holocene coastal glaciation of alaska holocene uctuations of the three cirque glaciers on the seward peninsula and ve groups of tidewater and land terminating glaciers along the northernmost gulf of alaska provide a proxy record of late holocene climatic change furthermore the movements of the coastal glaciers were relevant to late holocene native american migration the earliest expansion was recorded about 6850 yr bp by hubbard glacier at the head of yakutat bay in the gulf of alaska however its down fjord advance to the bay mouth was delayed until 2700 bp similarly expansions of the icy bay bering and mccarty glaciers occurred near their present termini by 3600 3000 bp compatible with marked cooling and precipitation increases suggested by the alaskan pollen record decrease in glacier activity 2000 bp was succeeded by advances of gulf coastal glaciers between 1500 and 1300 bp correlative with early medieval expansions across the northern hemisphere a medieval optimum encompassing at least a few centuries prior to ad 1200 is recognized by general retreat of land terminating glaciers but not of all tidewater glaciers little ice age advances of land based glaciers many dated with the precision of tree ring cross dating were centered on the middle 13th or early 15th centuries the middle 17th and the last half of the 19th century a d strong synchrony of these events across coastal alaska is evident 2000 elsevier science ltd all rights reserved

potential analogues for paleoclimatic variations in eastern interior alaska during the past 14 000 yr atmospheric circulation controls of regional temperature and moisture responses the paleoclimatic history of a region can be viewed as a series of surface temperature and moisture anomalies through time the effects of changes in large scale climatic controls e g insolation major circulation controls can be mediated by the influence of smaller scale controls e g topographic barriers coastlines this may result in heterogenous surface climatic responses at the regional and sub regional scale divergent paleoclimatic trajectories between regions may be explainable in terms of such meso scale patterns using modern analogues for paleoclimate we examine how the sequence of climatic variations in eastern interior alaska during the interval 12 000 0 14c yr bp could have been generated by specific atmospheric circulation patterns fossil pollen and lake level records document the long term trends in temperature and effective moisture for the region water balance modelling provides additional estimates of paleoprecipitation synoptic climatological patterns are described using the modern instrumental record of upper level and sea level pressure surface temperature and precipitation at 12 000 14c yr bp eastern interior alaska was cooler and drier than present a situation generated today by a southward displacement of the jet stream conditions warmer and drier than present at 9000 14c yr bp may have been generated by increased ridging north of alaska and a weakened westerly circulation warmer wetter conditions than present possibly prevailed in the late middle holocene these might reflect ridging over alaska and troughing further west cool wet conditions feature enhanced westerly flow into alaska through an eastward shift in the east asian trough and positive pressure anomalies in the north pacific they may be analogous to cold periods of the little ice age the analogues demonstrate how surface conditions in other parts of beringia may sometimes be similar to while at other times different from those in the eastern interior these broader spatial patterns provide hypotheses about past climates that can be tested with paleoclimatological data for example the widespread positive temperature anomalies associated with the warm dry 9000 14c yr bp analogue fit with the expansion northward of the eastern siberian treeline the anomalously cool conditions in northeast siberia associated with the warm wet analogue may explain the continued late middle holocene treeline advance in alaska while there was retreat in siberia

paleomagnetic modeling of seamounts near the hawaiian emperor bend abstract the hawaiian emperor seamount chain records the motion of the pacific plate relative to the hawaiian mantle hotspot for 80 m y a notable feature of the chain is the pronounced bend at its middle this bend had been widely credited to a change in plate motion but recent research suggests a change in hotspot motion as an alternative existing paleomagnetic data from the emperor chain suggest that the hotspot moved south during the late cretaceous and early tertiary but reached its current latitude by the age of the bend thus data from area of the bend are important for understanding changes in plume latitude in this study we analyze the magnetic anomalies of five seamounts annei daikakuji w daikakuji e abbott and colahan in the region of the bend these particular seamounts were chosen because they have been recently surveyed to collect multibeam bathymetry and magnetic data positioned with gps navigation inversions of the magnetic and bathymetric data were performed to determine the mean magnetization of each seamount and from these results paleomagnetic poles and paleolatitudes were calculated three of the five seamounts have reversed magnetic polarities two are normal and four contain a small volume of magnetic polarity opposite to the main body consistent with formation during the early cenozoic a time of geomagnetic field reversals although magnetization inhomogene ties can degrade the accuracy of paleomagnetic poles calculated from such models the seamounts give results consistent with one another and with other pacific paleomagnetic data of approximately the same age seamount paleolatitudes range from 13 7 to 23 7 with an average of 19 4 7 4 2 these values are indistinguishable from the present day paleolatitude of the hawaiian hotspot together with other paleomagnetic and geologic evidence these data imply that the hawaiian hotspot has moved little in latitude during the past 45 m y

late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

late holocene high resolution glacial chronologies and climate kenai mountains alaska recent retreat of outlet glaciers from the harding and grewingk yalik icefields has revealed a vast array of deposits on the eastern and western flanks of the kenai mountains that records multiple glacier advances into coastal forests during late holocene time treering dating together with radiocarbon and lichenometric analyses allows for the reconstruction of these glacial fluctuations to decadal precision over the past two thousand years the records of fluctuations are derived from 16 land terminating and seven tidewater glaciers in three fjord systems as well as two cirque glaciers three major intervals of holocene glacier expansions are evident they occurred about 3600 yr b p 600 a d and during the little ice age from 1300 to 1850 a d the earliest expansion beyond present ice margins is known only from the mccarty tidewater glacier the 600 a d event involved the simultaneous advance of land terminating and tidewater glaciers during the little ice age however tidewater glaciers were advancing several centuries prior to their land terminating neighbors those land terminating glaciers on the western mountain flank retreated from their little ice age maxima as much as two centuries before those on the eastern mountain flank land terminating tongues on the eastern more maritime mountain flank have shown more sensitivity to variations in winter precipitation during the little ice age and within recent decades than the more continental glaciers on the western flank that are affected more by summer temperatures the glacial and climatic records suggest that advances of the ice tongues from about 1420 to 1460 a d between 1640 and 1670 a d at about 1750 a d and from 1880 to 1910 a d reflected times of increased winter precipitation advances between 1440 to 1460 a d from 1650 to 1710 a d and from 1830 to 1860 a d followed intervals of lower summer temperatures

ocean atmosphere forcing of centennial hydroclimate variability in the pacific northwest reconstructing centennial timescale hydroclimate variability during the late holocene is critically important for understanding large scale patterns of drought and their relationship with climate dynamics we present sediment oxygen isotope records spanning the last two millennia from 10 lakes as well as climate model simulations indicating that the little ice age was dry relative to the medieval climate anomaly in much of the pacific northwest of north america this pattern is consistent with observed associations between the el nino southern oscillation enso the northern annular mode and drought as well as with proxy based reconstructions of pacific and atlantic ocean atmosphere variations over the past 1000 years the large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer term shifts in enso like dynamics and that an improved understanding of the centennial timescale relationship between external forcing and drought is necessary for projecting future hydroclimatic conditions in western north america

increased aridity during the early holocene in west greenland inferred from stable isotopes in laminated lake sediments abstract palaeoclimatic inferences from the greenland ice cores suggest that holocene climate was relatively uniform the ice core records primarily reflect hemispheric temperature related climate processes whereas lakes tend to reflect regional scale climatic variability stable isotopes in closed basin lakes are sensitive to changes in effective precipitation here we report stable isotope evidence 18 o and 13 c records from authigenic calcite in laminated lake sediments from two oligosaline closed basin lakes in southern west greenland sondre stromfjord the stable isotope profiles indicate a dynamic early to mid holocene climate as a strongly negative precipitation evaporation balance from 7000 to 5600 cal yr bp lowered lake levels throughout the region this interpretation of the stable isotope data is supported by a survey of modern lake water isotopic composition and fossil shorelines around many closed basin saline lakes which indicate higher lake levels in the past the increased aridity during the early holocene resulted from a shift in regional circulation patterns in the davis straits baffin bay area enhanced stability of the west greenland depression and the situation of a regional trough over the sondre stromfjord area caused weakened westerly airflow and strengthened outflow i e winds blowing off the ice sheet resulting in reduced precipitation in the region decreased precipitation coupled with higher insolation probably caused the negative precipitation evaporation balance

climatic forcing of carbon oxygen isotopic covariance in temperate region marl lakes carbon and oxygen stable isotopic compositions of lacustrine carbonate from a southeastern michigan marl lake display linear covariance over a range of 4 0 peedee belemnite pdb in oxygen and 3 9 pdb in carbon mechanisms of delta 13 c delta 18 o coupling conventionally attributed to lake closure in arid region basins are inapplicable to hydrologically open lake systems thus an alternative explanation of isotopic covariance in temperate region dimictic marl lakes is required we propose that isotopic covariance is a direct record of change in regional climate in short residence time temperate region lake basins summer meteoric precipitation is enriched in 18o relative to winter values and summer organic productivity enriches epilimnic dissolved inorganic carbon in 13c thus climate change toward longer summers and or shorter winters could result in greater proportions of warm month meteoric precipitation longer durations of warm month productivity and net long term enrichment in carbonate 18o and 13c isotopic covariance observed in the michigan marl lake cores is interpreted to reflect postglacial warming from 10 to 3 ka followed by cooler mean annual temperature a shift toward greater proportions of seasonal summer precipitation a shortening of the winter season or some combination of these three factors

holocene driftwood incursion to southwestern victoria island canadian arctic archipelago and its significance to paleoceanography and archaeology abstract holocene driftwood is found on postglacial raised beaches of wollaston peninsula victoria island the highest driftwood appears on the 12 to 13 m beach which formed about 4000 yr b p and is common on beaches 12 6 m in elevation the earliest paleoeskimo dwelling features also occur on the 12 to 13 m beach wood increases on the 5 to 6 m beach which formed about 2000 yr b p and is abundant below that level thus zonation of wood suggests the following hypotheses 1 that the coastal mackenzie current the source of modern driftwood did not operate before 4000 yr b p and lacked its present vigor or persistence until 2000 yr b p and 2 that the apparent sudden influx of driftwood at 4000 yr b p may have provided a fuel resource and or may have been related to conditions that enabled first peopling radiocarbon ages indicate that 1 the first wood arrived about 4700 yr b p 2 little wood arrived from 4700 2000 yr b p and 3 influx of wood was episodic after 2000 yr b p much of the wood that arrived after 1100 yr b p was redistributed by people and scattered on higher beaches explanation of the evident correlation between highest wood and highest dwelling features must await archaeological studies

thermal stresses and the bimodal distribution of elastic thickness estimates of the oceanic lithosphere observations of plate flexure beneath seamounts and at deep sea trenches suggest that the mechanical strength of the oceanic lithosphere increases with age the mechanical thickness h seems to follow the depth to a particular isotherm in the cooling plate model a detailed review of available estimates of elastic thickness te shows that the strength deduced from studies at seamounts is significantly different from the strength inferred at trenches and fracture zones whereas te beneath seamounts approximately follows the 400 c isotherm h at trenches follows the depth to the 700 800 c isotherms the cause of this bimodal distribution is not fully understood thermal bending stresses due to cooling of the lithosphere have been suggested to play an important role in the flexural deformation at transform faults and fracture zones and their distribution with depth is consistent with intraplate seismicity this paper evaluates the effects of thermal stresses on deformation beneath seamounts and at trenches and how their interaction with flexural stresses may modify plate strength the results indicate that thermal bending stresses will bias the moment curvature relationship such that a plate of a certain strength will appear relatively weaker beneath a seamount positive curvature but relatively stronger at a trench negative curvature this systematic bias appears to be in qualitative agreement with published te estimates for old lithosphere the theory predicts a diminishing amount of bias the general lack of sufficient te determinations from old ocean basins and the uncertainties associated with modeling of trenches prohibit a detailed analysis of this part of the te versus age relationship i conclude that the scatter in the elastic thickness estimates appears to be caused by a combination of lithospheric reheating during seamount emplacement bias introduced by thermal stresses and variable amount of yielding of the plate beneath seamounts in proportion to seamount size and lithospheric age at the time of loading

equilibrium and disequilibrium stable isotope effects in modern charophyte calcites implications for palaeoenvironmental studies abstract stable isotopes in fossil charophyte calcite may record palaeoenvironmental information but at present very little is known about isotopic records in modern chara stem encrustations or gyrogonites this problem is addressed with isotopic data from present day chara from a wide spread of freshwater environments in britain and ireland 13 c values of stem encrustations from low water flow environments lakes ponds ditches are more positive than their coexisting gyrogonite values by between 0 6 and 3 0 reflecting microenvironmental metabolic effects caused by photosynthesis in stronger water flows where dissolved inorganic carbon is well mixed stem encrustation 13 c values are close to equilibrium 18 o values in chara stem encrustations are not equilibrium values being typically offset to isotopically lighter compositions by about 1 5 relative to equilibrium by kinetic effects during rapid calcification gyrogonite 18 o values are less negative than coexisting stem encrustation values by between 0 7 and 1 7 there is no clear evidence that gyrogonite 18 o or 13 c values are influenced by extensive disequilibrium but the data are difficult to interpret further without new experimental studies isotopic records in fossil lacustrine chara marls mainly stem encrustation calcites should be interpreted with caution environmental records essentially of relative changes in late summer water temperature or hydrology may be preserved but these are unlikely to represent true equilibrium values gyrogonite calcification probably happens on a timescale of weeks such that isotopic data represent snapshots of the environmental conditions at the time of calcification the timing of calcification in chara may itself be variable depending on environment and temperature it is a major unknown that currently hinders interpretation of isotopic data

crustal structure of the continental margin of korea in the east sea japan sea from deep seismic sounding data evidence for rifting affected by the hotter than normal mantle abstract despite the various opening models of the southwestern part of the east sea japan sea between the korean peninsula and the japan arc the continental margin of the korean peninsula remains unknown in crustal structure as a result continental rifting and subsequent seafloor spreading processes to explain the opening of the east sea have not been adequately addressed we investigated crustal and sedimentary velocity structures across the korean margin into the adjacent ulleung basin from multichannel seismic mcs reflection and ocean bottom seismometer obs data the ulleung basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal the continental margin documents rapid transition from continental to oceanic crust exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of moho over a distance of about 50 km the crustal model of the margin is characterized by a high velocity up to 7 4 km s lower crustal hvlc layer that is thicker than 10 km under the slope base and pinches out seawards the hvlc layer is interpreted as magmatic underplating emplaced during continental rifting in response to high upper mantle temperature the acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption these features suggest that the evolution of the korean margin can be explained by the processes occurring at volcanic rifted margins global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the korean margin and in the ulleung basin

fractionation and deposition of indium and arsenic from the kusatsu and tamagawa acidic hot springs japan possible man made analogues for rare metal concentrations onto lake beds the kusatsu and tamagawa hot springs contain both toxic elements and rare metals used in high technology industries high acidity and significant discharge of these springs have led to the construction of dams and neutralization of spring waters by lime addition however the same neutralization process causes differing effects in the kusatsu and tamagawa areas this study focuses on the effects of neutralization on fractionation between arsenic as and indium in during river transport and precipitation of these elements on the lake beds the yubatake thermal waters in the kusatsu area are rapidly neutralized after addition of a lime suspension after this neutralization the dissolved as and in are nearly completely removed by sorption onto suspended hydrous ferric oxides hfo which then settle out and are added to sediments within a man made lake without significant fractionation in contrast the obuki thermal waters in the tamagawa area are neutralized by both addition of lime and by mixing with tributary streams leading to a gradual downstream increase in ph arsenic tends to be sorbed by hfo in upstream areas leading to wide dispersal of as across the entire watershed in comparison in is transported to the lake inlet as stable chloride and or sulfate complexes without significant removal with considerable portions being precipitated in a man made lake as a result in is effectively concentrated within downstream lake sediments

noble gas geochemistry in thermal springs abstract the composition of noble gases in both gas and water samples collected from horseshoe spring yellowstone national park was found to be depth dependent the deeper the sample collection within the spring the greater the enrichment in kr xe radiogenic 4he and 40ar and the greater the depletion in ne relative to 36ar the compositional variations are consistent with multi component mixing the dominant component consists of dissolved atmospheric gases acquired by the pool at the surface in contact with air this component is mixed in varying degree with two other components one each for gas and water entering the bottom of the pool the two bottom components are not in equilibrium in horseshoe spring the bubbles entering at the bottom strip the atmospheric derived pool gases from the surrounding water while en route to the surface if the original bottom bubbles are noble gas poor as in the case of horseshoe the acquired pool gases can then quickly obliterate the original bubble composition these results are used to demonstrate that yellowstone spring surface gas samples and perhaps similarly sampled thermal springs from other hydrothermal systems have gas abundances that depend more on spring morphology than processes occurring deeper in the hydrothermal system

a deglacial and holocene record of climate variability in south central alaska from stable oxygen isotopes and plant macrofossils in peat we used stable oxygen isotopes derived from bulk peat d 18 otom in conjunction with plant macrofossils and previously published carbon accumulation records in a w14 500 cal yr bp peat core ht fen from the kenai lowlands in south central alaska to reconstruct the climate history of the area we find that patterns are broadly consistent with those from lacustrine records across the region and agree with the interpretation that major shifts in d 18 otom values indicate changes in strength and position of the aleutian low al a semi permanent low pressure cell that delivers winter moisture to the region we find decreased strength or a more westerly position of the al relatively higher d 18 otom values during the bolling allerod holocene thermal maximum htm and late holocene which also correspond to warmer climate regimes these intervals coincide with greater peat preservation and enhanced carbon c accumulation rates at the ht fen and with peatland expansion across alaska the htm in particular may have experienced greater summer precipitation as a result of an enhanced pacific subtropical high a pattern consistent with modern d 18 o values for summer precipitation the combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation a strengthened al relatively lower d 18 otom values is most evident during the younger dryas neoglaciation and the little ice age consistent with lower peat preservation and c accumulation at the ht fen suggesting less precipitation reaches the leeward side of the kenai mountains during periods of enhanced al strength the peatlands on the kenai peninsula thrive when the al is weak and the contribution of summer precipitation is higher highlighting the importance of precipitation seasonality in promoting peat accumulation this study demonstrates that d 18 otom values in peat can be applied

a direct comparison between the historical record of lake level and the δ18o signal in carbonate sediments from lake turkana kenya we compared oxygen isotopic profiles from authigenic calcite in nine freeze cores from lake turkana kenya with the historical record of lake levels for the past 105 years 210pb dating of the cores indicates that sediment in two of the cores spans the complete historical record we observed spatial variability in 6180 and 617c values between cores and an offset from expected isotopic equilibrium values in several of the cores both of these characteristics can be explained by proximity to river input in model calculations of lake level we muted the spatial variability of the s1 o dataset by using a normalized and stacked record there is good agreement between the lake level history modeled using the normalized and stacked record and the historical record of lake level the lake level record derived from the s180 data indicates that lake level fluctuated by 15 m during the last century our model calculations indicate that s o records can be used to generate quantitative lake level curves even using datasets with significant spatial variability the isotopic composition of carbonates has been used in numerous lacustrine studies to determine paleoclimatic information fluctuations in the isotopic record preserved in carbonates are created mainly by variations in the temperature and composition of the water in which the carbonate formed in turn these variations can be caused by climatic changes in the lake basin carbonates are therefore potentially an archive of the paleoenvironment of a lake basin in tropical or closed basin settings shifts in the oxygenstable isotopic composition s180 of carbonates are often attributed to shifts in the evaporation to input e z ratio of a lake previous workers have used the relationship between changes in the s180 value of carbonates and the e z ratio of a lake basin to discuss qualitative changes in paleo lake levels although the relationship between the o composition of lake water and the various inputs and outputs to a basin has been described quantitatively gat 1984 phillips et al 1986 benson and white 1994 only one quantitative comparison between a historical lake level record and lake level determined from the ai80 composition of carbonates has been attempted li 1995

helium isotope studies of geothermal fields in the taupo volcanic zone new zealand abstract we report new measurements of 3he 4he and ne on 69 samples of gas from geothermal fields in the central section of the ne sw trending taupo volcanic zone tvz we find 3 he 4 he ratios in the range 5 9 7 3 times the atmospheric ratio 5 9 7 3ra typical of subduction zone systems in some areas near the boundaries of the volcanic zone the ratio is much lower 2 4ra the values in the wairakei field are extremely uniform and vary by only a few per cent from 7 2 ra in contrast the wells in the ohaaki broadlands field show a striking factor of two variation with the west bank section characterised by values near 6 ra while the east bank section has values as low as 3 0 ra this suggests that mixing of two types of geothermal source fluids may be occurring at ohaaki broadlands an inverse relationship has been found between the 3 he 4 he ratio of the gases and the b cl ratios in the associated fluids thus the helium isotope ratios appear to be affected both by the flux of mantle helium associated with mantle subduction and also by the presence of sedimentary rocks beneath the geothermal field leaching by the hot ascending fluid of radiogenic 4he together with boron from the underlying high boron low chloride mesozoic greywacke basement is thought to be the cause of this inverse relationship the co 2 3 he ratio in the tvz exceeds the morb ratio by a factor of up to 100 with higher values corresponding to higher b cl fluid ratios suggesting that the greywacke may also be the major source of the co2 we have also measured argon concentrations and isotopes on 19 samples in the ohaaki broadlands area in order to further elucidate the nature of the striking helium isotope variations the argon isotope ratios are relatively close to atmospheric indicating that the majority of the argon comes from recirculated groundwater the simplified boiling model of mazor et al 1990 has been used to calculate the 3 he heat ratio in the ohaaki broadlands and wairakei fields the values obtained fall within the range previously reported for mid ocean ridge systems this model has been extended and has led us to the conclusion that compared to the 3 he 4 he ratio the 3 he 36 ar asw ratio is a much better indicator of the potential geothermal heat the 4 he 40 ar na where na non atmospheric ratio of both the high mantle derived and low crustal derived 3 he 4 he end members of the analyses reported here is about 3 6 but for samples with low 3 he 36 ar ratio this ratio falls to values below 0 5 the value of 3 6 is in the range which is expected for the radiogenic component and although considerably lower than that often found in subduction type mantle gases it is still within the accepted range of values

correlation of gold in siliceous sinters with 3he4he in hot spring waters of yellowstone national park opaline sinter samples collected at yellowstone national park ynp were analyzed for gold by neutron activation and for other trace elements by the inductively coupled plasma optical emission spectroscopy icp oes method no correlation was found between au and as sb or total fe in the sinters although the sample containing the highest au also contains the highest sb there also was no correlation of au in the sinter with the h2s concentration in the discharged hot spring water or with the estimated temperature of last equilibration of the water with the surrounding rock the au in rhyolitic tuffs and lavas at ynp found within the yellowstone caldera show the same range in au as do those outside the caldera while thermal waters from within this caldera all have been found to contain relatively low dissolved au and to deposit sinters that contain relatively little au therefore it is not likely that variations in au concentrations among these sinters simply reflect differences in leachable au in the rocks through which the hydrothermal fluids have passed rather variations in h2s the concentration of total dissolved sulfide that result from different physical and chemical processes that occur in different parts of the hydrothermal system appear to exert the main control on the abundance of au in these sinters hydrothermal fluids at ynp convect upward through a series of successively shallower and cooler reservoirs where water rock chemical and isotopic reactions occur in response to changing temperature and pressure in some parts of the system the fluids undergo decompressional boiling and in other parts they cool conductively without boiling mixing of ascending water from deep in the system with shallow groundwaters is common all three processes generally result in a decrease in h2s and destabilize dissolved gold bisulfide complexes in reservoir waters in the ynp system thus different reservoirs in rocks of similar composition and at similar temperatures may contain waters with different h2s and au the h2s in a subsurface reservoir water is difficult to assess on the basis of analyses of hot spring waters because of uncertainties about steam loss during fluid ascent however the same processes that result in low h2s in reservoir waters also tend to result in decreases in the ratio of 3he4he r dissolved in that water values of r relative to this ratio in air ra attain values 15 in ynp thermal waters to date all of the thermal waters at ynp that have rra values 9 have been found to deposit sinters with relatively low gold concentrations these include all of the thermal waters that discharge from 180 215 c reservoirs at upper midway and lower geyser basins within the western part of the yellowstone caldera and thermal waters at norris geyser basin outside the yellowstone caldera where some of the waters flow directly to the surface from a reservoir where the temperature is about 300 c a high 3he4he ratio in thermal water discharged at the surface does not guarantee high gold concentrations in the sinter deposited by this water boiling with loss of steam the gas phase takes a separate route to the surface during rapid upflow from the shallowest reservoir to the surface decreases the h2s and total he dissolved in the residual liquid without appreciably changing the 3he4he ratio this is because the isotopic composition of the he of the initial bulk fluid is unchanged and there is too little time for much radiogenic 4he to build back into the liquid during this rapid ascent from the near surface reservoir however if boiling with phase separation and loss of steam occurs deep in the system the 3he4he ratio in the residual liquid now depleted in h2s and total he will be susceptible to dilution with radiogenic 4he that is acquired during the longer residence time underground some or all of the au that comes out of solution when an initial gold bisulfide complex breaks down as a result of loss of h2s may be swept up to the surface as solid probably colloidal particles depending on the rate of flow of the mixture of water and steam and the geometry of the channel where colloidal silica also forms as a result of this boiling free au apparently becomes attached to the colloidal silica and deposits where the silica deposits

oxygen isotope disequilibrium precipitation of calcite in lake arreso denmark lake carbonates are generally assumed to precipitate at or very close to oxygen isotopic equilibrium with the ambient water we present results from the eutrophic lake arreso northeastern sealand denmark that demonstrate disequilibrium precipitation of present day calcite according to the temperature equation of epstein et al these calcites are depleted in 18 o by 2 3 when compared to the expected equilibrium values core studies indicate that the development of disequilibrium conditions in lake arreso is correlated with the onset of an enhanced eutrophication a high precipitation rate is suggested as the mechanism responsible for the observed 18 o depletion of the calcite precipitates

evolution of paleo sea surface conditions over the last 600 years in the mackenzie trough beaufort sea canada abstract in order to document long term climate trends and predict future climate change for the arctic we need to look at the geological record to establish the link between historical and pre industrial sea surface parameters dinoflagellate cysts dinocysts are used as proxy indicators of sea surface parameters temperature salinity sea ice cover primary productivity jointly with transfer functions and a modern dinocyst reference database to reconstruct the evolution of sea surface conditions at decadal and multi decadal timescales here we present the fossil dinocyst assemblages established from three sediment cores collected along an inshore offshore transect in the mackenzie trough during the 2004 cases canadian arctic shelf exchange study cruise the chronology of each core was determined using 210 pb activity and ams 14 c measurements in core 912a sediment cores 912a 909b and 906b cover the last 600 200 and 100 years respectively palynomorph influxes increase from the bottom to the top of each core illustrating an increasing productivity over the last 600 years until 1850 ad when we observe a decrease of productivity until today we determined a succession of two assemblages over the last 600 years assemblage i at the base of each core is mostly composed of dinocysts from heterotrophic taxa the modern assemblage assemblage ii at the top of each core is mostly composed of dinocysts from autotrophic taxa quantitative reconstructions of sea surface parameters reveal a sharp increase in summer august temperature 2 to 5 c throughout the study area from 1400 ad until 1800 1850 ad after which the increase between 0 5 and 1 0 c is much slower until modern times

abrupt climate oscillations during the last deglaciation in central north america evidence from stable isotopes and a variety of proxies from two ontario lakes demonstrate that many of the late glacial to early holocene events that are well known from the north atlantic seaboard such as the gerzensee killarney oscillation also known as the intra allerod cold period younger dryas and preboreal oscillation also occurred in central north america these results thus imply that climatic forcing acted in the same manner in both regions and that atmospheric circulation played an important role in the propagation of these events

biologically induced calcite and its isotopic composition in lake ontario we studied water sediment trap and core samples from eastern lake ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so called whiting events calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors including temperature primary productivity and the abundance of pica cyanobacteria during the stratified period calcite precipitation is highly correlated to lake temperature because physical and biological factors interact to produce conditions favorable for whitings during warm years when the lake stratifies early in the seasonal cycle carbonate stratigraphies in multiple cores from eastern lake ontario revealed similar patterns of historical variation in percent carbonate an exponential rise in carbonate accumulation occurred in nine cores after 1930 culminating in peak values in the early 1980s this rise was related to historic increases in primary productivity resulting from increased phosphorus loading to lake ontario superimposed upon this rise were four peaks centered on 1940 1942 1957 1961 1971 1977 and 1983 that correlate with maxima in summer air temperature anomalies from the great lakes region and with strong el niiio events these peaks are also associated with maxima in s c values and minima in s180 values of carbonate lending support to our model that more calcite is precipitated with higher 6 c values during warm years when thermal stratitication occurs early in the seasonal cycle beginning in the mid 1980s calcite accumulation and its 6 c ratio began to decrease suggesting a reduction in primary productivity in surface waters probably related to lower phosphate concentrations in epilimnetic waters of lake ontario during the stratified period reduced summer p loading may be explained either by a lagged response to p abatement measures that began in the late 1970s or by decreased p loading from upstream lake erie beginning in the late 1980s as a result of the establishment of filter feeding zebra mussels

sediment isotope tracers from lake saarikko finland and implications for holocene hydroclimatology abstract multi component isotopic analyses on a sediment core from lake saarikko finland give insight into holocene climate changes in northern europe oxygen isotopic records from aquatic cellulose and authigenic carbonate reflect consistent similar trends in hydrological balance and are employed jointly to infer relative changes in lake water temperature other geochemical and isotopic tracers shed light on fluctuations in lake level and nutrient cycling facilitating the interpretation of the oxygen isotopic archives in the early holocene 10 000 9000 cal yr bp the lake level was low and dry conditions prevailed despite low temperatures higher lake levels and depleted oxygen isotopic values 9000 7500 cal yr bp were probably caused by several factors higher effective humidity an isotopically depleted precipitation source a cold event around 8300 cal yr bp and increased spring snowmelt in contrast higher summer temperatures lower effective humidity lower lake levels and enriched oxygen isotopic values were experienced during the mid holocene 7500 3300 cal yr bp the occurrence of the warmest inferred lake water and the most enriched cellulose oxygen isotope values 6000 5000 cal yr bp is consistent with a summer temperature maximum inferred from other proxy sources from the region the late holocene was characterized by higher effective humidity and higher lake levels increase in spring snowmelt and colder temperatures most likely related to the little ice age induced a drastic change in the lake hydrology and probably caused the formation of its present outlet 800 cal yr bp changes in the lake hydrological balance and climate variables inferred from oxygen isotopic records can be related to atmospheric circulation most clearly to changes in the dominance and strength of westerly air flow as well as summertime anticyclonic circulation

palaeohydrology of the southwest yukon territory canada based on multiproxy analyses of lake sediment cores from a depth transect lake level variations at marcella lake a small hydrologically closed lake in the southwestern yukon territory document changes in effective moisture since the early holocene former water levels driven by regional palaeohydrology were reconstructed by multiproxy analyses of sediment cores from four sites spanning shallow to deep water marcella lake today is thermally stratified being protected from wind by its position in a depression it is alkaline and undergoes bio induced calcification relative accumulations of calcium carbonate and organic matter at the sediment water interface depend on the location of the depositional site relative to the thermocline we relate lake level fluctuations to down core stratigraphic variations in composition geochemistry sedimentary structures and to the occurrence of unconformities in four cores based on observations of modern limnology and sedimentation processes twenty four ams radiocarbon dates on macrofossils and pollen provide the lake level chronology prior to 10 000 cal bp water levels were low but then they rose to 3 to 4 m below modern levels between 7500 and 5000 cal bp water levels were 5 to 6 m below modern but rose by 4000 cal bp between 4000 and 2000 cal bp they were higher than modern during the last 2000 years water levels were either near or 1 to 2 m below modern levels marcella lake water level fluctuations correspond with previously documented palaeoenvironmental and palaeoclimatic changes and provide new independent effective moisture information the improved geochronology and quantitative water level estimates are a framework for more detailed studies in the southwest yukon

reconstruction of paleohydrology and paleohumidity from oxygen isotope records in the bolivian andes cellulose inferred lake water n 18 o n 18 olw records from lago potosi lp a seasonally closed lake in a watershed that is not currently glaciated and lago taypi chaka kkota ltck previously reported in abbott et al 2000 quat sci rev 19 1801 1820 an overflowing lake in a glaciated watershed provide the basis for late pleistocene and holocene paleoclimatic reconstruction in the bolivian andes deconvolution of the histories of changing evaporative isotopic enrichment from source water n 18 o in the lake sediment records is constrained by comparison to the sajama ice core oxygen isotope profile whereas local hydrological influence is distinguished from the regional moisture balance history by the response of the different catchments to climate change overall variations in the lp n 18 olw record appear to be dominantly controlled by evaporative 18 o enrichment reflecting shifts in local effective moisture this record is used to generate a preliminary quantitative reconstruction of summer relative humidity spanning the past 11 500 cal yr on the basis of an isotope mass balance model results indicate that the late pleistocene was moist with summer relative humidity values estimated at 10 20 greater than present increasing aridity developed in the early holocene with maximum prolonged dryness spanning 7500 6000 cal yr bp at lp an interval characterized by summer relative humidity values that may have been 20 lower than present highly variable but dominantly arid conditions persist in the mid to late holocene with average summer relative humidity values estimated at 15 below present which then increase to about 10 20 greater than present by 2000 cal yr bp slightly more arid conditions characterize the last millennium with summer relative humidity values ranging from 5 10 lower than present similar long term variations are evident in the ltck n 18 olw profile except during the early holocene when lake water evaporative 18 o enrichment in response to low relative humidity appears to have been offset by enhanced inflow from 18 o depleted snowmelt or groundwater from the large catchment although some temporal offset is evident significant correspondence occurs between the isotope inferred paleohumidity reconstruction and other paleohydrological proxies from the region these

climate change in the turkana basin as deduced from a 4000 year long δo18 record abstract a model of the oxygen isotopic composition of lake turkana waters sheds insight into the paleoclimatic interpretation of a 18 o profile of inorganic calcite from a core taken from the lake the model indicates that high frequency fluctuations seen in the isotopic record are probably due to shifts in lake level while the long term increase of 1 4 seen from 4 to 2 kyr bp cannot be due solely to lake level change it must be due to changes in other climatic parameters such as the isotopic composition of the inflow these findings suggests that the abrupt change observed in lake turkana and many other african lakes at 4 ka was the precursor to a 2000 year long adjustment in the climate over the ethiopian plateau the isotopic record from lake turkana agrees with other paleoclimate records from the basin including the diatom stratigraphy and radiocarbon dates on exposed shoreline deposits

synoptic scale controls on the δ18o in precipitation across beringia oxygen isotope records of precipitation 18oprecip from beringia are thought to reflect synoptic scale circulation changes associated with the aleutian low to delineate the spatial pattern of 18oprecip associated with the two dominant modes of aleutian low circulation we combine modern 18oprecip and deuterium excess data with climate reanalysis and back trajectory modeling aleutian low strength and position are revealed to systematically affect regional moisture source and 18oprecip whereby a strengthened aleutian low causes lower higher 18oprecip in western eastern beringia we compare a new 100 year long 18o record from the aleutian islands with the north pacific index the primary indicator of aleutian low strength and find a significant positive relationship r 0 43 p 0 02 n 28 that tracks late twentieth century change this study demonstrates synoptic scale circulation controls on our isotope record and provides a coherent framework for interpreting existing and emerging paleoisotope data from the region

temperatures of the past 2000 years inferred from lake sediments southwest yukon territory canada abstract lake sediments from four sites in the southwest yukon territory canada provided paleotemperature records for the past 2000 yr an alpine and a forest site from the southeastern portion of the study area near kluane lake and another alpine forest pair of lakes from the donjek river area located to the northwest yielded chironomid records that were used to provide quantitative estimates of mean july air temperature prior to ad 800 the southwest yukon was relatively cool whereas after ad 800 temperatures were more variable with warmer conditions between ad 1100 and 1400 cooler conditions during the little ice age ad 1400 to 1850 and warming thereafter these records compare well with other paleoclimate evidence from the region

effective elastic thickness of the lithosphere along the easter seamount chain bathymetry and gravity data collected during legs 5 6 and 7 of the 1993 gloria expedition and the recently released 2 min altimetry derived global gravity grid are used to determine the effective elastic thickness of the lithosphere along the easter seamount chain esc forward modeling admittance and coherence methods yield consistent restfits with the exception of the eastern and western ends of the esc the effective elastic thickness along the chain is 1 4 km the thin elastic thickness for the majority of the esc seamounts is compatible with a young seafloor age at the time of loading derived from new radiometric ages of the seamounts along the chain and a magnetic isochron age interpretation of the nazca plate seafloor age the elastic thickness southeast of the nazca fracture zone is 6 km apparently because of the seafloor age discontinuity across the fracture zone the elastic thickness near the san felix island at the eastern end of the esc is even greater 11 km which is compatible with the estimated seafloor age at the time of loading a slight increase in the effective elastic thickness of the far western part of the esc suggests dynamic compensation or less thermal weakening of lithosphere above a plume channel versus directly above the plume center these findings combined with published geochemistry support a hotspot origin for the esc complicated by large scale plate boundary reorganizations and channeling of plume material to the east pacific rise

a 16 ka oxygen isotope record from genggahai lake on the northeastern qinghai tibetan plateau hydroclimatic evolution and changes in atmospheric circulation moisture source history and changes in atmospheric circulation are the most important attributes for portraying past climate changes and for estimating possible future trends however few climate records reflecting these attributes are available from the marginal zones of the asian summer monsoon here we present a record of the oxygen isotopic composition of authigenic carbonates delta 18 ocarb of sequential sediments from genggahai lake in the northeastern qinghai tibetan plateau qtp isotopic analyses were performed on the fine grained carbonate fraction 38 mu m mollusc shells and stem encrustations from submerged plants the stratigraphic variations of the delta o 18 record from the different carbonate components exhibit a remarkably similar pattern probably reflecting the fact that delta 18 ocarb variability was controlled primarily by changes in the oxygen isotopic composition of the lake water delta 18 olw disequilibrium effects and water temperature are precluded as major factors affecting the delta 18 ocarb variations genggahai lake is hydrologically open and characterized by a rapid discharge rate as indicated by analysis of the hydrological setting of the lake system and by the observed significant positive correlation between delta o 18 lw and the oxygen isotopic composition of the inflowing water delta o 18 1 under such hydrological conditions we argue that the isotopic signals of different moisture sources should be reflected in the carbonate isotopic composition furthermore placing the delta 18 ocarb record in the context of regional palaeoclimate archives we found that the isotopic signals particularly the negative shifts from the average values cannot be interpreted consistently despite a process of evaporative enrichment at the lake surface during the early to mid holocene low delta 18 ocarb values during 10 6 9 4 and 7 4 63 ka were associated with higher lake levels and thus the record may have been significantly affected by a strengthened asian summer monsoon at those times and hence by a positive moisture balance isotopic depletions with similar magnitudes occurred at 15 14 5 13 8 13 3 12 5 11 4 5 3 4 8 3 7 3 4 2 8 2 3 1 7 1 3 and 0 6 1 a i e within the lateglacial and the late holocene these negative shifts in delta 18 ocarb corresponded to lower lake level phases and most likely were a response to intensification of the mid latitude westerly circulation that may have transported significantly more o 18 depleted moisture to the region compared to that from the asian summer monsoon overall our results suggest that the alternating influence of the asian summer monsoon and the westerlies played a significant role in determining the pattern of atmospheric circulation on the northeastern qtp c 2017 elsevier ltd all rights reserved

a ring width based reconstruction of june july minimum temperatures since ad 1245 from white spruce stands in the mackenzie delta region northwestern canada abstract we present a reconstruction of june july minimum temperatures since ad 1245 for the mackenzie delta region based on a 29 site network of white spruce picea glauca ring width series most but not all trees experienced a divergent temperature growth response similar to the divergence that has affected other white spruce trees across yukon and alaska however divergence in the study region began as early as ad 1900 and we have documented our methods to avoid including divergent signals in the reconstruction calibration verification testing based on local temperature data and multi century coherence with nearby and large scale temperature proxy records confirm that our reconstruction is robust the reconstruction shows cool conditions in the late 13th early 18th and early 19th centuries corresponding with solar minima and increased volcanism these cool periods are interrupted by warm periods consistent with early to mid 20th century warmth the late 20th century is the warmest interval and the last decade is estimated to be 1 4 c warmer than any decade before the mid 20th century the reconstructed climate history corroborates other proxy based inferences and supports the notion that high latitude regions such as the mackenzie delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries

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

timing and climatic controls over neoglacial expansion in the northern coast mountains british columbia canada holocene sedimentary records from two lakes in white pass british columbia show that the onset of neoglacial sedimentation began c 2 ka cal bp prior to this time the lakes accumulated organicrich sediments with properties and sedimentation rates similar to adjacent lakes that have not had glacial influences during the holocene neoglaciation at white pass was coincident with the increased delivery of exotic tsuga heterophylla western hemlock pollen these results together with regional indications for increased delivery of hemlock pollen at 2 ka bp by a deepened low pressure in the northeastern pacific ocean suggest that increased moisture was important for the expansion of glaciers in the region in addition to longer term late holocene cooling

the bahia seamounts test of a hotspot model and a preliminary south american late cretaceous to tertiary apparent polar wander path abstract detailed bathymetric and magnetic data collected over the bahia seamounts in the western south atlantic brazil basin are analyzed six paleomagnetic poles are determined one from three seamounts sharing a ridge and five from isolated seamounts two poles fall near a continental late cretaceous south american pole and are assumed to be of late cretaceous age another seamount has a preliminary 40 ar 39 ar age of 62 4 ma we check this age and estimate the ages of other seamounts by rotating their poles into north american coordinates and comparing them with north american paleomagnetic reference poles these ages and the characteristic magnetic polarities of all bahia seamounts are used to test hotspot models of formation of the seamount group the northern and central bahia seamount chains could have formed from a single hotspot the southern bahia chain may require a second hotspot the two postulated hotspots were probably concurrent and separated by 150 to 200 km the paleomagnetic poles trace out a smooth curve from the late cretaceous poles to a pole that is indistinguishable from the spin axis which we estimate as having an early eocene age the pole ages remain preliminary until better age dates are found and rocks are recovered from more seamounts

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

holocene climate inferred from oxygen isotope ratios in lake sediments central brooks range alaska analyses of sediment cores from two lakes in the central brooks range provide temperature and moisture balance information for the past 8500 cal yr at century scale resolution two methods of oxygen isotope analysis are used to reconstruct past changes in the effective moisture precipitation minus evaporation and temperature effective moisture is inferred from oxygen isotope ratios in sediment cellulose from meli lake area 0 13 km 2 depth 19 4 m the lake has a low watershed to lake area ratio 7 and significant evaporation relative to input summer temperature shifts are based on oxygen isotope analyses of endogenic calcite from tangled up lake area 0 25 km 2 depth 3 5 m this basin has a larger watershed to lake area ratio 91 and less evaporation relative to input sediment oxygen isotope analyses from the two sites indicate generally more arid conditions than present prior to 6000 cal yr b p subsequently the region became increasingly wet temperature variability is recorded minimally at centennial scale resolution with values that are generally cool for the past 6700 cal yr the timing and direction of climate variability indicated by the oxygen isotope time series from meli and tangled up lakes are consistent with previously established late holocene glacier advances at 5000 cal yr b p in the central brooks range and high lake levels at birch lake since 5500 cal yr b p this unique use of oxygen isotopes reveals both moisture balance and temperature histories at previously undetected high resolution temporal scales for northern alaska during the middle to late holocene c 2001 university of washington

multi proxy holocene palaeoclimatic record from a saline lake in the canadian subarctic multi proxy palaeolimnological analyses of a postglacial sedimentary sequence at a centennial scale resolution from an athalassic saline lake in the yukon were conducted to infer patterns of holocene climatic change in the canadian subarctic using sediment mineralogy and biostratigraphy diatoms pigments diatominferred quantitative estimates of palaeosalinity were obtained by use of transfer functions developed from a calibration set of 219 lakes from western north america the sediment mineralogy and fossil pigments at the base of the core indicated a moderately deep non stratified lake dominated by clastic influx probably in a basin fed by glacial meltwater the early holocene history c 11 000 8100 14c yr bp was characterized by a relatively deep mesosaline lake with diatom inferred salinities approximating 20 g l 1 the occurrence of both aragonite and dolomite as well as elevated concentrations of chlorophyll and carotenoid pigments support the interpretation of deepwater anoxia and possibly

crustal structure volcanism and opening mode of the ulleung basin east sea sea of japan abstract a study of the ulleung basin in the southwestern east sea sea of japan based on single and multi channel seismic reflection profiles and ocean bottom seismometer obs data suggests that the basin formed largely by pull apart opening and the deep northern basin is underlain by thicker than normal oceanic crust 10 km thick probably formed during the earliest stage of seafloor spreading volcanic activity in association with basin opening occurred over much of the basin but it ceased first in the south while it continued in the north until recently the principal evidence for pull apart opening includes 1 an overall rhomboidal shape of the basin consisting of two basement lows and a median high known to be characteristic of pull apart basins 2 the location and orientation of the major volcanic sources suggesting more or less n s opening and 3 the strike slip fault system along the western basin margin which appears to have guided the pull apart opening the lack of extensional deformation along the western basin margin which would have been prevalent if sw japan had rotated away from the korean peninsula as suggested by paleomagnetic data is also not in favor of the alternative rotational opening of the basin the absence of graben and rift topography in the acoustic basement in the deep northern ulleung basin is indicative of the non brittle or ductile nature of the crust tau p analysis of the obs data reveals that the igneous crust consists of upper and lower layers with velocities typical of oceanic layers the velocity depth profiles with a two gradient velocity structure is also characteristic of oceanic crust however the lower layer is much thicker than oceanic layer 3 and the change of velocity gradient which occurs at around 6 5 km s in typical oceanic crust occurs at about 6 km s suggesting that the crust is not a typical oceanic crust the meager basin size and short opening period may suggest that the basin opening did not lead to the formation of full fledged oceanic crust but instead resulted in embryonic or incipient oceanic crust thickened by upper mantle thermal perturbations evoked by rifting

rapid hydrological changes during the holocene revealed by stable isotope records of lacustrine carbonates from lake igelsjon southern sweden a holocene sediment sequence from lake igelsjon south central sweden was studied by stable oxygen and carbon isotope analyses of different carbonate components the deposit which covers the time span from ca 11 500 cal bp to the present was laid down in a small kettle hole lake the hydrological balance of which is presently dominated by groundwater flow isotopic records obtained on bulk carbonates originating mainly from summer produced calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand likely reflecting pronounced hydrological variations corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts probably related to an extended calcification season the isotopic records were complemented by studies of modern isotope hydrology and our interpretations are based on a simplistic climate hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface volume ratio of the basin during the ice free season assumed periods of decreased lake volume in a relatively dry climate low lake level are characterised by enrichment in o 18 and c 13 resulting from increased evaporation inflow ratio and atmospheric equilibration respectively in clear contrast to this situation intervals of more humid climatic conditions give rise to increased lake volume high lake level possibly surface over flow and relatively depleted isotopic ratios relatively humid conditions which may correlate to a wide spread cooling event recorded by various proxies across the north atlantic region are indicated by distinct isotopic shifts at ca 8300 and 8000 cal bp bracketing a period of o 18 depletion the period between ca 8000 and 4000 cal bp was characterised by relatively dry and stable climatic conditions whereas the subsequent part of the holocene experienced a more humid and variable climate following marked and coherent depletions in o 18 and c 13 at ca 4000 cal bp c 2002 elsevier science ltd all rights reserved less

seismic evidence for stretched continental crust in the japan sea the japan sea is a major marginal sea in the western pacific comprised of basins and bathymetric highs technically these features were created by multiple rifting and spreading processes as exemplified in the creation of the japan basin and yamato basin however there are smaller scale features for which seismic crustal models have been inadequate to infer or verify their origin and evolution recent advances in marine seismological surveys enable us to obtain heterogeneous seismic crustal structures in sufficient detail to characterize these features in september of 1992 a seismic experiment was conducted to obtain the detailed seismic crustal structure in the southwestern part of the japan sea including the basin and bank areas seventeen ocean bottom seismometers obss were deployed on two lines explosives and airguns were fired as controlled seismic sources the model of the crust obtained in the northern tsushima basin is about 13 km thick including a 1 5 km thick sedimentary layer beneath the bank area the crust is 22 km thick and the upper crust is relatively homogeneous with a p wave velocity of about 6 km s the bank is interpreted to be a stretched continental crust fragment

a seismic experiment in the ulleung basin tsushima basin southwestern japan sea east sea of korea understanding the crustal structure of the ulleung basin tsushima basin in the southwestern japan sea east sea of korea is important for reconstructing the opening tectonics of the japan sea a korea and russia collaborative seismic experiment was carried out in 1991 to investigate the crustal structure of this basin using ocean bottom seismometers obss and large capacity air guns the results of the experiment reveal that the ulleung basin is floored by distinctive upper and lower crustal layers with velocities typical of layers 2 and 3 the lower crust however is unusually thick 7 8 km and the moho lies flat at 15 16 km depths though similar to the yamato basin in crustal thickness the ulleung basin has a much thicker sedimentary sequence and a slightly thinner lower crust in the center geophysical evidence thus shows that the crust under the ulleung basin has velocity range and crustal layering falling closer to those of normal oceanic crust than the yamato basin the formation mechanism of the thicker than normal lower crust should be clarified to better understand the complex opening process in the southern japan sea

environmental controls on the 2h 1h values of terrestrial leaf waxes in the eastern canadian arctic the hydrogen isotope composition of plant waxes preserved in lacustrine sediments is a potentially valuable tool for reconstructing paleoenvironmental changes in the arctic however in contrast to

geochemical and isotopic properties of fluids from gold bearing and barren quartz veins of the sovetskoye gold deposit siberia russia this paper reports on the comparative study of fluids trapped in inclusions in gold bearing and barren quartz veins at the sovetskoye gold deposit yeniseisky ridge siberia russia the host rocks are greenschist facies metasedimentary rocks of upper proterozoic age within the deposit some veins contain 10 to 25 ppm of au gold bearing veins others contain less than 1 ppm of au barren veins fluid inclusions trapped in barren veins are predominantly low salinity h2o 4 0 8 0 mass nacl equiv with variable contents of dissolved co2 12 5 mol ch4 1 3 mol and n2 1 7 mol homogenization temperatures vary from 200 to 410 c and the calculated pressures of entrapment are 1 5 kbars inclusion fluids trapped in the host schists are predominantly aqueous 97 6 99 3 mol h2o with co2 contents below 2 4 mol percent the fluids trapped in ore bearing quartz inclusions are different inclusions show higher homogenization temperatures up to 630 c and salinity up to 20 25 mass nacl equiv calculated pressures range from 0 7 to 2 0 kbars bulk gas chromatographic data of fluids extracted from native gold have contents of co2 that range from 29 3 to 62 0 mol percent n2 from 2 7 to 13 2 mol percent and ch4 from 0 0 to 2 8 mol percent in gold bearing quartz the contents of co2 range from 18 0 to 41 0 mol percent n2 from 0 1 to 0 2 mol percent and ch4 from 0 3 to 3 0 mol percent raman spectroscopic data of fluid from gold bearing quartz revealed co2 contents of individual inclusions as high as 98 2 mol percent n2 up to 66 4 mol percent and ch4 up to 88 7 mol percent fluids of the country rock schists which host gold bearing quartz veins are also enriched in co2 up to 49 5 mol the host rocks for both barren and gold bearing quartz veins show consistent ree patterns characterized by a negative eu anomaly fluids from barren quartz veins show similar ree patterns although with a less conspicuous negative eu anomaly whereas fluids from gold bearing quartz show a marked positive eu anomaly similar isotopic values of sulfur in pyrite pyrrhotite and arsenopyrite disseminated in country rocks 34s 14 7 21 6 and in barren 34s 12 9 19 9 and gold bearing quartz veins 34s 13 3 17 9 suggest that sulfur in sulfides was derived from the same source most likely being the adjacent country rocks co2 trapped in fluid inclusions of barren and gold bearing quartz has distinct isotopic compositions 13c 8 1 to 10 2 and 4 9 to 5 2 respectively and the 13c values are positively correlated with au contents in veins helium isotope composition of both types of quartz veins 3he 4he 0 04 0 05 ra for gold bearing veins and 3he 4he 0 02 ra for barren veins indicates a crustal provenance of mineral forming fluids the 40ar 39ar dating of sericite demonstrates that the barren veins 890 850 ma are significantly older than the gold bearing veins 830 730 ma on the basis of their ages barren veins are interpreted as synmetamorphic the age of the gold bearing veins corresponds to the age of the local granitoids 850 720 ma suggesting that the origin of the sovetskoye deposit is related to the tectonic activity syntetctonic magmatism

lake carbonate δ18o records from the yukon territory canada little ice age moisture variability and patterns abstract a 1000 yr history of climate change in the central yukon territory canada is inferred from sediment composition and isotope geochemistry from small groundwater fed seven mile lake recent observations of lake water 18 o lake level river discharge and climate variations suggest that changes in regional effective moisture precipitation minus evaporation are reflected by the lake s hydrologic balance the observations indicate that the lake is currently 18 o enriched by summer evaporation and that during years of increased precipitation when groundwater inflow rates to the lake increase lake water 18 o values decrease past lake water 18 o values are inferred from oxygen isotope ratios of fine grained sedimentary endogenic carbonate variations in carbonate 18 o supplemented by those in carbonate and organic 13 c c n ratios and organic carbon carbonate and biogenic silica accumulation rates document changes in effective moisture at decadal time scales during the early little ice age period to present results indicate that between ad 1000 and 1600 effective moisture was higher than today a shift to more arid climate conditions occurred after ad 1650 the 19th and 20th centuries have been the driest of the past millennium temporal variations correspond with inferred shifts in summer evaporation from marcella lake 18 o a similarly small stratified alkaline lake located 250 km to the southwest suggesting that the combined reconstructions accurately document the regional paleoclimate of the east central interior comparison with regional glacial activity suggests differing regional moisture patterns during early and late little ice age advances

anatomy of siliceous hot springs examples from yellowstone national park wyoming usa abstract numerous siliceous hot spring systems in the norris and lower geyser basins of yellowstone national park wyoming provide insights into spring geometries depositional facies and lithofacies associated with modern hot springs analyses of active cistern spring octopus spring deerbone spring and spindle geyser and inactive pork chop geyser siliceous hot springs have facilitated the construction of a facies model for siliceous hot spring deposits at yellowstone yellowstone s siliceous springs tend to group into four broad morphological categories siliceous spires and cones domal mounds terraced mounds and ponds siliceous spires cones are subconical accumulations up to 5 7 m high and about 2 m in diameter and are common deposits in yellowstone lake domal mounds are characterized by siliceous precipitates with a broad lens or shield geometry 2 3 m in vertical relief discharge channels and an areal accumulation of approximately 150 m2 in contrast terraced mounds have a stair step morphology a substantial pool 8 10 m in diameter shrubby precipitates and occupy areas of 2000 m2 siliceous ponds are variable in size have little outflow and exhibit low amounts of silica precipitation of these morphological varieties domal mounds and terraced mounds are thought to have the best long term preservation potential the four spring morphotypes are composed of up to eight cumulative hot spring depositional facies 1 vent 95 c 2 proximal vent precipitation of siliceous sinter is the result of abiotic and biotic processes abiotic precipitational processes are dominant in the vent area whereas biotic influences on the precipitate fabric become progressively more important downflow

an oxygen isotope record of holocene climate change in the south central brooks range alaska abstract understanding the ecological and socio economic impacts of climatic warming requires knowledge of associated changes in moisture balance reconstructions of holocene moisture balance variation offer indispensible baseline information against which recent changes can be evaluated we analyzed chara stem encrustations in the sediments of takahula lake located in the south central brooks range of alaska for oxygen and carbon isotope composition to infer climatic change over the past 8000 years to help constrain climatic interpretations of the sediment 18 o record we also analyzed water samples from takahula and other lakes in the region for oxygen and hydrogen isotope composition results show that winter precipitation dominates the water balance of these lakes and that post input evaporation is a key control of lake water isotope composition of takahula lake stratigraphic patterns in chara 18 o supplemented by those in 13 c and sediment lithology reveal distinct changes in effective moisture precipitation minus evaporation over the past 8000 years effective moisture was relatively high from 8000 to 5000 cal bp with marked fluctuations between 6800 and 5000 cal bp it then decreased to reach a minimum around 4000 cal bp and increased with fluctuations from 4000 to 2500 cal bp followed by a decreasing trend toward the present that was interrupted by a wet little ice age centered at 400 cal bp aridity during the 20th century was among the highest of the entire 8000 year record at the millennial timescale the temporal patterns of moisture balance shifts at takahula lake are broadly coherent with those inferred from previous paleoclimate records from the region the chara 18 o values around 5600 cal bp and during the little ice age are up to 5 lower than at present and 3 6 lower than that of the modern input water to the lake these exceptionally low values suggest that factors other than effective moisture must have contributed to the pronounced variations in the takahula lake 18 o record increased winter precipitation associated with a westerly aleutian low position may account for 1 of the 18 o decrease other factors leading to the 18 o depletion during these periods probably include decreased temperatures as well as increased lake ice cover and associated reductions in evaporation

stable isotopes in charophyte incrustations relationships with climate and water chemistry abstract age gradients of stable c and o isotopes were found in modern chara hispida calcite incrustations allowing seasonal changes in water chemistry to be observed gradients resulted from apical calcification in growing charophytes in a regional study of 12 species and varieties of charophytes the carbonate 13c differed significantly with low value and high value species such as chara globularis and c baltica respectively samples from lakes and other stagnant waters had significantly higher 13c values than those sampled from flowing water the differences were related mainly to photosynthesis charophyte 18o carbonate was not significantly different between species but water chemistry was important for brackish water lamprothamnium papulosum the overall 18o carbonate was positively correlated with groundwater 18o and it is suggested that more reliable environmental information is available from 18o than 13c in charophyte marls the mean charophyte carbonate 13c and 18o was 5 7 and 6 4 vpdb respectively environmental temperature estimates suggested that at some sites the carbonate was deposited close to isotopic equilibrium but in others a slight to moderate disequilibrium was indicated

geyserite in hot spring siliceous sinter window on earth s hottest terrestrial paleo environment and its extreme life siliceous hot spring deposits or sinters typically form in active terrestrial on land volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the earth s surface as silica charged geothermal fluids geyserites are sinters affiliated with the highest temperature 75 100 c natural geothermal fluid emissions comprising localized lithologically distinctive hydrothermal silica precipitates that develop around geysers spouters and spring vents they demarcate the position of hot fluid upflow zones useful for geothermal energy and epithermal mineral prospecting near vent areas also are extreme environment settings for the growth of microbial biofilms at near boiling temperatures microbial biosignatures e g characteristic silicified microbial textures carbon isotopes genetic material lipid biomarkers may be extracted from modern geyserite however because of strong taphonomic filtering and subsequent diagenesis fossils in geyserite are very rare in the pre quaternary sinter record which in and of itself is patchy in time and space back to about 400 ma only a few old examples are known such as geyserite reported from the devonian drummond basin australia devonian rhynie cherts scotland and a new example described herein from the spectacularly well preserved late jurassic 150 ma yellowstone style geothermal landscapes of patagonia argentina there geyserite is associated with fossil vent mounds and silicified hydrothermal breccias of the claudia sinter which is geologically related to the world class cerro vanguardia gold silver deposit of the deseado massif a part of the chon aike siliceous large igneous province tubular filament like micro inclusions from claudia were studied using integrated petrographic and laser micro raman analysis the results of which suggest a biological origin the putative fossils are enclosed within nodular geyserite a texture typical of subaerial near vent conditions overall this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of earth s highest temperature habitable terrestrial sedimentary environment hot spring depositional settings also may serve as analogs for early earth paleoenvironments because of their elevated temperature of formation rapid mineralization by silica and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures

late holocene moisture balance variability in the southwest yukon territory canada abstract analyses of sediment cores from marcella lake a small hydrologically closed lake in the semi arid southwest yukon provides effective moisture information for the last 4500 years at century scale resolution water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that marcella lake is currently enriched in 18 o by summer evaporation past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal charophyte stem encrustations a record of the 18 o composition of mean annual precipitation at jellybean lake a nearby evaporation insensitive system provides data of simultaneous 18 o variations related to decade to century scale shifts in aleutian low intensity position the difference between the two isotope records represents 18 o enrichment in marcella lake water caused by summer effective moisture conditions results indicate increased effective moisture between 3000 and 1200 cal bp and two marked shifts toward increased aridity at 1200 and between 300 and 200 cal bp these prominent late holocene changes in effective moisture occurred simultaneously with changes in aleutian low circulation patterns over the gulf of alaska indicated by jellybean lake the reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today

flexural isostasy and loading sequence of the dokdo seamounts on the ulleung basin in the east sea sea of japan abstract the isostatic compensation and loading sequence of the dokdo seamounts on the ulleung basin in the east sea are studied by a flexure model using gravity and bathymetric data the dokdo seamounts comprise dokdo dok island lying as a cluster of emerged small islets surmounting a large submerged volcanic edifice and two voluminous tablemounts simheungtaek and isabu in spite of their similarity in topographic expression a large difference of about 50 mgal between the observed gravity anomaly peaks over dokdo and the isabu tablemount implies different amounts of compensation a comparison between the observed and calculated gravity anomalies of the seamounts shows that the flexural compensation investigated in this study predicts well the observed data the flexure model suggests that the dokdo seamounts might be composed of high density volcanic rocks modeling results show that the flexural rigidity or effective elastic thickness of the lithosphere under dokdo is stronger or thicker than that under the isabu tablemount it implies that the age of lithosphere at the time of loading for isabu was younger than that for dokdo the effective elastic thicknesses associated with the dokdo seamounts approximately follow 200 400 c isotherms in the cooling plate model the results of this study and the former age dating of dokdo suggest that the isabu tablemount was formed first followed by dokdo after the opening of the east sea ceased

opening mode of the japan sea inferred from the palaeomagnetism of the japan arc the western edge of the pacific plate is marked by a chain of back arc basins stretching from the aleutians through japan and the philippines to new zealand most of the basins lie behind volcanic island arcs far from continents and are the result of extension of the oceanic lithosphere1 but the japan sea is bounded on one side by continental crust the sikhote alin and korean peninsula of the asian continent and on the other by an active arc with continental fragments it can thus be said to be associated more with continental rifting1 4 than with oceanic processes we report here palaeomagnetic data from the japan arc which indicate that since the early miocene north east japan has rotated counter clockwise through 47 around a vertical axis while south west japan has rotated clockwise through 56 refs 5 8 we attribute this differential rotation which took place concurrently between 21 and 11 myr ago to the back arc opening of the japan sea8 with a double door mode that is there are two fan shaped spreading basins facing each other such a fan shaped opening is probably peculiar to the geological phenomenon of rifting of a continental fragment from thick continental lithosphere

evolution of geothermal fluids deduced from chemistry plots yellowstone national park u s a mazor e and thompson j m 1982 evolution of geothermal fluids deduced from chemistry plots yellowstone national park u s a j volcanol geotherm res 12 351 360 large amounts of chemical data obtained in geothermal fields may readily be sorted out by the aid of a simple set of graphs that provide a clear over all picture and facilitate the understanding of geochemical processes taking place as a case study data from several hundred samples of the thermal springs at the well known yellow stone national park are discussed the pattern obtained seems to indicate 1 geochemical similarity between the spring groups of heart lake shoshone upper midway lower and norris geyser basins i e a geochemical uniformity of major spring groups located over 40 km apart 2 these groups may be described as originating from a common fluid most resembling the composition of norris waters accompanied by co and other volatiles that react with igneous rocks forming local variations 3 the secondary reactions occur at medium depth before the ascent to the surface 4 extensive concentration dilution processes occur during the ascent to the surface the water of the mammoth group may be described as originating from the same norris like fluid that has been diluted low na and ci contents and intensively reacted with carbonaceous rocks thus gaining in ca mg so and hco

coupled variations in helium isotopes and fluid chemistry shoshone geyser basin yellowstone national park abstract early studies of 3he 4he variations in geothermal systems have generally attributed these fluctuations to either differences in the source of the magmatic 3he rich helium or to local differences in the deep flux of magmatic 3he rich helium kennedy et al 1987 however show that near surface processes such as boiling and dilution may also drastically affect 3 he 4 he ratios of geothermal vapors helium isotope ratios were determined for several hot springs at shoshone geyser basin of yellowstone national park for this study along with other noble gas data stable isotope data and water and gas chemistry data for each spring were also compiled the water chemistry indicates that there is one deep hot thermal water in the area which is mixing with dilute meteoric water that has entered the system at depth spring hco3 concentrations correlate with 3 he 4 he values as in nearby lower geyser basin this correlation is attributed to variable amounts of deep dilution of thermal waters with a relatively cool water that inhibits boiling at depth thus preventing the loss of co2 and therefore hco3 and magmatic he in the most diluted samples oxygen and hydrogen isotope data also support a boiling and dilution model but to produce the observed fractionations the boiling event would have to be extensive with steam loss at the surface whereas the boiling that affected the helium isotope ratios was probably a small scale event with steam loss at depth it is possible that deep boiling occurred in the basin and that small amounts of steam escaped along fractures at about 500 m below the surface while all subsequently produced steam was lost near or at the surface

controls on recent alaskan lake changes identified from water isotopes and remote sensing 1 high latitude lakes are important for terrestrial carbon dynamics and waterfowl habitat driving a need to better understand controls on lake area changes to identify the existence and cause of recent lake area changes in the yukon flats a region of discontinuous permafrost in north central alaska we evaluate remotely sensed imagery with lake water isotope compositions and hydroclimatic parameters isotope compositions indicate that mixtures of precipitation river water and groundwater source 95 of the studied lakes the remaining minority are more dominantly sourced by snowmelt and or permafrost thaw isotope based water balance estimates indicate 58 of lakes lose more than half of inflow by evaporation for 26 of the lakes studied evaporative losses exceeded supply surface area trend analysis indicates that most lakes were near their maximum extent in the early 1980s during a relatively cool and wet period subsequent reductions can be explained by moisture deficits and greater evaporation

an anomalously thick layering of the crust of the yamato basin southeastern sea of japan the final stage of back arc spreading abstract the yamato basin is believed to have been formed by back arc spreading of the japanese islands a seismic velocity structure beneath the basin was modeled on the basis of seismic data acquired during the delp 85 wakashio cruise conducted by the japanese research group of the international lithosphere project ilp the dataset consists of multichannel reflection profiles airgun shot refraction profiles recorded by ocean bottom seismometers obss and explosion refraction profiles also recorded by the obss the model indicates that the crustal layering is twice as thick as in a normal oceanic basin but the velocity in each layer and that of the underlying uppermost mantle is very similar to that of oceanic basin crust the crust is 14 km thick at the middle of the oblong basin along its strike and thinner towards the rim of the basin tending toward 11 km stratigraphy of the sedimentary layer and the acoustic basement suggest that volcanism during the late stage of spreading is responsible for the thick layering and the seamount chain located along the spreading axis of the basin

hydrology mediated differential response of carbon accumulation to late holocene climate change at two peatlands in southcentral alaska abstract peatlands are among the largest reservoirs of terrestrial carbon in the northern hemisphere understanding how this reservoir will respond to climate changes is critical to assessing potential climate feedbacks peatland carbon accumulation rates pcar are controlled by the difference between production and decomposition which is affected by local and climatic factors including hydrology and temperature to better understand how local controls can influence the response of pcar to climate change we investigated modern hydrology paleohydrology and pcar at two nearby sphagnum dominated peatlands with different surficial geology lowland and moraine settings in southcentral alaska modern hydrological data indicated a higher rate of subsurface drainage at the lowland site suggesting greater hydrologic sensitivity to prolonged dry periods of the past we investigated past responses of these peatlands to well documented climatic changes like the medieval climate anomaly mca at 1000 600 cal yr bp and little ice age lia at 600 200 cal yr bp using water table depth wtd inferred from testate amoebae and pcar calculated from loss on ignition and 14 c dating analyses our results indicate that wtd and pcar remained relatively stable at the moraine site throughout the last 1100 years including the mca and lia however the lowland site experienced relatively stable wtd and higher pcar during the mca but highly variable wtd and lower pcar during the lia these differences suggest that hydrology and likely decomposition were the primary control on pcar at these peatlands our results highlight the importance of local scale controls like surficial geology in mediating the response of peatland hydrology and carbon accumulation to climate change

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

isotopic and hydrologic responses of small closed lakes to climate variability hydroclimate reconstructions from lake sediment oxygen isotope records and mass balance models abstract hydroclimate sensitivity simulations were conducted with a lake catchment hydrologic and isotope mass balance model adapted to two small closed lakes castor and scanlon located in the pacific northwest model simulations were designed to investigate the combined influences of persistent disequilibrium reddening and equifinality on lake water and sediment i e biogenic and endogenic carbonate mineral oxygen isotope 18 o values and to provide a basis for quantitative probabilistic climate reconstructions using lake sediment 18 o records simulation results indicate that within closed basin lakes changes in long term i e multi decadal precipitation amounts produce inconsistent responses in lake water and sediment 18 o values that are strongly influenced by lake basin outseepage and morphometry simulations of variable initial conditions in which randomly generated monthly climate data i e precipitation temperature and relative humidity were used to force the model during the equilibration period which precedes the application of instrumental climate data demonstrate that castor lake and scanlon lake have a somewhat limited isotopic memory of 10 years additional tests conducted using a monte carlo ensemble in which random climate data were used to force the model combined with 18 o analyses of water samples collected from 2003 to 2011 ad indicate that within small closed lakes in the pacific northwest november february precipitation is the strongest seasonal climatic control on sediment oxygen isotope values further a monte carlo based reconstruction of 20 year average november february precipitation amounts strongly correlates r 2 0 66 to instrumental values from the 20th century with all observed values falling within modeled 95 prediction limits indicating that probabilistic quantitative paleoclimate interpretations of lake sediment 18 o records are attainable

paleoposition of southwest japan at 16 ma implication from paleomagnetism of the miocene ichishi group abstract new paleomagnetic data from shallow marine sediments of the ichishi group suggest a clockwise tectonic rotation of southwest japan in the middle miocene samples have been collected from mud or tuff layers at 17 sites stability of remanent magnetization has been examined by using alternating field and thermal demagnetization the polarity sequence composed of four normal and seven reversed polarity sites is correlated to polarity epoch 16 15 2 17 6 ma based on micropaleontological assignment of the upper ichishi group to blow s zone n8 the mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast this result suggests that southwest japan was subjected to a clockwise rotation through 45 since 16 ma the clockwise rotation can be explained by the drift of southwest japan associated with the spreading of the japan sea during the middle miocene

colloidal transport of gold and silica in epithermal precious metal systems evidence from the sleeper deposit nevada bonanza vein gold ore from the sleeper deposit nevada was deposited at a depth of less than 500 m and exhibits a characteristic texture of alternating colloform bands of fine grained quartz and bands of opaline silica containing abundant electrum textural evidence indicates that the quartz bands recrystallized from a gel like amorphous precursor whereas the gold rich bands were deposited originally as amorphous precipitate formed by the coagulation of colloidal silica and gold particles gold and silica precipitated initially as colloidal particles at deeper levels in the hydrothermal system and were mechanically transported upward by the hydraulic action of the ore forming fluids coagulation of the colloidal particles may have been caused by solution cooling or boiling and catalyzed by hydrated polycationic al 3 aqueous species transport of gold as colloidal particles in epithermal systems indicates that at least in some instances higher gold content is possible than in true solution a gold enriched ore fluid appears necessary to explain the origin of the bonanza grade ore at the sleeper mine and the colloidal gold transport process locally might have played a role in the genesis of the more common disseminated epithermal precious metal deposits

enhanced late holocene enso pdo expression along the margins of the eastern north pacific abstract pacific climate is known to have varied during the holocene but spatial patterns remain poorly defined this paper compiles terrestrial and marine proxy data from sites along the northeastern pacific margins and proposes that they indicate 1 suppressed enso conditions during the middle holocene between 8000 and 4000 cal bp with a north pacific that generally resembled a la nina like or more negative pdo phase and 2 a climate transition between 4200 and 3000 cal bp that appears to be the teleconnected expression to a more modern like enso pacific compared to modern day conditions the compiled data suggest that during the middle holocene the aleutian low was generally weaker during the winter and or located more to the west while the north pacific high was stronger during the summer and located more to the north coastal upwelling off california was more enhanced during the summer and fall but suppressed during the spring oregon and california sea surface temperatures ssts were cooler the santa barbara basin had an anomalous record suggesting warmer ssts late holocene records indicate a more variable el nino like and more positive pdo pacific the aleutian low became more intensified during the winter and or located more to the east the north pacific high became weaker and or displaced more to the south coastal upwelling off california intensified during the spring but decreased during the fall oregon and california ssts became warmer recording the shoreward migration of sub tropical gyre waters during the fall while spring upwelling cooler sst increased in the santa barbara basin the high resolution proxy records indicate enhanced enso and pdo variability after 4000 cal bp off southern california 3400 cal bp off northern california and by 2000 cal bp in southwestern yukon a progressively northward migration of the enso teleconnection during the late holocene is proposed

late quaternary climatic change on the american north pacific coast temporal changes in solar radiation caused by variations in the earth s orbit figure prominently in current quaternary climate theory1 4 experimental design of atmospheric circulation models emphasizes the importance of solar radiation in the heating of interglacial land and ocean surfaces at different seasons of the year whereby monsoon type circulation seasonal shifting of regional cyclonic and anticyclonic centres develops while during glacial ages seasonality is greatly modified by the influence of ice sheets5 7 we investigated the late quaternary climate of the north pacific where according to modelling solar radiation in the early holocene at the time of the summer solstice is high and in the late holocene is relatively low we compared quantitative temperature and precipitation estimates from southern alaska obtained by application of transfer functions to fossil pollen records with estimates from western washington8 and southern british columbia9 data extending over 10 000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the north pacific ocean in the early holocene as monsoon type circulation became established with melting of glaciers the subtropical north pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present so that warmth and dryness high summer radiation increased in southern alaska the aleutian low pressure centre locus of cyclonic storm activity intensified during the late holocene resulting in colder and more humid coastal climate low summer radiation over much of the year and increased frequency of glacier growth in the cordillera

conditions leading to a recent small hydrothermal explosion at yellowstone national park porkchop geyser in yellowstone national park was the site of a small hydrothermal explosion on september 5 1989 in the early 1960s this was a quiescent spring with an intermittent seeping discharge infrequent geyser eruptions 3 5 m high started in 1971 and in 1985 the geyser began erupting as a perpetual spouter 6 9 m high perpetual spouting at the latter height continued until just before the catastrophic hydrothermal event when the geyser column suddenly rose to a height of 20 30 m followed immediately by the explosive ejection of sinter blocks up to 1 88 m in maximum dimension and formation of an irregular crater 13 9 m long and 11 7 m wide the ejected blocks show a variety of siliceous deposits indicative of changing environments of deposition with time and possibly of prior hydrothermal explosive activity at this site water samples from porkchop were collected and analyzed once in the 1920s again in 1951 ten times between 1960 and mid 1989 and once in january 1990 after the explosion chemical geothermometry shows an increase in the temperature of last water rock equilibration of about 60 to 70 c from 1962 through 1989 this may have been the result of drawing water progressively from different and hotter regions of a single reservoir or mixing waters from two different reservoirs with a progressively larger proportion of water being drawn from the hotter reservoir from 1962 through 1989 boiling of ascending fluids coming from hotter subsurface regions resulted in an increase in the proportion of steam to water discharged by the geyser a constriction at the exit of the geyser tube throttled the flow of water and steam and allowed water in shallow cavities adjacent to the geyser tube to become heated to the boiling point at pressures greater than normal hydrostatic we hypothesize that a sudden breaking loose of this constriction likely triggered by a seasonal increase in subsurface boiling throughout norris basin allowed water and steam to be discharged from porkchop much more rapidly than previously this resulted in a drop in pressure within the geyser tube causing water in adjacent connected chambers to become superheated an ensuing rapid flashing of superheated water to steam within relatively confined spaces resulted in the hydrothermal explosion

periglacial landscape dynamics in the western canadian arctic results from a thermokarst lake record on a push moraine herschel island yukon territory abstract ice rich permafrost landscapes are sensitive to climate and environmental change due to the melt out of ground ice during thermokarst development thermokarst processes in the northern yukon territory are currently not well documented lake sediments from herschel island 69 36 n 139 04 w in the western canadian arctic provide a record of thermokarst lake development since the early holocene a 727 cm long lake sediment core was analyzed for radiographic images magnetic susceptibility granulometry and biogeochemical parameters organic carbon nitrogen and stable carbon isotopes based on eight calibrated ams radiocarbon dates the sediment record covers the last 11 500 years and was divided into four lithostratigraphic units a to d reflecting different thermokarst stages thermokarst initiation at the study area began 11 5 cal ka bp from 11 5 to 10 0 cal ka bp lake sediments of unit a started to accumulate in an initial lake basin created by melt out of massive ground ice and thaw subsidence between 10 0 and 7 0 cal ka bp unit b the lake basin expanded in size and depth attributed to talik formation during the holocene thermal maximum higher than modern summer air temperatures led to increased lake productivity and widespread terrain disturbances in the lake s catchment thermokarst lake development between 7 0 and 1 8 cal ka bp unit c was characterized by a dynamic equilibrium where lake basin and talik steadily expanded into ambient ice rich terrain through shoreline erosion once lakes become deeper than the maximum winter lake ice thickness thermokarst lake sediments show a great preservation potential however site specific geomorphic factors such as episodic bank shore erosion or sudden drainage through thermo erosional valleys or coastal erosion breaching lake basins can disrupt continuous deposition a hiatus in the record from 1 8 to 0 9 cal ka bp in lake herschel likely resulted from lake drainage or allochthonous slumping due to collapsing shore lines before continuous sedimentation of unit d recommenced during the last 900 years

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

oxygen isotope records of holocene climate variability in the pacific northwest abstract oxygen isotope 18o measurements of authigenic carbonate from cleland lake southeastern british columbia paradise lake central british columbia and lime lake eastern washington provide a 9000 year holocene record of precipitation evaporation balance variations in the pacific northwest both cleland lake and paradise lake are small surficially closed basin systems with no active inflows or outflows lime lake is surficially open with a seasonally active overflow water isotope values from cleland and paradise plot along the local evaporation line indicating that precipitation evaporation balance is a strong influence on lake hydrology in contrast lime lake water isotope values plot on the local meteoric water line signifying minimal influence by evaporation to infer past hydrologic balance variations at a high temporal resolution we sampled the cleland paradise and lime lake sediment cores at 1 60 mm intervals 3 33 years per sample on average and measured the isotopic composition of fine grained

isotope signature of the younger dryas and two minor oscillations at gerzensee switzerland palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates oxygen and carbon isotope ratios in the carbonate of benthic ostracodes pseudocandona marchica and molluscs pisidium ssp were measured across the transitions bordering the younger dryas chronozone in littoral lacustrine cores from gerzensee switzerland the specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk carbonate oxygen isotope record 18occ if corrected for their vital offsets oxygen isotope ratios of pisidium and juvenile p marchica both formed in summer are almost identical to 18occ this bulk carbonate is mainly composed of encrustations of benthic macrophythes chara ssp also mainly produced during summer adult p marchica which calcify in winter show consistently higher 18o larger shifts across both transitions and short positive excursions compared with the summer forms especially during early preboreal despite such complexity the 18o of adult p marchica probably reflects more accurately the variations of the 18o of former lake water because during winter calcification temperatures are less variable and the water column isotopically uniform the difference between normalised 18o of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures in general the results indicate warmer summers during the late allerod and early preboreal compared with the younger dryas altogether the isotopic composition of lake water 18ol and of the dissolved inorganic carbonate 13cdic reconstructed from adult pseudocandona marchica as well as the seasonal water temperature contrasts indicate that the major shifts in the 18o of local precipitation at gerzensee were augmented by changes of the lake s water balance with relatively higher evaporative loss occurring during the allerod compared with the younger dryas it is possible that during the early preboreal the lake might even have been hydrologically closed for a short period we speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts

paleomagnetic evidence for motion of the hawaiian hotspot during formation of the emperor seamounts the bend in the hawaiian emperor chain is the best example of a change in plate motion recorded in a fixed hotspot frame of reference alternatively the bend might record primarily differences in motion of the hawaiian hotspot relative to the pacific lithosphere new paleomagnetic data from the emperor chain support the latter view althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain the best available paleomagnetic data suggest pacific hotspots may have moved at rates comparable to those of lithospheric plates 30 mm yr 1 in late cretaceous to early tertiary times 81 43 ma if correct this requires a major change in how we view mantle dynamics and the history of plate motions in the early to mid cretaceous 128 95 ma hotspots in the atlantic moved at similar rates these episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion such as the past 5 m y

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc

the impact of air mass circulation dynamics on late holocene paleoclimate in northwestern north america paleoclimate records from northern british columbia southwestern yukon and adjacent alaska suggest that late holocene climate may have been influenced by specific air mass circulation dynamics the aleutian lowpressure index alpi is a measure of sea level pressure fluctuations in the pacific northwest associated with the aleutian low al pressure system in this study we show that the al has a strong influence on historical climate change in the study area and explore the relationships between alpi polarity and changes in late holocene paleoclimate records analyses of weather station data in the study area indicate positive correlations r 0 63 between mean wintertime december march temperature and alpi values total wintertime snowfall accumulation and total precipitation show moderate and weak negative correlations respectively a late holocene increase in exotic western hemlock tsuga heterophylla pollen has been observed in regional paleoclimate studies a sustained positive alpi phase during the late holocene is considered as a causative mechanism under such conditions warm maritime air masses would more frequently penetrate inland potentially resulting in eastward pollen transfer enhanced growing conditions at coastal sites and an increase eastwards in the range limit of these species this study indicates that apparent conflicts in the timing and magnitude of late holocene climate change may be the result of a strong regional climate forcing mechanism that exhibits both temporal and geographical variation r 2002 elsevier science ltd and inqua all rights reserved