spatial zonation limits magnesite dissolution in porous media abstract we investigate how mineral spatial distribution in porous media affects their dissolution rates specifically we measure the dissolution rate of magnesite interspersed in different patterns in packed columns of quartz sand where the magnesite concentration v v was held constant the largest difference was observed between a mixed column containing uniformly distributed magnesite and a one zone column containing magnesite packed into one cylindrical center zone aligned parallel to the main flow of acidic inlet fluid flow parallel one zone column the columns were flushed with acid water at a ph of 4 0 at flow velocities of 3 6 or 0 36 m d breakthrough data show that the rate of magnesite dissolution is 1 6 2 times slower in the one zone column compared to the mixed column this extent of rate limitation is much larger than what was observed in our previous work 14 for a similar one zone column where the magnesite was packed in a layer aligned perpendicular to flow flow transverse one zone column two dimensional reactive transport modeling with crunchflow revealed that ion activity product iap and local dissolution rates at the grid block scale 0 1 cm vary by orders of magnitude much of the central magnesite zone in the one zone flow parallel column is characterized by close or equal to equilibrium conditions with iap k eq 0 1 two important surface areas are defined to understand the observed rates the effective surface area a e reflects the magnesite that effectively dissolves under far from equilibrium conditions iap k eq a i reflects the effective magnesite surface that lies along the quartz magnesite interface modeling results reveal that the transverse dispersivity at the interface of the quartz and magnesite zones controls mass transport and therefore the values of a e and a i under the conditions examined in this work the value of a e varies from 2 to 67 of the total magnesite bet surface area column scale bulk rates r mgco 3 b in units of mol s vary linearly with a e and a i using a e to normalize rates we calculate a rate constant 10 9 56 mol m 2 s that is very close to the value of 10 10 0 mol m 2 s under well mixed conditions at the grid block scale this implies that the laboratory field rate discrepancy can potentially be caused by differences in the effective surface area if we know the effective surface area of dissolution we will be able to use the rate constant measured in laboratory systems to calculate field rates for some systems in this work approximately 60 70 of the a e is at the magnesite quartz interface this implies that in some field systems where the detailed information that we have for our columns is not available the effective mineral surface area may be approximated by the area of grains residing at the interface of reactive mineral zones although it has long been known that spatial heterogeneities play a significant role in determining physical processes such as flow and solute transport our data are the first that systematically and experimentally quantifies the importance of mineral spatial distribution chemical heterogeneity on dissolution

new evidence from the western canadian arctic archipelago for the resubmergence of bering strait widespread molluscan samples were collected from raised marine sediments to date the last retreat of the nw laurentide ice sheet from the western canadian arctic archipelago at the head of mercy bay northern banks island deglacial mud at the modern coast contains hiatella arctica and portlandia arctica bivalves as well as cyrtodaria kurriana previously unreported for this area multiple h arctica and c kurriana valves from this site yield a mean age of 11 5 14c ka bp with 740 yr marine reservoir correction the occurrence of c kurriana a low arctic taxon raises questions concerning its origin because evidence is currently lacking for a molluscan refugium in the arctic ocean during the last glacial maximum elsewhere the oldest late glacial age available on c kurriana comes from the laptev sea where it is 10 3 14c ka bp and attributed to a north atlantic source this is 2000 cal yr younger than the mercy bay samples reported here making the laptev sea 3000 km to the west an unlikely source an alternate route from the north atlantic into the canadian arctic archipelago was precluded by coalescent laurentide innuitian and greenland ice east of banks island until 10 14c ka bp we conclude that the presence of c kurriana on northern banks island records migration from the north pacific this requires the resubmergence of bering strait by 11 5 14c ka bp extending previous age determinations on the reconnection of the pacific and arctic oceans by up to 1000 yr this renewed ingress of pacific water likely played an important role in re establishing arctic ocean surface currents including the evacuation of thick multi year sea ice into the north atlantic prior to the younger dryas geochron

marine and limnic radiocarbon reservoir corrections for studies of late and postglacial environments in georgia basin and puget lowland british columbia canada and washington usa models of late glacial environmental change in coastal areas are commonly based on radiocarbon ages on marine shell and basal lake sediments both of which may be compromised by reservoir effects the magnitude of the oceanic reservoir age in the inland waters of the georgia basin and puget lowland of northwestern north america is inferred from radiocarbon ages on shell wood pairs in saanich inlet and previously published estimates the weighted mean oceanic reservoir correction in the early and mid holocene is 720 90 yr slightly smaller than but not significantly different from the modern value the correction in late glacial time is 950 50 yr valley head sites yield higher reservoir values 1200 130 yr immediately after deglaciation the magnitude of the gyttja reservoir effect is inferred from pairs of bulk gyttja and plant macrofossil ages from four lakes in the region incorporation of old carbon into basal gyttja yields ages from bulk samples that are initially about 600 yr too old the reservoir age declines to less than 100 yr after the first millennium of lake development when these corrections are accounted for dates of deglaciation and late glacial sea level change in the study area are pushed forward in time by more than 500 yr

time evolution of the mineralogical composition of mississippi valley loess over the last 10 kyr climate and geochemical modeling abstract anthropogenic and natural climate change affect processes in the atmosphere biosphere hydrosphere and pedosphere the impact of climate on soil evolution has not been well explored largely due to slow rates and the complexity of coupled processes that must be observed and simulated the rates of mineral weathering in loess deposited 23 kyr ago and experiencing soil formation for 13 kyr are explored here using the witch model for weathering and the genesis model for climate simulation the witch model which uses rigorous kinetic parameters and laws with provision for the effect on rates of deviation from equilibrium can successfully simulate the depletion profiles in the soil for dolomite and albite if soil co2 is assumed to rise over the last 10 kyr up to about 30 40 the present atmospheric pressure and if the solubility product of the ca smectite is assumed equal to that of an fe iii rich ca montmorillonite such simulations document that dissolution behavior for silicates and carbonates are strongly coupled through ph and for ca smectite and feldspars through dissolved silica such coupling is not incorporated in simple geometric and analytical models describing mineral dissolution and therefore probably contributes to the long standing observation of discrepancies among laboratory and field mineral dissolution rates

a paleoclimate interpretation derived from pedogenic clay minerals from the piedmont province virginia abstract oxygen isotope ratios of pedogenic kaolinites were measured to estimate the ambient climate conditions during the formation of a saprolite in the piedmont province woodbridge va kaolinite is the predominant pedogenic clay mineral in this saprolite it is formed mostly from weathering of muscovite and to a lesser extent from weathering of microcline a dioctahedral smectite vermiculite phase formed by weathering muscovite is present in minor amounts the 18o 16o ratios indicate that most if not all the kaolinite formed in a cooler climatic regime in which meteoric waters were more depleted in 18o than most present meteoric waters it is possible that the pedogenic kaolinite formed shortly after or during the pleistocene glacial stage in north america this interpretation is consistent with the age of this saprolite derived from 10be dating methods the oxygen isotopic signatures of these kaolinites are not consistent with an older middle or early miocene age for this saprolite

constancy of silicate mineral weathering rate ratios between natural and experimental weathering implications for hydrologic control of differences in absolute rates abstract inverse models which apportion watershed effluxes geochemical mass balance over estimated mineral surface area give weathering rates for individual silicate minerals e g feldspar 1 3 orders of magnitude slower than laboratory rates comparisons of rates calculated from several recent watershed geochemical mass balance studies with experimentally determined rates reveal that the ratio of mineral weathering rates for a given silicate mineral pair determined in an internally consistent field study equals the ratio of rates for the same minerals in any internally consistent set of laboratory experimental data thus the coefficient which corrects the weathering rate for any mineral from a laboratory data set to a field setting is identical to the corresponding coefficient for any other mineral in the same data sets the correction factor linking experimental and natural rates must be independent of composition physical e g hydrologic controls rather than compositional or chemical controls cause the difference between weathering rates in nature and the laboratory because flow in natural weathering profiles is spatially heterogeneous not all of the potentially available surface in natural systems actually participates in reactions with pore fluids

constraining tectonic compression processes by reservoir pressure evolution overpressure generation and evolution in the kelasu thrust belt of kuqa foreland basin nw china abstract the kuqa foreland basin kfb immediately south of the south tianshan mountains is a major hydrocarbon producing basin in west china the kelasu thrust belt in the basin is the most favorable zone for hydrocarbon accumulations widespread overpressures are present in both the cretaceous and paleogene reservoirs with pressure coefficients up to 2 1 the tectonic compression process in kfb resulted from the south tianshan mountains uplift is examined from the viewpoint of the overpressure generation and evolution in the kelasu thrust belt the overpressure evolution in the reservoir sandstones were reconstructed through fluid inclusion analysis combined with pvt and basin modeling overpressures at present day in the mudstone units in the kelasu thrust belt and reservoir sandstones of the dabei gas field and the keshen zone are believed to have been generated by horizontal tectonic compression both disequilibrium compaction and horizontal tectonic compression are thought to contribute to the overpressure development at present day in the reservoir of the kela 2 gas field with the reservoir sandstones showing anomalously high primary porosities and low densities from wireline log and core data the overpressure evolution for the cretaceous reservoir sandstone in the kelasu thrust belt evolved through four stages a normal hydrostatic pressure 12 5 ma a rapidly increasing overpressure 5 3 ma an overpressure release 3 1 64 ma and overpressure preservation 1 64 0 ma overpressure developed in the second stage 5 3 ma was generated by disequilibrium compaction as tectonic compression due to the uplift of the tianshan mountains acted at the northern monocline of kfb from 5 ma to 3 ma which provided abundant sediments for the kfb and caused the anomalously high sedimentation rate during the n2k deposition from 3 ma to 1 64 ma the action of tectonic compression extended from the northern monocline to the kelasu thrust belt and returned to the northern monocline of kfb from 1 64 ma to present day therefore the horizontal tectonic compression was the dominant overpressure mechanism for the overpressure generation in the third stage 3 1 64 ma and overpressure caused by disequilibrium compaction from 5 ma to 3 ma was only preserved in the kela 2 gas field until present day

relationships between co2 thermodynamic limits on silicate weathering and the strength of the silicate weathering feedback abstract recent studies have suggested that thermodynamic limitations on chemical weathering rates exert a first order control on riverine solute fluxes and by extension global chemical weathering rates as such these limitations may play a prominent role in the regulation of carbon dioxide levels p co 2 over geologic timescales by constraining the maximum global weathering flux in this study we develop a theoretical scaling relationship between equilibrium solute concentrations and p co 2 based on equilibrium constants and reaction stoichiometry relating primary mineral dissolution and secondary mineral precipitation we test this theoretical scaling relationship against reactive transport simulations of chemical weathering profiles under open and closed system conditions representing partially and fully water saturated regolith respectively under open system conditions equilibrium bicarbonate concentrations vary as a power law function of p co 2 y k x n where n is dependent on reaction stoichiometry and k is dependent on both reaction stoichiometry and the equilibrium constant under closed system conditions bicarbonate concentrations vary linearly with p co 2 at low values and approach open system scaling at high p co 2 to describe the potential role of thermodynamic limitations in the global silicate weathering feedback we develop a new mathematical framework to assess weathering feedback strength in terms of both 1 steady state atmospheric p co 2 concentrations and 2 susceptibility to secular changes in degassing rates and transient carbon cycle perturbations which we term 1st and 2nd order feedback strength respectively finally we discuss the implications of these results for the effects of vascular land plant evolution on feedback strength the potential role of vegetation in controlling modern solute fluxes and the application of these frameworks to a more complete functional description of the silicate weathering feedback most notably the dependence of equilibrium solute concentrations on p co 2 may represent a direct weathering feedback largely independent of climate and modulated by belowground organic carbon respiration

the surface area and reactivity of granitic soils i dissolution rates of primary minerals as a function of depth and age deduced from field observations surface area normalised dissolution rates of the primary minerals in two distinct granitic soils located in 1 the dartmoor national park england and 2 glen dye scotland were determined as a function of depth each soil was sampled to a depth of 1 m the maximum soil ages based on 14c analysis of the humin fraction of the soil are 15 600 and 4400 years for the dartmoor and glen dye soil profiles respectively the measured bet surface areas of the soil minerals are close to 5 m2 g in the b and c horizons but decrease to less than 1 m2 g close to the surface retrieved geometric surface area normalised mineral dissolution rates are most rapid at the surface and at the bedrock soil interface this behaviour is interpreted to stem from a combination of the approach to equilibrium of the soil waters with depth and more rapid dissolution rates of fresh versus weathered surfaces at the soil surface the relative mineral dissolution rate order is found to be quartz feldspar mica with quartz geometric surface area dissolution rates as fast as 2 6 to 4 1 10 13 mol m2 s as observed in a number of past studies field based rates obtained in this study are significantly slower than corresponding rates obtained from laboratory studies suggesting that these latter rates may not accurately describe the reactivity of primary minerals in soils

a paleotemperature record derived from dissolved noble gases in groundwater of the aquia aquifer maryland usa low 14c activities in groundwater of the confined part of the aquia aquifer in southeastern maryland suggest that most of this water infiltrated at least 30 000 years ago however radiocarbon contents of the dissolved inorganic carbon seem to be affected by isotopic exchange possibly with secondary calcite deposits in the formation leading to overestimated 14c ages whereas the geochemistry of the aquia aquifer complicates the application of the widely used 14c dating method the accumulation of radiogenic he seems to provide a viable alternative for establishing a chronology the quasi linear increase of he concentrations with flow distance observed in the aquia aquifer can be explained entirely by accumulation of in situ produced radiogenic he u and th concentrations in aquia sand were measured in order to determine the accumulation rate of 4he with sufficient confidence to establish a he time scale concentrations of dissolved atmospheric noble gases were used to derive mean annual ground temperatures at the time of infiltration these noble gas temperatures ngts clearly show the presence of water that infiltrated under much cooler conditions than at present ngts are correlated with chloride concentrations corroborating the hypothesis that chloride variations in this aquifer constitute a climate signal in contrast the stable isotope ratios 180 and d do not provide a clear record of past climatic changes in the aquia aquifer and the correlation between ngts and stable isotope ratios is weak the ngt record suggests that mean annual temperatures in this midlatitude coastal site during the last glacial maximum lgm were 9 0 0 6 c colder than during the holocene this difference is slightly lower than estimates derived from pollen data for this region but considerably larger than the rather uniform cooling of about 5 c indicated by noble gas studies in more southern locations of north america the larger cooling is ascribed to the influence of the laurentide ice sheet which at its maximum extension came as close as 250 km to our study site

reactive transport model of the formation of oxide type ni laterite profiles punta gorda moa bay cuba oxide type ni laterite deposits are characterized by a dominant limonite zone with goethite as the economically most important ni ore mineral and a thin zone of hydrous mg silicate rich saprolite beneath the magnesium discontinuity fe less soluble is mainly retained forming goethite while ni is redeposited at greater depth in a fe iii and ni rich serpentine serpentine ii or in goethite where it adsorbs or substitutes for fe in the mineral structure here a 1d reactive transport model using crunchflow of punta gorda oxide type ni laterite deposit moa bay cuba formation is presented the model reproduces the formation of the different laterite horizons in the profile from an initial partially serpentinized peridotite in 106 years validating the conceptual model of the formation of this kind of deposits in which a narrow saprolite horizon rich in ni bearing serpentine is formed above peridotite parent rock and a thick limonite horizon is formed over saprolite results also confirm that sorption of ni onto goethite can explain the weight percent of ni found in the moa goethite

the younger dryas and the sea of ancient ice we propose that prior to the younger dryas period the arctic ocean supported extremely thick multi year fast ice overlain by superimposed ice and firn we re introduce the historical term paleocrystic ice to describe this the ice was independent of continental glacier ice and formed a massive floating body trapped within the almost closed arctic basin when sea level was lower during the last glacial maximum as sea level rose and the barents sea shelf became deglaciated the volume of warm atlantic water entering the arctic ocean increased as did the corresponding egress driving the paleocrystic ice towards fram strait new evidence shows that bering strait was resubmerged around the same time providing further dynamical forcing of the ice as the transpolar drift became established additional freshwater entered the arctic basin from siberia and north america from proglacial lakes and meltwater derived from the laurentide ice sheet collectively these forces drove large volumes of thick paleocrystic ice and relatively fresh water from the arctic ocean into the greenland sea shutting down deepwater formation and creating conditions conducive for extensive sea ice to form and persist as far south as 60 n we propose that the forcing responsible for the younger dryas cold episode was thus the result of extremely thick sea ice being driven from the arctic ocean dampening or shutting off the thermohaline circulation as sea level rose and atlantic and pacific waters entered the arctic basin this hypothesis focuses attention on the potential role of arctic sea ice in causing the younger dryas episode but does not preclude other factors that may also have played a role

holocene relative sea level history of franz josef land russia one of the largest uncertainties in ice volume changes during the late quaternary period is the extent of ice sheets over the barents and kara seas field research on central and eastern franz josef land russia provide new observations on postglacial emergence and deglaciation that further constrain the magnitude and timing of late weichselian glaciations radiocarbon dating of driftage from raised marine sequences place deglacial unloading prior to 9 4 ka at a number of localities within 1 to 2 km of the present glacier margin in situ shells from raised marine sediments yield 14c ages between 9 7 and 8 4 yr b p evidence that outlet glaciers were at or behind present margins by the early holocene period the altitude of the marine limit on franz josef land ranges from 49 to 20 m above sea level asl and is low compared to eastern svalbard 110 to 60 m asl the age of the marine limit ranges from 10 4 ka to ca 6 0 ka and exhibits greater diachrony where emergence is 35 m a low initial rate of emergence reflects glacio isostatic compensation offset by a eustatic rise in sea level and perhaps an additional component from renewed water loading of the barents sea after deglaciation the presence of raised beaches at 1 to 4 m asl that are 1 to 2 ka indicates that uplift is incomplete an exponential extrapolation of uplift data for franz josef land and eastern svalbard yields current maximum uplift estimates of 0 7 to 1 6 mm yr an inferred 5 5 m of uplift remaining these values are at least 50 to 80 lower than the inferred uplift residual for a modeled ice sheet in the barents and kara seas the discrepancy indicates that further refinement is needed for this ice sheet model the compilation of emergence data from franz josef land svalbard and novaya zemlya confine maximum glacio isostatic compensation to the barents sea comparatively minor ice sheet loads were over novaya zemlya and the southeastern barents sea emergence isobases since 5 and 9 ka descend northward across franz josef land indicating a diminishing glacio isostatic response into the arctic ocean

chemical weathering of a marine terrace chronosequence santa cruz california i interpreting rates and controls based on soil concentration depth profiles abstract the spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal california are interpreted in terms of chemical weathering rates and processes in regoliths up to 15 m deep and 226 kyrs old quartz normalized mass transfer coefficients indicate non stoichiometric preferential release of sr ca na from plagioclase along with lesser amounts of k rb and ba derived from k feldspar smectite weathering results in the loss of mg and concurrent incorporation of al and fe into secondary kaolinite and fe oxides in shallow argillic horizons elemental losses from weathering of the santa cruz terraces fall within the range of those for other marine terraces along the pacific coast of north america residual amounts of plagioclase and k feldspar decrease with terrace depth and increasing age the gradient of the weathering profile bs is defined by the ratio of the weathering rate r to the velocity at which the profile penetrates into the protolith a spreadsheet calculator further refines profile geometries demonstrating that the non linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface to volume ratios and at high residual feldspar concentrations at greater depth by the approach to thermodynamic saturation these parameters are of secondary importance to the fluid flux qh which in thermodynamically saturated pore water controls the weathering velocity and mineral losses from the profiles long term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute cl balances qh 0 025 0 17 m yr 1 during saturation controlled and solute limited weathering the greater loss of plagioclase relative to k feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics the steady state weathering rate under such conditions is defined as r q h m sol m total 1 s v b s the product of qh and the ratio of solubilized to solid state feldspar msat mtotal define the weathering velocity the weathering gradient bs reflects the kinetic rate of reaction where sv is the volumetric surface area of the residual feldspar both this rate expression and the spreadsheet calculations produce similar plagioclase weathering rates r 5 14 10 16 mol m 2 s 1 which agree with those reported for other environments of comparable climate and age weathering dependent concentration profiles are commonly described in literature the present paper provides methods by which these data can yield a more fundamental understanding of the weathering processes involved

simulation of surface dynamics during dissolution as a function of the surface orientation implications for non constant dissolution rates a b s t r a c t an important problem in geochemistry is the understanding of how changes occurring on a surface during dissolution affect the variability of measured dissolution rates in this study a new approach to study the effect of surface dynamics on dissolution rates is tested by coupling experimental data with a numerical model that simulates the retreat of surface profiles during dissolution we present specific results from the simulation of dissolution of fluorite surfaces the equations that determine the retreat of a surface are based on experimentally obtained equations that relate the retreat rate of a surface to a single variable the crystallographic orientation of the surface our results show that depending on the starting orientation different types of topography are developed similar to those observed experimentally during the initial dissolution phase changes of topography are rapid and associated with fast dissolution rates the progressively slower dissolution rates are coupled with the development of surface segments with orientations that dissolve at a slower rate consequently the overall retreat rate of a profile decreases during the simulation and tends to a near constant value the results show a close relationship between dissolution rates surface orientation and surface dynamics which suggests that the dissolution rate of a specific mineral phase is not constant but varies with dissolution time and surface structure this variability needs to be considered in the evaluation of experimentally derived dissolution rates future dissolution experiments and predictive kinetic models of dissolution 2014 elsevier b v all rights reserved

metal release from limestones at high partial pressures of co2 abstract co 2 leakage from underground co 2 sequestration and storage poses potential risks to degradation of water quality in shallow aquifers increased co 2 concentrations can result in decreased ph and lead to subsequent metal release from mineral dissolution or desorption from mineral surfaces dissolution of carbonate minerals present in aquifer sediments or rocks will buffer ph and is generally thought to reduce the potential risk of metal release in the event of a co 2 leak as a result much of the research on geochemical impacts of co 2 leakage has focused on siliciclastic aquifers with little to no carbonate minerals present however carbonate minerals contain trace amounts of metals in their crystal structure that will be released into solution with dissolution and may pose a risk to drinking water quality here we perform laboratory water rock experiments to analyze the potential for metal release due to carbonate mineral dissolution in limestone aquifers rock samples from three limestone aquifers were dissolved in batch reactors with varying partial pressures of co 2 from 0 01 to 1 bar in the headspace as co 2 dissolved into the fluid and decreased the ph the carbonate minerals dissolved and released metals into solution the concentrations of calcium magnesium strontium barium thallium uranium and cobalt increased but remained below any regulatory limits the concentrations of arsenic and nickel increased and exceeded primary drinking water standards set by the usepa and the state of california respectively potential sources of metals in the rocks were determined through detailed sample characterization using sequential extractions laser ablation inductively coupled mass spectrometry and high resolution mineralogical mapping with qemscan we found that calcite dissolution released more metals to solution than pyrite dissolution or metal desorption from mineral surfaces in these experiments geochemical models based on the experimental data were used to evaluate the relative importance of calcite dissolution versus pyrite dissolution over a 30 year time frame under both oxic and sub oxic conditions calcite dissolution is the dominant source of metals to solution immediately after exposure to co 2 pyrite dissolution becomes the dominant source at later times as the fluid reaches equilibrium with respect to calcite for all model scenarios the cumulative contribution of metals to solution was dominated by calcite dissolution results from this study suggest that the ph buffering benefit of carbonate mineral dissolution in the event of a co 2 leak may be offset by the potentially negative effect of trace metal release from the crystal structure this study highlights the need for detailed sample characterization at individual sites to identify sources of metals when assessing the potential risk of co 2 leakage into shallow aquifers

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

weathering rates as a function of flow through an alpine soil the effect of flow on release rates of solutes from soil in a 39 m2 alpine catchment in the colorado rockies was measured during the summers of 1990 1994 flow rates through the soil were varied by augmenting natural rainfall with deionized irrigation water daily water inputs averaged between 96 and 2161 day during the five field seasons and mean discharge inputs minus evapotranspiration varied from 35 to 175 1 day 1 volume weighted mean concentrations of base cations and silica decreased only moderately in response to the increased water inputs input fluxes of solutes in precipitation were similar in each of the study seasons but output fluxes of base cations and silica in surface outflow increased substantially in conjunction with the average water input rate for the season weathering rates calculated from the chemical fluxes increased substantially in response to increases in water input rates the increases appear to be largely attributable to enhanced transport of solutes from the soil matrix under high flow conditions at high flow physical flushing of micropores presumably occurs to a greater extent than during low flow periods because of greater soil wetness and higher hydrologic head increased flushing would also cause an increased rate of diffusion of solutes from microcracks in mineral surfaces and constricted pore spaces in response to an increased concentration gradient between those regions and adjacent areas in the soil matrix another consequence of the increased flushing that occurs during periods of high flow is that concentrations throughout the soil matrix tend to be lower which might increase chemical weathering rates of some silicate minerals such as microcline which are relatively close to saturation decreased si concentrations under high flow conditions appear to promote dissolution of amorphous aluminosilicates or desorption of si from mineral surfaces buffering si concentrations in the soil solutions thus both physical transport of solutes and subsequent chemical effects appear to be responsible for the positive relation observed between fluxes of weathering products and water input rates

determining mineral weathering rates based on solid and solute weathering gradients and velocities application to biotite weathering in saprolites abstract chemical weathering gradients are defined by the changes in the measured elemental concentrations in solids and pore waters with depth in soils and regoliths an increase in the mineral weathering rate increases the change in these concentrations with depth while increases in the weathering velocity decrease the change the solid state weathering velocity is the rate at which the weathering front propagates through the regolith and the solute weathering velocity is equivalent to the rate of pore water infiltration these relationships provide a unifying approach to calculating both solid and solute weathering rates from the respective ratios of the weathering velocities and gradients contemporary weathering rates based on solute residence times can be directly compared to long term past weathering based on changes in regolith composition both rates incorporate identical parameters describing mineral abundance stoichiometry and surface area weathering gradients were used to calculate biotite weathering rates in saprolitic regoliths in the piedmont of northern georgia usa and in luquillo mountains of puerto rico solid state weathering gradients for mg and k at panola produced reaction rates of 3 to 6 10 17 mol m 2 s 1 for biotite faster weathering rates of 1 8 to 3 6 10 16 mol m 2 s 1 are calculated based on mg and k pore water gradients in the rio icacos regolith the relative rates are in agreement with a warmer and wetter tropical climate in puerto rico both natural rates are three to six orders of magnitude slower than reported experimental rates of biotite weathering

combined effect of carbonate and biotite dissolution in landslides biases silicate weathering proxies abstract long term estimates of the dissolution of silicate rock are generally derived from a range of isotopic proxies such as the radiogenic strontium isotope ratio 87 sr 86 sr which are preserved in sediment archives for these systems to fairly represent silicate weathering the changes in isotopic ratios in terrestrial surface waters should correspond to changes in the overall silicate dissolution this assumes that the silicate mineral phases that act as sources of a given isotope dissolve at a rate that is proportional to the overall silicate weathering bedrock landsliding exhumes large quantities of fresh rock for weathering in transient storage and rapid weathering in these deposits is controlled primarily by dissolution of the most reactive phases in this study we test the hypothesis that preferential weathering of these labile minerals can decouple the dissolution of strontium sources from the actual silicate weathering rates in the rapidly eroding western southern alps wsa of new zealand we find that rapid dissolution of relatively radiogenic calcite and biotite in landslides leads to high local fluxes in strontium with isotopic ratios that offer no clear discrimination between sources these higher fluxes of radiogenic strontium are in contrast to silicate weathering rates in landslides that are not systematically elevated on a mountain belt scale radiogenic strontium fluxes are not coupled to volumes of recent landslides in large 100 km 2 catchments but silicate weathering fluxes are such decoupling is likely due first to the broad variability in the strontium content of carbonate minerals and second to the combination of radiogenic strontium released from both biotite and carbonate in recent landslides this study supports previous work suggesting the limited utility of strontium isotopes as a system to study silicate weathering in the wsa crucially however in settings where bedrock landsliding is a dominant erosive process there is potential for both random and systematic bias in isotope proxies if the most reactive phases exposed for dissolution by landslides disproportionately contribute to the proxy of choice this clearly suggests that the isotopic composition of marine sr is a proxy for periods of rapid mountain uplift and erosion rather than for the associated enhanced silicate weathering

chemical weathering in a tropical watershed luquillo mountains puerto rico ii rate and mechanism of biotite weathering abstract samples of soil saprolite bedrock and porewater from a lower montane wet forest the luquillo experimental forest lef in puerto rico were studied to investigate the rates and mechanisms of biotite weathering the soil profile at the top of a ridge in the rio icacos watershed consists of a 50 100 cm thick layer of unstructured soil above a 600 800 cm thick saprolite developed on quartz diorite the only minerals present in significant concentration within the soil and saprolite are biotite quartz kaolinite and iron oxides biotite is the only primary silicate releasing significant k and mg to porewaters although biotite in samples of the quartz diorite bedrock is extensively chloritized chlorite is almost entirely absent in the saprolite phyllosilicates phyllosilicate grains are present as 200 1000 m wide books below about 50 cm depth x ray diffraction xrd and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite lattice fringe images under transmission electron microscope tem show single layers of biotite altering to two layers of kaolinite suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries some single 14 a layers are also observed in the biotite under tem the degree of kaolinitization of individual phyllosilicate grains as observed by tem decreases with depth in the saprolite this tem work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low temperature environments the rate of release of mg in the profile calculated as a flux through the soil normalized per watershed land area is approximately 500 mol hectare 1 yr 1 1 6 10 9 molmg msoil 2 s 1 this rate is similar to the flux estimated from mg discharge out the rio icacos 1000 mol hectare 1 yr 1 or 3 5 10 9 molmg msoil 2 s 1 indicating that scaling up from the soil to the watershed is possible for mg release the rate of mg release from biotite normalized to brunauer emmett teller bet surface area is calculated using a mass balance equation which includes the density and volume of phyllosilicate grains porewater chemistry and flux and soil porosity the mean rates of biotite weathering calculated from k and mg release rates are approximately 6 and 11 10 16 molbiotite mbiotite 2 s 1 respectively significantly slower than laboratory rates 10 12 to 10 11 molbiotite mbiotite 2 s 1 the discrepancy in scaling down from the soil to the laboratory is probably explained by 1 differences in weathering mechanism between the two environments 2 higher solute concentrations in soil porewaters 3 loss of reactive surface area of biotite in the saprolite due to kaolinite and iron oxide coatings and or 4 unaccounted for heterogeneities in flow path through the soil

modelling weathering processes at the catchment scale the witch numerical model a numerical model of chemical weathering in soil horizons and underlying bedrock witch has been coupled to a numerical model of water and carbon cycles in forest ecosystems aspects to simulate the concentration of major species within the soil horizons and the stream of the strengbach granitic watershed located in the vosges mountains france for the first time simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis the model is able to reproduce the concentrations of most major species within the soil horizons as well as catching the first order seasonal fluctuations of aqueous calcium magnesium and silica concentrations however the witch model underestimates concentrations of mg2 and silica at the spring of the catchment stream and significantly underestimates ca2 concentration the deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock however the resulting increased ca2 release yields important smectite precipitation in the deepest model layer in contact with the bedrock and subsequent removal of large amount of silica and magnesium from solution in contrast the model accurately accounts for the concentrations of major species ca mg and silica measured in the catchment stream when precipitation of clay minerals is not allowed the model underestimation of mg2 and h4sio4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming in agreement with observations on other watersheds draining granitic rocks this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the strengbach watershed

stratigraphic constraints on late pleistocene glacial erosion and deglaciation of the chukchi margin arctic ocean at least two episodes of glacial erosion of the chukchi margin at water depths to 450 m and 750 m have been indicated by geophysical seafloor data we examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock the diamictons are estimated to form during the last glacial maximum lgm and an earlier glacial event possibly between ois 4 to 5d both erosional events were presumably caused by the grounding of ice shelves originating from the laurentide ice sheet broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor postglacial sedimentation evolved from iceberg dominated environments to those controlled by sea ice rafting and marine processes in the holocene a prominent minimum in planktonic foraminiferal 18 o is identified in deglacial sediments at an estimated age near 13 000 cal yr bp this 18 o minimum also reported elsewhere in the amerasia basin is probably related to a major laurentide meltwater pulse at the younger dryas onset the bering strait opening is also marked in the composition of late deglacial chukchi sediments

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

revision of the nw laurentide ice sheet implications for paleoclimate the northeast extremity of beringia and arctic ocean sedimentation abstract for the past half century reconstructions of north american ice cover during the last glacial maximum have shown ice free land distal to the laurentide ice sheet primarily on melville and banks islands in the western canadian arctic archipelago both islands reputedly preserve at the surface multiple laurentide till sheets together with associated marine and lacustrine deposits recording as many as three pre late wisconsinan glaciations the northwest corner of banks island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation banks glaciation considered to be of matuyama age 780 ka bp inside the limit of banks glaciation younger till sheets are ascribed to the thomsen glaciation pre sangamonian and the amundsen glaciation early wisconsinan stade the view that the western canadian arctic archipelago remained largely ice free during the late wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on banks and melville islands both dated to 22 ka bp these dates imply that these islands constitute the northeast extremity of beringia a fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of banks and melville islands including new dating of glacial and marine landforms and sediments on dundas peninsula southern melville island ams 14 c dates on ice transported marine molluscs within the most extensive laurentide till yield ages of 25 49 ka bp these dates require that late wisconsinan ice advanced northwestward from visount melville sound excavating fauna spanning marine isotope stage 3 laurentide ice that crossed dundas peninsula 300 m asl coalesced with melville island ice occupying liddon gulf coalescent laurentide and melville ice continued to advance westward through m clure strait depositing granite erratics at 235 m asl that require grounded ice in m clure strait as do streamlined bedforms on the channel floor deglaciation is recorded by widespread meltwater channels that show both the initial separation of laurentide and melvile ice and the successive retreat of laurentide ice southward across dundas peninsula into viscount melville sound sedimentation from these channels deposited deltas marking deglacial marine limit forty dates on shells collected from associated glaciomarine rhythmites record near synchronous ice retreat from m clure strait and dundas peninsula to north central victoria island 11 5 ka bp along the adjacent coast of banks island deglacial shorelines also record the retreat of laurentide ice both eastward through m clure strait and southward into the island s interior the elevation and age 11 5 ka bp of deglacial marine limit there is fully compatible with the record of ice retreat on melville island the last retreat of ice from mercy bay northern banks island previously assigned to northward retreat into m clure strait during the early wisconsinan is contradicted by geomorphic evidence for southward retreat into the island s interior during the late wisconsinan this revision of the pattern and age of ice retreat across northern banks island results in a significant simplification of the previous quaternary model our observations support the amalgamation of multiple till sheets previously assigned to at least three pre late wisconsinan glaciations into the late wisconsinan this revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking erratics were also widely observed armouring meltwater channels originating on the previously proposed never glaciated landscape an extensive late wisconsinan laurentide ice sheet across the western canadian arctic is compatible with similar evidence for extensive laurentide ice entering the richardson mountains yukon farther south and with the innuitian ice sheet to the north widespread late wisconsinan ice in a region previously thought to be too arid to sustain it has important implications for paleoclimate ice sheet modelling arctic ocean ice and sediment delivery and clarifying the northeast limit of beringia

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

the deglacial history of surface and intermediate water of the bering sea the lithology of deglacial sediments from the bering sea includes intervals of laminated or dysaerobic sediments these intervals are contemporaneous with the occurrence of laminated sediments from the california margin and gulf of california which suggests widespread low oxygen conditions at intermediate depths in the north pacific ocean the cause could be reduced intermediate water ventilation increased organic carbon flux or a combination of the two we infer abrupt decreases of planktonic foraminifer d 18 o at 14 400 and 11 650 yr bp which may be a combination of both freshening and warming on the shirshov ridge the abundance of sea ice diatoms of the genus nitzschia reach local maxima twice during the deglaciation the latter of which may be an expression of the younger dryas these findings expand the extent of the expression of deglacial millennial scale climate events to include the northernmost pacific r 2005 elsevier ltd all rights reserved

a multiisotope c and n modeling analysis of soil organic matter turnover and transport as a function of soil depth in a california annual grassland soil chronosequence 1 we examine soil organic matter som turnover and transport using c and n isotopes in soil profiles sampled circa 1949 1978 and 1998 a period spanning pulse thermonuclear 14c enrichment of the atmosphere along a 3 million year annual grassland soil chronosequence temporal differences in soil 14c profiles indicate that inputs of recently living organic matter om occur primarily in the upper 20 30 cm but suggest that om inputs can occur below the primary rooting zone a three pool som model with downward transport captures most observed variation in 14c percentages of c and n 13c and 15n supporting the commonly accepted concept of three distinct som pools the model suggests that the importance of the decadal som pool in n dynamics is greatest in young and old soils altered hydrology and possibly low ph and or p dynamics in highly developed old soils cause changes in soil c and n turnover and transport of importance for soil biogeochemistry models

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

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

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

a reactive transport model for examining tectonic and climatic controls on chemical weathering and atmospheric co2 consumption in granitic regolith we developed a 1d reactive transport model for examining how tectonic and climatic parameters namely uplift rate water seepage velocity and temperature control chemical weathering and atmospheric co2 consumption rates during regolith development the model consists of mass conservation equations describing how mineral and solute concentrations change temporally and spatially vertically during weathering of granite containing 30 plagioclase an20 and up to 3 accessory calcite the equations are coupled by volumetric weathering rates which depend on mineral abundances intrinsic dissolution rate constants and surface areas as well as the departure of pore water from thermodynamic equilibrium we numerically solve a non steady state non dimensional version of the model by eliminating the need to prescribe regolith thickness non dimensionalization introduces two key scaling parameters that drive variations in the model results the rock residence time r the time for rock to travel upward through the model domain and the water residence time w the time for water to travel downward through the model domain we use the model to examine fundamental properties of chemical weathering especially reaction front propagation with the primary aim of characterizing weathering regimes and identifying factors that maximize the dissolution of plagioclase because only silicate weathering regulates atmospheric co2 levels over geological timescales weathering regimes are commonly classified as transport or supply limited versus weathering or kinetically limited but as outgrowths of geomorphology these terms primarily refer to the role of r in regulating regolith thickness our findings suggest that the paradigm should be expanded to include kinetic controls determined by w both regimes can experience far from and near equilibrium mineral dissolution however transport limited regimes generally have lower w r ratios compared to kinetically limited regimes under transport limitation thick to thin reaction fronts propagate downward indefinitely yielding extensive mineral depletion deeply weathered regolith and high ratios of silicate to carbonate weathering under kinetic limitation thin to non existent reaction fronts evolve to steady state yielding minimal mineral depletion no regolith development and low ratios of silicate to carbonate weathering kinetically limited regimes typifying tectonically active mountain ranges have low long term atmospheric co2 consumption rates transport limited regimes typifying tectonically stable cratons also have low long term atmospheric co2 consumption rates but because much of the earth s surface is transport limited we infer that such environments have the greatest impact on the global atmospheric co2 consumption flux the model output leads us to hypothesize that the maximum contribution should occur for extensive regions of silicate bedrock consolidated in warm wet climates because the combination of tectonic stability high temperatures and rapid seepage velocities accelerates reaction front propagation facilitates calcite depletion and sustains deep regolith development over long timescales our findings point to the importance of internal climate feedbacks for stabilizing long term atmospheric co2 levels

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

postglacial to holocene history of the laptev sea continental margin palaeoenvironmental implications of benthic assemblages abstract bivalves ostracods and foraminifers were studied in four ams 14 c dated sediment cores from the laptev sea one from the upper continental slope with a date of 15 8 cal ka in its basal part and three from river palaeovalleys on the outer middle shelf aging back to 12 7 11 2 cal ka at the continental margin high relative proportions of cassidulina neoteretis planktic foraminifers and ostracods with north atlantic affinities provide evidence on past inflows of atlantic derived waters whereas freshwater inputs downslope sediment movements and ice rafting are documented by the presence of euryhaline brackish water and freshwater ostracods and low planktic benthic ratio atlantic derived subsurface waters reached the studied site by ca 16 cal ka i e prior to the establishment of the pathway across the barents sea shelf further west the strongest atlantic influence occurred prior to 12 cal ka and after 3 cal ka a cold low nutrient marine environment with a coastal polynya setting is reconstructed for the time 16 14 cal ka whereas between 12 7 and 11 2 cal ka freshwater influence reached its maximum during a time when the outer shelf was flooded and brackish water assemblages inhabited the estuarine parts of palaeovalleys following the temporal and spatial pattern of sea level rise these fluvially affected assemblages rapidly transformed into shallow marine faunas after ca 3 5 3 cal ka well pronounced changes in the benthic communities indicate a general climate cooling characterized by a more intensified surface and bottom water circulation regime

sea level data for parts of the bering chukchi shelves of beringia from 19 000 to 10 000 14c yr b p abstract sea level changes in beringia are especially significant because they affect the migration of land plants and animals between asia and north america and marine plants and animals between the pacific and arctic oceans previous studies of cores from the bering and chukchi shelves produced sea level curves evaluation of these data suggests that nine of the radiocarbon dated estimates of sea level position are most reliable for the time period 19 000 to 10 000 yr b p the trend of these nine points is proposed as the basis for a regional sea level curve for central beringia constraints on the data must be noted however by anyone using them

climate dependence of feldspar weathering in shale soils along a latitudinal gradient although regolith the mantle of physically chemically and biologically altered material overlying bedrock covers much of earth s continents the rates and mechanisms of regolith formation are not well quantified without this knowledge predictions of the availability of soil to sustain earth s growing population are problematic to quantify the influence of climate on regolith formation a transect of study sites has been established on the same lithology silurian shale along a climatic gradient in the northern hemisphere as part of the susquehanna shale hills critical zone observatory pennsylvania usa the climate gradient is bounded by a cold wet end member in wales and a warm wet end member in puerto rico in between mean annual temperature mat and mean annual precipitation map increase to the south through new york pennsylvania virginia tennessee and alabama the site in puerto rico does not lie on the same shale formation as the appalachian sites but is similar in composition soils and rocks were sampled at geomorphologically similar ridgetop sites to compare and model shale weathering along the transect focusing on the low concentration non nutrient element na we observe that the extent and depth of na depletion is greater where mean annual temperature mat and precipitation map are higher na depletion a proxy for feldspar weathering is the deepest reaction documented in the augerable soil profiles this may therefore be the reaction that initiates the transformation of high bulk density bedrock to regolith of low bulk density based on the shale chemistry along the transect the time integrated na release rate qna increases exponentially as a function of mat and linearly with map ny the only site with shale till parent material is characterized by a qna that is 18 times faster than pa an observation which is attributed to the increased surface area of minerals due to grinding of the glacier and kinetically limited weathering in the north a calculated apparent arrhenius type temperature dependence across the transect excluding ny for the dissolution of feldspar na depletion is 99 15 kj mol 1 a value similar to field measured values of the activation energy 14 109 kj mol 1 or laboratory measured values of the enthalpy of the albite reaction 79 8 kj mol 1 observations from this transect document that weathering losses of na from silurian shale can be understood with models of regolith formation based on chemical and physical factors such that weathering progresses from kinetically limited sites wales to al to the transport limited site in puerto rico significant advances in our ability to predict regolith formation will be made as we apply more quantitative models to such transect studies on shales and other rocks types

late weichselian iceberg surface melt and sediment production from the eurasian ice sheet results from numerical ice sheet modelling abstract results from a numerical ice sheet model were matched with geological evidence detailing the extent and timing of the late weichselian ice sheet in the eurasian arctic through simple adjustments in the model s environmental inputs the numerical model predicts the spatial and temporal variation in 1 subglacial sediment transport and deposition 2 rates of iceberg calving and 3 rates of supraglacial melting over the past 30 000 yr the ice sheet is characterised by a series of ice streams occupying bathymetric troughs in the barents sea and west of norway which act as sources for glacial sediment build up and iceberg production our model indicates that significant volumes of sediment are deposited over the bear island fan 3000 km 3 in 12 000 yr franz victoria trough fan 500 km 3 in 8000 yr and a series of smaller fans west of norway which combine to yield 4000 km 3 in 12 000 yr the norwegian channel ice stream operated for only 4000 yr during which time 400 km 3 of sediments were deposited on the adjacent fan the ice sheet experienced two major periods of iceberg production where the rate of calving increased by 50 at about 15 000 and 12 500 yr ago however the time dependent response of iceberg calving to sea level rise for individual ice streams is shown to be more complicated than the generalised ice sheet response the marine portions of the ice sheet decayed after 15 000 yr ago resulting in several embayments at the mouths of bathymetric troughs a second pulse of enhanced iceberg calving at 12 500 yr ago caused further decay of the marine ice sheet and the ice margin retreated back to the shorelines of island archipelagos in the northern barents sea ice loss through surface melting was restricted mostly to the southern margin of the ice sheet

the effect of land plants on weathering rates of silicate minerals abstract land plants and their associated microbiota directly affect silicate mineral weathering in several ways by generation of chelating ligands by modifying ph through production of co2 or organic acids and by altering the physical properties of a soil particularly the exposed surface areas of minerals and the residence time of water in laboratory experiments far from equilibrium 1 mm oxalate a strong chelator of al has a negligible effect on the dissolution rate of alkali feldspars but some effect on calcic feldspars and olivine by analogy to oxalate the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small except perhaps in microenvironments adjacent to roots and fungal hyphae the effect of ph on silicate mineral dissolution rate depends on ph below ph 4 5 the rate increases with decreasing ph in the circumneutral region the rate is ph independent and at ph values above around 8 the rate increases with increasing ph vegetation should thus cause an increase in weathering rate through the ph effect only where the ph is below 4 5 as an overall generalization the effect of plants on weathering rate through changes in soil solution chemistry is probably small for granitic rocks it may be greater for more mafic rocks it is the release of ca and mg from mafic rocks that has the greatest influence on the global co2 budget the effect of changes in soil physical properties on weathering rate can be major by binding fine particles plants can greatly increase weathering rates in areas of high physical erosion where erosion rates are lower the effect of plants is less clear on long timescales plants may decrease chemical weathering by binding secondary products and isolating unweathered minerals from meteoric water a major unknown in estimating the effect of the advent of land plants on weathering rates is the nature thickness particle size distribution permeability of the regolith on the pre silurian continents the indirect effect of vegetation through changing the regional distribution of precipitation may be as important as the direct effects

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

paleodeviations of radiocarbon marine reservoir values for the northeast pacific differences in the radiocarbon ages of coeval marine shells and wood from emergent glaciomarine sediments in the fraser lowland of southwestern british columbia and northwest washington indicate that a total marine radiocarbon reservoir value of 1 1 1 k y is applicable in the region this is 40 greater 300 yr than the 800 yr value currently used to correct the ages of both modern and late pleistocene marine shells from this area the glaciomarine sediments were deposited rapidly between ca 12 5 and 11 5 1 4 c k y b p paleodeviations of the marine reservoir value may illustrate that rapid environmental changes occurred during the last glacial to interglacial transition these variations are thought to have been caused by changes in both deep and surface ocean circulation and by variations in the production of atmospheric radiocarbon 1 4 c these findings may indicate a rapid reordering of oceanic atmospheric circulation in the region

beringian climate during the late pleistocene and holocene abstract the difference between the climates of the bering land bridge and asiatic western beringia 18 20 ka ago is discussed the climatic reconstructions of the bering land bridge and western beringia are based upon two methods first we discuss the ecological and thermal requirements of the thermophilic weevils coleoptera curculionidae in the genus stephanocleonus second we discuss the effect of climatic continentality on soil temperatures we suggest that for western beringia the climate was suitable for the warm steppe environment mean july air temperatures were at least 10 11 c and an annual sum of daily temperatures above 0 c sdd at the soil surface was up to 2500 c in contrast to these conditions the climate of the bering land bridge was very similar to that found in the modern arctic tundra zone

bridging the gap between laboratory measurements and field estimations of silicate weathering using simple calculations weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than those inferred from field studies simple calculations show that even if the field conditions were fully simulated in standard laboratory experiments it would be impossible to measure the slow rates of mineral dissolution that are observed in the field as it is not possible to measure the dissolution rates under typical field conditions one should extrapolate the available data to the field conditions to do this a rate law for the dissolution of plagioclase in the field was formulated by combining the far from equilibrium dissolution rate of weathered natural oligoclase at 25 c with the effect of deviation from equilibrium on dissolution rate of fresh albite at 80 c in contrast to the common view that laboratory experiments predict dissolution rates that are faster than those in the field the simulation based on this rate law indicates that laboratory dissolution experiments actually predict slower rates than those observed in the field this discrepancy is explained by the effect of precipitation of secondary minerals on the degree of saturation of the primary minerals and therefore on their dissolution rate indeed adding kaolinite precipitation to the simulation significantly enhances the dissolution rate of the plagioclase moreover a strong coupling between oligoclase dissolution and kaolinite precipitation was observed in the simulation we suggest that such a coupling must exist in the field as well therefore any attempt to predict the dissolution rate in the field requires knowledge of the rate of the secondary mineral precipitation

models of transport and reaction describing weathering of fractured rock with mobile and immobile water we propose models for calculating the rate of chemical weathering of minerals as a function of depth in the weathering zone a macropore network is assumed to be responsible for the transport of mobile water which removes soluble weathering products at the interface of that network and the matrix conditions of infrequent rainfall a and of very frequent rainfall b are separately modeled but both lead to a volumetric weathering rate with the general form 0exp z where the amplitude 0 and the equilibration length depend on the pore geometry of regolith and on parameters describing transport across the macropore matrix interface a or mineral dissolution b this is obtained with no assumption of steady state for regolith evolution extrapolating these end members into intermediate conditions the model is consistent with the exponential decay of regolith production rate versus depth reported by several authors and yields in a variety of regolith types in the range from centimeters to meters the velocity of the regolith bedrock interface also shows an exponential decay with weathering zone thickness and is enhanced by bedrock fractures when compared to models of unfractured bedrock when the residence time of fluid in the weathering zone f is large the bulk weathering rate rb is inversely proportional to this time and for small f rb reverts to the laboratory rate application to compiled data from several sites leads to estimates of a dissolution rate constant and specific surface area consistent with those of albite

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

paleoecology of late glacial peats from the bering land bridge chukchi sea shelf region northwestern alaska insect fossils and pollen from late pleistocene nonmarine peat layers were recovered from cores from the shelf region of the chukchi sea at depths of about 50 m below sea level the peats date to 11 300 11 000 yr b p and provide a limiting age for the regional pleistocene holocene marine transgression the insect fossils are indicative of arctic coastal habitats like those of the mackenzie delta region mean july temperatures 10 6 14 c suggesting that 11 000 yr ago the exposed chukchi sea shelf had a climate substantially warmer than modern coastal regions of the alaskan north slope the pollen spectra are consistent with the age assignment to the birch interval 14 000 9000 yr b p the data suggest a meadow like graminoid tundra with birch shrubs and some willow shrubs growing in sheltered areas

the role of trace minerals in chemical weathering in a high elevation granitic watershed estibere france chemical and mineralogical evidence we investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the pyrenees france the sites were located on glacial deposits derived from similar hercynian 300 ma granites characterized by the occurrence of zoned plagioclases and trace calcic phases epidote prehnite sphene apatite the surface waters at those sites show high ca na molar ratios 1 which could not be explained by the dissolution of the major plagioclase oligoclase present in the rocks the coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale the weathering of the trace calcic minerals which represent 1 of the total rock volume are responsible for more than 90 of the calcium export at the sites annual cationic fluxes 23 104 eq km2 yr calculated for the estibere watershed are among the highest reported for high elevation systems draining granitic rocks and 80 of this annual cationic flux can be attributed to the weathering of trace calcic phases calculations based on isotopic values 87sr 86sr go in the same direction except apatite the trace calcic phases appear to be mainly silicates thus the type of chemical weathering observed in the estibere watershed may have an influence on atmospheric co2 consumption by granite weathering however comparison with other watersheds draining granitic environments worldwide and with the two other sites in the pyrenees indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering e g high elevation catchments on glacial deposits other factors such as the date of glacial retreat the physical denudation rate the hydrological functioning of the watershed and the nature and structure of the soil cover are also important

evaluating u series tools for weathering rate and duration on a soil sequence of known ages four soil profiles of known age 40 250 600 and 3000 ka from the merced soil chronosequence in california were analysed for u and th isotopes and for major and trace element compositions to test the assumption that leaching of u series isotopes is a first order process with an invariant rate constant as frequently assumed when applying this isotopic tool to determine weathering duration and sediment residence time average 230 th 238 u values for each profile decrease from a high of 1 28 in the youngest soil 40 ka to 1 09 0 99 and 0 98 in the 250 ka 600 ka and 3000 ka soils respectively 234 u 238 u values also show variation across the 4 soils the simultaneous variation in 230 th 238 u and 234 u 238 u cannot be explained by a first order kinetic model with invariant rate constants and instead requires that leaching coefficients for the u series isotopes change with time the observed data is consistent with a two stage model that reflects an initial period of fast leaching of u and th from a readily weathered soil pool such as grain boundaries or defects followed by slow leaching from a more resistant soil pool application of such a two stage model may lead to significantly shorter calculated timescales of weathering than those obtained by the widely applied single stage model of u series weathering which assumes no change in leaching coefficients over time the results of this study have wide implications for published and future use of u series tools in weathering studies

the last glacial maximum on spitsbergen svalbard most scientists have concluded previously that the west coast of spitsbergen svalbard remained ice free during the late weichselian between 25 000 and 10 000 yr b p we conclude that the glaciation was more extensive terraces that were postulated to have been ice free are covered by a thin late weichselian till sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords isfjorden and van mijenfjorden terminated west outside of the fjord mouths basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of spitsbergen yielded ages of about 12 500 yr b p from which we conclude that the ice extended to the shelf edge based on the extent of amino acid diagenesis in radiocarbon dated molluscs the duration of the maximum extension of the late weichselian glaciation was short certainly less than 10 000 years during the ice free period preceding that glaciation at least back to 40 000 yr b p the glaciers on svalbard were not significantly larger than at present as shown by marine deposits close to the glacier snouts many radiocarbon dates place deglaciation of the outer coast at about 12 500 yr b p at about 10 000 yr b p the rest of the archipelago rapidly became ice free

chemical weathering rates of a soil chronosequence on granitic alluvium iii hydrochemical evolution and contemporary solute fluxes and rates although long term changes in solid state compositions of soil chronosequences have been extensively investigated this study presents the first detailed description of the concurrent hydrochemical evolution and contemporary weathering rates in such sequences the most direct linkage between weathering and hydrology over 3 million years of soil development in the merced chronosequence in central california relates decreasing permeability and increasing hydrologic heterogeneity to the development of secondary argillic horizons and silica duripans in a highly permeable younger soil 40 kyr old pore water solutes reflect seasonal to decadal scale variations in rainfall and evapotranspiration et this climate signal is strongly damped in less permeable older soils 250 to 600 kyr old where solutes increasingly reflect weathering inputs modified by heterogeneous flow elemental balances in the soils are described in terms of solid state exchange and pore water reservoirs and input output fluxes from precipitation et biomass solute discharge and weathering solute mineral nutrients are strongly dependent on biomass variations as evidenced by an apparent negative k weathering flux reflecting aggradation by grassland plants the ratios of solute na to other base cations progressively increase with soil age discharge fluxes of na and si when integrated over geologic time are comparable to solid state mass losses in the soils implying similar past weathering conditions similarities in solute and sorbed ca mg ratios reflect short term equilibrium with the exchange reservoir long term consistency in solute ratios when contrasted against progressive decreases in solid state ca mg requires an additional ca source probably from dry deposition amorphous silica precipitates from thermodynamically saturated pore waters during periods of high evapotranspiration and result in the formation of duripans in the oldest soils the degree of feldspar and secondary gibbsite and kaolinite saturation varies both spatially and temporally due to the seasonality of plant respired co2 and a decrease in organically complexed al in deeper pore waters k feldspar is in equilibrium and plagioclase is about an order of magnitude undersaturated hydrologic heterogeneity produces a range of weathering gradients that are constrained by solute distributions and matrix and macropore flow regimes plagioclase weathering rates based on precipitation corrected na gradients vary between 3 and 7 10 16 mol m 2 s 1 these rates are similar to previously determined solid state rates but are several orders of magnitude slower than for experimental plagioclase dissolution indicating strong inhibitions to natural weathering partly due to near equilibrium weathering reactions

holocene history of the bering sea bowhead whale balaena mysticetus in its beaufort sea summer grounds off southwestern victoria island western canadian arctic abstract the fossil remains of 43 bowhead whales were mapped on the raised beaches of western wollaston peninsula victoria island canadian arctic near the historic summer range limit of the bering sea stock in the beaufort sea the elevations and radiocarbon ages of the remains demonstrate that the bowhead ranged commonly into the region following the submergence of bering strait at ca 10 000 14c yr b p until ca 8500 14c yr b p during the same interval bowheads ranged widely from the beaufort sea to baffin bay subsequently no whales reached wollaston peninsula until ca 1500 14c yr b p late holocene populations evidently were small or occupations were brief in comparison to those of the early holocene although the late holocene recurrence may relate to the expansion of pioneering thule whalers eastward from alaska there are few thule sites and limited evidence of thule whaling in the area surveyed to support this suggestion

characterization of the reaction and transport properties of porous rhyolite and its application to the quantitative understanding of the chemical weathering rate abstract the chemical weathering of porous rhyolite from kozushima japan was studied and the factors controlling the weathering rate including advection diffusion and dissolution were characterized using laboratory experiments the results were used to analyze the reaction and transport rates and the relationship between the weathering rates obtained in the laboratory and field was evaluated a flow through dissolution experiment using a rhyolite core demonstrated that the dissolution rate r mol cm 2 s 1 in deionized water depends on time t days according to the relationship r 2 9 10 16 t 0 65 the dissolution rate was also dependent on the concentration of dissolved si according to the relationship r 1 n where c ceq ceq 230 mol l 1 and n 1 0 or 0 33 the hydraulic conductivity and diffusion coefficients were measured under water saturated and unsaturated conditions the saturated hydraulic conductivity was 10 times greater than the unsaturated conductivity and the saturated effective diffusion coefficient of dissolved si was 5 times greater than the unsaturated diffusion coefficient previous studies on the weathering of the rhyolites from kozushima have shown that the field dissolution rate over 52 000 years was 3 10 19 6 10 19 mol si cm 2 s 1 these values are 12 1000 times lower than the dissolution rates obtained in the laboratory over a reaction time of 277 days reactive transport analysis demonstrated that the effect of on the dissolution rate is enhanced as the water saturation decreases the rate decreasing effect of was large in the early stages of weathering and then gradually decreased with time the 52 000 year weathering period is inferred to have occurred following a decrease in the dissolution rate to a value close to the field rate during an early weathering stage and subsequent further decrease in the rate owing to the effect of

isotope stage 5 130 74 ka in greenland a review abstract marine and glacigene deposits dated with varying degrees of certainty to isotope stage 5 130 74 ka are exposed in coastal cliffs in 18 areas and localities in northern and eastern greenland dating methods include thermoluminescence tl u th methods and correlation with the deep sea record amino acid parameters are used for correlation between localities deposits from the last interglaciation isotope substage 5e are rare and have been found only at three localities in both west and east greenland their mollusc and foraminifer faunas indicate more vigorous sea surface circulation and sea surface temperatures some degrees higher than known from the holocene during this warm period ice sheet growth began in northwest greenland the ice sheet reached its maximum for the last ice age during the succeeding phase provisionally correlated with isotope substage 5d this was followed by a new warm period with increased influx of warm subarctic water and high summer temperatures on land provisionally correlated with isotope substage 5a in east greenland the observations indicate a more complex ice sheet history the record from greenland is very similar to that obtained in adjacent coastal areas of the high arctic implying that the rapid shifts from warm to cold during isotope stage 5 were especially conducive to the formation of the embryonic north american and scandinavian ice sheets at high northern latitudes probably because the pulses of warm water were required to advect sufficient moisture into these areas to allow the growth of continental ice sheets

variation in soil surface area in a chronosequence of soils from glen feshie scotland and its implications for mineral weathering rate calculations abstract the inorganic component of soil horizons from a chronosequence of six soils developed in glen feshie scotland shows an increase in surface area with soil age and a decrease in surface area with increasing depth in the soil profiles surface area increases due to the development of discontinuous porous coatings on mineral grains the preferential dissolution of specific areas of individual minerals resulting in complex highly irregular grain shapes and a general reduction in grain size due to dissolution the discontinuous coatings consist predominantly of oxalate extractable al si oxyhydroxides and account for between 61 and 94 of the total inorganic surface area failure to take into account the increase of mineral surface area with time can lead to predictions of decreasing mineral dissolution rate with soil age in contrast to laboratory studies which assume that mineral dissolution can reach a steady state the difference between total and reactive mineral surface area may help to explain the frequently reported result that laboratory measured mineral dissolution rates are up to several orders of magnitude greater than those measured in the field

simulating loss of primary silicate minerals from soil due to long term weathering using allogen comparison with soil chronosequence lake sediment and river solute flux data this paper presents allogen a process model of soil mineral chemical weathering though designed principally to aid interpretation of lake sediment geochemical records by providing mass balance constraints for competing interpretations the model is also applicable to more general questions about long term weathering and soil development the model is constructed around a generalised version of the mineral weathering submodel of profile modified to minimise the need for site specific data and to optimise performance for long term change comparison with observed weathering rate data river flux studies chronosequences and lake sediment chemical stratigraphy suggests that soil mineral depletion can be usefully simulated over timescales applicable to quaternary and holocene studies to illustrate this the plausibility of a weathering interpretation is demonstrated for sediment records at lake hope simpson and moraine lake and the lake chronosequence at glacier bay while long term soil mineral depletion appears predictable reliable simulation of past runoff quality is hampered by lack of a suitable long term model for soil carbon

using a reactive transport model to elucidate differences between laboratory and field dissolution rates in regolith the reactive transport model flotran was used to forward model weathering profiles developed on granitic outwash alluvium over 40 3000 ka from the merced california usa chronosequence as well as deep granitic regolith developed over 800 ka near davis run virginia usa baseline model predictions that used laboratory rate constants km measured fluid flow velocities v and bet volumetric surface areas for the parent material a o m were not consistent with measured profiles of plagioclase potassium feldspar and quartz reaction fronts predicted by the baseline model are deeper and thinner than the observed consistent with faster rates of reaction in the model reaction front depth in the model depended mostly upon saturated versus unsaturated hydrologic flow conditions rate constants controlling precipitation of secondary minerals and the average fluid flow velocity va unsaturated hydrologic flow conditions relatively open with respect to co2 g resulted in the prediction of deeper reaction fronts and significant differences in the separation between plagioclase and potassium feldspar reaction fronts compared to saturated hydrologic flow relatively closed with respect to co2 g under saturated or unsaturated flow conditions the rate constant that controls precipitation rates of secondary minerals must be reduced relative to laboratory rate constants to match observed reaction front depths and measured pore water chemistry additionally to match the observed reaction front depths va was set lower than the measured value v for three of the four profiles the reaction front gradients in mineralogy and pore fluid chemistry could only be modeled accurately by adjusting values of the product kma o m by assuming km values were constrained by laboratory data field observations were modeled successfully with tst like rate equations by dividing measured values of a o m by factors from 50 to 1700 alternately with sigmoidal or alinhibition rate models this adjustment factor ranges from 5 to 170 best fit models of the wetter hydrologically saturated davis run profile required a smaller adjustment to a o m than the drier hydrologically unsaturated merced profiles we attributed the need for large adjustments in va and a o m necessary for the merced models to more complex hydrologic flow that decreased the reactive surface area in contact with bulk flow water e g dead end pore spaces containing fluids that are near or at chemical equilibrium thus rate models from the laboratory can successfully predict weathering over millions of years but work is needed to understand how to incorporate changes in what controls the relationship between reactive surface area and hydrologic flow

contrasting glacial interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge distinct cyclicity in lithology and microfaunal distribution in sediment cores from the mendeleev ridge in the western arctic ocean water depths ca 1 5 km reflects contrasting glacial interglacial sedimentary patterns we conclude that during major glaciations extremely thick pack ice or ice shelves covered the western arctic ocean and its circulation was restricted in comparison with interglacial modern type conditions glacier collapse events are marked in sediment cores by increased contents of ice rafted debris notably by spikes of detrital carbonates and iron oxide grains from the canadian arctic archipelago composition of foraminiferal calcite n 18 o and n 13 c also shows strong cyclicity indicating changes in freshwater balance and or ventilation rates of the arctic ocean light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca 12 14 c kyr bp the prolonged period with low n 18 o and n 13 c values and elevated contents of iron oxide grains from the canadian archipelago in the lower part of the mendeleev ridge record is interpreted to signify the pooling of freshwater in the amerasia basin possibly in relation to an extended glaciation in arctic north america unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the mendeleev ridge and other mid depth locations throughout the arctic ocean such as the northwind and lomonosov ridges this correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for arctic ocean sediments 2003 elsevier b v all rights reserved

basalt weathering across scales abstract weathering of silicate minerals impacts many geological and ecological processes for example the weathering of basalt contributes significantly to consumption of atmospheric carbon dioxide co2 and must be included in global calculations of such consumption over geological timeframes here we compare weathering advance rates for basalt wd where d and indicate the scale at which the rate is determined and surface area measured respectively from the laboratory to the watershed scales data collected at the laboratory weathering rind soil profile and watershed scales show that weathering advance rate of basalt is a fractal property that can be described by a fractal dimension dr 2 3 by combining the fractal description of rates with an arrhenius relationship for basalt weathering we derive the following equation to predict weathering advance rates at any spatial scale from weathering advance rates measured at the bet scale w d k 0 a d r 2 e e a r t here k0 is the pre exponential factor 1 29 107 mm3 mm 2 yr 1 ea is the activation energy 70 kj mol 1 and a is a spatial constant related to the scale of measurement of bet surface area 10 7 mm the term a d r 2 is the roughness the roughness fractal dimension can be conceptualized as a factor related to both the thickness of the reaction front and the specific surface area within the reaction front however the above equation can also be written in terms of a surface fractal dimension and the hypothetical average grain radius these fractal dimensions provide insight into reaction front geometry and should vary with lithology once the surface area discrepancy has been accounted for using this method we find a one to two order of magnitude range in weathering advance rates measured at any scale or temperature that can be attributed to factors such as changes in erosional regime parent lithology mechanism climate composition of reacting fluid and biological activity our scaled equation when used to predict global basalt co2 consumption based upon global lithologic maps yields an uptake flux 1 75 1013 mol co2 yr 1 within the predicted error of fluxes estimated based upon riverine measurements

rapid sea level rise and holocene climate in the chukchi sea three new sediment cores from the chukchi sea preserve a record of local paleoenvironment sedimentation and flooding of the chukchi shelf 50 m by glacial eustatic sea level rise radiocarbon dates on foraminifera provide the first marine evidence that the sea invaded hope valley southern chukchi sea 53 m as early as 12 ka the lack of significant sediment accumulation since ca 7 ka in hope valley southeastern chukchi shelf is consistent with decreased sediment supply and fluvial discharge to the shelf as deglaciation of alaska concluded abundant benthic foraminifera from a site west of barrow canyon indicate that surface waters were more productive 4 6 ka and this productivity varied on centennial time scales an offshore companion to this core contains a 20 m record of the holocene these results show that carefully selected core sites from the western arctic ocean can have a temporal resolution equal to the best cores from other regions and that these sites can be exploited for high resolution studies of the paleoenvironment

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

importance of surface structure on dissolution of fluorite implications for surface dynamics and dissolution rates dissolution rates are usually calculated as a function of surface area which is assumed to remain constant ignoring the changes occurring on the surface during dissolution here we present a study

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

the role of magnesite spatial distribution patterns in determining dissolution rates when do they matter we systematically explore the role of magnesite distribution patterns in dictating its dissolution rates under an array of flow velocity and permeability contrast conditions using flow through column experiments and reactive transport modeling columns were packed with magnesite distributed within quartz matrix in different spatial patterns the mixed column has uniformly distributed magnesite while the zonation columns contain magnesite in different number of zones parallel to the main flow dissolution rates are highest under conditions that maximize water flowing through the magnesite zone this occurs under fast flow and high permeability or uniformly distributed magnesite zones under high flow and low permeability magnesite conditions dissolution only occurs at the magnesite quartz interface leading to rates an order of magnitude lower in the one zone columns than those in the mixed columns spatial patterns do not make a difference under low flow conditions when the system approaches equilibrium v 0 36 m d or under conditions where magnesite zones have higher permeability than quartz zone the bulk column scale rate depends on ae through rmgco3 b mol s 10 9 60 ae where ae is the surface area that effectively dissolves with iap keq 0 1 the rate constant of 10 9 60 is very close to 10 10 0 mol m 2 s under well mixed conditions suggesting the potential resolution of laboratory field rate discrepancy when ae instead of the total bet surface area at i s used the ae values are 1 3 orders of magnitude lower than at the effectively dissolving magnesite quartz interface areas vary between 60 and 100 of ae pointing the importance of reactive interfaces in heterogeneous porous media this work quantifies the significance of magnesite spatial distribution patterns it has important implications in understanding biogeochemical processes in the critical zone and in the deep subsurface where spatial variations in mineral properties prevail

paleoglaciological insights from the age and morphology of the jesse moraine belt western canadian arctic abstract the jesse moraine belt 350 km long was deposited by the northwest laurentide ice sheet on banks and victoria islands in the western canadian arctic archipelago during the last deglaciation the moraine belt is composed of ice cored controlled moraines that contrast markedly with adjacent glacial sediments deposited during preceding ice sheet retreat more than 80 radiocarbon ages from fossil molluscs illustrate that deposition of the moraine belt was brief occurring between 13 75 and 12 75 cal ka bp the chronology demonstrates that moraine deposition was coeval with ice sheet drawdown and ice streaming on adjacent victoria island detailed geomorphic mapping demonstrates that the moraine belt is the product of a regional change in ice marginal processes this involved a predominantly cold based ice margin giving way to polythermal bed conditions which were conducive to widespread deposition of controlled moraines and ice stream bedforms the expansion of warm based thermal regimes in the northwest laurentide ice sheet followed widespread ice sheet withdrawal from m clure strait and western amundsen gulf this suggests a re equilibration of regional ice divides in response to rapidly changing ice sheet margins and surface gradients the reconstructed dynamical behavior of the northwest laurentide ice sheet provides new insights regarding ice sheet responses to late glacial climate and relative sea level change among other variables

modelling chemical depletion profiles in regolith abstract chemical or mineralogical profiles in regolith display reaction fronts that document depletion of leachable elements or minerals a generalized equation employing lumped parameters was derived to model such ubiquitously observed patterns c c 0 c 0 c x 0 c x 0 exp ini k x 1 here c cx 0 and co are the concentrations of an element at a given depth x at the top of the reaction front or in parent respectively ini is the roughness of the dissolving mineral in the parent and k is a lumped kinetic parameter this kinetic parameter is an inverse function of the porefluid advective velocity and a direct function of the dissolution rate constant times mineral surface area per unit volume regolith this model equation fits profiles of concentration versus depth for albite in seven weathering systems and is consistent with the interpretation that the surface area m2 mineral m 3 bulk regolith varies linearly with the concentration of the dissolving mineral across the front dissolution rate constants can be calculated from the lumped fit parameters for these profiles using observed values of weathering advance rate the proton driving force the geometric surface area per unit volume regolith and parent concentration of albite these calculated values of the dissolution rate constant compare favorably to literature values the model equation useful for reaction fronts in both steady state erosional and quasi stationary non erosional systems incorporates the variation of reaction affinity using ph as a master variable use of this model equation to fit depletion fronts for soils highlights the importance of buffering of ph in the soil system furthermore the equation should allow better understanding of the effects of important environmental variables on weathering rates

radiocarbon chronology of depositional regimes in the western arctic ocean abstract the foraminiferal abundance and percentage of coarse ice rafted detritus ird define glacial deglacial and interglacial depositional regimes in ams radiocarbon dated box cores from the western arctic ocean sediment deposition rates are generally less than 0 5 cm ka for glacial regimes greater than this for deglacial regimes and greater than 1 2 cm ka for interglacial regimes these differences in deposition rates might account for the much lower average sedimentation rates for the last 780 ka of 1 3 mm ka in cores from the central arctic ocean if glacial regimes dominated this interval foraminiferal abundances are less than 500 g during glacial maxima and mostly higher than 2000 g during deglacial and interglacial regimes slightly higher coarse ird percentages occur in deglacial intervals 5 10 up to 30 compared with interglacial intervals mostly 5 which characterize the last 10 12 ka in the western arctic ocean glacial regimes occurred from about 40 to 11 ka except for a brief interglacial or deglacial interval around 24 28 ka in the central arctic ocean the coarsest deglacial events occurred prior to 45 ka the late wisconsin deglaciation sediments approximately 9 16 ka are difficult to detect in the central arctic ocean sediments because they are only slightly coarser than the holocene and in some box cores less coarse than the holocene a previously unrecognized coarse ird event occurred near the core tops 0 3 cm between 1500 and 3500 radiocarbon years ago in the western arctic ocean only sediment older than 40 ka is coarser than this recent ird event which might correspond to a neoglaciation recognized in the north atlantic and elsewhere

learning to read the chemistry of regolith to understand the critical zone the base of the critical zone includes the mantle of altered soil and rock regolith that changes in response to chemical physical and biological processes occurring at earth s surface these processes are recorded in the chemistry of the regolith and this long term record can often be deciphered for example on eroding ridgetops where flows are generally downward for water and upward for earth material element concentrations vary with depth to constitute depletion addition depletion enrichment and biogenic profiles models can be used to explore the records of mineral dissolution atmospheric input coupled dissolution precipitation and biolifting documented in these profiles these models enable interpretation of the effects of time climate rates of erosion and human and other biotic impacts on the profile patterns by testing quantitative models against the long term record of information in regolith we will learn to project changes arising from human and natural perturbations of the critic

the dissolution kinetics of a granite and its minerals implications for comparison between laboratory and field dissolution rates the present study compares the dissolution rates of plagioclase microcline and biotite chlorite from a bulk granite to the dissolution rates of the same minerals in mineral rich fractions that were separated from the granite sample the dissolution rate of plagioclase is enhanced with time as a result of exposure of its surface sites due to the removal of an iron oxide coating removal of the iron coating was slower in the experiment with the bulk granite than in the mineral rich fractions due to a higher fe concentration from biotite dissolution as a result the increase in plagioclase dissolution rate was initially slower in the experiment with the bulk granite the measured steady state dissolution rates of both plagioclase 6 2 1 2 10 11 mol g 1 s 1 and microcline 1 6 0 3 10 11 mol g 1 s 1 were the same in experiments conducted with the plagioclase rich fraction the alkali feldspar rich fraction and the bulk granite based on the observed release rates of the major elements we suggest that the biotite chlorite rich fraction dissolved non congruently under near equilibrium conditions in contrast the biotite and chlorite within the bulk granite sample dissolved congruently under far from equilibrium conditions these differences result from variations in the degree of saturation of the solutions with respect to both the dissolving biotite chlorite and to nontronite which probably was precipitating during dissolution of the biotite and chlorite rich fraction following drying of the bulk granite the dissolution rate of biotite was significantly enhanced whereas the dissolution rate of plagioclase decreased the presence of coatings wetting and drying cycles and near equilibrium conditions all significantly affect mineral dissolution rates in the field in comparison to the dissolution rate of fully wetted clean minerals under far from equilibrium laboratory conditions to bridge the gap between the field and the laboratory mineral dissolution rates these effects on dissolution rate should be further studied