development of a sea ice model for use in zonally averaged energy balance climate models abstract a sea ice model for use in zonally averaged energy balance climate models is presented which includes the following processes surface melting basal freezing and melting lateral melting from ice flee water or growth of new ice in leads snowfall and the formation of white ice ice advection and a parameterized ice and snow thickness distribution which represents the effects of small scale dynamics the ice growth equations of hibler are solved analytically thereby permitting a gradual increase in zonal ice fraction in fall and winter both lateral and vertical melting lead to a continuous decrease of ice fraction during ice decay the correlation between ice thickness and ice thickness sensitivity to the upward heat flux at the ice base is of opposite sign seasonally and latitudinally the parameterized feedback between ice thickness and the minimum permitted lead fraction is found to be very important to the ice simulation and is a process which needs to be studied using higher resolution

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

massive magnesium depletion and isotope fractionation in weathered basalts abstract magnesium isotopes have been shown to fractionate significantly during continental weathering however the degree and direction of fractionation varies from one study to the next and the main factors that control mg isotope fractionation during weathering have yet to be delineated here we report mg contents and isotopic compositions for two 10 m deep drill cores through bauxites developed on columbia river basalts crbs samples from these two drill cores have very low mgo contents 0 12 0 25 wt and variable but high 26mg values from 0 1 to up to 1 8 the heaviest isotopic composition ever reported for mg relative to the average values of fresh crbs 26mg 0 23 0 07 and mgo 5 9 wt these features reflect the near complete loss of mg in the isotopically heavy regolith the most highly weathered bauxites at the tops of the profiles have the lowest 26mg values reflecting the addition of isotopically light eolian dust excluding these samples 26mg in bauxites displays a weak positive correlation with gibbsite abundance suggesting that gibbsite preferentially retains 26mg in the bauxites the integrated mg isotopic fractionation factors between bauxite and fluid 26mgbauxite fluid inferred from rayleigh fractionation calculations vary from 0 05 to 0 4 which is similar to the range inferred from previous studies of igneous rock weathering profiles though none of these previous studies found the extremely heavy 26mg and massive mg depletion seen here collectively studies of weathering profiles suggest loss of isotopically light mg from the continents which must contribute to the very light 26mg seen in river water and seawater

chemical weathering of silicate rocks in karelia region and kola peninsula nw russia assessing the effect of rock composition wetlands and vegetation this study is aimed at assessing the effect of factors including lithology forest peatland coverage dissolved organic carbon and vegetation on chemical fluxes and concentrations of major elements in rivers the mean annual element concentrations and dissolved fluxes of acid and basic rock dominated watersheds of the karelia region and kola peninsula nw russia have been estimated from the chemical composition of river water samples collected in the summers of 1996 2000 and from annual discharge and chemical composition data of 16 watersheds collected from 1961 to 1975 the mean annual flux corrected for atmospheric input varies from 0 5 to 5 6 t km2 y and is dominated by alkali metals for the kola alkaline rocks and by calcium for the karelian granito gneisses the pure granitic and pure basaltic river chemical denudation rates in the baltic shield are 0 33 and 2 3 t km2 y respectively the cationic and silica fluxes of both granitic and basaltic watersheds are comparable with those of other boreal regions having similar runoff compositions and climate the cationic flux of the rivers is positively correlated with the basic rock fraction of the watershed whereas the dissolved organic carbon flux increases with the increasing peatland fraction the chemical composition of the river water is controlled by bedrock dissolution during dry periods and by plant litter degradation and washout of organic debris from the topsoil horizon during wet periods taking account the chemical composition of the plant litter and the biological turnover intensity it was estimated that the plant litter degradation in kola and karelia regions provides 10 40 of total annual dissolved riverine element flux

the influence of weathering processes on riverine magnesium isotopes in a basaltic terrain this study presents major trace element and mg isotope data for the dissolved load and suspended particulates of icelandic rivers draining dominantly basaltic catchments including both glacier fed and direct runoff rivers these samples provide the opportunity to understand the behaviour of mg isotopes during chemical weathering where variations due to lithology are not extant given the significant role of mg in the carbon cycle such variations may provide important information on the regulation of earth s climate hydrothermal waters groundwater precipitation glacial ice basalt glass olivine and representative soils have also been analysed the dissolved load shows a wide range of 26mg compositions compared to the parent basaltic glass 26mg 0 29 ranging from 0 96 to 0 64 while precipitation and hydrothermal waters possess 26mg values of 0 83 and 0 85 respectively with lower mg concentrations than the dissolved load biomass activity in vegetation and organic material in soils and rivers colloids appear to have little effect on the mg isotope compositions rather the data suggest that mg elemental and isotopic variations are largely controlled by the formation and stability of secondary phases in response to differing hydrological conditions in some samples seawater in the form of direct precipitation or glacial runoff also appears to be an important source of mg glacier fed rivers groundwaters and some direct runoff rivers with a high ph have higher 26mg than basalt which is most likely due to the incorporation of light mg isotopes in secondary minerals in contrast those direct runoff rivers which have a relatively low ph have low 26mg relative to basalt consistent with preferential incorporation of heavy mg isotopes into secondary phases although it is not possible to rule out some contribution from precipitation riverine suspended particulates are depleted in mobile elements and have 26mg compositions values both higher and lower than unweathered basalt in the glacier fed and direct runoff rivers where the 26mg of the dissolved phase is heavy due to the formation of secondary phases the suspended load is light because it contains more of those phases the opposite is true for the remainder of the direct runoff rivers which have low ph this could be due to dissolution of secondary minerals enriched in light mg which are unstable at low ph or the formation of new secondary phases

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

sea ice melting and floe geometry in a simple ice ocean model a coupled sea ice ocean numerical model has been developed that addresses the role of floe geometry during summertime melting the model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration the partition between melting on the top bottom and lateral side surfaces of floes is examined using time dependent simulations with differing initial average floe diameters the different parameterizations for bottom and lateral melting in the literature are also compared and found to vary significantly the results show that lateral melting is important only for floes with diameters less than o 30 m given atmospheric thermal forcing typical of the central arctic in summer this means that the decrease in ice concentration over the summer is a strong function of floe diameter in keeping with simple geometrical arguments in all cases about 80 of the net thermal energy that enters the ocean through leads goes toward melting ice while the rest warms the ocean

evidence of zn isotopic fractionation in a soil plant system of a pristine tropical watershed nsimi cameroon abstract the objective of this study is to determine for the first time the zinc zn isotopic composition of different soil horizons parent rocks litter and plants from a single pristine watershed three soil profiles from nsimi zoetele site south cameroon africa have been investigated the 66zn 66zn 66zn 64zn sample 66zn 64zn jmc 3 0749l 1 103 measured in the soils and rocks range from 0 05 to 0 64 in a typical hillslope soil profile developed in situ from a granitic parent rock we observe two important and systematic trends i a weathering regime in the saprolite horizon that involves strong zn depletion with no or slight fractionation compared to the fresh igneous rock and ii a shallower weathering regime with significant depletion in heavy zn isotopes in the most superficial soil horizons in contrast the soil profile of the swamp zone does not exhibit isotopic fractionation between the soil and the parent rock six plants and two litter samples were analyzed for their zn isotopic compositions 66zn varied from 0 75 to 0 91 among all samples plant roots and shoots are generally enriched in heavy isotopes 66zn of 0 42 to 0 76 relative to the litter layer 0 12 to 0 25 and most superficial soils similar to the controlled plant growth study of weiss et al weiss d j mason t f d zhao f j kirk g j d coles b j and horstwood m s a 2005 isotopic discrimination of zinc in higher plants new phytologist 165 703 710 negative 66zn values were obtained for tree leaves the most aerial part of the tree based on biomass data for the tropical forest vegetation is on average enriched in light isotopes compared to the litter and the superficial soil horizons which are the nutrients reservoirs due to the age of these soils and the complexity of pedogenetic processes it is difficult to explain the isotopic composition of the soils at present however the transformation of the saprolite horizon into a ferruginous horizon is associated with an enrichment in light zn isotopes this observation may be due to the adsorption of zn onto clays surfaces the uptake of zn by roots in the soils leads to an enrichment in heavy isotopes once the zn is in the xylem it will be transported within the plant during this transport both diffusion and active uptake of heavy isotopes by cells out of the xylem favour the mobility of light isotopes to the most aerial parts of the plants the difference in zn isotopic composition between the deep horizons and the superficial horizons of soils suggests that zn isotopes can be used to discriminate the source of zn and other metals leaving the catchment by river water

wintertime heat flux to the underside of east antarctic pack ice in the sea ice zone there is a delicate balance between the heat loss from the surface of the snow covered sea ice and the heat supplied to the underside of the ice by the deep ocean the difference between these two heat fluxes determines the amount of ice growth or melt in global atmospheric models the ocean heat flux is often prescribed and has been shown to be an important parameter in determining how thick sea ice will grow thermodynamically although this ocean heat flux is a critical component in climate models there are relatively few direct measurements in the antarctic sea ice region in this study we use measurements of the temperature gradient through the sea ice and of ice growth during a field experiment to estimate the ocean heat flux in the east antarctic region around 140 e 65 s during august 1995 we find an average ocean heat flux of 13 0 14 5 w m 2 this is more than twice the winter values reported in the western weddell sea under multiyear sea ice but similar to the 19 w m 2 that has been estimated for the entire weddell gyre during august 1995 the air temperature showed large variations ranging from near freezing to 30 c this resulted in the thicker ice floes 50 60 cm alternating between a no growth or melting condition and an active ice growth at the base however it is likely that the thicker 60 cm ridged portions of the floes were continually melting

the composition of the continental river weathering flux deduced from seawater mg isotopes this study establishes the magnesium isotopic composition of seawater and evaluates its constancy as a function of depth and geographic location it also provides results on the magnesium isotopic composition of river water samples draining specific lithologies in combination the results are used to obtain an average magnesium isotopic composition of 1 54 for the global continental weathering flux compared to the 2 value of the global ocean both relative to nist srm 980 analyses of modern and fossil carbonate secreting echinoderms suggest that these can serve as archives of seawater 26mg values it is demonstrated that these records of the magnesium isotopic composition of ancient oceans can be used to make important inferences about the relative contribution of different lithologies to the global continental weathering flux particularly carbonate versus silicate weathering preliminary results suggest that the composition of the continental weathering flux has not undergone dramatic changes during the phanerozoic

solute flux and mineral mass balance approaches to the quantification of plant effects on silicate weathering the weathering of calcium and magnesium silicate minerals on the continents has exerted a major control on atmospheric co 2 over geologic time and vascular plants may have played an important role in this process we have examined the role of plants in weathering in western iceland by two methods a solute flux approach and a mineral mass balance approach using the chemistry of weathering products and of waters draining adjacent areas of basaltic rocks that are either barren with a partial cover of mosses and lichens or populated by trees the study area was chosen to maximize vegetational differences and to minimize differences in microclimate slope and lithology while avoiding hydrothermal waters and anthropogenic acid rain solute flux results including data on cation uptake by growing trees indicate that the rate of weathering release of ca and mg to streams is about 4 times higher in vegetated areas than in bare areas mineral mass balance results show that trees increase plagioclase weathering by a factor of 2 and pyroxene weathering by a factor of 10 possibly as a result of preferential weathering of pyroxene by the vegetation biomass normalized weathering fluxes from the birch trees are greater than those from the conifers suggesting that angiosperms enhance weathering to a greater degree than gymnosperms results indicate a perpetual short term sink for atmospheric c as tree induced leakage of hco super 3 from the forest ecosystem to rivers and streams in addition to the finite sink of c in forest biomass the findings also suggest a major role for vascular plants as they invaded upland portions of the continents between 410 and 360 my ago in accelerating weathering and thereby lowering atmospheric co 2

lithium magnesium and uranium isotope behaviour in the estuarine environment of basaltic islands this study presents major and trace elements and uranium u lithium li and magnesium mg isotope data for dissolved and suspended particulate material from estuaries draining dominantly basaltic terrains in iceland borgarfjor ur and sao miguel povoacao in the azores archipelago the concentrations of dissolved sodium na calcium ca potassium k sulphate so4 mg and li and 7li 6li and 26mg 24mg isotope ratios vary directly as a function of the dissolved chloride concentration cl indicating that these species are non reactive in these estuaries however u appears to be affected either by colloid flocculation or the formation of fe oxyhydroxides in borgarfjor ur the major element composition of suspended particulate material in the estuary at borgarfjor ur shows that the detrital silicates delivered to the estuarine mixing zone are relatively unweathered accordingly the 26mg isotope composition of the suspended material is indistinguishable from that of the parent basalts however the 234u 238u activity ratios of the suspended material are significantly different from the parent basalt indicating rapid equilibration of the u isotopes between particles and seawater the li concentration and 7li isotope composition of the suspended load are also observed to increase with increasing cl consistent with ongoing weathering of detrital material and the formation of secondary minerals in seawater depending on the particle residence time in the estuary this process could remove as much as 15 25 of the global riverine input of li to the ocean

magnesium isotopes in permafrost dominated central siberian larch forest watersheds abstract to unravel the mg isotope fractionation pathways within the continuous permafrost zone in the larch deciduous forest of central siberia we measured the mg isotopic composition of two large siberian rivers nizhnaya tunguska and kochechum which flow into the yenisey a small forested stream and the major fluid and solid sources of mg in the watershed atmospheric precipitates surface suprapermafrost flow interstitial soil solutions plant biomass litter and mineral soils the obtained results indicate a significant seasonal variation in riverine water mg isotope signatures during the winter baseflow the mg isotope composition of large rivers is significantly lighter than the source basaltic rocks and the atmospheric depositions these differences support the presence of fluids enriched in lighter mg isotopes such as those affected by the mineral precipitation of secondary silicates or fluids that dissolve sedimentary carbonate rocks during the spring flood and in the summer and fall seasons the river fluid 26 mg values increased by 0 2 0 3 and approached the mg isotope composition of the ground vegetation dwarf shrubs mosses and the soil organic horizon overall the riverine waters were 0 3 0 7 lighter than the unaltered bedrock and the deep minerals soil horizons the mg isotopic compositions of larix gmelinii organs i e stem wood roots and needles exhibit a low variability however an enrichment of 0 2 0 3 in the 26 mg of larch needles in the course of the growing season from june to september can be observed this enrichment most likely demonstrates uptake of isotopically heavier mg by the plant in addition to the progressive thawing of the mineral soil deepening of the active layer of the soil overall the mg isotope approach indicates the important contribution of vegetation larch needles mosses and dwarf shrubs to the riverine mg isotope signature and helps to reveal the contribution of isotopically light carbonate rocks in the large rivers of the central siberian plateau

invisible polynyas modulation of fast ice thickness by ocean heat flux on the canadian polar shelf although the canadian polar shelf is dominated by thick fast ice in winter areas of young ice or open water do recur annually at locations within and adjacent to the fast ice these polynyas are detectable by eye and sustained by wind or tide driven ice divergence and ocean heat flux our ice thickness surveys by drilling and towed electromagnetic sounder reveal that visible polynyas comprise only a subset of thin ice coverage additional area in the coastal zone in shallow channels and in fjords is covered by thin ice which is too thick to be discerned by eye our concurrent surveys by ctd reveal correlation between thin fast ice and above freezing seawater beneath it we use winter time series of air and ocean temperatures and ice and snow thicknesses to calculate the ocean to ice heat flux as 15 and 22 w m2 at locations with thin ice in penny strait and south cape fjord respectively near surface seawater above freezing is not a sufficient condition for ocean heat to reach the ice kinetic energy is needed to overcome density stratification the ocean s isolation from wind under fast ice in winter leaves tides as the only source two tidal mechanisms driving ocean heat flux are discussed diffusion via turbulence generated by shear at the under ice and benthic boundaries and the internal hydraulics of flow over topography the former appears dominant in channels and the coastal zone and the latter in some silled fjords where and when the layering of seawater density permits hydraulically critical flow

multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the arctic ocean the conductive and oceanic heat fluxes and the mass balance of sea ice were investigated utilizing an ice mass balance buoy imb deployed in the arctic ocean after imb deployment the ice thinned from 1 95 m in late august to 1 46 m by mid october 2008 from then on ice growth until mid june 2009 increased the ice thickness to 3 12 m the ice temperature and consequently the conductive heat flux at the ice surface exhibited persistent high frequency variations due to diurnal and synoptic scale atmospheric forcing these signals propagated downward with damped magnitude and temporal lag the competition of oceanic and conductive heat flux dominated the low frequency variations of ice growth however high frequency variations in ice growth were controlled largely by the oceanic heat flux from mid november 2008 to mid june 2009 the average oceanic heat flux along a track from 86 2 n 115 2 w to 84 6 n 33 9 w was 7 1 w m2 this was in agreement with that derived from an imb deployed in 2005 about 1 5 to the north of our buoy we attributed the relatively high oceanic heat flux 10 15 w m2 observed during autumn and early winter to summer warming of the surface ocean upward mixing of warm deep water as observed when our buoy drifted over the shallow region of the lomonosov ridge 85 4 85 9 n 52 2 66 4 w demonstrated the impact of bathymetry on the oceanic heat flux under ice cover and consequently on the basal ice mass balance 2013 american geophysical union all rights reserved

observations of the summer breakup of an arctic sea ice cover the arctic sea ice cover evolves dramatically through the summer melt season floe size distribution fsd is a critical parameter used to examine this change as the ice cover transitions from large rectilinear plates in spring to an ensemble of discrete rounded floes by midsummer the fsd at a given time impacts the dynamic and thermodynamic behavior of the ice cover focusing on the seasonal marginal ice zone in the beaufort and chukchi seas from may to september 2014 we present qualitative and quantitative results derived from national technical means high resolution imagery and supported by ice mass balance buoy data results indicate that as melt accelerates floe breaking pattern and therefore fsd is heavily influenced by the distribution of melt ponds discrete element model results using morphological conditions derived from analyzed satellite imagery confirmed that breaking occurs along ponds and perpendicular to applied stress

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

ca isotope cycling in a forested ecosystem reports of large ca isotope fractionations between trees and soils prompted this study of a boreal forest ecosystem near la ronge saskatchewan to improve understanding of this phenomenon the results on five tree species black spruce trembling aspen white spruce jack pine balsam poplar confirm that nutrient ca uptake by plants favors the light isotopes thus driving residual ca in plant available soil pools towards enrichment in the heavy isotopes substantial within tree fraction occurs in tissues formed along the transpiration stream with low 44ca values in fine roots 2 mm intermediate values in stemwood and high values in foliage separation factors between different plant tissues are similar between species but the initial fractionation step in the tips of the fine roots is species specific and or sensitive to the local soil environment soil water 44ca values appear to increase with depth to at least 35 cm below the top of the forest floor which is close to the deepest level of fine roots the heavy plant fractionated signature of ca in the finely rooted upper soils filters downward where it is retained on ion exchange sites leached into groundwater and discharged into surface waters the relationship between ca uptake by tree fine roots and the pattern of 44ca enrichment with soil depth was modeled for two ca pools the forest floor litter and the underlying upper b mineral soil six study plots were investigated along two hillside toposequences trending upwards from a first order stream we used allometric equations describing the ca distribution in boreal tree species to calculate weighted average 44ca values for the stands in each plot and estimate ca uptake rates the 44ca value of precipitation was measured and soil weathering signatures deduced by acid leaching of lower b mineral soils steady state equations were used to derive a set of model ca fluxes and fractionation factors for each plot the model reproduces the increase in 44ca with depth found in forest floor and upper b soil waters transient model runs show that the forest ca cycle is sensitive to changes in plant ca uptake rate such as would occur during ontogeny or disturbance accordingly secular records of 44ca in tree ring cellulose have the potential to monitor changes in the forest ca cycle through time thus providing a new tool for evaluating natural and anthropogenic impacts on forest health another model run shows that by changing the size of the isotope fractionation factor and adjusting for differences in forest productivity that the range in ca isotope fractionation in forested ecosystems reported in the literature thus far is reproduced as a quantitative tool the ca cycling model produces a reasonable set of relative ca fluxes for the la ronge site consistent with environment canada s measurements for wet deposition in the region and simulated ca release from soil mineral weathering using the profile model but the sensitivity of the model is limited by the small range of fractionation observed in this boreal shield setting of 1 which limits accuracy if the model were applied to a site with a greater range in 44ca values among the principal ca fluxes it is capable of producing robust and reliable estimations of ca fluxes that are otherwise difficult to measure in forested ecosystems

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

seasonal evolution of an ice shelf influenced fast ice regime derived from an autonomous thermistor chain ice shelves strongly interact with coastal antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub ice platelet layer the close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology in this study we characterize the seasonal cycle of antarctic fast ice adjacent to the ekstrom ice shelf in the eastern weddell sea we used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain vertical sea ice temperature and heating profiles obtained daily between november 2012 and february 2014 were analyzed to determine sea ice and snow evolution and to calculate the basal energy budget the residual heat flux translated into an ice volume fraction in the platelet layer of 0 18 0 09 which we reproduced by a independent model simulation and agrees with earlier results manual drillings revealed an average annual platelet layer thickness increase of at least 4 m and an annual maximum thickness of 10 m beneath second year sea ice the oceanic contribution dominated the total sea ice production during the study effectively accounting for up to 70 of second year sea ice growth in summer an oceanic heat flux of 21 w m 2 led to a partial thinning of the platelet layer our results further show that the active heating method in contrast to the acoustic sounding approach is well suited to derive the fast ice mass balance in regions influenced by ocean ice shelf interaction as it allows subdiurnal monitoring of the platelet layer thickness

the effect of hydrothermal spring weathering processes and primary productivity on lithium isotopes lake myvatn iceland lithium isotopes are rapidly becoming one of the most useful tracers of silicate weathering processes but little is known on their behaviour in groundwaters and hydrothermal springs and how these sources might influence the weathering signal in surface waters this study presents lithium isotope compositions 7li for cold groundwaters 3 7 c and hydrothermal springs that were at geothermal temperatures 200 300 c but have cooled during transport 17 44 c both represent an important source of water and nutrients for lake myvatn iceland we also present a time series from the laxa river which is the single outflow from the lake the 7li values in the input springs to lake myvatn are highly variable 5 27 and correlate inversely with temperature and total dissolved solids these co variations imply that even in such waters the processes controlling 7li variations during weathering still operate that is the ratio of primary rock dissolution to secondary mineral formation where the latter preferentially incorporates 6li with a temperature dependent fractionation factor in high temperature geothermal waters 300 c secondary mineral formation is inhibited and has a low fractionation factor leading to little 7li fractionation even in waters that have cooled considerably over several months from their geothermal temperatures fractionation is still low and 7li values are similar to those reported from waters measured at 350 c in contrast cooler groundwaters promote relatively high proportions of clay formation which scavenge dissolved solids including 6li the time series on the laxa river the single outflow from lake myvatn shows little 7li variation with time over the 12 month sampling period 17 21 demonstrating that in contrast to tracers such as si isotopes li isotopes are unaffected by the significant seasonal phytoplankton blooms that occur in the lake thus these results clearly illustrate that li isotopes are ideally suited to constrain silicate weathering processes because fractionation by secondary mineral formation operates even when groundwater and hydrothermal inputs are significant and because li isotopes are demonstrably unaffected by phytoplankton or plant growth

decadal variation and trends in subsurface salinity from 1960 to 2012 in the northern south china sea observations suggest that subsurface waters in the northern south china sea nscs exhibited substantial low frequency variability with a striking decadal change in the southern limit of the 34 6 psu isohaline long term freshening of the subsurface waters started in 1960 was followed by salinification from 1975 and freshening occurred again from 1993 to 2012 the linear trends were 0 0076 0 0100 and 0 0078 psu yr respectively an analysis of the subsurface salinity budget reveals that the main underlying contributors to subsurface salinity are horizontal advection and vertical entrainment in particular advection driven by the luzon strait transport and vertical entrainment from the mixed layer are the key factors controlling variations on subsurface salinity diagnosis of the salinity budget further suggests that entrainment from the mixed layer played a more important role in the freshening periods than in the salinifying period

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

oceanic heat flux in the fram strait measured by a drifting buoy as one component of the arctic environmental drifting buoy two thermistor strings were installed through the ice to measure ice temperatures and determine oceanic heat fluxes as the buoy drifted from the arctic basin into the greenland sea ice temperature data between 14 dec 1987 and 2 jan 1988 were retrieved during this period the aedb progressed from approximately 81 n 4 e to 77 n 5 w this constituted the most rapid displacement of the entire drift coinciding with the entry of the floe into the marginal ice zone of fram strait once in the miz water temperatures increased most notably at a depth of 16 m where values changed from 1 8 c to more than 2 c bottom ablation rates of 34 mm day were observed between 21 and 28 dec during this excursion into warmer water the oceanic heat flux increased by a factor of 18 from 7 w m to 128 w m

heat flux at the ice ocean interface the role of the oceanic heat flux fw in the sea ice energy and mass balance is discussed and a method is described for determining fw from measurements of the temperature and thickness of sea ice results obtained using this method and data collected in the fall of 1988 during a drift in the eastern arctic northeast of fram strait are presented estimates of fw ranged from 0 to 37 w m 2 and varied in both time and space the gradual variation over the course of the drift reflects transformation of the west spitsbergen current into arctic water masses a significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under ice topographic features and turbulent energy and mass transfer in the boundary layer in addition there is a variability in the ice growth rate on horizontal scales of 0 1 to 1 m which is ascribed to the instability of the ice ocean phase boundary in the presence of turbulent flow these observations have implications for modeling and future experiments

the anatomy of a freezing lead winter leads are regions of intense ice growth with resultant large fluxes of heat to the atmosphere and salt to the ocean they constitute a major source of new ice in the arctic basin during the 1988 drift phase of the coordinated eastern arctic experiment we were afforded a unique opportunity to conduct a detailed long term study of a freezing lead measurements were made from september 17 to november 18 during which time the ice grew from open water to a thickness of 0 56 m cores were removed from the lead ice on a routine basis and analyzed for ice temperature salinity density and structure from these measurements the derived quantities of brine volume porosity heat flux to the atmosphere and salt flux to the ocean were computed in addition to this 2 month time series study of ice cores the spatial variation in lead ice properties was investigated on september 30 thin section studies of ice structure indicated that the upper 0 05 0 15 m of the ice sheet was granular and that the lower portion was columnar typically a portion of the granular layer was snow ice once the transition from granular to columnar ice had occurred granular ice did not reappear as the ice grew thicker the c axes of the ice crystals became aligned within the horizontal plane this alignment direction corresponded closely with the inferred direction of the current at the ice water interface vertical temperature profiles in the ice were approximately linear salinity profiles were usually c shaped with bulk salinities ranging from 9 to 6 before stabilizing at 6 for ice thicker than 0 35 m core data were used to compute the flux of heat to the atmosphere and the flux of salt to the ocean for seven time intervals during the experiment heat fluxes ranged from 89 to 29 w m2 with an average of 50 w m 2 roughly 3 times the corresponding value from multiyear ice the flux of salt from the lead ice to the ocean varied from 0 51 to 0 06 kg m 2 d 1 averaging 0 21 kg m 2 d 1

magnesium isotope systematics of the lithologically varied moselle river basin france abstract magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the moselle basin northeastern france this small basin is remarkable for its well constrained and varied lithology on a small distance scale and this is reflected in river water sr isotope compositions upstream where the moselle river drains silicate rocks of the vosges mountains waters are characterized by relatively high 87sr 86sr ratios 0 7128 0 7174 in contrast downstream of the city of epinal where the moselle river flows through carbonates and evaporites of the lorraine plateau 87sr 86sr ratios are lower down to 0 70824 magnesium in river waters draining silicates is systematically depleted in heavy isotopes 26mg values range from 1 2 to 0 7 relative to the value presently estimated for the continental crust and a local diorite 0 5 in comparison 26mg values measured in soil samples are higher 0 0 this suggests that mg isotope fractionation occurs during mineral leaching and or formation of secondary clay minerals on the lorraine plateau tributaries draining marls carbonates and evaporites are characterized by low ca mg 1 5 3 2 and low ca sr 80 400 when compared to local carbonate rocks ca mg 29 59 ca sr 370 2200 similar to other rivers draining carbonates the most likely cause of the mg and sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer 26mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year from 1 4 to 1 6 and from 1 2 to 1 4 respectively within the range defined for the underlying rocks downstream of epinal the compositions of the moselle river samples in a 26mg vs 87sr 86sr diagram can be explained by mixing curves between silicate carbonate and evaporite waters with a significant contribution from the vosgian silicate lithologies 70 temporal co variation between 26mg and 87sr 86sr for the moselle river throughout year is also observed and is consistent with a higher contribution from the vosges mountains in winter in terms of runoff and dissolved element flux overall this study shows that mg isotopes measured in waters rocks and soils coupled with other tracers such as sr isotopes could be used to better constrain riverine mg sources particularly if analytical uncertainties in mg isotope measurements can be improved in order to perform more precise quantifications

effects of biogeochemical processes on magnesium isotope variations in a forested catchment in the vosges mountains france abstract this study investigates the potential of mg isotopes as tracers of biogeochemical processes in a small forested catchment located on sandstones extremely poor in mg bearing minerals the average 26 mg is 0 63 0 12 and 0 0 14 for local rainwater and bedrock respectively from the c horizon to the upper eluvial e horizon soil 26 mg from 0 0 0 14 to 0 25 0 14 is close to the bedrock value while more than 70 of mg is lost suggesting a small isotopic shift during illite dissolution the surface soil horizon a h 26 mg is close to plant 26 mg and especially to the grass 26 mg value 0 49 the bulk 26 mg of trees and grass 0 32 and 0 41 respectively are higher than the average 26 mg values of the soil exchangeable fraction 0 92 to 0 42 and of rainwater 0 65 within plants roots are enriched in heavy isotopes whereas light isotopes are preferentially translocated and stored in the above ground parts in norway spruce the older needles forming the annual litterfall are isotopically lighter and strongly depleted in mg compared to more recent needles soil solution 26 mg shifts seasonally from low values lower than rainwater and close to litterfall during a high rainfall period in spring to higher values close to soil 26 mg in dryer periods of winter or summer at the watershed scale streamwater 26 mg varies between 0 85 0 14 and 0 08 0 14 and 26 mg values decrease linearly with discharge the high streamwater 26 mg at low flow close to bedrock 26 mg most likely reflects dissolution processes in the deep saprolite in relation to the very long water residence time conversely we suggest that low stream level 26 mg values are at least partly related to the contribution of surface flows from wet areas using a simple mass and isotopic balance approach we compute that mineral dissolution rates in the soil 0 35 kg mg ha 1 year 1 presently compensate for mg losses from the soil

the dynamics of si cycling during weathering in two small catchments in the black forest germany traced by si isotopes abstract silicon stable isotopes have emerged as a powerful proxy to investigate weathering because si uptake from solution by secondary minerals or by the vegetation causes significant shifts in the isotope composition in this study we determined the si isotope compositions of the principle si pools within two small catchments located on sandstone and paragneiss respectively in the temperate black forest germany at both settings clay formation is dominated by mineral transformation preserving largely the signature of parental minerals with 30si values of around 0 7 bulk soils rich in primary minerals are similar to bulk parental material with 30si values close to 0 4 topsoils are partly different because organic matter degradation has promoted intense weathering leading to 30si values as low as 1 0 water samples expose highly dynamic weathering processes in the soil zone 1 after spring snowmelt increased release of doc and high water fluxes trigger clay mineral dissolution which leads to 30si values down to 0 7 and 2 in course of the summer si uptake by the vegetation and secondary mineral formation drives dissolved si to typical positive 30si values up to 1 1 groundwater with 30si values of around 0 4 records steady processes in bedrock reflecting plagioclase weathering together with kaolinite precipitation an isotope mass balance approach reveals incongruent weathering conditions where denudation of si is largely driven by physical erosion erosion of phytoliths contributes 3 to 21 to the total si export flux which is in the same order as the dissolved si flux these results elucidate the si dynamics during weathering on catchments underlain of sedimentary origin prevailing on the earth surface and provide therefore valuable information to interpret the isotope signature of large river systems

strontium isotopes trace biological activity in the critical zone along a climate and vegetation gradient abstract weathering and ecosystem nutrition are intimately linked through the supply of fresh mineral nutrients from regolith and bedrock the geogenic nutrient pathway however the prominence of this link is dependent on the efficiency of nutrient recycling from plant litter the organic nutrient cycle isotope ratios of strontium sr an element that behaves similarly to ca in ecosystems confer two types of information radiogenic sr isotopes inform as to the sources of sr and the degree of weathering while stable sr isotopes constrain partitioning between compartments of the critical zone bedrock water secondary solids and plants to date however neither the reactions nor the mass balance between compartments that fractionate sr isotopes nor the fractionation factors involved are well understood here we present geochemical budgets of sr using radiogenic and stable sr isotopes and ca sr ratios at four sites along a substantial climate and primary production gradient in the coastal mountains of chile we found that sr release through weathering is isotopically congruent and released sr is not strongly isotopically fractionated either during secondary mineral formation or transfer into the exchangeable pool despite this the 88sr 86sr ratio of bio available sr which should reflect the ratio of dissolved sr is higher than that of rock and regolith we propose that this offset is caused by plants while 88sr 86sr in plant organs at the four study sites systematically increased from roots towards their leaves whole plant sr isotope compositions indicate preferential uptake of light sr into plants with a fractionation of up to 0 3 relative to the bio available pool despite this strong biological fractionation 88sr 86sr ratios in bio available sr do not covary with biomass production across our study sites because with greater plant growth sr is recycled more times after release by weathering an isotope neutral process rather the loss of sr from the ecosystem in solid organic material sets the isotope ratio of dissolved or bio available sr organic solids thus appear to constitute a significant export path of elements released during weathering with the removal of solid plant debris reducing the recycling factor of sr and possibly that of other mineral nutrients too

hydrography and vertical fluxes of heat and salt northeast of svalbard in autumn temperature and salinity data collected by a salargos buoy during october 1988 northeast of svalbard norway as part of the coordinated eastern arctic research experiment are analyzed as the buoy drifted across the continental slope the data show a transition from central arctic conditions where the thermocline lies below the halocline to shelf conditions where the two coincide surface waters on the shelf were above the freezing point losing heat to sea ice advected southward by the wind the atlantic inflow current was also observed on the continental slope with a maximum temperature above 3 c a storm caused upwelling and entrainment of this current leading to strong ice ocean heat fluxes and ice melting the resulting flux of fresh water stabilized the surface layer and shut off further entrainment this episodic process can lead to bigger heat losses from the atlantic inflow current than previously considered for ice covered conditions

modeling novel stable isotope ratios in the weathering zone when rock is converted to weathering products the involved processes can be fingerprinted using the stable isotope ratios of metals for example li mg ca fe sr and metalloids b si here we construct a framework for interpreting these novel stable isotope ratios quantitatively in the compartments of the weathering zone in a geomorphic context the approach is applicable to any novel stable isotope system and is based on a simple steady state mass balance model that represents the weathering zone from the scale of a soil column to that of entire continents our model is based on the assumption that the two main processes associated with isotope fractionation are formation of secondary precipitates such as clays and uptake of nutrients by plants the model results show that the isotope composition of a given element in the weathering zone compartments depends on 1 the ratio between the release flux to water through primary mineral dissolution and the erosion flux of isotopically fractionated solid material consisting of secondary precipitates and organic matter 2 the isotope fractionation factors associated with secondary mineral precipitation and uptake by plants a relationship is established between isotope ratios isotope fractionation factors and indexes for chemical weathering such as chemical depletion fractions cdf and elemental mass transfer coefficients derived from simple elemental concentration measurements from this relationship isotope fractionation factors can be calibrated from chemical and isotope data measured on field material furthermore we show how the ratio of solid export to dissolved export of a given element from the weathering system can be estimated from the comparison of the isotope composition between bedrock water and sediment this calculation can be applied to samples from soils from rivers and from the sedimentary record and does not require knowing the isotope fractionation factors involved in the reactions finally we apply the model to the oceanic li isotope record reconstructed from marine carbonate sediments in order to discuss changes in global geomorphic regimes through the cenozoic

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

using sea ice to measure vertical heat flux in the ocean results of an experiment performed at drifting ice station fram i in the arctic ocean northwest of spitzbergen during march may 1979 indicate that sensible heat flux from the ocean to the ice cover was less than 2 w m 2 the estimate is based on measurements of temperature gradient growth rate and salinity of young sea ice uncertainty in the magnitude of the heat flux results more from evidence of horizontal inhomogeneity in the growing ice sheet than from measurement errors

signatures of supercooling mcmurdo sound platelet ice near ice shelves around antarctica the ocean becomes supercooled and has been observed to carry small suspended ice crystals our measurements demonstrate that these small crystals are persistently present in the water column beneath the winter fast ice and when incorporated in sea ice they reduce the mean grain size of the sea ice cover by midwinter larger ice crystals below the ice water interface are observed to form a porous sub ice platelet layer with an ice volume fraction of 0 25 0 06 the magnitude and direction of the oceanic heat flux varied between 5 6 wm 2 upwards and 15 10 wm 2 downwards in may but by september it settled between 6 2 and 11 2 w m 2 the negative values imply that the ocean acts as a heat sink which is responsible for the growth of 12 of the ice thickness between june and september this oceanic contribution should not be ignored in models of antarctic sea ice thickness close to an ice shelf

experimental investigation of mg isotope fractionation during mineral dissolution and clay formation abstract silicate minerals are a major mg source to seawater through rivers and therefore it is important to determine the impact of dissolution and formation of mg rich primary and secondary minerals on the mg isotope signature of natural waters we dissolved biotite mineral in a plug flow reactor at controlled ph and t 25 c and synthesized to and tot phyllosilicates lizardite and kerolite respectively at t 90 150 and 250 c all leaching solutions during biotite dissolution are enriched in light isotopes compared to the biotite sample with a 1 1 range of 26mgbiotite solution at ph 1 mg isotopic steady state between the solution and biotite is established after 600 h while at ph 5 it is never reached even after 4 months a sequential leaching suggests that the solution 26mg values depend mostly on a balance between the relative proportions of labile and structural mg with different 26mg values ca concentrations and elementary ratios measured in output solutions during the incipient stage of dissolution indicate non negligible mg contribution from small amount of disseminated carbonate phases present within the biotite sample during synthetic clay formation both to and tot clays are significantly enriched in heavy isotopes and follow rayleigh fractionation equations for specific values of isotope fractionation factors at t 250 c a single isotope fractionation factor of 1 00059 0 00014 can explain the mg isotope evolution of both to and tot clays a similar isotope fractionation factor of 1 00054 0 00014 can be inferred from all tot synthesized at t 90 250 c a compilation of mg isotope fractionation factors during secondary phase formation highlights a difference between field and experimental investigations at low temperature more experiments are now necessary to determine the role of clay crystallochemistry at temperatures below 50 c

the effect of ocean heat flux on seasonal ice growth in young sound northeast greenland the seasonal ice cover plays an important role in the climate system limiting the exchange of heat and momentum across the air water interface among other factors sea ice is sensitive to the ocean heat flux in this study we use in situ oceanographic sea ice and meteorological data collected during winter 2013 2014 in young sound ys fjord in northeast greenland to estimate the ocean heat flux to the landfast ice cover during the preceding ice free summer incident solar radiation caused sea surface temperatures of up to 5 6 c subsequently this heat was transferred down to the intermediate depths but returned to the surface and retarded ice growth throughout winter two different approaches were used to estimate the ocean heat fluxes i a residual method based on a 1 d thermodynamic ice growth model and ii a bulk parameterization using friction velocities and available heat content of water beneath the ice the average heat flux in the inner ys varied from 13 w m 2 in october december to less than 2 w m 2 in january may an average heat flux of 9 w m 2 was calculated for the outer ys moreover we show that the upward heat flux in the outer fjord is strongly modulated by surface outflow which produced two maxima in heat flux up to 18 24 w m 2 during 26 december to 27 january and from 11 february to 14 march by may 2014 the upward ocean heat flux reduced the landfast ice thickness by 18 and 24 in the inner and outer ys respectively

unexpected calcium sources in deep soil layers in low fertility forest soils identified by strontium isotopes lorraine plateau eastern france forest ecosystems are often found on acid soils where calcium availability depends on two main inputs atmospheric deposition and the weathering of soil minerals and on the biological cycling of nutrients in the context of global change decreasing atmospheric inputs increasing biomass exportation climate change it is important to determine calcium sources to the ecosystem and tree nutrition to better understand how forest ecosystems will respond to these changes over time the aim of this study was to study and compare ca pools and cycling in two mature forest ecosystems clermont en argonne and azerailles developed on two contrasting polycyclic soils lorraine plateau eastern france and identify the ca sources contributing to ecosystem functioning at both sites soil ca pools were measured atmospheric deposition of ca was monitored from bulk precipitation and throughfall chemistry ca biological cycling was assessed by measuring litterfall and by a litter decomposition experiment strontium 87sr 86sr isotope data in the soil profile fine roots exchangeable pool bulk soil was used to estimate the distribution of sr and ca uptake in the soil profile and the relative contribution of mineral weathering in the soil layers to total ecosystems inputs despite important differences in ca availability in the topsoil between both sites tree growth and nutrition indicators showed no significant difference this discrepancy is not explained by the biological cycling of ca but may be partly explained by higher ca deposition at the ca poorer site strontium isotope data enabled to show important differences of ca sources for tree uptake at the ca poorer site deep soil layers 105 cm potentially represent from 32 to 100 of total sr uptake at the ca richer site results suggest that uptake is more evenly distributed in the soil profile sr isotope data coupled with a modeling approach suggest that two different mineral sources exist in the soil profile a radiogenic sr source in the topsoil 87sr 86sr 0 717 and a less radiogenic source in depth 87sr 86sr 0 717 the deep mineral source may represent from 40 to 86 of total sr inputs at the poorer site and from 25 to 86 at the richer site the origin of this deep strontium source is unclear but soil mineralogy suggests an allochthonous origin we hypothesize that this deep source originates from capillary rise of the groundwater aquifer this nutrient input to forest ecosystems is not commonly taken into account but may strongly participate in maintaining the chemical fertility of soils over time

annual cycle of landfast sea ice in prydz bay east antarctica 1 under the chinese national antarctic research expedition program in 2006 the annual thermal mass balance of landfast ice in the vicinity of zhongshan station prydz bay east antarctica was investigated sea ice formed from mid february onward and maximum ice thickness occurred in late november snow cover remained thin and blowing snow caused frequent redistribution of the snow the vertical ice salinity showed a question mark shaped profile for most of the ice growth season which only turned into an i shaped profile after the onset of ice melt the oceanic heat flux as estimated from a flux balance at ice ocean interface using internal ice temperatures decreased from 11 8 3 5 w m 2 in april to an annual minimum of 1 9 2 4 w m 2 in september it remained low through late november in mid december it increased sharply to about 20 0 w m 2 simulations applying the modified versions of stefan s law taking account the oceanic heat flux and ice atmosphere coupling compare well with observed ice growth there was no obvious seasonal cycle for the thermal conductivity of snow cover which was also derived from internal ice temperatures its annual mean was 0 20 0 04 w m 1 c 1

magnesium retention on the soil exchange complex controlling mg isotope variations in soils soil solutions and vegetation in volcanic soils iceland understanding the biogeochemical cycle of magnesium mg is not only crucial for terrestrial ecology as this element is a key nutrient for plants but also for quantifying chemical weathering fluxes of mg and associated atmospheric co2 consumption requiring distinction of biotic from abiotic contributions to mg fluxes exported to the hydrosphere here mg isotope compositions are reported for parent basalt bulk soils clay fractions exchangeable mg seasonal soil solutions and vegetation for five types of volcanic soils in iceland in order to improve the understanding of sources and processes controlling mg supply to vegetation and export to the hydrosphere bulk soils 26mg 0 40 0 11 are isotopically similar to the parent basalt 26mg 0 31 whereas clay fractions 26mg 0 62 0 12 exchangeable mg 26mg 0 75 0 14 and soil solutions 26mg 0 89 0 16 are all isotopically lighter than the basalt these compositions can be explained by a combination of mixing and isotope fractionation processes on the soil exchange complex successive adsorption desorption of heavy mg isotopes leads to the preferential loss of heavy mg from the soil profile leaving soils with light mg isotope compositions relative to the parent basalt additionally external contributions from sea spray and organic matter decomposition result in a mixture of mg sources on the soil exchange complex vegetation preferentially takes up heavy mg from the soil exchange complex 26mgplant exch 0 50 0 09 and changes in 26mg in vegetation reflect changes in bioavailable mg sources in soils this study highlights the major role of mg retention on the soil exchange complex amongst the factors controlling mg isotope variations in soils and soil solutions and demonstrates that mg isotopes provide a valuable tool for monitoring biotic and abiotic contributions of mg that is bioavailable for plants and is exported to the hydrosphere

investigation of magnesium isotope fractionation during granite differentiation implication for mg isotopic composition of the continental crust abstract high precision mg isotopic analysis was performed on a suite of well characterized i type granitoids and associated hornblende and biotite minerals from the dabie orogen in central china to address the behavior of mg isotopes during granite differentiation although these granitoids formed through different degrees of partial melting and fractional crystallization with large variations in elemental and mineral compositions their 26 mg values vary from 0 26 to 0 14 and are indistinguishable within our analytical precision 0 07 2 sd coexisting hornblendes and biotites in these granitoids display similar mg isotopic composition with 26 mg ranging from 0 31 to 0 14 in hornblendes and 0 23 to 0 12 in biotites the inter mineral fractionation factors 26 mg hbl bt 26 mg hbl 26 mg bt vary from 0 10 to 0 02 with an average 0 06 0 08 2 sd the limited inter mineral fractionation agrees with the theoretic prediction that mg cations in both hornblende and biotite are octahedrally coordinated with oxygen which restricts the magnitude of equilibrium isotope fractionation overall data from both bulk granitoids and associated mineral separates suggest that mg isotope fractionation during i type granite differentiation is limited collectively granitoids studied here have mg isotopic composition similar to that of terrestrial basalts and peridotites 26 mg 0 21 0 07 vs 0 25 0 07 2 sd confirming that magmatic processes do not significantly fractionate mg isotopes the continental crust in the dabie orogen as sampled by these i type granitoids has a mantle like mg isotopic composition given that significant mg isotope fractionation occurs during chemical weathering processes mg isotopes may potentially be used for tracing granite genesis in particular if sedimentary materials are involved in granite sources

increased mg release rates and related mg isotopic signatures during bacteria phlogopite interactions abstract phlogopite weathering experiments were carried out under aerobic conditions in a closed system to study mg isotopic fractionation during the dissolution and processes involved in the presence of bacterial strains four different bacterial strains with different metabolisms were chosen biotic experiments were performed in batch reactors at 24 c for 12 days in parallel abiotic phlogopite weathering experiments were also performed using organic and nitric acids citric and gluconic acids were used to model the effects of chelating agents produced by bacteria and nitric acid was used to model the effects of acidifying agents the results indicate that both decreases in ph and the production of metabolites during heterotrophic bacterial activities significantly accelerate the release of mg and si in solution also at a given ph the fraction of elements released in solution is greater in the presence of bacteria or citric acid compared to that released in the presence of nitric and gluconic acids magnesium isotopic analyses indicate that the solutions obtained using nitric acid and acidifying bacterial strains display on average 26mg values that are close to or slightly heavier by 0 4 than those of fresh phlogopite 1 2 0 08 in contrast in experiments performed with citric acid the mg leached into solution is slightly enriched in light isotopes by 0 3 relative to the initial phlogopite while its binding to organics is expected to be related to its preferential enrichment in heavy isotopes despite its small range of variations the 26mg values of solutions vary inversely with ph thus suggesting that secondary phases preferentially enriched in 26mg at the highest ph values may play a key role

the impact of water rock interaction and vegetation on calcium isotope fractionation in soil and stream waters of a small forested catchment the strengbach case this study aims to constrain the factors controlling the calcium isotopic compositions in surface waters especially the respective role of vegetation and water rock interactions on ca isotope fractionation in a continental forested ecosystem the approach is to follow changes in space and time of the isotopic composition and concentration of ca along its pathway through the hydro geochemical reservoirs from atmospheric deposits to the outlet of the watershed via throughfalls percolating soil solutions and springs the study is focused on the strengbach catchment a small forested watershed located in the northeast of france in the vosges mountains the 44 40ca values of springs brooks and stream waters from the catchment are comparable to those of continental rivers and fluctuate between 0 17 and 0 87 soil solutions however are significantly depleted in lighter isotopes 44 40ca 1 00 1 47 whereas vegetation is strongly enriched 44 40ca 0 48 to 0 19 these results highlight that vegetation is a major factor controlling the calcium isotopic composition of soil solutions with depletion in light calcium in the soil solutions from deeper parts of the soil compartments due to preferential 40ca uptake by the plants rootsystem however mass balance calculations require the contribution of an additional ca flux into the soil solutions most probably associated with water rock interactions the stream waters are marked by a seasonal variation of their 44 40ca with low 44 40ca in winter and high 44 40ca in spring summer and autumn for some springs nourishing the streamlet a decrease of the 44 40ca value is observed when the discharge of the spring increases with in addition a clear covariation between the 44 40ca and corresponding h4sio4 concentrations high 44 40ca values and low h4sio4 concentrations at high discharge low 44 40ca values and high h4sio4 concentrations at low discharge these data imply that during dry periods and low water flow rate the source waters carry a ca isotopic signature from alteration of soil minerals whereas during wet periods and high flow rates admixture of significant quantities of 40ca depleted waters vegetation induced signal from uppermost soil horizons controls the isotopic composition of the source waters this study clearly emphasizes the potential of ca isotopes as tracers of biogeochemical processes at the water rock vegetation interface in a small forested catchment