change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

last deglacial sea surface temperature evolution in the southeast pacific compared to climate changes on the south american continent abstract applying the alkenone method we estimated sea surface temperatures ssts for the past 33 kyr in two marine sediment cores recovered from the continental slope off mid latitude chile the sst record shows an increase of 6 7 c from the last ice age lia to the holocene climatic optimum while the temperature contrast between lia and modern temperatures is only about 3 4 c the timing and magnitude of the last deglacial warming in the ocean correspond to those observed in south american continental records according to our sst record the existence of a younger dryas equivalent cooling in the southeast pacific is much more uncertain than for the continental climate changes a warming step of about 2 5 c observed between 8 and 7 5 cal kyr bp may have been linked to the early to mid holocene climatic transition 8 2 7 8 cal kyr bp also described from equatorial africa and antarctica in principal variations in the latitudinal position of the southern pacific westerlies are considered to be responsible for sst changes in the peru chile current off mid latitude chile

a major widespread climatic change around 5300 cal yr bp at the time of the alpine iceman palaeoenvironmental and archaeological data from arbon bleiche lake constance switzerland give evidence of a rapid rise in lake level dated by tree ring and radiocarbon to 5320 cal yr bp this rise event was the latest in a series of three successive episodes of higher lake level between 5550 and 5300 cal yr bp coinciding with glacier advance and tree limit decline in the alps this west central european climate change may have favoured the quick burial and the preservation of the alpine iceman recently found in the tyrolean alps it has possible equivalents in many records from various regions in both hemispheres dating to 5600 5000 cal yr bp and corresponds to global cooling and contrasting patterns of hydrological changes this major mid holocene climate event marks the hypsithermal neoglaciation transition possibly resulting from a combination of different factors including orbital forcing changes in ocean circulation and variations in solar activity copyright 2004 john wiley sons ltd

sea ice and wind variability during the holocene in east antarctica insight on middle high latitude coupling abstract micropaleontological and biomarker data from two high accumulation marine sites from the coastal and continental shelf zone ccsz off east antarctica adelie land at 140 e and eastern prydz bay at 77 e are used to reconstruct holocene changes in sea ice and wind stress at the basin wide scale these data demonstrate congruent increase in sea ice concentration persistence and wind stress related sea surface turbulence in the two regions since 7 cal ka bp with a particularly strong signal since 4 5 3 5 cal ka bp comparison of these high latitude records with sea ice and turbulence records from the southern mid latitudes highlights distinctive climatic evolutions according to the different latitudinal bands sea ice persistence and turbulence increase in east antarctica ccsz are opposite to sea surface warming and sea ice retreat recorded after 4 5 3 5 cal ka bp in the east atlantic and indian sector between 55 and 45 s at the same period paleodata suggest sst cooling in all major coastal upwelling systems of the southern hemisphere caused by the northward transport of subpolar surface waters as a response to southern westerlies reinforcement we therefore propose as suggested for the northern hemisphere that holocene changes in the latitudinal insolation gradient primarily forced by obliquity and precession and amplified by sea ice and glacial ice expansions in the antarctic realm are responsible for the observed contrasted latitudinal patterns of southern latitudes

a solar irradiance trigger for millennial scale abrupt changes in the southwest monsoon 1 marine sedimentary records of the last glacial from tropical monsoon latitudes indicate climate fluctuations comparable to rapid changes in 18o recorded in greenland synchronizing two high resolution sedimentary records from the oman and pakistan margins we resolve millennial scale reversals in sea surface temperature sst gradient sst across the arabian sea which directly correspond with the majority of dansgaard oeschger d o events for the last 65 kyr the relative amplitude of individual monsoon and d o events appears comparable suggesting coupled and at least hemispheric forcing to explore this quasi cyclic forcing we compare alkenone based geologic data with modern satellite derived sst estimates between sites interstadial conditions fall within the range of monsoons during the holocene but stadial conditions have no analogs following published associations between eurasian winter snow cover ewsc and monsoon rainfall and el nino southern oscillation enso events and anomalous ewsc we find a good correlation between the southern oscillation index soi and arabian sea sst throughout the modern data set an apparent 11 year cyclicity in the soi reveals an association between the monsoon soi and solar output variability the soi primarily tracks solar total irradiance but the soi monsoon linkage becomes nonlinear during excursions of the soi associated with el nino events strong el ninos coincide precisely with minimum solar irradiance during the solar cycle which we attribute to threshold behavior in tropical pacific ssts and associated trade wind strength we propose that both short term interannual decadal and long term centennial millennial changes in solar output are consistent with records of enso variability monsoon intensity and d o event timing

triple water isotopologue record from wais divide antarctica controls on glacial interglacial changes in 17oexcess of precipitation measurements of the 17oexcess of h2o were obtained from ice cores in west and east antarctica combined with previously published results from east antarctica the new data provide the most complete spatial and temporal view of antarctic 17oexcess to date there is a steep spatial gradient of 17oexcess in present day precipitation across antarctica with higher values in marine influenced regions and lower values in the east antarctic interior there is also a spatial pattern to the change in 17oexcess between the last glacial maximum lgm and holocene periods at coastal locations there is no significant change in 17oexcess at both the west antarctic ice sheet divide site and at vostok east antarctica the lgm to early holocene change in 17oexcess is about 20 per meg atmospheric general circulation model gcm experiments show that both the observed spatial gradient of 17oexcess in modern precipitation and the spatial pattern of lgm to early holocene change can be explained by kinetic isotope effects during snow formation under supersaturated conditions requiring a high sensitivity of supersaturation to temperature the results suggest that fractionation during snow formation is the primary control on 17oexcess in antarctic precipitation variations in moisture source relative humidity play a negligible role in determining the glacial interglacial 17oexcess changes observed in antarctic ice cores additional gcm experiments show that sea ice expansion increases the area over which supersaturating conditions occur amplifying the effect of colder temperatures temperature and sea ice changes alone are sufficient to explain the observed 17oexcess glacial interglacial changes across antarctica

deglacial pattern of circulation and marine productivity in the upwelling region off central south chile abstract a high resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36 s off central south chile geob 7165 1 36 33 s 73 40 w 797 m water depth core length 750 cm indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka comparative analysis of several cores along the chilean continental margin 30 41 s suggests that the onset and the pattern of deglacial warming was not uniform off central south chile due to the progressive southward migration of the southern westerlies and local variations in upwelling marine productivity augmented rather abruptly at 13 14 ka well after the oceanographic changes we suggest that the late deglacial increase in paleoproductivity off central south chile reflects the onset of an active upwelling system bringing nutrient rich oxygen poor equatorial subsurface water to the euphotic zone and a relatively higher nutrient load of the antarctic circumpolar current during the last glacial maximum when the southern westerlies were located further north productivity off central south chile in contrast to off northern chile was reduced due to direct onshore blowing winds that prevented coastal upwelling and export production

dynamics of the millennial scale sea surface temperature and patagonian ice sheet fluctuations in southern chile during the last 70 kyr odp site 1233 abstract the ultra high sedimentation rates at odp site 1233 situated at 41 s off chile enabled the investigation of the millennial to multi centennial scale relationship and variability of the patagonian ice sheet pis extent as indicated by the fe relative concentration record and offshore sea surface temperatures sst during the last glacial period the close relationship of the fe record and the sst pattern as described previously for the 50 19 kyr time interval extends in the older part of the records 70 50 kyr during marine isotope stage mis 4 a delay of 500 yr of pis retreats relative to sst increases has been found similar to that described for the coldest part of mis 3 and 2 during early mis 3 60 56 kyr synchronous variability in both records resembles the deglacial to holocene time interval reflecting either a meltwater pulse or a dominant control of the fe input by rainfall changes related to a rather small pis results of spectral analysis on the detrended records show three main periodicity bands at 4 5 3 1 2 4 2 2 and 1 2 0 8 kyr the possible origins of these bands are discussed in terms of stochastic resonance and solar forcing

oxygen isotopes versus climap 18 ka temperatures a comparison from the tropical atlantic glacial interglacial differences in 18 o values of globigerinoides sacculifer have been mapped in the western and central tropical atlantic using data from surface and core sediments glacial interglacial differences in the western tropical atlantic if attributed to temperature changes only are at odds with temperature reconstructions performed by climap in the ceara rise region delta 18 o values exceeding 2 are recorded they can only be partly attributed to changes in the precipitation evaporation regime i e higher salinities and 18 o enriched precipitation an additional cooling of 1 2 c as compared to climap9s results is required to balance the 18 o record thus temperature changes from glacial to modern times amount to 2 3 c in the tropical atlantic off the northern coast of brazil

pollen distribution in marine surface sediments from chilean patagonia abstract southern south america is the only mid to high latitude continental landmass in the southern hemisphere and therefore represents one of the key areas to recover terrestrial records for the study of past and future climate variability at these latitudes during cruise md 159 of r v marion dufresne cores were taken off the chilean coast from 40 to 55 s in the open ocean and the fjords pollen spectra of 32 core top samples illustrate the relationships between pollen distribution in the sampled marine sediments and their transport from the vegetation onshore pollen concentrations show two distinct gradients 1 a north to south gradient controlled by latitudinal vegetation changes and by westerly winds and 2 from the fjords to the open ocean a gradient clearly controlled by wind fluvial inputs and pollen diagenesis linked to the distance from the coast and water depth the distribution of pollen percentages in these marine surface sediment samples reflects the local vegetation from the nearby continental area consequently pollen analyses from older sediments in these marine cores will be reliable tools to reconstruct past vegetational changes

high resolution planktic foraminiferal record of the last 13 300 years from the upwelling area off chile abstract a high resolution sedimentary record spanning the last deglacial and holocene periods was obtained by studying the deep sea sediment core gik 17748 2 retrieved from 2545 m water depth in the valparaiso basin chilean continental slope southeast pacific 32 45 00 s 72 02 00 w ams 14 c measurements and oxygen isotope analyses of the planktic foraminifera species globigerina bulloides and neogloboquadrina pachyderma dex indicate an age of 13 3 ams 14 c kyr b p at the base of the core 383 cm and sedimentation rates ranging between 9 and 92 cm kyr foraminiferal assemblages and accumulation rates were analysed in order to investigate variations in paleoceanography and paleoproductivity in the southern peru chile current during the last 13 kyr changes in foraminiferal assemblages indicate a sequence of three major hydrographic regimes at the site of the core 1 deglacial sediments are characterised by variable faunal compositions generally reflecting strong upwelling and high productivity 2 during the early and middle holocene upwelling and thus productivity decreased as indicated by an elevated relative abundance of n pachyderma dex and the importance of the subtropical surface water of the peru chile countercurrent increased as indicated by higher relative amounts of n dutertrei 3 for the last 3 kyr variable faunal assemblages indicate variable competing environmental conditions characterised on one hand by increased upwelling reflected by an elevated relative abundance of n pachyderma sin and on the other hand by warmer conditions deduced from a higher relative abundance of n dutertrei probably due to more frequent and more intense el nino events in addition hints for slightly cooler conditions between 11 4 and 10 7 kyr b p might be related to a younger dryas event in this region

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

late holocene marine productivity changes in northern patagonia chile inferred from a multi proxy analysis of jacaf channel sediments abstract a multi proxy approach based on organic organic carbon alkenones and c n and inorganic geochemical proxies biogenic opal inorganic carbon fe ti and ca preserved in the sediments of the jacaf channel cf7 pc33 44 21 s 72 58 w 510 m water depth chilean fjords yields evidence of major past productivity fluctuations in accordance with climatic changes over the last 1800 years the downcore record clearly shows two productivity climate modes the first period prior to 900 cal yr bp is characterized by decreased marine productivity and a reduced continental signal pointing to diminished precipitation and runoff in contrast the second period between 750 cal yr bp and the late 1800s top of core is illustrated by elevated productivity and an increased continental signal suggesting higher precipitation and runoff both time intervals are separated by a relatively abrupt transition of 150 years which roughly coincides with the beginning of the little ice age the increased content of freshwater diatoms and chrysophyte cysts that characterize the last 200 years of the latter mode coincides with a significant decrease in the carbonate content of the sediment together they further indicate increased terrigenous contributions and decreased marine carbonate productivity at the end of the little ice age the correspondence between our record and other paleoclimate studies carried out in south america and antarctica demonstrates that the chilean fjord area of northern patagonia is not just sensitive to local climatic variability but also to regional and possibly global variability

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

palaeoenvironmental conditions during the middle holocene at isla de los estados staaten island tierra del fuego 54 s argentina and their influence on the possibilities for human exploration abstract the middle holocene is a particular time period in which there are uneven environmental dynamics all along the southern portion of the continent whereas in the puna extreme aridity and high temperatures the so called hypsithermal period have been recorded a more humid and rainy phase dominated southern tierra del fuego the present paper explores the palaeoenvironmental situation of isla de los estados staaten island 54 38 54 55 s 63 48 64 46 w and its relationship with the archaeological record left behind by ancient canoeing people the considered period is characterized by exceptionally windy conditions the palaeoenvironmental information could be used as an explanation for the absence of cultural remains and also for the scarce archaeological record for peninsula mitre at the beginning of the middle holocene the diatom record shows a large amount of aulacoseira sp that could indicate either windy conditions or higher water levels at the site core the more distinctive changes in the diatom assemblages occurred at ca 5000 cal b p suggesting a shallower water level and more acidic conditions by 3000 cal b p the diatom species are strongly linked to peat and swampy environments however during the late holocene milder conditions might have favored seasonal travelling to the outer islands of the fuegian archipelago though no definitive or permanent settlements have been found

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

climatic controls of holocene fire patterns in southern south america holocene fire climate vegetation linkages are mostly understood at individual sites by comparing charcoal and pollen records with other paleoenvironmental proxy and model simulations this scale of reconstruction often obscures detection of large scale patterns in past fire activity that are related to changes in regional climate and vegetation a network of 31 charcoal records from southern south america was examined to assess fire history along a transect from subtropic to subantarctic biomes the charcoal data indicate that fire activity was greater than present at ca 12 000 cal yr bp and increased further and was widespread at 9500 cal yr bp fire activity decreased and became more spatially variable by 6000 cal yr bp and this trend continued to present atmospheric circulation anomalies during recent high fire years show a southward shift in westerlies and paleoclimate model simulations and data syntheses suggest that such conditions may have prevailed for millennia in the early holocene when the pole to equator temperature gradients were weaker and annual temperatures were higher than present in response to orbital time scale insolation changes

millennial scale changes of surface and deep water flow in the western tropical atlantic linked to northern hemisphere high latitude climate during the holocene there is increasing evidence that the preceding holocene climate was as unstable as the last glacial period although variations occurred at much lower amplitudes however low latitude climate records that confirm this variability are sparse here we present a radiocarbon dated holocene marine record from the tropical western atlantic aragonite dissolution derived from the degree of preservation of the pteropod limacina inflata records changes in the corrosiveness of the bottom water at the core site due to the changing influence of northern versus southern water masses the 18 o difference between the shallow living planktonic foraminifera globigerinoides sacculifer and the deep living globorotalia tumida is used as proxy for changes in the vertical stratification of the surface water hence the trade wind strength at this latitude we compared our data to high latitude records of the north atlantic region a good agreement is found between the aragonite dissolution and the strength in the island scotland overflow water which contributes significantly to the north atlantic deep water this suggests that large scale variations in the atlantic thermohaline circulation occurred throughout the holocene concurrently the comparison of our 18 o with the gisp2 glaciochemical records points to global holocene atmospheric reorganizations seen in both the tropics and high northern latitudes

oceanic climate and circulation changes during the past four centuries from radiocarbon in corals we analyzed radiocarbon in annual coral bands from the galapagos islands in the tropical east pacific to understand natural variability of past ocean circulation associated with climate change variability was observed on el nino timescales 3 7 years as well as at decadal and multi decadal periods low radiocarbon levels persisted for ten years during the early 1600s and for sixteen years during the early 1800s both coincident with periods of high volcanic aerosol loading in the atmosphere from massive eruptions intensification of tropical circulation at this time may be linked to climatically controlled changes in the structure of the tropical thermocline that is responsible for delivering cool upwelled waters to the tropical east pacific

climate variability at the southern boundaries of the namib southwestern africa and atacama northern chile coastal deserts during the last 120 000 yr abstract in this study we present grain size distributions of the terrigenous fraction of two deep sea sediment cores from the se atlantic offshore namibia and from the se pacific offshore northern chile which we unmix into subpopulations and which are interpreted as coarse eolian dust fine eolian dust and fluvial mud the downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern africa and northern chile for the last 120 000 yr the two records show a relatively wet last glacial maximum lgm compared to a relatively dry holocene but different orbital variability on longer time scales generally the northern chilean aridity record shows higher frequency changes which are closely related to precessional variation in solar insolation compared to the southwestern african aridity record which shows a remarkable resemblance to the global ice volume record we relate the changes in continental aridity in southwestern africa and northern chile to changes in the latitudinal position of the moisture bearing southern westerlies potentially driven by the sea ice extent around antarctica and overprinted by tropical forcing in the equatorial pacific ocean

integrated reconstruction of holocene millennial scale environmental changes in tierra del fuego southernmost south america abstract this study presents new paleoenvironmental data obtained from sedimentary cores from lago fagnano an elongated lake located at 54 s in southernmost south america data from palynomorphs pollen spores and algae and associated palynofacies as well as from diatom taxa retrieved from these cores compared with other regional proxies contribute to evaluate the similarities and differences in the climate patterns based on different proxies from southernmost patagonia the pollen analysis reveals that a grass steppe environment existed during the early holocene 11 300 8000 cal a bp followed by a major vegetation change characterized by development of forest steppe ecotone communities between 8000 and 6500 cal a bp under more humid conditions between 6500 and 4000 cal a bp expansion and colonization by nothofagus forests reflect an increase in effective moisture levels while openness in the forest communities characterizes the region after 1100 cal a bp the palynological organic matter combined with the algal content reflects hydrological changes occurring in the lake and its nutrient status probably in close relation with past climate oscillations all these past ecological changes are closely related to oscillations in precipitation and temperature as a response to the variations in the latitudinal position and or strength of the southern westerlies wind belt during the holocene

the southern westerlies in central chile during the two last glacial cycles as documented by coastal aeolian sand deposits and intercalating palaeosols abstract changes in the position and intensity of the southern westerly winds sww and related causal processes during the quaternary are controversial and not well understood here we present a record from continental central chile based on coastal aeolian sand and dunes with intercalated palaeosols reaching back 190 ka in time sixteen samples for luminescence dating and additional samples for geochemical procedures were analysed from three locations in the norte chico la serena los vilos las ventanas besides the recent bw horizons four palaeosols btb1 btb2 btb3 btb4 are identified they formed in periods with stable surface conditions and a relatively dense vegetation cover whereas sand accumulation reflects increased aeolian activity under dry conditions and in parts glacial sea level lowering three of these soils are well bracketed by luminescence data to

abrupt early to mid holocene climatic transition registered at the equator and the poles paleoclimatic records from equatorial east africa antarctica and greenland reveal that atmospheric circulation changed abruptly at the early to mid holocene transition to full postglacial conditions a climatic reorganization occurred at all three sites between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both marine and terrestrial records around the world

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

diatoms in southeast pacific surface sediments reflect environmental properties abstract diatom abundance and assemblage composition determined for 47 surface sediment samples from the southeast pacific 50 s 15 n combined with existing data for the peru and chile margins demonstrate responses to regional temperature upwelling and productivity high diatom abundances valves g mark the eastern equatorial pacific upwelling and the coastal upwelling areas in particular the upwelling centers off peru freshwater diatoms reflect the low salinity tongue off the chilean fjords diatom species composition distinguishes between coastal and eastern equatorial pacific upwelling conditions and records sea surface temperatures q mode factor analysis defines five floral assemblages factors 1 and 4 determined by the genus chaetoceros f1 and thalassionema f4 reflect coastal and equatorial upwelling conditions respectively factors 2 and 3 characterized by the genus thalassiosira and azpetia nodulifera can be associated with el nino conditions a 5th factor described by paralia sulcata records a near shore upwelling center off point concepcion central chile statistical transfer functions relate diatom species percentages to sea surface temperature and productivity with error estimates of 0 9 c and 23 gc m 2 yr respectively and provide new tools for estimating past temperature and productivity along the west coast of south america

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

major hydrological regime change along the semiarid western coast of south america during the early holocene water availability in the semiarid western coast of chile 30 32 s is conditioned by high interannual precipitation variability reflecting the transition between arid subtropical and moist mid latitude climates in the southeastern pacific ocean a paleoclimate reconstruction based on the latest pleistocene holocene geological record from the quebrada santa julia archeological site in chile 31 50 s and on modern meteorological mechanisms producing alluvial episodes in this region indicates a major change in the rainfall regime shortly after 8600 cal yr bp this together with other paleoclimate proxies along the west coast of south america 34 14 s suggests la nina like conditions 13 000 8600 cal yr bp based on sedimentological and geomorphologic evidence we hypothesized that the absence of heavy rainfall events in northern chile and the new hydrological regime that prevailed ca 8600 5700 cal yr bp in north central chile resulted from an increase in the large scale westerly flow over central chile as expected in near neutral enso conditions this atmospheric circulation anomaly is compatible with an equatorward shift of the influence of the southeast pacific subtropical anticyclone relative to the early holocene prior to the onset of modern enso variability

strontium isotope tracing of terrigenous sediment dispersal in the antarctic circumpolar current implications for constraining frontal positions the vigor of the glacial antarctic circumpolar current acc and the locations of frontal boundaries are important parameters for understanding the role of the southern ocean in global climate change toward the goal of understanding the locations of currents we present a survey of sr isotope ratios in terrigenous sediments around the perimeter of antarctica the pattern of the variations within the modern acc is used to suggest that terrigenous sediment from antarctica is injected into the acc via the ross and weddell gyres in the south north of the main acc the sr isotopes reflect continental contributions from africa australia new zealand and south america along a transect northward from the ross sea sr isotope ratios show a decrease from higher values in the south antarctic provenance to lower values in the north provenance from new zealand this otherwise monotonic decrease is interrupted within the acc by a zigzag to lower and then higher values which accompanies minimum terrigenous flux this zigzag requires contributions from two additional sediment sources beyond the main antarctic and new zealand end members the lower sr isotope ratios are attributable to greater contributions from basaltic sources within the current a consistent pattern around the acc the samples with higher sr isotope ratios point to an additional contributor possibly a wind transported component from australia during the lgm there is a systematic geographical variation in the sr isotope ratios similar to that of the holocene a small offset of the zigzag to the north approximately 1 2 may indicate a small northward shift of the southern boundary of the acc more highly resolved data are required to test whether this northward shift is really significant and whether it applies to other acc fronts during the lgm

impacts of andean uplift on the humboldt current system a climate model sensitivity study 1 using both an atmospheric global circulation model and a regional oceanic model we assess the impact of the andes uplift on the humboldt current system hcs with three topographic scenarios for the andes we show that the uplift played a crucial role in shaping the lower troposphere dynamics over the pacific ocean and in turn affected the physical characteristics of the system our results show that the uplift has triggered a marked southward shift of the hcs changing the latitudinal position of coastal upwelling areas as well as the strength of the south pacific gyre our oceanic modeling experiments show that the latitudinal pattern of sea surface temperatures is dramatically modified with reduced andes with anomalies reaching up to 3 c we discuss the feedbacks of these changes on south american climate as well as the potential onset of an altitudinal threshold that would have had triggered these changes

sea ice seasonality during the holocene adelie land east antarctica abstract thin sections of laminated cores from different antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale here we present the relative abundances of four diatom species and species groups fragilariopsis curta group as a proxy for yearly sea ice cover f kerguelensis as a proxy for summer sea surface temperature chaetoceros hyalochaete resting spores as a proxy for spring sea ice melting and the thalassiosira antarctica group as a proxy for autumn sea ice formation in core md03 2601 retrieved off adelie land on the antarctic continental shelf these abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years both the marine records and the simulated climate demonstrated a cooler early holocene 9000 7700 years bp a warmer mid holocene 7700 4000 years bp and a colder late holocene 4000 1000 years bp yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the mid holocene hypsithermal than during the late holocene neoglacial however diatom census counts and model output indicate that sea ice spring melting happened earlier in the season as expected but that autumn sea ice formation also occurred earlier in the season during the hypsithermal than during the colder neoglacial thereby following seasonal changes in local insolation

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

geoarchaeological evidence from peru for a 5000 years b p onset of el nino for the tropical west coast of south america where el nino southern oscillation enso is most pronounced archaeological and associated paleontological deposits in northern peru revealed a major climate change at about 5000 years before the present yr b p the data implied the presence of stable warm tropical water as far south as 10 s during the early mid holocene about 8000 to 5000 yr b p these data suggest that enso did not occur for some millennia preceding 5000 yr b p when global and regional climate was warmer than today

late quaternary environmental changes and latitudinal shifts of the antarctic circumpolar current as recorded by dinoflagellate cysts from offshore chile 41 s abstract the late quaternary organic walled dinoflagellate cyst record of site 1233 41 s offshore chile was studied with a 200 year resolution spanning the last 25 000 years the study provides the first continuous record of sub recent and recent dinoflagellate cysts in the southeast se pacific major changes in the composition of the cyst association cyst concentration and morphology of operculodinium centrocarpum reflect changes in sea surface temperature sst sea surface salinity sss palaeoproductivity and upwelling intensity these changes can be associated with latitudinal shifts of the circumpolar frontal systems the high cyst concentration high brigantedinium spp abundances low species diversity and the occurrence of certain cold water species are supportive for a 7 10 equatorward shift of the antarctic circumpolar current acc during the coldest phase of the last glacial maximum lgm between 25 and 21 1 cal ka bp deglacial warming initiated at 18 6 cal ka bp termination i 18 6 11 1 cal ka bp is interrupted by an unstable period of extreme seasonality rather than a cooling event between 14 4 and 13 2 cal ka bp synchronous with the antarctic cold reversal acr the holocene maximum is observed between 11 6 and 9 8 cal ka bp and is typified by the most southward position of the northern margin of the acc a cooling phase occurred during the early holocene until 7 cal ka bp and during the last 0 8 ka our data indicates that the se pacific 41 s climate has been influenced over the whole record by changes in the southern hemisphere sh high latitudes while during the mid to late holocene also a tropical forcing mechanism was involved including the el nino southern oscillation and the variable hadley cell intensity furthermore this study showed a relationship between the variable morphology of the spines processes of o centrocarpum and the combined variation of sea surface salinity and temperature sss sst ratio

paleoproductivity in the southern peru chile current through the last 33 000 yr abstract based on a multiparameter approach including organic carbon biogenic opal carbonate and the species composition of planktic foraminifera this paper provides the first qualitative assessment of the history of paleoproductivity on glacial interglacial time scales in the southern peru chile current pcc off chile which belongs to the least studied parts of the world ocean during the last glacial maximum lgm highest relative paleoproductivity of the last 33 kyr indicated by high accumulation rates of organic carbon biogenic opal and carbonate has been found contrasted by lowest values during the early and middle holocene this shift from high to low productivity is accompanied by a major change in the species composition of planktic foraminifera from a dominance of neogloboquadrina pachyderma sin to the dominance of n pachyderma dex the temporal pattern of paleoproductivity off chile is very similar to the history of the continental paleoclimate in the region which is supposed to be driven by the position of the southern westerlies this observation points to a functional relationship between the position of the southern westerlies and the history of paleoproductivity off chile assuming that atmospheric and oceanographic circulation are closely linked a northward displacement of the antarctic circumpolar current during the lgm in line with the northward movement of the southern westerlies would bring the main nutrient source closer to our core sites resulting in increased productivity however based on the available data it is not clear if the higher productivity in the southern pcc during the lgm reflects generally higher productivity during this time or only a regional displacement of the main productivity centers

last glacial holocene climate variability in the atlantic sector of the southern ocean abstract the southern ocean plays a major role in the glacial interglacial global carbon cycle however there is a substantial lack of information from its antarctic zone south of the polar front pf to understand key climate processes e g sea ice variability productivity changes co2 source region shifts of the southern westerly wind active in this region during the glacial interglacial transition due to the limited high resolution sediment records from this area to close this gap we investigated high resolution diatom records from a series of sediment cores from the atlantic and western indian sectors of the southern ocean between the modern pf and the winter sea ice wsi edge summer sea surface temperature ssst and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation as well as opal deposition these complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes southern ocean our reconstructions show that the last glacial lg sssts south of the modern pf are 1 3 c colder than modern conditions wsi expanded to the modern pf our data suggests effective carbon export in the antarctic zone during the lg deglacial two steps of warming support the bipolar seesaw mechanism antarctic zone is an important source region for the co2 deglacial increase the warming was more suppressed towards south due to continuous ice discharge from antarctica the sssts exceeded modern values during the early holocene optimum when wsi extent probably retreated south of its modern position the southern boundary of maximum opal deposition zone may have shifted to south of 55 s in the bouvet island area at this time the mid late holocene cooling with wsi re expanding to the bouvet island area probably related to enhanced cold water export by the weddell gyre from the developing cavity under the west antarctic ice shelf the cooling also suggests a northward shift of the southern westerly wind at least its southern boundary

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

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

early and mid holocene age for the tempanos moraines laguna san rafael patagonian chile data about the nature and timing of holocene events from the southern hemisphere especially in southern south america are required to provide insight into the extent and nature of past climate change in a region where land based records are restricted here we present the first use of single grain optically stimulated luminescence osl dating of a moraine sequence recording glacial advance along the western side of the patagonian icefields dates from the tempanos moraines at laguna san rafael lsr show that the san rafael glacier srg advanced to maximum holocene positions during the period 9 3 to 9 7 ka and at 5 7 ka outwash lying beneath the moraine in its northern portion dated to 7 7 ka indicates that the glacier front was also advanced at this time since these advances span both the regional early holocene warm dry phase 11 5 ka to 7 8 ka and the subsequent cooling and rise in precipitation in the mid late holocene since 6 6 ka we infer that the advances of the srg are not simply climate driven but that the glacier has also probably responded strongly to non climatic stimuli such as internal ice dynamics and the transition between calving and non calving many westwards flowing glaciers in patagonia were probably calving during much of the late pleistocene and holocene so we conclude that establishing robust glacial chronologies where climatic and non climatic factors cannot be distinguished is likely to remain a challenge

a geochemical and sedimentary record of high southern latitude holocene climate evolution from lago fagnano tierra del fuego abstract situated at the southern margin of the hemispheric westerly wind belt and immediately north of the antarctic polar frontal zone tierra del fuego is well positioned to monitor coupled changes in the ocean atmosphere system of the high southern latitudes here we describe a holocene paleoclimate record from sediment cores obtained from lago fagnano a large lake in southern tierra del fuego at 55 s to investigate past changes in climate related to these two important features of the global climate system we use an ams radiocarbon chronology for the last 8000 yr based on pollen concentrates thereby avoiding contamination from bedrock derived lignite our chronology is consistent with a tephrochronologic age date for deposits from the middle holocene volcan hudson eruption combining bulk organic isotopic 13 c and 15 n and elemental c and n parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret holocene climate and tectonic change during the last 8000 yr co variability and long term trends in c n ratio carbon accumulation rate and magnetic susceptibility reflect an overall holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin we attribute this variability to westerly wind derived precipitation increased wind strength and precipitation in the late holocene drives the nothofagus forest eastward and enhances run off and terrigenous inputs to the lake superimposed on the long term trend are a series of abrupt 9 negative departures in c n ratio which constrain the presence of seismically driven mass flow events in the record we identify an increase in bulk 13 c between 7000 and 5000 cal yr bp that we attribute to enhanced aquatic productivity driven by warmer summer temperatures the lago fagnano 13 c record shows similarities with holocene records of sea surface temperature from the mid latitude chilean continental shelf and antarctic air temperatures from the taylor dome ice core record in east antarctica mid holocene warming occurred simultaneously across the antarctic frontal zone and in particular in locations currently influenced by the antarctic circumpolar current

ice core evidence for secular variability and 200 year dipolar oscillations in atmospheric circulation over east antarctica during the holocene two holocene ice core records from east antarctica vostok and epica dome c were analysed for dust concentration and size distribution at a temporal resolution of 1 sample per 50 years a series of volcanic markers randomly distributed over the common part of the ice cores from 9 8 to 3 5 kyear bp ensures accurate relative dating 33 years dust size records from the two sites display oscillations structured in cycles with sub millennial and secular scale frequencies that are apparently asynchronous the power spectra of the composite sum of the two dust size records display spectral energy mostly for 150 to 500 year periodicities on the other hand the 200 year band is common to both records and the 200 year components of the two sites are out of phase 100 year lead or lag over 5 5 kyear a phenomenon also reflected by a significant 99 conf lev band in the power spectra of the composite difference of the two size records during long range transport mineral dust originating from the southern hemisphere continents is graded to a variable extent depending on the altitude and duration of atmospheric transport relatively coarse dust is associated with air mass penetration from the middle lower troposphere and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the antarctic plateau a hypothesis already proposed for the changes that occurred during the last glacial maximum to holocene transition delmonte et al 2004b moreover we assume that the overall fluctuation of air mass advection over antarctica depends on the meridional pressure gradient with respect to low latitudes i e the antarctic oscillation aao we therefore suggest a regional variability in atmospheric circulation over east antarctica the 150 500 year power spectrum of the composite parameter represents the long term variability of the aao imprinted by secular internal oscillations probably related to the southern ocean climatic system on the other hand the dust composite parameter suggests a persistent atmospheric dipole over east antarctica delivering coarser finer dust particles alternatively to vostok and dome c regions with a bi centennial periodicity indeed a seesaw phenomenon in dust size distribution was already observed at three east antarctic sites during the last deglaciation delmonte et al 2004b and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south pole interestingly the parameter shows a pronounced 200 year oscillation mode throwing new light on the unresolved question of a possible relationship between climate and solar activity

14c and 10be dated late holocene fluctuations of patagonian glaciers in torres del paine chile 51 s and connections to antarctic climate change abstract southern hemisphere holocene glacier chronologies are important for unraveling past climate change mid to high latitude teleconnections and regional to global climate forcing at present a significant number of glacier chronologies for patagonia are based on 14c dating which may afford only maximum or minimum limiting dates here we combine geomorphology and stratigraphy with radiocarbon 14c and beryllium 10 10be surface exposure age dating at three outlet glaciers zapata tyndall and pingo these glaciers drain the southernmost tip of the southern patagonian ice field at torres del paine national park chile 51 s after an expansion that we date at 3200 yr b p the torres del paine glaciers expanded to their last major late holocene maxima at 600 and 340 yr b p with the final dated readvance after 190 yr b p we use these data together with other patagonian glacier records to define the early mid and final glacial stages of the last millennium these cold events were separated by warm conditions that allowed the nothofagus forest to colonize deglaciated land the presence of near concurrent glacier fluctuations in patagonia and antarctic peninsula indicates widespread cooling punctuated the late holocene including the last millennium across much of the extratropical southern hemisphere we link this cooling to cold oceanographic atmospheric conditions forced by a northern shift or intensification of the southern westerly winds such scenario increased northward advection of cold antarctic circumpolar water along western patagonia and favored decreased upwelling of warm circumpolar deep water together with expanded sea ice around the antarctic peninsula

holocene antarctic climate variability from ice and marine sediment cores insights on ocean atmosphere interaction abstract holocene climate variability in the southeast atlantic sector of the southern ocean and antarctic is assessed and quantified through integration of available marine sediment core and antarctic ice core data we use summer sea surface temperature ssst and sea ice presence sip reconstructions from two marine sediment cores recovered north 50 s and south 53 2 s of the present day antarctic polar front apf as well as an atmospheric temperature and sea ice proxy from the epica ice core from dronning maud land edml we find reasonably good agreement in the timing of climate evolution in the analyzed series almost all records show a gradual glacial to holocene climate transition interrupted by the antarctic cold reversal around 13 000 cal yr bp and early holocene climatic optimum hco at about 11 000 cal yr bp during the early hco the seasonal ice cover retreats to south of 53 s it then readvances in the course of the mid to late holocene the maximum winter sea ice edge position during the recent 10 000 years varied mainly within 51 53 s with sporadic growth to north of 50 s a position similar to that during the last glacial the onset of the neoglacial period after ca 4000 yr bp is associated with a steepening of the ssst gradient between the marine core sites strengthening of the westerlies and cooling in the inland ice sheet the agreement in timing between elevated ssst during the early hco and decreased deuterium excess in edml and other ice cores from different locations in the east antarctic suggests that the retreat of sea ice during the early hco and weakening of the apf was a general feature of the east antarctic climate during that time

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

ice age vegetation and climate of subtropical chile abstract vegetation and climate of subtropical chile over the past 50 000 yr are reconstructed from pollen spores and other microfossils contained in a 10 7 m section of lacustrine deposits of laguna de tagua tagua 34 30 s 71 10 w controlled by 14 radiocarbon age determinations five pollen assemblages covering stratigraphic zones in the section represent plants on the upland and species inhabiting the lake basin surface pollen spectra from 58 stations approximately 30 40 s form an adjunct for interpreting past vegetation and climate from the fossil record temperature semi humid woodland of southern beech nothofagus dombeyi type and podocarp prumnopitys andina was apparently established about laguna de tagua tagua during the pleistocene contrasting existing semi arid broad sclerophyllous vegetation the woodland was extensive about the lake at the time of the last glacial maximum 25 000 14 000 yr b p and earlier 43 000 34 000 yr b p pollen from the families chenopodiaceae and amaranthaceae which characterize intervals of the pleistocene centered around 33 000 and 43 000 yr b p and the holocene suggests intervening episodes of relative aridity lake level fluctuations appear to follow the late quaternary climatic pattern implied by pollen assemblage data water in the lake was relatively high during development of southern beech podocarp woodland whereas during intervals of chenopod amaranth dominance lake levels were comparatively low excess precipitation over evaporation which during the pleistocene favored development of woodland of beech and podocarp is attributed to greater storm frequency conditions were apparently governed by strengthening of atmospheric circulation in the belt of southern westerly winds in the late glacial the temperate and more humid ice age climate with limited seasonality underwent transition to a subtropical semi arid mediterranean type that identifies the postglacial fluctuations in intensity of the southern westerlies marked by latitudinal movement of the polar front can account for past vegetation changes at laguna de tagua tagua

late holocene precipitation variability recorded in the sediments of reloncavi fjord 41 s 72 w chile we present reconstructions of late holocene changes in the source of organic matter and siliceous export production in the relocanvi fjord 41 s 72 w northern chilean patagonia based on organic carbon content 13corg n c ratio diatom assemblages and biogenic silica contents from three sediment cores the age models are based on a combination of 210pb profiles ams 14c dating and on the first occurrence of the diatom rhizosolenia setigera f pungens as a stratigraphic marker in the fjords the cores span the last 300 to 700 yr diatoms dominate the siliceous assemblages in the three cores 98 on average our results suggest that precipitation seasonality in the region of reloncavi was high in ce 1300 1400 and ce 1700 1850 with a clear decreasing trend since ce 1850 the latter trend is in agreement with instrumental records and tree ring reconstructions these fluctuations seem to be associated with the southern annular mode sam

southern ocean control on the extent of denitrification in the southeast pacific over the last 70 ka abstract temporal changes in oceanic denitrification the bacterial reduction of nitrate under suboxic conditions highlight the potential importance of n inventory changes and the production of n 2 o on the climate system at the same time the cause of the globally observed variation in denitrification remains unclear high resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from odp site 1234 on the chile margin record integrated denitrification changes within the peru chile upwelling system over the last 70 ka denitrification changes in the southeast pacific are coherent with antarctic climate changes recorded by the byrd ice core 18 o record and lead northern hemisphere climate events the southern hemisphere character of the chile margin 15 n record suggests that episodes of reduced denitrification in the se pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of subantarctic mode water samw which forms in the subantarctic zone of the southern ocean and feeds into the low latitude thermocline

asynchronous alkenone and foraminifera records from the benguela upwelling system abstract radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies including the investigation of temporal leads and lags the critical assumption is that temporal coupling between foraminifera and other sediment constituents including specific molecular organic compounds biomarkers of marine phytoplankton e g alkenones is maintained in the sediments to test this critical assumption in the benguela upwelling area we have determined radiocarbon ages of total c37 c39 alkenones in 20 samples from two gravity cores and three multicorer cores the cores were retrieved from the continental shelf and slope off namibia and samples were taken from holocene deglacial and last glacial maximum core sections the alkenone radiocarbon ages were compared to those of planktic foraminifera total organic carbon fatty acids and fine grained carbonates from the same samples interestingly the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples such age differences may be the result of different processes bioturbation associated with grain size effects lateral advection of recycled material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes based on the results of this study the age offsets between foraminifera and alkenones in sediments from the upper continental slope off namibia most probably do not result from particle selective bioturbation processes resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm s recorded near the core sites is the more likely explanation our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone based proxy data observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals i e the result of processes associated with particle settling and biological activity

early to mid holocene aridity in central chile and the southern westerlies the laguna aculeo record 34 s abstract central chile 32 35 s lies at the northern border of strong westerly influence and thus exhibits a steep precipitation gradient therefore the palaeoclimatic archives in the region are suitable for detecting past moisture changes the study of laguna aculeo 33 50 s 70 54 w presents a multiproxy holocene lake record including sedimentology geochemistry mineralogy pollen diatoms and radiocarbon dating 17 dates results indicate an arid early to mid holocene period about 9500 5700 cal yr b p after 5700 cal yr b p effective moisture increased progressively and around 3200 cal yr b p modern humid conditions were established numerous intercalated clastic layers reflect flood deposition during rainy winters a fluvial unit was deposited shortly before 9000 cal yr b p subsequently flood events were absent until 5700 but have become frequent since 3200 cal yr b p the frequency of flood layers possibly points to weak or no el nino activity during the early and mid holocene with a subsequent increase during the late holocene during the early and mid holocene the westerlies were probably blocked and hence deflected southward by the subtropical high pressure cell higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high pressure cell with intensified westerlies and possibly increased el nino activity

high concentrations of biogenic barium in pacific sediments after termination i a signal of changes in productivity and deep water chemistry abstract high concentrations of barium have been found in sediments deposited on the chilean continental slope after glacial termination i when compared to independent proxies of paleoproductivity the pattern of biogenic barium accumulation does not match the changes in paleoproductivity in this region and cannot be explained by changes in the terrigenous supply of barium alone this leaves an increased concentration of dissolved barium in sea water as the most likely cause of the observed barium anomalies based upon the accumulation rate of biogenic barium and the paleoproductivity index which was calculated from the accumulation rates of organic carbon biogenic opal and carbonate the changes in the concentration of dissolved barium in the pacific ocean in the course of the last glacial and through the holocene could be modelled this model shows that barium concentrations in the pacific during the last glacial were comparable to today 150 nmol kg1 the highest dissolved barium concentrations were calculated for the early and middle holocene 190 nmol kg1 the resulting pattern of variations in the barium concentration in the seawater agrees well with ba ca ratios in benthic foraminifera published in the literature the observed changes are probably driven by the holocene shoaling of the pacific carbonate compensation depth which is assumed to have caused an increased flux of previously carbonate bound barium from the sediment to the deep ocean waters leading to the observed longstanding maximum of dissolved barium in the pacific during the holocene

average process length variation of the marine dinoflagellate cyst operculodinium centrocarpum in the tropical and southern hemisphere oceans assessing its potential as a palaeosalinity proxy the study investigates the morphological variability of the dinoflagellate cyst operculodinium centrocarpum resting cyst of protoceratium reticulatum in core top samples distributed over the southern hemisphere and the tropics in relation to sea surface temperature sst and sea surface salinity sss at the corresponding sites the process lengths show a moderate inverse relationship to summer sst ssst r 0 44 and ssss ssst r 0 4 however lateral transport of cysts probably produced noise in the plots after excluding tropical and southern hemisphere sites considered to have been affected by long distance lateral transport the relationship between process length and density follows the equation sd 0 8422x 1016 9 r 0 55 with a root mean square error 0 63 kg m 3 while the negative correlation with ssst increases up to r 0 79 next to salinity this study thus highlights the importance of a second factor temperature affecting process length in the topics and the southern hemisphere oceans

late holocene sea surface temperature and precipitation variability in northern patagonia chile jacaf fjord 44 s abstract a high resolution multi proxy study including the elemental and isotopic composition of bulk organic matter land plant derived biomarkers and alkenone based sea surface temperature sst from a marine sedimentary record obtained from the jacaf fjord in northern chilean patagonia 44 20 s provided a detailed reconstruction of continental runoff precipitation and summer sst spanning the last 1750 yr we observed two different regimes of climate variability in our record a relatively dry warm period before 900 cal yr bp lower runoff and average sst 1 c warmer than present day and a wet cold period after 750 cal yr bp higher runoff and average sst 1 c colder than present day relatively colder ssts were found during 750 600 and 450 250 cal yr bp where the latter period roughly corresponds to the interval defined for the little ice age lia similar climatic swings have been observed previously in continental and marine archives of the last two millennia from central and southern chile suggesting a strong latitudinal sensitivity to changes in the southern westerly winds the main source of precipitation in southern chile and validating the regional nature of the lia our results reveal the importance of the chilean fjord system for recording climate changes of regional and global significance

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

oxygen 18 salinity relationship simulated by an oceanic general circulation model the distribution of h218o in the ocean is simulated using an oceanic general circulation model gcm surface isotopic fluxes prescribed to this model are derived from an atmospheric gcm which ensures their consistency the oceanic gcm is initialized with a homogeneous composition and redistributes isotopic gradients so as to equilibrate with the atmosphere a good agreement is found between the observations and the simulation concerning i the interbasin h218o gradients especially the atlantic being more enriched than the pacific as well as the meridional gradients and ii the h218o salinity relationship

a radiocarbon based assessment of the preservation characteristics of crenarchaeol and alkenones from continental margin sediments crenarchaeotal glycerol dibiphytanyl glycerol tetraether gdgt lipids and alkenones are two types of biomarkers derived from planktonic marine microorganisms which are used for reconstruction of sea surface temperature we determined the radiocarbon contents of the archaeal gdgt crenarchaeol and of alkenones isolated from continental margin sediments systematic differences were found between the two biomarkers with higher radiocarbon content in crenarchaeol than in the phytoplankton derived alkenones these differences can be explained by variable contributions of pre aged laterally advected material to the core sites crenarchaeol appears to be more efficiently degraded during transport in oxygen replete environments than alkenones whether this reflects the influence of chemical structure or mode of protection e g particle association is not known

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

palynological evidence for increased aridity on the central chilean coast during the holocene abstract the late quaternary vegetation of the semiarid coast of central chile is inferred from the palynological analysis of profiles from quereo 31 55 s and quintero 32 47 s prior to 11 400 yr b p wet conditions are suggested by the abundance of pollen indicators of swamp and aquatic taxa such as cyperaceae and myriophyllum and by the presence of traces of arboreal pollen since ca 10 000 yr b p a trend toward increasingly drier conditions is implied by the almost complete absence of arboreal and aquatic taxa and a general decrease in the diversity of the semiarid shrubland indicators from 3000 yr b p onward the pollen records show the reappearance of swamp and aquatic taxa presumably associated with wetter conditions which led to recolonization by forest taxa at 1720 yr b p in quintero the drier climate detected along the semiarid coast of central chile during most of the holocene extended inland to the andean foot hills within the present mediterranean type climate zone of chile and also affected the distribution of the winter deciduous nothofagus forests and the northern boundary of the temperate rain forests

marine radiocarbon reservoir effect along the northern chile southern peru coast 14 24 s throughout the holocene abstract through an extensive sampling and dating of pairs of associated shells and charcoal fragments combined with reanalysis of all the available previous data we reconstruct the evolution throughout the holocene of the regional marine radiocarbon reservoir effect r values along the northern chile southern peru area 14 24 s after elimination of the cases in which the terrestrial component yielded older ages than the marine shells to which they were associated the study is based upon data from 47 pairs of associated marine and terrestrial material our results suggest major changes in both the magnitude and variability range of r during the whole holocene period 1 between 10 400 and 6840 cal yr bp high values 511 278 yr probably result from a strengthened se pacific subtropical anticyclone and shoaling of equatorial subsurface waters during intensified upwelling events 2 between 5180 and 1160 cal yr bp lower values 226 98 yr may reflect a major influence of subtropical water and diminished coastal upwelling processes 3 during the last thousand years high values between 355 105 and 253 207 yr indicate an increased influence of 14 c depleted water masses and of enso for the early twentieth century a r value of 253 207 yr was calculated

high resolution reconstruction of southwest atlantic sea ice and its role in the carbon cycle during marine isotope stages 3 and 2 1 recent modeling suggests that changes in southern ocean sea ice extent potentially regulated the exchange of co2release between the ocean and atmosphere during glacials unfortunately a lack of high resolution sea ice records from the southern ocean has prevented detailed testing of these model based hypotheses with field data here we present high resolution records of southern ocean sea ice for the period 35 15 cal ka bp derived from diatom assemblages measured in three glacial sediment cores forming an 8 transect across the scotia sea southwest atlantic chronological control was achieved through a novel combination of diatom abundance stratigraphy relative geomagnetic paleointensity data and down core magnetic susceptibility and ice core dust correlation results showed that the winter sea ice edge reached its maximum northward extent of 53 s at least 3 north of its modern limit between 25 and 23 5 cal ka bp predating the last glacial maximum lgm maximum northward expansion of the summer sea ice edge also pre dated the lgm advancing to at least 61 s and possibly as far north as 55 s between 31 and 23 5 cal ka bp a 12 advance from its modern position a clear shift in the seasonal sea ice zone is evident following summer sea ice edge retreat at 23 5 cal ka bp potentially related to austral insolation forcing this resulted in an expanded seasonal sea ice zone between 22 5 cal ka bp and deglaciation our field data confirm that southern ocean sea ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre formed nutrients our data indicates that southern ocean sea ice was most effective as a physical barrier between 31 and 23 5 cal ka bp and as a mechanism capable of reducing vertical mixing between 22 5 cal ka bp and deglaciation however poor correlations with atmospheric co2 variability recorded in ice cores particularly the lack of a co2response during a rapid sea ice meltback event recorded at our study sites at the same time as antarctic isotopic maximum 2 suggest that southern ocean sea ice in the scotia sea did not play a controlling role in atmospheric co2 variation during the glacial