simulation of modern and middle cretaceous marine δ18o with an ocean atmosphere general circulation model 1 we have developed a coupled ocean atmosphere general circulation model the genesis mom model with the ability to transport and fractionate water isotopes in the ocean and atmosphere the model is used to predict modern and cretaceous precipitation and seawater 18o the model reproduces the large scale modern day isotopic distribution in the zonal mean the difference between simulated and observed seawater 18o is within 0 2 in the low and middle latitudes and within 1 at high latitudes in comparison to modern simulated cretaceous surface seawater 18o is systematically depleted by 0 3 at low and middle latitudes these differences are attributed to equilibrium fractionation during surface evaporation at low latitudes and an increased partitioning of 18o from the surface into the deep ocean due to intermediate and deep water formation in subtropical basins in the cretaceous we also find that regional seawater 18o is significantly influenced by the paleobathymetry and the resolution of oceanic gateways boundary conditions that are not well known for the past our simulation of cretaceous seawater 18o has major implications for oxygen isotope paleothermometry we conclude that conventional assumptions of past seawater 18o may lead to an overestimate of cretaceous sea surface temperatures especially at middle and high latitudes

nd isotopic excursion across cretaceous ocean anoxic event 2 cenomanian turonian in the tropical north atlantic late cretaceous fish debris from demerara rise exhibits a dramatic positive excursion of 8 nd units during ocean anoxic event 2 oae2 that is superimposed on extremely low nd t values 14 to 16 5 observed throughout the rest of the studied interval the oae2 nd excursion is the largest yet documented in marine sediments and the majority of the shift is estimated to have occurred over nd values on demerara rise are explained as the nd isotopic signature of the south american craton whereas eruptions of the caribbean large igneous province or enhanced mixing of intermediate waters in the north atlantic could have caused the excursion

did the rifting of the atlantic ocean cause the cretaceous thermal maximum the cretaceous thermal maximum was a major turning point in the history of earth s climate this interval of peak warmth in the turonian has been attributed to very high atmospheric pco2 resulting from rapid outgassing rates although crustal cycling rates peaked in the aptian albian interval on the basis of coupled ocean atmosphere model simulations of the middle cretaceous we hypothesize that the formation of an atlantic gateway could have contributed to the cretaceous thermal maximum differences between prerifting and postrifting climate experiments demonstrate substantial regional oceanographic changes in the north and south atlantic basins that are consistent with oxygen isotopic evidence used to infer a cretaceous thermal maximum the model results help reconcile the paleoclimate record inferred from foraminiferal d 18 o with our understanding of climate dynamics and cretaceous tectonism

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

tracing past ocean circulation to understand how ocean circulation and climate may change in the future we must first understand how the system operated in the past without man9s influence new inorganic isotopic tracers are now helping to elucidate past ocean circulation patterns but controversies remain regarding the relative influence of ocean circulation and weathering on the isotopic signals

paleotemperature and paleosalinity inferences and chemostratigraphy across the aptian albian boundary in the subtropical north atlantic 1 geochemical analyses of extraordinarily well preserved late aptian early albian foraminifera from blake nose ocean drilling program site 1049 reveal rapid shifts of 18o 13c and 87sr 88sr in the subtropical north atlantic that may be linked to a major planktic foraminifer extinction event across the aptian albian boundary the abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0 8 1 4 million years at the boundary contact but the values before and after the hiatus indicate that major oceanographic changes occurred at this time 87sr 88sr increase by 0 000 200 13c values decrease by 1 5 to 2 2 and 18o values decrease by 1 0 planktics to 0 5 benthics across the hiatus further both 87sr 88sr ratios and 18o values during the albian are anomalously high the 87sr 88sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter basin differences in seawater 87sr 88sr during the albian or revision of the seawater curve for 18o planktic values in some aptian samples likely reflect a diagenetic overprint but preservation is excellent in the rest of the section in well preserved material benthic foraminiferal values are largely between 0 5 and 0 0 and planktic samples are largely between 0 0 to 1 0 with a brief excursion to 2 0 during oae 1b using standard assumptions for cretaceous isotopic paleotemperature calculations the 18o values suggest bottom water temperatures at 1000 1500 m of 8 10 c and surface temperatures of 10 14 c which are 4 6 c and 10 16 c cooler respectively than present day conditions at the same latitude the cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present because of their exquisite preservation whole scale alteration of the analyzed foraminifera is an untenable explanation our proposed solution is a high evaporative fractionation factor in the early albian north atlantic that resulted in surface waters with higher 18o values at elevated salinities than commonly cited in cretaceous studies a high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and like the sr isotopes implies limited connectivity among the individual basins of the early cretaceous proto atlantic ocean

cretaceous deep water formation in the indian sector of the southern ocean 1 the role that meridional overturning circulation moc patterns played in poleward heat transport during the extreme warmth of the early to late cretaceous is a fundamental and unresolved question in climate dynamics in order to address this question we must determine where deep waters formed and how they may have circulated during periods of extreme warmth here we present late albian through maastrichtian 105 to 65 ma nd isotope records from deep sea drilling project dsdp and ocean drilling program odp sites in the proto indian ocean and the tropical pacific comparison of these data with previously published records indicates deep water formation in the indian sector of the southern ocean began at least 105 ma extending the record of high latitude convection back into the early cretaceous prior to the peak warmth of the mid cretaceous the growing body of data supports a mode of moc in part characterized by high latitude downwelling during the peak of greenhouse warmth of the mesozoic and cenozoic however this mode of moc likely was characterized by numerous locations of deep convection that were regionally important but not significant in terms of a globally overturning circulation due to paleogeographic and bathymetric barriers

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

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

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

new oxygen isotope evidence for long term cretaceous climatic change in the southern hemisphere a new composite 18 o record generated from calcareous fine fraction and bulk sediments from the exmouth plateau details long term cretaceous climatic change at mid latitudes in the southern hemisphere assessment of new and previously published 18 o data indicates that a mid cretaceous global climatic optimum was achieved sometime between the time of the cenomanian turonian boundary and the middle turonian when surface ocean paleotemperatures were the highest of the past 115 m y periods of cooling and warming that reversed the general patterns were superimposed on long term aptian turonian warming and turonian maastrichtian cooling trends respectively extrapolation of southern hemisphere paleotemperature trends to maastrichtian paleotemperature data from a low latitude pacific guyot implies that maximum mid cretaceous low latitude paleotemperatures could have been in excess of 33 c

formation of southern component water in the late cretaceous evidence from nd isotopes constraining deep ocean circulation during past greenhouse climatic periods such as the cretaceous is important for understanding meridional heat transfer processes controls on ocean anoxia and the relative roles of climate and tectonics in determining paleocirculation patterns ocean circulation models for the late cretaceous and early paleogene suggest that significant deep water production occurred in the southern ocean but cannot constrain when this process commenced or what the temporal relationship was between opening tectonic gateways and late cretaceous climatic cooling nd isotope data obtained from biogenic apatite fish teeth and bones are presented from lower bathyal and abyssal sites in the south atlantic and indian oceans during the mid cretaceous relatively radiogenic nd isotope values suggest that deep water circulation in these basins was sluggish with inputs likely dominated by seawater particle exchange processes and possibly easily weathered volcanic terranes in the campanian maastrichtian the nd isotopic composition of proto indian and south atlantic deep waters became less radiogenic suggesting the onset of deep water formation in the southern ocean southern component water scw consistent with paleogene reconstructions and ocean circulation models a combination of southern hemisphere cooling and the opening of tectonic gateways during the campanian likely drove the onset of scw

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

nearshore chlorophyll a events and wave driven transport 1 continuous records of temperature and chlorophyll a chl a fluorescence were used to characterize phytoplankton variability at two shallow intertidal stations on the northern california coast chl a records from spring and summer 2007 and 2008 were characterized by distinct peaks persisting for 1 5 to five days these peaks represent bloom events which often coincided between the two sites even though they are separated by 150 km blooms did not appear to be directly forced by individual upwelling episodes while some events were associated with reversals of upwelling favorable winds there was a stronger relationship between chl a peaks and peaks in surface swell height this relationship was dominant in spring and early summer but no longer evident by july we suggest that these nearshore chl a peaks are an accumulation of phytoplankton caused by convergence of onshore wave transport against the impermeable coastal boundary scaling arguments show this mechanism to be consistent with observed chl a increase rates this mechanism has not been previously considered as a forcing for blooms at rocky coasts and it may have significant implications for understanding coastal productivity larval dispersal and nearshore water quality

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

early diagenetic evolution of bone phosphate an x ray diffractometry analysis abstract a new crystallinity index ci based on the x ray powder diffractometric pattern of fossil bone carbonate hydroxylapatite is defined this ci value provides a semi quantitative way to estimate the diagenetic changes in archaeological and palaeontological bone phosphate the studied samples are 71 human bones from the french merovingian cemetery of saint linaire 1200 1700 bp 37 human bones from two necropoleis in niger 1000 5000 bp two cave bear bones from aldene cave southern france around 70 000 bp five bones of miocene mammals and 14 bones of mesozoic reptiles the main results are that 1 there is no correlation between the increase in the ci and the age of the sample even in one given locality 2 the ci seems to be related to the taphonomical conditions in archaeological and fossil bones 3 an increase in the ci is correlated with a loss in organic matter in one archaeological site but the quality of preservation of organic matter in fossil bones does not depend on the changes in the ci 4 the correlation between the increase in the ci and the decrease of co3amount in bones from the niger necropolies suggests a possible mechanism for the increase in crystallinity the changes of crystallinity reflect early diagenetic changes and depend on the burial environments

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

warm saline intermediate waters in the cretaceous tropical atlantic ocean during the cretaceous period warm deep and intermediate waters filled the oceans evidence from benthic foraminferal 18o and mg ca ratios suggests that the intermediate water masses in the proto atlantic ocean formed from high salinity waters sinking from shallow shelf seas

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

a simulation of mid cretaceous climate a series of general circulation model experiments utilizing genesis have been completed for the mid cretaceous based on geography variable atmospheric carbon dioxide concentrations 2 to 6 times present day concentrations and variable poleward oceanic heat flux 6 to 1 2 1015 w increased from present day by combining all three major variables co2 geography and oceanic heat flux the distribution of mid cretaceous temperatures can be achieved in the simulations increased co2 is required to promote global warmth and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of co2 four times present day co2 with 1 2 1015 w provided the best match to the distribution of mid cretaceous data the best match to the cretaceous observations was achieved with a globally averaged surface temperature increase of 6 2 c at the lower end of past estimates of mid cretaceous warmth this value may be a better estimate of mid cretaceous global warming finally the model experiments can be used to provide a paleocalibration of the global warming expected for a doubling of atmospheric carbon dioxide the best estimates for the mid cretaceous appear to be a 2 5 to 4 0 c sensitivity in the mid to upper range of the sensitivity of current climate models used to assess future global change

changes in north atlantic circulation at the end of the cretaceous greenhouse interval ocean circulation patterns during the late cretaceous greenhouse interval remain disputed marine sediment geochemistry suggests that the end of the greenhouse interval coincided with the onset or intensification of deep water formation in the north atlantic ocean

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

evidence for deep water production in the north pacific ocean during the early cenozoic warm interval the deep ocean circulation is responsible for a significant component of global heat transport in the present mode of circulation deep waters form in the north atlantic and southern oceans where surface water becomes sufficiently cold and dense to sink polar temperatures during the warmest climatic interval of the cenozoic era approximately 65 to 40 million years myr ago were significantly warmer than today and this may have been a consequence of enhanced oceanic heat transport however understanding the relationship between deep ocean circulation and ancient climate is complicated by differences in oceanic gateways which affect where deep waters form and how they circulate here i report records of neodymium isotopes from two cores in the pacific ocean that indicate a shift in deep water production from the southern ocean to the north pacific approximately 65 myr ago the source of deep waters reverted back to the southern ocean 40 myr ago the relative timing of changes in the neodymium and oxygen isotope records indicates that changes in cenozoic deep water circulation patterns were the consequence not the cause of extreme cenozoic warmth

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

effect of changes in d18o content of the surface ocean on estimated sea surface in past warm climate 1 using a coupled climate model of intermediate complexity including oxygen 18 climber 2 we investigate the evolution of the distribution of surface water 18o composition under warm climate conditions we then determine the impact of changes of the surface water 18o distribution on ocean surface temperatures inferred from calcite oxygen 18 our results show that published temperature reconstructions based on oxygen 18 from calcite are systematically biased by 2 to 4 c in the absence of major oceanic circulation changes and up to 7 c in the presence of major oceanic circulation changes as the bias introduced is shown to vary with latitude our work has major implications on past latitudinal temperature gradient reconstructions based on oxygen 18 measurements

influence of organic matrix on the post mortem destruction of molluscan shells to examine the role of organic constituents in the destruction of calcium carbonate skeletons we aged fresh shells of the bivalves nucula sulcata organic rich nacreous aragonites with low crystallite surface areas and cerastoderma edule organic poor porcellaneous aragonites high crystallite surface areas under both sterile and non sterile microbial conditions in aragonite undersaturated saturated and supersaturated seawaters for periods up to 11 months deterioration was tracked by sem and weight loss and compared to damage produced by reagents of specific effect the same qualitative sequence of damage was observed in all tanks for both species but rates of deterioration were geq 2 times higher in microbial than in sterile tanks at a given saturation state and were as high or higher in the microbial saturated and supersaturated tanks than in the sterile undersaturated tank damage to shell surfaces was limited almost entirely to loss of organic matrix which eventually exposed and

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

dissolved rare earth elements tracing lithogenic inputs over the kerguelen plateau southern ocean abstract dissolved rare earth elements rees were measured in the water masses upstream from and over the kerguelen plateau indian sector of the southern ocean upstream from the plateau the ree profiles were consistent with published data from the southern and indian oceans over the plateau a one box model yields a lithogenic nd flux from the dissolution of lithogenic material of 89 20 t nd y 1 and a corresponding dissolved iron input larger than 100 000 t fe y 1 however despite evidence of this significant lithogenic input dissolved fe is strongly depleted in the upper layers contrasting with the enriched ree concentrations this contrast stresses the different behaviours of ree and iron in the surface waters and the fact that strong fertilization does not imply dissolved fe replete waters

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

the maastrichtian record from shatsky rise northwest pacific a tropical perspective on global ecological and oceanographic changes we present new isotopic and micropaleontological data from a depth transect on shatsky rise that record the response of the tropical pacific to global biotic and oceanographic shifts during the mid maastrichtian results reveal a coupling between the upper ocean characterized by a weak thermocline and low to intermediate productivity and intermediate waters during the earliest maastrichtian oxygen and neodymium isotope data suggest a significant contribution of relatively warm intermediate water from the north pacific isotopic shifts through the early maastrichtian suggest that this warmer water mass was gradually replaced by cooler waters originating in the southern ocean although the cooler water mass remained dominant through the remainder of the maastrichtian it was displaced intermittently at shallow intermediate depths by north pacific intermediate water the globally recognized mid maastrichtian event similar to 69 ma manifested by the brief appearance of abundant inoceramid bivalves over shallow portions of shatsky rise is characterized by an abrupt increase similar to 2degrees 3degrees c in sea surface temperatures a greater flux of organic matter out of the surface ocean and warmer similar to 4degrees c intermediate waters results implicate simultaneous changes in surface waters and the sources distribution patterns of intermediate water masses as an underlying cause for widespread biotic and oceanographic changes during mid maastrichtian time

160 m y record of marine sedimentary phosphorus burial coupling of climate and continental weathering under greenhouse and icehouse conditions a compilation of all meaningful phosphate data published in the proceedings of the deep sea drilling project and the ocean drilling program is used here for the extraction of a 160 m y marine burial record of bulk phosphorus all sediment types 5648 measurements and a 100 m y marine burial record of biogenic phosphorus pelagic biogenic sediment types 1754 data these records serve as estimates for total and dissolved bioavailable phosphorus flux rates which in turn are highly dependent on total and chemical continental weathering rates respectively the similarity of both records indicates that in the past 100 m y changes in total weathering rates may have been tracked by changes in chemical weathering rates prior to 32 ma phosphorus burial and long term sea level change are positively correlated from 32 ma to the present this correlation is inverse this points to a fundamental change in feedback mechanisms between continental weathering phosphorus and climate which was probably linked to the onset of major glaciation