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

a full coverage high resolution topographic model of greenland computed from a variety of digital elevation data in this paper a new high resolution elevation model of greenland including the ice sheet as well as the ice free regions is presented it is the first published full coverage model computed with an average resolution of 2 km and providing an unprecedented degree of detail the topography is modeled from a wide selection of data sources including satellite radar altimetry from geosat and ers 1 airborne radar altimetry and airborne laser altimetry over the ice sheet and photogrammetric and manual map scannings in the ice free region the ice sheet model accuracy is evaluated by omitting airborne laser data from the analysis and treating them as ground truth observations the mean accuracy of the ice sheet elevations is estimated to be 12 13 m and it is found that on surfaces of a slope between 0 2 and 0 8 corresponding to approximately 50 of the ice sheet the model presents a 40 improvement over models based on satellite altimetry alone on coastal bedrock the model is compared with stereo triangulated reference points and it is found that the model accuracy is of the order of 25 35 m in areas covered by stereo photogrammetry scannings and between 200 and 250 m elsewhere

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

vertical and horizontal surface displacements near jakobshavn isbrae driven by melt induced and dynamic ice loss 1 we analyze global positioning system gps time series of relative vertical and horizontal surface displacements from 2006 to 2012 at four gps sites located between 5 and 150 km from the front of jakobshavn isbrae ji in west greenland horizontal displacements during 2006 2010 at kaga ilul and qeqe relative to the site aasi are directed toward north west suggesting that the main mass loss signal is located near the frontal portion of ji the directions of the observed displacements are supported by modeled displacements derived from nasa s airborne topographic mapper atm surveys of surface elevations from 2006 2009 and 2010 however horizontal displacements during 2010 2012 at kaga and ilul are directed more towards the west suggesting a change in the spatial distribution of the ice mass loss in addition we observe an increase in the uplift rate during 2010 2012 as compared to 2006 2010 the sudden change in vertical and horizontal displacements is due to enhanced melt induced ice loss in 2010 and 2012

a model computation of the temporal changes of surface gravity and geoidal signal induced by the evolving greenland ice sheet this paper deals with present day gravity changes in response to the evolving greenland ice sheet we present a detailed computation from a 3 d thermomechanical ice sheet model that is interactively coupled with a self gravitating spherical viscoelastic bedrock model the coupled model is run over the last two glacial cycles to yield the loading evolution over time based on both the ice sheet s long term history and its modern evolution averaged over the last 200 years results are presented of the absolute gravity trend that would arise from a ground survey and of the corresponding geoid rate of change a satellite would see from space the main results yield ground absolute gravity trends of the order of 1 gal yr 1 over the ice free areas and total geoid changes in the range between 0 1 and 0 3 mm yr 1 these estimates could help to design future measurement campaigns by revealing areas of strong signal and or specific patterns although there are uncertainties associated with the parameters adopted for the earth s rheology and aspects of the ice sheet model given the instrumental accuracy of a particular surveying method these theoretical trends could also be useful to assess the required duration of a measurement campaign according to our results the present day gravitational signal is dominated by the response to past loading changes rather than current mass changes of the greenland ice sheet we finally discuss the potential of inferring the present day evolution of the greenland ice sheet from the geoid rate of change measured by the future geodetic grace mission we find that despite the anticipated high quality data from satellites such a method is compromised by the uncertainties in the earth model the dominance of isostatic recovery on the current bedrock signal and other inaccuracies inherent to the method itself

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

crustal deformation across the southern patagonian icefield observed by gnss abstract geodetic gnss observations at 43 sites well distributed over the southern patagonian icefield region yield site velocities with a mean accuracy of 1 mm a and 6 mm a for the horizontal and vertical components respectively these velocities are analyzed to reveal the magnitudes and patterns of vertical and horizontal present day crustal deformation as well as their primary driving processes the observed vertical velocities confirm a rapid uplift with rates peaking at 41 mm a causally related to glacial isostatic adjustment gia they yield now an unambiguous preference between two competing gia models remaining discrepancies between the preferred model and our observations point toward an effective upper mantle viscosity even lower than 1 6 10 18 pa s and effects of lateral rheological heterogeneities an analysis of the horizontal strain and strain rate fields reveals some complex superposition with compression dominating in the west and extension in the east this deformation field suggests significant contributions from three processes gia a western interseismic tectonic deformation field related to plate subduction and an extensional strain rate field related to active patagonian slab window tectonics

mass balance of the greenland ice sheet at high elevations comparison of ice discharge from higher elevation areas of the entire greenland ice sheet with total snow accumulation gives estimates of ice thickening rates over the past few decades on average the region has been in balance but with thickening of 21 centimeters per year in the southwest and thinning of 30 centimeters per year in the southeast the north of the ice sheet shows less variability with average thickening of 2 centimeters per year in the northeast and thinning of about 5 centimeters per year in the northwest these results agree well with those from repeated altimeter surveys except in the extreme south where we find substantially higher rates of both thickening and thinning

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

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

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

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

recent postglacial rebound gravity change and mantle flow in fennoscandia summary the recent postglacial rebound of fennoscandia is investigated using sea level data levelling data and gravity data in particular an analysis is made of the repeated data obtained hitherto on the fennoscandian land uplift gravity line along latitude 63 methods for this analysis include an iterative procedure for computing the relation between gravity change and absolute land uplift the mass flow parameter and the geoid rise the remaining land uplift is also estimated the mass flow parameter c is used to characterize the relation between additional mass and additional volume due to rebound it is a number between 0 and 1 1 corresponding to full inflow of mantle below the rising crust and 0 to no inflow but some kind of decompression the main result is that c is significantly different from 0 at the 99 per cent level we find c 0 8 this means that models proposed of the present uplift based on pure decompression must be ruled out and that a viscous inflow of mantle is a necessary part of the ongoing uplift process on the other hand this process might be more complicated than a pure viscous flow

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

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

grounding line migration and high resolution calving dynamics of jakobshavn isbrae west greenland 1 we performed three field campaigns in 2004 2007 and 2010 at the southern margin of the jakobshavn isbrae west greenland in order to infer flow velocities and their changes from photogrammetric time lapse imagery with a temporal resolution of 20 min and a spatial spacing of about 30 m on the glacier surface area wide analysis of more than 3000 three dimensional trajectories at individual glacier positions allow for both the mapping of the grounding line and the detailed observation of flow variations during major calving events from 2004 to 2010 the grounding line of jakobshavn isbrae retreated 3 5 0 2 km considering previously published results the grounding line retreat amounts to 6 km since 1985 the glacier has an ephemeral floating tongue that can establish during the readvance of the glacier front and break apart after large calving events observations of a major calving event show that an acceleration of flow velocities coincides with the onset of the break up during which flow velocities of up to 70 m d can be reached moreover large vertical displacements of the glacier front in the order of 15 m and lowering of 8 m at positions 500 m beyond the calving front were observed 2 days before the calving event after the break up the glacier slowly adjusts to the new boundary conditions within the next 4 5 days flow velocity variations caused by calving were detected up to 1 km upstream only which indicates that individual calving events have no immediate effect on the large scale glacier dynamics

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

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

the response of the greenland ice sheet to climate changes in the 21st century by interactive coupling of an aogcm with a thermomechanical ice sheet model we present results from a greenhouse warming experiment obtained from an atmosphere ocean sea ice general circulation model that is interactively coupled with a three dimensional model of the greenland ice sheet the experiment covers the period 1970 2099 and is driven by the mid range intergovernmental panel on climate change sresb2 scenario the greenland model is a thermomechanical high resolution 20 km model coupled with a viscoelastic bedrock model the melt and runoff model is based on the positive degree day method and includes meltwater retention in the snowpack and the formation of superimposed ice the atmospheric oceanic general circulation model aogcm is a coarse resolution model without flux correction based on the laboratoire de meteorologie dynamique paris lmd 5 3 atmospheric model coupled with a primitive equation free surface oceanic component incorporating sea ice coupled large scale ice ocean clio by 2100 average greenland annual temperature is found to rise by about 4 5 c and mean precipitation by about 35 the total fresh water flux approximately doubles over this period due to increased runoff from the ice sheet and the ice free land but the calving rate is found to decrease by 25 the ice sheet shrinks equivalent to 4 cm of sea level rise the contribution from the background evolution is not more than 50 of the total predicted sea level rise we did not find significant changes in the patterns of climate change over the north atlantic region compared with a climate change run without greenland fresh water feedback

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

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

global mapping functions for the atmosphere delay at radio wavelengths i have developed expressions for calculating the ratios mapping functions of the line of sight hydrostatic and wet atmospheric path delays to their corresponding zenith delays at radio wavelengths for elevation angles down to 3 the coefficients of the continued fraction representation of the hydrostatic mapping function depend on the latitude and height above sea level of the observing site and on the day of the year the dependence of the wet mapping function is only on the site latitude by comparing with mapping functions calculated from radiosonde profiles for sites at latitudes between 43 s and 75 n the hydrostatic mapping function is seen to be more accurate than and of comparable precision to mapping functions currently in use which are parameterized in terms of local surface meteorology when the new mapping functions are used in the analysis of geodetic very long baseline interferometry vlbi data the estimated lengths of baselines up to 10 400 km long change by less than 5 mm as the minimum elevation of included data is reduced from 12 to 3 the independence of the new mapping functions from surface meteorology while having comparable accuracy and precision to those that require such input makes them particularly valuable for those situations where surface meteorology data are not available

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

improved ice loss estimate of the northwestern greenland ice sheet 1 we estimate ice volume change rates in the northwest greenland drainage basin during 2003 2009 using ice cloud and land elevation satellite icesat laser altimeter data elevation changes are often reported to be largest near the frontal portion of outlet glaciers to improve the volume change estimate we supplement the icesat data with altimeter surveys from nasa s airborne topographic mapper from 2002 to 2010 and nasa s land vegetation and ice sensor from 2010 the airborne data are mainly concentrated along the ice margin and thus have a significant impact on the estimate of the volume change our results show that adding airborne topographic mapper and land vegetation and ice sensor data to the icesat data increases the catchment wide estimate of ice volume loss by 11 mainly due to an improved volume loss estimate along the ice sheet margin furthermore our results show a significant acceleration in mass loss at elevations above 1200m both the improved mass loss estimate along the ice sheet margin and the acceleration at higher elevations have implications for predictions of the elastic adjustment of the lithosphere caused by present day ice mass changes our study shows that the use of icesat data alone to predict elastic uplift rates biases the predicted rates by several millimeters per year at gps locations along the northwestern coast

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

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

present day uplift patterns over greenland from a coupled ice sheet visco elastic bedrock model we present results from a fully coupled ice bedrock model calculation of the greenland ice sheet and the underlying earth during the last two glacial cycles the method treats the mutual interaction between the ice and the bedrock and yields the main glacial isostatic characteristics of the ice sheet evolution and the bedrock adjustment since the last glacial maximum by taking advantage of the splitting of the present day rate of bed uplift into a viscous and an elastic component these results allow one to distinguish between the bedrock response to the past and present ice sheet evolution respectively

a spectral formalism for computing three dimensional deformations due to surface loads 2 present day glacial isostatic adjustment using a spherically symmetric self gravitating linear viscoelastic earth model we predict present day three dimensional surface deformation rates and baseline evolutions arising as a consequence of the late pleistocene glacial cycles in general we use realistic models for the space time geometry of the final late pleistocene deglaciation event and incorporate a gravitationally self consistent ocean meltwater redistribution the predictions of horizontal velocity presented herein differ significantly in both their amplitude and their spatial variation from those presented in an earlier analysis of others which adopted simplified models of both the late pleistocene ice history and the earth rheology an important characteristic of our predicted velocity fields is that the melting of the laurentide ice sheet over canada is capable of contributing appreciably to the adjustment in europe the sensitivity of the predictions to variations in mantle rheology is investigated by considering a number of different earth models and by computing appropriate frechet kernels these calculations suggest that the sensitivity of the deformations to the earth s rheology is significant and strongly dependent on the location of the site relative to the ancient ice sheet the effects on the predictions of three dimensional deformation rates of altering the ice history or adopting approximate models for the ocean meltwater redistribution have also been considered and found to be important the former especially so finally for a suite of earth models we provide predictions of the velocity of a number of baselines in north america and europe we find that in general both radial and tangential motions contribute significantly to baseline length changes and that these contributions are a strong function of the earth model we have furthermore found a set of earth models which together with the ice 3g deglaciation chronology produce predictions of baseline length changes that are consistent with very long baseline interferometry measurements of baselines within europe

coal and coal macerals as source rocks for oil and gas abstract the role of coals in the generation and migration of hydrocarbons is discussed from the viewpoints of chemistry and petrology extract data and considerations of volatile matter and maturity suggests that under geochemical conditions most coals can give rise to oil as well as gas a distinction is drawn between release of absorbed oil and formation of hydrocarbons by thermal breakdown of the coal matrix itself the generation and preservation of oil require not only that suitable lipidic structures be present but that the product oil can escape before being cracked to gas exinite preferably in large discrete particles is the most oil prone maceral vitrinite can form oil but subsequent migration depends on the availability of cracks and fissures in the coal matrix the most highly reflecting forms of inertinite e g fusinite have no inherent capacity to generate oil low reflectance inertinite such as is common in many australian coals may have minor source potential a speculative attempt is made to quantify the oil generating capacity of coal macerals and mixtures as a general broad rule on a weight basis exinite can produce ten times more oil than vitrinite and a hundred times more than inertinite approximate calculations suggest that thermal maturation of coals can account for all the known oil and gas reserves in the gippsland and cooper basins of australia even if only 1 of generated hydrocarbons is trapped

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

apparent stability of gps monumentation from short baseline time series 1 long running short 1 km gps baselines offer an insight into the accuracy budget of geophysical estimates inferred from gps coordinate time series in this paper we report on analysis of 10 short baselines using data spanning several years and examine deviations from a constant baseline length annual signals with amplitude 0 5 mm are evident in various coordinate components at 6 of the 10 sites with amplitudes exceeding 2 5 mm on two baselines these signals are largely invariant to elevation cutoff angle multipath and phase center model errors are shown to probably have negligible effects at most sites at annual periods they are therefore likely real monument motions although linear thermal expansion is negligible at most sites linear trends 0 25 mm yr 1 are evident on four baselines in at least one coordinate component subdaily signals are present at all sites at k1 and its higher harmonics time correlated noise possibly in the form of flicker noise dominates despite many common signals being eliminated as a result of the small baseline lengths although it is around 1 order of magnitude smaller than for single site ppp solutions we constrain monument random walk motion to be no more than 0 5 mm yr 1 2 if these baseline motion results were representative of the 300 currently active igs sites 180 would have annual signals 0 5 mm in at least one coordinate component 120 would have linear rates 0 25 mm yr 1 and almost all sites would have subdaily k1 k2 signals of 0 1 mm each solely due to local site effects

geoid displacement about greenland resulting from past and present day mass changes in the greenland ice sheet 1 predictions are presented of secular changes in the geoid arising from glacial isostatic adjustment gia following the last glacial maximum and from presentday mass changes in the greenland ice sheet gis geoid displacement from ongoing gia is dominated by ice load changes outside of greenland at lower spherical harmonic degrees 2000 m spatial variability is noted when the presentday gis response is expanded to degree and order 32 this is detectable by grace when assuming an optimistic accuracy but is too small by a factor of ca 3 for an alternate accuracy estimate present day gis geoid displacement rates are generally less than the equivalent response from ice mass changes in antarctica patagonia and alaska index terms 1299 geodesy and gravity general or miscellaneous 1645 global change solid earth 1827 hydrology glaciology 1863 citation fleming k z martinec and j hagedoorn 2004 geoid displacement about greenland resulting from past and present day mass changes in the greenland ice sheet geophys res lett 31 l06617

palaeomagnetic evidence for a displaced terrain in western antartica an outstanding problem in antarctic tectonics is the relationship between the east antarctic craton and the late palaeozoic cenozoic orogenic belts that comprise western antarctica1 antarctic peninsula ellsworth land eights coast and marie byrd land see fig 1a related problems are the place of western antarctica in reconstructions of gondwanaland and the evolution of the pacific margin of gondwanaland we present here palaeomagnetic data derived from folded cambrian argillites that crop out in the ellsworth mountains which were collected during the 1979 80 austral field season although the early palaeozoic palaeomagnetic field of gondwanaland is characterized by rapid apparent polar wander at the present level of coverage the data are consistent with rotation of the ellsworth mountain block with respect to the east antarctic craton as postulated by schopf2 this result supports a microplate nature of western antarctica