pronounced zonal heterogeneity in eocene southern high latitude sea surface temperatures paleoclimate studies suggest that increased global warmth during the eocene epoch was greatly amplified at high latitudes a state that climate models cannot fully reproduce however proxy estimates of eocene near antarctic sea surface temperatures ssts have produced widely divergent results at similar latitudes with ssts above 20 c in the southwest pacific contrasting with ssts between 5 and 15 c in the south atlantic validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites here we present multiproxy data from seymour island near the antarctic peninsula that provides well constrained evidence for annual ssts of 10 17 c 1 sd during the middle and late eocene comparison of the same paleotemperature proxy at seymour island and at the east tasman plateau indicate the presence of a large and consistent middle to late eocene sst gradient of 7 c between these two sites located at similar paleolatitudes intermediate complexity climate model simulations suggest that enhanced oceanic heat transport in the south pacific driven by deep water formation in the ross sea was largely responsible for the observed sst gradient these results indicate that very warm ssts in excess of 18 c did not extend uniformly across the eocene southern high latitudes and suggest that thermohaline circulation may partially control the distribution of high latitude ocean temperatures in greenhouse climates the pronounced zonal sst heterogeneity evident in the eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

new constraints on atmospheric co2 concentration for the phanerozoic earth s atmospheric co2 concentration ca for the phanerozoic eon is estimated from proxies and geochemical carbon cycle models most estimates come with large sometimes unbounded uncertainty here we calculate tightly constrained estimates of ca using a universal equation for leaf gas exchange with key variables obtained directly from the carbon isotope composition and stomatal anatomy of fossil leaves our new estimates validated against ice cores and direct measurements of ca are less than 1000 ppm for most of the phanerozoic from the devonian to the present coincident with the appearance and global proliferation of forests uncertainties obtained from monte carlo simulations are typically less than for ca estimates from other approaches these results provide critical new empirical support for the emerging view that large 2000 3000 ppm long term swings in ca do not characterize the post devonian and that earth s long term climate sensitivity to ca is greater than originally thought key points a novel co2 proxy calculates past atmospheric co2 with improved certainty co2 is unlikely to have exceeded 1000 ppm for extended periods post devonian earth s long term climate sensitivity to co2 is greater than originally thought

coeval eocene blooms of the freshwater fern azolla in and around arctic and nordic seas abstract for a short time interval c 1 2 myr during the early middle eocene 49 myr the central arctic ocean was episodically densely covered by the freshwater fern azolla implying sustained freshening of surface waters coeval azolla fossils in neighboring nordic seas were thought to have been sourced from the arctic the recognition of a different azolla species in the north sea raised doubts about this hypothesis here we show that no less than five azolla species had coeval blooms and spread in the arctic and nw european regions a likely trigger for these unexpected azolla blooms is high precipitation prevailing by the end of the warmest climates of the early eocene climatic optimum eeco

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

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

thallium isotope evidence for a permanent increase in marine organic carbon export in the early eocene article the first high resolution thallium tl isotope records in two ferromanganese crusts fe mn crusts cd29 and d11 from the pacific ocean are presented the crusts record pronounced but systematic changes in 205 tl 203 tl that are unlikely to reflect diagenetic overprinting or changes in isotope fractionation between seawater and fe mn crusts it appears more likely that the fe mn crusts track the tl isotope composition of seawater over time the present day oceanic residence time of tl is estimated to be about 20 000 yr such that the isotopic composition should reflect ocean wide events new and published os isotope data are used to construct age models for these crusts that are consistent with each other and significantly different from previous age models application of these age models reveals that the tl isotope composition of seawater changed systematically between 55 ma and 45 ma using a simple box model it is shown that the present day tl isotope composition of seawater depends almost exclusively on the ratio between the two principal output fluxes of marine tl these fluxes are the rate of removal of tl from seawater via scavenging by authigenic fe mn oxyhydroxide precipitation and the uptake rate of tl during low temperature alteration of oceanic crust it is highly unlikely that the latter has changed greatly therefore assuming that the marine tl budget has also not changed significantly during the cenozoic the low 205 tl

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

seismic and geologic evidence for early paleogene deepwater circulation in the western north atlantic previous studies of paleogeography global climate and foraminiferal stable isotopes have suggested that paleogene deepwater circulation was significantly different from that of today extracting details of deepwater history from the western north atlantic has been hampered by oligocene erosion and the lack of ideally located drill holes we report the discovery of a seismic disconformity on the sw bermuda rise that we have tied to a late paleocene erosional event in deep sea drilling project dsdp boreholes from this region distribution of this new seismic marker reflector ab indicates that it was formed by cyclonically circulating bottom water entering the western north atlantic from the south we attribute this vigorous deep circulation to a southern ocean source analogous to the effects of modern antarctic bottom water this interpretation is supported by isotopic comparisons that show the paleocene southern ocean was enriched in 13c relative to the pacific we distinguish reflector ab from the overlying reflector au on the basis of superposition and ages obtained at dsdp sites and piston cores using one of the cores we have estimated that the youngest age for reflector au is earliest oligocene 36 6 34 0 ma while its oldest age has been previously established as late eocene laminated sediments beneath reflector ab are enriched in organic carbon indicating that the early paleocene deep western north atlantic was occasionally anoxic these low oxygen levels may have been the result of sluggish deep circulation and or low latitude production of warm saline deep water wsdw sediments immediately above reflector ab show that deposition resumed on the western bermuda rise site 387 by the latest paleocene to earliest eocene biochron np10 57 2 0 6 ma while deposition resumed on the central bermuda rise site 386 during the late paleocene erosion nondeposition continued across much of the bermuda rise widespread resumption of pelagic deposition in the early eocene is consistent with 13c evidence for reduced southern ocean influence at this time however lower eocene sediments record well oxygenated conditions and 13c and 18o comparisons indicate that there were two early eocene deepwater sources the southern ocean and wsdw pak and miller this issue

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

drake passage and cenozoic climate an open and shut case drake passage opening has often been viewed as a single discrete event possibly associated with abrupt changes in global circulation and climate at or near the eocene oligocene boundary a new plate tectonic model based on recent reinterpretations of the opening history of basins in the scotia sea suggests that an effective ocean gateway may have developed even earlier during the middle eocene this is consistent with a growing body of evidence from sediment core proxy data for eocene changes in southern ocean circulation and biological productivity the period between earliest opening after 50 ma and the latest eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins this shallow opening may have caused important changes in southern ocean circulation contributing to eocene cooling and the growth of antarctic ice sheets

tropical atlantic seasonal dynamics in the early middle eocene from stable oxygen and carbon isotope profiles of mollusk shells there are disagreements whether the tropical sea surface temperature during the warm early to early middle eocene was equal to the present temperature or significantly lower in order to determine the sea surface temperature of the eastern tropical atlantic in the early middle eocene we have established 18o and 13c profiles along the transect of growth of excellently preserved shells of turritella gastropods and a macoma bivalve from tropical west africa this method makes possible a distinction between the winter and the summer temperature the 18o and 13c data indicate sea surface temperatures of 29 31 c which declined to 23 25 c during seasonal upwelling these conditions are similar to those of today and suggest that significant seasonal dynamics prevailed in the early middle eocene tropics the new data further contradict that the tropics cooled during the generally warm early to early middle eocene as inferred in studies on foraminifera 18o

the ocean circulation in the southern hemisphere and its climatic impacts in the eocene abstract opening of southern ocean gateways may have had a controlling influence on the evolution of global climate the largest step in the history of cenozoic climate from an eocene greenhouse toward the modern glaciated state is correlated with opening of a deep water connection between the southern indian and southern pacific oceans this study synthesizes results from previous work assesses the possibility that ocean heat transport was much greater than modern during the globally warm eocene and explores the sensitivity of polar climate to large changes in ocean heat transport the magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes we find that ocean heat transport was unlikely to have been sufficiently greater than modern during the eocene to explain the change in the climate specifically in order to have significantly affected antarctic climate ocean heat transport changes would have had to change by an order of magnitude much greater than the largest change produced in our simulations in coupled climate model simulations changes in co2 concentrations from 1120 to 560 ppm supported by proxy records lead to significant antarctic responses in the absence of ocean heat transport changes the results show that antarctic snow accumulation is primarily controlled by changes in summer temperature not precipitation and that snow did not remain on antarctica during summer months in eocene even at low greenhouse gas concentrations greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks were more likely to have been the primary cause of antarctic glaciation than ocean heat transport changes

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

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

internal tides in the strait of gibraltar abstract analysis of moored current measurements in the strait of gibraltar is provided here the vertical internal displacements double amplitudes with a semidiurnal frequency are extremely large and sometimes exceed 200 m it is found that these displacements are associated with forced tidal internal waves over camarinal sill which crosses the strait the separation of tidal components showed that the amplitude of internal tide with m2 frequency is 69 m while the amplitudes of other components of the internal tide s2 k1 o1 are 3 5 times smaller the amplitudes of the waves decrease with the distance from the sill and at a distance of 50 km from the sill the amplitudes are 3 times smaller than over the sill the energy of internal tides is transferred to internal bore and turbulent mixing the wavelength of the internal tide was estimated on the basis of moored measurements the wavelength of the east propagated wave is 90 km while the west propagated wave is 60 km numerical modeling demonstr

relationship between glacial geology and streamwater chemistry in an area receiving acid deposition abstract seventy streams in southwestern new york state were sampled in june and again in december streamwater chemistry proved to be closely associated with glacial geology streams in glaciated area watersheds had higher ph alkalinity calcium and conductivity values than streams in unglaciated area watersheds within the glaciated area streams of the kent drift sheet had higher alkalinity calcium and conductivity values than streams of the olean drift sheet streamwater sulfates were also analyzed in december and were found to be highest in the kent drift sheet glacial geology of a watershed is well predicted by discriminant analysis of streamwater chemistry data additional buffering capacity provided by blacial till appears to override sulfate adsorption considerations in making the glaciated area streams less susceptible to atmospheric acid deposition

paleogene opening of drake passage the timing of events leading to the earliest connection between the pacific and atlantic oceans at drake passage is controversial but important because gateway opening probably had a profound effect on global circulation and climate a rigorous new analysis of marine geophysical data demonstrates a major change in the motion of the south american and antarctic plates at about 50 ma from n s to wnw ese accompanied by an eightfold increase in separation rate this would have led to crustal extension and thinning and perhaps the opening of small oceanic basins with the probable formation of a shallow b1000 m gateway during the middle eocene no change in south american antarctic motion is observed near the eocene oligocene boundary but a deep water connection developed between 34 and 30 ma when continued extension led to the initiation of seafloor spreading at the west scotia ridge these timings correlate with events seen in the oxygen isotope record from benthic foraminera and support the view that drake passage opening was the trigger for abrupt eocene oligocene climate deterioration and the growth of extensive antarctic ice sheets d 2005 elsevier b v all rights reserved

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

eocene paleoceanographic evolution at 20 30 s in the atlantic ocean abstract oceanographic changes in eocene bottom water have been traced with oxygen and carbon isotope values and gradients and benthic foraminiferal assemblages the south atlantic sections chosen for this study are located on an east west traverse depositional depths range from middle bathyal through abyssal the dsdp sites are located on the walvis ridge site 363 in the angola basin sites 522 523 the brazil basin site 19 hole 20c and on the rio grande rise site 357 in abyssal sites of the south atlantic the eocene bottom water environment can be divided into two distinct regimes the early eocene and the late eocene the middle eocene is transitional faunal distribution pattern indicate that source areas where bottom water formed were probably different between the two regimes during the early eocene warm saline water formed possibly in the tethyan ocean east of gibraltar there is good evidence that the late eocene bottom water of the south atlantic recorded at lower bathyal down to middle abyssal environments was formed in southern high latitude regions first invasion of cooler bottom water is recorded at upper abyssal depths around 46 ma earliest zone p12 site 19 from 40 ma late zone p15 onwards this signal is recorded at all sites except middle bathyal depth site 357 selected faunal parameters allow reconstruction of bottom water oxygenation episodically increased abundance of epifaunal species indicate a renewal of the bottom water accompanying these faunal changes 13 c values of benthic foraminefera increase whereas vertical 13 c benthic planktonic foraminifera gradients decrease

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

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

eocene silicoflagellate and ebridian paleoceanography in the central arctic ocean the silicoflagellate and ebridian assemblages in early middle eocene arctic cores obtained by iodp expedition 302 acex were studied in order to decipher the paleoceanography of the upper water column the assemblages in lithologic unit 2 49 7 45 1 ma one of the biosiliceous intervals were usually endemic as compared to the assemblages that occurred outside of the arctic ocean the presence of these endemic assemblages is probably due to a unique environmental setting controlled by the degree of mixing between the low salinity arctic waters and relatively high salinity waters supplied from outside the arctic ocean such as the atlantic and possibly the western siberian sea using the basin to basin fractionation model the early middle eocene arctic ocean corresponds to an estuarine circulation type which includes the modern day black sea the abundant down core occurrence of ebridians strongly suggests the past presence of low salinity waters and may indicate that low oxygen concentrations prevailed in the euphotic layer on the basis of the ecology of the modern ebridian hermesinum adriaticum

cyclicity in the middle eocene central arctic ocean sediment record orbital forcing and environmental response 1 continuous x ray fluorescence scanning of middle eocene 46 ma core m0002a 55x 236 241 m composite depth recovered during integrated ocean drilling program expedition 302 revealed a strong cyclical signal in some major and trace geochemical elements we performed a multiproxy study of the same core which included organic geochemical sedimentological and biological parameters and integrated our results with available geochemical and physical properties data the target was to look for cyclicity in the several proxies investigate their frequency and understand the environmental response to the potential forcing results indicate that a higher terrigenous component corresponds to lower organic carbon concentration smaller contributions by angiosperm pollen and spores organic walled dinoflagellate cysts and chrysophyte cysts lower productivity shorter growing season for flowering plants and lower stratification but higher contributions by bisaccate pollen and diatoms drier conditions on land more marine conditions and higher terrigenous sand ice rafted debris ird our investigation shows that physical proxy parameters hold cyclicity with periods of about 50 and 100 cm and that these frequency components are compatible with a milankovitchtype orbital forcing representing precession and obliquity respectively the longer 100 cm cyclicity is also present in the biological pollen dinoflagellate cysts and siliceous microfossils and in the sedimentological ird proxies the environmental signal derived from the integrated multiproxy analysis suggests that in an enclosed arctic ocean at time of ice sea ice and glacial ice initiation the biological proxies responded more strongly to growing season length darkness whereas the terrigenous components directly driven by sea ice and or glacial ice formation and extent responded more directly to seasonal insolation

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

oxygen isotope and paleobotanical estimates of temperature and δ18o latitude gradients over north america during the early eocene empirical estimates of climate parameters such as mean annual temperature mat are essential to describe both ancient climate and to ground truth climate model simulations of past climates in terrestrial settings no single proxy record is able to provide detailed temporal yet geographically widespread information and it thus becomes essential that paleoclimatic information obtained from different proxies be comparable as an example of how to compare estimates and to illustrate what can be learned by doing so we measured oxygen isotope ratios of phosphate in the tooth enamel of fossil mammals and the body scales of freshwater fish in order to estimate the mean annual temperature mat in which they lived the samples were collected from paleogene rocks of the bighorn green river and powder river basins of wyoming earliest eocene samples provide mat estimates that are similar to mat estimates for the same times and areas obtained from leaf margin analysis furthermore isotopic data from the paleocene eocene thermal maximum petm which has not yet yielded fossil floras indicate a significantly higher mat of 26 c we also used temperature estimates obtained by both methods to investigate paleoelevation and to reconstruct geographic patterns of mat over north america for the early eocene larger laramide basins have higher temperatures and lower inferred elevations compared to associated volcanic highlands where cooler temperatures are consistent with substantial elevations in turn latitudinal gradients in temperature indicate that warming centered on polar regions played an important role during the eocene hothouse lastly we show that the reconstructed eocene relation between oxygen isotope ratios of precipitation and mat is significantly different from the modern relation between these two variables because the relation has changed over time the modern correlation should not be used to estimate paleo mat from measurements of oxygen isotope ratios in fossil material

neogene overflow of northern component water at the greenland scotland ridge in the north atlantic ocean flow of north atlantic deep water nadw and of its ancient counterpart northern component water ncw across the greenland scotland ridge gsr is thought to have played an important role in ocean circulation over the last 60 ma the iceland plume has dynamically supported an area which encompasses the gsr consequently bathymetry of the gsr has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle here we reassess the importance of plate cooling and convective control on this northern gateway for ncw flow during the neogene period following wright and miller 1996 to tackle the problem benthic foraminiferal isotope data sets have been assembled to examine 13c gradients between the three major deep water masses i e northern component water southern ocean water and pacific ocean water composite records are reported on an astronomical timescale and a nonparametric curve fitting technique is used to produce regional estimates of 13c for each water mass confidence bands were calculated and error propagation techniques used to estimate ncw and its uncertainty despite obvious reservations about using long term variations of 13c from disparate analyses and settings and despite considerable uncertainties in our understanding of ancient oceanic transport pathways the variation of ncw through time is consistent with independent estimates of the temporal variation of dynamical support associated with the iceland plume prior to 12 ma 13c patterns overlap and ncw cannot be isolated significant long period variations are evident which are consistent with previously published work from 12 ma when lithospheric cooling probably caused the gsr to submerge completely long period 13c patterns diverge significantly and allow reasonable ncw estimates to be made our most robust result is a dramatic increase in ncw overflow between 6 and 2 ma when dynamical support generated by the iceland plume was weakest between 6 and 12 ma a series of variations in ncw overflow have been resolved

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

ocean and climate response to north atlantic seaway changes at the onset of long term eocene cooling abstract around the early middle eocene boundary the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the north atlantic ocean circulation interestingly these changes coincide with the first steps of cenozoic cooling from the paleogene greenhouse climate towards the modern icehouse the cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space as a result it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e g atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins in this study we attempt to identify thresholds in tectonic gateway passages and atmospheric co2 concentration using the fully coupled earth system model cosmos indeed the simulation of earth s past climates can unravel the physical processes driving deep water formation in a greenhouse world specifically we use cosmos to evaluate the impact of changes in the north atlantic gateways at the early middle eocene boundary on the north atlantic deep western boundary currents under low obliquity configuration we find that northern component waters start to form when the greenland scotland ridge reaches a threshold depth of deeper than 200 m while the arctic ocean is still shut off from the north atlantic in this scenario the relatively deep greenland scotland ridge allows for sufficient inflow of warm salty atlantic surface waters into the nordic seas to initiate convection during winter cooling opening the seaway towards the arctic leads to a cessation of northern component water formation as it allows for inflow of brackish surface waters into the northern nordic seas hindering northern component water formation

evolution of cenozoic seaways in the circum antarctic region abstract a complete circum antarctic seaway did not open until both the south tasman rise cleared the oates land coast of east antarctica and drake passage opened between the southern tip of south america and the northern end of the antarctic peninsula major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the south tasman rise and antarctica as very close to the eocene oligocene boundary with an unrestricted opening deeper than 2000 m dating from 32 ma timing of the opening of drake passage is more circumstantial because the exact motions of certain micro continental fragments are not known the motion of africa with respect to south america as well as the motion of east antarctica with respect to africa are well constrained for the cenozoic these major plate motions are used with the reasonable assumption of no cenozoic motion of the antarctic peninsula with respect to east antarctica to constrain the location of the antarctic peninsula with respect to the southern tip of south america for the critical period of late eocene to late oligocene uncertainty of motion of the south georgia and south orkney microcontinents and other possible continental fragments make an exact time for opening of drake passage difficult to ascertain even so the early oligocene position of the antarctic peninsula with respect to south america requires a through going deep water seaway to have been open at drake passage prior to 28 ma even given the unconstrained motion of various high standing crustal fragments in the scotia sea with reasonable assumptions concerning motion of the crustal fragments in the western and central scotia sea it is likely that drake passage or passage through powell basin was open to deep water circulation by 31 2 ma

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

evidence for glaciation in the northern hemisphere back to 44 ma from ice rafted debris in the greenland sea the widely accepted age estimate for the onset of glaciation in the northern hemisphere ranges between 2 and 15 million years ago ma however recent studies indicate the date for glacial onset may be significantly older we report the presence of ice rafted debris ird in 44 to 30 ma sediments from the greenland sea evidence for glaciation in the north atlantic during the middle eocene to early oligocene detailed sedimentological evidence indicates that glaciers extended to sea level in the region allowing icebergs to be produced ird may have been sourced from tidewater glaciers small ice caps and or a continental ice sheet

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

scotia sea regional tectonic evolution implications for mantle flow and palaeocirculation abstract the scotia sea and surrounding scotia arc have evolved over the past 40 ma by extension behind an east migrating subduction zone at the boundary between the south american sam and antarctic ant plates the considerable data set now available regional geology and geophysics earthquake seismology satellite altimetry global plate analyses suggest why east migrating subduction began what has been the driving force that has sustained it and what other processes have controlled the mode of back arc extension in the scotia sea a suite of six reconstructions has been developed based on this data set the reconstruction to 40 ma creates a compact cuspate continental connection between south america and the antarctic peninsula at the subducting pacific margin with fragments now dispersed around the scotia arc occupying positions within it compatible with their known geology the driving force has been subduction of south american ocean floor which began as a result of southward migration of the pole of south american antarctic plate rotation and a key modulator of back arc extension has been collision of ridge crest sections of the south american antarctic plate boundary with the east advancing trench cenozoic regional tectonic evolution has two other likely consequences which greatly increase its importance firstly this region saw the tectonic disruption of the final barrier to complete circum antarctic deep water flow that may have had a profound effect on palaeoclimate secondly it is possible that the rapid roll back of the hinge of subduction is related to shallow eastward flow in the sub lithospheric mantle both of these consequences are explored the reconstructions show that rapid roll back of the subduction hinge averaging 50 mm a over the last 40 ma with respect to the south american plate has been a feature of all of scotia sea evolution and provide a history of motion of several oceanic microplates most of which are now welded together within the scotia sea this will guide the location of seismometers and or dredge hauls to test the hypothesis of shallow mantle flow and help interpret the results the reconstructions also allow an assessment of the creation of deep water pathways that would have permitted the development of the present day antarctic circumpolar current acc an early miocene onset within the period 22 17 ma seems likely for the acc depending on the structure and palaeo elevation of davis bank and aurora bank sections of the north scotia ridge however the study shows there was a delay of one or more million years between initial provision of a deep water pathway and the major mid miocene change in global climate involving the general level of antarctic glaciation that may have been related if these changes were related then the delay suggests that other factors possibly rough elevated ocean floor but also non tectonic factors such as atmospheric co2 were important in determining palaeoclimate

onset of north atlantic deep water production coincident with inception of the cenozoic global cooling trend here we show that the onset of deep water overflow from the norwegian greenland sea into the north atlantic interpreted to represent the onset of a modern style north atlantic deep water mass commenced close to the early to middle eocene boundary this finding is based on the identification of a large elongate contourite sediment drift the judd falls drift in the faeroe shetland basin through detailed mapping of high resolution two dimensional and three dimensional seismic data this sediment drift covers an area of 9000 km2 in one of the critical present day deep water gateways into the north atlantic ocean interpretation of the body as a contourite drift is based on standard seismic stratigraphic diagnostic criteria including tridirectional onlap lensoid sediment geometry upslope progradational configurations of stacked onlap units and an erosional base cut in a deepwater setting the internal reflection configuration indicates that the drift was deposited under a southwest flowing current regime which we propose represents the onset of north atlantic deep water production with continual deep water flow until at least the latest eocene ca 35 million years ago ma onset of drift deposition is dated by several key boreholes as occurring at ca 50 49 ma across the early to middle eocene boundary and is coincident with independent geochemical evidence for major changes in the configuration of deep sea circulation patterns global biological production and the onset of cenozoic climatic cooling these temporal concurrences suggest a strong link between the initiation of north atlantic deep water production and cenozoic global climate evolution

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

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

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

deciphering the role of southern gateways and carbon dioxide on the onset of the antarctic circumpolar current 1 growth of antarctic ice sheet during the cenozoic 34 million years ago appears as a potential tipping point in the long term cooling trend that began 50 ma ago for decades the onset of the antarctic circumpolar current acc following the opening of the drake passage and of the tasman seaway has been suggested as the main driver of the continental scale antarctic glaciation however recent modeling works emphasized that the eocene oligocene atmospheric carbon dioxide co2 lowering could be the primary forcing of the antarctic glaciation questioning the acc theory here we investigate the response of the acc to changes in co2concentrations occurring from the late eocene to the late oligocene we used a fully coupled atmosphere ocean model foam with a mid oligocene geography we find that the opening of southern oceanic gateways does not trigger the onset of the acc for co2typical of the late eocene 840 ppm a cooler background climatic state such as the one prevalent at the end of the oligocene is required to simulate a well developed acc in this cold configuration the intensified sea ice development around antarctica and the resulting brine formation lead to a strong latitudinal density gradient in the southern ocean favoring the compensation of the ekman transport and consequently the acc our results imply that the acc has acted as a feedback rather than as a driver of the global cooling

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