strengthening and westward shift of the tropical pacific walker circulation during the mid holocene pmip simulation results abstractbased on the zonal mass streamfunction the mid holocene annual and seasonal changes in the tropical pacific walker circulation pwc are examined using numerical simulations from the paleoclimate modelling intercomparison project phases 2 and 3 compared to the pre industrial period the annual mean of the pwc intensity strengthened with an average increase of 0 26 1014 kg2 m 2 s 1 or 5 and both the western edge and center of the pwc cell shifted westward by an average of 4 and 3 respectively in the majority of the 29 models used for analysis during the mid holocene those changes were close related to an overall increase in the equatorial indo pacific east west sea level pressure difference and low level trade winds over the equatorial pacific annual mean pwc changes come mainly from boreal warm seasons in response to the mid holocene orbital forcing asian and north african monsoon rainfall was strengthened due to large scale surface warming in the northern hemisphere in boreal w

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

subaqueous melting of store glacier west greenland from three dimensional high resolution numerical modeling and ocean observations we present three dimensional high resolution simulations of ice melting at the calving face of store glacier a tidewater glacier in west greenland using the massachusetts institute of technology general circulation model we compare the simulated ice melt with an estimate derived from oceanographic data the simulations show turbulent upwelling and spreading of the freshwater laden plume along the ice face and the vigorous melting of ice at rates of meters per day the simulated august 2010 melt rate of 2 0 0 3 m d is within uncertainties of the melt rate of 3 0 1 0 m d calculated from oceanographic data melting is greatest at depth above the subglacial channels causing glacier undercutting melt rates increase proportionally to thermal forcing raised to the power of 1 2 1 6 and to subglacial water flux raised to the power of 0 5 0 9 therefore in a warmer climate store glacier melting by ocean may increase from both increased ocean temperature and subglacial discharge key points simulated melt agrees with estimates from a hydrographic survey of the glacier with more runoff glaciers will melt faster at constant ocean temperature 2013 american geophysical union all rights reserved

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

asynchronous behavior of outlet glaciers feeding godthabsfjord nuup kangerlua and the triggering of narsap sermia s retreat in sw greenland we thank w dryer and d podrasky for assistance with fieldwork and l kenefic for assisting with digitizing glacier front positions ch2 m hill polar services and air greenland provided logistics support the spot 5 images used for the 2008 dem were provided by the spirit program centre national d etudes spatiales france the digitalglobe worldview images used for the 2014 dem were obtained from p morin terminus positions were derived from landsat images courtesy of the u s geological survey funding was provided by the us national science foundation nsf office of polar programs opp grants nsf plr 0909552 and nsf plr 0909333 cassotto is supported by nasa under the earth and space science fellowship program grant nnx14al29h k k kjeldsen acknowledges support from the danish council research for independent research grant no dff 409000151 k kjaer is thanked for his support during the earlier phases of this study on ice weather stations are operated by geus denmark within the programme for monitoring of the greenland ice sheet promice j mortensen acknowledges support from iiknn greenland defrost project of the nordic centre of excellence program interaction between climate change and the cryosphere and the greenland ecosystem monitoring programme www g e m dk s rysgaard was funded by the canada excellence research chair programme additional funding was provided by the geophysical institute university of alaska fairbanks and greenland climate research centre scientific editor h fricker and reviewers h jiskoot and g cogley provided very constructive feedback that helped improve the paper

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

controls on the transport of oceanic heat to kangerdlugssuaq glacier east greenland this work was funded by nerc grant ne k014609 1 to peter nienow and andrew sole and a nerc studentship to donald slater edward hanna and david wilton acknowledge support from nerc grant ne h023402 1

linear response of east greenland s tidewater glaciers to ocean atmosphere warming predicting the retreat of tidewater outlet glaciers forms a major obstacle to forecasting the rate of mass loss from the greenland ice sheet this reflects the challenges of modeling the highly dynamic topographically complex and data poor environment of the glacier fjord systems that link the ice sheet to the ocean to avoid these difficulties we investigate the extent to which tidewater glacier retreat can be explained by simple variables air temperature meltwater runoff ocean temperature and two simple parameterizations of ocean atmosphere forcing based on the combined influence of runoff and ocean temperature over a 20 y period at 10 large tidewater outlet glaciers along the east coast of greenland we find that ocean atmosphere forcing can explain up to 76 of the variability in terminus position at individual glaciers and 54 of variation in terminus position across all 10 glaciers our findings indicate that i the retreat of east greenland s tidewater glaciers is best explained as a product of both oceanic and atmospheric warming and ii despite the complexity of tidewater glacier behavior over multiyear timescales a significant proportion of terminus position change can be explained as a simple function of this forcing these findings thus demonstrate that simple parameterizations can play an important role in predicting the response of the ice sheet to future climate warming

distributed subglacial discharge drives significant submarine melt at a greenland tidewater glacier this is the publisher s final pdf the article is copyrighted by american geophysical union and published by john wiley sons inc it can be found at http agupubs onlinelibrary wiley com agu journal 10 1002 28issn 291944 8007

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

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

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

the effect of meltwater plumes on the melting of a vertical glacier face abstractfreshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord terminating glaciers the discharge of the freshwater forms upwelling plumes in front of the glacier calving face this study simulates the meltwater plumes emanated into an unstratified environment using a nonhydrostatic ocean model with an unstructured mesh and subgrid scale mixing calibrated by comparison to established plume theory the presence of an ice face reduces the entrainment of seawater into the meltwater plumes so the plumes remain attached to the ice front in contrast to previous simple models ice melting increases with height above the discharge also in contrast to some simple models and the authors speculate that this overcutting may contribute to the tendency of icebergs to topple inwards toward the ice face upon calving the overall melt rate is found to increase with discharge flux only up to a critical value which depends on the channel size

fast retreat of zachariae isstrom northeast greenland after 8 years of decay of its ice shelf zachariae isstrom a major glacier of northeast greenland that holds a 0 5 meter sea level rise equivalent entered a phase of accelerated retreat in fall 2012 the acceleration rate of its ice velocity tripled melting of its residual ice shelf and thinning of its grounded portion doubled and calving is now occurring at its grounding line warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward sloping marine based bed its equal ice volume neighbor nioghalvfjerdsfjorden is also melting rapidly but retreating slowly along an upward sloping bed the destabilization of this marine based sector will increase sea level rise from the greenland ice sheet for decades to come

p and s wave tomography and anisotropy in northwest pacific and east asia constraints on stagnant slab and intraplate volcanism we determined three dimensional p and s wave velocities and p wave azimuthal anisotropic tomography of the northwest pacific subduction zones by inverting 1 225 086 p wave and 335 117 s wave arrival times from 13 413 earthquakes our results show some differences between p and s wave images for the stagnant pacific slab in the mantle transition zone mtz beneath northeast china the stagnant slab looks thicker in the p wave image than that in the s wave image which may reflects the effects of both hydration and lower temperature in the mtz though differences in the resolution of p and s wave tomography may also have some effects the changbai intraplate volcanism is caused by hot and wet upwelling in the big mantle wedge above the stagnant pacific slab our p wave anisotropy tomography shows that the fast velocity direction fvd in the subducting philippine sea plate beneath the ryukyu arc is ne sw trench parallel which is consistent with the spreading direction of the west philippine basin during its initial opening stage suggesting that it may reflect the fossil anisotropy a striking variation of the fvd with depth is revealed in the subducting pacific slab beneath the northeast japan arc which may be caused by slab dehydration that changed elastic properties of the slab with depth the fvd in the mantle wedge beneath the northeast japan and ryukyu arcs is trench normal which reflects subduction induced convection beneath the kuril and izu bonin arcs where oblique subduction occurs the fvd in the mantle wedge is nearly normal to the moving direction of the downgoing pacific plate suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow

tides modulate crevasse opening prior to a major calving event at bowdoin glacier northwest greenland retreat of calving glaciers worldwide has contributed substantially to sea level rise in recent decades mass loss by calving contributes significantly to the uncertainty of sea level rise projections at bowdoin glacier northwest greenland most calving occurs by a few large events resulting from kilometre scale fractures forming parallel to the calving front high resolution terrestrial radar interferometry data of such an event reveal that crevasse opening is fastest at low tide and accelerates during the final 36 h before calving using the ice flow model elmer ice we identify the crevasse water level as a key driver of modelled opening rates sea water level variations in the range of local tidal amplitude 1 m can reproduce observed opening rate fluctuations provided crevasse water level is at least 4 m above the low tide sea level the accelerated opening rates within the final 36 h before calving can be modelled by additional meltwater input into the crevasse enhanced ice cliff undercutting by submarine melt ice damage increase due to tidal cyclic fatigue crevasse deepening or a combination of these processes our results highlight the influence of surface meltwater and tides on crevasse opening leading to major calving events at grounded tidewater glaciers such as bowdoin

impact of two plumes interaction on submarine melting of tidewater glaciers a laboratory study idealized laboratory experiments investigate the glacier ocean boundary dynamics near a vertical glacier in a two layer stratified fluid discharge of meltwater runoff at the base of the glacier subglacial discharge enhances submarine melting in the laboratory the effect of multiple sources of subglacial discharge is simulated by introducing freshwater at freezing temperature from two point sources at the base of an ice block representing the glacier the buoyant plumes of cold meltwater and subglacial discharge water entrain warm ambient water rise vertically and interact within a layer of depth h2 if the distance between the sources x0 is smaller than h2 0 35 where is the entrainment constant the plume water detaches from the glacier face at the interface between the two layers and or at the free surface as confirmed by previous numerical studies and field observations a plume model is used to explain the observed nonmonotonic dependence of submarine melting on the sources separation the distance between the two sources influences the entrainment of warm water in the plumes and consequently the amount of submarine melting and the final location of the meltwater within the water column two interacting plumes located very close together are observed to melt approximately half as much as two independent plumes the inclusion or parameterization of the dynamics regulating multiple plumes interaction is therefore necessary for a correct estimate of submarine melting hence the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates and fjord stratification and circulation

seasonal to multiyear variability of glacier surface velocity terminus position and sea ice ice melange in northwest greenland glacier ice discharge which depends on ice velocity and terminus fluctuations is a primary component of greenland ice sheet mass loss some research suggests that ice melange influences terminus calving in turn affecting glacier velocity the details and broad spatiotemporal consistency of these relationships however is undetermined focusing on 16 northwestern greenland glaciers during 2009 through summer 2014 we examined seasonal surface velocity changes glacier terminus position and sea ice and ice melange conditions for a longer term analysis we also produced extended records of four glaciers from 1999 to 2014 there is a strong correspondence between seasonal near terminus sea ice melange conditions and terminus change with rigid ice melange conditions associated with advance and open water associated with retreat extended sea ice free periods and reduced rigid melange are also linked with anomalously large terminus retreat in all but one case sustained multiyear retreat of greater than 1 km during both the 15 year and 6 year records was accompanied by interannual velocity increases seasonal velocity patterns however correspond more strongly with runoff changes than terminus behavior projections of continued warming and longer sea ice free periods around greenland indicate that notable retreat over wide areas may continue this sustained retreat likely will contribute to multiyear speedup longer melt seasons and earlier breakup of melange may also alter the timing of seasonal ice flow variability

convection driven melting near the grounding lines of ice shelves and tidewater glaciers subglacial meltwater draining along the bed of fast flowing marine terminating glaciers emerges at the groundingline wheretheiceeithergoesafloattoformaniceshelforterminates inacalvingface theinputof freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice ocean interface this process is modeled using the theory of buoyant plumes that has previously been applied to the study of the larger scale circulation beneath ice shelves the plume grows through entrainment of ocean waters and the heat brought into the plume as a result drives melting at the ice ocean interface the equations are nondimensionalized by using scales appropriate for the region where the subglacial drainage rather than the subsequent addition of meltwater supplies the majority of the buoyancy forcing it is found that the melt rate within this region can be approximated reasonably well by a function that is linear in ocean temperature has a cube root dependence on the flux of subglacial meltwater and has a complex dependency on the slope of the ice ocean interface the model is used to investigate variability in melting induced by changes in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelves and tidewater glaciers the results show how warming ocean waters and increasing subglacial drainage both generate increases in melting near the grounding line

wind driven modulation of warm water supply to a proglacial fjord jorge montt glacier patagonia projections of sea level rise due to ice loss from the land to the ocean have been hampered by a lack of understanding of the role the ocean is playing in glacier retreat including the processes that contribute to the supply of warm water to the ice ocean interface here shipboard moored and weather station data collected off jorge montt a rapidly retreating glacier in patagonia are analyzed to understand the influence of wind forcing during summer synoptic scale down fjord wind events enhance an estuarine like two layer flow increasing the inflow of oceanic deep water during up fjord wind events the inflow of deep water is significantly reduced and a three layer exchange flow develops overall along fjord wind forcing is shown to modulate the inflow of warm water to the fjord by a factor of 2 5 the results sug gest that local channelized winds can be an important process modulating warm water supply and melting of tidewater glaciers

structure and dynamics of a subglacial discharge plume in a greenlandic fjord discharge of surface derived meltwater at the submerged base of greenland s marine terminating glaciers creates subglacial discharge plumes that rise along the glacier ocean interface these plumes impact submarine melting calving and fjord circulation observations of plume properties and dynamics are challenging due to their proximity to the calving edge of glaciers therefore to date information on these plumes has been largely derived from models here we present temperature salinity and velocity data collected in a plume that surfaced at the edge of saqqarliup sermia a mid sized greenlandic glacier the plume is associated with a narrow core of rising waters approximately 20 m in diameter at the ice edge that spreads to a 200 m by 300 m plume pool as it reaches the surface before descending to its equilibrium depth volume flux estimates indicate that the plume is primarily driven by subglacial discharge and that this has been diluted in a ratio of 1 10 by the time the plume reaches the surface while highly uncertain meltwater fluxes are likely two orders of magnitude smaller than the subglacial discharge flux the overall plume characteristics agree with those predicted by theoretical plume models for a convection driven plume with limited influence from submarine melting this article is protected by copyright all rights reserved

tidal modulation of buoyant flow and basal melt beneath petermann gletscher ice shelf greenland a set of collocated in situ oceanographic and glaciological measurements from petermann gletscher ice shelf greenland provides insights into the dynamics of under ice flow driving basal melting at a site 16 km seaward of the grounding line within a longitudinal basal channel two conductivity temperature ct sensors beneath the ice base and a phase sensitive radar on the ice surface were used to monitor the coupled ice shelf ocean system a 6 month time series spanning 23 august 2015 to 12 february 2016 exhibited two distinct periods of ice ocean interactions between august and december radar derived basal melt rates featured fortnightly peaks of 15 m yr 1 which preceded the arrival of cold and fresh pulses in the ocean that had high concentrations of subglacial runoff and glacial meltwater estimated current speeds reached 0 20 0 40 m s 1 during these pulses consistent with a strengthened meltwater plume from freshwater enrichment such signals did not occur between december and february when ice ocean interactions instead varied at principal diurnal and semidiurnal tidal frequencies and lower melt rates and current speeds prevailed a combination of estimated current speeds and meltwater concentrations from the two ct sensors yields estimates of subglacial runoff and glacial meltwater volume fluxes that vary between 10 and 80 m3 s 1 during the ocean pulses area average upstream ice shelf melt rates from these fluxes are up to 170 m yr 1 revealing that these strengthened plumes had already driven their most intense melting before arriving at the study site

volcanic eruptions in the longgang volcanic field northeastern china during the past 15 000 years the longgang volcanic field located in northeastern china is volcanically active with a number of eruptions during the quaternary but the chronology of the eruptions is poorly defined some tephra layers are well preserved in the annually laminated sediments of maar lakes in the region and facilitate the construction of a much improved chronological framework for the volcanic history of the area the results of our investigations reveal that three basaltic explosive eruptions occurred at ad 460 11460 cal yr bp and 14000 cal yr bp respectively the largest explosive basaltic eruption ad 460 produced a thick black scoria layer in the longgang volcanic field including lakes the tephra distribution and chronological data suggest that this eruption is likely to be from the jinlongdingzi volcano two basaltic flood eruptions occurred at jinlongdingzi the earlier basaltic eruption produced a lava flow that spread over a forest and encased standing trees two radiocarbon ages obtained from charcoal samples collected from the burned remains of these trees are 1828 1989 cal yr bp and 2164 2359 cal yr bp in the most recent stage of volcanism the lava flow extended only ca 2 km and flowed into lake dalongwan from the present status of the forest ecosystem which has not yet reached the fully mature successional stage we estimate that this lava is very young ca a few hundreds years old jinlongdingzi is a potentially dangerous volcano monitoring and assessment of the potential hazards in the longgang volcanic field should be carried out in the future

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

sensitivity of tidewater glaciers to submarine melting governed by plume locations this work was funded by nerc award ne p011365 1 calismo calving laws for ice sheet models to pi benn

rock magnetic studies on sediments from erlongwan maar lake long gang volcanic field jilin province ne china summary detailed rock magnetic investigations were carried out on two 23 m long sediment cores from erlongwan maar lake ne china the completely laminated sediment sequence of the lake is interrupted by 410 graded layers with thicknesses between 0 1 and 150 cm magnetite of psd size was identified as the main magnetic carrier mineral by temperature dependent measurements of the saturation magnetization and determination of hysteresis parameters the minerogenic components in the laminated sediments and the graded layers are nearly identical and their rock magnetic characteristics reflect the prevailing conditions anoxic or oxic during deposition the most reliable criteria for estimating the availability of oxygen is whether an increase in minerogenic influx is linked to a shift in the magnetic grain size spectrum to coarser oxic or finer anoxic grains comparison of different rock magnetic parameters indicative for magnetic grain size and coercitivity revealed that the s ratio which is known to reflect the presence of high coercive minerals is grain size indicative in sediments with a monomineralic magnetic composition

the impact of glacier geometry on meltwater plume structure and submarine melt in greenland fjords meltwater from the greenland ice sheet often drains subglacially into fjords driving upwelling plumes at glacier termini ocean models and observations of submarine termini suggest that plumes enhance melt and undercutting leading to calving and potential glacier destabilization here we systematically evaluate how simulated plume structure and submarine melt during summer months depends on realistic ranges of subglacial discharge glacier depth and ocean stratification from 12 greenland fjords our results show that grounding line depth is a strong control on plume induced submarine melt deep glaciers produce warm salty subsurface plumes that undercut termini and shallow glaciers produce cold fresh surface trapped plumes that can overcut termini due to sustained upwelling velocities plumes in cold shallow fjords can induce equivalent depth averaged melt rates compared to warm deep fjords these results detail a direct ocean ice feedback that can affect the greenland ice sheet

subsurface iceberg melt key to greenland fjord freshwater budget liquid freshwater fluxes from the greenland ice sheet affect ocean water properties and circulation on local regional and basin wide scales with associated biosphere effects the exact impact however depends on the volume timing and location of freshwater releases which are poorly known in particular the transformation of icebergs which make up roughly 30 50 of the loss of the ice sheet mass to liquid freshwater is not well understood here we estimate the spatial and temporal distribution of the freshwater flux for the helheim sermilik glacier fjord system in southeast greenland using an iceberg melt model that resolves the subsurface iceberg melt by estimating seasonal variations in all the freshwater sources we confirm quantitatively that iceberg melt is the largest annual freshwater source in this system type we also show that 68 78 of the iceberg melt is released below a depth of 20 m and seasonally about 40 100 of that melt is likely to remain at depth in contrast with the usual model assumptions iceberg melt also peaks two months after all the other freshwater sources peak our methods provide a framework to assess individual freshwater sources in any tidewater system and our results are particularly applicable to coastal regions with a high solid ice discharge in greenland iceberg melt is the largest annual freshwater source in a south greenland fjord with release largely below 20 m depth according to iceberg model simulations furthermore iceberg melt peaks later in the year than other sources of freshwater

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

crust structure beneath jilin province and liaoning province in china based on seismic ambient noise tomography abstract we imaged the crust structure beneath jilin province and liaoning province in china with fundamental mode rayleigh waves recorded by 60 broadband stations deployed in the region surface wave empirical green s functions were retrieved from cross correlations of inter station data and phase velocity dispersions were measured using a frequency time analysis method dispersion measurements were then utilized to construct 2d phase velocity maps for periods between 5 and 35 s subsequently the phase dispersion curves extracted from each cell of the 2d phase velocity maps were inverted to determine the 3d shear wave velocity structures of the crust the phase velocity maps at different periods reflected the average velocity structures corresponding to different depth ranges the maps in short periods in particular were in excellent agreement with known geological features of the surface in addition to imaging shear wave velocity structures of the volcanoes we show that obvious low velocity anomalies imaged in the changbaishan tianchi volcano the longgang jinlongdingzi volcano and the system of the dunmi fault crossing the jingbohu volcano all of which may be due to geothermal anomalies

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

ice motion of the patagonian icefields of south america 1984 2014 2015 american geophysical union all rights reserved we present the first comprehensive high resolution mosaic of ice velocity of the northern npi and southern patagonian icefields spi from multiple synthetic aperture radar and optical data collected between 1984 and 2014 the results reveal that many of the outlet glaciers extend far into the central ice plateaus which implies that changes in ice dynamics propagate far inside the accumulation area we report pronounced seasonal to interannual variability of ice motion on pio xi and jorge montt a doubling in speed of jorge montt a major slow down of o higgins significant fluctuations of upsala and a deceleration of san rafael which illustrate the need for sustained continuous time series of ice motion to understand the long term evolution of the rapidly thinning icefields the velocity product also resolves major ambiguities in glacier drainage in areas of relatively flat topography illustrating the need to combine topography and flow direction to map drainage basins

seismic evidence of on going sublithosphere upper mantle convection for intra plate volcanism in northeast china abstract a 3 d crustal and upper mantle s wave velocity model of ne china is constructed by inversion of phase velocity dispersion curves at 6 140 s periods from ambient noise tomography and two plane surface wave tomography the seismic data used in this study are collected from 120 china earthquake administration cea permanent stations and 127 portable stations of necessarray we observe strong low s wave velocity beneath the changbaishan volcano in the upper mantle to at least 200 km depth which is interpreted as a mantle upwelling beneath the changbaishan volcano that is consistent with the body wave tomographic image the songliao basin is dominated by a high velocity extending to at least 200 km depth built upon the observed velocity anomalies we propose a sub lithosphere mantle convection model for ne china in which the upwelling of upper mantle materials from the mantle transition zone to the changbaishan volcano could induce a local sub lithosphere convection in the upper mantle and the strong high velocity of the upper mantle beneath the songliao basin corresponds to the downwelling limb of this convection cell the downwelling beneath the songliao basin could also induce secondary local convection in the asthenosphere to the west leading to local asthenospheric upwelling beneath the abaga and halaha volcanoes in the xing an mongolia orogenic belt

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

a two dimensional glacier fjord coupled model applied to estimate submarine melt rates and front position changes of hansbreen svalbard we have developed a two dimensional coupled glacier fjord model which runs automatically using elmer ice and mitgcm software packages to investigate the magnitude of submarine melting along a vertical glacier front and its potential influence on glacier calving and front position changes we apply this model to simulate the hansbreen glacier hansbukta proglacial fjord system southwestern svalbard during the summer of 2010 the limited size of this system allows us to resolve some of the small scale processes occurring at the ice ocean interface in the fjord model using a 0 5 s time step and a 1 m grid resolution near the glacier front we use a rich set of field data spanning the period april august 2010 to constrain calibrate and validate the model we adjust circulation patterns in the fjord by tuning subglacial discharge inputs that best match observed temperature while maintaining a compromise with observed salinity suggesting a convectively driven circulation in hansbukta the results of our model simulations suggest that both submarine melting and crevasse hydrofracturing exert important controls on seasonal frontal ablation with submarine melting alone not being sufficient for reproducing the observed patterns of seasonal retreat both submarine melt and calving rates accumulated along the entire simulation period are of the same order of magnitude 100 m the model results also indicate that changes in submarine melting lag meltwater production by 4 5 weeks which suggests that it may take up to a month for meltwater to traverse the englacial and subglacial drainage network

dust records from varved lacustrine sediments of two neighboring lakes in northeastern china over the last 1400 years dust storms are natural phenomena described in chinese historical documents as early as 1150 bc these documents provide a way to evaluate proxy data from different natural records the minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern china were analyzed the area is located in the path of dust storms the minerogenic clastics in the studied maar lakes originate mainly from dust deposition general variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a tibet ice core and dust events as recorded in historical documents the minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength three periods of intensive dust events ad 1050 1330 ad 1590 1690 and the last 200 years have been identified during the past 1500 years the recent increasing pattern of clastic content could be linked to human activity in the dust source regions significantly most of the medieval warm period mwp was marked by a high frequency of dust storms

spatially distributed runoff at the grounding line of a large greenlandic tidewater glacier inferred from plume modelling understanding the drivers of recent change at greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming a poorly constrained component of tidewater glacier processes is the near terminus subglacial hydrology here we present a novel method for constraining near terminus subglacial hydrology with application to marine terminating kangiata nunata sermia in south west greenland by simulating proglacial plume dynamics using buoyant plume theory and a general circulation model we assess the critical subglacial discharge if delivered through a single compact channel required to generate a plume that reaches the fjord surface we then compare catchment runoff to a time series of plume visibility acquired from a time lapse camera we identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface yet we observe no plume we attribute these observations to spatial spreading of runoff across the grounding line persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration

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

east asian monsoon variability between 15 000 and 2000 cal yr bp recorded in varved sediments of lake sihailongwan northeastern china long gang volcanic field a palaeohydrological reconstruction on decadal scale for the period 15000 2000 cal yr bp based on calculated net accumulation rates for biogenic silica f bsio2 and additional proxies sedimentol

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

ice flow in greenland for the international polar year 2008 2009 a digital representation of ice surface velocity is essential for a variety of glaciological geologic and geophysical analyses and modeling here we present a new reference comprehensive high resolution digital mosaic of ice motion in greenland assembled from satellite radar interferometry data acquired during the international polar year 2008 to 2009 by the envisat advanced synthetic aperture radar asar the advanced land observation system alos s phase array l band sar palsar and the radarsat 1 sar that covers 99 of the ice sheet in area the best mapping performance is obtained using alos palsar data due to higher levels of temporal coherence at the l band frequency but c band frequency sar data are less affected by the ionosphere the ice motion map reveals various flow regimes ranging from patterned enhanced flow into a few large glaciers in the cold low precipitation areas of north greenland to diffuse enhanced flow into numerous narrow fast moving glaciers in the warmer high precipitation sectors of northwest and southeast greenland we find that the 100 fastest glaciers v 800m yr drain 66 of the ice sheet in area marine terminating glaciers drain 88 of greenland and basal sliding motion dominates internal deformation over more than 50 of the ice sheet this view of ice sheet motion provides significant new constraints on ice flow modeling copyright 2012 by the american geophysical union

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

observations and modeling of ocean induced melt beneath petermann glacier ice shelf in northwestern greenland we update observationally based estimates of subaqueous melt qm beneath petermann glacier ice shelf pgis greenland and model its sensitivity to oceanic thermal forcing tf and subglacial runoff qsg using the massachusetts institute of technology general circulation model mitgcm in a two dimensional domain with 20 m vertical and 40 m horizontal resolution at the grounding line we adjust the drag coefficient to match the observationally based qm with the inclusion of qsg the maximum melt rate qmmax is two times larger in summer and 1 3 larger annually than in winter qmmax increases above linear with tf and below linear with qsg we estimate that qmmax increased by 24 8 1 m yr beneath pgis from the 1990s to the 2000s from a 0 21 c warming in ocean temperature and a doubling in qsg hence contributing to its thinning if the pgis is removed we estimate that the modeled melt rate near the grounding line will increase 13 16 times

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

observation and parameterization of ablation at the base of ronne ice shelf antarctica parameterizations of turbulent transfer through the oceanic boundary layer beneath an ice shelf are tested using direct measurements of basal ablation observations were made in the southwestern part of ronne ice shelf about 500 km from open water the mean basal ablation rate was measured over a month long and a year long period using phase sensitive radar to record the thinning of the ice shelf ocean temperatures were observed within about 25 m of the ice shelf base over the period of the radar observations while the tidally dominated ocean currents were estimated from tidal analysis of collocated current observations from an earlier period ablation rates derived using these ocean data and a number of bulk parameterizations of turbulent transfer within the boundary layer are compared with the direct measurements the ablation rates derived using a parameterization that explicitly includes the impact of ocean currents on the turbulent transfer of heat and salt match the observations to within 40 with suitable tuning of the drag coefficient the mismatch can be reduced below the level of the observational errors equally good agreement can be obtained with two slightly simpler current dependent parameterizations that use constant turbulent transfer coefficients andtheoptimalvaluesforthecoefficientsatthis particularlocationon ronneice shelfaregiven

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

ice dammed lake drainage cools and raises surface salinities in a tidewater outlet glacier fjord west greenland the drainage of ice dammed lakes in the form of outburst floods in greenland is detected regularly by remote sensing and these events are expected to occur more frequently in a warmer climate however their impact on ice sheet stability and neighboring water bodies is still unknown in this interdisciplinary study we investigate lake drainages from the greenland ice sheet into a west greenland fjord by analyzing simultaneous time series of satellite observations and direct hydrographic measurements of temperature and salinity in the fjord satellite images show that in general lake drainages have occurred quasiperiodically during the last decade a particular sequence of drainage events was observed by satellite in 2009 and was analyzed together with the first direct hydrographic observations signs of ice dammed lake drainages were observed by a downstream mooring located just below the intertidal zone the release of freshwater occurred at the fjord subsurface at a tidewater outlet glacier the downstream in water sequence of property changes in relation to these drainage events was observed as an almost immediate decrease in surface layer temperature 2 c followed within a week by the arrival of a high saline pulse 5 units with elevated salinity lasting for several days during the passage during lake drainages large amounts of relatively warm and saline intermediate water are brought to the near surface layers by entrainment processes near the glacier front and this influences the hydrography of the fjord but also impacts the ecosystem through upwelling of nutrient rich intermediate water

direct observations of submarine melt and subsurface geometry at a tidewater glacier ice loss from the world s glaciers and ice sheets contributes to sea level rise influences ocean circulation and affects ecosystem productivity ongoing changes in glaciers and ice sheets are driven by submarine melting and iceberg calving from tidewater glacier margins however predictions of glacier change largely rest on unconstrained theory for submarine melting here we use repeat multibeam sonar surveys to image a subsurface tidewater glacier face and document a time variable three dimensional geometry linked to melting and calving patterns submarine melt rates are high across the entire ice face over both seasons surveyed and increase from spring to summer the observed melt rates are up to two orders of magnitude greater than predicted by theory challenging current simulations of ice loss from tidewater glaciers

bedrock morphology reveals drainage network in northeast baffin bay a subglacial drainage network underneath the paleo ice sheet off west greenland is revealed by a new compilation of high resolution bathymetry data from melville bay northeast baffin bay this drainage network is an indicator for ice streaming and subglacial meltwater flow toward the outer shelf repeated ice sheet advances and retreats across the crystalline basement together with subglacial meltwater drainage had their impact in eroding overdeepened troughs along ice stream pathways these overdeepenings indicate the location of a former ice sheet margin the troughs inherit characteristics of glacial and subglacial meltwater erosion most of the troughs follow tectonic weakness zones such as faults and fractures in the crystalline bedrock many of these tectonic features correspond with the orientations of major fault axes in the baffin bay region the troughs extend from the present sub glacial fjord systems at the greenland coast and parallel modern outlet glacier pathways the fast flowing paleo ice streams were likely accelerated from the meltwater flow as indicated by glacial landforms within and along the troughs the ice streams flowed along narrow tributary troughs and merged to form large paleo ice streams bedded in the major cross shelf troughs of melville bay apart from the troughs a rough seabed topography characterises the bedrock and we see a sharp geomorphic transition where ice flowed onto sedimentary rock and deposits

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

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

mechanisms of lava flow emplacement during an effusive eruption of sinabung volcano sumatra indonesia abstract the ongoing effusive phase of the eruption of sinabung volcano sumatra indonesia began in late december 2013 and has produced a 2 9 km long andesitic lava flow with two active secondary summit lobes frequent pyroclastic density currents pdcs with 5 km runout distance and associated plumes up to 5 km in height large intermediate to silicic composition lava flows of the type documented here are common at volcanoes around the world but they are infrequently observed while active this eruption provides a special opportunity to observe and study the mechanisms of emplacement and growth of an active andesitic lava flow we use visible and thermal satellite images to document the flow and describe the dominant processes driving emplacement of the lava over the course of the eruption effusion and flow advance rates were at their highest in january march 2014 a decrease in flow advance rate in late march 2014 from 20 to 70 m d 1 to

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

effect of near terminus subglacial hydrology on tidewater glacier submarine melt rates submarine melting of greenlandic tidewater glacier termini is proposed as a possible mechanism driving their recent thinning and retreat we use a general circulation model mitgcm to simulate water circulation driven by subglacial discharge at the terminus of an idealized tidewater glacier we vary the spatial distribution of subglacial discharge emerging at the grounding line of the glacier and examine the effect on submarine melt volume and distribution we find that subglacial hydrology exerts an important control on submarine melting under certain conditions a distributed system can induce a factor 5 more melt than a channelized system with plumes from a single channel inducing melt over only a localized area subglacial hydrology also controls the spatial distribution of melt which has the potential to control terminus morphology and calving style our results highlight the need to constrain near terminus subglacial hydrology at tidewater glaciers if we are to represent ocean forcing accurately

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

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

spreading of warm ocean waters around greenland as a possible cause for glacier acceleration we examine the pattern of spreading of warm subtropical origin waters around greenland for the years 1992 2009 using a high resolution 4km horizontal grid coupled ocean and sea ice simulation the simulation provided by the estimating the circulation and climate of the ocean phase ii ecco2 project qualitatively reproduces the observed warming of subsurface waters in the subpolar gyre associated with changes of the north atlantic atmospheric state that occurred in the mid 1990s the modeled subsurface ocean temperature warmed by 1 5 c in southeast and southwest greenland during 1994 2005 and subsequently cooled by 0 5 c modeled subsurface ocean temperature increased by 2 2 5 c in central and then northwest greenland during 1997 2005 and stabilized thereafter while it increased after 2005 by xu and others 2012 we show that the oceanic changes have very likely increased the subaqueous melt rates of the glacier fronts and in turn impacted the rates of glacier flow

bathymetry data reveal glaciers vulnerable to ice ocean interaction in uummannaq and vaigat glacial fjords west greenland marine terminating glaciers play a critical role in controlling greenland s ice sheet mass balance their frontal margins interact vigorously with the ocean but our understanding of this interaction is limited in part by a lack of bathymetry data here we present a multibeam echo sounding survey of 14 glacial fjords in the uummannaq and vaigat fjords west greenland which extends from the continental shelf to the glacier fronts the data reveal valleys with shallow sills overdeepenings 1300 m from glacial erosion and seafloor depths 100 1000 m deeper than in existing charts where fjords are deep enough we detect the pervasive presence of warm salty atlantic water aw 2 5 degrees c with high melt potential but we also find numerous glaciers grounded on shallow 200 m sills standing in cold 1 degrees c waters in otherwise deep fjords i e with reduced melt potential bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution

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

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

scalings for submarine melting at tidewater glaciers from buoyant plume theory abstractrapid dynamic changes at the margins of the greenland ice sheet synchronous with ocean warming have raised concern that tidewater glaciers can respond sensitively to ocean forcing understanding of the processes encompassing ocean forcing nevertheless remains embryonic the authors use buoyant plume theory to study the dynamics of proglacial discharge plumes arising from the emergence of subglacial discharge into a fjord at the grounding line of a tidewater glacier deriving scalings for the induced submarine melting focusing on the parameter space relevant for high discharge tidewater glaciers the authors suggest that in an unstratified fjord the often quoted relationship between total submarine melt volume and subglacial discharge raised to the power is appropriate regardless of plume geometry provided discharge lies below a critical value in these cases it is then possible to formulate a simple equation estimating total submarine melt volume as a function of discharge fjord temperature

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

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

subglacial discharge driven renewal of tidewater glacier fjords the classic model of fjord renewal is complicated by tidewater glacier fjords where submarine melt and subglacial discharge provide substantial buoyancy forcing at depth here we use a suite of idealized high resolution numerical ocean simulations to investigate how fjord circulation driven by subglacial plumes tides and wind stress depends on fjord width grounding line depth and sill height we find that the depth of the grounding line compared to the sill is a primary control on plume driven renewal of basin waters in wide fjords the plume exhibits strong lateral recirculation increasing the dilution and residence time of glacially modified waters rapid drawdown of basin waters by the subglacial plume in narrow fjords allows for shelf waters to cascade deep into the basin wide fjords result in a thin boundary current of shelf waters that flow toward the terminus slightly below sill depth wind forcing amplifies the plume driven exchange flow however wind induced vertical mixing is limited to near surface waters tidal mixing over the sill increases in fjord transport of deep shelf waters and erodes basin stratification above the sill depth these results underscore the first order importances of fjord glacier geometry in controlling circulation in tidewater glacier fjords and thus ocean heat transport to the ice

totten glacier subglacial hydrology determined from geophysics and modeling aurora subglacial basin asb which feeds totten glacier is a marine basin lying below sea level and contains up to 3 5m of global sea level equivalent rates of future sea level rise from this area are primarily dependent on the stability of totten ice shelf and the controls on ice flow dynamics upstream of the grounding line both of which may be influenced by subglacial hydrology we apply the glads subglacial hydrology model to asb to examine whether the spatial patterns of distributed and efficient drainage systems impact the dynamics of totten glacier we determine the most appropriate model configuration from our series of sensitivity tests by comparing the modeled basal water pressure and water depth results with specularity content data those data are derived from icecap radar surveys over the same region and represent regions of basal water accumulation the best match between simulated basal hydrology properties and specularity content shows a strong correspondence in regions of distributed water in the asb troughs for both water depth and water pressure but weak correspondence between water depth and specularity content near the grounding line this may be due to the presence of several large channels draining over the grounding line into the head of totten ice shelf which are likely not as well represented in the specularity content data as distributed systems these channels may have a significant impact on melt and therefore the stability of totten ice shelf within asb regions of high water pressure and greater water accumulation correspond well with regions of faster ice flow suggesting some control of basal hydrology on ice dynamics in this region

impact of a localized source of subglacial discharge on the heat flux and submarine melting of a tidewater glacier a laboratory study abstractidealized laboratory experiments have been conducted in a two layer stratified fluid to investigate the leading order dynamics that control submarine melting and meltwater export near a vertical ice ocean interface as a function of subglacial discharge in summer the discharge of surface runoff at the base of a glacier subglacial discharge generates strong buoyant plumes that rise along the glacier front entraining ambient water along the way the entrainment enhances the heat transport toward the glacier front and hence the submarine melt rate increases with the subglacial discharge rate in the laboratory the effect of subglacial discharge is simulated by introducing freshwater at freezing temperature from a point source at the base of an ice block representing the glacier the circulation pattern observed both with and without subglacial discharge resembles those observed in previous observational and numerical studies buoyant plumes rise vertically until they find either their neutrally b

a model for tidewater glacier undercutting by submarine melting dynamic change at the marine terminating margins of the greenland ice sheet may be initiated by the ocean particularly where subglacial runoff drives vigorous ice marginal plumes and rapid submarine melting here we model submarine melt driven undercutting of tidewater glacier termini simulating a process which is key to understanding ice ocean coupling where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area thus the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice ocean interface we suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume likely promoting calving of ice above it remains unclear however whether undercutting proceeds sufficiently rapidly to influence calving at greenland s fastest flowing glaciers