aspects of climate variability in the north atlantic sector discussion and relation to the greenland ice sheet project 2 high resolution isotopic signal this paper reviews aspects of climate variability in the north atlantic sector that may influence the seasonal to decadal scale isotopic signal in the greenland ice sheet project 2 gisp2 ice core interpretation of the isotopic signal and its spatial applicability at the seasonal level requires investigation into synoptic scale climatology we discuss possible climatic influences of 1 likely source regions of precipitation reaching the gisp2 site 2 the characteristics of cyclone activity over the north atlantic sector and 3 changes in major atmospheric features such as the mean sea level icelandic low and azores high pressure systems the north atlantic oscillation and the baffin trough next we evaluate correlations between the gisp2 deuterium isotopic signal and coastal temperatures with atmospheric pressure patterns thereby deriving climatic interpretations of the high resolution isotopic record the gisp2 site is influenced by both the icelandic low to the southeast and davis strait baffin bay storms to the southwest and west the north atlantic oscillation influences the gisp2 isotopic signal through the seesaw in winter temperatures between west greenland and northern europe agreement in excursion directions of gisp2 isotopes and east greenland and iceland temperature records is associated with different positions of the baffin trough in winter and also with anomalous 500 mbar net geostrophic flow linkages between isotopic excursion direction and atmospheric variability need to be explored further by comparison with additional seasonal data sets from other greenland ice cores

palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

the north atlantic oscillation and oceanic precipitation variability global north atlantic oscillation nao oceanic precipitation features in the latter half of the twentieth century are documented based on the intercomparison of multiple state of the art precipitation datasets and the analysis of the nao atmospheric circulation and sst anomalies most prominent precipitation anomalies occur over the ocean in the north atlantic where in winter a quadrupole like pattern is found with centers in the western tropical atlantic sub tropical atlantic high latitude eastern atlantic and over the labrador sea the extent of the sub tropical and high latitude center and the amount of explained variance over 50 are quite remarkable however the tropical atlantic center is probably the most intriguing feature of this pattern apparently linking the nao with itcz variability in summer the pattern is tripole like with centers in the eastern mediterranean sea the north sea baltic sea and in the sub polar atlantic in the eastern indian ocean the correlation is positive in winter and negative in summer with some link to enso variability the sensitivity of these patterns to the choice of the nao index is minor in winter while quite important in summer interannual nao precipitation anomalies have driven similar fresh water variations in these key regions in the sub tropical and high latitude atlantic in winter precipitation anomalies have been roughly 15 and 10 of climatology per unit change of the nao respectively decadal changes of the nao during the last 50 years have also influenced precipitation and fresh water flux at these time scales with values lower higher than usual in the high latitude eastern north atlantic labrador sea in the 1960s and the late 1970s and an opposite situation since the early 1980s in summer the north sea baltic region has been drier than usual during the period 1965 1975 when the nao was generally positive

lower timberline in central colorado during the past 15 000 yr a 15 000 yr paleoenvironmental record at the elevation of lower timberline in central colorado suggests two major paleoclimatic changes during that interval 1 at 10 000 yr b p from cool moist conditions to warm moist conditions and 2 at 4 000 yr b p to warm dry conditions this sequence can be interpreted as a shift from precipitation predominantly originating from pacific winter storms before 10 000 yr b p to a predominantly monsoonal type regime lasting until 4 000 yr b p to the present pattern contemporaneity of higher upper timberline and lower lower timberline during the 10 000 to 4 000 yr b p interval is not contradictory but a result of changes in those circulation patterns

the north atlantic oscillation signature in deuterium and deuterium excess signals in the greenland ice sheet project 2 ice core 1840 1970 the greenland ice sheet project 2 gisp2 core can enhance our understanding of the relationship between parameters measured in the ice in central greenland and variability in the ocean atmosphere and cryosphere of the north atlantic ocean and adjacent land masses seasonal summer winter to annual responses of d and deuterium excess isotopic signals in the gisp2 core to the seesaw in winter temperatures between west greenland and northern europe from a d 1840 to 1970 are investigated this seesaw represents extreme modes of the north atlantic oscillation which also influences sea surface temperatures ssts atmospheric pressures geostrophic wind strength and sea ice extents beyond the winter season temperature excursions inferred from the d record during seesaw extreme nao mode years move in the same direction as the west greenland side of the seesaw symmetry with the west greenland side of the seesaw suggests a possible mechanism for damping in the ice core record of the lowest decadal temperatures experienced in europe from a d 1500 to 1700 seasonal and annual deuterium excess excursions during seesaw years show negative correlation with d this suggests an isotopic response to a sst land temperature seesaw the isotopic record from gisp2 may therefore give information on both ice sheet and sea surface temperature variability cross plots of d and d show a tendency for data to be grouped according to the prevailing mode of the seesaw but do not provide unambiguous identification of individual seesaw years a combination of ice core and tree ring data sets may allow more confident identification of ga and gb extreme nao mode years prior to 1840

spatial variation in the influence of the north atlantic oscillation on precipitation across greenland 1 ice core derived accumulation records from greenland have been proposed as proxies for north atlantic oscillation nao reconstruction in a series of single site analyses accumulation records from ice cores drilled in western greenland were found to exhibit the strongest linear association with nao in this paper we expand on these findings by proposing a spatiotemporal statistical model to explore further the relationship between nao and the accumulation records from 35 firn and ice cores drilled in western and southern greenland in particular we propose a temporal extension of the bayesian spatially varying coefficient regression model which is fit using a markov chain monte carlo algorithm this model readily accommodates the irregular features of the data i e variation in record lengths and irregular spacing among ice core locations and the serial dependence within individual records using our statistical model we are able to exploit the spatial dependence structure of the derived accumulation nao relationship to explore the regional patterns in the strength of this relationship our findings support previous work that identified a region in western greenland where derived accumulation is most correlated with nao however we also identify a region further inland to the east and south where the estimated strength of the linear accumulation nao relationship is weaker but more certain than in the previously identified region thus our findings can be used to guide decisions regarding where to locate future drilling efforts in greenland by weighing the trade off between the potential strength of the accumulation nao relationship and its uncertainty

norwegian fjord sediments reveal nao related winter temperature and precipitation changes of the past 2800 years abstract the north atlantic oscillation nao is the leading mode of atmospheric circulation variability in the north atlantic region associated shifts of storm tracks precipitation and temperature patterns affect energy supply and demand fisheries and agricultural as well as marine and terrestrial ecological dynamics long term nao records are crucial to better understand its response to climate forcing factors and assess predictability and shifts associated with ongoing climate change a recent study of instrumental time series revealed nao as main factor for a strong relation between winter temperature precipitation and river discharge in central norway over the past 50 years here we compare geochemical measurements with instrumental data and show that primary productivity recorded in central norwegian fjord sediments is sensitive to nao variability this observation is used to calibrate paleoproductivity changes to a 500 year reconstruction of winter nao luterbacher et al 2001 conditioned on a stationary relation between our climate proxy and the nao we establish a first high resolution nao proxy record nao tfj from marine sediments covering the past 2800 years the nao tfj shows distinct co variability with climate changes over greenland solar activity and northern hemisphere glacier dynamics as well as climatically associated paleo demographic trends the here presented climate record shows that fjord sediments provide crucial information for an improved understanding of the linkages between atmospheric circulation solar and oceanic forcing factors

north atlantic oscillation dynamics recorded in greenland ice cores carefully selected ice core data from greenland can be used to reconstruct an annual proxy north atlantic oscillation nao index this index for the past 350 years indicates that the nao is an intermittent climate oscillation with temporally active coherent and passive incoherent phases no indication for a single persistent multiannual nao frequency is found in active phases most of the energy is located in the frequency band with periods less than about 15 years in addition variability on time scales of 80 to 90 years has been observed since the mid 19th century

precipitation over greenland retrieved by a dynamic method and its relation to cyclonic activity abstract in order to calculate the vertical motion over some high mountain regions such as greenland an equation without the quasigeostrophic approximation in coordinates has been developed a dynamic method for retrieving precipitation over greenland is based on this equation the retrieved annual mean precipitation distribution for 1987 and 1988 is in very good agreement with the observed annual accumulation pattern over the greenland ice sheet the major weather system producing precipitation over greenland is the frontal cyclone based on the precipitation characteristics greenland can be divided into five subregions precipitation over the north coastal and central interior regions primarily occurs in summer for the three other subregions if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed a clear relationship between precipitation and cyclonic activity emerges if a mean cyclone exists in the labrador sea heavy precipita

the diel cycle of water vapor in west greenland we present a study of the dynamics of small scale 100 km atmospheric circulation in west greenland which is dominated by interactions of marine and continental air masses water vapor concentration and isotopic ratios measured continuously over a 25 day period in kangerlussuaq greenland were used to monitor the convergence of easterly katabatic winds and westerly sea breezes that form a front between the dry isotopically depleted glacial air mass and the moist isotopically enriched marine air mass during the latter 16 days of the measurement period an interval with no large scale synoptic interference the inland penetration of the sea breeze controlled the largest day to day humidity and vapor isotopic variations kangerlussuaq experienced sea breezes in the afternoon on 9 days consistent with the long term average of such occurrences on 56 of days in july and august the inland position of the sea breeze front is controlled by the katabatic wind strength which is stronger during times of reduced cloud coverage and or higher pressure gradient between the coast and the greenland ice sheet the position and movement of the front will likely respond to changes in the general atmospheric circulation and regional radiation balance resulting from global warming which will in turn impact the local hydrological cycle and ecosystem processes

annual accumulation over recent centuries at four sites in central greenland 1 accurate accumulation records are fundamental to understanding mass balance of the greenland ice sheet ice cores can provide multicentury high resolution ground based point estimates of water accumulation in 2003 and 2004 four new ice cores were collected in the central western d4 and d5 and summit sandy and katie regions of greenland annual layer counting based on multiple glaciochemical parameters primarily hydrogen peroxide sea salt and dust proxies was used to date the ice cores resulting in annual dating the bottom depth ages for d4 d5 sandy and katie were estimated at 1738 1673 1844 and 1934 a d with mean annual accumulation rates of 41 4 35 2 22 4 and 22 4 cmweq yr 1 respectively these new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores spatial variability was quantified through an analysis of variance thereby allowing for more meaningful comparisons to atmospheric processes more regionally representative accumulation records were constructed for the central western and summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements these regional records exhibited 6 7 interannual variability 1 standard deviation of the mean and had lower spatial variability uncertainties than individual accumulation records correlations indicate that 20 of the variance in the central western region was explained by the north atlantic oscillation nao and suggests that an array of more northern ice cores may correlate more closely with nao

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

modeled variations of precipitation over the greenland ice sheet abstract a parameterization of the synoptic activity at 500 hpa and a simple orographic scheme are used to model the spatial and temporal variations of precipitation over the greenland ice sheet for 1963 88 from analyzed geopotential height fields produced by the national meteorological center nmc model coefficients are fitted to observed accumulation data primarily from the summit area of the ice sheet all major spatial characteristics of the observed accumulation distribution are reproduced apart from the orographic accumulation maximum over the northwestern coastal slopes the modeled time averaged total precipitation amount over greenland is within the range of values determined by other investigators from surface based observations a realistic degree of interannual variability in precipitation is also simulated a downward trend in simulated ice sheet precipitation over the 26 years is found this is supported by a number of lines of evidence it matches the accumulation trends during this peri

southeast greenland winter precipitation strongly linked to the icelandic low position abstractgreenland s largest precipitation flux occurs in its southeast se region during the winter controlled primarily by easterly winds and frequent cyclogenesis in the north atlantic several

the impact of cloud cover on the net radiation budget of the greenland ice sheet energy balancemodelsdrivenbyradiationandturbulentheatfluxeshave beenwidelyappliedto predictingtheresponse ofthegreenland ice sheetto climatechange however a lackof knowledge of the temporal and spatial distribution of cloudamount and type has necessitated the use of parameterizations or statistical models of cloud cover this deficiency results in large uncertainties in both shortwave and longwave radiation fluxes stereo matching of nadir and forward viewalongtrack scanning radiometer 2 atsr 2 image pairs has been shown to be a reliable method of retrieving cloud top height and further cloud properties can be derived from thermal imagery allowing classification into cloud type a1year cloud record for a transect across southern greenland derived from stereo matching is presented here and comparisons are made with climate re analysis data and ground observations the cloud cover data were used in a simple radiative transfer model and the impact of clouds on the net radiation fluxes was found to be considerable different cloud scenarios produced up to 40wm 2 difference in net radiation balance in theablationzone wherethealbedoislowerandmost variable thesensitivity to cloud cover fraction was less marked but the higher spatial resolution of the atsr 2 cloud record was reflected by a much more varied trend in radiation balance whether the net radiation balance increases or decreases with increased cloud cover was foundto be a function of the cloud amount andtype and also the surface albedo the sensitivity of the model to a 5 change in cloud amount was found to be comparable to a1k change in temperature this clearlydemonstratestheimportanceofreliable quantitativeclouddatainmass balanceand otherglaciological studies

modeled precipitation variability over the greenland ice sheet on the basis of the evaluation of recent greenland precipitation studies some of the deficiencies in the modeled precipitation are probably related to the topographic data employed in modeling in this paper the modern digital elevation data of ekholm 1996 is used if the horizontal pressure gradient force in coordinates is separated into its irrotational and rotational parts which are expressed by the equivalent geopotential and geo stream function respectively the topographic effect on the precipitation can be accurately modeled the equivalent geopotential and geo stream function are implemented in a fully consistent manner in the generalized equation in this paper a simplified large scale condensation without evaporation of condensate is also used these improvements are combined to yield an improved dynamic method two aspects of the precipitation distribution are refined by the improved dynamic method one is the 10 cm yr 1 contour near summit greenland and the other is a relative large precipitation area centered near the point 70 n 49 w extensive comparisons are made between the retrieved precipitation and the observed annual accumulation time series from 11 ice core sites on the ice sheet the modeled precipitation from the original method must use sealers to have a high degree of interannual correspondence between the measured accumulation and the retrieved precipitation but the retrieved precipitation from the improved method increases at all ice core sites and a good correspondence is obtained without any sealer being required the spatial average of multiyear mean error e j is 11 5 cm yr 1 for the modeled precipitation from the improved method while that for p from era 15 is 14 5 cm yr 1 the total mean error em is 3 0 cm yr 1 for the improved method while em for the p from era 15 is 4 0 cm yr 1 these two errors show that the precipitation modeled by the improved method is better than the p from era 15 thus the distribution of precipitation over the 11 sites retrieved by the improved dynamic method is considerably refined large downward trends in annual amounts are present in the precipitation retrieved by the improved dynamic method for all of greenland and its southern and central west coastal regions the modeled precipitation from the improved dynamic method and observed accumulation from ice cores are all in agreement with the thomas et al 1999 result that the southern greenland ice sheet above 2000 m is approximately in balance it also shows that local thickening and thinning areas of the ice sheet derived by airborne laser altimetry from 1993 to 1999 over the entire greenland above 2000 m krabill et al 2000 are approximately consistent with precipitation change retrieved by the improved dynamic method

recent ice sheet growth in the interior of greenland a continuous data set of greenland ice sheet altimeter height from european remote sensing satellites ers 1 and ers 2 1992 to 2003 has been analyzed an increase of 6 4 0 2 centimeters per year cm year is found in the vast interior areas above 1500 meters in contrast to previous reports of high elevation balance below 1500 meters the elevation change rate is 2 0 0 9 cm year in qualitative agreement with reported thinning in the ice sheet margins averaged over the study area the increase is 5 4 0 2 cm year or 60 cm over 11 years or 54 cm when corrected for isostatic uplift winter elevation changes are shown to be linked to the north atlantic oscillation

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

the north atlantic oscillation and its imprint on precipitation and ice accumulation in greenland interannual to decadal fluctuations in net precipitation and ice accumulation are examined over greenland it is shown that in western greenland these fluctuations are correlated with the north atlantic oscillation the analysis is based on two complementary data sources a highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the european centre for medium range weather forecasts and a composite ice accumulation record representative for the western part of central greenland it is suggested that western greenland snow accumulation is a good proxy for the nao index with the potential for the reconstruction of a long time series

apparent density mapping and 3d gravity inversion in the eastern alps1 power spectrum analysis of the bouger gravity values in the eastern alps suggests that the gravity field may be separated into long and short wavelength components the long wavelength component is assumed to be caused by alpine crustal thickening this long wavelength component was subjected to a gravimetric single density interface inversion procedure giving a gravimetric mohorovicic model which is generally in good agreement with moho depths derived by refraction and reflection seismology the residual high frequency gravity component correlates well with the main surface geological units in the eastern alps apparent density mapping by applying an inverse density deconvolution filter to the short wavelength gravity component gives density values for the upper crust which correspond well with averaged density values from rock samples

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

a freshwater jet on the east greenland shelf in august 1997 rrs discovery cruise 230 world ocean circulation experiment woce section a25 ran a hydrographic section into cape farewell on the southern tip of greenland the closest approach to the shore was 2 nm in a water depth of 160 m over the east greenland shelf analysis of the hydrographic data conductivity temperature depth ctd vessel mounted acoustic doppler current profiler and thermosalinograph has revealed a current flowing southwestward 15 km wide 100 m deep and centered 10 km offshore we believe it to be driven by meltwater runoff from greenland this feature which we call the east greenland coastal current egcc carries a little less than 1 sv 106 m3 s 1 with peak current speeds of 1 m s 1 at the surface the center of the egcc lies on a salinity front with maximum salinity contrast 4 practical salinity units psu between coast and shelf break and between surface and bottom a spot value of freshwater transport is 0 06 sv 1800 km3 yr 1 which is equivalent to 30 of the arctic freshwater gain the presence of the egcc and its continuity up the east greenland coast as far as denmark strait is confirmed in satellite sea surface temperature images and surface drifter tracks we estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be 25 per 1 c

on the mid pleistocene transition to 100 kyr glacial cycles and the asymmetry between glaciation and deglaciation times 1 a mechanism is proposed for the mid pleistocene transition from a dominant periodicity of 41 kyr to 100 kyr in glacial oscillations the same mechanism is shown to also explain the asymmetry between the long glaciation and short deglaciation phases of each cycle since that transition versus the symmetry of the 41 kyr oscillations prior to the transition these features arise naturally within the framework of the sea ice switch glacial cycle mechanism of gildor and tziperman 2000 as a result of the gradual cooling of the deep ocean during the pleistocene this cooling results in a change of the relation between atmospheric temperature and the rates of accumulation and ablation of continentals ice sheets it is this latter change that leads to the activation of the sea ice switch and therefore to the initiation of the 100 kyr oscillations the gradual glaciation and rapid deglaciations during these oscillations occur because the mean value of the ice sheet ablation is not far from the maximum rate of snow accumulation during warm periods this proximity of mean ablation and maximum accumulation rates is shown to be also a consequence of the mid pleistocene gradual cooling of the deep ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 1620 global change climate dynamics 3309 1640 global change remote sensing 4267 oceanography general paleoceanography keywords climate dynamics glacial cycles mid pleistocene transition 100 kyr 41 kyr

atmospheric circulation and cyclone frequency variations linked to the primary modes of greenland snow accumulation 1 data from 34 greenland firn cores extending from 1982 to 1996 are used to identify spatial accumulation variability patterns and their associated atmospheric circulation and cyclone frequencies the first principal component representing west central greenland accumulation is correlated to nao variability having increased southwesterly northeasterly flow over that area during high low accumulation winters the flow is linked to a relative increase in cyclone activity on the west central region of the ice sheet during high accumulation periods the second principal component represents accumulation over southeastern greenland where strong westerly flow leads to high accumulation and an increase in lee cyclones on the east and southeast coast the study provides evidence that increased cyclone activity occurs over or immediately adjacent to areas experiencing anomalously high accumulation and it is important to distinguish lee cyclones from icelandic cyclones as they produce opposite precipitation effects over the ice sheet

interannual variations of snow accumulation on the greenland ice sheet 1985 1996 new observations versus model predictions newly measured time series of net water equivalent accumulation from ice cores are reported for 11 sites located near the 2000 m contour of the greenland ice sheet many of these sites are located in regions where accumulation has not been previously measured we compared these new time series of annual accumulation with previously reported modeled precipitation covering the same time range because ice core accumulation records include both regional and local accumulation components we used adjacent ice core records at six multiple core sites to estimate the local component and extrapolated these results to the five single core sites we investigated the impact of this short scale spatial variability in accumulation on statistical comparisons between the observed accumulation and model precipitation although sealers were required to match the 12 year mean modeled precipitation to the mean observed accumulation a high degree of correspondence between observed interannual accumulation and scaled modeled precipitation was found at 7 of 11 locations the need for scaling and the low correspondence between model simulations and observations at some sites clearly indicate that model improvements are needed although very encouraging a more spatially distributed array of ice core accumulation measurements spanning the same time period as the precipitation modeling is necessary for continued model improvement and validation in agreement with earlier studies the large temporal variability in snow accumulation predicted by modeling and confirmed by ice cores indicates that the ice sheet elevation varies by tens of centimeters from year to year simply because of changing accumulation

the crustal structure of the eastern alps from a combination of 3d gravity modelling and isostatic investigations abstract the transition between european and adriatic crust is an important feature related to the plate collision that formed the european alps the diversity of seismic and geological information allows the construction of two alternative 3d density models which both match the observed gravity field different seismic experiments suggest a thickness for the adriatic crust between 30 and 40 km the thick crust model requires an unusually dense lower crust 3050 kg m 3 to reproduce the observed bouguer anomaly to evaluate the two alternative models the isostatic implications of the geometry and density distribution within both 3d models are investigated using local airy and regional vening meinesz isostasy airy isostatic investigations show that the eastern alps are not isostatically compensated and the residuals correlate strongly with exposed geological formations subsequently subsurface loading is an important factor controlling isostatic processes the different geometry and densities in the two 3d models imply different loading at the crust mantle boundary the subsurface loads calculated from the 3d density models were used to estimate regional isostasy by a convolution method in general small rigidity values d 21 nm are determined for the eastern alpine lithosphere in the model with a 40 km thick adriatic crust high flexural rigidities are inferred for the adriatic plate 100 10 21 nm but these values are unusual for an active orogenic region the results point to the interfingering of european and adriatic crust that results in the squeezing of european crust between adriatic crust and mantle with additional contamination by mantle material

climate driven fluctuations in freshwater flux to sermilik fjord east greenland during the last 4000 years the freshwater runoff from the glaciated and snow covered sermilik fjord catchment se greenland was estimated at annual resolution for the period 1900 2008 and at decadal resolution for the past four millennia our simulations were forced with available meteorological station data 1900 2008 and greenland ice core estimated temperature data 1899 bc ad 1980 from dye3 and gisp2 time series of estimated ice discharge 2000 2009 for the three major outlet glaciers helheim fenris and midgard indicate that 53 74 of the ice discharge variations could be explained by variations in areally averaged glacier terminus surface supraglacial runoff based on these data and together with calculated subglacial geothermal and frictional melting as well as net precipitation for the fjord area the sermilik fjord freshwater flux was deduced for the period 1900 2008 our simulations indicated that during the last century surface freshwater runoff has equaled 13 of the sermilik fjord average freshwater flux of 33

assessment of greenland albedo variability from the advanced very high resolution radiometer polar pathfinder data set the advanced very high resolution radiometer polar pathfinder app data set is used to examine the variability of the surface albedo over greenland analysis of the app albedo record from 1981 to 1998 show anomalously low albedo during 1995 and 1998 over most of the ice sheet as compared with the other years the low albedo encountered during these years suggests that the ice sheet experienced considerable melt in 1995 and 1998 particularly near the western margin of the ice sheet conversely anomalously high albedos were found in 1992 as a result of colder temperatures and hence less melt following the eruption of mount pinatubo the relationship between the annual north atlantic oscillation nao index and the mean summer albedo from all the stations reveals a positive correlation of 0 44 and a positive correlation of 0 55 for the southern part of the ice sheet therefore variations in the mean summer albedo over greenland can in part be explained by variations in the nao such that during periods of intensification of the normal mode of the nao the mean summer albedo is above normal trend analysis reveals an overall downward trend in surface albedo from 1981 to 1998 which agrees with recent trends in melt and precipitation however the trend was found not to be statistically significant but rather influenced by the low albedo in recent years

a comparison of quasigeostrophic and nonquasigeostrophic vertical motions for a model simulated rapidly intensifying marine extratropical cyclone abstract large scale departures from quasigeostrophic vertical motions are diagnosed for a model simulation of the qe ii storm 9 11 september 1978 the simulation was performed by the limited area mesoscale prediction system lamps initialized at 1200 utc 9 september 1978 the model cyclone intensified from a central pressure of 1003 mb to 976 mb in 24 h considerably short of the 59 mb 24 h 1 observed deepening but reasonable in comparison to other model simulations of this storm this diagnosis centers on a hydrostatic generalized omega equation which scales to the quasigeostiophic omega equation for small rossby number vertical motions were computed both from this generalized omega equation and the quasigeostrophic omega equation in order to examine the importance of nonquasigeostrophic effects the high correlation of vertical motions from a control experiment using most of the terms in the generalized omega equation with the vertical motions predicted by the model establishes the validity o

evaluation of recent precipitation studies for greenland ice sheet the retrieval of an accurate spatial and temporal record of contemporary greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales a comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of greenland there is general agreement on a long term greenland average of about 35 cm yr 1 and on long term values for regional scales although differences for outlying data sets exceed 50 of the observed glaciological estimate for particular regions a fundamental problem is the inadequate topographic representation of greenland in the numerical analyses nearly all of the data sets are overly dry for high elevation areas as seen from comparisons with glaciological observations from summit the east central region of greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses in contrast there is strong agreement among all methods on the temporal variability for the west central region over a 15 year period from the comparison it is concluded that none of the data sets is able to capture all of the regional scale features in general however the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of greenland s precipitation climatology in particular an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses in the north anomalously high precipitation is associated with cyclonic development near the fram strait for west central greenland the close agreement among methods is related to the dominant contribution of the mean circulation

exploring seasonal accumulation bias in a west central greenland ice core with observed and reanalyzed data the seasonality of accumulation in west central greenland is investigated to determine whether a summer bias exists in a multi century ice core recovered from crawford point cp such a bias would negatively affect the ice core s potential for reconstructing the history of winter circulation patterns including the north atlantic oscillation an automatic weather station aws installed at the cp site in 1995 records sub daily surface heights and affords a unique opportunity to assess the seasonal distribution of accumulation and test the performance of five gridded reanalysis datasets and a regional climate model simulated accumulation compares remarkably well with in situ measurements from both the aws and cp ice core demonstrating their potential to accurately represent accumulation in this region seasonal accumulation exhibits no summer maximum indicating that any concurrent precipitation maximum is likely offset by melt and or sublimation effects the lack of a strong seasonal accumulation bias implies that the cp ice core is well suited for future investigations of the history of winter circulation patterns

recent greenland accumulation estimated from regional climate model simulations and ice core analysis the accumulation defined as precipitation minus evaporation over greenland has been simulated with the high resolution limited area regional climate model hirham4 applied over an arctic integration domain this simulation is compared with a revised estimate of annual accumulation rate distribution over greenland taking into account information from a new set of ice core analyses based on surface sample collections from the north greenland traverse the region with accumulation rates below 150 mm yr21 in central northwest greenland is much larger than previously assumed and extends about 500 km farther to the south it is demonstrated that good agreement between modeled and observed regional precipitation and accumulation patterns exists particularly concerning the location and the values of very low accumulation in the middle of greenland the accumulation rates in the northern part of greenland are reduced in comparison to previous estimates these minima are connected with a prevailing blocking high over the greenland ice sheet and katabatic wind systems preventing humidity transports to central greenland the model reasonably represents the synoptic situations that lead to precipitation maxima of precipitation and accumulation occur at the southwestern and southeastern coasts of greenland and are connected with cyclonic activity and the main storm tracks around greenland the central region of the greenland ice sheet acts as a blocking barrier on moving weather systems and prohibits cyclones moving from west to east across this region and thus prevents moisture transports

the 1958 2009 greenland ice sheet surface melt and the mid tropospheric atmospheric circulation in order to assess the impact of the mid tropospheric circulation over the greenland ice sheet gris on surface melt as simulated by the regional climate model mar an automatic circulation type classification ctc based on 500 hpa geopotential height from reanalyses is developed general circulation correlates significantly with the surface melt anomalies for the summers in the period 1958 2009 the record surface melt events observed during the summers of 2007 2009 are linked to the exceptional persistence of atmospheric circulations favouring warm air advection the ctc emphasizes that summer 500 hpa circulation patterns have changed since the beginning of the 2000s this process is partly responsible for the recent warming observed over the gris

substantial thinning of a major east greenland outlet glacier aircraft laser altimeter surveys in 1993 and 1998 over kangerdlugssuaq glacier in east greenland reveal thinning over the 5 year interim of several meters for all surveyed areas within 70 km of the seaward ice front rising to 50 meters in the final 5 km such rapid thinning is best explained by increased discharge velocities and associated creep thinning most probably caused by enhanced lubrication of the glacier bed the calving ice front over the past decade has occupied approximately the same location as in 1966 velocity estimates for 1995 96 are about the same as those for 1966 and 1988 but significantly less than for 1999 suggesting that major thinning began after 1995

first deep seismic reflection images of the eastern alps reveal giant crustal wedges and transcrustal ramps 1 the alps are considered as a classical example for an orogen created by continental plate collision in this study we present new images obtained from deep seismic reflection profiling in the eastern alps between munich and venice which give rise to examine and revise existing concepts the seismic sections exhibit a prominent bi verging reflection pattern at crustal scale a major ramp like structure outcropping at the inn valley fault can be traced southward over 80 km into the mountain root where relics of the subducted penninic ocean are expected new models of the evolution of the eastern alps show an upper lower crustal decoupling along transcrustal thrust faults with opposite thrust directions of both the european and the adriatic african continents

precipitation over greenland and its relation to the north atlantic oscillation the equation method based on an equivalent isobaric geopotential height in coordinates has been used to retrieve the precipitation over greenland this approach is designed to accurately represent the topographic effects of the greenland ice sheet on atmospheric motion and precipitation the 11 year mean precipitation from 1985 to 1996 over all of greenland is 376 mm yr 1 which is close to the long term mean precipitation of 346 mm yr 1 estimated from glaciological data the precipitation over all of greenland shows that the largest value in 1986 is 472 mm yr 1 and the smallest value in 1995 is 309 mm yr 1 the major interannual variability of the atmospheric circulation in the north atlantic can be represented by the variation of the north atlantic oscillation nao index which is most pronounced during winter it is found that if the nao index increases the total precipitation over greenland decreases and vice versa the correlation coefficient between these two series for 1985 1995 is 0 75 the mean precipitation over southern greenland where the majority of precipitation falls is more closely related to the nao index in winter and their correlation coefficient is 0 80 this relationship can be understood from the composite maps of sea level pressure and greenland precipitation for the high and low index months during months of high nao index values the icelandic low is strong during months of low nao index values the monthly mean low is located to the southwest of greenland over the labrador sea precipitation amounts over the southeast coast of greenland are about 100 mm larger during the low nao index months than the high nao index months precipitation over all of greenland during the low nao index months is higher there are significant downward trends in annual precipitation from 1985 1995 for all of greenland and its southern and central west coastal regions amounting to about 3 per year

holocene climatic changes in greenland different deuterium excess signals at greenland ice core project grip and northgrip 1 water stable isotope measurements d and 18o have been conducted on the holocene part of two deep greenland ice cores greenland ice core project grip and northgrip located 320 km apart these combined measurements provide the first two continuous greenland holocene deuterium excess profiles d d 8 18o a parameter strongly influenced by changes in moisture sources we discuss here temporal and regional fluctuations of the deuterium excess within central to north greenland with a mean temporal resolution of 4 years although grip and northgrip exhibit similar annual mean surface temperatures and 18o levels a significant offset of modern deuterium excess is observed between the two sites we attribute this offset to a different mix of modern moisture sources pointing to regional scale differences in moisture advection toward greenland the common long term deuterium excess holocene increasing trend is probably related to the increased relative contribution of low latitude moisture to greenland snowfall in response to the change in the earth obliquity as symmetrically observed in antarctica three abrupt declines punctuate the grip excess record 8 2 4 5 and 0 35 ka bp suggesting associated reorganizations of the northern high latitudes hydrological cycle the 8 2 ka bp event is characterized by 1 a rapid cooling followed by a progressive warming and 2 a deuterium excess cooling restricted to grip therefore totally different from rapid events during glacial times by contrast the northgrip deuterium excess record is more stable we propose that a slightly larger proportion of moisture supplied by local storm tracks to grip induces an isotopic compensation mechanism between simultaneous site and source temperature coolings resulting in a rather temperature insensitive 18o profile together with well marked deuterium excess amplitudes northgrip 18o seems less biased by isotopic processes and should provide a more reliable past temperature record

gravity inferred crustal thickness of greenland abstract greenland s crust contains clues for understanding the dynamics of the earth s second largest ice sheet as well as the iceland hotspot over the past 100 ma however our knowledge of the sub ice crust is very limited due to the paucity of outcrops and seismic observations particularly in central greenland in order to augment these sparse constraints we modeled terrain and airborne free air gravity data which provide estimates for moho and related crustal thickness these estimates were obtained from the inversion of isostatically corrected terrain effects where the computed gravity effects of the terrain s rock water and ice components were subtracted from the terrain correlated free air anomalies the terrain correlated free air components were estimated from the correlation spectrum between the free air anomalies and the terrain s gravity effects which are assumed to reflect isostatic disturbances of the crustal terrain the results indicated an average crustal thickness of about 37 km for greenland with greater values by 5 10 km in the southern greenland archean blocks and caledonian foldbelt and comparably lower values in northern greenland the thinner crustal thickness estimates in the north are strongly correlated with the faster basal melt regions of the ice sheet and glaciers the crustal thickness map provides constraints for an improved interpretation of the iceland hotspot track in northern greenland at about 100 70 ma

atmospheric circulation variability associated with shallow core seasonal isotopic extremes near summit greenland seasonal back diffused 18o time series reconstructed for nine shallow firn cores from the greenland summit for 1959 1987 are evaluated in terms of 1 their spatial and temporal variability and 2 their association to the atmospheric circulation rotated principal component analysis evaluates spatial and temporal patterns of organization in the back diffused 18o ice core time series mean sea level pressure and 500 hpa height fields are obtained for winter and summer seasons that fall in the isotopically warmest and coldest thirds of the seasonal data the winter back diffused 18o data indicate that some degree of longitudinal separation takes place between isotopic records from western and eastern greenland in agreement with coastal station climatic data temporal variability is linked with statistical significance to the variability of the atmospheric circulation over the denmark strait as well as over the norwegian and barents seas the north atlantic oscillation nao and the mean icelandic low in the denmark strait affect isotopic variability over the cores west of the ice divide just as they have been shown to prominently affect west coast air temperature records isotopic variability at some ice cores east of the divide is influenced by pressure variability over the norwegian and barents seas although statistical significance is lower the nao appears insignificant in summer isotopic variability as the circulation in that season is very much localized and dominated by either ridging warm cases or troughs cold cases over eastern greenland and the arctic ocean results suggest that long term winter 18o variability can potentially be linked to climate variation over europe especially from the mediterranean basin northward to about 55 n and as far east as central siberia