phanerozoic evolution of atmospheric methane a simple geochemical box model for the global cycle of methane ch4 has been developed and applied to reconstruct the evolution of atmospheric ch4 over the entire phanerozoic according to the model the partial pressure of atmospheric ch4 pch4 increased up to approximately 10 ppmv during the carboniferous coal swamp era this implies a maximum radiative forcing of about 3 5 w m 2 via ch4 through its radiative forcing ch4 heated the average global surface temperature by up to 1 c the elevated pch4 values during the permian carboniferous cold period may have moderated the temperature decline caused by the coeval drawdown of atmospheric co2 additional runs with a global carbon model indicate that the heating induced by elevated pch4 favored the drawdown of atmospheric pco2 via enhanced rates of silicate weathering simulations with a state of the art climate model reveal that the effects of atmospheric ch4 on average global surface temperature also depend on the partial pressures of co2 the ch4 climate effect is amplified by high background levels of atmospheric co2 such that a coeval increase in the partial pressure of both greenhouse gases has a much stronger climate effect than previously anticipated

carbon geochemistry of cold seeps methane fluxes and transformation in sediments from kazan mud volcano eastern mediterranean sea abstract despite growing concerns about potential enhancement of global warming and slope failure by methane produced by gas hydrate dissociation much uncertainty surrounds estimates of gas hydrate reservoir sizes as well as methane fluxes and oxidation rates at the sea floor for cold seep sediments of the eastern mediterranean sea depth dependent methane concentrations and rates of anaerobic oxidation of methane aom are constrained by modeling the measured pore water sulfate profile the calculated dissolved methane distribution and flux are sensitive to the advective flow velocity which is estimated from the depth distributions of conservative pore water constituents na b near complete anaerobic oxidation of the upward methane flux of 6 0 mol m 2 yr 1 is supported by the depth distributions of indicative biomarkers and the carbon isotopic compositions of organic matter and dissolved inorganic carbon pore water and solid phase data are consistent with a narrow depth interval of aom 14 18 cm below the sediment water interface based on an isotopic mass balance the biomass of the microbial population carrying out oxidation of methane coupled to sulfate reduction at the given methane flux represents 20 of the total organic carbon which is a significant pool of in situ formed organic matter model results indicate that the asymptotic methane concentration is reached a few meters below the sediment surface the predicted asymptotic concentration is close to the in situ saturation value with respect to gas hydrate suggesting that the rate of shallow gas hydrate formation is controlled by the ascending methane flux the proposed model approach can be used to predict the formation of gas hydrate and to quantify methane fluxes plus transformation rates in surface sediments where fluid advection is an important transport mechanism

intermediate sulfur oxidation state compounds in the euxinic surface sediments of the dvurechenskii mud volcano black sea abstract the deep black sea is known to be depleted in electron acceptors for sulfide oxidation this study on depth distributions of sulfur species s ii s 0 s n 2 s 2 o 3 2 so 3 2 so 4 2 in the dvurechenskii mud volcano a cold seep situated in the permanently anoxic eastern black sea basin sorokin trough 2060 m water depth showed remarkable concentrations of sulfide oxidation products sulfite concentrations of up to 11 mol l 1 thiosulfate concentrations of up to 22 mol l 1 zero valent sulfur concentrations of up to 150 mol l 1 and up to five polysulfide species were measured in the upper 20 cm of the sediment electron acceptors found to be available in the dvurechenskii mud volcano dmv for the oxidation of hydrogen sulfide to sulfide oxidation intermediates are iron minerals and probably also reactive manganese phases up to 60 mol g 1 of reactive iron minerals and up to 170 mol l 1 dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow thus the source for the oxidative power in the dmv are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments leading to the formation of various sulfur intermediates in comparably high concentrations another possible source of sulfide oxidation intermediates in dmv sediments could be the formation of zero valent sulfur by sulfate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero valent sulfur sulfide oxidation intermediates which are produced by these processes do not reach thermodynamic equilibrium with rhombic sulfur especially close to the active center of the dmv due to a short equilibration time thus mud volcano sediments such as in the dmv can provide oxidizing niches even in a highly reduced environment like the abyssal part of the black sea

some new aspects of the transient ionization layer of comet siding spring origin in the martian upper atmosphere the close encounter of comet siding spring with mars resulted in the formation of a dense transient ionization layer in the martian upper atmosphere at altitudes between 80 and 120 km instruments on three spacecraft orbiting mars detected the presence of this layer as reported in previous publications in this study we reanalyzed the ionograms of the mars advanced radar for subsurface and ionospheric sounding marsis instrument on mars express to get further insight about the recurrence of the layer for this purpose data from three periapsis passes of marsis that took place 5 h 12 h and 19 h after peak dust deposition are used we found that the transient ionization layer was sustained at least for 19 h on the nightside and 12 h on the dayside while the peak density of the layer on the nightside gradually decreases from orbit to orbit it does not change much on the dayside some ionograms in all three orbits show two transient ionization layers that are separated by 60 km in apparent altitude these double layers occur preferentially in regions of strong vertical magnetic fields the bottom layer of the double structure is probably an oblique echo due to reflections from ionization bulges formed in regions of vertical magnetic fields at altitudes of the transient ionization layer horizontal bifurcation of the original layer is considered as another plausible mechanism for explaining the double layer structure

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

rapid soil accumulation in a frozen landscape polygonal patterned ground is a dominant geomorphic feature in the mcmurdo dry valleys antarctica in central beacon valley polygons are considered to be ancient expressions of stagnant surface processes and are thought to be stable for millions of years however the actual rate at which these polygons form and alter is not known we describe a detailed cross section of a polygon make several depth profiles of meteoric 10be along this cross section and use optically stimulated luminescence to date a few key samples at the center of this polygon while confirming conclusions of previous studies that the polygon shoulders are stable on a 100 k y time scale and experience little vertical sediment mixing our results also give clear evidence of eolian transport to the polygon center leading to a sediment accumulation rate of 3 cm k y 1 over the past 15 k y moreover the data suggest that the accumulated material is locally derived and hence surface erosion of the polygon shoulders must exist that cannot be recorded by meteoric 10be we conclude that polygon modification and soil accumulation under the apparent frozen conditions of beacon valley is an active and ongoing process

seismic and gpr surveys of mullins glacier mcmurdo dry valleys antarctica ice thickness internal structure and implications for surface ridge formation we present results from ground penetrating radar gpr and seismic surveys for the mullins valley debris covered glacier mullins glacier antarctica that yield local ice thickness estimates of 80 110 m in upper mullins valley and 150 m in upper beacon valley englacial debris in upper mullins glacier occurs as scattered cobbles and as discrete layers one extensive englacial debris layer which appears as a coherent reflector dipping 40 458 up valley intersects the ground surface within an 8m high ice cored ridge the largest of several ridges that mark the glacier surface field excavations reveal that this englacial interface consists of multiple debris bands that can be directly correlated with ridge microtopography englacial debris layers most probably originate as concentrated rockfall in ice accumulation zones and or as surface lags that form as dirty ice sublimes during periods of negative mass balance a similar pattern of surface ridges on friedman glacier 2 5 km west of mullins glacier suggests regional environmental changes are involved in ridge formation these observations carry implications for evaluating debris entrainment and surface ridge formation mechanisms in cold based debris covered glaciers and provide a glaciological framework for evaluating and interpreting paleoclimate records from mullins glacier

global methane emission through mud volcanoes and its past and present impact on the earth s climate mud volcanism is an abundant global phenomenon whereby fluid rich low density sediments extrude both on land and offshore methane which generally exceeds 90 vol of the gas phase is emitted at high rates during and after emplacement of the mud domes and is known for its high global warming potential gwp this comprehensive estimate of the annual contribution of mud volcano degassing assesses the significance of mud volcanism for the accumulation of greenhouse gases in the atmosphere a first order estimate for the earlier pre anthropogenic volume of methane released through mud volcanoes further supports their profound effect on the earth s climate since at least the paleozoic 570 ma

in situ benthic fluxes from an intermittently active mud volcano at the costa rica convergent margin along the erosive convergent margin off costa rica a large number of mound shaped structures exist built by mud diapirism or mud volcanism one of these mound 12 an intermittently active mud volcano currently emits large amounts of aqueous dissolved species and water chemosynthetic vent communities authigenic carbonates and methane plumes in the water column are manifestations of that activity benthic flux measurements were obtained by a video guided benthic chamber lander bcl deployed at a vent site located in the most active part of mound 12 the lander was equipped with 4 independent chambers covering adjacent areas of the seafloor benthic fluxes were recorded by repeated sampling of the enclosed bottom waters while the underlying surface sediments were recovered with the lander after a deployment time of one day one of the chambers was placed directly in the centre of an active vent marked by the occurrence of a bacterial mat while the other chambers were located at the fringe of the same vent system at a lateral distance of only 40 cm a transport reaction model was developed and applied to describe the concentration profiles in the pore water of the recovered surface sediments and the temporal evolution of the enclosed bottom water repeated model runs revealed that the best fit to the pore water and benthic chamber data is obtained with a flow velocity of 10 cm yr 1 at the centre of the vent the flux rates to the bottom water are strongly modified by the benthic turnover benthic filter the methane flux from below at the bacterial mat site is as high as 1032 mol cm 2 yr 1 out of which 588 mol cm 2 yr 1 is oxidised in the surface sediments by microbial consortia using sulphate as terminal electron acceptor and 440 mol cm 2 yr 1 are seeping into the overlaying bottom water sulphide is transported to the surface by ascending fluids 238 mol cm 2 yr 1 and is formed within the surface sediment by the anaerobic oxidation of methane aom 588 mol cm 2 yr 1 however sulphide is not released into the bottom water but completely oxidized by oxygen and nitrate at the sediment water interface the oxygen and nitrate fluxes into the sediment are high 781 and 700 mol cm 2 yr 1 respectively and are mainly driven by the microbial oxidation of sulphide benthic fluxes were much lower in the other chambers placed in the fringe of the vent system thus methane and oxygen fluxes of only 28 and 89 mol cm 2 yr 1 respectively were recorded in one of these chambers our study shows that the aerobic oxidation of methane is much less efficient than the anaerobic oxidation of methane so that methane which is not oxidized within the sediment by aom is almost completely released into the bottom water hence anaerobic rather than aerobic methane oxidation plays the major role in the regulation of benthic methane fluxes moreover we demonstrate that methane and oxygen fluxes at cold vent sites may vary up to 3 orders of magnitude over a lateral distance of only 40 cm indicating an extreme focussing of fluid flow and methane release at the seafloor

formation of patterned ground and sublimation till over miocene glacier ice in beacon valley southern victoria land antarctica a thin glacial diamicton informally termed granite drift occupies the floor of central beacon valley in southern victoria land antarctica this drift is 40 ar 39 ar analyses of presumed in situ ash fall deposits that occur within granite drift at odds with the great age of this ice are high centered polygons that cut granite drift if polygon development has reworked and retransported ash fall deposits then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice our results show that the surface of granite drift is stable at polygon centers and that enclosed ash fall deposits can be used to define the age of underlying glacier ice in our model for patterned ground development active regions lie only above polygon troughs where enhanced sublimation of underlying ice outlines high centered polygons the rate of sublimation is influenced by the development of porous gravel and cobble lag deposits that form above thermal contraction cracks in the underlying ice a negative feedback associated with the development of secondary ice lenses at the base of polygon troughs prevents runaway ice loss secondary ice lenses contrast markedly with glacial ice by lying on a d versus 18 o slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess the latter indicates that secondary ice lenses likely formed by melting downward percolation and subsequent refreezing of snow trapped preferentially in deep polygon troughs the internal stratigraphy of granite drift is related to the formation of surface polygons and surrounding troughs the drift is composed of two facies a nonweathered matrix supported diamicton that contains 25 striated clasts in the 16 mm fraction and a weathered clast supported diamicton with varnished and wind faceted gravels and cobbles the weathered facies is a coarse grained lag of granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies the concentration of cosmogenic 3 he in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice these profile patterns and the 3 he surface exposure ages of 1 18 0 08 ma and 0 18 0 01 ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr although granite drift is stable at polygon centers low frequency slump events occur at the margin of active polygons slumping together with weathering of surface clasts creates the large range of cosmogenic nuclide surface exposure ages observed for granite drift maximum rates of sublimation near active thermal contraction cracks calculated by using the two 3 he depth profiles range from 5 m m y to 90 m m y sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates nevertheless these rates are orders of magnitude lower than those computed on theoretical grounds during eruptions of the nearby mcmurdo group volcanic centers ash fall debris collects at the surface of granite drift either in open thermal contraction cracks or in deep troughs that lie above contraction cracks these deposits subsequently lower passively as the underlying glacier ice sublimes the fact that some regions of granite drift have escaped modification by patterned ground for at least 8 1 ma indicates long term geomorphic stability of individual polygons once established polygon toughs likely persist for as long as 10 5 10 6 yr our model of patterned ground formation which applies to the hyperarid cold desert polar climate of antarctica may also apply to similar sized polygons on mars that occur over buried ice in utopia planitia

fate of sediment during plate convergence at the mediterranean ridge accretionary complex volume balance of mud extrusion versus subduction and or accretion drilling results from two mud volcanoes on the mediterranean ridge accretionary complex as well as extensive geophysical surveys have provided new insights about the geometry of these domes at depth mud extrusion is related to buoyancy and plate convergence between africa and eurasia that caused back thrust faulting of accreted strata containing overpressured mud at depth the domes mainly consist of mud breccia formed of as much as 65 polymictic clasts embedded in a clayey matrix of presumed late miocene age volumetric estimates of extruded mud in a well studied area around the olimpi mud volcano field were balanced against sediment input at the deformation front the results demonstrate that only a small fraction of rock mass having entered the subduction zone since the messinian is needed to compensate for the mud expelled in the study area most of the sediment 95 or more is either subducted or incorporated into the accretionary prism the volume of gas expelled with the liquefied overpressured mud was estimated to range between 1 68 10 6 and 2 85 10 7 m 3 yr

depositional processes beneath coastal multi year sea ice the extent of multi year sea ice impacts climate processes worldwide such as ocean atmosphere carbon dioxide exchange and deep ocean current formation reconstructing these processes in the past and assessing the distribution of ecologically and climatically significant features such as polynas requires recognition of sediments deposited under multi year sea ice but little is known about their characteristics textural analysis of subaerial and sea floor sediment in explorers cove mcmurdo sound at the mouth of taylor valley antarctica augmented with observations of sedimentary structures and faunal components elucidates how sediment is transported to the sea floor and allows characterization of the deposits comparison of grain size characteristics of subaerial moraine delta and sea ice surface sediment and sea floor sediment from short cores taken at depths of 7 to 25 m indicates that the likely source of the moderately to poorly sorted sea floor sand is deltaic sediment small glacial meltwater streams have built deltas since taylor valley became ice free ca 7000 years ago windblown sediment accumulating on the multi year sea ice close to the coast typically is coarser grained than sediment on the sea floor this suggests that the transport of sediment through the ice to the sea floor is not the predominant mode of sediment transfer however supra sea ice sediment does move to the sea floor through local fractures the rate of sedimentation under multi year sea ice is low because of limited stream flow and biogenic sedimentation the ice cover inhibits primary productivity and dampens waves precluding physical re suspension the upper centimetres of sea floor sediment are churned by epifaunal scallops and brittle stars that leave no telltale biogenic structures and whose calcite ossicles and shells may be poorly preserved the resulting deposits under multi year sea ice are poorly sorted massive sand that provides little evidence of the bioturbators that have masked the indicators of the original physical depositional processes

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

stabilists strike again on page 412 of this issue1 sugden and colleagues announce that glacier ice in the dry valleys of east antarctica seems to have survived for over 8 million years under a thin layer of sediment this they argue testifies that stable polar conditions have persisted for at least that time

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area

degradation of glacial deposits quantified with cosmogenic nuclides quartermain mountains antarctica many glacial deposits in the quartermain mountains antarctica present two apparent contradictions regarding the degradation of unconsolidated deposits the glacial deposits are up to millions of years old yet they have maintained their meter scale morphology despite the fact that bedrock and regolith erosion rates in the quartermain mountains have been measured at 0 1 4 0 m ma 1 additionally ground ice persists in some miocene aged soils in the quartermain mountains even though modeled and measured sublimation rates of ice in antarctic soils suggest that without any recharge mechanisms ground ice should sublimate in the upper few meters of soil on the order of 103 to 105 years this paper presents results from using the concentration of cosmogenic nuclides beryllium 10 10be and aluminum 26 26al in bulk sediment samples from depth profiles of three glacial deposits in the quartermain mountains the measured nuclide concentrations are lower than expected for the known ages of the deposits erosion alone does not always explain these concentrations and deflation of the tills by the sublimation of ice coupled with erosion of the overlying till can explain some of the nuclide concentration profiles the degradation rates that best match the data range 0 7 12 m ma 1 for sublimation of ice with initial debris concentrations ranging 12 45 and erosion of the overlying till at rates of 0 4 1 2 m ma 1 overturning of the tills by cryoturbation vertical mixing or soil creep is not indicated by the cosmogenic nuclide profiles and degradation appears to be limited to within a few centimeters of the surface erosion of these tills without vertical mixing may partially explain how some glacial deposits in the quartermain mountains maintain their morphology and contain ground ice close to the surface for millions of years copyright 2010 john wiley sons ltd

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

fluid expulsion from the dvurechenskii mud volcano black sea part i fluid sources and relevance to li b sr i and dissolved inorganic nitrogen cycles significant sediment ocean chemical fluxes are produced by the expulsion of sedimentary fluids at continental margins although such fluxes could play a role in global geochemical cycles few quantitative estimates of their global or even regional significance exist we carried out a pore water geochemical study of fluids expelled from the dvurechenskii mud volcano dmv in the black sea with the aim of understanding the role played by mud volcanoes in black sea geochemical cycles the dmv is presently expelling highly saline fluids particularly enriched in geochemically important species such as li 1 5 mm b 2 17 mm ba2 0 57 mm sr2 0 79 mm i 0 4 mm and dissolved inorganic nitrogen din 22 mm a combination of geochemical indicators shows that this geochemical signature was acquired via organic matter and silicate alteration processes in the subsurface down to 3 km depth and near surface gas hydrate formation we used a simple transport model to estimate the benthic fluxes of these solutes at the dmv our results show that the dmv is expelling fluids at a rather low seepage rate 8 25 cm year 1 resulting in a total water flux of 9 4 10 5 km3 year 1 this gentle regime of fluid expulsion results in li b sr2 i and din fluxes between 3 8 104 and 2 1 106 mol year 1 surface biogeochemical processes affect the benthic fluxes of ba2 such that the deep ba2 flux is completely consumed through the precipitation of authigenic barite baso4 in surface sediments the black sea i cycle is likely to be affected by mud volcanism if the 50 known black sea mud volcanoes share the rather sluggish activity of the dmv mud volcano fluxes of li b sr and din instead are too small to affect black sea geochemical cycles on a global scale mud volcanism could play a role in the marine cycles of li b sr i and din if current estimates of mud volcano abundance are correct

estimates of methane output from mud extrusions at the erosive convergent margin off costa rica four mud extrusions were investigated along the erosive subduction zone off costa rica active fluid seepage from these structures is indicated by chemosynthetic communities authigenic carbonates and methane plumes in the water column we estimate the methane output from the individual mud extrusions using two independent approaches the first is based on the amount of ch4 that becomes anaerobically oxidized in the sediment beneath areas covered by chemosynthetic communities which ranges from 104 to 105 mol yr 1 the remaining portion of ch4 which is released into the ocean has been estimated to be 102 104 mol yr 1 per mud extrusion the second approach estimates the amount of ch4 discharging into the water column based on measurements of the near bottom methane distribution and current velocities this approach yields estimates between 104 105 mol yr 1 the discrepancy of the amount of ch4 emitted into the bottom water derived from the two approaches hints to methane seepage that cannot be accounted for by faunal growth e g focused fluid emission through channels in sediments and fractures in carbonates extrapolated over the 48 mud extrusions discovered off costa rica we estimate a ch4 output of 20 106 mol yr 1 from mud extrusions along this 350 km long section of the continental margin these estimates of methane emissions at an erosional continental margin are considerably lower than those reported from mud extrusion at accretionary and passive margins almost half of the continental margins are described as non accretionary assuming that the moderate emission of methane at the mud extrusions off costa rica are typical for this kind of setting then global estimates of methane emissions from submarine mud extrusions which are based on data of mud extrusions located at accretionary and passive continental margins appear to be significantly too high

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

a quantitative assessment of methane cycling in hikurangi margin sediments new zealand using geophysical imaging and biogeochemical modeling takahe seep located on the opouawe bank hikurangi margin is characterized by a well defined subsurface seismic chimney structure ca 80 500 m2 in area sub seafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure reaction transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas the dissolution of gas up to 3761 mmol m 2 yr 1 dwarfed the rate of methanogenesis within the simulated sediment column 2 6 mmol m 2 yr 1 dissolved methane is mainly consumed by anaerobic oxidation of methane aom at the base of the sulfate reduction zone and trapped by methane hydrate formation below it with maximum rates in the central part of the chimney 946 and 2420 mmol m 2 yr 1 respectively a seep wide methane budget was constrained by combining the biogeochemical model results with geophysical data and led to estimates of aom rates gas hydrate formation and benthic dissolved methane fluxes of 3 68 104 mol yr 1 73 85 104 mol yr 1and 1 19 104 mol yr 1 respectively a much larger flux of methane probably escapes in gaseous form through focused bubble vents the approach of linking geochemical model results with spatial geophysical data put forward here can be applied elsewhere to improve benthic methane turnover rates from limited single spot measurements to larger spatial scales

the oldest ice on earth in beacon valley antarctica new evidence from surface exposure dating abstract beacon valley antarctica contains unique remnants of glacier ice underneath a till layer covering the valley floor to constrain the age and evolution of this important indicator of antarctic paleoclimate we analyzed two dolerite erratics from the till surface and one from within the ice for cosmogenic helium and neon a conservative minimum exposure age of the older surface sample is 2 3 ma but taking into account erosion the true exposure age of this boulder is likely to be considerably higher the buried sample contains more than 20 times less cosmogenic noble gases than the old surface sample although its current shielding would imply only a three times lower production rate this indicates that the ice level has slowly been lowered by sublimation at the rate of a few m ma the high exposure age of the surface sample as well as the very low sublimation rate of the relict ice both support the conclusion that the remnant ice in beacon valley was deposited many million years ago sugden et al nature 376 1995 412 414 and has never been thinner than at present in addition we found that cosmogenic helium and neon are released quantitatively from pyroxene at temperatures of 1000 c respectively

modeling vapor diffusion within cold and dry supraglacial tills of antarctica implications for the preservation of ancient ice abstract we modeled water vapor diffusion within mullins till a relatively dry supraglacial till in southern victoria land antarctica that rests directly on mullins glacier purportedly one of the oldest alpine glaciers in the world like most supraglacial tills in cold desert environments mullins till contains three characteristic facies a weathered facies representing the oxidation of iron bearing minerals and the physical disintegration of surface rocks a sand wedge facies representing the episodic infill of thermal cracks associated with contraction crack polygons and an underlying fresh facies representing the addition of englacial debris sourced from rockfall as overlying ice sublimes using a one dimensional model for fickian vapor diffusion through porous media we show that the rate of subsurface ice sublimation varies by 5 5 beneath till facies and that over timescales of 10 5 years diffusion through porous sand wedges contributes to the development of deep troughs surrounding high centered polygons applying site specific meteorological data collected over a four year period we show that ice loss at the stagnant terminus of mullins glacier is 6 6 10 5 m a 1 a value that although low and assuming an ice thickness of 150 m is consistent with complete ice loss under current environmental forcing in 2 5 ma our sensitivity tests indicate that the vast majority of sublimation occurs during the summer months calculated summertime losses drop to zero with either a reduction in soil and ice surface temperatures of 6 4 c or an increase in atmospheric relative humidity from 44 to 75 both of which could arise from an increase in cloud cover over mullins glacier sublimation responses to meteorological forcing are not uniform across mullins glacier a summer increase in soil temperature of 2 c results in negligible change in ice sublimation at mullins terminus but a 27 increase in ice loss in upper mullins valley the key factor is the thickness of mullins till which is greater near the glacier terminus for till thicknesses exceeding 25 cm non linear variations in soil temperature result in downward vapor fluxes capable of producing thin cm scale lenses of secondary pore that cap the surface of buried glacier ice this downward vapor flow sourced from modern snowfall and or elevated atmospheric relative humidity is one of the key factors that enable long term preservation of buried glacier ice overall our results highlight the subtle relations among changes in till texture till thickness and meteorological forcing on the rate of subsurface ice loss and provide insight into the plausible range of conditions under which multi million year old ice can exist beneath thin supraglacial tills

an enhanced model of the contemporary and long term 200 ka sublimation of the massive subsurface ice in beacon valley antarctica a massive ice body buried under several decimeters of dry regolith in beacon valley antarctica is believed to be more than 1 ma old and perhaps over 8 1 ma however vapor diffusion models suggest that subsurface ice in this region is not stable under current climate conditions to better understand the controls on sublimation rates and stability of this massive ice we have modeled vapor diffusion using 12 years of climate and soil temperature data from 1999 to 2011 including field measurements of episodic snow cover and snowmelt events that have not been represented in previous models of ground ice sublimation the model is then extended to reconstruct the sublimation history over the last 200 ka using paleotemperatures estimated from ice core data from nearby taylor dome and a relationship between atmospheric temperature and humidity derived from our meteorological records the model quantifies the impact of episodic snow events they account for a nearly 30 reduction in the massive ice loss the sublimation rate of ground ice averages 0 11 mm a 1 between 1999 and 2011 in beacon valley parameterized with past environmental conditions and assuming the same regolith thickness the modeled sublimation rate of ground ice in beacon valley averages 0 09 mm a 1 for the last 200 ka comparable to the long term average rate estimated independently from various studies based on cosmogenic isotopes this study provides a realistic estimate of the long term sublimation history and supports the inference that the buried ice in beacon valley is older than 1 ma

solute and isotope geochemistry of subsurface ice melt seeps in taylor valley antarctica the mcmurdo dry valleys of antarctica are a polar desert region with watersheds dominated by glacial melt recent ground exploration reveals unusual surface fl ow seep features not directly supplied by glacial melt much of this seep water is potentially derived from permafrost snow patches refrozen precipitation accumulated in the subsurface buried glacier ice or even groundwater from the deep subsurface flow features that lack obvious glacier melt sources were identifi ed in archived aerial photographs of taylor valley this valley was surveyed for extant and extinct seeps and the locations of geomorphic features in fi active seeps were documented water samples from seeps were analyzed for major ions and stable isotopes of hydrogen and oxygen solute chemistry and isotopic signatures of seeps are distinct from those of nearby streams and glaciers with the seeps having elevated solute concentrations all but one seep had water isotopically heavier than water from nearby glaciers and streams suggesting that seep waters have been substantially modifi ed if they had been derived originally from the same meteoric sources that supply local glaciers and streams the seeps are important because they compose a previously overlooked component of the desert hydrological cycle seep features in the dry valleys are potential terrestrial analogs for the geologically young gullies observed on mars which are thought to be evidence of groundwater seepage and surface runoff

ground surface temperature and humidity ground temperature cycles and the ice table depths in university valley mcmurdo dry valleys of antarctica in the upper mcmurdo dry valleys 90 of the measured ice table depths range from 0 to 80 cm however numerical models predict that the ice table is not in equilibrium with current climate conditions and should be deeper than measured this study explored the effects of boundary conditions air vs ground surface temperature and humidity ground temperature cycles and their diminishing amplitude with depth and advective flows darcy flow and wind pumping on water vapor fluxes in soils and ice table depths using the rego vapor diffusion model we conducted a series of numerical experiments that illustrated different hypothetical scenarios and estimated the water vapor flux and ice table depth using the conditions in university valley a small high elevation valley in situ measurements showed that while the mean annual ground surface temperature approximates that in the air the mean annual ground surface relative humidity 85 ice was significantly higher than in the atmosphere 50 ice when ground surface temperature and humidity were used as boundary conditions along with damping diurnal and annual temperature cycles within the sandy soil rego predicted that measured ice table depths in the valley were in equilibrium with contemporary conditions based on model results a dry soil column can become saturated with ice within centuries overall the results from the new soil data and modeling have implications regarding the factors and boundary conditions that affect the stability of ground ice in cold and hyper arid regions where liquid water is rare

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

dating buried glacier ice using cosmogenic 3he in surface clasts theory and application to mullins glacier antarctica abstract we develop a modeling framework to describe the accumulation of terrestrial cosmogenic 3 he in antarctic debris covered glaciers the framework helps quantify the expected range in cosmogenic nuclide inventories for measured clasts at the surface of supraglacial debris we first delineate the physical factors that impact clast movement within and on top of debris covered glaciers including the effects of 1 ice ablation 2 erosion at the debris surface and 3 stochastic geomorphic processes that impact clast movement within and on top of supraglacial debris we then explicitly calculate the impact of each process in altering the total inventory of cosmogenic nuclides in surface clasts assuming basic elements of ice dynamics and debris entrainment are known the model results provide an estimate for the total accumulation of cosmogenic nuclides as well as the expected range in nuclide inventories for any clast at the surface of debris covered glaciers because the values are quantified the approach can be applied to help evaluate the robustness of existing and future cosmogenic datasets applied to these systems as a test we applied our model framework towards mullins glacier a cold based debris covered alpine glacier in the dry valleys of antarctica our simulated values for cosmogenic nuclide inventories compare well with those previously measured from fifteen surface cobbles along mullins glacier 3 he both in terms of expected ranges and absolute values and suggest that our model framework adequately incorporates most of the complicating factors that impact cosmogenic datasets for cold based debris covered glaciers relating these cosmogenic nuclide inventories to ice ages the results show that ice within mullins glacier increases non linearly ranging from 12 ka to 220 ka in areas of active flow to 1 6 ma in areas of slow moving to stagnant ice

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

a sporadic third layer in the ionosphere of mars the daytime martian ionosphere has been observed as a two layer structure with electron densities that peak at altitudes between about 110 and 130 kilometers the mars express orbiter radio science experiment on the european mars express spacecraft observed in 10 out of 120 electron density profiles a third ionospheric layer at altitude ranges of 65 to 110 kilometers where electron densities on average peaked at 0 8 10 10 per cubic meter such a layer has been predicted to be permanent and continuous its origin has been attributed to ablation of meteors and charge exchange of magnesium and iron our observations imply that this layer is present sporadically and locally

estimating the time of pockmark formation in the sw xisha uplift south china sea using reaction transport modeling carbon cycling and fluid seepage in marine sediments over the late quaternary were investigated at a now extinct pockmark located in a mega pockmark field in the sw xisha uplift nw south china sea measured particulate organic carbon poc content and porewater sulfate so4 2 dissolved inorganic carbon dic concentrations and 34s so4 2 distributions were used to constrain a non steady state reaction transport model and quantify poc mineralization rates as well as estimate the time when fluid flow ceased at the investigated pockmark an increase in poc content and 34s so4 2 and a decrease in sulfate concentrations in the upper ca 2m at the pockmark and a reference core implied an increase in the flux and reactivity of organic matter during the early holocene around 10kyrb p caused by enhanced primary productivity during the strengthened southwestern summer monsoon these features were simulated with the model assuming a holocene increase in poc flux and reactivity subsequently starting from an initial condition reminiscent of a modern active cold seep hydrate ridge hindcast simulations showed that fluid seepage at the pockmark ceased ca 39kyr ago this corresponds to a relative sea level high stand which is believed to be associated with gas hydrate stabilization the non steady state model presented in this contribution can also be used to constrain the time when fluid seepage ceased at other presently extinct cold seeps when suitable sediment and porewater data are available

stability of massive ground ice bodies in university valley mcmurdo dry valleys of antarctica using stable o h isotope as tracers of sublimation in hyper arid regions abstract to date studies of the stability of subsurface ice in the mcmurdo dry valleys of antarctica have been mainly based on climate based vapor diffusion models in university valley 1800 m a small glacier is found at the base of the head of the valley and adjacent to the glacier a buried body of massive ice was uncovered beneath 20 40 cm of loose cryotic sediments and sandstone boulders this study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable o h isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends the results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period the contrasting 18 o profiles and regression slope values between the uppermost 6 cm of the buried massive ice upward convex 18 o profile and s d 18o 5 1 and that below it progressive increase in 18 o and s d 18o 6 4 suggest independent post depositional processes affected the isotope composition of the ice the upward convex 18 o profile in the uppermost 6 cm is consistent with the ice undergoing sublimation using a sublimation and molecular diffusion model and assuming that diffusion occurred through solid ice the sublimation rate needed to fit the measured 18 o profile is 0 2 10 3 mm yr 1 a value that is more similar to net ice removal rates derived from 3 he data from cobbles in beacon valley till 7 0 10 3 mm yr 1 than sublimation rates computed based on current climate 0 1 0 2 mm yr 1 we suggest that the climate based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters particularly the nature and thermo physical properties of the overlying sediments i e temperature humidity pore structure and ice content grain size

methane discharge into the black sea and the global ocean via fluid flow through submarine mud volcanoes during the margasch cruise m52 1 in 2001 with rv meteor we sampled surface sediments from three stations in the crater of the dvurechenskii mud volcano dmv located in the sorokin trough of the black sea and one reference station situated 15 km to the northeast of the dmv we analysed the pore water for sulphide methane alkalinity sulphate and chloride concentrations and determined the concentrations of particulate organic carbon carbonate and sulphur in surface sediments rates of anaerobic oxidation of methane aom were determined using a radiotracer 14ch4 incubation method numerical transport reaction models were applied to derive the velocity of upward fluid flow through the quiescently dewatering dmv to calculate rates of aom in surface sediments and to determine methane fluxes into the overlying water column according to the model aom consumes 79 of the average methane flux from depth 8 9 10 6 mol a 1 such that the resulting dissolved methane emission from the volcano into the overlying bottom water can be determined as 1 9 10 6 mol a 1 if it is assumed that all submarine mud volcanoes smvs in the black sea are at an activity level like the dmv the resulting seepage represents less than 0 1 of the total methane flux into this anoxic marginal sea the new data from the dmv and previously published studies indicate that an average smv emits about 2 0 10 6 mol a 1 into the ocean via quiescent dewatering the global flux of dissolved methane from smvs into the ocean is estimated to fall into the order of 10 10 mol a 1 additional methane fluxes arise during periods of active mud expulsion and gas bubbling occurring episodically at the dmv and other smvs

formation and evolution of an extensive blue ice moraine in central transantarctic mountains antarctica mount achernar moraine is a terrestrial sediment archive that preserves a record of ice sheet dynamics and climate over multiple glacial cycles similar records exist in other blue ice moraines els

anaerobic methane oxidation by bacteria employing 14c methane uncontaminated with 14c carbon monoxide 14c labelled methane biologically prepared by methanobacterium thermoautotrophicum is widely used to determine methane oxidation rates however m thermoautotrophicum synthesizes carbon monoxide as a by product during methanogenesis in this study sulfate reducing bacteria utilizing the acetyl coa carbon monoxide dehydrogenase pathway were able to form 14co2 from 14ch4 containing 14co 14c labelled carbon monoxide was removed from 14ch4 by oxidation over hopcalite to carbon dioxide and fixation in sodium hydroxide solution measurable formation of 14co2 from purified 14c labelled methane by sulfate reducing bacteria was not observed therefore reported anaerobic methane oxidation rates in marine habitats measured with 14ch4 from m thermoautotrophicum are inclined to include carbon monoxide oxidation rates anaerobic oxidation of 14ch4 by sulfate reducing and acetogenic bacteria and methanogenic archaebacteria was tested only methanogenic species produced up to 900 ppm 14co2 from 14ch4 applied this observation and the absence of methane oxidation by sulfate reducing bacteria sustain the hypothesis that methanogenic archaebacteria in a syntrophic community might be responsible for the oxidation of methane in anaerobic habitats

fast growing till over ancient ice in beacon valley antarctica we analyze published cosmogenic 3he depth profiles through the till that covers relict glacier ice in beacon valley antarctica in order to derive rigorous constraints on the till thickness history and on the amount and rate of ice loss by sublimation the till is a residue of debris laden ice that sublimed the 3he profiles show that the lower 80 of the till formed in the past 310 43 k y under sublimation rates averaging 7 m m y 1 meters per million years such rapid recent growth of the till contradicts previous interpretations that it is older than 8 1 ma at an adjacent site where it encloses volcanic ash of this age we question whether the ash provides a valid age constraint for the ice cosmogenic nuclide analysis of the till where the ash was collected for dating should resolve this question

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

soil phosphorus cycling in an antarctic polar desert abstract soil phosphorus distribution and cycling in the mcmurdo dry valleys is poorly understood despite its importance for contemporary antarctic ecosystem processes we present data from sequential chemical extractions of phosphorus pools from dry valley soils and sediments on tills across a gradient of surface exposure ages and across potential weathering gradients in stream channels the geologically old but poorly weathered soils of the dry valleys have large phosphorus pools relative to in situ biological requirements these pools are dominated by unweathered p fractions comprising between 60 and 90 of total soil phosphorus among sites occurring on tills ranging in surface exposure ages of approximately 103 106 yrs variation in total phosphorus concentration and availability are related to differences in the initial p content of these tills ross sea tills contain basalts and kenyte which contribute to higher concentrations of phosphorus relative to soils developing on tills deposited by advances of the taylor glacier at local scales physicochemical gradients contribute to variation in weathering rates altering the distribution of phosphorus among chemical fractions which differ in their potential mobility and availability to microorganisms for example hyporheic stream sediments exhibit evidence of phosphorus weathering from primary minerals and loss relative to upland soils adjacent to stream channels dry valley landscapes glaciers lakes streams soils are hydrologically connected providing a mechanism for phosphorus weathering and mobilization in soils and sediments to contribute to the nutrient budgets of adjacent aquatic ecosystems we suggest that landscape history till composition and contemporary subsurface and stream hydrology are the primary controls over phosphorus cycling in the mcmurdo dry valleys

basin wide estimates of the input of methane from seeps and clathrates to the black sea numerous methane emitting bottom features such as seeps methane clathrate hydrates clathrates and mud volcanoes have been identified recently in the black sea the fluxes of methane from these sources averaged over large spatial scales are unknown here we take advantage of the fact that the black sea is a semi enclosed basin with restricted deep water circulation to establish first order estimates of basin wide fluxes of methane from these sources to the water column and atmosphere first we measured the natural radiocarbon content of methane 14c ch4 dissolved in the water column and emitted from seeps the 14c ch4 results showed that the dominant source of methane to the water column is emitted from seeps and a smaller source is diagenetically produced in relatively modern sediments the 14c ch4 results were then used to partition a basin wide total methane budget this analysis estimated the basin wide flux of methane from seeps and clathrates to the water column to be 3 60 to 4 28 tg yr 1 second a geochemical box model was used to calculate possible distributions of methane inputs from seeps and clathrates as well as provide additional estimates of the basin wide flux of methane from seeps and clathrates to the water column 4 95 to 5 65 tg yr 1 2006 elsevier b v all rights reserved

resurfacing time of terrestrial surfaces by the formation and maturation of polygonal patterned ground 1 to help interpret the polygonal patterned ground on mars we present recent findings about a similar form of patterned ground in a particularly cold and arid region on earth the dry valleys of antarctica in this region distinct arrays of interconnected polygons which we refer to herein simply as patterned ground characterize many surfaces reflecting a subsurface network of interconnected subvertical wedges of sand that grow incrementally as sand progressively fills soil fractures the fractures form initially as thermoelastic stresses arise during periods of rapid cooling of frozen ground and they continue to open and close in response to thermal cycles we describe the initiation and maturation of the patterned ground using data for the growth of sand wedges and for the evolution of crack patterns and microrelief over time scales ranging up to 106 years

regolith transport quantified by braking block mcmurdo dry valleys antarctica abstract the mcmurdo dry valleys of antarctica are today a hyper arid polar desert prior work has identified several in situ volcanic ashes 6 11 myr old resting on the surface regolith that suggests the persistent stability of the regolith surfaces and climate however our field observations of characteristic regolith bulges above and cavities below boulders that are lodged in the hillslope braking blocks contradict the apparent preservation of the regolith surfaces to quantify the regolith mobility we modeled the downslope regolith transport around large boulders in the dry valleys using a finite difference regolith transport model to guide our modeling effort we surveyed the detailed topography around one large boulder in the field model results fit the observed topography well and allow for the calculation of the minimum volume of regolith per unit width of slope that was mobilized 4 m3 1 m width to assess the general applicability of the braking block analysis on random boulders on hillslope we surveyed the topographic characteristics adjacent to 997 boulders on 10 separate hillslopes the bulge cavity development appears to be sensitive to 1 the adjacent obstructions that restrict the free movement of the regolith around the given boulder and 2 the inherent surface roughness even though theoretically boulders of all sizes should have a cavity bulge pair surrounding them the signal to noise ratio prevented us from extracting such measurements reliably on boulders whose diameter was smaller than about 1 m on boulders that sat on bedrock covered by a thin veneer of regolith and on boulders that were part of an actively aggrading talus the limiting minimum topographic diffusivity was found to be 10 6 m2 yr over time periods of millions of years this is enough to rework the surfaces and highlights the intriguing contradiction between the preserved ashes and the observed regolith transport

the thermal structure of the dvurechenskii mud volcano and its implications for gas hydrate stability and eruption dynamics the sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates if ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field the sediment temperature distribution not only limits the occurrence of gas hydrates but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates located in the sorokin trough in the northern black sea the dvurechenskii mud volcano dmv was in the focus of detailed investigations during the m72 2 and m73 3a cruises of the german r v meteor and the rov quest 4000 m in february and march 2007 a large number of in situ sediment temperature measurements were conducted from the rov and with a sensor equipped gravity corer gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer dapc the thermal structure of the dmv suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano accompanied by intermittent mud expulsion at the summit modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the dmv are very close to the stability limits changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation c 2009 elsevier ltd all rights reserved

an ionized layer in the upper atmosphere of mars caused by dust impacts from comet siding spring we report the detection of a dense ionized layer in the upper atmosphere of mars caused by the impact of dust from comet siding spring the observations were made by the ionospheric radar sounder on the mars express spacecraft during two low altitude passes approximately 7 h and 14 h after closest approach of the comet to mars during these passes an unusual transient layer of ionization was detected at altitudes of about 80 to 100 km with peak electron densities of 1 5 to 2 5 105 cm 3 much higher than normally observed in the martian ionosphere from comparisons to previously observed ionization produced by meteors at earth and mars we conclude that the layer was produced by dust from the comet impacting and ionizing the upper atmosphere of mars

production consumption and migration of methane in accretionary prism of southwestern taiwan to systematically quantify the production consumption and migration of methane along a continental margin 210 sediment cores were collected from offshore southwestern taiwan and analyzed for their gas and aqueous geochemistry these data combined with published results were used to calculate the diffusive methane fluxes across different geochemical transitions and to develop scenarios of mass balance to constrain deep microbial and thermogenic methane production rates within the accretionary prism the results showed that methane diffusive fluxes ranged from 2 71 10 3 to 2 78 10 1 and from 1 88 10 1 to 3 97 mmol m 2 d 1 at the sulfate methane transition zone smtz and sediment seawater interfaces respectively high methane fluxes tend to be associated with structural features suggesting a strong structural control on the methane transport a significant portion of ascending methane 50 is consumed by anaerobic oxidation of methane at the smtz at most sites indicating effective biological filtration gas compositions and isotopes revealed a transition from the predominance of microbial methane in the passive margin to thermogenic methane at the upper slope of the active margin and onshore mud volcanoes methane production and consumption at shallow depths were nearly offset with a small fraction of residual methane discharged into seawater the flux imbalance arose primarily due to the larger production of methane through deep microbial and thermogenic processes at a magnitude of 1 512 43 096 tg myr 1 methane and could be likely accounted for by the sequestration of methane into hydrate forms and clay absorption

million year old ice found under meter thick debris layer in antarctica cosmogenic nuclide measurements associated with buried glacier ice in ong valley in the transantarctic mountains suggest the preservation of ancient ice there are three glacial tills on the valley floor which have formed from the concentration of regolith contained within sublimating glacier ice two tills are less than 1 m thick and underlain by ice measurements of cosmogenic 10be 26al and 21ne show that i the youngest buried ice unit and corresponding till are at least 11 13 ka ii another ice unit and corresponding intermediate age till are at least 1 1 ma old under any circumstances and most likely older than 1 78 ma and iii the oldest till is at least 1 57 ma and most likely greater than 2 63 ma these observations highlight the longevity of ice under thin debris layers and the potential to sample ancient ice for paleoclimate paleoatmosphere information close to the present land surface

physical characteristics and occurrence rates of meteoric plasma layers detected in the martian ionosphere by the mars global surveyor radio science experiment 1 low altitude plasma layers are present in 71 of 5600 electron density profiles from the martian ionosphere obtained by the mars global surveyor radio science experiment these layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms the mean altitude of the meteoric layer is 91 7 4 8 km the mean peak electron density in the meteoric layer is 1 33 0 25 1010 m 3 the mean width of the meteoric layer is 10 3 5 2 km the occurrence rate of meteoric layers varies with season solar zenith angle and latitude seasonal variations in occurrence rate are particularly strong often exceeding an order of magnitude meteoric layer altitude peak electron density and width are all positively correlated with correlation coefficients of 0 3 0 4 other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties such as scale height solar zenith angle and solar flux have absolute values that are significantly smaller indicating lack of correlation the photochemical lifetime of plasma in meteoric layers is 12 days and depends on altitude

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the barbados accretionary wedge chemical isotopic and heat budgets are controlled by fluid flow and venting at convergent margins fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes which are common at the barbados convergent margin chemical and isotopic compositions of fluids collected from four mud volcanoes located east of the barbados deformation front at 13 50 n indicate venting is sufficiently rapid to prevent diffusion from seawater in sediments surrounding the mud volcanoes the rate of nonfocused fluid flow is 0 26 cm yr although this rate is 3 orders of magnitude slower than the flow from the mud volcanoes significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes chloride concentrations are depleted to a minimum of 211 mm 45 of seawater value primarily by mixing diagenetically altered pore fluids with an 18o enriched fresh water released from the dissociation of methane hydrate this reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes the geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions 1 clay mineral dehydration which releases h2o and influences a range of chemical and isotopic compositions 2 organic matter regeneration which increases alkalinity nh4 and br and decreases so42 concentrations 3 cation exchange with clay minerals which increases na and decreases nh4 concentrations 4 carbonate recrystallization and precipitation which decrease ca2 but increase sr2 concentrations and 5 conversion of volcanic ash to clay minerals which utilizes h2o and decreases mg2 concentrations the geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from 75 to 115 c thus at the regional geothermal gradients of 27 to 40 c km these temperatures indicate that the source regions are at 2 to 4 5 km depth

excess ground ice of condensation diffusion origin in university valley dry valleys of antarctica evidence from isotope geochemistry and numerical modeling abstract this study investigates the origin and age of ground ice in the uppermost 1 m of permafrost in university valley one of the upper valleys in the mcmurdo dry valleys of antarctica in contrast to other regions in the mdv mean daily air and soil temperatures at the coring sites are always below 0 c which allows for unique cryogenic processes to occur in the two cores that were analyzed excess ground ice was measured throughout ranging between 23 and 85 isotope geochemical trends in the ice rich permafrost indicate that the ground in core 5 65 cm long and the uppermost 52 cm of core 7 originated from condensation diffusion of water vapor whereas the ground ice between 57 90 cm in core 7 originated from freezing of liquid water using numerical modeling we show that the excess ground ice of condensation diffusion origin formed by the long term thermal contraction expansion of the cryotic sediments which allowed for the ice content to exceed pore filling capacity absolute age estimates of the sandy loam sediments based on optically stimulated luminescence dating indicate that soils have been accreting at the site for at least the last 170 36 ka years and this places an upper limit to the age of the ground ice absolute soil ages allowed us to link the change in ground ice origin in core 7 which took place around 152 12 ka years with shifts in climate conditions since marine isotope stage 5e interglacial period our findings offer a new process of ground ice emplacement in sediments in cold dry environments and allow an alternative explanation regarding the enigmatic origin of excess ground ice identified by mars odyssey and phoenix in the northern martian plain which is that overfilled pore ice can form by vapor deposition and repeated thermal cycling without the presence of melt water

predictions of the effects of mars s encounter with comet c 2013 a1 siding spring upon metal species in its ionosphere the infall of dust from the coma of comet c 2013 a1 siding spring and its subsequent ablation in the atmosphere of mars has the potential to affect the abundances of metal species in the atmosphere and ionosphere we develop relationships between properties of the dust population in the coma and densities of metal species in the atmosphere and ionosphere these can be used to predict the abundances of metal species in the atmosphere and ionosphere during the encounter given postencounter observations of the atmosphere and ionosphere they can also be used to infer relevant cometary properties although current predictions suggest that the influx of cometary dust will be comparable to the sporadic background the higher entry speed involved which leads to a greater production rate of ions during ablation means that metal ion abundances may be enhanced during and after the encounter

effects of the passage of comet c 2013 a1 siding spring observed by the shallow radar sharad on mars reconnaissance orbiter the close passage of comet c 2013 a1 siding spring to mars provided a unique opportunity to observe the interaction of cometary materials with the martian ionosphere and atmosphere using the sounding radar sharad shallow radar aboard mars reconnaissance orbiter in two nightside observations acquired in the 10 h following the closest approach the sharad data reveal a significant increase of the total electron content tec the observed tec values are typical for daylight hours just after dawn or before sunset but are unprecedented this deep into the night results support two predictions indicating that cometary pickup o ions or ions generated from the ablation of cometary dust are responsible for the creation of an additional ion layer

geochemical processes and chemosynthetic primary production in different thiotrophic mats of the hakon mosby mud volcano barents sea we have investigated if in a cold seep methane or sulfide is used for chemosynthetic primary production and if significant amounts of the sulfide produced by anaerobic oxidation of methane are oxidized geochemically and hence are not available for chemosynthetic production geochemically controlled redox reactions and biological turnover were compared in different habitats of the ha kon mosby mud volcano the center of the mud volcano is characterized by the highest fluid flow and most primary production by the microbial community depends on oxidation of methane the small amount of sulfide produced is oxidized geochemically with oxygen or is precipitated with dissolved iron in the medium flow peripheral beggiatoa habitat sulfide is largely oxidized biologically the oxygen and nitrate supply is high enough that beggiatoa can oxidize the sulfide completely and chemical sulfide oxidation or precipitation is not important an internally stored nitrate reservoir with average concentrations of 110 mmol l21 enables the beggiatoa to oxidize sulfide anaerobically the ph profile indicates sequential sulfide oxidation with elemental sulfur as an intermediate gray thiotrophic mats associated with perturbed sediments showed a high heterogeneity in sulfate turnover and high sulfide fluxes balanced by the opposing oxygen and nitrate fluxes so that biological oxidation dominates over geochemical sulfide removal processes the three habitats indicate substantial small scale variability in carbon fixation pathways either through direct biological use of methane or through indirect carbon fixation of methane derived carbon dioxide by chemolithotrophic sulfide oxidation

geomicrobiology and occluded o2 co2 ar gas analyses provide evidence of microbial respiration in ancient terrestrial ground ice abstract the study of ancient massive ground ice and sediment rich ice bodies not only allows an understanding of the stability of permafrost but also offers the possibility to understand the long term preservation and viability of microbes within these ice bodies although microorganisms have been identified in ancient bodies of ground ice and permafrost there still is a lack of convincing evidence that the microbes were metabolically active within the ice in this study we combine geomicrobiology methods with the measurements of occluded gasses in four ancient massive ground ice bodies to provide evidence of microbial respiration in our samples abundant cold adapted heterotroph microorganisms were identified using culture dependent and independent methods the occluded gas measurements with low o 2 ar less than 21 4 and 13 c co 2 as low as 25 2 values and high 18 o o 2 up to 16 3 values are suggestive of in situ consumption of o 2 by heterotrophic psychrophilic bacteria living within the ice matrix overall the multi disciplinary approach provides a strong set of tools from which to infer metabolic activity within bodies of ground ice the analysis of o 2 ar 18 o o 2 and 13 c co 2 from occluded gasses in ice are strong isotope biosignatures that could allow detecting evidence of life on other planetary icy bodies such as mars

in situ sediment temperature measurements and geochemical porewater data suggest highly dynamic fluid flow at isis mud volcano eastern mediterranean sea isis mud volcano is located on the upper slope of the nile deep sea fan and has been described as the surface expression of a deep seated gas chimney loncke l gaullier v mascle j vendeville b 2002 shallow structure of the nile deep sea fan interactions between structural heritage and salt tectonics consequences on sedimentary dispersal in ciesm ed turbidite systems and deep sea fans of the mediterranean and the black seas ciesm workshop series vol 17 monaco detailed geothermal and geochemical investigations of isis mv have been carried out during the nautinil 2003 and mimes 2004 cruises within the framework of the euro margins mediflux project sediment temperatures of more than 40 c at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of isis mv the microbathymetry along dive tracks of the submersible nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology at the center porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments whereas the chlorinity of cores taken at short distances away is equal to bottom water values applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies which points to a transient regime of variable fluid flow possibly accompanied by episodic mud eruptions numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud

pore water profiles and authigenic mineralization in shallow marine sediments above the methane charged system on umitaka spur japan sea umitaka spur situated on an unusual collisional plate boundary along the eastern margin of the japan sea hosts gas seeps pock marks collapse structures and gas hydrates piston cores were recovered from this ridge to understand carbon cycling pore fluid gradients and authigenic mineralization above a methane charged system we present the chemistry of fluids and solids from three cores adjacent to seep locations high fluxes of ch4 and alkalinity transport carbon from a deep zone of methanogenesis toward the seafloor methane however reacts with so42 across a shallow sulfate methane transition smt which generates additional alkalinity and hs a fraction of these ch4 oxidation products form authigenic carbonate and pyrite these minerals are not readily apparent from visual inspection of split cores because they exist as micritic coatings on microfossils or as framboidal pyrite they are however readily observed in chemical analyses as peaks of labile ca sr ba or s in sediment at or near the smt carbon inputs and outputs nicely balance across the smt in all three cores if one considers four relevant fluxes loss of alkalinity to the seafloor addition of methane from below addition of alkalinity from below and carbonate precipitation importantly in all cores the magnitude of the fluxes decreases in this order although some carbon rising from depth forms authigenic carbonate most 80 escapes to the ocean as alkalinity nonetheless authigenic fronts in sediment on umitaka spur are a significant reservoir of inorganic carbon given calculated pore fluid fluxes for ca and sr the fronts require tens of thousands of years to form suggesting that the present state and loss of carbon represent long lived processes

decadal topographic change in the mcmurdo dry valleys of antarctica thermokarst subsidence glacier thinning and transfer of water storage from the cryosphere to the hydrosphere abstract recent local scale observations of glaciers streams and soil surfaces in the mcmurdo dry valleys of antarctica mdv have documented evidence for rapid ice loss glacial thinning and ground surface subsidence associated with melting of ground ice to evaluate the extent magnitude and location of decadal scale landscape change in the mdv we collected airborne lidar elevation data in 2014 2015 and compared these data to a 2001 2002 airborne lidar campaign this regional assessment of elevation change spans the recent acceleration of warming and melting observed by long term meteorological and ecosystem response experiments allowing us to assess the response of mdv surfaces to warming and potential thawing feedbacks we find that locations of thermokarst subsidence are strongly associated with the presence of excess ground ice and with proximity to surface or shallow subsurface active layer water subsidence occurs across soil types and landforms in low lying low slope areas with impeded drainage and also high on steep valley walls glacier thinning is widespread and is associated with the growth of fine scale roughness pond levels are rising in most closed basin lakes in the mdv across all microclimate zones these observations highlight the continued importance of insolation driven melting in the mdv the regional melt pattern is consistent with an overall transition of water storage from the local cryosphere glaciers permafrost to the hydrosphere closed basin lakes and ponds as well as the ross sea we interpret this regional melting pattern to reflect a transition to arctic and alpine style hydrologically mediated permafrost and glacial melt

fluid source and methane related diagenetic processes recorded in cold seep carbonates from the alvheim channel central north sea integrated petrography mineralogy geochronology and geochemistry of cold seep carbonate crusts and free gas from the alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central north sea free gas isotope characteristics coupled with carbonate 13c values as low as 66 vpdb indicate a predominantly microbial methane source with minor thermogenic contribution we estimate that 70 of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane the early stage of crust growth is represented by microcrystalline aragonite and mg calcite 10 to 40 mol mgco3 cementing seafloor sediments consisting of clays quartz feldspar and minor detrital low mg calcite and dolomite typical association of aragonite cement with coarse grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction the later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts in contrast to early generation cements late generation cavity infills have rare earth elements and y patterns with small negative ce anomalies similar to seawater consistent with carbonate precipitation in a more open seawater dominated system aragonite u th ages indicate carbonate precipitation between 6 09 and 3 46 kyr bp in the northern part of the channel whereas in the southern part precipitation occurred between 1 94 and 0 81 kyr bp reflecting regional changes in fluid conduit position

interpretation of temperature measurements from the kaiko nankai cruise modeling of fluid flow in clam colonies during the kaiko nankai detailed submersible survey numerous measurements of the temperature gradient inside the sediment were performed on the deepest active zone of fluid venting which is situated on the anticline related to the frontal thrust using the ifremer t naut temperature probe operated from the submersiblenautile we thus obtained the temperature structure below different types of clam colonies associated with fluid venting we used the finite element method to model the thermal structure and fluid flow pattern of these vents and to determine the velocity of upward fluid flow through the colonies on a biological basis four types of clam colonies are defined each biological type has distinctive thermal characteristics and corresponds to a particular fluid flow pattern darcian flow velocity in the most active type of colony type a is of the order of 100 m a the total amount of fluid flowing through colonies in the studied area is estimated to be 200 m3 a 1 per metre width of subduction zone most of the flow is vented through type a colonies this value is more than one order of magnitude too high to be compatible with the amount of water available from steady state compaction of sediments in the whole wedge thermal arguments suggest that downwelling of seawater occurs around type a colonies and that seawater is then mixed with upcoming fluids at a depth of 1 or 2 metres furthermore finite element modeling shows that a salinity difference of a few parts per mil between the upcoming fluids and seawater is sufficient to drive convection around the colonies as water samples from a few vents indicate that the fluid source should actually be significantly less saline than seawater we propose that the very high fluid flows measured are a consequence of the dilution of the fluid of deep origin with seawater by a factor of 5 to 10

controls on authigenic carbonate precipitation at cold seeps along the convergent margin off costa rica five sediment cores from cold seeps at the forearc off costa rica were used to explore the relationship between fluid advection dissolved ca concentrations in upward migrating fluids and authigenic caco3 precipitation a numerical transport reaction model was used to determine rates of anaerobic oxidation of methane aom caco3 precipitation and benthic fluxes of solutes production of carbonate alkalinity and formation of authigenic carbonates is most intense at intermediate flow rates 3 40 cm a 1 and reduced under low and high flux conditions 0 1 and 200 cm a 1 dissolved ca concentrations observed in the vent fluids off costa rica cover a wide range between 4 and 31 mm clearly exceeding seawater concentrations at two locations systematic model runs showed that high ca concentrations in ascending fluids enhance the rate of authigenic carbonate production at moderate flow rates leading to an almost quantitative fixation of deeply derived ca in authigenic carbonates hence caco3 precipitation is not only controlled by ca diffusing into the sediment from bottom water but also by the ca concentration in ascending fluids thus ca enriched fluids offer a reason for enhanced subsurface caco3 precipitation and the occurrence of carbonate caps on dewatering structures in the central american fore arc based on average precipitation rates deduced from the systematic model runs it is possible to give a rough estimate of the global ca fixation at cold seeps 2 1010 mol ca a 1 which suggests that cold seeps are most likely not of key importance with respect to ca cycling in the ocean

antarctic blue ice moraines analogue for northern hemisphere ice sheets abstract this paper reviews the distribution character and age of blue ice moraines in antarctica and asks whether there are implications for the study of former pleistocene ice sheets in the northern hemisphere blue ice forms where acceleration of downslope katabatic winds removes snow and causes ice to ablate upward ice flow compensates for the surface ablation and in some places brings rock debris to the surface to form a blue ice moraine blue ice moraines occur where topography focuses katabatic winds notably outlet glaciers cutting through mountains and in the lee of nunataks and escarpments nearer the coast many antarctic blue ice moraines have been accumulating for millions of years the cyclic growth and decay of pleistocene ice sheets and the dominance of surface ablation near the ice sheet margins are clearly different yet there are aspects that apply to pleistocene ice sheets based on antarctic blue ice deposits equivalent deposits associated with former pleistocene ice sheets are likely to 1 lie in topographic sediment traps such as in side valleys or embayments next to outlet glaciers 2 occur in the lee of mountains 3 display a morphology indicating ice flow into the embayment or towards the mountain front 4 include a wide range of lithologies derived from the inland ice sheet yet consist wholly of local debris in places 5 accumulate a thick deposit perhaps over successive glaciations further 6 the location and intensity of moraine formation will change spatially and vertically in response to changes in the relative elevation of the surrounding mountains and its effect on ice flow the extent to which these criteria will help in interpreting the behaviour of pleistocene ice sheets is uncertain but we use examples from the greenland laurentide and eurasian ice sheets to suggest that the concept of enhanced ablation by katabatic winds encouraging surface moraine formation helps resolve several puzzles

methane seepage inferred from pore water geochemistry in shallow sediments in the western slope of the mid okinawa trough abstract widely distributed cold seeps are crucial sources of carbon to the seawater whereas anaerobic oxidation of methane aom and precipitation of authigenic carbonate might change the compositions of the methane rich fluids and thus reduce the outputs of dissolved carbon to seawater in this work we analyze the pore water compositions of four gravity cores with high methane concentration abnormalities in pore water or in overlying seawater in the western slope of the mid okinawa trough for the northern research area active weak methane seepage through the seafloor is identified in the vicinity of mud volcanoes sites c01 and c10 and strong emissions of gas and fluids may occur in the central mud volcanoes in a submarine canyon at the south c23 site exhibits rarely methane seepage while high rate transportation of methane from deep sediments and associated aom are identified at site c25 where small vertical faults and gas bearing layers are developed at the surrounding aom at site c25 is indicated by 1 quasi linearly decrease of sulfate concentrations with depths 2 intense increases of dissolved inorganic carbon dic concentrations and 3 significantly negative 13c values vary from 7 2 to 26 3 of dic organoclastic degradation in the shallow sediments is not obviously recognized in the study area because of the low concentrations of nh4 as well as negligible sulfate consumption at three of the four sites our data reveal that the cold systems are one of the dic sources the fluxes are ca 11 2 mmol m2 yr to the seawater in the okinawa trough which can be tracked by high depletion of 13c 13cdic ranges from 7 2 to 26 3 vpdb

chemical biological and hydrological controls on the 14c content of cold seep carbonate crusts numerical modeling and implications for convection at cold seeps understanding the hydrology of cold seep environments is crucial to perform accurate estimates of fluid and chemical fluxes at sedimentary wedges shallow convection processes may affect fluid flux estimates and could favor the destabilization of gas hydrate accumulations increasing the sediment ocean methane flux evidence for the occurrence of convection at cold seeps however is still limited we use the concentration of 14c d14c in carbonate crusts formed at cold seeps of the eastern mediterranean sea as a tracer for convective recirculation of seawater derived fluids a numerical model is applied to investigate the controls on 14c incorporation in cold seep carbonates our simulations show that increased amounts of ch4 in the expelled fluids result in elevated crust d14c while high ca2 and hco3 concentrations produce the opposite effect convection is the only transport process that can significantly increase crust d14c advection bioirrigation eddy diffusion and bioturbation instead have little effect on or produce a decrease of crust d14c in addition the presence of old or modern carbon mc in host sediments prior to cementation and the 14c decay associated to the time needed to form the crust contribute in defining the d14c of carbonate crusts we then use the model to reproduce the 14c content of the eastern mediterranean sea crusts to constrain the chemical and hydrological conditions that led to their formation some crusts contain relatively low amounts of 14c 945 0 d14c 930 2 which assuming no ageing after crust formation can be reproduced without considering convection other crusts from two sites the amsterdam and napoli mud volcanoes instead have a very high 14c content 899 0 d14c 838 4 which can only be reproduced by the model if convection mixes deep fluids with seawater order of magnitude calculations using the rayleigh criterion for convection suggest that the slow seepage about 10 cm year 1 of low salinity 20 fluids at the amsterdam sites could trigger haline convection there on the napoli mud volcano where high density brines are expelled density driven convection cannot take place and other processes possibly involving the rapid movement of free gas in the sediment could be important

removal of methane through hydrological microbial and geochemical processes in the shallow sediments of pockmarks along eastern vestnesa ridge svalbard the recent discovery of methane seeps in the arctic region requires a better understanding of the fate of methane in marine sediments if we are to understand the contributions of methane to arctic ecosystems and climate change to this goal we analyze pore water data from five sites along eastern vestnesa ridge a sediment drift off north west svalbard to quantify the consumption of dissolved methane across the sulfate methane transition zone which are 3 5 m below seafloor from the investigated sites we use transport reaction models to quantify the hydrology as well as the carbon mass balance in the sediments pore water profiles and our model results demonstrate that hydrological microbial and geochemical processes reactions efficiently remove methane carbon from fluid over different time scales we interpret the nonsteady state behavior of the first 50 70 cm of our pore water profiles from the active sites as an annual scale downward fluid flow due to a seepage related pressure imbalance such downward flow supplies sulfate which enhances methane consumption through anaerobic oxidation of methane aom within this depth range our steady state modeling confirms the efficiency of aom in consuming dissolved methane in the upper 0 8 1 2 m of sediments based on the phosphate profiles we estimate that aom at the active pockmarks may have been operating for the last two to four centuries precipitation of authigenic carbonate removes more than a quarter of the dissolved inorganic carbon produced by aom and fixes it as authigenic carbonate in the sediments a process that sequestrates methane carbon over geological time

basin scale estimates on petroleum components generation in the western black sea basin based on 3 d numerical modelling abstract a new numerical model reconstructing the depositional history 98 0 ma of the western black sea sub basin is presented the model accounts for changing boundary conditions i e water depth bottom water temperature heat flow evolution over time and estimates the rates and total amounts of the in situ biogenic methane generation and thermally driven organic matter maturation in the source rocks the overall thermogenic and biogenic gas generation predicted by the model is estimated at 1560 gt and 3100 gt respectively

bubble induced porewater mixing a 3 d model for deep porewater irrigation porewater data from vent sites of the northeastern shelf off sakhalin island sea of okhotsk exhibit bottom water concentrations down to a sediment depth of up to 300 cm below this depth solute concentrations rapidly change due to methanogenesis and anaerobic methane oxidation amo the profile shapes suggest an irrigation like process that mixes on a meter scale at these sites active gas emanation into the overlying water column and near surface gas hydrates are commonly observed we propose that methane gas bubbles rise through the soft surface sediments and cause mixing of the porewater mathematically the bubble induced irrigation can be described by eddy diffusion enhancing the diffusive transport of solutes by several orders of magnitude a 3 d numerical transport reaction model was developed to investigate the parameters defining the mixing process such as bubble rise velocity tube size tube distribution in the sediment and ebullition frequency model consistency with the field data requires eddy diffusivities 1 105 cm2 a tube densities of 4 tubes m2 equivalent to a tube spacing of 40 cm active gas seepage for more than a few weeks or months and moderate to low diagenetic reaction rates of solutes the corresponding methane gas fluxes that are predicted from the results of the model realizations range from 1 103 5 105 l m2 a due to bubble mixing solute fluxes in these sediments are increased by a factor of 3 and the maximum amo rate by a factor of 7

authigenic barite records of methane seepage at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanoes mvs are dynamic features that episodically expel gas charged fluids and mud onto the seafloor transferring various chemical constituents into the overlying water column the temporal variability in mv activity is however poorly understood so their importance as a source of methane ch4 and higher hydrocarbons for the oceanic carbon budget although thought to be significant cannot be properly constrained in this study the history of fluid and gas seepage at the carlos ribeiro mv gulf of cadiz is assessed via geochemical analyses and transport reaction modelling of pore fluids and barium ba rich layers ba fronts in sediment cores recovered along a transect from the eye to the periphery of the mv x ray fluorescence data reveal that ba fronts are absent at the eye while a single front with up to 1740 ppm ba is present at the margin of the summit three ba fronts occur at 45 85 and 130 cm depth within a mudflow to the southeast of the crater spectrometric analyses indicate that barite is the ba rich mineral in these layers upward advecting pore fluids are enriched in barium but depleted in calcium ca2 relative to seawater modelling of the ba2 and ca2 pore fluid profiles indicates that the positions of the ba fronts reflect both the present day hydrodynamic conditions as well as higher fluxes of methane in the past fluid advection appears to have decreased since 340 cal yr before present but degassing of the mudflow is ongoing and is potentially an important source of ch4

quantification of methane emission from bacterial mat sites at quepos slide offshore costa rica seafloor methane emission from the quepos slide on the submarine segment of the costa rica fore arc margin was estimated by extrapolating flux measurements from individual seeps to the total area covered by bacterial mats this approach is based on the combination of detailed mapping to determine the abundance of seeps and the application of a numerical model to estimate the amount of benthic methane fluxes model results suggest that the majority of the studied seeps transport rather limited amount of methane on average 177 mol cm 2 a 1 into the water column due to moderate upward advection allowing for intense anaerobic oxidation of methane aom on average 53 of the methane flux is consumed depth integrated aom rates 56 1 538 mol ch4 cm 2 a 1 are comparable with values reported from other active seep sites the overall amount of dissolved methane released into the water column from the entire area covered by bacterial mats on the quepos slide is estimated to be about 0 28 106 mol a 1 this conservative estimate which relies on rather accurate determinations of seafloor methane fluxes emphasizes the potential importance of submarine slides as sites of natural methane seepage however at present the global extent of methane seepage from submarine slides is largely unknown

ground ice recharge via brine transport in frozen soils of victoria valley antarctica insights from modeling δ18o and δd profiles abstract soils in the mcmurdo dry valleys antarctica contain ice and considerable amounts of salt ice often occurs at shallow depth throughout the dry valleys and other areas of hyperarid permafrost notably on mars this common occurrence of shallow ice is enigmatic however since according to published sublimation models it should disappear relatively quickly at rates of order 0 1 mm a 1 due to vapor loss to the atmosphere this loss may be offset by recharge from snowmelt infiltrating and freezing in the soil herein we present a first quantitative estimate of this recharge based on measured vertical profiles of d and 18 o that reveal considerable detail about the sources and sinks of ice we model these profiles taking into account the salt content and a soil temperature record along a 1 6 m depth profile of 10 ka old ice cemented soils in victoria valley antarctica the stable isotopes of ice are enriched in heavy isotopes at the top of the ice cement 20 cm depth both d and 18 o values plotted against depth exhibit a concave upward curve at depth the isotope composition is similar to that of lake victoria and modern meteoric water the concave shape of the isotope profile is suggestive of downward advection dispersion of snowmelt water enriched in heavy isotopes into the ice cement our advection dispersion model coupled with field data enables us to quantify the advective flux and dispersion of melt water into the ice the advective velocity and dispersion coefficient depend on the time since advection began and the ice to brine ratio they are respectively of the order of 10 11 10 10 m s 1 and 10 12 10 11 m 2 s 1 these values suggest that over the 10 ka time period a total of 190 mm water infiltrated into the ice cemented ground the isotope composition and deuterium excess values of the uppermost ice cement can be modeled from snowmelt water enriched in salts using open system rayleigh fractionation to develop the isotopic signature of the upper ice cement requires evaporation of 95 of the snowmelt water based on 190 mm brine infiltrating into the soil requires an initial total of 4 m of snowmelt water this corresponds to 0 4 mm a 1 suggesting that under the current climate condition water from snowmelt is sufficient to compensate modeled sublimation rates and therefore conserve ground ice in victoria valley