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

late weichselian relative sea level changes and ice sheet history in southeast greenland relative sea level rsl observations from the margins of the greenland ice sheet gis provide information regarding the timing and rate of deglaciation and constraints on geophysical models of ice sheet evolution in this paper we present the first rsl record for the southeast sector of the gis based on field observations completed close to ammassalik the local marine limit is c 69 m above sea level asl and is dated to c 11 k cal yrs bp thousand calibrated years before present and is a minimum date for ice free conditions at the study site rsl fell to c 24 m asl by 9 5 k cal yrs bp and continued to fall at a decreasing rate to reach close to present by 6 5 k cal yrs bp our chronology agrees with radiocarbon dates from offshore cores that indicate ice free conditions on the adjacent mid shelf by 15 k cal yrs bp we compare the new rsl data with predictions generated using two recently published glaciological models of the gis that differ in the amount and timing of ice loading and unloading over our study area these two gis models are coupled to the same earth viscosity model and background global ice model to aid in the data model comparison neither model provides a close fit to the rsl observations based on a preliminary sensitivity study using a suite of earth viscosity models we conclude that the poor data model fit is most likely due to an underestimate of the local ice unloading an improved fit could be achieved by delaying the retreat of a thicker ice sheet across the continental shelf a thick ice sheet extending well onto the continental shelf is in agreement with other recent observations elsewhere in east and south greenland

aster level 1 data processing algorithm the advanced spaceborne thermal emission and reflection radiometer aster is an advanced multispectral imager with high spatial spectral and radiometric performance built for the eos am1 polar orbiting spacecraft aster covers a wide spectral region from visible to thermal infrared with 14 spectral bands to meet this wide spectral coverage aster has three optical sensing subsystems visible and near infrared vnir shortwave infrared swir and thermal infrared tir in addition the vnir subsystem has two telescopes nadir and backward telescopes for stereo data acquisition this aster instrument configuration with multitelescopes requires highly refined ground processing for the generation of level 1 data products that are radiometrically calibrated and geometrically corrected the algorithm developed for the aster level 1 data processing is described

thermal gradient and geochronology of a paleozoic high grade terrane in the northeastern cathaysia block south china abstract the chencai terrane in the northeastern cathaysia block forms part of the northeast extension of the paleozoic orogeny in south china recent field investigations have revealed the occurrence of high grade rocks in this terrane including granulite facies metapelites khondalites and orthopyroxene bearing granulites however the thermal gradients and metamorphic history of this region have not been well constrained thus impeding a better understanding of the geodynamic history of the paleozoic orogeny in south china here we report results from a systematic study on the metamorphic pt conditions and geochronology of the orthopyroxene granulites and metasedimentary rocks metapelites from the chencai area the orthopyroxene granulites preserve granulite facies peak assemblage of opx grt pl kfs qtz and a retrograde p t trajectory peak pt conditions are 845 860 c and 0 83 0 86 gpa corresponding to a thermal gradient of 30 c km which is much hotter than the normal thermal gradient of continental crust mineral compositions of the metasedimentary rocks re equilibrated during retrograde metamorphism so that the peak pt conditions recorded by these rocks are much lower than those obtained from the orthopyroxene granulite peak pt conditions are 710 720 c 0 57 0 58 gpa for garnet biotite gneiss and 760 780 c 0 60 0 62 gpa for biotite garnetite zircon u pb dating shows that this episode of granulite facies metamorphism occurred at 430 450 ma and the detrital population shows minor or no contribution from the basement rocks of the cathaysia block the neoproterozoic rocks occurring along the jiangnan belt are considered to have provided the sedimentary source as indicated by the two main age peaks of 0 79 ga and 0 83 ga from the detrital zircon cores lu hf isotope data on the zircons indicates extensive alteration and little new zircon growth during the paleozoic metamorphism the ehf t values and model ages tdm1 of zircons suggest that the source rocks involved juvenile crustal components with hf model ages of 1 1 1 5 ga sedimentation of such a continental shelf sequence as well as the high thermal gradient of 30 c km confirm the previously proposed continental arc formation and maturation model in the chencai region

holocene environmental evolution of the se greenland shelf north and south of the denmark strait irminger and east greenland current interactions abstract holocene climatic and paleoceanographic development of the se greenland shelf is studied from cores md99 2317 and md99 2322 at sites north and south of the denmark strait respectively lithofacies ird counts calcium carbonate percentages benthic and planktic foraminiferal assemblages and oxygen isotope analyses and summer ssts reveal significant climate variations in the holocene driven by declining solar insolation and its interaction with waning continental ice sheets and changing atmospheric pressure patterns large changes in the east greenland and irminger currents and the greenland ice sheet are manifested as a 4 part division of the holocene an early holocene cold interval dominated by melting of the greenland ice sheet and polar front retreat extends from 11 8 to 9 5 cal kyr bp a cold interval from 9 5 to 8 1 cal kyr bp involved episodic cooling of the irminger current resulting from the last phases of laurentide ice sheet deglaciation and delayed the holocene optimum off east greenland by 3 kyr relative to peak summer solar insolation which likely helped to limit the early holocene melting of the greenland ice sheet the period 8 1 3 5 cal kyr bp represents a climatic optimum interval of maximum greenland ice sheet retreat and strong irminger current inflow to the denmark strait between 6 8 and 3 5 cal kyr bp the irminger current penetrated further north into the nordic seas than has been observed in recent decades this signal is consistent with diminished northerly winds a weaker greenland high and contracted subpolar gyre by 5 cal kyr bp periods of increased polar water and decreasing salinity in the irminger current suggest a transition toward expansion of the subpolar gyre and increased polar water in the egc the neoglacial interval from 3 5 to 0 2 cal kyr bp was cold and variable with increased freshwater forcing from the arctic ocean advance of the greenland ice sheet and southward advance of the polar front enhanced northerly winds and a strengthened greenland high are consistent with thicker and more extensive polar water and greatly diminished northward advection of irminger current in the denmark strait

response of jakobshavn isbrae greenland to holocene climate change rapid fluctuations in the velocity of greenland ice sheet gis outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future this significant short term variability highlights the need for geologic records of preinstrumental gis margin fluctuations in order to better predict future gis response to climate change using 10 be surface exposure ages and radiocarbon dated lake sediments we constructed a detailed chronology of ice margin fluctuations over the past 10 k y for jakobshavn isbrae greenland9s largest outlet glacier in addition we present new estimates of corresponding local temperature changes using a continuous record of insect chironomidae remains preserved in lake sediments we find that following an early holocene advance just prior to 8 ka jakobshavn isbrae retreated rapidly at a rate of 100 m yr 1 likely in response to increasing regional and local temperatures ice remained behind its present margin for 7 k y during a warm period in the middle holocene with sustained temperatures 2 c warmer than today then the land based margin advanced at least 2 4 km between a d 1500 1640 and a d 1850 the ice margin near jakobshavn thus underwent large and rapid adjustments in response to relatively modest centennial scale holocene temperature changes which may foreshadow gis response to future warming

late quaternary sedimentary processes and ocean circulation changes at the southeast greenland margin a study has been made of late quaternary depositional processes and bottom current activity on the southeast greenland margin using seismic sub bottom profiling and deep tow side scan sonar data as well as sediment core information the seabed data demonstrate the occurrence of strong southerly bottom currents prevailing on the slope and rise well defined longitudinal bedforms indicate maximum mean near bottom current velocities of up to at least 1 0 m s at the depth stratum of labrador sea water 800 1500 m similarly strong currents occur in denmark strait overflow water dsow at the base of the slope whereas more basinward the maximum dsow flow speed is lower iceberg plow marks were found down to about 700 m water depth both at the shelf edge and on the lower slope and rise the seafloor morphology is indicative of downslope sediment transport and mass flow deposition which is concluded to be a typically glacial feature after generally more sluggish deep water circulation during the last glacial maximum dsow basin ventilation was re established shortly before 13 3 ka on the shelf in front of the retreating greenland ice margin permanent or semi permanent sea ice conditions prevailed until about 12 5 ka at that time increased irminger current activity had resulted in warming and east greenland current egc controlled iceberg drift increased no evidence was found for a return to extreme glacial conditions or a ceasing of dsow flow during the younger dryas abundant coarse ird collected at greater water depth from shallow sub seabed strata has a provenance mainly in the northern part of east greenland 68 73 n which demonstrates the existence of a pre holocene egc system initially extending to beyond the shelf edge

the deglacial history of southeast sector of the greenland ice sheet during the last glacial maximum the southeast sector of the greenland ice sheet is currently experiencing rapid changes in mass balance and ice sheet dynamics at low elevations however to what extent these changes are typical of the behaviour of this sector of the ice sheet is uncertain as our understanding of the longer term controls on ice sheet dynamics in this region is limited two models exist for last glacial maximum lgm ice sheet configuration in east greenland the first minimum model envisages a restricted ice sheet with exposed nunataks in coastal areas and limited ice extent onto the continental shelf fed by ice flowing through bedrock troughs a second maximum model entails a thicker ice sheet with limited coastal nunataks and ice filling the coastal valleys and extending across the entire continental shelf radiocarbon dates on foraminifera collected from seabed cores on the southeast greenland continental shelf suggest that the ice sheet reached a maximum extent at ca 22 kcal yr before retreating perhaps as early as ca 17 kcal yr bp and reaching the present coast at ca 10 kcal yr bp this paper presents the results of a study designed to test these different ice sheet models based on geomorphological mapping and cosmogenic isotope analyses in the torqulertivit imiat valley an area to the east of the coastal town of ammassalik 26al and 10be measurements on abraded bedrock surfaces in terrain above local trimlines yield surface exposure ages of ca 11 8 9 9 ka this demonstrates warm based glacial erosion of high level surfaces ca 740 m asl followed by trimline formation during deglaciation and intense postglacial weathering our work constrains minimum ice thickness during the lgm to at least 740 m and supports a maximum ice sheet model in this sector of the gis ice sheet retreat from the continental shelf to the southern edge of sermilik fjord is dated to ca 11 1 9 7 ka and helps to constrain the timing of the early holocene retreat of the helheim glacier ice stream within the torqulertivit imiat valley age determinations from glacially abraded terrain above the local marine limit on the coast 11 1 9 7 ka and those from 10 km up valley 12 8 9 9 ka suggest rapid surface ablation during these intervals coincident with rapid atmospheric warming observed in the greenland ice core records

rapid response of helheim glacier southeast greenland to early holocene climate warming recent changes in speed thinning and retreat rates of marine terminating outlet glaciers have raised concerns about the future stability of the greenland ice sheet establishing a longer term record of outlet glacier retreat rates is essential to provide a context for present day observations and to improve and constrain numerical models of outlet glacier behavior new exposure dating 10be of streamlined bedrock surfaces and glacial erratic boulders of sermilik fjord southeast greenland the present day drainage route of helheim glacier documents rapid retreat 80 m a 1 of this major marine terminating outlet glacier at the close of the last glaciation the glacier front retreated 80 km to within 20 km of the present day 2010 position of helheim glacier in 1 ka ca 10 8 0 3 ka ago retreat followed rapidly rising air temperatures at the start of the holocene and at this temporal resolution there is no evidence that fjord geometry influenced glacier behavior the significant response to climatic amelioration at the end of the last glacial suggests a high sensitivity to abrupt temperature increases which has major implications for the future stability of present day greenlandic outlet glaciers in a warming climate

unstable ice stream in greenland during the younger dryas cold event past present and future ice sheet stability is closely linked to the dynamic behavior of major draining ice streams and surrounding ice shelves while short observational records document the recent variability and acceleration of ice streams the long term dynamics of ice streams remain poorly documented here we date the pjetursson s moraine on disko island greenland to 12 2 0 6 ka and demonstrate that the jakobshavn isbrae ji ice stream collapsed during the middle of the younger dryas yd cold interval we suggest that this collapse was due to the incursion of warm subsurface water under the ice shelf fronting the ji ice stream as well as increased surface air temperature and sea surface temperature seasonality starting at the beginning of the yd cold interval the triggered acceleration of the land based ji and the delivery of icebergs into disko bugt potentially contributed to heinrich event 0 at the end of the yd the collapse of the ji ice stream 12 2 0 6 ka ago demonstrates that calving marine based ice margins can respond rapidly to environmental changes it provides a new benchmark for marine terminating ice stream models

technical methodology for aster global dem at the core of the technical methodology for creating the advanced spaceborne thermal emission and reflection radiometer aster global digital elevation model gdem is the procedure for generating a global set of 1 latitude by 1 longitude tiles containing dem data in geographic latitude and longitude coordinates and with one arc second postings from scene based aster dems the aster gdem is comprised of all tiles which include at least 0 01 land in them each containing 3601 by 3601 elevation data points the tiles are created by stacking all observed scene dem data matched geographically to the tile container selecting valid data for each pixel removing abnormal data values and then averaging the remaining selected valid data to assign as the tile elevation data valid earth surface elevation values typically clump within a 40 m range and are assumed to be lower in elevation than residual cloud outliers the filtering process which assigns the tile elevation data is one of the most important parts of the gdem generation system the median based selection method is designed to efficiently select the valid data for each pixel the combination of cloud masked and non cloud masked data is another important part of the process to assign accurate elevation data for each pixel because the cloud masking capability is not perfect the algorithm used to combine both data is described the postprocessing for inland water bodies is successfully carried out to yield a flattened elevation value this postprocessing is essential to assign unique elevation values for each inland water body gdem tile elevation data include some residual anomalies mostly in areas with fewer than three valid stacked input scenes the correction method using existing reference data also is described

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

landscape chronology and glacial history in thule northwest greenland abstract constraining past responses of ice sheets to changes in climate enhances our ability to predict future changes in ice extent and sea level here we employ surficial geologic mapping stratigraphic analysis radiocarbon dating of marine mollusks and analysis of cosmogenic 10 be in glacially deposited boulders to make inferences about past ice extents in thule northwest greenland our work shows the existence of two distinct diamict units in the thule area we infer that one diamict was deposited by the main greenland ice sheet while the second was deposited by a subsequent outlet glacier re advance boulders in the two diamicts n 13 and n 15 respectively have similar bimodal distributions of cosmogenic 10 be ages both diamicts have a group of younger 10 be ages as well as a more diffuse group of considerably older 10 be ages 20 30 ka many of the boulders likely contain nuclides inherited from previous periods of exposure suggesting that glacial ice in the thule region has been cold based and non erosive in the past the landscape chronology we develop suggests that deglaciation after the last glacial maximum occurred 10 8 ka and was later followed by a re advance of outlet glaciers possibly in concert with the 9 3 ka or 8 2 ka cold events

the east greenland continental margin 65 n since the last deglaciation changes in seafloor properties and ocean circulation nine gravity cores collected on the east greenland continental margin off kangerdlugssuaq fjord reveal a drastic decrease in average sedimentation rates from the cross shelf through the continental slope from 43 2 cm kyrs to 2 2 cm kyrs respectively since the last deglaciation beginning at 2g cm2kyrs at 4000 yrs b p both caco3 and non caco3 accumulation rates became high g cm2kyrs since 3000 yrs b p these rates distinctly decreased melting of glaciers and current activity which drastically changed in space and time controlled the terrigenous sediment input and thus the grain size distribution and the physical properties of sediments across the shelf these observations suggest that current winnowing on sediments is one of the dominant processes at present this is seen in the acoustic reflectivity and in the acoustically hard seafloor particularly at the upper continental slope in addition icebergs transported southward along the continental margin have scoured the sediment surface in water depths 350m

rapid ice retreat in disko bugt supported by 10be dating of the last recession of the western greenland ice sheet 10 be dating abstract due to rising sea levels and warming ocean currents marine based sectors of the greenland and ant arctic ice sheets are particularly vulnerable to warming climate reconstructions of the timing of marine based ice margin fluctuations in greenland during the early holocene can provide context for historical and modern observations of ice sheet change here we generate a 10 be chronology of ice sheet retreat through disko bugt western greenland our new chronology consisting of twelve 10 be ages from sites surrounding and within disko bugt fills a gap in the history of the western margin of the greenland ice sheet and allows for a continuous composite record of ice margin recession between the continental shelf break and the current margin we constrain the onset of ice margin retreat from outer disko bugt to 10 8 0 5 ka when combined with previous chronologies these results place the final greenland ice sheet retreat out of disko bugt onto land at jakobshavn isfjord and qasigiaanguit at 10 1 0 3 ka and later at 9 2 0 1 ka in southeastern disko bugt the rate of retreat during this time period is between w50e450 m a 1 for central disko bugt and w50e70 m a 1 along the southern coast of disko bugt

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

asynchronous response of marine terminating outlet glaciers during deglaciation of the fennoscandian ice sheet this is the accepted manuscript version published version is available at http dx doi org 10 1130 g35299 1

be 10 ages from central east greenland constrain the extent of the greenland ice sheet during the last glacial maximum traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the east greenland continental margin during the last glacial maximum lgm ice to the shelf break south of scoresby sund and ice extending no further than to the inner shelf at and north of scoresby sund we report new 10be ages from erratic boulders perched at 250 m a s l on the kap brewster peninsula at the mouth of scoresby sund the average 10be ages calculated with an assumed maximum erosion rate of 1 cm ka and no erosion respectively 17 3 2 3 ka and 15 1 1 7 ka overlap with a period of increased sediment input to the scoresby sund fan 19 15 ka the results presented here suggest that ice reached at least 250 m a s l at the mouth of scoresby sund during the lgm and add to a growing body of evidence indicating that lgm ice extended onto the outer shelf in northeast greenland

characterizing fluvial systems at basin scale by fuzzy signatures of hydromorphological drivers in data scarce environments despite the relevance of river hydromorphology hymo for integrated water resource management consistent geomorphic information at the scale of whole river basin is still scarce especially in emerging economies in this paper we propose a new scalable and globally applicable framework to analyze and classify fluvial systems in data scarce environments the framework is based on a data driven analysis of a multivariate data set of 6 key hydro morphologic drivers derived using freely available remote sensing information and several in situ hydrological time series core of the framework is a fuzzy classifier that assigns a characteristic signature of hymo drivers to individual river reaches we demonstrate the framework on the red river basin a large trans boundary river basin in vietnam and china where human induced morphological change concretely endangering local livelihoods is contrasted by very limited hymo information the derived hymo information covers spatial scales from the entire basin to individual reaches it conveys relevant information on subbasin hydro morphologic characteristic as well as on local geomorphologic forms and processes the fuzzy classifier successfully distinguishes abrupt from continuous downstream change and spatially dissects the river system in segments with homogeneous hydro morphologic forcings successful numerical modelling of morphologic forms and process rates based on the hymo signatures indicates that the multivariate basin scale classification captures relevant morphological drivers outperforms an analysis based on local drivers only and can support river management from diverse morphology related perspectives over a wide range of scales

revisiting greenland ice sheet mass loss observed by grace in this paper we discuss a new method for determining mass time series for 16 hydrological basins representing the greenland system gs whereby we rely on gravity recovery and climate experiment grace mission data in the same analysis we also considered observed mass changes over ellesmere island baffin island iceland and svalbard ebis the summed contribution of the complete system yields a mass loss rate and acceleration of 252 28 gt yr and 22 4 gt yr2 between march 2003 and february 2010 where the error margins follow from two glacial isostatic adjustment gia models and three processing centers providing grace monthly potential coefficient sets we describe the relation between mass losses in the gs and the ebis region and found that the uncertainties in all areas are correlated the summed contribution of ellesmere island baffin island iceland and svalbard yields a mass loss rate of 51 17 gt yr and an acceleration of 13 3 gt yr2 between march 2003 and february 2010 the new regional basin reconstruction method shows that the mass loss within the southeastern basins in the gs has slowed down since 2007 while mass loss in western basins increased showing a progression to the north of greenland

the influence of ice marginal setting on early holocene retreat rates in central west greenland ice sheet reconstructions from diverse ice margin settings spanning multiple millennia are needed to assess the reaction of the greenland ice sheet gris to millennial scale climatic forcing and to place historical records in a longer term context here we present 18 new cosmogenic 10 be exposure ages and five new radiocarbon ages that constrain the early holocene retreat of the gris in the disko bugt region in both a marine and a land based setting results indicate similar rates of early holocene retreat of 40 50m a 1 from transects in torsukattak fjord marine setting and the naternaq area land based setting we compile seven previously published chronologies of deglaciation from west greenland which yield early holocene retreat rates ranging from 10 to 65m a 1 similar to those determined for our two study areas this work demonstrates that when averaged on millennial timescales retreat rates were remarkably similar along the western gris margin furthermore the retreat rates calculated here demonstrate that terrestrial sectors of ice sheets can retreat at net rates comparable to their marine counterparts copyright 2015 john wiley sons ltd

fluctuations of local glaciers in greenland during latest pleistocene and holocene time abstract this paper is the first to summarize research on fluctuations of local glaciers in greenland e g ice caps and mountain glaciers independent of the greenland ice sheet during latest pleistocene and holocene time in contrast to the extensive data available for fluctuations of the greenland ice sheet surprisingly little data exist to constrain local glacier extents much of the available research was conducted prior to wide spread use of ams radiocarbon dating and the advent of surface exposure and luminescence dating although there is a paucity of data generally similar patterns of local glacier fluctuations are observed in all regions of greenland and likely reflect changes in paleoclimate which must have influenced at least the margins of the inland ice absolute age data for late glacial and early holocene advances of local glaciers are reported from only two locations disko island and the scoresby sund region subsequent to late glacial or early holocene time most local glaciers were smaller than at present or may have disappeared completely during the holocene thermal maximum in general local glacier advances that occurred during historical time 1200 1940 ad are the most extensive since late glacial or early holocene time historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last 100 yrs in all but one area north greenland local glaciers are currently receding from historical extents

4 1 5 c abrupt warming 11 270 yr ago identified from trapped air in greenland ice nitrogen and argon isotopes in air trapped in a greenland ice core gisp2 show two prominent peaks in the interval 11 800 10 800 b p which indicate two large abrupt warming events the first abrupt warming 10 4 c is the widely documented event at the end of the younger dryas here we report on the second abrupt warming 4 1 5 c which occurred at the end of a short lived cooler interval known as the preboreal oscillation 11 270 30 b p a rapid snow accumulation increase suggests that the climatic transition may have occurred within a few years the character of the preboreal oscillation and the subsequent abrupt warming is similar to the dansgaard oeschger d o events in the last glacial period suggestive of a common mechanism but different from another large climate change at 8 200 b p in which cooling was abrupt but subsequent warming was gradual the large abrupt warming at 11 270 b p may be considered to be the final d o event prior to the arrival of the present stable and warm epoch

the deglaciation of coastal areas of southeast greenland large marine terminating glaciers around the margins of the greenland ice sheet have retreated accelerated and thinned over the last two decades relatively little is known about the longer term behaviour of the greenland ice sheet yet this information is valuable for assessing the significance of modern changes we address this by reporting 11 new beryllium 10 10be exposure ages from previously uninvestigated coastal areas across southeast greenland the new ages are combined with existing data from the region to assess the timing of glacier retreat after the last glacial maximum the results show that deglaciation occurred first in the north of the region 68 n and progressed southwards this north south progression is attributed to the influence of the warm irminger current on the ice margin areas in the south of the region were isolated from the warm waters by the shallow bathymetry of the continental shelf this demonstrates that oceanographic forcing paced the deglaciation of southeast greenl

ice flow patterns and precise timing of ice sheet retreat across a dissected fjord landscape in western norway abstract we reconstruct patterns of ice flow and retreat of the southwestern scandinavian ice sheet from 2900 field observations of glacial striae and elevation measurements of 60 ice marginal deltas from a high resolution lidar dem during the last glacial maximum ice flow was towards the west across the entire area including across several hundred meter deep north south oriented fjords during deglaciation ice flow adjusted to topography and the dominant flow direction switched towards the south west we use a shoreline diagram constructed from relative sea level curves to establish the age of each delta which allows us to constrain the timing of retreat with almost decadal precision rapid ice sheet retreat commenced at the onset of the holocene at 11 600 cal years bp retreat rates were 160 m a 1 in the deepest fjords 60 80 m a 1 in shallower fjords and even slower for land terminating margins the fastest retreat rates 240 m a 1 and 340 m a 1 were experienced in the largest fjords hardangerfjorden and sognefjorden which border the study area to the south and north crosscutting glacial striae indicate that calving bays developed during retreat along the widest fjords the combination of complex fjord topography with fast ice margin retreat by iceberg calving led to isolation of ice remnants on islands and peninsulas a process that accelerated the overall rate of deglaciation ice margin retreat paused between 11 300 11 100 cal years bp probably due to cooling during the preboreal oscillation

multi phased deglaciation of south and southeast greenland controlled by climate and topographic setting abstract to put recent greenland ice sheet gris ice loss into a longer term context we must understand its behavior during late glacial and early holocene warming previous results seem to suggest that there is a large contrast in the timing of deglaciation between south and southeast greenland however because of lack of available data in particular in southeast greenland it is difficult to assess how the ice sheet responded to major late glacial and early holocene climate changes in this study we use 41 new 10be ages to constrain the deglaciation chronology in 12 new locations from the coast to the present ice margin in south and southeast greenland we find that south greenland south of 61 5 n deglaciated between 14 8 and 11 9 ka whereas southeast greenland 61 5 n to 68 2 n deglaciated between 11 4 and 11 3 ka the deglaciation of the coastal low intermediate topography in south greenland coincides with increased air surface temperatures during the bolling allerod with fjords continuing to deglaciate into the early holocene in contrast the ice sheet persisted at the coast until the late glacial and early holocene in southeast greenland likely because of increased precipitation in the high alpine topography and fjord geometry and bathymetry e g width of fjords and presence of sills this multi phased deglaciation demonstrates a contrasting response of the southern gris to changes in climate and variations in topographic setting and that the spatial deglaciation of the gris was complex and likely did not respond to a single external climate forcing

spread of ice mass loss into northwest greenland observed by grace and gps 1 greenland s main outlet glaciers have more than doubled their contribution to global sea level rise over the last decade recent work has shown that greenland s mass loss is still increasing here we show that the ice loss which has been well documented over southern portions of greenland is now spreading up along the northwest coast with this acceleration likely starting in late 2005 we support this with two lines of evidence one is based on measurements fromthegravityrecoveryandclimateexperiment grace satellite gravity mission launched in march 2002 the other comes from continuous global positioning system gps measurements from three long term sites on bedrock adjacent to the ice sheet the grace results provide a direct measure of mass loss averaged over scales of a few hundred km the gps data are used to monitor crustal uplift caused by ice mass loss close to the sites the grace results can be used to predict crustal uplift which can be compared with the gps data in addition to showing that the northwest ice sheet margin is now losing mass the uplift results from both the gps measurements and the grace predictions show rapid acceleration in southeast greenland in late 2003 followed by a moderate deceleration in 2006 because that latter deceleration is weak southeast greenland still appears to be losing ice mass at a much higher rate than it was prior to fall 2003 in a more general sense the analysis described here demonstrates that gps uplift measurements can be used in combination with grace mass estimates to provide a better understanding of ongoing greenland mass loss an analysis approach that will become increasingly useful as long time spans of data accumulate from the 51 permanent gps stations recently deployed around the edge of the ice sheet as part of the greenland gps network gnet citation khan s a j wahr m bevis i velicogna and e kendrick 2010 spread of ice mass loss into northwest greenland observed by grace and gps geophys res lett 37 l06501 doi 10 1029 2010gl042460

rapid early holocene ice retreat in west greenland abstract the possible demise of the greenland ice sheet and its effect on global sea level rank among the most serious climate threats to society to improve our knowledge about the future behaviour of the ice margin we studied the ice sheet s response to early holocene warming in west greenland using 47 cosmogenic 10 be exposure ages 26 optically stimulated luminescence ages as well as 15 new and 28 previously published radiocarbon ages paired bedrock and boulder ages show that the entire area was covered by warm based ice during the last glacial maximum lgm although glacial erosion was insufficient to completely remove the upper rock surface containing 10 be inherited from a previous period of exposure in bedrock samples above an elevation of 800 m our compilation of 10 be and 14 c ages demonstrates that the ice sheet retreated from the outer coast to the present ice margin between c 11 4 and 10 4 cal ka bp in the godthabsfjord system and between 10 7 0 6 and 10 1 0 4 ka ago in buksefjord whereas the coast at sermilik became ice free at c 10 5 cal ka bp we find no significant changes in the retreat rates between the deep godthabsfjord system and the buksefjord sermilik region which is characterized by only a few narrow and shallow fjords however deglaciation was initiated c 700 900 years earlier in the godthabsfjord system indicating that the deep fjords probably triggered land based deglaciation by dynamic ice loss leading to an overall rapid early holocene ice retreat and drawdown of the ice sheet in west greenland these results demonstrate that even if there was a topographic control on the onset of deglaciation fast ice retreat is not restricted to deep fjord systems but may occur independently of the topographic setting

rapid early holocene retreat of a laurentide outlet glacier through an arctic fjord marine terminating outlet glaciers control the stability of ice sheets exposure ages and radiocarbon dates show that an arctic outlet glacier of the laurentide ice sheet rapidly retreated about 9 500 years ago and imply strong feedbacks between bathymetry and ice movement

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

accurate coastal dem generation by merging aster gdem and icesat glas data over mertz glacier antarctica abstract mertz glacier mg calved in february 2010 and a 70 years calving cycle of mg was reported recently because of the shallow mertz bank to better investigate the calving process a high accurate surface digital elevation model dem with accurate date marker over mg is urgently required for numerical modeling especially over the ice tongue however it is quite challenging to generate an accurate dem over high relief and steep slope regions to solve this problem a new method for accurate coastal dem production by merging aster gdem and icesat glas data is designed which can effectively discriminate accurate elevation data from aster gdem then a dem corresponding to the end of 2002 over mg is generated which has an accuracy of 0 99 17 50 m this dem is several times better in accuracy than the original aster gdem accuracy 8 17 54 31 m and two new characteristics of aster gdem have been found through analysis first aster gdem has elevation bias varying from 23 m to 28 m spatially correlated to aster ground tracks which was most probably caused by uncertainty of attitude measurements of aster second aster gdem grids with stacking number 4 can be effectively adjusted by ground control points so as to improve elevation accuracy additionally this dem has the best accuracy by comparing with other dems ramp dem 47 71 91 61 m icesat glas dem 1 01 30 33 bamber dem 1 07 33 04 m bedmap 2 dem 9 19 48 34 m and cryosat 2 dem 5 42 32 02 m the high performance of our dem in accuracy indicates that our method is effective and has a potential to be widely used to improve existing aster gdem along antarctic coast

freshwater forcing from the greenland ice sheet during the younger dryas evidence from southeastern greenland shelf cores abstract we present evidence for freshwater forcing from the greenland ice sheet during the last deglaciation explore its potential involvement in the younger dryas cooling and investigate the role of atlantic intermediate water in the retreat of the greenland ice sheet paleoceanographic conditions and ice sheet retreat history are interpreted from ird stable isotopes and foraminiferal assemblages in sediment cores retrieved along the length of the kangerlussuaq trough a cross shelf trough on the southeast greenland shelf the vedde ash 11 980 cal yr bp which is a marker bed within the younger dryas and the saksunarvatn tephra 10 180 cal yr bp an early holocene marker horizon have been located in these cores the tephra markers and calibrated 14c dates on foraminifers and molluscs provide the basis for the age models in the cores the stable isotope records indicate a 0 5 depletion of the 18o between 13 4 and 12 8 cal ka bp a pronounced light isotope event exceeding 1 5 on the inner shelf and 0 8 on the outer shelf occurs at the beginning of the younger dryas cold period 12 8 cal ka bp and ends by 12 cal ka bp immediately before deposition of the vedde ash the light isotope spikes are interpreted as glacial meltwater spikes associated with retreat of the adjacent greenland ice sheet associated with the light isotope events are episodic high percentages of the atlantic intermediate water benthic foraminiferal species cassidulina neoteretis which continue from the bolling allerod into the younger dryas high percentages of this species suggest that atlantic intermediate water entered the kangerlussuaq trough during the allerod and the younger dryas via the irminger current as it does today we conclude that advection of atlantic intermediate water into the kangerlussuaq trough south of the denmark strait promoted melting and retreat of the marine portions of the greenland ice sheet explaining the observed glacial meltwater spikes

using proglacial threshold lakes to constrain fluctuations of the jakobshavn isbrae ice margin western greenland during the holocene abstract the future response of the greenland ice sheet gis and its potential contribution to sea level rise are uncertain rapid changes of greenland s outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future this significant short term variability highlights the need for longer term geologic e g holocene records of ice margin fluctuations however a major challenge with reconstructing the gis during the holocene stems from it having been smaller than it is at present thus traditional glacial geologic approaches are not suitable we use radiocarbon dated sediment sequences from seven proglacial threshold lakes spanning 50 km of the western gis margin near jakobshavn isbrae to constrain the timing of early holocene deglaciation the duration that this sector of the western gis was smaller than its present configuration and the timing of its advance during neoglaciation our reconstructions suggest deglaciation 7300 cal yr bp minimum ice extent 6000 5000 cal yr bp and smaller than present ice configuration until at least 2300 cal yr bp for the ice margin south of jakobshavn isbrae and until 400 cal yr bp for the ice margin north of jakobshavn isbrae one relatively large proglacial lake that became briefly ice free during the middle holocene lies in a catchment that likely extends 10s of km inland beneath the gis suggesting significant middle holocene retreat of this portion of the gis the overall pattern of ice sheet change is inconsistent with existing ice sheet model reconstructions for this region but is consistent with numerous paleoclimate proxy and relative sea level data these continuous lacustrine records corroborate but provide closer age control than existing non continuous records of radiocarbon dated reworked bivalves from historical moraines in the region reconstructing ice margin change from proglacial threshold lakes is one of few approaches with the potential to constrain smaller than present ice sheet extent

the deglaciation and neoglaciation of upernavik isstrom greenland abstract we constrain the history of the greenland ice sheet margin during the holocene at upernavik isstrom a major ice stream in northwestern greenland radiocarbon dated sediment sequences from proglacial threshold lakes adjacent to the present ice margin constrain deglaciation of the sites to older than 9 6 0 1 ka this age of deglaciation is confirmed with 10 be ages of 9 9 0 1 ka from an island adjacent to the historical ice position the lake sediment sequences also constrain the ice margin to have been less extensive than it is today for the remainder of the holocene until 1100 to 700 yr ago when it advanced into two lake catchments the ice margin retreated back out of these lake catchments in the last decade the early holocene deglaciation in melville bugt one of few locations around greenland where a vast stretch of the current ice margin is marine based preceded deglaciation in most other parts of greenland earlier deglaciation in this ice sheet sector may have been caused by additional ablation mechanisms that apply to marine based ice margins furthermore despite ice sheet models depicting this sector of greenland as relatively stable throughout the holocene our data indicate a 20 km advance retreat cycle within the last millennium

glacier specific elevation changes in parts of western alaska the meltwater from glaciers in alaska contributes strongly to global sea level rise but accurate determination is challenging as only two comparatively small glaciers have long term measurements of annual mass balance gulkana and wolverine simple upscaling of their values to the entire region is error prone as their representativeness is unknown and might be biased alternatively differencing digital elevation models dems from two epochs provides overall volume changes for a longer period of time that can be converted to mass changes using appropriate density assumptions here we combine outlines from two glacier inventories to determine glacier specific elevation changes over a 50 year period for 3180 glaciers in western alaska using dem differencing this allows us to determine the representativeness of the land terminating gulkana and wolverine glaciers for the entire region and to exclude calving glaciers marine and lacustrine from the sample mean changes for all land terminating lake terminating and tidewater glaciers are 0 23 0 44 0 63 0 40 and 0 64 0 66 m a 1 respectively and 0 7 and 0 6 m a 1 for the two mass balance or benchmark glaciers thus fortuitously their changes better represent calving glaciers and the overall mean 0 63 1 14 m a 1 than the change of land terminating glaciers i e they are not representative for their own type different methods of considering potential dem artefacts provide variable mean changes but the same general result

a new inventory of mountain glaciers and ice caps for the antarctic periphery although the glaciers in the antarctic periphery make up a large fraction of all mountain glaciers and ice caps on earth a detailed glacier inventory of the region is lacking we compile such an inventory recording areas area altitude distributions terminus characteristics and volume estimates glaciers on the mainland are excluded the inventory is derived from the antarctic digital database and some manual digitization we additionally rely on satellite imagery digital elevation models and a flowshed algorithm to classify ice bodies we find 1133 ice caps and 1619 mountain glaciers covering a total of 132 867 6643 km 2 estimated total volume corresponds to 0 121 0 010 m sea level equivalent of the total glacier area 99 drains either into ice shelves 63 or into the ocean 36 the inventory will provide a database for glacier mass balance assessments modelling and projections and help to reduce the uncertainties in previous studies

active tectonics in 4d high resolution abstract with a little more than 100 years since the publication of seminal and field defining investigations active tectonics is still a relatively young sub discipline of structural geology this research field addresses the accumulation of strain due to plate tectonic motion and more importantly release thereof through the occurrence of earthquakes or other strain releasing events in that regard active tectonics aims to characterize the incremental steps of plate tectonics determining earthquake chronologies fault slip rates and other common objectives importantly feed into our understanding of for example fault mechanics and crustal rheology characterizing the recurrence of large and potentially devastating earthquakes is further motivated by seismic hazard assessment and risk mitigation the primary data source in active tectonics is surface and shallow subsurface evidence of faulting presenting itself in topographic and stratigraphic data sets respectively field observations and air photo interpretation of displaced stratigraphic and geomorphic markers were used almost 40 years ago to formulate end member models of earthquake recurrence technological developments since then especially within the last two decades have dramatically increased the abundance and resolution of topographic data sets and the ability to date stratigraphic units and geomorphic surfaces enabling the formulation of better informed conceptual models of earthquake recurrence here we provide an overview of the high resolution topographic data sets and dating methods that enabled the recent advances of active tectonics

glacial history and landscape evolution of southern cumberland peninsula baffin island canada constrained by cosmogenic 10be and 26al since the first application of cosmogenic nuclides to the study of glacial history and processes in 1990 increasing numbers of studies have used a variety of cosmogenic isotopes to quantify the exposure age and erosion rate of glaciated landscapes however obtaining chronological data from glaciated landscapes once covered by cold based nonerosive ice is challenging because these surfaces violate assumptions associated with simple cosmogenic exposure dating nonerosive glacial ice fails to completely remove nuclides produced during previous periods of exposure leaving behind rock surfaces with complex multigenetic nuclide inventories here we constrain the glacial history landscape evolution and efficiency of subglacial erosion in the pangnirtung fiord region of southern baffin island using over 300 paired analyses of in situ cosmogenic 10be and 26al simple exposure ages are 6 3 160 ka for 10be n 152 and 4 3 124 ka for 26al n 153 paired bedrock boulder samples have discordant ages simple exposure ages generally increase with elevation 10be and 26al ages for the same sample disagree and both boulders and bedrock yield multimodal age distributions all patterns suggestive of limited subglacial erosion measured 26al 10be ratios indicate that about one third of the samples in the data set experienced at least one period of pre holocene exposure followed by burial with limited erosion modeled two isotope minimum limiting exposure durations are as high as hundreds of thousands of years and minimum limiting burial durations range up to millions of years implying that parts of southern baffin island have been preserved beneath nonerosive glacial ice for much if not all of the quaternary a subset of the samples contains few nuclides inherited from prior periods of exposure and is thus useful for constraining the chronology of the most recent deglaciation using these samples we infer that deglaciation of most of the landscape occurred ca 11 7 ka and that the duval moraines a prominent feature of the last deglaciation formed ca 11 2 ka

a 10be chronology of lateglacial and holocene mountain glaciation in the scoresby sund region east greenland implications for seasonality during lateglacial time abstract thirty eight new cosmogenic 10 be exposure ages from the scoresby sund region of east greenland indicate that prominent moraine sets deposited by mountain glaciers date from 780 to 310 yr approximately during the little ice age from 11 660 to 10 630 yr at the end of the younger dryas cold interval or during preboreal time and from 13 010 to 11 630 yr during lateglacial time equilibrium line altitudes elas interpreted from lateglacial to early holocene moraines indicate summertime cooling between 3 9 and 6 6 c relative to today s value much less than the extreme younger dryas cooling registered by greenland ice cores mean annual temperatures of 15 c colder than today s value this apparent discrepancy between paleotemperature records supports the contention that younger dryas cooling was primarily a wintertime phenomenon 10 be ages of lateglacial and holocene moraines show that mountain glaciers during the little ice age were more extensive than at any other time since the early holocene epoch in addition 10 be ages of lateglacial moraines show extensive reworking of boulders with cosmogenic nuclides inherited from prior periods of exposure consistent with our geomorphic observations and cosmogenic exposure dating studies in other arctic regions

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

paired bedrock and boulder 10be concentrations resulting from early holocene ice retreat near jakobshavn isfjord western greenland we measured in situ cosmogenic 10 be in 16 bedrock and 14 boulder samples collected along a 40 km transect outside of and normal to the modern ice margin near sikuijuitsoq fjord in central west

ice sheet extent and early deglacial history of the southwestern sector of the greenland ice sheet the offshore and coastal geomorphology of southwest greenland records evidence for the advance and decay of the greenland ice sheet during the last glacial maximum regional ice flow patterns in the vicinity of sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf with an ice stream centred over holsteinsborg dyb high level periglacial terrain composed of blockfield and tors is dated to between 101 and 142 ka using 26al and 10be cosmogenic exposure ages these limit the maximum surface elevation of the last glacial maximum ice sheet in this part of southwest greenland to ca 750 810 m asl and demonstrate that terrain above this level has been ice free since mis 6 last glacial maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the outer hellefisk moraines exposure dates record ice surface thinning from 21 0 to 9 8 ka with downwasting rates varying from 0 06 to 0 12 m yr 1 this reflects strong surface ablation associated with increased air temperatures running up to the bolling interstadial gis1e at ca 14 ka and later marine calving under high sea levels the relatively late retreat of the itilleq ice stream inland of the present coastline is similar to the pattern observed at jakobshavn isbrae located 250 km north in disko bugt which also retreated from the continental shelf after ca 10 ka we hypothesise that the ice streams of west greenland persisted on the inner shelf until the early holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet

rapid response of helheim glacier in greenland to climate variability over the past century during the early 2000s the greenland ice sheet experienced the largest ice mass loss of the instrumental record 1 largely as a result of the acceleration thinning and retreat of large outlet glaciers in west and southeast greenland 2 5 the quasi simultaneous change in the glaciers suggests a common climate forcing increasing air 6 and ocean 7 8 temperatures have been indicated as potential triggers here we present a record of calving activity of helheim glacier east greenland that extends back to about ad 1890 based on an analysis of sedimentary deposits from sermilik fjord where helheim glacier terminates specifically we use the annual deposition of sand grains as a proxy for iceberg discharge our record reveals large fluctuations in calving rates but the present high rate was reproduced only in the 1930s a comparison with climate indices indicates that high calving activity coincides with a relatively strong influence of atlantic water and a lower influence of polar water on the shelf off greenland as well as with warm summers and the negative phase of the north atlantic oscillation our analysis provides evidence that helheim glacier responds to short term fluctuations of large scale oceanic and atmospheric conditions on timescales of 3 10 years the forcings behind the rapid increase in mass loss from the greenland ice sheet in the early 2000s ref 1 are still debated it is unclear whether the mass loss will continue in the near future and ifso atwhatrate theseuncertaintiesareaconsequenceofour limited understanding of mechanisms regulating ice sheet variability and the response of fast flowing outlet glaciers to climate variability in southeast greenland helheim glacier one of the regions largestglaciers thinned acceleratedandretreatedduringtheperiod 20032005

changes in ice front position on greenland s outlet glaciers from 1992 to 2007 1 previous studies in greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss raising greenland s contribution to sea level rise we examined ice front changes of 203 tidewater glaciers land terminating glaciers and glaciers terminating with ice shelves to understand greenland glacier behavior over three periods 1992 2000 2000 2006 and 2006 2007 we observed synchronous ice sheet wide increases in tidewater retreat during 2000 2006 relative to 1992 2000 coinciding with a 1 1 c increase in mean summer temperature at coastal weather stations rates of retreat for the southeast and east slowed during 2006 2007 when temperatures were slightly cooler than the 2000 2006 average our work suggests that regional greenland tidewater retreat responds strongly to climate change with higher temperatures corresponding to increasing retreat and helps confirm a link between ice thickness velocity and ice front position

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

the second chinese glacier inventory data methods and results the second chinese glacier inventory was compiled based on 218 landsat tm etm scenes acquired mainly during 2006 10 the widely used band ratio segmentation method was applied as the first step in delineating glacier outlines and then intensive manual improvements were performed the shuttle radar topography mission digital elevation model was used to derive altitudinal attributes of glaciers the boundaries of some glaciers measured by real time kinematic differential gps or digitized from high resolution images were used as references to validate the accuracy of the methods used to delineate glaciers which resulted in positioning errors of 10 m for manually improved clean ice outlines and 30 m for manually digitized outlines of debris covered parts the glacier area error of the compiled inventory evaluated using these two positioning accuracies was 3 2 the compiled parts of the new inventory have a total area of 43 087 km 2 in which 1723 glaciers were covered by debris with a total debris covered area of 1494 km 2 the area of uncompiled glaciers from the digitized first chinese glacier inventory is similar to 8753 km 2 mainly distributed in the southeastern tibetan plateau where no images of acceptable quality for glacier outline delineation can be found during 2006 10

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

hydraulic correction method hcm to enhance the efficiency of srtm dem in flood modeling abstract digital elevation model dem is one of the most important controlling factors determining the simulation accuracy of hydraulic models however the currently available global topographic data is confronted with limitations for application in 2 d hydraulic modeling mainly due to the existence of vegetation bias random errors and insufficient spatial resolution a hydraulic correction method hcm for the srtm dem is proposed in this study to improve modeling accuracy firstly we employ the global vegetation corrected dem i e bare earth dem developed from the srtm dem to include both vegetation height and srtm vegetation signal then a newly released dem removing both vegetation bias and random errors i e multi error removed dem is employed to overcome the limitation of height errors last an approach to correct the multi error removed dem is presented to account for the insufficiency of spatial resolution ensuring flow connectivity of the river networks the approach involves a extracting river networks from the multi error removed dem using an automated algorithm in arcgis b correcting the location and layout of extracted streams with the aid of google earth platform and remote sensing imagery and c removing the positive biases of the raised segment in the river networks based on bed slope to generate the hydraulically corrected dem the proposed hcm utilizes easily available data and tools to improve the flow connectivity of river networks without manual adjustment to demonstrate the advantages of hcm an extreme flood event in huifa river basin china is simulated on the original dem bare earth dem multi error removed dem and hydraulically corrected dem using an integrated hydrologic hydraulic model a comparative analysis is subsequently performed to assess the simulation accuracy and performance of four different dems and favorable results have been obtained on the corrected dem

cosmogenic exposure age evidence for rapid laurentide deglaciation of the katahdin area west central maine usa 16 to 15 ka abstract katahdin the highest peak in maine and part of the second highest mountain range in new england provides an opportunity to assess the timing and style of continental ice sheet surface lowering during deglaciation we collected 14 samples from boulders on the adjacent basin ponds moraine from bedrock and boulders on the upper part of the mountain and from boulders in the surrounding area to estimate the age at which they were exposed by deglaciation of the laurentide ice sheet measurements of in situ produced 10be which are consistent with measurements of 26al indicate that the katahdin edifice became exposed from under ice by 15 3 2 1 ka n 6 an age indistinguishable from the adjacent basin ponds moraine 16 1 1 2 ka n 5 a boulder in the lowlands several km south of the moraine dates to 14 5 0 8 ka and a boulder deposited at pineo ridge about 170 km se of katahdin dates to 17 5 1 1 ka these data show that samples collected over an elevation range of 1 6 km and a distance of 170 km all have exposure ages that are indistinguishable within uncertainties together these data suggest that the laurentide ice sheet surface dropped rapidly and the ice sheet margin retreated quickly across maine between about 16 and 15 ka perhaps influenced by calving of the marine based ice sheet in the st lawrence lowlands to the north and the penobscot basin to the south

evidence for the asynchronous retreat of large outlet glaciers in southeast greenland at the end of the last glaciation recent rapid changes in the marine terminating sectors of the greenland ice sheet gris have prompted concerns about the future stability of the ice sheet long term records of ice sheet behaviour provide valuable context to assess the magnitude of current change and may help resolve the mechanisms driving deglaciation we report 23 new 10be exposure ages which constrain the deglacial history of two large fjord systems in southeast se greenland we compare our chronologies with existing data from the centre of the sector to examine the timing and style of deglaciation at a regional scale glacial erratic 10be exposure ages demonstrate that kangerdlugssuaq fjord deglaciated at 11 8 ka at the end of the younger dryas yd 12 8 11 6 ka retreat at kangerdlugssuaq fjord coincided with known incursion of the warm irminger current ic onto the continental shelf this is inferred to have initiated retreat comparison with recently published results from sermilik fjord and new 10be ages from bernstorffs fjord indicates deglaciation occurred 1 ka later in the south of the se region sermilik fjord 10 9 ka and bernstorffs fjord 10 4 ka deglaciated later retreat likely occurred in response to dramatic climatic amelioration at the termination of the yd stadial we suggest that the disparate timing of deglaciation across the se region may be primarily explained by the varying influence of the warm ic glaciers in southern se greenland were isolated from warm atlantic waters during the yd by complex shelf bathymetry in all fjord settings ice retreat was rapid and persistent consistent with the absence of geomorphological evidence for stillstand or readvance events ice retreat was accompanied by rapid thinning and likely continued to well within present day ice sheet margins glacial erratic 10be age determinations and geomorphological observations show no evidence for holocene readvance events prior to the little ice age lia