hydrography and energetics of a cold subpolar fjord andvord bay western antarctic peninsula abstract fjords along the western antarctic peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change but much is unknown about the physical oceanography of these fjords this paper presents a comprehensive description of the physical environment of andvord bay a glacial fjord located in the gerlache strait on the northern end of the peninsula measurements were collected as part of the fjordeco program between november 2015 and march 2017 including during three research cruises and from a number of fixed installations sub surface moorings time lapse cameras and automatic weather stations andvord bay is located just north of a sill in the gerlache strait this sill inhibits the direct influence of warm upper circumpolar deep water from the shelf and deep waters in the fjord are therefore relatively cold as a result glaciers in andvord bay are not subject to the substantial ocean driven retreat observed farther south on the peninsula instead mass flux from the glaciers occurs mainly through calving the influence of meltwater in andvord bay is small compared to glacial fjords in the arctic and in the south shetland islands although summer freshening is evident in the fjord near surface layer likely as a result of glacial inputs the combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone providing advantageous conditions for phytoplankton blooms andvord bay is generally dynamically quiet compared to the ambient ocean with the exception of during local katabatic wind events exchange with the gerlache strait is weak although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside in addition deep convection may play a role in ventilating subsurface waters in winter

influence of the porewater geochemistry on fe and mn assimilation in laternula elliptica at king george island antarctica abstract a high input of lithogenic sediment from glaciers was assumed to be responsible for high fe and mn contents in the antarctic soft shell clam laternula elliptica at king george island indeed withdrawal experiments indicated a strong influence of environmental fe concentrations on fe contents in bivalve hemolymph but no significant differences in hemolymph and tissue concentrations were found among two sites of high and lower input of lithogenic debris comparing fe and mn concentrations of porewater bottom water and hemolymph from sampling sites mn appears to be assimilated as dissolved species whereas fe apparently precipitates as ferrihydrite within the oxic sediment or bottom water layer prior to assimilation by the bivalve hence we attribute the high variability of fe and mn accumulation in tissues of l elliptica around antarctica to differences in the geochemical environment of the sediment and the resulting fe and mn flux across the benthic boundary

anatomy of a glacial meltwater discharge event in an antarctic cove glacial meltwater discharge from antarctica is a key influence on the marine environment impacting ocean circulation sea level and productivity of the pelagic and benthic ecosystems the responses elicited depend strongly on the characteristics of the meltwater releases including timing spatial structure and geochemical composition here we use isotopic tracers to reveal the time varying pattern of meltwater during a discharge event from the fourcade glacier into potter cove northern antarctic peninsula the discharge is strongly dependent on local air temperature and accumulates into an extremely thin buoyant layer at the surface this layer showed evidence of elevated turbidity and responded rapidly to changes in atmospherically driven circulation to generate a strongly pulsed outflow from the cove to the broader ocean these characteristics contrast with those further south along the peninsula where strong glacial frontal ablation is driven oceanographically by intrusions of warm deep waters from offshore the fourcade glacier switched very recently to being land terminating if retreat rates elsewhere along the peninsula remain high and glacier termini progress strongly landward the structure and impact of the freshwater discharges are likely to increasingly resemble the patterns elucidated here this article is part of the theme issue the marine system of the west antarctic peninsula status and strategy for progress in a region of rapid change

internal accumulation on storglaciaren sweden in a multi layer snow model coupled to a distributed energy and mass balance model to investigate the internal accumulation on storglaciaren sweden we couple a multilayer snow model to a distributed energy and mass balance model the snow model describes the temperature density and water content evolution of the snow ice pack and includes the processes of percolation and refreezing of water the model is run for the period 9 may 2 september 1999 and validated against weather station and mass balance observations on the glacier the model performs reasonably well with an average summer mass balance for the location of stake observations of 1 56 m w e compared to 1 59 m w e observed however the amount of melt is overestimated in the higher parts of the accumulation area and underestimated in the lower parts of the ablation area the modelled mass balance is most sensitive to the albedo parameterization the chosen momentum and scalar roughness lengths and all parameters related to snowfall the modelled internal accumulation is 0 25 m w e which amounts to about 20 of the winter accumulation and results in a positive net balance for 1999 of 0 23 m w e the modelled internal accumulation is most sensitive to the initial subsurface temperature profile and the irreducible water content

hydrography of potter cove a small fjord like inlet on king george island south shetlands abstract the hydrography of potter cove king george island south shetlands is described in detail for one summer season recorded data are wind air temperature water temperature salinity and water colour from these information on surface circulation patterns and dynamics of suspended sediments are derived possible sources of sediment input are discussed as a result a complex interaction between wind forcing circulation and seasonal melt of high glacier surfaces emerges

ocean forcing of glacier retreat in the western antarctic peninsula in recent decades hundreds of glaciers draining the antarctic peninsula 63 to 70 s have undergone systematic and progressive change these changes are widely attributed to rapid increases in regional surface air temperature but it is now clear that this cannot be the sole driver here we identify a strong correspondence between mid depth ocean temperatures and glacier front changes along the 1000 kilometer western coastline in the south glaciers that terminate in warm circumpolar deep water have undergone considerable retreat whereas those in the far northwest which terminate in cooler waters have not furthermore a mid ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat we conclude that changes in ocean induced melting are the primary cause of retreat for glaciers in this region

redox conditions and trace metal cycling in coastal sediments from the maritime antarctic abstract redox sensitive trace metals mn fe u mo re nutrients and terminal metabolic products no 3 nh 4 po 4 3 total alkalinity were investigated for the first time in pore waters of antarctic coastal sediments the results of this study reveal a high spatial variability in redox conditions in surface sediments from potter cove king george island western antarctic peninsula particularly in the shallower areas of the bay the significant correlation between sulphate depletion and total alkalinity the inorganic product of terminal metabolism indicates sulphate reduction to be the major pathway of organic matter mineralisation in contrast dissimilatory metal oxide reduction seems to be prevailing in the newly ice free areas and the deeper troughs where concentrations of dissolved iron of up to 700 m were found we suggest a combination of several factors to be responsible for the domination of metal oxide reduction over sulphate reduction in these areas these include the increased accumulation of fine grained material with high amounts of reducible metal oxides a reduced availability of metabolisable organic matter and an enhanced physical and biological disturbance by bottom water currents ice scouring and burrowing organisms based on modelled iron fluxes we calculate the contribution of the antarctic shelf to the pool of potentially bioavailable iron feb to be 6 9 103 to 790 103 t yr 1 consequently these shelf sediments would provide an feb flux of 0 35 39 5 mg m 2 yr 1 median 3 8 mg m 2 yr 1 to the southern ocean this contribution is in the same order of magnitude as the flux provided by icebergs and significantly higher than the input by aeolian dust for this reason suboxic shelf sediments form a key source of iron for the high nutrient low chlorophyll hnlc areas of the southern ocean this source may become even more important in the future due to rising temperatures at the wap accompanied by enhanced glacier retreat and the accumulation of melt water derived iron rich material on the shelf

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

imaging the midlatitude sporadic e plasma patches with a coordinated observation of spaceborne insar and gps total electron content kilometer scale fine structures of midlatitude sporadic e es plasma patches have been directly imaged for the first time by an interferogram derived from l band advanced land observation satellite phased array type l band synthetic aperture radar data obtained over southwestern japan the synthetic aperture radar interferogram captured the eastern part of a large scale frontal structure of daytime midlatitude es which spans over 250 km in the east northeast to west southwest direction fine structures are characterized by frontal and disc shaped patches which are elongated in the same direction as the large scale frontal structure length and width of the disc shaped patches are 10 20 km and 5 10 km respectively and they are quasi periodically located with a typical separation of 10 15 km the kelvin helmholtz instability with the vertical shear of zonal winds is considered to be the most likely candidate for the generation mechanism of the frontal patch and disc shaped patches aligned in the zonal direction

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

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

progressive strain localization in a major strike slip fault exhumed from midseismogenic depths structural observations from the salzach ennstal mariazell puchberg fault system austria 1 analysis of a strike slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high strain fault core we focus on the ennstal segment of the 400 km long salzach ennstal mariazell puchberg semp strike slip fault system in the eastern alps which accommodated 60 km of left lateral displacement during oligo miocene time macroscopic and microscopic observations reveal a zoned fault featuring a high strain core at least 10 m wide within a fault zone that is at least 150 m wide grain size distribution analysis shows how the ennstal segment of the semp evolved our data reveal a 10 m wide high strain fault core characterized by a power law relationship of grain sizes d2 2 0 bordered by a 54 m wide transition zone where the largest and smallest grains are characterized by two power law relationships d2 2 0 and 1 6 respectively this zone is in turn bordered by a region with grain sizes that show a single low strain power law relationship of d2 1 6 we interpret these relationships to be the result of concentrated shear overprinting an initial low strain power law grain size distribution before strain localized to the core this is consistent with the theory that faults mature by smoothing geometrical complexities forming a highly localized high strain fault core the data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure

nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation crystal plasticity at sub seismic slip rates at 18 150 c a central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic seismic transitions in fault gouges and to identify microstructural indicators for such transitions we present new data on the slip stability of calcite fault gouges and on microstructural development down to the nanometer scale our experiments consisted of direct shear tests performed dry at slip rates of 0 1 10 m s at a constant normal stress of 50 mpa at 18 150 c the results show a transition from stable to potentially unstable slip above 80 c all samples recovered showed an optical microstructure characterized by narrow 30 40 m wide riedel and boundary shear bands marked by extreme grain comminution and a crystallographic preferred orientation cpo boundary shear bands sectioned using fib sem focused ion beam scanning electron microscopy revealed angular grain fragments decreasing from 10 to 20 m at the outer margins to 0 3 m in the shear band core where dense aggregates of nanograins also occurred transmission electron microscopy applied to foils extracted from boundary shears using fib sem combined with the optical cpo showed that these aggregates consist of calcite nanocrystals 5 20 nm in size with the 104 201 dislocation glide system oriented parallel to the shear plane and direction our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity because crystal plasticity is strongly thermally activated we infer that the transition to velocity weakening slip is likely due to enhanced crystal plasticity at 80 c this implies that tectonically active limestone terrains will tend to be particularly prone to shallow focus seismicity

the role of veining and dissolution in the evolution of fine grained mylonites the mcconnell thrust alberta microstructural observations of the mcconnell thrust fault rocks demonstrate the importance of vein formation and calcite dissolution in the evolution of the mcconnell thrust limestone mylonites the protolith to the mylonite is a micritic limestone the mylonite contains numerous discontinuous bedding parallel calcite veins that range from relatively undeformed except for twinning and undulose extinction to highly sheared the highly sheared veins show evidence for dynamic recrystallization and grain size reduction along grain and twin boundaries that can lead to complete recrystallization to a grain size of approximately 1 3 m the bulk of the calcite matrix within the mcconnell thrust mylonite is interpreted to have formed by dynamical recrystallization of veins the emplacement of relatively coarse grained veins promoted the activation of dislocation creep within the fault rocks of the thrust in the absence of the increase in grain size afforded by vein emplacement it is anticipated that the fine grained protolith would have deformed predominantly by solution transfer with grain boundary sliding and localized brittle shearing the layer parallel calcite veins are found in close proximity to sheared clay seams which are interpreted to represent the insoluble residue left behind after dissolution of calcite these clay seams may have contributed to the build up of high pore fluid pressures which if intermittently reaching lithostatic conditions during displacement would result in transient brittle failure and thrust surface parallel vein emplacement in an otherwise ductilely deforming rock

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

taxon specific epibenthic foraminiferal δ18o in the arctic ocean relationship to water masses deep circulation and brine release we determined 18ocib values of live rose bengal stained and dead epibenthic foraminifera cibicidoides wuellerstorfi cibicides lobatulus and cibicides refulgens in surface sediment samples from the arctic ocean and the greenland iceland and norwegian seas nordic sea this is the first time that a comprehensive 18ocib data set is generated and compiled from the arctic ocean for comparison we defined atlantic water aw upper arctic bottom water uabw and arctic bottom water abw by their temperature salinity characteristics and calculated mean equilibrium calcite 18oequ from summer sea water 18ow and in situ temperatures as a result in the arctic environment we compensate for cibicidoides and cibicides specific offsets from equilibrium calcite of 0 35 and 0 55 respectively after this taxon specific adjustment mean 18ocib values plausibly reflect the density stratification of principle water masses in the nordic sea and arctic ocean in addition mean 18ocib from aw not only significantly differs from mean 18ocib from abw but also 18ocib from within aw differentiates in function of provenience and water mass age furthermore in shallow waters brine derived low 18ow can significantly lower the 18ocib of cibicides spp and thus 18ocib may serve as a paleobrine indicator there is no statistically significant difference however between deeper water masses mean 18ocib of the nordic sea and of the eurasian and amerasian basins and no influence of low 18ow brines is recorded in recent uabw and abw 18ocib of c wuellerstorfi this may be due to dilution of a low 18ow brine signal in the deep sea and or to preferential incorporation of relatively high 18ow brines from high salinity shelves although our data encompass environments with seasonal sea ice and brine formation supposed to ultimately ventilate the deep arctic ocean 18ocib from uabw and abw do not indicate negative excursions this may challenge hypotheses that call for enhanced arctic brine release to explain negative benthic 18o spikes in deep sea sediments from the late pleistocene north atlantic ocean

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

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

surface velocity and ice discharge of the ice cap on king george island antarctica glaciers on king george island antarctica have shown retreat and surface lowering in recent decades concurrent with increasing air temperatures a large portion of the glacier perimeter is ocean terminating suggesting possible large mass losses due to calving and submarine melting here we estimate the ice discharge into the ocean for the king george island ice cap l band synthetic aperture radar images covering the time span january 2008 to january 2011 over king george island are processed using an intensity tracking algorithm to obtain surface velocity measurements pixel offsets from 40 pairs of radar images are analysed and inverted to estimate a weighted average surface velocity field ice thicknesses are derived from simple principles of ice flow mechanics using the computed surface velocity fields and in situ thickness data the maximum ice surface speeds reach 225 m a 1 and the total ice discharge for the analysed flux gates of king george island is estimated to be 0 720 0 428 gt a 1 corresponding to a specific mass loss of 0 64 0 38 m w e a 1 over the area of the entire ice cap 1127 km 2