observations of periglacial landforms in utopia planitia with the high resolution imaging science experiment hirise 1 the region of western utopia planitia 80 105 e 40 55 n displays several types of landforms similar to earth periglacial features including scallop shaped depressions and networks of polygonal terrains the scalloped depressions have been proposed to originate from thermokarstic processes such as sublimation and or melting of near surface ground ice using hirise imagery we characterize these depressions and several associated distinct polygon networks in unprecedented morphologic and topographic detail and investigate support for an ice based degradation process the scalloped depressions and interior polygons and ridges are found to evolve together mainly influenced by sublimation local proximity of ground ice to the surface and obliquity variations

beryllium isotopes in central arctic ocean sediments over the past 12 3 million years stratigraphic and paleoclimatic implications the upper 200 m of the sediments recovered during iodp leg 302 the arctic coring expedition acex to the lomonosov ridge in the central arctic ocean consist almost exclusively of detrital material the scarcity of biostratigraphic markers severely complicates the establishment of a reliable chronostratigraphic framework for these sediments which contain the first continuous record of the neogene environmental and climatic evolution of the arctic region here we present profiles of cosmogenic 10be together with the seawater derived fraction of stable 9be obtained from the acex cores the down core decrease of 10be 9be provides an average sedimentation rate of 14 5 1 m ma for the uppermost 151 m of the acex record and allows the establishment of a chronostratigraphy for the past 12 3 ma the age corrected 10be concentrations and 10be 9be ratios suggest the existence of an essentially continuous sea ice cover over the past 12 3 ma

sediment redistribution versus paleoproductivity change weddell sea margin sediment stratigraphy and biogenic particle flux of the last 250 000 years deduced from 230thex 10be and biogenic barium profiles high resolution 230thex and 10be and biogenic barium profiles were measured at three sediment gravity cores length 605 850 cm from the weddell sea continental margin applying the 230thex dating method average sedimentation rates of 3 cm kyr for the two cores from the south orkney slope and of 2 4 cm kyr for the core from the eastern weddell sea were determined and compared to 18o and lithostratigraphic results strong variations in the radionuclide concentrations in the sediments resembling the glacial interglacial pattern of the 18o stratigraphy and the 10be stratigraphy of high northern latitudes were used for establishing a chronostratigraphy biogenic ba shows a pattern similar to the radionuclide profiles suggesting that both records were influenced by increased paleoproductivity at the beginning of the interglacials however 230thex0 fluxes 0 stands for initial exceeding production by up to a factor of 4 suggest that sediment redistribution processes linked to variations in bottom water current velocity played the major role in controlling the radionuclide and biogenic barium deposition during isotope stages 5e and 1 the correction for sediment focusing makes the true vertical paleoproductivity rates deduced from the fluxes of proxy tracers like biogenic barium much lower than previously estimated very low 230thex0 concentrations and fluxes during isotope stage 6 were probably caused by rapid deposition of older resedimented material delivered to the weddell sea continental slopes by the grounded ice shelves and contemporaneous erosion of particles originating from the water column

global distribution of beryllium isotopes in deep ocean water as derived from femn crusts the direct measurement of the ratio of cosmogenic 10be t12 1 5 ma to stable terrigenously sourced 9be in deep seawater or marine deposits can be used to trace water mass movements and to quantify the incorporation of trace metals into the deep sea in this study a sims based technique has been used to determine the 10be9be ratios of the outermost millimetre of hydrogenetic ferromanganese crusts from the worlds oceans 10be9be ratios time corrected for radioactive decay of cosmogenic 10be using 234u238u are in good agreement with ams measurements of modern deep seawater ratios are relatively low in the north and equatorial atlantic samples 0 4 0 5 10 7 in the southwest atlantic ratios increase up to 1 10 7 they vary between 0 7 and 1 0 10 7 in indian ocean samples and have a near constant value of 1 1 0 2 10 7 for all pacific samples if the residence time of 10be 10be in deep water is constant globally then the observed variations in 10be9be ratios could be caused by accumulation of 10be in deep water as it flows and ages along the conveyor following a transient depletion upon its formation in the northern atlantic in this view both 10be and 9be reach local steady state concentration in pacific deep water and the global 10be 600 a an alternative possibility is that the be isotope abundances are controlled by local scavenging for this scenario 10be would vary according to local particle concentration and would 600 a in the central pacific but 10be 230 a in the atlantic mass balance considerations indicate that hydrothermal additions of 9be to the oceans are negligible and that the dissolved riverine source is also small furthermore aeolian dust input of 9be appears insufficient to provide the dissolved 9be inventory the dissolution of only a small proportion 2 of river derived particulates could in principle supply the observed seawater 9be content if true ocean margins would be the sites for 9be addition due to the particle reactive nature of be these would also be the primary sites of be removal a possible net result of horizontal water masses passing through these marginal areas might be a decrease in seawater 10be9be and establishment of a relatively constant 9be concentration as 10be 600 a is less than the apparent age of deep water in the pacific 1500 a the pacific record of 10be9be is not expected to show secular variations due to changes in deep water flow despite the large variations in 10be9be between different water masses because of this insensitivity to deep water flow however it is suggested that the 10be9be ratio determined in the authigenic phase of marine sediments or hydrogenetic precipitates should be a suitable tool for monitoring changes in continental input or cosmic ray intensity on longer time scales

periglacial geomorphology and landscape evolution of the tempe terra region mars a systematic survey was undertaken and an investigation carried out into the geomorphological characteristics of lobate debris aprons in the tempe terra region of mars based on the most recent high resolution sub 15 m per pixel imagery and on new topography data this study endeavoured to raise and discuss questions regarding their formation emplacement and modification deformation sequence as well as the role of a mantling deposit found at mid latitude locations on mars furthermore a model for the formation of debris aprons in the tempe terra mareotis fossae settings is proposed image survey in combination with basic morphometric observations within a geomorphological context provided additional insights into the source emplacement and modification of hillslope debris material our results imply that lobate debris aprons are not mainly relicts of remnant degradation but are substantially composed of mantling material probably deposited episodically in the course of planetary obliquity changes and over a long timespan as derived erosion rates suggest crater size frequency statistics and the derivation of absolute ages show ages of sub recent modification and document earlier resurfacing events

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

boulder movement at high northern latitudes of mars 1 we examine a narrow latitudinal band 60 n 70 n on mars to place constraints on the seasonally averaged velocity q of boulder movements over patterned ground these latitudes comprise a region of the northern lowlands where patterned ground covers nearly every surface here boulders meters in diameter are consistently found to be concentrated at or near the cracks that define the polygonal networks indicating a mobilization process because impact craters are the source for many boulders we can use craters and their degradation to estimate the time scales for boulder movement we study and catalog 1018 degraded impact craters 100 m d 1 km in 55 high resolution imaging science experiment hirise images we find that crater degradation occurs on a time scale 1 ma which is too recent for melting related mechanisms in a past warmer epoch clustering of boulders occurs at a time scale of a few ma or shorter which means that boulders on 5 20 m diameter polygons move at seasonal velocities q 1 10 m yr or faster

sensitivity and response of beryllium 10 in marine sediments to rapid production changes geomagnetic events a box model study the response and the sensitivity of the marine beryllium 10 flux to abrupt production changes e g caused by a geomagnetic event are investigated by using a simple box model the effect of mixing processes in the water column on the 10be flux is simulated and the influence of bioturbation on the sedimentary record is studied while the effect of the oceanic residence time is found to be small bioturbation can drastically change the shape and the amplitude of the modeled 10be peak the simulations indicate that 10be production peaks persisting for more than 1500 years are recorded well in deep sea sediments if bioturbation induced integration times are small tbio 1000 years while sediment cores with tbio 1000 years are found to be not well suited for stratigraphic purposes the results further show that the sedimentary 10be peak lags initial signal this time lag is almost independent of the event duration for tbio 1000 years ranging between about 400 and 600 years therefore the model results support the idea that marine 10be peaks corresponding to geomagnetic events can be used as a global time marker to match marine terrestrial and ice core chronologies on the millennial and if the time lag of 500 100 years is considered the submillennial timescale

particulate removal of230th and231pa in the biologically productive northern north pacific settling particles were collected by sediment traps at four stations in the high latitudes of the north pacific and analyzed for234th 232th 230th 228th and231pa in the northern north pacific including the bering sea the average activity ratio of unsupported230th to231pa in settling particles was 5 5 whereas that in the gulf of alaska in the eastern north pacific was about 14 the northern north pacific may be an efficient sink for231pa relative to230th because the average ratio in the world ocean is equal to the production ratio of 10 8 in seawater the activity ratios of230th 231pa of the settling particles agree well with those of the surface sediments at the respective stations this indicates that both nuclides in the surface sediments originated from settling particles and their dissolution or uptake during early diagenesis are not effective the ratio of the particulate nuclide flux f to the overlying water column production rate p did not correlate well with the total mass flux for230th however that for231pa increased almost linearly with increase in total mass flux and reached unity when the total mass flux was about 110 mg m2 d this suggests that231pa transported from oligotrophic regions is being actively removed in the biologically productive northern north pacific

modification of the dichotomy boundary on mars by amazonian mid latitude regional glaciation 1 restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat the unique fretted terrain located along the deuteronilus protonilus mensae northern mid latitude portion of the boundary has been long held to provide clues to dichotomy degradation processes we use new spacecraft data to show that fretted valleys display a multitude of characteristics typical of integrated valley glacial systems on earth multiple theater headed alcove like accumulation areas sharp arete like ridges typical of glacial erosion converging patterns of downslope valley flow valley lineation patterns typical of folding and shear wrap around features indicative of flow around obstacles and broad piedmont like lobes as the valley fill extends out into the northern lowlands the single integrated system containing these features covers about 30 000 km2 and is one of dozens of fretted valleys along the dichotomy boundary in this region these relationships suggest that the boundary area was subjected to very large scale regional glaciation during the amazonian recognition and documentation of this important late stage process provides information critical to reconstructing the original dichotomy boundary

landforms indicative of ground ice thaw in the northern high latitudes of mars the confirmation of near surface ground ice and perchlorates at the phoenix landing site suggest that high latitude ground ice thaw may be more easily achieved than previously envisaged providing the potential to drive significant distinctive morphogenesis we describe the results of a survey of 23 high resolution imaging science experiment hirise images covering 337 of longitude between latitudes 59 n and 79 n in which such morphogenesis is apparent confirming that thaw has been a regionally important morphological agent some of the strongest geomorphological indicators of cyclical ground ice thaw described are assemblages of sorted landforms including clastic patterned ground resulting from cryoturbation of ice rich regolith and lobate forms reflecting solifluction also described are braided gully fan systems sourced at thermokarst pits and channels that have evolved from enlarged thermal contraction cracks not only are these landforms indicative of thaw and flowing liquid but the incision of solifluction lobes by thermokarst gullies demonstrates that thaw has been responsible for polycyclic morphogenesis the presence of these landforms across the high northern latitudes of mars indicates that the regional importance of thaw has been underestimated this in turn has important implications for the development of better climate models and the search for life on mars

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

thermal contraction crack polygons on mars a synthesis from hirise phoenix and terrestrial analog studies thermal contraction crack polygons are complex landforms that have begun to be deciphered on earth and mars by the combined investigative efforts of geomorphology environmental monitoring physical models paleoclimate reconstruction and geochemistry thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice ranging in ice content from weakly cemented soils to debris covered massive ice relative to larger topographic features polygons may form rapidly and reflect climate conditions at the time of formation preserving climate information as relict landforms in the geological record polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer and to delimit subsurface ice conditions analysis of martian polygon morphology and distribution indicates that geologically recent thermal contraction crack polygons on mars form predominantly in an ice rich latitude dependent mantle more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content deposition and modification history and to assess microclimate variation on timescales of ka to ma analyses of martian polygon morphology guided by investigations of terrestrial analog thermal contraction crack polygons strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons implying the presence of an ice rich substrate that was fractured during and subsequent to obliquity driven depositional periods and continually modified by ongoing vapor equilibration processes

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

the dissolved beryllium isotope composition of the arctic ocean we present the first comprehensive set of dissolved 10 be and 9 be concentrations in surface waters and vertical profiles of all major sub basins of the arctic ocean which are complemented by data from the major arctic rivers mackenzie lena yenisey and ob the results show that 10 be and 9 be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the arctic basin 350 750 atoms g and 9 15 pmol kg respectively in marked contrast be isotope compositions in the upper 150 m are highly variable and show systematic variations cosmogenic 10 be concentrations range from 150 to 1000 atoms g and concentrations of terrigenous 9 be range from 7 to 65 pmol kg resulting in 10 be 9 be ratios atom atom between 0 5 and 14 10 8 inflowing atlantic water masses in the eurasian basin are characterized by a 10 be 9 be signature of 7 10 8 the inflow of pacific water masses across the bering strait is characterized by lower ratios of 2 3 10 8 which can be traced into the central arctic ocean possibly as far as the fram strait a comparison of the high dissolved surface 10 be and 9 be concentrations corresponding to low 10 be 9 be signatures of 2 10 8 in the eurasian basin with hydrographic parameters and river data documents efficient and rapid transport of be with siberian river waters across the siberian arctic shelves into the central arctic basin although significant loss and exchange of be on the shelves occurs in contrast fresh surface waters from the canada basin also show high cosmogenic 10 be contents but are not enriched in terrigenous 9 be resulting in high 10 be 9 be signatures of up to 14 10 8 this is explained by a combination of efficient scavenging of be in the mackenzie river estuary and the shelves and additional supply of cosmogenic 10 be via atmospheric fallout and melting of old sea ice the residence time of be in the deep arctic ocean estimated from our data is 800 years and thus similar to the average be residence time in the global ocean 2009 elsevier ltd all rights reserved

sorted clastic stripes lobes and associated gullies in high latitude craters on mars landforms indicative of very recent polycyclic ground ice thaw and liquid flows self organised patterns of stone stripes polygons circles and clastic solifluction lobes form by the sorting of clasts from fine grained sediments in freeze thaw cycles we present new high resolution imaging science experiment hirise images of mars which demonstrate that the slopes of high latitude craters including heimdal crater just 25 km east of the phoenix landing site are patterned by all of these landforms the order of magnitude improvement in imaging data resolution afforded by hirise over previous datasets allows not only the reliable identification of these periglacial landforms but also shows that high latitude fluviatile gullies both pre and post date periglacial patterned ground in several high latitude settings on mars because thaw is inherent to the sorting processes that create these periglacial landforms and from the association of this landform assemblage with fluviatile gullies we infer the action of liquid water in a fluvio periglacial context we conclude that these observations are evidence of the protracted widespread action of thaw liquids on and within the martian regolith moreover the size frequency statistics of superposed impact craters demonstrate that this freeze thaw environment is at least in heimdal crater less than a few million years old although the current martian climate does not favour prolonged thaw of water ice observations of possible liquid droplets on the strut of the phoenix lander may imply significant freezing point depression of liquids sourced in the regolith probably driven by the presence of perchlorates in the soil because perchlorates have eutectic temperatures below 240 k and can remain liquid at temperatures far below the freezing point of water we speculate that freeze thaw involving perchlorate brines provides an alternative low temperature hypothesis to the freeze thaw of more pure water ice and might drive significant geomorphological work in some areas of mars considering the proximity of heimdal crater to the phoenix landing site the presence of such hydrated minerals might therefore explain the landforms described here if this is the case then the geographical distribution of martian freeze thaw landforms might reflect relatively high temperatures but still below 273 k and the locally elevated concentration of salts in the regolith c 2010 elsevier inc all rights reserved

quasi conservative behaviour of 10be in deep waters of the weddell sea and the atlantic sector of the antarctic circumpolar current we present the first transect of dissolved 10be depth profiles across the antarctic circumpolar current acc in the atlantic sector north of the polar front the 10be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms g at depth deep water 10be concentrations of particular water masses are consistent with earlier results obtained further north south of the polar front and in the weddell sea the distribution of 10be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher up to 2000 atoms g than further north probably as a result of mixing and advection of water masses of pacific origin overall the deep water 10be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that 10be can be viewed as a quasi conservative tracer this provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the southern ocean such as 230th in deep waters north of the acc weddell gyre boundary awb 10be 230th has a relatively constant value 1 7 0 3 109 atoms dpm over a wide density range whereas south of the awb the ratio is significantly lower 1 1 0 2 109 atoms dpm this normalisation to 10be corroborates that 230th is enriched by 50 due to accumulation south of the awb as a consequence of minimal particulate fluxes the quasi conservative behaviour deduced from our results also implies that 10be can only be used as a tracer for southern ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly

sorted stone circles in elysium planitia mars implications for recent martian climate we have found sorted stone circles and polygons near the equator of mars using new 25 cm pixel nasa hirise high resolution imaging science experiment images the sorted circles occur in geologically recent catastrophic flood deposits in the equatorial elysium planitia region and are diagnostic of periglacial processes sorted polygons do not form from volcanic activity as has been suggested for non sorted polygons in this region these landforms indicate that i a long lived geologically recent active cryoturbation layer of ground ice was present in the regolith ii there was some degree of freeze thaw and thus iii there were sustained period s likely within the last 10 ma in which the martian climate was 40 to 60 k warmer than current models predict

distribution and orientation of northern hemisphere gullies on mars from the evaluation of hrsc and moc na data abstract martian gullies show morphologic characteristics that indicate the presence of a flowing liquid during their formation process however the current climate in the northern hemisphere of mars does not allow the existence of substantial amounts of liquid water and therefore an assessment of the regional distribution and characteristics of gullies is required in order to understand the most recent climatic development of mars we examined high resolution stereo camera hrsc and mars orbiter camera narrow angle moc na data covering the northern hemisphere in order to determine the distribution geological setting and orientation of gullied slopes we used these results to test the consistency of formation models proposed in earlier works and to define the climate dependence gully orientations were analyzed only at impact crater walls because craters have an azimuthally uniform distribution of slopes this is ideal when investigating the influence of insolation on the distribution and development of landforms we examined 230 hrsc and 21 000 moc na images and identified more than 2200 gullies on hrsc and more than 3100 gullies in moc na data both surveys show the highest densities of gullies between 35 n and 55 n and a shift of gully orientation at 40 n from pole facing slopes to slopes facing the equator orientation trends as well as the latitudinal distribution of identified gullies strongly support the view of gully formation caused by insolation climatic conditions this result suggests that formation mechanisms based on the assumption of atmospheric water ice deposition proposed in earlier work are more likely than processes related to groundwater flow further support for a theory related to deposition is gained through observation of the high occurrence of gullies at isolated knobs and hills which cannot be associated with formation models based upon groundwater flow

highly resolved beryllium 10 record from odp site 1089 a global signal abstract in this study a highly resolved beryllium 10 record from a rapidly accumulating sediment core located in the southern cape basin odp leg 177 site 1089 is presented to extract the global 10 be production signal from the sedimentary record a dedicated correction procedure is applied first sediment redistribution is quantified by applying thorium 230 normalization then lateral transport of 10 be and 230 th is assessed using simple box model calculations the model results indicate that only minor transport corrections have to be applied thus site 1089 combines the advantage of good time resolution with nearly negligible oceanic transport of 10 be leading to a favored site for the reconstruction of global 10 be production changes from marine sediments our results suggest that the transport corrected 10 be record at site 1089 reflects long term variations of the global 10 be production rate over the past 300 kyr the absolute values of the youngest holocene samples are in good agreement with the estimated recent long term averaged global 10 be production rate deduced from observations the variability of the 10 be flux over the past 300 kyr corresponds well to the expected range deduced from model calculations the comparison with other reconstructions of geomagnetic paleointensity and with records of cosmogenic nuclides further emphasizes the global character of this 10 be record therefore our results show that it is possible to quantitatively extract the global 10 be production rate from a single marine record if transport processes are corrected for since the error of a single reconstruction is large a combination of several highly resolved and transport corrected 10 be records may lead to a significantly improved reconstruction of geomagnetic variability and of global cosmic ray flux and over the past 300 kyr

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

sorted clastic polygons in the argyre region mars and possible evidence of pre and post glacial periglaciation in the late amazonian epoch abstract the argyre basin and associated rim materials in the southern highlands of mars are ancient having been formed by the impact of a large body 3 9 gya despite its age the regional landscape exhibits a wide range of geological geomorphological modifications and or features e g fluvial lacustrine aeolian glacial and periglacial collectively this bears witness to the dynamic evolution of the argyre region from the deep past through to perhaps the present day here we present three principal findings that point to at least two distinct episodes of periglaciation separated by a possible glacial interval during the very late amazonian epoch in eastern aonia terra at i e on the western flank of the argyre basin these findings are the product of our circum argyre study of all hirise images 35 65 s and 290 350 e 1 a the first periglacial episode involves the development of small sized 15 25 m in diam and clastically sorted polygons sps the sps are observed at eighteen locations within eastern at hitherto the presence of sps in this region has been reported at one location alone no other observations of sps in the southern hemisphere of mars have been documented morphologically similar landforms develop in cold climate permafrost landscapes on earth by means of periglacial processes i e freeze thaw cycling segregated ice formation cryoturbation and frost heave b we ascribe a periglacial origin to the sps in eastern at on the basis of this similarity of form and no less importantly on the close spatial association of the sps with blockfields whose weathered clastic products are the building blocks of periglacial sorting on earth gelifluction like lobes and possible wet gullies where similar assemblages occur in terrestrial permafrost landscapes the presence of liquid water and of boundary conditions tolerant of freeze thaw cycling are observed or inferred c fifteen of the eighteen sp locations are clustered longitudinally 44 4 57 5 s 289 9 302 4 e this is inconsistent with the latitudinal and obliquity driven dependency of freeze thaw cycling in the late amazonian epoch hypothesised by many workers in the discipline 2 the second periglacial episode is highlighted by the development of small sized and clastically non sorted polygons nsps these polygons could have formed by means of a dry cryotic process i e thermal contraction cracking 3 the nsps incise and thus postdate a light toned mantle thought by numerous workers to comprise an ice dust admixture at some of the locations where the putatively icy mantle has undergone apparent ablation underlying sps are observed this suggests that the sps predate the mantle and derivatively the nsps as well the proposed geochronology of wet based sp icy mantle dry based nsp periods and interval is entirely new to the community moreover it underlines the possibility that periglacial and glacial boundary conditions at least in our study area may have oscillated much more substantially in the very late amazonian epoch than many workers have thought possible

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

thermokarst in siberian ice rich permafrost comparison to asymmetric scalloped depressions on mars 1 on earth the thawing of permafrost deposits with high ground ice content results in massive surface subsidence and the formation of characteristic large thermokarst depressions slope asymmetries within thermokarst depressions suggest lateral growth which occurs due to thermoerosion and gravimetric mass wasting along these slopes it has been proposed that rimless asymmetrically shaped depressions called scalloped depressions on mars were formed by insolation driven ground ice sublimation we investigated a large thermokarst depression in ice complex deposits in the siberian arctic as a terrestrial analogue for scalloped depressions in martian volatile rich mantle deposits our results from field studies insolation modeling and geomorphometric analyses suggest lateral thermokarst development in a northern direction this conclusion is obvious due to steeper slope angles of the south facing slopes insolation and surface temperatures are crucial factors directly influencing thermokarst slope stability and steepness comparative analyses of martian scalloped depressions in utopia planitia were conducted using high resolution high resolution imaging science experiment context camera and thermal infrared thermal emission imaging system satellite data by direct analogy we propose that the lateral scalloped depression development on mars was primarily forced on the steep pole facing slopes in the equator ward direction insolation modeling confirms that this must have happened in the last 10 ma during an orbital configuration of higher obliquity than today development would have been maximized if the orbit was both highly oblique and highly eccentric and or the martian summer coincided with perihelion relatively short events of increasing sublimation or even thawing of ground ice led to fast slumping processes on the steep pole facing slopes

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

periglacial landforms at the phoenix landing site and the northern plains of mars 1 we examine potentially periglacial landforms in mars orbiter camera moc and high resolution imaging science experiment hirise images at the phoenix landing site and compare them with numerical models of permafrost processes to better understand the origin nature and history of the permafrost and the surface of the northern plains of mars small scale 3 6 m polygonal patterned ground is ubiquitous throughout the phoenix landing site and northern plains larger scale 20 25 m polygonal patterns and regularly spaced 20 35 m rubble piles localized collections of rocks and boulders are also common rubble piles were previously identified as basketball terrain in moc images the small polygon networks exhibit well developed and relatively undegraded morphology and they overlay all other landforms comparison of the small polygons with a numerical model shows that their size is consistent with a thermal contraction origin on current day mars and are likely active in addition the observed polygon size is consistent with a subsurface rheology of ice cemented soil on depth scales of about 10 m the size and morphology of the larger polygonal patterns and rubble piles indicate a past episode of polygon formation and rock sorting in thermal contraction polygons while the ice table was about twice as deep as it is presently the pervasive nature of small and large polygons and the extensive sorting of surface rocks indicates that widespread overturning of the surface layer to depths of many meters has occurred in the recent geologic past this periglacial reworking has had a significant influence on the landscape at the phoenix landing site and over the martian northern plains

10 be profiles in seawater a knowledge of the marine geochemical cycle of 10be is basic to the use of this long lived cosmogenic radioisotope half life 1 5 myr in geochronological and geophysical studies1 3 the first attempts at measuring 10be in seawater were made only recently using nuclear accelerator spectrometry and six concentration values from four locations have been reported4 6 this data base must be expanded to include detailed water column profiles so that the behaviour of 10be in the ocean can be more fully described a parallel case in point is the recent measurement7 of a detailed oceanic profile for the stable 9be we report here two water column profiles of 10be one in the drake passage near antarctica and the other in the san nicolas basin about 100 km off the coast of southern california the san nicolas basin profile clearly demonstrates the regulation of 10be distribution by particulate cycling the data confirm the earlier suggestion4 of particle uptake of 10be in the surface ocean they also furnish evidence for regeneration of 10be across the thermocline and near the sea floor and for mid water scavenging

modeling the development of martian sublimation thermokarst landforms abstract sublimation thermokarst landforms result from collapse of the surface when ice is lost from the subsurface on mars scalloped landforms with scales of decameters to kilometers are observed in the mid latitudes and considered likely thermokarst features we describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation over periods of tens of thousands of mars years under conditions similar to the present the model produces scallop like features similar to those on the martian surface starting from much smaller initial disturbances the model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth with morphologies similar to observed landforms on the martian northern plains in order to produce these landforms by sublimation substantial quantities of excess ice are required at least comparable to the vertical extent of the landform and such ice must remain in adjacent terrain to support the non deflated surface we suggest that martian thermokarst features are consistent with formation by sublimation without melting and that significant thicknesses of very clean excess ice up to many tens of meters the depth of some scalloped depressions are locally present in the martian mid latitudes climate conditions leading to melting at significant depth are not required

thermokarst lakes and ponds on mars in the very recent late amazonian past the history of water is fundamental to understanding the geological evolution of mars and to questions concerning the possible development of life on the red planet today mars is cold and dry it

oceanic 231pa 230th ratio influenced by particle composition and remineralization abstract we have investigated the role of particle compositions in affecting the distribution of 231pa and 230th in the ocean by separating sediments collected by sediment traps and cores into three size fractions and analyzed for their excess 231pa 231paex excess 230th 230thex and major chemical components the samples came from stations along 140 w in the equatorial pacific and from the blake outer ridge in the north atlantic results indicate that aluminosilicates clays are the major carrier of 231pa and 230th and the ratio 231paex 230thex in marine particulates decreases with increasing 232th concentration model simulation shows that sea floor sediments and trap collected particles have similar 231paex 230thex ratios in their biogenic components which are very close to the seawater ratio but are about one order higher than the ratios in coexisting clays preferential scavenging of 230th over 231pa by clays is primarily responsible for the 231pa 230th fractionation in the ocean the fractionation factor between 230th and 231pa fth pa varies from 10 for aluminosilicates to 1 for biogenic 232th free particles changes in fth pa as a function of particle composition exert primary controls on 231paex 230thex in marine particulates and bottom sediments and on the boundary scavenging of pa remineralization of biogenic particles in the water column may result in a decrease of 231paex 230thex our observations place an important constraint on the use of sediment 231paex 230thex as a paleoproductivity proxy namely in order to use down core variations of 231paex 230thex to assess past changes in surface productivity one must either verify or assume that the lithogenic particle flux and water column particle remineralization have remained essentially constant at the core site

the distribution of putative periglacial landforms on the martian northern plains in this investigation hirise images were surveyed across three regions of the northern plains of mars acidalia arcadia and utopia planitiae a sample of hirise images within each of these areas was examined the aim of the investigation was to determine the distribution of three varieties of landform clastic patterned ground lobate hill slope features and scalloped depressions these features are of importance as they are morphologically similar to terrestrial periglacial features examples of these landforms were found across the study areas scalloped depressions are common at mid latitudes in each of the three regions sorted patterned ground was not as widespread some examples of sorted patterned ground were found in all three study areas but the main concentration occurs in the north western region of acidalia planitia lobate hill slope features were the least common of the three landform types despite occurring infrequently several possible examples of lobate features were found to occur in proximity to other putative periglacial features it was found that lobate hill slope features and clastic patterns occurred further south than expected beyond the southern extent of many previous studies these features and by extension the processes that form them could thus occur more widely than previously thought it also appears that although putative periglacial features are often found in crater interiors they are not limited to these environments extensive areas of patterned ground were found on the inter crater plains lobate features and sorted stripes were often found on crater walls which would support the hypothesis that they are analogous to hill slope features on earth scalloped depressions were most often found in crater interiors or on crater ejecta although examples on the inter crater plains were not uncommon

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

distribution of10be and9be in the pacific ocean abstract the vertical distributions of10be and9be at three locations in the pacific 25 n 170 e 17 n 118 w 3 s 117 w are presented the results show that both isotopes exhibit nutrient like profiles from the surface to the bottom the increase for10be is two to threefold and that for9be is about fivefold while the inter station variations in surface water concentrations may reach a factor of two deep water values tend to be much more uniform averaging about 2000 atoms g for10be and 30 pm for9be a similar situation applies to the10be 9be ratio it varies approximately from 1 to 3 10 7 atom atom at shallow depths but tends toward a value close to 1 1 10 7 in the deep ocean the variation of10be 9be can be viewed as resulting from the fact that10be in a given parcel of water consists of two components recycled and primary the recycled component is that part of10be which has reached tracer equilibrium with9be as opposed to the primary component which upon entering the sea from the atmosphere has yet to equilibrate with9be through particle cycling and mixing processes it is estimated that 70 to nearly 100 of10be at the three stations are being recycled and the recycled beryllium bears an atomic ratio of10be 9be close to 1 10 7 the oceanic residence time of be is of the order of 1000 4000 years comparable to or slightly longer than the ocean mixing time

constraints on deep water formation from the oceanic distributions of 10be 1 an analysis of the oceanic distribution of cosmogenic 10be shows that deep waters are formed by descending of cold dense surface waters at a rate of 18 sv 106 m3 s 1 in the northern north atlantic and 21 sv of which 17 sv enters the pacific in the antarctic over the last mixing cycle of 800 years lending support to the estimates based on radiocarbon and nutrient distributions it also indicates that deep water production in the northern north atlantic is 50 higher averaging over the recent 100 years than over the last mixing cycle suggesting a possible increase in the thermohaline ventilation of the north atlantic during the past century

geologically recent gully polygon relationships on mars insights from the antarctic dry valleys on the roles of permafrost microclimates and water sources for surface flow we describe the morphology and spatial relationships between composite wedge polygons and mars like gullies consisting of alcoves channels and fans in the hyper arid antarctic dry valleys adv as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground gullies in the adv arise in part from the melting of atmospherically derived wind blown snow trapped in polygon troughs snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions ice cemented permafrost provides an impermeable substrate over which meltwater flows but does not significantly contribute to meltwater generation relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs and dissection of fans by expanding polygon troughs these observations suggest the continuous presence of meters thick ice cemented permafrost beneath adv gullies we document strong morphological similarities between gullies and polygons on mars and those observed in the adv inland mixed microclimate zone on the basis of this morphological comparison we propose an analogous top down melting model for the initiation and evolution of martian gullies that occur on polygonally patterned mantled surfaces

accumulation of biogenic and lithogenic material in the pacific sector of the southern ocean during the past 40 000 years the 230th normalization technique was applied to surface sediments and down core records from the pacific sector of the southern ocean between 120 w and 170 w in order to reconstruct vertical rain rates corrected for lateral redistribution of sediment preserved rain rates of opal organic carbon and biogenic ba all indicate that biological productivity south of the antarctic polar front apf was much lower than today during the last glacial maximum lgm probably in response to increased ice cover however by analogy with modern opal fluxes south of the acc we show that year round ice cover is not a prerequisite for very low rates of opal accumulation available records from north of the apf indicate little to no change in opal export in contrast to records from the indian and atlantic sectors which show enhanced opal export north of the apf during the lgm glacial records from north of 66 s in the pacific all show lithogenic fluxes that were greater than today but significantly lower than lithogenic fluxes in the glacial atlantic and indian sectors together these new records from the pacific sector show that during the lgm the three basins of the southern ocean were significantly more differentiated than today the observed inter basin distribution of lithogenic fluxes and opal burial and the presumed geographical distribution of increased dust input to the southern ocean during the lgm are consistent with an atlantic indian pacific gradient in the degree of iron stimulated diatom productivity within the zone lying between the apf and the subantarctic front previous studies which focused primarily on the atlantic sector may have overestimated the glacial increase in the strength of the biological pump in the southern ocean

accumulation rates of th 230 pa 231 and some transition metals on the bermuda rise abstract measurements of 238u 234u 230th 232th 231pa mn fe co ni cu and zn were made on 23 samples from core gpc 5 a 29 m giant piston core from a water depth of 4583 m on the northeastern bermuda rise 33 41 2 n 57 36 9 w this area is characterized by rapid deposition of sediment transported by abyssal currents unsupported 230th and 231pa are present throughout the core but because of large variations in the sedimentation rate show marked departures from exponential decay with depth the trend with depth of the 231 pa ex 230 th ex ratio is consistent with the average accumulation rate of 36 cm 1000 y reported earlier on the basis of radiocarbon dating and caco3 stratigraphy when expressed on a carbonate free basis concentrations of mn co ni cu zn 230thex and 231paex all show cyclic variations positively correlated with those of caco3 the correlations can be explained by a model in which all of these constituents including caco3 are supplied to the sediments from the water column at a constant rate concentration variations are controlled mainly by varying inputs of terrigenous detritus with low inputs occurring during interglacials and high inputs during glacials relationships between the metal and 230thex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column the results in g cm2 1000 y are 4300 1100 for mn 46 16 for ni and 76 26 for cu these rates are somewhat larger than ocean wide averages estimated by other methods and the absolute rate of 230th accumulation in gpc 5 averages about nine times higher than production in the overlying water column this part of the bermuda rise and similar bottom current deposits may act as important accumulators of elements scavenged from seawater

initiation and growth of martian ice lenses abstract water ice in the upper meters of the martian regolith is a major volatile reservoir although the geographic extent burial depth and thermal stability of this shallow ice are well understood its origin history and stratigraphy are not over the past decade a growing body of observational evidence has indicated that shallow ground ice exceeds the pore volume of its host soil over large regions of both martian hemispheres this is confounding given that 1 the physical theory that accurately predicts the location of ground ice also assumes that ice should be pore filling in the upper meter of regolith and 2 the phoenix spacecraft uncovered far more pore filling ice than excess ice at its landing site in the northern hemisphere the development of ice lenses by low temperature in situ segregation analogous to the processes that generate frost heave on earth has been hypothesized to explain shallow excess ice on mars we have developed a numerical model of ice lens initiation and growth in the martian environment and used it to test this hypothesis for the first time we carried out a large suite of numerical simulations in order to place quantitative constraints on the timing and location of ice lens initiation and on the magnitude of ice lens growth in a variety of host soils we find that ice lens initiation is a ubiquitous process in the martian high latitudes but the ultimate magnitude of lens growth or frost heave is sensitive to the properties of the host soil depending on the specific properties of martian soils in situ segregation may be a very slow process sufficient to explain the excess ice observed in the dodo goldilocks trench at the phoenix landing site but without regionally significant effects alternatively if clay sized particles or perchlorate salts are present in situ segregation may be a vigorous process that has significantly affected the stratigraphy of ground ice in the upper meter of regolith throughout the high latitudes

co evolution of polygonal and scalloped terrains southwestern utopia planitia mars abstract thermal contraction crack polygons and scalloped depressions two of the most common landforms found in utopia planitia mars have previously been linked to the presence of ice rich deposits in the subsurface although the formation and evolution of these features individually are relatively well understood little to no effort has been directed towards elucidating possible interactions that occur between them during their development thus the overarching goal of this research was to investigate if there is an evolutionary link between polygonal and scalloped terrains by correlating metrics representing polygon and scallop maturity a variety of statistical analyses were performed using hirise and mola datasets to quantify interactions between four sets of polygonal and scalloped terrains our results demonstrate the existence of a negative relationship between polygonal subdivision and surface elevation indicating that polygon networks become more evolved as the surface subsides these results suggest that the permafrost landscape in utopia planitia may once have been extremely ice rich and that multiple geomorphic processes may be responsible for its evolution ultimately this work demonstrates that landscape reconstruction is more complete when a system approach is followed quantifying interactions between landforms as opposed to examining an individual landform in isolation

melting history of antarctica during the past 60 000 years marked changes in the surface water hydrology of the southern ocean during the past 60 kyr are revealed by a detailed comparison of the oxygen isotopic composition of planktonic and benthic foraminifera from sediment cores and the surface water temperature estimated by a transfer function derived from the distribution of diatoms in the same sediments from 35 to 17 kyr bp the southern ocean polar front was covered by a melt water lid containing a significant contribution from melting icebergs calved from antarctic ice shelves these icebergs may have originated from a succession of surges of the ice shelves

evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate

a new global database of mars impact craters 1 km 1 database creation properties and parameters 1 impact craters have been used as a standard metric for a plethora of planetary applications for many decades including age dating geologic mapping and stratigraphic relationships as tracers for surface processes and as locations for sampling lower crust and upper mantle material utilizing craters for these and other investigations is significantly aided by a uniform catalog of craters across the surface of interest consequently catalogs of craters have been developed for decades for the moon and other planets we present a new global catalog of martian craters statistically complete to diameters d 1 km it contains 384 343 craters and for each crater it lists detailed positional interior morphologic ejecta morphologic and morphometric data and modification state information if it could be determined in this paper we detail how the database was created the different fields assigned and statistical uncertainties and checks in our companion paper robbins and hynek 2012 we discuss the first broad science applications and results of this work

transport of10be and9be in the ocean beryllium isotopes 10be and9be have been measured in suspended particles of 1 mm size collected by mid water sediment traps deployed in the eastern pacific at manop sites h 6 32 n 92 50 w water depth 3600 m and m 8 50 n 104 00 w 3100 m for comparison surface sediments from box cores taken from the two sites were also studied the concentrations of10be and9be in sediment trap particles are about an order of magnitude smaller than those in the bottom sediments which contain about 8 109 and 6 1016 atoms g 1 of10be and9be respectively the sediment trap samples collected from 50 m off the bottom showed significant 26 63 contributions from resuspended bottom sediments the10be 9be ratio in trap samples varies from 3 to 20 10 8 the variation may partly result from varied proportion of authigenic detrital material the fluxes of both isotopes exhibit a very strong seasonality the fluxes of10be into the traps at about 1500 m are estimated as 9 105 and 4 105 atoms cm 2 a 1 at sites h and m respectively these values are to be compared with the fluxes into the sediments of 4 5 105 atoms cm 2 a 1 at both locations good correlations exist between10be 9be and27al indicating that the primary carrier phase s for the beryllium isotopes in the water column may be aluminosilicates

concentrated perchlorate at the mars phoenix landing site evidence for thin film liquid water on mars 1 nasa s phoenix mission which landed on the northern plains of mars in 2008 returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site here we use spectral data from phoenix s surface stereo imager to map the distribution of perchlorate salts at the phoenix landing site and find that perchlorate salt has been locally concentrated into subsurface patches similar to salt patches that result from aqueous dissolution and redistribution on earth we propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface and for concentrating it in patches the thin films are interpreted to result from melting of minor ice covers related to seasonal and long term obliquity cycles

scavenging of 230th 231pa and 10be in the southern ocean sw pacific sector the importance of particle flux particle composition and advection abstract the scavenging of 230 th 231 pa and 10 be was studied in the pacific sector of the southern ocean along 170 w using measurements from surface sediments time series sediment traps and the water column all sediment traps collected an annual flux of 231 pa greater than the integrated rate of production by 235 u decay up to 5 5 times greater and a flux of 10 be greater than the global average deposition rate of 10 be up to 3 4 times greater fluxes of 230 th were on average close to the production rate in the overlying water column these large fluxes of 231 pa and 10 be and high unsupported 231 pa 231 th and 10 be 230 th ratios in the sediments are not associated with depletion of nuclides in the water column and therefore are not the result of the classical boundary scavenging mechanism we estimate that of the 231 pa and 230 th advected into the southern ocean as part of the large scale overturning circulation only those nuclides associated with the upper limb of this circulation i e those that pass through the surface as part of the wind driven ekman flow are scavenged efficiently the majority of the nuclides advected into the southern ocean and associated with the bottom water limb are not scavenged to the sediments of the southern ocean but are returned northward throughout the year the unsupported 231 pa 230 th and 10 be 230 th ratios of material reaching sediment traps at 1000 m at a given site increase with increasing particle flux this behavior is explained by a conceptual model in which th pa and be are scavenged reversibly by fine grained suspended particles at all depths while pa and be are in addition scavenged strongly by diatom rich aggregates in surface waters spatial variability in the annually averaged unsupported 231 pa 230 th and 10 be 230 th ratios of sinking particulate matter reflects primarily the variability in particle composition and in the ratio and quantity of nuclides upwelled to the mixed layer rather than variability in particle flux

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

beryllium 10 in deep sea sediments a tracer for the earth s magnetic field intensity during the last 200 000 years abstract we present a new approach for the reconstruction of the earth s magnetic field intensity during the last 200 000 years based on 10 be in deep sea sediments a simple box model that is able to describe boundary scavenging of 10 be in the ocean is used to study the sensitivity of 10 be to changes of water circulation and or varying particle rain rates the model is applied to separate transport and production signal in single 10 be records vertical sediment accumulation rates are used as input values for the model calculations the calculated scavenging factors are applied to correct the 10 be records for boundary scavenging the model corrected 10 be based paleointensity record correlates well with other records from very different archives

a model for sorted circles as self organized patterns sorted circles emerge as self organized patterns from a laterally uniform active layer that becomes laterally sorted as frost heave deforms the interface between a stone layer and an underlying soil layer in a three dimensional cellular model of the active layer cyclic freezing and thawing drives transport of stone and soil particles by 1 addition of ice particles representing soil expansion by frost heave 2 removal of ice particles representing soil consolidation during thawing 3 addition of void particles a discrete abstraction of soil compressibility representing soil expansion by water absorption 4 removal of void particles representing compaction and desiccation of underlying soil by frost heave 5 relaxation of surface morphology by soil creep and stone avalanche and 6 vertical sorting of stones and soil by illuviation these transport processes give rise to sorted circles which are characterized by a mean spacing of 3 6 m a 2 4 m wide soil domain surrounded by a 1 0 m wide 0 3 m high annulus of stones and a 750 year period of circulation in the soil domain all consistent with measured characteristics of sorted circles in western spitsbergen in the model instabilities on the stonesoil interface grow upward as soil plugs by drawing in soil from the surrounding subsurface soil layer soil plugs develop into sorted circles as they contact the ground surface simultaneously elevating an encircling annulus of stones sorted circles are dynamically maintained by circulation within the stone and soil domains initiation of soil plugs is driven by a positive feedback in which frost heave near the stone soil interface pushes soil toward more compressible soil regions where the soil layer is thicker the lateral component of these frost heave induced displacements is not reversed during thaw because soil consolidation as ice rich soil melts and drains and soil expansion as desiccated and compacted soil hydrates displace soil vertically further development of soil plugs and sorted circles is determined by an interplay between this positive feedback and amplitude dependent negative feedbacks that result from decoupling of the freezing front from the stone soil interface parameters outside the range in which sorted circles form can result for example in stone islands and labyrinthine patterns the initial wavelength of perturbations on the stone soil interface is accurately predicted using a linear stability analysis but increase in this wavelength through time reflects the nonlinearities that control the spacing of soil plugs and sorted circles namely interactions and mergers between neighboring forms

thermokarst processes and the origin of crater rim gullies in utopia and western elysium planitia abstract we have identified a number of gullies that could be aqueous in origin near or at the rim of several impact craters in utopia planitia and western elysium planitia 30 0 59 0 n 241 0 291 0 w based on the sharpness of their incisions and the general absence of superposed craters we ascribe a relatively recent origin to the gullies scalloped depressions are commonplace throughout the region as well as on the crater walls rims and floors near the areas of gully issuance occasionally the depressions cross cut the gully debris aprons suggesting that the formation of some depressions is even more recent than that of the gullies previous research has proposed that the depressions are collapse basins formed by thermokarst processes on earth thermokarst landforms occur in areas of low gradient topography where the permanently frozen ground permafrost is ice rich and has undergone a change in thermal equilibrium this change can be triggered by long term or episodic cyclic climate change and accompanying rises in mean temperatures towards 0 c as well as by rises in seasonally sustained summer temperatures well above 0 c in order to explain the origin of the rim or near rim gullies we invoke high obliquity and the possibility that this region of mars experienced obliquity driven rises in temperature atmospheric pressure and humidity sufficient to keep surface water and near surface ground ice stable for extended periods of time we propose that gully formation is closely related to local freeze thaw processes that in turn generate a thermokarst landscape of which the gullies are a part this geological and climatological scenario comprises the following steps 1 an inundation of meltwater at high obliquity due to the thawing of an atmospherically deposited snowpack or ice sheet and the subsequent saturation of the underlying regolith to tens of metres of depth 2 loss of water on the surface perhaps as obliquity decreases slightly followed by the progressive freezing of the saturated regolith this creates an aggrading mass of ice rich regolith 3 obliquity induced temperature rises that engender the thaw drainage and partial evaporation of the near surface ice rich regolith 4 localised formation of thermokarst collapse basins alases as water is evacuated from these basins 5 formation of gullies near or at some impact crater rims as the result of meltwater migration from nearby alases through the thawed regolith to the areas of gully issuance although the plains materials in this region are in part very old possibly hesperian or even noachian the mantling deposits and their deformation by thermokarst processes appears to be relatively young this suggests that recent climatic conditions could have been episodically warmer and wetter than had been previously thought

fractionation of 230th 231pa and 10be induced by particle size and composition within an opal rich sediment of the atlantic southern ocean this study centers on the question how sensitive are 231pa 230th and 10be 230th to sediment composition and redistribution the natural radionuclides 231pa 230th and 10be recorded in deep sea sediments are tracers for water mass advection and particle fluxes we investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records we present new data on particle size specific 231pa and 10be concentrations an additional separation step based on settling velocities led to the isolation of a very opal rich phase we find that opal rich particles contain the highest 231pa and 10be concentrations and higher 231pa 230th and 10be 230th isotope ratios than opal poor particles the fractionation relative to 230th induced by the adsorption to opal rich particles is more pronounced for 231pa than for 10be we conclude that bulk 231pa 230th in southern ocean sediments is most suitable as a proxy for past opal fluxes the comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites however a simulation shows that particle sorting by selective removal of sediment winnowing could change the isotope ratios consequently 231pa 230th should not be used as paleocirculation proxy in cases where a strong loss of opal rich material due to bottom currents occurred

distribution and evolution of scalloped terrain in the southern hemisphere mars abstract scalloped depressions are a unique martian surface morphology found in the northern and southern hemisphere latitude dependent dust and ice rich surface mantles these features exhibit a distinct asymmetric north south slope profile characterized by steep pole facing scarps flat floors and gentle equator facing slopes we examined high resolution stereo camera hrsc images of the southern hemisphere to determine their longitudinal distribution which revealed that a majority of scalloped terrain is located in the region of the southern wall of the hellas basin and northern malea planum a detailed map of this area was produced where scallops were found to contour the southern wall of the basin and where the ice rich mantle was seen to be thickest scalloped terrain is concentrated along the topographic highs near the amphitrites and peneus paterae and areal extent and depth decreases with increasing depth into the basin we also examined existing hypothesis for the formation and evolution of scalloped depressions using high resolution imaging science experiment hirise images and data from the thermal emission imaging system infrared themis ir and the thermal emission spectrometer tes our approach provides regional context for the development of scalloped terrains within the southern hemisphere and offers detailed evidence of scallop depressions forming around small cracks presumably caused by thermal contraction morphometric measurements show that scalloped depressions can be as much as 40 m deep with typical depths of between 10 and 20 m our observations of scallop formation and development in the southern hemisphere support a solar insolation model proposed by previous researchers e g morgenstern a hauber e reiss d van gasselt s grosse g schirrmeister l 2007 j geophys res 112 citeid e06010 lefort a russell p s thomas n mcewen a s dundas c m kirk r l 2009a j geophys res 114 e04005 lefort a russell p s thomas n 2009b icarus in press observations made using hirise images suggest that scalloped depressions most likely form from small cracks in the mantle which become larger and deeper through sublimation of interstitial ice from within the mantle sublimation is likely enhanced on equator facing slopes because of increased solar insolation which accounts for the asymmetric slope profile and hemispherical orientation and is demonstrated by themis ir images we suggest that sublimation lag deposits can possibly be removed by dust devils or strong slope winds related to the hellas basin offering an explanation as to why scalloped terrain is so abundant only in this area of the southern hemisphere daytime maximum summer temperatures suggest that sublimation in the study area of malea planum is possible under current conditions if the sublimation lag is removed while it cannot be ruled out that scalloped terrain in malea planum is presently evolving we attribute the extensive distribution to geologically recent obliquity excursions when conditions were more conducive to mesoscale modification of the ice rich mantle

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

scalloped terrains in the peneus and amphitrites paterae region of mars as observed by hirise abstract the peneus and amphitrites paterae region of mars displays large areas of smooth geologically young terrains overlying a rougher and older topography these terrains may be remnants of the mid latitude mantle deposit which is thought to be composed of ice rich material originating from airfall deposition during a high obliquity period less than 5 ma ago within these terrains there are several types of potentially periglacial features in particular there are networks of polygonal cracks and scalloped shaped depressions which are similar to features found in utopia planitia in the northern hemisphere this area also displays knobby terrain similar to the so called basketball terrains of the mid and high martian latitudes we use recent high resolution images from the high resolution imaging science experiment hirise along with data from previous mars missions to study the small scale morphology of the scalloped terrains and associated polygon network and knobby terrains we compare these with the features observed in utopia planitia and attempt to determine their formation process while the two sites share many general features scallops in peneus amphitrites paterae lack the diverse polygon network i e there is little variation in the polygon sizes and shapes and large curvilinear ridges observed in utopia planitia this points to a more homogeneous ice content within the substrate in the peneus amphitrites paterae region and implies that scallop formation is independent of polygon formation this work shows that as in utopia planitia sublimation of interstitial ice is a likely process explaining the formation of the scalloped depressions in the region of peneus amphitrites paterae therefore we provide a simplified scallop formation model based on sublimation of interstitial ice as proposed for utopia planitia we also show that the differences in scallop morphologies between the two regions may be explained by differences in near surface ice content sublimation rates and age of formation of the scalloped terrains

differential frost heave and sorted patterned ground field measurements and a laboratory experiment abstract small scale sorted stripes and circles dominate over the alpine regions in the upper engadin swiss alps most of these features are spaced at less than 30 cm intervals by coarse margins shallower than 5 cm monitoring of sorted stripes indicates that shallow diurnal freezing often induces differences in amount and timing of frost heave by needle ice growth between fine and coarse stripes while deeper diurnal freezing and seasonal freezing rarely differentiate heave amounts of the two materials a laboratory simulation is designed to explore the contribution of differential frost heave to the sorting process at the monitoring site the device consists of a fine part loam and a coarse part a granule layer mounted on loam freeze thaw tests with a granule mantle of 0 5 2 5 and 5 cm thick demonstrate that the heave amount on the coarse part is greatly reduced by the 5 cm thick mantle and that the coarse part always heaves later but subsides earlier than the fine as a result of this time lag in frost heaving lateral soil movement towards the coarse part is generated within the surficial soil differential heave associated with diurnal freeze thaw cycles is capable of sorting of the top 5 cm of soil

possible mechanism of boulder clustering on mars whatever causes small scale polygonal patterned ground diameter 20 m to form pervasively in the northern plains of mars appears to also cause boulders to cluster at polygon margins assuming that these polygons are caused by the seasonal thermal contraction and expansion of ice in the near surface to meters of depth we propose a mechanism that ratchets boulders towards the edges in seasonal cycles on present day mars during the contraction cooling phase a co2 frost layer embeds the boulders buffered by condensation and sublimation the solid co2 is isothermal and does not contract we propose that it locks the boulders in place while the h2o ice in the near surface continues cooling and contracts beneath them in spring summer seasons when the frost sublimates and heating of the surface begins the boulders freely move with the expanding near surface ice we show that over many seasons this process would lead to progressive boulder movement towards polygon edges with an estimated rate of boulder migration 0 1 mm yr under present mars conditions

enhanced scavenging of 231pa relative to 230th in the south atlantic south of the polar front implications for the use of the 231pa 230th ratio as a paleoproductivity proxy abstract the fractionation of 230th and 231pa was investigated throughout the atlantic sector of the southern ocean published scavenging models generally assume that the 231pa 230t ratio of surface sediments is primarily determined by the mass flux of particles this relationship holds north of the polar front where low primary productivity coincides with ratios of unsupported 231pa 230th xs 231pa 230th in surface sediments below the production ratio of both radionuclides in the water column however we observed high xs231pa 230th ratios conventionally interpreted as a high productivity signal in surface sediments south of the polar front especially throughout the weddell sea in contradiction with the low particle flux of this region measurements of both dissolved and particulate fractions of 231pa and 230th in the water column revealed a strong n s decrease in the th pa fractionation factor from typical open ocean values around 10 north of the polar front to values between 1 and 2 south of 60 s this observation clearly indicates that the high xs231pa 230th ratios in surface sediments south of the antarctic circumpolar current are produced by a n s increase in the relative scavenging efficiency of 231pa relative to 230th most probably due to a change in the chemical composition of particulate matter and not by a high mass flux it is speculated that biogenic opal suggested not to significantly fractionate231pa and 230th may explain the enhanced scavenging of 231pa to the south this assumption is further supported by extremely high 231pa 230th ratios up to 0 34 in material collected with sediment traps south of the polar front where fluxes are primarily determined by biogenic opal based on these results we conclude that in regions where the sedimenting flux is dominated by biogenic opal the 231pa 230th ratio is not a reliable indicator for the mass flux of particles thus limiting its use as a paleoproductivity proxy in the southern ocean

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

zebra stripes in the atacama desert fossil evidence of overland flow abstract some hillslopes in the hyperarid region of the atacama desert in northern chile have surface clasts organized into distinct contour parallel bands separated by bare soil we call the bands zebra stripes due to the contrast between the darkly varnished clasts and the light colored salt rich soil gravel that comprises the zebra stripes is sorted such that the coarsest clasts are at the downslope front and fine progressively upslope how and when the zebra stripes formed are perplexing questions particularly in a region experiencing prolonged hyperaridity using googleearth satellite imagery and field observations we report the first quantitative and qualitative observations of zebra stripes in order to test hypotheses of the mechanisms and timing of their formation we consider soil shrink swell seismic shaking and overland flow as possible formation mechanisms and find that overland flow is the most likely based on cosmogenic 10 be concentrations in surface clasts salt deposition rates from the atmosphere and content in the soils we propose that the salt rich soils began accumulating 10 6 y ago and the zebra stripes formed 10 3 10 4 y at the latest the zebra stripe pattern has been preserved due to the self stabilization of the clasts within the stripes and the continued absence of life which would disturb the surface as seen at a wetter site to the south we conclude that the occurrence of zebra stripes is diagnostic of a set of distinct characteristics of local and or regional precipitation soil hillslope form and bedrock type

particulate fluxes of 230th 231pa and 10be in the northeastern pacific ocean abstract measurements of 230th 231pa and 10be in sediment trap samples and holocene sediments collected along a transect in the northeastern pacific indicate that the removal of these nuclides from the ocean is greatly influenced by boundary scavenging more than 35 of the 230th at least 70 of the 231pa and as much as 85 of the 10be fluxes collected by sediment traps at a nearshore site located 120 km off shore are supplied by lateral transport of the dissolved nuclides from the open ocean these findings are consistent with the hypothesis that boundary scavenging is proportional to the oceanic residence times of the nuclides 10 40 y for 230th 100 y for 231 pa and 1000 y for 10be results of this study indicate that particle flux is a principal factor influencing scavenging of 230th 231pa and 10be from the water column the marine geochemistry of 10be in ocean margins is fundamentally different from that in the open ocean scavenging of 10be occurs throughout the water column at the margin area in this study in contrast to the pattern of 10be being removed only in the surface waters and then remineralized at depth in the open ocean aluminosilicate may be a major phase removing 10be from the water column in the open ocean but not at ocean margins nuclide accumulation rates in the underlying holocene sediments are all higher than the corresponding fluxes collected by sediment traps several possibilities that could account for this observation include downslope sediment transport deployment of the traps during a period when the particle flux was not representative of long term average conditions and scavenging of the nuclides from near bottom waters the high accumulation rate of authigenic mn in some holocene sediments which can be attributed to redox cycling of mn may have caused near bottom scavenging of 230th and 231pa as well as certain other trace elements such as ba cu and zn

26al 10be and u th isotopes in blake outer ridge sediments implications for past changes in boundary scavenging we have investigated the distributions of 26 al 10 be u th isotopes and stable 27 al and 9 be in core ch88 11p 30 40pn 74 41pw 3337 m from the blake outer ridge bor in the western north atlantic an area that is characterized by high terrigenous input results show authigenic 26 al 27 al of 6 2 8u10 314 atom atom authigenic 10 be 9 be of 0 5 2 6u10 38 atom atom 6 0 2 1 8u10 6 atoms g of 26 al and 5 3 15 1u10 8 atoms g of 10 be in the core over the last glacial interglacial cycle these values as well as total 230 thex 232 th and 10 be 9 be ratios were all at their minima during the last glacial maximum lgm reflecting intensified terrestrial influx to the area aluminosilicate material clays in this influx preferentially scavenged 230 th over the two other particle reactive nuclides 26 al and 10 be such that their boundary scavenging during lgm followed the order 230 ths 10 bes 26 al as opposed to 10 bev 230 ths 26 al in the holocene they appear at variance with the order 10 bes 26 alw 230 th as would be predicted from the relative particle reactivities of the three species these scavenging characteristics point to 10 be 26 al as a potentially more suitable proxy for paleoproductivity than 10 be 230 thex mass balance considerations for 26 al and 10 be show a five fold lgm to holocene increase in deep water circulation in the study area with little change in ocean productivity except during the deglaciation when it increased noticeably fl 2001 elsevier science b v all rights reserved

habitable periglacial landscapes in martian mid latitudes subsurface permafrost environments on mars are considered to be zones where extant life could have survived for the identification of possible habitats it is important to understand periglacial landscape evolution and related subsurface and environmental conditions many landforms that are interpreted to be related to ground ice are located in the martian mid latitudinal belts this paper summarizes the insights gained from studies of terrestrial analogs to permafrost landforms on mars the potential habitability of martian mid latitude periglacial landscapes is exemplarily deduced for one such landscape that of utopia planitia by a review and discussion of environmental conditions influencing periglacial landscape evolution based on recent calculations of the astronomical forcing of climate changes specific climate periods are identified within the last 10 ma when thaw processes and liquid water were probably important for the development of permafrost geomorphology no periods could be identified within the last 4 ma which met the suggested threshold criteria for liquid water and habitable conditions implications of past and present environmental conditions such as temperature variations ground ice conditions and liquid water activity are discussed with respect to the potential survival of highly specialized microorganisms known from terrestrial permafrost we conclude that possible habitable subsurface niches might have been developed in close relation to specific permafrost landform morphology on mars these would have probably been dominated by lithoautotrophic microorganisms i e methanogenic archaea

solifluction rates processes and landforms a global review abstract field data on the rates of solifluction and associated parameters are compiled from the literature in an attempt to evaluate factors controlling the spatial variability in solifluction processes and landforms with special attention on the climate solifluction relationship the analyzed data originate from 46 sites over a wide range of periglacial environments from antarctic nunataks to tropical high mountains solifluction broadly defined as slow mass wasting resulting from freeze thaw action in fine textured soils involves several components needle ice creep and diurnal frost creep originating from diurnal freeze thaw action annual frost creep gelifluction and plug like flow originating from annual freeze thaw action and retrograde movement caused by soil cohesion the depth and thickness of ice lenses and freeze thaw frequency are the major controls on the spatial variation in solifluction processes near the warm margin of the solifluction affected environment diurnal freeze thaw action induces shallow but relatively rapid movement of a superficial layer 5 10 cm thick on average often creating the thin stone banked lobes typically seen on tropical high mountains in addition to diurnal movement annual frost creep and gelifluction may occur on slopes with soil climates of seasonal frost to warm permafrost dislocating a soil layer shallower than 60 cm at a rate of centimeters per year and eventually producing medium size solifluction lobes in high arctic cold permafrost regions two sided freezing can induce plug like flow of a soil mass 60 cm or thicker the correlation between process and landform suggests that the riser height of lobes is indicative of the maximum depth of movement and prevailing freeze thaw type climate change may result in new different ground freezing conditions thereby influencing the surface velocity and maximum depth of soil movement soil moisture and topography also control solifluction high moisture availability in the seasonal freezing period enhances diurnal freeze thaw action and subsequent seasonal frost heaving the latter contributes to raising the moisture content of the thawed layer and promotes gelifluction during the thawing period the slope angle defines the upper limit of the surface velocity of solifluction a diagram correlating the potential frost creep with the actual surface velocity permits an inter site comparison of the relative magnitude of solifluction components physically based modelling of periglacial slope evolution requires synthetic and more detailed field monitoring and laboratory simulations of solifluction processes

periglacial mass wasting landforms on mars suggestive of transient liquid water in the recent past insights from solifluction lobes on svalbard abstract on earth periglacial solifluction is a slow mass wasting process related to freeze thaw activity we compare the morphology of small scale lobate features on mars to solifluction lobes in svalbard to constrain their processes of formation the analysis is based on high resolution satellite imagery of mars hirise 25 cm pxl aerial images of svalbard with a similar spatial resolution hrsc ax 20 cm pxl acquired through an air campaign in summer 2008 and ground truth obtained during two summer expeditions in 2009 and 2011 on svalbard we present a detailed study of two crater environments on mars displaying two types of lobate forms characterized as sorted clast banked and non sorted lobes on both svalbard and mars such lobes typically occur as clusters of overlapping risers lobe fronts pointing to differential velocities in the soil the martian small scale lobes have well defined arcuate risers and lobe treads surface lobe widths range between 14 and 127 m and tread lengths between 13 and 105 m riser height is estimated to be approximately 1 5 m the lobes on mars share the plan view morphology of solifluction lobes on svalbard and their morphometry is within the range of values of terrestrial solifluction lobes the lobes are distinct from permafrost creep landforms such as rock glaciers we show the results of a survey of 53 hirise images covering latitudes between 59 n and 81 n similar to svalbard the studied lobate features on mars occur in close spatial proximity to gullies and thermal contraction polygons the widespread distribution of the lobate forms in the northern hemisphere and their close association to ground ice and gullies are best explained by mass wasting processes related to frost creep gelifluction and or plug like flow this suggests a protracted process thousand to several thousands of years of freeze thaw activity at the northern high latitudes on mars age constraints on lobe deposits and superposition relationships with gullies and polygons imply a process involving liquid water within the last few million years

possible pingos and a periglacial landscape in northwest utopia planitia hydrostatic closed system pingos are small elongate to circular ice cored mounds that are perennial features of some periglacial landscapes the growth and development of hydrostatic pingos is contingent upon the presence of surface water freezing processes and of deep continuous ice cemented permafrost other cold climate landforms such as small sized polygonal patterned ground also may occur in the areas where pingos are found on mars landscapes comprising small elongate to circular mounds and other possible periglacial features have been identified in various areas including utopia planitia where water is thought to have played an important role in landscape evolution despite the importance of the martian mounds as possible markers of water most accounts of them in the planetary science literature have been brief and or based upon viking imagery we use a high resolution mars orbiter camera image eo300299 and superposed mars orbiter laser altimeter data tracks to describe and characterise a crater floor landscape in northwest utopia planitia 64 8 n 292 7 w the landscape comprises an assemblage of landforms that is consistent with the past presence of water and of periglacial processes this geomorphological assemblage may have formed as recently as the last episode of high obliquity a similar assemblage of landforms is found in the tuktoyaktuk peninsula of northern canada and other terrestrial cold climate landscapes we point to the similarity of the two assemblages and suggest that the small roughly circular mounds on the floor of the impact crater in northwest utopia planitia are hydrostatic pingos like the hydrostatic pingos of the tuktoyaktuk peninsula the origin of the crater floor mounds could be tied to the loss of ponded local water permafrost aggradation and the evolution of a sub surface ice core

the subantarctic and polar fronts in relation to deep water masses through the southwestern atlantic the two principal fronts within the antarctic circumpolar current acc the subantarctic front saf and the polar front pf are investigated with respect to their spatial patterns and relations to deep water masses from the northern drake passage to the western and southern argentine basin observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters east of drake passage the width of the polar frontal zone pfz increases rapidly when the saf turns sharply northward as a part of the falkland malvinas current while the pf remains oriented mainly toward the northeast found within this region of the pfz are mesoscale eddies the upper layers of which consist of subantarctic mode water from the pacific the contrasts in upper layer water properties that identify the saf can be traced the entire length of the falkland current to the brazil falkland confluence zone and then southward to the southern argentine basin there the saf turns eastward and later but perhaps not always merges with the pf north of ewing bank to form a single intense current core strongly influenced by bottom topography at times this eastward current loops southward through a gap in the falkland ridge into the georgia basin thereby supplying relatively warm and salty subantarctic water to the antarctic zone east of the gap the two fronts become separated and are once again distinct features in the vicinity of the islas orcadas rise at depth within drake passage and the western scotia sea the saf and pf are not lateral boundaries between distinct water masses but are instead identified by enhanced vertical displacements of property isopleths with the northward turn of the saf east of drake passage a thick layer of circumpolar deep water cdw is advected over the falkland plateau into the argentine basin there it is joined by waters entering the argentine basin via a deep spreading route through the georgia basin denser cdw deep water from the weddell sea and episodically deep water from the southeastern pacific ocean together these waters form a northward flow off the patagonian shelf that extends from the sea surface to the bottom most of which turns back toward the south with the falkland current return also flowing south along the seaward side of the falkland current return well away from the western boundary is the main core of north atlantic deep water nadw detatched masses of nadw are observed within the cdw at the western boundary as well as within the acc south of the saf in the south central argentine basin

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

distribution of mid latitude ground ice on mars from new impact craters new impact craters at five sites in the martian mid latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice near infrared spectra of the largest example confirm this composition and repeated imaging showed fading over several months as expected for sublimating ice thermal models of one site show that millimeters of sublimation occurred during this fading period indicating clean ice rather than ice in soil pores our derived ice table depths are consistent with models using higher long term average atmospheric water vapor content than present values craters at most of these sites may have excavated completely through this clean ice probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself

deposition and degradation of a volatile rich layer in utopia planitia and implications for climate history on mars 1 we investigate the surface morphology of a study area in western utopia planitia mars which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes polygonally fractured ground and thermokarst like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters we observe a latitudinal dependence of the degradation of this mantling deposit larger depressions whose floors reveal the underlying basement rocks cover a higher fraction of the total terrain in the southern part of the study area than in the northern part indicating a more intense degradation of the mantle in the south all depressions have an asymmetric cross section in north south direction interpreted to be the result of the different solar radiation on differently oriented slopes on the basis of our morphological observations we develop a conceptual model for landscape evolution in western utopia planitia it involves subaerial deposition of a layered ice rich mantle and its subsequent degradation by polygon formation and sublimation a terrestrial analog to the polygonally fractured mantling deposit and its thermokarst like depressions is the siberian ice complex or yedoma which consists of subaerial ice rich deposits and is connected to nonglaciated landscapes with highly continental cold climatic environmental conditions our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western utopia however the young age of the deposition and degradation implies climatic excursions in the very recent past on mars

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores