permian rifting related fayalite syenite in the panxi region sw china abstract within the panxi rift of the permian emeishan large igneous province elip sw china a 20 km 2 quartz bearing fayalite syenitic pluton intrudes the 260 ma baima igneous complex bic the fayalite syenite is dated using shrimp zircon u pb techniques at 252 2 5 ma the panxi fayalite syenite is mainly composed of alkali feldspar ferroan augite fayalite quartz and fe ti oxides and contains 61 8 63 7 wt sio 2 5 0 7 3 wt fe 2 o 3 t and 9 9 12 1 wt total alkalis belonging to an a type variety of ferroan alkalic metaluminous granitoids the fayalite syenite displays positive eu anomalies eu eu 0 9 8 9 and is enriched in lree la yb n 6 6 11 5 the nd values and 87 sr 86 sr initial ratios of the fayalite syenite range from 1 3 to 1 9 and from 0 7035 to 0 7068 respectively the fayalite syenite and the bic had the same mantle source however the 8 myr age gap between them suggests the fayalite syenite formed by remelting of underplated mafic magmas injected into the crust during elip magmatism the ages of the fayalite syenite and bic are coincident with two permian mass extinction events and suggest that elip may have influenced both

paleoenvironmental changes in the western mediterranean since the last glacial maximum high resolution multiproxy record from the algero balearic basin abstract the present study uses a multiproxy approach in order to further understand the evolution of climate responses in the western mediterranean as of the last glacial maximum sediments from odp site 975 in the algero balearic basin have been analysed at high resolution both geochemically and mineralogicallly the resulting data have been used as proxies to establish a sedimentary regime primary marine productivity the preservation of the proxies and oxygen conditions fluctuations in detrital element concentrations were mainly the consequence of wet arid oscillations productivity has been established using ba excess according to which marine productivity appears to have been greatest during cold events heinrich 1 and younger dryas the s1 time interval was not as marked by increases in productivity as was the eastern mediterranean in contrast the s1 interval was first characterized by a decreasing trend and then by a fall in productivity after the 8 2 ky bp dry cold event since then productivity has remained low here we report that there was an important redox event in this basin probably a consequence of the major oceanographic circulation change occurring in the western mediterranean at 7 7 ky bp this circulation change led to reventilation as well as to diagenetic remobilization of redox sensitive elements and organic matter oxidation comparisons between our paleoceanographic reconstruction for this basin and those regarding other mediterranean basins support the hypothesis that across the mediterranean there were different types of responses to climate forcing mechanism the algero balearic basin is likely to be a key area for further understanding of the relationships between the north atlantic and the eastern mediterranean basins

complementary constraints from carbon 13c and nitrogen 15n isotopes on the glacial ocean s soft tissue biological pump a three dimensional process based model of the ocean s carbon and nitrogen cycles including 13c and 15n isotopes is used to explore effects of idealized changes in the soft tissue biological pump results are presented from one preindustrial control run pictrl and six simulations of the last glacial maximum lgm with increasing values of the spatially constant maximum phytoplankton growth rate max which accelerates biological nutrient utilization mimicking iron fertilization the default lgm simulation without increasing max and with a shallower and weaker atlantic meridional overturning circulation and increased sea ice cover leads to 280 pg more respired organic carbon corg storage in the deep ocean with respect to pictrl dissolved oxygen concentrations in the colder glacial thermocline increase which reduces water column denitrification and with delay nitrogen fixation thus increasing the ocean s fixed nitrogen inventory and decreasing 15nno3 almost everywhere this simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well but it overestimates deep ocean 13cdic and underestimates 15nno3 at high latitudes increasing max enhances corg and lowers deep ocean 13cdic improving the agreement with sediment data in the model s antarctic and north pacific oceans modest increases in max result in higher 15nno3 due to enhanced local nutrient utilization improving the agreement with reconstructions there models with moderately increased max fit both isotope data best whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well the best fitting models reproduce major features of the glacial 13cdic 15n and oxygen reconstructions while simulating increased corg by 510 670 pg compared with the preindustrial ocean these results are consistent with the idea that the soft tissue pump was more efficient during the lgm both circulation and biological nutrient utilization could contribute however these conclusions are preliminary given our idealized experiments which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes the analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes whereas carbon isotopes are sensitive to circulation changes and indicate well the three dimensional corg distribution nitrogen isotopes are more sensitive to biological nutrient utilization

north atlantic ventilation of southern sourced deep water in the glacial ocean one potential mechanism for lowering atmospheric co2 during glacial times is an increase in the fraction of the global ocean ventilated by the north atlantic which produces deep water with a low concentration of unused nutrients and thus drives the ocean s biological pump to a high efficiency however the data indicate that during glacial times a water mass low in 13c 12c and 14c c occupied the deep atlantic apparently at the expense of north atlantic deep water nadw this water is commonly referred to as southern sourced because of its apparent entry into the atlantic basin from the south prompting the inference that it was ventilated at the southern ocean surface here we propose that this deep atlantic water mass actually included a large fraction of north atlantic ventilated water the chemical characteristics of which were altered by recirculation in the deep southern and indo pacific oceans in an ocean model sensitivity experiment that reduces antarctic bottom water formation and weakens its overturning circulation we find that a much greater fraction of nadw is transported into the southern ocean without contacting the surface and is entrained and mixed into the southern sourced deep water that spreads into the global abyssal ocean thus north atlantic ventilation takes over more of the ocean interior lowering atmospheric co2 and yet the abyssal atlantic is filled from the south with old water low in 13c 12c and 14c c consistent with glacial data

orbitally paced paleoproductivity variations in the timor sea and indonesian throughflow variability during the last 460 kyr 1 a high resolution 1 2 kyr multiproxy record from the timor sea in the easternmost indian ocean international marine global change images program core md01 2378 latitude 13 04 95 s longitude 121 47 27 e 1783 m water depth closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the indonesian throughflow spectral analysis of five different flux based productivity proxies indicates spectral power concentrated in the 100 kyr glacial interglacial and the 23 kyr and 19 kyr precessional periods paleoproductivity maxima lead ice volume benthic 18o maxima by 20 to 40 1300 to 2600 years at the precession band the spectral differences in tropical paleoproductivity records from the pacific and indian oceans suggest that local processes wind and circulation patterns driven by insolation are dominant in driving productivity rather than large scale tropical features in the timor sea productivity fluctuations over the last 460 kyr were strongly influenced by monsoonal wind patterns offshore nw australia 23 and 19 kyr and were also modulated by sea level related variations in the intensity of the indonesian throughflow 100 kyr

the effect of vertical nutrient redistribution on surface ocean δ13c processes that shift nutrients from mid to lower ocean depths may or may not increase the ocean s vertical carbon pump redistribution of 13c produced by these processes is compared in two box models a vertical three box ocean and a thirteen box ocean in the former there is no 13c fractionation laterally between surface waters and the ocean nutrient and 13c distributions are linearly correlated this correlation is not changed when these tracers become redistributed and if the model surface ocean is nutrient limited the surface 13c cannot change in the 13 box ocean there is a transfer of negative 13c from the cold surface water through the atmosphere into the warm ocean its 13c is therefore lower than it would be as a result of the carbon pump by itself if a middepth nutrient depletion occurs because of lower nutrients in antarctic waters the warm surface 13c increases if the vertical nutrient shift occurs because of ocean circulation or biological recycling changes the warm surface water 13c change depends on the ratio of its vertical co2 fluxes i e exchange of atmospheric co2 versus upwelling total co2 and net biological production if this ratio remains about the same then little change occurs in surface 13c and the 13c of pacific deep water decreases about 0 3 in this case no change in the average ocean 13c is required to explain observations from sediment data this would imply that the ice age land biota carbon mass was about the same as that of today the vertical co2 flux ratio could be an important consideration if greater wind driven upwelling is a factor in the nutrient redistribution

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

how well would modern day oceanic property distributions be known with paleoceanographic like observations author s gebbie g streletz gj spero hj abstract 2016 american geophysical union all rights reserved compilations of paleoceanographic observations for the deep sea now contain a few hundred points along the oceanic margins mid ocean ridges and bathymetric highs where seawater conditions are indirectly recorded in the chemistry of buried benthic foraminiferal shells here we design an idealized experiment to test our predictive ability to reconstruct modern day seawater properties by considering paleoceanographic like data we attempt to reconstruct the known modern day global distributions by using a state estimation method that combines a kinematic tracer transport model with observations that have paleoceanographic characteristics when a modern like suite of observations practical salinity seawater 18o 13cdic po4 no3 and o2 is used from the sparse paleolocations the state estimate is consistent with the withheld data at all depths below 1500 m suggesting that the observational sparsity can be overcome physical features such as the interbasin gradients in deep 13cdic and the vertical structure of atlantic 13cdic are accurately reconstructed the state estimation method extracts useful information from the pointwise observations to infer distributions at the largest oceanic scales at least 10 000 km horizontally and 1500 m vertically and outperforms a standard optimal interpolation technique even though neither dynamical constraints nor constraints from surface boundary fluxes are used when the sparse observations are more realistically restricted to the paleoceanographic proxy observations of 13c 18o and cd ca however the large scale property distributions are no longer recovered coherently at least three more water mass tracers are likely needed at the core sites in order to accurately reconstruct the large scale property distributions of the last glacial maximum

subsidence of the northern south china sea and formation of the bashi strait in the latest miocene paleoceanographic evidences from 9 myr high resolution benthic foraminiferal δ 18 o and δ 13 c records abstract we present astronomically tuned high time resolution 3 4 kyr benthic foraminiferal 18o and 13c records between 9 ma and 5 ma from ocean drilling program odp site 1143 in the southern south china sea scs we found that the late miocene ocean carbon shift lmocs which was linked with the late miocene early pliocene biogenic bloom also occurred in the northern and southern scs a marked deep water 13c gradient as much as 1 0 of the northern and southern scs was observed between 6 5 ma and 5 9 ma which was probably caused by the significant difference in paleoproductivity between the northern and southern scs the deep 13c gradient was likely produced by rapid tectonic subsidence in the northern scs at 6 0 ma and the final formation of the bashi strait at 6 5 ma a reversed benthic 13c gradient of the northern and southern scs was also observed between 1 2 ma and 0 35 ma which was probably caused by the consecutive closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma further semi enclosed the scs basin and made the paleoproductivity the major factor influencing the deep water 13c leading to the reversed deep water 13c gradient of the northern and southern scs between 1 2 ma and 0 35 ma

signature of the brazil malvinas confluence argentine basin in the isotopic composition of planktonic foraminifera from surface sediments we explored the potential to use the stable isotopic compositions of planktonic foraminifera as a proxy for the position of the brazil malvinas confluence bmc in the argentine basin for this purpose we measured the oxygen and carbon isotopic compositions of globigerinoides ruber pink and white varieties measured separately globigerinoides trilobus globigerina bulloides globorotalia inflata and globorotalia truncatulinoides left and right coiling forms measured separately from a latitudinal transect of 56 surface sediment samples from the continental slope off brazil uruguay and argentina between 20 and 48 s lowest oxygen isotopes values were found in g ruber pink followed by g ruber white and g trilobus reflecting the highly stratified near surface water conditions north of the bmc globigerina bulloides was present mainly south of the bmc and records subsurface conditions supporting earlier plankton tow studies globorotalia inflata and g truncatulinoides left and right were both available over the whole transect and calcify in the depth level with the steepest temperature change across the bmc accordingly the 18 o of these species depict a sharp gradient of 2 at the confluence with remarkably stable values north and south of the bmc our data show that the oxygen isotopic composition of g inflata and g truncatulinoides left and right are the most reliable indicators for the present position of the bmc and can therefore be used to define the past migration of the front if appropriate cores are available

what do benthic δ13c and δ18o data tell us about atlantic circulation during heinrich stadial 1 approximately synchronous with the onset of heinrich stadial 1 hs1 13c decreased throughout most of the upper 1000 2500 m atlantic and at some deeper north atlantic sites this early deglacial 13c decrease has been alternatively attributed to a reduced fraction of high 13c north atlantic deep water nadw or to a decrease in the nadw 13c source value here we present new benthic 18o and 13c records from three relatively shallow 1450 1650 m subpolar northeast atlantic cores with published data from other cores these data form a depth transect 1200 3900 m in the subpolar northeast atlantic we compare last glacial maximum lgm and hs1 data from this transect with data from a depth transect of cores from the brazil margin the largest lgm to hs1 decreases in both benthic 13c and 18o occurred in upper waters containing the highest nadw fraction during the lgm we show that the 13c decrease can be explained entirely by a lower nadw 13c source value entirely by a decrease in the proportion of nadw relative to southern ocean water or by a combination of these mechanisms however building on insights from model simulations we hypothesize that reduced ventilation due to a weakened but still active atlantic meridional overturning circulation also contributed to the low 13c values in the upper north atlantic we suggest that the benthic 18o gradients above 2300 m at both core transects indicate the depth to which heat and north atlantic deglacial freshwater had mixed into the subsurface ocean by early hs1

downstream variation in grain size along an alpine river analysis of controls and processes downstream variation in bed material size was studied along a 115 km reach of the piave river eastern alps italy this river drains a region producing high sediment yields and has a braided pattern along half of its length during the last century the river system has been affected by several human impacts hydroelectric dams diversions gravel mining which have strongly altered flow regime and sediment dynamics the aim of the study is to analyse the changes of bed material size in the downstream direction and to explain these changes in the light of both natural and anthropogenic factors surface material was sampled at 35 sites using the grid by number method the collected data give a detailed picture of the downstream variation in sediment size which is characterised by a complex pattern rather than by a simple decreasing trend an explanation of this variation was found through identification of discontinuities significant steps in the downstream trend and factors which can determine changes in sediment texture both natural lateral sediment sources and anthropogenic factors e g barrages are significant in this river system and they provide an explanation for most of the observed discontinuities seven out of eight discontinuities few tributaries disrupt downstream fining while as expected the barrages produce important changes in sediment texture fining processes were investigated in the lower part of the study reach where the lateral sediment sources and the barrages have minor effects on the bed material exponential models provide acceptable explanations of the downstream variations and give fining coefficients equal to 0 027 and 0 028 km 1 respectively for d50 and d84 evidence suggests that both abrasion and sorting are important in determining the downstream fining observed but it is likely that sorting is the dominant process

trace elements and isotope geochemistry c o fe cr of the caue iron formation quadrilatero ferrifero brazil evidence for widespread microbial dissimilatory iron reduction at the archean paleoproterozoic transition abstract the banded iron formation bifs of the caue formation quadrilatero ferrifero brazil are part of the great volume of bifs deposited worldwide around 2 45 ga samples of carbonate ankerite dolomite bif from this unit were collected from a drill core ca 600 m deep in the alegria region geochemical data suggest low clastic contamination y ho 37 7 and seawater like signatures with positive la and y anomalies no true ce anomalies and mean eu eu 1 62 u th shows a sharp increasing downwards pattern up to ca 15 below the 535 m mark values of 13c and 18o are all negative reaching a minimum of 10 0 and 24 6 respectively in the 540 560 m interval values of 56fe are mostly positive between 0 5 and 1 3 the higher values are attained in the same interval values of authigenic 53cr range between 0 01 and 0 26 with an increasing downwards pattern which mirrors the u th variation a possible explanation for both the low 13c and the high 56fe is the activity of microorganisms in the dissimilatory iron reduction dir of the precursor ferric oxides thus we put forward a model for deposition of the caue bifs that starts with the generation of fe ii aq through hydrothermal input to the deeper basin which upon reaching a chemocline in the platform border oxidizes to fe iii and settles as iron oxy hydroxides to the basin floor when reaching the sediment layer fe iii is then reduced by microbial activity to generate magnetite and iron rich carbonates with negative 13c and positive 56fe an important issue is how u vi and cr vi were mobilized to the basin to form the positive u th and 53cr excursions these could reflect oxidative continental weathering but an alternative possibility is that those elements became available through local oxygenation in continental microenvironments which would better explain the lack of ce redox cycling in either case our results together with a growing body of data for bif sequences of similar age around the world e g kuruman south africa and hamersley australia suggest that microbial mediated dir was a common and widespread mechanism for the genesis of bifs at the archean paleoproterozoic transition

carbon isotopes and habitat of polar planktic foraminifera in the okhotsk sea the carbonate ion effect under natural conditions the upper 500 or 1000 m of the water column in the okhotsk sea was sampled for living planktic foraminifera the polar species neogloboquadrina pachyderma sinistral strongly dominates the foraminiferal assemblage the subpolar to temperate species globigerina bulloides accounts for 10 25 other species account for up to 3 only the shell 18o and 13c values of the species n pachyderma sin are compared to water 18o values and 13c values of dissolved inorganic carbon dic the strong gradient in 18o composition and temperature in the upper water column is reflected in the 18o of n pachyderma sin relative to the values expected for inorganic calcite precipitated under equilibrium conditions n pachyderma sin displays a vital effect of about 1 in 18o the 13c composition of n pachyderma sin is about constant with water depth and the reflection of 13cdic in the foraminiferal shell seems to be masked by other effects most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column the gradient of 13cdic extends well below this depth therefore the lack of correlation can partly be attributed to this fact the remaining discrepancy between 13c of n pachyderma sin and 13cdic correlates with the carbonate ion concentration in the water column this leads to the conclusion that the carbonate ion effect cie which has been derived from culturing experiments for other species spero et al 1997 nature 390 497 500 is found here under natural conditions when the magnitude of the cie derived for g bulloides is applied to n pachyderma sin cie corrected 13c of n pachyderma sin is a direct reflection of 13cdic in the water column with a constant offset of 1 2

glacial and holocene stable isotope distributions in the southeastern indian ocean we have reconstructed glacial interglacial variations in cibicidoides wuellerstorfi 13c and 18o in the southeastern indian ocean using depth transects of cores from off western and southern australia we compare these new results with published stable isotope records to constrain glacial interglacial changes in indian ocean chemistry and circulation the strong last glacial maximum lgm deep water 13c depletions previously observed for the northeastern indian ocean did not extend throughout the low latitude glacial indian ocean we observe only a small lgm 13c decrease off southern australia in marked contrast to the strong lgm 13c depletions observed in many cores from the atlantic and western indian sectors of the southern ocean it is not yet clear whether the very low lgm 13c values in the deep northern and southwestern indian ocean are an artifact of surface ocean productivity or whether they reflect real gradients in deep water chemistry

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

deep south atlantic carbonate chemistry and increased interocean deep water exchange during last deglaciation abstract carbon release from the deep ocean at glacial terminations is a critical component of past climate change but the underlying mechanisms remain poorly understood we present a 28 000 year high resolution record of carbonate ion concentration a key parameter of the global carbon cycle at 5 km water depth in the south atlantic we observe similar carbonate ion concentrations between the last glacial maximum and the late holocene despite elevated concentrations in the glacial surface ocean this strongly supports the importance of respiratory carbon accumulation in a stratified deep ocean for atmospheric co 2 reduction during the last ice age after 9 mol kg decline during heinrich stadial 1 deep south atlantic carbonate ion concentration rose by 24 mol kg from the onset of bolling to pre boreal likely caused by strengthening north atlantic deep water formation bolling or increased ventilation in the southern ocean younger drays or both pre boreal the 15 mol kg decline in deep water carbonate ion since 10 ka is consistent with extraction of alkalinity from seawater by deep sea caco 3 compensation and coral reef growth on continental shelves during the holocene between 16 600 and 15 000 years ago deep south atlantic carbonate ion values converged with those at 3 4 km water depth in the western equatorial pacific as did carbon isotope and radiocarbon values these observations suggest a period of enhanced lateral exchange of carbon between the deep south atlantic and pacific oceans probably due to an increased transfer of momentum from southern westerlies to the southern ocean by spreading carbon rich deep pacific waters around antarctica for upwelling invigorated interocean deep water exchange would lead to more efficient co 2 degassing from the southern ocean and thus to an atmospheric co 2 rise during the early deglaciation

upwelling and productivity along the peru chile current derived from faunal and isotopic compositions of planktic foraminifera in surface sediments abstract we report on the spatial distribution of isotopic compositions of the two planktic foraminifera species globigerina bulloides and neogloboquadrina pachyderma dex and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the chilean continental slope between 23 s and 44 s both 13c and 18o data of n pachyderma dex show little variability in the study area north of 39 s the isotopic values of n pachyderma dex are heavier than those of g bulloides whereas south of 39 s this relation inverses this is indicative for a change from a well mixed deep thermocline caused by coastal upwelling north of 39 s to well stratified water masses in a non upwelling environment south of 39 s in addition the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39 s to a high nutrient non upwelling assemblage south of 39 s which is characterized by decreased contributions of upwelling indicators such as g bulloides n pachyderma sin and globigerinita glutinata in general we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23 s and 44 s off chile our data point to higher marine productivity at upwelling centers north of 25 s and at 30 33 s south of 39 s significant supply of nutrients by fluvial input most likely boosts the productivity

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

impact of end member mixing on depth distributions of δ13c cadmium and nutrients in the n atlantic ocean abstract the po 4 13 c and cd depth distributions measured in the n atlantic ocean during recent geotraces and clivar cruises are a result of biological and circulation processes with in situ uptake and remineralization of organic matter dominating in the upper 300 m and mixing of water masses dominating in the thermocline and deep sea the observed slopes of the no 3 po 4 preindustrial 13 c po 4 and by analogy cd po 4 along isopycnals deviate significantly from that expected from redfield in the thermocline and deep sea and in each case the observed slope is similar to the slopes of the end member water masses being mixed the depth increase in the cd po 4 slope resulting from end member mixing explains the observed kink at 1 m po 4 in the cd po 4 relationship in the n atlantic the observation that the po 4 preindustrial 13 c cd relationship in the modern n atlantic is heavily influenced by end member mixing throughout most of the water column complicates the use of 13 c and cd as proxies of the paleocean s nutrient distribution because changes in the po 4 13 c cd composition of locally and remotely produced end members water masses would change the po 4 13 c and cd depth distributions in the paleo n atlantic ocean