reconstructing twentieth century sea surface temperature variability in the southwest pacific a replication study using multiple coral sr ca records from new caledonia 1 coral based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation analytical expense and time constraints coral sr ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of amedee island new caledonia different sampling resolutions were examined in coral sr ca fortnightly and monthly and 18o fortnightly monthly and seasonally as well as similar scale subsampling of the daily in situ sea surface temperature sst record the mean coral sr ca 18o and sst values do not change as a function of sampling resolution the coral sr ca signal is highly reproducible the average absolute offset between coeval monthly sr ca determinations between any two coral time series is 0 035 0 026 mmol mol 1 0 65 c which is less than twice the analytical precision of the coral sr ca measurements the stack average of the monthly coral sr ca variations and monthly anomalies are significantly correlated with monthly in situ sst 1967 1992 r 0 96 and 0 64 respectively p 0 05 and n 302 and 1 grid monthly sst data product 1900 1999 r 0 95 and 0 56 respectively p 0 05 and n 1198 the coral sr ca sst reconstruction exhibits interannual and decadal timescale fluctuations that exceed those observed in the gridded sst record which may reflect true differences between sst at a shallow reef site and those averaged over a 1 grid box or inadequacies in the methodology used to create the gridded sst product when few observations are available a warming trend of 0 6 c is observed in the twentieth century coral sr ca sst record

el nino southern oscillation signal associated with middle holocene climate change in intercorrelated terrestrial and marine sediment cores north island new zealand a synchronous textural variation in intercorrelated high resolution sediment records from floodplain continental shelf and continental slope settings of the eastern north island new zealand provides evidence of increased storminess after ca 4 ka an upcore change in sediment texture reflects the transition to landsliding which supplanted fluvial incision as the dominant mode of sediment production in the middle holocene this signal which appears in all three records indicates a regional response to external forcing and records the impact of an intensified atmospheric circulation marking the establishment of the contemporary climate that is strongly influenced by the el nino southern oscillation the change in climate was a hemispheric event and in the southern hemisphere its timing is confirmed by independent proxy records from elsewhere in new zealand and the circum south pacific region

interdecadal decadal climate variability from multicoral oxygen isotope records in the south pacific convergence zone region since 1650 a d 1 in the south pacific interdecadal decadal oceanic and atmospheric variability referred to as the interdecadal pacific oscillation ipo is most pronounced in the south pacific convergence zone spcz salinity front region here we have used annual average oxygen isotope 18o time series from five coral cores collected from fiji and tonga in this region to construct a fiji tonga interdecadal decadal pacific oscillation f t idpo index of low frequency 9 and 55 years climate variability back to 1650 a d we first demonstrate the consistency between this f t idpo index and a mean sea level msl pressure based spcz position index spi 1891 2000 thus verifying the ability of coral 18o to record past interdecadal decadal climatic variations in this region back to 1891 the f t idpo index is then shown to be synchronous with the ipo index 1856 2000 suggesting that this coral based index effectively represents the interdecadal decadal scale climate variance back to 1650 the regularity of the f t idpo index indicates that interdecadal decadal variability in the spcz region has been relatively constant over the past 350 years with a mean frequency of 20 years variance peaks near 11 and 35 years there is a consistent antiphase correlation of the f t idpo index and the interdecadal decadal components in equatorial pacific coral 18o series from maiana and palmyra this observation indicates that the eastward expansion westward contraction of the eastern salinity front of the western pacific warm pool wpwp occurs simultaneously 1 year with the westward eastward shift of the spcz salinity front during positive ipo negative ipo phases this is the same relationship observed during the phases of the el nino southern oscillation

the southwest pacific ocean circulation and climate experiment spice the southwest pacific ocean circulation and climate experiment spice is an international research program under the auspices of clivar the key objectives are to understand the southwest pacific ocean circulation and the south pacific convergence zone spcz dynamics as well as their influence on regional and basin scale climate patterns south pacific thermocline waters are transported in the westward flowing south equatorial current sec toward australia and papua new guinea on its way the sec encounters the numerous islands and straits of the southwest pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes the transit in the coral solomon and tasman seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the el nino southern oscillation while the southward transports influence the climate and biodiversity in the tasman sea after 7 years of substantial in situ oceanic observational and modeling efforts our understanding of the region has much improved we have a refined description of the spcz behavior boundary currents pathways and water mass transformation including the previously undocumented solomon sea the transports are large and vary substantially in a counter intuitive way with asymmetries and gating effects that depend on time scales this paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions

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

mixed phase cloud phase partitioning using millimeter wavelength cloud radar doppler velocity spectra retrieving and quantifying cloud liquid drop contributions to radar returns from mixed phase clouds remains a challenge because the radar signal is frequently dominated by the returns from the ice particles within the radar sample volume we present a technique that extracts the weak cloud liquid drop contributions from the total radar returns in profiling cloud radar doppler velocity spectra individual spectra are first decomposed using a continuous wavelet transform the resulting coefficients of which are used to identify the region in the spectra where cloud liquid drops contribute by assuming that the liquid contribution to each doppler spectrum is gaussian shaped and centered on an appropriate peak in the wavelet coefficients the cloud liquid drop contribution may be estimated by fitting a gaussian distribution centered on the velocity of this peak to the original doppler spectrum the cloud liquid drop contribution to reflectivity the volume mean vertical air motion subvolume vertical velocity variance and ice particle mean fall speed can be estimated based on the separation of the liquid contribution to the radar doppler spectrum the algorithm is evaluated using synthetic spectra produced from output of a state of the art large eddy simulation model study of an arctic mixed phase cloud the retrievals of cloud liquid drop mode reflectivities were generally consistent with the original model values with errors less than a factor of 2 the retrieved volume mean vertical air velocities reproduced the updraft and downdraft structures but with an overall bias of approximately 0 06 m s 1 retrievals based on ka band atmospheric radiation measurement program zenith radar observations from barrow alaska during october 2011 are also presented

orbital forcing of climate over south africa a 200 000 year rainfall record from the pretoria saltpan late pleistocene variations in rainfall in subtropical southern african are estimated from sediments preserved in the pretoria saltpan a 200000 year old closed basin crater lake on the interior plateau of south africa we show that south african summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession as predicted by orbital precession geometry berger 1978 this south african record is out of phase with north african palaeomonsoon indices street and grove 1979 rossignol strick 1983 mcintyre et al 1989 the amplitude of the rainfall response to insolation forcing agrees with climate model estimates prell and kutzbach 1987 these results document the importance of direct orbital insolation forcing on both subtropical north and south african climate as well as the predicted antiphase sensitivity to precessional insolation forcing

changes in the south pacific convergence zone in ipcc ar4 future climate projections the response of the south pacific convergence zone spcz to climate change is examined using simulations from 16 coupled climate models under the a2 emission scenario carried out for the intergovernmental panel on climate change fourth assessment report characteristics of the austral summer spcz in the late twenty first century are compared with the late twentieth century the orientation and latitude of the spcz precipitation band the area and intensity of precipitation within the spcz and the eastern extent of the spcz changes in the spcz position are examined using a simple linear fit to the band of maximum precipitation and using a pattern matching technique both techniques find no consistent shift in the slope or mean latitude of the austral summer spcz however many models simulate a westward shift in the eastern edge of the spcz in austral summer with reduced precipitation to the east of around 150 w the westward contraction of the spcz is associated with a strengthening of the trade winds in the southeast pacific and an increased zonal sea surface temperature gradient across the south pacific the majority of models simulate an increase in the area of the spcz and in mean and maximum precipitation within the spcz defined by a 6 mm day precipitation threshold consistent with increased moisture convergence in a warmer climate changes in the spcz response to enso are examined using enso precipitation composites the spcz has a reduced slope and is shifted towards the equator in the a2 multi model mean el nino composite

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

modulation of station rainfall over the western pacific by the madden julian oscillation 1 rainfall data from 140 stations in the pacrain network in the tropical western pacific are analysed to assess the signal due to the madden julian oscillation mjo during northern winter the station rainfall difference between the wet and dry phases of the mjo is up to 6 mm day 1 compared to the climatological mean value of 12 mm day 1 the anomalies have a strong spatial coherence with over 80 of the individual point station anomalies having the same sign as the large scale rainfall anomaly as determined by the mainly satellite derived cmap rainfall product

first insights into mid holocene environmental change in central vanuatu inferred from a terrestrial record from emaotfer swamp efate island abstract here we present the first terrestrial record of mid holocene environmental changes in vanuatu this preliminary multi proxy analysis of core tfer 06 from emaotfer swamp efate island indicates changes in environmental conditions are mainly related to variations in climate over the last 6500 cal yr bp drier periods are broadly correlated with an increase in sustained el nino events recorded in the pacific on a decadal timescale the earliest change is the disappearance of mangroves adjacent to the site around 3200 cal yr bp this could well be due to both local tectonic uplift with subsequent hydrostatic adjustment and the onset of a drier period from c 3250 2500 cal yr bp the prevailing drier conditions can be linked to more persistent el nino conditions local volcanic events had limited ecological impact on the area freshwater diatoms indicate a hydroseral succession species living on submerged plants being common in muds from c 3250 1500 cal yr bp but rare in fibrous peat deposited later palaeoecological indicators of human impact have not been identified throughout this work

sensitivity of the australian summer monsoon to tilt and precession forcing abstract the response of the australian summer monsoon to orbital forcing is studied using a coupled general circulation model gcm with the focus on the relative roles of tilt and precession on the forcing of the northern australian summer monsoon it was found that unlike the northern hemisphere monsoons which are dominated by precession forcing the australian monsoon can be enhanced significantly not only by precession forcing but also by tilt forcing coupled to oceanic feedback the new insights obtained from a series of experiments with differing tilt precession configurations allow an interpretation of the australian late quaternary monsoon record in which insolation forcing plays a significant role

eastern margin variability of the south pacific convergence zone 1 the influence of low level inflow wind and its high frequency variability on the spatial characteristics of the eastern margin of the south pacific convergence zone spcz is examined compositing daily and 5 day mean low level wind precipitation and tropospheric moisture data reveals a clear relationship between high frequency zonal inflow variations and the eastern spcz margin with relaxation of trade wind intensity associated with increased moisture near the mean eastern spcz margin and an eastward displacement of the convection an idealized 2 dimensional model demonstrates that variations in dry air inflow cause tropospheric moisture and precipitation variations akin to those observed in this prototype factors affecting the extent of spcz variability are also important to the mean margin position spcz margin shifts under natural variability thus offer an observational target against which to evaluate simulated interactions of inflow air mass characteristics with convection

doppler velocity characteristics during tropical cyclones observed using scansar raw data doppler velocity can be derived by calculating doppler shift anomalies between predicted and estimated doppler centroids the predicted doppler centroid is calculated based on a geometric model of satellite assuming that the target is not moving the estimated doppler centroid can be directly extracted from the raw sar signal data by applying the average cross correlation coefficient method it is known that wind generated ocean waves can significantly contribute to doppler velocity due to the correlation between orbital motions of the waves and tilt and hydrodynamic modulated radar cross sections in addition to what sea surface current contributes in this study the characteristics of doppler velocities under hurricane conditions were investigated using radarsat 1 scansar raw data five different hurricanes hurricane dean hurricane ivan hurricane kyle hurricane lili and typhoon xangsane and sequential acquisitions of two hurricanes hurricane kyle and hurricane lili were selected to study the contribution of wind induced waves to doppler velocities and compared with in situ measurements of drifting buoys the results show that hurricane generated seas and associated winds and waves appear to be different from ordinary sea state this leads to lower estimates of doppler velocities than expected and much closer to sea surface current velocities

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

changes in the enso spcz relationship from past to future climates abstract the south pacific convergence zone spcz is the main climate feature of the southwest pacific it is characterized by a band of intense convective rainfall extending from the western pacific warm pool to french polynesia strong precipitation gradients within the spcz make local hydrologic conditions very sensitive to small displacements of this rainfall band as those caused by el nino and la nina events the associated rainfall fluctuations strongly impact the vulnerable southwest pacific countries they are recorded in environmental indicators such as corals used as proxies of past evolution of the el nino southern oscillation enso here we analyze a set of paleoclimate and future climate simulations and present evidence that changes in the background tropical state largely control the mean spcz location in contrast changes in the background tropical state do not directly control the interannual variability of the spcz location we show that changes in the interannual variability of the spcz location cannot be directly imputable to changes in the enso amplitude or rather the relationship between enso and the spcz location varies from one climate to another we thus demonstrate that the teleconnection mechanisms inferred from the modern climate cannot be directly extrapolated to other climates this study therefore calls for a cautious interpretation of climate reconstructions from environmental indicators in the southwest pacific with regard to enso variations

variability in the mean latitude of the atlantic intertropical convergence zone as recorded by riverine input of sediments to the cariaco basin venezuela abstract changes in the strength and position of the intertropical convergence zone itcz are an important component of climate variability in the tropical atlantic the cariaco basin located on the northern margin of venezuela is sensitive to tropical atlantic climate change and its sediments provide a record of past itcz behavior today the cariaco basin experiences two distinct seasons that reflect the annual migration of the atlantic itcz between january and march when the itcz lies south of the equator northeasterly trade winds sit directly over cariaco basin and strong coastal upwelling and dry conditions dominate beginning in june july as the itcz moves north local rainfall reaches a maximum and the upwelling diminishes or disappears here we summarize new and previously published data on the river derived terrigenous fraction of cariaco basin sediments as well as comparisons to other paleoclimate records which together suggest a coherent climatologic response in the tropical atlantic triggered by a pattern of itcz migration that mimics the seasonal cycle during periods of cooler north atlantic ssts on time scales ranging from the little ice age to the younger dryas to the cold stadials of the last glacial decreased detrital delivery to cariaco basin from local rivers suggests a southward shift in the mean latitudinal position of the itcz during warm interstadials and periods of holocene and deglacial warmth northward shifts in itcz position and its belt of convective rainfall are inferred from increased detrital delivery to the basin whether the rapid shifts in itcz position and precipitation recorded by cariaco basin sediments and other regional records reflect a response to forcing originating in the high latitude atlantic or to forcing potentially sourced in the tropics is a key question yet to be fully answered

a multiscale framework for the origin and variability of the south pacific convergence zone the diagonal south pacific convergence zone spcz is the major climatological precipitation feature over the pacific region during the northern hemisphere winter however the basic mechanisms that control its structure and variability are only partly understood here an analysis of the spcz is carried out in a multiscale framework this identifies two modes that dominate a westward shifted spcz and an enhanced spcz which occur independently of each other within both modes the primary mechanism for the initiation of precipitation is a transient synoptic wave propagating along the subtropical jet which is then refracted by the basic state toward the westerly duct over the central equatorial pacific individual vorticity centres in the wave become elongated with a diagonal northwest southeast tilt convection then occurs in a diagonal band in the poleward flow ahead of the cyclonic vorticity anomaly in the wave however latent heat release in the convection leads to upper tropospheric divergence and anticyclonic vorticity forcing which dissipates the wave shutting off the convective forcing and stopping the precipitation hence each individual wave or event only lasts a few days and contributes a discrete pulse of diagonally oriented precipitation to the region the sum of these events leads to the diagonal climatological spcz event occurrence is a stochastic process the probability of which is modified by lower frequency variability of the basic state including the madden julian oscillation mjo and el nino southern oscillation enso for example during periods of enhanced convection over the eastern indian ocean to western pacific mjo phases 3 6 and la nina the westerly duct expands westwards allowing synoptic waves to refract equatorwards earlier and increasing the probability of westward shifted spcz events hence both the existence and variability of the spcz depend fundamentally on scale interactions between dynamical processes on time scales ranging from daily to interannual copyright 2011 royal meteorological society

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

the southern oscillation part viii model sensitivity to sst anomalies in the tropical and subtropical regions of the south pacific convergence zone abstract we show by means of a general circulation model experiment that the atmospheric circulation over the south pacific ocean is sensitive to sea surface temperature anomalies in the tropical and subtropical regions of the south pacific convergence zone the possible implications for understanding the life cycle of an extreme event in the southern oscillation are discussed

the response of enso flavors to mid holocene climate implications for proxy interpretation the response of el nino southern oscillation enso to mid holocene boundary conditions remains an open question paleoclimate proxies and climate model simulations do not agree in the magnitude of the reduction of enso variability while recent proxy evidence from fossil corals from the central pacific show that the reduction in mid holocene enso variability compared to the end of the twentieth century is not different from the reduction during other holocene time intervals this is inconsistent with the interpretation of lake and ocean sediment records from the eastern pacific which show a significant reduction compared to all other holocene periods in order to reconcile the seemingly conflicting proxy evidence from the eastern and central pacific we hypothesize that enso remained active during the mid holocene however there was a change in the spatial pattern of the sea surface temperature anomalies also known as enso flavors using national center for atmospheric research s community climate system model version 4 forced with mid holocene orbital conditions we find that the frequency of occurrence of the strongest eastern pacific ep events decreases in the mid holocene and their variance is reduced by 30 while the frequency of central pacific cp events slightly increases and their variance does not change we also find a shift in the seasonality of ep events but not in that of cp events lastly mid holocene ep events develop more slowly and decay faster the differential response of enso flavors to mid holocene forcing is remotely forced by the west pacific where a weakening of the trade winds in early boreal spring in the mid holocene initiates an anomalous downwelling annual kelvin wave which reaches the eastern pacific during the enso development season weakens the upper ocean stratification and results in reduced enso upwelling feedback the simulated reduction in the ep flavor versus the cp flavor in the mid holocene is consistent with proxy evidence the teleconnection patterns of the two flavors with temperature precipitation and salinity are distinct and proxies from different regions of the pacific might be recording variability associated with only one of the flavors or some combination of their relative effects

the south pacific convergence zone spcz a review abstract the circulation features associated with the south pacific convergence zone spcz and its accompanying cloud band are reviewed and discussed the paper focuses on the following topics location structure and characteristics of the spcz theories and observations concerning its existence the significance and scope of the spcz in global scale circulation patterns quasi periodic changes in its location and strength and synoptic scale features within its regional influence e g cyclones subtropical jets it concludes with some challenging problems for the future

evaluation of the south pacific convergence zone in ipcc ar4 climate model simulations of the twentieth century abstract understanding how the south pacific convergence zone spcz may change in the future requires the use of global coupled atmosphere ocean models it is therefore important to evaluate the ability of such models to realistically simulate the spcz the simulation of the spcz in 24 coupled model simulations of the twentieth century is examined the models and simulations are those used for the fourth assessment report ar4 of the intergovernmental panel on climate change ipcc the seasonal climatology and interannual variability of the spcz is evaluated using observed and model precipitation twenty models simulate a distinct spcz while four models merge intertropical convergence zone and spcz precipitation the majority of models simulate an spcz with an overly zonal orientation rather than extending in a diagonal band into the southeast pacific as observed two thirds of models capture the observed meridional displacement of the spcz during el nino and la nina events the four models that use

the south pacific convergence zone in cmip5 simulations of historical and future climate the south pacific convergence zone spcz is evaluated in historical simulations from 26 coupled model intercomparison project phase 5 cmip5 models and compared with previous generation cmip3 models a subset of 24 cmip5 models are able to simulate a distinct spcz in the december to february djf austral summer although the position of the spcz in these models is too zonal compared with observations the spatial pattern of spcz precipitation is improved in cmip5 models relative to cmip3 models although the spurious double itcz precipitation band in the eastern pacific is intensified in many cmip5 models all cmip5 models examined capture some interannual variability of spcz latitude and 19 models simulate a realistic correlation with el nino southern oscillation in simulations of the twenty first century under the rcp8 5 emission scenario no consistent shift in the mean position of the djf spcz is identified several models simulate significant shifts northward and a similar number of models simulate significant southward shifts the majority of cmip5 models simulate an increase in mean djf spcz precipitation and there is an intensification of the eastern pacific double itcz precipitation band in many models most models simulate regions of increased precipitation in the western part of the spcz and near the equator and regions of decreased precipitation at the eastern edge of the spcz decomposition of spcz precipitation changes into dynamic and thermodynamic components reveals predominantly increased precipitation due to thermodynamic changes while dynamic changes lead to regions of both positive and negative precipitation anomalies

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

late quaternary vegetation change in the tari basin papua new guinea the changes in late quaternary vegetation at two sites in the tari basin central highlands of new guinea are presented haeapugua basin 1650 m altitude and tugupugua basin 2300 m altitude lie within the lower montane forest belt where the climate is characterised by high relative humidity and low seasonality pollen analysis mineral magnetics carbonised particle analysis and dating by radiocarbon and thermoluminescence techniques are employed to reconstruct the vegetation and sediment history the sequences include fragmentary interglacial interstadial records from before 50 000 yr b p and a continuous record from at least 28 000 yr b p to the present the study shows that prior to 21 000 yr b p vegetation in the basin was dominated by fluctuating proportions of tree taxa indicative of a forested environment the montane forest taxon nothofagus is important throughout the record although other tree taxa including castanopsis myrtaceae dacrydium and pandanus attain dominance at different times under the influence of a range of environmental factors the creation of an open environment around 21 000 yr b p is considered to be a consequence of the arrival of humans in the region the late glacial transition between 14 500 and 8500 yr b p is a period of climatic instability with landscape and vegetation adjustments proceeding at different rates across the highlands vegetational adjustments match modern ranges by about 8500 yr b p when swamp forest developed across the sites at the lower altitude site there are indications of anthropogenic forest disturbance associated with swamp forest clearance commencing around 1700 yr b p and intensifying through to the present forest clearance is recorded only after 700 yr b p at the higher site where agriculture was probably only sustainable after the introduction of sweet potato ipomoea batatas

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

glacial to holocene climate changes in the se pacific the raraku lake sedimentary record easter island 27 s abstract easter island se pacific 27 s provides a unique opportunity to reconstruct past climate changes in the south pacific region based on terrestrial archives although the general climate evolution of the south pacific since the last glacial maximum lgm is coherent with terrestrial records in southern south america and polynesia the details of the dynamics of the shifting westerlies the south pacific convergence zone and the south pacific anticyclone during the glacial interglacial transition and the holocene and the large scale controls on precipitation in tropical and extratropical regions remain elusive here we present a high resolution reconstruction of lake dynamics watershed processes and paleohydrology for the last 34 000 cal yrs bp based on a sedimentological and geochemical multiproxy study of 8 cores from the raraku lake sediments constrained by 22 ams radiocarbon dates this multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake high lake levels and clastic input dominated sedimentation in raraku lake between 34 and 28 cal kyr bp sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the glacial period between 28 and 17 3 cal kyr bp including the lgm period colder conditions contributed to a reduction of the tree coverage in the island the coherent climate patterns in subtropical and mid latitudes of chile and eastern island for the lgm more humid conditions suggest stronger influence of the antarctic circumpolar current and an enhancement of the westerlies the end of glacial period occurred at 17 3 cal kyr bp and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments deglaciation termination 1 between 17 3 and 12 5 cal kyr bp was characterized by an increase in lake productivity a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels dominance of organic deposition and algal lamination the timing and duration of deglaciation events in easter island broadly agree with other mid and low latitude circum south pacific terrestrial records the transition to the holocene was characterized by lower lake levels the lake level dropped during the early holocene ca 9 5 cal kyr bp and swamp and shallow lake conditions dominated till mid holocene partially favored by the infilling of the lacustrine basin during the mid to late holocene drought phases led to periods of persistent low water table subaerial exposure and erosion generating a sedimentary hiatus in the raraku sequence from 4 2 to 0 8 cal kyr bp the presence of this dry mid holocene phase also identified in low andean latitudes and in patagonian mid latitudes suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by el nino like dominant conditions have occurred at a regional scale the palm deforestation of the easter island attributed to the human impact could have started earlier during the 4 2 0 8 cal kyr bp sedimentary gap our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the polynesian people to the island if it occurred at ca ad 800 it coincided with the warmer conditions of the medieval climate anomaly whereas if it took place at ca ad 1300 it was favored by enhanced westerlies at the onset of the little ice age changes in land uses farming intensive cattle during the last century had a large impact in the hydrology and limnology eutrophication of the lake

large variations in the holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect this effect for a particular site region is generally assumed constant through time when calibrating marine 14c ages however recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late quaternary and holocene here we report marine radiocarbon reservoir correction r r for heron reef and moreton bay in southwestern sw pacific for the last 8 ka derived from 14c analysis of 230th dated corals most of our r r for the last 5 4 ka agree well with their modern value but large r r variability of 410 yr from trough to peak with possible decadal centennial fluctuations is evident for the period 5 4 8 ka the latter time interval also has significant variations with similar features in previously published r r values for other sites in the pacific including southern peru northern chile in southeastern se pacific the south china sea vanuatu and papua new guinea with the largest magnitude of 920 yr from se pacific the mechanisms for these large r r variations across the pacific during the mid holocene are complex processes involving 1 changes in the quantity and 14c content of upwelled waters in tropical east pacific tep frequency and intensity of ocean upwelling in the tep and contribution of subantarctic mode water to the upwelled waters which is influenced by the intensity and position of southern westerly winds and 2 variations in ocean circulation associated with climate change la nina el nino conditions intensity of easterly trade winds positions of the intertropical convergence zone and the south pacific convergence zone which control the spreading of the older upwelled surface waters in the tep to the western sites our results imply the need for employing temporal changes in r r values instead of constant modern values for age calibration of holocene marine samples not only for the sw pacific sites but also for other tropical and subtropical sites in the pacific

origin of the south pacific convergence zone abstract the importance of the presence of south america and australia to the existence and orientation of the south pacific convergence zone spcz during january is explored using the ecmwf t21 model each of the continents is removed from the model and replaced with an ocean surface and the resulting precipitation and circulation associated with the spcz are then compared to a perpetual january control run results show that the presence of south america and the equatorial pacific upwelling zone does not appear to be crucial to the spcz but that the removal of australia destroys the southern monsoon and substantially weakens the western part of the spcz this suggests that the northwest southeast orientation of the spcz during southern summer is more dependent on interactions with the midlatitude westerlies over the south pacific than on the distribution of sea surface temperature and land over the southern hemisphere

mechanisms of mid holocene precipitation change in the south pacific convergence zone abstractthe variability of the south pacific convergence zone spcz during the mid holocene is investigated using models archived in the paleoclimate modelling intercomparison project phase ii pmip2 database relative to preindustrial conditions mid holocene top of atmosphere insolation was relatively lower during austral summer december february djf which is the season when the spcz is at its peak intensity in response to this perturbation the pmip2 models simulate a displacement of the spcz to the southwest this spcz shift is associated with a sea surface temperature sst dipole with increased rainfall collocated with warm sst anomalies decomposing the djf precipitation changes in terms of a diagnostic moisture budget indicates that the spcz shift is balanced to leading order by a change in the mean moisture convergence changes to the broad area of upper level negative zonal stretching deformation where transient eddies can become trapped and subsequently generate deep convection suppo