holocene timberline and palaeoclimate of the northern uinta mountains northeastern utah usa clastic and organic sediments exposed in two stream cutbanks above modern timberline in the headwaters of the henrys fork drainage record multiple episodes of fluvial lacustrine and wetland deposition the location of the upper henrys fork at the boundary between modern summer wet winter dry and summer dry winter wet precipitation regimes suggests that changes in vegetation during the holocene were due primarily to variations in growing season temperature a radiocarbon date of 9310 6 70 bp on a salix fragment from the base of one exposure indicates that the upper reaches of the henrys fork were vegetated by riparian willows by the early holocene four other dates on wood and bulk organics ranging up to 4070 6 70 bp indicate that deposition continued through the middle holocene high picea pinus ratios and high percentages of artemisia pollen suggest that an open picea parkland was established at timberline by 9 5 ka cal bp in response to mean annual and july temperatures 1 0 c greater than at present

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

sedimentology and stable isotopes from a lacustrine to palustrine limestone deposited in an arid setting climatic and tectonic factors miocene pliocene opache formation atacama desert chile abstract field relations petrography gis and geochemistry of a late miocene pliocene limestone the opache formation calama basin atacama desert chile shows that depositional facies diagenetic histories and isotopes differ from eastern to western parts of the basin we recognize two facies lacustrine characterized by ostracod diatom mudstone and wackestone and palustrine characterized by both shallow water and pedogenic features gis analysis of the basin topography reveals an intrabasinal low in the eastern area and steeper hydrological gradients to the west with the calama constriction restricting flow between east and west petrography and geochemical results confirm that the calama constriction influenced depositional parameters ponding groundwater to the east forming a shallow lake and creating palustrine conditions to the west our analyses indicate that lake waters were less enriched in 13c or 18o than palustrine waters even though petrologic studies show that the lacustrine carbonates have a complex diagenetic history derived from groundwater rich in dissolved minerals this seemingly contrary observation can be reconciled if an important source of water for the western carbonates was sourced from the pacific ocean and was less evolved whereas eastern limestones precipitated from water which had become depleted in 18o during transport from the east today moisture from the pacific very rarely if ever reaches inland as far as calama indicating that during the late miocene mid pliocene breakdown in the temperature inversion due to weakened or absent upwelling in the cold coastal pacific current allowed moisture from the pacific to reach inland this changing atmospheric circulation pattern may have also affected upper level airflow that today blocks eastern sourced moisture from crossing the andes allowing it to reach farther westward into the atacama region during the late miocene pliocene together these moisture sources were sufficient to produce carbonate rich palustrine and lacustrine environments in the calama basin

hydrological factors in the interpretation of stable isotopic proxy data present and past a european perspective in the context of this paper stable isotopic proxies are those preserving directly or via known or calculable fractionation factors a record of 18o 16o and or 2h 1h in the water which contributed to their growth suitable proxies include amongst others tree ring cellulose bone phosphate lake sediment minerals and speleothem fluid inclusions a principal aim of studying isotopic proxies is to gain more information about past climates through a knowledge of how rainfall isotope compositions have changed over time however converting back from proxy to rainfall is not necessarily straightforward because however well the isotopic fractionation due to proxy growth or formation is understood a variety of modifying processes may have intervened between this and the actual rainfall events three main reservoirs of environmental water may contribute to the isotopic compositions of terrestrial proxy indicators surface waters soil moisture and groundwater each of these can in principle be isotopically modified compared to rainfall in the locality this review examines these effects and how they may change under different european climate types at the present day it is concluded that while groundwater isotopic compositions typically represent closely the bulk composition of rainfall under a variety of climatic regimes soil and particularly lake waters require detailed study if their isotope systematics are to be adequately understood the review also finds that to a large extent the present is the key to the past in terms of recharge processes during the late pleistocene though glaciation may have had profound isotopic consequences in certain areas while a more general aridity led to the apparent absence of recharge in most areas for much of the late devensian

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

skeletal oxygen and carbon isotope compositions of acropora coral primary polyps experimentally cultured at different temperatures we investigated temperature and growth rate dependency of skeletal oxygen and carbon isotopes in primary polyps of acropora digitifera scleractinia acroporidae by culturing them at 20 23 27 or 31 c calcification was most rapid at 27 and 31 c we obtained a 18o temperature relationship 0 18 c 1 consistent with reported ranges for porites indicating that juvenile acropora polyps can be used for temperature reconstruction a growth rate dependency of skeletal isotopes was detected in the experimental polyps cultured at lower water temperatures when the skeletal growth rate of these polyps was also low the estimated upper calcification flux limit for a kinetic isotope effect to be observed in the 18o growth rate relationship 0 4 0 7 g caco3 cm 2 yr 1 was similar to the calcification flux in porites corresponding to a linear extension rate of 5 mm yr 1 the maximum rate at which the kinetic isotope effect is evident this result suggests that the calcification flux can be used as a measure of growth rate related isotope fractionation that is the kinetic isotope effect in corals of different genera and at different growth stages

environmental controls on the late holocene carbonate sedimentation of a karstic lake in the middle atlas mountains lake afourgagh morocco the lake afourgagh sediment record and facies successions provide an outstanding example of environmentally controlled carbonate sedimentation afourgagh is a small shallow permanent lake located in the middle atlas mountains in morocco in a karstic context it is fed by ground waters that are relatively enriched in mg resulting from the leaching of the jurassic dolomitic bedrock of the catchment this eutrophic lake is episodically restricted and characterized by alkaline waters with a fluctuating high mg ca ratio the maximum extension of the holocene shoreline coincides with evidence of a lake stabilization level corresponding to the outflow of the lake through a wadi lakeshore terrace sediments deposited on an alluvial fan siltstone during the past ca 2500 cal yr bp comprise four main facies a littoral crust palaeosols palustrine silts and charophyte tufas which reflect different environments from the shoreline toward the deeper water in the more distal parts the charophyte tufas display a well expressed lamination punctuated by the development of microstromatolites on algae thalli the mineralogical composition of the carbonates is linked to the facies while the charophyte tufas are characterized by a relatively high content in aragonite in addition to low mg calcite the littoral crust is mainly composed of magnesite this pattern is related to the evolving chemistry of water due to the influence of charophyte proliferation during dry summers calcium carbonate precipitation on algae thalli both bioinduced and microbially mediated progressively induces an increase in the mg ca ratio of the lake water while the capillary evaporation of shallow ground waters causes precipitation of a magnesite precursor on the shoreline producing magnesite during early diagenesis this effect is characteristic of two episodes part of the roman warm period and the beginning of the dark age cold period the carbonate mineralogy of the different depositional sequences at afourgagh indicates lake level and water chemistry fluctuations under a climatic influence therefore among other regional records the lake afourgagh sedimentary record provides useful evidence for reconstructing these environmental changes

mineralogy and sr mg geochemistry of charophyte carbonates a new tool for paleolimnological research abstract the carbonate biominerals formed in the oogonial cells and on stems of charophytes reveal intra specific and species to species variations within the genus chara calcite high magnesian calcite hmc and aragonite may be present in both oogonium and stem calcifications and for the first time evidence is presented of polymineral calcification hmc aragonite within single oogonial cells the data indicate strong specific differences in the biological mechanisms of mineralization within this group of plants among the various species of the genus chara studied there is no correlation between the charophyte carbonate mineralogy and the salinity of water where they formed calcite hmc and aragonite may all be present in charophyte calcifications formed in low salinity waters on the contrary there is an overall relationship between the mineralogy of these carbonates and the mg ca ratio of the water in which they formed sr content in charophyte calcite and high mg calcite reflect directly the sr ca ratio of the host water whereas mg content in these carbonates probably depends on the temperature and the mg ca ratio of the water partitioning coefficients for mg and sr for some widespread species are discussed our results indicate that charophyte carbonates may be used as paleohydrochemical proxies and imply that special attention must be paid to the mineralogical control of charophyte carbonates when they are to be used in isotopic studies

salinity bias on the foraminifera mg ca thermometry correction procedure and implications for past ocean hydrographic reconstructions 1 mg ca in foraminiferal calcite has recently been extensively used to estimate past oceanic temperatures here we show however that the mg ca temperature relationship of the planktonic species globigerinoides ruber is significantly affected by seawater salinity with a 1 psu change in salinity resulting in a 1 6 c bias in mg ca temperature calculations if not accounted for such a bias could lead for instance to systematic overestimations of mg ca temperatures during glacial periods when global ocean salinity had significantly increased compared to today we present here a correction procedure to derive unbiased sea surface temperatures sst and 18osw from g ruber tmg ca and 18of measurements this correction procedure was applied to a sedimentary record to reconstruct hydrographic changes since the last glacial maximum lgm in the western pacific warm pool while uncorrected tmg ca data indicate a 3 c warming of the western pacific warm pool since the lgm the salinity corrected sst result in a stronger warming of 4 c

ph control on oxygen isotopic composition of symbiotic corals abstract boron carbon and oxygen isotopic compositions were determined at the micrometre scale by high resolution ion microprobe in a sample of modern coral massive hermatypic coral porites lutea the ion probe data show for b and o much larger isotopic variations at the micrometre scale than those measured at the millimetre scale by conventional techniques 18opdb values range from 10 6 0 9 to 0 2 0 5 and 11b values range from 18 6 1 5 to 30 6 1 6 by contrast 13c values show the same range of variations from 4 6 0 65 to 2 2 0 67 at the micrometre and millimetre scales the range of 11b values indicates that significant ph variations from 7 1 to 9 0 are present at the sites of calcification the largest 18o variations correspond to the highest 11b values i e to the highest phs this measurement of ph allows modelling the oxygen isotopic fractionation occurring during aragonite precipitation taking into account the rate of o isotopic equilibrium between dissolved carbonate species h2co3 hco3 and co32 and water via the two reactions of hydration and hydroxylation the full range of 18o values measured at the micrometre scale can be modelled for residence times of dissolved carbonates in the calcifying fluid ranging between 1 h and at maximum 12 h the ph controls the 18o of the growing carbonate through the relative fractions of dissolved carbonate species and through the kinetics of their isotopic equilibration with water via hydration and hydroxylation the so called vital effect systematically observed for 18o in corals can thus be understood as representing an average of rapid ph variations due to coral biology during coral growth selectively measuring 18o values in the zones of coral skeletons that have low 11b values i e formed at low ph should significantly improve the quality of palaeoclimatic reconstructions based on 18o values

late holocene paleoenvironmental change at mid elevation on the caribbean slope of the cordillera central dominican republic a multi site multi proxy analysis abstract high resolution proxy records from the circum caribbean region indicate significant variation in late holocene climate especially precipitation attributed primarily to shifts in the mean annual position of the intertropical convergence zone itcz the paleoenvironmental and cultural impacts of this late holocene climate variability have been analyzed intensively in the western caribbean and to a lesser extent in the southern caribbean however the occurrence and impacts of late holocene climate shifts in the eastern caribbean especially in island interiors has not been well documented here we present sediment records of late holocene paleoenvironmental change from two lakes located on the caribbean slope of the cordillera central in the dominican republic that span the last 3000 years sediment characteristics pollen charcoal biogenic carbonate assemblages and isotopic composition and bulk sedimentary carbon isotope values in laguna castilla and laguna de salvador indicate extreme shifts in hydrology vegetation and disturbance regimes in response to climate change and human activity in the lake watersheds close correspondence between the hydrological histories of the lakes and trace metal concentrations in sediments of the cariaco basin indicate that precipitation variability here responds to the same controls and may similarly reflect shifts in the mean annual position of the itcz human occupation of the watersheds appears to be closely linked to severe dry periods and may indicate larger scale cultural responses to precipitation variability on the island of hispaniola prehistoric human populations strongly affected vegetation and disturbance regimes in the lake watersheds impacts may have lasted several centuries and may have been more severe than impacts of modern populations

the significance ofcharavegetation in the precipitation of lacustrine calcium carbonate a significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and in addition macrophytes in the littoral zone lake wigry one of the largest lakes in poland north east poland is characterized by i carbonate sediments with a caco3 content exceeding 80 within the littoral zone and ii large areas of submerged vegetation dominated by charophytes macroscopic green algae characeae family it is claimed that charophytes are highly effective in utilizing hco3 and forming thick caco3 encrustations thus this study was aimed at evaluating the caco3 production by dense chara stands overgrowing the lake bottom reaching a depth of 4 m in late july 2009 the fresh and dry mass of plants the percentage contribution of calcium carbonate and the production of caco3 per 1 m2 were investigated along three transects at three depths 1 m 2 m and 3 m with each sample area equal to 0 0625 m2 per transect the composition and structure of phytoplankton and the physico chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake the greatest dry plant mass exceeded 1000 g m 2 and caco3 encrustations constituted from 59 to over 76 of the charophyte dry weight thus the maximum and average values of carbonates precipitated by charophytes were 685 5 and 438 g m 2 respectively which exceeded previously reported results a correlation of carbonate production with the depth of chara stands was detected and intermediate depths offered the most favourable conditions for carbonate precipitation 589 g m 2 on average as precipitated carbonates are ultimately stored in bottom deposits the results highlight the significance of charophytes in lacustrine caco3 sedimentation

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

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

simulation of stress waves in attenuating drill strings including piezoelectric sources and sensors a key element in drill steering and prediction of lithology ahead of the bit is the transmission of while drilling information from the bottom of the well to the rig operator and the geophysicists mud pulse telemetry based on pressure pulses along the drilling mud and extensional waves through the drill string is the most used technique the last method properly designed could transmit data rates up to 100 bits per second against the 1 or 2 bits per second achieved with pressure pulses in this work a time domain algorithm is developed for the propagation of one dimensional axial torsional and flexural stress waves including transducer sources and sensors in addition the equations include relaxation mechanisms simulating the viscoelastic behavior of the steel dielectric losses and any other losses such as those produced by the presence of the drilling mud the casing and the formation moreover the algorithm simulates the passbands and stopbands due to the presence of the coupling joints and pulse distortion and delay due to nonuniform cross section areas acoustic and electric pulses generated at one location in the string can be propagated and detected at any other location by piezoelectric and acoustic sensors such as pcb accelerometers clamp on ammeters force and strain transducers

new views of tropical paleoclimates from corals abstract corals offer a rich archive of past climate variability in tropical ocean regions where instrumental data are limited and where our knowledge of multi decadal climate sensitivity is incomplete in the eastern equatorial pacific coral isotopic records track variations in enso related changes in sea surface temperature further west corals record variability in sea surface temperature and rainfall that accompanies zonal displacement of the indonesian low during enso events these multi century records reveal previously unrecognised enso variability on time scales of decades to centuries outside the enso sensitive equatorial pacific long term trends towards recent warmer wetter conditions suggest the tropics respond to global forcings new coral paleothermometers indicate that surface ocean temperatures in the tropical southwestern pacific were depressed by 4 6 c during the younger dryas climatic event and rose episodically during the next 4000 yr high temporal resolution measurements of sr ca and 18 o in corals provide information about the surface ocean hydrologic balance and can resolve the seasonal balance between precipitation and evaporation radiocarbon measurements in corals coupled with ocean circulation models may be used to reconstruct near surface ocean circulation past mixing rates and the distribution of fossil fuel co2 in the upper ocean most recently seasonal to interannual variations in the radiocarbon of corals from the equatorial pacific have been linked to the redistribution of surface waters associated with the enso

charophyte growth in small temperate water bodies extreme isotopic disequilibrium and implications for the palaeoecology of shallow marl lakes abstract a small pond containing the charophyte chara hispida was monitored over a one year period for changes in growth water chemistry water level and stable isotopic composition chara growth was found to be seasonal with maximum growth occurring from late april to july during this period ph rose to 10 while the dissolved inorganic carbon dic and calcium fell as a result of photosynthesis and calcification large gradients in ph water temperature and irradiance were found within the chara sward and measurements showed that most growth and photosynthesis occurred within the upper 20 cm of the water column chara oospore formation was also found to be seasonal but dependent upon environmental conditions 18 o w rose rapidly during summer as evaporation progressed and this was correlated with the 18 o dic and to some extent with 18 o c of the chara encrusted calcite however extreme isotopic disequilibrium was observed between the 18 o c and the 18 o w and also between the 13 c c and the 13 c dic this arose from the high ph allowing atmospheric co 2 to enter the water and combine directly with oh it is concluded that within shallow eutrophic lakes containing chara swards inferences of climate e g air temperature cannot be made from observations of the isotopic composition of chara carbonates however in combination with other geochemical data disequilibrium events may be identifiable in ancient lake basins and taken as evidence for lake shallowing and or eutrophication

a snapshot of climate variability at tahiti at 9 5 ka using a fossil coral from iodp expedition 310 1 the integrated ocean drilling program iodp expedition 310 recovered drill cores from the drowned reefs around the island of tahiti 17 40 s 149 30 w many of which contained samples of massive corals from the genus porites herein we report on one well preserved fossil coral sample a 13 6 cm long porites sp dated by uranium series techniques at 9523 33 years monthly 18o and sr ca determinations reveal nine clear and robust annual cycles coral 18o and sr ca determinations estimate a mean temperature of 24 3 c 3 2 c colder than modern for tahiti at 9 5 ka however this estimate is viewed with caution since potential sources of cold bias in coral geochemistry remain to be resolved the interannual variability in coral 18o is similar between the 9 5 ka coral record and a modern record from nearby moorea the seasonal cycle in coral sr ca is approximately the same or greater in the 9 5 ka coral record than in modern coral records from tahiti paired analysis of coral 18o and sr ca indicates cold wet warm dry interannual anomalies opposite from those observed in the modern instrumental record

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

extensional wave stopband broadening across the joint of pipes of different thickness the stopband of pipe extensional waves is an interesting natural phenomenon this study demonstrates an important extension of this phenomenon that is the stopband can be effectively broadened by transmitting the waves across the joint of pipes of different thickness the theoretical and experimental results reveal the detailed process of stopband forming along the pipe and the band broadening across the pipe joint the result can be utilized to provide a method for logging while drilling acoustic isolation design

a 700 year macrophyte productivity record inferred from isotopes of macrophyte remains and bulk carbonates in lake koucha northeast qinghai tibetan plateau abstract the isotopic composition of total organic carbon toc in lakes has been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments however the main factors that affect the carbon isotopes of toc may vary in different lake sediment records limiting the ability of organic carbon isotopes to explain biogeochemical and environmental changes especially in lakes with a large number of aquatic plants in this study the 13c values of macrophyte remains and bulk carbonate in a sedimentary core from lake koucha were investigated to evaluate their paleoenvironmental implications we found that the bulk carbonate was dominated by authigenic carbonates formed in the lake and that their 18o and 13c values can be used to reconstruct environmental changes in the lake koucha area the macrophyte productivity derived from the carbon isotopic offset between the macrophyte remains and the bulk carbonate eremains bc in the lake koucha area agree well with total solar irradiance tsi records inferred from 10be and temperature records based on tree rings from the qinghai tibetan plateau although the distribution of macrophytes is related to water depth according past studies and our observations in the field our findings suggest that changes in macrophyte productivity may be primarily driven by temperature changes in the lake koucha area

isotopic evidence for hydrologic change related to the westerlies in sw patagonia chile during the last millennium abstract the southern hemisphere westerly winds influence the spatial distribution of precipitation in southern south america and play a significant role in the global carbon cycle yet little is known about how this important atmospheric circulation feature has varied in the past here we present a sediment core record of late holocene variability from lago guanaco a small closed basin lake located in torres del paine national park chilean patagonia the park is located in the core of the modern wind field and variations in the intensity of the atmospheric circulation directly influence the hydrology of this region we combine stable isotopic measurements of biogenic carbonate and bulk organic matter to identify two periods of increased evaporation between 900 550 and 400 50 calendar years before present cal yr bp the first interval is coincident with the medieval climate anomaly mca while the more recent period is broadly coincident with the timing of the little ice age lia during the lia interval we observe simultaneous monotonic increases in the 18 o of biogenic carbonate and nothofagus dombeyi type pollen which we interpret as indicative of significant changes in the intensity of the southern westerlies during the last millennium the isotopic and palynological variations in the guanaco record are coincident with geochemical variations found in an antarctic ice core record from siple dome suggesting that the signal preserved in lago guanaco is regional rather than local and that the lia intensification was accompanied by a poleward shift in the southern margin of the westerlies in addition we interpret four periods of increased lake productivity centered on 900 650 500 and 200 cal yr bp from simultaneous increases in the 13 c of bulk organic material and biogenic carbonate these increases in lake productivity are most likely tied to increases in summer temperatures

geochemical perspectives on coral mineralization corals open an exceptional window into many phenomena of geological geochemical climatic and paleontological interest from the paleozoic to the present corals provide some of the finest high resolution archives of marine conditions corals are likewise exceptional for chronometric purposes and even the terrestrial 14c timescale has now been calibrated against coral 230th 234u corals also represent a testing ground for basic ideas about mineralogy and geochemistry the shapes sizes and organization of skeletal crystals have been attributed to factors as diverse as mineral supersaturation levels and organic mediation of crystal growth the coupling between calcification and photosynthesis in symbiotic corals is likewise attributed to everything from photosynthetic alkalinization of the water to efforts by the coral to prevent photosynthetic alkalinization corals also leave a significant geochemical imprint on the oceans their aragonite skeletons accept about 10 times more strontium than does calcite hence the proportion of marine aragonite precipitation affects the oceanic chemical balance biological carbonates represent the biosphere s largest carbon reservoir hence calcareous organisms affect the ocean s ph co2 content and ultimately global temperatures through the greenhouse gas connection finally corals present some geochemical puzzles for ecology and conservation how do symbiotic corals obtain nutrients in some of the most nutrient deficient parts of the planet are global geochemical changes partially responsible for the widespread declines in coral reefs during recent decades we will address many of these issues but will concentrate on coral skeletal structure and calcification mechanism these topics bear most directly on the biomineralization process and generally affect the choice of skeletal materials and analytical techniques used in geochemical investigations the coral reef is probably the planet s most spectacular biomineralization product these grand and complex ecosystems build on the accumulated skeletal debris of countless generations of organisms especially calcareous algae and symbiotic

last glacial holocene geochronology of sediment cores from a high altitude tibetan lake based on ams 14c dating of plant fossils implications for paleoenvironmental reconstructions abstract we obtained three sediment cores from a high altitude lake lake pumoyum co altitude 5020 m asl on the southern tibetan plateau for reconstruction of environmental changes during the last glacial holocene transition in this study we established the first reliable chronology for sediment cores from lake pumoyum co ca 18 5 cal ka bp at the bottom by 14c analyses of terrestrial plant residue concentrates prc 125 m and aquatic plant residues the calibrated ages of the prc fraction in the surface sediment were nearly modern 0 1 0 1 cal ka bp and the 13c values 22 to 24 were agreed well with those of modern terrestrial c3 plants in addition we estimated 14c reservoir ages of macrophyte remains from changes in their 13c values the major climate boundary layers in the cores transitions to bolling allerod 14 5 0 5 cal ka bp younger dryas 12 8 0 1 cal ka bp and preboreal 11 6 cal ka bp were confirmed by our new 14c chronology the transition to the bolling allerod warm phase from the last glacial 14 5 0 5 cal ka bp coincided with an obvious lithologic boundary a rapid decrease in the abundance of the macrophyte remains in the lake pumoyum co sediment cores

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

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater insights into the biomineralization response to ocean acidification 1 we reared primary polyps new recruits of the common atlantic golf ball coral favia fragum for 8 days at 25 c in seawater with aragonite saturation states ranging from ambient 3 71 to strongly undersaturated 0 22 aragonite was accreted by all corals even those reared in strongly undersaturated seawater however significant delays in both the initiation of calcification and subsequent growth of the primary corallite occurred in corals reared in treatment tanks relative to those grown at ambient conditions in addition we observed progressive changes in the size shape orientation and composition of the aragonite crystals used to build the skeleton with increasing acidification densely packed bundles of fine aragonite needles gave way to a disordered aggregate of highly faceted rhombs the sr ca ratios of the crystals measured by sims ion microprobe increased by 13 and mg ca ratios decreased by 45 by comparing these variations in elemental ratios with results from rayleigh fractionation calculations we show that the observed changes in crystal morphology and composition are consistent with a 80 decrease in the amount of aragonite precipitated by the corals from each batch of calcifying fluid this suggests that the saturation state of fluid within the isolated calcifying compartment while maintained by the coral at levels well above that of the external seawater decreased systematically and significantly as the saturation state of the external seawater decreased the inability of the corals in acidified treatments to achieve the levels of calcifying fluid supersaturation that drive rapid crystal growth could reflect a limit in the amount of energy available for the proton pumping required for calcification if so then the future impact of ocean acidification on tropical coral ecosystems may depend on the ability of individuals or species to overcome this limitation and achieve the levels of calcifying fluid supersaturation required to ensure rapid growth

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

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

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

numerical modeling and interpretation of drillstring waves drill bit seismic and pilot seismograms contain drillstring periodicities from signal and environmental noise sources these coherent components are similar in seismic while drilling correlations and their joint contribution may cause distortions in signal processing numeric modeling of the drillstring transmission line is used to correctly interpret the axial and torsional events with similar propagating modes of signal and noise the reflection coefficients are computed for drillstrings of arbitrary materials and their average mechanical features are related to the axial and torsional group velocities obtained by the dispersion equations fitting of the periodical components in the real seismograms is used to automatically correct the drill bit pilot delays and to estimate the surface and downhole boundary conditions

the propagation of sound waves in drill strings deep wells are commonly drilled while steering the drill bit the steering process is completely controlled by the drilling rig operator a key element of this procedure is the measurement and communication of navigation information from the bottom of the well to the operator pressure pulses modulated onto the flow of the drill fluid are now employed in some cases to communicate this information however data rates are only a few binary bits per second with this method this drastically limits the quantity of data available to the operator as an alternative method elastic waves generated within the steel drill string can be used as a carrier signal to transmit data the drill string is commonly assembled from 10 m segments of threaded pipe and forms a periodic structure the elastic wavelengths of interest are shorter than this periodic length consequently these waves undergo significant dispersion this paper presents new data for the propagation of elastic waves in a 2 km drill string the influen

modern and late holocene dolomite formation manito lake saskatchewan canada abstract major advances have occurred in our understanding of modern dolomite formation and penecontemporaneous dolomitization over the past several decades manito lake located in west central saskatchewan canada is a large 65 km 2 deep z max 22 m perennial saline 45 ppt tds lake in which modern and late holocene dolomite coexists with other endogenic and authigenic carbonate precipitates including aragonite monohydrocalcite calcite and mg calcite like many other lacustrine dolomites manito lake dolomite is microcrystalline less than 1 m to 5 m ca rich and poor to moderately ordered it occurs as relatively pure hardgrounds and as a component of nearshore microbialites it also forms isopachous cements in consolidated siliciclastic shoreline sediments manito lake dolomite is most likely forming by mainly biomediated precipitation at or near the sediment water interface i in pore spaces of coarse siliciclastic sediments i e beachrock ii as fine laminae associated with microbialites and iii as a major component of mudstone hardgrounds and pavements

significance of shallow marine and non marine algae stable isotope δ18o compositions over long periods example from the palaeogene of the paris basin in this study we test the potentiality of using dasycladales and charophytes calcareous shallow marine and non marine algae respectively as palaeoclimatic recorders these algae mineralize their carbonate during short periods in summer throughout the palaeogene we compare the 18o variation of these two taxa to identify a possible common factor influencing their isotopic composition i e temperatures variations from a local environmental signal we sampled and isotopically analyzed eight species of charophytes and seven species of dasycladales from 23 formations ranging from the palaeocene to the oligocene series of the paris basin by comparing the 18o of these two groups living in different environment with that of shallow marine mollusks from a previous study we show that temperature variations are the main factor influencing their 18o compositions and that local environmental effects do not screen the global thermal signal maximum annual palaeotemperatures are calculated from the 18o of the dasycladales and indicate by comparison with the data from mollusks previously analyzed that dasycladales species used probably mineralized their carbonate in equilibrium with sea water dasycladales recorded the global climatic events already known for the palaeogene with high temperatures reached during the early eocene and middle eocene climatic optimums and relative cooling intervals during the lutetian the priabonian and the rupelian charophyte gyrogonites also recorded temperature variations in their 18o compositions but reconstituting reliable temperature values in non marine environments is not directly possible and requires constraining 18o of local continental water using other proxies these promising results show that carbonates mineralized from algae constitute a reliable support for palaeoclimatic information and should be more widely used in the fossil record

a 1000 year record of forest fire drought and lake level change in southeastern british columbia canada high resolution charcoal analysis of lake sediments and stand age information were used to reconstruct a 1000 year fire history around dog lake which is located in the montane spruce zone of southeastern british columbia macroscopic charcoal 125 um accumulation rates char from lake sediment were compared with a modern stand origin map and fire scar dates in the kootenay valley to determine the relative area and proximity of fires recorded as char peaks small fires close to the lake and larger more distant fires appear as similar sized peaks in the record this information reinforces previous findings where char peaks represent a complex spatial aggregation of local to extra local fires around a lake site char peaks indicate frequent stand destroying fires during the mediaeval warm period ad 1000 1300 and other significant fires at c 1360 1500 1610 and 1800 we also present a proxy measure of lake level changes based on a comparison of accumulation rates of chara globulanis type oospores

the effect of skeletal mass accumulation in porites on coral sr ca and δ18o paleothermometry 1 paleotemperature estimates based on coral sr ca have not been widely accepted because the reconstructed glacial holocene shift in tropical sea surface temperature 4 6 c is larger than that indicated by foraminiferal mg ca 2 4 c we show that corals over estimate changes in sea surface temperature sst because their records are attenuated during skeletogenesis within the living tissue layer to quantify this process we microprofiled skeletal mass accumulation within the tissue layer of porites from australasian coral reefs and laboratory culturing experiments the results show that the sensitivity of the sr ca and 18o thermometers in porites will be suppressed variable and dependent on the relationship between skeletal growth rate and mass accumulation within the tissue layer our findings help explain why 18o sst sensitivities for porites range from 0 08 c to 0 22 c and are always less than the value of 0 23 c established for biogenic aragonite based on this observation we recalibrated the coral sr ca thermometer to determine a revised sensitivity of 0 084 mmol mol c after rescaling most of the published sr ca sst estimates for the indo pacific region for the last 14 000 years 7 c to 2 c relative to modern fall within the 95 confidence envelope of the foraminiferal mg ca sst records we conclude that two types of calibration scales are required for coral paleothermometry an attenuated porites specific thermometer sensitivity for studies of seasonal to interannual change in sst and importantly the rescaled 0 084 mmol mol c sr ca sensitivity for studies of 20th century trends and millennial scale changes in mean sst the calibration scaling concept will apply to the development of transfer functions for all geochemical tracers in corals

growth rate influences on coral climate proxies tested by a multiple colony culture experiment abstract as application of coral based climate reconstruction has become more frequent at tropical sites increased attention is being paid to the potential ambiguities of coral thermometers that are intrinsic to the biomineralisation process including the so called vital effect the growth rate related kinetic effect and the co 3 2 effect here we studied how the growth rate influenced the skeletal oxygen and carbon isotope ratios 18 o and 13 c and the sr ca ratio in a common garden experiment involving the long term culture of porites australiensis clone colonies comparison of the seasonal minimum 18 o values during summer showed a negligible influence of the large intercolony variation in growth rate 2 10 mm yr 1 on 18 o variation but 18 o was relatively sensitive to temporary intracolony growth rate changes related to colony health in contrast the sr ca ratio was robust against both inter and intracolony growth rate variation we found a positive shift in 13 c in slower growing corals which we attributed to the kinetic behaviour of the calcification reaction the seasonal fluctuation in 13 c corresponded not to changes in light intensity nor to 13 c of dissolved inorganic carbon in seawater but to photosynthetic efficiency as measured by pulse amplitude photometry these findings support the inference that coral skeletal sr ca and 18 o in a long lived colony can function as a palaeoclimate archive by recording signals of clonal growth we also propose practical guidelines for the proper interpretation of coral records