sr and nd isotopes as tracers of north atlantic lithic particles paleoclimatic implications sr and nd isotopic compositions have been measured on the lithic fraction of last climatic cycle sediments from the north atlantic 40 n 60 n in order to identify the origins of the particles from the reconstruction of their transport pathways we deduce the mechanisms that explain their distributions the main source regions are the canadian shield mostly the area of baffin bay and western greenland the scandinavian shield the european region british isles and bay of biscay and iceland we observe a significant glacial interglacial contrast characterized by a dominant icelandic input via near bottom transport by north atlantic deep water nadw during the interglacials and a largely continent derived contribution of surface transported ice rafted detritus ird during the glacial period during the last glacial period the heinrich events abrupt massive discharges of ird originated not only from the laurentide ice sheet as heretofore envisioned but also from other sources three other major north atlantic ice sheets fennoscandian british isles and icelandic probably surged simultaneously discharging ice and ird into the north atlantic as opposed to theories implying a unique laurentide origin gwiazda et al 1995 driven by an internal mechanism mcayeal 1993 we confirm that the icelandic and the fennoscandian ice sheets also surged as recently proposed by other authors and we here also distinguish a possible detrital contribution from the british isles ice sheet this pan north atlantic phenomenon thus requires a common regional external forcing

variations of biogenic particle flux in the southern atlantic section of the subantarctic zone during the late quaternary evidence from sedimentary and variations of intensity and composition of biogenic particle flux at the northern boundary of the present polarfrontal zone in the atlantic sector of the southern ocean are indicators of major changes of paleoenvironmentalconditions on glacial interglacial time scales during the late quaternary in order to estimate those pastchanges sediment accumulation patterns of two piston cores one from just north and one just south of thepresent day position of the subantarctic front were reconstructed using the 230thex method large contributionsof laterally supplied material were quantified and used to correct sediment accumulation rates during the lastglacial focussing of biogenic opal dominated material exceeded the original contribution from the surfacewater above by a maximum factor of 8 7 the initial activity ratio of 231paex 230thex was used as tracer forbiogenic particle flux and composition and indicates that during the glacial stages 2 and 4 the area of high opalproductivity was situated above the location of the southern core whereas the northern core has not beenreached by this northward shift during the last 130 kyr as shown by the pattern of focussing corrected bulkaccumulation rates if the position of the antarctic polar front has remained at the northern boundary of thehigh opal productivity area during the last 130 kyr the results suggest that was located exactly between thetwo core sites during glacial stages 2 and 4 a two box modeling approach involving particle flux and boundaryscavenging intensity of 231pa was applied to estimate the possible range of the 231paex 230thex ratio recordedin southern ocean sediments previous estimates on the export of 231pa from the atlantic into the southernocean are corroborated but the model suggests a low sensitivity of the 231paex 230thex ratio in southern oceansediments to variations of the residence time of north atlantic deep water in the atlantic ocean

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

rates of formation of modern phosphorite off western mexico abstract phosphorite deposition represents a significant but poorly constrained sink in the marine p cycle this study establishes conclusively that phosphorite forms today throughout a widespread region along the upper continental slope off southern baja california mexico in this region o2 depleted 5 50 m bottomwater overlies the seafloor and a narrow range of suboxic to anoxic redox conditions prevail in the modern 0 18 000 yr old near surface 0 50 cm organic c rich 2 10 wt sediment interstitial gradients of total alkalinity ta and inferred effects of organic matter decay correlate directly with sedimentation rates calculated from 14c dating other porewater and solid phase data indicate that francolite currently precipitates authigenically at each of five study sites moderately high concentrations 20 100 m of dissolved inorganic phosphate dip produced in the upper 5 cm of sediment sustain francolite growth at slightly greater depths while the necessary f diffuses into the sediment from above neither organic matter decay nor fish bone dissolution seem capable of producing the steep near surface gradients of dip measured in this study at some sites dip production coincides spatially with the reversible production of dissolved fe2 but thorough evaluation of the possible link between these processes requires further study the mechanism responsible for the near surface enrichment of interstitial dip thus remains unidentified box cores from each site contain an unreworked sequence of up to six thin 1 3 cm discrete francolite rich horizons several of which qualify as true phosphorite 50 wt francolite estimated diffusional burial fluxes of inorganic p and f range respectively from 2 40 g cm 2 y 1 and 4 12 g cm 2 y 1 or the equivalent in francolite of 16 260 g cm 2 y 1 these present day accumulation rates lie within the range of those determined for several ancient phosphorite deposits and for the extensively studied region of modern phosphorite deposition off peru

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

tracking the sources of icebergs with lead isotopes the provenance of ice rafted debris in heinrich layer 2 the provenance of ice rafted debris ird deposited in the north atlantic before during and after heinrich event 2 has been determined through measuring the lead isotopic composition of single feldspar grains and multiple grain composites from the larger than 150 m size fraction from cores from the eastern and western north atlantic and from the labrador sea single grain analyses are used to identify the specific continental sources of the ird whereas composite samples are used to assess the relative ird contributions from different sources all single grains from heinrich layer 2 h 2 as well as h 2 composites plot along a correlation line on a 207pb 204pb versus 206pb 204pb diagram characteristic of the churchill province of the canadian shield this is yet another strong piece of evidence that this heinrich event was dominated by a massive iceberg discharge of the laurentide ice sheet lobe located over hudson bay in contrast single grains from the ambient glacial sediment above and below h 2 have multiple sources many of them also lie along the correlation line with h 2 grains but many others have pb signatures consistent with derivation from the grenville province and the appalachian range in north america and possibly from scandinavia and greenland composites from the ambient sediment generally lie well to the right of the h 2 reference line in agreement with the results of the single grain analyses the evidence provided by lead isotopes regarding the dominant role played by the hudson bay lobe of the laurentide ice sheet in the development of the heinrich events lends support to the binge purge model advanced by macayeal 1993a b that invokes trapping of geothermal heat by the base of the icecap and subsequent basal melting as the mechanism that triggered the heinrich events

the phosphorus cycle in coastal marine sediments the concentration of dissolved phosphate in sediment box cores from the laurentian trough in the gulf of st lawrence increased sharply across the sediment water interface from 2 0 mol po4 1 in the bottom water to 6 3 mot po4 1 in the top cm remained almost constant at this value down to 5 15 cm depth and then increased rapidly with further depth in the region of constant concentration phosphate is buffered by sorption equilibria with the sediment the production rate of phosphate the sorption capacity of the sediment and the thickness of the diffusive boundary layer at the sediment water interface appear to control the shape of the pore water profile even though the buffering places an upper limit on the concentration gradient across the sediment water interface and hence on the flux the phosphate flux to the overlying water is controlled by the production rate of phosphate within the sediment a model is proposed to relate sediment chemistry to phosphorus fluxes

quantitative resolution of eolian continental crustal material and volcanic detritus in north pacific surface sediment proxy records of continental climate and atmospheric circulation provided by analyses of eolian continental material extracted from marine sediment have resulted in significant new information concerning the behavior of these climate systems on various timescales these studies however currently are limited to certain geographic areas because no chemical or physical extraction procedure provides an unambiguous separation of eolian continental crustal material from other contaminants like volcanic detritus we employ a combined analytical and statistical procedure in an effort to extract a more refined eolian signal from areas that may be affected by volcanic detritus bulk surface sediment samples from 33 locations in the north pacific were treated using a conventional sequential extraction procedure to remove the carbonate silica and oxyhydroxide components and the residue was analyzed by instrumental neutron activation analysis inaa for la ce sm eu yb lu hf sc and th q mode factor analysis of these data shows that 99 of the variance is explained by two end members which we interpret to be continental crustal material and volcanic detritus five least squares normative analysis models were evaluated to estimate the relative amount of these end members in each sample the continental crustal component was approximated using a fine grained fraction of china loess and bulk loess the volcanic component was approximated using the compositions of average kurile kamchatka volcanic material a median ocean drilling program odp leg 145 ash and a median kurile basalt the model based on average kurile kamchatka volcanic material and the fine loess fraction gives the most accurate results central and east pacific samples typically contain up to 100 of the eolian continental crustal component while samples near japan kamchatka and the aleutians contain a majority of volcanic detritus however the highly variable composition of volcanic material can result in systematic errors up to 25 in samples dominated by volcanic detritus the geographic distribution of the compositional end members is consistent with a continental dust source originating in asia and being diluted by ash from the volcanic arcs of the pacific rim this improved identification and resolution of the eolian continental component realized in this approach should permit paleoclimatic reconstructions to be developed from sediments in significant portions of the world that were previously precluded from analysis because of limitations with chemical or physical extraction procedures

carbon and phosphorus cycling in anoxic sediments of the saanich inlet british columbia abstract uncertainty currently exists about the removal of carbon c and phosphorus p from the oceanic reservoir especially in low oxygen settings in this paper the cycling of c and p is examined in sediments from the anoxic saanich inlet cored by ocean drilling program odp leg 169s in 1996 at two sites although c org p org ratios are high and increase with depth in the saanich inlet this effect is due largely to a remobilization of p from an organic matter sink to an authigenic sink reducible sedimentary components act as temporary shuttles in this process even in this anoxic setting with the ultimate burial sink for the remobilized p being carbonate fluorapatite the effective c org p reactive molar ratio appears to be about 150 200 indicating some preferential loss of p compared to c during organic matter degradation but not approaching previously reported values of over 3000 in black shales reactive p accumulation rates in this basin range from 10 000 60 000 mol cm 2 kyr greatly exceeding the range of 500 8000 mol cm 2 kyr found in most continental margin settings including regions of modern phosphogenesis the initiation of marine sedimentation in the saanich inlet occurred after deglaciation and the high rates of p burial seen here may provide an end member example of the effects of sea level and margin sedimentation on the distribution of p within the marine p cycle

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

sedimentary patterns in the late quaternary southern ocean the spatial and temporal distribution of biogenic and lithogenic sediments in the late quaternary southern ocean reflects the zonal character of the antarctic circumpolar current and is basically controlled by glacial dynamics in antarctica sea ice distribution temperature gradients wind patterns and thermohaline ocean circulation carbonate patterns in most places reveal a decline in biogenic carbonate preservation during glacial periods mainly attributed to a reduced influx of north atlantic deep water and increased ocean stratification which modified deep water chemistry towards more corrosivity an important lithological feature of the southern ocean is the circumpolar opal belt which today is situated between the polar front and the seasonal sea ice limit to the south during the glacial periods the opal belt shifted to the north in response to a wider sea ice extension that reduced light availability and diatom productivity to the south biosiliceous productivity to the north likely was fueled by detrital iron supplied by aeolian dust input and or hemipelagic processes lithogenic fluxes generally increased during the glacial periods provenance studies on the origin and dispersal of detrital materials suggest combined effects of low sea level stands increased glaciogenic input and enhanced current transport to have caused elevated detrital fluxes the relative and absolute contribution of aeolian dust is difficult to decipher and awaits further clarification by integrated provenance studies of both marine sediments and more reference materials from the potential terrestrial source areas ice rafted debris ird represents a minor fraction of lithogenic sediments but can be used to infer both antarctic ice sheet dynamics and the fate of both sea ice and iceberg survival in the distal southern ocean future work should be concentrated on a better identification of ird origin in terms of volcaniclastic influences the distinction of east and west antarctic sediment sources and sea ice versus iceberg transportation

rapid precipitation changes in the tropical west pacific linked to north atlantic climate forcing during the last deglaciation abstract the cause of rapid hydrological changes in the tropical west pacific during the last deglaciation remains controversial in order to test whether these changes were triggered by abrupt climate change events in the north atlantic ocean variations in precipitation during the last deglaciation 18 10 ka were extracted from proxy records of chemical weathering and terrigenous input in the western philippine sea wps the evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration cia elemental ratios k al toc tn and ti ca 13corg terrigenous fraction abundance and flux data from international marine global change study program images core md06 3054 collected on the upper continental slope of eastern luzon northern philippines sediment deposited during the last glacial maximum lgm shows weathering equal to or slightly greater than holocene sediment in the wps this unusual state of chemical weathering which is inconsistent with lower air temperatures and decreased precipitation in luzon during the lgm may be due to reworking of poorly consolidated sediments on the eastern luzon continental shelf during the lgm sea level lowstand rapid changes in chemical weathering characterized by higher intensity during the heinrich event 1 h1 and younger dryas yd and lower intensity during the bolling allerod b a were linked to rapid variations in precipitation in the wps during the last deglaciation the higher terrigenous inputs during the lgm relative to those of the holocene were controlled by sea level changes rather than precipitation the terrigenous inputs show a long term decline during the last deglaciation punctuated by brief spikes during the h1 and yd related to sea level rises and rapid precipitation changes in the wps respectively the proxy records of chemical weathering and terrigenous input from eastern luzon suggest high rainfall during the h1 and yd events consistent with inferred rainfall patterns based on fe ca records from offshore mindanao rapid precipitation changes in the wps did not coincide with migrations of the intertropical convergence zone itcz but rather were related to state shifts of the el nino southern oscillation enso during the last deglaciation based on proxy records and modeling results we argue that the atlantic meridional overturning circulation amoc controlled rapid precipitation changes in the tropical west pacific through zonal shifts of enso or meridional migration of the itcz during the last deglaciation our findings highlight the dominant role of the north atlantic ocean in the tropical hydrologic cycle during the last deglaciation

genes diversity and geologic process on the pacific coast abstract we examine the genetics of marine diversification along the west coast of north america in relation to the late neogene geology and climate of the region trophically important components of the diverse west coast fauna including kelp alcid birds e g auks puffins salmon rockfish abalone and cancer crabs appear to have radiated during peaks of upwelling primarily in the late miocene and in some cases secondarily in the pleistocene phylogeographic barriers associated with mio pliocene estuaries of the mid california coast the pliocene opening of the gulf of california tectonic and eustatic evolution of the california bight as well as the influence of pleistocene and holocene climate change on genetic structure are assessed in a geologic context comparisons to east coast and western freshwater systems as well as upwelling systems around the globe provide perspective for the survey

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

glacial interglacial terrigenous provenance in the southeastern atlantic ocean the importance of deep water sources and surface currents identifying terrigenous sources in deep sea sediments may re veal temporal trends in paleocirculation and the relative role of eolian upwelled and hemipelagic fe sources to surface waters bulk elemental and isotopic geochemistry of deep sea sediments recovered during ocean drilling program leg 177 in the south eastern atlantic sector of the southern ocean reveal several im portant aspects of paleocirculation and terrigenous provenance the sites studied span 43 53 s and represent different oceano graphic settings relative to regional hydrography and sediment type bulk sediment geochemistry indicates that terrigenous prov enance varied over the past 600 k y site 1089 the northernmost site exhibits clear glacial interglacial variability in provenance while provenance appears to vary regardless of climate state at the more southerly sites site 1093 and 1094 nd and sr isotopes and sm nd ratios of the terrigenous fraction indicate that study sites have geochemically distinguishable provenance nd and sr isotopes further suggest that sites 1089 and 1094 both contain detrital com ponents that originated in south america over the past 30 k y however site 1089 is also influenced by southern african sources and the strength of the agulhas current the nd data support a more hemipelagic source for the terrigenous material rather than an eolian source based on comparisons with antarctic ice core data and known sea ice extent

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

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

sedimentary corg p ratios paleocean ventilation and phanerozoic atmospheric po2 the corg p ratios of organic rich facies tocn1 exhibit considerable variation through the phanerozoic from b10 1 in the permian phosphoria formation to n1000 1 in some devonian black shales relative to the composition of phytoplankton c p 106 1 which provide the bulk of organic c and p to organic rich marine sediments the range of phanerozoic sedimentary corg p ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of c and p remobilization enhanced preservationoforganiccatlowerredoxpotentials combinedwithenhancedsedimentaryretentionofremineralizedorganicpathigher redox potentials results in a strong relationship between benthic redox conditions and sedimentary corg p ratios the strong secular coherence of the phanerozoic corg p record i e limited variation within narrow time slices suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale such as atmospheric po2 inversion and scaling of the phanerozoic corg p record yields a new atmospheric po2 model that has strong similarities to existing models based on elemental and isotopic mass balances yet differs in some potentially significant respects in particular the new model suggests that atmospheric po2 wasmarkedlylowerduringtheearlytomiddlepaleozoicthanpreviouslyinferred duringmostofthedevonian atmospherico2levels mayhavebeensufficientlylow b13 astopreventthesustainedcombustionofplantmaterial thisfeatureofthemodelmayaccount for ananomalous gapinthefossilcharcoalrecordduringthedevonian theredox dependentburialofpintheoceanresults inpositive and negative feedback mechanisms that tend to stabilize atmospheric oxygen concentrations on geologic timescales temporal variations in the burial of p relative to c suggest that the strength of these feedback mechanisms varied over the phanerozoic 2007 elsevier b v all rights reserved

distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean abstract the southern ocean is the largest high nutrient low chlorophyll hnlc region of the world ocean it is now well recognized that the low biological productivity in this region is mainly due to the limitation of phytoplankton growth by iron however in the core of the southern ocean a massive bloom occurs annually above the kerguelen plateau in the context of keops kerguelen plateau and ocean compared study we investigated the three dimensional distribution of dissolved iron dfe concentrations southeast of the island we show that in surface waters dfe was low and not significantly different above and outside the plateau 0 090 0 034 and 0 073 0 014 nm respectively by contrast below 150 m major differences in vertical profiles of dfe were observed the deep waters above the plateau were clearly enriched with dfe concentrations up to 0 6 nm near the seafloor the regeneration from sinking biogenic material and the input from the sediments are very likely the major processes delivering dfe to the deep water the deep iron rich reservoir existing above the plateau was responsible for the natural iron fertilization of the surface water by two different mechanisms i winter mixing provided 5 times more dfe to the surface waters above the plateau than outside and ii enhanced vertical gradients of dfe and elevated vertical diffusivity resulted in an 8 fold higher diapycnal diffusive flux the natural iron fertilization presented major differences from artificial iron fertilization experiments carried out in the southern ocean the amount of dfe required to stimulate the biological activity is much less and the mode of addition is clearly different the quantification of the excess of dfe supplied in the naturally fertilized area leads to the conclusion that the natural iron fertilization is 10 150 times more efficient to export carbon below 200 m than in artificial fertilization experiments the bloom above the kerguelen plateau was contingent to iron fertilization but it was also sustained by continuous input of major nutrients thus the natural fertilization described here mimics quite well glacial period scenarios where iron fertilization of the southern ocean might have occurred from below

modeling the geochemical cycle of iron in the oceans and its impact on atmospheric co2 concentrations iron occurs at very low concentrations in seawater and seems to be a limiting factor for primary production in the equatorial pacific and the southern ocean the global distribution of iron is still not well understood because of a lack of data and the complex chemistry of iron we develop a 10 box model to study the oceanic distribution of iron and its effect on atmospheric co2 concentration subject to our assumptions we find that a lack of interocean fractionation of deep sea iron concentrations as suggested by johnson et al 1997a is not readily explained by a balance of eolian deposition scavenging and regeneration incorporation of organic complexation in the model as suggested by johnson et al to reduce the scavenging rate of iron when concentrations fall below some ligand stabilized concentration is one solution to this difficulty alternatively the deep sea concentration may be more variable than the current rather sparse data coverage suggests in the model deep sea iron concentrations are responsive to the atmospheric source even if we adopt stabilization of concentrations by a ligand as modeled by johnson et al l997a in the southern ocean where the model suggests iron supply has an important limiting effect on the biota more than 99 of the iron supply to the surface in the present day comes from upwelling and not from the local atmospheric flux in the context of glacial interglacial changes to atmospheric co2 the model suggests that increasing atmospheric iron to the entire global ocean by a factor of 2 leads to decreases in atmospheric co2 of 10 30 ppm depending on assumptions however in our model co2 concentrations are almost unaffected by changes in southern ocean atmospheric fluxes alone unless these are unrealistically large 100 times present day the effect on atmospheric carbon dioxide is slightly stronger if accompanied by increased stratification of the southern ocean the model suggests that eolian iron fertilization of the ocean could have importantly influenced glacial atmospheric co2 concentrations but that other processes must also be at work to account for the full magnitude of the glacial interglacial change

scavenged excess aluminum and its relationship to bulk titanium in biogenic sediment from the central equatorial pacific ocean we present results from chemical analyses of al and ti in surface sediment sampled along two cross equator latitudinal transects at 135w and 140w in the central equatorial pacific ocean although traditionally both al and ti are considered to reside exclusively within terrigenous phases in marine sediment these sediments present extremely high al ti ratios that are several times that of average shale and other potential crustal sources a sharp maximum in al ti is observed slightly south of the equator where sedimentary bulk accumulation rate bar is also highest reflecting elevated productivity in the overlying water caused by surface water divergence bulk al ti decreases sharply away 2 latitude to near crustal values at 4 north and south the latitudinal profiles of al ti are entirely unrelated to the concentration of the biogenic components as well as to the absolute accumulation of al and ti these results indicate the presence of a significant scavenged component of al sourced directly from seawater during particle settling the data from the two transects analytically and oceanographically confirms our earlier work that was based on the single 135w transect calculations of alexcess indicate that the highest al ti ratios correspond to 50 of the total al being unsupported by the small amount of terrigenous phases present these results are consistent with previous and ongoing studies of biogenic sediment suspended particulate matter and sediment trap material quantitative use of al as an index of terrigenous material may therefore lead to an overestimation by a factor of two of the true terrigenous load in marine sediment sedimentary rock and settling particles because bulk al ti appears to respond to sedimentary bar which in biogenic regimes is linked to surface water productivity downcore records of al ti in biogenic sediment may track productivity changes through time such al ti proxy records may be applicable in sediment of all ages unlike radionuclide tracers which are limited by radioactive decay to use over the past hundreds of kyr

modern climate forcing of terrigenous deposition in the tropics cariaco basin venezuela one approach to deciphering tropical quaternary paleoclimate records has been to study the composition of terrigenous material in order to infer past changes in hydrologic and atmospheric conditions here we present the inorganic geochemistry major and trace elements of modern sediment traps and shelf sediments in the tropical cariaco basin venezuela in order to characterize seasonal variation in deposition of the terrigenous component and to document linkages within the ocean atmosphere climate system we show that variation in the chemistry of terrigenous input to the basin is a sensitive monitor of the annual meridional migration of the intertropical convergence zone itcz additionally seasonal terrigenous relative abundances are decoupled from terrigenous absolute fluxes showing that abundances are not directly related to terrigenous delivery changes in mixing between local fluvial sediments fluvial and or eolian mafic material and saharan dust explains the observed seasonality the modern seasonal variations are significantly smaller than those observed in the glacial interglacial paleorecord indicating that climate sensitivity at the two time scales is very different a striking contrast in the behavior of ti al between the longer glacial interglacial time scale and the modern seasonality also suggests that long term terrigenous deposition is not linked simply to 100kyr shifting of the itcz the modern data can be reconciled with the glacial interglacial record by invoking generally drier conditions during glacial periods over tropical latitudes combined with intermittent wet conditions caused by precessional forcing 2007 elsevier b v all rights reserved

a 2400 yr record of natural events and anthropogenic impacts in intercorrelated terrestrial and marine sediment cores waipaoa sedimentary system new zealand the waipaoa sedimentary system spans 100 km from terrestrial upland to continental rise alluvial buffering has little effect on sediment flux at the outlet of this mesoscale dispersal system and hinterland to margin transport is accomplished rapidly because of this synergy the floodplain and shelf depocenters are sensitive to changes in sediment production in the hinterland and natural and anthropogenically forced changes in sediment source dynamics that occur at several temporal and spatial scales leave distinctive signals in the stratigraphic record manifested as variations in sediment properties these signals appear in intercorrelated sediment cores from a headwater riparian storage area and the major terrestrial and marine repositories for sediment discharged during the past 2 4 k y the signals represent the landscape response to vegetation and land use change short term fluctuations in climate that affect surface properties and processes and extreme storms and subduction thrust earthquakes extreme storms are the minimum geomorphologically effective event preserved in the sediment records lower magnitude storms that are integral components of the prevailing hydrometeorological regime create high frequency fluctuations in sediment properties and collectively contribute to event sequences of 100 yr duration events and event sequences comprise a hierarchy of temporally sensitive phenomena the impacts of which are conditioned by frequency and magnitude by contrast vegetation disturbance is a spatially sensitive phenomenon that directly impacts sediment source areas and lowers the threshold of landscape sensitivity to erosion for this reason the taupo eruption of 1 718 ka and the piecemeal vegetation changes that occurred after the arrival of polynesian settlers also generated strong depositional signals after european colonization deforestation of the hinterland altered landscape sensitivity and precipitated the transition to an erosional regime that impacted sediment production and dispersal across the entire magnitude frequency spectrum of events regulating sediment delivery to and transport in stream channels no other perturbation had such a profound impact on the late holocene depositional record

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

geochemistry petrogenesis and tectonic setting of metavolcanics and their implications for gold mineralisation in gadag gold field southern india gold bearing metavolcanics of gadag gold field ggf are represented by mafic metabasalt metabasaltic andesite intermediate metaandesite and felsic metadacite metarhyolite rocks mafic metavolcanic rocks are low k fe rich tholeiites and were derived by partial melting of the upper mantle sources with high fe mg ratios and low m values intermediate and felsic metavolcanics were formed by remelting of these tholeiites mainly in crustal regimes although a complete sequence of metavolcanic rocks from mafic to intermediate to felsic fractions occurs these products were not the result of differentiation from a single magma crustal contamination was involved in the formation of intermediate and felsic rocks a clear gap in the chemical composition as well as index of differentiation among the mafic intermediate and felsic fractions indicate that these metavolcanics constitute a typical bimodal character it is suggested that these metavolcanics were emplaced in an active continental margin or a continental island arc setting the petrogenetic processes of formation of fe rich tholeiites that evolved in an active continental margin or a continental island arc setting could have provided a favourable geochemical environment for gold mineralisation under the conditions of deformation and metamorphism

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

millennial scale instability of the antarctic ice sheet during the last glaciation records of ice rafted detritus ird concentration in deep sea cores from the southeast atlantic ocean reveal millennial scale pulses of ird delivery between 20 000 and 74 000 years ago prominent ird layers correlate across the polar frontal zone suggesting episodes of antarctic ice sheet instability carbon isotopes 13 c of benthic foraminifers a proxy of deepwater circulation reveal that south atlantic ird events coincided with strong increases in north atlantic deep water nadw production and inferred warming interstadials in the high latitude north atlantic sea level rise or increased nadw production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the weddell sea region of west antarctica

tectonic processes in papua new guinea and past productivity in the eastern equatorial pacific ocean phytoplankton growth in the eastern equatorial pacific ocean today accounts for about half of the new production the fraction of primary production fuelled by externally supplied nutrients in the global ocean the recent demonstration that an inadequate supply of iron limits primary production in this region1 supports earlier speculation that in the past fluctuations in the atmospheric deposition of iron bearing dust may have driven large changes in productivity2 but we argue here that only small 2 nm increases in the iron concentration in source waters of the upwelling equatorial undercurrent are needed to fuel intense diatom production across the entire eastern equatorial pacific ocean episodic increases in iron concentrations of this magnitude or larger were probably frequent in the past because a large component of the undercurrent originates in the convergent island arc region of papua new guinea which has experienced intensive volcanic erosional and seismic activity over the past 16 million years cycles of plankton productivity recorded in eastern equatorial pacific sediments may therefore reflect the influence of tectonic processes in the papua new guinea region superimposed on the effects of global climate forcing

terrigenous fe input and biogenic sedimentation in the glacial and interglacial equatorial pacific ocean many ocean regions important to the global carbon budget including the equatorial pacific ocean have low chlorophyll concentrations despite high levels of conventional nutrients iron may instead be the limiting nutrient and elevated input of terrigenous fe during windy glacial episodes has been hypothesized to stimulate oceanic productivity through time and thus regulate the oceanic and atmospheric co2 balance to test whether particulate fe input is related to the accumulation of biogenic matter in one important low chlorophyll high nutrient area that is the equatorial pacific ocean we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial interglacial cycles 600 000 years our data set includes new chemical data on total fe terrigenous and biogenic components in three cores as well as previously published mineralogic records of coljan input to the region chemical spectral and stratigraphic analysis indicates that 1 terrigenous input to the region shows no consistent pattern of either glacial or interglacial maxima 2 the accumulation of particulate fe is closely related to the accumulation of terrigenous matter linear r 2 0 81 0 98 3 there are no coherent spectral relationships between fe input and glacial periodicity i e 5180 in any of the orbital frequency bands 4 the linear and cross spectral correlations between fe or coljan input and caco3 concentration are most commonly the strongest observed relationships between fe and any biogenic component yet indicate a largely inverse pattern with higher fe being associated with low caco3 5 there is no consistent linear r 2 correlation or spectral coherence between the accumulation of fe and that of caco3 corg or opal thus in total there is no relationship between terrigenous fe input and sedimentary sequestering of carbon additionally although we cannot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositional change the fe ti ratio which monitors first order mineralogic changes records only slight variations that also are linearly and spectrally unrelated to glacial periodicity the bulk fe flux and the accumulation of any biogenic component finally we find that the paleoceanographic flux of fe is several order of magnitudes larger than modem observations of coljan fe input suggesting that the long term importance of fe input by dust storms which deliver fe on the order of the sedimentary burial may be underestimated the removal of particulate terrigenous fe from the recently discovered source within the equatorial undercurrent however remains unquanfified and may also prove significant

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

sedimentary iron records from the cape basin abstract the iron hypothesis suggests that dust derived fe delivered to the southern ocean during glacial intervals fueled primary productivity and led to co 2 drawdown clear support for a dustier glacial atmosphere comes from ice core records of dust concentrations furthermore there is unequivocal proof from open ocean fe fertilization experiments that primary productivity in the modern day southern ocean is limited by fe however substantial hemipelagic detrital sources dilute and obscure the eolian signal here we present records of fe concentrations total and reducible and fe fluxes to highlight the importance of hemipelagic fe sources to the cape basin we illustrate that on average only 7 of the fe flux to site 1089 can be accounted for by particle settling indicating that redistribution by bottom currents accounts for an order of magnitude more fe than particulate scavenging processes distribution by surface currents or eolian deposition we also find that on average only 7 of the fe content is easily reducible furthermore we speculate that a significant source of dissolved fe to the bottom waters may come from re suspended bottom sediments

productivity records from the southern ocean and the equatorial pacific ocean testing the glacial shelf nutrient hypothesis abstract quantifying variations in oceanic nutrient mass balances is central to understanding the links between biological productivity carbon cycle variations and climate one challenge in mass balance determinations is in developing appropriate proxies and applying them in a number of oceanic settings on comparable time scales on glacial timescales it is important to separate nutrient variations driven by external processes e g continental weathering dust inputs from those driven by internal processes i e changing loci of upwelling changes in nutrient inventories here we compare several upwelling regions as a first order analysis of phosphorus p inventory variations in the ocean sea level variations should have a profound impact on the continental margin sink of this biolimiting nutrient on glacial timescales new estimates for a shorter response time of p in the ocean suggest that variations in the p cycle play a role on marine biological productivity and thus the carbon cycle during glacial interglacial intervals although this glacial transfer of nutrients from shelves to the deep sea was postulated over two decades ago few quantitative data have been produced to support or refute this hypothesis supported by a more thorough understanding of p sedimentary geochemistry we present here detailed records of variations in oceanic p cycling on glacial timescales showing that the redistribution of this nutrient from marginal to deep sea sinks during glacial lowstands has had an impact on the oceanic p cycle furthermore p based records of export production from the southern and equatorial pacific oceans indicate that this redistribution of p resulted in higher oceanic dissolved p concentrations and increased oceanic productivity toward the end of glacials and the beginning of subsequent interglacials a 10 20 kyr lag between p based export production records and sea level supports the newer estimates of the marine p response time and indicates that this nutrient lag may be a heretofore unrecognized driver of other biological paleoproductivity records

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

the distribution and chemical speciation of dissolved and particulate phosphorus in the bering sea and the chukchi beaufort seas abstract water samples were collected from the bering sea and the chukchi beaufort seas during the 4th chinese arctic research expedition in summer 2010 to examine the abundance spatial distribution and phase partitioning of phosphorus p between dissolved and particulate inorganic and organic phases measurements of p species included dissolved inorganic p dip dissolved organic p dop and five particulate p species operationally defined by sequential extraction techniques inorganic p was generally the predominant form of both dissolved and particulate p comprising on average up to 91 13 of the dissolved phase and 72 23 of the particulate phase in the study area concentrations of dip in the water column of the chukchi sea and bering sea were considerably higher than those in the beaufort sea 3 m vs 1 m showing a strong influence of north pacific inflow waters the percentage of dop in the dissolved p pool was generally higher in surface waters than deeper waters and higher in the chukchi sea than in the bering sea consistent with their difference in primary productivity and reflecting sources of dop from the surface waters within the particulate p pool the labile p and ferric bound p were the two predominant species especially in the upper water column

the natural iron fertilization experiment keops kerguelen ocean and plateau compared study an overview when the first scientific voyages went to the southern ocean high levels of living biomass were observed in the vicinity of islands hart 1942 was the first to mention that the abundant biomass might be due to the release of oligoelements like iron from the island this hypothesis however remained unverified for more than half a century because of the experimental difficulties in properly manipulating water with subnanomolar iron concentrations when john martin formulated the iron hypothesis martin 1990 and provided the first supporting evidence of it he also suggested using the chlorophyll plume observed westward of the galapagos island in the equatorial pacific as a natural iron fertilization experiment

temporal relationship between cratonization and glaciation the vendian early cambrian glaciation in western gondwana abstract cratonization has long been said to favour glaciation cratons would be ideal cradles for the development of continental ice caps in western africa the widespread continental glaciation developed near the proterozoic paleozoic boundary can no longer be considered as vendian according to the recent discovery of an early cambrian microfauna in eastern senegal it extends until atdabanian time 530 520 ma the age of its beginning lacks in precision it can be vendian or early cambrian in the hoggar fold belt it constitutes the lower part of molassic intermontane sequences where it is about 30 40 ma younger than the pan african cratonization dated at 600 ma this extensive cratonization closed the old long lived pan african brasiliano cycle 1000 600 ma and is responsible for the aggregation of west gondwana in the south american paraguay belt glacial sequences also postdate brasiliano cratonization dated at 590 ma they are probably vendian overlain by an ediacara like fauna and slightly older than those of western africa the glaciation was restricted to the shoulders of rifted basins initiating the young short lived pan african brasiliano cycle 600 or slightly younger to 520 ma world distribution of continents indicate that the widespread late vendian early cambrian ice cap glaciation of west africa developed at middle latitudes 50 30 whereas the probably vendian glaciation of the paraguay belt restricted to local highlands occupied high to middle latitudes 60 in western gondwana glaciation and cratonization occurring near the proterozoic cambrian boundary appear as distinct and temporary unrelated phenomena

a sediment nutrient oxygen feedback responsible for productivity variations in late miocene sapropel sequences of the western mediterranean abstract cyclic sediments observed throughout the mediterranean during the late miocene have been related to precessional forcing of ocean stratification individual couplets typically 2 m thick sequences of sapropels and diatom rich marls can be reliably traced from western spain to crete and were formed in restricted marginal basins micropaleontological evidence indicates paradoxically that the organic carbon rich sapropels were formed under low productivity conditions marked by surface water stratification and deep anoxia whereas the diatom rich marls were formed under high productivity conditions marked by upwelling here we present geochemical evidence mainly from detailed phosphorus determinations and paleo redox proxies indicating that a sediment nutrient oxygen feedback herein dubbed the sno effect is in part responsible for driving the observed productivity variations during stratification anoxic conditions in these basins cause the release of the limiting nutrient phosphorus from reducible oxide phases in the sediments basin stagnation causes the buildup of phosphorus below the photic zone subsequent overturn driven by precessionally driven winds injects phosphorus rich bottom waters into the photic zone the biotic response to this overturn is high productivity in marls directly overlying the sapropels culminating in diatom mat formation exhaustion of the stored excess phosphorus results in lower productivity marls which grade back into sapropels due to lower wind stresses and the return of stagnant basin conditions these findings indicate that the sno effect may in part be responsible for precessional scale productivity variations observed in parts of the mediterranean and perhaps present in other restricted ocean basins like the miocene monterey formation and the modern santa barbara basin

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

glacial interglacial variations in marine phosphorus cycling implications for ocean productivity 1 using a box model of organic carbon c and phosphorus p cycling in the global ocean we assess the effects of changes in the continental supply of reactive p oceanic mixing and sea level on the marine p cycle on glacial interglacial timescales our model results suggest that mixing is a dominant forcing during early glaciation causing retention of p in the deep ocean thereby lowering primary production and associated organic c and p burial sea level fall is the dominant forcing during late glaciation when reduced coastal trapping of reactive p enhances its transfer to the open ocean restoring primary production and p burial during postglacial periods changes in circulation and weathering dominate open ocean processes and oceanic primary production peaks as primary production is reduced upon glaciation changes in the marine p cycle are unlikely to drive enhanced primary production and co2 drawdown during glaciation

a model of the iron cycle in the ocean the ironex ii in situ fertilization experiment showed decisively that availability of iron limits the growth of phytoplankton in equatorial pacific surface waters high nutrient low chlorophyll hnlc surface waters potentially iron limited are also found in the north pacific and the southern ocean a model of seawater iron geochemistry has been incorporated into a global ocean circulation and carbon cycle model and tuned to match the observed ocean fe distribution the model reproduces the observed hnlc areas in the equatorial pacific and southern ocean but predicts nutrient depletion in the north pacific a region of high dust fluxes from asia the model is based on the idea that the concentrations of organic iron binding ligands in seawater control the subsurface fe concentration and predicts that a majority 70 80 of the global carbon export production can be sustained by upwelling of dissolved iron in seawater rather than by atmospheric deposition the ocean iron cycle increases the efficiency of iron utilization in the biological pump buffers new production against interannual fluctuations in iron deposition and contributes several new intrinsic timescales to the ocean carbon cycle several hundred years for the ocean iron concentration and perhaps several thousand for the concentration of ligand in the deep sea ocean recycling of fe appears to play a major role in determining the strength of the biological pump in the ocean and the pco2 of the atmosphere

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

redox fluctuations trace metal enrichment and phosphogenesis in the 2 0 ga zaonega formation abstract the 2 0 ga zaonega formation zf holds one of the oldest phosphorites in the geologic record reaching 15 p2o5 understanding the depositional conditions that enabled sedimentary phosphorus enrichment in this unit will thus help us to interpret the significance of the temporal distribution of phosphorites in earth s early history here we use an array of major and trace element data to constrain the redox conditions in the water column and extent of basinal restriction during deposition of the zf we also present new selenium se abundance and isotopic data to provide firmer constraints on fluctuations across high redox potentials which might be critical for phosphogenesis we find that se isotope ratios shift over a range of 3 in the zf with the earliest stratigraphically resolved negative se isotope excursion in the geologic record implying at least temporarily suboxic waters in the basin furthermore we find that redox sensitive element rse enrichments coincide with episodes of p enrichment thereby implicating a common set of environmental controls on these processes together our dataset implies deposition under a predominantly anoxic water column with periodic fluctuations to more oxidizing conditions because of connections to a large oxic reservoir containing se oxyanions and other rse s as well as sulfate in the open ocean this is broadly consistent with the depositional setting of many modern and recent phosphorites thereby tying these ancient deposits to a common depositional mechanism in light of these data we propose that the broader prevalence of phosphogenesis in the paleoproterozoic era was driven by growth of the seawater oxidant reservoir namely sulfate thus enabling diagenetic apatite precipitation in basins with high rates of export production particularly by facilitating the activity of sulfide oxidizing bacteria this suggests that the muted authigenic p burial observed in marginal marine siliciclastic sedimentary rocks during other intervals of the precambrian was not merely a result of low dissolved p levels in the global deep ocean but also was influenced by sulfate scarcity and strongly reducing bottom water conditions

phosphorus accumulation in marine sediments and the oceanic phosphorus cycle ideas about key factors in the oceanic mass balance of dissolved reactive phosphate have changed substantially i present an integrated overview of these here with an emphasis on evaluating the burial sinks for p and defining areas needing further research the major source of reactive p to the ocean is river input reactive p is delivered to the oceanic sediment water interface primarily in particulate organic matter p scavenged by hydrothermal iron rich oxyhydroxide particles with uptake in proportion to deep water phosphate concentrations represents a substantially smaller flux to the sediment water interface diagenetic transformations are important influences on the form of reactive p burial in marine sediments p burial occurs with organic carbon burial and as p associated with iron rich oxyhydroxide particles and coatings formation of authigenic p rich phases presumably apatite at the expense of organic p and oxide associated p is significant in open ocean marine sediments the authigenic p sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on p burial in organic rich continental margin sediments

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

feedback between aeolian dust climate and atmospheric co2 in glacial time 1 enhanced aeolian supply of iron to the biota of the southern ocean during glacial periods is suspected to be an important contributory mechanism to the concurrently low observed mixing ratios of atmospheric co2 declining rates of dust deposition prior to the glacial terminations may be critical in driving the initial deglacial rise in co2 but the reasons behind the dust decline itself are as yet unknown here we show that the dust record from the vostok ice core can be qualitatively derived from a few general assumptions regarding the formation and aging of patagonian sources of aeolian material and the efficiency with which it is transported through the atmosphere we suggest that during glacial periods this dust supply becomes particularly sensitive to changes in global climate and that in turn climate is responsive to the dust due to iron fertilization this positive feedback may mean that during glacial periods the carbon cycle exhibits two quasi steady states characterized by distinct co2 concentrations recognition of this glacial subcycle may help to account for the timing and sequence of events at the terminations

reassessment of the oceanic residence time of phosphorus phosphorus p is an essential nutrient for the growth of all organisms and is believed to limit marine productivity especially on geologic time scales holland 1984 smith 1984 howarth 1988 codispoti 1989 as a result of the link between marine photosynthetic productivity and atmospheric co2 phosphorus along with other nutrients present in short supply in the euphoric zone have been cited as potential players in the ocean s role in climate change this link has been referred to as the nutrient co2 connection broecker 1982 model simulations which aim to quantify the role of oceanic nutrient inventories in promoting or enhancing climate change rely on the most currently formulated element budgets for the ocean in this paper significant modifications to the currently accepted marine phosphorus budget are proposed the modified p budget presented here requires a reassessment of phosphorus residence time in the ocean and a concomitant review of the role of p as a potential player in climate change over glacialinterglacial time scales element budgets constructed for the oceans consist of a mass balance between inputs and outputs for which the simplifying assumption is generally made that the ocean is in steady state with the specific element in question the fluvial p flux constitutes the bulk of the input term for the marine phosphorus budget atmospheric input is 10 of the fluvial input froelich et al 1982 burial with sediments is the mechanism for ultimate removal of p from the oceans for a system at steady state the input flux equals the output flux in the present paper we focus on the output flux burial with sediments for two reasons first the chemistry of phosphorus buried in sediment cores from which p burial fluxes are calculated has not been affected to the same degree as rivers by anthropogenic perturbation it is therefore simpler to quantify the output term of the p budget which can be extrapolated to pre anthropogenic times second detailed p speciation data permit us to quantify the burial flux of reactive p as contrasted with refractory p in sediments this distinction is significant because burial of reactive p constitutes removal of potentially bio available p from the oceans two types of modification to the marine phosphorus budget are proposed here first the locus of p burial is addressed specifically the importance of p burial in the deep sea is contrasted with p burial in continental margins second the burial flux is characterized in terms of reactive potentially bio available p vs refractory p this distinction is made possible by obtaining detailed p speciation data from application of the sedex method ruttenberg 1992 a selective leaching procedure which separates solid phase p into five reservoirs on the basis of chemical reactivity loosely sorbed p ferric iron bound p authigenic apatite biogenic apatite c a c o 3 bound p detrital apatite p and organic p detailed p spe

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

long term controls on ocean phosphorus and oxygen in a global biogeochemical model 1 in this study we use a biogeochemical ocean general circulation model hamocc originally developed for the carbon and silicon cycles and expand it with a description of the sedimentary phosphorus p cycle the model simulates the release of reactive p by aerobic and anaerobic degradation of organic matter in the sediment as well as formation and burial of fe oxide bound p and authigenic ca p minerals we also include pre anthropogenic inputs of p from atmospheric dust which is mostly in the form of detrital apatite model predicted total p concentrations and rates of reactive p burial for the deep sea agree reasonably well with observations in open ocean and near continental margin sediments as part of a sensitivity analysis we assess the long term response of ocean productivity and deep water oxygenation to increases in the riverine input of p and preferential release of p from sediments the simulations show that the feedback from preferential p regeneration accelerates the expansion of suboxia o2 2 5mm along continental margins and in the naturally suboxic areas in tropical subtropical regions on timescales of 10 100 ka for a case in which maximum p regeneration from sediments is enabled a large scale pattern of bottom water suboxia 30 of the total ocean area develops over the southeastern tropical and northern pacific ocean sectors

water level and redox fluctuations in a sichuan basin lacustrine system coincident with the toarcian oae abstract increasing cases have indicated that oceanic anoxic events oaes appear to have records in terrestrial sediments which provide valuably high resolution materials for the debated and challenging issues of oaes however the current works are preliminary and need more geological analyses to test here we present a case study in the lower jurassic da anzhai member of the toarcian ca 180 ma sichuan basin sw china the petrology and sedimentary facies of the da anzhai member were used to reconstruct the relative water level fluctuations in the sichuan basin which are revealed to be consistent with coeval changes in global sea levels the da anzhai member was deposited during a period of lake shallowing with enhanced salinities corroborated by the sr ba and s toc ratios when sea level was generally high after global transgression during the lake shallowing there were four complete secondary lacustrine deepening shallowing cycles over shorter time scales the total organic carbon contents and organic carbon isotopic stratigraphy show there was a basin wide terrestrial response to the t oae as recorded by the da anzhai member the enrichment factors of mo relative to paas moef and corg p values imply a dysoxic redox condition the terrestrial response of oaes is likely caused by changes in hydrological conditions which were related to the global warming triggered by the karoo ferrar large igneous province the associated organic carbon accumulation mechanism is a combined effect of elevated primary productivity and oxygen depleted preservation conditions our data suggest that oaes do have terrestrial response and induce organic carbon accumulation but the mechanisms are still not much clear and need further studies

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

terrigenous sediment export from the western margin of south africa on glacial to interglacial cycles abstract similar to many shelves globally pleistocene terrigenous sediment deposition on the western shelf of south africa is strongly influenced by high amplitude sea level fluctuations over glacial to interglacial climate cycles here variations in the glauconitic quartzose sand and terrigenous mud content of gravity cores from the western slope of south africa are used to evaluate the dynamics of shelf sediment export over climate cycles of the last 450 kyr calcareous ooze on the slope contains a mean of 0 2 to 8 wt glauconitic quartzose sand derived from erosion of neogene outer shelf sediments and 13 to 40 wt terrigenous mud sourced from the orange river quartz sand content on the slope increases during glacial periods and is sharply reduced across glacial terminations and throughout interglacial highstands relative sea level changes on the margin estimated from the quartz sand content on the slope are consistent with the timing but not amplitude of proposed eustatic sea level records a possible mechanism of sand erosion on the outer shelf is the vertical mixing forced by internal tides which may intensify over the shelf break as sea level is lowered during glacials turbidites are rare and bottom currents are generally capable of suspending mud but not sand except locally along the margin estimated variations in the bulk sedimentation rate and terrigenous mud mass accumulation rate on the slope suggest that export of terrigenous mud off the shelf during glacial lowstands is transported beyond the slope at intermediate and deeper water depths to the southern ocean

paleo ocean chemistry records in marine opal implications for fluxes of trace elements cosmogenic nuclides 10be and 26al and biological productivity abstract here we provide evidence suggesting that marine diatom opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray produced radionuclides 10 be and 26 al but also a record of temporal variations in a large number of trace elements such as ti fe zn and mn this finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics initial results from a sediment core taken near the present day position of the antarctic polar front odp site 1093 show dramatic changes in the intrinsic concentrations of be al ti fe mn and zn in the opal assemblages during the past 140 kyr bp the results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements the time series of total be al ti fe and 10 be in the sediment core are all well correlated with each other and with dust records in the polar ice cores the observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust in this case presumably from the patagonia this observation also allows determination of fluxes of dust contributed 10 be to the antarctica ice sheets however our data show that the relationships among the various metals are not perfectly linear during periods of higher dissolved concentrations of trace elements indicated by fe and ti the relative concentrations of bioreactive elements be al mn and zn are decreased by contrast the fe zn and fe mn ratios decrease significantly during each transition from cold to warm periods the relative behavior could be consistent with any of the following processes i enhanced biological productivity due to greater supply of the bioreactive elements e g zn during cold periods ii increased biological and inorganic scavenging of particle active elements e g be and al during early interglacial periods iii differential uptake removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate in any case with one sedimentary phase and in single sedimentary sections we now have the potential to compare directly a proxy for aeolian input of micronutrients e g fe or ti with a proxy for production e g 26 al al ratios we expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity which exhibit different sensitivities to global climate fluctuations and micronutrient inputs would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide martin j h 1990 glacial interglacial co 2 change the iron hypothesis paleoceanography 5 1 13 our present data from a single site do not show that increases in dissolved fe concentrations per se were responsible for increased biological productivity however a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides 10 be and 26 al from various oceanic provinces

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial

tracking the dispersal of hydrothermal plumes from the juan de fuca ridge using suspended matter compositions in 1988 and 1989 particles from on and off axis neutrally buoyant plumes over the juan de fuca ridge were sampled to study their changing composition with distance from the ridge crest plume depth and particle composition in off axis hydrothermal plumes were used to identify plume sources and trajectories iron and phosphorus concentrations and in particular p fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter phosphorus vanadium and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer sized particles of fe oxyhydroxide the p fe molar ratio 0 23 is essentially the same for vent fields along cleft and endeavour segments indicating that the scavenging processes are the same for both regions high p fe ratios are observed over the south and north cleft segment vent fields and to the west along the vance seamount chain the seamounts evidently function as a barrier bathymetrically steering the hydrothermal plumes to the west away from the ridge crest since particles from the endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the juan de fuca ridge copper concentrations in the plumes can be used to distinguish plume sources based on water column depth and elemental composition hydrothermal plume particles from specific vent fields on the juan de fuca ridge may be tracked as much as several tens of kilometers from their source using particle compositions