large sea ice outflow into the nares strait in 2007 1 sea ice flux through the nares strait is most active during the fall and early winter ceases in mid to late winter after the formation of ice arches along the strait and re commences after breakup in summer in 2007 ice arches failed to form this resulted in the highest outflow of arctic sea ice in the 13 year record between 1997 and 2009 the 2007 area and volume outflows of 87 103 km2 and 254 km3 are more than twice their 13 year means this contributes to the recent loss of the thick multiyear arctic sea ice and represents 10 of our estimates of the mean ice export at fram strait clearly the ice arches control arctic sea ice outflow the duration of unobstructed flow explains more than 84 of the variance in the annual area flux in our record seasonal stoppages are always associated with the formation of an arch near the same location in the southern kane basin additionally close to half the time another ice arch forms just north of robeson channel prior to the formation of the kane basin arch here we examine the ice export with satellite derived thickness data and the timing of the formation of these ice arches

sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

estimating sea ice area flux across the canadian arctic archipelago using enhanced amsr e 1 enhanced resolution advanced microwave scanning radiometer amsr e imagery is used to estimate daily sea ice area fluxes between the canadian arctic archipelago and the arctic ocean and baffin bay for the period september 2002 to june 2007 over the period amundsen gulf and m clure strait exported 54 103 km2 of sea ice area or roughly 77 km3 of sea ice volume each year into the arctic ocean export import into the arctic ocean through the queen elizabeth islands is small and uncertain since no estimates for july and august could be made due to atmospheric attenuation of the microwave signal lancaster sound exported 68 103 km2 of sea ice area or roughly 102 km3 of ice volume into baffin bay this produced a net loss of sea ice area of about 122 103 km2 or roughly 174 km3 a 1 which is presumed to be generated from within the archipelago itself mainly through the stationary and transient polynyas and leads that form each winter daily ice area fluxes for amundsen gulf ag and lancaster sound ls were as high as 2500 km2 d 1 and were event driven depending on synoptic scale atmospheric circulation and the mobility of the sea ice mean sea level pressure difference across each gate is moderately correlated with daily sea ice area fluxes despite the fact that free ice drift conditions are not always met in the region cross gradient and daily sea ice area flux for lancaster sound show a large number of counter gradient ice flux occurrences suggesting that local mesoscale winds nongeostrophic and perhaps ocean currents play a role in transporting sea ice through this gate monthly ice fluxes for the ag and ms gate were positively correlated with the ao index indicating that a strong beaufort sea high pressure and gyre correspond to more export into the beaufort sea monthly fluxes for the ls gate were positively correlated with the nao index indicating that strong southerly atmospheric circulation over baffin bay increases ice export into baffin bay from lancaster sound

young late amazonian near surface ground ice features near the equator athabasca valles mars abstract a suite of four feature types in a 20 km 2 area near 10 n 204 w in athabasca valles is interpreted to have resulted from near surface ground ice these features include mounds conical forms with rimmed summit depressions flatter irregularly shaped forms with raised rims and polygonal terrain based on morphology size and analogy to terrestrial ground ice forms these athabascan features are interpreted as pingos collapsing pingos pingo scars and thermal contraction polygons respectively thermal infrared mapping spectrometer themis data and geological features in the area are consistent with a sedimentary substrate underlying these features these observations lead us to favor a ground ice interpretation although we do not rule out volcanic and especially glaciofluvial hypotheses the hypothesized ground ice that formed the mounds and rimmed features may have been emplaced via the deposition of saturated sediment during flooding an alternative scenario invokes magmatically cycled groundwater the ground ice implicit in the hypothesized thermal contraction polygons may have derived either from this flooding ground water or from atmospheric water vapor the lack of obvious flood modification of the mounds and rimmed features indicates that they formed after the most recent flood inundated the area analogy with terrestrial pingos suggests that ground ice may be still extant within the positive relief mounds as the water that flooded down athabasca valles emerged via a volcanotectonic fissure from a deep aquifer any extant pingo ice may contain evidence of a deep subsurface biosphere

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

stratigraphical and morphological evidence for pingo genesis in the cerberus plains rootless debris cones or pseudocraters occur in platy patterned ground throughout the cerberus plains of mars and are thought to represent the products of explosive magma ice interaction lanagan et al 2001 geophys res lett 28 2365 2368 fagents et al 2002 in smellie j l chapman m g eds volcano ice interaction on earth and mars in geol soc spec publ vol 202 pp 295 317 requiring lava and water interspersed they are central to theories of multiple magmatic and aqueous flood events burr et al 2002 icarus 159 53 73 berman d c hartmann w k 2002 icarus 159 1 17 and widespread sheet volcanism keszthelyi et al 2000 j geophys res 105 15027 15049 in the region during the late amazonian a region reported to have been occupied by water bodies ranging from lakes to oceans scott et al 1995 map of mars showing channels and possible paleolake basins usgs miscellaneous investigations series map i 2461 1 30 000 000 the nature of the platy substrate is the subject of debate with evidence given for lava keszthelyi et al 2000 j geophys res 105 15027 15049 plescia j b 2003 icarus 164 79 95 and ice brakenridge g r 1993 lunar planet sci xxiv part 1 175 176 rice et al 2002 lunar planet sci xxxiii abstract 2026 murray et al 2005 nature 434 352 355 the superposition relationships of cones and platy deposits in the channels of the athabasca valles precludes a magmatic origin indicating later formation as permafrost mounds or pingos with implications for geologically recent flood volcanism age constraints on young surfaces and recent climate change on mars

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

recent changes in the exchange of sea ice between the arctic ocean and the canadian arctic archipelago 1 sea ice is exchanged between the arctic ocean and canadian arctic archipelago caa but has not been quantified over long time periods the corresponding mechanisms responsible for recent variability and change also remain unidentified to address this we estimated the sea ice area flux between the arctic ocean and the m clure strait and queen elizabeth islands qei from 1997 to 2012 for the months of may to november over the period there was a mean flux of 1 103 km2 21 103 km2 at the m clure strait and mean flux of 8 103 km2 8 103 km2 at the qei positive and negative flux signs correspond to arctic ocean ice inflow and outflow respectively the m clure strait had a mean flux of 5 103 km2 from may to september and a mean flux of 7 103 km2 from october to november the qei gates had a mean flux of 4 103 km2 from august to september with negligible ice exchange from may to july and october to november more frequent high sea level pressure anomalies over the beaufort sea and canadian basin since 2007 have reduced arctic ocean multiyear ice myi inflow into the m clure strait the presence of myi in the caa originating from the arctic ocean has been maintained by inflow at the qei which has increased since 2005 these recent increases in arctic ocean myi inflow into the qei can be attributed to increased open water area within the caa that have provided more leeway for inflow to occur

thermokarst lakes and ponds on mars in the very recent late amazonian past the history of water is fundamental to understanding the geological evolution of mars and to questions concerning the possible development of life on the red planet today mars is cold and dry it

arctic sea ice circulation and drift speed decadal trends and ocean currents 1 we examine the basinwide trends in sea ice circulation and drift speed and highlight the changes between 1982 and 2009 in connection to regional winds multiyear sea ice coverage ice export and the thinning of the ice cover the polarity of the arctic oscillation ao is used as a backdrop for summarizing the variance and shifts in decadal drift patterns the 28 year circulation fields show a net strengthening of the beaufort gyre and the transpolar drift especially during the last decade the imprint of the arctic dipole anomaly on the mean summer circulation is evident 2001 2009 and enhances summer ice area export at the fram strait between 2001 and 2009 the large spatially averaged trends in drift speeds winter 23 6 decade summer 17 7 decade are not explained by the much smaller trends in wind speeds winter 1 46 decade summer 3 42 decade notably positive trends in drift speed are found in regions with reduced multiyear sea ice coverage over 90 of the arctic ocean has positive trends in drift speed and negative trends in multiyear sea ice coverage the increased responsiveness of ice drift to geostrophic wind is consistent with a thinner and weaker seasonal ice cover and suggests large scale changes in the air ice ocean momentum balance the retrieved mean ocean current field from decadal scale average ice motion captures a steady drift from siberia to the fram strait an inflow north of the bering strait and a westward drift along coastal alaska this mean current is comparable to geostrophic currents from satellite derived dynamic topography

crystal molds on mars melting of a possible new mineral species to create martian chaotic terrain images sent back by the mars exploration rover opportunity from the meridiani planum show sulfate rich rocks containing plate shaped voids with tapered edges that are interpreted as crystal molds formed after a late stage evaporite mineral has been removed experimental studies of the mgso4 h2o system at low temperatures reveal that the triclinic phase mgso4 11h2o exhibits a crystal morphology that matches the shapes of these molds mgso4 11h2o melts incongruently above 2 c to a mixture of 70 epsomite mgso4 7h2o and 30 h2o by volume when this occurs while crystals are encased in sediment plate shaped voids remain the existence of ice low surface temperatures and the high sulfate content of surface rocks and soil on mars makes mgso4 11h2o a possible mineral species near the surface at high latitudes or elsewhere in the subsurface if an evaporite layer contained a significant amount of this phase incongruent melting would result in a rapid release of a large volume of water and could explain some of the landform features on mars that are interpreted as outflow channels mgso4 11h2o would not survive a sample return mission unless extraordinary precautions were taken

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

sea ice motion tracking from sequential dual polarization radarsat 2 images a new sea ice motion tracking algorithm that operates with two sequential synthetic aperture radar sar radarsat 2 scansar images is presented the feature tracking approach is based on the combination of the phase correlation and cross correlation methods an algorithm for selecting control points a matching technique an approach for filtering out error vectors and a confidence levels setting for output drift vectors were specifically developed in order to increase the system s robustness and accuracy we evaluated ice motion tracking results derived from hh and hv channels of radarsat 2 scansar imagery and formulated a condition where the hv channel is more reliable than the hh channel for ice tracking furthermore we found that the ice motion tracking from the hv channel is not affected by noise floor stripes which are prominent in the cross polarization radarsat 2 scansar images the developed sea ice tracking technology was implemented at the canadian ice service environment canada for operational use the system was successfully run to provide operational support of field work in the arctic ocean in compliance with the united nations convention on the law of the sea in the spring of 2010

sea ice draft observations in nares strait from 2003 to 2012 time series observation of sea ice draft and velocity from nares strait between 2003 and 2012 provides new insights on the statistical properties of sea ice leaving the arctic for the atlantic oceans median ice draft is 0 8 m but it varies annually from 1 5 m in 2007 2008 to 0 5 m in 2008 2009 probability density distributions of sea ice draft depend on location across the channel with thicker ice near canada and thinner ice near greenland nevertheless sea ice motion stops seasonally due to arching land fast ice that spans the 30 40 km wide channel for up to 190 days per year such as during the 2011 2012 winter in contrast the 2006 2010 period exhibits a single ice arch lasting 47 days in april may 2008 hence sea ice statistics are weighted by space not by time using sea ice velocities estimated from colocated velocity observations multiyear sea ice with drafts exceeding 5 m constitute between 9 2003 2004 and 16 2007 2008 of the observed sea ice the probability g d of this thick ridged multiyear ice decays exponentially with draft d at an e folding scale d0 of 3 0 0 2 m the trend of d0 with time is statistically indistinguishable from zero this observation suggests a steady export of multiyear sea ice at decadal time scales we speculate that our observations document the draining of the last reservoir of thick ice from the arctic ocean found to the north of ellesmere island and greenland

ice thickness in the northwest passage recently the feasibility of commercial shipping in the ice prone northwest passage nwp has attracted a lot of attention however very little ice thickness information actually exists we present results of the first ever airborne electromagnetic ice thickness surveys over the nwp carried out in april and may 2011 and 2015 over first year and multiyear ice these show modal thicknesses between 1 8 and 2 0 m in all regions mean thicknesses over 3 m and thick deformed ice were observed over some multiyear ice regimes shown to originate from the arctic ocean thick ice features more than 100 m wide and thicker than 4 m occurred frequently results indicate that even in today s climate ice conditions must still be considered severe these results have important implications for the prediction of ice breakup and summer ice conditions and the assessment of sea ice hazards during the summer shipping season

the 2017 reversal of the beaufort gyre can dynamic thickening of a seasonal ice cover during a reversal limit summer ice melt in the beaufort sea during winter 2017 the semi permanent beaufort high collapsed and the anticyclonic beaufort gyre reversed the reversal drove eastward ice motion through the western arctic causing sea ice to converge against banks island and halted the circulation of multiyear sea ice via the gyre preventing its replenishment in the beaufort sea prior to the reversal an anomalously thin seasonal ice cover had formed in the beaufort following ice free conditions during september 2016 with the onset of the reversal in january 2017 convergence drove uncharacteristic dynamic thickening during winter by the end of march despite seasonal ice comprising 97 of the ice cover the reversal created the thickest roughest and most voluminous regional ice cover of the cryosat 2 record within the beaufort sea previous work has shown that winter ice export can precondition the region for increased summer ice melt but that a short reversal during april 2013 contributed to a reduction in summer ice loss hence the deformed ice cover at the end of winter 2017 could be expected to limit summer melt in spite of this the beaufort ice cover fell to its fourth lowest september area as the gyre re established during april and divergent ice drift broke up the pack negating the reversal s earlier preconditioning our work highlights that dynamic winter thickening of a regional sea ice cover for instance during a gyre reversal offers the potential to limit summer ice loss but that dynamic forcing during spring dictates whether this conditioning carries through to the melt season

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

cerberus fossae elysium mars a source for lava and water cerberus fossae a long fracture system in the southeastern part of elysium has acted as a conduit for the release of both lava and water onto the surface the southeastern portion of the fracture system localized volcanic vents having varying morphology in addition low shields occur elsewhere on the cerberus plains three locations where the release of water has occurred have been identified along the northwest athabasca and grjota vallis and southeast rahway vallis portions of the fossae water was released both catastrophically and noncatastrophically from these locations a fluvial system that extends more than 2500 km has formed beginning at the lower flank of the elysium rise across the cerberus plains and out through marte vallis into amazonis planitia the timing of the events is late amazonian

an equatorial periglacial landscape on mars abstract we present evidence drawn from new 25 cm pixel hirise images of mars of landforms indicative of geologically recent thaw degradation of ice rich terrain near the martian equator we have focused our study on the head region of athabasca vallis a catastrophic flood carved outflow channel thought to have been active within the last 2 8 ma the geomorphology of the study area is characterised by a series of polygonally patterned surfaces that are bounded by erosional scarps the scarps are indented with cirque shaped niches that appear to be controlled in scale and form by the pre existing polygonal sculpture shallow basins defined by niche indented scarps are also seen and contain pitted mound and cone structures that are similar in form to terrestrial pingos associated with many of these scarps are dendritic channels and gullies blocky debris and hummocky terminal deposits together these correspond morphologically to terrestrial retrogressive thaw slumps which are landforms typical of thermokarst environments we have also observed an evolutionary sequence of morphologies beginning with subsidence of polygonised surfaces and ending with scarp bounded basins fed by inter polygon channels this is consistent with the former presence of surficial liquid water released by ground ice thaw and is again indicative of thermokarst moreover the observations of epigenetic polygons and channels and of polycyclic retrogressive thaw slumps suggest that thaw and standing water persisted for many seasonal cycles the assemblage of landforms the occurrence of polygons and pingo like forms within erosional basins and observations of fluvial like channels cross cutting pre existing surface features are consistent with a surface that has evolved significantly since it was originally emplaced this precludes this terrain being a volcanic i e primary landscape as has been suggested in the past the formation of this landform assemblage requires that there was thaw of ground ice and persistent liquid water at the surface given the geologically young flood deposits in which this assemblage occurs our observations point to a recent period in which mars climate supported thaw conditions in this region

sea ice of the northern canadian arctic archipelago 1 existing information concerning the pack ice and relevant climate variables of the canadian arctic archipelago north of parry channel is summarized this knowledge is enhanced by newly available data on ice thickness derived from 123 703 drill holes completed during the 1970s pack ice in this area is a mix of multiyear second year and first year ice types with the latter subordinate except in the southeast ice remains land fast for more than half the year and summertime ice concentration is high 7 9 tenths in a typical year less than 20 of the old ice and 50 of the first year ice melt there are large interannual fluctuations in ice coverage and some suggestion of a decadal cycle the average ice thickness in late winter is 3 4 m but subregional means reach 5 5 m the pack is a mix of two populations one consisting largely of multiyear ice imported from the zone of heavy ridging along the periphery of the beaufort gyre and the other consisting of a mix of relatively undeformed first year second year and multiyear ice types that grow and age within the basin the ice of the sverdrup basin is strongly influenced by a flux of heat approximately 10 w m 2 that originates in the atlantic derived waters of the arctic ocean the drift of ice through the basin is controlled in the present climate by the formation of stable ice bridges across connecting channels the drift is episodic relaxation of these controls in a warmer climate may cause deterioration in ice conditions in canadian arctic waters

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

exchange of sea ice between the arctic ocean and the canadian arctic archipelago 1 first estimates of sea ice exchange between the arctic ocean and the canadian arctic archipelago caa are obtained using six years 1997 2002 of radarsat ice motion over the period the mean annual flux of sea ice area from the amundsen gulf ag m clure strait ms and queen elizabeth islands qei are 85 26 103 20 24 103 and 8 6 103 km2 positive negative sign indicates arctic outflow inflow overall net sea ice area is exported from the caa rough estimates suggest a mean annual volume flux of 102 km3 into the canada basin ice types are largely seasonal near the ag flux gate mixed seasonal and multiyear at the ms gate and primarily multiyear at the qei gates sea ice at the qei flux gates remains land fast for most of the year cross strait gradient in sea level pressure explains more than 50 of the variance in the area flux at these passages the role of ice exchange during the anomalous decrease in multiyear ice coverage in the sverdrup basin during september 1998 is examined

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

orientation and distribution of recent gullies in the southern hemisphere of mars observations from high resolution stereo camera mars express hrsc mex and mars orbiter camera mars global surveyor moc mgs data 1 geologically recent small gullies on mars display morphologies consistent with erosion by water or by debris flows suggested formation models are divided into two main categories 1 groundwater or 2 melting of near surface ice snow sourced from the atmosphere we have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation more than 22 000 mars orbiter camera narrow angle moc na and 120 mars express high resolution stereo camera hrsc images in the southern hemisphere were searched for gullies discrete gullied slope sections with consistent orientation were recorded rather than individual gullies slope setting impact crater valley wall etc location and orientation were recorded for each slope section more than 750 moc images with gullies 900 distinct gullied slope sections and more than 40 hrsc images 380 distinct gullied slope sections were identified from both moc and hrsc gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference the preferred gully orientation for hrsc is southeast rather than south in moc owing to illumination effects that make gullies difficult to detect on south to southwest facing slopes in hrsc in both moc and hrsc surveys higher latitude gullies show less preference for pole facing than those at mid latitudes both data sets produced similar results demonstrating that our data are reliable we suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation

the angular velocities of the plates and the velocity of earth s centre from space geodesy summary using space geodetic observations from four techniques gps vlbi slr and doris we simultaneously estimate the angular velocities of 11 major plates and the velocity of earth s centre we call this set of relative plate angular velocities geodvel for geodesy velocity plate angular velocities depend on the estimate of the velocity of earth s centre and on the assignment of sites to plates most geodetic estimates of the angular velocities of the plates are determined assuming that earth s centre is fixed in an international terrestrial reference frame itrf and are therefore subject to errors in the estimate of the velocity of earth s centre in itrf2005 and itrf2000 earth s centre is the centre of mass of earth oceans and atmosphere cm the velocity of cm is estimated by slr observation of lageos s orbit herein we define earth s centre to be the centre of mass of solid earth ce we determine the velocity of ce by assuming that the portions of plate interiors not near the late pleistocene ice sheets move laterally as if they were part of a rigid spherical cap the geodvel estimate of the velocity of ce is likely nearer the true velocity of cm than are the itrf2005 and itrf2000 estimates because 1 no phenomena can sustain a significant velocity between cm and ce 2 the plates are indeed nearly rigid aside from vertical motion and 3 the velocity of cm differs between itrf2005 and itrf2000 by an unacceptably large speed of 1 8 mm yr 1 the velocity of earth s centre in geodvel lies between that of itrf2000 and that of itrf2005 with the distance from itrf2005 being about twice that from itrf2000 because the geodvel estimates of uncertainties in plate angular velocities account for uncertainty in the velocity of earth s centre they are more realistic than prior estimates of uncertainties geodvel differs significantly from all prior global sets of relative plate angular velocities determined from space geodesy for example the 95 per cent confidence limits for the angular velocities of geodvel exclude those of revel sella et al for 34 of the 36 plate pairs that can be formed between any two of the nine plates with the best constrained motion the median angular velocity vector difference between geodvel and revel is 0 028 myr 1 which is up to 3 1 mm yr 1 on earth s surface geodvel differs the least from the geodetic angular velocities that altamimi et al determine from itrf2005 geodvel s 95 per cent confidence limits exclude 11 of 36 angular velocities of altamimi et al and the median difference is 0 015 myr 1 geodvel differs significantly from nearly all relative plate angular velocities averaged over the past few million years including those of nuvel 1a the difference of geodvel from updated 3 2 myr angular velocities is statistically significant for all but two of 36 angular velocities with a median difference of 0 063 myr 1 across spreading centres eight have slowed down while only two have sped up we conclude that plate angular velocities over the past few decades differ significantly from the corresponding angular velocity averaged over the past 3 2 myr

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

recent changes in the dynamic properties of declining arctic sea ice a model study 1 results from a numerical model simulation show significant changes in the dynamic properties of arctic sea ice during 2007 2011 compared to the 1979 2006 mean these changes are linked to a 33 reduction in sea ice volume with decreasing ice concentration mostly in the marginal seas and decreasing ice thickness over the entire arctic particularly in the western arctic the decline in ice volume results in a 37 decrease in ice mechanical strength and 31 in internal ice interaction force which in turn leads to an increase in ice speed 13 and deformation rates 17 the increasing ice speed has the tendency to drive more ice out of the arctic however ice volume export is reduced because the rate of decrease in ice thickness is greater than the rate of increase in ice speed thus retarding the decline of arctic sea ice volume ice deformation increases the most in fall and least in summer thus the effect of changes in ice deformation on the ice cover is likely strong in fall and weak in summer the increase in ice deformation boosts ridged ice production in parts of the central arctic near the canadian archipelago and greenland in winter and early spring but the average ridged ice production is reduced because less ice is available for ridging in most of the marginal seas in fall the overall decrease in ridged ice production contributes to the demise of thicker older ice as the ice cover becomes thinner and weaker ice motion approaches a state of free drift in summer and beyond and is therefore more susceptible to changes in wind forcing this is likely to make seasonal or shorter term forecasts of sea ice edge locations more challenging

fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea yukon territory canada abstract patterns of coastal erosion in the arctic differ dramatically from those coasts in more temperate environments thick sea ice and shore fast ice limit wave based erosional processes to a brief open water season however despite this permafrost coasts containing massive ice ice wedges and ice bonded sediments tend to experience high rates of erosion these high rates of erosion reflect the combined thermal mechanical processes of thawing permafrost melting ground ice and wave action climate change in the arctic is expected to result in increased rates of coastal erosion due to warming permafrost increasing active layer depths and thermokarst rising sea levels reduction in sea ice extent and duration and increasing storm impacts with the most ice rich permafrost in the canadian arctic the southern beaufort sea coast between the tuktoyaktuk peninsula and the alaskan border is subject to high rates of erosion and retrogressive thaw slump activity under many climate change scenarios this area is also predicted to experience the greatest warming in the canadian arctic this paper presents results of a remote sensing study on the long term patterns of coastal erosion and retrogressive thaw slump activity for herschel island in the northern yukon territory using orthorectified airphotos from 1952 and 1970 and an ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools mean coastal retreat rates of 0 61 m yr and 0 45 m yr were calculated for the periods 1952 1970 and 1970 2000 respectively the highest coastal retreat rates are on north west facing shorelines which correspond to the main direction of storm related wave attack during the period 1970 2000 coastal retreat rates for south to south east facing shorelines displayed a distinct increase even though these are the most sheltered orientations however south to south east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south east exposures the number and the total area of retrogressive thaw slumps increased by 125 and 160 respectively between 1952 and 2000 as well the proportion of active retrogressive thaw slumps increased dramatically polycyclic retrogressive thaw slumps appear to develop in a periodic fashion related to retrogressive thaw slump stage and maximum inland extent

increasing mobility of high arctic sea ice increases marine hazards off the east coast of newfoundland heavy ice conditions along canada s east coast during spring 2017 presented hazardous conditions for the maritime industry and required the canadian coast guard to pull its research icebreaker ccgs amundsen off its scientific cruise to provide ice escort services and conduct search and rescue operations along newfoundland s northeast coast greater ice concentrations and a thicker ice pack than are typical of this area created the anomalous ice cover within this paper we present in situ observations of the ice cover confirming that pieces of multiyear sea ice from the high arctic were present within the ice cover and subsequently examine the transport pathway that connects the export of thick multiyear sea ice from the lincoln sea and canadian arctic archipelago to coastal communities in newfoundland we conclude with a discussion on how an increasingly mobile arctic sea ice cover may increase these ice hazards in the south

outflow of arctic ocean sea ice into the greenland and barents seas 1979 2007 abstract twenty nine years of arctic sea ice outflow into the greenland and barents seas are summarized outflow is computed at three passages fram strait between svalbard and franz josef land s fjl and between franz josef land and severnaya zemlya fjl sz ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration ic fields over the record the mean annual area outflow at the fram strait is 706 113 103 km2 it was highest in 1994 95 1002 103 km2 when the north atlantic oscillation nao index was near its 29 yr peak the strength of the transpolar drift stream tds was high during the late 1980s through the mid 1990s there is no statistically significant trend in the fram strait area flux even though there is a positive trend in the gradient of cross strait sea level pressure the outflow has not increased because of a negative trend in ic seasonally the area outflow during recent sum

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies