precessional climate cyclicity in late cretaceous early tertiary marine sediments a high resolution chronometer of cretaceous tertiary boundary events we report well dated late cretaceous and early tertiary precessional climatic cycles recorded by rhythmic carbonate maxima and minima in south atlantic deep sea sites spectral analyses of digitized sediment color a suitable carbonate proxy show prominent regularities in the spacing marl carbonate beds magnetostratigraphic dating over a number of magnetic chrons constrains the duration of the cycles which can be detected over at least 20 myr of sedimentation at 7 coring locations their mean absolute period of23 5 4 4kyr agrees closely with the predicted late cretaceous precessional period of 20 8 kyr because they can be matched to a physical forcing mechanism with a known repeat time the cycles offer a new high resolution tool to measure rates of climate change before and after the cretaceous tertiary k t boundary from counts of carbonate cycles we derive the position of the k t boundary within c29r at 350 kyr after the base of the reversal the constancy of cycle thickness linearly related to sedimentation rate and amplitude up to the boundary clay does not give evidence for climate instability preceding the boundary orbital chronometry records a step function decrease in sediment accumulation rate at the cretaceous tertiary boundary that is consistent with a geologically instantaneous event

paleoceanography a review for the gsa centennial the central problem of paleoceanography is the history of the circulation of the ocean although speculation about ancient oceanic circulation goes back to the past century the field of paleoceanography was founded in the 1950s as oxygen isotope studies suggested that oceanic deep waters were warmer in the past than they are today extensive coring of deep sea sediments by numerous expeditions after world war ii was followed by the ocean drilling programs providing a rich data base paleoceanographic interpretations have tried to explain the most obvious changes in sea floor sediments and their contained fossils changing paleotemperatures indicated by oxygen isotopes fluctuations in the calcium carbonate compensation depth accumulations of organic carbon rich sediments and the unexpected abundance of hiatuses in a setting which had been thought to be the ultimate sedimentary sink the result has been the intriguing discovery that although the positions and circulation of the major surface gyres is generally stable the deep circulation of the ocean may reverse on a variety of time scales it has been suggested that formation of north atlantic deep water which causes the uneven distribution of nutrients alkalinity and oxygen in the deep sea today may have been replaced by formation of north pacific deep water during the last deglaciation reversing the concentration gradients of nutrients alkalinity and oxygen on a longer time scale the present general circulation which is dominated by production of oxygen rich cold deep water in the subpolar regions today may have replaced a pre oligocene general circulation in which warm saline oxygen poor deep waters were formed in warm seas in the arid zones paleoceanography is still in its infancy many new clues to the history of the ocean are being discovered and many new ideas about conditions in the past are being developed the beginning of the next century should see continuing rapid growth and maturation in this exciting new field

cenozoic ice volume history development of a composite oxygen isotope record to view cenozoic ice volume and ocean temperature history a composite 18 o time series was constructed for tropical shallow dwelling planktonic foraminifers and for deep water benthic foraminifers we conclude that cenozoic benthic 18 o primarily reflect considerable deep ocean temperature variation and that tropical planktonic 18 o afford the best record of cenozoic ice volume the planktonic composite indicates the presence of a significant ice budget for the past 40 m y the difference between the benthic and planktonic 18 o composites suggests that low latitude production of warm saline bottom water dominated tertiary thermohaline circulation

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

reorganization of deep ocean circulation accompanying a late cretaceous extinction event deep ocean circulation may be a significant factor in determining global climate1 5 increases in the flux of warm saline waters from low to high latitudes would enhance the poleward transport of heat and thus help maintain the warm conditions at high latitudes typical of globally warm greenhouse periods but controversy exists1 2 as to whether the ocean s thermohaline circulation can transport enough heat to bring about the temperature distributions of these times such as the mid cretaceous and early eocene here we present stable isotope records of ocean temperature and salinity that indicate that bottom waters in late cretaceous oceans of the southern hemisphere became cooler and less saline at the same time about 70 myr ago as widespread biotic changes3 6 8 these findings support the idea that changes in deep ocean circulation can act as a climate switch

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

past co2 changes and tropical sea surface temperatures the relationship between past co2 variations and tropical climate change on time scales of millions of years is reviewed explanations for cretaceous and early cenozoic climate change often involve higher atmospheric co2 levels climate models predict that such increases should have been associated with warmer tropical sea surface temperatures ssts however sparse mid cretaceous 18o based sst estimates from low latitude calcareous plankton are 1 0 1 5 heavier than predicted initial evaluations indicate that changes in salinity may not alleviate model data discrepancies for calcareous 18o and that interpretation of altered latitudinal 18o gradients in terms of increased poleward heat transport due to warm saline bottom water wsbw formation would require very large levels of wsbw production at least 60 sv calcareous 18o records may not always record true sst patterns as 18o analyses from phosphatic groups which are less sensitive to diagenesis indicate ssts 5 c higher this latter conclusion is supported by a number of other fossil groups which indicate temperatures warmer than those estimated from calcareous 18o in order to more rigorously test the paleo co2 hypothesis and indeed the models used to forecast future climates it is desirable to intensify investigations of past climate change in low latitudes in order to determine whether these preliminary conclusions stand the test of further scrutiny

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

oxygen isotope evidence for high salinity surface seawater in the mid cretaceous gulf of mexico implications for warm saline deepwater formation on the basis of textural and geochemical criteria we have identified a suite of calcitic molluscs and radiaxial fibrous calcite cements in albian cenomanian limestones from the gulf coast region that have not suffered significant diagenetic alteration the 18o values of these preserved components 2 94 to 0 45 versus pdb are our best estimate for original marine calcite in the rocks and therefore should reflect the temperature and 18o of coeval seawater isotopic paleotemperatures for average ice free seawater 18o 1 per mil versus smow are 14 24 c lower than present day mean annual temperatures for western gulf of mexico surface waters 23 5 26 5 c and estimates for mid cretaceous subtropical seawater t modern t the oxygen isotopic composition of original marine calcite yield reasonable paleotemperatures if the 18o 16o ratio and hence the salinity of surface waters in the ancestral gulf of mexico were elevated due to evaporation applying a model for t s t reconstructions from calcite 18o values predicts salinities of 37 41 ppt and densities as t of 25 26 for contemporaneous seawater a comparison of model results for tethyan surface waters to those for mid cretaceous equatorial pacific waters suggests that tethyan waters were dense enough to sink through the pycnocline to considerable depths our results and interpretations support the proposal based on other lines of evidence that warm saline waters originating in subtropical seas were an important component in deepwater formation during the mid cretaceous

atlantic mediterranean water exchange during the late neocene the nature of water exchange between the mediterranean and the atlantic is examined for three time periods during the late neogene in order to assess the impact of flow patterns between these basins on bottom water conditions in the oceans the large volume of carbonates and evaporites deposited in the mediterranean during the messinian salinity crisis appears to have caused the open ocean to become more undersaturated in calcium carbonate resulting in increased dissolution of deep sea carbonates during the latest miocene during the earliest pliocene an estuarine type of flow existed between the atlantic and mediterranean waters entered the mediterranean at depth and flowed out at the surface benthic foraminiferal stable isotopic evidence from the north atlantic indicates that north atlantic deep water nadw was produced throughout the early pliocene and that the absence of saline mediterranean outflow did not have a significant effect on bottom water production eustatic lowering of sea level during the last glacial maximum 18 000 years b p reduced water exchange between the atlantic and the mediterranean as a result salinities in the mediterranean increased substantially but it seems unlikely that diminished nadw production during the last glacial episode can be attributed to a reduction in mediterranean outflow

deep water in the late maastrichtian ocean 1 stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late maastrichtian ocean given mean oceanic 18ow of 1 0 the temperature of the coolest intermediate depth waters was 5 7 c that of the deepest waters was 10 c and that of the warmest intermediate waters was 13 15 c the cool intermediate depth water mass probably originated in the high latitude southern ocean the deepest waters originated at least partly in the northern atlantic the source region for the warmest intermediate depth water mass is unknown although much of the late maastrichtian deep water was probably preconditioned for winter sinking by low or middle latitude evaporation no more than 11 of late maastrichtian deep water could have been directly actuated by low latitude sea surface evaporation at least in the southern atlantic and indian oceans heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures

late cretaceous oceans and the cool tropic paradox oxygen isotopic proxies of paleo sea surface temperatures ssts suggest that maastrichtian about 66 million years ago tropical ssts were lower than those of today they also demonstrate that maastrichtian latitudinal sst gradients were much lower than those of the present the low maastrichtian sst gradients indicate that meridional heat transport was much greater or latitudinal differences in the balance of radiation to and from the sea surface were much less extreme during the latest cretaceous than they are today or that both conditions were true these findings challenge traditional interpretations of greenhouse late cretaceous climates

water ice abundance and co2 band strength on the saturnian satellite phoebe from cassini vims observations abstract we have studied the near infrared spectrum of the saturn satellite phoebe a distant satellite observed before cassini s saturn orbit insertion using data from the visual and infrared mapping spectrometer vims on the cassini orbiter we have done a critical calibration of the dataset that involves careful correction of dark artifacts we model areally mixed water ice and non ice assumed segregated because of the low 3 albedo of the non ice material for several high and medium resolution observations of phoebe made near closest approach using a hapke roughness factor of 15 we find ice abundances from 0 1 to over 4 the ice grain radii vary from 1 to 10 m these are displayed on a projected map of phoebe with about 50 coverage about 33 coverage at better than 5 km spatial resolution detailed looks at the water ice spectral fits shows that the weak 1 05 and 1 25 m bands are missing in most of the spectra implying that the ice endmember is not pure ice but has a dark material mixed with it that lowers the albedo and suppresses these bands we made a model of ice contaminated with phoebe like dark material showing that a few percent of dark material lowers the albedo to 50 and suppresses the bands the dirty ice model produces better fits to the spectra and implies that the amount of dirty ice is about 1 5 times the amount of pure ice we have also calculated the co 2 band depth for these same observations and projected the results the co 2 band depth varies inversely with water ice abundance

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

sensitivity of the divide position at siple dome west antarctica to boundary forcing a linearized perturbation about a two dimensional vialov nye icesheet profile is used to investigate the sensitivity of the divide position at siple dome west antarctica to small changes in the accumulation pattern and in the elevation of its lateral boundaries at the margins of ice streams c and d relaxation time scales for the icesheet surface and divide position are derived from the perturbation theory for siple dome these time scales are short 450 800 years for surface adjustment and 200 350 years for divide position adjustment these short time scales indicate that siple dome responds quickly to forcing at its boundaries therefore the recent migration of the siple dome divide determined from previous work is probably a response to an ongoing sustained forcing rather than a response to a long past climate event such as the transition from the last glacial maximum to the holocene based on our analysis the inferred rate of migration of the siple dome divide could be attained be

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

interspecies variation in stable isotopic signals of maastrichtian planktonic foraminifera we measured stable isotopic signals of the largest specimens of all abundant species of planktonic foraminifera in late maastrichtian samples from three atlantic mid latitude and high latitude sites each sample is marked by a relatively small interspecies range of 18o values 1 2 to 0 8 each also exhibits an interspecies range of 13c values that resembles those of modern assemblages at similar latitudes 2 8 to 0 9 with greater ranges at lower latitudes these results indicate that late cretaceous planktonic foraminifera inhabited water masses characterized by a relatively narrow range of temperatures but may have occupied an array of niches as ecologically diverse as that of modern taxa maastrichtian taxa exhibit more complex relationships between skeletal morphology and vertical and seasonal paleohabitat affinities than previous paleoecologic models have assumed for example keeled taxa were not limited to cold or deep habitats and serial taxa appear to have occupied both warm near surface niches and the coolest or most saline habitats the isotopic differences between species indicate that apparent variation in maastrichtian stable isotopic signals strongly depends on the taxa analyzed narrowly constrained size fractions of rugoglobigerina species may provide a good estimate of relative variation in isotopic equilibria of near surface summer paleoconditions at low and middle latitudes gublerina species laeviheterohelix species and planoglobulina multicamerata appear the likeliest candidates for consistently tracking relative variation in isotopic equilibria of the coldest or most saline paleohabitats of maastrichtian planktonic foraminifera these isotopic results suggest that upper water column thermal gradients may have been only 3 to 5 c in mid latitude and high latitude regions they also suggest that the western and central atlantic mid latitude summer seasurface may have been much cooler or saltier in the maastrichtian than it is today finally they corroborate previous estimates of 10 c surface water at southern high latitudes

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

possible role of oceanic heat transport in early eocene climate increased oceanic heat transport has often been cited as a means of maintaining warm high latitude surface temperatures in many intervals of the geologic past including the early eocene although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically determining how additional oceanic heat transport would take place has yet to be accomplished that the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked using early eocene climate as an example we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early eocene conditions our interpolation of early eocene paleotemperature data indicate that an approximately 30 increase in poleward heat transport would be required to maintain eocene high latitude temperatures this increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early eocene rates either oceanic processes were very different from those of the present to produce the early eocene climate conditions or oceanic heat transport was not the primary cause of that climate we believe that atmospheric processes with contributions from other factors such as clouds were the most likely primary cause of early eocene climate