the structure biological activity and biogeochemistry of cryoconite aggregates upon an arctic valley glacier longyearbreen svalbard glacier surfaces support unique microbial food webs dominated by organic and inorganic debris called cryoconite observations from longyearbreen spitsbergen show how these aggregate particles can develop an internal structure following the cementation of mineral grains mostly quartz and dolomite by filamentous microorganisms measurements of carbon and dissolved o2 show that these microorganisms mostly cyanobacteria promote significant rates of photosynthesis average 17 gc g 1 d 1 which assist aggregate growth by increasing the biomass and producing glue like extracellular polymeric substances the primary production takes place not only upon the surface of the aggregates but also just beneath due to the translucence of the quartz particles however since total photosynthesis is matched by respiration average 19 gc g 1 d 1 primary production does not contribute directly to cryoconite accumulation upon the glacier surface the microorganisms therefore influence the surface albedo most by cementing dark particles and organic debris together rather than simply growing over it time lapse photographs show that cryoconite is likely to reside upon the glacier for years as a result of this aggregation these observations therefore show that a better understanding of the relationship between supraglacial debris and ablation upon glaciers requires an appreciation of the biological processes that take place during summer

constraining erosional input and deep water formation in the north atlantic using nd isotopes many marine radiogenic isotope records show both spatial and temporal variations reflecting both the degree of mixing of distinct sources in the oceans and changes in the distribution of chemical weathering on the continents however changes in weathering and transport processes may themselves affect the composition of radiogenic isotopes released into seawater the provenance of physically weathered material in the labrador sea constrained through the use of ar ar ages of individual detrital minerals has been used to estimate the relative contributions of chemically weathered terranes releasing radiogenic isotopes into the labrador sea a simple box model approach for balancing observed nd isotope variations has been used to constrain the relative importance of localised input in the labrador sea and the subsequent mixing of labrador sea water into north atlantic deep water the long term pattern of erosion and deep water formation around the north atlantic seems to have been a relatively stable feature since 1 5 ma although there has been a dramatic shift in the nature of physical and chemical weathering affecting the release of hf and pb isotopes the modelled nd isotopes imply a relative decrease in water mass advection into the labrador sea between 2 4 and 1 5 ma accompanied by a decrease in the rate of overturning possibly caused by an increased freshwater input into the labrador sea

surface energy balance and melt thresholds over 11 years at taylor glacier antarctica 11 years ablation 18 cm a 1 was dominated by sublimation with very few occurrences of melt 42 days during 11 years results also indicated that above freezing air temperatures did not necessarily result in melt and in turn melt occurred during subfreezing air temperatures under some conditions for air temperatures near freezing low wind speed was critically important for melt initiation according to the model subsurface melt away from rocks and sediment in the ice occurred three times more frequently than surface melt occurs no deeper than 50 cm below the glacier surface and was small never exceeding 8 by mass the magnitude of subsurface melting and the energy balance indicate that taylor glacier ice is intermediate in optical properties between snow and blue ice

238u234u230th disequilibrium in hydrogenous oceanic femn crusts palaeoceanographic record or diagenetic alteration abstract a detailed tims study of 234uexc 238u 230th 232th and th u ratios have been performed on the outermost margin of ten hydrogenous fe mn crusts from the equatorial pacific ocean and west central indian ocean th u concentration ratios generally decrease from the crust s surface down to 0 5 1 mm depth and growth rates estimated by uranium and thorium isotope ratios are significantly different in fe mn crusts from the peru basin and the west central indian ocean fe mn crusts from the same geographical area define a single trend in plots of ln 234uexc 238u vs ln 230th 232th and th u ratios vs age of the analysed fractions results suggest that l hydrogenous fe mn crusts remain closed systems after formation and consequently 2 the discrepancy observed between the 230th and 234u chronometers in fe mn crusts and the variations of the th u ratios through the margin of femn crusts are not due to redistribution of uranium and thorium isotopes after oxyhydroxide precipitation but rather to temporal variations of both th u and initial thorium activity ratios recorded by the fe mn layers implications of these observations for determination of fe mn crust growth rates are discussed variations of both th u and initial th activity ratios in fe mn crusts might be related to changes in particle input to seawater and or changes in ocean circulation during the last 150 ka

an improved estimate of microbially mediated carbon fluxes from the greenland ice sheet microbially mediated carbon fluxes on the surface of the greenland ice sheet gris were recently quantified by hodson and others 2010 using measurements of the surface coverage of debris cryoconite and rates of biological production associated with debris near the ice sheet margin we present updated models that do not assume the same spatial uniformity in key parameters employed by hodson and others 2010 because they make use of biomass distribution and biological production data from a 79 km transect of the gris further the models presented here also include for the first time biomass associated with both cryoconite holes and surficial algae the predicted annual carbon flux for a small 1600km2 section of ice surrounding the field transect is about four times that estimated using spatially uniform biomass and production in this area when surficial algae are included the model predicts about 11 times more carbon fixation via photosynthesis per year than the cryoconite only models we therefore suggest that supraglacial carbon fluxes from the gris have previously been underestimated by more than an order of magnitude and that the hitherto overlooked surficial algal ecosystem can be the most crucial contributor the gris is shown to be in a relatively stable state of net autotrophy according to our model and so a strong link between bare ice area and total carbon fluxes is evident the implication is a biomass feedback to surface albedo and enhanced ablation as a result climate predictions for the year 2100 show that greater carbon fixation could also result from climate warming

cryoconite hole connectivity on the wright lower glacier mcmurdo dry valleys antarctica cryoconite holes can be important sources and stores of water and nutrients on cold and polythermal glaciers and they provide a habitat for various forms of biota understanding the hydrological connectivity of cryoconite holes may be the key to understanding the transport of nutrients and biological material to the proglacial areas of such glaciers this paper aims to characterize and explain spatial variability in the connectivity of ice lidded cryoconite holes on a small piedmont glacier in the mcmurdo dry valleys through geochemical analysis of cryoconite hole waters solute concentrations in both surface and near surface ice and cryoconite holes vary greatly along the glacier centerline and all sample types displayed similar spatial patterns of variability using chloride as a tracer we estimated variations in cryoconite hole connectivity along the glacier centerline we found that a previously used mass transfer method did not provide reliable estimates of the time period for which cryoconite hole waters had been isolated from the atmosphere we attribute this to spatial variability in both the chloride content of the surface ice and surface ablation rates the approach may however be used to qualitatively characterize spatial variations in the hydrological connectivity of the cryoconite holes these results also suggest that ice lidded cryoconite holes are never truly isolated from the near surface drainage system

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

evolution of cryoconite holes and their contribution to meltwater runoff from glaciers in the mcmurdo dry valleys antarctica cryoconite holes are water filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment measurements on the ablation zones of four glaciers intaylorvalley antarctica show that cryoconite holes cover about 4 6 of the ice surface they typically vary in diameter from 5 to 145 cm with depths ranging from 4 to 56 cm in some cases huge holes form with 5 m depths and 30 m diameters un like cryoconite holes elsewhere these have ice lids up to 36 cm thick and melt from within each spring about one half of the holes are connected to the near surface hydrologic system and the remainder are isolated the duration of isolation estimated from the chlor ide accumulation in hole waters commonly shows ages of several years with one hole of 10 years the cryoconite holes in the mcmurdo dryvalleys create a near surface hydro logic system tens of cm below the ice surface the glacier surface itself is generally frozen and dry comparison of water levels between holes a few meters apart shows independent cycles of water storage and release most likely local freeze thaw effects control water passage and therefore temporary storage rough calculations indicate that the holes gen erate at least 13 of the observed runoff on the one glacier measured this hydrologic system represents the transition between a melting ice cover with supraglacial streams and one entirely frozen and absent of water abstract cryoconite holes are water filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment measurements on the ablation zones of four glaciers intaylorvalley antarctica show that cryoconite holes cover about 4 6 of the ice surface they typically vary in diameter from 5 to 145 cm with depths ranging from 4 to 56 cm in some cases huge holes form with 5 m depths and 30 m diameters un like cryoconite holes elsewhere these have ice lids up to 36 cm thick and melt from within each spring about one half of the holes are connected to the near surface hydrologic system and the remainder are isolated the duration of isolation estimated from the chlor ide accumulation in hole waters commonly shows ages of several years with one hole of 10 years the cryoconite holes in the mcmurdo dryvalleys create a near surface hydro logic system tens of cm below the ice surface the glacier surface itself is generally frozen and dry comparison of water levels between holes a few meters apart shows independent cycles of water storage and release most likely local freeze thaw effects control water passage and therefore temporary storage rough calculations indicate that the holes gen erate at least 13 of the observed runoff on the one glacier measured this hydrologic system represents the transition between a melting ice cover with supraglacial streams and one entirely frozen and absent of water

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

oceanwide imprint of large tectonic and oceanic events on seawater nd isotope composition in the indian ocean from 90 to 40 ma 1 we have analyzed four sediment cores from the southern indian ocean odp sites 757 758 1135 and 762 with high carbonate content in order to reconstruct the neodymium isotopic composition end of ancient intermediate south indian seawater from late cretaceous 90 ma to early eocene 40 ma the endvariations are highly consistent and exhibit reproducible patterns over a very large geographic area confirming the seawater origin of the signal combining geochemical constraints with paleogeographic reconstructions we highlight the respective roles of 1 large scale tectonic events 2 continental weathering from surrounding precambrian terrains 90 65 ma 3 oceanic circulation changes 50 40 ma and possibly 4 local volcanism of the ultra fast spreading south east indian ridge seir 60 50 ma on the nd isotopic composition of south indian seawater between 60 ma and 50 ma the regional nd isotopic variations closely mimic changes in seir spreading rate we suggest that the nd isotopic composition of seawater could be influenced by nd of volcanic origin in the vicinity of ultra fast spreading ridges 13 cm yr the india asia collision closed the equatorial seaway between asia and india and drastically changed oceanic circulation patterns in the indian ocean warm and more radiogenic pacific equatorial seawater was diverted to the south by the east indian coast a stronger mixing of this pacific seawater with south indian seawater would explain the rapid shift ofend from 50 ma 11 to 40 ma 8

differing controls over the cenozoic pb and nd isotope evolution of deepwater in the central north pacific ocean dissolved pb and nd isotope ratios of seawater as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts have been used as paleoenvironmental proxy tracers for the north pacific however all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part or only the young parts have been analyzed thus the pb and nd isotope compositions of north pacific deep waters prior to 20 ma are not well constrained we present new results for three ferromanganese crusts one of which cj01 shows no phosphatization and is located far away from the epr its age is inferred to be 75 ma and thus provides for the first time an opportunity to trace the nd and pb isotope evolution of central north pacific seawater back to the latest cretaceous the three crusts no matter whether phosphatized or not display very similar pb and nd isotope trends with age suggesting no modification of the pb and nd isotope distribution by post depositional phosphatization our data suggest that dissolved pb in deep waters of the central north pacific over the cenozoic and latest cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs for pb these trends broadly resemble the pb isotope evolution of the eolian silicate dust fraction of core ll44 gpc3 in the central north pacific we suggest that the isotope evolution of dissolved pb in central north pacific seawater has been mainly controlled by pb released from eolian dust from north america prior to 50 ma and after 40 ma from asia in contrast the nd isotope time series of the crusts are by no means similar to the nd isotope evolution of the silicate dust fraction in core gpc3 suggesting a decoupling from the pb and negligible contributions from dust to the dissolved nd in the central north pacific deep water the rise of nd isotope ratios of pacific seawater during the cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the pacific

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

biological processes on glacier and ice sheet surfaces glacial ice covers around 10 of the earth s continents a review of the literature suggests that microbes living on glaciers and ice sheets are an integral part of both the glacial environment and the earth s ecosystem

deep pacific caco 3 compensation and glacial interglacial atmospheric co 2 abstract benthic foraminiferal 13c suggests that there was a net shift of isotopically light metabolic co2 from the upper ocean into the deep ocean during the last glacial period according to the caco3 compensation hypothesis this should have caused a transient drop in deep ocean co32 that was eventually reversed by seafloor dissolution of caco3 the resulting increase in whole ocean ph may have had a significant impact on atmospheric co2 compounding any decrease that was due to the initial vertical co2 shift the opposite hypothetically occurred during deglaciation when co2 was returned to the upper ocean and atmosphere and deep ocean co32 temporarily increased followed by excess burial of caco3 and a drop in whole ocean ph the deep sea record of caco3 preservation appears to reflect these processes with the largest excursion during deglaciation as expected but various factors make quantification of deep sea paleo co32 difficult here we reconstruct deep equatorial pacific co32 over the last glacial interglacial cycle using benthic foraminiferal zn ca which is strongly affected by saturation state during calcite precipitation our data are in agreement with the caco3 compensation theory including glacial co32 concentrations similar to or slightly lower than today and a termination i co32 peak of 25 30 mol kg 1 the deglacial co32 rise precedes ice sheet melting consistent with the timing of the atmospheric co2 rise a later portion of the peak could reflect removal of co2 from the atmosphere ocean system due to boreal forest regrowth caco3 compensation alone may explain more than one third of the atmospheric co2 lowering during glacial times

nitrogen fixation on arctic glaciers svalbard telling j anesio a m tranter m irvine fynn t hodson a butler c wadham j 2011 nitrogen fixation on arctic glaciers svalbard journal of geophysical research biogeosciences 116 article number g03039

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

metabolic activity and diversity of cryoconites in the taylor valley antarctica 1 metabolic activity and biogeochemical diversity within cryoconites from the canada commonwealth howard and hughes glaciers in the mcmurdo dry valleys revealed the presence of a productive microbial refuge in this polar desert ecosystem fluorescent in situ hybridization showed a high percentage of cytophaga flavobacteria cells in cryoconite sediments 87 2 while b proteobacterial cells dominated the ice overlying the sediment layer 54 2 the biomass of bacterial cells in the sediments was also greater 4 82 mgc ml 1 than that in the overlying ice 0 18 mgc ml 1 and was related to bacterial productivity on the basis of thymidine incorporation which ranged from 36 ng cl 1 d 1 in the overlying ice to 3329 ng c l 1 d 1 in the sediment containing layers bacteria within both the sediments and overlying ice were able to actively incorporate and respire radio labeled glucose as well as 17 other dissolved organic carbon compounds the cryoconites in the taylor valley support an active diverse assemblage of organisms despite the fact that they may remain sealed from the atmosphere for decades given the density of the cryoconites in the dry valleys 4 6 of ablation zone surfaces flushing of the cryoconites during warm years could provide a vital nutrient and organic carbon source to the surrounding polar desert

structure and formation process of cryoconite granules on urumqi glacier no 1 tien shan china cryoconite granules are dark colored spherical aggregates of organic and inorganic material on glacier ice and are commonly observed on glaciers the world over the structure of cryoconite granules on urumqi glacier no 1 tien shan china was analyzed granules were distributed over the entire ice surface of the ablation area and ranged in size from 0 26 to 3 5 mm mean 1 1 mm the granule surface was densely covered with filamentous cyanobacteria microscopy of a thin section revealed various inner structures most granules had concentric layers of dense organic matter which are probably derived from annual growth of the granules by the activity of cyanobacteria the number of layers averaged 3 5 and ranged up to 7 which is likely to indicate their mean and maximum growth ages respectively some granules contained two or more subgranules showing that small granules had combined and enlarged such structures suggest that granule formation was mainly due to the activity of filamentous cyanobacteria and that the granules repeatedly grew and disintegrated over a cycle of several years on the glacier

evaluation of the application of rare earth elements to paleoceanography anomalous departures of rare earth elements ree from similarity of chemical behaviour are most evident in a comparison of ce with its neighbors under reducing conditions ce3 acts like other ree but oxidized ce4 is adsorbed on mn fe oxyhydroxides or organic particulates and consequently the remaining solution will tend to exhibit a negative ce anomaly in addition more subtle fractionations may emphasize the light or the heavy or the middle ree a pattern of ree may be recorded by immediate diagenesis on a suitable chemical substrate such as apatite fish debris conodonts carbonate or chert this record was originally thought to reflect the paleoredox conditions of primary deposition however any such primary record may be overprinted by late diagenetic alteration early analyses of ree in conodonts from a wide range of sediments suggested a prevalence of reducing conditions no ce anomaly in pre carboniferous oceans and more common oxidation negative ce anomaly in the late paleozoic however recent research by other investigators indicates that variations in cean are more diverse in origin and in particular many are distorted to an unknown extent by late diagenesis in any case it is now clear that geological age does not show a consistent relationship to the level of the ce anomaly the ce anomaly apparently does not play any regular role in the isotopic events that accompany prominent mass extinctions further research is required to understand and thus make useful the controls on the ce anomaly

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

hafnium and neodymium isotopes in seawater and in ferromanganese crusts the element perspective abstract hafnium and nd isotopes are increasingly used as paleoceanographic proxies comparing the mantle crust array and the seawater array in plots of e hf vs e nd it has been observed that for a given e nd value the corresponding e hf value is higher for seawater than it is for terrestrial rocks while this difference had initially been explained by significant hydrothermal input of mantle hf into seawater the currently favoured explanation is incongruent weathering of continental rocks producing radiogenic riverine hf input we here address this topic from the perspective of the behaviour of these two elements in seawater and in ferromanganese fe mn crusts we distinguish between a truly dissolved and a dissolved hf and nd pool the latter being comprised of truly dissolved and colloid bound colloidal hf and nd while there exists a hydrothermal pathway for colloid bound dissolved mantle hf into the oceans there is in marked contrast to nd no important riverine pathway for colloidal or truly dissolved continental hf owing to their respective chemical speciation in seawater there exists truly dissolved nd in the ocean while the amount of truly dissolved hf is insignificant neodymium is in exchange equilibrium between local seawater and both the hydrous fe and mn oxides hydrogenetic fe mn crusts are composed of due to continuous ad and desorption there is continuous isotopic re equilibration and the isotopic composition of nd in a fe mn crust reflects that of truly dissolved nd in local ambient seawater in contrast hf is only associated with the hydrous fe oxides on which it forms surface precipitates that do not exchange with seawater due to this lack of isotopic re equilibration the isotopic composition of hf in a fe mn crust is the average of that of all the hf scavenged during the lifetime of the hydrous fe oxide particles since the hf bearing hydrous fe oxides in a fe mn crust do not form from local ambient seawater at the crust s growth site but are advected as colloids or fine particles their hf isotopic composition depends on the origin and migration pathway of these colloids hence while nd isotopes in fe mn crusts provide reliable information on truly dissolved nd in local ambient seawater hf isotopes rather indicate the origin and pathway of hydrous fe oxide colloids and might differ from truly dissolved hf in local ambient seawater this may explain the occasional decoupling of nd and hf isotopes in fe mn crusts and supports the notion of a significant hydrothermal mantle signal of hf in seawater

global distribution of beryllium isotopes in deep ocean water as derived from femn crusts the direct measurement of the ratio of cosmogenic 10be t12 1 5 ma to stable terrigenously sourced 9be in deep seawater or marine deposits can be used to trace water mass movements and to quantify the incorporation of trace metals into the deep sea in this study a sims based technique has been used to determine the 10be9be ratios of the outermost millimetre of hydrogenetic ferromanganese crusts from the worlds oceans 10be9be ratios time corrected for radioactive decay of cosmogenic 10be using 234u238u are in good agreement with ams measurements of modern deep seawater ratios are relatively low in the north and equatorial atlantic samples 0 4 0 5 10 7 in the southwest atlantic ratios increase up to 1 10 7 they vary between 0 7 and 1 0 10 7 in indian ocean samples and have a near constant value of 1 1 0 2 10 7 for all pacific samples if the residence time of 10be 10be in deep water is constant globally then the observed variations in 10be9be ratios could be caused by accumulation of 10be in deep water as it flows and ages along the conveyor following a transient depletion upon its formation in the northern atlantic in this view both 10be and 9be reach local steady state concentration in pacific deep water and the global 10be 600 a an alternative possibility is that the be isotope abundances are controlled by local scavenging for this scenario 10be would vary according to local particle concentration and would 600 a in the central pacific but 10be 230 a in the atlantic mass balance considerations indicate that hydrothermal additions of 9be to the oceans are negligible and that the dissolved riverine source is also small furthermore aeolian dust input of 9be appears insufficient to provide the dissolved 9be inventory the dissolution of only a small proportion 2 of river derived particulates could in principle supply the observed seawater 9be content if true ocean margins would be the sites for 9be addition due to the particle reactive nature of be these would also be the primary sites of be removal a possible net result of horizontal water masses passing through these marginal areas might be a decrease in seawater 10be9be and establishment of a relatively constant 9be concentration as 10be 600 a is less than the apparent age of deep water in the pacific 1500 a the pacific record of 10be9be is not expected to show secular variations due to changes in deep water flow despite the large variations in 10be9be between different water masses because of this insensitivity to deep water flow however it is suggested that the 10be9be ratio determined in the authigenic phase of marine sediments or hydrogenetic precipitates should be a suitable tool for monitoring changes in continental input or cosmic ray intensity on longer time scales

astoria fan sediments dsdp site 174 cascadia basin hf nd pb constraints on provenance and outburst flooding abstract the astoria submarine fan located off the coast of washington and oregon has grown throughout the pleistocene from continental input delivered by the columbia river drainage system enormous floods from the sudden release of glacial lake water occurred periodically during the pleistocene carrying vast amounts of sediment to the pacific ocean deep sea drilling project dsdp site 174 located on the southern distal edge of the astoria fan is composed of 879 m of terrigenous sediment the section is divided into two major units separated by a distinct seismic discontinuity an upper turbidite fan unit unit i and an underlying finer grained unit unit ii both units have overlapping ranges of nd and hf isotope compositions with the majority of samples having e nd values of 7 1 to 15 2 and e hf values 6 2 to 20 0 the most notable exception is the uppermost sample in the section which is identical to modern columbia river sediment nd depleted mantle model ages for the site range from 2 0 to 1 2 ga and are consistent with derivation from cratonic proterozoic source regions rather than cenozoic and mesozoic terranes proximal to the washington oregon coast the astoria fan sediments have significantly less radiogenic nd and hf isotopic compositions than present day columbia river sediment e nd 3 to 4 goldstein s j jacobsen s b 1987 nd and sr isotopic systematics of river water suspended material implications for crustal evolution earth planet sci lett 87 249 265 and suggest that outburst flooding tapping proterozoic source regions was the dominant sediment transport mechanism in the genesis and construction of the astoria fan pb isotopes form a highly linear 207 pb 204 pb 206 pb 204 pb array and indicate the sediments are a binary mixture of two disparate sources with isotopic compositions similar to proterozoic belt supergroup metasediments and columbia river basalts the combined major trace and isotopic data argue that outburst flooding was responsible for depositing the majority top 630 m of the sediment in the astoria fan

changes in pacific ocean circulation following the miocene onset of permanent antarctic ice cover we integrate micropaleontological and geochemical records benthic stable isotopes neodymium isotopes benthic foraminiferal abundances and xrf scanner derived elemental data from well dated pacific ocean successions 15 12 7 ma to monitor circulation changes during the middle miocene transition into a colder climate mode with permanent antarctic ice cover together with previously published records our results show improvement in deep water ventilation and strengthening of the meridional overturning circulation following major ice expansion at 13 9 ma neodymium isotope data reveal however that the provenance of intermediate and deep water masses did not change markedly between 15 and 12 7 ma we attribute the increased 13c gradient between pacific deep and intermediate water masses between 13 6 and 12 7 ma to more vigorous entrainment of pacific central water into the wind driven ocean circulation due to enhanced production of intermediate and deep waters in the southern ocean prominent 100 kyr ventilation cycles after 13 9 ma reveal that the deep pacific remained poorly ventilated during warmer intervals at high eccentricity whereas colder periods low eccentricity were characterized by a more vigorous meridional overturning circulation with enhanced carbonate preservation the long term 13c decline in pacific intermediate and deep water sites between 13 5 and 12 7 ma reflects a global trend probably related to a re adjustment response of the global carbon cycle following the last 400 kyr carbon maximum cm6 of the monterey excursion

the hf isotopic composition of ferromanganese nodules and crusts and hydrothermal manganese deposits implications for seawater hf we present hf and pb isotopic data and chemical compositions of the outermost layers of marine ferromanganese deposits of different types hydrogenous and hydrothermal with a worldwide distribution the hf isotopic compositions display a broad range and refine previously reported regional differences as follows atlantic ocean hf 4to 2 indian ocean hf 2to 4 pacific ocean hf 3to 10 the most radiogenic hf isotopic compositions in the pacific samples are for hydrothermal manganese deposits that also have low 207pb204pb demonstrating that this signature reflects a contribution from hydrothermal venting of hf leached from oceanic volcanic rocks rather than from riverine inputs volcanic ash or eolian dust hafnium concentrations in the deposits increase from 20 ppb to 20 ppm with decreasing hf the hf and pb isotopic compositions for ferromanganese crusts define an apparent mixing trend between literature values of average continental crust and morb the range in hf for ferromanganese crusts is narrower than it is for 206pb204pb compared to the differences in isotopic composition of the sources of hf and pb this is consistent with hf having a longer residence time than pb the concentration of hf in ferromanganese crusts has been found to co vary with growth rate and inversely correlates with hf isotopic compositions hf isotope ratios may be used to determine not only the source of hf but possibly the source of fe and mn measurements of hf and hf concentrations in nodule tops bottoms and associated sediments show that the hf of nodules is sensitive to sedimentary oxic and sub oxic diagenetic processes and thus most nodules may not reliably reflect the isotopic composition of hf in seawater

distribution and sources of pre anthropogenic lead isotopes in deep ocean water from fe mn crusts abstract the lead isotope composition of ocean water is not well constrained due to contamination by anthropogenic lead here the global distribution of lead isotopes in deep ocean water is presented as derived from dated ca 100 ka surface layers of hydrogenetic fe mn crusts the results indicate that the radiogenic lead in north atlantic deep water is probably supplied from the continents by river particulates and that lead in pacific deep water is similar to that characteristic of island and continental volcanic arcs despite a short residence time in deep water 80 100 a the isotopes of lead appear to be exceedingly well mixed in the pacific basin there is no evidence for the import of north atlantic deep water derived lead into the pacific ocean nor into the north indian ocean this implies that the short residence time of lead in deep water prohibits advection over such long distances consequently any climate induced changes in deep water flow are not expected to result in major changes in the seawater pb isotope record of the pacific ocean

neodymium isotopic variations in northwest pacific waters abstract four vertical profiles of the concentration and isotopic composition of nd in seawater were obtained in the western north pacific two profiles from the kuroshio current regime showed congruently that although the nd concentration increases gradually with depth its isotopic composition varies significantly with depth depending upon the water mass occupying the water column the high salinity kuroshio waters originating from the north pacific tropical water nptw carry the least radiogenic nd nd 7 4 to 8 7 to this region at 250 m from the western margin continental shelves most likely from the east china sea the nd isotopic compositions in the north pacific intermediate water npiw that occurs at 600 to 1000 m in the subtropical region are fairly uniform at nd 3 7 the profile data from the 38 to 40 n kuroshio oyashio mixed water region off sanriku of honshu japan also suggest that the newest npiw with nd 3 2 is formed there by the mixing of various source waters and the radiogenic component of nd is derived mainly from the oyashio waters in the pacific deep water pdw below 1000 m the nd isotopic composition is neither vertically nor horizontally homogeneous suggesting that it serves as a useful tracer for sluggish deep water circulation as well two profiles from the izu ogasawara trench showed a minimum nd value at 2000 m suggesting that there exists a horizontal advective flow in the vicinity of honshu japan there is some evidence from other chemical properties to support this observation the waters below 4000 m including those within the trench in the subtropical region have nd values of around 5 suggesting that the deep waters are fed from the south along the western boundary ultimately from the antarctic bottom water aabw in the south pacific this extends up to 40 n along the japanese islands in the subarctic region 42 n the waters have more radiogenic nd with nd 4 0 throughout the water column presumably due to the supply of nd by weathering in such igneous provinces as the kuril kamchatska aleutian island chain the lateral inhomogeneity of the nd isotopic composition in pdw suggests that there may be different circulation and mixing regimes in the north pacific basin

the impact of early cretaceous gateway evolution on ocean circulation and organic carbon burial in the emerging south atlantic and southern ocean basins abstract organic carbon burial is an important driver of carbon cycle and climate dynamics on geological and shorter time scales ocean basins emerging during the early cretaceous break up of gondwana were primary sites of organic carbon burial implying that their tectonic and oceanographic evolution may have affected trends and perturbations in global climate via changes in local organic carbon burial assessing the role of individual ocean basins in the global carbon climate context requires a sound understanding of the processes that induced large scale changes in carbon burial and the timing of these changes here we reconstruct the oceanographic evolution and its links to organic carbon burial in the barremian to albian south atlantic and southern ocean basins which may have acted as carbon sinks of global importance our reconstruction is based on combined seawater neodymium isotope and sedimentological records obtained from multiple deep sea drill sites and a new general circulation model deep water circulation within and between those basins was primarily controlled by the opening of the shallow falkland plateau gateway between 118 ma and 113 ma and the deep georgia basin gateway by 110 ma for which we provide new age constraints based on biostratigraphic and carbon isotope data the opening of these gateways was accompanied by local to basin wide decreases in organic carbon burial suggesting that ocean circulation affected the oxygenation state via changes in deep water ventilation although our data do not provide quantitative information on the impact of changes in regional organic carbon burial on the global carbon cycle the synchronicity between the reduction of organic carbon burial in the south atlantic basin and global warming during the early albian points to a strong causal relationship

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

carbon fluxes through bacterial communities on glacier surfaces there is very little information about the activity of microbial communities on the surface of glaciers though there is an increasing body of evidence to show that they strongly influence the biogeochemistry of these habitats we measured bacterial abundance and production in cryoconite holes on arctic antarctic and alpine glaciers in order to estimate the role of heterotrophic bacteria within the carbon budget of glacial ecosystems our results demonstrate an active bacterial community on the surface of glaciers with doubling times that vary from a few hours to hundreds of days depending on the glacier and position water or sediments within the cryoconite hole however bacterial production is only 2 3 of the published literature values of community respiration from similar habitats indicating that other types of microbes e g eukaryotic organisms may also play a role in the c cycle of glaciers we estimate that only up to 7 of the organic c in cryoconite sediments is utilized by the heterotrophic bacterial community annually suggesting that the surface of glaciers can accumulate organic carbon and that this c may be important for biogeochemical activity downstream to adjacent ecosystems

a lead isotopic study of circum antarctic manganese nodules abstract lead isotope ratios in manganese nodules from the circum antarctic ocean display systematic geographical variations eastward in the direction of current movement from south of australia they progressively decrease in the pacific sector and into the western atlantic sector until 30 w from this longitude lead isotope ratios increase in the eastern atlantic sector and reach their highest values in the indian sector near 110 e south of western australia they abruptly decrease these two lead isotope domains correspond closely to the circum antarctic neodymium isotope domains previously recognized by albarede and goldstein 1992 however the intraocean isotopic variations are much clearer for pb than nd reflecting the shorter oceanic residence time of pb 102 y compared with nd 103 y and confirming that pb is a much more sensitive marine tracer throughout the circum antarctic ocean the lead isotopic changes follow the pattern of present day oceanic circulation the pb shows an overall continental signature which is strongest in the indian sector the most probable candidate as the source of the continental signal is north atlantic deep water nadw which enters the circum antarctic in the south atlantic as nadw mixes with circumpolar water lead isotope ratios increase eastward in the indian sector reflecting progressive loss of the pacific derived pb signal the abrupt decrease of lead isotope ratios between the indian and pacific sectors appears to be a consequence of addition of pacific seawater through the pacific lead isotope ratios gradually decrease eastward approaching values of east pacific rise metalliferous sediments ocean ridge basalts and south pacific mn nodules this trend results from an increasing influence of pacific ocean water containing a component derived from pacific volcanism the pacific signature persists into the argentine basin in the southwest atlantic ocean reflecting significant input of water from the drake passage northward into the atlantic the pacific pb component is seen in the atlantic and indian oceans near southern africa as well as in the atlantic and indian sectors of the circum antarctic lead and neodymium isotopes correlate in the atlantic indian sectors but not in the pacific sector reflecting differences in residence times and modes of water mass mixing the renewal of circum antarctic water occurs on a timescale which is short compared to the residence time of nd but long compared to pb as a result dissolved pb is subject to considerable changes over the timescale of circumpolar current movement while nd is less easily affected nadw is added locally in the south atlantic and moves eastward as a water mass as nadw mixes with circumpolar water cpw through the indian sector changes affecting nd pb in nadw and cpw occur in tandem and neodymium and lead isotopes are correlated through the pacific sector gradual addition of pacific seawater occurs over a large region and nd pb relationships are not coupled because simple isotopic mixing systematics are not conserved there neodymium and lead isotopes vary independently the consistency of lead isotope variations with present day ocean bottom water circulation is remarkable considering that the mn nodules as sampled reflect the integrated flux of pb over 105 106 y the oceanic mixing time is 103 y the residence time for pb is 102 y and the circulation time of the circumantarctic ocean is 30 y processes occurring over such different timescales can show such a relationship only if the system is stable over the longest time interval thus on average element sources and ocean circulation through the pleistocene have been similar to the present day despite significant perturbations during glacial periods

acquisition of the neodymium isotopic composition of the north atlantic deep water the north atlantic deep water nadw neodymium isotopic composition nd ic is increasingly used in oceanography and paleoceanography to trace large scale circulation and weathering processes notably to investigate past variations of the global thermohaline circulation although the present day nadw nd ic is well characterized at nd 13 5 the acquisition of this isotopic signature in other words the causes of this value has so far been very sparsely documented such an understanding is however fundamental to the interpretation of paleo records nd ic and rare earth element concentrations were measured at 9 stations within the north atlantic subpolar gyre signature cruise summer 1999 the comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the nadw the labrador sea water lsw nd 13 9 0 4 north east atlantic deep water neadw nd 13 2 0 4 and north west atlantic bottom water nwabw nd 14 5 0 4 acquire their nd ic through distinct water mass mixings and lithogenic inputs these different mechanisms acting upon water masses from very diverse sources seem to bring the nd ic of the three nadw layers to values close together and similar to that of the nadw it is suggested that sediment seawater interactions significantly lower the neadw and nwabw nd ic along the south east greenland margin since these interactions do not significantly modify the nd content of these water masses sediment remobilizations leading to the nd ic variations are probably associated with nd removal fluxes from the water mass toward the sediment a process called boundary exchange on the other hand lsw seems to acquire its nd ic from the subpolar mode waters from which it is formed by deep convection and no other mechanism needs to be invoked its unradiogenic signature could ultimately be linked to fresh water runoff from the canadian shield these conclusions should allow more precise interpretations of paleoceanographic nd ic records taking into account the distinct histories of the three nadw layers including distinct water mass mixings and distinct lithogenic inputs

reconstructing seawater circulation on the moroccan shelf of gondwana during the late devonian evidence from nd isotope composition of conodonts 1 the nd isotope composition of conodonts is used for the first time as a paleoceanographic proxy to reconstruct seawater circulation conodonts from two stratigraphic levels in the eastern anti atlas the lower part of the frasnian zone 11 base of the kellwasser facies and the boundary interval of the uppermost crepida rhomboidea zones top of the kellwasser facies were selected for reconstruction of seawater circulation on the moroccan shelf of gondwana during late devonian times the recognized lateral variations in nd values are in very good agreement with current related sedimentary features they provide evidence for communication of the moroccan shelf with the rheic ocean to the southwest and with the variscan sea to the north in the frasnian the general seawater flow was directed from the southwest to the east and was influenced by a local riverine input of low radiogenic nd from the south the west african craton and or the pan african ougarta belt and from the northwest the precambrian basement of the anti atlas the combined set of nd isotopic records and directional data from the middle famennian reveals a circulation pattern different from that of the frasnian it was dominated by a general westward flow with a countercurrent in the central tafilalt area the establishment of a new circulation system during the famennian suggests essential changes in paleogeography of the western part of the variscan realm

neodymium in modern foraminifera from the indian ocean implications for the use of foraminiferal nd isotope compositions in paleo oceanography abstract the use of the nd isotope composition of planktic foraminifera as a proxy for sea surface water is based on the assumption that nd is incorporated during initial calcification and preserved after foraminifera death subsequent transport through the water column and storage in the sediment pile to test this assumption nd concentrations are reported from foraminiferal tests collected from 20 to 3045 m depth multinets and sediment traps from offshore somalia and in the somali basin of the indian ocean nd partition coefficients calculated for two species globigerinoides ruber and globigerina bulloides sampled in the uppermost water column 100 m are 16 52 the measured nd ca ratio of living foraminifera is 8 nmol mol which is 8 190 times lower than reported in cleaned foraminifera from sediment cores 61 1500 nmol mol moreover the nd content of foraminiferal tests varies markedly within the water column 8 220 nmol mol ca recording a positive correlation with mn content r2 0 91 the observed changes in the nd concentration after foraminiferal death appear to reflect nd addition from deeper in the water column and imply a major disturbance of the primary nd isotope composition formed at the surface the high nd ca reported for cleaned foraminifera from sediment cores are interpreted to be a consequence of current cleaning techniques although cleaning successfully removes organics and secondary mn coatings into solution any released rare earth elements ree are subsequently re adsorbed onto the calcite cleaning removes elements with a 2 valency state into solution e g cd and mn but more reactive elements with higher valency states e g ree3 th4 are re absorbed onto residual carbonate it is concluded that although foraminifera clearly record temporal variations in nd isotope composition the relationship between these variations and changes in the sea surface nd isotope composition has yet to be established unambiguously further work is required to rule out the possibility that the nd in foraminifera represents a mixed signal derived from surface sediments and bottom and pore waters

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

near surface hydraulic conductivity of northern hemisphere glaciers the hydrology of near surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments to elucidate the hydrological characteristics of this near surface glacial weathering crust we describe the design and operation of a capacitance based piezometer that enables rapid economical deployment across multiple sites and provides an accurate high resolution record of near surface water level fluctuations piezometers were employed at 10 northern hemisphere glaciers and through the application of standard bail recharge techniques we derive hydraulic conductivity k values from 0 003 to 3 519 m day 1 with a mean of 0 185 0 019 m day 1 these results are comparable to those obtained in other discrete studies of glacier near surface ice and for firn and indicate that the weathering crust represents a hydrologically inefficient aquifer hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance the large range of k observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography our data demonstrate a greater complexity of near surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production the conductivities reported here coupled with typical supraglacial channel spacing suggest that meltwater can be retained within the weathering crust for at least several days not only does this have implications for the accuracy of predictive meltwater run off models but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments impurities microbes and nutrients to downstream ecosystems because continued atmospheric warming will incur rising snowline elevations and glacier thinning the supraglacial hydrological system may assume greater importance in many mountainous regions and consequently detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained

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

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

nd isotope composition of seep carbonates towards a new approach for constraining subseafloor fluid circulation at hydrocarbon seeps abstract the carbonates forming at deep sea hydrocarbon seeps provide an archive for the source and migration pathways of the seeping fluids interpretation of the archived isotopic and elemental signatures is however not straightforward because of mixing between the signals of fluids and ambient seawater limited understanding of subseafloor fluid circulation and effects of diagenetic alteration the nd isotope system is among the most widely used tracers of circulation patterns in modern and past oceans but to date nd isotopes have been rarely used in investigations of fluid migration pathways at hydrocarbon seeps to test the sensitivity of nd isotope signals of seep carbonates to record past interactions between the seeping fluids and 143nd enriched volcanic derived mineral components we performed nd sr and stable isotope analyses of the lower cretaceous barremian seep carbonates found in baska czech carpathians these seep deposits are directly underlain by a complex of mafic igneous rocks which the methane charged fluids must have passed through on their way to the seafloor the end t values measured in the seep carbonates are significantly more radiogenic than the inferred signal of contemporaneous local seawater and shifted towards the composition typical of the underlying basaltoids this is in agreement with the 87sr 86sr ratios which are markedly lower that the coeval seawater signature consistent co variance trends are observed among the measured end t 87sr 86sr and 13c values attesting increasing role of the volcanic derived fluid component with increasing contribution of methane derived carbon the results of the present approach reveal the potential of nd isotopes to fingerprint exotic fluid end members present in plumbing systems of both fossil and modern methane discharges the method can be of particular use in studies of seeps associated with plate margins where 143nd enriched igneous materials are commonly encountered in the basement or in the sediment column

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

hafnium isotope stratigraphy of ferromanganese crusts a cenozoic record of hafnium isotopic compositions of central pacific deep water has been obtained from two ferromanganese crusts the crusts are separated by more than 3000 kilometers but display similar secular variations significant fluctuations in hafnium isotopic composition occurred in the eocene and oligocene possibly related to direct advection from the indian and atlantic oceans hafnium isotopic compositions have remained approximately uniform for the past 20 million years probably reflecting increased isolation of the central pacific the mechanisms responsible for the increase in87sr 86sr in seawater through the cenozoic apparently had no effect on central pacific deep water hafnium

late quaternary variability of mediterranean outflow water from radiogenic nd and pb isotopes mediterranean outflow water mow is characterised by higher temperatures and salinities than other ambient water masses mow spreads at water depths between 500 and 1500 m in the eastern north atlantic and has been a source of salinity for the atlantic meridional overturning circulation in the north atlantic we used high resolution nd and pb isotope records of past ambient seawater obtained from authigenic ferromanganese coatings of sediments in three gravity cores at 577 1745 and 1974 m water depth in the gulf of cadiz and along the portuguese margin complemented by a selection of surface sediments to reconstruct the extent and pathways of mowover the past 23 000 years the surface and downcore nd isotope data from all water depths exhibit only a very small variability close to the present day composition of mowbut do not reflect the present day nd isotopic stratification of the water column as determined from a nearby open ocean hydrographic station in contrast the pb isotope records show significant and systematic variations which provide evidence for a significantly different pattern of the mow pathways between 20 000 and 12 000 years ago compared with the subsequent period of time

nd isotope signature of holocene baltic mn fe precipitates as monitor of climate change during the little ice age neodymium nd isotope profiles were analyzed on two baltic mn fe precipitates 99 2 and tl1 from shallow water 20 m of the mecklenburg bay the age range of these mn fe precipitates determined by 226raex ba dating reaches from recent growth back to 4300 and 1000 yr bp respectively over this time range the nd isotope composition varies from end 0 13 1 to 17 5 in the selected baltic precipitates indicating substantial changes in the nd isotope composition of the baltic sea the lowest end values were recorded during the time interval of the little ice age lia ad 1350 to 1850 these minimum values indicate either an increase of the input of less radiogenic nd from scandinavian archean proterozoic sources end about 22 to the baltic sea or a decrease of the input of more radiogenic nd from continental european sources end about 12 and or north sea water end about 10 variations of both erosive continental input and north sea inflow may indicate a direct response of the nd isotope signal in the baltic sea to climate changes during the lia and be related to cyclic shifts in the atmospheric circulation triggered by the north atlantic oscillation nao another aspect that possibly influenced the input of trace elements and nd isotopes into the baltic sea is the population development in the circum baltic area during the lia the lowest end values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland the reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the baltic sea by rivers which in turn may have resulted in a change of the nd isotope composition of baltic sea water

extreme hydrochemical conditions in natural microcosms entombed within antarctic ice cryoconite holes are near vertical tubes that form in the surface of glaciers when solar heated debris melts into the ice those that form in the mcmurdo dry valleys of antarctica are distinctive in that they have ice lids and are closed to the atmosphere for periods of years to decades photoautotrophs and heterotrophs grow within this closed environment perturbing the poorly buffered water chemistry yet maintaining the potential for photosynthesis microbial excretion and decomposition of organic matter produces dissolved organic carbon doc dissolved inorganic carbon ratios of 1 2 much of the dissolved nitrogen pool 80 100 exists as dissolved organic nitrogen don the don doc ratio is 1 11 mol mol typical of organic particulate material at the earth s surface the combination of photoautotrophy heterotrophy and weak chemical buffering within these microcosms promotes values of ph pco2 o2 saturation and percentage total dissolved nitrogen as don that reach 10 99 10 7 6 atm 160 and 100 respectively which are a unique combination among the surface waters on earth these ice sealed cryoconite holes could be important analogues of refugia on snowball earth and other icy planets

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

a robotic approach to mapping post eruptive volcanic fissure conduits volcanobot was developed to map volcanic vents and their underlying conduit systems which are rarely preserved and generally inaccessible to human exploration it uses a primesense carmine 1 09 sensor for mapping and carries an ir temperature sensor analog distance sensor and an inertial measurement unit imu inside a protective shell the first field test succeeded in collecting valuable scientific data but revealed several needed improvements including more rugged cable connections and mechanical couplers increased ground clearance and higher torque motors for uphill mobility the second field test significantly improved on all of these aspects but it traded electrical ruggedness for reduced data collection speed data collected by the volcanobots while intermittent yield the first insights into the cm scale geometry of volcanic fissures at depths of up to 25 m volcanobot was deployed at the 1969 mauna ulu fissure system on k lauea volcano in hawai i it collected first of its kind data from inside the fissure system we hypothesized that 1 fissure sinuosity should decrease with depth 2 irregularity should be persistent with depth 3 any blockages in the conduit should occur at the narrowest points and 4 the fissure should narrow with depth until it is too narrow for volcanobot to pass or is plugged with solidified lava our field campaigns did not span enough lateral or vertical area to test sinuosity the preliminary data indicate that 1 there were many irregularities along fissures at depth 2 blockages occurred but not at obviously narrow locations and 3 the conduit width remained a consistent 0 4 0 5 m for most of the upper 10 m that we analyzed

response of beryllium and radiogenic isotope ratios in northern atlantic deep water to the onset of northern hemisphere glaciation we present time corrected ratios of cosmogenic 10 be to continent sourced 9 be from two fe mn crusts located in the northwest atlantic in the vicinity of the origins of northern atlantic deep water nadw these initial 10 be 9 be ratios represent those of the ambient seawater at the time of crust deposition and are constant through the last 7 ma previously published isotope records of radiogenic nd and pb isotopes in these crusts show a decrease in e nd and an increase in 206 pb 204 pb over the last 5 ma these changes are consistent with a gradual increase in the strength of nadw production an increase in the labrador sea component of nadw or an increased erosional input into the labrador sea since the residence time and thus the advective length scales of dissolved be in deep water lie between those of nd and pb records of 10 be 9 be should contrary to what has been observed vary in phase with those of nd and pb if these variations are accounted for by changes in paleo circulation the observed variations in radiogenic nd and pb isotopes are therefore most likely to be explained with an increase in the flux of terrigenous matter in the area of the labrador sea which was possibly associated with ice rafting and selective leaching of pb isotopes an increase of the labrador sea component that contributes to nadw is also a possibility but based on the 10 be 9 be data presented here large scale changes in the thermohaline circulation can be discounted as cause for the radiogenic tracer variations

in situ quantification of supraglacial cryoconite morphodynamics using time lapse imaging an example from svalbard there is growing recognition of the significance of biologically active supraglacial dust cryoconite for glacial mass balance and ecology nonetheless the processes controlling the distribution transport and fate of cryoconite particles in the glacial system remain somewhat poorly understood here using a 216 hour time series of plot scale 0 04 m 2 images we quantify the small scale dynamics of cryoconite on longyearbreen svalbard we show significant fluctuations in the apparent cryoconite area and dispersion of cryoconite over the plot within the 9 day period of observations however the net movement of cryoconite across the ice surface averaged only 5 3 mm d 1 high resolution measurements of cryoconite granule motion showed constant random motion but weak correlation with meteorological forcing factors and no directional trends for individual particle movement the high resolution time series data suggest that there is no significant net transport of dispersed cryoconite material across glacier surfaces the areal coverage and motion of particles within and between cryoconite holes appears to be a product of differential melting leading to changes in plot scale microtopography local meltwater flow dynamics and weather dependent events these subtle processes of cryoconite redistribution may be significant for supraglacial albedo and have bearing on the surface energy balance at the glacier scale

comparison of cryoconite organic matter composition from arctic and antarctic glaciers at the molecular level abstract glacier surfaces are reservoirs that contain organic and inorganic debris referred to as cryoconite solar heating of this material results in the formation of water filled depressions that are colonized by a variety of microbes and are hypothesized to play a role in carbon cycling in glacier ecosystems recent studies on cryoconite deposits have focused on their contribution to carbon fluxes to determine whether they are a net source or sink for atmospheric co 2 to better understand carbon cycling in these unique ecosystems the molecular constituents of cryoconite organic matter com require further elucidation com samples from four glaciers were analyzed by targeted extraction of plant and microbial derived biomarkers in conjunction with non targeted nmr experiments to determine the com composition and potential sources several molecular proxies were applied to assess com degradation and microbial activity using samples from greenland the canadian arctic and antarctica com from canadian john evans glacier and greenlandic leverett glacier locations was more chemically heterogeneous than that from the antarctic likely due to inputs from higher plants mosses and sphagnum as suggested by the solvent extractable alkyl lipids and sterols and the detection of lignin and sphagnum derived phenols after cupric oxide chemolysis solid state 13 c nuclear magnetic resonance nmr experiments highlighted the bulk chemical functional groups of com allowing for a general assessment of its degradation stage from the alkyl o alkyl proxy whereas solution state 1 h nmr highlighted both microbial and plant contributions to base soluble extracts from these com samples the dominance of 1 h nmr signals from microbial protein peptides in base soluble extracts of com from antarctica joyce glacier and garwood glacier phospholipid fatty acid plfa biomarker detection and the absence of plant derived biomarkers in both the solvent and cupric oxide extracts suggests that this com is dominated by microbial derived material these results indicate that com carbon composition is dependent on the local glacier environment which may have a profound impact on carbon cycling and sequestration on glacier surfaces

excess dissolved ca in the deep ocean a hydrothermal hypothesis abstract variations in seawater alkalinity and dissolved calcium provide information essential to establishing the integrated deep ocean calcium carbonate dissolution flux high precision ca measurements reported here confirm earlier suggestions that the deep ocean contains higher levels of dissolved ca than expected from calcium carbonate dissolution only i propose that the mid depth ca excess is a manifestation of the circulation of seawater through hydrothermal systems at mid ocean ridges qualitative agreement with 3 he distributions and evidence for deep water mg depletions support this hypothesis the magnitude of the mid depth ca excess implies a total hydrothermal flux larger than expected from the corresponding excess in 3 he and points to the relative importance of low temperature diffuse fluxes versus high temperature discrete fluxes for elements such as ca the implied total hydrothermal flux for ca is consistent with its oceanic mass balance requirements and resolves several long standing problems associated with our understanding of the chemical evolution of the ocean and in particular its low alkaline content

the hf isotope composition of global seawater and the evolution of hf isotopes in the deep pacific ocean from fe mn crusts this paper presents a revised chemical purification method of hf for the measurement of hf isotope ratios of fe mn crusts on a new generation of double focusing multiple collector plasma source mass spectrometer mc icp ms by measuring surface scrapings of hydrogenetic fe mn crusts distributed over the three major ocean basins the present day hf isotope distribution of oceanic deep water is assessed in detail the results show an ehf provinciality correlated with those of other radiogenic isotope tracers such as nd and pb in agreement with previous studies this supports the use of hf isotopes as tracer of element source provenance and water masses fe mn crusts display the same present day hf nd isotope array as given before for mn nodules the smaller isotopic variability of hf compared with nd may either be caused by a more efficient mixing of hf than nd in the ocean due to a longer residence time or may be a consequence of a systematically more radiogenic hf than nd isotope signature delivered to the oceans by weathering of continental crust a hf isotope time series was measured on crust va13 2 to assess the hf isotope compositions of the central pacific deep water over the past 26 ma no consistency is observed between the hf and pb isotope time series in contrast hf and nd isotope time series display similar patterns which are however apparently offset by 2 ma prior to 14 ma differential diffusion of hf and nd does not explain this offset the smaller amplitude in the hf isotope variations compared with the nd isotopes rather argues for more efficient mixing of hf in the ocean we suggest that both isotope systems have responded in a similar way to the processes affecting the dissolved radiogenic isotope composition of pacific deep water during this time interval the parallel increase in ehf and end observed between 14 and 3 ma may probably be attributed to the increased inputs of hf and nd into the central pacific ocean derived from the weathering of the pacific islands arcs over the past 3 ma an increased aeolian continental input derived from asia most likely caused negative shifts in end and ehf recorded by va13 2 the fact that hf and nd isotope compositions plot along the present day array for fe mn crusts and mn nodules over the entire past 26 ma suggests that aeolian supply of hf to the pacific ocean has been a long term important feature

laser induced fluorescence emission life from lake fryxell antarctica cryoconites laser induced fluorescence emission life images were obtained in situ from a 27 cm long ice core at lake fryxell antarctica the excitation was accomplished with a simple 532 nm green laser pen light and the fluorescence images were captured with a small compact digital camera the targets for the experiment were mm scale cryoconite assemblages found in the ice covers of this perennially frozen antarctic lake the fluorescence response originates from photo pigments in cyanobacteria dominated cryoconite assemblages with phycoerythrin pe exhibiting the optimal target cross section this inexpensive low mass low energy method avoids manipulation of the in situ habitat and individual target organisms and does not disturb the microbial community or the surrounding ice matrix we establish the correlation between fluorescence intensity and pe concentration we show that cryoconite fluorescence response does not appear to decrease with depth in the ice cover in agreement with similar findings at lake untersee a perennially ice covered lake in dronning maud land antarctica optical reflection and refraction events at the air ice interface can complicate quantitative estimates of total pigment concentrations laser targeting of a single mm scale cryoconite can result in multiple neighboring excitation events secondary to reflection and refraction phenomena in the multiple air ice interface of the bubbles surrounding the primary target

evolution of nd and pb isotopes in central pacific seawater from ferromanganese crusts abstract hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts by analysing nd pb and be isotope profiles within crusts it is possible to reconstruct seawater tracer histories depth profiles of 10be 9be ratios in three pacific ferromanganese crusts have been used to obtain growth rates which are between 1 4 and 3 8 mm ma nd and pb isotopes provide intact records of isotopic variations in pacific seawater over the last 20 ma or more there were only small changes in pb isotope composition in the last 20 ma this indicates a constant pb composition for the erosional sources and suggests further that erosional nd inputs may have been uniform too end values vary considerably with time and most probably reflect changes in ocean circulation the end values of the crusts not only vary as a function of age but also as a function of water depth from 25 to 0 ma crust va13 2 from 4 8 km water depth has a similar pattern of end variation to the two shallower crusts from 1 8 and 2 3 km but about 1 0 to 1 5 units more negative this suggests that end stratification in pacific seawater as demonstrated for the present day has been maintained for at least 20 ma each crust shows a decrease in end from 3 5 ma to the present which is interpreted in terms of an increase in the nadw component present in the pacific from 10 to 3 5 ma ago the crusts show an increase in end this suggests a decreasing role for a deep water source with end less than circum pacific sources in this regard the panamanian gateway restriction from 10 ma with final closure at 3 5 ma may have played an important role in reducing access of atlantic derived nd to the pacific

organic matter content and quality in supraglacial debris across the ablation zone of the greenland ice sheet quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for regional and potentially global carbon flow estimations the concentration and quality of organic carbon oc is an important indicator of biogeochemical and physical processes that prevail in an ice sheet ecosystem here we determine the content and quality of oc in debris from the surface of the greenland ice sheet gris using microscopic chromatographic spectrophotometric and high temperature combustion techniques the total oc content in the debris increased with distance from the edge of the ice sheet from virtually zero to 6 dry weight at 50 km inland and there was a peak in the carbohydrate proportion and the microbial abundance at 6 km inland the highest galactose mannose arabinose xylose ratios indicating maximum autochthonous microbial production were found at 10 km inland we propose that three key processes influence the carbon cycling on the gris aeolian input of microbial inoculum and nutrients in situ biological c transformation and the wash away of supraglacial debris by meltwaters we show that all these processes have significant spatial variability while the total oc content of the debris on the ice sheet is probably controlled by the physical processes of wind transport and wash away by meltwater the microbial abundance and the quantity of the labile cell contained oc within the debris is likely to be driven by the balance between the wash away and the microbial productivity

viral dynamics in cryoconite holes on a high arctic glacier svalbard 1 viruses are an abundant and dynamic constituent of microbial communities in aquatic ecosystems in this study we characterized the abundance of viruses associated first with the bottom sediment and overlying water of cryoconite holes and second with shallow ice cores of two different glaciers in svalbard viral abundances were ca 10 100 times lower than the average for marine and freshwater ecosystems in temperate regions virus to bacterium ratios vbr average 10 range between 0 7 and 74 in the water and ice samples and a strong positive correlation between viral and bacterial abundance r 0 93 p 0 01 n 57 indicate that viruses most probably play an important role in controlling bacterial mortality and hence biogeochemical cycling on glaciers samples taken along a transect from the glacier ablation area to proglacial ponds in its forefield showed that viral abundance increased in response to a higher host availability which in turn probably resulted from an increase in temperature and higher mineral levels in the ponds in a transplantation experiment viruses from cryoconite holes were incubated with a bacterial community from a proglacial lake results from the transplantation experiment showed that viruses from cryoconite holes were able to infect bacteria from proglacial lakes and thus influence biogeochemical cycles across different glacial ecosystems our data therefore suggest that viruses in cryoconite holes may be able to infect a broad range of bacterial species

supraglacial weathering crust dynamics inferred from cryoconite hole hydrology water levels in cryoconite holes were monitored at high resolution over a 3 week period on austre broggerbreen svalbard these data were combined with melt and energy balance modelling providing insights into the evolution of the glacier s near surface hydrology and confirming that the hydrology of the near surface porous ice known as the weathering crust is dynamic and analogous to a shallow perched aquifer a positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust this likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance occasionally causing sudden drainage events a linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near surface ice porosity over the measurement period the transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long term storage loci for cryoconite at the glacier surface this study highlights the importance of the weathering crust as a crucial component of the hydrology ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces

on the relationship between nd isotopic composition and ocean overturning circulation in idealized freshwater discharge events using a cost efficient climate model the effect of changes in overturning circulation on neodymium isotopic composition nd is systematically examined for the first time idealized sequences of abrupt climate changes are induced by the application of periodic freshwater fluxes to the north atlantic na and the southern ocean so thus mainly affecting either the formation of north atlantic deep water nadw or antarctic bottom water aabw variations in nd reflect weakening and strengthening of the formation of nadw and aabw changes in ndof end members are relatively small relationships between nd and the strength of nadw or aabw are more pronounced for aabw than for nadw atlantic patterns of variations in nd systematically differ between na and so experiments additionally the signature of changes in nd in the atlantic and the pacific is alike in na but opposite in so experiments discrimination between na and so experiments is therefore possible based on the atlantic pattern of variations in nd and the contrariwise behavior of nd in the atlantic and the pacific in further experiments we examined the effect of variations in magnitudes of particle export fluxes within the examined range and although settling particles represent the only sink of nd their effects on nd are relatively small our results confirm the large potential of nd as a paleocirculation tracer but also indicate its limitations of quantitative reconstructions of changes in the atlantic meridional ocean circulation

world map of nd isotopes in sea floor ferromanganese deposits the nd isotopic compositions of hydrogenous ferromanganese encrustations and nodules largely reflect those of the overlying seawater integrated over the few millions of years over which they grow available nd isotope data on ocean floor hydrogenous deposits suggest control by nd from particulates blown from the continents and released by volcanic activity associated with subduction zones and midocean ridges the regional nd isotope variations display a marked similarity to the broad patterns of present day deep ocean circulation suggesting that the particulates that are the sources of oceanic nd travel along with water masses despite rapid 10 100 ka perturbations during glacial periods the long term patterns of water mass movements and oceanic fluxes of particulates have remained essentially stable over the last few million years

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 concentration and isotopic composition of diffusible nd in fresh and marine waters abstract variations in the nd isotopic composition of ocean water through time recorded in marine deposits are suggested to document changes in erosional input and ocean circulation thus characterization of the dissolved nd component in seawater is important but few attempts have been made to directly measure truly dissolved nd here we report nd data obtained using the technique of diffusive gradients in thin films dgt designed to measure in situ diffusible labile trace metals in aqueous solutions the method samples free ions and possibly very small complexes the concentration and isotopic composition of nd in fresh brackish and seawater have been determined with dgt analyzed with thermal ionization mass spectrometry and compared with filtered and bulk water samples concentrations measured in water samples and with dgt show that the relative amount of diffusible nd increases with salinity from being about 10 in the fresh water to 42 in seawater at each sampled site the isotopic composition of nd in the water shows a similar isotopic composition within errors with nd sampled using the dgt method these results indicate that there is a complete exchange between the particulate colloidal fraction and the truly dissolved phase therefore our findings suggest that solute nd reflects both the isotopic composition of the marine sediments and the bulk water

degassing of metals and metalloids from erupting seamount and mid ocean ridge volcanoes observations and predictions recently it has been reported that the element polonium degasses from mid ocean ridge and seamount volcanoes during eruptions published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions this process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems in this paper a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using 1 predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and 2 limited data from submarine volcanic effusives the latter include analyses of polonium and trace metals in near volcano water masses sampled following a submarine eruption at loihi seamount hawaii 1000 m bsl in 1996 the element volatility predictions and observations show good agreement considering the limited dataset some of the highest volatility main group and transition element enrichments in seawater over loihi are predicted by the degassing mass transfer model i present when expanded to cover all submarine volcanic activity it is predicted that exit fluxes of these elements are up to 102 103 greater by degassing than by normal mor hydrothermalism in contrast mor exit fluxes of low volatility alkali and alkaline earth elements are likely 102 106 greater from hydrothermal inputs degassing inputs to the ocean are probably highly episodic occurring almost entirely during eruptions these are times of enhanced and abnormal hydrothermalism as well although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities it is nevertheless possible to predict to what extent each process flavors the effluents of the other degassing at mid ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and or fluid ascent in the buoyant hydrothermal plumes above ridges

measuring rates of gross photosynthesis and net community production in cryoconite holes a comparison of field methods photosynthesis by microbes on the surfaces of glaciers and ice sheets has the potential to fix carbon alter the albedo of ice surfaces via the production of organic matter and so enhance ice melt it could also be important for supplying labile organic matter and nutrients to in situ and downstream ecosystems this study compares in situ 24 hour incubation methods for measuring rates of gross photosynthesis respiration and net community production ncp in cryoconite holes on three svalbard valley glaciers rates of gross photosynthesis and respiration measured by the co 2 method were closely balanced resulting in rates of ncp close to the detection limit mean of 1 3 g c g 1 d 1 consistent with previous measurements in arctic cryoconite holes this suggests that organic matter within cryoconite holes may be derived largely from allochthonous sources the molar ratio of o 2 to co 2 in incubations gave mean respiratory and photosynthetic quotients of 0 80 0 17 1 x sd and 1 24 0 20 1 x sd respectively the 14 c method typically underestimated rates of gross photosynthesis co 2 method by more than one order of magnitude and measured a rate closer to ncp

nd isotope evidence for the evolution of the paleocurrents in the atlantic and tethys oceans during the past 180 ma the nd isotopic composition of atlantic and tethys seawater as deduced from marine phosphorites varied considerably during the past 180 ma the early tethys and central atlantic seawater from 180 to 160 ma ago early middle jurassic had a nd isotopic signature identical to that of the pacific end 6 suggesting that pacific seawater entered the newly forming tethys basin however with time continental runoff draining into the young basin became more important and led to a decrease in the nd isotopic composition and finally a decoupling from the pacific ocean during the late early cretaceous 120 90 ma ago atlantic and tethys seawater reached continental crust like nd isotopic composition values end 10 which could reflect high weathering rates induced by the warm and humid climate at that time in the time span between 80 and 50 ma late cretaceous early tertiary the nd isotopic composition of both tethys and atlantic seawater strongly increased towards pacific seawater values in the case of the atlantic ocean this change has been correlated with the opening of the south atlantic which enabled the more radiogenic pacific seawater to travel westwards around the southern edge of africa into the south and finally the north atlantic in the case of tethys seawater we have to assume that during this period large masses of pacific seawater entered the tethys again directly through the indian tethys seaway the renewed importance of this seaway might be related to the late cretaceous early tertiary first order global sea level highstand the most abrupt change towards lower more crust like values occurred in the early miocene 25 17 ma ago in the south and north atlantic as well as in the tethys during this period the143nd 144nd isotope ratios dropped from 0 5124 end 4 2 down to 0 5122 end 8 this change indicates a diminishing influx of pacif seawater into the atlantic and tethys oceans and can be correlated with the breakdown of the circum equatorial circulation patterns of the world oceans due to plate tectonics from 20 to 17 ma ago miocene the nd isotopic composition of the atlantic ocean increased again and reached values as high as 0 5123 end 6 6 whereas tethys seawater remained at low values this decoupling can be correlated with the incipient complete isolation of the tethys the nd isotopic composition was henceforth controlled by the continental runoff from surrounding land masses the major increase in the nd isotopic composition observed in the atlantic can be related to the opening of the drake passage and establishment of the circum antarctic current system this allowed pacific seawater to enter directly the south atlantic around antarctica a renewed drop in the nd isotopic composition of atlantic seawater during the late miocene can be related to the onset of north atlantic bottom water formation and its subsequent upwelling

radiogenic isotope records of quaternary glaciations changes in the erosional source and weathering processes variations of global and regional silicate weathering rates and paleo ocean circulation patterns are estimated by using radiogenic isotope records but the effects of changes in provenance are generally ignored here sediment provenance has been constrained through the use of ar ar ages for individual detrital minerals from the labrador sea which can be compared directly to the radiogenic isotope compositions from the same core material dramatic changes in the radiogenic isotope composition of north atlantic deep water through the quaternary period are shown to reflect discrete changes in both sources and weathering processes accompanying northern hemisphere glaciation changes in the different radiogenic isotope systems reflect the influence of source physical weathering and chemical weathering and not simply changes in the underlying weathering rate or ocean circulation patterns that are typically inferred

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

a blue ice ecosystem on the margins of the east antarctic ice sheet freezing temperatures desiccation and high levels of solar radiation make the surface of the antarctic ice sheet one of earth s harshest habitats however our study in the vestfold hills area of east antarctica shows that favourable conditions for microbial production become established just beneath the surface of blue ice areas which collectively cover about 2 of the ice sheet periphery their translucent wind polished surface allows solar heating to create meltwater in a greenhouse type environment at depths of up to 1m melting is intensified around dark debris particles or cryoconite where we found microbiological activity to be greatest rates of photosynthesis average 2060 ngc g cryoconite 1 d 1 were adapted to low light intensities 10 of surface irradiance values and most likely dominated by cyanobacteria and chloroplastida a heterotrophic bacterial community was also found to be active within the cryoconite although average bacterial growth rates 5 7 ngc g cryoconite 1 d 1 were far lower than average community respiration 1870 ng c g cryoconite 1 d 1 the majority of the respired carbon was most likely associated with the autotrophs and several protists therefore blue ice areas constitute oases for microbial life around the periphery of earth s coldest ice sheet