a 200 000 year δ18o record of closed basin lacustrine calcite death valley california abstract a modified method from mccrea mccrea j m 1950 the isotopic chemistry of carbonates and a paleotemperature scale j chem phys 18 849 857 has been developed for analyzing carbon and oxygen isotopic compositions of lacustrine calcite in bulk saline lake sediments a two level climatic fluctuation model is suggested based on a continuous 200 000 year 18 o record of lacustrine calcite from a 186 m sediment core from badwater basin death valley california this record provides new approaches to the debate on the timing and driving forces of late quaternary climatic changes excursions in calcite 18 o track those of 18 o in sulfate in the death valley core as well as to those in marine carbonate specmap and polar ice in the summit ice core grip greenland the death valley record shows periodicities of 96 000 39 000 21 000 14 000 and 8000 years the longer term 96 000 39 000 and 21 000 years fluctuations match milankovitch orbital forcing and are thus likely to be global in origin the shorter term 14 000 and 8000 years fluctuations probably reflect regional climatic and or hydrologic forcing

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

contemporary rates of chemical denudation and atmospheric co2 sequestration in glacier basins an arctic perspective this paper presents new estimates of solute fluxes from five high arctic glacier basins in svalbard these estimates are combined with data from two other glacier basins to assess the effectiveness of chemical denudation on svalbard and to estimate rates of temporary or transient co2 drawdown we use a solute provenance model to partition solutes into marine aerosol atmospheric and crustal components and to estimate their annual fluxes crustally derived solute fluxes are equivalent to a mean chemical denudation rate of 350 meq m 2 a 1 for svalbard range 160 560 meq m 2 a 1 which lies within the global range of 94 4200 meq m 2 a 1 for 21 glacier basins in the northern hemisphere and is close to the continental average of 390 meq m 2 a 1 specific annual discharge is the most significant control upon chemical denudation in the glacierized basins and basin lithology is an important secondary control with carbonate rich and basaltic lithologies currently showing the greatest chemical denudation rates estimates of transient co2 drawdown are also directly associated with specific annual discharge and rock type on svalbard transient co2 drawdown lies in the range 110 3000 kg c km 2 a 1 whilst the range is 110 13000 kg c km 2 a 1 for the northern hemisphere glacial data set transient co2 drawdown is therefore usually low in the svalbard basins unless carbonate or basalt rocks are abundant the analysis shows that a large area of uncertainty in the transient co2 drawdown estimates exists due to the non stoichiometric release of solute during silicate hydrolysis silicate hydrolysis is particularly non stoichiometric in basins where the extent of glacierization is high which is most probably an artefact of high flushing rates through ice marginal and subglacial environments where k feldspars are undergoing mechanical comminution copyright 2000 john wiley sons ltd

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

appalachian blue ridge cover sequence ranges at least into the ordovician the first direct evidence that stratified rocks of the central core of the southern appalachian blue ridge range in age into the paleozoic comes from a pelmatozoan echinoderm column discovered within a unit directly above the murphy marble in north carolina before this discovery most geologists had considered all stratified rocks of the blue ridge east of the frontal imbricate thrust blocks to be late proterozoic or early cambrian the echinoderm fragment is in a lower amphibolite facies interbedded mica schist impure marble zone that lies directly above the murphy marble rocks above the murphy marble are dominantly turbiditic metaclastic rocks with minor carbonate and metavolcanic rocks interpreted as having formed within a successor basin unconformably above upper precambrian rift facies and lower paleozoic drift facies rocks of the laurentian passive margin an upper bound for the age of the successor basin in the murphy belt has not been established similar sequences in the talladega belt to the southwest and possibly the foothills belt to the west range at least into the devonian most appalachian tectonic models assert that during the taconic orogeny a middle ordovician synorogenic clastic wedge now located in the easternmost tennessee foreland salient was derived by erosion from the metamorphosed pre ordovician blue ridge basement and cover sequence to the east which was uplifted as part of an advancing taconic crystalline thrust wedge the presence of ordovician or younger rocks described here which were deposited east of the proposed taconic orogenic front suggests the need to modify models for taconic clastic wedge formation in the southern appalachians the results presented here also suggest that peak metamorphism in the region was post ordovician and thus was probably not contemporaneous with the taconic orogeny as previously thought

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

isotopic evidence of holocene climatic change in the san juan mountains colorado abstract the d of cellulose from 14c dated wood collected in the san juan mountains of southwestern colorado decreased by about 45 from 9600 to 3100 yr b p and an additional 25 to the present the wood samples are from trees that grew above present day tree line and reflect a time of warmer average summer temperatures these changes in d are interpreted to indicate a major change during the holocene in the sources of moisture in the seasonality of precipitation or in both

peat bank growth holocene palaeoecology and climate history of south georgia sub antarctica based on a botanical macrofossil record botanical macrofassil analysis of a more than 9000 years old radiocarbon dated peat sequence of a moss peat bank from south georgia shows a clear evolution in the vegetation seven ecological phases could be distinguished and they can be interpreted in terms of climate development during the holocene until 2200 years ago warnstorfia fontinatiopsis was the dominant moss species pointing to a wet environment lower numbers of this species in association with the presence of drier species are assumed to indicate drier periods such as occurring between ca 6000 5200 and 4400 3400 cal yr br the most prominent and definitive vegetation change took place around 2200 cal yr bp a polytilchum chollsodontium moss peat bank was formed which is still growing there today the forcing mechanism for this vegetation change is thought to be a temperature decrease rather than a precipitation decrease this conclusion is mainly based on the fact that today moss peat banks have their optimal occurrence range in the maritime antarctic a region were the mean annual temperature is ca 4 degrees c lower than on south georgia the remarkable change in the moss bank vegetation at 2200 cal yr bp raises the question whether this moment was only a short climatic deterioration or a definitive change to a cooler and wetter climate after a holocene climatic optimum period c 2008 elsevier ltd all rights reserved

retreating alpine glaciers increased melt rates due to accumulation of dust vadret da morteratsch switzerland the automatic weather station aws on the snout of the vadret da morteratsch switzerland has delivered a unique 12 year meteorological dataset from the ablation zone of a temperate glacier this dataset can be used to study multi annual trends in the character of the surface energy budget since 2003 there has been a substantial darkening of the glacier tongue due to the accumulation of mineral and biogenic dust the typical surface albedo in summer has dropped from 0 32 to 0 15 we have analysed the implications of the lowered albedo for the energy balance and the annual ablation for the 4 year period 2003 06 the decreased albedo caused an additional removal of about 3 5 m of ice calculations with an energy balance model show that the same increase in ablation is obtained by keeping the ice albedo fixed to 0 32 and increasing the air temperature by 1 7 k our analysis confirms that for retreating glaciers the deposition of dust from exposed side moraines on the glacier surface constitutes an important feedback mechanism the mineral dust stimulates the growth of algae lowers the surface albedo enhances the melt rates and thereby facilitates the further retreat of the glacier snout

holocene climate in the atlantic sector of the southern ocean controlled by insolation or oceanic circulation abstractthe holocene climate of the southern ocean is not well un derstood mainly because of the lack of high resolution reconstruc tions of ocean surface properties here we present a 12 500 yr long decadal scale record of holocene sea surface temperatures and sea ice presence from the polar front of the east atlantic southernocean the record shows gradual climate change with no abruptneoglacial cooling and an unprecedented late holocene warming the dominant forcing factor appears to be precessional insolation northern hemisphere summer insolation correlates to at least theearly to middle holocene climate trend spectral analysis revealscentennial scale cyclic climate changes with periods of 1220 1070 400 and 150 yr the record shows good correlation to east ant arctic ice cores and to climate records from south georgia andbunger oasis however the record shows out of phase behaviorwith regard to climate records from the western antarctic penin sula and the peru chile current such behavior hints at a climaticdivide through patagonia the drake passage and between westand east antarctica keywords southern ocean paleoclimate diatoms modern analogtechnique holocene insolation antarctic polar front introductionthe holocene climate variability has received less attention thanthe more dramatic changes during the last glacial period the holoceneis generally assumed to be a stable interglacial period when climatechanges in the north atlantic are transmitted to the rest of the worldthrough a strong thermohaline circulation imbrie et al 1992 thelarge uctuations of the last glacial period appear to continue into thisinterglacial although in a subdued manner bond et al 2001 the southern ocean has received even less attention than the highnorthern latitudes oceanic records are few and coarse they generallydisplay a warm early holocene followed by cooling labracherie etal 1989 pichon et al 1992 hodell et al 2001 similar to northatlantic climate e g koc and jansen 1994 high resolution recordsare restricted to antarctic ice cores which mostly display little climatevariability during the holocene jouzel et al 2001 an exception isthe taylor dome deuterium record in which the holocene appears tobe split by an abrupt cooling event ca 5 5 5 ka steig et al 1998 this cooling appears to t the late holocene global cooling trend por ter 2000 as a nonlinear response from the climate system to insolationchanges demenocal et al 2000 hodell et al 2001 high resolution holocene records available for southern oceanclimate reconstruction are rarely from the antarctic circumpolar cur rent proper e g domack et al 2001 stenni et al 2001 lamy et al 2002 with the exception of a multiproxy approach to holocene cli mate that includes a high resolution description of lithic fragments hodell et al 2001 we present data from site tn057 17 near the polar front in theeast atlantic southern ocean it is based on quantitative estimates ofsummer sea surface temperature ssst and sea ice presence sip utilizing the down core variability of diatom assemblages the recordshows good correlation to antarctic ice cores but a gradual change inphase relationships during the early holocene the record shows anin phase relationship with the ross sea region ice cores during thelate holocene the record shows an in phase relationship with the eastantarctic region ice cores antarctic polar frontthe antarctic polar front apf fig 1 is an important climateboundary in terms of air sea uxes and the heat and salt budgets ofthe oceans at the surface the apf is a steep sea surface temperaturegradient while the subsurface expression is the southern limit for sub duction of cold fresh antarctic surface water below warmer and moresaline subantarctic surface water orsi et al 1995 globally the apfcould be the southern limit of synchrony with northern hemisphereclimate broecker 1996 the apf is subject to large spring and sum mer blooms of diatoms fischer et al 2002 and achieves the largestbiogenic sedimentation rates of the diatom ooze belt of the southernocean burckle and cirilli 1987 it is these high sedimentation ratesof diatomaceous oozes and the sensitivity of diatoms especially to lightand temperature that make sites in the apf region suitable for pro ducing high resolution records of climate change

middle and late holocene paleotemperatures reconstructed from oxygen isotopes and gdgts of sediments from lake pupuke new zealand abstract quantitative holocene temperature reconstructions for southern hemisphere terrestrial environments are still restricted to few records and multi proxy methods are rarely applied to the same system here we test the applicability and comparability of temperature reconstructions inferred from different methodological approaches we combined sedimentary cellulose and diatom oxygen isotope data from lake pupuke north island new zealand to derive a record of lake water temperatures this record is complemented with mean annual air temperatures derived from the branched gdgt index mbt measured on the same sedimentary record the datasets of both reconstructions show little temperature variation for the period 1320 7110 cal bp the exceptions are a warmer period culminating between 1700 and 1600 cal bp reflected in both proxies and centennial scale intervals with cooler water temperatures at 3380 and 2750 cal bp recorded in the oxygen isotope based temperature reconstruction but not in the mbt inferred air temperature estimates we suggest that variations in lake circulation are the likely reason for deviations between temperature reconstructed from different proxies

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

glacier hydrochemistry solute provenance and chemical denudation at a surge type glacier in kuannersuit kuussuat disko island west greenland abstract in 1995 1998 han 11 km terrestrial surge of kuannersuit glacier an outlet glacier of the largest ice cap on disko island west greenland affected the catchment dramatically in order to estimate solute fluxes and provenances bulk meltwaters were sampled at the main subglacial outlet during the initial part of the quiescent phase the hydrochemistry is significantly influenced by a subglacial basaltic weathering regime with absence of carbonate minerals the results show that marine and aerosol derived solutes have minimal contribution to the total ion content whereas sequestration of atmospheric co 2 associated with carbonation of ca rich feldspar and reactive volcanic glass is more dominant than previously reported from glacierized catchments application of a sampling strategy dividing water samples into four groups to determine the content of dissolved hco 3 and co 3 2 shows that the cationic equivalent weathering rate range is 683 860 meq m 2 a 1 and solute flux ranges between 76 and 98 t km 2 a 1 the crustal denudation rate is estimated to 26 t km 2 a 1 and the transient co 2 drawdown amounts to 8500 13700 kg c km 2 a 1

carbonate and silicate weathering in two presently glaciated crystalline catchments in the swiss alps abstract we present a weathering mass balance of the presently glaciated rhone and oberaar catchments located within the crystalline aar massif central switzerland annual chemical and physical weathering fluxes are calculated from the monthly weighted means of meltwater samples taken from july 1999 to may 2001 and are corrected for precipitation inputs the meltwater composition issuing from the oberaar and rhone catchments is dominated by calcium which represents 81 and 55 of the total cation flux respectively i e 555 and 82 96 keq km 2 yr 1 the six to seven times higher ca2 denudation flux from the oberaar catchment is attributed to the presence of a strongly foliated gneissic zone the gneissic zone has an elevated calcite content as reflected by the 4 6 times higher calcite content of the suspended sediments from oberaar compared to rhone and a higher mechanical erosion rate resulting in a higher flux of suspended sediment the mean flux of suspended calcite of the oberaar meltwaters during the ablation period is 7 times greater than that of the rhone meltwaters taking the suspended calcite as a proxy for the total including sub glacial sediments weathering calcite surface area it appears that the available surface area is an important factor in controlling weathering rates however we also observe an increased supply of protons for carbonate dissolution in the oberaar catchment where the sulphate denudation flux is six times greater carbonic acid is the second important source of protons and we calculate that three times as much atmospheric co2 is drawn down short term in the oberaar catchment silica fluxes from the two catchments are comparable with each other but are 100 kmol km2 yr 1 lower than fluxes from physically comparable non glaciated basins

climatic implications of the natural variations of d h ratios in tree ring cellulose abstract natural variations in the deuterium composition of carbon bound hydrogen of cellulose nitrate from tree rings have been measured trees from edmonton have been analysed in detail and the d values of 5 year groups of rings show a strong temporal correlation with mean annual temperature at the growth site this is shown to result from the cellulose isotopic composition being related to the isotopic composition of soil water used during photosynthesis the soil water is in turn related to meteoric water which at this growth site appears to correlate temporally with mean annual temperature similar measurements from trees which grew in various areas of north america show a strong spatial correlation between d of cellulose and mean annual temperature the spatial functional relationship between d values and mean annual temperature at the growth site t is found to be d 5 5t 130 swhich compares with the spatial relationship between d of meteoric water and mean annual air temperature which is d 5 6t 100

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

a shift towards wetter and windier conditions in southern sweden around the prominent solar minimum 2750 cal a bp a variety of palaeoclimatic records show a shift towards cooler wetter and windier conditions in europe around 2800 cal a bp the shift broadly coincides with an increase of the atmospheric c 14 concentration suggesting a connection between solar activity variations and climate change here we investigate a peat record from undarsmosse in southern sweden in a previous study based on a low resolution chronology this record showed increased aeolian sand influx and sphagnum spore content around 2800 cal a bp indicating high storm activity and wetter conditions we applied the c 14 wiggle match dating technique on the same record to construct a robust chronology to evaluate the temporal relationship to solar forcing in addition we performed plant macrofossil analysis to determine local vegetation changes based on the new chronology a shift to a sphagnum dominated bog representing wetter conditions and the onset of a period with increased storminess occurred around 2700 cal a bp these changes are within age model uncertainties synchronous with climatic changes inferred from other sites in europe suggesting a shift in the larger scale atmospheric circulation possibly triggered by decreased solar activity less

hydrochemical characteristics of bulk meltwater from an entire ablation season longyearbreen svalbard the ionic and isotopic characteristics of bulk waters emanating from the cold based longyearbreen central svalbard in 2004 are examined to determine lithological hydrological and glaciological controls on water composition solute provenance and chemical denudation the geology consisted of reactive coal seams and associated sedimentary rocks acidity caused by microbial mediated oxidation of sulfides and to a lesser extent nitrogen bearing minerals was neutralized by congruent dissolution of dolomite and incongruent weathering of silicates in open system subglacial drainage channels the ablation season was divided into an early melt season a peak flow period and a late melt season the runoff distribution during these periods was 1 7 89 7 and 8 6 respectively whereas the solute flux distribution was 1 9 82 1 and 16 0 respectively comparisons between different annual solute flux estimation methods indicated that extrapolation of peak flow period data significantly underestimated both the early and late melt season solute fluxes about 3 8 of the solutes derived from sea salt spray 0 7 from acid aerosol deposition and 95 5 from crustal organic sources the physical and chemical conditions resulted in diffusion of co 2 rather than atmospheric drawdown the cation equivalent weathering rate and the crustal solute yield were 322 meq m 2 a 1 and 22 tkm 2 a 1 respectively which are within the regional range of svalbard however the chemical weathering intensity was as high as 940 meq m 3 owing to the relatively low specific discharge of 0 34 ma 1

late pleistocene holocene marine conditions in the ross sea antarctica evidence from the diatom record statistical analyses of diatom assemblages from radiocarbon dated sediment cores were used to reconstruct changing palaeoceanographic conditions in the western and west central ross sea antarctica from c 12 14c kyr bp to the present data from three kasten cores support a north to south time transgressive glacial interglacial transition assemblages at the base of each core suggest that glacial processes affecting frustule preservation were significant during the late pleistocene increasing biogenic silic and decreasing per centages of reworked species suggest that upper water column productivity instead of preservational processes increasingly dominates diatom assemblages during grounding line recession c 12to c 6 14c kyr bp a warm ing during the middle to late holocene c 6to c 3 14c kyr bp may have resulted in a spring sea ice melting prior to the annual inception of the ross sea polynya in the west central ross sea and b increased plateletice delivery due to increased melting beneath t

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

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

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

is palynology a credible climate proxy in the subantarctic pollen and spore analysis is the most successfully used palaeobotanical discipline for reconstructing holocene vegetation and climate history throughout the world subantarctic islands are very specific areas they are located in the circum antarctic southern ocean in latitudes that are under strong influence of the southern westerly winds and are characterised by a treeless phanerogam poor flora palynological research on many of these islands has resulted in diverging conclusions about how to infer climate history from pollen data in this study we compare pollen data with macrofossil data on the one hand and the palaeoenvironmental history based on a multiproxy record on the other hand of two peat sequences from two different subantarctic islands south georgia and ile de la possession iles crozet we conclude that palynology must be used with caution as a proxy for climate change on these islands especially when no other proxy data are available the upland lowland principle as it has been applied in pollen studies in the south indian ocean islands results in erroneous conclusions about climate change on ile de la possession more palaeoclimatic multiproxy and pollen studies in combination with pollen vegetation relationship studies can however contribute to a more reliable model of how to interpret pollen data in the subantarctic we want to stress that our conclusions are only based on holocene records consequently the question remains if palynology can be used as a palaeoclimatic proxy when climatic changes were more pronounced such as during the last glacial interglacial transition

paleoclimatic inferences from an isotopic investigation of groundwater in the central san juan basin new mexico groundwater from the ojo alamo and nacimiento aquifers in the central san juan basin new mexico has yielded 14c ages ranging from modern to 35 000 yr b p the pleistocene age samples are characterized by a stable isotope content about 25 lighter in d and 3 lighter in 18o than modern precipitation and groundwater we attribute this difference to a colder mean annual temperature and perhaps increased winter precipitation consideration of various factors controlling the stable isotope composition of the groundwater allows estimation of a 5 to 7 c temperature decrease during the late wisconsin accompanied by increased effective precipitation a similar estimate of the temperature change is obtained from noble gas paleothermometry these data support a model of moderately cooler late pleistocene climate in the american southwest characterized by summers with less precipitation than today but wetter winters

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

solar forced 2600 bp and little ice age highstands of the caspian sea abstract the level of the caspian sea the largest inland sea in the world has fluctuated capriciously in history with amplitudes up to 3 m in the last century to 25 m in the last millennium and to over 150 m since the last glacial there is little consensus about the causes and forecasts are contradictory mainly due to a lack of solid data about past sea levels before 1837 ad when instrumental observation started we studied the holocene turali barrier complex along the western caspian shore in dagestan russia barrier dynamics during the last 3 m sea level cycle in the past century show that only lagoonal deposits overridden by highstand barriers are suitable for dating former highstands in the holocene barrier complex we selected the most suitable sites for dating using ground penetrating radar gpr profiles outcrops and gravel pits we obtained 14 accelerator mass spectrometry ams 14c data on in situ double valved molluscs from highstand lagoonal deposits the results suggest that the last major highstands occurred around 2600 bp and in the little ice age and coincide with global cooling events associated with minima in solar activity this suggests that millennial precipitation changes in the volga river drainage basin are also forced by solar activity

a microbial driver of chemical weathering in glaciated systems glaciological processes under ice sheets provide sustainable ecosystems for microbes forming an aquatic environment through basal melting and providing nutrients and energy from bedrock microbes facilitate solute production in most earth surface environments but the balance of biotic and abiotic weathering in subglacial environment is presently unknown this study demonstrates an up to eightfold increase in dissolved major cations in biotic relative to abiotic weathering experiments using glacial sediments and meltwater this conclusion greatly expands our view of earth s biogeochemically active weathering zone by incorporating the large wet based portions of glaciated continents both at present and during earth s history the profound environmental significance is that microbial processes have the ability to maintain terrestrial chemical weathering rates in cooling climates during glacial advance

neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the north cascade mountains the most important weathering reaction that neutralizes incoming atmospheric acidity in the south cascade lake basin is weathering of calcite which occurs in trace amounts in veins on joint surfaces and as a subglacial surficial deposit although the basin is underlain by igneous and high grade metamorphic rocks weathering of plagioclase is quantitatively negligible the principal silicate weathering reaction is alteration of biotite to vermiculite these conclusions are based on mass balance calculations involving runoff compositions and on mineralogical observations for predictive modeling of the effects of increased acid deposition it is essential to identify the relevant weathering reactions feldspar weathering is commonly not an important source of solutes in alpine basins underlain by granitic rocks 30 references 2 figures 1 table

organic carbon export from the greenland ice sheet abstract glacial meltwater exports a unique type of organic carbon to marine systems distinct from non glacially derived riverine export potentially capable of stimulating downstream marine primary productivity here we describe for the first time the bulk level dissolved organic carbon doc and particulate organic carbon poc isotopic composition of glacial meltwater draining the greenland ice sheet gris these data in conjunction with an earlier study that investigated the molecular level composition of gris dissolved organic matter collectively describe the concentration radiocarbon content and lability of organic carbon in subglacial discharge from a land terminating outlet glacier during a melt season by scaling up our measurements across the ice sheet we estimate that the annual doc flux from the gris 0 08 tg y is equivalent to that from a small arctic river discharge q 3 y and that the annual poc flux from the gris 0 9 tg y may be comparable to that of a large arctic river q 200 km 3 y the doc flux is derived primarily from beneath the glacier subglacial 75 in the early season and from surface ice melt up to 100 transmitting through the subglacial environment at the peak of the meltseason the poc flux is primarily derived from the subglacial environment throughout the meltseason the early season low flow glacier discharge contains higher doc concentrations 0 5 4 1 mg l 1 and exports more enriched carbon 14 c doc 250 compared to the peak season high flow discharge when the concentrations are lower 0 1 0 6 mg l 1 and the 14 c is more depleted 14 c doc 400 conversely the poc export 1 4 13 2 mg l 1 14 c poc 250 shows no temporal variation in either concentration or radiocarbon content throughout the meltseason dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system confirming the influence of subglacial hydrology on the composition of the bulk carbon pools based on this work we conclude that 1 different mechanisms control the doc and poc flux from glacial systems 2 chemically distinct doc pools are accessed by seasonally evolving hydrological flow paths and 3 the gris can deliver labile carbon which may also be 14 c depleted to downstream proglacial and marine environments

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

an integrated palaeoenvironmental investigation of a 6200 year old peat sequence from ile de la possession iles crozet sub antarctica a 6200 year old peat sequence cored in a volcanic crater on the sub antarctic ile de la possession iles crozet has been investigated based on a multi proxy approach the methods applied are macrobotanical mosses seeds and fruits and diatom analyses complemented by geochemical rock eval6 and rock magnetic measurements the chronology of the core is based on 5 radiocarbon dates when combining all the proxy data the following changes could be inferred from the onset of the peat formation 6200 cal yr bp until ca 5550 cal yr br biological production was high and climatic conditions must have been relatively warm at ca 5550 cal yr bp a shift to low biological production occurred lasting until ca 4600 cal yr br during this period the organic matter is well preserved pointing to a cold and or wet environment at ca 4600 cal yr bp biological production increased again from ca 4600 cal yr bp until ca 4100 cal yr bp a hollow and hummock micro topography developed at the peat surface resulting in the presence of a mixture of wetter and drier species in the macrobotanical record after ca 4100 cal yr bp the wet species disappear and a generally drier acidic bog came into existence a major shift in all the proxy data is observed at ca 2800 cal yr br pointing to wetter and especially windier climatic conditions on the island probably caused by an intensification and or latitudinal shift of the southern westerly belt caused by a stronger wind regime erosion of the peat surface occurred at that time and a lake was formed in the peat deposits of the crater which is still present today c 2008 elsevier b v all rights reserved less

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

stable isotope evidence for microbial sulphate reduction at the bed of a polythermal high arctic glacier glacier beds may be host to a range of microbial communities which drive oxic waters towards anoxia along certain hydrological flowpaths chemical and isotopic signatures in meltwaters from finsterwalderbreen a polythermal glacier on sedimentary bedrock in svalbard show clear evidence for anoxia at the glacier bed increases in 34s and 18o of sulphate indicate that microbial sulphate reduction has resulted in significant decreases in sulphate concentration the 13c of the dissolved inorganic carbon dic is isotopically light 13c 8 which is consistent with the use of bedrock kerogen and or the necromass of sulphide oxidising bacteria as organic substrates for the sulphate reducing bacteria calculated rates of organic carbon mineralisation correspond to 10 of the total annual dic flux of the glacial meltwaters this microbial ecosystem is chemoautotrophically based ultimately being sustained by the kerogen and or bacterial necromass and sulphides in the bedrock this work suggests that glacier beds can be refugia for life when climatic and or atmospheric conditions are otherwise inclement and also supports the contention that microbial life is present in subglacial lake vostok

kinetic isotopic fractionation during carbonate dissolution in laboratory experiments implications for detection of microbial co2 signatures using δ13c dic laboratory experiments on reagent grade calcium carbonate and carbonate rich glacial sediments demonstrate previously unreported kinetic fractionation of carbon isotopes during the initial hydrolysis and early stages of carbonate dissolution driven by atmospheric co2 there is preferential dissolution of ca 12 co3 during hydrolysis resulting in 13 c dic values that are significantly lighter isotopically than the bulk carbonate the fractionation factor for this kinetic isotopic effect is defined as carb carb is greater on average for glacial sediments 17 4 than for calcium carbonate 7 8 for the 63 m size fraction a sediment concentration o f5gl 1 and closed system conditions at 5 c this difference is most likely due to the preferential dissolution of highly reactive ultra fine particles with damaged surfaces that are common in subglacial sediments the kinetic isotopic fractionation has a greater impact on 13 c dic at higher caco3 water ratios and is significant during at least the firs t6ho fcarbonate dissolution driven by atmospheric co2 at sediment concentrations o f5gl 1 atmospheric co2 dissolving into solution following carbonate hydrolysis does not exhibit any significant equilibrium isotopic fractionation for at least 6 h after the start of the experiment at 5 c this is considerably longer than previously reported in the literature thus kinetic fractionation processes will likely dominate the 13 c dic signal in natural environments where rock water contact times are short 6 24 h e g glacial systems headwaters in fluvial catchments and there is an excess of carbonate in the sediments it will be difficult apply conventional isotope mass balance techniques in these types of environment to identify microbial co2 signatures in dic from 13 c dic data copyright 2004

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

milankovitch paced termination ii in a nevada speleothem 1 the devils hole dh calcite record from the great basin nevada provided the first radiometrically dated time series of late pleistocene climate fluctuations in doing so dh suggested that the penultimate deglaciation termination ii t ii occurred at 142 3 ka which is 10 kyr before the associated rise in summer insolation helping to launch the causality problem for milankovitch the interpretation of the dh record has been subject to considerable discussion ever since we present the first attempt to reproduce the dh record of an early t ii in the great basin based on a stalagmite from lehman caves nevada which is 400 km northeast of devils hole our speleothem records at least the latter part of t ii over its period of growth from 133 129 ka which appears to disagree with the early timing of t ii in dh dh also exhibits important differences from many other paleoclimate records over the past two deglaciations though these are reduced somewhat after ice volume correcting dh 18o we suggest that the climatic signal in the dh record remains to be fully explained

solute acquisition in glacial melt waters ii argentiere french alps bulk melt waters with open system characteristics variations in dissolved cations total alkalinity sulphate and field ph are recorded for subglacial melt and bulk melt waters those emerging from the portal at argenticre france in peak and recession flow conditions calcium and bicarbonate are the major ions and the bulk melt waters are domonstrated to have acquired solutes by weat hering and dissolution in a system open to atmos pheric carbon dioxide subglaciaj melt waters have closed system characteristics are close to saturation with calcite and quartz and must be in near equ ilibrium with weathered particulates recession now bulk melt waters are chemi cally similar to subg lacial melt but have open system charac teristics either due to re equilibration with the atmosphere for ground water mixing

origin and fate of lake vostok water frozen to the base of the east antarctic ice sheet the subglacial lake vostok may be a unique reservoir of genetic material and it may contain organisms with distinct adaptations but it has yet to be explored directly the lake and the overlying ice sheet are closely linked as the ice sheet thickness drives the lake circulation while melting and freezing at the ice sheet base will control the flux of water biota and sediment through the lake here we present a reconstruction of the ice flow trajectories for the vostok core site using ice penetrating radar data and global positioning system gps measurements of surface ice velocity we find that the ice sheet has a significant along lake flow component persistent since the last glacial maximum the rates at which ice is frozen accreted to the base of the ice sheet are greatest at the shorelines and the accreted ice layer is subsequently transported out of the lake using these new flow field and velocity measurements we estimate the time for ice to traverse lake vostok to be 16 000 20 000 years we infer that most vostok ice analysed to date was accreted to the ice sheet close to the western shoreline and is therefore not representative of open lake conditions from the amount of accreted lake water we estimate to be exported along the southern shoreline the lake water residence time is about 13 300 years

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

landslides in blanket peat on subantarctic islands causes characteristics and global significance blanket peat on hillslopes in the british isles is known to be susceptible to mass movements a few such peat landslides had also been reported from southern hemisphere islands with climates that favour the formation of blanket bogs previous studies of peat landslides on subantarctic islands are re examined to address two primary hypotheses i that landslides in blanket peat are primarily controlled by natural intrinsic thresholds and ii that the general characteristics and failure mechanisms of the peat landslides on subantarctic islands do not differ significantly from british and irish examples peat slides on macquarie island and marion island are analysed to establish whether quantitative comparisons can be made with the stability of blanket peat in ireland the inventory surveys of the subantarctic islands indicate that there may be several hundred peat landslides perhaps three times more than in the british isles they appear to be common because of the combined effects of several factors including the constituent vegetation and the frequent moderate rainfall that promotes formation of smooth impermeable iron and organic pans at the base of the peat the absence of intense convective rainfall droughts and anthropogenic disturbance leads to the conclusion that the failures result from peat accumulation reaching natural maximum thicknesses with respect to intrinsic stability thresholds different vegetation on different slopes seems to influence the shear strength of blanket peat on macquarie island and in general the subantarctic peat landslides are shown to be visually similar but quantitatively different from irish examples

globally synchronous climate change 2800 years ago proxy data from peat in south america initial findings from high latitude ice cores implied a relatively unvarying holocene climate in contrast to the major climate swings in the preceding late pleistocene however several climate archives from low latitudes imply a less than equable holocene climate as do recent studies on peat bogs in mainland north west europe which indicate an abrupt climate cooling 2800 years ago with parallels claimed in a range of climate archives elsewhere a hypothesis that this claimed climate shift was global and caused by reduced solar activity has recently been disputed until now no directly comparable data were available from the southern hemisphere to help resolve the dispute building on investigations of the vegetation history of an extensive mire in the valle de andorra tierra del fuego we took a further peat core from the bog to generate a high resolution climate history through the use of determination of peat humification and quantitative leaf count plant macrofossil analysis here we present the new proxy climate data from the bog in south america the data are directly comparable with those in europe as they were produced using identical laboratory methods they show that there was a major climate perturbation at the same time as in northwest european bogs its timing nature and apparent global synchronicity lend support to the notion of solar forcing of past climate change amplified by oceanic circulation this finding of a similar response simultaneously in both hemispheres may help validate and improve global climate models that reduced solar activity might cause a global climatic change suggests that attention be paid also to consideration of any global climate response to increases in solar activity this has implications for interpreting the relative contribution of climate drivers of recent global warming

the ubiquitous nature of accessory calcite in granitoid rocks implications for weathering solute evolution and petrogenesis calcite is frequently cited as a source of excess ca sr and alkalinity in solutes discharging from silicate terrains yet no previous effort has been made to assess systematically the overall abundance composition and petrogenesis of accessory calcite in granitoid rocks this study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks calcite is found to be universally present in a concentration range between 0 028 to 18 8 g kg 1 mean 2 52 g kg 1 calcite occurrences include small to large isolated anhedral grains fracture and cavity infillings and sericitized cores of plagioclase no correlation exists between the amount of calcite present and major rock oxide compositions including cao ion microprobe analyses of in situ calcite grains indicate relatively low sr 120 to 660 ppm negligible rb and 87sr 86sr ratios equal to or higher than those of coexisting plagioclase solutes including ca and alkalinity produced by batch leaching of the granitoid rocks 5 co2 in di water for 75 d at 25 c are dominated by the dissolution of calcite relative to silicate minerals the correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation in longer term column experiments 1 5 yr reactive calcite becomes exhausted solute ca and sr become controlled by feldspar dissolution and 87sr 86sr by biotite oxidation some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration however the ubiquitous occurrence of calcite also suggests formation during late stage subsolidus magmatic processes this conclusion is supported by petrographic observations and 87sr 86sr analyses a review of thermodynamic data indicates that at moderate pressures and reasonable co2 fugacities calcite is a stable phase at temperatures of 400 to 700 c

millennial scale climate changes on south georgia southern ocean abstract the location of south georgia 54 s 36 w makes it a suitable site for the study of the climatic connections between temperate and polar environments in the southern hemisphere because the mass balance of the small cirque glaciers on south georgia primarily responds to changes in summer temperature they can provide records of changes in the south atlantic ocean and atmospheric circulation we use grey scale density weight loss on ignition and grain size analyses to show that the proportion of glacially eroded sediments to organic sediments in block lake was highly variable during the last 7400 cal yr b p we expect that the glacial signal is clearly detectable above noise originating from nonglacial processes and assume that an increase in glacigenic sediment deposition in block lake has followed holocene glacier advances we interpret proglacial lake sediment sequences in terms of summer climate warming and cooling events prominent millennial scale features include cooling events between 7200 and 7000 5200 and 4400 and 2400 and 1600 cal yr b p and after 1000 cal yr b p comparison with other terrestrial and marine records reveals that the south georgian record captures all the important changes in southern hemisphere holocene climate our results reveal a tentative coupling between climate changes in the south atlantic and north atlantic because the documented temperature changes on south georgia are anti phased to those in the north atlantic

terrestrial and submarine evidence for the extent and timing of the last glacial maximum and the onset of deglaciation on the maritime antarctic and sub antarctic islands this paper is the maritime and sub antarctic contribution to the scientific committee for antarctic research scar past antarctic ice sheet dynamics pais community antarctic ice sheet reconstruction the overarching aim for all sectors of antarctica was to reconstruct the last glacial maximum lgm ice sheet extent and thickness and map the subsequent deglaciation in a series of 5000 year time slices however our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub antarctic sector therefore in this paper we focus on an assessment of the terrestrial and offshore evidence for the lgm ice extent establishing minimum ages for the onset of deglaciation and separating evidence of deglaciation from lgm limits from those associated with later holocene glacier fluctuations evidence included geomorphological descriptions of glacial landscapes radiocarbon dated basal peat and lake sediment deposits cosmogenic isotope ages of glacial features and molecular biological data we propose a classification of the glacial history of the maritime and sub antarctic islands based on this assembled evidence these include type i islands which accumulated little or no lgm ice type ii islands with a limited lgm ice extent but evidence of extensive earlier continental shelf glaciations type iii seamounts and volcanoes unlikely to have accumulated significant lgm ice cover type iv islands on shallow shelves with both terrestrial and submarine evidence of lgm and or earlier ice expansion type v islands north of the antarctic polar front with terrestrial evidence of lgm ice expansion and type vi islands with no data finally we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

glaciomarine sedimentation and its paleoclimatic implications on the antarctic peninsula shelf over the last 15 000 years abstract analyses of sedimentological geochemical and micropaleontological parameters from radiocarbon dated sediment cores retrieved from the antarctic peninsula s western continental shelf reveal a detailed paleoclimatic and or paleoceanographic history over the last 15 000 radiocarbon years deglaciation of the outer shelf off anvers island commenced prior to at least 15 000 yr bp marked by the deposition of distal glaciomarine diamicton facies 2 beneath a floating ice shelf and lasted for 3800 years with increasing diatom abundance and total organic carbon toc over time a return to colder conditions occurred between 12 800 and 11 600 yr bp with a drop in toc content and diatom abundance which is coincident with the younger dryas event in the north atlantic region at this time an abrupt increase in percentage sea ice taxa as well as in the ratio of fragilariopsis curta fragilariopsis cylindrus thalassiosira antarctica suggests renewed ice shelf advance in contrast the inner shelf was deglaciated somewhat later about 11 000 yr bp that is 3000 years after the outer shelf prior to 11 000 yr bp deposition of proximal glaciomarine diamicton facies 1 close to the grounding line under a floating ice shelf and or persistent sea ice may have occurred on the inner shelf after this date deposition of distal glaciomarine diamicton facies 2 followed a climatic optimum is recognized between 6000 and 2500 yr bp coinciding with a mid holocene climatic optimum from several other antarctic sites e g the palmer deep during this time as the glacial system receded from the shelf greatly enhanced primary productivity occurred in open marine conditions resulting in the deposition of diatomaceous mud facies 3 and causing post depositional dissolution of calcareous benthic and planktonic foraminifers in sediment around 2500 yr bp the onset of the neoglacial diatomaceous sandy mud facies 4 characterized by a decrease in toc and diatom abundance reflects the formation of more extensive and seasonally persistent sea ice as evidenced by an increase in percentage of sea ice taxa and in the ratio of f curta f cylindrus t antarctica our results provide evidence of climatic change on the antarctic peninsula s western shelf that helps to refine the existence and timing of late pleistocene and holocene millennial scale climatic events in the southern hemisphere

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

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

elevated stream trace and minor element concentrations in the foreland of receding tropical glaciers globally the ongoing retreat of mountain glaciers will ultimately diminish fresh water supplies this has already begun in watersheds with greatly reduced glacial coverage still unknown are the affects of glacial retreat on downstream water quality including the threats to human and ecosystem health in the cordillera blanca retreating glaciers have exposed sulfide rich rock outcrops negatively affecting the quality of the glacial meltwater this study has evaluated glacial melt stream hydrogeochemistry in the sulfide bearing rio quilcay watershed 927 0 s 7722 0 w during the 2008 dry season surface water samples were collected from the upper 12 km of the watershed during the 2008 dry season dissolved 0 4 lm and unfiltered acidified ph 2 al co cu fe ni mn pb zn and dissolved major ions and organic c doc concentrations were quantified and ph and temperature were measured in the field twenty of 22 stream samples had ph values below 4 generating significantly p 0 01 a 0 05 greater cation denudation normalized to discharge than other worldwide glacier fed streams additionally dissolved trace and minor element concentrations were comparable to acid mine drainage non conservative dissolved element behaviors resulted from adsorption desorption reactions in tributary mixing zones at low ph values hydrous fe oxides acted as the dominant sorption surfaces the poor water quality observed in cordillera blanca headwaters coupled with the likely exposure of additional sulfide rich outcrops from ongoing glacial retreat may pose water quality challenges

subantarctic peatlands and their potential as palaeoenvironmental and palaeoclimatic archives subantarctic islands are located within the antarctic circumpolar current and the southern westerly wind belt the latter called southern westerlies making them unique terrestrial archives to investigate past changes in oceanic and atmospheric circulation patterns in the southern mid latitudes the islands are characterised by a treeless phanerogam poor flora in which bryophytes are of major importance several peat based holocene palaeoenvironmental and palaeoclimatic studies have recently been published for south georgia and ile de la possession iles crozet a range of techniques have been used in these studies mainly plant macrofossil analysis but also analyses of diatoms pollen and non pollen microfossils geochemical and geomagnetic measurements the records are chronologically constrained by radiocarbon dating this paper brings together these data in order to give an overview of the subantarctic peat based palaeoclimatic records a new plant macrofossil record for the island of south georgia is added evidence for millennial scale holocene climate variability was found for both islands of which the most striking one occurred in the late holocene however within the uncertainty of the age depth models the timing for this climate shift to wetter and or colder conditions on south georgia and windier wetter conditions on ile de la possession is different for both islands ile de la possession iles crozet seems to follow the northern hemisphere climate evolution as the event was dated to w2800 cal bp a well known climate event present in many peat based records in north western europe in contrast the south georgian late holocene climate records reveal a shift around w2200e2000 cal bp

evolution of the subglacial drainage system beneath the greenland ice sheet revealed by tracers predictions of the greenland ice sheet s response to climate change are limited in part by uncertainty in the coupling between meltwater lubrication of the ice sheet bed and ice flow1 2 3 this uncertainty arises largely from a lack of direct measurements of water flow characteristics at the bed of the ice sheet previous work has been restricted to indirect observations based on seasonal and spatial variations in surface ice velocities4 5 6 7 and on meltwater flux8 here we employ rhodamine and sulphur hexafluoride tracers injected into the drainage system over three melt seasons to observe subglacial drainage properties and evolution beneath the greenland ice sheet up to 57 km from the margin tracer results indicate evolution from a slow inefficient drainage system to a fast efficient channelized drainage system over the course of the melt season further inland evolution to efficient drainage occurs later and more slowly an efficient routing of water was established up to 41 km or more from the margin where the ice is approximately 1 km thick overall our findings support previous interpretations of drainage system characteristics thereby validating the use of surface observations as a means of investigating basal processes

solute acquisition in glacial melt waters i fjallsjokull south east iceland bulk melt waters with closed system characteristics l etude de la composition des eaux de surface cations alcalinite sulfates et ph montre des modifications par rapport aux precipitations par l acquisition de substances dissoutes provenant de l alteration et de la dissolution de debris rocheux dans un systeme ouvert aux gaz carbonique atmospherique les eaux resurgentes ont des compositions variables calcite qui peuvent provenir de l eau de surface

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

co2 evasion from the greenland ice sheet a new carbon climate feedback abstract decay of the greenland ice sheet gis figures prominently in climate change predictions but direct carbon cycle feedbacks are poorly constrained here we show that melting of the gis yields a previously unknown flux of co 2 to the atmosphere and we use a reactive transport model to examine if how and to what extent this flux will change as the ice sheet decays in a warmer world water emerges from beneath the isunnguata and russell glaciers in west greenland with co 2 partial pressures pco 2 3 10 supersaturated with respect to atmospheric equilibrium during downstream transport in the akuliarusiarsuup kuua river mineral weathering sequesters 75 of the excess co 2 as hco 3 a carbon sink on human timescales and the remaining 25 evades to the atmosphere scaled to all rivers draining the gis the evasion flux of 0 11 0 03 tg c year compares to fluxes reported for other rivers draining precambrian shield crystalline rocks and having similar dissolved carbonate systematics this flux is insufficient to influence modern day atmospheric co 2 levels and we find that higher meltwater discharge alone will cause only moderate future increases however more substantial increases could occur if meltwaters intersect basal ice known to have elevated pco 2 values worst case model scenarios yield evasion fluxes of 100 20 170 40 tg c year by 2100 these atmospheric co 2 inputs surpass those for arctic lakes and would augment by up to 25 those predicted for permafrost thaw our findings suggest that positive feedbacks linking greenhouse gas emissions arctic climate change and global warming may be stronger than previously realized

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

assessing meteoric water composition and relative humidity from18o and2h in wood cellulose paleoclimatic implications for southern ontario canada abstract an empirical model is presented that derives the initial isotopic composition of water used by terrestrial plants and the relative humidity that prevailed during photosynthesis from the isotopic composition of oxygen and carbon bound hydrogen in the plant cellulose the model uses fixed values for the fractionation factors that describe the evapotranspirative isotopic enrichment of leaf waters and the biochemical fractionations occurring during cellulose synthesis when applied to cellulose extracted from fossil plant matter the model can be used to generate quantitative estimates of the temperature and moisture regimes of the past the application of the model is demonstrated by consideration of 18o and 2h results on cellulose from fossil wood collected at brampton ontario the brampton data yield records of systematic changes in the temperature and moisture regimes of the eastern great lakes region over the past 11 500 a both mean annual temperature and photosynthetic humidity increased substantially from values much lower than the present at the end of the wisconsin stage to values higher than the present in the mid holocene the phase relation of the paleotemperature and paleohumidity curves engenders differentiation of the climatic history at brampton into four characteristic zones i a period of ameliorating climate predominantly much colder and drier than now lasting until about 7400 b p ii an early hypsithermal period of warm and dry conditions that transformed after 6000 a b p into iii the main hypsithermal time of warmth and pronounced moistness subsequent climatic detrioration led to establishment of iv cool moist conditions like the present sometime within the last few thousand years

holocene palaeoecology and climate history of south georgia sub antarctica based on a macrofossil record of bryophytes and seeds the results are presented of a detailed plant macrofossil analysis of a c 14 dated holocene organic sequence from a sub antarctic island south georgia in the peat infilling of a rock basin 31 bryophyte species and many of the principal species of the present day angiosperm flora associated with bog communities have been identified the zonation of the bryophytes and the seeds and fruits shows a striking correspondence with the sediment stratigraphy and indicates five ecological phases the first four reflect a succession from a minerotrophic shallow pool to an ombrotrophic warnstorfia polytrichum bog after the deposition of a greyish brown layer c 2200 c 14 years bp a wet deschampsia warnstofia sanionia rostkovia bog came into existence which is still present today the ecological phases are radiocarbon dated they can be interpreted in terms of climate development during the holocene climate ameliorated rapidly at about 10 000 c 14 years bp followed by a drier period around 7000 c 14 years bp the climate became wetter and the following c 2500 years probably represent the climatic optimum between 4500 and 2600 c 14 years bp drier conditions prevailed at the study site the most striking change occurred at 2600 c 14 years bp when a marked change in vegetation and ecology indicates much wetter conditions less

early to mid holocene aridity in central chile and the southern westerlies the laguna aculeo record 34 s abstract central chile 32 35 s lies at the northern border of strong westerly influence and thus exhibits a steep precipitation gradient therefore the palaeoclimatic archives in the region are suitable for detecting past moisture changes the study of laguna aculeo 33 50 s 70 54 w presents a multiproxy holocene lake record including sedimentology geochemistry mineralogy pollen diatoms and radiocarbon dating 17 dates results indicate an arid early to mid holocene period about 9500 5700 cal yr b p after 5700 cal yr b p effective moisture increased progressively and around 3200 cal yr b p modern humid conditions were established numerous intercalated clastic layers reflect flood deposition during rainy winters a fluvial unit was deposited shortly before 9000 cal yr b p subsequently flood events were absent until 5700 but have become frequent since 3200 cal yr b p the frequency of flood layers possibly points to weak or no el nino activity during the early and mid holocene with a subsequent increase during the late holocene during the early and mid holocene the westerlies were probably blocked and hence deflected southward by the subtropical high pressure cell higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high pressure cell with intensified westerlies and possibly increased el nino activity

patterns of water chemistry and discharge in the glacier fed kennicott river alaska evidence for subglacial water storage cycles runoff from the temperate kennicott glacier in the wrangell mountains alaska displays distinctive oscillations in discharge electrical conductivity and solute concentrations during the summer melt season in addition to daily fluctuations the kennicott river undergoes quasi cyclic changes in discharge over 12 to 18 day periods probably linked to weather induced variations in melt solute variations are lagged from discharge by several days solute concentrations peak during falling discharge and reach minima during rising discharge we explore probable weathering reactions through mass balance analysis the reactions responsible for most solute fluctuations are halite dissolution and h2co3 driven calcite dissolution while sulfide oxidation and associated calcite dissolution are significant but steady components of the solute flux halite dissolution is probably limited by the glacial abrasion rate calcite dissolution by carbonation co varies directly with the calculated pco2 of the runoff this result is not expected in an environment that is poorly connected to the atmosphere a possible explanation is that respiration by subglacial microbes produces co2 at the glacier bed the extent of sulfide oxidation is limited by availability of o2 and the lack of temporal variation in this reaction suggests that this limit operates in both the distributed system and subglacial conduits all solute variations are consistent with changes in subglacial water storage and are therefore indicative of changing efficiency of subglacial drainage through time

hydrochemistry of carbonate terrains in alpine glacial settings nearly 200 analyses of meltwaters ice and snow from three alpine glacial sites in carbonate terrain are summarized and discussed in terms of sources of solutes and kinetic controls on the progress of weathering reactions most data derive from the swiss glacier de tsanfleuron which is based on cretaceous and tertiary pure and impure limestones two other sites marmolada italian dolomites and the saskatchewan glacier alberta are based on a mixed calcitic dolomitic substrate most solutes originate from carbonate dissolution moreover where pyrite is present its oxidation supplies significant sulphate and forces more dissolution of carbonate the ratios sr2 ca2 and mg2 ca2 are much higher in tsanfleuron melt waters than local bedrock a phenomenon that can be reproduced in the laboratory at small percentages of dissolution these anomalous ratios are attributed to incongruent dissolution of traces of the metastable carbonates mg calcite and aragonite these phases also provide na to solution k is argued to originate mainly by ion exchange on clays with solute ca2 quartz and very minor feldspar dissolution are also inferred locally enhanced input from atmospheric sources is recognized by high cl and associated na the progress of weathering reactions has been evaluated by the trends in the data computer modelling and some simple laboratory experiments the most dilute samples show a trend towards removal of co2 to low partial pressures c 10 5 5 atmospheres reflecting initially rapid carbonate dissolution and relatively slow dissolution of gaseous co2 later addition of atmospheric co2 or acid from pyrite oxidation allows further carbonate dissolution but solutions show a wide range of saturations and co2 pressures as high as 10 2 2 where pyrite oxidation is important in a carbonate terrain measurement of electroconductivity corrected to 25 c and alkalinity in the field allows the following preliminary deductions where meq stands for milliequivalents formula presented where s is the minimum meq ca2 mg2 produced by simple dissolution of carbonate unconnected with pyrite oxidation as with any proxy method these deductions do not remove the need for chemical analysis of waters in a given study area copyright 1994 john wiley sons ltd

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

phase relationships between antarctic and greenland climate records comparison of climate records from antarctic and greenland ice cores shows that the two regions respond asynchronously during millennial scale climate changes the apparent out of phase relationship between the records has been described as a climate seesaw in which cooling in the northern hemisphere is balanced by warming in the southern hemisphere the same relationship has also been attributed to the initiation of climate change events in the southern hemisphere rather than the north atlantic as is conventionally assumed a simple statistical approach band pass filtering combined with lag correlation tests used to examine the phase relationships in more detail shows that neither an anti phase nor a phase lag relationship adequately describes the observations whereas antarctic and greenland climate records do exhibit approximate anti phase behavior about 50 of the time they are generally in phase during cooling a phase lead of southern hemisphere climate of 1000 1600 years is statistically indistinguishable from a lag of 400 800 years whether for dansgaard oeschger heinrich or longer duration events the seesaw or southern lead appearance of the data arises from the fundamentally different characteristics of the climate time series most importantly the absence of rapid warming events in antarctica comparable to those in greenland to be consistent with the observations climate models will need to capture these characteristics in addition to reproducing the correct phase relationships

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

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

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

holocene dynamics of the southern westerly winds over the indian ocean inferred from a peat dust deposition record abstract the southern westerly winds sww play a major role in climate variability in southern hemisphere mid and high latitudes regulating rainfall ocean circulation and the southern ocean carbon sink despite their importance little is known about millennial scale changes in the sww and how they have influenced the climate system in the past and interacted with the earth s surface elements such as dust nutrients and carbon here we present a dust record from a 6 6 kyr old peat core in amsterdam island ams situated at the northern edge of the sww 37 s in the southern indian ocean mineral dust flux was used to track atmospheric dust production long distance transport and subsequent deposition dust provenance was determined from rare earth element ree and nd isotopic signatures end in the peat core compared with a reference dataset of southern hemisphere dust sources using a multi proxy mixing model the end and ree ratios show a relatively uniform mixture of ca 40 local 15 southern african and 45 southern south american dust sources since 6 6 cal kyr bp however from 1910 ad onwards there is a doubling in the contribution from southern africa 32 two mineral dust flux minima occur at 6 2 4 9 cal kyr bp and 3 9 2 7 cal kyr bp interpreted as periods with equatorward shifted and or strengthened sww at the northern edge of the wind belt conversely periods of higher dust flux at 6 6 6 2 cal kyr bp 4 9 3 9 cal kyr bp and 1 4 cal kyr bp onwards are interpreted as poleward shifted and or weakened sww these interpretations are based on the findings that higher lower wind speeds lead to enhanced less removal of distal dust on the way to ams by wet deposition and turbulence published holocene sww records at the northern edge of the wind belt 33 41 s covering south america southern africa and australia show much variability over the last 6 6 kyr we suggest this reflects complex regional climate variability in the different sh longitudinal sectors indicating that sww are not zonally homogeneous at the northern edge of the wind belt the recent shift in dust provenance is not accompanied by enhanced total dust deposition at ams we therefore suggest that human impact e g land use changes and drier climate conditions in southern africa have led to enhanced dust mobilization

bi polar ocean linkages evidence from late holocene antarctic marine and greenland ice core records a continuous 14c dated palaeoenvironmental 4000 year proxy from the antarctic peninsula glacial marine record demonstrates pronounced cycles of elevated palaeoproductivity warm events that rec

rates of chemical denudation and co2 drawdown in a glacier covered alpine catchment solute fluxes from a glacier covered alpine catchment are partitioned into components derived from sea salt acid aerosol dissolution of atmospheric co2 and crustal weathering the bulk of solute is crustally derived coupled sulfide oxidation and carbonate dissolution so cd and carbonation of carbonate minerals generate approximately equal amounts of solute chemical denudation constitutes 1 5 of solid denudation but is significantly higher than the continental average co2 drawdown by weathering reactions varies directly with discharge and suspended sediment load and inversely with meltwater p co2 if it is generally true that flushing rates control co2 drawdown in glacier covered catchments then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial interglacial time scales

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd