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

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

the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

holocene history of the estuarine area surrounding portage alaska as recorded in a 93 m core a 93 m core obtained at portage alaska records four prograding cycles of estuarine deposition for the past 8230 100 years analyses of texture mineralogy paleontology and sedimentary structures enable definition of eight lithologic units mineralogic studies show that past and present sedimentation at portage has been largely mud and sand from the susitna river on the northwest side of cook inlet six radiocarbon dates from concentrated organic debris in the core and on the surface enable determination of sedimentation rates for four intervals and show rates to be higher and to vary more at depth than rates nearer the surface the glacier carved turnagain arm fiord has been receiving sediment for at least the past 14 000 years as estimated by extrapolation of calculated sedimentation rates to the thickness of unconsolidated sediment drilled at portage which totals approximately 300 m presently deposition is accomplished instantly as the result of tectonic subsidence and compaction of sediment

isolation basins sea level changes and the holocene history of the greenland ice sheet abstract isolation basins are natural topographic depressions that at various times in their history may be connected to or isolated from the sea by changes in relative sea level rsl they provide a valuable source of data for tracking large scale tens of meters changes in rsl over millennia as well as quiet water depositional environments where abrupt changes caused by tsunami iceberg roll or storms may be recorded in this paper we review isolation basins as sources of rsl data with a particular focus on their use in greenland to constrain the holocene history of the ice sheet a new rsl curve from disko fjord west greenland is presented which shows that local ice free conditions were established at c 11 k cal yr bp after which rsl fell rapidly from a marine limit at c 80 m to reach close to present sea level by c 4 k cal yr bp we compare this record with other isolation basin rsl data from six other sites in disko bugt and note a strong northwest southeast differential rebound across the area during the early and mid holocene that reflects variations in ice load history we compare the disko bugt data with other previously published isolation basin rsl records from sisimiut central west greenland nanortalik south greenland and ammassalik southeast greenland rsl fell below present during the early holocene at nanortalik c 10 k cal yr bp and during the mid to late holocene elsewhere before rising to present these differences reflect variations in the timing and amount of greenland ice load change since the last glacial maximum as well as non greenland processes notably the collapse of the laurentide forebulge and also changes in ice equivalent sea level isolation basin data have relatively small age and height uncertainties compared with other rsl indicators enabling them to resolve between different earth and ice sheet models especially during periods of large ice load and rsl change

lake sediment evidence for the date of deglaciation of the hidden lake area kenai peninsula alaska an abrupt environmental change is reflected in a core from hidden lake alaska by differences in sediment type chlorite crystallinity and content of organic carbon and water of the sediments this abrupt change in the sedimentary record occurred about 14 500 14c yr ago and probably marks the time of recession of the glacier from the hidden lake drainage basin deglaciation of the area was then underway and rock flour was being deposited in the lake after recession of the glacier from the hidden lake drainage basin rock flour was no longer introduced and organic matter content of the sediment increased by the dating of these changes in sediment type we show that retreat of glaciers in this area took place significantly earlier than previously estimated this agrees with the timing of retreat of alpine glaciers elsewhere in western north america

constraining landscape history and glacial erosivity using paired cosmogenic nuclides in upernavik northwest greenland high latitude landscape evolution processes have the potential to preserve old relict surfaces through burial by cold based nonerosive glacial ice to investigate landscape history and age in the high arctic we analyzed in situ cosmogenic 10 be and 26 al in 33 rocks from upernavik northwest greenland we sampled adjacent bedrock boulder pairs along a 100 km transect at elevations up to 1000 m above sea level bedrock samples gave significantly older apparent exposure ages than corresponding boulder samples and minimum limiting ages increased with elevation two isotope calculations 26 al 10 be on 20 of the 33 samples yielded minimum limiting exposure durations up to 112 k y minimum limiting burial durations up to 900 k y and minimum limiting total histories up to 990 k y the prevalence of 10 be and 26 al inherited from previous periods of exposure especially in bedrock samples at high elevation indicates that these areas record long and complex surface exposure histories including significant periods of burial with little subglacial erosion the long total histories suggest that these high elevation surfaces were largely preserved beneath cold based nonerosive ice or snowfields for at least the latter half of the quaternary because of high concentrations of inherited nuclides only the six youngest boulder samples appear to record the timing of ice retreat these six samples suggest deglaciation of the upernavik coast at 11 3 0 5 ka average 1 standard deviation there is no difference in deglaciation age along the 100 km sample transect indicating that the ice marginal position retreated rapidly at rates of 120 m yr 1

rise and fall of a hypothesized seismic gap source complexity in the mw 7 0 16 december 1857 southern italy earthquake abstract on 16 december 1857 a strong earthquake m 7 struck a large portion of the southern apennines about 150 km southeast of naples the earthquake was thoroughly investigated by irish engineer robert mallet who wrote an extensive report that is still regarded as a landmark in observational seismology because of the concentration of damage in the high agri valley and contrary to mallet s own findings for many years the earthquake was referred to as the val d agri earthquake and was believed by most investigators to have ruptured the 20 25 km normal fault lying beneath this intermontane basin the magnitude of the earthquake however and evidence for earthquake complexity suggest that the true rupture length has been so far underestimated we contend that the 1857 earthquake ruptured in a cascade fashion two adjacent and relatively well known faults first the smaller melandro pergola fault commonly believed to represent a seismic gap between the causative faults of the 1857 and of the 1980 irpinia m w 6 9 earthquakes and then the larger agri valley fault proper contemporary chronicles reported a time lapse of 2 3 min between the two ruptures thus effectively making them two independent shocks the rupture must have proceeded unilaterally from the northwestern edge of the melandro pergola fault where mallet placed the earthquake epicenter thus explaining the concentration of damage and attention by rescue crews and subsequent investigators in the southeastern portion of the high agri valley

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

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

new in situ 14c data indicate the absence of nunataks in west greenland during the last glacial maximum abstract in situ cosmogenic nuclide exposure age distributions on ice age nunataks act as past ice thickness indicators and provide valuable targets for ice sheet model simulations of the last glacial maximum several locations along west greenland have been identified as being potential nunataks due to their weathered nature and their high cosmogenic nuclide inventories with little evidence for ice sheet burial we present new in situ cosmogenic 14c measurements from four high elevation surfaces in the central uummannaq fjord system that were identified as potential nunataks in prior work building on previous work we model cosmogenic radionuclide production and decay and consider a range of ice sheet history scenarios since our results require more burial or shielding under ice than what independent methods suggest for holocene ice cap cover we propose that these locations were not nunataks during the last glacial maximum but rather were buried during the peak of the last glacial maximum however we cannot confirm whether these sites were buried by the greenland ice sheet or local glaciers

microfossil analysis of sediments representing the 1964 earthquake exposed at girdwood flats alaska usa abstract diatom pollen foraminifera and thecamoebian assemblages from an outcrop of peat and silt at girdwood flats in the upper turnagain arm of the cook inlet alaska record four phases of relative land and sea level changes the first phase is the development of freshwater swamp above high marsh sediments during relative land uplift caused by strain accumulation along the locked portion of the alaska aleutian subduction zone in second phase the top 2 cm of the peat all microfossil groups record pre seismic relative sea level rise relative land subsidence the third phase is rapid land subsidence 1 7 m during the earthquake of march 1964 that initiated intertidal silt accumulation above the peat the final phase is the colonisation of mudflat by salt marsh communities during post seismic land uplift the microfossil data compare favourably with sequences from washington oregon and british columbia that record late holocene submergence events caused by earthquakes the comparable changes in microfossil assemblages record the different phases of relative land and sea level changes and the magnitude of land subsidence caused by each earthquake expressed relative to the tidal range at the site these results raise the question whether preseismic sea level rise represents any kind of warning of large earthquakes

palaeoecological studies of holocene lake sediments from west greenland abstract colonisation by plants and animals and subsequent biotic development in west greenland was studied by analyses of macrofossils in four holocene lake sequences one of the lake basins located near the outer coast was deglaciated shortly after the transition from the last glacial stage to the holocene and a basal date of 12 100 11 300 cal years bp was obtained two of the lake basins located near the margin of the greenland ice sheet were deglaciated several millennia later the oldest sediments contain low diversity floras and faunas some of the first immigrants were chironomidae and daphnia pulex soon followed by other insects crustaceans and other invertebrates water mosses ranunculus confervoides hippuris vulgaris and potamogeton filiformis were among the first plants that colonised the lakes the earliest holocene terrestrial flora in west greenland was probably entirely herbaceous with salix herbacea and empetrum nigrum being some of the first woody plants to arrive a number of invertebrates are new to the fossil fauna of greenland and the ostracod ilyocypris bradyi that was found in one sequence from 7000 to 6500 cal years bp has not been recorded from greenland before

early holocene large scale meltwater discharge from greenland documented by foraminifera and sediment parameters records of foraminiferal assemblages combined with lithological properties grain size magnetic parameters and xrf data of marine sediment cores from west greenland coastal waters and the adjacent labrador sea document widespread early holocene meltwater discharge this discharge is concluded to originate from large scale melting of the greenland ice sheet gis having started prior to 8600 cal yr bp and ended at about 7700 7500 cal yr bp when the gis margin had withdrawn from the fjords and become mainly land based the benthic foraminiferal record from one of the coastal sites mainly reflects west greenland current wgc subsurface water properties and to a minor degree surface productivity the most significant feature in this record is an abrupt shift to a higher productivity regime around 7700 cal yr bp we suggest that the cessation of a widespread gis meltwater discharge at that time favoured an increased influence of sub surface water of atlantic origin and initiation of modern subpolar gyre circulation enabling labrador sea deep convection further offshore a record of planktonic foraminiferal assemblages shows an oceanographic change at ca 9500 cal yr bp whilst a gradual but marked change in the planktonic foraminiferal assemblage between 8800 and 7000 cal yr bp may be related to a narrowing of the wgc low salinity surface water belt the oceanic regime off west greenland prior to 7800 cal yr bp was thus characterised by the presence of a permanent and widespread meltwater surface layer presumably preventing deep convection in this region apart from indications of a slight decrease in meltwater discharge by the benthic foraminiferal fauna data neither of the records show any clear signal of a regionally important 8 2 ka event

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

new constraints on greenland ice sheet dynamics during the last glacial cycle evidence from the uummannaq ice stream system this paper presents the first assessment of the uummannaq ice stream system uiss in west greenland the uiss drained 6 of the greenland ice sheet gris at the last glacial maximum lgm the onset of the uiss is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break mapping cosmogenic radiogenic nuclide crn dating and model output reveal that glacially scoured surfaces up to 1266 m above sea level asl in fjord head areas were produced by warm based ice moving offshore during the lgm with the elevation of warm based ice dropping westwards to 700 m asl as the ice stream trunk zone developed marginal plateaux with allochthonous blockfields suggest that warm based ice produced till and erratics up to 1200 m asl but crn ages and weathering pits suggest this was pre lgm with only cold based ice operating during the lgm deglaciation began on the outer shelf at 14 8 cal kyrs b p with ubekendt ejland becoming ice free at 12 4 ka the uiss then collapsed with over 100 km of retreat by 11 4 ka 10 8 cal kyrs b p a rapid and complex response to bathymetric deepening trough widening and sea level rise coinciding with rapidly increasing air temperatures and solar radiation but which occurred prior to ocean warming at 8 4 cal kyrs b p local fjord constriction temporarily stabilized the unzipped uiss margins at the start of the holocene before ice retreat inland of the current margin at 8 7 ka

the recession of the inland ice margin during the holocene climatic optimum in the jakobshavn isfjord area of west greenland recent subsurface mapping of parts of the greenland inland ice margin in the region of jakobshavn isbrae indicates that the fjord system in the period of at least 2700 4700 calendar yr b p was more ice free than at present and that the front of the glacier was at least 15 km behind the present position the 14c datings of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for greenland s first settlers the sarqaq people who arrived in the region about 4000 yr ago to find hunting grounds 10 20 larger than the present

10be measurements in bedrock constrain erosion beneath the greenland ice sheet margin glacial erosion is a key process driving landscape evolution but it remains unclear what factors dictate the rate and which subglacial erosion occurs and moreover measurements of subglacial erosion that do not rely on sediment flux measurements are rare here we present in situ 10be measurements from bedrock surfaces in western greenland with well constrained ice cover histories to quantify the erosion rate beneath the greenland ice sheet margin during historical times we calculate an abrasion rate of 0 72 0 35 mm yr 1 and a likely total basin wide erosion rate abrasion quarrying of 1 1 8 mm yr 1 which are at least 1 order of magnitude higher than typical subglacial erosion rates in other polar landscapes a compilation of published 10be data suggest that the southwestern greenland ice sheet acts as a particularly effective erosional agent within the broader baffin bay greenland region over millennial to glacial interglacial timescales suggestive of a basal ice sheet thermal regime controlled by regional climate

cycle of earthquake induced aggradation and related tidal channel shifting upper turnagain arm alaska usa aggradation of intertidal sediment in upper turnagain arm a macrotidal estuary located in southern alaska near anchorage began because of subsidence caused by sediment consolidation and tectonic lowering of the land during the earthquake of march 27 1964 at the head of the arm decrease in percent sand of surface sediments with time and return of rodents pulmonate gastropods trees bushes and grasses to the intertidal region indicate that the rate of sediment deposition has slowed and the upper turnagain arm area has returned to a state of preearthquake equilibrium only 17 years after the event comparison of channel locations before and after the earthquake indicates the possibility of regional postseismic tilting of the estuary

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

post younger dryas deglaciation of the greenland western margin as revealed by spatial analysis of lakes lake shapes and their spatial distribution are important geomorphological indicators in previously glaciated areas their shapes are influenced by the underlying geological structure and processes of glacial sediment deposition or erosion since these processes act on large areas distribution of lakes can reflect the intensity of glacial erosional depositional processes and their spatial extent landsat imagery was used to extract lake outlines from a selected pilot study area on the widest ice free coastal margin of the south western greenland north of kangerlussuaq analysis included image classification and spatial analysis of lakes with elevation data using geographic information system gis tools a morphometric index was applied to extract kettle lakes as indicators of a specific glacial process ice stagnation analysis of their spatial distribution helped in the reconstruction of glacial dynamics in formerly glaciated terrain our results show that spatial lake distribution combined with elevation analysis can be used to identify zones of glacial erosion and deposition the highest concentrations of lakes within the study area occupy the elevation range between 164 and 361 m above sea level a s l this zone can be identified as an area where intensive glacial erosion took place in the past the widespread distribution of modeled kettle lake features within the same elevation range and across the study area suggests that the last deglaciation process was accompanied by abandonment of blocks of stagnant ice this conclusion is supported by surface exposure ages obtained in the same study area and published elsewhere copyright 2009 john wiley sons ltd

contrasting evidence of holocene ice margin retreat south western greenland constraining the greenland ice sheet s gris response to holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations ice sheet models predict enhanced ice retreat in south western greenland during the middle holocene however few geological observations corroborating the extensive retreat are available we present new data from lake sediment cores from the isua region south western greenland which provide constraints on holocene fluctuations of the gris margins our data indicate that the main gris margin was 30 km west of its present day extent by 5 7k cal a bp and had retreated to within 3 km of its present day margin by 4 6k cal a bp with subsequent re advances by 1 8 and at 1 7 1 3 and 0 5k cal a bp times of ice retreat are coeval with increasing temperatures in western greenland suggesting that temperature was a dominant factor in ice retreat the late retreat at isua is in contrast to the early retreat observed in the godthabsfjord area and is probably related to the lack of fjords extending to the present isua ice margin our data are not consistent with current ice sheet models that overestimate the middle holocene ice retreat in the isua region of south western greenland

cosmogenic nuclide exposure ages along a vertical transect in western norway implications for the height of the fennoscandian ice sheet 10 be and 26 al exposure ages for bedrock samples from a vertical transect at skala in western norway provide new constraints on the history of the fennoscandian ice sheet the weathered bedrock surface autochthonous block field mantling the summit of skala has an exposure age of 55 ka suggesting that this surface formed before the last glacial maximum 18 14 c ka or 21 calendar ka the block field is truncated by a glacial trimline at 1660 m above sea level glaciated bedrock below the trimline has an exposure age of 26 21 ka the range depends on assumptions about erosion rate ice therefore receded from this altitude at about the time of the last glacial maximum the 10 be age for bedrock immediately below a second lower trimline at skala suggests a glacial advance or stillstand at 18 13 ka consistent with previously documented readvances or stillstands at the western and southern margins of the ice sheet

the deglaciation history of the simplon region southern swiss alps constrained by 10be exposure dating of ice molded bedrock surfaces the deglaciation history of the swiss alps after the last glacial maximum involved the decay of several ice domes and the subsequent disintegration of valley glaciers at high altitude here we use bedrock exposure dating to reconstruct the temporal and spatial pattern of ice retreat at the simplon pass altitude 2000 m located 40 km southwest of the rhone ice dome eleven 10be exposure ages from glacially polished quartz veins and ice molded bedrock surfaces cluster tightly between 13 5 0 6 ka and 15 4 0 6 ka internal errors indicating that the simplon pass depression became ice free at 14 1 0 4 ka external error of mean age this age constraint is interpreted to record the melting of the high valley glaciers in the simplon pass region during the warm bolling allerod interstadial shortly after the oldest dryas stadial two bedrock samples collected a few hundred meters above the pass depression yield older 10be ages of 17 8 0 6 ka and 18 0 0 6 ka these ages likely reflect the initial downwasting of the rhone ice dome and the termination of the ice transfluence from the ice dome across the simplon pass toward the southern foreland there the retreat of the piedmont glacier in val d ossola was roughly synchronous with the decay of the rhone ice dome in the interior of the mountain belt as shown by 10be ages of 17 7 0 9 ka and 16 1 0 6 ka for a whaleback at 500 m elevation near montecrestese in northern italy in combination with well dated paleoclimate records derived from lake sediments our new age data suggest that during the deglaciation of the european alps the decay of ice domes was approximately synchronous with the retreat of piedmont glaciers in the foreland and was followed by the melting of high altitude valley glaciers after the transition from the oldest dryas to the bolling allerod when mean annual temperatures rose rapidly by 3 c

summary of quaternary geology of the municipality of anchorage alaska abstract quaternary geology of the upper cook inlet region is dominated by deposits of glacier retreats that followed repeated advances from both adjacent and more distant mountains at several levels high on the mountains there are remnant glacial deposits and other features of middle or older pleistocene age late pleistocene lateral moraines along the chugach mountain front represent successively younger positions of ice retreat from the last glacial maximum as the trunk glacier retreated northeastward up the anchorage lowland cook inlet transgressed the area depositing the bootlegger cove formation and tudor road deposits the glacier then readvanced to form the latest pleistocene elmendorf moraine a prominent feature that trends across the anchorage lowland extensive alluvium was deposited both concurrently and somewhat later as cook inlet regressed mountain valleys contain 1 locally preserved moraines possibly of early holocene age 2 poorly preserved moraine remnants of older late holocene age and 3 well preserved moraines formed mainly during the little ice age glaciers still occupy large parts of the mountains the upper ends of some mountain valleys and small cirques holocene landslide deposits including those formed during the great alaska earthquake of 1964 occur throughout the area especially along bluffs containing the bootlegger cove formation

the deglaciation of clyde inlet northeastern baffin island arctic canada the behaviour of ice sheets as they retreated from their last glacial maximum lgm positions provides insights into lateglacial and early holocene ice sheet dynamics and climate change thepatternofdeglaciationofthelaurentideicesheet lis inarcticfiordlandscapescannow bewelldatedusingcosmogenicexposuredating weusecosmogenicexposureandradiocarbonages to constrain the deglaciation history of clyde inlet a 120km long fiord on northeastern baffin island the lis reached the continental shelf during the lgm retreated from the coastal lowlands by 12 5 0 7ka n 3 and from the fiord mouth by 11 7 2 2ka n 4 rapid retreat from the outer fiord occurred 10 3 1 3ka n 6 with the terminus reaching the inner fiord shortly after 9 4ka n 2 where several moraine systems were deposited between ca 9 4 and ca 8 4ka these moraines represent fluctuations of the lis during the warmest summers since the last interglaciation and this suggests that the ice sheet was responding to increased snowfall before retreating from the head of clyde inlet the lis margin fluctuated at least twice between ca 7 9 and ca 8 5ka possibly in response to the 8 2ka cold event copyright 2006 john wiley sons ltd

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

a large earthquake occurring 700 800 years ago in aialik bay southern coastal alaska a conifer forest on the shore of verdant cove an inlet of aialik bay on the southeast coast of the kenai peninsula alaska was buried by high energy beach sediments shortly after 860 50 i4c years bp the switch from ocean distal forest to cobble beach indicates a radical change in depositional environment suggestive of rapid subsidence of 1 3 5 m the presence of hemlock a tree taxon sensitive to salt water exposure and the preserved cast of a tree trunk suggest that subsidence and burial occurred rapidly by 690 60 14c years bp forest peat was accumulating atop the beach sediments burying the forest and rapid spit progradation was underway spit progradation implies land emergence or stable sea level especially in this case where the spit has a limited sediment supply we infer that subsidence of the spit ca 860 50 14c years bp was followed by slow land emergence up to the time of the 1964 ad great earthquake when the area subsided coseismically 1 4 m the sudden drowning of the buried fore

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

glacial geological geomorphological research in west greenland used to test an ice sheet model abstract ice sheet modeling is an essential tool for estimating the effect of climate change on the greenland ice sheet the large spatial and long term temporal scale of ice sheet models limits the amount of data which can be used to test model results a framework for the analysis of glacial geological data to test ice sheet models is illustrated by a case study in west greenland a geological scenario of ice margin positions since the last glacial maximum is based on a review of existing literature and new datings of moraine systems ages of moraine systems and associated accuracy ranges are interpolated to a 1 1 km grid over an area of about 57 500 km 2 resampling to a 20 20 km grid on an ice sheet model coordinates permits a quantitative comparison with modeled ice marginal positions in view of the uncertainties in the geological scenario with moraine system ages having an absolute uncertainty of 700 to 3300 cal yr the greenland ice sheet model of huybrechts provides a reasonable simulation of the deglaciation pattern in central west greenland modeled timing of the position of the ice margin generally precedes the geological record by 900 yr the difference between geology and model is large for areas without proper geological information and small but still about 500 950 yr for well dated moraine systems model deficiencies in west greenland are probably related to the forcing function driving ablation estimates and especially the forcing function for sea level and the description of calving processes should he reviewed critically the simplified topography used by the model could also induce errors although topography used in models neglects possible important features such as ice streams we do not find any significant trend between differences and relief amplitude missing moraines on the southern part of the shelf and absence of geological information from beneath the present ice sheet affect the character and quality of the geological scenario

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

chronology of the last recession of the greenland ice sheet a new deglaciation chronology for the ice free parts of greenland the continental shelf and eastern ellesmere island canada is proposed the chronology is based on a new compilation of all published radiocarbon dates from greenland and includes crucial new material from southern northeastern and northwestern greenland although each date provides only a minimum age for the local deglaciation some of the dates come from species that indicate ice proximal glaciomarine conditions and thus may be connected with the actual ice recession in addition to shell dates dates from marine algae lake sediments peat terrestrial plants and driftwood also are included only offshore and in the far south have secure late glacial sediments been found other previous reports of late glacial sediments older than 11 5 cal kyr bp from onshore parts of greenland need to be confirmed most of the present ice free parts of greenland and nares strait between greenland and ellesmere island were not deglaciated until the early holocene copyright c 2002 john wiley sons ltd less

early permian sediment provenance and paleogeographic reconstructions in southeastern gondwana using detrital zircon geochronology northern perth basin western australia abstract the perth basin western australia forms part of a north trending belt of intracratonic rift basins that initiated in southeastern gondwana in the late paleozoic existing provenance studies have highlighted the dominance of proterozoic zircons derived from southerly terranes such as the albany fraser orogen leeuwin complex and more distant provinces in east antarctica with limited input from the adjacent archean western australian craton new u pb geochronology data were acquired using a sensitive high resolution ion microprobe shrimp ii on detrital zircons from lower permian formations exposed in the northeastern perth basin in contrast to previous studies archean zircons showing fine oscillatory zoning dominate the age spectra with up to 90 grains ranging between 3 0 and 2 6 ga indicating that granitic parent rocks of the adjacent craton were a major sediment source during the early permian a minor paleoproterozoic age population from the gascoyne complex of the capricorn orogen was likely transported southward and dispersed in the basin by a combination of longshore drift and tidal currents meso and neoproterozoic detritus became prominent only from the middle artinskian and may relate to the establishment of large northward flowing river systems draining the albany fraser province the prydz leeuwin belt and or the wilkes land in east antarctica this study shows that integrating depositional processes and stratigraphic evolution of sedimentary formations with provenance analysis can enhance reconstruction of dispersal pathways to and within basins

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

geodetic measurements in greenland and their implications we describe results from an ongoing experiment in greenland in which we are using absolute gravity and continuous global positioning system gps measurements to study vertical crustal motion at two locations along the edge of the ice sheet kellyville located about one third of the way up the western ice margin and kulusuk located along the eastern ice margin at about the same latitude as kellyville the gps measurements suggest average crustal uplift rates of 5 8 1 0 mm yr at kellyville and 2 1 1 5 mm yr at kulusuk there have not yet been enough absolute gravity occupations to permit useful secular gravity solutions at either location the negative uplift rate at kellyville is consistent with independent archeological and historical evidence that the southwestern edge of the continent has been subsiding over the last 3000 years but it is inconsistent with estimates of the earth s continuing viscoelastic response to melting ice during the early holocene which predict that kellyville is likely to be uplifting rather than subsiding by 2 0 3 5 mm yr the resulting 7 8 3 6 mm yr discrepancy between the observed and predicted uplift rates is too large to be caused by loading from present day changes in nearby ice however it is consistent with independent suggestions that the western ice sheet margin in this region may have advanced by 50 km during the past 3000 4000 years if this advance did occur and if the crustal subsidence it induces is not removed from altimeter measurements of greenland ice sheet elevations then the altimeter solutions could underestimate the true snow ice thickness change by 5 10 mm yr along portions of the western margin of the ice sheet

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

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

ice stream influence on west greenland ice sheet dynamics during the last glacial maximum this paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central west greenland and explores the evidence for a cross shelf ice stream at the last glacial maximum lgm to the east of sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow flowing ice sheet areas at the coast the effects of regional flow convergence caused by coastal fjord orientation routed ice into the sisimiut itilleq area where it formed an ice stream onset zone this funnelled ice into an offshore trough holsteinsborg dyb resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream holsteinsborg isbrae to the south of this striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast but were later redirected by the itilleq fjord ice which turned southwestward due to diffluent flow and deflection by holsteinsborg isbrae roches moutonnees in this area have low elongation ratios and high bedform density but do not provide unequivocal support for ice streaming as they are a product of both bedrock structure and changes in ice flow direction rather than enhanced flow velocities cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca 755 810 m above sea level in this region such ice thickness enabled holsteinsborg isbrae to reach the mid outer continental shelf during the lgm and to contribute to the formation of a trough mouth fan and the outer hellefisk moraines initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the bolling interstadial at ca 14 5 cal ka bp between 12 and 10 cal ka bp both increased air and ocean temperatures post the younger dryas and peak sea level rise up to the marine limit caused accelerated thinning and marginal retreat through calving although dating evidence suggests ice streams remained along the inner shelf coast boundary until at least ca 10 cal ka bp their longevity maintained by increased ice thickness and ice discharge copyright 2009 john wiley sons ltd

apogean perigean signals encoded in tidal flats at the fluvio estuarine transition of glacier creek turnagain arm alaska implications for ancient tidal rhythmites turnagain arm is a macrotidal fjord style estuary glacier creek is a small glacially fed stream which enters the estuary tangentially near girdwood alaska trenches and daily sedimentation measurements were made in a mudflat along the fluvio estuarine transition of glacier creek during several summers since 2003 each year the flats appear to erode during the winter and then accrete vertically in the spring and summer in each of the years studied tidal laminae in vertically thickening and thinning laminae bundles were deposited by twice daily tides in neap spring tidal cycles in 2004 bundles of thickening and thinning laminae couplets were noted in trenches cut into the flats five laminae bundles alternated between thicker and thinner bundles corresponding to the perigean high spring and apogean low spring tides well preserved apogean perigean cycles have rarely been documented in modern tidal flat sediments at this location vertical accretion of tidal rhythmites with well developed neap spring cyclicity is possible because of the near complete removal of the flat from the previous year which creates accommodation space for vertical accretion without significant reworking macrotidal conditions no reworking by infaunal invertebrates protection from the main tidal channel by a gravel bar and protection from storm waves and fluvial erosion by a recess in the sedge marsh that surrounds the flats all aid in preservation of rhythmites during aggradation the position of the flats relative to tidal range allows for accumulation of complete spring cycles and incomplete neap cycles in the summer of 2004 apogee and perigee were closely aligned with the new and full moons resulting in successive strong perigee and apogee tides which probably aided in the accumulation of successive thick thin spring cycles encoding the apogean and perigean tidal cycle the apogean perigean signal was not observed in subsequent years

precise cosmogenic 10be measurements in western north america support for a global younger dryas cooling event the inner titcomb lakes moraine in the wind river mountains wyoming has been dated with a precision of 5 using accelerator mass spectrometric measurements of cosmogenic 10be in surface samples from nine boulders resting on its crest the age of this moraine is 11 4 0 5 to 13 8 0 6 ka the range in age is due to the uncertainty in the 10be production rate and uncertainties in rock erosion rate and shielding of cosmic rays by snow additional exposure ages on bedrock and boulder surfaces that are stratigraphically younger and older than the inner titcomb lakes moraine conform with this age the exposure ages of the inner titcomb lakes moraine overlap the north atlantic younger dryas event 12 8 0 2 to 11 5 0 3 ka

greenland ice sheet increased coastal thinning repeated laser altimeter surveys and modelled snowfall summer melt show average ice loss from greenland between 1997 and 2003 was 80 12 km3 yr 1 compared to about 60 km3 yr 1 for 1993 4 1998 9 half of the increase was from higher summer melting with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation velocities of one large glacier almost doubled between 1997 and 2003 resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003 copyright 2004 by the american geophysical union

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

correction of in situ cosmogenic nuclide production rates for geomagnetic field intensity variations during the past 800 000 years we present integrated relative production rates for cosmogenic nuclides in rock surfaces which take into account reported variations of the geomagnetic field intensity during the past 800 000 yr the calculations are based on the model simulating cosmic ray particle interactions with the earth s atmosphere given by masarik and beer simulation of particle fluxes and cosmogenic nuclide production in the earth s atmosphere j geophys res 104 d10 12099 12111 1999 corrections are nearly independent on altitude between sea level and at least 5000 m the correction factors are essentially identical for all stable and radioactive cosmogenic nuclides with half lives longer than a few hundred thousand years at the equator integrated production rates for exposure ages between 40 000 to 800 000 yr are 10 to 12 higher than the present day values whereas at latitudes 40 geomagnetic field intensity variations have hardly influenced in situ cosmogenic nuclide production correction factors for in situ 14c production rates differ from those of longer lived nuclides they are always smaller than 2 because the magnetic field intensity remained rather constant during the past 10 kyr when the major fraction of the 14c extant today was produced

late holocene paleoseismology of a site in the region of maximum subsidence during the 1964 mw 9 2 alaska earthquake paleoseismology of the 1964 alaska earthquake sediment archives of coseismic deformation from regions of maximum coseismic displacement act as key datasets for the development and constraint of models of surface elevation change associated with holocene great earthquakes we present new lithologic and biostratigraphic investigations of a previously thought lost core from portage at the head of turnagain arm upper cook inlet which is within the zone of maximum coseismic subsidence during the ad 1964 alaska earthquake quantitative analysis of diatoms preserved over six peat silt couplets before the ad 1964 earthquake show six phases of rapid relative sea level rise radiocarbon dates from each contact show that all six correlate with independently modelled ages of great earthquakes recorded in the prince william sound segment of the aleutian megathrust during the last 4000 years as with the other sites in the upper cook inlet there is no evidence for an earthquake between the penultimate great earthquake 880 a bp and ad 1964 in contrast to those separately recorded at kodiak island and katalla correlation of the six earthquakes at portage with those at girdwood and no evidence for additional peat silt couplets support our previous interpretation that the extra three peat silt couplets at girdwood lacking evidence of intertidal sedimentation represent local scale changes in environment rather than coseismic subsidence and short recurrence intervals of great earthquakes

beryllium 10 exposure ages of erratic boulders in southern norway and implications for the history of the fennoscandian ice sheet the margins of the fennoscandian ice sheet fis during the last glacial maximum lgm are fairly well constrained yet the thickness of the fis and its temporal evolution are poorly known here we use beryllium 10 be 10 exposure ages of glacially transported boulders along three vertical transects in southern norway to determine past ice sheet elevations the ice surface elevation during the lgm at our westernmost site skala was likely at approximately 1440 in coinciding with a previously mapped trimline at our central site blaho the ice surface elevation at the lgm was at least at similar to 1620m likely closer to 1800m at elgahogna our easternmost site lgm ice was above the summit elevation of 1460m rapid deglaciation began at skala and blaho at approximately 13 5 14 5 10 beka and at approximately 12 be 10 ka at elgdhogna by approximately 9 be 10 ka the fis had thinned to below our lowest sample at each location periods of rapid thinning correlate with an exposure dated ice margin history as well as the glaciation curve for western scandinavia our data when combined with previous bedrock and blockfield highly weathered bedrock on summits exposure ages resolve a long standing debate over the age and geomorphic interpretation of blockfields and weathering zones in southern norway frozen bed low erosive ice clearly covered the summit blockfields at blaho and especially at elgdhogna where we find a large and progressive divergence between boulder and bedrock exposure ages with elevation we conclude that the lower limit of blockfields in these areas should be interpreted as an englacial thermal boundary rather than the upper limit of the lgm fis and that blockfields have survived multiple glacial cycles we also compare our deglaciation record with several models of the fis models that predict how the fis changed during deglaciation either through inversion of crustal rebound or through climate dependent forward modeling generally match our exposure ages reasonably well during deglaciation but predict larger lgm surface elevations than our data indicate on the other hand the climap maximum model which provides lgm elevations only agrees with our results fairly well c 2007 elsevier ltd all rights reserved

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

widespread early holocene deglaciation washington land northwest greenland abstract constraining the greenland ice sheet gis response to past climate change is imperative for understanding modern ice sheet sensitivity to rising temperatures in this study we investigate the response of the gis to warming during the last deglaciation across the currently ice free area of washington land in northwest greenland we apply 10be cosmogenic surface exposure dating to glacially transported boulders deposited across the landscape the interpretation of the dates offering insight into gis retreat after the last glacial maximum we find that the northwestern sector of the gis sustained full ice cover across washington land until 11 ka then began thinning with widespread ice retreat culminating by 8 5 1 1 ka the record of our new exposure ages indicates that deglaciation occurred 2 3 ka after abrupt warming at the end of the younger dryas cold period which suggests a delayed response of the gis to this regional warming

constraining holocene 10be production rates in greenland the absence of a production rate calibration experiment on greenland has limited the ability to link 10be exposure dating chronologies of ice margin change to independent records of rapid climate change we use radiocarbon age control on holocene glacial features near jakobshavn isbrae western greenland to investigate 10be production rates the radiocarbon chronology is inconsistent with the 10be age calculations based on the current globally averaged 10be production rate calibration data set but is consistent with the 10be production rate calibration data set from north eastern north america which includes a calibration site nearby on north eastern baffin island based on the best dated feature available from the jakobshavn isbrae forefield we derive a 10be production rate value of 3 98 0 24 atoms g a 1 using the st scaling scheme which overlaps with recently published reference 10be production rates we suggest that these 10be production rate data or the very similar data from north eastern north america are used on greenland copyright 2011 john wiley sons ltd

holocene glaciation of alaska and adjoining yukon territory canada abstract holocene glacial fluctuations between arctic central interior and southern maritime alaska are broadly synchronous this synchrony is evident from a review of work in 11 study areas with varying numbers of glaciers 3 100 glacier types subpolar cirque temperate valley tidewater surging and dating methodologies the pattern is temporally and spatially consistent with vegetation data and generally with climatic deteriorations culminating in the little ice age early holocene glacial advances are confirmed for 7 6 5 8 lichen ka bp at 4 of 97 glaciers in the brooks range advances also occurred by 5 85 and 5 7 ka bp at separate glacier tongues in the northern alaska range at least by 6 5 ka bp in lituya bay and possibly also in the malaspina and aleutian islands areas a sharp increase in glacier activity began by 4 4 ka bp in the arctic and glacier bay areas and by about 3 ka bp major glacier advances probably were initiated or well underway throughout alaska during holocene glacial maxima ice filled glacier and lituya bays as well as fjords of prince william sound and massive moraines buried forests in the northeastern st elias mountains area minor recession is recorded directly or implied in most of alaska about 2 ka bp or locally through the following millennium subsequently distinct but locally weak advances occurred by about 1 2 ka bp in most areas again followed by intervals of glacier recession most pervasive and ubiquitous were the little ice age advances initiated about 700 bp these generally culminated in two major advances between about 400 and 50 bp in the arctic those of a d 1600 dominated those of the late 1800s in the gulf of alaska those of the middle 1700s or late 1800s dominated large scale asynchronous advances and retreats of calving tidewater glaciers have been recorded during the twentieth century but most such movements are only indirectly related to climate

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

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

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

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

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

early deglacial onset of southwestern greenland ice sheet retreat on the continental shelf abstract the greenland ice sheet gris advanced onto the continental shelf during the last glacial period while deglacial records for when the gris withdrew onto the modern coastline are relatively abundant the timing of early gris retreat on the shelf is poorly constrained here we use planktic foraminiferal 18 o sediment grain size sedimentation rates and 14 c ages in southeastern davis strait core hu87033 008 to develop an early deglaciation chronology of the southwestern gris while on the continental shelf sedimentation rates and especially silt and clay fractions are high between 20 5 and 17 1 ka suggesting that the southwestern gris margin was near or at the shelf break where it released subglacially derived sediment laden meltwater a peak in sedimentation rates of 110 cm ka 1 between 19 3 ka and 18 6 ka combined with an initial decrease in planktic 18 o of 0 5 per mil suggests an early deglacial pull back of the gris margin from the shelf break with a concurrent increase in surface ocean meltwater discharge a subsequent planktic 18 o decrease of 1 0 per mil combined with a drop in silt and clay sedimentation rates at 18 17 ka likely record further gris retreat inland from the shelf break terrestrial 10 be surface exposure ages indicate that the gris margin remained on the continental shelf until 11 ka yet the cause of this subsequent ice margin stability on the inner shelf is not known our new records provide the first evidence that the southwestern gris margin may have begun to deglaciate at the same time as other northern hemisphere ice sheets as labrador sea water temperatures likely remained near glacial values until 15 ka we suggest that initial southwestern gris retreat was in response to rising global sea level from retreat of other ice sheets and or the initial deglacial rise in boreal summer insolation

the last deglaciation of the southeastern sector of the scandinavian ice sheet the scandinavian ice sheet sis was an important component of the global ice sheet system during the last glaciation but the timing of its growth to or retreat from its maximum extent remains poorly known we used 115 cosmogenic beryllium 10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice margin fluctuations of the sis between 25 000 and 12 000 years before the present the age of initial deglaciation indicates that the sis may have contributed to an abrupt rise in global sea level subsequent ice margin fluctuations identify opposite mass balance responses to north atlantic climate change indicating differing ice sheet sensitivities to mean climate state

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

cosmogenic exposure dating in arctic glacial landscapes implications for the glacial history of northeastern baffin island arctic canada cosmogenic exposure dating and detailed glacial terrain mapping from the clyde foreland baffin island arctic canada reveal new information about the extent and dynamics of the northeastern sector of the laurentide ice sheet lis during the last glacial maximum lgm the clyde foreland is composed of two distinct landscape zones 1 glacially scoured terrain proximal to the major sources of laurentide ice that flowed onto the foreland and 2 ice distal unscoured sectors of the foreland both zones are draped with erratics and dissected by meltwater channels indicating past ice cover we interpret the two landscape classes in terms of ice sheet erosive ability linked with basal thermal regime glacially scoured terrain was occupied by erosive warm based ice and unscoured terrain was last occupied by non erosive cold based ice cosmogenic exposure ages from 100 erratics from the two landscape types have different age distributions cosmogenic exposure ages from the glacially scoured areas suggest ice cover during the lgm followed by deglaciation between 15 and 12 ka in the unscoured lowlands the cosmogenic exposure ages have multiple modes ranging between 12 and 50 ka suggesting multiple periods of cold based ice cover during the last glacial cycle in landscapes covered by cold based ice large numbers of cosmogenic exposure ages are required for elucidating glacial histories

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

meteoric 10 be as a tracer of subglacial processes and interglacial surface exposure in greenland abstract in order to test whether sediment emerging from presently glaciated areas of greenland was exposed near or at earth s surface during previous interglacial periods we measured the rare isotope 10be contained in grain coatings of sediment collected at five ice marginal sites such grain coatings contain meteoric 10be 10bemet which forms in the atmosphere and is deposited onto earth s surface samples include sediment entrained in ice glaciofluvial sediment collected at the ice margin and subglacial sediment extracted during hot water drilling in the ablation zone due to burial by ice contemporary subglacial sediment could only have acquired substantial 10bemet concentrations during periods in the past when the greenland ice sheet was less extensive than present the highest measured 10bemet concentrations are comparable to those found in well developed long exposed soils suggesting subglacial preservation and glacial transport of sediment exposed during preglacial or interglacial periods ice bound sediment has significantly higher 10bemet concentrations than glaciofluvial sediment suggesting that glaciofluvial processes are sufficiently erosive to remove tracers of previous interglacial exposures northern greenland sites where ice and sediment are supplied from the ice sheet s central main dome have significantly higher 10bemet concentrations than sites in southern greenland indicating greater preglacial or interglacial landscape preservation in central greenland than in the south because southern greenland has more frequent and spatially extensive periods of glacial retreat but nevertheless has less evidence of past subaerial exposure we suggest that 10bemet measurements in glacial sediment are primarily controlled by erosional efficiency rather than interglacial exposure length

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

response of a land terminating sector of the western greenland ice sheet to early holocene climate change evidence from 10 be dating in the sondre isortoq region abstract the prevalence of land terminating greenland ice sheet margins is expected to increase as tidewater glaciers retreat onto land yet few studies have characterized the sensitivity of these slow moving margins to climatic variability the response of land terminating ice sheet sectors to climate forcing can be assessed by examining records of paleo ice margin positions preserved in ice sheet moraine systems in western greenland the extensive fjord stade moraine system was deposited by minor readvances or stillstands of the greenland ice sheet margin during early holocene net recession here we combine new moraine mapping and cosmogenic 10be exposure dating to constrain the timing of fjord stade moraine deposition in the sondre isortoq region we find that the fjord stade moraines are composed of a western stage and an eastern stage which we constrain to 9 7 0 7 ka n 7 1 sd and 9 0 0 3 ka n 7 1 sd respectively synchronous deposition of the fjord stade moraine complex across at least 350 km of western greenland implies a widespread response of the western greenland ice sheet to the 9 3 ka event furthermore these new moraine ages may correlate with laurentide ice sheet sourced freshwater pulses into the north atlantic ocean we also show that the response of the western greenland ice sheet to early holocene freshwater forcing was not restricted to fast flowing marine terminating outlet glaciers the land terminating margin in the sondre isortoq region halted or reversed its pattern of retreat in response to climatic change