climate variability in the early pliocene arctic annually resolved evidence from stable isotope values of sub fossil wood ellesmere island canada abstract tree ring analyses have contributed significantly to investigations of past climate stable isotope climate proxies 18o d and 13c values enhance traditional ring width data although poor preservation of ancient wood has tended to limit development of stable isotope proxy records to the holocene and the late pleistocene here we apply stable isotope techniques to wood that represent the remains of mixed coniferous boreal vegetation preserved in early pliocene 4 5 ma deposits at strathcona fiord ellesmere island canada ca 78 n four well preserved tree trunks identified through wood anatomical characteristics as larix larch from this high arctic site provide annually resolved sequences of up to 250 years from which we developed a high resolution record of pliocene climate stable oxygen isotope values in conjunction with ring width measurements were used to derive annually resolved temperature records for this site our ring width and isotope based reconstructions provide an annually resolved record up to 250 years of temperature and indicate growing season jj temperatures 15 8 5 0 c 11 8 5 1 c and mean annual temperatures mat 1 4 4 0 c 18 3 4 1 c warmer than present estimated isotope values of precipitation of 16 3 2 18o and 150 1 8 9 d were calculated from the isotopic values of wood cellulose relative humidity estimated from both 13c and d records ranged from 60 to 80 paleotemperature source water and humidity estimates are comparable to those of a modern boreal forest growing ca 15 20 south of modern ellesmere island

direction of unsaturated flow in a homogeneous and isotropic hillslope 1 the distribution of soil moisture in a homogeneous and isotropic hillslope is a transient variably saturated physical process controlled by rainfall characteristics hillslope geometry and the hydrological properties of the hillslope materials the major driving mechanisms for moisture movement are gravity and gradients in matric potential the latter is solely controlled by gradients of moisture content in a homogeneous and isotropic saturated hillslope absent a gradient in moisture content and under the driving force of gravity with a constant pressure boundary at the slope surface flow is always in the lateral downslope direction under either transient or steady state conditions however under variably saturated conditions both gravity and moisture content gradients drive fluid motion leading to complex flow patterns in general the flow field near the ground surface is variably saturated and transient and the direction of flow could be laterally downslope laterally upslope or vertically downward previous work has suggested that prevailing rainfall conditions are sufficient to completely control these flow regimes this work however shows that under time varying rainfall conditions vertical downslope and upslope lateral flow can concurrently occur at different depths and locations within the hillslope more importantly we show that the state of wetting or drying in a hillslope defines the temporal and spatial regimes of flow and when and where laterally downslope and or laterally upslope flow occurs

the younger dryas termination and north atlantic deep water formation insights from climate model simulations and greenland ice cores results from the gisp2 and grip ice cores show that the termination of the younger dryas yd climate event in greenland was a large and extremely fast climate change a reinitiation of north atlantic deep water formation following a shutdown and its associated winter release of heat to the atmosphere has been suggested as the most likely cause of this climate transition to test this idea two general circulation model experiments using genesis have been completed for yd time 12 000 calendar years ago one with low heat flux in the nordic seas 10 w m deep water shutdown and one with high nordic sea heat flux 300 w m active deep water formation comparison of greenland climate differences between these experiments with the ice core records shows that when deep water is turned on much of the yd termination warming is achieved the increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation which obscures the dominantly wintertime response to the specified forcing the winter storm track shift toward greenland contributes much of the climate change at the yd termination

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

recumbent folding of divide arches in response to unsteady ice divide migration arches in stratigraphic layers directly under a flow divide raymond bumps are predicted by models of steady ice sheet flow and have been observed in several ice domes here we model the evolution of these layers when a formerly stationary divide migrates rapidly to a new position then again becomes stationary leaving the arched layers in a flank position as they are then carried downstream with the flow these abandoned arches can develop into recumbent folds these folds can occur over a wide range of divide migration speeds the shearing flow that produces these recumbent folds also distributes the folded layers over a wide distance downstream from the original divide location if the divide offset is abrupt pre cores or material lines comprising core relative isochrones can be used to quickly identify portions of an abandoned raymond bump that would be overturned at any future ice core site downstream if as appears to be the case in greenland the divide is never stable long enough to produce a mature arch folds of this type would not occur the most likely place to find such folds might be the flank of an ice ridge bounded by unsteady ice streams

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

isotopic composition δ13c δ18o in wood and cellulose of siberian larch trees for early medieval and recent periods 1 we related tree ring width trw and isotopic composition 13c 18o of wood and cellulose from four larch trees larixcajanderi mayr to climate parameters the material was sampled in northeastern yakutia 70 n 148 e for the recent ad 1880 2004 and early medieval ad 900 1000 periods during the recent period june july and august air temperatures were positively correlated with 13c and 18o of wood and cellulose while july precipitation was negatively correlated furthermore the vapor pressure deficit vpd of july and august was significantly correlated with 13c of wood and cellulose but vpd had almost no influence on 18o comparative analyses between mean isotope values for the ad 900 1000 and ad 1880 2004 periods indicate similar ranges of climatic conditions with the exception of the period ad 1950 2004 while isotopic ratios in cellulose are reliably related to climatic variables during some periods those in whole wood showed even stronger relationships strong positive correlations between 18o of cellulose and greenland ice core gisp2 data were detected for the beginning of the medieval period r 0 86 p 0 05 indicating the reliability of isotope signals in tree rings for large scale reconstructions

stability of climate signal in carbon and oxygen isotope records and ring width from scots pine pinus sylvestris l in finland four hundred year long records of carbon and oxygen stable isotope ratios and ring width were measured from scots pine pinus sylvestris l from sites in northern and eastern finland responses of isotope ratios to temperature and precipitation were analysed for the 20th century carbon isotope ratios responded strongly to summer temperature at both sites whereas an influence of precipitation on the record was observed only at the site in eastern finland oxygen isotope ratios were less responsive to climatic variation than carbon at the high frequency level to shed light on the role of the possible divergence problem during last decades the climate responses were studied separately in the first and in the second half of the 20th century the responses to temperature were stable in the north but in eastern finland the significant period of summer occurred earlier during the later half of the century relationships between records were studied during the 400 a period all proxies correlated positively with each other although temporal changes occurred common forcing discovered in northern finland between carbon isotope and ring width records was weaker in the earlier period studied three climate reconstructions were created temperature reconstruction for northern finland and temperature and precipitation reconstructions for eastern finland copyright 2009 john wiley sons ltd

comparison of stable carbon and oxygen isotopes in picea glauca tree rings and sphagnum fuscum moss remains from subarctic canada stable isotope ratios from tree rings and peatland mosses have become important proxies of past climate variations we here compare recent stable carbon and oxygen isotope ratios in cellulose of tr

the southern ocean surface between marine isotope stages 6 and 5d shape and timing of climate changes summer sea surface temperature ssst and sea ice extent obtained at millennial to centennial resolution are presented for seven cores recovered in the atlantic and western indian antarctic zone from termination ii and the last interglacial s s i e marine isotope substage mis 5e the diatom based ssst estimates show that during the late mis 6 intensified export of cold waters from the weddell sea resulted in sssts close to 0 c in the central and eastern atlantic sector due to northward expansion of the winter sea ice edge by 3 5 latitude the sea ice seasonality was reduced such conditions have great potential for efficient year round reduction in air sea gas exchange and glacial co2 draw down the warming at termination ii started at 132 131 ka marked by rapid retreat of the sea ice edge the ssst increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2 5 and 3 5 c in the earliest mis 5e 128 125 ka besides a distinct cold reversal around 129 5 ka the warming was punctuated by short lived temperature rebounds with amplitudes of 1 1 5 c occurring at 200 300 yr frequency thus in the range of the periodicity of solar input increased chaetoceros spp abundance suggests meltwater events as the primary cause of the coolings the ssst optimum characterised by strongly enhanced biogenic sedimentation rates ended at ca 125 ka with the full re establishment of the global conveyor belt and beginning of the northern hemisphere climatic optimum at this time sssts decreased stepwise and stabilised on values slightly warmer than today showing in the following period of mis 5e only low amplitude oscillations during mis 5d a northward expansion of the sea ice field took place but sssts only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the southern ocean did not fall in a true glacial mode the tight correlation between southern ocean ssst and winter sea ice records and vostok atmospheric temperature and co2 records support the idea that the antarctic winter sea ice and southern ocean temperature exert a primary control on the atmospheric ocean co2 exchanges and hence on global climate reduction of the antarctic sea ice field and increase of ssst at the onset of termination ii could have been triggered by precessional changes influencing southern high latitude summer insolation positive feedback mechanisms reduction of surface albedo and release of co2 into the atmosphere and changes in global ocean circulation affected by a collapse or strong reduction in north atlantic deep water nadw production could have induced further reinforcement of the southern ocean warming

sensitivity of a greenland ice sheet model to ice flow and ablation parameters consequences for the evolution through the last climatic cycle sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice two types of experiments are performed steady state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the grip record the experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters deformation and sliding law coefficients geothermal flux and that it is low when the ice flow is fast on the other hand the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate the ice sheet extension shows the opposite sensitivity it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients for colder climates when there is no ablation the ice sheet extension depends on the sea level an interesting result is that the variations with time of the altitude at the ice divide summit do not depend on the parameters we tested the present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry it seems that compared to the parameter set most commonly used higher ablation rate coefficents must be used

ice core evidence of abrupt climate changes ice core records show that climate changes in the past have been large rapid and synchronous over broad areas extending into low latitudes with less variability over historical times these ice core records come from high mountain glaciers and the polar regions including small ice caps and the large ice sheets of greenland and antarctica

methodology for use of isotopic climate forcings in ice sheet models in ice sheet models an internally consistent calculation of climatic temperature forcing from ice core isotopic records requires that corrections be made for an ice core site s elevation changes such corrections can be important for two reasons first elevation change at an ice divide can be large compared to elevation change at the migrating ice margin resulting in erroneous estimates of marginal melt rate second the of precipitation at an ice divide responds less to regional climatic temperature changes than to local temperature changes of the same magnitude that are caused by elevation changes significant elevation change corrections may also be necessary for inferring the relationships used to calculate climatic temperature from a simple methodology incorporating both of these elevational effects is presented here further i recommend that the to temperature conversion relations used in ice sheet models should derive from independently reconstructed temperature and time series rather than from spatial correlations and justify this recommendation based on current understanding of the atmospheric isotopic distillation system

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

geometry distribution and fill of erosional scours in a heterolithic distal lower shoreface sandstone reservoir analogue grassy member blackhawk formation book cliffs utah usa

comparison of stable carbon isotope ratios in the whole wood cellulose and lignin of oak tree rings abstract the stable carbon isotope ratios 13c of whole wood cellulose and acid insoluble lignin from annual latewood increments of quercus robur l from modern and sub fossil wood were measured and their potential use as palaeoenvironmental indicators examined the resulting time series demonstrate a very high degree of coherence with 13c of cellulose isotopically enriched by approximately 3 compared to 13c of lignin the 13c values of all three components are influenced by the climate of july and august modern whole wood retains the strongest climate signal perhaps because its composition is closest to that of leaf sugars in sub fossil wood there is no evidence that differential decay leads to fractionation of carbon within either cellulose or lignin but differential decay can alter the cellulose to lignin ratio

landscape chronology and glacial history in thule northwest greenland abstract constraining past responses of ice sheets to changes in climate enhances our ability to predict future changes in ice extent and sea level here we employ surficial geologic mapping stratigraphic analysis radiocarbon dating of marine mollusks and analysis of cosmogenic 10 be in glacially deposited boulders to make inferences about past ice extents in thule northwest greenland our work shows the existence of two distinct diamict units in the thule area we infer that one diamict was deposited by the main greenland ice sheet while the second was deposited by a subsequent outlet glacier re advance boulders in the two diamicts n 13 and n 15 respectively have similar bimodal distributions of cosmogenic 10 be ages both diamicts have a group of younger 10 be ages as well as a more diffuse group of considerably older 10 be ages 20 30 ka many of the boulders likely contain nuclides inherited from previous periods of exposure suggesting that glacial ice in the thule region has been cold based and non erosive in the past the landscape chronology we develop suggests that deglaciation after the last glacial maximum occurred 10 8 ka and was later followed by a re advance of outlet glaciers possibly in concert with the 9 3 ka or 8 2 ka cold events

orbital forcing and role of the latitudinal insolation temperature gradient orbital forcing of the climate system is clearly shown in the earths record of glacial interglacial cycles but the mechanism underlying this forcing is poorly understood traditional milankovitch theory suggests that these cycles are driven by changes in high latitude summer insolation yet this forcing is dominated by precession and cannot account for the importance of obliquity in the ice age record here we investigate an alternative forcing based on the latitudinal insolation gradient lig which is dominated by both obliquity in summer and precession in winter the insolation gradient acts on the climate system through differential solar heating which creates the earths latitudinal temperature gradient ltg that drives the atmospheric and ocean circulation a new pollen based reconstruction of the ltg during the holocene is used to demonstrate that the ltg may be much more sensitive to changes in the lig than previously thought from this it is shown how lig forcing of the ltg may help explain the propagation of orbital signatures throughout the climate system including the monsoon arctic oscillation and ocean circulation these relationships are validated over the last eemian interglacial which occurred under a different orbital configuration to the holocene we conclude that lig forcing of the ltg explains many criticisms of classic milankovitch theory while being poorly represented in climate models

cool tropical temperatures shift the global δ18o t relationship an explanation for the ice core δ18o borehole thermometry conflict the discrepancy between central greenland borehole temperatures and the isotopic composition of last glacial maximum ice can be explained by a shift in the 5180 t relationship for the hydrological cycle linked to cooler tropical temperatures this concept is illustrated using a simple rayleigh distillation model an estimate for o a 5180 at lgm holocene of 0 37 o oc is determined with a simple graphical technique

delineating hydrological response units by geographical information system analyses for regional hydrological modelling using prms mms in the drainage basin of the river brol germany a modified concept of hydrological response units hrus for regional modelling of river basins using the prms mms model is presented the hrus are delineated by geographical information system gis analysis from physiographic basin properties such as topography soils geology rainfall and land use using a thorough hydrological systems analysis the hrus once classified by gis analysis preserve the three dimensional heterogeneity of the drainage basin the river brol basin a 216km 2 rheinisches schiefergebirge germany was selected to apply the concept in total 23 hrus were delineated and tested with the prms mms model using a 20 year hydrometeorological daily database the hydrological systems analysis revealed that interflow is the dominant flow process through the basin s slopes and the major contribution to groundwater recharge and river runoff this was accounted for by parameterizing the hrus in the model control file to drain their surplus water not used for satisfying the demand of evapotranspiration to a common conceptual subsurface storage this storage was simulated by interflow drainage to the groundwater aquifer in the valley floor which in turn drained to the channel network the prms mms model simulated the observed daily discharge very well and the fit was described by a daily correlation coefficient of r 0 91 the nasim and hspf models using different means to represent the basin s physiographic heterogeneity were applied to the brol basin as well but did not achieve this correlation the hru concept was found to be a reliable method for regional hydrological basin modelling and allows spatial up and downscaling future research on this concept will focus on incorporating the variable precipitation distribution into the classification of hrus and on the hydrodynamic routing of the modelled discharge additionally satellite imagery must be used for classifying land use in macroscale drainage basins

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

reducing uncertainties in δ13c analysis of tree rings pooling milling and cellulose extraction recent developments of on line methods have provided another boost to the determination of stable isotope ratios in organic material along with a significant increase in sample throughput the sample sizes decrease both of which are necessary conditions to acquire long time series from limited wood amounts in view of this new technique we reconsidered the most important factors influencing the measured isotopic signature which are 1 pooling 2 homogeneity and 3 cellulose extraction in most cases pooling i e mixing wood of the same year from different trees can be made in a simple way by mixing the whole wood available because mass weighted and unweighted isotope measurements were the same within the error more attention must be paid in homogenizing the sample theoretical considerations underpinned by experimental results suggest a fineness of 0 15 mm 115 mesh if cellulose is extracted and 0 1 mm 165 mesh for direct wood analysis many of previous studies did not achieve this fineness we find that wood is as good a climate proxy as cellulose this is shown by comparing correlations of wood and corresponding cellulose isotope values with meteorological data which are identical within the uncertainty

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

ch4 and δ18o of o2 records from antarctic and greenland ice a clue for stratigraphic disturbance in the bottom part of the greenland ice core project and the greenland ice sheet project 2 ice cores the suggestion of climatic instability during the last interglacial period eem based on the bottom 10 of the greenland ice core project grip isotopic profile has been questioned because the bottom record from the neighboring greenland ice sheet project 2 gisp2 core 28 km away is strikingly different over the same interval and because records of the 18o of atmospheric o2 from both cores showed unexpected rapid fluctuations here we present detailed methane records from the vostok antarctica grip and gisp2 cores over the relevant intervals the grip and gisp2 data show rapid and large changes in methane concentration which are correlative with variations of the 18o of the ice while the vostok record shows no such variations this discrepancy reinforces the suggestion that the bottom sections of the greenland records are disturbed by combining the methane data with measurements of 18o of o2 in the same samples we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the grip core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation

paired bedrock and boulder 10be concentrations resulting from early holocene ice retreat near jakobshavn isfjord western greenland we measured in situ cosmogenic 10 be in 16 bedrock and 14 boulder samples collected along a 40 km transect outside of and normal to the modern ice margin near sikuijuitsoq fjord in central west

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

on topographic controls of soil hydraulic parameter scaling at hillslope scales 1 most upscaling efforts for soil hydraulic parameters developed thus far have opted to ignore the effect of topography in their derivation of effective parameter values this approach which considers a flat terrain with no lateral flows is reasonable as long as the coarser support dimensions are of the order of a few hundred meters in such a scenario the upscaled characteristics of the parameters are governed predominantly by the texture and structure of the soil in the domain however when upscaling fine scale hydraulic parameter data to much larger extents hillslope scales and beyond topography plays a bigger role and can no longer be ignored efforts to model hydrologic processes and phenomena with particular emphasis on those occurring in the unsaturated zone are conducted at various scales we present here a study to isolate the influence of topographic variations on the effective upscaled soil hydraulic parameters under different hillslope configurations the power averaging operator algorithm was used to aggregate fine scale soil hydraulic parameters to coarser resolutions hydrologic scenarios were simulated using hydrus 3d for four different topographic configurations under different conditions to test the validity of the upscaled soil hydraulic parameters the outputs from the simulations fluxes and soil moisture states were compared across multiple scales for validating the effectiveness of the upscaled soil hydraulic parameters it was found that the power averaging algorithm produced reasonably good estimates of effective soil hydraulic parameters at coarse scales further a probable threshold dimension beyond which the topography dominates the soil hydraulic property variation was analyzed on the basis of only the topography the scaling algorithm was able to capture much of the variation in soil hydraulic parameters required to generate equivalent flows and soil moisture states in a coarsened domain

influence of lateral subsurface flow and connectivity on soil water storage in land surface modeling lateral surface subsurface flow and their connectivity play a significant role in redistributing soil water which has a direct effect on biological chemical and geomorphological processes in the root zone 1 m however most of the land surface models neglect the horizontal exchanges of water at the grid or subgrid scales focusing only on the vertical exchanges of water as one dimensional process to develop better hydrologic understanding and modeling capability in complex landscapes in this study we added connectivity based lateral subsurface flow algorithms in the community land model to demonstrate the impact of lateral flow and connectivity on soil water storage we designed three cases including the following 1 with complex surface topography only 2 with complex surface topography in upper soil layers and soil hydraulic properties with uniform anisotropy and 3 with complex surface topography and soil hydraulic properties with spatially varying anisotropy the connectivity was considered as an indicator for the variation of anisotropy in the case 3 which was created by wetness conditions or geophysical controls e g soil type normalized difference vegetation index and topographic index these cases were tested in two study sites er 5 field and er sub watershed in oklahoma comparing to the field gravimetric and remote sensing soil moisture observations through the analysis of spatial patterns and temporal dynamics of soil moisture predictions from the study cases surface topography was found to be a crucial control in demonstrating the variation of near surface soil moisture but not significantly affected the subsurface flow in deeper soil layers in addition we observed the best performance in case 3 representing that the lateral connectivity can contribute effectively to quantify the anisotropy and redistributing soil water in the root zone hence the approach with connectivity based lateral subsurface flow was able to better characterize the spatially distributed patterns of subsurface flow and improve the simulation of the hydrologic cycle

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

a multi proxy approach for revealing recent climatic changes in the russian altai for the first time we present a multi proxy data set for the russian altai consisting of siberian larch tree ring width trw latewood density mxd 13c and 18o in cellulose chronologies obtained for the period 1779 2007 and cell wall thickness cwt for 1900 2008 all of these parameters agree well between each other in the high frequency variability while the low frequency climate information shows systematic differences the correlation analysis with temperature and precipitation data from the closest weather station and gridded data revealed that annual trw mxd cwt and 13c data contain a strong summer temperature signal while 18o in cellulose represents a mixed summer and winter temperature and precipitation signal the temperature and precipitation reconstructions from the belukha ice core and teletskoe lake sediments were used to investigate the correspondence of different independent proxies low frequency patterns in trw and 13c chronologies are consistent with temperature reconstructions from nearby belukha ice core and teletskoe lake sediments showing a pronounced warming trend in the last century their combination could be used for the regional temperature reconstruction the long term 18o trend agrees with the precipitation reconstruction from the teletskoe lake sediment indicating more humid conditions during the twentieth century therefore these two proxies could be combined for the precipitation reconstruction

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

a tale of two ice sheets the vast laurentide ice sheet once covered the northern reaches of the american continent a combination of geological data and climate simulations suggests that it dwindled faster than has been projected for greenland s ice over the next century

a continuum mixture model of ice stream thermomechanics in the laurentide ice sheet 1 theory we employ a continuum mixture framework to incorporate ice streams in a three dimensional thermomechanical model of the laurentide ice sheet the ice mass is composed of a binary mixture of sheet ice which deforms by viscous creep and stream ice which flows by sliding and or sediment deformation at the bed dynamic and thermal evolutions are solved for each component in the mixture with coupling rules to govern transfer between flow regimes we describe two different transfer mechanisms 1 creep exchange the nourishment of ice streams by viscous creep inflow from the surrounding ice sheet and 2 bed exchange the activation growth and deactivation of ice streams perpetrated by transfers of bed area between flow constituents this paper develops the underlying mixture theory we express the governing equations for mass momentum and energy balance in a form suitable for direct incorporation in existing numerical models of ice thermomechanics a companion paper in this issue explores mixture and ice stream behavior in applications with the laurentide ice sheet

exploration of marine mammal paleogeography in the northern hemisphere over the cenozoic using beta diversity abstract previous studies on fossil marine mammal biogeography have identified several key geographical routes hypothesized to play a prominent role in their dispersal this study aims to assess the degree to which each route plays a role data on fossil marine mammal temporal and geographic distributions were derived from the paleobiology database we used a beta diversity metric the sorensen dice coefficient to measure faunal similarity across ocean basins over the cenozoic faunal similarity was high between the mediterranean and the atlantic but relatively low between the mediterranean and the pacific faunal similarity was observed across both halves of the north pacific for all four groups in this study modern high similarity values between the atlantic and the pacific were not observed in the fossil record and were established in the quaternary the strait of gibraltar is shown to be a pivotal passageway for the dispersal of marine mammals first in the eocene as sirenians and cetaceans leave the tethys sea and again as marine mammals reinvade the mediterranean following the messinian salinity crisis the central american seaway plays only a minor role in marine mammal dispersal modern faunal similarity is the result of recent dispersal events in the quaternary through the arctic ocean

simulating arctic climate warmth and icefield retreat in the last interglaciation in the future arctic warming and the melting of polar glaciers will be considerable but the magnitude of both is uncertain we used a global climate model a dynamic ice sheet model and paleoclimatic data to evaluate northern hemisphere high latitude warming and its impact on arctic icefields during the last interglaciation our simulated climate matches paleoclimatic observations of past warming and the combination of physically based climate and ice sheet modeling with ice core constraints indicate that the greenland ice sheet and other circum arctic ice fields likely contributed 2 2 to 3 4 meters of sea level rise during the last interglaciation

climate signals in δ 13 c of wood lignin methoxyl groups from high elevation larch trees abstract in this study a barely used method to measure 13c values from lignin methoxyl groups 13cmethoxyl of tree rings is applied to high alpine larch trees to test their potential as a climate proxy thirty seven larch trees larix decidua mill were sampled at a tree line site near simplon village in the valais switzerland samples were used to measure tree ring width and from five individuals 13cmethoxyl was determined at annual resolution from 1971 to 2009 and at pentadal resolution from 1747 to 2009 the physiological tree responses to increasing atmospheric co2 concentration since 1850 and the corresponding decrease in 13c suess effect were corrected using a range of published discrimination factors and approaches one of these approaches considers a flexible correction factor which minimizes the residuals with target climate data testing the response of the new 13cmethoxyl proxy to climate revealed significant correlations with june to august temperatures ranging from r 0 56 to 0 75 for annually and from r 0 41 to 0 87 for pentadally resolved data depending on the correction methods tree ring width also shows significant correlations with june to august temperature these results demonstrate the potential of 13cmethoxyl to serve as a summer temperature proxy in high elevation alpine environments

setting a chronology for the basal ice at dye 3 and grip implications for the long term stability of the greenland ice sheet abstract the long term stability of the greenland ice sheet gis is an important issue in our understanding of the climate system limited data suggest that the northern and southern sections extend well back into the pleistocene but most age constraints do not definitively date the ice here we re examine the grip and dye 3 ice cores to provide direct ice core observations as to whether the gis survived previous interglacials known to be warmer 130 ka or longer 430 ka than the present interglacial we present geochemical analyses of the basal ice from dye 3 1991 2035 m and grip 3020 3026 m that characterize and date the ice we analyzed the elemental and isotopic composition of o2 n2 and ar of trapped air in these two cores to assess the origin of trapped gases in silty ice dating of the trapped air was then achieved by measuring the paleoatmospheric 40ar 38ar and the 17o anomaly 17 of o2 the resulting age is a lower limit because the trapped air may be contaminated with crustal radiogenic 40ar the oldest average age of replicates measured at various depths is 970 140 ka for the grip ice core and 400 ka 170 ka for dye 3 17 data from dye 3 also argue strongly that basal ice in this core predates the eemian this confirms that the greenland ice sheet did not completely melt at southern greenland during the last interglacial nor did it completely melt at summit greenland during the unusually long interglacial 430 kyr before present

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

spatial and temporal oxygen isotope trends at the northern tree line in eurasia 1 the oxygen isotope ratio of ice cores and sea sediments is an extremely useful source of information on long term climatic changes a similar approach has been applied to the oxygen isotope ratio of tree rings to enable a pattern based reconstruction of the isotope variations on the continents we present an oxygen isotope map for northern eurasia spanning from norway to siberia that reflects the isotope distribution in the late 19th century and compare it with an equivalent map for the present day situation the average isotope values of 130 trees show a large east to west gradient and are highly correlated with the isotope distribution of precipitation surprisingly the 18o 16o ratio of the wood has been decreasing in the interior of the continent since the late 19th century in contrast to the strong temperature increase recorded by meteorological data from this isotope trend over time a change in the seasonality of precipitation can be inferred

the demise of the last interglacial recorded in isotopically dated speleothems from the alps abstract the transition from interglacial to glacial climate has attracted much attention in paleoclimatic research partly because orbital forcing dictates that such a return to a new ice age is inescapable albeit in the distant future only the detailed series of steps that leads to glacial inceptions remains poorly understood however and studies of past glacial inceptions are often compromised by incomplete records imprecise chronological control and or uncertainties associated with proxy transfer functions here we present results from u th dated speleothems from a cave in the austrian alps entrische kirche cave which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials the alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits we use high resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the last interglacial unprecedented in detail for central europe peak interglacial conditions are characterized by high 18 o values and high growth rates from ca 127 to 124 ka a major drop in 18 o by 3 occurred at ca 118 ka which coincided with cold event c26 in the north atlantic this isotopic shift which occurred at or close to isotopic equilibrium cannot be explained by simple uniform cooling modelling suggests that enhanced seasonality dominated by significant changes in winter precipitation are required to reconcile the isotope data with the fact that calcite deposition continued across the mis 5e d transition i e no cave freezing this period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free eventually speleothem growth terminated at ca 114 ka which is in line with widespread ice rafting in the north atlantic cold event c24 and the onset of fully stadial conditions during mis 5d

twentieth century trends in tree ring stable isotopes δ13c and δ18o of larix sibirica under dry conditions in the forest steppe in siberia 1 tree ring width density and ratio of stable isotopes 13c 12c and 18o 16o in wood and cellulose were determined for larch larix sibirica ledeb growing under water deficit conditions in the forest steppe zone in central siberia 54 24 n 89 57 e for the period 1850 2005 dendroclimatic analysis of the chronologies indicated precipitation to be the most important factor determining indicated parameters precipitation of june is significantly correlated with tree ring width and maximum density r 0 36 and 0 43 p 0 05 respectively relations of 13c and 18o to precipitation are similar but the most important month is july r 0 47 p 0 05 for 13c r 0 29 p 0 05 for 18o further 18o is positively related to the mean temperatures of july r 0 30 p 0 05 carbon and oxygen isotope ratios in wood and cellulose showed strong negative trends for the last 100 years the reason for this decrease could be the observed shift of the beginning of the vegetation period to earlier dates up to 1 week in spring and the increased use of precipitation water stored in the soil from october of the previous year although other explanations cannot be excluded in particular the physiological effect of increasing atmospheric co2 also responsible for lower 13c values thus an earlier start of the vegetation period could lead to tree ring formation during a period with higher water availability resulting in stronger isotopic fractionation and 13c depletion also reflected in a higher earlywood to latewood ratio at the same time highly 18o depleted water from october precipitation of the previous year is absorbed the incorporation of this isotopically lighter water during photosynthesis is reflected in the wood and cellulose of tree rings

paleocurrent direction measurements in a volcanic setting by means of anisotropy of magnetic susceptibility a case study from the lower miocene tepoztlan formation transmexican volcanic belt central mexico sources of ancient volcanic rocks are often unknown if they are either eroded and or covered by younger deposits this problem as well as the provenance of reworked volcaniclastic fluvial and mass flow deposits can be partially solved by the application of anisotropy of the magnetic susceptibility ams for massive and poorly sorted volcaniclastic rocks in particular this may be the only way of finding reliable transport directions and therefore allowing for paleogeographic reconstructions here we present a data set of 428 ams measurements and 249 measurements of sedimentary paleocurrent indicators from the miocene tepoztlan formation at the southern edge of the transmexican volcanic belt central mexico the highest degree of reliability of ams measurements is gained for data from lava samples and the lowest from mass flows sedimentary structures in sandstones and conglomerates such as trough cross stratification asymmetric ripple marks and the shape of scours and channels could be used to calibrate the results from ams data and to prove their reliability ams data on fluvial deposits point to a drainage system with a w e flow direction indicating an outflow of the river system into the ancient gulf of mexico

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

last interglacial arctic warmth confirms polar amplification of climate change the warmest millennia of at least the past 250 000 years occurred during the last interglaciation when global ice volumes were similar to or smaller than today and systematic variations in earth s orbital parameters aligned to produce a strong positive summer insolation anomaly throughout the northern hemisphere the average insolation during the key summer months m j j was ca 11 above present across the northern hemisphere between 130 000 and 127 000 years ago with a slightly greater anomaly 13 over the arctic greater summer insolation early penultimate deglaciation and intensification of the north atlantic drift combined to reduce arctic ocean sea ice allow expansion of boreal forest to the arctic ocean shore across vast regions reduce permafrost and melt almost all glaciers in the northern hemisphere insolation amplified by key boundary condition feedbacks collectively produced last interglacial summer temperature anomalies 4 5 c above present over most arctic lands significantly above the average northern hemisphere anomaly the last interglaciation demonstrates the strength of positive feedbacks on arctic warming and provides a potentially conservative analogue for anticipated future greenhouse warming

estimation of channel sinuosity from paleocurrent data a method using fractal geometry discussion the use of fractals to solve geological problems is an exciting new development in the earth sciences and ghosh 2000 is to be congratulated for his application of fractal geometry to estimate channel sinuosities from paleocurrent data in spite of the skepticism voiced by miall 1996 as to the validity of methods based on paleocurrent dispersal patterns any progress in this field is to be welcomed in fact although the technique proposed by ghosh 2000 represents an entirely new angle to solving the problem the results closely approximate those produced by the method of le roux 1992 as modified in 1994 fig 1 surely the good correlation between two independent techniques that are based purely on theoretical principles must indicate that there is some merit in the paleocurrent approach figure 1 comparison of sinuosity values for different consistency ratios using the methods of le roux 1994 and ghosh 2000 ghosh used a theoretical model considering the shape of a single meander but the method

a convex distribution of vegetation along a stony soil slope due to subsurface flow in the semiarid loess plateau northwest china abstract soil water vegetation interactions have been a research topic for decades landscape patterns can be shaped by soil water availability and in reverse the effects of subsurface flow on the soil water vegetation interactions are relatively less studied than the surface flow especially in the semiarid region this work is focused on how the larch larix principis rupprechtti interacted with soil water and how the convex pattern of the larch was formed along the stony soil slope in the semiarid loess plateau northwest china the soil water balance equation in soil water assessment tool swat was modified to include subsurface flow exchange between two adjacent hydrologic response units hrus the slope was then delineated into adjacent hrus to understand the hydrologic and ecological processes inside the slope the modified swat model on the slope was calibrated and validated by the field data the model was forced by a 55 year meteorological data series to investigate the larch soil water interactions and the formation of the convex distribution pattern over long term it is found that the subsurface flow has shaped the convex distribution of vegetation lai along the slope the subsurface flow occurs due to relatively high permeability of the stony soil and it affects the heterogeneities of soil water availability through the soil water storage capacity the concave spatial pattern of the soil water stress determines the vegetation growth along the slope in this semiarid region these understandings provide new knowledge about the influences of hydrological processes on vegetation distribution patterns along a slope which is useful in vegetation management under similar conditions

the effect of a holocene climatic optimum on the evolution of the greenland ice sheet during the last 10 kyr the holocene climatic optimum was a period 8 5 kyr ago when annual mean surface temperatures in greenland were 2 3 c warmer than present day values however this warming left little imprint on commonly used temperature proxies often used to derive the climate forcing for simulations of the past evolution of the greenland ice sheet in this study we investigate the evolution of the greenland ice sheet through the holocene when forced by different proxy derived temperature histories from ice core records focusing on the effect of sustained higher surface temperatures during the early holocene we find that the ice sheet retreats to a minimum volume of 0 15 1 2 m sea level equivalent smaller than present in the early or mid holocene when forcing an ice sheet model with temperature reconstructions that contain a climatic optimum and that the ice sheet has continued to recover from this minimum up to present day reconstructions without a warm climatic optimum in the early holocene result in smaller ice losses continuing throughout the last 10 kyr for all the simulated ice sheet histories the ice sheet is approaching a steady state at the end of the 20th century

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

modeling precipitation over ice sheets an assessment using greenland the interaction between ice sheets and the rest of the climate system at long time scales is not well understood and studies of the ice ages typically employ simplified parameterizations of the climate forcing on an ice sheet it is important therefore to understand how an ice sheet responds to climate forcing and whether the reduced approaches used in modeling studies are capable of providing robust and realistic answers this work focuses on the accumulation distribution and in particular considers what features of the accumulation pattern are necessary to model the steady state response of an ice sheet we examine the response of a model of the greenland ice sheet to a variety of accumulation distributions both observational datasets and simplified parameterizations the predicted shape of the ice sheet is found to be quite insensitive to changes in the accumulation the model only differs significantly from the observed ice sheet for a spatially uniform accumulation rate and the most important factor for the successful simulation of the ice sheet s shape is that the accumulation decreases with height according to the ability of the atmosphere to hold moisture however the internal ice dynamics strongly reflects the influence of the atmospheric circulation on the accumulation distribution

variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

ice core evidence for extensive melting of the greenland ice sheet in the last interglacial evidence from ice at the bottom of ice cores from the canadian arctic islands and camp century and dye 3 in greenland suggests that the greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka thousand years ago in contrast to earlier interpretations the presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed however the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller ice texture gas content and other evidence also suggest that the basal ice at each drill site is superimposed ice a type of ice typical of the early growth stages of an ice cap or ice sheet if the present day ice masses began their growth during the last interglacial the ice sheet from the earlier illinoian glacial period must have competely or largely melted during the early part of the same interglacial period if such melting did occur the 6 meter higher than present sea level during the sangamon cannot be attributed to disintegration of the west antarctic ice sheet as has been suggested

re evaluation of paleo accumulation parameterization over northern hemisphere ice sheets during the ice age examined with a high resolution agcm and a 3 d ice sheet model

global thermohaline circulation part i sensitivity to atmospheric moisture transport a global ocean general circulation model of idealized geometry combined with an atmospheric model based on observed transports of heat momentum and moisture is used to explore the sensitivity of the global conveyor belt circulation to the surface freshwater fluxes in particular the effects of meridional atmospheric moisture transports the numerical results indicate that the equilibrium strength of the north atlantic deep water nadw formation increases as the global freshwater transports increase however the global deep water formation that is the sum of the nadw and the southern ocean deep water formation rates is relatively insensitive to changes of the freshwater flux perturbations to the meridional moisture transports of each hemisphere identify equatorially asymmetric effects of the freshwater fluxes the results are consistent with box model results that the equilibrium nadw formation is primarily controlled by the magnitude of the southern hemisphere freshwater flux however the results show that the northern hemisphere freshwater flux has a strong impact on the transient behavior of the north atlantic overturning increasing this flux leads to a collapse of the conveyor belt circulation but the collapse is delayed if the southern hemisphere flux also increases the perturbation experiments also illustrate that the rapidity of collapse is affected by random fluctuations in the wind stress field

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

lateral moisture flow beneath a sandy hillslope without an apparent impeding layer part of a small drainage basin on the sevilleta national wildlife refuge about 25 km north of socorro nm was intensively instrumented with soil monitoring equipment to estimate natural ground water recharge soil moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand moisture content data were obtained by the neutron scattering technique and hydraulic head data were obtained using tensiometers in addition tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water the results indicate that there is a strong lateral component to unsaturated flow on a hillslope even in the absence of apparent sublayers of much lower permeability darcian calculations estimate the long term steady deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm the deep soil water flux downward varied by several orders of magnitude during the 17 month period of record

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

annually resolved temperature reconstructions from a late pliocene early pleistocene polar forest on bylot island canada abstract here we use 18o ratios measured in tree rings of crossdated sub fossil wood to reconstruct an annually resolved record of temperature and 18o of meteoric water for an interglacial late pliocene early pleistocene fossil forest found on bylot island nunavut canada our record represents the first crossdated record of pliocene wood mean annual temperatures determined in this study average 3 4 3 8 c which is 11 4 4 4 c warmer than present day bylot island 14 8 2 2 c june july temperatures average 13 5 1 1 c approximately 12 6 1 6 c warmer than present day meteoric water 18o values average 15 5 2 9 2 6 more enriched than present values of precipitation 18o our temperatures are comparable to mid pliocene modeled temperatures for the arctic 3 5 c warmer than present suggesting that interglacial warm periods in the late pliocene early pleistocene may have been as warm as the mid pliocene warm period that both the bylot island forest deposit and the kap kobenhavn deposit represent the remains of northern tree line vegetation that lived during warm interglacial periods within the overall cool plio pleistocene suggests that forest deposits in the arctic capture a snapshot of interglacial conditions during the plio pleistocene rather than the average pliocene climate and may not be suitable records to study pliocene cooling

marine to fluvial transition proterozoic upper rewa sandstone maihar india abstract the proterozoic upper rewa sandstone in central india is generally interpreted as entirely marine a detailed study in maihar madhya pradesh however reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints facies associations differ in stratal geometry and arrangement palaeocurrent direction and pattern as well as in grain size and sorting the fine grained marine association is dominated by tidal sheet deposits with characteristic rhythmic changes in thickness and style of cross stratification and their packages as well as local evidence of current reversals subordinate beach deposits are also present the major palaeocurrent direction is highly consistent and westward the coarse grained often granule rich sandstones of the fluvial association are embodied by four facies correlatable with flow stages and relative bed shear these braided stream deposits are preserved in vertical stacks of tabular sandbodies in response mainly to basin subsidence the palaeocurrent pattern is unimodal and northwestward but its dispersion covers 180 the rocks are poorly sorted and at places incorporate sand clasts although they are virtually mud free and mineralogically mature as in two other associations the medium to fine grained sandstones at the intermediate interval between the marine and fluvial associations are of distinct lensoid geometry they incorporate representatives from the previous two associations as well as translatent strata interdune erg deposits and possibly aeolian cross strata consequently the palaeocurrent pattern is polymodal with a spread over 270 an overall coarsening up trend in the fluvial part and thinning up trend in the tidal part imply progradation in spite of evidence of basin subsidence a high rate of sediment discharge from a perennial river system in a humid climate is suggested

the impact of greenland s deglaciation on the arctic circulation 2 the greenland ice sheet is the largest orographic feature of the arctic mountains of such a scale together with surface heating or cooling anomalies exert a strong influence on the atmospheric circulation of the northern hemisphere the impact of greenland s ice sheet on the atmospheric circulation is of importance due to its position in vicinity to the north atlantic storm tracks the impact of greenland s deglaciation on cyclone tracks has been investigated in a regional numerical weather prediction model

modelled nucleation centres of the pleistocene ice sheets from an ice sheet model with subgrid topographic and glaciologic parameterizations abstract ice sheet inception at the onset of the last glacial epoch ca 115 kyr bp is not well understood to cause the northern hemisphere to descend into ice age conditions internal climate system feedbacks must have acted to amplify relatively low amplitude orbital cooling trends while a number of plausible internal mechanisms have been proposed for this internal amplification the dramatic continental ice sheet expansion that is recorded in the marine sediment record is an enduring mystery global sea level lowering of at least 20 m and as much as 75 m over 10 kyr appears typical of the early stages of glacial inception this rate of ice sheet growth has not been freely captured in either glaciologic or climatic models is it because we do not adequately understand the relevant internal feedbacks or fail to capture them in models is it simply related to technical model limitations e g topographic resolution this paper explores the premise that model resolution poses a critical limitation on simulations of ice sheet nucleation i present a series of ice sheet nucleation simulations in north america and eurasia based on an ice sheet model that includes parameterizations of km scale topographic detail snow ice accumulation and melt and glacier dynamics model climate is based on perturbations to modern observational climatology even with this topographic detail and with simulations long enough to allow ice to advect downslope and spread over the terrain it remains difficult to induce a large scale glacierization in both north america and eurasia severe climate perturbations are required cold temperatures need to be accompanied by substantial increases in precipitation in the north atlantic and polar regions in order to accrue continental ice at the rate demanded by sea level reconstructions the simulations presented here are too simple to separate climate perturbations from internal system feedbacks but with modern precipitation rates a combined climate cooling net positive feedback of more than 8 c is required to establish large scale ice sheets in

high rates of sea level rise during the last interglacial period sea level during the last interglacial stood at least 4 m higher than at present with evidence of short term fluctuations of up to 10 m a new continuous sea level record from the red sea and coral ages suggest that during these fluctuations sea level changes were on the order of 1 6 m per century

determining the channel sinuosity of ancient fluvial systems from paleocurrent data abstract the classification of modern river channels is based primarily on their sinuosity values which can be determined directly from aerial photographs ancient channel systems are seldom sufficiently exposed to allow direct measurement of thalweg and valley lengths but paleocurrent directions can be used to calculate fairly accurate sinuosity values aerial photographs of four modern meander belts were studied to determine the relationship between local current directions within the meander belts and the actual sinuosity of the active river channels a value of 3 2 times the standard deviation gave the best approximation of the operational channel range resulting in a close correspondence between calculated and actual sinuosity values this method can therefore be used to estimate the s nuosity of ancient fluvial systems

early last interglacial greenland ice sheet melting and a sustained period of meridional overturning weakening a model analysis of the uncertainties proxy data suggest that the last interglacial lig 130 116 ka bp climate was characterized by higher temperatures a partially melted greenland ice sheet gis and a changed atlantic meridional overturning circulation amoc notwithstanding the uncertainties in lig palaeoclimatic reconstructions this setting potentially provides an opportunity to evaluate the relation between gis melt and the amoc as simulated by climate models however first we need to assess the extent to which a causal relation between early lig gis melt and the weakened amoc is plausible with a series of transient lig climate simulations with the loveclim earth system model we quantify the importance of the major known uncertainties involved in early lig gis melt scenarios based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early lig gis melting kept the amoc weakened notwithstanding this scenario is at the extreme end of the parameter space assuming that proxy based reconstructions of early lig amoc weakening offer a realistic representation of its past state this indicates that either 1 the amoc weakening was caused by other forcings than early lig gis melt or 2 the early lig amoc was less stable than indicated by our simulations and a small amount of gis melt was sufficient to keep the amoc in the weak state of a bi stable regime we argue that more intensive research is required because of the high potential of the early lig to evaluate model performance in relation to the amoc response to gis melt

oxygen and hydrogen isotopic ratios of water in precipitation beyond paleothermometry paleoclimatologists face a dilemma no sedimentary proxy is a pure recorder of quantitative climate information yet climate modelers and policy makers increasingly seek quantitative comparisons between instrumentally documented possibly anthropogenic climate changes and those produced naturally in the past in the second edition of his influential book bradley 1999 p 6 discussed the calibration of proxy records to learn past climate changes calibration involves using modern climatic records and proxy materials to understand how and to what extent proxy materials are climate dependent it is assumed that the modern relationships observed have operated unchanged throughout the period of interest the principle of uniformitarianism in other words one relates the characteristics of sediment to climate at different places for one time or at a place for short times and then uses that relation plus characteristics of older sediments to estimate the climatic conditions that produced those sedimentary characteristics bradley 1999 then extensively discussed the difficulties in applying this methodology in a complex world with imperfect recorders nonetheless the goal of using calibrated proxies for quantitative as well as qualitative paleoclimatic reconstruction is clear a prominent recent use of calibrated paleoclimatic data is the assessment of whether the probably anthropogenic warming of the latter 20th century moved beyond the band of natural variability of the prevailing climate bradley 2000 combined recent instrumental records with several longer proxy based reconstructions of surface temperature including that of mann et al 1999 based on this composite data set bradley 2000 argued that temperatures in the late 20th century were unique in the context of the entire millennium the proxy records were primarily based on tree ring data but included isotopic and major element geochemistry of corals and occurrence of melt layers and isotopic ratios of water in ice cores however broecker 2001 questioned the basis for the reconstruction of

architecture and origin of an amalgamated fluvial sheet sand lower castlegate formation book cliffs utah abstract amalgamated fluvial sheet sandstones in the stratigraphic record are often interpreted as the deposits of braided rivers alluvial sequence stratigraphic models show these sheet sandstones overlying sequence boundaries and deposited during low rates of base level rise and fall since sequence stratigraphic models rely on the balance between creation destruction of accommodation and sediment supply is the sheet like nature of these units controlled by channel style by aggradation rates tied to base level changes or a combination of both the lower member of the castlegate formation in the book cliffs of eastern utah u s a was selected to answer these questions regarding the origin and architecture of amalgamated sheet sandstones the lower castlegate is 60 m thick and is underlain by a regional sequence boundary delineation of the alluvial architecture utilized a combination of outcrop photography measured sections and paleochannel dimension estimation at two outcrops in the type area architectural components within the outcrops were defined and include 1 basal thalweg fill units 2 inclined sandy or heterolithic barform deposits and 3 overbank siltstone and mudstone thalweg fill units represent deposition in the topographically lowest part of the channel and are preferentially preserved thalweg units exist as single units or as a composite of multiple thalweg units overlying thalweg units inclined barform deposits are in places preserved and genetically linked to an underlying thalweg fill unit bar accretion directions when combined with paleocurrent indicators show that lateral downstream and upstream accretion all occur in the lower castlegate overbank deposits are rarely preserved but where present they typically overlie bar deposits the architectural components stack to form a threefold cyclic hierarchy of 1 channel bar systems 2 12 m thick 2 channel belts 2 16 m thick and 3 stacked channel belt complexes 17 40 m thick complete channel bar systems are rarely preserved and occur locally as a succession of multiple stacked thalweg fill units the lack of barforms within a composite thalweg unit suggests that channel migration is the dominant process controlling preservation within channel bar systems possibly associated with a component of local avulsion channel belts are composed of stacked channel bar systems capped by a barform the barform is preserved due to a regional avulsion moving the active channel to another location within the floodplain isolating it from potential reworking stacked channel belt complexes are characterized by alternations of thalweg dominated and barform dominated channel belts the mechanism responsible for deposition at the stacked channel belt complex scale may be creation destruction of accommodation associated with base level changes paleochannel reconstructions show that channel flow depths using bar and underlying thalweg thickness were up to 7 6 m channel depth estimates utilizing a cross bed set thickness of 26 cm averaged 4 6 7 7 m these values were used to calculate channel widths which were estimated at 143 365 m up to a maximum of approximately 1 km regional paleoflow within the lower castlegate was dominantly southeast directed the architectural components paleochannel characteristics and paleocurrent data suggest the lower castlegate member was deposited in low to intermediate sinuosity rivers influenced by autocyclic processes at smaller scales and allocyclic processes at the larger outcrop scale

estimation of channel sinuosity from paleocurrent data a method using fractal geometry abstract in ancient fluvial deposits exposure limitations seldom allow direct measurement of channel and valley lengths the requisite parameters for determination of channel sinuosity however sinuosity can be indirectly estimated from dispersion of paleocurrent data because it is observed in modern rivers that the migration paths of ripples and dunes usually follow the local orientation of the thalweg a natural channel can be described to be broadly sinuous in plan a magnified view of any small part of it is also sinuous in shape this scale independence of shape can be observed at smaller and yet smaller scales fractal patterns which also have this property are used here to model channel plan form at the scale of bedform migration paths it is assumed that the sinuosity of a fractal pattern represents the channel sinuosity over a single meander wavelength and the orientations of the smallest segments of the patterns are considered to represent the bedform migration directions an attempt has been made in this study to establish a functional relationship between the sinuosity of the patterns and the dispersion consistency ratio of its segment orientations from a number of fractal patterns of different sinuosity values the following relationship is noted ln sinuosity 2 49 0 0475 consistency 0 000234 consistency2 this relationship can be used to estimate from paleocurrent data the sinuosity of short stretches of ancient channels whose sinuosity was steady over time e g bank stabilized non migrating channels published data from a number of modern rivers are used to test the equation and the goodness of fit hypothesis cannot be rejected at 5 level of significance the lateral growth of a meander generally involves a gradual increase in the sinuosity of the thalweg a growing natural meander is modeled by grouping together a number of fractal patterns of different sinuosity values in a group the pattern having the maximum sinuosity value represents the thalweg at the last stage of growth while the rest of the patterns represent the thalwegs at intermediate stages of growth partial removal of earlier deposits by erosion associated with the growth of meander is taken into account by excluding the parts of the fractal patterns that represent the intermediate growth stages and lie outside final meander loop the segment orientations from all the patterns in each group are pooled and compared with the maximum sinuosity value from a number of such groups of different maximum values of sinuosity the relation between the consistency ratio and the maximum sinuosity is found to be ln sinuosity 4 2416 0 0801 consistency 0 0004 consistency2 an empirical test of this equation using data from a single ancient meandering river deposit yields satisfactory results

effects of age and environment on stable carbon isotope ratios in tree rings of riparian populus abstract stable carbon isotopes of riparian tree rings are enabling improved reconstruction of past climate variability but this advance is limited by difficulty distinguishing the effects of tree age from those of climate we investigated relative influence of age and climate trends in genus populus which dominates floodplain forests in europe asia and north america we related precipitation and river flow to annual variation in stable carbon isotope ratio 13c in trees with a broad distribution of ages spanning two hundred years on the floodplain of the lightly regulated little missouri river north dakota usa we examined a total of 845 rings from seven specimens of cottonwood tree populus deltoides w bartram ex marshall ssp monilifera aiton eckenwalder cottonwood 13c decreased from pith to bark in whole wood but this trend was almost completely eliminated in purified cellulose the 13c offset between whole wood and cellulose increased from pith to bark consistent with trends of decreasing cellulose and increasing hemicellulose as a proportion of whole wood while annual ring width was correlated with monthly precipitation from april through june 13c showed strong correlations only in june and july suggesting that these complementary proxies allow resolution of seasonal variation in water availability we conclude that past climate can be reconstructed from 13c of purified cellulose from cottonwood without detrending for tree age

depositional and tectonic setting of the archean moodies group barberton greenstone belt south africa the 3 22 3 10 ga old moodies group uppermost unit of the swaziland supergroup in the barberton greenstone belt bgb is the oldest exposed well preserved quartz rich sedimentary sequence on earth it is preserved in structurally separate blocks in a heavily deformed fold and thrust belt north of the inyoka fault moodies strata reach up to 3700 m in thickness detailed mapping correlation of measured sections and systematic analysis of paleocurrents show that the lower moodies group north of the inyoka fault forms a deepening and fining upward sequence from a basal alluvial conglomerate through braided fluvial tidal and deltaic sandstones to offshore sandy shelf deposits the basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying fig tree group dacitic volcanic rocks shoreline parallel transport and extensive reworking dominate overlying deltaic tidal and marine facies the lithologies and arrangement of moodies group facies sandstone petrology the unconformable relationship between moodies strata and older deformed rocks presence of at least one syndepositional normal fault and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower moodies group was deposited in one or more intramontane basins in an extensional setting thinner moodies sections south of the inyoka fault generally less than 1000 m thick may be correlative with the basal moodies group north of the inyoka fault and were probably deposited in separate basins a northerly derived southward thinning fan delta conglomerate in the upper part of the moodies group in the central bgb overlies lower strata with an angular unconformity this and associated upper moodies conglomerates mark the beginning of basin shortening by south to southeast directed thrust faulting along the northern margin of the bgb and suggest that the upper moodies group was deposited in a foreland basin timing orientation and style of shortening suggest that this deformation eventually incorporated most of the bgb into a major fold and thrust belt

tectonic events reflected by palaeocurrents zircon geochronology and palaeobotany in the sierra baguales of chilean patagonia abstract the sierra baguales situated north of the torres del paine national park in the magallanes region of southern chile shows a well exposed stratigraphic sequence ranging from the late cretaceous to late pliocene which presents a unique opportunity to study the evolution of sedimentological styles and trends palaeoclimate changes and tectonic events during this period the depositional environment changed from a continental slope and shelf during the cenomanian campanian tres pasos formation to deltaic between the campanian maastrichtian dorotea formation and estuarine in the lutetian bartonian man aike formation during the rupelian a continental environment with meandering rivers and overbank marshes was established rio leona formation this area was flooded in the early burdigalian estancia 25 de mayo formation during the patagonian transgression but emerged again during the late burdigalian santa cruz formation measured palaeocurrent directions in this mesozoic cenozoic succession indicate source areas situated between the northeast and east southeast during the late cretaceous east southeast during the middle eocene and southwest during the early oligocene to early miocene this is confirmed by detrital zircon age populations in the different units which can be linked to probable sources of similar ages in these areas the east southeastern provenance is here identified as the antarctic peninsula or its northeastern extension which is postulated to have been attached to fuegian patagonia during the eocene the southwestern and western sources were exhumed during gradual uplift of the southern patagonian andes coinciding with a change from marine to continental conditions in the magallanes austral basin as well as a decrease in mean annual temperature and precipitation indicated by fossil leaves in the rio leona formation the rain shadow to the east of the andes thus started to develop here during the late eocene early oligocene 34 ma long before the quechua phase of andean tectonics 19 18 ma that is generally invoked for its evolution at lower latitudes

regressive depositional architecture on a mesoproterozoic siliciclastic ramp sequence stratigraphic and nd isotopic evidences from bhalukona formation singhora group chhattisgarh supergroup central india abstract a paleo environmental and sequence stratigraphic study of the mesoproterozoic bhalukona formation singhora group central india provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the proterozoic siliciclastic ramp settings under falling and lowstand sea level conditions beside delineation of two diachronous surfaces process based facies analysis identified fourteen facies types that are grouped under five different facies associations paleo environments range among continental fluvial beach foreshore upper shoreface lower shoreface and wave dominated delta front from the paleocurrent measurement within the fluvial channel sandstones and measurement of crest line orientations of wave generated swash bedforms it is inferred that the bhalukona sea had nne ssw shoreline trajectory and the south easterly flowing river system carried sediment on the shoreline from a source in the west northwest such inference though in clear discordance with the earlier proposed south southeastern sediment source for the singhora basin finds support in the shift in e nd t t 1 42 ga values from 3 5 3 3 to 9 3 2 2 indicating change in sediment provenance at the early bhalukona sedimentation history sediments in the bhalukona formation derived from more evolved or older continental crustal sources in comparison to those of the underlying saraipalli formation a tectonic forcing behind the shift in sediment provenance and fall in relative sea level is inferred that established the forced regressive and lowstand shoreline in the singhora basin during the bhalukona time abrupt basin ward shift of facies tract and incision on shelf is exhibited by the occurrence of poorly sorted coarse granular bhalukona fluvial system carrying rip up mud clasts directly above the argillaceous highstand saraipalli shelf with 10 m incision and is inferred as the signal for forced regression and development of type i sequence boundary in low gradient proterozoic ramp settings without shelf slope break we interpret that the bhalukona fluvial system incised the coastal prism developed on the saraipalli highstand coastline the low gradient of the ramp however prompted long distance 15 km regression represented by the offlapped and detached delta front lobe away from the shoreline the slow steady rise in sea level onset of lowstand and establishment of a wave dominated coastline caused reworking of fluvial sediments in the basinal part within the wave base and resulted development of ravinement deposit basin ward the surface grades into correlative conformity with aggradational and weak retrogradational stacking the beach foreshore upper and lower shoreface in order of superposition record the lowstand depositional history the basin scale transgression is witnessed with formation of transgressive surface of erosion tse and establishment of the chuipalli shelf system dominantly beyond storm wave base taking into consideration 23 m preserved shoreface succession 1 m per year eustatic rise consistent with present day rate and average rate of shoreface retreat 0 5 m per year 11 5 km retreat for the bhalukona shoreline is estimated in its lowstand history

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

palaeogeographic reconstruction of sandstones using weighted mean grain size maps with examples from the karoo basin south africa and the sydney basin australia abstract although sandstone grain size maps can be a powerful means of reconstructing ancient depositional environments they have rarely been used in the past in this paper two case studies are presented to illustrate the potential of this technique where other more conventional methods may not be applicable in the first case a braided to anastomosing river system in the triassic molteno formation of the south african karoo basin is examined the weighted mean grain size map clearly portrays the distribution of channels and islands and compares very well with other methods of reconstruction the second case study examines an offshore shoal in the permian nowra sandstone of the sydney basin in australia here the grain size map shows a north northeasterly trend parallel to the orientation of the shoal with a zone of coarsest grains displaced to the east of the shoal crest this probably reflects the location of the breaker zone as grain size is an important factor controlling the porosity and permeability of sediments these maps can provide very useful information when exploring for epigenetic stratabound ore deposits such as uranium or planning production wells for oil and gas

air content along the greenland ice core project core a record of surface climatic parameters and elevation in central greenland we present here measurements of the air content of the ice v performed along the greenland ice core project grip ice core the main features of the long term trends are 1 a decrease of 13 between the last glacial maximum lgm and the earliest part of the holocene and 2 an increase of 8 during the holocene the results are discussed in terms of changes in atmospheric pressure surface elevation and porosity at close off the v record contains a significant signal of past changes of surface elevation in qualitative agreement with ice sheet modeling simulations it suggests a thickening of central greenland during the transition from the lgm to the early holocene and a significant thinning through the holocene period it also stresses the large influence on past v variations of changes in ice porosity which are not explained by the present day spatial relationship with temperature and may reflect changes in other surface climatic parameters like precipitation seasonality or wind stress the potential role of temporal variations of atmospheric pressure patterns is also evaluated air content results in the grip ice older than 110 ka indicate values approximately in the same range as those observed during the last 40 000 years with generally higher air content corresponding to isotopically warmer ice

peregrinations of the greenland ice sheet divide in the last glacial cycle implications for central greenland ice cores abstract the superb quality of the climate chronology archived in the summit greenland ice cores grip gisp2 testifies that the greenland ice sheet divide has been generally stable through the last glacial cycle the ice sheet has experienced a broad range of paleoclimate conditions ice sheet margin configurations and internal dynamical adjustments in glacial interglacial transitions however it is unlikely that the summit region escaped shifts in ice divide position geometry elevation and flow characteristics details of this dynamical history are important to several aspects of ice core studies the magnitudes of pure and simple shearing reconstruction of vertical ice velocity the explicit location of the ice divide and the divide residence time at different locations are all of interest in interpretation of climatic variables and physical properties of ice in the ice cores we apply a three dimensional thermomechanical ice sheet model to examine the evolution of these dynamical variables over the last 160 kyr in central greenland while a high elevation ice dome is present in the summit region throughout the simulation ice divide migrations of up to 150 km are predicted all points in the vicinity of the summit ice cores including the modern divide have been subject to flowline shifts and variable non zero shear deformation during the adjustment from glacial to holocene conditions from ca 10 ka to the present modelled divide peregrinations and strain rate history are consistent with the observed disturbance of deep ice in the grip and gisp2 ice cores which has muddled paleoclimate reconstructions for the last interglacial eemian period in greenland dynamical excursions are also evident north of the modern summit where the ngrip ice core is currently being drilled dahl jensen et al j glaciol 43 1997 300 306 however the prevailing flow direction and deformation regime at the ngrip site are much more stable than those at grip and gisp2 in the simulations combined with the greater depth of ice at this site this lends cautious optimism to the hope that eemian ice at ngrip may contain an intact record of eemian climate

irregular oscillations of the west antarctic ice sheet model simulations of the west antarctic ice sheet suggest that sporadic perhaps chaotic collapse complete mobilization of the ice sheet occurred throughout the past one million years the irregular behaviour is due to the slow equilibration time of the distribution of basal till which lubricates ice sheet motion this nonlinear response means that predictions of future collapse of the ice sheet in response to global warming must take into account its past history and in particular whether the present basal till distribution predisposes the ice sheet towards rapid change

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

sea level highstands over the last 500 000 years evidence from the ironshore formation on grand cayman british west indies abstract the ironshore formation up to 19 m thick in the rogers wreck point area of grand cayman is divided into the unconformity bounded units a b c and d the unconformities are highlighted by caliches and or terra rossa th u dates from aragonitic corals indicate that unit a formed at 400 ka unit b 346 ka unit c 229 ka and unit d 131 ka these ages correlate with the highstands of the last four interglacial periods and probably represent marine isotope stages 5 unit d 7 unit c 9 unit b and 11 unit a the limestones in units a d which have similar biotic and lithologic characteristics represent deposition in shallow water on a narrow coastal shelf unit a has a high faunal diversity and was deposited in open marine conditions whereas units b c and d were deposited in quieter water lagoons that probably had fringing reefs along their sea ward edges although grand cayman is located on the cayman ridge close to an active spreading center and transform fault the island has undergone little or no vertical movement over the last 500 ky available evidence indicates that sea level at the time of deposition of each unit relative to present sea level was unit a 9 0 to 5 5 m unit b 3 0 to 0 5 m unit c 2 5 to 1 1 m and unit d 2 5 to 6 0 m these data are good estimates of eustatic sea level highstands over the last 500 ky