global ice sheet system interlocked by sea level abstract denton and hughes 1983 quaternary research 20 125 144 postulated that sea level linked a global ice sheet system with both terrestrial and grounded marine components during late quaternary ice ages summer temperature changes near northern hemisphere melting margins initiated sea level fluctuations that controlled marine components in both polar hemispheres it was further proposed that variations of this ice sheet system amplified and transmitted milankovitch summer half year insolation changes between 45 and 75 n into global climatic changes new tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the antarctic ice sheet thus fitting the concept of a globally interlocked ice sheet system but recent atmospheric modeling results manabe and broccoli 1985 journal of geophysical research 90 2167 2190 suggest that factors other than areal changes of the grounded antarctic ice sheet strongly influenced southern hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres atmospheric carbon dioxide linked to high latitude oceans is the most likely candidate shackleton and pisias 1985 atmospheric carbon dioxide orbital forcing and climate in the carbon cycle and atmospheric co2 natural variations archean to present e t sundquest and w s broecker eds pp 303 318 geophysical monograph 32 american geophysical union washington d c but another potential influence was high frequency climatic oscillations 2500 yr it is postulated that variations in atmospheric carbon dioxide acted through an antarctic ice shelf linked to the grounded ice sheet to produce and terminate southern hemisphere ice age climate it is further postulated that milankovitch summer insolation combined with a warm high frequency oscillation caused marked recession of northern hemisphere ice sheet melting margins and the north atlantic polar front about 14 000 14c yr b p this permitted renewed formation of north atlantic deep water which could well have controlled atmospheric carbon dioxide w s broecker d m peteet and d rind 1985 nature london 315 21 26 combined melting and consequent sea level rise from the three warming factors initiated irreversible collapse of the interlocked global ice sheet system which was at its largest but most vulnerable configuration

retreat history of the east antarctic ice sheet since the last glacial maximum the east antarctic ice sheet eais is the largest continental ice mass on earth and documenting its evolution since the last glacial maximum lgm is important for understanding its present day and future behaviour as part of a community effort we review geological evidence from east antarctica that constrains the ice sheet history throughout this period 30 000 years ago to present this includes terrestrial cosmogenic nuclide dates from previously glaciated regions 14c chronologies from glacial and post glacial deposits onshore and on the continental shelf and ice sheet thickness changes inferred from ice cores and continental scale ice sheet models we also include new 14c dates from the george v land terre adelie coast shelf we show that the eais advanced to the continental shelf margin in some parts of east antarctica and that the ice sheet characteristically thickened by 300 400 m near the present day coastline at these sites this advance was associated with the formation of low gradient ice streams that grounded at depths of 1 km below sea level on the inner continental shelf the lambert amery system thickened by a greater amount 800 m near its present day grounding zone but did not advance beyond the inner continental shelf at other sites in coastal east antarctica e g bunger hills larsemann hills very little change in the ice sheet margin occurred at the lgm perhaps because ice streams accommodated any excess ice build up leaving adjacent ice free areas relatively unaffected evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the lgm an observation supported by ice cores which suggest that interior ice sheet domes were 100 m lower than present at this time ice sheet recession may have started 18 000 years ago in the lambert amery glacial system and by 14 000 years ago in mac robertson land these early pulses of deglaciation may have been responses to abrupt sea level rise events such as meltwater pulse 1a destabilising the margins of the ice sheet it is unlikely however that east antarctica contributed more than 1 m of eustatic sea level equivalent to post glacial meltwater pulses the majority of ice sheet recession occurred after meltwater pulse 1a between 12 000 and 6000 years ago during a period when the adjacent ocean warmed significantly large tracts of east antarctica remain poorly studied and further work is required to develop a robust understanding of the lgm ice sheet expansion and its subsequent contraction further work will also allow the contribution of the eais to post glacial sea level rise and present day estimates of glacio isostatic adjustment to be refined

insoluble particles in antarctic ice background aerosol size distribution and diatom concentration we have measured insoluble particle size distributions covering the radius range 0 05 1 31 m for six sections of ice core from dome c antarctica two of the sections are from the holocene two are from the last glacial maximum lgm and another two are from the period that preceded it our measurements lead us to the conclusion that the southern hemisphere insoluble background aerosol size distribution in the range of our measurements has not changed significantly over the 26 000 year period that we studied we also compared the concentration of diatoms in a sample of holocene ice with that in two samples of lgm ice and found that the concentration of diatoms whose largest dimension was equal to or greater than 10 m was 20 times larger during the lgm the same as the ratio we measured for the concentration of insoluble particles we interpret this to mean that the higher dust levels were mainly due to an increase in wind strength rather than to increased continental aridity

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

long term climatic changes indicated by crystal growth in polar ice the reconstruction of palaeotemperatures from polar ice samples is essentially based on the isotopic composition of the ice in this paper we propose a new and independent way to obtain such data by using crystal size change profiles from central antarctica dome c and vostok ice cores data we suggest that crystal growth rate is mainly driven by a built in memory9 of the surface temperature conditions at the time of deposition a semi empirical model of crystal grain growth is proposed leading to last glacial maximum holocene temperature change estimates in good agreement with isotope interpretations however the possible palaeocli matic application of this model suffers some limitations connected in particular with in situ strain conditions

interpreting ancient ice in a shallow ice core from the south yamato antarctica blue ice area using flow modeling and compositional matching to deep ice cores 1 we explore methods of dating a 101 m ice core from a bare ice ablation area in the yamato mountains dronning maud land east antarctica there are two unknowns the age of the ice at the surface and the age spanned by the core the ice crystal growth rate was used to estimate the age span of the core at about 5 kyr co2 ch4 and n2o data on the core were compared with well dated records from deep cores leading to two plausible matches both within isotope stage c detailed comparison of high resolution dep records from this core and the dome fuji core support the 55 61 kyr bp fit best oxygen isotope values in the core were then used to constrain the source elevation of the snow in the core and hence the velocities in a simple flow line model we inverted the ice core surface age age span and origin site and their confidence intervals in a sensitivity study of flow model parameter space the flow line model predicts good matches to the core by reducing glacial flow rates to 70 of present day accumulation rates by 45 with 10 confidence intervals the modeled surface age for the whole meteorite field yields maximum surface ages of about 90 kyr which is consistent with known but poorly constrained tephra dating meteorite terrestrial ages and the frequency of meteorite discoveries this approach can be used quite generally to link deep ice cores to surface outcrops on blue ice fields

a study of the seismogenic process beneath the south western foothills in taiwan in relation with the 2010 jiasian earthquake abstract a moderate earthquake occurred near the town of jiasian in kaohsiung county taiwan at 8 18 am local time on 4 march 2010 the epicenter was located about 60 km northeast of kaohsiung city about 70 aftershocks occurred during the same day in this study we invert a 3 d velocity structure beneath the southwestern part of taiwan furthermore we accurately determine the locations the focal mechanisms and the regional stress tensor from the inverted 3 d velocity model according to the results we can conclude 1 a low vp anomaly zone with a high vp vs ratio in the southwestern part of the research area may have been caused by the subducting oceanic lithosphere 2 a high vp anomaly zone with low vp vs ratio in the northeastern part of the research area demonstrates that there is an intervening continental sliver 3 based upon the inverted 3 d velocity model and the relocated seismicity we suppose that there might be a nw se trending blind fault which dips to the north 4 according to the results of the focal mechanisms of the jiasian earthquake sequence and the regional stress tensor inversion we can surmise that the possible blind fault may be a thrust fault with left lateral characteristic and 5 based upon the different tectonic process in this area we can conclude that the chishan transfer fault zone leads to a possible oblique slip fault locks and exhibit high seismic potential which caused the jiasian earthquake sequence

the relationship between a zonal index and blocking activity abstract the degree to which northern hemisphere blocking activity is controlled by variations in zonal mean conditions is investigated a set of northern hemisphere winter season 500 hpa analyzed fields is examined for blocks using an objective index defined solely from the eddy fields with this blocking index it is shown that in most regions enhanced blocking activity is associated with relatively strong zonally averaged winds around 30 n and weak winds around 50 60 n also the preferred zonal positions of blocks are related to the state of the zonal mean flow a similar analysis is carried out using data from a perpetual january gcm simulation and the same relationship between blocking activity and zonally averaged conditions is found to be valid to an even stronger degree for these data to investigate whether anomalous zonal mean flows are actually controlling the associated level of blocking activity two experiments with the gcm are performed in one experiment the zonal mean state of the gcm i

shear wave velocity model of the chukuo fault zone southwest taiwan from cross correlation of seismic ambient noise abstract the chia nan chiayi tainan area is in the southwestern taiwan and is located at the active deformation front of the collision of the eurasian continental plate and the philippine sea plate which causes complex folds as well as thrust fault systems in the area the chukuo fault zone is a boundary between the western foothill and the western coastal plain in the chia nan area the nature of the crustal structure beneath the fault zone especially the eastern part of the fault zone with mountain topography has not been well known in detailed due to lack of drilling data as well as its limitation in using other geophysical methods such as active source survey in this study we deployed an array with 11 broadband seismic stations to monitor the seismicity of the chukuo fault zone the array has recorded more than 1000 microearthquakes around this area it provides an opportunity to use p and s wave travel time data to investigate the both the crustal p and s velocity in the fault zone however due to the nature of the earthquake distribution the ray density is relatively low at depth between 0 and 7 km in addition the uncertainty of s wave reading for small earthquake also a limit in building precise s velocity profile thus we take the advantages of using cross correlation of seismic ambient noise to investigate crustal s velocity profile in the chukuo fault area especially in the mountain area where crustal faulting is a dominated phenomenon the results indicate that s wave velocity in the uppermost crust in the chukuo fault zone is shown to be slower than previous studies a low velocity layer exists at depth between 1 and 2 km in the east of the chukuo fault the low s velocity is related to a highly fractured upper crust due to intensive deformation caused by the orogenic process

the variability of antartic ice sheet response to the climatic signal high resolution numerical model experiments were carried out along two flowlines in dronning maud land antarctica one flowline passing through the central part of a coastal mountain range and one along a major continental ice stream shirase glacier results showed that ice sheet behaviour in response to the climatic signal locally differs response patterns are different for the inland ice sheet the coastal ice sheet and around marginal subglacial mountains modelled response time series were analyzed by lag correlation range and fractal analysis local differentiation in ice sheet response is primarily related to the sensitive interplay between surface accumulation patterns thermomechanical properties of the ice sheet and bedrock roughness

parameterization of the annual surface temperature and mass balance of antarctica this study entails the parameterization by means of a linear multiple regression analysis of the annual surface temperature and mass balance of antarctica the analysis was performed for the entire ice cap as well as for three separate regions ice shelves elevation less than 200 m the interior elevation above 1500 m and the escarpment region in between it was found that temperature can be parameterized very well in terms of elevation and latitude the latitudinal gradient on the ice shelves can be explained by the super adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves the surface mass balance can be parameterized reliably only in the interior where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere and a significant correlation with the shape of the dome the convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer this results in precipitation as radiative cooling in the inversion exceeds adiabatic warming an estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior based on regression results and a physical analysis of the precipitation processes in this region a temperature sensitivity analysis was performed for the current mass balance distribution for a 1 k rise in surface temperature the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea level lowering of 0 2 mm a 1 this is about 30 less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere

chemical composition of ice containing tephra layers in the byrd station ice core antarctica abstract the chemical composition of ice containing tephra volcanic ash layers in 22 sections of the byrd station ice core was examined to determine if the volcanic eruptions affected the chemical composition of the atmosphere and precipitation in the vicinity of byrd station the liquid conductivity acidity sulfate nitrate aluminum and sodium concentrations of ice samples deposited before during and after the deposition of the tephra layers were analyzed ice samples that contain tephra layers have on average about two times more sulfate and three to four times more aluminum than nonvolcanic ice samples the acidity of ice samples associated with tephra layers is lowered by hydrolysis of silicate glass and minerals average nitrate sodium and conductivity are the same in all samples because much of the sulfur and chlorine originally associated with these eruptions may have been scavenged by ash particles the atmospheric residence time of these volatiles would have been minimized therefore the eruptions probably had only a small effect on the composition of the antarctic atmosphere and a negligible effect on local or global climate

ice flow at the dome c ice divide based on a deep temperature profile we calculate the temperature distribution with depth at the dome c ice divide east antarctica for a number of vertical strain rate functions assuming two dimensional flow to solve the heat equation we use the dome c oxygen isotope profile and radar data to specify the surface and basal boundary conditions respectively two different sets of simple monotonie polynomials are used as strain rate test functions for a net surface warming of about 9 c through the wisconsinan holocene climatic transition we find that the best agreement to the measured 800 m dome c temperature profile results from a vertical strain rate of the form 1 z h p with h the ice thickness and p 2 5 using dated horizons in the oxygen isotope profile obtained by cross correlation with a marine sediment core we find virtually no change in accumulation rate at dome c since the end of the wisconsinan glacial

laboratory antarctica research contributions to global problems research in antarctica is becoming increasingly important in the large interdisciplinary studies of connections within the earth9s geosphere biosphere system four examples of broad research areas are discussed upper atmosphere research explores the sun earth interactions which are most intense in the polar regions the mass balance and dynamics of the large antarctic ice sheet and its paleoclimatic records recovered from deep ice cores are important indicators of past and present global changes antarctica and sediment cores from the southern ocean contain the history of inception and growth of the ice masses and their subsequent fluctuations and the long term history of paleoclimate the remarkable adaptations of antarctic biota to extreme cold and drought may allow through biotic monitoring the detection of changes in the ocean and climate of antarctica

a baseline antarctic gia correction for space gravimetry abstract within the past decade newly collected gps data and geochronological constraints have resulted in refinement of glacial isostatic adjustment gia models for antarctica these are critical to estimating and understanding ice mass changes at present day a correction needs to be made when using space gravity for ice mass balance assessments due to the fact that any vertical movements of the solid earth masquerade as changes in ice mass and these must be carefully removed the main upshot of the new antarctic gia models is a downward revision of negative ice mass trends deduced from the gravity recovery and climate experiment grace resulting from a reduced gia correction this revision places grace inferred trend in mass balance within the one sigma uncertainty of mass balance deduced by altimetry because uncertainties in holocene ice history and the low viscosity rheology beneath the west antarctic ice sheet wais continue to vex further improvement in predictions of present day gia gravity rate more emphasis has been given to regional scale gia models here we use a bayesian method to explore the gravimetric gia trend over antarctica both with and without the impact of a late pleistocene antarctic ice loads along with the contribution of oceanic loads we call this model without loads associated with antarctica a baseline for regional gia models to build upon we consider variations of the radial mantle viscosity profile and the volume of continental scale ice sheets during the last glacial cycle the modeled baseline gia is mainly controlled by the lower mantle viscosity and continental levering caused by ocean loading we find that the predicted baseline gia correction weakly depends on the ice history this correction averages to 28 4 16 5 41 9 95 confidence gt yr of which 23 6 5 3 are contributed by east antarctica in contrast with late pleistocene antarctic proximal ice included the total modeled mass trend due to gia is 73 7 30 1 114 7 gt yr a baseline gia correction of 28 4 gt yr is of order 50 of the mean net mass trend measured during the period 1992 2017 the statistical analysis provides tools for properly synthesizing any regional antarctic gia model with a self consistent far field component this may prove important for accounting for both global and regional 3 d variations in mantle viscosity

response of the east antarctica ice sheet to sea level rise a nonsteady ice flow model that explicitly includes longitudinal stresses is used to study the effects of marginal changes on the interior portions of an ice sheet sea level rise is found to cause a wave of thinning to propagate upglacier and this wave is slowed diffused and damped at the ice divide at dome c in central east antarctica post wisconsinan sea level rise is modeled as having caused 110 m thinning with response now 70 complete if accumulation rates increased by 10 at the same time then calculated net thinning has been only 75 m ice sheet response to changes in sea level and accumulation rate is relatively rapid response to temperature changes is an order of magnitude slower response times are shorter if the marginal position of an ice sheet is controlled

late cenozoic glacial history of the ross embayment antarctica abstract the ross ice drainage system comprises about 25 per cent of the surface area of the antarctic ice sheet its fluctuations during the late quaternary have been determined in two ways from analyses of three deep ice cores extracted at byrd west antarctica and at vostok and dome circe east antarctica and from the distribution stratigraphy and chronology of glacial drifts in the transantarctic mountains the ice core studies give time series records for the last 160 ka that correspond well with the marine isotope record and clearly show glacial interglacial stadial and interstadial intervals they also suggest that during glaciation maxima the polar plateau was characterised by an accumulation rate 50 per cent lower and temperature 7 9 c lower than present values glacial geological studies reveal a hiatus in the drift record between older miocene early pleistocene glacial sediments and drifts of the last two glaciations isotope stages 6 and 2 there are two leading but contradictory interpretations of the older drift sirius formation one is based primarily on biological data and favours partial deglaciation of antarctica in the pliocene early pleistocene followed by regrowth of the east antarctic ice sheet to dimensions larger than now and then substantial uplift of the transantarctic mountains the other is founded on glacial geological observations and implies a larger than present ice sheet over antarctica during the miocene and only 200 m of uplift subsequently for the late quaternary reconstructed ice surface profiles based on detailed mapping and dating of drift sheets show that large outlet glaciers from the east antarctic polar plateau became about 1000 m thicker during glaciation maxima while the plateau ice barely thickened at all this is attributed to extensive northward migration of the ice grounding line in the ross embayment as global sea level fell dates obtained from the drift sheets confirm that glaciers in the ross embayment area reached maximal limits at 190 160 ka bp and at 23 14 ka bp recession from the last glaciation maximum was underway by 13 ka bp and was complete by ca 6 ka bp alpine glaciers terminating in dry valleys fluctuate asynchronously with the ross embayment glaciers they retreat during glacial maxima when they become starved of accumulation and readvance during warmer intervals because of their dependence on grounding line position glacier fluctuations in much of antarctica are primarily led by sea level changes controlled by ice sheets in the northern hemisphere

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

climatology of tracked persistent maxima of 500 hpa geopotential height persistent open ridges and blocking highs maxima of 500 hpa geopotential height z500 pmz adjacent in space and time are identified and tracked as one event with a lagrangian objective approach to derive their climatological statistics with some dynamical reasoning a pmz starts with a core that contains a local eddy maximum of z500 and its neighboring grid points whose eddy values decrease radially to about 20 geopotential meters gpms smaller than the maximum it connects two consecutive cores that share at least one grid point and are within 10 of longitude of each other using an intensity weighted location the pmz ends at the core without a successor on each day the pmz impacts an area of grid points contiguous to the core and with eddy values decreasing radially to 100 gpms the pmzs identified and tracked consist of persistent ridges omega blockings and blocked anticyclones either connected or as individual events for example the pmz during 2 13 august 2003 corresponds to persistent open ridges that caused the extreme heatwave in western europe climatological statistics based on the pmzs longer than 3 days generally agree with those of blockings in the northern hemisphere more pmzs occur in djf season than in jja and their duration both exhibit a log linear distribution because more omega shape blocking highs and open ridges are counted the pmzs occur more frequently over northeast pacific than over atlantic europe during cool seasons similar results are obtained using the 200 hpa geopotential height in place of z500 indicating the quasi barotropic nature of the pmz

inferences from stable water isotopes on the holocene evolution of scharffenbergbotnen blue ice area east antarctica we show that it is possible to extract a high resolution annual paleoclimate record from the surface of a blue ice area bia the variability of the surface stable isotope values suggests that almost all the surface ice in scharffenbergbotnen bia east antarctica is of holocene age the isotopic changes across the bia show that the modern climate there is warmer than the climate in the early holocene optimum 11 kyr bp a volume conserving ice flow model for the bia constrained by isotopic variability and layer thicknesses and a series of 14 c ages indicate both that the bia has been smaller than now and that the surface velocities were considerably smaller during the last glacial maximum changes in ice sheet thickness drive the bia towards present day conditions the relatively young age of the majority of the bia also explains the lack of meteorite finds in this area and may be typical for many bias in low elevation nunatak areas

antarctic ice volume and contribution to sea level fall at 20 000 yr bp from raised beaches the contribution of the antarctic ice sheets to global sea level fall at the last glacial maximum lgm depends largely on how the extent and thickness of peripheral ice changed model studies1 3 suggest that there was widespread thickening from 500 m to more than 1 000 m of the ice sheet margins sufficient to induce a drop in sea level of at least 25 m geological evidence4 5 on the other hand indicates only limited ice expansion and a sea level fall of just 8 m here we use recent data on the altitudes and ages of raised beaches from the ross embayment and east antarctica to investigate the timing and extent of antarctic deglaciation these indicate that the ice margin during the lgm was thinner and less extensive than has been formerly thought and that its contribution to the drop in sea level was only 0 5 2 5 m deglaciation was well advanced by 10 kyr bp and was complete by 6 kyr bp these findings imply either that sea level during the lgm fell less than present estimates suggest or that an ice volume considerably greater than currently accepted must have been present in the northern hemisphere

soluble impurities in the byrd station ice core antarctica their origin and sources polar ice cores contain long and detailed records of paleoatmospheric composition paleoclimate and their evolution through time by making a complete ionic balance in melted samples of ice it is possible to evaluate the origin identification of chemical compounds and sources continental marine volcanic extraterrestrial of soluble impurities contained in these ice cores once these are known an attempt can be made to try and explain the cause of any observed changes in this paper we present results of analyses of the major soluble impurities h na nh4 k so4 no3 cl made on bulk samples selected at approximately 50 m intervals down the length of an ice core from byrd station antarctica 80 01 s 119 31 w 1530 m most samples are in ionic balance and it is therefore possible to suggest with which compounds the ionic impurities are linked these compounds include an important contribution from both sea salts nacl and na2so4 and strong acids approximately equal amounts of hno3 and h2so4 the cl na mole ratio is found to be quite stable throughout the core and hovers about the expected bulk sea water ratio in general the marine derived components at byrd station decreased by a factor of 2 between the late glacial maximum and holocene while the gas derived acid components decreased by a factor of only 1 5 some possible causes of these variations are suggested

on the age vs depth and optical clarity of deep ice at south pole the first four strings of phototubes for the amanda high energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the south pole during the 1995 96 season an addit

evolution of the temporal multifractal scaling properties of the chiayi earthquake ml 6 4 taiwan abstract variations in the fractal dimension of earthquakes have been suggested to be a precursor of a large earthquake however the physical characteristics and seismicity are always different along a large fault system and it is difficult to segment a large fault for further investigating therefore the fractal dimension of earthquakes on a given fault only reflects the average seismic characteristics of the area and may be unrelated to precursory activity in this paper the evolution of the temporal generalized fractal dimension dq of a seismic cluster within a small fault system associated with the chiayi earthquake ml 6 4 taiwan is investigated the earthquakes of this sequence are confined in small source volume and reflect the behavior of the local fault system our results show that the dq curve of the background stage is smooth with a low multifractal degree 0 36 and the seismicity is nearly monofractal in the chiayi region during the foreshock stage the seismicity becomes active such that not only the dq curve exhibits greater variability especially for the steep slope of dq curve at q 0 but also the temporal fractal dimension changes from nearly monofractal to multifractal in the aftershock stage the fluctuation of dq is large and the multifractal degree is up to 1 0 the temporal multifractal property becomes more pronounced as well finally when the seismicity returns to the background stage the dq curve becomes smooth and nearly monofractal again therefore the fluctuations in the dq spectrum of an earthquake cluster associated with a large earthquake not only give a clear picture of the temporal alterations in the seismogenic regimes but also illustrate their variability through time for a large earthquake in addition the variation of the slope of dq curve at q 0 in the foreshocks may be used as a precursor of a large earthquake

the connection between extreme stratospheric polar vortex events and tropospheric blockings the variations of tropospheric blockings and their connections with the stratospheric polar vortex during different stages of the life cycle of extreme stratospheric polar vortex events i e strong vortex sv events and weak vortex wv events are investigated the blocking frequency decreases over the euro atlantic sector and increases over the western north pacific during the onset and maturation stages of sv events there are more blocking days over the western north pacific and weakened upward planetary wave fluxes in the stratosphere during the maturation stage of shorter time scale sv events than during longer time scale sv events and the weakening of the upward planetary wave fluxes mainly results from the linear wave interference effect the blocking frequency is increased over the euro atlantic sector during the decline stage of sv events this increase is found to be related to the descending stratospheric zonal wind anomalies and the poleward displacement of the eddy driven jet stream which lasts for about 10 days and is associated with the descending positive stratospheric northern annular mode nam anomalies the increased blocking frequency leads to an enhancement of the planetary wave fluxes in the stratosphere via both the linear wave interference for shorter time scale sv events and nonlinear wave interference for longer time scale sv events effect the changes of the blocking frequency during the growth stage of wv events are almost opposite to those observed during the onset and maturation stages of sv events the blocking frequency decreases over the euro atlantic sector after the central dates of wv events which are related to the descending stratospheric zonal wind anomalies and the equatorward displacement of the eddy driven jet stream preceded by the descending negative stratospheric nam anomalies about 10 days we found that the nonlinear wave interference begins to make a considerable contribution to the weakening of the upward wave fluxes in the stratosphere after the central date of wv events and this is not emphasized in previous literature

ruptures in a highly fractured upper crust the 1999 chiayi m 6 4 earthquake sequence that occurred about one month after the 1999 chi chi m 7 6 earthquake is remarkably similar to the ruey li m 6 2 earthquake sequence which occurred one year before the big chi chi event both sequences were energetic and short in duration with events confined in small source volumes and the fault plane orientation of individual events in these sequences varied abruptly during the development of the dynamic rupture both occurred on the southern extension of the large chelungpu rupture causal to the chi chi event and in an area of highly fractured upper crust we consider that this faulting behavior is due to the rupture induced dynamic stress that interacts with the pre existing highly fractured upper crust and continually perturbs the local stress field this phenomenon appears to be typical of particularly active plate boundary regions with a highly fractured upper crust under intense tectonic loading

applying plant functional types to construct biome maps from eastern north american pollen data comparisons with model results abstract global biome models like biome1 convert climate model simulations of past climates into biome distributions and thus facilitate comparison of both climate and biome model results with biomes estimate from paleoecological data we adapted a biomization method recently developed for european pollen data for use with pollen data in eastern north america and then compared its estimated biomes with those derived from applying biome1 to the climate simulations from the ncar ccm1 national center for atmospheric research community climate model version 1 for 6000 years ago 6 ka we first tested the biomization method by seeing how well the biomes inferred from modern pollen data match observed biomes we found that modifications to the method were necessary in part to account for physiological differences between north american and european taxa and in part to cope with our choice of using just 23 major pollen taxa our modifications significantly improved the match between observed modern biomes and pollen derived biomes as measured by the kappa statistic we tested our tuning of the biomization method by matching its inferred 6 ka biomes to biomes estimated from pollen data using the modern analog technique the degree of agreement at 6 ka is close to that for today showing that 1 the biomization method and modern analog technique when applied to the same pollen data produce consistent results and 2 the modifications made to the biomization method are robust back to 6 ka we then used the results of the biomization method to test the biome maps simulated by biome1 which derives biome distributions from observed climate values for today and from the climatic simulations of the ccm1 for 6 ka only a fair agreement is seen and significant offsets exist in the placement of biomes by biome1 for today biome1 simulates the boundary between the temperate deciduous and cool mixed forests to be too far south and the steppe forest boundary to be too far west these model biases are also evident in the simulations at 6 ka despite the fact that ccm1 simulates warmer than present temperatures in the central united states to the north however biome1 correctly simulates the cool mixed forest and taiga boundary at 6 ka as more northwestward than at present

a deglacial model for antarctica geological constraints and glaciological modelling as a basis for a new model of antarctic glacial isostatic adjustment abstract we present a new reconstruction of the antarctic ice sheets between 20 ka bp and the present day our reconstruction is derived using a numerical model to generate a physically consistent ice surface across the whole of the continent we define the extent of the ice sheet at five time slices 20 15 10 5 and 0 ka bp assuming an equilibrium state for the 20 ka bp time slice and a transient state for the deglacial time slices the evolution of the ice sheet within the numerical model is driven by variations in temperature accumulation rate and relative sea level in order to reconstruct the concave profile of the ice sheet in marine grounded regions such as the ross and weddell seas we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams we find a strong dependence upon the basal sliding parameters and also the position of the grounding line we use an extensive data base of geological and glaciological data to constrain our ice sheet reconstruction grounding line extent is prescribed from marine geological data and we test ice sheet thickness against onshore geological data at 62 sites of the five time slices considered our 20 ka bp reconstruction is the best constrained by data and has an rms misfit of 147 6 m when compared to observations of ice thickness change between 20 ka bp and the present day across all time slices there are large regions of the ice sheet which are poorly constrained especially after 20 ka bp we estimate the spatial distribution of uncertainty in our ice sheet reconstruction and note that the solutions are least reliable in regions of complex topography we predict that the antarctic ice sheets contributed 9 1 5 m of eustatic sea level to the global ocean between 20 ka bp and the present and our reconstruction with minimum misfit contributes 8 m eustatic sea level during this period these values which we argue are an upper bound are lower than many previous estimates the reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

a comparison of deep antarctic ice cores and their implications for climate between 65 000 and 15 000 years ago abstract three ice cores drilled in the central part of the antarctic continent extend back to the last glacial period one from west antarctica byrd and two from east antarctica vostok and dome c this period is also partly covered by a few cores from the coastal areas in these cores climatic information is mostly derived from the isotopic profiles d or 18 o from which surface temperature and more indirectly precipitation rate can be estimated the main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period from ca 65 000 15 000 yr b p the time scales have been examined in detail and a new 40 000 yr chronology for the dome c core adopted special emphasis is placed on the link between the concentration of 10 be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers elevation changes of the ice sheet derived from gas content and isotopic data bear directly on interpretations of past temperature and precipitation rate changes

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

paleoclimatic tracers an investigation using an atmospheric general circulation model under ice age conditions 2 water isotopes the linear relationship observed between the water isotopic contents of precipitation and surface air temperatures leads to the use of the water isotopes h218o and hdo in paleoclimatology applied to the measurements of the isotopic content of paleowaters like groundwaters and deep ice cores this relationship is used to infer paleotemperatures however this interpretation of paleo isotopic contents is only valid if the isotope temperature relationship is not affected by climate change to address this problem we have developed a water isotope modeling inside an atmospheric general circulation model agcm and performed simulations of both the present day and last glacial maximum lgm climatic conditions agcms are indeed the only appropriate tools able to account the whole complexity of the atmospheric circulation for the present day climate preliminary results for january were presented by joussaume et al 1984 and are complemented by new simulations performed for both february and august climatic conditions with a higher resolution version of the model model results are well corroborated by observations they also exhibit some effects of the atmospheric circulation on the isotopic fields for the simulated lgm climate the model results compare well with paleoclimatic data of water isotopic contents except for a higher than observed spatial variability the overall patterns of the simulated 18o temperature relationship for the lgm climate are practically unchanged which tends to comfort the use of water isotopes in paleoclimatology however concerning the deuterium excess i e the relationship between oxygen 18 and deuterium the model results are not sufficiently valid to allow a discussion of the use of deuterium excess in paleoclimatology

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

late quaternary lake level changes and climates of australia abstract spatial and temporal patterns in lake level data from 38 sites in australia and papua new guinea provide a basis for reconstructing changes in water balance and atmospheric circulation during the past 30 000 years the reconstructions are consistent with hydrological changes inferred from pollen analysis and palaeowind directions inferred from dunes generally wetter conditions between 30 000 and 24 000 bp are consistent with a strong walker circulation with the sta near its present position general aridity at the glacial maximum until 12 000 bp with higher than present lake levels in the southeastern interior of australia implies that the southern margin of the subtropical anticyclone belt was expanded southward and the southern westerlies were correspondingly displaced this southward shift appears in all gcm simulations of the 18 000 bp climate and may be a result of the increased vigour of the northern hemisphere circulation a northward migration of the belt of high lake levels between 11 000 and 6000 bp suggests that the sta shifted back equatorward to north of its present position relaxation to modern conditions occurred after 6000 bp interrupted by an unexplained dry phase 6000 5000 bp in tasmania and queensland

magmatic and phreatomagmatic volcanic activity at mt takahe west antarctica based on tephra layers in the byrd ice core and field observations at mt takahe abstract the morphology grain size characteristics and composition of ash particles in 30 ka to 150 ka tephra layers from the byrd ice core were examined to characterize the eruptions which produced them and to test the suggestion that they were erupted from mt takahe a shield volcano in marie byrd land west antarctica volcanic deposits at mt takahe were examined for evidence of recent activity which could correlate with the tephra layers in the ice core coarse and fine ash layers have been recognized in the byrd ice core the coarse ash layers have a higher mass concentration than the fine ash layers and are characterized by fresh glass shards 50 m diameter many containing elongate pipe vesicles the fine ash layers have a lower mass concentration and contain a greater variety of particles typically mt takahe is the favored source for the tephra because a chemical analyses of samples from the volcano are distinctive being peralkaline trachyte and similar in composition to the analyzed tephra b mt takahe is a young volcano a speculative eruptive history for mt takahe is established by combining observations from mt takahe and the byrd ice core tephra initial eruptions at mt takahe were subglacial and then graded into alternating subaerial and subglacial activity the tephra suggest alternating subaerial magmatic and hydrovolcanic eruptions from 30 to 20 ka b p followed by a sustained period of hydrovolcanic eruptions from 20 to 14 ka b p which peaked at 18 ka b p

microparticle concentration variations linked with climatic change evidence from polar ice cores the microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation the ratio of the average particle concentration in the late glacial strata to that in the holocene strata is 6 1 for the core from dome c antarctica 3 1 for the core from byrd station antarctica and 12 1 for the core from camp century greenland whether this temporal correlation between increased atmospheric particle load and the lower surface temperatures is directly causal is unknown however the variations in these two parameters must be satisfactorily resolved in any successful hypothesis that addresses the causes of climatic change

a multifaceted climatology of atmospheric blocking and its recent linear trend abstract a dynamically based climatology is derived for northern hemisphere atmospheric blocking events blocks are viewed as large amplitude long lasting and negative potential vorticity pv anomalies located beneath the dynamical tropopause the derived climatology based on the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 provides a concise coherent and illuminating description of the main physical characteristics of blocks and the accompanying linear trends the latitude longitude distribution of blocking frequency captures the standard bimodal geographical distribution with major peaks over the north atlantic and eastern north pacific in all four seasons the accompanying pattern for the age distribution the genesis lysis regions and the track of blocks reveals that 1 younger blocks 1 4 days are more prevalent at lower latitudes whereas significantly older blocks up to 12 days are located at higher latitudes 2 genesis is confined predominantly t

systematic analysis of shear wave splitting in the aftershock zone of the 1999 chi chi taiwan earthquake shallow crustal anisotropy and lack of precursory variations we analyze shear wave splitting sws in a high quality waveform data set recorded at surface and downhole 0 2 km seismometers in a region around the 20 september 1999 m w 7 6 chi chi taiwan earthquake sequence the data set was generated by events in a 5 year period before during and after the mainshock the purpose is to investigate the depth extent of the crustal anisotropy and its possible temporal evolution in relation to the occurrence of large earthquakes results from downhole records show a stable polarization direction of the fast shear wave that matches well the local global positioning system gps velocity field a slightly different polarization direction of the fast shear wave is obtained from surface data this suggests a possible anisotropy change between the top 0 2 km structure and the deeper section of the crust measured time delays below the downhole station have an average value of 0 16 sec without systematic changes for sources from about 8 km to 20 km in depth estimates of time delays in the top 0 2 km of the crust based on shear waves reflected from the free surface give a constant 0 04 sec a likely depth distribution inferred from these two types of measurements and an s velocity model indicates that the crustal anisotropy in the region is dominated by the top 2 to 3 km the measured polarization directions and time delays give essentially constant values over the 2 7 year premainshock and 2 3 year postmainshock periods in the region adjacent to the chi chi rupture and within 10 km from the epicentral region of its two large m 6 0 aftershocks analysis of sws in waveforms produced by earthquake multiplets confirms further the lack of precursory temporal variations of crustal anisotropy in the immediate neighborhood of the chi chi earthquake sequence the results raise doubts on the general usefulness of sws measurements for earthquake forecasting an apparent coseismic increase in anisotropy time delay of approximately 10 is observed for depths 0 2 km however this value is clearly affected by spatial changes associated with different event locations before and after the chi chi mainshock

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

deuterium excess in an east antarctic ice core suggests higher relative humidity at the oceanic surface during the last glacial maximum a continuous deuterium excess profile d d 8 18o was obtained from the dome c ice core spanning 32 000 yr it exhibits significant variations over this period in particular d was 4 5 lower around 18 000 yr bp than over the past 7 500 yr interpreted as reflecting higher relative humidity estimated 90 over the oceanic areas providing moisture for antarctic precipitation

a 3 d model for the antarctic ice sheet a sensitivity study on the glacial interglacial contrast on the longer climatic time scales changes in the elevation and extent of the antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes and contribute significantly to world wide sea levels in this paper a 3 d time dependent thermomechanical model for the entire ice sheet is presented that is subsequently used to examine the effects of glacial interglacial shifts in environmental boundary conditions on its geometry the model takes into account a coupled ice shelf grounding line dynamics basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields ice flow is calculated on a fine mesh 40 km horizontal grid size and 10 layers in the vertical for grounded and floating ice and a stress transition zone in between at the grounding line where all stress components contribute in the effective stress in the flow law there is free interaction between ice sheet and ice shelf so that the entire geometry is internally generated a simulation of the present ice sheet reveals that the model is able to yield realistic results a series of sensitivity experiments are then performed in which lower temperatures reduced accumulation rates and lower global sea level stands are imposed either singly or in combination by comparing results of pairs of experiments the effects of each of these environmental changes can be determined in agreement with glacial geological evidence we found that the most pronounced changes show up in the west antarctic ice sheet configuration they appear to be essentially controlled by variations in eustatic sea level whereas typical glacial interglacial changes in temperature and ice deposition rates tend to balance one another these findings support the hypothesis that the antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea level teleconnections grounding occurs more readily in the weddell sea than in the ross sea and long time scales appear to be involved it may take up to 30 40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions according to these reconstructions a steady state antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation

predicted age depth scales for siple dome and inland wais ice cores in west antarctica geophysical data are used with ice flow models and generalized accumulation histories to estimate age and annual layer thickness versus depth for two anticipated ice core sites in west antarctica siple dome 81 65 s 148 81 w and an inland site on the west antarctic ice sheet wais this modeling experiment predicts that 104 year old ice is at 50 depth and 105 year old ice is at 90 depth at both sites both of these cores could contain climate information through the last glacial cycle with annual resolution through the holocene the predicted similarity in resolution and record length between the two cores suggests that they could be compared in detail to obtain both spatial and temporal information about the paleoclimate and history of the west antarctic ice sheet

climatic warming and basal melting of large ice sheets possible implications for east antarctica climatic warming is shown to be capable of inducing shear heating instability and basal melting in a model ice sheet that is creeping slowly downslope growth times of the instability are calculated from a nonlinear analysis of temperature and flow in the model ice sheet whose surface undergoes a prescribed increase of temperature the source of instability lies in the decrease of maximum ice thickness for steady downslope creep with increasing surface temperature a surface temperature increase of 5 to 10 k can cause instability on a 104 year time scale for realistic ice rheology the instability occurs suddenly after a prolonged period of dormancy the instability might be relevant to the east antarctic ice sheet warming associated with the holocene interglacial epoch that heralded the end of the last ice age may have set the east antarctic ice sheet on a course toward widespread instability some 104 years later the present co2 induced climate warming is also a potential trigger for instability and basal melting of the east antarctic ice sheet

upstream cyclone influence on the predictability of block onsets over the euro atlantic region abstractatmospheric blocking has been shown to be a phenomenon that models struggle to predict accurately particularly the onset of a blocked state following a more zonal flow this struggle is i

fault mechanics and the kinematics of block rotations in many strike slip tectonic settings large rotations up to 100 of crustal blocks have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which accommodate the relative motion between the blocks as regional deformation progresses simple geometrical considerations require that the faults must also rotate in this paper we show that on the basis of mechanical considerations the amount of fault rotation permissible under a stationary stress field is limited to 20 to 45 consequently block rotations that are larger than 40 or 45 require more than one set of accompanying faults to accommodate the block rotation examples of such multiple sets with 40 to 45 between them as predicted by the model were recognized in sistan iran in yerington the lake mead area nevada and in southern california

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

the enigma of the arthur s pass new zealand earthquake 2 the aftershock distribution and its relation to regional and induced stress fields the aftershock distribution of the 1994 arthur s pass earthquake mw6 7 is unusual for a reverse faulting event in that it extends 12 km nnw and 30 km sse of the actual fault plane which strikes ne sw we have used several methods to infer the regional stress field in the region including geodetic results earthquake mechanisms and inversion of p wave polarity data for the stress tensor orientation the inversion method is new and does not require the focal mechanisms of the events used it also incorporates the coulomb failure criterion all results point to a stress field favoring strike slip faulting not thrusting with near horizontal 1 and 3 principal axes striking at 298 and 28 using dislocation theory we calculate the stress induced by the arthur s pass earthquake and its largest aftershock a strike slip event and add this to the regional field there is a fair correspondence between the hypocenters of aftershocks away from the mainshock fault plane and regions of high induced coulomb failure stress cfs on optimally oriented fault planes however there are regions of high induced cfs that are devoid of aftershocks it appears that earthquake slip in this region of oblique 19 plate convergence is as observed elsewhere partitioned into components parallel and perpendicular to the plate margin most of the slip is parallel as occurs on the nearby dextral alpine fault the boundary between the pacific and australian plates however occasional reverse events such as the arthur s pass earthquake account for at least some of the perpendicular component of slip and the uplift that produced the southern alps

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

evolution of the east antarctic ice sheet a numerical study of thermo mechanical response patterns with changing climate an efficient numerical ice sheet model including time dependence and full thermo mechanical coupling has been developed in order to investigate the thermal regime and overall configuration of a polar ice sheet with respect to changing environmental conditions from basic sensitivity experiments in which a schematic east antarctic ice sheet is forced with a typical glacial interglacial climatic shift it is found that i the mutual interaction of temperature and deformation has a stabilizing effect on its steady state configuration ii in the transient mode this climatic transition initially leads to increased ice thickness due to enhanced accumulation after which this trend is reversed due to a warmer base timescales for this reversal are of the order of 103 years in marginal zones and of 104 years in interior regions iii horizontal heat advection plays a major role in damping possible runaway behaviour due to the dissipation strain rate feed back suggesting that creep instability is a rather unlikely candidate to initiate surging of the east antarctic ice sheet the model is then applied to four east antarctic flow lines only the flow line passing through wilkes land appears to be vulnerable to widespread basal melting due to enhanced basal warming following climatic warming time dependent modelling of the vostok flow line indicates that the vostok station area has risen about 95 m since the beginning of the present interglacial due to thermomechanical effects which is of particular interest in interpreting the palaeoclimatic signal of the ice core obtained there

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

the positive north atlantic oscillation with downstream blocking and middle east snowstorms impacts of the north atlantic jet abstracta recent study revealed that cold winter outbreaks over the middle east and southeastern europe are caused mainly by the northeast southwest ne sw tilting of european blocking eb associated with the positive phase north atlantic oscillation nao here the north atlantic conditions are examined that determine the eb tilting direction defined as being perpendicular to the dipole anomaly orientation using daily reanalysis data the nao events are classified into strong sjn and weak wjn north atlantic jet types a composite analysis shows that the eb is generally stronger and located more westward and southward during sjn events than during wjn events during sjn events the nao and eb dipoles exhibit ne sw tilting which leads to strong cold advection and large negative temperature anomalies over the middle east and southeastern europe in contrast northwest southeast nw se tilting without strong negative temperature anomalies over the middle east is seen during wjn events a nonline

a possible causal relationship between the 1998 ruey li sequence and the 1999 chi chi earthquake in taiwan we have investigated the causal relationship between two recent taiwan events the 1998 m 6 2 ruey li and the 1999 m 7 6 chi chi earthquakes it is found that both earthquakes are generated by ruptures essentially along nearby sections of a large through going fault zone along the western foothills of taiwan the rapid termination in 10 days of the m 6 2 ruey li sequence is interpreted by the presence of an asperity in terms of the peikang basement high which dominates the tectonic deformation in central western taiwan we have carried out the relocation of the aftershocks their fault plane solutions plus stress inversion waveform source slip inversion coulomb stress change calculations and regional strain energy calculations for the ruey li sequence so as to examine its causal relationship from different angles we have concluded that as both events are results of the same regional stress accumulation due to the plate convergence the ruey li earthquake sequence would likely have escalated into a much larger rupture including the chelungpu fault had it not been for the presence of the peikang basement high

west directed flow of the west antarctic ice sheet across eastern basin ross sea during the quaternary abstract detailed seismic stratigraphic correlations and contour mapping time structure and time thickness of near surface units in eastern basin ross sea outer continental shelf suggest that strata outcropping at ross bank were deposited as a terminal moraine in association with west directed advance of the west antarctic ice sheet grounding zone from marie byrd land during the grounding event there was a major shift from west directed ice sheet flow to north directed ice stream flow seismic correlation to age control at dsdp leg 28 sites 271 and 272 suggests a pre last glacial maximum quaternary age for this major grounding event