eolian deposition of trace elements onto taylor valley antarctic glaciers abstract the major ion and trace element chemistry in four 60 110 cm deep snow pits was examined from three antarctic taylor valley glaciers commonwealth canada and howard all located within 20 km of the ross sea taylor valley tv 77 30 s 163 15 e is part of the mcmurdo dry valleys mdv the largest ice free area in antarctica snow chemistry of these glaciers is strongly influenced by cross valley sw ne and ne sw winds that deposit eolian materials including mineral dust and soluble salts arsenic cd cu mo pb sb and sn in recent tv glacier snow are almost exclusively derived from eolian dust the relative magnitude of element variations with depth relate to the exposure of snow sites to prevalent winds eolian deposition is a primary source of these elements to canada glacier snow and supra and proglacial streams eolian processes are likely very important to the delivery and availability of nutrients and potentially toxic elements to dry valley antarctic ecosystems

geochemical and anthropogenic enrichments of mo in sediments from perennially oxic and seasonally anoxic lakes in eastern canada abstract we measured the vertical distributions of mo fe mn sulfide sulfate organic carbon major ions and ph in sediment porewater from one perennially oxic and three seasonally anoxic lacustrine basins in eastern canada as well as those of mo acid volatile sulfide fe mn al organic c 210pb and 137cs in sediment cores from the same sites the only input of anthropogenic mo to these lakes comes from atmospheric deposition the relatively monotonous distribution of mo in the porewater of three seasonally anoxic basins suggests that mo is not redistributed in the sedimentary column during periods of anoxia in contrast porewater mo profiles obtained at three sampling dates in a perennially oxic basin display sharp mo peaks below the sediment water interface indicating redistribution subsequent to deposition modeling of these latter porewater mo profiles with a diagenetic reaction transport equation coupled to comparisons among the various porewater and solid phase profiles reveal that mo is released at 1 2 cm depth as a consequence of the reductive dissolution of fe oxyhydroxides and scavenged both at the vicinity of the sediment water interface by re adsorption onto authigenic fe oxyhydroxides and deeper in the sediments where dissolved sulfide concentrations are higher the estimated rate constant for the adsorption of mo onto fe oxyhydroxides is 36 45 cm3 mol 1 s 1 diagenetic modeling indicates that authigenic mo in sediments of the perennially oxic basin represents about one third of the total solid phase mo in the first cm below the sediment water interface and only one tenth below this horizon if we assume that no authigenic mo is accumulated in the seasonally anoxic lake sediments we conclude that the sediment mo concentrations which are up to 3 16 times higher than the average lithogenic composition depending on the lake are mainly due to atmospheric deposition of anthropogenic mo and not to the formation of authigenic mo phases reconstructed historical records of the atmospheric mo deposition indicate maximum values in the 1970s and 1980s and significant decreases since then emissions to the atmosphere associated with the smelting of non ferrous ores and coal combustion appear to be the most important sources of anthropogenic mo

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

postglacial vegetation and fire history eastern klamath mountains california usa pollen and high resolution charcoal data from bluff lake and crater lake california indicate simi lar changes in climate vegetation and fire history during the last 15 500 years pollen data at bluff lake suggest that the vegetation between c 15 500 and 13 100 cal bp consisted of subalpine parkland with scattered pinus and abies after 13 100 cal bp a relatively closed forest of p monticola p contorta and abies developed and fire event frequency was low the inferred climate then was cooler and wetter than present pinus and quercus vaccinifoliadominated at both sites during the early holocene when conditions were warm and dry as climate became wetter and cooler in the late holocene abies spp at both sites and tsuga mertensi ana at crater lake increased in importance displacing pinus and quercus the two lake records have similar trends in fire history with high event frequencies at c 8400 4000 and 1000 cal bp and low values at c 4800 cal bp the fire and vegetation history at both sites suggests a similar response to large scale changes in climate during the holocene

holocene fire occurrence and alluvial responses at the leading edge of pinyon juniper migration in the northern great basin usa abstract fire and vegetation records at the city of rocks national reserve ciro south central idaho display the interaction of changing climate fire and vegetation along the migrating front of single leaf pinyon pinus monophylla and utah juniper juniperus osteosperma radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response and fossil woodrat neotoma middens revealed pinyon and juniper arrivals fire peaks occurred 10 700 9500 7200 6700 2400 2000 850 700 and 550 400 cal yr bp whereas 9500 7200 6700 4700 and 1500 1000 cal yr bp are fire free wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late holocene whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid holocene increased fires during the wetter and more variable late holocene suggest variable climate and adequate fuels augment fires at ciro utah juniper and single leaf pinyon colonized ciro by 3800 and 2800 cal yr bp respectively though pinyon did not expand broadly until 700 cal yr bp increased fire related deposition coincided with regional droughts and pinyon infilling 850 700 and 550 400 cal yr bp early and late holocene vegetation change probably played a major role in accelerated fire activity which may be sustained into the future due to pinyon juniper densification and cheatgrass invasion

timberline fluctuations and late quaternary paleoclimates in the southern rocky mountains colorado pollen and plant macrofossils from eight sedimentary basins on the west slope of the colorado rocky mountains document fluctuations in upper and lower timberline since the latest pleistocene by tracking climatically sensitive forest boundaries the moisture controlled lower timberline and the temperature controlled upper timberline paleoclimatic estimates can be derived from modern temperature and precipitation lapse rates pollen data suggest that prior to 11 000 yr b p a subalpine forest dominated by picea spruce and pinus pine grew 300 700 m below its modern limit the inferred climate was 2 5 c cooler and had 7 16 cm greater precipitation than today abies fir increased in abundance in the subalpine forest around 11 000 yr b p probably in response to cooler conditions with increased winter snow pollen and plant macrofossil data demonstrate that from 9000 to 4000 yr b p the subalpine forest occupied a greater elevational range than it does today upper timberline was 270 m above its modern limit suggesting that mean annual and mean july temperatures were 1 2 c warmer than today intensification of the summer monsoon coupled with increased summer radiation between 9000 and 6000 yr b p raised mean annual precipitation by 8 11 cm and allowed the lower limit of the subalpine and montane forests to descend to lower elevations the lower forest border began to retreat upslope between 6000 and 4000 yr b p in response to drier conditions and the upper timberline descended after 4000 yr b p when temperatures cooled to about 1 c warmer than today the modern climatic regime was established about 2000 yr b p when the summer precipitation maxima of the early and middle holocene were balanced by increased winter precipitation

biogenic calcite structures forming in lake fryxell antarctica stromatolites are organosedimentary structures produced by microorganisms which have been used extensively in the interpretation of precambrian and to a lesser extent phanerozoic history1 5 modern stromatolites are generally restricted to hot springs or warm hypersaline and or alkaline aquatic environments3 recently however we documented6 the presence of modern stromatolites in several cold perennially ice covered antarctic dry valley lakes here we report a finding in lake fryxell antarctica of biogenic calcite structures not observed in our previous study of other antarctic lakes these structures were laminated indurate unbranched and had either a vertical or horizontal orientation we infer that these calcite structures are biogenic in origin and hence stromatolitic based on the following evidence 1 the presence of an actively metabolizing algal mat on their surface and 2 an internal composition of filamentous blue green algal cell wall fragments diatom frustules and calcite crystals

variations in fire frequency and climate over the past 17 000 yr in central yellowstone national park a 17000 yr fire history from yellowstone national park demonstrates a strong link between changes in climate and variations in fire frequency on millennial time scales the fire history reconstruction is based on a detailed charcoal stratigraphy from cygnet lake in the rhyolite plateau region macroscopic charcoal particles were tallied from contiguous 1 cm samples of a 6 69 m long core and the data were converted to charcoal accumulation rates at evenly spaced time intervals intervals of high charcoal accumulation rates were interpreted as local fire events on the basis of information obtained from modern charcoal calibration studies in the yellowstone region the record indicates that fire frequency was moderate 4 fires 1000 yr during the late glacial period reached highest values in the early holocene 10 fires 1000 yr and decreased after 7000 calendar yr b p the present fire regime 2 3 fires 1000 yr was established in the past 2000 yr the charcoal stratigraphy correlates well with variations in july insolation through time which suggests that regional climate changes are responsible for the long term variations in fire frequency in the early holocene summer insolation was near its maximum which resulted in warmer effectively drier conditions throughout the northwestern united states at this time the fire frequency near cygnet lake was at its highest after 7000 calendar yr b p summer insolation decreased to present values the regional climate became cooler and wetter and fires were less frequent the cygnet lake record suggests that long term fire frequencies have varied continuously with climate change even when the vegetation has remained constant

new data for late pleistocene pinedale alpine glaciation from southwestern colorado abstract new cosmogenic surface exposure ages of moraine crest boulders from southwestern colorado are compared with published surface exposure ages of boulders from moraine complexes in north central colorado and in west central fremont lake basin wyoming 10be data sets from the three areas were scaled to a single 10be production rate of 5 4 at g yr at sea level and high latitude slhl which represents the average 10be production rate for two high altitude mid latitude sites in the western united states us and austria multiple nuclide ages on single boulders indicate that this 10be production rate yields ages comparable to those calculated with a commonly used 36cl production scheme the average age and age range of moraine crest boulders on terminal moraines at the southwestern colorado and wyoming sites are similar indicating a retreat from their positions 16 8 36cl ka cosmogenic ages in this paper are labeled 10be or 36cl ka or just ka when both 10be or 36cl ages are being discussed radiocarbon ages are labeled 14c ka calibrated radiocarbon are labeled cal ka and calendar ages are labeled calendar ka errors 1 associated with ages are shown in tables radiocarbon ages were calibrated using the data of hughen et al science 303 2004 202 this suggests a near synchronous retreat of pinedale glaciers across a 470 km latitudinal range in the middle and southern rocky mountains hypothetical corrections for snow shielding and rock surface erosion shifts the time of retreat to between 17 2 and 17 5 10be ka at pinedale wyoming and between 16 3 and 17 3 36cl ka at hogback mountain colorado

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

spatiotemporal variability of the precipitation dipole transition zone in the western united states 1 el nino southern oscillation related hydroclimatic variability in the western united states is characterized by a north south dipole pattern of precipitation anomalies with opposing signs here i use a high resolution dataset to analyze spatiotemporal patterns in the transition zone between the centers of opposite association results indicate that the transition zone is spatially limited west of the continental divide consisting of a narrow zone within the 40 42 n latitude band and portions of eastern washington eastern oregon and western colorado the transition zone was narrower when the southern oscillation index and the pacific decadal oscillation pdo were in a constructive phase and during the negative atlantic multidecadal oscillation phase although the transition zone has remained remarkably stationary across the great basin shifts likely pdo related have occurred over time in the west coast states implications for water resource planning in river basins underlying the transition zone vary by region

rates of sediment accumulation in pollen cores from small lakes and mires of eastern north america abstract data from 291 small lakes and mires in eastern north america provide information on the natural variability of rates of sediment accumulation in these environments over the last 18 000 yr accumulation rates were calculated by linear interpolation between radiocarbon and biostratigraphic dates from sediment cores taken for pollen analysis within the data set the rates were lognormally distributed with a mean accumulation rate of 91 cm 103 yr and a range from less than 1 to over 3500 cm 103 yr the accumulation rate data were divided into five subsets that were temporally or spatially distinct and therefore represent different geomorphic and climatic conditions at the time of deposition sediments deposited in basins north of 50 n south of 40 n and before 10 000 yr b p accumulated at much slower rates than sediments accumulating in midlatitude basins between 40 and 50 n between 10 000 and 330 yr b p sediment accumulation over the last 330 yr has on average been at rates four to five times faster than any time previously inorganic sediments that could be radiocarbon dated have accumulated at significantly lower rates than organic sediments reflecting differences in depositional processes for midlatitude basins during the holocene the most likely rate of continuous sediment accumulation within our data set is 65 cm 103 yr rates below 10 cm 103 yr are likely to be associated with nonconstant processes of sediment accumulation

late quaternary vegetation and climate of the wind river range wyoming abstract sediments from rapid lake document glacial and vegetation history in the temple lake valley of the wind river range wyoming over the past 11 000 to 12 000 yr radiocarbon age determinations on basal detrital organic matter from rapid lake 11 770 710 yr b p and temple lake 11 400 630 yr b p bracket the age of the temple lake moraine suggesting that the moraine formed in the late pleistocene this terminal pleistocene readvance may be represented at lower elevations by the expansion of forest into intermontane basins 12 000 to 10 000 yr b p vegetation in the wind river range responded to changing environmental conditions at the end of the pleistocene following deglaciation alpine tundra in the temple lake valley was replaced by a pinus albicaulis parkland by about 11 300 14 c yr b p picea and abies established by 10 600 14c yr b p grew with pinus albicaulis in a mixed conifer forest at and up to 100 m above rapid lake for most of the holocene middle holocene summer temperatures were about 1 5 c warmer than today by about 5400 14 c yr b p pinus albicaulis and abies became less prominent at upper treeline because of decreased winter snowpack and higher maximum summer temperatures the position of the modern treeline was established by 3000 14 c yr b p when picea retreated downslope in response to neoglacial cooling

efficient regional scale 3d potential field geophysical modelling to redefine the geometry of granite bodies beneath prospective geologically complex northwest tasmania in this study a regional model that defines the three dimensional geometry of the subsurface geology beneath the complex prospective northwestern tasmania has been developed this has been achieved using a series of potential field inversions constrained by surface geology geological sections seismic interpretations and a newly extended petrophysical dataset three major episodes of granitic magmatism are preserved in tasmania in the neoproterozoic cambrian and devonian granite bodies are hence considered important indicators of mineralization for explorers in an area of challenging vegetation topography and cover sequences forward modelling and property based inversions of the pre existing geological model show that the previously interpreted subsurface geometry is not compatible with potential field data four sub regions displayed a large discrepancy between calculated and observed data this study redefines the subsurface geometries of these sub regions through individual geometry inversions the density and magnetic susceptibility ranges of units are further refined through property inversions the modified geometry of the devonian granites in the four sub regions may be summarized as follows 1 the housetop granite is relatively thin 5 km thickness whereas 2 the heemskirk and meredith granites are very thick and granite extends to a shallower depth between these bodies than previously interpreted this region between plutons is thus a more prospective region than previously thought 3 for the first time an intrusive body underlying the eastern part of the rocky cape group has been identified its petrophysical properties are similar to that of a granite and its top is interpreted at a depth of 3 km this interpreted low density granitic unit may be either neoproterozoic or devonian 4 a new non magnetic low density cambrian granite with a minimum burial depth of 1 km is also modelled in 3d within the mount read volcanics in the south of the study area our approach whereby sub regions are identified for more detailed modelling enables new constraints to be introduced in a computationally efficient way and has general application to refining the geometry of key structures in prospective regions

the solubility of as2s3 and speciation of as in dilute and sulphide bearing fluids at 25 and 90 c abstract the solubility of synthetic crystalline as 2 s 3 in o 2 free dilute and sulphide bearing solutions has been determined at temperatures of 25 and 90 c the predominant dissolved as species are h 3 aso 0 3 and h 2 as 3 s 6 orpiment solubility is limited by the reactions 0 5as 2 s 3 3h 2 o h 3 aso 0 3 1 5hs 1 5h pk 25 23 11 0 11 pk 90 18 83 0 05 1 5as 2 s 3 1 5hs 0 5h h 2 as3s 6 pk 25 3 61 09 pk 90 3 42 0 06 a formational free energy for orpiment has been calculated as g 0 f 96 72 kj mol measured concentrations of as in hot springs of the taupo volcanic zone new zealand are consistent with those predicted using the solubility reactions and equilibrium constants of this study in sampled springs ph 2 6 97 100 of the dissolved as is present as h 3 aso 0 3 when h 3 aso 0 3 is the dominant as species orpiment deposition is likely to occur in response to fluid cooling in the sub aerial environment

mesoproterozoic tasmania witness to the east antarctica laurentia connection within nuna most recent paleogeographic reconstructions of the supercontinent nuna juxtapose the north australian craton mawson continent south australia east antarctica and laurentia between 1 6 ga and 1 3 ga but differ in their relative positioning the 10 km thick siliciclastic rocky cape group of tasmania was deposited in an opening marine basin on the margin of east antarctica during nuna breakup based on a similar detrital zircon signature and depositional age the rocky cape group has been correlated with the upper belt purcell supergroup in laurentia thus representing a key tie point within nuna here the detrital zircon age signature of mesoproterozoic rocky cape group quartzites is investigated by comparing new detrital zircon u pb hf isotopic data to an extensive compilation of zircon isotopic data from australia east antarctica and laurentia our analysis demonstrates that the rocky cape group is unlikely to have been sourced from any geological terrane exposed in presentday australia instead zircon u pb hf isotopic data from basement terranes in laurentia and east antarctica show striking similarities to the rocky cape group detrital signature paleocurrent data indicate that the majority of sediment in the rocky cape group was sourced from laurentia which was to the southeast present day coordinates of tasmania supporting a sweat like southwest united states east antarctica configuration for nuna we suggest that rifting left a thinned continental connection between east antarctica and laurentia onto which the lower middle rocky cape group was deposited between 1 45 and 1 30 ga

regionalization of fire regimes in the central rocky mountains usa article i nfo fire is one of the most important natural disturbances in the coniferous forests of the us rocky mountains the rocky mountains are separated by a climatic boundary between 40 and 45 n which we refer to as the central rocky mountains crm to determine whether the fire regime from the crm was more similar to the northern rocky mountains nrm or southern rocky mountains srm during the holocene a 12 539 yr old sediment core from long lake wyoming located in the crm was analyzed for charcoal and pollen these data were then compared to charcoal records from the crm nrm and srm during the younger dryas chronozone the fire regime was characterized as frequent at long lake the early and middle holocene fire regime was charac terized as infrequent a brief interval from 4000 to 3000 cal yr bp termed the populus period had a frequent fire regime and remained frequent through the late holocene at long lake in comparison to sites from the nrm and srm the fire regime at long lake was most similar to the srm during the past 12 539 cal yr bp these results suggest the disturbance regime in the crm has a greater affinity with those of the srm

the geochemistry of antarctic streams and their role in the evolution of four lakes of the mcmurdo dry valleys abstract major ion concentrations are reported for nineteen meltwater streams in the mcmurdo dry valleys antarctica and for the four lakes fed by these streams the most important solute acquisition processes for these flowing waters are dissolution of marine derived salts dissolution of calcite coatings derived from chemical weathering of parent rock and direct weathering of silicates although lakes joyce hoare and fryxell have undergone significant evaporative concentration the only simple salt which is predicted to form at present is calcite the shallow waters of all four lakes were supersaturated with respect to this mineral but were undersaturated with respect to other simple salts geochemical budgets however indicate that so4 k and mg in addition to ca and hco3 have been removed from some of these lakes over recent geological time bacterial sulfate reduction followed by precipitation of metal sulfides is likely to be a sink for sulfate sinks for mg and k are more problematic but may include formation of mgcalcites and in the case of k reverse weathering reactions the ages of the contemporary water columns as indicated by chloride budgets are relatively young and these lakes could have evolved their chemical compositions over a few thousand years of present stream flows it is not necessary to invoke trapped seawater or other salt sources to explain their evolution

holocene record of precipitation seasonality from lake calcite δ18o in the central rocky mountains united states a context for recent hydroclimatic extremes and variability is provided by a 10 k y sediment carbonate oxygen isotope 18 o record at 5 100 yr resolution from bison lake 3255 m above sea level in northwestern colorado united states winter precipitation is the primary water source for the alpine headwater lake in the upper colorado river basin and lake water 18 o measurements reflect seasonal variations in precipitation 18 o holocene lake water 18 o variations are inferred from endogenic sedimentary calcite 18 o based on comparisons with historic watershed discharge records and tree ring reconstructions drought periods i e drier winters and or a more rain dominated seasonal precipitation balance generally correspond with higher calcite 18 o values and vice versa early to middle holocene 18 o values are higher implying a rain dominated seasonal precipitation balance lower more variable 18 o values after ca 3500 yr ago indicate a snow dominated but more seasonally variable precipitation balance the middle to late holocene 18 o record corresponds with records of el nino southern oscillation intensification that supports a teleconnection between rocky mountain climate and north pacific sea surface temperatures at decade to century time scales

holocene fire and vegetation along environmental gradients in the northern rocky mountains abstract holocene records of fire vegetation and climate were reconstructed from four sites in the bitterroot range region of the northern rocky mountains in order to examine the vegetation and fire histories and evaluate the hypothesis proposed by whitlock and bartlein 1993 regarding the effects of increased summer insolation on precipitation patterns vegetation history in the series of sites was broadly similar in the late glacial period the pollen data suggest open parkland dominated by picea or alpine meadow which reflect conditions cooler and drier than present these open forests were replaced in the early to middle holocene by forests composed mainly of pinus and pseudotsuga which suggest conditions warmer than present modern forest compositions were in place by ca 3000 cal yr bp and small variations in the timing of the vegetation shifts reflect local differences among sites the long term trends in fire occurrence support the hypothesis proposed by whitlock and bartlein 1993 that precipitation regimes were sharpened during the early holocene summer insolation maximum but their location has remained unchanged as a result of topographic constraints sites located in areas currently summer dry were drier than present during the early holocene and fires were more frequent conversely sites located in the areas that are summer wet at present were wetter than present in the early holocene and fires were less frequent on millennial time scales it appears that the climate boundary is controlled by topography and does not shift

perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in west bengal india excess of 4600 m gk g 1 stable isotope ratios of waters from constructed perennial ponds indicate the ponds are chiefly recharged during the summer monsoon and subsequently undergo extensive evaporation during the dry winter season in contrast groundwaters with high as concentrations plot along the local meteoric water line lmwl near where the annual volume weighted mean precipitation values for d 2 ha ndd 18 o would plot the stable isotope data demonstrate that groundwaters are directly recharged by local precipitation without significant evaporation and thus are not recharged by nor mixed with the pond waters furthermore reactive transport modeling indicates that dissolved organic matter dom derived from pond waters does not fuel microbial respiration and as mobilization at depth in the underlying aquifer because travel times for pond derived dom exceed groundwater ages by thousands of years instead organic matter within the aquifer sediments must drive dissimilatory iron reduction and as release to groundwaters citation datta s a w neal t j mohajerin t ocheltree b e rosenheim c d white and k h johannesson 2011 perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in west bengal india geophys res lett 38 l20404 doi 10 1029 2011gl049301

geochemistry of rare elements in waters and sediments of alkaline lakes in the sasykkul depression east pamirs abstract the saline lakes tuzkul chukurkul sasykkul lakes of the sasykkul depression located in the semidesert part of the pamirs provide a prominent example of the evaporative concentration of alkaline waters in a closed basin under arid climate conditions chemical evolution of the lake waters has resulted in the development of residual na cl co3 so4 and na cl co3 brines the contents of a number of rare elements were determined in waters and sediments of the sasykkul depression lakes speciation modelling suggests that the main aqueous species of ag are chloride complexes cu pb zn mn are carbonate complexes be bi nb are hydroxocomplexes mo w as v are oxyanions it was established that the salt lake sediments are significantly enriched in b ba mo w u th high contents of trace elements are considered to be due to chemical weathering of rocks within the catchment basin significant contribution from thermal springs derived from the residual fluids associated with acid igneous and volcanic rocks and following evapoconcentration in a closed basin the processes of evaporative concentration solution complexation chemical precipitation and water sediment interaction lead to the partitioning of trace metals in the salt sediments

late holocene response of limber pine pinus flexilis forests to fire disturbance in the pine forest range nevada usa despite growing concerns that ecological stressors fire insect and pathogen outbreaks may force vegetation change few studies have attempted to use paleoecological data to understand small scale interactions between disturbance and vegetation using charcoal and pollen data we infer past fire episodes and subsequent vegetation responses for a limber pine pinus flexilis forest in northwestern nevada usa to determine local vegetation recovery from disturbance using superimposed epoch analysis we examined average vegetation and individual taxon responses to eight randomly selected fire events over the past 4 0 ka pollen evidence shows that on average fires produce a weak response of declining pinus while other taxa including artemisia and poaceae increase directly after fire episodes within 30 yr of a disturbance pollen data indicate ecosystem recovery to pre fire composition consistent with modern studies of fire recovery of limber pine forests similar to short term changes of pollen abundance long term vegetation responses indicate pinus abundance weakly declining and artemisia increasing when fire episodes are frequent however despite fire episode frequencies varying between 75 and 250 yr the overall vegetation structure has remained relatively stable over the past 4 0 ka our study contributes to the limited information on the disturbance ecology of isolated subalpine forests in the intermountain west

holocene vegetation fire and climate history of the sawtooth range central idaho usa the paucity of low and middle elevation paleoecologic records in the northern rocky mountains limits our ability to assess current environmental change in light of past conditions a 10 500 yr long vegetation fire and climate history from lower decker lake in the sawtooth range provides information from a new region initial forests dominated by pine and douglas fir were replaced by open douglas fir forest at 8420 cal yr bp marking the onset of warmer conditions than present presence of closed douglas fir forest between 6000 and 2650 cal yr bp suggests heightened summer drought in the middle holocene closed lodgepole pine forest developed at 2650 cal yr bp and fires became more frequent after 1450 cal yr bp this shift from douglas fir to lodgepole pine forest was probably facilitated by a combination of cooler summers cold winters and more severe fires than before five drought episodes including those at 8200 cal yr bp and during the medieval climate anomaly were registered by brief intervals of lodgepole pine decline an increase in fire activity and mistletoe infestation the importance of a holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

constraining the vandieland microcontinent at the edge of east gondwana australia abstract using airborne magnetic and marine gravity data the geological subdivisions of western tasmania have been interpreted north across bass strait into victoria the three westernmost tasmanian zones the king island rocky cape and burnie zones are inferred to form the largely concealed selwyn block in victoria the eastern tasmania zone correlates with the victorian tabberabbera zone thus the tasmanian tamar fracture zone corresponds with the victorian governor fault the victorian ceres gabbro is correlated with magnetic rocks west of king island that are tentatively considered to be neoproterozoic most of the cambrian felsic volcanic rocks of the tasmanian mount read volcanics lie above the burnie zone as do the similar rocks exposed in the jamieson licola and glen creek windows in central victoria reinterpretation of a victorian deep seismic reflection line indicates burnie zone equivalent rocks were thrust south west over rocky cape zone equivalents a link between western tasmania and central victoria is evident from upper devonian granites intruded into the selwyn block region the eastern end of the upper devonian cobaw complex and the warburton granodiorite contain calcsilicate enclaves interpreted to be derived from a northern equivalent to the smithton basin the mount disappointment granodiorite has high ni and cr contents and pseudomorphs after orthopyroxenes consistent with having been partly sourced from the underlying basaltic rocks like those on the eastern margin of the king island zone the magnetic responses under the strathbogie complex the cerberean caldera and the lysterfield granodiorite are attributed to metamorphism of part of an extension of the smithton basin probably equivalents to the 580 ma spinks creek volcanics quartzite cobbles in a devonian conglomerate in the south eastern melbourne zone may be derived from rocky cape group equivalents when integrated with the geological interpretation of tasmania we provide a stratotectonic map of the vandieland micro continent

vegetation fire and climate history of the northwestern great basin during the last 14 000 years the northwestern great basin lies in the transition zone between the mesic pacific northwest and xeric intermountain west the paleoenvironmental history based on pollen macroscopic charcoal and plant macrofossils from three sites in the northwestern great basin was examined to understand the relationships among the modern vegetation fire disturbance and climate the vegetation history suggests that steppe and open forest communities were present at high elevations from ca 11 000 to 7000 cal yr bp and were replaced by forests composed of white fir western white pine and whitebark pine in the late holocene over the last 11 000 years fires were more frequent in mid elevation forests 10 25 fire episodes 1000 years and rare in high elevation forests 2 5 fire episodes 1000 years applying modern pollen climate relationships to the fossil pollen spectra provided a means to interpret past climate changes in this region in the past 9000 years summer temperatures decreased from 1 to 41c and annual precipitation has increased 7 15 these results indicate that the millennial scale climate forcing driving vegetation changes can be quantified within the intermountain west in general and northwestern great basin in particular in addition fire can be considered an important component of these ecosystems but it does not appear to be a forcing mechanism for vegetation change at the resolution of these records r 2007 elsevier ltd all rights reserved

proterozoic crustal evolution of central east antarctica age and isotopic evidence from glacial igneous clasts and links with australia and laurentia abstract rock clasts entrained in glacial deposits sourced from the continental interior of antarctica provide an innovative means to determine the age and composition of ice covered crust zircon u pb ages from a suite of granitoid clasts collected in glacial catchments draining central east antarctica through the transantarctic mountains show that crust in this region was formed by a series of magmatic events at 2 01 1 88 1 85 1 79 1 57 1 50 1 41 and 1 20 1 06 ga the dominant granitoid populations are ca 1 85 1 45 and 1 20 1 06 ga none of these igneous ages are known from limited outcrop in the region in addition to defining a previously unrecognized geologic history zircon o and hf isotopic compositions from this suite have 1 mantle like 18o signatures 4 0 4 5 and near chondritic hf isotope compositions ehf 1 5 for granitoids of 2 0 ga age 2 mostly crustal 18o 6 0 8 5 and variable hf isotope compositions ehf 6 to 5 in rocks with ages of 1 88 1 85 1 79 and 1 57 ga in which the 1 88 1 79 ga granitoids require involvement of older crust 3 mostly juvenile isotopic signatures with low mantle like 18o 4 5 and radiogenic hf isotope signatures ehf 6 to 10 in rocks of 1 50 1 41 ga age with some showing crustal sources or evidence of alteration and 4 mixed crustal and mantle 18o signatures 6 0 7 5 and radiogenic hf isotopes ehf 3 to 4 in rocks of 1 2 ga age together these age and isotopic data indicate the presence in cratonic east antarctica of a large composite igneous province that formed through a punctuated sequence of relatively juvenile proterozoic magmatic events further they provide direct support for geological correlation of crust in east antarctica with both the gawler craton of present day australia and proterozoic provinces in western laurentia prominent clast ages of 2 0 1 85 1 57 and 1 45 ga together with sediment source linkages provide evidence for the temporal and spatial association of these cratonic elements in the columbia supercontinent abundant 1 2 1 1 ga igneous and metamorphic clasts may sample crust underlying the gamburtsev subglacial mountains indicating the presence of a mesoproterozoic orogenic belt in the interior of east antarctica that formed during final assembly of rodinia

a record of lateglacial holocene environmental change from a high elevation site in the intermountain west usa records of past vegetation and fire history can be complicated by changes in the depositional environment of a sampling location however these changes can alternatively be used as a measure of climate variability our study site ca 18 0 cal ka bp record from little brooklyn lake wyoming located near the crest of the snowy range records three moisture states initially the lake was likely a glacier fed pond indicated by the presence of pediastrum algae colonies around 13 0 cal ka bp this pond transitioned to a meadow environment suggested by the loss of pediastrum algae colonies and slow sedimentation rates meadow conditions were maintained until ca 5 0 cal ka bp when pediastrum algae colony abundance increased indicating the formation of a shallow lake from 18 0 to ca 5 0 cal ka bp the pollen record is suggestive of alpine vegetation conditions with relatively high spruce and herbaceous taxa low charcoal influx also characterizes the period between 18 0 and 5 0 cal ka bp after 5 0 cal ka bp the coincidence of the formation of shallow lake and pollen data indicating a shift to a spruce and fir forest suggests an increase in effective moisture fire remained rare in this basin over the entire record however once the lake established sedimentation rates and charcoal influx increased copyright 2013 john wiley sons ltd

arsenic speciation in mono lake california response to seasonal stratification and anoxia abstract mono lake is a closed basin alkaline hypersaline lake located at the western edge of the great basin in eastern california we studied the distribution of arsenic as species in the water column of mono lake between february and november 2002 this period captured the seasonal progression from winter mixing through summer thermal stratification to autumn overturn arsenic speciation was determined by ion chromatography inductively coupled plasma mass spectrometry of samples preserved in the field by flash freezing in liquid nitrogen we found that arsenic speciation was dominated 90 by arsenate when oxygen was detectable once levels fell below 6 mol l o 2 arsenic speciation shifted to dominance by reduced species arsenate and arsenite co occurred in a transition zone immediately below the base of the oxycline and low but significant concentrations of arsenate were occasionally detected in sulfidic hypolimnion samples thio arsenic species were the dominant form of as found in sulfidic waters maxima of thio arsenic species with stoichiometries consistent with mono di and trithio arsenic occurred in succession as sulfide concentration increased a compound with a stoichiometry consistent with trithio arsenic was the dominant as species 50 of total as in high sulfide 2 mmol l bottom water lower concentrations of total as in bottom water relative to surface water suggest precipitation of as s mineral phases in response to sulfide accumulation during prolonged anoxia

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

direct observations of aluminosilicate weathering in the hyporheic zone of an antarctic dry valley stream abstract this study focused on chemical weathering and bacterial ecology in the hyporheic zone of green creek a mcmurdo dry valley antarctica stream an in situ microcosm approach was used to observe dissolution features on the basal plane surface of muscovite mica four mica chips were buried in december 1999 and dug up 39 d later atomic force microscopy afm of the basal plane surfaces revealed small anhedral 10 a deep etch pits covering 4 of the surfaces from which an approximate basal plane dissolution rate of 8 3 10 18 mol muscovite cm 2 s 1 was calculated on the basis of the geometric surface area for the study period this is an integrated initial dissolution rate on a fresh surface exposed for a relatively brief period over the austral summer and should not be compared directly to other long term field rates the observation of weathering features on mica agrees with previous stream and watershed scale studies in the dry valleys which have demonstrated that weathering occurs where liquid water is present despite the cold temperatures afm imaging of mica surfaces revealed biofilms including numerous small

comparison of arsenic and molybdenum geochemistry in meromictic lakes of the mcmurdo dry valleys antarctica implications for oxyanion forming trace element behavior in permanently stratified lakes abstract water samples were collected for arsenic as and molybdenum mo analysis from different depths in lakes hoare and fryxell both of which are located in the taylor valley within the mcmurdo dry valleys of antarctica sampling depths within each lake were chosen to capture variations in as and mo concentrations and as speciation in the oxic mixolimnia and anoxic monimolimnia of these meromictic lakes arsenic concentrations ranged from 0 67 nmol kg 1 to 3 54 nmol kg 1 in lake hoare and from 1 69 nmol kg 1 to 17 5 nmol kg 1 in lake fryxell molybdenum concentrations varied between 5 05 nmol kg 1 and 43 nmol kg 1 in lake hoare and between 3 52 nmol kg 1 and 25 5 nmol kg 1 in lake fryxell concentrations of as and mo generally increased with depth in the mixolimnion of each lake consistent with uptake near the ice water interface by organic particles and or fe mn oxides oxyhydroxides followed by gravitational settling and regeneration remineralization at depth in the vicinity of the redoxcline arsenic concentrations either remained constant hoare or increased with depth fryxell in the anoxic monimolimnia whereas mo exhibited dramatic decreases in concentrations across the redoxcline in both lakes geochemical modeling predicts that as and mo occur as thioanions in the anoxic bottom waters of lakes hoare and fryxell and further that the contrasting behavior of both trace elements reflects the respective reactivity of their thioanions towards fe sulfide minerals such as mackinawite fes and or pyrite fes 2 more specifically the geochemical model suggests that fe sulfide mineral precipitation in the anoxic monimolimnia of both lakes regulates dissolved sulfide concentrations at levels that are too low for as sulfide minerals e g orpiment realgar to precipitate whereas mackinawite and or pyrite react s with particle reactive thiomolybdate anions possibly forming an fe mo s mineral that precipitates and hence leads to mo removal from solution

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

reconstructing south china in the mesoproterozoic and its role in the nuna and rodinia supercontinents abstract south china consisting of the yangtze and cathaysia blocks including hainan island is characterized by episodic magmatism and lithospheric scale tectonism during 1 7 1 0 ga and is important in the nuna and rodinia reconstruction three newly identified mesoproterozoic magmatic intervals at 1 76 1 60 ga 1 53 1 37 ga and 1 25 1 05 ga were accompanied by three mineralization events at 1 65 ga 1 45 ga and 1 05 ga these events are also recorded by detrital zircon from ca 1 05 ga equivalent sedimentary sequences in both western yangtze and central hainan island these findings indicate a common proterozoic tectonic history shared by central hainan and yangtze contradicting models invoking grenvillian aged tectonism in south china the yangtze block occupied an intracratonic position between laurentia and australia in nuna before it drifted away and docked to western australia and northern india in the reconfigured rodinia the cathaysia was located close to northern india during the proterozoic

postglacial fire vegetation and climate history in the clearwater range northern idaho usa the environmental history of the northern rocky mountains was reconstructed using lake sediments from burnt knob lake idaho and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large scale climate changes during the holocene vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold dry conditions from 14 000 to 12 000 cal yr b p abundant pinus pollen suggests warmer moister conditions than the previous period most sites record the development of a forest with pseudotsuga ca 9500 cal yr b p indicating warm dry climate coincident with the summer insolation maximum as the amplification of the seasonal cycle of insolation waned during the middle holocene pseudotsugawas replaced by pinus and abies suggesting cool moist conditions the fire reconstructions show less synchroneity in general the sites west of the continental divide display a fire frequency maximum around 12 000 8000 cal yr b p which coincides with the interval of high summer insolation and stronger than present subtropical high the sites on the east side of the continental divide have the highest fire frequency ca 6000 3500 cal yr b p and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late holocene this study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher than present fire frequency occurred in the past

authigenic monazite and detrital zircon dating from the proterozoic rocky cape group tasmania links to the belt purcell supergroup north america abstract the oldest known rocks in tasmania occur in the proterozoic rocky cape group a 10 km thick quartzarenite siltstone pelite dominated succession previously constrained to have been deposited between 1450 ma and 750 ma the rocky cape group contains the enigmatic fossil horodyskia string of beads and has the potential to place tasmania within supercontinent reconstructions detrital zircon and authigenic monazite grains dated via u pb laser ablation inductively coupled plasma mass spectrometry la icpms analysis yield a deposition window between c 1450 ma youngest zircon populations and c 1330 ma oldest authigenic monazite population for the 9 km thick lower middle units pedder river siltstone lagoon river quartzite balfour subgroup which hosts horodyskia detention subgroup the upper units 1 km include the irby siltstone which is younger than c 1310 ma this unit is likely separated from both the lower middle units and the overlying c 1900 ma grains were identified authigenic monazite age distributions are complex with multiple age domains within most samples the common pb corrected 206u 238pb ages defined by oldest grains in each sample identify three statistically significant groups 1 1358 1292 ma inclusive of two sigma errors lagoon river quartzite and pedder river siltstone 2 1283 1239 ma cowrie siltstone and balfour subgroup and 3 1085 9 ma detention subgroup we suggest monazite was precipitated during episodic fluid flow events at these three stages in various parts of the basin the original source for ree bearing fluids could be detrital monazite which is rarely preserved and or organic matter from the interbedded carbonaceous shales the rocky cape group has a shared provenance with the higher grade metasediments surprise bay and fraser formations of nearby king island the newly derived depositional ages also overlap and support the correlation of these rock associations on the basis of current datasets there are no obvious correlations that can be made with mesoproterozoic basins preserved in mainland australia instead an overlap in the timing of deposition similarities in detrital zircon signatures and analogous depositional environment suggests the c 1 45 1 37 ga upper belt purcell supergroup missoula and lemhi groups of western north america constitutes a plausible correlation with the tasmanian mesoproterozoic succession if the unexposed palaeoproterozoic basement of tasmania correlates with the transantarctic mountains region of east antarctica as previously proposed we suggest that the overlying mesoproterozoic sequences were deposited during rifting of the supercontinent nuna between proto australia including the mawson craton of antarctica and laurentia as predicted by the most recent palaeogeographic reconstructions both the tasmanian and western laurentian packages were affected by episodic post depositional fluid flow events between c 1 35 and 1 05 ga possible thermotectonic imprints of the subsequent assembly of rodinia

contrasting climatic histories for the snake river plain idaho resulting from multiple thermal maxima abstract ten sites near the snake river plain have consistent differences in their climatic histories sites at low elevation reflect the early holocene xerothermic of the pacific northwest whereas most climatic chronologies at high elevation indicate maximum warmth or aridity somewhat later ca 6000 yr ago this elevational contrast in climatic histories is duplicated at three sites from the central snake river plain for sites in such close proximity the different chronologies cannot be explained by changes in atmospheric circulation during the late quaternary rather the differences are best explained by the autecology of the plants involved and the changing seasonal climate the seasonal climatic sequence predicted by multiple thermal maxima explains the high and low elevation chronologies during the early holocene maximum insolation and intensified summer drought in july forced low elevation vegetation upward however moisture was not a limiting factor at high elevation where vegetation moved upward in response to increased length of growing season coincident with maximum september insolation 6000 yr ago

a 15 000 year record of vegetation and climate change from a treeline lake in the rocky mountains wyoming usa future climate projections predict warming at high elevations that will impact treeline species but complex topographic relief in mountains complicates ecologic response and we have a limited number of long term studies examining vegetation change related to climate in this study pollen and conifer stomata were analyzed from a 2 3 m sediment core extending to 15 330 cal yr bp recovered from a treeline lake in the rocky mountains of wyoming both pollen and stomata record a sequence of vegetation and climate change similar in most respects to other regional studies with sagebrush steppe and lowered treeline during the late pleistocene rapid upward movement of treeline beginning about 11 500 cal yr bp treeline above modern between 9000 and 6000 cal yr bp and then moving downslope 5000 cal yr bp reaching modern limits by 3000 cal yr bp between 6000 and 5000 cal yr bp sediments become increasingly organic and sedimentation rates increase we interpret this as evidence for lower lake levels

diel stream geochemistry taylor valley antarctica unlike temperate and polythermal proglacial streams the proglacial streams in taylor valley tv antarctica are derived primarily from glacier surface melt with no subglacial or groundwater additions solute responses to flow reflect only the interaction of glacial meltwater with the valley floor surrounding the stream channel we have investigated the major minor and trace element 24 h variations of two proglacial melt streams andersen creek and canada stream originating from the canada glacier in tv antarctica both streams exhibited diel mid austral summer diurnal flow variation with maximum flow being more than 50 times the minimum flow dissolved 0 4 m major minor and trace solute behaviors through diel periods were strongly controlled by the availability of readily solubilized material on the valley floor and hyporheic biological exchanges anderson creek had generally greater solute concentrations than canada stream because of its greater receipt of eolian sediment andersen creek also acquired greater solute concentrations in the rising limb of the hydrograph than the falling limb because of dissolution of eolian material at the surface of the stream channel coupled with minimal hyporheic biological exchange conversely canada stream had less available eolian sediment but a greater hyporheic biological exchange which preferentially removed trace and major solutes in the rising limb and released them in the falling limb given the dynamic nature of discharge eolian and hyporheic biological processes solute loads in tv streams are difficult to predict copyright 2012 john wiley sons ltd