the impact of groundwater depletion on spatial variations in sea level change during the past century continental groundwater loss during the past century has elevated sea level by up to 25 mm the mass unloading associated with this depletion locally uplifts earth s solid surface and depresses the geoid leading to slower relative sea level rise near areas of significant groundwater loss we computed spatial variations in sea level using a model of the solid earth s response to estimates of groundwater depletion during the past century and find large negative deviations of 0 4 mm yr along the coastlines of western north america and southern asia this approximately corresponds to the difference between rates of sea level rise measured by tide gauges in these regions since 1930 and average rates inferred from global reconstructions groundwater induced regional variations in sea level can be larger than those due to postglacial rebound and interseismic deformation and should become increasingly important in the future as both groundwater depletion and sea level rise accelerate

retreat of glaciar tyndall patagonia over the last half century we report measurements of ice surface elevation ice thickness and surface area for glaciar tyndall patagonia made in 1999 2002 the measurements together with previously published observations show acceleration over the last few decades of the rates of thinning and retreat of the main calving front the acceleration of shrinkage appears to be driven by a combination of climate and feedback processes the dominant feedback being increased melting associated with lowering of the glacier surface elevation feedback the melting capacity in the main terminus lake is now too small to be a major factor accelerating the retreat the glacier bed has low slope and remains below the elevation of the lake spillway for 14 km upstream from the 2000 calving front indicating the potential for extensive retreat under the influence of strong elevation feedback and increasing interaction with the lake as it enlarges

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

calving rates in fresh water new data from southern patagonia data relating to calving dynamics in fresh water are scarce especially for deep water sites a linear dependence of calving velocity vc onwater depth hw is commonly accepted for both tidewater and fresh water calving glaciers herewe use recent data from temperate patagonian glaciers to propose a revised relationship for calving in fresh water the new ratio is derived from glaciers calving rapidly into deep water documented using sequential satellite images and depth soundings the main data source is a detailed remotely sensed dataset of the rapidly retreating glaciarupsala complementedwith global positioning system field surveys and precise ice proximal bathymetric surveys the areaintegrated mean water depth between glacier positions in 1996 and 2000 is 490m with a maximum recorded depth of4700m in the same period image analysis reveals surface area loss of 1 37 km a 4 8 km and an average calving rate of 1880ma the resulting vc hw ratio is of a similar order of magnitude to that recently derived for nearby glaciar moreno but is well above the range of values commonly reported for lacustrine calving

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

water mass properties and exchange between the nordic seas and the northern north atlantic during the period 23 6 ka benthic oxygen isotopic evidence 1 twenty benthic oxygen isotope records from different water depths in the nordic seas and the north atlantic are compared during the last glacial maximum brine formation on continental shelves produced brine shelf water bsw sinking below 1500 m in the nordic seas open ocean convection in the nordic seas produced glacial north atlantic intermediate water gnaiw gnaiw overflowed the greenland scotland ridge and entrained depths above and at least partly below 2000 m in the north atlantic during the early deglaciation bsw enriched intermediate water masses in the nordic seas were formed these overflowed the greenland scotland ridge and influenced the north atlantic intermediate and deepwater masses in the bolling allerod ba open ocean convection increased and produced intermediate water in the nordic seas with outflow to the north atlantic however deep water with modern characteristics did not entrain water below 2000 m in the north atlantic in similar amounts as during the holocene a new period of brine formation during the younger dryas transported bsw to intermediate water masses in the norwegian sea there was also open ocean convection and meridional overturning in the nordic seas but it was probably reduced compared to the ba in the early holocene and mid holocene meridional overturning appears similar to that of today potential locations for large scale formation of bsw might have been broad and shallow 200 m areas of the north sea northeast of greenland and north of east siberia these settings should be favorable for bsw formation during cold periods

multispecies stable isotopes of benthic foraminifers reveal past changes of organic matter decomposition and deepwater oxygenation in the arabian sea 1 the stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western arabian sea was determined to evaluate deepwater oxygenation organic matter remineralization and early diagenetic processes during the past 190 000 years the 18o records reveal species specific metabolic effects susceptibility to changes in carbonate ion concentration and supralysoclinal calcite dissolution the foraminiferal 13c records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon 13cdic and in the microhabitat depth of infaunal species maximum 13cdic offsets between bottom and pore waters ranged between mean values of 0 8 and 1 2 corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2 7 ml l 1 intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well oxygenated deepwater masses during interglacials during interglacial maxima the 13c difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes

evolution of late glacial ice marginal lakes on the northwestern canadian shield and their influence on the location of the dubawnt lake palaeo ice stream abstract during deglaciation of the north american laurentide ice sheet large proglacial lakes developed in positions where proglacial drainage was impeded by the ice margin for some of these lakes it is known that subsequent drainage had an abrupt and widespread impact on north atlantic ocean circulation and climate but less is known about the impact that the lakes exerted on ice sheet dynamics this paper reports palaeogeographic reconstructions of the evolution of proglacial lakes during deglaciation across the northwestern canadian shield covering an area in excess of 1 000 000 km2 as the ice sheet retreated some 600 km the interactions between proglacial lakes and ice sheet flow are explored with a particular emphasis on whether the disposition of lakes may have influenced the location of the dubawnt lake ice stream this ice stream falls outside the existing paradigm for ice streams in the laurentide ice sheet because it did not operate over fined grained till or lie in a topographic trough ice margin positions and a digital elevation model are utilised to predict the geometry and depth of proglacial lakes impounded at the margin at 30 km increments during deglaciation palaeogeographic reconstructions match well with previous independent estimates of lake coverage inferred from field evidence and results suggest that the development of a deep lake in the thelon drainage basin may have been influential in initiating the ice stream by inducing calving drawing down ice and triggering fast ice flow this is the only location alongside this sector of the ice sheet where large 3000 km2 deep lakes 120 m are impounded for a significant length of time and exactly matches the location of the ice stream it is speculated that the commencement of calving at the ice sheet margin may have taken the system beyond a threshold and was sufficient to trigger rapid motion but that once initiated calving processes and losses were insignificant to the functioning of the ice stream it is thus concluded that proglacial lakes are likely to have been an important control on ice sheet dynamics during deglaciation of the laurentide ice sheet

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

mass fluxes and dynamics of moreno glacier southern patagonia icefield accumulation ablation calving and flow dynamics of moreno glacier one of the main outlet glaciers of the southern patagonia icefield were studied based on field campaigns and on spaceborne radar imagery acquired by sir c x sar ice velocities and ablation were measured through two summers and one winter the ice depth was sounded seismically at a transect 8 km above the calving front showing a maximum depth of 720 m the velocity field of the terminus was derived from sir c x sar data by means of interferometry and amplitude correlation the average specific annual net accumulation is 5540 500 mm water equivalent the bottom topography of the lake and the high ratio of calving flux to net accumulation explain the remarkable stability of moreno glacier throughout this century which is in contrast to the retreat of other glaciers in this region

mg ca ratios of the benthic foraminifera oridorsalis umbonatus obtained by laser ablation from core top sediments relationship to bottom water temperature 1 a laser ablation system connected to an inductively coupled plasma mass spectrometer was used to determine mg ca ratios of the benthic foraminifera oridorsalis umbonatus a set of modern core top samples collected along a depth transect on the continental slope off namibia 320 2300 m water depth 2 9 to 10 4 c was used to calibrate the mg ca ratio against bottom water temperature the resulting mg ca bottom water temperature relationship of o umbonatus is described by the exponential equation mg ca 1 528 e0 09 bwt the temperature sensitivity of this equation is similar to previously published calibrations based on cibicidoides species suggesting that the mg ca ratio of o umbonatus is a valuable proxy for thermocline and deep water temperature

detailed seismic stratigraphy of lago puyehue implications for the mode and timing of glacier retreat in the chilean lake district lago puyehue is a glacigenic lake in the chilean lake district 40 s with a complex deglaciation history a detailed seismic stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the lago puyehue basin than the neighbouring glacier from the lago rupanco basin because of their close proximity rupanco meltwater streams played an important part in the depositional processes of lago puyehue a timing discrepancy between the in lake ages of a sediment core and the outer lake ages of moraine deposits re opens the discussion on the timing of deglaciation in the southern hemisphere copyright 2011 john wiley sons ltd

a new projection of sea level change in response to collapse of marine sectors of the antarctic ice sheet we present gravitationally self consistent predictions of sea level change that would follow the disappearance of either the west antarctic ice sheet wais or marine sectors of the east antarctic ice sheet eais our predictions are based on a state of the art pseudo spectral sea level algorithm that incorporates deformational gravitational and rotational effects on sea level as well as the migration of shorelines due to both local sea level variations and changes in the extent of marine based ice cover if we define the effective eustatic value eev as the geographically uniform rise in sea level once all marine based sectors have been filled with water then we find that some locations can experience a sea level rise that is 40 per cent higher than the eev this enhancement is due to the migration of water away from the zone of melting in response to the loss of gravitational attraction towards the ice sheet load self attraction the expulsion of water from marine areas as these regions rebound due to the unloading and the feedback into sea level of a contemporaneous perturbation in earth rotation in the wais case this peak enhancement is twice the value predicted in a previous projection that did not include expulsion of water from exposed marine sectors of the west antarctic or rotational feedback the peak enhancements occur over the coasts of the united states and in the indian ocean in the wais melt scenario and over the south atlantic and northwest pacific in the eais scenario we conclude that accurate projections of the sea level hazard associated with ongoing global warming should be based on a theory that includes the complete suite of physical processes described above

buoyancy driven lacustrine calving glaciar nef chilean patagonia glaciar nef a 164 km 2 eastern outlet of hielo patagonico norte the northern patagonia icefield terminates in a proglacial lake that has formed in conjunction with 20th century glacier retreat the terminus is inferred to be transiently afloat a hinge calving mechanism is proposed in which buoyant forces impose a torque on the glacier tongue resulting in the release of coherent sections of the glacier tongue as tabular icebergs a simple model shows how torque and tensile stress reach a maximum at the up glacier limit of the buoyant zone and that glacier thinning causes this point to migrate up glacier empirical evidence supporting this model includes elevated thermo erosional notches 6 5 m above lake level and the ubiquitous presence since 1975 of tabular icebergs with surface areas 0 3 km 2 flow speeds of 1 2 1 3 m d 1 were measured near the terminus in february 1998 extrapolations from these short term data yield a calving rate of 785 835 m a 1 and a calving flux of 232 10 6 m 3 a 1 or 0 2 km 3 a 1 the calculated mean water depth at the terminus is 190 m this calving rate is higher than at grounded temperate glaciers calving in fresh water but is nevertheless almost an order of magnitude less than calving rates at both grounded and floating tidewater glaciers

the sea level budget along the northwest atlantic coast gia mass changes and large scale ocean dynamics sea level rise and decadal variability along the northwestern coast of the north atlantic ocean are studied in a self consistent framework that takes into account the effects of solid earth deformation and geoid changes due to large scale mass redistribution processes observations of sea and land level changes from tide gauges and gps are compared to the cumulative effect of gia present day mass redistribution and ocean dynamics over a 50 year period 1965 2014 gia explains the majority of the observed sea level and land motion trends as well as almost all interstation variability present day mass redistribution resulting from ice melt and land hydrology causes both land uplift and sea level rise in the region we find a strong correlation between decadal steric variability in the subpolar gyre and coastal sea level which is likely caused by variability in the labrador sea that is propagated southward the steric signal explains the majority of the observed decadal sea level variability and shows an upward trend and a significant acceleration which are also found along the coast the sum of all contributors explains the observed trends in both sea level rise and vertical land motion in the region as well as the decadal variability the sum of contributors also explains the observed acceleration within confidence intervals the sea level acceleration coincides with an accelerating density decrease at high latitudes

evolution of a debris covered glacier in the western himalaya during the last four decades 1971 2016 a multiparametric assessment using remote sensing and field observations abstract this study assesses the response of the panchi nala glacier bhaga basin western himalaya to climate change by monitoring multiple glacier parameters namely length area debris cover snowline altitude sla surface ice velocity siv and surface elevation change h these parameters were analysed using high resolution satellite images corona kh 4b and sentinel 2 msi and medium resolution ones landsat tm etm oli and terra aster acquired between 1971 and 2016 along with extensive field observations considering only dimensional changes the glacier appears to have low rates of recession 4 54 2 56 m y 1 and deglaciation 0 11 0 04 y 1 over the study period 1971 2016 however siv and h values reveal a significant slowdown 33 87 1992 93 2015 16 and an extensive lowering 1 62 0 06 m y 1 2000 2013 on the glacier the debris cover area and sla also increased by 23 50 1 74 and 287 63 m respectively during 1971 2016 increase in the mean winter minimum temperature and decrease in the winter snowfall are probably the main drivers of glacier depletion we conclude that the significant slowdown extensive surface lowering development of a proglacial lake and appearance of the supraglacial lakes collectively indicate a severe glacier degeneration this forewarns that the glacier may experience an accelerated pace of wastage in the future

thermo erosional notch development at fresh water calving tasman glacier new zealand controls on glacier calving rates are receiving increased scientific interest at fresh water calving glaciers limnological factors might be more important than glaciological ones measurements of thermo erosional notch development at the calving ice cliff of tasman glacier new zealand suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting notch formation rates typically vary between 10 and 30 cm d 1 maximum rate 65 cm d 1 in summer corresponding to an average calving rate of 34 m a 1 notch formation is slower than waterline melt and is controlled by water temperatures and circulation cliff geometry debris supply and water level fluctuations the latter shift the position of undercutting resetting the level of the notch formation process and thereby slowing it the geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation hence water temperatures in the lake are not necessarily indicative of the rate of notch formation the prediction of rate of notch formation from far field variables is hampered by the complex interaction of the influencing factors the significance of thermal undercutting as a calving rate controlling process decreases with increasing ice velocities calving rates and surface gradients

long term impact of the proglacial lake jokulsarlon on the flow velocity and stability of breiðamerkurjokull glacier iceland

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

what caused the low water phase of glacial lake agassiz abstract first order modeling suggests that a low water phase in late glacial lake agassiz can be explained through changes in the balance between evaporation precipitation and runoff rather than drainage the low water moorhead phase is often attributed to drainage through outlets opened by isostatic depression and retreat of the laurentide ice margin however new data indicate that the proposed outlets were ice covered during the moorhead phase instead the lake water levels dropped to the moorhead phase before the start of the younger dryas chronozone and remained there until 11 3 ka thus drainage seems to be an implausible explanation for younger dryas aged low water levels in lake agassiz an alternative explanation is that evaporation equaled or exceeded water inputs from the adjacent ice margin and the deglaciated parts of the drainage basin to evaluate whether this hypothesis is plausible we constructed a simple model that considers the paleo basin geometry hydrology and meltwater production from the adjacent ice margin modest hydrologic changes within the range of present day variability coupled with low meltwater production produce a closed basin shifts in the location of the polar jet driven by increased arctic albedo may explain our inferred hydrologic changes

recent glacier and glacial lake changes and their interactions in the bugyai kangri southeast tibet glaciers in the bugyai kangri are located in a transition zone from southeast tibet where monsoonal temperate glaciers dominate to inner tibet where continental glaciers dominate here we analyze glacier and glacial lake changes in this region using multi year inventories based on landsat images from 1981 2013 results show that the total area of 141 glaciers in the region decreased by 30 44 0 89 km 2 from 198 35 9 54km 2 1980s to 167 93 4 52 km 2 2010s the annual area shrinkage rate 0 48 a 1 is lower than that reported for southeastern tibet but higher than that of inner tibet both the number and total area of glacial lakes increased between 1981 and 2013 among all lakes proglacial lakes contribute most similar to 81 to the expansion the total area of ten proglacial lakes increased by 150 3 13 17 and of these ten lakes the four that expanded most sharply showed increased calving at their upper margins resulting in more rapid retreat of lake terminating glaciers than land terminating glaciers owing to rapid calving several lakes may undergo further growth in the near future increasing the potential risk of glacial lake outburst floods

contribution of global groundwater depletion since 1900 to sea level rise 1 removal of water from terrestrial subsurface storage is a natural consequence of groundwater withdrawals but global depletion is not well characterized cumulative groundwater depletion represents a transfer of mass from land to the oceans that contributes to sea level rise depletion is directly calculated using calibrated groundwater models analytical approaches or volumetric budget analyses for multiple aquifer systems estimated global groundwater depletion during 1900 2008 totals 4 500 km3 equivalent to a sea level rise of 12 6 mm 6 of the total furthermore the rate of groundwater depletion has increased markedly since about 1950 with maximum rates occurring during the most recent period 2000 2008 when it averaged 145 km3 yr equivalent to 0 40 mm yr of sea level rise or 13 of the reported rate of 3 1 mm yr during this recent period

mg ca temperature calibration for the benthic foraminifera melonis barleeanum and melonis pompilioides an important tool for deep sea temperature reconstruction is mg ca paleothermometry applied to benthic foraminifera foraminifera of the genus melonis appear to be promising candidates for temperature reconstructions due to their wide geographical and bathymetric distribution and their infaunal habitat which was suggested to reduce secondary effects from carbonate ion saturation co3 2 here we make substantial advances to previous calibration efforts and present new multi lab mg ca data for melonis barleeanum and melonis pompilioides from more than one hundred core top samples spanning in situ bottom temperatures from 1 to 16 c coupled with morphometric analyses of the foraminifer tests both species and their morphotypes seem to have a similar response of mg ca to growth temperature compilation of new and previously published data reveals a linear dependence of temperature on mg ca with a best fit of mg ca mmol mol 0 113 0 005 bwt c 0 792 0 036 r2 0 81 n 120 1 sd salinity bottom water co3 2 and varying morphotypes have no apparent effect on the mg ca temperature relationship but pore water co3 2 might have had an influence on some of the samples from the tropical atlantic

thermal regime of a supraglacial lake on the debris covered koxkar glacier southwest tianshan china a supraglacial lake was surveyed on the koxkar glacier in southwest tianshan from july to september 2007 and july to september 2008 and the temperature variation characteristics of the lake debris and debris free ice were analyzed at different depths to determine the thermal regimes in addition the discrepancies of temperature variation characteristics were investigated for different geomorphic units of the ablation zone of the koxkar glacier it was found that daily temperature variation curves for deep water are v shaped because meltwater from the glacier surface at temperatures of around 0 c feeds the lake and mixes with the relatively high temperature surface water during the day as the water temperature rises to approximately 4 c the mixed water sinks and forms a low temperature trough in the deep water of the lake in the middle of the day the vertical lapse rate of the lake water temperature against depth 0 33 c m has a magnitude lower than that of the debris 4 29 c m and that of the debris free ice 0 38 c m in the koxkar glacier s ablation zone the temperature curve for the surface water largely varied between the temperature curves for the debris at depths of 0 2 and 0 5 m the surface thermal condition of the ablation zone is significantly affected by the daily weather and there is a limited influence in debris at a depth of 1 m and in the lake at a depth of 5 m

interseismic uplift rates for western oregon and along strike variation in locking on the cascadia subduction zone 1 we quantify the spatial pattern of uplift rate in western oregon and northernmost california using tidal and leveling records to better understand the pattern of interseismic locking on the cascadia subduction zone we extend relative sea level time series of the six primary noaa tide gauges to include all observations from 1925 to 2006 previously unidentified bench mark instability biases portions of tidal records by 1 6 mm a 1 before correction we determine precise relative uplift rates at the six tidal sites with an adjustment that includes rates of differenced time series as additional constraints our analysis of national geodetic survey leveling data between tide gauges corrects errors in 1941 leveling and 184 secondary ties double the number of highest quality uplift rate estimates relative uplift rates from leveling are adjusted to the tidal rates accounting for uncertainties in both data types tidal and leveling uplift rates agree within error for all but one of the coastal segments where we infer systematic leveling error affects the 1988 line uplift rates are made absolute using an interval and location specific geocentric sea level rise rate of 2 3 0 2 mm a 1 total propagated one sigma errors for the absolute uplift rates of bench marks are 0 4 mm a 1 along strike changes in uplift rate near 45 n and 42 8 n require two distinct changes in locking depth as inferred from elastic dislocation modeling the along strike changes in locking on this portion of the cascadia subduction zone interface correlate to the western and southern extent of the mafic siletzia block in the fore arc

precise multielemental ratios in small foraminiferal samples determined by sector field icp ms inductively coupled plasma mass spectrometry icp ms holds two main advantages over other techniques for the measurement of foraminiferal elemental ratios 1 numerous trace metals may be precisely and simultaneously measured and 2 smaller samples may theoretically be used methods are presented for the precise determination of mg ca sr ca cd ca zn ca li ca u ca mn ca and fe ca by sector field icp ms analytical precision is largely independent of sample size over the range of 5 to 125 g caco3 eliminating the need for narrow target dilutions long term 1 precisions are as follows mg ca 0 54 sr ca 0 57 cd ca 1 8 zn ca 3 2 li ca 0 88 u ca 1 9 mn ca 0 97 and fe ca 1 4 for mg ca actual foraminiferal samples appear to give reliable results below 10 g caco3 postcleaning mass

vertical crustal displacement due to interseismic deformation along the san andreas fault constraints from tide gauges interseismic motion along complex strike slip fault systems such as the san andreas fault system safs can produce vertical velocities that are 10 times smaller than horizontal velocities caused by along strike variations in fault orientation and locking depth tide gauge stations provide a long 50 100 year recording history of sea level change due to several oceanographic and geologic processes including vertical earthquake cycle deformation here we compare relative sea level displacements with predictions from a 3 d elastic viscoelastic earthquake cycle model of the safs we find that models with lithospheric structure reflecting a thick elastic plate 50 km and moderate viscosities produce vertical motions in surprisingly good agreement with the relative tide gauge uplift rates these results suggest that sea level variations along the california coastline contain a small but identifiable tectonic signal reflecting the flexure of the elastic plate caused by bending moments applied at the ends of locked faults

the temporal significance of transitions from melting to calving termini at glaciers in the central southern alps of new zealand termini of valley glaciers in the central southern alps are undergoing a three phase sequence of retreat that began in the 1950s an initial phase of melting and slow downwasting under thickening supraglacial debris mantles is associated with stationary or slowly retreating termini this is followed by a transitional phase of disruption of insulating debris mantles allowing the rapid growth of shallow thermokarst lakes the shape and location of which vary according to glacier gradient and marginal topography a third phase of rapid calving retreat of ice cliffs into deepening proglacial lakes develops from the transitional phase at no stage are terminal responses simply related to climate present transitions to calving retreat are related to the morphology of glacier termini particularly to large outwash heads landform evidence indicates that similar calving phases do not appear to have occurred since late pleistocene deglaciation so that present changes to glacier termini are of great significance

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

a conceptual model of supra glacial lake formation on debris covered glaciers based on gpr facies analysis jordan r mertes acknowledges funding from michigan technological university and the michigan technological university 2016 fall finishing fellowship sarah s thompson acknowledges funding from the university centre in svalbard unis and the european commission fp7 mc ief

thermal structure of proglacial lakes in patagonia calving glaciers are rapidly retreating in many regions under the influence of ice water interactions at the glacier front in contrast to the numerous researches conducted on fjords in front of tidewater glaciers very few studies have been reported on lakes in which freshwater calving glaciers terminate to better understand ice water interactions at the front of freshwater calving glaciers we measured lakewater temperature turbidity and bathymetry near glaciar perito moreno upsala and viedma large calving glaciers of the southern patagonia icefield the thermal structures of these lakes were significantly different from those reported in glacial fjords there was no indication of upwelling subglacial meltwater instead turbid and cold glacial water discharge filled the region near the lake bottom this was because water density was controlled by suspended sediment concentrations rather than by water temperature near surface wind driven circulation reaches a depth of 180 m forming a relatively warm isothermal layer mean temperature of 5 6 c at perito moreno 3 4 c at upsala and 6 7 c at viedma which should convey heat energy to the ice water interface however the deeper part of the glacier front is in contact with stratified cold water implying a limited amount of melting there in the lake in front of glaciar viedma the region deeper than 120 m was filled entirely with turbid and very cold water at pressure melting temperature our results revealed a previously unexplored thermal structure of proglacial lakes in patagonia suggesting its importance in the subaqueous melting of freshwater calving glaciers

global depletion of groundwater resources 1 in regions with frequent water stress and large aquifer systems groundwater is often used as an additional water source if groundwater abstraction exceeds the natural groundwater recharge for extensive areas and long times overexploitation or persistent groundwater depletion occurs here we provide a global overview of groundwater depletion here defined as abstraction in excess of recharge by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction restricting our analysis to sub humid to arid areas we estimate the total global groundwater depletion to have increased from 126 32 km3 a 1 in 1960 to 283 40 km3 a 1 in 2000 the latter equals 39 10 of the global yearly groundwater abstraction 2 0 6 of the global yearly groundwater recharge 0 8 0 1 of the global yearly continental runoff and 0 4 0 06 of the global yearly evaporation contributing a considerable amount of 0 8 0 1 mm a 1 to current sea level rise

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

global geoid and sea level changes due to present day ice mass fluctuations we predict gravitationally self consistent global geoid and relative sea level rsl perturbations due to present day melting of ice complexes including the antarctic and greenland ice sheets and a suite of mountain glaciers and ice sheets classic analyses of sea level change indicate that these perturbations will depart significantly from eustatic i e geographically uniform trends e g woodward 1888 farrell and clark 1976 although this result has not always been appreciated in modern analyses mass flux of individual ice reservoirs will produce unique geometries of sea level change and this distinctiveness admits the possibility of using global geoid sea surface and rsl signatures of recent climate change to infer the ongoing mass balance of each reservoir rather than simply the net mass flux as an example we show that perturbations to the geoid arising from noneustatic water loads associated with each ice reservoir are sufficiently large at low degrees to be theoretically measurable within 5 years by the grace satellite mission we complete the study by reanalyzing tide gauge data at 23 sites selected by douglas 1997 in a recent analysis of global rsl rise traditionally estimates of global sea level rise are generated by taking the mean of a set of secular tide gauge trends that have been corrected for the influence of ongoing glacial isostatic adjustment gia related to the late pleistocene glacial cycles the common assumption in such studies is that the geographic scatter in the residual gia corrected trends is due to errors in the gia model or unmodeled processes e g tectonics we consider a large suite of gia model predictions and apply a least squares approach to the gia corrected tide gauge trends to estimate the weighting of various present day sea level signatures we find that the fit to the residual rsl trends is significantly improved and that the procedure is able to resolve a long standing observation of anomalously low sea level rates in europe this preliminary analysis which is relatively insensitive to changes in the assumed geometry of the present day mass balance assumes that ocean thermal expansion is globally uniform however the procedure can be easily extended to incorporate a realistic steric contribution once the geometry of the process is sufficiently well constrained

theoretical calving rates from glaciers along ice walls grounded in water of variable depths calving has been studied for glaciers ranging from slow polar glaciers that calve on dry land such as on deception island 63 0 s 60 6 w in antarctica through temperate alaskan tide water glaciers to fast outlet glaciers that float in fiords and calve in deep water such as jakobshavns isbrae 69 2 n 49 9 w in greenland calving from grounded ice walls and floating ice shelves is the main ablation mechanism for the antarctic and greenland ice sheets as it was along marine and lacustrine margins of former pleistocene ice sheets and is for tide water and polar glaciers

postglacial sea level change on a rotating earth summary we present a complete derivation of the equation governing long term sea level variations on a spherically symmetric self gravitating maxwell viscoelastic planet this new sea level equation extends earlier work by incorporating in a gravitationally self consistent manner both a time dependent ocean continent geometry and the in uence of contemporaneous perturbations to the rotation vector of the planet we also outline an e cient pseudo spectral numerical methodology for the solution of this equation and present a variety of predictions based on a suite of earth models of relative sea level rsl variations due to glacial isostatic adjustment gia these results show that the contribution to the predicted rsl signal from gia induced perturbations to the rotation vector can reach 7 8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum this result is sensitive to variations in the adopted lower mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness we also show that the rotationally induced component of rsl change is su cient to in uence previous estimates of late holocene melting events and ongoing sea level change due to giawhich were based on a rsl theory for a non rotating earth in particular estimates of antarctic melting over the last 5 kyr based on the amplitude of sea level highstands from the australian region may require an adjustment downwards of the order of 0 5 m of equivalent sea level rise furthermore present day rates of sea level change are perturbed by as much as 0 2 mm yr 1 by the rotational component of sea level change and this has implications for gia corrections of the global tide gauge record over the period from the last glacial maximum to the present we predict a distinctly non monotonic variation in the rotation induced component of rsl this is in agreement with our previous preliminary study milne mitrovica 1996 but contrasts signi cantly with predictions presented by han wahr 1989 and bills james 1996 we demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies we furthermore refute an assertion by bills james 1996 that previously published constraints on mantle viscosity and ice sheet histories which did not incorporate a rotation induced rsl component are largely invalidated by this omission

interannual flow dynamics driven by frontal retreat of a lake terminating glacier in the chinese central himalaya abstract most lake terminating glaciers in the himalaya retreat rapidly due to periodic frontal ice loss at their terminus but long term observations are still limited regarding their flow dynamics which is crucial for understanding the processes of ice mass loss and proglacial lake growth we present multi decadal surface velocity dynamics of the longbasaba glacier a rapid retreating lake terminating glacier in the chinese himalaya using an image feature tracking method applied on optical satellite images between 1989 and 2018 we show that in companion with rapid retreat 51 7 m a 1 its lower 5 km tongue experienced high interannual fluctuations in velocity comprising periodic acceleration and slowdown in 1989 1995 and 2001 2010 and a recent remarkable acceleration since 2012 the temporal variation of longitudinal velocity distribution indicates an upward propagation of the lake ward acceleration namely a downglacier inversion of strain from compression to extension this propagation is coupled to the retreat of the glacier front and occurs along the lowermost 1 1 5 km lake adjacent section as the proglacial lake expands the most recent acceleration of the near lake section since 2012 has likely facilitated a dynamic thinning on its upper sections where flow acceleration started two years later in 2014 this pattern contrasts markedly with a nearby decelerating land terminating glacier which has experienced a much slower retreat rate 7 8 m a 1 and the same magnitude of mean thinning rate at its lower part since 2000 our results confirm the strong influence of the proglacial lake on ice flow dynamics and suggest that lake ice interactions are important to consider when analyzing interpreting or modeling dynamics of rapidly retreating lake terminating glaciers in the himalayas as well as around the world

onset of calving at supraglacial lakes on debris covered glaciers of the nepal himalaya field surveys of supraglacial ponds on debris covered glaciers in the nepal himalaya clarify that ice cliff calving occurs when the fetch exceeds 80 m thermal undercutting is important for calving processes in glacial lakes and subaqueous ice melt rates during the melt and freeze seasons are therefore estimated under simple geomorphologic conditions in particular we focus on the differences between valley wind driven water currents in various fetches during the melt season our results demonstrate that the subaqueous ice melt rate exceeds the ice cliff melt rate when the fetch is 20 m and water temperature is 2 48c calculations suggest the onset of calving due to thermal undercutting is controlled by water currents driven by winds at the surface of the lake which develop with expanding water surface

ice sheet advance dynamics and decay configurations evidence from west central scotland abstract a 3700 km 2 area adjacent to the firth of clyde scotland is examined to constrain the development and dynamics of the western central sector of the last british and irish ice sheet results from geomorphological mapping lithostratigraphic investigations three dimensional geological modelling and field observations are combined to produce an empirically constrained five stage conceptual model of ice sheet evolution a previously published dates on interstadial organic deposits and mammalian fossils suggest that the main late devensian mld mis 2 glaciation of central scotland began after 35 ka cal bp during build up ice advanced from the western scottish highlands into the clyde and ayrshire basins glaciomarine muds and shelly deposits scavenged from the firth of clyde were redeposited widely as shelly tills and glacial rafts ice advance against reverse slopes generated and subsequently overtopped ice marginal sediment accumulations we hypothesise that some of these formed pre cursor ridges which were moulded into suites of ribbed moraine during the glacial cycle b sustained stadial conditions at the last glacial maximum lgm c 30 25 ka cal bp resulted in development of a major dispersal centre over the firth of clyde and southern uplands this dispersal centre locally preserved previously formed subglacial bedforms and fed a wide corridor of fast flowing ice east towards the firth of forth c initial deglaciation promoted a substantial re configuration of the ice surface with enhanced westward drawdown into the outer firth of clyde and eastward migration of an ice divide towards the clyde forth watershed d renewed ice sheet thickening over the firth of clyde may have accompanied growth of the irish ice sheet during the killard point stadial c 17 1 15 2 ka cal bp it was associated with limited bed modification subsequent ice sheet retreat was characterised by substantial meltwater production ponding and erosion e late stages of mld ice sheet retreat were punctuated by one or more significant ice margin oscillations discovery of de geer moraines at the site of a former proglacial lake in western ayrshire allows glacier flow at the ice margin to be approximated as 290 m a 1 during one such oscillation such velocities were probably enabled by basal sliding and shallow sediment deformation at this stage those parts of the mld ice sheet margin that were grounded in the firth of clyde were extremely vulnerable to collapse final disintegration of glacier ice in the clyde basin probably occurred early in the lateglacial interstadial greenland interstadial 1 coinciding with marine incursion to c 40 m above present day sea level

rapid thinning of lake calving yakutat glacier and the collapse of the yakutat icefield southeast alaska usa both lake calving yakutat glacier 337 km 2 alaska usa and its parent icefield 810 km 2 are experiencing strong thinning and under current climate conditions will eventually disappear comparison of digital elevation models shows that yakutat glacier thinned at area averaged rates of 4 76 0 06 m w e a 1 2000 07 and 3 66 0 03 m w e a 1 2007 10 simultaneously adjacent yakutat icefield land terminating glaciers thinned at lower but still substantial rates 3 79 and 2 94 m w e a 1 respectively for the same time periods indicating lake calving dynamics helps drive increased mass loss yakutat glacier terminates into harlequin lake and for over a decade sustained a 3 km long floating tongue which started to disintegrate into large tabular icebergs in 2010 such floating tongues are rarely seen on temperate tidewater glaciers we hypothesize that this difference is likely due to the lack of submarine melting in the case of lake calving glaciers floating tongue ice losses were evaluated in terms of overall mass balance and contribution to sea level rise the post little ice age collapse of yakutat icefield was driven in part by tidewater calving retreats of adjacent glaciers the lake calving retreat of yakutat glacier a warming climate and by the positive feedback mechanisms through surface lowering

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

ice foot development at temperate tidewater margins in alaska the presence of an ice foot at the base of temperate tidewater ice cliffs has been debated for nearly 100 years this paper presents evidence demonstrating ice feet at tidewater margins in glacier bay alaska ice feet are likely sources of many submarine icebergs originating at the ice margin the cause of ice foot development is unclear but may represent a change in fracture behavior near the bed where higher debris concentrations affect fracture propagation and calving ice foot formation can be favored by englacial discharge and sediment ramps along the glacier margin that can cause differential melting of the ice cliff the presence of ice feet is important to understanding ice proximal sediment dynamics because they are a primary source of debris rich icebergs and their calving affects sediment redistribution patterns

holocene glacier chronologies are high resolution global and inter hemispheric comparisons possible in the context of reconstruction of holocene glacier chronologies there has been a clear tendency during the past few decades towards imprecise use of the term high resolution furthermore it seems to be increasingly assumed that recently developed terrestrial cosmogenic nuclide dating tcnd is replacing earlier dating methods although recent glaciological knowledge clearly reveals the futility of oversimplified global and inter hemispheric correlation on the basis of few key sites such comparisons are widely attempted stimulated by the example of a recently published article relating to the southern alps of new zealand schaefer et al 2009 science 324 622 625 we highlight some related potential problems with the interpretation of holocene glacier chronologies in particular we consider 1 that the term high resolution should be applied only to decadal scale resolution or better and therefore not to tcnd based chronologies 2 that discontinuous moraine chronologies should not be ter

glacier calving a numerical model of forces in the calving speed water depth relation empirical data suggest that the rate of calving of grounded glaciers terminating in water is directly proportional to the water depth important controls on calving may be the extent to which a calving face tends to become oversteepened by differential flow within the ice and the extent to which bending moments promote extrusion and bottom crevassing at the base of a calving face numerical modelling suggests that the tendency to become oversteepened increases roughly linearly with water depth in addition extending longitudinal deviatoric stresses at the base of a calving face increase with water depth these processes provide a possible physical explanation for the observed calving rate water depth relation

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

glacial isostatic adjustment along the pacific coast of central north america abstract we infer the gia signal and its uncertainty along the central pacific coast of north america using 680 sea level index points and over 20 000 model runs sampling 700 1 d earth viscosity models and 29 ice sheet reconstructions due to the large spatial extent and different tectonic settings of the study area we divided it into three sub regions northern central and southern for which model parameters were inferred separately also given that this region is tectonically active the influence of this process as well as sediment isostatic adjustment was accounted for where possible by removing it from the data using published estimates our results indicate that it is not possible to produce an acceptable to for all of the rsl data with a single set of model parameters suggesting significant lateral variability in viscous structure specifically low viscosities 1019 1020 pas are inferred in the upper mantle within the northern region southwestern british columbia and northwest washington compared to those inferred 2 5 1020 pas for the central and southern regions extending from southern washington to southern california high quality model fits were obtained for all data except those from the northern region where no single parameter set was able to capture both the rapid and large rsl fall during the late glacial and the monotonic rise during the mid to late holocene at all localities this suggests the need for an earth model that incorporates departures from a linear maxwell rheology as applied here and or lateral variations in viscosity structure using our optimal model parameter sets we show that gia is a significant contributor to both contemporary vertical land motion and relative sea level change in our study region and so should be considered when interpreting observations of these signals and for making future relative sea level projections model output of present day vertical land motion at 483 gps stations and sea level change at 56 tide gauge stations is provided with estimated uncertainty so that these data can be used to study non gia processes more accurately

land water contribution to sea level from grace and jason 1measurements 1 we investigate the effect of water storage changes in the world s major hydrological catchment basins on global and regional sea level change at seasonal and long term time scales in a joint inversion using grace and jason 1 data we estimate the time dependent sea level contributions of 124 spatial patterns fingerprints including glacier and ice sheet melting thermal expansion changes in the terrestrial hydrological cycle and glacial isostatic adjustment particularly for hydrological storage changes we derive fingerprints of the 33 world s largest catchment basins assuming mass distributions derived from the leading eofs of total water storage in the watergap global hydrological model wghm from our inversion we estimate a contribution of terrestrial hydrological cycle changes to global mean sea level of 0 20 0 04 mm yr with an annual amplitude of 6 6 0 5 mm for august 2002 to july 2009 using only grace data in the inversion and comparing to hydrological changes derived from grace data directly using a basin averaging method shows a good agreement on a global scale but considerable differences are found for individual catchment basins up to 180 hydrological storage change estimates in 33 basins from the grace jason fingerprint inversion indicate a trend 46 smaller and an annual amplitude 43 bigger compared to wghm derived storage changes mapping the hydrological trends to regional sea level reveals the strongest sea level rise along the coastlines of south america max 0 9 mm yr and west africa max 0 4 mm yr whereas around alaska and australia we find the hydrological component of sea level falling min 2 0 mm yr and 0 9 mm yr

a secondary ionization mass spectrometry calibration of cibicidoides pachyderma mg ca with temperature an evaluation of c pachyderma mg ca using a new suite of warm water multicores from the florida straits shows that the slope of mg ca with temperature is shallower than previously thought using secondary ionization mass spectrometry we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is gaussian suggesting that the mg ca in these samples is not affected by the addition of a secondary high magnesium calcite in the walls the mg ca within a typical c pachyderma test varies by about 20 1 100 and the variability increases slightly in tests with higher mg ca the regression of c pachyderma mg ca with temperature has a slope of 0 13 0 05 mmol mol 1 per c indistinguishable from the slope observed in inductively coupled plasma mass spectrometry measurements from a different subset of the same multicores but about one half the slope of previously published calibrations the largest differences between the calibrations comes at the warm water end of the regression where previously published c pachyderma mg ca values from little bahama bank are at least 3 mmol mol 1 higher than observed in these new cores the reasons for this difference are not fully known but are most likely related to diagenesis at little bahama bank

calving speed and climatic sensitivity of new zealand lake calving glaciers calving speeds and calving mechanisms in fresh water contrast with those in tidewater we obtained calving speeds for six lake calving glaciers in new zealand s southern alps and surveyed the depths and temperatures of their ice contact lakes the glaciers are temperate grounded in shallow 20 m water and exhibit compressive flow at their termini these data increase the global dataset of fresh water calving statistics by 40 bringing the total to 21 glaciers for this dataset calving rates uc correlate positively with water depths hw r2 0 83 the relationship being expressed by uc 17 4 2 3 hw this is an order of magnitude lower than values of uc at temperate tidewater glaciers for a subset of 10 glaciers for which ice proximal water temperature tw data are available uc also correlates positively with tw supporting a physical relation between calving and melting at and below the water line fluctuations of new zealand lake calving glaciers in the period 1958 97 show that although the transition from non calving to calving dramatically increases frontal retreat rates the onset of calving does not isolate terminus change from climatic forcing in terms of climatic sensitivity lake calving glaciers occupy an intermediate position between tidewater glaciers least sensitive and non calving glaciers most sensitive

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

spatial variations in the rate of sea level rise caused by the present day melting of glaciers and ice sheets the redistribution of surface water mass associated with the melting of glacial ice causes uplift near areas of mass depletion depression of the seafloors and changes in the earth s gravitational field which perturb the ocean surface as a result local spatial variations exist in the rate of sea level rise tide gauges on continental coastlines measure a sea level rise 5 smaller than the global average tide gauges in the hemisphere opposite a source of continental mass depletion measure sea level rise 10 to 20 greater than the global average produced by that source while satellites make measurements 10 too low because most long duration tide gauges are in the northern hemisphere if the sources of sea level rise are unbalanced between the two hemispheres estimates of global sea level rise could be in error by 10 to 20 individual tide gauges could be more seriously unrepresentative if they are near regions of significant present day mass depletion

determination of multiple element calcium ratios in foraminiferal calcite by quadrupole icp ms a method has been developed for rapid and precise simultaneous determination of nine element ca ratios in foraminiferal tests directly from intensity ratios using external matrix matched standards on a quadrupole inductively coupled plasma mass spectrometer icp ms all quantification isotopes are determined in pulse mode to avoid cross calibration small argide 40ar26mg interferences on 66zn are corrected by using two additional mg and zn standards a stable signal conducive for high precision measurements is obtained by cone conditioning variable calcium concentration has negligible effect on li al mn and sr but ca concentrations for standards and samples need to be constrained at a similar level for precise measurements of zn cd and u aliquots of samples are first analyzed for ca concentrations on an inductively coupled plasma atomic emission spectrometer icp aes and the remaining solutions are diluted to ca concentration of 100 ppm for ratio measurements to assure data quality the long term reproducibility of the method yielded precisions of li ca 2 4 b ca 4 2 mg ca 1 4 al ca 14 mn ca 0 9 zn ca 2 8 1 2 7 8 mol mol and 5 1 0 5 1 2 mol mol sr ca 0 9 cd ca 2 4 0 07 0 24 mol mol and 4 8 0 01 0 07 mol mol and u ca 2 5 for foraminiferal samples as small as 60 g

calving processes at a grounded ice cliff repeat photographs and field survey reveal the mechanism of short term ice cliff evolution at maud glacier a temperate lake calving glacier in new zea land calving is cyclic each cycle involving four stages 1 waterline melting and collapse of the roof of a sub horizontal notch at the cliff foot 2 calving of ice flakes from the cliff face leading to a growing overhang from the waterline upwards and crack propagation from the glacier surface 3 large but infrequent calving of slabs in response to the devel oping overhang returning the cliff to an initial vertical profile 4 rare subaqueous cal ving of a submerged ice foot results indicate that the rate controlling process is the speed of waterline melting and that calving rate is independent of water depth at least at time scales of weeks to months slowly calving lake terminating glaciers have mass balances more negative than land terminating glaciers but nevertheless advance and retreat in response to mass balance driven changes in ice velocity