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

authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

oxygen minimum zone controlled mn redistribution in arabian sea sediments during the late quaternary 1 accumulation of labile mn is related to bottom water oxygen concentrations in this study we investigate the relation between oxygen minimum zone omz intensity and mn burial in arabian sea during the late quaternary mn carbonates in sediments of the deep arabian basin indicate that this part of the basin remained oxygenated for at least the last 185 kyr sequential leaching showed manganese carbonate enrichments with concentrations up to 3750 ppm in deep basin sediments these mn spikes must have formed diagenetically during periods of increased mn oxide fluxes to the deep basin associated with vertical extension of the omz this extension caused remobilization of mn oxides from a previously oxic slope resulting in increased mn accumulation in the deep basin mn relocation is evidenced by synchronous mn depletions in organic rich intervals in slope sediments mn records from the deep basin can thus be used as a qualitative proxy to reconstruct intermediate water oxygenation

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

late cretaceous and early paleogene nutrient and paleoproductivity records from blake nose western north atlantic ocean 1 we evaluate phosphorus p and biogenic barium bio ba as nutrient burial and export productivity indicators for the late cretaceous and early paleogene combining these with calcium carbonate caco3 organic carbon c and bulk caco3 c isotopes 13c sample ages span 36 71 ma 1 sample 0 5 m y for a depth transect of sites in the western north atlantic blake nose ocean drilling program leg 171b sites 1052 1051 and 1050 we use a multitracer approach including redox conditions to investigate export productivity surrounding the global paleocene 13c maximum 57 ma reducing conditions render most of the bio ba record not useful for export productivity interpretations p and organic c records indicate that regional nutrient and organic c burial were high at 61 and 69 ma and low during the paleocene 13c maximum a time of proposed global high relative organic c burial observed organic c burial changes at blake nose cannot explain this c isotope excursion

new evidence for subtropical warming during the late paleocene thermal maximum stable isotopes from deep sea drilling project site 527 walvis ridge the late paleocene thermal maximum lptm was a dramatic short term global warming event that occurred 55 ma warming of high latitude surface waters and global deep waters during the lptm has been well documented however current data suggest that subtropical and tropical sea surface temperatures ssts did not change during the event conventional paradigms of global climate change such as co2 induced greenhouse warming predict greater warming in the high latitudes than in the tropics or subtropics but nonetheless cannot account for the stable tropical subtropical ssts we measured the stable isotope values of well preserved late paleocene to early eocene planktonic foraminifera from south atlantic deep sea drilling project dsdp site 527 to evaluate the subtropical response to the climatic and environmental changes of the lptm planktonic foraminiferal 18o values at site 527 decrease by 0 94 from pre lptm to excursion values providing the first evidence for subtropical warming during the lptm we estimate that subtropical south atlantic ssts warmed by at least 1 4 c on the basis of possible changes in evaporation and precipitation the new evidence for subtropical sst warming supports a greenhouse mechanism for global warming involving elevated atmospheric co2 levels

early diagenetic processes during mn carbonate formation evidence from the isotopic composition of authigenic ca rhodochrosites of the baltic sea the formation of authigenic ca rich rhodochrosite acr in sapropelic sediments of the gotland basin baltic sea is governed by deepwater renewal processes whereby saline water from the north atlantic flushes the brackish anoxic baltic deeps the carbon and oxygen isotopic compositions of these mn carbonates suggest that acr formation takes place just below the sediment surface and that dissolved compounds from the deepwater column such as water and bicarbonate molecules were incorporated in acr during authigenesis porewaters near the sediment surface display 18 o values of 5 4 vsmow and are generally depleted in 18 o compared to the oxygen isotopic composition of water in equilibrium with mn carbonate solid solutions acr 18 o values are 4 6 this suggests that early burial diagenetic processes significantly modify the initial isotopic composition of water during mn carbonate formation the reduction of sulfate having 18 o values of 8 4 accounts for a permanent enrichment of porewater 18 o and observed 18 o values at depth equal to 4 6 however this process does not explain the observed disequilibrium in the oxygen isotopic composition between water and acr close to the sediment surface where mn carbonate formation takes place based on isotopic mass balance calculations we suggest that mno2 with 18 o values of 8 9 released oxygen enriched in 18 o into the anoxic porewaters close below the sediment surface this process should occur after oxygenation events during deepwater renewal when mno2 accumulates at the surface of anoxic sediments manganese carbonates formed in these waters display 18 o values of 1 0 heavier than values expected solely from the initial deepwater composition this quantitatively explains the discrepancy between paleosalinities calculated from acr 18 o based on mn carbonate water isotopic equilibrium fractionation and direct observations for the same period our results emphasize the important role of microbial mno2 reduction during rhodochrosite authigenesis and suggest that mn ii activity rather than alkalinity is the limiting component for sedimentary mn carbonate formation copyright 2002 elsevier science ltd

the palaeocene eocene carbon isotope excursion constraints from individual shell planktonic foraminifer records the palaeocene eocene thermal maximum petm is characterized by a global negative carbon isotope excursion cie and widespread dissolution of seafloor carbonate sediments the latter feature supports the hypothesis that the petm and cie were caused by the rapid release of a large mass greater than 2000gt c of 12c enriched carbon the source of this carbon however remains a mystery possible sources include volcanically driven thermal combustion of organic rich sediment dissociation of seafloor methane hydrates and desiccation and oxidation of soil sediment organics a key constraint on the source s is the rate at which the carbon was released fast rates would be consistent with a catastrophic event e g massive methane hydrate dissociation whereas slower rates might implicate other processes the petm carbon flux is currently constrained by high resolution marine and terrestrial records of the cie in pelagic bulk carbonate records the onset of the cie is often expressed as a single or multiple step excursion extending over 10 4 years individual planktonic shell records in contrast always show a single step cie with either pre excursion or excursion isotope values but no transition values benthic foraminifera records which are less complete owing to extinction and diminutive assemblages show a delayed excursion here we compile and evaluate the individual planktonic shell isotope data from several localities we find that the most expanded records consistently show a bimodal isotope distribution pattern regardless of location water depth or depositional facies this suggests one of several possibilities i the isotopic composition of the surface ocean atmosphere declined in a geologic instant 500yr ii that during the onset of the cie most shells of mixed layer planktonic foraminifera were dissolved or iii the abundances or shell production of these species temporarily declined possibly due to initial ph changes

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

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

use of multiproxy records on the agulhas ridge southern ocean ocean drilling project leg 177 site 1090 to investigate sub antarctic hydrography from the oligocene to the early miocene 1 ocean drilling program odp site 1090 on the agulhas ridge in the south atlantic sector of the southern ocean is ideally located to capture changes in southern ocean circulation patterns using samples taken from cored sediments we construct multiproxy records of productivity biogenic barium baex opal and caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox conditions u and mn enrichments to investigate hydrographic conditions associated with climatic shifts from the oligocene through the early miocene orbitally induced cyclicity in u and mn enrichments 100 kyr suggests shifts in deepwater characteristics however caco3 dissolution coincident with low u and mn enrichments does not indicate low oxygen corrosive waters similar to modern conditions these observations indicate that a well developed modern type antarctic circumpolar current acc did not yet exist over the period from 30 to 20 ma with two potential consequences the southern ocean was not functioning as a silica trap permitting a broader distribution of silica that may have facilitated organic carbon burial in the ocean in general and the lack of a deeply mixing acc may have facilitated organic carbon burial in the southern ocean both the relative high opal mars coincident with low caco3 mars and absolute high pr mars burial of organic carbon suggest a powerful mechanism for pco2 drawdown

black shale formation during the latest danian event and the paleocene eocene thermal maximum in central egypt two of a kind abstract the paleocene eocene thermal maximum petm 55 8 ma is considered as the most severe of a series of transient warming events hyperthermals that occurred during the early paleogene however the extent and magnitude of environmental changes during the short lived warming events pre and post dating the petm are still poorly constrained in this study we focus on the latest danian event lde 61 7 ma and compare it to the petm we present high resolution micropaleontological geochemical and mineralogical data of the petm and the lde in two adjacent sections from the gebel qreiya area in egypt there both events are characterized by a distinct set of event beds overlying an unconformity they are associated with intense carbonate dissolution and substantial changes in the benthic foraminifera fauna moreover both show an abrupt drop of siliciclastic input sediment starvation correlative to the onset of black shale formation and a strong enrichment in redox sensitive trace elements the evidence for enhanced detrital input during the onset of the petm and a longer recovery phase with enhanced phosphorus sedimentation during the petm attests a stronger environmental impact of this event compared to the lde according to rock eval and elemental analysis the petm as well as the lde event beds have up to 4 wt organic carbon small amounts of volatile hydrocarbons but high amounts of highly weathered and inert organic matter black carbon during pyrolysis the extremely high temperatures for the maximum release of hydrocarbons of the petm and lde samples correspond to thermal heating of 170 c which is incompatible with the sediment burial history therefore we suggest that the organic matter in both event deposits does not reflect well preserved marine biomass but predominantly represents a mixture of heavily weathered autochthonous marine material and allochthonous combustion residues differences in preservation and or type of organic matter are also likely to account for the divergent stable isotope anomalies of organic carbon the well known negative carbon isotope anomaly at the petm and a positive anomaly at the lde although warming water column stratification and enhanced nutrient input may have promoted anoxic conditions on the shelf during the lde as well as during petm our results support rapid sea level rise and clastic starvation as one important mechanism for black shale formation and carbon sequestration for both events this result underlines the similarity of both hyperthermal events in terms of environmental changes recorded on the southern tethyan margin with the petm showing an additional early phase of strong detrital input not revealed at the lde

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

the ecology of living stained deep sea benthic foraminifera from the sulu sea the distribution of living rose bengal stained deep sea benthic foraminifera was determined in the upper 20 cm of sediments of eight soutar box cores taken from two depth transects 510 4515 m in the thermospheric 10 c sulu sea despite the uniformity of bottom water temperatures salinities and dissolved oxygen levels below 1000 m significant faunal differences exist at different depths in the low oxygen 1 25 ml l below 1000 m basin the shallowest site 510 m is dominated 10 of the calcareous fauna by cibicidoides uvigerina 150 m and bolivina 63 m while siphonina is codominant with cibicidoides and uvigerina in the 1005 m core the 2000 m cores are dominated by cibicidoides gyroidinoides and oridorsalis while cibicidoides bradyi and oridorsalis umbonatus dominate the 3000 and 4000 m cores infaunal assemblages of valvulineria mexicana are found in the sediments of the 4515 m core relatively low bottom water oxygen values do not necessarily yield typical low oxygen taxa such as bolivina uvigerina chilostomella bulimina and globobulimina changes in the abundances of these taxa in fossil assemblages have been used as indicators of changes in ancient bottom water oxygen levels but may instead reflect organic carbon contents of the sediments an examination of the vertical distributions of foraminiferal assemblages from the 63 m and 150 m fractions reveals that taxa have microhabitat preferences similar to those observed in other regions taxa found in the upper 0 to 1 cm interval epifaunal include cibicidoides wuellerstorfi and hoeglundina elegans while taxa such as chilostomella and globobulimina reach maximum abundances in subsurface sediments and have infaunal microhabitat preferences cibicidoides bradyi and o umbonatus live in sediment depths from 0 to 4 cm and have transitional preferences with both epifaunal and infaunal occurrences intrageneric differences in test morphologies including pore distribution rounded peripheries and variable spire height are observed in cibicidoides and gyroidinoides and are suggested to be related to microhabitat preferences vertical distributions of a number of taxa found in both the 63 to 150 m and 150 m fractions are similar suggesting that juveniles and adults live under similar microhabitat conditions ontogenetic changes in microhabitat preferences of most species are not observed in this study and therefore would not be expected to account for isotopic vital effects reported for some taxa in previous studies

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

on the duration of magnetochrons c24r and c25n and the timing of early eocene global warming events implications from the ocean drilling program leg 208 walvis ridge depth transect 1 five sections drilled in multiple holes over a depth transect of more than 2200 m at the walvis ridge se atlantic during ocean drilling program odp leg 208 resulted in the first complete early paleogene deep sea record here we present high resolution stratigraphic records spanning a 4 3 million yearlong interval of the late paleocene to early eocene this interval includes the paleocene eocene thermal maximum petm as well as the eocene thermal maximum etm 2 event a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records and shipboard color data these records were used to refine the shipboard derived spliced composite depth for each site and with a record from odp site 1051 were then used to establish a continuous time series over this interval extensive spectral analysis reveals that the early paleogene sedimentary cyclicity is dominated by precession modulated by the short 100 kyr and long 405 kyr eccentricity cycles counting of precession related cycles at multiple sites results in revised estimates for the duration of magnetochrons c24r and c25n direct comparison between the amplitude modulation of the precession component derived from xrf data and recent models of earth s orbital eccentricity suggests that the onset of the petm and etm2 are related to a 100 kyr eccentricity maximum both events are approximately a quarter of a period offset from a maximum in the 405 kyr eccentricity cycle with the major difference that the petm is lagging and etm2 is leading a 405 kyr eccentricity maximum absolute age estimates for the petm etm2 and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of earth s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods nevertheless we provide two possible tuning options which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405 kyr eccentricity cycle for the entire paleogene

analysis of the non linearity in the pattern and time evolution of el nino southern oscillation in this study the observed non linearity in the spatial pattern and time evolution of el nino southern oscillation enso events is analyzed it is shown that enso skewness is not only a characteristic of the amplitude of events el ninos being stronger than la ninas but also of the spatial pattern and time evolution it is demonstrated that these non linearities can be related to the non linear response of the zonal winds to sea surface temperature sst anomalies it is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive el nino versus negative la nina and strong versus weak events exist which is mostly describing the difference between central and east pacific events central pacific events tend to be weak el nino or strong la nina events in turn east pacific events tend to be strong el nino or weak la nina events a rotation of the two leading empirical orthogonal function modes illustrates that for both el nino and la nina extreme events are more likely than expected from a normal distribution the bjerknes feedbacks and time evolution of strong enso events in observations as well as in coupled model simulations also show strong asymmetries with strong el ninos being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by la nina events in turn strong la nina events are preceded by el nino events and are more strongly forced by thermocline depth anomalies than by wind anomalies further the zonal wind response to sea surface temperature anomalies during strong el nino events is stronger and shifted to the east relative to strong la nina events supporting the eastward shifted el nino pattern and the asymmetric time evolution based on the simplified hybrid coupled rechoz model of enso it can be shown that the non linear zonal wind response to sst anomalies causes the asymmetric forcings of enso events this also implies that strong el ninos are mostly wind driven and less predictable and strong la ninas are mostly thermocline depth driven and better predictable which is demonstrated by a set of 100 perfect model forecast ensembles

correlation between isotope records in marine and continental carbon reservoirs near the palaeocene eocene boundary changes in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land the carbon isotope compositions of marine carbonate sediments from the late palaeocene vary considerably exhibiting a sudden decrease close to the palaeocene eocene boundary which coincides with deep sea benthic extinctions1 and with changes in ocean circulation here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel in using palaeosol carbonates to reconstruct the co2 content of the ancient atmosphere2 isotope shifts of this sort will have to be taken into account the sharp decrease in 13c 12c ratios in the late palaeocene provides a datum for precise correlation of marine and continental records and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals

evidence from authigenic uranium for increased productivity of the glacial subantarctic ocean authigenic uranium is precipitated in reducing sediments and therefore responds both to changes in particulate organic carbon flux to the sediment and to changes in the oxygen concentration of bottom waters by examining a large number of cores over a wide latitudinal and depth range in the atlantic sector of the southern ocean we hope to distinguish between a predominantly productivity driven authigenic u signal and a circulation or sediment focusing signal we find little to no authigenic u in holocene sediments throughout the south atlantic ocean glacial sediments north of 40 s lack authigenic u whereas sediments from the subantarctic zone show substantial enrichments in authigenic u relative to the holocene up to 5 3 ppm the widespread distribution of glacial u enrichment even in cores with no glacial interglacial change in mass accumulation rate implies that u deposition was not caused by an increased supply of organic carbon via sediment focusing authigenic u and organic carbon in a shallow core 1000 m from the subantarctic region show the same glacial increase found in the deep cores because this site was well ventilated during the last glacial maximum its record provides further evidence that increased glacial productivity of the subantarctic region contributed to the high concentrations of authigenic u found in the glacial sections of deep cores

scavenged excess aluminum and its relationship to bulk titanium in biogenic sediment from the central equatorial pacific ocean we present results from chemical analyses of al and ti in surface sediment sampled along two cross equator latitudinal transects at 135w and 140w in the central equatorial pacific ocean although traditionally both al and ti are considered to reside exclusively within terrigenous phases in marine sediment these sediments present extremely high al ti ratios that are several times that of average shale and other potential crustal sources a sharp maximum in al ti is observed slightly south of the equator where sedimentary bulk accumulation rate bar is also highest reflecting elevated productivity in the overlying water caused by surface water divergence bulk al ti decreases sharply away 2 latitude to near crustal values at 4 north and south the latitudinal profiles of al ti are entirely unrelated to the concentration of the biogenic components as well as to the absolute accumulation of al and ti these results indicate the presence of a significant scavenged component of al sourced directly from seawater during particle settling the data from the two transects analytically and oceanographically confirms our earlier work that was based on the single 135w transect calculations of alexcess indicate that the highest al ti ratios correspond to 50 of the total al being unsupported by the small amount of terrigenous phases present these results are consistent with previous and ongoing studies of biogenic sediment suspended particulate matter and sediment trap material quantitative use of al as an index of terrigenous material may therefore lead to an overestimation by a factor of two of the true terrigenous load in marine sediment sedimentary rock and settling particles because bulk al ti appears to respond to sedimentary bar which in biogenic regimes is linked to surface water productivity downcore records of al ti in biogenic sediment may track productivity changes through time such al ti proxy records may be applicable in sediment of all ages unlike radionuclide tracers which are limited by radioactive decay to use over the past hundreds of kyr

reversed deep sea carbonate ion basin gradient during paleocene eocene thermal maximum 1 the paleocene eocene thermal maximum petm 55 ma ago was marked by widespread caco3 dissolution in deep sea sediments a process that has been attributed to massive release of carbon into the ocean atmosphere system the pattern of carbonate dissolution is key to reconstructing changes in deep sea carbonate chemistry and ultimately the rate magnitude and location of carbon input here we show that during the petm the deep sea undersaturation was not homogeneous among the different ocean basins application of a sediment model to a suite of data records from different sites and ocean basins shows that a globally uniform decrease in deep sea carbonate ion concentration co32 is inconsistent with the data rather we demonstrate that deep sea co32 increased from the atlantic through the southern ocean into the pacific our results show that the petm deep sea co32 basin gradient during dissolution was reversed relative to the modern

depth dependency of the paleocene eocene carbon isotope excursion paired benthic and terrestrial biomarker records ocean drilling program leg 208 walvis ridge 1 the paleocene eocene thermal maximum petm coincided with a negative carbon isotope excursion cie in carbonate and organic matter in terrestrial and marine records consequently the petm global warming of 5 6 c has been attributed to the rapid emission of a large amount of isotopically light carbon into the ocean atmosphere system and the magnitude of the cie has been used to estimate the amount of carbon greenhouse gas emitted however there are large discrepancies between the magnitude of the cie in marine and in terrestrial material in different types of marine carbonate records bulk carbonate planktic and benthic foraminiferal carbonate and in marine carbonate records from different locations the marine carbonate record of the cie may be incomplete in most deep sea bathyal abyssal locations because of ocean acidification and widespread dissolution of seafloor carbonates we demonstrate that the cie in benthic foraminiferal stable isotope records is relatively abrupt and not as gradual as portrayed in bulk carbonate records along the walvis ridge depth transect se atlantic the benthic cie is about 1 5 at 3600 m paleodepth in contrast to about 3 5 at 1500 m paleodepth consistent with depth dependent truncation by carbonate dissolution strong covariance between the benthic record and the stable carbon isotope values of terrestrial n alkanes isolated from the same core i e site 1263 supports a relatively rapid excursion of at least 3 5 but no more than 5 0

an alternative age model for the paleocene eocene thermal maximum using extraterrestrial 3he a continuous age model for the brief climate excursion at the paleocene eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3he 3he et to the seafloor 3he et measurements from odp site 690 provide quantitative evidence for the rapid onset few kyr and short duration 120 kyr of global warming and of the associated disturbance to the earth s surficial carbon budget at this time these observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon possibly from seafloor methane hydrate as the proximal cause of the event however the 3he et technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre event values the 3he et based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle and so may indicate additional or accelerated mechanisms of carbon removal from the ocean atmosphere system during this period 3he et was also measured at odp site 1051 to test the validity of the site 690 chronology comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at site 1051 an observation consistent with sediment structures and previous age modeling efforts the site 1051 age model shows a 30 kyr period in which climate proxies return toward pre event values after which they remain invariant for 80 kyr if this rise represents the recovery interval identified at site 690 then the 3he et based age models of the two sites are in good agreement however alternative interpretations are possible and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion regardless of these details this work shows that the 3he et technique can provide useful independent evidence for the development and testing of astronomically calibrated age models

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

changes in dissolved oxygen in the southern ocean with climate change 1 climate models predict that increasing greenhouse gases in the atmosphere will change our climate however the range of observations available to assess these model predictions is limited we have utilized an ocean biogeochemical model to project the impact of climate change on the oxygen cycle in the ocean and the air sea exchange of oxygen with climate change our model predicts an outgassing of oxygen from the ocean in the model the southern ocean is the region that displays the largest change in the air sea exchange of oxygen with climate change the reduced oxygen uptake in the southern ocean is dominated by a reduction in convective mixing and in the subduction rate of bottom water which decreases the amount of dissolved oxygen in the southern ocean our model results suggest that dissolved oxygen is sensitive to changes in southern ocean circulation revealing the potential to use dissolved oxygen to test model predictions of climate change from southern ocean observations collected 28 years a part we observed a decrease in dissolved oxygen that was consistent with model climate change simulation this provides credibility to the climate model predictions additional analysis and observations of dissolved oxygen are needed to substantiate our climate model simulations

mobility and immobility of redox sensitive elements in deep sea turbidites during shallow burial during the first few tens of thousands of years after an organic rich turbidite is emplaced on an abyssal plain surficial oxidation of the unit occurs by downwards diffusion of bottom water o2 from work on piston cores it is known that a suite of redox sensitive elements form characteristic relocation peaks in such units around the deepest reaches upper few dm achieved by oxidation fossil oxic post oxic boundaries four individual turbidites now buried at depths of 130 230 m below seafloor mbsf obtained by odp leg 157 drilling on the madeira abyssal plain map have been investigated to determine the effects of burial diagenesis on these geochemical signals over 3 7 my porewater data indicate that post oxic conditions persist to around 130 mbsf on the map below which sulphate reduction predominates all four units have retained high total organic carbon corg contents 1 4 in their lower reaches despite the fact that bottom waters have previously oxidised this same organic matter in the turbidite tops to 0 2 the apparent inertness of the turbidite corg contrasts with the reactivity of organic matter observed in hemipelagic sediment from other odp investigations in all four cases low initial caco3 contents have been quantitatively removed along with corg oxidation with additional dissolution of carbonate by undersaturated bottom waters diagenetic fractions of the elements se cd sb tl and v are present in highly localised peaks and show no evidence of migration in different combinations the elements cu co ni and zn appear to have migrated over short 5 cm distances in thin mm dark coloured sulphide bands probably sourced by reduction of a mn oxyhydroxide host phase during early 70 ky burial two examples of local diagenetic pyritisation up to 20 wt fes2 are observed in the bodies of the two turbidites buried to 130 mbsf confirming that sulphate reduction is active at this level this diagenetic pyrite is associated with high concentrations of as and lesser enrichments of ni zn co se sb and possibly mo

latest on the absolute age of the paleocene eocene thermal maximum petm new insights from exact stratigraphic position of key ash layers 19 and 17 abstract we constructed a precise early eocene orbital cyclostratigraphy for dsdp site 550 leg 80 goban spur north atlantic utilizing precession related cycles as represented in a high resolution x ray fluorescence based barium core log based on counting of those cycles we constrain the exact timing of two volcanic ash layers in site 550 which correlate to ashes 19 and 17 of the fur formation in denmark the ashes relative to the onset of the paleocene eocene thermal maximum petm are offset by 862 kyr and 672 kyr respectively when combined with published absolute ages for ash 17 the absolute age for the onset of the petm is consistent with astronomically calibrated ages using the current absolute age of 28 02 ma for the fish canyon tuff fct standard for calibrating the absolute age of ash 17 is consistent with tuning option 2 in the astronomically calibrated paleocene time scale of westerhold et al 2008 westerhold t rohl u raffi i fornaciari e monechi s reale v bowles j and evans h f 2008 astronomical calibration of the paleocene time palaeogeography palaeoclimatology palaeoecology v 257 p 377 403 using the recently recalibrated absolute age of 28 201 ma for the fct standard is consistent with tuning option 3 in the astronomically calibrated paleocene time scale the new results do not support the existence of any additional 405 kyr cycle in the early paleocene astronomically tuned time scale

accumulation variability derived from an ice core from coastal dronning maud land antarctica a 100 m long ice core was retrieved from the coastal area of dronning maud land dml antarctica in the 2000 01 austral summer the core was dated to ad 1737 by identification of volcanic horizons in dielectrical profiling and electrical conductivity measurement records in combination with seasonal layer counting from high resolution oxygen isotope d 18 o data a mean long term accumulation rate of 0 29 m a 1 w e was derived from the high resolution d 18 o record as well as accumulation rates during periods in between the identified volcanic horizons a statistically significant decrease in accumulation was found from about 1920 to the present a comparison with other coastal ice cores from dml suggests that this is a regional pattern

anomalous shifts in tropical pacific planktonic and benthic foraminiferal test size during the paleocene eocene thermal maximum paleocene eocene warming and changes in oceanic hydrography should have significantly impacted the ecology of marine microorganisms both at the surface and on the seafloor we analyzed several key characteristics of foraminifera from two shatsky rise odp leg 198 cores spanning the p e boundary including the maximum test diameters of the largest calcareous trochospiral benthic foraminifera and largest shallow dwelling planktonic foraminifera and the stable carbon and oxygen isotope ratios of benthic foraminifera and bulk samples we also qualitatively constrained changes in bottom water dissolved oxygen concentrations by quantifying changes in benthic species abundances we find warming synchronous with an unusual increase in the size of surface water planktonic in contrast to deep water benthic foraminifera which decrease in size we suggest that a decline in bottom water dissolved oxygen is the primary mechanism responsible for the size reduction of pacific deep sea benthic foraminifera whereas the contemporaneous size increase of surface water planktonic foraminifera is attributed to an increase in thermal stratification and decrease in local nutrient supply

interpreting transient carbonate compensation depth changes by marine sediment core modeling 1 with the advent of computationally fast intermediate complexity models of earth s climate and carbon cycle the marine record can be interpreted much more directly than before specifically the mechanistic simulation of deep sea sediment cores provides an important step in bridging the model data divide here i use this methodology to help interpret the excursion in carbonate compensation depth ccd during the paleoceneeocene thermal maximum that is recorded in cores recovered from walvis ridge in the south atlantic by explicitly simulating the expected geological record of a massive co2 release in an earth system model i show how reduction in the intensity of subsurface mixing of the sediment by benthic animals substantially magnifies the recorded shoaling of the ccd conversely to quantify correctly the carbon release consistent with the observed ccd changes one must account for any bioturbational changes a reduction in sediment mixing intensity also appears to be important to reproducing the sharpness of the contact between carbonate rich late paleocene sediments and the overlying early eocene clay layer at walvis ridge assuming a relatively rapid approximately 1 ka duration co2 release further helps to account for some of the paleoceanographic observations finally interbasin differences in bioturbational regime help resolve some of the observed disparity in carbonate preservation between walvis ridge and sites outside of the atlantic although changes in ocean ventilation and circulation are also likely to play a critical role in this

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

solid phase manganese in southeast atlantic sediments implications for the paleoenvironment abstract in many deep sea sediments mn rich layers are observed at various levels in order to investigate their formation and preservation as well as their use to reconstruct past changes in the depositional environment downcore profiles of manganese and manganese carbonate from different early diagenetic environments in the southeast atlantic ocean were examined by geochemical analysis x ray diffraction and sem analysis the results were compared to pore water data and productivity regimes in sediments underlying areas of high to moderate surface water fertility mn is reduced and recycled to overlying waters or precipitated at the oxic suboxic boundary within the sediment forming subsurface mn spikes manganese carbonate is a characteristic feature of these early diagenetic mn enrichments in the cores from the equatorial divergence where glacial interglacial productivity changes have been recorded by geochemical and isotopical evidence manganese carbonate peaks occur at deglaciation phases decreased supply of organic matter though the total manganese contents are nearly constant indicating that manganese carbonate survives burying to anoxic sediments better than mn iv phases in sediments of the central walvis ridge underlying nutrient poor surface waters peaks of mn iv and manganese carbonate occur in glacial sections thus giving evidence of higher reduction rates through increased supply of the reducing organic matter the higher flux of organic matter is attributed to a higher surface water productivity during glacials on the central walvis ridge since the evaluation of paleoproductivity proxies in that area is ambigous the interpretation of manganese and manganese carbonate profiles is an important qualitative tool supporting glacial interglacial changes in paleoproductivity

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

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

late miocene early pliocene manganese redirection in the central indian ocean expansion of the intermediate water oxygen minimum zone decomposition of organic matter combined with density stratification generate a pronounced intermediate water oxygen minimum zone omz in the northwest indian ocean this zone currently lies between water depths of 200 and 2000 m and extends approximately 5000 km southeast from the arabian coast based upon benthic foraminiferal assemblage changes it has been suggested that this omz was even more extensive during the late miocene early pliocene 6 5 3 0 ma with a maximum volume and or intensity at approximately 5 0 ma while this inference may contribute to an understanding of the history of northwest indian ocean upwelling corroborating geochemical evidence for this interpretation has heretofore been lacking ocean drilling program odp sites 752 754 and 757 on broken and ninetyeast ridges are located within central indian ocean intermediate water depths 1086 1650 m but outside the present lateral dimensions of the indian ocean omz high resolution chemical analyses of sediment from these sites indicate significant reductions in the flux of mn and normalized mn concentrations between 6 5 and 3 0 ma that are most pronounced at approximately 5 0 ma because late miocene pliocene paleodepths for these sites were essentially the same as at present and because extremely low sedimentation rates 0 3 1 3 cm ky most likely precluded sedimentary metal oxide diagenesis we suggest that the observed mn depletions reflect diminished deposition of reducible mn oxyhydroxide phases within o2 deficient intermediate waters and that this effect was most intense at approximately 5 0 ma this interpretation implies that waters with less than 2 0 ml l o2 extended at least 1500 km beyond their present limits and is consistent with changes in benthic foraminifera assemblages we further suggest this expanded indian ocean omz is related to regionally and or globally increased biological productivity

identification and removal of mn mg rich contaminant phases on foraminiferal tests implications for mg ca past temperature reconstructions 1 the geochemical composition of foraminifera shells from an ocean drilling program site in the panama basin has been analyzed by several analytical techniques la icp ms icp ms xrd sem edx in order to identify and evaluate the occurrence of contaminant phases which may bias paleoenvironmental reconstructions la icp ms results on uncleaned tests indicate the presence of mnmg rich contaminant phases at the inner surfaces of the foraminiferal shells which have mn ca ratios up to 400 mmol mol 1 and mg ca ratios up to 50 mmol mol 1 we have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included the analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high mn values are associated with at least two different contaminant phases of which only one is linked to high mg values xrd analysis further reveals that the mn mg rich phase is the ca mn mg carbonate kutnahorite ca mn mg co3 2 our results demonstrate that the presence of kutnahorite like minerals can bias mg ca ratios toward higher values by 7 36 and lead to significant overestimation of past seawater temperatures by 0 9 up to 6 2 c in the case of these panama basin samples components 11 867 words 13 figures 3 tables

uranium diagenesis in sediments underlying bottom waters with high oxygen content we measured u in sediments both pore waters and solid phase from three locations on the middle atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments en433 1 212 mol c cm2 y oc426 120 10 mol c cm2 y en433 2 33 mol c cm2 y pore water oxygen goes to zero by 1 4 1 5 cm at en433 1 and oc426 and slightly deeper oxygen penetration depths were measured at en433 2 4 cm all of the pore water profiles show removal of u from pore waters calculated pore water fluxes are greatest at en433 1 0 66 0 08 nmol cm2 y and less at en433 2 and oc426 0 24 0 05 and 0 13 0 05 nmol cm2 y respectively solid phase profiles show authigenic u enrichment in sediments from all three locations the average authigenic u concentrations are greater at en433 1 and oc426 5 8 0 7 nmol g and 5 4 0 2 nmol g respectively relative to en433 2 4 1 0 8 nmol g this progression is consistent with their relative ordering of reduction intensity with greatest reducing conditions in sediments from en433 1 less at oc426 and least at en433 2 the authigenic u accumulation rate is largest at en433 1 0 47 0 05 nmol cm2 y but the average among the three sites on the mab is 0 2 nmol cm2 y pore water profiles suggest diffusive fluxes across the sediment water interface that are 1 4 1 7 times greater than authigenic accumulation rates at en433 1 and en433 2 these differences are consistent with oxidation and loss of u from the solid phase via irrigation and or bioturbation which may compromise the sequestration of u in continental margin sediments that underlie bottom waters with high oxygen concentrations previous literature compilations that include data exclusively from locations where o2 bw 150 m suggest compelling correlations between authigenic u accumulation and organic carbon flux to sediments or organic carbon burial rate sediments that underlie waters with high o2 bw have lower authigenic u accumulation rates than would be predicted from relationships developed from results that include locations where o2 bw 150 m

barite accumulation ocean productivity and sr ba in barite across the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm ca 55 ma was a period of extreme global warming caused by rapid emission of greenhouse gases it is unknown what ended this episode of greenhouse warming but high oceanic export productivity over thousands of years as indicated by high accumulation rates of barium ba may have been a factor in ending this warm period by carbon sequestration however ba has a short oceanic residence time 10 k y so a prolonged global increase in ba accumulation rates requires an increase in input of ba to the ocean increasing barite saturation we use a novel proxy for barite saturation sr ba in marine barite to demonstrate that the seawater saturation state with respect to barite did not change across the petm the observations of increased barite burial no change in saturation and the short residence time can be reconciled if ba burial decreased at continental margin and shelf sites due to widespread occurrence of suboxic conditions leading to ba release into the water column combined with increased biological export production at some pelagic sites resulting in ba sink reorganization

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

could changing ocean circulation have destabilized methane hydrate at the paleocene eocene boundary 1 during the paleocene eocene thermal maximum petm 55 ma marine and terrestrial carbon isotope values exhibit a negative shift of at least 2 5 indicative of massive destabilization of marine methane hydrates releasing 2000 gigatons of methane carbon the cause of the hydrate destabilization is unknown but has been speculated to be warming due to a change from high latitude to low latitude deepwater formation here we present results from a numerical ocean model indicating that a sudden switch of deepwater formation from southern to northern high latitudes caused middepth and deep ocean warming of 3 5 c the switch is caused by a slow increase in the intensity of the atmospheric hydrologic cycle as expected under increasing temperatures and consistent with petm sedimentary evidence deepened subtropical subduction prior to the thermohaline circulation switch causes warming of 1 4 c in limited areas at thermocline through upper intermediate depths which could destabilize methane hydrates gradually and at progressively greater depths warming accompanying a south to north switch in deepwater formation would produce sufficient warming to destabilize seafloor gas hydrates over most of the world ocean to a water depth of at least 1900 m

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity