vegetation and climate changes during the last two glacial interglacial cycles in the western mediterranean a new long pollen record from padul southern iberian peninsula abstract a new sediment core from padul padul 15 05 provides a long and continuous sedimentary and paleoenvironmental record of the last 200 kyr here we present a detailed palynological study from this sedimentary sequence with new vegetation and paleoenvironmental data and a climatic interpretation for the last two climatic cycles from the southern iberian peninsula in the western mediterranean region pollen analysis from this core shows orbital scale vegetation oscillations mainly forced by precession and eccentricity pointing into insolation as the principal factor controlling vegetation changes at this latitude the last two glacial interglacial cycles from mis 6 to the present as well as stadial and interstadial phases are well represented and characterized by significant oscillations in mediterranean forest in the area but several differences with respect to other mediterranean long pollen records can be recognized some of these disparities between regions seem to be more related to different precipitation rates linked to the specific geographical features e g strong topographic relief than to latitudinal differences between the sites in addition a lake level reconstruction based on palynological data was developed and compared with the previous reconstruction from this record representing local environmental changes in the padul wetland that seems to be related to precipitation evapotranspiration balance and therefore to changes in regional climate conditions during glacial stadial conditions recorded by maxima in xerophytes the p e increased due to very low evapotranspiration resulting in high lake levels while during warmer interglacial interstadial phases except for the mis 5e mainly represented in this record by maxima in the mediterranean forest water level decreased as a result of high evapotranspiration exceeding precipitation input the comparison of the new padul 15 05 pollen record with the two previous palynological studies from padul shows significant differences mainly due to disagreements in the age control of the sequences this study shows that an accurate age depth model becomes essential when interpreting long paleoenvironmental and paleoclimate records

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

paleoclimatic implications of holocene plant remains from the sierra bacha sonora mexico abstract a total of 93 plant taxa were identified from 11 packrat neotoma sp midden samples from the sierra bacha on the coast of the gulf of california near puerto libertad sonora mexico nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr b p sonoran desertscrub was present on rocky slopes throughout the holocene early holocene assemblages dominated by fouquieria columnaris boojum tree reflect vegetation and climate more like modern baja california with greater winter rainfall and cooler summers middle holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold water upwelling locally inhibits summer precipitation the results are similar to all previous midden reconstructions of early and middle holocene climates in the sonoran desert but contradict general atmospheric circulation model simulations

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

hydrological changes in the mediterranean sea over the last 30 000 years sea surface temperatures were reconstructed over the last 30 000 years from alkenone paleothermometry sst alk and planktonic foraminifera assemblages using the modern analog technique mat sst foram along two cores of the mediterranean sea md84 632 levantine basin and md04 2797 siculo tunisian strait oxygen isotope of planktonic foraminifera g bulloides for core md04 2797 and g ruber for core md84 632 were also determined sst alk in the levantine basin indicate colder values at the last glacial maximum lgm 14 c than earlier established from mat and a cooling amplitude of 6 7 c comparable to the central mediterranean sea climatic events such as the younger dryas yd and heinrich events 1 and 2 h1 and h2 were times of significant cooling in the two cores in the eastern basin values of local seawater oxygen isotope w indicate relatively saltier waters during the lgm and deglaciation than today with increasing w values higher salinity in the eastern basin and decreasing ones lower salinity in the central mediterranean sea during cold stadials the observed alterations of surface water properties t and w in the central and eastern mediterranean at the lgm are consistent with model experiments showing slightly lower evaporation in the mediterranean than today except for the eastern basin

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

quatermalacological analyses for modeling of the upper weichselian palaeoenvironmental changes in the carpathian basin abstract the late pleistocene environmental history of the carpathian basin can be regarded as one of the missing links to our understanding of the last glacial development of europe changes in the radiocarbon dated mollusc faunas of the loess areas along with the palaeogeographic interpretations implied by them seem to underlie the latest results gained from radiocarbon dated pollen analysis of the region changes in the mollusc fauna refer to nine short lived 1000 3000 years cyclical palaeoclimatological alterations which repeatedly transformed the palaeoecological conditions and vegetation in the carpathian basin between 34 and 12 kyr on the basis of malacological data the presence of a major palaeoclimatic trend could be assumed for periods of both warming and cooling in the carpathian basin the mildest july palaeotemperatures were recorded in the sw parts and the coldest ones were recorded in the ne parts of the basin humidity and vegetation cover displayed a large scale mosaic type heterogeneity reflecting the modifying effect of local factors it seem that the upper weichselian environment was mosaic or mosaic like in the carpathian basin and the different plants and animals spread from different ecological spots during periods of climate change when the distribution of the forest grassland ecotone or tundra like habitats changed

postglacial vegetation and climate dynamics in the seymour belize inlet complex central coastal british columbia canada palynological evidence from tiny lake a pollen based study from tiny lake in the seymour belize inlet complex of central coastal british columbia canada permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change open pinus parklands grew at the site during the early lateglacial when the climate was cool and dry but more humid conditions in the later phases of the lateglacial permitted mesophytic conifers to colonise the region early holocene conditions were warmer than present and a successional mosaic oftsugaheterophylla andalnus occurred at tiny lake climate cooling and moistening at 8740 70 14 c a bp initiated the development of closed late successional t heterophylla cupressaceae forests which achieved modern character after 6860 50 14 c a bp when a temperate and very wet climate became established the onset of early holocene climate cooling and moistening at tiny lake may have preceded change at more southern locations including within the seymour belize inlet complex on a meso to synoptic scale this would suggest that an early holocene intensification of the aleutian low pressure system was an important influence on forest dynamics in the seymour belize inlet complex and that the study region was located near the southern extent of immediate influence of this semi permanent air mass copyright 2008 john wiley sons ltd

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

the structure of the southwest monsoon winds over the arabian sea during the late quaternary observations simulations and marine geologic evidence each summer strong southwest winds produced by the asian monsoon blow across the nw arabian sea creating a broad region of upwelling characterized by cool sea surface temperatures and enriched phytoplankton biomass the integrated history of the summer plankton blooms is preserved in the form of distinct plankton fossil assemblages and sediment facies forming a continuous geologic record of wind driven upwelling and thus changes in the sw monsoon winds sediments have been recovered from two regions in the nw arabian sea one located along the oman continental margin and another located approximately 400 km offshore over the late quaternary these two sites record time series of upwelling that are substantially different to understand the source of the differences we examined the relationship between wind stress and upwelling at these sites using historical observations and model simulated wind fields in the coastal region upwelling is directly related to the ekman transport offshore and is thus linearly proportional to the alongshore wind stress farther offshore open ocean upwelling is driven by the positive curl in the wind stress in historical records we found little correlation between stronger winds and increased open ocean upwelling in the region offshore where the sediment cores were recovered the year with the strongest winds was accompanied by weaker wind stress curl and diminished upwelling indicated by warmer sea surface temperatures and decreased phytoplankton pigment content because the region of maximum wind stress curl moved nw that year in atmospheric general circulation model experiments using a range of summer insolation forcing we found large changes in the wind stress curl occur over some areas of the nw arabian sea however the offshore core locations lies outside of the region where changes in the sw monsoon drive large changes in open ocean upwelling in contrast to the coastal sites where upwelling is directly related to the wind stress the offshore sites appear to be located in a region where the wind stress curl does not change much over a large range of summer insolation there is some evidence from both the interannual and model fields that this location is affected more by movements in the position of the low level jet than by changes in the over all strength of the sw monsoon although more data are required to define these patterns these results indicate that the time series of open ocean upwelling observed in the geologic record from offshore sites may differ substantially from the coastal time series

initiation of the australian summer monsoon 14 000 years ago abstract definitive evidence for the onset of monsoon moisture in northern australia following the arid phase of the last glacial maximum has been elusive in large part due to the lack of long continuous sediment records here we report new evidence from two separate drainage basins in the kimberley region of monsoonal northwestern australia at both sites radiocarbon ages on basal biogenic materials in flood deposits indicate stream flow as high or higher than maximum historic levels began about 14 cal ka bp these results suggest that the australian summer monsoon was fully active several millennia earlier than previously expected the early onset of the monsoon and the widespread evidence for diminished monsoon activity in the late holocene cannot be reconciled with primary forcing of the australian monsoon by changes in low latitude summer insolation over australia

postglacial vegetation history of the mackenzie river basin abstract three radiocarbon dated cores from small lakes provide pollen records of postglacial vegetation change in the central mackenzie river basin these data are combined with previously published records to reconstruct vegetation development from central alberta to the mackenzie delta the paleoecological data demonstrate that a continuous corridor of herb and shrub dominated vegetation extended between beringia and the great plains of north america from deglaciaiton until about 10 000 yr b p the initial vegetation was replaced by spruce forests between 10 000 and 8500 yr b p significant vegetation change continued until approximately 500 yr b p when the muskeg dominated landscape typical of the present subarctic was established the initial herb and shrub vegetation was likely a reprise of conditions which existed during earlier pleistocene deglaciations these conditions may have provided a favorable environment for animals adapted to nonforested vegetation and promoted migration southward from beringia and northward from the great plains during the last deglaciation and earlier pleistocene deglaciations the sequence of postglacial vegetation change in the mackenzie basin likely reflects a combination of climatic change edaphic change and plant migration patterns and interactions

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

relative influences of the interdecadal pacific oscillation and enso on the south pacific convergence zone 1 the south pacific convergence zone spcz one of the most extensive features of the global atmospheric circulation is shown to vary its location according to both the polarity of the el nino southern oscillation enso and of the interdecadal pacific oscillation ipo we first demonstrate that the ipo can be regarded as the quasi symmetric pacific wide manifestation of the pacific decadal oscillation that has been described for the north pacific shifts in the position of the spcz related to enso on interannual time scales and to the ipo on decadal time scales appear to be of similar magnitude and are largely linearly independent a station pressure based index of variations in spcz latitude is shown to be significantly related to the polarity of the ipo when enso influences are accounted for movements of this sensitive section of the spcz have occurred in phase with those of the ipo since the 1890s

simulations of the last glacial maximum ice sheet surface climate implications for the interpretation of ice core air content this paper reports on analyses of the surface pressure surface wind and seasonality of temperature and precipitation in the central parts of greenland and antarctica as simulated by different general circulation models gcms for the present and for the last glacial maximum lgm climates these parameters in addition to the mean surface temperature influence the air content of the ice either directly or through their influence on the pore volume to correctly interpret the air content of the ice in terms of past ice sheet elevation changes the variations of these parameters must therefore be known most of the simulations discussed here have been carried out within the framework of the paleoclimate modeling intercomparison project moreover a stretched grid gcm has been used with a high resolution over the ice sheets we show that not taking into account changes of surface pressure at constant altitude between the lgm and today leads to an overestimation of past ice sheet elevation up to 150 m while wind speed changes are too weak to have a significant influence on ice core air content the results concerning changes of the amplitude or phase of the seasonal variations of precipitation and temperature are somewhat ambiguous most but not all of the models suggest an intensification of the seasonal cycle of surface temperatures over central greenland and to a lesser extent over central east antarctica neglecting these changes might lead to an underestimation of past elevation by up to 140 m for the greenland ice sheet but this number is subject to large uncertainties

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

vegetation history and palaeoclimate of the last glacial period at lago grande di monticchio southern italy a high resolution palynological study of a 51 m core from lago grande di monticchio southern italy has provided a palaeonvironmental record for the last glacill a annual lamination based chronology supported by radiometric and tephrochronological dates provides an absolute timescale for this record that spans 76 300 years correlations are established between the pollen stratigraphy the grip ice core 18o record and foraminiferal assemblages from atlantic core v23 81 both dansgaard oeschger and heinrich events are reflected by changes in the pollen stratigraphy revised dates are estimated for heinrich events h1 h6 a quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern italy associated with these and other fluctuations during the last glacial

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

tropical and high latitude forcing of enhanced megadroughts in northern china during the last four terminations abstract understanding the origin and evolutionary history of drought events is of great significance providing critical insight into future hydrological conditions under the changing climate due to the scarcity of drought proxies from northern china the occurrence and underlying mechanisms of the drought events remains enigmatic on longer timescales here we utilize microbial lipid proxies to reconstruct significant drought events over the last four ice age terminations in the southernmost section weinan section of the chinese loess plateau the abundance of archaeal isoprenoid gdgts glycerol dialkyl glycerol tetraethers relative to bacterial branched gdgts measured by ri b and bit indices is diagnostic of enhanced drought conditions the ri b and bit indices are stable and low high throughout most of the loess section spanning the last 350 thousand years but they do exhibit sharp transient peaks valleys during the intervals associated with the four ice age terminations and especially terminations ii and iv these enhanced drought events are non intuitively associated with a significant decrease in the relative abundance of c4 plants inferred by a decrease in the carbon isotope composition of bulk organic matter although the microbial records show some consistency with the weinan grain size profiles indicative of eastern asian winter monsoon variability they also show some apparent difference in fact some features of the microbial records exhibit strong similarities with marine sediment planktonic foraminiferal 13c records from the western pacific warm pool which reflect enso like changes during glacial terminations therefore enhanced droughts immediately before the interglacial warming in northern china could be explained at least in part by teleconnections in tropical ocean atmosphere circulation via shifts in the intertropical convergence zone itcz and associated jet stream over the asian continent according to our microbial biomarker data these enhanced megadroughts are apparently different both in terms of severity and causal mechanism from the more commonly discussed dry conditions observed during glacial periods

cyclic quaternary alluviation and terracing in a nonglaciated drainage basin on the north flank of the qinling shan central china abstract pleistocene alluvial terraces of the nonglaciated ba river drainage basin on the north flank of the qinling shan are capped by a succession of loess units and paleosols that correlate with the standard marine isotope chronology and are used to date the subjacent alluvial gravels alluvial fills were deposited during isotope stages 2 6 8 12 and 16 whereas terracing occurred during interglacial stages 1 5 7 11 and 15 the apparent absence of terraces dating to stage 14 and stage 4 may be due to the lesser intensity of these glaciations compared to that of stage 2 although disruption of the alluvial regime by local tectonism is a likely alternative for the lack of a stage 4 terrace a stage 10 terrace was not positively identified from available exposures its possible absence could be related to post stage 12 uplift aggradational episodes correlate with glaciations and loess deposition whereas degradational episodes correlate with interglaciations or interstades and soil formation implying that climate is the primary control on quaternary paleohydrology this in turn points to variations in the earth s orbital geometry as the major factor that modulates both climate and ultimately the fluvial system in the qinling shan in this region glaciations were dominated by a cold dry winter monsoon climate whereas during interstades and interglaciations a warmer and wetter climate prevailed implying strengthening of the summer monsoon both the loess paleosol and the alluvial records are consistent with climate model simulations spanning the last 18 000 yr that show a change from cold dry conditions during the last glacial maximum to a climate warmer and wetter than present during the first half of the holocene

calibrating grass phytolith assemblages in climatic terms application to late pleistocene assemblages from kansas and nebraska abstract the use of modern phytolith assemblages for the interpretation of fossil phytolith assemblages demonstrates the utility of phytolith analysis in reconstructing grassland vegetation and climate in the great plains of north america the modern data presented are the typical average assemblages for 34 modern localities taken throughout the great plains modern assemblage variability across the region is substantial this variability shows a coherent geographical pattern consistent with modern grassland composition these modern phytolith assemblages are calibrated in terms of modern climate data specifically july mean temperature seven fossil assemblages from three late pleistocene localities in the central great plains are presented two alternative phytolith temperature regression models are applied to these fossil assemblages to estimate paleo temperature resulting estimates are consistent with other efforts to calculate late pleistocene temperature departures in the region ca 8 0 to 7 0 c the fossil data also show rapid change in grassland composition and climate during the pleistocene holocene transition these results demonstrate how phytolith analysis can complement or substitute for pollen analysis in the great plains of north america

orbital forcing of arctic climate mechanisms of climate response and implications for continental glaciation progress in understanding how terrestrial ice volume is linked to earths orbital configuration has been impeded by the cost of simulating climate system processes relevant to glaciation over orbital time scales 10 3 10 5 years a compromise is usually made to rep resent the climate system by models that are averaged over one or more spatial dimensions or by three dimensional models that are limited to simulating par ticular snapshots in time we take advantage of the short equilibration time 310 years of a climate model consisting of a three dimensional atmosphere coupled to a simple slab ocean to derive the equilibrium climate response to accelerated variations in earths orbital configuration over the past 165 000 years prominent decreases in ice melt and increases in snowfall are sim ulated during three time intervals near 26 73 and 117 thousand years ago ka when aphelion was in late spring and obliquity was low there were also significant decreases in ice melt and increases in snowfall near 97 and 142 ka when eccentricity was relatively large aph elion was in late spring and obliquity was high or near its long term mean these glaciation friendly time intervals correspond to prominent and secondary phases of terrestrial ice growth seen within the marine d 18 o record both dynamical and thermal effects contribute to the increases in snowfall during these periods through increases in storm activity and the fraction of precipi tation falling as snow the majority of the mid to high latitude response to orbital forcing is organized by the properties of sea ice through its influence on radiative feedbacks that nearly double the size of the orbital forcing as well as its influence on the seasonal evolution of the latitudinal temperature gradient

soil fertility and slope processes in the western cumberland escarpment of kentucky influences on the development of horticulture in the eastern woodlands the archaeological record of dry rockshelters in the red river valley of eastern kentucky contains botanical remains of several weedy annual seed bearing plants that point to the independent development of agriculture during the late archaic and early woodland period the objective of this study is to gather quantitative data through the chemical and physical analysis of soils collected within a valley transect to gain insights into landscape processes and soil fertility that may have played a role in the early development of plant domestication and the location of garden plots in relation to rock shelter sites in the upper cumberland plateau region of eastern kentucky soils on upland benches formed in limestones have soil fertility values that are comparable to fertile floodplain soils upslope outcrops of calcareous bedrock are contributing basic cations to these bench soils additionally in comparison to other landscape positions these upland soils have high levels of organic carbon available p and greater c n ratios soil morphology radiocarbon dates and archaeological evidence indicate that many of the numerous earthflows and debris flows within the region are early to middle holocene in age these slides were likely generated by mid holocene climatic shifts in which the frequency and intensity of summer precipitation increased across the southeastern united states these slope failures may have contributed to the development of plant domestication by creating forest canopy gaps and disturbed soils in which weedy plants thrived

the late quaternary environmental history of batorliget n e hungary abstract a sedimentary sequence extending back into the last glacial has been obtained from batorliget marsh in n e hungary reconstruction of the environmental history of the region using the techniques of pollen analysis molluscan analysis and geochemistry has revealed an important late quaternary refugium during the last glacial a refugium for temperate flora and fauna existed within a landscape dominated by coniferous forest predominantly made up of pinus and picea the lateglacial postglacial transition at 10 000 yr b p resulted in a dramatic shift from coniferous but also including betula woodland to deciduous woodland following the lateglacial postglacial transition a highly diverse woodland became established in the early postglacial accompanied by an equally diverse molluscan assemblage this diversity remained throughout the early postglacial although the types present within the woodland changed a number of times at c 7000 yr b p anthropogenic disturbance resulted in the destruction of the mixed forest and the development of agricultural land the importance of this region as a refugial area both in the lateglacial and early postglacial is discussed and the influence that it had on the postglacial development of the fauna and flora of northeastern hungary is reviewed

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

variability in upwelling fields in the northwestern indian ocean 2 data model comparison at 9000 years b p theoretical investigations in the form of general circulation model gcm simulations and empirical studies of pollen lake levels and marine sediments suggest that the indian summer monsoon was intensified 9000 years ago at a time of increased summer radiation about 8 in the northern hemisphere the southwesterly summer monsoon winds and their pattern of wind stress curl cause coastal upwelling along the coast of arabia stronger summer winds therefore should intensify coastal upwelling incorporation of the broad scale gcm winds into a high resolution ocean model of the arabian sea produces distinct patterns of stronger upwelling at 9000 years b p to verify these patterns in the geologic record we mapped upwelling assemblages of planktonic foraminifera and estimated sea surface temperature sst to define the magnitude and spatial distribution of monsoonal upwelling at 9000 years b p we found that the upwelling assemblage increased in abundance and the august ssts were several degrees celsius cooler off arabia than present however in the central and eastern arabian sea the tropical assemblage increased and the ssts were warmer than present values the sst gradient across the arabian sea was greater 6 c at 9000 years b p than it is today 4 c these observations are consistent with the model results that show increased divergence upwelling and a thinner upper layer or shallower thermocline in the westernmost arabian sea and increased convergence downwelling and a thicker upper layer in the central and eastern arabian sea in this experiment the use of low resolution winds from a general circulation model ncar ccm in a high resolution ocean model seems to be appropriate for simulating the long term averages observed in the marine sediments

continental drift runoff and weathering feedbacks implications from climate model experiments changes in atmospheric carbon dioxide have been proposed as a major regulator of climate during the last 570 million years continental weathering and its variation over time are hypothesized to be important for controlling atmospheric carbon dioxide continental weathering is altered by changes in total runoff as well as changes in the size and elevation of the land masses to be weathered when paleogeographic information for the phanerozoic 570 m y ago to present is used in a global climate model the model exhibits substantial variations in precipitation evaporation and runoff even with dramatically different land ocean distributions an increase in global surface temperature leads to an increase in global precipitation but not always an increase in global runoff during the early phanerozoic 514 342 ma when the continents are relatively small and widely distributed runoff depends on continental evaporation and temperature as the continents migrate into subtropical latitudes global runoff decreases as global land temperatures and evaporation increase as the continents shift to higher latitudes global runoff increases as global land temperatures and evaporation decrease during the middle to late phanerozoic 306 ma present when large continental land masses predominate runoff depends on continental precipitation experiments with increased atmospheric co 2 for the middle ordovician 458 ma when the paleocontinent of gondwana was centered at subtropical latitudes and the early silurian 425 ma when gondwana had shifted to middle and high latitudes also point to a correlation between land mass location and runoff global runoff increases 15 with increased co 2 at 425 ma but remains unchanged for 458 ma even though global mean temperature and precipitation increase comparable amounts for the two time periods these results imply that weathering feedback between temperature and runoff may be dependent on land ocean configuration

changes during the holocene in the size of white tailed deer odocoileus virginianus from central illinois abstract white tailed deer odocoileus virginianus from central illinois varied in size during the holocene the record which extends back to 8450 yr b p indicates small deer through the mid holocene until 3650 yr b p after which size increases although influences of winter climate seasonality anthropogenic effects and other ecological factors should not be discounted an intriguing possible cause of the deer size shifts is insolation driven summer climate and its influence on food resources in the holocene small deer size is correlated with high summer insolation and with low winter insolation climatic models indicate that in spite of changes in insolation holocene winters did not vary greatly through time especially in contrast to summers which were dynamic physiological constraints peculiar to o virginianus make critical the quality of summer forage for determining final adult size summer temperature averaged 2 c warmer than present during the middle holocene which increased evaporation and probably reduced the period of availability of high quality forage low in fiber and high in protein consequently less fuel for growth was consumed by mid holocene deer and only small body size was achieved other possible causes e g bergmann s rule seasonality of clinal variation are considered with reference to central illinois deer but at present the most parsimonious explanation appears to be the summer insolation hypothesis

a diatom record of climate and hydrology for the past 200 ka from owens lake california with comparison to other great basin records abstract diatoms from lake sediments beneath owens lake playa inyo county california document a nearly continuous paleolimnological record of climate and hydrologic change since the penultimate glacial interglacial cycle based on a chronology established by radiocarbon tephrochronology and paleomagnetic control freshwater planktic diatoms especially species of stephanodiscus plagioclase feldspar rich sediments with high magnetic susceptibility and juniperus type pollen characterized the penultimate glaciation at owens lake saline diatoms dominated in the following interglacial period and there are several episodes during which freshwater planktic diatoms became abundant between 100 and 50 ka that may represent interstadial climatic conditions saline diatoms fell to low values after 50 ka but warm season aulacoseira species indicate episodes of significant summer precipitation in the hydrologic balance of owens lake prior to the last glacial maximum by 25 ka glacial environments were again characterized by abundant juniperus plagioclase feldspar and stephanodiscus species generally arid holocene climates were recorded in owens lake by short term fluctuations of saline and freshwater diatoms desiccation and oolitic sediments barren of diatoms comparison to paleoclimate records both north and south of owens lake suggest a southerly displacement of storm tracks originating from the aleutian low during glacial episodes

local holocene environmental indicators in upper mesopotamia pedogenic carbonate record vs archaeobotanical data and archaeoclimatological models abstract it has been suggested that pedogenic carbonate coatings on stones in archaeological sites can be used to reconstruct late quaternary environmental changes in the area of the fertile crescent this research compares a pedogenic carbonate record from southeastern turkey with three other local or regional sources of palaeoenvironmental information in order to evaluate the correlation of this new proxy with other independent data from the area 1 ancient plant macroremains from archaeological sites as ecological indicators 2 stable carbon isotope composition of ancient plant macroremains available in the literature and from our own investigations in six mid holocene archaeological sites and 3 modelled holocene precipitation and temperature changes in the northern fertile crescent comparison involved selected palynological and isotopic data from lacustrine sediments as well as speleothem isotopic records in near eastern locations available in the literature although the data show a certain amount of variation of proxy records on the regional scale for the northern fertile crescent upper mesopotamia they suggest three pronounced features of the holocene environmental history 1 a trend toward warmer temperatures may have affected the area during the early holocene between ca 10 000 6000 cal bp 2 increased moisture availability and relatively high temperatures in the mid holocene ca between 5000 and 4000 cal bp and 3 a significant decrease in moisture availability around 4000 cal bp further research is needed to enhance the chronological resolution of both pedogenic carbonate and plant macrofossil records this study stresses the complexity of the holocene palaeogeography of the near east and underlines the need for careful analysis of local sources of palaeonvironmental information in the region

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

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

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

the southern hemisphere westerlies in the australasian sector over the last glacial cycle a synthesis abstract the southern hemisphere westerlies in the southwest pacific are known to have waxed and waned numerous times during the last two glacial cycles though even semi continuous histories of the westerlies extend back no more than about 20 000 years we have good evidence for at least three scales of events a westerly maximum occurs at the last glacial maximum there is less conclusive evidence for another westerly maximum in the late holocene and for a minimum at ca 11 ka it is too early to ascribe even a cycle to these data but there are grounds to suggest that milankovitch precessional forcing may underlie the observed pattern there is also a quasi 2600 year cycle present in antarctic ice cores that appears to correlate to variation in westerly flow there is strong centennial scale variability in historical times the little ice age lia ca 1400 1850 was associated with a poleward shift in the circumpolar trough in the southern ocean strengthened westerly circulation over tasmania and a strengthening of southwesterly circulation and neoglaciation in southern new zealand while the preceding period 800 1400 ad was less certainly marked by reduced westerly flow from modern records we know that decadal and inter annual variability is important e g pacific decadal oscillation high latitude mode also known as the antarctic oscillation el nino southern oscillation only a minority of the proxies examined can identify changes on these temporal scales but data from tree rings ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale we conclude that westerly circulation is as strong now as at any time in the last glacial cycle in addition changes in latitudinal boundaries in the westerlies may be nearly as large in inter annual zonal shifts ca 2 maximum as in glaciation interglaciation movements ca 3 4 there is however reasonable evidence of strengthening weakening across much of the westerly belt at westerly maxima minima such as the lia early holocene

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

holocene monsoon changes inferred from lake sediment pollen and carbonate records northeastern cambodia major holocene monsoon changes in continental southeast asia are reconstructed from analysis of 14c dated changes in pollen and organic inorganic carbon in sediment cores taken from permanent closed basin volcanic lakes in ratanakiri province northeastern cambodia analysis focuses on the nature and timing of monsoon changes inferred from changes in vegetation and lake conditions these data provide the first well dated palynological record covering most of the holocene and continuous up to the present from a terrestrial site in mainland southeast asia the record from a 15 m core retrieved from kara lake representing the last 9300 years shows that the late glacial conditions ended about 8500 14c yr b p more than 1000 years later than sites in southwest china summer monsoon intensity increased over the period ca 8400 5300 14c yr b p similar to most other sites in the asian monsoon region a subsequent expansion of secondary forests at the expense of dense semievergreen forests suggest a drier climate leading to more frequent fire disturbance after ca 3500 14c yr b p disturbance frequency may have increased further with increasing seasonality from ca 2500 14c yr b p to the present dense forest has recovered in a mosaic with annually burned dry forest but climate may not be the main control on local vegetation dynamics in the late holocene

dissimilarity mapping between fossil and contemporary pollen spectra in europe for the past 13 000 years abstract the degree of analogy between fossil and contemporary pollen spectra in europe has been investigated using the chord distance dissimilarity measure no analog pollen spectra represent vegetation without a modern analog and hence by inference represent macroclimatic conditions different from any occurring in the region today such spectra have minimum chord distances that exceed a threshold value assessed using contemporary samples from the same and different vegetation u units contoured maps of minimum chord distance portray the changing patterns of analogous and no analog pollen spectra and hence vegetation units since 13 000 yr b p no analog vegetation units have been extensive in some regions for much of the holocene persisting as recently as 1000 years ago in many areas the chord distance measure has also been used to explore the patterns extent and rates of change in european pollen spectra since 13 000 yr b p pollen spectra changed rapidly during late glacial and early holocene times and during the last millennium paleoclimatic changes have brought about the major changes in the holocene paleovegetation of europe human impact upon european vegetation has obscured neither the contemporary relationship between pollen spectra and vegetation nor the climatically determined long term changes of vegetation across the continent since 13 000 yr b p

an overview of the post messinian paleoenvironmental history of the western mediterranean a review of the pliocene pleistocene paleoenvironmental history of the western mediterranean is presented based on micropaleontological and geochemical studies of ocean drilling program odp leg 107 material and marine outcrops in southern italy the calcareous plankton biochronology proposed for the mediterranean by rio et al 1990 and 1991a provides the necessary age control for determining the timing of major climatic and oceanographic changes in the region the early pliocene period in the mediterranean was not a time of warm stable climate rather it was marked by relatively high amplitude climatic oscillations in marginal areas these climatic oscillations resulted in the rhythmic deposition of limestone marl couplets which have an average duration of approximately 19 000 years it is proposed that these sedimentary couplets are the result of precessionally induced changes in monsoon intensity which in turn cause variability in coastal divergence and upwelling the 18o and the calcareous plankton foraminifera and coccoliths records for tyrrhenian sea odp site 653 reveal a cooling of surface waters at 3 1 ma coincident with this cooling is an increase in the frequency of diatomite formation in southern italy bianco section the global cooling at 2 4 ma and the associated expansion of northern hemisphere glaciation resulted in a shift to more arid conditions in the mediterranean region this climate change may have altered the mediterranean water balance resulting in the establishment of antiestuarine water exchange with the atlantic at this time the 18o record for site 653 is also marked by a sharp cooling across the pliocene pleistocene boundary in the boundary stratotype section at vrica this cooling is manifested as an increase in the abundance of the planktonic foraminifer neogloboquadrina pachyderma

sensitivity of the african and asian monsoons to mid holocene insolation and data inferred surface changes abstract orbital forcing alone is not sufficient to explain the massive northward penetration of monsoon rains in africa shown by data during the mid holocene 6000 yr ago feedbacks associated with changes in ssts and land surface cover may be necessary to produce a sufficient increase in the monsoon a step toward a better understanding of the respective role of oceans and land surfaces is to design sensitivity studies with prescribed forcings inferred from observations in the first study ssts are lowered in the upwelling regions offshore of west africa and somalia and increased in the bay of bengal and south china sea in the second simulation the modern sahara desert is replaced by a combination of xerophytic woods scrub and grassland in both cases the amount of water vapor advected from oceanic sources is increased north of 10 n in africa in response to the increased land sea temperature contrast thereby enhancing rainfall but the magnitude of the simulated changes is much larger when land s

controls on the east asian monsoon during the last glacial cycle based on comparison between hulu cave and polar ice core records previous studies have suggested a sound chronological correlation between the hulu cave record east asian monsoon and greenland ice core records which implies a dominant control of northern hemisphere climate processes on monsoon intensity we present an objective straightforward statistical evaluation that challenges this generally accepted paradigm for sub orbital variability we propose a more flexible global interpretation which takes into account a broad range of variability in the signal structures in the hulu cave and polar ice core records rather than a limited number of major transitions our analysis employs the layer counted greenland ice core chronology 2005 gicc05 which was developed for greenland records and has since been applied via methane synchronisation to the high resolution 18oice series from epica dronning maud land edml the gicc05 chronology allows these ice core records to be compared to the u th dated hulu cave record within relatively narrow 3 bounds of age uncertainty following previous suggestions our proposed interpretation suggests that the east asian monsoon is influenced by a combination of northern hemisphere pull which is more intense during boreal warm periods and southern hemisphere push which is more intense monsoon during austral cold periods our analysis strongly suggests a dominant control on millennial scale monsoon variability by southern hemisphere climate changes during glacial times when the monsoon is weak overall and control by northern hemisphere climate changes during deglacial and interglacial times when the monsoon is strong the deduced temporally variable relationship with southern hemisphere climate records offers a statistically more plausible reason for the apparent coincidence of major east asian monsoon transitions with northern hemisphere dansgaard oeschger do climate events during glacial times than the traditional a priori interpretation of strict northern hemisphere control

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

capillary water absorption characteristics of some cappadocian ignimbrites and the role of capillarity on their deterioration cappadocia stands out as one of the most important regions in turkey for its natural historical and cultural heritages the region is under the influence of wetting and drying and freezing and thawing weathering processes which are largely controlled by the water content water migrates through rock pores via different processes such as capillary water absorption which is one of the most common ways observed in the cappadocia region in this study a research program consisting mainly of laboratory studies was carried out to investigate the capillary water absorption characteristics of ignimbrites which are the host rocks of many natural and historical heritage structures in cappadocia accordingly xrd analyses mercury porosimeter and capillary water absorption tests were performed the pore size distribution which is a function of welding degree controls the capillary water absorption process of ignimbrites particularly ignimbrites that have a uniform pore size distribution of around 5 10 m reveal higher capillary water absorption potential ignimbrites have a considerable and variable potential in terms of capillarity and the capillarity plays a major role on the deterioration and decomposition of many of the historical and natural heritage structures in the cappadocia region

the effect of ocean dynamics in a coupled gcm simulation of the last glacial maximum general circulation models gcms of the climate system are powerful tools for understanding and predicting climate and climate change the last glacial maximum lgm provides an extreme test of the model s ability to simulate a change of climate and allows us to increase our understanding of mechanisms of climate change we have used a coupled high resolution ocean atmosphere gcm hadcm3 to simulate the equilibrium climate at the lgm the effect of ocean dynamics is investigated by carrying out a parallel experiment replacing the dynamic three dimensional ocean gcm with a static thermodynamic mixed layer ocean model changes to the ocean circulation and feedbacks between the ocean atmosphere and sea ice have an important influence on the surface response and are discussed the coupled model produces an intensified thermohaline circulation and an increase in the amount of heat transported northward by the atlantic ocean equatorward of 55 n which is at odds with the interpretation of some proxy records such changes which the thermodynamic mixed layer ocean model cannot produce have a large impact around the north atlantic region and are discussed in the study

sensitivity of the australian monsoon to insolation and vegetation implications for human impact on continental moisture balance general circulation model experiments test the geologically based correlation of high monsoon rainfall over interior australia with northern hemisphere insolation and evaluate the sensitivity of the australian monsoon to ecosystem change our results suggest that northern hemisphere insolation control on the intensity of the siberian high rather than summer insolation over the australian continent determines the strength of the australian monsoon on millennial time scales unlike a classic monsoon regime additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere atmosphere feedbacks linked to vegetation type and soil properties this sensitivity offers a resolution to the observed failure of the australian monsoon to penetrate the interior in the holocene postulated regular burning practiced by early humans may have converted a tree shrub grassland mosaic across the semiarid zone to the modern desert scrub thereby weakening biospheric feedbacks and resulting in long term desertification of the continent

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

variability in upwelling fields in the northwestern indian ocean 1 model experiments for the past 18 000 years a nonlinear reduced gravity ocean model is used to assess the effects of changes in the monsoon winds during glacial and interglacial conditions on the seasonal circulation in the northwestern indian ocean winds from the national center for atmospheric research community climate model simulations for 18 kyr b p the most recent glacial maximum and a period of weaker monsoon winds 9 kyr b p near the beginning of the present interglacial and a period of stronger monsoon winds and present day 0 kyr b p conditions are used to drive the model to a steady seasonal cycle strength of upwelling fields are inferred in each case by integrating upward displacements of the model pycnocline over the primary upwelling season of mid april to mid august in both the 0 kyr b p and the 9 kyr b p cases a broad band of upwelling and decreased model upper layer thickness extends along the coast of the arabian peninsula out 350 500 km offshore during the southwest monsoon this upwelling is driven by the strongly positive wind stress curl beneath the cyclonic side of the atmospheric findlater jet located to the north and west of the jet axis farther offshore in the anticyclonic region to the south and east of the jet axis the negative wind stress curl drives downwelling and increased upper layer thickness in the 9 kyr b p case the atmospheric jet is much stronger and narrower than in the 0 kyr b p case with stronger values of both positive and negative curl to the northwest and southeast respectively of the jet axis this drives much stronger upwelling to the northwest of the jet axis and downwelling to the southeast in the 18 kyr b p case the findlater jet is very weak and upwelling patterns are uniformly weak across the basin the spatial distribution and temporal variation of the upwelling fauna in the sediment record is consistent with the model upwelling fields in all three cases the ocean model thus provides the link between the climate model and the sedimentation data verifying the hypothesis that variations in upwelling driven by variations in the strength of the monsoon jet are responsible for the observed variations in the sediment record

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

the effect of volcanic aerosols on global climate abstract the surface temperature decrease after major volcanic eruptions has been demonstrated by a number of groups to be the order of a few tenths of a degree at first the stratospheric aerosol is usually restricted to a narrow range of latitudes and the volcanically induced temperature decrease is found to be nonuniform over the surface of the earth in fact because of the differential cooling of land and ocean there should always be volcanically induced temperature gradients these temperature gradients will induce a redistribution of air mass and anomalous sea level pressure gradients anomalous winds and anomalous climate on a global scale in this paper a hypothesis is presented which assumes that volcanic aerosols by reducing the solar radiation induces surface temperature gradients and sea level pressure gradients between the land and the oceans since cooling of the land occurs before the oceans there will be at first an increase of sea level pressure over land relative to the oceans conservation of total air mass on a global scale requires the sea level pressure over the ocean to be reduced because the majority of the land area is in the northern hemisphere the volcanically induced cooling will transfer air mass from the oceanic anticyclones in both the northern and southern hemisphere to the continents and especially to southern eurasia the anomalous sea level pressure pattern slp which would be obtained higher slp over southern eurasia and lower slp over the southern oceans is very close to the pattern first named by sir gilbert walker called the negative phase of the southern oscillation the positive phase of the southern oscillation can occur when no volcanic aerosols are present and the stratosphere is clear then the additional radiation and heating of the land increases the transfer of air mass from the northern hemisphere land mass to the world s oceans the positive phase of the global southern oscillation in this paper it will be shown that this hypothesis has the potential to explain the observed association between low latitude volcanic aerosols and the el nino southern oscillation it also has the potential to explain why el chichon s eruption induced a very strong el nino compared to the weaker el nino events induced by the eruptions of agung and krakatau it also explains why almost all monsoon countries experience below normal precipitation just prior to the maximum of the el nino warming the hypothesis also has the potential to explain why low and high latitude aerosols will affect the global climate system differently this hypothesis represents a return to the ideas of sir gilbert walker who first defined the southern oscillation as a global scale anomaly rather than an index between just two stations

glacier modeling and the climate of patagonia during the last glacial maximum ice cap modeling constrained by empirical studies provides an effective way of reconstructing past climates the former patagonian ice sheet is in a climatically significant location since it lies athwart the southern hemisphere westerlies and responds to the latitudinal migration of climatic belts during glacial cycles a numerical model of the patagonian ice cap for the last glacial maximum lgm is developed which is time dependent and driven by changing the mass balance altitude relationship it relies on a vertically integrated continuity model of ice mass solved over a finite difference grid the model is relatively insensitive to ice flow parameters but highly sensitive to mass balance the climatic input is adjusted to produce the best fit with the known limits of the ice cap at the lgm the ice cap extends 1800 km along the andes and has a volume of 440 000 km3 during the lgm the equilibrium line altitude ela was lower than at present by at least 560 m near latitude 40 s 160 m near latitude 50 s and 360 m near latitude 56 s the latitudinal variation in ela depression can be explained by an overall fall in temperature of about 3 0 c and the northward migration of precipitation belts by about 5 latitude annual precipitation totals may have decreased by about 0 7 m at latitude 50 s and increased by about 0 7 m at latitude 40 s the ela rises steeply by up to 4 m per kilometer from west to east as the westerlies cross the andes and this prevents ice growth to the east the limited decrease in temperature during the lgm could be related to the modest migration of the antarctic convergence between south america and the antarctic peninsula

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

mediterranean pluvial periods and sapropel formation over the last 200 000 years abstract three mediterranean deep sea cores have been studied to reconstruct the hydrological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200 60 kyr bp the isotopic and sea surface temperature records of planktonic foraminifera were used to estimate the oxygen isotopic composition of surface water w in the tyrrhenian sea and levantine basin our results show a strong w salinity decrease in both basins associated with each sapropel these w decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel s 1 centred at ca 8 kyr bp a strong precipitation increase transformed the whole mediterranean sea into a non concentration basin the low surface salinity was responsible for the water column stratification while nutrients brought in by the runoff enhanced productivity it resulted in a significant reduction in the rate of deep water oxygenation and sapropel formation in the eastern basin in addition the mediterranean sea 18 o record is very similar to that of the bay of bengal as the latter is very sensitive to the summer monsoon rain this similarity suggests that both glacial and interglacial sapropels result from enhanced monsoon like precipitation due to an increase in summer insolation driven by precession variations

late pleistocene holocene records from lake ulaan southern mongolia implications for east asian palaeomonsoonal climate changes a 5 88 m long core taken from lake ulaan was studied for high resolution paleoclimatic changes during the last 17 000 years the core sediments are divided into three units based on grain size distribution unit 1 top to 392 cm depth covering the last 11 200 years unit 2 392 530 cm 11 2 15 ka and unit 3 530 588 cm 15 0 16 7 ka these sediments were transported by local westerly winds units 1 and 3 and fluvial processes unit 2 based on major element compositions and geological setting of adjacent areas provenance of unit 1 sediments was interpreted to be the lake terrane and that of unit 2 to be the idermeg terrane unit 3 sediments were derived from the gobi altai terrane the records of total organic carbon c n ratio and weathering intensity suggest that paleoclimate in the source area of lake ulaan sediment was most humid during the early holocene humid during the mid holocene and dry in the late holocene the decrease of humidity through the holocene is a typical characteristic of the east asian monsoon region comparison with lacustrine records of other mongolia regions suggests that the northern boundary of east asian summer monsoon influence could have been located further north than previously assumed copyright 2013 john wiley sons ltd