variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

the role of lignite in the carbon cycle of lignite containing mine soils evidence from carbon mineralisation and humic acid extractions in many mine soils lignite carbon is present as a potential carbon source for micro organisms although the establishment of an active microbial community in reclaimed mine soils was recognised to be of great importance to reclamation success the organic substrates available for micro organisms have never been characterised in terms of bioavailability the objective of this study was to examine if lignite in mine soils is decomposed and transformed during biodegradation a chronosequence of lignite rich mine substrates consisting of lignite containing overburden material parent substrate for soil development a 14 years old mine soil and a 37 years old mine soil both rich in lignite in addition to recent carbon were sampled and incubated for 16 months carbon mineralisation was monitored and the soil respired co2 subjected to 14c activity measurements additionally the 14c activity of humic acids extracted from the soils was determined with the 14c activity data lignite carbon contribution was estimated these results show that lignite was decomposed in the lignite containing parent substrate as well as in the 14 and 37 years old mine soil over the whole incubation period the average decay rate of lignite being 0 025 and 0 007 g lignite c kg 1 c year 1 lignite carbon was part of the humic acid fraction indicating that lignite in the soil is oxidized during biodegradation a higher portion of lignite can be extracted as humic acids with increasing soil development thus lignite in soil can be mineralised as well as humified and must be considered in the soil carbon cycle

further rock magnetic and chronostratigraphic results on reversal excursions during the last 50 ka as derived from northern high latitudes and discrepancies in precise ams 14c dating summary a total of five sediment cores from three sites the arctic ocean the fram strait and the greenland sea yielded evidence for geomagnetic reversal excursions and associated strong lows in relative palaeointensity during oxygen isotope stages 2 and 3 a general similarity of the obtained relative palaeointensity curves to reference data can be observed however in the very detail results from this high resolution study differ from published records in a way that the prominent laschamp excursion is clearly characterized by a significant field recovery when reaching the steepest negative inclinations whereas only the n r and r n transitions are associated with the lowest values two subsequent excursions also reach nearly reversed inclinations but without any field recovery at that state a total of 41 accelerator mass spectrometry ams 14 c ages appeared to allow a better age determination of these three directional excursions and related relative palaeointensity variations however although the three sites yielded more or less consistent chronological as well as palaeomagnetic results a comparison to another site ps2644 in the iceland sea revealed significant divergences in the ages of the geomagnetic field excursions of up to 4 ka even on basis of uncalibrated ams 14 c ages this shift to older 14 c ages cannot be explained by a time transgressive character of the excursions because the distance between the sites is small when compared with the size of and the distance to the geodynamo in the earth s outer core the most likely explanation is a difference of reservoir ages and or mixing with old 14 c depleted co2 from glacier ice expelled

an icelandic freshwater radiocarbon reservoir effect implications for lacustrine 14c chronologies a freshwater radiocarbon 14c reservoir effect fre is a 14c age offset between the atmospheric and freshwater carbon reservoirs fres can be on the order of 10 000 14c yr in extreme examples and are a crucial consideration for 14c dating of palaeoenvironmental and archaeological samples correction for a fre may be possible provided the fre and the proportion of fre affected carbon within a sample can be accurately quantified however although such correction is desirable for affected samples it is essential that such correction is accurate in order to produce useful chronological information accuracy of fre correction can be limited by spatial variation in fre within a freshwater system but despite this there is currently a paucity of information to identify and quantify such variability within affected systems here we present results of a study that investigates the effects of spatial fre variation upon dating accuracy within the freshwater system of lake m vatn northern iceland a substantial fre 10 000 14c yr has previously been identified in archaeological and modern samples from the region which shows the potential for considerable spatial variability the study also assesses the use of 13c and 15n in age correction of affected samples the results show that benthic detritus and organisms at primary trophic levels from locations within the lake are affected by a fre of at least 3500 14c yr with clear spatial variation resulting in 14c age differences of up to 7670 14c yr between samples there is a broad correlation between stable isotope values and fre within the data set however large associated uncertainties currently preclude highly accurate and precise stable isotope based quantification of the proportion of fre affected carbon within archaeological and palaeoenvironmental samples from m vatn and the surrounding region

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

evidence for multiple paleomagnetic intensity lows between 30 and 50 ka bp from a western equatorial pacific sedimentary sequence abstract a paleomagnetic study was carried out on the radiocarbon dated md97 2134 core located in the western equatorial pacific southern papua new guinea margin rock magnetic investigations revealed changes of the magnetic mineralogy along the hemi pelagic sedimentary sequence but the reconstruction of past direction and relative paleointensity variations of the geomagnetic field remained feasible four successive paleointensity drops are recorded between 30 and 50 ka bp the largest one is associated with an abrupt swing of declination and inclination interpreted as a smoothed signature of the laschamp excursion 41 ka bp the succession of four events of weak intensity between 30 and 50 ka bp introduces a complex behaviour of the geomagnetic field in the time interval spanning over the laschamp and the mono lake excursions

the hydrochemistry of lake vostok and the potential for life in antarctic subglacial lakes our understanding of lake vostok the huge subglacial lake beneath the east antarctic ice sheet has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake the north of the lake where the overlying ice sheet is thickest is characterized by subglacial melting whereas freezing of lake water occurs in the south resulting in 210 m of ice accretion to the underside of the ice sheet the accreted ice contains lower concentrations of the impurities normally found in glacier ice suggesting a net transfer of material from meltwater into the lake the small numbers of microbes found so far within the accreted ice have dna profiles similar to those of contemporary surface microbes microbiologists expect however that lake vostok and other subglacial lakes will harbour unique species particularly within the deeper waters and associated sediments the extreme environments of subglacial lakes are characterized by high pressures low temperatures permanent darkness limited nutrient availability and oxygen concentrations that are derived from the ice that provides the meltwater copyright 2002 john wiley sons ltd

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

large subglacial lake beneath the laurentide ice sheet inferred from sedimentary sequences subglacial lakes identifi ed beneath the antarctic ice sheet belong to a rare category of unexplored environments on earth s surface the key to understanding the origin and longevity of subglacial lakes is likely contained in their sedimentary sequences here we explore the nature of a sedimentary succession in a deep tectonic trough identifi ed as a prime candidate for a large subglacial paleolake the trough is the 100 km long 620 m deep christie bay located in the east arm of the great slave lake canada high resolution seismic refl ection data and short sediment cores collected in the deep trough show a 150 m thick sequence of fi sedimentary lake fi ll separating glacial ice contact deposits from draped holocene lake sediments we interpret this sequence to consist of sediments that accumulated in a subglacial lake that covered an area larger than 130 km 2 the inferred presence of a subglacial paleolake is supported by results from hydrologic modeling of drainage pathways beneath the laurentide ice sheet during the last glacial maximum our data point toward the existence of a dynamic subglacial lake environment where sediments were delivered by discharge of meltwater from a subglacial water system a core sample of the sedimentary lake fi ll in christie bay may elucidate whether living organisms exist in subglacial lakes

interglacial environments of coastal east antarctica comparison of mis 1 holocene and mis 5e last interglacial lake sediment records we reconstruct terrestrial and freshwater environments of the last two quaternary interglacials in coastal east antarctica by examining multi proxy evidence in a lake sediment core the record from progress lake in the larsemann hills consists of two discrete sediment units the lower unit contains the first known evidence of antarctic coastal environments during a previous interglacial likely to be mis5e biogeochemical biological and sedimentological climate proxies revealed a productive biological community and an active hydrological regime consistent with the warmer conditions detected in continental ice cores at this time the diatom assemblage was similar to that currently found in the sub and maritime antarctic biome and included some sub antarctic endemic taxa that have not previously been reported from east antarctica this suggests southward expansion of the sub antarctic diatom biome during mis5e mosses were also present in the lake or the catchment but are rare in the region today two discrete periods of enhanced productivity show that the mis5e environment was not stable mis5e ended abruptly with a rapid transition to glacial conditions the lake was covered by a layer of firnified snow and ice and phototrophic biological activity ceased for a period of c 90 000 years the upper unit was deposited in mis1 after 3470 3687 cal yr bp after phototrophic biological production resumed lower species diversity pigment production an antarctic continental diatom assemblage and an absence of moss layers suggest cooler conditions during mis1

high resolution paleomagnetic records from holocene sediments from the palmer deep western antartic peninsula thick holocene sedimentary sections 45 m cored in the palmer deep by the united states antarctic program usap and during ocean drilling program odp leg 178 provide the first opportunity to examine past geomagnetic field behavior at high southern latitudes after removal of a low coercivity drilling overprint the sediments display a stable single component remanent magnetization two short cores that recovered the uppermost 2 6 m of sediment have inclinations that fluctuate about the present day inclination 57 measured at faraday station and several features with wavelengths of 10 to 20 cm appear to be correlative however shipboard measurements of inclination fluctuations on split core samples from three holes drilled at odp site 1098 do not correlate well with each other even though the intensity and susceptibility data correlate very well and the overall mean inclination for cores from each hole is consistent with the expected geocentric axial dipole gad inclination the correlation is improved dramatically by using inclinations measured on u channels taken from the pristine center of a split core consequently the anomalous directions and the resulting poor between hole correlation of inclinations obtained from shipboard data can be attributed to coring induced deformation which is common on the outer edge of odp piston cores and or measurement artifacts in the split core data our preferred inclination record is thus derived from u channel results the upper 25 m represents continuous sedimentation over the past 9000 yr with an average sedimentation rate exceeding 250 cm kyr 0 25 cm yr given that remanence measurements on u channels average over an interval 7 cm long we obtained independent measurements of the paleo geomagnetic field that average over only 30 yr this high resolution record is characterized by an inclination that fluctuates within 15 of the current gad inclination

paleoceanographic history around the tsugaru strait between the japan sea and the northwest pacific ocean since 30 cal kyr bp abstract the paleoceanographic history around the tsugaru strait since 30 0 cal kyr bp was reconstructed using ecological and biogeographical habitats of diatom species and q mode factor analysis of diatom flora in six piston cores at 30 0 17 5 cal kyr bp a fall in sea level and the intensification of the oyashio current caused erosion of submarine sediments near the shore in the eastern area of the strait and led to deposition of the third and second sequences of thinly laminated layers tl3 and tl2 in the japan sea at 17 5 11 5 cal kyr bp cooling intensified around the strait producing an inflow of oyashio water into the japan sea through the strait at 15 5 14 5 cal kyr bp a cold water mass around the strait developed from subarctic sea ice to arctic waters at 13 0 11 2 cal kyr bp the younger dryas cooling was clearly recorded by the increasing of oceanic cold water diatom species in the eastern area of the tsugaru strait but not in the japan sea at 15 5 13 0 cal kyr bp and 11 25 10 25 cal kyr bp the warming around the younger dryas resulted in the deposition of thinly laminated layers off shimokita in the eastern area of the strait at 9 5 cal kyr bp the oyashio current water intruded into deep depths in the mixed water region off sanriku at 9 5 7 0 cal kyr bp the fluctuation of 1 5 kyr intervals in the strength of the tsushima warm current system in the japan sea was initiated

effects of extreme heating on the elemental and isotopic compositions of an upper cretaceous coal abstract intrusion of igneous sills into coal seams in the maastrichtian vermejo formation of colorado new mexico rapidly and severely altered the organic matter content of the coal organic carbon concentrations drop from 65 in coal samples distant from sills to between 5 and 38 in coal samples close to a sill changes in organic matter c n ratios and 13 c values relative to distance from the sill indicate preferential losses of isotopically light forms of carbon from the coal the relatively high toc concentration elevated c n ratio and more negative 13 c value of coal closest to the sill suggest that rapid pyrolysis immobilized the thermal products as partially graphitized or mineral forms of carbon

a review of coastal palaeoclimate and relative sea level reconstructions using δ13c and c n ratios in organic material holocene reconstructions of relative sea level rsl and environmental change in the coastal zone have become progressively more numerous since the importance of assessing possible future sea level rises has become apparent traditionally this has been achieved using a combination of biological and physical indicators e g pollen diatoms foraminifera grain size etc in some circumstances microfossils can be rare or absent from holocene sediments and in these cases carbon isotope ratios 13c and organic carbon to total nitrogen ratios c n can be used because they have the potential to provide information as to the origin of organic material preserved in coastal environments the distinction in 13c and c n of the various sources of carbon to estuarine sediments has led to its wide use as a tracer of carbon pathways and storage in estuaries more recently these techniques have been applied to holocene sediments to decipher changes in palaeocoastal environments and thus position relative to sea level and or palaeoriver discharge which have direct relevance to palaeoclimate this paper reviews the studies that have utilised this technique and explores examples from a wide range of coastal environments saltmarshes estuaries lagoons isolation basins and fjords it also discusses the potential alteration of geochemical signatures as a result of decompositional processes organic matter decomposition has been shown to change sediment 13c and c n values and thus an understanding of the processes involved is necessary in order to have confidence in the palaeoenvironmental interpretation of holocene 13c and c n decompositional shifts in c n and particularly 13c can occur over a relatively short time period however it is the direction of change in 13c and c n rather than absolute values that is key for interpreting changes in relative sea level and thus such changes are commonly preserved

submarine landslide identified in md179 cores off joetsu area eastern margin of the sea of japan abstract gas hydrate is exposed on the sea floor and is buried in shallow sediments in the off joetsu area at the eastern margin of the sea of japan sediment cores recovered from topographic highs of the joetsu knoll and umitaka spur show pockmarks and mounds formed by gas hydrate dissociation but those from the un named ridge have no such topographic features all topographic highs and pockmarks mainly comprise bioturbated layers interbedded with thinly laminated tl layers which are common sea of japan sediments recovered sediments are however mostly disturbed by submarine landslides showing tilted horizons faults slump folds and breccia except that from the un named ridge the timing of events is well constrained by identification of the number of tl layers in some sediment cores landslides occurred both during the cold glacial period of the late mis3 to the last glacial maximum lgm and during the warm interglacial period of the post lgm all were caused by the explosive rise of gas hydrate formed at very shallow depths of the sea bottom by the supply of gas from the depth of the gas hydrate stability zone through gas chimney passages developed under the pockmarks seismic activity demands consideration as a factor because the off joetsu area is tectonically active

a high resolution relative paleointensity record from the gerlache boyd paleo ice stream region northern antarctic peninsula herein we document and interpret an absolute chronological dating attempt using geomagnetic paleointensity data from a post glacial sediment drape on the western antarctic peninsula continental shelf our results demonstrate that absolute dating can be established in holocene antarctic shelf sediments that lack suitable material for radiocarbon dating two jumbo piston cores of 10 m length were collected in the western bransfield basin the cores preserve a strong stable remanent magnetization and meet the magnetic mineral assemblage criteria recommended for reliable paleointensity analyses the relative paleomagnetic intensity records were tuned to published absolute and relative paleomagnetic stacks which yielded a record of the last 8500 years for the post glacial drape four tephra layers associated with documented eruptions of nearby deception island have been dated at 3 31 3 73 4 44 and 6 86 0 07 ka using the geomagnetic paleointensity method this study establishes the dual role of geomagnetic paleointensity and tephrochronology in marine sediments across both sides of the northern antarctic peninsula

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

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

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

impact of antarctic climate during the late quaternary records from zub lake sedimentary archives from schirmacher hills east antarctica abstract the antarctic continental margin is marked with ice free areas which are host to numerous freshwater lakes these lacustrine systems are rich in sedimentary deposits which archive in them the regional and general climatic variations these lakes respond to the seasonal variations in climate over glacial interglacial timescales and can be inferred from the sedimentary proxies in this study a 79 cm long radiocarbon dated sediment core retrieved from a peri glacial lake is analysed for elementary corg norg isotopic 13com 15nom and particle size sand silt clay the radiocarbon dated sections 0 65 cm extends up to 43 kyr bp the time series of sedimentary organic matter om proxies corg 3 5 3 c natomic ratio 11 3 and 13com 14 4 indicate that the om in this lake sedimentary record is an admixture of terrestrial and lacustrine biomass distinctly higher lower values during the holocene lgm suggests presence of terrestrial and aquatic aquatic biomass indicating ice free ice cover and warm cold holocene glacial conditions which would result in an increased decreased lake productivity and fluvial wind input of sand and clay silt higher sand content 30 24 and 15 kyr bp silt content 24 kyr bp corg and norg 24 kyr bp within the last glacial stage lgs indicates intermittent warming period in coherence with the antarctic isotope maximum aim the transition in values corg norg c n ratio 13com sand content starting at 16 6 kyr bp closely following antarctic deglaciation to reach holocene optimum values at 11 3 kyr bp documents the influence of antarctic climate on regional areas

pleistocene collapse of the west antarctic ice sheet some glacial sediment samples recovered from beneath the west antarctic ice sheet at ice stream b contain quaternary diatoms and up to 108 atoms of beryllium 10 per gram other samples contain no quaternary diatoms and only background levels of beryllium 10 less than 10 6 atoms per gram the occurrence of young diatoms and high concentrations of beryllium 10 beneath grounded ice indicates that the ross embayment was an open marine environment after a late pleistocene collapse of the marine ice sheet

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

paleogeography and paleoecology of the upper miocene zillingdorf lignite deposit austria abstract the zillingdorf deposit formed during the late miocene filling of lake pannon and contains austria s largest lignite reserves two lignite seams are present and developed within frequently flooded low lying mires in near shore environments high sulphur contents are due to the influence of the brackish water body of lake pannon during peat accumulation a transgression forced the nw se trending shoreline northeastwards differences in soluble organic matter som yield and hydrocarbon content of borehole samples and woody macrofossils are related to differences in the content and composition of free lipids of microbial origin and or hydrocarbons derived from the biogeochemical degradation of plant tissue variations of pristane phytane ratios are interpreted to reflect differences in the redox conditions of the mire peatification in an acidic and aerobic environment is further reflected by the predominance of aromatic over saturated hydrocarbons the presence of an intense complex mixture in the gc traces due to biodegradation processes high ratios for diasterenes relative to sterenes and high concentration ratios of hopanes to hop 17 21 ene of the respective samples gelification of plant tissue is governed by microbial activity as indicated by the positive relationship between gelification index and hopanoids concentration the composition of terpenoid biomarkers indicates the predominance of gymnosperms over angiosperms and increasing proportions of angiosperms in the peat forming vegetation with decreasing depth in the upper seam from the sesqui and diterpenoids present in the lignite and fossil wood remnants a predominant role of species of the coniferales families cupressaceae taxodiaceae are concluded the preservation of plant tissue is governed by the presence absence of decay resistant gymnosperms a general influence of the floral assemblage on the isotopic composition of organic carbon of the lignite 13c 27 2 to 24 6 is proposed decomposition of plant tissue and biogeochemical carbon cycling is assumed to further affect the 13c values of the lignite carbon isotope data of fossil wood remnants are consistent with their chemotaxonomical classification as gymnosperms 13c between 22 5 and 24 9 and angiosperms 13c between 25 5 and 26 6 respectively the 13c data of the extracted cellulose reveal clear differences between fossil wood from gymnosperms average 13c 20 3 and angiosperms mean 13c 22 9 the higher isotopic difference of about 3 5 between cellulose and fossil wood compared to that found in modern trees is explained by the smaller effect of 13c discrimination for cellulose when compared with wood during decomposition

on the age of the laschamp geomagnetic excursion abstract the laschamp geomagnetic excursion is a critical tie point found directly in deep sea sediment cores and revealed in polar ice as an abrupt change in the rate of cosmogenic nuclide flux despite the importance of this excursion to quantifying paleoclimate proxy records archived in sediment and ice and to providing an independent calibration of the radiocarbon calendar its timing remains poorly known previous k ar 40 ar 39 ar and u th isochron determinations from lava flows at the type locality in the massif central france vary widely are imprecise and suggest a mean age of about 46 2 2 5 ka 2 results of 6 new unspiked k ar and 13 40 ar 39 ar incremental heating experiments on subsamples from three sites on the laschamp and olby flows are concordant and give a weighted mean age of 40 4 1 1 ka 2 uncertainty including analytical sources only that is 10 younger than the previous estimates considering that the 40 k 40 ar decay constant is not known to a precision better than 2 4 the most probable radioisotopic age for the laschamp excursion is 40 4 2 0 ka 2 analytical plus decay constant uncertainties this new age for the laschamp excursion agrees precisely with that deduced from the napis 75 deep sea sediment paleointensity stack when calibrated against the gisp2 ice core chronology using the o isotopes in ice and the magnetic properties of the marine cores

theoretical framework and diagnostic criteria for the identification of palaeo subglacial lakes abstract the antarctic ice sheet is underlain by numerous subglacial lakes which comprise a significant and active component of its hydrological network these lakes are widespread and occur at a range of scales under a variety of conditions at present much glaciological research is concerned with the role of modern subglacial lake systems in antarctica another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath former ice sheets this is challenging both conceptually in identifying whether and where subglacial lakes may have formed and also distinguishing the signature of former subglacial lakes in the geological record in this work we provide a synthesis of subglacial lake types that have been identified or may theoretically exist beneath contemporary or palaeo ice sheets this includes a discussion of the formative mechanisms that could trigger onset of or drain subglacial lakes these concepts provide a framework for discussing the probability that subglacial lakes exist ed beneath other palaeo ice sheets indeed we conclude that the former mid latitude ice sheets are likely to have hosted subglacial lakes although the spatial distribution frequency and type of lakes may have differed from today s ice sheets and between palaeo ice sheets given this possibility we propose diagnostic criteria for identifying palaeo subglacial lakes in the geological record these criteria are derived from contemporary observations hydrological theory and process analogues and provide an observational template for detailed field investigations

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

mono lake excursion recorded in sediment of the santa clara valley california 1 two intervals recording anomalous paleomagnetic inclinations were encountered in the top 40 meters of research drill hole ccoc in the santa clara valley california the younger of these two intervals has an age of 28 090 330 radiocarbon years b p calibrated age 32 8 ka this age is in excellent agreement with the latest estimate for the mono lake excursion at the type locality and confirms that the excursion has been recorded by sediment in the san francisco bay region the age of an anomalous inclination change below the mono lake excursion was not directly determined but estimates of sedimentation rates indicate that the geomagnetic behavior it represents most likely occurred during the mono lake laschamp time interval 45 28 ka if true it may represent one of several recurring fluctuations of magnetic inclination during an interval of a weak geomagnetic dipole behavior noted in other studies in the region

limnological conditions in subglacial lake vostok antarctica subglacial lake vostok is located 4 km beneath the surface of the east antarctic ice sheet and has been isolated from the atmosphere for 15 million yr concerns for environmental protection have prevented direct sampling of the lake water thus far however an ice core has been retrieved from above the lake in which the bottom 85 m represents lake water that has accreted i e frozen to the bottom of the ice sheet we measured selected constituents within the accretion ice core to predict geomicrobiological conditions within the surface

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

diatoms in south pole ice implications for eolian contamination of sirius group deposits marine and nonmarine diatoms occur throughout a south pole ice core spanning the past 2000 yr similar diatoms occur in east and west antarctica at siple and taylor domes because there are no local diatom sources at these locations diatoms must have been carried by winds from coastal or extra antarctic sites our data demonstrate widespread historical eolian transport of diatoms to the antarctic ice sheets supporting the view that sirius group sediments were contaminated by late neogene diatoms long after they were deposited if so there is no reason to postulate a pliocene deglaciation event in east antarctica

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

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

metamorphosed palaeosols associated with cretaceous fossil forests alexander island antarctica fossil soils are present within mid cretaceous fluvial sediments of the fossil bluff group alexander island antarctica the palaeosols contain in situ fossil trees and rooted plants these palaeosols are typically composed of two dominant horizons an upper organic rich horizon with identifiable plant remains and a lower horizon with well developed blocky ped structures clay cutans and mottling these features are typical of modern soils in seasonally dry climates although evidence of flooding is apparent from interbedded fluvial sandstones and mudstones the palaeosols indicate that this high latitude mid cretaceous environment was predominantly seasonally dry the presence of the zeolites laumontite prehnite and pumpellyite indicates a later metamorphic overprint on the palaeosols resulting from burial diagenesis of this region at depths of about 3 8 5 2 km and temperatures of 150 170 c

late quaternary climates of east asia deduced from the total organic carbon contents of cored sediments md179 3304 3312 off joetsu city japan sea abstract total organic carbon toc and total nitrogen tn concentrations are analyzed with high temporal resolution ca 100 years for cores md179 3304 and md179 3312 taken from the japan sea off joetsu city the temporal changes in toc and tn concentrations vary quasi regularly in similar patterns the age models are formed on the basis of the dates of 14c dating marker tephra beds tl layers and marine isotope events with depth toc concentration is high in mis 1 and 5 low in mis 2 and 4 and slightly elevated in mis 3 with frequent short fluctuations this general trend is very similar to lr04 curve except for the reduced dominance of toc around the mis 5 5 substage as shown typically in mis 3 there are many peaks of toc in a short interval the details of these toc peaks can be correlated with the warm interstadials of the greenland ice core we can identify a sawtooth like decreasing trend of toc in mis 3 in contrast the decreasing trend of 18o in the ice core corresponds to an increasing trend of toc in mis 5 the most plausible explanation for the correlation of climate changes between east asia and the north atlantic is oscillation of the arctic polar front through time the detailed correspondence of toc concentrations of the japan sea sediments to other common paleoclimate proxies means that the toc concentrations of these sediments is an excellent paleoclimate record in far east asia although the genetic relationship between air temperature and biological productivity in the japan sea is as yet unknown

ridge asymmetry and deep aqueous alteration at the trench observed from rayleigh wave tomography of the juan de fuca plate using rayleigh wave tomography of noise removed ocean bottom seismometer obs data from the cascadia initiative we illuminate the structure of the upper mantle beneath the juan de fuca plate beneath the juan de fuca ridge there is strong asymmetry with a pronounced low velocity zone in the 25 65 km depth range extending to the west from the spreading axis this anomaly has velocities low enough to indicate the presence of melt the asymmetry in velocity structure and the much greater abundance of seamounts on the west flank of the ridge suggest that dynamic buoyant upwelling is important perhaps triggered by thermal or compositional anomalies beneath axial seamount in contrast there is no evidence for asymmetry in the axial zone or lower than expected velocities beneath the gorda ridge on the eastern flank of the juan de fuca ridge the shear velocity in the 25 65 depth range is higher than expected the lithosphere appears to be colder and thicker than predicted by standard plate cooling models perhaps caused by the downwelling counterpart of the upwelling on the west side of the ridge close to the trench there is a sharp decrease in shear velocity we interpret this as aqueous alteration caused by hydrothermal circulation through deep normal faults associated with bending of the plate beneath the astoria and nitinat fans where abyssal plain sediment is thickest the velocity decrease is much smaller which is consistent with a thick sediment cap that prevents hydrothermal alteration of the plate

geomagnetic intensity and inclination variations at hawaii for the past 98 kyr from core soh 4 big island a new study and a comparison with existing contemporary data abstract reliable thellier thellier paleointensity determinations were obtained from 321 out of 766 examined samples from the upper 200 units 675 m of core soh 4 drilled in the kilauea volcano the main trend of the soh 4 record is a marked decrease from values higher than present in the last 4 kyr to values about 40 smaller from about 20 kyr to the bottom of the sampled interval three main lows coinciding with shallow or negative inclinations observed in the record were identified with an excursion previously documented in hawaii and the mono lake and laschamps events for the last 15 kyr the soh 4 intensities are largely in agreement with the worldwide distribution of volcanic data in the 15 75 kyr interval the general lack of volcanic data makes comparison with the soh 4 data difficult the soh 4 record is similar to a composite record of paleointensity largely based on a recent north atlantic sedimentary paleointensity stack napis 75 the soh 4 record is also generally consistent with a record of geomagnetic field intensity obtained from a study of 36 cl in the grip ice core calculated with the assumption that the production rate of 36 cl is controlled only by the geomagnetic field one pronounced discrepancy between the different records is observed around 50 kyr bp when the sedimentary and cosmogenic based records document high intensities which are not observed in soh 4 these high intensities are also absent in a recent record based on the analyses of sea floor magnetic anomalies the histogram of vadms obtained from soh 4 is different from that obtained from the sedimentary or 36 cl based records and is more skewed than the distribution given by kono and tanaka for the last 2 5 million years

a detailed palaeointensity and inclination record from drill core soh1 on hawaii abstract a new record of absolute palaeointensity was obtained from drill core scientific observation hole 1 soh1 on kilauea volcano hawaii kilauea s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order three hundred and sixty samples were studied with the thellier thellier technique which gave 195 successful palaeointensity and 271 successful inclination determinations three geomagnetic excursions were observed which exhibited intensity reductions of about 50 initial age control from k ar and ar ar dating only constrained the total age between 20 and 120 ka the final age model was obtained by stretching the soh1 record relative to other hawaiian palaeomagnetic data this gave an age range of 0 45 ka for the flows and identified the excursions as the hilina pali mono lake and laschamp events the soh1 record of the hilina pali event is the most detailed ever incorporating data from around 40 flows this age model suggests that kilauea had a burst of activity at the soh1 site around 20 ka all available data was combined to form a composite record of palaeointensity and inclination on hawaii for 0 45 ka

technologies for retrieving sediment cores in antarctic subglacial settings accumulations of sediment beneath the antarctic ice sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies this paper briefly reviews the history of sediment sampling in subglacial environments it then outlines some of the technological challenges and constraints in developing the corers being used in sub ice shelf settings e g george vi ice shelf and larsen ice shelf under ice streams e g rutford ice stream at or close to the grounding line e g whillans ice stream and in subglacial lakes deep under the ice sheet e g lake ellsworth the key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures

exploring former subglacial hodgson lake antarctica paper ii palaeolimnology direct exploration of subglacial lakes buried deep under the antarctic ice sheet has yet to be achieved however at retreating margins of the ice sheet there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered one of these lakes hodgson lake 72 00 549 s 068 27 708 w has emerged from under more than 297 465 m of glacial ice during the last few thousand years this paper presents data from a multidisciplinary investigation of the palaeolimnology of this lake through a study of a 3 8 m sediment core extracted at a depth of 93 4 m below the ice surface the core was dated using a combination of radiocarbon optically stimulated luminescence and relative palaeomagnetic intensity dating incorporated into a chronological model stratigraphic analyses included magnetic susceptibility clast provenance organic content carbonate composition siliceous microfossils isotope and biogeochemical markers based on the chronological model we provisionally assign a well defined magnetic polarity reversal event at ca 165 cm in the lake sediments to the mono lake excursion ca 30 34 ka whilst osl measurements suggest that material incorporated into the basal sediments might date to 93 9 ka four stratigraphic zones a d were identified in the sedimentological data the chronological model suggests that zones a c were deposited between marine isotope stages 5 2 and zone a during stage 1 the holocene the palaeolimnological record tracks changes in the subglacial depositional environment linked principally to changing glacier dynamics and mass transport and indirectly to climate change the sediment composition in zones a c consists of fine grained sediments together with sands gravels and small clasts there is no evidence of overriding glaciers being in contact with the bed reworking the stratigraphy or removing this sediment this suggests that the lake existed in a subglacial cavity beneath overriding lgm ice in zone d there is a transition to finer grained sediments characteristic of lower energy delivery coupled with a minor increase in the organic content attributed either to increases in allochthonous organic material being delivered from the deglaciating catchment a minor increase in within lake production or to an analytical artefact associated with an increase in the clay fraction evidence of biological activity is sparse total organic carbon varies from 0 2 to 0 6 and cannot be unequivocally linked to in situ biological activity as comparisons of 13c and c n values with local reference data suggest that much of it is derived from the incorporation of carbon in catchment soils and gravels and possibly old co2 in meteoric ice we use the data from this study to provide guidelines for the study of deep continental subglacial lakes including establishing sediment geochronologies determining the extent to which subglacial sediments might provide a record of glaciological and environmental change and a brief review of methods to use in the search for life

subglacial lake mcgregor south central alberta canada abstract it is proposed that a lake here named subglacial lake mcgregor existed beneath the laurentide ice sheet at or near the last glacial maximum the lake resided in the ancient buried mcgregor and tee pee preglacial valleys which are now mostly filled with glacigenic deposits the greatest thickness of sediment in the valleys is in the form of chaotically deposited lake beds that were laid down in a subaqueous environment by a number of process gravity flow water transport and suspension settling topographic sedimentary and stratigraphic evidence point to a subglacial not a proglacial origin for the beds during the early stages of lake existence ice movement was significant as there are numerous sets of shear planes in the sedimentary beds this indicates that the lake filled lake sedimentation and drained shearing of the beds by overlying ice when ice contacted the bed often thus early in its history the lake s was were ephemeral during the later stages of lake existence the lake was relatively stable with no rapid draining or influx of sediment gradual drainage of the lake resulted in lowering of the ice onto the lake beds resulting in subglacial till deposition drainage was not a single continuous event rather it was characterized by multiple phases of near total drainage till deposition followed by water accumulation lake sedimentation water accumulation events became successively less significant reflected by thinning of lake beds and thickening of till beds higher in the stratigraphic sequence since subglacial lake sedimentation appears to be restricted to the subglacial valleys it is suggested that the valleys acted as a large scale interconnected cavity system that both stored and transported water it is also suggested that these acted as the main routes of water flow beneath the laurentide ice sheet

sediment fabrics oxygenation history and circulation modes of japan sea during the late quaternary abstract the quaternary hemipelagic sediments of the japan sea are characterized by centimeter to decimeter scale alternations of heavily bioturbated organic poor light layers and finely laminated organic rich dark layers these dark and light layers which can be correlated throughout the deeper part of the basin are considered to reflect changes in bottom water oxygenation however depositional mechanisms responsible for individual dark layers and causes of oxygen depletion are not fully understood two possible settings for deposition of organic rich dark layers are recognized one is a stratified ocean like the black sea where limited vertical advection results in euxinic conditions in the deeper parts of the basin the other is an upwelling region like the arabian sea where the oxygen minimum zone is intensified by enhanced nutrient upwelling and surface productivity in this study fabrics of hemipelagic sediments deposited in the japan sea during the last 160 ka were studied in three cores collected from different latitudes and water depths fabrics were classified into 4 classes based on corresponding bottom water oxygenation level five dark layer types were defined based on the distribution patterns of sediment fabric classes within each dark layer comparison of dark layer types at shallower and deeper sites in a chronologic framework provided evidence for five different modes of deep water circulation these circulation modes which reflect relative intensities of upwelling and density stratification appear to be related to global sea level changes as well as climate impact on the nature of water influx through the tsushima strait

age of the mono lake excursion and associated tephra abstract the mono lake excursion mle is an important time marker that has been found in lake and marine sediments across much of the northern hemisphere dating of this event at its type locality the mono basin of california has yielded controversial results with the most recent effort concluding that the mle may actually be the laschamp excursion earth planet sci lett 197 2002 151 we show that a volcanic tephra ash 15 that occurs near the midpoint of the mle has a date not corrected for reservoir effect of 28 620 300 14c yr bp 32 400 gisp2 yr bp in the pyramid lake basin of nevada given the location of ash 15 and the duration of the mle in the mono basin the event occurred between 31 500 and 33 300 gisp2 yr bp an age range consistent with the position and age of the uppermost of two paleointensity minima in the napis 75 stack that has been associated with the mle philos trans r soc london ser a 358 2000 1009 the lower paleointensity minimum in the napis 75 stack is considered to be the laschamp excursion philos trans r soc london ser a 358 2000 1009

exploring former subglacial hodgson lake antarctica paper i site description geomorphology and limnology at retreating margins of the antarctic ice sheet there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered this paper presents a site description of one of these lakes hodgson lake situated on southern alexander island west of the antarctic peninsula 72 00 549 s 68 27 708 w first we describe the physical setting of the lake using topographic and geomorphological maps second we determine local ice sheet deglaciation history and the emergence of the lake using cosmogenic isotope dating of glacial erratics cross referenced to optically stimulated luminescence dating of raised lake shoreline deltas formed during ice recession third we describe the physical and chemical limnology including the biological and biogeochemical evidence for life results show that the ice mass over hodgson lake was at least 295 m thick at 13 5 ka and has progressively thinned through the holocene with the lake ice cover reaching an altitude of c 6 5 m above the present lake ice sometime after 4 6 ka thick perennial ice cover persists over the lake today and the waters have remained isolated from the atmosphere with a chemical composition consistent with subglacial melting of catchment ice the lake is ultra oligotrophic with nutrient concentrations within the ranges of those found in the accreted lake ice of subglacial lake vostok total organic carbon and dissolved organic carbon are present but at lower concentrations than typically recorded in continental rain no organisms and no pigments associated with photosynthetic or bacterial activity were detected in the water column using light microscopy and high performance liquid chromatography increases in so4 and cation concentrations at depth and declines in o2 provide some evidence for sulphide oxidation and very minor bacterial demand upon o2 that result in small perhaps undetectable changes in the carbon biogeochemistry however in general the chemical markers of life are inconclusive and abiotic processes such as the diffusion of pore waters into the lake from its benthic sediments are far more likely to be responsible for the increased concentrations of ions at depth the next phases of this research will be to carry out a palaeolimnological study of the lake sediments to see what they can reveal about the history of the lake in its subglacial state and a detailed molecular analysis of the lake water and benthos to determine what forms of life are present combined these studies will test some of the methodologies that will be used to explore deep continental subglacial lakes

authigenic 10be 9be signature of the laschamp excursion a tool for global synchronisation of paleoclimatic archives authigenic 10be and 9be isotope concentrations have been measured in marine sediments deposited between 10 and 60ka bp in the western equatorial pacific and their ratio compared to the geomagnetic relative paleointensity rpi record obtained from the same core c l blanchet n thouveny t de garidel thoron new evidences of geomagnetic moment lows between 30 and 45ka bp from a sedimentary sequence of the west equatorial pacific quat sci rev in press over the studied time interval dated by radiocarbon and oxygen isotope stratigraphy three periods of reduced rpi occurring at 32 37 and 45ka according to the constructed age model are concomitant with three significant increases in atmospheric 10be production since the most prominent 10be 9be peak necessarily results from the weakest geomagnetic moment event i e that associated with the laschamp excursion we assign to this cosmogenic nuclide event the age of the laschamp excursion i e 40 4 2 0ka bp h guillou b s singer c laj c kissel s scaillet b r jicha on the age of the laschamp geomagnetic excursion earth planet sci lett 227 2004 331 343 cosmogenic nuclide production peaks provide critical complementary evidence for the identification of geomagnetic dipole lows linked to excursions and constitute accurate markers for global intercorrelation of paleoclimatic archives

wissard at subglacial lake whillans west antarctica scientific operations and initial observations a clean hot water drill was used to gain access to subglacial lake whillans slw in late january 2013 as part of the whillans ice stream subglacial access research drilling wissard project over 3 days we deployed an array of scientific tools through the slw borehole a downhole camera a conductivity temperature depth ctd probe a niskin water sampler an in situ filtration unit three different sediment corers a geothermal probe and a geophysical sensor string our observations confirm the existence of a subglacial water reservoir whose presence was previously inferred from satellite altimetry and surface geophysics subglacial water is about two orders of magnitude less saline than sea water 0 37 0 41 psu vs 35 psu and two orders of magnitude more saline than pure drill meltwater 0 002 psu it reaches a minimum temperature of 0 558c consistent with depression of the freezing point by 7 019 mpa of water pressure subglacial water was turbid and remained turbid following filtration through 0 45 mm filters the recovered sediment cores which sampled down to 0 8 m below the lake bottom contained a macroscopically structureless diamicton with shear strength between 2 and 6 kpa our main operational recommendation for future subglacial access through water filled boreholes is to supply enough heat to the top of the borehole to keep it from freezing

paleoceanographic changes of surface and deep water based on oxygen and carbon isotope records during the last 130 kyr identified in md179 cores off joetsu japan sea abstract we reconstructed the paleoenvironmental history of surface and deep water over the last 130 kyr from oxygen and carbon isotope ratios of planktonic and benthic foraminifera in two cores md179 3312 and md179 3304 from the joetsu basin eastern margin of the japan sea our data showed that paleoceanographic changes such as influx of surface currents and vertical circulation were associated with global glacial interglacial sea level change surface water conditions were influenced by the influx of tsushima current east china sea coastal or off shore waters through the tsushima strait during interglacial or interstadial stages and strongly affected by freshwater input during the glacial maximum during interglacial maximums such as marine isotope stages 1 and 5e development of well oxygenated bottom water was indicated a density stratified ocean with weak ventilation was inferred from the isotopic records of benthic foraminifera during the last glacial maximum local negative excursions in carbon isotopes during deglacial or interglacial periods may suggest the dissolution of gas hydrates or methane seep activities

paleoenvironmental implications from biomarker and stable isotope investigations on the pliocene velenje lignite seam slovenia a pliocene lignite seam up to 160 m thick occurs in the velenje basin slovenia the seam originated in a topogenous mire and evolved within a non marine transgressive setting differences in soluble organic matter yield and hydrocarbon content of borehole samples from the lignite are related to differences in the composition of free lipids of microbial origin and or hydrocarbons derived from the biogeochemical degradation of plant tissue variations of the redox conditions within the mire are reflected by pristane phytane ratios the abundance of terpenoid biomarkers indicates the predominance of gymnosperms over angiosperms which is consistent with palynomorphic spectra dominated by pollen of the sequoia taxodium metasequoia plant community rather than by angiosperms evidence is also provided that the content of land plant derived biomarkers and the preservation of plant tissue is controlled by the input of resin rich decay resistant conifers sections of the seam characterized by a high degree of gelification of humotelinite gelification index show high contents of hop 17 21 ene but low hopane concentrations the results suggest that the gelification of plant tissue may be governed by the activity of anaerobic rather than aerobic bacteria despite the minor variation in the proportions of gymnosperms versus angiosperms in the peat forming vegetation a general influence of the floral assemblage on carbon isotopic composition of the coals 13c 25 3 to 27 0 is proposed carbon cycling during biogeochemical decomposition of plant tissue by bacteria is assumed to affect the 13c value of the lignite petrographic and geochemical data of gelified and ungelified fossil wood provide evidence that gelification may be governed by microorganisms e g anaerobic bacteria different from those responsible for decreasing cellulose contents during early diagenetic aerobic degradation of wood based on the molecular composition of terpenoid biomarkers the wood fragments are identified as derived from gymnosperms the relative proportions of saturated versus aromatic hydrocarbon fractions of fossil gymnosperms display a general tendency towards lower values in gelified wood remains this indicates that bacteria involved in gelification of plant tissue may also be involved in aromatisation of diterpenoid hydrocarbons the chemotaxonomical classification of the macrofossils as gymnosperms is corroborated by the mean carbon isotopic compositions of the macrofossils 13c 24 5 and the extracted cellulose 13c 22 0 the higher isotopic difference of about 2 5 between cellulose and fossil wood compared to that found in modern trees can most probably be explained by the smaller effect of 13c discrimination for cellulose when compared with wood during decomposition chem geol 158 1999 121 compared with the coals the 13c values of wood and extracted cellulose are affected to a minor extent by microbial activity

high resolution paleomagnetic secular variations and relative paleointensity since the late pleistocene in southern south america abstract paleomagnetic inclination declination and relative paleointensity were reconstructed from the sediments of laguna potrok aike in the framework of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado here we present the u channel based full vector paleomagnetic field reconstruction since 51 2 ka cal bp the relative paleointensity proxy rpi was built by normalising the natural remanent magnetisation with the anhysteretic remanent magnetisation using the average ratio at 4 demagnetisation steps part of the chrm interval nrm arm 10 40 mt a grain size influence on the rpi was removed using a correction based on the linear relationship between the rpi and the median destructive field of the natural remanent magnetisation mdf nrm the new record is compared with other lacustrine and marine records and stacks from the mid to high latitudes of the southern hemisphere revealing consistent millennial scale variability the identification of the laschamp and possibly the mono lake geomagnetic excursions and a direction swing possibly associated to the hilina pali excursion at 20 ka cal bp nonetheless a global scale comparison with other high resolution records located on the opposite side of the earth and with various dipole field references hint at a different behaviour of the geomagnetic field around southern south america at 46 ka cal bp

depositional environment of the late miocene hausruck lignite alpine foreland basin insights from petrography organic geochemistry and stable carbon isotopes abstract lignites and fossil wood from two boreholes in the late miocene hausruck district alpine foreland basin austria were investigated with respect to organic carbon and total sulfur contents ash yields maceral composition organic geochemistry and stable carbon isotope ratios the lignites from the two sampled profiles differ in sulfur contents and petrography based facies indicators gelification index gi tissue preservation index tpi the results point to drier and more acidic conditions in the part of the mire sampled at drill site lukasberg whereas the lignites from kalletsberg formed under near neutral conditions due to a raised ground water table the different depositional environments are supported by the paleogeographic positions of the boreholes borehole lukasberg is located within a paleo valley whereas borehole kalletsberg is located at the deeper part of a basin situated south and southwest of the hausruck area environmental changes with time within the mire are confirmed by the molecular composition of the soluble organic matter som differences in pristane phytane ratio isomerisation of hopanes at position 17 concentrations of hopanes and in the ratio of hopanes to hop 17 21 enes are related to the extent of gelification of plant tissue sulfur content and ph values caused by differences in ground water table the variable contents of individual terpenoid hydrocarbons derived from land plants indicate that angiosperms and conifers contribute to peat formation in the hausruck district in variable proportions overall angiosperm biomarkers slightly predominate the tissue preservation index tpi within the kalletsberg profile is probably governed by the proportion of decay resistant conifers as indicated by the correlation between tpi and biomarker composition of the coals correlations between 13 c values of the lignites between 24 9 and 27 4 and their non hopanoid terpenoid composition indicate the major influence of changes in peat forming vegetation on the carbon isotopic composition of the coals in the hausruck district carbon isotope data of macrofossils are consistent with their taxonomical classification as conifers 13 c between 22 7 and 25 1 and angiosperms 13 c between 25 5 and 26 6 respectively the 13 c data of the extracted cellulose reveal clear differences between fossil wood from gymnosperms average 13 c 21 0 and angiosperms mean 13 c 23 4

a stacked record of relative geomagnetic paleointensity for the past 270 kyr from the western continental rise of the antarctic peninsula paleomagneticandrockmagnetic investigations were carriedout onfourgravity coresrecoveredfrom the westerncontinental rise of the antarctic peninsula during the sedano ii cruise of rv ogs explora the studied cores each about 6 5 m long were collected at a depth of 3700 4100 m below the sea level on the distal gentle side of sediment drift 7 and consist of very fine grained sediments spanning through various glacial interglacial cycles detailed analysis of the paleomagnetic and rock magnetic data allowed toreconstruct relative paleointensity rpi records nrm20 mt arm20 mt for eachcore weestablished arefined agemodel for the studied sequences by correlating individual sedano rpi curves to the global rpi stack sint 800 y guyodo j p valet global changes in intensity of the earth s magnetic field during the past 800 kyr nature 399 1999 249 252 the individual normalized sedano rpi records are in mutual close agreement they were thus merged in a rpi stacking curve spanning the last 270 kyr and showing a low standard deviation this study also points out that rpi records may provide a viable tool to date otherwise difficult to datesedimentarysequences suchasthosedepositedalongperi antarctic margins thenewrpichronologyindicatesthat thesampled sedimentary sequenceisyoungerthanpreviouslythought andallowsanew high resolutioncorrelation tooxygenisotope stages furthermore we recognized variations in the rock magnetic parameters that appear to be climatically driven with changes in therelative proportionoftwomagnetic mineralpopulationswithdistinctcoercivities rockmagnetic andlithological trendsobserved in the sedano cores indicate that during the climatic cycles of the late pleistocene this sector of the peri antarctic margin was subjected to subtle yet identifiable environmental changes confirming a relatively higher instability of the west antarctic ice sheet with respect to the east antarctic counterpart

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

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

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

paleomagnetic correlations between scandinavian ice sheet fluctuations and greenland dansgaard oeschger events 45 000 25 000 yr b p abstract two paleomagnetic excursions the skjong correlated with the laschamp about 41 000 gisp2 yr b p and the valderhaug correlated with the mono lake about 34 000 gisp2 yr b p have been identified in stratigraphic superposition in laminated clay deposited in ice dammed lakes in three large caves in western norway during both periods the margin of the scandinavian ice sheet advanced and reached the continental shelf beyond the outermost coastline the mild 4000 yr long alesund interstade when the coast and probably much of the hinterland were ice free separated the two glacial advances the two paleomagnetic excursions have also been indirectly identified as increased fluxes of 36cl and 10be in the grip ice core greenland this article presents a correlation between ice margin fluctuations of the scandinavian ice sheet and the stratigraphy of grip gisp cores using the paleomagnetic excursions and the 36cl and 10be peaks and thus circumventing the application of different dates or time scales some of the fluctuations of the scandinavian ice sheet were of the allerod younger dryas type in the sense that its margin retreated during mild interstades on greenland and readvanced during cold stades however some fluctuations were apparently not in phase with the greenland climate

holocene history of the larsen a ice shelf constrained by geomagnetic paleointensity dating a sedimentary record collected from beneath the former lar sen a ice shelf reveals the holocene history of the larsen a re gion the record begins with the transition from grounded ice to a floating ice shelf completed by 10 7 6 0 5 ka and ends with the modern recession the record contains several late holocene dia tomaceous ooze layers that suggest proximity to productive open water events radiocarbon ages obtained from these sediments were complicated by the presence of detrital and reworked carbon we have eliminated these complications and constructed a chro nology for the larsen a ice shelf history via tuning of the geo magnetic field paleointensity record with a reference curve this approach provides chronological control to sediment sequences that lack appropriate material for radiocarbon dating geomag netic paleointensity features with wavelengths of 2 3 k y can be recognized and interhemispherically correlated illustrating the po tential to use geomagnetic paleointensity variations as a global cor relation and dating tool at sub milankovitch time scales

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

evidence for the long term sedimentary environment in an antarctic subglacial lake lakes beneath the antarctic ice sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments however no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet and understanding of sediment pathways processes and structure in subglacial lake environments remains uncertain here we present an analysis of seismic data from subglacial lake ellsworth showing that the lake bed comprises very fine grained sediments deposited in a low energy environment with low water and sediment fluxes minimum sediment thickness is 6 m the result of prolonged low sedimentation rates based on the few available analogues we speculate this sediment age range is a minimum of 150 ka and possibly 1 ma sediment mass movements have occurred but they are rare and have been buried by subsequent sedimentation we present a new conceptual model of subglacial lake sedimentation allowing a framework for evaluating processes in subglacial lake environments and for determining future lake access locations and interpreting subglacial lake samples