seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic blooms this annual population overturning is marked by a 0 7 increase in d 18 o in both species the shell flux of n pachyderma peaks during the spring bloom and in late summer when stratification is close to its minimum and maximum respectively both export periods contribute about equally and account for 95 of the total annual flux shell fluxes of t quinqueloba show only a single broad pulse in summer thus following the seasonal stratification cycle the d 18 oo fn pachyderma reflects temperatures just below the base of the seasonal sml without offset from isotopic equilibrium the d 18 op attern oft quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 oo fn pachyderma therefore t quinqueloba also reflects temperature near the base of the sml but with a positive offset from isotopic equilibrium these offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species in the irminger sea the species consistently show a contrast in their flux timings their flux weighted dd 18 o will thus dominantly be determined by seasonal temperature differences at the base of the sml rather than by differences in their depth habitat consequently their sedimentary dd 18 o may be used to infer the seasonal contrast in temperature at the base of the sml citation jonkers l g j a brummer f j c peeters h m van aken and m f de jong 2010 seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic paleoceanography 25 pa2204 doi 10 1029 2009pa001849

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

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

a 550 000 year record of east asian monsoon rainfall from 10be in loess cosmogenic 10 be flux from the atmosphere is a proxy for rainfall using this proxy we derived a 550 000 year long record of east asian summer monsoon easm rainfall from chinese loess this record is forced at orbital precession frequencies with higher rainfall observed during northern hemisphere summer insolation maxima although this response is damped during cold interstadials the 10 be monsoon rainfall proxy is also highly correlated with global ice volume variations which differs from chinese cave 18 o which is only weakly correlated we argue that both easm intensity and chinese cave 18 o are not governed by high northern latitude insolation as suggested by others but rather by low latitude interhemispheric insolation gradients which may also strongly influence global ice volume via monsoon dynamics

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

geomagnetic dipole strength and reversal rate over the past two million years independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment1 2 and thus provide information regarding the processes governing the geodynamo so far this procedure has been limited to the past 800 000 years 800 kyr ref 3 which does not include any geomagnetic reversals here we present a composite curve that shows the evolution of the dipole moment during the past two million years this reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas which were used for calibration we show that at least during this period the time averaged field was higher during periods without reversals but the amplitude of the short term oscillations remained the same as a consequence few intervals of very low intensity and thus fewer instabilities are expected during periods with a strong average dipole moment whereas more excursions and reversals are expected during periods of weak field intensity we also observe that the axial dipole begins to decay 60 80 kyr before reversals but rebuilds itself in the opposite direction in only a few thousand years

glacial effects on weathering processes new insights from the elemental and lithium isotopic composition of west greenland rivers greenland is by far the dominant source of glacial runoff to the oceans but the controls on the chemical and isotopic composition of this runoff are poorly known to better constrain glacial effects on weathering processes we have conducted elemental and lithium isotope analyses of glacial and non glacial rivers in gneiss catchments in west greenland the glacial rivers have high total suspended solids 0 5 g l 1 and low total dissolved solids 12 scm 1 relative to the non glacial rivers and they contain a higher proportion of dissolved ca2 and k because of subglacial preferential weathering of trace carbonates and biotite the glacial rivers also have high so42 because of the oxidation of trace sulphides under the ice both glacial and non glacial rivers have high 7li respectively not vert similar 26 and not vert similar 30 relative to the rocks from which the li is derived not vert similar 8 saturation state modelling suggests that this is due to the formation of fe oxyhydroxides in the non glacial rivers with preferential uptake of 6li during inner sphere sorption of li on the fe oxyhydroxide surface glacial rivers however are undersaturated with respect to clay minerals and fe oxyhydroxides nevertheless leaching of suspended sediments indicates that not vert similar 65 of the li in these sediments is associated with fe oxyhydroxide phases and the 7li value of this li is low not vert similar 5 these results suggest that these fe oxyhydroxides formed under the ice as a product of sulphide oxidation with preferential uptake of 6li onto the mineral surface solubilisation of li from these fe oxyhydroxide phases is unlikely to represent a significant flux of li to the oceans moreover because the difference between the 7li values of glacial vs non glacial rivers is small glaciation has not had a significant impact on the li isotopic composition of the riverine flux delivered to the oceans in the past even at the height of the last deglaciation

glacier hydrochemistry solute provenance and chemical denudation at a surge type glacier in kuannersuit kuussuat disko island west greenland abstract in 1995 1998 han 11 km terrestrial surge of kuannersuit glacier an outlet glacier of the largest ice cap on disko island west greenland affected the catchment dramatically in order to estimate solute fluxes and provenances bulk meltwaters were sampled at the main subglacial outlet during the initial part of the quiescent phase the hydrochemistry is significantly influenced by a subglacial basaltic weathering regime with absence of carbonate minerals the results show that marine and aerosol derived solutes have minimal contribution to the total ion content whereas sequestration of atmospheric co 2 associated with carbonation of ca rich feldspar and reactive volcanic glass is more dominant than previously reported from glacierized catchments application of a sampling strategy dividing water samples into four groups to determine the content of dissolved hco 3 and co 3 2 shows that the cationic equivalent weathering rate range is 683 860 meq m 2 a 1 and solute flux ranges between 76 and 98 t km 2 a 1 the crustal denudation rate is estimated to 26 t km 2 a 1 and the transient co 2 drawdown amounts to 8500 13700 kg c km 2 a 1

role of seasonal transitions and westerly jets in east asian paleoclimate abstract the summer rainfall climate of east asia underwent large and abrupt changes during past climates in response to precessional forcing glacial interglacial cycles as well as abrupt changes to the north atlantic during the last glacial however current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity and do not account for the known complexity in the seasonal evolution of east asian rainfall which exhibits sharp transition from the spring regime to the meiyu and then again from the meiyu to the summer regime we explore the interpretation that east asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes following previous suggestions we focus on role of the westerly jet over asia namely that its latitude relative to tibet is critical in determining the stepwise transitions in east asian rainfall seasons in support of this linkage we show from observational data that the interannual co variation of june july august rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the meiyu summer and with more northward shifted westerlies for earlier transitions we similarly suggest that east asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions in particular the transition of the jet from south of the plateau to the north that determines the seasonal transition from spring rains to the meiyu in an extreme scenario which we speculate the climate system tended towards during stadial cold phases of d o stadials and periods of low northern hemisphere summer insolation the jet does not jump north of the plateau essentially keeping east asia in prolonged spring conditions we argue that this hypothesis provides a viable explanation for a key paleoproxy signature of d o stadials over east asia namely the heavier mean 18o of precipitation as recorded in speleothem records the southward jet position prevents the low level monsoonal flow which is isotopically light from penetrating into the interior of east asia as such precipitation there will be heavier consistent with speleothem records this hypothesis can also explain other key evidences of east asian paleoclimate changes in particular the occurrence of dusty conditions during north atlantic stadials and the southward migration of the holocene optimal rainfall

climate change shrinking glaciers under scrutiny melting glaciers contribute to sea level rise but measuring their mass loss over time is difficult an analysis of satellite data on earth s changing gravity field does just that and delivers some unexpected results the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports

observed runoff jokulhlaups and suspended sediment load from the greenland ice sheet at kangerlussuaq west greenland 2007 and 2008 this study fills the gap in hydrologic measurements of runoff exiting a part of the greenland ice sheet gris the kangerlussuaq drainage area west greenland the observations are of value for obtaining knowledge about the terrestrial freshwater and sediment output from part of the gris and the strip of land between the gris and the ocean in the context of varying ice sheet surface melt and influx entering the ocean high resolution stage discharge and suspended sediment load show a decrease in runoff of approx 25 and in sediment load of approx 40 from 2007 to 2008 in response to a decrease in the summer accumulated number of positive degree days during the 2007 and 2008 runoff season joekulhlaups are observed at kangerlussuaq drained from an ice dammed lake at the margin of the gris

subglacial water drainage storage and piracy beneath the greenland ice sheet meltwater drainage across the surface of the greenland ice sheet gris is well constrained by measurements and modeling yet despite its critical role knowledge of its transit through the subglac

the behaviour of magnesium and its isotopes during glacial weathering in an ancient shield terrain in west greenland the magnesium mg isotope composition of rivers is sensitive to changes in the balance of primary mineral dissolution and secondary mineral formation as these processes are regulated by climate then changes to the earth s climate system such as the onset of glaciation could potentially alter the isotopic behaviour of mg in rivers to investigate how mg isotopes behave during glacial weathering we have determined the mg concentration and mg isotope ratio for the dissolved suspended and bedload phases of glacial and non glacial rivers in west greenland this region is essentially monolithological and there is little biological activity hence isotope variations largely result from differences in weathering processes dissolved mg in rivers is always enriched in the light mg isotopes relative to the bedload 26mg 0 4 and the glacial rivers have lighter mg isotope compositions 26mg 1 to 1 3 than the non glacial rivers 26mg 0 6 enrichment of light mg in the dissolved load is consistent with the preferential uptake of heavy mg from solution during the formation of secondary silicate minerals however evidence from saturation state modelling suggests that little secondary mineral formation is likely to have occurred in the glacial rivers because the concentration of dissolved solids is very low moreover the glacial derived suspended sediment has identical mg isotope ratios to the bedload these observations suggest that the formation of secondary weathering minerals is not controlling the behaviour of mg isotopes in these rivers rather variations in the 26mg value of the dissolved load are attributed to incongruent weathering of the solid phase preferential dissolution of carbonate minerals which have low 26mg 1 1 to 5 2 imparts a more negative 26mg signal to the glacial river waters although our study indicates that the mg isotopic composition of the dissolved load is sensitive to changes in weathering congruence it is unlikely that glaciation will result in major changes in the 26mg composition of continental runoff

seasonal evolution of upper ocean horizontal structure and the remnant mixed layer 1 we discuss the seasonal evolution of upper ocean thermohaline structure at small horizontal scales the upper 350 m of a 1000 km long section in the subtropical north pacific was observed in winter spring and summer with 3 14 km horizontal resolution four vertical regions had distinct density and salinity structure the mixed layer remnant mixed layer high stratification layer and permanent thermocline the remnant mixed layer consists of water from the winter mixed layer left over after restratification the remnant mixed layer was most similar to the mixed layer in winter and spring and most similar to the high stratification layer below in summer the high stratification layer had elevated stratification that varied seasonally the permanent thermocline varied little seasonally and was horizontally and vertically uniform in comparison in all seasons density ratios showed that mixed layer s differences tended to compensate in density with the strongest tendency toward compensation in winter density ratios were temperature dominated in the remnant mixed layer consistent with salt fingering salinity anomalies were largest at the surface and decayed with depth in all seasons spectra of isopycnal depth and s anomalies along isopycnals are compared between the three seasons and four vertical layers isopycnal depth variance at 30 46 km wavelengths decreased from winter to spring to summer by a factor of 2 10 in stratified regions by treating salinity anomalies as a tracer the effective isopycnal diffusivity in the remnant mixed layer was estimated to be 1 4 m2 s 1 over 30 46 km wavelengths

organic carbon export from the greenland ice sheet abstract glacial meltwater exports a unique type of organic carbon to marine systems distinct from non glacially derived riverine export potentially capable of stimulating downstream marine primary productivity here we describe for the first time the bulk level dissolved organic carbon doc and particulate organic carbon poc isotopic composition of glacial meltwater draining the greenland ice sheet gris these data in conjunction with an earlier study that investigated the molecular level composition of gris dissolved organic matter collectively describe the concentration radiocarbon content and lability of organic carbon in subglacial discharge from a land terminating outlet glacier during a melt season by scaling up our measurements across the ice sheet we estimate that the annual doc flux from the gris 0 08 tg y is equivalent to that from a small arctic river discharge q 3 y and that the annual poc flux from the gris 0 9 tg y may be comparable to that of a large arctic river q 200 km 3 y the doc flux is derived primarily from beneath the glacier subglacial 75 in the early season and from surface ice melt up to 100 transmitting through the subglacial environment at the peak of the meltseason the poc flux is primarily derived from the subglacial environment throughout the meltseason the early season low flow glacier discharge contains higher doc concentrations 0 5 4 1 mg l 1 and exports more enriched carbon 14 c doc 250 compared to the peak season high flow discharge when the concentrations are lower 0 1 0 6 mg l 1 and the 14 c is more depleted 14 c doc 400 conversely the poc export 1 4 13 2 mg l 1 14 c poc 250 shows no temporal variation in either concentration or radiocarbon content throughout the meltseason dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system confirming the influence of subglacial hydrology on the composition of the bulk carbon pools based on this work we conclude that 1 different mechanisms control the doc and poc flux from glacial systems 2 chemically distinct doc pools are accessed by seasonally evolving hydrological flow paths and 3 the gris can deliver labile carbon which may also be 14 c depleted to downstream proglacial and marine environments

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

carbonate minerals in the global carbon cycle abstract carbonate minerals constitute earth s largest c reservoir this reservoir is considered unimportant to the global c cycle over long periods of time e g 10 6 yrs because it provides balanced sources and sinks of atmospheric co 2 as carbonate minerals precipitate and dissolve from carbonic acid respectively however carbonate mineral reactions may impact the carbon cycle at short time scales 10 2 to 10 5 yrs particularly when atmospheric pco 2 changes by several hundred ppm as exemplified by the paleocene eocene thermal maximum at transitions between glacial interglacial times and over the past century from anthropogenic inputs here i review recent literature about mechanisms in which carbonate minerals may impact the global carbon cycle carbonate mineral dissolution which increases dissolved inorganic carbon dic concentrations may represent a net atmospheric co 2 sink as primary productivity consumes dic resulting in organic c burial in fluvial systems of carbonate terrains alternatively carbonate minerals dissolved by sulfuric and nitric acids may represent an atmospheric source of co 2 with no rapid balancing atmospheric sink sulfuric acid dissolves carbonate minerals of modern carbonate platform sediments and water filled sinkholes and in the deep sea at the base of carbonate platform scarps in terrestrial landscapes sulfuric acid dissolves carbonate minerals of karst terrains hypogene caves and in comminuted glacial sediments nitric acid forms from oxidation of reactive n which has doubled in the past hundred years as humans fix atmospheric n 2 similar to some reactions involving sulfuric acid nitric acid dissolution of carbonate minerals represents a net source of atmospheric co 2 this source is concentrated in fertilized agricultural fields in carbonate terrains each of these processes represents a small flux relative to major c exchanges such as volcanic sources and silicate mineral weathering but collectively they could impact the c cycle at magnitudes similar to these major processes these impacts may increase as humans further alter elemental cycles of s and n

molecular characterization of dissolved organic matter associated with the greenland ice sheet abstract subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial interglacial timescales the likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores we examined the composition of carbon pools associated with different regions of the greenland ice sheet subglacial supraglacial proglacial in order to elucidate the type of dissolved organic matter dom present in the subglacial discharge over a melt season electrospray ionization esi fourier transform ion cyclotron resonance ft icr mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes specifically a larger proportion of protein like compounds were observed in the supraglacial samples and in the early melt season spring subglacial discharge in contrast the late melt season summer subglacial discharge contained a greater fraction of lignin like and other material presumably derived from underlying vegetation and soil these results suggest 1 that the majority of supraglacial dom originates from autochthonous microbial processes on the ice sheet surface 2 that the subglacial dom contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism and 3 that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season these conclusions are consistent with the hypothesis that given sufficient time e g overwinter storage resident subglacial microbial communities may oxidize terrestrial material beneath the greenland ice sheet

controls on the solute geochemistry of subglacial discharge from the russell glacier greenland ice sheet determined by radiogenic and stable sr isotope ratios abstract we used radiogenic and stable sr isotope ratios 87sr 86sr and 88 86sr to examine controls on solute acquisition in subglacial discharge from the russell glacier a land terminating lobe of the greenland ice sheet gris located in western greenland the study focused on two melt seasons in 2014 and 2015 subglacial discharge 87sr 86sr ratios are 13 000 ppm higher than those measured for bedload and suspended sediment digests and are more similar to those of bedload sediment leachates these results point to the preferential dissolution of minerals with high 87sr 86sr ratios analyses of mineral separates from bulk rocks demonstrate that biotite chlorite hornblende and k feldspar have relatively high 87sr 86sr ratios subglacial discharge 88 86sr values are 0 10 higher than those for bedload and suspended sediment digests isotope fractionation during secondary mineral formation and or adsorption cannot account for the difference between subglacial discharge and bedrock 88 86sr values as suspended and bedload sediment leachates and digests produced similar 88 86sr values and are within the range for bulk silicate earth consistent with the interpretation of 87sr 86sr ratios we attribute the difference to the preferential dissolution of minerals with high 88 86sr values mineral separates display a wide range of 88 86sr values 0 40 those having high 88 86sr values include hornblende and k feldspar as well as apatite and titanite taken together the preferential weathering of predominately silicate minerals explains the sr isotope geochemistry of subglacial discharge subglacial discharge from the russell glacier feeds the proglacial akuliarusiarsuup kuua river akr along a 32 km transect of the akr from the gris margin toward the coast riverine 87sr 86sr ratios increase from 0 722 to 0 747 in an approximately step wise pattern that corresponds to point source inputs of additional subglacial discharge major cation concentrations and 87sr 86sr ratios minimally vary along lengths of the transect with no hydrological inputs this suggests that proglacial chemical weathering is negligible and likely does not contribute significantly to gris solute fluxes in general this study supports the recent contention that silicate mineral weathering dominates the solute geochemistry of gris subglacial discharge in contrast to valley glaciers which typically show substantial contributions from carbonate and sulfide weathering regardless of primary bedrock composition ice sheet subglacial chemical weathering may therefore have a greater impact on long term atmospheric co2 drawdown than previously realized

the coupled release of ree and pb to the soil labile pool with time by weathering of accessory phases wind river mountains wy abstract rare earth element ree distributions and pb isotope compositions were explored in soils varying in age from ca 0 4 to 300 ka developed on moraines in the wind river mountains wyoming soil extracts 0 6 m hcl were used to examine the soil labile pool while the major element distribution in soil profiles was used to determine the extent of weathering at different soil depths the results show that the chondrite normalized ree patterns of the deepest bulk soil within each profile reflects the composition of the moraine till except for the oldest soil up to ca 12 ka the soil extract fraction is enriched in light ree indicating early release of light ree to the soil labile pool while that of the two oldest soils are relatively enriched in heavy ree in the soil extracts the la sm ratio normalized to the deepest soil la d sm d decreases systematically with soil age similarly the eu anomaly in the deepest soil from each profile eu d eu d decreases slightly with soil age in the three young soils however eu d eu d increases with soil age in the older soils the systematic trends of these two ratios indicate the depletion of light ree in young soils and the enrichment of eu and heavy ree in the older soils based on the pb isotope ratios the relative contribution of pb to the soil labile pool via mineral weathering of u or th rich phases was assessed for the different stages of weathering the whole soil profile 208 pb 204 pb ratio was found to decrease with soil age and with la d sm d whereas it increased with the eu d eu d ratio in each horizon pb isotope ratios 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratio generally decrease with soil age in order to overcome possible effects from parent material heterogeneity the amount of radiogenic pb as compared to the whole soil composition was calculated and this was found to decrease systematically with soil age

controls on magmatism in an island arc environment study of lavas and sub arc xenoliths from the tabar lihir tanga feni island chain papua new guinea the tabar lihir tanga feni tltf islands of papua new guinea mainly comprise high k calc alkaline and silica undersaturated alkaline rocks that have geochemical features typical for subduction related magmatism numerous sedimentary mafic and ultramafic xenoliths recovered from tubaf seamount located on the flank of lihir island provide a unique opportunity to study the elemental and isotopic composition of the crust and mantle wedge beneath the arc and to evaluate their relationships to the arc magmatism in the region the sedimentary and mafic xenoliths show that the crust under the islands is composed of sedimentary sequences and oceanic crust with pacific affinity a majority of the ultramafic xenoliths contain features indicating wide spread metasomatism in the mantle wedge under the tltf arc leaching experiments reveal that the metasomatized ultramafic xenoliths contain discrete labile phases that can account for up to 50 or more of elements such as cu zn rb u pb and light ree rare earth elements most likely introduced in the xenoliths via hydrous fluids released from a subducted slab the leaching experiments demonstrated that the light ree enrichment pattern can be more or less removed from the metasomatized xenoliths and the residual phases exhibit ree patterns that range from flat to light ree depleted sr nd isotopic data for the ultramafic residues show a coupled behavior of increasing 87sr 86sr with decreasing 143nd 144nd ratios the labile phases in the ultramafic xenoliths represented by the leachates show decoupling between sr and nd with distinctly more radiogenic 87sr 86sr than the residues both leachates and residues exhibit very wide range in their pb isotopic compositions indicating the involvement of three components in the mantle wedge under the tltf islands two of the components can be identified as pacific oceanic mantle and pacific sediments some of the ultramafic samples and clinopyroxene separates however exhibit relatively low 206pb 204pb at elevated 207pb 204pb suggesting that the third component is either indian ocean type mantle or australian subcontinental lithospheric mantle geochemical data from the ultramafic xenoliths indicate that although the mantle wedge in the area was extensively metasomatized it did not significantly contribute to the isotopic and incompatible trace element compositions of tltf lavas compared to the mantle samples the tltf lavas have very restricted pb isotopic compositions that lie within the pacific morb range indicating that magma compositions were dominated by melts released from a stalled subducted slab with pacific morb affinity interaction of slab melts with depleted peridotitic component in the mantle wedge followed by crystal fractionation most likely generated the geochemical characteristics of the lavas in the area

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

high export of dissolved silica from the greenland ice sheet silica is an essential element for marine life and plays a key role in the biogeochemistry of the ocean glacial activity stimulates rock weathering generating dissolved silica that is exported to coastal areas along with meltwater the magnitude of the dissolved silica export from large glacial areas such as the greenland ice sheet is presently poorly quantified and not accounted for in global budgets here we present data from two fjord systems adjacent to the greenland ice sheet which reveal a large export of dissolved silica by glacial meltwater relative to other macronutrients upscaled to the entire greenland ice sheet the export of dissolved silica equals 22 10 gmol si yr 1 when the silicate rich meltwater mixes with upwelled deep water either inside or outside greenland s fjords primary production takes place at increased silicate to nitrate ratios this likely stimulates the growth of diatoms relative to other phytoplankton groups

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

continental weathering fluxes during the last glacial interglacial cycle insights from the marine sedimentary pb isotope record at orphan knoll nw atlantic abstract regional weathering intensity must have changed dramatically at high latitudes during the quaternary as a consequence of repeated continental glaciation investigation of these glacial interglacial changes at high temporal resolution is possible with the recent development of pb isotopes in femn oxyhydroxide phases as a proxy for region specific weathering intensity where increases in the radiogenic component are thought to correspond to increased continental weathering fluxes here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from iodp sites u1302 3 on orphan knoll 3500 mbsl nw atlantic spanning the last 37 ka located at the eastern edge of the laurentide ice sheet lis site u1302 3 is well placed to monitor changes in weathering intensity associated with lis glacial history overall the data show a close correspondence to local surface water 18o with least radiogenic values during times of heavy 18o glacial maximum and most radiogenic values during times of light 18o holocene this supports the prediction that weathering intensity in glaciated regions of the north atlantic correlates with the exposure age of glacial debris superimposed on these background trends are extreme radiogenic excursions e g variation in 206pb 204pb from 19 2 21 0 contemporaneous with heinrich events and the younger dryas these data are substantially more radiogenic than existing records from the nw atlantic and most likely represent episodes of exceptionally high inputs of pre formed femn oxyhydroxides during drainage of the lis due to its extreme isotope composition at least in the nw atlantic region pb would appear to be a good proxy for the fluxes of weathered continental material and perhaps by inference nutrients to the surface ocean

local partitioning of the overturning circulation in the tropics and the connection to the hadley and walker circulations conceptually it is useful to partition the three dimensional tropical circulation into meridional and zonal components namely the hadley and walker circulations the averaging involved in their definitions can introduce ambiguities these problems can be circumvented by first partitioning the total vertical mass flux into components associated with overturning in the meridional and zonal directions respectively called here the local hadley and local walker circulations defining the local hadley and local walker circulations this way ensures the pair of two dimensional overturning circulations can be added to give the original three dimensional circulation even when the averages are taken over limited domains the method is applied to the vertical motion from the era interim reanalysis for the period 1979 to 2009 one important result is that the local hadley circulation responds much more strongly to enso than the local walker circulation even though the local walker circulation in the central pacific weakens during el nino years and strengthens and widens during la nina years

co2 evasion from the greenland ice sheet a new carbon climate feedback abstract decay of the greenland ice sheet gis figures prominently in climate change predictions but direct carbon cycle feedbacks are poorly constrained here we show that melting of the gis yields a previously unknown flux of co 2 to the atmosphere and we use a reactive transport model to examine if how and to what extent this flux will change as the ice sheet decays in a warmer world water emerges from beneath the isunnguata and russell glaciers in west greenland with co 2 partial pressures pco 2 3 10 supersaturated with respect to atmospheric equilibrium during downstream transport in the akuliarusiarsuup kuua river mineral weathering sequesters 75 of the excess co 2 as hco 3 a carbon sink on human timescales and the remaining 25 evades to the atmosphere scaled to all rivers draining the gis the evasion flux of 0 11 0 03 tg c year compares to fluxes reported for other rivers draining precambrian shield crystalline rocks and having similar dissolved carbonate systematics this flux is insufficient to influence modern day atmospheric co 2 levels and we find that higher meltwater discharge alone will cause only moderate future increases however more substantial increases could occur if meltwaters intersect basal ice known to have elevated pco 2 values worst case model scenarios yield evasion fluxes of 100 20 170 40 tg c year by 2100 these atmospheric co 2 inputs surpass those for arctic lakes and would augment by up to 25 those predicted for permafrost thaw our findings suggest that positive feedbacks linking greenhouse gas emissions arctic climate change and global warming may be stronger than previously realized

age of the orkendalen moraines kangerlussuaq greenland constraints on the extent of the southwestern margin of the greenland ice sheet during the holocene abstract although greenland ice core records register relatively stable holocene climate conditions the lower elevation margins of the greenland ice sheet gris experienced significant holocene fluctuations these fluctuations include ice sheet recession during the holocene thermal maximum 9 5 ka and advance during the little ice age lia a d 1350 1880 determining the extent and timing of these fluctuations is important for understanding the response of the gris to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models sets of moraines marking past extents of the southwestern gris margin occur in the kangerlussuaq region we focus on the orkendalen moraines a prominent moraine set located within 2 km of the modern ice margin and just outboard of the lia moraines we present the first 10be ages of the orkendalen moraines indicating they were deposited at 6 8 0 3 ka the geomorphic relationship between the orkendalen and lia moraines indicates that the ice sheet margin was inboard of its orkendalen extent between 6 8 ka and the culmination of the lia the age of the orkendalen moraines provides an important constraint on the extent of the southwestern gris during the middle holocene

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

10be in chinese loess we report a first series of10be measurements on chinese loess covering the last 750 000 years the10be concentration shows a tendency to decrease with increasing grain size leaching experiments with acid solutions show that10be is strongly bound to particles and therefore mobility due to dissolution can be excluded the10be record in loess shows features similar to those observed in 180 records from deep sea sediments which strongly reflect climatic variations this allows one to correlate the10be loess records with 180 deep sea records and to establish a time scale based on this time scale accumulation rates of loess and10be fluxes can be calculated these reveal generally higher values for cold arid and windy periods than for warm humid and calmer intervals

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

chemical weathering across the western foreland of the greenland ice sheet abstract proglacial streams deliver melt water and chemical weathering products including nutrients and radiogenic isotopes from continental ice sheets to the ocean weathering products are also delivered to the ocean in non glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides if weathering reactions differ in non glacial and proglacial stream catchments the streams could deliver different types and magnitudes of solutes to the ocean depending on relative discharge volumes unlike proglacial streams however little is known of non glacial stream solute compositions or discharge here we show specific discharges are similar from a proglacial stream draining the greenland ice sheet gris with several streams disconnected from the ice sheet we also evaluate weathering reactions across a 170 km transect in western greenland that contains one proglacial stream draining the gris and two coastal ice distal and three inland ice proximal areas with non glacial streams non glacial streams exhibit solute compositions and offsets between dissolved and bedload sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in stream weathering that consumes co2 about 5 times less co2 is consumed per liter in the proglacial than inland non glacial streams however arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total co2 weathering than proglacial stream one coastal area consumes less co2 per liter than the proglacial stream and another coastal area exhibits net co2 production these results indicate estimates for glacial foreland solute fluxes and co2 weathering consumption and production should include estimates from both non glacial and proglacial streams understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and co2 fluxes associated with continued ice sheet retreat

south greenland ice sheet collapse during marine isotope stage 11 varying levels of boreal summer insolation and associated earth system feedbacks led to differing climate and ice sheet states during late quaternary interglaciations in particular marine isotope stage mis 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410 000 to 400 000 years ago implying substantial mass loss from the greenland ice sheet gis there are however no model simulations and only limited proxy data to constrain the magnitude of the gis response to climate change during this super interglacial thus confounding efforts to assess climate ice sheet threshold behaviour and associated sea level rise here we show that the south gis was drastically smaller during mis 11 than it is now with only a small residual ice dome over southernmost greenland we use the strontium neodymium lead isotopic composition of proglacial sediment discharged from south greenland to constrain the provenance of terrigenous silt deposited on the eirik drift a sedimentary deposit off the south greenland margin we identify a major reduction in sediment input derived from south greenland s precambrian bedrock terranes probably reflecting the cessation of subglacial erosion and sediment transport as a result of near complete deglaciation of south greenland comparison with ice sheet configurations from numerical models suggests that the gis lost about 4 5 to 6 metres of sea level equivalent volume during mis 11 this is evidence for late quaternary gis collapse after it crossed a climate ice sheet stability threshold that may have been no more than several degrees above pre industrial temperatures

meltwater chemistry and solute export from a greenland ice sheet catchment watson river west greenland summary solute export from the greenland ice sheet gris to coastal regions around greenland is likely to increase in the future as a consequence of increasing icemelt production here we present hydrochemical characteristics solute and major ion exports and chemical denudation rates for 2007 2010 for the watson river sector of the gris that drains into the fjord kangerlussuaq the hydrochemistry is dominated by ca2 and hco3 with a relatively high molar k na ratio of 0 6 0 1 typical for meltwaters draining a gneissic lithology low molar ca2 na and mg2 na ratios indicate that weathering of disseminated carbonates contributes less than silicate weathering to the chemical composition the solute export varied between 33 103 2009 and 61 103 tons 2010 showing that increasing discharge leads to increasing solute export at the catchment scale deviations between ion yield estimates derived from use of discharge weighted and mean daily concentrations methods were generally less than 5 indicating that the choice of method is of less importance the chemical denudation rates ranged between 36 and 56 meq m 2 per year which are lower than previous records from glacierized catchments however when normalized by discharge the denudation rates are comparable to other arctic sites when extrapolating the results from the watson river catchment to the entire greenland for 2007 2010 the solute export from greenland meltwater varied between 7 1 106 and 7 8 106 tons whilst the major ion export was between 6 4 106 and 7 3 106 tons dissolved fe a potential biolimiting nutrient for primary productivity in the north atlantic had annual export rates from greenland between 15 103 and 52 103 tons

stable isotope evidence of dual arabian sea and bay of bengal vapour sources in monsoonal precipitation over north india abstract high resolution time series data of hydrogen d and oxygen 18o isotope values of precipitation have been generated for the first time at kolkata eastern india where the summer monsoon clouds from bay of bengal bob commence their journey over india use of a rayleigh cum two component mixing model and comparison of kolkata data with the international atomic energy agency iaea global network of isotopes in precipitation gnip data base of new delhi suggest that the precipitation at new delhi cannot be explained by simple continental effect of a bob vapour source alone traveling and raining successively along kolkata new delhi route it is necessary to invoke an admixture of 20 vapour originating from the arabian sea with the vapour coming from bob and finally causing summer monsoon rains at new delhi the findings have major implications to the regional water vapour budget over india

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

direct observations of evolving subglacial drainage beneath the greenland ice sheet simultaneous observations of moulins and boreholes in western greenland show that water delivery to the base of the ice sheet via moulins affects short term ice velocity fluctuations but not late season ice velocity decelerations increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system seasonal acceleration of the greenland ice sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed1 2 via crevasses and moulins vertical conduits connecting supraglacial water to the bed of the ice sheet as the melt season progresses the subglacial hydrologic system drains supraglacial meltwater more efficiently1 2 3 4 decreasing basal water pressure4 and moderating the ice velocity response to surface melting1 2 however limited direct observations of subglacial water pressure4 5 6 7 mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby 0 3 2 kilometres away boreholes indicating that moulins connect to an efficient channelized component of the subglacial hydrologic system which exerts the primary control on diurnal and multi day changes in ice velocity our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the paakitsoq region of western greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin connected channels to convey supraglacial melt instead these observations suggest that decreasing late season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt season dynamics affect ice velocity beyond the conclusion of the melt season8 9 10

hydrologic exchange and chemical weathering in a proglacial watershed near kangerlussuaq west greenland abstract the exchange of proglacial river water with active layer pore water could alter water chemical compositions in glacial outwash plains and oceanic solute fluxes to evaluate effects of this exchange we sampled watson river and adjacent pore water during the 2013 melt season at two sandurs in western greenland one in sandflugtdalen and the other near the confluence with sondre stromfjord we measured temperature specific conductivity and head gradients between the river and bank over a week long period at sandflugtdalen as well as sediment hydraulic conductivity and chemical compositions of waters from both sites specific conductivity of pore water is four to ten times greater than river water as solutes are concentrated from weathering reactions cryoconcentration and evaporation pore water compositions are predominantly altered by carbonate dissolution and sulfide mineral oxidation high concentrations of hco3 and so4 result from solute recycling and dissolution of secondary ca mg carbonate sulfate salts initially formed by near surface evaporation in the summer and at depth by freeze in of the active layer and cryoconcentration in the winter high hydraulic conductivity 10 5 to 10 4 m s and diurnal fluctuations of river stage during our study caused exchange of river and pore water immediately adjacent to the river channel with a net loss of river water to the bank pore water 6 m from the river continuously flowed away from the river approximately 1 8 of the river discharge through the sandflugtdalen was lost to the river bank during our 6 75 day study based on calculations using darcy s law although not sampled some of this water should discharge to the river during low river stage early and late in the melt season elevated pore water solute concentrations in sandurs and water exchange at diurnal and seasonal frequency should impact fluxes of solutes to the ocean although understanding the magnitude of this effect will require long term evaluation throughout the melt season

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

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

antarctic weathering and carbonate compensation at the eocene oligocene transition during the eocene oligocene transition a permanent ice sheet was established on antarctica marine sediment geochemistry indicates a period of intense weathering associated with the inception of the ice sheet

lead and strontium isotopes as monitors of experimental granitoid mineral dissolution abstract flow through dissolution experiments were carried out on crushed granitoid rock the elat granite and three mineral separates plagioclase perthite and biotite chlorite from this rock at ph 1 and 25 c major element concentrations were combined with pb and sr isotopic analyses of starting materials and output solutions and together enabled us to elucidate several important mechanisms related to granitoid rock weathering we observed an initial stage of rock dissolution

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects

sr nd pb isotope evidence for ice sheet presence on southern greenland during the last interglacial to ascertain the response of the southern greenland ice sheet gis to a boreal summer climate warmer than at present we explored whether southern greenland was deglaciated during the last interglacial lig using the sr nd pb isotope ratios of silt sized sediment discharged from southern greenland our isotope data indicate that no single southern greenland geologic terrane was completely deglaciated during the lig similar to the holocene differences in sediment sources during the lig relative to the early holocene denote however greater southern gis retreat during the lig these results allow the evaluation of a suite of gis models and are consistent with a gis contribution of 1 6 to 2 2 meters to the 4 meter lig sea level highstand requiring a significant sea level contribution from the antarctic ice sheet