discovery of new hydrothermal vent sites in bransfield strait antarctica we carried out a search for hydrothermal vents in the central basin of bransfield strait antarctica the zaps zero angle photon spectrometer chemical sensor and instrument package oregon state university ofos ocean floor observation system camera sled and tvg tv grab geomar were used to explore the water column and underlying seafloor these operations were supplemented with a series of dredges hydrothermal plumes over hook ridge at the eastern end of the basin are confined to the e ridge crest and se flank the plumes are complex and sometimes contain two turbidity maxima one widespread feature centered at 1150 m and a smaller more localized but broad maximum at 600 800 m we traced the source of the shallower plume to a sunken crater near the ridge crest using sensors on the zaps instrument package subsequently two tv grabs from the crater brought back hot soupy sediment 42 49 c overlain by hard siliceous crusts and underlain by a thick layer of volcanic ash we also recovered chimney fragments whose texture and mineralogy indicate venting temperatures in excess of 250 c native sulfur and fe sulfides occur in fractures and porous layers in sediment from throughout the area pore water data from the crater site are consistent with venting into a thin sediment layer and indicate phase separation of fluids beneath hook ridge the source of the deeper plumes at hook ridge has yet to be located we also explored a series of three parallel volcanic ridges west of hook ridge called three sisters we detected water column anomalies indicative of venting with the zaps package and recovered hydrothermal barites and sulfides from middle sister we spent considerable time photographing middle sister and hook ridge but did not identify classic vent fauna at either location we either missed small areas with our photography or typical mor vent fauna are absent at these sites

southern ocean bottom water of the australian new zealand sector the bottom water characteristics of the southeast indian ocean and southwest pacific ocean reveal northward transfer of cold water across the mid ocean ridge at the discordance zone near 120 e and at the balleny fracture zone near 155 e a principal northward flow which transfers cold continental margin waters of antarctic origin to lower latitudes within the south indian basin occurs to the east of kerguelen plateau within the south indian basin near the 0 c isotherm the s o2 and si relations display significant slope changes the more variable water below 0 c is of local origin while the water above 0 c represents larger scale regional effects

abyssal circulation and benthic foraminiferal changes near the paleocene eocene boundary a major change in cenozoic deep sea benthic foraminifera occurred in the atlantic indian and pacific oceans near the paleocene eocene boundary benthic foraminiferal abundance changes began at about 61 5 ma at pacific deep sea drilling project dsdp site 577 a major extinction event followed at 58 57 ma between zones p6a and p6b and a series of first appearances continued until circa 55 5 ma zone p6c these faunal changes occurred during a 6 c warming of pacific bottom water and may indicate that the primary cause was changing temperature other potential causes of the faunal turnover include global changes in surface ocean productivity and changing bottom water source regions comparison of benthic and planktonic 13c records requires no change in the ratio of oceanic phosphorous to carbon during the late paleocene to early eocene which weakens the case for but does not disprove a change in surface ocean productivity at this time interbasinal comparisons of benthic foraminiferal 13c records document that water with high 13c values filled the cape basin during the late paleocene and possibly the early eocene circa 61 57 ma but apparently did not extend into the western basins of the atlantic this pattern suggests a supply of antarctic source water for the cape basin and possible tectonic isolation of the western atlantic basins during at least part of the late paleocene carbon isotope comparisons show that bottom water supply to the cape basin was reduced in the early eocene eolian grain size data suggest that a decrease in zonal wind intensity occurred at the end of the paleocene these late paleocene climatic changes bottom water warming and decreased wind intensity correspond with evidence for an important global tectonic reorganization and extensive subaerial volcanism which may have contributed to climatic warming through increased supply of co2

influence of changing deep ocean circulation on the phanerozoic oxygen isotopic record isotopic segregation in seawater caused by changing ocean circulation may in part explain the enigmatic oxygen isotopic record of phanerozoic marine carbonates paleoceanographic evidence suggests that circulation of warm saline deep waters has occurred during at least two periods of warm global climate those saline deep waters should have preferentially stored 18o in the deep oceans corresponding depletion of 18o in surface waters would have resulted in lower 18o of marine carbonates deposited on continental shelves modeling of paleoceanographic isotopic data suggests that this storage effect is similar in magnitude but opposite in sign to that of modern enrichment of 18o in the oceans by glacial storage modeling of carbonate compositions through time that takes into account such storage effects as predicted by changing global climate suggests that large changes in the mean oceanic isotopic composition but neither extreme temperatures nor sudden changes in mean ocean compositions are needed to explain the isotopic record

nepheloid layer dynamics in the northern portuguese shelf abstract a general hydrographic and nephelometric survey of the nw portuguese continental shelf and upper slope was undertaken under winter and spring conditions the nepheloid layer dynamics along the shelf during three cruises were controlled principally by the following factors a the hydrography of the shelf slope waters i e the nepheloid layers followed isopycnals and water masses b prevalence of upwelling or downwelling circulation over the shelf c dispersion of material by river discharge mainly the douro river d resuspension of mid shelf fine deposits induced by swell e peculiar morphology with the presence of porto canyon and outer shelf rock outcrops the general circulation controls the seaward extension of the nepheloid layers in winter under dominant downwelling conditions an intense bottom nepheloid layer bnl was observed on the shelf due to river borne particle supply and remobilization of mid shelf muddy sediments depth 100 m in this period the bnl increased in thickness to the top of the slope following the isopycnals near the shelf break the bnl detached to form intermediate nepheloid layers inl small inls appear deeper in some areas of the slope a surface nepheloid layer snl appears in the surface water over the shelf and slope in spring biological particles mainly contribute to the snl which is separated from the bnl by a zone of clear water in winter the snl is restricted to the inner shelf where there are high inputs of fluvial particles downwelling circulation probably induces transport of shelf particles to deeper waters in the bnl in spring the predominant circulation was southward upwelling the water column was highly stratified and dispersion of particles in the snl was offshore

evolution and biogeography of paleogene microperforate planktonic foraminifera abstract microperforations with a maximum diameter less than 1 m characterize some paleogene planktonic foraminifera and 5 microperforate groups are distinguished differences occur in pore density and wall textures as well as in the coiling mode these groups are unrelated phylogenetically and the microperforate wall represents a morphological character of convergence parvularugoglobigerina the earliest group with smooth surface and scattered microperforations evolved immediately after the k t boundary in many localities the globoconusa group is characterized by a heavily pustulate wall and relatively coarser pores of lower density derived from guembelitria members of this group occur in almost every marine sequence of the lower paleocene with no latitudinal preference but they tend to dominate shallow water assemblages in epicontinental seas and possibly are related to coastal upwelling together with its immediate ancestor woodringina and the evolutionary offshoots zeauvigerina and tubitextularia the biserial chiloguembelina contains the largest number of species falling into 4 subgroups as here recognized the chiloguembelinids dominated the early paleocene the high latitude middle eocene and the late eocene early oligocene the middle eocene guembelitria triseriata cassigerinelloita amekiensis lineage is defined by triserial to triserial pseudoplanispiral coiling and occurs mainly in marginal seas and over oceanic rises in southern oceans the tenuitellids the latest group first occur in the late eocene become common in the oligocene miocene and extend into the quaternary and modern oceans with a high frequency in high latitudes of the oligocene tenuitellids are considered to be cold water indicators

planktonic foraminiferal biostratigraphy and mechanisms in the extinction of morozovella in the late middle eocene the muricate planktonic foraminiferal genera morozovella and acarinina were abundant and diverse during the upper palaeocene to middle eocene and dominated the tropical and subtropical assemblages a significant biotic turnover in planktonic foraminifera occurred in the latest middle eocene with a notable reduction in the acarininid lineage and the extinction of the morozovellids these genera are extensively employed as palaeoclimatic and biostratigraphic markers and therefore this turnover episode is an important event in the record of the cenozoic planktonic foraminifera sediments from the western north atlantic ocean drilling program site 1052 were examined in order to investigate these extinction events in terms of both timing and mechanisms biostratigraphic events of the middle and late eocene have been examined with a sampling resolution of approximately 3 kyr these have been calibrated to the magneto and astrochronology to accurately define the timing of key biostratigraphic events particularly the extinction of morozovella spinulosa which is a distinct biomarker for late middle eocene sediments high resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form the large acarininids acarinina praetopilensis terminate 10 kyr prior to the extinction of m spinulosa and small acarininids acarinina medizzai and acarinina echinata continue into the upper eocene high resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western north atlantic to reconstruct sea surface temperatures ssts and deep water temperatures and the structure of the water column around this major biotic turnover whilst the extinctions of m spinulosa and a praetopilensis occur during a long term cooling trend the biotic turnover in the muricate group does not appear to be related to significant climatic change sea surface temperatures decrease slowly prior to the extinction events and there is no evidence for a large temperature shift associated with the faunal changes the turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae d 2003 elsevier b v all rights reserved

isotopic interrogation of a suspected late eocene glaciation ephemeral polar glaciations during the middle to late eocene 48 34 ma have been proposed based on far field ice volume proxy records and near field glacigenic sediments although the scale timing and duration of these events are poorly constrained here we confirm the existence of a transient cool event within a new high resolution benthic foraminiferal 18o record at ocean drilling program odp site 738 kerguelen plateau southern ocean this event named the priabonian oxygen isotope maximum prom event lasted 140 kyr and is tentatively placed within magnetochron c17n 1n 37 3 ma based on the correlation to odp site 689 maud rise southern ocean a contemporaneous change in the provenance of sediments delivered to the kerguelen plateau occurs at the study site determined from the 63 m fraction of decarbonated and reductively leached sediment samples changes in the mixture of bottom waters based on fossil fish tooth nd were less pronounced and slower relative to the benthic 18o and terrigenous nd changes terrigenous sediment nd values rapidly shifted to less radiogenic signatures at the onset of the prom event indicating an abrupt change in provenance favoring ancient sources such as the paleoproterozoic east antarctic craton bottom water nd reached a minimum value during the prom event although the shift begins much earlier than the terrigenous nd excursion the origin of the abrupt change in terrigenous sediment provenance is compatible with a change in antarctic terrigenous sediment flux and or source as opposed to a reorganization of ocean currents a change in terrigenous flux and or source of antarctic sediments during the oxygen isotope maximum suggests a combination of cooling and ice growth in east antarctica during the early late eocene

ecological and evolutionary response of tethyan planktonic foraminifera to the middle eocene climatic optimum meco from the alano section ne italy abstract the enigmatic middle eocene climatic optimum meco is a transient 500 kyr warming event that significantly interrupted at 40 ma the long term cooling through the middle and late eocene eventually resulting in establishment of permanent antarctic ice sheet this event is still poorly known and data on the biotic response are so far scarce here we present a detailed planktonic foraminiferal analysis of the meco interval from a marginal basin of the central western tethys alano section northeastern italy the expanded and continuous alano section provides an excellent record of this event and offers an appealing opportunity to better understand the role of climate upon calcareous plankton evolution a sapropel like interval characterized by excursions in both the carbon and oxygen bulk carbonate isotope records represents the lithological expression of the post meco event in the study area and follows the 18 o negative shift interpreted as representing the meco warming high resolution quantitative analysis performed on both 38 m and 63 m fractions reveals pronounced and complex changes in planktonic foraminiferal assemblages indicating a strong environmental perturbation that parallels the variations of the stable isotope curves corresponding to the meco and post meco intervals these changes consist primarily in a marked increase in abundance of the relatively eutrophic subbotinids and of the small low oxygen tolerant streptochilus chiloguembelina and pseudohastigerina at the same time the arrival of the abundant opportunist eutrophic jenkinsina and pseudoglobigerinella bolivariana typical species of very high productivity areas also occurs the pronounced shift from oligotrophic to more eutrophic opportunist low oxygen tolerant planktonic foraminiferal assemblages suggests increased nutrient input and surface ocean productivity in response to the environmental perturbation associated with the meco particularly critical environmental conditions have been reached during the deposition of the sapropel like beds as testified by the presence of common giant and or odd morphotypes this is interpreted as evidence of transient alteration in the ocean chemistry the enhanced surface water productivity inferred by planktonic foraminiferal assemblages at the onset of the event should have resulted in heavier 13 c values the recorded lightening of the carbon stable isotope preceding the maximum warmth therefore represents a robust indication that it derives principally by a conspicuous increase of p co 2 the increased productivity of surface waters also supported by geochemical data may have acted as mechanism for p co 2 reduction and returned the climate system to the general eocene cooling trend the oxygen depleted deep waters and the organic carbon burial following the peak of the meco event represent the local response to the meco warming and suggest that high sequestration of organic matter if representing a widespread response to this event might have contributed to the decrease of p co 2 as well though the true mechanisms are still obscure several lines of evidence indicate a potential pressure on planktonic foraminiferal evolution during the meco event including permanent changes besides transient and ecologically controlled variations

did impacts volcanic eruptions or climate change affect mammalian evolution abstract in recent years it has become popular to attribute faunal change and mass extinction to impacts volcanic eruptions or climatic change how well do these supposed causes compare to the excellent record of cenozoic life especially that of fossil mammals two different cenozoic mammal diversity curves were compared and important climatic volcanic and impact horizons were examined in detail in no case is there a strong correlation between impacts eruptions or climatic events and any episode of mammalian turnover on the contrary most of the known impact eruption and climatic events of the cenozoic occurred during intervals of faunal stability conversely episodes of high turnover and faunal change among cenozoic mammals correlate with no known extrinsic causes apparently extrinsic environmental factors such as impacts eruptions and climate change have a minimal effect and intrinsic biological factors must be more important

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

suspended particulate matter and nepheloid layers over the southern margin of the cretan sea n e mediterranean seasonal distribution and dynamics seawater along the southern margin of the cretan sea may 1994 september 1995 has been found to have light transmission values ranging from 79 to 94 corresponding to spm values ranging from 1 5 mg l 1 to 0 2 mg l 1 the highest spm concentrations mostly of terrigenous origin were found close to the sea bed over the shelf break and upper slope the origins of spm in the surface waters 150 m is principally biogenic the occurrence of nepheloid layers at intermediate depths within the upper water column is mostly a result of density stratification the dynamics of spm distributions are governed by the 2 gyre system which induces a general onslope flow and so inhibits the seaward dispersion of the relatively more turbid coastal shelf waters this is in agreement with the virtual absence of suspensates of terrigenous origin offshore of the shelf break near bottom nepheloid layers bnl and detached intermediate nepheloid layers occur in the vicinity of the shelf break and over upper slope region these may be explained by resuspension induced by near bed current activity and breaking of internal waves high concentrations of spm near the seabed may be caused by anthropogenic trawling activity occasionally the formation of bnl may result from local seismic activity resulting in gravity driven mass movements

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

hantkeninid depth adaptation an evolving life strategy in a changing ocean the interplay between evolution paleoecology and environmental change is examined in a geochemical study of a group of eocene planktonic foraminifera the hantkeninids which are well known biostratigraphic inde fossils underwent spectacular long term evolution in the middle and upper eocene 49 0 33 7 ma a time when major global climate and oceanic changes were occurring we use oxygen and carbon isotope analysis of their shell calcite to investigate how their habitat changed as they evolved the hantkeninids originated in a deep water oxygen minimum environment but migrated into fully oxygenated near surface waters as global temperatures decreased and water column stratification declined this change in depth ecology coincided with pronounced morphological evolution involving changes in chamber shape and degree of inflation and modification of the primary aperture these developments are considered to be adaptations to a near surface habitat

atlantic eocene planktonic foraminiferal historical biogeography and paleohydrographic indices abstract analysis of a quantitative and synoptic data base of eocene atlantic planktonic foraminifera has illuminated many facets of foraminiferal faunal structure and composition reflective of bioprovince and useful for empirical establishment of ecologic and paleohydrographic indices tropical indigenes such as the morozovellids turborotaliids subquadrate acarininids and some globigerinathekids dissolve most rapidly along with juveniles of most species tropical faunas are high in diversity and dominance include oxygen minimum indices such as the biserial heterohelicids only in high productivity times such as the middle eocene are dominated by genera with high numbers of species and species consistently typical of warm water regions until the late eocene when faunas include a higher number of middle than lower latitude types truly tropical genera are replaced by subtropical eutrophic indicators such as the globigerinathekids and contract to the florida current region prior to their extinctions at the end of the middle eocene atlantic late paleogene tropical forms first appear in the gulf of mexico at the end of the middle eocene middle latitude faunas include high numbers of chiloguembelinids pseudohastigerinids small and biconvex morozovellids round and globigerinid form acarininids low spired subbotinids in the late middle eocene high spired subbotinids large and typical globigerinids in the late eocene these forms have intermediate dissolution susceptibilities middle latitude faunas are often high in diversity in midddle latitude frontal regions dominance is low even in warm intervals when tropical indigenes increase in number in middle latitude faunas especially in boundary currents low latitude species penetrate temperate areas also during cool eutrophic periods of vigorous circulation such as the late middle eocene typical of temperate slope faunas are high abundances of high spired subbotinids and small sized catapsydracids high latitude faunas are usually low in diversity except in the middle to late eocene when frontal regions were located in the southern labrador sea and over rockall bank typical forms are the low spired subbotinids until the late middle eocene globorotaloids catapsydracids tenuitellids and in the late eocene the biserial heterohelicids indigenous species are the most solution resistant and many are mesopelagic during warmings rare low latitude indices penetrate high latitudes subpolar faunas have greatest affinities with middle latitude faunas at these times

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

effects of the oligocene climatic events on the foraminiferal record from fuente caldera section spain western tethys abstract an expanded succession of upper priabonian upper eocene to chattian upper oligocene hemipelagic marls interbedded with turbiditic sandstone layers is present in the spanish fuente caldera section subbetic zone western tethys we analyzed foraminifera from this section quantitatively with emphasis on biostratigraphy and paleoecology benthic foraminifera indicate an upper to possibly upper middle bathyal depth of deposition for most of the studied section with paleobathymetric analysis made difficult because of the common presence of shallow water taxa some reworked by turbidites and others epiphytic taxa which may have been transported by turbidites or by floating plant material we identified three major biotic and paleoenvironmental events 1 the major planktonic foraminiferal turnover across the eocene oligocene boundary which includes several first and last occurrences as well as a decrease in the percentage of surface water dwellers possibly linked to global cooling 2 a dramatic sea level drop indicated by the presence of a 37 m thick sequence of calcarenites lower half of planktonic foraminiferal zone o2 31 5 ma with abundant trace fossils and allochthonous foraminifera this sea level fall which triggered erosion of material in shallow marine settings and transport by turbidity currents into the basin apparently post dated the major glacial expansion on the antarctic continent oi1 33 7 ma and predated the later major expansion oi2 through oi2b 27 30 5 ma thus may have been tectonically controlled 3 a warming event starting in the chattian lowermost part of zone o6 27 1 ma which could be correlated to the globally recognised late oligocene warming event but apparently started somewhat earlier 27 1 ma as compared to 26 5 ma

transport of suspended particulate matter in an antarctic fjord abstract vertical profiles of temperature salinity and light attenuation were used in conjunction with underwater photography and water samples to characterize the nature and dynamics of particle transport in an antarctic fjord most of the particles are sand sized 0 1 2 mm floccules comprised of individual grains in the 5 to 50 m size range the quartz silt grains are derived from basal debris laden meltwater originating from beneath the submerged valley glacier the meltwater buoyantly rises to form cold water interflows at mid water depths turbulent mixing near the seafloor also plays a role in the transport and break up of floccules together the midwater cold tongues and near bottom turbidity account for 87 of the total sediment load thus attesting to the importance of non surface transport mechanisms in polar fjords

evolutionary consequences of the latest paleocene thermal maximum for tropical planktonic foraminifera study of planktonic foraminiferal assemblages preserved in the central equatorial pacific odp site 865 reveal that genera which inhabited the near surface mixed layer diversified during the latest paleocene thermal maximum lptm this transient diversification gave rise to a suite of short lived 50 to several 100 ka distinctive morphotypes morozovella allisonensis sp nov m africana and acarinina sibaiyaensis that are restricted to the lptm interval parallel morphometric and stable isotopic data have been recorded from individual shells of members of the m velascoensis m allisonensis and a soldadoensis a sibaiyaensis lineages the single specimen isotope data confirm that m allisonensis and a sibaiyaensis are indeed stratigraphically restricted to the lptm carbon isotope excursion all specimens recorded anomalously low 13c values a stratigraphic succession of single specimen isotope data from within the 13c excursion interval was used to reconstruct the complex population dynamics which mediated the rapid 10 ka evolution of the lptm taxa these data reveal that local populations of ancestral m velascoensis temporarily collapsed with the descendant m allisonensis suddenly originating from a peripherally isolated population this pattern is most consistent with peripatric speciation overall the evolutionary transition from acarinina soldadoensis to a sibaiyaensis is most consistent with sympatric speciation although certain elements of this transition are suggestive of a parapatric mechanism we postulate that the rapid evolution of the lptm taxa a sibaiyaensis and m allisonensis was fostered by a deepening of the nutrient depleted mixed layer alternatively the lptm morphotypes m allisonensis and a sibaiyaensis may have been extreme ecophenotypic variants arrayed along an intensified ecological gradient support for this latter interpretation is derived from the morphometric data which clearly show the morphological intergradation of the lptm taxa with their respective ancestors thus the morphologic diversification seen during the lptm may represent failed speciations both scenarios invoke a temporary steepening of clinal gradients in response to intensified oligotrophy the strong size dependencies displayed by the 18o and 13c signatures of m allisonensis and a sibaiyaensis suggest that photosymbiosis facilitated the evolutionary success of the morozovellids and acarininids during the lptm

the nepheloid bottom layer and water masses at the shelf break of the western ross sea in the austral summers of 2000 2001 and 2002 2003 the italian clima project carried out two oceanographic cruises along the northwestern margin of the ross sea where the antarctic bottom water forms here there is an interaction between the water masses on the sea floor of the outer shelf and slope with a consequent evolution of benthic nepheloid layers and an increase in total particulate matter we observed three different situations a the presence of triads bottom structures characterized by a concomitant jump in turbidity temperature and salinity data and high re suspension phenomena related to the presence of the circumpolar deep water and its mixing with cold salty shelf waters associated with gravity currents b the absence of triads with high re suspension implying that when the gravity currents are no longer active the benthic nepheloid layer may persist until the suspended particles settle to the sea floor suggesting that the turbidity data can be used to study recent gravity current events and c the absence of turbidity and sediment re suspension phenomena supports the theory that a steady situation had been re established and the current interaction no longer occurred or had finished sometime before

the fram strait acoustic tomography system the deep and wide fram strait between greenland and spitzbergen is the main influx and efflux gate to the arctic basin although major resources are invested in measurements of current and temperature here http asof npoar no the flux estimates still have significant deficiencies and errors our objective is to build test validate and use an innovated integrated observing and modeling system including acoustic tomography for improved monitoring of volume heat and freshwater transports in the fram strait as part of the damocles ip developing arctic modeling and observing capabilities for long term environmental studies integrated project a first step acoustic tomography system is to be installed in the fram strait between east greenland and west spitzbergen in august 2008 the first step tomography system consists of one acoustic source near the svalbard shelf and one receiver array in the middle of the fram strait an extended acoustic system serving both tomography and glider navigation i

high resolution velocity and hydrographic observations of the drygalski trough gravity plume during the second cruise of the anslope project the hydrography and velocity fields within a descending gravity plume in the northwestern ross sea shelf area were sampled at high resolution the observations give insights into small scale fluctuations of the three dimensional velocity field in and around the core of a strong gravity current associated with peak velocities close to 2 m s there are two distinct layers of high acoustic backscatter at 300 khz near the seabed associated with increased velocity variance and richardson numbers near 0 25 suggesting that the high backscatter is caused by increased levels of turbulence resulting in increased acoustic bragg scattering c 2008 elsevier ltd all rights reserved

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

response of antarctic odp site 690 planktonic foraminifera to the paleocene eocene thermal maximum faunal evidence for ocean climate change 1 high resolution study of antarctic planktonic foraminiferal assemblages ocean drilling program site 690 weddell sea shows that these microplankton underwent a stepwise series of changes during the paleocene eocene thermal maximum petm initiation of this response coincides with the onset of the carbon isotope excursion cie but precedes the benthic foraminiferal mass extinction the top to bottom succession in the biotic response indicates that the surface ocean atmosphere was affected before the deep sea the earliest stage of the faunal response entailed a conspicuous turnover within the shallow dwelling genus acarinina and a succession of stratigraphic first appearances the genus morozovella large 180 m biserial planktonics and a wilcoxensis are all restricted to the lower cie within this petm section acarininid populations crashed as the ocean climate system ameliorated during the cie recovery reflecting atypical surface water conditions this transient decline in acarininids is paralleled by a marked increase in carbonate content of sediments it is postulated that this interval of carbonate enrichment and its unusual microfauna reflects enhanced carbon storage within reservoirs of the global carbon cycle other than the marine carbonate system sensu broecker et al 1993 ravizza et al 2001

a recount of ross sea waters abstract oceanographic observations within the ross sea have grown dramatically in recent years both in number and quality this has prompted a parallel recount of the circulation and structure of all water masses in the southwestern continental margins of the pacific ocean a high resolution set of horizontal property distributions was combined into a new climatology which in turn is the basis of a fine volumetric s census of all ross sea water masses inshore of the shelf break 700 m isobath the ross sea volume 25 10 4 km 3 partitioning into layers of neutral density n is 25 in the top layer n 3 of antarctic surface water aasw 22 in the middle layer 28 00 kg m 3 n 3 of oceanic thermocline water 12 and modified circumpolar deep water mcdw 10 and 53 in the bottom layer n 28 27 kg m 3 of shelf water sw 1 85 c 22 precursor of the antarctic bottom water aabw offshore aasw flows westward along the outer shelf and southward along the eastern coast past cape colbeck oceanic thermocline waters 28 00 kg m 3 n 3 cross the shelf break west of 170 w and follow southward paths along banks shoaling progressively to near the sea surface of the central and western inner shelves winter buoyancy loss converts aasw and oceanic thermocline water into denser types of mcdw and sw which move cyclonically toward the sills of major troughs the census shows a continuous mode of relatively dense mcdw 28 10 kg m 3 n 3 directly linked to the circumpolar deep water cdw offshore effectively ventilating and freshening the deep ocean at levels below the salinity maximum and above aabw mcdw outflows from the ross sea shelf are traced to the antarctic circumpolar current near 155 e into the australian antarctic basin along the northern flank of the southwest pacific ridge and to near 135 w past the eastern end of the ross gyre two sources of salty sw are inferred near the coastal polynyas in the terra nova bay and western ross ice shelf areas the latter contributes to a major outflow of ice sw that reaches the shelf break along 180 vertical mixing of mcdw and sw produce msw over the shelf continuing over the sills as new aabw export of low salinity aabw s

the paleocene eocene transition in the antarctic indian ocean inference from planktic foraminifera isotopic depth stratification and relative abundance studies of planktic foraminifera at odp site 738 reveal three major faunal turnovers during the latest paleocene and early eocene reflecting the climatic and structural changes in the antarctic surface ocean faunal event 1 occurred near the paleocene eocene boundary and is characterized by a faunal turnover in deep dwellers decreased relative abundance in intermediate dwellers and increased relative abundance in surface dwellers this event marks a temporary elimination of the vertical structure in the surface ocean over a period of more than 63 000 years that is apparently associated with the sudden shutdown of the antarctic intermediate water production the appearance of morozovellids before this event suggests that polar warming is the cause for the shutdown in the production of this water mass at this time warm saline deep water may have formed at low latitudes faunal event 2 occurred near the ap5a ap5b subzonal boundary and is characterized by a faunal turnover in deep dwellers with no apparent change in surface and intermediate dwellers increased individual size wall thickness and relative abundance in deep dwelling chiloguembelinids suggests the formation of a deep oxygen minima in the antarctic oceans during the maximum polar warming possibly as a result of upwelling of nutrient rich deep water faunal event 3 occurred in subzone ap6 and is characterized by a faunal turnover in surface dwellers and a delayed diversification in deep dwellers this event marks the onset of antarctic cooling a drastic decrease in the 13c 18o values of the deep assemblage in zone ap7 suggests an intensified thermocline and reduced upwelling following the polar cooling

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

oxygen and carbon isotopic composition and biogeographic distribution of planktonic foraminifera in the indian ocean five planktonic foraminiferal assemblages were encountered along a north south transect in the indian ocean with the following dominant species globorotalia truncatulinoides in the southern subtropical assemblage globigerinoides ruber globigerinella aequilateralis and globorotalia menardii in the northern subtropical assemblage globigerinoides sacculifer and pulleniatina obliquiloculata in the tropical assemblage neogloboquadrina dutertrei and globigerina bulloides in the tropical upwelling assemblage and globigernoides conglobatus in the tropical arabian sea assemblage oxygen and carbon isotopic analyses were performed on three surface dwelling species of planktonic foraminifera in tropical and subtropical waters 22 30 c the 18o of globigerinoides ruber and g sacculifer varies with surface water temperature and the slope of the isotope temperature regression line is similar to that of epstein et al 1953 for marine molluscs however foraminiferal 18o values are significantly lighter than those of molluscs indicating isotopic disequilibrium comparison between plankton tows taken within and below the mixed layer at the same stations shows that g ruber has similar low 18o values in both sets suggesting that it secretes its shell within the mixed layer by contrast g sacculifer has slightly higher 18o values below than within the mixed layer because it continues to secrete calcite below the thermocline no significant 18o variations with shell size were found on the other hand 13c values were strongly size dependent i e the smaller the size the lighter the 13c comparison of living g ruber and g sacculifer with recent specimens from the surface sediment shows that the living foraminifera are generally lighter in 18o than the fossils supporting independent observations that the latter have secreted additional calcite during gametogenesis when the organisms settle freely from the euphotic zone for about 12 h and pass through waters lower in temperature than the epipelagic waters where the foraminifera form the bulk of their shells

did photosymbiont bleaching lead to the demise of planktic foraminifer morozovella at the early eocene climatic optimum the symbiont bearing mixed layer planktic foraminiferal genera morozovella and acarinina were among the most important calcifiers of early paleogene tropical subtropical oceans a marked and permanent switch in the abundance of these genera is known to have occurred at low latitude sites at the beginning of the early eocene climatic optimum eeco such that the relative abundance of morozovella permanently and significantly decreased along with a progressive reduction in the number of species concomitantly the genus acarinina almost doubled its abundance and diversified here we examine planktic foraminiferal assemblages and stable isotope compositions of their tests at ocean drilling program site 1051 northwest atlantic to detail the timing of this biotic event to document its details at the species level and to test a potential cause the loss of photosymbionts bleaching we also provide stable isotope measurements of bulk carbonate to refine the stratigraphy at site 1051 and to determine when changes in morozovella species composition and their test size occurred we demonstrate that the switch in morozovella and acarinina abundance occurred rapidly and in coincidence with a negative carbon isotope excursion known as the j event 53 ma which marks the start of the eeco we provide evidence of photosymbiont loss after the j event from a size restricted 13c analysis however such inferred bleaching was transitory and also occurred in the acarininids the geologically rapid switch in planktic foraminiferal genera during the early eocene was a major evolutionary change within marine biota but loss of photosymbionts was not the primary causal mechanism

estimating greater paleodepths with ostracodes especially in past thermospheric oceans abstract modern ostracodes show significant morphologic and taxonomic changes with increasing depth deep psychrospheric faunas are less diverse and more cosmopolitan than shallow faunas individuals are larger rarer and blind their carapaces seem better designed relative to the mass of construction material used speciation is slower taxa are older longer ranging and for the most part now confined to abyssal and bathyal environments deep thermospheric ostracodes found in pre psychrospheric oceans or isolated basins are different their deep origin seems related to the ability of shelf species to submerge past what is a formidable thermal barrier to test morphologic changes that reflect faunal submergence in thermospheric oceans such as existed in the atlantic before about 40 m y b p the basis for an adaptive structural theory is explored this leads to a search for limits expressive of rapid change both in the structure of morphology and in water mass structure examination of the ostracodes from core samples of cretaceous age from nine d s d p sites in the south atlantic suggests that the rio grande rise walvis ridge aseismic system has both been a water mass barrier and yet remained deep at least mid bathyal over the last 100 m y no evidence of either shallow ostracodes from the shelves of africa south america or those of islands were found indicating that models proposed previously that there would have been an archipelago or shallow submerged causeway across the rio grande rise walvis ridge during the late cretaceous are probably in error

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

early paleogene temperature history of the southwest pacific ocean reconciling proxies and models we present a new multiproxy tex86 18o and mg ca marine temperature history for canterbury basin eastern new zealand that extends from middle paleocene to middle eocene including the paleocene eocene thermal maximum petm and early eocene climatic optimum eeco in light of concerns that proxy based sea surface temperature sst estimates are untenably warm for the southwest pacific during the eocene we review the assumptions that underlie the proxies and develop a preliminary paleo calibration for tex86 that is based on four multiproxy eocene records that represent an sst range of 15 34 c for the southwest pacific paleogene we show that tex86l exhibits the best fit with the eocene paleo calibration ssts derived from related proxies tex86h 1 tex86 exhibit a systematic warm bias that increases as tex86 values decrease a warm bias of 4 7 c where tex86 0 7 the tex86l proxy indicates that southwest pacific sst increased by 10 c from middle paleocene to early eocene with sst maxima of 26 28 c tropical during the petm and eeco and an sst minimum of 13 16 c cool warm temperate at the middle late paleocene transition 58 7 ma the base of the eeco is poorly defined in these records but the top is well defined in canterbury basin by a 2 5 c decrease in sst and bottom water temperature bwt in the latest early eocene 49 3 ma bwt falls from a maximum of 18 20 c in the eeco to 12 14 c in the middle eocene overall cooler temperatures are recorded in the mid waipara section which may reflect a deeper 500 m water depth and less neritic depositional setting compared with hampden and odp 1172 200 m water depth the high ssts and bwts inferred for the petm and eeco can be reconciled with eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto east australian current is taken into account

palaeoecology of late middle eocene planktic foraminifera and evolutionary implications the late middle eocene is marked by accelerated global cooling representing part of the long transitional interval separating the early eocene greenhouse and later oligocene icehouse climatic regimes this time interval is also regarded as having witnessed a decline in planktic foraminiferal diversity following the extinction of most of the muricate clade genera acarinina and morozovelloides at approximately 39 ma here we examine planktic foraminiferal assemblages recovered at odp site 1052 blake nose nw atlantic and by recording a high level of taxonomic diversity including several previously undocumented morphotypes we suggest that the diversity of late middle eocene planktic foraminifera may have been underestimated depth habitats of every species within these late middle eocene assemblages are reconstructed using oxygen and carbon stable isotope ratios furthermore because stable isotope analyses suggest that species of globoturborotalita appear to have generally calcified during winter months these taxa offer in combination with predominantly summer surface dwellers such as morozovelloides the potential to reconstruct patterns of seasonality during the late palaeogene using extremely well preserved glassy planktic foraminiferal calcite from a contemporaneous hemipelagic drill site detailed sem imaging of test microstructures and wall textures confirm that many modern features of foraminiferal ecology and test architecture had already evolved by the late middle eocene the common occurrence of the cancellate wall texture combined with the wide variety of reconstructed foraminiferal depth habitats indicates that there is no necessary relationship between foraminiferal wall textures and habitat and that wall textures are evolutionary conservative features of the foraminiferal test

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

atlantic eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography reconstruction of atlantic ocean vertical and meridional water characteristics is based on combined synoptic fossil census data stable isotope records and measurements of individual planktonic foraminiferal species correlations between planktonic foraminiferal indices and specific water types and or chemical conditions are used to trace seven stages in the history of atlantic circulation during eocene climatic changes 1 warm equable probably saline productive ocean of the early eocene characterized by lowest meridional and vertical thermal gradients and the maximal extent of tropical surface water 2 early middle eocene expansion of subtropical waters and faunas accompanying the first climatic cooling and eutrophication of equatorial surface waters 3 maximal partitioning of water types faunas and bioprovinces in middle eocene zone p11 accompanying maximum planktonic foraminiferal diversity accelerated near surface and deepwater cooling and intensified upwelling 4 latest middle eocene zone p14 maximal planktonic foraminiferal evolutionary overturn during accelerated cooling deep and surface water ventilation and transformation of tropical surface water habitat with the expansion of temperate water types and faunas this accompanied the reduction of meridional heat transport in boundary currents 5 late eocene bottom water and middle latitude cooling broadening of meridional temperature gradients and expanded oxygen minimum but faunal homogenization following the decreased import of mediterranean water ourflow 6 weakening and or shoaling of the nutricline an oxygen minimum and the thermocline preceding a diminution of primary productivity at the eocene oligocene boundary and 7 earliest oligocene low productivty ocean marked by diminished vertical thermal contrasts and homogeneous foraminiferal faunas dominated by small sized individuals the increased areal extent of upwelling with the outcropping of cooler waters over large geographic regions provides an important climatic forcing mechanism in the latest middle and late eocene

the evolutionary history of size variation of planktic foraminiferal assemblages in the cenozoic abstract the iterative evolutionary radiation of planktic foraminifers is a well documented macroevolutionary process here we document the accompanying size changes in entire planktic foraminiferal assemblages for the past 70 my and their relationship to paleoenvironmental changes after the size decrease at the cretaceous paleogene k p boundary high latitude assemblages remained consistently small size evolution in low latitudes can be divided into three major phases the first is characterized by dwarfs 65 42 ma the second shows moderate size fluctuations 42 14 ma and in the third phase planktic foraminifers have grown to the unprecedented sizes observed today our analyses of size variability with paleoproxy records indicate that periods of size increase coincided with phases of global cooling eocene and neogene these periods were characterized by enhanced latitudinal and vertical temperature gradients in the oceans and high diversity polytaxy in the paleocene and during the oligocene the observed minor size changes of the largely low diversity oligotaxic assemblages seem to correlate with productivity changes however polytaxy per se was not responsible for larger test sizes

foraminiferal turnover across the eocene oligocene transition at fuente caldera southern spain no cause effect relationship between meteorite impacts and extinctions we studied planktic and small benthic foraminifera from the fuente caldera section southern spain across the eocene oligocene transition benthic foraminifera indicate lower bathyal depths for the late eocene and earliest oligocene detailed highresolution sampling and biostratigraphical data allowed us to date precisely layers with evidence for meteorite impact ni rich spinel which occur in the lower part of the planktic foraminiferal globigerapsis index biozone and in the middle part of the small benthic foraminiferal cibicidoides truncanus bb4 biozone middle priabonian late eocene major turnovers of foraminifera occur at the eocene oligocene boundary only the impact did not occur at a time of planktic or benthic foraminiferal extinction events and the late eocene meteorite impacts did thus not cause extinction of foraminifera the most plausible cause of the eocene oligocene boundary extinctions is the significant cooling which generated glaciation in antarctica and eliminated most of the warm and surface dwelling foraminifera d 2005 elsevier b v all rights reserved

the isotopic signature of planktonic foraminifera from ne atlantic surface sediments implications for the reconstruction of past oceanic conditions the stable isotope compositions of the planktonic foraminifera globigerina bulloides globigerinoides ruber white and pink varieties globigerinoides trilobus globorotalia inflata and globorotalia truncatulinoides right and left coiling types were examined as recorders of north atlantic surface water properties based on 40 box core surface sediments between 60 and 30 n while g ruber white and pink varieties and g trilobus mainly reflect summer surface water conditions in their oxygen isotope composition g bulloides reflects temperatures of the northward migrating spring bloom february march in the south to may june in the north our data show that g bulloides cannot be regarded as an indicator for summer temperatures as deduced from duplessy et al s data gt inflata and gt truncatulinoides right and left coiling build their shells in the coldest waters compared with the other species and reflect temperatures between 100 and 400 m water depth the difference in oxygen isotope composition between g bulloides and g inflata serves as a proxy for water mass stratification g bulloides is the only species that gives a distinct pattern in its carbon isotopic composition showing a high correlation with the surface water phosphate values along the transect and may serve as a proxy for palaeonutrients and or productivity

tides of the northwestern ross sea and their impact on dense outflows of antarctic bottom water abstract moored and depth profile measurements of hydrography and currents during the 2003 2005 antarctic slope anslope program on the shelf slope region near drygalski trough sill in the northwest ross sea have revealed an energetic benthic outflow of cold dense antarctic bottom water aabw produced near the shelf break this outflow couples dense water production processes on the continental shelf to ventilation of the global deep ocean we use time series of bottom pressure and currents on the anslope moorings and a high resolution three dimensional primitive equation numerical model to explore the hypothesis that the tidal currents near the shelf break have a significant impact on outflow volume transport and hydrographic properties tidal currents exceed 1 m s 1 at spring tide over the outer shelf and upper slope tidal advection at spring tide carries water parcels 20 km across slope during a half tidal cycle sufficient to advect water from northern drygalski trough across the sill to the shelf break or similarly from the shelf break 500 m water depth down to the 1600 m isobath a tidally rectified lagrangian mean flow of order 0 05 0 1 m s 1 over the outer shelf and upper slope accompanies the spring tide thickness and water mass properties of the benthic layer over the sill and upper slope exhibit pronounced tidal cycles due to advection of hydrographic gradients and to energetic mixing that can extend more than halfway up from the seabed to the ocean surface maximum parameterized diapycnal diffusivity in the benthic layer at spring tides approaches 1 m 2 s 1 the addition of tides has a profound effect on time averaged outflows of aabw primarily through an increase in benthic layer thickness during spring tide downslope volume fluxes of aabw over the slope averaged over a tidal cycle are 2 5 times larger at spring tide than at neap indicating a need to include the effect of tides in large scale ocean models attempting to represent shelf water contributions to the global ocean circulation

the paleocene eocene thermal maximum as recorded by tethyan planktonic foraminifera in the forada section northern italy abstract the forada section in the venetian pre alps of northern italy represents an expanded record of the paleocene eocene thermal maximum petm at a depositional paleodepth of about 1 km 0 5 km high resolution planktonic foraminiferal analysis of this section in a time interval of approximately 1 3 myr across the paleocene eocene boundary reveals striking faunal changes that allow the identification of eight phases a h the late paleocene was represented by stable warm and oligotrophic surface water conditions phase a unstable environmental conditions start well before the onset of petm ca 150 kyr phase b and involved a change towards eutrophy as marked by the increase of subbotina and the concomitant decrease of morozovella this step is also characterized by enhanced fragmentation and dissolution the interval corresponding to the main body of the carbon isotope excursion cie is characterized by a marked increase of acarinina though with some differences in the species composition and relative abundance both in high and low latitudes particularly in the tethyan area forada is no exception to this pattern however at forada two prominent peaks in abundance of acarininids are recorded ca 30 kyr prior to the onset of the cie thus suggesting an increase in temperature heralding the onset of the petm phase c interestingly the lower peak in abundance of acarinina just precedes the 1 carbon isotope negative shift occurring below the onset of the main cie the basalmost eocene corresponding to the lower part of cie curve is represented by intense planktonic foraminiferal dissolution implying an extraordinary rise of the ccd this interval has an estimated duration of about 16 kyr phase d the dominance of acarininids in the lower part of the cie phase e f ca 14 and 22 5 kyr is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the forada depositional environment at that time these acarininids include at forada also the temporally constrained acarinina sibaiyaensis and a africana the morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the cretaceous anoxic events suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the petm the recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups e g biserials globanomalinids igorinids planorotalids and pseudohastigerinids occurring in the middle part of the cie ca 30 kyr after the onset of the petm indicates an initial environmental recovery phase g a new stable state is definitely reached in the upper part of the forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late paleocene conditions phase h however the perturbation during the petm produced significant changes in the ocean geochemistry that endured after the petm event as testified by the prominent high carbonate dissolution characterizing the marly levels and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages these striking oscillations were not present in the latest paleocene

isotopic and distributional evidence of a planktonic habit for the foraminiferal genusstreptochilus bro nnimann and resig 1971 abstract oxygen and carbon isotope analyses show that the biserial foraminiferal genusstreptochilus which was originally described from pelagic sediments on the eauripik rise and ontong java plateau lived deep in the upper water column within the oxygen minimum layer the species ofstreptochilus average from 4 to 19 of the foraminiferal assemblages in which benthic forms compose less than 1 or 2 specimens ofstreptochilus are selectively dissolved when in contact with the bottom water mass their rapid evolutionary turnover of less than a few million years and their wide areal distribution in the equatorial indo pacific are indicative of planktonic foraminifera aside from usefulness of the species ofstreptochilus as stratigraphic indices these neogene biserial planktonic foraminifera are potential indices of paleoceanographic stratification

early eocene palaeoceanography and palaeoclimatology of the eastern north atlantic stable isotope results for dsdp hole 550

neodymium and hafnium boundary contributions to seawater along the west antarctic continental margin highlights nd and hf are released from sediments to the water column in the amundsen sea embayment seawater nd and hf isotope compositions show opposed trends close to the marie byrd seamounts aabw is isotopically distinct in nd between the atlantic and the pacific sectors hf isotope variations occur between the sectors but not with depth in each sector abstract neodymium and hafnium isotopes and elemental concentrations sm nd hf zr have been measured in three water column profiles south of the antarctic circumpolar current in and to the east of the ross sea in conjunction with five bottom water samples from the amundsen sea embayment neodymium and hafnium both appear to be released from sediments in the embayment in the case of nd this is reflected in radiogenic isotope compositions endend up to 5 4 and highly elevated concentrations up to 41 pmol kg hafnium isotopes on the other hand are only very slightly altered relative to the open ocean sites and boundary release is most prominently indicated by elevated concentrations 1 pmol kg versus 0 7 pmol kg there is also a local input of both hf and nd at the marie byrd seamounts which leads to nd isotope compositions as radiogenic as 3 1 and hafnium shifted to less radiogenic compositions in local bottom water a compilation of the new data with literature data reveals a consistent view of the influence of antarctica on the nd isotope composition in lower circumpolar deep water lcdw and antarctic bottom water aabw sector specific nd addition shifts aabw formed in the atlantic sector to less radiogenic isotope compositions average end 9end 9 relative to lcdw average end 8 4end 8 4 whereas aabw in the pacific sector is shifted to more radiogenic values average end 7end 7 the evolution towards more radiogenic endend with depth in lcdw in the pacific sector is likely to reflect admixture of aabw but in addition is also controlled by boundary exchange with the slope as observed at the marie byrd seamounts hafnium isotopes are relatively homogeneous in the data set ranging between ehf 2ehf 2 and 3 8 for most samples excluding less radiogenic compositions in deep waters close to the marie byrd seamounts the hf isotope composition in the pacific sector is however slightly less radiogenic than in the atlantic corresponding to an average of 3 relative to an average of 3 8 this probably reflects unradiogenic hf inputs from antarctica to the pacific sector which are vertically homogenized by reversible scavenging the hf isotope heterogeneity in lcdw between both sectors is likely to indicate a shorter seawater residence time for hf than for nd which is consistent with the dissolved particulate phase partitioning of both elements

oligocene miocene biostratigraphy magnetostratigraphy and isotopic stratigraphy of the western north atlantic magnetostratigraphic records from western north atlantic deep sea drilling project dsdp sites 563 and 558 are correlated with the geomagnetic polarity time scale gpts berggren et ai 1984a 1984b using marine magnetic anomalies and selected biostratigraphic datum levels the magnetochronology established is used to make direct magnetobiostratigraphic correlations that agree with previous oligocene early miocene studies however we show that zones nn8 partim and nn9 and associated epoch 11 correlate with magnetic anomaly 5 chron csn this contrasts with previous indirect correlations of epoch 11 with anomaly sa and requires an upward adjustment of 1 5 2 0 m y for middle late miocene calcareous nannofossil zones we correlate the middle late miocene boundary with zone nn8 and earliest chron csn 10 4 ma

eocene sea temperatures for the mid latitude southwest pacific from mg ca ratios in planktonic and benthic foraminifera abstract we have used laser ablation inductively coupled plasma mass spectrometry la icp ms to measure elemental mg ca al ca mn ca zn ca sr ca and ba ca ratios of 13 species of variably preserved early to middle eocene planktonic and benthic foraminifera from new zealand the foraminifera were obtained from ashley mudstone mid waipara river south island which was deposited at bathyal depth ca 1000 m on the northern margin of the east facing canterbury basin at a paleo latitude of ca 55 s la icp ms data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings mineralisation and detrital sediment screened mg ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late early to early middle eocene ca 51 to 46 5 ma a time interval that spans the termination of the early eocene climatic optimum eeco during this time sea surface temperatures sst varied from 30 to 24 c and bottom water temperatures bwt from 21 to 14 c comparison of mg ca sea temperatures with published 18o and tex86 temperature data from the same samples hollis et al 2009 shows close correspondence indicating that la icp ms can provide reliable mg ca sea temperatures even where foraminiferal test preservation is variable agreement between the three proxies also implies that mg ca temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to eocene species although some species e g v marshalli show significant calibration differences the mg ca ratio of the eocene ocean is constrained by our data to be 35 50 lower than the modern ocean depending on which tex86 temperature calibration kim et al 2008 liu et al 2009 is used to compare with the mg ca sea temperatures sea temperatures derived from 18o analysis of foraminifera from waipara show amplified variability relative to the mg ca and tex86 proxies this amplified variability is probably a diagenetic effect although it is possible that this eocene 18o record contains an ice volume component the amplification signalling that temperature changes may have been accompanied by growth and collapse of ephemeral polar ice sheets on timescales of ca 0 5 myr

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

foraminifer test preservation and diagenesis comparison of high latitude eocene sites foraminifer tests are prone to diagenetic recrystallization on a micron scale that can affect their geochemical composition hence it is important to identify fossil material that is well preserved here we illustrate the textures of tests from several high latitude eocene sites using a combination of reflected light microscopy and high resolution scanning electron microscopy the sites are ocean drilling program odp site 647 in the labrador sea 53 n odp site 689 at maud rise in the weddell sea 64 s odp site 1135 kerguelen plateau c 59 s and outcrop samples from hampden beach new zealand palaeolatitude c 55 s the foraminifera studied from site 647 and hampden beach have glassy transparent tests that show only minor signs of diagenetic alteration whereas the foraminifera from sites 690 and 1135 are opaque and recrystallized we associate the better state of foraminifer preservation at the former sites with the high clay content of the sediments our observations suggest that site 647 and hampden beach may be useful for the establishment of high latitude sea surface temperatures and hence global temperature gradients in the eocene

antarctic bottom water production and export by tides in the ross sea 1 current measurements in the western ross sea show that antarctic bottom water is produced at the outer edge of the continental shelf by tidal stirring of antarctic surface water circumpolar deep water and shelf water current amplitudes during spring tides are greater than 1 m s sufficient to carry circumpolar deep water onto the shelf from offshore and stir at least the lower portion of the water column to a nearly homogeneous mixture the antarctic bottom water produced every day during spring tides does not appear to have a seasonal signal its export rate is estimated to be 1 95 1 85 10 6 m 3 s

orbitally forced climate change in late mid eocene time at blake nose leg 171b evidence from stable isotopes in foraminifera previous stable oxygen isotopic data from surface dwelling foraminifera indicate that eocene tropical sea surface temperatures ssts were significantly lower than at present here we show that stable isotopic analyses 180 13c of the late mid eocene mixed layer dweller morozovella spinulosa are consistent with in mid eocene mid latitudes ssts close to or slightly lower than modern temperatures at blake nose western north atlantic in contrast isotopic analyses of the benthic foraminiter nuttalides truempyi reveal a gradual fall in mean bottom water temperatures from 8 to 7 c over c 500 ka years these deep intermediate water temperatures are significantly higher than modern ones and are similar to intermediate and bottom water temperatures recorded from earlier in palaeogene and late cretaceous time large shifts arc seen in the 18o and 13c values of the planktonic foraminifers of up to 1 and 2 6 respectively that probably reflect temperature and nutrient fluctuations controlled by regional changes in upwelling intensity and runoff the surface to benthos 18o gradient decreases from 3 pdb to a minimum of c 0 5 pdb over 400 ka which could relate to the intensity of upwelling spectral analysis reveals precessional forcing in the foraminiferal 18o records which shows the direct influence of low latitude insolation on surface water stratification monsoonal wind systems may have forced the upwelling cycles and or freshwater input the benthic foraminifer 18o record also contains the obliquity cycle in addition to the precessional cycles indicating the inheritance of mid and high latitude forcing to subtropical deep waters

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

energetic plumes over the western ross sea continental slope rapid descent of dense drygalski trough western ross sea antarctica shelf water over the continental slope within 100 to 250 m thick benthic plumes is described speeds of up to 1 0 m s are recorded flowing at an average angle of 35 to the isobaths entraining ambient lower circumpolar deep water en route this process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor antarctic bottom water nonetheless a 4 hour duration pulse of undiluted shelf water was observed at depth 1407 m directly north of the drygalski trough moving at around 90 degrees to isobaths and at a speed of 1 4 m s thus the export of ross sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths punctuated by rapid downhill cascades

oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from hole 538a dsdp leg 77 gulf of mexico abstract a relatively extended oligocene pelagic sequence with good to medium recovery drilled during dsdp leg 77 in the gulf of mexico yielded rich and well diversified planktonic foraminiferal faunas planktonic foraminifera recorded in hole 538a span the interval from zone p19 through p22 evolutionary lineages were observed among the globoquadrinids the globigernitids and the globigerina ciperoensis and globigerinoides primordius groups quantitative analysis of planktonic foraminiferal assemblages shows that faunas fluctuate in abundance and species diversity throughout the sequence a few of these fluctuations that could be related to selective dissolution are mainly confined to the early mid oligocene a climatic curve was constructed using a warmer indicators turborotalia pseudoampliapertura globoquadrina tripartita dentoglobigerina globularis dentoglobigerina baroemoenensis globigerina ciperoensis and globigerinoides groups and cassigerinella chipolensis and as cooler indicators catapsydrax spp globorotaloides spp subbotina angiporoides group globigerina s str and the tenuitellids three major intervals are identifiable in the climatic curve interval 1 lower up to zone p20 predominantly cooler interval 2 intermediate up to the upper part of zone p21a with warm and cool fluctuations and interval 3 upper warmer with large positive peak due to abundant g angulisuturalis at the beginning of zone p21b with recooling midway in zone p22 in intervals 1 and 2 planktonic foraminiferal faunas are dominated by temperate forms interpretation of planktonic foraminiferal data suggests that cooler water conditions characterize the early mid oligocene during the mid oligocene most of zone p21a water masses exhibit peculiar characteristics transitional to the warmer waters prevailing during the late oligocene warmer conditions were not definitely settled in zone p22 however as indicated by the cooler episode following the warmest peak these climatic trends are inconsistent with those inferred from oxygen isotopes except at small scale in fact oxygen isotope values for oligocene atlantic ocean are too heavy thus too cool in comparison with the high abundance and diversity of warm taxa especially in zone p22 when values are lighter warmer as in zone p19 abundance and diversity of warm indices are too low to explain such a cool isotope values in presence of highly diversified and abundant warm planktonic foraminifera we suggest 1 that the oxygen isotope ratio used for estimating oligocene paleotemperatures might be 1 heavier than eocene values and further increased for the late oligocene this hypothesis implies the presence of a relatively extended ice cap in antarctica in the early and mid oligocene and probably an increase in ice volume during the late oligocene 2 heavier isotope values might be related to an increase in salinity or 3 by a combination of both ice cap and increase in salinity

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

biostratigraphic implications of the maastrichtian lower eocene sequence at the north gunna section farafra oasis western desert egypt abstract eleven planktic foraminiferal zones are established in the maastrichtian lower eocene sediments at the north gunna section farafra oasis western desert egypt the study section is composed of five rock units the khoman dakhla tarawan esna and farafra formations a hiatus at the k t boundary including the upper maastrichtian lower paleocene abathomphalus mayaroensis parasubbotina pseudobulloides zones has been detected moreover most of the esna formation in the study area is of early eocene age m subbotinae a pentacamerata zones rather than late paleocene as commonly observed in the neighbouring areas the zonal scheme developed here is correlated with other sequences and the p zonation of blow 1979 and berggren and miller 1988 are discussed

the climate of the eocene ocean oxygen isotope palaeotemperature estimates are presented for a number of deep sea sediment samples of eocene age covering a wide geographical area these are plotted on a geographical reconstruction for 50 ma the latitudinal temperature gradient at that time was less than half its present value surface temperature at high latitudes was about 10 c and at low latitudes little over 20 c it is concluded that ocean currents must have contributed a greater proportion of the poleward transport of heat than they do at present

environmental change in the subtropics during the late middle eocene greenhouse and global implications 1 oxygen isotope records from odp site 1052 blake nose subtropical north atlantic ocean indicate significant short term high amplitude variability up to 1 4 in about 2500 to 4000 years during the late middle eocene 37 9 37 5 ma these variations reflect a combination of changes in sea surface temperature and the oxygen isotope composition of the regional seawater in order to independently evaluate the magnitude of sst changes at blake nose and better understand the nature of environmental change during the late middle eocene we present planktonic foraminiferal mg ca data combined with 18o data from the same samples the calculated mg ca paleotemperatures indicate a decrease in ssts over the study interval from 33 to 28 c at the same time that previously published foraminiferal 18ocalcite values from the same samples also decrease thus the 18ocalcite values must reflect a significant component of seawater 18o change in order to reconcile the opposite paleotemperature trends reflected by both proxies calculated 18oseawater values decreased from 3 at 37 83 ma to 2 at 37 6 ma the combined trends of the sst and 18oseawater cannot be explained by an increase of continental ice over this time interval instead the data favor an overall weakening of the hydrological cycle as global climate transitioned from the greenhouse to icehouse

paleocene and eocene kaolinite distribution in the south atlantic and southern ocean antarctic climatic and paleoceanographic implications abstract clay mineral associations of paleocene and eocene age have been examined in six drilled sequences from the southern south atlantic and southern ocean these sites are located to provide three depth transects across intermediate water masses widespread abundance of pedogenic smectite at all locations suggests globally warm climates and alternating wet and dry seasons on the adjacent continental margins including antarctica as was the case during the late cretaceous remarkably kaolinite is observed only in paleocene eocene sediments at the highest latitudes of these sites and must have originated from antarctica the restriction of kaolinite to the antarctic region is inferred to have resulted from especially higher rainfall there during the paleocene eocene relative to the lower latitude areas examined this inferred high rainfall is considered to have resulted from globally warm temperatures that increased poleward latent heat transport compensating for a strong heat deficit in the antarctic region relative to the tropics kaolinite was not observed in the latest cretaceous maastrichtian sediments of maud rise antarctica kaolinite first appears in the clay mineralogical assemblages in the earliest paleocene 64 to 64 5 ma at a time of relatively cool intermediate waters and before a warming trend of surface waters currents at intermediate water depths transported fine terrigenous sediments from the antarctica during the latest paleocene and early eocene 59 to 52 ma at a time when the oxygen isotopic strongly in east antarctica during the latest paleocene and early eocene 59 to 59 ma at a time when the oxygen isotopic data indicate maximum warmth of surface and intermediate waters of the southern ocean these are interpreted to reflect a paleocene maximum of antarctic rainfall this development peaked at 57 3 m close to the paleocene eocene boundary a time of maximum warmth based on oxygen isotopic data increased illite content and associated chlorite and random mixed layer clays at the end of the middle eocene 41 ma suggest local development of poorly weathered soils on antarctica favored by a cooling of the southern ocean coeval extension of kaolinite into shallower water depths and similar clay mineral associations in shallower and deeper sites indicate the development of cooler conditions led to an increasing influence of antarctic environments upon intermediate water masses at high latitudes

rapid diversification of planktonic foraminifera in the tropical pacific odp site 865 during the late paleocene thermal maximum the planktonic foraminiferal generamorozovellaandacarininarapidly in 10 k y diversified during the late paleocene thermal maximum lptm giving rise to such morphotypes asm allisonensis new species m africana anda sibaiyaensis single specimen isotopicanalysisconfirmsthatm allisonensisanda sibaiyaensisarerestrictedtothelptm carbon isotope excursion recorded at ocean drilling program site 865 equatorial pacific ocean the short lived 50 to several 100 k y excursion taxa attest to the ephemeral effectsofthelptmonthecalcareousplankton single specimenoxygenisotopedatashow that evolution of m allisonensis and a sibaiyaensis was accompanied by migration to deeper water depths ancestralm velascoensisanda soldadoensiswere extremely rare or absent during the early stages of the lptm but immigrated back into the study area to coexist with their descendants in later lptm horizons photosymbiosis may have facilitatedthemorozovellidandacarininiddiversificationsduringtheoligotrophicconditionsof the lptm

the middle eocene climatic optimum meco a multiproxy record of paleoceanographic changes in the southeast atlantic odp site 1263 walvis ridge the middle eocene climatic optimum meco 40 ma was a transient period of global warming that interrupted the secular cenozoic cooling trend we investigated the paleoceanographic paleoenvironmental and paleoecological repercussions of the meco in the southeast atlantic subtropical gyre ocean drilling program site 1263 tex86 and 18o records support an 4 c increase in surface and deepwater temperatures during the meco there is no long term negative carbon isotope excursion cie associated with the early warming consistent with other sites and there is no short term negative cie 50 kyr during the peak of the meco in contrast to what has been observed at some sites this lack of a cie during the peak of the meco at site 1263 could be due to poor sediment recovery or geographic heterogeneity of the 13c signal benthic and planktic foraminiferal mass accumulation rates markedly declined during meco indicating a reduction of planktic foraminiferal production and export productivity vertical 13c gradients do not indicate major changes in water column stratification and there is no biomarker or micropaleontological evidence that hypoxia developed we suggest that temperature dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming the kinetics of biochemical reactions increase with temperature more so for heterotrophs than for autotrophs steady warming during meco may have enhanced heterotroph i e foraminiferal metabolic rates so that they required more nutrients these additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming the combination of warming and heterotroph starvation altered pelagic food webs increased water column recycling of organic carbon and decreased the amount of organic carbon available to the benthos

a comparison of eocene climate model results to quantified paleoclimatic interpretations abstract the integration of climate model results and geologic information offers considerable potential for deriving greater insight into the geologic record in this study climate model results and quantified climatic interpretations derived from proxy data are compared to assess model capabilities and to examine proxy data interpretations atmospheric general circulation model experiments were used to produce a range of possible representative eocene climate states based on current knowledge of the eocene record the climate model experiments incorporate two idealized endmembers of eocene ocean surface temperature distributions characterized by very different latitudinal gradients model results are compared to quantified interpretations of the climate of early eocene north america in an attempt to identify one of the sea surface temperature distributions as more likely to have existed during the eocene the comparisons do not produce a conclusive match between inferred paleoclimatic information and any single case of model results but some interesting insights become apparent model predictions of mean annual temperature and mean annual precipitation compare favorably to interpretations from geologic evidence but there are large differences between model results and interpreted paleoclimatic parameters of minimum surface temperature and mean annual temperature range several possible causes for these differences are discussed

near bottom particle flux in the abyssal northeast atlantic during a 17 month study at a site on the porcupine abyssal plain of the northeast atlantic approx 48 n 20 w the downward flux of particulate material within and above the benthic nepheloid layer bnl was measured using sediment traps 1455 m above bottom mab 3100 m depth and 90 mab 4465 m depth flux at 90 mab is usually higher than the primary flux at 3100 m depth and this enhancement is especially pronounced during the winter the additional material found in the near bottom trap comprises recently deposited resuspended material rebound flux but with an admixture of refractory sediment it is unlikely that scavenging of either bnl particles or dissolved material contributes greatly to the near bottom flux fluxes of metal tracers 232th and al and cyanobacteria into traps were used to examine the process of resuspension the ratio of tracer flux at 90 mab to that at 3100 m depth was taken as a measure of the strength of the resuspension process the resuspension factor rf and reflects clearly the enhanced resuspension in winter this seasonal variation appears to be related to both the magnitude of near bottom currents and to the wave height at the surface 40 days before it is also possible that recently deposited material forms a partly cohesive blanket on the sediment surface that restricts resuspension to the benthic boundary layer

late quaternary paleoceanography of the tropical atlantic 1 spatial variability of annual mean sea surface temperatures 0 20 000 years b p at least two modes of glacial interglacial climate change have existed within the tropical atlantic ocean during the last 20 000 years the first mode defined by cold glacial and warm interglacial conditions occurred symmetrically north and south of the equator and dominated the eastern boundary currents and tropical upwelling areas this pattern suggests that mode 1 is driven by a glacial modification of surface winds in both hemispheres the second mode of oceanic climate change defined by temperature extremes centered on the deglaciation was hemispherically asymmetrical with the northern tropical atlantic relatively cold and the southern tropical atlantic relatively warm during deglaciation a likely cause for this pattern of variation is a reduction of the presently northward cross equatorial heat flux during deglaciation no single mechanism accounts for all the data potential contributors to oceanic climate changes are linkage to high latitude climates modification of monsoonal winds by ice sheet and or insolation changes atmospheric co2 and greenhouse effects indirect effects of glacial meltwater and variations in thermohaline overturn of the oceans

the eocene oligocene planktic foraminiferal transition extinctions impacts and hiatuses biostratigraphic study and re examination of 22 late eocene to early oligocene sections provides data in support of three and possibly a fourth late eocene impact events in the g index zone during a period of about 1 ma of the middle priabonian between 34 7 and 35 7 ma no major species extinctions or significant species abundance changes directly coincide with these impact events species extinctions are gradual and selective affecting primarily cool temperature intolerant surface dwellers these extinctions began with the onset of global cooling during the early middle eocene and culminated near the eocene oligocene boundary the global cooling was associated with the isolation of antarctica as australia moved northward the development of a circum antarctic circulation growth of antarctic ice sheet beginning by late middle eocene time and a change from a thermospheric to thermohaline circulation we find no evidence that the multiple late eocene impact events directly contributed to the climatic deterioration already in progress

western ross sea continental slope gravity currents antarctic bottom water of the world ocean is derived from dense shelf water that is carried downslope by gravity currents at specific sites along the antarctic margins data gathered by the anslope and clima programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the ross sea when high salinity shelf water exits the shelf through drygalski trough joides trough immediately to the east offers an additional escape route for less saline shelf water while the glomar challenger trough still farther east is a major pathway for export of the once supercooled low salinity ice shelf water that forms under the ross ice shelf the drygalski trough gravity currents increase in thickness from 100 to 400 m on proceeding downslope from 600 m the shelf break to 1200 m upper slope sea floor depth while turning sharply to the west in response to the coriolis force during their descent the mean current pathway trends 35 downslope from isobaths benthic layer current and thickness are correlated with the bottom water salinity which exerts the primary control over the benthic layer density a 1 year time series of bottom water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of shelf water export through drygalski trough these cold 34 75 pulses correlate with strong downslope bottom flow extreme examples occurred during austral summer fall 2003 comprising concentrated high salinity shelf water 1 9 c 34 79 and approaching 1 5 m s 1 at descent angles as large as 60 relative to the isobaths such events were most common during november may consistent with a northward shift in position of the dense shelf water during austral summer the coldest saltiest bottom water was measured from mid april to mid may 2003 the summer fall export of high salinity shelf water observed in 2004 was less than that seen in 2003 this difference if real may reflect the influence of the large iceberg c 19 over drygalski trough until its departure in mid may 2003 when there was a marked decrease in the coldest saltiest gravity current adjacent to drygalski trough northward transport of cold saline recently ventilated antarctic bottom water observed in march 2004 off cape adare was 1 7 sv including 0 4 sv of high salinity shelf water

reevaluation of conflicting eocene tropical temperature estimates molluskan oxygen isotope evidence for warm low latitudes oxygen isotope data from planktonic foraminifera for the warm eocene epoch suggest that tropical sea surface temperatures ssts may have been cooler than at present such data have stimulated various explanations involving e g major changes in ocean heat transport however the planktonic data disagree with terrestrial climate proxies which suggest significantly warmer low latitude temperatures we examined this discrepancy by analyzing seasonal oxygen isotope variations in shallow marine mollusks from the mississippi embayment results indicate that mean annual ssts decreased from 26 27 c in the early eocene to 22 23 c in the oligocene agreeing well with temperatures inferred from terrestrial climate proxies these cooling trends with more significant winter cooling 5 c than summer cooling 3 c are consistent with the predicted consequences of decreasing atmospheric co 2 concentration through the paleogene suggesting that atmospheric co 2 change was a major controlling factor for paleogene climate change that winter sst estimates from the mollusks agree well with the foraminiferal sst estimates suggests that planktonic foraminiferal growth in low latitudes occurred mainly during the cooler winter months throughout the eocene we hypothesize that the unusual hydrography of eocene oceans shifted foraminiferal productivity primarily to winter biasing foraminiferal sst estimates of mean annual ssts