paleoredox changes across the paleocene eocene thermal maximum walvis ridge odp sites 1262 1263 and 1266 evidence from mn and u enrichment factors an understanding of sediment redox conditions across the paleocene eocene thermal maximum petm 55 ma is essential for evaluating changes in processes that control deep sea oxygenation as well as identifying the mechanisms responsible for driving the benthic foraminifera extinction sites cored on the flanks of walvis ridge ocean drilling program leg 208 sites 1262 1266 and 1263 allow us to examine changes in bottom and pore water redox conditions across a 2 km depth transect of deep sea sediments of petm age recovered from the south atlantic here we present measurements of the concentrations of redox sensitive trace metals manganese mn and uranium u in bulk sediment as proxies for redox chemistry at the sediment water interface and below all three walvis ridge sites exhibit bulk mn enrichment factors ef ranging between 4 and 12 prior to the warming values at crustal averages mn ef 1 during the warming interval and a return to pre event values during the recovery period u enrichment factors across the petm remains at crustal averages u ef 1 at site 1262 deep and site 1266 intermediate depth u enrichment factors at site 1263 shallow peaked at 5 immediately prior to the petm and dropped to values near crustal averages during and after the event all sites were lower in dissolved oxygen content during the petm before and after the petm the deep and intermediate sites were oxygenated while the shallow site was suboxic our geochemical results indicate that oxygen concentrations did indeed drop during the petm but not sufficiently to cause massive extinction of benthic foraminifera

stable carbon isotope patterns of marine biomarker lipids in the arctic ocean during eocene thermal maximum 2 the middle paleocene through early eocene long term gradual warming was superimposed by several transient warming events such as the paleocene eocene thermal maximum petm and eocene thermal maximum 2 etm2 both events show evidence for extreme global warming associated with a major injection of carbon into the ocean atmosphere system but the mechanisms of carbon injection and many aspects of the environmental response are still poorly understood in this study we analyzed the concentration and stable carbon isotopic delta c 13 composition of several sulfur bound biomarkers derived from marine photoautotrophs deposited in the arctic ocean at similar to 85 degrees n during etm2 the presence of sulfur bound biomarkers across this event points toward high primary productivity and anoxic bottom water conditions the previously reported presence of isorenieratene derivatives indicates euxinic conditions in the photic zone likely caused by a combination of enhanced primary productivity and salinity stratification the negative carbon isotope excursion measured at the onset of etm2 for several biomarkers ranges between 3 and 4 5 much larger than the similar to 1 4 recorded in marine carbonates elsewhere suggesting substantial enhanced isotopic fractionation by the primary producers likely due to a significant rise in pco 2 in the absence of biogenic carbonates in the etm2 section of our core we use coeval planktonic delta c 13 from elsewhere to estimate surface water delta c 13 in the arctic ocean and then apply the relation between isotopic fractionation and pco 2 originally calibrated for haptophyte alkenones to three selected organic biomarkers i e s bound phytane c 35 hopane and a c 25 highly branched isoprenoid this yields pco 2 values potentially in the range of four times preindustrial levels however these estimates are uncertain because of a lack of knowledge on the importance of pco 2 on photosynthetic isotopic fractionation

molybdenum behavior during early diagenesis insights from mo isotopes 1 we present molybdenum isotope and concentration data from 14 sites in the eastern pacific from the central california to the peru margin the environments studied have been chosen to represent a broad range in oxidation reduction redox potential which provide a framework for the behavior of this redox sensitive element manganese rich hemipelagic sediments from the eastern tropical pacific have a mean characteristic mo isotope signature 98 95mo 0 49 0 04 two times the standard deviation of the mean 2 sdom with n 14 that reflects fractionation between ocean water and authigenic mo associated with mn oxides authigenic fe mo s deposits from reducing continental margin settings also have a characteristic mo isotopic signature 98 95mo 1 64 0 04 2 sdom with n 136 both of these values are in contrast to highly sulfidic 11 m h2saq restricted basin environments which contain mo isotope values analytically indistinguishable from seawater in terms of the mo isotope composition the modern oceanic mo sink is dominated by continental margin type environments where 98 95mo 1 6 and mn rich sediments where 98 95mo approximately 0 5 with a minor contribution from euxinic settings where h2saq 11 m

high resolution deep sea carbon and oxygen isotope records of eocene thermal maximum 2 and h2 eocene thermal maximum 2 etm2 and h2 were two short lived global warming events that occurred 2 m y after the paleocene eocene thermal maximum petm ca 56 ma we have generated benthic foraminiferal stable carbon and oxygen isotope records of four sites along a depth transect on walvis ridge 3 5 1 5 km paleodepth southeast atlantic ocean and one site on maud rise weddell sea to constrain the pattern and magnitude of their carbon isotope excursions cies and deep sea warming at all sites etm2 is characterized by 3 c warming and a 1 4 cie the h2 event that occurred 100 k y later is associated with 2 c warming and a 0 8 cie the magnitudes of the 13 c and 18 o excursions of both events are signifi cantly smaller than those during the petm but their coherent relation indicates that the 13 c change of the exogenic carbon pool was similarly related to warming during these events despite the much more gradual and transitioned onset of etm2 and h2

neodymium isotopic reconstruction of late paleocene early eocene thermohaline circulation abstract high resolution fish tooth nd isotopic records for eight deep sea drilling project and ocean drilling program sites were used to reconstruct the nature of late paleocene early eocene deep water circulation the goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4 5 c warming of deep and bottom waters at the paleocene eocene boundary the paleocene eocene thermal maximum petm event the combined set of records indicates a deep water mass common to the north and south atlantic southern and indian oceans characterized by mean nd values of 8 7 and different water masses found in the central pacific ocean nd 4 3 and caribbean sea nd 1 2 the geographic pattern of nd isotopic values before and during the petm suggests a southern ocean deep water formation site for deep and bottom waters in the atlantic and indian ocean basins the nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the petm this finding is consistent with the pattern of warming established by recently published stable isotope records suggesting that deep and bottom water warming during the petm was gradual and the consequence of surface water warming in regions of downwelling

south pacific intermediate water oxygen depletion at the onset of the paleocene eocene thermal maximum as depicted in new zealand margin sections 1 extreme global warming and massive input of 13c depleted carbon into the exogenic carbon cycle characterize the paleocene eocene thermal maximum petm circa 55 5 ma previous work indicates that dissolved o2 concentrations dropped in some regions of the ocean during this event but spatial temporal and causal relationships between warming carbon input and o2 deficiency remain elusive we present lithologic carbon isotopic and trace fossil results from outcrops in new zealand that clarify this issue sections exposed at mead and dee streams in eastern marlborough south island contain expanded sedimentary intervals that were deposited before during and after the petm on an upper continental slope the petm in these intervals is characterized by enhanced siliciclastic deposition a hallmark negative carbon isotope excursion and a loss of bioturbation importantly however the latter only occurs during the prominent drop in 13c and not during its recovery our results suggest that south pacific intermediate waters became hypoxic coincident to carbon injection at the start of the petm while higher sea surface temperatures throughout the petm would have decreased the dissolved oxygen content of sinking surface waters we argue here that oxygen depletion was driven by some combination of elevated temperature water column stratification and intermediate water methane oxidation

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

on the duration of the paleocene eocene thermal maximum petm 1 the paleocene eocene thermal maximum petm is one of the best known examples of a transient climate perturbation associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean atmosphere system one key to quantifying the mass of carbon released identifying the source s and understanding the ultimate fate of this carbon is to develop high resolution age models two independent strategies have been employed cycle stratigraphy and analysis of extraterrestrial helium heet both of which were first tested on ocean drilling program odp site 690 these two methods are in agreement for the onset of the petm and initial recovery or the clay layer main body but seem to differ in the final recovery phase of the event above the clay layer where the carbonate contents rise and carbon isotope values return toward background values here we present a state of the art age model for the petm derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during odp leg 208 walvis ridge southeastern atlantic integrated with published records from site 690 weddell sea southern ocean odp leg 113 during leg 208 five paleocene eocene p e boundary sections sites 1262 to 1267 were recovered in multiple holes over a depth transect of more than 2200 m at the walvis ridge yielding the first stratigraphically complete p e deep sea sequence with moderate to relatively high sedimentation rates 1 to 3 cm ka where a is years a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records on the scale of precession cycles with a total duration of the petm now estimated to be 170 ka the revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and heet

global decline in ocean ventilation oxygenation and productivity during the paleocene eocene thermal maximum implications for the benthic extinction the prominent global warming event at the paleocene eocene boundary 55 ma referred to as the paleocene eocene thermal maximum petm was characterized by rapid temperature increase and changes in the global carbon cycle in

arctic late paleocene early eocene paleoenvironments with special emphasis on the paleocene eocene thermal maximum lomonosov ridge integrated ocean drilling program expedition 302 we reconstruct the latest paleocene and early eocene 57 50 ma environmental trends in the arctic ocean and focus on the paleocene eocene thermal maximum petm 55 ma using strata recovered from the lomonosov ridge by the integrated ocean drilling program expedition 302 the lomonosov ridge was still partially subaerial during the latest paleocene and earliest eocene and gradually subsided during the early eocene organic dinoflagellate cyst dinocyst assemblages point to brackish and productive surface waters throughout the latest paleocene and early eocene dinocyst assemblages are cosmopolitan during this time interval suggesting warm conditions which is corroborated by tex86 reconstructed temperatures of 15 18 c inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower eocene spectral analysis reveals that the cyclicity recorded in x ray fluorescence scanning fe data from close to eocene thermal maximum 2 53 ma presence confirmed by dinocyst stratigraphy is related to precession within the lower part of the petm proxy records indicate enhanced weathering runoff anoxia and productivity along with sea level rise on the basis of total organic carbon content and variations in sediment accumulation rates excess organic carbon burial in the arctic ocean appears to have contributed significantly to the sequestration of injected carbon during the petm

persistently declining oxygen levels in the interior waters of the eastern subarctic pacific abstract fifty years of measurements at ocean station papa osp 50 n 145 w show trends in the interior waters of the subarctic pacific that are both impacted by short term few years to bi decadal atmospheric or ocean circulation oscillations and by persistent climate trends between 1956 and 2006 waters below the ocean mixed layer to a depth of at least 1000 m have been warming and losing oxygen on density surfaces found in the depth range 100 400 m 26 3 27 0 the ocean is warming at 0 005 0 012 c y 1 whereas oxygen is declining at 0 39 0 70 mol kg 1 y 1 or at an integrated rate of 123 mmol m 2 y 1 decrease of 22 over 50 years during this time the hypoxic boundary defined as 60 mol o 2 kg 1 has shoaled from 400 to 300 m in the alaska gyre the 26 2 isopycnal occasionally ventilates whereas at osp 26 0 has not been seen at the ocean surface since 1971 as the upper ocean continues to stratify to interpret the 50 year record at osp the isopycnal transport of oxygenated waters within the interior of the subarctic pacific is assessed by using a slightly modified no parameter broecker w 1974 no a conservative water mass tracer earth and planetary science letters 23 100 107 the highest nitrate oxygen signature in interior waters of the north pacific is found in the bering sea gyre western subarctic gyre and east kamchatka current region as a consequence of winter mixing to the 26 6 isopycnal by mixing with low no waters found in the subtropics and okhotsk sea this signature is diluted as waters flow eastward across the pacific evidence of low no waters flowing north from california is seen along the coasts of british columbia and se alaska oxygen in the subsurface waters of the alaskan gyre was supplied 60 by subarctic and 40 by subtropical waters during woce surveys whereas such estimates are shown to periodically vary by 20 at osp other features discernable in the osp data include periods of increased ventilation of deeper isopycnals on an 18 year cycle and strong short term few month variability caused by passing mesoscale eddies the potential impacts of declining oxygen on coastal ecosystems are discussed

benthic foraminiferal extinction and repopulation in response to latest paleocene tethyan anoxia the latest paleocene benthic foraminiferal extinction event has been studied in two marlstone successions in the tethys at wadi nukhl egypt and torangly turkmenistan both sections yield a sapropelic layer at the level of the extinction event at nukhl this layer underlies a thin calcareous bed that has also been found in other middle east upper paleocene sections with the onset of anoxia at the tethyan sea floor the aerobic and oligotrophic gavelinella beccariiformis deep sea community collapsed eutrophic to mesotrophic and low oxygen conditions most likely resulting from enhanced organic carbon fluxes to the sea floor triggered an 100 200 k y repopulation sequence marked by downslope migration of several neritic communities that were dominated by opportunistic and tolerant taxa the initial ecosystem restoration was completed when an aerobic and oligotrophic nuttallides truempyi deep sea community became established we suggest that this repopulation mode could be typical for the central tethys

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

numerical investigation of salinity in controlling ore forming fluid transport in sedimentary basins example of the hyc deposit northern australia this paper presents the first hydrogeological model that fully couples transient fluid flow heat and solute transport associated with the formation of the hyc sedex deposit in the mcarthur basin northern australia numerical results reveal that salinity plays an important role in controlling hydrothermal fluid migration in particular it appears that it is the distribution of evaporitic units within a given basin rather than their absolute abundance that controls the development of free convection relatively saline conditions at the seafloor strengthen the thermally induced buoyancy force and hence promote free convection of basinal solutions whereas high salinities at the bottom counteract the thermal function of natural geothermal gradient and suppress the development of convective hydrothermal fluid circulation in the latter case higher thermal gradients are required to initiate substantial free convective fluid flow numerical experiments also suggest the position of an ore body with respect to its vent system may be controlled by the spatial and temporal salinity distributions in the basin vent distal ore formation a result of exhalation of brines that are denser than seawater and hence can flow away from the vent region is promoted by moderate salinity at the seafloor and higher salinity in the aquifer vent proximal ore accumulation a result of pluming upon exhalation of brines less dense than seawater is favored by the highest salinity conditions occurring near the level of the seafloor

coccolith sr ca records of productivity during the paleocene eocene thermal maximum from the weddell sea 1 a major perturbation of the global carbon cycle 55 million years ago believed to result from release of 1000 2000 gt of c from methane hydrates correlates with an intense but transient greenhouse warming event known as the paleocene eocene thermal maximum petm the rapid 105 years recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle enhanced marine productivity may be one important feedback but indicators for productivity changes have yielded conflicting results here we use a new independent indicator sr ca in coccolith carbonate which covaries with the productivity of coccolithophorid algae to investigate the biotic response in the most complete petm deep sea record which was recovered at odp site 690 in the weddell sea in the dominant coccolithophorid genus toweius a large 40 sr ca increase immediately after the gas hydrate release signals a dramatic productivity increase productivity levels remained high for 60 000 years but decreased to pre event levels by 120 000 years after the gas hydrate release productivity levels during the petm are higher than observed at any other time in our 400 000 year record other coccolithophorid genera chiasmolithus and discoaster show a brief modest 25 sr ca increase increase in productivity that lags behind the methane event by 50 000 years and is within the range of productivity variation elsewhere in the record the timing of the toweius productivity increase agrees well with os isotope records of globally increased weathering intensity which may have provided higher nutrient fluxes to stimulate algal productivity if this type of productivity response occurred globally it would also be consistent with the timing of c drawdown that may have returned temperatures to near pre event levels

comment on the diachroneity of alluvial fan lithostratigraphy a test case from southeastern ebro basin magnetostratigraphy by n swanson hysell and d l barbeau jr

terrestrial carbon isotope excursions and biotic change during palaeogene hyperthermals the earth s climate between 60 and 50 million years ago was punctuated by several abrupt warming events the largest of these being the palaeocene eocene thermal maximum carbon isotope records from the bighorn basin wyoming document these events in the terrestrial realm and show a consistent scaling between marine and terrestrial records across the three main events

authigenic molybdenum isotope signatures in marine sediments we present new mo isotope data from the mexican continen tal margin that in conjunction with previous data allow us to propose a mechanistic description of the mo isotope system in ma rine sediments we hypothesize that there are unique environmen tally dependent mo isotope signatures recorded in marine sedi ments that reflect the mechanisms responsible for authigenic mo accumulation open ocean anoxic sites defined as having dissolved oxygen and sulfide concentrations near zero in the overlying water exhibit a 98 95 mo isotope signature of 1 6 we believe this val ue reflects mo sulfide formation via diagenetic processes within sediments quantitative formation of mo sulfide within the sulfidic water column of euxinic environments results in sediment isotope values similar to the modern seawater value 2 3 as typified by samples from the highly sulfidic black sea in contrast to these reducing settings manganese oxide rich sediments have measured mo isotope values that are more negative relative to seawater than any other sediment samples analyzed to date similar to fe mn crusts 0 7 most measured mo isotope compositions of marine sediments from open ocean settings appear to reflect a mix ture of lithogenic mo 0 0 and the mo signature of a specific authigenic mo accumulation mechanism we therefore suggest that mo isotopes may record unique signatures that reflect the domi nant chemical mechanism for mo sequestration into sediments

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

a biogenic origin for anomalous fine grained magnetic material at the paleocene eocene boundary at wilson lake new jersey 1 the paleocene eocene thermal maximum which occurred 55 5 ma was caused by a massive release of carbon as indicated by an 3 negative carbon isotope excursion recorded in the marine atmospheric and terrestrial reservoirs one suggested source for the carbon a cometary impactor is based on the sudden appearance and high concentration of single domain sd magnetite in paleocene eocene p e boundary cores from the north atlantic continental margin we evaluate the potential sources of sd magnetite at the p e boundary by presenting new magnetic hysteresis low temperature magnetic remanence and transmission electron microscopy data from the north atlantic coastal ocean our results show a similar increase in sd material but demonstrate that the magnetic material has a biogenic origin these findings indicate that the high concentrations of sd magnetite immediately above the p e boundary are the result of unusual accumulations and or preservation of magnetotactic bacteria such bacteria typically occupy the oxic anoxic transition zone near the sediment water interface or in the water column the high abundances of sd magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of sd magnetite it may also indicate that the oxic anoxic redox boundary shifted into the water column the latter explanation implies transient eutrophy of the coastal ocean in this region most likely due to seasonally enhanced runoff and increased stratification and nutrient loading

patterns and magnitude of deep sea carbonate dissolution during eocene thermal maximum 2 and h2 walvis ridge southeastern atlantic ocean 1 eocene thermal maximum 2 etm2 or h1 53 7 ma represents a short lived warming episode associated with the injection of a large mass of 13c depleted carbon into the ocean atmosphere system the mass of injected carbon the extent of deep sea dissolution and the amount of warming during etm2 appear to be approximately half of those documented for the paleocene eocene thermal maximum petm 55 5 ma but the pattern of lysocline migration during etm2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms we present high resolution carbonate dissolution and bulk stable isotope records across etm2 and the successive h2 event 53 6 ma on a common age model for four sites along the walvis ridge depth transect 1500 to 3600 m paleowater depth to assess lysocline evolution the onset of etm2 is characterized by multiple depth dependent transitions of carbonate dissolution up to 96 of the total flux associated with rapid depletions in bulk carbonate carbon up to 1 1 5 and oxygen up to 0 7 1 5 isotope values h2 shows a 0 7 negative carbon isotope excursion with a coeval decrease in 18o of 0 5 and 80 of carbonate dissolution during etm2 the lysocline recovered within 30 ka we attribute this rapid recovery to terrestrial caco3 neutralization through enhanced chemical weathering of carbonates in soils and rocks according to theory carbonate dissolution was lower after recovery than prior to etm2 indicating carbonate ion oversaturation and a deeper position of the lysocline spectral analysis indicates that the changes in carbonate dissolution and 13c values were precession paced implying that weathering feedbacks and short term perturbations in the carbon cycle were important in determining early eocene background and hyperthermal ocean co32 conditions

fluvial discharge and sea level changes controlling black shale deposition during the paleocene eocene thermal maximum in the dababiya quarry section egypt abstract the formation of black shales along the tethyan margins at the paleocene eocene thermal maximum petm 55 ma may have been an important feedback mechanism to reduce the warming by excess carbon burial however the detailed evolution of sediment redox conditions during this event is still poorly constrained we address this issue by a high resolution mineralogical and geochemical investigation of the outer neritic dababiya quarry petm section in central egypt which serves as the global boundary stratotype section and point for the base of the eocene there the base of the petm beds corresponds to the onset of sediment lamination indicative of oxygen deficiency at the seafloor the absence of calcium carbonate and a major increase in phyllosilicate abundance and change in detritus sensitive trace elements is indicative of severe carbonate dissolution in addition to enhanced fluvial input erosion of coastal low lands and deposition during low or slightly rising sea level subsequently fully anoxic conditions were established for a short period during the peak phase of the petm as recorded by the strong relative enrichment of redox sensitive trace elements and organic carbon compared to background sediments the decoupling of the fe and mo contents from the detrital fraction may even indicate that euxinic conditions existed with free hydrogen sulfide in the water column concurrent to the onset of anoxia high carbonate and quartz contents as well as high elemental ratios of si al suggest a major drop of siliciclastic sediment supply sediment starvation most likely caused by a rapid sea level rise the final recovery phase of the petm is associated with a progressive restoration of the pre petm siliciclastic sedimentation temporary seasonal anoxic to dysoxic conditions and high phosphorus enrichment followed by carbonate dominated sedimentation and the return to well oxygenated conditions we conclude that after a period of strong fluvial discharge several parameters inherent to the petm e g warming water column stratification and enhanced fluvial discharge may have contributed to the development of anoxia and increased the burial efficiency of organic carbon by reducing water column oxygenation the temporal coincidence of sediment starvation and onset of black shale deposition during the petm suggests that a rapid sea level rise was an additional important triggering factor therefore our results support not only current views that tethyan continental shelf areas may have acted as large carbon sinks during the petm but also indicate that transgressions may have provided an important feedback mechanism for organic carbon drawdown during hyperthermal events

a molybdenum isotope record of eocene thermal maximum 2 implications for global ocean redox during the early eocene during the early eocene a series of short term global warming events hyperthermals occurred in response to the rapid release of carbon into the oceans and atmosphere in order to investigate the response of ocean redox to global warming we have determined the molybdenum isotope compositions 98 95 mo of samples spanning one such hyperthermal eocene thermal maximum 2 etm 2 54 1ma from integrated ocean drilling program expedition 302 site m0004a in the arctic ocean the highest 98 95 mo in our sample set 2 00 0 11 corresponds to the development of local euxinia at site m0004a during the peak of etm 2 which we interpret as recording the global seawater 98 95 mo at that time the etm 2 seawater 98 95 mo is indistinguishable from a recent estimate of seawater 98 95 mo from an earlier hyperthermal paleocene eocene thermal maximum petm 55 9ma 98 95 mo 2 08 0 11 it is argued that the similarity in seawater 98 95 mo during etm 2 and the petm was caused by the development of transient euxinia in the arctic ocean during each hyperthermal that allowed sediments accumulating in this basin to capture the long term 98 95 mo of early eocene seawater our new data therefore place a minimum constraint on the magnitude of transient global seafloor deoxygenation during early eocene hyperthermals

testing the cenozoic multisite composite δ18o and δ13c curves new monospecific eocene records from a single locality demerara rise ocean drilling program leg 207 until recently very few high quality deep ocean sedimentary sections of eocene age have been available consequently our understanding of eocene paleoceanography has become heavily reliant on composite records patched together from multiple sites in different ocean basins and generated using multiple taxa potential sources of local noise in the global signal here we test the reliability of the early to middle eocene composite 18o and 13c stratigraphies zachos et al 2001 by generating new monospecific records in benthic foraminiferal calcite from a single locality demerara rise in the tropical western atlantic ocean drilling program leg 207 we present new stable isotope correction factors for commonly used eocene benthic foraminiferal species we find that interspecies isotopic offsets are constant across the isotopic range supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera in general the 18o stratigraphy from demerara rise supports the validity of the eocene 18o composite while revealing a temporary warming punctuating middle eocene cooling this warming may correspond to the so called middle eocene climatic optimum previously documented in the southern ocean the composite and demerara rise records for 13c differ substantially by removing the intersite and intertaxa sources of uncertainty in 13c we obtain a clearer picture of carbon cycling during the eocene secular change in interocean 13c gradients through the eocene reveals that intervals of climatic warmth especially the early eocene are associated with very small water mass ageing gradients

paleoenvironmental implications of cenozoic sediments from the central arctic ocean iodp expedition 302 using inorganic geochemistry 1 integrated ocean drilling program iodp expedition 302 arctic coring expedition acex recovered a unique sediment record from the central arctic ocean revealing that this region underwent major environmental fluctuations since the late cretaceous major and trace element composition of 1 300 samples were determined using x ray fluorescence xrf the results show significant compositional variability of the sediments with depth that can be attributed to changes in a provenance and pathways of detrital material b paleoenvironmental conditions and depositional processes and c diagenetic overprint of the primary record in addition to existing lithological units we introduce new geochemical units for a more process related approach interpreting the acex record in detail via the geochemical signature of siberian flood basalts we are able to reconstruct the discontinuous rifting and deepening of the central lomonosov ridge during the paleogene accompanied by changing current regimes and the onset of sea ice eocene biosiliceous sedimentation took place in a relatively shallow setting under predominantly anoxic bottom water conditions causing a positive anoxia productivity feedback although water column stratification was repeatedly interrupted by ventilation events anoxic to sulfidic conditions were even more extreme after biosilica production ceased and significant amounts of pyrite were deposited on the lomonosov ridge especially in organic matter rich paleogene deposits diagenetic processes obscured the paleoenvironmental signals fundamental environmental changes occurred in the middle eocene but geochemical and micropaleontological proxies point not to the identical sediment depth after approximately 26 ma of non deposition or erosion the middle miocene record shows the transition to dominantly oxic bottom water conditions although suboxic diagenesis seemingly affected these deposits

molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the early jurassic relatively brief periods of severe paleoenvironmental change during the jurassic and cretaceous were associated with the widespread accumulation of organic rich marine deposits termed oceanic anoxic events oaes these intervals involved abrupt global warming of 5 10 c higher rates of continental weathering elevated extinction rates and large scale perturbations to the global carbon cycle the major oaes also overlapped temporally the emplacement of large igneous provinces however despite being known as oaes the extent of seawater anoxia at those times is undefined and the causative processes remain unclear here we show how changes in seawater molybdenum isotope ratios a proxy for seawater anoxia during the toarcian early jurassic oae define the onset and expansion of oxygen deficient conditions our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically broadly in line with precession driven changes in 13 corg despite their intermittent occurrence over geological history oaes have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day