europa s dynamic icy crust abstract europa s icy crust records active resurfacing by tectonic and thermal processes over tens of millions of years as rapidity demonstrated by a paucity of craters tidal working causes rotational torque surface stress internal heating and orbital evolution which can explain the formation of observed tectonic crack patterns ridges crustal displacement and chaotic terrain by processes involving connections between the surface and the underlying ocean through cracks melt sites and occasional impacts these processes were recent and thus most likely continue today the permeability of the crust allows exchange of materials including oxidants and exogenic organics from the surface and endogenic substances from the ocean such that a habitable biosphere might extend to within a few centimeters of the surface continual changes in environmental conditions in the ice crust such as deactivation of individual cracks after thousands of years due to non synchronous rotation and crustal thawing releasing any trapped organisms could provide drivers for biological adaptation as well as opportunity for evolution

timing of millennial scale climate change at siple dome west antarctica during the last glacial period using atmospheric methane and the isotopic composition of o2 as correlation tools we place the dd record of ice from the siple dome west antarctica ice core on a precise common chronology with the gisp2 greenland ice core for the period from 9 to 57 ka the onset of major millennial warming events in siple dome preceded major abrupt warmings in greenland and the pattern of millennial change at siple dome was broadly similar though not identical to that previously observed for the byrd ice core also in west antarctica the addition of siple dome to the database of well dated antarctic paleoclimate records supports the case for a coherent regional pattern of millennial scale climate change in antarctica during much of the last ice age and glacial interglacial transition

pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

the radiocarbon reservoir effect in proglacial lakes examples from antarctica abstract we studied the apparently old radiocarbon ages from lakes in the dry valleys of antarctica the radiocarbon reservoir effect in these lakes results from two components the inherited age and the residence age the inherited age is derived from input of old carbon primarily from subsurface melt of adjacent glaciers the residence age comes from in situ aging of lake water in an environment sealed from the atmosphere our results indicate that surface melt of glaciers introduces little ancient carbon to the lake system because of rapid gas equilibration with the atmosphere subsurface melt in lakes with large glacier cross sectional areas at the grounding line however can contribute a significant amount of ancient carbon leading to lake bottom reservoir effects in excess of 2700 yr this value can increase to 20 000 yr immediately at the grounding line in most lakes however surface melt far exceeds that from the subsurface and dilutes the effect of ancient carbon making the inherited age relatively low residence ages generally are on the order of a few thousand years but can be as much as 10 000 yr because a residence age is reset when the lake loses its ice cover and is exposed to wind driven mixing its magnitude can provide important information about lake history

aterian lithic technology and settlement system in the jebel gharbi north western libya the aterian represents one of the multiple facets of the middle stone age msa and has become increasingly important in the context of understanding modern human origins in this paper we present the results of our study on the aterian in the jebel gharbi north western libya from a regional point perspective a total of 1567 lithic objects were analysed for this work from twelve different aterian assemblages the results of this analysis show a wide range of economic behaviour possibly suggesting different site functions within the three main areas ain zargha jefara and wadi ghan it is unlikely that any of these assemblages represents a residential site instead we argue that the assemblages in the study are more likely to be the result of a logistic land use technologically they exhibit all the distinctive features of the aterian technocomplexes coexistence between levallois and blade technology presence of tanged pieces and bifacial foliates as well as of upper palaeolithic tools together with a majority of sidescrapers and endscrapers only a combination of these features and certainly not one of them alone can characterize an assemblage as aterian

antarctic lakes suggest millennial reorganizations of southern hemisphere atmospheric and oceanic circulation the phasing of millennial scale oscillations in antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change particularly those involving the southern ocean however records of millennial scale variability from antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores some of which show little variability through that time here we present new data from closed basin lakes in the dry valleys region of east antarctica that show high magnitude high frequency oscillations in surface level during the late pleistocene synchronous with climate fluctuations elsewhere in the southern hemisphere these data suggest a coherent southern hemisphere pattern of climate change on millennial time scales at least in the pacific sector and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes

ice age storm trajectories inferred from radar stratigraphy at taylor dome antarctica the taylor dome ice core east antarctica provides a climate record that extends through the previous interglacial we use ice dynamics modeling and geochemical records to infer the local accumulation rate history a pronounced accumulation reduction occurred during the last glacial maximum lgm the spatial gradient of accumulation across the surface of taylor dome indicates the modern local prevailing storm direction radar internal layering shows that this gradient was reversed during the lgm suggesting a reorganization of synoptic weather systems occurred possibly linked to the advance and retreat of the west antarctic ice sheet

cooling of the southern high latitudes during the medieval period and its effect on enso abstract a high resolution multiproxy study performed on a marine record from se pacific off southern south america was used to reconstruct past regional environmental changes and their relation to global climate particularly to el nino southern oscillation enso phenomenon during the last 2200 years our results suggest a sustained northward shift in the position of the zonal systems i e the southern westerly wind belt and the antarctic circumpolar current which occurred between 1300 and 750 yr bp the synchrony of the latitudinal shift with cooling in antarctica and reduced enso activity observed in several marine and terrestrial archives across south america suggests a causal link between enso and the proposed displacement of the zonal systems this shift might have acted as a positive feedback to more la nina like conditions between 1300 and 750 yr bp by steepening the hemispheric and tropical pacific zonal sea surface temperature gradient this scenario further suggests different boundary conditions for enso before 1300 and after 750 yr bp

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

a temperature index model of stream flow at below freezing temperatures in taylor valley antarctica we model runoff from glaciers in the mcmurdo dry valleys antarctica with summer december january average air temperatures from 1990 to 2002 for the purpose of estimating decades to millennial scale glacial runoff into lakes fryxell hoare and bonney the relationship between summer temperatures and melt is found to be exponential near the melting temperature we propose a variety of simple models that are calibrated using measured discharge from a number of streams draining from ten glaciers in taylor valley the surface melting rate is constrained by mass balance measurements from four of the glaciers a model based solely on temperature produced good results coefficient of determination r 2 0 71 for the south facing glaciers but poor results for the north facing glaciers r 2 2 0 73 for the north facing glaciers with little change from the south facing glaciers including a wind index did not improve the correlation between modeled and measured runoff

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

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

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

regional insolation forcing of late quaternary climate change in the southern hemisphere southern new zealand positioned within the important southwesterly wind system is a prime site for examining interhemispheric linkages in climate change a series of cores drilled in the okarito pakihi peat bog now provides a continuous record of vegetation and climate change that may become a benchmark for the region the data include clear evidence for modification of the global climate change signal in the southern hemisphere by local variation in the intensity of solar radiation in agreement with the milankovitch orbital forcing hypothesis1 it is often assumed that glacial interglacial climate transitions occurred synchronously in the northern and southern hemispheres of the earth it is difficult to test this assumption because of the paucity of long continuous climate records from the southern hemisphere that have not been dated by tuning them to the presumed northern hemisphere signals2 here we present an independently dated terrestrial pollen record from a peat bog on south island new zealand to investigate global and local factors in southern hemisphere climate changes during the last two glacial interglacial cycles our record largely corroborates the milankovitch model of orbital forcing but also exhibits some differences in particular an earlier onset and longer duration of the last glacial maximum our results suggest that southern hemisphere insolation may have been responsible for these differences in timing our findings question the validity of applying orbital tuning to southern hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change

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

glacier retreat in new zealand during the younger dryas stadial the younger dryas a period of sudden cooling in the northern hemisphere about 12 900 years ago is perhaps the best known example of abrupt climate change but the global extent of the younger dryas is a topic of intense debate particularly in the record of glacial behaviour in new zealand a new reconstruction of the growth and retreat patterns of glaciers in the southern alps in new zealand at the time of the younger dryas supports the suggestion that temperature reductions in the north caused warming and glacial retreat in the southern hemisphere through a series of climate feedbacks the younger dryas during which northern hemisphere temperatures cooled drastically in just a few years is perhaps the best known example of abrupt climate change but its global extent is under debate particularly in the record of glacial behaviour in new zealand these authors present evidence for glacial retreat in new zealand during the younger dryas supporting the hypothesis that northern hemisphere climate changes caused southern hemisphere warming through a series of climate feedbacks millennial scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions the presence of the younger dryas stadial 12 9 to 11 7 kyr ago is established throughout much of the northern hemisphere but the global timing nature and extent of the event are not well established evidence in mid to low latitudes of the southern hemisphere in particular has remained perplexing1 2 3 4 5 6 the debate has in part focused on the behaviour of mountain glaciers in new zealand where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent1 2 3 the interhemispheric behaviour of the climate system during the younger dryas thus remains an open question fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period here we show that new zealand s glaciers retreated after 13 kyr bp at the onset of the younger dryas and in general over the subsequent 1 5 kyr period our evidence is based on detailed landform mapping a high precision 10be chronology7 and reconstruction of former ice extents and snow lines from well preserved cirque moraines our late glacial glacier chronology matches climatic trends in antarctica southern ocean behaviour and variations in atmospheric co2 the evidence points to a distinct warming of the southern mid latitude atmosphere during the younger dryas and a close coupling between new zealand s cryosphere and southern high latitude climate these findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the north atlantic led to a strong interhemispheric thermal gradient8 during late glacial times in turn leading to increased upwelling and co2 release from the southern ocean9 thereby triggering southern hemisphere warming during the northern younger dryas

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

glacier advance in southern middle latitudes during the antarctic cold reversal the geographic extent of cooling associated with the antarctic cold reversal is unclear dating of glacial moraines in new zealand suggests that the cooling extended into the southern mid latitudes possibly as a result of the northward migration of the southern subtropical front