diffusive loss of argon in response to melt vein formation in polygenetic impact melt breccias many planetary surfaces in the solar system have experienced prolonged bombardment with each impact new rocks can be assembled that incorporate freshly generated impact melts with fragments of older rocks some breccias can become polygenetic containing multiple generations of impact melt products and can potentially provide important insights into the extensive bombardment history of a region however the amount of chronological information that can be extracted from such samples depends on how well the mineral isotopic systems of geochronometers can preserve the ages of individual melt generations without being disturbed by younger events we model the thermal evolution of impact melt veins and the resulting loss of ar from k bearing phases common in impact melt breccias to assess the potential for preserving the 40ar 39ar ages of individual melt generations our model results demonstrate that millimeter scale clast free melt veins cause significant heating of adjacent host rock minerals and can cause detectable ar loss in contact zones that are generally thinner than and at most about the same thickness as the vein width the incorporation of cold clasts in melt veins reduces the magnitudes of heating and ar loss in the host rocks and ar loss can be virtually undetectable for sufficiently clast rich veins quantitative evidence of the timing of impacts as measured with the 40ar 39ar method can be preserved in polygenetic impact melt breccias particularly for those containing mm scale bodies of clast bearing melt products

seasonal activity and morphological changes in martian gullies abstract recent studies of martian dune and non dune gullies have suggested a seasonal control on present day gully activity the timing of current gully activity especially activity involving the formation or modification of channels which commonly have been taken as evidence of fluvial processes has important implications regarding likely gully formation processes and necessary environmental conditions in this study we describe the results of frequent meter scale monitoring of several active gully sites by the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro the aim is to better assess the scope and nature of current morphological changes and to provide improved constraints on timing of gully activity on both dune and non dune slopes our observations indicate that 1 gully formation on mars is ongoing today and 2 the most significant morphological changes are strongly associated with seasonal frost and defrosting activity observed changes include formation of all major components of typical gully landforms although we have not observed alcove formation in coherent bedrock these results reduce the need to invoke recent climate change or present day groundwater seepage to explain the many martian gullies with pristine appearance

chloride bearing materials in the southern highlands of mars chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing spectrally distinct surface deposits consistent with chloride bearing materials have been identified and mapped using data from the 2001 mars odyssey thermal emission imaging system these deposits are found throughout regions of low albedo in the southern highlands of mars geomorphologic evidence from orbiting imagery reveals these deposits to be light toned relative to their surroundings and to be polygonally fractured the deposits are small

continental inputs of beryllium to the oceans abstract an understanding of the geochemistry of the cosmogenic radioisotope 10 be t 1 2 1 5 my and the stable isotope 9 be is necessary for the development of their use in deep sea sediments as a geochronometer and as a monitor of variations in cosmogenic nuclide production we examined these isotopes in oceanic regions strongly influenced by input of continental materials the effects of atmospheric aerosols were studied through examination of the water column chemistry of the mediterranean a basin strongly influenced by saharan dust while salinity transects through the amazon and ganges brahmaputra estuaries were used to investigate riverine fluxes to the oceans these results were used to quantify riverine and eolian fluxes they indicate that eolian dust is probably the most significant source of 9 be to the oceans changes in 10 be 9 be in the marine sedimentary record which are not associated with radioactive decay or variability in 10 be production can thus result from local or regional changes in dust inputs

transport processes induced by metastable boiling water under martian surface conditions liquid water on the martian surface is expected to be metastable owing to low atmospheric pressure experiments at martian conditions reveal that water and briny flows induce grain saltation and slope destabilization with geomorphic consequences

can the aluminum and titanium contents of ocean sediments be used to determine the paleoproductivity of the oceans in the central equatorial pacific settling particles collected with sediment traps have al ti values greater than those of a typical crustal source the al ti values of the sediment trap material are not well correlated with either the flux of organic carbon or with total particle mass suggesting that this ratio cannot be used as a simple index of paleoproductivity however the al ti values of some trap samples are more than 3 times the ratio for typical crustal materials indicating a noncrustal source of excess al numerical analysis using linear programming indicates that the excess al is associated with opal and that this biological component carries as much as 1200 ppm of al because of the low particulate fluxes of lithogenic material in the equatorial pacific and the relatively high opal content of equatorial sediment trap material opal appears to be the predominant conveyor of al to the equatorial sediments our sediment trap al ti values are similar to ratios previously measured in equatorial sediments suggesting that measurements of this element pair in ocean sediments may be an indicator of opal rain to the seafloor the particle reactive nature of al and ti means their ratios in sediments may be relatively insensitive to opal preservation or other diagenetic processes however the al ti values of raining particles are highly sensitive to the relative proportion of opal and lithogenic material where opal lithogenic ratios are less than 20 the al ti values are indistinguishable from a crustal source ratio in addition the amount of excess al associated with opal in settling particles may be a function of the concentration of al in the water column and of the processes that fractionate dissolved al and ti these issues must be evaluated before the al ti values of ocean sediments can be used as a reliable proxy of opal flux to the seafloor

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

the biogeochemistry of aluminum in the pacific ocean abstract vertical distributions and horizontal surface transects of dissolved and particulate al at several locations in the pacific ocean are presented here concentrations of dissolved al in the pacific range from 0 3 to 5 nmol kg in the surface waters from 0 1 to 1 nmol kg in mid depths and from 0 5 to 2 nmol kg in the deep waters from these data and published data from other regions it is evident that al has a unique oceanic chemistry relative to that of other metals external sources and rapid particle scavenging throughout the water column are the major controls on dissolved al distributions in the oceans vertical profiles generally exhibit a surface maximum a mid depth minimum and increasing concentrations toward the sediment water interface this suggests two sources of dissolved al one to the surface waters and one to the deep waters concentrations of dissolved al in surface waters are lowest within the eutrophic low salinity california current 0 3 1 nmol kg and increase westwardly into the subtropical gyre of the north pacific 5 nmol kg values in the south pacific gyre are fivefold lower these horizontal trends indicate that the primary source of dissolved al to the surface waters of the central pacific is from eolian input dissolved al supplied by rivers to the eastern north pacific appears to be rapidly scavenged in estuaries and or the highly productive coastal region the source of dissolved al to the deep waters is not known but could be due to a flux out of the sediments or a remineralization process suspended particulate al concentrations increase with depth at all stations and decrease with distance from the ocean boundary surface values range from 1 5 nmol kg near shore to 0 3 nmol kg in the central gyres of the pacific deep water concentrations range from 22 nmol kg near shore to 4 nmol kg in the north pacific central gyre and decrease to 1 3 nmol kg in the south pacific central gyre observed distributions indicate that suspended particulate al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting nepheloid layer out from ocean boundary regions particle residence times estimated are consistent with other reported values

two pulses of seasonal activity in martian southern mid latitude recurring slope lineae rsl abstract recurring slope lineae rsl are narrow dark features that incrementally lengthen down steep low albedo slopes when temperatures are warm subsequently fade and reoccur annually rsl could be caused by wet wet triggered debris or dry granular flow mechanisms we have classified 190 candidate and confirmed southern mid latitude sml rsl sites using six mars years of high resolution imagery to provide new constraints on rsl flow mechanisms we demonstrate that at least three confirmed sml rsl sites have at least two pulses of active lengthening we have also confirmed that rsl start much earlier than previously thought the first sml rsl pulse occurs from solar longitude ls 187 6 to 226 14 or 62 32 sols while the second pulse occurs from ls 260 26 to 329 29 or 113 89 sols even with the newly observed early pulse the total sml rsl active duration is still shorter than rsl found elsewhere on the planet no significant seasonal variations exist between the dominant n nw w slope face orientations the central peak of hale crater appears to be anomalous in that it has a third pulse that rejuvenates rsl late in the southern summer ls 330 1 to 348 19 or 48 26 sols these additional rsl pulses of activity add increased complexity to rsl behavior follow up missions may be needed to unambiguously discriminate between rsl mechanisms

a hydrological continuum in permafrost environments the morphological signatures of melt driven hydrology on earth and mars abstract this paper examines relationships between the morphology of cold desert hydrological features and the water sources and it relates the formation of diagnostic deposits and erosion patterns to environmentally controlled patterns of discharge in particular three sets of landforms found in the mcmurdo dry valleys of antarctica are compared to similar features on mars antarctic streams rivers to amazonian valleys terrestrial gullies to martian gullies and water tracks to recurring slope lineae similarities in landform morphology are highlighted for each set hydrological characteristics are aggregated or calculated and they are shown to scale comparably across the landforms for the terrestrial and martian groups accordingly a hydrological continuum is proposed linking the magnitude and the persistence of water sources in cold desert environments to flow response and the formation of diagnostic landforms this concept provides a framework for examining the relationships between climate hydrology and geomorphology in the cold desert environments of these two worlds

recurring slope lineae in equatorial regions of mars the presence of liquid water is a requirement of habitability on a planet possible indicators of liquid surface water on mars include intermittent flow like features observed on sloping terrains these recurring slope lineae are narrow dark markings on steep slopes that appear and incrementally lengthen during warm seasons on low albedo surfaces the lineae fade in cooler seasons and recur over multiple mars years recurring slope lineae were initially reported to appear and lengthen at mid latitudes in the late southern spring and summer and are more common on equator facing slopes where and when the peak surface temperatures are higher here we report extensive activity of recurring slope lineae in equatorial regions of mars particularly in the deep canyons of valles marineris from analysis of data acquired by the mars reconnaissance orbiter we observe the lineae to be most active in seasons when the slopes often face the sun expected peak temperatures suggest that activity may not depend solely on temperature although the origin of the recurring slope lineae remains an open question our observations are consistent with intermittent flow of briny water such an origin suggests surprisingly abundant liquid water in some near surface equatorial regions of mars dark streaks that appear on the surface of mars during warm seasons have been observed at the mid latitudes and tentatively attributed to the flow of briny water imagery from the mars reconnaissance orbiter over multiple mars years suggests that these seasonally active features are also present in equatorial regions where liquid surface water is not expected

tracing dust input to the global ocean using thorium isotopes in marine sediments thoromap continental dust input into the ocean atmosphere system has significant ramifications for biogeochemical cycles and global climate yet direct observations of dust deposition in the ocean remain scarce the long lived isotope thorium 232 232th is greatly enriched in upper continental crust compared to oceanic crust and mid ocean ridge basalt like volcanogenic material in open ocean sediments away from fluvial and ice rafted sources of continental material 232th is often assumed to be of predominantly eolian origin in conjunction with flux normalization based on the particle reactive radioisotope thorium 230 230th 232th measurements in marine sediments are a promising proxy for dust accumulation in the modern and past ocean here we present thoromap a new global data compilation of 230th normalized fluxes of 232th after careful screening we derive dust deposition estimates in the global ocean averaged for the late holocene 0 4 ka and the last glacial maximum lgm 19 23 ka thoromap is compared with dust deposition estimates derived from the community climate system model ccsm3 and ccsm4 two coupled atmosphere land ocean and sea ice models model data correlation factors are 0 63 ccsm3 and 0 59 ccsm4 in the late holocene and 0 82 ccsm3 and 0 83 ccsm4 in the lgm thoromap is the first compilation that is built on a single specific proxy for dust and that exclusively uses flux normalisation to derive dust deposition rates

slope elevation and thermal inertia trends of martian recurring slope lineae initiation and termination points multiple possible processes occurring on coarse sandy slopes abstract recurring slope lineae rsl are dark linear features on the surface of mars that advance incrementally downslope fading and re growing annually numerous hypotheses have been proposed to explain rsl formation including wet models that involve liquid water or brines and dry mechanisms involving liquid free mass wasting or solid vapor phase changes that trigger granular flow in part hypotheses to explain rsl formation rely on observations of the physical characteristics of the slopes on which rsl are present to determine if rsl exhibit physical characteristics typical of one particular formation mechanism we examined the initiation and termination points of over 10 000 rsl across 16 confirmed rsl sites to determine their slope elevation orientation and thermal inertia rsl typically form within an envelope of high elevations at each mapping site are oriented equatorward and west and have hillslope thermal inertia values consistent with sand and gravel notably the rsl begin and end at slopes above within and below the angle of repose required to trigger and sustain dry granular flows sensitivity testing indicates that these slope values are not a result of pixel scale noise discontinuous rsl are observed at several study sites the slope and thermal inertia values of the rsl as well as these additional geomorphic observations of discontinuous dark features are not consistent with the characteristics of dry flows in which continuous dust avalanches begin within the dynamic angle of repose and terminate within the static angle of repose although rsl are found to be common on coarse sandy and rocky slopes not all sandy slopes in rsl regions that are close to the angle of repose contain rsl we conclude that mechanisms other than dry mass wasting are needed to explain all of the observed geomorphic characteristics of rsl source and termination points

hirise observations of recurring slope lineae rsl during southern summer on mars abstract recurring slope lineae rsl are active features on mars that might require flowing water most examples observed through 2011 formed on steep equator facing slopes in the southern mid latitudes they form and grow during warm seasons and fade and often completely disappear during colder seasons but recur over multiple mars years they are recognizable by their incremental growth relatively low albedo and downhill orientation we examined all images acquired by hirise during l s 250 10 slightly longer than southern summer l s 270 360 of mars years 30 31 03 2011 10 2011 and supplemented our results with data from previous studies to better understand the geologic context and characteristics of rsl we also confirmed candidate and likely sites from previous studies and discovered new rsl sites we report 13 confirmed rsl sites including the 7 in mcewen et al mcewen et al 2011 science 333 6043 740 743 the observed seasonality latitudinal and slope orientation preferences and themis brightness temperatures indicate that rsl require warm temperatures to form we conclude that rsl are a unique phenomenon on mars clearly distinct from other slope processes that occur at high latitudes associated with seasonal co 2 frost and episodic mass wasting on equatorial slopes however only 41 82 out of 200 of the sites that present apparently suitable conditions for rsl formation steep equator facing rocky slopes with bedrock exposure in the southern mid latitudes 28 60 s contain any candidate rsl with confirmed rsl present only in 7 13 sites of those locations significant variability in abundance size and exact location of rsl is also observed at most sites indicating additional controls such as availability of water or salts that might be playing a crucial role

iron manganese and lead at hawaii ocean time series station aloha temporal variability and an intermediate water hydrothermal plume trace metal clean techniques were used to sample hawaii ocean time series hot station aloha on seven occasions between november 1998 and october 2002 on three occasions full water column profile samples were obtained on the other four occasions surface and near surface euphotic zone profiles were obtained together with three other published samplings this site may have been monitored for dissolved 0 4 or 0 2 m fe more frequently than any other open ocean site in the world low fe concentrations 2500 m the concentrations we observe 0 4 0 5 nmol kg 1 are significantly lower than some other deep north pacific stations but are similar to values that have been reported for a station 350 miles to the northeast we attribute these low deepwater values to transport of low fe antarctic bottom water into the basin and a balance between fe regeneration and scavenging in the deep water near surface waters have higher fe levels than observed in the lower euphotic zone significant temporal variability is seen in near surface fe concentrations ranging from 0 2 0 7 nmol kg 1 we attribute these surface fe fluctuations to variable dust deposition biological uptake and changes in the mixed layer depth this variability could occur only if the surface layer fe residence time is less than a few years and based on that constraint it appears that a higher percentage of the total fe must be released from north pacific aerosols compared to north atlantic aerosols surprisingly significant temporal variability and high particulate fe concentrations are observed for intermediate waters 1000 1500 m these features are seen in the depth interval where high 3he from the nearby loihi seamount hydrothermal fields has been observed the total fe 3he ratio implies that the hydrothermal vents are the source of the high and variable fe the vertical profile of mn at aloha qualitatively resembles other north pacific mn profiles with surface and intermediate water maxima but there are some significant quantitative differences from other reported profiles the 0 4 m mn concentration is highest near the surface decreases sharply in the upper 500 m then shows an intermediate water maximum at 800 m and then decreases in the deepest waters these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations it appears that there is a significant mn gradient throughout the water column from hot towards the northeast compared to the first valid oceanic pb data for samples collected in 1976 pb at aloha in 1997 1999 shows decreases in surface waters and waters shallower than 200 m pb concentrations in central north pacific surface waters have decreased by a factor of 2 during the past 25 yr from 65 to 30 pmol kg 1 surface water pb concentrations in the central north atlantic and central north pacific are now comparable we attribute the surface water pb decrease to the elimination of leaded gasoline in japan and to some extent by the u s and canada we attribute most of the remaining pb in pacific surface waters to asian emissions more likely due to high temperature industrial activities such as coal burning rather than to leaded gasoline consumption a 3 year mixed layer time series from the nearby hale aloha mooring site 1997 1999 shows that there is an annual cycle in pb with concentrations 20 higher in winter months this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher pb in the upper thermocline pb concentrations double between the surface and 200 m from 200 m to the bottom pb concentrations decrease to levels of 5 9 pmol kg 1 near the bottom for most of the water column thermocline and deepwater pb concentrations do not appear to have changed significantly during the 23 yr interval

petrological and thermal histories of a lunar breccia 73217 as inferred from pyroxene crystallization sequences exsolution phenomena and pyroxene geothermometry electron probe microanalyses x ray diffraction studies and pyroxene geothermometry of blue gray breccia 73217 indicate a record of an early plutonic period and a later thermal event the breccia contains two domains one breccia a contains coarse orthopyroxene clasts whereas the other breccia b contains coarse pigeonite clasts pyroxene trends deduced from pyroxene clasts from breccias a and b are analogous to the early and late fractionation stages respectively of terrestrial basic layered intrusions minor element compositions of both augite and ca poor pyroxenes from breccias a and b vary continuously with feo mgo feo ratio optical and x ray observations reveal that pyroxene clasts show a great variety of exsolution textures but that individual pyroxene grains show relatively simple and less intensive exsolution patterns there is no overlap in mineral compositions of pyroxenes as well as plagioclase and ilmenite clasts between breccias a and b these characteristics are consistent with a model that the coarse mineral clasts of both breccias a and b possibly originated from the same relatively small layered intrusion i e breccia a being derived from an early stage 1100 1060 c 20 c and b from a later stage of fractionation 1060 1050 c both breccias experienced a later common annealing event 1040 1070 c

the effects of continental margins and water mass circulation on the distribution of dissolved aluminum and manganese in drake passage a total of 232 samples were analyzed for concentrations of dissolved aluminum al and manganese mn in drake passage both al and mn were extremely low similar to 0 3 and 0 1 nm respectively in the surface layer of the middle drake passage most likely due to limited input and biological uptake scavenging elevated al 14 nm and mn 2 nm over the south american continental shelf are related to land run off whereas elevated concentrations 1 nm and 2 nm respectively near the antarctic peninsula are most likely related to sediment re suspension re suspension of sedimentary particles and pore waters influences the distribution of al and mn over the continental slopes on both sides of drake passage the influence of the continental margins and accumulated dust input potentially explains the higher al observed eastward in the atlantic section of the southern ocean in the northern drake passage elevated al similar to 0 8 nm and mn similar to 0 3 nm near the seafloor are most likely the result of bottom sediment re suspension by the relatively strong currents in the deep southern drake passage sediment re suspension associated with the inflow of weddell sea deep water appears to cause elevated al 1 nm and mn similar to 0 4 nm in the deep northern drake passage north atlantic deep water brings in elevated al and southeast pacific deep slope water brings in the signature of pacific hydrothermal vents elevated mn and delta he 3 were correlated in this water layer and are most likely originating from the volcanically active ridges in the pacific ocean

possible closed system pingo and ice wedge thermokarst complexes at the mid latitudes of utopia planitia mars abstract on earth hydrostatic or closed system pingos csps are perennial ice cored mounds formed by the freeze thaw cycling of water when or as thermokarst lakes lose their water by drainage or evaporation the mounds vary in shape from circular or sub circular to elongate are sub kilometre in their long axes and may reach decametres in height often the mounds show summit depressions radial fractures and single tiers or benches as the csps degrade small scale debris flows or slumps occur end stage degradation typically exhibits debris laden ramparts elevated metres above the surrounding terrain typically the csps originate and develop where deep and continuous permafrost is ice rich i e infused with excess ice as it is in the tuktoyaktuk coastlands of northern canada mid to northern alaska and northeast russia in these areas or regions the terrain often is populated by a thermokarst lakes and alases thermokarst lake basins absent of water b fields of small scale ice wedge polygons either low centred or high centred relative to the polygon margins and c melt water filled or emptied polygon margin troughs or corner pits individual troughs and pits connected by means of the local topographical gradient comprises beaded stream systems or networks here we report describe and discuss a suite of candidate csps at the mid latitudes of utopia planitia up 35 50 n 80 115 e the morphologies scale and height of the martian mounds as well as the surface textures and characteristics landscape features and spatially associated landforms are consistent with the csps observed in ice rich regions on earth the up mounds are nested in or reside adjacent to flat floored possibly thermokarstic depressions small scale polygons some of which exhibit low or high centres relative to their margins and connected polygon margin depressions or pits that mirror beaded stream systems in ice rich terrain on earth the size frequency distribution of craters in our study region precludes a surface younger than 100 ma thus the csp like mounds in up and the pre mound periglacial revisions of the landscape presented by us may be markers of freeze thaw cycling that occurred much earlier in the amazonian epoch than most of the current discussions about periglaciation in up suggest

a case study of recurring slope lineae rsl at tivat crater implications for rsl origins abstract the origin or origins of recurring slope lineae rsl on mars are enigmatic these seasonally dark linear features correlate with temperatures appropriate for liquid water or brine they also progress slowly downslope and fade disappear when inactive similar to shallow subsurface groundwater flows that wick moisture to the surface if liquid water or brine does indeed flow so near the surface and is sufficiently dilute it could have profound implications for the modern habitability of mars we present the results of a case study at tivat crater in the southern midlatitudes that provide new insights into rsl including their potential origins at tivat these results include comprehensive maps of rsl extents in four mars years detailed rsl evolution across one growth season rockfall markings and dust devil tracks in two well constrained years rsl and rockfall markings which are more widely distributed than rsl fade at the same time suggesting a fading mechanism that acts across tivat based on relative albedo analyses rsl and rockfall markings at tivat fade because their host slopes darken which is most easily explained by the widespread removal of dust such a dry fading mechanism would favor a dry origin for rsl we also present a wide range of other rsl observations including highly variable growth pooling like behavior where slopes shallow to roughly 30 and total areal extents that decrease each year across a span of five years we discuss the implications of these observations for various rsl formation models including a new conceptual model that primarily mobilizes dust taken together our observations seem to favor a dry mass movement origin for rsl at tivat but significant challenges remain for each examined model

seasonal slumps in juventae chasma mars dark topographic slumps several meters wide tens of meters in length and up to a meter in depth are observed on the slopes of juventae chasma jc valles marineris vm mars these slumps usually originate near the terminal points of recurring slope lineae rsl near their initiation points the slumps have topographic depressions due to the removal of materials near their lowermost reaches new materials are deposited in lobes over the course of three mars years ten active slumps have been observed in jc all of which formed in or near the same season areocentric longitude ls 0 120 mars color imager marci observations show low altitude atmospheric obscurations confined within the topography of the vm and jc in the seasons when the slumps form in one instance data from the compact reconnaissance imaging spectrometer for mars crism and marci show evidence of h2o ice in the atmospheric obscuration likely due to the formation of a low level afternoon cloud above a dust storm or mixing of condensate clouds with a diffuse dust cloud the presence of atmospheric obscurations with h2o ice near times when the slumps form is intriguing but no direct evidence currently exists to support that they aid in slump formation further monitoring of this site will help establish if rsl and or atmospheric events play a role in the creation of contemporary slumps

constraining oceanic dust deposition using surface ocean dissolved al we use measurements of ocean surface dissolved al a global biogeochemical elemental cycling bec ocean model and the global dust entrainment and deposition dead model to constrain dust deposition to the oceans our al database contains all available measurements with best coverage in the atlantic vertical profiles and seasonal data exist in limited regions observations show that surface dissolved al is distributed similarly to the dust deposition predicted by dead and other models there is an equatorial atlantic al maximum that decreases toward higher latitudes there are high al concentrations in the mediterranean sea and the arabian sea and low concentrations in the pacific and the southern ocean the ocean basins maintain more distinct al profiles than fe profiles in the upper ocean consistent with a weaker biological influence on al than fe the bec predicted surface dissolved al compares relatively well with observations the al distribution reflects the combined effects of al input from dust and al removal by particle scavenging and biological uptake by diatoms model observed biases suggest a southward shift of maximum dust deposition compared to current dust model predictions dead appears to overestimate deposition north of 30 n in the pacific and to underestimate deposition south of 30 n observed al concentrations and the ocean model predicted surface al lifetime provide a semi independent method to estimate oceanic dust deposition this technique indicates that dead may overestimate dust deposition to the north equatorial atlantic but underestimate in other atlantic regions the southern ocean and the arabian sea however spatial variations in aerosol al solubility may also contribute to the model observation mismatch our results have implications for all dust borne ocean nutrients including fe and demonstrate the potential of marine geochemical data to constrain atmospheric aerosol deposition fields

equatorial locations of water on mars improved resolution maps based on mars odyssey neutron spectrometer data abstract we present a map of the near subsurface hydrogen distribution on mars based on epithermal neutron data from the mars odyssey neutron spectrometer the map s spatial resolution is approximately improved two fold via a new form of the pixon image reconstruction technique we discover hydrogen rich mineralogy far from the poles including 10 wt water equivalent hydrogen weh on the flanks of the tharsis montes and 40 wt weh at the medusae fossae formation mff the high weh abundance at the mff implies the presence of bulk water ice this supports the hypothesis of recent periods of high orbital obliquity during which water ice was stable on the surface we find the young undivided channel system material in southern elysium planitia to be distinct from its surroundings and exceptionally dry there is no evidence of hydration at the location in elysium planitia suggested to contain a buried water ice sea finally we find that the sites of recurring slope lineae rsl do not correlate with subsurface hydration this implies that rsl are not fed by large near subsurface aquifers but are instead the result of either small

laboratory studies of perchlorate phase transitions support for metastable aqueous perchlorate solutions on mars abstract perchlorate salts recently discovered on mars are known to readily absorb water vapor from the atmosphere and deliquesce into the aqueous phase at room temperature here we study the deliquescence crystalline solid to liquid transition and efflorescence liquid to crystalline solid transition of perchlorate salts at low temperatures relevant to mars a raman microscope and environmental cell were used to determine the deliquescence relative humidity drh and efflorescence relative humidity erh of naclo 4 and mg clo 4 2 as a function of temperature and hydration state we find that the deliquescence of anhydrous naclo 4 is only slightly dependent on temperature and occurs at 38 rh the drh of naclo 4 h 2 o increases with decreasing temperature from 51 at 273 k to 64 at 228 k the drh of mg clo 4 2 6h 2 o also increases with decreasing temperature from 42 at 273 k to 64 at 223 k the efflorescence of both naclo 4 and mg clo 4 2 salt solutions occurs at a lower rh than deliquescence due to the kinetic inhibition of crystallization for all temperatures studied the erh values of naclo 4 and mg clo 4 2 are 13 and 19 respectively these results indicate perchlorate salts can exist as metastable supersaturated solutions over a wide range of rh and temperature conditions summer diurnal temperature and relative humidity cycles at low latitudes on mars could allow the surface salts to be aqueous for several hours per day

experimental investigation of the stability and evaporation of sulfate and chloride brines on mars abstract we have investigated the evaporation of concentrated magnesium and ferrous sulfate and magnesium and ferric chloride brines as possible sources for liquid water on the surface of mars with special emphasis on the effect of freezing and crystallization of solutions experimental evaporation rates range from 0 04 mm h 1 for 25 wt mgso4 at 271 9 k to 0 19 mm h 1 for 18 wt feso4 at 270 5 k for chloride solutions evaporation rates range from 0 09 mm h 1 for 40 wt fecl3 at 261 34 k to 0 43 mm h 1 for 20 wt mgcl2 at 267 2 k these evaporation rates are significantly lower than for pure water i e 1 35 mm h 1 at 273 k using the pitzer ion interaction model we show that the decrease in evaporation rate is due to lower water activity in concentrated solutions down to 0 91 for saturated mgso4 and 0 97 for saturated feso4 at their eutectic temperatures for saturated mgcl2 and fecl3 the calculated water activities are 0 57 and 0 60 at their respective eutectic temperatures in addition we show that the water activity drops significantly when salts are crystallizing down to 0 17 and 0 21 for mgso4 and feso4 respectively our experiments and calculations show that the water activity and evaporation rate are dependent on the hydration state of the precipitating salt which is in turn controlled by the temperature and the relative humidity low hydration state salts precipitate at lower humidity with lower evaporation rates our study suggests that martian brines could remain stable for longer periods of time at low temperatures and low humidity than previously thought brines formed from these salts would be a more stable source of water on mars thus beneficial for any putative martian life past and or present

recurring slope lineae and chlorides on the surface of mars recurring slope lineae rsl are dark streaks that appear on steep slopes on the martian surface while their apparent movement suggests liquid flow remote sensing studies have not found evidence of fresh water some rsl have been observed at temperatures below the freezing point of water if liquid water is present therefore it is likely in the form of a brine in contrast to studies of other dissolved species such as perchlorates this study explores the possibility of chloride as a dissolved component in rsl using thermal emission imaging system themis decorrelation stretch dcs products and hirise images the presence of chloride lag deposits at rsl sites was assessed on a global scale though faint potential chloride signatures were detected at two rsl sites emissivity spectra showed no significant variation from surrounding geology no other rsl showed indications of chlorides using a simple model the upper limit of chloride required for positive detection is estimated to be 30 15 g m2 the total brine required to produce a detectable lag deposit is 80 35 ml m2 at a eutectic concentration of calcium chloride over the last climate cycle brine production could be up to 8 3 x 10 4 ml m2 yr without producing a detectable lag deposit based on these results we conclude that chloride abundance is not the limiting factor for rsl generation rsl could be produced by capillary wicking of chloride rich brines to the surface where small amounts of brine produce lag deposits below the detection limits of currently orbiting instruments

dissolved aluminium cycling in the northern equatorial and subtropical gyre region of the indian ocean abstract dissolved aluminium hereafter dal concentrations have been determined on 34 full vertical water column profiles sampled along the two separate geotraces india transects gi 01 and gi 06 to understand the biogeochemical controls on dal distribution in the northern the bay of bengal the andaman sea and the arabian sea equatorial and subtropical gyre region of the indian ocean al released due to the partial dissolution of and or al desorption from the suspended lithogenic sediments supplied in a huge amount to the bay of bengal bob waters by the ganga brahmaputra g b river system indian peninsular rivers and sediment resuspension from the continental shelf and slope predominantly controls the dal distribution in the bob and results in an overall increase in the dal concentrations throughout the water column towards the northern bob and the eastern coast of india considering the steady state balance between the dal input from the lithogenic sediment flux in the upper water column and first order scavenging removal of dal the fractional solubility of al from the lithogenic sediments in the bob surface waters is estimated to be in the range of 1 1 4 7 advection of indonesian sea surface waters through the strait of malacca and dal input from the partial dissolution of resuspended terrigenous sediments sourced from the insular shelf of the nicobar islands set major controls on the dal distribution in the surface and upper thermocline waters of the southern andaman sea and the southern bob region near the nicobar islands rapid renewal of and vertical mixing in the deeper waters 1000 m relative to scavenging removal of dal results in near uniform dal concentrations 3 7 nm in the deeper waters at the center of the southern andaman sea in the south eastern arabian sea the continental outflow of mineral dust and advection of dal enriched bay of bengal surface waters control the dal distribution in the surface water layer dal in the surface waters of the equatorial indian ocean during the late winter sampling period of the gi 06 cruise is predominantly determined by the mixing between dal rich surface waters of the southern bob and relatively dal depleted surface waters of the southern arabian sea under the influence of the northeast monsoon current the scavenging residence time of dal in the deep waters of the equatorial indian ocean is estimated using a 1 d scavenging advection diffusion model and found to be in the range of 92 141 years deposition of australian dust and advection of indonesian throughflow water translates to the dal enrichment in the upper water column 3500 m advects across the ninety east ridge from the western australian basin to bring the dal rich waters to the northern end of the central indian ocean basin

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

dissolved aluminium in the mediterranean abstract three vertical profiles of dissolved al and nutrients are reported from the eastern basin of the mediterranean profiles of al concentrations resemble those of the nutrient elements except that a proportionally higher residual concentration remains in the surface layer concentrations of al in the surface water inflow from the north atlantic which contains between 10 and 20 nm around gibraltar are elevated to 55 59 and 75 nm at the stations occupied calculations indicate that these concentrations are probably produced by dissolution al from aeolian dust and advective mixing of al rich deep waters into the surface layer balanced by a biologically associated removal process the al removed from the surface layer redissolves in the deep water to raise al concentrations to about 160 nm samples were also recovered from anoxic deep brines in the tyro and bannock basins in the brines al concentrations fall to about 15 nm while si concentrations approach 270 nm

distribution of aluminium in waters of the north east atlantic 25 n to 35 n abstract dissolved al concentrations from the ne atlantic between 25 n and 35 n off the coast of nw africa range from 16 nm to 32 nm in a well mixed surface layer extending to 150 m depth increasing towards the maximum of the saharan dust plume mediterranean outflow water is detected as a high al anomaly corresponding to the salinity signal of the mediterranean water other than in surface and mediterranean waters al concentrations are invariant with depth but increase from 6 nm to 11 nm towards the continental margin the magnitude of the dissolved al signal in the surface layer is compatible with dissolution of al from the highest of present estimates of dust input to this area comparison with data from other areas indicates that al cannot be cycled through the oceans in parallel to silica as has been previously suggested

coupled al si geochemistry in an ocean general circulation model a tool for the validation of oceanic dust deposition fields 1 we introduced the marine cycle of al into a geochemical ocean general circulation model in order to assess the potential of modeled surface ocean dissolved al as a tracer for dust input to the world ocean the geochemical cycles of si and al have been coupled through the dynamics of diatoms aluminum is added to the ocean by deposition of continental aerosols followed by partial dissolution of the aluminosilicate fraction dissolved al interacts with suspended siliceous particles according to a reversible first order scavenging reaction dust fields are provided by atmospheric general circulation models a database of marine dissolved al measurements was collated the ocean model results for two different dust deposition fields andersen et al 1998 mahowald et al 1999 are compared with these data the model confirms a solubility of the aluminosilicate fraction between 1 5 and 3 0 modeled levels of dissolved al in surface waters mirror the delivery of dust to the surface ocean comparing dissolved al distributions resulting from the two different dust fields yields significant differences in ocean dissolved al distributions which reflect a differential contribution of individual source regions model results suggest a significant overestimation of the north african arabian desert source region for the dust field after mahowald et al 1999 dust input to the central pacific ocean appears to be of the correct order of magnitude this approach allows for a direct comparison of dust fields and proposes an independent check of the underlying parameterization of uplift transport and deposition of dust

aluminium in the northwest atlantic abstract a series of profiles between woods hole and bermuda has been measured on board ship for al the extrema in the upper waters can be explained by the accumulation of aeolian inputs in the thin summer mixed layer the depletion of the underlying winter water by scavenging during the spring bloom and the enrichment of the subtropical mode 18 c water by aeolian accumulation during winter and local convection before the spring bloom the pronounced minimum at mid depth is associated with the antarctic intermediate water and the underlying labrador sea med water complex presumably the aaiw and the med water are depleted by the ageing effect on this short residence time element during their transit to the area the lsw is formed from surface waters containing a large component of arctic waters extremely depleted in al advected south in the east greenland current the linear increase to the bottom is caused by mixing of enriched lower north atlantic deep water with the depleted bottom water and lsw cores the enrichment in the deep water appears to be produced by the entrainment of high al waters from the north european shelf by the gyre in the norwegian greenland sea and its injection into the denmark straits overflow waters in a manner recently described for the radiocaesium releases from the windscale reprocessing plant on the irish sea an additional contribution probably comes from the shelf north of iceland

nitrogen fixation in the south atlantic gyre and the benguela upwelling system 1 dinitrogen n2 fixation is recognized as an important input of new nitrogen n to the open ocean gyres contributing to the export of organic matter from surface waters however very little n2 fixation research has focused on the south atlantic gyre where dust deposition of iron fe an important micronutrient for diazotrophs is seasonally low recent modeling efforts suggest that n2 fixation may in fact be closely coupled to and greatest in areas of denitrification as opposed to the oceanic gyres one of these areas the benguela upwelling system lies to the east of the south atlantic gyre in this study we show that n2 fixation in surface waters across the south atlantic gyre was low overall 1 5 nmol n l 1 d 1 with highest rates seen in or near the benguela upwelling system up to 8 nmol n l 1 d 1 surface water dissolved fe dfe concentrations were very low in the gyre 0 3 nm or lower while soluble reactive phosphorus srp concentrations were relatively high 0 15 m n2 fixation rates across the entire sampling area were significantly positively correlated to dfe but also to srp and no3 thus high no3 concentrations did not exclude n2 fixation in the upwelling region which provides evidence that n2 fixation may be occurring in previously unrecognized waters specifically near denitrification zones however the gene encoding for a nitrogenase component nifh was not detected from known diazotrophs at some stations in or near the upwelling where n2 fixation was greatest suggesting the presence of unknown diazotrophs in these waters

dust deposition to the surface waters of the western and central north pacific inferred from surface water dissolved aluminum concentrations 1 dissolved al was determined on similar to 3500 surface water samples collected in the nw pacific during the 2002 intergovernmental oceanographic commission ioc contaminant baseline survey in addition dissolved al was determined on samples collected at 9 vertical stations occupied along the cruise track surface water al distributions when converted to annual mineral dust deposition measures and brown 1996 imply extremely low depositions mean values 0 3 g m 2 yr 1 to surface waters of the subarctic gyre despite the atmospheric transport of large amounts of mineral dust across this region from the desert regions of china the calculated deposition values are also much lower than the 1 10 g m 2 yr 1 predicted for this region by the gesamp model duce et al 1991 the lowest mineral dust depositions correspond to the high nutrient low chlorophyll hnlc region of the nw pacific which implies that the biogeochemical status of this region is the result of low atmospheric micronutrient input similar to other hnlc regions in the subtropical gyre the al derived dust deposition mean values 0 1 0 6 g m 2 yr 1 agrees well with the 1 g m 2 yr 1 predictions of the gesamp model enriched concentrations of dissolved al in the coastal waters near kauai from fluvial sources indicate the potential role of remote high islands in adding reactive trace elements to the nearby surface waters in the vertical profiles elevated dissolved al concentrations 4 8 nm were found to correspond to the potential density of the western pacific subtropical mode waters which form in the recirculation zone of the kuroshio

aerosol iron and aluminum solubility in the northwest pacific ocean results from the 2002 ioc cruise dust aerosol samples were collected across the western north pacific ocean during may june 2002 samples were analyzed for soluble aerosol fe ii fe ii fe iii and al as well as major cations and anions the aerosol samples were leached using a 10 second exposure to either filtered surface seawater or ultrapure deionized water yielding a measure of the instantaneous soluble fraction a variety of analytical methods were employed including 57fe isotope dilution high resolution icp ms energy dispersive x ray fluorescence graphite furnace aas ion chromatography and the felume chemiluminescent technique fe was found to be more soluble in ultrapure deionized water leaches especially during periods of higher dust concentrations fe solubility averaged 9 8 in ultrapure water leaches and 6 5 in seawater leaches significant correlations were found between both soluble aerosol fet and soluble fe ii concentrations and aerosol acidity however the percentages of soluble aerosol fet and fe ii did not correlate with aerosol acidity we also did not observe significant correlations between total and soluble aerosol fe concentrations and the concentrations of either particulate fe or dissolved fe in surface waters

the geochemistry of don juan pond evidence for a deep groundwater flow system in wright valley antarctica abstract don juan pond djp antarctica is one of the most unusual surface waters on earth because of its cacl 2 rich composition to investigate the evolution of pond waters during closed basin evaporation and to understand the source of brines responsible for the chemistry of djp we apply a newly developed low temperature aqueous model in the na k ca mg cl system to djp by modeling the closed basin evaporation of djp and comparing ionic ratios between djp surface water deep groundwater shallow groundwater and other surface chemistries in wright valley we find that djp is best explained by upwelling deep groundwater as opposed to recent hypotheses proposing shallow groundwater sources the early closed basin evolution of brines in our model accurately predicts observed chemistries in djp however late stage closed basin evaporation produces mg k rich brines and salts that do not match the cacl 2 rich brine in djp based on groundwater inflow rates to djp we estimate that even the most concentrated brines in djp have undergone closed basin evaporation for less than a year to explain the observed lack of mg 2 and k accumulation in djp over time and the surprisingly young age for the brines we deduce that djp is a localized upwelling from a regional groundwater flow through system in which evaporated djp brines are recycled back into the subsurface over yearly timescales the existence of a regional groundwater flow system beneath djp has implications for water and solute budgets in cold desert ecosystems and may provide clues for the formation of groundwater and aqueous flows on mars

characteristics of the numerous and widespread recurring slope lineae rsl in valles marineris mars abstract recurring slope lineae rsl are narrow 0 5 5 m dark features on mars that incrementally lengthen down steep slopes fade in colder seasons and recur annually these traits suggest that liquid water is flowing in the shallow subsurface of mars today here we describe high resolution imaging science experiment hirise observations of rsl within valles marineris vm we have identified 239 candidate and confirmed rsl sites within all the major canyons of vm with the exception of echus chasma about half of all the globally known rsl locations occur within vm and the areal density of rsl on coprates montes appears to be the greatest on the planet vm rsl are heterogeneously distributed as they are primarily clustered in certain areas while being conspicuously absent in other locations that appear otherwise favorable rsl have been found on many of the interior layered deposits ilds within vm such ild rsl appear to traverse bedrock instead of regolith like all other rsl forty six of the vm rsl sites show incremental lengthening and exhibit similar behavior in most of the canyons of vm but the rsl duration at one site in juventae chasma is significantly reduced furthermore the lengthening seasonality depends solely on slope orientation with typical vm rsl on a given slope lengthening for 42 74 of a mars year there are always rsl lengthening within vm regardless of the season if rsl are caused by water such a long active season at hundreds of vm rsl sites suggests that an appreciable source of water must be recharging these rsl thermophysical modeling indicates that a melting temperature range of 246 264 k is needed to reproduce the seasonal phenomenology of the vm rsl suggesting the involvement of a brine consisting of tens of wt salt the mechanism s by which rsl are recharged annually remain uncertain overall gaining a better understanding of how rsl form and recur can benefit the search for extant life on mars and could provide details about an in situ water resource

distribution of be al se and bi in the surface waters of the western north atlantic and caribbean abstract the mixed layer distributions of several trace elements have been determined along a detailed transect from rhode island to the panama canal when taken together with a new and existing profile data from the north atlantic and north pacific some general inferences emerge as to the processes controlling their concentrations in the surface waters the large enrichments in be observed in the upper waters of the north atlantic relative to the north pacific appear to be sustained mainly by fluvial inputs those of se are derived from atmospheric transport aluminium and bi also appear to have an aeolian source in the sargasso sea however in the tropical eastern pacific the al input may be fluvial on this cruise be al and the se species were analyzed on board ship within a few hours of collection the demonstration that this is feasible opens up the prospect of the application of large scale chemical hydrography to the study of the processes controlling the distribution and water column variability of trace elements in the oceans

the water content of recurring slope lineae on mars observations of recurring slope lineae rsl from the high resolution imaging science experiment have been interpreted as present day seasonally variable liquid water flows however orbital spectroscopy has not confirmed the presence of liquid h2o only hydrated salts thermal emission imaging system themis temperature data and a numerical heat transfer model definitively constrain the amount of water associated with rsl surface temperature differences between rsl bearing and dry rsl free terrains are consistent with no water associated with rsl and based on measurement uncertainties limit the water content of rsl to at most 0 5 3 wt in addition distinct high thermal inertia regolith signatures expected with crust forming evaporitic salt deposits from cyclical briny water flows are not observed indicating low water salinity if any and or low enough volumes to prevent their formation alternatively observed salts may be preexisting in soils at low abundances i e near or below detection limits and largely immobile these rsl rich surfaces experience 100 k diurnal temperature oscillations possible freeze thaw cycles and or complete evaporation on time scales that challenge their habitability potential the unique surface temperature measurements provided by themis are consistent with a dry rsl hypothesis or at least significantly limit the water content of martian rsl

the western qaidam basin as a potential martian environmental analogue an overview the early martian environment is interpreted as warmer and wetter before a significant change in its global climatic conditions irreversibly led to the current hyper arid environments this transition is one of the most intriguing processes of martian history the extreme climatic change is preserved in the salt deposits desiccated landscapes and geomorphological structures that were shaped by the evaporation of water however until a manned journey to mars is feasible many martian materials morphological structures and much of its evolutionary history will continue to be poorly understood in this regard searching and investigating martian analogues is still meaningful to find an earth environment with a whole set of martian structures distributed at a scale comparable to mars is even more important to test landing crafts and provide optimized working parameters for rovers the western qaidam basin in north tibetan plateau is such a martian analogue the area harbors one of the most extreme hyper arid environments on earth and contains a series of ancient lakes that evaporated at different evolutionary stages during the rise of the tibetan plateau large quantities of salts and geomorphological features formed during the transition of warmer and wet to colder and dry conditions provide unique references to study the modern martian surface and interpret the orbital data we present numerous similarities and results of investigations that suggest the qaidam basin as a potential analogue to study modern geomorphic processes on mars and suggest that this is an essential site to test future mars sample return missions

aluminium in the south atlantic steady state distribution of a short residence time element the aluminium concentrations of water samples from 18 hydrographic profiles and 35 surface samples in the south atlantic were determined on board ship during leg iii of the south atlantic ventilation experiment save the observed surface water distributions range 0 5 to 57 nm are though to arise from the partial dissolution of eolian transported continental dusts coupled with limited lateral transport by prevailing surface currents in the deep water the greatest enrichments are observed coincident with the depth of the lower north atlantic deep water the similarity between the al si ratios in this water mass in both the south and north atlantic is taken as evidence that no significant al additions are being made to this water during its transit the lower al concentrations observed in the water masses of antarctic origin approximately 3 nm are consistent with their formation in areas of limited dust input the somewhat higher values observed in the antarctic bottom water suggest that the shelf component of this water mass may have elevated al concentrations

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

dissolved al in and ce in the eastern indian ocean and the southeast asian seas in comparison with the radionuclides 210pb and 210po to carry out comparative geochemical investigation of refractory and reactive metals in different oceanic settings covering different s characteristics productivity dissolved oxygen profiles water and sediment discharge etc we have determined the vertical profiles of dissolved 0 04 m al in and ce as well as 210pb and 210po in the eastern indian ocean from 40 s in the southern ocean to 8 n in the bay of bengal and the southeast asian seas in the antarctic circumpolar region the concentrations of these refractory metals are very low presumably due to very low the atmospheric input and intensified scavenging resemblance in the vertical profiles of these metals is often seen in some other stations however there are also significant differences among their distributions for example in the magnitude of surface enrichment caused by the external input from eolian and fluvial coastal sources comparison of al distributions in surface waters with those of atmospherically derived 210pb suggests the relative importance of eolian input over fluvial coastal sources fluvial and coastal input appears to be insignificant for dissolved in but may be important for ce the mean residence time of al in the surface mixed layer was estimated to be 2 years which is similar to that of 210pb in the intermediate and deep waters the concentrations of each element vary with depth and location the range of variation is in the order of al ce in depending upon particle reactivity although dissolved al decreases along the water trajectory by particle scavenging variations of dissolved in and ce are relatively small which may be due to less scavenging for both elements compared with significantly high 4 pm dissolved ce throughout the water column in the bay of bengal dissolved al concentration remains low suggesting that it has higher affinity to particles and hence is scavenged by sinking particulate matter this is consistent with the observation that the dissolved al in the antarctic intermediate water aaiw decreases from 4 to 6 nm in the 30 s perth basin to 0 7 nm in the 10 s west australia basin along its trajectory using the chlorofluorocarbons cfcs ventilation age of aaiw fine 1993 the mean residence time of al in the intermediate and deep waters in the eastern indian ocean is estimated to be 17 yr approximately the same as that of 210pb 10 15 yr in the semiclosed basins of southeast asia the distributions of al in and ce are also very unique in the south china sea there is a strong sediment source for dissolved in and ce during the deepwater passage through the luzon strait

surface water dissolved aluminum and titanium tracers for specific time scales of dust deposition to the atlantic surface water distributions of dissolved al dal and dissolved ti dti were investigated along a meridional atlantic transect and related to dust deposition estimates in the zone of saharan dust deposition highest dal concentrations occurred in the tropical salinity minimum and suggest increasing al dissolution from saharan aerosols with wet deposition by contrast the dti distribution is not related to precipitation but agrees with the pattern of annual dust deposition in the zone of patagonian dust deposition elevated dti concentrations contrasted with decreased dal concentrations indicating excess dal scavenging onto biogenic particles in surface waters estimated residence times range from months to years for dal and are 10 times higher for dti this suggests that dal reflects seasonal changes in dust deposition while dti is related to longer temporal scales however spatial variations in input and removal processes complicate the quantification of dust deposition from surface water concentrations

thermal history recorded by the apollo 17 impact melt breccia 73217 abstract lunar breccia 73217 is composed of plagioclase and pyroxene clasts originating from a single gabbronorite intrusion mixed with a silica rich glass interpreted to represent an impact melt a study of accessory minerals in a thin section from this breccia 73217 52 identified three different types of zircon and anhedral grains of apatite which represent distinct generations of accessory phases and provide a unique opportunity to investigate the thermal history of the sample equant anhedral zircon grains that probably formed in the gabbronorite referred to as type 1 have consistent u pb ages of 4332 7 ma a similar age of 4335 5 ma was obtained from acicular zircon type 2 grains interpreted to have formed from impact melt a polycrystalline zircon aggregate type 3 occurs as a rim around a baddeleyite grain and has a much younger age of 3929 10 ma similar to the 3936 17 ma age of apatite grains found in the thin section a combined apatite type 3 zircon age of 3934 12 ma is proposed as the age of the serenitatis impact event and associated thermal pulse x ray mapping and electron probe analyses showed that ti is inhomogeneous in the zircon grains on the sub micrometer scale however model temperatures estimated from shrimp analyses of ti concentration in the 10 m diameter spots on the polished surfaces of type 1 and type 2 zircons range between about 1300 and 900 c respectively whereas ti concentrations determined for the type 3 zircon are higher at about 1400 1500 c a combination of u pb ages ti concentration data and detailed imaging and petrographic studies of the zircon grains shows that the gabbronorite parent of the zircon clasts formed shortly before the 4335 5 ma impact which mixed the clasts and the felsic melt and projected the sample closer to the surface where fast cooling resulted in the crystallization of acicular zircon type 2 the 3934 12 ma serenitatis event resulted in partial remelting of the glass and formation of polycrystalline zircon type 3 this event also reset the u pb system of apatite formed merrillite coronas around some apatite grains and probably re equilibrated some pyroxenes in the clasts although there have been arguments for pre 3 9 ga impacts based on other types of samples the age of the acicular zircon at 4335 5 ma provides the first evidence of impact melt significantly predating the lunar cataclysm our data combined with other chronological results demonstrate the occurrence of pre 3 9 ga impacts on the moon and suggest that the lunar impact history consisted of a series of intense bombardment episodes interspersed with relatively calm periods of low impact flux

atmospheric deposition of soluble trace elements along the atlantic meridional transect amt abstract we briefly review the role of atmospheric deposition measurements within the atlantic meridional transect amt programme and then go on to present new data on the soluble concentrations of a range of trace metals fe al mn ti zn v ni and cu and major ions in aerosols collected along the amt transect the results allow us to identify emission sources of the trace metals particularly in terms of the relative importance of anthropogenic versus crustal sources we identify strong gradients in concentrations and deposition for both crustal and anthropogenically sourced metals with much higher inputs to the north atlantic compared to the south atlantic reflecting stronger land based emission sources in the northern hemisphere we suggest anthropogenic sources of ni and v may include an important component from shipping we consider the extent to which these gradients are reflected in surface water concentrations of these metals based on the geotraces water column trace metal data we find there is a clear difference in the concentrations of surface water dissolved al and fe between the north and south atlantic gyres reflecting atmospheric inputs however for mn v or ni higher inputs to the north atlantic compared to the south atlantic are not clearly reflected in their water column concentrations

diffusion barriers at mars surface conditions salt crusts particle size mixtures and dust the diffusion coefficient of water vapor through porous media at mars like surface conditions is measured for a variety of complex particle size distributions and soil compositions micron sized dust simulants mixtures of sand and dust sized particles and salt encrusted sand are examined we find that while the value of the diffusion coefficient d can be reduced by up to a factor of 10 for heavily salt encrusted soils minimum observed d 0 4 0 04 cm 2 s 1 moderate amounts of salt only produce minor reductions in d mechanical packing of pure dust can lower d by a similar amount while mixtures of dust with sand sized particles produce at most a factor of 4 reduction we conclude that present day processes of aeolian redistribution moderate levels of salt encrustation and volatile loss from dirty ice would be inefficient at producing soil deposits and lags on mars that pose significant barriers to diffusion therefore subsurface ice deposits that are thermally unstable would not be protected against sublimative loss by such materials

a deep groundwater origin for recurring slope lineae on mars the recurring slope lineae on mars have been hypothesized to originate from snow melting deliquescence dry flow or shallow groundwater except for the dry flow origin these hypotheses imply the presence of surficial or near surface volatiles placing the exploration and characterization of potential habitable environments within the reach of existing technology here we present observations from the high resolution imaging science experiment heat flow modelling and terrestrial analogues which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere at depths of approximately 750 m spatial correlation between recurring slope lineae source regions and multi scale fractures such as joints and faults in the southern mid latitudes and in valles marineris suggests that recurring slope lineae preferably emanate from tectonic and impact related fractures we suggest that deep groundwater occasionally surfaces on mars in present day conditions observations and heat flow modelling suggest that briny groundwater surfacing from fractures forms recurring slope lineae on mars

an aeolian grainflow model for martian recurring slope lineae abstract recurring slope lineae rsl on mars have been enigmatic since their discovery their behavior resembles a seeping liquid but sources of water remain puzzling this work demonstrates that the properties of rsl are consistent with observed behaviors of martian and terrestrial aeolian processes specifically rsl are well explained as flows of sand that remove a thin coating of dust observed rsl properties are supportive of or consistent with this model which requires no liquid water or other exotic processes but rather indicates seasonal aeolian behavior these settings and behaviors resemble features observed by rovers and also explain the occurrence of many slope lineae on mars that do not meet the strict definition of rsl this indicates that rsl can be explained simply as aeolian features other processes may add complexities just as they could modify the behavior of any sand dune

spectral constraints on the formation mechanism of recurring slope lineae 1 recurring slope lineae rsl exhibit multiple lines of evidence for a wet origin in the southern midlatitudes they form on steep equator facing slopes that are warm during southern summer the formation temperature seasonality and other geomorphic characteristics are suggestive of water related formation perhaps dense brines we examined compact reconnaissance imaging spectrometer for mars images of all confirmed rsl sites from the southern midlatitudes and the equatorial region to understand the composition of rsl and or rsl associated deposits we did not detect any spectral signature attributable to water however a distinct and consistent spectral signature is observed at most sites indicating enhanced abundances or distinct grain sizes of both ferric and ferrous minerals in rsl related materials compared to adjacent non rsl slopes like the rsl themselves the strength of these signatures varies as a function of season the observed spectral changes may indicate removal of a fine grained surface component during rsl flow precipitation of ferric oxides and or wetting of the substrate

new observations of martian southern mid latitude recurring slope lineae rsl imply formation by freshwater subsurface flows abstract southern mid latitude sml recurring slope lineae rsl are narrow 0 5 5 m dark albedo features that emanate from bedrock and incrementally lengthen down steep slopes that preferentially face the equator we observe that sml rsl begin lengthening prior to southern summer at a solar longitude ls of 245 11 when mars global surveyor thermal emission spectrometer tes derived near maximum surface temperatures are 296 5 k and mars reconnaissance orbiter mars climate sounder mcs and mars odyssey thermal emission imaging system themis derived mid afternoon surface temperatures are 273 k sml rsl continue to lengthen for 104 38 sols with an average near maximum surface temperature of 298 5 k the sml rsl then stop lengthening at ls 314 12 when mid afternoon surface temperatures drop below 273 k they remain dark for another 116 41 sols until ls 16 14 as surface temperatures continue to fall although the rsl recharge mechanism remains unknown our observation that the vast majority of rsl lengthen only when mid afternoon surface temperatures are 273 k supports the hypothesis that they are formed by shallow subsurface liquid water flows without significant freezing point depression the number and length of rsl at multiple sites increased dramatically following the mars year 28 globe encircling dust storm we interpret this increase to be due to warmer subsurface temperatures created by a dust laden greenhouse effect that may be unique to the southern mid latitudes near ls 270 therefore sml rsl flow is quite sensitive to ground temperature and may only occur under favorable orbital parameters when mean insolation during the rsl lengthening season is above that of the current southern mid latitude mean insolation value this value is currently at a peak that has not been attained for the last 100 ka meanwhile the rsl poor northern mid latitude mean insolation is near a minimum and has a value 27 lower than the southern value if sml rsl are indeed formed by shallow subsurface freshwater flows then they may be some of the best locations on mars to explore for extant life

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

sulfate deposition in subsurface regolith in gusev crater mars excavating into the shallow martian subsurface has the potential to expose stratigraphic layers and mature regolith which may hold a record of more ancient aqueous interactions than those expected under current martian surface conditions during the spirit rover s exploration of gusev crater rover wheels were used to dig three trenches into the subsurface regolith down to 6 11 cm depth road cut the big hole and the boroughs a high oxidation state of fe and high concentrations of mg s cl and br were found in the subsurface regolith within the two trenches on the plains between the bonneville crater and the foot of columbia hills data analyses on the basis of geochemistry and mineralogy observations suggest the deposition of sulfate minerals within the subsurface regolith mainly mg sulfates accompanied by minor ca sulfates and perhaps fe sulfates an increase of fe2o3 an excess of sio2 and a minor decrease in the olivine proportion relative to surface materials are also inferred three hypotheses are proposed to explain the geochemical trends observed in trenches 1 multiple episodes of acidic fluid infiltration accompanied by in situ interaction with igneous minerals and salt deposition 2 an open hydrologic system characterized by ion transportation in the fluid subsequent evaporation of the fluid and salt deposition and 3 emplacement and mixing of impact ejecta of variable composition while all three may have plausibly contributed to the current state of the subsurface regolith the geochemical data are most consistent with ion transportation by fluids and salt deposition as a result of open system hydrologic behavior although sulfates make up 20 wt of the regolith in the wall of the boroughs trench a higher hydrated sulfate than kieserite within the boroughs or a greater abundance of sulfates elsewhere than is seen in the boroughs wall regolith would be needed to hold the structural water indicated by the water equivalent hydrogen concentration observed by the gamma ray spectrometer on odyssey in the gusev region copyright 2006 by the american geophysical union

surface ocean lower atmosphere interactions in the northeast pacific ocean gyre aerosols iron and the ecosystem response 1 here we report measurements of iron and aluminum in surface and subsurface waters during late march and late may of 2001 on transects between central california and hawaii a large cloud of asian dust was detected during april 2001 and there was a clear signal in surface water iron due to aerosol deposition on the may transect iron and aluminum concentrations increased synchronously by 0 5 and 2 nm along the southern portion of the transect which includes the hawaii ocean time series hot station from background values in march 0 1 to 0 2 nm fe these changes occurred in a ratio that is close to the crustal abundance ratio of the metals which indicates a soil aerosol source a vertical profile of dissolved iron was also measured at the hot station in late april and this profile also shows a large increase near the surface direct observations of aerosol iron concentration at mauna loa observatory on hawaii indicate that aerosol concentrations were significantly lower than climatological values during this period soil aerosol concentrations along the transect were estimated using the real time navy aerosol analysis and prediction system naaps the naaps results show a large meridional gradient with maximum concentrations in the boundary layer north of 30 n however the deposition of iron and aluminum to surface waters was highest south of 25 n near hawaii there were only weak signals in the ecosystem response to the aerosol deposition

subsurface ice on mars with rough topography high latitude ground ice on mars discovered by the gamma ray spectrometer suite is thought to be thermally stable owing to the presence of vapor in the martian atmosphere however local slopes can alter surface and subsurface temperatures substantially and hence allow ground ice to persist at locations where it would otherwise be unstable global statistics of the topography of mars are computed processed and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive this slope distribution is convolved with a new thermal model for the dependence of subsurface ice on slope to produce a prediction of the global ice distribution that includes the effect of topographic roughness in the highest latitudes slopes reduce the amount of buried ice while in lower latitudes the ice fraction increases widening the geographic boundary of the ice table at the high latitudes where ice is stable beneath horizontal ground the estimated reduction of ice is small compared to the existing ice volume areas in the midlatitudes with high surface roughness that have previously been predicted to be ice free are predicted to contain quantities of ice that may be detectable at present and accessible in the future slopes cause ground ice to be stable to latitudes of about 25 degrees in both hemispheres including for example areas within the northern olympus mons aureole deposits hecates tholus and hellas basin ice is unstable at equatorial latitudes even when accounting for surface slopes

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

spectral evidence for hydrated salts in recurring slope lineae on mars transient streaks that appear seasonally on martian slopes are consistent with brine flows but evidence of water or salts has been lacking analysis of spectral data reveals hydrated salts associated with the streaks confirming a briny origin

dissolution of nontronite in chloride brines and implications for the aqueous history of mars increasing evidence suggests the presence of recent liquid water including brines on mars brines have therefore likely impacted clay minerals such as the fe rich mineral nontronite found in martian ancient terrains to interpret these interactions we conducted batch experiments to measure the apparent dissolution rate constant of nontronite at 25 0 c at activities of water ah 2o of 1 00 0 01 m cacl 2 or nacl 0 75 saturated nacl or 3 00 mol kg 1 cacl 2 and 0 50 5 00 mol kg 1 cacl 2 experiments at ah 2o 1 00 0 01 m cacl 2 were also conducted at 4 0 c 25 0 c and 45 0 c to measure an apparent activation energy for the dissolution of nontronite apparent dissolution rate constants at 25 0 c in cacl 2 containing solutions decrease with decreasing activity of water as follows 1 18 10 12 9 10 14 mol mineral m 2 s 1 ah 2o 1 00 2 36 10 13 3 1 10 14 mol mineral m 2 s 1 ah 2o 0 75 2 05 10 14 2 9 10 15 mol mineral m 2 s 1 ah 2o 0 50 similar results were observed at 25 0 c in nacl containing solutions 1 89 10 12 1 10 13 mol mineral m 2 s 1 ah 2o 1 00 1 98 10 13 2 3 10 14 mol mineral m 2 s 1 ah 2o 0 75 this decrease in apparent dissolution rate constants with decreasing activity of water follows a relationship of the form log k diss 3 70 0 20 ah 2o 15 49 where k diss is the apparent dissolution rate constant and ah 2o is the activity of water the slope of this relationship 3 70 0 20 is within uncertainty of that of other minerals where the relationship between dissolution rates and activity of water has been tested including forsteritic olivine log r 3 27 0 91 ah 2o 11 00 olsen et al 2015 and jarosite log r 3 85 0 43 ah 2o 12 84 dixon et al 2015 where r is the mineral dissolution rate this result allows prediction of mineral dissolution as a function of activity of water and suggests that with decreasing activity of water mineral dissolution will decrease due to the role of water as a ligand in the reaction apparent dissolution rate constants in the dilute nacl solution 1 89 10 12 1 10 13 mol mineral m 2 s 1 are slightly greater than those in the dilute cacl 2 solutions 1 18 10 12 9 10 14 mol mineral m 2 s 1 we attribute this effect to the exchange of na with ca in the nontronite interlayer an apparent activation energy of 54 6 1 0 kj mol was calculated from apparent dissolution rate constants in dilute cacl 2 containing solutions at temperatures of 4 0 c 25 0 c and 45 0 c 2 33 10 13 1 3 10 14 mol mineral m 2 s 1 4 0 c 1 18 10 12 9 10 14 mol mineral m 2 s 1 25 0 c and 4 98 10 12 3 8 10 13 mol mineral m 2 s 1 45 0 c the greatly decreased dissolution of nontronite in brines and at low temperatures suggests that any martian nontronite found to be perceptibly weathered may have experienced very long periods of water rock interaction with brines at the low temperatures prevalent on mars with important implications for the paleoclimate and long term potential habitability of mars

formation of recurring slope lineae by liquid brines on present day mars 1 recurring slope lineae rsl are small scale seasonal flow features identified by mars reconnaissance orbiter that present several interesting characteristics such as an albedo contrast seasonal dependence and a strong preference for equator facing slopes all of these characteristics strongly suggest a thermally driven mechanism such as a liquid triggered or dominated flow here we investigate the possibility that these features are formed by melting of brines of various compositions via a combination of thermodynamic and kinetic numerical models results suggest that a solution with a freezing temperature of 223 k can best reproduce the observed seasonality relatively high surface evaporation rates at the rsl locations make the flows quickly disappear over a single season our model reproduces well the seasonality of rsl and can explain the preference for equator facing slopes suggesting that brine flows and therefore liquids are possible on a small time and space scale today on mars however if the rsl are indeed formed by brines it may indicate that a recharge mechanism is active in order to maintain a source of brine over even short geological timescales which would have important implications for the martian water cycle

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

sublimation rate of ice under simulated mars conditions and the effect of layers of mock regolith jsc mars 1 1 we have studied the sublimation of ice buried beneath 200 mm of jsc mars 1 model regolith under simulated mars conditions as expected even thin layers of regolith cause large decreases in sublimation rate up to one order of magnitude at 50 mm when the depth of the regolith was 50 to 200 mm we detected water desorbing from the overlying layers for which we were able to determine a desorption coefficient of 1 45 0 5 10 3 h 1 after allowing for the effect of desorption we found that the diffusion coefficient for water vapor through our regolith is 1 74 0 70 10 4 m2 s 1 in excellent agreement with theoretical values we thus find that a 1 m thick layer of ice buried below a meter of regolith resembling jsc mars 1 on mars at 235 k would last 800 years

topographic measurements of slope streaks on mars abstract slope streaks are enigmatic actively forming albedo features occurring on slopes in high albedo low thermal inertia dust rich equatorial regions on mars they are a specifically martian phenomenon with no direct analogs on the earth their morphology suggests that the streaks are initiated at their upslope tips and propagate down to their termini however the physical mechanism of their formation is uncertain we performed a large series of measurements of slopes associated with slope streaks using stereo pairs of high resolution orbital images obtained by hirise camera and generated several digital elevation models for selected streaks we found that 1 slopes at the upslope streak tips range widely however there is a strong indication that streaks can be initiated only on slopes steeper than 20 2 slopes of the streak termini show an even wider range with some streaks terminating at slopes as steep as their tips while others propagate all the way down to horizontal surfaces 3 the streaks can propagate stably for long many hundreds of meters distances and can turn following the topographic gradient on 10 15 slopes 4 no uphill propagation of streaks is detected over baselines of tens of meters 5 the slope streaks often propagate over 1 2 m high obstacles and can climb 1 2 m uphill over short meters distances we used these findings to assess the viability of two classes of hypotheses about slope streak formation mechanisms proposed earlier 1 dry some kind of run away avalanche like dry granular flow and 2 wet some kind of run away propagation of a front of percolating brines in the shallow subsurface no specific observation unambiguously proves or rejects either of the two mechanisms several of our findings are readily explained by the dry mechanism and cannot be easily explained with any kind of wet mechanism while other findings are closely consistent with the wet mechanism and are difficult to reconcile with the dry mechanism this situation might be explained by equifinality meaning that the streaks despite their similarity are formed by different physical processes alternatively some modifications to either the dry or wet mechanisms may be able to provide a coherent explanation it is also possible that new ideas are needed to understand the processes involved

seasonality of present day martian dune gully activity martian slope gullies are argued to be evidence for recent liquid water flow on the surface of mars to explain the source of water a wide range of environmental conditions and processes has been invoked however a lack of information about the environmental context or timing of gully activity makes it difficult to evaluate the theories here we present new observations of extensive gully modification over the past 6 mars years within dune gullies with slope gully morphology observed activity within 18 gullies in 7 dune fields constrains timing to winter which is consistent with observed slope gully activity these observations show that fluvial processes are unlikely to cause present day martian dune gully activity and imply that co 2 frost accumulation may play the dominant role

physical models and predictions for recurring slope lineae formed by wet and dry processes abstract the observation of low albedo elongated and transient features lengthening downhill on mars has attracted wide interest because of the possible role of aqueous fluids in their formation these recurring gravity driven processes called recurring slope lineae rsl remain mysterious in that although the influence of local climate conditions has been established their nature dry versus wet and the mechanisms that govern their growth and fading are debated we present three different physical models for the growth of rsl the first two are wet based models with different aqueous fluid evaporation models and the last is based on dry granular theory we discuss the prediction of each model with regards to the growth and fading of rsl and their morphology we finally discuss the strengths and weaknesses of these models in light of what we currently observe on mars we find that both wet and dry rsl scenario face challenges mostly regarding aspects of mass balance however water based scenarios provide a consistent framework to reconcile the different sets of morphological observations made on rsl

complex magmatic and impact history prior to 4 1 ga recorded in zircon from apollo 17 south massif aphanitic breccia 73235 abstract sample 73235 is one of several aphanitic impact melt breccias collected by the apollo 17 mission at stations 2 and 3 on the slopes of the south massif this study presents a detailed investigation of internal structures and u pb ages of large zircon grains from this breccia sample new data combined with the results of previous studies of zircon grains from the same location indicate that most zircon clasts in breccias from stations 2 and 3 formed during multiple magmatic events between 4 37 and 4 31 ga although the oldest zircon crystallized at about 4 42 ga and the youngest at 4 21 ga in addition zircons from the aphanitic breccias record several impact events prior to the 3 9 ga late heavy bombardment the results indicate that the zircons probably crystallized at different locations within the procellarum kreeep terrane and were later excavated and modified by several impacts and delivered to the same locality within separate ejecta blankets this locality became a source of material that formed the aphanitic impact melt breccias of the south massif during a 3 9 ga impact however the zircons showing old impact features are not modified by this 3 9 ga impact event suggesting that i this common source area was located at the periphery of excavation cavity and ii the 3 9 ga ages recorded by the zircon grains could date large basin forming events as significant as major later 3 9 ga collisions such as imbrium and serenitatis

photometric properties of mars soils analogs we have measured the bidirectional reflectance of analogs of dry wet and frozen martian soils over a wide range of phase angles in the visible spectral range all samples were produced from two geologic samples the standard jsc mars 1 soil simulant and hawaiian basaltic sand in a first step experiments were conducted with the dry samples to investigate the effects of surface texture comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures in a second step water was introduced to produce wet and frozen samples and their photometry investigated optical microscope images of the samples provided information about their microtexture liquid water even in relatively low amount resulted in the disappearance of the backscattering peak and the appearance of a forward scattering peak whose intensity increases with the amount of water specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice we discuss the implications of these measurements in terms of the expected photometric behavior of the martian surface from equatorial to circum polar regions in particular we propose some simple photometric criteria to improve the identification of wet and or icy soils from multiple observations under different geometries

correction to stability of perchlorate hydrates and their liquid solutions at the phoenix landing site mars 1 in the paper stability of perchlorate hydrates and their liquid solutions at the phoenix landing site mars by vincent f chevrier et al geophysical research letters 36 l10202 doi 10 1029 2009gl037497 2009 there is an error in figure 3b of the published paper the curve describing the gcm global circulation model results for humidity at the phoenix landing site is wrong the new figure gives the right humidity variations from the gcm the legend is the same as for the original figure 3b this error does not affect subsequent calculations and all the conclusions of the paper remain valid since they were based on the measured humidity data by the phoenix thermal and electrical conductivity prove tecp instrument rather than on the gcm model results 2 the description of the gcm results in the paper page 5 end of the first paragraph should be modified accordingly the gcm results on water vapor pressure show a similar trend than the tecp data with high daytime values up to 7 pa and low nighttime value down to 3 5 10 3 pa however the amplitude of pressure variations calculated form the gcm is higher than the tecp data which range from 2 10 3 to 2 pa this suggests some form of interaction of water vapor with the regolith compared to pure atmospheric processes

formation of aqueous solutions on mars via deliquescence of chloride perchlorate binary mixtures abstract perchlorate salts known to exist on mars can readily absorb water vapor and deliquesce into aqueous solutions even at low temperatures the multiple soluble ionic species such as chloride salts present in the martian subsurface may affect this deliquescence here we study the deliquescence solid to aqueous transition and efflorescence aqueous to solid transition of three perchlorate chloride mixtures kclo 4 kcl at 253 k naclo 4 nacl at 243 and 253 k and mg clo 4 2 mgcl 2 at 243 and 253 k a raman microscope with an environmental cell was used to monitor the phase transitions of internally mixed clo 4 cl particles as a function of the perchlorate mole fraction the eutonic relative humidity where deliquescence begins to occur regardless of clo 4 mole fraction deliquescence relative humidity drh where complete deliquescence occurs and efflorescence relative humidity erh were measured for several perchlorate mole ratios for each cation system at the temperatures studied the eutonic relative humidity was measured to be 28 rh for mg clo 4 2 mgcl 2 mixtures 38 rh for naclo 4 nacl mixtures and 82 rh for kclo 4 kcl mixtures the drh depends on the perchlorate mole ratio but is below the drh of the least deliquescent highest drh pure salt when humidity is lowered around an aqueous salt mixture we find that efflorescence occurs at an rh below the drh due to the kinetic inhibition of crystallization the erh values of the salt solutions were as low as 5 rh for mg clo 4 2 mgcl 2 mixtures as low as 13 rh for naclo 4 nacl mixtures and as low as 66 rh for kclo 4 kcl mixtures the low eutonic rh values for the na and mg 2 perchlorate chloride mixtures are important wherever mg clo 4 2 and mgcl 2 or naclo 4 and nacl coexist at the temperatures studied mixtures will contain a stable aqueous phase above 28 or 38 rh respectively regardless of the perchlorate mole fraction this liquid water may persist until 5 or 13 rh respectively

lead and aluminum in atlantic surface waters 50 n to 50 s reflecting anthropogenic and natural sources in the eolian transport lead and aluminum were measured with a 40 100 km resolution in surface water on two transects across the atlantic ocean one in may 1990 from cape town to the north sea the other in november 1990 from the north sea to the strait of magellan samples were drawn 14 m below surface at normal speed from a 2 m long snorkel system mounted on the bottom of the ship directly into a clean room area in the tropics both pb and al show maximum concentrations in the intertropical convergence zone itcz correlated with each other and with minimum salinities indicating wet deposition as their common source even in this area characterized by large inputs of mineral aerosols the pb al ratio shows that the major source of soluble lead 95 is anthropogenic at higher latitudes al is low throughout 10 20 nmol kg whereas enhanced pb values show the anthropogenic inputs off south africa northern argentina and especially western europe very low pb and especially al concentrations in the upwelling areas associated with the canary and benguela currents show that the enhanced biogenic particle fluxes cause an efficient scavenging of both lithogenic particles known to arrive here by dry deposition and of the adhering reactive trace metals

new and recent gully activity on mars as seen by hirise 1 fresh appearing gully deposits are found at tens of sites in the southern hemisphere of mars these deposits have latitudinal and azimuthal dependences similar to the overall preferences of southern hemisphere gullies suggesting that most gullies can undergo such events definite changes are seen at ten sites including two previously reported these include visible modification of gully channels and aprons those formation intervals constrained to better than one mars year tend to include winter and exclude summer suggesting seasonal activity this seasonal activity is consistent with proposed models for gully formation driven by co2 frost although at least some of the new deposits are probably due to dry granular flow with no volatile involvement as these deposits are capable of effecting distinct topographic changes to gully aprons and channels they represent a significant component of recent gully evolution

the role of dust deposition in determining surface water distributions of al and fe in the south west atlantic abstract underway dissolved al and fe determinations were made on surface water samples collected between 34 s and 8 n in the southern and tropical atlantic ocean using a towed surface water sampler the general distribution of dissolved al which ranged from 8 nm in the sub tropical gyre to 61 nm under the intertropical convergence zone itcz north of the equator corresponds clearly with atmospheric dust deposition patterns a striking correlation between al and surface water salinities between 28 s and 8 n further indicates that wet deposition is the predominant mechanism of delivery of this atmospheric source iron concentrations in contrast were more uniform varying between 0 6 and 0 8 nm south of the equator highest fe values up to 1 4 nm also were found associated with the maximum dust inputs at the itcz indicating an atmospheric source for this element whose input appears to be limited by the solubility of fe in sea water the lowest fe values 0 4 nm also were observed in the equatorial region and are assumed to result from the biological removal of fe from nutrient rich water masses originating in the nearby equatorial and coastal upwelling regions the high frequency data acquisition of the towed sampler revealed significant variations up to 50 in both al and fe concentrations over short distances most notably along the interface between the south equatorial and canary currents the high variability of a biologically important trace element such as fe in these dynamic regions is indicative of the interplay between chemical and biological patchiness in surface waters

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

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

combining seawater 232th and 230th concentrations to determine dust fluxes to the surface ocean abstract aeolian dust is a significant source of iron and other nutrients to the surface ocean but constraining the size of this flux is difficult chemical tracers such as al are useful but are limited by lack of information about their rate of removal from surface seawater in this study we test the use of th isotopes as an improved tracer of dust input by measuring 232 th and 230 th concentrations of upper ocean seawater at six stations along a meridional atlantic section that spans the saharan dust plume open ocean 232 th like al is dominantly derived from dust dissolution while 230 th is produced in seawater by u decay and provides an assessment of th removal rates the highest 232 th concentrations and 232 th 230 th ratios particularly in the surface waters are observed at stations expected to be influenced by input of saharan dust the pattern of 232 th concentration is in agreement with dissolved al distributions and seawifs aerosol imagery supporting the use of 232 th as a proxy for short term dust addition deeper in the water column 232 th concentration may also reflect longer term dust inputs in addition lateral input of 232 th from mediterranean outflow water is detected at 1000 m in the north atlantic surface water residence times are calculated separately from 230 th and 234 th using a simple scavenging model and values from the two isotopes are generally consistent with one another th 230 residence times appear to reflect the longer term value however rather than exhibiting the strong seasonal influence seen for 234 th these th residence times allow dust flux to the surface ocean to be calculated using the known concentration of th in dust and assumed values for the solubility of dust th in seawater resulting dust fluxes show good agreements with models of dust deposition if th solubility is 1 to 5 in the north atlantic yielding fluxes of 0 4 19 2 g m 2 yr 1 and 5 to 10 in the south atlantic fluxes of 0 2 0 7 g m 2 yr 1 despite the need for better constraints on the fractional solubility of dust th this study demonstrates the power of combining th isotope measurements to constrain dust fluxes to the surface ocean

the polygonal surface structures in the dalangtan playa qaidam basin nw china controlling factors for their formation and implications for analogous martian landforms