late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

reflection of linear internal tides from realistic topography the tasman continental slope abstractthe reflection of a low mode internal tide on the tasman continental slope is investigated using simulations of realistic and simplified topographies the slope is supercritical to the internal tide which should predict a large fraction of the energy reflected however the response to the slope is complicated by a number of factors the incoming beam is confined laterally it impacts the slope at an angle there is a roughly cylindrical rise directly offshore of the slope and a leaky slope mode wave is excited these effects are isolated in simulations that simplify the topography to separate the incident from the reflected signal a response without the reflector is subtracted from the total response to arrive at a reflected signal the real slope reflects approximately 65 of the mode 1 internal tide as mode 1 less than two dimensional linear calculations predict because of the three dimensional concavity of the topography it is also less than recent glider estimates likely as a result o

orbitally forced climate signals in mid pliocene nannofossil assemblages downcore cyclic variation in high resolution nannofossil abundance records from mid pliocene equatorial atlantic odp sites 662 and 926 demonstrate the direct response by several pliocene taxa notably discoaster sphenolithus and florisphaera profunda to orbitally forced climatic variation in particular these records display strong obliquity and precessional signals reflecting primarily high latitude southern hemisphere changes influencing upwelling intensity and local low latitude insolation driven climatic changes via the productivity and or turbidity influence of amazon sourced terrigenous material at sites 622 and 926 respectively in seasonal studies of coccolithophorid assemblages only part of the variation observed can be explained by abiotic processes so it is perhaps not surprising that in this study few pliocene nannofossil taxa demonstrate significant correlations with each other or with physical environmental parameters only some variance in nannofossil abundances can be explained by the primary controls of temperature and productivity the rest is attributed to nonlinear responses to climatic changes biotic processes such as grazing predation viral infection and competition and or abiotic factors for which there is no readily available proxy e g salinity the lack of strong consistent intra and inter relationships of the nannoflora and the environment reflects an ecologically complex differentiated original community producing a complex integrated signal transmitted into the fossil record

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

evidence for an earliest oligocene ice sheet on the antarctic peninsula there is growing consensus that development of a semipermanent ice sheet on antarctica began at or near the eocene oligocene e o boundary beyond ice rafted debris in oceanic settings however direct evidence for a substantial ice sheet at this time has been limited and thus far restricted to east antarctica it is unclear where glacier ice first accumulated and how extensive it was on the antarctic continent in the earliest oligocene sediments at the top of the eocene marine shelf section on seymour island antarctic peninsula include glacial marine deposits and a lodgment till with clasts derived from a variety of rock units on the peninsula dinoflagellate biostratigraphy and strontium isotope stratigraphy indicate an age at or very close to the e o boundary glacier ice extending to sea level in the northern peninsula at this time suggests the presence of a regionally extensive west antarctica ice sheet and thus an even more dramatic response to the forcing factors that facilitated high latitude ice expansion in the earliest oligocene

eocene oligocene global climate and sea level changes st stephens quarry alabama we integrate upper eocene lower oligocene lithostratigraphic magnetostratigraphic biostratigraphic stable isotopic benthic foraminiferal faunal downhole log and sequence stratigraphic studies from the alabama st stephens quarry ssq core hole linking global ice volume sea level and temperature changes through the greenhouse to icehouse transition of the cenozoic we show that the ssq succession is dissected by hiatuses associated with sequence boundaries three previously reported sequence boundaries are well dated here north twistwood creek cocoa 35 4 35 9 ma mint spring red bluff 33 0 ma and bucatunna chickasawhay the mid oligocene fall ca 30 2 ma in addition we document three previously undetected or controversial sequences midpachuta 33 9 35 0 ma shubuta bumpnose lowermost oligocene ca 33 6 ma and byram glendon 30 5 31 7 ma an 0 9 18 o increase in the ssq core hole is correlated to the global earliest oligocene oi1 event using magnetobiostratigraphy this increase is associated with the shubutabumpnose contact an erosional surface and a biofacies shift in the core hole providing a fi rst order correlation between ice growth and a sequence boundary that indicates a sea level fall the 18 o increase is associated with a eustatic fall of 55 m indicating that 0 4 of the increase at oi1 time was due to temperature maximum 18 o values of oi1 occur above the sequence boundary requiring that deposition resumed during the lowest eustatic lowstand a precursor 18 o increase of 0 5 33 8 ma mid chron c13r at ssq correlates with a 0 5 increase in the deep pacifi c ocean the lack of evidence for a sea level change with the precursor suggests that this was primarily a cooling event not an ice volume event eocene oligocene shelf water temperatures of 17 19 c at ssq are similar to modern values for 100 m water depth in this region our study establishes the relationships among ice volume 18 o and sequences a latest eocene cooling event was followed by an earliest oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall

evidence for annual records of phytoplankton productivity in the kimmeridge clay formation coccolith stone bands upper jurassic dorset uk the upper jurassic kimmeridge clay formation is a c org rich sequence of mudrocks that was deposited in a dysoxic basin which served unusually to preserve primary coccolithophorid proportions strikingly contrasting within this dark coloured formation are the white coccolith stone bands which contain pristinely preserved coccolithophorid assemblages preserving potentially primary coccolithophorid abundances with minimal diagenetic alteration using methodology described herein scanning electron microscopy sem observation of mum scale laminae within selected stone bands has revealed five distinctive types of microlamina type 1 being barren clay type 2 comprising coccoliths associated with varying amounts of clay or amorphous organic matter type 3 being purely coccolithic type 4 being of putative microbial origin and type 5 containing frequent calcispheres these are all described and illustrated here illustrated sequences of these are discussed with reference to an hypothetical model sequence based on modem records representing a kimmeridgian year of coccolithophorid productivity annual signals are thus interpreted based on the observations presented here and including summaries of the palynomorph records from the stone bands we comment on watznaueriacean palaeoecology and particularly the interpretation of watznaueria fossacincta barnesiae as an opportunistic growth maximising taxon c 2004 elsevier b v all rights reserved

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

the eocene oligocene preglacial glacial transition in the atlantic sector of the southern ocean odp site 690 abstract high resolution interdisciplinary analyses of the clay and coarse 40 m fractions of odp leg 113 site 690 eocene oligocene sediments on the flank of the maud rise provide information on paleoproductivity water masses paleoclimate and erosion in the antarctic range as well as on the cyclicity of these processes three time intervals are distinguished 1 1 the middle eocene characterized by a nearly pure smectites b productivity varying between relatively high values in the 42 44 ma interval to very low values after 42 ma and c cyclic variations which correspond to changes in clay mineral associations a warm saline deep water mass is inferred to have protected carbonate shells against dissolution at site 690 we interpret the abundant mica in the coarse fraction as distributed by intermediate currents 2 2 the latest middle eocene late eocene characterized by low productivity values increasing with time kaolinite and illite concentrations also increase since the middle late eocene boundary mixing in the water column which starts during a cooling event causes similar clay mineral assemblages at site 690 and at site 689 on top of maud rise 3 3 the oligocene separated from the eocene by a hiatus is characterized by high productivity highly increased amounts of illite and other minerals originating from erosion and physical weathering of antarctica and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400 450 kyr cyclicity six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a proto aabw type

sea level and climate signatures recorded in orbitally forced continental margin deposits over the last 1 myr new perspectives from the bohai sea abstract sediment accumulation in continental margins during the quaternary period was substantially influenced by both sea level fluctuations and climate changes however the response of sediment accumulation to these changes on an orbital timescale remains poorly understood for two main reasons the scarcity of sedimentary records with a high resolution chronology and the difficulty in distinguishing the role of sea level from regional climate signals here we present the results of sediment color reflectance c grain size and total organic carbon toc content of core bh08 212 4 m in length spanning the last 1 myr recovered from the bohai sea china the chronology of core bh08 on the orbital timescale is constrained by both magnetostratigraphy and astronomical tuning sedimentary facies analysis suggests that the sedimentary sequence is dominated by the alternation of a deltaic system and floodplain deposition principal components analysis of the grain size data reveals two principal components pcs including pc1 reflecting the 31 500 m fraction and pc2 reflecting the 18 66 m fraction comparison of sample scores on pc1 pc2 and c with the alternation of sedimentary environments reveals that pc1 and c reflect cycles of deltaic and floodplain deposition at 100 kyr and 40 kyr periodicities while pc2 exhibits a 20 kyr periodicity in addition to the 100 kyr and 40 kyr cycles we infer that pc1 and c are mainly sea level dependent whereas pc2 is controlled by the combination of changes in monsoon climate and sea level we suggest that milankovitch scale monsoon climate fluctuations controlled the sediments supply to the bohai sea during the last 1 myr while the redistribution of sediments by marine processes e g tidal currents has partially obscured the monsoonal signal in the grain size proxy e g pc1 which instead is sensitive to sea level change our results provide an example of the influence of climate and sea level on sediment accumulation in a shallow continental margin setting influenced by monsoonal climate in an icehouse world

calibration between eustatic estimates from backstripping and oxygen isotopic records for the oligocene eustatic estimates from the backstripping of oligocene sections are compared quantitatively with d 18 o data each of the nine oligocene d 18 o events maxima identified in previous studies correlates with a stratigraphically determined sea level lowstand oxygen isotopic records from planktonic foraminifers from western equatorial atlantic ocean drilling program odp site 929 indicate an isotopic increase of 0 16 per 10 m decrease in the depth of the ocean apparent sea level asl amplitudes of asl change also correlate with moderate and high resolution benthic foraminiferal d 18 o records from odp sites 803 western tropical pacific and 929 and from deep sea drilling project dsdp site 522 south atlantic ocean with an isotopic change of 0 22 per 10 m of asl change r 2 5 0 807 and 0 960 respectively and with records from odp site 689 southern ocean 0 13 per 10 m of asl change r 2 5 0 704 this correlation suggests that southern ocean deep water temperature changes were smaller than tropical sea surface temperature changes between million year scale glacials and interglacials it also suggests that the deep sea southern ocean records may provide the best means to calibrate sea level to oxygen isotopes

changes in calcareous nannofossil assemblages during the middle eocene climatic optimum clues from the central western tethys alano section ne italy we present a study focused on changes in calcareous nannofossil assemblages of the alano section during the middle eocene climatic optimum meco this warming event is characterized by a prominent perturbation both in oxygen and carbon stable isotopes around the chron c18r c18n transition ca 40 ma and lasting ca 500 600 kyr semi quantitative analyses on calcareous nannofossil assemblages have been carried out our results show that the meco interval coincides with a significant shift in the relative abundance of calcareous nannofossil taxa suggesting a relationship between biotic changes and stable isotope shifts paleoecological studies at species level and or based on morphometric criteria i e small placoliths sometimes show the opposite behaviour between changes observed at the genus level and those observed at lower taxonomic levels for instance a taxon thought to be better adapted to oligotrophic warm waters e g sphenolithus shows a prominent decrease if analyzed at genus level but an increase was instead recorded for s spiniger moreover taxa preferentially thriving in eutrophic cold waters as for instance small reticulofenestrids increase remarkably in abundance during this warming phase while medium large placoliths do not show any significant trend an increase in reworked mainly cretaceous specimens is also observed during the meco these lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea surface waters suggesting that an enhanced nutrient availability could have driven the make up of the calcareous nannofossil assemblages the increase in reworking may indicate an increase in terrigenous input due to increased chemical weathering likely produced by an enhanced hydrological cycle

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

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

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

paleoenvironmental evolution in a high stressed cold seep system vicchio marls miocene northern apennines italy abstract excellent exposures of miocene seep carbonates enclosed in marine marly sediments vicchio outcrops in the northern apennines italy offer the opportunity to highlight the evolution of a fossil seep ecosystem and the response of benthic communities to high stressed environmental conditions for this purpose seep related facies and molluscs within carbonate bodies have been studied coupled with benthic foraminiferal assemblages and carbon and oxygen isotopes in the enclosing marls the integrated planktonic foraminiferal and calcareous nannofossil biostratigraphy has allowed us to constrain the seepage within well calibrated bioevents and to stress the relationships with paleoclimatic and paleoceanographic variations during the middle miocene in the mediterranean area our biostratigraphic data indicate that the onset of the seepage approximates the mi3b cooling event 13 82 ma and the seepage system lasts for 400 kyr the evolution of the vicchio cold seep system passes through four phases 1 the onset of the seepage characterized by a pervasive flow of methane rich fluids is inferred by 13c depletion of marly sediments and by prevailing benthic foraminifera indicative of suboxic conditions at the sea floor 2 the methane flow becomes focused causing the precipitation of wide pinnacle like carbonate bodies which contain giants lucinids enclosing marls indicate well oxygenated conditions possibly enhanced by paleoceanographic variations connected to the mi3b cooling event 3 the appearance of the vesicomyid christineconcha cf c regab and the absence of lucinids in seep carbonates suggest stable methane rich fluid emissions higher flow rates locally favoured the flourishment of bacterial mats benthic foraminifera show abundance peaks of organic matter depending taxa 4 the reduced intensity of methane rich fluid flows favours the precipitation of stratiform carbonate bodies along strike the macrofauna is characterized by the presence of both vesicomyidae and giant lucinids foraminiferal assemblages in the enclosing marls indicate the restoration of well oxygenated conditions

biogeographic gradients of middle eocene oligocene calcareous nannoplankton in the south atlantic ocean middle eocene oligocene calcareous nannoplankton have been analyzed quantitatively for eight dsdp and odp sites ranging from the equatorial zone to 65 s latitude in the south atlantic ocean there is a general decrease in calcareous nannoplankton species diversity from the middle eocene through the oligocene and species diversity also decreases towards the higher latitudes similar to findings of other studies the drop of the species diversity of calcareous nannoplankton across the eocene oligocene boundary is not drastic delineation of latitudinal distribution patterns of individual species or groups and r mode cluser analysis permit the classification of warm water taxa coccolithus formosus discoasters helicosphaerids and sphenoliths temperate water taxa coccoliths pelagicus cyclicargoliths floridanus group reticulofenestra bisecta reticulofenestra samodurovii reticulofenestra umbilica and cool water taxa chiasmoliths isthmolithus recurvus and reticulofenestra daviesii the abundance of warm water taxa plummets whereas the abundance of cool water taxa sharply increases across the eocene oligocene boundary at the middle and high latitude sites reflecting a profound cooling event in these areas polar ordination and similarity analyses reveal that steep latitudinal biogeographic gradients had been established at least by the middle eocene the gradient greatly increases near the eocene oligocene boundary indicating more severe and permanent cooling at the high latitudes the biogeographic gradient data of this study conflict with the widely accepted inference from the oxygen isotopic data that the thermal gradients between mid latitudes and high latitudes are low or nearly flat for the paleogene oceans lower surface water salinities in the high latitudes may have lowered the 18o values of the planktonic microfossils but apparently did not have significant effect on latitudinal distribution patterns of calcareous nannoplankton which offers an independent means for estimating latitudinal thermal gradients

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

evolution of deep sea sediments across the paleocene eocene and eocene oligocene boundaries abstract the composition and distribution of deep sea sediments is the result of a multitude of climatic biotic and oceanic conditions relating to biogeochemical cycles and environmental change here we utilize the extensive sediment archives of the international ocean discovery program iodp and its predecessors to construct maps of deep sea sediment type across two critical but contrasting boundaries in the paleogene one characterised by an interval of extreme warmth paleocene eocene and the other by global cooling eocene oligocene ocean sediment distribution shows significant divergence both between the latest paleocene and paleocene eocene thermal maximum petm across the eocene oligocene transition eot and in comparison to modern sediment distributions carbonate sedimentation in the latest paleocene extends to high southern latitudes disappearance of carbonate sediments at the petm is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon cycle perturbation biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early paleogene ocean in the southern ocean we attribute the low in biosiliceous burial to the warm deep water temperatures which would have impacted biogenic silica preservation in the late eocene our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial pacific enhanced biosiliceous deposits in the late eocene equatorial pacific and south atlantic are due to increased productivity and the spin up of the oceans our compilation documents the enhanced global carbonate sedimentation in the early oligocene confirming that the drop in the carbonate compensation depth was global

tidal energy loss internal tide radiation and local dissipation for two layer tidal flow over a sill abstracta simple analytical model for tidal energy loss at fjord sills and its partitioning into local dissipation and radiated internal tides is presented the analytical model builds on a two layer assumption with quasi steady nonlinear flow over the sill and wave radiation in the far field when the interface is situated above sill level upstream and downstream propagating internal waves are generated as the bottom layer flow becomes partially blocked because of a hydraulic control over the sill when this control sets in energy is lost in the transition from supercritical flow over the sill to subcritical flow downstream of the sill the analytical model is compared with observations at the drobak sill in the oslo fjord and with idealized numerical simulations with a nonhydrostatic primitive equation model the overall good agreement between observations analytical model and numerical model results indicates that the hydraulic control over the sill is a key player for both the generation of inter

resonant amplification of subinertial tides in a submarine canyon 1 tidal oscillations dominate the flow field in many submarine canyons observations have shown that semidiurnal tidal energy in submarine canyons is significantly amplified with respect to adjacent shelves this amplification is thought to be caused by focusing of propagating internal tides incident from the open ocean or local in canyon generation on critical canyon floor slopes these mechanisms require freely propagating internal tides with superinertial frequencies we present results from a moored array in a canyon at 44 n where the observed velocities reached over 0 8 m s 1 the canyon flow field was highly unusual because it was dominated by the subinertial diurnal tide this occurred despite the fact that the barotropic tide was predominantly semidiurnal the diurnal tide was dramatically amplified in the canyon its velocities increasing toward the seafloor and canyon head the diurnal oscillations also exhibited marked modulation in time by the background barotropic forcing length scales suggest that the diurnal tide should be resonant in the canyon an analytical framework is used to explain the mechanisms behind the strong diurnal currents observed by the moored array in the model along shelf barotropic flow sets up a double kelvin wave response in the canyon generating along canyon velocities which are subsequently amplified by resonance the pattern of the model predictions is in excellent agreement with the observed velocity pattern

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

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

stepwise transition from the eocene greenhouse to the oligocene icehouse the eocene oligocene transition is the largest global cooling in the cenozoic period a comparison of three independent proxies from the continental shelf and deep ocean reveals a three step transition to cold glacial conditions with ice sheets 25 larger than their present size

tidal conversion and turbulence at a model ridge direct and large eddy simulations direct and large eddy simulations are performed to study the internal waves generated by the oscillation of a barotropic tide over a model ridge of triangular shape the objective is to go beyond linear theory and assess the role of nonlinear interactions including turbulence in situations with low tidal excursion number the criticality parameter defined as the ratio of the topographic slope to the characteristic slope of the tidal rays is varied from subcritical to supercritical values the barotropic tidal forcing is also systematically increased numerical results of the energy conversion are compared with linear theory and in laminar flow at low forcing they agree well in subcritical and supercritical cases but not at critical slope angle in critical and supercritical cases with higher forcing there are convective overturns turbulence and significant reduction as much as 25 of the radiated wave flux with respect to laminar flow results analysis of the baroclinic energy budget and spatial modal analysis are performed to understand the reduction the near bottom velocity is intensified at critical angle slope leading to a radiated internal wave beam as well as an upslope bore of cold water with a thermal front in the critical case the entire slope has turbulence while in the supercritical case turbulence originates near the top of the topography where the slope angle transitions through the critical value the phase dependence of turbulence within a tidal cycle is examined and found to differ substantially between the ridge slope and the ridge top where the beams from the two sides cross

bryozoan beds in northern italy as a shallow water expression of environmental changes during the oligocene isotope event 1 abstract shifts in carbonate producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm the shallow marine calcare di nago formation exposed in the san valentino section northern italy covers the late eocene and earliest oligocene the succession is characterized by the occurrence of light dependent biota such as coralline algae and larger benthic foraminifera in the uppermost part of the section however the fossil association is dominated by bryozoans which are filter feeder organisms this ca 12 m thick interval locally contains up to 86 bryozoans while coralline algae as well as larger benthic foraminifera are absent coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds whereas orthophragminids do not recover the gradual disappearance of larger foraminifera and coralline algae within the bryozoan dominated deposits is coeval with a pronounced positive shift in 13c based on its biostratigraphic position this positive shift is interpreted to be linked to the positive shift in 13c recognized in deep sea records shortly above the eocene oligocene boundary which in turn is associated to the positive shift in 18o leading to the oi 1 oligocene isotope event 1 cooling phase total phosphorus content increases in the bryozoan beds suggesting enhanced nutrient supply to the neritic ecosystem this phosphorous peak is coeval with the globally recognized increment in ocean productivity around the oi 1 and 13c positive shift thus disappearance of light dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower sea surface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters resulting from enhanced primary productivity as bryozoan beds occur in several italian localities around the eocene oligocene boundary they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice house earth

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

energetics of barotropic and baroclinic tides in the monterey bay area abstracta detailed energy analysis of the barotropic and baroclinic m2 tides in the monterey bay area is performed the authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy this approach is implemented in the stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans results from three dimensional high resolution suntans simulations are analyzed to estimate the tidal energy partitioning among generation radiation and dissipation a 200 km 230 km domain including all typical topographic features in this region is used to represent the monterey bay area of the 152 mw energy lost from the barotropic tide approximately 133 mw 88 is converted into baroclinic energy through internal tide generation and 42 56

a simple parameterization of turbulent tidal mixing near supercritical topography abstract a simple parameterization for tidal dissipation near supercritical topography designed to be applied at deep midocean ridges is presented in this parameterization radiation of internal tides is quantified using a linear knife edge model vertical internal wave modes that have nonrotating phase speeds slower than the tidal advection speed are assumed to dissipate locally primarily because of hydraulic effects near the ridge crest evidence for high modes being dissipated is given in idealized numerical models of tidal flow over a gaussian ridge these idealized models also give guidance for where in the water column the predicted dissipation should be placed the dissipation recipe holds if the coriolis frequency f is varied as long as hn w f where n is the stratification h is the topographic height and w is a width scale this parameterization is not applicable to shallower topography which has significantly more dissipation because near critical processes dominate the observed turbul

remote impacts of the 18 6 year period modulation of localized tidal mixing in the north pacific 1 the impact of the 18 6 year period modulation of the localized strong tidal mixing on the annual mean sea surface temperature sst in the open north pacific ocean is analyzed in a numerical experiment using an ocean general circulation model oscillatory sst anomalies induced in this model move eastward along the boundary between the subarctic and the subtropical gyres from the western boundary to the central pacific in about 10 years with a speed slower than that of the surface currents anomalous currents in the upper 300 m play an important role in inducing sst anomalies these anomalous currents are coupled to subsurface density anomalies and could be related to eastward moving low mode second or higher baroclinic long rossby waves these results suggest that the 18 6 year modulation of localized strong tidal mixing can influence large scale sst and or heat flux and thus climate as a result of remote impacts associated with changes in the mid depth density structure induced locally where mixing is strong that move horizontally into the open ocean

preliminary simulations of internal waves and mixing generated by finite amplitude tidal flow over isolated topography much recent observational evidence suggests that energy from the barotropic tides can be used for mixing in the deep ocean here the process of internal tide generation and dissipation by tidal flow over an isolated gaussian topography is examined using two dimensional numerical simulations employing the mitgcm four different topographies are considered for five different amplitudes of barotropic forcing thereby allowing a variety of combinations of key nondimensional parameters while much recent attention has focused on the role of relative topographic steepness and height in modifying the rate of conversion of energy from barotropic to baroclinic modes here attention is focused on parameters dependent on the flow amplitude for narrow topography large amplitude forcing gives rise to baroclinic responses at higher harmonics of the forcing frequency tall narrow topographies are found to be the most conducive to mixing dissipation rates in these calculations are most efficient for the narrowest topography

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

post sampling dissolution and the consistency of nannofossil diversity measures a case study from freshly cored sediments of coastal tanzania abstract this study investigates the potentially deleterious effect of prolonged sample storage on the reliability of calcareous nannofossil species abundance and community diversity measures and their subsequent interpretation as paleoceanographic proxies nannofossil assemblages from two freshly cored successions of hemipelagic clay were documented over a one year period using a series of paired smear slides the first made from sediment samples within a day of coring and the second either 6 months or 1 year later diversity measured by shannon s h is consistent between the two sets for the majority of samples however significant changes both positive and negative were recorded in a number of cases and appear to be largely due to variations in smear slide thickness and not to post sampling dissolution there is no significant change in nannofossil fragmentation or abundance over time although the relative abundances of small dissolution susceptible placoliths of reticulofenestra minuta do appear to decrease with time in some samples counts of mineral grains show that there is a significant loss of fine 1 2 m cubic pyrite within months of drilling and this combined with the decline in abundance of r minuta suggests that limited pyrite oxidation coupled to carbonate dissolution is occurring geochemical analyses confirm that these sediments contain significant concentrations of sulphate one year after sample recovery which may be the result of gypsum formation associated with the oxidation of pyrite estimates of pyrite oxidation suggest that up to 3 of the original calcium carbonate has dissolved in the year after coring which could account for the observed loss of small placoliths effects of this kind are almost certainly confined to hemipelagic sequences rich in organic matter and or reduced iron but are frequently offset by the exceptional preservation of calcareous microfossils that can occur within such sediments

tidally forced lee waves drive turbulent mixing along the arctic ocean margins in the arctic ocean limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong however mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to arctic ocean state are poorly understood we present measurements from the shelf north of svalbard that show abrupt isopycnal vertical displacements of 10 50 m and intense dissipation associated with cross isobath diurnal tidal currents of 0 15 m s 1 energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water during a 6 hr turbulent event high frequency internal waves were present the full 300 m depth water column became turbulent dissipation rates increased by a factor of 100 and turbulent heat flux averaged 15 w m 2 compared with the background rate of 1 w m 2 plain language summary turbulent mixing in the arctic ocean water column affects sea ice variability through transport of subsurface heat toward the surface this turbulent mixing is concentrated along the margins mainly driven by tidal flow over sloping topography however processes of energy transfer from tides to turbulence in the arctic are poorly understood and the magnitudes and locations of mixing are poorly constrained here we present detailed measurements from the shelf north of svalbard showing a turbulent event driven by moderate tidal currents the energy is trapped and accumulated at the time of maximum downslope flow and is released at the turn of the tide when the entire water column becomes highly turbulent our observations imply that this process is an important source of mixing in the arctic ocean

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

shelf and open ocean calcareous phytoplankton assemblages across the paleocene eocene thermal maximum implications for global productivity gradients abrupt global warming and profound perturbation of the carbon cycle during the paleocene eocene thermal maximum petm ca 55 ma have been linked to a massive release of carbon into the ocean atmosphere system increased phytoplankton productivity has been invoked to cause subsequent co2 drawdown cooling and environmental recovery however interpretations of geochemical and biotic data differ on when and where this increased productivity occurred here we present high resolution nannofossil assemblage data from a shelf section the u s geological survey usgs drill hole at wilson lake new jersey and an open ocean location ocean drilling program odp site 1209 paleoequatorial pacific these data combined with published biotic records indicate a transient steepening of shelf offshelf trophic gradients across the petm onset and peak with a decrease in open ocean productivity coeval with increased nutrient availability in shelf areas productivity levels recovered in the open ocean during the later stages of the event which coupled with intensified continental weathering rates may have played an important role in carbon sequestration and co2 drawdown

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

double ridge internal tide interference and its effect on dissipation in luzon strait abstractluzon strait between taiwan and the philippines features two parallel north south oriented ridges the barotropic tides that propagate over these ridges cause strong internal waves and dissipation the energy dissipation mechanisms and the role of the baroclinic wave fields in this dissipation are investigated using numerical simulations with the massachusetts institute of technology general circulation model mitgcm the model is integrated over two dimensional configurations along a zonal transect at 20 6 n for a maximum duration of a spring neap cycle nearly all dissipation occurs at the steep ridge crests due to high mode turbulent lee waves with horizontal scales of several kilometers and vertical scales of hundreds of meters the spatial structure and timing of the predicted velocities and dissipation agree with observations and confirm the existence of these lee waves the lee wave strength is greatly affected by the internal waves generated at the other ridge when semidiurnal barotropic

calcareous nannofossils in extreme environments the messinian salinity crisis polemi basin cyprus the rapidly changing and extreme environmental conditions of the early messinian salinity crisis are reflected in abrupt variations in nannofossil assemblages within the messinian units kalavasos formation from the polemi basin during the messinian sedimentary and microfossil data indicate that the polemi basin was a semi enclosed shallow water basin subject to repeated influxes of marine and freshwater this is supported by the absence of many open marine nannoplankton e g discoaster and by the presence of neritic littoral and freshwater diatoms whilst calcareous nannoplankton are known to occupy near shore habitats they are rarely preserved in such environments due to terrigenous and clastic influx the shallow and eutrophic environments of the messinian polemi basin therefore provide an unusual opportunity to investigate which extinct nannofossil taxa occupied marginal marine environments nannoplankton diversity 3 to 11 species is low in comparison to the open ocean and the assemblages are extremely uneven with high dominance one of five species reticulofenestra minuta reticulofenestra antarctica helicosphaera carteri umbilicosphaera jafari and sphenolithus abies was observed to dominate in all of the assemblages these were broadly distributed marine species but capable of opportunistic behaviour salinity and nutrient levels are thought to be the primary factors controlling the overall nature of the nannoplankton assemblages using the associated diatom and sedimentological evidence we infer the palaeoecology of key nannofossil taxa and speculate on the palaeoenvironments of the messinian polemi basin r antarctica is thought to have dominated in normal salinity mesotrophic shallow water environments h carteri in shallow brackish eutrophic environments u jafari in hypersaline conditions r minuta in eutrophic conditions with an abnormal salinity from brackish to hypersaline and s abies in mesotrophic deeper and normal salinity environments d 2005 elsevier b v all rights reserved

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

piston core record of late paleogene 31 ma to recent seafloor hydrothermal activity in the southwest pacific basin a large diameter piston core containing 8 35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote southwest pacific basin 31 42 194 s 143 30 331 w 5082 m water depth providing unique insight into hydrothermal activity and eolian sedimentation there since the early oligocene a combination of fish teeth sr isotope stratigraphy and inaa geochemical data reveals an exponentially decreasing hydrothermal flux 31 ma to the present although hydrothermal sedimentation related to seafloor spreading explains this trend a complex history of late eocene early oligocene ridge jumps propagating rifts and plate tectonic reorganization of south pacific seafloor could have also played a role a possible hiatus in deposition as recorded by changes in core composition just below 2 m depth is beyond the resolution of the fish teeth sr isotope dating method employed here however the timing of this interval may be coincident with extinction of the pacific farallon ridge at 20 ma a low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth consistent with dust generating continental sources far to the west australia new zealand this is the first long term paleoceanographic record obtained from within the south pacific bare zone rea et al 2006 an anomalous region where pacific seafloor has largely escaped sediment accumulation since the late cretaceous

breaking of unsteady lee waves generated by diurnal tides 1 diapycnal mixing caused through breaking of large amplitude internal lee waves generated by sub inertial diurnal tides which are modulated with a 18 6 year period is hypothesized to be fundamental to both the intermediate layer ventilation and the bi decadal oscillation around the north pacific ocean the first observational evidence of such wave breaking is presented here the breaking wave observed had 200 m height and 1 km width and its associated diapycnal mixing was estimated to be 1 5 m2 s 1 with a temporal average 104 times larger than typical values in the open oceans our estimate suggests that a similar mixing process occurs globally particularly around the pacific and antarctic oceans

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

energy flux and dissipation in luzon strait two tales of two ridges abstractinternal tide generation propagation and dissipation are investigated in luzon strait a system of two quasi parallel ridges situated between taiwan and the philippines two profiling moorings deployed for about 20 days and a set of nineteen 36 h lowered adcp ctd time series stations allowed separate measurement of diurnal and semidiurnal internal tide signals measurements were concentrated on a northern line where the ridge spacing was approximately equal to the mode 1 wavelength for semidiurnal motions and a southern line where the spacing was approximately two thirds that the authors contrast the two sites to emphasize the potential importance of resonance between generation sites throughout luzon strait baroclinic energy energy fluxes and turbulent dissipation were some of the strongest ever measured peak to peak baroclinic velocity and vertical displacements often exceeded 2 m s 1 and 300 m respectively energy fluxes exceeding 60 kw m 1 were measured at spring tide at the wester

topographic form drag on tides and low frequency flow observations of nonlinear lee waves over a tall submarine ridge near palau abstracttowed shipboard and moored observations show internal gravity waves over a tall supercritical submarine ridge that reaches to 1000 m below the ocean surface in the tropical western pacific

internal hydraulic jumps and overturning generated by tidal flow over a tall steep ridge abstract recent observations from the hawaiian ridge indicate episodes of overturning and strong dissipation coupled with the tidal cycle near the top of the ridge simulations with realistic topography and stratification suggest that this overturning has its origins in transient internal hydraulic jumps that occur below the shelf break at maximum ebb tide and then propagate up the slope as internal bores when the flow reverses a series of numerical simulations explores the parameter space of topographic slope barotropic velocity stratification and forcing frequency to identify the parameter regime in which these internal jumps are possible theoretical analysis predicts that the tidally driven jumps may occur when the vertical tidal excursion is large which is shown to imply steep topographic slopes such that dh dxn 1 the vertical length scale of the jumps is predicted to depend on the flow speed such that the jump froude number is of order unity the numerical results agree with the theoreti

biotic signals from nannoflora across the iridium anomaly in the upper eocene of the massignano section evidence from statistical analysis abstract strong evidence for a major late eocene impact including an iridium rich layer and shocked quartz has been found in the massignano section central italy stratotype of the eocene oligocene boundary quantitative calcareous nannofossils analyses have been performed and classical and multivariate statistical techniques have been applied to assess the paleonvironmental effect of this impact on the nannoflora abundance patterns indicate 1 a warming episode just above the iridium layer 2 a subsequent slight cooling trend probably related to the global cooling during late eocene to early oligocene 3 marked fluctuations in the trophic resources and an increase in near shore taxa in the upper part of the interval 4 increase in low nutrient taxa in biotite rich layers just above the iridium level possibly related to lowered productivity linked to volcanic activity all these signals appear most likely to be the result of long term climatic changes rather than to short term effects of extraterrestrial impact in addition cluster analysis was performed on the assemblage data this delineated similarities among different taxa and grouped samples with similar assemblages several groups related to temperature trophic and unknown preference conditions have been distinguished a consistent difference in the abundances of the taxa and in their correlation has been detected between samples above and below the iridium level this change appears to be related to two important sedimentary features which are found in the interval above the iridium occurrence 1 the presence of biotite rich layers linked to increasing volcanism and 2 a conspicuous color transition from reddish to greenish related to changes in sedimentary environments e g variations in trace element abundance these environmental changes rather than the impact may have affected the nannoflora assemblages

pacific abyssal transport and mixing through the samoan passage versus around the manihiki plateau abstractthe main source feeding the abyssal circulation of the north pacific is the deep northward flow of 5 6 sverdrups sv 1 sv 106 m3 s 1 through the samoan passage a recent field campaign

eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica paleoecological and paleoceanographic implications abstract the evolution of the southern ocean climate during the late eocene late oligocene interval is examined through high resolution quantitative calcareous nannofossil analyses on samples from the southern ocean sections on maud rise and kerguelen plateau we determined the abundance patterns of the counted species to clarify the biostratigraphy which we correlated with high resolution magnetostratigraphy roberts a p bicknell s j byatt j bohaty s m florindo f harwood d m 2003a magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 in florindo f cooper a k o brien p a eds antarctic cenozoic palaeoenvironments geologic record and models palaeogeogr palaeoclimatol palaeoecol 198 145 168 florindo f roberts a p in press eocene oligocene magnetobiochronology of odp sites 689 and 690 maud rise weddell sea antarctica geol soc am bull and used this data to interpret paleoceanographic changes through the late eocene to late oligocene percentage plots of the individual species compared with r mode principal component and cluster analysis results allowed us to divide the assemblages into three groups temperate water taxa cool water taxa and no temperature affinity taxa we attempt correlations between these paleoecological groups and the major sea surface temperature sst variations with tectonic and paleoceanographic changes in the southern ocean during the late eocene the nannofossil assemblage data reveal that there were several minor sst decreases coolings from 36 to 34 ma before the eocene oligocene e o boundary a sharp cooling event dated at 33 54 ma earliest oligocene occurred about 160 kyr after the e o boundary which is dated at 33 7 ma relatively stable cool conditions are interpreted to persist until the latest oligocene when an increase in abundance of temperate water taxa which corresponds to an antithetical decrease in abundance of cool water indicators is recorded on the basis of our dating the opening of the drake passage allowing shallow water circulation began by 33 54 ma at the latest while the establishment of deep water connections through the tasmanian gateway occurred at 33 ma as suggested by exon et al proc odp init rep 189 2001 1

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

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

the influence of subinertial internal tides on near topographic turbulence at the mendocino ridge observations and modeling abstractshipboard measurements of velocity and density were obtained in the vicinity of a small channel in the mendocino ridge where flows were predominantly tidal measured daily inequalities in transport are much greater than those predicted by a barotropic tide model with the strongest transport associated with full depth flows and the weakest with shallow surface confined flows a regional numerical model of the area finds that the subinertial k1 diurnal tidal constituent generates topographically trapped waves that propagate anticyclonically around the ridge and are associated with enhanced near topographic k1 transports the interaction of the baroclinic trapped waves with the surface tide produces a tidal flow whose northward transports alternate between being surface confined and full depth full depth flows are associated with the generation of a large amplitude tidal lee wave on the northward face of the ridge while surface confined flows are largely nonturbulent the regional model demons

observations of diurnal coastal trapped waves with a thermocline intensified velocity field abstractusing 18 days of field observations we investigate the diurnal d1 frequency wave dynamics on the tasmanian eastern continental shelf at this latitude the d1 frequency is subinertial an

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

internal tide convergence and mixing in a submarine canyon abstractobservations from eel canyon located on the north coast of california show that elevated turbulence in the full water column arises from the convergence of remotely generated internal wave energy the incoming semidiurnal and bottom trapped diurnal internal tides generate complex interference patterns the semidiurnal internal tide sets up a partly standing wave within the canyon due to reflection at the canyon head dissipating all of its energy within the canyon dissipation in the near bottom is associated with the diurnal trapped tide while midwater isopycnal shear and strain is associated with the semidiurnal tide dissipation is elevated up to 600 m off the bottom in contrast to observations over the flat continental shelf where dissipation occurs closer to the topography slope canyons are sinks for internal wave energy and may have important influences on the global distribution of tidally driven mixing

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

antarctic control on tropical indian ocean sea surface temperature and hydrography 1 we reconstructed the surface hydrography of the south equatorial current in the western indian ocean for the last 65 000 years using a marine sediment core record results show that tropical indian ocean temperatures resemble temperatures from antarctic ice cores with warm and cold fluctuations synchronous with the antarctic cold reversal and the antarctic warm events a1 a4 the most likely thermal link involves subantarctic mode water samw which forms north of the subpolar frontal zone and spreads northward into the indian ocean this subsurface water mass is the prime suspect because of a stronger temperature response in the thermocline recorded by the foraminifer n dutertrei than in surface water g ruber

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

the eocene oligocene transition changes in sea level temperature or both abstract the eocene oligocene transition eot 34 ma reflects the onset of major antarctic glaciation the primary geochemical signature of the eot is two 300 kyr spaced shifts in increasing deep sea oxygen isotope values possibly reflecting both global cooling and or increasing ice volume a way to assess the respective contribution of continental ice is to quantify concomitant glacio eustatic sea level change this is usually expressed in relatively shallow marine depositional settings one potentially suitable region is in the vicentinian alps ne italy where marginal marine deposits document sea level changes during the eot by correlating stable isotope bio and magnetostratigraphic information between three distant regions we are able to relate the shallow marine sections to the pacific oxygen isotope record from ocean drilling program odp site 1218 of coxall et al 2005 microfacies sedimentological and biotic analysis suggests that associated with the first isotope shift eot 1 sea level fell 20 m and with the ultimate shift the oligocene isotope event 1 oi 1 sea level fell some 50 60 m distribution patterns of temperature sensitive dinoflagellates from a coeval central italian section reveal that the early stages of the eot were accompanied by sea surface cooling whereas no sustained cooling is noted in association with the oi 1 this suggests that the initial eot shift s reflect a mixed signal of ice volume and temperature whereas the oi 1 primarily reflects expansion of the antarctic cryosphere

sustained full water column observations of internal waves and mixing near mendocino escarpment abstract the relative strength and spatiotemporal structure of near inertial waves niw and internal tides it are examined in the context of recent moored observations made 19 km south of mendocino escarpment an abrupt ridge step feature in the eastern pacific in addition to strong internal tide generation steps and ridges give rise to the possibility of shadowing wherein near inertial energy is prevented from reaching depths beneath a characteristic intersecting the ridge top a combination of two moored profilers and a long range acoustic doppler current profiler adcp yielded velocity and shear measurements from 100 to 3640 m 60 m above bottom and isopycnal depth strain and overturn inferred turbulence dissipation rate from 1000 to 3640 m sampling intervals 20 min in the upper 1000 m and 1 5 h below that were fast enough to minimize aliasing of higher frequency internal wave motions the 67 day long record is easily sufficient to isolate niw and it via bandpass filtering and to capture

tidally driven processes leading to near field turbulence in a channel at the crest of the mendocino escarpment abstractin situ observations of tidally driven turbulence were obtained in a small channel that transects the crest of the mendocino ridge a site of mixed diurnal and semidiurnal tides diurnal tides are subinertial at this latitude and once per day a trapped tide leads to large flows through the channel giving rise to tidal excursion lengths comparable to the width of the ridge crest during these times energetic turbulence is observed in the channel with overturns spanning almost half of the full water depth a high resolution nonhydrostatic 2 5 dimensional simulation is used to interpret the observations in terms of the advection of a breaking tidal lee wave that extends from the ridge crest to the surface and the subsequent development of a hydraulic jump on the flanks of the ridge modeled dissipation rates show that turbulence is strongest on the flanks of the ridge and that local dissipation accounts for 28 of the energy converted from the barotropic tide into baroclinic motion

equatorial heat accumulation as a long term trigger of permanent antarctic ice sheets during the cenozoic abstract growth of the first permanent antarctic ice sheets at the eocene oligocene transition eot 33 7 million years ago indicates a major climate shift within long term cenozoic cooling the driving mechanisms that set the stage for this glaciation event are not well constrained however owing to large uncertainties in temperature reconstructions during the eocene especially at lower latitudes to address this deficiency we used recent developments in coccolith biogeochemistry to reconstruct equatorial atlantic sea surface temperature sst and atmospheric pco2 values from pelagic sequences preceding and spanning the eot we found significantly more variability in equatorial ssts than previously reported with pronounced cooling from the early to middle eocene and subsequent warming during the late eocene thus we show that the antarctic glaciation at the eocene oligocene boundary was preceded by a period of heat accumulation in the low latitudes likely focused in a progressively contracting south atlantic gyre which contributed to cooling high latitude austral regions this prominent redistribution of heat corresponds to the emplacement of a strong meridional temperature gradient that typifies icehouse climate conditions our equatorial coccolith derived geochemical record thus highlights an important period of global climatic and oceanic upheaval which began 4 million years before the eot and superimposed on a long term pco2 decline drove the earth system toward a glacial tipping point in the cenozoic

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

a paleogene calcareous microfossil konservat lagerstatte from the kilwa group of coastal tanzania microfossil assemblages and their shell geochemistry are widely used in paleocean ography but they can be significantly altered by subtle variations in preservation state clay rich hemipelagic sediments of the paleogene kilwa group of coastal tanzania host calcareous microfossils that are exceptionally preserved as evidenced by morphological taxonomic and geochemical data the planktonic foraminifera are preserved as glassy translucent tests with original microgranular wall textures that resemble well preserved modern specimens and they arguably yield geochemical values that are relatively unaffected by recrystallization the calcareous nannofossils are extraordinarily diverse and represented by unique assemblage compositions that include dissolution susceptible taxa especially holo coccoliths and rhabdoliths and fragile and very small 3 mu m heterococcoliths many of which are new taxa notably the extant deep photic zone taxon gladiolithus is documented for the first time in the pre quaternary fossil record the kilwa group calcareous nannofossil diversities are consistently higher than all coeval assemblages and provide a benchmark against which to compare other paleogene biodiversity data highest diversities are preserved in hemipelagic clay rich lithologies and the greatest losses occur in lithified carbonate rich sediments most of the lost diversity however is confined to distinct taxonomic groups holococcoliths and syracosphaerales and in general the preservational potential of paleogene coccolithophores was greater than in the modern oceans because a larger proportion of the biodiversity fell within the larger size fractions for both foraminifera and coccolithophores incorporation into impermeable clay rich sediments that have never been deeply buried appears to have been critical in producing this konservat lagerstatte preservation

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

oligocene climate dynamics a planktonic and benthic foraminiferal stable isotope stratigraphy of the oligocene equatorial pacific ocean drilling program site 1218 was generated at 6 kyr resolution between magnetochrons c9n and c11n 2n 26 4 30 ma on a newly developed astronomically calibrated timescale our data allow a detailed examination of oligocene paleoceanography the evolution of the early cryosphere and the influence of orbital forcing on glacioeustatic sea level variations spectral analysis reveals power and coherency for obliquity 40 kyr period and eccentricity 110 405 kyr orbital bands with an additional strong imprint of the eccentricity and 1 2 myr obliquity amplitude cycle driving ice sheet oscillations in the southern hemisphere planktonic and benthic foraminifera 18o are used to constrain the magnitude and timing of major fluctuations in ice volume and global sea level change glacial episodes related to obliquity and eccentricity variations occurred at 29 16 27 91 and 26 76 ma corresponding to glacioeustatic sea level fluctuations of 50 65 m alteration of high latitude temperatures and antarctic ice volume had a significant impact on the global carbon burial and equatorial productivity as cyclic variations are also recorded in the carbon isotope signal of planktonic and benthic foraminifera the water column carbon isotope gradient and estimated percent carbonate of bulk sediment we also investigate the implications of a close correspondence between oxygen and carbon isotope events and long term amplitude envelope extrema in astronomical calculations during the oligocene and develop a new naming scheme for stable isotope events on the basis of the 405 kyr eccentricity cycle count

calcareous nannofossil events around the eocene oligocene boundary in the umbrian appenines italy abstract six pelagic sections from the umbrian area have been investigated to provide a detailed biostratigraphy and magnetostratigraphy at the eocene oligocene boundary data from calcareous nannofossils benthonic and planktonic foraminifera show that no catastrophic extinctions occurred at the boundary but that the latter is characterized by sequential events the last occurrences of discoaster barbadiensis and d saipanensis are found at an older level than the extinction of hantkenina which marks the eocene oligocene boundary variations in abundance of several calcareous nannofossil species have been observed close to the boundary an increase of isthmolithus recurvus a cold water indicator just below the eocene oligocene boundary seems to be a peculiar event well recognizable also in spain and in some dsdp sites from the south atlantic

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

direct breaking of the internal tide near topography kaena ridge hawaii abstract barotropic to baroclinic conversion and attendant phenomena were recently examined at the kaena ridge as an aspect of the hawaii ocean mixing experiment two distinct mixing processes appear to be at work in the waters above the 1100 m deep ridge crest at middepths above 400 m mixing events resemble their open ocean counterparts there is no apparent modulation of mixing rates with the fortnightly cycle and they are well modeled by standard open ocean parameterizations nearer to the topography there is quasi deterministic breaking associated with each baroclinic crest passage large amplitude small scale internal waves are triggered by tidal forcing consistent with lee wave formation at the ridge break these waves have vertical wavelengths on the order of 400 m during spring tides the waves are nonlinear and exhibit convective instabilities on their leading edge dissipation rates exceed those predicted by the open ocean parameterizations by up to a factor of 100 with the disparity in

numerical and analytical estimates of m2 tidal conversion at steep oceanic ridges abstract numerical calculations of the rate at which energy is converted from the external to internal tides at steep oceanic ridges are compared with estimates from analytic theories the numerical calculations are performed using a hydrostatic primitive equation ocean model that uses a generalized s coordinate system as the vertical coordinate the model regional ocean modeling system roms estimates of conversion compare well with inviscid and nondiffusive theory in the sub and supercritical regimes and are insensitive to the strength of viscosity and diffusivity in the supercritical regime the nondissipative analytic solution is singular all along the internal tide beams because of dissipation the roms solutions are nonsingular although the density gradients are strongly enhanced along the beams the agreement between model and theory indicates that the prominent singularities in the inviscid solution do not compromise the estimates of tidal conversion and that the linearization used in derivi

internal tide radiation from mendocino escarpment abstract strong semidiurnal internal tides are observed near mendocino escarpment in full depth profile time series of velocity temperature and salinity velocity and density profiles are combined to estimate the internal tide energy flux divergence of this flux demonstrates that its source is the barotropic tide interacting with the escarpment a baroclinic energy flux of 7 kw m 1 radiates from the escarpment corresponding to 3 of the 220 kw m 1 fluxing poleward in the surface tide energy and energy flux are concentrated in packets that emanate from the flanks of the ridge surmounting the escarpment and one site 90 km north of the escarpment coherent beamlike structure along semidiurnal ray paths remains identifiable until the first surface reflection beyond the first surface reflection north of the escarpment the energy flux drops by 2 kw m 1 and beams are no longer discernible turbulence as inferred from finescale parameterizations is elevated by over two orders of magnitude relative to th