sea ice production over the laptev sea shelf inferred from historical summer to winter hydrographic observations of 1960s 1990s the winter net sea ice production nsip over the laptev sea shelf is inferred from continuous summer to winter historical salinity records of 1960s 1990s while the nsip strongly depends on the assumed salinity of newly formed ice the nsip quasi decadal variability can be linked to the wind driven circulation anomalies in the laptev sea region the increased wind driven advection of ice away from the laptev sea coast when the arctic oscillation ao is positive implies enhanced coastal polynya sea ice production and brine release in the shelf water when the ao is negative the nsip and seasonal salinity amplitude tends to weaken these results are in reasonable agreement with sea ice observations and modeling

mapping of sea ice production in the arctic coastal polynyas 1 high ice production in coastal polynyas over the continental shelves in the arctic ocean is responsible for the formation of cold saline water which contributes to the maintenance of the arctic ocean halocline the accurate detection of coastal polynyas including an estimate of thin ice thickness is essential for the estimation of sea ice production this paper presents an algorithm that estimates thin ice thickness using special sensor microwave imager ssm i data in the arctic ocean detection and estimation of sea ice thicknesses of 0 15 m are based on the ssm i 85 and 37 ghz polarization ratios pr85 and pr37 through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer avhrr data in the three different arctic coastal polynyas thus for the entire arctic ocean the algorithm can be used for the detection of coastal polynyas and for the estimation of sea ice production through combination with heat flux calculation this study provides the first circumpolar mapping of sea ice production in coastal polynyas over the entire arctic ocean high ice production is confined to the major arctic coastal polynyas with the highest ice production rate being in the north water polynya this study also presents the interannual variability of sea ice production in the 10 major coastal polynyas from 1992 to 2007 in general interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature the mapping also provides surface heat and salt flux conditions in the ice covered region which have not been well understood to date

sorbing tracer experiments in a crystalline rock fracture at aspo sweden 3 effect of microscale heterogeneity we study the impact of microscale 10 3 10 2 m heterogeneity in material and structural properties on sorbing tracer transport in a single crystalline fracture of the true 1 tests mesoscale

sorbing tracer experiments in a crystalline rock fracture at aspo sweden 2 transport model and effective parameter estimation 1 transport and retention of sorbing tracers in a single altered crystalline rock fracture on a 5 m scale is investigated we evaluate the results of a comprehensive field study referred to as

supercooled water in an arctic polynya observations and modeling in situ field measurements of an active polynya in storfjorden svalbard during april 2006 are presented a surface heat flux estimated to be 400 w m 2 produced frazil ice that was advected away from the fast ice edge during the end of a polynya event driven by cold winds from the northeast conductivity temperature and depth casts from the fast ice edge of the polynya were calibrated by accompanying water samples and reveal a supercooling event that lasted for 3 days in a 5 m deep water column surface salinity reached 35 9 psu from brine release during ice growth the maximum supercooling measured was 0 037 0 005 c below the in situ freezing point near the surface and 0 016 0 005 c at the bottom the mean supercooling gradient was 0 020 0 005 c between the surface and the bottom these measurements are consistent with results from a one dimensional frazil ice model confirming that such supercooling levels can be expected frazil ice concentrations in the water were modeled to be lower than 0 02 g l 1 due to advection in the surface layer seven frazil grease ice samples taken from a place where advection was blocked along the fast ice edge showed a mean salinity of 26 2 psu indicating 25 frazil ice and 75 sea water in the grease ice the water column salinity decreased during the measurement period due to less saline water replacing newly formed brine enriched shelf water flowing down to deeper parts of storfjorden the supercooling ceased when the wind direction turned to the east with higher air temperatures and warmer and less saline water being pushed into storfjorden by the northward ekman transport these are the first in situ observations from an active arctic polynya with concurrent sampling of hydrography and frazil ice and the supercooling is the maximum observed in recent years with modern and accurate instrumentation

polynya impacts on water properties in a northeast greenland fjord abstract polynyas are an important yet poorly understood phenomena of high latitude oceans a storm event during late december 2013 with down fjord winds of up to 25 m s forced the collapse of the landfast ice over the young sound ys fjord outlet in northeast greenland this storm created a coastal polynya that was further maintained by several consecutive wind events until early march 2014 during the polynya period three landfast ice tethered oceanographic moorings recorded an enhanced surface layer 0 40 m transport towards the mouth of ys and a layer below 40 140 m flowing into the fjord and supplying the interior with cool and saline water from the polynya subsequent ctd transects in may 2014 reveal that this lower layer contained polynya originated cool saline and oxygen enriched water with oxygen concentrations significantly exceeding values from the previous summer salt balance bulk estimates show that the polynya generated a sufficient amount of brine to ventilate the fjord interior

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

diffusion controlled tracer retention in crystalline rock on the field scale 1 tracer retention is a key process for the barrier function of crystalline rock to any contaminant here we investigate the nature of retention mechanisms and their field scale parametrization using results of a comprehensive tracer transport experiment in crystalline rock on the field scale aspo hard rock laboratory sweden a method for identifying dominant retention mechanisms and inferring key parameters on the site scale is presented taking advantage of multiple tracer tests with a wide range of sorption affinities retention is shown to be diffusion controlled for the considered site robust features of tracer migration can be reasonably well predicted within a rock volume on at least 200 m scale by combining independent information with a simple model

impact of the arctic ocean atlantic water layer on siberian shelf hydrography this paper examines the role of the arctic ocean atlantic water aw in modifying the laptev sea shelf bottom hydrography on the basis of historical records from 1932 to 2008 field observations carried out in april may 2008 and 2002 2009 cross slope measurements a climatology of bottom hydrography demonstrates warming that extends offshore from the 30 50 m depth contour bottom layer temperature time series constructed from historical records links the laptev sea outer shelf to the aw boundary current transporting warm and saline water from the north atlantic the aw warming of the mid 1990s and the mid 2000s is consistent with outer shelf bottom temperature variability for april may 2008 we observed on shelf near bottom warm and saline water intrusions up to the 20 m isobath these intrusions are typically about 0 2 c warmer and 1 1 5 practical salinity units saltier than ambient water the 2002 2009 cross slope observations are suggestive for the continental slope upward heat flux from the aw to the overlying low halocline water lhw the lateral on shelf wind driven transport of the lhw then results in the bottom layer thermohaline anomalies recorded over the laptev sea shelf we also found that polynya induced vertical mixing may act as a drainage of the bottom layer permitting a relatively small portion of the aw heat to be directly released to the atmosphere finally we see no significant warming up until now over the laptev sea shelf deeper than 10 15 m in the historical record future climate change however may bring more intrusions of atlantic modified waters with potentially warmer temperature onto the shelf which could have a critical impact on the stability of offshore submarine permafrost

effective matrix diffusion in kilometer scale transport in fractured crystalline rock concentrations of tritium 3h and dichlorodifluoromethane cfc 12 in water samples taken from glacial drift and fractured crystalline rock over 4 km2 in central new hampshire are interpreted to identify a conceptual model of matrix diffusion and the magnitude of the diffusion coefficient dispersion and mass transfer to and from fractures has affected the 3h concentration to the extent that the peak 3h concentration of the 1960s is no longer distinguishable because of heterogeneity in the bedrock the sparsely distributed chemical data do not warrant a three dimensional transport model instead a one dimensional model of cfc 12 and 3h migration along flow lines in the glacial drift and bedrock is used to place bounds on the processes affecting kilometer scale transport arid model parameters are varied to reproduce the measured relation between 3h and cfc 12 rather than their spatial distributions a model of mass exchange to and from fractures that is dependent on the time varying concentration gradient at fracture surfaces qualitatively reproduces the measured relation between 3h and cfc 12 with an upper bound for the fracture dispersivity approximately equal to 250 m and a lower bound for the effective matrix diffusion coefficient equal to 1 m2 yr 1 the diffusion coefficient at the kilometer scale is at least 3 orders of magnitude greater than laboratory estimates of diffusion in crystalline rock the large diffusion coefficient indicates that diffusion into an immobile fluid phase rock matrix is masked at the kilometer scale by advective mass exchange between fractures with large contrasts in trarismissivity the measured transmissivity of fractures in the study area varies over more than 6 orders of magnitude advective mass exchange from high permeability fractures to low permeability fractures results in short migration distances of a chemical constituent in low permeability fractures over an extended period of time before reentering high permeability fractures viewed at the kilometer scale this process is analogous to the chemical constituent diffusing into and out of an immobile fluid phase

transport and retention from single to multiple fractures in crystalline rock at aspo sweden 2 fracture network simulations and generic retention model hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges neuman 2005 in this work we use

wintertime warming of an arctic shelf in response to large scale atmospheric circulation 1 observations on the west spitsbergen shelf have shown that the dynamic response of the shelf to wind forcing has a profound effect on the heat content of the water hydrographic and atmospheric data have been analysed with respect to the relative importance of surface heat fluxes and advective processes on ocean temperature during the arctic winter of 2005 06 periods of sustained along shelf winds generated upwelling and cross shelf exchange causing extensive flooding of the coastal waters with warm atlantic water from the west spitsbergen current the winter temperature of the west spitsbergen shelf reverted to that typical of fall interrupting the normal cycle of sea ice formation in the region

observations of supercooling and frazil ice formation in the laptev sea coastal polynya this paper examines a hydrographic response to the wind driven coastal polynya activity over the southeastern laptev sea shelf for april may 2008 using a combination of environmental satellite envisat advanced synthetic aperture radar asar and terrasar x satellite imagery aerial photography meteorological data and sbe 37 salinity temperature depth and acoustic doppler current profiler land fast ice edgemoored instruments when asar observed the strongest end of april polynya event with frazil ice formation the moored instruments showed maximal acoustical scattering within the surface mixed layer and the seawater temperatures were either at or 0 02 c below freezing we also find evidence of the persistent orizontal temperature and salinity gradients across the fast ice edge to have the signature of geostrophic flow adjustment as predicted by polynya models

seasonal surface layer dynamics and sensitivity to runoff in a high arctic fjord young sound tyrolerfjord 74 n runoff from the greenland ice sheet local glaciers and snowmelt along the northeastern greenland coastline has a significant impact on coastal water masses flowing south toward denmark strait very few direct measurements of runoff currently exist in this large area and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice measurements from the zackenberg research station located in young sound tyrolerfjord in northeast greenland 74 n provide some of the few observations of hydrographic hydrologic and atmospheric parameters from this remote area here we analyze measurements from the fjord and also measurements in the ambient water masses which are found in the outer fjord and between the fjord and the east greenland current and validate and apply a numerical model of the fjord a model sensitivity study allows us to constrain runoff estimates for the area we also show that a total runoff between 0 9 and 1 4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the fjord this indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the greenland ice sheet in this region may be up to 50 larger than the current estimate model simulations indicate the presence of a cold low saline coastal water mass formed by runoff from fjords north of the young sound tyrolerfjord system simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the fjord

redox fluctuations in the early ordovician oceans an insight from chromium stable isotopes abstract chromium cr stable isotopes are a useful tracer of changes in redox conditions because changes in its oxidation state are accompanied by an isotopic fractionation recent co precipitation experiments have shown that cr vi is incorporated into the calcite lattice suggesting that carbonates are a potential sink for dissolved cr in the ocean and could effectively capture the cr isotope composition of ambient seawater thus the cr isotopic composition 53cr of carbonates has the potential to record changes in the oxygenation state of ancient oceans to test the potential of this system we measured 53cr values of limestones and dolostones from an early ordovician marine carbonate platform cerro la silla section of the precordillera san juan argentina an increasing number of studies support the hypothesis that the early ordovician oceans were stratified with respect to oxygen and that the global ocean experienced multiple episodes of anoxic expansion and contraction making this time period ideal for testing the usefulness of the cr isotope system the most prominent feature of the cerro la silla cr isotope profile is a positive excursion of 0 5 during the late tremadocian accompanied by exceptionally low cr concentrations

oxidative release of chromium from archean ultramafic rocks its transport and environmental impact a cr isotope perspective on the sukinda valley ore district orissa india abstract this study investigates cr isotope fractionation during soil formation from archean 3 1 3 3 ga ultramafic rocks in a chromite mining area in the southern singhbhum craton orissa india the cr isotope signatures of two studied weathering profiles range from non fractionated mantle values to negatively fractionated values as low as 53 cr 1 29 0 04 local surface waters are isotopically heavy relative to the soils this supports the hypothesis that during oxidative weathering isotopically heavy cr vi is leached from the soils to runoff the impact of mining pollution is observed downstream from the mine where surface water cr concentrations are significantly increased accompanied by a shift to less positive 53 cr values relative to upstream unpolluted surface water a microbial mat sample indicates that microbes have the potential to reduce and immobilize cr vi which could be a factor in controlling the hazardous impact of cr vi on health and environment the positive cr isotope signatures of the brahmani estuary and coastal seawater collected from the bay of bengal further indicate that the positively fractionated cr isotope signal from the catchment area is preserved during its transport to the sea isotopically lighter cr vi downstream from the mine is probably back reduced to cr iii during riverine transport leading to similar cr isotope values in the estuary as observed upstream from the mine

impact of siberian coastal polynyas on shelf derived arctic ocean halocline waters hydrographic and stable oxygen isotope h218o h216o sampling was carried out within the west new siberian wns coastal polynyas in the southern laptev sea in late winters 2008 and 2009 the impact of sea ice formation on the water column was quantified by a salinity lower case delta 18o mass balance several stations had vertically homogeneous physical properties in april may 2008 and featured polynya formed local bottom water with elevated signals of brine released during sea ice formation and elevated fractions of river water the polynya formed bottom water was fresher than surrounding bottom waters at other stations salinity lower case delta 18o correlation showed well defined mixing lines for bottom and surface layers in march april 2009 surface waters were strongly influenced by lena river water and local polynya activity with elevated brine signals reached to intermediate depth but did not penetrate the bottom layer in the highly stratified water column inventory values of sea ice formation were comparable in both years but freshwater distributions from the preceding summers were different therefore the observed difference in the impact of polynya activity on the water column is not primarily controlled by the amount of sea ice formed during winter but by preconditioning from the preceding summer only in years when the river plume is mostly absent in the polynya region stratification is weak and allows winter sea ice formation to reach the bottom layer thus summer stratification controls the influence of local polynya water on the shelf s bottom hydrography and as bottom water is exported impacts on the source water of shelf derived halocline waters

discrete fracture network interpretation of field tracer migration in sparsely fractured rock field tracer migration in sparsely fractured rock is analyzed with a discrete fracture network model that has been calibrated on fracture and flow data from the stripa 3d experiment in sweden comparison between transport simulations in the flow calibrated discrete model and tracer tests of the field experiment confirms the fracture network parameters obtained from the flow analysis except for the variance of the fracture conductivities which had to be increased the discrete model reproduces the uneven spatial distribution of flow and tracers the complex dispersive behavior and channeling effects that have been observed in the field experiment as a result of flow channeling transport occurs along preferential paths whose transport properties may substantially deviate from the medium average properties for example porosity and wetted fracture surface area available to sorption may be reduced by almost 2 orders of magnitude compared to the medium average values

tracer attenuation in groundwater the self purifying capacity of aquifers strongly depends on the attenuation of waterborne contaminants i e irreversible loss of contaminant mass on a given scale as a result of coupled transport and transformation processes a general formulation of tracer attenuation in groundwater is presented basic sensitivities of attenuation to macrodispersion and retention are illustrated for a few typical retention mechanisms tracer recovery is suggested as an experimental proxy for attenuation unique experimental data of tracer recovery in crystalline rock compare favorably with the theoretical model that is based on diffusion controlled retention non fickian hydrodynamic transport has potentially a large impact on field scale attenuation of dissolved contaminants

significance of fracture rim zone heterogeneity for tracer transport in crystalline rock 1 conducting fractures of crystalline rock are typically altered over long periods of time the fracture rim zone a result of these alterations will as a rule have different physical and chemical properties from the unaltered fresh rock depending on various microscopic and macroscopic factors of the alterations in this paper we study the impact of rim zone heterogeneity exemplified by a decreasing porosity trend as inferred from the aspo hard rock laboratory site sweden on short and long term tracer transport our main finding is that this particular rim zone structure will have a dominant effect on transport of moderately to strongly sorbing tracers on experimental time scales and a notable effect on application time scales the findings of this work lend further support to the interpretation of the relatively strong retention reported by cvetkovic et al the fracture rim zone porosity structure may provide an additional safety margin for sorbing radionuclides in crystalline rock at sites where fracture alteration is prevalent

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

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

flow dependence of matrix diffusion in highly heterogeneous rock fractures diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties the flow dependence of matrix diffusion is quantified by a random variable transport resistance denoted as t l and computed from the flow field by following advection trajectories the numerical methodology for simulating fluid flow is mesh free using fup basis functions a generic statistical model is used for the transmissivity field featuring three correlation structures i highly connected non multi gaussian ii poorly connected or disconnected non multi gaussian and iii multi gaussian the moments of are shown to be linear with distance irrespective of the structure after approximately 10 integral scales of ln t percentiles of are found to be linear with the mean when considering all three structures taking advantage of this property a potentially useful relationship is presented between percentiles and the fracture mean water residence time that integrates all structures with high variability it can be used in discrete fracture network simulations where t statistical data on individual fractures are not available

mixing of the storfjorden overflow svalbard archipelago inferred from density overturns observations were made of the dense overflow from storfjorden from a survey conducted at closely spaced stations in august 2002 the field data set consists of conventional ctd conductivity temperature depth profiles and short term moored current meters and thermistor strings finestructure estimates were made by calculating thorpe scales over identified overturns using 0 1 dbar verticallyaveraged density profiles dissipation rate of turbulent kinetic energy per unit mass e is estimated assuming proportionality between thorpe and ozmidov length scales vertical eddy diffusivity kz is estimated using osborn s model assuming a constant mixing efficiency survey averaged profiles suggest enhanced mixing near the bottom with values of kz and e when averaged within the overflow equal to 10x10 4 m 2 s 1 and 3x10 8 w kg 1 respectively kz is found to decrease with increasing buoyancy frequency as n 1 2 0 3 albeit values of n covered only 0 5 8 cph 1 cph 2 3600 s 1 values of heat flux obtained using kz suggest that the plume gains a considerable amount of heat 45 25 w m 2 when averaged over the thickness of the plume from overlying waters of atlantic origin this value is lower than but considering the errors in estimates of kz comparable with 100 w m 2 the rate of change of heat in the overflow derived from sections across the sill and 80 km downstream

circulation and fjord shelf exchange during the ice covered period in young sound tyrolerfjord northeast greenland 74 n abstract fjords around greenland connect the greenland ice sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing runoff topography fjord shelf exchange tides waves and seasonal growth and melt of sea ice limited knowledge exists on circulation in high arctic fjords particularly those not impacted by tidewater glaciers and especially during winter when they are covered with sea ice and freshwater input is low here we present and analyze seasonal observations of circulation hydrography and cross sill exchange of the young sound tyrolerfjord system 74 n in northeast greenland distinct seasonal circulation phases are identified and related to polynya activity meltwater and inflow of coastal water masses renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale by the end of winter there is two layer circulation with outflow in the upper 45 m and inflow extending down to approximately 150 m tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the m2 tidal constituent 0 26 m s 1 and that residual currents 0 02 m s 1 were relatively small during the ice covered period tidal pumping a tidally driven fjord shelf exchange mechanism drives a salt flux that is estimated to range between 145 kg s 1 and 603 kg s 1 extrapolation of these values over the ice covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the ice covered period

stochastic simulation of radionuclide migration in discretely fractured rock near the aspo hard rock laboratory we study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network the rock volume is on a 1

sea ice production and water mass modification in the eastern laptev sea a simple polynya flux model driven by standard atmospheric forcing is used to investigate the ice formation that took place during an exceptionally strong and consistent western new siberian wns polynya event in 2004 in the laptev sea whether formation rates are high enough to erode the stratification of the water column beneath is examined by adding the brine released during the 2004 polynya event to the average winter density stratification of the water body preconditioned by summers with a cyclonic atmospheric forcing comparatively weakly stratified water column beforehand the model performance is tested through a simulation of a well documented event in april 2008 neglecting the replenishment of water masses by advection into the polynya area we find the probability for the occurrence of density driven convection down to the bottom to be low our findings can be explained by the distinct vertical density gradient that characterizes the area of the wns polynya and the apparent lack of extreme events in the eastern laptev sea the simple approach is expected to be sufficiently rigorous since the simulated event is exceptionally strong and consistent the ice production and salt rejection rates are likely to be overestimated and the amount of salt rejected is distrusted over a comparatively weakly stratified water column we conclude that the observed erosion of the halocline and formation of vertically mixed water layers during a wns polynya event is therefore predominantly related to wind and tidally driven turbulent mixing processes

fractionation behavior of chromium isotopes during coprecipitation with calcium carbonate implications for their use as paleoclimatic proxy interest in chromium cr isotope incorporation into carbonates arises from the observation that cr isotopic composition of carbonates could be used as a paleoclimate proxy to elucidate past fluctuations of oxygen contents in atmosphere and hydrosphere the use of cr isotopes to track paleoenvironmental changes for example related to the rise of oxygen during the archaean and protoerozoic needs careful assessment of the signal robustness and necessitates a thorough understanding of the cr cycle in earth system processes we conducted experiments testing the incorporation of chromate into the calcite lattice to investigate isotopic changes facilitated by the coprecipitation process our experiments indicate enrichment in cr concentration in the precipitates compared to the solutions consistent with previous reports of cr enrichment in chemical sediments compared to ambient seawater the fractionation of cr isotopes during calcium carbonate coprecipitation was assumed to be small based on previously published data of modern seawater and modern non skeletal marine carbonates however results from this study for rapidly precipitated calcium carbonate in the presence of chromate show a tendency for preferential incorporation of heavy cr isotopes in the precipitates resulting in increasing relative isotope difference between precipitate and initial solution 53cr p is from 0 06 to 0 18 with increasing initial cr concentration of the solution sample precipitation in the presence of chromate also showed the presence of vaterite calcium carbonate crystals were also precipitated in a double diffusion silica hydrogel over a longer period of time resulting in samples consisting of micrometric millimetric calcite crystals which were again significantly enriched in heavy cr isotopes compared to the initial solutions they average irrespective of the initial cr concentration a relative isotope difference 53cr p is of 0 29 0 08 2 whereas silica hydrogel samples show a preferential retention of light cr isotopes these results imply that in previous studies the 53cr seawater signals inferred from carbonates may be too positive or at lower cr concentrations typical for seawater marginal to no cr isotope fractionation can be expected this might have implications for the use of cr isotopic signals recorded in ancient marine carbonates in relation to ambient seawater and pave the way for future work to enable a reliable application of the cr isotope proxy