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

debris flows and water tracks in northern victoria land continental east antarctica a new terrestrial analogue site for gullies and recurrent slope lineae on mars although the present environmental conditions on mars prohibit the generation of significant volumes of liquid water observations of several very young landforms such as gullies and recurrent slope lineae have been interpreted as signals for aqueous processes to explore the range of conditions under which such features can be formed on earth a field site in northern victoria land east antarctica was geomorphologically investigated despite the small size of the icefree area the site displays gullies water tracks and other traces of liquid water the gullies show clear evidence of sediment transport by debris flows and are typical of paraglacial processes on steep slopes in a recently deglaciated area water tracks appear in different forms and seem to recur seasonally in the austral summer melting of snow and surface glacier ice is the major water source for both debris flows and water tracks the observations presented here highlight the potential for hyperarid polar deserts to generate morphogenetically significant amounts of meltwater the gullies are morphologically analogous to martian gullies and water tracks on steep slopes appear very similar to recurrent slope lineae the observations suggest that even small icefree sites in continental antarctica may enable observations which can serve as a basis for working hypotheses in mars analogue studies and future field work should consider more areas in antarctica in addition to the mcmurdo dry valleys to search for mars analogue landforms

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

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

an analysis of an arctic channel network using a digital elevation model abstract drainage basins possess spatial patterns of similarity that can be characterized by universal qualities in the fractal dimension and the cumulative area distribution features called water tracks often drain hillslopes in basins with permafrost and impose significant control on the hydrologic response of watersheds we analyzed the arrangement of channel networks and water tracks in imnavait creek in northern alaska to determine if basins with permafrost possess the same universal characteristics as basins without permafrost using digital elevation models dems we explored the hillslope channel scaling regimes the spatial distribution of mass through the cumulative area distribution and the fractal characteristics of channel networks in the kuparuk river basin in northern alaska fractal analysis slope area analysis and field mapping suggest that water tracks are positioned on the hillslopes where channels should occur fully developed channel networks however possess certain universal characteristics in aggregation patterns that are manifested in a common cumulative area distribution imnavait creek possesses those universal characteristics only above the scale of the hillslope water track or when the drainage areas reach the main channels in the valley bottom our interpretation is that a rudimentary channel network formed on the hillslopes but never developed into a mature channel network because permafrost is limiting erosion consequently the undissected hillslopes are extensive given the dependence of permafrost on a cold climate a warming climate and subsequent degradation of permafrost may have significant impacts on the erosional development of channel networks in the arctic

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

islands as eddy transformation and generation hotspots cabo verde case study abstract deep ocean islands have long been associated with the generation of oceanic eddies in their wakes however their interaction with incoming eddies has seldom been considered this study focuses on the characterization of background and locally generated mesoscale eddies in the cabo verde archipelago between 2003 and 2014 special attention is given to the interaction of incoming eddies with the bathymetry of the islands along with their impacts on the local generation of eddies island induced wind shear effects are also considered in addition some examples of the biological response to background and locally generated eddies are discussed this is achieved by combining remote sensing satellite observations for wind sea surface height and chlorophyll a chla surface concentrations the results show that the interaction between incoming background eddies and the archipelago is a recurrent phenomenon which results in eddy deflection splitting merging intensification and termination sorted by highest to lowest number of occurrences local island induced disturbances are also significant mainly due to atmospheric effects such processes result in the generation of island induced eddies and in wind mediated eddy intensification and confinement more often observed in the leeward group nonetheless it is strongly suggested that many of the locally generated eddies are a direct product or by product of the interaction of background eddies with the islands with respect to the biological realm a locally generated cyclonic eddy is observed to originate a pronounced phytoplankton bloom in the vicinity of the tallest island nonetheless background eddies generated off the african coast are often associated with enhanced chla concentrations when they intersect the archipelago such observations challenge the idea that local biological productivity in deep oceanic islands is exclusively driven by island induced mechanisms

water tracks and permafrost in taylor valley antarctica extensive and shallow groundwater connectivity in a cold desert ecosystem water tracks are zones of high soil moisture that route water downslope over the ice table in polar environments we present physical hydrological and geochemical evidence collected in taylor valley mcmurdo dry valleys antarctica which suggests that previously unexplored water tracks are a significant component of this cold desert land system and constitute the major flow path in a cryptic hydrological system geological geochemical and hydrological analyses show that the water tracks are generated by a combination of infiltration from melting snowpacks melting of pore ice at the ice table beneath the water tracks and melting of buried segregation ice formed during winter freezing the water tracks are enriched in solutes derived from chemical weathering of sediments as well as from dissolution of soil salts the water tracks empty into ice covered lakes such as lake hoare resulting in the interfingering of shallow groundwater solutions and glacier derived stream water adding complexity to the geochemical profile approximately four orders of magnitude less water is delivered to lake hoare by any given water track than is delivered by surface runoff from stream flow however the solute delivery to lake hoare by water tracks equals or may exceed the mass of solutes delivered from stream flow making water tracks significant geochemical pathways additionally solute transport is two orders of magnitude faster in water tracks than in adjacent dry or damp soil making water tracks salt superhighways in the antarctic cold desert accordingly water tracks represent a new geological pathway that distributes water energy and nutrients in antarctic dry valley cold desert soil ecosystems providing hydrological and geochemical connectivity at the hillslope scale

regional variations in the influence of mesoscale eddies on near surface chlorophyll eddies can influence biogeochemical cycles through a variety of mechanisms including the excitation of vertical velocities and the horizontal advection of nutrients and ecosystems both around the eddy periphery by rotational currents and by the trapping of fluid and subsequent transport by the eddy in this study we present an analysis of the influence of mesoscale ocean eddies on near surface chlorophyll chl estimated from satellite measurements of ocean color the influences of horizontal advection trapping and upwelling downwelling on chl are analyzed in an eddy centric frame of reference by collocating satellite observations to eddy interiors as defined by their sea surface height signatures the influence of mesoscale eddies on chl varies regionally in most boundary current regions cyclonic eddies exhibit positive chl anomalies and anticyclonic eddies contain negative chl anomalies in the interior of the south indian ocean however the opposite occurs the various mechanisms by which eddies can influence phytoplankton communities are summarized and regions where the observed chl response to eddies is consistent with one or more of the mechanisms are discussed this study does not attempt to link the observed regional variability definitively to any particular mechanism but provides a global overview of how eddies influence chl anomalies

brine formation via deliquescence by salts found near don juan pond antarctica laboratory experiments and field observational results abstract the observed darkening of water tracks near don juan pond djp as well as the formation of wet patches elsewhere in the mcmurdo dry valleys is attributed at least partially to deliquescence a process by which salts absorb atmospheric water vapor and form brine coupled with liquid phase growth when the atmospheric relative humidity exceeds the water activity here we perform laboratory experiments to investigate the temperature and relative humidity conditions necessary for deliquescence to occur in calcium chloride rich sediments collected from the djp watershed we use a raman microscope equipped with an environmental cell to study both deliquescence and efflorescence recrystallization of the soluble salt component of djp soils between 30 and 15 c in this temperature range we find that the soluble salt component of the djp sediments begins to deliquesce between 19 and 46 rh slightly higher than the deliquescence relative humidity of the primary pure component calcium chloride we find a limited hysteresis between deliquescence and efflorescence but much greater supersaturation of the salt brine can occur at temperatures above 0 c the relative humidity conditions were varied either slowly over 8 h to observe near equilibrium phases or rapidly over

hydraulic conductivity of active layer soils in the mcmurdo dry valleys antarctica geological legacy controls modern hillslope connectivity abstract spatial variability in the hydraulic and physical properties of active layer soils influences shallow groundwater flow through cold desert hydrological systems this study measures the saturated hydraulic conductivity and grain size distribution of 90 soil samples from the mcmurdo dry valleys mdv antarctica primarily from taylor valley to determine what processes affect the spatial distribution of saturated hydraulic conductivity in a simple mineral soil dominated natural hillslope laboratory we find that the saturated hydraulic conductivity and the grain size distribution of soils are organized longitudinally within taylor valley soils sampled down valley near the coast have a higher percentage of fine sized sediments fine sand silt clay and lower saturated hydraulic conductivities than soils collected up valley near taylor glacier 1 3 10 2 vs 1 2 10 1 cm s soils collected mid valley have intermediate amounts of fines and saturated hydraulic conductivity values consistent with a hydrogeologic gradient spanning the valley from high inland to low near the coast these results suggest the organization of modern soil properties within taylor valley is a relict signature from past glaciations that have deposited soils of decreasing age toward the mouth of the valley modified by fluvial activity acting along temporal and microclimate gradients

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

impact of eddies on surface chlorophyll in the south indian ocean a unique feature of the subtropical south indian ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies off western australia this anomalous behavior is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients further off shore two mechanisms have been suggested to explain the eddy chlorophyll relationship i eddies originating from the australian coast maintain their chlorophyll anomaly while propagating westward and ii eddy induced ekman upwelling downwelling enhances dampens nutrient supply in anticyclonic cyclonic eddies here we describe the relationship between eddies and surface chlorophyll within the south indian ocean and discuss possible mechanisms to explain the anomalous behavior in light of new analyses performed using satellite chlorophyll data we show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire south indian ocean basin from 20 to 28 s particularly in winter using self organizing maps we analyze the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity our analysis suggests that multiple mechanisms may underlie the observed eddy chlorophyll relationship based on argo float data we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer while shallower mixing in cyclonic eddies is expected to reduce it this could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies

dynamical processes within an anticyclonic eddy revealed from argo floats mesoscale eddies play a significant role in supplying the nutrients required for phytoplankton blooms and redistributing biomass in the ocean however how eddies influence nutrient flux and biomass distribution remains unclear here we reveal two important dynamical processes radial displacement and vertical fluctuations within an anticyclonic eddy by analyzing observations from argo floats the argo floats in the eddy were displaced toward the eddy edge due to the imbalance of radial momentum vertical fluctuations below the mixed layer resulted in alternating upwelling and downwelling in the inner and outer parts of the eddy high salinity deep water was uplifted tens of meters by the upwelling and further extended to the surface with the aid of wind effects vertical motions associated with the fluctuations penetrated to the depths of several hundred meters these processes represent crucial dynamical mechanisms for the motion of particles in mature anticyclonic eddies

satellite observations of mesoscale eddy induced ekman pumping abstractthree mechanisms for self induced ekman pumping in the interiors of mesoscale ocean eddies are investigated the first arises from the surface stress that occurs because of differences between surface wind and ocean velocities resulting in ekman upwelling and downwelling in the cores of anticyclones and cyclones respectively the second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient resulting in dipoles of ekman upwelling and downwelling the third mechanism arises from eddy induced spatial variability of sea surface temperature sst which generates a curl of the stress and therefore ekman pumping in regions of crosswind sst gradients the spatial structures and relative magnitudes of the three contributions to eddy induced ekman pumping are investigated by collocating satellite based measurements of sst geostrophic velocity and surface winds to the interiors of eddies identified from their sea surface height signatures on average e

evaluation of wet and dry recurring slope lineae rsl formation mechanisms based on quantitative mapping of rsl in garni crater valles marineris mars abstract recurring slope lineae rsl are narrow 0 5 5 m low albedo features that incrementally lengthen down steep slopes during warm seasons fade in colder seasons and recur each mars year to reduce the effort involved in manually mapping and analyzing each rsl in garni crater we developed mapping and automated analysis of rsl maarsl to analyze a set of orthorectified high resolution imaging science experiment hirise images and a digital elevation map maarsl along with manual mapping allowed us to detect rsl compute descriptive statistics and characterize changes over time we mapped 2910 rsl in 22 orthoimages from mars year my 31 solar longitude ls 133 0 to my32 ls 323 7 the maarsl results confirmed that rsl lengthening and fading occur concurrently on slopes with the same orientation and many times within some individual rsl slope angles of rsl and a slope slump show that some rsl start stop and have mean slope angles that are below the angle of repose our analysis shows that rsl are actively lengthening on at least one slope facing direction in all hirise observations of the crater we also found that ne n and nw facing rsl in garni crater lengthened during times of increasing shortwave insolation while s and sw facing rsl lengthened during increasing and decreasing shortwave insolation a non orthorectified hirise image acquired shortly after the my34 dust storm and shows rsl on every slope facing direction which is anomalous with respect to observations prior to the dust storm we find that dust removal and deposition could explain the darkening and fading respectively of rsl and could also explain the apparent lack of material being transported observations of rsl lengthening and fading occur concurrently on slopes could suggest overprinting of dry granular flows dry flows could also explain the significant lengthening activity of every slope facing direction after a fresh layer of dust was deposited via the my34 dust storm alternatively briny shallow subsurface flows are consistent with observations of rsl on slopes below the angle of repose and those that exhibit concurrent lengthening and fading however the most significant problem with briny rsl flows is accessing a source of briny water and removing excess salt from the regolith

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

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

satellite observations of chlorophyll phytoplankton biomass and ekman pumping in nonlinear mesoscale eddies nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms the relative importance of these two processes depends on the polarity of an eddy cyclones versus anticyclones and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation eddies originating in the eastern south indian ocean are unique in that anticyclones typically associated with downwelling contain elevated levels of chlorophyll a enhanced primary production and phytoplankton communities generally associated with nutrient replete environments from analysis of 9 years of concurrent satellite measurements of sea surface height chlorophyll phytoplankton carbon and surface stress we present observations that suggest eddy induced ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the south indian ocean the biological response to this eddyinduced ekman upwelling is evident only during the austral winter during the austral summer the biological response to eddy induced ekman pumping occurs deep in the euphotic zone beyond the reach of satellite observations of ocean color

chemical weathering trends in fine grained ephemeral stream sediments of the mcmurdo dry valleys antarctica abstract we investigated chemical weathering trends within the fine grained 40 m 2 g utilization of mfw mafic felsic weathered and a cn k al 2 o 3 cao na 2 o k 2 o plots however are more effective in discerning the extent and nature of chemical weathering in these stream systems ca and na depletion observed within the sediments exhibiting the highest surface area in delta stream suggest that chemical weathering may result in pitting and or incongruent dissolution of pyroxenes and feldspars as well as the development of amorphous and or nanophase weathering products in contrast clark glacier stream sediments do not have similar leaching trends in the fine grained sediment fraction and exhibit minimal weathering overall this may suggest that fine grained material is being trapped on top of the clark glacier surface and has not yet been transported into the weathering environment of the hyporheic zone due to timing of sampling alternatively complete dissolution of very fine grained sediment could be occurring in this stream transect and is therefore not preserved in the fine sediment fraction overall the magnitude of chemical weathering observed between the two stream systems is ultimately related to the nature of the underlying drift cold and wet based drift deposition dispersal patterns of eolian fines and variable stream discharge rates thus incorporation of local fine grained sediment derived from the underlying glacial drift deposits and distributed via the varying wind regimes within the hyper arid climate into active stream channels may facilitate incongruent mineral dissolution and development of weathering products and ultimately influence the composition and concentration of meltwater stream solutes

geologic context of recurring slope lineae in melas and coprates chasmata mars one of the major mars discoveries of recent years is the existence of recurring slope lineae rsl which suggests that liquid water occurs on or near the surface of mars today these dark and narrow features emerge from steep rocky exposures and incrementally grow fade and reform on a seasonal basis and are detected in images from the high resolution imaging science experiment camera rsl are known to occur at scattered midlatitude and equatorial sites with little spatial connection to one another one major exception is the steep low albedo slopes of melas and coprates chasmata in valles marineris where rsl are detected among diverse geologic surfaces e g bedrock and talus and landforms e g inselbergs and landslides new images show topographic changes including sediment deposition on active rsl slopes midwall locations in coprates and melas appear to have more areally extensively abundant rsl and related fans as compared with other rsl sites found on mars water budget estimates for regional rsl are on the order of 105 to 106 m3 of fluid for depths of 10 to 100 mm and suggest that a significant amount of near surface water might be present many rsl are concentrated near local topographic highs such as ridge crests or peaks which is challenging to explain via groundwater or ice without a recharge mechanism collectively results provide additional support for the notion that significant amounts of near surface water can be found on mars today and suggest that a widespread mechanism possibly related to the atmosphere is recharging rsl sources

ageostrophic secondary circulation in a subtropical intrathermocline eddy abstractvertical motions play a key role in the enhancement of primary production within mesoscale eddies through the introduction of nutrients into the euphotic layer however the details of the vertical velocity field w driving these enhancements remain under discussion for the first time the mesoscale w associated with an intrathermocline eddy is computed and analyzed using in situ high resolution three dimensional 3d fields of density and horizontal velocity by resolving a generalized omega equation valid for high rossby numbers in the seasonal pycnocline the diagnosed w reveals a multipolar structure with upwelling and downwelling cells located at the eddy periphery in the main pycnocline w is characterized by a dipolar structure with downwelling velocities upstream of the propagation path and upwelling velocities downstream maximum values of w reach 6 4 m day 1 an observed enhancement of chlorophyll a at the eddy periphery coincides with the location of the upwelling and downwelling cells a

mesoscale eddy characteristics in the interior subtropical southeast indian ocean tracked from the leeuwin current system abstract two oppositely rotating mesoscale eddies originating from the leeuwin current were captured during a research cruise in the interior southeast indian ocean in august 2012 a few hundred kilometers off the west coast of australia the two eddies had different vertical structures the anticyclonic eddy had stronger vertical shear above 200 m and a less stratified thermocline below the mixed layer while the cyclonic eddy had a more barotropic structure in the upper 500 m compared with the same types of eddies sampled in 2003 close to the australian coast the 2012 anticyclonic eddy had a larger radius deeper isothermal depths and higher peak velocity whereas the 2012 cyclonic eddy had a similar structure with the 2003 survey we use an argo float and three surface drifters deployed and trapped in the anticyclonic eddy to track its evolution over a 4 month period the eddy was observed to propagate 1000 km further to the west indicating that the leeuwin current properties of the eddy may be preserved for over 2000 km off the west coast of australia the eddy appeared to have experienced radial excursions relative to the eddy center with periodicity of 4 6 days and 15 days during their anticlockwise motions the radial movements of the drifters appeared to be constrained by the radial momentum balance within the eddy the importance of eddy distortions to ocean primary production in anticyclonic eddies in the southeast indian ocean warrants further studies

thermal behavior of horizontally mixed surfaces on mars abstract current methods for deriving thermal inertia from spacecraft observations of planetary brightness temperature generally assume that surface properties are uniform for any given observation or co located set of observations as a result of this assumption and the nonlinear relationship between temperature and thermal inertia sub pixel horizontal heterogeneity may yield different apparent thermal inertia at different times of day or seasons we examine the effects of horizontal heterogeneity on mars by modeling the thermal behavior of various idealized mixed surfaces containing differing proportions of either dust sand duricrust and rock or slope facets at different angles and azimuths latitudinal effects on mixed surface thermal behavior are also investigated we find large several 100 j m 2 k 1 s 1 2 diurnal and seasonal variations in apparent thermal inertia even for small 10 admixtures of materials with moderately contrasting thermal properties or slope angles together with similar results for layered surfaces mellon m t putzig n e 2007 lunar planet sci xxxviii abstract 2184 this work shows that the effects of heterogeneity on the thermal behavior of the martian surface are substantial and may be expected to result in large variations in apparent thermal inertia as derived from spacecraft instruments while our results caution against the over interpretation of thermal inertia taken from median or average maps or derived from single temperature measurements they also suggest the possibility of using a suite of apparent thermal inertia values derived from single observations over a range of times of day and seasons to constrain the heterogeneity of the martian surface

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

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

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

hydrological characteristics of recurrent slope lineae on mars evidence for liquid flow through regolith and comparisons with antarctic terrestrial analogs abstract on the basis of their morphology and seasonal thermal characteristics recurrent slope lineae rsl on mars have been inferred to be a possible result of the flow of a liquid likely a saline brine through the upper portions of the martian regolith in this note we analyze repeat hirise imaging of rsl to show that the downslope growth rate of recurrent slope lineae is well fit by an elementary groundwater flow model that also describes the downslope propagation of antarctic water tracks terrestrial analogs to rsl and that the apparent permeability of rsl bearing slopes is consistent with the observed sandy regolith substrate

modified jeffery model influence of particle concentration on mineral fabric in moderately concentrated suspensions 1 a modified jeffery model involving particle interactions allows the simulation of preferred orientation of crystals and the anisotropy of magnetic susceptibility in magmatic flow with up to 40 of rigid particle fraction numerical simulations are compared to analogue and natural fabrics a study of the role of particle concentration shows that the increasing percentage of crystal fraction in dilute suspensions leads to progressive attenuation of the fabric intensity and cyclicity at high strains in simple shear flow the lineation converges to a constant value close to the shear plane with increasing particle concentration the fabric diverges from the shear direction reflecting the effect of increased crystal tiling the model can be applied to quantify mineral preferred orientations of crystal mushes in magmatic fabric studies

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

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

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

response to comment on eddy wind interactions stimulate extraordinary mid ocean plankton blooms the alternative mechanism proposed by mahadevan et al is an unlikely explanation for our observations because their model predicts a bloom at the periphery of the eddy whereas the observations show it located at the eddy center and because the vertical displacements caused by the nonlinear ekman effect are too small to lead to an extraordinary biological response in this eddy

impacts of the mesoscale ocean atmosphere coupling on the peru chile ocean dynamics the current induced wind stress modulation the ocean dynamical responses to the surface current wind stress interaction at mesoscale are investigated in the south east pacific using a high resolution regional ocean atmosphere coupled model two simulations are compared one includes the surface current in the wind stress computation while the other does not in the coastal region absolute wind velocities are different between the two simulations but the wind stress remains very similar as a consequence the mean regional oceanic circulation is almost unchanged on the contrary the mesoscale activity is strongly reduced when taking into account the effect of the surface current on the wind stress this is caused by a weakening of the eddy kinetic energy generation near the coast by the wind work and to intensified offshore eddy damping we show that above coherent eddies the current stress interaction generates eddy damping through ekman pumping and eddy kinetic energy dissipation through wind work this alters significantly the coherent eddy vertical structures weakening the temperature and vorticity anomalies and increasing strongly the vertical velocity anomalies associated to eddies

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

transient upwelling hot spots in the oligotrophic north pacific 1 vertical exchange between deep nutrient rich and nutrient depleted surface waters controls the physical supply of nutrients into the euphotic zone in the oligotrophic waters of the subtropical north pacific ocean sea surface temperature and ocean color satellite images are used in this study to show that submesoscale chlorophyll patches are locally intensified these patches are associated with surface temperature fronts and regions of strong stretching of the eddying flow the latter are identified by calculating the finite size lyapunov exponents of the geostrophic flow derived from the sea surface height field from altimetry surface frontogenesis and nonlinear ekman pumping nlep arise as natural candidates for the sporadic generation of large vertical velocities that could favor the formation of these features a high resolution regional numerical model simulation confirms that large vertical velocities are indeed associated with strong density fronts and gradients of relative vorticity using the q vector divergence as a proxy for frontogenetically generated vertical velocities yields good agreement with the model vertical velocities particularly in regions where they are large the pattern and magnitude of nlep suggests that it is also contributing to the strong vertical motions although nlep and model vertical velocities are not necessarily in phase surface frontogenesis and nlep provide a possible explanation for the episodic injection of nutrients at the submesoscale which are then horizontally stirred and modulated by the unstable manifolds of the flow field given that these surface intensified processes would be biogeochemically more effective when the pycnocline is shallow they could also serve as one possible explanation for the late summer chlorophyll blooms that are known to occur in the region

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

vertical velocity dynamics and mixing in an anticyclone near the canary islands abstractthe complex structure of the vertical velocity field inside an anticyclonic eddy located just south of the canary islands is analyzed through a high resolution ocean model based on the flo

microscopy analysis of soils at the phoenix landing site mars classification of soil particles and description of their optical and magnetic properties the optical microscope onboard the phoenix spacecraft has returned color images 4 m pixel 1 of soils that were delivered to and held on various substrates a preliminary taxonomy of phoenix soil particles based on color size and shape identifies the following particle types generic names in brackets 1 reddish fines mostly unresolved that are spectrally similar to though slightly darker than global airborne dust red fines 2 silt to sand sized brownish grains brown sand 3 silt to sand sized black grains black sand and 4 small amounts of whitish fines possibly salts white fines most particles have a saturation magnetization in the range 0 5 2 am2 kg 1 as inferred from their interaction with magnetic substrates the particle size distribution has two distinct peaks below 10 m fines and in the range 20 100 m grains respectively and is different from that of ripple soils in gusev crater in particular medium to large sand grains appear to be absent in phoenix soils most sand grains have subrounded shape with variable texture a fractured grain observed on sol 112 reveals evidence of micrometer sized crystal facets the brown sand category displays a large diversity in color including shiny almost colorless particles potential source regions for these grains may be the tharsis volcanoes or heimdal crater 20 km east of the landing site the black grains are suggested to belong to a more widespread population of particles with mafic mineralogy the absence of black brown composite grains is consistent with different formation pathways and source regions for each grain type

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