optically stimulated luminescence osl dating of coastal aeolian sand accumulation in sanday orkney islands scotland optically stimulated luminescence osl dating of sand has been used to identify periods of enhanced aeolian activity at two coastal archaeological sites in orkney that coincide with periods of holocene climatic deterioration recorded elsewhere in both scotland and w europe areas of tofts ness sanday were settled from the neolithic abandoned in the late neolithic early bronze age reoccupied and permanently abandoned in the iron age sand layers above the neolithic soils have been osl dated to about 4000 bp correlating well with a period of increased aeolian activity elsewhere in w europe osl dating of aeolian sands above midden deposits and a bronze age burial at lopness on sanday suggest dune development by 3000 bp although both sites also contain sand that was deposited during the little ice age several possible mechanisms may have contributed to an increase in aeolian activity during the holocene that led to the abandonment of these sites although volcanic eruptions in iceland cannot be disc

rectification of the madden julian oscillation into the enso cycle an ocean general circulation model forced with idealized purely oscillating wind stresses over the western equatorial pacific similar to those observed during the madden julian oscillation mjo developed rectified low frequency anomalies in sst and zonal currents compared to a run in which the forcing was climatological the rectification in sst resulted from increased evaporation under stronger than normal winds of either sign from correlated intraseasonal oscillations in both vertical temperature gradient and upwelling speed forced by the winds and from zonal advection due to nonlinearly generated equatorial currents the net rectified signature produced by the mjo like wind stresses was sst cooling about 0 48c in the west pacific and warming about 0 18c in the central pacific tending to flatten the background zonal sst gradient it is hypothesized that in a coupled system such a pattern of sst anomalies would spawn additional westerly wind anomalies as a result of sst induced changes in the low level zonal pressure gradient this was tested in an intermediate coupled

luminescence dating of proglacial sediments from the eastern alps the potential of optically stimulated luminescence osl for dating proglacial deposits is tested here at three last glacial key sites in the eastern alps this was undertaken using both sand sized feldspar and quartz grains as well as fine silt sized material the samples reveal rather poor luminescence intensities of the investigated quartz grains and it is also clearly demonstrated that several of the deposits were incompletely bleached prior to deposition bleaching experiments were carried out and different approaches for extracting the aliquots where the osl was completely bleached prior to burial were tested applying different osl measurement techniques and analytical procedures we investigated which approach was most appropriate for dating known age proglacial sediments best results were achieved using single aliquot regenerative dose methodology on coarse grain quartz and feldspar samples in combination with the approach of preusser et al 2007 luminescence dating of proglacial sediments from switzerland boreas in press for ed calculation

late holocene palaeoenvironmental changes at lake esmeralda vega island antarctic peninsula based on a multi proxy analysis of laminated lake sediment we have studied laminated sediments from lake esmeralda vega island in order to reconstruct its history we describe both inorganic and organic components of the sediment using a combination of the following analytical methods x ray fluorescence xrf x ray diffraction xrd magnetic susceptibility measurement chemical analysis for determination of cation exchange capacity grain size determination geochemical analyses total inorganic carbon tic total organic carbon toc total sulphur ts spectrophotometry high pressure liquid chromatography and diatom assemblage and faunal remains characterization the geochronology of the core was based on modelling optically stimulated luminescence ages and supported by laminae counting the dating results imply a maximum age of 400 years for the 177 cm long core and a period covered of 200 years suggesting quasi annual laminae formation such a young age contradicts previous findings based on radiocarbon dating geomorphological evidence indicates that river capture isolated the lake catchment from upslope sediment delivery effectively terminating accumulation 230 years ago conversely our short term palaeoenvironmental record yields a subdecadal temporal resolution which is unparalleled in comparison with other antarctic palaeolimnological studies our interpretations of the geochemical and mineralogical proxy data give us insight into the past lake catchment and waterbody evolution and lead us to recognize periods of enhanced weathering bottom anoxia and to distinguish major lake level changes

on land ice loss and glacial isostatic adjustment at the drake passage 2003 2009 1 land glacier extent and volume at the northern and southern margins of the drake passage have been in a state of dramatic demise since the early 1990s here time varying space gravity observations from the gravity recovery and climate experiment grace are combined with global positioning system gps bedrock uplift data to simultaneously solve for ice loss and for solid earth glacial isostatic adjustment gia to little ice age lia cryospheric loading the present day ice loss rates are determined to be 26 6 gt yr and 41 5 9 gt yr in the southern and northern patagonia ice fields npi spi and antarctic peninsula ap respectively these are consistent with estimates based upon thickness and flux changes bounds are recovered for elastic lithosphere thicknesses of 35 h 70 km and 20 h 45 km and for upper mantle viscosities of 4 8 1018 pa s and 3 10 1019 pa s using a half space approximation for npi spi and ap respectively using an iterative forward model strategy antarctic peninsula ice models with a prolonged lia extending to a d 1930 are favored in all 2 fits to the gps uplift data this result is largely decoupled from earth structure assumptions the gia corrections account for roughly 20 60 of the space determined secular gravity change collectively the on land ice losses correspond to volume increases of the oceans equivalent to 0 19 0 045 mm yr of sea level rise for the last 15 years

ice dammed lateral lake and epishelf lake insights into holocene dynamics of marguerite trough ice stream and george vi ice shelf alexander island antarctic peninsula abstract we present new data regarding the past dynamics of marguerite trough ice stream george vi ice shelf and valley glaciers from ablation point massif on alexander island antarctic peninsula this ice free oasis preserves a geological record of ice stream lateral moraines ice dammed lakes ice shelf moraines and valley glacier moraines which we dated using cosmogenic nuclide ages we provide one of the first detailed sediment landform assemblage descriptions of epishelf lake shorelines marguerite trough ice stream imprinted lateral moraines against eastern alexander island at 120 m at ablation point massif during deglaciation lateral lakes formed in the ablation and moutonnee valleys dammed against the ice stream in george vi sound exposure ages from boulders on these shorelines yielded ages of 13 9 to 9 7 ka following recession of the ice stream george vi ice shelf formed in george vi sound an epishelf lake formed at 15 20 m asl in ablation and moutonnee valleys dated from 9 4 to 4 6 ka suggesting that the lake was stable and persistent for some 5000 years lake level lowering occurred after this with the lake level at 12 m at 3 1 0 4 ka and at 5 m asl today a readvance of the valley glaciers on alexander island at 4 4 0 7 ka is recorded by valley glacier moraines overlying epishelf lake sediments we speculate that the glacier readvance which occurred during a period of warmth may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of george vi ice shelf

optically stimulated luminescence dating of large storm events in northern scotland climate changes over the holocene have directly impacted on both coastal processes and human use of coastal areas this paper presents results from the dating of wind blown sand deposits collected from coastal and archaeological sites in northern scotland archaeological remains are frequently found interspersed with sand deposits and represent distinct periods of occupation of settlement sites within the local landscapes in some cases storm events sufficiently inundate the sites with sand to result in periodic abandonment storm events can also have dramatic results on adjacent rock coastlines with storm boulder ridges emplaced by large waves burying sand deposits on cliff top sites work has been undertaken using a quartz sar protocol to date sand deposition at two archaeological sites in orkney and a cliff top site in shetland these dates provide chronological information which help to construct regional chronologies of climatic instability and environmental change and allow the sar osl method to be assessed as an accurate sediment dating tool in this context

application of the osl dating for stratigraphic correlation of late weichselian and holocene sediments in the lithuanian maritime region abstract the lithuanian maritime region of the baltic sea is notable for widely spread sandy sediments of different stages of baltic sea development from post glacial late weichselian to recently settled marine sediments the osl dating of about 70 sandy sediments was performed during the large scale 1 50 000 geological mapping of this region for some boreholes radiocarbon 14 c dating and palaeobotanical studies were also carried out a good agreement of the osl ages with 14 c dating results and palaeobotanical data has been revealed for marine lacustrine and aeolian sediments the overestimation of osl ages for baltic ice lake sediments is caused by a very rapid sedimentation and the resultant insufficient bleaching

development of a regional glycerol dialkyl glycerol tetraether gdgt temperature calibration for antarctic and sub antarctic lakes a b s t r a c t a regional network of quantitative reconstructions of past climate variability is required to test climate models in recent studies temperature calibration models based on the relative abundances of sedimentary glycerol dialkyl glycerol tetraethers gdgts have enabled past temperature reconstructions in both marine and terrestrial environments nevertheless to date these methods have not been widely applied in high latitude environments due to poor performance of the gdgt temperature calibrations at lower temperatures to address this we studied 32 lakes from antarctica the sub antarctic islands and southern chile to 1 quantify their gdgt composition and investigate the environmental controls on gdgt composition and 2 develop a gdgt temperature calibration model for inferring past temperatures from antarctic and sub antarctic lakes gdgts were found in all 32 lakes studied and in 31 lakes branched gdgts brgdgts were the dominant compounds statistical analyses of brgdgt composition in relation to temperature ph conductivity and water depth showed that the composition of brgdgts is strongly correlated with mean summer air temperature msat this enabled the development of the first regional brgdgt temperature calibration for use in antarctic and sub antarctic lakes using four brgdgt compounds gdgt ib gdgt ii gdgt iii and gdgt iiib a key discovery was that gdgt iiib is of particular importance in cold lacustrine environments the addition of this compound significantly improved the model s performance from r2 0 67 rmsep loo leave one out 2 23 c rmsep h h block 2 37 c when applying the re calibrated global gdgt

underwater bleaching of signals from sediment grains new experimental data abstract the results of an underwater bleaching experiment are reported the purpose of the experiment was to evaluate the degree to which thermoluminescence tl and optically stimulated luminescence osl signals are reduced by a three hour exposure to light at different water depths samples of quartz and feldspar separates were annealed in the laboratory and then given fixed doses of laboratory beta radiation before exposure the results indicate that a three hour light exposure is sufficient to zero the optical signals down to water depths of 10 m for feldspar infra red stimulated luminescence and 12 14 m for quartz osl the tl results for the same quartz and feldspar samples exhibit some bleaching effects with tl signals at 14 m water depth being reduced to 50 65 of the initial value scatter of the tl results limits their interpretation

relative sea level curves for the south shetland islands and marguerite bay antarctic peninsula this paper presents preliminary relative sea level curves for the marguerite bay region and for the south shetland islands the marguerite bay curve is constrained by both new and previously published 14c dates on penguin remains and shells and on two isolation basins dating back to 6500 14c yr bp extrapolation back to the marine limit yields a minimum deglaciation date for marguerite bay of ca 9000 14c yr bp analysis of beach clasts suggests that there was a period of increased wave activity perhaps related to a reduction in summer sea ice extent between ca 3500 and ca 2400 14c yr bp the curve for the south shetland islands is derived entirely from published 14c dates from isolation basins and on whalebone penguin bone and seal bone the curve shows an initial relative sea level fall which was interrupted by a period in the mid holocene when relative sea level rose to a highstand of between 14 5 and 16 m above mean sea level amsl before falling again

late quaternary environmental changes in marguerite bay antarctic peninsula inferred from lake sediments and raised beaches the antarctic peninsula is one of the fastest warming regions on earth but its palaeoenvironmental history south of 63 latitude is relatively poorly documented relying principally on the marine geological record and short ice cores in this paper we present evidence of late quaternary environmental change from the marguerite bay region combining data from lake sediment records on horseshoe island and pourquoi pas island and raised beaches at horseshoe island pourquoi pas island and calmette bay lake sediments were radiocarbon dated and analysed using a combination of sedimentological geochemical and microfossil methods raised beaches were surveyed and analysed for changes in clast composition size and roundness results suggest a non erosive glacial regime could have existed on horseshoe island from 35 780 38 650 33 380 or 32 910 34 630 31 370 cal yr bp onwards there is radiocarbon and macrofossil evidence for possible local deglaciation events at 28 830 29 370 28 320 cal yr bp immediately post dating antarctic isotopic maximum 4 and 21 110 21 510 20 730 interpolated cal yr bp coinciding with or immediately post dating antarctic isotopic maximum 2 the holocene deglaciation of horseshoe island commenced from 10 610 11 000 10 300 cal yr bp at the same time as the early holocene temperature maximum recorded in antarctic ice cores this was followed by the onset of marine sedimentation in the narrows pourquoi pas island before 8850 8480 9260 cal yr bp relative sea level high stands of 40 79 m above present at pourquoi pas island and 40 55 m above present at calmette bay occurred sometime after 9000 cal yr bp and suggest that a thicker ice sheet including grounded ice streams was present in this region of the antarctic peninsula than that recorded at sites further north isolation of the narrows lake basin on pourquoi pas island shows relative sea level in this region had fallen rapidly to 19 41 m by 7270 7385 7155 cal yr bp chaetoceros resting spores suggest high productivity and stratified surface waters in the narrows after 8850 9260 8480 cal yr bp and beach clasts provide evidence of a period of increased wave energy at approximately 8000 yr bp lake sediment and beach data suggest an extended period of regional warming sometime between 6200 and 2030 cal yr bp followed by the onset of neoglacial conditions from 2630 and 2030 cal yr bp in narrows lake and col lake 1 respectively diatom and 13c vs c n and macrofossil evidence suggest a potential increase in the number of birds and seals visiting the narrows lake catchment sometime after 2100 2250 2000 cal yr bp with enhanced nutrient enrichment evident after 1150 1230 1080 cal yr bp and particularly from c 460 540 380 cal yr bp a very recent increase in gomphonema species and organic carbon in the top centimetre of the narrows lake sediment core after c 410 490 320 cal yr bp and increased sedimentation rates in the col lake 1 sediment core after c 400 490 310 cal yr bp may be a response to the regional late holocene warming of the antarctic peninsula

the effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments abstract the natural optically stimulated luminescence osl response of quartz grains extracted from a range of recent glaciofluvial and other glaciogenic sediments from western greenland is presented all samples were deposited within the last 10 years many only days or hours before collection consequently we would expect to measure zero or very small d e values had optical resetting of the osl signal been complete in the case of most samples d e values in the range 0 5 10 gy are observed while higher values are observed for a handful of samples however the regenerated osl growth curves constructed after daylight exposure of at least several hours also show large apparent d e values negative x axis intercepts corresponding samples from four different locations in the indian himalaya display similar osl characteristics the measurement of several regenerated osl growth curves omitting the preheat procedure which normally precedes osl measurement confirms that a significant degree of thermal transfer is occurring during the preheating it is this thermal transfer of charge during the preheat which is responsible for a significant contribution to the large apparent d e values observed for the regenerated osl growth in this paper we describe combined osl and tl measurements which have been used to monitor the charge transfer in detail for one sample an attempt is made to describe the charge transfer behaviour and we discuss methods appropriate to eliminating the unwanted effects of this phenomenon during osl dating preliminary results from the application of these techniques are presented and the implications of these observations for the osl dating of glaciogenic sediments are discussed

late quaternary glacial history of george vi sound area west antarctica during the last glacial maximum in west antarctica separate ice caps developed on alexander island and on palmer land became confluent in george vi sound and discharged northward from latitude 72 s radiocarbon 32 000 yr and amino acid approximately 120 000 yr age determinations on shell fragments hiatella solida found in basal till suggest a wisconsin age for the glaciation that incorporated them the pattern of ice flow differed from that deduced for this area in the climap reconstruction following the maximum stage there was a stadial event when outlet valley glaciers flowed from smaller ice caps into george vi sound more widespread recession permitted the george vi ice shelf to deposit palmer land erratics on eastern alexander island before isostatic recovery raised them to final elevations of about 82 m the ice shelf may have been absent at about 6500 yr b p when large barnacles bathylasma corolliforme were living in the sound small glaciers readvanced to form at least two terminal moraines before the ice shelf re formed and incorporated the barnacle shells into its moraine on alexander island the shells gave a 14c age corrected for antarctic conditions of about 6500 yr b p and an amino acid ratio consistent with a holocene age valley glaciers readvanced over the ice shelf moraine before oscillations of both valley glaciers and the ice shelf led to the formation of the present sequence of contiguous ice cored moraines probably during the little ice age such oscillations may represent a climatic control not yet observed in the dry valleys of victoria land the only other part of antarctica studied in detail for glacier fluctuations

bunger hills east antarctica ice free at the last glacial maximum optically stimulated luminescence dating of glaciofluvial and glacial lake shoreline sediments indicates that the bunger hills area in coastal east antarctica was largely ice free by the last glacial maximum lgm deglaciation commenced as early as 30 ka and the southern hills were completely exposed by 20 ka the sediments do not record evidence of an lgm readvance previous reconstructions of lgm ice limits for the area are incompatible with this new evidence

recent ice loss from the fleming and other glaciers wordie bay west antarctic peninsula satellite radar interferometry data from 1995 to 2004 and airborne ice thickness data from 2002 reveal that the glaciers flowing into former wordie ice shelf west antarctic peninsula discharge 6 8 0 3 km3 yr of ice which is 84 30 percent larger than a snow accumulation of 3 7 0 8 km3 yr over a 6 300 km2 drainage basin airborne and icesat laser altimetry elevation data reveal glacier thinning at rates up to 2 m yr fifty km from its ice front fleming glacier flows 50 percent faster than it did in 1974 prior to the main collapse of wordie ice shelf we conclude that the glaciers accelerated following ice shelf removal and have been thinning and losing mass to the ocean over the last decade this and other observations suggest that the mass loss from the northern part of the peninsula is not negligible at present copyright 2005 by the american geophysical union

glacial rebound and sea level change an example of a relationship between mantle and surface processes lambeck k 1993 glacial rebound and sea level change an example of a relationship between mantle and surface processes in r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 15 37 the problem of glacial rebound provides an outstanding example of the relationship between surface and mantle processes on time scales of 103 to 105 years changes in surface loading of ice and melt water associated with the growth and decay of the great ice sheets deform the surface of the planet and induces flow in the mantle a measure of the earth s response to the changing surface loads and internal deformation is provided by observations of past sea levels relative to the present level and inversion of these observations provides constraints on both the models of the rheological response of the earth to loading and on models of the ice sheets constraints on ice sheet models include the total volume of the grounded ice at the time of maximum glaciation the global rates of melting of the ice sheets the thickness of the ice at maximum glaciation the extent of ice cover over shallow seas such as the north sea and the barents sea and the role of antarctica in the global ice balance constraints on mantle parameters include the effective lithospheric thickness and the effective viscosity of the mantle some recent results for both sets of parameters are discussed

holocene relative sea level change and deglaciation on alexander island antarctic peninsula from elevated lake deltas abstract field data constraining the rate and spatial pattern of deglaciation and relative sea level rsl change on the antarctic peninsula ap are relatively sparse but are needed to improve regional ice sheet and rsl change models and contribute to better model predictions of future sea level rise we investigated the geomorphology sedimentology and quartz fraction single aliquot regeneration optically stimulated luminescence sar osl geochronology of elevated deltas around two epishelf lakes ablation lake al and moutonnee lake ml alexander island antarctic peninsula al and ml are dammed by george vi ice shelf and maintain a direct hydraulic connection to the sea hence their water levels are controlled by changes in rsl our aim was to provide new terrestrial constraints on rsl and deglaciation for the southern ap by comparing the formation processes age and altitude of the al and ml deltas with 1 existing rsl curves for the ap 2 isostatically coupled ap ice sheet models and 3 existing ap deglaciation history and sar osl ages from elevated deltas around the nearby inland hodgson lake hl although there was insufficient quartz in the ml samples for sar osl dating the 4 6 0 4 ka sar osl age of the elevated delta at al represents the last time active deltas were forming higher than present day lake level and implies 1 a fall in rsl of up to 14 4 m since the mid holocene in this part of alexander island which is consistent with existing field based rsl chronologies for the ap 2 relatively smaller ice masses than suggested by some but not all isostatically coupled ice sheet models since the mid holocene and 3 significant mid holocene thinning of the ap ice sheets which is consistent with regional sediment core data and cosmogenic exposure ages and the 4 4 0 7 ka sar osl age of the lowermost hl delta

optically stimulated luminescence dating of late quaternary glaciogenic sediments in the upper hunza valley validating the timing of glaciation and assessing dating methods we present a comprehensive comparison of optically stimulated luminescence osl ages with cosmogenic radionuclide crn ages and the first study to validate crn dates from boulders on moraine ridges using luminescence dates from glaciogenic sediments from associated moraines accomplished from both direct and stratigraphic relationships between crn and osl sampling sites both quartz and k feldspars extracted from 12 late quaternary glaciogenic sediments were studied using single aliquot osl techniques rapid signal saturation in preliminary additive dose infrared stimulated k feldspar luminescence growth data was interpreted as evidence of insufficiently bleached latent luminescence and these data gave rise to overestimated ages in the majority of samples further analysis concentrated on replicated single aliquot regenerative dose sar measurements of quartz minerals using blue green stimulation the sar sensitivity correction method repeatedly failed in two of the samples and a further sample exhibited significant thermal transfer nevertheless three of the eight glacial successions in the upper hunza valley were defined using quartz luminescence although we discuss the possibility of inherited components in the crn data in terms of paleoclimatic interpretations both dating techniques give concordant results

the deglacial history of nw alexander island antarctica from surface exposure dating recent changes along the margins of the antarctic peninsula such as the collapse of the wilkins ice shelf have highlighted the effects of climatic warming on the antarctic peninsula ice sheet apis however such changes must be viewed in a long term millennial scale context if we are to understand their significance for future stability of the antarctic ice sheets to address this we present nine new cosmogenic 10be exposure ages from sites on nw alexander island and rothschild island adjacent to the wilkins ice shelf that provide constraints on the timing of thinning of the alexander island ice cap since the last glacial maximum all but one of the 10be ages are in the range 10 2 21 7 ka showing a general trend of progressive ice sheet thinning since at least 22 ka until 10 ka the data also provide a minimum estimate 490 m for ice cap thickness on nw alexander island at the last glacial maximum cosmogenic 3he ages from a rare occurrence of mantle xenoliths on rothschild island yield variable ages up to 46 ka probably reflecting exhumation by periglacial processes

predictions of antarctic crustal motions driven by present day ice sheet evolution and by isostatic memory of the last glacial maximum detectable crustal motion and secular rate of change of solid surface gravity may be produced by the earth s response to present day and past ice mass changes in antarctica scenarios of present day ice mass balance previously utilized to explore the global geodetic signatures of the antarctic ice sheet produce elastic crustal responses that are typically bounded by uplift rates 5 mm yr horizontal motion 1 mm yr and solid surface gravity change rates 1 gal yr in a restricted locality one scenario produces uplift rates slightly in excess of 10 mm yr and correspondingly enhanced horizontal and gravity rates in contrast the viscoelastic response to ice mass changes occurring since last glacial maximum lgm exceeds 5 mm yr uplift over substantial portions of west antarctica for a wide range of plausible choices of timing and magnitude of deglaciation and mantle viscosity similarly viscoelastic gravity rate predictions exceed 1 gal yr decrease over large regions confirming suggestions that a global positioning system gps and absolute gravity based program of crustal monitoring in antarctica could potentially detect postglacial rebound a published revision to the climap model of the antarctic ice sheet at lgm herein called the d91 model features a substantially altered west antarctic ice sheet reconstruction this revision predicts a spatial pattern of present day crustal motion and surface gravity change that diverges strikingly from climap based models peak d91 crustal rates assuming deglaciation begins at 12 kyr and ends at 5 kyr are around 16 mm yr uplift 2 mm yr horizontal and 2 5 gal yr gravity tabulated crustal response predictions for selected antarctic bedrock sites indicate critical localities in the interior of west antarctica where expected responses are large and d91 predictions differ from climap based models by a factor of 2 or more observations of the postglacial rebound signal in antarctica might help constrain antarctic mass balance and contribution to sea level rise over the past 20 000 years

lake ice conveyor deposits geomorphology sedimentology and importance in reconstructing the glacial history of the dry valleys during the last glacial maximum lgm lake ice conveyors transported glacial debris across the surface of large proglacial lakes in the dry valleys region of antarctica the resulting sediments and landform assemblages are keys to interpreting the glacial history of the dry valleys and potentially other areas of antarctica paleoconveyor deposits occur in taylor miers wright and victoria valleys as well as in many other parts of the region sediments typically consist of stratified to massive sand and or silt grading upward into poorly sorted gravel cobbles and boulders these sediments make up a variety of landforms including mounds and moat line cross valley and longitudinal ridges the classic landform assemblage also displays an associated moraine bank as well as deltas and shorelines

testing an approach to osl dating of late devensian glaciofluvial sediments of the british isles in the british and irish isles the understanding of expansion and retreat of the last ice sheet in marine isotope stage mis 2 has been hindered by a lack of chronological control for the timing of its maximum extent and subsequent retreat stages in this research a suite of lithofacies from a former distal ice marginal sandur at orrisdale isle of man were identified and selected for optically stimulated luminescence dating different size fractions of quartz grains were extracted from selected lithofacies types with the aim of identifying which depositional environments and grain size fractions are best suited for optical dating tests have been undertaken to identify the luminescence properties of this quartz including preheat dose recovery and constant wave optically stimulated luminescence osl decay curve fitting equivalent dose distributions for all samples were wide and positively skewed indicative of heterogeneous bleaching a comprehensive statistically based decision making protocol has been defined in order to find the appropriate statistical model for burial dose estimation ages in the range of 17 14 ka have been obtained which agree with the expected geologically constrained chronology the orrisdale formation is contemporaneous with heinrich event 1 and the killard point stadial identified in eastern ireland ca 16 4 ka the suggested approach for osl dating of glaciofluvial sediments has the potential for much wider application to high latitude or temperate areas where there is an abundance of such sediments and where improved chronological control is much needed copyright 2009 john wiley sons ltd

modelling antarctic sea level data to explore the possibility of a dominant antarctic contribution to meltwater pulse ia abstract we compare numerical predictions of glaciation induced sea level change to data from 8 locations around the antarctic coast in order to test if the available data preclude the possibility of a dominant antarctic contribution to meltwater pulse ia mwp ia results based on a subset of 7 spherically symmetric earth viscosity models and 6 different antarctic deglaciation histories indicate that the sea level data do not rule out a large antarctic source for this event our preliminary analysis indicates that the weddell sea is the most likely source region for a large 9 m antarctic contribution to mwp ia the ross sea is also plausible as a significant contributor 5 m from a sea level perspective but glacio geological field observations are not compatible with such a large and rapid melt from this region our results suggest that the lambert glacier component of the east antarctic ice sheet experienced significant retreat at the time of mwp ia but only contributed 0 15 m eustatic sea level change all of the ice models considered under predicted the isostatic component of the sea level response in the antarctic peninsula and the soya coast region of the east antarctic ice sheet indicating that the maximum ice thickness in these regions is underestimated it is therefore plausible that ice melt from these areas the antarctic peninsula in particular could have made a significant contribution to mwp ia

glacier acceleration and thinning after ice shelf collapse in the larsen b embayment antarctica 1 ice velocities derived from five landsat 7 images acquired between january 2000 and february 2003 show a two to six fold increase in centerline speed of four glaciers flowing into the now collapsed section of the larsen b ice shelf satellite laser altimetry from icesat indicates the surface of hektoria glacier lowered by up to 38 6 m in a six month period beginning one year after the break up in march 2002 smaller elevation losses are observed for crane and jorum glaciers over a later 5 month period two glaciers south of the collapse area flask and leppard show little change in speed or elevation seasonal variations in speed preceding the large post collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics

patterns of spatio temporal paraglacial response in the antarctic peninsula region and associated ecological implications abstract the antarctic peninsula ap constitutes the warmest region of antarctica although 98 of the surface is still covered by glaciers the region shows contrasting geographic and climatic properties which have conditioned past and present glacial activity this paper constitutes a review of the spatial and temporal patterns of paraglacial activity across the ap bridging the geomorphological and ecological perspectives the number and extent of ice free environments has increased since the last glacial maximum particularly during the early holocene and the 20th century following deglaciation the redefinition of coastlines and the uplift of landmasses proceeded differently in the three sectors of ap with maximum uplift in the western sector 40 m a s l the minimum on the north 20 4 m a s l and intermediate in the eastern sector 30 m there are also differences in the levels of raised beaches with the highest complexity in the northern ap 5 7 levels and the lowest in the eastern ap 3 levels the transition from glacial to periglacial conditions paraglacial stage also differed greatly between the three sectors with the absence of rock glaciers in the western sector the development almost exclusively of glacier derived rock glaciers in the eastern ap and the majority of talus derived rock glaciers in the northern ap the development of protalus lobes block streams and other periglacial features was highly dependent on the cold warm based character of individual glaciers this characteristic determines the existence or absence of permafrost following deglaciation which in turn conditions the type and intensity of geomorphic processes in newly exposed ice free areas more recently following the post 1950s regional warming there have still been important differences between the three sectors in the development of paraglacial environments permafrost degradation has occurred in newly exposed areas accelerating mass wasting and sediment redistribution and changing hydrological processes especially in the northern and western ap while sudden glacial outburst flooding has occurred in the eastern ap the most apparent major ecological response to this recent warming is greening due to vegetation expansion which is more evident where paraglacial and periglacial processes are less intense the accurate characterization of the different paraglacial responses existing in the ap enables a better understanding of future environmental responses in this climatically sensitive region where climate models forecast significant environmental change for during forthcoming decades

antarctic peninsula ice sheet evolution during the cenozoic era the antarctic peninsula region is currently undergoing rapid environmental change resulting in the thinning acceleration and recession of glaciers and the sequential collapse of ice shelves it is important to view these changes in the context of long term palaeoenvironmental complexity and to understand the key processes controlling ice sheet growth and recession in addition numerical ice sheet models require detailed geological data for tuning and testing therefore this paper systematically and holistically reviews published geological evidence for antarctic peninsula ice sheet variability for each key locality throughout the cenozoic and brings together the prevailing consensus of the extent character and behaviour of the glaciations of the antarctic peninsula region major contributions include a downloadable database of 186 terrestrial and marine calibrated dates an original reconstruction of the lgm ice sheet and a new series of isochrones detailing ice sheet retreat following the lgm glaciation of antarctica was initiated around the eocene oligocene transition in east antarctica palaeogene records of antarctic peninsula glaciation are primarily restricted to king george island where glacigenic sediments provide a record of early east antarctic glaciations but with modification of far travelled erratics by local south shetland island ice caps evidence for neogene glaciation is derived primarily from king george island and james ross island where glaciovolcanic strata indicate that ice thicknesses reached 500 850 m during glacials this suggests that the antarctic peninsula ice sheet draped rather than drowned the topography marine geophysical investigations indicate multiple ice sheet advances during this time seismic profiling of continental shelf slope deposits indicates up to ten large advances of the antarctic peninsula ice sheet during the early pleistocene when the ice sheet was dominated by 40 kyr cycles glacials became more pronounced reaching the continental shelf edge and of longer duration during the middle pleistocene during the late pleistocene repeated glacials reached the shelf edge but ice shelves inhibited iceberg rafting the last glacial maximum lgm occurred at 18 ka bp after which transitional glaciomarine sediments on the continental shelf indicate ice sheet retreat the continental shelf contains large bathymetric troughs which were repeatedly occupied by large ice streams during pleistocene glaciations retreat after the lgm was episodic in the weddell sea with multiple readvances and changes in ice flow direction but rapid in the bellingshausen sea the late holocene epoch was characterised by repeated fluctuations in palaeoenvironmental conditions with associated glacial readvances however this has been subsumed by rapid warming and ice shelf collapse during the twentieth century

flow dynamics and till genesis associated with a marine based antarctic palaeo ice stream geophysical and geological data indicate that during the last glacial cycle a palaeo ice stream drained the antarctic peninsula ice sheet apis through marguerite bay to the edge of the continental shelf via a bathymetric trough marguerite trough mega scale glacial lineations msgl in outer marguerite trough are formed in an acoustically transparent sediment unit consisting of a soft deformation till the association of msgl with deformation till indicates that bed deformation occurred beneath the ice stream and the thickness of the subglacial deforming layer was on the order of several metres msgl within outer marguerite trough are related to a pre existing thick sequence of soft sediments on the outer shelf and are inferred to have formed by a combination of subglacial sediment deformation by attenuation from a point source and groove ploughing morphologically the msgl differ in several respects from those documented elsewhere and this variation suggests a polygenetic origin for this subglacial landform an initial advance of the apis across the marguerite bay continental shelf at the lgm deposited a stiff subglacial till following this advance the ice margin within marguerite trough retreated 70 100 km before stabilising and depositing a grounding zone wedge an ice stream then developed in the trough and extended to the shelf edge forming a soft deformation till development of the ice stream may have been a glacio dynamic response to regional deglaciation subsequent retreat of the marguerite trough ice stream was underway by 13 490 uncorrected 14c years before present based on the geophysical and core data ice stream retreat appears to have been rapid and it contrasts with reconstructions of palaeo ice streams from other locations in antarctica this implies marked regional variations in antarctic ice stream dynamics during late quaternary deglaciation

gravity evidence of very thin crust at the gakkel ridge arctic ocean abstract gakkel ridge the active spreading center in the arctic ocean is the slowest spreading portion of the global mid ocean ridge system total spreading rates range from 0 6 cm yr in the east where the ridge disappears beneath the laptev shelf to 1 3 cm yr in the west near greenland bathymetry and gravity surveys of four sections of the gakkel ridge were carried out in 1996 by the u s navy nuclear submarine uss pogy as part of scicex 96 in order to sample variations in seafloor morphology and gravity anomalies as a function of spreading rate the ridge axis throughout the survey area is characterized by a continuous axial rift valley similar to that observed at other slow spreading ridges the continuous rift axis suggests that well organized seafloor spreading is occurring at total spreading rates of less than 1 cm yr in three faster spreading 1 13 1 24 cm yr western survey areas located between 7 e and 54 e the gakkel ridge is deep compared with other ridge axes axial depths range between 4600 and 5100 m and ridge flanks at about 3200 m the ridge flank morphology is very blocky and is characterized by large scarps and deep fault bounded troughs very large amplitude free water anomalies with peak to trough amplitudes of 85 150 mgal are observed centered on the axis of the gakkel ridge modeling of the free water anomalies by varying the crustal thickness and average crustal density including the gravity effect of the cooling of the mantle away from the axis implies that if the average crustal density is less than 2900 kg m3 the crustal thickness must be less than 4 km the axial rift valley at the fourth survey area near 98 e where the total spreading rate is 0 99 cm yr is buried by sediments the axis in this region is associated with a continuous 70 mgal gravity minimum implying the presence of a large buried rift valley the rift flanks at 95 e are at a depth of greater than 3800 m 600 m deeper than the average depth at the gakkel ridge axis west of 60 e simple isostatic calculations suggest that the crust in this region may be vanishingly thin beneath the sediment cover these observations indicate a relationship between melt production and seafloor spreading rate at very slow spreading rates suggesting that ultra slow spreading may suppress melt production or delivery at the gakkel ridge

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

oceanic and atmospheric forcing of early holocene ice shelf retreat george vi ice shelf antarctica peninsula we use lake sediment records from an epishelf lake on alexander island to provide a detailed picture of the holocene history of george vi ice shelf gvi is core analyses included micropaleontology diatoms foraminifera stable isotope 18o 13c geochemistry total organic carbon toc total nitrogen tn c n ratios and grain size analyses these data provide robust evidence for one period of past ice shelf absence during the early holocene the timing of this period has been constrained by 10 ams 14c dates performed on mono specific foraminifera samples these dates suggest that gvi is was absent between c 9600 cal yr bp and c 7730 cal yr bp this early holocene collapse immediately followed a period of maximum holocene warmth that is recorded in some antarctic ice cores and coincides with an influx of warmer ocean water onto the western antarctic peninsula ap shelf at c 9000 cal yr bp the absence of a currently extant ice shelf during this time interval suggests that early holocene ocean atmosphere variability in the ap was greater than that measured in recent decades

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

structure and sedimentology of george vi ice shelf antarctic peninsula implications for ice sheet dynamics and landform development collapse of antarctic ice shelves in response to a warming climate is well documented but its legacy in terms of depositional landforms is little known this paper uses remote sensing structural glaciological and sedimentological data to evaluate the evolution of the c 25000 km 2 george vi ice shelf sw antarctic peninsula the ice shelf occupies a north south trending tectonic rift between alexander island and palmer land and is nourished mainly by ice streams from the latter region the structure of the ice shelf is dominated by inherited foliation and fractures and with velocity data indicates a largely compressive flow regime the formation of a moraine complex at the margin of the ice shelf is controlled by debris entrained within foliation and folds this englacial debris is of basal origin and includes both local mesozoic sedimentary and volcanic lithologies and exotic crystalline rocks from palmer land folding of basal ice to a high level in the source glaciers on palmer land is required to bring the debris to the surface these results have implications for understanding flow dynamics of ice shelves under compressive flow and debris entrainment and moraine formation associated with palaeo ice shelves supplementary material photographs of ice shelf morphology ice facies and ice structure detailed descriptions of ice facies including foliation logs supporting evidence for interpreting sedimentary facies complete dataset of sedimentological data including triangular plots of clast shape clast roundness histograms particle size distribution of sand size and lower and pie chart of local clasts versus exotic clasts from palmer land and a table summarizing the characteristics of representative clasts in the ice shelf moraine based on thin section analysis with indication of their provenance are available at http www geolsoc org uk sup18831

lake highstands in the pensacola mountains and shackleton range 4300 2250 cal yr bp evidence of a warm climate anomaly in the interior of antarctica we surveyed and dated the former shorelines of one lake in the shackleton range and two lakes in the pensacola mountains situated inland of the weddell sea embayment antarctica between 80 and 85 s these are amongst the highest latitude lakes in the antarctic and are located in areas where there is little or no holocene climate and hydrological information surveys of the lake shorelines show that past water levels have been up to 15 7 17 7 and 69 5 m higher than present in the three study lakes ams radiocarbon dating of lake derived macrofossils showed that there was a sustained period of higher water levels from approximately 4300 and until sometime after 2250 cal yr bp this is interpreted as being the result of an increased number of meltwater events and or degree days above freezing relative to the present the closest comparable ice cores from the dominion range in the transantarctic mountains 85 s 166 e and the plateau remote ice core on the continental east antarctic ice sheet 84 s 43 e

relative sea level history of marguerite bay antarctic peninsula derived from optically stimulated luminescence dated beach cobbles abstract calmette bay within marguerite bay along the western side of the antarctic peninsula contains one of the most continuous flights of raised beaches described to date in antarctica raised beaches extend to 40 8 m above sea level masl and are thought to reflect glacial isostatic adjustment due to the retreat of the antarctic peninsula ice sheet using optically stimulated luminescence osl we dated quartz extracts from cobble surfaces buried in raised beaches at calmette bay the beaches are separated into upper and lower beaches based on osl ages geomorphology and sedimentary fabric the two sets of beaches are separated by a prominent scarp one of our osl ages from the upper beaches dates to 9 3 thousand years ago ka as of 1950 consistent with previous extrapolation of sea level data and the time of ice retreat from inner marguerite bay however four of the seven ages from the upper beaches date to the timing of glaciation we interpret these ages to represent reworking of beaches deposited prior to the last glacial maximum lgm by advancing and retreating lgm ice ages from the lower beaches record relative sea level fall due to holocene glacial isostatic adjustment we suggest a holocene marine limit of 21 7 masl with an age of 5 5 7 3 ka based on osl ages from calmette bay and other sea level constraints in the area a marine limit at 21 7 masl implies half as much relative sea level change in marguerite bay during the holocene as suggested by previous sea level reconstructions no evidence for a relative sea level signature of neoglacial events such as a decrease followed by an increase in rsl fall due to ice advance and retreat associated with the little ice age is found within marguerite bay indicating either 1 no significant neoglacial advances occurred within marguerite bay 2 rheological heterogeneity allows part of the antarctic peninsula i e the south shetland islands to respond to rapid ice mass changes while other regions are incapable of responding to short lived ice advances or 3 the magnitude of neoglacial events within marguerite bay is too small to resolve through relative sea level reconstructions although the application of reconstructing sea level histories using osl dated raised beach deposits provides a better understanding of the timing and nature of relative sea level change in marguerite bay we highlight possible problems associated with using raised beaches as sea level indices due to post depositional reworking by storm waves

kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central lower michigan usa abstract in association with an undergraduate honors seminar at michigan state university we studied two small kame deltas in north central lower michigan these recently identified deltas provide clear evidence for a previously unknown proglacial lake glacial lake roscommon in this large basin located in an interlobate upland our first goal was to document and characterize the geomorphology of these deltas because both deltas are tied to ice contact ridges that mark the former position of the retreating ice margin within the lake our second goal was to establish the age of one of the deltas thereby constraining the timing of ice retreat in this part of michigan for which little information currently exists both deltas are composed of well sorted fine and medium sands with little gravel and have broad nearly flat surfaces and comparatively steep fronts samples taken from the upper 1 5 m of the deltas show little spatial variation in texture aside from a general fining toward their outer margins gullies on the outer margins of both deltas probably postdate the formation of the deltas proper we suggest that they formed by runoff during a permafrost period subsequent to lake drawdown we named the ice lobe that once covered this area the mackinac lobe because it had likely advanced into the region across the mackinac straits area five of six optically stimulated luminescence osl ages from one of the deltas had minimal scatter and were within 1000 years of one another with a mean age of 23 1 0 4 ka these ages suggest that the mackinac lobe had started to retreat from the region considerably earlier than previously thought even while ice was near its maximum extent in illinois and indiana and the remainder of michigan was ice covered this early retreat which appears to coincide with a short lived warm period indicated from the greenland ice core formed an opening that was at least occasionally flooded thick and deep fine textured deposits which underlie much of the region probably date to this time our work provides the first evidence of this extremely early ice retreat from central lower michigan occurring almost 4000 years before the southern margin of the ice saginaw lobe had started its retreat from the state

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

optical dating studies of quartz and feldspar sediment extracts abstract continuing developmental work into optical dating has led to some clarification of the optical behaviour of quartz and feldspar sediment extracts we have verified the key assumption intrinsic to the method that the optical signal is zeroed completely upon exposure to daylight we also show that the rate of zeroing in optical dating is much more rapid than it is in tl dating studies concerned with the extraction of the thermally stable signal from laboratory irradiated samples showed that problems may arise from medium to high temperature preheating of young samples optical alternatives to thermal stabilization were tested using dye and krypton lasers using a krypton laser we have succeeded in obtaining an equivalent dose of 0 0 0 7 gy for the quartz from a modern intertidal sand and an average dose of 120 22 gy for the feldspar extract of a 70 ka sand unit both were obtained using six wavelengths from the infrared to the violet and no dependence on wavelength was found we found that the photon energies of infrared and deep red light can stimulate luminescence in unirradiated quartz and feldspar extracts of sediments this was not expected and suggests that the process of trap emptying is more complex than we had envisioned but implies a far greater than expected degree of technical flexibility for the optical dating method

modeling the growth and decay of the antarctic peninsula ice sheet a model of the growth and decay of the antarctic peninsula ice sheet during the last glacial interglacial cycle is used to identify the main controls on ice sheet behavior using as input glaciological assumptions derived by w f budd and i n smith 1982 annals of glaciology 3 4249 bedrock topography isostatic compensation and mass balance relationships the model is driven by sea level change over the last 40 000 yr in association with assumed changes in the rate of melting beneath ice shelves an ice sheet dome over 3 5 km thick grows on the offshore shelf and straits west of the antarctic peninsula and reaches a maximum at 18 000 yr b p collapse begins at 14 000 yr b p but becomes rapid and continuous after 10 000 yr b p the present stable ice cover is achieved at 6500 yr b p ice growth and decay are characterized by thresholds which separate periods of steady state from periods of rapid transition the thresholds usually relate to topography tests show that ice sheet behavior is most sensitive to sea level change basal marine melting and accumulation and is less sensitive to isostasy spatial variation in accumulation calving rates and ice flow parameterization tests of the model against field evidence show good agreement in places as well as discrepancies which require further work o

glacier surge after ice shelf collapse the possibility that the west antarctic ice sheet will collapse as a consequence of ice shelf disintegration has been debated for many years this matter is of concern because such an event would imply a sudden increase in sea level evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the larsen ice shelf on the antarctic peninsula before its collapse in 1995 satellite images and airborne surveys allowed unambiguous identification of active surging phases of boydell sjogren edgeworth bombardier and drygalski glaciers this discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves

volume of antarctic ice at the last glacial maximum and its impact on global sea level change abstract the volume of antarctic ice at the last glacial maximum is a key factor for calculating the past contribution of melting ice sheets to late pleistocene global sea level change at present there are large uncertainties in our knowledge of the extent and thickness of the formerly expanded antarctic ice sheets and in the timing of their release as meltwater into the world s oceans this paper reviews the four main approaches to determining former antarctic ice volume namely glacial geology glacio isostatic studies glaciological modelling and ice core analysis and attempts to reconcile these to give a best estimate for ice volume in the ross sea there was a major expansion of grounded ice at the last glacial maximum accounting for 2 3 3 2 m of global sea level at some time in the weddell sea a large grounded ice sheet corresponding to c 2 7 m of global sea level extended to the shelf break however this ice expansion has not yet been confidently dated and may not relate to the last glacial maximum around east antarctica there was thickening and advance offshore of ice in coastal regions ice core evidence suggests that the interior of east antarctica was either close to its present elevation or thinner during the last glacial so the effect of east antarctica on sea level depends on the net balance between marginal thickening and interior thinning suggested east antarctic contributions vary from a 3 5 5 m lowering to a 0 64 m rise in global sea level the antarctic peninsula ice sheet thickened and extended offshore at the last glacial maximum with a sea level equivalent contribution of c 1 7 m thus the antarctic ice sheets accounted for between 6 1 and 13 1 m of global sea level fall at the last glacial maximum this is substantially less than has been suggested by most previous studies but the maximum figure matches well with one modelling estimate the timing of antarctic deglaciation is not well known in the ross sea terrestrial evidence suggests deglaciation may have begun at c 13 000 yr bp 1 but that grounded ice persisted until c 6 500 yr bp marine evidence suggests the western ross sea was deglaciated by c 11 500 yr bp deglaciation of the weddell sea is poorly constrained grounded ice in the northern antarctic peninsula had retreated by c 13 000 yr bp and further south deglaciation occurred sometime prior to c 6 000 yr bp many parts of coastal east antarctica apparently escaped glaciation at the lgm but in those areas that were ice covered deglaciation was underway by 10 000 yr bp with existing data the timing of deglaciation shows no firm relation to northern hemisphere driven sea level rise this is probably due partly to lack of antarctic dating evidence but also to the combined influence of several forcing mechanisms acting during deglaciation

mountain glaciers and ice caps around antarctica make a large sea level rise contribution the intergovernmental panel on climate change ipcc estimates that the sum of all contributions to sea level rise for the period 1961 2004 was 1 1 0 5 mm a 1 leaving 0 7

glacial lake victoria a high level antarctic lake inferred from lacustrine deposits in victoria valley we present evidence of a large lake glacial lake victoria that existed in victoria valley in the dry valleys region of antarctica between at least 20 000 and 8600 14c yr bp at its highstands glacial lake victoria covered 100 km2 and was ca 200 m deep the chronology for lake level changes comes from 87 ams radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present day lakes on the valley floor the existence of glacial lake victoria as well as other large lakes in the dry valleys indicates a climate regime significantly different from that of today at the last glacial maximum and in the early holocene copyright 2002 john wiley sons ltd

ice sheet and solid earth influences on far field sea level histories previous predictions of sea level change subsequent to the last glacial maximum show significant systematic discrepancies between observations at tahiti huon peninsula and sunda shelf during lateglacial time 14 000 to 9000 calibrated years before the present we demonstrate that a model of glacial isostatic adjustment characterized by both a high viscosity lower mantle 4 1022 pa s and a large contribution from the antarctic ice sheet to meltwater pulse ia 15 meters eustatic equivalent resolves these discrepancies this result supports arguments that an early and rapid antarctic deglaciation contributed to a sequence of climatic events that ended the most recent glacial period of the current ice age

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

geological constraints on glacio isostatic adjustment models of relative sea level change during deglaciation of prince gustav channel antarctic peninsula the recent disintegration of antarctic peninsula ice shelves and the associated accelerated discharge and retreat of continental glaciers has highlighted the necessity of quantifying the current rate of antarctic ice mass loss and the regional contributions to future sea level rise observations of present day ice mass change need to be corrected for ongoing glacial isostatic adjustment a process which must be constrained by geological data however there are relatively little geological data on the geometry volume and melt history of the antarctic peninsula ice sheet apis after termination 1 and during the holocene so the glacial isostatic correction remains poorly constrained to address this we provide field constraints on the timing and rate of apis deglaciation and changes in relative sea level rsl for the north eastern antarctic peninsula based on geomorphological evidence of former marine limits and radiocarbon dated marine freshwater transitions from a series of isolation basins at different altitudes on beak island relative sea level fell from a maximum of c 15 m above present at c 8000 cal yr bp at a rate of 3 91 mm yr 1 declining to c 2 11 mm yr 1 between c 6900 2900 cal yr bp 1 63 mm yr 1 between c 2900 1800 cal yr bp and finally to 0 29 mm yr 1 during the last c 1800 years the new beak island rsl curve improves the spatial coverage of rsl data in the antarctic it is in broad agreement with some glacio isostatic adjustment models applied to this location and with work undertaken elsewhere on the antarctic peninsula these geological and rsl constraints from beak island imply significant thinning of the north eastern apis by the early holocene further they provide key data for the glacial isostatic correction required by satellite derived gravity measurements of contemporary ice mass loss which can be used to better assess the future contribution of the apis to rising sea levels

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

early holocene retreat of the george vi ice shelf antarctic peninsula the recent collapse of several antarctic peninsula ice shelves has been linked to rapid regional atmospheric warming during the twentieth century new high resolution lake sediment records of holocene ice shelf behavior show that the george vi ice shelf was absent beginning ca 9595 calibrated cal yr b p but reformed by ca 7945 cal yr b p this retreat immediately followed a period of maximum holocene warmth that is recorded in some ice cores and occurred at the same time as an influx of warmer ocean water onto the antarctic peninsula shelf the absence of the ice shelf suggests that early holocene ocean atmosphere variability in the antarctic peninsula was greater than that measured in recent decades

luminescence characterisation of quartz rich cover sands from ne thailand abstract the genesis of a several meter thick cover sand layer which is widely distributed in mainland se asia has been the subject of much debate being considered by some to be an aeolian mantle of late pleistocene early holocene origin and by others to represent a holocene biomantle samples were collected from three sites in nw thailand in 1998 to assess the potential of luminescence studies for characterisation and chronometric studies of the layer the material is a quartz rich iron stained sand with high luminescence sensitivities a pronounced 325 c tl peak and high sensitivity to phototransfer and osl a number of methods for estimating stored dose were assessed of which additive tl and regenerative osl procedures produced good laboratory results these methods have been used to produce stored dose and apparent age profiles for one of the sites the data are consistent with a late pleistocene holocene aeolian deposition process possibly modified in the upper layers by bioturbation however the possibility that the recorded profiles are the result of heterogeneous mixing of bleached and unbleached grains within the biomantle model cannot at this stage be excluded the material has excellent luminescence properties and it is likely that further luminescence studies will be able to distinguish between the formation models and contribute significantly to understanding of these regionally significant sediments

dating quaternary lacustrine sediments in the mcmurdo dry valleys antarctica abstract reports of erroneously old 14c dates for modern antarctic materials have thrown doubt into 14c chronologies the carbon reservoir effect purported to exist in quaternary lacustrine sediments of the mcmurdo dry valleys was investigated by studying 14c distribution and testing alternate dating techniques our results show that the carbon reservoir effect is not pervasive stream and near shore microbial mats and dissolved inorganic carbon dic in the surface waters of lake fryxell are in equilibrium with modern 14co2 the surface waters of lake hoare and lake bonney however have dic 14c ages of 1650 and 2080 yr b p respectively these older age estimates are suggested to be due to the direct input of large amounts of glacial melt with relict dic on the other hand lake fryxell receives only a minor component of its inflow directly from a glacier while a large component must travel long distances in numerous shallow ephemeral streams after leaving local valley glaciers this mode of melt water input allows the water to equilibrate with modern co2 before entering the lake bottom water 14c ages for lake hoare closely match surface sediment ages supporting the widely published period 1200 yr b p after a 1650 yr reservoir correction when most dry valley lakes apparently evaporated to small brine ponds and or disappeared completely lake bonney bottom water is 8000 yr b p carbon dating is shown to be a viable technique for lake edge deposits and possibly lake bottom deposits where a correction to the sediment surface age can be obtained however we conclude that deep water paleolake deposits can not be reliably dated using 14c alone because of an inability to determine the age of the reservoir correction i e accounting for the initial carbon reservoir plus the age of the bottom water a suite of alternative and complimentary dating techniques were tested on modern and late holocene lacustrine deposits these include thermoluminescence tl 210pb 137cs and paleomagnetism of these techniques tl or the more sensitive optically stimulated luminescence holds the most promise for correcting lake sediment 14c ages tl dating of the modern lake hoare sediments showed an 1000 yr relict signal this signal is unaffected by the age of the lake water both 210pb and 137cs occurred in very low levels in the sediments and do not appear to be viable dating techniques for the perennially ice covered lakes of the mcmurdo dry valleys paleomagnetism was not suited to the coarse grained nature of lake hoare bottom sediments but could be a useful alternative given a finer sediment type

new relative sea level curves for the southern scott coast antarctica evidence for holocene deglaciation of the western ross sea here we present new relative sea level rsl curves developed from holocene aged raised beaches along the southern scott coast of the western ross sea antarctica fifty four dates of marine shells seal skin and elephant seal remains incorporated within raised beaches during storms afford a chronology for these curves all of the curves show the same pattern and timing of rsl change within a small range of error the best dated curve suggests that final unloading of grounded ross sea ice from the southern scott coast and mcmurdo sound region occurred shortly before 6500 14c yr bp this age is consistent with glacial geological evidence that places deglaciation between 5730 and 8340 14c yr bp our data strongly suggest that grounding line retreat of the ross sea ice sheet southward through the mcmurdo sound region occurred in mid and late holocene time if this is correct then rising sea level could not have driven ice recession to the present day grounding line on the siple coast because global deglacial sea level rise was essentially accomplished by mid holocene time copyright 1999 john wiley sons ltd

reconstruction of ice sheet changes in the antarctic peninsula since the last glacial maximum this paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the antarctic peninsula ice sheet apis from the last glacial maximum lgm through deglaciation to the present day these data are used to reconstruct grounding line retreat in 5 ka time steps from 25 ka bp to present glacial landforms and subglacial tills on the eastern and western antarctic peninsula ap shelf indicate that the apis was grounded to the outer shelf shelf edge at the lgm and contained a series of fast flowing ice streams that drained along cross shelf bathymetric troughs the ice sheet was grounded at the shelf edge until 20 cal ka bp chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains as well as cosmogenic nuclide dates on erratics and ice moulded bedrock retreat in the east was underway by about 18 cal ka bp the earliest dates on recession in the west are from bransfield basin where recession was underway by 17 5 cal ka bp ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid shelf the timing of initial retreat decreased progressively southwards along the western ap shelf the large ice stream in marguerite trough may have remained grounded at the shelf edge until about 14 cal ka bp although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka bp between 15 and 10 cal ka bp the apis underwent significant recession along the western ap margin although retreat between individual troughs was asynchronous ice in marguerite trough may have still been grounded on the mid shelf at 10 cal ka bp in the larsen a region the transition from grounded to floating ice was established by 10 7 10 6 cal ka bp the apis had retreated towards its present configuration in the western ap by the mid holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier by the start of the holocene mid to late holocene retreat was diachronous with stillstands re advances and changes in ice shelf configuration being recorded in most places subglacial topography exerted a major control on grounding line retreat with grounding zone wedges and thus by inference slow downs or stillstands in the retreat of the grounding line occurring in some cases on reverse bed slopes

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

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

geomorphological evidence and cosmogenic 10be 26al exposure ages for the last glacial maximum and deglaciation of the antarctic peninsula ice sheet this paper presents the first systematic attempt to map the last glacial maximum lgm configuration of the southern and central parts of the antarctic peninsula ice sheet and to determine the timing of onshore ice sheet retreat geomorphologic evidence shows that the lgm ice sheet expanded to form two ice domes in palmer land and merged with an expanded and thicker west antarctic ice sheet in the weddell sea ice from the antarctic peninsula merged with alexander island ice in george vi sound cosmogenic 10 be and 26 al data from 29 erratics on nunataks yield model ages between 7 2 ka and older than 1 ma the data set contains a high proportion of erratics with evidence of nuclide inheritance once these ages have been excluded the cosmogenic ages suggest that thinning of the west side of the antarctic peninsula ice sheet to near present configuration was almost complete by the early holocene these data combined with previously published 14 c data exclude the possibility that the west side of the antarctic peninsula ice sheet has been thinning throughout the holocene as has been demonstrated for some other sectors of the west antarctic ice sheet on the east side of the antarctic peninsula ice sheet thinning was under way prior to the early holocene but our data do not constrain the ice sheet behavior more recently than 7 2 ka

extending the geochronometry of arctic lake cores beyond the radiocarbon limit by using thermoluminescence reconstructing detailed paleoclimatic paleoenvironmental histories from pleistocene sediments in the arctic is an ongoing challenge because of the difficulty of measuring accurate timescales beyond the range of radiocarbon 14c dating important archives of such histories are arctic lakes that exist outside the known extent of the last major glaciations to develop reliable geochronometry of sediment cores from arctic and other lakes we applied thermoluminescence tl sediment dating methods to 24 samples 8 reported earlier but some reanalyzed here selected from cores from squirrel and joe lakes in northwestern alaska a sequence of 23 14c ages from the upper parts of these cores permitted tests of the zeroing assumption of tl dating that all fine silt grains were exposed to daylight before final burial we performed multiple tl tests on most samples to isolate stable tl signals and measured tl emissions spectra to help characterize samples tl ages generally agree with the 30 kyr age depth trend derived from 14c dating and extend the timescale apparently to 180 ka for squirrel lake and to at least 60 ka for joe lake an anomalously old tl result from squirrel lake is attributed to failure of the tl zeroing assumption within that sediment horizon in the lower joe lake core we assign a timing of 45 ka to 50 ka for the beginning of an apparently climatic warming interval these results identify and quantify the main tl sources of tl age inaccuracy and the preferred tl protocols for accurate tl sediment dating in northern high latitude lake deposits they also provide the first direct chronology beyond the 14c dating range for these lakes