reappraisal of early paleogene ccd curves foraminiferal assemblages and stable carbon isotopes across the carbonate facies of perth abyssal plain bulk carbonate content planktic and benthic foraminiferal assemblages stable isotope compositions of bulk carbonate and nuttallides truempyi benthic foraminifera and non carbonate mineralogy were examined across 30 m of carbonate rich paleogene sediment at deep sea drilling project dsdp site 259 on perth abyssal plain off western australia carbonate content mostly reflecting nannofossil abundance ranges from 3 to 80 and generally exceeds 50 between 35 and 57 mbsf a clay rich horizon with a carbonate content of about 37 occurs between 55 17 and 55 37 mbsf the carbonate rich interval spans planktic foraminiferal zones p4c to p6b 57 52 ma with the clay rich horizon near the base of our zone p5 upper p6b throughout the studied interval benthic species dominate foraminiferal assemblages with scarce planktic foraminifera usually of poor preservation and limited species diversity a prominent benthic foraminiferal extinction event bfee occurs across the clay rich horizon with an influx of large acarinina immediately above the 13c records of bulk carbonate and n truempyi exhibit trends similar to those observed in upper paleocene lower eocene 57 52 ma sediment from other locations two successive decreases in bulk carbonate and n truempyi 13c of 0 5 and 1 0 characterize the interval at and immediately above the bfee despite major changes in carbonate content foraminiferal assemblages and carbon isotopes the mineralogy of the non carbonate fraction consistently comprises expanding clay heulandite zeolite quartz feldspar sodic or calcic minor mica and pyrolusite mno2 the uniformity of this mineral assemblage suggests that site 259 received similar non carbonate sediment before during and after pelagic carbonate deposition the carbonate plug at site 259 probably represents a drop in the ccd from 57 to 52 51 ma as also recognized at other locations

a cenozoic record of the equatorial pacific carbonate compensation depth atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks these feedbacks involve the erosion of silicate rocks and organic carbon bearing rocks the integrated effect of these processes is reflected in the calcium carbonate compensation depth which is the oceanic depth at which calcium carbonate is dissolved here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial pacific ocean the carbonate compensation depth tracks long term ocean cooling deepening from 3 0 3 5 kilometres during the early cenozoic approximately 55 million years ago to 4 6 kilometres at present consistent with an overall cenozoic increase in weathering we find large superimposed fluctuations in carbonate compensation depth during the middle and late eocene using earth system models we identify changes in weathering and the mode of organic carbon delivery as two key processes to explain these large scale eocene fluctuations of the carbonate compensation depth

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

faunal turnovers in central pacific benthic foraminifera during the paleocene eocene thermal maximum abstract although it is well known that the paleocene eocene thermal maximum petm coincided with a major benthic foraminiferal extinction event the detailed pattern of the faunal turnover has not yet been clarified our high resolution benthic foraminiferal and carbon isotope analyses at the low latitude pacific ocean shatsky rise have revealed the following record of major faunal transitions 1 an initial turnover which involved the benthic foraminiferal extinction event bfe the bfe marked by a sharp transition from pre extinction fauna to disaster fauna represented by small sized bolivina gracilis expresses the onset of the petm and the abrupt extinction of about 30 of taxa this faunal transition lasted about 45 74 kyr after the initiation of the petm and was followed by 2 the appearance of opportunistic fauna represented by quadrimorphina profunda which existed for about 74 91 kyr after the initiation of the petm these two faunas which appeared after the extinction event are characterized by low diversity and dwarfism possibly due to lowered oxygen condition and decreased surface productivity the second pronounced turnover involved the gradual recovery from opportunistic fauna to the establishment of recovery fauna which coincided with the recovery about 83 91 kyr after its initiation

sedimentary trace element constraints on the role of north atlantic igneous province volcanism in late paleocene early eocene environmental change abstract a growing body of geologic evidence suggests that emplacement of the north atlantic igneous province naip played a major role in global warming during the early paleogene as well as in the transient paleocene eocene thermal maximum petm event a 5 million year record of major and trace element abundances spanning 56 to 51 ma at deep sea drilling project sites 401 and 549 confirms that the majority of naip volcanism occurred as subaerial flows thus the trace element records provide constraints on the nature and scope of the environmental impact of the naip during the late paleocene early eocene interval subaerial volcanism would have injected mantle co2 directly into the atmosphere resulting in a more immediate increase in atmospheric greenhouse gas abundances than co2 input through submarine volcanism the lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the petm any connection between naip volcanism and petm warming had to occur through the atmosphere

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

paleogene deepwater mass composition of the tropical pacific and implications for thermohaline circulation in a greenhouse world 1 the pacific ocean likely exerted the greatest marine influence on climate during the greenhouse interval of the paleogene the first step toward assessing the role of pacific deepwater circulation in global heat transport is a comprehensive reconstruction of deepwater mass composition and circulation patterns we present new deepwater mass nd isotope data from odp leg 199 sites 1215 1217 1219 and 1221 to augment the existing coverage provided by ferromanganese crust and fossil fish debris data the new data corroborate the notion that the pacific ocean operated in a bimodal pattern with deepwater sources in both the southern ocean and north pacific for much of the early to middle paleogene in addition the data indicate that there was little to no influence of atlantic waters on the deepwater composition of the tropical pacific the available deepwater nd isotope data provide refined constraints on the geographic and depth range of influence of both a southern ocean and north pacific deepwater mass from 65 to 45 ma the deep tropical pacific was the mixing location of deep waters sourced from the southern ocean and the north pacific the southern ocean deepwater mass extended from 1800 m to abyssal depths until 53 6 ma it circulated northward in the western pacific at least as far as the paleolocation of fe mn crust cld01 5 n paleolatitude and in the eastern portion of the pacific as far as site 1215 10 n paleolatitude a north pacific deepwater mass extended from at least 2400 m to 2900 m water depth from 65 to 54 ma south to shatsky rise paleolatitude 10 15 n and possibly as far as site 1215 700 km to the south of shatsky rise sites 1209 and 1211

high resolution deep sea carbon and oxygen isotope records of eocene thermal maximum 2 and h2 eocene thermal maximum 2 etm2 and h2 were two short lived global warming events that occurred 2 m y after the paleocene eocene thermal maximum petm ca 56 ma we have generated benthic foraminiferal stable carbon and oxygen isotope records of four sites along a depth transect on walvis ridge 3 5 1 5 km paleodepth southeast atlantic ocean and one site on maud rise weddell sea to constrain the pattern and magnitude of their carbon isotope excursions cies and deep sea warming at all sites etm2 is characterized by 3 c warming and a 1 4 cie the h2 event that occurred 100 k y later is associated with 2 c warming and a 0 8 cie the magnitudes of the 13 c and 18 o excursions of both events are signifi cantly smaller than those during the petm but their coherent relation indicates that the 13 c change of the exogenic carbon pool was similarly related to warming during these events despite the much more gradual and transitioned onset of etm2 and h2

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

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

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

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

multispecies stable isotopes of benthic foraminifers reveal past changes of organic matter decomposition and deepwater oxygenation in the arabian sea 1 the stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western arabian sea was determined to evaluate deepwater oxygenation organic matter remineralization and early diagenetic processes during the past 190 000 years the 18o records reveal species specific metabolic effects susceptibility to changes in carbonate ion concentration and supralysoclinal calcite dissolution the foraminiferal 13c records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon 13cdic and in the microhabitat depth of infaunal species maximum 13cdic offsets between bottom and pore waters ranged between mean values of 0 8 and 1 2 corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2 7 ml l 1 intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well oxygenated deepwater masses during interglacials during interglacial maxima the 13c difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes

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

eustatic variations during the paleocene eocene greenhouse world we reconstruct eustatic variations during the latest paleocene and earliest eocene 58 52 ma dinoflagellate cysts grain size fractions and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the paleocene eocene thermal maximum petm the same trend is recognized in published records from other sites around the world together the data indicate a eustatic rise during the petm beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion cie at 55 5 ma although correlations are tentative we recognize other global transgressions during chrons c25n and c24n the latter may be associated with eocene thermal maximum 2 53 5 ma or the x event 52 ma these results suggest a link between global sea level and hyperthermal intervals potentially because of the melting of small alpine ice sheets on antarctica thermal expansion of seawater or both however the early onset of sea level rise relative to the cie of the petm suggests contributions from other mechanisms perhaps decreasing ocean basin volume on sea level rise copyright 2008 by the american geophysical union

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

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

ecological evidence from live dead comparisons of benthic foraminiferal faunas off cape blanc northwest africa abstract a comparison of live and dead benthic foraminiferal faunas in a five station sample transect off cape blanc suggests that interspecific differences in living dead l d ratios are to a large extent determined by seasonal differences in reproduction it is proposed that many epifaunal and superficial infaunal species show a highly opportunistic behaviour with a majority of the foraminifera being produced in a relatively short period of the year the density of deeper infaunal taxa on the contrary would be much more stable over time sites with large contrasts in l d ratios between deep intermediate infaunal and epifaunal shallow infaunal taxa should be subject to important seasonal variations in the downward flux of organic matter this study suggests that important ecological information can be gained from live dead comparisons

widespread and synchronous change in deep ocean circulation in the north and south atlantic during the late cretaceous modern thermohaline circulation plays a role in latitudinal heat transport and in deep ocean ventilation yet ocean circulation may have functioned differently during past periods of extreme warmth such as the cretaceous the late cretaceous 100 65 ma was an important period in the evolution of the north atlantic ocean characterized by opening ocean gateways long term climatic cooling and the cessation of intermittent periods of anoxia oceanic anoxic events oaes however how these phenomena relate to deep water circulation is unclear we use a proxy for deep water mass composition neodymium isotopes end to show that at north atlantic odp site 1276 deep waters shifted in the early campanian 78 83 ma from end values of 7 to values of 9 consistent with a change in the style of deep ocean circulation but 10 myr after a change in bottom water oxygenation conditions a similar but more poorly dated trend exists in end data from dsdp site 386 the campanian end transition observed in the north atlantic records is also seen in the south atlantic and proto indian ocean implying a widespread and synchronous change in deep ocean circulation although a unique explanation does not exist for the change at present we favor an interpretation that invokes late cretaceous climatic cooling as a driver for the formation of southern component water which flowed northward from the southern ocean and into the north atlantic and proto indian oceans

an extraterrestrial 3he based timescale for the paleocene eocene thermal maximum petm from walvis ridge iodp site 1266 in the deep sea the paleocene eocene thermal maximum petm is often marked by clay rich condensed intervals caused by dissolution of carbonate sediments capped by a carbonate rich interval constraining the duration of both the dissolution and subsequent cap carbonate intervals is essential to computing marine carbon fluxes and thus testing hypotheses for the origin of this event to this end we provide new high resolution helium isotope records spanning the paleocene eocene boundary at odp site 1266 in the south atlantic the extraterrestrial 3he 3he et concentrations replicate trends observed at odp site 690 by farley and eltgroth 2003 by assuming a constant flux of 3he et we constrain relative changes in accumulation rates of sediment across the petm and construct a new age model for the event in this new chronology the zero carbonate layer represents 35 kyr some of which reflects clay produced by dissolution of paleocene pre petm sediments above this layer carbonate concentrations increase for 165 kyr and remain higher than in the latest paleocene until 234 48 34 kyr above the base of the clay the new chronology indicates that minimum 13 c values persisted for a maximum of 134 27 19 kyr and the inflection point previously chosen to designate the end of the cie recovery occurs at 217 44 31 kyr this allocation of time differs from that of the cycle based age model of rohl et al 2007 in that it assigns more time to the clay layer followed by a more gradual recovery of carbonate rich sedimentation the new model also suggests a longer sustained 13 c excursion followed by a more rapid recovery to pre petm 13 c values these differences have important implications for constraining the source s of carbon and mechanisms for its subsequent sequestration favoring models that include a sustained release of carbon after an initial pulse

a strait outflow circulation process study the case of the alboran sea abstract a three dimensional primitive equation model is used to investigate the physical processes governing the exchanges of water between the mediterranean sea and the atlantic ocean at the level of the strait of gibraltar the circulation is driven by connecting two reservoirs filled with waters of different densities the motion starts from rest and is initiated by removing the dam separating them at the initial time the results are in agreement with observations in the strait the light atlantic water flows into the mediterranean basin in the surface layer while the denser mediterranean water moves toward the ocean as a deep current after a spinup time interval of three days the flow transport in the strait reaches a quasi stationary value of 0 9 sv sv 106 m3 s 1 as it enters the alboran sea the flow of atlantic water experiences a transition regime where the surface current is transformed into a shallow buoyant jet after several days of integration this flow intrudes into the alboran bas

a transient deep sea circulation switch during eocene thermal maximum 2 ever since its discovery eocene thermal maximum 2 etm2 53 7 ma has been considered as one of the little brothers of the paleocene eocene thermal maximum petm 56 ma as it displays similar characteristics including abrupt warming ocean acidification and biotic shifts one of the remaining key questions is what effect these lesser climate perturbations had on ocean circulation and ventilation and ultimately biotic disruptions here we characterize etm2 sections of the ne atlantic deep sea drilling project sites 401 and 550 using multispecies benthic foraminiferal stable isotopes grain size analysis xrf core scanning and carbonate content the magnitude of the carbon isotope excursion 0 85 1 10 and bottom water warming 2 2 5 c during etm2 seems slightly smaller than in south atlantic records the comparison of the lateral 13c gradient between the north and south atlantic reveals that a transient circulation switch took place during etm2 a similar pattern as observed for the petm new grain size and published faunal data support this hypothesis by indicating a reduction in deepwater current velocity following etm2 we record a distinct intensification of bottom water currents influencing atlantic carbonate accumulation and biotic communities while a dramatic and persistent clay reduction hints at a weakening of the regional hydrological cycle our findings highlight the similarities and differences between the petm and etm2 moreover the heterogeneity of hyperthermal expression emphasizes the need to specifically characterize each hyperthermal event and its background conditions to minimalize artifacts in global climate and carbonate burial models for the early paleogene

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

sedimentary record of the mid pleistocene climate transition in the southeastern south atlantic odp site 1090 abstract one important goal of leg 177 of the ocean drilling program odp was to explore the nature of the mid pleistocene climate transition mpt on the southern hemisphere a suitable mpt record was encountered at site 1090 in the southeastern south atlantic where a 44 m thick sequence of quaternary diatom bearing foraminiferal muds and oozes was recovered on the agulhas ridge environmental responses to the mpt comprised changes in terrestrial climate biological productivity and regional ocean circulation as inferred from compositional sediment data and clay mineralogy a shift towards more arid conditions occurred between 900 and 800 ka in southern africa changes in palaeoceanography already started earlier since 1150 ka northward displacements of the polar front appeared during glacial periods and shifted the area of dominant diatom deposition towards site 1090 likewise glacial interglacial contrasts in regional conveyor circulation strengthened after 1200 ka and became most severe after 650 ka however while changes in regional conveyor circulation likely responded in tune with global ice volume changes and show the onset of 100 kyr cycles after 1200 ka an unusual 130 kyr pattern characterises the pattern of frontal movements between 1200 ka and 650 ka probably in response to imperfect adaptation of regional climate to the global 100 kyr climate cycles

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

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

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

on the duration of magnetochrons c24r and c25n and the timing of early eocene global warming events implications from the ocean drilling program leg 208 walvis ridge depth transect 1 five sections drilled in multiple holes over a depth transect of more than 2200 m at the walvis ridge se atlantic during ocean drilling program odp leg 208 resulted in the first complete early paleogene deep sea record here we present high resolution stratigraphic records spanning a 4 3 million yearlong interval of the late paleocene to early eocene this interval includes the paleocene eocene thermal maximum petm as well as the eocene thermal maximum etm 2 event a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records and shipboard color data these records were used to refine the shipboard derived spliced composite depth for each site and with a record from odp site 1051 were then used to establish a continuous time series over this interval extensive spectral analysis reveals that the early paleogene sedimentary cyclicity is dominated by precession modulated by the short 100 kyr and long 405 kyr eccentricity cycles counting of precession related cycles at multiple sites results in revised estimates for the duration of magnetochrons c24r and c25n direct comparison between the amplitude modulation of the precession component derived from xrf data and recent models of earth s orbital eccentricity suggests that the onset of the petm and etm2 are related to a 100 kyr eccentricity maximum both events are approximately a quarter of a period offset from a maximum in the 405 kyr eccentricity cycle with the major difference that the petm is lagging and etm2 is leading a 405 kyr eccentricity maximum absolute age estimates for the petm etm2 and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of earth s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods nevertheless we provide two possible tuning options which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405 kyr eccentricity cycle for the entire paleogene

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

changes in calcareous nannofossil assemblages across the paleocene eocene transition from the paleo equatorial pacific ocean quantitative analyses of selected calcareous nannofossils in deep sea sections recovered from the paleo equatorial pacific odp leg 199 provide new information about biostratigraphy biochronology and the evolutionary history of calcareous nannofossils across the paleocene eocene transition interval the sediment cores from odp leg 199 represent the first continuous paleocene eocene boundary sections ever to be sampled in the central equatorial pacific ocean calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as ericsonia discoaster fasciculithus rhomboaster and tribrachiatus focus is given to the evolution of the rhomboaster tribrachiatus lineage in the lower eocene interval at site 1215 and on the stratigraphic relationship of these taxa relative to species in the genus fasciculithus critical intervals of north atlantic dsdp site 550 have also been re examined the tribrachiatus digitalis morphotype was described at site 550 from an interval affected by down hole contamination partly originating from within the tribrachiatus orthostylus range the t digitalis morphotype represents an evolutionary transitional form between t contortus and t orthostylus entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species the subzonal subdivision of zone np10 hence collapses lithological and colour variability reflecting orbital cyclicity occur in the lower eocene of site 1215 permitting a relative astronomical age calibration of the tribrachiatus taxa the distinct rhomboaster spp discoaster araneus association also occurs in the paleo equatorial pacific ocean together with a marked decrease in diversity of fasciculithus spp site 1220 reveals a short peak abundance of thoracosphaera spp just above the p e boundary interval which probably reflects a stressed surface water environment

climate sensitivity to arctic seaway restriction during the early paleogene abstract the opening and closing of ocean gateways affects the global distribution of heat salt and moisture potentially driving climatic change on regional to global scales between 65 and 45 million years ago ma during the early paleogene exchange between the arctic and global oceans occurred through two narrow and shallow seaways the greenland norway seaway and the turgai strait sediments from the arctic ocean suggest that during this interval the surface ocean was warm brackish and episodically enabled the freshwater fern azolla to bloom the precise mechanisms responsible for the development of these conditions in the paleogene arctic remain uncertain here we show results from an isotope enabled atmosphere ocean general circulation model which indicate that northern hemisphere climate would have been very sensitive to the degree of oceanic exchange through the arctic seaways we also present modelled estimates of seawater and calcite 18o for the paleogene by restricting these seaways we simulate freshening of the surface arctic ocean to 6 psu and warming of sea surface temperatures by 2 c in the north atlantic and 5 10 c in the labrador sea our results may help explain the occurrence of low salinity tolerant taxa in the arctic ocean during the eocene and provide a mechanism for enhanced warmth in the north western atlantic we propose that the formation of a volcanic land bridge between greenland and europe could have caused increased ocean convection and warming of intermediate waters in the atlantic if true this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the paleocene eocene thermal maximum petm

high resolution nannofossil biochronology of middle paleocene to early eocene at odp site 1262 implications for calcareous nannoplankton evolution abstract over the last several decades debates on the tempo and mode of evolution have centered on the question whether morphological evolution preferentially occurs gradually or punctuated i e with long periods of stasis alternating with short periods of rapid morphological change and generation of new species another major debate is focused on the question whether long term evolution is driven by or at least strongly influenced by changes in the environment or by interaction with other life forms microfossils offer a unique opportunity to obtain the large datasets as well as the precision in dating of subsequent samples to study both these questions we present high resolution analyses of selected calcareous nannofossils from the deep sea section recovered at odp site 1262 leg 208 in the south eastern atlantic the studied section encompasses nannofossil zones np4 np12 equivalent to cp3 cp10 and chrons c27r c24n we document more than 70 biohorizons occurring over an about 10 myr time interval 62 5 ma to 52 5 ma and discuss their reliability and reproducibility with respect to previous data thus providing an improved biostratigraphic framework which we relate to magnetostratigraphic information and present for two possible options of a new paleocene stratigraphic framework based on cyclostratigraphy this new framework enabled us to tentatively reconstruct steps in the evolution of early paleogene calcareous nannoplankton through documentation of transitional morphotypes between genera and or species and of the phylogenetic relations between the genera fasciculithus heliolithus discoasteroides and discoaster as well as between rhomboaster and tribrachiatus the exceptional record provided by the continuous composite sequence recovered at walvis ridge allows us to describe the mode of evolution among calcareous nannoplankton new genera and or new species usually originated through branching of lineages via gradual but relatively rapid morphological transitions as documented by the presence of intermediate forms between the end member ancestral and descendant forms significant modifications in the calcareous nannofossil assemblages are often related to significant changes in environmental conditions but the appearance of structural innovations and radiations within a single genus also occurred during stable environmental conditions these lines of evidence suggest that nannoplankton evolution is not always directly triggered by stressed environmental conditions but could be also driven by endogenous biotic control

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

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

on the sensitivity of ocean circulation to arctic freshwater input during the paleocene eocene thermal maximum abstract the paleocene eocene thermal maximum petm 55 ma ago corresponds to a time characterized by extreme global warming caused by a massive carbon input into the ocean and atmosphere climate proxies from sedimentary records suggest that fresh water flow from an ice free arctic into the remainder of the global ocean increased due to tectonic changes enhanced runoff and thermal expansion in this study we use the community climate system model version 3 ccsm 3 including a carbon cycle model to examine the sensitivity of the ocean circulation to freshwater outflow from the arctic ocean during the petm and whether these changes may have contributed to an additional warming during the petm two experiments the first with freshwater exchange between the arctic and pacific oceans and the second between the arctic and atlantic oceans are compared with a reference experiment with exchange between the arctic and indian oceans and with independent stratigraphic and geochemical records from the ocean drilling program odp as freshwater is transported from the arctic into the north pacific ocean stratification is enhanced in the north pacific due to a significant reduction in surface salinity as a consequence intermediate to deep water sources shift from both hemispheres in the pacific ocean to a dominant source in the south pacific ocean and an additional source in the northern tethys ocean this simulated shift of deep water sources during the petm is in agreement with recent nd isotope measurements the circulation patterns in the pacific are similar to those inferred from stable isotope reconstructions but contradicting a strong north atlantic deep water source during the petm freshwater input into the pacific ocean results in a warming of intermediate water masses of 2 c in the north pacific when freshwater flow is routed from the arctic into the atlantic ocean surface density changes are too small to change vertical stratification substantially contrary to a previous study in summary based upon circulation patterns and temperature increases due to freshwater flux through the bering strait arctic freshwater input into the north pacific may have contributed to methane hydrate destabilization an event suggested to have accelerated warming during the petm

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

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

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

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

millennial scale changes in atmospheric co2 levels linked to the southern ocean carbon isotope gradient and dust flux the rise in atmospheric co2 concentrations observed at the end of glacial periods has at least in part been attributed to the upwelling of carbon rich deep water in the southern ocean1 2 the magnitude of outgassing of dissolved co2 however is influenced by the biological fixation of upwelled inorganic carbon and its transfer back to the deep sea as organic carbon the efficiency of this biological pump is controlled by the extent of nutrient utilization which can be stimulated by the delivery of iron by atmospheric dust particles3 changes in nutrient utilization should be reflected in the 13c gradient between intermediate and deep waters here we use the 13c values of intermediate and bottom dwelling foraminifera to reconstruct the carbon isotope gradient between thermocline and abyssal water in the subantarctic zone of the south atlantic ocean over the past 360 000 years we find millennial scale oscillations of the carbon isotope gradient that correspond to changes in dust flux and atmospheric co2 concentrations as reported from antarctic ice cores4 5 we interpret this correlation as a relationship between the efficiency of the biological pump and fertilization by dust borne iron as the correlation is exponential we suggest that the sensitivity of the biological pump to dust borne iron fertilization may be increased when the background dust flux is low

latest on the absolute age of the paleocene eocene thermal maximum petm new insights from exact stratigraphic position of key ash layers 19 and 17 abstract we constructed a precise early eocene orbital cyclostratigraphy for dsdp site 550 leg 80 goban spur north atlantic utilizing precession related cycles as represented in a high resolution x ray fluorescence based barium core log based on counting of those cycles we constrain the exact timing of two volcanic ash layers in site 550 which correlate to ashes 19 and 17 of the fur formation in denmark the ashes relative to the onset of the paleocene eocene thermal maximum petm are offset by 862 kyr and 672 kyr respectively when combined with published absolute ages for ash 17 the absolute age for the onset of the petm is consistent with astronomically calibrated ages using the current absolute age of 28 02 ma for the fish canyon tuff fct standard for calibrating the absolute age of ash 17 is consistent with tuning option 2 in the astronomically calibrated paleocene time scale of westerhold et al 2008 westerhold t rohl u raffi i fornaciari e monechi s reale v bowles j and evans h f 2008 astronomical calibration of the paleocene time palaeogeography palaeoclimatology palaeoecology v 257 p 377 403 using the recently recalibrated absolute age of 28 201 ma for the fct standard is consistent with tuning option 3 in the astronomically calibrated paleocene time scale the new results do not support the existence of any additional 405 kyr cycle in the early paleocene astronomically tuned time scale

multiple early eocene hyperthermals their sedimentary expression on the new zealand continental margin and in the deep sea the paleocene eocene thermal maximum petm ca 55 5 ma was a geologically brief interval characterized by massive influx of isotopically light carbon extreme changes in global climate and profound variations in earth system processes an outstanding issue is whether it was an isolated event or the most prominent example of a recurring phenomenon recent studies of condensed deep sea sections support the latter but this finding remains uncertain here we present and discuss lithologic and carbon isotope records across two lower eocene outcrops on south island new zealand the petm manifests as a marl rich horizon with a significant negative carbon isotope excursion cie above in sediment deposited between 54 and 53 ma are four horizons with similar though less pronounced expressions marl beds of all five horizons represent increased terrigenous sedimentation presumably linked to an accelerated hydrological cycle five corresponding clay rich horizons and cies are found in deep sea records although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution the presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 c depleted carbon during the early eocene

understanding long term carbon cycle trends the late paleocene through the early eocene 1 the late paleocene to the early eocene 58 52 ma was marked by significant changes in global climate and carbon cycling the evidence for these changes includes stable isotope records that reveal prominent decreases in i 18 oa ndi 13 c suggesting a rise in earth s surface temperature 4 i c and a drop in net carbon output from the ocean and atmosphere concurrently deep sea carbonate records at several sites indicate a deepening of the calcite compensation depth ccd here we investigate possible causes e g increased volcanic degassing or decreased net organic burial for these observations but from a new perspective the basic model employed is a modified version of geocarb iii however we have coupled this well known geochemical model to loscar long term ocean atmosphere sediment carbon cycle reservoir model which enables simulation of seawater carbonate chemistry the ccd and ocean i 13 c we have also added a capacitor in this case represented by gas hydrates that can store and release 13 c depleted carbon to and from the shallow geosphere over millions of years we further consider accurate input data e g i 13 c of carbonate on a currently accepted timescale that spans an interval much longer than the perturbation several different scenarios are investigated with the goal of consistency amongst inferred changes in temperature the ccd and surface ocean and deep ocean i 13 c the results strongly suggest that a decrease in net organic carbon burial drove carbon cycle changes during the late paleocene and early eocene although an increase in volcanic activity might have contributed importantly a drop in net organic carbon burial may represent increased oxidation of previously deposited organic carbon such as stored in peat or gas hydrates the model successfully recreates trends in earth surface warming as inferred from i 18 o records the ccd and i 13 c at the moment however our coupled modeling effort cannot reproduce the magnitude of change in all these records collectively similar problems have arisen in simulations of short term hyperthermal events during the early paleogene paleocene eocene thermal maximum suggesting one or more basic issues with data interpretation or geochemical modeling remain

terrestrial carbon isotope excursions and biotic change during palaeogene hyperthermals the earth s climate between 60 and 50 million years ago was punctuated by several abrupt warming events the largest of these being the palaeocene eocene thermal maximum carbon isotope records from the bighorn basin wyoming document these events in the terrestrial realm and show a consistent scaling between marine and terrestrial records across the three main events

magnetostratigraphic re calibration of the paleocene eocene boundary interval in holes 550 and 549 goban spur eastern north atlantic a magnetostratigraphic reinvestigation of the paleocene eocene boundary intervals in dsdp holes 550 and 549 goban spur has removed uncertainties associated with the previously published magnetostratigraphic information for these chronostratigraphically important sections in hole 550 levels assigned to nannoplankton zones np4 and 5 previously considered to be of normal polarity carry a reverse polarity characteristic magnetisation which is correlated with geomagnetic chron c26r unconformably overlying these levels is a thin interval of reversely magnetised sediment which records the latter part of chron c25r chron c25n is redefined and its lower upper boundaries are placed respectively at 425 08 and 422 12 mbsf in hole 550 chron c24r extends upwards62 4 m respectively the start and end of chron c24n 3n are placed at 359 69 and 349 41 mbsf in this hole within core 28 just above c24n 3n is a record of chron c24n 2n as well as interval of indeterminate polarity within c24n 2r the problematic issue of assigning numerical ages to the various events associated with the paleocene eocene transition in hole 550 is then discussed the remanence in hole 549 is difficult to interpret because magnetic inclinations in the interval previously assigned to chrons c25n and c24r are typically 20o compared with the60o expected for the paleogene sediments at this site acknowledging the complexities of this record we have constructed the magnetostratigraphy for this hole based on results from the present study and previous work h a townsend the paleomagnetism of sediments acquired from the goban spur on the deep sea drilling project leg 80 in p c de graciansky c w poag et al eds initial reports dsdp 80 1985 389 410 contrary to the previous study we are not able to fix the base of chron c25n it is located either in the lower part of core 18 where the core pieces are too small to be used reliably for paleomagnetic studies or in the gap between cores 18 and 19 the chron c25n 24r boundary is blurred 351 to 353 mbsf because of the shallow inclination problem chron c24n 3n which is characterised by inclinations of35o has its lower upper boundaries at318 and 307 62 mbsf respectively an apparent record of chron c24n 2n based on two samples is present between 305 53 and 304 65 mbsf 1998 elsevier science b v all rights reserved

insights from the paleogene tropical pacific foraminiferal stable isotope and elemental results from site 1209 shatsky rise 1 stable isotope and elemental measurements were conducted on foraminifera from a sequence of calcareous pelagic ooze at ocean drilling program site 1209 to document the thermal evolution of the north pacific water column over shatsky rise and to address long standing questions about the nature of oceanic circulation in the early paleogene a major change in seasonality and water column structure in the early eocene marks a change in tropical pacific climate and circulation just prior to the early eocene climatic optimum subsequent long term cooling is interrupted by a transient positive 18o excursion identified in planktonic and benthic foraminifera during the late early eocene that is interpreted as evidence for ephemeral formation of deep water from a low latitude saline source paired analysis of benthic mg ca and 18o was undertaken to assess the relative contribution of temperature and seawater oxygen isotope composition to the benthic 18o record stratigraphic trends of benthic 18o and mg ca decouple during two intervals in the early eocene and early middle eocene although variable seawater 18o is the most likely candidate to explain decoupling of benthic 18o and mg ca it is difficult to argue for substantial change in continental ice volume during a presumably ice free interval of time

what caused the long duration of the paleocene eocene thermal maximum 1 paleorecords show that the paleocene eocene thermal maximum petm 56 ma was associated with a large carbon cycle anomaly and global warming 5 k which persisted for at least 50 kyr conventional carbon cycle climate models that include a single initial carbon input pulse over 10 kyr fail to reproduce the long duration of the petm without invoking additional slow carbon release over more than 50 kyr hereafter referred to as bleeding however a potential carbon source for the bleeding as well as its release mechanism has hitherto remained elusive here i present first principle calculations of heat transfer in marine sediments which demonstrate that a bottom water temperature anomaly as generated during the petm takes tens of thousands of years to penetrate the top few hundred meters of deep sea sediments while the initial temperature rise has been suggested to cause dissociation of the majority of oceanic methane hydrate within 10 kyr my calculations reveal a long tail of hydrate dissociation causing smaller but continued carbon release substantially beyond 10 kyr in addition i suggest that temperature enhanced metabolic processes in marine sediments and the absence of methane hydrate deposition during the petm contributed to prolonged carbon input during the event enhanced fluxes of methane over this time scale would have sustained the carbon isotope excursion and amplified long term greenhouse warming by elevating atmospheric concentrations of steady state ch4 or in oxidized form co2

early eocene palaeoceanography and palaeoclimatology of the eastern north atlantic stable isotope results for dsdp hole 550

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

bottom current pathways in the argentine basin revealed by mean silt particle size regional circulation patterns in the deep sea are very difficult to determine because of time constraints on the acquisition of large physical oceanographic data sets from abyssal depths in addition the large number of long term 1 yr current meter arrays needed to delineate bottom current pathways are extremely costly an alternative method for inferring benthic flow patterns described here is to map the mean size of the silt fraction of sediment on the sea floor because of the availability of a large number of core samples in the argentine basin the particle size approach provides a useful method for determining bottom current pathways in that deep basin

patterns and magnitude of deep sea carbonate dissolution during eocene thermal maximum 2 and h2 walvis ridge southeastern atlantic ocean 1 eocene thermal maximum 2 etm2 or h1 53 7 ma represents a short lived warming episode associated with the injection of a large mass of 13c depleted carbon into the ocean atmosphere system the mass of injected carbon the extent of deep sea dissolution and the amount of warming during etm2 appear to be approximately half of those documented for the paleocene eocene thermal maximum petm 55 5 ma but the pattern of lysocline migration during etm2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms we present high resolution carbonate dissolution and bulk stable isotope records across etm2 and the successive h2 event 53 6 ma on a common age model for four sites along the walvis ridge depth transect 1500 to 3600 m paleowater depth to assess lysocline evolution the onset of etm2 is characterized by multiple depth dependent transitions of carbonate dissolution up to 96 of the total flux associated with rapid depletions in bulk carbonate carbon up to 1 1 5 and oxygen up to 0 7 1 5 isotope values h2 shows a 0 7 negative carbon isotope excursion with a coeval decrease in 18o of 0 5 and 80 of carbonate dissolution during etm2 the lysocline recovered within 30 ka we attribute this rapid recovery to terrestrial caco3 neutralization through enhanced chemical weathering of carbonates in soils and rocks according to theory carbonate dissolution was lower after recovery than prior to etm2 indicating carbonate ion oversaturation and a deeper position of the lysocline spectral analysis indicates that the changes in carbonate dissolution and 13c values were precession paced implying that weathering feedbacks and short term perturbations in the carbon cycle were important in determining early eocene background and hyperthermal ocean co32 conditions

time scale controversy accurate orbital calibration of the early paleogene 1 timing is crucial to understanding the causes and consequences of events in earth history the calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating uncertainties in the computations of earth s orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 ma attempts to construct a robust astronomically tuned time scale for the early paleogene by integrating radioisotopic and astronomical dating are only partially consistent here using the new la2010 and la2011 orbital solutions we present the first accurate astronomically calibrated time scale for the early paleogene 47 65 ma uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the fish canyon standard comparison with geological data confirms the stability of the new la2011 solution back to 54 ma subsequent anchoring of floating chronologies to the la2011 solution using the very long eccentricity nodes provides an absolute age of 55 530 0 05 ma for the onset of the paleocene eocene thermal maximum petm 54 850 0 05 ma for the early eocene ash 17 and 65 250 0 06 ma for the k pg boundary the new astrochronology presented here indicates that the intercalibration and synchronization of u pb and 40ar 39ar radioisotopic geochronology is much more challenging than previously thought

a middle eocene carbon cycle conundrum a 500 000 year long period of warmth in the middle eocene was marked by high atmospheric carbon dioxide concentrations and prolonged dissolution of carbonate in the deep oceans numerical simulations attempting to capture these features identify gaps in our understanding of the causes of this and similar perturbations

testing the impact of seasonal phytodetritus deposition on δ13c of epibenthic foraminifer cibicidoides wuellerstorfi a 31 000 year high resolution record from the northwest african continental slope 1 studies of temporal changes of ocean circulation and deepwater ventilation often rely on 13c records of epibenthic foraminifer cibicidoides wuellerstorfi however primary productivity related overprints may distort the signal and simulate a chemical age of ambient water mass that is too old and simulates poorly ventilated ambient bottom waters to further constrain the use of c wuellerstorfi 13c records from high productivity areas we analyzed a 14cams dated gravity core from the upwelling regime off northwest africa at 12 n we compare this new record with 37 radiocarbon dated 13c records from the eastern atlantic ocean between 45 n and 25 s that are bathed by the same water mass only during heinrich events 1 and 2 when the investigated core site off northwest africa experienced year round sustained deposition of organic matter the 13c values at this site faithfully record deepwater ventilation states during times of predominantly seasonal deposition of fresh phytodetritus however 13c values were significantly lower than at the reference sites this underscores that reconstruction of paleocirculation and deep ocean ventilation using c wuellerstorfi 13c from regions that experienced seasonal phytodetritus deposition needs to be validated by additional proxies that are not affected by local productivity

testing the cenozoic multisite composite δ18o and δ13c curves new monospecific eocene records from a single locality demerara rise ocean drilling program leg 207 until recently very few high quality deep ocean sedimentary sections of eocene age have been available consequently our understanding of eocene paleoceanography has become heavily reliant on composite records patched together from multiple sites in different ocean basins and generated using multiple taxa potential sources of local noise in the global signal here we test the reliability of the early to middle eocene composite 18o and 13c stratigraphies zachos et al 2001 by generating new monospecific records in benthic foraminiferal calcite from a single locality demerara rise in the tropical western atlantic ocean drilling program leg 207 we present new stable isotope correction factors for commonly used eocene benthic foraminiferal species we find that interspecies isotopic offsets are constant across the isotopic range supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera in general the 18o stratigraphy from demerara rise supports the validity of the eocene 18o composite while revealing a temporary warming punctuating middle eocene cooling this warming may correspond to the so called middle eocene climatic optimum previously documented in the southern ocean the composite and demerara rise records for 13c differ substantially by removing the intersite and intertaxa sources of uncertainty in 13c we obtain a clearer picture of carbon cycling during the eocene secular change in interocean 13c gradients through the eocene reveals that intervals of climatic warmth especially the early eocene are associated with very small water mass ageing gradients

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

carbonate ion effect on mg ca sr ca and stable isotopes on the benthic foraminifera oridorsalis umbonatus off namibia abstract we investigate the influence of carbonate system parameters carbonate ion concentration co32 carbonate ion saturation co32 on the trace element and stable isotope ratios in the endobenthic foraminifera oridorsalis umbonatus data from modern core top samples from the namibian continental slope suggest that the shell composition of this species is influenced by the chemistry of the pore water for these organic rich sediments the impact of ocean bottom water properties on both pore water and shell chemistry is surprisingly small sr ca correlates positively with co32 and to a lesser extent with co32 which is opposed to previous results a co32 decrease of 10 mol kg leads to an increase of 0 05 mmol mol in sr ca we observe a correlation between shell 18o corrected for temperature and 18o seawater and co32 however the variability of the corrected 18o is close to the analytical limit no clear dependences were observed for 13c and mg ca

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

sensitivity of seawater oxygen isotopes to climatic and tectonic boundary conditions in an early paleogene simulation with giss modele r 1 an isotope enabled ocean atmosphere general circulation model giss modele r is used to estimate the spatial gradients of the oxygen isotopic composition of seawater 18osw where is the deviation from a known reference material in per mil during the early paleogene 45 65 ma understanding the response of 18osw to changes in climatic and tectonic boundary conditions is important because records of carbonate 18o document changes in hydrology as well as changes in temperature and global ice volume we present results from an early paleogene configuration of modele r which indicate that spatial gradients of surface ocean 18osw during this period could have been significantly different to those in the modern ocean the differences inferred from modele r are sufficient to change early paleogene sea surface temperature estimates derived from primary carbonate 18o signatures by more than 2 c in large areas of the ocean in the north atlantic indian and southern oceans the differences in 18osw inferred from our simulation with modele r are in direct contrast with those from another 18o tracing model study which used different but equally plausible early paleogene boundary conditions the large differences in 18osw between preindustrial and early paleogene simulations and between models emphasizes the sensitivity of 18osw to climatic and tectonic boundary conditions for this reason absolute estimates of eocene paleocene temperature derived from carbonate 18o alone are likely to have larger uncertainties than are usually assumed

variations in the oceanic vertical carbon isotope gradient and their implications for the paleocene eocene biological pump 1 variations in the efficiency of the biological pumping of carbon from the surface to the deep ocean have been invoked to explain changes in atmospheric pco2 and thus climate on a variety of timescales we compiled published paleocene and eocene foraminiferal carbon isotope data and adjusted them to a uniform timescale to investigate changes in the biological pump in the early cenozoic eight basinal time series were binned into 0 01 ma increments and five water column depth horizons the carbon isotope data reveal remarkably coherent trends in surface thermocline and deep water carbon isotope values through the paleocene and eocene these data were used to drive a three box ocean carbon isotope model to estimate long term relationships among changes in atmospheric pco2 organic and inorganic carbon burial and biological pumping our model results provide evidence for two different modes of organic carbon cycling during the paleocene and earliest eocene atmospheric pco2 drawdown was driven externally by terrestrial organic carbon burial after the earliest eocene variations in atmospheric pco2 resulting from imbalances in organic carbon cycling appear to have been driven by variations in the biological pump a temporary decline in biological pump efficiency at 50 ma may have led to increased atmospheric pco2 increased weathering and nutrient delivery to the oceans and enhanced organic carbon burial thus a biological pump driven increase in atmospheric pco2 created a counterintuitive inverse relationship between organic carbon burial and atmospheric pco2 with no indication of the burial event in the surface water carbon isotope record

two types of surface wind response to the east china sea kuroshio front abstracteffects of the sea surface temperature sst front along the east china sea kuroshio on sea surface winds at different time scales are investigated in winter and spring the climatological vector wind is strongest on the sst front while the scalar wind speed reaches a maximum on the warm flank of the front and is collocated with the maximum difference between sea surface temperature and surface air temperature sst sat the distinction is due to the change in relative importance of two physical processes of sst wind interaction at different time scales the sst front induced sea surface level pressure slp adjustment sf slp contributes to a strong vector wind above the front on long time scales consistent with the collocation of baroclinicity in the marine boundary layer and corroborated by the similarity between the thermal wind and observed wind shear between 1000 and 850 hpa in contrast the sst modulation of synoptic winds is more evident on the warm flank of the sst front large ther

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