a strong wind event on the ross ice shelf antarctica a case study of scale interactions abstractin situ observations satellite imagery numerical weather prediction and reanalysis fields are used to investigate the synoptic and mesoscale environment of a strong wind event swe at mcmurdo station ross island region on the ross ice shelf antarctica on 10 october 2003 the swe occurred during the passage of a sequence of three mesoscale low pressure systems from the central ross ice shelf to the southwest ross sea a potential vorticity pv analysis showed that the lows drew air of continental origin down the glacial valleys of the transantarctic mountains and onto the ice shelf as a katabatic drainage flow however the analysis indicated that the air mass associated with the swe was of recurved maritime origin drawn in by the second mesoscale low l2 this air mass approached mcmurdo station from the south where interactions with the orography played a critical role in the early stages of the event when the wind speed was less than 10 m s 1 the air was deflected around the topograph

importance of latent heating in mesocyclones for the decay of cold air outbreaks a numerical process study from the pacific sector of the southern ocean abstractin this study the dynamical mechanisms shaping the evolution of a marine cold air outbreak cao that occurred over the ross amundsen and bellingshausen seas in june 2010 are investigated in an isentropic framework the drainage of cold air from west antarctica into the interior ross sea its subsequent export and the formation of a dome of cold air off the sea ice edge are shown to be intimately linked to a lower tropospheric cyclone as well as the cyclonic breaking of an upper level potential vorticity trough the dome formation is accompanied by an extreme deepening of the boundary layer whose top reaches to the height of the low lying tropopause within the trough potentially allowing for deep stratosphere troposphere exchange a crucial finding of this study is that the decay of the cao is essentially driven by the circulation associated with a train of mesocyclones and the release of latent heat in their warm sectors sensitivity experiments with switched off fluxes of sensible and late

a steep fan at coprates catena valles marineris mars as seen by hrsc data 1 we investigate a steep fan like deposit in the coprates catena region using the new high resolution stereo camera hrsc data and other martian data sets water flowing in a 45 km long sapping valley entered a deep trough and formed a stepped fan 1100 m high above the trough floor with a mean slope of 7 4 the origin of the fan is uncertain however we favor an alluvial sheetflood dominated deposition for the sedimentary feature though there is weak evidence for a possible stationary water level 500 m above the floor and a fan delta origin regional morphotectonics and previous geological mapping suggest that groundwater related aqueous sedimentation could have been active from hesperian to early amazonian implying favorable climatic conditions for the flow and possible ponding of water during that period

groundwater controlled valley networks and the decline of surface runoff on early mars 1 fluvial erosion on early mars was dominated by valley networks created through a combination of groundwater processes and surface runoff a reduced greenhouse effect due to co 2 loss together with a declining geothermal heat flux promoted the growth of a cryosphere and a hesperian hydrologic regime dominated by outflow channel formation we test the hypothesis that the transition from valley network to outflow channel formation was preceded by a more subtle evolution characterized by a weakening of surface runoff leaving groundwater processes as the dominant final source of valley network erosion our hypothesis supported by a terrestrial analog in the atacama desert of chile is related to the groundwater sapping reactivation hypothesis for densely dissecting highland valley networks on mars suggested by baker and partridge in 1986 and focuses on the age analysis of large sparsely dissecting valley networks such as nanedi valles nirgal vallis valleys in fretted terrain and tributaries of outflow channels and valles marineris chasmata we find that these features are consistently late noachian to hesperian in age younger than noachian densely dissecting dendritic valley networks in the southern highlands in the tharsis region the observation of dense and sparse valley network morphologies on hesperian terrain suggests that while surface runoff gave way to groundwater processes consistent with our hypothesis the transition may have occurred later than elsewhere on the planet the volcanic nature of tharsis suggests that geothermal heat and volatile production led to episodically higher volumes of surface runoff in this region during the hesperian

inversion of relief a component of landscape evolution inversion of relief occurs when materials on valley floors are or become more resistant to erosion than the adjacent valley slopes as erosion proceeds the valley floor becomes a ridge bounded by newly formed valleys on each side areas of lava flows contain many examples of inversion of relief but it is also common in areas of duricrusts inversion of relief is so widespread in some areas that it should be regarded as a general component in a model of landscape evolution inversion of relief has some important implications drainage lines will shift significantly over time slope soil relationships catenas have to be reassessed because the regolith on the upper part of a hill slope may have developed under very different conditions from those existing at present the resulting catena is not a simple expression of soils and response to landscape position this also has important implications for geochemistry where present day ridge tops were once valley floors geochemical signatures will reflect lateral water movement in the old landscape rather than simple in situ weathering and vertical redistribution in the present landscape finally inversion of relief can produce erosion surfaces of very low relief that cannot be termed peneplains pediplains or etchplains because they have a very different genesis this underlines the importance of determining the complexities of landscape evolution before such genetic terms are applied to any landscape

hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the ross ice shelf antarctica numerical simulations and surface based observations show that katabatic winds persistently converge toward and blow across the siple coast part of west antarctica onto the ross ice shelf about 14 of the time during winter april to august 1988 thermal infrared satellite images reveal the horizontal propagation of this negatively buoyant katabatic airstream for about 1000 km across the ice shelf to its northwestern edge a trajectory that nearly parallels the transantarctic mountains this takes place when the pressure field supports such airflow and is caused by synoptic scale cyclones that decay near and or over marie byrd land the northwestward propagation of the katabatic winds is accompanied by other changes in the hemispheric long wave pattern an upper level ridge develops over wilkes land resulting in an enhancement of the split jet in the pacific ocean then more frequent and or intensified synoptic scale cyclones are steered toward marie byrd land where they become nearly stationary to the northeast of the climatological location the resulting isobaric configuration accelerates the katabatic winds crossing siple coast and supports their horizontal propagation across the ross ice shelf an immediate impact of this katabatic airflow that crosses from the ice shelf to the ross sea is expansion of the persistent polynya that is present just to the east of ross island this polynya is a conspicuous feature on passive microwave images of antarctic sea ice and plays a central role in the salt budget of water masses over the ross sea continental shelf the impact of this katabatic airflow upon mesoscale cyclogenesis over the south pacific ocean is also discussed

morphology stratigraphy and mineralogical composition of a layered formation covering the plateaus around valles marineris mars implications for its geological history an extensive layered formation covers the high plateaus around valles marineris mapping based on hirise ctx and hrsc images reveals these layered deposits lds crop out north of tithonium chasma south of ius chasma around west candor chasma and southwest of juventae chasma and ganges chasma the estimated area covered by lds is not vert similar42 300 km2 they consist of a series of alternating light and dark beds a 100 m in total thickness that is covered by a dark unconsolidated mantle possibly resulting from their erosion their stratigraphic relationships with the plateaus and the valles marineris chasmata indicate that the lds were deposited during the early to late hesperian and possibly later depending on the region before the end of the backwasting of the walls near juventae chasma and probably before louros valles sapping near ius chasma their large spatial coverage and their location mainly on highly elevated plateaus lead us to conclude that lds correspond to airfall dust and or volcanic ash the surface of lds is characterized by various morphological features including lobate ejecta and pedestal craters polygonal fractures valleys and sinuous ridges and a pitted surface which are all consistent with liquid water and or water ice filling the pores of lds lds were episodically eroded by fluvial processes and were possibly modified by sublimation processes considering that lds correspond to dust and or ash possibly mixed with ice particles in the past lds may be compared to dissected mantle terrains currently observed in mid to high latitudes on mars which correspond to a mantle of mixed dust and ice that is partially or totally dissected by sublimation the analysis of crism and omega hyperspectral data indicates that the basal layer of lds near ganges chasma exhibits spectra with absorption bands at not vert similar1 4 m and not vert similar1 9 m and a large deep band between not vert similar2 21 and not vert similar2 26 m that are consistent with previous spectral analysis in other regions of lds we interpret these spectral characteristics as an enrichment of lds in opaline silica or by al phyllosilicate rich layers being overlain by hydroxylated ferric sulfate rich layers these alteration minerals are consistent with the aqueous alteration of lds at low temperatures

comprehensive analysis of glaciated martian crater greg abstract the 66 km diameter martian crater greg east of hellas hosts various distinctive features including dendritic valleys filled with chevron textured masses south wall and lobate tongues a few kilometers long north wall we analyze these features by various quantitative techniques to illuminate martian geologic and climatic history crater retention model ages indicate that greg is at least 1 3 gy old but surface layers of mantles and glacial features are orders of magnitude younger properties of the dendritic valleys combined with climate models suggest that fluvial activity began under a thicker warmer atmosphere soon after the crater s formation the oldest exposed fluvial systems have surface crater retention ages of a few hundred my indicating runoff in recent geologic time much of greg is covered by ice rich mantle deposits for which we infer gradual accumulation and depths of order 30 85 m they mask pre existing landforms the lobate tongues are interpreted as glaciers with mean slope of 10 2 2 3 and average thickness of 33 19 m our calculations and data suggest that these glaciers were originally ice rich and that their surface layers have been depleted by volatile loss the glaciers probably formed when ice rich mantle deposits reached critical thickness and flowed downhill the top 5 10 m of the mantle and glaciers show crater survival times of order a few my to 15 my which remarkably is the time since the last 1 4 episodes of obliquity 45 global climate models affirm that greg lies in one of two non polar areas with extremes of ice deposition during high obliquity epochs this match with observations supports the use of such models in studies of planetary climate change

the formation of valles marineris 1 tectonic architecture and the relative roles of extension and subsidence 1 the formation of the valles marineris troughs on mars is widely held to involve some combination of horizontal extension and vertical subsidence or collapse but the specific tectonic mechanism is poorly understood this study uses boundary element models of valles marineris formation to evaluate a range of fault dip angles for two end member models of trough formation simple extensional tectonism and extension together with vertical accommodation at the base of the lithosphere representing either viscous lower crustal flow or some other form of deep seated collapse the models are constrained by the lack of footwall uplift on the plateau surface outside the troughs and the lack of significant tectonic failure of the plateau in response to the stress changes induced by valles marineris formation the results demonstrate that trough formation by extensional tectonism alone generates large surface uplifts in the surrounding plateau and enormous stresses in the lithosphere in conflict with the observations the only mechanism that is compatible with both the observed topography and the limitations imposed by the finite strength of the lithosphere is trough formation through displacement along steeply dipping to subvertical border faults together with vertical accommodation at the base of the subsiding fault block fault dips are constrained to be greater than or equal to 85 leading to a ratio of vertical subsidence to horizontal extension exceeding 5 7 and a maximum extension of less than 4 6 km these results confirm earlier studies suggesting that trough formation involved a substantial component of vertical subsidence or collapse with only modest amounts of total extension

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

morphology and composition of the surface of mars mars odyssey themis results the thermal emission imaging system themis on mars odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness implying temporal changes in the processes or environments during or after their formation kilometer scale exposures of bedrock are observed elsewhere airfall dust completely mantles the surface over thousands of square kilometers mars has compositional variations at 100 meter scales for example an exposure of olivine rich basalt in the walls of ganges chasma thermally distinct ejecta facies occur around some craters with variations associated with crater age polar observations have identified temporal patches of water frost in the north polar cap no thermal signatures associated with endogenic heat sources have been identified

terraces and gilbert type deltas in crater lakes in ismenius lacus and memnonia mars paleolacustrine environments have been widely recognized from landform associations on the surface of mars in contrast to paleolakes in more open areas putative crater lakes commonly display well developed sedimentary landforms especially wave formed terraces and gilbert type deltas this study focuses on terraces and deltas of western memnonia and ismenius lacus as on earth these landforms provide important indications of water dynamics and sedimentary processes the putative martian paleolakes must have been active for thousands of years to have permitted the water movement and wave formation necessary to form one or more terraces fan shaped landforms at the mouths of channels entering crater lake areas may indicate various channel water interaction of these gilbert type deltas are particularly informative their presence indicates multiple flooding events whereby the inlet channels conveyed coarse grained sediment to the crater lake both terraces and deltaic progradation indicate that the crater lakes of memnonia and ismenius lacus were active for long time periods at least for thousands of years during the post heavy bombardment period of the later martian history the unequivocal presence of standing bodies of water of relatively long durations indicates that climatic settings very different from those prevailing today must have occurred at least locally and temporarily during parts of the martian planetary history

meltback of hesperian aged ice rich deposits near the south pole of mars evidence for drainage channels and lakes ponding minimum volumes 10 12 m 3 overtopping downcutting and further drainage of material through a series of craters and into the prometheus basin near the edge of the current cap topography data show that water filled some craters to depths of at least 200 m and possibly as much as 600 m materials derived from melting of this lobe of the daf drained over a lateral distance of 600 km and a vertical height of 800 m partially emptying into the prometheus basin these combined observations imply that meltback of the older volatile rich deposit was a widespread event occurring on both sides of the deposit over a distance of at least 1800 km and in an area possibly as much as 2 9 10 6 km 2 candidate top down and bottom up melting scenarios are examined the presence of associated hesperian aged volcanic deposits and possible subglacial edifices suggests that local and regional basal heating was a major factor in generating the meltwater that formed the drainage features index terms 6225 planetology solar system objects mars 5416 planetology solid surface planets glaciation 5470 planetology solid surface planets surface materials and properties 3309 meteorology and atmospheric dynamics climatology 1620 5418 planetology solid surface planets heat flow keywords mars polar glaciers hesperian channels water

effect of regional slope on drainage networks drainage networks that develop under conditions of no structural control and homogeneous lithology are generally dendritic depending upon the shape and inclination of the surface on which they form an experimental study was designed to investigate the effect of an increase of slope on the evolution and development of dendritic drainage patterns as slope steepens the pattern changes from dendritic at 1 slope to subdendritic at 2 to subparallel at 3 to parallel at 5 and higher the change from a dendritic type pattern to a parallel type pattern occurs at a low slope between 2 and 3 and primary channel junction angles decrease abruptly from about 60 to 43

a case study of a ross ice shelf airstream event a new perspective abstract a case study illustrating cloud processes and other features associated with the ross ice shelf airstream ras in antarctica is presented the ras is a semipermanent low level wind regime primarily over the western ross ice shelf linked to the midlatitude circulation and formed from terrain induced and large scale forcing effects an integrated approach utilizes moderate resolution imaging spectroradiometer modis satellite imagery automatic weather station aws data and antarctic mesoscale prediction system amps forecast output to study the synoptic scale and mesoscale phenomena involved in cloud formation over the ross ice shelf during a ras event a synoptic scale cyclone offshore of marie byrd land draws moisture across west antarctica to the southern base of the ross ice shelf vertical lifting associated with flow around the queen maud mountains leads to cloud formation that extends across the ross ice shelf to the north the low level cloud has a warm signature in thermal infrare

interaction of katabatic winds and near surface temperatures in the antarctic 1 a two dimensional mesoscale model was applied to simulate wintertime katabatic winds in the antarctic coastal region simulations were made for a constant slope angle with the slope height varying and for fixed slope heights with the slope angle varying thermal wind opposed the katabatic flow near the foot of the slope but enhanced it over the high plateau the steeper and higher the slope the stronger the effect on the plateau the 2 m potential temperature decreased down the slope toward sea ice because 1 the katabatic wind resulted in the accumulation of cold near surface air over the sea ice and the lower parts of the slope 2 over the flat sea ice zone the stratification was stronger and 3 the shallow slope was within the strong surface inversion from over the sea ice with a slope aspect ratio of 5 m km 1 and a slope height below 1000 m 2 m temperature t2m decreased down the slope but for slope heights of 1500 m and more t2m increased down the slope adiabatic warming and because of the stronger wind enhanced turbulent mixing of the warmer air from aloft contributed to the warming for slope angles ranging from 1 to 20 m km 1 with a small slope height of 500 m t2m decreased down the slope but not monotonically whereas with a slope height of 2000 m yielding stronger winds and larger adiabatic warming t2m increased monotonically down the slope the model results were supported by observations from several antarctic sites with different topographic conditions

impact of iceberg c 19 on ross sea primary production 1 for the second time in 26 months a large iceberg c 19 calved off the face of the ross ice shelf rather than breaking up as did its predecessor b 15 the iceberg c 19 remained largely intact eventually stopping temporarily near pennell bank before moving out of the southwestern ross sea the presence of c 19 restricted advection of sea ice out of the region resulting in unusually high sea ice cover during the spring and summer consequently phytoplankton blooms in the region were diminished dramatically and primary production was reduced by over 90 relative to normal years calving events over the last two decades indicate that reduced primary productivity may be a typical consequence of large icebergs that drift through the southwestern ross sea during spring and summer

distribution and characteristics of mesoscale cyclones in the antarctic ross sea eastward to the weddell sea abstract the mesoscale cyclone activity observed in the portion of antarctica that faces the south pacific ocean and weddell sea area is summarized from a study of 1991 in general area normalized results reveal much greater mesoscale cyclonic activity over the ross sea ross ice shelf and southern marie byrd land than on both sides of the antarctic peninsula more than 50 of the observed mesoscale vortices are of the comma cloud type the average diameter of mesoscale vortices is approximately 200 km near terra nova bay 270 km near byrd glacier and 280 km near siple coast near the antarctic peninsula the average diameter is about 370 km over the bellingshausen sea and 380 km on the weddell sea side the largest percentage of deep vortices occurs over the bellingshausen sea sector 38 of all cases where convective instability frequently occurs over the ross sea ross ice shelf and weddell sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700

supraglacial and proglacial valleys on amazonian mars abundant evidence exists for glaciation being an important geomorphic process in the mid latitude regions of both hemispheres of mars as well as in specific environments at near equatorial latitudes such as along the western flanks of the major tharsis volcanoes detailed analyses of glacial landforms lobate debris aprons lineated valley fill concentric crater fill viscous flow features have suggested that this glaciation was predominantly cold based this is consistent with the view that the amazonian has been continuously cold and dry similar to conditions today we present new data based on a survey of images from the context camera ctx on the mars reconnaissance orbiter that some of these glaciers experienced limited surface melting leading to the formation of small glaciofluvial valleys some of these valleys show evidence for proglacial erosion eroding the region immediately in front of or adjacent to a glacier while others are supraglacial eroding a glacier s surface these valleys formed during the amazonian consistent with the inferred timing of glacial features based on both crater counts and stratigraphic constraints the small scale of the features interpreted to be of glaciofluvial origin hindered earlier recognition although their scale is similar to glaciofluvial counterparts on earth these valleys appear qualitatively different from valley networks formed in the noachian which can be much longer and often formed integrated networks and large lakes the valleys we describe here are also morphologically distinct from gullies which are very recent fluvial landforms formed during the last several million years and on much steeper slopes 20 30 for gullies versus 10 for the valleys we describe these small valleys represent a distinct class of fluvial features on the surface of mars glaciofluvial their presence shows that the hydrology of amazonian mars is more diverse than previously thought

mineralogy of the nili fossae region with omega mars express data 2 aqueous alteration of the crust 1 nili fossae is a region with fresh exposures of old material omega spectral data have revealed a strong diversity of minerals in the nili fossae region including mafic minerals and phyllosilicates phyllosilicates are found to be primarily fe rich smectites a type of clay minerals these phyllosilicates are observed only on the noachian crust in four types of locations three are without any signatures other than phyllosilicates on 1 smooth layered deposits 2 massive exhumed material and 3 crater ejecta and one type of location is associated with olivine 4 over an altered mafic unit this diversity suggests a widespread liquid water activity and a variety of alteration processes the formation of phyllosilicates underwent considerable reduction if not cessation by the time of formation of syrtis major lava flows in the hesperian period phyllosilicates are spatially and chronologically disconnected from the fluvial and depositional landforms observed in the nili fossae region observations suggest that these landforms formed after the extensive formation of phyllosilicates during short periods of time and or temperatures close to freezing

light toned strata and inverted channels adjacent to juventae and ganges chasmata mars 1 light toned layered deposits on the plains adjacent to juventae and ganges chasmata have been identified and analyzed with several instruments onboard the mars reconnaissance orbiter including hirise ctx and crism beds exhibit variations in brightness color polygonal fracturing and erosional properties that are not seen in light toned layered deposits within the chasmata at both juventae and ganges the light toned layered deposits along the plains have associated features we interpret as fluvial including sinuous ridges inverted channels that exhibit light toned layering and an extensive valley system for the ganges deposit the strong correlation between the inverted channels and light toned layered deposits suggests an association with fluvial lacustrine processes although pyroclastic and eolian activity may also be involved in their emplacement the identification of potential fluvial lacustrine layered deposits and associated valley networks suggests surface water flow in the valles marineris region that occurred for sustained periods during the hesperian 3 7 3 0 gyr

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

noachian hesperian geologic history of the echus chasma and kasei valles system on mars new data and interpretations abstract new high resolution datasets have prompted a mapping based study of the 2500 km long echus chasma and kasei valles system that utilizes geomorphic details stratigraphic relations and cratering statistics derived from the new datasets our results suggest that between the hesperian and amazonian epochs on mars 3 7 ga to recent the study area was affected by at least 4 episodes of widespread volcanic activity and 4 periods of episodic fluvio glacial activity this paper discusses the noachian to hesperian 2 6 ga history of the study area during which time in the hesperian three of the volcanic episodes took place along with the first two episodes of fluvio glacial activity highlights of our new findings and refinements from this time period include 1 two ancient western floods sourced from tharsis that occurred around 3 61 and 3 4 ga and carved the east trending path of north kasei valles 2 uranius dorsum with 58 aligned cones along its length that was emplaced in north kasei around 3 6 ga between these periods of early flooding 3 possible ash deposits surrounding echus chasma one of which contains narrow dendritic valley systems that may have been carved over a period of about 10 000 yr and 4 evidence that suggests glaciers and near surface ice may have contributed to erosion of local units

mechanisms and timescales of fluvial activity at mojave and other young martian craters mojave crater and five other relatively young late hesperian to amazonian age martian craters exhibit channelized alluvial fans that are sourced from bedrock eroded catchments these catchments emerge from the crests of sloping surfaces suggesting a formation mechanism that involved precipitation the evidence for fluvial activity at all six craters is restricted to their interiors and the immediate surrounding regions detailed mapping at mojave reveals the highest density of channels catchments and fans interior to the crater similar landforms are identified outside of the crater but not beyond 200 km from the rim irregular pits on the floor of mojave interpreted as degassing structures from hot impact melt directly superpose several fan surfaces and partly destroy the fan toes this suggests that sediment was mobilized immediately after crater formation while the crater was still hot based on the patterns and timing of channel fan development at all six craters we favor several hypotheses for the precipitation mechanism 1 snowfall and melt on young hot impact craters 2 impact plume precipitation and 3 degassing of volatiles from impact melt terrain scenario 1 suggests a different global or regional climate relative to modern conditions requiring equatorial and midlatitude snowfall accumulation scenarios 2 and 3 do not necessarily require unique climate conditions as water may have been mobilized from the target or the impactor

fluvial and lacustrine activity on layered deposits in melas chasma valles marineris mars 1 valley networks on mars are the most obvious features attesting that different geologic processes and possibly climatic conditions existed in the past themis images reveal valley networks within melas chasma in valles marineris a hesperian age canyon system the valley networks in melas chasma are dense and highly organized and the heads of the valleys are scattered at different elevations all these features suggest that the networks were fed by precipitation the morphological details reveal inner channels on some valley floors attesting that water flowed within these valleys on the dem the valleys flow into a completely enclosed depression the edge of this feature follows a mola contour line and the depression shows many sedimentary morphologies suggesting lacustrine environment these landforms are located on remnants of layered deposits possibly composed of sulfate layers suggesting that fluvial activity could have contributed to the erosion of the layered terrains in valles marineris collectively the features in melas chasma are a maximum of hesperian in age these results suggest that warm wet environmental conditions on mars persisted through the hesperian and were present during the formation of valles marineris the evidence for a paleolake in melas chasma attests to adequate environmental conditions for life development through the hesperian period

ice shelf microtopography observed using satellite thermal imagery small anomalies in ice shelf surface temperature correlate with measured microtopography clear sky thermal infrared tir images of the brunt ice shelf antarctica frequently show persistent patterns of anomalous snow surface temperatures the anomalous signatures appear as stripes orientated along the ice flowline and are of the order of 5 k in magnitude the positional persistence of the stripes suggests a topographic mechanism for their formation in order to test this hypothesis the tir stripes are compared to a digital terrain model dtm derived from a kinematic global positioning system survey of the ice shelf ridges and valleys are seen in the dtm the ridges correspond to the warmer tir stripes the valleys to the colder areas in order to investigate the mechanism that couples elevation with thermal signature two comparable but contrasting sets of clear sky infrared images are presented along with surface meteorological data the first shows strong tir stripes whilst the second despite similar snow and air temperature profiles shows a weaker signature and smaller sensible heat flux h two possible mechanisms are presented which explain the tir signature surface elevation mapping onto the vertical air temperature profile or alternatively enhanced surface sensible heat flux on elevated areas at present there is insufficient information to resolve this uncertainty

evidence for a short period of hydrologic activity in newton crater mars near the hesperian amazonian transition 1 hesperian amazonian aged valleys and alluvial fans distributed in regional clusters throughout the southern middle to low latitudes were formed during a period of fluvial runoff and erosion which acted over a smaller spatial and temporal scale than the older classical martian valley networks dated to the noachian hesperian boundary in order to explore the potential sources of water which formed these younger valleys we calculated the expected sediment transport and water discharge rates for a valley and alluvial fan located in newton crater 40 s 159 e over a wide range of water filled channel depths and sediment grain sizes in order to constrain the formation timescale and required water volume depending on the depth of the water filled channel within the valley the alluvial fan was likely emplaced over 0 1 to 10 years of fluvial activity involving between 1 8 and 5 7 km 3 of water these results imply water runoff rates of between 1 and 10 cm d over a typical 300 km2 drainage area possible processes for delivering water to these drainages include high obliquity snowpack melting via volcanism or impacts resulting in either scattered local to regional melting events or a brief global warming event an extended perhaps episodic period of fluvial activity lasting hundreds of years driven by insolation induced melting of high obliquity snowpacks is another possibility

sea ice variability and primary productivity in the ross sea antarctica from methylsulphonate snow record 1 the ross sea contains the most biologically productive continental shelf in antarctica and is a region where the annual formation of sea ice drives substantial amounts of bottom water formation we present snow pit chemistry data from mt erebus saddle that provide a quantitative proxy to reconstruct summer sea ice conditions and rates of marine primary production the methylsulphonate ms record is strongly correlated with changes in the area of open water r2 0 903 p 0 05 caused by differences in atmospheric circulation and the sea ice damming effect of large icebergs b 15 and c 19 which calved from the ross ice shelf in 2000 and 2002 respectively furthermore ms and phytoplankton net primary production correlate significantly r2 0 927 p 0 01 our results demonstrate the potential of the mt erebus saddle ice core to reconstruct sea ice and primary productivity variability in the ross sea beyond the observational record

mineralogy of juventae chasma sulfates in the light toned mounds mafic minerals in the bedrock and hydrated silica and hydroxylated ferric sulfate on the plateau 1 juventae chasma contains four light toned sulfate bearing mounds denoted here as a d from west to east inside the trough mafic outcrops at the base of the mounds and in the wall rock and light toned layered deposits of opal and ferric sulfates on the plateau hyperspectral visible near infrared compact reconnaissance imaging spectrometer for mars crism spectra were used to identify monohydrated and polyhydrated sulfate phs outcrops of layered material on the bright mounds most of the monohydrated sulfate signatures closely resemble those of szomolnokite feso4 h2o characterized by a water band near 2 08 m while some areas exhibit spectral features more similar to those of kieserite mgso4 h2o with a band centered closer to 2 13 m the largest phs outcrops occur on the top of mound b and their spectral features are most consistent with ferricopiapite melanterite and starkeyite but a specific mineral cannot be uniquely identified at this time coordinated analyses of crism maps mars orbiter laser altimeter elevations and high resolution imaging science experiment images suggest that mounds a and b may have formed together and then eroded into separate mounds while mounds c and d likely formed separately mafic minerals low ca pyroxene high ca pyroxene and olivine are observed in large 2 10 km wide outcrops in the wall rock and in smaller outcrops 50 500 m across at the floor of the canyon most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals the plateau region northwest of juventae chasma is characterized by an abundance of light toned layered deposits one region contains two spectrally unique phases exhibiting a highly stratified terraced pattern crism spectra of one unit eroded into swirling patterns with arc like ridges exhibit a narrow 2 23 m band assigned to hydroxylated ferric sulfate a thin layer of a fractured material bearing an opaline silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate bearing light toned layered deposits hydrothermal processes may have produced an acidic environment that fostered formation of the hydrated silica and hydroxylated ferric sulfate units

geomorphic study of fluvial landforms on the northern valles marineris plateau mars 1 fluvial landforms are observed on the plateau near echus chasma and other locations on the valles marineris plateau using high resolution 10 to 50 m pixel mars express images and topography branching valleys have a 20 to 100 m deep v shape profile typical of fluvial processes their incision occurred in a thin 150 m and weak dark unit that overlies the plateau basement the valleys are distributed close to watershed boundaries as expected for overland flows and different from pure glacial or hydrothermal processes the 2d geometry of valley networks show drainage densities reaching 1 3 km 1 that indicate a strong 2d extension stage that usually requires a minimum of thousands of years as established from terrestrial examples however the 3d valley geometry shows a limited incision and a lack of concavity suggesting a limited development in time millions of years of evolution are unlikely many outlets connect to the heads of canyons of echus chasma that might involve sapping processes these canyons might have formed coevally with shallow valleys their difference in geometry is a consequence of the difference in lithology which induced a difference in the erosion capacity and an enhanced infiltration conducing to sapping valleys are submitted to modification by aeolian processes sometimes leading to the formation of inverted channels as observed more broadly through the region these landforms formed late in the early mars history and might be considered as examples of episodic fluvial events due to short term climate changes and or regional fluvial activity after the noachian

raised channel systems as indicators of palaeohydrologic change a case study from oman abstract the aim of this paper is to determine the extent to which raised channel systems may be used as indicators of long term paleohydrologic change and hence of broader paleoenvironmental changes in arid areas during the cenozoic the paper reviews the paleohydrologic significance of former drainage systems in arid areas and demonstrates the application of paleohydrologic methods to the analysis of the long term evolution of a complex series of exhumed multistorey raised channel systems in interior oman the paper discusses the range of possible autocyclic and allocyclic controls on changes in channel behaviour through time as a means of establishing the paleoenvironmental significance of observed changes in paleochannel pattern morphology sedimentology and stability the paper identifies some of the major allocyclic controls including climatic changes and particularly the seasonality magnitude frequency and distribution of rainfall events during the cenozoic together with the degree of continentality and hence the strength and persistence of arid wind systems base level changes due to eustatic fluctuations and or tectonic activity may also act to control long term patterns of aggradation followed by large scale landscaping lowering however long term fan ageing associated with progressive aggradation and steepening of paleochannel systems may also eventually lead to fanhead trenching independent of any external controls in addition progressive expansion of the drainage network and resulting river capture can lead to marked increases in water and sediment supplies to the fluvial system the paper also emphasizes the difficulties involved both in differentiating the wide range of possible controls on paleohydrologic response and also in developing an accurate and precise chronology for desert paleodrainage systems and in their correlation with non fluvial sedimentological sequences the raised channel systems of interior oman consist of heavily desert varnished chert and or ophiolite rich gravels dating from some time during the plio pleistocene period the paleochannels from sinuous gravel ridges rising the observed changes have resulted from a complex combination of both internally and externally generated environmental changes during the cenozoic progressive extension of the drainage network on to the ophiolite massif of the mountain source area resulted in river capture and a concomitant increase both in paleodischarges and in supplies of ophiolitic sediments to the paleodrainage system the early sinuous channels may have developed under a humid to sub humid climate in which perennial or seasonal flows allowed the distinct meander paleochannels to form ephemeral flows characterized by flash flood regimes were probably associated with the later distributary systems which may reflect semi arid to arid climatic conditions the large scale deflation of the interfluve sediments which resulted in the eventual exhumation of the cemented gravel capped multistorey paleochannel sequence is also likely to have occurred during periods of marked continentality probably during periods of low sea level associated with the quaternary glaciations

chaos terrain storms and past climate on mars 1 we model the atmospheric response to a chaos forming event at juventae chasma north of valles marineris mars using the mars regional atmospheric modeling system mrams interactions between lake driven convergence topography and the regional wind field steer lake induced precipitation to the southwest mean snowfall reaches a maximum of 0 9 mm h water equivalent peak snowfall 1 7 mm h water equivalent on the sw rim of the chasm more than 80 of vapor released by the lake is trapped in or next to the lake as snow radiative effects of the thick cloud cover raise mean plateau surface temperature by up to 18 k locally we find that the area of maximum modeled precipitation corresponds to the mapped juventae plateau channel networks at echus chasma modeled precipitation maxima also correspond to mapped plateau channel networks this is consistent with the earlier suggestion that valles marineris plateau layered deposits and interbedded channel networks result from localized precipitation however snowpack thermal modeling shows temperatures below freezing for the 12 mbar co2 atmosphere used in our mrams simulations this is true even for the most favorable orbital conditions and whether or not the greenhouse effect of the lake storm is included moderately higher co2 pressures or non co2 greenhouse forcing is very likely required for melting and plateau channel network formation under a faint young sun required warming is 10 k global temperatures need not be higher than today in these localized precipitation scenarios the rest of the planet remains dry

late hesperian to early amazonian midlatitude martian valleys evidence from newton and gorgonum basins 1 numerous shallowly incised valleys extend from the upper interior rims of newton and gorgonum basins across smooth interior basin deposits these valleys are a few meters to 300 m wide and may have experienced discharges over all or most of their width implying that they are in fact incised channels in newton crater these valleys extend up to 75 km to near the center of the basin floor in gorgonum basin the valleys terminate at what we interpret to be a former ice covered lake these valleys appear to be examples of scattered shallowly incised valleys found throughout the midlatitudes of mars superimposed upon the widespread mantling deposits within the region on the basis of crater count age dating the interior valleys in newton and gorgonum basins were formed at about the hesperian to amazonian transition the runoff through the valleys may have occurred due to episodic melting of snow and ice that had accumulated on the crater rims temperatures warm enough to cause extensive melting may have occurred during optimal orbital and obliquity configurations because of intensive volcanism releasing greenhouse gasses or as a result of a brief episode of warming from a large impact somewhere on mars the valleys were formed at about the same time as major outflow channels were active along the highlands lowlands boundary water delivered to the northern lowlands by the outflow channels may have been recycled as snow and ice deposits within the martian midlatitudes the episodic melting of such deposits may have formed the midlatitude valleys

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

topography of valley networks on mars from mars express high resolution stereo camera digital elevation models 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands the geometry of valley networks can be studied using mars orbiter laser altimeter mola altimetry which is sufficient to map large valleys without a detailed 3 d shape of valley networks imaging from the mars express high resolution stereo camera hrsc is used to generate digital elevation models dems with resolution 50 m and vertical accuracy 60 m we studied valleys near huygens crater and in the aeolis region both in the noachian bedrock and on the west echus plateau in hesperian bedrock hrsc dems in these areas show that 1 drainage density is 3 times higher than is observed in mola data 2 degree of ramification is 1 order more than with mola 3 transverse valley profiles show a v shape more accurately and a minimum depth of 20 m and 4 higher drainage density shows greater headward extension that is not correlated to greater valley depth the deepest valleys 400 m are found in the huygens region where the density in the dem is 0 1 km 1 compared to shallow valleys 100 m of the echus region where the density is higher 0 3 km 1 these regional differences are due to spatially variable preservation and bedrock lithology longitudinal profiles suggest variations in duration of activity profile concavity is only developed in some noachian terrains valleys visible in hrsc images correspond to topographic features in dems showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage

a description of the ross ice shelf air stream ras through the use of self organizing maps soms 1 the low level wind field across the ross ice shelf region antarctica is studied through the method of self organizing maps soms emphasis is placed on identifying and characterizing the ross ice shelf air stream ras the ras is a dominant northward stream of air resulting in significant transport of atmospheric mass from the interior of antarctica two soms are created for the lowest model level 13 m and the 5th lowest model level 150 m from archived real time numerical weather prediction output of the antarctic mesoscale prediction system amps a verification of the som for the lowest model level is completed by comparing select nodes to automatic weather station wind rose plots the winds depicted in the lowest model level som are dominated by the position of the cyclone in the ross sea and the changes in wind speeds on the antarctic plateau the 5th lowest model level provides a better depiction of the ras the ras is found to be present primarily when associated with a cyclone in the ross sea there is a strong seasonality to the ras with the ras occurring frequently during the winter months and rarely during the summer months the structure and position of the ras is strongly dependent on the position of the ross sea cyclone

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

localized precipitation and runoff on mars 1 we use the mars regional atmospheric modeling system mrams to simulate lake storms on mars finding that intense localized precipitation will occur for lake size 103 km2 mars has a low density atmosphere so deep convection can be triggered by small amounts of latent heat release in our reference simulation the buoyant plume lifts vapor above condensation level forming a 20 km high optically thick cloud ice grains grow to 200 m radius and fall near or in the lake at mean rates up to 1 5 mm h 1 water equivalent maximum rates up to 6 mm h 1 water equivalent because atmospheric temperatures outside the surface layer are always well below 273 k supersaturation and condensation begin at low altitudes above lakes on mars in contrast to earth lake effect storms lake storms on mars involve continuous precipitation and their vertical velocities and plume heights exceed those of tropical thunderstorms on earth for lake sizes 102 5 to 103 5 km plume vertical velocity scales linearly with lake area convection does not reach above the planetary boundary layer for lakes 103 km2 or for atmospheric pressure o 102 mbar instead vapor is advected downwind with little cloud formation precipitation occurs as snow and the daytime radiative forcing at the land surface due to plume vapor and storm clouds is too small to melt snow directly 10 w m 2 however if orbital conditions are favorable then the snow may be seasonally unstable to melting and produce runoff to form channels we calculate the probability of melting by running thermal models over all possible orbital conditions and weighting their outcomes by probabilities given by long term integrations of the chaotic diffusion of solar system orbital elements with this approach we determine that for an equatorial vapor source sunlight 15 fainter than at present and snowpack with albedo 0 28 0 35 melting may occur with 4 0 1 probability this rises to 56 12 if the ancient greenhouse effect was modestly 6 k greater than today

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

3d morphometry of valley networks on mars from hrsc mex dems implications for climatic evolution through time 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands eight dense branching valley networks were studied in noachian terrains of huygens newcomb and kepler craters south tyrrhena terra and thaumasia in hesperian terrains of echus plateau and west eberswalde craters and in amazonian terrains of alba patera using images and digital elevation models from the mars express high resolution stereo camera to determine 2d and 3d morphometric parameters extracted geomorphic parameters show similar geometry to terrestrial valleys drainage densities organization from bifurcation ratios and lengths ratios hack exponent consistent with terrestrial values of 0 6 and progressive deepening of valleys with increasing strahler order in addition statistics on valley depths indicate a deeper incision of noachian valleys compared to younger post noachian valleys 100 m for noachian ones showing a strong difference in fluvial erosion these characteristics show that dense martian valley networks formed by overland flows in relation to a global atmospheric water cycle in noachian epoch and confirm that the later stages of activity may be related to shorter duration of activity distinct climatic conditions and or regional processes or conditions

effects of obliquity and water vapor trace gas greenhouses in the early martian climate 1 we explore possible mechanisms for the generation of warm wet climates on early mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions the presence of both water vapor a strong greenhouse gas and other trace greenhouse gases such as so2 in a predominantly co2 atmosphere may act under certain conditions to elevate surface temperatures above the freezing point of liquid water at least episodically variations in obliquity are explored to investigate whether these periodic variations in insolation at mars can broaden the regions or seasons where warm temperatures can exist we use the mars weather research and forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by johnson et al 2008 while achieving temperatures above 273 k globally remains challenging the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions which can help to explain the presence of fluvial surface features e g valley networks and hydrous minerals of post noachian age a period when alternate methods do not convincingly explain the sustainability of liquid water furthermore we find that global warming can be achieved with the presence of a darker surface globally which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

birdseyes fenestrae shrinkage pores and loferites a reevaluation abstract birdseyes birdseye limestone fenestrae fenestral fabric shrinkage pores and loferites are considered similar if not synonymous when occurring in lime mudstone or syndepositional dolomite especially in association with mudcracks and stromatolites compaction experiments indicate however that in the absence of early cementation these rugs can be completely obliterated whereas mudcracks and stromatolites remain relatively unchanged lumping of burrows and root tubes under the general terms birdseyes or fenestrae such as for example tubular fenestrae burrow fenestrae or root tube fenestrae is discouraged they should be called burrows or root tubes because the birdseyes fenestrae and shrinkage pores are so intimately associated with tidal flats in the minds of most geologists submarine cementation of pelletal and oolitic botryoidal grainstone under 5 to 6 m of water on the bahama banks has resulted in rugs provocatively similar to many birdseyes and fenestrae generally attributed to peritidal conditions in the literature birdseyes and fenestrae in ancient grainstones cannot therefore be reliably identified without consideration of the sedimentary sequence and assoc ated sedimentary structures

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

mars reconnaissance orbiter observations of light toned layered deposits and associated fluvial landforms on the plateaus adjacent to valles marineris abstract we have used data from the mars reconnaissance orbiter to study 30 80 m thick light toned layered deposits on the plateaus adjacent to valles marineris at five locations 1 south of ius chasma 2 south of western melas chasma 3 south of western candor chasma 4 west of juventae chasma and 5 west of ganges chasma the beds within these deposits have unique variations in brightness color mineralogy and erosional properties that are not typically observed in light toned layered deposits within valles marineris or many other equatorial areas on mars reflectance spectra indicate these deposits contain opaline silica and fe sulfates consistent with low temperature acidic aqueous alteration of basaltic materials we have found valley or channel systems associated with the layered deposits at all five locations and the volcanic plains adjacent to juventae ius and ganges exhibit inverted channels composed of light toned beds valleys channels and light toned layering along the walls of juventae and melas chasmata are most likely coeval to the aqueous activity that affected the adjacent plateaus and indicate some hydrological activity occurred after formation of the chasmata although the source of water and sediment remains uncertain the strong correlation between fluvial landforms and light toned layered deposits argues for sustained precipitation surface runoff and fluvial deposition occurring during the hesperian on the plateaus adjacent to valles marineris and along portions of chasmata walls

evolution of vertical knickpoints waterfalls with resistant caprock insights from numerical modeling 1 vertical knickpoints waterfalls mark a prominent process transition zone whose governing mechanics is not represented by conventional stream power incision models we examine the evolution of vertical knickpoints with resistant caprock utilizing numerical simulations that explicitly represent 1 face failure mechanisms 2 flow acceleration and amplified erosion above a knickpoint lip 3 deposition and removal of coarse debris below the knickpoint and 4 base level lowering or tectonic uplift rates our model demonstrates that knickpoint retreat rate where the subcaprock is weak or vertically jointed and base level fall rates are steady is likely to become tied to downstream conditions and equal to the downstream incision rate divided by channel gradient mechanically this coupling occurs where the subcaprock reaches a threshold height for failure in shear or buckling or where the weathering rate of the subcaprock is higher than the downstream incision wave velocity vi ds the height of the subcaprock face can influence its gravitational stability and the knickpoint lateral erosion rate and lead to a feedback between downstream incision and retreat rate retreat rate can be lower than vi ds during transients which could be long 106 years and set by the weathering rate of the subcaprock or influenced by lag debris evacuation key variables other than discharge can be important in setting retreat rates these include base level lowering rate the rock strength of stratigraphic units downstream of the knickpoint and the size and flux of sediment contributed from above the knickpoint or from the canyon walls two types of oversteepened reaches can form in association with a vertical knickpoint 1 an upstream free fall induced oversteepened reach whose length is longer than the flow acceleration zone and 2 a downstream coarse debris induced oversteepened reach although the model was constructed with caprock type knickpoints in mind some of its elements and insights are also relevant to homogenous substrates

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

satellite observations of katabatic wind propagation for great distances across the ross ice shelf abstract five winter months april august 1988 of thermal infrared satellite images were examined to investigate the occurrence of dark warm signatures across the ross ice shelf in the antarctic continent these features are inferred to be generated by katabatic winds that descend from southern marie byrd land and then blow horizontally across the ice shelf significant mass is added to this airstream by katabatic winds blowing from the major glaciers that flow through the transantarctic mountains from east antarctica these negatively buoyant katabatic winds can reach the northwestern edge of the shelf a horizontal propagation distance of up to 1000 km 14 of the time where the airstream crosses from the ice shelf to the ice covered ross sea a prominent coastal polynya is formed because the downslope buoyancy force is near zero over the ross ice shelf the northwestward propagation of this katabatic air mass requires pressure gradient support the study shows that the extended horizontal propagat

phyllosilicates in the mawrth vallis region of mars 1 omega mars express has discovered large outcrops rich in phyllosilicates in the region of mawrth vallis mars around 20 w 25 n the region is located in noachian highly cratered terrains close to the limit of the martian dichotomy where the outflow channel mawrth vallis cuts the highlands we have examined this region using omega spectra of the surface from 0 9 m to 2 6 m with spatial sampling from 500 m to 3 km offering a full coverage of the region omega spectra show two broad bands centered at 1 m and 2 2 m revealing the presence of clinopyroxene on dark surfaces phyllosilicates have been identified by absorption bands at 1 4 m 1 9 m and 2 2 or 2 3 m comparison with laboratory spectra reveals similarities with al oh smectites such as montmorillonites or fe or mg oh smectites such as nontronite a precise location of the phyllosilicate rich areas on visible hrsc images indicates that they are placed exclusively on bright outcrops mostly on the plateaus dated to the noachian period on hrsc and moc images the phyllosilicate rich outcrops reveal strong erosional features such as numerous residual buttes composed of layers a few meters thick the phyllosilicate rich unit corresponds to a geological unit more than 100 m thick over a horizontal extension approximately of 300 km 400 km this unit implies a large volume of altered rocks either in situ or after transport and deposition in noachian terrains revealing a different climatic and geologic environment from the present one

ancient glaciation on mars a large number of anomalous landforms on mars can be attributed to glaciation including the action of ice and meltwater glacial landscapes are concentrated south of lat 33 and in the northern plains suggesting vast austral and boreal ice sheets crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in martian history thus mars may have had a relatively warm moist climate and dense atmosphere much later than previously believed

most mars minerals in a nutshell various alteration phases formed in a single environment in noctis labyrinthus 1 a closed depression in the noctis labyrinthus region of mars at 10 4 s 98 6 w believed to have formed in the late hesperian holds an inner pit partially filled with several hundred meters of stratified material compact reconnaissance imaging spectrometer for mars crism visible near infrared reflectance data reveal signatures of numerous hydrated minerals including halloysite kaolinite fe smectite si oh bearing phases and fe sulfates polyhydrated monohydrated and hydroxylated types including jarosite we use crism data high resolution imagery hirise and hrsc high resolution stereo camera derived elevation to analyze the morphology composition and stratigraphy of these materials we propose an alteration sequence including formation of acid sulfate solutions from groundwater and magmatic sulfur which then locally altered the basaltic bedrock and layered sediments mainly deposited from volcanic tephra forming fe smectite and fe sulfates the mineral variability can mostly be explained by local variations in the ph of the altering fluids with original acidity being buffered by dissolution of primary minerals and by variable fluid input and evaporation and or freezing rates resulting in various water rock ratios this site shows local formation of almost all classes of minerals identified thus far on mars without invoking global conditions processes related to local volcanic activity and associated hydrothermalism were able to produce during an era in which the climate is believed to have been cold a large variety of hydrated minerals this study highlights the importance of the geological setting of hydrated minerals in the understanding of mars geologic and climatic evolution

a 200 year sulfate record from 16 antarctic ice cores and associations with southern ocean sea ice extent chemistry data from 16 50 115m deep sub annually dated ice cores are used to investigate spatial and temporal concentration variability of sea salt ss so4 2 and excess xs so4 2 over west antarctica and the south pole for the last 200 years low elevation ice core sites in western west antarctica contain higher concentrations of so4 2 as a result of cyclogenesis over the ross ice shelf and proximity to the ross sea polynya linear correlation analysis of 15 west antarctic ice core so4 2 time series demonstrates that at several sites concentrations of ssso4 2 are higher when sea ice extent sie is greater and the inverse for xsso4 concentrations of xsso4 2 from the south pole site east antarctica are associated with sie from the weddell region and west antarctic xsso4 2 concentrations are associated with sie from the bellingshausen amundsen ross region the only notable rise of the last 200 years in xsso4 around 1940 is not related to sie fluctuations and is most likely a result of increased xsso4 2 production in the mid low latitudes and or an increase in transport efficiency from the mid low latitudes to central west antarctica these high resolution records show that the source types and source areas of ssso4 2 and xsso4 2 delivered to eastern and western west antarctica and the south pole differ from site to site but can best be resolved using records from spatial ice core arrays such as the international trans antarctic scientific expedition itase

satellite derived maps of arctic and antarctic sea ice motion 1988 to 1994 standard image processing methods applied to 85 5 ghz special sensor microwave imager ssm i data provide previously unseen details about sea ice motion in the arctic and southern oceans means calculated from daily ice motions for 1988 1994 confirm the basic circulation patterns established from drifting stations and buoys but extend these observations to illustrate less well known transport patterns in the arctic coastal zones and sub arctic seas in the antarctic the gridded motion fields show a nearly continuous westward transport along the antarctic coast with well defined regions of exchange between this east wind drift and the antarctic circumpolar current this detailed view of mean ice motion in the southern ocean is unique and presents a comprehensive overview not previously available for antarctic ice motions

a validation of the antarctic mesoscale prediction system using self organizing maps and high density observations from snowweb abstractthis study compares high resolution output 1 1 km horizontal grid length from twice daily forecasts produced by the antarctic mesoscale prediction system amps with a dense observational network east of ross island covering 10 000 km2 15 snowweb stations significantly increased the number of observation stations in the area to 19 during the 2014 15 austral summer collocated virtual stations created from amps output are combined with observations producing a single dataset of zonal and meridional wind components used to train a self organizing map som the resulting som is used to individually classify the observational and amps datasets producing a time series of classifications for each dataset directly comparable to the other analysis of class composites shows two dominant weather patterns low but directionally variable winds and high but directionally constant winds linked to the ross ice shelf airstream ras during ras events the amps and snowweb data displayed good temporal cl

martian geomorphology from fractal analysis of drainage networks 1 an alternative approach to conventional planetary terrain analysis is proposed martian terrains represented by topography based on the mars orbiter laser altimetry mola data are represented as a series of drainage basins regardless of the historical presence or absence of actual fluid flow a fractal analysis of each drainage network computationally extracted from an underlying terrain yields a network descriptor a list of four numbers that describes the traits of a network network descriptors are used for a quantitative characterization and classification of martian surfaces we have extracted and analyzed 387 drainage networks from 74 martian locations representing all major epochs and geological units to investigate whether their network descriptors are capable of differentiation between different epochs and geological units we have found that our approach can distinguish morphologically different terrains but only in a statistical sense in particular the method could be used to measure the degree of surface cratering and thus the age of the surface in addition for surfaces that are not heavily cratered the method is capable of distinguishing between different geological units we have found no global trends in the character of martian drainage networks their network descriptors show no systematic dependence on location or elevation our analysis reveals that all noachian surfaces grouped in the npld geological unit have very similar network descriptors regardless of prominence and integration of their visible fluvial features the comparison between statistical description of npld and terrestrial drainage networks shows overall similarities but also some marked differences because of these differences the notion of sustained rainfall on mars during the noachian epoch is inconsistent with our findings but a limited rainfall is compatible with our results