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

a high resolution14c dated sediment sequence from southwest sweden age comparisons between different components of the sediment a macrofossil rich glaciomarine marine lacustrine sediment from a soft water lake in southwestern sweden has provided an opportunity to 14c date different components of its sediments bulk sediment dates are 100 to 500 yr older than fragile terrestrial macrofossils of corresponding levels with a mean age difference of ca 300 yr this is explained by the presence of old and reworked organic material in the sediment five age comparisons between terrestrial macrofossils and periostraca of marine bivalves probably arctica islandica of allerod age give a mean age difference of 380 yr i e slightly greater than the present reservoir age of 340 30 yr for the swedish west coast this difference is roughly the same as for the marine macroalga desmarestia aculeata a date from shell carbonate fragments of mytilus edulis yields an age that is more than 1000 yr older than corresponding periostraca and terrestrial macrofossils and 500 1000 yr older than the age of the supposed deglaciation of the site altogether this indicates a larger marine reservoir effect during the allerod than at present 1998 john wiley sons ltd

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

greenland glacial history and local geodynamic consequences summary space time reconstructions of the continental ice sheets that existed at last glacial maximum lgm have previously been produced using two entirely independent methodologies one based upon the use of theoretical models of ice sheet accumulation and flow and one based upon the geophysical inversion of relative sea level rsl histories from previously ice covered regions the analyses described in this paper demonstrate the significant advantages that derive from the simultaneous application of both methods to the particular case of greenland we thereby show that the ice 4g reconstruction of the glaciation history of this region from lgm to present which was based upon the geophysical inversion of rsl data alone was reasonably accurate in the peripheral regions where rsl data were available but inaccurate in the interior of the ice sheet which was unconstrained by such information we test the new model of greenland glacial history determined by the simultaneous application of the constraints that derive from ice sheet modelling and the geophysical inversion of rsl data by employing recently published geodetic inferences of mass balance over the entire interior region of the ice sheet and of gps measurements of vertical crustal motion these observations which were not employed to constrain the ice sheet reconstruction provide significant support for the new glacial history for greenland that our analyses have led us to infer

reconstructing recent relative sea level changes in west greenland local diatom based transfer functions are superior to regional models we present the results of an investigation into the potential of salt marshes in the aasiaat area west greenland for recent relative sea level rsl reconstruction we use 64 modern diatom samples to develop a transfer function that has a rmsep of 0 16 m and an r2 of 0 84 we combine these with a similar data set from sisimiut 250 km south of aasiaat standardising the data to account for tidal range differences an aasiaat sisimiut and a combined model is used to reconstruct rsl change from two recently deposited sediment sections all three models predict similar rsl change for sediment deposited in low marsh settings but for sediment deposited in high marsh environments the models differ our preferred aasiaat model reconstructs rsl rise from c 0 6 m at c 570 cal yr bp to stabilise within 0 20 m of present after 400 cal yr bp model differences are related to variations in the high marsh upland vegetation zones diatom assemblages and organic content between sites that are likely related to differences in tidal range we conclude that a local transfer function model is superior to a combined site model for rsl reconstruction in west greenland

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

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

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

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

lateglacial to holocene relative sea level changes in the bjarkarlundur area near reykholar north west iceland this paper presents results from seven isolation basins to investigate the relative sea level history from the lateglacial and the mid to late holocene from the bjarkarlundur area near reykholar on the reykjanes peninsula in north west iceland results presented help to constrain the timing and rate of relative sea level rsl change since deglaciation and also the timing of deglaciation itself in the bjarkarlundur area the marine limit is estimated to be approximately 80 m above sea level based on an isolation basin with sill altitude at 79 1 m the maximum age of this marine limit and hence local deglaciation is estimated at 12 2 14c ka bp relative sea level then fell rapidly during the late bolling early allerod at a rate of approximately 35 mm 14c a 1 to below 50 m by 11 4 14c ka bp after this the rate of rsl fall decreased significantly during the late allerod and younger dryas chronozones averaging 6 mm 14c a 1 between 11 4 and 9 7 14c ka bp based on isolation basins with sill altitudes of 51 1 and 41 1 m our data constrain any possible fluctuation in rsl produced by regrowth of ice during the younger dryas to below 10 m after 9 7 14c ka bp the rate of rsl fall increased significantly to approximately 23 mm 14c a 1 to at least 9 0 14c ka bp if eustatic sea level rise is taken into account and the calibrated timescale is used actual crustal uplift rates are estimated at 56 and 46 mm cal a 1 during lateglacial and early holocene times respectively during the mid to late holocene rsl then rose to at least 1 m above present day levels gradually falling to the present day level from 3 1 14c ka bp these results demonstrate the potential of isolation basin data for investigating the timing and rate of rsl change in iceland this can add important well constrained information on rsl when combined with data from raised beaches copyright 2009 john wiley sons ltd

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

holocene sea level reconstruction in the young sound region northeast greenland a relative sea level curve over the holocene is constructed for the young sound region in northeastern greenland the reconstruction is derived by dating the heights of raised beach ridges in coastal plains using optically stimulated luminiscence osl and by dating palaeoterrestrial surface levels now buried beneath the intertidal frame using the 14 c technique the relative sea level curve reveals a rapid fall of at least 10 mm a 1 from ca 9500 to 7500 a ago which slowed to 2 mm a 1 until it reached the present sea level ca 3000 a ago this part of the curve is based on the raised beach ridge data thereafter relative sea level continued to fall to reach a minimum level at about 0 5 m below the present sea level ca 2300 a ago since then relative sea level has experienced a slow rise of about 0 2 mm a 1 this part of the curve uses the data from the palaeoterrestrial surfaces the study supplements other estimates of holocene relative sea level changes and supports the observations of a decreasing trend in the timing of the cross point and in minimum relative sea level from south to north greenland copyright 2011 john wiley sons ltd

late holocene land and sea level changes in the british isles implications for future sea level predictions abstract four decades of palaeosea level research in the british isles have produced a large dataset of age altitude curves of postglacial sea level changes patterns of late holocene relative sea level change reveal the persistent influence of the british irish ice sheet and the larger scandinavian ice sheet on contemporary rates of vertical land movements the shennan and horton 2002 map of late holocene relative land movements has been used in future sea level rise predictions by the united kingdom climate impact programme in their 2002 assessment ukcip02 but has been mistaken for a map of absolute land movements in this paper land motion data for britain are extracted from the shennan and horton 2002 relative sea level data and a new map of crustal land movements is presented which also includes ireland this procedure takes into account the regional 20th century sea level rise 0 14 m and the process of ocean syphoning i e a global fall in sea level of 0 3 mm yr due to gia induced ocean floor lowering and re distribution of ocean mass the calculated land motion rates also depend on the global late holocene ice equivalent sea level change given by the intergovernmental panel on climate change as 0 0 0 2 mm yr accounting for these processes reduces the misfit between geological observations of vertical land motion and those independently derived from gravity aligned global positioning system ag gps measurements and shows that ukcip02 has underestimated land subsidence in southern britain and over estimated land uplift in scotland both by 0 1 0 2 mm yr a best fit between gps and geological estimates of land movements in britain is achieved for a global long term eustatic sea level fall of ca 0 2 mm yr suggesting some global ice expansion in the late holocene rather than melt if this is correct uplift rates in scotland would be lower and subsidence rates in southern britain would be faster by 0 4 0 5 mm yr than estimated by ukcip02 more high quality late holocene relative sea level data are required to quantify vertical land motion as accurately as possible especially near large coastal population centres for input into regional scenarios of future sea level rise

a below the present late holocene relative sea level and the glacial isostatic adjustment during the holocene in the malay peninsula abstract this study has reconstructed the holocene relative sea level history in the relatively tectonically stable malay peninsula with two specific objectives quantifying the sea level indicative meanings of mangrove sediments and producing new high quality sea level index points in this study a wetland on the east coast of the peninsula was extensively surveyed the elevational relationship between habitat zones and their pollen and diatom assemblages was established and a number of indicative meanings were precisely quantified for this wetland this quantified relationship is extrapolated to other coastal sites of the peninsula for re calibration of previously published mangrove based sea level data the reconstructed sea level history from the new and re calibrated data demonstrates a period of rapid sea level rise at a rate of 15 8 3 9 mm a between 10 500 cal a bp at 35 0 4 3 m and 9000 cal a bp at 14 2 1 6 m the rate of rising sea level was gradually reduced to zero from 9000 to 5000 cal a bp and by the end of this period the relative sea level reached a highstand of c 3 3 0 2 m over the past 5000 years relative sea level fell to its lowest point at 0 6 0 1 m by 800 cal a bp this far field sea level history has been driven by the global ice volume change and glacial isostatic adjustment and it matches well with the modelled ice volume equivalent sea level

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

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

gps measurements of vertical crustal motion in greenland we have analyzed 5 years of continuous global positioning system gps measurements taken at kellyville just off the western margin of the ice sheet in southern greenland a fit to the vertical component gives a negative secular uplift rate of 5 8 1 0 mm yr a negative rate i e a subsidence is consistent with archeological and historical evidence that the surrounding region has been subsiding over the last 3 kyr however it is inconsistent with estimates of the earth s continuing viscoelastic response to melting ice prior to 4 ka years ago which predict that kellyville should be uplifting rather than subsiding by 2 0 3 5 mm yr the resulting 7 8 3 6 mm yr discrepancy is too large to be the result of loading from present day changes in nearby ice we show instead that it is consistent with independent suggestions that the western ice sheet margin in this region of greenland may have advanced by 50 km during the past 3 4 kyr

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

relative sea level change in west greenland during the last millennium relative sea level rsl data provide important long term century to millennial scale constraints on ice load history in greenland in this paper we present the results of a litho bio and chronostratigraphic study designed to reconstruct rsl during the last millennium from salt marsh deposits recovered from a field site near to the town of sisimiut west greenland the stratigraphy at three marshes typically records an upwards transition from freshwater to salt marsh deposits we use a quantitative transfer function and subjective model to reconstruct palaeomarsh elevation and changes in mean tide level mtl from 16 sediment profiles from these marshes these palaeomarsh elevations are placed in a chronological framework established by 18 radiocarbon dated index points both models yield similar results and show mtl rose from 0 60 0 20 m at c 600 cal a bp to reach 0 10 0 20 m at c 400 cal a bp after this time mtl remained close to present 0 20 m until the present day although low sedimentation rates limit the resolution of our reconstructions during this interval the initial rise in rsl can be explained by the dominance of non greenland processes notably the collapse of the laurentide forebulge over local greenland solid earth uplift caused by postglacial ice unloading this is despite some reloading of the crust that occurred during the neoglacial expansion of the greenland ice sheet in this part of west greenland the slow down in rsl at 400 cal a bp does not record either a change in the rate of laurentide forebulge collapse or a change in eustatic sea level we argue instead that this slow down records the effects of a sustained reduction in local greenland ice mass that persists over most of the past 400 years the latter interval is widely acknowledged as a period of generally cooler than present conditions associated with the later stages of the little ice age during this period field evidence suggests that in many areas the ice sheet had reached its maximum late holocene extent it is not obvious at this stage how to reconcile an expanding ice sheet with a reduction in ice load during this interval although we hypothesise it could reflect one or more of i a change in ice sheet dynamics ii reduced mass accumulation caused by cold and dry conditions and iii a lagged response to earlier periods of climate warming

salt marshes as archives of recent relative sea level change in west greenland abstract temperate latitude salt marshes are a proven environment from which high precision 0 10 0 20 m relative sea level rsl records can be developed over recent decades and centuries such records provide an important link between millennial histories of rsl change and instrumental records the high latitude salt marshes in greenland have not previously been explored as potential archives of recent rsl change here we develop four diatom based transfer functions using contemporary diatom data collected from three salt marshes located 40 km south of the coastal town of sisimiut west greenland our preferred model has a good fit between observed and predicted elevations r 2 0 94 and a root mean square error prediction of 0 19 m we apply the four models to a short sediment profile collected from one of the marshes that formed between c 600 cal year bp and the present three of the four models predict the same trend in which rsl rose from 0 55 0 19 m mean tide level mtl to 0 05 0 19 m mtl between c 600 and 400 cal year bp at a rate of c 2 7 mm year 1 after 400 cal year bp rsl slowed and remained stable until the present day the results of this study demonstrate that greenland salt marshes are potentially valuable archives of data for developing quantitative estimates of rsl change during the last few centuries thereby bridging the gap between existing millennial scale approaches and more recent direct observations of ice sheet behaviour and associated vertical land motions

century scale relative sea level changes in west greenland a plausibility study to assess contributions from the cryosphere and the ocean this paper interprets high resolution relative sea level rsl reconstructions obtained from recently deposited salt marsh sediments in greenland the primary aim of this study is to determine the relative contribution to the rsl observations from local to regional ice mass changes as well as density related steric variations in the adjacent ocean at sites in west greenland rsl rise slows from 3 mm yr to 0 mm yr at 400 years bp and is stable thereafter in south greenland a similar rsl slowdown is also observed but this occurs approximately 200 yrs later substantial contributions from oceanographic changes are ruled out as dominant drivers of the rsl slowdown in western greenland but could be more important at nanortalik model sensitivity tests indicate that the rsl data are not compatible with a dominant dynamic ice loss via the jakobshavn isbrae outlet glacier as the region of ice loss and the resulting sea level trends are too localised regional changes in ice thickness related to surface mass balance changes can explain the observed rsl signals but only if there is dominant mass loss during the period 400 years bp to present this conclusion is unaffected even when uncertainties in earth viscosity structure are taken into account however it is plausible that some of the rsl fall may be due to reduced ice growth at the onset of the little ice age a high resolution mass balance history of the greenland ice sheet over the past few millennia and the influence of lateral earth structure on predictions of rsl change are identified as priority areas of study in order to confidently separate local transient e g elastic and gravitational rsl changes from the long term viscous contribution associated primarily with deglacial changes

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

induced seismicity in the geysers geothermal area california a simultaneous inversion for hypocenters velocities and station delays was performed from the p arrival times of 55 microearthquakes and four explosions distributed throughout a 90 by 100 km region centered at the geysers geothermal area in northern california the resulting one dimensional layered model shows velocity increasing with depth from 4 4 km s at the surface to 5 9 km s at 8 km and deeper we relocated 7215 earthquakes which occurred between may 1975 and february 1982 using the new velocity model these relocations show a significant spatial clustering near production wells in the steam field that was not apparent in earlier studies we infer from the spatial and temporal pattern of seismicity that the seismicity at the geysers is induced by geothermal production activities with the expansion of power production by approximately 70 in 1979 1980 seismic activity has developed near the new production areas seismicity has also expanded northwestward of the present production area although there are no active steam wells in this area statistical cross correlations between the number of earthquakes per month and both steam withdrawal per month and injection volume per month were calculated for the wells studied we find no consistent pattern of correlation between injection and seismicity likewise we find little or no correlation between steam withdrawal and seismicity for steam wells in production longer than 7 years two mechanisms remain plausible for inducing seismicity at the geysers volumetric contraction due to mass withdrawal may perturb the stress field and cause faulting in reservoir rock already near failure due to the regional stress field alternatively aseismic deformation due to regional tectonic stress may be converted to stick slip seismic deformation due to an increase of coefficient of friction along fault surfaces such as could occur from exsolution of dissolved silica into fractures neither mechanism would be likely to show strong correlation between production and seismicity rates however we expect seismicity to continue in the geysers and for seismicity to appear in areas where new production occurs

relative sea level history from the lambert glacier region east antarctica and its relation to deglaciation and holocene glacier readvance we present a relative sea level rsl history constrained by ams radiocarbon dated marine freshwater transitions in isolation basins from a site adjacent to the lambert glacier east antarctica the rsl data suggest an initial ice retreat between c 15 370 and 12 660 cal yr b p within this period meltwater pulse ia mwp ia between c 14 600 14 200 and 14 100 13 700 cal yr b p occurred an exceptionally large ice melting event inferred from far field sea level records the rsl curve shows a pronounced highstand of approximately 8 m between c 7570 7270 and 7250 6950 cal yr b p that is consistent with the timing of the rsl highstand in the nearby vestfold hills this is followed by a fall in rsl to the present in contrast to previous findings the isolation of the lakes in the larsemann hills postdates the isolation of lakes with similar sill heights in the vestfold hills an increase in rsl fall during the late holocene may record a decline in the rate of isostatic uplift in the larsemann hills between c 7250 6950 and 2847 2509 cal yr b p that occurred in response to a documented mid holocene glacier readvance followed by a late holocene retreat

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

relative sea level changes since 15 000 cal yr bp in the nanortalik area southern greenland we present new results for relative sea level change for southern greenland for the interval from 9000 cal yr bp to the present together with earlier work from the same region this yields a nearly complete record from the time of deglaciation to the present isolation and or transgression sequences in one lake and five tidal basins have been identified using lithostratigraphic analyses sedimentary characteristics magnetic susceptibility saturated induced remanent magnetisation sirm organic and carbonate content and macrofossil analyses ams radiocarbon dating of macrofossils and bulk sediment samples provides the timescale relative sea level fell rapidly and reached present day level at similar to 9300 cal yr bp and continued falling until at least 9000 cal yr bp between 8000and6000cal yrbpsea level reached its lowest level of around similar to 10m below highest astronomical tide at around 5000 cal yr bp sea level had reached above 7 8 m below highest astronomical tide and slowly continued to rise not reaching present day sea level until today the isostatic rebound caused rapid isolation of the basins that are seen as distinct isolation contacts in the sediments in contrast the late holocene transgressions are less well defined and occurred over longer time intervals the late holocene sea level rise may be a consequence of isostatic reloading by advancing glaciers and or an effect of the delayed response to isostatic rebound of the laurentide ice sheet one consequence of this transgression is that settlements of palaeo eskimo cultures may be missing in southern greenland copyright c 2006 john wiley sons ltd

improving the reliability of bulk sediment radiocarbon dating abstract radiocarbon dated chronologies are the most extensively applied dating technique when investigating the last 45 000 years in lake and marine sediments a single macrofossil or several microfossils are the preferred sample material because they have a 14c age that accurately reflects the time of deposition however absence of macro or microfossils are a recurring challenge often it is necessary to use bulk sediment samples for radiocarbon dating but they frequently yield ages clearly exceeding the depositional timeframe due to occurrence of organic material of older origin until now it has not been possible to assess if the dating result of a bulk sediment sample is reliable or to adequately explain the mechanisms behind age disagreement between bulk and macro and microfossils in this study we investigate the age offset between paired bulk and macrofossil ages in sediment cores from three lakes in se and e greenland furthermore we distinguish three quantifiable main carbon sources in the samples a recent terrestrial organic fragments b recent aquatic organic matter and c reworked land derived old carbon through pyrolysis organic geochemistry organic petrographic microscopy and isotopic fractionization our results show that the offset between bulk humic fraction and macrofossil radiocarbon ages in three similar lakes range from 9 14c yr to 20 1 14c kyr we observe a reduced age offset between bulk and macrofossil ages and thereby a higher reliability of bulk humic fraction ages correlated with increased values of toc c n ratio and high co2 release in pyrolysis s3 value we recommend that future studies presenting bulk sediment chronologies apply pyrolysis organic geochemistry organic petrographic microscopy and isotopic fractionization as demonstrated here to select reliable sediment intervals for bulk dating and retrieve more robust results

new observations on the relative sea level and deglacial history of greenland from innaarsuit disko bugt relative sea level rsl data derived from isolation basins at innaarsuit a site on the south shores of the large marine embayment of disko bugt west greenland record rapid rsl fall from the marine limit ca 108 m at 10 300 9900 cal yr b p to reach the present sea level at 3500 cal yr b p since 2000 cal yr b p rsl rose ca 3 m to the present when compared with data from elsewhere in disko bugt our results suggest that the embayment was deglaciated later and more quickly than previously thought at or slightly before 10 300 cal yr b p the northern part of disko bugt experienced less rebound ca 10 m at 6000 cal yr b p compared with areas to the south submergence during the late holocene supports a model of crustal down warping as a result of renewed ice sheet growth during the neoglacial there is little evidence for west to east differences in crustal rebound across the southern shores of disko bugt

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

implicit ice in the global theory of glacial isostatic adjustment the inference of ice sheet paleo topography with respect to sea level is herein shown to require accounting for an accurately calculable additional ice mass beyond that which is explicitly required as input to the integral equation for relative sea level history

age of the fjord stade moraines in the disko bugt region western greenland and the 9 3 and 8 2 ka cooling events abstract retreat of the western greenland ice sheet during the early holocene was interrupted by deposition of the fjord stade moraine system the fjord stade moraine system spans several hundred kilometers of western greenland s ice free fringe and represents an important period in the western greenland ice sheet s deglaciation history but the origin and timing of moraine deposition remain uncertain here we combine new and previously published 10 be and 14 c ages from disko bugt western greenland to constrain the timing of fjord stade moraine deposition at two locations 60 km apart at jakobshavn isfjord the northern of two study sites we show that jakobshavn isbrae advanced to deposit moraines ca 9 2 and 8 2 8 0 ka in southeastern disko bugt the ice sheet deposited moraines ca 9 4 9 0 and 8 5 8 1 ka our ice margin chronology indicates that the greenland ice sheet in two distant regions responded in unison to early holocene abrupt cooling 9 3 and 8 2 ka as recorded in central greenland ice cores although the timing of fjord stade moraine deposition was synchronous in jakobshavn isfjord and southeastern disko bugt within uncertainties we suggest that jakobshavn isbrae advanced while the southeastern disko bugt ice margin experienced stillstands during the 9 3 and 8 2 ka events based on regional geomorphology and the distribution of 10 be ages at each location the contrasting style of ice margin response was likely regulated by site specific ice flow characteristics jakobshavn isbrae s high ice flux results in an amplified ice margin response to a climate perturbation both warming and cooling whereas the comparatively low flux sector of the ice sheet in southeastern disko bugt experiences a more subdued response to climate perturbations our chronology indicates that the western greenland ice sheet advanced and retreated in concert with early holocene temperature variations and the 9 3 and 8 2 ka events although brief were of sufficient duration to elicit a significant response of the western greenland ice sheet

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

sea level changes since the last glacial maximum an appraisal of the ipcc fourth assessment report the ipcc fourth assessment report ar4 stated that global sea level rose by about 120 m between the last glacial maximum lgm and 3 2 ka and did not rise again until the late 19th century a review of relevant literature demonstrates that the rise may have been larger by 10 15 m that the timing of stabilisation is poorly constrained within the last 7 ka bp and that the onset of modern rates of sea level rise is not synchronous and uniform across the globe the lgm lowstand as defined in the ar4 is based on the classic barbados sea level history but the sea level curve from this island may not be an accurate eustatic approximation if glacial isostatic adjustment gia processes were significant as suggested by various authors the barbados sea level curve revealed the existence of meltwater pulse mwp 1a at around 14 000 cal a bp questions about the source and causal mechanism of mwp 1a are still being explored by field scientists and gia modellers these problems have direct relevance for contemporary measurements of ice mass changes because space geodetic measurements rely on information provided by gia models to separate land motion from ice mass changes global patterns of holocene sea level change are controlled by regional sea level variability not only through isostatic and tectonic processes but also through steric effects longer wavelength gravitational changes produced by changing ice ocean mass flux and hemispheric scale perturbations in the earth s rotation eustasy is therefore merely a concept not a measurable quantity constraining the late holocene ice melt contribution to global sea level rise and determining regional sea level rise patterns in the 18th and 19th centuries are important future tasks for sea level scientists these will establish the baseline contributions to 20th and 21st century sea level rise and will help to determine the causes of modern rates of sea level rise constraining historical sea level accelerations and short term ice mass flux will aid models of ice sheet dynamics and help to reduce current uncertainties in future sea level predictions the ar4 shows that regional sea level variability is clearly present in sea level change patterns for the past 50 a and an important challenge for the next ipcc assessment is to incorporate this variability into regional future sea level rise scenarios copyright 2009 john wiley sons ltd

a comparison of observed and theoretical postglacial relative sea level in atlantic canada two extreme models of late wisconsinan ice cover in atlantic canada and the northeastern u s a are shown to produce postglacial relative sea level curves that bracket existing field observations at six sites throughout the region this suggests that the true late wisconsinan ice distribution is probably intermediate to the two contrasting reconstructions proposed both ice models predict the existence of four relative sea level zones an innermost zone closest to the centre of glaciation in which relative sea level falls continuously throughout postglacial time an outermost zone in which it rises continuously and two transitional zones in which it first falls and then rises in varying proportions according to the distance from the ice margin the distinctive forms of the relative sea level curves are probably representative of each of the zones and are unlikely to be significantly perturbed even by large local ice readvances they therefore establish patterns with which future field data are expected to conform the form that the geological record of relative sea level change is likely to take within each zone is discussed and promising settings for the collection of new data are proposed the common practice of separating relative sea level into an isostatic and a eustatic component is analysed and shown to be incorrect as usually applied the practice is also shown to be unnecessary because the models discussed in this paper predict changes in relative sea level that can be compared directly with the observations

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

late holocene environment and climatic changes in ameralik fjord southwest greenland evidence from the sedimentary record sedimentological and geochemical xrf data together with information from diatom and benthic foraminiferal records of a 3 5 m long gravity core from ameralik fjord southern west greenland is used for reconstructing late holocene environmental changes in this area the changes are linked to large scale north atlantic ocean and climate variability ams 14c dating of benthic foraminifera indicates that the sediment core records the last 4400 years and covers the termination of the holocene thermal maximum htm the late htm 4 4 3 2 ka bp is characterized by high accumulation rates of fine silty sediments related to strong meltwater discharge from the inland ice the htm benthic foraminiferal fauna demonstrates the presence of well ventilated saline bottom water originating from inflow of subsurface west greenland current water of atlantic irminger sea origin the hydrographic conditions were further characterized by limited sea ice probably related to a mild and relatively windy winter climate af

relative sea level change in greenland during the last 700 yrs and ice sheet response to the little ice age this paper presents new evidence regarding relative sea level rsl changes and vertical land motions at three sites in greenland since 1300 a d a time interval that spans the later part of the medieval climate anomaly mca and the little ice age lia we observe rsl rise at two sites in central west greenland from c 0 80 0 20 m at c 1300 a d to c 0 20 m 0 25 m at c 1600 a d after which rsl slowed and then stabilised at a third site in south greenland we observe rsl rise from c 1 40 0 20 m at c 1400 a d until c 1750 a d after which rsl slowed and was stable during at least the latter part of the 20th century the c 1600 a d rsl slow down seen at the two former sites is surprising because it occurs during the lia when one might expect the ice sheet to be gaining mass and causing rsl to rise we interpret this rsl slowdown to indicate a period of enhanced regional mass loss from central west greenland since c 1600 a d and propose two hypotheses for this loss first a reduction in precipitation during cold and dry conditions and second higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards the latter hypothesis is compatible with a well established temperature seesaw between western greenland and northern europe and potentially a previously identified shift from a positive to generally more negative nao conditions around 1400 to 1600 a d our study shows how rsl data from greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern europe the ice sheet in west greenland gained mass

glacimarine sedimentary processes and depositional environments in an embayment fed by west greenland ice streams abstract the extent and behaviour of the central west greenland sector of the greenland ice sheet gis during the last glacial maximum lgm and the following deglaciation remains poorly constrained to investigate deglacial marine environments and sedimentary processes in an area fed by several lgm ice streams we now report findings from a 3 5 khz sub bottom profiler survey acquired in and around disko bay in 2009 sediment thicknesses and volumes in three glaciated areas disko bay southern vaigat and egedesminde dyb are fully constrained for the first time acoustic facies types and distributions were also mapped the largest sediment thicknesses 256 m and widest variation in acoustic character was observed in disko bay adjacent to the mouth of jakobshavns isfjord significant sediment thicknesses were also observed in isolated basins in the egedesminde dyb trough and in a trough in southern vaigat strait up to 110 m given low modern sedimentation rates these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through disko bay and into both the jakobshavns and torssukatak fjord systems in central west greenland our results highlight similarities in deglacial sedimentary processes across the study area when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment laden meltwater plumes and melting icebergs we estimate the sediment flux for the palaeo jakobshavn ice stream while the ice margin was stable at a fjord entrance sill to be 1 6 3 6 10 7 m 3 a 1 assuming a flux at the upper end of our range for the torssukatak fjord system requires the grounded ice margin to be stable for about 450 years during retreat the sediment fluxes we estimate are within the range of previously calculated fluxes for other arctic and antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation even during periods of quasi stability retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice distal sedimentation by rainout of iceberg rafted detritus ird and hemipelagic material accumulation rates drop to 2 mm a 1 this study demonstrates the variability in glacimarine processes and environments on high latitude continental margins and highlights the importance of local factors such as bedrock morphology as well as glacio dynamic factors on sedimentation

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

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

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

deglaciation landforms and c 14 chronology of the lac guillaume delisle area eastern hudson bay a report on field evidence abstract this paper presents new field data pertaining to the deglaciation of the lac guillaume delisle area aiming to establish its emplacement in time and space between the breaching of the laurentide ice sheet lis over hudson bay and the final ice disintegration over northern quebec and labrador the deglaciation of the east coast of hudson bay started at 8200 cal bp in the south western sector of the lac guillaume delisle estuary when the marine limit was at 271 m above sea level asl by 8000 cal bp frontal moraines and proximal glacio marine sediments were deposited in the transverse valleys along the coastal cuesta ridges at a mean elevation of 250 m asl they are associated with a regional topographic pinning event of the western margin of the quebec labrador ice sheet qlis on the high coastal relief at that time the coastal relief encouraged a change in deglaciation mode from fast calving in the open and deep tyrrell sea to a tidewater ice sheet controlled by the topography the ice front thereafter retreated eastward under very large and fast crustal unloading where ice contact deltas fed by short sandar and eskers were deposited between 7900 and 7400 cal bp between 240 and 195 m asl as the ice front was receding inland and lost contact with tyrrell sea a series of deposits and landforms characterize this modification in the sedimentation regime when the ice sheet margin changed from tidewater to terrestrial dating shows that the deglaciation of the western margin of qlis on land was very fast i e faster than when the front of the ice sheet was in contact with the tyrrell sea as the fall of the relative sea level continued a large volume of paraglacial sediments was deposited in the river valleys making up vast fluvial terraces and deltas between 6500 and 5800 cal bp between 125 and 100 m asl since then land emergence has continued at a rate of about 1 3 m century downcutting by rivers post glacial deltaic sedimentation and shoreline changes still continue today

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

holocene relative sea level changes in the inner bredefjord area southern greenland in this paper we present new relative sea level data from southern greenland a key area for understanding the greenland ice sheet gis response to climate change within fourteen lakes and marine lagoons from the inner part of bredefjord nordre sermilik in southern greenland isolations revealed by stratigraphic and palaeoecological analyses are dated and relative sea levels reconstructed due to coastal emergence caused by the gis retreat within the area the relative sea level fell rapidly in the early holocene between at least c 9600 and c 7300 cal yrs bp attaining a rate of 2 cm per year between 9600 and 8000 cal yrs bp spatial variability in relative sea level changes is show for southern greenland from a comparison with the nanortalik and the qagortoq areas the regression occurred about 2000 years later in the inner bredefjord area compared to the nanortalik area and about 1000 years later compared to the qaqortoq area this is a consequence of earlier deglaciation in areas located at the outer coast between c 8000 cal yrs bp and the present day relative sea level was lower than today the lowest relative sea level in the inner bredefjord area of between 5 4 and 15 m a h a t above highest astronomical tide was reached between 7000 and 1000 cal yrs bp the neoglacial readvance together with the collapse of the laurentide peripheral bulge is probably responsible for the transgression in the inner bredefjord area as has been indicated from the nearby sites qagortoq and nanortalik our relative sea level reconstructions showing spatial variability within southern greenland have implications for glacial isostatic adjustment gia modelling and the understanding of the gis ice sheet dynamics the early holocene regression is consistent with the recession of the southern sector of the gis from the shelf edge at c 22 000 cal yrs bp reaching inland of the present day outer coast by c 12 000 cal yrs bp and its present margin by c 10 500 cal yrs bp c 2013 elsevier ltd all rights reserved

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

slabs in the lower mantle and their modulation of plume formation numerical mantle convection models indicate that subducting slabs can reach the core mantle boundary cmb for a wide range of assumed material properties and plate tectonic histories an increase in lower mantle viscosity a phase transition at 660 km depth depth dependent thermal expansivity and depth dependent thermal diffusivity do not preclude model slabs from reaching the cmb we find that ancient slabs could be associated with lateral temperature anomalies 500 c cooler than ambient mantle plausible increases of thermal conductivity with depth will not cause slabs to diffuse away regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the cmb even for radially simple mantle structures the observation from tomography showing only a few continuous slab like features from the surface to the cmb may be a result of complex plate kinematics not mantle layering there are important consequences of deeply penetrating slabs our models show that plumes preferentially develop on the edge of slabs in areas on the cmb free of slabs plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin however in areas beneath slabs the basal thermal boundary layer would be thicker and plume formation infrequent beneath slabs a substantial amount of hot mantle can be trapped over long periods of time leading to mega plume formation we predict that patches of low seismic velocity may be found beneath large scale high seismic velocity structures at the core mantle boundary we find that the location buoyancy and geochemistry of mega plumes will differ from those plumes forming at the edge of slabs various geophysical and geochemical implications of this finding are discussed

the role of the earth s mantle in controlling the frequency of geomagnetic reversals a series of computer simulations of the earth s dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic field generation in the fluid core eight different patterns of heat flux from the core to the mantle are imposed over the core mantle boundary spontaneous magnetic dipole reversals and excursions occur in seven of these cases although sometimes the field only reverses in the outer part of the core and then quickly reverses back the results suggest correlations among the frequency of reversals the duration over which the reversals occur the magnetic field intensity and the secular variation the case with uniform heat flux at the core mantle boundary appears most earth like this result suggests that variations in heat flux at the core mantle boundary of the earth are smaller than previously thought possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin or because of enhanced heat flux in the mantle s zones of ultra low seismic velocity

modulation of mantle plumes and heat flow at the core mantle boundary by plate scale flow results from laboratory experiments we report results from analog laboratory experiments in which a large scale flow is imposed upon natural convection from a hot boundary layer at the base of a large tank of corn syrup the experiments show that the subdivision of the convective flow into four regions provides a reasonable conceptual framework for interpreting the effects of large scale flow on plumes region i includes the area of the hot thermal boundary layer tbl that is thinned by the large scale flow thereby suppressing plumes region ii encompasses the critically unstable boundary layer where plumes form region iii is the area above the boundary layer that is devoid of plumes region iv comprises the area of hot upwelling and plume conduits quantitative analysis of our experiments results in a scaling law for heat flux from the hot boundary and for the spatial extent of plume suppression when applied to the earth s core mantle boundary cmb our results suggest that large scale mantle flow due to sinking lithospheric plates can locally thin the tbl and suppress plume formation over large fractions of the cmb approximately 30 of heat flow from the core may be due to increased heat flux from plate scale flow furthermore cmb heat flux is non uniformly distributed along the cmb with large areas where heat flux is increased on average by a factor of 2 as a consequence the convective flow pattern in the outer core may be affected by cmb heat flux heterogeneity and sensitive to changes in plate scale mantle flow becauseofplumesuppressionanddfocusingtofhotmantlefromthecmbintozonesofupwellingflow plumeconduits hotspots