late quaternary palaeoenvironment of northern guatemala evidence from deep drill cores and seismic stratigraphy of lake peten itza long sediment cores were collected in spring 2006 from lake peten itza northern guatemala in water depths ranging from 30 to 150 m as part of an international continental scientific drilling program project the sediment records from deep water consist mainly of alternating clay gypsum and carbonate units and in at least two drill sites extend back 200 kyr most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes a revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin from ca 200 to ca 85 ka sediments are dominated by carbonate clay silt often interbedded with sandy turbidites indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate at ca 85 ka an exposure horizon consisting of gravels coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation indicating dry climate conditions from ca 85 to ca 48 ka transgressive carbonate clay sediments overlain by deep water clays suggest a lake level rise and subsequent stabilization at high stage from ca 48 ka to present the lithology is characterized by alternating clay and gypsum units gypsum deposition correlates with heinrich events i e dry climate whereas clay units coincide with more humid interstadials

multi proxy evidence of millennial climate variability from multiple bahamian speleothems abstract northern hemisphere tropical paleoclimate records support significant changes associated with dansgaard oeschger d o events and heinrich stadials 1 to 6 during the last 64 000 years however few absolutely dated terrestrial records from the western atlantic span the last six heinrich stadials here we present geochemical results from three new stalagmites collected from a cave in the bahamas which encompass heinrich stadials 1 to 6 we build on a previous study of the 13 c and 18 o values of the calcite and 18 o value of fluid inclusions from a single stalagmite from the same cave spanning the last three heinrich stadials absolute geochronometry using u th equilibrium series demonstrates that the stalagmites formed between 63 8 and 13 8 kyr bp the 13 c and 18 o values of the calcite show higher values associated with heinrich stadials 1 6 and lower values during the d o interstadial events the sr ca ratios of the calcite are shown to be relatively invariant while in two of the samples the mg ca ratios track the 13 c values increases in the 18 o values across heinrich stadials 1 6 are interpreted as being driven by lower temperatures the two deeper occurring stalagmites demonstrate increased mg ca ratios and 13 c values during heinrich stadials 1 and 2 which are interpreted as a signal of reduced flow rates in the epikarst and increased water rock interactions as a result of increased aridity which potentially occurred across all six heinrich stadials the observed reductions in mean annual temperature and amount of precipitation across heinrich stadials are proposed to be driven by a reduction in sea surface temperatures in the north atlantic and an expanded bermuda high during d o interstadials the bahamas cave records likely indicate warmer and or wetter climate however the isotopic shifts are not as significant as the isotopic excursions associated with heinrich stadials

precise and accurate isotope fractionation factors α17o α18o and αd for water and caso4 2h2o gypsum gypsum caso4 2h2o is a hydrated mineral containing crystallization water also known as gypsum hydration water ghw we determined isotope fractionation factors 17o 18o and d between ghw and free water of the mother solution in the temperature range from 3 c to 55 c at different salinities and precipitation rates the hydrogen isotope fractionation factor dgypsum water increases by 0 0001 units per c between 3 c and 55 c and salinities 150 g l of nacl the dgypsum water is 0 9812 0 0007 at 20 c which is in good agreement with previous estimates of 0 981 0 001 at the same temperature the 18ogypsum water slightly decreases with temperature by 0 00001 per c which is not significant over much of the temperature range considered for paleoclimate applications between 3 c and 55 c 18ogypsum water averages 1 0035 0 0002 this value is more precise than that reported previously e g 1 0041 0 0004 at 25 c and lower than the commonly accepted value of 1 004 we found that nacl concentrations below 150 g l do not significantly affect 18ogypsum water but dgypsum water increases linearly with nacl concentrations even at relatively low salinities suggesting a salt correction is necessary for gypsum formed from brines unlike oxygen isotopes the dgypsum water is affected by kinetic effects that increase with gypsum precipitation rate as expected the relationship of the fractionation factors for 17o and 18o follows the theoretical mass dependent fractionation on earth 0 529 0 001 we provide specific examples of the importance of using the revised fractionation factors when calculating the isotopic composition of the fluids

quantitative estimates of tropical temperature change in lowland central america during the last 42 ka determining the magnitude of tropical temperature change during the last glacial period is a fundamental problem in paleoclimate research large discrepancies exist in estimates of tropical cooling inferred from marine and terrestrial archives here we present a reconstruction of temperature for the last 42 ka from a lake sediment core from lake peten itza guatemala located at 17 n in lowland central america we compared three independent methods of glacial temperature reconstruction pollen based temperature estimates tandem measurements of 18o in biogenic carbonate and gypsum hydration water and clumped isotope thermometry pollen provides a near continuous record of temperature change for most of the glacial period but the occurrence of a no analog pollen assemblage during cold dry stadials renders temperature estimates unreliable for these intervals in contrast the gypsum hydration and clumped isotope methods are limited mainly to the stadial periods when gypsum and biogenic carbonate co occur the combination of palynological and geochemical methods leads to a continuous record of tropical temperature change in lowland central america over the last 42 ka furthermore the gypsum hydration water method and clumped isotope thermometry provide independent estimates of not only temperature but also the 18o of lake water that is dependent on the hydrologic balance between evaporation and precipitation over the lake surface and its catchment the results show that average glacial temperature was cooler in lowland central america by 5 10 c relative to the holocene the coldest and driest times occurred during north atlantic stadial events particularly heinrich stadials hss when temperature decreased by up to 6 to 10 c relative to today this magnitude of cooling is much greater than estimates derived from caribbean marine records and model simulations the extreme dry and cold conditions during hss in the lowland central america were associated with fresh water forcing in the north atlantic which led to reduced atlantic meridional overturning circulation cooling of the north atlantic southern advance of sea ice and southward shift of the intertropical convergence zone although some models correctly predict the sign of temperature and precipitation changes they consistently underestimate the degree of observed cooling and decreased precipitation over land in lowland central america

internal reflecting horizons in spitsbergen glaciers a single pronounced internal reflecting horizon has been observed on radio echo sounding from over 30 glaciers in spitsbergen they are often present along the entire length of the glacier remaining at a fairly constant depth 100 200 m below the ice surface echo strength data from radio echo sounding have been used to obtain reflection coefficients for these horizons of between 15 and 25 db combined with results of ice core studies the possible causes of this internal layer are investigated the presence of water is found to be the most likely explanation indicating the existence at depth of a layer of temperate ice

petrographical palynological and geochemical analyses of the hub and harbour seams sydney coalfield nova scotia canada implications for facies development abstract benched channel samples and continuous block samples of the hub and harbour seams from the sydney basin nova scotia were studied to define the variations in petrography geochemistry and palynology of the seams and to interpret the depositional environments of the precursor mires petrographic compositions of the seams are very similar with high vitrinite content low inertinite moderate liptinite and negligible clastic mineral content pyrite content is moderate there is little variation in petrographic composition between benches in either seam there are marked variations in petrographic compositions at the lithotype scale petrographic facies parameters indicate deposition of the bulk of both seams under fairly uniform conditions in relatively wet mires unusually wet or dry periods were rare the palynological assemblages of both seams indicate a middle to late westphalian d age the common to abundant palynomorphs are derived from arborescent and herbaceous lycopsids tree ferns and other ferns and sphenopsids the palynological assemblages support the petrographic interpretation of relatively wet mires cordaites pollen florinites is rare suggesting that there was little contribution from plants growing in dry or upland areas the absence of the densospore miospore phase and the petrographic data indicate there were no periods in which domed mires occurred the distinctive dull bands occurring in the hub and harbour seams are characterised by low vitrinite contents high inertinite content high liptinite and common detrital minerals sporinite showing varying degrees of degradation is commonly highly concentrated in thin bands the geochemistry is marked by much higher hi values than normally reported for coals but other indices are typical for coals of this rank the palynological assemblages of the dull bands are dominated by tree fern spores and other ferns with only a minor contribution by sphenopsid spores the dull bands were deposited during periods of inundation of mires relatively low mineral content indicates that the distributary channels which flooded the mires were quite distant from the depositional sites of the samples

siderite clumped isotope thermometry a new paleoclimate proxy for humid continental environments abstract clumped isotope measurements can be used to exploit the paleoclimatic potential of pedogenic siderite feco3 however the applicability of this method is held back by the lack of clumped isotope calibrations of mineralogies other than calcite and aragonite here we present an inorganic calibration of siderites grown in the laboratory between 21 and 51 c linear regression of 47 values and temperature 106 t2 k yields the following relationship r2 0 997 47 rf 0 0356 0 0018 10 6 t 2 0 172 0 019 we demonstrate that this calibration is indistinguishable from calcite at current levels of analytical precision our observations suggest that there is likely no large systematic bias in the clumped isotope acid fractionation factors between the two different carbonate minerals we also present clumped isotope measurements of a natural siderite collected from holocene sediments of the mississippi river delta we find that siderites record warm season marsh water temperatures instead of mean annual temperatures as it has long been presumed this finding has important implications for the accuracy of siderite stable isotope and clumped isotope based climate reconstructions

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

radio echo sounding of svalbard glaciers peculi arities of radio echo sound ing of mountain gl aciers and ice fields between nunataks from terrestria l vehicles and from heli copters are consi dered in this paper the possibility of using compar atively high frequen cies of up to 865 mhz for sounding suc h glaciers is demonst rated on the basis of expe rimental data results of airbo rne radio echo so unding of svalba rd gl aciers of various types dimensions and regime obtained with the help of the 620 m hz airbo rne equipment of high resolution are shown returns from the gla cier bed have been obtained on the majority of glaciers unde r in vestigation the firn regions of ice fields with temp erate regimes flowing between nuna taks are mostly an exception depre ssion in the glacier bed with the ice thic kne ss up to 540 m as well as int ernal reflecting boundaries have been detected in some glaciers ic e volum es of glaciers have been determined from the airborne radio echo sounding data with the use of a parabolic appr oximation to the cross section glacier profiles good correl ational dependence between ice volume and surface area of glaciers has been established and is use d to estimate the ic e and water resources in sva lbard glaciers

cold surface layer thinning on storglaciaren sweden observed by repeated ground penetrating radar surveys 1 a characteristic feature of ground penetrating radar gpr surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface cts hence providing a possible tool for mapping thermal structure with high accuracy comparison of detailed temperature measurements in bore holes and gpr profiles at 345 mhz and 800 mhz center frequencies on storglaciaren sweden show that the cts can be detected and mapped with an accuracy of about 1 m at both frequencies a comparison between comprehensive gpr surveys of the cold surface layer separated by 12 years 1989 2001 shows a substantial and complex thinning of the cold layer an overall decrease of 8 3 m 22 of average thickness of the cts depth is much larger than uncertainties in cts depth determinations the stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of cts there is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning however small increase in average winter air temperature a limiting factor for the temperature gradient through the cold surface layer may provide a partial explanation the weaker temperature gradient reduces the transport of latent heat from the cts thus slowing down its downward migration

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

vegetation response to abrupt climate changes in western europe from 45 to 14 7k cal a bp the bergsee lacustrine record black forest germany

clumped isotope fractionation during phosphoric acid digestion of carbonates at 70 c the application of clumped isotopes 47 in carbonate minerals as a sensitive temperature proxy in paleo environments depends on a well constrained clumped isotope fractionation for the necessary step of phosphoric acid digestion of the carbonate mineral to produce co2 published estimates for clumped isotope fractionations vary and the effect of different carbonate mineralogies is still under debate differences in the sample preparation design and sample digestion temperatures are potential sources for varying acid fractionations and could be a source for discrepant 47 temperature calibrations observed in different laboratories to evaluate the clumped isotope acid fractionation at 70 c and simultaneously account for a potential cation effect we analyzed a set of eight carbonate minerals calcite aragonite dolomite and magnesite that were driven to a stochastic isotope distribution by heating them to temperatures of 1000 c our study reveals significant cation and mineral specific differences for the 47 acid fractionation of carbonate minerals digested at 70 c or 100 c the 47 acid fractionation at 70 c for calcite is 0 197 0 002 for aragonite 0 172 0 003 whereas dolomite has a significantly larger acid fractionation of 0 226 0 002 for magnesite digested at 100 c we observed a 47 acid fractionation of 0 218 0 020 projected to an acid digestion at 25 c our acid fractionation for calcite of 0 260 is statistically indistinguishable from existing studies we further show that the 47 of the calcite standards eth 1 and eth 2 of 0 265 and 0 267 respectively are in the range of the determined acid fractionation projected to 25 c suggesting that they have an identical and near stochastic isotope distribution the observed differences in the 47 acid fractionation between calcite and aragonite 47 0 025 and between calcite and dolomite 47 0 029 does not correlate with the phosphoric acid fractionation of oxygen isotopes but rather depends on the radius of the cation as well as on the mineral structure our results reveal that the acid fractionation of dolomite at 70 c is significantly distinct from the one of calcite but at 90 c the two are within error of each other due to the different acid fractionation temperature dependence of calcite and dolomite thus it is necessary to use a mineral specific 47 acid fractionation factor for dolomite to avoid differences in the final 47 signal from dolomites digested at 90 c and dolomites digested at lower temperatures similar effects may apply also to other carbonates such as magnesite and siderite however their mineral specific 47 acid fractionation at digestion temperatures around 90 c might be also similar to the one of calcite so that potential differences could be within the range of the analytical error

deglacial abrupt climate change in the atlantic warm pool a gulf of mexico perspective 1 during the last deglaciation greenland ice core and north atlantic sediment records exhibit multiple abrupt climate events including the younger dryas cold episode 12 9 11 7 ka however evidence for the presence of the younger dryas in the gulf of mexico gom and the relationship between gom sea surface temperature sst and high latitude climate change is less clear we present new mg ca sst records from two varieties of the planktonic foraminifer globigerinoides ruber white and pink to assess northern gom sst history from approximately 18 4 10 8 ka thirty five accelerator mass spectrometry ams 14c dates from orca basin core md02 2550 provide excellent age control and document high sedimentation rates 40 cm kyr g ruber white and pink mg ca sst data exhibit increases 4 6 0 6 c and 2 2 0 5 c respectively from at least 17 8 16 6 ka with nearly decadal resolution that are early relative to the onset of the bolling allerod interstadial moreover g ruber white sst decreases at 16 0 14 7 ka 1 0 0 5 c and 12 8 11 6 ka 2 4 0 6 c correlate to the oldest and younger dryas in greenland and cariaco basin the g ruber pink sst record which reflects differences in seasonality and or depth habitat is often not in phase with g ruber white and closely resembles antarctic air temperature records overall it appears that orca basin sst records follow antarctic air temperature early in the deglacial sequence and exhibit enhanced seasonality during greenland stadials

a revised calibration of the clumped isotope thermometer abstract a growing number of materials and environmental settings are studied using the carbonate clumped isotope 47 thermometer the method has been applied in both biogenic and non biogenic carbonate systems in marine and terrestrial settings over a wide range of geological timescales the current 47 temperature calibration gives good temperature estimates for most biogenic materials however systematic biases are commonly observed at low temperatures in this study we report additional calibration data that covers a wider temperature range at more evenly distributed temperatures and are measured at higher analytical precision than the original calibration combining these data with the original calibration yields a 47 t relationship that is similar to the original calibration though slightly less steep 47 0 0526 0 0025 10 6 t 2 0 0520 0 0284 this revised calibration is in better agreement with biogenic carbonates including those grown at low temperatures the difference between the original and revised calibrations is significant for carbonates forming below 16 c or above 49 c 47 values of 0 68 and 0 56 additionally we include a comprehensive analysis of the sources of error associated with 47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision as an illustration we apply the revised calibration and uncertainty analysis to 3 previously published studies at low temperatures the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded in light of our 47 errors analysis in cases where the temperature signals are small we find that replicate analyses are critical to identify a temperature signal

a high resolution temporal record of environmental changes in the eastern caribbean guadeloupe from 40 to 10 ka bp abstract in neotropical regions fossil bat guano accumulated over time as laminated layers in caves hence providing a high resolution temporal record of terrestrial environmental changes additionally cave settings have the property to preserve such organic sediments from processes triggered by winds deflation abrasion and sandblasting and intense rainfall leaching away this study reports both stable carbon and nitrogen isotope compositions of frugivorous bat guano deposited in a well preserved stratigraphic succession of blanchard cave on marie galante guadeloupe these isotopic data are discussed with regard to climate changes and its specific impact on eastern caribbean vegetation during the late pleistocene from 40 to 10 ka cal bp guano 13 c values are higher than modern ones suggesting noticeable vegetation changes this provides also evidence for overall drier environmental conditions during the pleistocene compared to today meanwhile within this generally drier climate shifts between wetter and drier conditions can be observed large temporal amplitudes in both 13 c and 15 n variations reaching up to 5 9 and 16 8 respectively also indicate these oceanic tropical environments have been highly sensitive to regional or global climatic forcing stable isotope compositions of bat guano deposited from 40 to 35 ka bp the last glacial maximum and the younger dryas reveal relatively wet environmental conditions whereas at least from the end of the heinrich event 1 and the bolling period the region experienced drier environmental conditions nevertheless when considering uncertainties in the model age the isotopic record of blanchard cave show relatively similar variations with known proxy records from the northern south america and central america suggesting thus that the blanchard cave record is a robust proxy of past itcz migration teleconnections through global atmospheric pattern suggest that islands of the eastern caribbean basin could be also under the influence of a bipolar temperature gradients that impact the mean location of the itcz with a southern hemisphere imprint during the glacial period and a more significant role of northern hemisphere during the last deglaciation

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

on the fidelity of shell derived δ18oseawater estimates article i nfo 18 oseawater a robustproxyforsurfacesalinity we assessthe fidelity of shell derived 18 oseawater estimates for the surface dwelling foraminifer globigerinoides ruber white using an atlantic meridional coretop transect spanning basin scale temperature and salinity gradients shell derived and observed 18 oseawater values are well correlated r 2 0 77 but a large systematic bias is observed shell mg ca ratios are significantly elevated above values expected from observed and isotopic calcification temperatures in the saline subtropical gyres of both hemispheres this temperature independent shell mg ca ratio variability termed excess mg ca i s highly correlated with surface salinity r 2 0 77 and the observed salinity dependence 27 4 is much higher than indicated by culture studies 6 2 our coretop data are used to develop new atlantic basin temperature and salinity calibration equations that are accurate 1 1 c and 0 20 respectively precise r 2 0 82 and 0 81 respectively and verifiable using previously published data these results are valid for the relatively high salinities of the subtropical atlantic 35 5 37 3 we discover that inclusion of other published data from lower salinity regions b35 indicates little or no excess mg ca taken together these results point to a strongly non linear positive salinity effect on shell mg ca ratios that significantly affects the accuracy of sst and 18

late pleistocene and mid holocene climate change derived from a florida speleothem abstract a stalagmite collected from brooksville ridge cave in west central florida was deposited from 30 to 20 kyr bp encompassing heinrich event 2 h2 and from 5 to 4 kyr bp the later part of the mid holocene the h2 event in the speleothem occurs at 24 kyr bp which is temporally similar to its timing in other paleoclimate reconstructions however the oxygen and carbon isotope values indicate the climate in florida was relatively warm and wet for a glacial period rather than extremely cool and dry as seen in other regions the higher temperatures and increased precipitation compared to the preceding climate state produced a shift towards enhanced vegetation growth dense forest during this period one possible cause is the faltering of the north atlantic thermohaline circulation due to increased glacial meltwater input thereby preventing heat transfer via the gulf stream from the tropics to the northerly latitudes this change in the circulation would lead to warmer gulf of mexico and subtropical atlantic sea surface temperatures ssts these higher ssts would promote an increase in convective thunderstorm activity due to higher evaporation rates however to give this shift some paleoclimate perspective the average mid holocene speleothem oxygen isotope values were more depleted by 1 indicating even warmer temperatures and higher precipitation amounts compared to the glacial period additionally the carbon isotopes show a 3 shift towards more negative values indicating a more heavily forested west central florida the variability within both the mid holocene and late pleistocene data support the possibility of atmospheric teleconnections between the tropics subtropics and northerly latitudes contributing to shorter term shifts in precipitation amount superimposed on the larger scale glacial interglacial isotopic composition of the speleothem

on the thermal regime of an arctic valley glacier a study of white glacier axel heiberg island n w t canada from 1974 to 1981 a total of 32 bore holes was drilled on white glacier and vertical ice temperature profiles measured the data obtained allowed the construction of three longitudinal and four transverse profiles of the two dimensional temperature distributions thus an extensive layer of temperate or near temperate ice was discovered close to the bedrock in the lowest part of the glacier tongue it was also found that the temperature distribution cannot be in a steady state since there is a temperature minimum 100 150 m below the glacier surface in the accumulation area a simple numerical model calculation shows that this minimum can be mostly explained by the general climatic warming since 1880 the 10 m temperatures show diffuse relations to climatic conditions and balance zones a simple scheme for extrapolating surface temperatures is discussed

radio echo sounding of spitsbergen glaciers problems in the interpretation of layer and bottom returns comparaison des sondages de glaciers du spitsbezg par un equipement 60 mhz spri mk iv et des sondages sovietiques sur 440 et 620 mhz les fortes differences observees sont attribuees a la forte absorption et grande dispersion sur le lit rocheux des sondages sovietiques

caribbean hydroclimate and vegetation history across the last glacial period abstract we present a new speleothem trace element and stable isotope record which extends previous paleoclimate evidence from cuban speleothems to the last 96 ka multiple proxies were used to reconstruct caribbean hydroclimate and vegetation variability on orbital to millennial timescales in particular our proxies indicate a shift to more abundant c4 compared to c3 vegetation and or reduced soil activity during the last glacial maximum our results confirm the close link of caribbean precipitation to north atlantic climate variability insolation and the strength of the amoc the associated variations in caribbean ssts and the shift of the itcz led to substantial changes of the hydrological cycle during heinrich stadials and the younger dryas climatic conditions in cuba were comparably cool and or dry in contrast warm dansgaard oeschger cycles were accompanied by wetter conditions this is in agreement with previous evidence for the holocene when north atlantic cold warm events coincided with drier wetter conditions in cuba however our record suggests that this connection was less dominant during mis 4 to 2 displayed by a weaker response of cuban precipitation proxies to north atlantic climatic shifts than during mis 5 in particular we hypothesize that this weaker connection was mediated by the southerly shifted itcz inducing a weakening of the northern branch of the caribbean low level jet which usually transports moisture into the northern caribbean this is strikingly evident during the deglacial when driest and or coolest conditions prevailed in western cuba from hs 1 into the younger dryas including the bolling allerod interstadial

comparison of radio echo sounding 30 1000 mhz and high resolution borehole temperature measurements at finsterwalderbreen southern spitsbergen svalbard

climate change in lowland central america during the late deglacial and early holocene the transition from arid glacial to moist early holocene conditions represented a pro found change in northern lowland neotropical climate here we report a detailed record of changes in moisture availability during the latter part of this transition 11 250 to 7500 cal yr bp inferred from sediment cores retrieved in lake peten itza northern guatemala pollen assemblages demon strate that a mesic forest had been largely established by 11 250 cal yr bp but sediment properties indicate that lake level was more than 35 m below modern stage from 11 250 to 10 350 cal yr bp during the preboreal period lithologic changes in sediments from deep water cores 50 m below modern water level indicate several wet dry cycles that suggest distinct changes in effective moisture four dry events designated pbe1 4 occurred centred at 11 200 10 900 10 700 and 10 400 cal yr bp and correlate with similar variability observed in the cariaco basin titanium record and glacial meltwater pulses into the gulf of mexico after 10 350 cal yr bp multiple sediment proxies suggest a shift to a more persistently moist early holocene climate comparison of results from lake peten itzawith other records from the circum caribbean demonstrates a coherent climate response during the entire span of our record furthermore lowland neotropical climate during the late deglacial and early holocene period appears to be tightly linked to climate change in the high latitude north atlantic we speculate that the observed changes in lowland neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the intertropical convergence zone and azores bermuda high pressure system this mechanism operated on millennial to submillennial timescales and may have responded to changes in solar radiation glacial meltwater north atlantic sea ice and the atlantic meridional overturning circulation moc copyright 2005 john wiley sons ltd

laurentide ice sheet meltwater and abrupt climate change during the last glaciation 1 a leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the north american laurentide ice sheet lis which may have routed fresh water between the gulf of mexico gom and the north atlantic affecting north atlantic deep water variability and regional climate paired measurements of 18o and mg ca of foraminiferal calcite from gom sediments reveal five episodes of lis meltwater input from 28 to 45 thousand years ago ka that do not match the millennial scale dansgaard oeschger warmings recorded in greenland ice we suggest that summer melting of the lis may occur during antarctic warming and likely contributed to sea level variability during marine isotope stage 3

triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo humidity reconstruction abstract atmospheric relative humidity is an important parameter affecting vegetation yet paleo humidity proxies are scarce and difficult to calibrate here we use triple oxygen 17 o and 18 o and hydrogen d isotopes of structurally bound gypsum hydration water ghw extracted from lacustrine gypsum to quantify past changes in atmospheric relative humidity an evaporation isotope mass balance model is used together with monte carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of ghw and with statistically robust estimates of uncertainty we apply this method to reconstruct the isotopic composition of paleo waters of lake estanya ne spain and changes in normalized atmospheric relative humidity rh n over the last glacial termination and holocene from 15 to 0 6 cal kyrs bp the isotopic record indicates the driest conditions occurred during the younger dryas yd 12 13 cal kyrs bp we estimate a rh n of 40 45 during the yd which is 30 35 lower than today because of the southward displacement of the polar front to 42 n it was both windier and drier during the yd than the bolling allerod period and holocene mean atmospheric moisture gradually increased from the preboreal to early holocene 11 to 8 cal kyrs bp 50 60 reaching 70 75 rhn from 7 5 cal kyrs bp until present day we demonstrate that combining hydrogen and triple oxygen isotopes in ghw provides a powerful tool for quantitative estimates of past changes in relative humidity

a 43 ka record of paleoenvironmental change in the central american lowlands inferred from stable isotopes of lacustrine ostracods we present a continuous ostracod isotope 18o and 13c record from lake peten itza peten guatemala in the northern lowland neotropics that spans the last 43 cal ka bp variations in oxygen and carbon isotopes closely follow lithologic variations which consist of alternating gypsum and clay deposits that were deposited under relatively dry and wet climate respectively during the last glacial period the greatest 18o and 13c values coincide with gypsum deposited during lake lowstands under arid climate conditions that were correlated previously with north atlantic heinrich events in contrast interstadials and the entirety of the last glacial maximum 24 19 cal ka bp are marked by clay deposition and lower 18o and 13c values reflecting higher lake levels and relatively moister climate isotope results and pollen data along with independently inferred past water levels show the early deglacial period 19 15 cal ka bp was the time of greatest aridity and lowest lake stage of the past 43 ka this period occurred during heinrich stadial 1 hs 1 when an extensive tropical megadrought has been postulated stager et al 2011 heinrich stadial 1 is represented by two episodes of gypsum precipitation and high 18o and 13c values in peten itza interrupted by an intervening period of lower 18o and 13c and clay deposition centered on 17 cal ka bp the two periods of inferred maximum cold and or arid conditions at 17 5 and 16 1 cal ka bp coincide approximately with two pulses of ice rafted debris ird recorded off southern portugal bard et al 2000 at 15 cal ka bp coinciding with the start of the bolling allerod period 18o and 13c decrease and gypsum precipitation ceases indicating a transition to warmer and or wetter conditions gypsum precipitation resumed while 18o and 13c increased at the start of the younger dryas at 13 1 cal ka bp and continued until 10 4 cal ka bp near the onset of the holocene precipitation changes during the last glacial period in the northern hemisphere neotropics were closely linked with freshwater forcing to the high latitude north atlantic and sensitive to changes in the location of meltwater input climate was coldest driest when meltwater directly entered the high latitude north atlantic permitting sea ice expansion and weakening of atlantic meridional overturning circulation amoc which resulted in a more southerly position of the intertropical convergence zone itcz upon deglaciation when meltwater was directed to the gulf of mexico at 17 ka and during the bolling allerod period 15 13 ka precipitation increased in the northern hemisphere neotropics as north atlantic sea ice retreated and the itcz shifted northward results from lake peten itza offer some support for the meltwater routing hypothesis of clark et al 2001

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

calibration and application of the clumped isotope thermometer to foraminifera for high resolution climate reconstructions the reconstruction of past ocean temperatures is fundamental to the study of past climate changes therefore considerable effort has been invested in developing proxies for seawater temperatures one of the most recent and promising new proxy is carbonate clumped isotope thermometry in particular because it is based on thermodynamic equilibrium and not on biogeochemical proxies here we present a new calibration of the clumped isotope thermometer to foraminifera based on seven species of planktic and benthic foraminifera spanning a growth temperature range of 2 28 c we used a newly developed technique for the measurements of small samples to improve the applicability of this method to paleoceanography our data have a comparable precision 0 005 0 013 and confirm previous calibration studies based on biogenic and inorganic calcite we discuss possible sources of uncertainty such as over underestimation of the calcification temperatures species specific vital effects ph variations between the seawater and the vacuole water of the species and possible kinetic effects on the clumped isotope calibration to validate our calibration study and test the applicability of our measuring technique to paleoclimate and paleoceanographic studies we measured the isotope composition of globigerinoides ruber white at high resolution in a sediment core covering the last 700 years in the gulf of taranto mediterranean sea the results show that it is necessary to average a relatively large number of analyses to achieve a consistent temperature signal for the detection of small sea surface temperature changes although with the current analytical system clumped isotope thermometry is only applicable to the analysis of relatively large sst changes in marine sediments further technical improvements may make this a very powerful technique for paleoceanographic studies

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

late quaternary glaciation and equilibrium line altitudes of the mayan ice cap guatemala central america abstract the sierra los cuchumatanes 3837 m guatemala supported a plateau ice cap and valley glaciers around montana san juan 3784 m that totaled 43 km 2 in area during the last local glacial maximum former ice limits are defined by sharp crested lateral and terminal moraines that extend to elevations of 3450 m along the ice cap margin and to ca 3000 3300 m for the valley glaciers equilibrium line altitudes elas estimated using the area altitude balance ratio method for the maximum late quaternary glaciation reached as low as 3470 m for the valley glaciers and 3670 m for the mayan ice cap relative to the modern altitude of the 0 c isotherm of 4840 m we determined ela depressions of 1110 1436 m if interpreted in terms of a depression of the freezing level during maximal glaciation along the modern lapse rate of 5 3 c km 1 this ela indicates tropical highland cooling of 5 9 to 7 6 1 2 c our data support greater glacial highland cooling than at sea level implying a high tropical sensitivity to global climate changes the large magnitude of ela depression in guatemala may have been partially forced by enhanced wetness associated with southward excursions of the boreal winter polar air mass

stable isotope proxy records in tropical terrestrial environments abstract the tropics refers to an area that is loosely equatorial characterized by relatively high temperatures at low altitude comparatively low seasonal contrast in temperatures and generally high or highly seasonal rainfall the stable isotopes of carbon oxygen and hydrogen are increasingly important tools of relevance to understanding trajectories and mechanisms of past environmental change in the tropics in the case of carbon this is because at the broadest level the carbon isotope composition of organic and carbon containing inorganic proxy materials formed in the tropics can be read as being derived from the balance between c3 tree and c4 grass photosynthesis hence providing a relative measure of vegetation type and indirectly climate likewise changes in the oxygen and hydrogen isotope composition of many proxy materials again at the broadest level can be read as indicative of changes in hydrological conditions and or altitude in the past this review provides an entry point into the literature relating to the use of stable isotopes as terrestrial environmental proxies for past environmental change with a focus on the measurement and interpretation of stable isotope data from the wide range of proxy materials preserved in tropical environments

temperature dependence of oxygen and clumped isotope fractionation in carbonates a study of travertines and tufas in the 6 95 c temperature range conventional carbonate water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials in spite of a large number of studies however there are still large uncertainties in both 18o and 47 based temperature calibrations for this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates in this study we analyzed oxygen carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines tufa and cave deposits from natural springs and wells together these samples cover a temperature range from 6 to 95 c travertine samples were collected close to the vents of the springs and from pools and tufa samples were collected from karstic creeks and a cave the majority of our vent and pool travertines and tufa samples show a carbonate water oxygen isotope fractionation comparable to the one of tremaine et al 2011 with some samples showing higher fractionations no significant difference between the calcite water and aragonite water oxygen isotope fractionation could be observed the 47 data from the travertines show a strong relationship with temperature and define the regression 47 0 044 0 005 106 t2 0 205 0 047 the ph of the parent solution mineralogy and precipitation rate do not appear to significantly affect the 47 signature of carbonates compared to the temperature effect and the analytical error the tufa samples and three biogenic calcites show an excellent fit with the travertine calibration indicating that this regression can be used for other carbonates as well this work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6 c to 95 c

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

an 85 ka record of climate change in lowland central america drill cores obtained from lake peten itza peten guatemala contain a 85 kyr record of terrestrial climate from lowland central america that was used to reconstruct hydrologic changes in the northern neotropics during the last glaciation sediments are composed of alternating clay and gypsum reflecting relatively wet and dry climate conditions respectively from 85 to 48 ka sediments were dominated by carbonate clay indicating moist conditions during marine isotope stages mis 5a 4 and early 3 the first gypsum layer was deposited at 48 ka signifying a shift toward drier hydrologic conditions and the onset of wet dry oscillations during the latter part of mis 3 peten climate varied between wetter conditions during interstadials and drier states during stadials the pattern of clay gypsum wet dry oscillations during the latter part of mis 3 48 23 ka closely resembles the temperature records from greenland ice cores and north atlantic marine sediment cores and precipitation proxies from the cariaco basin the most arid periods coincided with heinrich events when cold sea surface temperatures prevailed in the north atlantic meridional overturning circulation was reduced and the intertropical convergence zone itcz was displaced southward a thick clay unit was deposited from 23 to 18 ka suggesting deposition in a deep lake and pollen accumulated during the same period indicates vegetation consisted of a temperate pine oak forest this finding contradicts previous inferences that climate was arid during the last glacial maximum lgm chronozone 21 2 ka at 18 ka peten climate switched from moist to arid conditions and remained dry from 18 to 14 7 ka during the early deglaciation moister conditions prevailed during the warmer bolling allerod 14 7 12 8 ka with the exception of a brief return to dry conditions at 13 8 ka that coincides with the older dryas and meltwater pulse 1a the onset of the younger dryas at 12 8 ka marked the return of gypsum and hence dry conditions the lake continued to precipitate gypsum until 10 3 ka when rainfall increased markedly in the early holocene

similarities and dissimilarities between the last two deglaciations and interglaciations in the north atlantic region abstract sea surface temperatures ssts recorded by alkenones and oxygen isotopes in the alboran basin are used here to describe at an unprecedented fine temporal resolution the present interglaciation pig initiated at 11 7 ka bp the last interglaciation lig onset approximately at 129 ka and respective deglaciations similarities and dissimilarities in the progression of these periods are reviewed in comparison with ice cores and stalagmites cold spells coeval with the heinrich events h described in the north atlantic include multi decadal scale oscillations not previously obvious up to 4 c in less than eight centuries within the stadials associated with h1 and h11 ca 133 ka and 17 ka respectively these abrupt oscillations precede the accumulation of organic rich layers deposited when perihelion moves from alignment with nh spring equinox to the summer solstice a reference for deglaciations events observed during the last deglaciation at 17 ka 14 8 ka and 11 7 ka are reminiscent of events occurred during the penultimate deglaciation at ca 136 ka 132 ka and 129 ka respectively the sst trend during the pig is no more than 2 c from 20 c to 18 c up to 0 2 c ka the trend is steeper during the lig i e up to a 5 c change from the early interglaciation to immediately before the glacial inception from 23 c to 18 c up to 0 4 c ka events are superimposed upon a long term trend towards colder ssts beginning with sst maxima followed by temperate periods until perihelion aligned with the nh autumn equinox before ca 5 3 ka for the pig and 121 ka for the lig a cold spell of around eight centuries at 2 8 ka during the pig was possibly mimicked during the lig at ca 118 ka by a sst fall of around 1 c in a millennium these events led interglacial sst to stabilise at around 18 c the glacial inception barely evident at the beginning ca 115 ka north atlantic event c25 after perihelion passage in the nh winter solstice culminated with a sst drop of at least 2 c in two millennia event c24 ca 111 ka the little ice age 0 7 ka also occurred after the latest perihelion passage in the nh winter solstice and could be an example of how a glacial pre inception event following an interglaciation might be

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

links between tropical rainfall and north atlantic climate during the last glacial period the last glacial period was marked by dramatic climate fluctuations sediment records from the cariaco basin and the arabian sea suggest that cooling in the north atlantic region was tightly coupled with a southward displacement of the intertropical convergence zone and a weakening of the indian summer monsoon

late glacial temperature and precipitation changes in the lowland neotropics by tandem measurement of δ18o in biogenic carbonate and gypsum hydration water we applied a new method to reconstruct paleotemperature in the tropics during the last deglaciation by measuring oxygen isotopes of co occurring gypsum hydration water and biogenic carbonate in sediment cores from two lakes on the yucatan peninsula oxygen and hydrogen isotope values of interstitial and gypsum hydration water indicate that the crystallization water preserves the isotopic signal of the lake water and has not undergone post depositional isotopic exchange with sediment pore water the estimated lake water 18o is combined with carbonate 18o to calculate paleotemperature three paired measurements of 1200 yr old gypsum and gastropod aragonite from lake chichancanab mexico yielded a mean temperature of 26 c range 23 29 5 c which is consistent with the mean and range of mean annual temperatures mat in the region today paired measurements of ostracods gastropods and gypsum hydration water samples were measured in cores from lake peten itza guatemala spanning the late glacial and early holocene period 18 5 10 4 ka the lowest recorded temperatures occurred at the start of heinrich stadial hs 1 at 18 5 ka inferred temperatures from benthic ostracods ranged from 16 to 20 c during hs 1 which is 6 10 c cooler than mat in the region today whereas temperatures derived from shallow water gastropods were generally warmer 20 25 c reflecting epilimnetic temperatures the derived temperatures support previous findings of greater tropical cooling on land in central america during the late glacial than indicated by nearby marine records temperature increased in two steps during the last deglaciation the first occurred during the bolling allerod b a from 14 7 to 13 ka when temperature rose to 20 24 c towards the end of this period the second step occurred at 10 4 ka near the beginning of the holocene when ostracod inferred temperature rose to 26 c reflecting modern hypolimnetic temperature set during winter whereas gastropod derived temperature attained 30 c reflecting modern summer epilimnetic temperature

intra seasonal changes in deformation profiles revealed by borehole studies storglaciaren sweden in 1985 1987 and 1988 we measured deformation of bore holes in the ablation zone of storglaciaren a different hole was used each year deformation profiles were determined for four consecutive time periods between mid july and early september all three holes were in an area where the glacier lies in an overdeepened part of the bed up glacier from a riegel the first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin despite large standard errors variations in the deformation profiles during the melt season are broadly consistent with other data we thus believe that they are real and that they reflect changes in the stress field resulting from changes in drag at the bed a decrease in drag early in the melt season coupled with convergence of the bed contours towards the riegel is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year also noteworthy but perhaps problematical was an abrupt transverse shear of m at a depth of 25 m near the center of the glacier injuly 1985 the shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas