biogenic sedimentation and geochemical properties of deep sea sediments of the demerara slope abyssal plain influence of the amazon river plume abstract the amazon river plume has a major impact on sedimentation at abyssal depths throughout a broad area 450 000 km2 and far 500 1000 km from the river mouth as the plume mixes into the north atlantic ocean it may support ecological niches favorable for n2 fixation driven by the symbiosis between diatoms and diazotrophic cyanobacteria this proposed diatom diazotroph association dda should result in increased carbon export from a limited region of plume influence here we used 32 multicores collected throughout the demerara abyssal slope and plain at depths ranging from 3000 to 5000m to assess patterns and rates of export and accumulation of organic carbon corg or poc and biogenic sio2 bsi sediment accumulation rates were determined from 14c ages of foraminifera obtained at 2 5 depths from 9 cores and were further constrained by 230th measurements the sedimentation rate 1 5 cm ky 1 representing the average accumulation over the past 8000 years was combined with corg and bsi sediment concentrations to establish biogenic matter burial fluxes burial of poc represents 4 16 of the corg raining to the deep sea floor which is high for water depths 4000 m burial of bsi represents 1 9 of the total bsi rain clastic sedimentation dominates regions underlying the plume while carbonate sedimentation dominated otherwise sediment mixing bioturbation was studied in 13 cores using 210pb as a tracer and showed no spatial patterns diffusional mixing coefficients ranged from 0 03 to 3 2 cm year 1 values consistent with other deep sea mixing rates however sites with the highest mixing rates did not have the highest corg content sediment focusing was studied in at 7 sites using 230th as a tracer surficial sediments had focusing factors that ranged from 1 to 2 indicating little sediment redistribution biogenic sedimentation in general and bsi deposition in particular is not concentrated in the region of dda abundance the nw axis of primary plume trajectory is coincident with the maximum deposition and burial of poc and bsi but not caco3

sediment dispersal in the argentine basin evidence from visible light spectra abstract visible light reflectance spectra were determined for each of 236 core top samples from the argentine basin and surrounding areas the spectra were analyzed by taking the first derivative of the raw spectral curves and factor analyzing the first derivative values using wavelengths as variables we used a four factor solution that explains about 90 of the cumulative variance factors were evaluated by comparing factor loadings to first derivative curves from known minerals and mineral combinations by the mapped distributions of the factor scores and by comparison to factors from other areas the four factors represent in order of decreasing variance goethite terrigenous vs pelagic sedimentation organic matter and chlorite the goethite and chlorite factors are useful for interpreting sediment influx and dispersal goethitecomes from the falkland plateau and the argentine continental margin once introduce to the deep ocean goethite appears to be transported primarily by isobath parallel currents chlorite on the other hand is transported into the argentine basin by antarctic bottom water aabw and from the falkland plateau however along the falkland plateau chlorite is transported normal to the slope probably by gravitational processes

long chain alkenones and alkyl alkenoates as palaeotemperature indicators their production flux and early sedimentary diagenesis in the eastern north atlantic the production and fate of long chain alkenones and alkenoates was examined with regard to their use as palaeotemperature indicators alkenoate abundances were higher than previously reported for other regions and more strongly correlated with temperature than was alkenone unsaturation u37k suggesting biogeographical variability in alkenone and alkenoate production in surface waters we define the aa36 ratio to parameterize alkenoate abundance and present an empirical temperature calibration derived from our euphotic zone samples for use in the north atlantic t 17 35 25 12 u37k 26 73 aa36 93 90 u37k aa36 significant diagenetic losses of alkenones and alkenoates were found within the water column and near surface sediments in spite of diagenetic losses the temperature signal recorded by these compounds in the sediments remains largely unaltered and corresponds to the euphotic zone water temperature during the springtime period of maximum coccolithophorid production and flux rather than the average annual sea surface temperature

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

a reexamination of late pleistocene boreal forest reconstructions for the southern high plains previous paleoecological research on the southern high plains resulted in development of a late quaternary chronology of pollen analytical episodes and the proposal that boreal forest existed in the region in the late pleistocene these interpretations are now considered untenable because 1 a number of the radiocarbon ages are questionable 2 there are serious problems of differential pollen preservation and reproducibility of the pollen data 3 there is an absence of supporting geological or paleontological data and 4 the soils of the area contain none of the distinctive pedological characteristics produced by a boreal forest available data suggest that the region was primarily an open grassland or grassland with some nonconiferous trees through most of the quaternary

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

carbonate dissolution on the muir seamount western north atlantic interglacial glacial changes abstract although the history of carbonate dissolution has been studied for many years few records of dissolution through an entire glacial cycle are available for the western north atlantic north american basin using 14 cores from the muir and siboney seamounts located about 240 km northeast of bermuda changes in carbonate dissolution were examined over the last 125 000 years the core depth range spans more than 3000 m 1780 m 4980 m insuring that major changes in dissolution will be recorded weight percent carbonate was plotted as a function of water depth for five stratigraphically defined levels to determine temporal changes in the sedimentary lysocline and calcite compensation depth ccd during the holocene the lysocline is located between 4050 m and 4350 m the ccd is not pre ent even in the deepest sample 4980 m the late glacial 18 000 years b p lysocline may have shoaled to about 2500 m whereas during early glacial time 72 000 years b p it deepened to about 3400 m the mid glacial carbonate maximum 60 000 years b p interstadial is marked by a deepening of the lysocline to about 3800 m during the entire glacial episode the ccd aappears to have remained fixed at 4650 m the last interglacial 125 000 years b p was a time favorable to carbonate preservation the lysocline was deeper than 4650 m the deepest core containing sediments of this age increased glacial dissolution appears to result from changes in deep circulation the establishment of the ccd during glacial time is interpreted as indicating increased antarctic bottom water flow the lysocline on the other hand may reflect the degree of stagnation of north atlantic deep water

recent sedimentation on the new jersey slope and rise radiocarbon dating and sedimentological studies of closely spaced cores indicate movement during the holocene of sediments on the new jersey continental slope and upper rise between wilmington and lindenkohl canyons the uneven time stratigraphic thickness of the late quaternary sediment sections between cores and the nonuniform deposition rate at any given core site and among core sites show that the sediment blanket in canyon and intercanyon areas has been affected by downslope gravity driven pocesses during the holocene to the present the reduced rate of deposition on the slope and upper rise between the late pleistocene and the present is largely due to decreased off shelf transport in response to the eustatic rise in sea level very old radiocarbon dates at core tops result from emplacement of older reworked materials from upslope or from truncation of sections by mass wasting processes exposing older material at the sea floor these processes also account for an irregular sequence of dated sections within cores and stratigraphic irregularities of the surficial cover from core to core marked variability in deposition rates on the slope and upper rise is largely a function of topographic configuration proximity and accessibility to sediment source and transport processes seaward of the shelf break moreover higher accumulation rates on the upper rise are attributed primarily to slope bypassing bypassing prevalent during the late pleistocene has continued periodically to the present

a comparison of sediment accumulation chronologies by the radiocarbon and 230thexcess methods abstract four northeast atlantic cores which exhibited well correlated linear progressions of conventional radiocarbon age with depth were analysed to provide 230 th excess profiling data the current evaluation of marine radiocarbon data suggests that conventional radiocarbon ages consistently underestimate true time this deficit progressively increases from 4 to 22 ky bp as a result steady state sediment accumulation rate models based on conventional radiocarbon ages are expected to be in error by up to 17 dependent on the period over which the estimates are made when proxy timescales from the radiocarbon and 230 th excess data for the four cores are compared over periods between 0 11 5 and 0 18 2 ky bp the trend of cumulative time derived from the 230 th excess profiling data is shown to be consistent with the expected trend of conventional radiocarbon age vs the best current estimate of true time this agreement supports the use of 230 th excess as a tracer for detailed estimates of changing deep sea sediment accumulation fluxes

authigenic uranium in atlantic sediments of the last glacial stage a diagenetic phenomenon cores from three different atlantic localities equatorial cape verde rise and porcupine abyssal plain are shown to have anomalous high u contents 5 8 ppm total in sediments laid down during the last glacial stage 12 24 ky bp radiocarbon data demonstrate that the sediments hosting the peak u levels were accumulated at rates similar to those immediately above and below all the cores exhibit maximum mn levels characteristic colour changes and maximum u levels in the same sequence with increasing depth in core on the evidence of the similarities between the cores and pore water u data from a porcupine abyssal plain site it is proposed that the authigenic u enrichments are syndiagenetic and possibly active no correlation is observed between sediment authigenic u and corg contents the source of enrichment is bottom water u which has diffused downwards into the sediments to be sorbed at a particular redox level located 10 30 cm below the oxic post oxic boundary marked by the colour change the magnitude of the enrichments is caused by the persistence of this boundary at a particular level as a result of the decrease in mean sediment accumulation rate between the last glacial stage 5 2 up to at least 19 1 cm ky 1 and the holocene 2 2 4 1 cm ky 1 similar accumulation rate contrasts are expected to be widespread in the atlantic and the implications for previous reported work particularly from the mid atlantic ridge are discussed

rare earth elements in manganese nodules from the south atlantic ocean as indicators of oceanic bottom water flow abstract the mineralogy and geochemistry of a suite of nine manganese nodules from the south atlantic have been determined the ce la ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the antarctic bottom water as has previously been successfully carried out in the pacific ocean the ce la ratios of the nodules decrease in the sequence lazarev sea weddell sea 10 4 and 9 7 east georgia basin 6 5 and 7 1 argentine basin 5 0 but then increase in the brazil basin 6 2 and angola basin 9 8 and 15 1 a further decrease was observed in the cape basin 7 6 an extremely high ce la ratio of 24 4 had already been determined for nodules sampled north of the nares abyssal plain in the western north atlantic these data reflect the more complicated pattern of bottom water flow in the south atlantic than in the south pacific the penetration of more oxygenated north atlantic deep water into the south atlantic accounts for the higher ce la ratios in the nodules from the angola and brazil basins based on this study the flow path of the antarctic bottom water could only be traced as far north as the argentine basin the unique geochemistry of nodules from the central angola basin high mn fe and ce la ratios high contents of ni cu zn and mo appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules

late quaternary sedimentation in the western north atlantic stratigraphy and paleoceanography abstract a detailed analysis of stratigraphic indices was undertaken to study paleoclimatic change in the western north atlantic three stratigraphic indicators carbonate content globorotalia menardii and uvigerina peregrina were tested in ten radiocarbon dated cores from the north american continental margin of these carbonate content appears to be most accurate carbonate content exhibits two major increases from late glacial time to the present estimated ages of the average of the mid point of these increase are 13 200 b p and 8600 b p an absolute chronology was established down fifteen cores using these stratigraphic indicators and the radiocarbon dates sea surface temperature sst estimates derived from planktonic foraminifera were mapped at 2000 yr intervals from 2000 b p to 14 000 b p sst warms rapidly from 12 000 to 8000 b p reaches a maximum between 8000 and 6000 b p and gradually cools after 6000 b p bottom waters were monitored with uvigerina peregrina and dissolution indices the disappearance of uvigerina suggests that the water type it lives in low o 2 started to thin from both the top and bottom by 13 000 b p and by 7300 b p had disappeared fragmentation of planktonic foraminifera was used as an index of dissolution in most cores dissolution was intense during late glacial time lessened during early postglacial time and resumed in the late postglacial

temperature and circulation changes in the eastern north atlantic during the last 150 000 years evidence from the planktonic foraminiferal record during the last 150 000 years the circulation of the subtropical gyre in the eastern north atlantic has changed in response to glacial interglacial variations in climate maps and time series constructed from planktonic foraminifera recovered from 18 piston cores show the nature of this response paleontological chemical and lithologic indices are used to establish a stratigraphy in the cores numerical analysis of the paleontological data yields estimates of the sea surface temperatures sst and salinity maps of these estimates and of the interpreted circulation have been constructed for 18 28 73 93 125 and 150 000 years b p 18o stages 2 3 4 5 b 5 e 6 the analysis yielded six major results 1 1 in the southern sargasso sea faunal abundances and sst have remained essentially constant for the last 150 000 years 2 2 in the northwestern part of the study area between 30 n and 40 n faunal variations were large but sst variations small 2 3 c during the last 150 000 years sst remained stable due to different ecological water types of similar temperature range exchanging dominance downcore 3 3 in the northern part of the study area between 40 45n sst remained warm in the west and decreased to glacial level minima in the east between 120 and 80 000 years b p 18o substages 5 d to 5 a the large west east gradients may have been maintained by a meridional flow of the north atlantic current around the azores plateau 4 4 along the canary current there were generally monotonic decreases in sst during the last climatic cycle 5 5 the advance of ice that culminated in the wisconsin maximum at 18 000 years b p was accompanied by rising sst in both the vicinity of the azores and along the southern part of the canary current 6 6 inferred increases in the velocities of the north atlantic current occurred at approximately the same time as all seven of the major polar advances of the last 150 000 years and are associated with stable or rising temperatures these sst patterns may have resulted from increased north atlantic current velocities advecting warm source waters more rapidly into the mid latitudes the increased velocities may have been due to a combination of reinforcing factors increased wind stress steepening of the thermocline due to increased cooling of 18 c water south of the gulf stream and increased baroclinicity that resulted when the low temperature north atlantic polar front migrated southward toward the stable gyre center

fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge abstract a geochemical investigation has been conducted of a suite of four sediment cores collected from directly beneath the hydrothermal plume at distances of 2 to 25 km from the rainbow hydrothermal field as well as a large biogenic component 80 caco3 these sediments record clear enrichments of the elements fe cu mn v p and as from hydrothermal plume fallout but only minor detrital background material systematic variations in the abundances of hydrothermal elements are observed at increasing distance from the vent site consistent with chemical evolution of the dispersing plume further pronounced ni and cr enrichments at specific levels within each of the two cores collected from closest to the vent site are indicative of discrete episodes of additional input of ultrabasic material at these two near field locations radiocarbon dating reveals mean holocene accumulation rates for all four cores of 2 7 to 3 7 cm kyr 1 with surface mixed layers 7 to 10 cm thick from which a history of deposition from the rainbow hydrothermal plume can be deduced deposition from the plume supplies elements to the underlying sediments that are either directly hydrothermally sourced e g fe mn cu or scavenged from seawater via the hydrothermal plume e g v p as holocene fluxes into to the cores surface mixed layers are presented which typically are an order of magnitude greater than background authigenic fluxes from the open north atlantic one core collected closest to the vent site indicates that both the concentration and flux of hydrothermally derived material increased significantly at some point between 8 and 12 14c kyr ago the preferred explanation is that this variation reflects the initiation intensification of hydrothermal venting at the rainbow hydrothermal field at this time perhaps linked to some specific tectonic event in this fault controlled hydrothermal setting

organic carbon distribution in the north atlantic ocean during the last glacial maximum abstract the organic carbon content of eighty two last glacial maximum lgm sediment samples from the north atlantic ocean was determined with a coulometer organic carbon in these sediments averaged about 0 5 by weight slightly higher than in modern sediments factors that control organic carbon distribution were examined in two ways by mapping the spatial distribution of organic carbon during the lgm and by comparing organic carbon content to sediment characteristics in general sediment organic content increases with increasing sedimentation rate increasing clay content and decreasing carbonate content the spatial distribution of lgm organic content is similar in most respects to the mapped modern distribution the primary exception being areas of high organic content one area of high organic content off nortwest africa is situated in the same area geographically but is larger than its modern counterpart perhaps indicating that wind driven upwelling was more intense and or widespread during the lgm the two other areas of high organic carbon content the north american margin and west of the mid atlantic ridge mar at about 40 n have no modern counterpart on the north american margin south of cape cod organic carbon content is generally 0 6 and in several samples is 0 9 the increased organic carbon content of sediment in this area appears to be related to an increase in sedimentation rate and the concomitant increase in inorganic nutrients the area west of the mar is more perplexing and appears to be related to changes in lgm surface circulation

benthic recycling of biogenic debris in the eastern tropical atlantic ocean abstract distributions of pore water o2 no 2 no 3 nh 4 si oh 4 po3 4 mn2 f and t a were determined at 15 stations in the eastern equatorial atlantic while overall profile characteristics are consistent with previous models of organic matter diagenesis profile shapes suggest that a deep reaction layer rich in organic c is also present at many sites while it is unlikely that the oxidation of organic c in this layer has had a major effect on the ocean c cycle pore water profile shapes are significantly altered despite exposure to seawater so2 4 concentrations for 1000 years decomposition of the organic matter in the layer appears to be restricted to oxic and suboxic processes these results suggest major differences in organic carbon decomposition and preservation under oxic suboxic and anoxic conditions present day benthic fluxes are largest adjacent to the eastern boundary coastal upwelling region and similar in magnitude to values reported for the eastern pacific preliminary estimates suggest that the benthic respiration in the eastern 1 3 of the north atlantic south of 20 n may alone account for 20 of the total deep north atlantic respiration combining these results with estimates of organic c burial and deep water column decomposition suggests that this region is a major location of organic c input into the deep sea

a poisoned chalice deep sea sediments often carry information about past temperatures in the upper ocean directly above their location but as mccave cautions in this perspective interpretation of the sediments can be complicated by deep sea processes for example material transported laterally in the deep ocean may distort the upper ocean signal in the sediments a report by ohkouchi illustrates such processes at bermuda rise the study yields a detailed understanding of deep sea sediment transport processes aiding the interpretation of sediment records at this site and sounding a warning for others

early diagenesis of lipid biomarker compounds in north atlantic sediments near surface sediments 0 45 mm depth interval from the iceland basin 59 n 21 w 3070 m water depth and biscay abyssal plain 48 n 17 w 4105 m water depth were sectioned at millimeter scale resolution to assess alterations in key lipid biomarkers during early diagenesis inventories g cm 2 in the topmost 45 mm of biomarkers from presumed terrestrial sources c20 linear n alkanes n alkanoic acids n alkanols and from phytoplankton sources phytosterols long chain alkenones and alkenoates were 1 5 4 times more abundant in the iceland basin core than in the biscay abyssal plain core indicating greater sedimentary inputs and or preservation at the iceland basin site biomarker concentrations varied significantly over millimeter scale depth intervals pronounced subsurface concentration maxima were present at both sites at the biscay abyssal plain site steep concentration gradients in the uppermost few mm of the sediment column indicate extensive diagenetic losses at or near the sediment water interface strong covariance was seen in the concentrations of various compounds within each class e g long chain n alkanes n alkanols n alkanoic acids and long chain alkenones and alkyl alkenoates indicating that individual compounds within each class are associated with the same organic matrix and have similar degradation and mixing rates thus biomarker indices for assessment of land derived inputs cpi c29 c31 acl and sea surface temperature ipt remain largely unaltered by early diagenetic processes in oxic abyssal sediments in spite of extensive bioturbation and degradative losses within the uppermost few centimeters of the sediment column

calcium carbonate preservation patterns in the central north atlantic during the last 150 000 years abstract the dissolution record of the canary and eastern north american basins was examined in 15 cores spanning the last 150 000 years stratigraphic control was based on fluctuations in percent carbonate and 18 0 16 0 dissolution changes were determined based on variations in percent planktonic foraminiferal fragments and benthonic foraminifera results indicate three main dissolution events coincident with 18 0 stages 2 4 and 6 the lysocline apparently shallowed about 300 m in the canary basin at these times there is no simple linear relationship between dissolution intensity and ice volume dissolution was more intense during stage 4 than during stage 2 even though 18 0 records indicate the reverse is true for ice volume also carbonate preservation during the lower part of stage 3 is comparable to stages 1 and 5e a comparison of atlantic pacific carbonate dissolution patterns indicates a tendency for out of phase preservation patterns in 18 0 stages 1 and 2 and an in phase dissolution event during stage 4 the out of phase pattern may partially reflect variations in the production rate of north atlantic deep water the in phase dissolution peak correlates with a major cooling regression transport of organic carbon from transient shallow reservoirs into the deep sea could have contributed to formation of such a pattern however additional evidence from longer atlantic pacific records is needed before the shelf basin model can be more fully evaluated

climate change possible influence of ocean upwelling and nutrient concentration the relaxation time of the ocean phosphate system is close to 105 yr the behaviour of this system is here explored using a simple box model this approach illustrates that changes in upwelling in low to mid latitudes might exert a significant influence on the atmospheric pco2 and that the long term relaxation behaviour of the ocean phosphate system would rend to enhance the importance of the 100 kyr frequency component in the climatic record

present water mass calcium carbonate corrosiveness in the eastern south atlantic inferred from ultrastructural breakdown of globigerina bulloides in surface sediments abstract the atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite lysocline however calculations and models that attribute the calcite lysocline to the critical undersaturation depth hydrographic or chemical lysocline and not to the depth at which significant calcium carbonate dissolution is observed sedimentary calcite lysocline strongly overestimate the preservation potential of calcareous deep sea sediments significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep guinea and angola basin and below 4400 m in the cape basin our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the south atlantic ocean in particular coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic co2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic lysocline

the mid pleistocene climate transition as documented in the deep south atlantic ocean initiation interim state and terminal event abstract the mid pleistocene transition mpt of the global climate system initiated by a shift towards much larger northern hemisphere ice shields at around 920 ka and ending with predominance of 100 kyr ice age cyclicity since about 640 ka is one of the fundamental enigmas in quaternary climate evolution climate proxy records not exclusively linked to global ice volume are necessary to advance understanding of the mpt here we present a high resolution pleistocene magnetic susceptibility time series of 12 sediment cores from the subtropical south atlantic essentially reflecting dissolution driven variations in carbonate accumulation controlled by changes in deep water circulation in addition to characteristics known from 18o records the data sets reveal three remarkable features intimately related to the mpt 1 an all pleistocene minimum of carbonate accumulation in the south atlantic at 920 ka 2 a mpt interim state of reduced carbonate deposition indicating that the mpt period may have been a discrete state of the pleistocene deep water circulation and climate system and 3 a terminal mpt event at around 540 530 ka documented in several peculiarities such as thick laminated layers of the giant diatom ethmodiscus rex

depth dependent carbonate dissolution changes in the eastern north atlantic during the last 170 000 years abstract previous studies have shown that dissolution increased in the north atlantic during glacial 13o stages 2 4 and 6 the relative intensity of the events is similar in cores between 3000 4600 m with the stage 4 event being the most intense canary basin cores deeper than 4600 m show a different pattern of dissolution itensity for example stage 6 dissolution was more intense than stage 4 the divergent dissolution patterns at depths 4600 m may indicate the presence of a discrete water mass at abyssal depths during some glacial episodes an analysis of stage 6 records in different parts of the atlantic suggests that the water mass at that time may have been the antarctic bottom water

classification of deep sea fine grained sediments abstract most deep sea sediments contain one or more biogenic components and one dominant nonbiogenic component usually clay or silty clay we present a descriptive classification scheme in which deep sea fine grained sediments are placed within a three component system of calcareous biogenic siliceous biogenic and nonbiogenic components in a three step procedure the user assesses whether the dominant component is biogenic or nonbiogenic whether the dominant biogenic component is siliceous or calcareous and what the relative abundances of the biogenic components are within limits of 10 25 and 50 the terminology proposed is that commonly used by many sedimentologists with some refinements and greater precision in the use of terms

atlantic sediments glacial interglacial comparisons to assess the regional effects of glaciation on sedimentation in the atlantic ocean we compare sediment types distributions and rates between recent core top and last glacial maximum lgm 18 000 years b p stratigraphic levels based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than recent during both the recent and lgm carbonate content shows an east west asymmetry with western basins exhibiting lower carbonate values input of ice rafted detritus into the north atlantic during lgm time interrupts this topographic control on carbonate distribution considerably farther south than at present in the south atlantic this effect is minor comparison of lgm and recent sediment distributions indicates that the lgm seafloor was dominated by biogenic oozes calcareous clays and clays while the recent is dominated by biogenic oozes and marls coarse grained detritus is much more prevalent in lgm sediments derived not only from glacial input but also from fluvial and aeolian sources sedimentation rates calculated from lgm to recent sediment thickness in cores are 4 cm 1000 yr for most of the ocean higher rates are typical of the continental margin off the amazon river the north american basin and a small region off west equatorial africa

paleoceanography of the deep western boundary undercurrent on the north american continental margin for the past 25 000 yr temporal fluctuations of silt mean particle size and foraminiferal indices were used to examine fluctuations in velocity and position of the axis of the deep western boundary undercurrent dwbuc on the north american continental margin from 25 to 17 ka the dwbuc axis was 500 m shallower and farther inshore than its present position on the lower rise current speed was high from 25 to 20 ka and then waned until 17 ka between 17 and 7 ka the major axis of the dwbuc shallowed to 4000 m current speed increased from 17 to 11 ka but slowed from h to 7 ka since 7 ka the dwbuc axis has deepened to its modern position at 4900 m the zone of maximum carbonate dissolution remained below the dwbuc the most intense dissolution was from 22 to 9 ka and 5 to 2 ka highest abundance of uvigerina and highest percent benthic foraminifera were immediately above the dwbuc from 22 to 7 ka after which values of both parameters fell to near zero

transport of carbonate sediment in the western north atlantic evidence from oxygen and carbon isotopes abstract in most deep ocean environments the carbonate component is usually considered to be of pelagic origin deposited on the sea bed without extensive transport even when evidence exists that carbonate fractions have been transported the transport is usually viewed as being intrabasinal stable isotope analyses 18 o and 13 c of the carbonate contained in the fine fraction m of eight cores from the north american continental margin and the west flank of the mid atlantic ridge mar suggest that carbonate sedimentation patterns may be influenced by transport to a greater extent than previously recognized in holocene sections of all the cores the fine fraction and foraminiferal isotopic signals are comparable in cores from the flanks of the mar the fine fraction and foraminiferal isotopic signals remain comparable during the entire glacial interglacial cycle on the north american margin however the pattern is strikingly different starting about 10 ka and extending back into glacial times the fine fraction isotopic signal in margin cores becomes increasingly depleted reaching a value of 8 pdb the foraminiferal signal from these same cores follows the typical glacial interglacial pattern and gets heavier during glacial time the holocene correspondence of foraminiferal and fine fraction isotope curves throughout the north american basin suggests that both have the same intrabasinal pelagic source however in late glacial age sediments from the north american margin the divergence of foraminiferal and fine fraction isotope signals indicates different sources for each component based on the isotopic signals and the timing of changes in the signal a substantial proportion of the fine fraction carbonate on the north american margin appears to be derived from diagenetically altered carbonate rock this fine carbonate sediment probably resulted from physical erosion of carbonate rock by glacial processes and deposition in the north american basin by the retreating wisconsin glacier

fluids and trace element transport in subduction zones melt inclusion data from primitive arc basalts from mexico and kamchatka show clear positive correlations of fluid mobile element h 2 o ratios with the cl h 2 o ratio suggesting that the trace element content of subduction zone fluids is strongly enhanced by complexing with chloride this effect is observed for large ion lithophile lile elements e g rb and sr but also for the light rare earth elements ree e g la and ce as well as for u the correlations of these elements with cl h 2 o cannot be explained by the addition of sediment melts or slab melts to the mantle source since cl has no effect on the solubility or partitioning of these elements in silicate melt systems on the other hand the observed relationship of trace element abundance with cl is consistent with a large body of experimental data showing greatly enhanced partitioning into aqueous fluid upon addition of chloride accordingly it appears that a dilute cl bearing aqueous fluid is the main carrier of lile light ree and u from the slab to the source of melting in arcs moreover elevated ce h 2 o ratios clearly correlate with fluid salinity and therefore are not suitable as a slab geothermometer from a synopsis of experimental and melt inclusion data it is suggested that the importance of sediment or slab melting in the generation of arc magmas is likely overestimated while the effects of trace element scavenging from the mantle wedge may be underestimated moreover establishing reliable data sets for the fluid mineral partition coefficients of trace elements as a function of pressure temperature and salinity requires additional efforts since most of the commonly used experimental strategies have severe drawbacks and potential pitfalls

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

magnetic characterization of holocene sedimentation in the south atlantic surface sediment samples representative for the tropical and subtropical south atlantic 15 n to 40 s were investigated by isothermal magnetic methods to delineate magnetic mineral distribution patterns and to identify their predominant holocene climatic and oceanographic controls individual parameters reveal distinct yet frequently overlapping regional sedimentation characteristics a probabilistic fuzzy c means cluster analysis was applied to five concentration independent magnetic properties assessing magnetite to hematite ratios and diagnostic of bulk and fine particle magnetite grain size and coercivity spectra the resultant 10 cluster structures establish an oceanwide magnetic sediment classification scheme tracing the major terrigenous eolian and fluvial fluxes authigenic biogenic magnetite accumulation in high productivity areas transport by ocean current systems and effects of bottom water velocity on depositional regimes distinct dissimilarities in magnetic mineral inventories between the eastern and western basins of the south atlantic reflect prominent contrasts of both oceanic and continental influences

parasound echosounding comparison of analogue and digital echosounder records and physical properties of sediments from the equatorial south atlantic abstract the new parasound echosounding system krupp atlas elektronik gmbh kae recently installed on the german research vessel meteor proved to be a very useful tool in high frequency sediment echography during two recent cruises in the equatorial atlantic conventional echosounder records provide only a qualitative picture of the structure of sedimentary sequences in contrast the main advantages of the parasound system are its ability to change frequency and signal length of the incident signal and its access to seismogram data via an interface for digital data acquisition first we present some examples of typical echosounder records from the african continental margin off angola which illustrate the capabilities of the new instrument these records facilitate lateral correlation of even small scale sediment structures secondly we compare synthetic seismograms calculated from measured physical properties of sediment cores with analogue echosounder records this shows that strong changes in lithology due to turbidites or sand layers as well as climatically controlled variations in carbonate content can be correlated directly both with whole core physical property logs and with seismic reflections in the parasound echograms finally we focus on digitized echosounder records obtained at coring stations and compare these data with synthetic seismograms derived from the core logs this procedure enables us to evaluate the relative importance of interference phenomena vis a vis lithological variations in the generation of reflection horizons in deep sea sediment sequences depending on the wavelength of the source signal small layers either with sharp or gradational changes in lithology and physical properties may be undetectable by seismic methods owing to destructive interference in contrast often even very weak reflections in echosounder records can be related to small variations in lithology and thus to physical properties

holocene sediment fluxes in the northeast atlantic from 230thexcess and radiocarbon measurements radiocarbon and 230thexcess data from six ne atlantic box cores are considered the cores form a transect from the porcupine abyssal plain over the east thulean rise to the southern end of feni drift the chronology for the cores is established from bulk sediment carbonate radiocarbon data and reveals that sections exhibiting constant accumulation rates can be identified in all the cores with rates of 3 0 3 5 cm kyr 1 on the plain through the holocene and late holocene rates of 4 3 6 6 cm kyr 1 elsewhere five out of the six cores show accumulations of more 230thexcess than is produced in the overlying water column with the greatest inventories up to 225 of production in the cores from the rise and drift a size fraction comparison between two cores from the plain and rise reveals that the higher overall accumulation rates and 230thexcess inventories in the off plain cores are due to an increased fine 5 m component fraction whereas the flux of coarser material is similar to that received on the plain this suggests that the higher fluxes of materials observed are physically rather than biogeochemically driven and also that drift formation has been continuously active in the late holocene sections of all the cores where regular accumulation is defined by the radiocarbon data are modeled first by a linear radiocarbon age depth model and second by a constant rain 230thexcess 0 model prorated for the observed core inventories these modeling approaches yield historical mass accumulation rate estimates which are generally in reasonable agreement 30 but the differences observed appear to be well organized in time rather than random

magnetic characterisation of present day deep sea sediments and sources in the north atlantic the north atlantic plays a key role in global climate through formation of north atlantic deep water which drives the thermohaline circulation to understand past and future climate change it is essential to understand the processes occurring within the present day north atlantic but ocean wide studies of present day sediment distribution and sources are relatively sparse here we use magnetic measurements to characterise the surface sediments of the north atlantic and identify the major climatic and oceanographic controls on their magnetic signatures the magnetic data and subsequent cluster analysis identify distinct spatial patterns of sediment sources and transport pathways much of the sedimentary magnetic signal appears to be controlled by detrital inputs especially of windblown dust and ice rafted debris ird with a range of different sources these sediment transport pathways can be validated by making direct comparison of the sediment magnetic properties with source rocks and soils and with iceberg trajectory and observation data the spatial distributions of the ird dominated sediments substantiate those mapped previously using lithological tracers provide additional spatial information on sediment sources and pathways and suggest that deep water currents are less significant than proposed in controlling present day sediment mineralogy and distribution the data form a present day basis for comparison with glacial stage ird and dust distributions and modes of ocean circulation

impact of shallow living radiolarian flux variations on north atlantic cycladophora davisiana percentages abstract the cause of high cycladophora davisiana percentages a deep living maximum abundance 200 m radiolarian species in high latitude 45 late pleistocene deep sea sediments has been much debated in this paper we show that in four subpolar north atlantic cores these late pleistocene high percentages 20 result more from a reduction of other radiolarian flux predominantly shallow living species c davisiana flux relative to holocene flux these findings are similar to those reported from the north pacific hays et al 2013 in both oceans the late pleistocene to holocene shallow living species flux increase is larger than the concomitant decrease of c davisiana flux similarly high c davisiana percentages 20 found today in okhotsk sea holocene sediments kruglikova 1975 robertson 1975 morley and hays 1983 result from low radiolarian concentrations in the overlying dicothermal layer 20 150 m where year round temperatures are near 0 c it is likely that the high c davisiana percentages in north atlantic late pleistocene sediments were caused by a similar overlying stratification that had important biological consequences for radiolarians and other plankton a more significant time transgressive increase in shallow and others radiolarian assemblage flux occurs initially in the southernmost core in mid holocene ultimately recorded at the northernmost site during the late holocene here flux of the deep assemblage and c davisiana also increases

oceanographic control of biogenic opal and diatoms in surface sediments of the southwestern atlantic based on 66 surface sediment samples collected in the sw atlantic ocean between 27 and 50 s this study presents an overview of the spatial distribution of biogenic opal and diatom concentrations and diatom assemblages biogenic opal has highest values in the deepest pelagic stations and decreases toward the slope diatoms closely follow the spatial trend of opal diatom assemblages reflect the present day dominant hydrographical features antarctic diatoms are the main contributors to the preserved diatom community in core top sediments with coastal planktonic and tropical subtropical diatoms as secondary components dominance of antarctic diatoms between 35 and 50 s in the pelagic realm mirrors the northward displacement of antarctic source water masses characterized by high nutrient content and low salinity northward of ca 35 s the highest contribution of tropical subtropical pelagic diatoms typical for nutrient poor and high salinity waters matches the main southward path of the brazil current mixing of antarctic and tropical waters down up to 45 s is clearly illustrated by the diatom assemblage concentrations of biogenic opal and diatoms rather reflect the path of predominant water masses but are less correlated with surface water productivity in the sw atlantic

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

alteration of magnetic mineralogy at the sulfate methane transition analysis of sediments from the argentine continental slope on the argentine continental slope off the rio de la plata estuary the sulfate methane transition smt has been encountered at shallow depths of a few meters below the seafloor at around this horizon where sulfate diffusing downward from the bottom water is met and reduced by methane rising from deeper in the sediment column intense alteration affects the detrital magnetic mineral assemblage less than 10 of the dominant primary low coercivity ferrimagnetic titano magnetite remains after alteration in the upper part of the suboxic environment underlying the iron redox boundary which is located at a depth of 0 1 m approximately 60 of the finer grained detrital fraction is already dissolved while the high coercivity minerals are relatively unaffected in the suboxic environment large portions 40 are diagenetically dissolved in the sulfidic smt zone nevertheless the characteristics of the magnetic residue are entirely controlled by a high coercivity mineral assemblage unlike common observations that diagenetic alteration produces coarser magnetic grain sizes in suboxic milieus a distinct overall fining is found in the sulfidic zone different factors should contribute to this effect scanning electron microscope analysis combined with x ray microanalysis identified fine grained titano magnetite preserved as inclusions in silicates and between high ti titanohematite lamellae and possibly of prime importance a comprehensive fragmentation of larger grains in the course of maghemitization the only secondary iron sulfide mineral detected is pyrite which is present as clusters of euhedral crystals or directly replaces titano magnetite the thermomagnetic measurements did not provide evidence for the presence of ferrimagnetic sulfides such as greigite different from other studies reporting a marked magnetic enhancement at around the smt due to the precipitation and preservation of such metastable ferrimagnetic sulfides a complete pyritization process will cause a distinct magnetic depletion like in the present case 2005 elsevier b v all rights reserved

bioturbation and holocene sediment accumulation fluxes in the north east atlantic ocean benthic boundary layer experiment sites bioturbation and holocene sediment accumulation are quantified in the three experimental areas of the benthic boundary layer benbo programme by means of the natural radionuclides 14c and 210pb and the artificial radionuclides 137cs and 241am the holocene accumulation rates determined by the radiocarbon method are 4 4 and 6 5 cm kyr 1 at sites b rockall plateau 1100 m water depth and c feni drift 1925 m water depth respectively accumulation at site a situated between feni drift and porcupine bank at 3570 m water depth was interrupted by an erosional event in the mid holocene which removed 0 25 m or more of the uppermost sediment present at that time the estimated accumulation rate since that event is 2 1 cm kyr 1 different estimates of surficial bioturbation mixing depths at site b are returned by the 210pbexcess and 14c methods with the former indicating 10 cm and the latter unusually deep at 17 cm at site c 210pbexcess and the fallout radionuclides 137cs and 241am are present in two distinctly separated depth zones with the deepest mixing down to 15 cm similar to the 14c mixed layer depth this is ascribed to deep burrowing by sipunculid or echiuran worms at site c and similar deep mixing is inferred to be necessary at site b to produce the differences in mixed layer depths derived from the longer and shorter lived radionuclide profiles although the deep burrowing episodes must be rare 1 event per 102 yr the greater accumulation rate at site c compared with site b is produced by an enhanced flux of current driven clay and silt sized material this fine material both dilutes the caco3 content of the site c sediment and is responsible for the higher corg content observed at site c compared with site b unlike the site b and c sediments which are fine grained the coarse 63 125 m size fraction is the most abundant size class in the late holocene sediments at site a suggesting that the sediments at this location are winnowed

distribution of major elements in atlantic surface sediments 36 n 49 s imprint of terrigenous input and continental weathering 1 numerous studies use major element concentrations measured on continental margin sediments to reconstruct terrestrial climate variations the choice and interpretation of climate proxies however differ from site to site here we map the concentrations of major elements ca fe al si ti k in atlantic surface sediments 36 n 49 s to assess the factors influencing the geochemistry of atlantic hemipelagic sediments and the potential of elemental ratios to reconstruct different terrestrial climate regimes high concentrations of terrigenous elements and low ca concentrations along the african and south american margins reflect the dominance of terrigenous input in these regions single element concentrations and elemental ratios including ca e g fe ca are too sensitive to dilution effects enhanced biological productivity carbonate dissolution to allow reliable reconstructions of terrestrial climate other elemental ratios reflect the composition of terrigenous material and mirror the climatic conditions within the continental catchment areas the atlantic distribution of ti al supports its use as a proxy for eolian versus fluvial input in regions of dust deposition that are not affected by the input of mafic rock material the spatial distributions of al si and fe k reflect the relative input of intensively weathered material from humid regions versus slightly weathered particles from drier areas high biogenic opal input however influences the al si ratio fe k is sensitive to the input of mafic material and the topography of andean river drainage basins both ratios are suitable to reconstruct african and south american climatic zones characterized by different intensities of chemical weathering in well understood environmental settings

tracking rainfall in the northern mediterranean borderlands during sapropel deposition the role of mid latitude precipitation in the hydrological forcing leading to the deposition of sapropels in the mediterranean sea remains unclear the new gdec 4 2 borehole east corsica margin northern tyrrhenian sea provides the first precisely dated evidence for enhanced rainfall in the western mediterranean during warm intervals of interglacial periods over the last 547 kyr comparison of gdec 4 2 proxy records with pollen sequences and speleothems from the central and eastern mediterranean reveals that these pluvial events were regional in character and occurred probably in response to the intensification of the mediterranean storm track along the northern mediterranean borderlands in autumn winter our dataset suggests that the timing of maxima of the mediterranean autumn winter storm track precipitation coincide with that of the north african summer monsoon and sapropel deposition besides highlighting a close coupling between mid and low latitude hydrological changes our findings suggest that during warm intervals of interglacial periods the reduced sea surface water salinities together with the high flux of nutrient and organic matter produced by the monsoonal nile and wadi systems floods were maintained throughout the winter by the mediterranean rainfall this provides an important additional constraint on the hydrological perturbation causing sapropel formation

millimeter scale profiling of abyssal marine sediments role of bioturbation in early sterol diagenesis abstract near surface sediments from an abyssal northeast atlantic site were sectioned using a newly designed precision core extruder pce downcore profiles of excess 210 pb and sterols showed pronounced millimeter scale variability reflecting specific degradation and bioturbation processes excess 210 pb and sterol concentrations decreased sharply in the uppermost 5 mm and pronounced subsurface maxima were present stonol stenol ratios and the relative abundance of cholesterol increased below 10 mm indicating biodegradation involving 5 double bond hydrogenation c 24 dealkylation and or de novo synthesis sterol profiles indicate that early diagenesis of labile compounds is dominated by processes operating near the sediment water interface and that the penetration of labile material into oxic sediments is largely controlled by advective processes associated with infaunal feeding rather than diffusive like mixing

ocean circulation at the last glacial maximum a combined modeling and magnetic proxy based study 1 formation of north atlantic deep water nadw is an important component of the ocean thermohaline circulation but debate exists over the ocean circulation state during glacial stages some geological and modeling studies suggest decreased nadw and increased formation of southern ocean deep water during the last glacial maximum lgm others indicate similar or higher rates of nadw advection here we test three different potential lgm ocean states by comparing the modeled iceberg trajectories each produces with magnetically mapped patterns and sources of lgm ice rafted debris ird the three lgm states are characterized by vigorous nadw formation deepwater production in the southern ocean and a third intermediate state with southern ocean deepwater formation but also some north atlantic intermediate water formation cluster analysis of sediment magnetic properties was used to characterize north atlantic ird patterns and sources which match most closely iceberg trajectories arising from some combination of the southern sinking and intermediate ocean circulation states the magnetic data indicate two major ird sources fennoscandia and greenland iceland and one minor source the st lawrence region the model and magnetic data suggest that the lgm north atlantic circulation was dominated by a cyclonic central north atlantic gyre separated from the north atlantic current which was displaced south of 42 n

sediment accumulation rates west of the mid atlantic ridge 35 n abstract although carbonate curves have a long history of use for temporal correlation only limited agreement concerning the reasons for down core carbonate variations has been reached in this study these variations are examined by analyzing absolute accumulation rates of both carbonate and terrigenous sediment components carbonate content was determined in nine cores from approximately 3000 5000 m water depth down core variation in carbonate was correlated to an oxygen isotope curve to establish a down core time stratigraphy weight percent carbonate carbonate accumulation rate and terrigenous sediment accumulation rate were plotted as a function of water depth and time 0 130 000 yrs b p the weight percent carbonate plot indicates that carbonate content decreases with increasing water depth however the carbonate accumulation rate data demonstrates that this decrease in weight percent carbonate does not result from a decrease in the carbonate accumulation rate in the deeper cores the accumulation rate of carbonate actually increases in these deep cores the increase in carbonate accumulation rate is offset by a larger increase in the accumulation rate of terrigenous sediment resulting in a decrease in weight percent carbonate high accumulation rates of both carbonate and terrigenous sediment in cores below 4250 m appears to result from transport and redeposition of sediment most of the carbonate sediment deposited in these deep cores appears to be derived from shallow areas of the mid atlantic ridge mar the terrigenous sediment probably results from deposition by deep currents

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

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

the high velocity core of the western boundary undercurrent at the base of the u s continental rise the western boundary undercurrent is a high velocity contour following bottom current that flows southwesterly on the u s atlantic continental margin a high velocity core of the western boundary undercurrent is delineated by an analysis of underlying sediments which are characterized by coarse particle sizes and efficiently aligned magnetic grains in a zone from 4440 meters at the base of the rise to 5200 meters on the adjacent abyssal plain

new techniques in sediment core analysis an introduction marine sediment cores are the fundamental data source for information on seabed character depositional history and environmental change they provide raw data for a wide range of research including studies of global climate change palaeoceanography slope stability oil exploration pollution assessment and control and sea floor surveys for laying cables pipelines and siting of sea floor structures during the last three decades a varied suite of new technologies have been developed to analyse cores often non destructively to produce high quality closely spaced co located downcore measurements characterizing sediment physical properties geochemistry and composition in unprecedented detail distributions of a variety of palaeoenvironmentally significant proxies can now be logged at decadal and in some cases even annual or subannual scales allowing detailed insights into the history of climate and associated environmental change these advances have had a profound effect on many aspects of the earth sciences particularly palaeoceanography in this paper we review recent advances in analytical and logging technology and their application to the analysis of sediment cores developments in providing access to core data and associated datasets and data mining technology in order to integrate and interpret new and legacy datasets within the wider context of sea floor studies are also discussed despite the great advances in this field however challenges remain particularly in the development of standard measurement and calibration methodologies and in the development of data analysis methods new data visualization tools and techniques need to be developed to optimize the interpretation process and maximize scientific value amplified collaboration environments and tools are needed in order to capitalize on our analysis and interpretation capability of large multi parameter datasets sophisticated yet simple to use searchable internet databases with universal access and secure long term funding and data products resulting in user defined data mining query and display so far pioneered in the usa and australia provide robust models for efficient and effective core data stewardship

depositional fluxes palaeoproductivity and ice rafting in the ne atlantic over the past 30 ka over the last 30 ka sediment flux to the northeast atlantic ocean has been strongly influenced by the growth and decay of northern hemisphere ice sheets input of ice rafted detritus the migration of the polar front and associated changes in patterns of biological productivity we examined cores from 47 n to 60 n along 20 w to determine the flux of components including carbonate organic carbon and terrigenous material and divided into size fractions during the glacial period fine carbonate flux was low and ice rafted input high burial flux during the holocene became dominated by coccolith and foraminiferal carbonate with minor organic matter and biogenic silica estimates of palaeoproductivity are ambiguous a method which corrects for water depth and sedimentation rate suggests no clear glacial to holocene change whereas a method based on percentage of organic carbon suggests increased productivity from glacial to holocene of around 60 sites of sediment focusing saw a change from enhanced fine terrrigenous flux in the glacial to enhanced fine carbonate in the holocene after compensating for sediment focusing glacial ice rafted flux distribution shows a decrease from south to north across the area reflecting cyclonic surface water circulation deposition of ice rafted detritus during heinrich events h1 and h2 led to enhanced preservation of organic matter immediately beneath the layers indicating a rapid accumulation rate

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

terrigenous fluxes at the celtic margin during the last glacial cycle the sedimentary sections of three cores from the celtic margin provide high resolution records of the terrigenous fluxes during the last glacial cycle a total of 21 14 c ams dates allow us to define age models with a resolution better than 100 yr during critical periods such as heinrich events 1 and 2 maximum sedimentary fluxes occurred at the meriadzek terrace site during the last glacial maximum lgm detailed x ray imagery of core md95 2002 from the meriadzek terrace shows no sedimentary structures suggestive of either deposition from high density turbidity currents or significant erosion two paroxysmal terrigenous flux episodes have been identified the first occurred after the deposition of heinrich event 2 canadian ice rafted debris ird and includes ird from european sources we suggest that the second represents an episode of deposition from turbid plumes which precedes ird deposition associated with heinrich event 1 at the end of marine isotopic stage 2 mis 2 and the beginning of mis 1 the highest fluxes are recorded on the whittard ridge where they correspond to deposition from turbidity current overflows canadian icebergs have rafted debris at the celtic margin during heinrich events 1 2 4 and 5 the highresolution records of heinrich events 1 and 2 show that in both cases the arrival of the canadian icebergs was preceded by a european ice rafting precursor event which took place about 1 1 5 kyr before two rafting episodes of european ird also occurred immediately after heinrich event 2 and just before heinrich event 1 the terrigenous fluxes recorded in core md95 2002 during the lgm are the highest reported at hemipelagic sites from the northwestern european margin the magnitude of the canadian ird fluxes at meriadzek terrace is similar to those from oceanic sites 2002 elsevier science b v all rights reserved

sediment flux patterns in the northeastern atlantic variability since the last interglacial abstract the distribution of terrigenous and carbonate absolute accumulation rates in the northeastern atlantic during the last climatic cycle shows that climate and sediment accumulation are closely coupled either directly or through oceanic circulation and eustatic variation the strong contrast between the glacial and holocene flux distribution is related to oceanic circulation changes either surface circulation which governs both the ice rafting supply and the planktonic biogenic production or more particularly deep circulations via the reinitiation of the iceland scotland overflow glacial erosion and the low sea level stand enhance the terrigenous supply but the holocene deep circulation reinforcement leads to important material reworking as a consequence an almost constant average sediment flux is obtained 4g 2 ky 1 during the holocene compared to 4 7 g cm 2 ky 1 during the glacial period during the holocene period the notable increase in mean carbonate flux from 1 5 to 3 g cm 2 ky 1 is associated with carbonate biogenic production but the carbonate flux distribution shows the influence of redistributive agents on margins fluxes do not simply decrease from continental sources to the oceanic basin eustatic drops leads to a shift in the areas of preferential accumulation from the upper to the lower slope during the deglacial warming period the fluxes are respectively an average of two and three times higher than during the holocene and the glacial periods their importance highlights the major impact of rapid climatic changes finally local conditions the location of terrigenous sources and the presence of contour currents are among the many factors which will modify the trends observed on a global scale

global deep sea burial rate of calcium carbonate during the last glacial maximum global databases concentrations rates in holocene and last glacial of calcium carbonate and mass accumulation maximum sediments were used to estimate the deep sea sedimentary calcium carbonate burial rate during these two time intervals sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region mean noncarbonate accumulation rates were estimated within each of nine regions determined by the distribution and nature of the accumulation rate data for core top sediments data coverage 67 of the high calcite the regions of reasonable encompass 75 sediments globally and within these regions we estimate an accumulation rate of 55 9 3 6x1011 mol yr 1 the same regions cover 48 of glacial high caco3 sediments the smaller fraction is due to a shift of calcite deposition to the poorly sampled south pacific and total 44 1 6 0x1011 mol yr 1 projecting to 100 coverage south and total 44 1 6 0x1011 both estimates yields accumulation estimates of 8 3x1012 mol yr 1 today and 9 2x1012 mol yr 1 during glacial time this is little better than a guess given the incomplete data coverage but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decreasein shallow water burial during glacial time

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

determining the composition of late quaternary marine sediments from nuv vis and nir diffuse reflectance spectra abstract as the length of marine cores increases and sampling intervals decrease the need for rapid and inexpensive means of determining sediment composition has become apparent in this study we examine one potentially useful technique for assessing compositional changes in marine cores diffuse reflectance spectrophotometry we examined nearultraviolet visible and near infrared reflectance spectra from five data sets each data set consists of calibration samples and test samples the calibration samples spectra were related to a sediment component using multiple linear regression the resulting regression or calibration equations were then evaluated using the test samples calibration equations were written relating spectra to several sediment components including carbonate atlantic and east pacific rise odp site 847 organic carbon content atlantic and east pacific rise and opal content east pacific rise the correlation coefficients for the regression equations ranged from a high of 0 99 for carbonate and opal at odp site 847 to a low of 0 97 for atlantic carbonate indicating that spectral variations are highly correlated to sediment composition all of the equations include a substantial number of variables from shorter visible and longer near ultraviolet wavelengths suggesting that these wavelengths are especially important for devices designed specifically to scan marine cores although equations for estimating organic and carbonate content appear independent of other sediment components the opal equation is strongly dependent on carbonate content indicating that opal concentration is correlated to carbonate content tests of the calibration equations indicated that all our equations reasonably estimate the pattern of changes either down core or in surface sediments where our spectral estimates have difficulty is with absolute values frequently over or underestimating observed values by a substantial amount within these limitations diffuse reflectance spectrophotometry can be a useful tool for characterizing marine cores and as our understanding of the relationship between spectra and mineralogy improves so will estimates of absolute values

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition