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

residual circulations due to bottom roughness variability under tidal flows abstract tidal flows over irregular bathymetry are known to produce residual circulation flows due to nonlinear interaction with gradients of depth using the depth averaged vorticity equations the generation of residual vorticity and residual flows due to variation of the frictional coefficient are examined the authors find that the contribution due to bottom roughness variations can be as large as that arising from gradients of depth and velocity specific cases are considered on the northern california shelf georges bank and the u s south atlantic bight the generation of residual vorticity is a strong function of the length scales at which roughness or depth vary length scales of bottom roughness variation are commonly within the range of greatest effect e g sand patchiness cobbly outcrops etc the site specific cases show that the bottom roughness variability can generate as much residual circulation as that expected from depth variability the implication for numerical modeling studies

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

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

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

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 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

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

progressive soft sediment deformation within a subglacial shear zone a hybrid mosaic pervasive deformation model for middle pleistocene glaciotectonised sediments from eastern england this paper presents a hybrid pervasive and mosaic model for the progressive deformation of a stratified diamicton complex in eastern england within an active subglacial shear zone sedimentary evidence from undeformed low strain zones towards the base of the sediment pile indicates that the tectonised sediments were originally deposited as a series of subaqueous flows in a glaciolacustrine basin these sediments have subsequently been deformed during a progressive subglacial shearing event this event is divided into three stages ductile folding and sediment remobilisation d1 brittle faulting in the form of reidel shears d2 and hydrofracturing and sediment remobilisation d3 the dominant control on the pattern and style of deformation appears to relate to the rate of thrust induced till accretion and the aquifer properties and pore water content and or pressure of the deforming sediments

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

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

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

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

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

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

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

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

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

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