present day vertical crustal deformations in west greenland from repeated gps observations summary a gps network consisting of 10 sites was established in the ice free area of west greenland and was observed for the first time in 1995 in 2002 a complete re observation was carried out these repeated gps observations served as a basis for the determination of vertical crustal deformations the data analysis was performed using the bernese software version 5 0 for the central site kangerlussuaq a negative uplift rate subsidence of 3 1 1 1 mm yr 1 was obtained related to the reference frame igb00 the regional pattern is characterized by an east west gradient of up to 4 mm yr 1 between the outer coast and the subsiding area along the present ice margin which can be explained to a great extent as a result of the late holocene re advance of the greenland ice sheet relative sea level changes could be calculated taking the present eustatic sea level rise into account the present day sea level rises at the outer coast between maniitsoq and paamiut and in the large fjords with increasing rates of more than 4m m yr 1 in their innermost parts these findings are in agreement with the general picture obtained from geomorphological and archaeological research for sisimiut and the disko bay area the present sea level change is almost zero whereas the crustal uplift rate for ilulissat was observed to be 1 6 mm yr 1 w econclude that this present vertical uplift rate in ilulissat is affected by the retreat of the ice margin during the last 150 yr and the present negative mass balance of the jakobshavn isbrae and its drainage basin

quaternary redox transitions in deep crystalline rock fractures at the western margin of the greenland ice sheet when planning for long term deep geological repositories for spent nuclear fuel knowledge of processes that will influence and change the sub surface environment is crucial for repositories in nor

controls upon the last glacial maximum deglaciation of the northern uummannaq ice stream system west greenland the uummannaq ice stream system uiss was a convergent cross shelf ice stream system that operated in west greenland during the last glacial maximum lgm this paper presents new evidence constraining the geometry and evolution of the northern sector of the uiss and considers the factors controlling its dynamic behaviour geomorphological mapping 21 new terrestrial cosmogenic nuclide tcn exposure ages and radiocarbon dating constrain lgm warm based ice stream activity in the north of the system up to 1400 m a s l intervening plateaux areas either remained ice free or were covered by cold based icefields beyond the inner fjords topography and bathymetry forced ice flow southwards into the uummannaq trough where it coalesced with ice from the south and formed the trunk zone of the uiss deglaciation of the uiss began at 14 9 cal ka bp rapid retreat from the lgm limit was forced by an increase in air temperatures and rising sea level enhanced by the bathymetric over deepening of the uummannaq and igdlorssuit sund troughs ice reached the inner fjord confines in the northern uummannaq area by 11 6 ka and experienced an ice marginal stabilisation in rink karrat fjord for up to 5 ka this was a function of topographic constriction and bathymetric shallowing and occurred despite continued climatic forcing in the neighbouring ingia fjord this did not occur following this period of stability ice within rink karrat fjord retreated reaching the present ice margin or beyond after 5 ka the presence of a major ice stream within a mid fjord setting during the mid holocene and the holocene thermal maximum 11 5 ka is in direct contrast to records of other ice streams throughout west greenland which suggest ice had retreated beyond its present margin by 9 7 ka this demonstrates the potential importance of topographic control on calving margin stability and its ability to override climatic forcing

increased aridity during the early holocene in west greenland inferred from stable isotopes in laminated lake sediments abstract palaeoclimatic inferences from the greenland ice cores suggest that holocene climate was relatively uniform the ice core records primarily reflect hemispheric temperature related climate processes whereas lakes tend to reflect regional scale climatic variability stable isotopes in closed basin lakes are sensitive to changes in effective precipitation here we report stable isotope evidence 18 o and 13 c records from authigenic calcite in laminated lake sediments from two oligosaline closed basin lakes in southern west greenland sondre stromfjord the stable isotope profiles indicate a dynamic early to mid holocene climate as a strongly negative precipitation evaporation balance from 7000 to 5600 cal yr bp lowered lake levels throughout the region this interpretation of the stable isotope data is supported by a survey of modern lake water isotopic composition and fossil shorelines around many closed basin saline lakes which indicate higher lake levels in the past the increased aridity during the early holocene resulted from a shift in regional circulation patterns in the davis straits baffin bay area enhanced stability of the west greenland depression and the situation of a regional trough over the sondre stromfjord area caused weakened westerly airflow and strengthened outflow i e winds blowing off the ice sheet resulting in reduced precipitation in the region decreased precipitation coupled with higher insolation probably caused the negative precipitation evaporation balance

the response of the southern greenland ice sheet to the holocene thermal maximum to determine the long term sensitivity of the greenland ice sheet to a warmer climate we explored how it responded to the holocene thermal maximum 8 5 cal kyr b p calibrated to calendar years before present i e a d 1950 when lake records show that local atmospheric temperatures in greenland were 2 4 c warmer than the present records from five new threshold lakes complemented with existing geological data from south of 70 n show that the ice margin was retracted behind its present day extent in all sectors for a limited period between ca 7 and 4 cal kyr b p and in most sectors from ca 1 5 to 1 cal kyr b p in response to higher atmospheric and ocean temperatures ice sheet simulations constrained by observations show good correlation with the timing of minimum ice volume indicated by the threshold lake observations the simulated volume reduction suggests a minimum contribution of 0 16 m sea level equivalent from the entire greenland ice sheet with a centennial ice loss rate of as much as 100 gt yr for several millennia during the holocene thermal maximum our results provide an estimate of the long term rates of volume loss that can be expected in the future as regional air and ocean temperatures approach those reconstructed for the holocene thermal maximum

uv induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate 1 sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass independent sulfur isotopic signature acquired when volcanic so2 experiences uv photooxidation the volcanic data are consistent with laboratory so2 photooxidation experiments using uv light at 248 nm maximum absorption of ozone whereas sulfur isotopic anomalies previously observed in archean samples are consistent with photodissociation at 190 220 nm a mechanism of so2 photooxidation occurring in the early stage of a stratospheric volcanic plume in the range of 220 320 nm weak band absorption of so2 is also proposed since mass independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of so2 to uv radiation their measurements might therefore offer the possibility to determine the degree of uv penetration in the ozone absorption window for the present and past atmospheres they can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records offering the possibility to reassess the climatic impact of past volcanic eruptions

borehole measurements indicate hard bed conditions kangerlussuaq sector western greenland ice sheet the hydrological processes and sliding dynamics of the greenland ice sheet are closely linked to the structural framework of its bed establishing whether the ice mass rests on bedrock relatively clear of rock debris a thick deformable till layer or some intermediate combination is therefore key to understanding the ice sheet response to changes in meltwater inputs here we report on direct observations of the ice bed interface along a flow line transect in the ablation zone of the western greenland ice sheet our measurements are derived from a network of 32 boreholes that vary from 100 m deep near the ice margin to 830 m deep 46 km upflow from the terminus we performed a suite of experiments and sampling techniques in the holes to investigate the bed conditions in contrast to previous geophysical and drilling studies elsewhere in greenland which have suggested that the ice rests on a thick layer of sediment we find no evidence for a thick sediment cover on the bed of the kangerlussuaq sector of the ice sheet our observations imply that this area has a relatively clean and hard bed and that this facilitates a basal hydraulic system governed by ice bedrock interactions the lack of sediment cover on the bed could be due to recent deglaciation and advance of this sector of the ice sheet and or variable rates of erosion and preferential routing of sediment through bedrock troughs

paleoecological studies of a holocene lacustrine record from the kangerlussuaq sondre stromfjord region of west greenland abstract a lacustrine sediment record from the kangerlussuaq region west greenland has resulted in a pollen macrofossil and sediment stratigraphy that encompasses the last 5000 14 c yr deglaciation of the area and subsequent development of a nearby floodplain occurred before 5000 yr b p since that time eolian sand and silt deposition appear to have been continuous with a significant increase ca 1000 14 c yr b p pollen analysis shows little change in the character of the vegetation throughout the record fluctuations in herb pollen taxa indicate changes in the extent and development of eolian sand sheets the oldest pollen zone records relatively little pollen accumulation and low taxa diversity this is followed by a zone of high pollen accumulation presumably a phase of highest vegetation density from 4400 to 3400 14 c yr b p thereafter declining pollen accumulation rates reveal a gradual environmental deterioration macrofossil analyses record significant limnological changes with an early eutrophic phase followed by a masotrophic phase and a reversal to more eutrophic conditions in the final phase the preserved record illustrates the interactions of deglaciation eolian activity regional vegetation and limnological change

a revised chronology for the fjord stade moraine in disko bugt west greenland this paper re evaluates the age of the fjord stade moraine in disko bugt a large marine embayment in west greenland previous work suggests that this moraine is part of a widespread moraine complex present throughout west greenland which formed ca 9300 cal yr bp in response to either a regional climate change or the effects of topographic controls on ice sheet recession we present the results of a relative sea level study using data from eight isolation basins that straddle the fjord stade moraine in southeast disko bugt our results suggest that the moraine here formed between ca 8400 and 7700 cal yr bp this is later than previously thought and similar in timing to a widespread cooling event recorded in the greenland ice core records this chronological similarity raises the possibility that the fjord stade moraine in the study area records an ice marginal response to a major short lived climatic cooling during the early holocene the so called 8200 event

spatial and temporal variability of lake ontogeny in south western greenland abstract holocene palaeolimnological records of diatoms and carotene a proxy for aquatic production from four lakes in the low arctic region of south western greenland were used to investigate the role of climate on lake ontogeny two of the lakes are located in the maritime coastal region near sisimiut and two inland close to the head of kangerlussuaq fjord where there is a more continental climate diatom records from the four lakes at1 at4 ss1381 ss8 had similar long term ontogeny trends independent of climatic setting and the changes are interpreted as responses to first order weathering controls on catchment lake chemistry short term excursions from these broad trends occurred in one coastal site at4 caused by intense erosion of the steep catchment and at inland sites where temporary hydrological closure and lake level decline occurred during the mid holocene 8000 5000 cal a bp algal production as carotene was more closely and consistently correlated with climatic changes it peaked during the mid holocene the warmest period of the holocene at all sites and there were transient increases in production in inland lakes during the medieval climate anomaly and little ice age because of fertilization through increased aeolian dust deposition a synthesis of seven palaeolimnological records from this region identified that only the mid holocene was correlated with diatom stratigraphic zones and there was considerable among site variability in later holocene lake response to climate forcing in this area comparable long term trends in species assemblage turnover dca ca axis 1 scores clearly demonstrate that lakes have predictable ontogeny trends in this region characterised by maximum alkalinity and nutrient availability in the first few millennia followed by progressive oligotrophication and alkalinity loss however individual lake and catchment characteristics lake morphology catchment geomorphology when modified by climatic change vegetation cover erosion weathering rates aeolian dust deposition lake level can diverge from this ontogeny template leading to complex ecological transitions in lakes from this region

deglaciation of the greenland and laurentide ice sheets interrupted by glacier advance during abrupt coolings abstract understanding patterns of ice sheet deglaciation is key for predicting the rate of future ice sheet melt yet the processes underlying deglaciation remain elusive the early holocene 11 7 ka to 8 2 ka greenlandian stage represents the most recent period when the laurentide and greenland ice sheets underwent large scale recession moreover this ice sheet recession occurred under the backdrop of regional temperatures that were similar to or warmer than today and comparable to those projected for the upcoming centuries reconstructing laurentide and greenland ice sheet behavior during the early holocene and elucidating the mechanisms dictating this behavior may serve as a partial analog for future greenland ice sheet change in a warming world here we present 123 new 10be surface exposure ages from two sites on baffin island and southwestern greenland that constrain the behavior of the laurentide and greenland ice sheets and an independent alpine glacier during the early holocene on baffin island we focus on a unique area where moraines deposited by the laurentide ice sheet rest directly adjacent to moraines deposited by an independent alpine glacier sixty one 10be ages reveal that advances and or stillstands of the laurentide ice sheet and an alpine glacier occurred in unison around 11 8 ka 10 3 ka and 9 2 ka sixty two 10be ages from southwestern greenland indicate that the greenland ice sheet margin experienced re advances or stillstands around 11 6 ka 10 4 ka 9 1 ka 8 1 ka and 7 3 ka our results reveal that ice sheets respond to climate perturbations on the same centennial timescale as small alpine glaciers we hypothesize that during the warming climate of the early holocene freshening of the north atlantic ocean induced by ice sheet melt resulted in regional cooling and brief periods of ice sheet stabilization superimposed on net glacier recession these observations point to a negative feedback mechanism inherent to melting ice sheets in the baffin bay region that slows ice sheet recession during intervals of otherwise rapid deglaciation

the influence of decadal to millennial scale ice mass changes on present day vertical land motion in greenland implications for the interpretation of gps observations 1 we show predictions of present day vertical land motion in greenland using a recently developed glacial isostatic adjustment gia model calibrated using both relative sea level rsl observations and geomorphological constraints on ice extent predictions from our gia model are in agreement with the relatively small number of gps measurements of absolute vertical motion from south and southwest greenland this suggests that our model of ice sheet evolution over the holocene period is reasonably accurate the uplift predictions are highly sensitive to variations of upper mantle viscosity thus depending on the earth model adopted different periods of ice loading change dominate the present day response in particular regions of greenland we also consider the possible influence of more recent changes in the ice sheet by applying a second ice model specifically a surface mass balance smb model which covers the period 1866 to 2005 predictions from this model suggest that decadal scale smb changes over the past 140 years play only a small role in determining the present day viscous response at the sub mm yr level in most locations for a range of earth model parameters high rates of peripheral thinning from 1995 to 2005 predicted using the smb model produce large elastic uplift rates 6 mm yr in west and southwest greenland this suggests that in some areas close to the ice margin modern surface mass balance changes have a dominant control on present day vertical land motion

geodetic measurements of postglacial adjustments in greenland 1 we analyze data from seven continuous global positioning system gps receivers and one tide gauge all located along the edge of the greenland ice sheet to determine vertical uplift rates we compare our results with predictions based on the ice 5g deglaciation model of peltier 2004 results from the gps receiver at kellyville 1 2 1 1 mm a and from the tide gauge at nuuk 2 2 1 3 mm a indicate that ice 5g overestimates the subsidence rates at those locations by 2 1 and 1 1 mm a respectively kellyville and nuuk are located along the southwestern margin of the greenland ice sheet and the observed negative uplift rates are consistent with independent evidence that the ice margin along the southwestern edge readvanced during the last 8 ka to its current position the ice 5g glaciation deglaciation history includes a readvance between the latitudes of 62 n and 72 n the gps measurements suggest the ice 5g readvance may be too large or mistimed our gps results at qaqortoq located at the southern tip of greenland suggest a secular subsidence rate of 0 3 1 1 mm a while ice 5g predicts an uplift rate of 1 0 mm a ice 5g assumes no ice sheet readvance in south greenland including no readvance of the qassimiut lobe the difference of 1 3 1 1 mm a can tentatively be explained as due to a 33 km readvance of the qassimiut lobe during the last 3 ka for the other gps sites the observed predicted uplift rates are 3 6 1 1 0 1 mm a at thule 0 0 1 1 2 0 mm a at scoresbysund and 0 4 1 1 1 7 mm a at kulusuk for thule kulusuk and scoresbysund the differences between the observed and predicted rates are on the order of 1 3 3 7 mm a though with opposite signs and indicate that ice 5g does not exactly reproduce the correct rebound signal at those locations

large fractionations of c and h isotopes related to methane oxidation in arctic lakes microbial oxidation of methane ch4 plays a central role in carbon cycling in arctic lakes reducing potential ch4 emissions associated with warming isotopic signatures of ch4 13c and 2h are indicators of microbial oxidation wherein the process strongly enriches 13c and 2h in residual ch4 we present 13c and 2h measurements obtained from sampling the water column and sediment for dissolved ch4 from three small arctic lakes in western greenland under both open water and ice covered conditions from 2013 to 2014 despite substantial variations in aquatic chemistry among the lakes 13c and 2h of ch4 suggested that ch4 was produced predominantly by acetoclastic methanogenesis in the littoral sediments and hydrogenotrophic methanogenesis in the profundal sediments in all of the lakes surprisingly large variations for both 13c and 2h of ch4 were observed with 13c extending from 72 to 7 4 and 2h from 390 to 250 the ch4 isotopic values reported here were significantly more enriched p 0 0001 in both 13c and 2h than values reported from other arctic freshwater environments as is characteristic of methanotrophy the enrichment in 13c and 2h was associated with low ch4 concentrations we suggest that the ch4 most enriched in 13c and 2h may reflect unusually efficient methanotrophic communities in arctic ice margin lakes this study provides the first measurement of 2h for ch4 in an arctic freshwater environment at concentrations 10 m the extreme enrichment of 13c and 2h of ch4 from arctic methanotrophy has significant implications for interpreting sources and sinks of ch4 without knowledge of local geology stable isotope values of ch4 higher than 30 for 13c and 150 for 2h could be misinterpreted as thermogenic geothermal or abiogenic origins given crystalline bedrock and the strong positive correlation between 13c and 2h throughout the water columns in three arctic lakes confirms that ch4 heavily enriched in 13c and 2h is the result of methanotrophy

late holocene relative sea level rise and the neoglacial history of the greenland ice sheet in west greenland early and mid holocene relative sea level rsl fall was replaced by late holocene rsl rise during the neoglacial after 4 3 cal ka bp thousand calibrated years before present here we present the results of an isolation basin rsl study completed near to the coastal town of sisimiut in central west greenland rsl fell from 14 m above sea level at 5 7 cal ka bp to reach a lowstand of 4 0 m at 2 3 1 2 cal ka bp before rising by an equivalent amount to present differences in the timing and magnitude of the rsl lowstand between this and other sites in west and south greenland record the varied interplay of local and non greenland rsl processes notably the reloading of the earth s crust caused by a neoglacial expansion of the greenland ice sheet gis and the subsidence associated with the collapse of the laurentide ice sheet forebulge this means that the timing of the sea level lowstand cannot be used to infer directly when the gis advanced during the neoglacial the rise in late holocene rsl is contrary to recently reported bedrock uplift in the sisimiut area based on repeat gps surveys this indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late holocene and that there has been a switch from subsidence to uplift at some point in the last thousand years or so

modelled ice sheet margins of three greenland ice sheet models compared with a geological record from ice marginal deposits in central west greenland ice sheet modelling is an essential tool for estimating the effect of climate change on the greenland ice sheet the large spatial and long term temporal scale ofice sheet models limits the amount of data which can be used to test model results the geological record is useful because it provides test material on the timescales typical for the memory of ice sheets millennia this paper compares modelled ice marginal positions with a geological scenario of ice marginpositions since the last glacial maximum to the present in west greenland morphological evidence of ice margin positions is provided by moraines moraine systems are dated by 14c dated marine shells and terrestrial peat we compared three greenland ice sheet models there are distinct differences inmodelled ice margin positions between the models and between model results and the geological record disagreement between models and the geologicalrecord in the near coastal area are explained by the insufficient treatment of marginal processes in a tidewater environment a smaller than present ice sheetaround the warm period in the holocene holocene climatic optimum only pops up when an unsmooth forcing is used this underlines the importance ofshort term variations in climatic variables in determining ice margin positions in the past but also in the future

testing models of mid to late holocene sea level change north queensland australia understanding the nature of global ice equivalent eustatic sea level changes during the mid to late holocene is important to our understanding of how ice sheets will respond to future climate change this study re analyses the indicative meaning and age control of existing relative sea level rsl data from cleveland bay north queensland australia and presents new rsl data from a foraminifera based transfer function as a preliminary test of global geophysical models in this region during the mid to late holocene the foraminifera based transfer function produces reliable rsl estimates consistent through the mid to late holocene at different locations in cleveland bay analysis of the combined rsl database reveals that rsl rose above present between 8 and 6 2 ka cal bp with the peak of the sea level highstand c 2 8 m above present at c 5 ka cal bp remaining relatively stable above 1 5 m from 6 2 until at least 2 3 ka cal bp falling to present in the last millennia this long period of sea level above present in the mid to late holocene suggests a gradual rather than abrupt end to global ice melt which must have continued into the late holocene this new analysis also shows no evidence for episodic fluctuations within the highstand although they cannot be entirely ruled out by this study this study demonstrates that more sea level data needs to be collected from locations uncontaminated by glacio isostasy hydro isostasy and tectonic effects in order to better constrain the late holocene melt histories of the large polar ice sheets

carbon dating reveals a seasonal progression in the source of particulate organic carbon exported from the greenland ice sheet surface melt from the greenland ice sheet gris collects particulate organic carbon poc as it drains into subglacial environments and transports it downstream where it serves as a microbial substrate we hypothesized that older poc is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer to test this poc samples were collected from a meltwater river exiting the gris over an ablation season and 14c dated resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area we found that poc ages increased from 5000 to 9000 years b p until peak discharge and catchment size afterward significant fluctuations in poc age were observed interpreted to result from periods of high and low subglacial hydrological pressure and sediment supply and subsequent exhaustion these observations suggest a seasonal progression in the source of poc exported from the gris and provide evidence for a seasonally evolving subglacial drainage system

the holocene sedimentary history of the kangerlussuaq fjord valley fill west greenland abstract west greenland has been intensively studied to reconstruct and better understand past relative sea level changes and deglacial history this study extends these efforts by linking sea level and deglacial history to the sedimentary infill successions of kangerlussuaq fjord and associated landward valleys based on published and new land and sea based geophysical data radiocarbon dates and geological observations we have characterized the infill and reconstructed the sedimentation history during the holocene based on a revised sea level curve and data presented in this paper we defined three depositional phases phase i 7000 yr bp is represented by dominant glaciomarine deposition associated with a tide water glacier system as the greenland ice sheet gis continued to retreat it became land based during phase ii 7000 1500 yr bp two separate depocenters formed keglen delta depocenter arose from a temporary stabilization phase of the gis and prograded rapidly over the glaciomarine deposits of phase i further inland proglacial lake formation and subsequent sedimentary infill associated with the ongoing gis retreat is represents the second depocenter the watson river connected both depocenters by a flood plain which transferred sediment from the gis to the keglen delta ongoing sea level fall due to glacio isostastic uplift combined with a gradually cooler and dryer climate resulted in terrace formation along the watson river flood plain around 4000 yr bp the gis margin reached its most landward location and began to advance to its present location the final phase phase iii

implications for deglaciation chronology from new ams age determinations in central west greenland abstract new evidence has been obtained for the age of the umivit keglen and orkendalen moraine systems close to the present ice sheet margin in central west greenland the umivit keglen moraine system is dated at 7500 to 6500 14 c yr b p which is older than the previously assumed date of 7300 to 6000 14 c yr b p the orkendalen system is now dated at 6200 to 5600 14 c yr b p against earlier estimates of 300 to 700 14 c yr b p the new age is based on ams radiocarbon dated organic material within depressions between morainic ridges belonging to the orkendalen system a major implication of the new age is that ice margin positions prevailed for about 6000 years behind the present ice sheet margin the retreat behind the present margin could be substantial and in the light of deglaciation rates prior to the orkendalen phase may be ca 10 s of kilometers rather than kilometers circumstantial evidence is found for the retreat of the ice sheet margin behind its present position during the holocene climatic optimum the results placed into a time frame of deglaciation since the last glacial maximum enable comparison with greenland ice sheet models and ice core records

palaeohydrology of kangerlussuaq sondre stromfjord west greenland during the last 8000 years major fluctuations of hydroclimate in west greenland are recorded in paleoshoreline terraces that encircle several lakes near kangerlussuaq greenland 67 01 n 50 40 w geomorphic and stratigraphic analyses were used to construct a lake level curve for hunde so a large closed basin lake in this region changes in lake volume associated with lake level fluctuations were cal culated and a water balance model was used to determine the primary factors influencing lake volume and the changes in those factors necessary to affect reconstructed lake level change sensitivity tests suggest that mean annual precipitation and the relative proportion of summer versus winter precipitation are the primary climate drivers of lake level change temperature effects are less important unless coupled with changes in one of the other variables two pluvial periods occurred centered around 4600 and 2000 cal yr bp with mean annual precipitation estimated at 130 mm and 70 mm higher than modern respectively in contrast a low stand prior to 6070 cal yr bp with water levels as much as 18 m below modern was a result of summer temperatures 2 3 above modern coupled with a 14 day increase in the length of the iceoff period and a reduction in mean annual precipitation of 80 mm relative to modern

spectral roughness and glacial erosion of a land terminating section of the greenland ice sheet spectral roughness offers a significant potential for understanding the evolution of glaciated landscapes here we present the first roughness study combining a high resolution 250 to 500 m dem

constraints on the greenland ice sheet since the last glacial maximum from sea level observations and glacial rebound models abstract geomorphological descriptions of changes in the extent of the greenland ice sheet gis have been combined with glacial isostatic adjustment models to reproduce the sea level history of greenland since the last glacial maximum lgm the contribution to past sea level change around greenland due to ice load changes outside of that region has been considerable 10 s of meters while still contributing a rise of several mm yr 1 today the isostatic contribution to relative sea level around greenland from changes in the gis is found by iteratively perturbing preliminary ice models with different lgm extents and deglaciation starting times the resulting first order model that provides the best agreement between observed and predicted sea level contributes 3 1 and 1 9 m water equivalent of additional ice relative to present day ice volumes at the lgm and younger dryas respectively the gis in most areas does not appear to have extended far onto the continental shelf the exceptions being southern most southwest greenland and northern east greenland as well as at the coalescence of the northwest greenland and innuitian ice sheets changes in ice thickness since the lgm were 500 m along the present day outer coast and 1500 m along some parts of the present day ice margin the observed mid to late holocene fall in sea level to below the present day level and the subsequent transgression seen in some areas implies that the gis retreated behind the present day margin by distances of the order of 40 km before readvancing

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

holocene evolution of the western greenland ice sheet assessing geophysical ice sheet models with geological reconstructions of ice margin change abstract geophysical ice sheet models are used to predict future ice sheet dimensions and in turn these projections help estimate the magnitude of eustatic sea level rise before models can confidently predict ice sheet behavior they must be validated by being able to duplicate the geological record of ice sheet change here we review geological records of greenland ice sheet gris change with emphasis on the warmer than present middle holocene and compare these records to published studies that numerically simulate gris behavior through the holocene geological records are concentrated in west and southwest greenland which are also the regions where the gris margin likely experienced the greatest distance of inland retreat during the middle holocene several records spanning from melville bugt to jakobshavn isfjord in western greenland indicate the gris achieved its minimum extent between 5 and 3 ka and farther south in the kangerlussuaq region new data presented here indicate the ice margin reached its minimum extent between 4 2 and 1 8 ka in the narsarsuaq region in southern greenland the gris likely achieved its minimum configuration between 7 and 4 ka we highlight key similarities and discrepancies between these reconstructions and model results and finally we suggest that despite some degree of inland retreat the west and southwest gris margin remained relatively stable and close to its current position through the holocene thermal maximum

dating of the narssarssuaq stade in southern greenland following the holocene thermal maximum the greenland ice sheet began to expand and many local glaciers formed the maximum extent of most outlet glaciers from the inland ice was reached around 100 to 200 years ago however some exceptions have been recorded in southern greenland the neoglacial narssarssuaq stade marks an older re advance that exceeded the historical advance the dating of the narssarssuaq stade has been much debated here we present new radiocarbon dates from a sediment core collected from a small lake within the moraines formed during this stade a minimum age for the narssarssuaq stade of around 1200 yr bp is suggested from the dates

subglacial permafrost evidencing re advance of the greenland ice sheet over frozen ground abstract greenland ice sheet gris covers an area of 1 7 million km2 it has been an important source of climate information and the air temperature history of greenland is well known however the thermal history and temperature conditions of the greenland bedrock are poorly known there are only few records on the temperature of the proglacial bedrock and no records on bedrock temperature underneath the ice sheet the greenland analogue project gap recently investigated hydrological hydrogeological and geochemical processes in kangerlussuaq west greenland because permafrost has a major hydrological impact in arctic regions the cryogenic structure of the bedrock was an important research topic from previous studies it was already known that kangerlussuaq is located within the zone of continuous permafrost temperature profiling in a new research borehole extending horizontally 30 m underneath the ice sheet revealed that permafrost is 350 m deep at the ice margin this result raised the question how far the permafrost extends under the ice sheet in order to investigate the thermal properties we made a series of electromagnetic em soundings at the ice margin area on proglacial area and on the ice sheet and detected that subglacial permafrost extends at least 2 km from the ice margin to inland we also observed a patchy unfrozen sediment layer between the ice and the frozen bedrock possible existence of subglacial sediments and their role in ice dynamics has been debated in many recent papers our successful campaign shows that geophysics can be used for bedrock investigations through thick ice which is known to be challenging for electromagnetic methods our results provide the first direct evidence supporting the proposed holocene ice re advance over frozen ground and contribute to the discussion on the rapid climate changes in past to the future of the ice sheet under warming climate and hydrogeology at the ice margin

geologic methane seeps along boundaries of arctic permafrost thaw and melting glaciers in the arctic permafrost and glaciers form a cryosphere cap that traps methane leaking from hydrocarbon reservoirs restricting flow to the atmosphere aerial surveys and ground based measurements reveal the release of radiocarbon depleted methane along boundaries of permafrost thaw and retreating glaciers in alaska and greenland

radiocarbon dated evidence of worldwide early holocene climate change radiocarbon dated glacial deposits from several different areas of the world indicate that alpine glaciers and ice caps in parts of both the northern and southern hemispheres expanded in response to climate change in early holocene time these data suggest that a worldwide episode of cooler climate similar in scope to the more recent neoglaciation occurred ca 8 500 7 500 yr b p

rapid last deglacial thinning and retreat of the marine terminating southwestern greenland ice sheet abstract marine terminating outlet glaciers are a major source of modern ice loss from the greenland ice sheet gris but their role in gris retreat during the last deglaciation is not well constrained here we develop deglacial outlet glacier retreat chronologies for four regions in southwest and south greenland to improve understanding of spatial variations in centennial to millennial scale ice loss under a warming climate we calculate 10be surface exposure ages of boulders located in fjords near the towns of qaqortoq paamiut nuuk and sisimiut our northernmost study site sisimiut deglaciated earliest at 18 ka to 15 ka with an average thinning rate of 0 1 0 3 m yr 1 inland retreat from sisimiut to the modern ice margin took 7 ka at an average retreat rate of 15 20 m yr 1 a 10be dated moraine 25 km from the modern gris margin deposited at 8 ka suggests a possible ice margin still stand but this does not change overall retreat rates after retreat from the small coastal sisimiut fjords the gris margin was mainly land terminating in this region in contrast earliest exposure occurred at 12 ka near qaqortoq and 11 10 ka near nuuk and paamiut with ice thinning at rates of 0 2 0 3 m yr 1 to instantaneous within measurement uncertainty ice retreat inland through the extensive nuuk paamiut and qaqortoq fjord systems to near modern ice margins occurred in

using in situ cosmogenic 10be to identify the source of sediment leaving greenland we use the concentration of in situ 10be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to greenland s sediment budget we sampled along the western eastern and southern margins of the greenland ice sheet and collected sediment sourced from glacerized n 19 and non glacerized terrain n 10 from channels where sediment from glacerized and non glacerized terrain is mixed n 28 from holocene glacial fluvial terraces n 4 and from one sand dune in situ 10be concentrations in sediment range from 1600 to 34 000 atoms g 1 the concentration of in situ 10be in sediment sourced from non glacerized terrain is significantly higher than in sediment sourced from glacerized areas in mixed channel sediment and in terrace sediment that was deposited during the holocene to constrain the timing of landscape exposure for the deglaciated portion of the narsarsuaq field area in southern greenland we measured in situ 10be concentration in bedrock n 5 and boulder n 6 samples paired bedrock and boulder ages are indistinguishable at 1 uncertainty and indicate rapid exposure of the upland slopes at 10 5 ka the isotope concentration in sediment sourced from non glacerized terrain is higher than in sediment sourced from glacerized terrain because the non glacerized landscape has been exposed to cosmic radiation since early holocene deglaciation sediment from glacerized areas contains a low but measurable concentration of 10be that probably accumulated at depth during a prolonged period of exposure probably before the establishment of the greenland ice sheet the concentration of 10be in mixed fluvial sediment and in terrace sediment is low and similar to the concentration in sediment from glacerized areas which indicates that the greenland ice sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled copyright 2014 john wiley sons ltd

gps measurements of crustal uplift near jakobshavn isbrae due to glacial ice mass loss 1 we analyze 2006 2009 data from four continuous global positioning system gps receivers located between 5 and 150 km from the glacier jakobshavn isbrae west greenland the gps stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from jakobshavn isbrae all stations experienced uplift but the uplift rate at kangia north only 5 km from the glacier front was about 10 mm yr 1 larger than the rate at ilulissat located only 45 km further away this suggests that most of the uplift is due to the unloading of the earth s surface as jakobshavn thins and loses mass our estimate of jakobshavn s contribution to uplift rates at kangia north and ilulissat are 14 6 1 7 mm yr 1 and 4 9 1 1 mm yr 1 respectively the observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from nasa s airborne topographic mapper atm which shows that jakobshavn lost mass at an average rate of 22 2 km3 yr 1 between 2006 and 2009 at kangia north and ilulissat the predicted uplift rates computed using thinning estimates from the atm laser altimetry are 12 1 0 9 mm yr 1 and 3 2 0 3 mm yr 1 respectively the observed rates are slightly larger than the predicted rates the fact that the gps uplift rates are much larger closer to jakobshavn than further away and are consistent with rates inferred using the atm based glacier thinning model shows that gps measurements of crustal motion are a potentially useful method for assessing ice mass change models

directly dating postglacial greenlandic land surface emergence at high resolution using in situ 10be postglacial emergence curves are used to infer mantle rheology delimit ice extent and test models of the solid earth response to changing ice and water loads such curves are rarely produced by direct dating of land emergence rather most rely on the presence of radiocarbon datable organic material and inferences made between the age of sedimentary deposits and landforms indicative of former sea level here we demonstrate a new approach 10 be dating to determine rates of postglacial land emergence in two different settings in southern greenland narsarsuaq igaliku we date directly the exposure as relative sea level fell of gravel beaches and rocky outcrops allowing determination of rapid post younger dryas emergence in western greenland kangerlussuaq we constrain holocene isostatic response by dating the sequential stripping of terrace sediment driven by land surface uplift relative sea level fall and resulting fluvial incision the technique we employ provides high temporal and elevation resolution important for quantifying rapid emergence immediately after deglaciation and less rapid uplift during the middle holocene 10 be constrained emergence curves can improve knowledge of relative sea level change by dating land emergence along rocky coasts at elevations and locations where radiocarbon datable sediments are not present and without the lag time needed for organic material to accumulate

holocene palaeosols and aeolian activities in the umimmalissuaq valley west greenland aeolian sand sheets and active dunefields preserve an ancient holocene land surface represented by palaeosols that occur around the present ice margin in the kangerlussuaq area west greenland to determine the relation between holocene aeolian activities and periods of soil formation both substantially dependent on the deglaciation history palaeosols aeolian sand sheets and dunefields were analysed using field data grain size analyses optically stimulated luminescence dating and ams 14c data in an area of about 15 km2 of the umimmalissuaq valley palaeosols are developed close to the ice margin 60 wt are comparable with aeolian sand sheets currently formed at greater distances 4 5 km from the present ice margin we propose a transport distance for fine aeolian sediments in which the palaeosols are formed of at least 4 km from inboard of the present ice margin soil for

numerical modeling of glacial sediment production and transport during deglaciation abstract we aim to improve the understanding of sediment fluxes originating from ice sheet outlet glaciers in order to explain the evolution of sedimentary fjord fills a numerical glacial erosion and sediment flux process model has been developed to quantify sediment generation and subglacial transport dynamic ice sheet cover is generated from topography and climate parameters affecting the glacial net mass balance pressure temperature and velocity characteristics of the ice sheet force erosion at the glacier bed bed erodability depends on bedrock hardness and potential shielding by sediment after erosion sediment is either stored at the bed or transported either by meltwater or englacially within basal ice model experiments show ice retreat is driven by valley topography rapid retreat occurs in the flatter valley stretches and slower retreat in the steeper parts of a glacial valley distinct depocenters of exposed sediment develop during retreat predicted erosion rates in the glaciated valley range from 37 to 56 mm yr for different climate scenarios which is well within the range of reported field reconstructions erosion is significantly accelerated beneath warm based ice and the effect of an enlarged warm based footprint during warming compensates for decreasing ice mass topographic shielding of bedrock by previously eroded material in large areas constrains erosion by a factor 4 simulated glacier retreat and melt water flux initially occur at a high rate and subsequently decelerate while sediment delivery exhibits a distinct lagging of several thousands of years behind the meltwater flux upon the transition from glaciation to deglaciation the subglacial system is in a sediment starved state late deglacial erosion and sub and englacial sediment storage cause a lagging sediment delivery to downstream periglacial fluvial and lacustrine domains

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

age of the orkendalen moraines kangerlussuaq greenland constraints on the extent of the southwestern margin of the greenland ice sheet during the holocene abstract although greenland ice core records register relatively stable holocene climate conditions the lower elevation margins of the greenland ice sheet gris experienced significant holocene fluctuations these fluctuations include ice sheet recession during the holocene thermal maximum 9 5 ka and advance during the little ice age lia a d 1350 1880 determining the extent and timing of these fluctuations is important for understanding the response of the gris to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models sets of moraines marking past extents of the southwestern gris margin occur in the kangerlussuaq region we focus on the orkendalen moraines a prominent moraine set located within 2 km of the modern ice margin and just outboard of the lia moraines we present the first 10be ages of the orkendalen moraines indicating they were deposited at 6 8 0 3 ka the geomorphic relationship between the orkendalen and lia moraines indicates that the ice sheet margin was inboard of its orkendalen extent between 6 8 ka and the culmination of the lia the age of the orkendalen moraines provides an important constraint on the extent of the southwestern gris during the middle holocene

earliest holocene south greenland ice sheet retreat within its late holocene extent early holocene summer warmth drove dramatic greenland ice sheet gis retreat subsequent insolation driven cooling caused gis margin readvance to late holocene maxima from which ice margins are now retreating we use 10be surface exposure ages from four locations between 69 4 n and 61 2 n to date when in the early holocene south to west gis margins retreated to within these late holocene maximum extents we find that this occurred at 11 1 0 2 ka to 10 6 0 5 ka in south greenland significantly earlier than previous estimates and 6 8 0 1 ka to 7 9 0 1 ka in southwest to west greenland consistent with existing 10be ages at least in south greenland these 10be ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late holocene temperatures in the early holocene current south greenland ice margin retreat suggests that south greenland may have now warmed to or above earliest holocene summer temperatures

a continuous record of holocene eolian activity in west greenland eolian landforms are widespread alongside proglacial valley sandurs in west greenland and comprise low relief sand sheets climbing dunes and upland loess sedimentary facies mainly reflect distance to outwash source zones and the influence of vegetation cover the sediments show stratification types typical for poorly to moderately vegetated sand sheets alternately laminated silt peat sequences and unstratified loess twenty five accelerator mass spectrometry 14c dates provide the basis for the chronostratigraphy of the inland eolian deposits 14c dates from interstratified sand sheets suggest that the bulk of eolian sands were deposited prior to 3400 cal yr b p and after 550 cal yr b p this two phase formation for the inland dunes most likely reflects local changes in proglacial floodplain development and meltwater rerouting associated with a significant recession of the greenland ice sheet during the mid holocene climate optimum subsequent floodplain regeneration and renewed sand sheet formation after 550 cal yr b p followed when the ice margin readvanced to its present position in contrast atmospheric deposition of regionally derived silt in upland peat mires has been continuous since at least 4750 cal yr b p silt influx data demonstrate a strongly episodic history of the intensity of eolian activity over the past five millennia which tentatively reflects alternating periods of winter aridity associated with the variable incursion of maritime air masses over the interior ice free areas of west greenland

deglaciation of a major palaeo ice stream in disko trough west greenland recent work has confirmed that grounded ice reached the shelf break in central west greenland during the last glacial maximum lgm here we use a combination of marine sediment core data including glacimarine lithofacies and ird proxy records and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the greenland ice sheet gris across the shelf retreat of this outlet which contained the ancestral jakobshavns isbrae ice stream from the outer shelf in disko trough was rapid and progressed predominantly through iceberg calving however minor pauses in retreat tens of years occurred on the middle shelf at a trough narrowing forming subtle grounding zone wedges by 12 1 cal kyr bp ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf where it was pinned and stabilised for at least 100 years during this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice mass loss fine grained sediments muds were deposited alternately with ird rich sediments diamictons forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles high influxes of subglacial meltwater emanating from the nearby ice margins deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons this is the first example of this glacimarine lithofacies from a continental shelf setting and we suggest that the calving bay configuration of the ice margin plus the switching between calving and melting as ablation mechanisms facilitated its deposition by channelling meltwater and icebergs through the inner trough the occurrence of a major stillstand on the inner shelf in disko trough demonstrates that the ice dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the gris during retreat

the greenland ice sheet during the last glacial cycle current ice loss and contribution to sea level rise from a palaeoclimatic perspective abstract during the last interglacial lig period between 130 and 116 thousand years before present ka bp the greenland ice sheet gris was considerably reduced in size contributing to a global mean sea level msl rise of 0 5 4 2 m relative to the present this is not sufficient to explain the 6 9 m msl rise estimated for the lig which implies that a significant contribution to the lig highstand came from antarctica following the lig the gris grew and attained its maximum volume of about 12 m global sea level equivalents sles between 18 and 16 ka bp since then the gris margins have retreated on an order of several hundred km following a general pattern of lagged response to changes in high latitude summer insolation and global greenhouse gas concentrations on shorter timescales and over smaller spatial scales the combination of internal ice sheet dynamics and external climate dynamics has often resulted in a more complex and asynchronous behaviour of the ice sheet margin the gris probably reached its minimum holocene extent around 4 ka bp and modelling studies suggest that it contributed to a rise in global msl of less than 0 2 m relative to the present at this time a period of steady growth followed the holocene minimum and in many areas the ice sheet advanced beyond its present limits during the little ice age i e the last few centuries currently the gris occupies an area of 1 7 10 6 km 2 and features a volume of 2 96 10 6 km 3 which amounts to 7 4 m sle observations show that the rate of mass loss from the gris has been accelerating over the past few decades and ice sheet modelling indicates that we have to go back to the last deglaciation around 10 ka bp in order to find sustained melt rates that were higher than those experienced over the last decade the future development of the gris will have a profound influence on sea level both globally and regionally but there are large uncertainties related to how the gris will respond to future global warming based on a range of modelling studies employing different emission scenarios the gris is expected to contribute about 0 1 0 3 m to global msl rise by the end of the 21st century in a longer time perspective modelling suggests that melting of the gris may replace ocean thermal expansion as the most important factor in future sea level rise potentially contributing with 0 7 2 6 m sle within the next 500 years multi millennial simulations show that the entire ice sheet 7 4 m sle might disappear completely within less than three thousand years under high emission scenarios i e with atmospheric co 2 reaching four times preindustrial levels

fault patterns associated with extensional fault propagation folding abstract extensional fault propagation drape folds are a common type of structure in rift basins and a number of oil and gas fields produce from these structures the detailed geometry and trap volumes are dependent on the relationship between the basement faults and the overlying folds and associated secondary faults in the sedimentary cover experimental models were used to study the 3 d geometry and secondary fault patterns of drape folds associated with single faults and two or more intersecting faults two layer clay models consisting of stiff and soft clay were used to model the deformation zones in the basement and sedimentary cover respectively extension on single basement faults normal to the direction of extension results in the development of a deformation zone with expanding width in which the fault density initially increases and then remains approximately constant extension on terminating faults results in conical drape folds with faults oblique to the fold axis along the propagating tip basement faults oblique to the direction of extension are characterized by oblique secondary faults along the boundaries of the deformation zone which curve into a direction normal to the extension direction in the center trapdoor fault geometries associated with two or more intersecting faults result in a triangular uplift with maximum relief at the apex the difference in relief between the flanks and the apex is greatest in the case of propagating basement faults en echelon secondary faults initiate on the flanks and extend into the apex area curving into orientations that are closer to normal to the regional direction of extension the width of the fault zone and the total fault length increase with increasing extension the fault density initially increases and then remains approximately constant with increasing extension

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

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

a model of greenland ice sheet deglaciation constrained by observations of relative sea level and ice extent an ice sheet model was constrained to reconstruct the evolution of the greenland ice sheet gris from the last glacial maximum lgm to present to improve our understanding of its response to climate change the study involved applying a glaciological model in series with a glacial isostatic adjustment and relative sea level rsl model the model reconstruction builds upon the work of simpson et al 2009 through four main extensions 1 a larger constraint database consisting of rsl and ice extent data model improvements to the 2 climate and 3 sea level forcing components 4 accounting for uncertainties in non greenland ice the research was conducted primarily to address data model misfits and to quantify inherent model uncertainties with the earth structure and non greenland ice our new model termed huy3 fits the majority of observations and is characterised by a number of defining features during the lgm the ice sheet had an excess of 4 7 m ice equivalent sea level iesl which reached a maximum volume of 5 1 m iesl at 16 5 cal ka bp modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors southwest and southeast greenland began to retreat from the continental shelf by 16 to 14 cal ka bp thus responding in part to the bolling allerod warm event c 14 5 cal ka bp subsequently ice at the southern tip of greenland readvanced during the younger dryas cold event in northern greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the younger dryas to present day conditions upon entering the holocene 11 7 cal ka bp the ice sheet soon became land based during the holocene thermal maximum htm 9 5 cal ka bp air temperatures across greenland were marginally higher than those at present and the gris margin retreated inland of its present day southwest position by 40 60 km at 4 cal ka bp which produced a deficit volume of 0 16 m iesl relative to present in response to the htm warmth our optimal model reconstruction lost mass at a maximum centennial rate of c 103 4 gt yr our results suggest that remaining data model discrepancies are affiliated with missing physics and sub grid processes of the glaciological model uncertainties in the climate forcing lateral earth structure and non greenland ice particularly the north american component finally applying the huy3 greenland reconstruction with our optimal earth model we generate present day uplift rates across greenland due to past changes in the ocean and ice loads with explicit error bars due to uncertainties in the earth structure present day uplift rates due to past changes are spatially variable and range from 3 5 to 7 mm a including earth model uncertainty

preliminary 10be chronology for the last deglaciation of the western margin of the greenland ice sheet the now acknowledged thinning of the greenland ice sheet raises concerns about its potential contribution to future sea level rise in order to appreciate the full extent of its contribution to sea level rise reconstruction of the ice sheet s most recent last deglaciation could provide key information on the timing and the height of the ice sheet at a time of rapid climate readjustment we measured 10be concentrations in 12 samples collected along longitudinal and altitudinal transects from sisimiut to within 10 km of the isunguata sermia glacier ice margin on the western coast of greenland along the longitudinal transect we collected three perched boulders and two bedrocks in addition we sampled seven perched boulders along a vertical transect in a valley within 10 km of the isunguata sermia glacier ice margin our pilot dataset constrains the height of the ice sheet during the last glacial maximum lgm between 500 m and 840 m including the 120 m relative sea level depression at the time of the lgm 21 ka bp from the transect we estimate the thinning of the ice sheet at the end of the deglaciation between 12 3 1 5 10be ka n 2 and 8 3 1 2 10be ka n 3 to be 6 cm a 1 over this time period direct dating of the retreat of the western margin of the greenland ice sheet has the potential to better constrain the retreat rate of the ice margin the thickness of the former ice sheet as well as its response to climate change copyright 2008 john wiley sons ltd

limnological controls on stable isotope records of late holocene palaeoenvironment change in sw greenland a paired lake study stable isotope records are increasingly being used in palaeoenvironmental studies of arctic lakes here we compare stable isotope and elemental records 13c 15n c n with high resolution xrf derived geochemical and colour data from low arctic lakes ss1220 and ss85 in southwest greenland lake ss1220 sediments are laminated gyttja whereas ss85 consist of homogeneous gyttja both records cover the last c 5000 years 13c and carbon content suggest that organic matter in both lakes is predominantly autochthonous the c n variability ranging between 11 and 15 is interpreted to be a function of nitrogen deficiency which is further supported by 15n values at ss1220 falling close to atmospheric 15natmosphere although some changes in the geochemical stratigraphies presented here can be related to regional environmental change i e hydrology effective precipitation aeolian activity these effects are filtered through the lake catchments these changes alter the nutrient supply and hence lake productivity which appear to be the primary controls on the stable isotope data we suggest that information of past environmental change can only be gained from the stable isotope composition of lake sediments when there is a reasonable understanding of limnological processes and records may be lake specific

carbonaceous particles reveal that late holocene dust causes the dark region in the western ablation zone of the greenland ice sheet a dark region in the western ablation zone of the greenland ice sheet is caused by outcropping ice layers that contain more dust than the surrounding brighter ice these higher amounts of dust were deposited in the accumulation zone of the ice sheet and travelled with the ice to the ablation zone to deduce the period and the causes of this higher dust deposition carbonaceous particles in ice samples from the dark region and from brighter reference ice were analysed and used for dating samples including ice from directly below the surface contain high amounts of modern organic carbon probably from microorganisms on the ice surface deeper samples reveal low amounts of carbonaceous particles which are originally deposited in the accumulation zone the amount of outcropping carbonaceous particles in the dark region seems significantly higher than in the reference ice one of the samples that contained material initially deposited in the accumulation zone was dated and revealed late holocene ages coinciding with a period of enhanced eolian activity in the nearby tundra therefore variable eolian activity during the holocene effected dust fluxes towards the ice and hence leads to albedo variations in the present ablation zone of the ice sheet