increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

production and destruction control of biogenous sedimentation in the tropical atlantic 0 300 000 years b p late pleistocene signals of calcium carbonate organic carbon and opaline silica concentration and accumulation are documented in a series of cores from a zonal meridional depth transect in the equatorial atlantic ocean to reconstruct the regional sedimentary history spectral analysis reveals that maxima and minima in biogenous sedimentation occur with glacial interglacial cyclicity as a function of both 1 primary production at the sea surface modulated by orbitally forced variation in trade wind zonality and 2 destruction at the seafloor by variation in the chemical character of advected intermediate and deep water from high latitudes modulated by high latitude ice volume from these results a pattern emerges in which the relative proportion of signal variance from the productivity signal centered on the precessional 23 kyr band decreases while that of the destruction signal centered on the obliquity 41 kyr and eccentricity 100 kyr periods increases below 3600 m ocean depth

metal contents of phytoplankton and labile particulate material in the north atlantic ocean abstract phytoplankton contribute significantly to global c cycling and serve as the base of ocean food webs phytoplankton require trace metals for growth and also mediate the vertical distributions of many metals in the ocean we collected bulk particulate material and individual phytoplankton cells from the upper water column

variability of upwelling off nw africa during the latest quaternary diatom evidence diatom abundance and species composition were quantitatively studied in two latest quaternary 130 ka to the present sequences from the continental margin of northwest africa off this region coastal upwelling is well developed under the influence of the ne trade winds variations in diatom abundance in these cores are inferred to represent changes caused by varying degrees of the upwelling fertility times of high productivity are marked by high relative frequencies of chaetoceros while low productivity is marked by the dominance of aulacoseira granulata upwelling increased during glacial episodes isotopic stages 2 4 and 6 relative to isotopic stages 1 and 5 during the late holocene primary productivity levels are similar to those for stage 5 but in the early holocene upwelling intensities seem to have been weaker than today the paleoproductivity reconstruction based on the diatom record is supported by paleoproductivity estimations based on the organic carbon content of the sediments sarnthein et al 1987a

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

mapping climatological seasonal variations of surface currents in the tropical atlantic using ship drifts the seasonal variability of current velocities in the tropical atlantic was studied by grouping ship drift velocity observations into 2 5 boxes and calculating monthly mean velocity values these values were used to calculate and map the annual mean velocity the seasonal variation about the mean the annual and semiannual harmonics and the first two empirical orthogonal functions eofs the seasonal variation is primarily zonal in the equatorial band and in the north equatorial countercurrent necc and primarily alongshore near the coast of south america maxima of seasonal variation of 23 cm s are centered in the necc near 6 n 42 5 w and in the gulf of guinea near 2 n 7 5 w most 80 of the variance in the necc and along the western boundary of the area studied has an annual period most of the variance along the equator in the mid atlantic has a semiannual period over the whole region 49 of the seasonal variance is explained by the annual harmonic and 69 is explained by a combination of the annual and semiannual harmonics the second eof contains 29 of the variance of the data set and shows a simultaneous speeding slowing of the major equatorial currents the south equatorial current sec the north brazil current the necc and the guinea current along their principal axes of variation with a concurrent slowing speeding of the guyana current and the brazil current the pattern of variation resembles a large equatorial gyre centered along 4 n that flows clockwise from may to september and counterclockwise most of the rest of the year the first eof accounts for 35 of the variance and shows a simultaneous speeding slowing of eastward velocity from 5 s to 10 n except in the western sec the western end of the north brazil current and the guinea current the out of phase fluctuations apparent in the western sec near the equator are explained by the slowing and reversal of the south equatorial current near 2 n 40 w between april and june this slowing of the sec is associated with the start up of the necc which accelerates eastward in may june and july and flows eastward across the atlantic from july through december the sec divides seasonally near the eastern tip of brazil where residual alongshore velocities are northward for half the year peaking during may and june and southward for the other half of the year a second division can be seen north of the amazon where the north brazil current continues up the coast into the guyana current during the first half of the year but partially retroflects into the necc during the last half of the year a fast eastward flow in the necc coincides with below average velocities in the guyana current and above average velocities in the western sections of the north brazil current and the sec north of the equator

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

an overview of dissolved fe and mn distributions during the 2010 2011 u s geotraces north atlantic cruises geotraces ga03 abstract high resolution dissolved fe dfe and dissolved mn dmn distributions were obtained using a trace metal clean rosette during the geotraces ga03 zonal transect cruises usgt10 and usgt11 across the north atlantic ocean this manuscript provides a general overview of the dfe as well as dmn and dissolved al dal distributions that reveal several fe inputs at varying depths across the study region elevated dfe concentrations correlate with elevated dal concentrations in the surface waters of the subtropical gyre indicating a significant atmospheric source of fe in contrast there is no apparent significant dust source for mn in the subsurface waters dfe maxima are a result of the remineralization process as revealed by their correspondence with dissolved oxygen minima within the oxygen minimum the ratio of dfe to apparent oxygen utilization aou is lower than would be expected from the measured fe content of surface water phytoplankton suggesting that a significant amount of dfe that is remineralized at depth 63 90 is subsequently scavenged from the water column the rate of remineralization which is based on the slope of dfe aou plot is similar across a wide area of the north atlantic in addition to the remineralization process sedimentary inputs are apparent from elevated dmn signals in the eastern basin particularly near the african coast in the western basin sedimentary input is also occurring along the advective flow path of the upper labrador sea water ulsw as ulsw transits along the north american continental shelf region the largest dfe anomaly 68 nm which also corresponds to a dmn anomaly up to 33 nm is seen in the neutrally buoyant hydrothermal plume sampled over the mid atlantic ridge and that signal is visible for 500 km to the west of the ridge

concentrations provenance and flux of aerosol trace elements during us geotraces western arctic cruise gn01 abstract the arctic region is undergoing significant changes in climate with a notable decrease in summertime sea ice coverage over the past three decades this trend means an increasing proportion of arctic ocean surface waters can receive direct deposition of material from the atmosphere potentially influencing marine biogeochemical cycles and delivery of pollutants to the arctic ecosystem here we present aerosol concentrations of selected trace elements al ti v mn fe co ni cu zn cd and pb measured during the us geotraces western arctic cruise gn01 also known as hly1502 in august october 2015 concentrations of lithogenic elements al ti v mn fe and co were similar to those measured in remote and predominantly marine influenced air masses in previous studies reflecting the remoteness of the arctic ocean from major dust sources concentrations of ni cu zn pb and cd showed significant enrichments over crustal values and were often of similar magnitude to concentrations measured over the north atlantic in air masses of north american or european provenance we use 7be inventory and flux data from gn01 to estimate a bulk atmospheric deposition velocity during the study period and combine it with our aerosol concentrations to calculate atmospheric deposition fluxes of the trace elements in the arctic region during late summer the resulting estimates for mineral dust and fe deposition fall at the low end of global estimates and confirm the arctic ocean as a low dust environment during the summer months this article is part of a special issue entitled conway geotraces edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean empirical estimates for island sites in the north atlantic the results of several recent studies challenge the reigning paradigm that continental soil dust provides the only significant atmospheric source of dissolved iron to the surface ocean this evidence includes correlations between the operational solubility of aerosol iron and atmospheric loadings of black carbon and aluminum normalized vanadium and nickel each of which are associated with emissions from the combustion of fossil fuel oil these observations suggest that the relative solubility of aerosol iron hence the eolian flux of soluble iron to the surface ocean may be significantly impacted by anthropogenic oil combustion products using recent field data from the bermuda region we have developed an empirical method to estimate the solubility of aerosol iron using bulk aerosol concentrations of fe v and al we apply this method to a large body of published data from the aeroce program for north atlantic island sites on tenerife barbados bermuda and ireland where the relative proportions of anthropogenic aerosols range from minor to major respectively our aerosol iron solubility estimates suggest that anthropogenic emissions contribute approximately 70 and 85 of the annual dry deposition of soluble iron to the surface ocean near bermuda and ireland respectively implying that human activities have profoundly affected the iron budget of the north atlantic region the annual mean dry deposition of soluble iron at barbados and izana is dominated by soil dust the anthropogenic contribution at these two sites ranges from 12 to 30 and is highly dependent on the soil dust solubility of fe employed in the model the low end 12 estimate appears to be more representative of these high dust sites

biogeochemistry of dissolved arsenic in the temperate to tropical north atlantic ocean abstract the biogeochemical cycle of arsenic was examined in the water column across the north atlantic from 39 to 17 n as part of the us geotraces north atlantic study geotraces section ga03 results show limited nutrient like distribution of as5 and upper ocean maxima in as3 and methylated as as found in many other studies in the oligotrophic water masses microbial communities i e phytoplankton appear to favor the reduction to as3 instead of methylation as detoxification of as5 taken up during phosphorus p limitation due to their chemical similarities the depth integrated average concentrations in the mixed layer depth of as3 in the western and eastern atlantic ocean were 1 30 1 14 nmol l 1 n 4 and 0 65 n 2 respectively and rose to 3 30 nmol l 1 n 2 in the central atlantic ocean no pattern was observed for as5 15 7 2 8 nmol l 1 n 8 and methylated species were detected occasionally below 0 41 nmol l 1 in the mixed layer based on significant correlations between phosphate alkaline phosphate activity apa a conventional proxy for p limitation and as3 we conclude that as3 is a good proxy for p limitation within the upper water column similar to our earlier evaluation of surface data mass balances for the mixed layer show that atmospheric inputs of as5 can compensate for the losses via export fluxes and microbial reduction to as3 the cycling of as3 is more complex with sources from as5 reduction and losses due to photochemical and microbial induced oxidation the resulting residence time of as3 with respect to these processes can be as short as 0 7 3 days unlike as5 atmospheric inputs of as3 cannot balance the oxidative losses and the short residence time further limits horizontal and vertical advective diffusive inputs it appears that reduction of as5 coupled with detoxification and general microbial reduction are the sources of as3 in the oceanic mixed layer while as3 production during as5 detoxification has been well studied the generic microbial reduction of as5 to as3 requires a more thorough investigation

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

meridional distribution of dissolved manganese in the tropical and equatorial pacific abstract the distribution of dissolved mn dmn was studied in the tropical and equatorial pacific along a meridional transect beginning at station aloha 22 45 n 158 w extending southwards to 7 s along 158 w results show that in the surface ocean 6000 km from the continents which suggests that dmn in the deep open ocean is strongly affected by remineralization the dmn aou linear relationship n 37 r 0 87 that we found in this work is consistent with culture studies and can be applied to mn models to reproduce the observed open ocean mn concentrations in deep waters

sapropelic deposits in a sediment from the guinea basin south atlantic until recently it has been generally thought that a stagnant water column is a prerequisite to the formation of organic rich deposits in deep water marine sediments a belief best exemplified by studies on the eastern mediterranean sapropels many workers have assumed that following the hydrological isolation of the deep waters stagnation of the eastern mediterranean basins and the concomitant development of anoxic conditions occurred before the deposition of the sapropelic layers1 10 opposing arguments suggesting a role for increased marine productivity have however been put forward both specifically with respect to the eastern mediterranean sapropels11 12 and more generally regarding deep water organic rich deposits13 15 we report here the discovery of sapropelic layers 0 5 organic carbon 16 in a recent sediment core from a deep water site in the guinea basin it is thought most unlikely that stagnant conditions could prevail in the water column at this site and preliminary analyses of the sediments suggest that the organic rich deposits have been a direct result of increased productivity in the overlying water column the most recent occurring about 18 000 yr ago and coinciding with the last glacial maximum

hydrographic and current observations on the continental slope and shelf of the western equatorial atlantic abstract hydrographic and current profiling data from december 1980 and current meter data obtained between september 1980 and november 1981 from the continental slope and shelf of the western equatorial atlantic between 2 and 7 n are used to describe the character of the north brazil coastal current nbcc system hydrographic data and the profiling results show that the nbcc has three distinct branches during the boreal fall in the near surface a strong current flows northwestward parallel to the coast at least as far as 6 n current speed within the near surface nbcc over a one year period were between 75 and 250 cm s 1 while the transport in december 1980 was between 15 and 20 106 m3 s 1 there was a southeastward near surface flow farther offshore which appears to be the return of the nbcc the ultimate destination of which is the north equatorial countercurrent offshore of the southeastward flow was a portion of a low salinity lens of amazon water the waters within and below the thermocline

marine sepiolite in middle permian carbonates of south china implications for secular variation of phanerozoic seawater chemistry abstract it is now widely accepted that the composition of seawater varied significantly during the phanerozoic and that the mg ca ratio of seawater is a major factor in synchronized secular oscillations in the mineralogical composition of marine evaporites and nonskeletal as well as biogenic carbonates however the nature of the mg sink is still subject to debate we describe early diagenetic sepiolite from the chihsia formation middle permian of south china the mg incorporated in sepiolite likely was furnished by stabilization of high mg calcite and silica was derived from siliceous fossils two factors facilitated the accumulation of sepiolite in the chihsia formation the first is a chihsian depositional environment of an intra oceanic carbonate platform that lacked detrital terrestrial input which enhanced the availability of biogenic silica for sepiolite formation the second is the chemical composition of permian seawater as the precipitation of high mg calcite was aided by a high mg ca ratio associated with an aragonite sea the formation of sepiolite is significant in constraining the recycling flux of mg during recrystallization of carbonate sediments with a high proportion of high mg calcite periods of aragonite seas worldwide major occurrences of marine sepiolite and palygorskite in the phanerozoic correlate with periods of aragonite seas this temporal distribution implies that minerals of the sepiolite palygorskite group play an important role in the geochemical recycling of mg and that major sepiolite and palygorskite deposits indicate episodes of high mg concentrations in seawater the formation of sepiolite also was probably related to an abundance of silica secreting organisms which interacted with the chemical evolution of phanerozoic seawater in addition authigenic sepiolite and palygorskite are not indicators of arid and semiarid climates

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

geologic time series from deep sea sediments time scales and distortion by bioturbation abstract in order to evaluate the time and frequency domain characteristics of geologic time series obtained from deep sea sediments two important problems must be considered first an accurate time scale must be established for the sediment records to be studied an accurate time scale is a basic requirement for such techniques as spectral and cross spectral analysis secondly the distortion of a geologic time series by sedimentation processes such as bioturbation must be considered if inferences are to be made about the mechanisms controlling climatic and oceanographic processes reflected in the geologic record recently it has been suggested that the periodic components in paleoclimatic records which can be related to variations in the earth s orbital parameters can be used as a means for providing very detailed control for late pleistocene sediment sections a time scale is estimated by tuning an individual frequency component in a climate record to an orbital parameter the tuning procedure commonly uses the technique of bandpass filtering which removes all frequency components except the one equivalent to an orbital parameter and then adjusting the geologic time scale so that the filtered record and orbital record align since bandpass filtering will produce a periodic record from any data set a question is raised as to the circularity of this tuning approach a series of numerical experiments using synthetic time series are used to determine if the tuning of a geologic record artificially induces improved correlation and increased periodic character in a climatic record these experiments indicate that the tuning does not artificially induce these effects thus it is suggested that the careful use of orbital tuning provides a powerful means of defining a geologic time scale the degree to which bioturbation distorts a paleoclimatic record is studied by comparing the spectra of oxygen isotopic records obtained from cores with sedimentation rates ranging from 1 to 12 cm 1000 yr 1 it is shown that the systematic change in the variance spectra of these records that is predicted by models of bioturbation cannot be observed for sedimentation rates greater than 2 cm 1000 yr 1 this can be explained in part if bioturbation is a function of sedimentation rates if this is the case then bioturbation must proceed to depth of tens to hundreds of centimeters however it seems likely that the degree to which bioturbation alters the climate signal preserved in deep sea sediment cores has been overestimated

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

reconstructing past particle fluxes in the tropical atlantic ocean using a research strategy analogous to modern sediment trap studies sediment accumulation patterns on submarine rises can be interpreted in terms of past ocean chemistry and circulation we have followed this research strategy to reconstruct the history of surface water productivity and deep water chemistry and circulation in the eastern equatorial atlantic sierra leone rise and western equatorial atlantic ceara rise during the last glacial maximum 18 000 b p on shallow sections of these rises at depths with little carbonate particle degradation we assume that the accumulation of skeletal carbonate approximates the carbonate production rate in surface water during the last glacial maximum the rate of carbonate productivity was lower in the eastern atlantic than it is today while the western atlantic exhibited no glacial interglacial difference in carbonate productivity based on the difference in carbonate accumulation rates between shallow and deep cores on the rises we observed greater dissolution in both basins during the last glaciation the eastern atlantic always had a lower rate of dissolution than the western atlantic despite having deep water with a lower 13c during the last glacial maximum organic carbon accumulation in the eastern atlantic increased with depth in the water column during the last glaciation suggesting that there was a bathymetric decrease in dissolved oxygen concentration at that time these observations are consistent with a glacial decrease in the production rate of northern source deep water during the last glaciation at that time the mixing zone between northern source and southern source deep water migrated to the north in the atlantic resulting in a greater proportion of corrosive southern source deep water in the western atlantic and entering the eastern atlantic through low latitude fracture zones today the ratio of northern and southern components entering the eastern atlantic is about 4 1 based on 13c and carbonate accumulation our best estimate of this ratio during the last glaciation is 1 1

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

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

impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron evidence from the sargasso sea we report empirical estimates of the fractional solubility of aerosol iron over the sargasso sea during periods characterized by high concentrations of saharan dust summer 2003 and by low concentrations of aerosols in north american maritime north atlantic air masses spring 2004 and early summer 2004 we observed a strong inverse relationship between the operational solubility of aerosol iron defined using a flow through deionized water leaching protocol and the total concentration of aerosol iron whereby the operational solubility of aerosol iron was elevated when total aerosol iron loadings were low this relationship is consistent with source dependent differences in the solubility characteristics of our aerosol samples and can be described by a simple mixing model wherein bulk aerosols represent a conservative mixture of two air mass end members that carry different aerosol types saharan air which contains a relatively high loading of aerosol iron 27 8 nmol fe m 3 that has a low fractional solubility 0 44 and north american air which contains a relatively low concentration of aerosol iron 0 5 nmol fe m 3 that has a high fractional solubility 19 historical data for aerosols collected on bermuda indicate that the low iron loadings associated with north american air masses are typically accompanied by elevated v al fe al and v mn mass ratios in the bulk aerosol relative to saharan dust which are indicative of anthropogenic fuel combustion products the identification of similar compositional trends in our sargasso sea aerosol samples leads us to suggest that the elevated solubility of iron in the aerosols associated with north american air masses reflects the presence of anthropogenic combustion products which contain iron that is readily soluble relative to iron in saharan soil dust we thus propose that the source dependent composition of aerosol particles specifically the relative proportion of anthropogenic combustion products is a primary determinant for the fractional solubility of aerosol iron over the sargasso sea this hypothesis implies that anthropogenic combustion emissions could play a significant role in determining the atmospheric input of soluble iron to the surface ocean

a new mechanism for decreasing north atlantic deep water production rates during the pleistocene geological data suggest that north atlantic deep water nadw production rates decreased during the pleistocene we apply a coupled ice mixed layer model for vertical overturn in the marginal ice zone hakkinen 1987a to propose an explanation for such a decrease the model predicts that prevailing wind direction is important in preconditioning of the water column along the marginal ice zone miz because it affects rates of upwelling and mixing of surface and subsurface waters processes that result in deep water formation at present prevailing wind directions during the winter in the greenland sea are northeasterly because ice has a larger drag coefficient than water ekman transport is greater under the ice than in open water this configuration causes divergence along the miz mixing of surface and subsurface waters and vertical overturn during the glacial maximum however the prevailing winds along the miz polar front were predominantly westerly modeling studies suggest that ice age changes in the prevailing winds would have significantly increased the depth of the mixed layer and decreased entrainment equal to mixing rates in agreement with geological data mixing changes due to westerly winds are greater than mixing changes due to a lower salinity layer under the present wind regime changes due to winds are so large that further changes in boundary conditions low salinity surface layer result in only minor additional reductions in vertical mixing still the maximum reduction occurs when the two processes are considered together a situation that may be applicable to the younger dryas event during the last deglaciation when a meltwater lid may have developed in the subpolar north atlantic our study suggests that wind induced changes in mixed layer depth along the miz represent a viable mechanism for decreasing past nadw production rates

a linear analysis of equatorial atlantic ocean thermocline variability abstract observed variations in the atlantic ocean s equatorial thermocline are compared at four locations with simulations using an analytical reduced gravity model the comparison shows the essential features of the seasonal wind forced thermocline response to be accounted for by a linear superposition of equatorial long waves evolving basinwide tending to bring the zonal pressure gradient into balance with the wind stress a frequency response function is derived whose properties provide a basis for discussing the large scale features of the equatorial atlantic ocean s seasonal cycle for example its evolution along the equator the maximum upwelling region observed in the gulf of guinea and the secondary upwelling season also observed there clarification is also given to the issue of remote versus local forcing for these features

copper distribution and speciation across the international geotraces section ga03 abstract copper cu distribution and speciation were characterized along a zonal section in the north atlantic ocean from lisbon portugal to woods hole massachusetts as part of the u s geotraces program dissolved cu profiles displayed many of the same features identified by other researchers including sub surface scavenging and a linear increase with depth but many also exhibited unique properties and geographic trends concentrations ranged from 0 43 nm at the surface to 3 07 nm near the seafloor the highest concentrations were measured in deep waters to the west of cape verde and northwest of the canary islands while the lowest concentrations were measured in upper waters mostly between mauritania and cape verde the westernmost sampling sites overlying or adjacent to the u s east coast continental shelf featured surface maxima that decreased in magnitude moving east toward bermuda reflecting declining inputs from cu enriched coastal waters and north american aerosols free cu cu 2 concentrations were tightly controlled by organic complexation and scavenging across the section with values varying between 1 54 fm and 1 07 pm these results provide the first evidence that cu 2 concentrations are strongly complexed throughout the water column even in boundary zones where dissolved cu concentrations are elevated because of local sources strong organic ligands l acted as a buffer for cu 2 restricting concentrations to a narrow range 10 100 fm throughout most of the water column cu 2 and dissolved cu were strongly scavenged by suspended particulate matter within several benthic nepheloid layers and a hydrothermal plume above the trans atlantic geotraverse tag vent field on the mid atlantic ridge mar

comparative analysis of sulfur isotope behavior in the basins with evaporites of chloride and sulfate types abstract the pripyat trough and the caspian depression are examples of basins with chloride and sulfate type evaporite formations respectively patterns of sulfur isotope distribution in these basins are essentially different sulfur isotopic composition of sulfate minerals in the caspian depression becomes lighter from the gypsum stage 34 s 13 9 0 3 toward the chloride stage 12 7 0 2 an opposite isotopic trend occurs in the pripyat trough 34s are respectively 22 8 1 0 and 25 3 0 5 pyrite formed in the chloride stage in the caspian depression is significantly depleted in 34s with respect to the initial sulfate of the basin 34 s sulfate py 22 5 2 1 34s sulfate py in the pripyat trough is lower 17 6 1 2 diagenetic anhydrites from the intersaliferous and subsaliferous formations are enriched in 34s relative to the sulfur isotope values measured from the anhydrites in the main salts this enrichment is higher in the pripyat trough average 34s 2 7 5 2 than in the caspian depression 0 9 2 1 the above differences are well explained in the terms of chemical systems that are limited or unlimited with respect to sulfur during the sulfate reduction process brines act as sulfur limited systems in chloride type basins and as sulfur unlimited systems in sulfate type ones

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

atmospheric deposition of soluble trace elements along the atlantic meridional transect amt abstract we briefly review the role of atmospheric deposition measurements within the atlantic meridional transect amt programme and then go on to present new data on the soluble concentrations of a range of trace metals fe al mn ti zn v ni and cu and major ions in aerosols collected along the amt transect the results allow us to identify emission sources of the trace metals particularly in terms of the relative importance of anthropogenic versus crustal sources we identify strong gradients in concentrations and deposition for both crustal and anthropogenically sourced metals with much higher inputs to the north atlantic compared to the south atlantic reflecting stronger land based emission sources in the northern hemisphere we suggest anthropogenic sources of ni and v may include an important component from shipping we consider the extent to which these gradients are reflected in surface water concentrations of these metals based on the geotraces water column trace metal data we find there is a clear difference in the concentrations of surface water dissolved al and fe between the north and south atlantic gyres reflecting atmospheric inputs however for mn v or ni higher inputs to the north atlantic compared to the south atlantic are not clearly reflected in their water column concentrations

climatically sensitive eolian and hemipelagic deposition in the cariaco basin venezuela over the past 578 000 years results from al ti and k al al ti and k al ratios in bulk sediment are used to interpret wind blown and hemipelagic sources of deposition to a 578 kyr record in the cariaco basin venezuela ocean drilling program site 1002 graphical and cross spectral analyses indicate that these ratios vary extremely closely with planktonic foraminiferal 18o with both ratios being significantly higher during interglacials and lower during glacials k al indicates that during glacials the lower sea level that results in relative basin isolation increases the relative proportion of kaolinite derived from local rivers draining the relatively humid venezuelan margin al ti decreases during glacials suggesting greater proportions of eolian rutile sourced from the northern sahara due to increased wind strength and or aridity this interpretation is consistent with previous studies of the chemistry and mineralogy of saharan derived eolian matter in the caribbean and with a mass balance determining the effect of changes in eolian rutile accumulation on the bulk sedimentary al ti ratio

the elemental composition of the deep particle flux in the sargasso sea abstract the elemental composition of the deep particle flux at 500 m 1500 m and 3200 m was measured at the oceanic flux program ofp time series site in the northern sargasso sea from september 2000 to march 2015 the results clearly show that the deep particle flux is sourced from two components an extrinsic flux component that is derived from and temporally coupled with recent surface export fluxes and an intrinsic flux component that is derived from chemical scavenging and suspended particle aggregation within the deep water column elemental fluxes show a seasonal cycle that is closely tied to the overlying cycle in primary production fluxes of biogenic minerals and nutrient elements peak during the late winter spring maximum in overlying primary production a small late winter spring peak in fluxes of non biogenic elements suggests that intrinsic flux generation within the deep water column also covaries with overlying production and the extrinsic flux flux elemental composition also shows a marked seasonal cycle that reflects dilution of the intrinsic flux in the late winter and spring with fresh biogenic materials sourced from recent overlying production factor of four increases in lithogenic element fluxes and lithogenic element ratios indicate that the source of the deep lithogenic flux is not saharan dust but north american margin sediments that have been resuspended and advected to the region via gulf stream recirculation high rates of authigenic mineral precipitation accompany organic matter degradation in mesopelagic waters the excess mn flux i e flux not supported by lithogenic minerals increases by an order of magnitude between 500 m and 1500 m and the excess ba flux increases by a factor of three there is a major reorganization of element associations with flux carrier phases with increasing depth in particular the geochemical behavior and flux of p becomes increasingly independent of organic carrier phases and the geochemical behavior of fe co ni cu and to a lesser extent v and pb becomes increasingly controlled by manganese oxide scavenging this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

rare earth elements in marine sediments and geochemical standards abstract a comparison was made of sediment dissolution methods used for analysis of rare earth elements ree and major elements fe al ti zr p dissolution by hf and lithium metaborate fusion were compared in seven geochemical standards and twenty marine sediments using hf dissolution of shelf and slope sediments this author previously observed that these marine sediments were significantly depleted in heavy ree hree relative to the crustal abundance i e shale this observation plus published ree compositions of river particles lead to the conclusion that the riverine input of particles to the oceans cannot be assumed to have the crustal abundance for ree comparisons of fusion total to hf dissolutions for marine sediments show that the latter method misses between 20 and 100 of the hree i e dy er yb lu and large percentages of zr in contrast fusion and hf dissolution yield similar concentrations for the light la ce nd and middle eu gd ree and other major elements the fusion data show that the marine sediments are more similar in ree composition to shales than previously reported by this author who underestimated the contribution of hf insoluble residues to the concentration of hree the heavy mineral zircon is the most likely cause of this observation zircons known to be enriched in hree were identified by x ray diffraction as a major component of the hf insoluble residues geochemical standards also have a significant but usually smaller fraction of their hree associated with hf insoluble phases these compositional differences have significance with respect to interpreting river inputs oceanic abundances and diagenesis of ree

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

estimates of the transport of trace metals from the ocean to the atmosphere the bubble interfacial microlayer sampler bims was used in the north atlantic to determine the enrichment factors relative to sodium and the ocean efsea for a series of trace metals on bubble derived atmospheric sea salt particles no enrichment was found for k and mg within the analytical precision of 10 mean efsea values determined for al co cu fe mn pb v and zn ranged from 10 to 20 000 positive correlations were found between bubble generation depth and the efsea values for fe pb sc and zn estimates suggest that the ocean is the primary global source of atmospheric k and mg that it is potentially a nontrivial 5 20 of the total source of atmospheric cu v and possibly zn and that it is an insignificant source of al co fe mn pb and sc in the remote north pacific during certain periods of the year the ocean may be the primary source for all these elements present on aerosol particles with diameters greater than 3 m

complementary roles of orbital insolation and north atlantic deep water during late pleistocene interglacials a long standing dilemma of the milankovitch hypothesis involves the observation that the holocene deglaciation was comparable in extent to previous late pleistocene interglacials even though insolation forcing was less in this paper we propose an explanation that is based on an observed complementary relationship between eccentricity and north atlantic deep water nadw production rates a 13c record from the south atlantic indicates that nadw production rates are high when eccentricity is low stages 1 11 and vice versa for the holocene the inferred stronger thermohaline circulation injects approximately the same heat into the high latitude north atlantic 9 w m as the insolation differences between the early holocene and last interglacial peak we utilize an energy balance model to calculate that the excess heat from the holocene thermohaline increase can explain at least 50 65 and 100 of the energy budget shortfall from milankovitch forcing over the laurentide and fennoscandian ice sheets respectively we suggest that the observed complementary relationship between milankovitch and nadw reflects a coupling due to a reverse monsoonal effect over the north atlantic during times of high eccentricity and strong land sea contrast enhanced heating over land results in increased subsidence over the ocean which causes circulation and precipitation changes these processes could lower ocean salinities and decrease thermohaline circulation thus deglaciation can progress through either mechanism with the total heat balance for each interglacial being approximately the same however the combined effect of increased insolation and reduced thermohaline circulation for the last interglacial yields slightly warmer 1 0 c temperatures in mid and high latitude northern hemisphere land areas than in the holocene this result is approximately in line with geologic data from these regions

what controls opal preservation in tropical deep sea sediments measurements of opal preservation in deep sea sediment cores have been presented in three ways the opal concentration as a fraction of total dry weight opaltot the opal concentration normalized to calcite free dry weight opalcalcite free and me opal accumulation rate opal mar it is tempting to interpret changes in these indices as indicators of rates of biological production in past oceans based on theoretical constraints we argue that in typical tropical and subtropical sediments both opalcalcite free and opal mar reflect a significant artifact of dilution by other phases thus the band of high opalcalcite free in the equatorial pacific appears to be caused in large part by the high calcite in that region rather than by high opal productivity the best candidate for a reliable paleoproductivity proxy appears to be opaltot unfortunately present day opaltot data from tropical and subtropical regions show little or no systematic trend with the rain rate of opal pore water silica concentration data reveal that the apparent pore water opal solubility is not constant but correlates regionally with the rain rate of opal to the seafloor a model that treats opal as a single homogeneous phase with a single well defined solubility product predicts a strong dependence of opal concentration on rain rate in stark contrast to the data and a constant asymptotic pore water si two models representing opal as multiple heterogeneous phases with different solubilities are able to reproduce the observed asymptotic pore water si rain rate relationship but not the lack of rain rate trend in the opal concentration data only by assuming a systematic trend in the quality of opal i e the solubility as a function of opal production can we reproduce the observed pattern of opal preservation the implication of this study is that changes in opal preservation in the geologic record cannot simply be interpreted in terms of changes in surface ocean productivity until our understanding of opal diagenesis can be improved

cycling of lithogenic marine particles in the us geotraces north atlantic transect in this paper we present describe and model the first size fractionated 0 8 51 m 51 m water column particulate trace metal results from the us geotraces north atlantic zonal transect in situ pumping survey with a focus on the lithogenic tracer elements al fe and ti this examination of basin wide full depth distributions of particulate elements elucidates many inputs and processes some for bulk lithogenic material others element specific which are presented via concentration distributions elemental ratios size fractionation dynamics and steady state inventories key lithogenic inputs from african dust north american boundary interactions the mediterranean outflow hydrothermal systems and benthic nepheloid layers are described using the refractory lithogenic tracer ti we develop a 1 d model for lithogenic particle distributions and test the sensitivities of size fractionated open ocean particulate ti profiles to biotically driven aggregation disaggregation rates vertical sinking speeds and dust input rates we discuss applications of this lithogenic model to particle cycling in general and to poc cycling specifically

geochemical composition of aeolian dust and surface deposits from the qatar peninsula abstract the trace metal geochemistry of atmospheric dust and terrestrial surface particles were studied on the qatar peninsula from february 2014 to november 2015 we included samples of the mega dust storm event on 01 02 april 2015 atmospheric dust samples were collected using passive dust traps terrestrial surface deposits of recent dust accumulation and traffic particulate from roads were also sampled all samples were total acid digested and analyzed for major and trace elements using icp oes analyzer the concentration of thirteen elements ca mg ag as cd cr cu mo ni se sn sr zn were enriched in atmospheric dust samples relative to upper continental crust ucc calcium was especially enriched by up to 435 relative to ucc about 33 of the total sample mass was caco3 reflecting the composition of surface rocks and soils in the source areas of the elements typically associated with anthropogenic activity ag ni and zn were most enriched relative to ucc with enrichment factors ef of 182 233 and 209 respectively other metals which normally reflect anthropogenic sources including pb and v were not significantly enriched with enrichment factors of 25 and 3 respectively major elements al mn fe were depleted 58 35 and 5 respectively relative to ucc due to the large dilution effect of the enrichment of caco3 back trajectories were determined at the date of sampling for each sample using the noaa hysplit model these showed that the source of the dust particles was almost equally divided between northerly and southerly sources except one sample which appeared to originate from the west more variability in particle source locations were observed during the winter months october to march samples from the mega dust storm were solubilized using an acetic acid hydroxylamine hydrochloride leach procedure to obtain an upper estimate of the potential contribution of bioactive elements to surface seawater the leach procedure solubilized a significant fraction of almost all elements ca was the element most affected 81 removed because of the carbonate minerals present bioactive elements like fe 25 and p 58 were also significantly solubilized because river input is so small to the arabian gulf this solubilized fraction of dust is likely a major source of nutrients to surface seawater enrichment factors were also calculated with respect to the average composition of terrestrial surface deposits tsd samples are not enriched significantly with respect to major components ef

seasonal variations of the subsurface thermal structure in the gulf of guinea abstract the subsurface thermal structure in the gulf of guinea is analyzed using the historical hydrographic data file of particular interest is the rapid vertical displacement of the thermal structure from the warm march may season to the cold july august season this displacement field is trapped at the equator with vertical and meridional scales appropriate to a second or third mode baroclinic kelvin wave it has a maximum amplitude between 4 w and 10 w with a node near 2 e south of 4 s no seasonal displacement of the thermocline underlies the seasonal variation in the sea surface temperature along the eastern boundary north of the equator to 3 e the displacement field vanishes thus the coastal upwelling associated with a vertical displacement tightly bound to the northern coast from 2 e to 10 w appears detached from the equatorial regime

dissolved al in the zonal n atlantic section of the us geotraces 2010 2011 cruises and the importance of hydrothermal inputs abstract the distribution of dissolved aluminium determined during ga03 the us geotraces north atlantic transects us gt nazt shows large inputs to the basin from three main sources atmospheric deposition outflow from the mediterranean and inputs from hydrothermal sources along the mid atlantic ridge mar the partial dissolution of atmospheric aerosols emanating from the sahara yield high concentrations of dissolved al in the surface waters of the basin and are used to estimate the geographical pattern of dust deposition the mediterranean outflow delivers a large source of dissolved al to the intermediate waters of the eastern basin and its subsequent distribution within the basin can be explained by simple isopycnal mixing with surrounding water masses hydrothermal venting at the trans atlantic geotraverse tag hydrothermal field in the mar produces a neutrally buoyant plume that introduces copious quantities of dissolved al with concentrations of up to 40 nm to the deeper waters of the north atlantic that can be seen advecting to the west of the mar the concentration of dissolved al in the deep waters of the eastern basin of the atlantic can be accounted for by admixing the mar al enriched plume water and antarctic bottom water aabw as they pass through the vema fracture zone the data sets show no evidence for biological remineralisation of dissolved al from si carrier phases in deep waters

dry deposition of trace elements to the western north atlantic 1 data for al fe na sb se v and zn in aerosol particles from bermuda are used in combination with parameterized dry deposition velocities to investigate trace element recycling on atmospheric sea salt during july and august which are in the high dust season 10 of the monthly mean aerosol na can be ascribed to crustal sources rather than sea salt but in general the contribution of mineral dust to na dry deposition is small 1 relative to that from sea salt in fall and winter 10 to 20 of the aerosol al a commonly used indicator of mineral dust is attributable to recycled sea salt but the dust fluxes then are small and longer term averages show a recycling effect of only 1 to 5 on dry deposition the percentage of recycled fe appears to be even less than for al noncrustal non sea salt nc nss sources account for 70 of the aerosol sb se v and zn but differences in the dry deposition velocities for three particle types strongly affect their air sea exchange dust can account for more than half of the new dry deposition inputs of v and zn while the amounts of sb and se recycled on sea spray approach or exceed their new inputs from dust and the nss nc sources

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

trace element concentrations elemental ratios and enrichment factors observed in aerosol samples collected during the us geotraces eastern pacific ocean transect gp16 abstract atmospheric deposition is an important source of bioactive trace elements to the open ocean but observations of this flux are sparse atmospheric deposition of aerosol iron is of particular interest as it can play an important role in supporting primary production in the global ocean yet it represents a key uncertainty that hampers accurate numerical modeling of the marine iron cycle we report concentrations of atmospheric trace elements from samples collected as part of the 2013 us geotraces gp16 zonal transect of the eastern pacific ocean the cruise transected a relatively dusty region which coincided with the peruvian upwelling zone before entering the much less dusty region of the subtropical gyre the aerosol chemical composition and elemental ratios indicate crustal sources for al ti v mn and fe while the analyses suggest that cu cd and pb originate from anthropogenic emissions dry deposition fluxes were calculated by applying characteristic deposition velocities based on the expected particle size associated with each element bulk deposition which includes wet and dry deposition was calculated using the inventory of 7be in the upper water column soluble aerosol iron flux estimates were compared with vertical iron fluxes within the water column to assess the relative importance of atmospheric deposition to the marine iron cycle in the region atmospheric deposition was insignificant relative to the upwelling input of iron in the areas near the continental sources but increased in relative importance seaward of the coastal upwelling zone even as the magnitude of deposition decreased away from the coast this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

reduced advection into atlantic ocean deep eastern basins during last glaciation maximum causes of change in deep water 13c can be either global or local in extent global causes include 1 climatically induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1 and 2 erosion and deposition of organic rich continental shelf sediments during sea level fluctuations which change the mean oceanic carbon phosphorus ratio2 regional gradients of 13c are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow changes in a single geological record of benthic foraminiferal 13c can result from any combination of these global and abyssal circulation effects by sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity we can assume that each 13c record was equally affected by global causes of 13c variation the differences seen between the 13c records must therefore reflect changes in the distribution of 13c in the deep ocean we interpret these differences in distribution in terms of changes in the ocean s abyssal circulation benthic foraminiferal carbon isotopic evidence from a suite of sierra leone rise cores indicates that the deeper parts of the eastern atlantic basins underwent a reduction in o2 during the maximum of the last glaciation reduced advection of o2 rich deep water through low latitude fracture zones associated with increased delivery of organic matter to the deep ocean lowered the 13c of deep water co2 at all depths below the sill separating the eastern and western atlantic basins 3 this decreased advection into the eastern atlantic ocean coincides with the overall decrease in deep water production in the north atlantic during the last glacial maximum4 7

river fluxes of dissolved silica to the ocean were higher during glacials ge si in diatoms rivers and oceans two centric marine diatom species thalassiosira oceanica and thalassiosira antarctica were grown in batch cultures to determine the incorporation of germanium ge and silicon si into siliceous shells opal the results were modeled as ge si isotope fractionation during exponential growth diatoms take up and incorporate ge si from solution without major discrimination against ge during stationary phase growth near silica limitation the antarctic species t antarctica discriminates slightly against ge but integrated ge si opal produced over the latter portion of the growth cycle is indistinguishable from the initial solution ratio these results confirm experiments using radioactive 68ge that showed absence of fractionation during diatom silica uptake azam and volcani 1981 in contrast to two box ocean models that invoke 50 ge discrimination by diatoms to explain the observed excess surface ocean germanium concentration murnane and stallard 1988 froelich et al 1989 and late pleistocene ocean sediment ge si opal records mortlock et al 1991 runs of a 10 box ocean ge and si model pandora with 50 discrimination reproduce the excess surface ocean ge but introduces curvature into the deep ocean ge versus si relationship that is not observed in the oceans thus 50 fractionation is not supported by either cultures or models if diatoms do not fractionate ge si then late pleistocene ge si opal variations in piston cores are caused not by changes in local biosiliceous production and silica utilization mortlock et al 1991 but rather by whole ocean changes in ge si seawater the marine ge si opal record of the last 450 kyr can be modeled as transient oceanic responses to instantaneous continental climate transitions consistent with the chemical weathering model of murnane and stallard 1990 glacial periods are characterized by lower continental weathering intensity lower ge si riv and two fold higher dissolved silica river fluxes marine ge si opal records thus contain a history of ocean silica chemistry that reflect rapid global changes in continental weathering

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

a master of the earth h d holland and his contributions to geochemistry abstract h d holland was one of the great geochemists of modern times as a professor at princeton university for 22 years and at harvard for 33 he mentored 24 graduate students and 24 postdoctoral researchers he was a member of the u s national academy of sciences and a president of the geochemical society he co authored 179 publications in 64 years from 1949 to 2012 including four books he edited one other book and with karl turekian co edited the ten volume treatise on geochemistry his contributions to geochemistry were mainly in economic geology hydrothermal processes and especially the chemistry and evolution of the earth s atmosphere and oceans a topic to which he devoted nearly half of his publications his most significant contributions documented changes in the composition of seawater through geologic time and the rise of oxygen in earth s atmosphere he pioneered the use of mineral sequences in marine evaporite deposits and fluid inclusions in evaporite minerals to determine the composition of ancient seawater he collected extensive data on paleosols and used them to calibrate the oxygen content of the ancient atmosphere documenting its rise in the great oxidation event that peaked between 2 41 and 2 32 ga and writing extensively about the causes of this event one of the most significant in earth history

late quaternary deep ocean circulation a review of paleoceanographic studies dealing with late quaternary deep water circulation in the oceans is presented these studies which are based on the analysis of deep sea benthic foraminiferal faunal and geochemical data and sedimentological data are discussed in light of physical oceanographic conditions in the modern ocean we include in this review a re evaluation of benthic foraminiferal data from north atlantic and southern ocean piston cores and suggest that the dominance of uvigerina during glacial intervals reflects increased amounts of organic carbon at the sea floor compared to modern values a number of geochemical studies have suggested that the production or characteristics of north atlantic deep water nadw changed during glacial times although these changes have been thought to result from a cessation of overflow water from the norwegian greenland seas it is suggested here that seasonal sea ice cover was possible over southern portions of the norwegian sea during glacial intervals the presence of seasonally open water would have allowed norwegian sea overflow water to have been produced although perhaps at lower volumes and with different hydrographic properties than at present the record of antarctic bottom water aabw circulation does not show a simple relationship with paleoclimatic oscillations indicating that changes in oceanographic conditions in the southern ocean had little effect on aabw formation the aabw record contrasts with the glacial interglacial cycles of nadw suggesting no direct link between aabw and nadw circulation a variety of data suggests that changes in pacific deep water circulation occurred as a result of glacial production of north pacific deep water or from an increased flux of southern ocean water

elemental ratios and enrichment factors in aerosols from the us geotraces north atlantic transects abstract the north atlantic receives the highest aerosol dust input of all the oceanic basins dust deposition provides essential bioactive elements as well as pollution derived elements to the surface ocean the arid regions of north africa are the predominant source of dust to the north atlantic ocean in this study we describe the elemental composition li na mg al p sc ti v cr mn fe co ni cu zn as se rb sr cd sn sb cs ba la ce nd pb th u of the bulk aerosol from samples collected during the us geotraces north atlantic zonal transect 2010 11 in order to highlight the differences between a saharan dust end member and the reported elemental composition of the upper continental crust ucc and the implications this has for identifying trace element enrichment in aerosols across the north atlantic basin as aerosol titanium ti is less soluble than aerosol aluminum al it is a more conservative tracer for lithogenic aerosols and trace element to ti ratios however the presence of ti rich fine aerosols can confound the interpretation of elemental enrichments making al a more robust tracer of aerosol lithogenic material in this region

on the origin of fluids included in phanerozoic marine halite basic interpretation strategies abstract in addition to the use of janecke units in the nacl kcl mgcl 2 na 2 so 4 h 2 o nacl kcl mgcl 2 cacl 2 h 2 o system to classify brine origins a fast and efficient method is described to identify inclusions of evaporated seawater in ancient marine halite the method is based on the calculation of degrees of evaporation for various elements de element of brines created by different salt forming processes the de element patterns of the fluid inclusions serve as fingerprints and are characteristic of different brine types of known origin

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

further studies on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds upper ocean temperature data obtained during the seasonal response of the equatorial atlantic experiment and the francais ocean et climat dans l atlantique equatorial program are used to describe the variations of the thermocline observed along the equator from february 1983 to september 1984 in response to rapid seasonal changes in zonal wind stress the thermocline underwent sequences of upwelling followed by downwelling or conversely depending upon whether the winds were intensifying or relaxing these sequences increased systematically in magnitude and duration to the east both the sequential behavior and its zonal inhomogeneity represent departures from the slowly varying and in phase climatological description of the annual thermocline response an analytical reduced gravity equatorial long wave model forced by zonal wind stress distributions representative of the variations observed along the equator was employed to reconcile the differences between the 1983 1984 synoptic measurements and the climatologically averaged description qualitative agreements between the model results and the data were found for many salient features of the annual cycle including the zonal pressure gradient calculated by finite difference the features in the model arise as interference patterns between directly forced and reflected kelvin and long rossby waves that are generated with each change in the wind stress the manner in which the wind stress changes from year to year is therefore crucial to the equatorial ocean s response

late quaternary carbonate sedimentation at the sierra leone rise eastern equatorial atlantic ocean abstract in the eastern equatorial atlantic ocean changes in the concentration of carbonate in late quaternary sediments resulted from reduced production of carbonate in surface waters and increased dilution with non carbonate sediments during glacial maxima during glacial stages production of carbonate in surface water measured as its accumulation rate in shallow undissolved cores decreased by one half the glacial accumulation rate of non carbonate components increased 1 5 to 4 times over holocene values the greatest increases occurred in the deepest cores carbonate dissolution during stages 2 3 and 4 increased the proportion of foraminiferal fragments and decreased the accumulation rate of susceptible species in the deep sites in shallow sites slightly increased dissolution can be detected during stage 3 while greatly increased dissolution occurred during stage 4 bathymetric profiles of foraminiferal fragmentation and accumulation document a shoaling of the foraminiferal lysocline by 1000 m during glacial isotopic stages we present a mass balance model of sediment accumulation for carbonate and insoluble components and from this model we estimate the rate of downslope transport and dissolution of carbonate at the sierra leone rise our results show that during stage 4 the rate of carbonate loss to dissolution was greater than the rate observed today or during other interglacial stages the calculated rates of dissolution for stages 2 and 3 are not significantly different from those calculated for stage 1

partitioning of dissolved iron and iron isotopes into soluble and colloidal phases along the ga03 geotraces north atlantic transect abstract the size partitioning of dissolved fe dfe 56 fe of 1 3 to 1 5 relative to dfe 56 fe 0 5 in the surface ocean where sfe and cfe cycle independently and identical sfe and dfe isotope ratios below 250 m where sfe and cfe are constantly partitioned and exchanged

late pleistocene paleoclimatology of the central equatorial pacific flux patterns of biogenic sediments high resolution records of the concentration and mass accumulation rate mar or flux of biogenic sediments from core rc11 210 in the central equatorial pacific are compared for the entire late pleistocene the fluxes of calcium carbonate and organic carbon correlate well the opal flux pattern shows no direct correlation with the other two rather opal flux maxima correlate with slopes of i e both precede and follow the organic carbon and carbonate mar peaks organic carbon and calcite therefore may both be better indicators of past productivity than opal which is an indicator of transition at this location we interpret the sequence low biogenic fluxes high opal fluxes high carbonate carbon and opal fluxes as representing the transition from low to high sea surface biological productivity the phase relationships for eccentricity of the biogenic sedimentation records were compared to those of other climatic indications including the oxygen isotope record of ice volume the ice core co2 record the pacific 13c record the deep nutrient cd ca record and the eolian grain size record of wind intensity we find that starting from maximum ice volume phase angle of 0 the phase relationships of the 100 000 year periodicity show in the first quadrant maximum wind intensity 30 and maximum calcite and carbon flux 45 occurring first followed by maximum opal flux 75 and then maximum deep nutrients 95 minimum pacific 13c occurs at a phase angle of 155 the maximum co2 in the vostok record and minimum ice volume is at 180 thus in the eccentricity climate cycle glacial conditions lead to stronger wind driven circulation which enhances productivity which in turn results in enhanced oceanic and atmospheric carbon dioxide and minimum ice volume

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition