the tajikistan superbolide of july 23 2008 i trajectory orbit and preliminary fall data the results of the atmospheric trajectory radiant heliocentric orbit and preliminary strewn field calculations for an extremely bright slow moving fireball are presented in the evening hours of july 23 2008 a bright object entered earth s atmosphere over tajikistan the fireball had a 20 3 maximum absolute magnitude and a spectacularly long persistent dust trail remained visible over a widespread region of tajikistan for about 28 minutes after sunset the fireball was also recorded by a visible light satellite system at 14 h 45 min 25 s ut and the dust trail was imaged by video and photocameras a unique aspect of this event is that it was detected by two infrasound and five seismic stations too the bolide was first recorded at a height of 38 2 km reached its maximum brightness at a height of 35 0 km and finished at a height of 19 6 km the first breakup occurred under an aerodynamic pressure of approximately 1 6 mpa similar to the values derived for breakups of the scarcely reported meteorite dropping bolides the fireball s trajectory and dynamic results suggest that meteorite survival is likely the meteoroid followed an apollo like asteroid orbit comparable to those derived for previously recovered meteorites with accurately known orbits

spatial distribution of live benthic foraminifera in the rhone prodelta faunal response to a continental marine organic matter gradient abstract benthic foraminifera were collected in the rhone prodelta gulf of lions mediterranean sea an enriched zone with high organic matter content in june 2005 sediment cores were sampled at depths ranging from 20 to 100 m four distinct foraminiferal assemblages were determined in the study area reflecting the geographical distribution of the impact of river supply the living foraminiferal faunas present a typical picture with strongly impoverished faunas composed exclusively of stress tolerant taxa fursenkoina fusiformis bulimina aculeata leptohyalis scottii and adelosina longirostra in the immediate vicinity of the river mouth this assemblage is well adapted to a high input of continental organic matter and a minimum oxygen penetration depth into the sediment to the southwest under the main corridor followed by the river plume high organic input with a dominantly terrestrial signature more refractory may be stressful for many taxa which need organic matter of a more labile quality in this area nonion scaphum nonionella turgida and rectuvigerina phlegeri are present in low densities on the edge of this area these taxa show much higher densities a greater proportion of marine organic carbon could explain their increasing abundances in this area towards the east and towards the deepest stations in the outer part of the enriched zone biodiversity increases faunas at these stations have intermediate densities and contain a number of taxa cassidulina carinata epistominella vitrea valvulineria bradyana nonionella iridea bradyi at the deepest stations bolivina dilatata spathulata and textularia porrecta at the eastern stations that seem to benefit from more marine organic matter the comparison of geochemical measurements and foraminiferal data strongly suggests that the spatial distribution of foraminifera in the rhone prodelta is mainly governed by the quality and the quantity of organic matter reaching the sediment water interface since bottom waters are well oxygenated 215 260 mol l and oxygen penetration into the sediment is less than 1 cm at all stations benthic ecosystem oxygenation appears to have only a minor impact on regional differences in faunal distribution

successive foraminiferal faunas and inferred palaeoenvironments associated with the postglacial holocene marine transgression gulf st vincent south australia gulf st vincent is one of a pair of elongate triangular shallow water embayments into the southern coast of continental australia from the southern floor of this embayment within a shallow basi

late quaternary paleoproductivity and deep water circulation in the eastern south atlantic ocean evidence from benthic foraminifera abstract two late quaternary sediment cores from the northern cape basin in the eastern south atlantic ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition the locations of the cores were selected such that both of them presently are bathed by north atlantic deep water nadw and past changes in deep water circulation should be recorded simultaneously at both locations however the areas are different in terms of primary production one core was recovered from the nutrient depleted walvis ridge area whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high recent data served as the basis for the interpretation of the late quaternary faunal fluctuations and the paleoceanographic reconstruction during the last 450 000 years nadw flux into the eastern south atlantic ocean has been restricted to interglacial periods with the strongest dominance of a nadw driven deep water circulation during interglacial stages 1 9 and 11 at the continental margin high productivity faunas and very low epibenthic 13c values indicate enhanced fluxes of organic matter during glacial periods this can be attributed to a glacial increase and lateral extension of coastal upwelling the long term glacial interglacial paleoproductivity cycles are superimposed by high frequency variations with a period of about 23 000 yr enhanced productivity in surface waters above the walvis ridge far from the coast is indicated during glacial stages 8 10 and 12 during these periods cold nutrient rich filaments from the mixing area were probably driven as far as to the southeastern flank of the walvis ridge

multidecadal variations in the early holocene outflow of red sea water into the arabian sea we present holocene stable oxygen isotope data from the deep arabian sea off somalia at a decadal time resolution as a proxy for the history of intermediate upper deep water these data show an overall 18o reduction by 0 5 between 10 and 6 5 kyr b p superimposed upon short term 18o variations at a decadal centennial timescale the amplitude of the decadal variations is 0 3 prior and up to 0 6 subsequent to 8 1 kyr b p we conclude from modeling experiments that the short term 18o variations between 10 and 6 5 kyr b p most likely document changes in the evaporation precipitation balance in the central red sea changes in water temperature and salinity cause the outflowing red sea water to settle roughly 800 m deeper than today

benthic foraminiferal faunal and isotopic changes as recorded in holocene sediments of the northwest indian ocean 1 historically the holocene has been considered an interval of relatively stable climate however recent studies from the northern arabian sea netherlands indian ocean program 905 suggested high amplitude climate shifts in the early and middle holocene based on faunal and benthic isotopic proxy records we examined benthic foraminiferal faunal and stable isotopic data from ocean drilling program odp site 723 and total organic carbon data from odp site 724 oman margin 808 and 593 m water depths respectively at site 723 the mid holocene shift in 18o values of infaunal benthic species uvigerina peregrina 1 4 is 3 times larger than that of epifaunal benthic species cibicides kullenbergi recorded at site niop 905 off somalia however none of the five other benthic species we measured at hole 723a exhibits such a shift in 18o we speculate that the late holocene 18o decrease in u peregrina represents species specific changes in ecological habitat or food preference in response to changes in surface and deep ocean circulation while the stable isotopic data do not appear to indicate a middle holocene climatic shift our total organic carbon and benthic faunal assemblage data do indicate that the early holocene deep arabian sea was influenced by increased ventilation perhaps by north atlantic deep water and or circumpolar deep water incursions into the indian ocean leading to remineralization of organic matter and a relatively weak early holocene oxygen minimum zone in the northwest arabian sea in spite of strong summer monsoon circulation

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

enhanced arabian sea intermediate water flow during glacial north atlantic cold phases abstract during the last glacial period polar ice cores indicate climate asynchrony between the poles at the millennial time scale yet surface ocean circulation in large parts of the globe varied in tune with greenland temperature fluctuations suggesting that any anti phase behavior to a substantial degree must lie in the deeper global ocean circulation which is poorly understood outside the atlantic ocean here we present data from the north western indian ocean which indicate that the timing of maxima in northward extensions of glacial antarctic intermediate water gaaiw coincides with dramatically reduced thermohaline overturn in the north atlantic associated with the heinrich ice surge events he the repeated expansion of the gaaiw during hes recorded far north of the equator in the arabian sea suggests that southern hemisphere driven intermediate water mass variability forms an integral part of the inter hemisphere asynchronous climate change behavior at the millennial time scale

recent benthic foraminiferal assemblages in deep high energy environments from the gulf of cadiz spain the benthic environment in the gulf of cadiz north eastern atlantic is strongly affected by the mediterranean outflow water undercurrent mow which flows northwards along the western iberian margin at 500 1500 m water depth foraminiferal census counts of living and dead assemblages from 27 surface samples ranging from 103 to 1917 m water depth and the examination of hard substrates reveal a close correlation of the fauna with the local hydrography and sediment facies four different faunal groups are separated by factor analysis of the living fauna assemblage 1 contains typical lower slope species and dominates samples from the lower mow core layer and in the north atlantic deep water below shelf edge foraminifera are common in assemblage 2a which shows the highest proportions in samples from 103 to 272 m assemblage 2b is dominated by upper slope species and suspension feeders that are frequent in the upper mow core layer and in distal settings between 396 and 901 m species from assemblage 3 prefer epibenthic habitats and are recorded with high proportions exclusively in the immediate flow paths of the upper mow between 496 and 881 m colonisation structures and species composition of epibenthic assemblages from the proximal facies largely differ from those in distal settings in general epibenthic foraminifers only use elevated substrates under the influence of near bottom flow under high current velocities epibenthic foraminifers prefer large and heavy objects they colonise high attachment levels where a maximum yield of advected food particles can be achieved in distal settings at lower flow velocities the elevation height does not exceed 20 mm above the surrounding sediment surface this level is related to a hydrologic transition layer with high concentrations of suspended particles the comparison of microhabitat preferences and faunal structure under high and low current velocities reveal that substrate stability may be a confining environmental variable for endobenthic and shallow epibenthic foraminifers the observations also indicate that the preferential settling height of epibenthic foraminifera is related to the highest lateral flux rates of food particles within reach from the sea floor a dynamic selection of elevated microhabitats is only used by 7 8 of all species recognised in the gulf of cadiz area

rotational aspects of stratified gap flows and shallow fohn observations of fohn in the alps and other mountainous regions suggest that the underlying dynamics is often affected by gap like features in elongated ridge like topography to assess the dynamics of these flows idealized numerical experiments are conducted with a hydrostatic numerical model using f plane geometry and a free slip lower boundary condition the topography is taken to be a two dimensional ridge oriented in the west east direction with a valley transect of depth h across it the upstream flow is westerly with a constant wind speed u and constant brunt vaisala frequency n the control parameters defined by this setting are a dimensionless gap depth n h u the ratio between ridge height and gap depth h h a rossby number describing the south north width of the ridge and additional parameters associated with the shape of the gap with intermediate rossby numbers ro 1 the setting resembles that of shallow alpine south fohn cases which are characterized by a cross alpine flow essentially confined to valley transects for small dimensionless gap depths and large rossby numbers the flow follows the predictions of linear theory and takes on an approximately symmetric pattern with respect to the ridge line for n h u 1 flow separation and splitting takes place upstream and downstream of the gap respectively the flow within the gap decouples from the flow aloft and is driven by the geostrophic south north pressure gradient to yield a fohn like flow it is demonstrated that the limit f 0 is singular i e the flow solution does not converge towards the symmetric f 0 solution and that there exist multiple stationary solutions for f 0 two with northerly and southerly flow across the gap respectively and one with north south symmetry the existence of these multiple steady states is related to a wake instability yet vortex shedding is suppressed by the presence of the ridge downstream of the gap additional simulations are presented which demonstrate that a transient external forcing can induce transitions between the multiple flow solutions the relationship of the idealized setting to alpine shallow fohn is discussed and additional experiments are conducted to assess the effects of surface friction and of an inversion present to the south of the ridge

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

east african mid holocene wet dry transition recorded in palaeo shorelines of lake turkana northern kenya rift abstract the wet early to mid holocene of tropical africa with its enhanced monsoon ended with an abrupt shift toward drier conditions and was ultimately replaced by a drier climate that has persisted until the present day the forcing mechanisms the timing and the spatial extent of this major climatic transition are not well understood and remain the subject of ongoing research we have used a detailed palaeo shoreline record from lake turkana kenya to decipher and characterise this marked climatic transition in east africa we present a high precision survey of well preserved palaeo shorelines new radiocarbon ages from shoreline deposits and oxygen isotope measurements on freshwater mollusk shells to elucidate the holocene moisture history from former lake water levels in this climatically sensitive region in combination with previously published data our study shows that during the early holocene the water level in lake turkana was high and the lake overflowed temporarily into the white nile drainage system during the mid holocene 5270 300 cal yr bp however the lake water level fell by 50 m coeval with major episodes of aridity on the african continent a comparison between palaeo hydrological and archaeological data from the turkana basin suggests that the mid holocene climatic transition was associated with fundamental changes in prehistoric cultures highlighting the significance of natural climate variability and associated periods of protracted drought as major environmental stress factors affecting human occupation in the east african rift system

the effects of solar irradiation changes on the migration of the congo air boundary and water levels of paleo lake suguta northern kenya rift during the african humid period 15 5 ka bp abstract the water level record from the 300 m deep paleo lake suguta northern kenya rift during the african humid period ahp 15 5 ka bp helps to explain decadal to centennial intensity variations in the west african monsoon wam and the indian summer monsoon ism this water level record was derived from three different sources 1 grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments 2 the altitudes and ages of paleo shorelines within the basin and 3 the results of hydro balance modeling providing important insights into the character of water level variations abrupt or gradual in the amplifier paleo lake suguta the results of these comprehensive analyses suggest that the ahp highstand in the suguta valley was the direct consequence of a northeastwards shift in the congo air boundary cab which was in turn caused by an enhanced atmospheric pressure gradient between east africa and india during a northern hemisphere insolation maximum rapidly decreasing water levels of up to 90 m over less than a hundred years are best explained by changes in solar irradiation either reducing the east african indian atmospheric pressure gradient and preventing the cab from reaching the study area or reducing the overall humidity in the atmosphere or a combination of both these effects in contrast although not well documented in our record we hypothesize a gradual end of the ahp despite an abrupt change in the source of precipitation when a decreasing pressure gradient between asia and africa prevented the cab from reaching the suguta valley the abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during october whether or not this is the case the water level record from the suguta valley demonstrates the importance of both orbitally controlled insolation variations and short term changes in solar irradiation as factors affecting the significant water level variations in east african rift lakes

the distribution of living benthic foraminifera on the continental slope and rise off southwest norway abstract surface sediment samples taken by corer from 45 stations on the norwegian continental margin and in the norway basin have been investigated for their benthic foraminiferal content unlike previous studies the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages the additional living assemblage is characterized by the arenaceous speciescribrostomoides subglobosum that dominates between 1400 and 2000 m water depth but is rare in the dead faunal data trifarina angulosa and to a lesser extent cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth where it is associated with strong bottom currents and warm saline atlantic water of the north atlantic drift on the slope between 600 and 1200 m water depth themelonis zaandami species assemblage dominates particularly in areas characterized today by rapid sedimentation of terrigeneous material between 1000 and 1400 m depth where the slope is covered by fine grained organic rich terrigeneous mud the living foraminiferal assemblage is characterized bycassidulina teretis andpullenia bulloides below 1400 m three foraminiferal assemblages are found c subglobosum is found from 1400 to 2000 m cibicidoides wuellerstorfi andepistominella exigua predominantly live from 2000 to 3000 m water depth and below 3000 m oridorsalis umbonatus andtriloculina frigida dominate the fauna all of theelphidium excavatum tests found in this study and thecassidulina reniforme tests found above 500 m water depth were found to be reworked analysis of the sediment grain size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofc wuellerstorfi ande exigua is positively correlated to relatively coarse caused by planktic foraminifera and organic rich sediments whereas high frequencies ofo umbonatus andt frigida coincide with low organic carbon content we suggest thatc wuellerstorfi is adapted to deep sea environments with relatively high food supply tolerating relatively low interstitial water oxygen content whereaso umbonatus may tolerate lower food supply prefering well oxygenated interstitial waters

the influence of the ne winter monsoon on productivity changes in the gulf of aden nw arabian sea during the last 530ka as recorded by foraminifera abstract benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the gulf of aden nw arabian sea that spans the last 530 ka the benthic foraminifera were grouped into four principal assemblages using q mode principal component analyses comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity the benthic foraminiferal productivity indicators coupled with the record of globigerina bulloides a planktic foraminifer known to be sensitive to productivity changes in the region all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages this trend is opposite to the productivity pattern related to the sw summer monsoon of the arabian sea and indicates the role of the ne winter monsoon on the productivity of the gulf of aden a period of exceptionally enhanced productivity is recognized in the gulf of aden region between 60 and 13 kyr indicating the intensification of the ne winter monsoon to its maximal activity contemporaneous indication of increased productivity in other parts of the arabian sea unexplained so far by the sw summer monsoon variability might be related to the intensification of the ne winter monsoon another prominent event of high productivity second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr these two events seem to correspond to periods of similar orbital positioning of rather low precession and eccentricity amplitude for a relatively long period glacial boundary conditions seem to control to a large extent the ne winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the ne monsoonal variability following the identification of productivity events related to the ne winter monsoon in the gulf of aden it is possible now to extend this observation to other parts of the arabian sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records

atmospheric circulation patterns during late pleistocene climate changes at lake malawi africa abstract the climate of tropical africa transitioned from an interval of pronounced orbitally paced megadroughts to more humid and stable conditions approximately 70 000 years ago scholz et al 2007 the regional atmospheric circulation patterns that accompanied these climatic changes however are unclear due to a paucity of continental paleoclimate records from tropical africa extending into the last interglacial we present a new 140 kyr record of the deuterium hydrogen isotopic ratio of terrestrial leaf waxes d wax from drill cores from lake malawi southeast africa that spans this important climatic transition d wax shifts from highly variable and relatively d depleted to more stable and d enriched around 56 ka contemporary with the onset of more humid conditions in the region moisture source and transport history dominate the d wax signal at lake malawi with local rainfall amount playing a secondary role for much of the paleorecord analysis of modern moisture sources for lake malawi suggests that d depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier d depleted air mass currently located in central southern africa to the lake malawi catchment this d depleted air mass is associated with the descending limb of the hadley cell which implies significant changes in the hadley circulation during the megadroughts and related changes in the position of the intertropical convergence zone over africa these findings demonstrate the ability of d wax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance and elucidate potential mechanisms for pronounced hydrological change in southeast africa during the late pleistocene

bipolar seesaw in the northeastern tropical atlantic during heinrich stadials two sst records based on mg ca of g ruber pink from the continental slope off west africa at 15 n and 12 n shed new light on the thermal bipolar seesaw pattern in the northeastern tropical atlantic during periods of reduced atlantic meridional overturning circulation amoc associated with heinrich stadials h1 to h6 the two records indicate that the latitudinal position of the bipolar seesaw s zero anomaly line between cooling in the north and warming in the south gradually shifted southward from h6 to h1 a conceptual model is presented that aims to provide a physically consistent mechanism for the southward migration of the seesaw s fulcrum the conceptual model suggests latitudinal movements of the intertropical convergence zone driven by a combination of orbital forced changes in the meridional temperature gradient within the realm of the hadley cell and the expansion of the northern hemisphere cryosphere as a major factor

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

benthic foraminiferal response to late glacial and holocene sea level rise and rainfall variability off east africa analogous to west and north africa east africa experienced more humid conditions between approximately 12 and 5 kyr bp relative to today while timing and extension of wet phases in the north and west are well constrained this is not the case for the east african humid period here we present a record of benthic foraminiferal assemblages and sediment elemental compositions of a sediment core from the east african continental slope in order to provide insight into the regional shallow indian ocean paleoceanography and east african climate history of the last 40 kyr during glacial times the dominance of a benthic foraminiferal assemblage characterized by bulimina aculeata suggests enhanced surface productivity and sustained flux of organic carbon to the sea floor during heinrich stadial 1 h1 the nuttallides rugosus assemblage indicates oligotrophic bottom water conditions and therefore implies a stronger flow of southern sourced aaiw to the study site during the east african humid period the saidovina karreriana assemblage in combination with sedimentary c n and fe ca ratios suggest higher river runoff to the indian ocean and hence more humid conditions in east africa between 8 5 and 8 1 kyr contemporaneous to the globally documented 8 2 kyr event a severe reduction in river deposits implies more arid conditions on the continent comparison of our marine data with terrestrial studies suggests that additional moisture from the atlantic ocean delivered by an eastward migration of the congo air boundary during that time period could have contributed to east african rainfall since approximately 9 kyr the gaining influence of the millettiana millettii assemblage indicates a redevelopment of the east african fringe reefs

recent abyssal benthic foraminiferal biofacies of the eastern equatorial indian ocean abstract study of recent abyssal benthic foraminifera from core top samples in the eastern equatorial indian ocean has identified distinctive faunas whose distribution patterns reflect the major hydrographic features of the region above 3800 m indian deep water idw is characterized by a diverse and evenly distributed biofacies to which globocassidulina subglobosa pyrgo spp uvigerina peregrina and eggerella bradyi are the major contributors nuttalides umbonifera and epistominella exigua are associated with indian bottom water ibw below 3800 m within the ibw fauna n umbonifera and e exigua are characteristic of two biofacies with independent distribution patterns nuttalides umbonifera systematically increases in abundance with increasing water depth the e exigua biofacies reaches its greatest abundance in sediments on the eastern flank of the ninetyeast ridge and in the wharton cocos basin the hydrographic transition between idw and ibw coincides with the level of transition from waters supersaturated to waters undersaturated with respect to calcite and with the depth of the lysocline carbonate saturation levels possibly combined with the effects of selective dissolution on the benthic foraminiferal populations best explain the change in faunas across the idw ibw boundary and the bathymetric distribution pattern of n umbonifera the distribution of the e exigua fauna cannot be explained with this model epistominella exigua is associated with the colder more oxygenated ibw of the wharton cocos basin the distribution of this biofacies on the eastern flank of the ninetyeast ridge agrees well with the calculated bathymetric position of the northward flowing deep boundary current which aerates the eastern basins of the indian ocean

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

the tropical rainbelt and productivity changes off northwest africa a 31 000 year high resolution record abstract benthic foraminiferal assemblage compositions and sedimentary geochemical parameters were analyzed in two radiocarbon dated sediment cores from the upwelling area off nw africa at 12 n to reconstruct productivity changes during the last 31 kyr high latitude cold events and variations in low latitude summer insolation influenced humidity wind systems and the position of the tropical rain belt over this time period this in turn caused changes in intensity and seasonality of primary productivity off the southern northwest african continental margin high accumulation rates of benthic foraminifera carbonate and organic carbon during times of north atlantic melt water events heinrich 2 25 4 to 24 3 kyr bp and 1 16 8 to 15 8 kyr bp indicate high productivity dominance of infaunal benthic foraminiferal species and high numbers of deep infaunal specimens during that time indicate a strong and sustained supply of refractory organic matter reworked from the upper slope and shelf a more southerly position of the tropical rainbelt and the northeast trade wind belt during heinrich 2 and 1 may have enhanced wind intensity and almost permanent upwelling driving this scenario a phytodetritus related benthic fauna indicates seasonally pulsed input of labile organic matter but generally low year round productivity during the last glacial maximum 23 to 18 kyr bp the tropical rainbelt is more expanded to the north than during heinrich events and relatively weak ne trade winds resulted in seasonal and weak upwelling thus lower productivity high productivity characterized by a seasonally high input of labile organic matter is indicated for times of orbital forced warming such as the african humid period 9 8 to 7 kyr bp an intensified african monsoon during boreal summer and the northernmost position of the tropical rainbelt within the last 31 kyr resulted in enhanced river discharge from the northward extended drainage area initiating intense phytoplankton blooms in the late holocene 4 to 0 kyr bp strong carbonate dissolution may have been caused by even more enhanced organic matter fluxes to the sea floor increasing aridity on the continent and stronger ne trade winds induced intensive seasonal coastal upwelling

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas