spruce trees from a melting ice patch evidence for holocene climatic change in the colorado rocky mountains usa in september 2006 we found the remains of timber sized spruce trees picea engelmannii on the floors of melting ice patches at altitudes of 3465 3480 m in the mummy range of north central colorado the ice patches occupy northeast facing recesses in which windblown snow scoured from a tundra upland to the southwest accumulates deeply we hypothesize that the upland was timbered during the early to middle holocene dense forest vegetation intercepted snow preventing it from blowing to the recesses and allowing trees to become established there neoglacial cooling led to gradual deforestation of the upland renewed transport and deposition of snow by wind and death of the ice patch trees radiocarbon dates show that the trees died between 3860 15 and 3780 20 14c yr bp c 4200 cal yr bp the trunks show decay similar to that of historic log structures built above timberline during the late nineteenth and early twentieth centuries suggesting that they have been protected by ice for all but a

distribution and transport of hydrocarbons in surface sediments of the alaskan outer continental shelf abstract surface sediments from the outer continental shelf of alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by noaa blm sediments were collected from the proposed oil lease areas of beaufort sea southeastern bering sea norton sound navarin basin gulf of alaska kodiak shelf and lower cook inlet data on normal and branched alkanes and di and triterpenoids from capillary gas chromatography gc and gas chromatography mass spectrometry gc ms indicate that the area displays little evidence of petroleum hydrocarbons i e seeps except at a few isolated stations beaufort sea sediments have the highest hydrocarbon budget whereas kodiak shelf sediments have the lowest the molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin norton sound and cook inlet sediments contain the highest levels of terrigenous lipids and kodiak shelf the lowest the abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time the distribution of polynuclear aromatic hydrocarbons pah is complex and shows a pyrolytic origin the data on perylene strongly favor the hypothesis that it is performed from terrigenous precursors and transported into the marine environment with no apparent in situ generation polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in gulf of alaska and kodiak shelf sediments two stations north of kalgin island in lower cook inlet and one in southeastern bering sea show typical weathered petroleum distribution of n alkanes and triterpenoids probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

evaluation of proposed early holocene advances of alpine glaciers in the north cascade range washington state usa constraints provided by palaeoenvironmental reconstructions many palaeoenvironmental reconstructions from across western north america indicate that the early to mid holocene was warmer and drier than present the wide distribution of these records suggests that relatively mild and arid conditions were regionally ubiquitous during the early holocene in contrast two recently proposed advances of alpine glaciers in the cascade range of washington state corresponding to equilibrium line altitude depressions of 350 to 450 m are placed in the early holocene the juxtaposition of the proposed major expansion of early holocene alpine glaciers with the constraint provided by a number of palaeoenvironmental reconstructions from directly adjacent areas results in palaeoclimatic gradients that are untenable the apparent diachronous behaviour of adjacent palaeoenvironmental records may be an artifact of dating errors

lower timberline in central colorado during the past 15 000 yr a 15 000 yr paleoenvironmental record at the elevation of lower timberline in central colorado suggests two major paleoclimatic changes during that interval 1 at 10 000 yr b p from cool moist conditions to warm moist conditions and 2 at 4 000 yr b p to warm dry conditions this sequence can be interpreted as a shift from precipitation predominantly originating from pacific winter storms before 10 000 yr b p to a predominantly monsoonal type regime lasting until 4 000 yr b p to the present pattern contemporaneity of higher upper timberline and lower lower timberline during the 10 000 to 4 000 yr b p interval is not contradictory but a result of changes in those circulation patterns

climatic significance of late pleistocene insect fossils from marias pass montana a small insect fossil assemblage was recovered from late pleistocene lake sediment below the mount st helens jy ash near marias pass montana the insect fauna contains several arctic alpine and open ground beetles including bembidion sulcipenne hyperboroides and possibly holoboreaphilus nordenskioeldi this fauna in conjunction with the plant macrofossil evidence suggests that at about 11 400 bp tree line was at least 450 m lower than present

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

effect of vegetation on an ice age climate model simulation a growing number of studies suggest that vegetation changes can significantly influence regional climate variations herein we utilize a climate model genesis with a land surface vegetation package to evaluate the potential role of the very large vegetation changes that occurred during the last glacial maximum lgm in particular we focus on the potential response to a significant reduction in the area of tropical rainforest simulations employed a global vegetation reconstruction for the lgm and climate long range investigation mapping and prediction climap sea surface temperature sst estimates results indicate that expansion of dryland vegetation causes a 15 30 additional lgm cooling for australia 0 4 c and africa 0 9 c respectively turnover from conifer to tundra also causes cooling of 2 4 c or more in western europe and siberia however for the largest rainforest area amazon basin inclusion of realistic vegetation increased modeled temperatures 2 4 c and decreased precipitation by 10 35 these latter results are similar to those obtained with sensitivity experiments of the effects of future amazon deforestation initial assessment of the potential effect of decreased stomatal resistance due to lower ice age co2 levels indicates little significant response to this effect comparison of model predicted low elevation lgm temperature changes with estimates from proxy data indicate that inclusion of realistic vegetation estimates for the lgm results in slightly more than 50 agreement between models and data for low elevation sites in low mid latitudes data at variance with model predictions would appear to be explainable by considering additional changes in vegetation ice age dust or a 1 2 c cooling below climap values this conclusion is at variance with a 3 4 c tropical cooling suggested by some studies for explaining estimated land temperature changes during the lgm in some western european sites model temperatures are colder than proxy data by 2 8 c this model data discrepancy may be explained by less sea ice in the subpolar north atlantic than stipulated by climap a conclusion consistent with new marine data from that region

geomorphic and climatic change over the past 12 900 yr at swiftcurrent lake glacier national park montana usa abstract glaciated alpine landscapes are sensitive to changes in climate shifts in temperature and precipitation can cause significant changes to glacier size and terminus position the production and delivery of organic mass and in the hydrologic energy related to the transport of water and sediment through proglacial environments a sediment core representing a 12 900 yr record collected from swiftcurrent lake located on the eastern side of glacier national park montana was analyzed to assess variability in holocene and latest pleistocene environment the spectral signature of total organic carbon content toc since 7 6 ka matches that of solar forcing over 70 500 yr timescales periodic inputs of dolomite to the lake reflect an increased footprint of grinnell glacier and occur during periods when sediment sinks are reduced glacial erosion is increased and hydrologic energy is increased grain size carbon nitrogen c n ratios and toc broadly define the termination of the younger dryas chronozone at swiftcurrent lake as well as major holocene climate transitions variability in core parameters is linked to other records of temperature and aridity in the northern rocky mountains over the late pleistocene and holocene

oxygen isotope records of goethite from ferricrete deposits indicate regionally varying holocene climate change in the rocky mountain region u s a oxygen isotopes of goethite from ferricrete deposits were measured from both northern and southern rocky mountain localities to assess geographic variability in regional holocene paleoclimate change a f3 7xincrease in oxygen isotope values of 14 c dated goethites in the northern rocky mountains suggests a regional scale relative increase in amounts of isotopically heavy summer precipitation since the early holocene in contrast oxygen isotope values from the southern rocky mountains increase abruptly f2 1xat f6200 14 c yr b p then decrease f2 4xbetween f2000 14 c yr b p and the present we interpret this period of relatively high y 18 o values as evidence for a middle holocene warm period combined with a relatively strong summer monsoon these variable climate records suggest that the rocky mountains of the western united states have had a spatially heterogeneous holocene climate history d 2003 university of washington all rights reserved

bacterial and algal hydrocarbons in sediments from a saline antarctic lake ace lake capillary gas chromatography mass spectrometry c gc ms and iatroscan thin layer chromatography flame ionisation detection tlc fid were used to study hydrocarbon distributions in a sediment core from ace lake a saline meromictic lake in the vestfold hills of antarctica hydrocarbons were abundant in most core sections up to 125 g g dry wt particularly in near surface samples and the distributions were very complex major constituents were identified as phytane 2 6 10 15 19 pentamethyleicosane tetrahydrosqualene a mixture of phytenes cholesta 3 5 diene and fern 7 ene smaller amounts of sterenes and hopenes were also present the predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present phytenes were abundant in all core sections and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria phytadienes were minor constituents at all depths studied an unusual feature of some distributions was the high concentrations of fern 7 ene which was the major hydrocarbon in the 20 25 cm core section this alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments a possible source might be from purple non sulphur bacteria high concentrations of straight chain c29 and c34 alkenes were also found in these sediments but their origin has not been determined major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago the present condition of permanent anoxic bottom waters probably developed only in the last 1000 years

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

palaeoecology of postglacial treeline shifts in the northern cascade mountains canada abstract postglacial changes in vegetation and chironomid communities at a subalpine lake in the engelmann spruce subalpine fir zone in the northern cascade mountains british columbia indicate patterns of treeline and climate fluctuation during the holocene in late glacial sediments of cabin lake pollen assemblages representative of alpine vegetation and cold stenothermous chironomids indicate cold conditions prior to the holocene in the early holocene 10 090 to 7000 14 c yr bp co occurrence of spruce fir parkland and a warm adapted chironomid community indicates a warm and probably dry climate in the mid holocene inferred forest closure suggests that precipitation increased and a mixture of warm and cold adapted chironomids indicates temperatures warmer than present but cooler than in the early holocene this period between 7000 and 3200 14 c yr bp represents a transitional climate in which temperature gradually declined culminating in cool neoglacial conditions this transitional interval may correspond with the mesothermic period proposed for lowland sites in southern british columbia palaeobotanical evidence suggests that moist subalpine forest began to establish around 4800 14 c yr bp with minimum temperatures and maximum precipitation between 2435 and ca 1700 14 c yr bp corresponding with neoglacial advances throughout the northern cordillera a cool late holocene 3200 14 c yr bp to present is also supported by a further decline in warm adapted chironomids comparisons with other study sites in the pacific northwest reveal that regional climatic changes were a major factor in driving biotic changes in this area

new pollen and beetle analyses at the mary jane site colorado evidence for late glacial tundra conditions analyses of fossil pollen and beetles from a late pinedale peat deposit from the upper fraser river colorado allow a reassessment of previously published paleoenvironmental evidence from the site between 13 800 and at least 12 600 yr b p the environment was an open tundra indicative of a cold dry climate scattered spruce trees were probably present at the site by the end of the record ca 12 300 yr b p

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

paleoenvironmental interpretations of holocene insect fossil assemblages from the la poudre pass site northern colorado front range abstract a sequence of peats from the la poudre pass site northern front range colorado rockies yielded abundant insect fossil assemblages studied intervals ranged in age from nearly 10 000 yr b p to about 5400 yr b p seventy named insect taxa were extracted from the peat among these are a mixture of aquatic and terrestrial species several taxa from the lowest 10 cm are indicative of climatic conditions found today in montane forest regions although conifers were probably not present at the site until several centuries after the initiation of peat deposition later insect assemblages contain a mixture of both tundra and forest faunal elements suggesting the close proximity of altitudinal tree limit to the site from about 9500 yr b p through the uppermost level studied 5400 yr b p

reconstructing the late holocene history of a subalpine environment charlevoix quebec using fossil insects in southern quebec charlevoix canada reconstructions of the subalpine insect assemblages were made in environments that were transformed by fire during the late holocene since 4500 bp the ecological requirements of beetle species likely to be found as fossils were studied by collecting living beetles in pitfall traps in forest suibalpine and alpine environments the late holocene changes of insect assemblages were reconstructed by recovering fossil insects from 13 peat sections modem beetle assemblages are valuable indicators of tree cover well developed podzol soils under peat as well as numerous spruce charcoal remains overlaying the podzol in all sampling sites suggest that a dense spruce cover was present before the beginning of the accumulation of peat and was eliminated by fire 4570 800 bp ground beetle and bark beetle assemblages at the base of the peat sections contained a mixture of forest and open environment species indicating that the postfire environment was a subalpine one w

hydrocarbon geochemistry of the puget sound region ii sedimentary diterpenoid steroid and triterpenoid hydrocarbons cyclic components of the aliphatic hydrocarbon mixtures extracted from puget sound sediment cores include a suite of c19 and c20 diterpenoid hydrocarbons of which fichtelite sandaracopimaradiene and isopimaradiene have been identified although apparently also derived from vascular plants these diterpenoid hydrocarbons have relative abundances distinctly different from the co existing plant wax n alkane suite five c27 c28 and c29 diasteranes and four c29 c30 and c31 17 h 21 h hopanes occur in relatively constant proportion as components of a highly weathered fossil hydrocarbon assemblage these chromatographically resolved cycloalkanes along with the strongly covarying unresolved complex mixture have been introduced to puget sound sediments from adjacent urban centres at increasing levels over the last 100 yr in the absence of any major oil spill naturally occurring triterpenoid hydrocarbons including hop 22 29 ene diploptene are also present a new group of c30 polyenes has been detected which contains compounds apparently structurally related to a co existing bicyclic c25 diene and to c20 and c25 acyclic multibranched hydrocarbons described in a previous paper barrick et al 1980

numerical modeling of the snowmass creek paleoglacier colorado and climate in the rocky mountains during the bull lake glaciation mis 6 abstract well preserved moraines from the penultimate or bull lake glaciation of snowmass creek valley in the elk range of colorado usa present an opportunity to examine the character of the high altitude climate in the rocky mountains during marine oxygen isotope stage 6 this study employs a 2 d coupled mass energy balance and flow model to assess the magnitudes of temperature and precipitation change that could have sustained the glacier in mass balance equilibrium at its maximum extent during the bull lake glaciation variable substrate effects on glacier flow and ice thickness make the modeling somewhat more complex than in geologically simpler settings model results indicate that a temperature depression of about 6 7 c compared with the present 1971 2000 ad would have been necessary to sustain the snowmass creek glacier in mass balance equilibrium during the bull lake glaciation assuming no change in precipitation amount or seasonality a 50 increase or decrease from modern precipitation would have been coupled with 5 2 c and 9 1 c bull lake temperature depressions respectively uncertainty in these modeled temperature depressions is about 1 c

a hydrocarbon biomarker record for the last 40 kyr of plant input to lake heqing southwestern china multi proxy records relating to climate and vegetation have been obtained for a core spanning the last 40 kyr from the heqing lake basin 26 n 100 e 2200 m asl yunnan province of southwestern china compound specific carbon isotope records for the vascular plant leaf wax hydrocarbons the c23 c33 n alkanes and for the algal hydrocarbons the c23 and c25 n alkenes and a c30 cyclobotryococcatriene all show a shift of circa 3 in d 13 c values from mis 3 to the end of mis 2 followed by a rapid return to lighter values this shift from 32 to 29 for the n alkanes and n alkenes most likely derives from bicarbonate utilization by aquatic plants in the lake rather than increased c4 photosynthesis thus both pollen data and hydrocarbon data appear to reveal a rise and fall in the contributions of submerged and or floating plants during mis 2 2004 elsevier ltd all rights reserved

the effect of holocene temperature fluctuations on the evolution and ecology of neotoma woodrats in idaho and northwestern utah abstract animals respond to climatic change by adapting or by altering distributional patterns how an animal responds is influenced by where it is positioned within its geographic range the probability of extirpation is increased near range boundaries here we examine the impact of holocene climatic fluctuations on a small mammalian herbivore the bushy tailed woodrat neotoma cinerea at five locations within south central idaho and northwestern utah previous work demonstrated that woodrats adapt to temperature shifts by altering body size we focus here on the relationship between body mass temperature and location within the geographic range body mass is estimated by measuring fossil fecal pellets a technique validated in earlier work overall we find the predicted phenotypic response to climate change animals were larger during cold periods and smaller during warmer episodes however we also identify several time periods when changes in environmental temperature exceeded the adaptive flexibility of n cinerea a smaller bodied species the desert woodrat n lepida apparently invaded lower elevation sites during the mid holocene despite being behaviorally and physically subordinate to n cinerea analysis of contemporary patterns of body size and thermal tolerances for both woodrat species suggests this was because of the greater heat tolerance of n lepida the robust spatial relationship between contemporary body size and ambient temperature is used as a proxy to reconstruct local climate during the holocene

saturated and olefinic hydrocarbons in recent sediments from the baltic sea abstract saturated and olefinic hydrocarbons in the top sections of contemporary sediments from four stations in the baltic sea teili 1 f 81 eb 1 and xv 1 were analysed by capillary gas chromatography and gc ms techniques the 0 2 2 4 4 5 and 10 11 cm sections showed a small unresolved complex mixture ucm however in all these sections a strong predominance of odd over even carbon numbered compounds exists indicating an insignificant petroleum hydrocarbon input in the areas studied the resolved hydrocarbons are of mixed marine autochthonous and terrigenous origin the 0 5 cm sections contained the highest proportions of short chain and branched chain hydrocarbons derived mostly from algae and bacteria in general an increase was observed in the ratios of saturated to unsaturated and of longer chain to short chain hydrocarbons with increasing depth because of the facile diagenesis of unsaturated components and faster biodegradation of short chain hydrocarbons in addition between one and seven hydrocarbons the exact structure of which could not be assigned were detected in the samples most of these components were cyclic and unsaturated and a number were triterpenes

monazite chemical weathering rare earth element behavior and paleoglaciohydrology since the last glacial maximum for the loch vale watershed colorado usa rare earth element ree release from weathering of accessory monazite ree po4 since the last glacial maximum at 18 1 ka was investigated in sediment recovered from an outlet lake within the glaciated loch vale watershed colorado usa labile rees in the sediments reveal monazite weathering increased during the younger dryas chronozone ydc 13 2 to 11 1 ka when alpine glaciers advanced as climate cooled and bedrock comminution increased monazite dissolution peaked at approximately the pleistocene holocene transition 10 5 ka during the holocene ree concentrations decline reflecting a reduction in monazite weathering the ree cerium ce may occur as trivalent or tetravalent cations and the ce anomaly ce n ce n in sediment permits interpretations of paleoredox conditions the ce n ce n decreases from 18 1 ka to the pleistocene holocene boundary initially oxidizing conditions within the watershed increased because of enlargement of the proglacial area as the ice retreated at the onset of the ydc oxidation further escalated in response to enhanced chemical weathering associated with glacial advance a more stable holocene climate and landscape resulted in relatively small changes in ce n ce n values slightly decreasing ce n ce n values over the last several hundred years are consistent with present day stream water values and may reflect the onset of present day hydrobiogeochemical conditions

how travertine veins grow from top to bottom and lift the rocks above them the effect of crystallization force travertine mounds form at the mouth of springs where co 2 degassing drives carbonate precipitation from water flowing from depth building of such mounds commonly involves the successive stratigraphic deposition of carbonate layers that precipitate from waters rising from depth along vertical to horizontal open fissures that are episodically sealed by radiating crystals much more intriguing structures can also be observed such as widespread horizontal white veins of carbonate with vertical aragonite fibers parallel or oblique to the stratigraphic travertines which extend laterally over distances of several tens of meters and could represent up to 50 of the total volume of the travertine mound using highly precise u th dating the growth direction of these horizontal veins is shown to be from top to bottom and this fact clearly indicates that they developed within the mound over a period of 1000 yr for the vein analyzed a vein growth mechanism is proposed that is able to uplift the rock above the vein thanks to the force of crystallization the possible development of such structures in other places and the consequences of reverse growth direction when interpreting travertine data are discussed

overview of the recent sediment hydrocarbon geochemistry of atlantic and gulf coast outer continental shelf environments abstract an overview of the hydrocarbon geochemistry of recent marine sediments from the u s atlantic and gulf of mexico outer continental shelf ocs regions is presented hydrocarbon levels along the atlantic ocs are fairly uniform ranging between in the north atlantic eastern gulf south texas gulf and coastal louisiana sediments a linear relationship exists between total hydrocarbon and total organic carbon concentrations indicating that each area consists of a geochemical province defined by a source input or depositional regime specific to the region the use of trace parameter bulk parameter ratios such as total hydrocarbon or individual pah concentrations total organic carbon content in defining such provinces and thus in serving as a basis for evaluating variations in source inputs as part of future surveys is demonstrated this approach views the hydrocarbon content and composition of atlantic and gulf coast ocs sediments as points on a spectrum defined by input types sources and deposition patterns sedimentation and erosion which conceptually link all the regions into a unified system

pulses of carbon dioxide emissions from intracrustal faults following climatic warming carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels an analysis of a 135 000 palaeorecord shows that pulses of carbon dioxide leakage from a natural reservoir in utah are associated with episodes of glacial unloading

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

mineral growth in rocks kinetic rheological models of replacement vein formation and syntectonic crystallization abstract we model three cases of coupling between mineral growth kinetics and mechanical response of the rock i dispersed spherical crystals growing by replacement in a hydrostatically stressed elastic rock ii growth of veins or vein networks accommodated by viscous relaxation of surrounding rock and iii syntectonic crystallization in a rock undergoing bulk pure shear such models for the microscopic environment of mineral growth together with additional assumptions or knowledge about rheological behavior and aggregate geometry provide refined estimates of the behavior of a macroscopic volume element which could be combined with geochemical reaction transport models crucial in the models are the various consequences pressure solution creep fracturing of the local stress that is necessarily generated by mineral growth in rocks other than in pores in the first model the dispersed spherical crystals of mineral a are assumed to grow within a spherical volume of rock consisting of mineral b the mineralized zone mz itself embedded in elastic rock the macroscopic stress in the mz and the far field stress in the surrounding rock are uniform and hydrostatic mineral growth of the a crystals is driven by supersaturation with respect to mineral a is accommodated by replacement of b grains and leads to an expansion of the mz described by an infinitesimal strain the radial growth rate of a spherical crystal of mineral a with replacement of mineral b is da dt k a r tln a k b v 0 b k b v 0 b k a v 0 a where ka and kb are kinetic constants r is the gas constant t the temperature in kelvin and v0a and v0b are specific volumes reference saturation states of mineral a a 1 and host mineral b b 1 are specified at the far field hydrostatic stress 0 the microscopic environment of each crystal of a is modeled by a representative volume element rve consisting of a sphere of mineral a embedded in a spherical shell of mineral b in each rve stress is neither uniform nor hydrostatic the model links the local microscopic stress with the macroscopic stress in the mz and surrounding rock the second model refers to veins that make room for themselves by growing not to veins that form by cementation of previously opened or opening cracks if the growth of mineral a as propagating veins or as an interconnected vein network takes place by deformation and expansion of the mz with the deformation itself driven by the stress arising from the supersaturation driven growth the surrounding rock undergoes deformation and is treated as viscous the rate of growth in vein width w is dw dt 2 k a rtln a sv 0 a 1 m where m 16 kav0ac2 3b3 is the medium viscosity c is the vein radius and each vein is treated as centered in a spherical rve of radius b s is an effective tensile stress required for vein propagation for a vein network in which veins surround equant polyhedra of rock of radius b we set c b and drop the term in s for simplicity veins may also widen by replacement the ratio of vein widening by expansion to that by replacement is dw dt expansion dw dt replacement 3 b 16 3 b 16 k a v 0 a k b v 0 b k b v 0 b k a v 0 a both mechanisms of accommodation contribute equally when 3b 16kbv0b at higher viscosity replacement is dominant the incipient growth of a cylindrical crystal with circular cross section in a medium deforming in pure shear simulates syntectonic crystallization both dissolution and deformation of the host accommodate growth in the model the crystal tends to grow faster in the direction of maximum rate of extension in this direction the host mineral may either dissolve to accommodate growth or precipitate to form a pressure shadow accommodation by host dissolution is greatest in the direction of maximum rate of shortening

algal and archaeal polyisoprenoids in a recent marine sediment molecular isotopic evidence for anaerobic oxidation of methane 1 analyses of 13c contents of individual organic molecules in a marine sediment show that crocetane 2 6 11 15 tetramethylhexadecane an isomer of phytane is produced by microorganisms that use methane as their main source of carbon the sediments lie at a water depth of 68 m in the kattegat the strait between denmark and sweden crocetane appears first 185 cm below the sediment water interface in the zone marking the transition from sulfate reduction to methanogenesis its 13c value is 90 10 versus vienna pee dee belemnite vpdb its structure which includes four isoprene units arranged symmetrically around a tail to tail linkage suggests that it is produced by a member of the archaea growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters the source organism apparently functions as a methane consuming member of the microbial consortium responsible for the anaerobic oxidation of methane hoehler et al 1994 in which as first demonstrated quantitatively in these sediments iversen and jorgensen 1985 electrons are transferred from methane to sulfate the presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2 6 10 15 19 pentamethylicosane pmi and of ether bound phytane and biphytane the pmi reaches a minimum value of 47 well below the transition zone its isotopic depletion could reflect either methanogenic or methanotrophic sources the ether bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane

spatial and temporal variations in meteoric 10be inventories and long term deposition rates colorado front range abstract atmospherically derived cosmogenic nuclides such as meteoric 10 be offer great potential in quaternary science because they can be used as landform geochronometers and as sediment tracers use of meteoric 10 be inventories for determining landform age soil residence time or erosion rates requires knowing the long term rate of deposition for this cosmogenic nuclide to the earth s surface here we present meteoric 10 be inventories measured at 6 dated sites near the boulder creek critical zone observatory front range colorado each site lies on a relatively stable landform broad moraine or fluvial terrace at slopes between 10 be deposition precipitation dryfall and dust deposition calculated from measured inventories at these sites range from 0 4 to 5 0 10 6 atoms cm 2 yr 1 none of the inventories match expected primary meteoric 10 be deposition rates that global latitude based models or precipitation specific models predict for this region meteoric 10 be inventories and calculated deposition rates at the three older 90 ka sites fall below 0 3 0 7 model predictions inventories and rates at the three pinedale age sites lgm 21 15 ka are higher 1 5 4 than model predictions previous analysis of soils in the front range over the same timeframe as these sites indicate that long term dust accumulation rates are low and associated secondary meteoric 10 be deposition is unlikely to account for the deviation from model predictions at the pinedale age sites in particular long term dustfall would have to be 1 2 orders of magnitude higher to add the meteoric 10 be required to account for measured inventories low inventories at older sites are consistent with loss of meteoric 10 be through physical erosion or selective removal of near surface soil enriched in meteoric 10 be time averaged rates of total meteoric 10 be deposition for these sites are minima we speculate that higher inventories at pinedale age sites reflect the addition of meteoric 10 be due to snowdrifts and or interflow associated with landform location increasing the effective precipitation related primary meteoric 10 be deposition at the sampled sites given these constraints and the spatial variation observed around the front range we suggest that 1 5 0 2 10 6 atoms cm 2 yr 1 is an appropriate long term meteoric 10 be deposition rate to use across much of the front range region that receives 45 55 cm of precipitation a year this long term total meteoric 10 be deposition rate is 30 50 higher than that predicted by global or annual precipitation specific models emphasizing that local calibration of deposition rates is essential for geomorphic studies around the globe

crystallization pressure versus crack seal as the mechanism for banded veins banded fibrous veins are often pointed to as evidence for episodic crack opening driven by oscillations in fluid pressure or bulk strain advances in understanding the geochemistry of precipitation data on veins and experiments suggest that pressure due to growing crystals may be an alternate explanation for many observations on these types of veins we propose that some veins originate at sites of precipitation and then propagate due to the pressure exerted by the crystal growth as materials precipitate the vein walls are pushed apart the resulting veins have shapes typical for mode i cracks except that mechanically crystallization pressure replaces the role of internal fluid pressure in their propagation a nonzero remote differential stress serves to align veins mechanical and geochemical considerations suggest that this process will be most important in fine grained rocks such as greenschist grade pelites where diffusion from sites of dissolution rather than advection is the dominant mass transport process veins may owe their orientation to tectonism but their initiation and growth are due to processes that supersaturate the pore fluid veins formed by this mechanism involve cracking to the extent that precipitation forces an original flaw to extend during precipitation cyclic quartz mica bands may indicate geochemical self organization at the vein wall driven by pressure solution enhanced supersaturation in the pore fluid and nonlinear precipitation kinetics at the vein wall

the beaver meadow complex revisited the role of beavers in post glacial floodplain development we evaluate the validity of the beaver meadow complex hypothesis used to explain the deposition of extensive fine sediment in broad low gradient valleys previous work establishes that beaver damming forms wet meadows with multi thread channels and enhanced sediment storage but the long term geomorphic effects of beaver are unclear we focus on two low gradient broad valleys beaver meadows and moraine park in rocky mountain national park colorado usa both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes we examine the geomorphic significance of beaver pond sediment by determining the rates and types of sedimentation since the middle holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition sediment analyses from cores and cutbanks indicate that 33 50 of the alluvial sediment in beaver meadows is ponded and 28 40 was deposited in channel in moraine park 32 41 is ponded sediment and 40 52 was deposited in channel radiocarbon ages spanning 4300 years indicate long term aggradation rates of 0 05 cm yr 1 the observed highly variable short term rates indicate temporal heterogeneity in aggradation which in turn reflects spatial heterogeneity in processes at any point in time channel complexity increases directly downstream of beaver dams the increased complexity forms a positive feedback for beaver induced sedimentation the multi thread channel increases potential channel length for further damming which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped channel complexity decreased significantly as surveyed beaver population decreased beaver meadows and moraine park represent settings where beaver substantially influence post glacial floodplain aggradation these findings underscore the importance of understanding the historical range of variability of valley bottom processes and implications for environmental restoration copyright 2011 john wiley sons ltd

response of bushy tailed woodrats neotoma cinerea to late quaternary climatic change in the colorado plateau abstract temperature profoundly influences the physiology and life history characteristics of organisms particularly in terms of body size because so many critical parameters scale with body mass long term temperature fluctuations can have dramatic impacts we examined the response of a small mammalian herbivore the bushy tailed woodrat neotoma cinerea to temperature change from 20 000 yr b p to present at five sites within the colorado plateau our investigations focused on the relationship between temperature plant composition and abundance and woodrat size body size was estimated by measuring fossil fecal pellets a technique validated in earlier work we found significant and highly covariable patterns in body mass over the five locations suggesting that responses to temperature fluctuations during the late quaternary have been very similar although woodrat mass and the occurrence of several plant species in the fossil record were significantly correlated in virtually all instances changes in woodrat size preceded changes in vegetational composition these results may be due to the greater sensitivity of woodrats to temperature or to the shorter generation times of woodrats as compared to most plants an alternative hypothesis is that winter temperatures increased before summer ones woodrats are highly sensitive to warmer winters whereas little response would be expected from forest woodland plants growing at their lower limits our work suggests that woodrat size is a precise paleothermometer yielding information about temperature variation over relatively short term temporal and regional scales

possible origin of n alkanes with a remarkable even to odd predominance in recent marine sediments abstract n alkane distributions with a remarkable even to odd predominance c16 c24 were found in marine surface sediments the previously proposed diagenetic reduction of the corresponding n fatty acids could not be considered as a source for these n alkane based on a comparison of compositional features of n alkane n fatty acid and n alcohol distributions carbon isotope analyses and other geochemical parameters the data indicate that the even predominant n alkanes were derived directly from marine bacteria

differential response of vegetation to postglacial climate in the lower salmon river canyon idaho late pleistocene to holocene terrestrial climate and vegetation records in the lower salmon river canyon of idaho are interpreted from the stable isotopic composition of soil carbonates and from aeolian sedimentation frequencies carbonate and sediment samples from six sections were processed and analyzed with the resulting isotopic and grainsize data organized in relation to a normalized time series developed from an associated radiocarbon chronology this record is interpreted in regards to changes in aridity temperature and wind speed during the late quaternary and is further compared with regional paleoenvironmental records lowered n 18 o and n 13 c concentrations before 20 000 yr bp are interpreted as reflecting late wisconsinan cold conditions after 18 000 yr bp climatic conditions show warmer periods punctuated by sharp returns to colder temperatures and increased c3 flora by 12 000 yr bp higher resolution data show very unstable climatic conditions across the pleistocene holocene boundary reflected in wide variations in n 18 o and n 13 c and aeolian sand deposition during the period between 12 000 and 9000 yr bp the lower salmon river canyon is thought to have experienced marked seasonality with summers and winters respectively warmer and colder than today this climatic scenario was accompanied by an initial instability in canyon vegetation following the establishment of a low energy floodplain in the canyon after 10 000 yr bp a pattern of c3 dominant riparian flora appears during the middle holocene climatic and vegetative variability is much reduced from the preceding period after 4000 yr bp soil carbonate isotopes reflect a trend toward cooler climate conditions and more mesic vegetation populations 2002 elsevier science b v all rights reserved

a 12 000 year radiocarbon date of deglaciation from the continental divide of northwestern montana during the pinedale late wisconsinan glaciation an outlet glacier from a mountain ice field flowed eastward across the continental divide through marias pass in northwestern montana this outlet glacier was the major source of the two medicine glacier a large piedmont glacier that extended from the mountain front east about 55 km onto the plains an accelerator mass spectrometry radiocarbon age of 12 194 145 bp aa 9530 was obtained from a wood fragment underlying a glacier peak tephra and a mount saint helens set j tephra in a section of lake sediments near marias pass this radiocarbon age provides a minimum date of deglaciation for the marias pass area that is about 800 years older than a previous estimate furthermore the radiocarbon age indicates that the two medicine glacier was no longer being supplied by its major source and if it still existed was only as a dying stagnant ice mass

palynological evidence for late and postglacial environmental change in central colorado abstract a sediment core recovered from lost park 39 17 30 n 105 32 30 w elevation 3079 m provides palynological evidence for postglacial vegetational and environmental change in the central front range of colorado pine spruce woodland was the dominant vegetation type throughout the 12 000 yr long record nonarboreal taxa however showed substantial changes from 11 800 to 9100 14 c yr b p high artemisia levels suggest steppe vegetation indicative of a climate cooler than that at present with an annual precipitation regime dominated by winter moisture the pollen spectra of this interval resemble modern spectra at two sites within colorado and wyoming comparisons of modern climatic data suggest that lost park may have experienced winter temperatures 3 to 3 5 c colder than those at present and monthly winter precipitation levels 3 5 cm higher than those at present during this late glacial time lower artemisia coupled with increases in poaceae pollen suggest a shift to warmer conditions dominated by summer monsoon precipitation around 9100 14 c yr b p increased charcoal occurrences between 6000 and 4000 14 c yr b p may suggest the onset of drier summer conditions that would be expected with a waning summer monsoon circulation at that time since 1800 14 c yr b p a resurgence in artemisia pollen suggests a return to relatively cool and or dry conditions similar to the present climate

unsteady late pleistocene incision of streams bounding the colorado front range from measurements of meteoric and in situ 10be 1 dating of gravel capped strath terraces in basins adjacent to western u s laramide ranges is one approach to document the history of late cenozoic fluvial exhumation we use in situ 10be measurements to date the broad surfaces adjacent to the eastern edge of the rocky mountains in colorado and compare these calculated ages with results from meteoric 10be measurements we analyze three sites near boulder colorado gunbarrel hill table mountain and pioneer that have been mapped as the oldest terrace surfaces with suggested ages ranging from 640 ka to the plio pleistocene transition our in situ 10be results reveal abandonment ages of 95 129 ka at table mountain 175 27 ka at pioneer and ages of 251 10 ka and 307 15 ka at gunbarrel hill all are far younger than previously thought inventories of meteoric 10be support this interpretation yielding ages that are comparable to table mountain and 20 lower than pioneer in situ ages we argue that lateral beveling by rivers dominated during protracted times of even moderate glacial climate and that vertical incision rates of several mm yr likely occurred during times of very low sediment supply during the few interglacials that were characterized by particularly warm climate conditions in contrast to the traditional age chronology in the area our ages suggest that the deep exhumation of the western edge the high plains occurred relatively recently and at an unsteady pace

hydrocarbon geochemistry of siliciclastic microbial laminated deposits from puck bay poland abstract samples of siliciclastic organic rich microbial laminated deposits from the brackish water environment of the puck bay southern baltic sea were analyzed by means of gas chromatography and mass spectrometry the distribution of extractable hydrocarbon fraction was examined gc ms investigations revealed that there occur n alkanes from c 16 to c 35 hopanoids and isoprenoids pristane and phytane in spite of a number of subfossilized cyanobacteria and microalgae in the composition of the n alkane fraction long chain alkanes predominate high contents of c 22 and c 24 alkanes relative abundance and variety of hopanoids two of which have not been described previously seems to be better indicators of the presence of cyanobacteria and microalgae and of their biodegraded remains

sediment cores representative of contrasting environments in salt flats of the moknine continental sabkha eastern tunisia sedimentology bulk features of organic matter alkane sources and alteration the moknine continental sabkha exhibits particularly contrasting situations in terms of inundation silting up evaporite deposition vegetation and detrital material input following extensive preliminary studies eight representative cores were selected marked differences in sedimentology were observed between the cores they are accounted for by the present and past position of the core in the sabkha the depth of the zone and the extent of detrital material input from oueds examination of 58 sections from the cores showed conspicuous differences in organic matter abundance and aliphaticity not related to the nature of the facies and also in the abundance of the total lipid extracts and aliphatic hydrocarbons alkane distributions in the 58 sections and their variations reflect the complex and variable interrelationships in the contrasting environments of the sabkha between the i nature of the different types of sources bacteria cyanobacteria microalgae and higher plants ii composition of these different sources and iii extent of bacterial degradation of the alkanes from primary sources

holocene and latest pleistocene glacial chronology glacier national park montana moraines of two different age groups have been identified fronting the present day glaciers and snowfields in glacier national park montana the subdued vegetated moraines of the older group have been found at 25 sites mainly in the central part of the lewis range these older moraines are in places overlain by the mazama ash although the exact age of the moraines has not been determined by radiocarbon dating vegetative evidence and correlation with other pre altithermal age moraines in the rocky mountains suggest that these older moraines date from 10 000 bp or earlier whether these moraines are the product of a separate advance after the end of the wisconsin glaciation or are simply the product of the last advance or stillstand of wisconsin glaciers before final deglaciation is not known moraines of the younger group consisting of fresh bouldery rubble are common throughout glacier park tree ring analyses indicate that some of these younger moraines were deposited by advances that culminated du

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

organic matter sources and early diagenetic alterations in arctic surface sediments lena river delta and laptev sea eastern siberia ii molecular and isotopic studies of hydrocarbons abstract the hydrocarbons extracted from three surface sediment samples from the delta of the lena river and adjacent areas of the laptev sea were examined to derive information on their source s natural vs anthropogenic terrestrial vs marine the abundance nature distribution and individual stable carbon isotope ratios of these hydrocarbons were determined it thus appeared that the laptev samples are characterized by i a negligible level of oil pollution due to anthropogenic and or natural petrogenic inputs ii an almost exclusive occurrence of long chain predominantly odd carbon numbered n alkanes and iii some differences in the level of bacterial alteration with a relatively higher degradation of the n alkanes in the seaward sediment a non terrestrial origin is proposed for these n alkanes based on the present results and on previous observations on carboxylic acid moieties and the pyrolysis products of the three surface sediments such hydrocarbons are probably not derived from the epicuticular waxes of higher plants but chiefly correspond to autochthonous products likely of algal origin these observations added to recent results on samples from other types of marine environments stress that an abundance of long chain predominantly odd n alkanes in extracts should not be systematically considered alone as evidence for a major contribution of higher plant waxes the relatively low contribution of terrestrial n alkanes in the laptev sediments should result from the combination of i a major dilution of the terrestrial input due to high primary productivity in summer promoted both by a large influx of nutrients provided by the lena river and by the specific conditions in such an arctic environment and ii the high level of degradation of the organic material transported by the lena river thus the latter probably provided a low input of lipids from terrestrial sources to the laptev samples

accelerator dating of a mixed assemblage of late pleistocene insect fossils from the lamb spring site colorado abstract fossil insects from the late glacial deposits at the lamb spring archaeological site near denver colorado are relatively abundant and diverse providing considerable paleoecological data for the site the late pleistocene insect fauna from the site comprises 72 identified taxa principally beetles however the fauna presented an interpretive problem because it contained a mixture of prairie and alpine tundra species this was initially considered to be the result of a mixing of faunal elements during the climatic transition of late glacial times a no modern analog fauna accelerator dating of insect fossil specimens from the two ecological groups helped resolve the paleoecological problem fossil specimens of the prairie associated species were dated at 17 850 550 yr b p while specimens of the tundra associated species yielded an age of 14 500 500 yr b p these dates reveal that what appeared to be an ecological mixing was probably a taphonomic problem wherein full glacial age fossils were probably reworked into latest wisconsin sediments while both faunal assemblages reflect climatic conditions substantially colder than present initial results suggest that the full glacial fauna represents a cold dry grassland or steppe environment while the younger fauna suggests moister and more tundra like conditions

late pleistocene climate inferred from the reconstruction of the taylor river glacier complex southern sawatch range colorado abstract ice surface topography of a late pleistocene glacier complex herein named the taylor river glacier complex trgc was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps during the last glacial maximum lgm the trgc covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and or upland ice fields equilibrium line altitudes elas for the glaciers of the trgc were estimated using the accumulation area ratio method assuming that ratio to be 0 65 0 05 elas thus derived ranged from about 3275 to 3400 m with a mean of 3340 60 m a degree day model ddm was used to infer the climatic significance of the lgm ela with no appreciable differences in precipitation with respect to modern climate the ela implies that mean summer temperatures during the lgm were 7 6 c cooler than today the ddm was also used to determine the temperatures required to maintain steady state mass balances for each of the reconstructed glaciers the required reductions in summer temperature vary little about a mean of 7 1 c the sensitivity of these results to slight 25 changes assumed for lgm precipitation are less than 0 5 c even under an lgm climate in which precipitation is assumed to be substantially different 50 than the present mean summer temperatures must be on the order of 7 0 to 8 5 c lower to depress equilibrium lines to lgm altitudes the greater sensitivity of the ela to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation

antiphasing between rainfall in africa s rift valley and north america s great basin the beginning of the bolling allerod warm period was marked in greenland ice by an abrupt rise in 18o an abrupt drop in dust rain and an abrupt increase in atmospheric methane content the surface waters in the norwegian sea underwent a simultaneous abrupt warming at about this time a major change in the pattern of global rainfall occurred lake victoria latitude 0 which prior to this time was dry was rejuvenated the red sea which prior to this time was hypersaline freshened lake lahontan which prior to this time had achieved its largest size desiccated whereas the chronologic support for the abruptness of the hydrologic changes is firm only for the red sea in keeping with evidence obtained well away from the northern atlantic in the santa barbara basin and the cariaco trench the onset and end of the millennial duration climate events were globally abrupt if so the proposed linkage between the size of african closed basin lakes and insolation cycles must be reexamined

late quaternary loess in northeastern colorado part ii pb isotopic evidence for the variability of loess sources a new application of the pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late wisconsin loess in the central great plains of eastern colorado samples of the peoria loess collected throughout the study area contain k feldspar derived from two isotopically and genetically distinct sources 1 glaciogenic material from early and middle proterozoic crystalline rocks of the colorado province and 2 volcaniclastic material from the tertiary white river group exposed on the northern great plains pb isotopic compositions of k feldspar in loess from two dated vertical sections at beecher island and last chance colorado vary systematically implying climatic control of source availability we propose a model whereby relatively cold conditions promoted the advance of front range valley glaciers discharging relatively little glaciogenic silt but strong winds caused eolian erosion of white river group silt due to a decrease in vegetation cover during warmer periods valley glaciers receded and discharged abundant glaciogenic silt while surfaces underlain by the white river group were stabilized by vegetation isotopic data from eastern colorado loess sections record two warm cold warm cycles during late wisconsin time between about 21 000 and 11 000 radiocarbon yr b p similar to results from other studies in the united states and greenland

aliphatic hydrocarbons in great barrier reef organisms and environment abstract this investigation was undertaken to assess the chemical nature occurrence and possible origin of petroleum hydrocarbons in the great barrier reef ecosystem aliphatic hydrocarbons in surface sediments water and a suite of seven species from widely separated coral reefs in the great barrier reef area were analysed by gas chromatography and by gas chromatography coupled with mass spectrometry the hydrocarbons found were substantially of biogenic origin the major components were n pentadecane n heptadecane pristane and mono alkenes based on heptadecane and were believed to originate from benthic algae and phytoplankton there was no evidence to suggest that lipid content had any influence on hydrocarbon content hydrocarbons from the organisms and sediments have characteristic composition patterns which would be altered by the presence of petroleum hydrocarbons an unresolved complex mixture usually considered indicative of petroleum contamination was found in greater than trace amounts only in holothuria sea cucumber and acropora coral from the capricorn group and in some sediment samples from the capricorn group and lizard island area

late quaternary loess in northeastern colorado part i age and paleoclimatic significance loess in eastern colorado covers an estimated 14 000 km 2 and is the westernmost part of the north american midcontinent loess province stratigraphic studies indicate there were two periods of loess deposition in eastern colorado during late quaternary time the first period spanned ca 20 000 to 12 000 14 c yr b p ca 20 14 ka and correlates reasonably well with the culmination and retreat of pinedale glaciers in the colorado front range during the last glacial maximum the second period of loess deposition occurred between ca 11000 and 9000 14 c yr b p this interval may be holocene or may correlate with a hypothesized younger dryas glacial advance in the colorado front range sedimentologic mineralogic and geochemical data indicate that as many as three sources could have supplied loess in eastern colorado these sources include glaciogenic silt derived from the colorado front range and two bedrock sources volcaniclastic silt from the white river group and clays from the pierre shale the sediment sources imply a generally westerly paleowind during the last glacial maximum new carbon isotope data combined with published faunal data indicate that the loess was probably deposited on a cool steppe implying a last glacial maximum july temperature depression relative to the present of at least 5 6 c overall loess deposition in eastern colorado occurred mostly toward the end of the last glacial maximum under cooler and drier conditions with generally westerly winds from more than one source

hydrocarbon and fatty acid distributions in rostherne lake sediment england abstract hydrocarbon and carboxylic acid distributions in the top 30 cm section of a contemporary lacustrine sediment rostherne mere cheshire england of age 0 150 yr present variations which can be correlated with changes in input of organic material as well as the effects of early diagenesis thus the higher proportions of short chain and branched lipids in the top 0 7 cm sediment section are as expected on the basis of the relatively greater contribution of algal and other microbial matter to the surface sediment layer similarly the increase in the ratio of saturated to unsaturated straight chain acids with depth is in accord with the more facile diagenesis of the unsaturated components acid hydrolysis of solvent extracted sediment afforded lipid fractions featuring a more significant microbial contribution than pre hydrolysis extracts as denoted by the greater abundance of c15 and c17iso and anteiso branched acids also no trend with depth in the ratio of saturated to unsaturated acids was observed for post hydrolysis extracts indicating that bound compounds may be somewhat protected relative to soluble lipids a contribution from petroleum derived hydrocarbons to the sediment apparent from the complex branched cyclic b c alkane distributions decreases with depth and is virtually absent from the 18 30 cm sediment section

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge