the paleocene eocene transition at mead stream new zealand a southern pacific record of early cenozoic global change mead stream in marlborough new zealand exposes a spectacular 650 m thick stratigraphic section of well bedded micritic limestone chert and marl that was deposited on a south pacific upper continental slope from late cretaceous to middle eocene the 200 m upper paleocene lower eocene succession was examined for its lithology bulk carbonate carbon isotopes and assemblages of radiolarians calcareous nannoplankton and foraminifera so that it could be placed into a global context the interval displays several prominent carbon isotope anomalies and is correlated with south pacific radiolarian zones rp5 to rp9 and calcareous nannofossil zones np6 8 to np12 additionally planktic foraminiferal zones p4 to p6b are identified in uppermost paleocene and lower eocene strata mead stream has a near continuous paleocene lower eocene sediment record and three globally significant climate events the late paleocene carbon isotope maximum pcim the initial eocene thermal maximum ietm and the early eocene climatic optimum eeco have obvious expressions the pcim is a 50 m thick interval of biosiliceous micritic limestone in which 13c is 3 the lower part contains two organic rich biosiliceous mudstone units that may represent expansion of an oxygen minimum zone omz during a global increase in marine biological productivity the ietm is a 4 m thick interval in which 13c drops below 1 5 in a pattern seen at other locations the basal 2 4 m is a distinctive recessed marl rich unit that is defined herein as the dee marl the ietm is marked by a rapid decline in the nannoplankton genus fasciculithus short lived occurrences of discoaster cf araneus and morozovella aequa aequa and significant radiolarian faunal turnover owing to impoverished benthic faunas the benthic foraminiferal extinction event bfee is poorly defined the onset of the eeco is marked by a 1 negative 13c excursion a transition from limestone rich to marl rich facies and a marked decrease in radiolarian abundance compacted sedimentation rates vary between 1 4 2 7 cm kyr for upper paleocene lower eocene strata at mead stream although individual beds with average thickness of 10 cm were deposited too fast to directly represent cycles in orbital parameters time series analysis of bed thicknesses suggests that groups of beds may record milankovitch scale periodicity perhaps with a significant obliquity component thus the relative frequency and thickness of marl and limestone beds in this section is shown to be strongly influenced by climatic changes at a wide range of temporal scales from suborbital and orbital cycles to aberrant short term events and long term trends predominance of marl in ietm and eeco intervals indicates that episodes of extreme global warming resulted in reduced oceanic productivity and increased terrestrial discharge in the high latitude southwestern pacific

enhanced terrestrial weathering runoff and surface ocean carbonate production during the recovery stages of the paleocene eocene thermal maximum 1 the carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the paleocene eocene thermal maximum petm circa 55 ma the rapid release of large quantities of carbon into the ocean atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion cie the brevity 120 220 kyr of the petm reflects the rapid enhancement of negative feedback mechanisms within earth s exogenic carbon cycle that served the dual function of buffering ocean ph and reducing atmospheric greenhouse gas levels detailed study of the petm stratigraphy from ocean drilling program site 690 weddell sea reveals that the cie recovery period which postdates the cie onset by 80 kyr is represented by an expanded 2 5 m thick interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate collectively the micropaleontological and sedimentological changes preserved within the cie recovery interval reflect a transient state when ocean atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths a prominent peak in the abundance of the clay mineral kaolinite is associated with the cie recovery interval indicating that continental weathering runoff intensified at this time as well robert and kennett 1994 such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering runoff and carbonate precipitation helped sequester carbon during the petm recovery period e g dickens et al 1997 zachos et al 2005

jurassic and cretaceous paleomagnetic data from the southern alps italy jurassic and cretaceous paleomagnetic data from 46 sites in the venetian alps trento plateau and se lombardian basin have been compiled nine of these site mean directions have been previously published the sites can be divided into four age groups senonian hauterivian barremian kimmeridgian tithonian and callovian oxfordian for three of the age groups positive regional fold tests indicate at the 99 confidence level that the characteristic magnetization components predate the deformation structural mapping in the venetian alps allowed us to assign sites to individual thrust sheets and we observe no significant relative rotation of thrust sheets in the nappe pile indeed we observe remarkable consistency in mean direction throughout the entire sampling area for each of the four age groups the senonian and hauterivian barremian pole positions lie close to coeval poles on african apparent polar wander paths apwps this result is consistent with previous analyses of middle and late cretaceous data from the venetian alps the new jurassic poles deviate significantly from recently published african apwps reflecting either the poor definition of the african apwp in the late jurassic or about 20 anticlockwise rotation of the southern alps relative to africa during early cretaceous time the former of the two possibilities is favored by a new late jurassic early cretaceous pole from north america and by early permian paleomagnetic data from the southern alps which are consistent with coeval african data implying that the movement of the southern alps was similar to that of africa since early permian

new evidence for subtropical warming during the late paleocene thermal maximum stable isotopes from deep sea drilling project site 527 walvis ridge the late paleocene thermal maximum lptm was a dramatic short term global warming event that occurred 55 ma warming of high latitude surface waters and global deep waters during the lptm has been well documented however current data suggest that subtropical and tropical sea surface temperatures ssts did not change during the event conventional paradigms of global climate change such as co2 induced greenhouse warming predict greater warming in the high latitudes than in the tropics or subtropics but nonetheless cannot account for the stable tropical subtropical ssts we measured the stable isotope values of well preserved late paleocene to early eocene planktonic foraminifera from south atlantic deep sea drilling project dsdp site 527 to evaluate the subtropical response to the climatic and environmental changes of the lptm planktonic foraminiferal 18o values at site 527 decrease by 0 94 from pre lptm to excursion values providing the first evidence for subtropical warming during the lptm we estimate that subtropical south atlantic ssts warmed by at least 1 4 c on the basis of possible changes in evaporation and precipitation the new evidence for subtropical sst warming supports a greenhouse mechanism for global warming involving elevated atmospheric co2 levels

turbulent heat and momentum fluxes in the upper ocean under arctic sea ice we report observations of heat and momentum fluxes measured in the ice ocean boundary layer from four drift stations between january and june 2015 covering from the typical arctic basin conditions in the nansen basin to energetic spots of interaction with the warm atlantic water branches near the yermak plateau and over the north spitsbergen slope a wide range of oceanic turbulent heat flux values are observed reflecting the variations in space and time over the five month duration of the experiment oceanic heat flux is weakly positive in winter over the nansen basin during quiescent conditions increasing by an order of magnitude during storm events an event of local upwelling and mixing in the winter time nansen basin highlights the importance of individual events spring time drift is confined to the yermak plateau and its slopes where vertical mixing is enhanced wind events cause an approximate doubling of oceanic heat fluxes compared to calm periods in june melting conditions near the ice edge lead to heat fluxes of o 100 w m 2 the combination of wind forcing with shallow atlantic water layer and proximity to open waters leads to maximum heat fluxes reaching 367 w m 2 concurrent with rapid melting observed ocean to ice heat fluxes agree well with those estimated from a bulk parameterization except when accumulated freshwater from sea ice melt in spring probably causes the bulk formula to overestimate the oceanic heat flux this article is protected by copyright all rights reserved

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

latest paleocene earliest eocene cyclostratigraphy using core photographs for reconnaissance geophysical logging abstract i present a new method for reconnaissance cyclostratigraphic study of continuously cored boreholes the generation of detailed sediment color logs by digitizing ocean drilling program odp core photographs the reliability of the method is tested by comparison with the spectrophotometer color log for the uppermost paleocene lowermost eocene section chron c24r at odp hole 1051a the color log generated from hole 1051a core photographs is essentially identical to the spectrophotometer log the method is applied to the chron c24r section at holes 1051a and 690b producing the first high resolution geophysical log for the latter section i calculate astronomically calibrated durations between bio and chemostratigraphic events within chron c24r by correlating the cyclostratigraphies for holes 1051a and 690b these durations are significantly different from previous estimates indicating that the chronology of events surrounding the paleocene eocene boundary will have to be revised this study demonstrates that useful geophysical logs can be generated from digitized odp and dsdp core photographs the method is of practical use for sections lacking high resolution logs as is the case for most lower paleogene sections

combined airborne laser and radar altimeter measurements over the fram strait in may 2002 knowledge of sea ice thickness is critical for the prediction of future climate and for assessing the significance of changes in thickness sea ice thickness can be calculated from radar or laser satellite altimetry measurements of freeboard however a lack of knowledge of snow depth introduces significant uncertainties into these calculations this paper compares the first coincident airborne laser and radar altimetry data over sea ice collected during the laser radar altimetry lara field campaign lara was a flight of opportunity that provided valuable data to explore techniques to validate satellite measurements of ice freeboard and the possibility of combining laser and radar measurements over snow covered sea ice to calculate the snow depth two new methods were created to analyse these data sets a new radar retracker and a radar power simulator which models radar returns from the laser data we present the first quantitative analysis of data from the lara laser and radar altimeters and demonstrate the potential of combining laser and radar altimetry to estimate snow depth lara elevation estimates compare well with elevations from the radar altimeter onboard ers 2 at the sub meter level and the study provides lessons for future validation of satellite altimetry data over sea ice laser elevations are consistently higher than the radar elevations over snow covered sea ice as lara was a flight of opportunity no coincident in situ measurements were available nevertheless the difference between the reflecting surface of the laser and radar is consistent with snow depth from climatology and the analysis techniques developed in this paper will be useful for future radar and laser altimetry comparisons

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

abrupt hydrographic changes in the equatorial pacific and subtropical atlantic from foraminiferal mg ca indicate greenhouse origin for the thermal maximum at the paleocene eocene boundary 1 the paleocene eocene boundary peb was marked by an extraordinary climatic event hypothesized to originate from a large perturbation to the carbon cycle which fueled global warming the rapid dissociation of oceanic methane hydrates the pattern of surface warming interpreted from existing sea surface temperature records is not consistent with a greenhouse origin for this event which would have fueled sea surface warming globally although oxygen isotope 18o based reconstructions indicate polar warming results for the tropics and subtropics are ambiguous because of uncertainties associated with interpreting planktonic foraminiferal 18o to remedy this we have constructed high resolution temperature records based on mg ca of multiple species of both surface and thermocline dwelling planktonic foraminifera across the peb in the equatorial pacific and subtropical atlantic during the carbon isotope excursion cie surface temperatures increased by 3 5 4 c and thermocline temperatures warmed by 3 c estimates of surface water and thermocline salinity based on paired mg ca and 18o data indicate a pattern of hydrographic changes in the equatorial and subtropical oceans that is different from previously proposed with a more vigorous hydrologic cycle during warming the pattern of warming and salinity changes are consistent with this being a greenhouse induced global warming event and the timing of hydrographic changes relative to the cie supports the hypothesis that gradual warming of intermediate deep waters triggered methane hydrate dissociation

warm atlantic water explains observed sea ice melt rates north of svalbard warm atlantic water aw that flows northward along the svalbard west coast is thought to transport enough heat to melt regional arctic sea ice effectively despite this common assumption quantitative requirements necessary for aw to directly melt sea ice fast enough under realistic winter conditions are still poorly constrained here we use meteorological data satellite observations of sea ice concentration and drift and model output to demonstrate that most of the sea ice entering the area over the yermak plateau melts within a few weeks simulations using the los alamos sea ice model cice in a 1 d vertically resolved configuration under a relatively wide range of in situ observed atmospheric and ocean forcing show a good fit to observations simulations require high frequency atmospheric forcing data to accurately reproduce vertical heat fluxes between the ice or snow and the atmosphere moreover we switched off hydrostatic equilibrium to properly reproduce ice and snow thickness when observations showed that ice had a negative freeboard without surface flooding and snow ice formation this modeling shows that realistic melt rates require a combination of warm near surface aw and storm induced ocean mixing however if aw is warmer than usual 5 c then lower mixing rates are sufficient our results suggest that increased winter storm frequency and increased heat content of the aw may work together in reducing future sea ice cover in the eurasian basin

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

the apectodinium acme and terrestrial discharge during the paleocene eocene thermal maximum new palynological geochemical and calcareous nannoplankton observations at tawanui new zealand manifestations of profound perturbations in biogeochemical systems during the paleocene eocene thermal maximum petm include a prominent global negative 13c and a pronounced increase in the relative abundance of dinoflagellate cysts dinocysts assigned to the genus apectodinium while motile representatives of apectodinium were most likely thermophilic and heterotrophic the underlying causes of this dinoflagellate response are not well understood here we provide new insight by examining the palynology chemistry and calcareous nannoplankton across the petm in a continental slope section at tawanui new zealand across the petm marked changes in the relative abundance of apectodinium vary antithetically with significant changes in the 13c of carbonate and organic matter in general the high relative abundance of apectodinium relates to enhanced concentrations of dinocysts signifying a bloom of apectodinium in surface waters during the petm changes in apectodinium and 13c records correspond to variations in many other parameters including a smaller negative shift in bulk carbonate 13c than expected increased terrestrial palynomorphs elevated toc and c n ratios lower carbonate contents higher sio2 and al2o3 contents and lower si al ratios all of these variations can be explained by an increase in delivery of terrigenous material to the continental margin a peak in the relative abundance of glaphyrocysta dinocysts at the onset of the petm may indicate greater down slope transport of neritic material changes in calcareous nannoplankton abundances suggest increased nutrient availability in surface waters during the petm the combined results show that apectodinium dominated assemblages global perturbations in carbon isotopes and enhanced terrigenous delivery closely correspond in time at tawanui a sudden and massive carbon injection to the ocean atmosphere system may have enhanced weathering and increased terrigenous inputs to continental margins during the petm we further suggest that these inputs caused the apectodinium acme by elevating primary productivity in marginal seas

palaeocene oceans and climate an isotopic perspective abstract the early cenozoic was a time of climatic and oceanographic transition from the cretaceous greenhouse world to the icehouse world of the neogene 18 o measurements shed light on ocean temperature and possible polar ice fluctuations during this interval while 13 c measurements monitor fluctuations in ocean productivity deep water circulation and atmospheric co 2 the major features from 18 o analysis of the early cenozoic are general cooling of surface waters with some evidence for transient cooling across the k t boundary surface water temperatures were at a cenozoic maximum in the early eocene whereas deep waters cooled then warmed during the palaeocene the 13 c of bulk carbonates is at a minimum at the start of the cenozoic due to the profound crisis in ocean surface water productivity associated with the extinctions of marine plankton at the cretaceous tertiary boundary thereafter 13 c values increase in bulk carbonates as well as planktonic and benthonic foraminifera to their cenozoic maximum in the late palaeocene c 60 ma after which time they again decrease over an interval of c 4 5 m y to a cenozoic low in the early eocene the increase in 13 c values characteristic of the palaeocene period is probably related to a combination of increasing surface water productivity and accelerated burial of organic carbon conversely the decline in 13 c into the early eocene is probably related to a decrease in ocean productivity and a deceleration in the rate of organic carbon burial benthic 13 c comparisons suggest that deep waters appear to have been predominantly formed in the high southern latitudes with the exception of a short lived interval near the palaeocene eocene boundary possibly associated with a transient climatic anomaly the late palaeocene thermal maximum the thermal change of palaeocene deep waters may be related to the changing productivity of surface waters by controlling atmospheric co 2 flux in a similar way to that proposed for the control of the pleistocene glacial cycles

interdecadal changes in snow depth on arctic sea ice snow plays a key role in the growth and decay of arctic sea ice in winter it insulates sea ice from cold air temperatures slowing sea ice growth from spring to summer the albedo of snow determines how much insolation is absorbed by the sea ice and underlying ocean impacting ice melt processes knowledge of the contemporary snow depth distribution is essential for estimating sea ice thickness and volume and for understanding and modeling sea ice thermodynamics in the changing arctic this study assesses spring snow depth distribution on arctic sea ice using airborne radar observations from operation icebridge for 2009 2013 data were validated using coordinated in situ measurements taken in march 2012 during the bromine ozone and mercury experiment bromex field campaign we find a correlation of 0 59 and root mean square error of 5 8 cm between the airborne and in situ data using this relationship and icebridge snow thickness products we compared the recent results with data from the 1937 1954 1991 soviet drifting ice stations the comparison shows thinning of the snowpack from 35 1 9 4 to 22 2 1 9 cm in the western arctic and from 32 8 9 4 to 14 5 1 9 cm in the beaufort and chukchi seas these changes suggest a snow depth decline of 37 29 in the western arctic and 56 33 in the beaufort and chukchi seas thinning is negatively correlated with the delayed onset of sea ice freezeup during autumn

new chronology for the late paleocene thermal maximum and its environmental implications the late paleocene thermal maximum lptm is associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle we have developed a new orbital chronology for ocean drilling program odp site 690 weddell sea southern ocean by using spectral analysis of high resolution geochemical records the lptm interval spans 11 precessional cycles yielding a duration of 210 to 220 k y the 13 c anomaly associated with the lptm has a magnitude of about 2 5 to 3 we show that about 2 of the excursion occurs within two steps that each were less than 1000 yr in duration the remainder developed through a series of steps over 52 k y the timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial further we are able to correlate the records between odp sites 690 and 1051 western north atlantic on the scale of 21 k y cycles which demonstrates that the details of the 13 c excursion are recognizable between distant sites comparison of cycle records at sites 690 and 1051 suggests that sediment representing the interval 30 k y just prior to and at the onset of the lptm are missing in the latter location this unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k y of the start of the lptm

effect of frequent winter warming events storms and snow on sea ice growth a case from the atlantic sector of the arctic ocean during the n ice2015 campaign

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

meteorological conditions in a thinner arctic sea ice regime from winter to summer during the norwegian young sea ice expedition n ice2015 atmospheric measurements were made over arctic sea ice north of svalbard from winter to early summer january june 2015 during the norwegian young sea ice n ice2015 expedition these measurements which are available publicly represent a comprehensive meteorological data set covering the seasonal transition in the arctic basin over the new thinner sea ice regime winter was characterized by a succession of storms that produced short lived less than 48 h temperature increases of 20 to 30 k at the surface these storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering north atlantic storms into the high arctic nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling radiatively clear state the strength and depth of these inversions were similar to those during the surface heat budget of the arctic ocean sheba campaign in contrast atmospheric profiles during the opaquely cloudy state were different to those from sheba due to differences in the synoptic conditions and location within the ice pack storm events observed during spring summer were the result of synoptic systems located in the barents sea and the arctic basin rather than passing directly over n ice2015 these synoptic systems were driven by a large scale circulation pattern typical of recent years with an arctic dipole pattern developing during june surface temperatures became near constant 0 c on 1 june marking the beginning of summer atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes

coccolith sr ca records of productivity during the paleocene eocene thermal maximum from the weddell sea 1 a major perturbation of the global carbon cycle 55 million years ago believed to result from release of 1000 2000 gt of c from methane hydrates correlates with an intense but transient greenhouse warming event known as the paleocene eocene thermal maximum petm the rapid 105 years recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle enhanced marine productivity may be one important feedback but indicators for productivity changes have yielded conflicting results here we use a new independent indicator sr ca in coccolith carbonate which covaries with the productivity of coccolithophorid algae to investigate the biotic response in the most complete petm deep sea record which was recovered at odp site 690 in the weddell sea in the dominant coccolithophorid genus toweius a large 40 sr ca increase immediately after the gas hydrate release signals a dramatic productivity increase productivity levels remained high for 60 000 years but decreased to pre event levels by 120 000 years after the gas hydrate release productivity levels during the petm are higher than observed at any other time in our 400 000 year record other coccolithophorid genera chiasmolithus and discoaster show a brief modest 25 sr ca increase increase in productivity that lags behind the methane event by 50 000 years and is within the range of productivity variation elsewhere in the record the timing of the toweius productivity increase agrees well with os isotope records of globally increased weathering intensity which may have provided higher nutrient fluxes to stimulate algal productivity if this type of productivity response occurred globally it would also be consistent with the timing of c drawdown that may have returned temperatures to near pre event levels

an osmium isotope excursion associated with the late paleocene thermal maximum evidence of intensified chemical weathering in the latest paleocene an abrupt shift to more negative 13c values has been documented at numerous marine and terrestrial sites bralower et al 1997 cramer et al 1999 kaiho et al 1996 kennett and stott 1991 koch et al 1992 stott et al 1996 thomas and shackleton 1996 zachos et al 1993 this carbon isotope event cie is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4 6 c kennett and stott 1991 and more moderate warming in the subtropics thomas et al 1999 here we report 187os 188os isotope records from the north atlantic and indian oceans which demonstrate a 10 increase in the 187os 188os ratio of seawater coincident with the late paleocene cie this excursion to higher 187os 188os ratios is consistent with a global increase in weathering rates the inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate which acts to stabilize earth s climate walker et al 1981 estimates of the duration of late paleocene cie bains et al 1999 bralower et al 1997 norris and rohl 1999 rohl et al 2000 in conjunction with the os isotope data imply that intensified chemical weathering in response to warm humid climates can occur on timescales of 104 105 years this interpretation requires that the late paleocene thermal maximum os isotope excursion be produced mainly by increased os flux to the ocean rather than a transient excursion to higher 187os 188os ratios in river runoff although we argue that the former is more likely than the latter we cannot rule out significant changes in the 187os 188os ratio of rivers

barium and the late paleocene δ13c maximum evidence of increased marine surface productivity deep sea sediment ba ba al2o3 sample 15 ba aluminosilicate records show increasing values synchronous with the evolution of the late paleocene global 13c maximum reflecting an increase in marine surface primary production and biogenic barite formation at this time at two oligotrophic locations deep sea drilling project dsdp sites 384 and 527 in the north and south atlantic respectively ba increases from 160 360 ppm in the early paleocene to 1100 3000 ppm during the 13c maximum at equatorial dsdp site 577 positioned within or near the high productivity zone ba increases from 15 500 ppm in the early paleocene to 25 400 ppm in conjunction with late paleocene maximum 13c values linear fitted correlation plots of sediment ba content versus surface water 13c in all three regions support barite originating in the euphotic zone the early to late paleocene relative increase in ba illustrates how burial rates of corg relative to al2o3 accelerated by a factor of 1 8 and 6 0 in the eutrophic and oligotrophic areas respectively a tentative estimate weighing our result for the entire ocean suggests that accumulation rates of organic carbon increased by a factor of 2 during the late paleocene 13c maximum

the blast in the past the rapidity and amount of carbon being released through human agency have been thought to be unprecedented not so it emerges from the evidence of anomalies in the ratios of carbon isotopes in an ocean core it seems that around 55 million years ago there was an equivalently swift and massive blast of carbon into the ocean and atmosphere the source was probably methane hydrates that are usually locked up in huge deposits on continental shelves

magnetostratigraphic and cyclostratigraphic calibration of a prospective palaeocene eocene stratotype at zumaia basque basin northern spain detailed magnetostratigraphic work at the palaeocene eocene boundary interval in the zumaia section has led to a precise delineation of the position of polarity chron c25n from 35 0 m or 35 7 m to 25 2 m below the base of the carbon isotopic excursion that marks the palaeocene eocene boundary this chronostratigraphic constraint suggests that the lithological carbonate marl couplets making up most of the studied section are the expression of orbital precession cycles and confirms the expanded and continuous nature of the section with mean sediment accumulation rates of 2 5 cm kyr 1 the new data render zumaia a unique land based marine section with available magnetostratigraphic data coupled to cyclostratigraphy the revised chronostratigraphic framework presented supports previous cyclostratigraphic calibration of the latest palaeocene geomagnetic timescale it should facilitate better assessment of the different chemobiostratigraphic events that span this critical interval as a consequence of past climate and oceanographic change consequently the zumaia section is proposed as a candidate global stratotype section and point gssp for the palaeocene eocene boundary

rare earth elements in limestone marlstone couplets from the albian cenomanian cismon section venetian region northern italy assessing ree sensitivity to environmental changes abstract we have studied the ree distribution through the albian cenomanian interval of a stratigraphic succession cismon section scaglia variegata formation venetian prealps consisting of rhythmically alternating carbonate rich and carbonate poor strata which are the sedimentary expression of systematic variations of surface fertility and bottom water redox conditions in the depositional basin limestone semicouplets show seawater like shale normalized patterns hree enriched with negative ce anomalies and high er nd ratios indicating a clear dependence on the ree chemistry of surface seawaters marlstones and shales exhibit flatter patterns more moderate ce anomalies and low er nd good correlations between er nd ce ce and mn suggest that superimposed on ree signatures imparted by detrital and biogenic phases the ree composition shows evidence of their sensitivity to palaeoredox conditions resulting in ree fractionation and ce cycling ree data are consistent with results from previous stratigraphic and geochemical major and trace elements investigations in reflecting palaeoenvironmental conditions rhythmically varying from efficiently mixed seawater during the limestone deposition to oxygen depleted bottom waters at the time of marlstone deposition

thermal conductivity of landfast antarctic and arctic sea ice 1 we present final results from a program to measure the thermal conductivity of sea ice with in situ thermistor arrays using an amended analysis of new and previously reported ice temperatures results from landfast first year fy ice near barrow alaska and mcmurdo sound antarctica are consistent with predictions from effective medium models but 10 15 higher than values from the parameterization currently used in most sea ice models we observe no previously reported anomalous near surface reduction which is now understood to have been an artifact nor a convective enhancement to the heat flow although our analysis is limited to temperatures below 5c at which brine percolation is restricted results for landfast multiyear my ice in mcmurdo sound are also consistent with effective medium predictions and emphasize the density dependence we compare these and historical measurements with effective medium predictions and the representation commonly used in sea ice models developed originally for my arctic ice we propose an alternative expression derived from effective medium models appropriate for both my and fy ice that is consistent with

critical role of snow on sea ice growth in the atlantic sector of the arctic ocean during the norwegian young sea ice n ice2015 campaign in early 2015 a deep snow pack was observed almost double the climatology for the region north of svalbard there were significant amounts of snow ice in second year ice syi while much less in first year ice fyi here we use a 1 d snow ice thermodynamic model forced with reanalyses to show that snow ice contributes to thickness growth of syi in absence of any bottom growth due to the thick snow growth of fyi is tightly controlled by the timing of growth onset relative to precipitation events a later growth onset can be favorable for fyi growth due to less snow accumulation which limits snow ice formation we surmise these findings are related to a phenomenon in the atlantic sector of the arctic where frequent storm events bring heavy precipitation during autumn and winter in a region with a thinning ice cover

observations of flooding and snow ice formation in a thinner arctic sea ice regime during the n ice2015 campaign influence of basal ice melt and storms seven ice mass balance instruments deployed near 83 n on different first year and second year ice floes representing variable snow and ice conditions documented the evolution of snow and ice conditions in the arctic ocean north of svalbard in january march 2015 frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution four instruments documented flooding and snow ice formation flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy increased temperature and heat propagation through the underlying ice slush then progressively transformed into snow ice flooding resulted from two different processes i after storm induced breakup of snow loaded floes and ii after loss of buoyancy due to basal ice melt in the case of breakup when the ice was cold and not permeable rapid flooding probably due to lateral intrusion of seawater led to slush and snow ice layers at the ocean freezing temperature 1 88 c after the storm the instruments documented basal sea ice melt over warm atlantic waters and ocean to ice heat flux peaked at up to 400 w m 2 the warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow ice 3 c the n ice2015 campaign provided the first documentation of significant flooding and snow ice formation in the arctic ice pack as the slush partially refroze snow ice formation may become a more frequently observed process in a thinner ice arctic

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

reply to comment by timothy j bralower d clay kelly and deborah j thomas on coccolith sr ca records of productivity during the paleocene eocene thermal maximum from the weddell sea

ocean to ice heat flux at the north pole environmental observatory 1 data from drifting buoys deployed in april 2002 as part of the north pole environmental observatory project have been analysed to estimate ocean heat flux in the time period from 1 may 2002 to 11 mar 2003 prior to late january the observatory remained in deep water but subsequently drifted directly over the yermak plateau a relatively shallow feature north of svalbard while over deep water heat flux was dominated by storage and release of solar energy in the ocean boundary layer during summer the most likely annual average value for 2002 was 2 6 w m 2 less than previous determinations in the western arctic over yermak plateau heat flux at the interface came from mixing of warmer water into the boundary layer from below when the observatory was in water with depths less than 1200 m the average heat flux was around 22 w m 2

mode and tempo of the paleocene eocene thermal maximum in an expanded section from the venetian pre alps mode and tempo of an expanded paleocene eocene thermal maximum section in the venetian pre alps

an expanded cretaceous tertiary transition in a pelagic setting of the southern alps central western tethys abstract an integrated micropalaeontological planktonic foraminifera and calcareous nannofossils mineralogical and stable isotope investigation was carried out across the cretaceous tertiary k t boundary in a previously undescribed hemipelagic section forada section cropping out in the piave river valley southern alps belluno province ne italy our results suggest that an apparently complete k t transition with an expanded basal danian is preserved in the forada section the k t boundary is marked by a ca 1 5 cm thick clay interval intercalated in the pelagic carbonates of the scaglia rossa formation the boundary clay characterised by an iridium anomaly is constituted by a basal 1 2 mm thick green layer and an overlying red layer below the boundary clay the calcareous nannofossil micula murus zone and the planktonic foraminiferal plummerita hankteninoides zone that characterise the terminal maastrichtian in complete sections have been identified virtually all the calcareous plankton biohorizons normally utilised in the early danian have been recognised interestingly the ranking of the various biohorizons is the same observed elsewhere if considering the single plankton groups separately while several inconsistencies emerge if considering the relative succession of the two calcareous plankton groups simultaneously we caution to infer hiatuses on a section based only on the spacing of the biohorizons of a single group because of the risk of diachroneities in the stressed early danian environment by comparing the distance of the key biohorizons i e the first occurrence fo of cruciplacolithus primus and the last occurrence lo of parvularugoglobigerina eugubina from the boundary clay at forada and in other complete classical sections we have inferred that the early danian is expanded in the forada section the section seems ideally suited for studying the recovery pattern of the pelagic ecosystem and calcareous plankton communities in the aftermath of the k t catastrophe in a pelagic setting of the western central tethys the adaptive radiation of planktonic foraminifera was very rapid in contrast with the delayed diversification of coccolithophores the latter show a ca 21 cm thick dead zone that is followed by a long lasting survival interval ca 180 cm thick that might represent some 200 kyr dominated by persistent cretaceous coccolithophores and calcareous dinoflagellate thoracosphaera spp the temporal pattern in recovery of the coccolithophore and planktonic foraminiferal communities is decoupled as well pointing to their varying sensitivities to the k t perturbation it appears that the ecospace occupied by coccolithophores in the terminal maastrichtian was occupied in the initial danian by the calcareous dinoflagellates thoracosphaera spp that remained a significant component of the assemblage up to the base of the prinsius dimorphosus zone of romein romein a j t 1979 lineages in early paleogene calcareous nannoplankton utrecht micropaleontological bulletins 22 231 pp probably in the early chron c29n on the contrary planktonic foraminifera seem to reach stable conditions earlier in the late cruciplacolithus primus zone the early danian interval considered is also characterised by low sr ca ratio of the biogenic carbonates that would suggest dramatically low coccolithophore productivity conditions in agreement with previous flux studies we speculate that the altered ecological structure of phytoplankton community and the low productivity of coccolithophores severely affected the efficiency of the transfer of organic carbon from the photic zone to the deep ocean thus supporting the early danian living ocean model of d hondt et al d hondt s donaghay p zachos j c luttenberg d lindinger m 1998 organic carbon fluxes and ecological recovery from the cretaceous tertiary mass extinction science 282 276 279

dramatic interannual changes of perennial arctic sea ice linked to abnormal summer storm activity 1 the perennial september arctic sea ice cover exhibits large interannual variability with changes of over a million square kilometers from one year to the next here we explore the role of changes in arctic cyclone activity and related factors in driving these pronounced year to year changes in perennial sea ice cover strong relationships are revealed between the september sea ice changes and the number of cyclones in the preceding late spring and early summer in particular fewer cyclones over the central arctic ocean during the months of may june and july appear to favor a low sea ice area at the end of the melt season years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks they lack the normal maximum in cyclone activity over the central arctic ocean and cyclones that track from eurasia into the central arctic are largely absent fewer storms are associated with above average mean sea level pressure strengthened anticyclonic winds an intensification of the transpolar drift stream and reduced cloud cover all of which favor ice melt it is also shown that a strengthening of the central arctic cyclone maximum helps preserve the ice cover although the association is weaker than that between low cyclone activity and reduced sea ice the results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season

comparison of freeboard retrieval and ice thickness calculation from als asiras and cryosat 2 in the norwegian arctic to field measurements made during the n ice2015 expedition we present freeboard measurements from airborne laser scanner als the airborne synthetic aperture and interferometric radar altimeter system asiras and cryosat 2 siral radar altimeter ice thickness measurements from both helicopter borne and ground based electromagnetic sounding and point measurements of ice properties this case study was carried out in april 2015 during the n ice2015 expedition in the area of the arctic ocean north of svalbard the region is represented by deep snow up to 1 12 m and a widespread presence of negative freeboards the main scattering surfaces from both cryosat 2 and asiras are shown to be closer to the snow freeboard obtained by als than to the ice freeboard measured in situ this case study documents the complexity of freeboard retrievals from radar altimetry we show that even under cold below 15 c conditions the radar freeboard can be close to the snow freeboard on a regional scale of tens of kilometers we derived a modal sea ice thickness for the study region from cryosat 2 of 3 9 m compared to measured total thickness 1 7 m resulting in an overestimation of sea ice thickness on the order of a factor 2 our results also highlight the importance of year to year regional scale information about the depth and density of the snowpack as this influences the sea ice freeboard the radar penetration and is a key component of the hydrostatic balance equations used to convert radar freeboard to sea ice thickness

limited range of interspecific vital effects in coccolith stable isotopic records during the paleocene eocene thermal maximum 1 small but significant differences exist among stable carbon and oxygen isotopic excursions measured in coccolith dominated bulk carbonate and planktic foraminifera during the paleocene eocene thermal maximum petm one hypothesis suggests that the bulk carbonate isotopic record is compromised by changing nannofossil assemblages since modern nannofossils show a large 5 permil range of interspecific vital effects new techniques are employed here to separate different size fractions of coccoliths from petm sediments at odp site 690 for isotopic analysis removing a major portion of the variation in nannofossil assemblages isotopic compositions of coarse and fine coccolith fractions dominated by coccoliths of genus chiasmolithus and toweius respectively differ by less than 0 5 permil for both oxygen and carbon the near monogeneric toweius record closely parallels the main trends in the bulk carbonate isotope records including multiple steps in the negative carbon isotopic excursion suggesting that the trends in the bulk carbonate record are not artifacts of changing species assemblages because both coccolithophorids and symbiont bearing foraminifera like acarinina must inhabit the photic zone it is unlikely that the 103 year lags in isotope event onset between coccoliths and acarinina reflect true time transgressive invasion of isotopically depleted co2 into the water column the small range of vital effects among paleocene coccoliths is unlikely to result from diagenetic homogenization and instead may reflect more similar carbon acquisition strategies of paleocene coccolithophorid algae due to larger and or more similar cell sizes and higher atmospheric carbon dioxide the small range of vital effects suggests that bulk carbonate records are likely reliable for other early and pre cenozoic sediments where foraminifera are often scarce

reply to discussion on middle jurassic shear zones at cap de creus eastern pyrenees spain a record of pre drift extension of the piemonte ligurian ocean journal of the geological society london 174 289 300 we welcome the discussion by elena druguet jordi carreras and jochen mezger druguet et al 2017 of our paper vissers et al 2017 b in which we report jurassic 40ar 39ar ages from shear zones at cap de creus nw spain the authors argue that our interpretation of these results and the inferred development of the cap de creus shear zones during jurassic stretching and opening of the piemonte ligurian ocean contradicts structural and tectonic evidence and that it is not sufficiently supported by geochronological data below we first consider their structural and tectonic arguments from the tectonic palaeogeographical scale down to the smaller field scale and then proceed to discuss our ar ar results druguet et al 2017 note that prior to the oligo miocene rifting event the corso sardinian block was fixed east of ne iberia hence that the rocks at cap de creus were not located at the jurassic pre drift continental margin and that the northern cap de creus shear zones could not have formed as normal faults related to continental rifting this palaeogeographical argument builds on a previous hypothesis by stampfli borel 2002 stampfli et al 2002 and stampfli hochard 2009 in which iberia the corso sardinian block and the brianconnais domain formed one single microcontinent this hypothesis however must be discarded on the basis of recent palaeomagnetic work on sardinia by advokaat et al 2014 showing that between late jurassic and eocene time sardinia underwent no vertical axis rotations relative to eurasia and was fixed to europe in a rotated position that results from post eocene deformation whereas all available evidence indicates that iberia was located much further west and underwent some 35 counterclockwise rotation during the cretaceous van hinsbergen et al 2017 vissers et al 2017 a sardinia

palaeoenvironmental turnover across the palaeocene eocene boundary at the stratotype section in dababiya egypt based on benthic foraminifera the global stratotype section and point for the palaeocene eocene p e boundary was defined at dababiya quarry egypt at the base of the carbon isotope excursion cie we present the first detailed analysis of palaeocene eocene benthic foraminifera from dababiya in order to infer the palaeoenvironmental turnover across the p e boundary at dababiya the cie coincides with a major turnover in foraminiferal assemblages the last occurrence of angulogavelinella avnimelechi at the base of the cie may be correlated to the main phase of extinction of deep sea benthic foraminifera benthic foraminifera indicate that stressful conditions such as oxygen deficiency carbonate dissolution and changes in food supply persisted at the sea floor over most of the cie interval the main phase of recovery of benthic foraminifera is recorded c 250 cm above the p e boundary and it may be linked to increased productivity and oxygenation at the sea floor

could changing ocean circulation have destabilized methane hydrate at the paleocene eocene boundary 1 during the paleocene eocene thermal maximum petm 55 ma marine and terrestrial carbon isotope values exhibit a negative shift of at least 2 5 indicative of massive destabilization of marine methane hydrates releasing 2000 gigatons of methane carbon the cause of the hydrate destabilization is unknown but has been speculated to be warming due to a change from high latitude to low latitude deepwater formation here we present results from a numerical ocean model indicating that a sudden switch of deepwater formation from southern to northern high latitudes caused middepth and deep ocean warming of 3 5 c the switch is caused by a slow increase in the intensity of the atmospheric hydrologic cycle as expected under increasing temperatures and consistent with petm sedimentary evidence deepened subtropical subduction prior to the thermohaline circulation switch causes warming of 1 4 c in limited areas at thermocline through upper intermediate depths which could destabilize methane hydrates gradually and at progressively greater depths warming accompanying a south to north switch in deepwater formation would produce sufficient warming to destabilize seafloor gas hydrates over most of the world ocean to a water depth of at least 1900 m

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard