the bering land bridge a moisture barrier to the dispersal of steppe tundra biota the bering land bridge blb connected the two principal arctic biological refugia western and eastern beringia during intervals of lowered sea level in the pleistocene fossil evidence from lowland blb organic deposits dating to the last glaciation indicates that this broad region was dominated by shrub tundra vegetation and had a mesic climate the dominant ecosystem in western beringia and the interior regions of eastern beringia was steppe tundra with herbaceous plant communities and arid climate although western and eastern beringia shared many species in common during the late pleistocene there were a number of species that were restricted to only one side of the blb among the vertebrate fauna the woolly rhinoceros was found only to the west of the blb north american camels bonnet horned musk oxen and some horse species were found only to the east of the land bridge these were all steppe tundra inhabitants adapted to grazing the same phenomenon can be seen in the insect faunas of the western and eastern beringia the steppe tundra beetle fauna of western beringia was dominated by weevils of the genus stephanocleonus a group that was virtually absent from eastern beringia the dry adapted weevils lepidophorus lineaticollis and vitavitus thulius were important members of steppe tundra communities in eastern beringia but were either absent or rare in western beringia the leaf beetles chrysolina arctica c brunnicornis bermani and galeruca interrupta circumdata were typical members of the pleistocene steppe tundra communities of western beringia but absent from eastern beringia on the other hand some steppe tundra adapted leaf beetles managed to occupy both sides of the blb such as phaedon armoraciae much of the blb remains unstudied but on biogeographic grounds it appears that there was some kind of biological filter that blocked the movements of some steppe tundra plants and animals across the blb

arsenic in groundwater from mineralised proterozoic basement rocks of burkina faso this study describes the hydrogeochemistry and distributions of as in groundwater from a newly investigated area of burkina faso groundwaters have been sampled from hand pumped boreholes and dug wells close to the town of ouahigouya in northern burkina faso although most analysed groundwaters have as concentrations of less than 10 g l 1 they have a large range from 0 5 to 1630 g l 1 the highest concentrations are found in borehole waters all dug wells analysed in this study have as concentrations of 10 g l 1 skin disorders melanosis keratosis and more rare skin tumour have been identified among the populations in three villages in northern burkina faso two within the study area although detailed epidemiological studies have not been carried out similarities with documented symptoms in other parts of the world suggest that these are likely to be linked to high concentrations of as in drinking water the high as groundwaters observed derive from zones of au mineralisation in birimian lower proterozoic volcano sedimentary rocks the au occurring in vein structures along with quartz and altered sulphide minerals pyrite chalcopyrite arsenopyrite however the spatial variability in as concentrations in the mineralised zones is large and the degree of testing both laterally and with depth so far is limited hence concentrations are difficult to predict on a local scale from available data the groundwater appears to be mainly oxic and the dissolved as occurs almost entirely as as v although concentrations are highest in groundwaters with dissolved o2 concentrations 2 mg l 1 the source is likely to be the oxidised sulphide minerals and secondary fe oxides in the mineralised zones positive correlations are observed between dissolved as and both mo and w which are also believed to be derived from ore minerals and oxides in the mineralised zones the discovery of high as concentrations in some groundwaters from the birimian rocks of northern burkina faso reiterates the need for reconnaissance surveys in mineralised areas of crystalline basement

diagenetic cycling of arsenic in amazon shelf sediments in order to help elucidate major natural controls on the diagenetic behavior of as vertical profiles of total dissolved and solid phase as were measured in amazon shelf deposits a deltaic region little influenced by human activity arsenic distributions are typically characterized by subsurface porewater maxima and surficial solid phase enrichment maximum porewater as concentrations 2 4 m are an order of magnitude greater than levels reported in most other coastal marine environments and elevated concentrations extend several meters below the sediment surface dissolved as varies inversely with easily leachable as 40 140 nmol g 1 in the solid phase and directly with increases in solid phase fe ii these patterns reflect a strong redox coupling with fe whereby oxidized as is associated with fe oxyhydroxides in surface sediments then subsequently reduced and released upon burial in the extensive suboxic zone upward diffusion and intense physical reworking of sediments presumably releases the dissolved arsenic fraction to the water column or allows for re adsorption in surface sediments arsenic porewater concentrations generally increase away from the river in some cases regular seasonal variations are evident apparently corresponding to nonsteady state ingrowth of diagenetic profiles following extensive sediment reworking during rising river flow the massive cycling of as in amazon shelf sediments is likely due to the combined effects of intense chemical weathering in regions of the drainage basin production of oxides and a turbulent physical regime present on the shelf both of which promote sedimentary cycling of fe and coupled elements during early diagenesis

multiple water isotope proxy reconstruction of extremely low last glacial temperatures in eastern beringia western arctic abstract precipitation isotopes are commonly used for paleothermometry in high latitude regions here we present multiple water isotope proxies from the same sedimentary context perennially frozen loess deposits in the klondike goldfields in central yukon canada representing parts of marine isotope stages mis 4 3 and 2 allowing us to uniquely corroborate fractionations and temperature conversions during these late pleistocene cold stages we include new and existing proxy data from relict wedge ice a direct archive for snowmelt relict pore ice an archive for bulk soil water integrating year round precipitation and hydrated volcanic glass shards and fossil plant waxes which are also thought to integrate year round precipitation but are subject to large fractionations in some cases our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean new transfer functions calibrated specifically for northern north america d precip 3 1 c 1 t 155 and 18 o precip 0 41 c 1 t 20 2 and novel insights on the apparent net fractionation correction for eastern beringian steppe tundra plant waxes e wax precip 59 10 the snowmelt origin of wedge ice ensures a relatively constrained winter spring seasonality of contributing precipitation as supported by the consistency between water isotope measurements from late holocene wedge ice and modern winter spring precipitation wedge ice dating to the transitional mis 3 2 is isotopically depleted relative to modern spring winter precipitation by an amount that indicates a temperature depression of 14 5 c below modern the soil water origin of pore ice and other proxies integrating year round precipitation from soil water allows for a more variable precipitation seasonality the isotopic composition of modern pore ice is consistent with mean annual precipitation however the isotopic composition of pore ice during mis 3 2 converges on wedge ice values signalling an increase in the ratio of cold to warm season precipitation integrated by pore ice during glacial times possibly due to drier summers as supported by the fossil record and climate model simulations in the study region water isotope proxies integrating year round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality as detected here and thus are best interpreted as upper bound estimates based on these proxies we estimate that annual temperatures during mis 4 3 2 and 2 were depressed below the modern climate to a maximum of 18 c 16 c and 21 c 4 5 c respectively our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate and may be particularly important for studies of the major climate transformations over glacial interglacial timescales

geochemistry of iron ochres and mine waters from levant mine cornwall abstract the geochemistry of metal rich mine waters and mineral precipitates from the levant mine cornwall has been examined sulphide oxidation at levant mine has produced a wide range of secondary sulphides oxides chlorides sulphates and carbonates in a gossan environment the mine waters display a wide variation in alkalinity ph chloride sulphate sodium potassium and heavy metal content which can be explained by variable degrees of mixing between acidic metal rich rock drainage waters and neutral to alkaline sea waters transition metals are soluble in the acidic mine waters with concentrations up to 665 mg l cu 41 mg l zn 76 mg l mn 6 mg l co and 2500 mg l total fe the production of acid rock drainage and leaching of metals can be related to sulphide oxidation where these metal rich acidic waters mix with infiltrated sea water neutralization occurs and some metals are precipitated principally cu where pools of mine drainage are stagnant native copper and cuprite are precipitated frequently observed replacing iron pipes and rail tracks and wooden shaft supports due to electrode potential differences in these solutions dissolved copper species are also reduced by interaction with wood derived organic species precipitation of iron oxyhydroxides caused by a ph increase also occurs and leads to coprecipitation of other metals including cd co ph mn ag and zn thus limiting the release of dissolved metals in solution from the mine however the release of suspended metal rich ochres in mine discharge waters with high ph zn cd mn ni sn sb as bi cu co and ag will still present a potential environmental hazard

stratigraphic context of old crow tephra holitna lowland interior southwest alaska abstract a thick deposit of old crow tephra was discovered in a bluff exposure along the middle holitna river near the kulukbuk hills 61 20 n latitude 157 10 w longitude in interior southwest alaska this locality is the southwesternmost known deposit of old crow tephra in alaska thickness and grain size data from this site support a source volcano in the eastern aleutian arc pleistocene stratigraphic sequences in the lowland are dominated by upward fining eolian sand sheet deposits and loess separated by organic silt these deposits record at least two episodes of regional glaciation and an intervening nonglacial period marine oxygen isotope stage 3 stage 5 or both old crow tephra crops out near the top of the lower upward fining eolian unit indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation the sequence of eolian deposits that contain old crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6 whereas the overlying eolian sequence formed during the last glaciation stage 2 this stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission track and thermoluminescence ages of ca 140 000 10 000 yr b p

arsenic enrichment in groundwater of west bengal india geochemical evidence for mobilization of as under reducing conditions abstract the mechanism of as release and source s of as has been investigated in a small part of a watershed in the murshidabad district of west bengal analyses include major ion and trace element concentrations as well as o h and s isotope ratios of groundwater surface water and a thermal spring the results indicate that all water samples belong to the ca hco 3 type except for the thermal spring which is of the na hco 3 type shallow and deeper groundwaters have distinct hydrochemical features high as contents were registered only in the deeper groundwater horizon factor analysis and the distribution pattern of major and trace elements indicate that as is present in the aquifer as a scavenged phase by fe iii and to a lesser extent by mn iv phases the release of as into the groundwater occurs gradually in successive stages corresponding to the actual redox state in the aquifer the main stage of as release is related to the bacterial reduction of fe iii to fe ii i e to the simultaneous dissolution of fe oxyhydroxides low redox conditions in highly polluted areas are indicated by low so 4 concentration and high 34 s values during bacterial so 4 reduction residual so 4 in groundwater is depleted in the lighter s isotope 32 s however the cause of the gradual decrease of the redox state in the groundwater is still not well understood

late wisconsin environments of the bering land bridge abstract late wisconsin paleobotanical and fossil insect data from the central and northern sectors of the bering land bridge indicate widespread mesic shrub tundra environments even during the last glacial maximum vegetation before the last glacial maximum was a birch heath graminoid tundra with few or no steppe elements shrubs were not an important element of the vegetation but were present in small numbers during the interval 20 000 14 000 yr bp land bridge vegetation was dominated by birch graminoid tundra with small ponds containing aquatic plants heaths were relatively unimportant insects from this interval were indicative of arctic climate with drier tundra than during the late glacial during the late glacial interval 14 000 11 000 yr bp land bridge vegetation was dominated by birch heath graminoid tundra with small ponds choked with aquatic plants the insect record indicates open ground habitats dominated by mesic tundra by 11 000 yr bp insect data suggest that summer temperatures on the emergent bering shelf were warmer than present day upland regions in western alaska summer temperatures on the chukchi shelf were warmer than the present day north slope of alaska contrary to previous hypotheses we found no evidence of steppe tundra on the land bridge new accelerator mass spectrometer ams 14c dates show that much of the land bridge was above sea level and thus available for human and animal migration until as late as 11 000 yr bp

late quaternary vegetation of chukotka northeast russia implications for glacial and holocene environments of beringia abstract two lake records from the kankaren region of southern chukotka when combined with other palynological and macrofossil data document spatial and temporal variations in the regional vegetation history since 21 000 14c 25 400 cal yr bp full glacial environments were severely cold and arid in central and northern chukotka whereas southern sites experienced conditions that were relatively moist although still drier than present southern chukotka may represent a western extension of environments of the land bridge proper including a possible moisture barrier to intercontinental migration shrub betula tundra established earliest in southern chukotka 15 800 14 000 14c 19 000 16 700 cal yr bp 13 000 14c 15 300 cal yr bp central and north pinus pumila earliest in the north 9600 14c 11 100 cal yr bp 7600 14c 8400 cal yr bp south and shrub alnus earliest in both the south and north 12 000 11 000 14c 13 800 12 900 cal yr bp these patterns support the presence of cryptic refugia for betula and alnus in chukotka during the full glaciation in contrast p pumila probably migrated into chukotka from populations located in the northern coastal lowlands and from mountainous regions of southwestern beringia evidence for a thermal optimum 11 000 8000 14c 12 900 9000 cal yr bp is strong in northern chukotka but is absent in central and southern areas

late wisconsin climate in northeastern usa and southeastern canada reconstructed from fossil beetle assemblages mean july and january temperatures are reconstructed from radiocarbon dated fossil beetle assemblages yielding a synthesis of palaeoclimatic history of the regions south of the laurentide ice sheet in north america from 35 000 to 8500 yr bp mean july temperatures close to the last glacial maximum were 11 12 c colder than present mean january temperatures were possibly 10 19 c colder mutual climatic range analyses of the beetle assemblages show warming of mean summer temperatures as early as 13 7 kyr although ice proximal sites were consistently about 5 c cooler than ice distal sites late glacial mean summer temperatures peaked between 12 and 11 kyr then remained fairly constant through the early holocene mean winter temperatures did not reach modern values until after 10 kyr

two step deglaciation at the oxygen isotope stage 6 5e transition the zeifen kattegat climate oscillation comparison of marine lacustrine and terrestrial records from twenty four sites suggests the existence of a younger dryas type climate oscillation just prior to the oxygen isotope stage 6 5e boundary these records include results from biostratigraphic pedostratigraphic and speleothem studies as well as analyses of stable isotope compositions of marine records and ice cores the climate oscillation is named after the warm zeifen interstadial and the cold kattegat stadial the zeifen interstadial may be related to a major meltwater pulse in the baffin bay labrador sea norwegian sea region the climate oscillation is presumably in part a result of a variation in ocean circulation especially in the strength of the north atlantic drift but changes in the atmospheric circulation also played an important role the geographically widespread distribution of the oscillation suggests that the two step deglaciation influenced both the northern and southern hemispheres c 1996 elsevier science ltd

identifying bias in cold season temperature reconstructions by beetle mutual climatic range methods in the pliocene canadian high arctic abstract well preserved beetle elytra from the fossil and subfossil record are used by palaeoclimatologists to estimate past temperatures beetle derived estimates of temperature across the pliocene arctic are consistently lower than those derived from other palaeoclimate proxies here we test if that pattern is attributable to either the modern dataset or specific mutual climatic range method mcrm we used a global dataset of observations global biodiversity information facility for modern beetles as opposed to a north american regional dataset and a consistent mcrm for comparison to vegetation derived estimates termed cracle climate reconstruction analysis using coexistence likelihood estimation rather than different mcrm methods for each analysis beetle derived estimates from one site beaver pond are consistently much lower than the vegetation derived estimates stable isotope results from flora and fauna and summer temperatures from bacterial tetraethers the reanalysis of beetle data produced a small reduction in proxy estimate mismatch overall we found good agreement among proxy estimates of maximum temperature of the warmest month for two of the three sites in the canadian arctic but increasingly poorer agreement for warmest quarter coldest quarter and minimum temperature of the coldest month this pattern may be due to beetles avoidance mechanisms and a climate space different from modern calibration sets during the pliocene beetle derived temperature estimates especially cold season should be interpreted with caution when reconstructing palaeoclimates

late quaternary mis 3 to mis 1 stratigraphic transitions in a highland beringian landscape along the kuskokwim river alaska stratigraphic records extending to marine oxygen isotope stage mis 3 57 000 29 000 cal yr bp or older in beringia are extremely rare three stratigraphic sections in interior western alaska show near continuous sedimentological and environmental progressions extending from at least mis 3 if not older through mis 1 14 000 cal yr bp present the kolmakof sue creek and vabm vertical angle bench mark kuskokwim sections along the central kuskokwim river once a highland landscape at the fringe of central and eastern beringia contain aeolian deposition and soil sequences dating beyond 50 000 14 c yr bp thick peaty soil shallow lacustrine and tephra deposits represent the mis 3 interstade or older sand sheet and loess deposits wedge cast development and very thin soil development mark the later mis 3 period and the transition into the mis 2 stade 29 000 14 000 cal yr bp loess accumulation with thicker soil development occurred between 16 000 13 500 cal yr bp at the mis 2 and mis 1 transition after 13 500 cal yr bp loess accumulation waned and peat development increased throughout mis 1 these stratigraphic sequences represent transitions between a warm and moist period during mis 3 to a cooler and more arid period during mis 2 then a return to warmer and moister climates in mis 1

linking glacier extent and summer temperature in ne russia implications for precipitation during the global last glacial maximum abstract it is generally assumed that during the global last glacial maximum glgm i e 18 24 ka bp dry climatic conditions in ne russia inhibited the growth of large ice caps and restricted glaciers to mountain ranges however recent evidence has been found to suggest that glacial summers in ne russia were as warm as at present while glaciers were more extensive than today as a result we hypothesize that precipitation must have been relatively high in order to compensate for the high summer temperatures and the resulting glacial ablation we estimate precipitation abundance by mass balance calculations for the palaeo glaciers on kamchatka and in the kankaren range using a degree day modelling ddm approach and find that precipitation during the glgm was likely comparable to or even exceeded the modern average we suggest that stronger than present southerly winds over the northwest pacific may have accounted for the abundant precipitation the ddm results imply that summer temperature rather than aridity limited glacier extent in the southern pacific sector of ne russia during the glgm

late pleistocene and holocene seasonal temperatures reconstructed from fossil beetle assemblages in the rocky mountains abstract mutual climatic range mcr analysis was applied to 20 fossil beetle assemblages from 11 sites dating from 14 500 to 400 yr b p the fossil sites represent a transect of the rocky mountain region from northern montana to central colorado the analyses yielded estimates of mean july and mean january temperatures the oldest assemblage 14 500 yr b p yielded mean july values of 10 11 c colder than present and mean january values 26 30 c colder than present postglacial summer warming was rapid as indicated by an assemblage dating 13 200 yr b p with mean july values only 3 4 c cooler than modern by 10 000 yr b p several assemblages indicate warmer than modern mean summer and winter values by 9000 yr b p mcr reconstructions indicate that both summer and winter temperatures were already declining from an early holocene peak mean july values remained above modern levels and mean january values remained below modern levels until 3000 yr b p a series of small scale oscillations followed

late quaternary vegetation and climate history of the central bering land bridge from st michael island western alaska pollen analysis of a sediment core from zagoskin lake on st michael island northeast bering sea provides a history of vegetation and climate for the central bering land bridge and adjacent western alaska for the past 30 000 14 c yr b p during the late middle wisconsin interstadial 30 000 26 000 14 c yr b p vegetation was dominated by graminoid herb tundra with willows salix and minor dwarf birch betula nana and ericales during the late wisconsin glacial interval 26 000 15 000 14 c yr b p vegetation was graminoid herb tundra with willows but with fewer dwarf birch and ericales and more herb types associated with dry habitats and disturbed soils grasses poaceae dominated during the peak of this glacial interval graminoid herb tundra suggests that central beringia had a cold arid climate from 30 000 to 15 000 14 c yr b p between 15 000 and 13 000 14 c yr b p birch shrub ericales sedge moss tundra began to spread rapidly across the land bridge and alaska this major vegetation change suggests moister warmer summer climates and deeper winter snows a brief invasion of populus poplar aspen occurred ca 11 000 9500 14 c yr b p overlapping with the younger dryas interval of dry cooler climate during the latest wisconsin to middle holocene the bering land bridge was flooded by rising seas alder shrubs alnus crispa colonized the st michael island area ca 8000 14 c yr b p boreal forests dominated by spruce picea spread from interior

the mutual climatic range method of palaeoclimate reconstruction based on insect fossils new applications and interhemispheric comparisons abstract the mutual climatic range mcr method of palaeoclimate reconstruction has been employed in europe for the last decade a quantitative calibrated method mcr has many advantages over qualitative methods more recent applications deal with eastern and central north america and the method is also being developed for desert and arctic faunas the climate envelopes for north american beetles have been compiled using a 25 km gridded north american climate database that pairs climate parameters with modern collection sites modern tests of the reliability of the mcr method for north american species yielded similar results to prior european tests linear regressions of predicted on observed values yielded equations used to calibrate the mcr estimates work is under way to develop mcr estimates of mean annual precipitation for fossil assemblages from the desert southwest where moisture conditions may play a more important role in determining beetle species ranges an examination of british and north american mean july temperature reconstructions during the late wisconsinan glacial interval compares and contrasts three sets of records the north american records show no indication of the younger dryas cooling that is clearly marked in records from northwest europe the mcr method adds vigour to our reconstructions and allows us to compare between regions and with other palaeoenvironmental methods

arsenic speciation in soil porewaters from the ashanti mine ghana abstract at the ashanti au mine in southwest ghana arsenopyrite constitutes an important part of the hypogene ore assemblage often hosting significant concentrations of au the oxidation of arsenopyrite either through lateritic weathering or during mineral processing releases as into the environment the speciation of as in soil porewaters both from uncontaminated soils and those overlain by mine waste has been assessed in aerobic soils overlying weathered au as mineralization in the bedrock as was present in concentrations of 189 1025 ppm in soil and porewater concentrations ranged from 86 2 to 557 g l 1 arsenic in these waters was found to be largely present as arsenate approximately 78 95 of the total as with arsenite monomethylarsonic acid mmaa and dimethylarsinic acid dmaa also present where arsenite concentrations are greater than arsenate no organoarsenical species were observed in the uncontaminated soils overlying unmineralized bedrock background as concentrations were in the range of 12 5 20 2 ppm and porewater concentrations ranged from 11 2 to 20 g l 1 in these porewaters arsenate was the dominant species no organoarsenical species were observed in these waters suggesting that there is a possible threshold level of total as concentration required above which methylation of as by soil microorganisms takes place in the acidic soils contaminated by mine tailings arsenite was the major species present up to 45 of total as in the aerobic soils and 79 of total as in the anaerobic soils although the soils were underlain by the unmineralized bedrock soil as concentration ranged from 40 5 to 1290 ppm and as concentration in extracted porewaters from anaerobic soils ranged from 70 2 to 110 g l 1 and in aerobic soil from 70 8 to 599 g l 1 in the aerobic soils mmaa dmaa and arsenate were also present but only arsenate was found along with arsenite in the anaerobic soil porewaters

toward a geochemical mass balance of major elements in lake qinghai ne tibetan plateau a significant role of atmospheric deposition abstract sediments in lake qinghai archive important information about past environmental changes in order to faithfully interpret the sediment records and constrain the elemental cycles it is critical to trace various sources of sediments in the lake the results show that the elemental input output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate mar of lake qinghai sediments a realistic model must include contributions of dry wet atmospheric deposition that allow the major element mass balance for the lake to be defined the budget estimation is based on mass balances of si and al which are relatively immobile and carried to the lake via particulate forms estimated annual budget of dry atmospheric deposition is 1 3 0 3 103 kt a accounting for 65 of the total inputs to the lake sediments assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake the resultant flux of 300 45 g m2 a falls within the flux average of the desert area 400 g m2 a and the loess plateau 250 g m2 a consistent with the geographical setting of lake qinghai the role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account this highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide the results also indicate that nearly all ca input was preserved in the lake sediments under modern conditions consistent with ca2 supersaturation of the lake water

middle to late wisconsinan climate and ecological changes in northern alaska evidences from the itkillik river yedoma abstract continuous paleoenvironmental records covering the period prior to the last glacial maximum in northeastern beringia are sparse this study presents a multi proxy analysis of a 35 m high yedoma exposure located on the right bank of the itkillik river in alaska the exposure accumulated over 39 thousand years kyr during the middle wisconsinan interstadial and the late wisconsinan glacial advance we identified five stratigraphic units based on pollen carbon and ice content and isotopic composition 18o of the sediments middle wisconsinan climate in northern alaska promoted peat accumulation prior to 33 6 cal kyr bp calibrated kyr before present reconstructed july air temperatures were 1 2 c lower than current at 34 8 cal kyr bp consistent with the timing of the interstadial climatic optimum in interior alaska and yukon colder by up to 4 c and drier conditions characterize the transition from interstadial to glacial conditions between 33 6 and 29 8 cal kyr bp late wisconsinan 29 8 17 9 cal kyr bp july air temperatures were 2 3 c lower than today with grassland vegetation dominated by poaceae artemisia and forbs in contrast to the modern cyperaceae dominance moister and warmer environmental conditions after 17 9 cal kyr bp correspond to the late glacial to early holocene interval

arsenic distributions in porewaters and sediments of puget sound lake washington the washington coast and saanich inlet b c solid phase as mn al and excess 210pb and dissolved total as as 3 as 5 mn 2 fe 2 po 34 nh 4 and h2s profiles in 12 cores from puget sound lake washington the washington coast and saanich inlet b c are presented typically strong correlations between solid phase as and mn concentration maxima in surficial sediments are a result of intense as scavenging in the overlying waters by mn or ferich phases or solid phase as dissolution at depth followed by upward diffusion and co precipitation with mn or fe oxides at or near the sediment water interface atypically anthropogenic inputs cause high sedimentary as concentrations without accompanying high mn levels sedimentary as fluxes are an order of magnitude greater in puget sound and lake washington than off the washington coast and in saanich inlet porewater total as concentration profiles exhibit sub surface maxima with magnitudes 10 60 times greater than in overlying bottom waters porewater maxima in marine environments are proportional to associated solid phase as concentrations these maxima consistently occur within 1 0 cm of the bottom of the 210pb derived surface mixed layer suggesting solid phase as release to porewater in response to a redox gradient across this mixing boundary dissolved as behavior beneath these maxima indicates as removal to solid phases in marine but not lacustrine porewaters porewater as 3as 5 ratios are 1 0 for washington coastal environments and usually between 1 0 4 0 for puget sound and lake washington as 5 is below the detection limit in porewaters of saanich inlet when the overlying bottom water is anoxic but as 3as 5 ratios as low as 2 8 exist in near surface porewater under oxic bottom water conditions

postglacial climates inferred from a lake at treeline southwest yukon territory canada abstract pollen chironomid and ostracode records from a lake located at alpine treeline provide regional paleoclimate reconstructions from the southwest yukon territory canada the pollen spectra indicate herbaceous tundra existed on the landscape from 13 6 11 ka followed by birch shrub tundra until 10 ka although picea pollen dominated the assemblages after 10 ka low pollen accumulation rates and picea percentages indicate minimal treeline movement through the holocene chironomid accumulation rates provide evidence of millennial scale climate variability and the chironomid community responded to rapid climate changes ostracodes were found in the late glacial and early holocene but disappeared due to chemical changes of the lake associated with changes in vegetation on the landscape inferred mean july air temperature total annual precipitation and water depth indicate a long term cooling with increasing moisture from the late glacial through the holocene during the younger dryas 12 9 11 2 ka cold and dry conditions prevailed the early and mid holocene were warm and dry with cool wet conditions after 4 ka and warm dry conditions since the end of the little ice age

oxygen isotope record of sea level and climate variations in the sulu sea over the past 150 000 years the sulu sea is located in the warm pool of the western pacific ocean where mean annual temperatures are the highest of anywhere on earth because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change changes in the oxygen isotope composition of planktonic foraminifera from sulu sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial interglacial and millenial timeseales and such records have been obtained for the late pleistocene epoch and the last deglaciation1 3 here i present results that extend the millenial time resolution record back to 150 000 years before present on timescales of around 10 000 years the sulu sea oxygen isotope record matches changes in sea level deduced from coral terraces on the huon peninsula4 this is particularly the case during isotope stage 3 an interglacial period 23 000 to 58 000 years ago where the sulu sea oxygen isotope record deviates from the specmap deep ocean oxygen isotope record5 thus these results support the idea4 6 that there were higher sea levels and less continental ice during stage 3 than the specmap record implies and that sea level during this interglacial was just 40 50 metres below present levels the subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought

arctic north american seasonal temperatures from the latest miocene to the early pleistocene based on mutual climatic range analysis of fossil beetle assemblages late tertiary and early quaternary fossil beds in the arctic regions of north america have yielded abundant well preserved remains of plants and arthropods documenting the existence of coniferous forests in the high arctic latitudes nearly all of the beetle coleoptera specimens in these fossil assemblages represent extant species we have applied the mutual climatic range mcr method of paleotemperature analysis to fossil beetle assemblages from 11 sites to estimate mean summer t max and winter t min temperatures we found that arctic t min values during the latest miocene and pliocene were substantially warmer than they are today the mcr estimates therefore support the scenario derived from the paleobotanical data namely that arctic pliocene climates were far less continental several pliocene age assemblages from the high arctic yielded t max estimates 9 10 c warmer than modern values at the sites this is the same degree of warming required to allow coniferous forests to grow in the high arctic by 3 million years bp a cooling trend is marked in the paleobotanical and fossil beetle evidence from alaska all assemblages dating between 5 7 and 2 million years bp yielded calibrated t max values between 12 4 and 13 8 c regardless of location thus the insect fossil data support the theory that there was far less latitudinal gradation in temperatures during the late pliocene than there is today our reconstructions suggest regional climatic cooling especially winter temperatures began by at least 2 million years bp

consolidation and incipient oxidation of alkaline arsenopyrite bearing mine tailings macraes mine new zealand abstract fine grained ca 15 m arsenopyrite bearing mine tailings have been exposed to drying and oxidation for 4 a pending relocation the tailings are still partly covered by a pond of decanted pore waters the water table in drying tailings has lowered by 1 3 m and desiccation cracks up to 2 cm wide have formed on the 1 m scale extending through the unsaturated zone tailings in the unsaturated zone have similar pore water contents to saturated tailings typically 16 32 wt water saturated tailings retain alkaline ph ca 10 from the mine cyanidation plant but ph lowers progressively towards ca 7 near the surface or near desiccation cracks in the unsaturated zone the redox state of the tailings changes in parallel with ph with an empirical relationship eh mv 55 ph 290 water in the remnant decant pond reflects this relationship also unsaturated tailings have variable but low permeabilities typically 10 3 to 10 4 m day and more permeable horizons have allowed incursion of oxygenated air and or rain water from desiccation cracks sulphide grains in all tailings examined are unaltered sulphides and solutions in the tailings are out of thermodynamic equilibrium predicted from the redox ph conditions due to kinetic constraints incursion of rain water locally facilitates deposition from pore waters of insoluble fe oxide and arsenate minerals thus fixing as in the dry unsaturated tailings

geochemical controls of elevated arsenic concentrations in groundwater ester dome fairbanks district alaska abstract ester dome an upland area near fairbanks alaska was chosen for a detailed hydrogeochemical study because of the previously reported elevated arsenic in groundwater and the presence of a large set of wells amenable to detailed sampling ester dome lies within the fairbanks mining district where gold bearing quartz veins typically containing 2 3 vol sulfide minerals arsenopyrite stibnite and pyrite have been mined both underground and in open cuts gold bearing veins on ester dome occur in shear zones and the sulfide minerals in these veins have been crushed to fine grained material by syn or post mineralization movement groundwater at ester dome is circumneutral ca hco 3 to ca so 4 type and ranges from dilute specific conductance of 48 s cm to more concentrated specific conductance as high as 2070 s cm in general solute concentrations increase down hydrologic gradient redox species indicate that the groundwaters range from oxic to sub oxic low dissolved oxygen fe iii reduction no so 4 reduction waters with the highest fe concentrations as high as 10 7 mg l are the most anoxic dissolved as concentrations range from 3 mo f or u such that desorption of arsenic from clays or oxides also does not control arsenic mobility oxidation of arsenopyrite and dissolution of scorodite in the near surface environment appears to be the primary control of dissolved as in this upland area more specifically the elevated as concentrations are spatially associated with sulfidized shear zones and localities of gold bearing quartz veins consistent with this interpretation elevated dissolved sb concentrations as high as 59 g l also correlated with occurrences of hypogene sulfide minerals were measured in samples with high dissolved as concentrations

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

responses of an arctic landscape to lateglacial and early holocene climatic changes the importance of moisture many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes and their sensitivities to climate change are poorly understood stratigraphic records of land surface processes and vegetation change in the arctic foothills of northern alaska reveal how tundra landscapes responded to climatic changes between 13 000 and 8000 14 c yr bp peat deposition began and shrub vegetation became widespread ca 12 500 14 c yr bp probably in response to the advent of warmer and wetter climate increased slope erosion caused rapid alluviation in valleys and populus trees spread northward along braided floodplains before 11 000 14 c yr bp lake levels fell and streams incised their floodplains during the younger dryas yd 11 000 10 000 14 c yr bp a hiatus in records of populus suggest that its geographic range contracted and pollen records of other species suggest a cooler and drier climate during this interval basal peats dating to the yd are rare suggesting that rates of paludification slowed immediately after 10 000 14 c yr bp lake levels rose streams aggraded rapidly again intense solifluction occurred and populus re invaded the area moist acidic tundra vegetation was widespread by 8500 14 c yr bp along with wet organic rich soils most of these landscape scale effects of climatic change involved changes in moisture although low temperature is the most conspicuous feature of arctic climate shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions r 2002 elsevier science ltd all rights reserved

late glacial and holocene landscapes of central beringia abstract new palynological and sedimentological data from st lawrence island present a rare view into late glacial and holocene environments of the central bering land bridge the late glaciation was a time of dynamic landscape changes in south central beringia with active thermokarst processes including the formation and drainage of thaw lakes the presence of such a wet unstable substrate if widespread probably would have had an adverse impact on food sources and mobility for many of the large mammal populations the establishment of betula shrub tundra on the island suggests late glacial summers that were warmer than present consistent with regional paleoclimatic interpretations however the increasing proximity to the bering sea as postglacial sea levels rose modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of beringia at this time the mid to late holocene is marked by more stable land surfaces and development of sphagnum and cyperaceae peat deposits the accumulation of organic deposits decline of shrub betula and decrease in thermokarst disturbance suggest that conditions were cooler than the previous a recent decline in peat accumulation at the study sites may relate to local geomorphology but similar decreases have been noted for other arctic regions

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

late pleistocene environments of the western noatak basin northwestern alaska glacial lake noatak formed repeatedly during middle and late pleistocene time as expanding glaciers from the delong mountains blocked the noatak river valley downcutting by the noatak river has exposed thick sediment successions in bluffs up to 86 m high two river bluffs nk 26 and nk 29a contain correlative organic rich flood plain deposits that were formed during and after deposition of the old crow tephra at about the transition between oxygen isotope stage 6 and oxygen isotope stage 5 at the beginning of the last interglaciation both bluffs also contain older interglacial or interstadial flood plain deposits of uncertain age pollen and beetle remains were recovered from the older and younger flood plain deposits at each bluff pollen from the younger flood plain deposits suggests tundra vegetation with local dominance of sedge juniperus abundances were locally high especially around the time of old crow tephra deposition mutual climatic range mcr estimates from the insect fossil assemblages suggest that mean summer temperatures tmax near the time of old crow tephra deposition were about 2 c colder than modern mean winter temperatures were very similar to those of today a younger sample from the same interglacial deposit yielded a tmax estimate of 2 c warmer than modern signaling interglacial warming pollen from the older interglacial deposit at nk 29a suggests mesic tundra with boreal forest more distant than it is today mcr analysis of a possibly correlative older interglacial deposit at nk 26 suggests a tmax about 2 c below present

a framework for interpreting paleoclimatic variations in eastern beringia abstract paleoclimatic variations in a particular region can be viewed as the outcome of the superimposition of the effects of a number of large scale controls a framework for understanding paleoclimatic variations in a region can be established by considering the long term history of those controls jointly with climatic modeling results that illustrate how regional climates respond to changes of individual controls the relevant controls of late quaternary paleoclimatic variations in eastern beringia include 1 the size of the ice sheet which influences both atmospheric circulation and temperature 2 insolation which influences mainly temperature and seasonality 3 carbon dioxide concentration in the atmosphere which influences temperature and 4 feedbacks involving sea ice sea surface temperatures and snow cover which reinforce the insolation effects we review the results of a number of paleoclimatic experiments with general circulation models to illustrate the potential response of eastern beringia to the variations of these controls we then present a framework for understanding paleoclimatic variations in eastern beringia by describing the likely responses of the climate of this region to the known variations in the controls in addition we discuss key times during the quaternary when particular combinations of the controls give rise to natural experiments which lend themselves to the testing of particular hypotheses our understanding of the nature of climatic variations at high latitudes should increase through examination of paleoclimatic evidence that documents the response of the region at those key times

differential insect and mammalian response to late quaternary climate change in the rocky mountain region of north america abstract of the 200 beetle species identified from rocky mountain late pleistocene insect faunal assemblages 23 are no longer resident in this region none of the 200 species is extinct in contrast to this only 8 of 73 identified mammal species from rocky mountain late pleistocene assemblages are no longer resident in the rockies and 12 species are now extinct since both groups of organisms are highly mobile it would appear that their responses to the large scale fluctuations of climate associated with the last 125 000 years have been considerably different most strikingly contrasting with the insects there are no mammals in the rocky mountain late pleistocene fossil record that are found exclusively today in the pacific northwest pnw region the pnw does have a distinctive modern mammalian fauna but only one of these keen s myotis has a fossil record outside the pnw region in the eastern and central united states no modern pnw vertebrate species have been found in any rocky mountain fossil assemblages based on these data it appears that there has been little or no mammalian faunal exchange between the pnw region and the rocky mountains during the late pleistocene or holocene this is in stark contrast to the fossil beetle record where pnw species are a substantial component in many faunas right through to the late holocene

an extensive middle to late pleistocene tephrochronologic record from east central alaska abstract chester bluff cb in yukon charley rivers national preserve ycnp alaska contains an extensive middle to late pleistocene tephra record within thick loess deposited on a terrace the regionally prominent old crow oc tephra 140 10 ka gi tephra 560 80 ka of fairbanks the preido hill prh tephra of the klondike and vt tephra 77 8 4 1 ka of both the klondike and fairbanks were found at cb the presence of these tephra beds will aid in correlating disparate paleoenvironmental records across eastern beringia there are 15 new tephra beds 11 from the wrangell volcanic field wvf and or hayes volcano one from the aleutian arc alaska peninsula aaap and three unclassified beds cb is normally magnetized indicating the entire sequence is of bruhnes age

holocene climate changes in eastern beringia nw north america a systematic review of multi proxy evidence abstract reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change this review summarizes available information from diverse holocene paleoenvironmental records across eastern beringia alaska westernmost canada and adjacent seas and it quantifies the primary trends of temperature and moisture sensitive records based in part on midges pollen and biogeochemical indicators compiled in the recently published arctic holocene database and updated here to v2 1 the composite time series from these proxy records are compared with new summaries of mountain glacier and lake level fluctuations terrestrial water isotope records sea ice and sea surface temperature analyses and peatland and thaw lake initiation frequencies to clarify multi centennial to millennial scale trends in holocene climate change to focus the synthesis the paleo data are used to frame specific questions that can be addressed with simulations by earth system models to investigate the causes and dynamics of past and future climate change this systematic review shows that during the early holocene 11 7 8 2 ka 1 ka 1000 cal yr bp rather than a prominent thermal maximum as suggested previously temperatures were highly variable at times both higher and lower than present approximate mid 20th century average with no clear spatial pattern composited pollen midge and other proxy records average out the variability and show the overall lowest summer and mean annual temperatures across the study region during the earliest holocene followed by warming over the early holocene the sparse data available on early holocene glaciation show that glaciers in southern alaska were as extensive then as they were during the late holocene early holocene lake levels were low in interior alaska but moisture indicators show pronounced differences across the region the highest frequency of both peatland and thaw lake initiation ages also occurred during the early holocene during the middle holocene 8 2 4 2 ka glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka as reflected in most proxy types following the middle holocene thermal maximum temperatures decreased starting between 4 and 3 ka signaling the onset of neoglacial cooling glaciers in the brooks and alaska ranges advanced to their maximum holocene extent as lakes generally rose to modern levels temperature differences for averaged 500 year time steps typically ranged by 1 2 c for individual records in the arctic holocene database with a transition to a cooler late holocene that was neither abrupt nor spatially coherent the longest and highest resolution terrestrial water isotope records previously interpreted to represent changes in the aleutian low pressure system around this time are here shown to be largely contradictory furthermore there are too few records with sufficient resolution to identify sub centennial scale climate anomalies such as the 8 2 ka event the review concludes by suggesting some priorities for future paleoclimate research in the region

improving the accuracy of small vertebrate based palaeoclimatic reconstructions derived from the mutual ecogeographic range a case study using geographic information systems and uda oda discrimination methodology abstract understanding past climate and the mechanisms of climate change remain major challenges in scientific research the mutual ecogeographic range mer method for climatic reconstruction uses the current geographical distribution of fossil assemblages to infer palaeoclimatic conditions current species distributions used in the mer method are usually obtained from biogeographic atlases that record the absence presence of species in a 10 10 km grid a 10 10 km area is quite broad and the method only records presence absence without considering the real area occupied by any given species thus the method overlooks the fact that environmental heterogeneity is strongly related to topography and climatic conditions may change abruptly over a few kilometres to improve the accuracy of small vertebrate palaeoclimatic reconstructions derived from the mer method we developed the uda oda discrimination methodology which is applied to stratigraphic units xb and upper unit v from el salt alcoi spain we identified the occupied distribution area oda which denotes realistic occupied areas where the species may be present and the uda uncertain distribution area where the species may be absent we achieved this by combining the species distribution recorded in the atlases and the species environmental requirements described in the literature climate values resulting from the mer method and our uda oda discrimination methodology showed significant differences extrapolating values from areas that are more similar to the areas occupied by the different species today yielded more representative climatic parameters for the assemblage tested resulting in a more accurate palaeoclimatic reconstruction moreover the discrimination analysis proposed here allows us to work with species whose distribution is currently disturbed which was not possible using the mer method

macrofossil and pollen evidence for full glacial steppe within an ecological mosaic along the bluefish river eastern beringia abstract plant and insect macrofossil assemblages dating to the full glacial late wisconsinan are rare from eastern beringia here we present an assemblage of fossil pollen insect and plant macrofossils recovered from alluvium at the bluefish exposure northern yukon territory nine ams radiocarbon ages place these data between ca 18 880 16 440 14c yr bp 22 313 19 597 cal yr bp these data indicate that xeric steppe rich in bunchgrasses poa and elymus artemisia frigida and diverse forbs was interspersed within a mosaic of local vegetation types including mid rich fens mesic graminoid meadows steppe tundra and herb tundra macrofossils and minor pollen of tundra forbs suggest steppe tundra plant associations within midslope elevations and discontinuous herb tundra on high elevation uplands on exposed bedrock ridges the composition and distribution of local vegetation was dependent on available moisture drainage aspect and elevation compositional and physiognomic similarities can be made with extrazonal steppe dominated dry slopes and high elevation steppe tundra ecotones in central alaska and yukon territory our paleoecological data reflect environments inhabited by the diverse late pleistocene bluefish caves fauna including woolly mammoth horse steppe bison and saiga antelope

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

mutual climatic range reconstructions of seasonal temperatures based on late pleistocene fossil beetle assemblages in eastern beringia abstract the mutual climatic range mcr method of paleoclimate reconstruction has been employed by paleoentomologists for the last decade a quantitative calibrated method mcr has many advantages over qualitative methods the method has now been developed for arctic faunas climate envelopes for beetle species found in eastern beringia have been compiled using a 25 km gridded north american climate database that pairs climate parameters with modern collection sites linear regressions of predicted on observed values yielded equations used to calibrate the mcr estimates this study presents the initial results from the mcr analysis of 46 fossil beetle assemblages from alaska and the yukon territory the assemblages range in age from about 150 000 9200 yr bp isotope stage six assemblages yielded estimates of mean july temperature tmax 4 5 c colder than at present assemblages associated with the old crow tephra oct dated approximately 140 000 yr bp likewise indicated tmax values well below modern levels isotope stage 5e faunas showed tmax values as much as 3 5 c warmer than modern early wisconsinan assemblages showed climatic cooling with tmax levels dropping as low as 6 c colder than at present a mid wisconsinan interstadial period is marked by warming of mean summer temperatures to near modern levels at some sites last glacial maximum assemblages reflect cooling of tmax to a level about 6 4 c colder than at present although most assemblages from this period yielded mean january temperatures above modern levels warming of summer temperatures began at least by 12 500 yr bp and warmer than modern tmax values were recorded from all assemblages between then and 9200 yr bp

the mobility of gold in tropical rain forest soils the complex mineralogical and chemical system of a tropical rain forest weathering profile at the ashanti mine ghana was characterized to evaluate the role of inorganic and organic processes with the potential to mobilize gold in the rain forest soils the concentration of gold has been measured in bulk saprolite soil samples and in pore water extractions from the saprolite and soil horizons from the sansu prospect at ashanti gold concentration in the ground waters varied from below the detection limit 0 01 mu g l to a maximum of 84 4 mu g l at the water table average gold concentration in the soil pore waters is 3 6 mu g l the gold in the pore waters is present as either soluble gold or as suspended particles less than 0 45 mu m in size despite the presence of significant gold concentrations in the soil pore waters gold concentration in soils over the auriferous shear zones is up to 400 times greater than over the nonauriferous country rocks suggesting a limited gold mobility similarly a close correlation between gold held in the solid soil fraction and in soil pore waters reveals very little in the way of supergene gold enrichment conversely the gold is dissolved and reprecipitated over a range of a few centimeters the high concentration of gold in the soil pore waters at ashanti is a reflection both of the high gold content of the hypogene ore and of the efficiency of supergene fluids in the tropical rain forest environment to leach the gold but not retain it in a mobile form solubility calculations indicate that gold complexing in the soils appears to be dominated by auoh h 2 o au cn 2 super au s 2 o 3 2 super 3 au nh 3 2 super and a gold fulvate complex selective extraction of gold from organic and inorganic soil fractions reveals that the element is largely concentrated as native gold a significant proportion up to 28 is concentrated in the light organic fraction of the near surface soils which is dominated by fulvic acid the role of gold adsorption by clays and hydrous fe mn oxides appears to be small with less than 1 percent of the gold being present in an easily exchangeable form gold appears relatively immobile in the lower saprolite with gold values in solution being below the detection limit 0 01 mu g l higher up in the saprolite gold appears to be dissolved by hydroxide and thiosulfate complexes in the upper saprolite and by fulvate cyanide and hydroxide complexes in the soils due to the in situ nature of gold dissolution and reprecipitation even short lived species such as thiosulfate and cyanide can play an important role in the supergene chemistry of gold in the ashanti soils halide complexes are not considered important owing to their low concentration in the ground waters cl 9 mg l and the unrealistically high eh low ph conditions required humic acids are also not considered important in the dissolution of gold as they are only sparingly soluble in the ph range of the ashanti soils 4 2 6 8

eastern beringia and beyond late wisconsinan and holocene landscape dynamics along the yukon coastal plain canada terrestrial permafrost archives along the yukon coastal plain northwest canada have recorded landscape development and environmental change since the late wisconsinan at the interface of unglaciated beringia i e komakuk beach and the northwestern limit of the laurentide ice sheet i e herschel island the objective of this paper is to compare the late glacial and holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice analyses at these sites involved a multi proxy approach including sedimentology cryostratigraphy palaeoecology of ostracods stable water isotopes in ground ice hydrochemistry and ams radiocarbon and infrared stimulated luminescence irsl dating ams and irsl age determinations yielded full glacial ages at komakuk beach that is the northeastern limit of ice free beringia herschel island to the east marks the late wisconsinan limit of the northwest laurentide ice sheet and is composed of ice thrust sediments containing plant detritus as young as 16 2 cal ka bp that might provide a maximum age on ice arrival late wisconsinan ice wedges with sediment rich fillings on herschel island are depleted in heavy oxygen isotopes mean delta o 18 of 29 1 parts per thousand this together with low d excess values indicates colder than modern winter temperatures and probably reduced snow depths grain size distribution and fossil ostracod assemblages indicate that deglaciation of the herschel island ice thrust moraine was accompanied by alluvial proluvial and eolian sedimentation on the adjacent unglaciated yukon coastal plain until similar to 11 cal ka bp during a period of low glacio eustatic sea level the late glacial holocene transition was marked by higher than modern summer temperatures leading to permafrost degradation that began no later than 11 2 cal ka bp and caused a regional thaw unconformity cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone thermokarst activity led to the formation of ice wedge casts and deposition of thermokarst lake sediments these were subsequently covered by rapidly accumulating peat during the early holocene thermal maximum a rising permafrost table reduced peat accumulation and extensive ice wedge growth resulted from climate cooling starting in the middle holocene until the late 20th century the reconstruction of palaeolandscape dynamics on the yukon coastal plain and the eastern beringian edge contributes to unraveling the linkages between ice sheet ocean and permafrost that have existed since the late wisconsinan

late quaternary climate change in the awatere valley south island new zealand using a sine model with a maximum likelihood envelope on fossil beetle data we present a new climatic reconstruction method appropriate for biological proxies where modern distributions are poorly defined and data sets are small the technique uses a sine function in conjunction with maximum likelihood estimates of best high and best low values for the distribution of each species to demonstrate the model we present temperature reconstructions for the last glacial maximum lgm and holocene from beetle fossil assemblages from the awatere valley new zealand the temperature estimates are determined by the mutual overlap of the climate range for all the species in the assemblage the overlap is then compared with modern physio chemical conditions for our example we estimate the lgm summer february mean temperature was about 3 5 4degreesc cooler and july winter mean daily minimum temperature was about 4 5degreesc cooler than present day temperatures the maximum likelihood estimates broaden the reconstructed temperature ranges to 2 5 5degreesc cooler for february temperatures and 3 5 6 0degreesc cooler for mean minimum daily temperature of the coldest month july these estimates are consistent with lgm temperature estimates of 4 7degreesc from other climate proxy indicators estimates of holocene temperatures are very similar to modern estimates are compared with results from the established mutual climatic range mcr technique and the results are compatible mcr is less robust than the sine model approach for these data because it requires the pre determination of the critical physiochemical controls and assumes gaussian distributions in climate space the sine model is conceptually superior to traditional bioclim modelling with which it shares many features because bioclim also assumes gaussian distributions and the sine model allows attribute testing of the data sets which are not possible with bioclim c 2004 elsevier ltd all rights reserved

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

arsenic content and groundwater geochemistry of the san antonio el triunfo carrizal and los planes aquifers in southernmost baja california mexico the san antonio el triunfo mining district located at a mountainous region 45 km south east of la paz baja california has been worked since the late 1700s mine waste material produced during 200 years of mineral extraction area poses a risk of local groundwater pollution and eventually regional pollution to the carrizal west basin and the los planes east basin aquifers there are different types of deposits in the mining area these are dominated by epithermal veins in which arsenopyrite is an important component carrillo and drever 1998a concluded that even though the amount of mine waste is relatively small in comparison to the large scale area significant as in groundwater derived from the mine waste piles is found locally in the groundwater this paper shows the results of geochemical analyses of groundwater samples from the san antonio el triunfo area and the carrizal and los planes aquifers during several years of monitoring 1993 1997 the highest values of total dissolved solids tds and as are in the mineralized area where the mining operations occurred 1500 ppm tds and 0 41 ppm as the lowest concentrations of tds and as are in general away from the mineralized area 500 ppm tds and 0 01 ppm as sulfate and bicarbonate alkalinity are in general high near the mineralized area and low away from it the arsenic concentrations vary seasonally especially after the heavy summer thunderstorms geochemical modeling minteqa2 and netpath and analysis of the regional geochemical evolution of the groundwater from the mining area towards the aquifer of los planes shows that the most likely hydrochemical processes include dilution precipitation of calcite and adsorption of as onto surfaces of iron oxyhydroxides ferrihydrite these processes act as natural controls to the extent and amount of as pollution in the carrizal and los planes aquifers

paleoenvironmental reconstruction of the last glacial maximum inferred from insect fossils from a tephra buried soil at tempest lake seward peninsula alaska abstract sediments and vegetation dated 21 570 cal yr bp were buried under tephra on the northern seward peninsula this buried surface has yielded plant macrofossils in growth position as well as numerous insect fossils excellently preserved in permafrost it appears that many of the insects were buried alive by the volcanic ash the species composition and ecological affinities of this fossil fauna are typical of alaskan late pleistocene steppe tundra environments the assemblages are dominated by the weevil lepidophorus lineaticollis one of the most common species in eastern beringian pleistocene fossil assemblages many other members of the ancient steppe tundra insect community are preserved in these assemblages including the pill beetle morychus sp and weevils of the genus coniocleonus in alaska most of these species but not all of them survived the pleistocene holocene environmental transition but are restricted today to relict patches of steppe like vegetation faunal diversity is low in spite of the recovery of more than 1000 individual insects and mites including more than 600 beetles this reflects the small number of species adapted to the cold dry environments of the lgm in eastern beringia they represent an ecosystem which no longer exists

rissian eemian and wurmian coleoptera assemblages from la grande pile vosges france abstract the grande pile peat bog sequence is one of the few west european sites that cover the entire time span of the last major climatic cycle 140 000 years a recent program of coring has provided material for insect analysis the aim of this palaeoentomological study is to interpret the environmental and climatic evolution from the end of the rissian glaciation to the holocene using subfossil coleoptera the studied samples yielded 394 taxa of coleoptera half of them identified to species level 19 of which do not belong to the present day french fauna the large number of taxa suggests a wide variety of habitats and provides much detailed palaeoecological evidence for the period studied the lowermost sediments of the sequence corresponding to the end of the rissian glaciation were deposited under very cold conditions in a tundra environment this is succeeded by a forest period in which two cool interludes of grassland environment occur although these periods are decidedly poor in tree dependent coleoptera they do not contain any really cold adapted taxa they divide the forest phase into three periods the first one corresponding to the eemian interglacial shows an early stage in which the beetle fauna is characterized by species dependent on deciduous trees a later stage in which this fauna is mixed with many conifer dependent elements some of which e g platypus oxyurus suggest warmer and perhaps wetter climatic condition than today the two later woodland periods yielded coleopteran assemblages rather similar to those recorded in the second part of the eemian i e with both deciduous and conifer dependent taxa there is some evidence to suggest that these two periods were slightly cooler than the eemian proper marked climatic deterioration becomes obvious in the upper half of the sedimentary sequence attributed to the last glacial period wurm with the reappearance of tundra beetle assemblages sediment and insect evidence suggest that the climate was extremely cold and continental at la grande pile at about 30 000 b p a comparison of the insect analysis with previous palynological works enables precise correlation between the results provided by these two independent approaches however large numbers of running water coleoptera in the forest periods replaced by standing water coleoptera in cold periods raise questions concerning the lacustrine origin of the sedimentation at la grande pile

old crow tephra found at the palisades of the yukon alaska abstract a 20 cm thick volcanic ash layer at the palisades along the yukon river is geochemically correlated with the old crow tephra a buried organic and wood rich layer above the old crow tephra probably records the last interglaciation the recognition of the old crow tephra provides the first chronologic information on the age of the thick sequence of pleistocene sediments at the palisades an important ice age mammal site in central alaska and a key locakity for the reconstruction of the history of the yukon river and the last interglaciation in central alaska

late pleistocene paleoecology of arctic ground squirrel urocitellus parryii caches and nests from interior alaska s mammoth steppe ecosystem usa botanical analyses of fossil and modern arctic ground squirrel urocitellus parryii caches and nests have been used to reconstruct the past vegetation from some parts of beringia but such archives are understudied in alaska five modern and four fossil samples from arctic ground squirrel caches and nests provide information on late pleistocene vegetation in eastern beringia modern arctic ground squirrel caches from alaska s arctic tundra were dominated by willow and grass leaves and grass seeds and bearberries which were widespread in the local vegetation as confirmed by vegetation surveys late pleistocene caches from interior alaska were primarily composed of steppe and dry tundra graminoid and herb seeds graminoid cuticle analysis of fossil leaves identified calamagrostis canadensis koeleria sp and carex albonigra as being common in the fossil samples stable carbon isotopes analysis of these graminoid specimens indicated that plants using the c3 photosynthetic pathways were present and functioning with medium to high water use efficiency fossil plant taxa and environments from ground squirrel caches in alaska are similar to other macrofossil assemblages from the yukon territory which supports the existence of a widespread mammoth steppe ecosystem type in eastern beringia that persisted throughout much of the late pleistocene

pleistocene graminoid dominated ecosystems in the arctic abstract we review evidence obtained from analyses of multiple proxies floristics mammal remains paleoinsects pollen macrofossils plant cuticles phytoliths stable isotopes and modeling that elucidate the composition and character of the graminoid dominated ecosystems of the pleistocene arctic the past thirty years have seen a renewed interest in this now extinct biome sometimes referred to as tundra steppe steppe tundra in north american sources while many questions remain converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the arctic confirming earlier conjectures completed in the 1960s 1980s a variety of still existing species of grasses and forbs played key roles in the species assemblages of the time but their mixtures were not analogous to the tundras of today local mosaics based on topography proximity to the ice sheets and coasts soil heterogeneity animal disturbance and fire regimes were undoubtedly present however inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity these past ecosystems were maintained by a combination of dry and cold climate and grazing pressure disturbance by large e g mammoth and horse and small e g ground squirrels mammals some recent studies from eastern beringia alaska suggest that more progress will be possible when analyses of many proxies are combined at local scales

late pleistocene climates of beringia based on analysis of fossil beetles thirty one fossil beetle assemblages from central and eastern beringia alaska the yukon territory and the now submerged bering land bridge have yielded seasonal temperature estimates for the interval 43 550 9250 14c yr before present yr b p estimates of the mean temperature of the warmest tmax and coldest tmin months were derived by the mutual climatic range method assemblages from northern and western sites show a mid wisconsin interstadial tmax warming from 35 000 30 000 yr b p this warming is less pronounced in assemblages for interior regions there is little or no beetle evidence for the spread of coniferous forest in eastern beringia during this interstade except for in parts of the yukon territory during the last glacial maximum tmax values were depressed by about 2 2 5 c in arctic regions of beringia and by about 4 c in the interior tmin values were about 8 c colder in both regions tmax and tmin values rose rapidly at northern sites after 12 000 yr b p seasonal temperatures peaked at 11 000 yr b p just as the bering land bridge was inundated this was followed by a sharp climatic cooling between 11 000 and 10 000 yr b p the equivalent of a younger dryas cooling in eastern beringia

low and high frequency climate variability in eastern beringia during the past 25 000 yearsthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new temperature and precipitation reconstructions for the past 25 000 cal years bp from across eastern beringia based on a network of pollen diagrams an updated modern pollen calibration database and an improved methodology using the modern analogue technique mat time series show july temperatures were around 4 c lower during full glacial and january temperatures were about 2 c lower than present annual temperatures rose beginning around 16 000 cal years bp reaching a maximum around 12 000 cal year bp the warming was more rapid in southern beringia annual precipitation varied by 250 mm during the past 25 000 cal years bp maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal years bp that vary regionally suggesting holocene atmospheric circulation changes at multiple time and space scales orbitally forced seasonality changes during the late glacial and early holocene resulted in reversed seasonal temperature reconstructions due to me

the mutual climatic range technique is usually not the area of sympatry technique when reconstructing paleoenvironments based on faunal remains abstract names applied to particular analytical techniques must be explicit and distinctive the potential that two distinct techniques of paleoenvironmental reconstruction that use ancient faunal remains each with a particular name might be confused in the future has recently become a reality the name mutual climatic range mcr coined and developed in the 1980s and concerning the modern climatic not geographic co occurrence of species represented in a prehistoric collection of remains has been applied multiple times to a different technique first published in 2009 the new mcr technique is very similar to a distinct one developed in the 1950s and 1960s that focuses on the location of the geographic co occurrence of species in an assemblage relative to the location of the deposit producing the remains the older method has been known as the area of sympatry aos technique since 1966 histories of the aos and original mcr techniques suggest they were developed independently the new mcr technique seems to have been developed without knowledge of the two earlier ones to avoid future confusion of one technique with the other it is suggested that the new one be renamed the utm mcr technique because rather than use isopleths of climatic variables as the aos technique does it considers climatic variables within 10 10 km utm squares

late quaternary paleoclimate of western alaska inferred from fossil chironomids and its relation to vegetation histories abstract fossil chironomidae assemblages with a few chaoboridae and ceratopogonidae from zagoskin and burial lakes in western alaska provide quantitative reconstructions of mean july air temperatures for periods of the late middle wisconsin 39 000 34 000 cal yr b p to the present inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination paleotemperature trends reveal substantial differences in the timing of climatic warming following the late wisconsin at each site although chronological uncertainty exists zagoskin lake shows early warming beginning at about 21 000 cal yr b p whereas warming at burial lake begins 4000 years later summer climates during the last glacial maximum lgm were on average 3 5 c below the modern temperatures at each site major shifts in vegetation occurred from 19 000 to 10 000 cal yr b p at zagoskin lake and from 17 000 to 10 000 cal yr b p at burial lake vegetation shifts followed climatic warming when temperatures neared modern values both sites provide evidence of an early postglacial thermal maximum at 12 300 cal yr b p these chironomid records combined with other insect based climatic reconstructions from beringia indicate that during the lgm 1 greater continentality likely influenced regions adjacent to the bering land bridge and 2 summer climates were at times not dominated by severe cold

old crow tephra 140 10 ka constrains penultimate reid glaciation in central yukon territory abstract old crow tephra 140 10 ka is closely associated with deposits from the penultimate reid glaciation along the pelly river in central yukon territory the elevation of the tephra above present base level and association with deglacial sediments suggests a close minimum age estimate confirming a mis 6 age for the reid glaciation this is in contrast to a mis 4 age for the penultimate gladstone glaciation in southwest yukon this study demonstrates that the assumed synchrony of the penultimate advance of the cordilleran ice sheet has little support and regional controls on the mass balance of source regions of the ice sheet are more important than previously considered