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

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

nd and pb isotope time series from atlantic ferromanganese crusts implications for changes in provenance and paleocirculation over the last 8 myr high resolution nd and pb isotope time series for the last 8 myr are reported for four atlantic ferromanganese crusts dated by 10be 9be chronology these are compared to new high resolution and high precision pb isotope time series and recently published nd isotope time series for two previously studied crusts from the nw atlantic ocean these records allow a more detailed examination of atlantic deepwater variability over the time period of intensification of northern hemisphere glaciation nhg changes in the pb isotope time series started after 3 ma but were most dramatic over the last 1 8 myr coinciding with changes of pb isotopes in the arctic ocean this latter change post dates the intensification of nhg at 3 1 to 2 5 ma and reflects an increase in the input of material eroded from the archean shield of canada and greenland shifts in nd and pb isotope compositions in a crust from the blake plateau occur before 5 ma and most prominent at 8 ma suggest that water masses from either the pacific or southern ocean influenced the isotope composition of this crust the relatively high end values around 8 ma recorded by the blake plateau crust are explained by a contribution of eastward flowing pacific water through the panama gateway into the caribbean sea this high end signal decreased between 8 and 5 ma suggesting that the supply of pacific water into the caribbean became restricted this is earlier than the caribbean seawater salinity increase at 4 2 ma deduced from 18o data and may indicate that there was only a surface water connection between the caribbean and pacific between 5 and 4 2 ma the closure of the panama gateway to intermediate and deep water exchange 200 m depth apparently occurred much earlier than the intensification of northern hemisphere glaciation at 3 1 2 5 ma and cannot therefore have been a direct cause of this climatic change but may as recently argued only have been a necessary precondition

permian to early triassic magnetostratigraphy from the central european basin in poland implications on regional and worldwide correlations abstract permian early triassic rocks sampled in 15 outcrops 93 hand samples and 11 unoriented boreholes 630 hand samples from the polish part of the central european basin were studied paleomagnetically in spite of extensive remagnetization affecting 50 of samples from the boreholes a magnetic polarity sequence was compiled the polarity pattern is not only common for many sections from the investigated area but also convergent with the global synthetic magnetostratigraphic scale the lower rotliegend early permian rocks contain a reversed polarity record while the upper rotliegend late permian early triassic sediments are characterized by mixed polarity magnetization within the buntsandstein part of that mixed megazone 14 magnetic zones were found buntsandstein sedimentation started with a normal polarity zone which may be compared with that of early griesbachian defined in several places in the world the polarity record noted in the middle buntsandstein sediments could indicate significant stratigraphic gaps or condensations near the middle buntsandstein and rot boundary the comparison of the upper buntsandstein polarity with the early middle triassic magnetostratigraphic data from other basins suggests that the majority or even all the rot sediments should be included in the anisian

multiple early triassic greenhouse crises impeded recovery from late permian mass extinction the late permian mass extinction was not only the most catastrophic known loss of biodiversity but was followed by unusually prolonged recovery through the early triassic opinion has been divided on whether delayed recovery was a legacy of especially profound ecological disruption or due to additional environmental perturbations new records from the sydney basin in southeastern australia now reveal five successive late permian and early triassic spikes of unusually high atmospheric co2 and profound chemical weathering these successive atmospheric co2 greenhouse crises coincided with unusually warm and wet paleoclimates for a paleolatitude of 61 s successive transient greenhouse crises punctuated long term cool dry and low co2 conditions and may account for the persistence of low diversity and small size in early triassic plants and animals

rare earth elements and neodymium isotopes in sedimentary organic matter abstract we report rare earth element ree and neodymium nd isotope data for the organic fraction of sediments collected from various depositional environments i e rivers n 25 estuaries n 18 open ocean settings n 15 and cold seeps n 12 sedimentary organic matter som was extracted using a mixed hydrogen peroxide nitric acid solution 20 h2o2 0 02 m hno3 after removal of carbonate and oxy hydroxide phases with dilute hydrochloric acid 0 25 m hcl a series of experimental tests indicate that extraction of sedimentary organic compounds using h2o2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates however this contamination is expected to be minor for ree because measured concentrations in h2o2 leachates are about two orders of magnitude higher than in the above mentioned phases the mean ree concentrations determined in the h2o2 leachates for samples from rivers estuaries coastal seas and open ocean settings yield relatively similar levels with ree 109 86 ppm mean s n 58 the organic fractions leached from cold seep sediments display even higher concentration levels 285 150 ppm mean s n 12 the h2o2 leachates for most sediments exhibit remarkably similar shale normalized ree patterns all characterized by a mid ree enrichment compared to the other ree this suggests that the distribution of ree in leached sedimentary organic phases is controlled primarily by biogeochemical processes rather than by the composition of the source from which they derive e g pore river or sea water the nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions in contrast the som extracted from marine sediments display end values that typically range between the end signatures for terrestrial organic matter inferred from the analysis of the sedimentary detrital fractions and marine organic matter inferred from the analysis of local surface seawater a notable exception is the case of organic matter om fractions leached from cold seep sediment samples which sometimes exhibit end values markedly different from both terrigenous and surface seawater signatures this suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes recycling pore water ree characterized by a distinct isotopic composition overall our results confirm that organic matter probably plays an important role in the oceanic ree budget through direct scavenging and remineralization within the water column both the high ree abundances and the shape of shale normalized patterns for leached som also suggest that om degradation in sub surface marine sediments during early diagenesis could control to a large extent the distribution of ree in pore waters benthic fluxes of organic bound ree could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins neodymium isotopes could provide useful information for tracing the origin terrestrial versus marine and geographical provenance of organic matter with potential applications in paleoceanography in particular future studies should further investigate the potential of nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation

variable eocene miocene sedimentation processes and bottom water redox conditions in the central arctic ocean iodp expedition 302 abstract in 2004 integrated ocean drilling program expedition 302 arctic coring expedition acex to the lomonosov ridge drilled the first central arctic ocean sediment record reaching the uppermost cretaceous 430 m composite depth while the neogene part of the record is characterized by grayish yellowish siliciclastic material the paleogene part is dominated by biosiliceous black shale type sediments the lithological transition between paleogene and neogene deposits was initially interpreted as a single sedimentological unconformity hiatus of 26 ma duration separating eocene from miocene strata more recently however continuous sedimentation on lomonosov ridge throughout the cenozoic was proclaimed questioning the existence of a hiatus in this context we studied the elemental and mineralogical sediment composition around the paleogene neogene transition at high resolution to reconstruct variations in the depositional regime e g wave current activity detrital provenance and bottom water redox conditions already below the hiatus mineralogical and geochemical proxies imply drastic changes in sediment provenance and or weathering intensity in the hinterland and point to the existence of another earlier gap in the sediment record the sediments directly overlying the hiatus the zebra interval are characterized by pronounced and abrupt compositional changes that suggest repeated erosion and re deposition of material regarding redox conditions euxinic bottom waters prevailed at the eocene lomonosov ridge and became even more severe directly before the hiatus with detrital sedimentation rates decreasing authigenic trace metals were highly enriched in the sediment this continuous authigenic trace metal enrichment under persistent euxinia implies that the arctic trace metal pool was renewed continuously by water mass exchange with the world ocean so the eocene arctic ocean was not fully restricted above the hiatus extreme positive ce anomalies are clear signs of a periodically well oxygenated water column but redox conditions were highly variable during deposition of the zebra interval significant mn enrichments only occur above the zebra interval documenting the miocene establishment of stable oxic conditions in the arctic ocean in summary extreme and abrupt changes in geochemistry and mineralogy across the studied sediment section do not suggest continuous sedimentation at the lomonosov ridge around the eocene miocene transition but imply repeated periods of very low sedimentation rates and or erosion

neodymium isotope constraints on chemical weathering and past glacial activity in svalbard abstract neodymium nd isotopes in leached authigenic components of marine sediments have been increasingly used as a tracer of past ocean water masses despite the general assumption that the nd isotopic composition of solutes released during chemical weathering fingerprints the source rocks on continents preferential dissolution of easily dissolvable phases may result in significant deviations in nd isotopic composition between the solutes and the source rocks with potential implications for the utility of nd isotopes in paleoenvironmental studies here we present the nd isotopic compositions of leached and detrital fractions separated from bedrock and marine sediment samples from the svalbard archipelago our goal is to further understand the behaviour of nd isotopes during chemical weathering in glacial catchments and evaluate how glacier fluctuations and associated weathering congruency may have affected the export of dissolved nd isotope signatures to seawater our results confirm that terrestrial weathering on svalbard causes considerable nd isotopic decoupling between the leached and detrital fractions of fjord sediments end resulting from the preferential dissolution of marine precipitates in glaciated catchments dominated by sedimentary rocks we also show that the degree of nd isotopic decoupling has fluctuated in response to climate variability on svalbard during the holocene which is also as suggested by the occurrence of generally higher end values during periods of glacier advances in sediment cores retrieved from two different fjords dicksonfjorden and woodfjorden we posit that the high end values can be ascribed to incongruent chemical weathering of fresh rock flour produced by glacial abrasion this finding suggests that the degree of nd isotopic decoupling could be used as a new proxy for tracing glacial fluctuations and associated glacier derived nutrient inputs to the marine realm

the large scale evolution of neodymium isotopic composition in the global modern and holocene ocean revealed from seawater and archive data neodymium isotopic compositions 143nd 144nd or end have been used as a tracer of water masses and lithogenic inputs to the ocean to further evaluate the faithfulness of this tracer we have updated a global seawater end database and combined it with hydrography parameters temperature salinity nutrients and oxygen concentrations carbon isotopic ratio and radiocarbon of dissolved inorganic carbon archive end data are also compiled for leachates foraminiferal tests deep sea corals and fish teeth debris from the holocene period 10 000 years at water depths 1500 m property property plots show clear correlations between seawater end and the other variables suggesting that large scale water mass mixing is a primary control of deepwater end distribution at 200 m basin scale seawater t s end diagrams demonstrate the isotopic evolution of different water masses seawater and archive end values are compared using property property plots and t s end diagrams archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the pacific both positive and negative offsets exist in the northern north atlantic applying multiple regression analysis to deep 1500 m seawater data we established empirical equations that predict the main large scale deepwater end trends from hydrography parameters large offsets from the predicted values are interpreted as a sign of significant local regional influence dominant continental influence on seawater and archive end is observed mainly within 1000 km from the continents generally seawater and archive end values form gradual latitudinal trend in the atlantic and pacific at depths 600 m consistent with the idea that nd isotopes help distinguish between northern southern sourced water contributions at intermediate and deep water depths

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

sedimentary fe mn oxyhydroxides as paleoceanographic archives and the role of aeolian flux in regulating oceanic dissolved ree in the marine environment authigenic ferromanganese fe mn oxides precipitate from seawater incorporating many dissolved trace elements such as nd pb whose isotopic composition is a direct proxy for ambient seawater thus isotopic studies of the fe mn oxyhydroxide component leached from sedimentary records can provide information on changes in erosional input or ocean circulation changes such studies may be complicated however by the presence of detrital material containing a fe mn oxide component which may mask the true seawater signal in addition the formation of fe mn oxyhydroxides in the marine environment remains poorly understood in particular the phase carbonates detrital particles that controls the delivery of authigenic fe mn oxides to the sediments has not yet been determined in this study we have analysed the ree and nd isotopic compositions of fe mn oxyhydroxide fractions dispersed in marine sediment cores from the cape and angola basins in the se atlantic cruise images ii for the angola basin deep sea core located at 1000 km south of the congo river mouth both the ree and nd isotopic compositions nd measured in recent fe mn oxyhydroxide fractions are typical of congo river borne fe mn oxides this shows that preformed fe mn oxides associated with detrital fractions can locally contaminate the seawater signal recorded by authigenic oxyhydroxides by contrast examination of ree distributions nd isotope data and mass accumulation rates in cape basin sediments shows paradoxically that the flux of fe mn oxides to sediments is controlled by aeolian particles from the nearby namib desert even though their ree and nd compositions point clearly to an authigenic origin it is proposed that partial dissolution of aeolian dust occurs in the water column releasing into solution its easily leachable fe mn component the dissolved fe2 and mn2 would then fuel the reprecipitation of authigenic fe mn oxyhydroxides scavenging additional dissolved trace elements from the ocean most probably from deep water masses in this case calculations suggest that aeolian deposition acts as a net sink for dissolved nd in the cape basin rather than a source and allows us to estimate the rate of removal of dissolved nd associated with atmospheric deposition yielding a global oceanic residence time for nd nd of between 500 and 1400 years

changing redox conditions at cold seeps as revealed by authigenic carbonates from alaminos canyon northern gulf of mexico anaerobic oxidation of methane in anoxic sediments at cold seeps often leads to formation of authigenic carbonates close to the seafloor along continental margins recent work however indicated that the redox conditions in sediments may vary to some degree during seepage activity in order to shed new light on the extent of this variability authigenic carbonates from alaminos canyon lease block 645 of the northern gulf of mexico have been characterized by means of inorganic and organic geochemistry the carbonates were collected from seep deposits representing various seafloor morphologies including extensive pavements mounds fractured carbonate slabs surrounded by dense bivalve shells and vestimentiferan tubeworm colonies the deposits almost entirely consist of aragonite the 18o values of aragonite vary from 2 6 to 5 8 v pdb suggesting precipitation in slight disequilibrium with the surrounding pore fluids the 13c values of aragonite between 33 9 and 20 4 v pdb agree with variable amounts of carbonate derived from oxidation of thermogenic methane and crude oil methane was primarily oxidized in an anaerobic process as revealed by the presence of 13c depleted molecular fossils of methane oxidizing archaea 13c values as negative as 118 and sulfate reducing bacteria 13c values as negative as 97 the syntrophic partners in the anaerobic oxidation of methane the observed inventories of molecular fossils in the authigenic carbonates mirror those of known consortia of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria namely the anme 2 desulfosarcina desulfococcus dss and anme 3 desulfobulbus dbb consortia in contrast the same carbonates exhibit shale normalized rare earth elements patterns that all display real negative ce anomalies ce ce 0 78 suggesting that at least temporarily oxic conditions prevailed the episodic occurrence of oxic conditions is confirmed by the presence of molecular fossils of aerobic methanotrophic bacteria including 4 methylcholesta 8 14 24 dien 3 ol and two bacteriohopanepolyols aminotetrol and aminotriol the 13c values of the biomarkers of aerobic methanotrophs are as negative as 58 and are consequently less 13c depleted than the molecular fossils of the prokaryotes performing anaerobic oxidation of methane a pattern in accord with culture experiments overall our results suggest that redox conditions at cold seeps are variable this variability probably reflects changes in seepage flux the combination of an inorganic and an organic geochemical approach used here is promising to better assess the variability and diversity of past fluid and gas expulsion at seeps

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

rare earth elements in the nw indian ocean abstract dissolved rare earth element ree distributions have been determined at three stations in the high productivity nw indian ocean nwio upwelling zone dissolved ree distributions within the well oxygenated surface waters and deep portions of the water column are similar to those reported previously from other open ocean locations at depth dissolved ree concentrations are intermediate between those of the atlantic and pacific oceans consistent with the continuous regeneration and enrichment of the strictly trivalent rees in and the progressive oxidative removal of ce from the deep ocean within the mid depth oxygen minimum zone dissolved ree concentrations exhibit a notable enrichment superimposed upon these typical oceanic profiles further dissolved ce concentrations are preferentially enriched within the suboxic horizon compared to the rest of the series indicating the reduction of insoluble ce iv to dissolved ce iii at these depths by analogy with our previous studies of ree distributions in anoxic basins we propose that the more modest enrichments of the strictly trivalent rees observed in the nwio suboxic zone must derive from uptake through scavenging within the well oxygenated portions of the water column and regeneration from sediments and settling particles within the more reducing conditions of the oxygen minimum zone

evolution of deepwater mixing and weathering inputs in the central atlantic ocean over the past 33 myr the isotopic composition of nd in present day deep waters of the central and northeastern atlantic ocean is thought to fingerprint mixing of north atlantic deep water with antarctic bottom water the central atlantic romanche and vema fracture zones are considered the most important pathways for deep water exchange between the western and eastern atlantic basins today we present new nd isotope records of the deepwater evolution in the fracture zones obtained from ferromanganese crusts which are inconsistent with simple water mass mixing alone prior to 3 ma and require additional inputs from other sources the new pb isotope time series from the fracture zones are inexplicable by simple mixing of north atlantic deep water and antarctic bottom water for the entire past 33 myr the distinct and relatively invariable nd and pb isotope records of deep waters in the fracture zones appear instead to have been controlled to a large extent by contributions from saharan dust and the orinoco amazon rivers thus the previously observed similarity of nd and pb isotope time series from the western and eastern north atlantic basins is better explainable by direct supply of labrador seawater to the eastern basin via a northern pathway rather than by advection of north atlantic deep water via the romanche and vema fracture zones

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

sr_nd_pb isotope systematics in amazon and congo river systems constraints about erosion processes abstract 87 sr 86 sr 143 nd 144 nd 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb isotopic ratios and rb sr sm nd u pb and th concentrations have been measured in the suspended loads of the congo and amazon rivers and their tributaries in the dissolved load 87 sr 86 sr rb sr nd sm u pb and th concentrations are also reported these results show that nd sm th and pb are almost insoluble and that their mass balance is controlled by particulates whereas rb sr and u are fractionated between soluble and particulate phases the 87 sr 86 sr ratios can only be interpreted after computing the amount of carbonate recycling and the partitioning for silicates between soluble and insoluble this paper presents a method based on the lead isotopic system that can be used to test the steady state of erosion which is tacitly assumed in many river and erosion studies the results presented show that the steady state is validated in each river of the congo basin and in the lowland rivers of the amazon basin but in not verified in the rivers from the andes rio solimoes and rio madeira 87 sr 86 sr 206 pb 204 pb and 208 pb 204 pb ratios are positively correlated and negatively correlated with 143 nd 144 nd ratios a number of arguments indicate that these correlations are mixing lines the end members being orogenic and shield components respectively for the amazon basin analysis of the river loads shows that the orogenic zone is favoured some 5 times more than the shield on an equal area basis this leads to a reinterpretation of sm nd data for shales and casts some doubts upon the proposition of secular variations in the sm nd ratio of the continental crust

manganese and iron in indian ocean waters abstract the first vertical profiles of dissolved mn and fe for the nw indian ocean are reported the area is characterized by seasonal upwelling and a broad oxygen minimum zone in intermediate waters the dissolved fe profile exhibits a maximum 5 1 nm in the oxygen minimum zone with low values both in surface waters 0 3 nm and deep waters around 1 nm mn concentrations in the surface waters are elevated 2 0 4 3 nm and decrease rapidly in an offshore direction below the first 25 m concentrations decrease dramatically 0 5 1 3 nm indicating removal by oxidation and particle scavenging further down various mn maxima are observed which can be related to hydrographic features sigma 1 1 intermediate water originating from the red sea lost its dissolved o2 while flowing northward along the omani coast and exhibits a strong mn maximum 4 6 6 5 nm coincident with the deep o2 minimum 2 2 at the two inshore stations in the gulf of oman this is overlain by relatively modest mn maxima 2 7 nm related to arabian gulf overflow water 3 3 finally the strong mn maxima 4 4 5 6 nm in the oxygen minimum zone at the two offshore stations are related to yet another watermass below these various maxima concentrations decrease gradually to values as low as 90 pm at 2000 meters depth towards the seafloor concentrations increase again leading to a modest bottom water maximum 0 7 1 5 nm the overall vertical distributions of mn and fe are strikingly similar also in actual concentrations to those previously reported for the eastern equatorial pacific an area also characterized by an extensive o2 minimum zone

organic rich sediments in ventilated deep sea environments relationship to climate sea level and trophic changes sediments on the namibian margin in the se atlantic between water depths of 1000 and 3600 m are highly enriched in hydrocarbon prone organic matter such sedimentation has occurred for more than 2 million years and is geographically distributed over hundreds of kilometers along the margin so that the sediments of this region contain a huge concentrated stock of organic carbon it is shown here that most of the variability in organic content is due to relative dilution by buried carbonates this reflects both export productivity and diagenetic dissolution not differences in either water column or bottom water anoxia and related enhanced preservation of organic matter these observations offer a new mechanism for the formation of potential source rocks in a well ventilated open ocean in this case the south atlantic the organic richness is discussed in terms of a suite of probable controls including local wind driven productivity upwelling trophic conditions transfer efficiency diagenetic processes and climate related sea level and deep circulation the probability of past occurrences of such organic rich facies in equivalent oceanographic settings at the edge of large oceanic basins should be carefully considered in deep offshore exploration

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

importance of vertical geochemical processes in controlling the oceanic profiles of dissolved rare earth elements in the northeastern indian ocean vertical profiles of dissolved rare earth elements rees were obtained in the bay of bengal and the andaman sea the ree concentrations at various depths in the bay of bengal are the highest in the indian ocean this is attributable ultimately to the large outflow of the ganges brahmaputra and irrawaddy rivers but the dissolved ree flux to surface waters alone cannot explain the large and near constant ree enrichment throughout the entire water column the underlying fan sediments serve as not a source but a sink for dissolved ree iii s absence of excess 228ra in the deep waters suggests that lateral input of dissolved rees from slope sediments is also small in these regions partial 0 3 dissolution of detrital particles which are carried by the rivers and lateral surface currents and subsequently settle through the water column appears to be a predominant source for the dissolved rees vertical profiles showing an almost linear increase with depth are common features for the light and middle rees everywhere but their concentration levels are variable from basin to basin and from element to element this suggests that their oceanic distributions respond quickly to the variation of particle flux and its ree composition through reversible exchange equilibrium with suspended and sinking particles much like the case for th the relative importance of the vertical geochemical processes of reversible scavenging over the horizontal basin scale ocean circulation with passive regeneration like nutrients decreases systematically from the light to the heavy rees using a model the mean oceanic residence times of rees in the bay of bengal are estimated to range from 37 years for ce to 140 1510 years for the strictly trivalent rees in the deep water of the andaman sea isolated from the bay of bengal by the andaman nicobar ridge maximum sill depth of 1800 m the ree concentrations are almost uniform presumably due to rapid vertical mixing the ree iii concentrations are similar to that of 1250 m depth water in the bay of bengal consistent with other oceanographic properties however the ree composition of the deep water appears to be altered slightly by preferential scavenging of the light ree iii at the bottom boundary of the basin

neodymium isotopes and concentrations in caribbean seawater tracing water mass mixing and continental input in a semi enclosed ocean basin we present the first full water column nd isotope end and concentration data for caribbean seawater as well as for stations close to the orinoco river mouth and in the florida straits the surface inflow into the southeastern caribbean via the guyana current is characterized by an endsignature of 10 9 which is a consequence of the mixing of relatively unradiogenic endsignatures 13 6 supplied by the orinoco river with contributions from the amazon river 10 despite the proximity to land sub surface and intermediate waters within the caribbean largely retain the endsignatures of their source water masses in the atlantic in contrast the deep waters of the caribbean show endsignatures at least 3 endunits more radiogenic than the inflowing upper north atlantic deep water unadw a endshift from 13 to 9 7 can be explained by addition of radiogenic nd to the deep caribbean through weathering inputs from land however in order to balance such large shifts in endwith at the same time modest increases in nd concentrations nd must also be removed from seawater within the basin it is suggested that the long residence time of deep waters in the caribbean allows significant interaction of seawater with sinking particles and seafloor sediments resulting in more radiogenic values these findings have implications for the use of endas a proxy for paleocirculation in restricted basins in which the residence times of the deep waters are long

neodymium isotopes in planktonic foraminifera a record of the response of continental weathering and ocean circulation rates to climate change the neodymium nd isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka here we present the first nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative reductive techniques the data along with mn ca ratios suggest that cleaned foraminifera provide a reliable record of nd in seawater and hold out the prospect of using nd in foraminifera to examine changes in seawater that accompany glacial interglacial climatic cycles the principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic fe mn coatings these contain large amounts of nd and other trace elements but can be cleaned off using highly reducing reagents mn ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range 10 100 mol mol that has yielded success in studies of transition elements in forams mass balance modelling suggests that for residual mn ca ratios 100 mol mol nd added to the foram in the coating will never shift the measured nd isotope composition significantly away from the seawater value acquired by the foram test in the water column additionally nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids finally core top planktonic foraminifera for two sites have nd isotope compositions that are identical to local surface seawater the data we present here for labrador sea forams over the past 2 5 m y are interpreted in terms of changes in the seawater isotopic composition the data show a pronounced shift from end values of 12 to 19 in the period 2 5 1 5 ma this change is interpreted to result from the initiation of northern hemisphere glaciation and the increased derivation of labrador sea nd via ice rafting from archaean terranes in central canada in combination with stable isotope and foraminiferal relative species abundance data the new nd data are consistent with the surface hydrography of the labrador sea being dominated by a fluctuating balance between cold polar waters containing unradiogenic nd and warm subtropical waters containing more radiogenic nd the major change in labrador sea nd that is observed in the past 2 5 ma can on its own account for the change in the nd isotope composition of north atlantic deep water over the same time period

nd isotopic compositions of eastern mediterranean sediments tracers of the nile influence during sapropel s1 formation abstract nd isotopic composition of eastern mediterranean sediments are used to investigate the influence of nile flux variations during the formation of the youngest sapropel s1 four box cores located on an east west transect around 35 n at increasing distance from the nile source were studied nd 0 signatures were measured in the lithogenic alumino silicate residue fraction and the authigenic biogenic carbonates organic matter and fe mn oxyhydroxides fraction of the sediment after 1 m hcl leaching the nd 0 profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sediments these profiles follow the gaussian shaped ba al profile shape which defines s1 the nd 0 variations can be related to changes in the proportions of two continental sources of particulate material nile particles and saharan aerosols a simple mixing model reveals that the contribution of nile particulates to the sediments increases relative to saharan aerosols during sapropel formation indicating a higher nile discharge and a decrease in eolian input at that time for the cores located closest to the nile fan the nd 0 signatures of the leachable fraction are always higher in the sapropel layer 5 to 4 than in the adjacent sediments 6 the sapropel layer nd 0 values increase with decreasing distance to the nile towards values close to the nile particulates all the results obtained on the leachable fraction point towards a massive input of nile freshwater during s1 deposition

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

glacial interglacial variations in the neodymium isotope composition of seawater in the bay of bengal recorded by planktonic foraminifera this study presents neodymium isotope and elemental data for cleaned planktonic foraminifera from odp site 758 in the southernmost reaches of the bay of bengal in the north east indian ocean cleaning experiments using oxidative reductive techniques suggest that diagenetic fe mn oxyhydroxide coatings can be effectively removed and that the measured nd isotope composition reflects the composition of seawater from which the foraminiferal calcium carbonate was precipitated modern core top pulleniatina obliquiloculata and globorotalia menardii give end values of 10 12 0 16 and 10 28 0 16 respectively indistinguishable from recent direct measurements of surface seawater in this area a high resolution nd isotope record obtained from g menardii for the past 150 kyr shows systematic variations end 3 on glacial interglacial timescales the timing of those variations shows a remarkable correspondence with the global oxygen isotope record which suggests a process controlling the nd isotope composition that responds in phase with global climate cycles palaeoclimate reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the indian subcontinent and a decrease in the flux of river water delivered to the bay of bengal thus changes in the riverine input of nd a change in either flux or composition most likely caused the isotope variations although changes in dust source or local ocean circulation may have also played a role these results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans and illustrate the potential of nd isotopes in foraminifera for high resolution palaeoceanographic reconstruction

recording changes in enadw composition over the last 340 ka using high precision lead isotopes in a fe mn crust we report high precision pb triple spike data and u th isotopic ages on a high resolution depth profile from a fe mn crust 121dk northeastern atlantic 24 n 21 w 2000 m our results bring important information particularly on the origin of the pb isotopic composition of the northeastern atlantic deep water and more generally on the use of pb isotopes as a paleo proxy to reconstruct weathering inputs to the north atlantic ocean growth rates determined using 230th ex and 230th 232th ex 2 9 0 2 and 3 0 3 mm ma respectively are found to be more reliable than 234uex sensitive to sea water contamination and are similar to the 10be results 3 0 3 mm ma very small variations in 206pb 204pb 18 942 18 964 208pb 204pb 39 057 39 083 and 207pb 204pb 15 696 15 701 are resolved defining linear trends in pb isotope diagrams high precision pb triple spike analysis of samples from crust bm1969 05 northwestern atlantic 39 n 61 w 1829 m are found to entirely reproduce the multi collector plasma source mass spectrometry data recently published this interlaboratory cross calibration establishes that the west north atlantic deep water wnadw does not represent a suitable pb contributor to the northeastern atlantic and rather suggests that the pb isotopic composition of wnadw is significantly altered before or during transport toward the northeastern atlantic basin the pb isotopic compositions of both suspended loads from the amazon mouth and offshore sediment cores are consistent on average with crust 121dk we therefore propose that the change in pb isotopic composition of wnadw may be caused by input of suspended particle loads from the amazon and possibly orinoco rivers or by interaction with sediments deposited by those rivers we speculate further that the short term compositional variations observed in this study may be caused by fluctuations in the relative contributions of amazon tributaries to the bulk composition supplied to the ocean because these tributaries sample terrains of drastically different ages phanerozoic andes and precambrian amazonian shield

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

temporal relationships of carbon cycling and ocean circulation at glacial boundaries evidence from high sedimentation rate south atlantic deep sea cores indicates that global and southern ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice sheet growth and retreat respectively no consistent lead lag relationships are observed during abrupt millennial warming events during the last ice age allowing for the possibility that ocean circulation triggered some millenial climate changes at the major glacial interglacial transitions the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets

towards explaining the nd paradox using reversible scavenging in an ocean general circulation model abstract the isotopic composition of the rare earth element neodymium nd has the potential to serve as water mass tracer because it is naturally tagged by continental sources with distinct ages and lithologies however in order to understand the limitations of this approach we need to know more about the physical and biogeochemical processes controlling the distribution of nd in the modern ocean for example nd isotope ratios behave quasi conservatively while concentrations in the water column generally increase with depth showing a broadly nutrient like behaviour we define this decoupling of nd concentrations and isotopic compositions as the nd paradox for the first time we model nd concentrations and isotopic compositions simultaneously and address the hypothesis that the nd paradox can be explained by a combination of lateral advection and reversible scavenging we impose a reversible scavenging model of nd removal from the ocean on the ocean circulation fields from the mit general circulation model using the transport matrix method we conclude that reversible scavenging is an active and important component in the cycling of nd in the ocean in the absence of an adequate alternative explanation reversible scavenging should be considered a necessary component in explaining the nd paradox

increased input of circumpolar deep water borne detritus to the glacial se atlantic ocean analysis of radiogenic isotopes in marine sediments can provide useful information on the provenance and transport of detrital material directly relevant to paleoceanographic investigations here we show that the detrital nd isotopic composition of recent se atlantic marine sediments matches the complex modern day hydrography in these same cores glacial interglacial isotopic variations are consistent with previous investigations using different paleoceanographic proxies which have shown that the relative influence of north atlantic deep water nadw into the south atlantic was reduced during glacial periods in a novel departure however we also calculate the mass accumulation rates of terrigenous material delivered by each of circumpolar deep water cdw and nadw to demonstrate that the accumulation of detritus delivered by cdw was enhanced significantly in the glacial south atlantic this enhanced transport flux could be explained by an increased flow of cdw into the glacial south atlantic and or an increased concentration of suspended terrigenous material transported by glacial cdw

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

an improved method for extracting marine sediment fractions and its application to sr and nd isotopic analysis the radiogenic isotopic composition of both detrital and fe mn fractions in marine sediments can be used in paleoceanography to infer changes of bottom water circulation we have examined various chemical techniques for the analysis of sr and nd isotope ratios in these fractions and present a robust method that can be used to separate both the fe mn oxides and the detrital fraction from a marine sediment sample for isotopic analysis our sequential leaching procedure involves the use of 10 acetic acid followed by 1 m hydroxylamine hydrochloride in 25 acetic acid to remove the carbonate component and the fe mn oxide fraction respectively the applicability of our chemical procedure is illustrated with examples from a marine sediment core raised from the northern cape basin southeast atlantic ocean

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

trace element behaviour at cold seeps and the potential export of dissolved iron to the ocean seawater samples were collected by submersible above methane seeps in the gulf of guinea regab and baboon pockmarks in order to investigate the behaviour of iron fe manganese mn and rare earth elements ree during fluid seepage our aim was to determine whether cold seeps may represent potential sources of dissolved chemical species to the ocean dissolved 0 45 m filtered samples and total dissolvable unfiltered samples concentrations were determined over 50 m long vertical transects above the seafloor and at various discrete locations within the pockmarks we show that substantial amounts of fe and mn are released into seawater during seepage of methane rich fluids mn is exported almost quantitatively in the dissolved form more than 90 of total mn mean mndiss 12 11 nmol kg 12 11 nmol kg although a significant fraction of fe is bound to particulate phases the dissolved iron pool still accounts on average for approximately 20 percent of total iron flux at vent sites mean fediss 22 11 nmol kg 22 11 nmol kg this dissolved fe fraction also appears to remain stable in the water column in contrast there was no evidence for any significant benthic fluxes of pore water ree associated with fluid seepage at the studied sites overall our results point towards distinct trace element behaviour during fluid seepage with potential implications for the marine geochemical budget the absence of any dissolved ree enrichments in bottom waters clearly indicates effective removal in sub surface sediments most likely precipitation of authigenic mineral phases at cold seeps i e carbonates represents a net sink for these elements while mn appears to behave near conservatively during fluid seepage the observed relative stability of dissolved fe in the water column above seepage sites could be explained by complexation with strong organic ligands and or the presence of fe bearing sulfide nanoparticles as reported previously for submarine hydrothermal systems considering the ubiquitous occurrence of methane vents at ocean margins cold seeps could represent a previously unsuspected source of dissolved fe to the deep ocean

rare earth elements and nd isotopes as tracers of modern ocean circulation in the central mediterranean sea abstract seawater rare earth element ree concentrations and nd isotopic composition end are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater however their measurements are basically lacking in the mediterranean sea water column this study analyzes 9 seawater stations around the central mediterranean sea to clarify the relative importance of external sources vertical biogeochemical processes and lateral water mass transport in controlling ree and end distributions concentrations of ree do not show nutrient like profiles with depth likely indicative of relatively young waters with limited accumulation of remineralized ree light ree lree present a non conservative behavior which largely peak at surface waters and rapidly decrease with depth the negative correlation of surface lree enrichment with offshore distance highlights the influence of continental input from the western italian coast to the tyrrhenian surface waters in contrast to other regions with reported boundary exchange this process does not modify the end values here on the other side distributions of dissolved heavy ree hree and end display a conservative behavior that can be explained by mixing of western maw and wmdw and eastern liw and emdw originated waters we test this hypothesis with an optimum multi parameter analysis ompa including hree and end parameters even though the limited data set consistent results of water mass fractions are obtained for the four main water masses although with some particularities while liw takes on major importance when considering hree in the model emdw fractions are preferentially detected with end this latter finding implies a noticeable deep water flux across the sicily strait into the western mediterranean that was not clearly evidenced before

tracing water mass mixing and continental inputs in the southeastern atlantic ocean with dissolved neodymium isotopes abstract in contrast to the vigorous deep ocean circulation system of the north and southwestern atlantic ocean no systematically sampled datasets of dissolved radiogenic neodymium nd isotope signatures exist to trace water mass mixing and provenance for the more restricted and less well ventilated angola basin and the cape basin in the southeastern atlantic ocean where important parts of the return flow of the atlantic meridional overturning circulation are generated here to improve our understanding of water mass mixing and provenance we present the first full water column nd isotope expressed as end values and concentration data for a section across the western angola basin from 3 to 30 s along the zero meridian and along an e w section across the northern cape basin at 30 s sampled during geotraces cruise ga08 compared with the southwestern atlantic basin we find overall less radiogenic end signatures reaching 17 6 in the uppermost 200 m of the angola and cape basins in the western angola basin these signatures are the consequence of the admixture of a coastal plume originating near 13 s and carrying an unradiogenic nd signal that likely resulted from the dissolution of fe mn coatings of particles formed in river estuaries or near the west african coast the highly unradiogenic nd isotope signatures in the upper water column of the northern cape basin in contrast originate from old archean terrains of southern africa and are introduced into the mozambique channel via rivers like the limpopo and zambezi these signatures allow tracing the advection of shallow waters via the agulhas and benguela currents into the southeastern atlantic ocean the nd isotope compositions of the deep water masses in both basins primarily reflect conservative water mass mixing with the only exception being the central angola basin where the signatures are significantly overprinted by terrestrial inputs bottom waters of the cape basin show excess nd concentrations of up to 6 pmol kg 20 originating from resuspended bottom sediments and or dissolution of dust but without significantly changing the isotopic composition of the waters due to similar end values of particles and bottom waters ranging between 9 6 and 10 5 given that bottom waters within the cape basin today are enriched in nd non conservative nd isotopic effects may have been resolvable under past glacial boundary conditions when bottom waters were more radiogenic

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

influence of the amazon river on the nd isotope composition of deep water in the western equatorial atlantic during the oligocene miocene transition highlights records of seawater endend are highly unradiogenic across the omt at ceara rise strong influence of amazon particulate nd on seawater endend at ceara rise point sourced riverine nd influences seawater far from continental shelf regional sedimentary nd flux can be confused with water mass mixing signals abstract dissolved and particulate neodymium nd are mainly supplied to the oceans via rivers dust and release from marine sediments along continental margins this process together with the short oceanic residence time of nd gives rise to pronounced spatial gradients in oceanic 143nd 144nd ratios endend however we do not yet have a good understanding of the extent to which the influence of riverine point source nd supply can be distinguished from changes in mixing between different water masses in the marine geological record this gap in knowledge is important to fill because there is growing awareness that major global climate transitions may be associated not only with changes in large scale ocean water mass mixing but also with important changes in continental hydroclimate and weathering here we present endend data for fossilised fish teeth planktonic foraminifera and the fe mn oxyhydroxide and detrital fractions of sediments recovered from ocean drilling project odp site 926 on ceara rise situated approximately 800 km from the mouth of the river amazon our records span the mi 1 glaciation event during the oligocene miocene transition omt 23 ma we compare our endend records with data for ambient deep atlantic northern and southern component waters to assess the influence of particulate input from the amazon river on nd in ancient deep waters at this site endend values for all of our fish teeth foraminifera and fe mn oxyhydroxide samples are extremely unradiogenic end 15end 15 much lower than the endend for deep waters of modern or oligocene miocene age from the north atlantic end 10end 10 and south atlantic end 8end 8 this finding suggests that partial dissolution of detrital particulate material from the amazon end 18end 18 strongly influences the endend values of deep waters at ceara rise across the omt we conclude that terrestrially derived inputs of nd can affect endend values of deep water many hundreds of kilometres from source our results both underscore the need for care in reconstructing changes in large scale oceanic water mass mixing using sites proximal to major rivers and highlight the potential of these marine archives for tracing changes in continental hydroclimate and weathering

climate driven glacial interglacial variations in the osmium isotope composition of seawater recorded by planktic foraminifera abstract this study presents osmium os isotope and elemental data for cleaned planktic foraminifera authigenic fe mn oxyhydroxides and pelagic carbonate host sediments from odp site 758 in the southernmost reaches of the bay of bengal the os in the bulk sediments appears to be dominantly hydrogeneous sourced by carbonate and fe mn oxyhydroxide but variations in this particular core are controlled by the presence of volcanic ash fe mn oxyhydroxide leachates of the bulk sediments from holocene samples also yield an os isotope composition close to that of seawater but the record diverges from that of foraminifera at a depth corresponding to the oxic post oxic boundary suggesting diagenetic mobilization of os at depths below this holocene planktic foraminifera cleaned using oxidative reductive techniques also give os isotope compositions indistinguishable from modern seawater but the record obtained for the past 150 kyr shows strong covaraitions of 187 os 188 os with both the local and global oxygen isotope record with less radiogenic os isotope compositions during glacial intervals these results indicate that foraminifera provide a robust record of seawater os isotope compositions and comparison of the data obtained here with records from the other major oceans demonstrate global changes in 187 os 188 os over this time interval while the covariation with oxygen isotopes suggest a process controlling the os isotope composition that is in phase with global climate cycles global excursions to relatively unradiogenic 187 os 188 os during glacial intervals are consistent with decreased input of radiogenic continental material reflecting cooler temperatures and reduced continental runoff modelling indicates that the shift to unradiogenic values during glacial intervals could be caused by an 30 decrease in the global river flux with an 5 change in river composition if the residence time of os in the oceans is 5 ka then the post glacial recovery to present day seawater values is consistent with a corresponding increase in the river flux of around 30 however if the residence time of os is closer to 40 ka as is suggested by the global river flux then this demands either significant changes in both the riverine os flux and composition of around 40 and 30 respectively that closely follow the oxygen isotope record or else a short lived post glacial pulse of weathering some 75 greater than the steady state flux in either case these results clearly indicate that climatic changes affect both the flux and composition of weathered material delivered to the oceans on glacial interglacial timescales

diagenetic uptake of rare earth elements by bioapatite with an example from lower triassic conodonts of south china abstract the distribution patterns of rare earth elements rees are frequently used as proxies for ancient seawater chemistry or paleomarine environmental conditions however recent work has shown that diagenesis can lead to remobilization and inter elemental fractionation of rees and that these effects often occur in conjunction with redox reactions in sediment porewaters here we review existing literature on the diagenetic fluxes of rees in marine sediments and porewaters in order to systematize existing knowledge on this subject rees undergo significant redistribution among sediment phases during both early and late diagenesis as a consequence of adsorption and desorption processes remobilization of rees commonly leads to inter elemental fractionation variously leading to enrichment or depletion of the light middle or heavy ree fractions further ree remobilization can be facilitated by redox changes e g through reductive dissolution of host phases in suboxic and anoxic porewaters characteristic ree distribution patterns develop through these processes 1 a flat distribution signifying predominantly terrigenous siliciclastic influence 2 a middle ree bulge probably due to adsorption of light and heavy rees to mn and fe oxyhydroxides respectively and 3 heavy ree enrichment indicative of hydrogenous seawater influence note all patterns in this paper are normalized to the ree composition of average upper continental crust or ucc in the second part of this study we undertake an analysis of the ree distributions in conodonts and whole rock samples from west pingdingshan a permian triassic boundary section in south china using ree th and y ho ratios we show that almost all of the conodont samples have a strong diagenetic overprint and that the hydrogenous ree fraction is small and not isolatable furthermore the conodonts contain two diagenetic ree components one characterized by low ree 100 300 ppm high ree th ratios 1000 strong middle ree enrichment and eu eu ratios of 1 5 2 0 and the second by high ree 300 2000 ppm low ree th ratios 20 30 little or no middle ree enrichment and eu eu ratios of 1 0 the first component exhibits a pronounced middle ree bulge that represents an early diagenetic signature associated with suboxic conditions possibly related to adsorption of rees onto fe mn oxyhydroxides in the shallow subsurface environment the second component shows a flat ree distribution that is similar to both our whole rock samples and average ucc indicating derivation from rees released from detrital siliciclastics e g clay minerals probably at a range of burial depths from shallow to deep failure of the conodont samples to yield an isolatable hydrogenous component demonstrates that bioapatite does not always preserve a primary marine ree signature given that bioapatite rees have been widely used for this purpose often on the assumption of minimal or no diagenetic influence our findings are likely to necessitate a re evaluation of the results of many earlier studies in general we counsel caution in inferring a hydrogenous origin for rees in bioapatite owing to frequent diagenetic alteration of ree distributions

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

cathodoluminescence in quaternary carbonate deposits abstract the cathodoluminescent oscillatory and sectoral growth zones common in crystals formed in ancient limestone successions in a variety of putative environments appear to be rare or absent from recent and pleistocene marine carbonate sequences the factors controlling cathodoluminescence and reasons for this disparity are examined the cathodoluminescent zones in the cements of ancient rocks have been interpreted as responses to variations in the redox potential of formative pore waters during crystal growth although similar cathodoluminescent behaviour is recorded from some deposits including travertines and quaternary speleothems formed in what are thought to have been strongly oxidizing environments the apparent absence of cathodoluminescence in the most recent and pleistocene marine deposits that presumably reflect deposition and diagenesis in environments that are also characteristically oxidized therefore seems anomalous the controlling influences on cathodoluminescence are reviewed together with evidence relating to observations of pleistocene marine deposits and likely conditions of formation but where it is present the mechanism s for its development remain elusive

seismicity and tectonics of a continent island arc collision zone at the island of taiwan a collision between the eurasian plate continental margin and a volcanic island arc on the philippine sea plate about 4 m y ago uplifted the island of taiwan many lines of geological and geophysical evidence suggest that the collision is still active today and is currently propagating southward due to plate interaction geological and tectonic settings have become more complicated since the onset of the collision the collision suture is along the longitudinal valley lv in eastern taiwan seismic studies including earthquake monitoring and seismic refraction lines conducted in 1985 in eastern taiwan and its offshore area using land seismic stations and ocean bottom seismographs have generated results that better constrain the present day plate interaction both the crustal velocity structure and earthquake hypocenter distribution suggest that the subduction of the philippine sea plate along the ryukyu trench extends to the east coast of taiwan near about 23 5 n very high seismicity with dominant right lateral strike slip faulting is found in the back arc region behind the ryukyu trench this seismic activity is interpreted as a result of plate convergence and back arc wrenching due to the relative motion between the okinawa platelet and the eurasian plate the region close to the lv in eastern taiwan showed only shallow and a relatively low level of seismicity during this experiment with higher seismicity to the east of the lv the lack of intermediate depth events suggests that subduction is no longer active along the collision zone and the difference in seismicity between the regions east and west of the lv reflects the difference in strength of the adjacent continental and island arc crusts to the south of the lv seismicity continued southward with intermediate depth events distributed mainly to the east of taiwan along a nearly vertical benioff zone this supports the argument that convergence and collision are still active south of taiwan

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

north atlantic deep water export to the southern ocean over the past 14 myr evidence from nd and pb isotopes in ferromanganese crusts the intensity of north atlantic deep water nadw production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate here we present a new approach to reconstruct the overall strength of nadw export from the north atlantic to the southern ocean over the past 14 myr applying the deep water nd and pb isotope composition as recorded by ferromanganese crusts and nodules we present the first long term nd and pb isotope time series for deep southern ocean water masses which are compared with previously published time series for nadw from the nw atlantic ocean these data suggest a continuous and strong export of nadw or a precursor of it into the southern ocean between 14 and 3 ma an increasing difference in nd and pb isotope compositions between the nw atlantic and the southern ocean over the past 3 myr gives evidence for a progressive overall reduction of nadw export since the onset of northern hemisphere glaciation nhg the nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37 depending on location

the potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past dissolved rare earth element ree concentration data from intermediate and deep seawater form an array characterized by higher middle ree enrichments mree mree in the north atlantic and a progressive increase in heavy to light ree ratios hree lree as water masses age the rees in foraminifera are fractionated towards higher mree mree and lower hree lree relative to seawater calculations based on a scavenging model show that the ree patterns in uncleaned core top foraminifera resemble those adsorbed onto calcite particulate organic material and hydrous ferric oxides but the full extent of the ree fractionation measured in foraminifera was not reproduced by the model however differences in the hree lree mree mree ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater ree distribution under oxic conditions the hree lree and mree mree compositions of uncleaned foraminifera at the sediment seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth in suboxic sedimentary environments all uncleaned foraminiferal ree concentrations are elevated relative to core top values indicating addition of rees from pore waters the hree lree ratio is highest when sedimentation rates were greatest lippold et al 2009 and when high fe ca ratios in the uncleaned foraminifera indicate that fe was mobile in sediments that have not experienced suboxic conditions during burial uncleaned foraminifera preserve the seawater signal taken up at the sediment seawater interface and are therefore suggested to be a suitable archive of changes in the ree signal of past bottom waters this article is protected by copyright all rights reserved

palaeomagnetic data for permian and triassic rocks from drill holes in the southern sydney basin new south wales abstract a section 300 m thick across the permian triassic boundary has been sampled in the southern coalfield of the sydney basin new south wales 55 samples mainly grey to drab sandstones were collected from 9 diamond drill holes which penetrated the entire narrabeen group and the upper part of the conformably underlying illawarra coal measures as well as a sill emplaced into the coal measures the samples included fully oriented cores additional reconnaissance samples from two further drill holes were also studied partial alternating field demagnetization and petrography indicate the magnetic remanence to be a stable drm partial thermal demagnetization above 300 c or 400 c caused large increases in magnetic susceptibility partial chemical demagnetization did not cause significant changes in remanence directions for the coal cliff sandstone basal narrabeen group triassic the palaeomagnetic pole position normal was calculated to be at 59 n 322 e dp 27 dm 29 which agrees with previously published data for the uppermost coal measures permian the pole position was calculated as 58 n 340 e dp 09 dm 10 data for samples from the lower to middle coal measures yield a pole position which is between the new permian triassic pole position and that for the underlying middle permian igneous rocks the top of the reversed kiaman magnetic interval permian may be near the tongarra coal and appin formation boundary early late permian

assessment of seawater nd isotope signatures extracted from foraminiferal shells and authigenic phases of gulf of guinea sediments the radiogenic neodymium nd isotope composition of foraminiferal shells provides a powerful archive to investigate past changes in sources and mixing of water masses however seawater nd isotope ratios extracted from foraminiferal shells can be biased by contaminant phases such as organic matter silicates or ferromanganese coatings the removal of which requires rigorous multiple step cleaning of the samples here we investigate the efficiency of flow through and batch cleaning methods to extract seawater nd isotope compositions from planktonic foraminifera in a shelf setting in the gulf of guinea that is strongly influenced by riverine sediment inputs nd isotope analyses of reductively and oxidatively cleaned mono specific planktonic foraminiferal samples and reductively cleaned mixed benthic foraminifera were complemented by analyses of non reductively cleaned mono specific planktonic foraminiferal samples fe mn coatings of de carbonated bulk sediment leachates and the residual detrital fraction of the same sediment al ca and mn ca ratios of fully cleaned foraminiferal samples reveal indistinguishable levels of cleaning efficiency between the batch and the flow through methods and the nd isotope compositions obtained from application of both methods are identical within error furthermore non reductively cleaned foraminiferal samples have the same nd isotope composition as reductively cleaned foraminifera at our study sites close to the niger river mouth the nd isotope composition of the foraminifera agree with the seawater nd isotope composition of nearby stations based on the combined extracted nd isotope signatures and element to calcium ratios as well as rare earth element distribution patterns we infer that the planktonic foraminiferal nd isotope signatures reflect bottom water pore water signatures the isotopic composition of the bulk de carbonated sediment leachates fe mn coatings differs significantly from the foraminiferal data at this site and probably reflects particles that acquired their ferromanganese pre formed pre formed ferromanganese coatings in nearby rivers therefore in such river influenced shelf settings foraminiferal shells should be used to obtain unbiased bottom seawater signatures

authigenic pb isotopes from the laurentian fan changes in chemical weathering and patterns of north american freshwater runoff during the last deglaciation climate dependent chemical weathering trends have a strong impact on the dissolved pb isotopic composition of continental runoff during glacial terminations so that this tracer can be used to reconstruct the impact of the north american deglaciation on aspects of freshwater runoff and ocean chemistry here we present authigenic fe mn oxyhydroxide derived pb isotope records from lower laurentian fan sediments that trace the local deglacial continental runoff signal through the gulf of st lawrence we use these records to investigate changes in the pb isotopic composition of the north american runoff and their relationship to deglacial processes the new pb isotope records are very similar to those from the subtropical deep nw atlantic locations though the new data are at higher resolution and exhibit much greater amplitudes of change due to their laurentide ice sheet proximal setting unradiogenic compositions 206pb 204pb as low as 18 8 at 18 5 ka during the latest glacial change towards highly radiogenic compositions during the early holocene 206pb 204pb 20 1 at 11 2 ka late holocene 206pb 204pb values return to intermediate values around 206pb 204pb 19 6 these new data support previous inferences that the pb isotopic composition of the deep atlantic is controlled during deglaciation by changes in the pattern and intensity of continental chemical weathering in more detail the most significant change in the entire pb isotope record starts at 12 5 ka and lasts until about 11 ka this observation of strong pb isotopic changes across a climatically cold period in the north atlantic region suggests that at this location pb isotopic compositions recorded in deep marine authigenic fe mn oxyhydroxides not only trace deglacial changes in chemical weathering intensity but also highly depend on major freshwater runoff routes in interior north america our data suggest a gradual opening of the eastward freshwater runoff route in the course of the younger dryas

petrographic rare earth elements and isotope constraints on the dolomite origin of ordovician majiagou formation jizhong depression north china abstract dolomites from the ordovician majiagou formation are considered as major hydrocarbon reservoir rocks in the yangshuiwu area jizhong depression however the origin of the dolomites remains unclear this study utilizes a composite analysis of seawater normalized rare earth elements rees petrography and isotopes c o and sr to trace dolomitizing fluids and processes three types of dolomite are identified planar s to nonplanar microcrystalline type d1 dolomite

provenance of terrigenous detritus of the surface sediments in the bering and chukchi seas as derived from sr and nd isotopes implications for recent climate change in the arctic regions abstract strontium and nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the chukchi and bering seas over the past 100 years regional distributions of the sr and nd isotopes of the surface sediments show higher sr isotope ratios and lower nd isotope ratios in the chukchi sea 87 sr 86 sr 0 7106 0 7150 e nd 10 1 to 8 3 and lower sr isotope ratios and higher nd isotope ratios in the eastern bering sea 0 7045 0 7109 8 6 to 3 0 in addition the rb and sr contents and ree patterns e g eu eu changed noticeably across the bering strait these variations mean that the sediments in the bering and chukchi seas have clearly distinct sources the terrigenous detritus in the chukchi sea is mainly derived from northeastern siberia 87 sr 86 sr 0 711 e nd 9 and bering strait inflow essentially from the yukon river and additionally from the mackenzie river basin including the canadian shield 0 732 0 734 14 the detritus in the eastern bering sea mainly consists of two components the continental material from the yukon river basin mainly underlain by mesozoic and paleozoic rocks in the alaskan mainland 0 708 0 709 9 to 8 and the aleutian arc volcanics 0 703 6 to 10 transported northward by the alaska coastal and bering shelf waters the eastern bering sediments over the past 100 years show slight variations of the sr isotope ratio and relatively wide variations of the nd isotope ratio and the variations and trends of the time series of the northeastern bering sea in the sr nd isotope diagram are probably controlled by changes in the grain size of the detritus from the yukon river basin some of the e nd time series show periodic fluctuations correlating with the annual mean surface air temperature sat for the arctic the e nd value is low in the high sat period and high in the low sat period in the warm period the yukon river was likely to supply a higher amount of the fine grain material with a relatively low e nd value such as surficial overburden probably because partial melting of continental glaciers and permafrosts in the alaskan mainland increased more detailed analysis with high time resolution is needed to clearly understand the effects the sat have on the arctic continental and marine environments

separating biogeochemical cycling of neodymium from water mass mixing in the eastern north atlantic abstract the radiogenic neodymium nd isotope ratio 143nd 144nd expressed in e nd is being used as a tracer in paleo and modern ocean circulation however the mechanisms controlling input distribution and internal cycling are far from understood for example globally nd concentration nd commonly follows patterns of nutrient tracers generally increasing with depth below the thermocline while e nd tends to reflect the water masses which has often been referred to as the nd paradox here we present dissolved nd isotopes and concentrations at unprecedented vertical and spatial resolution from the eastern part of the us geotraces north atlantic zonal transect gulf of cadiz mauritanian shelf cape verde islands the nd of all samples ranges from 12 3 to 36 7 pmol kg with lowest nd usually found within the layer of highest chlorophyll a levels chl max suggesting removal through scavenging the nd isotope compositions range between e nd 13 4 and 9 9 with lower values at the surface within the extension of the saharan dust plume and a benthic nepheloid layer bnl less negative values are found in oligotrophic surface waters mediterranean outflow water mow and near the cape verde islands overall water mass mixing derived from e nd is best visible at the strait of gibraltar where mow enters the atlantic ocean most of the sub thermocline e nd varies within a small range with poor water mass distinction due to the dominance of north atlantic deep water high surface nd associated with more negative e nd is interpreted to be the result of dust deposition and dissolution local nd maxima with no apparent change in e nd compared to ambient seawater observed within a zone of minimum oxygen concentration omz at 500 m depth off mauritania suggest minor input of lithogenic nd but a rather high contribution through desorption of previously scavenged nd that is saharan dust in this area has only a minor influence on the isotope composition of water below the uppermost surface layer the low e nd values and elevated nd within the bnl on the other hand indicate release from detrital material our new high resolution dataset gives valuable insights into the nd distribution near continental margins influenced by high atmospheric inputs and changing oxygen conditions we show how vertical and lateral processes overlap to produce the observed nd distribution bringing us forward in understanding the nd paradox