true polar wander driven by late stage volcanism and the distribution of paleopolar deposits on mars article i nfo the areal centroids of the youngest polar deposits on mars are offset from those of adjacent paleopolar deposits by 5 10 we test the hypothesis that the offset is the result of true polar wander tpw the motion of the solid surface with respect to the spin axis caused by a mass redistribution within or on the surface of mars in particular we consider the possibility that tpw is driven by late stage volcanism during the late hesperian to amazonian there is observational and qualitative support for this hypothesis in both north and south observed offsets lie close to a great circle 90 from tharsis as expected for polar wander after tharsis formed we calculate the magnitude and direction of tpw produced by mapped late stage lavas for a range of lithospheric thicknesses lava thicknesses eruption histories and prior polar wander events we find that if tharsis formed close to the equator the stabilizing effect of a fossil rotational bulge located close to the equator leads to predicted tpw of b2 too small to account for observed offsets if however tharsis formed far from the equator late stage tpw driven by low latitude late stage volcanism would be 6 33 similar to that inferred from the location of paleopolar deposits a volume of 4 4 1 3 10 19 kg of young erupted lava can account for the offset of the dorsa argentea formation from the present day south rotation pole this volume is consistent with prior mapping based estimates and would imply a mass release of co2 by volcanic degassing similar to that in the atmosphere at the present time the south polar layered deposits are offset from the present rotation pole in a direction that is opposite to the other paleopolar deposits this can be explained by either a sequential eruption of late stage lavas or an additional contribution from a plume beneath elysium we predict that significant volcanic activity occurred during the time interval represented by the basal unit planum boreum unconformity planum boreum postdates the promethei lingula lobe and that the north polar deposits span a substantial fraction of solar system history if the additional contribution to tpw from plumes is small then we would also predict that tharsis montes formation postdates the promethei lingula lobe of the south polar layered deposits we conclude with a list of observational tests of the tpw hypothesis

the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

hydrogen isotope evidence for loss of water from mars through time 1 the high d h of the martian atmosphere 5 6 terrestrial is considered strong evidence for the loss of martian water to space the timing and magnitude of the loss of water from mars can be constrained by measurements of d h in martian meteorites previous studies of martian meteorites have shown a large range in d h from terrestrial values to as high as the current martian atmosphere here we show that the ancient 4 ga mars meteorite alh84001 has a d h 4 terrestrial and that the young 0 17 ga shergotty meteorite has a d h 5 6 terrestrial we also find that the young los angeles shergottite has zoning in d h that can be correlated to igneous growth zoning strongly suggesting assimilation of d enriched water during igneous crystallization near the martian surface in contrast to previous studies we find higher and less variable d h ratios in these three meteorites our results suggest a two stage evolution for martian water a significant early loss of water to space prior to 3 9 ga followed by only modest loss to space in the last 4 billion years the current martian atmospheric d h has remained essentially unchanged for the last 165 ma

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

a probabilistic case for a large missing carbon sink on mars after 3 5 billion years ago abstract mars has a thin 6 mbar co2 atmosphere currently there is strong evidence for paleolakes and rivers formed by warm climates on mars including after 3 5 billion years ga ago which indicates that a co2 atmosphere thick enough to permit a warm climate was present at these times since mars no longer has a thick co2 atmosphere it must have been lost one possibility is that martian co2 was lost to space oxygen escape rates from mars are high enough to account for loss of a thick co2 atmosphere if co2 was the main source of escaping o but here using h isotope ratios o escape calculations and quantification of the surface o sinks on mars we show for the first time that o escape from mars after 3 5 ga must have been predominantly associated with the loss of h2o not co2 and therefore it is unlikely that 250 mbar martian co2 has been lost to space in the last 3 5 ga because such results require highly unfavored o loss scenarios it is possible that the presence of young rivers and lakes on mars could be reconciled with limited co2 loss to space if crater chronologies on mars are sufficiently incorrect that all apparently young rivers and lakes are actually older than 3 5 ga or if climate solutions exist for sustained runoff on mars with atmospheric co2 pressure

paleotemperature and paleosalinity inferences and chemostratigraphy across the aptian albian boundary in the subtropical north atlantic 1 geochemical analyses of extraordinarily well preserved late aptian early albian foraminifera from blake nose ocean drilling program site 1049 reveal rapid shifts of 18o 13c and 87sr 88sr in the subtropical north atlantic that may be linked to a major planktic foraminifer extinction event across the aptian albian boundary the abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0 8 1 4 million years at the boundary contact but the values before and after the hiatus indicate that major oceanographic changes occurred at this time 87sr 88sr increase by 0 000 200 13c values decrease by 1 5 to 2 2 and 18o values decrease by 1 0 planktics to 0 5 benthics across the hiatus further both 87sr 88sr ratios and 18o values during the albian are anomalously high the 87sr 88sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter basin differences in seawater 87sr 88sr during the albian or revision of the seawater curve for 18o planktic values in some aptian samples likely reflect a diagenetic overprint but preservation is excellent in the rest of the section in well preserved material benthic foraminiferal values are largely between 0 5 and 0 0 and planktic samples are largely between 0 0 to 1 0 with a brief excursion to 2 0 during oae 1b using standard assumptions for cretaceous isotopic paleotemperature calculations the 18o values suggest bottom water temperatures at 1000 1500 m of 8 10 c and surface temperatures of 10 14 c which are 4 6 c and 10 16 c cooler respectively than present day conditions at the same latitude the cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present because of their exquisite preservation whole scale alteration of the analyzed foraminifera is an untenable explanation our proposed solution is a high evaporative fractionation factor in the early albian north atlantic that resulted in surface waters with higher 18o values at elevated salinities than commonly cited in cretaceous studies a high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and like the sr isotopes implies limited connectivity among the individual basins of the early cretaceous proto atlantic ocean

atmospheric origin of martian interior layered deposits links to climate change and the global sulfur cycle since the first photogeologic exploration of mars vast mounds of layered sediments found within the valles marineris troughs interior layered deposits ilds have remained unexplained recent spectroscopic results showing that these materials contain coarse grained hematite and sulfate suggest that they are fundamentally similar to layered sulfate deposits seen elsewhere on mars and are therefore a key piece of the global aqueous history of mars in this work we constrain the origin of the ilds by considering mass balance equations one model involving formation of the ilds by groundwater upwelling requires that a significant fraction of the global martian sulfur budget was concentrated in the valles marineris at the time when the ilds formed it also necessitates high deposition and erosion rates in the hesperian we favor an alternative model in which the ilds formed in a configuration similar to what is observed today through atmospherically driven deposition of ice dust and volcanogenic sulfuric acid such a model is easily compatible with the global sulfur budget and does not require significant erosion rates or large volumes of liquid water we propose that formation of sulfate rich layered sediments on mars was governed through time by volcanogenic so 2 and h 2 o emission rates and dust production against a backdrop of obliquity variation in a largely cold and dry climate

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

origin and evolution of a cold based tropical mountain glacier on mars the pavonis mons fan shaped deposit 1 each of the large tharsis montes volcanoes in the equatorial region of mars has an unusual amazonian aged fan shaped deposit on its west northwestern flank on the basis of viking orbiter data the origin of these deposits has been variously ascribed to volcanic mass wasting tectonic and glacial processes using new mgs and odyssey data combined with recent developments in the study of cold based glaciers we reassess the geology and mode of origin for these deposits with particular emphasis on pavonis mons the deposits share three characteristic facies including 1 a ridged facies consisting of tens to 100 parallel concentric ridges around the margins of the deposits 2 a knobby facies composed of irregular hills and hummocks and 3 a smooth facies of broad lobate plains that superposes all other units within the deposits on the basis of morphology topography superposition relationships and close terrestrial analogs in the dry valleys of antarctica we interpret the pavonis fan shaped deposit as the depositional remains of a cold based glacier that formed on the northwestern flank in recent martian history we interpret the ridged facies as drop moraines formed around the margins of a retreating cold based glacier the knobby facies as a sublimation till derived from in situ down wasting of cold based glacial ice and the smooth facies as extant debris covered glacial ice in addition to the three main facies the fan shaped deposit at pavonis mons contains several unique features including arcuate scarps high relief flow like features and radial ridges which suggest that volcanism played a role during its formation using recent results from mars general circulation model simulations we outline a model of glacier formation involving atmospheric deposition of water ice on the northwestern flanks of the tharsis montes during periods of high mean obliquity reconstructed ice sheet profiles for each of the tharsis montes glaciers suggest that the ice sheets attained average thicknesses of 1 6 2 4 km values that are consistent with a cold based glacial origin analysis of crater size frequency distributions using new data indicates that the age of the glaciation lies within the late amazonian 10 200 ma thus our results suggest that multiple phases of tropical mountain glaciation occurred on mars within the past few hundred myr and that significant amounts of near surface equatorial ice may remain within the deposit today

strong water isotopic anomalies in the martian atmosphere probing current and ancient reservoirs we measured maps of atmospheric water h2o and its deuterated form hdo across the martian globe showing strong isotopic anomalies and a significant high deuterium hydrogen d h enrichment indicative of great water loss the maps sample the evolution of sublimation from the north polar cap revealing that the released water has a representative d h value enriched by a factor of about 7 relative to earth s ocean vienna standard mean ocean water vsmow certain basins and orographic depressions show even higher enrichment whereas high altitude regions show much lower values 1 to 3 vsmow our atmospheric maps indicate that water ice in the polar reservoirs is enriched in deuterium to at least 8 vsmow which would mean that early mars 4 5 billion years ago had a global equivalent water layer at least 137 meters deep

mercury anomalies in upper aptian lower albian sediments from the tethys realm abstract the upper aptian lower albian stratigraphic interval documents important perturbations in the carbon cycle associated with the oceanic anoxic event 1b oae 1b tentatively connected with pulses in volcanic activity and the formation of the southern kerguelen plateau however uncertainties in existing age models for this interval preclude a robust and definitely convincing cause effect connection between these two events a sedimentary record from the poggio le guaine section umbria marche basin shows anomalously high levels of mercury during the upper aptian lower albian interval the persistence of the anomalies of hg after normalization against toc al and fe suggests that chemical and physical processes related to organic matter scavenging adsorption onto clay minerals hydrous iron oxides and sulphur only played a secondary role as mechanisms for hg accumulation in the sediments in agreement with previous studies in which anomalous enrichments of hg in sedimentary records were interpreted as monitors of enhanced volcanic activity we speculate that the hg enrichments documented in the poggio le guaine section reflect a rapid increase in atmospheric hg content associated with a massive release of volcanic hg and possibly suggest a multi phase emplacement of the southern kerguelen plateau skp as a realistic source nonetheless comparison of hg profiles and micropalaeontological data from the poggio le guaine section reasonably excludes the possibility that the global biotic turnover horizon documented in the upper aptian could be directly attributed to the volcanic pulses of the skp emplacement

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

three dimensional radar imaging of structures and craters in the martian polar caps abstract over the last decade observations acquired by the shallow radar sharad sounder on individual passes of the mars reconnaissance orbiter have revealed the internal structure of the martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate however a complete picture of the cap interiors has been hampered by interfering reflections from off nadir surface features and signal losses associated with sloping structures and scattering foss et al the leading edge 36 43 57 2017 https doi org 10 1190 tle36010043 1 addressed these limitations by assembling three dimensional data volumes of sharad observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously the radar volumes provide unprecedented views of subsurface features readily imaging structures previously inferred from time intensive manual analysis of single orbit data e g trough bounding surfaces a buried chasma and a basal unit in the north massive carbon dioxide ice deposits and discontinuous layered sequences in the south our new mapping of the carbon dioxide deposits yields a volume of 16 500 km 3 11 larger than the prior estimate in addition the radar volumes newly reveal other structures including what appear to be buried impact craters with no surface expression our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a hesperian age for the substrate consistent with that of the surrounding plains as determined from statistics of surface cratering rates planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits the radar volumes also provide new topographic data between the highest latitudes observed by the mars orbiter laser altimeter and those observed by sharad in general mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes

the formation and stability of buried polar co2 deposits on mars abstract shallow radar soundings of the south polar layered deposits spld have revealed buried co 2 ice with as many as three distinct layers separated by thinner layers of water ice bierson et al 2016 this layering is suggestive of formation by cyclical processes such as obliquity eccentricity and advance of perihelion if obliquity is the main driver then there were many opportunities for co 2 deposits to have formed within the last 3 5 4 myr to persist however co 2 deposits must be followed by the deposition of an insulating layer of porous water ice that can seal in the co 2 to survive the obliquity maxima that follow we suggest that the existing deposits were formed within the last 350 kyr each obliquity minimum was quickly followed by a period in which perihelion occurred in the northern summer southern winter solstice under these conditions an enhanced deposition of low porosity fine grained water ice could occur on the winter pole a similar series of depositions and burials by water ice could have occurred between 2 75 and 2 2 million years ago but these deposits were unlikely to have survived the many high obliquity swings that occurred between 2 2 ma and 400 ka the formation and burial of co 2 ice could also have occurred in similar fashion earlier during the last 100 myr in which the southern polar layered deposits were formed although at current times the geothermal flux may be too low to cause basal melting of co 2 deposits in earlier times deposits formed in deeper scarps and valleys could have led to basal co 2 melting and sequestration into the regolith by extension basal melting and sequestration in the regolith may provide an explanation for the fate of the thick co 2 atmosphere pco 2 0 5 bar implied by climate models of early mars

methane bursts as a trigger for intermittent lake forming climates on post noachian mars lakes existed on mars later than 3 6 billion years ago according to sedimentary evidence for deltaic deposition the observed fluviolacustrine deposits suggest that individual lake forming climates persisted for at least several thousand years assuming dilute flow but the lake watersheds little weathered soils indicate a largely dry climate history with intermittent runoff events here we show that these observational constraints although inconsistent with many previously proposed triggers for lake forming climates are consistent with a methane burst scenario in this scenario chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate using numerical simulations we find that outgassed methane can build up to atmospheric levels sufficient for lake forming climates if methane clathrate initially occupies more than 4 of the total volume in which it is thermodynamically stable such occupancy fractions are consistent with methane production by water rock reactions due to hydrothermal circulation on early mars we further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake forming climates to less than a million years consistent with observations we conclude that methane bursts represent a potential pathway for intermittent excursions to a warm wet climate state on early mars

effect of mars atmospheric loss on snow melt potential in a 3 5 gyr mars climate evolution model post noachian martian paleochannels indicate the existence of liquid water on the surface of mars after about 3 5 gya irwin et al 2015 palucis et al 2016 in order to explore the effects of variations in co2 partial pressure and obliquity on the possibility of surface water we created a zero dimensional surface energy balance model we combine this model with physically consistent orbital histories to track conditions over the last 3 5 gyr of martian history we find that melting is allowed for atmospheric pressures corresponding to exponential loss rates of dp dt t 3 73 or faster but this rate is within 0 5 of the rate calculated from initial measurements made by the mars atmosphere and volatile evolution maven mission if we assume all the escaping oxygen measured by maven comes from atmospheric co2 lillis et al 2017 tu et al 2015 melting at this loss rate matches selected key geologic constraints on the formation of hesperian river networks assuming optimal melt conditions during the warmest part of each mars year irwin et al 2015 stopar et al 2006 kite et al 2017a b the atmospheric pressure has a larger effect on the surface energy than changes in mars s mean obliquity these results show that initial measurements of atmosphere loss by maven are consistent with atmospheric loss being the dominant process that switched mars from a melt permitting to a melt absent climate jakosky et al 2017 but non co2 warming will be required if 2 gya paleochannels are confirmed or if most of the escaping oxygen measured by maven comes from h2o

north polar deposits of mars extreme purity of the water ice 1 the polar layered deposits are the largest reservoir of water on the surface of mars the physical properties of the ice and their spatial distribution are largely unknown 140 000 data points from the sounding radar sharad on the mars reconnaissance orbiter were analyzed over the gemina lingula region one fourth of the north polar layered deposits area maps of the dielectric properties of the bulk ice were drawn up there is no basal melting signature a drop of the dielectric constant in north west of gemina lingula could be explained by an abrupt 250 meter uplift of the base the bulk ice of the studied region has an average dielectric constant of 3 10 0 12 and a loss tangent 0 0026 0 0005 analytic interpretations shown the volume of ice is pure at 95 the impurities have a radial distribution with higher concentrations at margins

amazonian aged fluvial valley systems in a climatic microenvironment on mars melting of ice deposits on the interior of lyot crater valley networks regional drainage patterns suggesting liquid water stability at the surface are confined to early in the history of mars the noachian hesperian boundary and before prior to a major climate transition to the hyperarid cold conditions of the amazonian several later fluvial valley systems have been documented in specific hesperian and early amazonian environments and are thought to have formed due to local conditions here we describe fluvial valley systems within lyot crater that have the youngest well constrained age reported to date middle or late amazonian for systems of this size tens of km these valleys are linked to melting of near surface ice rich units extend up to 50 km in length follow topographic gradients and deposit fans the interior of lyot crater is an optimal micro environment since its low elevation leads to high surface pressure and temperature conditions at its location in the northern mid latitudes are sufficient for melting during periods of high obliquity this micro environment in lyot apparently allowed melting of surface ice and the formation of the youngest fluvial valley systems of this scale yet observed on mars

the imprint of atmospheric evolution in the d h of hesperian clay minerals on mars the deuterium to hydrogen d h ratio in strongly bound water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of these minerals curiosity s sample analysis at mars sam experiment measured thermally evolved water and hydrogen gas released between 550 c and 950 c from samples of hesperian era gale crater smectite to determine this isotope ratio the d h value is 3 0 0 2 times the ratio in standard mean ocean water smow the d h ratio in this 3 billion year old mudstone that is half that of the present martian atmosphere but substantially higher than that expected in very early mars indicates an extended history of hydrogen escape and desiccation of the planet

aeolian bedforms yardangs and indurated surfaces in the tharsis montes as seen by the hirise camera evidence for dust aggregates abstract hirise images of mars with ground sampling down to 25 cm pixel show that the dust rich mantle covering the surfaces of the tharsis montes is organized into ridges whose form and distribution are consistent with formation by aeolian saltation other dusty areas near the volcanoes and elsewhere on the planet exhibit a similar morphology the material composing these reticulate bedforms is constrained by their remote sensing properties and the threshold curve combined with the saltation suspension boundary both of which vary as a function of elevation atmospheric pressure particle size and particle composition considering all of these factors dust aggregates are the most likely material composing these bedforms we propose that airfall dust on and near the volcanoes aggregates in situ over time maybe due to electrostatic charging followed by cementation by salts the aggregates eventually reach a particle size at which saltation is possible aggregates on the flanks are transported downslope by katabatic winds and form linear and accordion morphologies materials within the calderas and other depressions remain trapped and are subjected to multidirectional winds forming an interlinked honeycomb texture in many places on and near the volcanoes light toned low thermal inertia yardangs and indurated surfaces are present these may represent duststone formed when aggregates reach a particle size below the threshold curve such that they become stabilized and subsequently undergo cementation

martian surface near surface water inventory sources sinks and changes with time today a 34 m global equivalent water layer gel lies in the martian polar layered deposits and shallow ground ice during the amazonian 3 m was outgassed and 31 m was lost to space and to the surface leaving 62 m at the end of hesperian during the hesperian volcanic outgassing added 5 m 7 m was lost and 40 m gel of groundwater was added to form outflow channels leaving 24 m carryover of surface water from the noachian into the hesperian the hesperian budget is incompatible with a northern ocean during this era these figures are for near surface water substantial amounts of water may have existed as deep ground ice and groundwater our estimate of approximately 24 m near surface water in the late noachian is insufficient to support an ocean at that time also and favors episodic melting of an icy highlands to produce the fluvial and lacustrine features

a recent ice age on mars evidence for climate oscillations from regional layering in mid latitude mantling deposits 1 two end member hypotheses have been proposed to account for the emplacement and distribution of ice in the near subsurface of mars at mid to high latitudes during recent spin axis orbital variation induced climate change in the first diffusion of atmospheric water vapor into and out of a porous regolith forms ice cemented soils whose latitudinal stability migrates as a function of orbitally controlled climatic conditions in the alternative hypothesis atmospheric deposition of ice snow and dust produces dusty ice rich layers during periods of higher obliquity new image data reveal meters thick layered deposits exposed on mid latitude pole facing slopes supporting the latter hypothesis these observations suggest that the near surface ice detected by the grs instrument suite and the phoenix lander at high latitudes is linked to thick buried ice that was atmospherically deposited during recent ice ages and that significant amounts of subsurface ice may remain today in the 30 50 mid latitude regions where fresh craters imaged by hirise expose abundant ice

sequence and relative timing of large lakes in gale crater mars after the formation of mount sharp the quantification of lake levels in gale crater is important to define the hydrologic and climatic history experienced by the sedimentary deposits found by curiosity we propose that there were at least three major lake stands within gale each persisted 1000 years and all occurred after mount sharp reached close to its current topographic form deltaic deposits off the southern rim of gale derived from incision of farah vallis and corresponding deposits off the southern flank of mount sharp define the highest lake level which had a mean depth of 700 m canyons similar in form to farah vallis enter into craters and or the crustal dichotomy near gale from the south suggesting that the highest lake was supplied by a large scale flow system the next lake level established after a period of drying and rewetting is defined by four deltaic features three sourced from mount sharp and one from the western rim of gale as well as the termination of gullies around the northern rim of gale this second lake level had a mean depth of 300 m the presence of the gullies suggests more locally sourced water lake levels then rose another 100 m as evidenced by two deltaic deposits derived from the rim of gale and the termination of a second set of gullies post lake reduced hydrologic activity continued evidenced by a time of fan building including peace vallis the sequence of events suggests an episodic shift through time from relatively wet regional conditions to a drier environment with local runoff

high resolution chemostratigraphy of the late aptian early albian oceanic anoxic event oae 1b from the poggio le guaine section umbria marche basin central italy an integrated study of multiple geochemical proxies 13ccarb 13corg toc hi caco3 trace elements al ratios of the late aptian early albian oceanic anoxic event oae 1b has been performed on the pelagic sedimentary sequence of poggio le guaine umbria marche basin central italy a comparison of the newly collected stable isotope carbon curve with the records from the vocontian basin se france dsdp site 545 and hole 1049c provided a reliable and precise identification of the four main prominent black shale levels 113 jacob kilian urbino paquier and leenhardt that characterize the oae 1b the studied record shows an increase in the marine organic carbon accumulation rate in particular in the 113 jacob and urbino paquier levels in the other black shales toc values are 1 with evidence of degraded marine organic matter completely anoxic conditions were never established during the sediment deposition although evidence of oxygen depletion at the bottom of the basin is clearly documented by the distribution pattern of redox sensitive trace metals the results suggest an increase in organic carbon burial rates during the oae 1b due to the effect of enhanced surface productivity as supported by a major increase in ba al and reduced bottom water ventilation notably the kilian and urbino paquier levels from the plg section are characterized by the absence of correlative shifts in 13ccarb and 13corg the increase in the 13corg values in these levels is explained by an increase in the relative contribution of 13c enriched marine planktonic archaeal biomass while the concomitant negative excursions recorded in the 13ccarb could reflect a major contribution of isotopically light terrestrial carbonate ions from increased continental runoff during documented more humid conditions

mossbauer mineralogy of rock soil and dust at meridiani planum mars opportunity s journey across sulfate rich outcrop basaltic sand and dust and hematite lag deposits additonal co authors p gutlich e kankeleit t mccoy dw mittlefehldt f renz me schmidt b zubkov sw squyres re arvidson

evaluation of saltation flux impact responders safires for measuring instantaneous aeolian sand transport intensity the measurement of aeolian sand transport rates on small scales is of interest to the development and testing of detailed models of sand movement by wind this paper reports on laboratory evaluations and preliminary field tests of a new design of a piezo electric impact responder called a safire capable of measuring saltation impacts at a frequency of 20 hz the advantages of the safire are 1 that it provides high frequency measurements 2 that it presents a minimal obstruction to the wind flow no scour observed in the field and 3 that it is of a relatively low cost laboratory calibrations were performed with a vertical gravity flume generating known sand grain fluxes using both mixed sand and specific size fractions initial tests investigated three fundamental characteristics correspondence between digital and analogue signals generated by the instrument directional response of the probe and linearity of instrument response to mass flux instrument calibration included determination of the momentum threshold required for the sensor to register a grain impact based on this lower limit and the known distribution of grain size and speed at different fall heights a prediction is made as to the sand grain flux the safire ought to measure which is then compared with the signal response the result of this comparison is an assessment of the instrument s efficiency in counting saltating grains these safires were also deployed in the field as part of a larger investigationof spatio temporal transport variability thisexperiment providedthe opportunity to compare the instrument s performancewithtraditional sandtraps andthispaperdevelopsmethodsandassumptionsrequiredtoconvertmeasurements from impact responders to traditional mass transport rates the evaluations indicate that improvements to the instrument production process are required to ensure a standard momentum threshold among individual instruments furthermore the sensor design needs to be reconsidered in order to eliminate the variation in response depending on azimuth direction so that the sensor is uniformly omni directional d 2003 elsevier b v all rights reserved

dynamic and isotopic evolution of ice reservoirs on mars abstract the layered polar caps of mars have long been thought to be related to variations in orbit and axial tilt we dynamically link mars s past climate variations with the stratigraphy and isotopic composition of its ice by modeling the exchange of h2o and hdo among three reservoirs the model shows that the interplay among equatorial mid latitude and north polar layered deposits npld induces significant isotopic changes in the cap the diffusive properties of the sublimation lags and dust content in our model result in a cap size consistent with current mars the layer thicknesses are mostly controlled by obliquity variations but the precession period of 50 kyr dominates the variations in the isotopic composition during epochs of relatively low and nearly constant obliquity such as at present isotopic sampling of the top 100 m may reveal climate oscillations unseen in the layer thicknesses and would thus probe recent precession driven climate cycles

carbon sequestration on mars on earth carbon sequestration in geologic units plays an important role in the carbon cycle scrubbing co 2 from the atmosphere for long term storage while carbonate is identified in low abundances within the dust and soils of mars at 1 wt in select meteorites and in limited outcrops no massive carbonate rock reservoir on mars has been identified to date here we investigate the largest exposed carbonate bearing rock unit the nili fossae plains combining spectral thermophysical and morphological analyses to evaluate the timing and carbon sequestration potential of rocks on mars we find that the olivine enriched 20 25 basalts have been altered by low temperature in situ carbonation processes to at most 20 fe mg carbonate thus limiting carbon sequestration in the nili fossae region to 0 25 12 mbar of co 2 during the late noachian early hesperian before or concurrent with valley network formation while this is large compared to modern day co 2 reservoirs the lack of additional comparably sized post late noachian carbonate bearing deposits on mars indicates ineffective carbon sequestration in rock units over the past 3 7 b y this implies a thin atmosphere 500 mbar during valley network formation extensive post noachian atmospheric loss to space or diffuse deep sequestration by a yet to be understood process in stark contrast to earth s biologically mediated crust atmosphere carbon reservoir ratio of 10 4 10 5 mars ratio is a mere 10 10 3 even if buried pre noachian crust holds multiple bars

rapid oxidation of mercury hg at volcanic vents insights from high temperature thermodynamic models of mt etna s emissions a major uncertainty regarding the environmental impacts of volcanic hg is the extent to which hg is deposited locally or transported globally an important control on dispersion and deposition is the oxidation state of hg compounds hg 0 is an inert insoluble gas while hg ii occurs as reactive gases or in particles which deposit rapidly and proximally near the volcanic vent using a new high temperature thermodynamic model we show that although hg in etna s magmatic gases is almost entirely hg 0 i e gaseous elemental mercury significant quantities of hg ii are likely formed at etna s vents as gaseous hgcl2 when magmatic gases are cooled and oxidised by atmospheric gases these results contrast with an earlier model study and allow us to explain recent measurements of hg speciation at the crater rim of etna without invoking rapid 1 min low temperature oxidation processes we further model hg speciation for a series of additional magmatic gas compositions compared to etna hg ii production i e hg ii hgtot is enhanced in more hcl rich magmatic gases but is independent of the hg hbr and hi content of the magmatic gases hg ii production is not strongly influenced by the initial oxidation state of magmatic gases above nno although production is hindered in more reduced magmatic gases the model and results are widely applicable to other open vent volcanoes and may be used to improve the accuracy of chemical kinetic models for low temperature hg speciation in volcanic plumes

the fate of early mars lost water the role of serpentinization the fate of water which was present on early mars remains enigmatic we propose a simple model based on serpentinization a hydrothermal alteration process which may produce magnetite and store water our model invokes serpentinization during about 500 to 800 myr while a dynamo is active which may have continued after the formation of the crustal dichotomy we show that the present magnetic field measured by mgs in the southern hemisphere is consistent with a 500 m thick global equivalent layer of water trapped in serpentine serpentinization results in the release of h 2 the released h atoms are lost to space through thermal escape increasing the d h ratio in water reservoirs exchanging with atmosphere we show that the value of the d h ratio in the present atmosphere 5 is consistent with the serpentinization of a 500 m thick water gel we reassess the role of non thermal escape in removing water from the planet by considering an updated solar wind ionosphere interaction representation we show that the contribution of oxygen escape to h isotopic fractionation is negligible our results suggest that significant amounts of water up to a 330 1030 m thick gel present at the surface during the noachian similar to the quantity inferred from the morphological analysis of valley networks could be stored today in subsurface serpentine 1 the study like earth mars has been endowed with large amounts of water during accretion equivalent to the content of several terrestrial oceans corresponding to a several 10 km thick global equivalent layer the present inventory of observable water on mars mainly within the polar caps is quite smaller in the range from 20 30 m the mega regolith capacity is large with up to 500 gel m potentially trapped in the cryosphere and hypothetically several additional hundreds of meters up to 500 m of ground water surviving at depth below the cryosphere 1 a 500 m thick gel is generally assumed to be required to explain the formation of outflow channels 2 and most of this water could be trapped today as water ice and possibly deep liquid water in the subsurface and also possibly under the form of hydrated minerals

elevated primary productivity of calcareous nannoplankton associated with ocean anoxic event 1b during the aptian albian transition early cretaceous 1 previous isotopic investigations of aptian albian oceanic anoxic event oae 1b from the western north atlantic blake nose posited that increased sea surface temperatures and decreased salinity led to stratification of the upper water column resulting in lowered dissolved oxygen and enhanced organic matter preservation we examined calcareous nannofossils from the same site in the western north atlantic blake nose to evaluate changes in surface water conditions prior to during and after the aptian albian oae1b the results of our analysis conflict somewhat with the previous interpretation that oae1b at blake nose was linked to water column stratification the signal from calcareous nannofossils indicates that in the late aptian prior to oae1b oligotrophic conditions in the surface waters were replaced by mesotrophic conditions that persisted throughout the oae event and into the early albian we speculate that increased surface water productivity facilitated to some degree the development of oae1b at blake nose

boninitic volcanism in the oman ophiolite implications for thermal condition during transition from spreading ridge to arc the discovery of boninite a typical high mgo andesite in the oman ophiolite is reported the boninites in the oman ophiolite occur as lavas and dikes of the alley volcanic sequence that overlie or crosscut the spreading ridge derived lavas geotimes volcanic sequence and sheeted dikes the phenocryst mineral assemblage and the major and trace element compositions observed for these boninites resemble those of the izu mariana forearc boninites indicating that the alley boninites represent primitive melt generated by partial melting of hydrous peridotite the occurrence of boninite provides strong thermal and chemical constraints on the formation of the oman ophiolite that require hot hydrous shallow mantle 1250 c at 30 km depth to have underlain the proto oman ophiolite at the time of boninite generation the initiation of subduction of the young hot oceanic lithosphere and obduction of the future oman ophiolite near the spreading ridge and the resultant melting of the highly depleted shallow mantle wedge metasomatized by slab derived fluid represent the most favorable mechanism for the genesis of the alley boninites

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

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

low palaeopressure of the martian atmosphere estimated from the size distribution of ancient craters the decay of the martian atmosphere which is dominated by carbon dioxide is a component of the long term environmental change on mars from a climate that once allowed rivers to flow to the cold and dry conditions of today the minimum size of craters serves as a proxy for palaeopressure of planetary atmospheres because thinner atmospheres permit smaller objects to reach the surface at high velocities and form craters the aeolis dorsa region near gale crater on mars contains a high density of preserved ancient craters interbedded with river deposits and thus can provide constraints on atmospheric density at the time of fluvial activity here we use high resolution images and digital terrain models from the mars reconnaissance orbiter to identify ancient craters in deposits in aeolis dorsa that date to about 3 6 gyr ago and compare their size distribution with models of atmospheric filtering of impactors we obtain an upper limit of 0 9 0 1 bar for the martian atmospheric palaeopressure rising to 1 9 0 2 bar if rimmed circular mesas interpreted to be erosionally resistant fills or floors of impact craters are excluded we assume target properties appropriate for desert alluvium if sediment had rock mass strength similar to bedrock at the time of impact the paleopressure upper limit increases by a factor of up to two if mars did not have a stable multibar atmosphere at the time that the rivers were flowing as suggested by our results then a warm and wet co 2 h 2o greenhouse is ruled out and long term average temperatures were most likely below freezing

planetary surface dating from crater size frequency distribution measurements multiple resurfacing episodes and differential isochron fitting abstract the analysis of crater size frequency distributions and absolute densities forms the basis of current approaches for estimating the absolute and relative ages of planetary surfaces users of the neukum system of crater dating have conventionally used a cumulative presentation of the data but because of the recent proliferation of interest in identifying resurfacing ages it is worth emphasising the utility of the differential presentation of crater data in identifying resurfacing events and particularly in distinguishing the signature of short lived events such as volcanic flows from long acting processes such as aeolian erosion the work describes some additional considerations for making isochron fits to differentially plotted crater populations with respect to the removal of a binning bias for incrementally differentially plotted data the hartmann approach has not typically employed the fitting of isochrons but differential fitting would be a natural choice for this system and is implemented in the craterstats software a revised calculation of the martian epoch boundary times in both chronology systems is provided

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

atmospheric collapse and transport of carbon dioxide into the subsurface on early mars 1 the present climate of mars is extremely cold and dry and is characterized by a very thin co2 atmosphere on the other hand geological evidence suggests that the martian climate in the past might have been warm and wet suggesting that the atmospheric co2 pressure would have been several bars higher however the fate of the abundant co2 is still unclear here we propose a possible scenario for the evolution of co2 on mars numerical results suggest that co2 in the early atmosphere would have reduced by a runaway condensation to form large co2 ice caps then the large co2 ice caps should have shrunk by basal melting and most of co2 has percolated into subsurface of the ice caps the co2 would have formed clathrate hydrate and carbonate minerals and may still reside in the subsurface of mars this could explain the apparent shortage of co2 on the present martian surface

mars global digital dune database mgd3 north polar region mc 1 distribution applications and volume estimates the mars global digital dune database mgd3 now extends from 90 n to 65 s the recently released north polar portion mc 1 of mgd3 adds 844 000 km2 of moderate to large size dark dunes to the previously released equatorial portion mc 2 to mc 29 of the database the database available in gis and tabular format in usgs open file reports makes it possible to examine global dune distribution patterns and to compare dunes with other global data sets e g atmospheric models mgd3 can also be used by researchers to identify areas suitable for more focused studies the utility of mgd3 is demonstrated through three example applications first the uneven geographic distribution of the dunes is discussed and described second dune derived wind direction and its role as ground truth for atmospheric models is reviewed comparisons between dune derived winds and global and mesoscale atmospheric models suggest that local topography may have an important influence on dune forming winds third the methods used here to estimate north polar dune volume are presented and these methods and estimates 1130 km3 to 3250 km3 are compared with those of previous researchers 1158 km3 to 15 000 km3 in the near future mgd3 will be extended to include the south polar region published in 2011 this article is a us government work and is in the public domain in the usa