germanium silicon fractionation in the weathering environment abstract we present a detailed study of germanium behavior in the soil weathering environment as an important step toward using the ge si system as a tracer of silicate weathering processes in both modern and ancient environments intensely weathered soils developed on hawaiian basalts have bulk soil ge si ratios 2 to 10 times higher than fresh basalt e g 10 to 25 mol mol vs 2 5 mol mol soil ge concentrations increase with si and decrease with fe suggesting that ge sequestration is related to accumulation of secondary soil silicates rather than retention in soil fe oxy hydroxides sequential extractions of these soils suggest that ge si fractionation takes place by ge sequestration during the initial precipitation of secondary soil aluminosilicates principally allophane further si loss and changes in mineralogy as these soils age result in little additional ge si fractionation ge si ratios in granitic soils and saprolites are strongly influenced by relative weathering rates of primary minerals kaolinite has a ge si ratio 5 9 mol mol higher than the plagioclase from which it forms 3 1 mol mol whereas accumulation of primary quartz ge si 0 5 mol mol prevents granitic soils from attaining high ge si ratios laboratory synthesis of allophane confirms that ge is preferentially partitioned into the solid phase upon precipitation of secondary aluminosilicates from solution

salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

sensitivity of eddy induced heat transport to diabatic forcing compensation of the poleward eddy heat transport by the heat transport of an eddy induced mean meridional overturning cell is a common feature in many eddy resolving ocean models it has been argued that this is the result of the weak thermal driving of the ocean as the actual air sea coupling is scale dependent it might be questioned whether the approximation of weak thermal driving is relevant for the oceanic eddy field in this paper the role of diabatic forcing in modifying eddy mean flow interaction is investigated emphasis has been placed on the sensitivity of the eddy induced change in heat transport to the sea surface thermal boundary condition experiments have been performed with a multilayer isopycnic primitive equation model of an idealized north atlantic subtropical and subpolar gyre for different values of the air sea coupling solutions with and without transient eddies have been compared the air sea coupling mostly affects the upper ocean thermal and velocity fields a decrease of the coupling timescale pushes the separation point of the midlatitude jet further northward and induces a tight recirculation southwest of the separated jet these effects are enhanced by the eddies in the present model there is compensation of the eddy heat transport for sea surface temperature sst relaxation times longer than 150 days a breakdown of the compensation occurs for sst relaxation times shorter than 50 days the average upper layer depth is 200 m in between is a transition regime for strong thermal driving the eddy induced change in total heat transport is of the same order as the eddy heat transport

structure and dynamics of the sea of okhotsk marginal ice zone from ocean satellite radar sensing data radar images of the sea of okhotsk ice cover are analyzed the images were obtained by side looking radars slr installed on the ussr ocean series of satellites since september 1983 slr operates at wavelength 3 15 cm at vertical polarization a swath width is 460 km at a spatial resolution of 1 3 km satellite optical images air reconnaissance and meteorological information are used to interpret sea ice radar contrasts the radar images permit monitoring of the formation and transformation of the ice cover and its displacement under the influence of winds and currents radar contrast is enhanced in the marginal ice zone on account of the great difference in the scattering properties of pancake ice and grease ice in the marginal ice zone different regular motions are registered for ice edge waves ice bands and jets eddies and mushroomlike structures with dimensions ranging between 10 20 and 100 120 km

a model study on internally generated variability in subtropical mode water formation internally generated variability in the subtropical gyre is studied as a possible mechanism for the observed interannual to decadal variability in subtropical mode water formation an isopycnic ocean model with idealized geometry and forcing which mimics the north atlantic subtropical gyre is used for this purpose the horizontal resolution is sufficiently high and the friction and diffusion sufficiently low for the flow to become barotropically and baroclinically unstable two modes of low frequency variability are found both modes consist of westward propagating thickness anomalies the anomalies have a first baroclinic modal structure with a maximum amplitude at the thermocline one mode has a timescale of 8 years and a basin wide spatial scale the other has a timescale of 4 5 years and a smaller spatial scale the modes appear to be damped when the diffusion is high in that case the 8 year mode can be excited by a spatially coherent stochastic wind stress the evolution of the modes is determined by an interaction between the mean flow and the low frequency variability itself the modes are instabilities of the mean flow determined by the basic stratification it appears that coupling to the atmosphere and a parameterization of surface mixing are necessary for the low frequency variability to appear in the mixed layer the coupling and surface mixing do not play a role in generating the modes it is concluded that these internally generated modes may play a role in the observed variability in mode water formation

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

effects of velocity shear in advective mixed layer models abstract a general multidimensional model of the upper mixed layer of oceans and lakes is presented the density profile is approximated as uniform over the depth of the layer such an assumption is not made for the distribution of the horizontal velocity component as there is no observational evidence for it in fact many observations indicate that important velocity shears exist in regions where advection can be expected to play an important role in the dynamics of the mixed layer such as lakes near upwelling and frontal areas and in equatorial oceanic regions it is shown that vertical shear in the horizontal velocity field combined with a horizontal density gradient can result in the production or absorption of mechanical energy production results if the velocity shear tends to destabilize the density profile consumption if the tendency is stabilizing so that work against gravity must be done to mix the stabler density profile to uniformity in the mechanical energy equation this effect of th

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

the effects of mesoscale eddies on the main subtropical thermocline abstract the effects of mesoscale eddies on the main subtropical thermocline are explored using a simply configured wind and buoyancy driven primitive equation numerical model in conjunction with transformed eulerian mean diagnostics and simple scaling ideas and closure schemes if eddies are suppressed by a modest but nonnegligible horizontal diffusion and vertical diffusion is kept realistically small the model thermocline exhibits a familiar two regime structure with an upper advectively dominated ventilated thermocline and a lower advective diffusive internal thermocline and together these compose the main thermocline if the horizontal resolution is sufficiently high and the horizontal diffusivity is sufficiently low then a vigorous mesoscale eddy field emerges in the mixed layer and upper mode water regions the divergent eddy fluxes are manifestly across isopycnals and so have a diabatic effect beneath the mixed layer the mean structure of the upper i e ventilated thermocline is still

heat transport by mesoscale eddies in an ocean circulation model abstract the role of mesoscale eddies in the poleward heat transport in the ocean is investigated in particular the compensation of poleward eddy heat transport by an eddy induced mean meridional circulation is examined a multilayer isopycnic primitive equation model of an idealized western north atlantic is presented to test whether compensation also occurs within an isopycnic model and when the poleward eddy heat transport becomes comparable to the mean transport also in this model configuration compensation of the poleward eddy heat transport arises it is brought about by a westward eddy heat transport in the midlatitude jet which results in a pressure drop across the basin and consequently in a modified mean meridional overturning this compensation is discussed within the framework of wave mean flow interaction it is demonstrated that compensation results from eddy mean flow interaction when the diabatic forcing is sufficiently weak rings are recaptured before their sst anomaly is modified s

germanium silicon fractionation in a tropical granitic weathering environment abstract germanium silicon ge si ratios were determined on quartz diorite bedrock saprolite soil primary and secondary minerals phytolith soil and saprolite pore waters and spring water and stream waters in an effort to understand ge si fractionation during weathering of quartz diorite in the rio icacos watershed puerto rico the ge si ratio of the bedrock is 2 mol mol with individual primary mineral phases ranging between 0 5 and 7 mol mol the ratios in the bulk saprolite are higher 3 mol mol than values measured in the bedrock the major saprolite secondary mineral kaolinite has ge si ratios ranging between 4 8 and 6 1 mol mol the high ge si ratios in the saprolite are consistent with preferential incorporation of ge during the precipitation of kaolinite bulk shallow soils have lower ratios 1 1 1 6 mol mol primarily due to the residual accumulation of ge poor quartz ge si ratios measured on saprolite and soil pore waters reflect reactions that take place during mineral transformations at discrete depths spring water and baseflow stream waters have the lowest ge si ratios 0 27 0 47 mol mol reflecting deep initial weathering reactions resulting in the precipitation of ge enriched kaolinite at the saprolite bedrock interface mass balance calculations on saprolite require significant loss of si and al even within 1 m above the saprolite bedrock interface higher pore water ge si ratios 1 2 mol mol are consistent with partial dissolution of this ge enriched kaolinite pore water ge si ratios increase up through the saprolite and into the overlying soil but never reach the high values predicted by mass balance perhaps reflecting the influence of phytolith recycling in the shallow soil

river fluxes to the sea from the oceanʼs 10be 9be ratio the ratio of the meteoric cosmogenic radionuclide 10be to the stable isotope 9be is proposed here to be a flux proxy of terrigenous input into the oceans the ocean s dissolved 10be 9be is set by 1 the flux of meteoric 10be produced in the atmosphere 2 the denudational flux of the rivers discharging into a given ocean basin 3 the fraction of 9be that is released from primary minerals during weathering meaning the 9be transported by rivers in either the dissolved form or adsorbed onto sedimentary particles and incorporated into secondary oxides and 4 the fraction of riverine 10be and 9be actually released into seawater using published 10be 9be data of rivers for which independent denudation rate estimates exist we first find that the global average fraction of 9be released during weathering into river waters and their particulate load is 20 and does not depend on denudation rate we then evaluate this quantitative proxy for terrigenous inputs by using published dissolved seawater be isotope data and a compilation of global river loads we find that the measured global average oceanic dissolved 10be 9be ratio of about 0 9 10 7 is satisfied by the mass balance if only about 6 of the dissolved and adsorbed riverine be is eventually released to the open ocean after escaping the coastal zone when we establish this mass balance for individual ocean basins good agreement results between 10be 9be ratios predicted from known river basin denudation rates and measured ocean 10be 9be ratios only in the south atlantic and the south pacific the 10be 9be ratio is dominated by advected be and in these basins the ratio is a proxy for ocean circulation as the seawater 10be 9be ratio is faithfully recorded in marine chemical precipitates the 10be 9be ratio extracted from authigenic sediments can now serve to estimate relative changes in terrigenous input into the oceans back through time on a global and on an ocean basin scale

lead and lead isotopes in agricultural soils of europe the continental perspective abstract lead isotopes are widely used for age dating for tracking sources of melts sediments pb products food and animals and for studying atmospheric pb contamination for the first time a map of a pb isotope landscape at the continental scale is presented agricultural soil samples ap horizon 0 20 cm collected at an average density of 1 site 2500 km2 were analysed for pb concentration and pb isotopes 206pb 207pb 208pb lead concentrations vary from 1 6 to 1309 mg kg with a median of 16 mg kg isotopic ratios of 206pb 207pb range from 1 116 to 1 727 with a median of 1 202 the new data define the soil geochemical pb background for european agricultural soil providing crucial information for geological environmental and forensic sciences public health environmental policy and mineral exploration the european continental scale patterns of pb concentrations and pb isotopes show a high variability dominated by geology and influenced by climate lead concentration anomalies mark most of the known mineralised areas throughout europe some local pb anomalies have a distinct anthropogenic origin

springtime c band sar backscatter signatures of labrador sea marginal ice measurements versus modeling predictions during the march 1987 labrador ice margin experiment limex 87 two independent investigations were conducted to determine the c band backscattering cross section of the marginal pack ice along the newfoundland coast in one experiment data from a recently calibrated c band airborne scatterometer were combined with c band synthetic aperture radar sar data to measure the normalized scattering cross section of the ice at incidence angles from 10 degrees to 74 degrees to within or 2 db in the other experiment detailed measurements of ice surface roughness and surface properties were made and the radar cross sections were predicted from a scattering model in the present study measured and model results are combined and shown to be fully compatible by extension the results are expected to apply to any rubbled sea ice surface when surface scattering dominates

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

comparing results from two continental geochemical surveys to world soil composition and deriving predicted empirical global soil pegs2 reference values analytical data for 10 major oxides al2o3 cao fe2o3 k2o mgo mno na2o p2o5 sio2 and tio2 16 total trace elements as ba ce co cr ga nb ni pb rb sr th v y zn and zr 14 aqua regia extracted elements ag as bi cd ce co cs cu fe la li mn mo and pb loss on ignition loi and ph from 3526 soil samples from two continets australia and europe are presented and compared to 1 the composition of the upper continetal crust 2 published word soil awerage values and 3 data from other continetal scale soil surveys it cab be demonstrated that average upper continetal crust values do not provide reliable estimates for natural concentrations of elements in soil for many elements there exist substantial differences between published world aoil averages and the median concentrations observed on two continets direct comparison with other continetal datasets is hampered by the fact that often mean instead of the statistically more robust median is reported using a database of the worldwide disstribution of lithological units it can be demonstrated that lithology is a poor predictor of soil chemistry climate related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis to overcome existing shortcomings of predicted global or world soil geochemical reference values we propose preliminary empirical global soil reference values based on analytical results of a representative number of soil samples from two continets pegs2

does eddy subduction matter in the northeast atlantic ocean 1 mesoscale eddies are an important contributor to subduction in the gulf stream region and the antarctic circumpolar current but is eddy subduction also important in the relatively quiescent interior of the world s subtropical gyres observations from the subduction experiment of the northeast atlantic do not have the spatial resolution necessary to calculate eddy subduction and answer this question regional numerical models can diagnose subduction but their representativeness is unknown furthermore water mass budgets in an open ocean domain show that the simulated properties of subducted water directly depend upon uncertain open boundary conditions and surface fluxes to remedy these problems a state estimate of the ocean circulation is formed by constraining an eddy permitting general circulation model to observations by adjusting the model parameters within their uncertainty the resulting estimate is self consistent with the equations of motion and has the necessary resolution for diagnosing subduction in the northeast atlantic during 1991 1993 the time variable circulation contributes less than 1 sv of net subduction while the total subduction is 4 sv eddy volume fluxes of 40 m yr in the north equatorial current and the azores current however are significant and rival the subduction by ekman pumping locally furthermore a state estimate at 1 6 resolution has 2 3 sv more subduction in the density bands centered around 24 0 kg m3 and 26 0 kg m3 than a 2 state estimate this result implies that the inability to accurately simulate mesoscale phenomena and surface fluxes in climate models would lead to an accumulation of errors in water mass properties over 10 20 years even in the interior of the subtropical gyre

introduction to the pomme special section thermocline ventilation and biogeochemical tracer distribution in the northeast atlantic ocean and impact of mesoscale dynamics conducted in the northeast atlantic ocean 15 20 21 20 w 38 n 45 n the programme ocean multidisciplinaire meso echelle pomme is a research project aimed at a better understanding of the biological production and the carbon budget of the region in relation to the formation mechanisms of the 11 12 c mode water of the northeast atlantic with the help of two research vessels several tens of floats and drifters and nine moorings the field experiment was carried out between autumn 2000 and autumn 2001 with a more intensive phase in the winter and early spring of 2001 the field experiment resolved small several kilometers to regional several hundred kilometers scales and daily to seasonal variability a first analysis of the rich data set focused on the large scale and the mesoscale variability it shows that the distribution of water mass characteristics and biological activity is strongly influenced by the mesoscales in this supposedly quiet transition zone between the subtropical and subpolar gyres the seasonal variability however presents an imprint of the large scale structures with a clear north south gradient in properties and budgets this region is found on an annual average to be a sink of atmospheric co2 smaller scales associated with fronts and filaments were clearly observed in many fields temperature but also chlorophyll oxygen biogenic particles etc with modeling studies suggesting that they play a significant role in subduction ventilation and transport of biogeochemical tracers in the pomme region

microwave and physical properties of sea ice in the winter marginal ice zone surface based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the fram strait during march and april 1987 synthetic aperture radar imagery downlinked from an aircraft was used to select study sites the surface based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types exhibiting expected separation between young first year and multiyear ice gradient ratios calculated for both active and passive data appear to allow clear separation of ice types when used jointly surface flooding of multiyear floes resulting from excessive loading and perhaps wave action causes both active and passive signatures to resemble those of first year ice this effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft or satellite borne sensors

continental erosion and large scale relief a worldwide investigation of continental erosion is carried out by the study of large drainage basins on the basis of hydrological data environmental factors and basin relief distribution inside each basin mean geochemical and mechanical denudation rates are defined a multicorrelation analysis shows that the mechanical denudation rates ds are uncorrelated with environmental factors and correlated with mean basin elevation h while chemical denudation rates dd are insensitive to relief but correlated with mean annual precipitation furthermore two linear relationships between h and ds are detected 1 ds m 10 yr 419 10 6 h m 0 245 with v explained variance 95 1 this law concerns basins related to orogenies younger than 250 ma the negative intercept is interpreted as a continental sedimentation rate of 245 m m y an alternative model in which one invokes a critical elevation separating erosion from sedimentation is equally successful and leads to lower sedimentation rates 60 110 m m y for both models one derives from the slope of the adjustments erosion time constants on the order of 2 5 m y 2 ds m 10 yr 61 10 6 h m with v 86 5 this law concerns basins related to older orogenies the null intercept suggests the lack of continental storage because of the more important dispersion of the data the erosion time constant is calculated separately for each basin it ranges from 15 to 360 m y the tectonic implications of these results are discussed in particular the short time constant 2 5 m y agrees with orogenic uplift rates on the order of 1 mm yr observed in active mountain chains

eddy subduction in a model of the subtropical gyre abstract subduction is the process by which fluid transfers from the mixed layer to the interior of the ocean south of the gulf stream extension 18 mode water is formed in a region of high subduction rates in this region there is high mesoscale eddy activity in the present study the role of eddies in modifying the large scale subduction into mode water is investigated an eddy resolving isopycnic ocean model with mixed layer physics included and coupled to an atmospheric anomaly model is used for this purpose the geometry and forcing of the model are idealized annual mean subduction rates into mode water up to 200 m yr 1 are found south of the gulf stream extension the eddy contribution to the annual subduction is estimated by comparing the annual mean subduction rates obtained from monthly mean quantities with the total subduction rates i e eddy plus mean contributions the latter are determined by integrating the detrainment rates over the period when fluid is irreversibly detrained eddy

gulf stream velocity structure through inversion of hydrographic and acoustic doppler data near surface velocities from a shipborne acoustic doppler instrument are used together with conductivity temperature depth and o2 data to make estimates of geostrophic velocities off of cape hatteras the data set consists of two transects across the gulf stream at approximately 73 w and 71 w made by the r v endeavor in august 1982 an inversion technique is applied which makes use of both the acoustic doppler data and property conservation requirements the method produces estimates of the absolute flow field across the two sections with formal errors of 1 2 cm s at the time of the observations the net gulf stream transports are estimated to be 116 2 109 kg s at 73 w and 161 4 109 kg s at 71 w a southwestward deep western boundary current transport is estimated at 4 1 109 kg s taken together with recent gulf stream transport estimates of similar accuracy made in june 1982 the results are in general larger than historical transport estimates in this region

mixed layer thermocline interaction in a three dimensional isopycnic coordinate model abstract the annual buildup and obliteration of the seasonal thermocline and the associated ventilation of the permanent thermocline in a wind and thermally driven ocean basin are simulated numerically the model developed for this purpose is a combination of a single layer model of the oceanic mixed layer based on a simple closure of the turbulence kinetic energy equation and a three dimensional isopycnic coordinate model of the stratified oceanic interior the joint model set in a rectangular ocean basin is forced by annually varying wind stress and radiative plus turbulent heal fluxes approximating zonnaly averaged conditions over the north atlantic special emphasis is placed on the description of the mixed layer detrainment process which requires distributing mixed layer water of continuously variable density among constant density interior layers the truncation errors associated with this process are found to be numerically tolerable the quasi lagrangian character of the model s vertical coo

gemas source distribution patterns and geochemical behaviour of ge in agricultural and grazing land soils at european continental scale abstract agricultural soil ap horizon 0 20 cm and grazing land soil gr horizon 0 10 cm samples were collected from a large part of europe 33 countries 5 6 million km 2 as part of the gemas geochemical mapping of agricultural and grazing land soil soil mapping project gemas soil data have been used to provide a general view of element mobility and source rocks at the continental scale either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes the survey area includes a diverse group of soil parent materials with varying geological history a wide range of climate zones and landscapes the concentrations of ge in european soil were determined by icp ms after an aqua extraction and their spatial distribution patterns generated by means of a gis software the median values of ge and its spatial distribution in ap and gr soils are almost the same 0 037 vs 0 034 mg kg respectively the majority of ge anomalies is related to the type of soil parent material namely lithology of the bedrock and minor influence of soil parameters such as ph toc and clay content metallogenic belts with sulphide mineralisation provide the primary source of ge in soil in several regions in europe e g in scandinavia germany france spain and balkan countries comparison with total ge concentrations obtained from the baltic soil survey shows that aqua regia is a very selective method with rather low efficiency and cannot provide a complete explanation for ge geochemical behaviour in soil additionally large differences in ge distribution are to be expected when different soil depth horizons are analysed

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

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

enhanced chemical weathering of rocks during the last glacial maximum a sink for atmospheric co2 abstract it has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric co2 on the continents may have at least partly contributed to the low co2 concentrations during the last glacial maximum lgm variations in continental erosion could thus be one of the driving forces for the glacial interglacial climate cycles during quaternary times to test such an hypothesis a global carbon erosion model has been applied to a lgm scenario in order to determine the amount of co2 consumed by chemical rock weathering during that time in this model both the part of atmospheric co2 coming from silicate weathering and the part coming from carbonate weathering are distinguished the climatic conditions during lgm were reconstructed on the basis of the output files from a computer simulation with a general circulation model only the predicted changes in precipitation and temperature have been used whereas the changes in continental runoff were determined with an empirical method it is found that during the lgm the overall atmospheric co2 consumption may have been greater than today by about 20 mainly because of greater carbonate outcrop area related to the lower sea level on the shelves this does not however affect the atmospheric co2 consumption by silicate weathering which alone has the potential to alter atmospheric co2 on the long term silicate weathering and the concomitant atmospheric co2 consumption decreased together with a global decrease of continental runoff compared to present day both by about 10 nevertheless some uncertainty remains because the individual lithologies of the continental shelves as well as their behavior with respect to chemical weathering are probably not well enough known the values we present refer to the ice free continental area only but we tested also whether chemical weathering under the huge ice sheets could have been important for the global budget although glacial runoff was considerably increased during lgm weathering under the ice sheets seems to be of minor importance

geochemical and mineralogical distribution of germanium in the khusib springs cu zn pb ag sulfide deposit otavi mountain land namibia abstract the khusib springs deposit in the otavi mountain land namibia is a small though high grade carbonate hosted cu zn pb ag as sb ge deposit of the tsumeb type containing approximately 300 000 t of ore grading 10 cu 1 8 pb and 584 ppm ag a lens shaped sulfide orebody up to 10 m thick and elongated parallel to bedding replaces limestone locally brecciated of the lower tsumeb subgroup damara supergroup in the northern limb of a large ne trending synclinal structure a prominent zone of dolomite alteration surrounds the orebody in a drill core through the orebody the uppermost 2 m are enriched in zn up to 5 and ag up to 3350 ppm but lower in ge 26 v 2 as ge 6 s 32 forming small usually geochemical and mineralogical features of sulfide ores from khusib springs resemble some sulfide ores of the pipe shaped polymetallic ge rich tsumeb deposit similar to the latter ore formation probably occurred during d 2 deformation and metamorphism and involved highly saline hot brines up to 370 c chetty d frimmel h e 2000 the role of evaporites in the genesis of base metal sulfide mineralization in the northern platform of the pan african damara belt namibia geochemical and fluid inclusion evidence from carbonate wall rock alteration mineralium deposita 35 364 376 carrying sulfur derived from evaporite sequences a polyphase mineralization involving three successive stages is proposed early sphalerite pyrite chalcopyrite bornite mineralization is replaced by tennantite enargite galena and ge bearing colusite a late stage mineralization overprints parts of the orebody at lower temperatures leading to precipitation of schalenblende cu and ag rich digenite tetrahedrite and pearceite polybasite the occurrence of small but high grade ge rich cu zn pb ag deposits in the lower tsumeb subgroup has important consequences on the mineral potential of the area because prospecting for cu rich ores has been traditionally performed in the uppermost tsumeb subgroup only in relation to paleokarst structures

an eddy resolving numerical model of the ventilated thermocline abstract a three dimensional primitive equation numerical model is used to study the effects of mesoscale eddies within the subtropical thermocline solutions are obtained for an ocean bounded by idealized topography are driven by simple wind and buoyancy forcing at the surface results using an eddy resolving fine grid are compared to those using a noneddy resolving coarser grid relatively little difference is realized in the basic mean flow patterns of the two solutions however more significant differences are seen in the distributions of a passive tracer and the potential vorticity mixing by eddies in the westward flowing sector of the subtropical gyre is quite effective in homogenizing these quantities on isopycnals whereas previous theory has predicted homogenization of potential vorticity on long time scales within recirculating gyres the present model demonstrates homogenization on a much shorter time scale across recirculating ventilating flow boundaries anomalous potential vorticity th

towards identification of optimum radar parameters for sea ice monitoring modele theorique permettant de prevoir la diffusion par la glace multi annuelle et par la glace de premiere annee en conditions froides les resultats experimentaux montrent que les bandes de frequence ku et x ainsi que les angles d incidence superieure a 30 sont les meilleurs pour distinguer les types de glace de mer

eddy dynamics in a primitive equation model sensitivity to horizontal resolution and friction a primitive equation model of an idealized ocean basin driven by simple study wind and buoyancy forcing at the surface is used to study the dynamics of mesoscale eddies model statistics of a six year integration using a fine grid 1 6 0 2 with reduced coefficients of horizontal friction are compared to those using a coarser grid 1 3 0 4 but otherwise identical configuration eddy generation in both model cases is primarily due to the release of mean potential energy by baroclinic instability horizontal reynolds stresses become significant near the midlatitude jet of the fine grid case with a tendency for preferred energy transfers from the eddies to the mean flow using the finer resolution eddy kinetic energy nearly doubles at the surface of the subtropical gyre and increases by factors of 3 4 over the jet region and in higher latitudes the spatial characteristics of the mesoscale fluctuations are examined by calculating zonal wavenumber spectra and velocity autocorrelation functions with the higher resolution the dominant eddy scale remains approximately the same in the subtropical gyre but decreases by a factor of 2 in the subpolar areas the wavenumber spectra indicate a strong influence of the model friction in the coarse grid case especially in higher latitudes using the coarse grid there is almost no separation between the energetic eddy scale and the scale where friction begins to dominate leading to steep spectra beyond the cutoff wavenumber using the finer resolution an inertial subrange with a k 3 power law begins to emerge in all model regions outside the equatorial belt despite the large increase of eddy intensity in the fine grid model effects on the mean northward transport of heat are negligible strong eddy fluxes of heat across the midlatitude jet are almost exactly compensated by changes of the heat transport due to the mean flow

germanium geochemistry and mineralogy abstract germanium is enriched in the following geologic environments 1 1 iron meteorites and terrestrial iron nickel 2 2 sulfide ore deposits particularly those hosted by sedimentary rocks 3 3 iron oxide deposits 4 4 oxidized zones of ge bearing sulfide deposits 5 5 pegmatites greisens and skarns and 6 6 coal and lignitized wood in silicate melts ge is highly siderophile in the presence of native iron nickel otherwise it is highly lithophile among silicate minerals ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz in deposits formed from hydrothermal solutions ge tends to be enriched mostly in either sulfides or in fluorine bearing phases it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites greisens and skarns in sulfide deposits that formed from solutions having low to moderate sulfur activity ge is concentrated in sphalerite in amounts up to 3000 ppm sulfide deposits that formed from solutions having higher sulfur activity allowed ge to either form its own sulfides particularly with cu or to substitute for as sn or other metals in sulfosalts the ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids or is due to the incorporation of ge from the country rocks particularly from those containing organic material germanium bonds to lignin derivative organic compounds that are found in peat and lignite accounting for its common concentration in coals and related organic material germanium is precipitated from water together with iron hydroxide accounting for its concentration in some sedimentary and supergene iron oxide deposits it also is able to substitute for fe in magnetite in a variety of geologic environments in the oxidized zone of ge bearing sulfide deposits ge is concentrated in oxides hydroxides and hydroxy sulfates sometimes forming its own minerals it is particularly enriched in some iron and manganese bearing oxides and hydroxides including goethite up to 5300 ppm and hematite up to 7000 ppm

role of the seasonal cycle in the subduction rates of upper southern ocean waters abstracta kinematic approach is used to diagnose the subduction rates of upper southern ocean waters across seasonally migrating density outcrops at the base of the mixed layer from an eulerian viewpoint the term representing the temporal change in the mixed layer depth which is labeled as the temporal induction in this study i e stemp h t where h is the mixed layer thickness and t is time vanishes over several annual cycles following seasonally migrating density outcrops however the temporal induction is attributed partly to the temporal change in the mixed layer thickness averaged over a density outcrop following its seasonally varying position and partly to the lateral movement of the outcrop position intersecting the sloping mixed layer base neither the temporal induction following an outcrop nor its integral over the outcrop area vanishes over several annual cycles instead the seasonal eddy subduction which arises primarily because of the subannual correlations between the seasonal

the relationship between water mass formation and the surface buoyancy flux with application to phillips red sea model abstract a buoyancy flux across the sea surface between the outcropping of isopycnals must be balanced by a subsurface diapycnal buoyancy flux if this flux were only advective its derivative with respect to buoyancy would provide a direct estimate of the buildup of volume between isopycnals or rate of water mass formation a diapycnal velocity however requires diapycnal mixing which also causes a diapycnal buoyancy flux and it is shown that there is no reason to expect a simple relationship between the advective and diffusive fluxes for a surface layer with vigorous vertical mixing and weak horizontal mixing however the diapycnal diffusive flux of buoyancy is small and the flow through the base of the mixed layer can be derived from the derivative of the surface buoyancy flux with respect to buoyancy these points are illustrated by examination of the phillips similarity solution for the convective circulation driven in a channel by a uniform surface buoyancy loss

silicate rock weathering and atmospheric soil co2 uptake in the amazon basin estimated from river water geochemistry seasonal and spatial variations abstract using the data of the camrex project 1982 1984 on the water geochemistry of the amazon river and its main tributaries it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric soil co2 taking into account seasonal and spatial variations this study confirms the important role of the andes in the fluvial transport of dissolved and particulate material by the amazon and it shows for the first time that the silicate weathering rate and atmospheric soil co2 consumption are higher in the andes than in the rest of the amazon basin the seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge the average weathering rate estimated for the whole amazon basin 15 m my is comparable to other estimations made for other tropical equatorial environments a comparison between physical and chemical weathering rates of silicate rocks for the amazon basin and for each tributary basin show that in the andes and in the amazon trough the soil thicknesses are decreasing whereas in the shield the soil profiles are deepening

on the role of interior mixing and air sea fluxes in determining the stratification and circulation of the oceans abstract the problem of determining the eastern boundary basic stratification and the buoyancy driven circulation of the oceans is addressed a global integral constraint relating the interior stratification and the air sea heat fluxes is derived based on the condition that the total mass of water of given density is constant in a steady state ocean this constraint is then applied to two simple analytic models the first is a continuous nonlinear diffusive model of the lower mid depth and bottom circulation below the influence of the wind driven circulation it shows the tendency of the vertical density profile to look like an exponential profile in the presence of mixing the integral constraint is used to relate the stratification and circulation of the bottom and mid depth waters to the air sea heat fluxes at the surface where the deep densities outcrop the second model is a layered one of the wind driven circulation mid depth and bottom water the eastern boundary stratification of the model i

backscatter characteristics of the winter ice cover in the beaufort sea the microwave backscatter statistics of the sea ice cover in the winter beaufort sea are characterized using c band synthetic aperture radar sar data collected by the european earth resources satellite 1 sea ice backscatter signatures were sampled from sar image data collected during the winter of 1991 1992 and winter of 1992 1993 the spatial and temporal variabilities of the backscatter signatures of different ice types are discussed the results show considerable seasonal stability of the backscatter signature of multiyear ice as well as of first year ice small amplitude regional variations of the multiyear ice backscatter can be observed consistent contrast between multiyear ice and first year ice is maintained throughout the season the highest radiometric variability is observed in sea ice in leads on the basis of these observations the backscatter from the principal ice types multiyear and first year are consistent with scatterometer observations and can be easily identified under winter conditions correlations of the regional variations of multiyear ice signatures to physical processes are suggested

a reactive transport model for marcellus shale weathering abstract shale formations account for 25 of the land surface globally and contribute a large proportion of the natural gas used in the united states one of the most productive shale gas formations is the marcellus a black shale that is rich in organic matter and pyrite as a first step toward understanding how marcellus shale interacts with water in the surface or deep subsurface we developed a reactive transport model to simulate shale weathering under ambient temperature and pressure conditions constrained by soil and water chemistry data the simulation was carried out for 10 000 years since deglaciation assuming bedrock weathering and soil genesis began after the last glacial maximum results indicate weathering was initiated by pyrite dissolution for the first 1000 years leading to low ph and enhanced dissolution of chlorite and precipitation of iron hydroxides after pyrite depletion chlorite dissolved slowly primarily facilitated by the presence of co2 and organic acids forming vermiculite as a secondary mineral a sensitivity analysis indicated that the most important controls on weathering include the presence of reactive gases co2 and o2 specific surface area and flow velocity of infiltrating meteoric water the soil chemistry and mineralogy data could not be reproduced without including the reactive gases for example pyrite remained in the soil even after 10 000 years if o2 was not continuously present in the soil column likewise chlorite remained abundant and porosity remained small if co2 was not present in the soil gas the field observations were only simulated successfully when the modeled specific surface areas of the reactive minerals were 1 3 orders of magnitude smaller than surface area values measured for powdered minerals small surface areas could be consistent with the lack of accessibility of some fluids to mineral surfaces due to surface coatings in addition some mineral surface is likely interacting only with equilibrated pore fluids an increase in the water infiltration rate enhanced weathering by removing dissolution products and maintaining far from equilibrium conditions we conclude from these observations that availability of reactive surface area and transport of h2o and gases are the most important factors affecting rates of marcellus shale weathering of the in the shallow subsurface this weathering study documents the utility of reactive transport modeling for complex subsurface processes such modelling could be extended to understand interactions between injected fluids and marcellus shale gas reservoirs at higher temperature pressure and salinity conditions

diffusive transport of water in porous fresh to altered mid ocean ridge basalts abstract studying diffusive transport in porous rocks is of fundamental importance in understanding a variety of geochemical processes including element transfer primary mineral dissolution kinetics and precipitation of secondary phases here we report new findings on the relationship between diffusive transport and textural characteristics of the pore systems on the example of mid oceanic ridge basalts having different degree of alteration but very similar bulk pore volume diffusion processes in porous basalts were studied in situ using h 2 o d 2 o exchange experiments the effective diffusion coefficients of water molecules increase systematically from 5 05 10 11 to 1 19 10 10 m 2 s for fresh and moderately altered basalts and from 2 40 10 11 to 6 72 10 11 m 2 s for completely altered basalt as temperature increases from 5 to 50 c the activation energy of the diffusion process increases from 12 29 0 71 kj mol for fresh and moderately altered basalts to 14 3 1 33 kj mol for completely altered basalt the results indicate that neither the bulk porosity nor the degree of alteration can be used as proxies for the efficiency of element transport during morb water interaction the formation of secondary phases that replace primary minerals and fill the pore space in the rock leads to the formation of tiny pores and phases with large specific surface area these factors might have a dominant control on the transport properties of altered basaltic rocks

production regimes in the northeast atlantic a study based on sea viewing wide field of view sensor seawifs chlorophyll and ocean general circulation model mixed layer depth 1 a 5 year time series of sea viewing wide field of view sensor seawifs ocean color images schl is compared with mixed layer depths mld and atmospheric forcings from the clipper model of the north atlantic 1998 2002 this comparison is done over the region 16 22 w 30 50 n where subpolar mode waters are formed and which overlaps the region of the 2001 programme ocean multidisciplinaire meso echelle pomme experiment at sea three production regimes are identified on the basis of the seasonal cycling of schl and mld the well known subpolar and subtropical regimes and a midlatitude regime the midlatitude regime is characterized by a single broad bloom weaker than the subpolar spring bloom and stronger than the subtropical fall bloom which starts in fall as an entrainment bloom and peaks in spring as a restratification bloom this specific regime is found between 35 n and 40 n 2 in the northeast atlantic it corresponds to winter mlds between ze the depth of the euphotic layer and 2ze i e it lays between the region where the winter mld is greater than sverdrup s critical depth subpolar regime and the region where the mixing is never deeper than the well lit layer subtropical regime the very specific characteristics of the midlatitude regime strengthen the biological carbon pump since production is active in winter within the waters to be subducted the midlatitude regime also may provide an explanation for the unexpectedly low f ratios sometimes observed during the bloom in the region north atlantic bloom experiment pomme a large interannual variability is observed for the three regimes in terms of the timing and the intensity of the blooms and of the geographical boundaries of the regimes these variabilities appear to be mainly driven by the synoptic and the low frequency atmospheric variabilities it is also shown that in addition to the northward propagation of the subpolar spring bloom from 41 n 1 3 to 50 n the fall entrainment bloom propagates southward over the whole latitudinal range 35 50 n

structure and cycle of decadal variability of upper ocean temperature in the north pacific abstract yearly upper ocean in situ temperature anomaly data for the period 1961 90 are analyzed to reveal spatial structure and evolution of decadal variability in the north pacific ocean an eof analysis has been performed on individual temperature anomaly fields at upper ocean standard levels as well as simultaneously on the entire upper ocean data to depict the combined three dimensional structure in a coherent manner time evolution of anomaly fields is depicted by using a regression analysis the analyses detect the principal basin scale structure of decadal warm period dwp and decadal cold period dcp there is a well defined subsurface thermal anomaly pattern characterized by a prominent seesaw structure with opposite anomaly polarity between the midlatitude north pacific and the subtropical regions during a dwp a positive temperature anomaly is found in the central midlatitude upper ocean with the maximum at about 100 m depth this is accompanied by a corresponding negative anomaly in the

physical pathways for carbon transfers between the surface mixed layer and the ocean interior 1 although they are key components of the surface ocean carbon budget physical processes inducing carbon fluxes across the mixed layer base i e subduction and obduction have received much less attention than biological processes using a global model analysis of the preindustrial ocean physical carbon fluxes are quantified and compared to the other carbon fluxes in and out of the surface mixed layer i e air sea co2gas exchange and sedimentation of biogenic material model based carbon obduction and subduction are evaluated against independent data based estimates to the extent that was possible we find that climatological physical fluxes of dissolved inorganic carbon dic are two orders of magnitude larger than the other carbon fluxes and vary over the globe at smaller spatial scale at temperate latitudes the subduction of dic and to a much lesser extent 10 the sinking of particles maintain co2undersaturation whereas dic is obducted back to the surface in the tropical band 75 and southern ocean 25 at the global scale these two large counter balancing fluxes of dic amount to 275 5 pgc yr 1 for the supply by obduction and 264 5 pgc yr 1 for the removal by subduction which is 3 to 5 times larger than previous estimates moreover we find that subduction of organic carbon dissolved and particulate represents 20 of the total export of organic carbon at the global scale we evaluate that of the 11 pgc yr 1 of organic material lost from the surface every year 2 1 pgc yr 1 is lost through subduction of organic carbon our results emphasize the strong sensitivity of the oceanic carbon cycle to changes in mixed layer depth ocean currents and wind

limex 87 ice surface characteristics implications for c band sar backscatter signatures ice surface characterization data collected in 1987 during the labrador ice margin experiment are analyzed to estimate the changes in snow and ice properties at the onset of melt surface measurements were made from an ice research vessel on several days some of which had coincident remote sensing flights at a number of locations in the marginal ice zone these data are used as input parameters in a simple scattering model to simulate the effects of variations in material properties upon c band scattering signatures

c band scatterometer measurements of multiyear sea ice before fall freeze up in the canadian arctic backscatter signatures of multiyear sea ice myi during the late summer and early fall season before the fall freeze up in the canadian arctic archipelago caa have been obtained through the use of a ship based polarimetric scatterometer the device operates in c band and measurements were conducted in swaths from incidence angles of 20 deg 60deg three characteristic sites on myi floes were investigated in the high arctic and the central arctic regions in situ snow and sea ice thermophysical data were collected at each site in conjunction with local scatterometer measurements the thermophysical data were subsequently analyzed using dielectric modeling techniques and coupled with the backscattering measurements sigmadeg observed backscatter values and ratios were found to be in agreement with literature data with volumetric scattering as the dominant scattering mechanism

effects of the mixed layer time variability on kinematic subduction rate diagnostics abstract an eddy resolving primitive equation general circulation model is used to estimate water mass subduction rates in the north atlantic ocean subtropical gyre the diagnostics are based on the instantaneous kinematic approach which allows the calculation of the annual rate of water mass subduction at a given density range following isopycnal outcrop positions over the annual cycle it is shown that water mass subduction is effected rapidly 1 2 months as the mixed layer depth decreases in spring consistent with stommel s hypothesis and occurs mostly over the area of deep late winter mixed layers 150 m across the central north atlantic in the density range 26 27 2 annual subduction rates o 100 200 m yr 1 are found south and east of the gulf stream extension in the density range of subtropical mode waters from roughly 26 2 to 26 6 in the northeastern part of the subtropical gyre annual subduction rates are somewhat larger o 250 m yr 1 from a density of about 26 9 east of the nort

a high resolution simulation of the ocean during the pomme experiment mesoscale variability and near surface processes 1 this article is the second part of a modeling study of upper ocean mesoscale physical processes in an area of the northeast atlantic that was extensively sampled during the programme ocean multidisciplinaire meso echelle pomme experiment october 2000 september 2001 the model is a high resolution regional version of the ocean general circulation model opa integrated from february to may 2001 the mesoscale upper ocean dynamics has been carefully validated in a first paper paci et al 2005 in the present article the simulation is used to analyze the contribution of mesoscale eddies to the mixed layer processes during the period that controls the annual subduction rate and the characteristics of the subducted water mesoscale eddies account for a significant part of the mixed layer heat salt and water budgets through mesoscale and submesoscale structures acting on the horizontal advective terms they represent respectively 52 and 66 of the horizontal advection of temperature and salinity and 70 of the lateral induction they also induce an earlier and more intense restratification the domain averaged detrainment appears to be reduced by more than 15 by mesoscale eddies and reaches about 0 8 sv however these eddies increase the density of the detrained water some dense water likely to be involved in the formation of subpolar mode water is detrained by them in a way that maximizes its chance to be effectively subducted in the area

germanium sequestration by soil targeting the roles of secondary clays and fe oxyhydroxides abstract germanium is a trace element that behaves similarly to silicon and shows promise as a tracer of silicate weathering processes sequestration of ge by clay minerals is thought to be the dominant mechanism responsible for ge si fractionation during weathering in some environments ge may be sequestered by iron oxyhydroxides we examine ge behavior in soils along a well characterized climate gradient on the hawaiian island of maui to clarify the relationship between fe geochemistry and soil ge si ratios all of the sites are developed on basaltic lavas and tephras approximately 400 ky old are highly si depleted and have ge si ratios higher than parent material sites experiencing less than 3300 mm rain yr host oxidized highly weathered basaltic soils in which fe is present as secondary fe oxyhydroxide minerals in contrast the wetter sites 3340 mm yr show extensive fe reduction mobilization and loss we show that ge sequestration is independent of fe redox behavior along the gradient and thus precipitation of fe oxyhydroxides is not a major factor contributing to ge si fractionation during weathering instead elevated soil ge si ratios reflect partitioning of ge into secondary clay minerals plus additional retention of ge by refractory non silicates

modelling of atmospheric co2 consumption by chemical weathering of rocks application to the garonne congo and amazon basins modelling of atmospheric co consumption by chemical weathering of rocks application to the garonne congo and amazon basins

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

assessing the role of submarine groundwater discharge as a source of sr to the mediterranean sea abstract submarine groundwater discharge sgd has been identified as an important source of sr to the ocean and the sgd driven sr flux to the global ocean has been recently re evaluated beck et al 2013 however the uncertainty of this value is still high because of the uncertainties related to the determination of sgd flow rates and the paucity of 87 sr 86 sr data in sgd end members as carbonates have high sr concentrations and are subjected to intense heightened weathering they might significantly influence the sgd input of sr to the ocean here we present data on sr concentrations and 87 sr 86 sr ratios in three carbonate dominated sites of the western area of the mediterranean sea a semi enclosed basin characterized by abundant coastal carbonates the 87 sr 86 sr ratios in groundwater were lower compared to modern seawater 0 70916 as expected for areas dominated by carbonate lithologies concentrations of sr and 87 sr 86 sr ratios in groundwater showed conservative mixing in the studied subterranean estuaries by using sgd flow rates reported in the literature for the study areas a flow weighted fresh sgd end member characterized by a sr concentration of 27 30 m and a 87 sr 86 sr ratio of 0 707834 0 708020 was calculated for the eastern coast of the iberian peninsula integrating these sr data with literature data i e values of sr concentration and 87 sr 86 sr ratio from other lithologies as well as sgd flow rates we also calculated the fresh sgd driven sr flux to the entire mediterranean sea obtaining a value of 0 34 0 83 10 9 mol y 1 with a 87 sr 86 sr of 0 7081 0 7086 thus for the entire mediterranean basin sgd is globally a source of sr less radiogenic compared to seawater the sgd sr flux to the mediterranean sea represents 5 6 of the sgd sr flux to the global ocean and the mediterranean sgd end member has higher sr concentration 5 12 m than the global sgd end member 2 9 m this confirms the significant role of carbonate lithologies on sgd driven sr fluxes to seawater the fresh sgd driven sr flux to the mediterranean sea is about 20 50 of the riverine sr input and significantly higher than the input through atmospheric dust deposition therefore sgd should be considered as an important continental source of sr to the basin

ventilation of the north atlantic and north pacific subduction versus obduction abstract ventilation in the north atlantic and north pacific is examined by analyzing the levitus climatological data and the hellerman and rosenstein wind stress data ventilation between the permanent pycnocline and the overlying seasonal pycnocline and mixed layer consists of two physical processes subduction and obduction subduction takes place mainly in the subtropical basin where surface water is irreversibly transferred into the permanent pycnocline below obduction takes place in the subpolar basin where water from the permanent pycnocline is irreversibly transferred into the mixed layer above veatilation in the north atlantic and north pacific can be clarified into four physically different regions the subductive region the obductive region the ambiductive region where both subduction and obduction take place and the insulated region where neither subduction nor obduction occurs although the total subduction rates in these two oceans are comparable the total obduction rates are considera

on the thermodynamics of subduction abstract the thermodynamic processes attendant on the transfer of fluid between a surface mixed layer and a stratified thermocline beneath are discussed for a parcel of fluid in the mixed layer to pass into the stratified thermocline to subduct it must be stratified by buoyancy input this buoyancy can be supplied by local air sea exchange and or by lateral advective processes a series of experiments is described in which a mixed layer coupled to an ideal fluid thermocline undergoes differing seasonal cycles in one limit the mixed layer is held fixed in a steady winter configuration in the other the mixed layer is more realistically shallow over most of the year and deepens briefly in late winter it is shown that the annual subduction rate sann depends to first order only on late winter mixed layer properties however the annual mean air sea buoyancy exchange is sensitive to the details of the seasonal cycle and becomes vanishingly small as the effective subduction period shortens in this lim

observation of sea ice using the 36 ghz surface contour radar in january 1984 a 36 ghz scanning pencil beam radar was used at 175 m altitude over ice in the greenland sea to produce high spatial resolution 3 m by 5 m topographic and backscattered power maps incidence angles from nadir to approximately 300 offnadir were included in the data set when the radar maps were compared with the ice topography indicated by simultaneous photography and an analysis of the shadows of the ridges cast by the low sun angle 3 5 it was found that the backscattered power data sharply delineated many of the features observed in the photography the elevation data were less impressive but still consistent with the general variation of the topography

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy resolving ogcm of the western north pacific abstract the effects of mesoscale eddies on the subduction and distribution of the north pacific subtropical mode water stmw are investigated using an eddy resolving ocean general circulation model ogcm first the subduction rate is calculated and the contribution of eddies to the subduction of stmw is estimated it is found that eddy subduction significantly contributes to the total subduction of stmw second eddy thickness transport and diapycnal flux are directly diagnosed to investigate the large scale eddy induced transport process of stmw the large southward eddy thickness transport in the stmw core density is consistent with eddy subduction the eddy transport on the isopycnal surface of stmw is directed down the thickness gradient and traverses the mean flow the meridional eddy transport streamfunction indicates two eddy circulation cells south of 30 n associated with the circulation of stmw these cells flatten density surfaces similar to the effect of the gent and mcwilliams gm schem

mode water variability in a model of the subtropical gyre response to anomalous forcing abstract the response of mode water formation to typical atmospheric forcing anomalies is studied as a possible mechanism for generating the observed interannual to decadal variability in mode water an isopycnal model of the north atlantic subtropical gyre coupled to a mixed layer model is used for this purpose geometry and forcing are idealized the control run shows that mode water is a well ventilated water mass formation rates up to 200 m yr 1 are found at the outcrop of the mode water layer in a series of experiments the sensitivity to the position of the anomalous forcing and to the timescale of the forcing is examined the anomalous forcing has a dipole pattern that mimics the spatial structure of the north atlantic oscillation anomalous cooling induces a positive thickness anomaly in the mode water layer at the center of the gyre and a negative anomaly at the eastern side of the gyre the response to anomalous heat flux forcing appears to be sensitive to the position of the forcing anomaly

an eddy resolving numerical model of the ventilated thermocline time dependence abstract a primitive equation eddy resolving numerical model is used to study the inherent time scales of variability in the subtropical ocean assuming temporally constant surface forcing three primary scales arise mesoscale variability of roughly 50 day period zonally elongated barotropic bands of 1 1 year period and basin scale undulations of approximately 4 year period the latter are identified as first baroclinic mode rossby waves associated with bursts of ventilation at isopycnal outcrops as a result the equatorward transport required by sverdrup theory in the subtropics occurs not as a broad sluggish drift throughout the interior but as a succession of more intense flows that slowly propagate westward the zonally elongated bands agree in characteristics to those predicted from theory of homogeneous turbulence eddy energy that is generated by baroclinic instability leaks from baroclinic to barotropic mode and thereafter due to rotational constraints seeks low zonal wavenumbers the gr

eddy induced heat transport in a coupled ocean atmospheric anomaly model the midlatitude meridional heat transport in the ocean can be partitioned into a transport by the mean flow and an eddy transport this heat transport has been studied in several ocean only models surprisingly it was found that eddy resolving and coarse resolution models have similar total heat transport this is caused by a compensation mechanism in which poleward eddy transport is counterbalanced by an eddy induced meridional circulation recently it was shown that this compensation depends on details of the atmospheric forcing and in fact only occurs for weak thermal coupling where thermal coupling is defined as the rate of change of the surface heat flux with respect to the sea surface temperature sst the thermal coupling varies with the spatial scale of the sst anomaly to study the actual strength of this coupling on the eddy length scale the authors have coupled an isopycnic ocean model with embedded mixed layer to an atmospheric anomaly model by comparing coarse resolution and eddy resolving simulations it is found that 1 the thermal coupling is strong on the eddy length scale and 2 the aforementioned compensation does not occur consequences for the temperature boundary condition in ocean only models the gent and mcwilliams eddy parameterization and climate modeling are discussed

a perspective on the future of physical oceanography the ocean flows because it is forced by winds tides and exchanges of heat and freshwater with the overlying atmosphere and cryosphere to achieve a state where the defining properties of the ocean such as its energy and momentum do not continuously increase some form of dissipation or damping is required to balance the forcing the ocean circulation is thought to be forced primarily at the large scales characteristic of ocean basins yet to be damped at much smaller scales down to those of centimetre sized turbulence for decades physical oceanographers have sought to comprehend the fundamentals of this fractal puzzle how the ocean circulation is driven how it is damped and how ocean dynamics connects the very different scales of forcing and dissipation while in the last two decades significant advances have taken place on all these three fronts the thrust of progress has been in understanding the driving mechanisms of ocean circulation and the ocean s ensuing dynamical response with issues surrounding dissipation receiving comparatively little attention this choice of research priorities stems not only from logistical and technological difficulties in observing and modelling the physical processes responsible for damping the circulation but also from the untested assumption that the evolution of the ocean s state over time scales of concern to humankind is largely independent of dissipative processes in this article i illustrate some of the key advances in our understanding of ocean circulation that have been achieved in the last 20 years and based on a range of evidence contend that the field will soon reach a stage in which uncertainties surrounding the arrest of ocean circulation will pose the main challenge to further progress it is argued that the role of the circulation in the coupled climate system will stand as a further focal point of major advances in understanding within the next two decades supported by the drive of physical oceanography towards a more operational enterprise by contextual factors the basic elements that a strategy for the future must have to foster progress in these two areas are discussed with an overarching emphasis on the promotion of curiosity driven fundamental research against opposing external pressures and on the importance of upholding fundamental research as the apex of education in the field

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

geochemical fingerprinting and source discrimination of agricultural soils at continental scale 2108 agricultural soil samples ap horizon 0 20 cm were collected in europe 33 countries area 5 6 million km2 as part of the recently completed gemas geochemical mapping of agricultural and grazing land soil soil mapping project gemas soil data have been used to provide a general view of element origin and mobility with a main focus on source parent material and source rocks at the continental scale either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes the survey area covers a large territory with diverse types of soil parent materials with distinct geological history and a wide range of climate zones and landscapes to normalize the chemical composition of european agricultural soil mean values and standard deviation of the selected elements have been compared to model compositions of the upper continental crust ucc and mean european river suspended sediment some elements are enriched relative to the ucc al p pb zr whereas others such as mg na and sr are depleted the concept of the ucc extended normalization pattern has been applied to selected elements the mean values of rb k y ti al si zr ce and fe are very similar to the values from the ucc model even when standard deviations indicate slight enrichment or depletion zirconium has the best fit to the ucc model using both mean value and standard deviation lead and cr are enriched in european soil when compared to the ucc model but their standard deviation values span a large particularly towards very low values which can be interpreted as a lithological effect gemas soil data have been normalized to al and na taking into account the main lithologies of the ucc in order to discriminate provenance sources additionally sodium normalization highlights variations related to the soluble and insoluble behavior of some elements e g k rb versus ti al si v y zr ba and la respectively their reactivity e g fe mn zn and association with carbonates e g ca and sr maps of europe showing the spatial distribution of normalized compositions and element ratios reveal difficulties with the use of classical element ratios because of the large lithological differences in compositions of soil parent material the ratio maps and color composite images extracted from the gemas data can help to discriminate the main lithologies in europe at the regional scale but need to be used with caution due to the complexity of superimposed processes responsible for the soil chemical composition

impact of atmospheric co2 levels on continental silicate weathering 1 anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric co2 concentrations since the beginning of the industrial revolution here we use the b witch model to quantify the impact of increased co2 concentrations on co2 consumption by weathering of continental surfaces b witch couples a dynamic biogeochemistry model lpj and a process based numerical model of continental weathering witch it allows simultaneous calculations of the different components of continental weathering fluxes terrestrial vegetation dynamics and carbon and water fluxes the co2 consumption rates are estimated at four different atmospheric co2 concentrations from 280 up to 1120 ppmv for 22 sites characterized by silicate lithologies basalt granite or sandstones the sensitivity to atmospheric co2 variations is explored while temperature and rainfall are held constant first we show that under 355 ppmv of atmospheric co2 b witch is able to reproduce the global pattern of weathering rates as a function of annual runoff mean annual temperature or latitude for silicate lithologies when atmospheric co2 increases evapotranspiration generally decreases due to progressive stomatal closure and the soil co2 pressure increases due to enhanced biospheric productivity as a result vertical drainage and soil acidity increase promoting co2 consumption by mineral weathering we calculate an increase of about 3 of the co2 consumption through silicate weathering mol ha 1 yr 1 for 100 ppmv rise in co2 importantly the sensitivity of the weathering system to the co2 rise is not uniform and heavily depends on the climatic lithologic pedologic and biospheric settings

effect of oceanic advection on the potential predictability of sea surface temperature abstract the effect of oceanic advection on the predictability of sea surface temperature sst is investigated in the framework of a linear stochastic model an analytical solution of a one dimensional model shows that even though advection can give rise to a pair of low frequency normal modes no enhancement in the predictability is found in terms of domain averaged error variance however a predictable component analysis shows that advection can play a role in redistributing the predictable variance when forced with a spatially coherent stochastic forcing advection enables certain regions to be more predictable than others this analytical result is further examined in a more realistic two dimensional north atlantic model with observed mean currents it is shown that the predictability of sst averaged over the whole north atlantic basin is determined by the thermal damping time scale 3 months not the advective time scale 6 years however the most predictable pattern reveals that the predicta