high resolution stable isotope profiles of modern elephant loxodonta africana tusk dentin and tail hair from kenya implications for identifying seasonal variability in climate ecology and diet in ancient proboscideans abstract stable isotope ratios in tissues of large mammalian herbivores record diet and climate information integrated over large spatial areas and can be used to study modern and fossil ecosystems sound interpretation of data requires that tissue growth rates be determined accurately and that ecological and behavioral variables that influence stable isotope ratios of tissues be measured and related to experienced environmental conditions assessed through field observations remote sensing data and meteorological records if well understood in modern herbivores stable isotopes from closely related extinct taxa have tremendous potential for resolving paleodiet paleoenvironment and paleoclimate of terrestrial ecosystems we present multiyear high resolution i e weekly stable isotope records from bioapatite in tusk dentin 13cdentin and 18odentin and tail hair 13chair and 15nhair of an african elephant loxodonta africana from kenya that was fitted with a gps collar intermittently over a five year period and observed for nearly a decade gps and observational data provide behavioral life history and location information normalized difference vegetation index ndvi precipitation and isotopic data from plants and water provide further constraints for interpreting isotope profiles we determine tusk and hair growth rates using a combination of histological and geochemical approaches including bomb curve radiocarbon that confirm approximately weekly resolution in the stable isotope profiles tusk dentin isotope profiles spanning the periods 1982 to 1987 and 2000 to 2006 record weekly variability in 13cdentin where increases of up to 4 5 from baseline values due to diet switches from predominantly c3 browsing to mixed c3 browsing and c4 grazing occur during the twice yearly biannual rainy seasons the 13chair values show a similar trend the 13c profiles served as a proxy for seasonal changes in rainfall vegetation and diet the 18o of tusk bioapatite varied approximately biannually up to 5 likely reflecting increases in the proportion of plant water ingested during the wet season using a least squares inverse filter we show that ndvi can be used to predict 13c of dentin and vice versa offering the possibility to reconstruct seasonal changes in vegetation and rainfall in the geologic past our results demonstrate that high resolution tusk isotope profiles serve as a proxy for seasonality of diet and precipitation and thus can be used to reconstruct aspects of elephant life history vegetation and climate at unprecedented resolution from modern and fossil proboscidean samples

molybdenum isotope signatures in continental margin marine sediments abstract we present molybdenum isotope data for four sediment profiles from continental margin settings each profile has a distinctive average isotope composition ranging from 98 95 mo 0 5 to 1 3 relative to j and m laboratory standard this range lies between the modern ocean water value 2 3 and the values typical of mo adsorbed onto mn oxides 0 7 0 1 an important finding of this study is the apparent co variation between the mo isotope composition and the accumulation rate of authigenic mo under reducing conditions this relationship suggests that the chemical processes responsible for mo accumulation under reducing conditions produce an isotope signature in marine sediments in addition to the relationship between mo accumulation and the mo isotope signature there is also a relationship between these parameters and the rate of organic carbon oxidation and burial these relationships suggest that the mo isotope signature of reducing sediments may serve as a tracer for the cycling of organic carbon in continental margin sediments however additional data will be required to refine any such relationships

controls on mo isotope fractionations in a mn rich anoxic marine sediment gullmar fjord sweden abstract molybdenum isotopes have emerged as an important tool for determining the spatial extent of past ocean redox conditions however our understanding of mo cycling and associated isotopic fractionations in modern and ancient continental margin sediments is limited restricting attempts to fully utilize the potential of mo isotopes this is particularly the case with regard to the relative significance of mo isotope fractionations associated with biogeochemical mn and fe oxide cycling under conditions of low dissolved sulfide to rectify this we have investigated sediments from gullmar fjord sweden which contain high concentrations of mn oxides and exhibit a strong redox zonation between mn and fe reduction a combination of dissolved and particulate mo isotope measurements with porewater and solid phase mn and fe characterization reveals that the main influence on porewater 98 mo compositions is exerted by adsorption and desorption processes during reductive dissolution of both mn and fe oxyhydr oxide minerals in areas enriched in mn oxides distinctively low solid phase 98 mo values are observed 1 0 and 0 4 which occur due to the large mo isotope fractionation associated with mo adsorption to mn oxides however where mn oxide concentrations are lower authigenic 98 mo is largely controlled by fe oxyhydr oxide minerals resulting in more positive 98 mo isotopic compositions 0 5 and 2 our results suggest that for modern anoxic marine sediments where deposition occurs beneath an oxic to suboxic water column 98 mo is dominantly controlled by the relative availability of mn and fe oxides and the production of dissolved sulfide

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

dietary resource partitioning among three coeval proboscidean taxa anancus capensis mammuthus subplanifrons loxodonta cookei from the south african early pliocene locality of langebaanweg e quarry abstract the co existence of megaherbivores in present day ecosystems is uncommon during the early pliocene three large proboscidean taxa anancus capensis mammuthus subplanifrons and loxodonta cookei co existed in the strongly c3 dominated langebaanweg lbw environment on the southwestern coast of south africa it is expected that this would have required at least some resource partitioning to investigate whether how dietary resources were partitioned we have measured 13c and 18o in tooth enamel from the molars of a capensis n 13 m subplanifrons n 3 and l cookei n 20 13c values for a capensis are more tightly clustered and the mean more negative than for l cookei and m subplanifrons anancus capensis probably favoured shady wooded parts of the lbw environment where it mainly browsed loxodonta cookei and m subplanifrons spent more time in open habitats and were dietarily flexible the preference for browse of a capensis may have contributed to its extinction whereas the dietary flexibility of the genus loxodonta meant it was able to survive to the present we did not find significant differences in 18o values between the three taxa which suggests that they drank from the same water sources as expected if they were all resident in the lbw palaeoenvironment our study shows that the carrying capacity of the c3 dominated lbw environment was high

establishing chronologies from isotopic profiles in serially collected animal tissues an example using tail hairs from african elephants while the use of stable isotopes in wildlife ecological research is growing rapidly development of methods to establish time specific isotope data from continuously growing animal tissues are lacking using serially collected tail hairs from wild african elephants loxodonta africana we develop and compare four techniques to collate temporal isotope chronologies from metabolically inert tissues for which formation growth overlapped in time the influence of variation in within hair growth rates and other sources of error in the presented techniques are explored and found to be inconsequential relative to the 5 day tissue sampling interval using a floating point regression approach we find a high degree of correlation between independently derived isotope profiles from the same and different individuals in the study ecosystem remotely sensed normalized difference vegetation index ndvi data is compared with the isotope derived diet chronologies from five elephants developed independently diet shifts from browse to grass occurring at the onset of the wet season were highly synchronized while early dry season diets varied across individuals these methods are applicable across a variety of keratinous tissues and even teeth and as demonstrated by our results can be implemented using profiles from different individuals or relating profiles to environmental variation seasonality as such the presented methods allow the establishment of high resolution temporal data on diet movement and climatic conditions experienced by an organism in many research settings

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

authigenic sulfide and carbonate mineral formation in holocene sediments of the baltic sea formation of authigenic sulfides and carbonates in holocene 14c dated sediments is interpreted based on analyses of cations fes s fes2 s corg and sulfur isotopes mineral distribution was studied in thin sections and mineral morphology with sem eds the sediments were deposited in the gotland deep baltic sea during freshwater and brackish stages calcium rich rhodochrosite mnco3 occurs in concentrations up to 17 dw in brackish water sediments and are mainly confined to 0 02 0 5 mm thick laminae the frequency with which these laminae occur suggests that they formed with a periodicity of one to a few years and their purity suggests that formation took place in a few weeks we propose that these carbonate laminae resulted from oxic water inflow to the euxinic basin mn ii dissolved in the water column was rapidly oxidized and large amounts of mn oxides reached the sediment reduction of these mn oxides in a high alkalinity environment facilitated rhodochrosite precipitation at the sediment surface pyrite in the brackish water sediments formed at or above the sediment water interface in an iron limited environment due to alternating oxic and euxinic conditions fes was oxidized resulting in a high fes2 sfes s ratio median 170 formation of iron sulfides in the freshwater sediments occurred below the sediment water interface in a sulfate limited environment as a result of the rapid exhaustion of reactive iron in the brackish water sediments excess h2s diffused downwards to pyritize the uppermost part of the underlying freshwater sediments

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

iron and manganese shuttles control the formation of authigenic phosphorus minerals in the euxinic basins of the baltic sea microanalysis of epoxy resin embedded sediments is used to demonstrate the presence of authigenic iron fe ii phosphates and manganese mn calcium ca carbonate phosphates in the deep euxinic basins of the baltic sea these minerals constitute major burial phases of phosphorus p in this area elevating the total p burial rate above that expected for a euxinic depositional environment particle shuttles of fe and mn oxides into the deep euxinic basins act as drivers for p bearing mineral authigenesis while fe ii phosphates are formed continuously in the upper sediments following the sulfidization of fe oxyhydroxides and release of associated p mn ca carbonate phosphates are formed intermittently following inflow events of oxygenated north sea water into the deep basins the mechanism of fe ii phosphate formation differs from previously reported occurrences of vivianite formation in marine sediments by occurring within rather than below the sulfate methane transition zone the spatial distribution of both authigenic phases in baltic sediments varies in accordance with the periodic expansion of anoxia on centennial to millennial timescales the results highlight the potential importance of authigenic p bearing minerals other than carbonate fluorapatite for total p burial in euxinic basins

the manganese and iron shuttle in a modern euxinic basin and implications for molybdenum cycling at euxinic ocean margins a meaningful application of mo as a paleo redox proxy requires an understanding of mo cycling in modern reducing environments stagnant euxinic basins such as the black sea are generally regarded as model systems for understanding euxinic systems during early earth history however drawing direct parallels between the black sea and open marine euxinic margins is somewhat complicated by differences in the seawater residence time between these two environments we report sediment and pore water mo u mn and fe data for a euxinic basin with a short seawater residence time the weakly restricted gotland deep in the baltic sea here prolonged periods of euxinia alternate with brief inflow events during which well oxygenated saline water penetrates into the basin during these inflow events dissolved mn and fe that has accumulated within the euxinic deep water can be oxidized and precipitated co variations of mo and u within the sediment suggest that these inflow and oxygenation events may favor mo accumulation in the sediment through adsorption to freshly oxidized mn and fe solid phases once mo is sequestered within the deeper euxinic water and sediments mo retention can be further facilitated by conversion to thiomolybdate species and interactions with organic matter and metal sulfides by comparing our data with those from previous studies where a mn and fe shuttle for mo has been demonstrated we identify two prerequisites for the occurrence of this mechanism first there must be a water column oxic anoxic redox boundary this provides a solubility contrast for mn and fe second the residence time of seawater in the system has to be short weeks to a few years the latter criterion can be met through regular inflow in weakly restricted basins or upwelling in oxygen minimum zones at open marine continental margins based on prior work we suggest that similar conditions to those currently represented by the gotland deep may have prevailed at euxinic ocean margins during the proterozoic a boundary between euxinic and oxic water masses overlying the continental shelf may have resulted in accelerated mo transport through the water column with mn and fe oxyhydr oxides we propose that this mechanism along with mo isotope fractionation during adsorption could contribute to the light mo isotope composition observed in open marine euxinic sediment facies of the proterozoic

a 400 year record of environmental change in an euxinic fjord as revealed by the sedimentary biomarker record a 400 year sedimentary record of the euxinic kyllaren fjord was investigated using organic biogeochemical geochemical and sedimentological approaches accumulation rates of a suite of biomarkers and in some cases their stable carbon isotopic composition were determined biomarkers were separated into three different groups terrestrial derived general aquatic marine derived and aquatic marine derived but related to high primary productivity variations in bulk sediment parameters and biomarker accumulation rates with depth were used to interpret the sedimentary record we infer that in the first half of the 19th century an environmental change occurred caused by a change in either the precipitation regime vegetation and or land use the data also show that in the last century and especially in the last decades a distinct increase in primary productivity occurred most likely this is caused by a natural eutrophication due to the transformation of the fjord from an open to a confined system by the building of a partially open dam in 1954 possibly combined with anthropogenic eutrophication a concurrent shoaling of the fjord chemocline may have had a mediating effect in the change towards a higher productivity by enhancing nutrient and carbon recycling enhanced carbon recycling is reflected by decreased 13c values of several biomarkers

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

uranium and molybdenum isotope systematics in modern euxinic basins case studies from the central baltic sea and the kyllaren fjord norway abstract recent investigations have revealed significant fractionation of 238u 235u between organic rich sediments of anoxic marginal seas and seawater indicating redox dependent u isotope fractionation this study explores the conditions controlling u isotope fractionation in selected modern anoxic basins baltic sea landsort and gotland deeps and the kyllaren fjord in norway and compares u with mo isotope fractionation therefore the concentrations and isotope compositions of dissolved u and mo from the water column and organic rich sediments from three currently anoxic basins have been analysed the water column samples from the kyllaren fjord display a moderate depletion of u and a strong depletion of mo with increasing depth these variations are associated with a decrease in 238u and an increase in 98mo with depth from 0 35 to 0 70 and from 2 4 to 2 6 respectively from the u isotope composition of the deep euxinic water column of the kyllaren fjord a minimum value of 238ured 0 7 for the u isotope fractionation during reduction is inferred due to the high sedimentation rate in the kyllaren fjord surface sediment samples are only moderately enriched in u and mo 4 g g and 6 g g to 37 g g respectively and display 238u and 98mo averages of 0 26 0 10 and 2 18 0 21 respectively water column samples from the baltic sea display a minor decrease in the u and mo concentrations and only negligible u and mo isotope fractionation compared to open seawater the sediment layers from the baltic sea landsort deep which were deposited under mostly anoxic conditions are moderately enriched in u up to 8 g g and highly enriched in mo up to 222 g g however u and mo isotopic compositions are significantly lighter with 238u of 0 36 0 08 and 98mo of 0 04 0 11 than those of typical organic rich sediments from anoxic basins these findings reveal that compared to mo the u isotopic composition of sediments in restricted and strongly euxinic basins like the kyllaren fjord is significantly more dependent on 1 the extent of u removal from the water column which is lower than that of mo and on 2 the sedimentation rate i e the fraction of authigenic u relative to detrital u in the sediment which is also lower compared to that of mo in more open and only temporarily euxinic basins such as the investigated basins of the baltic sea strong mo is coupled with weak u isotope fractionation between water and sediment these signatures were likely the result of isotope fractionation under weakly sulfidic conditions and the generation of isotopically light mo during frequently occurring flushing events with oxygen rich water from the open sea this implies that mo and u isotope signatures of sediments only record paleo water column redox conditions of restricted basins if the water column was permanently stratified

molybdenum isotope fractionation in pelagic euxinia evidence from the modern black and baltic seas here we present stable isotope data for vertical profiles of dissolved molybdenum of the modern euxinic water columns of the black sea and two deeps of the baltic sea dissolved molybdenum in all water samples is depleted in salinity normalized concentration and enriched in the heavy isotope 98mo values up to 2 9 compared to previously published isotope data of sedimentary molybdenum from the same range of water depths furthermore 98mo values of all water samples from the black sea and anoxic deeps of the baltic sea are heavier than open ocean water the observed isotope fractionation between sediments and the anoxic water column of the black sea are in line with the model of thiomolybdates that scavenge to particles under reducing conditions an extrapolation to a theoretical pure mos42 solution indicates a fractionation constant between mos42 and authigenic solid mo of 0 5 0 3 measured waters with all thiomolybdates coexisting in various proportions show larger but non linear fractionation the best explanation for our field observations is mo scavenging by the thiomolybdates dominantly but not exclusively present in the form of mos42 the mo isotopic compositions of samples from the sediments and anoxic water column of the baltic sea are in overall agreement with those of the black sea at intermediate depth and corresponding sulphide concentrations the more dynamic changes of redox conditions in the baltic deeps complicate the black sea derived relationship between thiomolybdates and mo isotopic composition in particular the occasional flushing mixing of the deep waters affects the corresponding water column and sedimentary data 98mo values of the upper oxic waters of both basins are higher than predicted by mixing models based on salinity variations the results can be explained by non conservative behaviour of mo under suboxic to anoxic conditions in the shallow bottom parts of the basin most pronounced on the nw shelf of the black sea

molybdenum in the northeast pacific ocean1 the concentration of dissolved molybdenum has been determined in several profiles from the northeast pacific ocean the salinity normalized concentration is essentially constant in all open ocean samples 107 nm 1 2 5 nm the dissolved distribution is not significantly affected by biological cycling

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

uranium isotopes distinguish two geochemically distinct stages during the later cambrian spice event a b s t r a c t anoxic marine zones were common in early paleozoic oceans 542 400 ma and present a potential link to atmospheric po2 via feedbacks linking global marine phosphorous recycling primary production and organic carbon burial uranium u isotopes in carbonate rocks track the extent of ocean anoxia whereas carbon c and sulfur s isotopes track the burial of organic carbon and pyrite sulfur primary long term sources of atmospheric oxygen in combination these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million year time scales here we report high precision uranium isotopic data in marine carbonates deposited during the late cambrian spice event at ca 499 ma documenting a well defined 0 18 negative 238 u excursion that occurs at the onset of the spice event s positive 13

orphans tales seasonal dietary changes in elephants from tsavo national park kenya the similarity of y 13 c and y 15 n patterns in hairs of different individuals from the tsavo east orphaned elephant herd indicates that a single hair represents the dietary preferences and behavior of the entire group multiple tail hairs from the same individual collected at different times allows a chronology to be established because of the overlap in isotope patterns in hair and there is a very high correlation between hair from different individuals in the same group forward modeling using a threecomponent isotope turnover model for hair allows a precise estimate of diet of these elephants over a 2 year interval elephants from tsavo east national park in kenya feed predominantly on c3 leaves although they have a significant fraction of c4 grass in their diet for a short time at the beginning of the rainy season the overall integrated diet for the elephants studied is between 10 and 15 c4 grass although it reaches up to 60 for short intervals stable carbon isotope analyses of elephant tooth enamel show that the average integrated dietary preference of elephants in tsavo national park remained less than 25 grass between 1940 and the present d 2004 elsevier b v all rights reserved

century long record of mo isotopic composition in sediments of a seasonally anoxic estuary chesapeake bay abstract a double spike method was used to obtain mo isotope data for sediments and waters of the seasonally anoxic chesapeake bay and its primary tributary the susquehanna river the dissolved mo distribution in the estuary is non conservative reflecting minor mo loss to the sediments although removal of mo to the sediments does not have a large influence on the isotopic composition of the water column the 98mo of dissolved mo in most of the estuary is dominated by seawater six samples with salinity 15 have an average 98mo 2 17 0 12 which agrees well with a 98mo value for the cass 4 seawater standard of 2 23 a single sample of susquehanna river water has a 98mo of 1 02 consistent with recent findings of positive 98mo in rivers worldwide susquehanna river sediments in contrast have 98mo 0 1 the difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin the 98mo values for estuarine sediments are offset from values in the overlying water most samples deposited before 1925 have 98mo less than 0 similar to the susquehanna sediments subsequently there is an increase in the variability of 98mo with values ranging up to 0 8 the transition to increased variability coincides with the onset of authigenic mo deposition which was previously attributed to escalating summertime anoxia authigenic mo concentrations correlate poorly with 98mo in core samples suggesting that independent mechanisms influence the two parameters authigenic mo concentrations may be controlled by shifting pore water h2s levels while 98mo may be primarily affected by annual variations in mn refluxing

late middle to late pleistocene paleoecology and paleoenvironments in the coastal plain of rio grande do sul state southern brazil from stable isotopes in fossils of toxodon and stegomastodon abstract stable isotopes 13 c 18 o in teeth of extinct mammals have been used as indicators of diets and climate conditions which in turn are used for paleoenvironmental reconstructions the first analysis of stable isotopes in pleistocene mammals from southern brazil is reported here the analyzed taxa were the notoungulate toxodon and the proboscidean stegomastodon from late middle to late pleistocene fossiliferous beds exposed along chui creek in the coastal plain of rio grande do sul state the 13 c isotopes indicate that toxodon was a mixed feeder that fed mostly on c4 plants while stegomastodon was a browser to mixed feeder with preference for c3 plants with less c4 plants in the diet compared to modern african elephants comparison with carbon isotopic values in fossils of these taxa from other late quaternary localities in south america shows an increased proportion of c3 plants in the diets of both toxodon and stegomastodon in higher latitudes the values of 18 o in both taxa seem to reflect the isotopic composition of the ingested water rather than the isotopic content in the plants of which they fed on and the observed variations are likely to mirror variations of the patterns of precipitation paleoclimatic inferences and possible causes for the pseudo extinction of these taxa in southern brazil are also discussed

hydrogen sulphide release to surface waters at the precambrian cambrian boundary changes in environmental conditions at the precambrian cambrian transition around 542 million years ago have been suggested as a possible explanation for the apparent rapid increase in abundance of multicellular organisms known as the cambrian explosion the nature of the environmental changes is still a matter of debate however wille et al now report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of about 542 million years with the help of a box model of the oceanic molybdenum cycle they find that intense upwelling of hydrogen sulphide rich deep ocean water best explains the observed early cambrian molybdenum isotope signal this suggests that the early cambrian animal radiation may have been triggered by a major change in ocean circulation following a long period during which the ocean was stratified with sulphidic deep water this paper reports molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 million years the findings suggest that the early cambrian animal radiation may have been triggered by a major change in ocean circulation terminating a long period during which the proterozoic ocean was stratified with sulphidic deep water animal like multicellular fossils appeared towards the end of the precambrian followed by a rapid increase in the abundance and diversity of fossils during the early cambrian period an event also known as the cambrian explosion 1 2 3 changes in the environmental conditions at the precambrian cambrian transition about 542 myr ago have been suggested as a possible explanation for this event but are still a matter of debate1 2 3 here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 myr we find a transient molybdenum isotope signal immediately after the precambrian cambrian transition using a box model of the oceanic molybdenum cycle we find that intense upwelling of hydrogen sulphide rich deep ocean water best explains the observed early cambrian molybdenum isotope signal our findings suggest that the early cambrian animal radiation may have been triggered by a major change in ocean circulation terminating a long period during which the proterozoic ocean was stratified with sulphidic deep water

a new particulate mn fe p shuttle at the redoxcline of anoxic basins abstract pelagic redoxclines of anoxic basins and deeps form the suboxic transition between oxygenated surface and anoxic or even sulfidic bottom waters intense element cycling favoured by elevated microbial activity causes steep gradients of physico chemical parameters nutrients and redox sensitive trace metals this study presents a conceptual model for authigenic particle formation at pelagic redoxclines which is based on the tight coupling of mn fe and p cycles besides the well known occurrence of mn oxides textural sem edx and geochemical icp oes icp ms analyses of particles from the redoxclines of the black sea and the baltic sea gotland basin landsort deep evidence the existence of earlier postulated fe oxyhydroxo phosphates and emphasize mixed phases consisting of mn oxides and fe oxyhydroxo phosphates as a new solid species most of the analyzed particles are star shaped of about 5 m in size and occur as single particles or aggregates without any morphological differences between mn oxides fe oxyhydroxo phosphates and mixed phases throughout the redoxcline these minerals show a general succession with maximum abundance of mn oxides above the redoxcline followed by mixed phases and almost pure fe phosphates within and below the redoxcline respectively molar fe p ratios of single particles argue against the formation of known pure fe phosphates like vivianite or strengite at the lower end of the redox transition zone but are consistent with recent experimental findings for colloidal p bearing hydrous ferric oxides moreover morphological similarities suggest the formation of irregular fe oxyhydroxo coatings due to oxidation of upward diffusing fe 2 by oxygen and stepwise replacement of mn iv by fe iii on sinking mno x particles followed by immediate adsorption or even co precipitation of phosphate batch type experiments using biogenic mno x particles demonstrate the efficient potential of fe 2 oxidation by sinking mno x particles when entering sulfidic waters mno x particles are progressively reduced leading to an increasing relative abundance of fe and p rich particles in deeper parts of the water column these particles are also reductively dissolved thereby releasing fe 2 and phosphate to the water column this mn fe p shuttle likely affects phosphate transport throughout the water column and thus impacts primary production at least over longer time scales furthermore the particulate mn fe p shuttle must have played an important role for the cycling of p and certain trace metals in ancient ocean basins e g during certain periods of cretaceous black shale formation and should be considered in future mass balances and modeling approaches dealing with oxic anoxic interfaces of aquatic ecosystems

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

concentration oxidation state and particulate flux of uranium in the black sea abstract in contrast to its unreactive behavior in the open ocean uranium is removed from seawater to sediments of anoxic marine basins four biogeochemical processes have been proposed to account for this removal active uptake by organisms whose remains are preserved by the anoxic conditions of the sediments complexation of u vi by particulate organic matter chemical reduction of soluble u vi to insoluble u iv which is scavenged to the sediments by settling particles and precipitation of uranium within the sediments themselves the black sea is the largest anoxic marine basin in the world today waters below 150 200 m are anoxic and h2s levels build up to about 400 mol 1 1 in the bottom water maximum depth 2200 m concentrations of total u and the oxidation state of dissolved u were measured throughout the water column while particulate u fluxes were determined from time series sediment trap samples collected in the deep anoxic zone bottom waters were depleted in u by 40 relative to the initial u content of the water two independent methods gave residence times of dissolved u in the deep water column of about 103 years uranium occurred throughout the water column as soluble chemically labile reducible u vi rather than the thermodynamically favored u iv uranium is neither reduced to u iv by the high levels of h2s nor is it rapidly scavenged from the water column as would be expected for strongly hydrolyzed tetravalent actinides like u iv fluxes of particulate authigenic u measured with sediment traps are at least two orders of magnitude less than the rate of authigenic u burial in black sea sediments therefore the first three processes listed above contribute negligibly to the deposition of u in the sediments of anoxic marine basins such as the black sea the dominant removal process must involve precipitation of u in the sediments rather than scavenging from the water column

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

sulfidity controls molybdenum isotope fractionation into euxinic sediments evidence from the modern black sea molybdenum mo isotope fractionation has recently been introduced as a new proxy in oceanography and biogeochemistry it is therefore fundamental to understand the processes controlling mo partitioning into modern marine environments this study identifies the availability of dissolved sulfide as the dominant control on overall mo removal from the water column in euxinic systems mo isotopic composition of surface sediments from different localities of the black sea demonstrates complete fixation of mo only below 400 m water depth above a critical concentration of 11 mol l 1 aqueous hydrogen sulfide in the bottom water the mo isotopic composition of these sediments reflects the homogeneous seawater isotopic composition of 2 3 in contrast significant mo isotope fractionation into less euxinic sediments is evident at shallower depths in the black sea as well as in temporarily euxinic deeps of the baltic sea consistent with the observed lower maximum sulfide concentrations in the respective water columns therefore mo isotope signatures in the modern black sea constrain the processes responsible for global mo removal from the ocean by euxinic sediments furthermore models of past ocean anoxia reconstruction have to consider that the seawater mo isotopic composition is not per se archived in euxinic sediments

redox dependent changes in manganese speciation in baltic sea sediments from the holocene thermal maximum an exafs xanes and la icp ms study manganese mn enrichments in sediments of the deep basins of the baltic sea are believed to consist of ca mn carbonates that form from mn oxides following periodic inflows of oxygen rich north sea waters however a range of mn bearing mineral phases that besides mn carbonates e g ca rhodochrosite can include mn sulfides are known to be present in marine sediments with formation mechanisms that are sensitive to redox conditions in this study we use high resolution synchrotron exafs and xanes combined with la icp ms and micro xrf to investigate the nature of the mn enrichments in sediments from the holocene thermal maximum approx 8000 4000 cal yr bp at a site in the northern gotland basin analyses were performed on epoxy embedded sediment sequences we specifically address the role of changes in redox conditions in bottom waters as inferred from sediment molybdenum mo contents for mn sequestration we find that an up core increase in mo indicating a transition into more anoxic and sulfidic euxinic bottom water conditions is accompanied by a decline in total sediment mn contents while mn carbonates dominate the mn mineral fraction in the low mo interval in the more sulfidic high mo interval mn is associated with framboidal pyrite mn fe ratios in the sulfidic interval vary between the investigated sequences but reach values of up to 7 7 mol this exceeds ratios previously reported for sedimentary pyrite and exafs spectra indicate that sulfide bound mn is predominately tetrahedrally coordinated when mn fe ratios are high this suggests that mn is incorporated in other fe s phases such as mackinawite besides pyrite there is also evidence for the presence of a low concentration of mn associated with detrital aluminosilicates throughout the investigated intervals our results suggest that increased bottom water euxinia inhibited the formation of mn carbonate at this site during the holocene thermal maximum possibly due to a more rapid reduction of mn oxides in more sulfidic bottom waters c 2014 elsevier b v all rights reserved less

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

when do black shales tell molybdenum isotope tales molybdenum mo isotopes in ancient sediments are promising recorders of global ocean paleoredox conditions organic rich black shales can be used to reconstruct ancient ocean mo isotope compositions if these sediments record the isotopic composition of contemporaneous seawater comparison of 98 95 mo in two devonian shale sequences of similar age the new york oatka creek and geneseo formations reveals that this assumption cannot be applied to all organic rich shales although both sequences contain laminated intervals elevated organic carbon and enrichments of redox sensitive metals the mean 98 95 mo differs systematically between the formations by 0 59 independent paleoredox indicators reveal that portions of the oatka creek formation were deposited under pervasively euxinic anoxic and sulfidic conditions whereas conditions during deposition of the geneseo formation were intermittently euxinic to suboxic oxygen deficient but not sulfidic in the water column we infer that reconstruction of ancient ocean 98 95 mo from organic rich shales requires independent verification of persistent local euxinia with these considerations in mind our data point to 98 95 mo in the devonian oceans 0 6 lighter than in today9s oceans consistent with expanded anoxia

coupled molybdenum iron and uranium stable isotopes as oceanic paleoredox proxies during the paleoproterozoic shunga event the paleoproterozoic era was a time of remarkable importance in the redox evolution of earth s atmosphere and oceans here we present a multi proxy study of mo u and fe isotopes together with fe speciation of black shales and siltstones from the upper zaonega formation of the onega basin in karelia we attempt to better understand oceanic redox conditions during the 2 05 ga shunga event as the next step following the great oxidation event goe and the lomagundi carbon isotope excursion event a cautious examination of the fe speciation data shows that the studied section was deposited under dominantly euxinic conditions anoxic and sulfidic and that the lower part of the section experienced metamorphism through which pyrite was altered to pyrrhotite during this episode the system was closed with respect to fe but not sulfur the mo and u isotopic compositions corrected for detrital input were not affected by the metamorphism and loss of s and are fairly uniform throughout the entire section the fe isotope compositions are exceptionally heavy in the lower part of the section up to 56 fe irmm 14 0 83 and become lighter towards the upper intervals which also show significant mo and u enrichments we suggest that this pattern reflects changes in the position of the deposition site relative to the redox structure of the water column the upper part was deposited within a locally euxinic portion of the basin where h 2s availability was highest removal of mo and u was more efficient and precipitated pyrite captured relatively non fractionated dissolved fe in other words quantitative uptake of fe was favored in contrast the lower interval was deposited on the lower margin of a euxinic wedge where h 2s availability was lower and removal of mo and u was less efficient pyrite precipitation in this part of the water column reflected a more fractionated dissolved fe reservoir due to more protracted non quantitative fe uptake because of less efficient pyrite formation under lower sulfide conditions and greater access to the large oceanic pool of fe the u isotopic signal was corrected for detrital contribution giving compositions similar to the riverine input and suggesting that co precipitation into carbonates was the main process of u removal at this time we estimate the mo isotope composition of the contemporaneous ocean to be 98 mo sw 0 85 0 21 this is the lowest value yet reported for the proterozoic ocean suggesting that the oceanic mo cycle was dominated by euxinic and anoxic sinks with negligible mo removal into oxic environments recent studies have proposed a sharp increase in ocean atmosphere oxygen levels during the lomagundi event followed by a dramatic crash our results from black shales of the 2 05 ga shunga event are consistent with a post lomagundi decrease in biospheric oxygen levels

re os and mo isotope systematics of black shales from the middle proterozoic velkerri and wollogorang formations mcarthur basin northern australia joint application of the mo isotope paleoredox proxy and re os deposition age geochronometer to euxinic black shales has potential for tracing the evolution of ocean redox chemistry over geological time here we report new re os and mo isotope data for the mesoproterozoic velkerri formation roper group and paleoproterozoic wollogorang formation tawallah group mcarthur basin northern australia new re os ages of 1361 21 ma 2 n 14 mean square of weighted deviates mswd 1 3 model 1 and 1417 29 ma 2 n 12 mswd 1 3 model 1 constrain the depositional age of the velkerri formation and its contained biomarkers as well as acritarchs and microfossils from the roper group black shales from the upper velkerri formation have high mo abundances 105 119 ppm and degree of pyritization dop values 0 90 0 92 implying quantitative conversion of molybdate moo42 to thiomolybdate mos42 in overlying bottom waters the average 97 95mo 0 72 0 10 2 n 6 of these shales is consistent with previous data but represents a significantly more precise determination for global seawater 97 95mo at 1 4 ga this value is lighter than present day seawater by 0 85 and reflects expanded strongly euxinic deep ocean conditions h2s aq 11 m relative to oxic suboxic and weakly intermittently euxinic h2s aq 11 m marine deposition in the 1 4 ga oceans mass balance modelling suggests mo removal into strongly euxinic and oxic sediments may have comprised 30 70 and less than 15 respectively of the oceanic mo sink at 1 4 ga as opposed to 5 and 35 today respectively the re os radioisotope system in organic rich shales serves as a test for post depositional alteration that could affect the usefulness of paleoredox tracers such as mo stable isotopes re os isotope data for the wollogorang formation black shales are scattered and yield a highly imprecise date of 1359 150 ma 2 n 21 mswd 85 model 3 this age is younger than u pb zircon ages from interbedded tuffs that constrain the age of deposition at ca 1730 ma in conjunction with previous petrological geochemical and paleomagnetic data the re os isotope data suggest hydrothermal fluid flow through the wollogorang formation possibly associated with formation of the ca 1640 ma mcarthur river pb zn ag sedimentary exhalative deposit resulted in post depositional mobilization of re and os based on the degree of deviation of the re os data from a 1730 ma reference line open system behavior of re and os was greatest near the base of the black shale unit wollogorang formation black shales are enriched in mo 41 58 ppm but are characterized by variable 97 95mo 0 3 0 8 and dop 0 57 0 92 the lightest 97 95mo values occur near the base of the black shale unit based on the re os systematics hydrothermal fluids have probably overprinted the authigenic 97 95mo signature in those shales however the heaviest 97 95mo values in the wollogorang formation come from stratigraphically higher shales and are similar to those observed for the velkerri formation and thus may reflect seawater 97 95mo at 1 73 ga

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

seasonal and regional characterization of horizontal stirring in the global ocean 1 recent work on lagrangian descriptors has shown that lyapunov exponents can be applied to observed or simulated data to characterize the horizontal stirring and transport properties of the oceanic flow however a more detailed analysis of regional dependence and seasonal variability was still lacking in this paper we analyze the near surface velocity field obtained from the ocean general circulation model for the earth simulator ofes using finite size lyapunov exponents fsle we have characterized regional and seasonal variability our results show that horizontal stirring as measured by fsles is seasonally varying with maximum values in summer time fsles also strongly vary depending on the region we have first characterized the stirring properties of northern and southern hemispheres then the main oceanic basins and currents we have finally studied the relation between averages of fsle and some eulerian descriptors such as eddy kinetic energy eke and vorticity over the different regions

reconstruction of δ13c of chemocline co2 aq in past oceans and lakes using the δ13c of fossil isorenieratene abstract high abundances of the diaromatic carotenoid isorenieratene derived from photosynthetic green sulfur bacteria chlorobiaceae were found just below the chemocline in an anoxic fjord in norway throughout the annual cycle the stable carbon isotope composition of this carotenoid co varied with the 13c of co2 aq and is independent of the co2 and isorenieratene concentration this constant isotopic fractionation p of isorenieratene versus co2 4 1 was subsequently used in the reconstruction of 13c of co2 at the chemocline in ancient oceans and lakes these reconstructions indicate that 13c of co2 at the chemocline is often influenced by isotopically light co2 formed by remineralization of organic matter this process can depending on the depth and stability of the chemocline also effect the isotopic composition of the phytoplankton and thus isotopic records of sedimentary inorganic and organic carbon

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