remagnetization of the paleogene tibetan himalayan carbonate rocks in the gamba area implications for reconstructing the lower plate in the india asia collision netherlands organization for scientific research nwo 825 15 016 institute for rock magnetism irm at the university of minnesota instruments and facilities program of nsf

study of the impact of ice formation in leads upon the sea ice pack mass balance using a new frazil and grease ice parameterization abstractleads are cracks in sea ice that often form because of deformation during winter months leads expose the ocean to the cold atmosphere resulting in supercooling and the formation of frazil ice crystals within the mixed layer here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the los alamos sea ice model cice the frazil ice module considers an initial cooling of leads followed by a steady state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice the grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice simulations of the sea ice cover in the arctic and antarctic are performed and compared to a model that treats leads the same as the open ocean the processes of ice formation in the new module slow down the refreezing o

a model of sea ice formation in leads and polynyas cracks in the sea ice cover break the barrier between the ocean and atmosphere exposing the ocean to the cold atmosphere during the winter these cracks are known as leads within the continuous sea ice pack and polynyas near land or ice shelves sea ice formation starts with frazil ice crystals in supercooled waters which grow and precipitate to the ocean surface to form grease ice eventually consolidating into a layer of solid sea ice that grows downward in this study a numerical model is formulated to simulate the formation of sea ice in a lead or polynya from frazil ice to a layer of new sea ice the simulations show the refreezing of a lead within 48 h of its opening grease ice covers the lead typically within 3 10 h and consolidates into sea ice within 15 30 h this study uses its model to simulate an observed polynya event in the laptev sea showing the vertical distribution of frazil ice and water supercooling sensitivity studies are used to investigate the dependence of ice growth on the ambient environment with the surface wind speed shown to be of greatest importance to lead exposure time and total ice growth the size and distribution of frazil crystals and the time taken for the lead to freeze over is shown to be highly dependent upon the ambient forcing and lead geometry

interpretation of ph and eh trends in a fluvial sand aquifer system ground waters and aquifer materials from a shallow fluvial sand aquifer system 1 km long flow path were sampled and analyzed to determine the hydrogeochemical processes affecting ph and eh measured pt electrode potential the aquifer system is a fine grained sand k 10 3 cm s composed principally of quartz and plagioclase 70 of all grains with minor biotite partially altered to vermicuiite and trace amounts of calcite acid neutralization capacity measurements and x ray diffractograms suggest that acid precipitation recharging the aquifer undergoes a two step neutralization process the first step involves reactions with the surfaces of mineral grains mainly with plagioclase and biotite and the second step involves an irreversible neutralization involving biotite alteration to vermiculite and carbonate mineral dissolution during migration through deep confined parts of the aquifer ground waters attain equilibrium with calcite a thermodynamically based redox model of a closed oxidant system satisfactorily accounts for the sequential reduction of dissolved oxygen ferric oxides and sulfate in the aquifer by the oxidation of dissolved organic carbon and for oxygen only ferrous iron because of the problems of using pt electrodes in ground waters it is recommended that eh measurements be supplemented with dissolved oxygen and sulfide measurements

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

structural evolution of the yushu nangqian region and its relationship to syncollisional igneous activity east central tibet field mapping geochronological analyses and cross section construction reveal a protracted deformation history and a minimum of 61 km of cenozoic ne sw shortening in present coordinates across the yushu nangqian thrust belt in northern tibet cenozoic contraction started prior to 51 ma and was followed first by northwest striking right slip faulting and later by northwest striking left slip faulting renewed ne sw contraction is expressed by folding of neogene strata and thrusting which again was followed by northwest striking left slip faults late neogene deformation is expressed by local north striking normal faults shortening across the yushu nangqian belt appears to be accommodated by thin skinned thrusting which raises the question of how the deformation was accommodated in the lower crustal levels to resolve this problem we perform geochemical analysis of igneous rocks dated as 51 49 and 38 37 ma the rocks exhibit geochemical signatures characteristic of subduction which implies that coeval crustal thickening in northeastern tibet was most likely induced by continental subduction

polynya flux model solutions incorporating a parameterization for the collection thickness of consolidated new ice previous polynya flux models have specified a constant value for the collection thickness of frazil ice h at the polynya edge in certain circumstances this approach can cause the frazil ice depth h within the polynya to exceed h a result which violates assumptions made in the formulation of the ice flux balance equations at the polynya edge to overcome this problem a parameterization for h is derived in terms of the depth of frazil ice arriving at the polynya edge and the component normal to the polynya edge of the frazil ice velocity relative to the velocity of the consolidated ice pack thus h is coupled to the unknown polynya edge using the new parameterization for h an analysis of the unsteady one dimensional opening of a coastal polynya is presented analytical solutions are also derived using the new parameterization for h for steady state two dimensional polynyas adjacent to a semi infinite and finite length coastal barrier the latter case representing a prototype island in all cases the solutions show close qualitative and quantitative agreement with those derived using a constant value for h however the steady state two dimensional polynya edge can in certain circumstances exhibit a corner at the point where the offshore equilibrium width is reached precise conditions for the existence of a corner are derived in terms of the orientation of the frazil ice velocity u and the consolidated ice velocity u upper and lower bounds are also obtained for the area of the steady state island polynya and it is shown that over a large range of orientations of u and u the area exceeds that associated with the island polynya with constant h finally two simulations of the st lawrence island polynya are presented using the new parameterization for h and the results are compared with the h constant theory

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

mineral stimulation of subsurface microorganisms release of limiting nutrients from silicates abstract microorganisms play an important role in the weathering of silicate minerals in many subsurface environments but an unanswered question is whether the mineral plays an important role in the microbial ecology silicate minerals often contain nutrients necessary for microbial growth but whether the microbial community benefits from their release during weathering is unclear in this study we used field and laboratory approaches to investigate microbial interactions with minerals and glasses containing beneficial nutrients and metals field experiments from a petroleum contaminated aquifer where silicate weathering is substantially accelerated in the contaminated zone revealed that phosphorus p and iron fe bearing silicate glasses were preferentially colonized and weathered while glasses without these elements were typically barren of colonizing microorganisms corroborating previous studies using feldspars in laboratory studies we investigated microbial weathering of silicates and the release of nutrients using a model ligand promoted pathway a metal chelating organic ligand 3 4 dihydroxybenzoic acid 3 4 dhba was used as a source of chelated ferric iron and a carbon source to investigate mineral weathering rate and microbial metabolism in the investigated aquifer we hypothesize that microbes produce organic ligands to chelate metals particularly fe for metabolic processes and also form stable complexes with al and occasionally with si further the concentration of these ligands is apparently sufficient near an attached microorganism to destroy the silicate framework while releasing the nutrient of interest in microcosms containing silicates and glasses with trace phosphate mineral inclusions microbial biomass increased indicating that the microbial community can use silicate bound phosphate inclusions the addition of a native microbial consortium to microcosms containing silicates or glasses with iron oxide inclusions correlated to accelerated weathering and release of si into solution as well as the accelerated degradation of the model substrate 3 4 dhba we propose that silicate bound p and fe inclusions are bioavailable and microorganisms may use organic ligands to dissolve the silicate matrix and access these otherwise limiting nutrients

frazil ice entrainment of sediment large tank laboratory experiments laboratory experiments that simulate natural ice formation processes and sediment entrainment in shallow water are presented a 10 30 cm s 1 current was forced with impellers in a 20 m long 1 m deep indoor tank turbulence in the flow maintained a suspension of sediments at concentrations of 10 20 mg l 1 at 0 5 m depth low air temperatures 15 c and 5 m s 1 winds resulted in total upward heat fluxes in the range 140 260 w m 2 the cooling produced frazil ice crystals up to 2 cm in diameter with concentrations up to 4 5 g l 1 at 0 5 m depth considerable temporal variability with time scales of 1 min was documented a close to constant portion of the smaller frazil crystals remained in suspension after some hours the larger crystals which made up most of the ice volume accumulated as slush at the surface current measurements were used to calculate the turbulent dissipation rate and estimates of vertical diffusion were derived after 5 8 hours sediment concentrations in the surface slush were normally close to those of the water after 24 hours however they were 2 4 times higher data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil ice production rates as well as sufficiently strong turbulence waves do not seem to increase sediment entrainment significantly

acquisition of chemical remanent magnetization during experimental ferrihydrite hematite conversion in earth like magnetic field implications for paleomagnetic studies of red beds abstract hematite bearing red beds are renowned for their chemical remanent magnetization crm if the crm was acquired substantially later than the sediment was formed this severely compromises paleomagnetic records to improve our interpretation of the natural remanent magnetization the intricacies of the crm acquisition process must be understood here we contribute to this issue by synthesizing hematite under controlled earth like field conditions 100 t crm was imparted in 90 oriented samples with varying inclinations the final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides when the magnetic field intensity is 40 t the crm records the field direction faithfully however for field intensities 40 t the crm direction may deviate considerably from that of the applied field during synthesis the crm intensity normalized by the isothermal remanent magnetization crm irm 2 5 t increases linearly with the intensity of growth field implying that crm could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties crm in hematite has a distributed unblocking temperature spectrum from 200 to 650 c while hematite with a depositional remanent magnetization drm has a more confined spectrum from 600 to 680 c because it is usually coarser grained and more stoichiometric therefore the thermal decay curves of crm with their concave shape are notably different from their drm counterparts which are convex these differences together are suggested to be a potential discriminator of crm from drm carried by hematite in natural red beds and of significance for the interpretation of paleomagnetic studies on red beds

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

fate of organic matter during aquifer storage and recovery asr of reclaimed water in a carbonate aquifer abstract understanding the fate of injected organic matter and the consequences of subsequent redox processes is essential to assess the viability of using reclaimed water in aquifer storage and recovery asr a full scale field trial was undertaken at bolivar south australia where two asr cycles injected approximately 3 6 105 m3 of reclaimed water into a carbonate aquifer over a 3 a period organic c within reclaimed water was predominantly in the dissolved fraction ranging from 1 to 2 mmol l 1 10 20 mg l 1 markedly higher than potable supply and stormwater previously reported as source waters for asr between 20 and 24 of the injected dissolved organic c doc was mineralised through reaction with injected o2 and no3 furthermore this was achieved mainly within the first 4 m of aquifer passage despite the presence of residual doc so4 reduction was not induced within the bulk of the injected plume it was only near the asr well during an extended storage phase where deeply reduced methanogenic conditions developed indicating variable redox zones within the injectant plume the quality of water recovered from the asr well indicated that the organic c content of reclaimed water does not restrict its application as a recharge source for asr

temporal variations in parameters reflecting terminal electron accepting processes in an aquifer contaminated with waste fuel and chlorinated solvents abstract a fundamental issue in aquifer biogeochemistry is the means by which solute transport geochemical processes and microbiological activity combine to produce spatial and temporal variations in redox zonation in this paper we describe the temporal variability of teap conditions in shallow groundwater contaminated with both waste fuel and chlorinated solvents teap parameters including methane dissolved iron and dissolved hydrogen were measured to characterize the contaminant plume over a 3 year period we observed that concentrations of teap parameters changed on different time scales and appear to be related in part to recharge events changes in all teap parameters were observed on short time scales months and over a longer 3 year period the results indicate that 1 interpretations of teap conditions in aquifers contaminated with a variety of organic chemicals such as those with petroleum hydrocarbons and chlorinated solvents must consider additional hydrogen consuming reactions e g dehalogenation 2 interpretations must consider the roles of both in situ at the sampling point biogeochemical and solute transport processes and 3 determinations of microbial communities are often necessary to confirm the interpretations made from geochemical and hydrogeological measurements on these processes

remagnetization of carbonate rocks in southern tibet perspectives from rock magnetic and petrographic investigations netherlands organization for scientific research nwo with a rubicon grant 825 15 016 institute for rock magnetism irm at the university of minnesota instruments and facilities program of nsf erc starting grant 306810 nwo vidi 864 11 004

ice ocean interactions during shallow convection under conditions of steady winds three dimensional numerical studies abstract a three dimensional hydrodynamic ocean model coupled to a thermohydrodynamic model for young sea ice is applied to study shallow haline convection in the central greenland sea with an emphasis on sub mesoscale ice ocean interactions two types of young sea ice are distinguished i e frazil and pancake ice both acting different on surface heat salt and momentum fluxes two scenarios are considered a continued frazil ice production during steady winds and b the same scenario but with the intermittent formation of pancake ice during a short intervening period of low winds brine release due to new ice production creates shallow convection in both cases under conditions of continued frazil ice production ice streaks develop at the sea surface finally becoming oriented roughly parallel to the wind these streaks are the result of convective plumes that induce organized patterns of convergent and divergent surface currents frazil ice is herded into convergence zones where it becomes as thick as 6 m within 24 h the studies suggest a strong relationship between streak spacing and the penetration depth of convection given by an aspect ratio in the range of 2 3 after pancake ice has been formed however the organized ice streaks vanish developing into complex patterns of pancake ice this finding is in agreement with recent field observations in the greenland sea is odden ice tongue with the existence of pancake ice moreover the surface averaged buoyancy flux decreases and is determined from the integral of local sub mesoscale ice ocean interactions

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

self potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes abstractlarge amplitude 100 mv negative electric self potential anomalies are often observed in the vicinity of buried metallic objects and ore bodies or over groundwater plumes associated with organic contaminants to explain the physical and chemical mechanisms that generate such electrical signals a controlled laboratory experiment was carried out involving two metallic cylinders buried with vertical and horizontal orientations and centered through and in the capillary fringe within a sandbox the 2d and 3d self potential sp data were collected at several time steps along with collocated ph and redox potential measurements large dipolar sp and redox potential anomalies developed in association with the progressive corrosion of the vertical pipe although no anomalies were observed in the vicinity of the horizontal pipe this discrepancy was due to the orientation of the pipes with the vertical pipe subjected to a significantly larger eh gradient accounting for the electrical conductivity dis

identifying goethite and hematite from rock magnetic measurements of soils and sediments we describe a sequence of experiments involving the acquisition of isothermal remanent magnetization irm in high 2 t fields followed by orthogonal demagnetization and the cooling and heating of remanent magnetization mr over the temperature range 196 c to 680 c the main aim of these experiments is to improve the basis for identifying the imperfect antiferromagnetic minerals contributing to the magnetic properties of natural soil and sediment samples which often contain complex mineral mixtures the procedures developed are first applied to a series of ore and synthetic samples of hematite and goethite each characterized by x ray diffraction xrd spectra and second to controlled mixtures of the two minerals the results confirm the mineral diagnostic nature of the experiments used they are subsequently used to identify goethite and hematite contributions to the rock magnetic properties of a variety of soils and recent sediments goethite can be unambiguously identified often accompanied by hematite in the majority of the samples studied despite indications from the synthetic mixtures that the ratio of goethite to hematite may have to exceed an order of magnitude before the goethite signatures are readily recognizable the rock magnetic tests are a much more sensitive basis for recognizing the presence of goethite in natural samples than are xrd analyses the results suggest that goethite s contribution to the rock magnetic properties of soil and sediment samples may often have been underestimated

challenges in isolating primary remanent magnetization from tethyan carbonate rocks on the tibetan plateau insight from remagnetized upper triassic limestones in the eastern qiangtang block abstract carbonate rocks widely used for paleomagnetically quantifying the drift history of the gondwana derived continental blocks of the tibetan plateau and evolution of the paleo meso neo tethys oceans are prone to pervasive remagnetization identifying remagnetization is difficult because it is commonly undetectable through the classic paleomagnetic field tests here we apply comprehensive paleomagnetic rock magnetic and petrographic studies to upper triassic limestones in the eastern qiangtang block our results reveal that detrital biogenic magnetite which may carry the primary natural remanent magnetization nrm is rarely preserved in these rocks in contrast authigenic magnetite and hematite pseudomorphs after pyrite and monoclinic pyrrhotite record three episodes of remagnetization the earliest remagnetization was induced by oxidation of early diagenetic pyrite to magnetite probably related to the collision between the northeastern tibetan plateau and the qiangtang block after closure of the paleo tethys ocean in the late triassic the second remagnetization residing in hematite and minor goethite which is the further subsurface oxidation product of pyrite magnetite is possibly related to the development of the localized cenozoic basins soon after india asia collision in the paleocene the youngest remagnetization is a combination of thermoviscous and chemical remanent magnetization carried by authigenic magnetite and pyrrhotite respectively our analyses suggest that a high supply of organic carbon during carbonate deposition prevailing sulfate reducing conditions during early diagenesis and widespread orogenic fluid migration related to crustal shortening during later diagenesis have altered the primary remanence of the shallow water tethyan carbonate rocks of the tibetan plateau we emphasize that all paleomagnetic results from these rocks must be carefully examined for remagnetization before being used for paleogeographic reconstructions future paleomagnetic investigations of the carbonate rocks in orogenic belts should be accompanied by thorough rock magnetic and petrographic studies to determine the origin of the nrm

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

a paleomagnetic reinvestigation of the upper devonian perry formation evidence for late paleozoic remagnetization america we undertook a reinvestigation of the upper devonian perry formation of coastal maine and adjacent new brunswick thermal demagnetization of samples from the redbeds yielded a characteristic direction d 166 l 4 that fails a fold test comparison of the corresponding paleopole 312 e 41 s with previously published paleozoic poles for north america suggests that the sediments were remagnetized in the late carboniferous after the removal of a steep northerly component the volcanics also reveal a shallow and southerly direction d 171 1 25 without tilt correction no stability test is available to date the magnetization of the volcanics however similarity of several of the directions to those seen in the sediments raises the suspicion that the volcanics are also remagnetized although the paleopole without tilt correction 303 e 32 s could be taken to indicate an early carboniferous age for the remagnetization scatter in the data suggests that the directions are contaminated by the incomplete removal of a steeper component due to present day field thus it is more likely that the volcanics were remagnetized at the same time as the sediments isothermal remanent magnetization irm acquisition curves blocking temperatures coercivities and reflected light microscopy indicate that the magnetization is carried by hematite in the sediments and by both magnetite and hematite in the volcanics it is therefore likely that the remagnetization of the perry formation involved both thermal and chemical processes related to the variscan alleghe nian orogeny our results indicate that previously published directions for the perry formation were based on the incomplete resolution of two magnetic components these earlier results can no longer be considered as representative of the devonian geomagnetic field

remagnetization of red beds on the tibetan plateau mechanism and diagnosis red beds are important targets for paleomagnetic studies yet discriminating secondary chemical remanent magnetization crm from primary depositional remanent magnetization drm in them remains challenging here we reanalyze the thermal demagnetization data of and conduct comprehensive rock magnetic mossbauer spectroscopic and petrographic studies on red beds from four cenozoic basins on the eastern tibetan plateau china the gongjue nangqian shanglaxiu and jinggu basins the red beds in the latter two basins are remagnetized as are most nangqian red beds the gongjue red beds and some nangqian red beds retain a drm our results reveal that detrital titano magnetite and hematite are well preserved in red beds retaining the drm whereas remagnetized red beds contain large amounts of authigenic hematite and goethite with detrital fe bearing minerals strongly altered postdepositional diagenetic alteration induced by heating and or fluid circulation related to magmatism and or crustal deformation is probably the main reason for the remagnetization hematite carrying the crm in remagnetized red beds has wide distribution of grain size and unblocking temperature spectra while hematite carrying the drm is usually coarse and has confined unblocking temperature spectrum this can be used as a criterion for diagnosing remagnetization nanoscale goethite appears to occur only in remagnetized red beds another sensitive criterion for discriminating crm from drm these property based criteria constrain the origin of the nrm in red beds better than the classic paleomagnetic field tests our research emphasizes that integrated rock magnetic mossbauer spectroscopic and petrographic studies provide robust tools to diagnose remagnetization in red beds

distribution of terminal electron accepting processes in an aquifer having multiple contaminant sources abstract concentrations of electron acceptors electron donors and h2 in groundwater were measured to determine the distribution of terminal electron accepting processes teaps in an alluvial aquifer having multiple contaminant sources upgradient contaminant sources included two separate hydrocarbon point sources one of which contained the fuel oxygenate methyl tertbutyl ether mtbe infiltrating river water was a source of dissolved no3 so4 and organic carbon doc to the downgradient part of the aquifer groundwater downgradient from the mtbe source had larger concentrations of electron acceptors dissolved o2 and so4 and smaller concentrations of teap end products dissolved inorganic c fe2 and ch4 than groundwater downgradient from the other hydrocarbon source suggesting that mtbe was not as suitable for supporting teaps as the other hydrocarbons measurements of dissolved h2 indicated that so4 reduction predominated in the aquifer during a period of high water levels in the aquifer and river the predominant teap shifted to fe3 reduction in upgradient areas after water levels receded but remained so4 reducing downgradient near the river this distribution of teaps is the opposite of what is commonly observed in aquifers having a single contaminant point source and probably reflects the input of doc and so4 to the aquifer from the river results of this study indicate that the distribution of teaps in aquifers having multiple contaminant sources depends on the composition and location of the contaminants and on the availability of electron acceptors

paleomagnetism of eocene red beds in the eastern part of the qiangtang terrane and its implications for uplift and southward crustal extrusion in the southeastern edge of the tibetan plateau abstract a primary magnetic component with the acquisition time of 56 0 43 2 ma was isolated between 580 c and 685 c from the eocene gonjo and ranmugou formations in the eastern part of the qiangtang terrane tibetan plateau the tilt corrected site mean direction is d s 35 5 i s 29 3 k 45 9 95 3 2 the site mean inclination increased from 29 3 to 41 6 after multiple inclination shallowing corrections giving a paleopole of 57 9 n 192 1 e a 95 2 9 comparison of the paleogene paleomagnetic data for the qiangtang terrane and lhasa terrane reveals that both terranes experienced latitudinal crustal shortening before 54 43 ma indicating the uplift of southern and central tibet in the early eocene subsequently since 35 4 2 4 ma the north of the qiangtang terrane experienced 1300 410 km of crustal shortening indicating the uplift of the northern tibetan plateau the lhasa terrane and qiangtang terrane have not experienced further crustal shortening since the late eocene and the southeastern part of tibet cannot have provided abundant crustal material to accommodate the significant crustal southward extrusion in the southeastern edge of the tibetan plateau the crust of the tengchong terrane and shan thai block did not experience significant southward extrusion since the late oligocene early miocene the indochina block was situated in the north of the qiangtang terrane before the oligocene and since the early oligocene the indochina block began to experience southward extrusion from the north of the qiangtang terrane which absorbed part of the crustal shortening in the north of the qiangtang terrane

paleomagnetism of the middle late jurassic to cretaceous red beds from the peninsular thailand implications for collision tectonics abstract jurassic to cretaceous red sandstones were sampled at 33 sites from the khlong min and lam thap formations of the trang syncline 7 6 n 99 6 e the peninsular thailand rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620 690 c an easterly deflected declination d 31 1 i 12 2 95 13 9 n 9 in stratigraphic coordinates is observed as pre folding remanent magnetization from north trang syncline whereas westerly deflected declination d 342 8 i 22 3 95 12 7 n 13 in geographic coordinates appears in the post folding remanent magnetization from west trang syncline these observations suggest an occurrence of two opposite tectonic rotations in the trang area which as a part of thai malay peninsula received clockwise rotation after jurassic together with shan thai and indochina blocks between the late cretaceous and middle miocene this area as a part of southern sundaland block experienced up to 24 5 11 5 counter clockwise rotation with respect to south china block this post cretaceous tectonic rotation in trang area is considered as a part of large scale counter clockwise rotation experienced by the southern sundaland block including the peninsular malaysia borneo and south sulawesi areas as a result of australian plate collision with southeast asia within the framework of sundaland block the northern boundary of counter clockwise rotated zone lies between the trang area and the khorat basin

migration of contaminants in groundwater at a landfill a case study 6 hydrogeochemistry multilevel point samplers located on a longitudinal cross section through the plume of contaminated groundwater in the sand aquifer at the abandoned borden landfill were used to obtain a suite of small volume samples for analysis of major ions and of minor and trace level inorganic constituents calcium is the dominant cation and sulphate and bicarbonate are the dominant anions in the contaminant plume with maximum concentrations of 400 2000 and 1200 mg l 1 respectively beneath the landfill the most highly contaminated water in the aquifer has total dissolved solids of 4000 mg l 1 sulphate and iron are the only inorganic constituents that exceed the recommended limits for drinking water the plume contains above background concentrations of dissolved zinc and manganese no heavy metals or other hazardous inorganic trace elements occur at levels above the maximum limits for drinking water the plume contains levels of total dissolved organic carbon that are above background levels ranging from 30 mg l 1 beneath the landfill to 5 mg l 1 near the front of the plume the landfill which is almost entirely above the water table contains high partial pressures of carbon dioxide and methane the high carbon dioxide levels induce substantial dissolution of calcite which occurs in sand layers in the landfill and in the aquifer immediately below the landfill calcite dissolution is the origin of much of the dissolved inorganic carbon and some of the calcium in the plume most of the sulphate and much of the calcium in the plume appears to be derived from gypsum in construction debris in the landfill groundwater beneath the landfill is saturated with respect to gypsum and slightly supersaturated with respect to calcite some of the dissolved iron in the plume results from the release under reducing conditions of iron from ferric iron coatings on sand grains located in the aquifer beneath the landfill and in the layers in the refuse dissolved iron concentrations appear to be limited by the solubility of siderite dissolved sulphide is present at only very low concentrations and is probably controlled by ferrous sulphide solubility exchange of cations between the aquifer material and the leachate contaminated groundwater is an apparent cause of calcium release and subsequent precipitation of calcite in the plume as much of 80 of the k 20 of the mg2 and 15 of the na in the plume exists on the exchange sites the effects of dispersive and geochemical attenuation were evaluated from the ratios of chloride to other species along a central flow path from the landfill to the front of the plume platinum electrode measurements and electrochemical potentials calculated from equilibrium speciation of analysed constituents varied over a wide range of values and provided poor agreement among methods for the same sample only potentials derived from the iron redox couples and pt electrode measurements exhibited fair agreement for any one sample the rather narrow range of pt electrode potential values along the central flow line through the plume suggest that the electrochemical potentials are buffered apparently as a result of fe oh 3 s ag feco3 s equilibria

chemical overprint on the natural remanent magnetization of a subtropical red soil sequence in the bose basin southern china 1 we present a high resolution paleomagnetic investigation of the subtropical red soil sequence at the damei section bose basin southern china maghemite with low coercivities and fine grained hematite with high coercivities but relatively low unblocking temperatures were identified as main carriers of the natural remanent magnetization nrm strong chemical weathering occurring under subtropical climatic conditions in southern china led to a chemical remanent magnetization crm overprint that is sufficiently strong to mask the primary nrm analysis of the bose basin soil sequence indicates that the crm has a large lock in depth 4 m this example shows that magnetostratigraphic studies on red soil sequences in subtropical tropical southern china should be interpreted with caution

use of dissolved and vapor phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the subsurface 1 at many sites contaminated with petroleum hydrocarbons methanogenesis is a significant degradation pathway techniques to estimate ch4 production consumption and transport processes are needed to understand the geochemical system provide a complete carbon mass balance and quantify the hydrocarbon degradation rate dissolved and vapor phase gas data collected at a petroleum hydrocarbon contaminated site near bemidji minnesota demonstrate that naturally occurring nonreactive or relatively inert gases such as ar and n2 can be effectively used to better understand and quantify physical and chemical processes related to methanogenic activity in the subsurface in the vadose zone regions of ar and n2 depletion and enrichment are indicative of methanogenic and methanotrophic zones and concentration gradients between the regions suggest that reaction induced advection can be an important gas transport process in the saturated zone dissolved ar and n2 concentrations are used to quantify degassing driven by methanogenesis and also suggest that attenuation of methane along the flow path into the downgradient aquifer is largely controlled by physical processes slight but discernable preferential depletion of n2 over ar in both the saturated and unsaturated zones near the free phase oil suggests reactivity of n2 and is consistent with other evidence indicating that nitrogen fixation by microbial activity is taking place at this site

nanogoethite as a potential indicator of remagnetization in red beds red beds are well known for recording stable natural remanent magnetization nrm however discriminating primary nrm from secondary remanence in red beds is difficult the paleogene nangqian red beds in eastern tibetan plateau variably record an overprint related to nearby magmatism and thus provide a great opportunity to characterize remagnetization in red beds through comprehensive rock magnetic mossbauer spectroscopic and petrographic analyses we find that remagnetization was controlled by temperature remagnetized red beds contain abundant authigenic hematite and goethite with some larger grains unblocking at the neel temperatures and the remainder nanoparticles unblocking at lower temperatures in contrast red beds retaining primary nrm are characterized by dominance of detrital hematite and magnetite presence of fine grained authigenic hematite and absence of authigenic goethite and magnetite high temperature behaviors of nrm susceptibility are indicative of remagnetization but the presence of goethite appears to be a more sensitive criterion for diagnosing remagnetization in red beds

insights into the early tibetan plateau from u th he thermochronology the central songpan ganzi belt located on the eastern margin of the tibetan plateau has a similar high elevation and low relief to parts of central tibet thermochronological studies from the central tibetan plateau reveal a history of slow exhumation rates 1 since 45ma however the exhumation history of the central songpan ganzi belt is unknown to address this we conducted an apatite and zircon u th he thermochronology study of bedrock samples collected across the central songpan ganzi belt and into central parts of the tibetan plateau zircon u th he ages range from 54 2 7 5 to 146 5 10 0ma and the majority of apatite u th he ages fall between 74 7 19 0 and 35 7 9 4ma thermal history models of these data show rapid cooling in the late mesozoic and much slower cooling diagnostic of low rates of erosion throughout most of the cenozoic the late mesozoic rapid cooling is consistent with the existence of significant topography and relief at least in some parts of the songpan ganzi belt at that time we find no evidence for a regional miocene acceleration in erosion although three samples from the headwaters of the salween and mekong rivers gave younger ahe ages between 15 and 16ma that reflect an acceleration in river incision supplementary material laser ablation inductively coupled plasma mass spectrometry zircon u pb data from central and eastern tibet are available at www geolsoc org uk sup18647

goethite as a potential source of magnetic nanoparticles in sediments goethite is an important iron bearing mineral found in nearly all types of soils and sediments that typically occurs as particles of nanoscale crystallites here we show that poorly crystalline nanophase goethite can undergo dehydroxylation and alteration to produce strongly magnetic fe oxide nanoparticles after moderate reductive heating synthetic oriented aggregates of nanogoethite were converted to stoichiometric sub micron magnetite in contrast oxidative heating produced only nanocrystalline hematite we present a novel characterization of the products of nanogoethite alteration which represents an important pathway for the production of both superparamagnetic and stable single domain magnetic particles in a wide variety of sedimentary environments including soils and lacustrine and marine settings in which goethite is commonly present in nature the mechanism of magnetite formation observed in our experiments could contribute to the widespread phenomenon of magnetic enhancement in many soil types and could be responsible for secondary magnetizations often observed to accompany diagenesis in sedimentary rocks thus nanogoethite may be an important precursor of fine magnetic particles and magnetic remanence carriers in the environment particularly in soils and catchment areas affected by wildfire as well as in sediments subjected to deep burial diagenesis and low grade metamorphism

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

remagnetization mechanisms in triassic red beds from south china paleogeographic reconstructions based on paleomagnetic data rely on the reliability of the natural remanent magnetization nrm as a primary geomagnetic signal remagnetizations however can be common in many rock types including late paleozoic and mesozoic red beds and they complicate paleogeographic interpretations extracting the primary nrm from partially remagnetized rocks and understanding the remagnetization mechanism are important in these contexts we carried out a systematic paleomagnetic study of red bed samples from the triassic huangmaqing formation nanjing 32 0 n 118 9 e south china two nrm components carried by secondary and primary hematite are isolated in 47 of the 94 samples studied where the latter component has a direction in stratigraphic coordinates of d 29 2 i 34 6 95 10 9 47 samples from 6 sites that yields a paleopole of 60 8 n 228 1 e dp dm 12 5 7 2 which is consistent with triassic pole positions for the south china block a secondary chemical remanent magnetization crm d 227 1 i 80 8 95 7 3 is documented in all 94 samples from 10 sites and is carried by pigmentary hematite that is inferred to have been generated by magnetite oxidation during orogenic activity this secondary component has steep inclinations and is interpreted to have been influenced by a combination of the remanence carried by original parent magnetite the orogenic stress field and the prevailing geomagnetic field direction during deformation this crm direction is recorded commonly by red beds from the south china block and is significant for regional tectonic studies in the area

biogeochemical transformation of fe minerals in a petroleum contaminated aquifer abstract the bemidji aquifer in minnesota usa is a well studied site of subsurface petroleum contamination the site contains an anoxic groundwater plume where soluble petroleum constituents serve as an energy source for a region of methanogenesis near the source and bacterial fe iii reduction further down gradient methanogenesis apparently begins when bioavailable fe iii is exhausted within the sediment past studies indicate that geobacter species and geothrix fermentens like organisms are the primary dissimilatory fe reducing bacteria at this site the fe mineralogy of the pristine aquifer sediments and samples from the methanogenic source and fe iii reducing zones were characterized in this study to identify microbiologic changes to fe valence and mineral distribution and to identify whether new biogenic mineral phases had formed methods applied included x ray diffraction x ray fluorescence xrf and chemical extraction optical transmission and scanning electron microscopy and mossbauer spectroscopy all of the sediments were low in total fe content 1 and exhibited complex fe mineralogy the bulk pristine sediment and its sand silt and clay sized fractions were studied in detail the pristine sediments contained fe ii and fe iii mineral phases ferrous iron represented approximately 50 of fetot the relative fe ii concentration increased in the sand fraction and its primary mineralogic residence was clinochlore with minor concentrations found as a ferroan calcite grain cement in carbonate lithic fragments fe iii existed in silicates epidote clinochlore muscovite and fe iii oxides of detrital and authigenic origin the detrital fe iii oxides included hematite and goethite in the form of mm sized nodular concretions and smaller sized dispersed crystallites and euhedral magnetite grains authigenic fe iii oxides increased in concentration with decreasing particle size through the silt and clay fraction chemical extraction and mossbauer analysis indicated that this was a ferrihydrite like phase quantitative mineralogic and fe ii iii ratio comparisons between the pristine and contaminated sediments were not possible because of textural differences however comparisons between the texturally similar source where bioavailable fe iii had been exhausted and fe iii reducing zone sediments where bioavailable fe iii remained indicated that dispersed detrital crystalline fe iii oxides and a portion of the authigenic poorly crystalline fe iii oxide fraction had been depleted from the source zone sediment by microbiologic activity little or no effect of microbiologic activity was observed on silicate fe iii the presence of residual ferrihydrite in the most bioreduced anoxic plume sediment source implied that a portion of the authigenic fe iii oxides were biologically inaccessible in weathered lithic fragment interiors little evidence was found for the modern biogenesis of authigenic ferrous containing mineral phases perhaps with the exception of thin siderite or ferroan calcite surface precipitates on carbonate lithic fragments within source zone sediments

paleocene eocene syncontractional sedimentation in narrow lacustrine dominated basins of east central tibet sedimentologic stratigraphic compositional and structural data from four elongate basins 30 km long in the nangqian yushu region of east central tibet near the headwaters of the mekong and yangtze rivers indicate nonmarine sedimentation synchronous with paleocene eocene northeast southwest shortening sedimentation in the nangqian niuguoda xialaxiu and shanglaxiu basins involved 1 mud and carbonate accumulation in offshore to nearshore lacustrine environments and 2 gravel and sand deposition in fan delta to alluvial fan environments localized near basin margins growth strata in both fine and coarse grained deposits primarily in upper levels of basin fill provide evidence for sedimentation contemporaneous with motion on fold thrust structures provenance data collected from 25 measured stratigraphic sections including 1500 paleocurrent measurements and 150 conglomerate compositional analyses show that each basin was fed sediment from several directions by proximal source areas composed of carboniferous triassic rocks the source area proximity and a stratigraphic variability among the basins suggest that each basin evolved independently and was filled by sediment derived from relatively small drainage networks 103 km2 age control for basin fill is based on paleogene fossils 38 37 ma 40ar 39ar ages from volcanic rocks interbedded with uppermost strata of the nangqian basin and 51 49 ma 40ar 39ar ages from igneous rocks that intrude and unconformably overlie strata of the shanglaxiu basin strata containing middle cretaceous palynomorph and ostracod assemblages are present only locally in the lowermost part of the nangqian basin although the tectonic setting for cretaceous sedimentation is unclear early tertiary basin development was controlled by thin skinned fold thrust deformation we interpret the narrow widths of paleocene eocene basins to be a result of thrust spacing which in turn may have been controlled by the depth to the decollement 5 km deep according to our balanced cross section from which imbricate thrusts ramped up through the carboniferous triassic section sedimentologic and provenance evidence for internal drainage limited unroofing and relatively low average sediment accumulation rates in these syncontractional plateau interior basins indicates generally small drainage systems short main stem rivers shallow regional slopes and limited denudation in east central tibet during early tertiary time such geomorphic conditions which are similar to the modern low relief interior of the tibetan plateau suggest that the deeply incised mekong and yangtze rivers of eastern tibet were not established until after the termination of paleogene basin development in the region

changes in the sorption capacity of coastal plain sediments due to redox alteration of mineral surfaces chemical characteristics of grain coatings in a coastal plain sandy aquifer on the eastern shore of virginia were investigated where sediments have been exposed to distinct groundwater redox conditions dissolved o2 was 5 0 to 10 6 mg l 1 in the regionally extensive aerobic groundwater whereas in a narrow leachate plume it was only 0 001 to 0 9 mg l 1 the amount of dissolved fe in the aerobic groundwater was only 0 005 to 0 01 mg l 1 but it was 12 to 47 mg l 1 in the anaerobic zone the amount of extractable fe was an order of magnitude higher for the aerobic sediments than for the anaerobic sediments indicating that reductive dissolution removed the oxide coatings the capacity for anion sorption on the sediment surfaces as indicated by the sorption of 35so42 was an order of magnitude higher in the aerobic vs anaerobic sediments the presence of anaerobic groundwater did not significantly alter the amount of extractable al oxides on the surface of the sediments and those coatings helped to maintain a high surface area the removal of the fe oxides from the grain surfaces under anaerobic conditions was solely responsible for the significant reduction of so4 sorption observed this loss of capacity for anion sorption could lead to more extensive transport of negatively charged constituents such as some contaminant chemicals or bacteria that may be of concern in groundwater

microbial colonization and weathering of silicates in a petroleum contaminated groundwater abstract the influence of native microorganisms on mineral dissolution and precipitation was examined in a petroleum contaminated aquifer near bemidji minnesota in situ microcosms containing clean silicate fragments were established in the contaminated microbially active groundwater over one year periods the recovered minerals were then examined by sem and esem for microbial colonization patterns and weathering features these experiments reveal distinct patterns of colonization and weathering associated with microbial attachment and growth microcline anorthoclase and oligoclase were widely colonized and the colonized surfaces deeply weathered with secondary clays precipitated on some uncolonized surfaces other feldspars in contrast were uncolonized and unweathered specific mineral removal rate was estimated from etch pit depth while bulk weathering rate was estimated from the rate of change of silica concentration in the groundwater in this system the primary control of silicate dissolution is apparently microbial colonization and metabolic activity

chemical hydrogeology in natural and contaminated environments abstract chemical hydrogeology including organic and inorganic aspects has contributed to an increased understanding of groundwater flow systems geologic processes and stressed environments most of the basic principles of inorganic chemical hydrogeology were first established by investigations of organic free regional scale systems for which simplifying assumptions could be made the problems of groundwater contamination are causing a shift of emphasis to microscale systems that are dominated by organic chemical reactions and that are providing an impetus for the study of naturally occurring and manmade organic material along with the decrease in scale physical and chemical heterogeneity become major controls current investigations and those selected from the literature demonstrate that heterogeneity increases in importance as the study site decreases from regional scale to macroscale to microscale increased understanding of regional scale flow systems is demonstrated by selection of investigations of carbonate and volcanic aquifers to show how application of present day concepts and techniques can identify controlling chemical reactions and determine their rates identify groundwater flow paths and determine flow velocity and determine aquifer characteristics the role of chemical hydrogeology in understanding geologic processes of macroscale systems is exemplified by selection of investigations in coastal aquifers phenomena associated with the mixing zone generated by encroaching sea water include an increase in heterogeneity of permeability diagenesis of minerals and formation of geomorphic features such as caves lagoons and bays ore deposits of manganese and uranium along with a simulation model of ore forming fluids demonstrate the influence of heterogeneity and of organic compounds on geochemical reactions associated with genesis of mineral deposits in microscale environments importance of heterogeneity and consequences of organic reactions in determining the distributions and concentrations cf constituents are provided by several studies including infiltration of sewage effluent and migration of creosote in coastal plain aquifers these studies show that heterogeneity and the dominance of organically controlled reactions greatly increase the complexity of investigations

dating degassed groundwater with 3h 3he the production of gases in groundwater under contaminated locations by geochemical and biological processes is not uncommon degassing of these gases from groundwater and repartitioning of noble gases between water and gas phase distorts groundwater dating by 3h 3he we observed noble gas concentrations below atmospheric equilibrium in 20 out of 34 groundwater samples from agriculturally polluted sandy areas in the netherlands from the absence of nitrate in degassed samples we conclude that denitrification causes degassing the 22ne 20ne ratios show that degassing had attained solubility equilibrium and had not caused isotopic fractionation by diffusion to correct for the loss of tritiogenic 3he due to degassing we present a single step equilibrium degassing model we use the total dissolved gas pressure at the monitoring screen to estimate the depth and timing of degassing which is essential to estimate travel times from degassed samples by propagating the uncertainties in the underlying measurements and assumptions through the travel time calculations we found a travel time uncertainty of 3 years a we therefore conclude that 3h 3he dating can produce valuable information on groundwater flow even at sites with strong degassing copyright 2007 by the american geophysical union

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

the superparamagnetism of yucca mountain tuff yucca mountain tuff contains small titanomagnetite grains with narrow size distributions in the superparamagnetic range schlinger et al 1988 magnetic measurements on three samples comprising hysteresis loops at low and ambient temperatures acquisition and demagnetization of isothermal remanent magnetization thermal demagnetization of the saturation remanence and of a low temperature thermoremanence and frequency and temperature dependent susceptibilities allow evaluation of the magnetic properties in terms of neel s 1949 single domain theory precise grain volume distributions have been obtained by applying the blocking volume concept to thermal demagnetization results in contrast an attempt to derive mean particle volumes by fitting a langevin curve to the room temperature magnetization curves fails probably because the precondition for the langevin function kv kt 1 is not met it is only for the sample with the smallest grains and in weak fields 20 mt that a langevin fit provides a reasonable volume estimate there is good agreement between the experimental results and the calculated frequency and temperature dependence of susceptibility thus verifying that neel s theory is sufficient for the magnetic description of single domain assemblages spanning the superparamagnetic stable single domain boundary however some deviations between modeled and measured susceptibilities exist and the physical causes may include size dependent anisotropy nonuniform magnetizations and also an uncertain preexponential time constant 0 while 0 10 11 s gives the best fit for the sample with the largest grains 0 10 9 s is more reasonable for the others thus 0 may indeed be size and temperature dependent as predicted by brown 1959 the commonly cited parameter fd frequency dependence of susceptibility reaches 30 at room temperature rt for one sample with a blocking temperatures just below rt while fd 0 at rt for a superparamagnetic sample with smaller grains these results thus exemplify that fd is not limited to 15 as a number of studies suggest and that fd 0 must not be taken to imply the absence of superparamagnetic grains

iron reduction in the sediments of a hydrocarbon contaminated aquifer abstract sediments sampled at a hydrocarbon contaminated glacial outwash sandy aquifer near bemidji minnesota were analyzed for sediment associated fe with several techniques extraction with 0 5 m hcl dissolved poorly crystalline fe oxides and small amounts of fe in crystalline fe oxides and extracted fe from phyllosilicates use of ti citrate edta bicarbonate results in more complete removal of crystalline fe oxides the average hcl extractable fe iii concentration in the sediments closest to the crude oil contamination 16 2 mol g has been reduced by up to 30 from background values 23 8 mol g as a result of fe iii reduction in contaminated anoxic groundwater iron ii concentrations are elevated in sediments within an anoxic plume in the aquifer iron ii values under the oil body 19 2 mol g are as much as 4 times those in the background sediments 4 6 mol g indicating incorporation of reduced fe in the contaminated sediments a 70 increase in total extractable fe at the anoxic oxic transition zone indicates reoxidation and precipitation of fe mobilized from sediment in the anoxic plume scanning electron microscopy detected authigenic ferroan calcite in the anoxic sediments and confirmed abundant fe iii oxyhydroxides at the anoxic oxic boundary the redox biogeochemistry of fe in this system is coupled to contaminant degradation and is important in predicting processes of hydrocarbon degradation

53 43 ma deformation of eastern tibet revealed by three stages of tectonic rotation in the gongjue basin the gongjue basin from the eastern qiangtang terrane is located in the transition region where the regional structural lineation curves from east west oriented in tibet to north south oriented in yunnan in this study we sampled the red beds in the basin from the lower gongjue to upper ranmugou formations for the first time covering the entire stratigraphic profile the stratigraphic ages are bracketed within 53 43 ma by new detrital zircon u pb ages constraining the maximum deposition age to 52 5 1 5 ma rock magnetic and petrographic studies indicate that detrital magnetite and hematite are the magnetic carriers positive reversals and fold tests demonstrate that the characteristic remanent magnetization has a primary origin the gongjue and ranmugou formations yield mean characteristic remanent magnetization directions of d s i s 31 0 21 3 and d s i s 15 9 22 0 respectively the magnetic inclination of these characteristic remanent magnetizations is significantly shallowed compared to the expected inclination for the locality however the elongation inclination correction method does not provide a meaningful correction likely because of syn depositional rotation rotations relative to the eurasian apparent polar wander path occurred in three stages stage i 33 3 3 4 clockwise rotation during the deposition of the gongjue and lower ranmugou formations stage ii 26 9 3 7 counterclockwise rotation during deposition of the lower and middle ranmugou formation and stage iii 17 7 3 3 clockwise rotation after 43 ma the complex rotation history recorded in the basin is possibly linked to sinistral shear along the qiangtang block during india indentation into asia and the early stage of the extrusion of the northwestern indochina blocks away from eastern tibet

the physical properties of sea ice in the odden ice tongue abstract the odden ice tongue developed prominently during the winter of 1992 1993 but did not appear at all during the two subsequent winters of the esop period during 1992 1993 the in situ sea ice characteristics within odden were studied on four occasions in addition to direct observation and aerial photography the measurement programme included retrieval and on board analysis of frazil and pancake ice samples wave measurements within odden and near surface ctd measurements to examine the effect of melt on the upper ocean reported in brandon and wadhams 1999 the near surface hydrography beneath the odden ice tongue deep sea research in press this paper reports on the characteristics of the frazil and pancake ice observed and sampled during this season expanding on early results reported in wadhams et al 1996 journal of geographical research 101 c8 18 213 18 235 by combining the results of in situ sampling with the analysis of passive microwave and sar data of the sea ice extent through the winter it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

characterisation of organic matter in a shallow reducing arsenic rich aquifer west bengal abstract elevated arsenic in groundwaters extensively exploited for irrigation and drinking water in west bengal and bangladesh is causing serious impacts on human health a key mechanism for the genesis of arsenic as in these waters is microbially mediated reductive transformation of arsenic bearing fe iii hydrated oxides the role of organic c in this process whether from in situ organic matter om i e om from within the sediment or from other sources is widely recognised despite this there is a paucity of data about the characteristics of om in these as rich aquifers extraction and analysis of the polar and apolar fractions from seven different sediments from a known groundwater as hotspot in west bengal revealed om characteristic of the original terrestrial depositional environment however this was overprinted by abundant hydrocarbons with thermally mature e g petroleum distributions these hydrocarbons included abundant high molecular weight n alkanes and unresolved complex mixtures ucms as well as thermally mature distributions of hopanes and steranes additionally at certain depths surface sands 8 and 13 m deeper sands 25 m the om appeared to be biodegraded with the preferential removal of petroleum sourced n alkanes suggesting that indigenous microbes within the aquifer can utilise this carbon source the presence of this previously unreported source of bioavailable organic carbon is of importance as it has the potential to promote microbial activity and subsequent as release in the aquifers

combined 14c and δ13c analysis of petroleum biodegradation in a shallow contaminated aquifer the contamination of soil and groundwater by the accidental release of petroleum hydrocarbons is a common problem that affects drinking water supplies and in situ biodegradation is a promising option for removing contaminants with relatively low costs and minimal health risks total petroleum hydrocarbons tph 13c and 14c isotope ratios in dissolved inorganic carbon dic and other geochemical indicators have been analyzed to demonstrate the effectiveness of in situ biodegradation at a contaminated site the 13c and 14c isotope ratios ranged from 5 4 to 18 4 and from 35 1 to 67 pmc respectively some groundwater samples were contaminated with petroleum hydrocarbons with low 14c and 13c contents indicating the existence of microbial non methanogenic biodegradation whereas low 14c and high 13c contents were associated with the highest tph concentrations confirming that microbial methanogenic biodegradation occurred in these areas differences in the 13c and 14c isotope ratios between monitoring wells in uncontaminated and contaminated areas suggest that the percentage of the dic produced by methanogenic biodegradation decreased from 28 5 32 0 to 5 94 6 67 along the flow direction and became almost zero in downgradient areas and at the edge of the contamination plume

modeling of carbon cycling and biogeochemical changes during injection and recovery of reclaimed water at bolivar south australia 1 managed aquifer recharge is an increasingly popular technique to secure and enhance water supplies among a range of recharging techniques single well aquifer storage and recovery asr is becoming a common option to either augment drinking water supplies or facilitate reuse of reclaimed water for the present study a conceptual biogeochemical model for reclaimed water asr was developed and incorporated into an existing reactive multicomponent transport model the conceptual and numerical model for carbon cycling includes various forms of organic and inorganic carbon and several reactive processes that transfer carbon within and across different phases the major geochemical processes considered in the model were microbially mediated redox reactions driven by the mineralization of organic carbon mineral dissolution precipitation and ion exchange the numerical model was tested and applied for the analysis of observed data collected during an asr field experiment at bolivar south australia the model simulation of this experiment provides a consistent interpretation of the observed hydrochemical changes the results suggest that during the storage phase dynamic changes in bacterial mass have a significant influence on the local geochemistry in the vicinity of the injection extraction well farther away from the injection extraction well breakthrough of cations is shown to be strongly affected by exchange reactions and in the case of calcium by calcite dissolution

primary and secondary red bed magnetization constrained by fluvial intraclasts author s swanson hysell nl fairchild lm slotznick sp abstract 2019 american geophysical union all rights reserved the magnetization of hematite bearing sedimentary rocks provides critical records of geomagnetic reversals and paleogeography however the timing of hematite remanent magnetization acquisition is typically difficult to constrain while detrital hematite in sediment can lead to a primary depositional remanent magnetization alteration of minerals through interaction with oxygen can lead to the postdepositional formation of hematite in this study we use exceptionally preserved fluvial sediments within the 1 1 billion year old freda formation to gain insight into the timing of hematite remanence acquisition and its magnetic properties this deposit contains siltstone intraclasts that were eroded from a coexisting lithofacies and redeposited within channel sandstone thermal demagnetization petrography and rock magnetic experiments on these clasts reveal two generations of hematite one population of hematite demagnetized at the highest unblocking temperatures and records directions that rotated along with the clasts this component is a primary detrital remanent magnetization the other component is removed at lower unblocking temperatures and has a consistent direction throughout the intraclasts this component is held by finer grained hematite that grew and acquired a chemical remanent magnetization following deposition resulting in a population that includes superparamagnetic nanoparticles in addition to remanence carrying grains the data support the interpretation that magnetizations of hematite bearing sedimentary rocks held by g400 nm grains that unblock close to the neel temperature are more likely to record magnetization from the time of deposition this primary magnetization can be successfully isolated from cooccurring authigenic hematite through high resolution thermal demagnetization

thickness structure and properties of level summer multiyear ice in the eurasian sector of the arctic ocean in august and september 1991 thickness structure and properties of level multiyear ice were studied at 66 locations in the eurasian sector of the arctic ocean the mean ice thickness was 2 86 m with 0 31 m of freeboard including 0 08 m deteriorated ice of mean density 370 kg m 3 on the basis of the study of ice cores 61 of the ice cover consisted of undeformed columnar ice the remaining 39 consisted of a mixture of ice types including frazil 18 and deformed ice 9 through microstructural studies six main classes of pores could be identified the mean density of the ice cover increased from 720 kg m 3 at the top to 880 kg m 3 below 0 4 m depth sea ice salinities mean value 2 1 correlate with ice thickness on average salinity profiles exhibit a linear increase from values close to 0 at the top to 2 at 1 m depth with less steep salinity gradients below sampling from different depths within the ice cover indicates that the brine in summer sea ice is strongly stratified the influence of meltwater percolation is evident with salinities around 5 and ph values 15 and 8 at greater depths brine volumes ranging from 80 to 150 are controlled by the thermodynamic equilibrium between the solid and liquid phases gas volumes decrease from 200 at the top to 50 below 1 m depth pore microstructure is highly variable even on small scales salinity and other ice properties do not vary to a large degree between different regions the evolution of level multiyear sea ice is discussed with particular reference to hidden occurrence of deformed ice and the importance of ablation processes

paleomagnetism of late jurassic to early cretaceous red beds from the cardamom mountains southwestern cambodia tectonic deformation of the indochina peninsula abstract late jurassic to early cretaceous red beds of the phuquoc formation were sampled at 33 sites from the sihanoukville and koah kong areas of the phuquoc kampot som basin southwestern cambodia two high temperature remanent components with unblocking temperature ranging 650 670 c and 670 690 c were identified the magnetization direction for the former component d 5 2 i 18 5 with 95 3 1 in situ reveals a negative fold test that indicates a post folding secondary nature however the latter component carried by specular hematite is recognized as a primary remanent magnetization a tilt corrected mean direction of d 43 4 i 31 9 95 3 6 was calculated for the primary component at 11 sites corresponding to a paleopole of 47 7 n 178 9 e a 95 3 6 when compared with the 130 ma east asian pole a southward displacement of 6 0 3 5 and a clockwise rotation of 33 1 4 0 of the phuquoc kampot som basin as a part of the indochina block with respect to east asia were estimated this estimate of the clockwise rotation is 15 larger than that of the khorat basin which we attribute to dextral motion along the wang chao fault since the mid oligocene the comparison of the herein estimated clockwise rotation with the counter clockwise rotation reported from the da lat area in vietnam suggests the occurrence of a differential tectonic rotation in the southern tip of the indochina block during the southward displacement of the indochina block the non rigid lithosphere under its southern tip moved heterogeneously while the rigid lithosphere under the khorat basin moved homogeneously

crude oil in a shallow sand and gravel aquifer ii organic geochemistry abstract crude oil spilled from a pipeline break in a remote area of north central minnesota has contaminated a shallow glacial outwash aquifer part of the oil was sprayed over a large area to the west of the pipeline and part of it accumulated in an oil body that floats at the water table to the east of the point of discharge total dissolved organic carbon tdoc concentrations in shallow groundwater collected in the oil spray area reach 16 mg l this is nearly an order of magnitude higher than the tdoc concentrations of native groundwater 2 3mg l the additional tdoc derives from the partial degradation of petroleum residues deposited at the land surface and transported to the aquifer by vertical recharge in the vicinity of the oil body tdoc concentrations in groundwater are 48 mg l 58 of the tdoc being composed of non volatile organic c the majority of the volatile doc 63 is a mixture of low molecular weight saturated aromatic and alicyclic hydrocarbons derived from the oil downgradient from the oil body along the direction of groundwater flow concentrations of all measured constituents of the tdoc pool decrease concentrations begin to decline most rapidly however in the zone where dissolved o 2 concentrations begin to increase 50m downgradient from the leading edge of the oil within the anoxic zone near the oil body removal rates of isometric monoaromatic hydrocarbons vary widely this indicates that the removal processes are mediated mainly by microbiological activity molecular and spectroscopic characterization of the tdoc and its spatial and temporal variation provide evidence of the importance of biogeochemical processes in attenuating petroleum contaminants in this perturbed subsurface environment

estimating 14c groundwater ages in a methanogenic aquifer this paper addresses the problem of 14c age dating of groundwaters in a confined regional aquifer affected by methanogenesis increasing ch4 concentrations along the groundwater flow system and 13c and 14c isotopic data for dissolved inorganic carbon dissolved organic carbon and ch4 clearly show the effect of methanogenesis on groundwater chemistry inverse reaction path modeling using netpath indicates the predominant geochemical reactions controlling the chemical evolution of groundwater in the aquifer are incongruent dissolution of dolomite ion exchange methanogenesis and oxidation of sedimentary organic matter modeling of groundwater 14c ages using netpath indicates that a significant part of groundwater in the alliston aquifer is less than 13 000 years old however older groundwater in the range of 15 000 23 000 years is also present in the aquifer this paper demonstrates that 14c ages calculated using netpath incorporating the effects of methanogenesis on the carbon pools provide reasonable groundwater ages that were not possible by other isotopic methods

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

carbonate stable and clumped isotopic evidence for late eocene moderate to high elevation of the east central tibetan plateau and its geodynamic implications

wave rafting and the equilibrium pancake ice cover thickness 1 pancake ice the circular floes formed during ice growth in a wave field forms in many polar and subpolar seas vertical thin sections of cores taken from the ice cover in these regions show distinct layering structure these observations suggest wave rafting could play a significant role in defining the ice cover thickness much more so than thermodynamic growth although wave rafting is intuitively apparent no previous study relating the resulting ice cover to wave characteristics has been conducted in this study we utilize both laboratory experiments and numerical simulations to determine the rafting process we propose a theory that predicts a final equilibrium thickness provided that the incoming wave is kept constant the equilibrium thickness from the theory is proportional to the square of the wave amplitude and the square of the floe diameter and is inversely proportional to the cube of the wavelength this theory relates the final ice cover thickness to the wave characteristics and the size and surface properties of the pancake ice floes this theory also provides a way to calculate the speed with which the boundary between the single layer pancake ice floes and the equilibrium rafted ice cover propagates we conduct laboratory experiments with plastic model pancake ice to create rafting we perform computer simulations with a three dimensional discrete element model that simulates the movement of disc shaped floes in the wave field we compare the theoretical result with the laboratory experiments and a numerically simulated rafting process both the laboratory and the computer simulation results compare favorably with the theory

feldspars as a source of nutrients for microorganisms phosphorus and nitrogen are essential macronutrients necessary for the survival of virtually all living organisms in groundwater systems these nutrients can be quite scarce and can represent limiting elements for growth of subsurface microorganisms in this study we examined silicate sources of these elements by characterizing the colonization and weathering of feldspars in situ using field microcosms we found that in carbon rich anoxic groundwaters where p and n are scarce feldspars that contain inclusions of p minerals such as apatite are preferentially colonized over similar feldspars without p a microcline from s dakota which contains 0 24 p 2 o 5 but 1 mu mol g nh 4 super was heavily colonized and deeply weathered a similar microcline from ontario which has no detectable p or nh 4 super was barren of attached organisms and completely unweathered after one year anorthoclase 0 28 p 2 o 5 approximately 1 mu mol g nh 4 super was very heavily colonized and weathered whereas plagioclase specimens 0 01 p 1 mu mmol g nh 4 super were uncolonized and unweathered in addition the observed weathering rates are faster than expected based on laboratory rates we propose that this system is particularly sensitive to the availability of p and the native subsurface microorganisms have developed biochemical strategies to aggressively scavenge p or some other essential nutrient such as fe super 3 from resistant feldspars the result of this interaction is that only minerals containing p will be significantly colonized and these feldspars will be preferentially destroyed as the subsurface microbial community scavenges a limiting nutrient

self reversed magnetization held by martite in basalt flows from the 1 1 billion year old keweenawan rift canada in some basalt flows of the 1 1 billion year old keweenawan rift exposed at mamainse point ontario there is a magnetic phase that holds a remanence antiparallel to the populations of magnetite and hematite that are typical of flows in the succession the paleomagnetic and geological context of this component demonstrates that it is not a chemicaloverprint whoseremanence is attributableto a subsequently reversed geomagnetic field but that the component is a self reversal of the primary magnetization here we use rock magnetic experiments and mossbauer spectroscopy to show that this phase occurs in the most oxidized flowsandisheldbya fine grainedpopulationofhematitethatacquiredits self reversedremanencethrough interactions with a phase of lower blocking temperature we propose that this self reversed hematite is a manifestation of the self reversal phenomena that has been observed to occur experimentally during the transformation of maghemite to hematite and thathas been attributed to negative exchange coupling across the crystal lattices we suggest that hematite formed in association with iron silicates in the basalt flows carries a remanence reflective of the field in which it formed but that martite hematite pseudomorphed after magnetite which formed through the progressive oxidation of magnetite to maghemite with subsequent inversion to hematite carries the self reversed remanence this study marks the second time that a naturally occurring self reversed magnetization has been attributed to this mechanism and marks the oldestreportedinstanceof anytypeof self reversedremanence themartitethatformsthrough thisprocess has the ability to retain a record of the negative exchange coupling from the time of its formation for hundreds of millions of years

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

observations of hydrography and downflow of brine enriched shelf water in the storfjorden polynya svalbard 1 observations of hydrography and currents in the active storfjorden polynya during fieldwork in april 2004 and 2006 are presented the polynya adds salt from its efficient ice production usually increasing the density 0 15 kg m 3 downflow of dense water from the coastal polynya to the deeper basin enclosed by the storfjorden sill was captured in both years april 2006 had a period of strong heat loss and intense frazil ice growth in the polynya this created downflow of brine enriched shelf water bsw with a maximum salinity of 35 25 i e an increased density 0 4 kg m 3 above that of the source water in april 2004 the salinity remained lower than bsw s 34 8 reflecting the fresh source water in fall 2003 due to the heavy ice conditions in the western barents sea that year a portion 0 05 sv of such source water probably enters storfjorden through freemansundet where the mean current transports less saline and warmer water from the northwestern barents sea freemansundet has additionally a strong tidal current peaking at 53 cm s 1 dominated by the m2 component the tidal wave propagates through the narrow sound producing shallow water components and a locally well mixed water column the estimated ice production in winter 2004 twice as large as that of winter 2006 could not overcome this less saline well mixed source water bsw downflow within storfjorden was both observed and modeled to occur in areas with steep bathymetry our observations show that high resolution hydrographical data spacing less than 0 5 km are necessary to resolve such downflow consistent with the observed polynya water salinity current data at the sill showed weaker overflow in 2004 than in 2006 overflow of bsw was observed on the eastern part of the storfjorden sill in april 2006 indicating that overflow occurs across the entire sill width during the freezing period current temperature and salinity data from the overflow indicate a time lag of 12 18 days between the bsw production and the sill this downflow overflow link is confirmed by a numerical experiment and analytical scaling making results applicable to other polynyas

effect of water washing on c15 hydrocarbon fraction of crude oils from northwest palawan philippines recognition and subsequent correlation of biodegraded and or water washed oils with their unaltered counterparts has been a long recognized problem in petroleum geochemistry because water washing and biodegradation can occur concurrently it is difficult to delineate the individual effects of these two oil altering processes especially on the c15 hydrocarbon fraction both processes can cause an oil to become enriched in sulfur and to have a lower api gravity owing to loss of the more volatile components thus the altered oil may appear to be a high sulfur crude of low maturity altered and unaltered oil fractions extracted from cores of a water washed carbonate reservoir offshore northwest palawan were studied to observe the effect of alteration on correla ion parameters water washing resulted in the following changes 1 depletion of 13c in the c15 branched cyclic alkane fraction whereas virtually no change occurred in isotope composition of the aromatic fraction 2 selective loss of dibenzothiophenes followed by loss of aromatic hydrocarbons and 3 virtually no change in steranes or tricyclic and pentacyclic terpanes with the exception of enhancement of 17 agr h norhopane and decrease of 18 agr h trisnorhopane in situations of severe water washing mild biodegradation also occurred as indicated by the loss of n alkanes and possible selective loss of n alkanes having less than 25 carbon atoms relative to branched alkanes cycloalkanes and aromatic components because cycloalkanes and aromatic hydrocarbons are not generally preferentially utilized by bacteria as long as n alkanes are present the changes observed in these two fractions most likely result from water washing because of the potential for extreme compositional changes in the n alkane and aromatic fractions the most useful correlation parameters between the altered and unaltered oils are sterane and terpane distributions stable carbon isotope ratios are also useful however more studies of oils in which water washing is known to have occurred need to be made to explain the general response or various responses of the isotopic composition of oils to water washing

crude oil in a shallow sand and gravel aquifer iii biogeochemical reactions and mass balance modeling in anoxic groundwater abstract crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near bemidji minnesota the degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body the concentrations of fe2 mn2 and ch4 eh measurements and the 13c ratios of the total inorganic c indicate that the plume became more reducing ver a 5 a period however the size of the contaminant plume remained stable during this time field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment in anaerobic microcosm experiments conducted under field conditions almost complete degradation 98 was observed for benzene in 125 d and for toluene in 45 d concentrations of aqueous fe2 and mn2 increased in these experiments indicating that the primary reactions were hydrocarbon degradation coupled with fe and mn reduction mass transfer calculations on a 40 m flowpath in the anoxic zone downgradient from the oil body indicated that the primary reactions in the anoxic zone are oxidation of organic compounds precipitation of siderite and a ferroan calcite dissolution of iron oxide and outgassing of ch4 and co2 the major difference in the two models presented is the ratio of co2 and ch4 that outgasses both models indicate quantitatively that large amounts of fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume

grease ice in basin scale sea ice ocean models the first stage of sea ice formation is often grease ice a mixture of sea water and frazil ice crystals over time grease ice typically congeals first to pancake ice floes and then to a solid sea ice cover grease ice is commonly not explicitly simulated in basin scale sea ice ocean models though it affects oceanic heat loss and ice growth and is expected to play a greater role in a more seasonally ice covered arctic ocean we present an approach to simulate the grease ice layer with as basic properties the surface being at the freezing point a frazil ice volume fraction of 25 and a negligible change in the surface heat flux compared to open water the latter governs grease ice production and a gradual transition to solid sea ice follows with 50 of the grease ice solidifying within 24 hours the new parameterization delays lead closing by solid ice formation enhances oceanic heat loss in fall and winter and produces a grease ice layer that is variable in space and time results indicate a 10 30 increase in mean winter arctic ocean heat loss compared to a standard simulation with instant lead closing leading to significantly enhanced ice growth

an attempt to understand the behavior of dissolved organic carbon in coastal aquifers of pondicherry region south india groundwaters of the coastal region are significant and serve as a fragile ecosystem in the sedimentary terrain the pondicherry region is characterized by different geological formations of distinct geological epochs cretaceous tertiary and quaternary ninety three samples were collected from specific aquifers with respect to spatial distribution alluvium 31 upper cuddalore 13 lower cuddalore 13 other tertiary 7 cretaceous 24 and mixed multiple completion aquifer 5 the collected samples were analyzed for major ions ca2 mg2 na k hco3 cl po42 so42 f and doc stables isotopes of 18o d and 13c were also analyzed along with heavy metals like al ba fe sr cd and zn the 18o ranges between 6 85 and 2 15 and d ranges between 43 94 and 19 41 the distribution of these environmental isotopes in groundwater of this layered aquifer sequence was also attempted a comparison of the isotopic data with the rainfall local meteoric water line with a equation of d 7 398 18o 5 067 indian meteoric water line and global meteoric water line was performed the 13c values for groundwater ranges from 5 3 to 18 1 the result indicates that the groundwater in the study area is mainly meteoric in origin and few samples show evidence of evaporation the dissolved organic carbon doc is a very important component in biogeochemical cycling of elements characterized by high susceptibility to leaching the range of the doc in the study area is 0 16 mg l factor analysis was applied to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry the alluvium aquifers show a complex hydrogeochemistry than the older aquifers the major factor influencing the hydrogeochemistry of the region is rock water interaction and anthropogenic processes hence metal mobility of the groundwater shows the correlation of metal bonding and doc the relation between the doc and heavy metal concentration in the aquifers was also identified

secular variation in permian red beds from dome de barrot se france the do me de barrot red beds se france were deposited during the permo carboniferous reversed superchron pcrs near the palaeo equator the natural remanent magnetisation nrm resides in detrital hematite which is very resistant against thermal demagnetisation microprobe analyses reveal the presence of titanium in hematite grains indicating the volcanic and thus detrital origin therefore the nrm is a detrital remanent magnetisation and nrm variations reflect changes in the geomagnetic field tuning of the proxy parameter magnetic susceptibility to periods of the earth orbit during permian times provides relative time control the inferred average sedimentation rate is 11 8 cm 1000 yr 31 the variation in nrm directions is similar to present day secular variation sv this suggests that sv was not suppressed during at least part of the pcrs fl 2000 elsevier science b v all rights reserved

paleomagnetic constraints on the mesozoic cenozoic paleolatitudinal and rotational history of indochina and south china review and updated kinematic reconstruction abstract paleomagnetic data have long been used to hypothesize that the cenozoic extrusion of the indochina block along the left lateral ailao shan red river fault as a result of the india asia collision may have been associated with a major southward paleolatitude shift of as much as 10 15 and a vertical axis rotation of as much as 25 40 however although numerous paleomagnetic studies have been conducted in the southeast margin of the tibetan plateau and in the indochina region during the last few decades the detailed rotation as well as the latitudinal displacement of the indochina block remain controversial because of apparently contradicting paleomagnetic results geological constraints also yield contrasting estimates on the amount of displacement along different segment of the ailao shan red river fault 700 200 km in the northwest but only 250 km in the southeast in this paper the available paleomagnetic data from the southeast margin of the tibetan plateau and indochina as well as the south china block from jurassic and younger rocks are compiled and critically reviewed using the new paleomagnetic toolkit on paleomagnetism org our results show that 1 the south china block has declinations that reveal no significant rotations relative to eurasia since latest jurassic inclinations are consistently shallower than expected which is likely the result of inclination shallowing in sedimentary rocks 2 there is no paleomagnetically resolvable southward motion of the indochina block with respect to eurasia based on the paleomagnetic data paleomagnetic inclinations are in fact lower than expected probably due to inclination shallowing in sediments 3 paleomagnetic declinations reveal large more or less coherently rotating blocks in the northern indochina domain and the se tibetan margin that rotated up to 70 clockwise much more than the 10 15 rotation of the stable se part of the indochina block these blocks are bounded by fold thrust belts and strike slip faults which we interpret to have accommodated these block rotations during the cenozoic we designed a new tool on the online open access portal paleomagnetism org that allows testing whether euler rotations in a kinematic reconstruction fulfill paleomagnetic data using this tool we built a first order kinematic reconstruction of rotational deformation of northwest indochina in cenozoic we show that the northwestern part of indochina extruded 350 km more along the ailao shan red river fault than the southeastern part accommodated by internal northwest indochina rotation and deformation estimates of 250 km of extrusion of the southeastern part of the indochina then predicts 600 km of left lateral motion along the northwestern part of the ailao shan red river fault which reconciles the small and large estimates that prevail in the literature of extrusion of indochina from the tibetan realm during the cenozoic india asia collision

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed