el nino la nina and sahel precipitation during the middle holocene simulations with a synchronously coupled atmo sphere land ocean sea ice model indicate el nino la nina like events in the eastern tropical pacific ocean during the middle holocene 6 ka with similar intensities and frequencies as at present 0 ka july august september sahel precipitation shifts northward as expected from proxy data for present day interannual decadal variability of western sahel precipi tation is correlated with both pacific el nino la nina sea sur face temperature sst anomalies and the atlantic dipole teleconnections at 6 ka between sahel precipitation and el nino la nina sst anomalies are absent with tropical atlantic ssts asserting a dominant influence these results illustrate potential problems with using present day teleconnection patterns in interpreting past climate variability from proxy data

onset of aridity and dune building in central australia sedimentological and magnetostratigraphic evidence from lake amadeus abstract sediments from lake amadeus a groundwater discharge playa in central australia comprise a surface playa sequence the winmatti beds varying between 0 6 and 3 m in thickness overlying a long sequence of fairly uniform fluvial lacustrine clays the uluru clay the latter extends down to at least 15 m the maximum depth cored during this study and possibly down to 65 m below the present playa surface in the cores studied the brunhes matuyama boundary 0 73 ma was identifiable in all the upper sediments typically at a depth of between 1 and 2 m but below this there are two plausible chronological interpretations of the palaeomagnetic data deposition rates are very low typically no more than 1 5 cm ka in the uluru clay beds and down to 0 2 cm ka in the winmatti beds these rates suggest that the fluvial lacustrine phase lasted for at least 5 ma the boundary between the uluru clay and the winmatti beds bears a close correspondence to the boundary between the blanchetown clay a lacustrine sequence and the tyrrell beds a playa sequence in palaeo lake bungunnia in what is now the murray basin in southeastern australia however the transition occurs at about 0 9 ma or possibly 1 6 ma at lake amadeus whereas it has been dated palaeomagnetically at less than 0 73 ma probably 0 5 ma in lake bungunnia records from other locations in southeastern australia likewise support a major change from wetter to drier conditions at or shortly after the matuyama brunhes polarity transition thus the current evidence from lake amadeus indicates that in central australia the onset of aeolian and saline gypseous deposits characteristic of arid zone facies may have pre dated the corresponding change in the southeastern part of the continent by about 0 4 ma or possibly by about 1 1 ma in common with most playas in central australia lake amadeus is surrounded by a ring of gypseous dunes derived from material deflated from the surface of the playa magnetostratigraphic evidence from auger island in the middle of lake amadeus suggests that the oldest gypseous dune formation on the island must have pre dated the start of the jaramillo subchron at 0 98 ma or possibly the start of the brunhes epoch 0 73 ma thus making these the oldest dated dunes in australia the age of the auger island dunes is probably characteristic of other gypseous dunes around the margins of playas in central australia

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

distribution and texture of the bottom sediments in a semi enclosed coastal inlet the izmit bay from the eastern sea of marmara turkey thirty one surficial sediment samples were collected from the floor of izmit bay with a grab onboard the rv bilim in summer 1987 and analysed for their grain size total carbonate and organic carbon distribution low calcareous terrigenous mud 2 45 caco3 with a relatively high silt percentage was the principal sediment type found on the floor of izmit bay sediments rich in sand and gravel usually occur in the narrow and shoal areas of the bay where biogenic and topography related hydrodynamic conditions are dominant factors controlling the nature of bottom deposits the carbonates are made up almost entirely of the remains of calcareous organisms organic carbon concentrations of the sediments 0 35 1 62 are probably associated with the high primary production rates in this region thus the rates of sedimentation in the izmit bay calculated from the organic carbon and primary productivity data are estimated to be up to 70 cm 1000 years

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

lake lewis basin central australia environmental evolution and osl chronology abstract lake lewis is the furthest from the coast of australia s salt lakes and lies at the southern edge of influence of the australian monsoon regime the macdonnell ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain we describe lacustrine fluvial and aeolian environments of the basin and report optically stimulated luminescence osl dates from representative sediments a long period of generally wetter conditions during most of the pleistocene is represented by thick uniform lacustrine clay beneath and near lake lewis this is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin which indicate fluctuating climatic conditions osl results show that dune building in the basin commenced before 95 ka when salinity at the depocentre was high dune building peaked around 23 21 ka osl ages of fluvial deposits show that floods occurred during the last 20 ka following the last phase of maximum aridity in the region

marine transgression and dune initiation on western cape york northern australia abstract the chronostratigraphy of the coastal dunes on the western side of northern cape york differs from the general pattern of dune emplacement identified on easterly facing coasts across northern australia two episodes of dune emplacement are suggested by morphology prior to the establishment of the modern foredune tl dating and comparative soil profile development indicate the possibility of three episodes based on a small number of tl dates it is possible to associate dune emplacements at about 11 200 yrs b p 8300 yrs b p and 5200 yrs b p with shoreline disturbance and the destruction of shoreline vegetation by rising sea level stabilisation of the 11 200 yrs b p unit may be due to a short marine regression roughly around the time of the younger dryas the 8300 yrs b p unit probably stabilised due to changed environmental conditions and the 5200 yrs b p unit represents the cessation of post glacial sea level rise in northern australia

land surface feedbacks and palaeomonsoons in northern africa we ran a sequence of climate model experiments for 6000 years ago with land surface conditions based on a realistic map of palaeovegetation lakes and wetlands to quantify the effects of land surface feedbacks in the saharan region vegetation induced albedo and moisture flux changes produced year round warming forced the monsoon to 17 25 n two months earlier and shifted the precipitation belt 300 km northwards compared to the effects of orbital forcing alone the addition of lakes and wetlands produced localised changes in evaporation and precipitation but caused no further extension of the monsoon belt diagnostic analyses with biome and continental hydrology models showed that the combined land surface feedbacks although substantial could neither maintain grassland as far north as observed 26 n nor maintain lake megachad 330 000 km

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

thermoluminescence dating of dunes at cape st lambert east kimberleys northwestern australia abstract quaternary lithostraigraphic units in coastal dunes have been dated in the dune field at cape st lambert near the mouth of the berkeley river in the east kimberley region northwestern australia using coarse fraction thermoluminescence tl dating twelve tl dates were measured four main chronostratigraphic units were identified the oldest dunes appear to have been produced from offshore deposits reworked by rising sea level about 5000 years ago two sequences of younger stable dunes derive from the river mouth sediments of the berkeley river and date to about 3000 years ago and 1600 years ago respectively the presently active dunes appear to have been initiated within the last 1000 years a period of increased climatic variability from 3000 yrs b p to the present appears to be responsible for most of the late holocene units identified at cape st lambert

a radiocarbon chronology from the playa lake tyrrell northwestern victoria australia abstract dating sediments with a low organic carbon content has proved a considerable problem in playa palaeoenvironments conversion of organic carbon contained in sediments to strontium carbonate eases handling of the otherwise large samples needed to obtain radiocarbon dates from such material concentrated carbon samples were used to erect a chronology of sedimentation in the upper levels of lake tyrrell after 10 000 yr b p and comparisons made between radiocarbon ages for comparable stratigraphic horizons in cores from two sites in the northern basin of the lake reference is also made to a third series of dates which have a bearing upon the earlier history of deflation from the lake basin

australasian evidence for mid holocene climate change implies precessional control of walker circulation in the pacific abstract at its simplest the pacific cell of the walker circulation may be regarded as a thermal circulation driven by the temperature contrast between the west and east pacific evidence from australasia is summarized indicating that this circulation was greatly weakened in the early holocene but was enhanced at about 5000 bp the initial effect of this enhancement was the intensification of the northern australian monsoon within the australian tropics but this was reversed abruptly after 3700 bp the enhancement is attributed to an increased polar equator pressure gradient after 5000 bp with consequent intensification of the overall circulation pattern in the southern hemisphere including the mid latitude westerlies and the trade winds this in turn appears to be a result of increased southern hemisphere seasonality driven by the precessional cycle it is proposed that increased wind speeds off south america after 5000 bp in both mid and low latitudes enhanced upwelling and reduced sea surface temperatures ssts this created a greater east west surface temperature contrast across the pacific compounding a pre existing trend towards enhanced circulation and flipping climates in the southern hemisphere pacific basin from an early holocene mode to a late holocene mode under reduced circulation conditions early holocene climates at low latitudes in the southern hemisphere may have been dominated by monsoonal heat transfers

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

paleoclimate reconstruction along the pole equator pole transect of the americas pep 1 examples are presented of inter hemispheric comparison of instrumental climate and paleoclimate proxy records from the americas for di erent temporal scales despite a certain symmetry of seasonal precipitation patterns along the pep 1 transect decadal variability of winter precipitation shows di erent characteristics in terms of amplitude and frequency in both the last 100 and last 1000 years such di erences in variability are also seen in a comparison of time series of di erent el nin8 o southern oscillation proxy records from north and south america however these di erences do not appear to a ect the spatial correlation with paci c sea surface temperature patterns local and regional di erences in response to climate change are even more pronounced for records with lower temporal resolution and inter hemispheric synchroneity may or may not be indicative of the same forcing this aspect is illustrated in an inter hemispheric comparison of the last 1000 years of glacier variability and of the full and lateglacial lake level history 1999 elsevier science ltd all rights reserved

the enigma of a late pleistocene wetland in the flinders ranges south australia abstract lying in a semi arid region the flinders ranges have rocky weathering limited hillslopes and streams within the ranges are active only during rare downpours when they transport boulders gravel and coarse sand however silt and clay rich valley fill deposits incised by present streams occur as terraces and terrace remnants such deposits are not accumulating today in and upstream of brachina gorge in the central ranges these remnant valley fills are exposed in bank sections up to 18 m high at some localities exposures show horizontal centimetre scale beds of fine sand and clayey silt that can be traced for several hundred metres and contain gastropods diatoms and phytoliths consistent with sluggish shallow water flow under fresh to brackish conditions ams 14 c and osl dating shows that these valley fill deposits accumulated between 33 and 17 ka an interval that embraces the last glacial maximum lgm formerly thought to be lake beds aust j earth sci 46 1999 61 the valley fills are shown here to have accumulated in a fluvial wetland that extended westward from the middle reaches of brachina creek through brachina gorge and joined with aggraded fan deposits beyond the ranges aggradation of this wetland requires a substantial reduction of both rainfall variability and evaporation which would be favoured by the low temperatures and reduced incursions of summer rainfall this is consistent with climatic reconstructions by miller et al nature 385 1997 241 and johnson et al science 284 1999 1150 for lake eyre north of the flinders ranges at the lgm demise of the wetland was heralded by a major influx of coarse alluvium followed by channelling and dissection erosion was interrupted by an episode of aggradation and floodplain widening represented by remnants of a wide terrace inset below the primary wetland surface this episode which is interpreted as a return to lower climatic variability ceased with establishment of the present climatic regime which has resulted in stripping of the late pleistocene deposits from much of the brachina valley

hydroclimatic interpretation of quaternary shorelines on south australian playas abstract the catchment of lake eyre is one of the world s largest internally drained basins the playas near its depocentre the driest region of australia contain a partial record of quaternary climatic and hydrologic events for the last full glacial cycle and probably beyond ancient beach ridges marginal to lakes eyre frome callabonna and blanche have been dated using thermoluminescence tl to provide evidence for major changes in the hydrological regime of the basin beach ridges around lake eyre provide evidence of high lake stands up to 27 m above the present lake floor during what probably corresponds to the middle to latter part of marine oxygen isotope stage 5 there is evidence also for even higher lake stands associated with earlier isotope stages three tl dates identify a period of aeolian activity during stage 4 and a further 5 tl dates from lakes eyre and frome indicate that high lake stands occurred between about 55 and 40 ka corresponding with stage 3 the stage 5 and stage 3 high stands both relate to periods of enhanced fluvial activity previously identified in the lake eyre basin and elsewhere in australia in contradiction with other work a few tl dates from some playas suggest a possible major episode of high lake levels immediately preceding or at the start of the last glacial maximum lgm 26 22 ka this may relate to a sharp temperature suppression and an increase in runoff by rivers fed from monsoons in the north while a set of relatively low elevation late holocene beaches have been dated on two of the playas a period of enhanced precipitation and stream flow in the early to mid holocene appears not to have formed higher beaches possibly due to high temperatures and evaporation rates at that time the filling of lake eyre during and since stage 5 appears to have been to no more than to a level of 12 m australian height datum ahd possibly due a spillway at about this elevation in the form of the warrawoocara channel connecting lake eyre with playas to the southeast lakes gregory blanche callabonna and frome such overflows from one large basin to another would have had a major impact on the hydrology of the region in addition to enhanced runoff essential for the maintenance of high lake levels must have been local temperatures and evaporation rates significantly reduced from present day levels

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

the onset of the australian monsoon during winter monex synoptic aspects abstract a case study is presented of the onset of the southern hemisphere summer monsoon at longitudes near australia during december 1978 the numerical analyses comprising this case study are used in conjunction with station data and operational manually derived analyses for other years to investigate the following 1 the case or definition of monsoon onset 2 the three dimensional structure of the troposphere during an active monsoon situation and 3 the flow changes preceding and during the transition from a period of suppressed to a period of enhanced cumulonimbus activity over tropical australia a well defined onset occurs in six of the seven years considered onset defined as a satellite observed large scale increase in tropical convection is consistent with that determined by the wind criterion of troup 1961 in 1978 onset occurs in two stages an increase in convergence followed by an increase in convection the monsoon cloudiness exists entirely in the region of low level westerly win

mid holocene land surface conditions in northern africa and the arabian peninsula a data set for the analysis of biogeophysical feedbacks in the climate system large changes in the extent of northern subtropical arid regions during the holocene are attributed to orbitally forced variations in monsoon strength and have been implicated in the regulation of atmospheric trace gas concentrations on millenial timescales models that omit biogeophysical feedback however are unable to account for the full magnitude of african monsoon amplification and extension during the early to middle holocene 9500 5000 years b p a data set describing land surface conditions 6000 years b p on a 1 1 grid across northern africa and the arabian peninsula has been prepared from published maps and other sources of palaeoenvironmental data with the primary aim of providing a realistic lower boundary condition for atmospheric general circulation model experiments similar to those performed in the palaeoclimate modelling intercomparison project the data set includes information on the percentage of each grid cell occupied by specific vegetation types steppe savanna xerophytic woods scrub tropical deciduous forest and tropical montane evergreen forest open water lakes and wetlands plus information on the flow direction of major drainage channels for use in large scale palaeohydrological modeling the data set is available in digital form by anonymous ftp

sensitivity of paleoclimate simulation results to season definitions according to the milankovitch theory slow variations of the earth s orbital parameters change the amplitude of the seasonal cycle of insolation and are considered to be the main forcing mechanism of glacial interglacial cycles because of the precession and changes in eccentricity the length of seasons also varies no absolute phasing is then possible between the insolation curves of two different periods various solutions to compare different periods have been given either for astronomical computations e g berger and loutre 1991 laskar et al 1993 or for model simulations e g kutzbach and otto bliesner 1982 mitchell et al 1988 but the sensitivity of model results to the different possible solutions has never been quantified our results based on simulations of the last interglacial climate 126 kyr b p where changes in the length of the seasons are large clearly show that phase leads or lags between the various solutions used introduce biases in the analysis of insolation and climate change of the same order of magnitude as the milankovitch forcing our main conclusions are that 1 when comparing various model simulations the date of the vernal equinox i e the phasing of the seasonal cycle of insolation as well as the definition of seasons must be the same for all models in order to avoid artificial differences 2 seasons based on astronomical positions are preferred to seasons defined with the same lengths as today since they better account for the phasing of insolation curves however insolation is not the only forcing in most atmospheric general circulation model simulations we also discuss the impact of the calendar hidden behind the definition of the seasonal cycle of the other boundary conditions such as sea ice or sea surface temperatures

african hydroclimatic variability during the last 2000 years abstract the african continent is characterised by a wide range of hydroclimate regimes ranging from humid equatorial west africa to the arid deserts in the northern and southern subtropics the livelihoods of much of its population are also vulnerable to future climate change mainly through variability in rainfall affecting water resource availability a growing number of data sources indicate that such hydroclimatic variability is an intrinsic component of africa s natural environment this paper co authored by members of the pages africa 2k working group presents an extensive assessment and discussion of proxy historical and instrumental evidence for hydroclimatic variability across the african continent spanning the last two millennia while the african palaeoenvironmental record is characterised by spatially disjunctive datasets with often less than optimal temporal resolution and chronological control the available evidence allows the assessment of prominent spatial patterns of palaeomoisture variability through time in this study we focus sequentially on data for six major time windows the first millennium ce the medieval climate anomaly 900 1250 ce the little ice age 1250 1750 ce the end of the lia 1750 1850 ce the early modern period 1850 1950 and the period of recent warming 1950 onwards this results in a continent wide synthesis of regional moisture balance trends through history allowing consideration of possible driving mechanisms and suggestions for future research

environmental humidity changes inferred from multi indicators in the jianghan plain central china during the last 12 700 years abstract time sequence of the jz 2010 profile derived from ams 14 c dating and the content of the sediment elements ti rb and sr the rb sr values as well as the granularity and the magnetic susceptibility are utilized to reconstruct the environmental humidity changes in the jianghan plain since 12 700 cal bp the comprehensive analyses of multiple alternative indicators indicate that the regional moisture turned from relatively dry to wet after the late glacial period and reached its optimum until the mid holocene however the trend was punctuated by several decreased humidity phases beginning with the severe dry event approximately 4400 4100 cal bp the environment was dry as a whole with modest humidity from approximately 3900 cal bp humidity changes in the study area are dominated by the east asian monsoon system which is under the influence of the gradual southward migration of the itcz driven by the summer solar insolation changes in the northern hemisphere due to orbital forcing as the first attempt to apply rb sr value and ti concentration in tracing moisture evolution in a region with typical subtropical humid climate this study highlights the different effects and consequences of the proxies throughout the palaeoenvironmental change process and the impacts of regional topography that sustained tectonic subsidence since the cretaceous as well as the southeast tilt that opened the plain to the summer monsoon moreover the fluctuation of magnetic susceptibility is associated with the granularity feature the reduction oxidation conditions and the impact of human factors on the natural sedimentary environments during the historic period in the jianghan plain

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

global ocean response to orbital forcing in the holocene 1 global upper ocean evolution in the holocene is studied in two coupled ocean atmosphere models under orbital forcing conditions at 3 6 8 and 11 ka the annual mean sea surface temperature sst changes in the early to mid holocene are found to be forced mainly by the annual mean insolation forcing with an overall symmetric response of colder equator 1 c in the arctic this sst change is consistent with a synthesis of mid holocene paleo sst records in contrast the temperature response in the thermocline is dominated by an antisymmetric pattern with a cooling warming in the northern southern hemisphere midlatitudes the thermocline response is determined predominantly by surface water subduction and ultimately the insolation forcing in local late winter

quaternary stratigraphy geochronology and evolution of the magela creek catchment in the monsoon tropics of northern australia abstract magela creek a major tributary of the east alligator river in northern australia has left a detailed sedimentary record of a fluvial landscape dominated by climatic and eustatic changes associated with quaternary glacial interglacial cycles uranium series dates from young pisoliths in floodplain deposits indicate that ferruginisation is probably ongoing under present conditions while ferricretes in degraded terraces that flank the lower valley reveal a fluvial history extending back to early pleistocene or tertiary time inset within this older alluvium is a valley fill which from thermoluminescence dates was initiated about 300 kyr ago with each glacial climate change and associated fall in sea level distinct palaeochannels have been eroded into these floodplains infilling later with alluvium when climate and base level conditions were conducive to fluvial deposition radiocarbon dates show that the most recent palaeochannel beneath the modern magela creek last started to fill by downstream progradation and vertical accretion of bedload sand about 8 kyr the palaeochannel filled at an accelerating rate probably as a result of declining stream competence associated with drier conditions in the late holocene augmented by the backwater effects of sea level rise continued aggradation blocked the mouths of tributary valleys along magela creek forming alluvial dammed tributary lakes and deferred junction tributary streams from about 300 kyr cyclic episodes of channel incision and sediment evacuation in this tropical monsoon river valley have become less effective possibly because increasing aridity in the late quaternary has reduced the erosional effectiveness of australia s northern rivers reduced flow regime and rising sea level in the late holocene has resulted in the latest phase of alluvial accretion

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

the climate of europe 6000 years ago palaeoclimates across europe for 6000 y bp were estimated from pollen data using the modern pollen analogue technique constrained with lake level data the constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration p e is consistent with the regional change in moisture balance as indicated by lakes an artificial neural network was used for the spatial interpolation of lake level changes to the pollen sites and for mapping palaeoclimate anomalies the climate variables reconstructed were mean temperature of the coldest month tc growing degree days above 5 c gdd moisture availability expressed as the ratio of actual to equilibrium evapotranspiration and p e the constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies especially for p e the reconstructions indicate clear spatial and seasonal patterns of holocene climate change which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations winter temperatures tc were 1 3 k greater than present in the far n and ne of europe but 2 4 k less than present in the mediterranean region summer warmth gdd was greater than present in nw europe by 400 800 k day at the highest elevations and in the alps but 400 k day less than present at lower elevations in s europe p e was 50 250 mm less than present in nw europe and the alps but was 10 15 greater than present in s europe and p e was 50 200 mm greater than present in s and e europe

a holocene pollen record from lowland tropical australia a pollen record from a dunefield lake on groote eylandt northern australia is presented this is the first substantially complete holocene terrestrial record from the seasonally humid lowland tropics of northern australia the lake originated as a seasonal swamp prior to 10 000 bp a progressive rise in water tables occurred until a permanent lake was established at about 9000 bp from 9000 to 7500 bp the lake shows evidence of disruption in the surrounding dunefield prior to 7500 bp an open grassland covered the dunefield after 7500 bp the area was rapidly colonized by eucalyptus open forest and acacias these types remain dominant to the present the data suggest that conditions continuously ameliorated from the base of the record to the mid holocene and there is evidence of an effective precipitation maximum at about 4000 bp effective precipitation declined after 3800 bp but a recovery took place about 1000 bp

palynology and palaeoclimatic implications of two holocene sequences from southwestern australia results from two palynological investigations of holocene lake and swamp deposits from southwestern western australia are presented these are used to assess the validity of the existing palaeoclimatic evidence for holocene climates which is contradictory the boggy lake sequence from the far southwest of western australia shows that while vegetation changes have taken place over the last ca 4500 years these cannot be attributed to climatic change palaeoecological interpretations of earlier work at the site are shown to have an insecure basis the loch mcness swamp sequence from further north shows only minor vegetation changes since ca 9000 yr b p which cannot be attributed with certainty to climatic causes the investigations do not support earlier claims of mid holocene climates wetter than present or of an extensive arid phase in the mid to late holocene

morphology and chronostratigraphy of a coastal dunefield groote eylandt northern australia a coastal dunefield on groote eylandt in the gulf of carpentaria northern australia is stratigraphically described and dated using the coarse fraction thermoluminescence dating technique four phases of dune activity have been identified 1 modern active transverse and parabolic dunes 2 a parabolic dunefield apparently stabilized less than 2000 yr bp 3 a parabolic dunefield stablized between 6000 and 4800 yr bp 4 a basal dunefield unit emplaced prior to 100 000 yr bp the current dune systems are an expression of dune activation and stabilization events in the holocene but were formed from the deflation of an extensive pre holocene dunefield the destruction of the pre holocene dunefield appears to have been caused by sea level rise at the end of the pleistocene and during the early holocene the ages derived from the dunefield accord well with chronostratigraphic investigations of coastal dune systems elsewhere in northern australia and support theories of regional environmental change during the holocene

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

modeling climate shift of el nino variability in the holocene a coupled ocean atmosphere general circulation model is used to investigate climatic shift of el nino in the holocene the model simulates a reduced enso intensity in the early and mid holocene in agreement with paleoclimate record the enso reduction is proposed to be caused by both an intensified asian summer monsoon and a warm water subduction from the south pacific into the equatorial thermocline

enrichment and toxicity of trace metals in near shore bottom sediments of cuddalore se coast of india in order to identify contaminating trace metals and their sources studies on trace metals are often included in routine environmental monitoring programs twenty five near shore bottom sediment samples from the inner shelf region near cuddalore of the bay of bengal were analysed for sediment texture organic matter carbonate caco3 concentrations and total trace metal concentrations ttms fe mn cr cu ni co pb zn and cd in order to evaluate geochemical processes such as enrichment and their origin the presence of carbonates 2 5 5 8 indicates the dominance of calcareous shells in the region a relatively high percentage of organic matter 0 2 3 9 is attributed to the predominance of finer sediments entering through the minor rivers high concentrations of ttms in fine and organic rich sediments are influenced by municipal and industrial sources which contention is well supported by correlations of ttms concentrations with fe mn fractions geoaccumulation index igeo calculations indicate that cr cu ni pb and cd concentrations are above the values expected from their presence in the discharge of effluents from the industrial zones bordering the shoreline comparing the findings of the present study with those from different parts of the world cr cu ni pb appear to be enriched in the sediments of the region

time slice analysis of the australian summer monsoon during the late quaternary using the fast ocean atmosphere model we use the fast ocean atmosphere model foam to investigate the variation in the australian summer monsoon over the last 55 000 years a synthesis of palaeoenvironmental observations is used to constrain the model for six time slices 55 35 21 11 6 and 0 ka both inter hemispheric forcing and the seasonal timing of local insolation changes play key and interacting roles on the evolution and intensity of the monsoon during the onset to the monsoon a heat low develops to the west of australia over the indian ocean in all time slices but with varying strengths divergent outflow from asia converges with the cyclonic flow to bring increased rainfall to northern australia and the maritime continent the relative importance of a low pressure pull and the high pressure push varies according to the strength of the pressure anomalies only in the middle holocene is the low pressure pull the dominant forcing mechanism at 21 ka the climate shift to colder mean temperatures determines the large scale dynamics of the monsoon the general picture that emerges from these results is consistent with available palaeodata but highlights the importance of a broad regional perspective to ascribe the driving mechanisms at different times copyright 2006 john wiley sons ltd

tropical pacific variability in the ncar climate system model a 300 yr simulation with the ncar climate system model csm version 1 captured only 60 of the observed enso signal and exaggerated the interannual variability of sst in the western tropical pacific here a simulation with a new version of the csm which significantly improves the spatial and temporal patterns of tropical pacific variability is described maximum sst variability is shifted to the central and eastern pacific a better simulation of the equatorial pacific thermocline structure results in nino 3 and nino 4 statistics com parable to the observed estimates for the last century the evolution of sst and subsurface temperature anomalies is in excellent agreement with observed events the majority of events evolve as a standing mode with weak sst anomalies occurring in the northern spring in the eastern tropical pacific and maximum anomalies covering the eastern tropical pacific ocean to the date line by the following northern winter at the same time subsurface temperature anomalies spread eastward and upward along the tropical thermocline the delayed oscillator and wyrtki s buildup hypothesis are consistent with aspects of the csm simulation on the equator a westerly wind stress anomaly in the central pacific forces off equatorial upwelling anomalies which propagate westward reaching the western boundary about one half year later this upwelling signal then propagates eastward along the equator arriving 2 months before cooling in the eastern pacific basin the tropical pacific atmospheric response to warm oceanic events also agrees with observational analyses with a negative southern oscillation pattern in sea level pressure wind stress anomalies and low level convergence to the west of the maximum sst anomalies and enhanced deep convection and precipitation in the central and eastern tropical pacific

stratigraphy sedimentology chronology and palaeohydrology of quaternary lacustrine deposits at madigan gulf lake eyre south australia abstract madigan gulf is a large bay at the southern end of lake eyre north a major ephemerally flooded playa in arid central australia at the southwestern margin of a vast 1 300 000 km2 internal drainage basin the stratigraphy and chronology of the quaternary sequence in the gulf is described from 8 cores and a cliff exposure at the gulf margin a number of depositional environments are recognised and their distinctive sedimentary components are described facies recognised include deep and shallow water lacustrine environments dominated by surface water processes and dry or ephemerally flooded playa environments dominated by groundwater controlled processes sedimentary components include terrigenous clastics from river inflow and shoreline erosion carbonates of detrital inorganic or biological origin and gypsum and halite evaporites carbonates and gypsum evaporites precipitated within the basin are frequently reworked as clastic components the establishment of a preliminary chronology for the sequence by the application of thermoluminescence uranium thorium disequilibrium amino acid racemization and radiocarbon dating techniques has allowed a reconstruction of the last 130 ka of lake eyre palaeohydrology the wettest phase occurred during the last interglacial early in oxygen isotope stage 5 when an enlarged lake eyre was up to 25 m deep subsequently there has been a number of dry periods separating successively less effective wet phases culminating in the deposition of a substantial halite salt crust around the time of the glacial maximum the dry interludes are characterised by deflation of salts and sediment from the basin a process controlled by lowering of the watertable the record from madigan gulf demonstrates the dramatic and repetitive impact of lake deflation on the quaternary record of lake eyre in the early holocene a minor but mostly perennial lacustrine event was terminated at about 3 4 ka when the modern ephemeral playa regime was established the major catchment of lake eyre is located in the monsoon watered areas of northern australia as demonstrated by large floodings of the modern ephemeral regime major lacustrine episodes must indicate enhanced monsoon precipitation in northern australia in the holocene the lake has not risen to levels achieved during the early stage 5 lacustral phase indicating a marked reduction in the effectiveness of the monsoon in the present interglacial by comparison with its predecessor

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

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

late quaternary spatio temporal limnological variations in the altiplano of bolivia and peru abstract between the western and eastern andean cordilleras in peru and bolivia there are three main lacustrine basins lake titicaca lake poopo and the group of coipasa uyuni for the past few millennia highly variable environmental conditions have been recorded in their sediments today a latitudinal meteorological gradient influences the lakes status leading to specific deposits and ostracod communities lake titicaca in the north is oligohaline whereas lake poopo further south is polyhaline in the south the coipasa uyuni depression is characterized by a 12 000 km2 surficial salt crust during the late pleistocene ca 40 000 to 25 000 yr b p the water depth and salinity in paleolake poopo fluctuated widely and paleolake titicaca was slightly larger than at present sedimentation was mostly biocarbonate in the shallower areas and it was detrital organic in the deepest zones during the holocene a dry period transformed lake poopo into a salar with evaporite precipitation lake titicaca registered a large decline in water level 8100 3600 yr b p initially inducing gypsum precipitation followed by short influxes of water with an ostracod faunal composition similar to that of the modern brines of lake poopo lake titicacas present condition only appeared between 2200 and 1500 yr b p

accumulation of contaminant metals in marine sediments of halifax harbour nova scotia environmental factors and historical trends abstract sediments in halifax harbour have accumulated contaminant metals hg cu zn and pb as a result of discharge of untreated sewage and industrial waste leaching of land fill waste and surface drainage concentrations of contaminants in210pb dated sediment cores became significant about 1880 and rose rapidly after 1900 reaching maximum concentrations in the decades between 1950 and 1980 mean concentrations of hg increased from 0 2 g g 1 in pre 1890 sediments to 1 6 g g 1 in the 20th century similar enrichments for cu changed the concentration from 26 to 88 g g 1 for zn from 90 to 250 g g 1 and for pb the increase was from 12 to 206 g g 1 statistical factor analyses of geochemical data have been used to identify 1 primary contaminants directly associated with waste discharge these include total and organic bound forms of cu zn and pb 2 secondary contamination attributed to leaching and modification of primary contaminants include acid labile forms of zn ni and cu 3 diagenetic modification of buried sediments are identified by total and labile forms of mn 4 dispersion of contaminants from land surface drainage are characterized by fine grained aluminosilicates historical trends in the changing dominance of these environmental factors reflect changes in industrial activity urban growth and changes in the use of metals in paints domestic and industrial chemicals and in the combustion of fuels

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

response of the african monsoon to orbital forcing and ocean feedbacks in the middle holocene simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the northern hemisphere 6000 years ago could have increased tropical atlantic sea surface temperatures in late summer the simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern africa by more than 25 percent compared with the middle holocene simulation with prescribed modern sea surface temperatures and provided better agreement with paleorecords of enhanced monsoons

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

late quaternary environmental change in the interior south american tropics new insight from leaf wax stable isotopes stable isotope analysis of leaf waxes in a sediment core from laguna la gaiba a shallow lake located at the bolivian margin of the pantanal wetlands provides new perspective on vegetation and climate change in the lowland interior tropics of south america over the past 40 000 years the carbon isotopic compositions 13c of long chain n alkanes reveal large shifts between c3 and c4 dominated vegetation communities since the last glacial period consistent with landscape reconstructions generated with pollen data from the same sediment core leaf wax 13c values during the last glacial period reflect an open landscape composed of c4 grasses and c3 herbs from 41 20 ka a peak in c4 abundance during the last glacial maximum lgm 21 ka suggests drier or more seasonal conditions relative to the earlier glacial period while the development of a c3 dominated forest community after 20 ka points to increased humidity during the last deglaciation within the holocene large changes in the abundance of c4 vegetation indicate a transition from drier or more seasonal conditions during the early mid holocene to wetter conditions in the late holocene coincident with increasing austral summer insolation strong negative correlations between leaf wax 13c and d d values over the entire record indicate that the majority of variability in leaf wax d d at this site can be explained by variability in the magnitude of biosynthetic fractionation by different vegetation types rather than changes in meteoric water d d signatures however positive d d deviations from the observed 13c d d trends are consistent with more enriched source water and drier or more seasonal conditions during the early mid holocene and lgm overall our record adds to evidence of varying influence of glacial boundary conditions and orbital forcing on south american summer monsoon precipitation in different regions of the south american tropics moreover the relationships between leaf wax stable isotopes and pollen data observed at this site underscore the complementary nature of pollen and leaf wax 13c data for reconstructing past vegetation changes and the potentially large effects of such changes on leaf wax d d signatures

abandoned orange footed scrubfowl megapodius reinwardt nests and coastal rainforest boundary dynamics during the late holocene in monsoonal australia abstract the late holocene history of monsoon rainforest retreat in northern australia was explored by radiocarbon dating abandoned orange footed scrubfowl megapodius reinwardt nests scrubfowl can only build nests large heaps of soil and leaf litter in coastal rainforests in northern australia a detailed study from a site with a known history of rainforest contraction demonstrated that it is impossible to accurately determine the date of rainforest boundary retreat by radiocarbon dating abandoned scrubfowl nests nonetheless radiocarbon dates from abandoned nests at three sites on the coast of the northern territory suggested that the rainforests contracted sometime within the late holocene it is argued that the cause of such localised rainforest contraction is the combined effect of tropical cyclone damage and subsequent severe fires occurring in the storm debris and not regional climatic change a cause shown to be inconsistent with existing ecological and geomorphological data the observed maintenance of rainforest boundaries under a regime of aboriginal burning and the geographically patchy occurrence of abandoned scrubfowl nests does not support the idea that aborigines have been the primary cause of widespread rainforest retreat in the late holocene

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

quantifying the role of biosphere atmosphere feedbacks in climate change coupled model simulations for 6000 years bp and comparison with palaeodata for northern eurasia and northern africa the lmd agcm was iteratively coupled to the global biome1 model in order to explore the role of vegetation climate interactions in response to mid holocene 6000 y bp orbital forcing the sea surface temperature and sea ice distribution used were present day and co2 concentration was pre industrial the land surface was initially prescribed with present day vegetation initial climate anomalies differences between agcm results for 6000 y bp and control were used to drive biome1 the simulated vegetation was provided to a further agcm run and so on results after five iterations were compared to the initial results in order to identify vegetation feedbacks these were centred on regions showing strong initial responses the orbitally induced high latitude summer warming and the intensification and extension of northern hemisphere tropical monsoons were both amplified by vegetation feedbacks vegetation feedbacks were smaller than the initial orbital effects for most regions and seasons but in west africa the summer precipitation increase more than doubled in response to changes in vegetation in the last iteration global tundra area was reduced by 25 and the southern limit of the sahara desert was shifted 2 5 n north to 18 n relative to today these results were compared with 6000 y bp observational data recording forest tundra boundary changes in northern eurasia and savana desert boundary changes in northern africa although the inclusion of vegetation feedbacks improved the qualitative agreement between the model results and the data the simulated changes were still insufficient perhaps due to the lack of ocean surface feedbacks

early holocene aridity in tropical northern australia thermoluminescence ages from a longitudinal dunefield in tropical northern australia suggest that complete dune activation occurred here either continuously or sporadically between approximately 8 2 ka and 5 9 ka this period in australia is normally ascribed to one of increasingly warm and wet conditions towards the holocene climatic optimum however elsewhere this time 8 ka coincides with a brief period of global climate change recognized in 18 o records from antarctica methane records of the greenland summit ice cores changes to deep sea benthic foraminferal composition and atmospheric 14 c variations in tropical africa two distinct phases of aridity have been dated at approximately 8 ka and 6 ka the coincidence of aeolian reacti vation episodes in this north australian dunefield with brief phases of early holocene climate change elsewhere suggests possible global climatic teleconnections at this time

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

flood geomorphology of the katherine gorge northern territory australia the katherine gorge is a narrow deep canyon system developed in resistant sandstone the tropical monsoonal climate results in rare flood events of very large magnitude these floods flush sand sized sediment as washload through the gorge but local accumulations are preserved as slack water deposits at tributary mouths paleoflood hydrologic analysis of the deposits employing step backwater flow modeling allows quantitative estimates to be made of geomorphically significant flows for an annual exceedence probability of 10 2 the gorge may experience discharges of 6 000 m 3 s mean velocities of 7 5 m s flow depths of 15 to 45 m stream powers per unit area as great as 1 10 4 watts m 2 and bed shear stresses of 1 5 10 3 n m 2 such flows are required to transport boulders 3 m or more in intermediate diameter that occur at large scale riffles at maximum stage pools reach depths of 45 m and are preferentially developed at vertical joint intersections in the rock probably through intense hydraulic action pool and riffle development thus reflects the channel boundary characteristics for extreme flow conditions additional indicators of especially intense flow phenomena include potholes flutes abraded facets on rock bar surfaces and scabland development on upland bedrock surfaces

the characteristics and source of laminated mud at lake barrine northeast australia abstract in a small 1 km 2 crater lake in the australian upland tropics 17 15 s 145 38 e 721 m a s l laminated mud has accumulated throughout the past 5 ka it is limited to a central region below 50 67 m of water where it is protected by a monimolimnion the contents of the laminae e g total lake products organic detritus diatoms pollen grains vivianite crystals distinguish two contrasting types namely detritus rich and detritus poor judged against radiocarbon dates over long sequences these couplets are not annual gravimetric mineralogical and chemical observations on the mud and on suspended organic and inorganic matter caught through several periods indicate some diagenetic changes across the mud water interface diatom analyses do not assist in relating mud type to source or period of origin the most likely mechanism of lamination is that continuous deposition of clay with small and varied detrital accompaniment is periodically enhanced by greater detrital input this occurs in some but not all periods of winter isothermy when ground temperatures fall to zero and below on several consecutive nights this leads to the stirring of sediments in water shallower than 50 m and their relocation in the deeper meromictic zone fine variations in e g diatom content partly independent of lamination type probably contain a wealth of detail about the lake s environmental history

late pleistocene record of cyclic eolian activity from tropical australia suggesting the younger dryas is not an unusual climatic event in the gulf of carpentaria northeastern australia 30 ka of lacustrine sedimentation provides a record of cyclic deposition of eolian dust 60 m just preceding the holocene adjacent layers containing eolian particles 60 m in a core from carpentaria relate to perhaps intermittent periods of eolian activity involving sediment deflation and thus aridity in northern australia each spanning at least 600 yr major peaks of dust deposition occurred about every 2 25 ka such amplitude of cyclicity has already been recognized elsewhere on the globe for other phenomena including waxing and waning of north american and european mountain glaciers oxygen isotope records from greenland and antarctic ice cores changes in deep sea benthic foraminiferal composition oxygen isotope records of deep sea foraminifera and atmospheric 14 c variations we propose that the cold younger dryas event that affected the northern hemisphere is matched by a significant dry event in the tropical region of northern australia and that the timing of this event fits well into the 2 25 ka cyclic pattern described here thus the younger dryas is a phenomenon of global significance and is not an odd event contrary to current belief in addition we propose that activation of dunes in northeastern australia over periods of 600 yr corresponds to perhaps intermittently stronger easterly trade winds during such periods the intertropical convergence zone may not have extended as far south as it does today

on the equivocal fate of late pleistocene callitris vent cupressaceae woodlands in arid south australia fossil pollen assemblages suggest callitris cupressaceae dominated woodlands were prominent elements in landscapes near lake frome and lake eyre during latest pleistocene times callitris woodlands were present at lake eyre before 30 000 bp but became fragmented and disappeared in the lead up to the last glacial maximum callitris was again prominent from approximately 10 000 bp until about 5000 bp after which time it vanishes from the pollen record and presumably the region at lake frome callitris was abundant between 16 000 bp and 13 000 bp before declining to low modern levels from 11 000 bp at both sites the latest pleistocene or holocene decline in callitris occurrence and its eventual extinction in the vicinity of lake eyre broadly corresponds with archaeological indications of increasing human presence in the landscape in the absence of evidence of significant climatic changes at the times in question these observations lend tentative support to arguments that the composition and structure of modern zone vegetation has been significantly modified by aboriginal land management practices although the charcoal record is ambiguous fire is argued to be the principle agent of the changes wrought during human re colonisation of lands around lake frome and lake eyre

late quaternary environmental change and human impact around lake bolac western victoria australia the late quaternary history of the lake bolac region is reconstructed from sedimentary and pollen analysis of lake and swamp sequences and is supported by archaeological remains from lunette sediments freshwater deposits recovered from lake turangmoroke appear to date from the last glacial period when the vegetation was composed of herbfield and grassland subsequent dry conditions at the end of the pleistocene caused the deflation of some accumulated sediments on refilling the lake had become saline as moisture availability increased casuarina woodland dominated by allocasuarina verticillata became the regional vegetation cover domination by casuarina ended ca 8000 7000 yr bp probably as a result of rising saline ground water tables casuarinas were replaced to some degree by eucalypts augmented by the development of a riverine eucalyptus camaldulensis woodland swamp deposition commenced in the channel of neighbouring fiery creek at ca 4000 yr bp most likely as the result of a reduction in stream flow with decreased precipitation despite suggestions of significant impact on the vegetation by aboriginal people from other sites in southeastern australia there is no evidence of any alteration here from periods of occupation dated to around 13 000 yr bp and after 3500 yr bp the period of european occupation though is marked by significant changes in fire patterns reduced tree cover loss of floristic diversity increased erosion rates and salinity levels and decreased water levels journal ot quaternary science

mid holocene climate in new caledonia southwest pacific coral and pmip models monthly resolved results abstract the mid holocene climate is characterized by an insolation seasonality decrease in the southern hemisphere but measurements of its actual impact on monthly resolved sea surface temperature sst in the southwest pacific region are still insufficient a new caledonian 5 5 ka cal bp coral provides a 20 year long seasonally resolved record of ocean surface conditions as inferred from coral sr ca and ba ca results were compared to monthly series of paleoclimate modeling intercomparison project phase 2 pmip2 model simulations anomalous stable isotope and u ca values are observed in a restricted area of the skeleton related to dissolution features the mid holocene sst seasonal amplitude mean and variability are higher than presently in new caledonia the increased seasonal amplitude in the mid holocene being most probably due to the occurrence of colder winters other southwest pacific mid holocene coral data showed also such an increased seasonal amplitude this could mean that the south pacific convergence zone spcz was weaker or reached locations more northerly than at present which could fit with northward shifts of the inter tropical convergence zone itcz during south hemisphere winter inversely strong rainfalls during the summer deduced from the ba ca signal and reconstructed sea surface salinity sss were interpreted as reflecting pronounced southwestward shifts of the spcz in summer as those occurring today during la nina events none of the six pmip2 models used reproduce the proxy based mid holocene increase of sst seasonal amplitude model maps show a less intense spcz in winter that would be consistent with higher sst seasonal amplitude finally we stress the need for more seasonally resolved data to validate this enhanced mid holocene sst seasonal amplitude in the southwest pacific region and to better understand the underlying mechanisms

holocene evolution of coastal wetlands in wet tropical northeastern australia pollen in sediments drilled from the innisfail coastal plain northeast queensland australia was examined to reconstruct the evolution of holocene wetlands in a wet tropical environment in contrast to monsoonal australia stable environmental conditions created by year round rainfall and low tidal range caused abrupt unidirectional transitions in wetland zonation as marine influence changed this has enabled a detailed reconstruction of the marine transgression and subsequent progradation mangroves colonized in response to marine transgression at c 7400 bp as riverine mangroves of low salt tolerance migrated up the mulgrave river these were replaced around 7000 bp by extensive rhizophora dominated mangroves coinciding with the development of a rhizophora dominated community in wyvuri embayment mangroves reached their greatest extent as sea level rise slowed towards 6000 bp with a stillstand indicated by a brief return to terrestrial conditions at one site high freshwater input depressed salt i

dynamical and boundary forcing characteristics of regional components of the asian summer monsoon abstract in this paper the authors present a description of the internal dynamics and boundary forcing characteristics of two major subcomponents of the asian summer monsoon asm that is the south asian monsoon sam and the east southeast asian monsoon eam the description is based on a new monsoon climate paradigm in which the variability of asm is considered as the outcome of the interplay of a fast and an intermediate monsoon subsystem under the influence of slow external forcings two sets of regional monsoon indices derived from dynamically consistent rainfall and wind data are used in this study results show that the internal dynamics of sam are representative of a classical monsoon system in which the anomalous circulation is governed by rossby wave dynamics where anomalous vorticity induced by an off equatorial heat source is balanced by the advection of planetary vorticity on the other hand the internal dynamics of eam are characterized by a hybrid monsoon system featuring m

holocene flood frequency across the central alps solar forcing and evidence for variations in north atlantic atmospheric circulation the frequency of large scale heavy precipitation events in the european alps is expected to undergo substantial changes with current climate change hence knowledge about the past natural variability of floods caused by heavy precipitation constitutes important input for climate projections we present a comprehensive holocene 10 000 years reconstruction of the flood frequency in the central european alps combining 15 lacustrine sediment records these records provide an extensive catalog of flood deposits which were generated by flood induced underflows delivering terrestrial material to the lake floors the multi archive approach allows suppressing local weather patterns such as thunderstorms from the obtained climate signal we reconstructed mainly late spring to fall events since ice cover and precipitation in form of snow in winter at high altitude study sites do inhibit the generation of flood layers we found that flood frequency was higher during cool periods coinciding with lows in solar activity in addition flood occurrence shows periodicities that are also observed in reconstructions of solar activity from 14 c and 10 be records 2500 3000 900 1200 as well as of about 710 500 350 208 suess cycle 150 104 and 87 gleissberg cycle years as atmospheric mechanism we propose an expansion shrinking of the hadley cell with increasing decreasing air temperature causing dry wet conditions in central europe during phases of high low solar activity furthermore differences between the flood patterns from the northern alps and the southern alps indicate changes in north atlantic circulation enhanced flood occurrence in the south compared to the north suggests a pronounced southward position of the westerlies and or blocking over the northern north atlantic hence resembling a negative nao state most distinct from 4 2 to 2 4 kyr bp and during the little ice age south alpine flood activity therefore provides a qualitative record of variations in a paleo nao pattern during the holocene additionally increased south alpine flood activity contrasts to low precipitation in tropical central america cariaco basin on the holocene and centennial time scale this observation is consistent with a holocene southward migration of the atlantic circulation system and hence of the itcz driven by decreasing summer insolation in the northern hemisphere as well as with shorter term fluctuations probably driven by solar activity

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

on the weakening relationship between the indian monsoon and enso analysis of the 140 year historical record suggests that the inverse relationship between the el nino southern oscillation enso and the indian summer monsoon weak monsoon arising from warm enso event has broken down in recent decades two possible reasons emerge from the analyses a southeastward shift in the walker circulation anomalies associated with enso events may lead to a reduced subsidence over the indian region thus favoring normal monsoon conditions additionally increased surface temperatures over eurasia in winter and spring which are a part of the midlatitude continental warming trend may favor the enhanced land ocean thermal gradient conducive to a strong monsoon these observations raise the possibility that the eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong enso events

the asian australian monsoon and el nino southern oscillation in the ncar climate system model features associated with the asian australian monsoon system and el nino southern oscillation enso are described in the national center for atmospheric research ncar global coupled climate system model csm simulation characteristics are compared with a version of the atmospheric component of the csm the ncar ccm3 run with time evolving ssts from 1950 to 1994 and with observations the csm is shown to represent most major features of the monsoon system in terms of mean climatology interannual variability and connections to the tropical pacific this includes a representation of the southern oscillation links between strong asian australian monsoons and associated negative sst anomalies in the eastern equatorial pacific the equatorial sst gradient across the pacific in the csm is shown to be similar to the observed with somewhat cooler mean ssts across the entire pacific by about 18 28c the seasonal cycle of ssts in the eastern equatorial pacific has the characteristic signature seen in the observations of relatively warmer ssts propagating westward in the first half of the year followed by the reestablishment of the cold tongue with relatively colder ssts propagating westward in the second half of the year like other global coupled models the propagation is similar to the observed but with the establishment of the relatively warmer water in the first half of the year occurring about 1 2 months later than observed the seasonal cycle of precipitation in the tropical eastern pacific is also similar to other global coupled models in that there is a tendency for a stronger than observed double itcz year round particularly in northern spring but with a well reproduced annual maximum of itcz strength north of the equator in the second half of the year time series of area averaged ssts for the nino3 region in the eastern equatorial pacific show that the csm is producing about 60 of the amplitude of the observed variability in that region consistent with most other global coupled models global correlations between nino3 time series global surface temperatures and sea level pressure slp show that the csm qualitatively reproduces the major spatial patterns associated with the southern oscillation lower slp in the central and eastern tropical pacific when nino3 ssts are relatively warmer and higher slp over the far western pacific and indian oceans with colder water in the northwest and southwest pacific indices of asian australian monsoon strength are negatively correlated with nino3 ssts as in the observations spectra of time series of indian monsoon australian monsoon and nino3 sst indices from the csm show amplitude peaks in the southern oscillation and tropospheric biennial oscillation frequencies 3 6 yr and about 2 3 yr respectively as observed lag correlations between the nino3 sst index and upper ocean heat content along the equator show eastward propagation of heat content anomalies with a phase speed of about 0 3 m s21 compared to observed values of roughly 0 2 m s21 composites of el nino la nina events in the csm show similar seasonal evolution to composites of observed events with warming cooling of greater than several tenths of a degree beginning early in northern spring of year 0 and diminishing around northern spring of year 11 but with a secondary resurgence in the csm events later in northern spring of year 11 the csm also shows the largest amplitude enso sst and low level wind anomalies in the western tropical pacific with enhanced interannual variability of ssts extending northeastward and southeastward toward the subtropics compared to largest interannual sst variability in the central and eastern tropical pacific in the observations

thermoluminescence and excess 226ra decay dating of late quaternary fluvial sands east alligator river australia thermoluminescence tl dating was applied to seven samples of siliceous fluvial sands from the east alligator river of northern australia giving ages ranging from modern to 6000 yr b p two methods of estimating the equivalent dose ed total bleach and regenerative were applied to the 90 to 125 m quartz fraction of the samples in order to determine the reliability and internal consistency of the technique high resolution and spectroscopy were used to measure radionuclide contents these measurements revealed an excess 226ra activity compared with 230th this excess decreased with depth and was used directly to derive mean sedimentation rates and thus sediment ages both this method and one 14c date confirmed the validity of the tl values which increased systematically with depth and were consistent with site stratigraphy tl was of limited use in the dating of these late holocene deposits because of age uncertainties of 500 to 1600 yr resulting from a significant residual ed this residual probably resulted from incomplete bleaching during reworking upstream of the sampling site for pleistocene deposits the residual ed will be less significant because of higher total eds and tl dates will be correspondingly more accurate

late holocene coupled moisture and temperature changes on the northern tibetan plateau the northern tibetan plateau involves complex interactions between the mid latitude westerly circulation and the subtropical asia monsoon circulation acting as a bridge communicating high and low latitude climatic processes previous studies from the region suggest relatively wet conditions in cold periods during the late holocene for instance the little ice age lia however the inference of such temperature moisture association is subject to the large uncertainty in lacustrine 14c chronology due to the particularly large lake reservoir effect in the region here we take a different approach by reconstructing paired temperature and moisture records from the same sediment cores to assess the temperature moisture association independent of chronology uncertainty we use alkenone indices uk 37 and c37 4 to reconstruct high resolution temperature and moisture changes simultaneously from two lakes in the qaidam basin northern tibetan plateau over the last 2500 years characterized by marked climatic variability our paired records confirm the warm dry and cold wet association in arid northwestern china during the late holocene opposite to the warm wet and cold dry association in subtropical asian monsoonal regions our moisture records further suggest substantially drier conditions during the medieval warm period mwp than the current warm period lastly the temperature and moisture changes inferred from our records can be well correlated with solar irradiance changes suggesting a possible link between solar forcing and natural climate variability during the late holocene on the northern tibetan plateau

ams radiocarbon dating in the study of arid environments examples from lake eyre south australia abstract sediments containing small amounts of carbon are difficult to date using traditional radiocarbon techniques this has resulted in less than satisfactory attempts to establish reliable chronologies for sedimentation and environmental change in the australian arid zone we describe here the first application of the ams technique to the radiocarbon dating of salt lake core samples using a chemical pretreatment methodology based on pollen extraction techniques these results indicate that fine grained charcoal and pollen have a similar source and depositional mechanism the data from lake eyre imply a last glacial maximum deposition for the major buried halite layer an early holocene return to lacustrine conditions with a late holocene reduction of net sediment inout to madigan gulf as the present playa conditions were established

changes in vegetation and seasonal climate since the last full glacial at lake frome south australia abstract results are presented from stratigraphy radiocarbon and pollen analysis from lake frome south australia close to the summer winter rainfall boundary at 30 south latitude the pollen sequence shows that tree vegetation was minor around 18 000 yr b p the landscape was dominated by chenopod low shrublands and ephemeral tubuliflorae vegetation by 17 000 yr b p callitris moved in and rose to 25 of the pollen sum values of casuarina myrtaceous shrubs acacia dodonaea and cyperaceae also rose at about the same time between 17 000 and 14 500 yr b p callitris and eucalyptus dominated the tree vegetation with callitris reaching its maximum values eucalpt woodlands were associated with undershrubs belonging to myrtaceae acacia dodonaea and gyrostemonaceae whereas callitris woodlands had probably supported only a sparse understorey chenopodiaceae today distributed mainly in the winter rainfall zone continued to show high values 25 gramineae today associated with high summer rainfall generally remained below 20 the sporadic presence of a number of taxa which now grow in temperate areas further south suggest that average annual temperatures were a little lower than at present from 14 500 to 13 000 yr b p there was a sudden decline in the values of callitris and a more gradual decline in chenopodiaceae and dodonaea the rise of ephemeral vegetation together with a fall in chenopodiaceae would indicate that winter precipitation had started to decline between 13 000 and 4500 yr b p chenopodiaceae and tubuliflorae ephemerals declined and gramineae rose to its highest values tribulus pollen a subtropical tropical taxon first appeared 13 000 yr b p overall plants from the summer rainfall zone became more prominent and taxa from the temperate south declined summer monsoon incursions apparently strengthened and temperature increased during this phase since 4500 yr b p both chenopodiaceae and tubuliflorae returned to high values whereas gramineae declined values of acacia and myrtaceous shrubs rose but those of casuarina declined and callitris remained extremely low these changes were accompanied by the onset of playa environments which have since persisted vegetation during this phase suggests that summer precipitation declined and summer monsoon incursions became rare during the late holocene

paleoenvironmental controls on vertebrate bearing abandoned channels in the upper carboniferous abstract a paleoenvironmental study of the vertebrate bearing sapropelic coal that underlies the upper freeport coal westphalian d upper carboniferous at linton ohio identifies a hierarchy of physical and chemical controls that influenced the formation of this deposit surface and subsurface data from previous work and field study of extensive exposures show that the fossiliferous cannel occurs at the bottom of an approximately 15 m deep abandoned river meander within a sandstone dominated multistorey sediment body storeys of this sediment body fine upward and consist of varying proportions of sandstones and siltstones within lateral accretion beds that are interpreted as point bar deposits associated channel fills are generally organic rich and composed of coals such as the linton cannel or carbonaceous mudstones maximum observed channel depth is approximately 18 m and the maximum thickness of the multistorey sediment body reaches nearly 40 m the sandstone dominated sediment body that contains the linton cannel trends northwestwardly and contrasts with mudstone dominated coarsening upward sequences that were deposited contemporaneously in adjoining areas this lithic pattern suggests that fluvial activity was restricted to a persistent topographic low that may have resulted from movement along the transylvania fault zone a previously documented basement controlled feature rapid subsidence on the southern side of this structure confined the fluvial system and favored the preservation of deposits within the meander belt including the fossil bearing sapropelic channel fill at linton the low inorganic content and oxbow like outline of the linton fossil deposit and its lateral relationship to other storeys in the multistorey channel sequence indicate that the abandoned meander was closed rapidly by neck cutoff and in the absence of clastic influx filled by sapropelic peat remains of aquatic to terrestrial animals that lived in or near the oxbow lake slowly rotted in this scavenger free anaerobic setting because of the substantial depth of the original meander and a lack of coarse grained fill materials a prolonged period of sapropelic filling insured the preservation of an abundant and diverse autochthonous vertebrate assemblage most westphalian tetrapod deposits represent sapropelic peats and muds and share some of the taphonomic attributes of the linton deposit the high degree of autochthony evidenced by westphalian vertebrate accumulations indicates that taphonomic controls of low lying peat forming alluvial and delta plain systems differ significantly from those of well drained alluvial valley settings