tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis abstract tem photomicrographs show that organic matter in the continental margin sediments that we have examined is primarily patchy in distribution and occurs as 1 discrete discontinuous blebs and micro blebs of differentiated and undifferentiated protoplasm 2 bacterial cells and associated muco polysaccharide networks and 3 localized smears generally associated with clay minerals and domain junctions in clay rich flocs not as thin uniform grain coatings or as infillings of nicks or etch pits on sediment grains with high degrees of surface roughness this occurrence contradicts recent assertions that most organic matter in continental margins occurs as monolayer or monolayer equivalent coatings on mineral grains and inorganic bioclastic particles our results are based on tem photomicrographs of samples from the northern california continental slope that fall within the monolayer equivalent envelope defined by mayer 1994 marine snow from the overlying nepheloid layer and sediments from eckernforde bay in the baltic sea these samples were prepared specifically to preserve and image in situ sediment fabric and organic constituents textural evidence suggests that low permeabilities caused by the interaction between the organic inorganic and biologic components of the clay size fraction play a major role in determining organic matter preservation on continental margins

greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

seasonal evolution of water contributions to discharge from a greenland outlet glacier insight from a new isotope mixing model the greenland ice sheet gris subglacial hydrological system may undergo a seasonal evolution with significant geophysical and biogeochemical implications we present results from a new isotope mixing model to quantify the relative contributions of surface snow glacial ice and delayed flow to the bulk meltwater discharge from a small 5k m 2 land terminating gris outlet glacier during melt onset may and at peak melt july we use radioactive 222 rn and stable isotopes 18 o deuterium to differentiate the water source contributions atmospherically derived 7 be further constrains meltwater transit time from the glacier surface to the ice margin we show that 1 222 rn is a promising tracer for glacial waters stored at the bed and 2 a quantitative chemical mixing model can be constructed by combining 222 rn and the stable water isotopes applying this model to the bulk subglacial outflow from our study area we find a constant delayed flow stored component from melt onset through peak melt this component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land terminating sections of the gris undergoes a seasonal evolution from a distributed to a channelized system

on the origin of a phosphate enriched interval in the chattanooga shale upper devonian of tennessee a combined sedimentologic petrographic and geochemical study abstract the devonian chattanooga shale contains an uppermost black shale interval with dispersed phosphate nodules this interval extends from tennessee to correlative strata in kentucky indiana and ohio and represents a significant period of marine phosphate fixation during the late devonian of north america it overlies black shales that lack phosphate nodules but otherwise look very similar in outcrop the purpose of this study is to examine what sets these two shales apart and what this difference tells us about the sedimentary history of the uppermost chattanooga shale in thin section the lower black shales pbs show pyrite enriched laminae and compositional banding the overlying phosphatic black shales phbs are characterized by phosbioclasts have a general banded to homogenized texture with reworked layers and show well defined horizons of phosphate nodules that are reworked and transported in the phbs up to 8000 particles of p debris per cm2 occur in reworked beds whereas the background black shale shows between 37 88 particles per cm2 in the pbs the shale matrix contains between 8 16 phosphatic particles per cm2 the shale matrix in the phbs contains 5 6 inertinite whereas just 1 inertinite occurs in the pbs the shale matrix in both units is characterized by flat ree patterns shale normalized whereas phosbioclast rich layers in the phbs show high concentrations of rees and enrichment of mrees negative ce anomalies are common to all samples but are best developed in association with phosbioclasts redox sensitive elements co u mo are more strongly enriched in the pbs when compared to the phbs trace elements associated with organic matter cu zn cd ni show an inverse trend of enrichment deposited atop a sequence boundary that separates the two shale units the phbs unit represents a transgressive systems tract and probably was deposited in shallower water than the underlying pbs interval the higher phosphate content in the phbs is interpreted as the result of a combination of lower sedimentation rates with reworking winnowing episodes three types of phosphatic beds that reflect different degrees of reworking intensity are observed strong negative ce anomalies and abundant secondary marcasite formation in the phbs suggests improved aeration of the water column and improved downward diffusion of oxygen into the sediment the associated oxidation of previously formed pyrite resulted in a lowering of pore water ph and forced dissolution of biogenic phosphate phosphate dissolution was followed by formation of secondary marcasite and phosphate repeated episodic reworking caused repetitive cycles of phosphatic dissolution and reprecipitation enriching mrees in reprecipitated apatite a generally deeper seated redox boundary favored p remineralization within the sediment matrix and multiple repeats of this process in combination with wave and current reworking at the seabed led to the formation of larger phosphatic aggregates and concentration of phosphate nodules in discrete horizons

tracking millennial scale holocene glacial advance and retreat using osmium isotopes insights from the greenland ice sheet high resolution os isotope stratigraphy can aid in reconstructing pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine os residence time this paper presents new os isotope data from ocean cores adjacent to the west greenland ice sheet that have excellent chronological controls cores msm 520 and da00 06 represent distal to proximal sites adjacent to two west greenland ice streams core msm 520 has a steadily decreasing os signal over the last 10 kyr 187os 188os 1 35 0 81 in contrast os isotopes from core da00 06 proximal to the calving front of jakobshavn isbrae highlight four stages of ice stream retreat and advance over the past 10 kyr 187os 188os 2 31 1 68 2 09 1 47 our high resolution chemostratigraphic records provide vital benchmarks for ice sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change variations in os isotope composition from sediment and macro algae seaweed sourced from regional and global settings serve to emphasize the overwhelming effect weathering sources have on seawater os isotope composition further these findings demonstrate that the residence time of os is shorter than previous estimates of 104 yr

hydro biogeochemical coupling beneath a large polythermal arctic glacier implications for subice sheet biogeochemistry 1 we analyze the interannual chemical and isotopic composition of runoff from a large high arctic valley glacier over a 5 year period during which drainage evolved from a long residence time drainage system feeding an artesian subglacial upwelling sgu at the glacier terminus to a shorter residence time drainage system feeding an ice marginal channel imc increased icemelt inputs to the sgu are thought to have triggered this evolution this sequence of events provides a unique opportunity to identify coupling between subglacial hydrology and biogeochemical processes within drainage systems of differing residence time the biogeochemistry of the sgu is consistent with prolonged contact between meltwaters and subglacial sediments in which silicate dissolution is enhanced anoxic processes e g sulphate reduction prevail and microbially generated co2 and sulphide oxidation drive mineral dissolution solute in the imc was mainly derived from moraine pore waters which are added to the channel via extraglacial streams these pore waters acquire solute predominantly via sulphide oxidation coupled to carbonate silicate dissolution we present the first evidence that microbially mediated processes may contribute a substantial proportion 80 in this case of the total glacial solute flux which includes coupling between microbial co2 generation and silicate carbonate dissolution the latter suggests the presence of biofilms in subglacial ice marginal sediments where local perturbation of the geochemical environment by release of protons organic acids and ligands stimulates mineral dissolution these data enable inferences to be made regarding biogeochemical processes in longer residence time glacial systems with implications for the future exploration of antarctic subglacial lakes and other wet based ice sheet environments

advective flow through the upper continental shelf driven by storms buoyancy and submarine groundwater discharge data from monitoring wells on the carolina usa continental shelf require a reevaluation of pore water exchange across the seafloor temperature salinity and 226ra data from 3 offshore wells require rapid and frequent pore water exchange to depths of several meters through sands and other permeable sediments the exchange is driven by tidal pumping storms buoyancy and submarine groundwater discharge tidal pumping causes semidiurnal temperature cycles in one well that can only be explained by rapid fluid flow the effect of large storms is evident in sudden temperature changes 2 4 m below the seabed in two wells these changes require considerable pore water exchange sudden cooling of the ocean may cause pore waters to become buoyant with respect to the ocean and trigger pore water convection to several meters depth as observed in one well the wells also display frequent large factor of ten changes in 226ra activity this requires a substantial input of 226ra enriched fluids to replace 226ra that is lost during exchange events these data support a fourth flow process which is groundwater seeping from the underlying limestone the pore spaces in the overlying sand provide a temporary reservoir for these fluids we conclude that pore water residence times in 2 4 m thick sands on this continental margin are on the order of a few months or less

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

transport and reaction of iron and iron stable isotopes in glacial meltwaters on svalbard near kongsfjorden from rivers to estuary to ocean abstract glacial meltwater has been suggested as a significant source of potentially bioavailable iron to the oceans however the supply of dissolved iron dfe in glacial meltwaters is poorly constrained as few sites have been studied and because the chemical processing of fe during transport from glaciers to the adjacent coastal ocean is not well understood in order to better constrain glacial fluxes of dfe to the ocean iron concentrations iron stable isotopes 56fe and other supporting chemical and physical measurements were made along a 4 km long glacial meltwater river on svalbard and in estuarine waters that it flows into dissolved iron concentrations in the bayelva river decreased from a maximum of 734 nm near the glacier to an average value of 116 nm near the mouth of the river measurements in the kongsfjorden estuary suggest that 3 to 10 nm of dfe from the bayelva river is stabilized in glacial waters by the time it mixes into the ocean incubation of bayelva river waters over two weeks in both the light and dark show similar results with the majority of dfe being quickly precipitated and 4 to 7 nm fe stabilized in the dissolved phase evidence suggests that fe is most likely lost from the dissolved phase by aggregation and adsorption of nanoparticulate and colloidal fe to particles dissolved 56fe was between 0 11 and 0 09 for all river samples and did not vary systematically with dfe concentrations we infer that the fe is lost from the dissolved phase by a process that fractionates fe isotopes by less than 0 05 indicating that the fe bonding environment does not change during precipitation this is consistent with doc loss that is much faster than predicted photo oxidation rates suggesting that doc is also lost through adsorption and precipitation dissolved fe concentrations in the bayelva river 15 734 nm and fe concentrations which are stabilized in the dissolved phase 4 7 nm are much lower than some previous estimates of fe in glacial meltwaters with roughly 80 of dfe lost during transit in the bayelva river and roughly 90 of the remaining dfe lost in the estuary this may mean that glaciers are a less significant source of dissolved fe to the global oceans than has been previously hypothesized that cold base glaciers of the type studied here do not contribute significantly to the dissolved fe flux or that the flux of reactive particulate fe to the oceans is more important than the dissolved flux in arctic regions with similar proglacial environments bedrock composition weathering intensity and as precipitation of colloidal and nanoparticulate fe may all play an important role in regulating the glacial meltwater iron flux to the ocean

iron cycling and stable fe isotope fractionation in antarctic shelf sediments king george island iron fe fluxes from reducing sediments and subglacial environments are potential sources of bioavailable fe into the southern ocean stable fe isotopes 56fe are considered a proxy for fe sources and reaction pathways but respective data are scarce and fe cycling in complex natural environments is not understood sufficiently to constrain respective 56fe endmembers for different types of sediments environmental conditions and biogeochemical processes we present 56fe data from pore waters and sequentially extracted sedimentary fe phases of two contrasting sites in potter cove king george island antarctic peninsula a bay that is affected by fast glacier retreat sediments close to the glacier front contain more easily reducible fe oxides and pyrite and show a broader ferruginous zone compared to sediments close to the icefree coast where surficial oxic meltwater streams discharge into the bay pyrite in sediments close to the glacier front predominantly derives from eroded bedrock for the high amount of easily reducible fe oxides proximal to the glacier we suggest mainly subglacial sources where fe liberation from comminuted material beneath the glacier is coupled to biogeochemical weathering processes likely pyrite oxidation or dissimilatory iron reduction dir our strongest argument for a subglacial source of the highly reactive fe pool in sediments close to the glacier front is its predominantly negative 56fe signature that remains constant over the whole ferruginous zone this implies in situ dir does not significantly alter the stable fe isotope composition of the accumulated fe oxides the nonetheless overall light 56fe signature of easily reducible fe oxides suggests pre depositional microbial cycling as it occurs in potentially anoxic subglacial environments the strongest 56fe depletion in pore water and most reactive fe oxides was observed in sediments influenced by oxic meltwater discharge the respective site showed a condensed redox zonation and a pore water 56fe profile typical for in situ fe cycling we demonstrate that the potential of pore water 56fe as a proxy for benthic fe fluxes is not straight forward due to its large variability in marine shelf sediments at small spatial scales 2 4 at the site proximal to oxic meltwater discharge vs 0 9 at the site proximal to the marine glacier terminus both at 2 cm sediment depth the controlling factors are multifold and include the amount and reactivity of reducible fe oxides and organic matter the isotopic composition of the primary and secondary ferric substrates sedimentation rates and physical reworking bioturbation ice scraping the application of 56fe geochemistry may prove valuable in investigating biogeochemical weathering and fe cycling in subglacial environments this requires however similarly to the use of 56fe for the quantification of benthic fluxes that the spatial and temporal variability of the isotopic endmember is known and accounted for since geochemical data from subglacial environments are very limited further studies are needed in order to sufficiently assess fe cycling and fractionation at glacier beds and the composition of discharges from those areas

modelling rates of sedimentation from icebergs abstract icebergs transport debris from ice masses into the glacimarine environment but iceberg production debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters a model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts the flux of basal debris calved through a 1 m width of tidewater margin is h d c 100 v c where h d and c are basal debris rich ice thickness and sediment content and v c is iceberg calving rate iceberg basal melting for any horizontal interval d x away from the calving glacier is dy m b d x v b where m b is iceberg melt rate and v b is horizontal iceberg velocity sediment release for any x increment depends on iceberg debris concentration and previous berg melt history model parameters vary with the nature of climatic conditions on a continuum from cold polar environments e g high canadian arctic antarctic peninsula through sub polar environments e g baffin island svalbard to more temperate environments e g se alaska these parameters include glacier flow velocity glacier thermal regime basal debris rich ice thickness and marine water temperature model results suggest that iceberg sedimentation rates are lowest for high polar settings and most rapid in warm maritime and some sub polar areas however icebergs in cold waters transport debris to significantly greater distances from the parent glacier the model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings

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

detrital sediment fluxes from continents to oceans abstract detrital sediment is carried from land to the sea by three agents rivers glaciers and winds the shoreline is an arbitrary boundary within the detrital sediment transport system which extends from a site of origin across areas of temporary storage to a site of long term deposition the most important of the agents moving sediment across the land is river transport estimated to be in the order of 20 10 12 kg of sediment annually at present analysis of drainage basins indicates that relief and runoff are the most important factors in determining the sediment load of rivers the competence of rivers to transport sediment is governed by the volume flow gradient and the sediment load itself today most large rivers are fed by snowmelt in highland areas runoff from rainfall in the drainage basin and groundwater inflow along the river course water is lost to evaporation and groundwater infiltration river courses can often be divided into two segments a degradational section in which the gradient is relatively steep and little temporary storage of sediment takes place and an aggradational section where the gradient is sharply reduced through meandering and where large scale temporary sediment storage forms a flood plain lakes trap sediment inland and prevent its transport to the sea today many high and mid latitude rivers are interrupted by lakes of glacial origin there are also some large areas of internal drainage that deliver no sediment to the sea the load carried by rivers has been markedly altered by human activity and may have doubled over the past few thousand years only to be reduced in the past century by the widespread construction of dams the ancient use of fire in hunting and its subsequent use in clearing land has increased erosion extensive deforestation and cultivation processes have also increased the sediment supply dam construction is a relatively new factor and affects the sediment transport system by trapping sediment before it can reach the sea the resulting lower sediment supply from rivers is at least in part compensated by increased coastal erosion glacial erosion is difficult to estimate there is an ongoing controversy whether ice sheets are effective erosive agents or not estimates of the present global flux of glacial detritus range from 0 8 50 10 12 kg annually with the lower value most probable the dust flux is in the order of 0 5 to 0 9 10 12 kg annually but may vary greatly with time

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

seasonally resolved diatom δ18o records from the west antarctic peninsula over the last deglaciation understanding the response of the antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st century warming a unique diatom 18o record derived from a high resolution deglacial seasonally laminated core section off the west antarctic peninsula wap is presented here by extracting and analysing single species samples from individual laminae season specific isotope records were separately generated to show changes in glacial discharge to the coastal margin during spring and summer months as well as documenting significant intra annual seasonal variability during the deglaciation with increased discharge occurring in summer relative to spring further intra seasonal variations are apparent between individual taxa linked to the environment that individual diatom species live in whilst deglacial 18o are typically lower than those for the holocene indicating glacial discharge to the core site peaked at this time inter annual and inter seasonal alternations in excess of 3 suggest significant variability in the magnitude of these inputs these deglacial variations in glacial discharge are considerably greater than those seen in the modern day water column and would have altered both the supply of oceanic warmth to the wap as well as regional marine atmospheric interactions in constraining changes in glacial discharge over the last deglaciation the records provide a future framework for investigating links between annually resolved records of glacial dynamics and ocean climate variability along the wap

biochemical vs detrital mechanism of remanence acquisition in marine carbonates a lesson from the k t boundary interval abstract an apparently complete carbonate rich cretaceous tertiary boundary interval in odp section 119 738c 20r 5 from the southern kerguelen plateau provides a unique insight into processes of magnetization acquisition in marine carbonates the boundary interval is characterized by a 1 m thick clay rich zone distinct depositional lamina are preserved within the basal 15 cm of this zone the upper part is bioturbated previous studies have demonstrated that the bulk of the detrital fraction in the laminated and bioturbated carbonates has the same local source and hence the two intervals likely had similar initial detrital assemblages magnetic properties of these rocks however differ significantly the laminated sediments have a higher content of non silicate bound iron yet approximately an order of magnitude lower intensity of the natural remanent magnetization compared to the bioturbated rocks our detailed rock magnetic study indicates that in the bioturbated interval the dominant iron bearing phase is single domain magnetite likely of biogenic origin in the laminated interval apart from a small ferromagnetic fraction with multi domain like behavior non silicate bound iron is mainly sequestered in paramagnetic phases likely poorly crystalline oxyhydroxides it appears that a shut down of biological productivity after the k t event allowed preservation of the initial detrital early authigenic iron phases that are dominated by reactive iron oxyhydroxides with recovery of the normal biological activity as evidenced by resumption of bioturbation the oxyhydroxides had been replaced with biogenic magnetite thus produced biochemical magnetization led to a several fold increase in the remanence our results suggest that in areas where bioavailable iron constitutes a significant part of the detrital input such as in pelagic marine environments distant from clastic sources the biochemical remanent magnetization may be the dominant process of magnetization acquisition

sources and mechanisms for the enrichment of highly reactive iron in euxinic black sea sediments the deep basinal euxinic sediments of the black sea are enriched in iron that is highly susceptible to sulfidization compared to oxic suboxic continental margin sediments in the black sea and oxic dysoxic continental margin and deep sea sediments worldwide a mass balance treatment of iron speciation data from three deep basin sediment cores shows that this enrichment is due to a combination of 1 highly reactive iron bearing phases sulfides and oxides whose ultimate source was by diagenetic mobilization from the shelf wijsman and others 2001 and 2 enhanced iron reactivity in the lithogenous component of deep basinal sediments the cause of the enhanced reactivity of lithogenous iron is problematical possible mechanisms include microbial oxidation of non reactive iron silicates and the preferential deposi tion of a fine grained reactive iron enriched lithogenous component in the deep basin by the fractionation of the lithogenous flux during transport across the shelf the application of paleoredox indicators based on iron reactivity degree of pyritization indicator of anoxicity should take into account that the availability of highly reactive iron and hence the concentration of reactive iron phases in the sediment is controlled by a variety of chemical physical and biological factors some of which are not related directly to redox conditions in the water column

substantial iron sequestration during green clay authigenesis in modern deep sea sediments pyrite formation has been considered a key iron sink in organic rich marine sediments analyses of sediments from the ivory coast ghana marginal ridge demonstrate that iron can be buried at greater rates during green clay formation

the dual beam mini doas technique measurements of volcanic gas emission plume height and plume speed with a single instrument the largest error in determining volcanic gas fluxes using ground based optical remote sensing instruments is typically the determination of the plume speed and in the case of fixed scanning instruments also the plume height we here present a newly developed technique capable of measuring plume height plume speed and gas flux using one single instrument by simultaneously collecting scattered sunlight in two directions the angle between the two measurement directions is fixed removing the need for time consuming in field calibrations the plume height and gas flux is measured by traversing the plume and the plume speed is measured by performing a stationary measurement underneath the plume the instrument was tested in a field campaign in may 2005 at mt etna italy where the measured results are compared to wind fields derived from a meso scale meteorological model mm5 the test and comparison show that the instrument is functioning and capable of estimating wind speed at the plume height

mineral deposits and earth evolution mineral deposits are not only primary sources of wealth generation but also act as windows through which to view the evolution and interrelationships of the earth system deposits formed throughout the last 3 8 billion years of the earth s history preserve key evidence with which to test fundamental questions about the evolution of the earth these include the nature of early magmatic and tectonic processes supercontinent reconstructions the state of the atmosphere and hydrosphere with time and the emergence and development of life the interlinking processes that form mineral deposits have always sat at the heart of the earth system and the potential for using deposits as tools to understand that evolving system over geological time is increasingly recognized this volume contains research aimed both at understanding the origins of mineral deposits and at using mineral deposits as tools to explore different long term earth processes

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

early diagenesis and trace element accumulation in north american arctic margin sediments abstract concentrations of redox sensitive elements s mn mo u cd re were analyzed in a set of 27 sediment cores collected along the north american arctic margin naam from the north bering sea to davis strait via the canadian archipelago sedimentary distributions and accumulation rates of the elements were used to evaluate early diagenesis in sediments along this section and to estimate the importance of this margin as a sink for key elements in the polar and global oceans distributions of mn total s and reduced inorganic s demonstrated that diagenetic conditions and thus sedimentary carbon turnover in the naam is organized regionally undetectable or very thin layers

thermal subsidence and compaction in sedimentary basins application to baltimore canyon trough cooling with the subsidence of continental crust is likely to be an important mechanism for the formation of sedimentary basins if the lithosphere was initially very thin and sedimentation continued to fill the basin to the original depth of basement a similarity solution is possible in this paper the similarity solution is extended to include sediment compaction and a depth dependent thermal conductivity the similarity solution is also used to determine the thermal evolution and petroleum potential of sedimentary basins experience with similarity solutions in many branches of applied physics indicates that they commonly give good results even when the required assumptions are rather poor approximations an empirical subsidence relation valid for older basins is al o extended to include sediment compaction these results are applied to the evolution of the baltimore canyon trough on the outer continental margin of the eastern united states as given by the cost b 2 well good agreement is obtained with both the subsidence record and the present thermal gradient it is predicted that optimal thermal conditions for the conversion of kerogens to petroleum occur between depths of 4 and 6 km

importance of flood plain sedimentation for river sediment budgets and terrigenous input to the oceans insights from the brahmaputra jamuna river recent authors have suggested that a significant proportion of the worldwide terrigenous sediment budget is trapped landward of the river ocean boundary in high load tectonically active basins to test this idea modern flood plain sediment accumulation rates were determined along a 110 km reach of the brahmaputra locally jamuna river using 137cs geochronology of sediment cores and geographic information system gis extrapolation to adjacent areas 137cs accumulation rates decrease exponentially away from the channel from 4 cm yr on the natural levees to 1 cm yr within a few tens of kilometers basinward important controls on sedimentation in this area include proximity to distributary channels local topography and interannual variability of the flood pulse model results indicate that an average of 23 m t yr of sediment are sequestered in this section of the flood plain extrapolated basinwide as much as 39 71 of the river sediment budget may be trapped landward of the ganges brahmaputra mouth

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications

diagenesis of iron in proglacial sand deposits of late and post weichselian age abstract iron diagenesis was studied in quaternary sand deposits of a temperate climate using an integrated approach of sedimentary petrography and groundwater chemistry the iron bearing minerals amphiboles pyroxenes magnetite and ilmenite are all extensively altered quantitatively amphiboles and pyroxenes are by far the most important goethite and lepidocrocite are the most important of the iron oxyhydroxide weathering products and they coat quartz and feldspars as well as amphiboles and pyroxenes however lepidocrocite is absent in the unsaturated zone hematite is only present associated with magnetite and ilmenite total iron contents of the sediments range from 0 3 0 9 percent with 30 80 percent as coatings on quartz and feldspar grains 25 60 percent in the amphibole and pyrox ne fraction and only 2 15 percent in the magnetite and ilmenite fraction therefore amphiboles and pyroxenes are the most important sources of iron for these diagenetic processes the groundwater has a ph between 5 5 and 6 0 and contains 10 30 m fe2 and a low total of dissolved solids subtraction of the contribution of the dissolved solids from atmospheric precipitation indicates higher ph and hco3 sio2 ca2 na m and fe2 concentrations due to mineral reactions in the aquifer stability relationships for iron bearing minerals under the assumption of anoxic conditions show strong undersaturation for iron bearing silicates while undersaturation for magnetite and ilmenite is much less the saturation state for magnetite is strongly dependent on the iron oxide phase formed by incongruent dissolution the surfaces of iron silicates and magnetite are highly etch pitted indicating that mineral dissolution is controlled by surface reactions rather than by diffusion through alteration products the rate of mineral alteration is slow in comparison with groundwater flow thus diagenetic changes occur in the deposit as a whole rather than as a diagenetic front advancing through the deposit the abundance of feooh on all detrital grains suggests that this proglacial deposit could develop into a red bed during further diagenesis this possibility should be considered in the paleoclimatic interpretation of red beds

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

sources of iron for pyrite formation in marine sediments more than two hundred aerobic continental margin aerobic deep sea dysaerobic and anaerobic euxinic sediments have been examined for their variations in different operationally defined iron fractions each of which represents a different reactivity towards dissolved sulfide aerobic continental margin deep sea and dysaerobic sediments contain similar contents of highly reactive iron dithionite soluble iron plus pyrite iron poorly reactive iron iron soluble in hcl less that soluble in dithionite and unreactive iron total iron less that soluble in hcl by contrast non turbidite euxinic samples from the black sea as well as euxinic samples from the cariaco basin and framvaren are enriched in highly reactive iron these sediments contain a small lithogenous fraction and a large biogenous organic c rich fraction which decays by sulphate reduction in an iron rich water column to form pyrite rich sediment other anaerobic euxinic samples from the black sea orca basin and kau bay contain lower concentrations of biogenous sediment and are not therefore enriched in highly reactive iron degrees of pyritization dop for all the aerobic dysaerobic and anaerobic euxinix samples except those low in biogenous material are consistent with analogous ancient sediments and indicate that most pyrite formation occurs form the highly reactive iron fraction

chemical and physical characteristics of iron oxides in riverine and glacial meltwater sediments abstract the speciation and grain size distribution of iron have been examined in several riverine and glacial sediments in order to evaluate controls on the concentrations and modes of occurrence of iron oxides in weathering derived particulates three operationally defined fractions have been recognised relating to the reactivity of iron towards dissolved sulphide 1 highly reactive iron fe hr consisting of ferric oxides 2 poorly reactive iron fe pr consisting of magnetite and some sheet silicate iron and 3 unreactive residual silicate iron fe u the finer fractions of each riverine and glacial suite are enriched in fe hr and usually also have higher fe hr fet ratios however coarser fractions may also have elevated fe hr contents and relationships of fe hr to both surface area and al indicate that iron oxides dominantly occur in association with the surfaces of aluminosilicate minerals which are common in finer grained fractions but may also be relatively enriched in coarser fractions a similar range of fe hr surface loadings is evident in the riverine and glacial meltwater suites from 0 6 to 1 8 mg fe m 2 for the riverine sediments and 0 5 to 1 5 mg fe m 2 for the glacial meltwater sediments despite wide variations in catchment bedrock lithology and climatic conditions significantly lower iron oxide loadings 0 1 mg fe m 2 were found in subglacial sediments most fe hr is closely associated with organic c although the latter occurs as blebs or smears rather than continuous coatings e g ransom et al 1997 ransom b bennett r h baerwald r shea k 1997 tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis mar geol 138 1 9 electron microscope observations show that iron oxides may occur as nanoparticulate 10 20 nm spheres at the edges of sheet aluminosilicate minerals as crystalline oxides infilling surface pits in coarser grained aluminosilicate minerals and occasionally as discrete crystalline oxides the similar occurrences of iron oxides in both riverine and glacial environments indicates that the delivery of reactive iron oxides to the oceans during glacial interglacial cycles will be affected by the masses and grain size characteristics of sediments delivered by glacial and riverine fluxes rather than by differences in iron mineralogy these delivery rates will be modified by behaviour of the oxide nanoparticles during transport from the continents

estimation of the global amount of submarine gas hydrates formed via microbial methane formation based on numerical reaction transport modeling and a novel parameterization of holocene sedimentation this study provides new estimates for the global offshore methane hydrate inventory formed due to microbial ch4 production under quaternary and holocene boundary conditions a multi 1d model for particular organic carbon poc degradation gas hydrate formation and dissolution is presented the novel reaction transport model contains an open three phase system of two solid compounds organic carbon gas hydrates three dissolved species methane sulfates inorganic carbon and one gaseous phase free methane the model computes time resolved concentration profiles for all compounds by accounting for chemical reactions as well as diffusive and advective transport processes the reaction module builds upon a new kinetic model of poc degradation which considers a down core decrease in reactivity of organic matter various chemical reactions such as organic carbon decay anaerobic oxidation of methane methanogenesis and sulfate reduction are resolved using appropriate kinetic rate laws and constants gas hydrates and free gas form if the concentration of dissolved methane exceeds the pressure temperature and salinity dependent solubility limits of hydrates and or free gas with a rate given by kinetic parameters global input grids have been compiled from a variety of oceanographic geological and geophysical data sets including a new parameterization of sedimentation rates in terms of water depth we find prominent gas hydrate provinces offshore central america where sediments are rich in organic carbon and in the arctic ocean where low bottom water temperatures stabilize methane hydrates the world s total gas hydrate inventory is estimated at 0 82 x 10sup13 m3 2 10 x 10sup15 m3 ch4 at stp conditions or equivalently 4 18 995 gt of methane carbon the first value refers to present day conditions estimated using the relatively low holocene sedimentation rates the second value corresponds to a scenario of higher quaternary sedimentation rates along continental margins our results clearly show that in situ poc degradation is at present not an efficient hydrate forming process significant hydrate deposits in marine settings are more likely to have formed at times of higher sedimentation during the quaternary or as a consequence of upward fluid transport at continental margins

organic carbon fluxes to the ocean from high standing islands the transfer of terrestrially derived yet poorly quantified organic carbon to the oceans is an important yet unagreed upon proportion of the world s carbon budget the few data that exist suggest that high standing oceanic islands in the southwest pacific may make important contributions to the overall terrestrial flux of particulate organic carbon poc to the oceans we have determined the poc flux from several streams in new zealand with those data and previous measurements from taiwan and papua new guinea we estimate the poc flux from high standing islands in the southwest pacific to be 48 1012 g c yr 1 a value slightly lower than previous estimates these islands which make up only 3 of earth s landmass contribute 17 35 of the estimated poc entering the world s oceans annually and thus may be important sources of terrestrial carbon to the ocean anthropogenic activities especially deforestation and forest harvesting have probably exacerbated the natural flux few to no data exist for many of these islands and thus a more detailed assessment awaits further measurements

a pb isotope tracer of ocean ice sheet interaction the record from the ne atlantic during the last glacial interglacial cycle abstract ice sheet ocean interactions are both a response to climate forcing and a source of climate feedback releasing freshwater to the surface ocean and influencing climate and atmospheric co2 through changes in ocean circulation documenting the outcomes of these interactions for recent glacial cycles is important given current and future scenarios of polar ice retreat however this is currently hampered by lack of accurate constraints on ice sheet development and demise marine sedimentary pb isotope records have potential to investigate these aspects of ice sheet feedbacks at high temporal resolution because of the sensitivity of the pb isotope composition to continental weathering intensity and solute flux here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from odp site 980 on feni drift 2168 mbsl rockall trough ne atlantic spanning the last 43 ka the location of site 980 at the northern edge of the british irish ice sheet biis makes it well placed to monitor changes in biis development as it responded to migration of the polar front during the last glacial interglacial cycle the data reveal millennial scale cyclicity in pb isotope composition reminiscent of dansgaard oeschger cycles from the start of the record until heinrich event 2 43 24 ka characterised by extreme shifts to radiogenic compositions i e variation in 206pb 204pb from 18 9 to 20 5 the period 24 17 5 ka is also characterised by exceptionally radiogenic and highly variable pb isotope compositions associated with the rapid and repeated expansion and collapse of the biis the presence of such radiogenic pb isotope compositions during periods of maximum ice sheet activity support interpretation of the subglacial environment as an active weathering environment contributing to biogeochemical cycles through the transport vectors of meltwater release and debris laden ice calving

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

pliocene deglacial event timelines and the biogeochemical response offshore wilkes subglacial basin east antarctica abstract significantly reduced ice coverage in greenland and west antarctica during the warmer than present pliocene could account for 10 m of global mean sea level rise any sea level increase beyond this would require contributions from the east antarctic ice sheet eais previous studies have presented low resolution geochemical evidence from the geological record suggesting repeated ice advance and retreat in low lying areas of the eais such as the wilkes subglacial basin however the rates and mechanisms of retreat events are less well constrained here we present orbitally resolved marine detrital sediment provenance data paired with ice rafted debris and productivity proxies during three time intervals from the middle to late pliocene at iodp site u1361a offshore of the wilkes subglacial basin our new data reveal that pliocene shifts in sediment provenance were paralleled by increases in marine productivity while the onset of such changes was marked by peaks in ice rafted debris mass accumulation rates the coincidence of sediment provenance and marine productivity change argues against a switch in sediment delivery between ice streams and instead suggests that deglacial warming triggered increased rates of iceberg calving followed by inland retreat of the ice margin timescales from the onset of deglaciation to an inland retreated ice margin within the wilkes subglacial basin are on the order of several thousand years this geological evidence corroborates retreat rates determined from ice sheet modeling and a contribution of 3 to 4 m of equivalent sea level rise from one of the most vulnerable areas of the east antarctic ice sheet during interglacial intervals throughout the middle to late pliocene

distributions sources and transformations of dissolved and particulate iron on the ross sea continental shelf during summer we report water column dissolved iron dfe and particulate iron pfe concentrations from fifty stations sampled across the ross sea during austral summer january february of 2012 concentrations of dfe and pfe were measured in each of the major ross sea water masses including the ice shelf water and off shelf circumpolar deep water despite significant lateral variations in hydrography macronutrient depletion and primary productivity across several different regions on the continental shelf dfe concentrations were consistently low 0 1 nm in surface waters with only a handful of stations showing elevated concentrations 0 20 0 45 nm in areas of melting sea ice and near the franklin island platform across the study region pfe associated with suspended biogenic material approximately doubled the inventory of bioavailable iron in surface waters our data reveal that the majority of the summertime iron inventory in the ross sea resides in dense shelf waters with highest concentrations within 50 m of the seafloor higher dfe concentrations near the seafloor are accompanied by an increased contribution to pfe from authigenic and or scavenged iron particulate manganese is also influenced by sediment resuspension near the seafloor but unlike pfe is increasingly associated with authigenic material higher in the water column together these results suggest that following depletion of the dfe derived from wintertime convective mixing and sea ice melt recycling of pfe in the upper water column plays an important role in sustaining the summertime phytoplankton bloom in the ross sea polynya

how surface complexes impact boron isotope fractionation evidence from fe and mn oxides sorption experiments abstract although the ph dependence of boron isotope fractionation between solution and precipitating minerals has been widely used in earth sciences especially for reconstructing ancient seawater ph the mechanisms by which boron adsorbs on solids or coprecipitates in minerals are still poorly known here we have investigated boron isotopic fractionation during its adsorption on goethite feooh and birnessite k0 1mno2 2 0 9h2o as a function of solution ph at t 25 c and i 0 1 m maximum partition coefficients kd between adsorbed and aqueous boron equal to 39 and 34 for goethite and birnessite respectively are observed at ph 8 9 b adsorption at the surface of goethite induces its strong ph dependent isotopic fractionation ranging from 40 10b enrichment on goethite at ph 10 during adsorption on birnessite at acid and neutral ph boron isotopic fractionation is lower than during its sorption on goethite 15 decreases increases with increasing ph above ph 8 and reverses at ph 9 11b enrichment 23 at ph 10 8 is observed at birnessite surface based on combined infrared drift spectroscopic analysis and modeling of b speciation at oxides solution interfaces the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral boron inner sphere complexes on goethite surface and tetrahedral inner sphere and trigonal outer sphere and inner sphere complexes on birnessite surface b isotopic fractionation is strongly dependent on the structure of surface complexes formed the high steric strain induced by the formation of trigonal boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation isotopically lighter sorbed boron than that following the formation of tetrahedral bidendate binuclear complexes conversely the formation at birnessite surface of trigonal complexes having almost the same isotopic composition than aqueous boric acid accounts for the heavier isotopic composition of birnessite than goethite boron both at acid and alkaline ph these results show that in nature 11b enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of ph that changes boron speciation in solution and at solid surfaces this is typically the case for soil solution in fe and mn rich environments and in seawater in addition the markedly different isotopic fractionation factor at the same ph of boron sorbed on goethite and birnessite at ph 8 2 is equal to 0 967 and 0 986 for goethite and birnessite respectively may be used to determine past ocean ph values without requiring knowledge of past isotopic composition

the low temperature geochemical cycle of iron from continental fluxes to marine sediment deposition suspended sediments from 34 major rivers geographically wide spread and 36 glacial meltwater streams have been examined for their variations in different operationally defined iron fractions fehr iron oxides soluble in dithionite fepr iron soluble in boiling hcl but not in dithionite and feu total iron less that soluble in boiling hcl river particulates show a close association between fehr and total iron fet reflecting the effects of chemical weathering which derive oxide iron from and retain it in close association with total iron consistent with this continental scale average fehr fet ratios vary with runoff ratios average river runoff per unit area average precipitation per unit area by contrast the diminished effects of chemical weathering produce no recognizable association of fehr with fet in glacial particulates and instead both fepr and feu are closely correlated with fet reflecting essentially pristine mineralogy a comparison of the globally averaged compositions of riverine particulates and marine sediments reveals that the latter are depleted in fehr fepr and fet but enriched in feu the river and glacial particulate data are combined with estimates of authigenic hydrothermal atmospheric and coastal erosive iron fluxes from the literature to produce a global budget for fehr f e pr f e u and fet this budget suggests that the differences between riverine particulates and marine sediments can be explained by i preferentially removing fehr from the riverine particulate flux by deposition into inner shore reservoirs such as floodplains salt marshes and estuaries and ii mixing the resulting riverine particulates with fehr depleted glacial particulates preliminary measurements of inner shore sediments are consistent with i above phanerozoic and modern normal marine sediments have similar iron speciation characteristics which implies the existence of a long term steady state for the iron cycle this steady state could be maintained by a glacioeustatic feedback where fehr enriched riverine particulates are either more effectively trapped when sealevel is high small ice masses diminished glacial erosion or are mixed with greater masses of fehr depleted glacial particulates when sealevel is low large ice masses enhanced glacial erosion further important controls on the steady state for fehr operate through the formation of euxinic sediments and ironstones which also provide sealevel dependent sinks for fehr enriched sediment

debris in icebergs and rates of glaci marine sedimentation observations from spitsbergen and a simple model debris distribution and content in spitsbergen icebergs varies but basal debris rich layers often 1 m thick are the most important sources of iceberg rafted material angular iceberg rafted clasts in the glaci marine record imply the presence of nunataks or valley walls rather than unbroken ice sheet surfaces indicating paleo ice mass configuration calculated iceberg melt rates imply that most iceberg rafted debris is released within spitsbergen fjords sedimentation from icebergs is calculated as 1 mm a 1 for inner mollerfjorden and 8 mm a 1 for inner kongsfjorden an order of magnitude lower than total sediment inputs turbid subglacial meltwater is a more important debris source a simple model is proposed to calculate the flux of basal debris in icebergs and iceberg sedimentation rates

inputs of glacially derived dissolved and colloidal iron to the coastal ocean and implications for primary productivity 1 glacial meltwaters draining shield bedrock under the greenland ice sheet gis contain 0 4 m total dissolved fe tdfe with an average flow weighted concentration of 53 nm the concentrations of 0 03 and 0 03 0 4 m fe vary over the ablation period with weighted means for each of these fractions being respectively 22 4 nm and 30 8 nm these concentrations are lower estimates as an adjacent larger glacier a more representative source of glacial meltwater had higher dissolved fe concentrations and reactions of meltwaters with proglacial sediments could also enhance dissolved fe concentrations this source of tdfe is additional to the reactive oxyhydr oxide phases identified by raiswell et al 2006 that are also introduced to adjacent polar seas from glaciers the fe concentrations in the shield bedrock underlying the gis are lower than those of other crustal rocks 4 0 cf 6 2 but we argue that these fe concentrations are not limiting on the total dissolved fe concentrations we measure the biogeochemical weathering processes operating on the subglacial debris and suspended sediment in our catchment are likely to be similar to those in other glaciated catchments therefore the meltwater fe concentrations reported here can be used to give a first estimate of global fluxes of meltwater dissolved fe to coastal polar waters a lower estimate of the global flux of tdfe from glacial meltwaters is 75 106 moles fe a this glacial meltwater input of fe to adjacent polar waters will be greatest around greenland where there are highest annual meltwater discharges however the greatest impact of this source of glacial meltwater fe is anticipated to be in antarctic high nutrient low chlorophyll hnlc waters where phytoplankton productivity is typically limited by availability of fe for antarctic waters the estimated meltwater fe tdfe input is about 10 of that suggested to come from sea ice melting but glacial inputs continue throughout the austral summer ablation period after sea ice melt is complete

nanogeochemistry nanostructures emergent properties and their control on geochemical reactions and mass transfers abstract nanogeochemistry a newly emerging research field attempts to understand geochemical reactions and mass transfers at nanometer scales especially with regards to the formation of nanostructures in geochemical systems emergent properties of these structures and their controls on geochemical processes the research also includes use of nanotechnology to design new materials and engineering approaches for effective natural resource extraction and environmental management at the core of this new research field is the concept that as the size of a material is reduced to nanometers novel physical or chemical properties of the material may emerge that can be drastically different from those of the corresponding bulk phase and the material properties then become size dependent nanostructures which frequently occur in geologic materials may directly control mineral phase stability mineral water interface chemistry geochemical reaction kinetics geo fluid migration and transport and even global biogeochemical cycles as a whole this paper aims to provide a comprehensive review of recent progress in nanogeochemical research the review is focused on two general types of nanostructures nano solid phases and nanopores nanofluids with an emphasis on the occurrence of each nanostructure in natural environments the associated emergent properties and the potential geochemical implications stemming from an increasing interest in shale gas research a special discussion is provided on gas oil disposition and migration in unconventional low permeability reservoirs wherein shale is treated as a nanocomposite material nanogeochemistry is a relatively young research field and much remains to be explored there is an urgent need for systematically characterizing specific nanostructures over the whole nanometer size range and developing a general theoretical framework for data analysis and synthesis there is also a need for developing experimental and modeling techniques to extrapolate the knowledge obtained from simple model systems to complex natural systems

from black and white to colour in the silurian abstract ironstones and iron rich limestones regularly occur as components of time specific intervals of the palaeozoic as well as in younger times brett et al 2012 this issue silurian sediments deposited at high latitudes along the peri gondwana border are characterized by black and white limestone and graptolitic shale sequences those in the carnic alps southern austria additionally contain colourful pink to red limestones and ironstones laminated structures such as the ferruginous coatings around skeletal fragments mostly trilobites and some cephalopods and echinoderms and stromatolitic features along discontinuity surfaces display dark red green white and brownish colours due to the presence of goethite magnetite hematite chamosite calcite and subordinate apatite confocal laser raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceous matter associated with fossilized microbial structures in the form of stromatolites filaments and coccoids suggesting a microbial role in the colouring of the silurian world of the carnic alps iron concentrations up to 30 that of matrix and surrounding non ferruginous rocks suggest blooms of iron microbe activity in response to the time specific occurrence of chemically charged sea water during global biotic events

key role of organic complexation of iron in sustaining phytoplankton blooms in the pine island and amundsen polynyas southern ocean primary productivity in the amundsen sea southern ocean is among the highest in antarctica the summer phytoplankton bloom in 2009 lasted for 470 days in both the pine island and amundsen polynyas such productive blooms require a large supply of nutrients including the trace metal iron fe the organic complexation of dissolved fe was investigated in the amundsen sea during the spring of 2009 to better understand the potential role of ligands in enhancing the local stock of dissolved fe the main sources of fe and ligands to the amundsen sea are thought to be melting sea ice and the circumpolar deep water cdw which is modified mcdw on the continental shelf and upwells beneath the coastal glaciers and ice shelves upwelling of relatively warm mcdw is also responsible for the rapid melting of the pine island glacier pig and surrounding ice shelves resulting in additional release of fe into surface waters at upwelling stations near ice shelves organic ligands were nearly saturated with fe thus enhancing the stock of fe and its availability to the phytoplankton community however ligands had little capacity to buffer additional fe input from glacial melt in these coastal upwelling regions much of the glacial fe supply is lost due to vertical export of fe via scavenging and precipitation conversely within the phytoplankton bloom in the nearby coastal polynyas the uptake of fe combined with the production of organic matter enhanced the abundance of relatively unsaturated organic ligands capable of stabilizing additional fe supplied from glacial melt these unsaturated dissolved organic ligands combined with the continuous input of fe dissolved and particulate from glacial melt appear to favor the solubilization of fe thus increasing the stock of bioavailable fe and fueling the phytoplankton bloom

water pressure coupling of sliding and bed deformation iii application to ice stream b antarctica geophysical studies and glaciological analyses suggest strongly that ice stream b west antarctica moves primarily by pervasive deformation of a meters thick subglacial till analysis of the longitudinal profile of the ice stream up stream of the ice plain suggests that basal sliding is slow everywhere that effective pressure decreases slowly down stream and that the strain rate of pervasive shear is proportional to the basal shear stress and inversely proportional to the square or cube of the effective pressure discrete shearing may occur beneath the pervasively deforming zone these and other hypotheses which build on the analyses of the first two papers in this series can be tested in the field

sea surface temperature control on the distribution of far traveled southern ocean ice rafted detritus during the pliocene the flux and provenance of ice rafted detritus ird deposited in the southern ocean can reveal information about the past instability of antarctica s ice sheets during different climatic conditions here we present a pliocene ird provenance record based on the 40ar 39ar ages of ice rafted hornblende grains from ocean drilling program site 1165 located near prydz bay in the indian ocean sector of the southern ocean along with the results of modeled sensitivity tests of iceberg trajectories and their spatial melting patterns under a range of sea surface temperatures ssts our provenance results reveal that ird and hence icebergs in the prydz bay area were mainly sourced from i the local prydz bay region and ii the remote wilkes land margin located at the mouth of the low lying aurora subglacial basin a series of ird pulses reaching up to 10 times background ird flux levels were previously identified at site 1165 between 3 3 and 3 0 ma our new results reveal that the average proportion of ird sourced from distal wilkes land margin doubles after 3 3 ma our iceberg trajectory melting models show that slower iceberg melting under cooling ssts over this middle pliocene interval allowed wilkes land icebergs to travel farther before melting hence declining ssts can account for a large part of the observed ird provenance record at site 1165 in early pliocene ird layers sampled at suborbital resolution around 4 6 ma we find evidence for significant increases in icebergs derived from wilkes land during very warm interglacials this is suggestive of large scale destabilization of the east antarctic ice sheet in the aurora subglacial basin as far traveled icebergs would have to overcome enhanced melting in warmer ssts our results highlight the importance of considering ssts when interpreting ird flux and provenance records in distal locations

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

evaluation of high frequency paleoenvironmental variation using an optimized cyclostratigraphic framework example for c s fe analysis of devonian mississippian black shales central appalachian basin u s a abstract stratigraphic successions are rarely sampled at sufficiently dense spacing to permit evaluation of paleoenvironmental variation at the shortest fundamental frequency operative in the depositional system of interest often because that frequency remains undetermined here we provide an example of a sampling strategy optimized for recovery of high frequency paleoenvironmental signals based on 1 full core analysis using a continuous survey tool such as x radiography followed by 2 fine sampling of selected small scale cycles that record significant short term paleoenvironmental variation we show that this strategy results in recovery of high frequency paleoenvironmental signals that are completely missed by low density sampling protocols permitting key insights into depositional and early diagenetic processes that may otherwise by overlooked the present case study is based on c s fe systematics of the cleveland and sunbury shales which belong to the upper devonian lowermost carboniferous black shale succession of the central appalachian basin in eastern north america in these units the fundamental scale of paleoenvironmental variation is recorded by pervasive decimeter scale 5 to 20 cm thick compositional cycles that are readily visible in outcrop in which high organic layers weather out as resistant ledges we identified these cycles in drillcores using x radiography which proved to be an effective proxy for compositional variation owing to control of bulk density primarily by total organic carbon toc content we then sampled selected dm scale cycles n 21 at a centimeter spacing generating short high resolution multiproxy chemostratigraphic records including toc sulfur and fe concentrations fepy fehr a redox proxy 34spyrite and organic maceral content this analysis yielded the novel insight that all proxies related to authigenic iron sulfides e g stotal and spyrite fetotal and fepyrite fepy fehr and 34spyrite covary negatively with toc within the dm scale cycles we interpret the unusual pattern of negative toc pyrite covariation in the cleveland and sunbury shales to have resulted from differential distributions of labile organic matter om which drove h2s production via microbial sulfate reduction msr and reactive fe which controlled pyrite formation labile om was concentrated in high toc layers whereas reactive fe was concentrated in low toc layers possibly as fe oxyhydroxide coatings on silt grains as a consequence of which part of the h2s generated in the high toc layers diffused upward into the low toc layers before becoming fixed as pyrite this process is evidenced by several contrasts between high toc and low toc layers 1 higher spyrite concentrations and fepy fehr values in the latter 2 concentration of pyrite in the lower part of low toc layers immediately above high toc layers and 3 higher 34spyrite values in the latter reflecting late diagenetic formation of the h2s that diffused upward into the low toc layers to our knowledge this process has not been documented previously in ancient marine shales probably owing to insufficiently high resolution analysis in earlier studies

iron and manganese speciation and cycling in glacially influenced high latitude fjord sediments west spitsbergen svalbard evidence for a benthic recycling transport mechanism abstract glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese phases to the coastal ocean in high latitude regions little is known about the fate and biogeochemical cycling of glacially derived iron and manganese in the coastal marine realm sediment and porewater samples were collected along transects from the fjord mouths to the tidewater glaciers at the fjord heads in smeerenburgfjorden kongsfjorden and van keulenfjorden along western svalbard solid phase iron and manganese speciation determined by sequential chemical extraction could be linked to the compositions of the local bedrock and hydrological weathering conditions below the local glaciers the concentration and sulfur isotope composition of chromium reducible sulfur crs in kongs and van keulenfjorden sediments largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers the varying input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the pathways of organic carbon mineralization in the sediments of the three fjords high reducible iron and manganese oxide concentrations and elevated metal accumulation rates coupled to low input of fresh organic matter lead to a strong expression of dissimilatory metal oxide reduction evidenced in very high porewater iron up to 800 m and manganese up to 210 m concentrations in kongsfjorden and van keulenfjorden sediment reworking by the benthic macrofauna and physical sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese cycling in these fjords on going benthic recycling of glacially derived dissolved iron into overlying seawater where partial re oxidation and deposition occurs facilitates the transport of iron across the fjords and potentially into adjacent continental shelf waters such iron dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond by contrast low delivery of reducible iron oxyhydr oxide phases and elevated organic carbon mineralization rates driven by elevated input of fresh marine organic matter allow organoclastic sulfate reduction to dominate carbon remineralization at the outer smeerenburgfjorden sites which may limit iron fluxes to the water column

large flux of iron from the amery ice shelf marine ice to prydz bay east antarctica the antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide co2 sink through the photosynthetic fixation of co2 via the biological pump sustaining such high productivity requires a large supply of the essential micronutrient iron fe however the pathways for fe delivery to these zones vary spatially and temporally our study is the first to report a previously unquantified source of concentrated bioavailable fe to antarctic surface waters we hypothesize that fe derived from subglacial processes is delivered to euphotic waters through the accretion fe storage and subsequent melting fe release of a marine accreted layer of ice at the base of the amery ice shelf ais using satellite derived chlorophyll a data we show that the soluble fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required fe necessary to sustain the large annual phytoplankton bloom in prydz bay our finding of high concentrations of fe in ais marine ice and recent data on increasing rates of ice shelf basal melt in many of antarctica s ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt currently the distribution volume and fe concentration of antarctic marine ice is poorly constrained this uncertainty combined with variable forecasts of increased rates of ice shelf basal melt limits our ability to predict future fe supply to antarctic coastal waters

speciation and spatial distribution of solid phase iron in surface sediments of the east china sea continental shelf abstract speciation and reactivity characterization of solid phase fe in marine sediments are of significance to understanding its heterogeneous mineralogy and crystallinity the diagenetic cycling of fe and its regulating roles on many other elements in sediments in this study a combination of sequential and single step extractions was used for the determination of seven fe pools in surface sediments of the east china sea ecs continental shelf 1 carbonate associated fe fe ii carb plus acid volatile sulfide fe fe ii avs 2 easily reducible amorphous poorly crystalline fe oxides fe ox1 3 reducible crystalline fe oxides fe ox2 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u total fe fe t in the sediments is largely determined by terrestrial aluminosilicate particles as indicated by a great similarity of the fe t with that of the yangtze river and global riverine particulates the size of fe prs is found to be the largest pool followed by fe u fe ox2 fe mag fe ii avs carb fe ox1 and fe py the large fe prs may result from neoformation of fe rich clay minerals via reverse weathering and subsequent ageing the small sizes of fe ii avs carb and fe py pools is believed to be the result of low so 4 reduction due to generally low labile organic matter together with the oxic suboxic dynamic environments of the surface sediments the occurrence of fe ox1 fe ox2 and fe prs in the sediments is closely associated with the clay fraction as indicated by a high spatial correlation between the former and the latter highly reactive fe fe hr in the sediments is comparable to that in global marine sediments but apparently lower than in the yangtze river and global riverine particulates due probably to sequestration in the yangtze estuary the ratios of fe hr fe t fe pr fe t and fe u fe t in the ecs surface sediments consistently show more similarity to those in the yangtze river particulates than in the global continental margin or deep sea sediments the surface sediments maintain a high level of buffering capacity toward sulfidation suggested by a large fraction of highly reactive fe iii oxides fe iii hr in fe hr

reconstructing oxygen deficiency in the glacial gulf of alaska combining biomarkers and trace metals as paleo redox proxies abstract marine anaerobic oxidation of ammonium anammox plays a central role in the nitrogen cycle of modern oxygen deficient zones odzs the newly developed bacteriohopanetetrol stereoisomer bht x biomarker for anammox which is largely unaffected by early diagenesis allows for the reconstruction of the presence and dynamics of past odzs from the sedimentary record of continental margins in this study we investigate the development and dynamics of the odz in the gulf of alaska goa between 60 and 15 cal ka bp using records of redox sensitive trace metals tm and the bht x anammox biomarker from iodp site u1419 700 m water depth the biomarker record indicates that the odz in the goa was in concert with global climate fluctuations in the late pleistocene anammox was more pronounced during warmer periods and diminished during cooler periods as indicated by correlation with the 18o signal obtained by the north greenland ice core project ngrip trace metal enrichments however do not match the trend in bht x systematic metal enrichments in intervals where biomarkers point to more intense water column deoxygenation are not observed we suggest that this proxy discrepancy was caused by environmental factors other than water column redox conditions with opposing effects on the tm and biomarker records two of the most widely used redox indicators mo and u are not significantly enriched throughout the sediment record at site u1419 site u1419 experienced some of the highest sedimentation rates 100 1000 cm ka 1 ever reported for late pleistocene continental margin sediments leading to a continuous and rapid upward migration of the sediment water interface we suggest that despite water column and seafloor oxygen depletion significant sedimentary enrichments of these redox sensitive trace metals were prevented by a limited time for their diffusion across the sediment water interface and subsequent enrichment as authigenic phases thus depositional conditions were ideal for biomarker preservation but prevented significant authigenic trace metal accumulations similar discrepancies between organic and inorganic redox proxies could exist in other high sedimentation rate environments potentially putting constraints on paleo redox interpretations in such settings if they are based on trace metal enrichments alone

first data on trace metal level and behaviour in two major arctic river estuarine systems ob and yenisey and in the adjacent kara sea russia dissolved and colloidal trace element concentrations cd cu fe ni and pb were determined in the ob and yenisey river estuary systems and in the adjacent kara sea in september 1993 the data show a natural low concentration level of dissolved 0 4 m trace metals cd cu fe ni and pb in the two rivers and in the kara sea as compared to world unpolluted rivers and the central arctic ocean suggesting that the region studied is pristine with respect to trace metals the pathway of trace metals transported from rivers to the ocean seems to be complicated and largely influenced by biogeochemical processes taking place in the estuarine mixing zone colloidal material 104 daltons 0 4 m in addition to its significant contribution to the so called dissolved fraction has been shown to play a fundamental role in determining the behaviour of both conservative and non conservative trace metals during estuarine mixing hence colloids may control to a large extent the fate of dissolved trace metals as well as their net input from the rivers to the kara sea

weathering fluxes and sediment provenance on the sw scottish shelf during the last deglaciation the reconstruction of past ice sheet dynamics can shed a light on long term ice stream activity and in turn provide constraints on the response of modern ice sheets to climate change the hebrides ice stream his flowed across part of the western scottish shelf to the shelf break during the last glacial cycle and drained a large portion of the northern sector of the british irish ice sheet to investigate the deglacial dynamics of the his following the last glacial maximum lead pb isotope records were extracted from the femn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of his during its retreat these provide timing and some source information of glacially weathered inputs to the marine environment the femn oxyhydroxide fraction in the samples is dominated by allochthonous particles pre formed and shows a marked decrease from radiogenic 20 05 206pb 204pb at 21 cal ka bp to less radiogenic pb isotope compositions 19 48 towards the windermere interstadial 15 4 13 ka this decrease represents a reduction in the flux of subglacially derived radiogenic pb to the continental shelf is interpreted as being associated with the break up of the ice stream in western scotland around that time the pb sr and nd isotopic signatures of the detrital fraction indicate a preponderance of moine sourced fine sediments originated from the nw highlands in the core locations from 21 to 15 cal ka bp dimlington stadial windermere interstadial most likely dictated by the orientation of ice flow tidal and oceanic current directions and sediment delivery in contrast ice rafted debris in a 21 cal ka bp old basal diamicton contains volcanic derived material suggesting different provenance for different grain sizes the femn oxyhydroxide 208pb 204pb ratio shows an unusual inversion relative to the other pb isotope ratios and is attributed to the introduction of secondary weathering phases from a source with contrasting 208pb 204pb but similar 206pb 204pb and 207pb 204pb in the detrital fraction the inversions are constrained to periodic spikes which may indicate an increased contribution from a high th u source potentially the neighbouring archaean amphibolitic lewisian basement in the outer hebrides this study demonstrates how geochemical investigation on continental shelves can be used to constrain the timing activity and flow sources of palaeo ice streams

contributions from glacially derived sediment to the global iron oxyhydr oxide cycle implications for iron delivery to the oceans estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving and their sediment loads the combined total 2900 tg yr 1 of the suspended sediment load in meltwaters 1400 tg yr 1 and the sediment delivered by icebergs 1500 tg yr 1 are within the range of earlier estimates high resolution microscopic observations show that suspended sediments from glacial meltwaters supraglacial and proglacial sediments and sediments in basal ice from arctic alpine and antarctic locations all contain iron oxyhydr oxide nanoparticles which are poorly crystalline typically 5 nm in diameter and which occur as single grains or aggregates that may be isolated or attached to sediment grains nanoparticles with these characteristics are potentially bioavailable a global model comparing the sources and sinks of iron present as oxyhydr oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans beyond the continental shelf iceberg delivery of sediment containing iron as oxyhydr oxides during the last glacial maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric co2 to the levels observed in ice cores

direct effect of ice sheets on terrestrial bicarbonate sulphate and base cation fluxes during the last glacial cycle minimal impact on atmospheric co2 concentrations chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates solute fluxes from small valley glaciers are usually a linear function of discharge representative glacial solute concentrations can be derived from the linear association of solute flux with discharge these representative glacial concentrations of the major ions are f25 of those in global river water a 3 d thermomechanically coupled model of the growth and decay of the northern hemisphere ice sheets was used to simulate glacial runoff at 100 year time steps during the last glacial cycle 130 ka to the present the glacially derived fluxes of major cations anions and si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration a second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations the fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans the glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric co2 the potential change in atmospheric co2 concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant being 1 ppm d 2002 elsevier science b v all rights reserved

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere

soil processes and nutrient bioavailability in the rhizosphere of bolax gummifera in a subantarctic environment martial mountains ushuaia argentina abstract the aim of this study was to explore the effects of plants on the underlying substrate and the possible environmental implications of such effects in an extreme environment for this purpose we sampled the rhizosphere soil of bolax gummifera which is one of the most characteristic vascular plants in the martial mountains tierra del fuego argentina where plant cover is typically sparse superficial 0 5 cm rh5 and subsuperficial 5 15 cm rh15 samples of b gummifera rhizosphere and bulk soil were collected from a small homogeneous area and the following parameters were analyzed particle size ph total organic carbon toc total nitrogen tn total fe tfe fe and al associated with organic matter soluble in sodium pyrophosphate c pyro amorphous fe oxyhydroxides extracted with ammonium oxalate fe oxa crystalline fe oxyhydroxides extracted with sodium dithionite fe dit bioavailable plant nutrients soluble in mehlich 3 extractant and clay mineralogy several differences were found between rhizosphere soil rs and bulk soil the toc was 8 times higher and the tn and c pyro were 4 times higher in the rhizosphere than in the bulk soil mineralogical results suggest a slightly higher degree of chemical weathering mainly affecting biotite and amphibole minerals in the rs than in bulk soil consistent with significantly higher nutrient bioavailability in rs ca mg k co and fe on the other hand the higher concentrations of c and metals extracted with sodium pyrophosphate suggest the formation of more metal organic complexes in the rhizosphere than in the bulk soil this metal fraction is considered as readily mobilizable and available and can be leached from the soil to continental and coastal waters this effect will be enhanced in cold climates by expansion of plant cover due to the increased temperature expected under climate change