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

the importance of the terrestrial weathering feedback for multimillennial coral reef habitat recovery 1 modern day coral reefs have well defined environmental envelopes for light sea surface temperature sst and seawater aragonite saturation state arag we examine the changes in global coral reef habitat on multimillennial timescales with regard to sst and aragusing a climate model including a three dimensional ocean general circulation model a fully coupled carbon cycle and six different parameterizations for continental weathering the uvic earth system climate model the model is forced with emission scenarios ranging from 1 000 pg c to 5 000 pg c total emissions we find that the long term climate change response is independent of the rate at which co2 is emitted over the next few centuries on millennial timescales the weathering feedback introduces a significant uncertainty even for low emission scenarios weathering parameterizations based on atmospheric co2 only display a different transient response than weathering parameterizations that are dependent on temperature although environmental conditions for sst and aragstay globally hostile for coral reefs for millennia for our high emission scenarios some weathering parameterizations induce a near complete recovery of coral reef habitat to current conditions after 10 000 years while others result in a collapse of coral reef habitat throughout our simulations we find that the multimillennial response in sea surface temperature sst substantially lags the aragonite saturation recovery in all configurations this implies that if corals can naturally adapt over millennia by selecting thermally tolerant species to match warmer ocean temperatures prospects for long term recovery of coral reefs are better since arag recovers more quickly than sst

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

examining possible effects of seawater ph decline on foraminiferal stable isotopes during the paleocene eocene thermal maximum 1 a large body of paleoceanographic data for the paleocene eocene thermal maximum petm is based on foraminiferal stable carbon and oxygen isotope composition 13c and 18o however the proxy records could be biased due to a ph effect on stable isotopes during times when the ocean became more acidic as has been demonstrated for modern planktonic foraminifera in this paper we calculate the possible ranges of the ph effect on 13c and 18o during the petm based on the relative ph decline ph from the preperturbation steady state simulated by a carbon cycle model and the empirical relationships obtained from culture experiments with planktonic foraminifera the model is configured with eocene paleogeography and simulates ph for surface intermediate and deep water in the major ocean basins in response to various carbon input scenarios 2000 to 5000 pg c for an array of scenarios the modeled ph of the surface ocean ranges from 0 1 to 0 28 units this suggests that 13c of planktonic foraminifera may be increased by up to 2 1 and 18o may be increased by up to 0 7 corresponding to over 3 c error in paleotemperature estimate under conditions in which the model best simulates the global caco3 dissolution pattern we find marked differences in the deep sea ph between the atlantic 0 4 and pacific oceans 0 1 this would imply that the magnitude of the negative 13c and 18o excursions of benthic foraminifera in the atlantic ocean was dampened by up to 2 8 and 0 9 at maximum respectively relative to a constant ph scenario

ferrimagnetic iron sulfide formation and methane venting across the paleocene eocene thermal maximum in shallow marine sediments ancient west siberian sea

high resolution records of the late paleocene thermal maximum and circum caribbean volcanism is there a causal link two recently drilled caribbean sites contain expanded sedimentary records of the late paleocene thermal maximum a dramatic global warming event that occurred at ca 55 ma the records document significant environmental changes including deep water oxygen deficiency and a mass extinction of deep sea fauna intertwined with evidence for a major episode of explosive volcanism we postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the earth s environment

recovering the true size of an eocene hyperthermal from the marine sedimentary record 1 hyperthermals episodes of abrupt global warming associated with the massive injection of carbon into the oceans and atmosphere represent possible analogs for future climate change however uncertainties in their magnitude rate and duration arising as a result of mixing processes and changes in carbonate preservation as the sediment record is formed complicate their use in constraining climate sensitivity and the role of carbon cycle feedbacks here we use cgenie an earth system model of intermediate complexity to assess likely magnitude and rate of carbon input taking a small hyperthermal event from the early middle eocene c22nh3 49 2ma as a case study we develop an iterative method combined with a sediment model simulating the formation and mixing of deep sea sediments to converge on an estimate for the true magnitude of the carbon cycle perturbation in the atmosphere and ocean that drives the event in inverting the 0 95 benthic 13 cexcursion recorded atocean drilling program site 1258 we obtain an estimate of at least 1 45 for the atmospheric co2 13 c excursion that drove event c22nh3 we also assess controls on intersite variation of event shape in model sediments and find that sedimentation rate is the strongest determinant of modeled event size with higher sedimentation rate sites recording the atmospheric signal more accurately our revised estimate for the size of c22nh3 implies a total carbon input almost two thirds higher than would be deduced if the recorded 13 c excursion magnitude was taken at face value

multiple early eocene benthic foraminiferal assemblage and δ13c fluctuations at dsdp site 401 bay of biscay ne atlantic abstract within the last decade several early eocene hyperthermals have been detected globally these transient warming events have mainly been characterized geochemically using stable isotopes carbonate content measurements or xrf core scanning yet detailed micropaleontological records are sparse limiting our understanding of the driving forces behind hyperthermals and of the contemporaneous paleoceanography here detailed geochemical and quantitative benthic foraminiferal records are presented from lower eocene pelagic sediments of deep sea drilling project site 401 bay of biscay northeast atlantic in calcareous nannofossil zone np11 several clay enriched levels correspond to negative 13c and 18o bulk rock excursions with amplitudes of up to 0 75 suggesting that significant injections of 12c enriched greenhouse gasses and small temperature rises took place coeval with several of these hyperthermal events the benthic foraminiferal record reveals increased relative abundances of oligotrophic taxa e g nuttallides umbonifera and a reduction in the abundance of buliminid species followed by an increase of opportunistic taxa e g globocassidulina subglobosa and gyroidinoides spp these short lived faunal perturbations are thought to be caused by reduced seasonality of productivity resulting in a decreased corg flux to the seafloor moreover the sedimentological record suggests that an enhanced influx of terrigenous material occurred during these events additionally the most intense 13c decline here called level gives rise to a small yet pronounced long term shift in the benthic foraminiferal composition at this site possibly due to the reappraisal of upwelling and the intensification of bottom water currents these observations imply that environmental changes during smaller hyperthermal events are also reflected in the composition of deep sea benthic communities on both short

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

atmospheric pco2 reconstructed across five early eocene global warming events abstract multiple short lived global warming events known as hyperthermals occurred during the early eocene 56 52 ma five of these events the paleocene eocene thermal maximum petm or etm1 h1 or etm2 h2 i1 and i2 are marked by a carbon isotope excursion cie within both marine and terrestrial sediments the magnitude of cie which is a function of the amount and isotopic composition of carbon added to the ocean atmosphere system varies significantly between marine versus terrestrial substrates here we use the increase in carbon isotope fractionation by c3 land plants in response to increased pco2 to reconcile this difference and reconstruct a range of background pco2 and peak pco2 for each cie provided two potential carbon sources methane hydrate destabilization and permafrost thawing organic matter oxidation although the uncertainty on each pco2 estimate using this approach is low e g median uncertainty 23 18 this work highlights the potential for significant systematic bias in the pco2 estimate resulting from sampling resolution substrate type diagenesis and environmental change careful consideration of each of these factors is required especially when applying this approach to a single marine terrestrial cie pair given these limitations we provide an upper estimate for background early eocene pco2 of 463 248 131 ppmv methane hydrate scenario to 806 127 104 ppmv permafrost thawing organic matter oxidation scenario these results which represent the first pco2 proxy estimates directly tied to the eocene hyperthermals demonstrate that early eocene warmth was supported by background pco2 less than 3 5 preindustrial levels and that p co 2 1000 ppmv may have occurred only briefly during hyperthermal events

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

carbonate saturation dynamics during the paleocene eocene thermal maximum bathyal constraints from odp sites 689 and 690 in the weddell sea south atlantic abstract spatiotemporal patterns of carbonate dissolution provide a critical constraint on carbon input during an ancient 55 5 ma global warming event known as the paleocene eocene thermal maximum petm yet the magnitude of lysocline shoaling in the southern ocean is poorly constrained due to limited spatial coverage in the circum antarctic region this shortcoming is partially addressed by comparing patterns of carbonate sedimentation at the site 690 petm reference section to those herein reconstructed for nearby site 689 biochemostratigraphic correlation of the two records reveals that the first 36 ka of the carbon isotope excursion cie signaling petm conditions is captured by the site 689 section while the remainder of the cie interval and nearly all of the cie recovery are missing due to a coring gap a relatively expanded stratigraphy and higher carbonate content at mid bathyal site 689 indicate that dissolution was less severe than at site 690 thus the bathymetric transect delimited by these two petm records indicates that the lysocline shoaled above site 689 1 100 m while the calcite compensation depth remained below site 690 1 900 m in the weddell sea region the ensuing recovery of carbonate sedimentation conforms to a bathymetric trend best explained by gradual lysocline deepening as negative feedback mechanisms neutralized ocean acidification further biochemostratigraphic evidence indicates the tail end of the cie recovery interval at both sites has been truncated by a hiatus most likely related to vigorous production and advection of intermediate waters

neodymium isotopic reconstruction of late paleocene early eocene thermohaline circulation abstract high resolution fish tooth nd isotopic records for eight deep sea drilling project and ocean drilling program sites were used to reconstruct the nature of late paleocene early eocene deep water circulation the goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4 5 c warming of deep and bottom waters at the paleocene eocene boundary the paleocene eocene thermal maximum petm event the combined set of records indicates a deep water mass common to the north and south atlantic southern and indian oceans characterized by mean nd values of 8 7 and different water masses found in the central pacific ocean nd 4 3 and caribbean sea nd 1 2 the geographic pattern of nd isotopic values before and during the petm suggests a southern ocean deep water formation site for deep and bottom waters in the atlantic and indian ocean basins the nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the petm this finding is consistent with the pattern of warming established by recently published stable isotope records suggesting that deep and bottom water warming during the petm was gradual and the consequence of surface water warming in regions of downwelling

the palaeocene eocene carbon isotope excursion constraints from individual shell planktonic foraminifer records the palaeocene eocene thermal maximum petm is characterized by a global negative carbon isotope excursion cie and widespread dissolution of seafloor carbonate sediments the latter feature supports the hypothesis that the petm and cie were caused by the rapid release of a large mass greater than 2000gt c of 12c enriched carbon the source of this carbon however remains a mystery possible sources include volcanically driven thermal combustion of organic rich sediment dissociation of seafloor methane hydrates and desiccation and oxidation of soil sediment organics a key constraint on the source s is the rate at which the carbon was released fast rates would be consistent with a catastrophic event e g massive methane hydrate dissociation whereas slower rates might implicate other processes the petm carbon flux is currently constrained by high resolution marine and terrestrial records of the cie in pelagic bulk carbonate records the onset of the cie is often expressed as a single or multiple step excursion extending over 10 4 years individual planktonic shell records in contrast always show a single step cie with either pre excursion or excursion isotope values but no transition values benthic foraminifera records which are less complete owing to extinction and diminutive assemblages show a delayed excursion here we compile and evaluate the individual planktonic shell isotope data from several localities we find that the most expanded records consistently show a bimodal isotope distribution pattern regardless of location water depth or depositional facies this suggests one of several possibilities i the isotopic composition of the surface ocean atmosphere declined in a geologic instant 500yr ii that during the onset of the cie most shells of mixed layer planktonic foraminifera were dissolved or iii the abundances or shell production of these species temporarily declined possibly due to initial ph changes

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

constraints on ocean acidification associated with rapid and massive carbon injections the early paleogene record at ocean drilling program site 1215 equatorial pacific ocean massive amounts of 13c depleted carbon rapidly entered the ocean more than once during the early paleogene providing a geological framework for understanding future perturbations in carbon cycling

extinction and recovery of benthic foraminifera across the paleocene eocene thermal maximum at the alamedilla section southern spain abstract a complete succession of lower bathyal upper abyssal sediments was deposited across the paleocene eocene thermal maximum petm at alamedilla betic cordillera southern spain where the benthic foraminiferal turnover and extinction event associated with the negative carbon isotope excursion cie across the petm have been investigated detailed quantitative analyses of benthic foraminifera allowed us to distinguish assemblages with paleoecological and paleoenvironmental significance pre extinction fauna extinction fauna survival fauna including disaster and opportunistic fauna and recovery fauna these assemblages have been associated with significant parts of the 13 c curve for which a relative chronology has been established the correlation between the benthic turnover the 13 c curve the calcite and silicate mineral content and sedimentation rates allowed us to establish the sequence of events across the petm at alamedilla the benthic extinction event bee affected 37 of the species and it has been recorded over a 30 cm thick interval that was deposited in c a 10 ky suggesting a gradual but rapid pattern of extinction the beginning of the bee coincides with the onset of the cie 0 ky and with an interval with abundant calcite and it has been recorded under oxic conditions at the seafloor as inferred from the benthic foraminiferal assemblages and the reddish colour of the sediments we conclude that dissolution and dysoxia were not the cause of the extinctions which were probably related to intense warming that occurred before the onset of the cie the bee is immediately overlain by a survival interval dominated by agglutinated species the glomospira acme the low calcite content recorded within the survival interval may result from the interaction between dilution of the carbonate compounds by silicicate minerals as inferred from the increased sedimentation rates and the effects of carbonate dissolution triggered by the shoaling of the ccd we suggest that glomospira species disaster fauna may have bloomed opportunistically in areas with methane dissociation in and around the north atlantic the disaster fauna was rapidly replaced by opportunistic taxa which point to oxic and possibly oligotrophic conditions at the seafloor the ccd gradually dropped during this interval and calcite preservation improved towards the recovery interval during which the 13 c values and the calcite content recovered c a 71 25 to 94 23 ky and stabilized 94 23 ky coeval with a sharp decrease in sedimentation rates

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

evolution of deep sea sediments across the paleocene eocene and eocene oligocene boundaries abstract the composition and distribution of deep sea sediments is the result of a multitude of climatic biotic and oceanic conditions relating to biogeochemical cycles and environmental change here we utilize the extensive sediment archives of the international ocean discovery program iodp and its predecessors to construct maps of deep sea sediment type across two critical but contrasting boundaries in the paleogene one characterised by an interval of extreme warmth paleocene eocene and the other by global cooling eocene oligocene ocean sediment distribution shows significant divergence both between the latest paleocene and paleocene eocene thermal maximum petm across the eocene oligocene transition eot and in comparison to modern sediment distributions carbonate sedimentation in the latest paleocene extends to high southern latitudes disappearance of carbonate sediments at the petm is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon cycle perturbation biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early paleogene ocean in the southern ocean we attribute the low in biosiliceous burial to the warm deep water temperatures which would have impacted biogenic silica preservation in the late eocene our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial pacific enhanced biosiliceous deposits in the late eocene equatorial pacific and south atlantic are due to increased productivity and the spin up of the oceans our compilation documents the enhanced global carbonate sedimentation in the early oligocene confirming that the drop in the carbonate compensation depth was global

variations to calcareous nannofossil caco 3 content during the middle eocene c21r h6 hyperthermal event 47 4 ma in the gorrondatxe section bay of biscay western pyrenees abstract the carbonate content of calcareous nannofossils is dependent on seawater composition one of the factors that affect seawater chemistry and consequently the degree of calcification in coccolithophores is temperature as seen in present day warming oceans the depth at which carbonates are dissolved calcite compensation depth ccd can rise due to an increase in hco 3 and decrease in ph leading to a major dissolution on the seabed and burndown similar processes have also been deduced for eocene hyperthermal events such as the petm and etm2 this study reports changes in coccolith carbonate mass from a hemipelagic setting gorrondatxe at 1500 m paleodepth during the core of a minor eocene hyperthermal event namely the c21r h6 event 47 44 47 32 ma image analysis techniques were used to determine differences in the carbonate mass of selected calcareous nannofossil taxa revealing species specific patterns the caco 3 mass of chiasmolithus solitus decreased by 50 over the course of the c21r h6 event and many specimens also lost their crossed central bars an additional indication of mass loss reticulofenestra sp 3 5 m showed a similar trend but the percentage of mass lost was lower toweius pertusus interpreted as being reworked mirrored the behaviour of chiasmolithus solitus suggesting that the caco 3 mass loss may have occurred on the seabed rather than in the water column in general it can be concluded that the lysocline rose to 1500 m paleobathymetry in the bay of biscay during the c21r h6 event formation of corrosive bottom water in the north atlantic ocean is regarded as being responsible for the rise in the lysocline

south pacific intermediate water oxygen depletion at the onset of the paleocene eocene thermal maximum as depicted in new zealand margin sections 1 extreme global warming and massive input of 13c depleted carbon into the exogenic carbon cycle characterize the paleocene eocene thermal maximum petm circa 55 5 ma previous work indicates that dissolved o2 concentrations dropped in some regions of the ocean during this event but spatial temporal and causal relationships between warming carbon input and o2 deficiency remain elusive we present lithologic carbon isotopic and trace fossil results from outcrops in new zealand that clarify this issue sections exposed at mead and dee streams in eastern marlborough south island contain expanded sedimentary intervals that were deposited before during and after the petm on an upper continental slope the petm in these intervals is characterized by enhanced siliciclastic deposition a hallmark negative carbon isotope excursion and a loss of bioturbation importantly however the latter only occurs during the prominent drop in 13c and not during its recovery our results suggest that south pacific intermediate waters became hypoxic coincident to carbon injection at the start of the petm while higher sea surface temperatures throughout the petm would have decreased the dissolved oxygen content of sinking surface waters we argue here that oxygen depletion was driven by some combination of elevated temperature water column stratification and intermediate water methane oxidation

extraction of high resolution carbonate data for palaeoclimate reconstruction temporal variations in the calcium carbonate content of deepsea sediments provide direct stratigraphic as well as important palaeoenvironmental information relating to the global carbon cycle here i present an algorithm that allows carbonate content and porosity to be accurately predicted from saturated bulk density in equatorial pelagic carbonates applying the algorithm to continuous laboratory measurements of density made on dsdp and oop cores yields a nearly continuous carbonate record for the upper 200 m of the sediment section long ultra high resolution carbonate curves of this type should yield new insight into the evolution of the carbon chemistry of the oceans as well as the role of external milankovitch forcing in the development of the carbonate system the algorithm can also be applied to quantitative high resolution seismic data thereby enabling detailed carbonate records to be extracted from remotely derived geophysical data

persistent environmental change after the paleocene eocene thermal maximum in the eastern north atlantic the paleocene eocene thermal maximum petm 56 ma is associated with abrupt climate change carbon cycle perturbation ocean acidification as well as biogeographic shifts in marine and terrestrial biota that were largely reversed as the climatic transient waned we report a clear exception to the behavior of the petm as a reversing climatic transient in the eastern north atlantic deep sea drilling project site 401 bay of biscay where the petm initiates a greatly prolonged environmental change compared to other places on earth where records exist the observed environmental perturbation extended well past the 13 c recovery phase and up to 650 kyr after the petm onset according to our extraterrestrial 3he based age model we observe a strong decoupling of planktic foraminiferal 18 o and mg ca values during the petm 13 c recovery phase which in combination with results from helium isotopes and clay mineralogy suggests that the petm triggered a hydrologic change in western europe that increased freshwater flux and the delivery of weathering products to the eastern north atlantic this state change persisted long after the carbon cycle perturbation had stopped we hypothesize that either long lived continental drainage patterns were altered by enhanced hydrological cycling induced by the petm or alternatively that the climate system in the hinterland area of site 401 was forced into a new climate state that was not easily reversed in the aftermath of the petm

the calcite lysocline as a constraint on glacial interglacial low latitude production changes we investigate the response of the calcite lysocline to changes in the export production of the low latitude surface ocean the combined equatorial tropical and subtropical regions we employ different caco3 throughput schemes in a time dependent ocean carbon cycle model to separate the caco3 production lysocline balance from the other components of the model response and to estimate the effect of dissolution driven by organic matter decomposition in surface sediments with this model we carry out three experiments based on previous hypotheses for the cause of glacial interglacial atmospheric co2 variations 1 a simple increase in low latitude production 2 a decrease in its caco3 organic carbon rain ratio and 3 an increase in the depth of organic carbon regeneration none of these changes when taken alone can lower atmospheric co2 to glacial levels without violating observations of the glacial lysocline depth if a low latitude production increase were accompanied by a decrease in the caco3 organic carbon rain ratio then these simultaneous changes could lower atmospheric co2 to observed glacial levels without causing a significant change in the ocean average depth of the lysocline however even with these simultaneous changes the required increase in production is 50 or more of the modern rate of production

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

nd isotopic structure of the pacific ocean 70 30 ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world the oceanic meridional overturning circulation moc is a crucial component of the climate system impacting heat and nutrient transport and global carbon cycling past greenhouse climate intervals present a paradox because their weak equator to pole temperature gradients imply a weaker moc yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients to investigate the mode of moc that operated during the early cenozoic we compare new nd isotope data with nd tracer enabled numerical ocean circulation and coupled climate model simulations assimilation of new nd isotope data from south pacific deep sea drilling project and ocean drilling program sites 323 463 596 865 and 869 with previously published data confirm the hypothesized moc characterized by vigorous sinking in the south and north pacific 70 to 30 ma compilation of all pacific nd isotope data indicates vigorous distinct and separate overturning circulations in each basin until 40 ma simulations consistently reproduce south pacific and north pacific deep convection over a broad range of conditions but cases using strong deep ocean vertical mixing produced the best data model match strong mixing potentially resulting from enhanced abyssal tidal dissipation greater interaction of wind driven internal wave activity with submarine plateaus or higher than modern values of the geothermal heat flux enable models to achieve enhanced moc circulation rates with resulting nd isotope distributions consistent with the proxy data the consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients

warming the fuel for the fire evidence for the thermal dissociation of methane hydrate during the paleocene eocene thermal maximum dramatic warming and upheaval of the carbon system at the end of the paleocene epoch have been linked to massive dissociation of sedimentary methane hydrate however testing the paleocene eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events the cause of the paleocene eocene thermal maximum carbon isotope excursion remains speculative primarily due to uncertainties in the timing and duration of the paleocene eocene thermal maximum we present new high resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from ocean drilling program site 690 weddell sea southern ocean demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming both of these findings support the thermal dissociation of methane hydrate as the cause of the paleocene eocene thermal maximum carbon isotope excursion furthermore the data reveal that the methane derived carbon was mixed from the surface ocean downward suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation

an alternative model for caco3 over shooting during the petm biological carbonate compensation decreased caco3 content of deep sea sediments argues for rapid and massive acidification of the oceans during the paleocene eocene thermal maximum petm 56 ma bp in the course of the subsequent recovery from this acidification sediment caco3 content came to exceed pre petm levels known as over shooting past studies have largely attributed the latter to increased alkalinity input to the oceans via enhanced weathering but this ignores potentially important biological factors we successfully reproduce the caco3 records from walvis ridge in the atlantic ocean including over shooting using a biogeochemical box model replication of the caco3 records required 1 introduction of a maximum of 6500 gtc of co2 directly into deep ocean waters or 8000 gtc into the atmosphere 2 limited deep water exchange between the indo atlantic and pacific oceans 3 the disappearance of sediment bioturbation during a portion of the petm and 4 most central to this study a 50 reduction in net caco3 production during acidification in our simulations over shooting is an emergent property generated at constant alkalinity input no weathering feedback as a consequence of attenuated caco3 productivity this occurs because lower net caco3 production from surface waters allows alkalinity to build up in the deep oceans alkalinization thus promoting deep water super saturation restoration of caco3 productivity later in the petm particularly in the indo atlantic ocean leads to greater accumulation of caco3 ergo over shooting which returns the ocean to pre petm conditions over a time scale greater than 200 ka

sedimentary record of a tsunami during roman times bay of cadiz spain abstract historical data show that the gulf of cadiz has been exposed to destructive tsunamisduring at least the past 2000 yr the last tsunami was generated by the ad 1755 lisbon earthquake which affected the atlantic coasts of spain portugal and morocco today these littoral areas areintensely populated and the expected damage could be much greater tsunami studies are of greatimportance in helping to determine the recurrence interval of these events the presence of washover fan deposits on the inland margin of the valdelagrana spit bar cadiz spain indicates the occurrence of a high energy marine event ca 2300 cal yr bp historical geomorphological sedimentological palaeontological and geochronological data suggest that atsunami could have affected the area during roman times copyright 2002 john wiley sons ltd journal of quaternary science keywords tsunami deposits grain size palaeontology gulf of cadiz south spain introduction investigations of the geological records of past tsunamis arean important tool in helping to determine the recurrenceinterval of such events in a region these investigations arealso the only way of determining the prehistoric occurrenceand tsunami hazard in areas of infrequent seismic activity however at present it is dif cult to distinguish betweentsunami deposits and those laid down by other high energyevents such as a storm surge or hurricane recent work bygoff et al 2001 has helped to identify a series of diagnosticcriteria for tsunami deposits and research is underway tohighlight the differences between these and other high energyevents goff and chagu e goff in preparation j goff personalcommunication 2002 wave hydrodynamics the speci ccoastal setting morphology orientation availability and typeof sediments depositional environments tsunami magnitudeand tidal range are all factors that help to de ne the type andpreservation of tsunami deposits furthermore the ability todetermine the tsunamigenic source largely depends upon thepalaeoseismic and historical record e g goff et al 2001

global decline in ocean ventilation oxygenation and productivity during the paleocene eocene thermal maximum implications for the benthic extinction the prominent global warming event at the paleocene eocene boundary 55 ma referred to as the paleocene eocene thermal maximum petm was characterized by rapid temperature increase and changes in the global carbon cycle in

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

a model for orbital pacing of methane hydrate destabilization during the palaeogene the early eocene was marked by a series of abrupt warming events numerical modelling suggests that the events were the result of nonlinear interactions between orbital forcing ocean circulation and the carbon cycle a series of transient global warming events1 2 occurred during the late palaeocene and early eocene about 59 to 50 million years ago the events although variable in magnitude were apparently paced by orbital cycles2 3 4 and linked to massive perturbations of the global carbon cycle5 6 however a causal link between orbital changes in insolation and the carbon cycle has yet to be established for this time period here we present a series of coupled climate model simulations that demonstrate that orbitally induced changes in ocean circulation and intermediate water temperature can trigger the destabilization of methane hydrates we then use a simple threshold model to show that progressive global warming over millions of years in combination with the increasing tendency of the ocean to remain in a more stagnant state can explain the decreasing magnitude and increasing frequency of hyperthermal events throughout the early eocene our work shows that nonlinear interactions between climate and the carbon cycle can modulate the effect of orbital variations in this case producing transient global warming events with varying timing and magnitude

sedimentary response to paleocene eocene thermal maximum carbon release a model data comparison possible sources of carbon that may have caused global warming at the paleocene eocene boundary are constrained using an intermediate complexity earth system model confi gured with early eocene paleogeography we fi that 6800 pg c 13 c of 22 is the smallest pulse modeled here to reasonably reproduce observations of the extent of seafl oor caco 3 dis solution this pulse could not have been solely the result of methane hydrate destabilization suggesting that additional sources of co 2 such as volcanic co 2 the oxidation of sedimentary organic carbon or thermogenic methane must also have contributed observed contrasts in dissolution intensity between atlantic and pacifi c sites are reproduced in the model by reduc ing bioturbation in the atlantic during the event simulating a potential consequence of the spread of low oxygen bottom waters

no place to retreat heavy extinction and delayed recovery on a pacific guyot during the paleocene eocene thermal maximum modern global change threatens alpine ecosystems by forcing species to migrate to higher elevations and potentially eliminating alpine habitat altogether here we show that an analogous restriction of suitable habitat operates on submarine mountains during the paleocene eocene thermal maximum petm ca 55 96 ma ostracodes underwent local extinction on the crest of allison guyot in the central pacific ocean which lost 64 of its ostracode species richness 14 species reduced to three species and as much as 94 of ostracode abundance for 1 1 m y before recolonization rebuilt biodiversity and abundance over the next 200 k y biotic changes may reflect an increase in current speeds acidification and a decrease in food supply owing to a temperature driven increase in metabolic rates notably continental margin ostracodes also underwent extinction during the petm 25 38 loss but unlike allison guyot faunas could quickly repopulate the continental slope the absence of refugia for isolated seamounts prolonged the reduction in biodiversity initiated by the petm a pattern that may be expected for modern seamount faunas in an era of future global change

ocean chemistry and atmospheric co2 sensitivity to carbon perturbations throughout the cenozoic 1 we assess the response of atmospheric co2 pco2 and ocean chemistry to carbon perturbations placing modern carbon cycle sensitivity in the context of the cenozoic we use the carbon cycle model loscar to study the effect of perturbations over the past 67 ma our results indicate that atmospheric co2 and surface ocean ph were slightly more sensitive to carbon perturbations during the miocene 15 ma ago compared to modern conditions and less sensitive during the earlier part of the cenozoic we find that the sensitivity to carbon input at the paleocene eocene boundary 56 ma ago was most likely lower compared to modern conditions further we show that the cenozoic evolution of steady state pco2 and seawater mg ca ratios is critical for the system s sensitivity to a carbon release

reversed deep sea carbonate ion basin gradient during paleocene eocene thermal maximum 1 the paleocene eocene thermal maximum petm 55 ma ago was marked by widespread caco3 dissolution in deep sea sediments a process that has been attributed to massive release of carbon into the ocean atmosphere system the pattern of carbonate dissolution is key to reconstructing changes in deep sea carbonate chemistry and ultimately the rate magnitude and location of carbon input here we show that during the petm the deep sea undersaturation was not homogeneous among the different ocean basins application of a sediment model to a suite of data records from different sites and ocean basins shows that a globally uniform decrease in deep sea carbonate ion concentration co32 is inconsistent with the data rather we demonstrate that deep sea co32 increased from the atlantic through the southern ocean into the pacific our results show that the petm deep sea co32 basin gradient during dissolution was reversed relative to the modern

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

co2 driven ocean circulation changes as an amplifier of paleocene eocene thermal maximum hydrate destabilization changes in ocean circulation have been proposed as a trigger mechanism for the large coupled climate and carbon cycle perturbations at the paleocene eocene thermal maximum petm ca 55 ma an abrupt warming of oceanic intermediate waters could have initiated the thermal destabilization of sediment hosted methane gas hydrates and potentially triggered sediment slumps and slides in an ensemble of fully coupled atmosphere ocean general circulation model aogcm simulations of the late paleocene and early eocene we identify such a circulation driven enhanced intermediate water warming critically we find an approximate twofold amplification of atlantic intermediate water warming when co2 levels are doubled from 2x to 4x preindustrial co2 compared to when they are doubled from 1x to 2x this warming is largely focused on the equatorial and south atlantic and is driven by a significant reduction in deep water formation from the southern ocean this scenario is consistent with altered petm circulation patterns inferred from benthic carbon isotope data and the intensity of deep sea carbonate dissolution in the south atlantic the linkage between intermediate water warming and gas hydrate destabilization could provide an important feedback in the establishment of peak petm warmth

an alternative age model for the paleocene eocene thermal maximum using extraterrestrial 3he a continuous age model for the brief climate excursion at the paleocene eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3he 3he et to the seafloor 3he et measurements from odp site 690 provide quantitative evidence for the rapid onset few kyr and short duration 120 kyr of global warming and of the associated disturbance to the earth s surficial carbon budget at this time these observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon possibly from seafloor methane hydrate as the proximal cause of the event however the 3he et technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre event values the 3he et based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle and so may indicate additional or accelerated mechanisms of carbon removal from the ocean atmosphere system during this period 3he et was also measured at odp site 1051 to test the validity of the site 690 chronology comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at site 1051 an observation consistent with sediment structures and previous age modeling efforts the site 1051 age model shows a 30 kyr period in which climate proxies return toward pre event values after which they remain invariant for 80 kyr if this rise represents the recovery interval identified at site 690 then the 3he et based age models of the two sites are in good agreement however alternative interpretations are possible and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion regardless of these details this work shows that the 3he et technique can provide useful independent evidence for the development and testing of astronomically calibrated age models

impact of dissolution on the sedimentary record of the paleocene eocene thermal maximum the input of massive amounts of carbon to the atmosphere and ocean at the paleocene eocene thermal maximum petm 55 53 ma resulted in pervasive carbonate dissolution at the seafloor at many sites this dissolution also penetrated into the underlying sediment column the magnitude of dissolution at and below the seafloor a process known as chemical erosion and its effect on the stratigraphy of the petm are notoriously difficult to constrain here we illuminate the impact of dissolution by analyzing the complete spectrum of sedimentological grain sizes across the petm at three deep sea sites characterized by a range of bottom water dissolution intensity we show that the grain size spectrum provides a measure of the sediment fraction lost during dissolution we compare these data with dissolution and other proxy records electron micrograph observations of samples and lithology the complete data set indicates that the two sites with slower carbonate accumulation and less active bioturbation are characterized by significant chemical erosion at the third site higher carbonate accumulation rates more active bioturbation and possibly winnowing have limited the impacts of dissolution however grain size data suggest that bioturbation and winnowing were not sufficiently intense to diminish the fidelity of isotopic and microfossil assemblage records

deep sea redox across the paleocene eocene thermal maximum large amounts of 13c depleted carbon were released to the oceans and atmosphere during a period of abrupt global warming at the paleocene eocene thermal maximum petm 55 ma investigations of qualitative sedimentologic and paleontologic redox proxies such as bioturbation and benthic assemblages from pelagic and hemipelagic sections suggest transient reductions in bottom water oxygen during this interval possibly on a global scale here we present bulk sediment manganese mn and uranium u enrichment factors ef in atlantic and pacific deep sea cores to constrain relative paleoredox changes across the petm mn ef range from 1 to 9 in atlantic sites 1 to 35 in southern ocean sites and are at crustal averages ef 1 in pacific sites u ef range from 1 to 5 in atlantic sites 1 to 90 in southern ocean sites and are at crustal averages in pacific sites our results indicate suboxic conditions prior to during and in the recovery from the petm at intermediate depth sites in the atlantic and southern ocean while the pacific sites remained relatively oxygenated the difference in oxygenation between the atlantic and pacific sites leads us to suggest the source for isotopically light carbon release during the petm was in the atlantic

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

calcareous nannoplankton changes across the early toarcian oceanic anoxic event in the western tethys 1 calcareous nannoplankton were profoundly affected by environmental perturbations coincident with the early toarcian oceanic anoxic event t oae we quantify the abundance of nannofossils across the t oae at three locations in western europe where the event is marked by a prominent negative carbon isotope excursion cie data were treated by statistical analysis and the shannon diversity index was applied in order to describe nannofossil assemblage changes related to paleoenvironmental evolution in the basal toarcian before the t oae high proportions of taxa with an affinity for low temperature e g p liasicus t patulus bussonius occurred this observation is consistent with interpretations of published oxygen isotope records during the t oae the lowest abundance of nannofossils is observed but there is a peak of a coccolith calyculus from an organism that probably thrived in low saline surface waters depleted of nitrate at the end of the perturbation the lowest diversities of nannofossils occurred and assemblages are dominated by crepidolithus crassus a deep dweller this interval corresponded to progressive reoxygenation of deep water and the reoccupation of the deep photic zone by nannoplankton the highest abundance of nannofossils is recorded above the cie and testifies to the recovery of the entire nannoplankton community the t oae was widespread perhaps global and probably linked to major changes in the atmosphere and hydrosphere however the record of this event varies in the basins surrounding the western tethys suggesting regional imprints on the global signal the regional variability may attest to establishment of effective connections between the arctic and tethys oceans which allowed cool low saline water formed at high latitudes to stream toward the western tethys

oceanic calcium changes from enhanced weathering during the paleocene eocene thermal maximum no effect on calcium based proxies 1 during the paleocene eocene thermal maximum petm 55 myr ago prominent climatic and biogeochemical changes took place in the atmosphere ocean and on land for example deep sea temperatures rose by 5 c to 6 c while sea surface temperatures at high latitudes increased by up to 9 c in the sedimentary record the onset of the petm is marked by widespread dissolution of calcium carbonate on the seafloor in addition there is evidence for globally higher humidity precipitation and increased weathering during the petm both calcium carbonate dissolution and enhanced weathering probably affected the seawater calcium concentration here we investigate implications that possible changes in the ocean s calcium inventory may have had on boron calcium b ca and magnesium calcium mg ca ratios which are used as proxies for deep water carbonate chemistry and temperature respectively we also examine effects on 44ca of seawater which is used as an indicator for variations in the marine calcium cycle we focus on the magnitude of change in the ocean s calcium ion concentration as a result of the carbon perturbation which resulted in increased weathering fluxes and the dissolution of calcite on the ocean floor during the petm different ranges of carbon input scenarios and their effect on ocean chemistry were examined using the long term ocean atmosphere sediment carbon cycle reservoir loscar model we found that under the most plausible scenario the calcium ion concentration change ca2 was less than 0 7 and around 2 in the most extreme scenario our results show that b ca and mg ca proxies were not affected within analytical precision by changes in oceanic calcium due to weathering and carbonate dissolution during the petm the most extreme scenario ca2 2 would result in 4 mol kg 1 uncertainty in reconstruction of co32 the same scenario affects the temperature reconstruction by 0 2 c the effect on the ocean s calcium isotope budget was insignificant as well resulting in 44casw of less than 0 05

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

influences of high and low latitude processes on african terrestrial climate pleistocene eolian records from equatorial atlantic ocean drilling program site 663 high and low latitude forcing of terrestrial african paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from ocean drilling program site 663 in the eastern equatorial atlantic terrigenous eolian dust and phytolith savannah grass cuticle accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high latitude forcing the abundance of freshwater diatoms melosira transported from dry african lake beds varies coherently at 23 19 kyr orbital periodicities and at a phasing which implicates low latitude precessional monsoon forcing modeling studies demonstrate that african climate is sensitive to both high and low latitude boundary conditions african monsoon intensity is modulated by direct insolation variations due to orbital precession whereas remote high latitude forcing can be related to cool north atlantic sea surface temperatures ssts which promote african aridity and enhance dust transporting wind speeds the site 663 terrigenous and phytolith records covary with north atlantic sst variability at 41 n site 607 we suggest that pleistocene african climate has responded to both high latitude north atlantic sst variability as well as low latitude precessional monsoon forcing the high latitude influence dominates the sedimentary record prior to circa 2 4 ma terrigenous variations occurred primarily at precessional periodicities 23 19 kyr indicating that african climate was largely controlled by low latitude insolation variations prior to the onset of high amplitude glacial interglacial climate change

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

abundant early palaeogene marine gas hydrates despite warm deep ocean temperatures gas hydrates have been suggested as a carbon source for palaeogene hyperthermal events but warm seafloor temperatures are thought to have limited their accumulation numerical simulations suggest that enhanced organic carbon sedimentation and methanogenesis could have compensated for the smaller area of hydrate stability abrupt periods of global warming between 57 and 50 million years ago known as the early palaeogene hyperthermal events were associated with the repeated injection of massive amounts of carbon into the atmosphere1 2 3 4 the release of methane from the sea floor following the dissociation of gas hydrates is often invoked as a source5 however seafloor temperatures before the events were at least 4 7 c higher than today1 which would have limited the area of sea floor suitable for hosting gas hydrates6 7 palaeogene gas hydrate reservoirs may therefore not have been sufficient to provide a significant fraction of the carbon released here we use numerical simulations of gas hydrate accumulation8 at palaeogene seafloor temperatures to show that near present day values of gas hydrates could have been hosted in the palaeogene our simulations show that warmer temperatures during the palaeogene would have enhanced the amount of organic carbon reaching the sea floor as well as the rate of methanogenesis we find that under plausible temperature and pressure conditions the abundance of gas hydrates would be similar or higher in the palaeogene than at present we conclude that methane hydrates could have been an important source of carbon during the palaeogene hyperthermal events

the paleocene eocene carbon isotope excursion in higher plant organic matter differential fractionation of angiosperms and conifers in the arctic abstract a study of upper paleocene lower eocene p e sediments deposited on the lomonosov ridge in the central arctic ocean reveals relatively high abundances of terrestrial biomarkers these include dehydroabietane and simonellite derived from conifers gymnosperms and a tetra aromatic triterpenoid derived from angiosperms the relative percentage of the angiosperm biomarker of the summed angiosperm conifer biomarkers was increased at the end of the paleocene eocene thermal maximum petm different when observed with pollen counts which showed a relative decrease in angiosperm pollen stable carbon isotopic analysis of these biomarkers shows that the negative carbon isotope excursion cie during the petm amounts to 3 for both conifer biomarkers dehydroabietane and simonellite comparable to the magnitude of the cie inferred from marine carbonates but significantly lower than the 4 5 of the terrestrial c29 n alkane m pagani n pedentchouk m huber a sluijs s schouten h brinkhuis j s sinninghe damste g r dickens and the iodp expedition 302 expedition scientists 2006 arctic s hydrology during global warming at the paleocene eocene thermal maximum nature 442 671 675 which is a compound sourced by both conifers and angiosperms conspicuously the angiosperm sourced aromatic triterpane shows a much larger cie of 6 and suggests that angiosperms increased in their carbon isotopic fractionation during the petm our results thus indicate that the 4 5 c29 n alkane cie reported previously represents the average cie of conifers and angiosperms at this site and suggest that the large and variable cie observed in terrestrial records may be partly explained by the variable contributions of conifers and angiosperms the differential response in isotopic fractionation of angiosperms and conifers points to different physiological responses of these vegetation types to the rise in temperature humidity and greenhouse gases during the petm

the dan c2 hyperthermal event at gubbio italy global implications environmental effects and cause s abstract the dan c2 event is an early danian transient 100 kyr hyperthermal episode centered at 65 2 ma which records shifts in carbon reservoirs and ocean warming in the northwestern and southeastern sectors of the atlantic ocean here we present and discuss high resolution biochronostratigraphic and magnetic susceptibility data and geochemical records from the western tethyan contessa highway section gubbio italy which provide the first direct evidence of the dan c2 event beyond the atlantic ocean and point to the supra regional possibly global significance thereof at contessa highway the dan c2 event exhibits stressed ecological responses among calcareous nannoplankton and foraminifera which highlight marked environmental perturbation affecting the geobiosphere and resulting in enhanced eutrophication of the sea surface waters and carbonate dissolution as well as lowered oxygen content along the water column and at the sea bottom as for other early paleogene hyperthermal events the cause of the dan c2 event might likely to be found in changes potentially astronomically paced in the distribution of carbon within surface biosphere reservoirs however the role played by the concurrent third and last phase of deccan volcanism with its huge release of greenhouse gases into the atmosphere would be also taken into account in addition here we provide first evidence of a further short lived 38 kyr hyperthermal event not known up to now and that we term the lower c29n event

history of carbonate ion concentration over the last 100 million years abstract instead of having been more or less constant as once assumed it is now apparent that the major ion chemistry of the oceans has varied substantially over time for instance independent lines of evidence suggest that calcium concentration ca2 has approximately halved and magnesium concentration mg2 approximately doubled over the last 100 million years on the other hand the calcite compensation depth and hence the caco3 saturation has varied little over the last 100 my as documented in deep sea sediments we combine these pieces of evidence to develop a proxy for seawater carbonate ion concentration co32 over this period of time from the calcite saturation state which is proportional to the product of ca2 times co32 but also affected by mg2 we can calculate seawater co32 our results show that co32 has nearly quadrupled since the cretaceous furthermore by combining our co32 proxy with other carbonate system proxies we provide calculations of the entire seawater carbonate system and atmospheric co2 based on this reconstructed atmospheric co2 is relatively low in the miocene but high in the eocene finally we make a strong case that seawater ph has increased over the last 100 my

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

particulate δ15n in laminated marine sediments as a proxy for mixing between the california undercurrent and the california current a proof of concept the measurements of particulate 15n in coastal marine laminated sediments provide a high resolution proxy for fluctuations in the intensity of denitrification in the water column in the eastern tropical north pacific oxygen minimum zone this denitrification signal is transported northward by the california undercurrent thus serving as a tracer of ocean circulation this is verified through comparisons between salinity in the thermocline off southern california santa monica basin and the difference between 15nsed within age equivalent sediments from a southern pescadero slope and northern santa monica basin site trends in this parameter 15nsed relate to pacific decadal oscillation pdo phase changes between 1900 and 1990 we hypothesize that the decline in 15nsed during warm pdo phases is due to a strengthening of the california undercurrent transporting 15n enriched nitrate from the eastern tropical north pacific northward the deviation from this trend after 1990 suggests recent changes in circulation and or california current water nutrient biogeochemistry

sudden spreading of corrosive bottom water during the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum was associated with warming and seafloor carbonate dissolution numerical simulations suggest that the spread of deep corrosive water from the north atlantic can explain the observed dissolution patterns

interpreting transient carbonate compensation depth changes by marine sediment core modeling 1 with the advent of computationally fast intermediate complexity models of earth s climate and carbon cycle the marine record can be interpreted much more directly than before specifically the mechanistic simulation of deep sea sediment cores provides an important step in bridging the model data divide here i use this methodology to help interpret the excursion in carbonate compensation depth ccd during the paleoceneeocene thermal maximum that is recorded in cores recovered from walvis ridge in the south atlantic by explicitly simulating the expected geological record of a massive co2 release in an earth system model i show how reduction in the intensity of subsurface mixing of the sediment by benthic animals substantially magnifies the recorded shoaling of the ccd conversely to quantify correctly the carbon release consistent with the observed ccd changes one must account for any bioturbational changes a reduction in sediment mixing intensity also appears to be important to reproducing the sharpness of the contact between carbonate rich late paleocene sediments and the overlying early eocene clay layer at walvis ridge assuming a relatively rapid approximately 1 ka duration co2 release further helps to account for some of the paleoceanographic observations finally interbasin differences in bioturbational regime help resolve some of the observed disparity in carbonate preservation between walvis ridge and sites outside of the atlantic although changes in ocean ventilation and circulation are also likely to play a critical role in this

anomalous shifts in tropical pacific planktonic and benthic foraminiferal test size during the paleocene eocene thermal maximum paleocene eocene warming and changes in oceanic hydrography should have significantly impacted the ecology of marine microorganisms both at the surface and on the seafloor we analyzed several key characteristics of foraminifera from two shatsky rise odp leg 198 cores spanning the p e boundary including the maximum test diameters of the largest calcareous trochospiral benthic foraminifera and largest shallow dwelling planktonic foraminifera and the stable carbon and oxygen isotope ratios of benthic foraminifera and bulk samples we also qualitatively constrained changes in bottom water dissolved oxygen concentrations by quantifying changes in benthic species abundances we find warming synchronous with an unusual increase in the size of surface water planktonic in contrast to deep water benthic foraminifera which decrease in size we suggest that a decline in bottom water dissolved oxygen is the primary mechanism responsible for the size reduction of pacific deep sea benthic foraminifera whereas the contemporaneous size increase of surface water planktonic foraminifera is attributed to an increase in thermal stratification and decrease in local nutrient supply

solar system chaos and the paleocene eocene boundary age constrained by geology and astronomy astronomical calculations reveal the solar system s dynamical evolution including its chaoticity and represent the backbone of cyclostratigraphy and astrochronology an absolute fully calibrated astronomical time scale has hitherto been hampered beyond 50 million years before the present ma because orbital calculations disagree before that age here we present geologic data and a new astronomical solution zb18a showing exceptional agreement from 58 to 53 ma we provide a new absolute astrochronology up to 58 ma and a new paleocene eocene boundary age 56 01 0 05 ma we show that the paleocene eocene thermal maximum petm onset occurred near a 405 thousand year kyr eccentricity maximum suggesting an orbital trigger we also provide an independent petm duration 170 30 kyr from onset to recovery inflection our astronomical solution requires a chaotic resonance transition at 50 ma in the solar system s fundamental frequencies

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago

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

understanding the causes and consequences of past marine carbon cycling variability through models abstract on geological time scales the production and degree of recycling of biogenic carbon in the marine realm and ultimately its removal to sediments exerts a dominant control on atmospheric co 2 and hence variability in climate this is a highly complex system involving a myriad of inter connected biological chemical and physical processes for this reason alone linking observations often highly abstracted in the form of proxies to the primary processes involved and ultimately to explanatory hypotheses for specific geological events and transitions is challenging the past few decades have seen a progressive improvement in theoretical and process based understanding of the various components that make up the marine carbon cycle and hand in hand with this the development of numerical model representations of the complete system models have also been designed and or adapted with paleoclimate questions in mind and applied to quantitatively explore the role of the marine carbon cycle in both perturbations and long term geologic evolutionary trends in global climate and possible feedbacks between them however we must ask whether paleoclimate models incorporate sufficiently appropriate representations of the dynamics and sensitivities of the marine carbon cycle and indeed whether in the geological context we really know what these dynamics are here we provide a comprehensive overview of how marine carbon cycling and the biological carbon pump is treated in available paleoclimate models with the aim of critically evaluating their ability to help interpret past marine carbon cycle and climate dynamics to this end we first provide an overview of commonly used paleoclimate models and some of their associated paleo applications drawing from a wide range of global carbon cycle box models and earth system models of intermediate complexity emics secondly we review and evaluate the three dominant processes involved in the cycling of organic and inorganic carbon in the marine system and how they are represented in models namely biological productivity at the ocean surface remineralisation dissolution of particulate carbon within the water column and the benthic pelagic coupling at the seafloor we generate and employ illustrative examples using the model genie to show how different parameterisations of water column and sediment processes can lead to significantly different model projections our compilation reveals the prevalence of static parameterisations of marine carbon cycling among existing paleoclimate models which are commonly empirically derived from present day observations although such approaches tend to represent carbon transfer in the modern ocean well they are potentially compromised in their ability to reflect the true degree of freedom and strength of feedbacks with respect to past climate events particularly those characterised by environmental boundary conditions that differ fundamentally from today finally we discuss the importance of using models of different complexities and how questions of model uncertainty may start to be addressed

large terrestrial and marine carbon and hydrogen isotope excursions in a new paleocene eocene boundary section from tanzania recent onshore drilling expeditions in tanzania have yielded sediments spanning much of the late cretaceous and paleogene which show exceptionally good preservation of both calcareous microfossils and organic matter the interval of the paleocene eocene thermal maximum petm was recovered at tanzania drilling project tdp site 14 in 2004 the petm interval was identified using planktonic foraminifer and nannofossil biostratigraphy carbon isotopic measurements of planktonic foraminifera from the genus subbotina show a maximum measured negative shift in 13c values of approximately 4 5 which is significantly larger than has been observed for most deep sea foraminifer records higher plant derived n alkanes yield a ca 6 5 negative shift through the same interval as carbon isotope fractionation in higher plants varies amongst taxa and is influenced by humidity it is possible that this remarkably large shift in the n alkane 13c values records environmental and vegetation changes as well as changes in the 13c value of the ocean atmosphere reservoir however dramatic increases in humidity appear to be unlikely as higher plant biomarker d values shift to higher rather than lower values taken together the records suggest that the magnitude of the carbon isotope excursion cie in the ocean atmosphere reservoir may have been larger than has generally been accepted this has important implications for the source and quantity of 13c depleted carbon released at the petm

warming and environmental changes in the eastern north sea basin during the palaeocene eocene thermal maximum as revealed by biomarker lipids analysis of sediments deposited at different latitudes around the world during the palaeocene eocene thermal maximum petm 56 ma have revealed a globally profound warming phase regionally varying from 5 8 c such records from europe have not yet been obtained we studied the variations in sea surface and continental mean annual air temperatures sst and mat respectively and the distribution patterns and stable carbon isotopes of higher plant derived n alkanes in two proximal petm sections fur and store baelt denmark from the epicontinental north sea basin a negative carbon isotope excursion cie of 4 7 was recorded in land plant derived n alkanes similar to what has been observed for other petm sections however differences observed between the two proximal sites suggest that local factors such as regional vegetation and precipitation patterns also influenced the cie the presence of s bound isorenieratene derivatives at the onset of the petm and increased organic carbon contents points to a rapid shift in depositional environment from well oxygenated to anoxic and sulfidic these euxinic conditions are comparable with those during the petm in the arctic ocean ssts inferred from tex86 show relatively low temperatures followed by an increase of 7 c across the petm at the fur section a remarkably similar temperature record was obtained for mat using the mbt cbt proxy however the mat record of the store baelt section did not reveal this warming

expanded oxygen minimum zones during the late paleocene early eocene hints from multiproxy comparison and ocean modeling anthropogenic warming could well drive depletion of oceanic oxygen in the future important insight into the relationship between deoxygenation and warming can be gleaned from the geological record but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions we use i ca in benthic foraminifera to reconstruct late paleocene through early eocene bottom and pore water redox conditions in the south atlantic and southern indian oceans and compare our results with those derived from mn speciation and the ce anomaly in fish teeth we conclude that waters with lower oxygen concentrations were widespread at intermediate depths 1 5 2 km whereas bottom waters were more oxygenated at the deepest site in the southeast atlantic ocean 3 km epifaunal benthic foraminiferal i ca values were higher in the late paleocene especially at low oxygen sites than at well oxygenated modern sites indicating higher seawater total iodine concentrations in the late paleocene than today the proxy based bottom water oxygenation pattern agrees with the site to site o2 gradient as simulated in a comprehensive climate model community climate system model version 3 but the simulated absolute dissolved o2 values are low 35 mol kg while higher o2 values 60 100 mol kg were obtained in an earth system model grid enabled integrated earth system model multiproxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved

late lutetian thermal maximum crossing a thermal threshold in earth s climate system recognizing and deciphering transient global warming events triggered by massive release of carbon into earth s ocean atmosphere climate system in the past are important for understanding climate under elevated pco 2 conditions here we present new high resolution geochemical records including benthic foraminiferal stable isotope data with clear evidence of a short lived 30 kyr warming event at 41 52 ma the event occurs in the late lutetian within magnetochron c19r and is characterized by a 2 c warming of the deep ocean in the southern south atlantic the magnitudes of the carbon and oxygen isotope excursions of the late lutetian thermal maximum are comparable to the h2 event 53 6 ma suggesting a similar response of the climate system to carbon cycle perturbations even in an already relatively cooler climate several million years after the early eocene climate optimum coincidence of the event with exceptionally high insolation values in the northern hemisphere at 41 52 ma might indicate that earth s climate system has a thermal threshold when this tipping point is crossed rapid positive feedback mechanisms potentially trigger transient global warming the orbital configuration in this case could have caused prolonged warm and dry season leading to a massive release of terrestrial carbon into the ocean atmosphere system initiating environmental change

a simple model for the caco3 saturation state of the ocean the strangelove the neritan and the cretan ocean 1 a simple model of the caco3 saturation state of the ocean is presented it can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration it should also attract researchers unfamiliar with complex biogeochemical models despite its limitations the model calculated caco3 saturation state of today s ocean agrees well with observations in general the model reveals three distinctly different modes of operation the strangelove ocean of high supersaturation which is dominated by inorganic caco3 precipitation 2 the neritan ocean of indefinite saturation dominated by biogenic shallow water caco3 precipitation and 3 the cretan ocean of low saturation dominated by biogenic pelagic caco3 precipitation in the latter mode the deep ocean co32 is remarkably stable provided that the biogenic production of caco3 exceeds the riverine flux of ca2 and co32 this explains the overall constancy of the saturation state of the ocean documented over the last 100 ma the model is then used to address diverse questions one important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

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

comment on coccolith sr ca records of productivity during the paleocene eocene thermal maximum from the weddell sea by heather m stoll and santo bains

long climatic time series from sediment physical property measurements abstract with an accurate understanding of the lithologic dependence of pre compaction porosity in pelagic sediments it should be possible to calculate mass accumulation rate histories of sedimentary phases to generate proxy carbonate logs from core density scans and from seismic profiles and to reconstruct the mechanical and chemical processes that occur during burial and lithification we demonstrate that routinely made continuous gamma ray attenuation porosity evaluator grape wet bulk density measurements of sediments show a positive relationship to carbonate content in a variety of pelagic environments mineralogically related differences in packing rather than differences in grain density appear to control wet bulk density variations a hyperbolic model calibrated at dsdp odp drill ites quantifies the relationship of density to carbonate content in different pelagic environments the curvilinear relationships appear to converge to a similar wet bulk density 1 71 0 07 g cm3 porosity 58 at 100 carbonate content but they exhibit differing porosity at zero carbonate content wet bulk densities for a given carbonate content depend on the non carbonate mineralogy and grain size and increase systematically from opal to clay to quartz lithic fragment dominated settings because contrasts in sediment wet bulk density control the seismic response of unlithified sediments it should be possible to generate carbonate profiles remotely in carbonate rich settings after core calibration of the seismic system our model can generate long proxy carbonate curves with a typical sample spacing of 0 6 1 cm from existing grape data bases in equatorial pacific equatorial atlantic and northern atlantic locations over the past 6 m y these time series are used to investigate the long term evolution of climate in the milankovitch frequency band as well as to reconstruct patterns of carbonate sedimentation over time sedimentation bears the imprint of milankovitch cyclicity superimposed on long term trends the switch in carbonate sedimentation from 41 kyr periodicity during the matuyama chron to dominant 100 kyr periodicity in brunhes chron previously described in the north atlantic occurs in equatorial atlantic and pacific locations as well the lithological dependency of porosity in uncompacted pelagic sediments also has important implications for understanding later compaction and diagenetic modification of pelagic sediments in particular the grape observations suggest that differential burrow flattening observed in lithified limestone marl alternations results from mechanical and pressure solution compaction of strata that had strong primary porosity differences rather than from diagenetic unmixing of carbonate

palaeoceanography corrosive circulation an ancient carbon release resulted in widespread dissolution of carbonates at the sea floor numerical simulations suggest that the pattern of dissolution can be explained by a top down invasion of corrosive bottom waters from the north atlantic

a palaeogene perspective on climate sensitivity and methane hydrate instability the palaeoceneeocene thermal maximum petm a rapid global warming event and carbon cycle perturbation of the early palaeogene provides a unique test of climate and carbon cycle models as well as

tempo and scale of late paleocene and early eocene carbon isotope cycles implications for the origin of hyperthermals abstract the upper paleocene and lower eocene are marked by several prominent 1 carbon isotope 13c excursions cie that coincide with transient global warmings or thermal maxima including the paleocene eocene thermal maximum petm the cie which are recorded mainly in marine sedimentary sequences have also been identified in continental sequences occurred episodically and yet appear to be paced or triggered by orbital forcing to constrain the timing and scale of the cie relative to long term baseline variability we have constructed a 4 52 million year myr long high resolution 3 kyr bulk sediment carbon isotope record spanning the lower eocene to upper paleocene c25r c24n from a pelagic sediment section recovered at odp site 1262 in the southeast atlantic this section which was orbitally tuned utilizing high resolution core log physical property and geochemical records is the most stratigraphically complete upper paleocene to lower eocene sequence recovered to date time series analysis of the carbon isotope record along with a high resolution fe intensity record obtained by xrf core scanner reveal cyclicity with variance concentrated primarily in the precession 21 kyr and eccentricity bands 100 and 400 kyr throughout the upper paleocene lower eocene in general minima in 13c correspond with peaks in fe i e carbonate dissolution both of which appear to be in phase with maxima in eccentricity this covariance is consistent with excess oceanic uptake of isotopically depleted carbon resulting in lower carbonate saturation during periods of high eccentricity this relationship includes all late paleocene and early eocene cie confirming pacing by orbital forcing the lone exception is the petm which appears to be out of phase with the 400 kyr cycle though possibly in phase with the 100 kyr cycle reinforcing the notion that a mechanism other than orbital forcing and or an additional source of carbon is required to account for the occurrence and unusual scale of this event