226ra in marine barite new constraints on supported 226ra abstract following the pioneering work of paytan et al a paytan et al geochim cosmochim acta 60 1996 4313 4319 new investigations have been undertaken on marine barite separated from central and western equatorial pacific sediments these investigations are designed to achieve a better quantification of supported 226 ra activities in the separated samples enabling the use of excess 226 ra 226 ra ex in marine barite as a tool for dating holocene sediments instrumental neutron activation analysis allowed first to measure significant 238 u activities in the separated samples attributable to highly insoluble minerals that like barite are resistant to the chemical treatment used in this study tio 2 minerals zircon monazite within these u rich minerals 226 ra activities are in secular equilibrium with 238 u second the study of the 226 ra signal in old barite samples that do not contain any residual 226 ra ex activities provided accurate constraints on the amount of 226 ra produced by unsupported 230 th the remaining 226 ra activities corrected for the 238 u contribution appeared to decrease with depth with a slope comparable to that defined by the bulk 230 th ex activities the consistency of this deep trend allowed its extrapolation upwards to the sediment top in order to obtain an estimate of the 226 ra activities produced by unsupported 230 th in the holocene barite samples the total correction for supported 226 ra in the holocene barite samples used in this study therefore consists of the sum of 226 ra activities in secular equilibrium with 238 u within minerals and 226 ra activities produced by unsupported 230 th thus estimated the resulting correction is low for samples separated from central equatorial pacific sediments compared with both the total 226 ra activities measured in barite and results of previous studies the magnitude of the correction is nevertheless higher for samples from western equatorial pacific sediments which display a lower barite purity the corrected 226 ra in barite profiles are in agreement with the general trend observed for long half life radionuclides with a similar mixed layer in the sediment top thus adding confidence in the use of this tool below the mixed layer the exponential decay of 226 ra ex activities in barite allowed the determination of sedimentation rates that agree with the estimates for the two investigated sites ultimately one of the main uses for the 226 ra in barite dating method will be its application to holocene sediments from the southern ocean where dating is often problematic

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

on suspended barite and the oxygen minimum in the southern ocean particulate ba profiles were measured in the indian sector of the southern ocean the largest fraction 80 of this barium is present as barite microcrystals the profiles of total barium are characterized by a subsurface maximum between 200 and 500 m depth in the vicinity of the oxygen minimum highest barium values are found just south of the polar front while lowest values occur close to the antarctic divergence between the divergence and the polar front a tight inverse relationship is observed between oxygen in the oxygen minimum and barium in the barium maximum this relationship disappears north of the polar front since suspended barite is known to be of biological origin the correlation of barite with oxygen suggests that the observed decrease of oxygen in the oxygen minimum between the divergence and the polar front is due to local consumption of oxygen it is proposed that deep low oxygen water is advected towards the divergence where upwelling occurs and where this water subsequently partly spreads out to the north north east as entrained by the antarctic circumpolar current oxidation of locally produced organic matter with which barite crystals are associated consumes oxygen and sets free individual discrete barites as a result oxygen decreases and barite increases away from the divergence with barite integrating former biological processes

the southern ocean s biological pump during the last glacial maximum ice core records from antarctica show large 80 ppm and regular climate related changes in atmospheric co2 with minimum values during glacial periods and maximum values during peak interglacials the suggested role of the southern ocean in driving these changes is based on either the potential for increased utilization of surface nutrients or the potential for decreased ventilation of deep waters during glacial times several recent studies have invoked increased stratification of the southern ocean to explain lower glacial atmospheric co2 levels in terms of reduced exchange of co2 between the deep sea and the atmosphere a northward displacement and or substantial weakening of the westerly winds during glacial periods are implicit in the scenarios that invoke enhanced stratification however both circulation models and proxy results argue against a weakening of the westerlies in fact the mean flow of the antarctic circumpolar current and wind driven upwelling during the last glacial maximum lgm are thought to be at least as vigorous as those which exist today given these boundary conditions we offer two competing scenarios for ecosystem structure and export production of the glacial southern ocean the first scenario satisfies all proxy records for nutrient utilization and phytoplankton growth rate and requires increased relative to today nitrate utilization south of the antarctic polar front apf by phytoplankton other than diatoms together with a shift in the zone of maximum diatom growth from south interglacials to north glacials of the apf the second scenario has reduced growth of all phytoplankton species south of the apf during glacials and a shift in the zone of maximum export production to the north of the polar front the principal weakness of the first scenario is that there is little sedimentary evidence to support the increased export of particulate organic carbon required by the inferred increase in nitrate utilization south of the apf the principal weakness of the second scenario is that it requires a change in the isotopic fractionation of nitrogen by phytoplankton growing south of the polar front for reasons presently unknown the southern ocean s biological pump at the lgm has yet to be characterized unequivocally

reconstruction of primary productivity from the barium contents in surface sediments of the south atlantic ocean abstract the aim of the present study is an evaluation of the applicability of biogenic barium as a proxy for productivity for this purpose 190 surface sediment samples from the south atlantic ocean were analysed for their barium and aluminium concentrations biogenic barium is estimated by subtracting the calculated terrigenous barium obtained from the terrigenous ba al ratio and the amount of al in the sample from the total ba content in the sample based on the accumulation rates of biogenic barium export production is estimated using three different algorithms proposed by paleoceanography 7 1992 163 global biogeochem cycles 9 1995 289 geomar report 38 1995 105 primary productivity was calculated from these different export productions and compared with measurements of recent primary productivity in the overlying surface waters only the primary productions calculated on the basis of the algorithm of paleoceanography 7 1992 163 yield productivity values comparable to those existing in ocean surface waters this study further reveals that it is not sufficient to use a constant generally applicable organic carbon biogenic barium ratio as is postulated by global biogeochem cycles 9 1995 289 this ratio has to be assessed regionally for the sediments of the cape basin in the eastern south atlantic ocean a new algorithm is developed which gives plausible primary productivities for the overlying surface waters

equatorial pacific productivity and dust flux during the mid pleistocene climate transition received 6 may 2005 revised 30 august 2005 accepted 19 september 2005 published 17 december 2005 1 we present a helium isotope record for core tt013 114pc from the central equatorial pacific 140 w 4 n 4432 m water depth spanning a period of 1 million years we focus on the time interval from 560 to 800 kyr largely coinciding with the mid pleistocene climate transition mpt when the dominant period of the earth s climate variability shifted from 41 kyr to 100 kyr the terrigenous 4 he concentrations from our study correlate very well with published titanium concentrations in this core strongly supporting the use of terrigenous 4 he as a monitor of continental dust normalizing titanium and terrigenous 4 he concentrations to 3 he suggests that the dust supply during the mpt was approximately 30 lower compared to the subsequent period 560 100 kyr the 3 he normalized barium aluminum and phosphorus concentrations trace elements with a predominantly biogenic source in these sediments are relatively constant this is in contrast to previous studies that reported an apparent rise of titanium normalized productivity proxies rather than a significant increase in productivity during the mpt we conclude that the dust flux to the central equatorial pacific was reduced and that the export productivity was approximately constant during this period of climate reorganization

quantifying export production in the southern ocean implications for the ba xs proxy the water column and sedimentary baxs distribution around the crozet plateau is used to decipher the controls and timing of barite formation and to evaluate how export production signals are recorded in sediments underlying a region of natural fe fertilization within the fe limited southern ocean export production estimated from preserved vertical sedimentary baxs accumulation rates are compared with published export fluxes assessed from an integrated study of the biological carbon pump to determine the validity of baxs as a quantitative proxy under different fe supply conditions typical of the southern ocean detailed assessment of the geochemical partitioning of ba in sediments and the lithogenic end member allows appropriate correction of the bulk ba content and determination of the baxs content of sediments and suspended particles the upper water column distribution of baxs is extremely heterogeneous spatially and temporally organic carbon baxs ratios in deep traps from the fe fertilized region are similar to other oceanic settings allowing quantification of the inferred carbon export based on established algorithms there appears to be some decoupling of poc and ba export in the fe limited region south of the plateau the export production across the crozet plateau inferred from the baxs sedimentary proxy indicates that the fe fertilized area to the north of the plateau experiences enhanced export relative to equivalent southern ocean settings throughout the holocene and that this influence may also have impacted the site to the south for significant periods this interpretation is corroborated by alternative productivity proxies opal accumulation 231paxs 230thxs baxs can be used to quantify export production in complex settings such as naturally fe fertilized volcanoclastic areas providing appropriate lithogenic correction is undertaken and sediment focusing is corrected for along with evaluation of barite preservation

glacial interglacial changes in subarctic north pacific stratification since the first evidence of low algal productivity during ice ages in the antarctic zone of the southern ocean was discovered there has been debate as to whether it was associated with increased polar ocean stratification or with sea ice cover shortening the productive season the sediment concentration of biogenic barium at ocean drilling program site 882 indicates low algal productivity during ice ages in the subarctic north pacific as well site 882 is located southeast of the summer sea ice extent even during glacial maxima ruling out sea ice driven light limitation and supporting stratification as the explanation with implications for the glacial cycles of atmospheric carbon dioxide concentration

an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years eleven sediment samples taken downcore and representing the past 26 kyr of deposition at manop site c 0 57 2 n 138 57 3 w were analyzed for lipid biomarker composition biomarkers of both terrestrial and marine sources of organic carbon were identified in general concentration profiles for these biomarkers and for total organic carbon toc displayed three common stratigraphic features in the time series 1 a maximum within the surface sediment mixed layer 4 ka 2 a broad minimum extending throughout the interglacial deposit and 3 a deep pronounced maximum within the glacial deposit using the biomarker records a simple binary mixing model is described that assesses the proportion of terrestrial to marine toc in these sediments best estimates from this model suggest that 20 of the toc is land derived introduced by long range eolian transport and the remainder is derived from marine productivity the direct correlation between the records for terrestrial and marine toc with depth in this core fits an interpretation that primary productivity at site c has been controlled by wind driven upwelling at least over the last glacial interglacial cycle the biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr b p diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr

a comparison of early paleogene export productivity and organic carbon burial flux for maud rise weddell sea and kerguelen plateau south indian ocean 1 marine biological productivity has been invoked as a possible climate driver during the early paleogene through its potential influence on atmospheric carbon dioxide concentrations however the relationship of export productivity the flux of organic carbon c from the surface ocean to the deep ocean to organic c burial flux the flux of organic c from the deep ocean that is buried in marine sediments is not well understood we examine the various components involved with atmosphere to ocean c transfer by reconstructing early paleogene carbonate and silica production using carbonate and silica mass accumulation rates mars export productivity using biogenic barium bio ba mars organic c burial flux using reactive phosphorus p mars redox conditions using uranium and manganese contents and the fraction of organic c buried relative to export productivity using reactive p to bio ba ratios our investigations concentrate on paleocene eocene sections of sites 689 690 from maud rise and site 738 from kerguelen plateau in both regions export productivity organic c burial flux and the fraction of organic c buried relative to export productivity decreased from the paleocene early eocene to the middle eocene a shift is indicated from an early paleogene two gyre circulation in which nutrients were not efficiently recycled to the surface via upwelling in these regions to a circulation more like the present day with efficient recycling of nutrients to the surface ocean export productivity was enhanced for kerguelen plateau relative to maud rise throughout the early paleogene possibly due to internal waves generated by the plateau regardless of gyre circulation

greater supply of patagonian sourced detritus and transport by the acc to the atlantic sector of the southern ocean during the last glacial period reconstructing past detrital flux and provenance in the southernocean provides information about changes in source regions associated with climate variations and transport pathways we present a lastglacial maximum lgm to holocene comparison of 230th normalised fluxes combined with sediment provenance data pb nd and sr isotopes from a latitudinal core transect in the eastern atlanticsector of the southernocean odp leg 177 cores we compare the radiogenic isotopic composition ic of detritus in these cores to that of cores proximal to potential source areas we observe a well defined latitudinal holocene gradient in both detrital flux and provenance of sediment high detrital fluxes in the north are associated with terrigenous material derived from southern africa while low detrital fluxes in the south are associated with supply from southern south america west antarctica and the south sandwich islands the data suggest that this well defined holocene gradient in detrital flux and sediment provenance is controlled by the flow of the antarctic circumpolar current acc and the position of its frontal zones the lgm is characterised by 2 to 6 times higher than modern detrital fluxes at most odp leg 177 sites the lgm detrital fluxes do not show a latitudinal trend and suggest a greatersupply of glaciogenic detritussourced from southern south america glacialpatagonian outwash sediments 5 m fraction were analysed and compared to the bulk compositions of the marine sediments the pb ic of the patagonian sediments is very similar to the glacial ic of sediments in the scotia sea and at 49 s latitude in the eastern atlanticsector we propose that the glacial ic of sediments is controlled by increased delivery of patagoniandetritus initially supplied by glaciers and then transported at depth via the acc

ba distribution in surface southern ocean sediments and export production estimates 1 we present excess ba baxs data i e total ba corrected for lithogenic ba for surface sediments from a north south transect between the polar front zone and the northern weddell gyre in the atlantic sector and between the polar front zone and the antarctic continent in the indian sector focus is on two different processes that affect excess ba accumulation in the sediments sediment redistribution and excess ba dissolution the effect of these processes needs to be corrected for in order to convert accumulation rate into vertical rain rate the flux component that can be linked to export production in the southern ocean a major process affecting ba accumulation rate is sediment focusing which is corrected for using excess 230 th this correction however may not always be straightforward because of boundary scavenging effects a further major process affecting excess ba accumulation is barite dissolution during exposure at the sediment water column interface export production estimates derived from excess 230 th and barite dissolution corrected baxs accumulation rates i e excess ba vertical rain rates are of the same magnitude but generally larger than export production estimates based on water column proxies 234 th deficit in the upper water column particulate excess ba enrichment in the mesopelagic water column we believe export production values based on excess ba vertical rain rate might be overestimated due to inaccurate assessment of the baxs preservation rate barite dissolution has in general been taken into account by relating it to exposure time before burial depending on the rate of sediment accumulation however the observed decrease of excess ba content with increasing water column depth or increasing hydrostatic pressure illustrates the dependence of barite preservation on degree of saturation in the deep water column in accordance with available thermodynamic data therefore correction for barite dissolution would not be appropriate by considering only exposure time of the barite to some uniformly undersaturated deep water but requires also that regional differences in degree of undersatuation be taken into account index terms 1050 geochemistry marine geochemistry 4835 4850 4835 oceanography biological and chemical inorganic marine chemistry keywords excess ba sediment southern ocean export production

late quaternary variations in sea surface temperatures and their relationship to orbital forcing recorded in the southern ocean atlantic sector late quaternary summer sea surface temperatures ssts have been derived from radiolarian assemblages in the east atlantic sector of the southern ocean in the subantarctic and the polar frontal zone glacial ssts oxygen isotope stages 2 4 6 and 8 were 3 5 c cooler than today indicating northward displacements of the isotherms about 2 4 of latitudes during interglacials ssts almost reached modern levels oxygen isotope stages 7 and 9 or exceeded them by 2 3 c oxygen isotope stages 1 and 5 5 in the subantarctic atlantic ocean changes in sst and calcium carbonate content of the sediment precede variations in global ice volume in the range of the main milankovitch frequencies comparisons with the timing of north atlantic deep water nadw proxy records suggests that this early response in the subantarctic atlantic ocean is not triggered by the flux of nadw to the southern ocean

late quaternary sediment dating and quantification of lateral sediment redistribution applying230thex a study from the eastern atlantic sector of the southern ocean high resolution records of the natural radionuclide230th were measured in sediments from the eastern atlantic sector of the antarctic circumpolar current to obtain a detailed reconstruction of the sedimentation history of this key area for global climate change during the late quaternary high resolution dating rests on the assumption that the230thex flux to the sediments is constant short periods of drastically increased sediment accumulation rates up to a factor of 8 were determined in the sediments of the antarctic zone during the climate optima at the beginning of the holocene and the isotope stage 5e by comparing expected and measured accumulation rate of230thex lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above were calculated we show that lateral contributions locally were up to 6 5 times higher than the vertical particle rain rates at other locations only 15 of the expected vertical particle rain rate were deposited

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

biostratigraphic characterization and quaternary microfossil palaeoecology in sediment drifts west of the antarctic peninsula implications for cyclic glacial interglacial deposition abstract the sedano project recovered 19 gravity cores on sediment drifts from the pacific continental margin of the antarctic peninsula camerlenghi et al 1997a high resolution terrigenous sedimentary record of the sediment drifts on the antarctic peninsula pacific margin in ricci c a ed the antarctic region museo nazionale dell antartide siena pp 705 710 fifteen cores were sampled with the aim of developing an integrated biostratigraphy and palaeoecology based on calcareous nannofossils diatoms planktonic and benthic foraminifera framed in a depositional process reconstruction barren gray laminated and brown bioturbated hemipelagic sediments characterize glacial and interglacial cycles respectively analyses from both intervals allow comparison between microfossil occurrence in glacial and interglacial cycles the unit boundaries were drawn more accurately by means of the microfossil distribution on the basis of micropalaeontological and sedimentological evidence interglacial unit c is correlated to oxygen isotope stage 5 thus dating the unit boundaries at 127 and 70 ka peaks in diatom abundance correlate well with interglacial units and indicate high productivity and an open ocean environment a calcareous nannofossil cold taxa association is present in most cores examined and its consistent distribution within interglacial unit c indicates key environmental relationships the occurrence of calcareous nannofossils has been related to temperature tolerance sea ice cover reduction nutrient availability and factors limiting primary productivity our results confirm that coccolithophorids occurred at southern high latitudes in the western marginal basins of the antarctic peninsula during short periods of the late quaternary a foraminiferal assemblage made up of sinistral neogloboquadrina pachyderma and few benthics occurs only in interglacial units correlation of microfossil occurrences with climatic cycles adds information on their palaeoecology and palaeoproductivity in the southern high latitudes

provenance of glacial marine sediments under the mcmurdo ross ice shelf windless bight antarctica heavy minerals and geochemical data abstract sea floor sediments beneath the mcmurdo ross ice shelf in a 900 m deep depression behind ross island have been cored through access holes at two sites at site 1 31 cm of mud and lesser sand deposited over the last 22 ka overlies a 30 cm thick diamictite of the last glacial maximum at site 2 the entire core is mud deposited over the last 12 ka analyses of very fine sand sized heavy minerals and geochemical analyses of the sand and silt fractions have been carried out on samples from both sites to track variations in sediment provenance through the late quaternary the heavy minerals were identified by optical and electron scanning microscope sem edax analysis major and trace elements were determined on fused glass discs by x ray fluorescence xrf spectrometry heavy mineral assemblages have high concentrations of pyroxenes titanoaugite augite pigeonite low ca augite and enstatite olivines and glass grains amphiboles mg hornblende actinolite and kearsutite oxides titanite and titanomagnetite and stable minerals epidote garnet and apatite are present in minor amounts olivine titanoaugite and glass dominate the heavy mineral assemblages both in upper part of core 1 and in all of core 2 in the diamictite an increase of augite pigeonite low ca augite hornblende and stable minerals are observed the sediment geochemistry is linked to their mineralogical composition both in the sand and in the silt fractions k and rb trends probably represent variations in alkali feldspar and or mica content the variation of si al ratio is due to sialic minerals and or to quartz content variation mg ca ti sr are probably comprised in femic minerals the sets of analyses show that the sediments are a mix of local mcmurdo volcanic group mvg rocks and transantarctic mountains tam source rocks to the south and west the diamicton was a strong tam provenance suggesting that the main ice streams drained into the ross sea from the west at least prior to 18 ky and later than 25 ky the overlying mud is dominated by a mvg signal sediments in the two sampled sites derive from basal melting of the ice sheet which entrapped debris from mvg cropping out to the south of the ross embayment small quantities of minerals from the tam can be supplied by marine currents inflowing under the shelf from nw

barium in sediments off northwest africa a tracer for paleoproductivity or meltwater events 1 high resolution down core analyses of the solid phase content of total barium batot and total organic carbon toc back to 25 kyr b p were performed on a gravity core from the upper continental slope off cape yubi morocco the observed discrepancy between the two potential paleoproductivity proxies batot and toc initiated supplementary examinations of the pore water the geochemistry of the clay fraction x ray diffraction analyses and the application of a sequential ba extraction method of selected samples additionally we analyzed down core samples of the planktonic foraminifera turborotalita quinqueloba and globorotalia inflata for their ba ca ratios these analyses which were performed for the first time on these species were used to reconstruct past oceanic ba concentrations we suggest that in the study area which is characterized by high accumulation rates the preserved toc content is a valuable proxy for past primary productivity whereas the solid phase batot contents appear to be affected by other mechanisms and factors peaks of total barium content in the clay fraction and of ba ca ratios in the planktonic foraminifera shells found during the younger dryas and the heinrich 1 event are likely to result from increased meltwater influx into the northern north atlantic we suggest that ba enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the canary islands total barium contents of the clay fraction batot clay and ba ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

palaeoclimate and palaeoenvironmental changes through the onset of the valanginian carbon isotope excursion evidence from the polish basin abstract the valanginian weissert episode of environmental change is associated with a positive carbon isotope excursion cie in 13ccarb and 13corg records and a crisis in pelagic and neritic carbonate production the cie was interpreted to represent the first oceanic anoxic event oae of the cretaceous linked with the formation of the parana etendeka large igneous province lip recent studies suggest though that the extent of oceanic anoxia was limited to high latitude epicontinental seas and the pacific and that the parana etendeka lip postdates the valanginian cie with these new interpretations the palaeoenvironmental changes behind the observed perturbation of the carbon cycle remain to be elucidated here we present sedimentological and geochemical results from a drill core near w wal central poland the excavated succession is of particular interest due to its near shore depositional setting within the former polish basin and its preservation up to 17 wt of aragonite the core consists of lower to upper valanginian silty to sandy clays deposited under fully marine conditions on top of an upper jurassic karstified limestone a change in weathering mode from very humid and highly hydrolysing towards less humid and seasonally contrasted conditions is indicated by the abrupt change from a kaolinite to a smectite dominated clay mineral association near the boundary between the early and late valanginian moreover two phosphate rich horizons were identified which correlate in time to northern tethyan occurrences in the helvetic alps the lower level is associated with the early valanginian transgression and corresponds to peak humidity recorded in the w wal core the upper layer corresponds to the paroxysmal phase of the valanginian crisis in carbonate production in the w wal core evidence for anoxic conditions during the valanginian cie is lacking the climatic conditions and changes identified in the polish basin are different from those of the northern tethyan area where an increase in humidity is observed near the early late valanginian boundary the contrasting climate conditions are probably an expression of latitudinal shifts in the position of the northern mid latitude humid belt

organic accumulation in the lower chihsia formation middle permian of south china constraints from pyrite morphology and multiple geochemical proxies article i nfo the organic rich chihsia formation middle permian on the yangtze platform western hubei south china is considered to be the major hydrocarbon source rock in south china the lower part of the chihsia formation reported here was deposited in an intrashelf basin and is characterised by black laminated marlstones shales intercalated with dark grey limestones dolomites in which metre scale shallowing or cleaning upward cycles are ubiquitous each cycle is composed of basal marlstone shale and upper lime stone the organic matter is concentrated exclusively in the shaley bases of these cycles and shows system atic cyclic variations in abundance up through the succession an integrated approach of pyrite morphology and multiple geochemical proxies was used to determine the mechanism of organic accumulation in the organic rich sediments many redox proxies including pyrite framboid size distribution c s fe relation ships iron speciation and 34 s values of pyrite suggest deposition beneath the dysoxic bottom water which evolved into a more oxic water body when the organic poor limestones were deposited however the coincidence of increased abundance of total organic carbon toc with increased ba and mo contents in dicates that organic matter accumulation was controlled mainly by primary productivity these data indicate that increased organic accumulation resulted mainly from higher organic carbon export with increased nutri ent flux during superimposed sea level rises of different orders this in turn could have increased the oxygen consumption by respiration of microorganisms and organic matter decay leading to the depletion of oxygen in the water columns furthermore the rapid sedimentation rate further limited bioturbation and organic matter decomposition facilitating the preservation of buried organic matter

productivity fluctuations in the southeastern arabian sea during the last 140 ka abstract detailed analyses of multiple geochemical productivity proxies such as calcium carbonate biogenic opal biogenic ba organic carbon and total nitrogen have been carried out on a sediment core from the southeastern arabian sea to trace the palaeoproductivity fluctuations over the last 140 ka high calcium carbonate biogenic opal biogenic ba contents wt and their mass accumulation rates g cm2 ka suggest higher productivity during major interglacials than in the glacials organic carbon content

export production in the new zealand region since the last glacial maximum increased export production ep in the subantarctic zone saz of the southern ocean due to iron fertilisation has been proposed as a key mechanism for explaining carbon drawdown during the last glacial maximum lgm this work reconstructs marine ep since the lgm at four sites around new zealand for the first time in this region 230 thorium normalised fluxes of biogenic opal carbonate excess barium and organic carbon are presented in subtropical waters and the saz these flux variations show that ep has not changed markedly since the lgm the only exception is a site currently north of the subtropical front here we suggest the subtropical front shifted over the core site between 18 and 12ka driving increased ep to understand why ep remained mostly low and constant elsewhere lithogenic fluxes at the four sites were measured to investigate changes in dust deposition at all sites lithogenic fluxes were greater during the lgm compared to the holocene the positive temporal correlation between the antarctic dust record and lithogenic flux at a site in the tasman sea shows that regionally increased dust deposition contributed to the high glacial lithogenic fluxes additionally it is inferred that lithogenic material from erosion and glacier melting deposited on the campbell plateau during the deglaciation 18 12ka from these observations it is proposed that even though increased glacial dust deposition may have relieved iron limitation within the saz around new zealand the availability of silicic acid limited diatom growth and thus any resultant increase in carbon export during the lgm therefore silicic acid concentrations have remained low since the lgm this result suggests that both silicic acid and iron co limit ep in the saz around new zealand consistent with modern process studies

west antarctic ice sheet retreat driven by holocene warm water incursions glaciological and oceanographic observations coupled with numerical models show that warm circumpolar deep water cdw incursions onto the west antarctic continental shelf cause melting of the undersides of floating ice shelves because these ice shelves buttress glaciers feeding into them their ocean induced thinning is driving antarctic ice sheet retreat today here we present a multi proxy data based reconstruction of variability in cdw inflow to the amundsen sea sector the most vulnerable part of the west antarctic ice sheet during the holocene epoch from 11 7 thousand years ago to the present the chemical compositions of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced cdw upwelling controlled by the latitudinal position of the southern hemisphere westerly winds forced deglaciation of this sector from at least 10 400 years ago until 7 500 years ago when an ice shelf collapse may have caused rapid ice sheet thinning further upstream and since the 1940s these results increase confidence in the predictive capability of current ice sheet models

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

iron deficiency limits phytoplankton growth in antarctic waters enrichment experiments were performed in the ross sea to test the hypothesis that iron deficiency is responsible for the phytoplankton s failure to use up the luxuriant major nutrient supplies found in these and all other offshore antarctic ocean waters nitrate uptake rates in the controls without added trace elements ranged from 0 58 to 1 22 mol kg 1 d 1 the addition of 1 to 5 nmol of unchelated fe per liter resulted in rates that were 2 to 10 times higher 2 54 to 6 00 mol no3 kg 1 d 1 rates in bottles with 2 nmol mn added were identical to those in the controls 0 57 to 1 04 mol no3 kg 1 d 1 total decreases in no3 were balanced by increases in particulate organic n these results suggest that fe deficiency is the primary reason that the present day southern ocean biological pump is shut off in contrast iron was 50 times more abundant during the last glacial maximum greater fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric c02 these results also imply that large scale southern ocean fe fertilization is feasible at least in terms of the total amounts of fe required i e 100 000 to 500 000 tons yr 1

high resolution record of export production in the eastern equatorial pacific across the eocene oligocene transition and relationships to global climatic records 1 understanding changes in export production through time provides insight into the response of the biological pump to global climate change particularly during periods of rapid climate change in this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the eocene oligocene transition eot in addition we consider if these export production variations are dominantly controlled by orbitally driven climate variability to accomplish these objectives we report changes in export production in the eastern equatorial pacific eep from site u1333 across the eot reconstructed from a high resolution record of marine barite accumulation rates bar bar fluctuations suggest synchronous declines in export production associated with the two step increases in oxygen isotopes that define the transition the reduction in productivity across the eot suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition we also report a previously undocumented peak in eep export productivity before the eot onset this peak is consistent with export production proxies from the southern ocean potentially implying a global driver for this precursor event we propose that this enhanced export production and the associated carbon sequestration in the late eocene may have contributed to the pco2 drawdown at the onset of antarctic glaciation

the southern ocean surface between marine isotope stages 6 and 5d shape and timing of climate changes summer sea surface temperature ssst and sea ice extent obtained at millennial to centennial resolution are presented for seven cores recovered in the atlantic and western indian antarctic zone from termination ii and the last interglacial s s i e marine isotope substage mis 5e the diatom based ssst estimates show that during the late mis 6 intensified export of cold waters from the weddell sea resulted in sssts close to 0 c in the central and eastern atlantic sector due to northward expansion of the winter sea ice edge by 3 5 latitude the sea ice seasonality was reduced such conditions have great potential for efficient year round reduction in air sea gas exchange and glacial co2 draw down the warming at termination ii started at 132 131 ka marked by rapid retreat of the sea ice edge the ssst increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2 5 and 3 5 c in the earliest mis 5e 128 125 ka besides a distinct cold reversal around 129 5 ka the warming was punctuated by short lived temperature rebounds with amplitudes of 1 1 5 c occurring at 200 300 yr frequency thus in the range of the periodicity of solar input increased chaetoceros spp abundance suggests meltwater events as the primary cause of the coolings the ssst optimum characterised by strongly enhanced biogenic sedimentation rates ended at ca 125 ka with the full re establishment of the global conveyor belt and beginning of the northern hemisphere climatic optimum at this time sssts decreased stepwise and stabilised on values slightly warmer than today showing in the following period of mis 5e only low amplitude oscillations during mis 5d a northward expansion of the sea ice field took place but sssts only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the southern ocean did not fall in a true glacial mode the tight correlation between southern ocean ssst and winter sea ice records and vostok atmospheric temperature and co2 records support the idea that the antarctic winter sea ice and southern ocean temperature exert a primary control on the atmospheric ocean co2 exchanges and hence on global climate reduction of the antarctic sea ice field and increase of ssst at the onset of termination ii could have been triggered by precessional changes influencing southern high latitude summer insolation positive feedback mechanisms reduction of surface albedo and release of co2 into the atmosphere and changes in global ocean circulation affected by a collapse or strong reduction in north atlantic deep water nadw production could have induced further reinforcement of the southern ocean warming

grain size effects on th 230 xs inventories in opal rich and carbonate rich marine sediments abstract excess thorium 230 230thxs as a constant flux tracer is an essential tool for paleoceanographic studies but its limitations for flux normalization are still a matter of debate in regions of rapid sediment accumulation it has been an open question if 230thxs normalized fluxes are biased by particle sorting effects during sediment redistribution in order to study the sorting effect of sediment transport on 230thxs we analyzed the specific activity of 230thxs in different particle size classes of carbonate rich sediments from the south east atlantic and of opal rich sediments from the atlantic sector of the southern ocean at both sites we compare the 230thxs distribution in neighboring high vs low accumulation settings two grain size fractionation methods are explored we find that the 230thxs distribution is strongly grain size dependent and 50 90 of the total 230thxs inventory is concentrated in fine material smaller than 10 m which is preferentially deposited at the high accumulation sites this leads to an overestimation of the focusing factor and consequently to an underestimation of the vertical flux rate at such sites the distribution of authigenic uranium indicates that fine organic rich material has also been re deposited from lateral sources if the particle sorting effect is considered in the flux calculations it reduces the estimated extent of sediment focusing in order to assess the maximum effect of particle sorting on we present an extreme scenario in which we assume a lateral sediment supply of only fine material comparing 230thxs normalized mass fluxes biased by sorting effects with uncorrected mass fluxes we suggest that 230thxs normalization is still a valid tool to correct for lateral sediment redistribution however differences in focusing factors between core locations have to be evaluated carefully taking the grain size distributions into consideration

pleistocene variability of the subtropical convergence at east tasman plateau evidence from planktonic foraminiferal mg ca odp site 1172a combined measurements of mg ca and stable oxygen isotopes in tests of the planktonic foraminifer g bulloides from ocean drilling program odp site 1172a east tasman plateau allowed us to reconstruct sea surface temperature sstmg ca sea surface salinity sss and hence variations in the subtropical convergence stc in the southwestern tasman sea over the last four major glacial interglacial changes during interglacials the commonly enhanced sstmg ca and sss correspond to a lowered marine productivity and a lowered terrigenous flux implying that the stc separating cool high nutrient subantarctic surface water from warm saline oligotrophic subtropical surface water and hence the band of zonal westerlies responsible for the eolian dust flux were located south of east tasman plateau the warm east australian current was well established during warm periods and propagated far south during glacial times sstmg ca and sss were lower while both marine productivity and eolian flux increased such conditions prevailed during glacial marine isotope stages mis 12 mis 10 and to a lesser degree mis 6 and implied the extended northward influence of subantarctic surfacewater and a shift of the stc to 44 s the overall climatic signal at site 1172a appears to be largely attenuated when compared to published climate records from comparable latitudes to the west and to the east sstmg ca amplitudes were more pronounced in the subantarctic indian ocean and at chatham rise they exhibit a consistent pattern suggesting that latitudinal shifts of the stc occurred synchronously in the subantarctic indian ocean and at chatham rise but were largely damped at east tasman plateau due to the influence of the east australian current

organic carbon accumulation over the last 16 kyr off vancouver island canada evidence for increased marine productivity during the deglacial abstract the organic carbon content of marine sediments is commonly used as a proxy for export production however in continental margin sediments a large fraction of the organic matter may be of terrestrial origin and it is necessary to correct the total organic carbon data accordingly radiocarbon dating of bulk organic carbon organic geochemistry and isotope data 13c and 15n are used here to characterize the type of organic matter present in core jt96 09 collected at a water depth of 920 m on the slope off western canada the quantities of marine and terrestrial organic carbon are then estimated using the 13c data the 16 kyr record obtained from core jt96 09 suggests that accumulation of total organic carbon was highest during the late glacial and deglacial but geochemical data indicate that as much as 70 of this carbon is terrestrial in origin when the palaeo record is corrected for this terrigenous input it is observed that accumulation of marine organic matter and presumably marine export production increased at the end of the last glacial contemporaneous with the bolling and that it peaked during the allerod data from other palaeoproductivity proxies i e bio barium opal and alkenones also indicate relatively high productivity during the deglacial these results indicate a return to modern upwelling conditions and high marine export production at 14 3 calendar kyr bp and a period of enhanced upwelling relative to the present during the allerod

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

geophysical monitoring of moisture induced landslides a review author s whiteley js chambers je uhlemann s wilkinson pb kendall jm abstract 2018 the authors geophysical monitoring of landslides can provide insights into spatial and temporal variations of subsurface properties associated with slope failure recent improvements in equipment data analysis and field operations have led to a significant increase in the use of such techniques in monitoring geophysical methods complement intrusive approaches which sample only a very small proportion of the subsurface and walk over or remotely sensed data which principally provide information only at the ground surface in particular recent studies show that advances in geophysical instrumentation data processing modeling and interpretation in the context of landslide monitoring are significantly improving the characterization of hillslope hydrology and soil and rock hydrology and strength and their dynamics over time this review appraises the state of the art of geophysical monitoring as applied to moisture induced landslides here we focus on technical and practical uses of time lapse methods in geophysics applied to monitoring moisture induced landslide the case studies identified in this review show that several geophysical techniques are currently used in the monitoring of subsurface landslide processes these geophysical contributions to monitoring and predicting the evolution of landslide processes are currently underrealized hence the further integration of multiple parametric and geotechnically coupled geophysical monitoring systems has considerable potential the complementary nature of certain methods to map the distribution of subsurface moisture and elastic moduli will greatly increase the predictive and monitoring capacity of early warning systems in moisture induced landslide settings

tracers of ocean paleoproductivity and paleochemistry an introduction new developments in ocean paleoproductivity and paleochemistry have involved the application of tracers that record seawater composition that document sedimentary fluxes and that may be used to infer oceanic processes these include the use of cd ca and ba ca ratios in benthic foraminifera rare earth element patterns of chemical sediments uranium series nuclides in carbonate sediments and studies of the origins of chemical fluxes and anomalies in sedimentary profiles

polar stratification a critical view from the southern ocean oceanic stratification represents an effective mechanism to reduce vertical mixing of the water column thereby locking up carbon dioxide co2 in the deep sea and preventing air sea exchange of co2 it has been proposed that enhanced stratification of the upper water column in polar oceans during late cenozoic cooling episodes limited the upwelling of co2 rich deep waters and thus co2 release to the atmosphere resulting in a net global drawdown of atmospheric co2 increased stratification in the subarctic northwest pacific during both the onset of northern hemisphere glaciation at 2 73 ma and late quaternary glacial periods has been recently linked to enhanced ocean stratification south of the antarctic polar front apf in the pacific and atlantic sectors of the southern ocean increased stratification of southern ocean surface waters was mainly deduced from a reduction of biological production during these cooling episodes manifested by the decrease of geochemical proxies for productivity such as biogenic opal and barium in the marine sediment records however the records chosen from the southern ocean do not provide evidence for a more stratified upper water column rather the observed decrease in biological productivity is likely to have resulted from an expansion of annual sea ice coverage the sediment records suggest that south of the apf in the pacific and atlantic sectors of the southern ocean extensive sea ice may have contributed to the global co2 drawdown during glacial periods with hypothetical glacial increase of stratification in today s permanent open ocean zone merely being an add on caused by this expansion

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

variations of terrestrial input and marine productivity in the southern ocean 48 s during the last two deglaciations various biomarkers n alkanes n alcohols and sterols have been studied in a piston core tsp 2pc taken from the southern ocean to reconstruct the paleoenvironmental changes in the subantarctic region for the last two deglaciations mass accumulation rates of terrestrial higher molecular weight n alkanes and n alcohols and marine dinosterol and brassicasterol biomarkers increased significantly at the last two glacials and stayed low during interglacial peaks early holocene and the eemian these records indicate that the enhanced atmospheric transport of continental materials and the increased marine biological productivity were synchronously linked in the southern ocean at the last two glacials this suggests that increased glacial dust inputs have relieved iron limitation in the subantarctic southern ocean these two processes however were not linked at the cooling phase from the eemian to marine isotope stage mis 5d during this period paleoproductivity may have been influenced by the latitudinal migration of the high production zone associated with the antarctic polar front

constraining the oceanic barium cycle with stable barium isotopes highlights we present a ba isotope data set of seawater river waters and biogenic particles ba isotope signatures of upper ocean waters are heavier than river and deep waters adsorption of lighter ba isotopes on biogenic particles induces the fractionation ba isotopes trace land sea interactions and ocean mixing processes decoupling of ba from major nutrients confirms ba to be a biointermediate element abstract the distribution of barium ba concentrations in seawater resembles that of nutrients and ba has been widely used as a proxy of paleoproductivity however the exact mechanisms controlling the nutrient like behavior and thus the fundamentals of ba chemistry in the ocean have not been fully resolved here we present a set of full water column dissolved ba dba isotope 137badba profiles from the south china sea and the east china sea that receives large freshwater inputs from the changjiang yangtze river we find pronounced and systematic horizontal and depth dependent 137badba gradients beyond the river influence characterized by generally light signatures 0 0 to 0 3 0 3 the 137badba values in the upper water column are significantly higher 0 9 0 9 than those in the deep waters 0 5 0 5 moreover 137badba signatures are essentially constant in the entire upper 100 m in which dissolved silicon isotopes are fractionated during diatom growth resulting in the heaviest isotopic compositions in the very surface waters combined with the decoupling of dba concentrations and 137badba from the concentrations of nitrate and phosphate this implies that the apparent nutrient like fractionation of ba isotopes in seawater is primarily induced by preferential adsorption of the lighter isotopes onto biogenic particles rather than by biological utilization the subsurface 137badba distribution is dominated by water mass mixing the application of stable ba isotopes as a proxy for nutrient cycling should therefore be considered with caution and both biological and physical processes need to be considered clearly however ba isotopes show great potential as a new tracer for land sea interactions and ocean mixing processes

the southern ocean at the last glacial maximum a strong sink for atmospheric carbon dioxide analysis of satellite ocean color sea surface temperature and sea ice cover data reveals consistent patterns between biological production iron availability and physical forcings in the southern ocean the consistency of these patterns in conjunction with information on physical conditions during the last glacial maximum lgm enables estimates of export production at the lgm the lgm southern ocean experienced increased wind speeds colder sea surface and atmospheric temperatures increased deposition of atmospheric dust and a greatly expanded winter sea ice cover these variations had strong effects on southern ocean ecology and on air sea fluxes of co2 the seasonal ice zone siz was much larger at the lgm 30 million km2 than at present 19 million km2 the antarctic polar front pf likely marked the northern boundary of this expanded siz throughout the southern ocean as it does today in the drake passage region a large northward shift in the position of the pf during glacial times is unlikely due to topographic constraints north of the pf the increased flux of aeolian dust during glacial times altered phytoplankton species composition and increased export production and as a result this region was a stronger sink for atmospheric co2 than in the modern ocean south of the pf interactions between the biota and sea ice strongly influence air sea gas exchange over seasonal timescales the combined influence of melting sea ice and increased aeolian dust flux with its associated iron increased both primary and export production by phytoplankton over daily monthly timescales during austral spring summer resulting in a strong flux of co2 into the ocean heavy ice cover would have minimized air sea gas exchange over much of the rest of the year thus an increased net flux of co2 into the ocean is likely during glacial times even in areas where annual primary production declined we estimate that export production in the southern ocean as a whole was increased by 2 9 3 6 gt c yr 1 at the lgm relative to the modern era altered seasonal sea ice dynamics would further increase the net flux of co2 into the ocean thus the southern ocean was a strong sink for atmospheric co2 and contributed substantially to the lowering of atmospheric co2 levels during the last ice age

environmental change in the sea of okhotsk during the last 1 1 million years on the basis of two sedimentary records from the central sea of okhotsk we reconstruct the closely coupled glacial interglacial changes in terrigenous flux marine productivity and sea ice coverage over the past 1 1 myr the correspondance of our sedimentary records to the china loess grain size record china loess particle timescale chiloparts suggests that environmental changes in both the sea of okhotsk area and in se asia were closely related via the siberian atmospheric high pressure cell during full glacial times our records point to a strong siberian high causing northerly wind directions the extension of the sea ice cover and a reduced amur river discharge deglacial maxima of terrigenous flux were succeeded by or synchronous to high productivity events marine productivity was strengthened during glacial terminations because of an effective nutrient utilization at times of enhanced water column stratification and high nutrient supply from fluvial runoff and sea ice thawing during interglacials se monsoonal winds prevailed analogous to today s summer situation of a pronounced mongolian heat low and a strong hawaiian high strong freshwater discharge induced by high precipitation rates in the amur drainage area and a seasonally reduced and mobile sea ice cover favored marine productivity although being considerably lower than during the terminations and a lowered flux of ice rafted detritus

sedimentary basin evolution gravity flows volcanism and their impacts on the formation of the lower cretaceous oil shales in the chaoyang basin northeastern china abstract no detailed research has been carried out on the oil shales that are interbedded with gravity flow deposits and volcaniclastic rocks in the third member of the jiufotang formation in order to study the impact of basin evolution gravity flows and volcanism on oil shale formation petrology sedimentology sequence stratigraphy organic geochemistry and elemental geochemistry were used to characterise the oil shales extensional tectonic subsidence is suggested as the controlling factor for basin evolution the predominant maceral in the oil shales is sapropelinite suggesting organic matter was derived from mainly aquatic organism especially algae element indices u cu mo zn sr ba th g g zr g g and the chemical index of alteration cia show that the water conditions during deposition of the oil shales were anoxic and brackish with little terrigenous detrital input and a cold and dry palaeoclimate gravity flows were accompanied by the input of terrestrial detritus and a degree of oxygenation of the bottom waters reducing oil shale formation volcanic eruptions ejected intermediate acidic ashes not only leading to climate cooling but also either enhancing algal blooms by a fertilisation effect due to minor volcanic ash input or inhibiting algal blooms by a poisoning effect due to major volcanic ash input there is synchronicity between the occurrence of rifting gravity flows volcanism and earthquakes the best periods for oil shale formation were during intermissions between tectonic movement when there were few gravity flows volcanic eruptions or earthquakes high bioproductivity and lake expansion along with an anoxic environment were the main controlling factors for high quality oil shale formation there is a series of oil shale bearing rift basins formed in northeastern china that share a similar geological setting so this research provides a useful example for future resource exploration of coeval oil shales in northeastern china

the spatial structure of the 128 ka antarctic sea ice minimum we compare multi ice core data with 18o model output for the early last interglacial antarctic sea ice minimum the spatial pattern of 18o across antarctica is sensitive to the spatial pattern of sea ice retreat local sea ice retreat increases the proportion of winter precipitation depleting 18o at ice core sites however retreat also enriches 18o because of the reduced source to site distance for atmospheric vapor the joint overall effect is for 18o to increase as sea ice is reduced our data model comparison indicates a winter sea ice retreat of 67 59 and 43 relative to preindustrial in the atlantic indian and pacific sectors of the southern ocean a compilation of southern ocean sea ice proxy data provides weak support for this reconstruction however most published marine core sites are located too far north of the 128 000 years b p sea ice edge preventing independent corroboration for this sea ice reconstruction plain language summary the antarctic isotope and temperature maximum which occurred approximately 128 000 years before present b p during the warmer than present last interglacial period is associated with a major retreat of antarctic sea ice understanding the details of this major sea ice retreat is crucial in order to understand the sensitivity of the southern hemisphere sea ice system and to evaluate the performance of climate model simulations in response to future warming this work uses a multi ice and ocean core data model evaluation to assess the magnitude and spatial pattern of this sea ice retreat our results suggest that sea ice retreat was greatest in the atlantic and indian sectors of the southern ocean and less in the pacific sector these results may have had serious implications for the stability of marine terminating glaciers around the antarctic ice sheet and their contribution to the last interglacial sea level rise these results also support a hypothesized slowdown in northward ocean heat transport during the early last interglacial

water depth and diagenetic constraints on the use of barium as a palaeoproductivity indicator sediments underneath the high productivity areas of the coastal upwclling and equatorial divergence zones in the pacific and indian oceans are enriched in barium and on this basis the barium content of the sediments has long been suggested as a potential palaeoproductivity indicator analyses of sediments from the peru margin corroborate the pattern of enhanced barium accumulation in areas of high primary productivity in the deep ocean but also show that this pattern cannot be extended to shallow water deposits sediments from the peru shelf lack any barium enrichment whereas this element is significantly enriched in slope and basinal deposits in water columns deeper than 2000 m this depth effect is further illustrated at site 682 located in the rapidly subsiding lima basin the quaternary sequence deposited at water depths 3000 m is enriched in organic carbon opal and biogenic barium the miocene sediments although deposited under highly productive waters associated with a coastal upwclling centre do not show an enrichment in the barium record corresponding to the very high organic carbon and opal levels a pattern that is consistent with deposition in shallow basins in addition to the effect of water depth on the barium distribution overprinting of primary signals can be observed in sediments from upwclling areas undergoing strong anoxic diagenesis microcrystalline barite is partly dissolved in intervals depleted in interstitial sulphate as shown for sediments from the peru margin dissolution of barite in sulphate depleted intervals of deep water sections leads to high barium concentrations near the termination of the sulphate reducing zone where downward sulphate and upward barium diffusion foster local barite precipitation in diagenetic fronts the barium distribution in sedimentary oxic and suboxic environments at deep water depositional sites has a high potential as a palaeoproductivity indicator however barium accumulation as a proxy for ocean fertility should be used with caution in areas of varying water depths and in anoxic diagenetic environments where sulphate depletion undcrsatur ates the interstitial waters with respect to barite

the impact of sediment provenance on barium based productivity estimates abstract biogenic barium in marine sediments has been suggested to be a reliable proxy of export productivity from the surface ocean and algorithms have been developed to link these properties however problems arise when the proposed algorithms are applied to predominantly terrigenous sediments a major source of error is incorrect estimates of the terrigenous ba al ratio in normative calculations of the amount of biogenic barium in the sediment compared to an often used global average ba al ratio much better results can be obtained by estimating the terrigenous ba al ratio from exponential regression of the ba al ratios of surface sediments obtained from continental slope transects this method has been applied to surface sediments from the chilean continental slope the calculated regional terrigenous ba al ratios could be verified with purely terrigenous samples from chilean rivers the resulting accumulation rates of biogenic barium on the chilean continental slope reliably reproduce the regional pattern of primary productivity in the southern peru chile current indicating the potential of biogenic barium as a useful paleo productivity proxy

the energetic 2010 mw 7 1 solomon islands tsunami earthquake summary on 2010 january 3 a moment magnitude mw 7 1 earthquake struck the solomon islands very near the san cristobal trench causing extensive landslides and surprisingly large tsunami waves because of the unique proximity of islands to the trench 20 km and earthquake a post seismic survey successfully identified unexpected widespread coseismic subsidence towards the trench up to 80 cm with no discernable post seismic deformation approximately 1000 km from the earthquake ocean bottom pressure sensors measured 1 2 cm open ocean tsunami waves though spatially limited the local tsunami wave heights up to 7 m were comparable to the much larger adjacent 2007 mw 8 1 earthquake the seismically determined focal mechanism broad scale subsidence tsunami amplitude and open ocean wave heights are all explained by an extremely shallow low angle thrust adjacent to the impinging subduction of the two seamounts near the trench this event belongs to a potentially new class of shallow tsunami earthquakes that is not identified as deficient in radiated seismic energy

228ra 226ra and 226ra ba ratios in the western mediterranean sea barite formation and transport in the water column 226ra 228ra and ba distributions as well as 228ra 226ra and 226ra ba ratios were measured in seawater suspended and sinking particles at the dyfamed station in the western mediterranean sea at different seasons of year 2003 in order to track the build up and fate of barite through time the study of the 228raex 226raex ratios raex ra activities corrected for the lithogenic ra of suspended particles suggests that baex baex ba concentrations corrected for the lithogenic ba mostly barite formation takes place not only in the upper 500 m of the water column but also deeper i e throughout the mesopelagic layer temporal changes in the 228raex 226raex ratios of sinking particles collected at 1000 m depth likely reflect changes in the relative proportion of barite originating from the upper water column with a high 228ra 226ra ratio and formed in the mesopelagic layer with a low 228ra 226ra ratio 228raex 226raex ratios measured in sinking particles collected in the 1000 m trap in april and may suggest that barite predominantly formed in the upper water column during that period while barite found outside the phytoplankton bloom period february and june appears to form deeper in the water column combining ratios of both the suspended and sinking particles provides information on aggregation disaggregation processes high 226raex baex ratios were also found in suspended particles collected in the upper 500 m of the water column because celestite is expected to be enriched in ra bernstein r e byrne r h and schijf j 1998 acantharians a missing link in the oceanic biogeochemistry of barium deep sea res ii 45 491 505 acantharian skeletons may contribute to these high ratios in shallow waters the formation of both acantharian skeletons and barite enriched in 226ra may thus contribute to the decrease in the dissolved 226ra activity and 226ra ba ratios of surface waters observed between february and june 2003 at the dyfamed station

deglacial biogenic opal peaks revealing enhanced southern ocean upwelling during the last 513 ka abstract strength of southern ocean upwelling controls the exchange of carbon dioxide co 2 between deep ocean reservoirs and atmosphere as well as the communication of dissolved silicon with the euphotic zone of the southern ocean the silicon supply could limit diatom opal productivity in the high latitudes of southern ocean and the subsequent burial of biogenic opal in underlying sediments here we report a record of biogenic opal export off the prydz bay south of the polar front of the southern ocean indicating strengthened upwelling during the past five glacial terminations in all five terminations i v opal peaks occur in line with northern hemisphere summer insolation intensity as well as the existing irds indicating that freshwater injection associated with retreat of the northern hemisphere ice sheets could be the cause of enhanced upwelling in the southern ocean during terminations this could in turn promote co 2 outgassing finally accelerating the completion of the terminations in addition the enhanced upwelling could export the si rich deep water to low latitudes via antarctic intermediate water aaiw and subantarctic mode water samw potentially leading to deglacial opal peaks in subtropical north atlantic

biogenic barium and the detrital ba al ratio a comparison of their direct and indirect determination biogenic barium concentrations obtained from direct determination by a three step sequential extraction procedure are compared to those obtained from the widely used indirect normative calculation based on total digestion a comparison of the biogenic barium from the direct sequential extraction and the indirect normative calculation clearly shows that the detrital ba al ratio is the critical factor in the normative approach and that erroneous assumptions based on this ratio may introduce significant errors to the calculated biogenic barium overall the crustal average ba al ratio of 0 005 0 01 is much higher than our directly determined global average of 0 0037 this would result in an underestimation of the biogenic barium and thus of the primary productivity calculated using the ba flux obtained from the normatively calculated ba record using our ba al det ratio of 0 0037 leads to normatively calculated biogenic barium results that are in reasonable agreement with the biogenic barium from sequential extraction for samples of the atlantic pacific and indian ocean our directly determined regional ba al det ratios deviate from those calculated or assumed from hinterland ratios and our global average ba al det is lower than the one commonly reported therefore in sediments with a significant terrigenous fraction the sequential extraction technique is always required

reconstructing export production at the ne atlantic margin potential and limits of the ba proxy barium ba aluminium al and zirconium zr were measured in sediment trap material deployed at two margin settings of the ne atlantic the bay of biscaye at goban spur and the nw iberian margin the particulate organic carbon poc ba ratios of the trapped material in both margin environments are clearly higher compared to the open ocean although lateral advection of poc may partly explain these higher poc ba ratios for margin systems it is clear that the yield of authigenic particulate ba during organic matter degradation in the water column is lower in margin environments in order to assess export production in margin settings we optimised transfer functions based on trapped ba fluxes that were originally elaborated for open ocean settings calculations of export production based on trapped ba flux and poc ba ratio were compared with calculations based on trapped poc flux only export production based on ba flux show greater internal consistency amongst traps along the same mooring suggesting that this approach has advantages over the one based on poc flux only estimated export productions are of the same order of magnitude as estimates of new production but systematically fall short of the latter this systematic discrepancy needs further investigation

barium in hemipelagic sediment of the northwest pacific coupling with biogenic carbonate 1 geochemical analyses were performed on three cores of hemipelagic sediment from the northwest pacific ocean eastern edge of shikoku basin dating from the last interglacial and glacial periods the objective of this work is to delineate the relations between excess sedimentary barium ba ex content and biogenic opal carbonate and organic carbon contents calculated ba ex values show variable degrees of correlation with biogenic sediment fractions the mass accumulation rate mar of ba ex covaries with the mars of biogenic fractions and in particular with the mar of biogenic carbonate r2 0 68 and toc r2 0 50 variable relations between barium and biogenic fractions in hemipelagic sediment provide detailed insight into the behavior of sedimentary barium it appears that a significant proportion of the barium is affiliated with the carbonate fractions based on this strong correlation carbonate dissolution rates of the last glacial to interglacial periods are estimated assuming that the mars of carbonate and ba ex covary variation of the ba ca ratio in sediments reflects the extent of postdepositional carbonate dissolution the record of sedimentary ba ca ratios exhibits striking difference between sediment of the glacial and interglacial periods with a higher positive correlation during glacial intervals and a lower correlation during interglacial intervals this pattern is the result of enhanced carbonate dissolution during interglacial times sedimentary ba ca ratios may therefore be a useful tool for estimating the relative extent of carbonate dissolution ba ex curves and patterns in sedimentary ba ca ratios resemble the established pacific carbonate dissolution record i e enhanced dissolution during interglacial times and reduced dissolution during glacial times as suggested by previous studies variations in sedimentary ba ca ratios strongly support an interpretation of pronounced glacial interglacial fluctuation in carbonate dissolution in the northwest pacific ocean an especially pronounced dissolution event is evident at 75 kyr during the transition interval form interglacial to glacial conditions this suggests that ba ex may be used as a proxy for evaluating carbonate dissolution in hemipelagic settings but further study of the association between barium content and carbonate dissolution will be required to confirm this

barium accumulation in the arabian sea controls on barite preservation in marine sediments in this study a new sequential extraction technique is used to investigate the particulate barium ba phases in sediments from the arabian sea to determine the processes controlling ba accumulation in marine sediments the total solid phase ba concentration in arabian sea surface sediments increases with water depth from 200 ppm at 500 meters below sea surface mbss to 1000 ppm at 3000 mbss the sedimentary ba composition consists of three major fractions barite ba incorporated in aluminosilicates and ba associated with mn fe oxides accumulation of barite which is the most important ba fraction in sediments located below 2000 mbss increases gradually with water depth the ba al ratio of the terrigenous fraction varies significantly across the arabian basin as the result of differences in grain size and provenance of the terrigenous sediment ba associated with mn oxides is a relatively minor fraction compared with bulk ba concentrations and it only accumulates in well oxygenated sediments below the present day oxygen minimum zone the water depth dependent accumulation of barite in the arabian sea is not related to the continuous formation of barite in settling organic particles or ba scavenging by mn oxyhydroxides but is primarily controlled by differences in ba preservation upon deposition a good correlation between the barite saturation index and the barite accumulation rate in the upper 2000 m of the water column may indicate that the degree of barite saturation of the bottom water is the main environmental factor regulating the burial efficiency of barite organic matter degradation bioturbation diagenetic mn cycling and the crystallinity of the accumulating barite may play additional roles copyright 2001 elsevier science ltd

biogenic opal in southern ocean sediments over the last 450 000 years implications for surface water chemistry and circulation we present records of biogenic opal percentage and burial rate in 12 piston cores from the atlantic and indian sectors of the southern ocean these records provide a detailed quantitative description of changing patterns of opal deposition over the last 450 kyr the striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the southern ocean under different global climate conditions three broad depositional patterns can be distinguished northernmost records 39 42 s latitude are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity records from cores just north of the present antarctic polar front 46 49 s show even larger increases in opal burial rate during glacial intervals but have variance concentrated in the 100 and 23 kyr bands southernmost records 51 55 s are completely out of phase with those to the north with greatly reduced opal burial rates during glacial periods taken as a whole the opal records show no evidence for the increased total antarctic productivity predicted by recent geochemical models of atmospheric co2 variability the areal expansion of southern ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial interglacial opal patterns the excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region however local circulation changes may act to modify this basic signal possibly accounting for the observed differences in the opal variance spectra

particulate barium fluxes in the ross sea we present particulate barium data collected using sequencing sediment traps in the ross sea region of the southern ocean data were collected in 1991 92 1994 95 and 1996 98 from two separate field programs samples were collected at 200 m depth and 75 m above the seafloor 450 765 m depth ba fluxes in the shallow traps at all sites are uniformly low and the barium to organic carbon ba corg ratios in these traps typically agree within a factor of two both spatially and temporally deeper trap fluxes are as much as an order of magnitude larger than shallow trap fluxes in addition the ba corg ratio in the deeper traps varies by more than an order of magnitude with the ratio decreasing with increasing rates of organic carbon flux increases in the deeper trap fluxes may result from horizontal transport of material from other regions of the ross sea resuspension of previously deposited sediment and increases in biogenic ba formation with depth data presented here and within the contemporary literature lead us to speculate that much of the biogenic ba may be formed in the water column at depths greater than 200 m also the factor of 10 range in the ba corg ratio in combination with the depth dependence of biogenic barium formation leads us to conclude that biogenic barium formation may depend on the rate at which particles sink independent of the causal mechanism the variations in this ratio imply that using an algorithm that relates barium export to carbon export may be imprudent in regions of highly variable carbon flux

barium in planktonic foraminifera abstract reconstructions of ba distributions in ancient oceanic surface waters could provide new insight into paleoceanographic change calcite shells of planktonic foraminifera potentially provide a means of reconstructing such paleo ba distributions if lattice bound ba can be determined on shells recovered from deep sea cores planktonic foraminifera shells from a series of cores were purified of non lattice bound ba associated with organic or sedimentary phases by a combination of physical agitation oxidative reductive steps acid leaches and a novel alkaline dtpa step to dissolve barite a sequential dissolution of a large sample of cleaned shells of the planktonic foraminifer globigerinoides conglobatus indicates homogeneous distribution of ba in the shell material comparison of shells from sediments sediment traps and plankton tows indicates no significant differences in the ba content of the purified shells cleaned samples of the planktonic foraminifera globigerinoides sacculifera g ruber g conglobatus orbulina spp and globoquadrina dutertrei from the equatorial pacific north atlantic and mediterranean sea have ba ca ratios between 0 6 and 1 0 mol mol 0 8 to 1 4 ppm variation in foraminiferal ba contents between the three basins is consistent with the trend in surface seawater ba the calculated distribution coefficient for ba incorporation in these five species based on these data is 0 19 0 05 several species of the non spinose planktonic foraminifera globorotalia have ba ca ratios ranging from 2 to 13 mol mol these high ba contents might be explained by differences in the way these foraminifera precipitate their shells a temporal record of ba ca in samples of globigerinoides and orbulina from a core in the northwest atlantic suggests that the ba concentration of surface waters at this site has not changed by more than 20 over the last 14 kyr

does sedimentary organic δ13c record variations in quaternary ocean co2 aq ocean surface water co2 aq variations based on glacial interglacial changes in sediment delta 13corg are shown to compare favorably with reconstructions based on ice core co2 in particular an approximate 80 microatmospheres increase in atmospheric pco2 during the last glacial interglacial transition is calculated to correspond to a 3 4 micromolar increase in ocean surface water co2 aq at atmospheric equilibrium a widespread marine delta 13corg decrease of 1 2 accompanied this event and was not preceded by an equivalent isotopic change in surface water total dissolved inorganic carbon these observations support the hypothesis that co2 aq influences photosynthetic isotope fractionation between marine inorganic and organic carbon pools and therefore that plankton sediment delta 13corg may serve as a proxy for surface water co2 aq

foraminiferal reconstruction of barium distributions in water masses of the glacial oceans foraminiferal ba can be used to reconstruct the distribution of deeply regenerated chemical components in past oceans the ba contents of benthic foraminifera recovered from cores in the atlantic ocean indicate that waters deeper than 2900 m had 30 60 higher ba during the last glacial maximum lgm these changes are consistent with previously observed glacial nutrient enrichments based on foraminiferal cd and 13c increases in deepwater nutrient contents in the atlantic can be explained by reductions in north atlantic deep water formation during the lgm ba ca of benthic foraminifera from the glacial sections of intermediate depth atlantic cores are equal to or lower than holocene values this ba evidence argues against the mediterranean as a greatly increased source to atlantic intermediate waters during the lgm since the mediterranean is enriched in ba today and apparently remained enriched during the lgm benthic foraminiferal ba from the glacial sections of cores from the eastern equatorial pacific suggest that deep waters of the glacial pacific were about 25 lower in ba at 3000 m taken together the foraminiferal evidence indicates that the ba content of deep waters of the atlantic antarctic and pacific were similar at the lgm since foraminiferal cd distributions indicate that cd remained significantly lower in the deep atlantic relative to the pacific at the last glacial maximum a seven box ocean model is used to explore several scenarios for reconciling lgm ba and cd distributions while the changed distribution of both tracers suggests diminishment in the flux of nutrient depleted waters to the deep atlantic during the lgm increased atlantic upwelling rates and consequently enhanced ba particle fluxes can account for the the lack of ba fractionation between the deep atlantic and pacific the model suggests that ba can be transferred efficiently to the deep atlantic by enhanced upwelling because the vast majority of the ba is regenerated in the deep atlantic box

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

export productivity and carbonate accumulation in the pacific basin at the transition from a greenhouse to icehouse climate late eocene to early oligocene 1 the late eocene through earliest oligocene 40 32 ma spans a major transition from greenhouse to icehouse climate with net cooling and expansion of antarctic glaciation shortly after the eocene oligocene e o boundary we investigated the response of the oceanic biosphere to these changes by reconstructing barite and caco3 accumulation rates in sediments from the equatorial and north pacific ocean these data allow us to evaluate temporal and geographical variability in export production and caco3 preservation barite accumulation rates were on average higher in the warmer late eocene than in the colder early oligocene but cool periods within the eocene were characterized by peaks in both barite and caco3 accumulation in the equatorial region we infer that climatic changes not only affected deep ocean ventilation and chemistry but also had profound effects on surface water characteristics influencing export productivity the ratio of caco3 to barite accumulation rates representing the ratio of particulate inorganic c accumulation to corg export increased dramatically at the e o boundary this suggests that long term drawdown of atmospheric co2 due to organic carbon deposition to the seafloor decreased potentially offsetting decreasing pco2 levels and associated cooling the relatively larger increase in caco3 accumulation compared to export production at the e o suggests that the permanent deepening of the calcite compensation depth ccd at that time stems primarily from changes in deep water chemistry and not from increased carbonate production

228ra 226ra and 226ra ba ratios to track barite formation and transport in the water column abstract we measured 228 ra ex 226 ra ex and 226 ra ex ba ex ratios in suspended and sinking particles collected at the oceanic flux program ofp time series site in the western sargasso sea and compared them to seawater ratios to provide information on the origin and transport of barite baso 4 in the water column the 228 ra ex 226 ra ex ratios of the suspended particles down to 2000 m are nearly identical to those of seawater at the same water depth these ratios are much lower than expected if suspended barite was produced in surface waters and indicate that barite is produced throughout the mesopelagic layer the 228 ra ex 226 ra ex activity ratios of sinking particles collected at 1500 and 3200 m varied mostly between 0 1 and 0 2 which is intermediate between the seawater ratio at these depths ex ba total ba lithogenic considered to be mainly barite present in the sinking flux is a mixture of crystals formed recently in the upper water column formed several years earlier in the upper water column or formed recently in deeper waters we observe a sizeable temporal variability in the 228 ra ex 226 ra ex ratios of sinking particles which indicates temporal variability in the relative proportion of barite crystals originating from surface with a high 228 ra ex 226 ra ex ratio and mesopelagic with a low 228 ra ex 226 ra ex ratio sources however we could not discern a clear pattern that would elucidate the factors that control this variability the 226 ra ba ratios measured in seawater are consistent with the value reported from the geosecs expeditions 2 3 dpm mol 1 below 500 m depth but are significantly lower in the upper 500 m high 226 ra ex ba ex ratios and elevated sr concentrations in suspended particles from the upper water column suggest preferential uptake of 226 ra over ba during formation of srso 4 skeletons by acantharians which must contribute to barite formation in shallow waters deeper in the water column the 226 ra ex ba ex ratios of suspended particles are lower than those of seawater since 228 ra ex 226 ra ex ratios demonstrate that suspended barite at these depths has been produced recently and in situ their low 226 ra ex ba ex ratios indicate preferential uptake of ba over ra in barite formed in mesopelagic water

eocene to miocene terrigenous inputs and export production geochemical evidence from odp leg 177 site 1090 abstract changes in ocean circulation and climate during the cenozoic led to the development of the antarctic circum polar current acc and permanent antarctic ice sheets however the timing of the opening of the drake passage and the establishment of the acc is poorly constrained we present geochemical proxies of terrigenous inputs and export production at a single site in the southeastern atlantic ocean that suggest the drake passage had opened to intermediate and deep water by 32 8 ma two separate styles of sedimentation and geochemical composition of terrigenous material are observed with the change in sediment geochemical characteristics occurring at 32 8 ma middle to late eocene records are highly variable while latest eocene to early miocene records exhibit cyclic variations in elemental records and terrigenous material based on al ti ratios metal sources change from continental crust to oceanic crust sources at the eocene oligocene transition which we suggest reflects a change in deep water circulation phosphorus metal ratios indicate that there are two distinct intervals of enhanced export production one in the middle eocene and one throughout the eocene oligocene transition elevated al ti ratios greater than any lithic source in the middle eocene provide evidence of particulate scavenging and thus increased export production barium ratios further support changes in productivity in the middle eocene and at the eocene oligocene transition permanent changes in the ba concentration record in the early oligocene further support a change in deep water circulation due to the opening and deepening of the drake passage at 32 8 ma

sedimentation on the continental rise west of the antarctic peninsula over the last three glacial cycles abstract the continental rise west of the antarctic peninsula includes a number of large sediment mounds interpreted as contourite drifts cores from six sediment drifts spanning some 650 km of the margin and 4 of latitude have been dated using chemical and isotopic tracers of palaeoproductivity and diatom biostratigraphy interglacial sedimentation rates range from 1 1 to 4 3 cm ka glacial sedimentation rates range from 1 8 to 13 5 cm ka and decrease from proximal to distal sites on each drift late quaternary sedimentation was cyclic with brown biogenic burrowed mud containing ice rafted debris ird in interglacials and grey barren laminated mud in glacials foraminiferal intervals occur in interglacial stages 5 and 7 but not in the holocene processes of terrigenous sediment supply during glacial stages differed meltwater plumes were more important in stages 2 4 turbidity currents and ice rafting in stage 6 the terrigenous component shows compositional changes along the margin more marked in glacials the major oxides al2o3 and k2o are higher in the southwest and cao and tio2 higher in the northeast there is more smectite among the clay minerals in the northeast magnetic susceptibility varies along and between drifts these changes reflect source variations along the margin interglacial sediments show less clear trends and their ird was derived from a wider area downslope processes were dominant in glacials but alongslope processes may have attained equal importance in interglacials the area contrasts with the east antarctic continental slope in the se weddell sea where ice rafting is the dominant process and where interglacial sedimentation rates are much higher than glacial the differences in glacial setting and margin physiography can account for these contrasts

a comparison of multiple proxies for export production in the equatorial pacific 1 several commonly used paleoproductivity proxies were compared to evaluate the validity of assumptions and limitations associated with each proxy export production fluxes cexport over glacial interglacial timescales were calculated from previously developed proxy specific algorithms at ttn013 pc72 and ttn013 pc114 both located in the equatorial pacific comparison of data from the same core intervals yields conflicting results despite calibrations based on the same core top samples the periodicity of marine barite excess ba and excess al based cexport records is similar the relative magnitude of cexport when calculated using excess ba and algorithms based on sediment trap data is significantly different than records based on core top calibrations particularly during glacial intervals at both sites bulk sedimentary al ti and ba ti ratios covary however these ratios do not correspond with the downcore records of their respective excess concentrations and their accumulation rates or with contemporaneous records based on marine barite excess ba and excess al accumulation although downcore records based on sediment mass accumulation rates may be compromised by sediment focusing this process cannot explain all the differences observed among the various data sets presented here this implies that some or all of these proxies do not exclusively respond to changes in export production the contradictions among these data highlight the importance of addressing inconsistencies among paleoproxies and re examining assumptions imbedded in proxy fundamentals prior to applying paleoproductivity proxies and interpreting paleoceanographic records

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores