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

differential patterns of benthic foraminiferal extinctions near the paleocene eocene boundary in the north atlantic and the western tethys bathyal benthic foraminifera and stable isotopes from the caravaca and zumaya sections of spain indicate that the mass extinction near the paleocene eocene p e boundary upper planktic foraminiferal zone p6a was rapid coinciding with a negative 13c shift of 2 4 the onset of dark grey shale deposition and increased carbonate dissolution prior to the extinction event diverse benthic foraminiferal assemblages and high 13c values suggest the presence of a stable intermediate deep watermass rich in oxygen and saturated in calcium carbonate in both caravaca and zumaya sections after the extinction event small finely agglutinated haplophragmoides glomospira and thin walled epifaunal taxa nuttallides truempyi dominate in the north atlantic zumaya section this assemblage indicates sluggish circulation bottom waters undersaturated in calcium carbonate and dysaerobic conditions low oxygen conditions prevailed for the succeeding 400 kyr and are characterized by 1 2 fluctuations in benthic 13c in the western tethys caravaca section infaunal taxa buliminids dominate after the extinction event and prevailed through the succeeding 400 to 450 kyr of decreased 13c values indicating low oxygen conditions despite these common features benthic foraminiferal assemblages from these two sections exhibit significant differences during the extinction event at the zumaya section the extinction event occurred over less than 50 kyr and resulted in a sudden reduction in species richness after the 13c shift in contrast at the caravaca section species diversity declined gradually beginning prior to and in concert with the gradually declining 13c values this gradual change occurred over a period of 250 kyr and culminated in a 4 13c shift these differences in 13c values and benthic assemblages between caravaca and zumaya suggest that the p e oceanographic changes that triggered the benthic foraminiferal mass extinction exhibited its first manifestation in the tethys region

provincialism associated with the paleocene eocene thermal maximum temporal constraint sudden global warming 55 ma is associated with remarkable biotic events among both terrestrial and marine organisms the marine microplankton were especially affected with a rapid diversification among tropical planktonic foraminifera a global acme of the dinoflagellate apectodinium complex and sudden changes in abundance patterns among the calcareous nannoplankton additionally and in contrast with the former two groups the latter group showed marked provincialism with the distinctive rhomboaster spp discoaster araneus association rd restricted to a broadly crescent shaped area extending through the tethys seaway and the north and south atlantic oceans we show here that this geographically restricted association was also temporally restricted the stratigraphic occurrence of the rhomboaster spp d araneus association is correlative with the earliest eocene carbon isotope excursion the relative abundance of this association is highest in the interval of minimum 13c values and sharply decreases as the 13c increases toward preexcursion values we propose that the rhomboaster spp d araneus association constitutes a stratigraphic proxy for the carbon isotope excursion and represents an unique response to the paleocene eocene thermal maximum petm with a temporal span on the order of 175 kyr

carbonate saturation dynamics during the paleocene eocene thermal maximum bathyal constraints from odp sites 689 and 690 in the weddell sea south atlantic abstract spatiotemporal patterns of carbonate dissolution provide a critical constraint on carbon input during an ancient 55 5 ma global warming event known as the paleocene eocene thermal maximum petm yet the magnitude of lysocline shoaling in the southern ocean is poorly constrained due to limited spatial coverage in the circum antarctic region this shortcoming is partially addressed by comparing patterns of carbonate sedimentation at the site 690 petm reference section to those herein reconstructed for nearby site 689 biochemostratigraphic correlation of the two records reveals that the first 36 ka of the carbon isotope excursion cie signaling petm conditions is captured by the site 689 section while the remainder of the cie interval and nearly all of the cie recovery are missing due to a coring gap a relatively expanded stratigraphy and higher carbonate content at mid bathyal site 689 indicate that dissolution was less severe than at site 690 thus the bathymetric transect delimited by these two petm records indicates that the lysocline shoaled above site 689 1 100 m while the calcite compensation depth remained below site 690 1 900 m in the weddell sea region the ensuing recovery of carbonate sedimentation conforms to a bathymetric trend best explained by gradual lysocline deepening as negative feedback mechanisms neutralized ocean acidification further biochemostratigraphic evidence indicates the tail end of the cie recovery interval at both sites has been truncated by a hiatus most likely related to vigorous production and advection of intermediate waters

source related variations of ground motions in 3 d media application to the newport inglewood fault los angeles basin summary deterministic earthquake scenario simulations are playing an increasingly important role in seismic hazard and risk estimation our aim is to calculate a substantial number of different finite source scenarios embedded in a 3 d structure for a particular fault or fault system by pre calculating numerical green s functions ngfs a large seismic fault is divided into subfaults of appropriate size for which synthetic green s functions at the surface are calculated and stored consequently ground motions from arbitrary kinematic sources can be simulated for the whole fault or parts of it by superposition to illustrate this approach and its functionalities we simulate m 7 up to 0 5 hz scenario earthquakes for a simplified model of the newport inglewood ni fault in the los angeles la basin we quantify the variations of surface ground motion e g peak ground velocity pgv and synthetic seismograms due to source parameters e g hypocentre location and corresponding slip history the results show a complex behaviour with dependence of absolute pgv and its variation on asperity location source directionality and local structure and demonstrate the necessity to combine 3 d structural and finite source effects to quantify ground motion characteristics and their variations

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

late paleocene middle eocene benthic foraminifera on a pacific seamount allison guyot odp site 865 greenhouse climate and superimposed hyperthermal events we investigated the response of late paleocene middle eocene 60 37 5 ma benthic foraminiferal assemblages to long term climate change and hyperthermal events including the paleocene eocene thermal maximum petm at ocean drilling program odp site 865 on allison guyot a seamount in the mid pacific mountains seamounts are isolated deep sea environments where enhanced current systems interrupt bentho pelagic coupling and fossil assemblages from such settings have been little evaluated assemblages at site 865 are diverse and dominated by cylindrical calcareous taxa with complex apertures an extinct group which probably lived infaunally dominance of an infaunal morphogroup is unexpected in a highly oligotrophic setting but these forms may have been shallow infaunal suspension feeders which were ecologically successful on the current swept seamount the magnitude of the petm extinction at site 865 was similar to other sites globally but lower diversity postextinction faunas at this location were affected by ocean acidification as well as changes in current regime which might have led to increased nutrient supply through trophic focusing a minor hyperthermal saw less severe effects of changes in current regime with no evidence for carbonate dissolution although the relative abundance of infaunal benthic foraminifera has been used as a proxy for surface productivity through bentho pelagic coupling we argue that this proxy can be used only in the absence of changes in carbonate saturation and current driven biophysical linking

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

stable isotope stratigraphy and paleoclimatology of the paleogene bighorn basin wyoming usa abstract climatic warming from the late paleocene into the early eocene had profound effects on atmospheric and marine circulation marine thermal gradients and benthic biota in addition marine carbon isotope values decreased substantially in both surface and deep waters because carbon is rapidly exchanged between reservoirs at the earth s surface such as marine surface water the atmosphere land plants and materials that obtain carbon from plants e g soil minerals and herbivores carbon isotope fluctuations provide time lines linking the marine and continental records we analyzed the carbon isotope composition of paleosol carbonates and mammalian tooth enamel from stratigraphic sections in northwestern wyoming carbon isotope correlation demonstrates that a short interval of extreme high latitude warming coincided precisely with the first appearance of several important modern mammalian orders in addition oxygen isotope analyses of fossils and paleosol carbonates provide information about climatic conditions on land in the paleogene we reconstructed the oxygen isotope composition of local meteoric water using biogenic minerals paleocene eocene meteoric water was significantly 18 o depleted indicating substantial loss of water vapor during its transport to the region soil temperature was calculated as a proxy for mean annual temperature assuming oxygen isotope equilibrium between soil carbonate and meteoric water calculated temperatures were plausible 10 25 c but highly variable prohibiting high resolution analysis of local temperature variations in response to global climatic warming

bathyal ostracodes from the florida hatteras slope the straits of florida and the blake plateau abstract epibathyal ostracodes from the florida hatteras slope the blake plateau and the straits of florida were studied to determine the relationship of numerous genera and species to bottom water environmental conditions such as dissolved oxygen and bottom water temperatures from a total of 100 samples 44 samples evenly distributed between 200 and 1100 m water depth and having an average of 325 specimens were examined in detail using occurrence data from the adjacent continental shelf carapace preservation rose bengal staining and population data indigenous death assemblages were distinguished from transported or reworked fossil specimens the percent of transported specimens varied as follows blake plateau 90 of the samples and usually constitute 10 to 30 of each trachyleberidea bairdoppilata saida paranesidea ambocythere bythocypris cytherella bradleya henryhowella and polycopidae occur in 45 to 80 of the samples in varying percentages the upper depth limits of 39 taxa occur at or just below the thermocline suggesting a relationship to temperature australoecia quasibuntonia cytheropteron ruggieriella saida ambocythere trachyleberidea macrocypris krithe thalassocythere andcytherella are most common or restricted to the o2 minimum zone conversely anchistrocheles bradleya henryhowella androckallia are most common below 750 m in well oxygenated water with temperatures below 8 c the results show that 1 ostracodes display a narrow depth zonation controlled by dissolved oxygen and water temperature 2 species diversity is very high for a bathyal zone 3 ostracodes can be used to identify the source of sediment that has been transported downslope and 4 some taxa are useful in recognizing low oxygenated water in cenozoic deposits

ostracod faunas and water masses across the continental margin off southwestern africa changes in composition of modern benthic ostracod faunas across the continental margin of southwestern africa occur at boundaries between and within major water masses a mixed layer antarctic intermediate water aaiw boundary at 200 m an aaiw salinity minimum zone at 650 m an aaiw bathyal thermocline at 1000 m and the aaiw north atlantic deep water nadw boundary at 1500 m in addition two population changes occur within the nadw at 1 8 2 0 km and 2 0 3 0 km the antarctic bottom water assemblage is sparse and poorly preserved

deep sea ostracode turnovers through the paleocene eocene thermal maximum in dsdp site 401 bay of biscay north atlantic abstract previous low resolution studies suggest that ostracodes in contrast with deep sea foraminifera largely survived the massive environmental changes of the paleocene eocene thermal maximum petm in a new high resolution study from the continental slope 1800 m paleodepth ne atlantic we also find extensive survivorship of ostracode faunas but this is accompanied by a temporary drop in species diversity and ecological diversity during the petm there are 12 common ostracode species before the petm that are reduced to only two species at the same time as the benthic foraminiferal extinction event all but three species reappear in the later parts of the petm and statistical analysis suggests that most of the apparent lazarus species might be found with sufficient sampling of petm faunas we find no evidence for an excursion fauna of ostracodes as has been detected in calcareous nannofossils planktic foraminifera and benthic foraminifera however the ostracode assemblages changed from a relatively diverse ecological assemblage before and after the petm to one dominated by infaunal species typical of low oxygen conditions during the petm the absence of major extinction and the temporary nature of species disappearances are comparable to turnovers in shallow marine ostracodes and stands in sharp contrast to the 50 species level extinction in benthic foraminifers

perturbation at the sea floor during the paleocene eocene thermal maximum evidence from benthic foraminifera at contessa road italy abstract detailed analyses of the benthic foraminiferal assemblages extracted with the cold acetolyse method together with high resolution geochemical and mineralogical investigations across the paleocene eocene p e boundary of the classical succession at contessa road western tethys allowed to recognize and document the paleocene eocene thermal maximum petm interval the position of the benthic extinction event bee and the early recovery of benthic faunas in the aftermath of benthic foraminiferal extinction the stratigraphical interval spanning the p e boundary consists of dominantly pelagic limestones and two prominent marly beds benthic foraminifera indicate that these sediments were deposited at lower bathyal depth not deeper than 1000 1500 m the carbon isotope excursion cie interval is characterized by high barite abundance with a peak at the base of the same stratigraphic interval indicating a complete although condensed record of the early cie a succession of events and changes in the taxonomic structure of benthic foraminifera has been recognized that may be of use for supra regional stratigraphic correlation across the p e boundary interval the composition of the benthic foraminiferal assemblages dominated by infaunal taxa indicates mesotrophic and changing conditions on the sea floor during the last 45 kyr of the paleocene the bee occurs at the base of the cie within the lower marly bed and it is recorded by the extinction of several deep water cosmopolitan taxa then the lysocline ccd rose and severe carbonate dissolution occurred preservation deteriorated the faunal density and simple diversity dropped to minimum values and a peak of glomospira spp has been observed stress tolerant and opportunistic groups represented mainly by bi and triserial taxa dominate the low diversity post extinction assemblages indicating a benthic foraminiferal recovery under environmental unstable conditions probably within a context of sustained food transfer to the bottom a three phase pattern of faunal recovery is recognizable at first the lysocline ccd started to descend and then recovered small sized bulimina oridorsalis umbonatus and tappanina selmensis rapidly repopulated the severely stressed environment later on siphogenerinoides brevispinosa massively returns dominating the assemblage together with other buliminids nuttallides truempyi and anomalinoides sp 1 finally a marked drop in abundance of s brevispinosa is followed by a bloom of the opportunistic and recolonizer agglutinated pseudobolivina that for the first time is recorded within the main cie a second interval of dissolution but less severe than the previous one has been recognized within the upper marly bed uppermost part of the main cie interval and it is interpreted as a renewed less pronounced shoaling of the lysocline ccd that interrupted the recovery of benthic faunas this further rise likely represents a response to persistent instability of ocean geochemistry in this sector of the tethys before the end of the cie in the cie recovery and post cie intervals the composition of the benthic foraminiferal assemblages suggests mesotrophic and unstable conditions at the sea floor according to the geochemical proxy for redox conditions the deposition of the petm sediments at contessa road occurred in well oxygenated waters leading out a widespread oxygen depletion as major cause of the bee changing oceanic productivity carbonate corrosivity and global warming appear to have played a much more important role in the major benthic foraminiferal extinction at the p e boundary

nannoplankton malformation during the paleocene eocene thermal maximum and its paleoecological and paleoceanographic significance the paleocene eocene thermal maximum petm is characterized by a transient group of nannoplankton belonging to the genus discoaster our investigation of expanded shelf sections provides unprecedented detail of the morphology and phylogeny of the transient discoaster during the petm and their relationship with environmental change we observe a much larger range of morphological variation than previously documented suggesting that the taxa belonged to a plexus of highly gradational morphotypes rather than individual species we propose that the plexus represents malformed ecophenotypes of a single species that migrated to a deep photic zone refuge during the height of petm warming and eutrophication anomalously high rates of organic matter remineralization characterized these depths during the event and led to lower saturation levels which caused malformation the proposed mechanism explains the co occurrence of malformed discoaster with pristine species that grew in the upper photic zone moreover it illuminates why malformation is a rare phenomenon in the paleontological record

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

the southern italy earthquake of 23 november 1980 an unusual pattern of faulting abstract a complex rupture history for the 23 november 1980 magnitude 6 9 italian earthquake resulted in an unusual pattern of two high angle subperpendicular normal faults forming the corner of a down dropped crustal block evidence for this interpretation is from aftershocks the pattern of strong ground motion focal mechanism of the mainshock and two critically placed leveling profiles quantitative modeling of leveling profiles using smoothly varying dislocation segments provides confirmation of the fault pattern and specific verification of the existence of a secondary fault which is suborthogonal to the primary fault rupture began on the nw trending main fault with downward motion of the northeast block about 40 sec after initial motion began rupture initiated on an orthogonal ne trending subsidiary fault propagating away from the main fault this fault pattern is consistent with tectonic extension in a northeasterly direction

the latest paleocene crisis in the deep sea ostracode succession at maud rise southern ocean during the late paleocene thermal maximum ca 55 50 ma mid bathyal ostracodes at maud rise in the southern ocean ocean drilling program site 689 underwent a sudden dramatic turnover synchronous with a global extinction in deep sea benthic foraminifers and with large scale short lived negative excursions in the stable isotope record of foraminiferal calcite a previously stable and long lived ostracode assemblage dominated by heavily calcified chiefly epifaunal taxa was replaced within 10 k y by a taxonomically novel association of small thin walled opportunistic and generalist forms that persisted for 25 40 k y thereafter ostracode faunas recovered and common bathyal formsreturned althoughspeciesweresmallerand orless heavilycalcifiedthanbeforethe turnover the complex fabric of change in ostracode shell morphology and assemblage composition and structure reflects both long term and sudden perturbations in seawater chemistry at this site ostracode data are in agreement with the hypothesis that the latest paleoceneextinctionsinthedeepseawerecausedbyachangeinthedominantsourcearea of intermediate water mass from high altitudes to the subtropics these data also suggest that warm saline waters persisted at maud rise for the next 100 k y

the platycopid signal deciphered responses of ostracod taxa to environmental change during the cenomanian turonian boundary event late cretaceous in se england abstract a multi proxy investigation of the cenomanian turonian boundary event ctbe near dover in southern england previously demonstrated that coincident with a major global positive carbon stable isotope excursion during oceanic anoxic event 2 oae 2 the diversity of nanoplankton dinoflagellates planktonic and benthonic foraminifera and ostracods was severely reduced this was attributed to decreasing levels of dissolved oxygen consequent on an intensification and expansion of the oceanic oxygen minimum zone omz into shelf seas in the case of the ostracods it was noted that as podocopid taxa became locally extinct platycopids became the dominant component of the fauna subsequently the platycopid signal hypothesis psh claimed that dominance of platycopids in ostracod assemblages could be regarded as a signal of dysaerobic conditions on the sea floor based on the premise that the filter feeding platycopids able to pass more water over their respiratory surface were better equipped than other benthonic ostracods to survive in water of reduced oxygen concentration the psh has been widely accepted and applied in palaeoenvironmental reconstructions of stratigraphic intervals ranging from the palaeozoic to the quaternary however the modern biological and ecological support claimed for the platycopid signal has been challenged platycopids are occasionally dominant in modern omzs but often they are not and in any case the same can be said about some podocopids apparently precise calibration scales published by some authors are not justified by available data furthermore platycopid signal indications of dysaerobic intervals in the english chalk succession often conflict with the evidence of macrofossils and trace fossils here we review old and new data from two ctbe sites in se england dover and eastbourne and advance an alternative interpretation of the platycopid signal based on the concept of the spread of oceanic oligotrophic conditions into the european chalk sea during oae2 we propose that ostracod assemblages overwhelmingly dominated by platycopids signify oligotrophy because living platycopids appear to be adapted to filter feed on nano and picoplankton which are predominant in oligotrophic conditions

the platycopid signal of oxygen depletion in the ocean a critical evaluation of the evidence from modern ostracod biology ecology and depth distribution abstract the use of relative abundances of filter feeding platycopid ostracods in estimating past levels of dissolved oxygen in the ocean the platycopid signal hypothesis is examined paying particular attention to evidence from faunistic biological and ecological studies the degree of support for the hypothesis has been overstated available data on ostracod depth distribution show that previous claims for platycopid dominance in the oxygen minimum zone in different oceanic regions are misleading and based on only a few studies observations and experimental studies on living platycopids are limited in scope and should be treated with caution we conclude that previously published and widely applied calibrations of platycopid abundance against dissolved oxygen levels are inadequately justified by the available data any further application of the platycopid signal technique should necessarily address these criticisms

cenozoic bathyal and abyssal ostracods beneath the oligotrophic south pacific gyre iodp expedition 329 sites u1367 u1368 and u1370 abstract this study reports on paleocene through pleistocene deep sea ostracod assemblages from carbonate sequences recovered at integrated ocean drilling program iodp sites u1367 u1368 and u1370 during expedition 329 to the south pacific gyre spg the spg has the lowest surface primary productivity in the world oceans and the sedimentary system beneath it has the lowest rates of organic matter flux to the seafloor in the ocean results show that this oligotrophic oceanic environment supported abundant and diverse ostracod faunas during the oligocene and the middle miocene suggesting that ostracods are capable of exploiting low levels of food availability in the deep ocean the spg records revealed ostracod assemblages following major global climatic transitions the cretaceous paleocene 65 5 ma and the eocene oligocene 33 5 ma transitions and the middle miocene climatic optimum 14 ma the danian ostracod assemblage is scarce and characterized by paraphysocythere spp and anebocythereis hostizea high faunal turnover by the early oligocene gives rise to an assemblage predominantly characterized by typical lower bathyal and abyssal genera krithe poseidonamicus argilloecia and cytheropteron that are indicative of cold moderately oxygenated conditions and signal the cooling of the deep ocean after the e o transition an increase in abundance of robust epifaunal taxa bradleya henryhowella dutoitella pennyella and rugocythereis and a pronounced decrease argilloecia and cytheropteron characterize the middle miocene and pleistocene assemblages and indicate the presence of more corrosive bottom waters and enhanced oligotrophic conditions in the spg however low variability in the ostracod assemblage taxonomic composition and stratigraphic distribution at sites u1367 and u1368 suggest that mostly stable paleoceanographic conditions existed in the south pacific gyre during the early to the late oligocene and from the middle to late miocene u1368 declines in ostracod abundances toward the top of the sedimentary sequences at these sites are synchronous with the late oligocene warming and the late miocene carbonate crash in the equatorial pacific but they seem to also overlap the time when the site locations subsided below the calcium carbonate compensation depth ccd as they moved away from the east pacific rise