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

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

ross ice shelf oxygen isotopes and west antarctic climate history the ross ice shelf 18o profile at station j 9 covers at least the last 30 000 yr it identifies the depth in the core of ice from i the last glacial interglacial transition 266 to 286 m and ii the 1000 m surface elevation about 140 m various processes contribute to the 18o change observed in the core i climatic warming mainly caused by a decrease in winter sea ice extent around antarctica of about 6 latitude early in the glacial interglacial transition ii decreasing ice sheet thickness later in the glacial interglacial transition and during the holocene and iii decreases in elevation and effective distance from the open ocean as the source of the ice in the core shifts along the flow line toward j 9 average 18o values of the last 3000 yr imply a fairly stable climate yet shorter 102 to 103 yr 18o climatic oscillations up to 6 are seen in both the holocene and the glacial portion of the record

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

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

the younger dryas termination and north atlantic deep water formation insights from climate model simulations and greenland ice cores results from the gisp2 and grip ice cores show that the termination of the younger dryas yd climate event in greenland was a large and extremely fast climate change a reinitiation of north atlantic deep water formation following a shutdown and its associated winter release of heat to the atmosphere has been suggested as the most likely cause of this climate transition to test this idea two general circulation model experiments using genesis have been completed for yd time 12 000 calendar years ago one with low heat flux in the nordic seas 10 w m deep water shutdown and one with high nordic sea heat flux 300 w m active deep water formation comparison of greenland climate differences between these experiments with the ice core records shows that when deep water is turned on much of the yd termination warming is achieved the increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation which obscures the dominantly wintertime response to the specified forcing the winter storm track shift toward greenland contributes much of the climate change at the yd termination

a major widespread climatic change around 5300 cal yr bp at the time of the alpine iceman palaeoenvironmental and archaeological data from arbon bleiche lake constance switzerland give evidence of a rapid rise in lake level dated by tree ring and radiocarbon to 5320 cal yr bp this rise event was the latest in a series of three successive episodes of higher lake level between 5550 and 5300 cal yr bp coinciding with glacier advance and tree limit decline in the alps this west central european climate change may have favoured the quick burial and the preservation of the alpine iceman recently found in the tyrolean alps it has possible equivalents in many records from various regions in both hemispheres dating to 5600 5000 cal yr bp and corresponds to global cooling and contrasting patterns of hydrological changes this major mid holocene climate event marks the hypsithermal neoglaciation transition possibly resulting from a combination of different factors including orbital forcing changes in ocean circulation and variations in solar activity copyright 2004 john wiley sons ltd

late quaternary diatom assemblages from prydz bay eastern antarctica abstract the paleo depositional environment of inner prydz bay east antarctica has been reconstructed for the past 21 320 14c yr b p using diatom assemblages and sediment facies from a short 352 cm long gravity core between 21 320 and 11 650 14c yr b p compact tillite and diamicton are present in the core and diatom frustules are rare to absent these data suggest that an ice sheet grounded over the site during the last glacial maximum following glacial retreat siliceous muddy ooze was deposited from 11 650 to 2600 14c yr b p in an open marine setting during this stage diatom frustules are abundant and well preserved and thalassiosira antarctica resting spores and fragilariopsis curta dominate the assemblage this assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today since 2600 14c yr b p sea ice and ice edge diatom species have become more abundant and neoglacial cooling is inferred the assemblage is similar to that forming currently in prydz bay where sea ice is absent

sedimentological and stable isotope evolution of lakes in the vestfold hills antarctica the sedimentological chemical and isotopic characteristics of sediment cores from three slightly saline to hypersaline lakes highway ace and organic lakes and two marine inlets ellis fjord and taynaya bay in the vestfold hills antarctica have been examined sections of the cores deposited in marine environments are characterized by uniform regularly laminated fine grained organic rich sediments with uniform organic 13c values 18 0 to 19 4 vs pdb and sulfur contents in contrast sediments deposited in lacustrine environments are extremely heterogeneous varying from finely laminated mat like sequences to poorly sorted clastic rich sediments authigenic monohydrocalcite and aragonite occur in some lake sediments the 13c values of organic matter in the lacustrine sediments exhibit an extremely wide range 10 5 to 25 3 that can be related to variations in physico chemical conditions in the lake waters strongly negative organic 13c values coupled with high sulfur contents are indicative of an anoxic zone in the overlying lake waters whereas less negative organic 13c values coupled with low sulfur contents are indicative of well mixed oxic conditions particularly high organic 13c values result during high levels of microbial activity in the lakes due to high rates of photosynthetic co2 fixation the large shifts in organic 13c are not necessarily accompanied by any change in macroscopic sedimentological characteristics illustrating the utility of isotopic investigations in these environments the 13c composition of authigenic carbonate in hypersaline organic lake sediments provides a record of changes in palaeoproductivity while the 18o of the carbonate provides information on rates of meltwater input and evaporation in the lake 14c dating suggests that highway lake was isolated from the sea by isostatic uplift at least 4600 yr before present b p whereas organic lake was isolated at approximately 2700 yr b p apparent emergence rates calculated from the 14c ages range from 1 0 to 2 1 mm yr 1 the reservoir effect in the lacustrine and marine environments is variable but probably does not exceed 1000 yr in any of the lakes examined

circumpolar distribution of holocene marine fossils in antarctic beaches abstract the composite frequency of radiocarbon ages for holocene marine fossils from beaches around antarctica is significantly different than random variations in the frequency of fossil ages coincide with the timing of holocene climate changes inferred from antarctic ice cores sub antarctic lakes polar and alpine moraines and sea level extant antarctic marine species that occur as fossils in beaches may reflect coastal meltwater impacts associated with ice sheet marginal fluctuations that were circumpolar during the holocene

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 1 geophysical results in the 1994 1995 and 1998 austral field seasons geophysical research efforts in the ross sea focused on acquiring a high resolution database designed to permit 1 reconstruction of the maximum extent and configuration of the ice sheet during the last glacial maximum i e oxygen isotope stage 2 2 reconstruction of conditions at the base of the ice sheet and 3 assessment of the relative retreat history of the ice sheet following the last glacial maximum five seismic facies are distinguished on the basis of external geometry relationships among features bounding surface amplitude intensity of internal acoustic signature and geometry of internal reflectors seismic facies 1 is a transparent draping unit correlated to diatomaceous mud interpreted as being deposited under open marine conditions seismic facies 2 and 3 are comprised of units displaying subdued massive internal signatures with smooth lower bounding surfaces and hummocky upper surfaces characterized by glacial lineations these units are interpreted to be grounding zone proximal deposits overridden by the expanded ice sheet seismic facies 2 may be a deforming till unit seismic facies 4a is characterized by an internally massive to chaotic signature an erosional often flat lower surface and a hummocky upper surface displaying glacial lineations this unit is interpreted to be till and is divided into deposits associated with the most recent glacial expansion 4a and with an earlier pre last glacial maximum expansion 4b seismic facies 5 is an acoustically laminated ponded and draping deposit interpreted to contain proglacial and sub ice shelf materials deposited continuously since the last interglacial period the associations of these units provide context for the interpretation of the ice edge maximum position conditions at the base of the ice sheet and the relative retreat history of the region there is compelling evidence for a much expanded ice sheet in the ross sea during the last glacial maximum in the western ross sea the maximum grounding position is marked by an isolated grounding zone wedge and placed in the vicinity of coulman island approximately 150 km from the continental shelf edge in the central ross sea the maximum grounding position is close to the continental shelf break based primarily on the presence of an extensive 60 m thick sheet like deposit with a fluted upper surface streaming ice may have occupied bathymetric lows on the continental shelf as suggested by 1 the configuration of bathymetry 2 the presence of glacially eroded troughs 3 the concentration of sediment interpreted to be deforming till within the middle to outer shelf reaches of the troughs and 4 the fluted nature of the upper surface absolute rates of streaming ice flow relative to inter ice stream areas are not implied the western ross sea continental shelf deposits record the retreat history of ice derived predominantly from the east antarctic ice sheet and glaciers of the transantarctic mountains ice flow on the continental shelf is interpreted to have remained fixed in position restricted by the walls of the troughs on the inner shelf of the western ross sea the ice flowed over and eroded lithified sedimentary strata slower moving ice occupied flat topped banks a single grounding zone wedge occurs on the western ross sea central shelf no substantial deposits are observed on the inner continental shelf this lack of grounding zone features reflects a restricted sediment supply and a relatively steady rapid retreat of the ice sheet during retreat ice flow acted independently in each major trough and on the bank tops ice retreated from victoria land basin drygalski trough before it retreated from joides basin ice remained on the bank tops shedding material into the abandoned troughs grounded ice in the central ross sea was derived predominantly from an expanded west antarctic ice sheet the ice sheet remained grounded on the continental shelf edge after retreat of ice from the western ross sea expanded ice eroded the inner shelf and deposited sheets of till on the central and outer shelf ice stream drainage shifted laterally as recorded by rounded laterally accreting ridges that separate bathymetric troughs the central ross sea is the repository for larger volumes of sediment derived from ice flow across basins of relatively thick unlithified sedimentary deposits two till sheets mark grounding zone positions in the central ross sea reflecting the higher sediment supply and a stepped deglaciation ice remained grounded on the pennell bank to the west a series of moraines marks the retreat of ice across the bank mega scale glacial lineations and other streamlined subglacial geomorphic features occur across the continental shelf primarily within the troughs the lineations substantiate the maximum reconstruction and support the interpretation of a deforming substrate beneath the outer reaches of the expanded ice sheet this deforming substrate may have contributed to the onset of deglaciation features associated with meltwater are rare or absent suggesting that basal meltwater played a minor role in retreat of the ice sheet

ross sea paleo ice sheet drainage and deglacial history during and since the lgm onshore and offshore studies show that an expanded grounded ice sheet occupied the ross sea embayment during the last glacial maximum lgm results from studies of till provenance and the orienta

triple water isotopologue record from wais divide antarctica controls on glacial interglacial changes in 17oexcess of precipitation measurements of the 17oexcess of h2o were obtained from ice cores in west and east antarctica combined with previously published results from east antarctica the new data provide the most complete spatial and temporal view of antarctic 17oexcess to date there is a steep spatial gradient of 17oexcess in present day precipitation across antarctica with higher values in marine influenced regions and lower values in the east antarctic interior there is also a spatial pattern to the change in 17oexcess between the last glacial maximum lgm and holocene periods at coastal locations there is no significant change in 17oexcess at both the west antarctic ice sheet divide site and at vostok east antarctica the lgm to early holocene change in 17oexcess is about 20 per meg atmospheric general circulation model gcm experiments show that both the observed spatial gradient of 17oexcess in modern precipitation and the spatial pattern of lgm to early holocene change can be explained by kinetic isotope effects during snow formation under supersaturated conditions requiring a high sensitivity of supersaturation to temperature the results suggest that fractionation during snow formation is the primary control on 17oexcess in antarctic precipitation variations in moisture source relative humidity play a negligible role in determining the glacial interglacial 17oexcess changes observed in antarctic ice cores additional gcm experiments show that sea ice expansion increases the area over which supersaturating conditions occur amplifying the effect of colder temperatures temperature and sea ice changes alone are sufficient to explain the observed 17oexcess glacial interglacial changes across antarctica

holocene palaeoenvironmental reconstruction in norteastern brazi inferred from polen charcoal and carboon isotope records soils in the barreirinhas region maranhao state were sampled for 613 c analysis and buried charcoal fragments in the soils were radiocarbon dated three soil profiles collected in forested areas around the lagoa do caqo and one in a woody savanna mixture of non arboreal and arboreal species located approximately 10 km southeast of the lagoa were studied a high resolution pollen record was obtained from lake sediments showing that forest vegetation was predominant in the area in the early holocene from approximately 10 000 14c yr bp the pollen spectrum gradually changed suggesting the dominance of open savanna communities these were transformed to a more forested landscape woody savanna from approximately 7500 yr bp the lake sediments also record evidence of fire indicated by buried charcoal particles at several soil depths during the holocene the 613 c analysis of soil organic matter som indicates that from between approximately io0000 yr bp and 9000 yr bp to 4000 yr bp a woody savanna

application of tandem accelerator mass spectrometer dating to late pleistocene holocene sediments of the east antarctic continental shelf abstract glacial recession from the antarctic continental shelf is recorded by glacial marine diamictons sands and overlying siliceous oozes in order to clarify the chronology for this sequence use was made of the university of arizona tandem accelerator mass spectrometer tams for 14 c dating small samples of benthic and planktonic foraminifera were selectively removed from diamictons graded sands and surface sediments which were recovered from the wilkes land continental shelf and slope east antarctica organic carbon was also utilized as a source for tams dating of the siliceous oozes and muds uncorrected ages varied from 14 260 140 to 3230 200 yr b p carbon fixed by phytoplankton and foraminifera is strongly influenced by old glacial derived co 2 thus reservoir corrections of up to 5500 yr are needed for the 14 c dates iceberg turbation reworks foraminifera so that dates from resulting deposits diamictons are interpreted as maximum ages the consistency of corrected ages from the shelf along with the sedimentologic interpretation suggests a rather recent recession perhaps mid holocene for this portion of the east antarctic ice sheet further application of the tams method should help clarify other problems concerning the late quaternary glacial history of antarctica

factors influencing the distribution of diatoms and other algae in the ross sea quantitative microscopic analyses of sediment trap samples collected in the ross sea between january 1990 and february 1992 reveal striking temporal and spatial differences in algal bloom composition and size trap samples from the southwestern ross sea site a 76 30 s 167 30 e were dominated by the diatom fragilariopsis curia maximum of 92 a species associated with both sea ice and the retreating ice edge in the ross sea this species was probably seeded by melting congelation ice highest flux of diatom valves to both upper and lower traps in the 1991 1992 season occurred as a distinct event in mid february 1991 after which flux decreased by 1 to 3 orders of magnitude as overall flux decreased an increase in relative abundance of chaetoceros resting spores and the open water species thalassiosira antarctica was observed in the lower trap suggesting some localized lateral advection in the south central ross sea site b 76 30 s 175 w algal diversity was much higher with a greater contribution of nondiatom material the prymnesiophyte phaeocystis antarctica dinoflagellates and cysts of unknown affinity were much more common than at site a as were the diatoms fragilariopsis cylindrus fragilariopsis kerguelensis and thalassiosira gracilis highest diatom flux occurred later february 20 to march 6 1991 at this site and was an order of magnitude lower as compared to maximum flux at site a distinct differences in bloom size and composition between sites a and b may be a function of upper water column structure differences in the amount of sea ice melting and the type of sea ice present at the time of ice breakout congelation versus pack ice despite rich surface productivities lower silica flux to the seafloor at site b results from the higher proportion of nonsiliceous algae at site c 72 30 s 172 30 e in the northwestern ross sea diatoms again dominated algal flux however assemblage composition differed from that observed at both sites a and b relative abundance of f curta was lower averaging 60 70 while the remainder of the assemblage was made up of f cylindrus other more robust species of fragilariopsis and chaetoceros resting spores algal flux at site c is intermediate in style between sites a and b significantly spatial differences in diatom assemblages noted above appear to be reflected in seafloor surface sediments suggesting that downcore diatom data provide an interpretable record of paleoproductivity in the ross sea

stability of tunnels according to depth and variability of rock mass parameters abstract even with the most recent advances in rock mechanics the stability assessment of underground tunnels continues to involve many uncertainties in the parameters which can significantly affect the calculated factors of safety in the present work a straight characterization which can help to evaluate the risk of a tunnel collapse with respect to the depth of excavation is proposed following a consolidated limit analysis approach and by means of the hoek brown failure criterion the galleries are divided into shallow intermediate and deep according to the variability of the mechanical parameters of the rock mass with depth a solution to the problem of impending collapse in the case of variable rock properties is proposed and examples are presented and discussed both from an analytical and a numerical standpoint

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

2d and 3d stability analysis of tunnel roof collapse in stratified rock a kinematic approach abstract this paper aims to predict the potential roof collapse of deep tunnels subjected to water table level changes and deterioration of rock overlying the tunnel crown the effect of partly weathered rock masses is represented with lower mechanical parameters meanwhile the pore water pressure is taken as external loads acting on the rock bank below the water table without consideration of capillary effect under the combined effects of the above two conditions a novel and comprehensive failure mechanism is postulated for analyses of roof stability of tunnels both two dimensional 2d and three dimensional 3d collapse mechanisms formed by multi surfaces are proposed in kinematic analyses where upper bound solutions of the failure mechanism are derived based on variational principle and stepwise optimization technique validation of the proposed approach is carried out which showed consistencies of failure mechanisms with analytical and numerical results presented in published literatures parametric studies with rectangular and circular tunnel cross sections are also conducted in 2d and 3d analyses so as to depict the effect of weathered parameters and pore water on incipient falling blocks the output from these parametric studies could potentially provide useful reference for engineers in the design and construction of deep buried tunnels

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

extreme avalanche runout a comparison of empirical models the prediction of snow avalanche runout distances and the probability of exceeding the predicted positions is the first and most important step required before making decisions about placement of facilities or control structures in snow avalanche prone terrain there are two main prediction methods for calculating runout distances 1 procedures linked to the selection of friction coefficients in avalanche dynamic models and 2 empirical statistical prediction based on terrain parameters for a set of extreme runout distances for the mountain range in question within the second method there are presently two competing empirical approaches to prediction i ordinary least squares regression analysis related to angles measured for the path profile in question and ii extreme value prediction of runout based on a gumbel distribution of a dimensionless terrain parameter in this paper a comparison of the two empirical methods with emphasis on the slope steepness in the runout zone is provided the comp

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

glacial interglacial variations in methanesulfonate msa in the siple dome ice core west antarctica methanesulfonate msa in the siple dome ice core is a record of the deposition of biogenic sulfur to the west antarctic ice sheet covering the past 100 kyr siple dome msa levels were low during the last glacial maximum and increased to higher holocene levels with a several kyr lag relative to the deglacial warming the positive correlation between msa and temperature at siple dome is similar to that in greenland ice cores renland gisp2 and grip and stands in contrast to the negative correlation observed at vostok east antarctica the siple dome msa data suggest that the sign of the high latitude dust sulfur climate feedback is negative at least for the pacific sector of the high latitude southern ocean these results challenge the idea that fertilization by increased dust deposition led to widespread increased dms emissions from this region of the glacial southern ocean

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

using the sunspot cycle to date ice cores for many ice cores the snow accumulation rate is too low to preserve annual stratigraphy precluding direct measurement of annual layer thickness for selected holocene sections of the taylor dome core east antarctica we instead use high resolution 10be measurements to establish a nominal 11 year thickness taking advantage of the solar cycle in cosmogenic isotope production we compare measured thicknesses with the layer thickness profile predicted by a finite element ice flow model the results are in good agreement supporting the assumption that the length of the solar cycle has remained essentially constant throughout the holocene for ice cores where annual layers are not preserved the 10be 11 year layer method can be used as an independent check on flow model estimates of layer thickness and to estimate past accumulation rates it should be possible to accurately date ice cores by counting 11 year layers detected with continuous high resolution 10be measurements

holocene sediment records from the continental shelf of mac robertson land east antarctica geochemical records are presented for five sediment cores from basins on the continental shelf of mac robertson land east antarctica the cores contain 2 4 m thick sequences of hemipelagic siliceous mud and ooze smo deposited under seasonally open marine conditions the inner and middle shelf smo sequences are massive dark olive green material whereas the outer shelf smo sequences are dark olive material interspersed with light olive green layers 1 10 cm thick the biogenic material is dominated by marine diatoms including fragilariopsis curta fragilariopsis cylindrus and chaetoceros spp in the dark colored smo and corethron criophilum in the light colored layers radiocarbon dates suggest that the cores provide continuous accumulation records extending from 1 kyr before present b p back as far as 4 15 kyr b p with estimated accumulation rates of 0 07 5 mm yr 1 the three core records from the middle and outer shelf suggest six episodes of increased accumulation of biogenic material at 5 5 kyr b p all three cores 1 2 and 6 2 kyr b p two of the three cores and 3 8 and 10 8 kyr b p one core most of which coincide with corethron layers we interpret these features as the result of enhanced diatom production over the outer shelf possibly related to climatic warm periods the absence of such features in the inner shelf core records is thought to reflect a relatively constant level of seasonal diatom production in adjacent waters maintained by a coastal polynya

oxygen isotope δ18o evidence of holocene hydrological changes at signy island maritime antarctica a record of holocene hydrological changes has been produced from variations in oxygen isotope composition delta 18 o preserved in freshwater lake sediments from maritime antarctica small amounts 5 of authigenic carbonate have been extracted from a non marl sediment core from sombre lake signy island 60 degrees 43 s 45 degrees 38 w oxygen isotope and particle size analysis provide a sensitive record of hydrological events in the lake arising from local and regional climate phenomena the climate affects delta o 18 through snowpack volume and glacier activity in the catchment lakewater temperatures the input versus evaporation balance and the duration of seasonal lake ice cover the most depleted negative delta o 18 values are associated with influxes of meltwater at times of glacier advance or retreat enriched positive delta o 18 values occur during more arid warmer conditions with longer periods of open water in summer this isotope record can be used to determine century scale to decadal variability in air circulation and moisture origin strong similarities with other holocene proxy records from the weddell sea and antarctic peninsula region are apparent including the mid holocene climate optimum followed by the neoglacial and most recently late twentieth century climatic warming the oxygen isotope record from sombre lake illustrates the importance of remote islands in contributing to our understanding of teleconnections in atmospheric and oceanographic circulation sea ice extent air temperatures and precipitation in the southern ocean

estimating extreme avalanche runout for the columbia mountains and fernie area rocky mountains of british columbia canada extreme snow avalanche runout is typically estimated using a combination of historical and vegetation records as well as statistical and dynamic models the two classes of statistical models and runout ratio are based on estimating runout distance past the point which is typically defined as the point where the avalanche slope incline first decreases to 10 the parameters for these models vary from mountain range to mountain range in canada and runout ratio parameters have been published for the combined rocky and purcell mountains and for the british columbia coast mountains despite active development no suitable tall avalanche path model parameters have been published for the columbia mountains or for the lizard range area around fernie b c using a dataset of 65 avalanche paths statistical model parameters have been derived for these regions

the taylor dome antarctic 18o record and globally synchronous changes in climate abstract the 18 o 16 o profile of a 554 m long ice core through taylor dome antarctica shows the climate variability of the last glacial interglacial cycle in detail and extends at least another full cycle taylor dome shares the main features of the vostok record including the early climatic optimum with later cool phase of the last interglacial period in antarctica taylor dome 18 o fluctuations are more abrupt and larger than those at vostok and byrd station although still less pronounced than those of the greenland gisp2 and grip records the influence of the atlantic thermohaline circulation on regional ocean heat transport explains the partly north atlantic character of this antarctic record under full glacial climate marine isotope stage 4 late stage 3 and stage 2 this marine influence diminished and taylor dome became more like vostok varying degrees of marine influence produce climate heterogeneity within antarctica which may account for conflicting evidence regarding the relative phasing of northern and southern hemisphere climate change

magnitude and geographic variation of the radiocarbon content in antarctic marine life implications for reservoir corrections in radiocarbon dating abstract radiocarbon age estimates on marine derined materials from the antarctic appear old in comparison with the terrestrial radiocarbon timescale as a result of significantly depleted 14 c concentrations in antarctic seas we review measurements of 14 c concentrations in modern antarctic marine life from south georgia the shetland islands and antarctic peninsula and suggest correction factors required to relate radiocarbon measurements on fossil marine materials from these areas to the conventional radiocarbon timescale for dates based on shells seaweeds sealbones and penguin bones the minimum correction factor for south georgia is ca 750 years and for the south shetland islands and antarctic peninsula it may be up to 1250 1300 years for whalebones a minimum correction of 1000 years may apply over a wide geographic area for comparison we also review radiocarbon measurements on marine species and seawater from other sectors of the antarctic in high latitudes correction factors of ca 1400 years are generally applicable to shell seal and penguin samples

palaeoclimatic significance of late quaternary diatom assemblages from southern windmill islands east antarctica abstract the late quaternary palaeoenvironmental history of the southern windmill islands east antarctica has been reconstructed using diatom assemblages from two long well dated sediment cores taken in two marine bays the diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late pleistocene during the following glacial the windmill islands were covered by grounded ice preventing any in situ bioproductivity following deglaciation a sapropel with a well preserved diatom assemblage was deposited from 10 500 cal yr bp between 10 500 and 4000 cal yr bp total organic carbon corg and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures hydrological conditions in coastal bays were characterised by combined winter sea ice and open water conditions this extensive period of glacial retreat was followed by the holocene optimum 4000 to 1000 cal yr bp which occurred later in the southern windmill islands than in most other antarctic coastal regions diatom assemblages in this period suggest ice free conditions and meltwater stratified waters in the marine bays during summer which is also reflected in high proportions of freshwater diatoms in the sediments the diatom assemblage in the upper sediments of both cores indicates neoglacial cooling from 1000 cal yr bp which again led to seasonally persistent sea ice on the bays the holocene optimum and cooling trends in the windmill islands did not occur contemporaneously with other antarctic coastal regions showing that the here presented record reflects partly local environmental conditions rather than global climatic trends

late quaternary foraminiferal assemblages from western ross sea antarctica in relation to the main glacial and marine lithofacies abstract investigations on foraminifers from upper pleistocene holocene sediments were carried out on twelve cores from the western ross sea continental margin drygalski joides north victoria land basins as part of a progetto nazionale di ricerche in antartide p n r a multidisciplinary project data on the foraminiferal frequency species diversity tests abundance and their state of preservation were presented as a synthesis of 404 core samples to establish their relationships with the main glacial and marine lithofacies of this area a total of 126 benthic species pertaining to 73 genera have been identified just few taxa such as cibicides spp globocassidulina spp trifarina angulosa and miliammina spp being the most ubiquitous and in some cases the dominant species of these paleoenvironments two variants of neogloboquadrina pachyderma including thin and thick shelled forms have been recovered we propose to use these results to provide the degree of glacial control during the last glacial maximum and the following holocene retreat of the ice sheets high test fragmentation low diversity and density tests reflect higher glacial influence of the ice sheet in the drygalski basin whereas the decreasing percentage of fragmentation and a relative increase of density and diversity in drygalski joides and north victoria land basins indicate the paleoenvironmental passage from the ice sheet to the ice shelf condition the ice shelf retreat is well evidenced in the joides basin by a succession of levels barren of foraminifers alternating with high density levels rich in t angulosa followed by a total disappearance of the calcareous foraminifers open marine settings indicative of lower glacial influence and increased corrosiveness of the water masses is testified by the miliammina foraminiferal assemblage during the holocene in drygalski and joides basins cores on the contrary rich and abundant benthic and planktonic assemblages characterize the holocene paleoenvironment of the north victoria land area indicating that the water masses were less corrosive with respect to the other areas in addition to the glacial reworking of the tests and the dissolution due to the corrosive water mass conditions the volcaniclastic sediments recovered in the north victoria land basin cores also affected the condition of test preservation in volcaniclastic sediments older than about 20 ka bp the foraminifers concentration tends to zero and when present their tests are highly damaged or completely broken

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

effect of soil infilled joints on the stability of rock wedges formed in a tunnel roof abstract the use of an equivalent continuum for a rock mass is not always suitable for situations where the failure is structurally controlled by discontinuities as in the case of wedges in the tunnel roof in these instances discontinuum approaches are usually preferred rock joints that are filled with soft infill are likely to be the weakest planes in a rock mass having a dominant influence on its overall shear behaviour in this case the joint material model adopted for the discontinuities should be able to describe important mechanisms such as asperity sliding and shearing post peak behaviour asperity deformation and the effect of the soft infilling the latest version of a soil infilled joint model is discussed here it describes more comprehensively than previous models the occurrence of dilation and compression with lateral displacements and also represents the hardening mechanism related to asperity interference as observed in the laboratory that cannot be readily captured by the existing joint models an analytical approach for the analysis of rock wedges structurally controlled by soil infilled joints and a numerical simulation based on a metro station collapse which occurred in brazil in 2007 are presented

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

dry flowing avalanche run up and run out the prediction of run up and run out of dry flowing avalanches is very important for land use planning design of run out zone defenses and construction of risk maps in avalanche terrain in this paper we present a numerical dynamics model to predict the stop position of the tip of these avalanches when friction coefficients internal and external initial flow depth and incoming speed are specified for known path geometry in the run out zone we also compare our model to that in the swiss guidelines and to field examples the results of these calculations clearly define model differences and the implications of different choices of friction coefficients

synchronous climate changes in antarctica and the north atlantic central greenland ice cores provide evidence of abrupt changes in climate over the past 100 000 years many of these changes have also been identified in sedimentary and geochemical signatures in deep sea sediment cores from the north atlantic confirming the link between millennial scale climate variability and ocean thermohaline circulation it is shown here that two of the most prominent north atlantic events the rapid warming that marks the end of the last glacial period and the bolling allerod younger dryas oscillation are also recorded in an ice core from taylor dome in the western ross sea sector of antarctica this result contrasts with evidence from ice cores in other regions of antarctica which show an asynchronous response between the northern and southern hemispheres

the ross sea s contribution to eustatic sea level during meltwater pulse 1a abstract radiocarbon dates obtained from ross sea sediments combined with constraints on maximum ice extent based on sedimentological data and ice sheet modeling results indicate that the ross embayment antarctica is unlikely to have been a substantial contributor to meltwater pulse mwp 1a at 12 5 14c ka the ice sheet in the ross embayment during the last glacial maximum is estimated to have contained ice volume equivalent to 3 6 m eustatic sea level rise and does not show evidence of rapid retreat grounded ice advance occurred during initial late pleistocene eustatic rise and ice sheet retreat began coeval with or subsequent to mwp 1a chronological and sedimentological data from the ross embayment indicate that deglaciation in this region has occurred throughout the holocene and the maximum possible contribution of eustatic rise from the ross embayment is

evidence from diatoms for holocene climate fluctuation along the east antarctic margin diatom assemblages in two holocene sediment cores gc1 and gc2 from the mac robertson shelf east antarctica are compared with modern sedimentary diatom assemblages from the same area open marine deposition commenced in iceberg alley gc1 on the outer continental shelf 10 7 adj 14 c kyr bp

holocene climate variability from the lake sediment core in schirmacher oasis region east antarctica multiproxy approach abstract a 1 62 m sediment core was retrieved from one of the landlocked freshwater lakes l 6 in the schirmacher oasis so east antarctica during the 24th indian antarctic expedition 2004 2006 the sediment core samples were analyzed for total organic carbon toc biogenic silica bsi grain size and elemental concentration ratios mg ca and mn fe the sediment core represents the time period of last 11 6 cal ka bp as ascertained by ams 14 c radiocarbon dates the sedimentation accumulation rate variation of 13 6 cm ka from 11 6 to 10 cal ka bp reveals a warm phase followed by a low sedimentation accumulation rate of 2 9 cm ka from 10 ka bp to 3 1 ka bp indicating a cold period in the region the sedimentation accumulation rate again increased from 3 1 cal ka bp to recent with a maximum of 88 cm ka which reveals the initiation of glacier retreat or ice free conditions in the study area the total organic carbon toc is

a preliminary analysis of failure mechanisms in karst and man made underground caves in southern italy abstract natural and anthropogenic caves may represent a potential hazard for the built environment due to the occurrence of instability within caves that may propagate upward and eventually reach the ground surface inducing the occurrence of sinkholes in particular when caves are at shallow depth the effects at the ground surface may be extremely severe apulia region southern italy hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities the latter being mostly represented by underground quarries the pliocene pleistocene calcarenite a typical soft rock was extensively quarried underground by digging long and complex networks of tunnels with time these underground activities have progressively been abandoned and their memory lost so that many apulian towns are nowadays located just above the caves due to urban expansion in the last decades therefore a remarkable risk exists for society which should not be left uninvestigated the present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties aimed at exploring the progression of instability of the cavities numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass and the distinct element method for jointed rock mass conditions both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated along with the consequent failure mechanisms in particular degradation processes of the rock mass as a consequence of wetting and weathering phenomena in the areas surrounding the caves have been simulated the results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes as detected in situ has been noticed

climatic interpretation of the recently extended vostok ice records a new ice core drilled at the russian station of vostok in antarctica reached 2755 m depth in september 1993 at this depth the glaciological time scale provides an age of 260 ky bp 25 we refine this estimate using records of dust and deuterium in the ice and of 18o of o2 in the entrapped air 18o of o2 is highly correlated with insolation over the last two climatic cycles if one assumes that the egt chronology overestimates the increase of age with depth by 12 for ages older than 112 ky bp this modified age depth scale gives an age of 244 ky bp at 2755 m depth and agrees well with the age depth scale of walbroeck et al in press derived by orbital tuning of the vostok d record we discuss the temperature interpretation of this latter record accounting for the influence of the origin of the ice and using information derived from deuterium excess data we conclude that the warmest period of stage 7 was likely as warm as today in antarctica a remarkable feature of the vostok record is the high level of similarity of proxy temperature records for the last two climatic cycles stages 6 and 7 versus stages 1 5 this similarity has no equivalent in other paleorecords

preservation efficiencies and accumulation rates for biogenic silica and organic c n and p in high latitude sediments the ross sea rates of biogenic sediment accumulation biogenic silica and organic c n and p and pore water flux have been established for a variety of depositional environments in the ross sea on the basis of 14c measurements in kasten cores sediment accumulation rates ranged from 250 cm kyr 1 in the coastal basin of granite harbor to 1 2 cm kyr 1 in the shelf and slope environments of the northern and eastern ross sea burial of biogenic material was most rapid in the southwestern ross sea where biogenic silica accumulation rates ranged from 2 to 31 g cm 2 kyr 1 and organic carbon accumulation rates ranged from 0 05 to 1 4 g cm 2 kyr 1 in the northern and eastern ross sea biogenic silica and organic carbon accumulation rates typically equaled 0 02 0 03 g sio2 cm 2 kyr 1 and 0 002 0 004 g c cm 2 kyr 1 flux core measurements were used to estimate seabed regeneration rates for biogenic silica organic carbon and phosphorus pore water fluxes in general showed much less variability across the ross sea than did the biogenic accumulation rates pore water silicate fluxes in the study area ranged from 0 6 to 5 3 g sio2 cm 2 kyr 1 whereas carbon fluxes ranged from 0 1 to 1 2 g c cm 2 kyr 1 and phosphate fluxes varied from 0 006 to 0 012 g p cm 2 kyr 1 seabed preservation efficiencies were calculated for biogenic silica organic carbon and phosphorus by combining the solid phase and pore water data the seabed preservation efficiencies for biogenic silica 1 86 were greater than for organic carbon 1 71 at all nine stations examined the preferential preservation of biogenic silica relative to organic carbon also was apparent in ross sea sediments because the biogenic silica organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment water interface sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data p preservation efficiencies remained relatively high 24 65 even when the accumulation rates were low 1 2 cm kyr 1 because of the near zero phosphate fluxes out of the seabed of the total p in the seabed 0 04 0 09 wt approximately 25 existed in the form of organic p the total amount of biogenic silica accumulating on the ross sea shelf is 2 3 1012 g sio2 yr 1 which is approximately an order of magnitude less than the ledford hoffman et al 1986 estimate that was based on 210pb chronologies biogenic silica accumulation rates in the southern central and western ross sea increased during the mid and late holocene reaching their maximum values during the past 500 to 1000 years

chronology of late wisconsin ice retreat from the western ross sea antarctica lithologic data from marine sedimentary cores and accelerator mass spectrometer ams radiocarbon dates indicate that grounded ice did not advance to the western ross sea continental shelf edge during the last glacial maximum lgm a chronology of the timing of ice retreat was provided by 26 ams dates obtained from 12 cores dates ranging from 20 to 29 ka suggest that the outer continental shelf beyond ca lat 74 s was not covered by grounded glacial ice prior to and during the early stages of the lgm 14c dates just above transitions from subglacial diamictons to marine muds indicate that the area around the drygalski ice tongue was deglaciated by at least 11 5 ka the ross ice shelf reached its present day position near ross island by about 7 ka a hiatus of about 15 ka is apparent in radiocarbon dates in cores from the outer continental shelf the hiatus is interpreted to represent an absence of sedimentation caused by the presence of an ice shelf

deglacial paleoclimate of the american sector of the southern ocean late glacial holocene records from the latitude of canal beagle 55 s argentine tierra del fuego abstract paleoclimate at the time of deglaciation 14 000 10 000 14 c yr b p in different sectors of the southern ocean has followed a continuous warming trend but also warming broken by a transitory episode the younger dryas stadial event during which on the order of a millennium colder conditions prevailed evidence is from antarctic ice cores deep sea cores glacier fluctuations and pollen and beetle records reasons for the apparent nonuniformity include differential sensitivity of each sector to climatic change uneven dating control and the variable forcing response nature of biota used as climatic indicators establishing the late glacial paleoclimate of the southern ocean is of significance as it bears on comprehending the character of deglaciation in a global context with the object of investigating further the sequence of deglacial climatic events pollen stratigraphic studies at canal beagle at the southern extremity of south america were extended westward to the vicinity of ushuaia and lapataia supplementing work done previously at caleta robalo puerto harberton and bahia moat at ushuaia pollen frequency and influx records of the late glacial as well as the holocene chronologically controlled by 25 14 c age determinations are from four sphagnum empetrum mires results obtained at sites dating from 12 500 to 12 000 yr b p show late glacial climatic variability most indicative among tundra communities of grass and dwarf shrub heath is a drop both in frequency and influx of the singular arboreal component nothofagus at the time of the younger dryas when estimated summer january temperature was 3 c lower than at present at ushuaia in general terms the late glacial pattern is not unlike the northwestern european sequence sensu walker 1995 which exhibits a late glacial interstadial 13 000 11 000 yr b p followed by a younger dryas stadial 11 000 10 000 yr b p within limits of the chronology in the american sector there is no indication as shown by marine cores from the southern ocean and by antarctic ice cores that deglacial climatic events at higher latitudes of the southern hemisphere exemplified by the younger dryas lead similar events in the northern hemisphere uninterrupted warming evident in the marine and ice cores occurred after 11 600 11 500 yr b p at canal beagle in contrast the trend toward steadily milder climate indicated by continuous expansion of nothofagus frequency followed in the early holocene after 10 000 yr b p early holocene nothofagus woodland containing grass and composites replaced tundra under a warmer and drier set of conditions coupled with burning estimated summer temperature averaged 1 c higher than today and annual precipitation 100 mm less pollen influx remained generally low until about 5000 yr b p when the rate of nothofagus greatly increased together with increase in the rate of empetrum a characteristic mire component the implication is of late holocene spread of both closed forest and mire the result of greater precipitation and lower temperatures while burning abated summer temperatures evidently varied within about 0 5 c and precipitation by 100 mm compared with the present renewed albeit fluctuating glacial activity is recorded after 5000 yr b p under a variable cooler and more humid late holocene climatic regime

evidence from wavelet analysis for a mid holocene transition in global climate forcing a strong mid holocene transition has been identified by wavelet analyses in several sea ice cover records from the circum antarctic area ice core records taylor dome byrd and tropical marine records the results are compared with those previously published in a synthesis of north atlantic records and with 4 new records from the norwegian and icelandic seas and from a coastal site in ireland these new records confirm the previous pattern for the north atlantic area extend this pattern nearly to the arctic circle and include a continental record we further tested the possibility of extending this scheme using continental records from south america the holocene pattern proposed here confirms the importance of external forcing during the early holocene solar activity 1000 years cyclicity and 2500 years during the entire holocene even if the signal is disturbed by meltwater fluxes the second part of the holocene is then marked by the gradual appearance of internal forcing thermohaline circulation around 1500 years associated with a stabilisation of the signal coupling between ocean and atmosphere seems to play a fundamental role in the observed frequencies which vary accordingly in the atlantic circum antarctic and pacific areas the north atlantic area seems to be the instigator of thermohaline circulation as shown by its sensitivity to meltwater discharges during the early holocene even though each sector is independent with regards to its frequency content around 1600 years for atlantic area around 1250 years for antarctica the holocene methane pattern still under debate ruddiman w f 2003a orbital insolation ice volume and greenhouse gases quaternary science review 22 1597 1629 ruddiman w f 2003b the anthropogenic greenhouse era began thousands of years ago climatic change 61 261 293 could be explained by a more efficient thermohaline circulation around the mid holocene with an anthropogenic effect initiated at not vert similar2500 bp as shown by the inter hemispheric gradient

geochemical characterization of a marine sediment core from the joides basin ross sea antarctica abstract the chemical fractionation of ten metals al ti cr fe cd cu mn pb zn and ni is reported for a marine sediment collected in the joides basin ross sea antarctica to evaluate their mobility and availability the bcr sequential extraction procedure was applied on 11 sections of the sediment the analyses performed both by icp oes and gf aas highlighted that most of the elements were in the residual phase showing a strong binding with the matrix and a low availability the bcr sequential procedure allowed us to have an insight into the chemical properties of the sediment and provided useful information about the redox state of the sediment itself and important indication on the availability and partitioning of different metals a chemometric treatment was applied on the dataset and it showed a separation between the superficial and the deep sections of the core the first being more influenced by the presence of mn and the second by an increase in al ti fe cr and pb concentrations

snow avalanche runout from two canadian mountain ranges field measurements on maximum runout from two different mountain ranges in canada are presented and compared the coast mountains in british columbia and the rocky mountains we include a statistical analysis of topographic terrain parameters such as starting zone catchment area horizontal reach vertical drop and relevant slope angles following mcclung and mears 1991 we derived a dimensionless parameter which is a measure of runout for each avalanche and we found that the runout ratios defined below for a given mountain range obey a gumbel distribution consistent with previous results in addition we found that the runout ratios for both mountain ranges have a length scale dependence which is potentially very important for land use planning procedures the mean value of the runout ratio decreases significantly as the horizontal reach increases together with data from other mountain ranges our results show that path length effects will have to be incorporated when using statistical prediction methods for engineering zoning purposes the runout ratio is defined as the quotient of two lengths x x where is the horizontal distance from the 10 point to the maximum runout position and x is the horizontal distance from the start position to the point where slope angle first declines to 10

late pleistocene holocene sedimentary fluxes of organic carbon and biogenic silica in the northwestern ross sea antarctica eight sediment gravity cores collected from thejoides and drygalski basins were analysed in order to understand late pleistocene holocene biogenic dux changes in the ross sea driven by paleoenvironmental changes core lithologies and magnetic susceptibility depth profiles were used for core logging and stratigraphic corre lation nineteen ams radiocarbon dates of bulk organic matter were used to set chrono logical constraints and calculate sediment accumulation rates these rates which vary from 1 4 38 cm ka i were used to obtain the burial f1uxes of biogenic components the highest f uxes occur in the deepest parts o the basins toc 0 05 0 2 g cm 2 ka i biogenic silica 1 5 5 g cm 2 ka i whereas topographic highs show the lowest values toc 0 010 1 g cm 2 ka i biogenic silica 0 1 1 4 g cm 2 ka i dramatic changes in both physical properties and fluxes record the establishment of open marine sedimentation conditions which occurred first in thejoides basin and then with a delay of ca 6000 years in the drygalski basin both toc and biogenic silica ouxes increase through the holocene though slightly difterently the high f1uxes of both lobe and biogenic ba suggest that sedi ment accumulation at basin sites is strongly influenced by lateral transport

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

evidence for an early holocene climatic optimum in the antarctic deep ice core record in the interpretation of the antarctic deep ice core data little attention has been given to the holocene part of the records as far as translation of the stable isotope content in terms of temperature is concerned this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no 14c dating has yet been available for this type of sequence in this article we focus on the dome c and vostok cores and on a new 850 m long ice core drilled out at komsomolskaia by the soviet antarctic expeditions these three sites are located in east antarctica on the antarctic plateau in a region essentially undisturbed by ice flow conditions so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal our results compare well with the proximal records of southern hemisphere high latitudes and support the existence of a warmer climatic optimum between 10 and 6 ka y bp maximum temperatures are reached just at the end of the last deglaciation which confirms previous observations at high latitudes in contrast with later dates for the atlantic and hypsithermal optima in europe and north america

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

upper bound analysis of progressive failure mechanism of tunnel roofs in partly weathered stratified hoek brown rock masses abstract a reliable prediction of roof stability in stratiform or deteriorated rock banks remains a difficult problem in tunnel engineering while it is still one of the most classical engineering issues needed to be investigated so as to provide relevant reference to practical projects in previous research homogeneous geomaterials were adopted to determine the analytic solutions of collapse profile in hoek brown rock masses however when rock heterogeneities are considered in different rock layers the results gained from existing collapse mechanisms would underestimate the dimensions of falling blocks thus in this paper a new curved failure mechanism constructed with two continuous lines intersecting at the interface namely progressive failure mechanism is employed to derive the analytic solutions of the shape and region of roof collapse on the basis of upper bound theorem and variational approach the corresponding results calculated are in well accordance with the existing findings which shows sound agreement and validity of the proposed mechanism and from which one can notice that additional detaching blocks would occur apart from the initial collapsing block when there exist various rock layers with different mechanical parameters due to physical erosion or other factors such as weathering process to investigate the influence of different parameters on the range of roof failure special attention is given to some examples of square and circular tunnels and the results computed can give some instruction for practical engineering projects

distinguishing subglacial till and glacial marine diamictons in the western ross sea antarctica implications for a last glacial maximum grounding line analyses of lithology stratigraphy and tephra from marine sediment cores collected from the western ross sea during cruises eltanin 32 and 52 and deep freeze 80 and 87 indicate that subglacial till does not extend to the continental shelf edge subglacial till occurs as the lowest unit in most cores landward south of approximately 74 s while seaward of approximately 74 s the lowest diamicton units are glacial marine diamictons glacial marine diamictons are distinguished from subglacial tills by the presence of higher and more variable total organic carbon content downcore distinct tephra layers stratification higher diatom and foraminifera abundances higher sand content and radiocarbon dates in chronological order downcore sand sized tephra layers from two cores on the outer continental shelf are interpreted as single eruptive events one likely to have been derived from the mount melbourne volcano and the other from the pleiades volcano radiocarbon dates from sediment above and below the tephra layer in one of these cores df87 32 show that deposition indicative of open water conditions occurred between 22 and 26 ka in the western ross sea

geological analysis and stability assessment of a sea arch in palinuro southern italy abstract the study aims to describe the geological and geostructural layouts of an unstable sea arch located in a very attractive tourist area of southern italy on the basis of ad hoc field surveys and laboratory tests the problems of an in depth geo mechanical characterization of the rock mass are discussed in details and its main strength parameters are derived an indirect assessment of the possible geostatic stress field due to the neotectonic events which affected this sector of apennine range during the last 100 000 years is proposed and validated by means of numerical non linear fe analyses the results suggest that the presence of a lateral thrust acting into the promontory located at the back of the arch is very likely and its effects would agree well with the failures occurred in the past on the arch surfaces it is concluded that any possible intervention should be carefully designed on the basis of the highlighted factors and further investigations

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 2 sedimentologic and stratigraphic signature sedimentologic geotechnical geochemical and accelerator mass spectrometer ams radiocarbon data from two marine geologic cruises in the ross sea have allowed us to constrain facies relationships and temporal changes in the west antarctic ice sheet the selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality chirp subbottom reflection system a complex but consistent succession of facies documents a number of environments from subglacial to open marine massive mud rich diamictons have low water contents contain in places a calcareous microfossil assemblage show minimal textural variation and contain low and uniform total organic carbon values this reflects a subglacial setting this unit passes upward into a stratified thin granulated facies consisting of pelletized sandy muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble sized clasts this facies reflects the lift off zone or thin water film between the basal debris and sea floor overlying this unit are silty clays that contain a well sorted very fine grained sand component there are no coarse grains within this unit this facies is in part laminated and reflects deposition beneath an ice shelf near and away from the grounding line zone the ice shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open marine setting a sandy volcaniclastic rich subfacies marks the transition from ice shelf to open marine environments found at the calving line the 86 ams radiocarbon dates on organic matter provide an accurate chronology for 19 cores ice shelf conditions were established in the outer drygalski trough by 11 0 25 ka and perhaps earlier this transition took place in the joides basin by 10 8 ka the calving front of the ross ice shelf passed over the drygalski trough at 74 s by 9 5 0 25 ka the timing of deglaciation in the ross sea calls into question current models for the contribution of antarctic glacial ice to holocene sea level rise and suggests that recession was relatively gradual and more closely aligned with northern hemisphere deglaciation and its associated eustatic pulse

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

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

formulation of ice shelf dynamic boundary conditions in terms of a coulomb rheology coastal boundaries where fast flowing ice shelves shear past stagnant grounded ice are typically riven with surface crevasses seawater filled basal crevasses and tidal strand cracks here we formulate a boundary condition describing stress transmission through these fractured boundaries in terms of the coulomb law as a result of this formulation agreement between finite element simulations of the ross ice shelf flow and field observations is improved over agreement obtained with formulations which do not account for ice failure our results additionally suggest that shear stress transmitted through ice shelf boundaries is lower than previously thought

palaeoproductivity in the ross sea antarctica during the last 15 kyr bp and its link with ice core temperature proxies a detailed study of organic carbon content obtained from two sediment cores collected in the joides basin western ross sea antarctica was carried out the variations observed during the last deglaciation and the holocene were compared to the high resolution climatic records epica dc and taylor dome preserved in the ice the importance of the carbon content as a proxy for palaeoclimatic and palaeoenvironmental changes was investigated a dramatic decrease in the ross sea palaeoproductivity was observed during the antarctic cold reversal 12 5 14 kyr bp another decrease in total organic carbon in the second half of the holocene after 5 6 kyr bp confirms the climate worsening observed in previous studies

seasonal precipitation timing and ice core records this is a commentary on global circulation model experiments of moisture source changes in greenland urging caution in how they are applied because they have important implications for paleoclimate reconstruction from ice cores the work comes from preliminary find is of a ice core gisp2 of the authors the authors conclude that at present anomalies in greenland ice core records should not be interpreted solely in terms of source region variations the combined use of oxygen 18 d and ionic species in the new summit greenland cores should make it possible to answer empirically some of the questions raised by the gcm experiments as to the interpretation of oxygen 18 records in terms of temperature 4 refs 1 fig

glacio isostasy and glacial ice load at law dome wilkes land east antarctica abstract the holocene sea level high stand or marine limit in wilkes land east antarctica reached 30 m above present sea level at a few dispersed sites the most detailed marine limit data have been recorded for the windmill islands and budd coast at the margin of the law dome ice cap a dome of the east antarctic ice sheet eais relative sea level lowering of 30 m and the associated emergence of the windmill islands have occurred since 6900 14c corr yr b p numerical modeling of the earth s rheology is used to determine the glacio isostatic component of the observed relative sea level lowering glaciological evidence suggests that most of eais thickening occurred around its margin with expansion onto the continental shelf consequently a regional ice history for the last glacial maximum lgm was applied in the glacio isostatic modeling to test whether the observed relative sea level lowering was primarily produced by regional ice sheet changes the results of the modeling indicate that the postglacial 13 000 to 8000 14c yr b p removal of an ice load of between 770 and 1000 m from around the margin of the law dome and adjacent eais have produced the observed relative sea level lowering such an additional ice load would have been associated with a 40 to 65 km expansion of the law dome to near the continental shelf break together with a few hundred meters of ice thickening on the adjoining coastal slope of the eais up to 2000 m elevation whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes the glacio isostatic response at the windmill islands results from a combination of regional and to a lesser extent antarctic wide effects the correspondence between the holocene relative sea level lowering interpreted at the margin of the law dome and the lowering interpreted along the remainder of the wilkes land and oates land coasts 105 160 e suggests that a similar ice load of up to 1000 m existed along the eais margin between wilkes land and oates land