Dry hydroclimates in the late Palaeocene-early Eocene hothouse world

Domain: earth_science
Published: 2024-08-15
Editorial outcome: minor_revision

Abstract
Extremeglobalwarmingcanproducehydroclimatechangesthatremain
poorlyunderstoodforsub-tropicallatitudes.LatePalaeocene-earlyEocene
(LPEE;~58-52Ma)proto-MediterraneanzonesofthewesternTethysoffer
opportunitiestoassesshydroclimateresponsestomassivecarboncycleper-
turbations.Here,wereconstructLPEEhydroclimateconditionsofthese
regionsandfindthatcarboncycleperturbationsexertedcontrolsonorbitally
forcedhydroclimatevariability.Long-term(~6Myr)carboncyclechanges
inducedagradualprecipitation/moisturereduction,whichwasexacerbated
bysomeshort-lived(<200kyr)carboncycleperturbationsthatcausedrapid
warmingandexceptionallydryconditionsinwesternTethyancontinental
areas.Hydroclimaterecoveryfollowingthegreatestshort-livedglobalwarm-
ingeventstook~24-27kyr.Theseobservationssupportthenotionthat
anthropogenicallydrivenwarmingcancausewidespreadaridificationwith
impactsthatmaylasttensofthousandsofyears.

Introduction
Human-driven greenhouse gas emissions induce detrimental envir- temporal extent of global warming influences on the hydrological
onmentalimpactsthatmaylastthousandsofyearsifimportantcli- cycle,remainpoorlyconstrained.
matechangemitigationstrategiesarenotadopted1,2.Anthropogenic Thesharedsocio-economicpathway(SSP;seeTab.S1forunab-
global warming is expected to cause substantial hydrological cycle breviated acronyms) 8.5 of the IntergovernmentalPanel on Climate
variations that threaten water security in diverse regions3–5. Model Change (IPCC) comprises massive carbon emissions and predicts a
experiments have used historical data to suggest that continental hothouseclimatestate(>5-10°Ctemperatureincrease)overthenext
Mediterraneanzones–i.e.,southernEuropeandnorthernAfrica–may two centuries2. This severe globalwarming scenario is predicted to
experience intensified aridityin thenextthree decades3,6. However, causemajorhydroclimate variations,icemelting,sea levelrise,and
the severity and persistence of drought associated with different triggering of negative carbon cycle feedbacks that can potentially
possibleglobalwarmingscenariosmayhavebeenunderestimatedby extendthelifetimeofhuman-inducedglobalwarmingformorethan
modelsimulations4,5.Geologicalhydroclimatereconstructionsofsub- 100kyr2,10.Theseprojectedconditionsareroughlysimilartothoseof
tropical Mediterranean regions indicate contrasting drier or wetter the late Palaeocene-early Eocene (LPEE, ~58–52Ma), which records
responsestodiverseglobalwarmingevents7–9.Hence,theimpactsof multiple global warming events that produced SSP 8.5-like climatic
extremeclimaticconditionsonMediterraneanhydroclimates,andthe scenarios2,11,12.AlthoughLPEEglobalwarmingeventsdevelopedunder
contrasting continental configurations with respect to the current magnitudes, which were triggered by orbitally forced and/or
tectonic setting, and had slower carbon release rates compared to volcanism-related mechanisms24,25. These events are recognised by
anthropogenic global warming11,13,14, geological LPEE records have negativecarbonisotopeexcursions(CIEs)andincludehyperthermals
been interpreted to offer a suitable opportunity to assess potential such as the Palaeocene-Eocene Thermal Maximum (PETM; ~56Ma).
global warming impacts of SSP 8.5-like climatic conditions on the Thiseventwasthelargesthyperthermalandhasbeenassociatedwitha
hydrological cycle9,11,14–16. Therefore, LPEE hydroclimate reconstruc- carbon release of 3000–10,000 Gt13,25. Succeeding hyperthermals
tionsofproto-Mediterraneanareascanprovideinsightsintohydro- includetheEoceneThermalMaximum(ETM)2(~54Ma)andETM3
logical cycle responses of sub-tropical regions to increased (~53Ma), which had considerably smaller environmental impacts
temperatures and can enable estimation of the typical duration of andmagnitudesthanthePETM22,26.Forinstance,carbonreleaseesti-
globalwarmingcontrolsonthehydrologicalcycle.
mates for the ETM 2range onlybetween ~2600Gtand ~3800Gt26.
LPEE hothouse climates were characterised by orbitally forced Smaller LPEE carbon cycle perturbations also occurred between
carbon cycle/temperature variations on eccentricity and precession hyperthermals, and were called the F, H2, I1, I2, L1, and L2
timescales17–19. These orbitally paced patterns were superimposed events19,21,22(Fig.1a).
upon a~5-Myr-long temperature increase that correlates with Short-lived LPEE carbon cycle perturbations have been divided
decreasing stable oxygen (δ18O) and carbon (δ13C) isotope signals intoapeakphase,withtemperatureincreases,oceanacidification,and
(Fig. 1a). This long-term carbon cycle perturbation resulted from a major hydroclimate changes, and a succeeding recovery phase of
gradual organic carbon burial reduction and/or increased volcanic acceleratedcarbonsequestration19,21–23(Fig.S1).Thisperiod,whichis
activity12,20,andwaspunctuatedbyshort-lived(<200kyr)carboncycle markedbyirreversibleδ13Ctransitionsfrommorenegativetomore
perturbationsthatsystematicallyoccurredunderenhancedseasonal positivevalues,isassumedtohaverestoredenvironmentalchanges
contrastconditionsclosetobothlong(~400kyr)andshort(~100kyr) induced by global warming to pre-event-like settings. Accelerated
eccentricitymaxima21–24.Short-livedLPEEcarboncycleperturbations carbon removal occurred during the first ~6-26 kyr of the recovery
wereassociatedwithisotopicallylightcarboninjectionsofdifferent phase due to optimisation of the oceanic biological pump19,27. This
processwasenhancedinproportiontotheinitialmagnitudeofthe LPEEsub-tropicalregionsincludeproto-Mediterraneanzonesof
light carbon injection that triggered each short-lived LPEE global western Tethyan continental areas, where dry hydroclimates with
warmingevent,anditsduration(~6–26kyr)coincidedwiththatofthe intermittent extreme precipitation events are recorded in the
ocean acidification recovery19. However, the incidence of carbon PETM28,30–32,34.Theseareaswerelocatedatroughlysimilarlatitudesas
sequestration on other processes, such as LPEE hydroclimate varia- modern Mediterranean zones41–44, which are influenced by seasonal
bility, is still poorly understood, partially because hydroclimate precipitationsystems(e.g.,monsoonsandwinterstormtracks)that
recoverytimescalesareyettobeconstrained.
aresensitivetopressureandmoisturedivergencechanges45,46.Spatial
Continental hydroclimate reconstructions indicate global wet- contrastsintheresponsesofthoseseasonalprecipitationsystemsto
becomes-wetter and dry-becomes-drier hydroclimate responses increasedtemperaturescangeneratewetterordrierconditionsacross
(hereaftercalledwet-wetteranddry-drier)duringpeakPETMandETM different modern southern Europe and northern Africa3,45,46. During
2 conditions9,11,14,28. This pattern, which would be expected to be the Neogene-Quaternary, orbitally forced precipitation patterns
especiallyintensifiedovertheoceanbyincreasedlower-tropospheric caused important Mediterranean hydroclimate fluctuations47. How-
watervapourtransport29,hasbeenassociatedwithpolaramplification, ever,thepossibilityofunderlyingcontrolbyorbitalforcingandglobal
atmosphericcirculationandtemperaturegradientchangesinducedby warmingonLPEEproto-Mediterraneanhydroclimatesremainselusive.
LPEE global warming9. PETM and ETM 2 dry-drier hydroclimate LPEEproto-Mediterraneanhydroclimatevariabilitycanberecor-
responseshavebeenfoundoversomesub-tropicalcontinentalinter- ded by detrital minerals contained within western Tethyan marine
iorsasaresultofreducedmoisturedivergenceandweakmeridional sedimentarysections,suchasthesub-tropicalContessaRoadsection
temperaturegradients9,28,30–35.Theseregionshavebeenconsiderably (Fig.1b;seeMethods).ThissectionhasrecordsofLPEEcarboncycle
less studied than high and tropical latitudes, where wet-wetter perturbations in marine pelagic carbonates of the Scaglia Rossa
hydroclimate responses have been identified28,36–39; however, some Formation19(Fig.2a,S1).Thisunitcontainslimestonesthatalternate
sedimentaryrecordsalsoprovideevidenceofcontrastinghydrological withmarls,whichusuallycoincidewithshort-livedLPEEcarboncycle
responsesbetweenthePETMandsucceedingshort-livedcarboncycle perturbations19.Thesemarlylayerscontainlowplanktonicandhigh
perturbations(i.e.,dry-becomes-wetter40). agglutinatedforaminiferacontentsandhadeitherreducedorsimilar
sedimentationratescomparedtolimestones19,21.Thesefeaturesindi-
catethatContessaRoadsedimentationdependedmainlyonbiogenic
CaCO deposition/dissolution patterns, which is corroborated by
3
orbitally driven CaCO dissolution cycles thathave been associated
3
with ocean/atmosphere light carbon concentration shifts21,22,24
(Fig.S2).DespitetheminorterrigenouscomponentofContessaRoad
sediments21,41,thissectionalsocontainsdetritalmineralswithinaeolian
dustfractions,whichareinterpretedaserosionproductsfromwestern
Tethyan continental rock massifs in northern Africa and southern
Europe21,42–44. The terrigenous fraction of Scaglia Rossa carbonates
includeshaematite,maghemite,andmagnetite44,48,49,whichserveas
proxiesforcontinentalhydroclimatevariability32,50,51.Nevertheless,the
relationshipbetweenhydrologicalcyclevariationsrecordedbythese
mineralsandLPEEglobalwarmingeventshasyettobeinvestigated.
Here,wecharacteriseContessaRoadsedimentationpatterns,witha
focus on magnetic minerals, to reconstruct western Tethyan con-
tinentalhydroclimates.Wepresent~4Myr-longhigh-resolutionX-ray
fluorescence(XRF)androckmagneticrecords(seeMethods)toassess
theinfluenceoforbitalcontrolsontheLPEEhydrologicalcycle,andto
exploretheimpactsofbothlong-termclimatictrendsandshort-lived
carbon cycle perturbations on proto-Mediterranean hydroclimates.
Our observations offer opportunities to gauge pre-anthropogenic
hydroclimate recovery timescales, which provides insights into
potentialhydroclimateresponsesofMediterraneanregionstoahot-
houseSSP8.5globalwarmingscenario.

Results
ContessaroadCaCO sedimentation
3
TheContessaRoadsectionmainlyconsistsofreddishlimestoneswith
highbiogeniccontents(CaandCaCO ),andlowdetritalelement(e.g.,
3
Fe, Ti, Si, Al, Zr and Rb) and bulk-rock (BR) magnetic mineral con-
centration parameter values (e.g., BR saturation remanent magneti-
sation(M ),andBRhardisothermalremanentmagnetisation(HIRM)).
rs
These rocks alternate with reddish marls with low Ca and CaCO
3
contents, and high detrital element and BR magnetic mineral con-
centrationparametervalues(Fig.2b–e,S3,S4).
ContessaRoadcontainstwointervalsthatdifferfromthetypical
alternatingreddishlimestone/marlsedimentationpattern.Thefirstis
a~600kyr-longintervalaftertheFevent,whichisreferredtohereas
theearlyEoceneterrigenouszone(EETZ).Thisintervalhasthehighest
detritalelementandBRmagneticmineralconcentrationsandcontains
severalconsecutivemarlsthatdonotcoincidewithmajorCIEevents
(Fig.2).Thesecondanomalousintervalspans~200kyrfollowingthe
ETM3.WerefertothisperiodastheearlyEocenelowmagnetisation
zone (EELMZ; Supplementary information), which contains whitish
limestonesthatrecordthelowestBRmagneticmineralconcentration
valuesatContessaRoad(Fig.2d,e,S4).

Contessaroadmagneticminerals
MagneticmineralassemblagesofScagliaRossacarbonatesconsistofa
mixture of high and low coercivity phases43,44,48. Temperature-
dependent magnetic susceptibility (χ-T) curves for 7 of 10 repre-
sentativeContessaRoadsamples(seeMethods)containagradualχ
dropduringheatingfrom~300°C,andasinglecoolingpeakat~450-
500°C(Fig. 3,S5,S6). Thesefeatures arecompatiblewithtransfor-
mationofpedogenicfine-grainedmaghemiteintohaematite52.AnETM
2samplehasnoindicationofaχdropat~300°C;nevertheless,thatχ-T
curvehasa~615-630°Cheatingdropthatisindicativeofmaghemite53,
whichispresentinalmostallContessaRoadsamples(Fig.3,S5,S6).χ-
Tcurvesalsocontaindropsat~580°Cforthreesamples,whichindi-
catethatmagnetiteis presentinreducedproportionscomparedto
maghemite(Fig.3b,d).Three-axisthermaldemagnetisationresults54
for representative Contessa Road samples (see Methods) typically
revealgradualmagnetisationdropsto675°Cforallaxes(Fig.3a–e),
which is diagnostic of pedogenic red pigmentary haematite55. This
mineralgivesreddishhuestotheScagliaRossacarbonates44,48,which
persists across most Contessa Road limestones and marls (Fig. 4a).
Scanningelectronmicroscope(SEM)imagingandSEM-basedenergy
dispersiveX-rayspectroscopy(EDXS)analysesindicatethatFe-Al-rich
minerals(e.g.,maghemite,magnetiteandredpigmentaryhaematite)
appearintheclayfractionsurroundingCa-richbioclasts(Fig.4b–f,S7).
Visual observations (Fig. 4a) and high-temperature rock magnetic
experimentssuggestthatredpigmentaryhaematiteisnotpresentin
thewhitishcarbonatesoftheEELMZ.Three-axisthermaldemagneti-
sationresultsforthisintervalrevealamagnetisationdropat~675°C
for the hard axis, which is interpreted to reflect the presence of
specularhaematite55(Fig.3).Thisbehaviourisnotidentifiedinother
samples.IntheEELMZ,amagnetisationdropalsooccursforallaxesat
~80°C, which indicates the presence of goethite exclusively in this
ContessaRoadinterval54(Fig.3f).
Theaboverockmagneticexperimentsrevealthathighcoercivity
magneticmineralassemblagesatContessaRoadmainlycontainpig-
mentary haematite, while low coercivity magnetic mineral assem-
blagespredominantlyconsistofmaghemitealthoughsomemagnetite
is also present. Variability in the concentration of these minerals is
estimated here on a carbonate free basis(CFB) (see Methods). CFB
calculations remove CaCO sedimentation controls on magnetic
3
mineralconcentrationparameters50,whichallowsclearidentification
ofmagneticmineralcontentchangesatContessaRoad(Fig.5,S8).M -
rs
CFBreflectsconcentrationvariationsofallmagneticminerals,which
indicatesalong-termLPEEmagneticmineralconcentrationdecrease
(transitionfromredtopinkdotsinFig.5a)punctuatedbythehighest
CaCO sedimentation andlowestM -CFBvaluesduringtheEETZandEELMZ,respectively
3 rs
(Fig.5a).HaematitecontentvariationsareidentifiedusingHIRM-CFB.
IncontrasttoM -CFB,HIRM-CFBinitiallyhasagraduallyincreasing
rs
trend before the PETM that reaches maximum values across PETM
marls(Fig.5b).HighHIRM-CFBvaluesatthePETMpeakarefollowed
byanabruptdropthatcoincideswithlimestonesthatmarkthePETM
recovery(changefromredtopinkdotsinFig.5b).ThePETMintervalis
thenfollowedbyanearlyEocenehaematitecontentdecreasewiththe
lowest values across the EELMZ and slight increases during some
short-lived carbon cycle perturbations (Fig. 5b). Maghemite and
magnetite content variations are recognised using anhysteretic
remanent magnetisation (ARM). ARM-CFBdecreases gradually from
beforethePETM,withlowestvaluesacrossPETMmarlylayers.This
gradual decrease is punctuated by limestones with pre-PETM ARM-
CFBvalues(Fig.5c).ThePETMintervalisthenfollowedbyalong-term
earlyEocenetrendtowardmorenegativeARM-CFBvalues(transition
fromredtopinkdotsinFig.5c).ARM-CFBdecreasesarealsoidentified
duringsomeshort-livedcarboncycleperturbations.
MagneticmineralcompositionalvariationsatContessaRoadare
estimatedusingcoercivityofremanence(B )andS-ratio(Fig.5d,e,
cr
S9). High B and low S-ratio values are interpreted to reflect the
cr
compositionaldominanceofhaematite,whilelowB andhighS-ratio
cr
values indicate the compositionalpredominanceof maghemite and
magnetite50,51. B and S-ratio reveal a gradual transition from pre-
cr
dominantlylowpre-PETMcoercivitiestohighercoercivitiesinPETM
marls(Fig.5d,e).Thesetrendsculminateinanabruptchangetolow
B and high S-ratios in limestones that mark the PETM recovery
cr
(Fig.5d,e).ThePETMintervalisthenfollowedbyalong-termcom-
positionaltransitionfromlowtohighcoercivitiesintheearlyEocene.
However,highB andlowS-ratiovaluesacrossmostshort-livedcar-
cr
boncycleperturbationsandduringtheEELMZinterruptthispattern
(Fig.5d,e).

Methods
TheContessaRoadsection
The Cretaceous-Palaeogene Contessa Road section (lat. 43°22'47”N;
long.12°33'50”E)isamarinesedimentarysectionlocatednorthwestof
thetownshipofGubbio,Italy.Thissectionwasdepositedinthewes-
ternTethyan Umbria-Marchebasinand recordsLPEEpelagiccarbo-
nate sedimentation of the Scaglia Rossa Formation41. Deposition of
these LPEE carbonates occurred between magnetochrons C24r and
C23r,andbetweencalcareousnannofossilzonesNP8/9andNP12over
the~30-48mstratigraphicdepthintervalatContessaRoad(Fig.S1).
The0mdepthatContessaRoadcoincideswiththeK/Pgboundary;
positive depths correspond to younger strata21. CaCO -based and
3
δ13C-based astrochronological age models have been used to refine
Contessa Road age constraints19,21,24. These age models reveal that
majorhyperthermalssuchasthePETM,ETM2andETM3arerecorded
withinmarlylayersat~31.3m,~40m,and~46mdepths,respectively19,21
(Fig.S1).Piedrahitaetal.19developedthemostrecentLPEEchronology
forContessaRoad.Theyinitiallydividedthesectionintotwooutcrops
(Fig.S1).OutcropArangesbetween30mand33mdepthatContessa
RoadandcontainsaPETMrecord,whileoutcropBrangesfrom~33m
to~48mdepthatContessaRoadandcontainsrecordsoftheF,ETM2,
H2, I1, I2, ETM 3, L1 and L2 events19,21. The J event is also indicated
tentatively in this outcrop; however, its δ13C expression is not well
developed19(Fig.S1;19).Piedrahitaetal.19identifiedorbitalsignatures
in high-resolution BR-χ and δ13C records. BR-χ was interpreted to
indicateCaCO contentchanges,whileδ13Cwasassociatedwithlight
3
carbon concentration variability. Therefore,BR-χ presents thesame
variations of detrital element patterns, and δ13C anti-correlate with
detrital element indices19,21,24,62. Long and short eccentricity cycles
withinBR-χandδ13CweretunedtotheZB18aastronomicalsolution23
(Fig. S2); hence,aCaCO dissolutionindicatorsuchas PC1 repre-
3 dis
sentsthesamevariabilitydescribedbyPiedrahitaetal.19.Tuningtothe
ZB18a astronomical solution allowed transfer of Contessa Road
recordsfromthedepthdomaintothetimedomain(Fig.S1,S2).Ana-
lysesforthisstudywereperformedonthesamesamplesasPiedrahita
etal.19;therefore,allofourrecordsarepresentedinthetimedomain.

Sampling
TheLPEEContessaRoadintervalwassampledat1-cmresolutionin
hyperthermalsandincontinuous2-cmstratigraphicintervalsinother
partsofthesection.Ca,CaCO andδ13CdatafortheLPEEContessa
3
RoadrecordwerepresentedbyPiedrahitaetal.19.XRFFe,SiandCa
resultsarefromPiedrahitaetal.24onlyforthePETMinterval(outcropA
inFig.S1);allremainingXRF,rockmagneticandSEMdataweregen-
eratedinthisstudyattheAustralianNationalUniversityandtheChi-
neseAcademyofSciences.

X-rayfluorescencemeasurements
Samples were cut to expose flat surfaces for XRF measurements.
Analyses were made using a third generation Avaatech XRF Core
ScannerwithaCanberraX-PIPSsilicondriftdetectoroperatedat10kV
(current=0.5mA,counttime=60s,nofilter)and30kV(current=
0.5mA,counttime=60s,Pd-Thickfilter).Allsampleswerecleaned
andfixedoverplasticholdersfordiscreteXRFmeasurementsusinga
16mm2samplearea.Samplespacinginthecorescantablewas~20cm
to avoid interference between measurements. Standards were run
betweenmeasurementsetstotestmeasurementreliability.RawX-ray
spectrawereanalysedviaiterativeleastsquaresanalysisintheWinAxil
softwarefromCanberraEurisys.

Rockmagnetism
Samples were cut into ~1cm cubes for ARM and hysteresis measure-
ments.ARMmeasurementsweremadewitha2GEnterprisescryogenic
magnetometer.ARMswereinducedusinga140-mTalternatingfieldand
a0.05-mTdirectcurrentbiasfield.Hysteresisloopsweremeasuredwith
aPrincetonMeasurementsCorporationvibratingsamplemagnetometer
3900to±1Tmaximumfieldswitha2-mTfieldstep.Saturationrema-
nentmagnetisation(M ),saturationmagnetisation(M),coercivity(B),
rs s c
low-field χ (χ ), and high-field χ (χ ) were calculated from hysteresis
lf hf
loops.Usingtheupper(M+(H))andlower(M-(H))hysteresisbranches,
weestimatedasymmetricremanenthystereticmagnetisationderived
curve (M ) from ð1ÞM ðHÞ=ðM+ðHÞ(cid:2) M(cid:2)ðHÞÞ=2, where H corre-
rh rh
spondstothemagneticfieldstrengthandMtomagnetisation68.Using
theM curve,weestimatedB ≈B asð2ÞM ðB Þ=ðM ð0TÞ=2Þ,HIRM
rh rh cr rh rh rh
ð3ÞðM ð1:0TÞ(cid:2)M ð0:3TÞÞ, L-ratio ð4ÞðM ð0:3TÞ=M ð0:1TÞÞ, and
rh rh rh rh
S-ratioð5ÞðM ð0:3TÞ=M ð0TÞÞ.WeusedBurrtypeXIIdistributions68of
rh rh
M curvestounmixmagneticmineralcomponentstoseparatecoer-
rh
civitycomponents(seeSupplementaryresults).
Temperature-dependent magnetic analyses were made for
representativesamples.Sampleswerecrushedforχ-Tmeasurements,
whichwereperformedinanargonatmospherewithanAGICOMFK1-
FA Kappabridge equipped with a CS-3 furnace. Three-axis thermal
demagnetisation was performed using samples that were cut into
rectangular cuboids. Soft-, medium- and high-coercivity isothermal
remanent magnetisation fractions were induced with direct current
fieldsof0.05T,0.3Tand2.7Talongthreeorthogonalsampleaxes.
SampleswerethendemagnetisedthermallyinanASCTD-48SCoven
andmeasuredona2GEnterprisescryogenicmagnetometer.
Bulk-rock(BR)magneticmineralconcentrationparameterswere
normalisedwithrespecttosamplemass.Anexampleofthesecalcu-
lationsisgivenbyBR-M inthefollowingequation:
rs
Br(cid:2)M ðAm2kg (cid:2)1Þ= M rs ðAm2Þ ð6Þ
rs
SamplemassðkgÞ

Carbonate-free basis (CFB) magnetic mineral concentration
parameterswereestimatedusingthehigh-resolutionCaCO recordof
3
Piedrahitaetal.19,whichmakesitpossibletosubtractmathematically
theCaCO contentofeachanalysedsampleforsubsequentdatanor-
3
malisation. An example of CFB calculations is given by M -CFB as
rs
follows:
(cid:4) (cid:5)
(cid:1) (cid:3)
M (cid:2)CFB Am2kg (cid:2)1 = M rs Am2 ð7Þ
rs ðSamplemassðkgÞ*ð100%(cid:2)CaCO ð%ÞÞ
3 1
whereð8Þð100%(cid:2)CaCO ð%ÞÞisthesamplemasspercentagethatdoes
3
notconsistofCaCO .
3

Principalcomponentanalysis(PCA)
Differentdatasetswerestandardisedtoperformprincipalcomponent
analysis(PCA).AninitialPCAwasperformedusingdetritalandbio-
genic XRF elements (referred to here as PCA ) to identify CaCO
3
dissolutionpatternsatContessaRoad.AsecondPCAwascarriedout
withXRFelements,CFBmagneticmineralconcentrationparameters,
B and S-ratio (referred to here as PCA ) to assess relationships
cr all
betweenterrigenousinputs,CaCO dissolutionandmagneticmineral
3
compositiononContessaRoadcarbonates.Finally,athirdPCAwas
performed using M -CFB, ARM-CFB, HIRM-CFB, B and S-ratio
rs cr
(referred to here as PCA ) to characterise magnetic mineral con-
arid
tent and compositional variations associated with western Tethyan
hydroclimatevariability.

Spectralanalysis
PC1 andHIRM-CFBweredividedintointervalstoavoidtheEETZ
dis
andtheEELMZ.Thesetwoperiodshaddifferentsedimentationpat-
terns to those that record orbitally controlled CaCO dissolution
3
cyclesthroughtherestoftheContessaRoadsection21.Threeinter-
vals(PETM,postEETZ-preEELMZintervalandpostEELMZinterval)
aretreatedseparatelytoexploreorbitalsignalsatContessaRoad.All
recordswereinterpolatedtotheaveragesamplingresolutionofeach
interval,whichvariesbetween~2kyrand~4kyr.Allrecordswerethen
detrendedwithlocallyestimatedscatterplotsmoothing(LOESS)fil-
ters and local regression windows equivalent to 35% of record
lengths. Spectral analyses were carried out using the Acycle
Software69 with the periodogram and multi-taper methods. Short
eccentricity and precession signals were isolated using Gaussian
bandpass filterswithbandwidthsof 0.010±0.003(1σ) cycleskyr−1
(~75–140 kyr) for short eccentricity, and 0.044±0.010 (1σ) cycles
kyr−1(~18–29kyr)forprecession.Allfilteredsignalswerethennor-
malisedbetween-1and1toallowamplitudecomparisonsbetween
orbitalsignalsofdifferentintervals.
Cross-spectral analysis was performed using the Lomb-Scargle
FouriertransformintheRedFit-Xsoftware70.Thissoftwarewasusedto
generatesquaredcoherencyandphasespectraforPC1 andHIRM-
dis
CFB for each interval in which orbital signals are studied–i.e., the
PETM,postEETZ-PreEELMZandpostEELMZintervals.

Scanningelectronmicroscopeobservations
Representativesampleswerecut,embeddedinanepoxyresinmount,
andpolishedtomakecrosssections.Sampleswerethencarboncoated
toproduceaconductivelayerforSEMobservationswithaThermo
FisherApreoSEMequippedwithaBrukerQUANTAXenergydispersive
X-ray spectrometer. These instruments allow the identification of
morphological features and chemical composition of samples. SEM
observationswereperformedwitha~10mmworkingdistance,15kV
acceleratingvoltageand6.4nAcurrent.

Dataavailability
All data generated in this study are provided in the Supplementary
Information/Source Data file. Source data are provided for all rock
magnetic and X-ray fluorescence measurements. Source data are
providedwiththispaper.

Codeavailability
ThePCAcodeusedinthismanuscriptisavailableatFigShare(https://
doi.org/10.6084/m9.figshare.25522990).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study analyses the concentrations and properties of magnetic minerals from the lower Eocene Contessa road section (Italy) in order to deduce the paleoenvironmental and paleoclimatic evolution of the western Mediterranean area. The manuscript confirms the results from previous studies carried out in this section and elsewhere, which showed that pelagic sedimentation in the area was astronomically forced and several short-lived (<200 ky-long) carbon-cycle perturbations occurred when long and short eccentricity maxima overlapped. Additionally, the authors found that western Mediterranean conditions became generally drier as the early Eocene climate became progressively warmer (eventually leading to the early Eocene climatic optimum), although this trend was interrupted during a ~500 ky-long wetter interval at approximately 55 Ma. They also deduce that extremely dry conditions occurred during the short-lived carbon cycle perturbations and that the recovery to pre-event conditions was fast (23-27 ky). They suggest that these results may be relevant to our understanding of the evolution and impact of anthropogenic global warming.\n\nThe manuscript is a potentially good fit for the journal and its readers. The authors have gone to great lengths with their research and show a sound understanding of the subject. However, there are some loose ends and there is room for improvement in terms of methodology and how the results are interpreted and presented.\n\nMAJOR ISSUES\n(1) It is not clear how CFB parameters were obtained. For example, was the carbonate content of each sample separated using physicochemical treatments in the laboratory (i.e., were samples decarbonated) and were the mineralogical properties of the residue subsequently analysed? Alternatively, was the carbonate content subtracted by theoretical calculations? The method used should be more clearly explained. The former method would probably also allow for the identification of clay and magnetic mineral phases by X ray diffraction, which would help to support (or refute) some of the authors’ interpretations.\n(2) Why all magnetic minerals are interpreted to be detrital and why some (e.g., magnetite) are not (partly) biogenic or authigenic should also be more clearly explained. In addition, pigmentary haematite in red bed sequences is usually secondary and probably formed in the order of 105-106 years after deposition (Kodama, 2012). Could this affect the interpretation of shorter hydroclimate variations?\n(3) From the very beginning (line 108) the authors state that the variations in the carbonate/clay ratio throughout the succession record variations in the rate of carbonate deposition or dissolution, later favouring dissolution as the main controlling factor (line 227). The line of reasoning should be more clearly explained. Initially, they ignore that clay (and magnetic mineral) content could also vary as a consequence of changes in the rate of terrigenous sediment input over time (i.e., terrigenous dilution). This possibility is only considered later in the manuscript, and restricted to the interpretation of the EETZ (lines 241-248). In order to address these issues further, the authors could obtain some terrigenous input proxies (e.g., Ti/Al and Zr/Al ratios) throughout the succession.\n(4) PCA2all scores are used as a proxy of variations in the rates of detrital input and CaCO3 dissolution over time. However, each of the factors identified by the PCA analysis should represent only one controlling mechanism, not two (i.e., PCA2all should represent variations in either detrital input or CaCO3 dissolution, but not in both). Furthermore, both Ca (i.e., carbonates) and magnetic parameters show negative loadings in PCA2all, suggesting that they are related. Consequently, why do the authors relate negative PCA2all values only with detrital supplies in Fig. 6e? Why does Ca increase in EETZ? In addition, matrices of all PCA analyses (tables with loadings between variables and principal components) should also be provided in the supplementary material in order to know which variables are relevant to each component and their statistical significance.\n(5) Regarding spectral analysis and orbital forcing, it should be emphasized that the power spectra are rather noisy and spiky (Fig. 7), meaning that there are significant periodicities that the authors seem to ignore. The original data used for the spectral analysis should be provided in the supplementary material in order to allow replication. In addition, the authors are perhaps too optimistic when stating that “the coincidence between PC1dis short eccentricity and ZB18a astronomical solution indicates that the filtered PC1dis precession signal is a good indicator of precession-related light carbon concentration/CaCO3 dissolution variations” (lines 281-283). The fact that the filtered PC1dis eccentricity signal is similar to the eccentricity solution in ZB18 does not necessarily mean that the precession signal also has to match. In fact, the amplitude of precession cycles does not fit that of eccentricity cycles. In order to reinforce their interpretation, the authors should try to correlate their precession cycles with those from other records. Although there are no precession solutions for the studied time interval (lines 279-280), some studies carried out in partly coeval successions have identified the record of early Eocene precession cycles (e.g., Westerhold et al., 2007, 2017). My impression is that the filtered HIRM-CFB precession signal is probably not reliable, as it displays only five precession cycles in the PETM (Fig. 8), which are too few for the estimated 170-200 ky duration of this event (the 9.5 precession cycles obtained in the filtered PC1dis signal seem to be more reasonable). Consequently, the discussion about the environmental significance of the differences between the filtered PC1dis and HIRM-CFB precession signals seems to be too speculative (lines 285-293). Taking into account that the filtered HIRM-CFB eccentricity signal also departs from the filtered PC1dis and ZB18 eccentricity signals, my impression is that the HIRM-CFB record is not suitable for filtering. This would mean that the discussion about the filtered HIRM-CFB eccentricity signal is also speculative (lines 298-314).\n(6) In this work, the authors seem to misunderstand the relationship between eccentricity cycles and seasonal contrast. More specifically, they suggest that eccentricity maxima produce enhanced seasonal contrast (lines 314-315 and 326-327). In reality, seasonal contrast is determined by precession cycles, not by eccentricity cycles. Precessional variations in insolation determine the temperature contrast between summer and winter, along with the consequent annual distribution of precipitation, storminess, organic productivity, etc. In the northern hemisphere, precessional seasonality is minimized (mild summers and winters) when boreal summers occur at aphelion and winters at perihelion (i.e., high precession index), but seasonality increases (warmer summers and cooler winters) when summers occur at perihelion and winters at aphelion (i.e., low precession index). Periodic variations in the eccentricity of the Earth’s orbit modulate the amplitude of precession-driven seasonality. Thus, at eccentricity maxima both maximized and minimized seasonality occur during one single precession cycle. Conversely, during eccentricity minima seasonality remains similar (i.e., intermediate) regardless of the precession index. This should be taken into account in the discussion in lines 315-337. In this regard, it is very unlikely that “eccentricity minima periods … with relatively stable seasonal contrast … produced wetter conditions … which may have enhanced fluvial haematite transport to Contessa” (lines 318-321). Fluvial sediment input increases with seasonality, reaching maximum values under dry subhumid precipitation regimes with three to five wet months per year (Cecil and Dulong, 2003). These conditions generally occur at eccentricity maxima and low precession index. Similarly, rather than the minimum eccentricity configurations suggested in lines 329-333, “amplified seasonal precipitation and intermittent extreme precipitation events” are more likely during high seasonality conditions developed at maximum eccentricity and low precession index.\n\nOTHER ISSUES\nThere are too many acronyms in the manuscript, making it difficult to read.\nBoth haematite (text) and hematite (Fig. 5) are used. Please homogenize.\nHow stratigraphic thickness (Fig. S1) was transformed into age/time (e.g., Fig. 2) should be explained (age model).\nLine 61: “short-lived (~200 kyr) carbon cycle perturbations”. Maybe <200 kyr is more appropriate, as most events were significantly shorter than 200 ky and even the PETM was also probably shorter (170-200 kyr).\nLines 73-79: the wet-wetter and dry-drier evolutions may be too simplistic. Hydroclimates changed throughout some hyperthermal events.\nLines 138-139: Most of the other marl levels do seem to coincide with CIEs. In this regard, why was the J event (Fig. S1) not displayed in the other figures? Would it not fit the model and coincide with the long eccentricity maximum at ca. 53.2 Ma in Fig. S2?\nLines 149: The X drop at 300ºC does not occur in EETZ and ETM2, and is rather subtle in pre-ETM2, meaning that it is clearly visible in only 50% of the cases. Furthermore, the Curie temperature of some iron sulphides (e.g., greigite) is also approximately 300ºC. The potential occurrence (or absence) of sulphides should be discussed.\nLines 151-152: If only two out of five cases show the drop in X at 615-630ºC, why is the interpretation extrapolated to “almost ALL Contessa Road samples”?\nLines 186: Fig. 5b, and not 6b.\nLines 210-215: Unclear line of reasoning, please elaborate on this.\nLine 220: “Despite the terrigenous origin” (singular).\nLine 240-241: All marl layers coincide with positive PC2all positive peaks, not only the so-called “dissolution horizons” (see also comment on lines 138-139).\nLine 263: “deduced from” instead of “indicated”.\nLines 288-293: Unclear line of reasoning. Even if this discussion were pertinent (see general comment 5), increased light C and haematite concentrations could also result from increased fresh water (i.e., fluvial) supplies, which would suggest that terrigenous dilution was the main controlling mechanism for the compositional variations observed throughout the succession, rather than variations in carbonate deposition/dissolution (see general comment 3).\nLines 343-345: Unclear, please rephrase.\nLine 367: Fig. 9, rather than 8.\nLine 378: The 27-kyr recovery of the PETM seems to be subjective, as peak hyperthermal conditions may have been reached significantly earlier according to Fig. 9a.\nLines 403 and 407: Remove “depth” and “depths”, respectively.\nLine 416. Use “They” instead of “Piedrahita13”.\nLine 495: “Thin”, rather than “thick”?\nLine 677: “heating and cooling” … “red and blue”.\nSuppl. lines 13-15: Visually it seems that Sr maxima occur at hyperthermals.\nSuppl. Lines 55-56: Goethite is a high coercivity mineral. Does this sentence refer to haematite content?\nSuppl. line 58: EDXS show elemental occurrences/abundances, but not mineralogy. It cannot be concluded that “clay minerals are compositionally similar across all intervals”.\nSuppl. line 69: This section is highly speculative and does not reach any conclusion. Superfluous?\nSuppl. lines 80-81: Productivity can increase without higher terrigenous input (e.g., upwelling).\nFig. S4: What do low coercitivy components represent and why are magnetite and maghemite not distinguished? Why is goethite not represented in EELMZ? Mean coercitivity values and dispersion could be included.\n\nREFERENCES\nCecil and Dulong, 2003. SEPM Spec. Publ., 77, 21–27.\nKodama, 2012. Paleomagnetism of Sedimentary Rocks: Process and Interpretation, 157 pp. Wiley-Blackwell, Oxford.\nWesterhold et al., 2007. Paleoceanography 22, PA220.\nWesterhold et al., 2017. Clim. Past 13, 1129-1152.", "reviewer_2": "This paper is a high-resolution study of the Palaeocene-Eocene interval in the important and well-studied Contessa Road section in Gubbio, Italy. Although extensive palaeomagnetic, biostratigraphic and isotopic work has been done on this succession, this study uses an environmental magnetic and geochemical approach which allows the authors to infer terrestrial rather than palaeoceanographic conditions. It thus complements a number of papers from around the Tethyan margin examining the terrestrial response to the PETM (e.g. Bolle et al., Schmitz et al., 2003; Schmitz et al., 2007; Dallanave et al., 2012). Few of these studies extend beyond the PETM to a detailed consideration of other Eocene carbon cycle perturbation events, and this is an important contribution of this paper.\n\nThe main findings of this paper are as follows:\nA. There was a long-term aridification of the western Tethys over 58-52 Ma\nB. This was punctuated by carbon cycle perturbations which produced even drier conditions\nC. Recovery from these perturbations to pre-event hydroclimate conditions consistently took 23-27 kyr, regardless of the size of the perturbation\n\nThese arguments are underpinned by an interpretation of the magnetic mineral content of the sediments as follows:\n1. The magnetic fraction is primarily composed of maghemite and pigmentary hematite, both of which are primarily detrital\n2. Absolute concentration of both high and low-coercivity components with respect to overall non-carbonate content shows a long-term decrease, but hematite:maghemite ratio shows a long-term increase\n3. Hematite:maghemite ratio also increases during some of the hyperthermals and short carbon-cycle perturbations\n4. Reduced overall magnetic fraction and increased hematite proportion is inferred to indicate aridity\n\nMy main comments are some questions about points 1 and 4, some consideration of the interpretation of principal components, and an assessment of the findings on the basis of interpretations 1-4.\nFollowing this I have appended line-by-line comments.\n\n1. The magnetic fraction is primarily composed of maghemite and pigmentary hematite, both of which are primarily detrital\nThis is argued on the basis of Figure 3, which shows temperature-dependence of magnetic susceptibility and 3-component thermal demagnetisation diagrams for selected samples. It is argued that “almost all” Contessa Road samples show evidence of maghemite as a fall in MS around 300C (maghemite converting to hematite) and/or a fall in MS around 625C (maghemite Curie temperature). On the basis of the six samples shown, I can see these features in only three (PETM initial phase, PETM recovery phase, and EELMZ, which is subsequently discussed only in the supplementary information). Meanwhile, it is mentioned that two of the samples (PETM recovery and Pre-ETM 2) show evidence for magnetite, which I agree with. I would also interpret EETZ, ETM2 and EELMZ as potentially indicating magnetite. It may be that all or almost all of the samples not shown here contain the two features associated with maghemite – if this is the basis for the statement, it should be explicitly stated and perhaps quantified (what percentage of the samples show these features).\n\nThe 3-component thermal demagnetisation is said to show a pigmentary hematite signature (gradual demagnetisation to 675C), with the exception of the EELMZ. I found this convincing. It seems to me there is also some evidence of magnetite in PETM recovery and EETZ.\n\nI note that previous publications on the same outcrop, as well as on other outcrops of broadly the same formation, have also inferred a mixture of hematite, magnetite and maghemite. However, much more weight has previously been given to the contribution of both biogenic and detrital magnetite in lower parts of this succession (Abrejevitch et al., 2015; Coccioni et al., 2019), both of which are largely dismissed here. A previous study of this succession inferred that the hematite is primarily early post-depositional and authigenic, a possibility which is not discussed here (Abrejevitch et al., 2015). The maghemite could also be pre- or post-depositional oxidation of either detrital or biogenic magnetite, which is again not considered here.\n\nOverall, I think that given the importance of the detrital origin and mineralogy of the magnetic fraction to the argument in later parts of the paper, more could be done here to discuss possible other interpretations of the magnetic results and explain why they are not preferred. The supplementary material makes reference to IRM unmixing curves. It is interesting that these curves show fewer components than similar analyses for older parts of the Contessa Road section (Abrejevitch et al., 2015; Coccioni et al., 2019). These data could potentially help to test the argument that the soft component is primarily detrital rather than biogenic.\n\n2. Absolute concentration of both high and low-coercivity components with respect to overall non-carbonate content shows a long-term decrease, but hematite:maghemite ratio shows a long-term increase\nThis seems convincingly demonstrated by Figure 5.\n\n3. Hematite:maghemite ratio also increases during some of the hyperthermals and short carbon-cycle perturbations\nAgain, this is convincingly demonstrated by Figure 5 and Figure 9, although there are other short-lived increases of similar magnitude which do not coincide with carbon-cycle perturbations.\n\n4. Reduced overall magnetic fraction and increased hematite proportion is inferred to indicate aridity\nThe argument made here is that aridity in the source area led to reduced ferrihydrite formation, thus reducing the possibility of subsequent formation of maghemite and then hematite. However, the aridity promoted the formation of hematite from any ferrihydrite or maghemite that was formed, thus producing a situation where both magnetic components were reduced in absolute terms but the ratio of hematite to maghemite increased. This makes a number of assumptions: 1. that the magnetic signal is controlled almost entirely by input of detrital maghemite and hematite. 2. That the detrital maghemite comes almost entirely from ferrihydrite oxidation rather than oxidation of detrital or pedogenic magnetite. 3. That the signal is a proxy for source area soil conditions. 1 and 2 are discussed above. The third assumption leaves out the possibility of post-depositional reductive dissolution in the sediments, which would similarly both reduce the overall magnetic content and increase the hematite/maghemite ratio, due to the lower stability of maghemite in these conditions. A variation on this (with the dissolution occurring prior to deposition) is proposed by Abrejevitch et al. (2015) for a similar (though more extreme) set of magnetic features in the Gubbio section below the K-Pg boundary. The hypothesis of source area aridity is plausible, but as with the identification of the minerals, I think it is important to discuss other possibilities and explain why this one is preferred.\n\nInterpretation of Principal Components\nSeveral parts of the argument are based on the interpretation of principal components. PC1(dis) is interpreted as primarily representing carbonate dissolution. I see no issue with this, and this interpretation is backed up by previous studies of this section (e.g. Galeotti et al., 2010). PC1(all) is also interpreted as representing carbonate dissolution. This is more interesting, as the magnetic concentration parameters relative to detrital input are all positively loaded on this PC, suggesting that during periods of reduced net carbonate sedimentation, either detrital sediments became more magnetic (perhaps due to increased ferrihydrite -> maghemite -> hematite and/or increased production of pedogenic magnetite) or there was an alternate process which increased the magnetic mineral fraction relative to the detrital fraction as a whole. This is similar to the pattern seen in Coccioni et al (2019), which they interpreted as increased biogenic magnetite production by magnetotactic bacteria due to high nutrient levels. Given the importance of Bcr and S-ratio to the later arguments about aridity, it would be interesting to see a PCA(all) that also included these parameters.\n\nThe interpretation of PC2(all) is interesting. In L242-245 it is argued that the fact that CFB magnetic mineral parameters and Ca both show negative loadings on this PC indicates that there was also significant terrigenous input during times of reduced carbonate dissolution. However, the elements identified as proxies for terrigenous input are positively loaded on this PC, i.e. anticorrelated to the magnetic parameters and Ca, so the interpretation of this as representing increased terrigenous input seems unsupported. What this seems to me to indicate is that the underlying process was something that resulted in reduced terrigenous/increased carbonate input but simultaneously in magnetic enhancement of the non-carbonate fraction. I note that the loadings of the magnetic parameters on this PC are quite low, and the discussion does not return to PC2(all) again, so perhaps a detailed consideration is not so important. However, I do think the current interpretation should be revised.\n\nThe most important PC interpretation from the point of view of the main arguments of the paper is PC1(arid), which represents the anticorrelation between overall magnetic concentration (including absolute carbonate-free concentrations of all coercivity components) and proportion of the magnetic fraction represented by harder minerals (implicitly hematite). This is the basis of the argument discussed above in point 4, and so I will not discuss it further here.\n\nReturning to the findings:\nA. Long-term aridification of the western Tethys over 58-52 Ma\nIf the identification of the magnetic minerals as detrital hematite and maghemite and the interpretation of PC1(arid) as a source area soil aridity signal are both accepted, this is a well-supported finding.\n\nB. Punctuation by carbon cycle perturbations which produced even drier conditions\nBased on Figure 9, I can see the argument for increased aridity during the first part of the PETM and the first part of ETM2. L1 and L2 are also convincing. H2 and I1 look pretty marginal, I2 I don’t see at all, and ETM3 seems to be less arid by comparison with the immediately preceding period. F and the final phase of the PETM both seem to have increased humidity. Overall, this is a pretty complicated picture.\n\nC. Recovery from these perturbations to pre-event hydroclimate conditions over 23-27 kyr\nThis argument is based on three hyperthermals: the PETM, ETM2 and ETM3. Here I think there needs to be a discussion of how the peak of the event is identified and how you identified the point at which conditions returned to pre-event baselines (or indeed, how you quantified pre-event baselines). As it is, the “peak” of the PETM has similar values of PC1(arid) to a prior peak a few tens of thousands of years earlier, and the “recovery to pre-event conditions” is actually a change to conditions significantly more humid than those immediately before the PETM. The peak of ETM2 is clearer, but again, the “recovery” is set at significantly lower aridity that the values immediately before the event. The most arid conditions for ETM3 occur before the onset of the event as indicated by the shaded bar, and the “recovery” is truncated by the intervention of the EELMZ. Given this, I think it is quite speculative to argue that there is a relatively constant time interval over which hyperthermals return to “normal” conditions. If there was a clearer discussion of how these points were identified, it is possible that this problem could be resolved, although I would also emphasise in the text that there are only three data points to go on.\n\nLine by line comments:\nL38-40 – statement needs a reference\nL 44 – reveal - > reconstruct\nL81 – “should have” -> “are assumed to have”?\nL84 “optimized” -> “optimization of the”\nL91-93 – This sentence is a little unclear as to whether the dry drier response has been reconstructed for the interior continental areas or the continental margins/Mediterranean zones. A quick glance at the papers cited suggests that they generally seem to support increased humidity with periods of aridity during the PETM and ETM2 for the coastal areas, potentially indicating extreme rainfall events rather than increased background humidity, with some evidence for increased overall aridity in continental interiors.\nL109 – indicated -> interpreted\nL148 – “generally contain” -> “are generally characterised by”\nL181 – HIRM-CFB has a gradually increasing trend -> HIRM-CFB initially has a gradually increasing trend\nL181-2 – present tense for describing results\nL182 – “high HIRM-CFB values are followed by…” -> “high HIRM-CFB values at the peak of the PETM are followed by…”\nL192 – interesting there is no obvious drop in ARM at the EELMZ\nL194 – indicated -> estimated\nL199 – Not sure punctuated is the right word. Culminates in?\nL210-215 – I think I see what you’re getting at here, but this argument is currently unclear. You state that the haematite cannot be authigenic because if it were, increased magnetic concentrations would correlate with increased haematite concentrations. However, Figure 5 indicates that increased magnetic concentrations do correlate with increased haematite concentrations. I think what you are arguing is that the proportion of haematite in the magnetic fraction increases as magnetic content decreases, i.e. there is an enhancement of haematite relative to softer minerals as magnetic content decreases. (NB I also discuss this argument above in terms of possible other explanations for this pattern.)\nL216 – “Scaglia Rossa carbonates also contain maghemite and magnetite, which have been interpreted to mainly have detrital origins despite likely biogenic magnetite occurrences41,42” The two works cited here (Abrejevitch et al., 2015 and Coccioni et al., 2019) do not support the statement as given according to my reading of them. Coccioni et al. (2019) did not discuss maghemite at all and Figure 3(c) in that paper seems to indicate a biogenic magnetite component ranging around 30-40% and a detrital magnetite component of 10-15%. Abrejevitch et al. (2015) mentioned the possibility of maghemite but focused on magnetite and found detrital and biogenic magnetite contributing approximately equal amounts to the overall magnetisation with the exception of their low susceptibility zone (Fig 7 of that paper). See my comments above on the importance of discussing the interpretation of the mineralogy in more detail.\nL233-234 – “This implies that increased CaCO3 dissolution was accompanied by increased magnetic mineral inputs at Contessa Road (Fig. 6b-d)” – see the discussion above about the interpretation of PC1(all). This sentence is a little unclear as it is not immediately obvious that these increased magnetic inputs are increased relative to terrigenous inputs, i.e. the terrigenous (or more accurately non-carbonate) material is more magnetic. L236-237 – mainly CaCO3 dissolution makes sense, but one wonders why the non-carbonate material is more magnetic.\nL241 and following – I would use “troughs” rather than “negative peaks”, as when you then use the word “peaks” in the following discussion it becomes unclear whether you are talking about negative or positive extremes.\nL244-248 – if the PC2(all) negative peaks represent major terrigenous input, why are the detrital elements positively correlated with this axis? See discussion of PC interpretations, above.\nL255-259 – could the maghemite also come from other transformations (e.g. of magnetite)?\nL311-312 – this statement needs a reference, either to a published source or your own argument in an earlier section\nL295-323 – I found this argument a little confusing. So sometimes drier conditions/high seasonal contrast -> enhanced haematite production/transportation and other times wetter conditions/low seasonal contrast has this effect? Any ideas about why each of these mechanisms only seems to work sometimes? Might a wavelet analysis be useful to get an easier visual on power in the short eccentricity band?\nL325 – repetitive -> consistent\nL325-333 – again, I found this argument hard to follow. It would be good to clarify the connections between the systematic dry conditions and the strengthened hydroclimate variability/amplified seasonal precipitation/intermittent extreme precipitation. I think the argument here is that during short eccentricity maxima in hyperthermals, summers were drier and winters were wetter, while during eccentricity minima there was more consistent rainfall year-round, but this does not seem to fit with the “systematic dry conditions”.\nL352 – HIRM-> HIRM-CFB\nL367-68 – I think your data support the interpretation put forth by earlier studies and the earlier sections of this paper about extreme events, but I’m not sure I’d use the word “verify”.\nL372 – I don’t think the figure ref is correct here or in L374\nL376-377 – could this “non-linear response” be simply that once you get to a certain level of aridity, you don’t form any precursors any more, so the proxy is only sensitive within a particular aridity range?\nL377-379 – see my comments above\nL384 – “all” is a bit overegging it here – you have only studied a small number of events here\nL407 – “depths” – this is a bit confusing, as my understanding from Fig S1 is that the succession is measured according to a height above a stratigraphic datum (K/Pg boundary), therefore increasing with elevation/decreasing with age, whereas “depth” is usually used for depth below ground surface/datum, therefore decreasing with elevation/increasing with age. Suggest clarification, maybe “depths” -> “height above K-Pg boundary” with suitable acronym thereafter?\nL407-408 clarify that the ranges (30-33 m and 33-48 m) are for the outcrop coverage, not for the thermal events.\nL416 – Piedrahita -> Piedrahita et al.\nL417 – “that represent” -> “, which are proxies for”\nL463-471 – give the software used to carry out the PCA.\nL645-646 – date is wrong on this reference, should be 1981\n\nFigures: as a general comment, some of these figures use a lot of different colours to indicate different types of information. For accessibility reasons, ideally this information would be conveyed in other ways too, for example different coloured lines could also be differentiated using dots vs dashes, or points by using different symbols. If you have not already done so, I recommend https://www.fabiocrameri.ch/colourmaps/ and accompanying software/publications for making sure that accessible colour maps are used.\n\nFig 1 – The d13C/d18O/temp axis is reversed here compared to all other figures. Just for ease of reading it might be worth making it consistent.\nFig caption 2 – indicate meaning of shaded bands for d13C and CaCO3 wt % time series\nFig 3: Needs subfigure labels.\nYou have made a distinction here between the PETM initial phase and the PETM recovery – it would be good to have the boundary between these two phases marked on other figures, like Fig 2 and Fig 5.\nFig 8 –How were these intervals of good coincidence and bad coincidence chosen? Just by eyeballing? Also note that the caption states that the HIRM-CFB signal/orbital solution coincidence is good across short-lived carbon-cycle perturbations but these are not indicated with the blue boxes.\n\nSupp info L43-45 – given that the CFB magnetic parameters are calculated relative to detrital (or rather, non-carbonate) input, this would seem to indicate that these trends reflect magnetic enhancement of the detrital fraction at times of high carbonate dissolution, rather than simply detrital input – unless there is a significant non-detrital, non-carbonate fraction of the sediment, but the paper does not mention this.\nL90-91 What about terrigenous XRF values across the EELMZ?\nSupp fig 1 – An age axis on this figure would be helpful.\nSupp fig 5 – recommend switching the order of HIRM and ARM so that they are close to the coercivity components they are said to resemble, for ease of visual comparison. Note that the HIRM/High coercivity resemblance is v close, the ARM/low coercivity somewhat less so.\nSupp fig 7 – recommend reversing axis on S-ratio for ease of visual comparison.\n\nReferences\nAbrajevitch, A., Font, E., Florindo, F., & Roberts, A. P. (2015). Asteroid impact vs. Deccan eruptions: The origin of low magnetic susceptibility beds below the Cretaceous–Paleogene boundary revisited. Earth and Planetary Science Letters, 430, 209-223.\nBolle, M. P., & Adatte, T. (2001). Palaeocene-early Eocene climatic evolution in the Tethyan realm: clay mineral evidence. Clay minerals, 36(2), 249-261.\nCoccioni, R., Frontalini, F., Catanzariti, R., Jovane, L., Rodelli, D., Rodrigues, I. M., ... & Galbrun, B. (2019). Paleoenvironmental signature of the selandian-thanetian transition event (STTE) and early late paleocene event (ELPE) in the Contessa Road section (western Neo-Tethys). Palaeogeography, Palaeoclimatology, Palaeoecology, 523, 62-77.\nDallanave, E., Agnini, C., Muttoni, G., & Rio, D. (2012). Paleocene magneto-biostratigraphy and climate-controlled rock magnetism from the Belluno Basin, Tethys Ocean, Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 337, 130-142.\nGaleotti, S., Krishnan, S., Pagani, M., Lanci, L., Gaudio, A., Zachos, J. C., ... & Lourens, L. (2010). Orbital chronology of Early Eocene hyperthermals from the Contessa Road section, central Italy. Earth and Planetary Science Letters, 290(1-2), 192-200.\nSchmitz, B., & Pujalte, V. (2003). Sea-level, humidity, and land-erosion records across the initial Eocene thermal maximum from a continental-marine transect in northern Spain. Geology, 31(8), 689-692.\nSchmitz, B., & Pujalte, V. (2007). Abrupt increase in seasonal extreme precipitation at the Paleocene-Eocene boundary. Geology, 35(3), 215-218.", "reviewer_3": "The study by Piedrahita presented several interesting records of western Tethyan hydroclimate during the early Eocene. Those records are at orbital time scale resolution and contain highly valuable information of sensitivity of western Tethyan hydroclimate to carbon cycle perturbations. Given my expertise, my review only focuses on the staging of this study and discussions of climatic implications of these records.\n\n1. I found the staging of this manuscript a bit problematic. The wet-gets-wetter and dry-gets-dryer paradigm describes the hydroclimate response dominated by tropospheric moistening without changing circulation in response to CO2 increase (Held and Soden, 2006, J. Clim.), which leads to additional moisture being carried away from regions of divergence towards regions of convergence. However, the subtropical drying inferred from this paradigm, which is used to stage this study, only applies to the OCEAN! On land, P>=E in general, which implies either balanced (no net runoff) or slightly converging moisture flux (with net runoff). As a result, increasing tropospheric humidity can only increase or maintain P-E on land (Seager and Vecchi, 2010, PNAS; Byrne and O’Gormon, 2015, J. Clim.). Moreover, key components of subtropical terrestrial hydrological cycle such as monsoons (characterized by summer precip) and Mediterranean climate (characterized by winter precip) are controlled by regional circulation patterns that are departures from the zonal mean Hadley circulation. Tropospheric humidification can lead to enhanced monsoon rainfall even without any change or weakened monsoon circulation (Endo and Kitoh, 2014, GRL). In the Mediterranean region, drying over the land is explained by enhanced mass divergence due to strengthened high pressure system in the nearby region (Seager et al., 2014, J. Clim.). Finally, there is an inherent time scale difference between project future change in hydroclimate and the reconstructed early Eocene hydroclimate change presented here. The former does not involve slow feedback in the climate system such as vegetation and ice sheet (does not apply to this study), which are important for the latter (e.g., Lunt et al., 2010 Nat. Geo., Feng et al., 2022; Nat. Comm.). To me, the introduction and discussion could be revised to more accurately reflect knowledge on terrestrial and particularly Mediterranean hydroclimate as well as a long-term climate change perspective that deep time paleoclimate records can bring.\n\n2. The clarity of the discussion on “Orbitally forced LPEE hydroclimate variability in the western Tethys” could be improved. For example, “short eccentricity maxima” can be more explicitly written as northern hemisphere summer perihelion during the short eccentricity cycle. It is useful to be explicit given that eccentricity by itself does not affect insolation. Also, the linkage between changing seasonal cycle and the mean hydroclimate state was never explained. Kutzbath et al, 2020 (PNAS) might be a good starting point to explain how the seasonal changes in insolation driven by precession cycle can result in mean state changes of precipitation and P-E. They showed a linkage through shifting winter storm track.", "reviewer_author_response": "Response to reviews for:\nDry hydroclimates in the late Palaeocene-early Eocene hothouse world\nVictor A. Piedrahita1, Andrew P. Roberts2, Eelco J. Rohling2,3, David Heslop2, Xiang Zhao2, Simone Galeotti4,5, Fabio Florindo5,6, Katharine M. Grant2, Pengxiang Hu2, Jinhua Li1\n\nWe thank the reviewers for their comments, which have helped to clarify and improve our manuscript.\nAll reviewer comments are repeated below in black with responses in blue. We are grateful for, but do not provide responses to, supportive introductory comments.\n\nReviewer #1 (Remarks to the Author):\n\nComment 1: It is not clear how CFB parameters were obtained. For example, was the carbonate\ncontent of each sample separated using physicochemical treatments in the laboratory (i.e., were\nsamples decarbonated) and were the mineralogical properties of the residue subsequently analysed?\nAlternatively, was the carbonate content subtracted by theoretical calculations? The method used\nshould be more clearly explained. The former method would probably also allow for the identification\nof clay and magnetic mineral phases by X ray diffraction, which would help to support (or refute)\nsome of the authors’ interpretations.\n\nOur CFB estimates are from the high resolution wt.% CaCO record of Piedrahita et al. (2023), from\n3\nwhich we normalize magnetic parameters using mass fractions without CaCO . We now explain this\n3\nin the materials and methods section with an example of bulk-rock (BR) and CFB normalizations of\nM (lines 568-577).\nrs\n\nComment 2: Why all magnetic minerals are interpreted to be detrital and why some (e.g., magnetite)\nare not (partly) biogenic or authigenic should also be more clearly explained. In addition, pigmentary\nhaematite in red bed sequences is usually secondary and probably formed in the order of 105-106 years\nafter deposition (Kodama, 2012). Could this affect interpretation of shorter hydroclimate variations?\n\nWe have added a section “Origin of Contessa Road magnetic minerals” to address this. Initially, we\ndiscuss the hypothesis of Channell et al. (1982), who suggested that haematite formed at the expense\nof goethite during oxic periods. In contrast, periods with reducing settings would have inhibited\nmaghemite and haematite formation. These variations are not compatible with the LPEE Contessa\nRoad magnetic mineral record. Furthermore, we now indicate that sedimentary and fossil evidence\nreveal reduced organic inputs to the post K/Pg Contessa Road record (Coccioni et al., 2019), and\ninsignificant reductive diagenesis via organic matter degradation and microbial oxidant consumption\n(e.g., Roberts, 2015). Lack of reductive diagenesis also contrasts with the hypothesis of Abrajevitch et\nal. (2015), who interpreted that oxic diagenesis following a period of reducing conditions generated\nhaematite at the expense of detrital Fe oxyhydroxides. This assumption also implies continental Fe\noxyhydroxide transformation (Jiang et al., 2022). Combined evidence indicates that the western Tethys\nhad dry hydroclimates, which is compatible with haematite rather than goethite formation. Hence, we\nsuggest that most haematite and maghemite is detrital. Following the reviewer’s suggestion, we also\ndiscuss the possibility of haematite formation via post-depositional alteration of Fe-rich minerals\n(Kodama, 2012). We now clarify that this mechanism is not compatible with compositional\nenrichments of haematite and lowered magnetic mineral concentrations at Contessa Road. This\nsupports our interpretation of the detrital origin of haematite (lines 230-288).\nScaglia Rossa carbonates is restricted to central ridges in FORC diagrams and IRM unmixing\ncomponents with ~20-50 mT coercivities. These features can also be related to detrital maghemite/\nmagnetite. Furthermore, conclusive evidence for biogenic magnetite occurrences at Contessa Road\nhas not been presented (Liu et al., 2023). Even considering this, we generated different IRM unmixing\nassessments that include and exclude biogenic magnetite components. These analyses reveal that\ndetrital magnetic mineral contents would have been larger than biogenic magnetite contents (lines 272-\n288, S22- S49).\n\nComment 3: From the very beginning (line 108) the authors state that the variations in the\ncarbonate/clay ratio throughout the succession record variations in the rate of carbonate deposition or\ndissolution, later favouring dissolution as the main controlling factor (line 227). The line of reasoning\nshould be more clearly explained. Initially, they ignore that clay (and magnetic mineral) content could\nalso vary as a consequence of changes in the rate of terrigenous sediment input over time (i.e.,\nterrigenous dilution). This possibility is only considered later in the manuscript, and restricted to the\ninterpretation of the EETZ (lines 241-248). In order to address these issues further, the authors could\nobtain some terrigenous input proxies (e.g., Ti/Al and Zr/Al ratios) throughout the succession.\n\nThanks. We have added multiple lines of evidence to indicate that terrigenous dilution is not significant\nat Contessa Road. Initially, we indicate that Contessa Road marls have low planktonic and high\nagglutinated foraminifera contents, with either reduced or similar sedimentation rates compared to\nlimestones. These features indicate that CaCO deposition/dissolution was the prevailing\n3\nsedimentation mechanism at Contessa Road. Furthermore, PC2 analyses confirm that enhanced\nall\ndetrital inputs did not cause terrigenous dilution (lines 127-133, 311-328; Fig. 6, S14).\nWe have not used Ti/Al and Zr/Al ratios here because Contessa Road Al signals are below the core\nscanner detection limit. Hence, Al is not presented. Other available data ratios are not estimated\nbecause our data are not transformed into absolute concentrations. We rather present semi-quantitative\nXRF data. When ratios are calculated, absolute concentrations and semi-quantitative data may produce\ndifferent results. This is illustrated in the image below with unpublished data from Miocene eastern\nPacific sediments. Semi-quantitative XRF data (counts) and absolute concentrations (ppm) correlate\nwell for K and Ti. However, when Ti/K ratios are estimated, result for the two data sets differ. We,\ntherefore, avoid this kind of normalization and indicate that terrigenous dilution is restricted at\nContessa Road from published foraminifera assemblages and sedimentation rate data (Galeotti et al.,\n2023; Piedrahita et al., 2023), and with new the new PC2 analyses.\nall\n2\n50000 16500\n45000\n40000 16000\n35000\n30000 15500\n25000\n20000 15000\n15000\n10000 14500\n5000\n0 14000\n13.3 13.4 13.5 13.6 13.7 13.8 13.9\nComment 4: PCA2all scores are used as a proxy of variations in the rates of detrital input and CaCO\n3\ndissolution over time. However, each of the factors identified by the PCA analysis should represent\nonly one controlling mechanism, not two (i.e., PCA2all should represent variations in either detrital\ninput or CaCO3 dissolution, but not in both). Furthermore, both Ca (i.e., carbonates) and magnetic\nparameters show negative loadings in PCA2all, suggesting that they are related. Consequently, why\ndo the authors relate negative PCA2all values only with detrital supplies in Fig. 6e? Why does Ca\nincrease in EETZ? In addition, matrices of all PCA analyses (tables with loadings between variables\nand principal components) should also be provided in the supplementary material in order to know\nwhich variables are relevant to each component and their statistical significance.\n\nFollowing this suggestion, we have added correlation matrices for all PCAs. We also better explain\nthe PC2 significance. PC2 contains negative loadings for Ca and CFB magnetic concentration\nall all\nparameters, and positive loadings for detrital elements that anti-correlate with Ca. These patterns\nindicate that positive scores are related to enhanced CaCO dissolution and reduced magnetic mineral\n3\ninputs, while negative scores reveal enhanced CaCO preservation and increased magnetic mineral\n3\ninputs. Most of the PC2 record has values close to 0, which indicates reduced CaCO dissolution\nall 3\naccompanied by minimal detrital mineral inputs. These results validate previous evidence that CaCO\n3\n3\nstnuoc mpp\nK\nAge (Ma)\nK (counts) K (ppm)\n50000 5100\n4900\n45000\n4700\n40000\n4500\n35000 4300\n4100\n30000\n3900\n25000\n3700\n20000 3500\n13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9\nstnuoc mpp\nTi\nAge (Ma\nTi (counts) Ti (ppm)\n1.8 0.31\n1.6 0.305\n1.4\n0.3\n1.2\n1 0.295\n0.8 0.29\n0.6 0.285\n0.4\n0.2 0.28\n0 0.275\n13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9\nstnuoc/stnuoc\nmpp/mpp\n50000\n45000\n40000\n35000\n30000\n25000\n20000\n15000\n10000\n5000\n0\n14000 14500 15000 15500 16000 16500\nTi/K\nAge (Ma\nTi/K (counts/counts) Ti/K (ppm/ppm)\nstnuoc\nK\nppm\n50000\n45000\n40000\n35000\n30000\n25000\n20000\n4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000\nstnuoc\nTi\nppm\n1.8\n1.7\n1.6\n1.5\n1.4\n1.3\n1.2\n1.1\n1\n0.9\n0.8\n0.275 0.28 0.285 0.29 0.295 0.3 0.305 0.31\nstnuoc/stnuoc\nTi/K\nppm/ppm\ndeposition/dissolution were the main sedimentation drivers (Galeotti et al., 2010). Positive PC2\nall\npeaks generally coincide with positive PC1 and PC1 peaks, which confirms that positive PC2\ndis all all\nscores reveal enhanced CaCO dissolution. Alternatively, well-defined negative peaks only occur\n3\nacross the EETZ. This interval also contains positive peaks associated with CaCO dissolution;\n3\nhowever, negative PC2 peaks in the EETZ coincide with high CaCO contents (we added a new Fig.\nall 3\nS14 to enable identification of this relationship). This PC2 pattern confirms that, although detrital\nall\nminerals were constantly present during deposition, high detrital inputs did not cause terrigenous\ndilution (lines 311-328, Fig. S6, S13, S14).\n\nComment 5: Regarding spectral analysis and orbital forcing, it should be emphasized that the power\nspectra are rather noisy and spiky (Fig. 7), meaning that there are significant periodicities that the\nauthors seem to ignore. The original data used for the spectral analysis should be provided in the\nsupplementary material in order to allow replication. In addition, the authors are perhaps too optimistic\nwhen stating that “the coincidence between PC1dis short eccentricity and ZB18a astronomical solution\nindicates that the filtered PC1dis precession signal is a good indicator of precession-related light\ncarbon concentration/CaCO3 dissolution variations” (lines 281-283). The fact that the filtered PC1dis\neccentricity signal is similar to the eccentricity solution in ZB18 does not necessarily mean that the\nprecession signal also has to match. In fact, the amplitude of precession cycles does not fit that of\neccentricity cycles. In order to reinforce their interpretation, the authors should try to correlate their\nprecession cycles with those from other records. Although there are no precession solutions for the\nstudied time interval (lines 279-280), some studies carried out in partly coeval successions have\nidentified the record of early Eocene precession cycles (e.g., Westerhold et al., 2007, 2017). My\nimpression is that the filtered HIRM-CFB precession signal is probably not reliable, as it displays only\nfive precession cycles in the PETM (Fig. 8), which are too few for the estimated 170-200 ky duration\nof this event (the 9.5 precession cycles obtained in the filtered PC1dis signal seem to be more\nreasonable). Consequently, the discussion about the environmental significance of the differences\nbetween the filtered PC1dis and HIRM-CFB precession signals seems to be too speculative (lines 285-\n293). Taking into account that the filtered HIRM-CFB eccentricity signal also departs from the filtered\nPC1dis and ZB18 eccentricity signals, my impression is that the HIRM-CFB record is not suitable for\nfiltering. This would mean that the discussion about the filtered HIRM-CFB eccentricity signal is also\nspeculative (lines 298-314).\n\nThanks. We now present results from two spectral analysis techniques (periodograms and multi-taper\nmethod). Short eccentricity and precession are present within PC1 and HIRM-CFB (Fig. 7, S15), as\ndis\nvalidated by squared coherency spectra (Fig. 7) and explained in the text. Following this suggestion,\nwe also clarified that our power spectra have statistically significant spectral peaks that do not\ncorrespond to short eccentricity or precession. Some peaks may be associated with obliquity; however,\nthey do not appear consistently in all intervals, so we have not studied them in detail (lines 376-419).\nTo address reviewer concerns about the number of precession cycles, we re-filtered our signals with a\nbandpass filter of 0.044 ± 0.010 (1σ) cycles kyr−1 (~18-29 kyr) for precession, which indicates the\nsame number of cycles in the PC1 and HIRM-CFB records (Fig. 8) and confirms that the HIRM-\ndis\nCFB records precession. We do not compare our precession signals with other records for several\nreasons. There is not a conclusive number of precession cycles for the LPEE; hence it is not clear if\nsome astrochronological age models miss some precession cycles. Some age models are floating\nchronologies assuming constant 21 kyr durations for each precession cycle (e.g., Westerhold et al.,\n2007), while others are based on tuning to different astronomical solutions (e.g., La2004, La2010a,\nZb18a). These contrasting methods produce age models with different numbers of precession cycles,\nwhich hinders stratigraphic correlation. We are confident that our recalculated filtering assessments\n4\nand new power spectra reliably indicate precession signatures within the HIRM-CFB record (Fig. 7,\n8, S15). To allow replication of our results, all datasets will be available in the FigShare data repository\nthat Nature Communications suggest to use.\nTo clarify the significance of the filtered PC1 precession signal, we explain temperature and light\ndis\ncarbon concentration controls on biogenic CaCO sedimentation (Littler et al., 2014; Zeebe et al.,\n3\n2017). Higher temperatures/light carbon concentrations promote CaCO dissolution, which is\n3\nindicated by PC1 precession maxima. Similarities between amplitude modulation patterns of the\ndis\nPC1 precession signal and the filtered PC1 short eccentricity signal (Fig. S16) confirm that this\ndis dis\nprecession signal can be used as an indicator of temperature/light carbon concentration controls on\nCaCO dissolution. Following this suggestion and comment 6, we now explain that the opposite\n3\nrelationship between PC1 and HIRM-CFB precession signals indicate temperature control on\ndis\nhaematite formation and western Tethyan hydroclimates. This helped us to relate insolation and\nhaematite formation, which allowed identification of dry/wet periodic variations that enhanced and\ninhibited haematite production, respectively. This pattern is similar to that described for well-studied\nNeogene-Quaternary Mediterranean sediments, which signals that proto-Mediterranean and\nMediterranean hydroclimates have been driven by orbitally-forced dry/wet cycles (Bosmans et al.,\n2015; Rohling et al., 2015; Kutzbach et al., 2020) (lines 330-432). We explain the short eccentricity\nsignal in response to Comment 6 below.\n\nComment 6: In this work, the authors seem to misunderstand the relationship between eccentricity\ncycles and seasonal contrast. More specifically, they suggest that eccentricity maxima produce\nenhanced seasonal contrast (lines 314-315 and 326-327). In reality, seasonal contrast is determined by\nprecession cycles, not by eccentricity cycles. Precessional variations in insolation determine the\ntemperature contrast between summer and winter, along with the consequent annual distribution of\nprecipitation, storminess, organic productivity, etc. In the northern hemisphere, precessional\nseasonality is minimized (mild summers and winters) when boreal summers occur at aphelion and\nwinters at perihelion (i.e., high precession index), but seasonality increases (warmer summers and\ncooler winters) when summers occur at perihelion and winters at aphelion (i.e., low precession index).\nPeriodic variations in the eccentricity of the Earth’s orbit modulate the amplitude of precession-driven\nseasonality. Thus, at eccentricity maxima both maximized and minimized seasonality occur during\none single precession cycle. Conversely, during eccentricity minima seasonality remains similar (i.e.,\nintermediate) regardless of the precession index. This should be taken into account in the discussion\nin lines 315-337. In this regard, it is very unlikely that “eccentricity minima periods … with relatively\nstable seasonal contrast … produced wetter conditions … which may have enhanced fluvial haematite\ntransport to Contessa” (lines 318-321). Fluvial sediment input increases with seasonality, reaching\nmaximum values under dry subhumid precipitation regimes with three to five wet months per year\n(Cecil and Dulong, 2003). These conditions generally occur at eccentricity maxima and low precession\nindex. Similarly, rather than the minimum eccentricity configurations suggested in lines 329-333,\n“amplified seasonal precipitation and intermittent extreme precipitation events” are more likely during\nhigh seasonality conditions developed at maximum eccentricity and low precession index.\n\nThanks. We reworked our interpretations by explaining the influence of precession driven insolation\nvariability on HIRM-CFB and indicated that short eccentricity maxima amplified the precession\nexpression, which enhanced seasonal contrast. We suggest that these conditions, and short-lived\ncarbon cycle perturbations, intensified the hydrological cycle and produced orbitally paced dry\nconditions in short eccentricity timescales (lines 330-432).\nAlthough some authors have suggested authigenic magnetic mineral formation in Scaglia Rossa\ncarbonates (Channell et al., 1982; Abrajevitch et al., 2015; Coccioni et al., 2019), they also indicate\n5\nthat detrital magnetic minerals occur within aeolian dust fractions in this unit. Maghemite/haematite\nproduction occurs under dry conditions (Jiang et al., 2022); taking into account the preferential detrital\norigin of Contessa Road magnetic minerals (this study), and the required conditions to enhance fluvial\ntransport (see reviewer comment ), we, as suggested by previous studies, assume that Contessa Road\nmagnetic minerals were mainly transported by wind (Coccioni et al., 2019). This requires re-\ninterpretation of intervals in which the HIRM-CFB short eccentricity signal is out-of-phase with\nrespect to the ZB18a astronomical solution (Zeebe and Lourens, 2019). We have added the long\neccentricity signal of ZB18a and find that some out-of-phase HIRM-CFB short eccentricity cycles\nappear during long eccentricity minima. We use this relationship to suggest that short eccentricity\npaced dry hydroclimates occurred only by a combination of enhanced seasonal contrast (partially\nmodulated by long eccentricity maxima) and global warming. Nevertheless, these processes cannot\nexplain why some short eccentricity cycles match ZB18a during intervals without short-lived carbon\ncycle perturbations. We also suggest that HIRM-CFB was not sensitive to short eccentricity when the\nprecession-related seasonal contrast was reduced by long eccentricity forcing. However, this process\ncannot explain the short eccentricity variability through the whole record. We discard the influence of\nhaematite transport from far regions and post-depositional magnetic mineral alteration as causes for\nthe out-of-phase HIRM-CFB short eccentricity cycles with respect to Zb18a. We also indicate that\nprecession signal clipping may contribute to the HIRM-CFB short eccentricity signal development\n(e.g., Walters et al., 2023). However, we have no evidence to conclusively determine the significance\nof out-of-phase HIRM-CFB short eccentricity cycles; hence, we focus on the dry conditions promoted\nby enhanced seasonal contrast and short-lived carbon cycle perturbations (lines 388-432).\n\nComment 7: There are too many acronyms in the manuscript, making it difficult to read.\n\nWe removed several acronyms and only kept two new abbreviations that are not used in previous\nstudies, the early Eocene terrigenous zone (EETZ) and the early Eocene low magnetization zone\n(EELMZ). For convenience, we produced a table that includes all acronyms (Table S1).\n\nComment 8: Both haematite (text) and hematite (Fig. 5) are used. Please homogenize.\n\nThanks, we now only use haematite.\n\nComment 9: How stratigraphic thickness (Fig. S1) was transformed into age/time (e.g., Fig. 2) should\nbe explained (age model).\n\nThe Contessa Road age model was produced by Piedrahita et al. (2023). We now explain that the\nastrochronological age model was generated via short eccentricity tuning of bulk rock-χ and δ13C to\nthe ZB18a astronomical solution. We used the same samples as Piedrahita et al. (2023), so all of our\nrecords are presented in terms of age (lines 497-532).\n\nComment 10: Line 61: “short-lived (~200 kyr) carbon cycle perturbations”. Maybe <200 kyr is more\nappropriate, as most events were significantly shorter than 200 ky and even the PETM was also\nprobably shorter (170-200 kyr).\n\nThanks. We have made this change (line 71).\n\nComment 11: Lines 73-79: the wet-wetter and dry-drier evolutions may be too simplistic.\nHydroclimates changed throughout some hyperthermal events.\n\nWe now explain the mechanisms that controlled wet-wetter and dry-drier hydroclimate responses and\nindicate that some continental sediment records reveal contrasting hydroclimate responses between\nthe PETM and other short-lived carbon cycle perturbations (e.g., dry-becomes-wetter) (lines 98-121).\n\nComment 12: Lines 138-139: Most of the other marl levels do seem to coincide with CIEs. In this\nregard, why was the J event (Fig. S1) not displayed in the other figures? Would it not fit the model\nand coincide with the long eccentricity maximum at ca. 53.2 Ma in Fig. S2?\n\nThe J event does not have a well-defined CIE at Contessa Road (Piedrahita et al., 2023). Therefore,\nwe have not labelled it in our records. This is now explained (lines 513-515).\n\nComment 13: Line 149: The X drop at 300ºC does not occur in EETZ and ETM2, and is rather subtle\nin pre-ETM2, meaning that it is clearly visible in only 50% of the cases. Furthermore, the Curie\ntemperature of some iron sulphides (e.g., greigite) is also approximately 300ºC. The potential\noccurrence (or absence) of sulphides should be discussed.\n\nThanks. We now include new χ-T analyses, in which maghemite transitions are evident for 8 samples.\nThis suggests that most Contessa Road intervals contain maghemite (lines 169-192, Fig. 3, S5, S6).\nWe now point out that first-order reversal curves from Contessa Road do not contain evidence of\nmagnetic iron sulphides (Coccioni et al., 2019) (lines 249-252).\n\nComment 14: Lines 151-152: If only two out of five cases show the drop in X at 615-630ºC, why is\nthe interpretation extrapolated to “almost ALL Contessa Road samples”?\n\nThanks. We modified the text to clarify that this transition is not evident in most samples. However, a\n~615-630°C χ drop in an ETM 2 sample is useful for indicating that most LPEE Contessa Road\nsamples contain maghemite (lines 169-192, Fig. 3, S5, S6).\n\nComment 15: Line 186: Fig. 5b, and not 6b.\n\nThanks. We made this change (line 206).\n\nComment 16: Lines 210-215: Unclear line of reasoning, please elaborate on this.\n\nThanks. We rearranged the text to indicate that increased magnetic mineral contents potentially\nproduce more haematite because more oxidizable material is available (lines 254-261).\n\nComment 17: Line 220: “Despite the terrigenous origin” (singular).\n\nThanks. We made this change (line 291).\n\nComment 18: Lines 240-241: All marl layers coincide with positive PC2all positive peaks, not only\nthe so-called “dissolution horizons” (see also comment on lines 138-139).\n\nThanks. We rearranged the text and refer to marly layers (line 321-322).\n\nComment 19: Line 263: “deduced from” instead of “indicated”.\n\nWe re-wrote this sentence “Specifically, orbital controls on Contessa Road sedimentation are indicated\nby enhanced CaCO dissolution during long eccentricity, short eccentricity, and precession maxima”\n3\n(lines 336-338).\n\nComment 20: Lines 288-293: Unclear line of reasoning. Even if this discussion were pertinent (see\ngeneral comment 5), increased light C and haematite concentrations could also result from increased\nfresh water (i.e., fluvial) supplies, which would suggest that terrigenous dilution was the main\ncontrolling mechanism for the compositional variations observed throughout the succession, rather\nthan variations in carbonate deposition/dissolution (see general comment 3).\n\nAs the reviewer has indicated, this comment contains elements from previous suggestions. We now\nclarify that LPEE Contessa Road terrigenous dilution was insignificant (see comments 3 and 4) and\nexplain the hydroclimate conditions that HIRM-CFB precession signals reveal (see comment 5).\n\nComment 21: Lines 343-345: Unclear, please rephrase.\n\nThanks. We now indicate that haematite content drops coincide with haematite enrichments within\nmagnetic mineral fractions. We added a sentence to explain the paleoclimatic significance of this\npattern (lines 437-444).\n\nComment 22: Line 367: Fig. 9, rather than 8.\n\nThanks. We made this change across the whole paragraph (lines 452, 458, 459).\n\nComment 23: Line 378: The 27-kyr recovery of the PETM seems to be subjective, as peak\nhyperthermal conditions may have been reached significantly earlier according to Fig. 9a.\n\nWe now explain how we estimated this interval. Hyperthermal recovery timescales, which are marked\nby irreversible δ13C transitions from more negative to more positive δ13C values, coincide with\nhydroclimate recovery periods, as recognized by irreversible negative to positive PC1 transitions.\narid\nThis constrains a ~27-kyr hydroclimate recovery period for the PETM (lines 467-485).\n\nComment 24: Lines 403 and 407: Remove “depth” and “depths”, respectively.\n\nWe now indicate that 0 m depth at Contessa Road occurs at the K/Pg boundary. Positive depths\ncorrespond to younger strata; hence, we keep depth and depths (lines 504, 509).\n\nComment 25: Line 416. Use “They” instead of “Piedrahita13”.\n\nWe rewrote this section and removed this sentence (line 498-524).\n\nComment 26: Line 495: “Thin”, rather than “thick”?\n\nThanks. We replaced this word with “cross” (line 611).\n\nComment 27: Line 677: “heating and cooling” … “red and blue”.\n\nThanks. We made this change (Fig. 3).\n\nComment 28: Suppl. lines 13-15: Visually it seems that Sr maxima occur at hyperthermals.\n\nCorrect. However, Sr does not consistently co-vary with Ca or detrital element patterns. We now clarify\nthis (lines S11-S20).\n\nComment 29: Suppl. Lines 55-56: Goethite is a high coercivity mineral. Does this sentence refer to\nhaematite content?\n\nThanks. We now clarify that high coercivity minerals at Contessa Road are mainly haematite. We also\nindicate that goethite is only present in the EELMZ (lines S28-S30, S66-S72).\n\nComment 30: Suppl. line 58: EDXS show elemental occurrences/abundances, but not mineralogy. It\ncannot be concluded that “clay minerals are compositionally similar across all intervals”.\n\nThanks. The short supplementary information section that describes SEM EDXS data repeated\nmaterial from the main text (lines 211-216), so we removed it while retaining Fig. S7.\n\nComment 31: Suppl. line 69: This section is highly speculative and does not reach any conclusion.\nSuperfluous?\n\nFollowing the reviewer’s suggestion, we clarified this section. This discussion suggests that goethite\nin the EELMZ may indicate wet conditions following the ETM 3. However, we cannot exclude\nsediment bleaching by depositional infiltration of reducing waters, as described by Lowrie et al. (1990)\nfor other Contessa Road intervals. We agree that this section is speculative, but we kept it to note that\nthe EELMZ differs from the rest of the LPEE Contessa Road record (lines S75-S106).\n\nComment 32: Suppl. lines 80-81: Productivity can increase without higher terrigenous input (e.g.,\nupwelling).\n\nThanks. We have rephrased this part of the text to indicate that organic matter degradation is related\nto increased productivity (Roberts, 2015). We indicate that such conditions, which promote reductive\ndiagenetic periods, were unlikely at Contessa Road during the LPEE (lines S81-S88).\n\nComment 33: Fig. S4: What do low coercitivy components represent and why are magnetite and\nmaghemite not distinguished? Why is goethite not represented in EELMZ? Mean coercitivity values\nand dispersion could be included.\n\nWe have added B and DP values (Fig. S10). We also indicated that low coercivity components (left\nc\npanel in Fig. S10) mainly indicate detrital magnetite and maghemite. These minerals are not separated\nin different components because their coercivities are very similar (lines S40-S43). The EELMZ has\na similar IRM distribution compared to the other samples. So, we note that high coercivity components\nare mainly related to haematite except for the EELMZ, which has goethite. Our new IRM unmixing\nresults require major changes in the figures (see lines S23-S49, Fig. S10, S11).\n\nReviewer #2 (Remarks to the Author)\n\nComment 1: The magnetic fraction is primarily composed of maghemite and pigmentary hematite,\nboth of which are primarily detrital. This is argued on the basis of Figure 3, which shows temperature-\ndependence of magnetic susceptibility and 3-component thermal demagnetisation diagrams for\nselected samples. It is argued that “almost all” Contessa Road samples show evidence of maghemite\nas a fall in MS around 300C (maghemite converting to hematite) and/or a fall in MS around 625C\n(maghemite Curie temperature). On the basis of the six samples shown, I can see these features in only\nthree (PETM initial phase, PETM recovery phase, and EELMZ, which is subsequently discussed only\nin the supplementary information). Meanwhile, it is mentioned that two of the samples (PETM\nrecovery and Pre-ETM 2) show evidence for magnetite, which I agree with. I would also interpret\nEETZ, ETM2 and EELMZ as potentially indicating magnetite. It may be that all or almost all of the\nsamples not shown here contain the two features associated with maghemite – if this is the basis for\nthe statement, it should be explicitly stated and perhaps quantified (what percentage of the samples\nshow these features).\n\nThanks. We now include new χ-T analyses and plots with and without cooling curves, which makes it\npossible to assess maghemite transitions. We identified well-developed ~300°C χ drops in 6 of 10\nsamples (Fig. S6a, b, c, g, h and i). A further sample has a slight transition that may be due to\nmaghemite (Fig. S6j) and another has a ~615-630°C χ drop that can be associated with maghemite.\nSo, 8 of 10 samples contain this mineral. We clearly identify magnetite transitions in only three\nsamples (Fig. S6c, e, g). We detail these observations to indicate that maghemite is the predominant\nlow coercivity magnetic mineral at Contessa Road (lines 169-192; Fig. 3, S5, S6).\n\nComment 2: The 3-component thermal demagnetisation is said to show a pigmentary hematite\nsignature (gradual demagnetisation to 675C), with the exception of the EELMZ. I found this\nconvincing. It seems to me there is also some evidence of magnetite in PETM recovery and EETZ.\nI note that previous publications on the same outcrop, as well as on other outcrops of broadly the\nsame formation, have also inferred a mixture of hematite, magnetite and maghemite. However, much\nmore weight has previously been given to the contribution of both biogenic and detrital magnetite in\nlower parts of this succession (Abrejevitch et al., 2015; Coccioni et al., 2019), both of which are\nlargely dismissed here. A previous study of this succession inferred that the hematite is primarily early\npost-depositional and authigenic, a possibility which is not discussed here (Abrejevitch et al., 2015).\nThe maghemite could also be pre- or post-depositional oxidation of either detrital or biogenic\nmagnetite, which is again not considered here.\nOverall, I think that given the importance of the detrital origin and mineralogy of the magnetic fraction\nto the argument in later parts of the paper, more could be done here to discuss possible other\ninterpretations of the magnetic results and explain why they are not preferred. The supplementary\nmaterial makes reference to IRM unmixing curves. It is interesting that these curves show fewer\ncomponents than similar analyses for older parts of the Contessa Road section (Abrejevitch et al.,\n2015; Coccioni et al., 2019). These data could potentially help to test the argument that the soft\ncomponent is primarily detrital rather than biogenic.\n\nWe now include a new section “Origin of Contessa Road magnetic minerals”, in which we discuss the\nhypothesis that haematite is a post-depositional alteration product at Contessa Road. Channell et al.\n(1982) suggested that oxic periods produced haematite at the expense of goethite. In contrast, reducing\nperiods inhibited maghemite and haematite formation. This interpretation is not consistent with the\nEELMZ carbonates, which contain maghemite and goethite. Furthermore, the Channell et al. (1982)\nhypothesis requires reductive diagenesis activity, which is not evident according to sedimentary and\nfossil assemblages that indicate insignificant organic inputs to Contessa Road after the K/Pg event\n(Coccioni et al., 2019), and unlikely organic matter degradation and microbial oxidant consumption\n(e.g., Roberts, 2015). This interpretation is validated by first-order reversal curve diagrams that do not\ncontain evidence of iron sulphides (Coccioni et al., 2019) (lines 230-270).\nAbrajevitch et al. (2015) indicated that oxic diagenesis, after a period of reducing diagenesis, formed\nhaematite at the expense of detrital Fe oxyhydroxides. Reductive diagenesis is unlikely in the studied\ninterval. This interpretation, thus, implies that unstable Fe oxyhydroxides were transformed into other\nminerals in continental environments (Jiang et al., 2022). Wet and cold conditions transform Fe\noxyhydroxides into goethite, which is incompatible with proxy and model data that reveal dry LPEE\nwestern Tethyan hydroclimates. These patterns enable us to interpret that haematite and maghemite at\nContessa Road are mainly detrital. We also explore the possibility that haematite formed by post-\ndepositional alteration of Fe-rich minerals. However, this magnetic mineral formation mechanism is\nnot indicated by long-term magnetic concentration reductions and haematite compositional\nenrichments at Contessa Road (lines 230-270).\nFinally, FORC diagram central ridges and IRM unmixing components with ~20-50 mT coercivities\nhave been used to indicate biogenic magnetite in Scaglia Rossa Formation K/Pg and Paleogene\nrecords. However, this evidence is inconclusive of biogenic magnetite as these FORC and IRM\nunmixing features can also be associated with detrital maghemite/magnetite (e.g., Liu et al., 2023). We\nalso performed new IRM unmixing assessments that include biogenic magnetite components and\nfound that if biogenic magnetite is present, its proportion in magnetic mineral assemblages is smaller\nthan detrital magnetite/maghemite (lines 272-288, S22-S49; Fig, S10, S11, S12).\n\nComment 3: Absolute concentration of both high and low-coercivity components with respect to\noverall non-carbonate content shows a long-term decrease, but hematite:maghemite ratio shows a\nlong-term increase. This seems convincingly demonstrated by Figure 5. Hematite:maghemite ratio\nalso increases during some of the hyperthermals and short carbon-cycle perturbations.\nAgain, this is convincingly demonstrated by Figure 5 and Figure 9, although there are other short-lived\nincreases of similar magnitude which do not coincide with carbon-cycle perturbations.\n\nThanks. We now indicate that some intervals that do not coincide with short-lived carbon cycle\nperturbations had dry conditions. We attribute this pattern to larger long-term warming controls on\nproto-Mediterranean hydroclimate variability compared to short-lived carbon cycle perturbations.\nThis interpretation indicates that younger (earliest Eocene) strata record drier conditions and explains why\nsome intervals without short-lived carbon cycle perturbations record significant dry (lines 434-465).\n\nComment 4: Reduced overall magnetic fraction and increased hematite proportion is inferred to\nindicate aridity. The argument made here is that aridity in the source area led to reduced ferrihydrite\nformation, thus reducing the possibility of subsequent formation of maghemite and then hematite.\nHowever, the aridity promoted the formation of hematite from any ferrihydrite or maghemite that was\nformed, thus producing a situation where both magnetic components were reduced in absolute terms\nbut the ratio of hematite to maghemite increased. This makes a number of assumptions: 1. that the\nmagnetic signal is controlled almost entirely by input of detrital maghemite and hematite. 2. That the\ndetrital maghemite comes almost entirely from ferrihydrite oxidation rather than oxidation of detrital\nor pedogenic magnetite. 3. That the signal is a proxy for source area soil conditions. 1 and 2 are\ndiscussed above. The third assumption leaves out the possibility of post-depositional reductive\ndissolution in the sediments, which would similarly both reduce the overall magnetic content and\nincrease the hematite/maghemite ratio, due to the lower stability of maghemite in these conditions. A\nvariation on this (with the dissolution occurring prior to deposition) is proposed by Abrejevitch et al.\n(2015) for a similar (though more extreme) set of magnetic features in the Gubbio section below the\nK-Pg boundary. The hypothesis of source area aridity is plausible, but as with the identification of the\nminerals, I think it is important to discuss other possibilities and explain why this one is preferred.\n\nThanks. (1) Magnetic minerals at Contessa Road are now discussed in relation to their mainly detrital\norigins in a new discussion section (see comment 2). (2) We now indicate in a new discussion section\n(see comment 2) that magnetite to maghemite/hematite transformation was not significant at Contessa\nRoad. Also, we indicate maghemite prevalence over magnetite (see comment 1), which indicates that\nmagnetite may have not been as common as maghemite and haematite in detrital source areas for\nContessa Road. Considering this aspect and the detrital origin of maghemite and haematite (see\ncomment 2), we can assume that ferrihydrite occurrences in western Tethyan continental areas\npreceded maghemite and haematite formation. Dry conditions required for ferrihydrite transformation\ninto haematite coincide with proxy and model data that reveal dry LPEE western Tethyan conditions.\n(3) Yes, reductive diagenesis can cause preferential dissolution of low coercivity magnetic minerals\nover haematite. We now indicate that sedimentary and fossil assemblages at Contessa Road suggest\nreduced organic sediment inputs after the K/Pg boundary that inhibited reductive diagenesis via\norganic matter degradation and microbial oxidant consumption (Roberts, 2015). First-order reversal\ncurve diagrams from Contessa Road do not contain evidence of magnetic iron sulphides, which also\nsupports the absence of reductive diagenesis (Coccioni et al., 2019) (lines 245-252) and our\ninterpretations of hydroclimate controls on Contessa Road magnetic mineral assemblages.\n\nComment 5: Interpretation of Principal Components.\nSeveral parts of the argument are based on the interpretation of principal components. PC1(dis) is\ninterpreted as primarily representing carbonate dissolution. I see no issue with this, and this\ninterpretation is backed up by previous studies of this section (e.g. Galeotti et al., 2010). PC1(all) is\nalso interpreted as representing carbonate dissolution. This is more interesting, as the magnetic\nconcentration parameters relative to detrital input are all positively loaded on this PC, suggesting that\nduring periods of reduced net carbonate sedimentation, either detrital sediments became more\nmagnetic (perhaps due to increased ferrihydrite -> maghemite -> hematite and/or increased\nproduction of pedogenic magnetite) or there was an alternate process which increased the magnetic\nmineral fraction relative to the detrital fraction as a whole. This is similar to the pattern seen in\nCoccioni et al (2019), which they interpreted as increased biogenic magnetite production by\nmagnetotactic bacteria due to high nutrient levels. Given the importance of Bcr and S-ratio to the later\narguments about aridity, it would be interesting to see a PCA(all) that also included these parameters.\nThe interpretation of PC2(all) is interesting. In L242-245 it is argued that the fact that CFB magnetic\nmineral parameters and Ca both show negative loadings on this PC indicates that there was also\nsignificant terrigenous input during times of reduced carbonate dissolution. However, the elements\nidentified as proxies for terrigenous input are positively loaded on this PC, i.e. anticorrelated to the\nmagnetic parameters and Ca, so the interpretation of this as representing increased terrigenous input\nseems unsupported. What this seems to me to indicate is that the underlying process was something\nthat resulted in reduced terrigenous/increased carbonate input but simultaneously in magnetic\nenhancement of the non-carbonate fraction. I note that the loadings of the magnetic parameters on\nthis PC are quite low, and the discussion does not return to PC2(all) again, so perhaps a detailed\nconsideration is not so important. However, I do think the current interpretation should be revised.\nThe most important PC interpretation from the point of view of the main arguments of the paper is\nPC1(arid), which represents the anticorrelation between overall magnetic concentration (including\nabsolute carbonate-free concentrations of all coercivity components) and proportion of the magnetic\nfraction represented by harder minerals (implicitly hematite). This is the basis of the argument\ndiscussed above in point 4, and so I will not discuss it further here.\n\nAs suggested, we performed PCA analysis including B and S-ratio (see below and compared to\ncr\noriginal analyses). B and S-ratio addition does not change significantly the CFB rock magnetic\ncr\nconcentration and XRF loadings. PC1 and PC2 scores are also similar between analyses, which\nindicates that B and S-ratio are not important in that PCA. This is likely a result of the reduced\ncr\ninfluence of two parameters compared to six records that represent CaCO dissolution (Ca reductions\n3\nand Fe, Si, Ti, Rb, and Zr increases reveal CaCO dissolution) and nine CFB magnetic concentration\n3\nrecords. XRF detrital elements in pelagic carbonates do not represent terrigenous inputs. Instead, they\ncharacterize Ca reductions (Zachos et al., 2005; Westerhold et al., 2007; Zachos et al., 2010; Littler et\nal., 2014; Piedrahita et al., 2022). This is confirmed at Contessa Road by unchanged/reduced\nsedimentation rates of marly layers compared to limestones (Fig. S2; Galeotti et al., 2022; Piedrahita\net al., 2023). Considering similarities between the requested PCA analysis and our original assessment,\nwe retain our initial analysis and better explain the significance of PC2 (lines 311-328).\nall\nPC2 has positive loadings for detrital elements that anti-correlate with negative Ca loadings and\nall\ncorrelate poorly with CFB magnetic concentration parameters. Therefore, positive scores can be\nrelated to enhanced CaCO dissolution and reduced magnetic mineral inputs, and negative scores can\n3\nbe associated with enhanced CaCO deposition/preservation and increased magnetic mineral inputs.\nall\nto 0. This pattern indicates reduced CaCO dissolution and minimal detrital inputs (see comment 2\n3\nwhere we indicate that Contessa Road magnetic minerals are mainly detrital). Positive PC2 peaks\nall\ncan be associated with CaCO dissolution, as confirmed by their coincidence with positive PC1 and\n3 dis\nPC1 peaks. Well-developed negative PC2 peaks are only identified across the EETZ. These peaks\nall all\ncoincide with high CaCO contents (see this relationship in Fig. S14) and indicate that terrigenous\n3\ndilution was insignificant at Contessa Road. This interpretation is consistent with calcareous\nnannofossil assemblages and sedimentary patterns that indicate that CaCO deposition/dissolution\n3\nwere the main drivers of Contessa Road sedimentation (lines 290-328, Fig. S6, S14).\n\nComment 6: Long-term aridification of the western Tethys over 58-52 Ma. If the identification of the\nmagnetic minerals as detrital hematite and maghemite and the interpretation of PC1(arid) as a source\narea soil aridity signal are both accepted, this is a well-supported finding.\n\nThanks. The main condition that the reviewer has pointed out to use PC1 as a soil aridity index was arid\nhaving detrital magnetic minerals formed by the ferrihydrite→maghemite→haematite transformation.\nThis is now detailed in a new discussion section that explains that Contessa Road magnetic minerals\nare mainly detrital (see comment 2). This implies that maghemite and haematite should have been\nformed at the expense of ferrihydrite, which suggests that PC1 can be used as dry/wet index (see\narid\ncomment 4; lines 230-270, 434-465).\n\nComment 7: Punctuation by carbon cycle perturbations which produced even drier conditions.\nBased on Figure 9, I can see the argument for increased aridity during the first part of the PETM and\nthe first part of ETM2. L1 and L2 are also convincing. H2 and I1 look pretty marginal, I2 I don’t see at\nall, and ETM3 seems to be less arid by comparison with the immediately preceding period. F and the\nfinal phase of the PETM both seem to have increased humidity. Overall, this is a pretty complicated\npicture.\n\nWe now give a better explanation of Fig. 9. PETM and ETM 2 were dry. However, some intervals\nwithout short-lived carbon cycle perturbations or with smaller events were also dry. We indicate that\nthis is a consequence of long-term warming, which exerted larger controls on proto-Mediterranean\nhydroclimate variability than short-lived carbon cycle perturbations. This explains why PC1 reveals\narid\ndry conditions in the youngest part of our record. We now emphasise (Abstract) that only some short-\nlived carbon cycle perturbations punctuated long-term aridification (lines 22-34, 434-465).\n\nComment 8: Recovery from these perturbations to pre-event hydroclimate conditions over 23-27 kyr.\nThis argument is based on three hyperthermals: the PETM, ETM2 and ETM3. Here I think there needs\nto be a discussion of how the peak of the event is identified and how you identified the point at which\nconditions returned to pre-event baselines (or indeed, how you quantified pre-event baselines). As it\nis, the “peak” of the PETM has similar values of PC1(arid) to a prior peak a few tens of thousands of\nyears earlier, and the “recovery to pre-event conditions” is actually a change to conditions significantly\nmore humid than those immediately before the PETM. The peak of ETM2 is clearer, but again, the\n“recovery” is set at significantly lower aridity that the values immediately before the event. The most\narid conditions for ETM3 occur before the onset of the event as indicated by the shaded bar, and the\n“recovery” is truncated by the intervention of the EELMZ. Given this, I think it is quite speculative to\nargue that there is a relatively constant time interval over which hyperthermals return to “normal”\nconditions. If there was a clearer discussion of how these points were identified, it is possible that this\nproblem could be resolved, although I would also emphasise in the text that there are only three data\npoints to go on.\n\nWe now clarify how we estimated hydroclimate recovery timescales. Hyperthemal recovery, which is\nmarked by irreversible δ13C transitions from more negative to more positive δ13C values, coincide with\nirreversible PC1 transitions from negative to more positive values. These transitions enable\narid\nestimation of hydroclimate recovery periods. PC1 changes from negative to positive values during\narid\nthe PETM recovery, and transitions from negative PC1 values to close to 0 during the ETM 2\narid\nrecovery; this reveals a ~24-27 kyr hydroclimate recovery timescale. As noted, ETM 3 hydroclimate\nrecovery is difficult to define due to the EELMZ. We now explain this. Although only two events have\nwell-defined hydroclimate recovery timescales, we emphasise that the narrow range of estimates for\nevents with very different magnitudes (Lourens et al., 2005; Zeebe et al., 2009; Zachos et al., 2010;\nShaffer et al., 2016; Gutjahr et al., 2017; Harper et al., 2019) suggests that recovery may have been\noptimized. This would imply that hydrological cycle changes followed the same pattern as other\nprocesses (e.g., carbon sequestration) that were also optimized during LPEE hyperthermal recovery\n(lines 452-495).\n\nComment 9: L38-40 – statement needs a reference\n\nThanks. We added suitable references (Milly et al., 2005; Ault et al., 2014; Moon et al., 2018) (line\n39).\n\nComment 10: L 44 – reveal - > reconstruct\n\nThanks. We made this change (line 44).\n\nComment 11: L81 – “should have” -> “are assumed to have”?\n\nWe have made this change (line 100).\n\nComment 12: L84 “optimized” -> “optimization of the”\n\nWe have made this change (line 88-89).\n\nComment 13: L91-93 – This sentence is a little unclear as to whether the dry drier response has been\nreconstructed for the interior continental areas or the continental margins/Mediterranean zones. A\nquick glance at the papers cited suggests that they generally seem to support increased humidity with\nperiods of aridity during the PETM and ETM2 for the coastal areas, potentially indicating extreme\nrainfall events rather than increased background humidity, with some evidence for increased overall\naridity in continental interiors.\n\nThanks. We clarify that sub-tropical regions include proto-Mediterranean zones of western Tethyan\ncontinental areas, which experienced dry conditions with intermittent extreme precipitation events\n(lines 111-113).\n\nComment 14: L109 – indicated -> interpreted\n\nWe have made this change (line 135).\n\nComment 15: L148 – “generally contain” -> “are generally characterised by”\n\nThanks. Following a previous reviewer’s suggestion, we specify that 7 of 10 samples have χ drops\nduring heating from ~300°C. So, the expression “generally contain” was removed (lines 169-172).\n\nComment 16: L181 – HIRM-CFB has a gradually increasing trend -> HIRM-CFB initially has a\ngradually increasing trend.\n\nThanks. We made this change (line 205).\n\nComment 17: L181-2 – present tense for describing results\n\nThanks. We have replaced reached by reaches (line 206).\n\nComment 18: L182 – “high HIRM-CFB values are followed by…” -> “high HIRM-CFB values at\nthe peak of the PETM are followed by…”\n\nThanks. We made this change (line 206-208).\n\nComment 19: L192 – interesting there is no obvious drop in ARM at the EELMZ.\n\nWe agree. There are no obvious ARM drops at the EELMZ. We use this to explain that low coercivity\nminerals were not dissolved during the EELMZ, which makes this interval different from other whitish\ncarbonates intervals (e.g., across the K/Pg boundary; Abrajevitch et al., 2015) (lines S75-S106).\n\nComment 20: L194 – indicated -> estimated\n\nWe have made this change (line 223).\n\nComment 21: L199 – Not sure punctuated is the right word. Culminates in?\n\nThanks. We made this change (line 223).\n\nComment 22: L210-215 – I think I see what you’re getting at here, but this argument is currently\nunclear. You state that the haematite cannot be authigenic because if it were, increased magnetic\nconcentrations would correlate with increased haematite concentrations. However, Figure 5 indicates\nthat increased magnetic concentrations do correlate with increased haematite concentrations. I think\nwhat you are arguing is that the proportion of haematite in the magnetic fraction increases as magnetic\ncontent decreases, i.e. there is an enhancement of haematite relative to softer minerals as magnetic\ncontent decreases. (NB I also discuss this argument above in terms of possible other explanations for\nthis pattern.)\n\nThanks. We rearranged the text to indicate that increased magnetic mineral contents potentially\nproduce more haematite because more oxidizable material is available (lines 254-261).\n\nComment 23: L216 – “Scaglia Rossa carbonates also contain maghemite and magnetite, which have\nbeen interpreted to mainly have detrital origins despite likely biogenic magnetite occurrences41,42”\nThe two works cited here (Abrejevitch et al., 2015 and Coccioni et al., 2019) do not support the\nstatement as given according to my reading of them. Coccioni et al. (2019) did not discuss maghemite\nat all and Figure 3(c) in that paper seems to indicate a biogenic magnetite component ranging around\n30-40% and a detrital magnetite component of 10-15%. Abrejevitch et al. (2015) mentioned the\npossibility of maghemite but focused on magnetite and found detrital and biogenic magnetite\ncontributing approximately equal amounts to the overall magnetisation with the exception of their low\nsusceptibility zone (Fig 7 of that paper). See my comments above on the importance of discussing the\ninterpretation of the mineralogy in more detail.\n\nThanks. We changed the references accordingly in a new section “Origin of Contessa Road magnetic\nminerals” (lines 230-288). We explain that biogenic magnetite is not clearly identified at Contessa\nRoad and indicate that even if this mineral is present, detrital magnetite/maghemite contents are larger\nin our samples (lines S22-S49). This point is also raised in some comments above, so we reply in more\ndetail above (see comment 2).\n\nComment 24: L233-234 – “This implies that increased CaCO3 dissolution was accompanied by\nincreased magnetic mineral inputs at Contessa Road (Fig. 6b-d)” – see the discussion above about the\ninterpretation of PC1(all). This sentence is a little unclear as it is not immediately obvious that these\nincreased magnetic inputs are increased relative to terrigenous inputs, i.e. the terrigenous (or more\naccurately non-carbonate) material is more magnetic. L236-237 – mainly CaCO3 dissolution makes\nsense, but one wonders why the non-carbonate material is more magnetic.\n\nThanks. We now remark that PC1 has positive detrital element and CFB magnetic concentration\nall\nparameter loadings, and negative Ca loadings. Hence, PC1 does not separate CaCO dissolution from\nall 3\ndetrital magnetic mineral inputs. In contrast, detrital sedimentation and CaCO dissolution are\n3\nseparated by PC2 . This component explains the terrigenous/biogenic balance and its relationship\nall\nwith magnetic mineral contents (see comment 5). We now indicate that although positive PC1 scores\nall\ncould suggest that CaCO dissolution coincided with increased magnetic mineral inputs, this pattern\n3\nis not evident across all marly layers. PC1 positive peaks coincide with positive PC1 peaks that\nall dis\nrepresent a clean CaCO dissolution signal. Therefore, we suggest that PC1 mainly reveals CaCO\n3 all 3\ndeposition/dissolution patterns, consistent with the reviewer’s interpretation (“L236-237 – mainly\nCaCO3 dissolution makes sense”) (lines 290-328).\n\nComment 25: L241 and following – I would use “troughs” rather than “negative peaks”, as when you\nthen use the word “peaks” in the following discussion it becomes unclear whether you are talking\nabout negative or positive extremes.\n\nThanks. Some astrochronology studies only use the word “troughs” to refer to minimum values in\ncyclical time series. To avoid potential misunderstanding, we keep our original expression; however,\nwe always indicate when we refer to either positive or negative values (lines 290-328).\n\nComment 26: L244-248 – if the PC2(all) negative peaks represent major terrigenous input, why are\nthe detrital elements positively correlated with this axis? See discussion of PC interpretations, above.\n\nThanks. Yes, detrital elements (Fe, Si, Ti, Rb, and Zr) have positive PC2 loadings; however, these\nall\nelements do not represent detrital input variability. In contrast, XRF detrital elements in pelagic\ncarbonates characterize biogenic CaCO variability (e.g., Zachos et al., 2005; Westerhold et al., 2007;\nContessa Road (Piedrahita et al., 2022) and confirmed here by the excellent anti-correlation of detrital\nelements with Ca in PCA. Detrital magnetic mineral inputs do not necessarily correlate with increased\nCaCO dissolution according to PC2 . For a detailed explanation, see our response to Comment 5.\n3 all\n\nComment 27: L255-259 – could the maghemite also come from other transformations (e.g. of\nmagnetite)?\n\nThanks. We now explain that maghemite is much more common than magnetite in the LPEE Contessa\nRoad record. This allows us to suggest that haematite formed at the expense of maghemite following\nthe ferrihydrite→maghemite→haematite transformation rather than by magnetite alteration. This\ninterpretation is also supported by proxy and model evidence that reveal dry LPEE western Tethyan\nhydroclimates that were optimal for the ferrihydrite→maghemite→haematite transformation. Also,\nwe indicate that post-depositional magnetic mineral alteration was not a significant haematite\nformation mechanism at Contessa Road (lines 169-192, 230-270).\n\nComment 28: L311-312 – this statement needs a reference, either to a published source or your own\nargument in an earlier section\n\nThanks. We now explain in detail that Contessa Road magnetic minerals are detrital (see comment 5)\nearlier in the text (lines 230-288).\n\nComment 29: L295-323 – I found this argument a little confusing. So sometimes drier conditions/high\nseasonal contrast -> enhanced haematite production/transportation and other times wetter\nconditions/low seasonal contrast has this effect? Any ideas about why each of these mechanisms only\nseems to work sometimes? Might a wavelet analysis be useful to get an easier visual on power in the\nshort eccentricity band?\n\nThanks. We re-interpret our orbital signals following this suggestion. We add power spectra to confirm\nthe orbital signals using statistical criteria (Fig. 7, S15), so wavelet analyses are not required. We\nclarify that higher temperatures/light carbon concentrations promote CaCO dissolution, as indicated\n3\nby PC1 precession maxima (Littler et al., 2014; Zeebe et al., 2017). Thus, the opposite relationship\ndis\nbetween PC1 and HIRM-CFB precession signals reveals temperature control on haematite formation\ndis\nand western Tethyan hydroclimates. Precession-control on temperature gave us the possibility to\nassociate seasonality with haematite formation. Precession-driven insolation maxima conditions have\nbeen interpreted to coincide with CaCO dissolution, which in the northern hemisphere intensifies\n3\nseasonal precipitation and may have inhibited haematite formation. This mechanism implies that\nprecession-driven insolation minima conditions caused drying in western Tethyan continental\nregions, which follows the same hydroclimate variability pattern of Neogene-Quaternary\nMediterranean zones (e.g., Bosmans et al., 2015; Kutzbach et al., 2020) (lines 370-386).\nEccentricity control on precession suggests that the amplified precession expression, and its associated\nenhanced seasonal contrast during long and short eccentricity maxima, plays a role in western Tethyan\nhydroclimates. Our records indicate that enhanced seasonal contrast, with short-lived carbon cycle\nperturbations, accelerated the hydrological cycle and produced orbitally paced dry conditions in short\neccentricity timescales (lines 330-432).\nAlthough some authors have suggested authigenic magnetic mineral formation in Scaglia Rossa\ncarbonates (Channell et al., 1982; Abrajevitch et al., 2015; Coccioni et al., 2019), they also indicate\nthat detrital magnetic minerals occur within aeolian dust fractions in this unit. Maghemite/haematite\nproduction occurs under dry conditions (Jiang et al., 2022); taking into account the preferential detrital\norigin of Contessa Road magnetic minerals (this study), and the required conditions to enhance fluvial\ntransport (see reviewer comment ), we, as suggested by previous studies, assume that Contessa Road\nmagnetic minerals were mainly transported by wind (Coccioni et al., 2019). This requires re-\ninterpretation of intervals in which the HIRM-CFB short eccentricity signal is out-of-phase with\nrespect to the ZB18a astronomical solution (Zeebe and Lourens, 2019). We have added the long\neccentricity signal of ZB18a and find that some out-of-phase HIRM-CFB short eccentricity cycles\nappear during long eccentricity minima. We use this relationship to suggest that short eccentricity\npaced dry hydroclimates occurred only by a combination of enhanced seasonal contrast (partially\nmodulated by long eccentricity maxima) and global warming. Nevertheless, these processes cannot\nexplain why some short eccentricity cycles match ZB18a during intervals without short-lived carbon\ncycle perturbations. We also suggest that HIRM-CFB was not sensitive to short eccentricity when the\nprecession-related seasonal contrast was reduced by long eccentricity forcing. However, this process\ncannot explain the short eccentricity variability through the whole record. We discard the influence of\nhaematite transport from far regions and post-depositional magnetic mineral alteration as causes for\nthe out-of-phase HIRM-CFB short eccentricity cycles with respect to Zb18a. We also indicate that\nprecession signal clipping may contribute to the HIRM-CFB short eccentricity signal development\n(e.g., Walters et al., 2023). However, we have no evidence to conclusively determine the significance\nof out-of-phase HIRM-CFB short eccentricity cycles; hence, we focus on the dry conditions promoted\nby enhanced seasonal contrast and short-lived carbon cycle perturbations (lines 388-432).\n\nComment 30: L325 – repetitive -> consistent\n\nWe made this change (line 390).\n\nComment 31: L325-333 – again, I found this argument hard to follow. It would be good to clarify the\nconnections between the systematic dry conditions and the strengthened hydroclimate\nvariability/amplified seasonal precipitation/intermittent extreme precipitation. I think the argument\nhere is that during short eccentricity maxima in hyperthermals, summers were drier and winters were\nwetter, while during eccentricity minima there was more consistent rainfall year-round, but this does\nnot seem to fit with the “systematic dry conditions”.\n\nThanks. Our new explanation on how precession-driven insolation affected western Tethyan\nhydroclimate variability supports the idea that short eccentricity forcing caused large hydroclimate\nvariations, which under short-lived global warming conditions, were even more extreme. We have\nadded references that support the idea that Eocene global warming strengthened the hydrological\ncycle, and studies that indicate that dry western Tethyan hydroclimate responses to LPEE global\nwarming were a consequence of reduced seasonal precipitation. We indicate that proto-Mediterranean\nhydroclimates were similar to either a Quaternary Mediterranean-type climate with winter storm track\nactivity, or to a monsoon-type climate that reached western Tethyan regions. We do not have enough\ninformation to specify which seasonal precipitation system controlled western Tethyan hydroclimate\nvariability, so we do not clarify the seasons of precipitation increase (lines 349-402).\n\nComment 32: L352 – HIRM-> HIRM-CFB\n\nThanks. We made this change (line 448).\n\nComment 33: L367-68 – I think your data support the interpretation put forth by earlier studies and\nthe earlier sections of this paper about extreme events, but I’m not sure I’d use the word “verify”.\n\nThanks. We changed the paragraph to remove this word (lines 452-465).\n\nComment 34: L372 – I don’t think the figure ref is correct here or in L374\n\nThanks. We refer to Fig. 9 with our PC1 index (lines 452, 458, 459).\narid\n\nComment 35: L376-377 – could this “non-linear response” be simply that once you get to a certain\nlevel of aridity, you don’t form any precursors any more, so the proxy is only sensitive within a\nparticular aridity range?\n\nThanks. Our orbitally paced HIRM-CFB signals and their relationship with orbital insolation changes\nsuggest that haematite precursors formed continuously. Following this suggestion, we now better\nexplain why we argue that PC1 indicates non-linear proto-Mediterranean hydroclimate responses to\narid\nLPEE light carbon injections. We indicate that small short-lived carbon cycle perturbations such as L1\nand L2 had similar dry conditions to those of major events, which we argue is partially associated with\nthose non-linear hydroclimate responses to short-lived events and with long-term warming controls on\nhydroclimate variability. Major evidence for non-linear western Tethyan hydroclimate responses is\ngiven by the PETM and ETM 2 recovery timescales. These events had different temperature (the\nPETM was warmer) and carbon releases. However, their hydroclimate recovery timescales were\nsimilar (~27 kyr for the PETM and ~24 kyr for the ETM 2). This indicates that recovery was\nindependent of the size of the initial climate perturbation and suggests non-linear responses that were\nlikely associated with optimized carbon removal. We added some new references (Walters et al., 2023;\nMeijer et al., 2024) to non-linear hydroclimate responses to Eocene global warming (lines 452-485).\n\nComment 36: L377-379 – see my comments above\n\nThanks. See reply to comment 35.\n\nComment 37: L384 – “all” is a bit overegging it here – you have only studied a small number of\nevents here\n\nThanks. We rephrased the text to indicate that higher temperatures potentially disrupt hydroclimate\nvariability (lines 481-485).\n\nComment 38: L407 – “depths” – this is a bit confusing, as my understanding from Fig S1 is that the\nsuccession is measured according to a height above a stratigraphic datum (K/Pg boundary), therefore\nincreasing with elevation/decreasing with age, whereas “depth” is usually used for depth below ground\nsurface/datum, therefore decreasing with elevation/increasing with age. Suggest clarification, maybe\n“depths” -> “height above K-Pg boundary” with suitable acronym thereafter?\n\nThanks. We now indicate that the K/Pg boundary is recognized at 0 m depth at Contessa Road, and\nremark that positive depths are associated with younger strata (lines 505-506).\n\nComment 39: L407-408 clarify that the ranges (30-33 m and 33-48 m) are for the outcrop coverage,\nnot for the thermal events.\n\nWe made this change (lines 511-513).\n\nComment 40: L416 – Piedrahita -> Piedrahita et al.\n\nWe made this change (lines 515).\n\nComment 41: L417 – “that represent” -> “, which are proxies for”\n\nThanks. We rewrote the first two parts of the Materials and methods and removed this expression (lines\n498-532).\n\nComment 42: L463-471 – give the software used to carry out the PCA.\n\nWe used our own PCA code, which does not differ from that of any commercial software. Although\nPCA is used in many studies using different software, we can make our code public if required.\n\nComment 43: L645-646 – date is wrong on this reference, should be 1981\n\nThanks. In our new version of the manuscript this reference was removed.\n\nComment 44: Figures: as a general comment, some of these figures use a lot of different colours to\nindicate different types of information. For accessibility reasons, ideally this information would be\nconveyed in other ways too, for example different coloured lines could also be differentiated using\ndots vs dashes, or points by using different symbols. If you have not already done so, I\nrecommend https://www.fabiocrameri.ch/colourmaps/ and accompanying software/publications for\nmaking sure that accessible colour maps are used.\n\nThanks. We followed these guidelines to use more suitable colour combinations.\n\nComment 45: Fig 1 – The d13C/d18O/temp axis is reversed here compared to all other figures. Just\nfor ease of reading it might be worth making it consistent.\n\nWe reversed the δ13C record, but not the δ18O record to indicate the opposite LPEE relationship\nbetween δ13C, δ18O, and temperature (Fig. 1).\n\nComment 46: Fig caption 2 – indicate meaning of shaded bands for d13C and CaCO3 wt % time\nseries\n\nThanks. We indicate now that shaded bands refer to 2 standard errors.\n\nComment 47: Fig 3: Needs subfigure labels.\n\nWe added sublabels for the thermal transitions.\n\nComment 48: You have made a distinction here between the PETM initial phase and the PETM\nrecovery – it would be good to have the boundary between these two phases marked on other figures,\nlike Fig 2 and Fig 5.\n\nThanks. We indicate the PETM peak and recovery in Fig. S1.\n\nComment 49: Fig 8 –How were these intervals of good coincidence and bad coincidence chosen? Just\nby eyeballing? Also note that the caption states that the HIRM-CFB signal/orbital solution coincidence\nis good across short-lived carbon-cycle perturbations but these are not indicated with the blue boxes.\n\nThanks. We clarify that rectangles with black dashed lines indicate intervals where HIRM-CFB short\neccentricity signals do not coincide with ZB18a and state that these observations are based on visual\ncomparison and cross-spectral analysis (lines 404-408). We removed rectangles with blue dashed lines.\n\nComment 50: Supp info L43-45 – given that the CFB magnetic parameters are calculated relative to\ndetrital (or rather, non-carbonate) input, this would seem to indicate that these trends reflect magnetic\nenhancement of the detrital fraction at times of high carbonate dissolution, rather than simply detrital\ninput – unless there is a significant non-detrital, non-carbonate fraction of the sediment, but the paper\ndoes not mention this.\n\nThanks. Normalized rock magnetic concentrations allow comparison of magnetic mineral contents on\nan equal basis. Hence, data normalization by non-carbonate fractions does not imply that magnetic\ncontents are increased when CaCO dissolution is enhanced. This can be identified by comparing our\n3\nmagnetic concentration records. BR magnetic concentration records have increases that coincide with\nCaCO dissolution, which reveals that they indicate CaCO deposition/dissolution changes. In\n3 3\ncontrast, CFB magnetic concentration values are not necessarily higher when CaCO dissolution is\n3\nincreased (Fig. S4, S8). To clarify, we indicate in the Materials and methods section how our estimates\nare obtained. We also explain our bulk-rock (BR) and CFB normalizations of M (lines 568-576).\nrs\n\nComment 51: L90-91 What about terrigenous XRF values across the EELMZ?\n\nThanks. We now indicate that XRF detrital element concentrations across the EELMZ are low, while\nCa/CaCO is high. We explain that this pattern indicates reduced CaCO dissolution (lines S81-S84).\n3 3\n\nComment 52: Supp fig 1 – An age axis on this figure would be helpful.\n\nThanks. The Contessa Road age model is not totally linear with respect to depth. This does not allow\naddition of an age x-axis. However, we added the Contessa Road age model to the y-axis (Fig. S1).\n\nComment 53: Supp fig 5 – recommend switching the order of HIRM and ARM so that they are close\nto the coercivity components they are said to resemble, for ease of visual comparison. Note that the\nHIRM/High coercivity resemblance is v close, the ARM/low coercivity somewhat less so.\n\nThanks. We made these changes (Fig. S4, S8).\n\nComment 54: Supp fig 7 – recommend reversing axis on S-ratio for ease of visual comparison.\n\nThanks. To keep the same format as the other plots in the figure we did not switch the y-axis. However,\nwe plotted the S-ratio as suggested in Fig. 5.\n\nReviewer #3 (Remarks to the Author):\n\nComment 1: 1. I found the staging of this manuscript a bit problematic. The wet-gets-wetter and dry-\ngets-dryer paradigm describes the hydroclimate response dominated by tropospheric moistening\nwithout changing circulation in response to CO increase (Held and Soden, 2006, J. Clim.), which\n2\nleads to additional moisture being carried away from regions of divergence towards regions of\nconvergence. However, the subtropical drying inferred from this paradigm, which is used to stage this\nstudy, only applies to the OCEAN! On land, P>=E in general, which implies either balanced (no net\nrunoff) or slightly converging moisture flux (with net runoff). As a result, increasing tropospheric\nhumidity can only increase or maintain P-E on land (Seager and Vecchi, 2010, PNAS; Byrne and\nO’Gormon, 2015, J. Clim.). Moreover, key components of subtropical terrestrial hydrological cycle\nsuch as monsoons (characterized by summer precip) and Mediterranean climate (characterized by\nwinter precip) are controlled by regional circulation patterns that are departures from the zonal mean\nHadley circulation. Tropospheric humidification can lead to enhanced monsoon rainfall even without\nany change or weakened monsoon circulation (Endo and Kitoh, 2014, GRL). In the Mediteya les\npregunte region, drying over the land is explained by enhanced mass divergence due to strengthened\nhigh pressure system in the nearby region (Seager et al., 2014, J. Clim.). Finally, there is an inherent\ntime scale difference between project future change in hydroclimate and the reconstructed early\nEocene hydroclimate change presented here.\n\nThanks. First, we now remark that dry-drier-wet-wetter hydroclimate responses are exacerbated in the\nocean because higher temperatures increase lower-tropospheric water vapor (Held and Soden, 2006).\nFollowing this comment, we indicate that diverse factors control continental hydroclimate variability\n(e.g., atmospheric circulation, temperature gradients, and polar amplification). We also clarify that\nalthough dry-drier-wet-wetter hydroclimate responses are interpreted to predominate during the LPEE,\nsome records reveal that some dry areas may have experienced wetter conditions as a response to\nLPEE short-lived carbon cycle perturbations. However, we also point out that sub-tropical LPEE\nregions have been interpreted to experience dry-drier hydroclimate responses to global warming,\nwhich were associated with reduced moisture divergence and weak meridional temperature gradients\n(lines 98-109).\nFollowing this comment, we add elements to indicate that hydroclimate variability in the\nMediterranean Basin and surrounds is driven partially by seasonal precipitation systems that include\nmonsoons and winter storm tracks. We thank the reviewer for suggesting the studies of Endo and Kitoh\n(2014) and Seager et al. (2014), which usefully indicate that seasonal precipitation systems respond to\npressure and moisture divergence changes, which can cause either increased or reduced humidity and\nproduce contrasting hydroclimate responses across different areas–i.e., while some areas become\nwetter, other areas become simultaneously drier. This provides better introductory statements for our\ntest of western Tethyan hydroclimate variability (lines 111-121). We also improved description of\nsimilarities between LPEE climatic conditions and SPP 8.5 climatic scenarios to indicate that our\nrecords provide insights into potential effects of extreme global warming on sub-tropical\nhydroclimates. We also add references to suggest that although LPEE short-lived carbon cycle\nperturbations occurred under different conditions with respect to anthropogenic global warming (e.g.,\ndifferent tectonic setting and carbon release rates), these events have been interpreted to offer\nopportunities to assess hydroclimate responses to high temperatures (lines 49-64).\n\nComment 2: 2. The clarity of the discussion on “Orbitally forced LPEE hydroclimate variability in\nthe western Tethys” could be improved. For example, “short eccentricity maxima” can be more\nexplicitly written as northern hemisphere summer perihelion during the short eccentricity cycle. It is\nuseful to be explicit given that eccentricity by itself does not affect insolation. Also, the linkage\nbetween changing seasonal cycle and the mean hydroclimate state was never explained. Kutzbath et\nal, 2020 (PNAS) might be a good starting point to explain how the seasonal changes in insolation\ndriven by precession cycle can result in mean state changes of precipitation and P-E. They showed a\nlinkage through shifting winter storm track.\n\nThanks. We significantly changed interpretations of orbital signals. We indicate that filtered PC1\ndis\nprecession reveals temperature/light carbon concentration controls on CaCO sedimentation. PC1\n3 dis\nprecession maxima, which coincide with enhanced CaCO dissolution, are associated with increased\n3\ntemperatures/light carbon concentrations that promote lysocline shoaling. This effect is identified\nwidely in CaCO , δ18O, and δ13C data from multiple LPEE pelagic carbonate sections and is associated\n3\nwith precession-driven insolation maxima conditions (Littler et al., 2014; Barnet et al., 2019). This\norbital configuration characterizes reduced haematite formation, as indicated by the opposite\nrelationship between the precession signals of PC1 and HIRM-CFB. Hence, northern hemisphere\ndis\ninsolation maxima (perihelion in the northern hemisphere summer) inhibited haematite production,\nlikely as a consequence of intensified seasonal precipitation, which is a pattern expected in sub-tropical\nareas of the northern hemisphere during precession minima (e.g., Kutzbach et al., 2020). This implies\nthat precession-driven insolation minima conditions caused drying in western Tethyan continental\nregions, which follows the same hydroclimate variability pattern of Neogene-Quaternary\nMediterranean zones, and suggests that LPEE proto-Mediterranean hydroclimates were controlled,\nat least at some level, by orbitally forced dry/wet cycles (lines 370-386).\nFollowing this suggestion, we also explain that short eccentricity plays a role in western Tethyan\nhydroclimate variability via its influence on precession, which is amplified during short eccentricity\nmaxima and causes enhanced seasonal contrast. We interpret that these conditions, with short-lived\ncarbon cycle perturbations, accelerated the hydrological cycle and produced dry conditions during\nshort eccentricity maxima (lines 388-402).\n\nREVIEWERS' COMMENTS\nReviewer #2 (Remarks to the Author):\n\nPlease note in the following that I have been asked to address the comments made by Reviewer 1 as\nwell as my own.\n\nThe authors have done significant extra work to clarify and support their arguments. It is clear that\nthey have carefully considered my comments on the original manuscript and either made appropriate\nchanges or explained why no change is necessary. I have a few additional comments, which I have\ncombined below with the responses to comments by Reviewer 1.\n\nReviewer 1 Comment 2\nThe reviewer comments that with respect to the magnetic minerals, there are some major questions\noutstanding:\n1. Could the haematite and maghemite be authigenic?\n2. Could the haematite be late diagenetic?\n3. Could the magnetite be biogenic?\n\n1. Could the haematite and maghemite be authigenic?\nPrevious models for the alternation between red (haematite-rich) and white (haematite-poor)\nlithologies at this site have argued for an authigenic origin for the haematite, as follows: model 1\n(Channel et al., 1982) suggests that intervals with reducing conditions did not produce haematite\nwhile those with oxic conditions did; model 2 (Abrajevitch et al., 2015) suggests haematite was\nformed in intervals that were subject to reducing conditions followed by oxic conditions. The authors\nargue that neither of these models can be applied to the late Palaeocene-early Eocene interval due to\nthe lack of any evidence for reducing conditions in either the white or the red units (no iron sulphides,\nno evidence for major organic carbon input). Furthermore, the white lithology contains maghemite but\nnot haematite, which differs from the magnetic assemblage present in white lithologies underpinning\nmodel 2, and is incompatible with reducing conditions.\nI am convinced by this argument with respect to the white lithology. Given that in order to form\npigmentary haematite in subaqueous sediments, there must be dissolved iron in the pore waters, and\nthat this iron is usually argued to proceed from dissolution deeper in the sediment due to reducing\nconditions, this would also seem to support the authors’ argument that the pigmentary haematite in\nthe overlying intervals is not authigenic. I note that one of the arguments in favour of an authigenic\norigin for the pigmentary haematite in Channel et al. (1982) is that colours sometimes change within\nbedding units – I wonder if this occurs in the interval studied here? If not, this could be noted for\nfurther support.\n\n2. Could the haematite be late diagenetic?\nReviewer 1 notes that pigmentary haematite is considered to usually form 105-106 years after\ndeposition. The authors argue that this cannot be the case here because the proportion of haematite\nincreases as the overall magnetic content decreases, which seems reasonable. This argument could be\nstrengthened by including references to other marine intervals where detrital pigmentary haematite\nhas been inferred.\n\n3. Could the magnetite be biogenic?\nThe authors have done significant work to address the possibility of biogenic magnetite in the section.\nThis is a very difficult question to solve without a positive TEM ID; however, the IRM unmixing work is\na good approach and indicates that the main low-coercivity signal is likely to be detrital. Another way\nto support this might be to consider what effect the biogenic magnetite might have on the story if it is\npresent. For example, subtracting the proportions of the low-coercivity signal that could potentially be\nbiogenic magnetite in each interval and seeing if it makes a major difference to the overall patterns.\nJust eyeballing it it looks like any potential biogenic contribution is higher in the later periods, so\nwould be more likely to strengthen the observed trend of reduced low coercivity/increased high\ncoercivity rather than weaken it.\n\nOverall, with the respect to Reviewer 1 Comment 2, I think the authors have done the important work\nof clarifying their reasoning so that the reader can judge for themselves. While they could potentially\nadd one or two more lines of evidence, I do not think this is indispensable and leave it up to the editor\nto decide.\n\nReviewer 1 Comment 3: Interpretation of the clay/carbonate ratio.\nAs far as I am aware, this question has been addressed in multiple previous studies, all of which came\nto the conclusion that the detrital/carbonate ratio in these rocks was primarily controlled by carbonate\ndissolution. I think this previous evidence is sufficiently clarified in lines 127-133 of the revised MS.\nHowever, I think the new discussion of PC2all as evidence for lack of terrigenous dilution is confusing –\nI will discuss this in the next comment. I also find the part of Figure 6 used to indicate carbonate\ndissolution / terrigenous input to be quite confusing. It looks like it’s saying that when PC2all is\npositive, carbonate dissolution is increased and terrigenous input is decreased, while when PC2all is\nnegative, carbonate dissolution is decreased and terrigenous input is increased. However, the PCA\ndiagram seems to indicate that positive PC2all = increased carbonate dissolution and increased\nterrigenous inputs while negative PC2all = decreased carbonate dissolution and decreased\nterrigenous inputs. I think the use of arrows, pos/neg signs and colours all in the same key is making\nthis harder to interpret than it needs to be. (Having said this, if PC2all is reinterpreted as representing a single\ncontrolling process, this will become much easier to represent – see below.)\n\nReviewer 1, Comment 4: the interpretation of PC2all\nHere the reviewer comments that a single principal component (PC) should represent a single\nenvironmental process, whereas here PC2all is interpreted to represent both variations in carbonate\ndissolution and variations in terrigenous input. I agree with this and further note that both PC1all and\nPC2all are interpreted here as due to carbonate dissolution, where the purpose of PCA is to separate\nout different processes and so the same process should not be assigned to more than one PC (that is,\nassuming that the PCs can be interpreted as environmental processes at all, which is not always the\ncase). The discussion added by the authors does not solve this problem, as they still interpret positive\nPC2all as representing both enhanced carbonate dissolution and increased terrigenous input and\nPC1all as representing carbonate dissolution.\nI am not sure I agree with the comment made by the authors in the rebuttal that “Most of the PC2all\nrecord has values close to 0, which indicates reduced CaCO3 dissolution\naccompanied by minimal detrital mineral inputs.” Values close to 0 would suggest average values, so if\n(for example) PC2all represents terrigenous input then values close to 0 represent periods where\nterrigenous input is close to the long-term average value.\nSimilarly, “Positive PC2all peaks generally coincide with positive PC1dis and PC1all peaks, which\nconfirms that positive PC2all scores reveal enhanced CaCO3 dissolution.” What this suggests to me is\nthat whatever process is controlling PC2all often varies in tandem with whatever process is controlling\nPC1dis and PC1all, not that they are both the same process. This is particularly clear when we\nconsider that, as the authors note, there are intervals across the EETZ where PC2all has negative\npeaks when wt% carbonate is relatively high.\nThe reviewer also requests a set of correlation matrices showing how each variable is loaded onto\neach PC. I may be misunderstanding the caption for Fig S13, but it seems to me that these matrices\nshow the correlations of the variables to each other, rather than their loading onto the PCs. I agree\nthat a table showing the loadings of each variable on each PC would be very useful for assessing how\nimportant each inferred process is for each variable.\nThe new PCA included in the response to reviewer 2 is useful and I would include it over the\noriginal PCAall, not because it changes the shape of the two components (as the authors make clear, it does\nnot), but because it provides more information to help explain the PCs, particularly PC2all.\n\nAn interpretation of the two PCs should have the following characteristics:\n1. Processes for the two PCs are independent\n2. Only one process is invoked for each PC\n3. PC1all should explain why the concentration of magnetic material in the CFB terrigenous fraction is\nincreased when this PC is positive\n4. PC1 all should explain why the average coercivity is decreased when this PC is positive\n5. PC2all should explain why the concentration of magnetic material in the CFB terrigenous fraction is\nnot really correlated with this PC\n6. PC2all should explain why the average coercivity is increased when this PC is positive\n7. PC2all should explain why there are points across the EETZ when wt%CaCO3 is high while this\nPC is negative\nMy suspicion is that PC1all = carbonate dissolution/insolation and PC2all = terrigenous input/aridity\n(drier = more aeolian input = higher haematite proportion).\n\nReviewer 1, Comment 5: Interpretation of the precessional signal.\nReviewer 1 comments that the spectral analyses reveal noisy signals with some significant peaks\noutside the eccentricity and precession bands. The authors have changed their main method of\nspectral analysis (from MTM to periodogram, although MTM is still presented in the supplementary\nmaterial). The periodogram doesn’t look very different to my eyes in terms of where the significant\npeaks are located. They now mention in the text that non-eccentricity/precession peaks occur but that\nthey are out of the scope of the paper. I think this is fine. Reviewer 1 further requests that the original\ndata for spectral analysis be made available, and the authors have stated that they will share this.\nReviewer 1 comments that the fact that PC1dis variability on eccentricity timescales matches the ZB18\nsolution does not mean that PC1dis variability on precessional timescales would match a precession\nsolution were one available. Reviewer 1 also comments that the amplitude of precession modulation in\nPC1dis does not match the eccentricity signal (presumably in PC1dis). The authors have added a new\nsupplementary figure showing the modulation of precessional-scale variability in comparison to the\neccentricity signal of PC1dis. This is not a perfect match, but it is reasonable, and the presence of the\nnew figure allows the reader to evaluate the evidence for themselves. Reviewer 1 suggests\ncomparison of the precessional signal in PC1dis to other coeval records; the authors state this is not\nlikely to be helpful as these records do not agree in terms of precession variability across this interval.\nThis seems fair, although if this reasoning is not explicitly stated in the paper it would be good to\ninclude it and also make reference to these other studies that reconstruct precession from this\ninterval.\nReviewer 1 suggests the HIRM-CFB record is not reliable for identifying orbital-scale cyclicity due to its\nfailure to identify the correct number of precession cycles across the PETM and its failure to match the\nZB18 solution on eccentricity timescales. The authors seem to suggest they have changed their\nfiltering method, although it is not clear how as the bandpass filters described in the methods section\nhave not changed. However, the HIRM-CFB precessional signal does now seem to have the correct\nnumber of cycles across the PETM. The fact that the HIRM-CFB filtered eccentricity signal does not\nmatch the ZB18/PC1dis signal across a substantial part of the interval is not addressed in the authors’\nreviewer response.\nThe text written in response to this comment (lines 362-365 of the revised MS) states that the HIRM-\nCFB precession signal is out of phase with the PC1dis precession signal, based on visual inspection of\nFig 8c and the phase analysis in the bottom row of Fig 7. I did not find this very convincing – the\nphase relationship in Fig 8c looks very variable to me, with some parts of the record very much out of\nphase and other very much in phase. Although there are leads/lags of ~10 kyr identified in the PETM\nand EELMZ phase spectra, the majority of the record falls into the central interval, where the lead/lag\nis max 4 kyr.\n\nReviewer 1 comment 6: Climatic interpretation of spectral analysis.\nReviewer 1 questions the connections drawn between the precession and eccentricity signals in PC1dis\nand HIRM-CFB and seasonality, noting that in the Northern Hemisphere, maximum precession =\nminimum seasonality and minimum precession = maximum seasonality. Eccentricity modulates this,\nwith maximum eccentricity producing both maximum and minimum seasonalities in a given precession\ncycle, while minimum eccentricity produces little contrast in seasonality across a given precession\ncycle. Reviewer 1 further notes that seasonal precipitation, extreme precipitation events and fluvial\ninput increase with increased seasonality.\nThe discussion in lines 370-385 of the revised MS is consistent with this, with maximum precession\nargued to represent times of greater aridity/higher HIRM-CFB, and vice versa. However, the discussion\nin lines 388-402 as well as the response to the reviewer do not seem to have taken the reviewer’s\nconcerns into account. Maximum eccentricity is still identified as producing maximum seasonal\ncontrast in lines 394-395, although the reviewer’s point was that maximum eccentricity modulates\nprecession such that both maximum seasonal contrast and minimum seasonal contrast occur (in the\nNorthern Hemisphere, at minimum and maximum precession, respectively). Thus, given that most of\nthe LPEEs last for several precession cycles, they cannot be said to be simply times of maximum\nseasonal contrast.\nThe authors also argue in lines 396-397 that maximum seasonal contrast at eccentricity maxima\nproduces dry conditions/reduced seasonal precipitation, although they have argued the opposite in\nlines 370-385 (maximum seasonal contrast = wetter conditions/increased seasonal precipitation,\nconsistent with Reviewer 1 and, e.g., Bosmans et al., 2015). This identification of eccentricity maxima\nwith enhanced seasonal contrast is repeated in lines 410-411. If high seasonal contrast is considered\nto produce overall wetter conditions due to enhanced seasonal and monsoonal precipitation and\nincreased extreme precipitation events, as argued in lines 370-385, then periods of maximum\neccentricity should be characterised by both enhanced dry (maximum precession/minimum seasonal\ncontrast/minimum seasonal precipitation) and enhanced wet (minimum precipitation/maximum seasonal\ncontrast/maximum seasonal precipitation) conditions. I could see an argument where the\nhaematite precursors are produced during the wet periods and then the haematite itself is produced\nand transported during the dry periods, and thus the enhancement of both types of climate during\neccentricity maxima and LPEEs results in overall increased average haematite in the sediments. I\ncould also see an argument where the increased temperatures during LPEEs enhance the increase in\nhaematite formation and transport at times of minimum seasonal contrast (and therefore minimum\nseasonal precipitation), which would also occur at times of maximum eccentricity. However, at\npresent, the argument about how eccentricity modulation of precession produces the observed\nhaematite variations is not clear to me.\n\nReviewer #3 (Remarks to the Author):\n\nThe authors have done a nice job revising the staging of the manuscript and interpretation of the\neccentricity signal in their records. One last suggestion, the authors probably would want to consider\nremoving or rewriting sentences/wordings related to the long-lasting effect of anthropogenic CO2\nemissions (lines 33 to 34, 37 to 38). More recent studies generally agree that once 0 emission is\nreached, CO2 level in the atmosphere will fall, and global warming will stop (e.g., Matthews and\nWeaver 2010, Nat. Geo). This is due to the net absorption of CO2 by the ocean and land. These\nstatements can be considered as erroneous in the eyes of researchers who study modern climate.\n\nResponse to reviews for:\nDry hydroclimates in the late Palaeocene-early Eocene hothouse\nworld\nVictor A. Piedrahita1, Andrew P. Roberts2, Eelco J. Rohling2,3, David Heslop2, Xiang Zhao2,\nSimone Galeotti4,5, Fabio Florindo5,6, Katharine M. Grant2, Pengxiang Hu2, Jinhua Li1\n\nWe thank the reviewers for their new comments, which have helped to improve our manuscript.\nReview comments are repeated below in black with responses in blue.\n\nReviewer #2 (Remarks to the Author)\n\nComment 1: Please note in the following that I have been asked to address the comments made\nby Reviewer 1 as well as my own. The authors have done significant extra work to clarify and\nsupport their arguments. It is clear that they have carefully considered my comments on the original\nmanuscript and either made appropriate changes or explained why no change is necessary. I have\na few additional comments, which I have combined below with the responses to comments by\nReviewer 1.\n\nWe thank the reviewer for their supporting comments about our initial review and for their\nadditional comments and suggestions to improve our manuscript.\n\nComment 2: The reviewer comments that with respect to the magnetic minerals, there are some\nmajor questions outstanding:\n1. Could the haematite and maghemite be authigenic?\n2. Could the haematite be late diagenetic?\n3. Could the magnetite be biogenic?\n\nWe reply to these questions in response to comments 3, 4, and 5 below.\n\nComment 3: Could the haematite and maghemite be authigenic? Previous models for the\nalternation between red (haematite-rich) and white (haematite-poor) lithologies at this site have\nargued for an authigenic origin for the haematite, as follows: model 1 (Channel et al., 1982)\nsuggests that intervals with reducing conditions did not produce haematite while those with oxic\nconditions did; model 2 (Abrajevitch et al., 2015) suggests haematite was formed in intervals that\nwere subject to reducing conditions followed by oxic conditions. The authors argue that neither of\nthese models can be applied to the late Palaeocene-early Eocene interval due to the lack of any\nevidence for reducing conditions in either the white or the red units (no iron sulphides, no evidence\nfor major organic carbon input). Furthermore, the white lithology contains maghemite but not\nhaematite, which differs from the magnetic assemblage present in white lithologies underpinning\nmodel 2, and is incompatible with reducing conditions. I am convinced by this argument with\nrespect to the white lithology. Given that in order to form pigmentary haematite in subaqueous\nsediments, there must be dissolved iron in the pore waters, and that this iron is usually argued to\nproceed from dissolution deeper in the sediment due to reducing conditions, this would also seem\nto support the authors’ argument that the pigmentary haematite in the overlying intervals is not\nauthigenic. I note that one of the arguments in favour of an authigenic origin for the pigmentary\nhaematite in Channel et al. (1982) is that colours sometimes change within bedding units – I wonder\nif this occurs in the interval studied here? If not, this could be noted for further support.\n\nWe thank the reviewer for their support of our explanation for the origin of magnetic minerals at\nContessa Road. Channell et al. (1982) suggested that rock colour variations between reddish and\npinkish tones result from goethite and pigmentary haematite content changes in this section. This\nargument does not apply to the late Palaeocene-early Eocene portion of the record because goethite\noccurrences are limited to a short interval (lines 190-192). Considering that several quantitative\ntechniques, which we have not measured for Contessa Road, have been developed to recognize\nsediment colour variations since Channell et al. (1982) (e.g., redness over greenness), we decided\nto avoid using visual changes between reddish/pinkish tones to identify magnetic mineral\nformation processes.\n\nComment 4: Could the haematite be late diagenetic? Reviewer 1 notes that pigmentary haematite\nis considered to usually form 105-106 years after deposition. The authors argue that this cannot be\nthe case here because the proportion of haematite increases as the overall magnetic content\ndecreases, which seems reasonable. This argument could be strengthened by including references\nto other marine intervals where detrital pigmentary haematite has been inferred.\n\nFollowing the reviewer’s suggestion, we include Jiang et al. (2022) as a supporting reference\nbecause they detail the environmental conditions under which haematite forms (line 257).\n\nComment 5: Could the magnetite be biogenic? The authors have done significant work to address\nthe possibility of biogenic magnetite in the section. This is a very difficult question to solve without\na positive TEM ID; however, the IRM unmixing work is a good approach and indicates that the\nmain low-coercivity signal is likely to be detrital. Another way to support this might be to consider\nwhat effect the biogenic magnetite might have on the story if it is present. For example, subtracting\nthe proportions of the low-coercivity signal that could potentially be biogenic magnetite in each\ninterval and seeing if it makes a major difference to the overall patterns. Just eyeballing it it looks\nlike any potential biogenic contribution is higher in the later periods, so would be more likely to\nstrengthen the observed trend of reduced low coercivity/increased high coercivity rather than\nweaken it.\n\nThanks for this suggestion. As the reviewer indicates, TEM observations are the only way to reveal\nbiogenic magnetite occurrences conclusively. Following this suggestion, we also compare low\ncoercivity detrital mineral proportions with biogenic magnetite in Fig. S12. We note that even if\nbiogenic magnetite occurred consistently across different intervals, its contribution would have\nbeen smaller than that of detrital magnetic minerals. This supports our interpretation of the detrital\norigin of magnetic minerals at Contessa Road (lines S35-S50).\n\nComment 6: Overall, with the respect to Reviewer 1 Comment 2, I think the authors have done\nthe important work of clarifying their reasoning so that the reader can judge for themselves. While\nthey could potentially add one or two more lines of evidence, I do not think this is indispensable\nand leave it up to the editor to decide.\n\nThanks for this supportive comment on our explanation. We added lines of evidence for the origin\nof the Contessa Road magnetic minerals as indicated in response to Comments 3, 4, and 5.\n\nComment 7: Interpretation of the clay/carbonate ratio. As far as I am aware, this question has been\naddressed in multiple previous studies, all of which came to the conclusion that the\ndetrital/carbonate ratio in these rocks was primarily controlled by carbonate dissolution. I think this\nprevious evidence is sufficiently clarified in lines 127-133 of the revised MS. However, I think the\nnew discussion of PC2all as evidence for lack of terrigenous dilution is confusing – I will discuss\nthis in the next comment. I also find the part of Figure 6 used to indicate carbonate dissolution /\nterrigenous input to be quite confusing. It looks like it’s saying that when PC2all is positive,\ncarbonate dissolution is increased and terrigenous input is decreased, while when PC2all is\nnegative, carbonate dissolution is decreased and terrigenous input is increased. However, the PCA\ndiagram seems to indicate that positive PC2all = increased carbonate dissolution and increased\nterrigenous inputs while negative PC2all = decreased carbonate dissolution and decreased\nterrigenous inputs. I think the use of arrows, pos/neg signs and colours all in the same key is making\nthis harder to interpret than it needs to be. (Having said this, if PC2all is reinterpreted as representing a single\ncontrolling process, this will become much easier to represent – see below.)\n\nWe thank the reviewer for these suggestions. When scores and loadings are combined, a positive\n(negative) outcome indicates values greater (less) than the mean. Furthermore, the magnitude of\nthe value also indicates how far the value deviates from the mean, with a larger magnitude\ncorresponding to a greater deviation. In PCA, positive scores of a PC indicate higher values of\nvariables with positive loadings and lower values of variables with negative loadings.\nAlternatively, negative scores of a PC indicate lower values of variables with positive loadings and\nhigher values of variables with negative loadings (see Jolliffe, I. T. 2002. Principal Component\nAnalysis. Springer). Therefore, negative PC2 scores cannot represent decreased terrigenous\nall\ninputs because CFB magnetic mineral concentration parameters have negative loadings (y-axis in\nFig 6b). The pattern described by the reviewer in this comment for Fig. 6b is correct for PC1 .\nall\nFollowing the reviewer’s suggestion in Comment 9, we now include B and S-ratio in our PCA\ncr all\nassessment. PC2 now contains positive detrital element and B loadings, and negative CFB\nall cr\nmagnetic mineral concentration parameters, Ca and S-ratio loadings. These patterns reveal that\npositive scores indicate enhanced CaCO dissolution with reduced magnetic mineral inputs;\n3\nhowever, magnetic mineral fractions in this case are dominated by haematite, as indicated by the\npositive B and negative S-ratio loadings. Alternatively, negative scores reveal better CaCO\ncr 3\npreservation accompanied by higher detrital inputs. Here, positive B and negative S-ratio loadings\ncr\nindicate that magnetic mineral fractions are enriched in low coercivity magnetic minerals.\nFollowing this suggestion, we also modified Fig. 6 and removed colours and arrows to make the\nPCA interpretation simpler (lines 290-330; Fig. 6).\n\nComment 8: The interpretation of PC2all. Here the reviewer comments that a single principal\ncomponent (PC) should represent a single environmental process, whereas here PC2all is\ninterpreted to represent both variations in carbonate dissolution and variations in terrigenous input.\nI agree with this and further note that both PC1all and PC2all are interpreted here as due to\ncarbonate dissolution, where the purpose of PCA is to separate out different processes and so the\nsame process should not be assigned to more than one PC (that is, assuming that the PCs can be\ninterpreted as environmental processes at all, which is not always the case). The discussion added\nby the authors does not solve this problem, as they still interpret positive PC2all as representing\nboth enhanced carbonate dissolution and increased terrigenous input and PC1all as representing\ncarbonate dissolution. I am not sure I agree with the comment made by the authors in the rebuttal\nthat “Most of the PC2all record has values close to 0, which indicates reduced CaCO3 dissolution\naccompanied by minimal detrital mineral inputs.” Values close to 0 would suggest average values,\nso if (for example) PC2all represents terrigenous input then values close to 0 represent periods\nwhere terrigenous input is close to the long-term average value.\nSimilarly, “Positive PC2all peaks generally coincide with positive PC1dis and PC1all peaks, which\nconfirms that positive PC2all scores reveal enhanced CaCO3 dissolution.” What this suggests to me is\nthat whatever process is controlling PC2all often varies in tandem with whatever process is controlling\nPC1dis and PC1all, not that they are both the same process. This is particularly clear when we\nconsider that, as the authors note, there are intervals across the EETZ where PC2all has negative\npeaks when wt% carbonate is relatively high.\n\nWe thank the reviewer for their suggestions to improve our explanations about PCA .\nall\nWe agree\nthat sometimes PCs cannot be interpreted to reveal even a single environmental process. In our\nPCA , diverse variables associated with different paleoenvironmental are included. PCA\nall all\nassesses relationships between CaCO dissolution, magnetic mineral concentration, and magnetic\n3\nmineral composition indices. PC1 has positive loadings for detrital elements, CFB magnetic\nall\nmineral concentration parameters and S-ratio, and negative loadings are found for B and Ca.\ncr\nDistances from the origin (loading) for all these variables are similar, which indicates that each\nvariable plays a role in the different PCs. Therefore, there are no statistical arguments to assume\nthat each PC should represent a single environmental process. Following the reviewer’s suggestion,\nwe added B and S-ratio to PCA , which allows simplification of our interpretations. PC1\ncr all all\nloadings indicate that positive PC1 peaks reveal enhanced CaCO dissolution accompanied by\nall 3\nhigh magnetic mineral inputs with compositional prevalence of low coercivity minerals. For PC2 ,\nall\nwe identified positive detrital element and B loadings, and negative Ca, CFB magnetic mineral\ncr\nconcentration parameter and S-ratio loadings. These arrangements suggest that positive PC2\nall\nscores represent CaCO dissolution accompanied by reduced magnetic mineral inputs; however,\n3\nthe remaining magnetic mineral fractions are compositionally dominated by haematite.\nAlternatively, negative PC2 scores, which are exclusively identified with pronounced peaks\nall\nacross the EETZ, indicate reduced CaCO dissolution and low coercivity magnetic mineral\n3\nenrichment. Our new simplified explanation for PCA allows removal of sentences like “Most of\nall\nthe PC2all record has values close to 0, which indicates reduced CaCO3 dissolution accompanied\nby minimal detrital mineral inputs” and “Positive PC2all peaks generally coincide with positive\nPC1dis and PC1all peaks, which confirms that positive PC2all scores reveal enhanced CaCO3\ndissolution”, which confused the reviewer (lines 290-330).\n\nComment 9: The reviewer also requests a set of correlation matrices showing how each variable\nis loaded onto each PC. I may be misunderstanding the caption for Fig S13, but it seems to me that\nthese matrices show the correlations of the variables to each other, rather than their loading onto\nthe PCs. I agree that a table showing the loadings of each variable on each PC would be very useful\nfor assessing how important each inferred process is for each variable.\nThe new PCA included in the response to reviewer 2 is useful and I would include it over the\noriginal PCAall, not because it changes the shape of the two components (as the authors make\nclear, it does not), but because it provides more information to help explain the PCs, particularly\nPC2all.\n\nAn interpretation of the two PCs should have the following characteristics:\n1. Processes for the two PCs are independent\n2. Only one process is invoked for each PC\n3. PC1all should explain why the concentration of magnetic material in the CFB terrigenous\nfraction is increased when this PC is positive\n4. PC1 all should explain why the average coercivity is decreased when this PC is positive\n5. PC2all should explain why the concentration of magnetic material in the CFB terrigenous\nfraction is not really correlated with this PC\n6. PC2all should explain why the average coercivity is increased when this PC is positive\n7. PC2all should explain why there are points across the EETZ when wt%CaCO3 is high while this\nPC is negative\n\nMy suspicion is that PC1all = carbonate dissolution/insolation and PC2all = terrigenous\ninput/aridity (drier = more aeolian input = higher haematite proportion).\n\nWe thank the reviewer for their suggestions to improve our explanations about PCA .\nall\nWe now\ninclude B and S-ratio in our analysis and added a Tab. S2 that has all the loadings associated with\ncr\neach PCA carried out in this study. We address each question of this comment individually bellow.\n1. Our new PCA interpretations reveal different processes. (1) Positive PC1 peaks reveal\nall all\nenhanced CaCO dissolution and increased magnetic mineral inputs compositionally\n3\nenriched in low coercivity minerals. (2) Pronounced negative PC1 peaks are not indicated.\nall\nHowever, negative PC1 values reveal that typical CaCO sedimentation at Contessa Road\nall 3\nis accompanied by reduced terrigenous inputs, which in this case are compositionally\ndominated by haematite over other magnetic minerals. (3) Positive PC2 peaks indicate\nall\nenhanced CaCO dissolution and reduced magnetic mineral inputs. Remaining magnetic\n3\nmineral fractions of this component are compositionally dominated by haematite.\nAlternatively, negative PC2 peaks indicate reduced CaCO dissolution (better CaCO\nall 3 3\npreservation) and increased magnetic mineral inputs enriched in low coercivity minerals.\nProcesses\nassociated with different components are summarized in the table below in terms of\nmagnetic mineral inputs, CaCO dissolution, and prevalence of low coercivity over high\n3\ncoercivity magnetic minerals. This table also indicates that each quadrant in the PC1 -\nall\nPC2 plot is associated with contrasting processes.\nall\nComponent / Magnetic mineral CaCO dissolution Compositional\ncoercivity minerals\nover high coercivity\nminerals\nPositive PC1 Increased Increased Increased\nall\nNegative PC1 Decreased Decreased Decreased\nall\nPositive PC2 Decreased Increased Decreased\nall\nNegativePC2 Increased Decreased Increased\nall\n2. We explain that the similar loadings of the different CaCO dissolution, magnetic mineral\n3\nconcentration, and magnetic mineral composition indices assessed in PCA do not allow\nall\nus to relate each component exclusively to a single palaeoenvironmental process (see\nComment 8).\n3. PC1 (x-axis in Fig. 6b) has positive detrital element and CFB magnetic concentration\nall\nparameter loadings that indicate that positive scores reveal enhanced CaCO dissolution\n3\nand increased magnetic mineral inputs compositionally enriched in low coercivity minerals.\n4. Magnetic mineral fractions indicated by positive PC1 scores are enriched in low over high\nall\ncoercivity magnetic minerals.\n5. CFB magnetic concentration parameters have negative loadings that indicate that PC2\nall\nindeed is partially controlled by these variables. This pattern indicates that negative PC2\nall\nscores reveal higher magnetic mineral inputs enriched in low coercivity minerals (negative\nS-ratio and CFB magnetic concentration parameter loadings).\n6. Positive PC2 peaks reveal enhanced CaCO dissolution periods that were coincident with\nall 3\nreduced magnetic mineral deposition. This reduced terrigenous sediment flux was\ncompositionally dominated by haematite over magnetite and maghemite.\n7. Negative PC2 peaks are associated with reduced CaCO dissolution (high wt%CaCO\nall 3 3\nvalues) and high magnetic mineral contents. This indicates that biogenic sedimentation was\nnot disturbed by terrigenous inputs, which suggests, along with sedimentation rate estimates\nand calcareous nannofossil assemblages, that dilution was not significant at Contessa Road.\nWe appreciate the reviewer’s suggestion about the interpretation of PCA . However, we\nall\ndemonstrate that positive and negative loadings play different roles that involve multiple\nenvironmental processes. Alternative carbonate dissolution (PC1 ) and dry/wet variability\ndis\n(PC1 ) indices were generated in our study (lines 290-330).\narid\n\nComment 10: Interpretation of the precessional signal. Reviewer 1 comments that the spectral\nanalyses reveal noisy signals with some significant peaks outside the eccentricity and precession\nbands. The authors have changed their main method of spectral analysis (from MTM to\nperiodogram, although MTM is still presented in the supplementary material). The periodogram\ndoesn’t look very different to my eyes in terms of where the significant peaks are located. They\nnow mention in the text that non-eccentricity/precession peaks occur but that they are out of the\nscope of the paper. I think this is fine. Reviewer 1 further requests that the original data for spectral\nanalysis be made available, and the authors have stated that they will share this.\n\nThanks for this supportive comment. All of our datasets have been uploaded to FigShare following\nrecommendations of Nature Communications.\n\nComment 11: Reviewer 1 comments that the fact that PC1dis variability on eccentricity timescales\nmatches the ZB18 solution does not mean that PC1dis variability on precessional timescales would\nmatch a precession solution were one available. Reviewer 1 also comments that the amplitude of\nprecession modulation in PC1dis does not match the eccentricity signal (presumably in PC1dis).\nThe authors have added a new supplementary figure showing the modulation of precessional-scale\nvariability in comparison to the eccentricity signal of PC1dis. This is not a perfect match, but it is\nreasonable, and the presence of the new figure allows the reader to evaluate the evidence for\nthemselves. Reviewer 1 suggests comparison of the precessional signal in PC1dis to other coeval\nrecords; the authors state this is not likely to be helpful as these records do not agree in terms of\nprecession variability across this interval. This seems fair, although if this reasoning is not\nexplicitly stated in the paper it would be good to include it and also make reference to these other\nstudies that reconstruct precession from this interval.\n\nFollowing the reviewer’s suggestion, we now indicate that precession signals within CaCO\n3\nrecords have been widely identified although they have differences among diverse records. We\nincluded supporting references for these statements such as Galeotti et al. (2010), Zachos et al.\n(2010), Litter et al. (2014), Zeebe et al. (2017), and Piedrahita et al. (2022) (lines 354-359).\n\nComment 12: Reviewer 1 suggests the HIRM-CFB record is not reliable for identifying orbital-\nscale cyclicity due to its failure to identify the correct number of precession cycles across the PETM\nand its failure to match the ZB18 solution on eccentricity timescales. The authors seem to suggest\nthey have changed their filtering method, although it is not clear how as the bandpass filters\ndescribed in the methods section have not changed. However, the HIRM-CFB precessional signal\ndoes now seem to have the correct number of cycles across the PETM. The fact that the HIRM-\nCFB filtered eccentricity signal does not match the ZB18/PC1dis signal across a substantial part of\nthe interval is not addressed in the authors’ reviewer response.\n\nIn our first submission, Reviewer #1 noticed that our HIRM-CFB plot was incorrect. We\naccidentally plotted a 0.026±0.003 cycles kyr−1 filtered signal. We addressed that issue and plotted\na 0.044 ± 0.010 cycles kyr−1 filtered signal that contains all precession components. This filtered\nsignal has ~9 precession cycles (Fig. 8c), which is the same as identified for PC1 , with the correct\ndis\nnumber of cycles expected for a ~170-200 kyr PETM duration (lines 599-617) (see figure below).\nWe understand that the reviewer is addressing comments from two reviews. We are grateful for\nthat, but we would like to respectfully indicate that in our past review, we presented several\narguments that explain why the HIRM-CFB eccentricity signal does not match the ZB18a\nastronomical solution in some parts of the Contessa Road record (see Comment 6-Reviewer #1 and\nComment 29, Reviewer #2). We indicated that most out-of-phase HIRM-CFB short eccentricity\ncycles coincide with long eccentricity minima periods and suggested that this pattern may indicate\nthat only global warming events synchronous with enhanced precession-driven haematite\nformation could promote hydroclimate variations that can be recorded in the short eccentricity\nband. Nevertheless, we also pointed out that some HIRM-CFB short eccentricity cycles are in-\nphase with ZB18a, and do not coincide with short-lived carbon cycle perturbations. Therefore, we\nsuggested that HIRM-CFB may have not been sensitive enough to short eccentricity when the\nprecession cycle amplitude was reduced by long eccentricity forcing. However, one long\neccentricity maxima interval has HIRM-CFB short eccentricity cycles that do not match ZB18a.\nWe also considered that source area changes and post-depositional alteration may explain the origin\nof those out-of-phase short eccentricity cycles, although these processes are not identified at\nContessa Road. Finally, we proposed that precession signal clipping could play a role in short\neccentricity cyclicity development (e.g., Walters et al., 2023). We were unable to indicate\nconclusively the process that drove out-of-phase HIRM-CFB short eccentricity cycles. Hence, we\nemphasised that we focus on the impacts of enhanced orbitally-driven seasonal contrast and short-\nlived carbon cycle perturbations on western Tethyan hydroclimate variability (lines 414-442).\n\nComment 13: The text written in response to this comment (lines 362-365 of the revised MS)\nstates that the HIRM-CFB precession signal is out of phase with the PC1dis precession signal,\nbased on visual inspection of Fig 8c and the phase analysis in the bottom row of Fig 7. I did not\nfind this very convincing – the phase relationship in Fig 8c looks very variable to me, with some\nparts of the record very much out of phase and other very much in phase. Although there are\nleads/lags of ~10 kyr identified in the PETM and EELMZ phase spectra, the majority of the record\nfalls into the central interval, where the lead/lag is max 4 kyr.\n\nThanks. We indicate that PC1 and HIRM-CFB precession signals are typically out of phase. Yes,\ndis\nsome precession cycles in these records are in-phase; however, these parts of the records are limited\nto two (2) precession cycles at ~53 Ma, two (2) precession cycles between ~53.5 Ma and 54 Ma,\nfive (5) precession cycles between 54 Ma and 54.5 Ma, and one (1) precession cycle at ~54.6 Ma.\nThese 10 precession cycles represent 7% of the 135 precession cycles identified in our records.\nThis small proportion cannot be even detected by phase spectra, which consistently reveal lag/lead\nrelationships. Therefore, we interpret HIRM-CFB precession to be mostly out of phase with PC1 .\ndis\nThis pattern is similar to that identified in orbitally forced Neogene-Quaternary Mediterranean\nsediments, as now indicated in the text with appropriate references (lines 369-373).\n\nComment 14: Climatic interpretation of spectral analysis. Reviewer 1 questions the connections\ndrawn between the precession and eccentricity signals in PC1dis and HIRM-CFB and seasonality,\nnoting that in the Northern Hemisphere, maximum precession = minimum seasonality and\nminimum precession = maximum seasonality. Eccentricity modulates this, with maximum\neccentricity producing both maximum and minimum seasonalities in a given precession cycle,\nwhile minimum eccentricity produces little contrast in seasonality across a given precession\ncycle. Reviewer 1 further notes that seasonal precipitation, extreme precipitation events and fluvial\ninput increase with increased seasonality.\nThe discussion in lines 370-385 of the revised MS is consistent with this, with maximum precession\nargued to represent times of greater aridity/higher HIRM-CFB, and vice versa. However, the\ndiscussion in lines 388-402 as well as the response to the reviewer do not seem to have taken the\nreviewer’s concerns into account. Maximum eccentricity is still identified as producing maximum\nseasonal contrast in lines 394-395, although the reviewer’s point was that maximum eccentricity\nmodulates precession such that both maximum seasonal contrast and minimum seasonal contrast\noccur (in the Northern Hemisphere, at minimum and maximum precession, respectively). Thus,\ngiven that most of the LPEEs last for several precession cycles, they cannot be said to be simply\ntimes of maximum seasonal contrast.\n\nThanks. We modified the text accordingly and following Comment 6 (Reviewer #1). We indicate\nthat short eccentricity maxima strengthened insolation control and caused wet phases with\naccelerated chemical weathering during precession-driven insolation maxima, and dry phases with\nexpanded arid zones during subsequent precession-driven lower-insolation periods (lines 393-412).\n\nComment 15: The authors also argue in lines 396-397 that maximum seasonal contrast at\neccentricity maxima produces dry conditions/reduced seasonal precipitation, although they have\nargued the opposite in lines 370-385 (maximum seasonal contrast = wetter conditions/increased\nseasonal precipitation, consistent with Reviewer 1 and, e.g., Bosmans et al., 2015). This\nidentification of eccentricity maxima with enhanced seasonal contrast is repeated in lines 410-411.\nIf high seasonal contrast is considered to produce overall wetter conditions due to enhanced\nseasonal and monsoonal precipitation and increased extreme precipitation events, as argued in lines\n370-385, then periods of maximum eccentricity should be characterised by both enhanced dry\n(maximum precession/minimum seasonal contrast/minimum seasonal precipitation) and enhanced\nwet (minimum precipitation/maximum seasonal contrast/maximum seasonal precipitation) conditions.\nI could see an argument where the haematite precursors are produced during the wet periods and then\nthe haematite itself is produced and transported during the dry periods, and thus the enhancement of\nboth types of climate during eccentricity maxima and LPEEs results in overall increased average\nhaematite in the sediments. I could also see an argument where the increased temperatures during\nLPEEs enhance the increase in haematite formation and transport at times of minimum seasonal\ncontrast (and therefore minimum seasonal precipitation), which would also occur at times of\nmaximum eccentricity. However, at present, the argument about how eccentricity modulation of\nprecession produces the observed haematite variations is not clear to me.\n\nThanks. We now remark that short eccentricity maxima enhanced haematite formation with wet\nphases related to precession-driven insolation maxima, and dry phases induced by reduced\nprecession-driven insolation. We indicate that amplified orbital controls and/or non-linear\nhydroclimate responses to short-lived carbon cycle perturbations reduce seasonal precipitation and\nproduced HIRM-CFB short eccentricity maxima coeval with ZB18a (lines 393-412). Accordingly,\nwe rephrased lines 410-411 (now lines 420-421) and replaced “enhanced seasonal contrast” with\n“enhanced precession-driven haematite production”.\n\nReviewer #3 (Remarks to the Author):\n\nComment 1: The authors have done a nice job revising the staging of the manuscript and\ninterpretation of the eccentricity signal in their records. One last suggestion, the authors probably\nwould want to consider removing or rewriting sentences/wordings related to the long-lasting effect\nof anthropogenic CO2 emissions (lines 33 to 34, 37 to 38). More recent studies generally agree that\nonce 0 emission is reached, CO2 level in the atmosphere will fall, and global warming will stop\n(e.g., Matthews and Weaver 2010, Nat. Geo). This is due to the net absorption of CO2 by the ocean\nand land. These statements can be considered as erroneous in the eyes of researchers who study\nmodern climate.\n\nThanks. We modified the text to clarify that long-term global warming impacts are expected if\nclimate change mitigation policies are not adopted (lines 32-34, 37-38).\n\nREVIEWERS' COMMENTS\nReviewer #2 (Remarks to the Author):\n\nThanks to the authors for their detailed consideration of my comments. They have addressed all my\nconcerns. I look forward to seeing the study in print!"}, "author_response": ""}]

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