slow release of fossil carbon during the palaeocene eocene thermal maximum a brief period of warming 55 9 myr ago has been attributed to the release of massive amounts of carbon geochemical and model data suggest the peak rate of carbon emission during this interval was relatively slow and significantly lower than present day levels of carbon emissions to the atmosphere

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

a model for the simulation of combined major and trace element liquid lines of descent abstract variations of major and trace element partition coefficients as functions of temperature and composition have severely limited the range of composition for quantitative modeling of the differentiation of natural magmatic systems application of a two lattice melt model greatly reduces compositional dependence for trace elements this allows the temperature dependence of isobaric trace element partitioning to be evaluated independently thus making it possible to model an expanded range of conditions and compositions the first goal of this investigation was to construct a model to simulate major and trace element systematics of natural differentiation processes by combining trace element partitioning with a major element phase equilibrium model nielsen 1985b the second goal was the application of this model to the simulation of magma chamber recharge assimilation eruption and fractional crystallization these simulations indicate that the proportions of minerals fractionating from an open system are not necessarily the same as those in a closed system recharge or assimilation will drive a magma composition off the cotectic along which it is evolving however fractionation will drive the liquid back towards the cotectic in a recharged magma chamber as the recharge flux increases the fractionating mineral proportions will be increasingly biased towards those phases which appear first from the primitive magma the bulk partition coefficient for an open system can be considerably different 5 10 or more for some elements compared to a closed system paired assimilation and fractional crystallization are often cited as the mechanisms responsible for the origin of high al basalts and andesites however the addition of an al rich assimilant into a fractionating basaltic magma will increase the proportion of plagioclase to the extent that al in the derived liquids will be effectively buffered or even decrease the assimilation of forsteritic olivine by reaction keleman and ghiorso 1986 increases the proportions of pyroxene and olivine thus reducing the fe enrichment and al depletion characteristic of low pressure basalt fractionation

late cenozoic arctic ocean sea ice and terrestrial paleoclimate sea otter remains found in deposits of two marine transgressions bigbendian and fishcreekian of the alaskan arctic coastal plain which occurred between 2 4 and 3 ma suggest that during these two events the southern limit of seasonal sea ice was at least 1600 km farther north than at present in alaskan waters perennial sea ice must have been severely restricted or absent and winters were warmer than at present during these two sea level highstands paleomagnetic faunal and palynological data indicate that the later transgression fishcreekian occurred during the early part of the matuyama reversed polarity chron amino acid diagenesis in fossil mollusks suggests that since the later transgression the effective diagenetic temperature edt in the deposits has been about 16 c which is about 7 c colder than modern values and slightly colder than the edt calculated for the past 125 ka such a low edt suggests that permafrost and perennial sea ice have been present nearly continuously since this transgression permafrost probably was absent however during the earlier bigbendian transgression permafrost and extensive perennial sea ice may have been initiated during the late stages of climatic cooling that spanned the gauss normal matuyama reversed polarity chron boundary and led into the first major late cenozoic glaciation of the northern hemisphere

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

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

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

spatiotemporal patterns of carbonate sedimentation in the south atlantic implications for carbon cycling during the paleocene eocene thermal maximum abstract rapid carbon input into the ocean atmosphere system caused a dramatic shoaling of the lysocline during the paleocene eocene thermal maximum petm a transient 170 kyr global warming event that occurred roughly 55 ma carbon cycle models invoking an accelerated carbonate silicate feedback mechanism to neutralize ocean acidification predict that the lysocline would subsequently deepen to depths below its original position as the marine carbonate system recovered from such a perturbation to test this hypothesis records of carbonate sedimentation and preservation for petm sections in the weddell sea odp site 690 and along the walvis ridge depth transect odp sites 1262 1263 and 1266 were assembled within the context of a unified chronostratigraphy the meridional gradient of undersaturation delimited by these records shows that dissolution was more severe in the subtropical south atlantic than in the weddell sea during the petm a spatiotemporal pattern inconsistent with the view that atlantic overturning circulation underwent a transient reversal deepening of the lysocline following its initial ascent is signaled by increases in caco3 and coarse fraction content at all sites carbonate preservation during the recovery period is appreciably better than that seen prior to carbon input with carbonate sedimentation becoming remarkably uniform over a broad spectrum of geographic and bathymetric settings these congruent patterns of carbonate sedimentation confirm that the lysocline was suppressed below the depth it occupied prior to carbon input and are consistent with the view that an accelerated carbonate silicate geochemical cycle played an important role in arresting petm conditions

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

salinity of the eocene arctic ocean from oxygen isotope analysis of fish bone carbonate stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle eocene samples 55 to 45 ma recently recovered from the lomonosov ridge by integrated ocean drilling program expedition 302 the arctic coring expedition the 18o values of the eocene samples ranged from 6 84 to 2 96 vienna peedee belemnite with a mean value of 4 89 compared to 2 77 for a miocene sample in the overlying section an average salinity of 21 to 25 was calculated for the eocene arctic compared to 35 for the miocene with lower salinities during the paleocene eocene thermal maximum the azolla event at 48 7 ma and a third previously unidentified event at 47 6 ma at the azolla event where the organic carbon content of the sediment reaches a maximum a positive 13c excursion was observed indicating unusually high productivity in the surface waters

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

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 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

climate model and proxy data constraints on ocean warming across the paleocene eocene thermal maximum article constraining the greenhouse gas forcing climatic warming and estimates of climate sensitivity across ancient large transient warming events is a major challenge to the palaeoclimate research community here we provide a new compilation and synthesis of the available marine proxy temperature data across the largest of these hyperthermals the paleocene eocene thermal maximum petm this includes the application of consistent temperature calibrations to all data including the most recent set of calibrations for archaeal lipid derived palaeothermometry this compilation provides the basis for an informed discussion of the likely range of petm warming the biases present in the existing record and an initial assessment of the geographical pattern of petm ocean warming to aid interpretation of the geographic variability of the proxy derived estimates of petm warming we present a comparison of this data with the patterns of warming produced by high pco2 sim ulations of eocene climates using the hadley centre atmosphere ocean general circulation model aogcm hadcm3l on the basis of this comparison and taking into account the patterns of intermediate water warming we estimate that the global mean surface temperature anomaly for the petm is within the range of 4 to 5 c

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

depth dependency of the paleocene eocene carbon isotope excursion paired benthic and terrestrial biomarker records ocean drilling program leg 208 walvis ridge 1 the paleocene eocene thermal maximum petm coincided with a negative carbon isotope excursion cie in carbonate and organic matter in terrestrial and marine records consequently the petm global warming of 5 6 c has been attributed to the rapid emission of a large amount of isotopically light carbon into the ocean atmosphere system and the magnitude of the cie has been used to estimate the amount of carbon greenhouse gas emitted however there are large discrepancies between the magnitude of the cie in marine and in terrestrial material in different types of marine carbonate records bulk carbonate planktic and benthic foraminiferal carbonate and in marine carbonate records from different locations the marine carbonate record of the cie may be incomplete in most deep sea bathyal abyssal locations because of ocean acidification and widespread dissolution of seafloor carbonates we demonstrate that the cie in benthic foraminiferal stable isotope records is relatively abrupt and not as gradual as portrayed in bulk carbonate records along the walvis ridge depth transect se atlantic the benthic cie is about 1 5 at 3600 m paleodepth in contrast to about 3 5 at 1500 m paleodepth consistent with depth dependent truncation by carbonate dissolution strong covariance between the benthic record and the stable carbon isotope values of terrestrial n alkanes isolated from the same core i e site 1263 supports a relatively rapid excursion of at least 3 5 but no more than 5 0

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

latest cretaceous paleocene deep sea ostracode fauna at iodp site u1407 western north atlantic with special reference to the cretaceous paleogene boundary and the latest danian event abstract during the paleocene the marine plankton community recovered its diversity after a severe diversity loss at the cretaceous paleogene k pg boundary in general changes in paleocene deep sea ostracode faunas are poorly understood it is still unclear how the deep sea ostracode faunas changed during compelling events such as the k pg boundary 66 04 ma and the latest danian event lde 62 18 ma a transient paleocene warming event in this report we describe a study on the latest cretaceous late paleocene ostracodes from integrated ocean drilling program site u1407 off newfoundland in the northwestern atlantic thirty six ostracode taxa were obtained from 202 discrete samples that were collected from the interval between 66 3 and 57 3 ma near the k pg boundary 8 2 of 25 of the maastrichtian taxa became extinct the extinction rate is estimated to be at most 0 12 e msy 1 which is equal to extinction rate of 12 per one million years and is in the same range as the background level extinction rate comparing the extinction rates between different ocean basins such as maud rise and blake nose the ostracode extinction at the k pg boundary displays striking geographical heterogeneity between the maastrichtian and danian the ostracode faunas change from a biofacies dominated by shallow bathyal taxa to one dominated by deep bathyal taxa during the lde ostracode faunas display an increase in their benthic ostracode accumulation rates and taxonomic diversity as well as an increase in the relative abundance of krithe crassicaudata simultaneously with a decline in carbonate content a similar change is commonly documented in fauna from the northeastern atlantic during the paleocene eocene thermal maximum petm 56 0 ma in contrast to the petm fauna an extinction event is not recognized near the danian selandian boundary the ostracodes show an increase in export productivity after the danian the ostracodes form a community that appears to tolerate warm and acidified water export productivity remains high during the selandian and thanetian

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

the paleocene eocene thermal maximum how much carbon is enough the paleocene eocene thermal maximum petm 55 53 million years before present was an abrupt warming event that involved profound changes in the carbon cycle and led to major perturbations of marine and terrestrial ecosystems the petm was triggered by the release of a massive amount of carbon and thus the event provides an analog for future climate and environmental changes given the current anthropogenic co2 emissions previous attempts to constrain the amount of carbon released have produced widely diverging results between 2000 and 10 000 gigatons carbon gtc here we use the uvic earth system climate model in conjunction with a recently published compilation of petm temperatures to constrain the initial atmospheric co2 concentration as well as the total mass of carbon released during the event thirty six simulations were initialized with varying ocean alkalinity river runoff and ocean sediment cover simulating various combinations of pre petm co2 levels 840 1680 and 2520 ppm and total carbon releases 3000 4500 7000 and 10 000 gtc we find that both the 840 ppm plus 7000 gtc and 1680 ppm plus 7000 10 000 gtc scenarios agree best with temperature reconstructions bottom waters outside the arctic and north atlantic oceans remain well oxygenated in all of our simulations while the recovery time and rates are highly dependent on ocean alkalinity and sediment cover the maximum temperature anomaly used here to constrain the amount of carbon released is less dependent on this slow acting feedback

centennial to decadal vegetation community changes linked to orbital and solar forcing during the dan c2 hyperthermal event formed close to the k pg boundary the boltysh meteorite crater ukraine preserves 400 m of lacustrine sedimentary rocks that include a record of the early danian dan c2 hyperthermal event abundant pollen spores and algae recovered from these sediments have yielded a cyclic record of plant ecology change paced by c 21 kyr orbital precession cycles new higher resolution sampling across the inception of the dan c2 hyperthermal event has identified oscillations in vegetation community ecology at sub orbital periods of c 2 kyr c 200 years and c 11 years these are consistent with possible hallstatt devreis suess and schwabe solar cycles respectively rapid regime shift from savanna to a mesic forest ecosystem was paced by c 21 kyr precession with the shift probably occurring in c 2 kyr i e possible hallstatt oscillations between mesic and winterwet dominated plant communities increased in intensity suggestive of ecological flickering supplementary material detrended correspondence and changepoint analysis palynological frequency data for dca groups and core photographs are available at https doi org 10 6084 m9 figshare c 3803893

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

the dynamics of global change at the paleocene eocene thermal maximum a data model comparison we integrate published stable isotopic chemical mineralogical and biotic data from the onset of the paleocene eocene thermal maximum petm at site 690 maud rise in the southern ocean the integrated data set documents a sequence of environmental steps including warming of the ocean from the surface downward and modification of its thermal and nutrient structure acidification of the deep ocean and the onset of continental weathering the age of the events with respect to the onset of the petm is calibrated with three different age models the relative and absolute timing of the steps are compared with simulated temperature salinity calcite saturation and dissolved po4 and o2 at different depths in the ocean generated with the uvic earth system climate model of intermediate complexity the simulation supports the top to bottom transfer of heat and carbon and generally agrees with age models in terms of the durations of leads and lags in temperature c isotope and biotic responses moreover the simulation shows that stratification increased and the nutricline strengthened at the onset of the petm these environmental changes explain the abundance of deep dwelling nannoplankton and foraminifera during the early part of the event the modeled calcite saturation is consistent with a harsh deep sea habitat at the time of the benthic foraminiferal extinction

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

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