monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

geochemical and isotopic evidence for paleoredox conditions during deposition of the devonian mississippian new albany shale southern indiana the upper part of the new albany shale is divided into three members in ascending order these are 1 the morgan trail member a laminated brownish black shale 2 the camp run member an interbedded brownish black and greenish gray shale and 3 the clegg creek member also a laminated brownish black shale the morgan trail and camp run members contain 5 to 6 total organic carbon toc and 2 sulfide sulfur isotopic composition of sulfide in these members ranges from 5 0 to 20 0 c s plots indicate linear relationships between abundances of these elements with a zero intercept characteristic of sediments deposited in a non euxinic marine environment formation of diagenetic pyrite was carbon limited in these members the clegg creek member contains 10 to 15 toc and 2 to 6 sulfide sulfur isotopic compositions of sulfide range from 5 0 to 40 the most negative values occur in the uppermost clegg creek member and are characteristic of syngenetic pyrite formed within an anoxic water column abundances of carbon and sulfur are greater and uncorrelated in this member consistent with deposition in as euxinic environment in addition dop degree of pyritization values suggest that formation of pyrite was generally iron limited throughout clegg creek deposition but sulfur isotopes indicate that syngenetic water column pyrite becomes an important component in the sediment only in the upper part of the member at the top of the clegg creek member a zone of phosphate nodules and trace metal enrichment coincides with maximal toc values during euxinic deposition phosphate and trace metals accumulated below the chemocline because of limited vertical circulation in the water column increased productivity would have resulted in an increased flux of particulate organic matter to the sediment providing an effective sink for trace metals in the water column phosphate and trace metals released from organic matter during early diagenesis resulted in precipitation of metal rich phosphate nodules

a reappraisal of kerogen formation abstract comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass kerogen and fossil fuels

low oxygen events in the laurentian channel during the holocene geochemical and micropaleontological analyses were carried out on a 35 cm box core cr06 tce spanning the last 6000 years in the esquiman channel a northeast arm of the laurentian channel in the gulf of st lawrence a 0 6 decrease of 18o in benthic foraminifer globobulimina auriculata shells characterizes the upper 10 cm of the core and suggests a warming of the bottom waters this change is concomitant with increased percentages of the low oxygen tolerant benthic foraminifer species brizalina subaenariensis and the atlantic water species oridorsalis umbonatus although a precise timing cannot be established notably because of the smoothing effect of bioturbation the amplitude of the trend recorded in the esquiman channel is coherent with that of the regional warming observed in the bottom water of the main axis of the laurentian channel over the last century warm bottom water conditions however are not exclusive to the recent time interval as shown by data from the lower part of the core which are also characterized by low 18o values in g auriculata and occurrence of both b subaenariensis and o umbonatus such data suggest the existence of low oxygen and relatively high temperature conditions in the bottom water of the esquiman channel about 4 to 6 kyrs ago likely related to enhanced inflow of atlantic water in the gulf of st lawrence through the cabot strait and the laurentian channel these results highlight the sensitivity of bottom water properties in the gulf of st lawrence to changes in the western north atlantic circulation

geochemical evidence for variations in delivery and deposition of sediment in pleistocene light dark color cycles under the benguela current upwelling system abstract distinctive light dark color cycles in sediment beneath the benguela current upwelling system indicate repetitive alternations in sediment delivery and deposition geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid pleistocene intervals from odp sites 1082 and 1084 concentrations of total organic carbon toc vary between 3 5 and 17 1 concentrations of caco3 vary inversely to toc and al which suggests that both carbonate dissolution and terrigenous dilution contribute to the light dark cycles opal concentrations are independent of both toc and caco3 therefore eliminating diatom production and lateral transport of shelf material as causes of the light dark cycles 13corg and 15ntot values do not vary across light dark sediment intervals implying that the extent of relative nutrient utilization did not change the stable 15ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the toc rich layers parallel changes in concentrations of indicator trace elements and toc imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen cu ni and zn are enriched in the darker sediment as a consequence of greater organic matter delivery redox sensitive metals vary due to loss mn and ba or enrichment mo under reducing conditions created by toc oxidation organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution sulfate reduction and the concentration of metals thus export production is considered ultimately responsible for the generation of the color cycles

postglacial vegetation history of the mackenzie river basin abstract three radiocarbon dated cores from small lakes provide pollen records of postglacial vegetation change in the central mackenzie river basin these data are combined with previously published records to reconstruct vegetation development from central alberta to the mackenzie delta the paleoecological data demonstrate that a continuous corridor of herb and shrub dominated vegetation extended between beringia and the great plains of north america from deglaciaiton until about 10 000 yr b p the initial vegetation was replaced by spruce forests between 10 000 and 8500 yr b p significant vegetation change continued until approximately 500 yr b p when the muskeg dominated landscape typical of the present subarctic was established the initial herb and shrub vegetation was likely a reprise of conditions which existed during earlier pleistocene deglaciations these conditions may have provided a favorable environment for animals adapted to nonforested vegetation and promoted migration southward from beringia and northward from the great plains during the last deglaciation and earlier pleistocene deglaciations the sequence of postglacial vegetation change in the mackenzie basin likely reflects a combination of climatic change edaphic change and plant migration patterns and interactions

coupled primary production benthic foraminiferal assemblage and sulfur diagenesis in organic rich sediments of the benguela upwelling system abstract episodically deposited dark organic rich pleistocene and late pliocene sediments from the lower continental slope off southwest africa reveal complex interactions between changes in primary production benthic foraminiferal assemblage and anaerobic microbial processes the organic rich layers contain diatom assemblages characteristic of intense seasonal coastal upwelling whereas stratigraphically adjacent sediments reflect pelagic primary production coastal upwelling dominated depositional intervals coincide with periods of enhanced carbon flux to the seafloor enhanced organic carbon export during dark layer deposition was accompanied by decreases in the diversity of benthic foraminifera to few opportunistic species adapted to high phytodetritus accumulation rates and low o 2 conditions in all sediments the sulfur isotopic composition of pyrite indicates redox cycling of sulfide close to the sediment water interface the sulfur isotopic evidence and the permanent presence of abundant low o 2 adapted benthic foraminifera throughout the organic rich layers suggest an oxygenated benthic environment efficient oxidation of sulfide and removal of sulfide by sulfidization of organic matter inhibited buildup of toxic hydrogen sulfide from bacterial sulfate reduction at the sediment water interface these data imply that in continental slope sediments underneath productive surface waters benthic dysoxic conditions are maintained by the lateral advection of dissolved oxygen to support a small but well adapted benthic community

spatial characteristics of sediment trace metals in an eastern boundary upwelling retention area st helena bay south africa a hydrodynamic biological pump hypothesis st helena bay a retention zone located in the southern benguela upwelling system is an important fish nursery however it suffers from seasonal bottom water hypoxia causing major economic losses anoxic conditions are linked to sulfide fluxes from bottom sediments defined by a high sedimentation rate of organic matter it is proposed that trace metals may play an important role in alleviating part of the ecological stress by forming sulfide complexes in such systems a spatially intensive data set of sediment biogeochemical characteristics showed that poc and trace metals cr cu zn ni etc accumulated in the central zone of the bay furthermore trace metal concentrations were strongly correlated with both poc and al to explain the observed biogeochemical relationships in st helena bay we propose a hypothesis that links the upwelling retention hydrodynamics primary productivity and sediment trace metal distribution trace metals are incorporated into phytoplankton cells in the euphotic zone but rapidly sediment along with particulate organics on their senescence both the biological pump and the dispersion of particulates are primarily controlled by the hydrodynamics prevalent within st helena bay which also govern the retention zone in the shadow of one of the major upwelling cells the dynamics of entrainmentestratification drives the productivity while a residual cyclonic gyre concentrates the surface productivity within the bay bed shear stresses spatially constrain the accumulation of biogenic organic matter which governs the trace metal biogeochemistry of the sediments along a narrow terrigenous mud belt 2005 elsevier ltd all rights reserved

petrographic and geochemical study of organic matter in surficial laminated sediments from an upwelling system mejillones del sur bay northern chile a study of recent laminated sediments accumulated in the oxygen minimum zone of mejillones bay northern chile shows that the organic matter is autochthonous and deposited under varying oceanographic conditions sedimentary units dominated by light laminations have low values of total organic carbon total nitrogen and sulphur and chaotoceros content coupled with high values of yellow amorphous organic matter these were deposited under conditions of low primary productivity favoring the recycling of the major part of metabolizable organic matter in the water column and the accumulation only of non metabolizable organic matter in the bottom sediments in contrast a unit rich in dark laminations with high values of total organic carbon total nitrogen and sulphur shows high values of brown and black aom and chaetoceros content this sedimentary unit reflects increased flocculation of organic particles during a period of high productivity and fast transit of organic material through the column water thus diminishing the recycling of metabolizable organic matter and its accumulation with non metabolizable organic matter in the sediments finally a unit characterized by presence of both light and dark laminations was formed by abrupt alternations of the two oceanographic states described previously

paleoenvironments of the latest cretaceous oil shale sequence southern tethys israel as an integral part of the prevailing upwelling system abstract the late cretaceous succession in israel is part of an extensive high productivity upwelling regime that persisted over 20 m y in the southern margins of tethys the deposition of a 40 m thick organic rich carbonate oil shale sequence in the negev israel indicates a major change in the evolution of this high productivity regime and reorganization of the marine ecosystem during the latest campanian early maastrichtian time the main objective of this study was to reconstruct changes in surface water productivity and seafloor oxygenation during the deposition of the oil shale member osm and transitions with the underlying phosphate and overlying marl members using high resolution records of planktic and benthic foraminifera and total organic carbon toc content the updated age of the osm determined by integrating planktic foraminifera calcareous nannofossils and inoceramids suggests that this sequence spans a maximum of 1 85 m y from 71 6 to 69 85 ma with a sedimentation rate of at least 2 4 cm kyr five distinct planktic p types and benthic b type foraminiferal assemblages were distinguished in the studied sequence the change from p type 5 to p type 1 along the sequence correlates with a distinct decrease in toc content 18 0 0 1 wt and signifies an upward decline in surface productivity based on this relationship it was inferred that species of globigerinelloide s principally globigerinelloides asper are the best tracers for extreme eutrophic surface water whereas heterohelicids are associated with more mesotrophic conditions the transition in time from assemblages b types 5 to 1 mainly reflects a change from the predominance of praebuliminids and neobuliminids to a more diversified rotaliid dominated assemblage indicating an increase in bottom water aeration the appearances of planktic foraminifera coincident with the establishment of benthic rotaliid fauna at the phosphate oil shale member transition mark the most prominent change in the upwelling sequence this change probably reflects moderate weakening of the eutrophic surface water productivity and a regional sea level rise resulting in seafloor deepening and improved seafloor aeration a further step in the decrease in toc content to 5 5 8 wt occurs in the uppermost part of the osm latest campanian and corresponds to the transitions to assemblages p type 1 and b type 1 this change suggests a shift to mesotrophic conditions additional increase in bottom and pore water aeration and thus the demise of the upwelling activity in the southern tethys

geochemistry of inorganic and organic sulphur in organic rich sediments from the peru margin abstract we have determined 1 the abundance and isotopic composition of pyrite monosulphide elemental sulphur organically bound sulphur and dissolved sulphide 2 the partition of ferric and ferrous iron 3 the organic carbon contents of sediments recovered at two sites drilled on the peru margin during leg 112 of the ocean drilling program sediments at both sites are characterised by high levels of organically bound sulphur obs obs comprises up to 50 of total sedimentary sulphur and up to 1 of bulk sediment the weight ratio of s to c in organic matter varies from 0 03 to 0 15 mean 0 10 such ratios are like those measured in lithologically similar but more deeply buried petroleum source rocks of the monterey and sisquoc formations in california the sulphur content of organic matter is not limited by the availability of porewater sulphide isotopic data suggest that sulphur is incorporated into organic matter within a metre of the sediment surface at least partly by reaction with polysulphides most inorganic sulphur occurs as pyrite pyrite formation occurred within surface sediments and was limited by the availability of reactive iron but despite highly reducing sulphidic conditions only 35 65 of the total iron was converted to sulphide 10 30 of the total iron still occurs as fe iii in surface sediments the isotopic composition of pyrite is similar to that of both iron monosulphide and dissolved sulphide either pyrite like monosulphide formed by direct reaction between dissolved sulphide and detrital iron and or the sulphur species responsible for converting fes to fes2 is isotopically similar to dissolved sulphide likely stoichiometries for the reaction between ferric iron and excess sulphide imply a maximum resulting fes2 fes ratio of 1 1 where pyrite dominates the pool of iron sulphides at least some pyrite must have formed by reaction between monosulphide and elemental sulphur and or polysulphide elemental sulphur s0 is most abundant in surface sediments and probably formed by oxidation of sulphide diffusing across the sediment water interface in surface sediments s0 is isotopically heavier than dissolved sulphide fes and fes2 and is unlikely to have been involved in the conversion of fes to fes2 polysulphides are thus implicated as the link between fes and fes2

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

the early matuyama diatom maximum off sw africa benguela current system odp leg 175 abstract several sites of ocean drilling program leg 175 between 20 and 30 s 1081 1082 1083 1084 and 1085 in the benguela current system show a distinct opal and diatom maximum within the late pliocene and early quaternary spanning the lower half of the matuyama reversed polarity chron mdm matuyama diatom maximum this maximum is centered around 2 0 2 6 ma and follows a rapid increase of diatom deposition near 3 1 ma within the mdm we recognized intervals dominated by the antarctic subantarctic species thalassiothrix antarctica which have the aspect of diatom mats the mdm and the mats developed during a time of sustained southern ocean influence 3 2 1 6 ma probably reflecting a period of seasonally pulsed continuous advection of subantarctic waters into the benguela oceanic current the onset and cessation of the mdm raises questions about modes in the operation of the silica cycle and the relation of these to major oceanographic events a depositional model for the late pliocene is proposed which involves positional changes in a longshore system of fronts substantial equatorward excursions of subantarctic waters during mdm time and subsurface waters greatly enriched in silicate

organic carbon accumulation and preservation in surface sediments on the peru margin concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen minimum zone on the peru margin were studied in samples from deck deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12 and 13 5 s the source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of of organic carbon obtained in the present study 20 3 to 21 6 pdb and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition organic carbon contents are highest up to 16 on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations 5 mol kg even at these low concentrations of dissolved oxygen however the surface sediments that were recovered from these depths are dominantly unlaminated strong currents up to 30 cm s associated with the poleward flowing peru undercurrent were measured at depths between 160 and 300 m on both transects the seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats extensive authigenic mineral crusts and or thick organic flocs constant advection of dissolved oxygen although in low concentrations active resuspension of surficial organic matter activity of organisms and transport of fine grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen deficient conditions dissolved oxygen concentrations ultimately may be the dominant affect on organic matter characteristics but reworking of fine grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region

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

transport and reduction of sulfate and immobilization of sulfide in marine black shales in fine grained sediments in which the amount of reduced sulfur retained in stable phases substantially exceeds that present initially in pore waters rates of sulfate reduction may have equaled or exceeded rates of sulfate transport resulting in enrichment of sup 34 s in pore waters and reduction products abundance and isotopic compositions of reduced sulfur compounds can be used to calculate the extent of sulfide retention and improve reconstructions of carbon sulfur oxidation reduction redox budgets the miocene monterey formation and upper devonian new albany shale represent distinct types of black shales that accumulated under different conditions of sulfate reduction our results suggest that the rate of sulfate reduction was controlled largely by mass transport in the monterey and by the reduction process itself in the new albany sulfide was more efficiently retained in the monterey thus each mole of sulfide in the new albany represents a greater amount of sedimented organic carbon removed during sulfate reduction 30 refs 4 figs 1 tab

a late wisconsin and holocene vegetation history from the central brooks range implications for alaskan palaeoecology abstract five pollen diagrams reveal late wisconsin and holocene vegetation changes in the walker lake alatna valley region of the central brooks range approximately 100 km west of the area studied by d a livingstone 1955 ecology 36 587 600 new insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate picea glauca and p mariana pollen three major pollen zones are identified 1 a basal herb zone characterized by high percentages of cyperaceae gramineae salix and artemisia and low total pollen influx 2 a shrub betula zone with increased total pollen influx and very high percentages of betula pollen predominantly in the size range of b nana and b glandulosa and 3 and alnus zone dominated by alnus pollen lakes currently within the boreal forest or near tree line show relatively high percentages of picea pollen in the alnus zone several striking vegetation changes occurred between ca 10 000 and 7000 yr b p between ca 11 000 and 10 000 yr b p populus balsamifera pollen percentages as great as 30 indicate that this species was present at low elevation sites near walker lake these populations declined abruptly ca 10 000 yr ago and have never regained prominence about 8500 yr b p picea glauca pollen reached 10 15 indicating the arrival of p glauca in or near the study area p glauca populations evidently decreased ca 8000 yr ago when picea pollen percentages and influx fell to low values about 7000 yr b p alnus pollen percentages and influx rose sharply as alder shrubs became established widely picea once more expanded ca 5000 yr ago but these populations were dominated by p mariana rather than p glauca which increased slowly at this time and may still be advancing northward some vegetation changes have been remarkably synchronous over wide areas of interior alaska and probably reflect responses of in situ vegetation to environmental changes but others may reflect the lagged responses of species migrating into new areas

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

sulfate reduction in surface sediments of the southeast atlantic continental margin between 15 38 s and 27 57 s angola and namibia sulfate reduction rates in the surface sediments from 17 stations from an along slope transect 1 300 m and from a cross slope transect 855 4 766 m were determined in the continental margin sediments of the benguela upwelling system profiles at all sites in the upwelling area showed increasing sulfate reduction rates from near zero at the surface to a peak at 2 5 cm up to 29 nmol cm 23 d 21 and then decreasing exponentially with depth to near background rates at 10 20 cm depth 2 nmol cm 23 d 21 depth integrated sulfate reduction rates were greatest at 1 300 m and decreased exponentially with water depth along the transect following the 1 300 m isobath depthintegrated sulfate reduction rates were highest in the north cape basin 1 16 6 0 23 mmol m 22 d 21 decreased over the walvis ridge 0 67 6 0 02 mmol m 22 d 21 and were lowest in the south angola basin 0 31 6 0 23 mmol m 22 d 21 depth integrated sulfate reduction rates were consistent with the known pattern of coastal upwelling intensities and were also strongly correlated with surface organic carbon concentrations sulfate reduction rates both as a function of depth and in comparison with sediment trap data indicated that lateral downslope transport of organic carbon occurs sulfate reduction was estimated to account for 20 90 of the published rates of total oxygen consumption for the sediments at 1 300 m depth and 3 16 of sediments from 2 000 to 3 000 m depth comparison of the sulfate reduction rate profiles with the published diffusive oxygen uptake rates showed that the kinetics of oxygen utilization in the surface sediments are much faster than those for anaerobic organic carbon remineralization although the underlying cause of the difference was not clear

impacts of the spatial extent of pollen climate calibration set on the absolute values range and trends of reconstructed holocene precipitation abstract pollen based quantitative reconstructions of past climate variables is a standard palaeoclimatic approach despite knowing that the spatial extent of the calibration set affects the reconstruction result guidance is lacking as to how to determine a suitable spatial extent of the pollen climate calibration set in this study past mean annual precipitation pann during the holocene since 11 5 cal ka bp is reconstructed repeatedly for pollen records from qinghai lake 36 7 n 100 5 e north east tibetan plateau gonghai lake 38 9 n 112 2 e north china and sihailongwan lake 42 3 n 126 6 e north east china using calibration sets of varying spatial extents extracted from the modern pollen dataset of china and mongolia 2559 sampling sites and 168 pollen taxa in total results indicate that the spatial extent of the calibration set has a strong impact on model performance analogue quality and reconstruction diagnostics absolute value range trend optimum generally these effects are stronger with the modern analogue technique mat than with weighted averaging partial least squares wa pls with respect to fossil spectra from northern china the spatial extent of calibration sets should be restricted to radii between ca 1000 and 1500 km because small scale calibration sets 1500 km radius will include taxa with very different pollen climate relationships

a late pliocene diatom ge si record from the southeast atlantic abstract as a result of both culture and sediment core studies the ratio of germanium ge to silicon si in diatom shells has been proposed as a proxy for monitoring whole ocean changes in seawater ge si a ratio affected by changes in continental weathering however because of the difficulties of extracting and cleaning diatom frustules from deep sea sediments only samples from highly pure diatom oozes in the antarctic region have been previously analyzed here we present data on diatom ge si ratios ge si opal for the time interval between 3 1 and 1 9 ma from a mid latitude coastal upwelling area where significant terrigenous sediment input complicated the sample processing and analyses in general our ge si opal values show the same decreasing trend after 2 6 ma than previously measured in antarctic sediments shemesh et al 1989 paleoceanography 4 221 231 but with a noisier background that may reflect the local imprint of proximal continental input superimposed upon global changes in the ocean reservoir the time of initiation of large scale north hemisphere glaciation at 2 6 ma is characterized by a declining pattern of diatom ge si ratios which could have resulted from a global increase in the input of riverine si due to enhanced silica weathering and or equatorward northward intrusions of subantarctic waters enriched in silica high ge si opal ratios are associated with high opal contents from the same sediment samples and with warm climate as indicated by depleted benthic foraminiferal 18 o values from the north and equatorial atlantic cold periods signified by enriched benthic 18 o values on the contrary are associated with lower ge si opal ratios we interpret diatom ge si values to reflect the prevailing weathering state on the continents with greater chemical weathering during warm and wet periods of the pliocene and less during cooler and drier intervals

relationships between primary productivity and bottom water oxygenation off northwest africa during the last deglaciation the upwelling region off northwest africa is one of the most productive regions in the world ocean this study details the response of surface and deep water environments off mauritania northwest africa to the rapid climate events of the last deglaciation especially the bolling allerod 15 5 13 5 ka bp and younger dryas 13 5 11 5 ka bp a high accumulation rate gravity core geob7926 2 recovered at 208 n 188 w was analysed for the grain size distribution of the terrigenous sediment fraction the organic carbon content diatom and benthic foraminifera communities humid conditions were observed during the bolling allerod with a high contribution of fluvial sediment input during the younger dryas intensified trade winds caused a larger sediment input of aeolian dust from the sahara and more intense upwelling with higher primary productivity as indicated by high diatom concentrations the abrupt and large increase of organic matter caused low oxygen conditions at the sea floor reflected by the poor benthic foraminiferal fauna and the dominance of the low oxygen tolerant foraminiferal species bulimina exilis this is surprising since low oxygen conditions have not been recorded during modern times at the sea floor in this region despite present day intensive upwelling and high primary productivity after the younger dryas more humid conditions returned diatom abundance decreased and b exilis was replaced by typical deep sea species as found in the region today indicating the return of more oxygenated conditions at the sea floor copyright 2011 john wiley sons ltd

holocene development of boreal forests and fire regimes on the kenai lowlands of alaska several studies have noted a relationship between vegetation type and fire frequency yet despite the importance of ecosystem processes such as fire the long term relationships between disturbance climate and vegetation type are incompletely understood we analysed pollen plant macrofossils and sedimentary charcoal from three lakes within the kenai lowlands to determine postglacial relationships between disturbance climate and vegetation for the boreal forest of southwest alaska an herb tundra was established in the lowlands following deglaciation by 13 000 cal bp salix alnus and probably betula kenaica expanded in the area after 10 700 cal bp followed by picea glauca by 8500 cal bp picea mariana became established by 4600 cal bp the early holocene was probably the driest time during the postglacial as determined by aquatic plant macrofossils and climate models lake levels reached near modern conditions by at least 8000 cal bp mean fire intervals mfi were longest during the shrubherb tundra phase 1389 65 yr decreased after expansion of b kenaica salix and populus 779 49 yr and picea glauca 819 41 yr and increased again with the arrival of p mariana 1309 66 yr unlike previous studies our data demonstrate the highest fire frequencies during the early to mid holocene and less frequent fire during the late holocene when p mariana forests dominated the lowlands early holocene forests of p glauca and b kenaica existed in summers that were longer and drier than today while the increasingly wetter and cooler climates of the late holocene probably hindered forest fire around paradox lake perhaps because of less frequent summer drought

organic geochemical changes in pliocene sediments of odp site 1083 benguela upwelling system the intensification of the northern hemisphere glaciation inhg was a major event in the development of the current climate state and as one of the most productive regions in the world s oceans the behaviour of the benguela upwelling system bus following the inhg is of wide interest to investigate post inhg changes in productivity and organic matter accumulation total organic carbon and biomarker accumulation rates were determined for sediments from cop site 1083 and compared to alkenone derived sea surface temperatures and nitrogen isotopic compositions these data indicate that the interval between 2 6 and 2 4 ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern bus the upwelling is reflected by significant changes in alkenone derived sst estimates between glacial and interglacial intervals with a total variability of 16 degrees c the studied interval is also characterized by large changes in organic matter export as reflected by changes in toc and biomarker accumulation rates which show maxima during ois 98 and during the transition from ois 97 to 96 intervals of elevated toc are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower caco 3 suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released co 2 being consumed by caco 3 dissolution however in apparent contrast to recent pleistocene sediments at the same site organic matter export after the inhg was not solely driven by upwelling intensity of the three pliocene glacial interglacial cycles examined ois 101 to 96 each is unique with respect to the timing and magnitude of changes in organic matter accumulation each is also characterized by different algal assemblages as inferred from biomarker distributions with ois 97 and 96 particularly dominated by diatoms we suggest that these differences reflect the important but evolving role of southern ocean waters in the pliocene bus nutrient depletion of so waters occurred during parts of pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates c 2009 elsevier b v all rights reserved

sulfate reduction and methanogenesis in a thioploca dominated sediment off the coast of chile continental shelf sediments of the central chile upwelling area are dominated by the presence of dense mats of the filamentous sulfur depositing bacterium thioploca spp we examined rates and pathways of s and methane cycling in these sediments along a transect from the bay of concepcion to the continental slope sulfate reduction rates 170 4670 nmol cm 3 d 1 were equal to or exceeded rates reported for other subtidal marine sediments elemental s and pyrite were the dominant end products of sulfate reduction in thioploca mats on the continental shelf whereas in the highly reducing beggiatoa dominated sediments of the nearby bay of concepcion acid volatile s was the principal end product dissolved organic c values were lowest at the stations with the highest sulfate reduction rates and increased offshore sediment porewater methane concentrations in all surface sediments were low 12 nmol cm 3 and methane production rates at the station most dominated by thioploca were extremely low 0 5 nmol cm 3 d 1 low methane production rates and concentrations were matched by low methane oxidation rates 0 1 nmol cm 3 d 1 radio tracer studies showed that methane production was almost exclusively from methylamines substrates which are noncompetitive with sulfate reduction rather than from acetate or co2 h2 bacterial mpn most probable number counts also indicated the presence of a methylotrophic population of methanogens surprisingly high numbers of autotrophic acetogenic bacteria were found suggesting that the bacterial population involved in anaerobic doc degradation is more complex than expected in spite of the high sulfate reduction rates sulfide concentrations in the shelf and slope were low or undetectable 0 5 m and sulfate concentrations were never depleted below bottom water levels down to depths of 25 30 cm calculations suggest that thioploca were oxidizing a maximum of 35 of sulfide production not enough to prevent sulfate depletion either other sulfide oxidizers were also present or transient hydrodynamic conditions coupled with bioturbation resulted in oxidation of the sediments

dated wood from alaska and the yukon implications for forest refugia in beringia abstract postulations on the existence of forest refugia in parts of beringia during the last glacial have been in large part based on ambiguous evidence existing data on radiocarbon dated and identified fossil wood and macrofossils from alaska and northwest canada are synthesized here and are augmented by results of palynological studies in an effort to show the persistence of some and total extinction of other tree and large shrub species possible dispersal routes taken by species that reinvaded beringia in postglacial times are also reconstructed from the fossil record macrofossil and pollen evidence when combined with climatic factors makes cottonwood a good candidate for survival during the last glacial larch and aspen are also candidates though the evidence for them is less positive pollen and macrofossils of alder are very scarce in deposits of the last glacial age and if it survived at all it was probably in very isolated vegetatively reproducing clones shrub birch may have been present in beringia but tree birch probably was reintroduced during the holocene spruce also appears to have been absent in alaska from about 30 000 to 11 500 yr ago and probably reinvaded beringia from a refugium south of the laurentide ice sheet

subsurface activity of benthic foraminifera in relation to porewater oxygen content laboratory experiments in a series of laboratory experiments we examined the migratory activity of some common benthic foraminifera in relation to subsurface oxygen concentrations in porewaters our results clearly demonstrate that foraminifera are capable of migrating through anoxic sediments reinforcing the idea that some common benthic foraminifera are facultative anaerobes we observed that migration was not completely random there seemed to be a bias towards upward migration when buried without a subsurface oxic zone although this migration can be taken as a response to the absence of oxygen it was not directly linked to gradients of oxygen as these were not present at that depth and a large portion of the assemblages continued to inhabit deeper sediment layers the relatively higher percentage of soft shelled foraminifera in the oxic zone suggests that they may be less tolerant to anoxic conditions than hard shelled foraminifera this possible differential tolerance may be one factor that will determine the survival or success of different species buried in deeper sediment layers

the interplay between the surface and bottom water environment within the benguela upwelling system over the last 70 ka the benguela upwelling system bus located between 30 and 20 s is one of the fundamental high productivity systems of the world ocean the bus has previously been studied in terms of primary productivity and ecology over glacial interglacial timescales however the response and coupling with the benthic environment have received little attention here for the first time we present a high resolution reconstruction of the bus highlighting the link between surface and benthic productivity and their response to climatic and oceanographic changes over the last 70 ka the study is based on benthic foraminiferal faunal analysis together with analyses of diatom assemblages grain size of the terrigenous fraction and stable o and c isotopic and bulk biogenic components of core geob3606 1 we reveal significant shifts in benthic foraminiferal assemblage composition tight coupling existed between the surface and bottom water environment especially throughout marine isotope stages 4 and 3 mis4 and mis3 due to the high export production the site has essentially experienced continuous low oxygen conditions however there are time periods where the hypoxic conditions were even more notable two of these severe hypoxic periods were during parts of mis4 and mis3 where we find an inverse relationship between diatom and benthic foraminifera accumulation meaning that during times of extremely high phytodetritus export we note strongly suppressed benthic productivity we also stress the importance of food source for the benthos throughout the record shifts in export productivity are attributed not only to upwelling intensity and filament front position but also regional global climatic and oceanographic changes had significant impact on the bus dynamics

extension of carbon flux estimation to oxic sediments based on sulphur geochemistry and analysis of benthic foraminiferal assemblages a case history from the eocene of hungary abstract the amount and type of organic matter om chemical and mineralogical compositions and the amount and isotopic ratio of sulphur were measured and benthic foraminiferal assemblages were analysed in a 70 m thick core section comprising marine marls from the eocene of hungary on the basis of benthic foraminiferal oxygen index bfoi the studied sediments were deposited under a range of anoxic to oxic bottom water conditions the amount of corg mineralised during early burial was calculated in two steps first carbon mineralised by sulphate reduction was calculated from the amount of sedimentary sulphur corrected for escaped oxidised h2s by taking into account the isotopic composition of sulphur then on analogy of recent sediments which are deposited with a similar rate of sedimentation and beneath bottom waters of similar o2 content carbon loss by aerobic respiration was estimated a good stratigraphic control and knowledge of variation of mineralogical composition along the section permitted to estimate past variation of local organic carbon flux cflux from calculated original corg contents during deposition of the studied strata cflux first decreased from 1 16 to 0 41 g corg m2 y then it progressively increased to 1 81 g corg m2 y changes in local cflux are explained by changes in water depth flux of terrestrial organic components and availability of nutrients liberated by alteration of products of the coeval pyroclastic activity

late quaternary history of tundra vegetation in northwestern alaska pollen analysis of a new core from joe lake indicates that the late quaternary vegetation of northwestern alaska was characterized by four tundra and two forest tundra types these vegetation types were differentiated by combining quantitative comparisons of fossil and modern pollen assemblages with traditional qualitative approaches for inferring past vegetation such as the use of indicator species although imprecisely dated the core probably spans at least the past 40 000 yr a graminoid salix tundra dominated during the later and early portions of the glacial record the middle glacial interval and the transition from glacial to interglacial conditions are characterized by a graminoid betula salix tundra a populus forest betula shrub tundra existed during the middle potion of this transition being replaced in the early holocene by a betula alnus shrub tundra the modern picea forest shrub tundra was established by the middle holocene these results suggest that the composition of modem tundra communities in northwestern alaska developed relatively recently and that throughout much of the late quaternary tundra communities were unlike the predominant types found today in northern north america although descriptions of vegetation variations within the tundra will always be restricted by the innate taxonomic limitations of their herb dominated pollen spectra the application of multiple interpretive approaches improves the ability to reconstruct the historical development of this vegetation type

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

regulation of bacterial sulfate reduction and hydrogen sulfide fluxes in the central namibian coastal upwelling zone abstract the coastal upwelling system off central namibia is one of the most productive regions of the oceans and is characterized by frequently occurring shelf anoxia with severe effects for the benthic life and fisheries we present data on water column dissolved oxygen sulfide nitrate and nitrite pore water profiles for dissolved sulfide and sulfate 35 s sulfate reduction rates as well as bacterial counts of large sulfur bacteria from 20 stations across the continental shelf and slope the stations covered two transects and included the inner shelf with its anoxic and extremely oxygen depleted bottom waters the oxygen minimum zone on the continental slope and the lower continental slope below the oxygen minimum zone high concentrations of dissolved sulfide up to 22 mm in the near surface sediments of the inner shelf result from extremely high rates of bacterial sulfate reduction and the low capacity to oxidize and trap sulfide the inner shelf break marks the seaward border of sulfidic bottom waters and separates two different regimes of bacterial sulfate reduction in the sulfidic bottom waters on the shelf up to 55 of sulfide oxidation is mediated by the large nitrate storing sulfur bacteria thiomargarita spp the filamentous relatives beggiatoa spp occupy low o 2 bottom waters on the outer shelf sulfide oxidation on the slope is apparently not mediated by the large sulfur bacteria the data demonstrate the importance of large sulfur bacteria which live close to the sediment water interface and reduce the hydrogen sulfide flux to the water column modeling of pore water sulfide concentration profiles indicates that sulfide produced by bacterial sulfate reduction in the uppermost 16 cm of sediment is sufficient to account for the total flux of hydrogen sulfide to the water column however the total pool of hydrogen sulfide in the water column is too large to be explained by steady state diffusion across the sediment water interface episodic advection of hydrogen sulfide possibly triggered by methane eruptions may contribute to hydrogen sulfide in the water column

late pliocene climate in the southeast atlantic preliminary results from a multi disciplinary study of dsdp site 532 abstract site 532 on the walvis ridge was sampled at 4000 to 800 year intervals from 2 24 to 2 60 ma spanning the three large glacial advances of the late pliocene an age model was created by correlating the oxygen isotope record to site 607 with linear interpolations between tie lines the resultant age model differs from that in the site reports by more than 800 000 years due to misidentification of a magnetic boundary sedimentation rates varied by an order of magnitude at this site with minimum accumulation during glacial events interglacial intervals were charactrized by high marine production and high summer precipitation on land while glacials had very low production and arid continental climate during the large glacial events stages 96 100 conditions of low production and continental aridity reached their greatest intensity but there is no evidence of a permanent mode shift in either marine or terrestrial records calcite concentration has a strong variation at obliquity frequencies with maxima during interglacials but occasionally shows a large amplitude at precessional frequencies as well so that high concentrations occur in a few glacial intervals as a result color variation is not a reliable guide to glacial scale cycles at this site composition of the phytoplankton assemblage is diverse and highly variable and we have not been able to distinguish a clear indicator of upwelling related production spectral analysis reveals obliquity and precessional signals in the pollen data while several diatom records contain combination tones indicating that these data represent a complicated response to both local and high latitude forcing

decoupling of bio and geohopanoids in sediments of the benguela upwelling system bus abstract geohopanoids derive from bacteriohopanepolyol bhp precursors however knowledge of the specific sources and diagenetic fate of both compound classes in marine sediments is fragmentary we studied the relationship between bhps and geohopanoids in a sediment core from the central benguela upwelling system bus including deposits over the last 75 ka the bus is a palaeo oceanographically stable setting where primary production is largely controlled by variation in upwelling intensity and therefore nutrient supply marine production in the bus was generally higher during glacial than during interglacial times as reflected in the levels of sedimentary total organic carbon geohopanoids at the study site consisted mainly of extractable hopanes and hopanols and occurred in the highest amounts during glacial periods a minor but still considerable fraction of geohopanoids was sulfur linked to geomacromolecular organic matter among these s bound hopane moieties 17 h 21 h trishomohopane c33 was the predominant compound suggesting a diagenetic overprint of bhps before linkage among the bhps a rare bacteriohopanetetrol with likely 22s configuration was observed this structural feature was lacking in the geohopanoids which all had the 22r configuration different behaviour of bhp and geohopanoid concentrations as well as 13c discrepancies indicate a decoupling of bio and geohopanoids geohopanoids most likely reflect laterally transported fossil organic matter whereas bhps are indigenous to the upper water column of the study site and may relate to past upwelling intensity nutrient levels hence care has to be taken using geohopanoids and other biomarkers for palaeoreconstruction in settings where sedimentation processes are not fully understood

controls on c s ratios in hemipelagic upwelling sediments the relationship between organic carbon and reduced sulfur concentrations was investigated in hemipelagic sediments underlying highly productive regions of the ocean and oxic to suboxic waters the benguela upwelling area peru and oman margins at all three sites the degree of pyritization averaged close to 0 4 indicating that reactive iron was probably not limiting for pyrite formation complete sulfate reduction occurred in the upper sections of the sediments from the oman and peru margins however dissolved sulfate never decreased below 5 mm in the benguela upwelling sediments the authors attribute this to more advanced organic matter degradation at the benguela upwelling site c s ratios increased with increasing organic carbon concentrations at all sites for sediments with greater than 3 wt toc the c s ratio averaged about 1 3 and 1 8 times the normal marine ratio of 2 8 at the benguela upwelling and peru margin sites respectively but 2 9 times this value in the oman margin sediments they hypothesize that the quality of the organic matter undergoing burial and rates of near interfacial transport processes are the dominant controls on sulfur burial in these sediments

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

environmental changes and growth history of a cold water carbonate mound propeller mound porcupine seabight on and off mound sediment cores from propeller mound hovland mound province porcupine seabight were analysed to understand better the evolution of a carbonate mound the evaluation of benthic foraminiferal assemblages from the off mound position helps to determine the changes of the environmental controls on propeller mound in glacial and interglacial times two different assemblages describe the holocene and marine isotope stage mis 2 and late mis 3 31 kyr bp the different assemblages are related to changes in oceanographic conditions surface productivity and the waxing and waning of the british irish ice sheet biis during the last glacial stages the interglacial assemblage is related to a higher supply of organic material and stronger current intensities in water depth of recent coral growth during the last glaciation the benthic faunas showed high abundances of cassidulinid species implying cold bottom waters and a reduced availability of organic matter high sedimentation rates and the domination of elphidium excavatum point to shelf erosion related to sea level lowering 50 m and the progradation of the biis onto the shelf a different assemblage described for the on mound core is dominated by discanomalina coronata gavelinopsis translucens planulina ariminensis cibicides lobatulus and to a lower degree by hyrrokkin sarcophaga these species are only found or show significantly higher relative abundances in on mound samples and their maximum contribution in the lower part of the record indicates a higher coral growth density on propeller mound in an earlier period they are less abundant during the holocene however this dataset portrays the boundary conditions of the habitable range for the cold water coral lophelia pertusa which dominates the deep water reefal ecosystem on the upper flanks of propeller mound the growth of this ecosystem occurs during interglacial and interstadial periods whereas a retreat of corals is documented in the absence of glacial sediments on mound glacial conditions with cold intermediate waters a weak current regime and high sedimentation rates provide an unfavourable environmental setting for lophelia corals to grow a late pleistocene decrease is observed in the mound growth for propeller mound which might face its complete burial in the future as it already happened to the buried mounds of the magellan mound province further north

benthic foraminifera off west africa 1 n to 32 s do live assemblages from the topmost sediment reliably record environmental variability abstract recent benthic foraminifera 125 m were investigated from multicorer samples on a latitudinal transect of 20 stations between 1 n and 32 s along the upper slope off west africa samples were selected from a narrow water depth interval between 1200 and 1500 m so that changes in water masses are minimized but changes in surface productivity are important and the only significant environmental variable live rose bengal stained benthic foraminifera were counted from the surface sediment down to a maximum of 12 cm dead foraminifera were investigated in the top 5 cm of the sediment only five live and five dead benthic foraminiferal assemblages were identified using q mode principal component analysis matching distinct primary productivity provinces characterized by different systems of seasonal and permanent upwelling differences in seasonality quantity and quality of food supply are the main controlling parameters on species composition and distribution of the benthic foraminiferal faunas to test the sensitivity of foraminiferal studies based on the uppermost centimeter of sediment only a comparative q mode principal component analysis was conducted on live and dead foraminiferal data from the top 1 cm of sediment it has been demonstrated that on the upper slope off west africa most of the environmental signals as recorded by species composition and distribution of the total live and dead assemblages i e including live and dead foraminifera from the surface sediment down to 12 cm and 5 cm respectively can be extracted from the assemblages in the top centimeter of sediment only on the contrary subsurface abundance maxima of live foraminifera and dissolution of empty tests strongly bias quantitative approaches based on the calculation of standing stocks and foraminiferal numbers in the topmost centimeter

recent eutrophication and consequent hypoxia in the bottom waters of the lower st lawrence estuary micropaleontological and geochemical evidence micropaleontological and geochemical analyses were carried out on two sediment box cores ah00 2220 and cr02 23 recovered in the lower st lawrence estuary lsle in order to document recent temporal variations of primary productivity and carbon fluxes to the bottom waters these reveal a ten fold increase in the accumulation rate of dinoflagellate cysts and benthic foraminifera in the sediment over the last four decades which can be interpreted as a recent increase in pelagic and benthic production furthermore the appearance of the benthic foraminiferal species brizalina subaenariensis and bulimina exilis which are tolerant of low oxygen concentrations and high organic fluxes in the upper 20 cm of the cores may reflect significant changes in bottom water conditions over the last 40 yrs variations in the microfossil abundances in core ah00 2220 are strongly correlated with an increase in organic carbon oc content from 1 1 to 1 6 and to a shift in the isotopic signature of the latter 13 corg from 24 8 to 24 0 similarly a concomitant decrease in the corg n ratio from 15 to 12 an increase in organic carbon content from 1 3 to 1 9 and an increase in 13 corg from 24 5 to 23 5 were observed in core cr02 23 all of which suggest an enhanced accumulation of marine over terrestrial oc in the lsle our results imply that a significant increase in marine productivity in the lsle occurred since the 1960 s 2006 elsevier b v all rights reserved

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

planktic foraminifera from the mid cretaceous barremian early albian of the north sea basin palaeoecological and palaeoceanographic implications abstract a marine cretaceous succession barremian albian of a cored borehole bgs 81 40 located in the central north sea basin has been examined with respect to its planktic and benthic foraminiferal content as well as for calcareous nannofossils the distribution patterns of foraminifera and calcareous nannofossils allow for a two fold division of the investigated interval 1 the barremian earliest aptian interval which reflects a marine temporary restricted setting this is indicated by sporadic occurrences of planktic foraminifera with very rare planispiral forms suggesting short term connections of the boreal and tethyan realms the benthic foraminiferal assemblages indicate aerobic sometimes dysaerobic bottom water conditions high abundances of nannoconids in the barremian suggest enhanced stratification and or warm oligotrophic surface water 2 the late aptian early albian interval which was characterised by an open oceanic environment with cool and aerobic surface water conditions planktic foraminifera are more abundant and diverse than in the lower interval trochospiral hedbergellids dominate the foraminiferal assemblages the episodic occurrences of planispiral clavate and trochospiral flattened planktic morphotypes indicate the existence of a seaway between the boreal and the tethyan realms aerobic to dysaerobic bottom water conditions are suggested by the composition of the benthic foraminiferal assemblages high abundances of cool water taxa within the calcareous nannofossil assemblages indicate a cooling trend across the latest aptian and earliest albian

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

isotopic composition and speciation of sulfur in the miocene monterey formation reevaluation of sulfur reactions during early diagenesis in marine environments the timing and pathways of early diagenetic sulfur transfer from dissolved species in pore waters to solid inorganic and organic compounds in sediments have been studied in the miocene monterey formation santa maria basin onshore california correlation between concentrations of total organic carbon toc and total sulfur ts in addition to concentrations of titanium aluminum total iron and reactive iron have been used to infer organic matter reactivity redox conditions and relative rates of clastic and biogenic input for each lithofacies isotopic compositions of six sulfur species acid volatile disulfide kerogen bitumen sulfate and elemental have provided information regarding relative timing of sulfur incorporation sulfate diffusivity in the upper centimeters of the sediments and the sources of sulfur for individual species isotopically the disulfide species expresses the greatest fractionation relative to estimated values of miocene seawater sulfate 22 cdt on average disulfide is depleted in 34s by 10 4 relative to kerogen and by 9 9 relative to acid volatile sulfide the 34s of bitumen shows no systematic change relative to 34skeregon suggesting the presence of migrated bitumen isotopic similarity of sulfate and elemental sulfur to sulfides and bitumen indicates that sulfate and elemental sulfur are chemical and or biological oxidation products derived from sulfides and bitumen consistent ordering of isotopic values for sulfur species disulfide acid volatile sulfide kerogen indicates that pyrite precipitated nearest to the sediment water interface under mildly reducing conditions and with little or no decrease in sulfate concentration relative to seawater enrichment of 34s in acid volatile sulfide and kerogen sulfur resulted from formation of these species at greater depths or in restricted micro environments under more reducing conditions and with low concentrations of porewater sulfate the formation of acid volatile sulfide after pyrite but during early diagenesis is significant because it implies more strongly reducing conditions than are generally recognized in deep water marine sediments

persistent warmth across the benguela upwelling system during the pliocene epoch a feature of pliocene climate is the occurrence of permanent el nino like or el padre conditions in the pacific ocean from the analysis of sediment cores in the modern northern benguela upwelling we show that the mean oceanographic state off southwest africa during the warm pliocene epoch was also analogous to that of a persistent benguela el nino at present these events occur when massive southward flows of warm and nutrient poor waters extend along the coasts of angola and namibia with dramatic effects on regional marine ecosystems and rainfall we propose that the persistent warmth across the pliocene in the benguela upwelling ended synchronously with the narrowing of the indonesian seaway and the early intensification of the northern hemisphere glaciations around 3 0 3 5 ma the emergence of obliquity related cycles in the benguela sea surface temperatures sst after 3 ma highlights the development of strengthened links to high latitude orbital forcing the subsequent evolution of the benguela upwelling system was characterized by the progressive intensification of the meridional sst gradients and the emergence of the 100 ky cycle until the modern mean conditions were set at the end of the mid pleistocene transition around 0 6 ma these findings support the notion that the interplay of changes in the depth of the global thermocline atmospheric circulation and tectonics preconditioned the climate system for the end of the warm pliocene epoch and the subsequent intensification of the ice ages

low and high frequency climate variability in eastern beringia during the past 25 000 yearsthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new temperature and precipitation reconstructions for the past 25 000 cal years bp from across eastern beringia based on a network of pollen diagrams an updated modern pollen calibration database and an improved methodology using the modern analogue technique mat time series show july temperatures were around 4 c lower during full glacial and january temperatures were about 2 c lower than present annual temperatures rose beginning around 16 000 cal years bp reaching a maximum around 12 000 cal year bp the warming was more rapid in southern beringia annual precipitation varied by 250 mm during the past 25 000 cal years bp maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal years bp that vary regionally suggesting holocene atmospheric circulation changes at multiple time and space scales orbitally forced seasonality changes during the late glacial and early holocene resulted in reversed seasonal temperature reconstructions due to me

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

phosphate oxygen isotopes insights into sedimentary phosphorus cycling from the benguela upwelling system abstract marine sediments are the main sink in the oceanic phosphorus p cycle the activity of benthic microorganisms is decisive for regeneration reflux or burial of inorganic phosphate pi which has a strong impact on marine productivity recent formation of phosphorites on the continental shelf and a succession of different sedimentary environments make the benguela upwelling system a prime region for studying the role of microbes in p biogeochemistry the oxygen isotope signature of pore water phosphate 18op carries characteristic information of microbial p cycling intracellular turnover of phosphorylated biomolecules results in isotopic equilibrium with ambient water while enzymatic regeneration of pi from organic matter produces distinct offsets from equilibrium the balance of these two processes is the major control for 18op our study assesses the importance of microbial p cycling relative to regeneration of pi from organic matter from a transect across the namibian continental shelf and slope by combining pore water chemistry sulfate sulfide ferrous iron pi steady state turnover rate modeling and oxygen isotope geochemistry of pi we found 18op values in a range from 12 8 to 26 6 both in equilibrium as well as pronounced disequilibrium with water our data show a trend towards regeneration signatures disequilibrium under low mineralization activity and low pi concentrations and microbial turnover signatures equilibrium under high mineralization activity and high pi concentrations these findings are opposite to observations from water column studies where regeneration signatures were found to coincide with high mineralization activity and high pi concentrations it appears that preferential pi regeneration in marine sediments does not necessarily coincide with a disequilibrium 18op signature we propose that microbial pi uptake strategies which are controlled by pi availability are decisive for the alteration of the isotope signature this hypothesis is supported by the observation of efficient microbial pi turnover equilibrium signatures in the phosphogenic sediments of the benguela upwelling system

interplay between sedimentary organic matter and dissolved oxygen availability in a coastal zone of the humboldt current system mejillones bay northern chile abstract geochemical and petrographical analyses were done in 26 surficial sediment samples from mejillones bay northern chile to investigate the processes that participate in the preservation of sedimentary organic matter annual variability of chlorophyll a and dic 13 c measured in surface waters of three different parts of mejillones bay did not show any significant spatial variability in biological productivity on the other hand bottom dissolved oxygen showed strong changes associated with water depth and season surface sediment composition was statistically analyzed displaying organic facies which are in agreement with the principal zones of bottom oxygenation annual mean condition identified in this bay in the oxic coastal zone 1 ml l 1 the total carbon tc total nitrogen tn total organic carbon toc hydrogen index hi and oxygen index oi were 1 3 0 1 0 4 355 8 mg hc g toc and 237 6 mg co 2 g toc respectively these results and the presence of almost exclusively dispersed amorphous organic matter suggest an environment where most metabolizable organic matter is degraded within the water column and or in the sediment water interface in the microxic hemipelagic zone 1 located deeper than 65 m the tc tn toc hi and oi were 10 5 1 0 6 6 529 7 mg hc g toc and 103 1 mg co 2 g toc respectively these values and the presence of abundant agglomerated amorphous organic matter suggest a better preservation of metabolizable and non metabolizable compounds we can conclude that biological productivity and dissolved oxygen exert a similar influence on the sedimentary organic matter but the characteristics and quantity of organic material preserved in bottom sediments of this bay are controlled principally by the availability of dissolved oxygen at the sediment water interface according to this conclusion we suggest that the sedimentary record of mejillones bay must be interpreted in paleoceanographic terms primarily in relation to the temporal variability of dissolved oxygen more than biological productivity the oi seems to be a good proxy of paleoxygenation in this coastal system

biogeochemical changes within the benguela current upwelling system during the matuyama diatom maximum nitrogen isotope evidence from ocean drilling program sites 1082 and 1084 1 the matuyama diatom maximum mdm is a time of peak opal accumulation from 2 6 to 2 0 ma within the benguela current upwelling system that was initiated by increased influence of southern ocean water on the eastern south atlantic we measured opal total organic carbon toc and caco3 fluxes and c and n stable isotopes in sediments deposited from 2 4 to 1 95 ma at sites 1082 and 1084 to explore the biogeochemical dynamics within the benguela region the infusion of southern ocean water delivered dissolved nutrients and southern ocean flora and fauna resulting in local opal accumulation increasing up to 8 g cm2ky and the production of diatom mats some 15n measurements of diatom bound organic matter indicate that the mats grew within the benguela region the bulk sediment 15n records are taken to reflect changes in the 15n of nitrate in the incoming water where lower values at 2 4 ma reflect less nitrate utilization in the antarctic a long term increase in relative nitrate uptake in the southern ocean is evidenced by the gradual increase in 15n toward 1 9 ma

a late pleistocene glacial chronology for the southern brooks range stratigraphic record and regional significance radiocarbon dates from 11 measured sections in the koyukuk region provide a chronology of the last pleistocene glaciation glaciers were advancing strongly by 24 000 yr ago they built moraines near the south flank of the brooks range retreated briefly about 22 000 to 20 000 yr b p then readvanced at least one more time into their terminal zones glaciation was accompanied by alluviation of the koyukuk and kobuk drainage systems and by periglacial processes that resemble those taking place today farther north and at higher altitudes moraines near the south flank of the range were being revegetated by 13 500 yr b p a strong final readvance into end moraine belts of some northern valleys occurred about 13 000 to 12 500 yr ago and this event may be synchronous with less extensive glacier readvances in upper valleys of the koyukuk region upper valleys were largely deglaciated by 11 800 yr b p dated stratigraphic sections from the northern alaska range show similar ages for initiation and close of glaciation and also suggest a possible interstadial episode about 20 000 yr ago scanty records of fluctuations during ice wastage probably reflect the general scarcity of datable wood peat and organic soils between about 19 500 and 13 500 yr ago the brooks range and alaska range chronologies closely approximate glacial successions determined else where in eastern beringia and in siberia advance and retreat of glaciers throughout this region evidently were associated with widespread climatic changes that also controlled the late wisconsin history of the laurentide ice sheet the itkillik ii and late itkillik phases of former usage are part of a single glaciation that was entirely separate from the preceding itkillik i ice advance for this reason the local term walker lake glaciation is here extended to the last major glaciation of the entire southern brooks range and use of itkillik phases should be discontinued the term itkillik glaciation is hereby restricted to the next older ice advance in accord with its original definition cold and dry conditions during the last glaciation of eastern beringia are indicated by 1 relatively small mountain glaciers 2 slight 200 m depression of glaciation limits below modern values 3 periglacial features indicating severe frost action on slopes with little protective plant cover 4 widespread accretion of eolian sand 5 low pollen influx rates 6 scarcity of radiocarbon datable organic remains and 7 general absence of carbonaceous paleosols plant growth may have been much more restricted than generally believed with relatively low capacity to support grazing animals and human hunting bands