rapid circulation of warm subtropical waters in a major glacial fjord in east greenland the recent rapid increase in mass loss from the greenland ice sheet is primarily attributed to an acceleration of outlet glaciers oceanographic data obtained in summer 2008 show that subtropical waters that reside year round in the shelf ocean off greenland continuously enter a large glacial fjord in east greenland and contribute to melting at the glacier terminus the recent rapid increase in mass loss from the greenland ice sheet1 2 is primarily attributed to an acceleration of outlet glaciers3 4 5 one possible cause of this acceleration is increased melting at the ice ocean interface6 7 driven by the synchronous warming8 9 10 of subtropical waters offshore of greenland however because of the lack of observations from greenland s glacial fjords and our limited understanding of their dynamics this hypothesis is largely untested here we present oceanographic data collected in sermilik fjord east greenland by ship in summer 2008 and from moorings our data reveal the presence of subtropical waters throughout the fjord these waters are continuously replenished through a wind driven exchange with the shelf where they are present all year the temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus key controls on the melting rate are the volume and properties of the subtropical waters on the shelf and the patterns of along shore winds suggesting that the glaciers acceleration has been triggered by a combination of atmospheric and oceanic changes our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice sheet margins

dynamics of a turbulent buoyant plume in a stratified fluid an idealized model of subglacial discharge in greenland fjords abstractthis study reports the results of large eddy simulations of an axisymmetric turbulent buoyant plume in a stratified fluid the configuration used is an idealised model of the plume generated by a subglacial discharge at the base of a tidewater glacier with an ambient stratification typical of greenland fjords the plume is discharged from a round source of various diameters and characteristic stratifications for summer and winter are considered the classical theory for the integral parameters of a turbulent plume in a homogeneous fluid gives accurate predictions in the weakly stratified lower layer up to the pycnocline and the plume dynamics are not sensitive to changes in the source diameter in winter when the stratification is similar to an idealised two layers case turbulent entrainment and generation of internal waves by the plume top are in agreement with the theoretical and numerical results obtained for turbulent jets in a two layer stratification in summer instead the stratification

spreading of greenland meltwaters in the ocean revealed by noble gases we present the first noble gas observations in a proglacial fjord in greenland providing an unprecedented view of surface and submarine melt pathways into the ocean using optimum multiparameter analysis noble gas concentrations remove large uncertainties inherent in previous studies of meltwater in greenland fjords we find glacially modified waters with submarine melt concentrations up to 0 66 0 09 and runoff 3 9 0 29 radiogenic enrichment of helium enables identification of ice sheet near bed melt 0 48 0 08 we identify distinct regions of meltwater export reflecting heterogeneous melt processes a surface layer of both runoff and submarine melt and an intermediate layer composed primarily of submarine melt intermediate ocean waters carry the majority of heat to the fjords glaciers and warmer deep waters are isolated from the ice edge the average entrainment ratio implies that ocean water masses are upwelled at a rate 30 times the combined glacial meltwater volume flux

irminger water variability in the west greenland current 1 we examine the historical variability of irminger water iw along 3 sections across the west greenland current over 1950 2005 significant variability in the salinity size and position of the iw core are seen over time some of the saltiest and warmest iw ever recorded have been seen since 1995 comparable to previous maximums in the 1960s during these periods the volume of iw is also larger leading to larger transports into the labrador sea for the period 1984 2005 transports at cape farewell are 3 8 0 9 sv 7 5 2 2 1013 j and 8 5 1 8 msv of salt referenced to 35 0 lsw formation is also correlated to iw transport at cape farewell with a lag of one year 0 51

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

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

the subglacial cavity and implied dynamics under nioghalvfjerdsfjorden glacier ne greenland seismic depth soundings on nioghalvfjerdsfjor den glacier nfg ne greenland reveal an overdeepened trough under thefloating glacier the maximum depth of the trough reaches more than 900m below sea level mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8ma 1 the geometry of the cavity and water mass characteristics from ctd measurements suggest the existence of a well de ned regional circulation system warm saline and rather densewaterfollows theinwardinclining basalslope through the deep valley of dijmphna sund towards the grounding line shallow ridges at the eastern glacier front prevent this watermassenteringfromthatdirection thecomparatively cold fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east the abundance of subglacial melt water east of nfg is most probably one of the main reasons for the semi permanent sea ice cover in this region cold water masses upwelling in the northeast water polynia and detected by satellite remote sensing are very likely influenced and mod ied by the subglacial melt water production

channelized bottom melting and stability of floating ice shelves 1 the floating ice shelf in front of petermann glacier in northwest greenland experiences massive bottom melting that removes 80 of its ice before calving into the arctic ocean detailed surveys of the ice shelf reveal the presence of 1 2 km wide 200 400 m deep sub ice shelf channels aligned with the flow direction and spaced by 5 km we attribute their formation to the bottom melting of ice from warm ocean waters underneath drilling at the center of one of channel only 8 m above sea level confirms the presence of ice shelf melt water in the channel these deep incisions in ice shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously

surface velocities and ice front positions of eight major glaciers in the southern patagonian ice field south america from 2002 to 2011 abstract the patagonian ice fields are known to have undergone rapid retreat of frontal positions and significant thinning of its glaciers over the past decades however surface velocities have been measured at only a few of these glaciers thus it remains uncertain if and to what extent the glacier dynamics has changed over time and contributed to ice loss in these ice fields in this study we examine the temporal evolution of flow velocities and ice front positions at eight major glaciers in the southern patagonian ice field spi hielo patagonico sur by using advanced synthetic aperture radar asar images from the environmental satellite envisat launched in 2002 by the european space agency and advanced land observation satellite phased array type l band synthetic aperture radar alos palsar data recorded from 2002 to 2011 the examined eight glaciers include glaciar jorge montt occidental pio xi or bruggen o higgins viedma upsala perito moreno and grey not all the glaciers revealed significant changes in frontal positions and flow velocities in the study period we detected significant temporal velocity changes at glaciar upsala jorge montt occidental and pio xi among these four glaciers glaciars upsala jorge montt and occidental revealed significant acceleration and terminus retreat and were undergoing dynamic thinning the markedly different absolute velocities but equally large longitudinal near terminus stretching at the three glaciers support a calving model based on crevasse depth criteria which predict a calving position where crevasse depths are equal to ice thickness crevasse depths are controlled by the longitudinal stretching rate meanwhile glaciar pio xi revealed complex spatial and temporal evolution in surface velocities without significant retreat and its dynamics remains enigmatic

21st century evolution of greenland outlet glacier velocities earlier observations on several of greenland s outlet glaciers starting near the turn of the 21st century indicated rapid annual scale and large 100 increases in glacier velocity combining data from several satellites we produce a decade long 2000 to 2010 record documenting the ongoing velocity evolution of nearly all 200 of greenland s major outlet glaciers revealing complex spatial and temporal patterns changes on fast flow marine terminating glaciers contrast with steady velocities on ice shelf terminating glaciers and slow speeds on land terminating glaciers regionally glaciers in the northwest accelerated steadily with more variability in the southeast and relatively steady flow elsewhere intraregional variability shows a complex response to regional and local forcing observed acceleration indicates that sea level rise from greenland may fall well below proposed upper bounds

ice stream retreat following the lgm and onset of the west greenland current in uummannaq trough west greenland the deglacial history and oceanography of uummannaq trough central west greenland continental shelf was investigated using foraminiferal sedimentological and bathymetric records together with a radiocarbon chronology providing a timeline for the retreat of glacial ice after the last glacial maximum lgm to map ice stream retreat data were collected from cores from the outer jr175 vc45 and jr175 vc43 and inner jr175 vc42 uummannaq trough a large ice stream fed by confluent glaciers draining the interior of the greenland ice sheet extended across the outer shelf during the lgm and was in retreat by 15 0 cal kyr bp foraminiferal data indicate that the warm west greenland current wgc was established prior to 14 0 cal kyr bp which is the hitherto earliest record of atlantic water found on the west greenland shelf for each of the cores foraminifera indicate that ice sheet retreat was followed quickly by incursion of the wgc suggesting that the warm water may have enhanced ice retreat prior to the younger dryas cold event the radiocarbon chronology indicates that the ice sheet retreated to the mid shelf where it subsequently stabilised and formed a large grounding zone wedge gzw after the younger dryas around 11 5 cal kyr bp the ice retreated rapidly from the gzw and into the fjords

the internal seiches in gullmar fjord part i dynamics abstract internal seiche motions with period 1 3 days in gullmar fjord are investigated based on mooring data with high vertical and time resolution the period and structure of the internal seiches are well described by a simple analytical three layer model taking into account blocking of the basin water at the sill energy budgets for forcing and damping of the seiches are estimated the internal seiches are forced by direct wind stress on the surface and by internal coastal waves of frequency close to the seiches the latter contribution being a little larger the e folding timescale for the internal seiche damping is approximately equal to the seiche periods which means that the seiches are effectively damped but also that the forcing must be in near resonance in order to maintain the observed seiche motions in the basin water the seiches manifest themselves with large vertical motions and clear upward phase propagation the phase propagation is related with a continuous rather than strictly layer

quantifying energy and mass fluxes controlling godthabsfjord freshwater input in a 5 km simulation 1991 2012 abstractfreshwater runoff to fjords with marine terminating glaciers along the greenland ice sheet margin has an impact on fjord circulation and potentially ice sheet mass balance through increasing heat transport to the glacier front here the authors use the high resolution 5 5 km hirham5 regional climate model allowing high detail in topography and surface types to estimate freshwater input to godthabsfjord in southwest greenland model output is compared to hydrometeorological observations and while simulated daily variability in temperature and downwelling radiation shows high correlation with observations typically 0 9 there are biases that impact the results in particular overestimated albedo leads to underestimation of melt and runoff at low elevations in the model simulation 1991 2012 the ice sheet experiences increasing energy input from the surface turbulent heat flux up to elevations of 2000 m and shortwave radiation at all elevations southerly wind anomalies and declining

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

automated remote sensing of sediment plumes for identification of runoff from the greenland ice sheet the viability of employing sediment plumes emanating from outlets along the western margin of the greenland ice sheet as indicators of runoff is assessed an automated sediment plume quantification system based on daily 250 m moderate resolution imaging spectroradiometer modis band 1 reflectance imagery is developed coherent plumes are identified using spectral thresholds and polygon tracing validation employs imagery quality control procedures and manual verification of plume areas outlets at land terminating margins with wide and straight fjord geometries deliver the most accurate and consistent results plume area observations are also possible at marine terminating margins with relatively static fronts and low proximal sea ice concentrations variability in plume area is examined with reference to special satellite microwave imager ssm i derived daily melt extent at the hydrologic catchment scale at annual timescales plume areas tend to co vary with surface melt extent indicating that more mass is lost by runoff during years of extensive melting some synchronicity in plume areas from different catchments is apparent at seasonal and daily timescales plumes from individual outlets primarily relate to catchment specific melting

influence of glacial water and carbonate minerals on wintertime sea ice biogeochemistry and the co2 system in an arctic fjord in svalbard the effect of freshwater sources on wintertime sea ice co2 processes was studied from the glacier front to the outer tempelfjorden svalbard in sea ice glacier ice brine and snow march april 2012 was mild and the fjord was mainly covered with drift ice in contrast to the observed thicker fast ice in the colder april 2013 this resulted in different physical and chemical properties of the sea ice and under ice water data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in april 2012 contained on average 54 of frozen in glacial meltwater this was five times higher than in april 2013 where the ice was frozen seawater in april 2012 the largest excess of sea ice total alkalinity at carbonate ion co32 and bicarbonate ion concentrations hco3 relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral enriched glacial water in april 2013 the excess of these variables was mainly due to ikaite dissolution as a result of sea ice processes dolomite dissolution increased sea ice at twice as much as ikaite and calcite dissolution implying different buffering capacity and potential for ocean co2 uptake in a changing climate

role of greenland freshwater anomaly in the recent freshening of the subpolar north atlantic the cumulative greenland freshwater flux anomaly has exceeded 5 000 km3 since the 1990s the volume of this surplus freshwater is expected to cause substantial freshening in the north atlantic analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s the sources of this freshening are yet to be determined in this study the relationship between the surplus greenland freshwater flux and this freshening is tested by analyzing the propagation of the greenland freshwater anomaly and its impact on salinity in the subpolar north atlantic based on observational data and numerical experiments with and without the greenland runoff a passive tracer is continuously released during the simulations at freshwater sources along the coast of greenland to track the greenland freshwater anomaly tracer budget analysis shows that 44 of the volume of the greenland freshwater anomaly is retained in the subpolar north atlantic by the end of the simulation this volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50 100 m however in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations therefore the simulations suggest that the accelerated greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening impacts on salinity in the subpolar seas of the freshwater transport through fram strait and precipitation are discussed

the mean age of ocean waters inferred from radiocarbon observations sensitivity to surface sources and accounting for mixing histories a number of previous observational studies have found that the waters of the deep pacific ocean have an age or elapsed time since contact with the surface of 700 1000 yr numerical models suggest ages twice as old here the authors present an inverse framework to determine the mean age and its upper and lower bounds givenglobaloceandataanalysisproject glodap radiocarbonobservations andthey show that the potential range of ages increases with the number of constituents or sources that are included in the analysis the inversion requires decomposing the world ocean into source waters which is obtained here using the total matrix intercomparison tmi method at up to 2 83 28 horizontal resolution with 11 113 surface sources the authors find that the north pacific at 2500 m depth can be no younger than 1100 yr old which is older than some previous observational estimates accounting for the broadness of surface regions where waters originate leads to a reservoir age correction of almost 100 yr smaller than would be estimated with a two or three water mass decomposition and explains some of the discrepancy with previous observational studies a best estimate of mean age is also presented using the mixing history along circulation pathways subject to the caveats that inference of the mixing history would benefit from further observations and that radiocarbon cannot rule out the presence of extremely old waters from exotic sources the deep north pacific waters are 1200 1500 yr old which is more in line with existing numerical model results

laboratory investigations of iceberg capsize dynamics energy dissipation and tsunamigenesis 1 we present laboratory experiments designed to quantify the stability and energy budget of buoyancy driven iceberg capsize box shaped icebergs were constructed out of low density plastic hydrostatically placed in an acrylic water tank containing freshwater of uniform density and allowed or forced if necessary to capsize the maximum kinetic energy translational plus rotational of the icebergs was 15 of the total energy released during capsize and radiated surface wave energy was 1 of the total energy released the remaining energy was directly transferred into the water via hydrodynamic coupling viscous drag and turbulence the dependence of iceberg capsize instability on iceberg aspect ratio implied by the tank experiments was found to closely agree with analytical predictions based on a simple hydrostatic treatment of iceberg capsize this analytical treatment along with the high reynolds numbers for the experiments and considerably higher values for capsizing icebergs in nature indicates that turbulence is an important mechanism of energy dissipation during iceberg capsize and can contribute a potentially important source of mixing in the stratified ocean proximal to marine ice margins

emerging impact of greenland meltwater on deepwater formation in the north atlantic ocean the greenland ice sheet has experienced increasing mass loss since the 1990s1 2 the enhanced freshwater flux due to both surface melt and outlet glacier discharge is assuming an increasingly important role in the changing freshwater budget of the subarctic atlantic3 the sustained and increasing freshwater fluxes from greenland to the surface ocean could lead to a suppression of deep winter convection in the labrador sea with potential ramifications for the strength of the atlantic meridional overturning circulation4 5 6 here we assess the impact of the increases in the freshwater fluxes reconstructed with full spatial resolution3 using a global ocean circulation model with a grid spacing fine enough to capture the small scale eddying transport processes in the subpolar north atlantic our simulations suggest that the invasion of meltwater from the west greenland shelf has initiated a gradual freshening trend at the surface of the labrador sea although the freshening is still smaller than the variability associated with the episodic great salinity anomalies the accumulation of meltwater may become large enough to progressively dampen the deep winter convection in the coming years we conclude that the freshwater anomaly has not yet had a significant impact on the atlantic meridional overturning circulation

the impact of melting ice on ocean waters abstract ice melts when it is in contact with ocean waters that have temperatures above the in situ freezing point the product is a mixture of meltwater and seawater having properties intermediate between those of the two components density is one of the properties that is affected and this has important implications for how the melt induced changes are eventually manifested although the direct impact of melting is to cool and dilute the ocean subsequent convection can carry the products of melting to parts of the water column where they are comparatively warm and salty these principles are illustrated with a set of observations from the continental shelf of the amundsen sea measurements made near a floating glacier are used to calculate the concentration of meltwater in the water column concentrations approaching 2 are associated with comparatively high temperatures low dissolved oxygen concentrations and negligible stable isotope anomalies the impact of drifting icebergs on the southern ocea

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

does calving matter evidence for significant submarine melt abstract during the summer in the northeast pacific ocean the alaska coastal current sweeps water with temperatures in excess of 12 c past the mouths of glacierized fjords and bays the extent to which these warm waters affect the mass balance of alaskan tidewater glaciers is uncertain here we report hydrographic measurements made within icy bay alaska and calculate rates of submarine melt at yahtse glacier a tidewater glacier terminating in icy bay we find strongly stratified water properties consistent with estuarine circulation and evidence that warm gulf of alaska water reaches the head of 40 km long icy bay largely unaltered a 10 20 m layer of cold fresh glacially modified water overlies warm saline water the saline water is observed to reach up to 10 4 c within 1 5 km of the terminus of yahtse glacier by quantifying the heat and salt deficit within the glacially modified water we place bounds on the rate of submarine melt the submarine melt rate is estimated at 9 m d 1 at least half the rate at which ice flows into the terminus region and can plausibly account for all of the submarine terminus mass loss our measurements suggest that summer and fall subaerial calving is a direct response to thermal undercutting of the terminus further demonstrating the critical role of the ocean in modulating tidewater glacier dynamics

the dynamics of a subglacial salt wedge marine terminating glaciers such as those along the coastline of greenland often release meltwater into the ocean in the form of subglacial discharge plumes though these plumes can dramatically alter the mass loss along the front of a glacier the conditions surrounding their genesis remain poorly constrained in particular little is known about the geometry of subglacial outlets and the extent to which seawater may intrude into them here the latter is addressed by exploring the dynamics of an arrested salt wedge a steady state two layer flow system where salty water partially intrudes a channel carrying fresh water building on existing theory we formulate a model that predicts the length of a non entraining salt wedge as a function of the froude number the slope of the channel and coefficients for interfacial and wall drag in conjunction a series of laboratory experiments were conducted to observe a salt wedge within a rectangular channel for experiments conducted with laminar flow reynolds number re 800 good agreement with theoretical predictions are obtained when the drag coefficients are modelled as being inversely proportional to re however for fully turbulent flows on geophysical scales these drag coefficients are expected to asymptote toward finite values adopting reasonable drag coefficient estimates for this flow regime our theoretical model suggests that typical subglacial channels may permit seawater intrusions of the order of several kilometres while crude these results indicate that the ocean has a strong tendency to penetrate subglacial channels and potentially undercut the face of marine terminating glaciers

a break in self similarity in the lunigiana garfagnana region northern apennines 1 in this study stable source parameters are determined for small earthquakes in the lunigiana garfagnana region using an empirical methodology based on coda envelope measurements that are significantly less affected by the source radiation pattern directivity and heterogeneous path variation than traditional direct wave measurements we find evidence that the scaled energy er m0 increases with moment and source spectra are not self similar for 3 0 mw 4 6 the calibration procedure allows for an independent check of three important features 1 that the empirical path corrections provide consistent amplitude measurements for the same event at different stations distances and azimuths 2 that the long period levels of the source spectra are consistent with independent m0 derived from long period waveform modeling 3 that small event spectra are flat below a conservative estimate of the corner frequency and thereby effectively accounting for near site attenuation

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

submarine melting of the 1985 jakobshavn isbrae floating tongue and the triggering of the current retreat 1 photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of jakobshavn isbrae west greenland the thickness of the floating tongue determined from hydrostatic equilibrium tapers from 940 m near the grounding zone to 600 m near the terminus feature tracking on orthophotos shows speeds on the july 1985 ice tongue to be nearly constant 18 5 m d 1 indicating negligible dynamic thinning the thinning of the ice tongue is mostly due to submarine melting with average rates of 228 49 m yr 1 0 62 0 13 m d 1 between the summers of 1984 and 1985 the cause of the high melt rate is the circulation of warm seawater thermal forcing of up to 4 2 c beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone we believe that this buoyancy driven convection is responsible for a deep channel incised into the sole of the floating tongue a dramatic thinning retreat and speedup began in 1998 and continues today the timing of the change is coincident with a 1 1 c warming of deep ocean waters entering the fjord after 1997 assuming a linear relationship between thermal forcing and submarine melt rate average melt rates should have increased by 25 57 m yr 1 sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed

large scale changes in greenland outlet glacier dynamics triggered at the terminus the recent dramatic retreat of many outlet glaciers of the greenland ice sheet has raised concerns over greenland s contribution to future sea level rise simulations with a numerical ice flow model indicate that the recent rates of mass loss in greenland s outlet glaciers are transient and should not be extrapolated into the future

ocean circulation and properties in petermann fjord greenland the floating ice shelf of petermann glacier interacts directly with the ocean and isthought to lose at least 80 of its mass through basal melting based on three opportunisticocean surveys in petermann fjord we describe the basic oceanography the circulationat the fjord mouth the hydrographic structure beneath the ice shelf the oceanic heatdelivered to the under ice cavity and the fate of the resulting melt water the 1100 m deepfjord is separated from neighboring hall basin by a sill between 350 and 450 m deep fjord bottom waters are renewed by episodic spillover at the sill of atlantic water from thearctic glacial melt water appears on the northeast side of the fjord at depths between200 m and that of the glacier s grounding line about 500 m the fjord circulation isfundamentally three dimensional satellite imagery and geostrophic calculations suggest acyclonic gyre within the fjord mouth with outflow on the northeast side tidal flowsare similar in magnitude to the geostrophic flow the oceanic heat flux into the fjordappears more than sufficient to account for the observed rate of basal melting cold low salinity water originating in the surface layer of nares strait in winter intrudes farunder the ice this may limit basal melting to the inland half of the shelf the melt rate andlong term stability of petermann ice shelf may depend on regional sea ice cover andfjord geometry in addition to the supply of oceanic heat entering the fjord

subglacial hydrology at rink isbrae west greenland inferred from sediment plume appearance marine terminating outlet glaciers discharge most of the greenland ice sheet s mass through frontal ablation and meltwater runoff while calving can be estimated by in situ and remote sensing observations submarine melting and subglacial meltwater transport are more challenging to quantify here we investigate the subglacial hydrology of rink isbrae a fast flowing west greenland tidewater glacier using time lapse photography modeled runoff estimates and daily satellite imagery from 2007 to 2011 we find that sediment plumes appear episodically at four distinct locations across the terminus and last between 2 h and 17 d this suggests short term variability in discharge and the existence of persistent pathways the seasonal onset of sediment plumes occurs before supraglacial lake drainages shortly after the onset of runoff and only after the wintertime ice melange has begun disintegrating plumes were also visible after the cessation of runoff 23 5 d which is indicative of subglacial storage the lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front

katabatic wind driven exchange in fjords the general issue of katabatic wind driven exchange in fjords is considered using an idealized numerical model theory and observations two regimes are identified for fjords narrower than a viscous boundary layer width the exchange is limited by a balance between wind and friction in lateral boundary layers for the nonlinear viscous parameterization used here this boundary layer thickness depends on the properties of the fjord such as stratification and length as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant for wider fjords typical of east greenland the balance is primarily between wind the along fjord pressure gradient and acceleration in general agreement with previous two layer nonrotating theories it is expected that o 10 of the surface layer will be flushed out of the fjord by a single wind event application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in sermilik fjord the presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness in which cases the exchange is reduced it is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east greenland represent an important mechanism of exchange between the fjord and shelf with implications for the renewal of warm salty waters at depth and for the export of glacial freshwater in the upper layer

surface expression of a wall fountain application to subglacial discharge plumes abstractwe use laboratory experiments and theoretical modeling to investigate the surface expression of a subglacial discharge plume as occurs at many fjords around greenland the experiments cons

synchronous retreat and acceleration of southeast greenland outlet glaciers 2000 06 ice dynamics and coupling to climate a large portion of the recent increase in the rate of mass loss from the greenland ice sheet is from increased outlet glacier discharge along its southeastern margin while previous investigations of the region s two largest glaciers suggest that acceleration is a dynamic response to thinning and retreat of the calving front it is unknown whether this mechanism can explain regional acceleration and what forcing is responsible for initiating rapid thinning and retreat we examine seasonal and interannual changes in ice front position surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006 while substantial seasonality in front position and speed is apparent nearly all the observed glaciers show net retreat thinning and acceleration with speed up corresponding to retreat the ratio of retreat to the along flow stress coupling length is proportional to the relative increase in speed consistent with typical ice flow and sliding laws this affirms that speed up results from loss of resistive stress at the front during retreat which leads to along flow stress transfer large retreats were often preceded by the formation of a flat or reverse sloped surface near the front indicating that subsequent retreats were influenced by the reversed bed slope many retreats began with an increase in thinning rates near the front in the summer of 2003 a year of record high coastal air and sea surface temperatures this anomaly was driven in part by recent warming suggesting that episodes of speed up and retreat may become more common in a warmer climate

oceanic boundary conditions for jakobshavn glacier part i variability and renewal of ilulissat icefjord waters 2001 14 jakobshavnglacier west greenland has respondedtotemperaturechangesinilulissaticefjord intowhich it terminates thisstudycollectedhydrographicobservationsinsideilulissaticefjordandfromadjacentdiskobay between2001and2014 thewarmestdeepdiskobaywaterswereblockedbytheentrancesillanddidnotreach jakobshavn glacier in the fjord basin the summer mean temperature was 2 88c from 2009 to 2013 excluding 2010 whenitwas 18c cooler despitethisvariability summerpotential densities in the basinwereinthe narrow range of 27 20 su 27 31kgm 23 and basin water properties matched those of disko bay in this layer each summer this relation has likely held since at least 1980 basin waters from 2009 and 2011 13 were therefore similar tothosein1998 99 whenjakobshavn glacier began toretreat whilebasin watersin2010wereascoolas in the 1980s the 2010 basin temperature anomaly was advected into disko bay not produced by local atmospheric variability this anomaly also shows that ilulissat icefjord basin waters were renewed annually or faster time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually outside of summer fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month in model simulations of the fjord circulation subglacial discharge from jakobshavn glacier could drive renewal of the fjord basin over a single summer while baroclinic forcing from outside the fjord could not because of the sill at the mouth

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

a 2000 year record of ocean influence on jakobshavn isbrae calving activity based on marine sediment cores the greenland ice sheet has experienced significant mass loss in recent years a substantial component of this is attributable to the retreat of marine terminating outlet glaciers which lose mass

hydrologic response of the greenland ice sheet the role of oceanographic warming the response of the greenland ice sheet to ongoing climate change remains an area of great uncertainty with most previous studies having concentrated on the contribution of the atmosphere to the ice mass balance signature here we systematically assess for the first time the influence of oceanographic changes on the ice sheet the first part of this assessment involves a statistical analysis and interpretation of the relative changes and variations in sea surface temperatures ssts and air temperatures around greenland for the period 1870 2007 this analysis is based on hadisst1 and reynolds oi v2 sst analyses in situ sst and deeper ocean temperature series surface air temperature records for key points located around the greenland coast and examination of atmospheric pressure and geopotential height from ncep ncar reanalysis second we carried out a novel sensitivity experiment in which ssts were perturbed as input to a regional climate model and document the resulting effects on simulated greenland climate and surface mass balance we conclude that sea surface ocean temperature forcing is not sufficient to strongly influence precipitation snow accumulation and melt runoff of the ice sheet additional evidence from meteorological reanalysis suggests that high greenland melt anomalies of summer 2007 are likely to have been primarily forced by anomalous advection of warm air masses over the ice sheet and to have therefore had a more remote atmospheric origin however there is a striking correspondence between ocean warming and dramatic accelerations and retreats of key greenland outlet glaciers in both southeast and southwest greenland during the late 1990s and early 2000s copyright 2008 john wiley sons ltd

heat sources for glacial melt in a sub arctic fjord godthabsfjord in contact with the greenland ice sheet 1 recent warming of subpolar mode water off greenland has been suggested to accelerate the mass loss from tidal outlet glaciers of the greenland ice sheet we present a comprehensive analysis of water masses dynamics and interannual hydrographic variability in godthabsfjord a sill fjord in contact with tidal outlet glaciers on the west coast of greenland through seasonal observations we recognize an intermediate baroclinic circulation mode driven by tidal currents and an associated important local heat source for the fjord during summer this results in significant warming and freshening of the intermediate layer of the main fjord and the increase in heat content is equivalent to melting of 2 1 km3 of glacial ice this is comparable to 8 km3 glacial ice discharge estimated from the kangiata nun ta sermia calving front per year during winter the external heat source in the west greenland current enters the fjord as intermittent inflows of either cold 2 c dense water in pulses of 1 to 3 months duration four distinct circulation modes are observed in the fjord of which all can contribute to glacial ice melt an important aspect of the ice distribution in the fjord is that only a minor fraction is exported out of the fjord

oceanographic regime shift during 1997 in disko bay western greenland data from a long time series of temperature salinity and nutrient measurements in disko bay west greenland reveal a marked change in the water characteristics during recent years seasonal dynamics in the upper 150 m of the water column were highly affected by the seasonality in meteorological conditions while the deeper water strata were more stable and were primarily influenced by large scale circulation patterns there was a marked increase in the average water temperatures at 200 m depth in spring 1997 with the long term average increasing from 1 30 c to 2 25 c weekly data from 1996 to 1997 show that the sudden change in bottom water occurred in april 1997 due to the inflow of a larger proportion of north atlantic water which propagated north along the coast before entering the bay further support for this inflow was found when tracing the relative proportion of atlantic water in the bay using inorganic nutrients these changes in the oceanography of the bay will not only lead to further glacial retreat but will also affect the local marine ecosystem by changing the relative dominance of major copepod species that overwinter in bottom waters of the bay

glacial weathering sulfide oxidation and global carbon cycle feedbacks connections between glaciation chemical weathering and the global carbon cycle could steer the evolution of global climate over geologic time but even the directionality of feedbacks in this system remain to be resolved here we assemble a compilation of hydrochemical data from glacierized catchments use this data to evaluate the dominant chemical reactions associated with glacial weathering and explore the implications for long term geochemical cycles weathering yields from catchments in our compilation are higher than the global average which results in part from higher runoff in glaciated catchments our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals to evaluate the effects of glacial weathering on atmospheric pco 2 we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon dic generated by weathering reactions compared with nonglacial weathering glacial weathering is more likely to yield alkalinity dic ratios less than 1 suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of co 2 to the atmosphere back of the envelope calculations indicate that oxidative fluxes could change ocean atmosphere co 2 equilibrium by 25 ppm or more over 10 ky over longer timescales co 2 release could act as a negative feedback limiting progress of glaciation dependent on lithology and the concentration of atmospheric o 2 future work on glaciation weathering carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

seasonal variability of the circulation system in a west greenland tidewater outlet glacier fjord godthabsfjord 64 n many tidewater outlet glacier fjords surround the coast of greenland and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet thus fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet however very few observational studies describe the seasonal dynamics of fjord circulation here we present the first continuous current measurements april november from a deep mooring deployed in a west greenland tidewater outlet glacier fjord four distinct circulation phases are identified during the period and they are related to exchange processes with coastal waters tidal mixing and melt processes on the greenland ice sheet during early summer warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s 1 in late summer the average velocity decreases to 3 cm s 1 during a period with significant subglacial freshwater discharges during this period a large variability in current velocities is also observed the associated average heat transport in an intermediate depth range corresponds to 568 gw in early summer and is reduced to 287 gw in late summer these heat fluxes are at the higher end of previously reported fluxes our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and thereby potentially to glacial melt we suggest that intermediate heat transport may play a similar important role in other fjords around greenland

oceanic transport of surface meltwater from the southern greenland ice sheet meltwater runoff from the greenland ice sheet alters ocean surface salinity numerical simulations show that meltwater from southeastern greenland is transported to the labrador sea more efficiently than that from southwestern greenland

bathymetry constrains ocean heat supply to greenland s largest glacier tongue mass loss from the greenland ice sheet has increased over the past two decades currently accounting for 25 of global sea level rise this is due to increased surface melt driven by atmospheric warming and the retreat and acceleration of marine terminating glaciers forced by oceanic heat transport we use ship based profiles bathymetric data and moored time series from 2016 to 2017 of temperature salinity and water velocity collected in front of the floating tongue of the 79 north glacier in northeast greenland these observations indicate that a year round bottom intensified inflow of warm atlantic water through a narrow channel is constrained by a sill the associated heat transport leads to a mean melt rate of 10 4 3 1 m yr 1 on the bottom of the floating glacier tongue the interface height between warm atlantic water and colder overlying water above the sill controls the ocean heat transport s temporal variability historical hydrographic data show that the interface height has risen over the past two decades implying an increase in the basal melt rate additional temperature profiles at the neighbouring zachariae isstrom suggest that ocean heat transport here is similarly controlled by a near glacier sill we conclude that near glacier sill controlled ocean heat transport plays a crucial role for glacier stability ocean heat transport underneath the floating tongue of 79 north glacier greenland is controlled by a sill in the inflow channel according to ship based and mooring data as well as bathymetric data

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

response of an antarctic peninsula fjord to summer katabatic wind events abstractfjords along the western antarctic peninsula are episodically exposed to strong winds flowing down marine terminating glaciers and out over the ocean these wind events could potentially be

ocean regulation hypothesis for glacier dynamics in southeast greenland and implications for ice sheet mass changes synchronous acceleration and thinning of southeast se greenland glaciers during the early 2000s was the main contributor that resulted in the doubling of annual discharge from the ice sheet we show that this acceleration was followed by a synchronized and widespread slowdown of the same glaciers in many cases associated with a decrease in thinning rates and we propose that ice sheet ocean interactions are the first order regional control on these recent mass changes sea surface temperature and mooring data show that the preceding dynamic thinning coincides with a brief decline in the cold east greenland coastal current egcc and east greenland current we suggest this decline was partly induced by a reduction in ice sheet runoff which allowed warm water from the irminger current to reach the se greenland coast a restrengthening of the cold waters coincides with the glaciers subsequent slowdown we argue that this warming and subsequent cooling of the coastal waters was the cause of the glaciers dynamic changes we further suggest that the restrengthening of the egcc resulted in part from cold water input by increased glacier calving during the speedup and increased ice sheet runoff we hypothesize that the main mechanism for ice sheet mass loss in se greenland is highly sensitive to ocean conditions and is likely subject to negative feedback mechanisms copyright 2010 by the american geophysical union

holocene history of the helheim glacier southeast greenland abstract helheim glacier ranks among the fastest flowing and most ice discharging outlets of the greenland ice sheet gris after undergoing rapid speed up in the early 2000s understanding its long term mass balance and dynamic has become increasingly important here we present the first record of direct holocene ice marginal changes of the helheim glacier following the initial deglaciation by analysing cores from lakes adjacent to the present ice margin we pinpoint periods of advance and retreat we target threshold lakes which receive glacial meltwater only when the margin is at an advanced position similar to the present we show that during the period from 10 5 to 9 6 cal ka bp the extent of helheim glacier was similar to that of todays after which it remained retracted for most of the holocene until a re advance caused it to reach its present extent at c 0 3 cal ka bp during the little ice age lia thus helheim glacier s present extent is the largest since the last deglaciation and its holocene history shows that it is capable of recovering after several millennia of warming and retreat furthermore the absence of advances beyond the present day position during for example the 9 3 and 8 2 ka cold events as well as the early neoglacial suggest a substantial retreat during most of the holocene

interannual variability of the subpolar mode water properties over the reykjanes ridge during 1990 2006 combining hydrographic data from the ovide observatoire de la variabilite interannuelle a decennale observatory of the interannual to decadal variability section greenland portugal with argo and historical ctd data over the period 1990 2006 we estimate the variability of the core properties of a variety of subpolar mode water spmw observed on the eastern flank of the reykjanes ridge this spmw acquires its core properties in the winter mixed layer along the eastern side of the reykjanes ridge we find that the february sea surface temperature along the ridge is a proxy for its core temperature the sources of this mode water are water masses advected by the mean cyclonic circulation in the iceland basin a density compensated tendency for cooling and freshening of the spmw core properties is observed in the early 1990s it stops in 1996 and is followed by an increase in temperature and salinity 1 41 c and 0 11 psu and a decrease in density 0 12 kg m 3 until at least 2003 during the entire period the data do not show any significant modification in the depth of the mode water core while they suggest that the thickness of the layer shrank the variability of the local air sea freshwater and heat fluxes cannot explain the observed salinity and temperature variations they are most likely related to the modifications of the properties of the spmw sources due to the recently evidenced changes driven by the north atlantic oscillation in the relative contributions of subtropical waters and subpolar waters in the iceland basin

contrasts in the response of adjacent fjords and glaciers to ice sheet surface melt in west greenland neighboring tidewater glaciers often exhibit asynchronous dynamic behavior despite relatively uniform regional atmospheric and oceanic forcings this variability may be controlled by a combination of local factors including glacier and fjord geometry fjord heat content and circulation and glacier surface melt in order to characterize and understand contrasts in adjacent tidewater glacier and fjord dynamics we made coincident ice ocean atmosphere observations at high temporal resolution minutes to weeks within a 10 000 km 2 area near uummannaq greenland water column velocity temperature and salinity measurements reveal systematic differences in neighboring fjords that imply contrasting circulation patterns the observed ocean velocity and hydrography combined with numerical modeling suggest that subglacial discharge plays a major role in setting fjord conditions in addition satellite remote sensing of seasonal ice flow speed and terminus position reveal both speedup and slow down in response to melt as well as differences in calving style among the neighboring glaciers glacier force budgets and modeling also point toward subglacial discharge as a key factor in glacier behavior for the studied region individual glacier and fjord geometry modulate subglacial discharge which leads to contrasts in both fjord and glacier dynamics

turbulent plumes from a glacier terminus melting in a stratified ocean the melting of submerged faces of marine terminating glaciers is a key contributor to the glacial mass budget via direct thermodynamic ablation and the impact of ablation on calving this study considers the behavior of turbulent plumes of buoyant meltwater in a stratified ocean generated by melting of either near vertical calving faces or sloping ice shelves we build insight by applying a turbulent plume model to describe melting of a locally planar region of ice face in a linearly stratified ocean in a regime where subglacial discharge is insignificant the plumes rise until becoming neutrally buoyant before intruding into the ocean background for strong stratifications we obtain leading order scaling laws for the flow including the height reached by the plume before intrusion and the melt rate expressed in terms of the background ocean temperature and salinity stratifications these scaling laws provide a new perspective for parameterizing glacial melting in response to a piecewise linear discretization of the ocean stratification

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

impact of periodic intermediary flows on submarine melting of a greenland glacier the submarine melting of a vertical glacier front induced by an intermediary circulation forced by periodic density variations at the mouth of a fjord is investigated using a nonhydrostatic ocean general circulation model and idealized laboratory experiments the idealized configurations broadly match that of sermilik fjord southeast greenland a largely two layers system characterized by strong seasonal variability of subglacial discharge consistent with observations the numerical results suggest that the intermediary circulation is an effective mechanism for the advection of shelf anomalies inside the fjord in the numerical simulations the advection mechanism is a density intrusion with a velocity which is an order of magnitude larger than the velocities associated with a glacier driven circulation in summer submarine melting is mostly influenced by the discharge of surface runoff at the base of the glacier and the intermediary circulation induces small changes in submarine melting in winter on the other hand submarine melting depends only on the water properties and velocity distribution at the glacier front hence the properties of the waters advected by the intermediary circulation to the glacier front are found to be the primary control of the submarine melting when the density of the intrusion is intermediate between those found in the fjord s two layers there is a significant reduction in submarine melting on the other hand when the density is close to that of the bottom layer only a slight reduction in submarine melting is observed the numerical results compare favorably to idealized laboratory experiments with a similar setup