palaeomagnetism of devonian ring complexes from the bayuda desert sudan new constraints on the apparent polar wander path for gondwanaland summary the approach of gondwana and or microplates derived from its northern margins towards laurentia and the closure of the intervening palaeo tethys is a controlling factor in the geodynamic evolution of the atlantic bordering continents during the early and mid palaeozoic however the currently available palaeomagnetic data for gondwana especially for the geodynamically critical silurian to devonian interval are still rather sparse and are compatible with a number of palaeogeographic scenarios in order to address this issue 114 samples 18 sites have been collected from a series of high level acidic intrusive rocks rhyolitic lavas and tuffs of mid devonian age 377 5 ma rb sr along the southern escarpment of the gilif hills sudan 17 83 n 32 67 e detailed demagnetization experiments revealed the presence of three directionally distinct components of magnetization labelled a b and c the overall mean direction of component a dec 0 9 inc 29 8 95 4 6 k 91 1 n 12 sites is indistinguishable from either the direction of the present field or the geocentric axial dipole field in northern sudan mixed polarities suggest a recent or pleistocene age of this component component b also displays mixed polarities the site mean directions for this component average to 6 5 declination 40 2 inclination with 95 7 0 and k 48 1 based on 10 sites and yield a palaeomagnetic pole at 48 8 s 23 5 e dp 5 1 1 dm 8 4 maghaemite and haematite have been identified to be the predominant magnetic phases in samples which carry component a and or b both a and b are the probable results of low temperature oxidation of magnetite although the age of component b can not be directly determined it is inferred by correlation with published data to reflect a late carboniferous overprint component c identified in 11 sites 39 samples is characterized by a very steep downward magnetization dec 296 2 inc 79 3 95 10 8 k 18 7 n 11 sites which corresponds to a palaeomagnetic pole position in the southwestern corner of libya 25 9 n 11 6 e dp 19 6 dm 20 6 maximum blocking temperatures of component c generally below 580 c are indicative of magnetite as carrier of this remanence the results of thermal remanent magnetization experiments demonstrate that component c is a thermo remanent magnetization probably primary and suggest this component to be representative for the direction of the earth s magnetic field during emplacement of the gilif hills volcanic rocks in mid devonian times the position of the resulting palaeomagnetic pole lends new support to geodynamic scenarios advocating the existence of a wide approx 5000 km pre hercynian ocean during devonian times the simplest reconciliation of component b with the reference apparent polar wander path is achieved by assuming it to be of carboniferous age and by invoking a westward cusp in the carboniferous part of the apparent polar wander path taken at face value the age of this cusp coincides with large scale post orogenic right lateral strike slip movements in hercynian europe and north africa this interpretation does not require the apparent polar wander apw loop and very high rates of plate motion implied by some alternative models however if it is valid it will require reinterpretation of the remanence age of one west african intrusive suite and of some eastern australian palaeozoic rocks

stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice covered antarctic lake lake hoare 77 degrees 38 s 162 degrees 53 e is an amictic oligotrophic 34 m deep closed basin lake in taylor valley antarctica its perennial ice cover minimizes wind generated currents and reduces light penetration as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere the biological community of lake hoare consists solely of microorganisms both planktonic populations and benthic microbial mats lake hoare is one of several perennially ice covered lakes in the mcmurdo dry valleys that represent the end member conditions of cold desert and saline lakes the dry valley lakes provide a unique opportunity to examine lacustrine processes that operate at all latitudes but under an extreme set of environmental conditions the dry valley lakes may also offer a valuable record of catchment and global changes in the past and present furthermore these lakes are modern day equivalents of periglacial lakes that are likely to have been common during periods of glacial maxima at temperate latitudes we have analyzed the dissolved inorganic carbon dic of lake hoare for delta 13c and the organic matter of the sediments and sediment trap material for delta 13c and delta 15n the delta 13c of the dic indicates that 12c is differentially removed in the shallow oxic portions of the lake via photosynthesis in the anoxic portions of the lake 27 34 m a net addition of 12c to the dic pool occurs via organic matter decomposition the dissolution of caco3 at depth also contributes to the dic pool except near the canada glacier where a substantial amount of allochthonous organic matter enters the lake the organic carbon being deposited on the lake bottom at different sites is isotopically similar suggesting an autochthonous source for the organic carbon preliminary inorganic carbon flux calculations suggest that a high percentage of the organic carbon fixed in the water column is remineralized as it falls through the water column at nearby lake fryxell the substantial relative to lake hoare glacial meltstream input overprints fryxell s shallow water biological delta 13c signal with delta 13c depleted dic in contrast lake hoare is not significantly affected by surface water input and mixing and therefore the delta 13c patterns observed arise primarily from biological dynamics within the lake organic matter in lake hoare is depleted in 15n which we suggest is partially the result of the addition of relatively light inorganic nitrogen into the lake system from terrestrial sources

high resolution ground penetrating radar profiles of perennial lake ice in the mcmurdo dry valleys antarctica horizon attributes unconformities and subbottom penetration abstractground penetrating radar gpr is not commonly used to study lake ice and in general the ground based use of radar frequencies greater than 500 mhz in cryosphere geophysics is rare due to a general interest in deeper stratigraphy and the difficulty of extensive profiling over rough snow surfaces our goal was to find further information on the origin of the deposition and formation of intra ice layers bottom topography and subbottom deposits using gpr with pulses centered near 850 mhz on two permanently ice covered lakes in the mcmurdo dry valleys antarctica the profiles were obtained using a one person sled operation over lake bonney which is typical of lakes in the region having an ice thickness that ranges between 3 and 5 m and lake vida where the maximum ice depth is at least 27 m lake bonney exhibits a semicontinuous sediment horizon at approximately a 2 m depth and several minor horizons in contrast lake vida contains unconformably eroded and folded continuous reflection horizo

plio pleistocene sedimentation in ferrar fiord antarctica a 166 m thick plio pleistocene sequence of glacial sediments has been cored in ferrar fiord in the southwestern corner of the ross sea antarctica the core has the following lithofacies massive diamictite 33 of the core interpreted as lodgement or waterlain till weakly stratified diamictite 25 waterlain till or proximal glaciomarine sediment well stratified diamictite 8 proximal glaciomarine or glaciolacustrine sediment sandstone 25 sand of aeolian or supraglacial origin mudstone 7 derived from subglacial debris and transported offshore in suspension and minor amounts of rhythmite and tuff the range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian derived sand and the low proportion of mudstone facies the core can be divided into two sequences based on composition and texture the sequence from 162 to 100 mbsf metres below the sea floor comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds it is pliocene in age 4 9 2 0 ma and records several advances and retreats of ice through the transantarctic mountains and across the drill site from the west the sequence from 100 mbsf to the sea floor of pleistocene age consists of alternations of diamictite interpreted as lodgement and waterlain till and sandstone of aeolian origin deposited in a glaciolacustrine setting similar to ice covered lakes in the dry valleys today these sediments have a high volcanic component and hence are thought to have been derived by the grounding and advance of the ross ice shelf from the east past volcanic ross island this change in source is attributed to the rising transantarctic mountains increasingly containing east antarctic ice the pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation with alternations of till and glaciolacustrine sand mudstones from the pliocene sequence beneath include palynomorphs indicating times when the landscape was at least partially vegetated but contain no evidence of meltwater influence

quantifying transient post overwash aquifer recovery for atoll islands in the western pacific marine overwash events for atoll islands in the pacific and indian oceans which cause salinization of fresh groundwater because of infiltrating seawater pose a significant challenge for island community sustainability in regard to water supply understanding transient fresh groundwater development during a post overwash period for a range of island sizes geologic characteristics and rainfall patterns is essential for water management this paper presents a methodology for quantifying this development for an atoll nation with methods applied to the 32 atolls of the federated states of micronesia fsm in the western pacific using the numerical groundwater modelling code sutra overwash events and post overwash freshwater seawater dynamics are simulated for the range of island widths 200 to 1100 m geologic characteristics hydraulic conductivity corresponding to leeward and windward islands and rainfall patterns western central and eastern regions present in the fsm thereby providing results for each atoll island results show that 10 17 8 12 and 6 12 months are required to achieve 60 freshwater lens recovery for leeward islands in the western central and eastern fsm respectively with variation due to rainfall rate and island width in contrast 4 9 months is required for 60 recovery for windward islands however the natural thinness of the lend on windward islands typically precludes extensive use of groundwater under average rainfall conditions overwash characteristics depth duration and seasonal timing did not significantly affect recovery times for the region of lowest rainfall western fsm 6 10 months is required to achieve potable groundwater at the typical depth of hand dug wells results provide water resource managers and atoll island communities with important information regarding timing of potential fresh groundwater use following an overwash event copyright 2015 john wiley sons ltd

mineralogical and geochemical analyses of antarctic lake sediments a study of reflectance and mossbauer spectroscopy and c n and s isotopes with applications for remote sensing on mars abstract we analyzed lake bottom sediments from the dry valleys region of antarctica to study the influence of water chemistry on the mineralogy and geochemistry of these sediments as well as to evaluate techniques for remote spectral identification of potential biomarker minerals on mars lakes from the dry valleys region of antarctica have been investigated as possible analogs for extinct lake environments on early mars sediment cores were collected in the present study from perennially ice covered lake hoare in the taylor valley these sediments were taken from a core in an oxic region of the lake and another core in an anoxic zone differences between the two cores were observed in the sediment color fe ii fe iii ratio the presence of pyrite the abundance of fe s and some trace elements and the c n and s isotope fractionation patterns the results of visible infrared reflectance spectroscopy 0 3 25 m mossbauer spectroscopy 77 and 4 k and x ray diffraction are combined to determine the mineralogy and composition of these samples the sediments are dominated by plagioclase k feldspar quartz and pyroxene algal mats grow on the bottom of the lake and organic material has been found throughout the cores calcite is abundant in some layers of the sediment core from the shallow oxic region and pyrite is abundant in the upper sediment layers of the core from the deep anoxic region of lake hoare analysis of the spectroscopic features due to organics and carbonates with respect to the abundance of organic c and carbonate contents was performed in order to select optimal spectral bands for remote identification of these components in planetary regoliths carbonate bands near 4 and 6 8 m 2500 and 1500 cm 1 were detected for carbonate abundances as low as 0 1 wt co2 organic features at 3 38 3 42 and 3 51 m 2960 2925 and 2850 cm 1 were detected for organic c abundances as low as 0 06 wt c the 13c and 15n trends show a more complex organic history for the anoxic region sediments than for the oxic region sediments the biogenic pyrite found in the core from the anoxic zone is associated with depleted 34s values and high organic c levels and could be used as a potential biomarker mineral for paleolakes on mars

the permanent ice cover of lake bonney antarctica the influence of thickness and sediment distribution on photosynthetically available radiation and chlorophyll a distribution in the underlying water column the thick permanent ice cover on the lakes of the mcmurdo dry valleys antarctica inhibits spatial lake sampling due to logistical constraints of penetrating the ice cover to date most sampling of these lakes has been made at only a few sites with the assumption that there is a spatial homogeneity of the physical and biogeochemical properties of the ice cover and the water column at any given depth to test this underlying assumption an autonomous underwater vehicle auv was deployed in lake bonney taylor valley measurements were obtained over the course of 2 years in a 100 100 m horizontal sampling grid at a 0 2 m vertical resolution additionally the auv measured the ice thickness in water equivalent and collected images looking up through the ice which were used to quantify sediment distribution on the surface and within the ice satellite imagery was used to map sediment distribution on the surface of the ice we present results of the spatial investigation of the sediment distribution on the ice cover and its effects on biological processes with particular emphasis on photosynthetically active radiation par the surface sediment is a secondary controller of the ice cover thickness which in turn controls the depth integrated par in the water column our data revealed that depth integrated par was negatively correlated with depth integrated chlorophyll a r 0 88 p 0 001 n 83 which appears to be related to short term photoadaptation of phytoplanktonic communities to spatial and temporal variation in par within the water column

antarctic paleolake sediments and the search for extinct life on mars evidence of lakes in mars history is substantial the proposed similarities between the ancient martian environment and certain modern environments on earth have led exobiologists to study antarctic lakes as analogs to those purported to have existed on mars we have investigated modern sedimentation processes especially with respect to 13c of carbonate and organic matter in lakes in the mcmurdo dry valleys region of east antarctica and assessed various paleolake deposits with respect to their utility as martian analogs and targets for future mars exobiology missions three main types of paleolake deposit were identified and assessed strand lines perched deltas and lacustrine sand mounds deltas are usually identified as good targets but our research shows that authigenic carbonates are not readily identifiable in the sediments large deltas although most likely to attract attention through remote sensing generally are difficult sites for discovery of paleobiological matter and 13c signals follow no coherent pattern lacustrine sand mounds on the other hand contain abundant authigenic carbonate and freeze dried organic matter and appear to be excellent records of paleolimnological conditions the advantage of studying lake bottom deposits versus lake edge deposits is retrieval of a stable lake wide signal deltas are therefore most useful in that they are generally large scale features capable of drawing attention to a region of potential for the discovery of smaller lacustrine sand mounds

nature and stability of atoll island shorelines gilbert island chain kiribati equatorial pacific islands rimming pacific atolls typically form narrow low lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea level rise as these low islands form the only habitable land for many island nations understanding the character of shorelines and the rates and controls that operate to bring about changes is an issue of central importance the purpose of this study is to unravel the characteristics of coastal change on atoll islands of the gilbert island chain of the equatorial pacific nation of kiribati especially as they relate to autogenic shoreline processes and el nino southern oscillation variability integration of field observations differential global positioning system data historical aerial photographs and ultra high resolution remote sensing images demonstrates the nature spatial patterns and rates of change from 17 islands on maiana and aranuka atolls the results illustrate that between 2005 and 2009 ca 50 of the shorelines on these islands displayed a discernable shift in position some shorelines were accretionary at net rates up to ca 8 m year 1 and others were erosional up to ca 18 m year 1 long term net rates of change on maiana between 1969 and 2009 were lower than short term net rates measured between 2005 and 2009 both short term and long term observations illustrate some of the greatest change occur near terminations of the largest north south oriented islands associated with longshore movement of coarse sand and gravel direct hits by tropical depressions and marked seasonality factors interpreted as being essential in island growth and shoreline dynamics elsewhere do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics similarly observations over four years suggested that shoreline variability probably is not influenced directly by marked sea level change although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long term increase in the rate of sea level rise within this framework of global change local anthropogenic effects autogenic shoreline processes and el nino southern oscillation influenced wind and wave variability control many aspects of these dynamic shorelines these results provide quantitative insights into the character and variability of rates of shoreline change information essential for evaluating and mitigating the vulnerability of island nations such as kiribati

light transmission and reflection in perennially ice covered lake hoare antarctica we have investigated the transmission and albedo of the perennial ice cover on lake hoare antarctica our database consists of year round measurements of the photosynthetically active radiation 400 700 nm under the ice measurements of the spatial variation of the under ice light in midsummer and spectrally resolved measurements from 400 to 700 nm of the albedo and transmission of the ice cover in early november and in midsummer january our results show that the transmission decreases in the first part of summer dropping by a factor of 4 from november to january we suggest that this is due to heating in the upper layers of the ice cover and the formation of tyndall figures later in the summer when a significant liquid water fraction occurs within the ice cover the transmission increases in the fall when the ice cover freezes solid the transmission drops markedly the spectrally resolved measurements from 400 to 700 nm show that 2 5 of the incident light in this spectral region penetrates the 3 5 m thick ice cover we have analyzed the spectral data using a two stream scattering solution to the radiative transfer equation with three vertical layers in the ice cover a surficial glaze of scattering ice 1 cm thick overlies a layer of sandy bubbly ice about a meter thick and below this is a thick layer of sand free ice with bubbles we find that the ice cover is virtually opaque at wavelengths longer than 800 nm the net transmission of solar energy is 2 significant changes in the thickness of the ice cover have been reported at lake hoare these are due primarily to changes in the thickness of the bottom layer only because this layer is relatively clear the effect on the transmission through the ice cover from these changes is less than would be predicted assuming a homogeneous ice cover

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

lake hoare antarctica sedimentation through a thick perennial ice cover lake hoare in the dry valleys of antarctica is covered with a perennial ice cover more than 3 m thick yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom rough topography on the ice covering the lake surface traps sand that is transported by the wind in late summer vertical conduits form by melting and fracturing making the ice permeable to both liquid water and gases cross sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits this is the primary sedimentation mechanism in the lake sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m this conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1 5 m despite the close spacing of the cores the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate apparently sand descends into the lake from discrete highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time in some locations on the lake bottom distinctive sand mounds have been formed by this process they are primary sedimentary structures and appear unique to the perennially ice covered lacustrine environment in some locations they are tens of centimetres high and gently rounded with stable slopes in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose a simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria eukaryotic algae and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites

sedimentation in ice covered lake hoare antarctica the sedimentation mechanisms that occur in ice covered lake hoare antarctica are examined to determine how sediment enters the lake and how the sedimentation pattern affects blue green algal growth at the lake bottom the 3 m thick ice cover contains pebbly sand as much as 2 m below the surface sediment with similar texture and mineralogy is found at the lake bottom this evidence together with the lack of sediment in the inflowing stream and the markedly different texture of sediment from the other terrains around the lake suggest that most of the sediment at the lake bottom comes in through the ice cover sand grains intermittently migrate through porous ice on the surface water filled vertical gas channels penetrating two thirds of the ice cover and possibly through cracks in the ice that act as conduits the algae at the lake bottom are able to survive in part because sediment that comes through the ice cover does not obliterate them

reflectance spectroscopy and geochemical analyses of lake hoare sediments antarctica implications for remote sensing of the earth and mars abstract visible to infrared reflectance spectroscopic analyses 0 3 25 m have been performed on sediments from the dry valleys region of antarctica sample characterization for these sediments includes extensive geochemical analyses and x ray diffraction xrd the reflectance spectra and xrd indicate major amounts of quartz feldspar and pyroxene in these samples and lesser amounts of carbonate mica chlorite amphibole illite smectite and organic matter calcite is the primary form of carbonate present in these lake hoare sediments based on the elemental abundances and spectroscopic features the particle size distribution of the major and secondary components influences their detection in mixtures and this sensitivity to particle size is manifested differently in the volume scattering and surface scattering infrared regions the christiansen feature lies between these two spectral regimes and is influenced by the spectral properties of both regions for these mixtures the christiansen feature was found to be dependent on physical parameters such as particle size and sample texture as well as the mineralogy semiquantitative spectroscopic detection of calcite and organic material has been tested in these quartz and feldspar rich sediments the relative spectral band depths due to organics and calcite correlate in general with the wt c from organic matter and carbonate the amounts of organic matter and carbonate present correlate with high br and u abundances and high ca and sr abundances respectively variation in the elemental abundances was overall minimal which is consistent with a common sedimentary origin for the forty two samples studied here from lake hoare

particulate matter in pack ice of the beaufort gyre ice observations and sediment samples were collected in the beaufort gyre in 1988 fine sediment occurred in very small patches of turbid ice as thin spotty surface layers in mud pellets or in old snowdrifts the latter were widespread south of 74 n containing an estimated 22 tonnes of silt and clay km 2 average particle concentration in sea ice 40 mg l 1 was much higher than in sea water 0 8 mg l 1 or in new snow but the sediment load was significantly smaller and of finer texture compared to that observed in a shelfal source area after a major entrainment event

a complex microbiota from snowball earth times microfossils from the neoproterozoic kingston peak formation death valley usa a thin carbonate unit associated with a sturtian age 750 700 million years ago glaciogenic diamictite of the neoproterozoic kingston peak formation eastern california contains microfossil evidence of a once thriving prokaryotic and eukaryotic microbial community preserved in chert and carbonate stratiform stromatolites oncoids and rare columnar stromatolites also occur the microbial fossils which include putative autotrophic and heterotrophic eukaryotes are similar to those found in chert in the underlying preglacial units they indicate that microbial life adapted to shallow water carbonate environments did not suffer the significant extinction postulated for this phase of low latitude glaciation and that trophic complexity survived through snowball earth times

sediment oxygen profiles in a super oxygenated antarctic lake perennially ice covered lakes are found in the mcmurdo dry valleys of southern victoria land antarctica in contrast to temperate lakes that have diurnal photic periods antarctic and arctic lakes have a yearly photic period an unusual feature of the antarctic lakes is the occurrence of o2 at supersaturated levels in certain portions of the water column here we report the first sediment o2 profiles obtained using a microelectrode from a perennially ice covered antarctic lake sediment cores collected in january and october 1987 from lake hoare in taylor valley show oxygenation down to 15 and in some cases 25 cm the oxygenation of sediments several centimeters below the sediment water interface is atypical for lake sediments and may be characteristic of perennially ice covered lakes there is a significant difference between the observed january and october sediment o2 profiles several explanations may account for the difference including seasonality a time dependent model is presented which tests the feasibility of a seasonal cycle resulting from the long photoperiod and benthic primary production in sediments overlain by a highly oxygenated water column

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

trapping of aeolian sediments and build up of the ice cover of a dry based antarctic lake among the perennially frozen lakes of the dry valleys of south victoria land antarctica some are dry based i e frozen to the bottom one of these is studied here by a multiparametric investigation isotopic composition in da nd 18 o ions gas and ice texture analyses a sediment layer about 10 cm thick appearing at a depth of 3 5m is also studied by grain size x ray diffraction and scanning electron microscope analyses the information retrieved indicates that this ice block lake results from a build up in two steps and explains how aeolian sediments were included as a layer into the ice copyright 2002 john wiley sons ltd