constraints on the core mantle boundary topography from p4kp pcp differential travel times 1 p4kp pcp differential travel times are examined to infer the core mantle boundary cmb topography a total of 362 p4kp pcp times are measured with a measurement error of 0 5 s the travel times are corrected for the earth s hydrostatic ellipticity and mantle heterogeneity using a p wave tomographic model spherical harmonic expansion up to degree 4 is adopted for model parameterization the p wave velocity heterogeneity is then estimated in the lowermost 150 km of the mantle to overcome the problem of underestimation of the velocity perturbation at the base of the mantle in the global 3 d p wave mantle model subsequently the cmb topography is inferred using the residues of the above processes since the odd degree components of the cmb topography are insensitive to the p4kp pcp times only the components of degrees 2 and 4 are solved for the resultant features indicate that the maximum amplitude of the cmb topography does not exceed 2 km with an uncertainty of less than 0 5 km a numerical test confirms that the pattern of degree 4 is more reliable with less amplitude recovery the obtained degree 4 pattern shows an amplitude of less than 1 km and indicates the presence of depressions under the circum pacific the central pacific and south africa

deglacial chronology from county donegal ireland implications for deglaciation of the british irish ice sheet in the north of ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum we constrain the timing of three subsequent events by accelerator mass spectrometry 14 c dating of marine microfaunas from muds at corvish county donegal early and rapid deglaciation of the continental shelf off northwestern ireland occurred before 17 1 k 14 c years bp when marine muds formed in trawbreaga bay ice subsequently readvanced into the bay some time between 15 0 and 14 0 k 14 c years bp and compressed contemporary sea stacks and beach cobbles into a ridge at ballycrampsey early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 c ages between 16 0 and 15 2 k 14 c years bp the deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14 1 k 14 c years bp the early deglaciation in the north at c 17 k 14 c years bp is correlative with deglaciation recorded in the irish sea basin western ireland and northeastern scotland indicating a response of the entire british irish ice sheet to early warming of the north atlantic ocean that resulted in a loss of up to two thirds of its mass subsequent ice sheet readvance between 15 0 and 14 1 k 14 c years bp in the north is part of a widespread response of the british irish ice sheet to heinrich event 1 during the killard point stadial high relative sea levels that accompanied deglaciation at 17 k 14 c years bp and again at 14 1 k 14 c years bp indicate substantial loading and attendant isostatic depression by the british irish ice sheet

a tropical mechanism for northern hemisphere deglaciation 1 we investigate the role of the tropics in the melting and reforming of the laurentide ice sheet on glacial timescales using an atmospheric general circulation model it is found that warming of tropical sea surface temperatures ssts from glacial boundary conditions as observed at the end of glacial periods causes a large increase in summer temperatures centered over the ice sheet forming regions of canada this highlatitude response to tropical change is due to relatively small changes in the circulation of the extratropical atmosphere which lead to changes in the vertical profiles of temperature and moisture in the extratropical atmosphere the maximum perturbation in the summer radiative balance over the laurentide ice sheet 25 w m 2 due to the changes in the local atmospheric water vapor inventory is much larger than that induced by glacial to interglacial changes in atmospheric co2 these changes via an atmospheric bridge between the tropics and extratropics represent a mechanism for deglaciations which is consistent with timing constraints in contrast a cold perturbation to tropical sst for interglacial boundary conditions results in only very small changes in the delivery of water vapor to the laurentide region and therefore almost no cooling over the canadian region this implies that tropical ssts could play a more important role in melting ice sheets in the northern hemisphere than in reforming them possibly providing a mechanism which could help to explain the rapidity of deglaciation relative to glacial inception

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

tropical climate at the last glacial maximum inferred from glacier mass balance modeling model derived equilibrium line altitudes elas of former tropical glaciers support arguments based on other paleoclimate data for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum lgm relative to the present lgm elas were maintained by air temperatures that were 3 5 to 6 6 c lower and precipitation that ranged from 63 wetter in hawaii to 25 drier on mt kenya africa our results imply the need for a 3 c cooling of lgm sea surface temperatures in the western pacific warm pool sensitivity tests suggest that lgm elas could have persisted until 16 000 years before the present in the peruvian andes and on papua new guinea

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

evidence of quaternary glaciation in the dominican republic some implications for caribbean paleoclimatology abstract the existence of glacial geomorphological and sedimentological features in the cordillera central of the dominican republic 3087 m maximum elevation such as cirques aretes glacial channels roches moutonnees moraines and bog filled depressions suggests the existence of former cirque glaciers and a snowline at 2200 2300 m the present day lower periglacial limit defined as the elevation at which average minimum temperature reaches 0 c is at approximately 2800 m the difference between this glacial snowline and that determined in central and south america and mexico is explained as due to the massenerhebung effect at present this effect predicts a lowering of the lower periglacial limit by 1100 1200 m and a former late pleistocene snowline at 2300 2500 m these data suggest that the glacial average temperature gradient in the dominican republic was higher than today possibly greater than 1 c per 100 m elevation further suggesting a drier climate than today

past climate and the role of ocean heat transport model simulations for the cretaceous a series of general circulation model experiments using global environmental and ecological simulation of interactive systems genesis were executed to evaluate the sensitivity of simulated mid cretaceous climate to small perturbations in ocean heat transport three experiments were performed 1 mixed layer ocean with no ocean heat transport zeroq 2 ocean heat transport specified as required for genesis to best match modern observations oneq and 3 doubled ocean heat transport twoq the oneq experiment represents an ocean heat transport which is actually about 15 of the values given by carissimo et al 1985 from modern observations as a sensitivity experiment these model simulations represent a doubling of the role of the ocean however relative to the observations they represent small perturbations to the total poleward heat transport in the model with the exception of the tropics no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport however relatively small increases in ocean heat transport resulted in a number of significant differences between simulations including tropical cooling polar warming weakened equator to pole surface temperature gradients weakened midlatitude jets decreased land sea pressure contrast and decreased midlatitude storminess the experiments indicate that changes in ocean heat transport which are well within the realm of possibility for earth history can have significant climatic impact although ocean heat transport may be a significant factor in explaining cretaceous polar warmth the changes specified in these experiments alone are not sufficient to explain the polar warmth of the cretaceous

quaternary environmental change in equatorial regions with particular reference to vegetation history a bibliography abstract it was thought for a long time that equatorial regions had remained virtually unchanged at least since the tertiary period it is only from the late tertiary that we can talk of the present disposition of land and sea about the equator our teaching has supposed that these regions were the hearth from which general spread to the remainder of the planet s surface by gradual adaptation and speciation this warm humid zone has been seen as a refuge for species unable to maintain temperature ranges in the face of stresses and fluctuations to north and south the diversity of species in rain forest environments was assumed to reflect their essential stability so indeed it may but not in quite the manner supposed originally by ecologists the variety of species present in the various regions of rain forest are greatly different with african exhibiting a relatively poor list compared with south america this as it turns out may well be a function of disturbance during the last 25 years and gathering momentum within the last decade a variety of studies have demonstrated that the concept of equatorial biological stasis is no longer tenable evidence for equatorial environmental changes is derived from theoretical as well as empirical studies regarding the former various attempts have been made to model the earth s atmosphere at different periods of the pleistocene and there is now fairly good agreement about the consequences for equatorial regions of a general global cooling namely a critical drying at lower elevations the empirical evidence is derived on the one hand from stratigraphic studies of peats and lake muds and also the analysis of ocean cores it is also derived from studies of the geographical ranges of plant and animal species

oxygen isotope analyses and deep sea temperature changes implications for rates of oceanic mixing since the first measurements were made more than thirty years ago1 analysis of oxygen isotopes in foraminifera from deep sea sediments has gained widespread use as a palaeoclimatic and stratigraphic indicator isotopes stages are commonly used to define the ice ages2 but controversy still remains regarding the relative contributions of temperature and ice volume change to the down core 18o record for the past decade temperature has commonly been considered a trivial portion of the signal3 recent reports however suggest that as much as one third of the measured 18o variations can be ascribed to cooler glacial maximum temperatures4 5 this interpretation requires mean deep ocean temperatures 0 c through much of late quaternary time here we explore some of the consequences of this hypothesis for the heat budget of the deep sea and conclude that either thermohaline overturn must have been faster than at present or that cooling of the deep ocean at the glacial maximum may have been overestimated

dynamical and observational constraints on tropical pacific sea surface temperatures at the last glacial maximum asynchronously coupled atmosphere and ocean general circulation model simulations are used to examine the consequences of changes in the west east sea surface temperature sst gradient across the equatorial pacific at the last glacial maximum lgm simulations forced by the climap sst for the lgm where the west east sst gradient across the pacific is reduced compared to present produce a reduction in the strength of the trade winds and a decrease in the west east slope of the equatorial thermocline that is incompatible with thermocline depths newly inferred from foraminiferal assemblages stronger than present trade winds and a more realistic simulation of the thermocline slope are produced when eastern pacific ssts are 2 c cooler than western pacific ssts our study highlights the importance of spatial heterogeneity in tropical ssts in determining key features of the glacial climate

ohmic dissipation in the earth s outer core resulting from the free inner core nutation abstract the diurnal tidal forces can excite a normal mode of the earth s core the free inner core nutation ficn which is characterized by a tilt of the rotation axis of the inner core with respect to the rotation axis of the outer core the differential rotation between the inner core and the outer core induces fluid motions in the outer core and gives rise to ohmic dissipation in the presence of the earth s internal magnetic field nutation measurements can reflect such dissipation if it is sufficiently strong and thus can provide insights into the properties and dynamics of the earth s core in this study we perform a set of numerical calculations of the linear perturbations in the outer core induced by the ficn at very low ekman numbers as small as 10 11 our numerical results show that the back reaction of the magnetic field notably alters the structure and length scale of the perturbations induced by the ficn and thus influences the ohmic dissipation resulting from the perturbations when the ekman number is sufficiently small ohmic dissipation tends to be insensitive to the fluid viscosity and to the magnetic diffusivity which allows us to estimate the ohmic dissipation associated with the ficn without relying on an extrapolation in contrast to the results of buffett 2010b the estimated ohmic dissipation based on our numerical calculations is too weak to account for the observed damping of the ficn mode this also implies that nutation measurements cannot provide effective constraints on the strength of the magnetic field inside the earth s outer core

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

the use of land snail shells in paleoenvironmental reconstruction fossil land snail shells constitute a valuable source of paleoenvironmental information for the quaternary they can be dated by a variety of methods including radiocarbon amino acid racemization and epimerization and perhaps also thu and esr the vast majority of paleoenvironmental studies based on land snail shells have examined the faunal composition of fossil assemblages from which a variety of paleoenvironmental characteristics such as biome temperature and moisture conditions have been reconstructed still there are a number of problems involved in using this approach and these are discussed shell morphology has occasionally been used to reconstruct such factors as rainfall and temperature stable isotope studies on quaternary land snails include analysis of 18o values of organic matter in the shells to reconstruct c4 plant distributions from which rainfall amounts can be inferred and analysis of 18o values of shell carbonate from which trends in the oxygen isotope composition of rainfall can be reconstructed stable carbon isotopes of shell carbonate have also been studied but their interpretation is not clear amino acid epimerization analysis dalloisoleucinel isoleucine ratios of land snail shells has been used for estimation of paleotemperatures some potential uses of land snail shells for paleoenvironmental reconstruction include the study of stable isotopes of h and n periodic growth lines and deposits of pedogenic carbonates on the shells

nature of environmental changes in south america at the last glacial maximum abstract a review is given of geomorphological evidence suggesting the nature of environmental changes in south america during the last glaciation maximum lgm the data are from glacial geocryogenic alluvial colluvial and aeolian systems and span 68 of latitude making the most complete land transect of major climatic systems in the southern hemisphere glaciers in the northern and central andes may have reached their maximal extent by 27 000 yr b p reduced precipitation at the lgm caused by lower temperatures and lower atmospheric humidity probably led to slight glacier recession in the tropical andes icefields in the southern andes were most expansive when global temperature and sea level were lowest because pacific westerlies supplied abundant moisture and western outlets advancing across the continental shelf were constrained by sea level low gradient river networks became incised by at least 100 m into narrow channels as global sea level fell by 120 m during the lgm draw down of water tables possibly impacted the forest cover enhancing the drying influence of reduced sea surface temperature and atmospheric humidity as forest and grass covers diminished in extent effecting greater atmospheric cooling because of reduced evapotranspiration and convective condensation colluvial and aeolian processes became more active and widespread almost 25 of the continent is covered with palaeo aeolian features presumed to have been active when airflow was stronger due to steeper atmospheric pressure and temperature gradients at the lgm substantial changes in precipitation totals and incidence and in ground water availability probably eliminated modern type tropical rainforest except in areas currently receiving ca 5000 mm of annual rainfall equivalent changes in vegetation cover spread across much of the guyana and brazilian highlands and throughout the southern temperate regions

late quaternary glaciation in the tropics future research directions abstract glacier snowline depressions in the tropics of 800 1000 m indicate an atmospheric cooling of 5 7 c during the late pleistocene such a temperature depression and the presence of large glaciers in the tropics in the past suggests that on glacial interglacial time scales the tropics have undergone substantial climatic and hydrologic change however uncertainties in the chronology of glaciation the response of glacial mass balance in the tropics to a variety of climate forcings and the relation of proxy records in alpine regions to synoptic tropical paleoclimate limit the full utility of the snowline proxy future research in these three areas will provide information on the phasing of climate change in the tropics in comparison to higher latitude regions and the correspondence of tropical glaciation to large scale changes in precipitation temperature and solar radiation

late pleistocene ice age scenarios based on observational evidence ice age scenarios for the last glacial interglacial cycle based on observations of boyle and keigwin concerning the north atlantic thermohaline circulation and of barnola et al concerning atmospheric co sub 2 variations derived from the vostok ice cores are herein analyzed northern hemisphere continental ice sheets are simulated with an energy balance model ebm that is asynchronously coupled to vertically integrated ice sheets models based on the glen flow law the ebm includes both a realistic land sea distribution and temperature albedo feedback and is driven with orbital variations of effective solar insolation with the addition of atmospheric co sub 2 and ocean heat flux variations but not in their absence a complete collapse is obtained for the eurasian ice sheet but not for the north american ice sheet we therefore suggest that further feedback mechanisms perhaps involving more accurate modeling of the dynamics of the mostly marine based laurentide complex appears necessary to explain termination i 96 refs 12 figs 2 tabs

evidence of the younger dryas in central america abstract three sites provide records that address whether the younger dryas was manifest in central america marine records from barbados and the cariaco basin are discussed as well as possible climatic forcing mechanisms sequences from montane la chonta bog costa rica and lowland lake quexil guatemala record a temperature decline of 1 5 2 5 c dated between 11 070 10 400 14c years bp and ca 12 000 10 300 14c years bp respectively the record from lake la yeguada panama does not include cooling although significant reorganization of local communities occurred during the younger dryas chronozone colder tropical ssts throughout deglaciation contributed to sub regional climatic variation more intense monsoonal activity and cooler air temperatures however the temperature reversals are not associated with the coldest tropical ssts which occurred during meltwater pulses the temperature reversals appear to be a response to extra tropical conditions presumably in the north atlantic which suggests that younger dryas cooling extended as far south as costa rica in panama monsoonal conditions may have blocked cooler temperatures precipitation continued to increase throughout deglaciation due to strong forcing by seasonal solar insolation in central america while desiccation events occurred to the north and south

small changes in the sea surface temperature during the last 20 000 years molecular evidence from the western tropical pacific one of the most controversial problems of glacial paleoclimatology is the conservative change in tropical sea surface temperature sst in contrast with the large high altitude temperature change in the western tropical pacific in this report sst was estimated for the last 20 000 years using alkenones preserved in marine sediments recovered from a site 800 km north of new guinea the uk37 unsaturation degree of long chain alkenones synthesized by planktonic prymnesiophyte algae record suggests that sst decreased at most 1 5 c at the last glacial maximum this small changes in sst of the western tropical pacific is concordant with results previously reported in uk37 studies from the eastern equatorial pacific and the equatorial atlantic the uk37 based sst estimates are in good agreement with the climap results and planktonic foraminifera 18o but much smaller than those ca 5 c obtained from coral sr ca and 18o thermometries and glacial vegetation reconstruction

anthropogenic sulfate and asian dust signals in snow from tien shan northwest china snow samples were collected from a 0 5 m snowpack at glacier no i and near bogda feng eastern tien shan northwest china samples that were melted in the field were analyzed for chloride nitrate sulfate sodium potassium magnesium calcium and microparticles eight samples were returned frozen and were analyzed for the above ions plus ammonium acetate formate methylsulfonate and hydrogen peroxide there was no significant difference in measured major ion concentrations between the melted and frozen samples measured cations in both sets of samples were two to three times greater than measured anions calcium and sodium are the dominant cations while sulfate is the dominant measured anion high ion burdens are associated with dusty layers in the snowpack indicating that dust from the vast arid regions of central asia is the dominant source for major ions in tien shan snow the significant increase in sulfate and decrease in the cation anion ratio in bogda eng snow relative to glacier no i snow suggest that anthropogenic emissions from urtimqi are an important source of sulfate to precipitation downwind from the city

reply to comments by p j webster and n a streten regarding surface circulation of the indian ocean during the last glacial maximum approximately 18 000 ybp

aridity of the mediterranean sea at the last glacial maximum a reinterpretation of the δ18o record paleoclimate data show conflicting evidence for aridity in the mediterranean basin at the last glacial maximum lgm two recent modeling studies of the lgm mediterranean using water balance biome and ocean general circulation models respectively suggest that evaporation over the basin was reduced at the lgm compared with today in apparent conflict with these results is the strongly enhanced 18o signature of the lgm mediterranean surface waters particularly in the eastern basin which has been ascribed to a much higher salinity in an alternative interpretation presented here a box model of the balance between paleoclimate model evaporation and rainfall and paleoceanographic model advective terms shows that the observed lgm 18o signature can be reproduced without the need for an enhanced salinity with advection playing the dominant role in the 18o budget the box model also shows that the 18o data alone are insufficient to determine the type of exchange between the eastern and western basins the results emphasize that regional paleoceanographic water balances should consider all relevant processes and not just the evaporative flux

abrupt changes in early holocene tropical sea surface temperature derived from coral records for many high latitude regions of the globe it is now clear that the transition to modern climate following the last glacial maximum was punctuated by a number of rapid and substantial climate oscillations1 2 in contrast relatively little is known about how the tropics responded to the deglaciation because few high resolution records are available from lower latitudes corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated using either 14c or 230th and because past sea surface temperatures can be recovered from the sr ca ratios in coral skeletons here we use this technique to derive several early holocene sea surface temperature records from a coral drill core recovered from espiritu santo vanuatu in the tropical southwest pacific ocean these records indicate that sea surface temperatures in this region were depressed by as much as 6 5 c below modern values at 10 350 calendar years bp but rose very abruptly during the following 1 500 years this temperature increase lags the post younger dryas increase observed in a coral record from the tropical atlantic ocean3by about 3 000 years an unexpected phase shift that may ultimately shed light on the mechanisms of deglacial climate change

constraints on southern hemisphere tropical climate change during the little ice age and younger dryas based on glacier modeling of the quelccaya ice cap peru 2015 the authors improving the late quaternary paleoclimate record through climate interpretations of low latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past present and future climate change paleotemperature reconstructions at low latitude glaciers are uniquely fruitful because they can provide both site specific information and enhanced understanding of regional scale variations due to the structure of the tropical atmosphere we produce little ice age lia and younger dryas yd paleoclimate reconstructions for the huancane outlet glacier of the quelccaya ice cap qic and low latitude southern hemisphere regional sea surface temperatures ssts using a coupled ice flow and energy balance model we also model the effects of long term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the huancane glacier length we find temperature to be the dominant climate driver of glacier length change also we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record necessitating that these features were formed during past colder climates to constrain our lia reconstruction we incorporate the qic ice core record finding a lia air temperature cooling at the ice cap of between 0 7 c and 1 1 c and 0 4 c and regional ssts cooling of 0 6 c for the yd paleoclimate reconstructions we propose two limits on the precipitation rate since the ice core record does not extend into the pleistocene 1 the precipitation rate scales with the clausius clapeyron relationship upper limit on cooling and 2 the precipitation rate increases by 40 lower limit on cooling which is an increase about twice as great as the regional increases realized in gcm simulations for the period the first limit requires 1 6 c cooling in ice cap air temperatures and 0 9 c cooling in ssts and the second limit requires 1 0 c cooling in ice cap air temperatures and 0 5 c cooling in ssts our temperature reconstructions are in good agreement with the magnitude and trend of gcm simulations that incorporate the forcing mechanisms hypothesized to have caused these climate change events

core mantle boundary topography from short period pcp pkp and pkkp data abstract we use a total of 839 369 pcp pkpab pkpbc pkpdf pkkpab and pkkpbc residual travel times from bull seism soc am 88 1998 722 grouped in 29 837 summary rays to constrain lateral variation in the depth to the core mantle boundary cmb we assumed a homogeneous outer core and the data were corrected for mantle structure and inner core anisotropy inversions of separate data sets yield amplitude variations of up to 5 km for pcp pkpab pkpbc and pkkp and 13 km for pkpdf this is larger than the cmb undulations inferred in geodetic studies and moreover the pcp results are not readily consistent with the inferences from pkp and pkkp although the source receiver ambiguity for the core refracted phases can explain some of it this discrepancy suggest that the travel time residuals cannot be explained by topography alone the wavespeed perturbations in the tomographic model used for the mantle corrections might be too small to fully account for the trade off between volumetric heterogeneity and cmb topography in a second experiment we therefore re applied corrections for mantle structure outside a basal 290 km thick layer and inverted all data jointly for both cmb topography and volumetric heterogeneity within this layer the resultant cmb model can explain pcp pkp and pkkp residuals and has approximately 0 2 km excess core ellipticity which is in good agreement with inferences from free core nutation observations joint inversion yields a peak to peak amplitude of cmb topography of about 3 km and the inversion yields velocity variations of 5 in the basal layer the latter suggests a strong trade off between topography and volumetric heterogeneity but uncertainty analyses suggest that the variation in core radius can be resolved the spherical averages of all inverted topographic models suggest that the data are best fit if the actual cmb radius is 1 5 km less than in the earth reference model used i e the average outer core radius would be 3478 km

comparison of foraminiferal coccolithophorid and radiolarian paleotemperature equations assemblage coherency and estimate concordancy the imbrie kipp method of paleotemperature estimation is rigorously tested by comparing atlantic temperature equations independently derived from the microfossils of three biotic groups the foraminifera coccolithophorida and radiolaria this method consists of two steps factor analysis of the modern sea bed data of the individual groups which resolves discrete biogeographic assemblages and regression analysis of the modern assemblage data with observed sea surface temperature data to obtain paleotemperature equations assemblage biogeography shows a simple subdivision into warm low latitude and cold high latitude for all biotic groups between biotic groups there is greater similarity among high latitude assemblages than low latitude ones correlating the assemblage data with observed sea surface temperatures to produce temperature distribution patterns shows differences of less than 2 c in their optimum and critical temperatures regression analysis produced accurate temperature equations for each biotic group all with standard errors of estimate of less than or equal to 2 c multiple correlation coefficients were all greater than 0 970 applying these equations to two multiple biotic data sets the modern and ice age sea bed data and comparing their temperature estimates using the standard error pooled shows over 87 concordancy for both data sets unlike the modern data the discordancy among temperature estimates of the ice age data shows a distinct geographic distribution its cause is believed to be oceanographic a difference in the water mass structure between the modern and ice age ocean

planktonic foraminiferal assemblages preserved in surface sediments correspond to multiple environment variables abstract here we investigate the relationships between modern planktonic foraminiferal species assemblages from atlantic and pacific core top sediment samples and 35 water column and preservation properties using canonical correspondence analysis cca cca finds two faunal dimensions axes that are most highly correlated to the environmental variables and describes each axis in terms of the best linear combination of environmental variables cca axis 1 30 4 of the faunal variance is related primarily to mean annual sea surface temperature sst r 0 96 cca axis 2 7 9 of the faunal variance is related to environmental variability associated with an inverse relationship between sst and surface salinity as well as pycnocline phosphate concentrations the seasonal range in nitrate concentrations water depth and chlorophyll concentrations at the sea surface based on this clustering of nutrient and chlorophyll on axis 2 we infer an ecological response to oceanic fertility no evidence is found for a unique dissolution influence suggesting that sea floor carbonate ion concentration cannot be estimated reliably from planktonic foraminiferal assemblages our results support the use of foraminiferal assemblages to estimate mean annual sst

stratification of the top of the core due to chemical interactions with the mantle 1 chemical interactions between the core and the mantle have been proposed as a mechanism to transfer o and si to the core adding light elements to the top of the core creates a stratified layer which grows by chemical diffusion into the underlying convecting region we develop a physical model to describe the evolution of the layer and estimate physical properties to aid in its detection the interface between the stratified layer and the convecting interior is defined by the onset of double diffusive instabilities oscillatory instabilities arise from the interplay of a stable compositional stratification and an unstable thermal stratification due to a superadiabatic heat flow at the core mantle boundary double diffusive convection in the region of neutral stratification establishes the base of the layer and sets the rate of entrainment of excess light element into the interior of the core growth of the layer by diffusion is interrupted by nucleation of the inner core which segregates light elements into the convecting part of the core for calculations using o as the sole light element we find that the base of the stratified layer retreats toward the core mantle boundary as the radius of the inner core increases representative but uncertain model parameters yield a present day layer thickness of 60 to 70 km we also calculate the anomaly in p wave velocity relative to the value for a well mixed core the velocity anomaly decreases almost linearly across the layer with a peak value of 2 at the core mantle boundary this anomaly should be large enough to detect in seismic observations although the sign of the anomaly is opposite to estimates obtained in previous seismic studies we suggest possible explanations for this discrepancy and speculate about the implications for the structure of the earth s interior

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

annual cycles of u ca in coral skeletons and u ca thermometry abstract we have discovered annual variations in the 238 u 40 ca ratio of porites coral skeletons measurements were made using thermal ionization mass spectrometric techniques yielding precisions of 2 2 for 238 u 40 ca and l 2 for 88 sr 40 ca coralline aragonite subsamples weighed 2 mg enabling submillimeter sampling resolution corresponding to monthly temporal resolution the annual nature of the cycles was confirmed by comparison with annual banding observable in x radiographs for two modern and one fossil sample the amplitude of the u ca variation ranges from 6 to 23 well outside of analytical error as annual u ca cycles appear to be a general feature of primary coralline aragonite the preservation of such features will be important in identifying unaltered coral for u series dating studies u ca variations mimic and are in phase with annual variations in 88 sr 40 ca for a given fractional shift in sr ca the fractional shift in u ca is about 6 times larger for the two modern corals 238 u 40 ca is strongly anticorrelated with measured temperature suggesting that 238 u 40 ca has potential as a paleothermometer if temperature is the only significant control on coralline 238 u 40 ca we reach the following conclusions from analyses of fossil samples a vanuatu sample which grew halfway through the last deglaciation gives u ca temperatures 4 to 5 c below modern values u ca thermometry applied to published data for barbados corals indicates that 1 temperature generally correlates with sea level 2 glacial temperatures stages 2 and 4 were 4 to 6 c lower than interglacial temperatures stages 7a 5e and 1 and 3 temperatures rose from glacial to interglacial values early in the last deglaciation thermometry applied to papua new guinea corals indicates that 1 temperatures were 5 to 6 c lower than interglacial temperatures from 13 to 10 ky bp then rose to present values 9 ky bp 2 the temperature depression between 13 and 10 ky bp is consistent with low temperatures observed in vanuatu during the same time interval and 3 the papua new guinea deglacial temperature history differs from that of barbados the results generally support estimates of tropical temperatures obtained from sr ca thermometry and snow line elevation data but disagree with those based on foram transfer functions a thermodynamic model suggests that coralline 238 u 40 ca may also be sensitive to marine carbonate ion concentration raising the possibility that some of the observed glacial interglacial 238 u 40 ca variation may result from glacial interglacial carbonate ion changes however the key experiments that might establish a coralline 238 u 40 ca carbonate ion relationship have yet to be performed

high resolution climate simulation of the last glacial maximum the climate of the last glacial maximum lgm is simulated with a high resolution atmospheric general circulation model the ncar ccm3 at spectral truncation of t170 corresponding to a grid cell size of roughly 75 km the purpose of the study is to assess whether there are significant benefits from the higher resolution simulation compared to the lower resolution simulation associated with the role of topography the lgm simulations were forced with modified climap sea ice distribution and sea surface temperatures sst reduced by 1 c ice sheet topography reduced co2 and 21 000 bp orbital parameters the high resolution model captures modern climate reasonably well in particular the distribution of heavy precipitation in the tropical pacific for the ice age case surface temperature simulated by the high resolution model agrees better with those of proxy estimates than does the low resolution model despite the fact that tropical ssts were only 2 1 c less than the control run there are many lowland tropical land areas 4 6 c colder than present comparison of t170 model results with the best constrained proxy temperature estimates noble gas concentrations in groundwater now yield no significant differences between model and observations there are also significant upland temperature changes in the best resolved tropical mountain belt the andes we provisionally attribute this result in part as resulting from decreased lateral mixing between ocean and land in a model with more model grid cells a longstanding model data discrepancy therefore appears to be resolved without invoking any unusual model physics the response of the asian summer monsoon can also be more clearly linked to local geography in the high resolution model than in the low resolution model this distinction should enable more confident validation of climate proxy data with the high resolution model elsewhere an inferred salinity increase in the subtropical north atlantic may have significant implications for ocean circulation changes during the lgm a large part of the amazon and congo basins are simulated to be substantially drier in the ice age consistent with many but not all paleo data these results suggest that there are considerable benefits derived from high resolution model regarding regional climate responses and that observationalists can now compare their results with models that resolve geography at a resolution comparable to that which the proxy data represent

asynchronous maximum advances of mountain and continental glaciers the last maximum glacier advance in many mountain ranges appears to have predated the last maximum advance of the wisconsinan continental ice sheets 20 000 years b p published evidence from widely spaced localities in north and south america europe asia and hawai i suggests that some mountain glaciers extended farther during one or more stades early in the last glaciation roughly 115 000 30 000 years b p than at its end when low global temperature and high precipitation presumably were most favorable for the growth of glaciers variations in the timing of glacier advances in different mountain ranges suggest that alpine glaciers are dependent on regional climate as well as global conditions their study might provide sensitive tests for theories of global climate change glacial deposits are often used as time markers in neotectonic and geomorphic studies and their ages sometimes are inferred from distant measurements or from proxy histories of global climate change undated geomorphic features such as moraines sharply incised streams and river terraces which commonly have been associated with the last maximum glacier advance 20 000 years b p or last deglaciation 13 000 years b p may actually be older by a factor of 2 to 4 or more conversely deposits assigned to the maximum advances of the penultimate global glaciation 130 000 years b p may actually date from early in the most recent glacial cycle and be younger by a comparable factor rates of faulting or folding estimated from displacements or deformation and the assumed ages of such geomorphic features might be too great or too small by corresponding factors

global calibration of gephyrocapsa coccolith abundance in holocene sediments for paleotemperature assessment 1 a global sea surface temperature calibration based on the relative abundance of different morphotypes within the coccolithophore genus gephyrocapsa in holocene deep sea sediments is presented there is evidence suggesting that absolute sea surface temperature for a given location can be calculated from the relative abundance of gephyrocapsa morphotypes in sediment samples with a standard error comparable to temperature estimates derived from other temperature proxies such as planktic foraminifera transfer functions a total of 110 holocene sediment samples were selected from the pacific indian and atlantic oceans covering a mean sea surface temperature gradient from 13 6 to 29 3 c standard multiple linear regression analyses were applied to this data set linking the relative abundance of gephyrocapsa morphotypes to sea surface temperature the best model revealed an r2 of 0 83 with a standard residual error of 1 78 c for the estimation of mean sea surface temperature this new proxy provides a unique opportunity for the reconstruction of paleotemperatures with a very small amount of sample material due to the minute size of coccoliths permitting examination of thinly laminated sediments e g a pinhead of material from laminated sediments for the reconstruction of annual sea surface temperature variations such fine scale resolution is currently not possible with any other proxy application of this new paleotemperature proxy may allow new paleoenvironmental interpretations in the late quaternary period and discrepancies between the different currently used paleotemperature proxies might be resolved

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

last glacial maximum equilibrium line altitude and paleo temperature reconstructions for the cordillera de merida venezuelan andes abstract the pattern and magnitude of glacier equilibrium line altitude ela lowerings in the tropics during the last glacial maximum lgm are topics of current debate in the northern tropics paleo ela data are particularly limited inhibiting the ability to make regional and large scale paleoclimatic inferences to improve these records nine paleo glaciers in the venezuelan andes were reconstructed based on field observations aerial photographs satellite imagery and high resolution digital topographic data paleo glacier equilibrium line altitudes elas were estimated using the accumulation area ratio aar and the area altitude balance ratio aabr methods during the local lgm in venezuela 22 750 to 19 960 cal yr bp elas were 850 to 1420 m lower than present local lgm temperatures were are at least 8 8 2 c cooler than today based on a combined energy and mass balance equation to account for an ela lowering this is greater than estimates using an atmospheric lapse rate calculation which yields a value of 6 4 1 c cooler the paleo glacial data from the venezuelan andes support other published records that indicate the northern tropics experienced a greater ela lowering and possibly a greater cooling than the southern hemisphere tropics during the lgm

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

late quaternary palaeoceanography of the western woodlark basin solomon sea and manus basin bismarck sea papua new guinea from planktic foraminifera and radiocarbon dating abstract foraminiferal assemblages and radiocarbon dates from three cores collected in the western woodlark basin and one from the manus basin have provided information on late quaternary sedimentation rates and characteristics of water masses in the western woodlark basin where turbidites and slumps are present sedimentation rates vary from a few tens of cm 1000 year to 140 cm 1000 year with background rates decreasing eastwards from new guinea from 7 cm 1000 year to 3 7 cm 1000 year in the manus basin during the past 16 000 years the sedimentation rate was 15 5 cm 1000 year in the western woodlark basin the lysocline has deepened by at least 900 m over the past 23 500 years it was above 2680 m before 23 500 years ago at 3145 m about 13 000 years ago and is now at 3500 m during the past 30 000 years variations in the mean annual temperatures of surface waters in the western woodlark basin were about 3 c and about 4 5 c in the manus basin there were cool intervals at 19 500 and 13 000 years ago a poorly developed early holocene warm interval 10 000 8500 years ago was followed by a cooler interval with a minimum 8000 years ago the holocene climatic optimum occurred 5000 years ago with temperatures higher than at present

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

investigating the sensitivity of the atmospheric general circulation model echam 3 to paleoclimatic boundary conditions we present atmospheric simulations of three different time slices of the late quaternary using the echam 3 general circulation model in t42 resolution in this work we describe the results of model runs for the time slices 6000 years bp last climate optimum 21 000 bp last glacial maximum and 115 000 years bp glacial inception although the solar insolation is known for all time slices a complete data set of the other boundary conditions which are necessary for running the atmospheric model exists only for the last glacial maximum in the form of the climap reconstruction for the other two time slices which are interglacial states like the modern climate sea surface temperatures land albedo and ice sheet topography are kept at modern values and only the solar insolation is changed appropriately the response of the model to solar insolation changes is quite reasonable the modelled anomalies are small and roughly opposite in sign for 6000 bp and 115 000 bp respectively in the case of last glacial maximum the glacial ice sheet topography and ice albedo produce a much larger climate anomaly in the model however to enable a real test of model performance under glacial boundary conditions the climap sea surface temperatures which are now known to be partly inaccurate should be replaced by an updated state of the art reconstruction

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

late quaternary lake level changes and climates of australia abstract spatial and temporal patterns in lake level data from 38 sites in australia and papua new guinea provide a basis for reconstructing changes in water balance and atmospheric circulation during the past 30 000 years the reconstructions are consistent with hydrological changes inferred from pollen analysis and palaeowind directions inferred from dunes generally wetter conditions between 30 000 and 24 000 bp are consistent with a strong walker circulation with the sta near its present position general aridity at the glacial maximum until 12 000 bp with higher than present lake levels in the southeastern interior of australia implies that the southern margin of the subtropical anticyclone belt was expanded southward and the southern westerlies were correspondingly displaced this southward shift appears in all gcm simulations of the 18 000 bp climate and may be a result of the increased vigour of the northern hemisphere circulation a northward migration of the belt of high lake levels between 11 000 and 6000 bp suggests that the sta shifted back equatorward to north of its present position relaxation to modern conditions occurred after 6000 bp interrupted by an unexplained dry phase 6000 5000 bp in tasmania and queensland

subdivision of glacial deposits in southeastern peru based on pedogenic development and radiometric ages the cordillera vilcanota and quelccaya ice cap region of southern peru 13 30 14 00 s 70 40 71 25 w contains a detailed record of late quaternary glaciation in the tropical andes quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history secondary iron and clay increase linearly in quelccaya soils and clay accumulates at a linear rate in vilcanota soils which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils in contrast logarithmic rates of iron buildup in soils in the cordillera vilcanota reflect chemical weathering high concentrations of secondary iron in vilcanota tills may mask the role of eolian input to these soils soil age estimates from extrapolation of field and laboratory data suggest that the most extensive late quaternary glaciation occurred 70 000 yr b p this provides one of the first semiquantitative age estimates for maximum ice extent in southern peru and is supported by a minimum limiting age of 41 520 14c yr b p a late glacial readvance culminated 16 650 cal yr b p in the cordillera vilcanota following rapid deglaciation of unknown extent an advance of the quelccaya ice cap occurred between 13 090 and 12 800 cal yr b p which coincides approximately with the onset of the younger dryas cooling in the north atlantic region moraines deposited 394 cal yr b p in the cordillera vilcanota and 300 cal yr b p on the west side of the quelccaya ice cap correlate with little ice age moraines of other regions

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

tropical climatic variation on the pacific slopes of the ecuadorian andes based on a 25 000 year pollen record from deep sea sediment core tri 163 31b marine sediments from 3 37 s 83 58 w yield a well dated pollen record of equatorial andean vegetation moderate development of podocarpus high montane rainforest 34 000 28 000 yr b p and increase of high andean grassland pollen 28 000 16 000 yr b p imply an extended dry cool glacial period following a brief interstade rapid stepwise expansion in coastal and montane forest pollen characterizes the deglacial interval the general correspondence between pollen and oxygen isotope variations in tri 163 31b suggests that tropical climatic variations in the northern andes were basically coherent with northern hemisphere glacier variations

comparing proxies for the reconstruction of lgm sea surface conditions in the northern north atlantic abstract within the frame of the multiproxy approach for the reconstruction of the glacial ocean margo project sea surface conditions of the last glacial maximum lgm 23 19 ka were reconstructed using different proxies which were calibrated to a standardized modern hydrography in the north atlantic the revised lgm margo data set provides a comprehensive coverage including the nordic seas the data set includes reconstruction based on planktonic foraminifer assemblages dinocyst assemblages alkenone coccolithophorid biomarkers and mg ca ratios in planktonic foraminifers several hydrological features of the lgm north atlantic can be identified that are supported by all four proxies they include an extensive perennial sea ice cover along the eastern canadian and greenland margins seasonally ice free central north atlantic and norwegian sea and the winter sea ice limit being located at about 55 n all proxies also suggest significantly colder than modern sea surface conditions in the southeastern part of the north atlantic and a more zonal temperature pattern than at present with a steep sst gradient of the order of 10 c between 40 n and 45 n however in the nordic seas large discrepancies remain well above the level of uncertainty of the sst reconstructions these discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions high interannual interdecadal variability or taphonomic processes affecting some of the proxies the average lgm sst in the nordic seas cannot at present be assessed with confidence however the existing evidence suggests that highly variable sea surface conditions and at least occasional advection of north atlantic waters may have characterised the glacial nordic seas

comparing reconstructed pleistocene equilibrium line altitudes in the tropical andes of central peru glacier equilibrium line altitude ela and the difference between modern and palaeo ela can be interpreted as a proxy for climate change one issue in ela reconstruction is that different methods of ela reconstruction may produce a range of results for the same palaeoglacier when a range of methods is used to reconstruct elas across a region resulting variations may be related to the method rather than the past climate palaeoclimatic interpretation of elas that were reconstructed by different methods may prompt spurious inferences if the ela range is the result of methodological differences rather than climatic variation we address the relationship and degree of variation between methods by comparing terminus to headwall altitude ratio thar accumulation area ratio aar and accumulation area balance ratio aabr methods for palaeoglaciers in four valleys in the tropical andes valleys in the eastern cordillera of the peruvian andes bordering the junin plain 11 s 76 w ca 4100 m a s l are presently ice free but were glaciated repeatedly during the pleistocene we use a combination of 90 m shuttle radar topography mission srtm data 15 m advanced spaceborne thermal emission and reflection radiometer aster data and 1 25 000 topographic maps to reconstruct elas within each of three groups of moraines map based thar and aabr estimates of ela tend to be highest followed by dem derived thar elas with aar reconstructed elas somewhat lower in this region ela estimates for the local last glacial max imum llgm range from ca 4250 to 4570 m a s l with elas of ca 220 to 550 m depending on valley and method used within individual valleys elas for the same palaeoglaciers calculated by different methods vary by 100 m elas of the llgm glaciers and those of the largest glaciers to occupy the junin valleys 65 ka are not markedly different from each other regardless of the method used in their calculation which is largely a reflection of the valley hypsometry in the region our analysis suggests relatively low decreases in temperature during glacial periods in the region ca 2 5 1 c copyright 2005 john wiley sons ltd

full glacial summer temperatures in eastern north america as inferred from wisconsinan vegetational zonation abstract a variety of types of fossil evidence pollen macrofossils and snails document the occurrence of boreal forest species at low latitudes of eastern north america duringthe last full glacial 18 000 yr b p both the northern and southern boundaries of boreal coniferous forest are determined by limiting values of summer warmth knowledge of these limiting factors permits construction of a gradient of wisconsinan summer temperatures the reconstructed temperature departures are 5 12 c for the eastern part of the continent south of the ice with temperature departures of no less than 5 6 c along the gulf coast information regarding occurrence of tundra and depression of treeline in the appalachian mountains provides another estimate of summer temperature depression that is in agreement with these results comparison with proxy data from other parts of the world shows that the degree of temperature depression is of about the same degree as that postulated for the tropics rind and peteet 1985 lui and colinvaux 1985 on the basis of the elevational shifts in vegetational zones and snowline quantitative estimates of past temperatures or temperature departures of the type produced here are valuable because they permit comparison with model simulations of the full glacial climate the depression in summer temperatures indicated is lower than most recent modeling results using climap boundary conditions and adds to suggestions that the reconstructed sea surface temperatures used as boundary conditions in simulations of glacial and holocene climates may be in error

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

empirical ocean tide models estimated from topex poseidon altimetry three empirical ocean tide models are determined from repeat cycles 10 to 78 of the topex poseidon t p altimeter mission the three models investigate the effects of the satellite orbit ephemeris on the ocean tides determined from t p altimetry and the effect of extracting the free core nutation resonance in the definition of the diurnal ocean tide admittance the altimetric data series use the joint gravity model jgm 2 geopotential orbit ephemeris and the preliminary jgm 3 orbit ephemeris computed at the university of texas center for space research the altimetric data from the t p mission are shown to have the precision necessary to estimate the monthly and fortnightly ocean tides in each bin inclusion of existing models of the ocean tides in the polar latitudes not sampled by the altimeter demonstrates the importance of these latitudes on spherical harmonic representations of the ocean tides the ocean tides are first estimated in bins of size 2 834 in longitude by 1 in latitude and then smoothed to 1 by 1 grids within 66 latitude the orthotide response formalism of groves and reynolds 1975 is used to represent the diurnal and semidiurnal ocean tides while a constant admittance is assumed across narrow bandwidths around each of the monthly mm fortnightly mf and termensual mt tidal components comparisons of the t p ocean tide models to tide gauge observations indicate their accuracies to be of the order of 2 3 cm the t p derived ocean tide models remove approximately 20 cm2 more of the t p measured sea surface variance than the cartwright and ray 1991 tide model and show a 19 cm2 and 15 cm2 improvement over the schwiderski 1980a b and cartwright and ray 1991 tide models respectively when compared to tide gauge estimates of the ocean tides

palaeoceanographic change in the northeastern south china sea during the last 15000 years the sedimentary succession of piston core rc26 16 dated by 14 c accelerator mass spectrometry provides a nearly continuous palaeoceanographic record of the northeastern south china sea for the last 15 000 yr planktic foraminiferal assemblages indicate that winter sea surface temperatures ssts rose from 18 c to about 24 c from the last glacial to the holocene a short lived cooling of 1 c in winter temperature centred at about 11 000 14 cy r ago may reflect the younger dryas cooling event in this area summer ssts have remained between 27 c and 29 c throughout the record the temperature difference between summer and winter was about ca 9 c during the last glacial much higher than the holocene value of ca 5 c during the late holocene a short lived cooling event occurred at about 4000 14 cy r ago oxygen and carbon isotopic gradients between surface 0 50 m and subsurface 50 100 m waters were smaller during the last glacial than those in the holocene the fluctuation in the isotopic gradients are caused most likely by changes in upwelling intensity smaller gradients indicate stronger upwelling during the glacial winter monsoon the fauna derived estimates of nutrient content of the surface waters indicate that the upwelling induced higher fertility and biological productivity during the glacial the winter monsoon became weaker during the holocene the carbonate compensation depth and foraminiferal lysocline were shallower during the holocene except for a short lived deepening at about 5000 14 c yr ago a preservation peak of planktic foraminifera and calcium carbonate occurred between 13400 and 12 000 14 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

hydrospheric transports the oxygen isotope record and tropical sea surface temperatures during the last glacial maximum a model is developed to consider explicitly the effect of glacial to holocene changes in transports of fresh and salt water on the distribution of oxygen isotopes in seawater and therefore on the calibration of the foraminiferal 18o paleothermometer the published foraminiferal isotopic record is shown to be consistent with glacial surface temperatures at low latitudes cooler than today by about 4 c in the atlantic and indian oceans and about 2 c in the pacific given glacial transport patterns supported by the geologic record if in addition net vapor transport from the indian and atlantic oceans to the pacific was enhanced significantly during glacial times relative to today the isotopic record would be consistent with a sea surface cooler by up to 5 c throughout the tropics at the last glacial maximum as expected based on proxies for continental surface temperatures

geochemical response to variable streamflow conditions in contaminated and uncontaminated streams 1 seasonal variations in stream inorganic geochemistry are not well documented or understood we sampled two mining impacted and two relatively pristine streams in western montana over a 12 month period collecting samples every 4 weeks with supplemental sampling at least weekly during spring runoff we analyzed all samples for dissolved operationally defined as 0 2 m and total recoverable concentrations generally the trace elements al as cu fe mn and zn did not correlate linearly with streamflow while the major elements e g ca k and mg did suspended sediment total recoverable metals and h followed clockwise hysteresis rotations driven by short term flushing events during the very early stages of spring runoff mining impacted sites had higher concentrations of many trace elements than did relatively pristine sites one of the mining impacted sites exhibited strong geochemical responses to spring rain events in the basin the results underscore the need to sample streams frequently during changing hydrologic and climatic conditions in order to accurately monitor surface water quality and to determine solute and particulate loads both contaminant and noncontaminant

the effects of mantle anelasticity on nutations earth tides and tidal variations in rotation rate summary we model the effects of mantle anelasticity on luni solar nutations on tidal deformation on tidal variations in rotation rate and on the eigenfrequency of the free core nutation our results can be used to invert observations to solve for the anelastic contributions to the shear and bulk moduli of the upper and lower mantle we use specific anelastic models to numerically estimate the effects of anelasticity on these geodetic observables we compare our nutation estimates with observational results among our conclusions 1 mantle anelasticity is likely to be the most important source of damping for the free core nutation 2 present vlbi nutation results are in principle accurate enough to usefully bound anelasticity at diurnal periods but the discrepancy between the vlbi observed nutations and the 1984 iau nutation model cannot be explained by anelasticity and is not yet well enough understood to allow anelasticity to be determined from the data

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

geographical distributions of organic walled dinoflagellate cysts in surficial sediments of the benguela upwelling region and their relationship to upper ocean conditions the organic walled cyst content of 41 surface sediment samples from the south eastern south atlantic ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions in order to obtain insight into which environmental factors influence the distribution of individual cyst species the cyst associations have been compared with oceanographic characteristics of the overlying water masses i e temperature salinity density and stratification gradients the associations and relationships have been established by visual examination of the dataset and the multivariate ordination techniques detrended correspondence analysis and canonical correspondence analysis special attention has been given to the factors of transport and preservation of the cysts five associations have been recognised as being characteristic of 1 areas influenced by coastal upwelling and or river outflow 2 open ocean 3 agulhas current and southern benguela current 4 benguela current and 5 walvis bay shelf break area the factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column nutrient concentration and seasonality variations in sea surface temperatures and salinities have only minor effect on cyst distribution

simulation of the ice age atmosphere january and july means a simulation of the atmospheric state under ice age conditions 18 000 years before present is presented the t21 atmospheric general circulation model agcm originally developed at the european centre for medium range weather forecasts was used for the calculation of six annual cycles results of the near surface climatology 2 m temperature 10 m wind and precipitation averaged over the last five model years are presented the presentation is restricted to january and july means in order to demonstrate the glacial changes in summer and winter the model s response to ice age boundary conditions was quite consistent with paleogeological data on land and with agcm experiments of other studies although the differences between the mean climate states of the model atmosphere under glacial and modern boundary conditions were statistically significant the basic structure of the simulated atmospheric circulation was not altered substantially

the late quaternary vegetational and climatic history of easter island easter island occupies an exceptionally isolated position in the south pacific ocean it is entirely volcanic and is famous for its giant statues late quaternary sediments have been investigated in three craters rano raraku rano aroi and rano kao giving a continuous record over the past 30 ka pollen records indicate that the island was formerly forested palynological and sedimentological evidence suggests a late pleistocene climate slightly cooler and drier than the present deforestation by people occurred mainly between 1200 and 800 yr bp this may have led to an ecological disaster and to the decline of the megalithic civilization the depauperation of the present native flora owes more to human activity than to isolation

chemical stratification at the top of earth s core constraints from observations of nutations abstract dissipation due to tidally driven flow in the earth s liquid core is detected in observations of nutations one source of dissipation is due to electromagnetic core mantle coupling but this mechanism requires a high electrical conductivity on the mantle side of the boundary and a strong radial magnetic field an alternative mechanism is viable in the presence of fluid stratification at the top of the core stratification causes the fluid close to the core mantle boundary to be trapped by the effects of topography further from the boundary the stratified fluid is swept past the mantle with the underlying tidal flow shear in the flow induces electric currents where the fluid is permeated with a radial magnetic field the resulting dissipation is only weakly dependent on the electrical conductivity of the mantle and the required strength of the radial magnetic field can be lowered for a representative calculation we explain the observed dissipation with a radial field of 0 5 mt and a mantle conductivity of 1000 s m provided the buoyancy frequency in the stratified layer is 0 09 s 1 such a strong stratification has recently been proposed on the basis of chemical interactions between the core and the mantle nutation observations support the presence of stratification to the extent that the resulting dissipation mechanism is more compatible with conventional estimates for the radial magnetic field and the mantle conductivity

palaeotemperature estimation methods sensitivity test on two western equatorial pacific cores abstract this study examines three methods of estimating past sea surface temperature sst imbrie and kipp s transfer function method ikm the modern analogue technique mat and the weighted averaging method wam by testing a number of experimental transfer functions on two western equatorial pacific cores rc17 177 and erdc 93p it is shown that sst estimation is sensitive to the number of factors and to the selection of core top samples in the calibration the most plausible result was given by an equation which is calibrated from a restricted region which is sufficiently large to fully cover the potential range of down core sst estimates the mat gave spurious sst estimates probably due to the failure of the dissimilarity coefficient the wam persistently gave lower sst estimates than the ikm because of the averaging effect of the method but the sst time series estimated by the two methods show almost identical fluctuation patterns the tolerance weighting approach in the wam may be inappropriate because tolerances of different species may have different implications all the above methods are affected by the distribution of calibration samples

estimates of sea surface temperature in the coral sea at the last glacial maximum the climap 1981 reconstruction of the coral sea found relatively little cooling 2 c in the low latitudes 10 s but a warming off australia at about 25 s the small low latitude changes are of interest because terrestrial pollen and snowline data from the new guinea highlands imply that surface temperatures may have been 6 to 9 c colder at the last glacial maximum lgm the purpose of this paper is to evaluate these conclusions on the basis of additional core sites new oxygen isotope stratigraphy and new sea surface temperature sst estimates using the modern analog technique mat in the northern coral sea planktonic foraminifer assemblages consist of tropical subtropical species that show little change over the past 20 kyr quantitative estimates of sst using the modern analog technique mat confirm the climap 1981 conclusion that little or no temperature change occurred in this tropical region at the lgm thus reinforcing the conflict with terrestrial evidence in the southern region 25 s two cores indicate that foraminifer faunas became more subtropical at the lgm the mat estimates for the lgm are 3 to 4 c colder than modern producing a steeper thermal gradient in the southern coral sea these data remove the warm sst anomaly along the eastern coast of australia and indicate that during the lgm cool high latitude waters were displaced northward along the coast of australia into the southern coral sea

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation