timing and origin of recent regional ice mass loss in greenland within the last decade the greenland ice sheet gris and its surroundings have experienced record high surface temperatures mote 2007 box et al 2010 ice sheet melt extent fettweis et al 2011 and record low summer sea ice extent nghiem et al 2007 using three independent data sets we derive for the first time consistent ice mass trends and temporal variations within seven major drainage basins from gravity fields from the gravity recovery and climate experiment grace tapley et al 2004 surface ice velocities from inteferometric synthetic aperture radar insar rignot and kanagaratnam 2006 together with output of the regional atmospheric climate modelling racmo2 gr ettema et al 2009 and surface elevation changes from the ice cloud and land elevation satellite icesat sorensen et al 2011 we show that changing ice discharge d surface melting and subsequent run off m r and precipitation p all contribute in a complex and regionally variable interplay to the increasingly negative mass balance of the gris observed within the last decade interannual variability in p along the northwest and west coasts of the gris largely explains the apparent regional mass loss increase during 2002 2010 and obscures increasing m r and d since the 1990s in winter 2002 2003 and 2008 2009 accumulation anomalies in the east and southeast temporarily outweighed the losses by m r and d that prevailed during 2003 2008 and after summer 2010 overall for all basins of the gris the decadal variability of anomalies in p m r and d between 1958 and 2010 w r t 1961 1990 was significantly exceeded by the regional trends observed during the grace period 2002 2011 2012 elsevier b v

glacier calving rates due to subglacial discharge fjord circulation and free convection we would like to thank the new hampshire space grant consortium award nnx15ah79h for the training grant to fund kms the conocophillips ludin northern area program under the crios project and the dartmouth graduate studies travel fund for their financial support to conduct fieldwork and travel for data dissemination the polar geospatial center for arranging access to the worldview 2 imagery the uk natural environmental research council nerk oceans 2025 and northern sea program for mooring work support with further support from the research council of norway nfr projects circa 214271 cleopatra 178766 cleopatra ii 216537 and marine night 226471 alex hart and the geosciences mechanical workshop at the university of edinburgh for manufacturing the time lapse camera enclosure that was used in this study colin oriffiths for overseeing the collection of mooring data in kongsfjorden since 2002 esa for processing the copernicus sentinel data 2016

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

sudden increase in tidal response linked to calving and acceleration at a large greenland outlet glacier 1 large calving events at greenland s largest outlet glaciers are associated with glacial earthquakes and near instantaneous increases in glacier flow speed at some glaciers and ice streams flow is also modulated in a regular way by ocean tidal forcing at the terminus at helheim glacier analysis of geodetic data shows decimeter level periodic position variations in response to tidal forcing however we also observe transient increases of more than 100 in the glacier s responsiveness to such tidal forcing following glacial earthquake calving events the timing and amplitude of the changes correlate strongly with the step like increases in glacier speed and longitudinal strain rate associated with glacial earthquakes the enhanced response to the ocean tides may be explained by a temporary disruption of the subglacial drainage system and a concomitant reduction of the friction at the ice bedrock interface and suggests a new means by which geodetic data may be used to infer glacier properties citation de juan j et al 2010 sudden increase in tidal response linked to calving and acceleration at a large greenland outlet glacier geophys res lett 37 l12501

the production scheme of cycladophora davisiana radiolaria in the okhotsk sea and the northwestern north pacific implication for the paleoceanographic conditions during the glacials in the high latitude oceans 1 the sediment trap study clearly unraveled that the distinct peaks of c davisiana fluxes occurred during summer to autumn in both the okhotsk sea and the northwestern north pacific the production of c davisiana is closely related to the microbial production in the intermediate water in the okhotsk sea the distinct microbial biomass in the intermediate water which is associated with the seasonal sea ice rejected brine water during winter may support the high c davisiana abundance therefore the significantly high c davisiana abundance during the last glacial maximum lgm in the high latitude open oceans implies the distinct microbial biomass in the intermediate water caused by the seasonal sea ice coverage analogous to the present okhotsk sea

estimating ocean heat transports and submarine melt rates in sermilik fjord greenland using lowered acoustic doppler current profiler ladcp velocity profiles submarine melting at the ice ocean interface is a significant term in the mass balance of marine terminating outlet glaciers however obtaining direct measurements of the submarine melt rate or the ocean heat transport towards the glacier that drives this melting has been difficult due to the scarcity of observations as well as the complexity of oceanic flows here we present a method that uses synoptic velocity and temperature profiles but accounts for the dominant mode of velocity variability to obtain representative heat transport estimates we apply this method to the sermilik fjord helheim glacier system in southeastern greenland using lowered acoustic doppler current profiler ladcp and hydrographic data collected in summer 2009 we find a mean heat transport towards the glacier of 29 10 9 w implying a submarine melt rate at the glacier face of 650 m a 1 t he resulting adjusted velocity profile is indicative of a multilayer residual circulation where the meltwater mixture flows out of the fjord at the surface and at the stratification maximum

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

nonlinear response of iceberg side melting to ocean currents icebergs calving into greenlandic fjords frequently experience strongly sheared flows over their draft but the impact of this flow past the iceberg is not fully captured by existing parameterizations we present a series of novel laboratory experiments to determine the dependence of submarine melting along iceberg sides on a background flow we show for the first time that two distinct regimes of melting exist depending on the flow magnitude and consequent behaviour of melt plumes side attached or side detached with correspondingly different meltwater spreading characteristics when this velocity dependence is included in melt parameterizations melt rates estimated for observed icebergs in the attached regime increase consistent with observed iceberg submarine melt rates we show that both attached and detached plume regimes are relevant to icebergs observed in a greenland fjord further depending on the regime iceberg meltwater may either be confined to a surface layer or distributed over the iceberg draft

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

heat salt and freshwater budgets for a glacial fjord in greenland abstractin greenland s glacial fjords heat and freshwater are exchanged between glaciers and the ocean submarine melting of glaciers has been implicated as a potential trigger for recent glacier acceleration and observations of ocean heat transport are increasingly being used to infer the submarine melt rates the complete heat salt and mass budgets that underlie such methods however have been largely neglected here a new framework for exploring glacial fjord budgets is developed building on estuarine studies of salt budgets the heat salt and mass transports through the fjord are decomposed and new equations for calculating freshwater fluxes from submarine meltwater and runoff are presented this method is applied to moored records from sermilik fjord near the terminus of helheim glacier to evaluate the dominant balances in the fjord budgets and to estimate freshwater fluxes throughout the year two different regimes are found in the nonsummer months advective transports are balanced by

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

characteristics of ocean waters reaching greenland s glaciers interaction of greenland s marine terminating glaciers with the ocean has emerged as a key term in the ice sheet mass balance and a plausible trigger for their recent acceleration our knowledge of the dynamics however is limited by scarcity of ocean measurements at the glacier ocean boundary here data collected near six marine terminating glaciers 79 north kangerdlugssuaq helheim and petermann glaciers jakobshavn isbrae and the combined sermeq kujatdleq and akangnardleq are compared to investigate the water masses and the circulation at the ice ocean boundary polar water of arctic origin and atlantic water from the subtropical north atlantic are found near all the glaciers property analysis indicates melting by atlantic water aw found at the grounding line depth near all the glaciers and the influence of subglacial discharge at depth in summer aw temperatures near the glaciers range from 4 58c in the southeast to 0 168c in northwest greenland consistent with the distance from the subtropical north atlantic and cooling across the continental shelf a review of its offshore variability suggests that aw temperature changes in the fjords will be largest in southern and smallest in northwest greenland consistent with the regional distribution of the recent glacier acceleration

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

tracking icebergs with time lapse photography and sparse optical flow leconte bay alaska 2016 2017 we present a workflow to track icebergs in proglacial fjords using oblique time lapse photos and the lucas kanade optical flow algorithm we employ the workflow at leconte bay alaska where we ran five time lapse cameras between april 2016 and september 2017 capturing more than 400 000 photos at frame rates of 0 5 4 0 min 1 hourly to daily average velocity fields in map coordinates illustrate dynamic currents in the bay with dominant downfjord velocities exceeding 0 5 m s 1 intermittently and several eddies comparisons with simultaneous acoustic doppler current profiler adcp measurements yield best agreement for the uppermost adcp levels 12 m and above in line with prevalent small icebergs that trace near surface currents tracking results from multiple cameras compare favorably although cameras with lower frame rates 0 5 min 1 tend to underestimate high flow speeds tests to determine requisite temporal and spatial image resolution confirm the importance of high image frame rates while spatial resolution is of secondary importance application of our procedure to other fjords will be successful if iceberg concentrations are high enough and if the camera frame rates are sufficiently rapid at least 1 min 1 for conditions similar to leconte bay

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

the role of horizontal resolution for polar low simulations polar lows are intense mesoscale cyclones that mainly occur during the winter over the sea in polar regions owing to their small spatial scale with a diameter between 200 and 1000 km simulating polar lows is a challenging task in this study we investigated how increased resolution of a numerical weather prediction model impacts its ability to simulate polar lows we focused on a polar low that was successfully captured by three different flights during the ipy thorpex field campaign in 2008 verifying model results against campaign data showed that decreasing the horizontal grid spacing from 12 to 4 km significantly improved the simulation of the developing polar low and a further decrease to 1 km gave further improvement a model run with latent heating reduced to 10 indicated an extensive influence of diabatic heating in this polar low case and we suggest that the improved model performance at higher resolution could be connected to the model s handling of convection additional simulations starting 24 h later showed that the initial conditions were important for the model performance and when simulating another polar low case we found that the model failed to produce the polar low independent of the resolution this shows that while higher resolution indeed may give improved predictions of polar lows other factors like synoptic situation lateral boundaries and the initial condition may also be important copyright 2011 royal meteorological society

an improved mass budget for the greenland ice sheet extensive ice thickness surveys by nasa s operation icebridge enable over a decade of ice discharge measurements at high precision for the majority of greenland s marine terminating outlet glaciers prompting a reassessment of the temporal and spatial distribution of glacier change annualmeasurements for 178 outlet glaciers reveal that despite widespread acceleration only 15 glaciers accounted for 77 of the 739 29 gt of ice lost due to acceleration since 2000 and four accounted for 50 among the top sources of loss are several glaciers that have received little scientific attention the relative contribution of ice discharge to total loss decreased from 58 before 2005 to 32 between 2009 and 2012 as such 84 of the increase in mass loss after 2009 was due to increased surface runoff these observations support recentmodel projections that surface mass balance rather than ice dynamics will dominate the ice sheet s contribution to 21st century sea level rise

applicability of large scale convection and condensation parameterization to meso γ scale hirlam a case study of a convective event abstract this paper presents a case study of a single cold air outbreak event with widespread convective precipitation over southern finland on 25 may 2001 the purpose of the study is to investigate the applicability of the convection and condensation scheme of the high resolution limited area model hirlam on meso scales the study concentrates on the issue of grid size dependent convection parameterization an explicit approach without the convection scheme is also examined at the same time the performance of an experimental nonhydrostatic version of hirlam is evaluated model simulations are conducted with three different horizontal grid spacings 11 5 6 and 2 8 km model results are compared to observed radar reflectivity data utilizing a radar simulation model which calculates radar reflectivities from three dimensional model output the best results are obtained using nonhydrostatic dynamics and a grid size dependent convection scheme with a 5 6 km grid interval however even the best conf

recent large increases in freshwater fluxes from greenland into the north atlantic 1 freshwater fw fluxes from river runoff and precipitation minus evaporation for the pan arctic seas are relatively well documented and prescribed in ocean gcms fluxes from greenland on the other hand are generally ignored altogether despite their potential impacts on ocean circulation and marine biology here we present a reconstruction of the spatially distributed fw flux from greenland for 1958 2010 we find a modest increase into the arctic ocean during this period fluxes into the irminger basin however have increased by fifty percent 6 3 0 5 km3 yr 2 in less than twenty years this greatly exceeds previous estimates for the ice sheet as a whole the rate of increase since 1992 is 16 9 1 8 km3 yr 2 the cumulative fw anomaly since 1995 is 3200 358 km3 which is about a third of the magnitude of the great salinity anomaly gsa of the 1970s if this trend continues into the future the anomaly will exceed that of the gsa by about 2025

the effects of changing resolution on mesocale modelling of line convection and slantwise circulations in fastex iop16 data are presented from modelling a rapidly developing cyclone in intensive observation period 16 of the fronts and atlantic storm tracks experiment using the new non hydrostatic version of the met office unified model at a number of different horizontal and vertical resolutions the model produces a good representation of the system including multiple fronts with line convection cloud heads and slantwise cross frontal circulations similar to those seen in the observations results from the model with various grid lengths from 60 km nested down to 2 km with 45 vertical levels show that more realistic detail is produced as the grid length is reduced but that the large scale structures remain consistent by spectral analysis it is found that structures on scales shorter than approximately five grid lengths are attenuated the line convection at the fronts is aliased onto the grid length scale except in the 2 km model where evidence of a three dimensional structure starts to appear the 2 and 4 km models have also been run with enhanced vertical resolutions it is concluded that whilst a 24 km 45 level model is sufficient to represent the overall frontal structure a model with resolution at least 2 km in the horizontal and 90 vertical levels is required to represent small scale multiple slantwise circulations similar to those observed in the dropsonde data crown copyright 2003

mechanisms behind the temporary shutdown of deep convection in the labrador sea lessons from the great salinity anomaly years 1968 71 abstractfrom 1969 to 1971 convection in the labrador sea shut down thus interrupting the formation of the intermediate dense water masses the shutdown has been attributed to the surface freshening induced by the great salinity anomaly gsa a freshwater anomaly in the subpolar north atlantic the abrupt resumption of convection in 1972 in contrast is attributed to the extreme atmospheric forcing of that winter here oceanic and atmospheric data collected in the labrador sea at ocean weather station bravo and a one dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail these results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean they are also relevant to present day conditions given the increased ice melt in the arctic ocean and from the greenland ice sheet the analysis herein shows that the shutdown was initiat

rapid submarine melting driven by subglacial discharge leconte glacier alaska 1 we show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers this buoyant discharge draws in warm seawater entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice to capture the effects of subglacial discharge on submarine melting we conducted 4 days of hydrographic transects during late summer 2012 at leconte glacier alaska a major rainstorm allowed us to document the influence of large changes in subglacial discharge we found strong submarine melt fluxes that increased from 9 1 1 0 to 16 8 1 3 m d 1 ice face equivalent frontal ablation as a result of the rainstorm with projected continued global warming and increased glacial runoff our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems these effects must be considered when modeling glacier response to future warming and increased runoff

impact of fjord dynamics and glacial runoff on the circulation near helheim glacier greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord s externally forced currents and stratification the presence of light arctic and dense atlantic waters in the fjord in particular causes meltwater to be exported at depth and influences the vertical distribution of heat along the ice margin our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters we conclude that the shape and stability of greenland s glaciers may be strongly influenced by the layering of the arctic and atlantic waters in the fjord as well as their variability

iceberg properties and distributions in three greenlandic fjords using satellite imagery icebergs calved from tidewater glaciers represent about one third to one half of the freshwater flux from the greenland ice sheet to the surrounding ocean using multiple satellite datasets we quantify the first fjord wide distributions of iceberg sizes and characteristics for three fjords with distinct hydrography and geometry sermilik fjord rink isbrae fjord and kangerlussuup sermia fjord we estimate average total iceberg volumes in summer in the three fjords to be 6 4 1 5 1 7 0 40 and 0 16 0 09 km 3 respectively iceberg properties are influenced by glacier calving style and grounding line depth with variations in size distribution represented by exponents of power law distributions that are 1 95 0 06 1 87 0 05 and 1 62 0 04 respectively the underwater surface area of icebergs exceeds the subsurface area of glacial termini by at least one order of magnitude in all three fjords underscoring the need to include iceberg melt in fjord freshwater budgets indeed in sermilik fjord we calculate summertime freshwater flux from iceberg melt of 620 m 3 s 1 140 m 3 s 1 similar in magnitude to subglacial discharge the method developed here can be extended across greenland to assess relationships between glacier calving iceberg discharge and freshwater production

rates of southeast greenland ice volume loss from combined icesat and aster observations 1 repeat satellite laser altimetry is critical for observing the rapidly changing mass balance of the greenland ice sheet however sparse sampling and high surface slopes over rapidly thinning coastal outlet glaciers may result in underestimation of mass loss here we supplement icesat derived surface elevation changes with differenced aster digital elevation models of outlet glaciers in southeastern greenland the region with the largest concentrated change in outlet glacier mass loss we estimate a 2002 2005 regional volume loss rate of 108 km3 yr our results are consistent with drainage scale grace and mass budget estimates when differences in observation periods are taken into account the two largest glaciers kangerdlugssuaq and helheim account for only 28 of the mass loss illustrating the combined importance of smaller glaciers and the need for complete observational coverage additionally we find that rapid concentrated thinning within the outlets represents a small contribution to the total volume change compared to dispersed inland thinning

iceberg meltwater fluxes dominate the freshwater budget in greenland s iceberg congested glacial fjords freshwater fluxes from the greenland ice sheet have increased over the last two decades due to increases in liquid i e surface and submarine meltwater and solid ice i e iceberg fluxes to predict potential ice sheet ocean climate feedbacks we must know the partitioning of freshwater fluxes from greenland including the conversion of icebergs to liquid i e meltwater fluxes within glacial fjords here we use repeat 0 5 m resolution satellite images from two major fjords to provide the first observation based estimates of the meltwater flux from the dense matrix of floating ice called melange we find that because of its expansive submerged area 100 km2 and rapid melt rate 0 1 0 8 m d 1 the ice melange meltwater flux can exceed that from glacier surface and submarine melting our findings suggest that iceberg melt within the fjords must be taken into account in studies of glacial fjord circulation and the impact of greenland melt on the ocean

modeling the impact of glacial runoff on fjord circulation and submarine melt rate using a new subgrid scale parameterization for glacial plumes the injection at depth of ice sheet runoff into fjords may be an important control on the frontal melt rate of tidewater glaciers here we develop a new parameterization for ice marginal plumes within the massachusetts institute of technology general circulation model mitgcm allowing three dimensional simulation of large 500 km2 glacial fjords on annual or longer time scales we find that for an idealized fjord without shelf driven circulation subglacial runoff produces a thin strong and warm down fjord current in the upper part of the water column balanced by a thick and slow up fjord current at greater depth although submarine melt rates increase with runoff due to higher melt rates where the plume is in contact with the ice front we find that annual submarine melt rate across the ice front is relatively insensitive to variability in annual runoff better knowledge of the spatial distribution of runoff controls on melt rate in those areas not directly in contact with plumes and feedback mechanisms linking submarine melting and iceberg calving are necessary to more fully understand the sensitivity of glacier mass balance to runoff driven fjord circulation

parameterization of convective precipitation in mesoscale numerical models a critical review abstract current approaches for incorporating cumulus convection into mesoscale numerical models are divided into three groups the traditional approach utilizes cumulus parameterization at convectively unstable points and explicit nonparameterized condensation at convectively stable points the fully explicit approach uses explicit methods regardless of stability the hybrid approach parameterizes convective scale updrafts and downdrafts but detrains a fraction of parameterized cloud and precipitation particles to the grid scale this allows the path and phase changes of such particles to be explicitly predicted over subsequent time steps the traditional approach provides the only alternative for numerical models with grid spacing too large to resolve mesoscale structure as grid spacing falls below 50 km the traditional approach becomes increasingly likely to violate fundamental scale separation requirements of parameterization particularly if mesoscale organization of convection is parameterize

a model of icebergs and sea ice in a joint continuum framework the ice melange a mixture of sea ice and icebergs often present in front of outlet glaciers in greenland or ice shelves in antarctica can have a profound effect on the dynamics of the ice ocean system the current inability to numerically model the ice melange motivates a new modeling approach proposed here a continuum sea ice model is taken as a starting point and icebergs are represented as thick and compact pieces of sea ice held together by large tensile and shear strength selectively introduced into the sea ice rheology in order to modify the rheology correctly an iceberg tracking procedure is implemented within a semi lagrangian time stepping scheme designed to exactly preserve iceberg shape through time with the proposed treatment sea ice and icebergs are considered a single fluid with spatially varying rheological properties mutual interactions are thus automatically included without the need for further parametrization an important advantage of the presented framework for an ice melange model is its potential to be easily included within sea ice components of existing climate models

a laboratory study of iceberg side melting in vertically sheared flows abstractan earlier study indicates that the side melting of icebergs subject to vertically homogeneous horizontal velocities is controlled by two distinct regimes which depend on the melt plume be

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

spatial and temporal melt variability at helheim glacier east greenland and its effect on ice dynamics this is the publisher s version also available electronically from http onlinelibrary wiley com

seasonal variability in the dynamics of marine terminating outlet glaciers in greenland recent studies indicate that the dynamics of fast flowing marine terminating outlet glaciers of the greenland ice sheet may be sensitive to climate and ocean forcing on sub annual timescales observations of seasonal behavior of these glaciers at such high temporal resolution however are currently few here we present observations of front position flow speed near surface air temperature and ocean conditions for six large marine terminating glaciers in the uummannaq region of west greenland to investigate controls on short term glacier dynamics as proposed by other studies we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange our data suggest that high sea surface temperature anomalously low sea ice concentration and reduced melange formation in early 2003 have triggered multi year retreat of several glaciers in the study area which is consistent with other regions in greenland of the stable glaciers only rink isbrae exhibits a seasonal speed variation that correlates with variations in front position with the others undergoing mid summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution drainage of supraglacial lakes and water filled crevasses results in substantial decreases in speed 40 60 on fast flowing glaciers our results demonstrate that attempts to model ice sheet evolution must take into account short timescale flow dynamics resulting from drainage events and oceanographic conditions

the dansgaard oeschger cycles discovered in the up stream source region of the north pacific intermediate water formation 1 millennial scale oceanographic oscillations were identified in the southern okhotsk sea based on high resolution measurements of total organic carbon toc c n ratios and biogenic opal employing core md01 2412 53 m with the bottom age of 115 ka the oscillations are linked with the dansgaard oeschger d o climatic cycles inadequate data existed in the source regions of the north pacific intermediate water npiw formation thus far we report the first decisive documentation of the d o cycles in the up stream source region of the npiw illustrating that the d o cycles observed in the down stream regions e g santa barbara basin due to expansion of the npiw were in part governed by the climatic variations occurred in the okhotsk sea increases in toc and c n ratios reflect abrupt sea level rises associated with 14 interstadial events over the past 115 kyrs attributing to the downward transport of eroded continental shelf sediments

roles of the okhotsk sea and gulf of alaska in forming the north pacific intermediate water recently obtained world ocean circulation experiment woce sections and pre woce hydrography are used to study the water mass structure and formation and transformation of north pacific intermediate water npiw five neutral density surfaces are selected and mapped encompassing npiw from 400 to 900 m in the subtropical latitudes with a distance of 100 m between a pair of surfaces npiw is defined as a subtropical gyre salinity minimum which is well followed by a neutral density surface n 26 9 formation and transformation of npiw is examined by the mapped turner angle on neutral density surfaces apparent diffusive double diffusion is found in the alaskan gyre on n 26 5 neutral surface in the northwest subpolar gyre and the okhotsk sea on n 26 9 neutral surface and mainly in the okhotsk sea on the two deep neutral surfaces n 27 2 and n 27 4 these diffusive regions indicate transformation sources for npiw along with additional information of potential vorticity and stream function it is found that there are two different npiw formation sources one in the gulf of alaska characterized by high potential vorticity and the other in the okhotsk sea characterized by low potential vorticity the former lies shallower at n 26 2 26 5 but its effect deepens to npiw core density level at n 26 8 on the basis of potential vorticity distribution the latter includes the influence of the northwest subpolar gyre and extends much deeper to n 27 4 we call them gulf of alaska intermediate water gaiw and okhotsk intermediate water oiw respectively gaiw contributes to npiw in the eastern part of the subtropical gyre east of date line whilst oiw dominates in the west and entire lower part of npiw seasonal flow stream function mapped on neutral surfaces shows that the contribution of gaiw to npiw occurs mainly in the wintertime because in winter a significant northward shift of zero wind stress curl makes the gulf of alaska an additional source for npiw

effect of a sheared flow on iceberg motion and melting icebergs account for approximately half the freshwater flux into the ocean from the greenland and antarctic ice sheets and play a major role in the distribution of meltwater into the ocean global climate models distribute this freshwater by parameterizing iceberg motion and melt but these parameterizations are presently informed by limited observations here we present a record of speed and draft for 90 icebergs from sermilik fjord southeastern greenland collected in conjunction with wind and ocean velocity data over an 8 month period it is shown that icebergs subject to strongly sheared flows predominantly move with the vertical average of the ocean currents if as typical in iceberg parameterizations only the surface ocean velocity is taken into account iceberg speed and basal melt may have errors in excess of 60 these results emphasize the need for parameterizations to consider ocean properties over the entire iceberg draft

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

a new present day temperature parameterization for greenland near surface air temperature 2 m over the greenland ice sheet gris is parameterized using data from automatic weather stations located on land and on the ice sheet the parameterization is expressed in terms of mean annual temperatures and mean july temperatures both depending linearly on altitude latitude and longitude the temperature parameterization is compared to a previous study and is shown to be in better agreement with observations the temperature parameterization is tested in a positive degree day model to simulate the present 1996 2006 mean melt area extent of the gris the model accounts for firn warming rainfall and refreezing of meltwater with different degree day factors for ice and snow under warm and cold climate conditions the simulated melt area extent is found to have reasonable agreement with satellite derived observations

numerical experiments on subaqueous melting of greenland tidewater glaciers in response to ocean warming and enhanced subglacial discharge the largest dischargers of ice in greenland are glaciers that terminate in the ocean and melt in contact with sea water studies of ice sheet ocean interactions have mostly focused on melting beneath near horizontal floating ice shelves for tidewater glaciers melting instead takes place along the vertical face of the calving front here we modify the massachusetts institute of technology general circulation model mitgcm to include ice melting from a calving face with the freshwater outflow at the glacier grounding line we use the model to predict melt rates and their sensitivity to ocean thermal forcing and to subglacial discharge we find that melt rates increase with approximately the one third power of the subglacial water flux and increase linearly with ocean thermal forcing our simulations indicate that consistent with limited field data melting ceases when subglacial discharge is shut off and reaches several meters per day when subglacial discharge is high in the summer these results are a first step toward a more realistic representation of subglacial discharge and of ocean thermal forcing on the subaqueous melting of tidewater glaciers in a numerical ocean model our results illustrate that the ice front melting process is both complex and strongly time dependent

quantifying flow regimes in a greenland glacial fjord using iceberg drifters funded by the national science foundation grant numbers oce 1130008 arc 0909274 and the university of oregon

greenland ice sheet mass balance reconstruction part ii surface mass balance 1840 2010 abstractmeteorological station records ice cores and regional climate model output are combined to develop a continuous 171 yr 1840 2010 reconstruction of greenland ice sheet climatic surface mass balance bclim and its subcomponents including near surface air temperature sat since the end of the little ice age independent observations are used to assess and compensate errors melt water production is computed using separate degree day factors for snow and bare ice surfaces a simple meltwater retention scheme yields the time variation of internal accumulation runoff and bare ice area at decadal time scales over the 1840 2010 time span summer june august sat increased by 1 6 c driving a 59 surface meltwater production increase winter warming was 2 0 c substantial interdecadal variability linked with episodic volcanism and atmospheric circulation anomalies is also evident increasing accumulation and melt rates bare ice area and meltwater retention are driven by increasing sat as a con

seasonal variability of submarine melt rate and circulation in an east greenland fjord 1 the circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front the model configuration and water properties are based on data collected in sermilik fjord near helheim glacier a major greenland outlet glacier the approximately two layer stratification of the fjord s ambient waters causes the meltwater plume at the glacier front to drive a double cell circulation with two distinct outflows one at the free surface and one at the layers interface in summer the discharge of surface runoff at the base of the glacier subglacial discharge causes the circulation to be much more vigorous and associated with a larger melt rate than in winter the simulated double cell circulation is consistent in both seasons with observations from sermilik fjord seasonal differences are also present in the vertical structure of the melt rate which is maximum at the base of the glacier in summer and at the layers interface in winter simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge to changes in water temperature and to the height of the layers they are also consistent with those inferred from simplified one dimensional models based on the theory of buoyant plumes our results also indicate that to correctly represent the dynamics of the meltwater plume care must be taken in the choice of viscosity and diffusivity values in the model

changes in the dynamics of marine terminating outlet glaciers in west greenland 2000 2009 1 recent changes in the dynamics of greenland s marine terminating outlet glaciers indicate a rapid and complex response to external forcing despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along greenland s northwestern margin it is unclear whether west greenland glaciers have undergone the synchronous speed up and subsequent slow down as observed in southeastern glaciers earlier in the decade to investigate changes in west greenland outlet glacier dynamics and the potential controls behind their behavior we derive time series of front position surface elevation and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west greenland from 2000 to 2009 using these data we look for relationships between retreat thinning acceleration and geometric parameters to determine the first order controls on glacier behavior our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales though nearly all glaciers retreated and thinned over the decade we found no direct relationship between retreat acceleration and external forcing applicable to the entire region in regard to geometry we found that following retreat 1 glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and 2 thinning rates declined more quickly for glaciers with steeper slopes overall glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west greenland

evaluation of the relative contribution of meteorological and oceanic forces to the drift of ice islands offshore newfoundland on 29 april 2015 four beacons were deployed onto an ice island in the strait of belle isle to record positional data the ice island later broke up into many fragments four of which were tracked by the beacons the relative influences of wind drag current drag coriolis force sea surface height gradient and sea ice force on the drift of the tracked ice island fragments were analyzed using atmospheric and oceanic model outputs the sea ice force was calculated as the residual of the fragments net forces and the sum of all other forces this was compared against the force obtained through ice concentration dependent relationships when sea ice was present the sea ice forces calculated from the residual approach and concentration dependent relationships were significant only when sea ice was present at medium high concentrations in the vicinity of the ice island fragments the forces from ocean currents and sea surface tilt contributed the most to the drift of the ice island fragments wind however played a minimal role in the total force governing the drift of the four ice island fragments and coriolis force was significant when the fragments were drifting at higher speeds