viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

fracture patterns at lava ice contacts on kokostick butte or and mazama ridge mount rainier wa implications for flow emplacement and cooling histories abstract cooling lava commonly develop polygonal joints that form equant hexagonal columns such fractures are formed by thermal contraction resulting in an isotropic tensional stress regime however certain linear cooling fracture patterns observed at some lava ice contacts do not appear to fit the model for formation of cooling fractures and columns because of their preferred orientations these fracture types include sheet like ladder like rectangular fracture pattern intermediate pseudo aligned individual column bounding fractures and pseudopillow straight to arcuate fractures with perpendicular secondary fractures caused by water infiltration fractures that form the edges of multiple columns along a single linear fracture despite the relatively common occurrence of these types of fractures at lava ice contacts their significance and mode of formation have not been fully explored this study investigates the stress regimes responsible for producing these unique fractures and their significance for interpreting cooling histories at lava ice contacts data was collected at kokostick butte dacite flow at south sister or and mazama ridge andesite flow at mount rainier wa both of these lava flows have been interpreted as being emplaced into contact with ice and linear fracture types have been observed on their ice contacted margins two different mechanisms are proposed for the formation of linear fracture networks one possible mechanism for the formation of linear fracture patterns is marginal bulging melting of confining ice walls will create voids into which flowing lava can deform resulting in margin parallel tension causing margin perpendicular fractures if viewed from the ice wall these fractures would be steeply dipping linear fractures another possible mechanism for the formation of linear fracture types is gravitational settling pure shear during compression and settling can result in a tensional environment with similar consequences as marginal inflation in addition to this horizontally propagating cooling fractures will be directly influenced by viscous strain caused by the settling of the flow this would cause preferential opening of fractures horizontally resulting in vertically oriented fractures it is important to note that the proposed model for the formation of linear fractures is dependent on contact with and confinement by glacial ice the influence of flow or movement on cooling fracture patterns has not been extensively discussed in previous modeling of cooling fractures rapid cooling of lava by the interaction with water and ice will increase the ability to the capture and preserve perturbations in the stress regime

morphologic and topographic analyses of debris aprons in the eastern hellas region mars this paper presents new detailed analyses of small scale morphologic and topographic characteristics of martian debris aprons that support viking based interpretations of debris aprons as ice rich flow features derived from local uplands fifty four debris apron complexes in the eastern hellas region of mars were examined using mars global surveyor data sets including mars orbiter camera images and mars orbiter laser altimeter topographic profiles consistent patterns in a suite of small scale surface textures and geomorphic features observed throughout the population reflect a history of viscous flow and surface degradation through wind ablation and loss of contained ice a wide variety of shapes seen in topographic profile reveal variations in distribution of contained ice and different stages of apron development and degradation the results of this study provide new evidence consistent with multiple models of apron formation including rock glacier debris covered glacier and ice rich landslide models typical eastern hellas debris aprons formed from a series of large scale events emplacing debris that was enriched initially or later by ground ice complemented by small scale mass wasting of multiple styles and postemplacement flow of apron masses

hirise observations of fractured mounds possible martian pingos 1 early images from the high resolution imaging science experiment hirise camera have revealed small fractured mounds in the martian mid latitudes hirise resolves fractures on the mound surfaces indicating uplift and shows that the mound surface material resembles that of the surrounding landscape analysis of mars orbiter camera moc images shows that in utopia planitia the mounds lie almost exclusively between 35 45 n this range coincides with the peak abundance latitudes of several landforms attributed to ground water or ice including gullies and suggests a ground ice related origin the best terrestrial analogues for the observed mound morphology are pingos although some differences are noted the presence of uncollapsed pingos would indicate the presence of near surface ground ice in the martian mid latitudes at depths greater than the 1 meter sampled by orbital spectrometers pingo formation may require near surface liquid water which is consistent with a shallow groundwater model for the origin of gullies

rapid magma ascent recorded by water diffusion profiles in mantle olivine mechanisms and rates of magma ascent play a critical role in eruption dynamics but remain poorly constrained phenomena water dissolved in mantle minerals as hydrogen and partitioned into the magma during ascent may provide clues to quantifying magma ascent rates prior to eruption we determined the dehydration profiles in olivine crystals from peridotite mantle xenoliths within the pali aike alkali basalt from patagonia chile the results demonstrate that the amount of water stored in the uppermost mantle has likely been underestimated due to water loss during transport using experimental diffusion data for hydrogen we estimate that the xenoliths reached the surface from 60 70 km depth in several hours a surprisingly rapid rise comparable to ascent rates for kimberlite magmas

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

steady state geotherm thermal disturbances and tectonic development of the lower lithosphere underneath the gibeon kimberlite province namibia the gibeon kimberlite province of southern namibia comprises more than 75 group 1 kimberlite pipes and dykes from the gibeon townsland 1 pipe 38 upper mantle xenoliths 23 garnet lherzolites and 15 garnet harzburgites were collected and minerals were analysed by electron microprobe for major elements pressures and temperatures of crystallisation for xenoliths with either coarse equant porphyroclastic and mosaic porphyroclastic textures were estimated by a number of combinations of geothermometers and geobarometers judged to be reliable and accurate for peridotites by brey and kohler 1990 the p t estimates for equilibrated xenoliths agree within the errors of the methods and plot within the stability field of graphite the p t values for coarse equant xenoliths fall close to a geothermal gradient of about 44 mw m2 within a very restricted pressure range the porphyroclastic xenoliths yield similar and higher temperatures at similar depths in these xenoliths ca in orthopyroxene and ca in olivine increase towards the rims and are high in the neoblasts indicating a stage of transient heating at depth the mosaic porphyroclastic xenolith minerals yield the highest temperatures are unzoned and indicate internal mineral equilibrium the depth of origin for the xenoliths from gibeon townsland 1 ranges from 100 to 140 km the cold coarse equant peridotites are relatively enriched garnet lherzolites with comparatively to the hot peridotites low modal orthopyroxene contents whereas the hot mosaic porphyroclastic peridotites are depleted garnet harzburgites with high modal amounts of orthopyroxene this is opposite to the findings for peridotites from the kaapvaal craton where the cold peridotites are depleted harzburgites with high modal orthopyroxene and many of the hot peridotites are fertile lherzolites with low modal abundance of orthopyroxene we present a model in which the high temperature depleted garnet harzburgites are equated to the cold coarse equant peridotites from the kaapvaal craton it is envisaged that this material was detached and transported laterally by an upwelling deflected plume

modeling of the influence of sea ice cycle and langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the west antarctic peninsula

analysis of antarctic peninsula glacier frontal ablation rates with respect to iceberg melt inferred variability in ocean conditions marine terminating glaciers on the antarctic peninsula ap have retreated accelerated and thinned in response to climate change in recent decades ocean warming has been implicated as a trigger for these changes in glacier dynamics yet little data exist near glacier termini to assess the role of ocean warming here we use remotely sensed iceberg melt rates seaward of two glaciers on the eastern and six glaciers on the western ap from 2013 to 2019 to explore connections between variations in ocean conditions and glacier frontal ablation we find iceberg melt rates follow regional ocean temperature variations with the highest melt rates mean 10 cm d 1 at cadman and widdowson glaciers in the west and the lowest melt rates mean 0 5 cm d 1 at crane glacier in the east near coincident glacier frontal ablation rates from 2014 to 2018 vary from 450 m a 1 at edgeworth and blanchard glaciers to 3000 m a 1 at seller glacier former wordie ice shelf tributary variations in iceberg melt rates and glacier frontal ablation rates are significantly positively correlated around the ap spearman s 0 71 p value 0 003 we interpret this correlation as support for previous research suggesting submarine melting of glacier termini exerts control on glacier frontal dynamics around the ap

searching for evidence of hydrothermal activity at apollinaris mons mars a multidisciplinary approach involving various remote sensing instruments is used to investigate apollinaris mons a prominent volcano on mars as well as the surrounding plains for signs of prolonged hydrologic and volcanic and possibly hydrothermal activity the main findings include 1 evidence from laser altimetry indicating the large thickness 1 5 2 km at some locations of the fan deposits draping the southern flank contrary to previous estimates coupled with possible layering which point to a significant emplacement phase at apollinaris mons 2 corroboration of robinson et al robinson m s mouginis mark p j zimbelman j r wu s s c ablin k k howington kraus a e 1993 icarus 104 301 323 hypothesis regarding the formation of incised valleys on the western flanks by density current erosion which would indicate magma water interaction or alternatively volatile rich magmas early in the volcano s history 3 mounds of diverse geometric shapes many of which display summit depressions and occur among faults and fractures possibly marking venting 4 strong indicators on the flanks of the volcano for lahar events and possibly a caldera lake 5 ubiquitous presence of impact craters displaying fluidized ejecta in both shield forming flank and caldera materials and materials that surround the volcano that are indicative of water rich target materials at the time of impact 6 long term complex association in time among shield forming materials and medusae fossae formation the findings point to a site of extensive volcanic and hydrologic activity with possibly a period of magma water interaction and hydrothermal activity finally we propose that the mound structures around apollinaris should be prime targets for further in situ exploration and search for possible exobiological signatures

crease structures indicators of emplacement rates and surface stress regimes of lava flows crease structures are features commonly found on lava flow surfaces and consist of a fracture with curved walls that extend outward from a linear valley these crease structures are found on flows of nearly all compositions and crystallinities we have mapped the distributions of crease structures on many flows in the western united states and found that 1 axial length is not dependent upon composition and crystallinity 2 adjacent crease structures are generally aligned in an en echelon pattern 3 crease structures located adjacent to flow margins are generally perpendicular to these margins and 4 at mount st helens washington large lobe bisecting crease structures are found on lobes situated on slopes of less than 20 degrees a primary surface feature found on many crease structures is striations striations are sets of long stripes on the walls of the crease structure that extend approximately parallel to the axis of the central valley and they appear to be analogous to those found on the faces of cyclically fractured basalt columns observations of developing crease structures on 6 of the nearly 20 mount st helens dome lobes show that they form throughout the extrusion of flows situated on slopes of less than 20 degrees but only at the very beginning and or end of extrusion of flows on steeper slopes these observations imply that crease structures form when the lava flow is forced to spread laterally either as the flow advances over a flat area or as the down slope movement stagnates near the end of extrusion causing the rate of spreading to exceed the downslope rate of flow this lateral spreading of lava results in the concentration of tensile stress along a line oriented perpendicular to the direction of spreading the cooled crust of the extrusion is therefore torn apart about this line of tensile stress concentration forming a central valley that exposes hot ductile material from the flow interior to the atmosphere the presence of striations on many crease structure walls implies that the emplacement mechanism is similar to that suggested for columnar basalts where each striation is produced by incremental fracturing the stress responsible for crease structure formation is due to both cooling and lateral spreading of lava calculations show that stress due to spreading is three orders of magnitude higher than that due to cooling fracture advance times were calculated using a simple one dimensional conductive cooling model adjusted for the special geometry of the crease structure the model closely approximates measured crease structure emplacement times at mount st helens and gives reasonable estimates for crease structures found on older silicic lava flows we then used this model to calculate emplacement times of entire domes that consist of a single crease structure by dividing the dome volume by the formation time we are able to calculate extrusion rates for these older domes these values which include the first flow rate estimates reported for rhyolitic lavas 0 03 106 m 3 s similar to average flow rates of 0 7 40 m 3 s calculated for mount st helens dacite lobes from detailed topographic maps

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

a first description of the antarctic peninsula coastal current abstract we present hydrographic and shipboard adcp data collected during the fall april june and winter july august and moored velocity observations collected from 2001 to early 2002 on the west antarctic peninsula wap shelf during the southern ocean global ecosystems dynamics so globec program in fall a geostrophically balanced buoyant current flows southward along the coast this antarctic peninsula coastal current apcc forms during the ice free season and extends from adelaide island to alexander island although its path inside marguerite bay is uncertain during the fall of 2001 the apcc had a volume transport of 0 32 0 13 sv and a freshwater transport relative to a reference salinity of 34 4 of 126 50 km 3 yr 1 from early july to late october the apcc disappears from the coast as the freshwater input from the coast diminishes and sea ice forms on the shelf an examination of the relative sizes of the freshwater sources suggests runoff from land and precipitation over the ocean are the primary sources for the apcc

global distribution composition and abundance of olivine on the surface of mars from thermal infrared data 1 we used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of fo91 fo68 fo53 fo39 fo18 and fo1 olivine samples to mars global surveyor thermal emission spectrometer tes data over low albedo regions of mars the fo91 fo68 fo53 and fo39 spectral end members were confidently identified on mars a range of compositions wider than inferred from martian meteorites small less than hundreds of square kilometers occurrences of the fo91 spectral end member are present in the rims of the argyre and hellas impact basins and may represent martian mantle materials the fo68 spectral end member is common throughout the highlands chasmata outflow channels and nili fossae region the fo53 spectral end member occurs in eastern syrtis major the nili fossae region and smooth floored craters of the highlands although less abundant than fo68 and fo53 the distribution of the fo39 spectral end member suggests that some olivine on mars is more fe rich than olivine in martian meteorites global maps of olivine show that 1 materials containing 10 20 of olivine are common in the southern highlands of mars 2 olivine is most common near the topographic dichotomy boundary and 3 olivine becomes uncommon near the poles suggesting that it may be influenced by topography and or latitude climate olivine is found in early noachian to amazonian terrains some of which may be coeval with phyllosilicate and sulfate deposits detected by omega implying that any early noachian wet period of mars climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today

pyroclastic activity at home plate in gusev crater mars home plate is a layered plateau in gusev crater on mars it is composed of clastic rocks of moderately altered alkali basalt composition enriched in some highly volatile elements a coarse grained lower unit lies under a finer grained upper unit textural observations indicate that the lower strata were emplaced in an explosive event and geochemical considerations favor an explosive volcanic origin over an impact origin the lower unit likely represents accumulation of pyroclastic materials whereas the upper unit may represent eolian reworking of the same pyroclastic materials

alteration of hydrovolcanic basaltic ash observations with visible and near infrared spectrometry ash of basaltic composition that is produced by hydrovolcanic activity occurs frequently on earth and may be much more widespread on mars altered basaltic tephras from tuff rings and tuff cones across the basin and range were examined using visible and near infrared vis ir reflectance spectrometry and a variety of other techniques it was found that vis ir spectrometry is sensitive to subtle changes in the hydration and oxidation state of these tephras hydration produces an increase in overall reflectance with gradual development of water and hydroxyl absorptions at 1 4 m and 1 9 m the oxidation of basaltic tephras can be observed spectrally through changes in the position and slope of the fe3 o2 charge transfer edge inflections on that edge due to ferric oxide minerals and changes in the position and depth of the 1 m iron crystal field band significantly in the tuffs examined ferrous and ferric iron minerals produce one composite absorption feature rather than two resolvable bands different styles of alteration were noted between thinly bedded tuff ring deposits emplaced by high energy largely dry pyroclastic surge and massively bedded tuff cone deposits emplaced by wetter lower energy pyroclastic flow the former class of tephras become hydrated and only moderately oxidized with some limited development of dioctahedral smectite clay minerals and minimal palagonitization the latter class of tephras are highly palagonitized which implies a high degree of hydration and oxidation in fact in the most highly altered tephras all the fe2 that is initially in the volcanic glass is converted to fe3 within nanophase and bulk ferric oxide phases in the palagonite there is also more extensive development in the tuff cone beds of zeolite and phyllosilicate minerals the differences in reflectance spectra of altered basaltic tephras can be traced back to initial differences in the water magma ratio extant at the volcanic vent thus vis ir spectrometry holds the potential to be used as a tool for investigations into the volcanic history and paleoclimate of volcanic terrains

modification of deep waters in marguerite bay western antarctic peninsula caused by topographic overflows circumpolar deep water cdw intrudes from the mid layers of the antarctic circumpolar current onto the shelf of the western antarctic peninsula providing a source of heat and nutrients to the regional ocean it is well known that cdw is modified as it flows across the shelf but the mechanisms responsible for this are not fully known here data from underwater gliders with high spatial resolution are used to demonstrate the importance of detailed bathymetry in inducing multiple local mixing events clear evidence for overflows is observed in the glider data as water flows along a deep channel with multiple transverse ridges the ridges block the densest waters with overflowing water descending several hundred metres to fill subsequent basins this vertical flow leads to entrainment of overlying colder and fresher water in localised mixing events initially this process leads to an increase in bottom temperatures due to the temperature maximum waters descending to greater depths after several ridges however the mixing is sufficient to remove the temperature maximum completely and the entrainment of colder thermocline waters to depth reduces the bottom temperature to approximately the same as in the source region of marguerite trough similarly it is shown that deep waters of palmer deep are warmer than at the same depth at the shelf break the exact details of the transformations observed are heavily dependent on the local bathymetry and water column structure but glacially carved troughs and shallow sills are a common feature of the bathymetry of polar shelves and these types of processes may be a factor in determining the hydrographic conditions close to the coast across a wider area

frozen melt rock reaction in a peridotite xenolith from sub arc mantle recorded by diffusion of trace elements and water in olivine this research was supported by natural environment research council algorithm doctoral studentship nerc 10 000497448 to pete tollan

identity and emplacement of domical structures in the western arcadia planitia mars 1 morphologic morphometric and thermophysical aspects of domical structures in a restricted part of the mars northern plains were characterized using mars odyssey and mars global surveyor data the majority of domical structures consist of relatively high thermal inertia subcircular to irregularly shaped core bodies surrounded by adjacent relatively low albedo low thermal inertia annuli and dispersed aureoles of apparently disaggregated material core profiles vary considerably from low to high aspect ratios elongate arms of material extend from the central summit regions in some of the structures core features include apparent blocky surface texture summit fissures and pits apparent summit and flank ruptures suggestive of eruption of material and concentric and straight summit ridges core heights range from 30 to 400 m mean 160 m diameters range from 620 to 3090 m mean 1550 m aspect ratios range from 0 02 to 0 36 mean 0 11 and volumes range from 0 1 to 1 8 km3 an additional morphologic type consists of subcircular domical mounds that are apparently covered by plains materials we propose that the majority of the structures are partially extrusive cryptodomes and lava domes whereas the mounds are entirely intrusive cryptodomes

martian mud volcanism terrestrial analogs and implications for formational scenarios the geology of mars and the stratigraphic characteristics of its uppermost crust mega regolith suggest that some of the pervasively occurring pitted cones mounds and flows may have formed through processes akin to terrestrial mud volcanism a comparison of terrestrial mud volcanism suggests that equivalent martian processes likely required discrete sedimentary depocenters volatile enriched strata buried rheological instabilities and a mechanism of destabilization to initiate subsurface flow we outline five formational scenarios whereby martian mud volcanism might have occurred a rapid deposition of sediments b volcano induced destabilization c tectonic shortening d long term load induced subsidence and e seismic shaking we describe locations within and around the martian northern plains that broadly fit the geological context of these scenarios and which contain mud volcano like landforms we compare terrestrial and martian satellite images and examine the geological settings of mud volcano provinces on earth in order to describe potential target areas for piercement structures on mars our comparisons help to evaluate not only the role of water as a functional component of geological processes on mars but also how martian mud volcanoes could provide samples of otherwise inaccessible strata some of which could contain astrobiological evidence

on the characteristics of circumpolar deep water intrusions to the west antarctic peninsula continental shelf 1 hydrographic and current velocity observations collected from march 2001 to february 2003 on the west antarctic peninsula shelf as part of the southern ocean global ecosystems dynamics program are used to characterize intrusions of upper circumpolar deep water ucdw and lower circumpolar deep water lcdw onto the shelf and marguerite bay ucdw is found on the middle and outer shelf along marguerite trough which connects the shelf break to marguerite bay and at another location farther south ucdw intrudes in the form of frequent four per month and small horizontal scales 4 km warm eddy like structures with maximum vertical scales of a few hundred meters however no evidence of ucdw intrusions was found in marguerite bay lcdw was found in several deep depressions connected to the shelf break including marguerite trough forming a tongue of relatively dense water 95 m thick on average that reaches into marguerite bay through marguerite trough a steady advective diffusive balance for the lcdw intrusion is used to make an estimation of the average upwelling rate and diffusivity in the deep layer within marguerite trough which suggest the lcdw layer is renewed approximately every six weeks

distribution of upper circumpolar deep water on the warming continental shelf of the west antarctic peninsula we use autonomous underwater vehicles to characterize the spatial distribution of upper circumpolar deep water ucdw on the continental shelf of the west antarctic peninsula wap and present the first near synoptic measurements of mesoscale features eddies containing ucdw on the wap thirty three subsurface eddies with widths on the order of 10 km were detected during four glider deployments each eddy contributed an average of 5 8 x 1016 j to the sub pycnocline waters where a cross shelf heat flux of 1 37 x 1019 j yr 1 is required to balance the diffusive loss of heat to overlying winter water and to the near coastal waters approximately two thirds of the heat coming onto the shelf diffuses across the pycnocline and one third diffuses to the coastal waters long term warming of the sub pycnocline waters is a small residual of this balance sixty percent of the profiles that contained ucdw were part of a coherent eddy between 20 and 53 of the lateral onshore heat flux to the wap can be attributed to eddies entering marguerite trough a feature in the southern part of the shelf which is known to be an important conduit for ucdw a northern trough is identified as additional important location for eddy intrusion

thermal diffusivity and conductivity of olivine wadsleyite and ringwoodite to 20 gpa and 1373 k abstract we present results of lattice thermal diffusivity measurements on mg0 9fe0 1 2sio4 olivine and its high pressure polymorphs wadsleyite and ringwoodite under mantle conditions we used the angstrom method on cylindrical samples in multianvil apparatus at pressures up to 20 gpa and temperatures up to 1373 k because of the fine polycrystallinity of the specimens 30 40 m or less there is strong scattering absorption of light and suppression of radiative transport so that the lattice vibrational component is the dominant heat transfer mode lattice thermal conductivities were calculated from the thermal diffusivity results using heat capacity and equation of state data olivine thermal conductivities are consistent with previous results obtained at 1 atm e g j am ceramic soc 38 1954 107 j geophys res 77 1972 6966 science 283 1999 1699 thermal conductivity increases by approximately 30 at the transition from olivine to wadsleyite corresponding to the 410 km discontinuity and a further but smaller increase may occur at the transition from wadsleyite to ringwoodite for each of these phases lattice conductivity closely follows a t 1 2 dependence on temperature t phys rev 119 1960 507 j geophys res 79 1974 703 brown 2002 if such a dependence applies to other silicates and complex crystals there should be a useful way to estimate conductivities at high temperatures from room temperature measurements

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

phyllosilicate and hydrated silica detections in the knobby terrains of acidalia planitia northern plains mars here we report detections of fe mg phyllosilicates and hydrated silica in discrete stratigraphic units within the knobby terrains of acidalia planitia made using data acquired by compact reconnaissance imaging spectrometer for mars fe mg phyllosilicates are detected in knobs that were eroded during southward retreat of the dichotomy boundary a second later unit now eroded to steep sided platforms embaying the knobs contains hydrated silica which may have formed via localized vapor weathering thin film leaching or transient water that resulted in surface alteration these are then overlain by smooth plains with small cones hypothesized to be mud volcanoes which previous studies have shown to have no hydrated minerals in spite of acidalia s location within the putative northern ocean collectively the data record a history of aqueous processes much like that in the southern highlands with progressively less intensive aqueous chemical alteration from the noachian to amazonian

water mass properties and circulation on the west antarctic peninsula continental shelf in austral fall and winter 2001 abstract hydrographic measurements made during the us southern ocean global ocean ecosystem dynamics cruises which took place from april to june and july to september 2001 provide a description of changes in water mass distributions and circulation patterns in the marguerite bay region of the west antarctic peninsula continental shelf that result from seasonal variability and offshore forcing by the southern boundary of the antarctic circumpolar current acc the primary seasonal change in water mass properties is the reduction in antarctic surface water and replacement by a thick winter water layer the primary effect of the acc is to pump warm 1 5 c salty 34 65 34 7 and nutrient rich circumpolar deep water cdw onto the continental shelf below 200 m at specific sites that correspond to bathymetric features such as marguerite trough the cdw intruded onto the continental shelf moved across shelf and entered marguerite bay this flow pattern was observed during both cruises suggesting that onshelf intrusions of cdw are a regular occurrence on this shelf the number of cdw intrusions observed suggests that 4 6 events can occur in a year regions where cdw intrusions occur are characterized by surface waters that are above freezing in winter diffusive heat fluxes based on estimated diffusivities are insufficient for the observed rate of temperature decay of cdw intrusions localized bathymetrically controlled vertical mixing is suggested as the primary heat transfer mechanism the hydrographic and acoustic doppler current profiler measurements show a southwesterly flowing coastal current along adelaide island that enters the north side of marguerite bay and exits around alexander island this current which may result from seasonal coastal buoyancy forcing was present in fall and winter but was better developed in fall this current may be part of a larger cyclonic gyre that overlies the northern part of the area surveyed during the two cruises

pitted cones and domes on mars observations in acidalia planitia and cydonia mensae using moc themis and tes data 1 domes and cones with summit pits located in acidalia planitia and cydonia mensae were studied using moc and themis images and a tes derived thermal inertia map north of 40 5 n latitude the features have a dome like morphology and south of that latitude the morphology is more cone like layering is apparent in the summit craters of fresher looking southern cones and asymmetric aprons were observed in some instances some of the northern domes also display layering in their summit craters but asymmetric aprons were not observed the northern domes can also display multiple summit pits or no summit pits at all and can occur in association with higher albedo pancake features the northern domes are higher in albedo but have apparent thermal inertias that are lower than the surrounding plains the apparent thermal inertia values of the southern cones range from values comparable to the surrounding plains to slightly lower from the tes thermal inertia map we infer that the thermal inertia values of the pitted cones are between those of basaltic fine dust and sand while those of the surrounding plains are closer to that of basaltic sand while a unique interpretation of the origin of the pitted cones is not possible with the available data we do not find compelling evidence to suggest an origin related to either basaltic volcanism or ground ice instead an origin for these features through some combination of mud volcanism and evaporite deposition around geysers and or springs is most consistent with the observations

ice flow and rock glaciers on mars several geologic features suggest the presence of rock glaciers on the surface of mars these features include lobate debris aprons concentric crater fill and lineated valley fill the lateral extent of these rock glaciers can range from 5 km to over 20 km a simple time marching model is developed and used here to demonstrate the ability of ice and ice rock mixtures to flow under martian conditions for temperatures lower than about 220 k even pure ice becomes too rigid to flow and a glacier 5 km long could not have formed results from this model indicate temperatures 20 to 40 k higher than present average midlatitude temperatures 210 k an ice content of no less than 80 and a net accumulation rate of at least 1 cm year 1 are required to produce rock glaciers of the size seen on mars

endogenous growth of a miocene submarine dacite cryptodome rebun island hokkaido japan momo iwa rebun island hokkaido japan is a dacite cryptodome 200 300 m across and 190 m high the dome is inferred to have intruded wet poorly consolidated sediment in a shallow marine environment the internal structure of the dome is concentric with a massive core banded rim and narrow brecciated border all of which are composed of compositionally uniform feldspar phyric dacite boundaries between each of the zones are distinct but gradational the massive core consists of homogeneous coherent unfractured dacite and is characterized by radial columnar joints 60 200 cm across the banded rim encircles the massive core and is 40 m wide it is characterized by large scale flow banding parallel to the dome surface the flow banding comprises alternating partly crystalline and more glassy bands 80 150 cm thick the outermost brecciated border is up to 80 cm thick and consists of in situ breccia and blocky peperite the in situ breccia comprises polyhedral dacite clasts 5 20 cm across and a cogenetic granular matrix the blocky peperite consists of polyhedral dacite clasts 0 5 2 cm across separated by the host sediment mudstone the internal structures of the dome suggest endogenous growth involving a continuous magma supply during a single intrusive phase and simple expansion from the interior although much larger the internal structures of momo iwa closely resemble those of lobes in subaqueous felsic lobe hyaloclastite lavas

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions the influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions has been investigated by performing a series of high temperature triaxial compression experiments samples with melt fractions of 0 02 0 12 were deformed under water saturated conditions at temperatures between 1373 and 1473 k and a confining pressure of 300 mpa in a gas medium apparatus at constant differential stress and temperature the rate of deformation increased rapidly but systematically with increasing melt fraction in the diffusion creep regime at a given differential stress samples with melt fractions of 0 02 and 0 12 deformed a factor of 2 and 20 respectively faster than a melt free sample in the dislocation creep regime a sample with a melt fraction of 0 12 deformed a factor of 40 faster than a melt free sample for partially molten olivine basalt aggregates deformed under hydrous conditions the dependence of creep rate on melt fraction can be expressed in the form 0 exp where 26 for diffusion creep and 31 for dislocation creep the results of this study combined with reasonable estimates for the spatial variation in the concentrations of water and melt as well as for the geotherm and the activation volume for creep provide constraints on the viscosity structure of earth s upper mantle as an example we present a viscosity profile for the mantle wedge above a subducting plate demonstrating that the viscosity in that region can vary by 3 orders of magnitude over a depth of 60 km due to the combined effects of water and melt weakening

visible to near infrared optical properties of pure synthetic olivine across the olivine solid solution olivine exhibits highly diagnostic absorption features across visible to near infrared vnir wavelengths due to electronic transitions of fe2 in its crystal structure the properties of these absorptions vary with composition enabling compositional analysis of olivine through vnir spectroscopy both in the laboratory and through remote sensing previous analyses of these trends have relied on natural olivine samples which are influenced by the presence of minor cations that can affect the diagnostic absorptions we conduct a systematic analysis of a suite of synthetic pure mg fe olivine samples with vnir 300 2600 nm reflectance spectroscopy and quantitative spectral deconvolutions from the full suite of samples described and characterized by dyar et al 2009 we identify a small suite of well characterized and chemically pure olivine samples that demonstrates consistent and reliable spectral reflectance properties across visible to near infrared wavelengths this suite covers the stoichiometric olivine solid solution from x mg mg fe 0 to x 70 fo to fo70 because of their tight compositional control these synthetic samples improve on previous analyses of natural samples the results of this study provide a new standard for spectral reflectance properties of olivine across visible to near infrared wavelengths for the compositions present in the suite we present updated data on the trends in olivine band position as a function of olivine composition which are the basis for remote compositional evaluation of olivine with visible to near infrared reflectance spectroscopy for these reasons these improved olivine band position trends are of major importance to remote compositional analyses of terrestrial planets

internal structure and emplacement of an upper pliocene dacite cryptodome milos island greece the upper pliocene kalogeros cryptodome is exposed on the northeastern part of milos greece the dacite cryptodome is 800 1300 m across and at least 120 m high it is inferred to have intruded wet unconsolidated pumiceous sediments in a shallow marine environment the kalogeros cryptodome includes five facies the coherent dacite facies 80 vol consists of massive non vesicular dacite and is characterised by radial columnar joints 20 250 cm across the banded dacite facies 15 vol encircles the coherent core and is up to 40 m thick it comprises alternating bands 0 5 4 m thick of pale grey and black dacite the fractured dacite facies less than 1 vol forms an irregular zone 1 3 m thick at the outer margin of the cryptodome the outermost massive dacite breccia facies less than 2 vol consists of blocky to polyhedral dacite clasts 1 40 cm in diameter and is characterised by domains of jigsawfit and clast rotated breccia the stratified dacite breccia 2vol is clast to matrix supported monomictic poorly sorted and composed of dacite clasts up to several metres in diameter the facies association collectively records endogenous growth of a cryptodome that involved a continuous magma supply during a single intrusive phase and simple expansion inflation during emplacement the margins of the kalogeros cryptodome were quench fragmented forming an outer domain of intrusive hyaloclastite and intensely fractured dacite the near solid outer carapace insulated the hotter less viscous interior laminar shear accompanied inflation generating large scale flow banding around the outer part of the core once stagnant concentric isotherms were established within the cryptodome and controlled the orientation of columnar joints cryptodomes are characterised by a well developed internal concentric distribution of distinctive textural domains modest autoclastic breccia and the absence of redeposited autoclastic facies

benthic foraminiferal record of holocene deep water evolution in the palmer deep western antarctic peninsula benthic foraminiferal data from ocean drilling program site 1098 indicate significant changes in deep water conditions of the palmer deep western antarctic peninsula margin throughout the holocene 13 ka to present the earliest holocene represents a period of transition from the last glacial maximum lgm cold bottom waters similar to saline shelf water ssw dominated the middle holocene the late holocene in the palmer deep has been characterized by alternating dominance of circumpolar deep water cdw and saline shelf water these changes have global oceanographic and climatic implications we suggest that the middle holocene bottom water record in the absence of circumpolar deep water on the western antarctic peninsula shelf indicates high saline shelf water production and or weakened circumpolar deep water production during the middle holocene climatic optimum the late holocene benthic foraminiferal record indicates rapidly fluctuating sea ice conditions and may indicate a teleconnection between the south pacific and southern ocean thus having implications related to the southern oscillation index

clustering within rootless cone groups on iceland and mars effect of nonrandom processes 1 this study aims at quantifying the spatial distribution of cones within rootless cone groups rcgs our data set consists of 1 seven icelandic rcgs identified through field investigations 2 seven candidate rcgs on mars identified through mars orbiter camera moc and thermal emission imaging system themis images and 3 four groups of impact craters on mars also identified through moc and themis images to determine if they can be remotely distinguished from the rcgs purely on the basis of their spatial distribution several independent statistical techniques are used including nearest neighbor analysis analysis of variance anova and linear alignment detection analysis our results indicate that the spatial distribution of each rcg is not random within a cone group cones preferentially form near existing cones the presence of at least one significant linear cone alignment in each rcg and strong linear alignments in some groups suggests that rootless cones form as the surface signature of preferred lava pathways an anova on mean nearest neighbor distances reveals the martian cone groups to be statistically indistinguishable from the icelandic rcgs supporting existing interpretations that they represent rootless cone groups a similar anova showed that the martian cone groups do not resemble the martian impact crater clusters studied the impact craters have significantly greater nearest neighbor distances and show no evidence of aggregation within a crater group

petrology and eruption styles of kick em jenny submarine volcano lesser antilles island arc basaltic magmas erupted from the kick em jenny submarine volcano have assimilated amphibole bearing crustal material the mgo content of the basalts ranges from 12 to 4 wt and some of the more evolved members of the suite may have eventually become saturated with amphibole as well as olivine plagioclase clinopyroxene and titanomagnetite major element and trace element compositions are consistent with processes dominated by assimilation fractional crystallization analysis of glassy melt inclusions mgo 2 9 wt in olivine phenocrysts suggests that pre eruption melt water contents may have been as high as 5 wt glass compositions are interpreted to reflect eruption related loss of water submersible observations and dredge sampling of the volcano have revealed two styles of eruption explosive tephra producing eruptions and non explosive dome forming lava eruptions the contrasting styles of eruption are thought to be due principally to the rate and extent of eruption related degassing of 5 wt juvenile h2o although magma interactions with external water may also play a role in explosive eruptions

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

shelf ocean exchange and hydrography west of the antarctic peninsula a review the west antarctic peninsula wap is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat reduction of sea ice cover and shifts

widespread weathered glass on the surface of mars low albedo sediments cover 10 7 km 2 in the northern lowlands of mars but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations here we use near infrared spectra acquired by the mars express omega observatoire pour la mineralogie l9eau les glaces et l9activite imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron bearing glass and silica enriched leached rinds on glass this interpretation is supported by observations of low albedo soil grains with possible rinds at the phoenix mars lander landing site in the northern lowlands by comparison with the extensive glass rich dune fields and sand sheets of iceland we propose an explosive volcanic origin for these glass rich sediments we also propose that the glassy remnant rinds on the sediments are the result of postdepositional alteration as these rinds are commonly formed in arid terrestrial volcanic environments during water limited moderately acidic leaching these weathered glass rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid infrared spectra suggesting that they may be representative of global processes our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on mars and also raise the possibilities that glass rich volcaniclastics are a major source of eolian sand on mars and that widespread surficial aqueous alteration has occurred under amazonian climatic conditions

discovery of columnar jointing on mars we report on the discovery of columnar jointing in marte valles mars these columnar lavas were discovered in the wall of a pristine 16 km diameter impact crater and exhibit the features of terrestrial columnar basalts there are discontinuous outcrops along the entire crater wall suggesting that the columnar rocks covered a surface area of at least 200 km 2 assuming that the rocks obliterated by the impact event were similarly jointed we also see columns in the walls of other fresh craters in the nearby volcanic plains of elysium planitia amazonis planitia which include marte vallis and in a well preserved crater in northeast hellas

morphology and texture of particles along the spirit rover traverse from sol 450 to sol 745 1 we quantified and classified the shape roundness size and texture of 935 loose surface particles along the spirit rover traverse from sols 450 745 to assess origin transport and other alteration mechanisms that altered particles during and after formation variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries texture is divided into four types vesicular smooth and flat faceted rough and flat faceted and very rough sphericity and roundness are intermediate and low respectively comparable to particles moved by high energy transport or to crushed particles this indicates intermittent high energy emplacement or modification of a single lithology rather than systematic continuous low energy abrasion or wear over time comparison with particle morphology at other mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide scale chemical alteration was active at a significant enough level to alter macromorphology in particular particle morphology at the mars pathfinder site shows stronger evidence of abrasion than along the spirit traverse suggesting mars pathfinder particles have undergone abrasion processes that particles in this study area have not additionally morphology indices have correlation coefficients near zero indicating that a fluvial transport mechanism is likely not responsible for morphology morphology and texture are instead related to origin and composition rather than subsequent modification morphology and texture support a volcanic origin possibly without modification but most likely altered primarily by ballistic impact implying that the spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact derived morphology

submarine analogs to venusian pancake domes abstract the morphology and dimensions of the largediameter steep sided flat topped pancake domes on venusmake them unlike any type of terrestrial subaerial volcano comparisons between images of hawaiian seamounts andpancake domes show similarities in shapes and secondaryfeatures the morphometry of pancake domes is closer to thatof pacific seamounts than subaerial lava domes consideringboth morphology and morphometry seamounts seem a betteranalog to the pancake domes the control of volatileexsolution by pressure on venus and the seafloor can causelavas to have similar viscosities and densities although thelatter will be counteracted by high buoyancy underwater however analogous effects of the venusian and seafloorenvironments alone are probably not sufficient to producesimilar volcanoes rather venusian lavas of variouscompositions may behave like basalt on the seafloor ifappropriate rates and modes of extrusion and planetary thermalstructure are a so considered introduction

the international bathymetric chart of the southern ocean ibcso version 1 0 a new bathymetric compilation covering circum antarctic waters the international bathymetric chart of the southern ocean ibcso version 1 0 is a new digital bathymetric model dbm portraying the seafloor of the circum antarctic waters south of 60 degrees s

quantitative morphology of rocks at the mars pathfinder landing site 1 we adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on mars based on two dimensional equations and particle outlines whereby images of particles obtained remotely may yield dimensionless numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history our test site was the particle rich rock garden at the mars pathfinder landing site a location where the primary geologic processes and lithology have been determined by other means a total of 575 particles were assessed in terms of size sphericity elongation and roundness qualitative roundness was determined for 460 particles particles are mostly pebble to cobble sized and have an average sphericity of 0 75 elongation of 0 63 and relative roundness of 0 083 69 of particles are subangular or subrounded particle sphericity is unimodal with a size sphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at vikings 1 and 2 this matches the predictions for a site with the single overall lithology implied from other analyses roundness data indicate one or possibly two particle populations representing the primary processes that likely affected particle roundness most strongly impact and catastrophic flooding finally we tested a hypothesis suggesting that darker smaller more angular particles comprise a population transported through impact cratering while larger less dark more rounded particles are associated with catastrophic flood transport the opposite result is seen larger particles throughout the rock garden are more angular than smaller ones

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

feedbacks between ice cover ocean stratification and heat content in ryder bay western antarctic peninsula a multiyear all season time series of water column physical properties and sea ice conditions in ryder bay at the western antarctic peninsula wap is used to assess the effects on the ocean of varying ice cover reduced ice cover leads to increased mixing and heat loss in the winter the reduction in stratification persists into the following summer preconditioning the water column to a greater vertical extent of surface driven mixing this leads to an increased amount of heat from insolation being mixed down affecting approximately the top 100 m the increased heat uptake in summer exceeds the heat lost the preceding winter giving the initially counter intuitive effect that enhanced winter cooling generates warmer temperatures in the following summer and autumn this process is therefore a positive feedback on sea ice as reduced sea ice leads to increased heat content in the ocean the following autumn it also causes increased winter atmospheric temperatures due to the increased winter heat loss from the ocean in the deeper part of the water column heat and carbon stored in the circumpolar deep water cdw layer are released by deep mixing events at these depths conditions are restored by advection and vertical mixing on multiyear time scales in recent years stronger deep mixing events in winter have led to a persistent reduction in cdw temperatures at the study site ocean glider data demonstrate the representativeness of these results across the wider region of marguerite bay within which ryder bay is situated

ocean acidification and calcium carbonate saturation states in the coastal zone of the west antarctic peninsula the polar oceans are particularly vulnerable to ocean acidification the lowering of seawater ph and carbonate mineral saturation states due to uptake of atmospheric carbon dioxide co2 high spatial variability in surface water ph and saturation states for two biologically important calcium carbonate minerals calcite and aragonite was observed in ryder bay in the coastal sea ice zone of the west antarctic peninsula glacial meltwater and melting sea ice stratified the water column and facilitated the development of large phytoplankton blooms and subsequent strong uptake of atmospheric co2 of up to 55 mmol m 2 day 1 during austral summer concurrent high ph 8 48 and calcium carbonate mineral supersaturation aragonite 3 1 occurred in the meltwater influenced surface ocean biologically induced increases in calcium carbonate mineral saturation states counteracted any effects of carbonate ion dilution accumulation of co2 through remineralisation of additional organic matter from productive coastal waters lowered the ph 7 84 and caused deep water corrosivity aragonite 0 9 in regions impacted by circumpolar deep water episodic mixing events enabled co2 rich subsurface water to become entrained into the surface and eroded seasonal stratification to lower surface water ph 8 21 and saturation states aragonite 1 8 relative to all surface waters across ryder bay uptake of atmospheric co2 of 28 mmol m 2 day 1 in regions of vertical mixing may enhance the susceptibility of the surface layer to future ocean acidification in dynamic coastal environments spatially resolved studies are essential to elucidate the natural variability in carbonate chemistry in order to better understand and predict carbon cycling and the response of marine organisms to future ocean acidification in the antarctic coastal zone

the freshwater system west of the antarctic peninsula spatial and temporal changes climate change west of the antarctic peninsula is the most rapid of anywhere in the southern hemisphere with associated changes in the rates and distributions of freshwater inputs to the ocean here results from the firstcomprehensivesurveyofoxygenisotopesinseawaterinthisregionareusedtoquantifyspatialpatternsof meteoric water glacial discharge and precipitation separately from sea ice melt high levels of meteoric water are found close to the coast due to orographic effects on precipitation and strong glacial discharge concentrations decrease offshore driving significant southward geostrophic flows up to 30 cm s 21 these produce high meteoric water concentrations at the southern end of the sampling grid where collapse of the wilkins ice shelf may also have contributed sea ice melt concentrations are lower than meteoric water and patchier because of the mobile nature of the sea ice itself nonetheless net sea ice production in the northern part of the sampling grid is inferred combined with net sea ice melt in the south this indicates an overall southwardicemotion thesurveyiscontextualizedtemporallyusingadecade longseriesofisotopedatafrom a coastal antarctic peninsula site this shows a temporal decline in meteoric water in the upper ocean contrary to expectations based on increasing precipitation and accelerating deglaciation this is driven by the increasingoccurrenceofdeeperwintermixedlayersandhaspotentialimplications forconcentrations oftrace metals supplied to the euphotic zone by glacial discharge as the regional freshwater system evolves the continuing isotope monitoring described here will elucidate the ongoing impacts on climate and the ecosystem

the partitioning of water between olivine orthopyroxene and melt synthesised in the system albite forsterite h2o coexisting forsterite enstatite and silicate glass were synthesised from a water bearing basalt analogue in programmed cooling experiments at 1 0 1 5 2 0 and 2 5 gpa hydrous species in each phase were characterised and quantified using infrared absorbance spectroscopy al 3 related hydroxyl defects with vibrational energies between 3400 3200 cm 1 dominate the hydroxyl budget of synthetic forsterite the vibrational characteristics of these defects indicate that similar absorptions in febearing systems result from fe 3 related oh species this interpretation resolves a previously recognised but unexplained relationship between oxygen fugacity and hydroxyl speciation in experimentally annealed olivines and suggests that the intensities of bands at 3400 3300 cm 1 could form the basis of an oxybarometer oh defect speciation in enstatite is similar to that in aluminous crystals synthesised at high water fugacity and many natural orthopyroxenes hydroxyl speciation in orthopyroxene is not therefore controlled by water activity total water contents of synthetic enstatites from any single experiment vary enormously this heterogeneity is attributed to variable contributions from a non intrinsic broad band hydrous component intrinsic hydroxyl concentrations dissolved in enstatite are identical in all crystals from an experiment the partitioning of water between forsterite enstatite and coexisting silicate melt is independent of pressure temperature and total water content over the range of conditions studied as long as the influence of these parameters on phase compositions is taken into account dh2o fo melt 0 0001 0 0003 n 4 and is insensitive to pressure or olivine aluminium contents dh2o en melt is strongly controlled by al2o3 concentration and ranges from 0 003 0 016 n 6 two samples contain both forsterite and enstatite and yield dh2o en fo 25 1

chemical multispectral and textural constraints on the composition and origin of rocks at the mars pathfinder landing site rocks at the mars pathfinder site are probably locally derived textures on rock surfaces may indicate volcanic sedimentary or impact generated rocks but aeolian abration and dust coatings prevent unambiguous interpretation multispectral imaging has resolved four spectral classes of rocks gray and red which occur on different surfaces of the same rocks pink which is probably soil crusts and maroon which occurs as large boulders mostly in the far field rocks are assigned to two spectral trends based on the position of peak reflectance the primary spectral trend contains gray red and pink rocks maroon rocks constitute the secondary spectral trend the spatial pattern of spectral variations observed is oriented along the prevailing wind direction the primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks the secondary spectral trend is apparently due to coating by a different mineral probably maghemite or ferrihydrite a chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit a flood deposit succeeded by smaller cobbles possibly deposited by impact and followed by aeolian erosion and deposition nearly linear chemical trends in alpha proton x ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust a conclusion supported by a correlation between sulfur abundance and red blue spectral ratio extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock the chemistry and normative mineralogy of the sulfur free rock resemble common terrestrial volcanic rocks and its classification corresponds to andesite igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias however the spectral mottling expected on conglomerates or breccias is not observed in any apxs analyzed rocks interpretation of the rocks as andesites is complicated by absence of a 1 m pyroxene absorption band plausible explanations include impact glass band masking by magnetite or presence of calcium and iron rich pyroxenes and olivine which push the absorption band minimum past the imager s spectral range the inferred andesitic composition is most similar to terrestrial anorogenic icelandites formed by fractionation of tholeiitic basaltic magmas early melting of a relatively primitive martian mantle could produce an appropriate parent magma supporting the ancient age of pathfinder rocks inferred from their incorporation in hesperian flood deposits although rocks of andesitic composition at the pathfinder site may represent samples of ancient martian crust inferences drawn about a necessary role for water or plate tectonics in their petrogenesis are probably unwarranted

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

spectral evidence of volcanic cryptodomes on the northern plains of mars abstract the composition and detailed morphology of dome shaped features located in western arcadia planitia and just west of utopia planitia were examined in this study utilizing data from mars reconnaissance orbiter and mars odyssey sensors the domes have diameters averaging 1 5 km and heights averaging 160 m and are generally dark toned although some are lighter toned or have split dark and light toned surfaces the domes are surrounded by annular deposits comprising with increasing distance from the domes dark toned aprons light toned aureoles and dark toned aureoles compact reconnaissance imaging spectrometer for mars crism data over several areas in the western arcadia region show that spectra from the flanks of several domes have 1 and 2 m absorption features consistent with the presence of olivine and a high ca pyroxene nominally augite modified gaussian model mgm analysis of these spectra indicates fe rich olivine compositions the tops of domes and the aprons surrounding many domes have negative sloping flat spectra in the near infrared which is consistent with tachylite rich glassy compositions high resolution imaging science experiment hirise images over several domes indicate that relatively high thermal inertia values associated with the tops of domes can be attributed to boulder strewn surfaces hirise images also reveal that light toned aureoles around domes consist of crenulated ground resembling brain terrain textures previously described for ice rich concentric crater fill elsewhere on the northern plains the plains surrounding the domes also display lineations that are interpreted to be lava channels or tubes the combination of volcanic and ice related features are consistent with the domes having formed as cryptodomes in the near sub surface we suggest that the domes could be basaltic in composition if the magmas were degassed and or highly crystallized and thus more viscous than typical basaltic magmas the intrusion of these magmas into an ice rich horizon would have produced a pervasively jointed chilled margin on the domes which once the domes were exposed would have mechanically weathered to form the dark aprons the domes could have served as local centers for ice accumulation during periods of high orbital obliquity which ultimately would have led to the formation of the brain terrain surrounding the features the domes represent late stage volcanic products on the northern plains of mars and associated features provide more evidence for the role that ice accumulation and modification has played in recent martian history

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

magmatic intrusions and deglaciation at mid latitude in the northern plains of mars abstract on earth igneous rocks are generally affected by magmatic differentiation and the volume of intrusive bodies is considered to be 5 10 times larger than the volume of volcanic rocks in contrast in the case of mars the occurrence of olivine phyric basalts at gusev crater mcsween h y 2006 j geophys res planets 111 e10 e02s10 the primitive nature of at least four picritic shergottites grott m 2013 planet space sci 174 49 111 and the chemical composition of major volcanic provinces baratoux d toplis m j monnereau m gasnault o 2011 nature 472 338 341 suggest that primary melts of the mantle may have commonly reached the surface these observations together with sparse morphologic evidence of intrusions in comparison with other terrestrial planets raise the issue of the conditions for the formation and occurrence of sub surface zones of magma storage on mars in this respect a series of two types of young amazonian domes located at mid latitudes in western arcadia planitia east of phlegra montes previously interpreted as surface expressions of intrusive bodies farrand w h lane m d edwards b r yingst r a 2011 icarus 211 139 156 are examined here a fraction of the domes consist of upraised plain material whereas others distinguished by a massive core and a large aspect ratio could be partially exhumed intrusions or extrusions of viscous differentiated magma the latter interpretation is however not compatible with the mafic compositions inferred from orbital visible and near infrared spectroscopic observations the thicknesses and radii of both types of domes appear to be related through a power law relationship with exponents close to 1 or 5 4 these exponent values are not compatible with extrusive morphologies but are characteristic of intrusions magma below an elastic layer michaut c 2011 j geophys res 10 1029 2010jb008108 we conclude that all types of domes are intrusive bodies the large aspect ratios of some of these features may be reconciled with a mafic composition and a shallow emplacement a few hundred meters as well as a relatively large injection rate magma emplacement below an ice rich horizon that was subsequently removed offers a plausible scenario for their partial exhumation this scenario is supported by independent signs of ice removal and deflation events in the northern plains the formation of these intrusions appear therefore to be related to an unusual context of magma ascent below a thick and low density ice rich horizon

basaltic lava domes lava lakes and volcanic segmentation on the southern east pacific rise meter scale dsl 120 sonar mapping and coregistered argo ii photographic observations reveal changes in eruptive style that closely follow the third order structural segmentation of the ridge axis on the southern east pacific rise 17 11 18 37 s near segment ends we observe abundant basaltic lava domes which average 20 m in height and 200 m in basal diameter and have pillow lava as the dominant lava morphology the ubiquity of pillow lava suggests low effusion rate eruptions the abundance of lava domes suggests that the fissure eruptions were of sufficient duration to focus and produce a line of volcanic edifices near segment centers we observe fewer but larger lava domes voluminous drained and collapsed lava lakes and smooth lobate and sheet lava flows with very little pillow lava the abundance of sheet flows suggests that high effusion rate eruptions are common fewer lava domes and large lava lakes suggest that fissure eruptions do not focus to point sources this pattern was observed on eight third order ridge segments suggesting that a fundamental volcanic segmentation of the ridge occurs on this scale the third order segment boundaries also correlate with local maxima in the seismic axial magma chamber reflector depth throughout the study area and decreased across axis width of the region of seismic layer 2a thickening along the one segment where sufficient cross axis seismic lines exist the geochemically defined magmatic segment boundaries in the study area match the locations of our volcanic segment boundaries although rock sampling density is not adequate to constrain the variation across all the third order volcanic segments that we identify these observations suggest that variation in the processes of crustal accretion along axis occurs at a length scale of tens of kilometers on superfast spreading 140 km myr full rate mid ocean ridges

block size distributions on silicic lava flow surfaces implications for emplacement conditions we determined block size distributions on the surfaces of holocene silicic lava flows at the inyo domes and the medicine lake volcano and studied the development of blocks on the active mount st helens and mount unzen lava domes to better understand the emplacement history of young viscous flows we measured block chord lengths along perpendicular 25 m long transects within vent jumbled and ridged morphologic units vent regions generally contain the largest average block sizes and largest range of average blocks whereas ridged areas tend to have the smallest average blocks observations at the active mount st helens and mount unzen lava domes show that block size distributions reflect stress conditions during flow high extrusion rates produce small primary blocks and lead to rapid fracturing of the flow surface whereas low extrusion rates allow large slabs to form in the vent area and lead to less severe fragmentation a dramatic increase in the size of blocks evident in active vent regions may indicate a significant decrease in eruption rate and thus could signal the cessation of extrusion however if the extrusion rate is too high or the cooling rate too low a rigid crust and accompanying blocks will not form on an eruptive time scale blocks may fracture through mechanical and thermal processes as they move downslope most silicic lava flows reach a steady state downslope where the average block size at the surface remains in the 20 30 cm size range with increasing distance from the vent fines blocks 12 cm do not accumulate on the flow surface because they slip toward the flow interior through void spaces between surface blocks we therefore expect long silicic lava flows to have blocky surfaces throughout their lengths an important consideration for evaluation of planetary lava flow emplacement

small edifice features in chryse planitia mars assessment of a mud volcano hypothesis abstract small edifice features that are less than a few kilometers in diameter and up to a few hundred meters in height are widely distributed in chryse planitia on mars they exhibit a broad range of morphological properties that are here classified as type 1 steep sided cones typically with a summit crater type 2 nearly flat features with single or multiple central summit craters or cones and type 3 nearly circular features in plan view characterized by steep sides and a broadly flat summit area their origins have not been determined with certainty but our study utilizing the high resolution imaging science experiment hirise images supports the interpretation of mud volcanism based on the observed morphological characteristics of these small edifices and comparisons with terrestrial analogs additionally hydrated minerals detected on these edifice features in data from the compact reconnaissance imaging spectrometer for mars crism further support the mud volcano hypothesis injection features such as clastic mega pipes and sand blow features may coexist with the mud volcanoes alternative mechanisms such as magmatic volcanism are not excluded but they have less support from our remote sensing observations further confirmation or rejection of the mud volcano hypothesis will require in situ investigation by landers or rovers

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

sulfates in the north polar region of mars detected by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer observed the northern circumpolar regions of mars at a resolution of a few kilometers an extended region at 240 e 85 n with an area of 60 kilometers by 200 kilometers exhibits absorptions at wavelengths of 1 45 1 75 1 94 2 22 2 26 and 2 48 micrometers these signatures can be unambiguously attributed to calcium rich sulfates most likely gypsum this region corresponds to the dark longitudinal dunes of olympia planitia these observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains

rootless cones on mars a consequence of lava ground ice interaction fields of small cratered cones on mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow melting and vaporization of the ice and subsequent explosive expansion of the vapour act to excavate the lava and construct a rootless cone around the explosion site similar features are found in iceland where flowing lava encountered water saturated substrates the martian cones have basal diameters of c 30 1000 m and are located predominantly in the northern volcanic plains high resolution mars orbiter camera images offer significant improvements over viking data for interpretation of cone origins a new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features this is consistent with the likely low availability of water ice in the martian regolith the scarcity of impact craters on many of the host lava flows indicates very young ages suggesting that ground ice was present as recently as less than 10 l00 ma and may persist today rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on mars which is of key significance in understanding the evolution of the martian climate the location of water in liquid or solid form is of great importance to future robotic and human exploration strategies and to the search for extraterrestrial life

the infrared signature of water associated with trivalent cations in olivine abstract forsterite crystals were synthesised under water saturated conditions at 1400 c and 1 5 gpa doped with trace amounts of either b al sc ti v cr mn fe co ga y zr in sm gd dy tm or lu the common and intense hydroxyl stretching bands in the infrared spectra of spinel peridotite olivine at 3572 and 3525 cm 1 were only reproduced in the presence of ti those samples where the trace element substitutes as the trivalent cation on the mg 2 site were identified from a systematic variation in concentration with the trivalent ionic radius the hydroxyl region of all samples is essentially identical except for between 3300 and 3400 cm 1 this region is characterised by one or more bands with the energy of the most intense feature being correlated with the ionic radius of the trivalent cation the integrated intensity of these hydroxyl bands also correlates with the concentration of the trivalent cation these correlations provide unambiguous evidence that bands or peaks in this region correspond to water at defect sites associated with trivalent cations trivalent peaks are sometimes observed in samples of mantle olivine and most likely indicate water associated with fe 3 the water at this site is not incorporated under normal mantle conditions and should not be included in estimates of the water capacity of mantle olivine these results emphasise the importance of identifying the infrared signature of different water substitution mechanisms

post eruptive development of the ukinrek east maar since its eruption in 1977 a d in the periglacial area of south west alaska maar eruptions form small initially steep walled basins that contain important archives for the climatic and palaeoenvironmental history in continental areas the two ukinrek maars in south western alaska erupted between 30 march and 9 april 1977 and are the best documented maars that have erupted in historical time this study presents a preliminary analysis of geomorphology hydrology magnetic susceptibility geochemistry and sedimentology data of a field study in august 2004 these results photographs and topographic surveys are combined for reconstructing the post eruptive evolution of ukinrek east maar within less than 30 years the initially polygonal shape of the crater with nearly vertical crater walls has developed into an almost elliptic form with slopes of 35 inclination on debris fans between a few escarpments the water table and the crater floor have risen significantly and the crater diameter depth ratio increased from 3 4 to 5 7 whereas the average height of the crater rim remained almost constant the main sub aerial resedimentation process is formation of rock falls rock slumps and scree resulting in debris flows and turbidites within the lake that is ice covered throughout about half of the year distal lake sediments consist of laminated minerogenic clayey sandy silts that document frequent turbidity currents from the linear sedimentation rate of only ca 5 mm year 1 in 17 cm long cores it may be concluded that the largest portion of the crater sediments formed within the first few months of the maar history however this has to be confirmed by future studies

spatial variation in seabed temperatures in the southern ocean implications for benthic ecology and biogeography the antarctic seabed has traditionally been regarded as cold and thermally stable with little spatial or seasonal variation in temperature here we demonstrate marked spatial variations in continental shelf seabed temperature around antarctica with the western antarctic peninsula shelf significantly warmer than shelves around continental antarctica as a result of flooding of the shelf by circumpolar deep water from the antarctic circumpolar current the coldest shelf seabed temperatures are in the weddell sea ross sea and prydz bay as a consequence of seasonal convection associated with strong air sea heat fluxes and sea ice formation these waters constitute the dense precursors of antarctic bottom water and can descend down the adjacent slope to inject cold water into the southern ocean deep sea deep sea seabed temperatures are coldest in the weddell sea and are progressively warmer to the east there is a distinct latitudinal gradient in the difference between seabed temperatures on the shelf and in the deep sea with the deep sea warmer by up to similar to 2 k at high latitudes and colder by similar to 2 k around sub antarctic islands these differences have important consequences for benthic ecology and biogeography understanding the evolutionary history of the antarctic marine biota and the impact of regional climate change

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

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

seasonality of warm water intrusions onto the continental shelf near the totten glacier warm modified circumpolar deep water mcdw from the southern ocean drives rapid basal melt of the totten ice shelf on the sabrina coast east antarctica affecting the mass balance of the grounded totten glacier recent observations show that mcdw intrudes onto the continental shelf through a depression at the shelf break here we investigate such intrusions by combining 1 new oceanographic and bathymetric observations collected for two consecutive years by profiling floats in the depression south of the shelf break 2 oceanographic measurements collected by conductivity temperature depth instrumented seals on continental slope and 3 an ocean model the depression provides a pathway for persistent inflow of warm 0 1 c mcdw to the inner shelf in austral autumn and early winter mcdw intrusions were up to 0 5 c warmer and were are 75 m thicker than in spring and summer the seasonality of the flow on the continental slope explains the seasonality of the intrusions the mcdw layer on the continental slope is warmer and thicker to the east of the depression than to the west in autumn and early winter a strong top to bottom westward current antarctic slope current transports the warmer and thicker mcdw layer along the slope and is diverted poleward at the eastern entrance of the depression a bottom intensified eastward current antarctic slope undercurrent develops in other months allowing cooler and thinner intrusions to enter the depression from the west our study illustrates how circulation on the antarctic slope regulates the ocean heat delivery to the continental shelf and ultimately to the ice shelves

subaqueous basaltic lava dome and carapace breccia on king george island south shetland islands antarctica on king george island during latest oligocene earliest miocene time submarine eruptions resulted in the emplacement of a small ca 500 m estimated original diameter basalt lava dome at low head the dome contains a central mass of columnar rock enveloped by fractured basalt and basalt breccia the breccia is crystalline and is a joint block deposit lithic orthobreccia interpreted as an unusually thick dome carapace breccia cogenetic with the columnar rock it was formed in situ by a combination of intense dilation fracturing and shattering caused by natural hydrofracturing during initial dome effusion and subsequent endogenous emplacement of further basalt melt now preserved as the columnar rock muddy matrix with dispersed hyaloclastite and microfossils fills fractures and diffuse patches in part of the fractured basalt and breccia lithofacies the sparse glass rich clasts formed by cooling contraction granulation during interaction between chilled basalt crust and surrounding water together with muddy sediment they were injected into the dome by hydrofracturing local steam fluidisation and likely explosive bulk interaction the basalt lava was highly crystallised and degassed prior to extrusion together with a low effusion temperature and rapid convective heat loss in a submarine setting these properties significantly affected the magma rheology increased the viscosity and shear strength and influenced the final dome like form of the extrusion conversely high heat retention was favoured by the degassed state of the magma minimal undercooling a thick breccia carapace and viscous shear heating which helped to sustain magmatic eruption temperatures and enhanced the mobility of the flow

evidence for amazonian highly viscous lavas in the southern highlands on mars we have identified small scale volcanic edifices two cones and three domes with associated flows within terra sirenum a region situated in the martian southern highlands based on thermal morphological and morphometrical properties and the determination of absolute model ages we conclude that these features were formed by volcanic activity of viscous lavas in the mid amazonian epoch relatively recently in martian history if our hypothesis is correct this small volcanic field represents rare evidence of young volcanic activity in the martian highlands in which martian equivalents of terrestrial lava domes and coulees might be present on earth such landforms are usually formed by highly viscous evolved lavas i e andesitic to rhyolitic for which observational evidence is sparse on mars hence this field might be one of only a few where martian evolved lavas might be investigated in detail