impact of atmospheric deposition biogeochemical cycling and water mineral interaction on ree fractionation in acidic surface soils and soil water the strengbach case leaf litter contains not only important quantities of elements derived from decomposition of organic matter but also atmospheric compounds this is illustrated by sr and nd isotope data from soils of the strengbach catchment which show that soil litter contains more than 50 of atmospheric sr and nd downward migrating soil water becomes strongly acidic during flow through litter and humus layers ph 3 8 4 at 5 10 cm depth causing not only intense mobilization of elements in the underlying acid brown and podzolic soils at depths between 10 and 50 cm but also the downward transfer of some litter derived compounds the sr and nd isotope data allow to quantify that soil water from 10 to 70 cm depth contains 45 to 65 of litter derived nd and sr sequential leaching experiments have been performed on soil samples in order to recover adsorbed trace elements or those fixed in acid soluble mineral phases such as fe mn oxyhydroxides and phosphate minerals the isotope data of these leachates of the uppermost soil horizons point similarly to the presence of important quantities of litter derived sr and nd in the uppermost 30 cm of the soils with the exception of the litter layer the soil profiles are substantially depleted in ca and p down to 50 cm depth which can be related to low apatite and plagioclase contents these minerals have probably been preferentially weathered and ca and p have been removed by percolating soil water and plant uptake leaching of primary granite derived apatite controls rare earth element ree fractionation only below 50 cm depth rhabdophane ree po4 has been observed as secondary replacement mineral of apatite this replacement is reflected by ca p ratios that are low at the surface and which increase regularly with depth implying that some of the apatite derived p has been integrated into newly formed rhabdophane and some of the p and ca have been exported either by soil solutions or plant uptake during downward transport litter derived elements are adsorbed on soil particles and or coprecipitate with authigenic minerals such as fe mn oxyhydroxide or rhabdophane alternatively litter derived elements may remain in solution or like ca be absorbed by vegetation the soil solutions from the uppermost 30 cm of the soil profiles and the corresponding soil leachates show very similar ree distribution patterns and are compared to the waters of the strengbach stream which drains the forested catchment strongly enriched in light rare earth elements lree however soil solutions from 60 to 70 cm depth are compared to litter strongly lree depleted and show stream water like ree distribution patterns it is suggested that this evolution of the ree in the soil solutions is due to the following processes taking place above 50 cm depth 1 precipitation of lree rich phosphate minerals like rhabdophane 2 diminution of the formation of organic dissolved or colloidal phases in association with fe mn and al oxyhydroxides and 3 preferential lree uptake by vegetation below 50 cm the ree distribution patterns are further modified by dissolution precipitation reactions and adsorption the combination of all these fractionation processes finally leads to the ree patterns of the strengbach stream at the catchment outlet

did antarctic sea ice expansion cause glacial co2 decline 1 recently stephens and keeling 2000 have put forward an appealing theory for explaining the decrease in glacial atmospheric co2 they argue that a compact sea ice cover extending southward of 55 s trapped large amounts of co2 beneath the sea surface thus accounting for the lower atmospheric concentrations an atmosphere ocean box model in which sea ice area is prescribed allows them to simulate 80 of the co2 drawdown however glacial co2 levels can be attained in their model only when the fraction of ice covered area southward of the antarctic polar front rises to 99 100 we present simulations with a coupled sea ice upper ocean model indicating that ice area fractions so large might have not prevailed even under rather extreme glacial conditions the combination of our glacial ice coverage estimates with the ice area co2 relation derived by stephens and keeling suggests that co2 sequestration under sea ice could account for at most 15 50 of the total glacial co2 decline

the granular sea ice model in spherical coordinates and its application to a global climate model abstract the granular sea ice model gran from tremblay and mysak is converted from cartesian to spherical coordinates in this conversion the metric terms in the divergence of the deviatoric stress and in the strain rates are included as an application the gran is coupled to the global earth system climate model from the university of victoria the sea ice model is validated against standard datasets the sea ice volume and area exported through fram strait agree well with values obtained from in situ and satellite derived estimates the sea ice velocity in the interior arctic agrees well with buoy drift data the thermodynamic behavior of the sea ice model over a seasonal cycle at one location in the beaufort sea is validated against the surface heat budget of the arctic ocean sheba datasets the thermodynamic growth rate in the model is almost twice as large as the observed growth rate and the melt rate is 25 lower than observed the larger growth rate is due to thinner ice at the beginning of

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

probing silicate weathering reactions in soils with b isotopes abstract the determination of the mechanisms and extent of soil mineral weathering can be challenging and the caveats reside in 1 difficulty identifying minerals that are actually involved in weathering reactions 2 non stoichiometric release of cations during weathering processes due to coupled dissolution precipitation and transformation reactions and 3 impact of vegetation activity on elemental cycles in upper soil horizons to better characterize mechanisms controlling mineral weathering in soils and trace the evolution of b concentration and isotope ratios during chemical weathering quantitative mineralogical analyses were coupled to b isotopes in a group of minerals biotite muscovite k feldspar and albite samples were selected along an alocrisol alumic cambisol wrb fao soil profile from the bedrock at 130 cm depth up to 20 cm depth developed on granitic bedrock in the breuil chenue forest france the samples consist of residual primary minerals associated with weathering secondary phases vermiculite kaolinite in varying proportions the b isotopic compositions of the most pristine minerals span a very narrow range of values around 31 whereas all secondary phases point to a much heavier value around 16 regardless of mineralogy our results also show a mineral dependent evolution of b concentration or isotopic composition as weathering progresses no variation is observed during dissolution of k feldspars b behaves like a very mobile element in micas biotite and muscovite whereas it concentrates in weathered products derived from albite however rates of b concentrations and changes in isotopic compositions appear to be much faster than those inferred from mineralogy or major element concentrations determined by xrd and bulk chemical analyses respectively these results indicate that b is involved in very early weathering reactions and raises the question of its actual location in the structure of the various soil minerals as well as its pathway to solution

a theoretical model coupling chemical weathering and physical erosion in landslide dominated landscapes a current theory that links the uplift of the himalayas to the drawdown of atmospheric co2 assumes that rates of chemical weathering are enhanced by accelerated physical erosion due to the increased exposure of fresh minerals although several studies have concluded that weathering rates do increase with erosion rates there is disagreement over the form of that relationship some find a linear relationship between weathering rate and erosion rate others however find that weathering is only approximately proportional to the square root of physical erosion such that changes in erosion rate are not matched by equivalent changes in weathering rate defining the nature of the relationship is critical because it determines the sensitivity of changes in weathering rate to changes in erosion rate in this study a theoretical model that couples erosion by landslides with chemical weathering processes was derived to explore the nature of this relationship in rapidly eroding landscapes results from the model suggest that where landsliding is the dominant erosional process the rate of chemical weathering is only proportional to the erosion rate raised to the 0 6 power therefore even if weathering rate is wholly dependent on erosion rate increases in erosion will not be matched by equivalent increases in chemical weathering 2007 elsevier b v all rights reserved

regolith formation rate from u series nuclides implications from the study of a spheroidal weathering profile in the rio icacos watershed puerto rico abstract a 2 m thick spheroidal weathering profile developed on a quartz diorite in the rio icacos watershed luquillo mountains eastern puerto rico was analyzed for major and trace element concentrations sr and nd isotopic ratios and u series nuclides 238 u 234 u 230 th 226 ra in this profile a 40 cm thick soil horizon is overlying a 150 cm thick saprolite which is separated from the basal corestone by a 40 cm thick rindlet zone the sr and nd isotopic variations along the whole profile imply that in addition to geochemical fractionations associated to water rock interactions the geochemical budget of the profile is influenced by a significant accretion of atmospheric dusts the mineralogical and geochemical variations along the profile also confirm that the weathering front does not progress continuously from the top to the base of the profile the upper part of the profile is probably associated with a different weathering system lateral weathering of upper corestones than the lower part which consists of the basal corestone the associated rindlet system and the saprolite in contact with these rindlets consequently the determination of weathering rates from 238 u 234 u 230 th 226 ra disequilibrium in a series of samples collected along a vertical depth profile can only be attempted for samples collected in the lower part of the profile i e the rindlet zone and the lower saprolite similar propagation rates were derived for the rindlet system and the saprolite by using classical models involving loss and gain processes for all nuclides to interpret the variation of u series nuclides in the rindlet saprolite subsystem the consistency of these weathering rates with average weathering and erosion rates derived via other methods for the whole watershed provides a new and independent argument that in the rio icacos watershed the weathering system has reached a geomorphologic steady state our study also indicates that even in environments with differential weathering such as observed for the puerto rico site the radioactive disequilibrium between the nuclides of a single radioactive series here 238 u 234 u 230 th 226 ra can still be interpreted in terms of a simplified scenario of congruent weathering incidentally the u th ra disequilibrium in the corestone samples confirms that the outermost part of the corestone is already weathered

ice deformation near sheba 1 the deformation rate of sea ice is a key parameter for determining the evolution of the ice thickness distribution it determines the rate of new ice formation through opening and the rate of ridging through closing and shear an extensive suite of ground based and satellite based measurements of ice motion is used to construct a daily time series of the ice velocity and deformation in the vicinity of the surface heat budget of the arctic ocean sheba ice camp that is suitable for forcing a model of the ice thickness distribution the velocity is interpolated to a square grid that remains centered on the camp has a spacing of 25 km is 400 km on a side and is determined for a 371 day period from 2 october 1997 to 7 october 1998 velocity measurements from buoys advanced very high resolution radiometer avhrr special sensor microwave imager ssmi and radarsat geophysical processing system rgps are merged using optimal interpolation and a kalman filter approach the deformation rate is taken directly from the rgps measurements when available the daily total deformation rate measured on a scale of 100 km near the camp averaged 2 21 d 1 and the standard deviation was 1 78 d 1 the divergence was positive in the early winter and negative through most of the spring and summer there were two major opening closing events one in january and one at the end of july the net divergence over the year was very near zero the vorticity indicated a net rotation of 87 over the year with the winter showing strong anticyclonic turning and the summer showing strong cyclonic turning

a random discontinuous model of sea ice motion the rate at which the sea ice pack spreads apart exposing the warm ocean to the cold atmosphere controls the air sea heat exchange in the arctic and the production of ice mass the rate of spreading or opening can be estimated from observations of ice motion using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces in a region intersected by many cracks some cracks will typically be opening while others are closing in this case the total of the openings will exceed the average divergence of the region a few measurements of the ice motion cannot resolve the openings at each crack so that any estimate of opening will be accompanied by estimation errors the random model adopted here imagines the leads to be distributed according to the poisson distribution and the relative displacements at any crack to be gaussian under these assumptions it is determined how the total opening is related to the average deformation and how this relationship depends on the size of the region and on the number of points used to determine the average deformation

sources of weathering derived solutes in two granitic catchments with contrasting forest growth chemical weathering is one of the controlling factors for landform evolution here we present deductions about the location and rate of chemical weathering within catchments based on chemical observations of soil water groundwater springs and streams in two granitic catchments with contrasting forest growth conditions forested and non vegetated and soil development the two catchments are located in the tanakami mountains of central japan and share the same climate in both catchments sio2 and na are the dominant weathering derived solutes in the first order stream using hydrological evidence the contribution to the sio2 and na fluxes from soil and bedrock were partitioned despite the difference in mean soil depth net fluxes of sio2 and na from the soil profile do not differ much between the two catchments suggesting low levels of easily weatherable minerals in the forest soil net sio2 and na fluxes from bedrock are about three times greater in the forested catchment than in the bare catchment and these differences contribute largely to the difference in net fluxes from the catchments net fluxes of sio2 and na from the forested catchment are about twice those from the bare catchment part of this increase may be related to the greater proton production in forested catchment consequently about 60 to 70 of the net sio2 and na fluxes from the non vegetated catchment and 70 to 90 from the forested catchment are derived from bedrock suggesting that the contribution of bedrock to the export of these weathering products increased with forest growth and soil formation copyright 2004 john wiley sons ltd

observing the yield curve of compacted pack ice 1 a method for observing the yield curve of compacted pack ice is developed based on the characteristic analysis of the stress field within the pack ice the analysis shows that the slope of the yield curve is associated with the angle between intersecting linear kinematic features thus by measuring the intersection angles we can inversely estimate the yield curve applying this method to the observed angles generates a curved diamond yield curve which possesses almost all the advantages identified by the other methods however due to the limited data available more observations are favored to refine this yield curve

contrasts in sea ice deformation and production in the arctic seasonal and perennial ice zones 1 four years 1997 2000 of radarsat geophysical processor system rgps data are used to contrast the sea ice deformation and production regionally and in the seasonal siz and perennial piz ice zones ice production is of seasonal ice in openings during the winter three day estimates of these quantities are provided within lagrangian elements initially 10 km on a side a distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter regional divergence over the winter could be up to 30 spatially the highest deformation is seen in the siz north of coastal alaska both ice deformation and production are higher in the siz deformation related ice production in the siz 0 5 m is 1 5 2 3 times that of the piz 0 3 m this is connected to ice strength and thickness atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability seasonal ice growth in ice fractures accounts for 25 40 of the total ice production of the arctic ocean uncertainties in these estimates are discussed by itself this deformation ice production relationship could be considered a negative feedback when thickness is perturbed however the overall effect on ice production in the face of increasing seasonal and thinner weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones

large scale comparison between buoy and ssm i drift and deformation in the eurasian basin during winter 1992 1993 a method for comparing sea ice velocity divergence and shear at the large scale between buoys and special sensor microwave imager ssm i is presented for initial testing the method is applied in the eurasian basin because of its relatively simple circulation dominated by the wind using eight argos buoys 11 strain rate arrays 100 600 km in size are constructed daily 100 km resolution sea ice motion derived from ssm i 85 ghz brightness temperatures is sampled 100 1000 km from the center of the buoy arrays over this range of possible scales a minimum rms difference rmsd for deformation is used to identify an optimal inclusion radius of 600 km corresponding to a length scale of 1000 km this length scale is typical of local storms confirming a strong connection between wind and observed sea ice motion on the basis of all 11 arrays an average rmsd of 2 48 0 05 cm s 1 for velocity vector and 8 8 0 9 10 8 s 1 using all four deformation components ui j is found at the optimal inclusion radius corresponding to average correlation coefficients of 0 896 0 002 and 0 729 0 030 respectively rmsd are found to scale with the temporal and spatial uncertainties of the ssm i suggesting that even better results can be achieved with higher resolution instruments

rapid and widespread dispersal of flood sediment on the northern california margin the dispersal of flood sediment from small river systems is a poorly studied yet potentially important aspect of active continental margin sedimentation in january 1995 during a flood with a 30 yr return period the eel river northern california delivered an estimated 25 3 106 t metric tons of fine grained 62 m sediment to the ocean the flood formed a distinct layer on the sea bed that was centered on the 70 m isobath extended for 30 km along shelf and 8 km across shelf and was as thick as 8 5 cm but contained only 6 106 t of sediment thus 75 of the flood derived sediment did not form a recognizable deposit but was instead rapidly and widely dispersed over the continental margin stratigraphic models of and compilations of sediment flux to active continental margins need to take the dispersive nature of small river systems into account

the architecture of an anisotropic elastic plastic sea ice mechanics constitutive law the architecture for a new large scale anisotropic constitutive law intended for use in a sea ice dynamics model is presented here this architecture accounts directly for refrozen lead systems in the pack ice strength with an anisotropic failure surface and in the ice thickness distribution with an oriented thickness distribution the lower limit 5 km of the model resolution is controlled by the fracture spacing of old thicker ice and the maximum lead width the upper limit of the model resolution 100 km is controlled by curvature in the lead directions and variations in the lead width these in turn are controlled by the variations in internal ice stress due to driving forces winds and currents which set the time resolution this architecture features abrupt changes in the failure surface and the associated flow rule that cannot be averaged over a time step in addition the principal stress normal to a new lead must be zero as it opens this model has subscale simulations that allow for the inclusion of phenomena such as ridging rafting buckling and fracture on the behavior of the ice with this new ice constitutive law it is possible to test directly the ice failure strength plastic flow rule and ice thickness distribution the data most useful for this testing come from ice stress and position buoys together with synthetic aperture radar deformation data some data comparisons have already been made

comparisons of sea ice velocity fields from ers 1 sar and a dynamic model numerical models for sea ice thickness distribution and velocity are used for ice dynamics research and ice forecasting in the modeling work ers 1 sar is an excellent tool in particular by providing spatial ice velocity fields as described in the present baltic sea study ice velocities were extracted from sar data with 3 and 6 day time intervals using the optical flow method a considerable stiffening of the ice pack was observed due to the change in the character of ice deformation under compression from rafting to ridging as the minimum ice thickness increased from 10 to 3o cm the coastal alignment was strong in the ice motion and the coastal boundary layer width was 20 30 km an analysis of the sar data with an ice dynamics model showed that the observed overall ice velocity field could be produred using the hibler viscous plastic ice rheology the compressive strength of the ice over 10 km sc ales was 2 5x 10 4 n m 2 50 for ridging and negligible for rafting of very thin ice the shear strength was significant and the normal yield ellipse aspect ratio of 2 was valid the 3 day time interval is val id for updating an ice model but for detailed ice dynamics investigations a data frequency of 1 d 1 or higher would be preferable

seasonal ice area and volume production of the arctic ocean november 1996 through april 1997 1 the radarsat geophysical processor system rgps produces estimates of sea ice motion deformation and thickness of the arctic ocean sea ice cover from time sequential synthetic aperture radar sar imagery acquired by radarsat based on these products we summarize the evolution of a region of the arctic ocean ice cover in terms of its area change ice volume production and multiyear ice coverage over a 6 month period between 7 november 1996 through 30 april 1997 this region encompasses a large part of the western arctic ocean the initial ice area covers 2 52 106 km2 at the end of april this region covers 2 59 106 km2 a net divergence of 3 over the period thin ice 0 20 cm typically covers 2 of this area the rgps estimates only the thickness distribution of sea ice volume produced by openings and closings of the ice cover since the initial observation thus only the ice volume of the seasonal ice cover can be determined between november 1996 and april 1997 1000 km3 0 4 m of sea ice is produced the amount stored in undeformed ice and ridged ice is dependent on the character of the redistribution function the rgps products also provide estimates of multiyear ice coverage from the time series of multiyear ice coverage we estimate that nearly 83 of the area is covered by multiyear ice for more detailed examination of the regional dependence of ice cover deformation volume production and my ice coverage the larger region is divided into five subregions where possible we provide an analysis of the errors in the above estimates in cases where quantification of the uncertainty is not feasible we list the potential error sources there are remaining sources of uncertainty in these calculations that remain unquantified but at this time there are no adequate in situ or remote sensing data for comprehensive evaluation of the above estimates

234u 238u activity ratios in freshwaters as tracers of hydrological processes the strengbach watershed vosges france abstract 234u 238u and 87sr 86sr isotopic ratios as well as major and trace u ba sr rb element concentrations were analyzed in dissolved loads of the strengbach stream vosges france in order to constrain the sources of u isotopes 234u 238u to river waters the variations of the 234u 238u activity ratios along the stream indicate a clear dependence between the 234u 238u activity ratios of the surface waters and the different types of rocks forming the watershed with near equilibrium values for the waters draining granites and high 234u 238u disequilibria 1 4 for those flowing over carbonates the high 234u 238u disequilibria are related to a supply of 234u enriched groundwaters located within the carbonate rocks the 234u 238u activity ratios of the waters at the outlet of the catchment collecting the sources of the stream on the granitic lithology decrease from 1 02 to 0 96 when the discharge of the stream increases such a tendency requires mixing between a water body enriched in 234u which weathered the granitic bed rock at secular equilibrium and a water with a 234u 238u activity ratio below unity representing a mobilization of u from material that has already been weathered comparison of the geochemical characteristics of waters collected during the year and those collected during a flood event reveals the involvement of two different weathered end members depending on the hydrological conditions during the year the dissolved u transported by the river originates from bed rock and deep horizons of the weathering profile whereas a significant part of u during the flood event is supplied by superficial horizons of soils probably complexed by organic colloids these results outline the potential of 234u 238u activity ratios to investigate hydrological processes and emphasize that their use as tracers of rock weathering should be made cautiously

early cenozoic crust at the norwegian continental margin and the conjugate jan mayen ridge multichannel seismic profiles at the voring plateau margin off norway and the northern jan mayen ridge have provided a framework for the early tertiary evolutionary history of these areas which were adjacent prior to the opening of the norwegian sea we propose that their paleogene evolution is quite similar and that the two acoustic basement reflectors ee and jo were formed in the early eocene by extrusion of flow basalts from the time of opening to about anomaly 23 time oceanic seafloor was generated by icelandic type spreading during that time the central jan mayen fracture was the main transform the seaward dipping reflector sequences are flow basalts generated by the icelandic spreading the existence of less well developed dipping sequences seaward of the primary ones probably reflects that these regions submerged later because of higher initial elevation during the early eocene subaerial spreading episode which is related to the north atlantic volcanic province basalt flows also covered the adjacent thinned and heavily intruded continental crust it is proposed that the continent ocean boundary is located just landward of anomaly 24b a short distance seaward of the voring plateau escarpment reflector k is only recognized landward of this boundary in a region of transitional crust the escarpment experienced syndepositional faulting and the most elevated parts of the voring marginal high did not subside below shallow water depths before oligocene miocene time we suggest that the voring margin and the jan mayen ridge represent volcanic passive margins the evolution of this margin type may relate to initial uplift due to rifting in previously thinned crust

influence of acid atmospheric inputs on surface water chemistry and mineral fluxes in a declining spruce stand within a small granitic catchment vosges massif france abstract the characteristics of surface and soil waters draining an old declining spruce stand and their chemical behaviour under acid input influence within a small catchment are described using open field precipitations throughfalls soil solutions spring and streamwater data element fluxes are calculated in the different ecosystem compartments and the proton mass balance has been assessed the results show the importance of acid occult deposits and more generally of acid atmospheric inputs in explaining present soil acidification this acidification is characterized by the base cation deficiencies observed in spruce thereby showing symptoms of decline however stream waters and spring waters are not yet acidified owing to the neutralization of acid inputs by weathering in the regolith nevertheless streamwater chemistry is dominated by strong acid anions which are not characteristic of waters draining granitic bedrock in pristine areas

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

regolith evolution on the millennial timescale from combined u th ra isotopes and in situ cosmogenic 10be analysis in a weathering profile strengbach catchment france abstract u th ra disequilibria cosmogenic in situ 10be concentrations and major and trace element concentrations have been analyzed in a 2 m deep weathering profile sampled at the summit of the granitic strengbach catchment france the data have been used to independently estimate both the long term regolith production and denudation rates and the weathering and erosion rates modeling of the 238u 234u 230th 226ra disequilibrium variations in the lower part of the profile yields a regolith production rate of 12 4 mm kyr 30 10 t km2 yr while modeling of the high resolution 10be concentration profile leads to an exposure age of 19 7 2 2 kyr an inherited concentration of 15 000 1 000 at g in quartz and a mean denudation rate of 22 10 mm kyr 37 15 t km2 yr the consistency between production and denudation rates suggests that on a millennial timescale the regolith mass balance at the summit of the catchment is close to a steady state even if the watershed may have been impacted by quaternary climatic changes and by recent anthropogenic perturbations e g 20th century acid rain and recent afforestation efforts the results also indicate that physical erosion is likely the dominant long term process of regolith denudation in the catchment furthermore the comparison of the long term production and denudation rates and of weathering and erosion rates determined from the depth profile analyses with the current weathering and erosion rates estimated at the outlet of the watershed based on monitoring of the water chemistry and sediment fluxes suggests that physical erosion may have varied more than the chemical weathering flux during the last 150 kyr although very few other sites with u series in situ 10be and stream monitoring data are available for comparison the current data suggest that 1 the mass balance steady state of regolith might be commonly achieved in soil mantled landscapes and 2 physical erosion has varied much more than chemical weathering in mid mountain catchments over the last 10 150 kyr these results highlight the importance of the combined analysis of u series nuclides and in situ 10be in the same weathering profile for the determination of key geomorphic parameters which are important to constraining landscape stability and the responses of landscapes to natural or anthropogenic forcing

sea ice type maps from alaska synthetic aperture radar facility imagery an assessment synthetic aperture radar sar imagery received at the alaska sar facility is routinely and automatically classified on the geophysical processor system gps to create ice type maps we evaluated the wintertime performance of the gps classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm the rms difference for multiyear ice is about 6 while the inconsistency in supervised classification is about 3 the algorithm separates first year from multiyear ice well although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first year ice distribution maps these results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the arctic

hydrograph separation using isotopic chemical and hydrological approaches strengbach catchment france the streamflow components were determined in a small catchment located in eastern france for a 40 mm rain event using isotopic and chemical tracing with particular focus on the spatial and temporal variations of catchment sources precipitation soil solution springwater and streamwaters were sampled and analysed for stable water isotopes 18o and 2h major chemical parameters so42 no3 cl na k ca2 mg2 nh4 h h4sio4 alkalinity and conductivity dissolved organic carbon doc and trace elements al rb sr ba pb and u 18o si doc ba and u were finally selected to assess the different contributing sources using mass balance equations and end member mixing diagrams isotopic hydrograph separation shows that the pre event water only contributes to 2 at the beginning of the stormflow to 13 at the main peak flow doc associated to si and u to ba allow to identify the different contributing areas upper layers of the saturated areas deep layers of the hillslope and rainwater the streamflow 70 originates from the deep layers of the hillslope the remaining being supplied by the small saturated areas the combination of chemical both trace and major elements and isotopic tracers allows to identify the origin of water pathways during the first stage of the storm event a significant part of the runoff 30 39 comes from the small extended saturated areas located down part of the basin overland runoff then groundwater ridging during the second stage the contribution of waters from the deep layers of the hillslope in the upper subcatchment becomes more significant the final state is characterised by a balanced contribution between aquifers located in moraine and downslopes indeed this study demonstrates the interest of combining a variety of hydrometric data geochemical and isotopic tracers to identify the components of the streamwater in such conditions

boron isotopes in different grain size fractions exploring past and present water rock interactions from two soil profiles strengbach vosges mountains abstract in the present study we test the ability of b isotopes to trace past and present weathering reactions in the case of two forest soils formed by a polyphasic sequence involving early hydrothermal alteration of the bedrock and pedogenesis we provide b chemical and isotopic compositions in two 2 m soil profiles sampled in the strengbach watershed vosges france the two soils belong to different soil series an ochreous podzol haplorthod and a brown acidic soil dystrochrept developed on the same granitic bedrock but differently affected by hydrothermal alteration separated granulometric fractions and bulk soil samples have been analyzed coarse particles are mostly composed of primary minerals and show a clear anti correlation between 11 b and mg al reflecting various grades of the early hydrothermal alteration the finest particles clay size fractions deviate from this hydrothermal trend and are diagnostic of pedogenic processes occurring after b exchange with the surrounding 11 b rich soil solution examination of the b distribution in different particle size fractions also indicates that b is transferred from the coarse sand fraction in deeper soil layers to the clay fraction in the upper layers the intermediate size fractions are found to play only a secondary role in the soil forming reactions the two soils show distinct b isotope profiles which are consistent with the different pedogenic processes that govern their formation in the podzolic soil 11 b can be explained by a simple model in which pedogenesis occurs by continuous dissolution of primary minerals and precipitation of secondary ones in the brown acid soil a more complex model that includes the precipitation of clay minerals in the deep horizon and their gradual dissolution in the upper soil layers accounts for the observed results additionally residual hydrothermal illites are more resistant to weathering and are found in the clay fraction where they were directly inherited from the dislocation of coarser grains in which they were encapsulated on a broader scale the large b isotopic fractionation during water rock interactions greatly facilitates the quantification of matter exchange between soil solutions and solids and the determination of global weathering rates the data from the present study demonstrate that the determination of b isotopes in different particle size fractions can reveal the relative importance of source and process effects during weathering

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

geochemical and isotopic sr u monitoring of soil solutions from the strengbach catchment vosges mountains france evidence for recent weathering evolution abstract this study presents the results of a geochemical and isotope u and sr study of soil solutions from two experimental sites in the strengbach catchment one under spruce trees and the other under beech trees the soil solution data combined with the data from soil and vegetation samples indicate that the dissolved u filtered to 0 45 m in the soil solutions is primarily of lithogenic origin implying that the colloidal u is secondarily associated with organic matter or organo metallic complexes present in the soil solutions the uranium activity ratios and sr isotope ratios of soil solutions are used to decipher the nature of the minerals that control the lithogenic contribution to the soil solutions a comparison of soil solution data collected over the period 2004 2006 with those collected over the period 1993 2010 indicates a decrease in the ca and k exported by the soil solutions between 1998 and 2004 at the spruce site and a significantly smaller decrease at the beech site in addition the sr isotope ratios of the soil solutions vary significantly between these two periods at the spruce site but not or much less at the beech site such observations suggest that the forest ecosystem at the spruce site is in a transient state associated with recent changes in weathering reactions the data also suggest that the comparison of u and sr isotopes in soil solutions and plant samples could be a relevant method for determining whether a forest ecosystem is in a steady or transient state

open water production in arctic sea ice satellite measurements and model parameterizations sequential synthetic aperture radar sar images from the ers 1 spacecraft were routinely used as input to the geophysical processor system at the alaska sar facility from 1992 through 1994 to produce sea ice displacement vectors on a 5 km grid we have combined some 5000 of these products consisting of nearly 700 000 displacement vectors into a set of 914 strips or mosaics of ice motion that span mostly 3 day intervals for each strip we compute the opening and closing of leads based on the change in area of the 5 km grid cells we also compute the area averaged deformation or strain invariants of the motion the small scale several kilometer lead activity can be parameterized fairly well in terms of the large scale several hundred kilometer strain invariants sea ice models implicitly contain such a parameterization through their constitutive equations the well known model of hibler 1979 that uses a viscous plastic rheology and an elliptical yield curve is in good agreement with our data the variance in the data about this theoretical relationship is less than that suggested by a random model of sea ice motion the data also indicate that shearing deformation contributes to the opening and closing of leads models with two categories or levels of ice thickness generally do not take shearing deformation into account in the evolution of the ice concentration nor do they redistribute ice as a result of ridging we show how to add these features to two level models however we argue that three level models consisting of open water thin ice and thick ice are much better suited to the proper treatment of open water production and we present such a model

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

ice atmosphere interactions during sea ice advance and retreat in the western antarctic peninsula region 1 the seasonal evolution of sea ice extent concentration and drift in the western antarctic peninsula wap region along with regional atmospheric synoptic variability are described for a winter period 1992 when sea ice advance and retreat were both anomalously early daily time series of winds opening and closing of the sea ice cover and volume fluxes in and out of the wap region indicate that synoptic variability in meridional winds determines whether the ice edge advances or retreats on daily to weekly timescales the importance of this finding is that the dynamics as opposed to the thermodynamics initiate and thereby dominate in the production of ice edge anomalies further the abrupt mid winter shift from persistently positive to negative ice edge anomalies indicates that there was a distinct change in the regional atmospheric circulation the ice atmosphere interactions in the winter of 1992 are then compared to those in the winter of 1990 when sea ice advance and retreat were both late instead of early but again the mid winter shift was abrupt the comparison highlights possible circumpolar and tropical polar atmospheric linkages in the south pacific that involve changes in the amplitude phase of the semi annual oscillation sao which in turn appear

identification of sea ice types in spaceborne synthetic aperture radar data an approach for identification of sea ice types in spaceborne synthetic aperture radar sar image data is presented the unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look up tables containing the expected backscatter signatures of different ice types measured by land based scatterometer the particular look up table used for labeling a segmented image is selected based on the seasonal and meteorological conditions at the time of data acquisition the extensive scatterometer observations and experience accumulated in field campaigns during the last 10 years were used to construct these look up tables these tables are expected to evolve as sea ice observations from the european ers 1 sar become available this paper presents the classification approach its expected performance the dependence of this performance on radar system performance and expected ice scattering characteristics results using both aircraft and simulated ers 1 sar data are presented the results are compared to limited field ice property measurements and coincident passive microwave imagery an algorithm based on this experimental approach has been implemented in the geophysical processor system at the alaska sar facility for classification of sea ice data in ers 1 c band sar data the importance of an integrated postlaunch program for validation and improvement of this approach is discussed

a 5 year satellite climatology of winter sea ice leads in the western arctic the distribution of openings leads and polynyas in polar sea ice is not well known this study estimates the large scale distribution and variability of leads in the arctic of the western hemisphere in winter using a 5 year record of defense meteorological satellite program thermal and visible band imagery the occurrence density and orientation of leads are derived from gridded maps made at 10 day intervals their mean value and interannual seasonal and monthly variabilities are estimated lead densities are observed to be highest in early winter decreasing 20 from november through april the highest densities are observed in the central canada basin and the lowest are in the east siberian sea there is limited interannual variability in the positions of maximum and minimum densities preferred lead orientations are identified as generally north south in the beaufort sea sector and east west in the east siberian sea sector with transitional orientations in the intermediate area the mean distributions of lead density and orientation are observed to be associated with large scale mean fields of ice divergence and shear respectively

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

the relation between ice deformation oceanic heat flux and the ice thickness distribution in the arctic ocean a one dimensional ocean model coupled with an ice model where the ice cover is partitioned into a number of thickness categories is used to investigate how the ice thickness distribution in the arctic ocean depends on the two deformation processes export net divergence and ridging the model standard case generates vertical profiles of temperature salinity and an ice thickness distribution similar to the observations the standard case oceanic heat flux agrees well with recently deduced heat fluxes from arctic ice dynamics joint experiment aidjex data the oceanic heat flux is about 18 w m 2 during summer and about 1 w m 2 during winter it is found that the mean ice thickness decreases with increasing ice export in close agreement with other investigations however the dependence of the mean ice thickness on ridging activity is found to be very weak the change of the mean ice thickness is only 12 cm when increasing the ridging activity in the model from 0 to 0 4 yr 1 where the larger value represents an estimate of the actual ridging activity in the arctic ocean in a sensitivity study different types of ridging and albedo parameterizations are tested and this weak dependence is found to be very robust other properties of the model ice cover are sensitive to ridging though the equilibrium thickness of undeformed ice decreases with both export and ridging activity the annual maximum open water fraction and the amplitude of the seasonal thickness variation increases with export and ridging

failure envelope of first year arctic sea ice the role of friction in compressive fracture 1 new experiments have been performed on the brittle compressive failure of columnar grained first year sea ice with the s2 growth texture harvested from the floating cover on the arctic ocean the ice was proportionally loaded biaxially across the columns at 10 c at 1 5 10 2 s 1 i e within the regime of brittle behavior the results when combined with earlier measurements of tensile strength by richter menge and jones 1993 allow the complete brittle failure envelope to be constructed the envelope is symmetric about the loading path r 2 1 1 owing to the isotropic character of the material within the horizontal plane of the ice sheet but is asymmetric with respect to the compressive compressive and tensile tensile quadrants owing to the relative weakness of the material under tension the compressive strength reaches a maximum along the loading path r 0 5 terminal failure occurs through either splitting unconfined loading coulombic shear faulting under lower confinement r 0 2 or spalling under higher confinement 0 2 r 1 an integral component of compressive failure under low confinement is the internal friction coefficient its value under the conditions of the experiments i 0 92 0 09 is deduced from the failure envelope the internal friction coefficient is shown through postterminal failure measurements to be closely similar to the coefficient of friction at the onset of sliding along the coulombic faults granite exhibits similar behavior modeling reveals that the terminal failure stress under low confinement can be reasonably well described in terms of the comb crack mechanism schulson et al 1999 renshaw and schulson 2001 of brittle compressive failure comparison with observations and measurements in the field indicate that the failure processes that operate on the smaller scale are similar to at least some of those that operate on the larger scale implying that the physics of failure may be scale independent

symmetric conjugation of continent ocean boundary structures along the norwegian and east greenland margins abstract a characteristic structural feature of the norwegian continental margin that has been described from multichannel seismic data as well as dsdp and odp drilling is a major buildup of layered extrusive basaltic rocks forming wedges that dip seaward along the entire margin models for their origin describe them as either products of a late stage intra continental rift phenomenon with the volcanic rocks overlying attenuated continental crust or as an integral component of the oceanic crust formed during the first few million years of seafloor spreading in the norwegian greenland sea from studies of the norwegian margin alone it was not possible to unequivocally distinguish between the two proposed models so an investigation of the conjugate portions of the east greenland margin was undertaken which used two ship multichannel seismic acquisition as its focus we found that the wedges were not only present on the east greenland margin but that details of their along strike variability are mirrored on both margins together with their spatial relationship to the oldest magnetic lineation pattern the wedges are relatively small in the northern part of the margin where they occur almost entirely landward of lineation 24 moving south we see that the wedges broaden encroach into the pattern of lineation 24 then develop into two separate wedges the seaward of which is associated with lineation 23 lineations 24 and 23 on both margins are distorted when associated with wedges we believe that these data lend strength to a tectonic association of the wedges with nascent plate boundary processes their observation in many margins throughout the world suggest that a prolific volcanic phase may be commonly associated with the inception of a divergent plate boundary and we believe that the most likely mechanism to generate the excess volcanism is the convective partial melting scheme recently proposed by mutter and buck 1986 and mutter et al in press

determination of the age distribution of sea ice from lagrangian observations of ice motion a procedure for monitoring the local age distribution of the arctic sea ice cover is presented the age distribution specifies the area covered by ice in different age classes in our approach a regular array of grid points is defined initially on the first image of a long time series and an ice tracker finds the positions of those points in all subsequent images of the series these lagrangian points mark the corners of a set of cells that move and deform with the ice cover the area of each cell changes with each new image or time step a positive change indicates that ice in a new age class was formed in the cell a negative change is assumed to have ridged the youngest ice in the cell reducing its area the ice in each cell ages as it progresses through the time series the area of multiyear ice in each cell is computed using an ice classification algorithm any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first year ice we thus have a fine age resolution in the young end of the age distribution and coarse resolution for older ice the age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing degree days and ice thickness or using a more complicated thermodynamic model we describe a general scheme for implementing this procedure for the arctic ocean from fall freeze up until the onset of melt in the spring the concept is illustrated with a time series of five ers 1 sar images spanning a period of 12 days such a scheme could be implemented with radarsat sar imagery to provide basin wide ice age and thickness information

modeling sea ice as a granular material including the dilatancy effect abstract a dynamic sea ice model based on granular material rheology is presented the sea ice model is coupled to both a mixed layer ocean model and a one layer thermodynamic atmospheric model which allows for an ice albedo feedback land is represented by a 6 m thick layer with a constant base temperature a 10 year integration including both thermodynamic and dynamic effects and incorporating prescribed climatological wind stress and ocean current data was performed in order for the model to reach a stable periodic seasonal cycle the commonly observed lead complexes along which sliding and opening of adjacent ice floes occur in the arctic sea ice cover are well reproduced in this simulation in particular shear lines extending from the western canadian archipelago toward the central arctic often observed in winter satellite images are present the ice edge is well positioned both in winter and summer using this thermodynamically coupled ocean ice atmosphere model the results also yield a sea ic

lithium isotope systematics in a forested granitic catchment strengbach vosges mountains france abstract over the last decade it has become apparent that li isotopes may be a good proxy to trace silicate weathering however the exact mechanisms which drive the behaviour of li isotopes in surface environments are not totally understood and there is a need to better calibrate and characterize this proxy in this study we analysed the li concentrations and isotopic compositions in the various surface reservoirs soils rocks waters and plants of a small forested granitic catchment located in the vosges mountains strengbach catchment france ohge http ohge u strasbg fr li fluxes were calculated in both soil profiles and at the basin scale and it was found that even in this forested basin atmospheric inputs and litter fall represented a minor flux compared to input derived from the weathering of rocks and soil minerals which together represent a minimum of 70 of dissolved li li isotope ratios in soil pore waters show large depth dependent variations average dissolved 7 li decreases from 1 1 to 14 4 between 0 and 30 cm but is 30 7 at 60 cm this range of li isotopic compositions is very large and it encompasses almost the entire range of terrestrial li isotope compositions that have been previously reported we interpret these variations to result from both the dissolution and precipitation of secondary phases large isotopic variations were also measured in the springs and stream waters with 7 li varying from 5 3 to 19 6 7 li increases from the top to the bottom of the basin and also covaries with discharge at the outlet these variations are interpreted to reflect isotopic fractionations occurring during secondary phase precipitation along the water pathway through the rocks we suggest that the dissolved 7 li increases with increasing residence time of waters through the rocks and so with increasing time of interaction between waters and solids a dissolution precipitation model was used to fit the dissolved li isotopic compositions it was found that the isotopic compositions of springs and stream waters are explicable by an isotopic fractionation of 5 to 14 best fit 10 8 in agreement with li incorporation into clay in soil solutions it was found that isotopic fractionation during secondary precipitation is larger at least 23 suggesting a major role for different secondary phases such as iron oxides that maybe incorporate li with a higher isotope fractionation

modeling the high frequency component of arctic sea ice drift and deformation abstract buoy observations of sea ice drift show that sea ice motion and deformation contain substantial high frequency variability at subdaily timescales however numerical simulations of the sea ice dynamics normally do not include processes on such short timescales instead by applying traditional water drag formulations for the ocean sea ice boundary layer the inertial frequencies tend to be omitted in the spectra of modeled sea ice motion and deformation due to fictitious ocean damping here a dynamic thermodynamic sea ice model is presented that includes inertial embedding of the sea ice into the oceanic boundary layer to reproduce sea ice motion and deformation not only at daily and lower frequencies but also at subdaily frequencies up to 2 cycles per day and higher comparison with buoy data shows that the embedded model much more successfully simulates the observed sea ice motion in regard to the high frequency component the results demonstrate that both inertial embedding of the sea ice oc

annual cycles of sea ice motion and deformation derived from buoy measurements in the western arctic ocean over two ice seasons data collected by two buoy arrays that operated during the ice seasons of 2014 2015 and 2016 2017 were used to characterize annual cycles of ice motion and deformation in the western arctic ocean an anomalously strong and weak beaufort gyre in 2014 2015 and 2016 2017 induced generally anticyclonic and cyclonic sea ice drift during 2014 2015 and 2016 2017 respectively cyclonic ice motion resulted in higher contributions of ice divergence to total ice deformation in 2016 2017 than in 2014 2015 in 2014 the autumn ice concentration and multiyear ice coverage were higher than in 2016 consequently the response of ice motion to wind forcing was weak and less ice deformation was observed in autumn 2014 during the autumn winter transition the ice wind speed ratio ice deformation rate and its spatial and temporal scaling exponents and localization of ice deformation decreased markedly in both 2014 2015 and 2016 2017 as a result of freeze up and consolidation of ice floes such dynamic behavior was maintained through to spring with the further thickening of ice cover ice deformation increased due to weakened ice strength as summer approached the amplitude of the annual cycle of ice deformation rate in the western arctic ocean in 2014 2015 and especially in 2016 2017 was larger than that observed during the surface heat budget of the arctic ocean sheba program in 1997 1998 we attribute this phenomenon to ice loss during the recent summers especially of thick multiyear ice

large scale drift of arctic sea ice retrieved from passive microwave satellite data a method of determining the large scale sea ice drift using 85 5 ghz special sensor microwave imager data are presented a cross correlation method is applied to sequential images of gridded data covering the entire arctic individual correlation results are validated with ice velocities derived from buoy data the satellite derived mean drift values and the variabilities of the ice drift correspond closely with the buoy data similarly time series of buoy data and associated satellite data are in good agreement even over large time periods an example of a satellite retrieved 3 day mean drift field demonstrates the potential of the method for providing large scale ice circulation patterns mean drift fields of the winter periods 1987 1988 and 1992 1993 indicate a considerable interannual variability of the sea ice drift pattern in the arctic ocean the arctic region is divided into seven larger areas and the area flux between these regions has been derived the kara sea and the laptev sea show the largest area ice export with 0 02 and 0 015 km 2 s 1 respectively the central arctic export through fram strait amounts to 0 12 sv during the winter of 1992 1993 with a maximum of 0 15 sv in january

erosion and weathering fluxes in granitic basins the example of the strengbach catchment vosges massif eastern france abstract this work reports on regular observations of the suspended sediment and bedload flux at the outlet of the granitic strengbach catchment 0 8 km over the period 2004 2010 along with the analysis of the dissolved load the data set allows a first determination of the physical erosion flux 3 3 t km 2 yr 1 exported out of the strengbach watershed and how it compares to the chemical weathering flux of basic cations the data indicate that the erosion rate carried by the bedload 1 7 t km 2 yr 1 can reach one third of the total erosion rate 5 t km 2 yr 1 in the strengbach watershed the accuracy of these rates is estimated to be 20 the study also indicates that the estimated values for the net annual weathering flux calculated for the watershed can differ by a factor of two or more depending on the corrections applied and the assumptions retained for the watershed s functioning from an uncorrected weathering flux of basic cations of 4 76 t km 2 yr 1 to an atmosphere corrected weathering flux of 2 t km 2 yr 1 for the period 2004 2010 the weathering budgets determined for the strengbach catchment fit the general trend defined between the weathering rate and runoff for other granitic watersheds this suggests that the anthropogenic impact due to acid perturbation or forest management has a relatively weak influence on the weathering intensity within the watershed the relationship between weathering and erosion rates determined for the strengbach catchment does not significantly differ from those established for other previously studied granitoid catchments

effect of sea ice rheology in numerical investigations of climate 1 plastic sea ice rheologies that employ teardrop and parabolic lens yield curves and allow varying biaxial tensile stresses have been developed these rheologies together with the previously developed ellipse and mohr coulomb ellipse rheologies are implemented in a thickness and enthalpy distribution sea ice model to examine the rheological effect in numerical investigations of arctic climate the teardrop lens and ellipse rheologies obey a normal flow rule and result in a two peak shear stress distribution the first peak is at the zero shear stress the second is near 16 000 n m 1 for the ellipse and two lens rheologies and near 30 000 n m 1 for the two teardrop rheologies the location of the second peak depends on the fatness of the yield curve and the amount of biaxial tensile stress allowed in contrast the mohr coulomb ellipse rheology based on coulombic friction failure does not tend to create the second peak the incorporation of biaxial tensile stress tends to increase ice thickness in most of the arctic a fatter yield curve tends to increase the frequency of large shear stresses an increased frequency of large shear stresses in conjunction with the inclusion of biaxial tensile stress tends to reduce ice speed and ice export to enhance ice ridging in the arctic interior and to reduce ice ridging in the coastal areas which has a significant impact on arctic spatial ice mass distribution and the total ice budget the teardrop rheologies reduce spatial bias of modeled ice draft against submarine observations more than others by changing ice motion deformation and thickness the choice of plastic rheology also considerably affects the simulated surface energy exchanges particularly in the arctic marginal seas

contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of greenland and the canadian arctic archipelago regional variability in monthly cryosat 2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large scale ice drift for five winters december to april 2011 2015 over a region of persistent convergence north of the coasts of greenland and the canadian arctic archipelago deformation explains 34 of the overall variance up to 69 in 2014 2015 in monthly thickness changes approximately 42 56 or 0 6 m of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear the estimated area averaged growth of 0 12 0 03 m month compares favorably with measurements from ice mass balance buoys examination of the time variable thickness distributions shows areas covered by ice 3 m increased albeit at fairly coarse resolution this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process

arctic sea ice as a granular plastic an important consideration in understanding sea ice mechanics is the integration of observed sea ice behavior on a floe neighborhood scale 1 10 km into ice dynamics on a regional scale o 50 km we investigate sea ice kinematics from october 1993 through april 1994 using relative motions from 13 drifting buoys with global positioning system navigation in a 20 km array centered on the sea ice mechanics initiative ice camp and we compare these motions to synthetic aperture radar sar derived ice velocities over a 100 by 500 km region in the beaufort sea there is excellent correspondence between the deformation of the buoy array and that from the sar inferred ice dynamics from analysis of the two major northerly wind convergence events of the winter are consistent with a granular hardening plastic conceptual model for beaufort sea ice under continued northerly winds the ice from the alaskan shore to the camp failed in shear and convergence in a progressive manner away from the coast the continuum scale o 10 km is an order of magnitude larger than the grain i e floe size o 1 km the ice motion often forms aggregates of 20 200 km separated by narrow 10 km shear zones similar to granular materials at moderate forcing i e wind stress multiplied by fetch the ice appears to fail along slip lines that occur at an acute angle to each other and to the direction of the wind forcing characteristic of a plastic material at critical state with longer fetch the ice appears to fail in compression perpendicular to the wind direction sea ice appeared to harden on a regional scale after the first event during the second northerly wind event there was a sea ice breakout toward the west apparently due to a lack of lateral confining stress our observations suggest that the ice floes advect through relatively stationary stress fields created by the wind forcing and coastal boundaries for example while the sar and advanced very high resolution radiometer images indicated the presence of the shear feature at the same geographic location for nearly a week buoys would show shearing only for several days as they transited across the region of shear there is a high correspondence between the major internal ice deformation events and persistent weather patterns on a 3 to 5 day temporal scale this implies that sar data collection and analysis for regional sea ice dynamics should be consistent with the wind forcing and have a sampling of less than 3 days

the force balance of sea ice in a numerical model of the arctic ocean the balance of forces in the sea ice model of hibler 1979 is examined the model predicts that internal stress gradients are an important force in much of the arctic ocean except in summer when they are significant only off the northern coasts of greenland and the canadian archipelago a partition of the internal stress gradient between the pressure gradient and the viscous terms reveals that both are significant although they operate on very different timescales the acceleration term is generally negligible while the sum of coriolis plus sea surface tilt is small thus the seasonal average force balance in fall winter and spring is mostly between three terms of roughly equal magnitudes air drag water drag and internal stress gradients this is also true for the monthly average force balance however we find that there is a transition around the weekly timescale and that on a daily basis the force balance at a particular location and time is often between only two terms either between air drag and water drag or between air drag and internal stress gradients the model is in agreement with the observations of thorndike and colony 1982 in that the correlation between geostrophic wind forcing and the model s ice velocity field is high this result is discussed in the context of the force balance we show that the presence of significant internal stress gradients does not preclude high wind ice correlation a breakdown of the internal stress gradient into component parts reveals that the shear viscous force is far from negligible which casts strong doubt on the theoretical validity of the cavitating fluid approximation in which this component is neglected finally the role of ice pressure is examined by varying the parameter p we find a strong sensitivity in terms of the force balance as well as ice thickness and velocity

sea ice kinematics and surface properties from radarsat synthetic aperture radar during the sheba drift 1 satellite data are important for providing the large scale context of the surface heat budget of the arctic ocean sheba station and for characterizing the spatial variability of the sea ice in its vicinity the canadian radarsat satellite collected 195 synthetic aperture radar sar images of the sheba site over the course of the 1 year drift the radarsat geophysical processor system rgps used these images to compute the spatial pattern of ice motion within 100 km of the sheba station by tracking features in sequential images from the ice motion data the divergence and shear of the pack ice are estimated the divergence is large from november to january followed by a gradual convergence from february through july the character of the ice motion changes at the end of july from piecewise rigid motion to free drift the ice motion reverts to its winterlike character in late september thus the kinematic summer runs from late july to late september the radar backscatter also goes through seasonal transitions capturing the abrupt onset of melt 29 may and freeze up 15 august the concentration of multiyear ice is about 94 in the fall and its backscatter signature remains stable through spring multiyear and first year ice cannot be distinguished during the summer melt season when the mean backscatter is negatively correlated with the surface air temperature the thermodynamic summer runs from late may to mid august index terms 4207 oceanography general arctic and antarctic oceanography 4275 oceanography general remote sensing and electromagnetic processes 0689 4540 oceanography physical ice mechanics and air sea ice exchange processes keywords sea ice synthetic aperture radar sar sheba

compressive shear faults within arctic sea ice fracture on scales large and small 1 we examined fracture features within arctic sea ice as revealed by landsat 7 and radarsat imagery by an aerial survey and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression regardless of scale which spans the range from kilometers to millimeters the features look alike they consist mainly of narrow lineaments that traverse the field of view plus wing like and comb like secondary cracks the lineaments occasionally intersect and generally exhibit either right lateral or left lateral relative movement like strike slip faults within earth s crust we term them brittle compressive shear faults they form through the linking of en echelon arrays of deformation induced secondary cracks from an application of wing crack and comb crack mechanics we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses to account for the brittle behavior of the sea ice cover we applied a recent model of the ductile to brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators in identifying the nature of sea ice fracture features we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation via the operation of scale independent mechanisms

opening and closing of sea ice leads digital measurements from synthetic aperture radar the coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques an algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar sar digital images the pair of images is classified into leads and ice correcting for variation in brightness with range displacements are determined automatically on a regular 2 km grid on a 100 km square scene by cross correlation an algorithm groups together cells which cover a lead event the lead area change is estimated for each cell group by counting lead pixels before and after deformation all positive changes are summed to obtain the amount of opening and all negative changes give closing errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0 2 of the area of the scene for comparison the measured opening and closing are in the range of 1 to 3 of the scene area in ice models the openings and closings of leads are parameterized in terms of the large scale deformation sar allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation in this image pair for which the deformation is nearly pure shear we find relatively small amounts of opening and closing consistent with previous observations and with parameterizations in most models the large values of opening and closing predicted by the poisson gauss kinematic model are not in evidence

influence of mass diffusion in sea ice dynamical models the mixing of floes of different thickness caused by repeated deformation of the ice cover is modeled as diffusion and the mass balance equation for sea ice accounting for mass diffusion is developed the effect of deformational diffusion on the ice thickness balance is shown to reach 1 of the divergence effect which describes ridging and lead formation this means that with the same accuracy the mass balance equation can be written in terms of mean velocity rather than mean mass weighted velocity which one should correctly use for a multicomponent fluid such as sea ice with components identified by floe thickness mixing diffusion of sea ice also occurs because of turbulent variations in wind and ocean drags that are unresolved in models estimates of the importance of turbulent mass diffusion on the dynamic redistribution of ice thickness are determined using empirical data for the turbulent diffusivity for long time scale prediction k5 days where unresolved atmospheric motion may have a length scale on the order of the arctic basin and the time scale is larger than the synoptic time scale of atmospheric events turbulent mass diffusion can exceed 10 of the divergence effect however for short time scale prediction for example 5 days the unresolved scales are on the order of 100 km and turbulent diffusion is about 0 1 of the divergence effect because inertial effects are small in the dynamics of the sea ice pack diffusive momentum transfer can be disregarded

the source of calcium in wet atmospheric deposits ca sr isotope evidence tracing the origin of calcium in wet atmospheric deposits is important for environmental studies since it is a dominant acid neutralising cation and an essential nutrient here we present the first calcium isotope ratio measurements for rain and snow samples from northeastern and southern locations france switzerland luxembourg california and japan suggest a carbonate origin only at a local scale in a forested watershed vosges mountains france the ca isotopic compositions of rainwater indicate that the rainwater becomes admixed with throughfall solution which is a mixing product of ca from dissolved atmospheric dust particles and leave excretions if this proves to be widely true the contribution of ca from the canopy could be very important for the neutralisation of acid rain and of the corresponding soil system in forested watersheds in such cases ca and sr cycles are decoupled in the lower atmosphere in contrast to sr isotopes ca isotopes can be applied to tracing processes occurring in the biosphere

from biological to lithological control of the b geochemical cycle in a forest watershed strengbach vosges abstract there is a fast growing interest in understanding the coupling between mineralogical and biological processes responsible for the migration of elements through continental ecosystems this issue has fundamental impacts at the soil plant scale because it can explain the tight links between soil and plant development and at the watershed scale because it gives a direct access to the water quality in the present study we performed an extended investigation of the bio geochemical cycle of boron which is an element known to be suitable for investigating water rock interactions and vegetation cycling new b data are provided along the hydro bio geochemical continuum in a forest ecosystem strengbach basin vosges france from rainwaters down to the outlet of the basin including systematic analyses of throughfalls soil solutions springs and brooks scattered in the watershed at the watershed scale we evidence a relationship between the b isotopic composition of river waters and the weathering regime outlining a predominant control of the parent rock mineralogy on the b geochemical behavior at the soil plant scale it appears that the b geochemical cycle is controlled by the vegetation cycling which is characterized by an uncommon easy to distinguish b isotopic composition 11b ranging from about 30 to 45 each year the amount of b being involved in the vegetation cycle is about four times greater than that of b being exported out of the watershed at 10 cm depth in soil where the plant roots are expected to be the most active we observe a marked seasonal oscillation of the b isotopic values which is interpreted as resulting from the vegetation activity a mass balance calculation based on the assumption that that 10b is preferentially accumulated in the biomass tends to indicate that the soil plant system does not behave at steady state with respect to b because of the very distinct b isotopic signature of vegetation and minerals in soil box modeling allows to quantify the part of the b fluxes involved in the vegetation cycling and the mineral reactions respectively this calculation reveals a clear correlation between the amount of b derived from soil weathering and the amount of b absorbed by plant roots this result clearly supports the idea that a coupling exists between mineral weathering and plant activity for the study of which b isotopes appear particularly suitable

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

lack of bedrock grain size influence on the soil production rate abstract our study deals with the part played by bedrock grain size on soil formation rates u and th series disequilibria were measured in two soil profiles developed from two different facies of the same bedrock i e fine and coarse grain size granites in the geomorphically flat landscape of the experimental breuil chenue forest site morvan france the u and th series disequilibria of soil layers and the inferred soil formation rate 1 2 mm ky 1 are nearly identical along the two profiles despite differences in bedrock grain size variable weathering states and a significant redistribution of u and th from the uppermost soil layers this indicates that the soil production rate is more affected by regional geomorphology than by the underlying bedrock texture such a production rate inferred from residual soil minerals integrated over the age of the soil is consistent with the flat and slowly eroding geomorphic landscape of the study site it also compares well to the rate inferred from dissolved solutes integrated over the shorter time scale of solute transport from granitic and basaltic watersheds under similar climates however it is significantly lower than the denudation or soil formation rates previously reported from either cosmogenic isotope or u series measurements from similar climates and lithologies our results highlight the particularly low soil production rates of flat terrains in temperate climates moreover they provide evidence that the reactions of mineral weathering actually take place in horizons deeper than 1 m while a chemical steady state of both concentrations and u series disequilibria is established in the upper most soil layers i e above 70 cm depth in such cases the use of soil surface horizons for determining weathering rates is precluded and illustrates the need to focus instead on the deepest soil horizons

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

silicate weathering rate and its controlling factors a study from small granitic watersheds in the jiuhua mountains abstract silicate weathering is intimately linked to global climate to investigate the controlling factors of silicate weathering rate we collected monthly or half monthly river water samples from ten small granitic watersheds in the jiuhua mountains mass balance calculation shows that agricultural activity atmospheric input silicate weathering carbonate weathering and evaporite dissolution contribute 2 0 16 9 58 7 13 5 and 8 9 cations to the river water respectively the disproportionate contribution of carbonate rocks with an exposed area of there is no correlation between silicate weathering rates swr and the suspended solid concentrations an index of physical erosion rate but there is a strong positive correlation between swr and temperature consistent with the kinetic limited chemical weathering regime in alpine areas a compilation of literature data from global small granitic watersheds in different climatic zones shows positive correlations between temperature runoff and swr a multiple linear regression between swr temperature and runoff yielded an adjusted r squared of 0 61 showing that climatic factors can account for 61 of the variation in swr in addition for catchments where the elevation difference between the highest point of the headwater and sampling point an approximate topographical parameter exceeds 400 m the r squared value obtained from the temperature and swr regression analysis is significantly increased indicating that temperature is likely the most important factor controlling silicate weathering in the alpine region where a kinetic limited regime dominates

the impact of vegetation on ree fractionation in stream waters of a small forested catchment the strengbach case previous studies on waters of a streamlet in the vosges mountains eastern france have shown that strontium and rare earth elements ree mainly originate from preferential dissolution of apatite during weathering however stream water ree patterns normalized to apatite are still depleted in the light ree lree la sm pointing to the presence of an additional lree depleting process vegetation samples are strongly enriched in lree compared to stream water and their sr and nd isotopic compositions are comparable with those of apatite and stream water thus the preferential lree uptake by vegetation might lead to an additional lree depletion of surface runoff in the forested catchment mass balance calculations indicate that the yearly lree uptake by vegetation is comparable with the lree export by the streamlet and therefore might be an important factor controlling lree depletion in river water this is underlined by the observation that rivers from arctic and boreal regions with sparse vegetation appear to be less depleted in lree than rivers from tropical environments or boreal environments with a dense vegetation cover

heterogeneous geochemistry of catchment acidification abstract many ions in catchment runoff are primarily controlled by heterogeneous reactions the mass law governing heterogeneous equilibria leads directly to a simple general expression for catchment acid buffering which can be estimated from bulk catchment runoff composition this analysis requires no particular assumptions or data regarding catchment minerals water flowpaths reaction pathways or equilibrium constants thus a catchment s vulnerability to acidification can be assessed directly from its runoff chemistry critical tests using data from four intensively studied catchments hubbard brook usa and sogndal risdalsheia and birkenes norway reveal catchment scale buffering behavior that is quantitatively comparable to that predicted from bulk runoff composition theoretical predictions and field data both indicate that reversing acidification at the acidified norwegian catchments would require large decreases in sulfate concentrations long term acidification will occur where leaching of base cations accelerated by add anion loading exceeds resupply from mineral weathering where the rate of depletion of adsorbed base cations can be estimated the resulting acidification of runoff can be predicted analytically base cation leaching partly offset by mineral weathering and acting in conjunction with declining acid anion loading appears responsible for the long term decline in base cation concentrations at hubbard brook a general method is proposed for evaluating the effects of spatial variability in catchment buffering mechanisms spatially averaged catchment runoff will generally yield whole catchment buffering predictions that closely approximate the spatially averaged buffering properties of a collection of geochemically diverse source regions mechanistic prediction of catchment buffering does not require identifying discrete source regions characterizing their individual geochemical properties or tracing the hydrologic flowpaths that connect them this considerably simplifies the problem of predicting whole catchment buffering behavior

assimilating satellite concentration data into an arctic sea ice mass balance model 1979 1985 using satellite ice concentration data observed buoy velocities and a thermodynamic ice growth model we compute the time histories of the thickness distributions of four ice types level and ridged first year ice and level and ridged multiyear ice these histories are computed for seven regions covering the arctic ocean with a 10 day time step for 1979 through 1985 a blend of observed buoy motions and wind driven free drift velocities drives the advective and ridging parts of the model while climatological growth and melt rates determine the ice thickness the model adjusts the thickness distributions so that the modeled concentrations of open water first year ice and multiyear ice match the concentrations derived by kalman filtering of satellite passive microwave observations the major adjustment is to reduce modeled ice concentrations in summer and particularly in the peripheral seas to account for unmodeled melt the model includes an ice salinity parameterization which along with changes in ice volume gives the salt or freshwater flux from the ice our results show that the arctic ice cover consists primarily of multiyear ice 60 by area and 82 by volume and that most of this ice is ridged the average ice thickness is 2 7 m with a seasonal variation of 30 and an interannual variation of 10 the study also shows that for each cell and the arctic as a whole the changes in ice volume caused by growth minus melt approximately balance the changes caused by import minus export the annual ice export through fram strait varies from 1100 to 3000 km3 primarily because of variations in ice velocity all regions except the chukchi sea have a net ice growth a net export and a net salt input to the ocean surface the annual mean salt flux to the ocean surface from net ice production is 7 3 kg m 2 downward fluxes along the transpolar drift stream are larger than elsewhere the largest downward flux of 33 kg m 2 yr 1 in the nansen basin can be attributed to the strong divergence near fram strait a companion paper steele et al this issue uses these fluxes and ice velocities to derive the arctic ocean freshwater balance

meso and microscale sea ice motion in the east siberian sea as determined from ers 1 sar data synthetic aperture radar sar derived ice motion vectors and sar interferometry were used to study the sea ice conditions in the region between the coast and 75 n 560 km in the east siberian sea in the vicinity of the kolyma river ers 1 sar data were acquired between 24 december 1993 and 30 march 1994 during the 3 day repeat ice phase of the satellite the time series of the ice motion vector fields revealed rapid 3 day changes in the direction and displacement of the pack ice longer term 1 month trends also emerged which were related to changes in large scale atmospheric circulation on the basis of this time series three sea ice zones were identified the near shore stationary ice zone a transitional ice zone and the pack ice zone three 3 day interval and one 9 day interval interferometric sets amplitude correlation and phase diagrams were generated for the end of december the begining of february and mid march they revealed that the stationary ice zone adjacent to the coast is in constant motion primarily by lateral displacement bending tilting and rotation induced by atmospheric oceanic forcing the interferogram patterns change through time as the sea ice becomes thicker and a network of cracks becomes established in the ice cover it was found that the major features in the interferograms were spatially correlated with sea ice deformation features cracks and ridges and major discontinuities in ice thickness

geomorphic and climatic controls on chemical weathering in the high himalayas of nepal article i nfo the hypothesis that co2 consumption by chemical weathering is enhanced by the exposure of fresh minerals provides a mechanism linking tectonic geomorphic and atmospheric processes we present data from the high himalayas of nepal indicating a positive linear relationship between cation weathering rate and suspended sediment yield because of a steep precipitation gradient across the field area the weathering rates are normalized according to runoff to isolate erosion as the controlling factor adjusted for runoff increases in weathering rates do not keep pace with increasing erosion rates where suspended sediment yieldsn2000 t km 2 y this result supports studies that predict a nonlinear relationship between denudation and weathering in rapidly eroding landscapes in addition we document a decoupling of the weathering of si and silicate cations from a glacierized watershed the proportions of silicate derived na and k are high relative to si during the warm summer months and then drop when subfreezing temperatures arrive in the fall we propose that during the summer glacial abrasion creates fresh mineral surfaces that favor the release of cations and abundant meltwater flushes these weathering products from the subglacial bed as temperatures fall below freezing and the production of meltwater slows dramatically river discharge becomes dominated by groundwater bearing the chemical signature of more congruent weathering reactions

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

on modeling the anisotropic failure and flow of flawed sea ice the failure and flow of sea ice on scales small and large is characterized by the propagation of oriented leads and cracks in this paper a theory for the dynamical treatment of anisotropic oriented flaws in sea ice is developed and used to examine the interaction of these oriented flaws under idealized stress forcing the essential idea of the theory is to take one or more oriented weak leads imbedded in thick ice a constitutive law for both the thin and thick ice is taken to be similar to laboratory observations which are consistent with mohr coulomb like failure application of normal continuum mechanics boundary conditions leads to anisotropic flow and failure characteristics of this anisotropic composite under both near and far field forcing the local failure characteristics show that there is a preferred orientation for failure with the intersection between leads increasing as confinement increases for spatially separated interacting flaws the theory predicts a preference for the weakening of flaws in a narrow range of angles of 10 20 relative to the principal far field stress imbedding isolated flaws leads to simulated damage directions consistent with local failure characteristics in the case where the ice is considered to have available flaws in all directions fracture propagation is found to proceed by picking out oriented flaws alternating in direction along large scale damage strikes with individual flaw alignments of 20 relative to far field principal stresses the mechanisms responsible for these results and how this anisotropic sea ice rheology might be implemented in current dynamic thermodynamic sea ice models are discussed