the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

opening the gateways for diatoms primes earth for antarctic glaciation the abrupt onset of antarctic glaciation during the eocene oligocene transition 33 7 ma oi1 is linked to declining atmospheric pco2 levels yet the mechanisms that forced pco2 decline remain elusive biogenic silicon cycling is inextricably linked to both long and short term carbon cycling through the diatoms siliceous walled autotrophs which today account for up to 40 of primary production it is hypothesised that during the late eocene a sharp rise in diatom abundance could have contributed to pco2 drawdown and global cooling by increasing the proportion of organic carbon buried in marine sediment diatom and sponge silicon isotope ratios 30si are here combined for the first time to reconstruct the late eocene early oligocene ocean silicon cycle and provide new insight into the role of diatom productivity in antarctic glaciation at odp site 1090 in the southern ocean a 0 6 rise in diatom 30si through the late eocene documents increasing diatom silicic acid utilisation with high near modern values attained by the earliest oligocene a concomitant 1 5 decline in sponge 30si at odp site 689 on the maud rise tracks an approximate doubling of intermediate depth silicic acid concentration in the high southern latitudes intermediate depth silicic acid concentration peaked at 31 5 ma coincident with the final establishment of a deepwater pathway through the tasman gateway and drake passage these results suggest that upwelling intensification related to the spin up of a circum antarctic current may have driven late eocene diatom proliferation organic carbon burial associated with higher diatom abundance and export provides a mechanism that can account for pco2 drawdown not only at but also prior to antarctic glaciation as required by a pco2 threshold mechanism for ice sheet growth

warm ocean processes and carbon cycling in the eocene sea surface and subsurface temperatures over large parts of the ocean during the eocene epoch 55 5 33 7 ma exceeded modern values by several degrees which must have affected a number of oceanic processes here we focus on the effect of elevated water column temperatures on the efficiency of the biological pump particularly in relation to carbon and nutrient cycling we use stable isotope values from exceptionally well preserved planktonic foraminiferal calcite from tanzania and mexico to reconstruct vertical carbon isotope gradients in the upper water column exploiting the fact that individual species lived and calcified at different depths the oxygen isotope ratios of different species tests are used to estimate the temperature of calcification which we converted to absolute depths using eocene temperature profiles generated by general circulation models this approach along with potential pitfalls is illustrated using data from modern core top assemblages from the same area our results indicate that during the early and middle eocene carbon isotope gradients were steeper and larger through the upper thermocline than in the modern ocean this is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm eocene ocean leading to more efficient recycling of organic matter and reduced burial rates of organic carbon

middle eocene to early oligocene paleoceanography of the antarctic ocean maud rise odp leg 113 site 689 change from a low to a high productivity ocean the sediment record from the middle eocene about 45 ma to the early oligocene about 33 ma on maud rise site 689 weddell sea paleodepth 1400 1650 m has been studied by means of a coarse fraction analysis in order to reconstruct variations in surface water productivity and bottom water masses productivity has been estimated using carbonate dissolution and accumulation rates of radiolaria diatoms benthonic and planktonic foraminifers sponge debris ostracods and echinoids accumulation rates of bolboforma spp vary parallel to these proxies productivity increased with time three episodes were found in which productivity increased sharply and productivity varied cyclically with a period of 430 ky the middle eocene ca 45 44 37 26 ma was a period of generally low productivity no opal was deposited and carbonate preservation was excellent during periods of a slight increase in productivity accumulation rates of benthonic and planktonic foraminifers ostracods and echinoids increased in spite of an increase in carbonate dissolution in the period ca 41 62 43 07 ma productivity rose in three distinct pulses clinoptilolite formed from biogenous opal is a common mineral in these sediments these three productivity maxima coincide with a mica rich unit mica probably originated from erosion on antarctica and was transported by an intermediate water depth current in the late eocene ca 36 9 34 95 ma productivity increased considerably and opal skeletons were deposited carbonate dissolution increased but planktonic foraminifer accumulation rates were not markedly decreased in periods of higher productivity because productivity increase exceeded or equalled rises in dissolution rates increasing opal accumulation rates coincided with increases in the rates for benthonic foraminifers sponge debris ostracods and echinoids in the late eocene early oligocene period 34 95 33 05 ma a further increase in productivity led to a strong dissolution of planktonic foraminifers in high productivity periods the productivity increase is probably due to the increasing pole equator temperature gradient which led to stronger atmospheric and oceanic turnover and mixing in the oceans in the uppermost late eocene two unusual layers suggest changes in bottom water masses affecting the seafloor at site 689 a sediment interval with especially well preserved carbonate microfossils underlies an interval that has poor carbonate preservation despite evidence of low productivity these intervals suggest a change in bottom water conditions from warm saline deep water wsdw which favors carbonate preservation to antarctic bottom water aabw which promotes carbonate dissolution cooling of surface waters over a period of 300 ky led to a thickening of the deep aabw layer and an upward shift of the overlying wsdw until the aabw finally reached the top of the maud rise in the area of site 689 this period of aabw influence on top of the maud rise lasted 200 ky

pattern of first and last appearance in diatoms oceanic circulation and the position of polar fronts during the cenozoic 1 first and last occurrences of 389 diatom species from the first global cenozoic record are used to reconstruct the position of major oceanographic boundaries first appearances and extinctions group in three latitudinal bands middle to high northern latitudes equatorial region and high southern latitudes sparse paleogene occurrences were limited to southern high latitudes along the equivalent of the modern antarctic polar front its late middle eocene to middle miocene position varied within 10 and within a 20 band from middle miocene to present suggesting an association with global cooling first and last occurrence events appear in the two remaining latitudinal regions during the eocene and increase in a stepwise fashion mimicking significant cooling events at about 16 ma first and last appearances shift from the north atlantic to the north pacific low latitude data suggest low surface water productivity prior to 40 ma while increased abundance from the middle miocene correlates with expansion of the east antarctic ice sheet

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

paleogene tropical pacific clues to circulation productivity and plate motion 1 stratigraphic data from 63 deep sea drilling project and ocean drilling program odp sites that sample the lower neogene and paleogene sediments of the tropical pacific have been compiled and put on the biostratigraphic and paleomagnetic timescale refined by odp leg 199 scientists sediment accumulation rates have been calculated for ten intervals ranging in age from 10 to 56 ma and have been plotted for the midpoint of each interval at the associated paleoposition for each site used a fixed hot spot model was used for reconstruction of the pacific lithospheric plate all such reconstructed intervals show the development of a tongue of high accumulation rates associated with the oceanographic divergence at the geographic equator the development of this equatorial band is weakest between 46 and 56 ma the time of the peak warmth in paleogene climate possible motion of the hawaiian hot spot or true polar wander between 46 and 56 ma appears to have had little effect on the plate rotation estimate of the position of the equator in addition to temporal changes in the calcite compensation depth and in productivity the biggest change in the patterns of sediment accumulation rates in the eastern tropical pacific was the development of a relatively strong divergence between 6 and 10 n near the region of divergence between the modern north equatorial current and the north equatorial counter current changes in the equatorial circulation appear to be associated in time with the opening and closing of oceanic gateways particularly the complex closing of the caribbean pacific gateway

size related stable isotope changes in late cretaceous planktic foraminifera implications for paleoecology and photosymbiosis abstract the paleoecology of cretaceous planktic foraminifera during the late cenomanian to coniacian period 95 86 ma remains controversial since much of the tropical marine record is preserved as chalk and limestone with uncertain geochemical overprints here we present 13c and 18o data from sieve size fractions of monospecific samples of exceptionally well preserved planktic foraminifera recovered during ocean drilling program leg 207 demerara rise western tropical atlantic our results suggest that all species studied hedbergella delrioensis heterohelix globulosa marginotruncana sinuosa whiteinella baltica grew primarily in surface waters and did not change their depth habitat substantially during their life cycle comparison of size related ontogenetic trends in 13c in cretaceous and modern foraminifera further suggests that detection of dinoflagellate photosymbiosis using 13c is confounded by physiological effects during the early stages of foraminifer growth raising doubts about previous interpretations of photosymbiosis in small foraminifera species we propose that obligate photosymbiosis involving dinoflagellates may not have evolved until the campanian or maastrichtian since our survey of cenomanian coniacian species does not find the 18o and 13c size related trends observed in modern foraminifer dinoflagellate symbioses

radiolarian magnetobiochronology and faunal turnover across the middle late eocene boundary at ocean drilling program site 1052 in the western north atlantic ocean quantitative radiolarian assemblage analysis has been conducted on middle and upper eocene sediments zones rp16 to rp18 from ocean drilling program site 1052 in order to establish the radiolarian magnetobiochronology and determine the nature of the faunal turnover across the middle late eocene boundary in the western north atlantic ocean we recognize and calibrate forty five radiolarian bioevents to the magneto and cyclo stratigraphy from site 1052 to enhance the biochronologic resolution for the middle and late eocene our data is compared to sites in the equatorial pacific leg 199 to access the diachrony of biostratigraphic events eleven bioevents are good biostratigraphic markers for tropical subtropical locations south of 30 n the primary markers lowest occurrences of cryptocarpium azyx and calocyclas bandyca which are tropical zonal boundary markers for zones rp17 and rp18 provide robust biohorizons for correlation and age determination from the low to middle latitudes and between the atlantic and pacific oceans some other radiolarian bioevents are highly diachronous 1 million years between oceanic basins a significant faunal turnover of radiolarians is recognized within chron c17n 3n 37 7 ma where 13 radiolarian species disappear rapidly in less than 100 kyr and 4 new species originate the radiolarian faunal turnover coincides with a major extinction in planktonic foraminifera we name the turnover phase the middle late eocene turnover mlet assemblage analysis reveals the mlet to be associated with a decrease in low mid latitude taxa and increase in cosmopolitan taxa and radiolarian accumulation rates the mlet might be related to increased biological productivity rather than to surface water cooling

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

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

new evidence for the hawaiian hotspot plume motion since the eocene abstract a thick mound of fossiliferous sediments reflecting high biogenic productivity at the equator can be used to determine latitudinal motion of the pacific lithospheric plate plate motion estimates based on the latitudinal movement of equatorial facies are independent of paleomagnetic data and hotspot tracks and thus permit further testing of kinematic models we have determined the northward motion of the pacific plate for the last 53 myr based on the position of the paleoequator as shown by equatorial sediment facies between 26 and 69 dsdp and odp sites sample the past 53 myr in the tropical pacific based on the mapped patterns of accumulation rates in these sites we were able not only to determine the position of the paleoequator but also to estimate the equatorial great circle and hence the relative position of the spin axis since the early eocene the northward motion of the pacific plate inferred from the change in latitude of dated hawaiian chain seamounts relative to the hawaiian hotspot is consistently higher than that deduced from the analyses of equatorial sediment facies such a difference results from a latitudinal shift of the hawaiian hotspot during the last 53 myr all together our observations and recent paleomagnetic results from the detroit nintoku and koko seamounts j a tarduno r a duncan d w scholl r d cottrell b steinberger t thordarson b c kerr c r neal f a frey m torii m c carvallo the emperor seamounts southward motion of the hawaiian hotspot plume in earth s mantle science 301 2003 1064 1069 1 are consistent with a progressive southward motion of the hawaiian mantle plume since the late cretaceous our results suggest that the hawaiian hotspot moved at 32 mm yr to the se during the past 43 million years and that the pacific plate moved 12 northward since 53 ma at an average rate of 25 mm yr

paleoproductivity nutrient burial climate change and the carbon cycle in the western equatorial atlantic across the eocene oligocene boundary paleoproductivity nutrient burial and carbon cycling were investigated across the eocene oligocene e o boundary begin to end 36 9 32 7 ma at 40 kyr resolution timescale of shackleton et al 1999 at ocean drilling program site 925 on the ceara rise in the western equatorial atlantic 3040 m present water depth 748 26 850 70 mbsf downcore bulk sediment records of biogenic barium total reactive phosphorus biogenic silica and calcium carbonate are interpreted to represent export production net nutrient burial biogenic opal production and inorganic carbon burial respectively the global positive excursion in 13c subsequent to the e o boundary is recorded at site 925 export production appears to have been externally forced by orbital parameters at eccentricity frequencies during the study interval based on spectral analysis of the biogenic barium and reactive phosphorus records biogenic silica production or preservation increased after the eocene oligocene boundary to a higher baseline although overall productivity and nutrient burial did not increase based on barium and reactive phosphorus records thus although absolute production did not increase at this site a shift in relative abundance of siliceous versus carbonate productivity may have resulted in a change in relative organic carbon burial this may have contributed to the positive excursion in global oceanic 13c subsequent to the eocene oligocene boundary although the silica maximum persists after the carbon isotope excursion ends

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

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

planktonic foraminiferal turnover diversity fluctuations and geochemical signals across the eocene oligocene boundary in tanzania a major turnover in planktonic foraminifera occurred across the eocene oligocene e o boundary new drill holes through the e o boundary in southern tanzania contain extremely well preserved and diverse assemblages of planktonic foraminifera here we document a 1 2 million year record of assemblages diversity and stable isotope fluctuations through this critical interval which is often dissolved and or recrystallised in carbonate rich facies the e o boundary is marked by the abrupt extinction of all five remaining species of the family hantkeninidae and a distinct size reduction in the genus pseudohastigerina the boundary is preceded over a short stratigraphic interval by the extinction of turborotalia cerroazulensis turborotalia cocoaensis and turborotalia cunialensis quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages we compare diversity fluctuations to the stable isotope record of pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species a major shift in the evenness occurs at 33 8 ma associated with the extinction of the t cerroazulensis group suggesting acute ecological disturbance we propose that the extinction of the t cerroazulensis group at 33 8 ma was directly related to cooling of sea surface temperatures while the extinction of hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes after the extinctions renewed origination and diversification occurred leading to a characteristic oligocene planktonic foraminifer assemblage

the biostratigraphy and paleobiology of oligocene planktonic foraminifera from the equatorial pacific ocean odp site 1218 planktonic foraminifera from a continuous oligocene succession with clear magnetochronology and sediment cycles at ocean drilling program site 1218 equatorial pacific ocean were studied in the interval from 27 to 30 ma paragloborotalia taxa are common and we examined their size relative abundance and stable isotopes multispecies stable isotope data indicate the depth habitats of oligocene planktonic foraminifera and suggest that globoquadrina venezuelana and dentoglobigerina globularis were probably mixed layer dwellers with paragloborotaliids recording heavier 18 o signatures consistent with a thermocline habitat cyclic variations in the abundance of paragloborotalia match eccentricity 100 kyr variations in percent carbonate and 13 c suggesting orbitally forced upwelling in the equatorial pacific ocean and that paragloborotalia were responding directly to changes in surface water productivity the high resolution biostratigraphy calibrated to the magnetochronology constrains the extinction of paragloborotalia opima which marks the top of planktonic foraminifera biozone o5 p21b at 27 456 ma the highest occurrence of p opima is associated with a 50 size decrease in paragloborotalia pseudocontinuosa taxa within chron 9n in addition we find the extinction of chiloguembelina cubensis is consistent with other deep sea sections within chron 10n at 28 426 ma marking the o4 o5 p21a p21b boundary

orbital control on carbon cycle and oceanography in the mid cretaceous greenhouse we established a new high resolution carbonate carbon isotope record of the albian interval of the marne a fucoidi formation central apennines italy which was deposited on the southern margin of the western tethys ocean bulk carbonate sampled with 10 15 cm spacing was used for the construction of a continuous carbon isotope curve through the albian stage spectral analyses reveal prominent 400 kyr cyclicity in the 13c curve which correlates with milankovitch long eccentricity changes cycles occurring in our record resemble those observed in several cenozoic 13c records suggesting that a link between orbital forcing and carbon cycling existed also under mid cretaceous greenhouse conditions based on comparisons with cenozoic eccentricity carbon cycle links we hypothesize that 400 kyr cycles in the mid cretaceous were related to a fluctuating monsoonal regime coupled with an unstable oceanic structure which made the oceanic carbon reservoir sensitive to orbital variations in the tethys these oceanographic conditions lasted until the late albian and then were replaced by a more stable circulation mode less sensitive to orbital forcing

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

middle eocene to early oligocene paleoceanography from agulhas ridge southern ocean ocean drilling program leg 177 site 1090 1 the agulhas ridge off the tip of africa between the atlantic and indian oceans is ideally located to capture the evolution of paleogene early neogene circulation patterns associated with global cooling multiproxy records of productivity biogenic barium baex opal caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox state of deep waters u enrichment from ocean drilling program odp site 1090 reflect hydrographic shifts in this region between the middle eocene and early oligocene 39 33 ma several peaks in increased export productivity and burial of organic matter occurred within the late eocene 36 5 34 and 33 7 ma which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pco2 to a threshold level that facilitated large ice sheet development on antarctica in the earliest oligocene our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle eocene to early oligocene by facilitating increases in the relative or absolute burial of organic carbon

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

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

coupled productivity and carbon isotope records in the southwest pacific ocean during the late miocene early pliocene biogenic bloom biogenic components of sediment accumulated at high rates beneath frontal zones of the indian and pacific oceans during the late miocene and early pliocene the 13c of bulk and foraminiferal carbonate also decreased during this time interval although the two observations may be causally linked and signify a major perturbation in global biogeochemical cycling no site beneath a frontal zone has independent records of export production and 13c on multiple carbonate phases across the critical interval of interest deep sea drilling project dsdp site 590 lies beneath the tasman front tf an eddy generating jetstream in the southwest pacific ocean to complement previous 13c records of planktic and benthic foraminifera at this location late neogene records of caco3 mass accumulation rate mar ca ti ba ti al ti and of bulk carbonate and foraminiferal 13c were constructed at site 590 the 13c records include bulk sediment bulk sediment fractions 63 m and 5 25 m and the planktic foraminifera globigerina bulloides globigerinoides sacculifer with and without sac and orbulina universa using current time scales caco3 mars ca ti al ti and ba ti ratios are two to three times higher in upper miocene and lower pliocene sediment relative to overlying and underlying units a significant decrease also occurs in all 13c records all evidence indicates that enhanced export production the biogenic bloom extended to the southwest pacific ocean between ca 9 and 3 8 ma and this phenomenon is coupled with changes in 13c the chron c3ar carbon shift however caco3 mars peak ca 5 ma whereas elemental ratios are highest ca 6 5 ma foraminiferal 13c starts to decrease ca 8 ma whereas bulk carbonate 13c begins to drop ca 5 6 ma temporal discrepancies between the records can be explained by changes in the upwelling regime at the tf perhaps signifying a link between changes in ocean atmosphere circulation change and widespread primary productivity

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

paleoenvironmental conditions for the development of calcareous nannofossil acme during the late miocene in the eastern equatorial pacific repeated monospecific coccolithophore dominance intervals acmes of specimens belonging to the noelaerhabdaceae family including the genus reticulofenestra and modern descendants emiliania and gephyrocapsa occurred during the neogene such acme was recognized during the late miocene 8 6 ma at a time of a major reorganization of nannofossil assemblages resulting in a worldwide temporary disappearance of larger forms of the genus reticulofenestra r pseudoumbilicus and the gradual recovery and dominance of its smaller forms 5 m in this study we present a multiproxy investigation of late miocene sediments from the east equatorial pacific integrated ocean drilling program site u1338 where small reticulofenestrid type placoliths with a closed central area known as small dictyococcites spp 3 m formed an acme we report on oxygen and carbon stable isotope records of multispecies planktic calcite and alkenone derived sea surface temperature our data indicate that during this 100 kyr long acme the east equatorial pacific thermocline remained deep and stable local surface stratification state fails to explain this acme and thus contradicts the model based hypothesis of a southern ocean high latitude nutrient control of the surface waters in the east equatorial pacific instead our findings suggest that external forcing such as an extended period of low eccentricity may have created favorable conditions for the small dictyococcites spp growth

distribution and composition of hydrothermal plume particles from the ashes vent field at axial volcano juan de fuca ridge in 1986 and 1987 buoyant and neutrally buoyant hydrothermal plume particles from the ashes vent field within axial volcano were sampled to study their variations in composition with height above the seafloor individual mineral phases were identified using standard x ray diffraction procedures elemental composition and particle morphologies were determined by x ray fluorescence spectrometry and scanning electron microscopy x ray energy spectrometry techniques the vent particles were primarily composed of sphalerite anhydrite pyrite pyrrhotite chalcopyrite barite hydrous iron oxides and amorphous silica grain size analyses of buoyant plume particles showed rapid particle growth in the first few centimeters above the vent orifice followed by differential sedimentation of the larger sulfide and sulfate minerals out of the buoyant plume the neutrally buoyant plume consisted of a lower plume which was highly enriched in fe s zn and cu and an upper plume which was highly enriched in fe and mn the upper plume was enriched in fe and mn oxyhydroxide particles and the lower plume was enriched in suspended sulfide particles in addition to the fe and mn oxyhydroxide particles the chemical data for the water column particles indicate that chemical scavenging and differential sedimentation processes are major factors controlling the composition of the dispersing hydrothermal particles short term sediment trap experiments indicate that the fallout from the ashes vent field is not as large as some of the other vent fields on the juan de fuca ridge

late oligocene initiation of the antarctic circumpolar current evidence from the south pacific the antarctic circumpolar current acc is a key feature of the southern ocean its development may have helped cool antarctica and initiate southern hemisphere glaciation the deep circulation of the acc must have been established after both the tasman gateway between antarctica and australia and the drake passage between south america and antarctica opened however estimates for acc initiation range over 20 m y from the middle eocene to early miocene a new piston core of upper oligocene to holocene sediments from the south pacific has allowed us to delimit the formation of the acc to the late oligocene ca 25 23 ma upper oligocene current worked sediments and a hiatus to the upper miocene result from the beginning of the modern acc flow i e when strong currents and mixing throughout the water column were established previously published nd isotope data date the first intrusion of pacific water into the atlantic much earlier the discrepancy with our results can be reconciled by the different methods measuring different flow regimes tracer methods such as nd are sensitive to relatively small and shallow incursions of water whereas pelagic erosional regimes require vigorous deep flow

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

major shifts in calcareous phytoplankton assemblages through the eocene oligocene transition of tanzania and their implications for low latitude primary production a high resolution record of exceptionally well preserved calcareous nannofossil assemblages from tanzania is marked by two key transitions closely related to the climatic events of the eocene oligocene transition eot the first transition at similar to 34 0 ma precedes the first positive shift in delta o 18 and coincides with a distinct interval of very low nannofossil abundance and a cooling in sea surface temperatures sst the second at similar to 33 63 ma is immediately above the eocene oligocene boundary eob and is associated with a significant drop in nannofossil diversity both transitions involve significant reductions in the abundance of holococcoliths and other oligotrophic taxa these changes in calcareous phytoplankton assemblages indicate 1 a widespread and significant perturbation to the low latitude surface ocean closely tied to the eob 2 a potential role for reduced carbonate primary production at the onset of global cooling and 3 a significant increase in nutrient availability in the low latitude surface ocean through the eot

missing organic carbon in eocene marine sediments is metabolism the biological feedback that maintains end member climates 1 ocean chemistry is affected by pco2 in the atmosphere by increasing the dissolution of solid calcium carbonate and elevating the dissolved inorganic carbon concentrations in seawater positive feedbacks between the ocean and atmosphere can maintain high atmospheric pco2 and affect global climate we report evidence for changes in the oceanic carbon cycle from the first high quality organic carbon corg data set of eocene sediments beneath the equatorial pacific upwelling region leg 199 of the ocean drilling program eocene corg mass accumulation rates mars are 10 times lower than holocene rates even though expected corg mars estimated from biogenic barium mars an indicator of biological production equal or exceed modern fluxes what happened to the missing corg recent advances in ecology and biochemical kinetics show that the metabolism of nearly all animals marine and terrestrial is positively correlated by first principles to environmental temperatures the approximately 10 c abyssal temperature difference from eocene to holocene should have radically reduced pelagic corg burial as we observe we propose that higher basal metabolism and nutrient utilization recycling rates in the eocene water column and surface sediments precluded corg sediment burial in the pelagic ocean increased rates of metabolism nutrient utilization and lowered corg sedimentation caused by increased temperature may have acted as a biological feedback to maintain high atmospheric pco2 and hothouse climates conversely these same parameters would reverse sign to maintain low pco2 when temperatures decrease thereby maintaining icehouse conditions during cold climate regimes

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

export productivity and carbonate accumulation in the pacific basin at the transition from a greenhouse to icehouse climate late eocene to early oligocene 1 the late eocene through earliest oligocene 40 32 ma spans a major transition from greenhouse to icehouse climate with net cooling and expansion of antarctic glaciation shortly after the eocene oligocene e o boundary we investigated the response of the oceanic biosphere to these changes by reconstructing barite and caco3 accumulation rates in sediments from the equatorial and north pacific ocean these data allow us to evaluate temporal and geographical variability in export production and caco3 preservation barite accumulation rates were on average higher in the warmer late eocene than in the colder early oligocene but cool periods within the eocene were characterized by peaks in both barite and caco3 accumulation in the equatorial region we infer that climatic changes not only affected deep ocean ventilation and chemistry but also had profound effects on surface water characteristics influencing export productivity the ratio of caco3 to barite accumulation rates representing the ratio of particulate inorganic c accumulation to corg export increased dramatically at the e o boundary this suggests that long term drawdown of atmospheric co2 due to organic carbon deposition to the seafloor decreased potentially offsetting decreasing pco2 levels and associated cooling the relatively larger increase in caco3 accumulation compared to export production at the e o suggests that the permanent deepening of the calcite compensation depth ccd at that time stems primarily from changes in deep water chemistry and not from increased carbonate production

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

a comparison of early paleogene export productivity and organic carbon burial flux for maud rise weddell sea and kerguelen plateau south indian ocean 1 marine biological productivity has been invoked as a possible climate driver during the early paleogene through its potential influence on atmospheric carbon dioxide concentrations however the relationship of export productivity the flux of organic carbon c from the surface ocean to the deep ocean to organic c burial flux the flux of organic c from the deep ocean that is buried in marine sediments is not well understood we examine the various components involved with atmosphere to ocean c transfer by reconstructing early paleogene carbonate and silica production using carbonate and silica mass accumulation rates mars export productivity using biogenic barium bio ba mars organic c burial flux using reactive phosphorus p mars redox conditions using uranium and manganese contents and the fraction of organic c buried relative to export productivity using reactive p to bio ba ratios our investigations concentrate on paleocene eocene sections of sites 689 690 from maud rise and site 738 from kerguelen plateau in both regions export productivity organic c burial flux and the fraction of organic c buried relative to export productivity decreased from the paleocene early eocene to the middle eocene a shift is indicated from an early paleogene two gyre circulation in which nutrients were not efficiently recycled to the surface via upwelling in these regions to a circulation more like the present day with efficient recycling of nutrients to the surface ocean export productivity was enhanced for kerguelen plateau relative to maud rise throughout the early paleogene possibly due to internal waves generated by the plateau regardless of gyre circulation

middle eocene regional climate instability evidence from the western north atlantic high resolution 3 k y d 18 o records from middle eocene mixed layer dwelling planktonic foraminifera from the western north atlantic show pronounced 1 variability the magnitude of change is greater than that seen in open ocean pleistocene records but could not have been caused by ice volume and or sea level fluctuations instead the oxygen isotope shifts resulted primarily from large oscillations in sea surface temperatures and indicate that the regional paleoceanography of the middle eocene western north atlantic was not consistently warm or stable the large shifts in sea surface temperatures could reflect variations in the position of the gulf stream relative to blake nose or variations in upwelling intensity

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

eocene biogenic silica accumulation rates at the pacific equatorial divergence zone 2 the eocene biosiliceous oozes of the tropical pacific are an easily recognizable sediment type having a reddish brown color and sugary texture these sediments are dominated by radiolarian tests with traces of terrigenous debris hydrothermal oxides a few diatoms and little if any carbonate the paucity of carbonate is a result of the very shallow pacific calcite compensation depth ccd of the eocene 3300 m rea and lyle 2005 and references therein the dominance of radiolarian tests over those of diatoms is an enigma in that diatoms usually dominate siliceous rich sediments of the oligocene and neogene the opal rich character of these eocene sediments is commonly associated with the development of cherts within the sections 3 these unusual characteristics of eocene radiolarian oozes have prompted some authors to puzzle over how so much silica could have been delivered to the sea floor during

factors influencing the distribution patterns of recent deep sea benthic foraminifera east of new zealand southwest pacific ocean abstract this study investigates which combination of environmental factors most strongly influences the distribution patterns of benthic foraminferal tests 0 63 m in a region bisected by the subtropical front east of new zealand seafloor sample sites extend from outer shelf 90 m to abyssal 4700 m depths across substrates ranging from biogenic terrigenous gravelly sand to hemipelagic mud and occur under the influence of antarctic intermediate water aaiw and circumpolar deep waters as well as receiving detritus from both subtropical and subantarctic surface water masses elevated values of the planktic foraminiferal fragmentation index and reworked small paleogene planktic foraminifera at outer shelf and bathyal depths coincide with areas of strong bottom currents q mode cluster analysis on the census counts of 398 benthic species clusters the 66 samples into three large groups shallow bathyal abyssal and at a lower level 10 mappable associations are recognised a combination of canonical correspondence analysis and a correlation coefficient matrix was used to relate the faunal data to a set of measured environmental proxies these analyses show that factors that have a relationship with depth are the most significant in determining foraminiferal distribution the principal environmental factors which appear to most strongly influence this benthic foraminiferal distribution are dissolved oxygen content in bottom waters sustainability of organic carbon flux rates seasonality of food supply lateral advection of water masses bottom water carbonate corrosiveness energetic state at the benthic boundary layer grain size composition of substrate salinity and temperature of the bottom waters shallow water associations 90 1250 m dominated by cassidulina carinata and trifarina angulosa occur within coarse substrates under well oxygenated high energy regimes and sustained food input the occurrence of the bathyal associations 230 2840 m dominated by c carinata alabaminella weddellensis and abditodentrix pseudothalmanni closely mirrors the distribution of aaiw within a region of variable food supply the sustainability of food supply combined with bottom water type and associated ventilation and dissolution strongly influence the composition of abyssal associations 1200 4700 m mostly dominated by epistominella exigua and a weddellensis

radiolarian faunal turnover and paleoceanographic change around eocene oligocene boundary in the central equatorial pacific odp leg 199 holes 1218a 1219a and 1220a continuous eocene through oligocene sedimentary sedimentary sections were obtained at holes 1218a 1219a and 1220a drilled during leg 199 of the ocean drilling program in the central equatorial pacific quantitative analysis of radiolarian assemblages between the upper eocene through lower oligocene sedimentary successions revealed that major faunal changes of radiolarians occurred in the late eocene 35 5 35 7 ma subchron c16n1 around the eocene oligocene boundary 33 7 33 8 ma upper subchron c13r and in the early oligocene 30 9 31 3 ma uppermost subchron c12r the faunal change in the late eocene is characterized by a stepwise decrease of tropical eocene species and an increase in cosmopolitan probably cool water tolerant radiolarians however without a significant change in species diversity and radiolarian accumulation rates the stratigraphic level of this late eocene turnover came after the late eocene impact event and may have been more related to global cooling and associated oceanographic changes than to asteroid impact the turnover around the eocene oligocene boundary corresponding to the oi 1 event is the most critical during the eocene oligocene transition many biotic events such as a sudden drop of species diversity an increase in the cosmopolitan radiolarian group a large number of species turnovers and a drop in radiolarian accumulation rates occurred at or just above this level together these indicators suggest a major restructuring of radiolarian assemblages from the high diversity eocene fauna to a low diversity oligocene one the third turnover event within early oligocene is represented by a replacement of dominant species with a sudden decrease in radiolarian accumulation rates however this oligocene turnover is not consistent with other major 18o isotope events such as oi 1b and oi 2

extinction and environmental change across the eocene oligocene boundary in tanzania the eocene oligocene transition between ca 34 and 33 5 ma is the most profound episode of lasting global change to have occurred since the end of the cretaceous diverse geological evidence from around the world indicates cooling ice growth sea level fall and accelerated extinction at this time turnover in the oceanic plankton included the extinction of the foraminifer family hantkeninidae which marks the eocene oligocene boundary in its type section another prominent extinction affected larger foraminifera which resulted in the loss of some of the world s most abundant and widespread shallow water carbonate secreting organisms however problems of correlation have made it difficult to relate these events to each other and to the global climate transition as widely recorded in oxygen and carbon isotope records from deep sea cores here we report new paleontological and geochemical data from hemipelagic sediment cores on the african margin of the indian ocean tanzania drilling project sites 11 12 and 17 the eocene oligocene boundary is located between two principal steps in the stable isotope records the extinction of shallow water carbonate producers coincided with an extended phase of ecological disruption in the plankton and preceded maximum glacial conditions in the early oligocene by 200 k y

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

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

radiolarians decreased silicification as an evolutionary response to reduced cenozoic ocean silica availability it has been hypothesized that increased water column stratification has been an abiotic universal driver affecting average cell size in cenozoic marine plankton gradually decreasing cenozoic radiolarian shell weight by contrast suggests that competition for dissolved silica a shared nutrient resulted in biologic coevolution between radiolaria and marine diatoms which expanded dramatically in the cenozoic we present data on the 2 components of shell weight change size and silicification of cenozoic radiolarians in low latitudes increasing cenozoic export of silica to deep waters by diatoms and decreasing nutrient upwelling from increased water column stratification have created modern silica poor surface waters here radiolarian silicification decreases significantly r 0 91 p 0 001 from 0 18 shell volume fraction in the basal cenozoic to modern values of 0 06 a third of the total change occurred rapidly at 35 ma in correlation to major increases in water column stratification and abundance of diatoms in high southern latitudes southern ocean circulation present since the late eocene maintains significant surface water silica availability here radiolarian silicification decreased insignificantly r 0 58 p 0 1 from 0 13 at 35 ma to 0 11 today trends in shell size in both time series are statistically insignificant and are not correlated with each other we conclude that there is no universal driver changing cell size in cenozoic marine plankton furthermore biologic and physical factors have in concert by reducing silica availability in surface waters forced macroevolutionary changes in cenozoic low latitude radiolarians

response of abyssal benthic foraminifera to mid oligocene glacial events in the eastern equatorial pacific ocean odp leg 199 abstract we investigated oligocene and early miocene benthic foraminiferal faunas 105 m in size from ocean drilling program leg 199 site 1218 4826 m water depth and 3300 to 4000 m paleo water depth and site 1219 5063 m water depth and 4200 to 4400 m paleo water depth to understand the response of abyssal benthic foraminifera to mid oligocene glacial events in the eastern equatorial pacific ocean two principal factor assemblages were recognized the factor 1 assemblage common nuttallides umbonifer is related to either an influx of the southern component water scw possibly carbonate undersaturated or a decrease in seasonality of the food supply from the surface ocean the factor 2 assemblage is characterized by typical deep sea taxa living under variable trophic conditions possibly with a seasonal component in food supply the occurrence of abyssal benthic foraminifera faunas during the mid oligocene depends on either the effect of scw or the seasonality of food resources the factor 1 assemblage was most common near 76ol c11r 73ol c10rn and 67ol c9n ca 30 2 29 1 and 26 8 ma respectively by palike et al 2006 this indicates that the effect of scw increased or the seasonal input of food from the surface ocean to benthic environments was weakened close to these glacial events in contrast the huge export flux of small biogenic carbonate particles close to these glacial events might be responsible for carbonate rich sediments buffering carbonate undersaturation changes in deep water masses or the periodicity of food supply from the surface ocean and variation in surface carbonate production affected by orbital forcing had an impact on the mid oligocene faunas of abyssal benthic foraminifera around the intervals of glacial events in the eastern equatorial pacific ocean the factor 1 assemblage decreased sharply at 30 ma 29 8 ma by palike et al 2006 30 0 ma by ck95 and returned to dominance after 29 ma 28 6 ma by palike et al 2006 28 8 ma by ck95 it is likely that the effect of scw possibly carbonate undersaturated has intensified since the late oligocene the faunal transition of benthic foraminifera in the eastern equatorial pacific ocean at 29 ma might be attributable to the influence of northern component water ncw input to the southern ocean and the subsequent formation of scw at about that time

equatorial pacific productivity changes near the eocene oligocene boundary there is general agreement that productivity in high latitudes increased in the late eocene and remained high in the early oligocene evidence for both increased and decreased productivity across the eocene oligocene transition eot in the tropics has been presented usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the eot itself a complete record of the eocene oligocene transition was obtained at three drill sites in the eastern equatorial pacific ocean odp site 1218 and iodp sites u1333 and u1334 four paleoproductivity proxies that have been examined at these sites together with carbon and oxygen isotope measurements on early oligocene planktonic foraminifera give evidence of ecologic and oceanographic change across this climatically important boundary export productivity dropped sharply in the basal oligocene 33 7 ma and only recovered several hundred thousand years later however overall paleoproductivity in the early oligocene never reached the average levels found in the late eocene and in more modern times changes in the isotopic gradients between deep and shallow living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early oligocene that on average affected accumulation rates of barite benthic foraminifera and opal as well as diatom abundance near 33 5 ma an interval with abundant large diatoms beginning at 33 3 ma suggests an intermediate thermocline depth which was followed by further shoaling a dominance of smaller diatoms and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera

evidence for late oligocene establishment of the antarctic circumpolar current removal of the last impediment to circum antarctic flow opening of the drake passage between antarctica and south america is essential to establishment of the acc and has been placed in both the earliest oligocene and earliest miocene on the basis of paleomagnetic reconstructions the tasman gateway between antarctica and tasmania notably deepened following 33 5 ma completion of the acc circuit has been seen as the key to major growth of the east antarctic ice sheet by thermal isolation of the continent an alternative argument attributes ice sheet growth to changes in atmospheric pco2 we present evidence on current strength and water mass properties suggesting a clear increase in flow speed and homogeneity of southern ocean water masses in the latest oligocene after about 23 95 ma marking establishment of the acc attributable to deep opening of drake passage the mi 1 glaciation may be a consequence establishment of a permanent low altitude ice sheet does not appear to take place prior to mid miocene cooling

cenozoic mass accumulation rates in the equatorial pacific based on high resolution mineralogy of ocean drilling program leg 199 1 we use continuous mineralogy logs derived from multisensor track physical properties data and reflectance spectroscopy to calculate high resolution carbonate opal and terrigenous mass accumulation rates mar for the eight sites cored during ocean drilling program leg 199 in the equatorial pacific the largest change in equatorial pacific sedimentation patterns of the last 55 myr occurs at the greenhouse icehouse transition shortly after the eocene oligocene boundary calcite compensation depth deepened dramatically the equatorial zone of opal accumulation narrowed and the intertropical convergence zone shifted to the equator during the paleogene the opal equatorial accumulation bulge extended to about 12 n whereas the neogene bulge extended only to about 7 n very low eocene carbonate mar was followed by much higher oligocene and early miocene mar with the carbonate equatorial bulge extending to 4 n terrigenous mars indicate the paleoposition of the intertropical convergence zone and a pliocene pleistocene increase in asian dust flux

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

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

multiproxy record of abrupt sea surface cooling across the eocene oligocene transition in the gulf of mexico the eocene oligocene transition eot ca 33 34 ma was a time of pronounced climatic change marked by the establishment of continental scale antarctic ice sheets the timing and extent of temperature change associated with the eot is controversial here we present multiproxy eot climate records 15 34 k y resolution from st stephens quarry alabama usa derived from foraminiferal mg ca d18o and tex86 we constrain sea surface temperatures ssts in the latest eocene and early oligocene and address the issue of climatic cooling during the eot paleotemperatures derived from planktic foraminifera mg ca and tex86 are remarkably consistent and indicate late eocene subtropical ssts of 28 c there was substantial and accelerated cooling of ssts 3 4 c through the latest eocene precursor d18o shift eot 1 prior to oligocene isotope 1 oi 1 our multispecies planktic foraminiferal d18o records diverge at the e o boundary 33 7 ma signifying enhanced seasonality in the earliest oligocene in the gulf of mexico

eocene to miocene terrigenous inputs and export production geochemical evidence from odp leg 177 site 1090 abstract changes in ocean circulation and climate during the cenozoic led to the development of the antarctic circum polar current acc and permanent antarctic ice sheets however the timing of the opening of the drake passage and the establishment of the acc is poorly constrained we present geochemical proxies of terrigenous inputs and export production at a single site in the southeastern atlantic ocean that suggest the drake passage had opened to intermediate and deep water by 32 8 ma two separate styles of sedimentation and geochemical composition of terrigenous material are observed with the change in sediment geochemical characteristics occurring at 32 8 ma middle to late eocene records are highly variable while latest eocene to early miocene records exhibit cyclic variations in elemental records and terrigenous material based on al ti ratios metal sources change from continental crust to oceanic crust sources at the eocene oligocene transition which we suggest reflects a change in deep water circulation phosphorus metal ratios indicate that there are two distinct intervals of enhanced export production one in the middle eocene and one throughout the eocene oligocene transition elevated al ti ratios greater than any lithic source in the middle eocene provide evidence of particulate scavenging and thus increased export production barium ratios further support changes in productivity in the middle eocene and at the eocene oligocene transition permanent changes in the ba concentration record in the early oligocene further support a change in deep water circulation due to the opening and deepening of the drake passage at 32 8 ma

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

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

spatial and temporal distribution of biogenic carbonate and opal in deep sea sediments from the eastern equatorial pacific implications for ocean history since 1 3 ma abstract high resolution records of glacial interglacial variations in biogenic carbonate opal and detritus derived from non destructive core log measurements of density p wave velocity and color r 0 9 from 15 sediment sites in the eastern equatorial sampling resolution is 1 kyr clear response to eccentricity and precession forcing for the peru basin we generate a high resolution 21 kyr increment orbitally based chronology for the last 1 3 ma spectral analysis indicates that the 100 kyr cycle became dominant at roughly 1 2 ma 200 300 kyr earlier than reported for other paleoclimatic records the response to orbital forcing is weaker since the mid brunhes dissolution event at 400 ka a west east reconstruction of biogenic sedimentation in the peru basin four cores 91 85 w distinguishes equatorial and coastal upwelling systems in the western and eastern sites respectively a north south reconstruction perpendicular to the equatorial upwelling system 11 cores 11 n 8 s shows high carbonate contents 50 between 6 n and 4 s and highly variable opal contents between 2 n and 4 s carbonate cycles b 6 b 8 b 10 b 12 b 14 m 2 and m 6 are well developed with b 10 430 ka as the most prominent cycle carbonate highs during glacials and glacial interglacial transitions extended up to 400 km north and south compared to interglacial or interglacial glacial carbonate lows our reconstruction thus favors glacial interglacial expansion and contraction of the equatorial upwelling system rather than shifting north or south elevated accumulation rates are documented near the equator from 6 n to 4 s and from 2 n to 4 s for carbonate and opal respectively accumulation rates are higher during glacials and glacial interglacial transitions in all cores whereas increased dissolution is concentrated on peru basin sediments close to the carbonate compensation depth and occurred during interglacials or interglacial glacial transitions

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

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

os isotope chemostratigraphy applied to organic rich marine sediments from the eocene oligocene transition on the west african margin odp site 959 1 the known temporal relationship between the benthic foraminiferal 18o record and the marine os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the west african margin ocean drilling program odp site 959 although organic rich sediments require significant corrections for in situ decay of 187re to 187os these results demonstrate the utility of the marine os isotope record for chemostratigraphic correlation of organic rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences revision of the odp site 959 chronology shifts the age assignment of an interval of biosiliceous organic rich sediment deposition from the oligocene to the late eocene and earliest oligocene likely culminating with the first major glaciation of the oligocene oi1 we speculate that enhanced organic carbon burial over much of the west african margin may have contributed to drawdown of atmospheric carbon dioxide before and during the oi1 event and suggest that os isotope chemostratigraphy provides a valuable tool for further exploring this possibility

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

paleogeographic controls on the onset of the antarctic circumpolar current development of the antarctic circumpolar current acc during the cenozoic is controversial in terms of timing and its role in major climate transitions some propose that the development of the acc was instrumental in the continental scale glaciation of antarctica and climate cooling at the eocene oligocene boundary here we present climate model results that show that a coherent acc was not possible during the oligocene due to australasian paleogeography despite deep water connections through the drake passage and tasman gateway and the initiation of antarctic glaciation the simulations of ocean currents compare well to paleoenvironmental records relating to the physical oceanography of the oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the acc we conclude that the northward motion of the australasian land masses and the reconfiguration of the tasman seaway and drake passage are necessary preconditions for the formation of a strong coherent acc

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

a near field sea level record of east antarctic ice sheet instability from 32 to 27 myr 1 fossil facies and isotope analyses of an early high paleolatitude 55 s section suggests a highly unstable east antarctic ice sheet from 32 to 27 myr the waxing and waning of this ice sheet from 140 to 40 of its present volume caused sea level changes of 25 m ranging from 30 to 50 m related to periodic glacial 100 000 to 200 000 years and shorter interglacial events the near field gippsland sea level gsl curve shares many similarities to the far field new jersey sea level njsl estimates however there are possible resolution errors due to biochronology taphonomy and paleodepth estimates and the relative lack of lowstand deposits in njsl that prevent detailed correlations with gsl nevertheless the lateral variations in sea level between the gsl section and njsl record that suggest ocean siphoning and antisiphoning may have propagated synchronous yet variable sea levels

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

high resolution record of export production in the eastern equatorial pacific across the eocene oligocene transition and relationships to global climatic records 1 understanding changes in export production through time provides insight into the response of the biological pump to global climate change particularly during periods of rapid climate change in this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the eocene oligocene transition eot in addition we consider if these export production variations are dominantly controlled by orbitally driven climate variability to accomplish these objectives we report changes in export production in the eastern equatorial pacific eep from site u1333 across the eot reconstructed from a high resolution record of marine barite accumulation rates bar bar fluctuations suggest synchronous declines in export production associated with the two step increases in oxygen isotopes that define the transition the reduction in productivity across the eot suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition we also report a previously undocumented peak in eep export productivity before the eot onset this peak is consistent with export production proxies from the southern ocean potentially implying a global driver for this precursor event we propose that this enhanced export production and the associated carbon sequestration in the late eocene may have contributed to the pco2 drawdown at the onset of antarctic glaciation

a potential barrier to deep antarctic circumpolar flow until the late miocene the central scotia sea located between the south american and antarctic plates is an integral part of the marine conduit that permits eastward deep water flow from the pacific ocean to the atlantic ocean the geologic history of the central scotia sea is therefore critical for a full understanding of the initiation and subsequent evolution of the complete deep antarctic circumpolar current widely believed to have been a key factor in the history of antarctic glaciation here we present new evidence on the nature and age of the central scotia sea floor multibeam surveys and the first dredged samples indicate that a now submerged remnant volcanic arc may have formed a barrier to deep eastward oceanic circulation until after the mid miocene climatic optimum inception and development of a full deep antarctic circumpolar current may therefore have been important not in the drop in global temperatures at the eocene oligocene boundary as long surmised but in the subsequent late miocene global cooling and intensification of antarctic glaciation

links between iron input and opal deposition in the pleistocene equatorial pacific ocean iron is often a limiting nutrient in ocean regions that have a constant supply of other macro nutrients and changes in iron supply over time have been linked to fluctuations in primary productivity marine sediments from the equatorial pacific ocean show that over the past million years iron input was linked to the export and burial of biogenic silica

onset and role of the antarctic circumpolar current for some time onset of the antarctic circumpolar current acc was considered to have caused or stabilised full antarctic glaciation recently however the importance of the acc in this role has been questioned in order to understand the relationship between the acc and antarctic glaciation and thence the importance of ocean circulation to palaeoclimate we need to determine the development history of both processes to this end we summarise all published estimates of acc onset the time of onset of shallow circulation or deep is uncertain whether based on tectonic studies or the interpretation of changes in the sediment record two potential final barriers to circumpolar flow have been identified south of tasmania and south of south america the former is well constrained by tectonics and marine geology to before 32 ma for a deep gap with a shallow gap in place by 35 5 ma at the latest these ages fit nicely with the onset of full antarctic glaciation at 33 34 ma although some workers question the causality estimates of the time of opening of the latter range widely whether based on tectonics or sedimentary geology from as recently as 6 ma to as early as 41 ma with the gap depth uncertain also resolution of the tectonics based uncertainties by additional survey being most probably both time consuming and inconclusive and the geological estimates being open to alternative interpretations we define an optimal strategy for additional sampling and measurement designed to resolve the time of onset more certainly possibly also resolving between deep and shallow opening and thereby constraining the acc role sample sites would have to be close to likely final barriers to avoid extraneous influence and within modern zones of acc influence ideally would form a depth transect and would have continuous mixed terrigenous and biogenic sections a wide range of carefully selected parameters would be measured at each r 2007 elsevier ltd all rights reserved

regional differences in pelagic productivity in the late eocene to early oligocene a comparison of southern high latitudes and lower latitudes paleoproductivity patterns at the eocene oligocene boundary in southern high latitudes and in the equatorial oceans were synthesized from the literature three odp dsdp sites from the southern ocean sites 689 748 and 511 were compared with three dsdp odp sites from the equatorial oceans sites 574 462 and 959 paleoproductivity was estimated by multiple sedimentological biological and geochemical proxies changes in paleoproductivity at the eocene oligocene boundary mainly took place in the southern high latitudes at site 689 the benthic foraminiferal fauna also indicates an increase in seasonality in equatorial oceans there are no indications for a shift to higher paleoproductivity at the eocene oligocene boundary on the contrary at site 959 sedimentology documents decreasing paleoproductivity in the oligocene major changes in temperature and ocean circulation in southern high latitudes versus only minor changes in the lower latitudes were probably responsible for the geographically different changes in paleoproductivity d 2004 elsevier b v all rights reserved

productivity and sea surface temperature changes recorded during the late eocene early oligocene at dsdp site 511 south atlantic this study investigates paleoenvironmental changes during the eocene oligocene transition eot at deep sea drilling project dsdp site 511 south atlantic as inferred from lipid biomarker long chain diols alkenones and calcareous nannofossil accumulation rates as well as changes in sedimentation regime i e relative contributions of total organic carbon toc calcium carbonate and biogenic silica sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 indicate a progressive but significant cooling 8 c from 34 5 ma to 33 6 ma consistent with estimates derived from other temperature proxies tex86 18o at the same site and for the same time interval this cooling is associated with a marked increase in primary productivity as indicated by high accumulation rates of biogenic silica toc alkenones long chain diols and calcareous nannofossils together these results are consistent with an enhancement of upwelling conditions favorable to the development of siliceous organisms at dsdp site 511 possibly induced by the oi 1 glaciation in antarctica that occurred during this period

coupled climate impacts of the drake passage and the panama seaway tectonically active gateways between ocean basins have modified ocean circulation over earth history today the atlantic and pacific are directly connected via the drake passage which forms a barrier to the time mean geostrophic transport between the subtropics and antarctica in contrast during the warm early cenozoic era when antarctica was ice free the drake passage was closed instead at that time the separation of north and south america provided a tropical seaway between the atlantic and pacific that remained open until the isthmus of panama formed in the relatively recent geological past ocean circulation models have previously been used to explore the individual impacts of the drake passage and the panama seaway but rarely have the two gateways been considered together and most explorations have used very simple atmospheric models here we use a coupled ocean ice atmosphere model gfdl s cm2mc to simulate the impacts of a closed drake passage both with and without a panama seaway we find that the climate response to a closed drake passage is relatively small when the panama seaway is absent similar to prior studies although the coupling to a dynamical atmosphere does increase the temperature change however with a panama seaway closing drake passage has a much larger effect due to the cessation of deep water formation in the northern hemisphere both gateways alter the transport of salt by ocean circulation with the panama seaway allowing fresh pacific water to be imported to the north atlantic and the drake passage preventing the flow of saline subtropical water to the circum antarctic a flow that is particularly strong when the panama seaway is open thus with a panama seaway and a closed drake passage the southern ocean tends to be relatively salty while the north atlantic tends to be relatively fresh such that the deep ocean is ventilated from the circum antarctic ensuing changes in the ocean heat transport drive a bi polar shift of surface ocean temperatures and the intertropical convergence zone migrates toward the warmer southern hemisphere the response of clouds to changes in surface ocean temperatures amplifies the climate response resulting in temperature changes of up to 9 c over antarctica even in the absence of land ice feedbacks these results emphasize the importance of tectonic gateways to the climate history of the cenozoic and support a role for ocean circulation changes in the glaciation of antarctica

chains clumps and strings magnetofossil taphonomy with ferromagnetic resonance spectroscopy magnetotactic bacteria produce intracellular crystals of magnetite or greigite the properties of which have been shaped by evolution to maximize the magnetic moment per atom of iron intracellular bacterial magnetite therefore possesses traits amenable to detection by physical techniques typically narrow size and shape distributions single domain size and arrangement in linear chains and often crystal elongation past strategies for searching for bacterial magnetofossils using physical techniques have focused on identifying samples containing significant amounts of single domain magnetite or with narrow coercivity distributions searching for additional of traits would however increase the likelihood that candidate magnetofossils are truly of biological origin ferromagnetic resonance spectroscopy fmr is in theory capable of detecting the distinctive magnetic anisotropy produced by chain arrangement and crystal elongation here we present analyses of intact and lysed magnetotactic bacteria dilutions of synthetic magnetite and sedimentary samples of modern carbonates from the great bahama bank oligocene miocene deep sea muds from the south atlantic and pleistocene lacustrine deposits from mono basin california we demonstrate that fmr can distinguish between intact bacterial magnetite chains collapsed chains and linear strings of magnetite formed by physical processes we also show that sediments in which the magnetization is likely carried by bacterial magnetite have fmr spectra resembling those of intact or altered bacterial magnetite chains