the last 7500 cal yr b p of westerly rainfall in central chile inferred from a high resolution pollen record from laguna aculeo 34 s abstract we report multiproxy analyses of a sediment core obtained from laguna aculeo that spans the past 7500 years laguna aculeo 33 50 s 70 55 w is one of the few natural inland lakes located in the mediterranean zone of central chile near the northern margin of the influence of the southern westerlies the record shows elevated pollen counts of halophytes and seasonally drying of the lake basin prior to 5700 cal yr b p indicating severe aridity and warmer than present conditions this was followed by the establishment of a fresh water lake along with an increase in arboreal and herbaceous plant diversity between 5700 and 3200 cal yr b p an intensification of this trend started at 3200 cal yr b p along with the abrupt decrease of halophytes until 100 cal yr b p within this humid period pollen accumulation rates show large amplitude fluctuations coeval with numerous turbidite layers suggesting a highly variable and torrential rainfall pattern this intense and variable precipitation regime is probably associated with the el nino southern oscillation enso phenomenon we suggest that the modern mediterranean climate of central chile was established at 3200 cal yr b p paleovegetation and paleolimnological changes starting at 100 cal yr b p correlate with documented human activity surrounding the lake

pollen sequence from the chilean lake district during the llanquihue glaciation in marine oxygen isotope stages 4 2 pollen stratigraphy of a core taken from a fen at fundo nueva braunau 40 17 499s 73 04 839w situated 2 km beyond the western border of llanquihue age glacial drift spans an age range from an estimated 60 000 70 000 bp to about 14 000 14 c yr bp marine oxygen isotope stages 4 2 the location at present is in the contact zone of valdivian evergreen forest and lowland deciduous beech forest early and late in the pollen record as indicated by assemblages of southern beech nothofagus dombeyi type and grass gramineae the site was located in subantarctic parkland intervening assemblages represent expansion of valdivian north patagonian evergreen forest 49 355 to about 40 000 14 c yr bp and north patagonian evergreen forest subantarctic parkland approximately 40 000 to 30 000 14 c yr bp climate over the time span was under the storm regime of the southern westerlies and apparently uninterruptedly wet when subantarctic parkland expanded cold conditions with summer temperatures estimated at 8 9 c 7 c lower than present resulted in episodes of glacier maxima climate moderated during the period of forest expansion at which time glaciers were in a state of recession contrasting with the continuously wet climate of the lake district for the period of record climate in semi arid arid subtropical chile underwent extended intervals of precipitation data from both the terrestrial and marine realm implicate the southern westerlies as the cause of intensified storm activity at lower latitudes copyright 2000 john wiley sons ltd

tree ring evidence of little ice age glacier advances in southern tibet the history of late holocene glacier fluctuations in eastern tibet was studied by determining the ages of trees growing on glacier deposits maximum tree ages yield minimum ages of ad 1760 and 1780 for moraine formation at the maximum extent of the little ice age glacier advances in two glacier forefields subsequent moraines could be dated to the beginning of the nineteenth and the beginning of the twentieth century larch trees from a third glacier forefield in southeastern tibet show evidence of glacier activity from 1580 to 1590 from the end of the eighteenth to the beginning of the nineteenth century and from 1860 to 1880 one glacier at mt gyalaperi recently advanced in both 1951 and 1987 periods of glacier advances can partly be correlated with periods of growth reductions in chronologies of total ring width and maximum latewood density derived from trees growing on slopes above the glacier valleys correlation functions with meteorological data suggest that maximum latewood density of subalpin

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

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

characteristics of late quaternary monsoonal glaciation on the tibetan plateau and in east asia abstract glaciers fed by monsoonal precipitation are mainly located on the tibetan plateau and easternmost asia these are characterized by simultaneous accumulation and ablation in summer season the southeast part of the tibetan plateau experiences monsoonal precipitation in excess of 1000 mm yr resulting in maritime temperate glaciers in contrast precipitation in the middle and northwest part of the tibet plateau decreases from 1000 to 200 mm yr resulting in the formation of continental cold glaciers during the last glacial the regions of heavy monsoonal precipitation were restricted to the southeast corner of the plateau the westerly weak precipitation zone shifted southward and occupied the major northwest part of the plateau where the extreme continental type glaciers greatly expanded in the eastern margin of asia including taiwan central japan hokkaido and probably mount changbai maritime type glaciers were more extensive because of higher monsoonal precipitation especially heavy snowfall in northwest japan owing to the rich moisture content of the winter monsoon over the japan sea the millennial scale monsoon intensity and glacial cycle in the tibetan plateau are strongly affected by the precession cycle and the orbit inclination cycle which dominate the solar irradiance variation in low latitudes as the high radiation and strong monsoon caused the warmer and wetter climate during 40 30 ka the low radiation produced a weak monsoon and large depression of temperature and precipitation around 21 ka this climatic pattern differs from that in the high latitudes where the eccentricity cycle is prominent the temperature during the last glacial maximum lgm was 6 9 c lower than today on the tibetan plateau and the equilibrium line altitude was depressed by about 1000 m in the southeast part and in the east south and west margins of the plateau where precipitation was high the equilibrium line depression was 500 300 m in the inner and especially the west part of the plateau this variation in equilibrium lines might be caused by the combined effect of the decrease in precipitation the expansion of extreme continental glaciers and the active uplift of glaciated mountains the estimation of a glaciated area of about 350 000 km2 in the tibetan plateau and roughly 500 000 km2 in high asia based on observations of prominent features of lgm glacier extension may be the direct evidence that shows there was no quaternary unified ice sheet developed in the tibetan plateau

a winter precipitation reconstruction ce 1810 2012 in the southeastern tibetan plateau and its relationship to salween river streamflow variations we established a tree ring width series from one yunnan douglas fir pseudotsuga forrestii stand near the mingyong glacier terminus of meili snow mountain southeastern tibetan plateau correlation analyses indicated that radial growth of yunnan douglas firs is largely controlled by variations in winter november march precipitation the precipitation reconstruction model accounts for 37 of the actual precipitation variance during the common period 1954 2012 spatial correlations with the gridded precipitation data reveal that the winter precipitation reconstruction represents regional precipitation changes over the southeastern tibetan plateau by comparing our results with other regional tree ring records a distinctive amount of common dry and humid periods were found our winter precipitation reconstruction shows profound similarities with salween river streamflow signals as well as regional glacial activity cross wavelet analysis reveals solar and enso influences on precipitation and streamflow variations in the southeastern tibetan plateau

iron isotope constraints on fe cycling and mass balance in oxygenated earth oceans the fe isotope composition of proterozoic to modern clastic sedimentary rocks and aerosols defines a range ind 56 fe values that is only slightly more variable than the range of fe isotope com positions measured in terrestrial igneous rocks indicating that chemical weathering sedimentary transport and diagenesis play only a minor role in producing fe isotope variations in environ ments where fe redox conditions have been controlled by current levels of atmospheric oxygen in contrast the fe isotope composi tions of hot fluids 300 8c from mid ocean ridge mor spread ing centers define a narrow range that is shifted to lower d 56 fe values by 0 2 0 5 as compared to igneous rocks these new data allow a conceptual model for the fe isotope composition of the oxic oceans that predicts large ranges in fe isotope composition under conditions of changing aerosol and mor fe fluxes such as during periods of major worldwide glaciation

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

climate variability over the last 9900 cal yr bp from a swamp forest pollen record along the semiarid coast of chile abstract we present a fossil pollen analysis from a swamp forest in the semiarid coast of chile 32 05 s 71 30 w at the northern influence zone of southern westerly wind belt a 10 000 cal yr bp calendar years before 1950 palynological sequence indicates a humid phase characterized by dense swamp forest taxa dated between 9900 and 8700 cal yr bp the presence of pollen starved sediments with only scant evidence for semiarid vegetation indicates that extreme aridity ensued until 5700 cal yr bp the swamp forest recovered slowly afterwards helped by a significant increase in moisture at 4200 cal yr bp a new swamp forest contraction suggests that another slightly less intense drought occurred between 3000 and 2200 cal yr bp the swamp forest expansion begins again at 2200 cal yr bp punctuated by a highly variable climate comparisons between the record presented here with other records across the region imply major variations in the extent of the southern westerlies during the holocene this variability could have been caused either by latitudinal displacements from the present mean position of southern westerlies wind belt or by changes in the intensity of the south pacific subtropical anticyclone both of which affect winter precipitation in the region

moisture changes and fluctuations of the westerlies in mediterranean central chile during the last 2000 years the laguna aculeo record 33 50 s abstract the multi proxy study of lacustrine sediments from laguna aculeo 33 50 s provides detailed information about moisture changes in the lowlands of mediterranean central chile during the last 2000 years the lake lies just at the northern border of the strong westerlies influence with dry summers and humid winters geochemical sedimentological and diatom analyses provide evidence for an arid period between cal 200 bc and ad 200 and a subsequent increase in moisture after cal ad 200 abundant clastic layers in the core represent flood events periods with a higher frequency of flood events indicate an increased intensity of the westerlies more winter frontal system activity and possibly enso related variability probably comparable to modern conditions in mediterranean central chile periods of high clastic input occur around cal ad 200 400 500 700 especially around cal ad 1300 1700 and around ad 1850 1998 during the last 50 years at least eight flood events were detected correlating mainly with el nino years a very short drier period also occurred in the late 1960s in recent decades human impact has resulted in a eutrophication of the lake

late pleistocene early holocene paraglacial and fluvial sediment history in the turbio valley semiarid chilean andes abstract the transitional character of climatic conditions confers great relevance to paleoclimate studies in the semiarid region where glacial and holocene geomorphologic records are scarce here we present the paraglacial and fluvial evolution of the turbio valley 30 s using both field observations and 14 c ams chronology two key sites at the uppermost turbio valley show glacial margins which likely formed during the 17 12 ka central andean pluvial event and earlier 37 27 ka episodes associated with glacial advances reported elsewhere in the semiarid andes likewise two episodes of subsequent paraglacial response are identified a first episode corresponds to early holocene fine grained deposits 11 500 7800 cal yr bp extending far downstream 40 km from the glacial margins these deposits and coeval debris cones 11 000 5500 cal yr bp are the result of arid conditions with occasional runoffs that were unable to export sediments along the trunk valley the second episode corresponds to disconformably overlying fluvial gravels extending 70 km downstream from the glacial margin indicative of an increase in the fluvial transport capacity occurring not long after 5500 cal yr bp fluvial transport increase resulted from a late holocene shift to wetter climate conditions representing a forcing factor which enhanced the paraglacial response

mid holocene radiocarbon ages in the subtropical andes 29 35 s climatic change and implications for human space organization this article discusses the distribution of radiocarbon age signatures obtained from archeological sites between 29 and 35 s in central chile and midwest argentina the goal of this analysis is to establish bases from which to interpret regional trends in the distribution of the archaeological record that connect these areas which have been traditionally considered to be geographically decoupled we propose a standardized methodology for selecting ages that provide a reliable human signature variations in date frequencies in a regional scale are discussed with the use of summed probability distributions radiocarbon voids at the regional level previously identified in midwest argentina are explored regional chronological information is compared to the available paleoenvironmental records thereby emphasizing the possible role of climate pulses in the spatial organization of human populations significant arid conditions between 7800 and 5700 cal bp are coincidental with a focused occupation of the andes mountains an area which may have offered stable resources and thus was more effectively occupied than other environmental bands

recent accelerating mass loss of southeast tibetan glaciers and the relationship with changes in macroscale atmospheric circulations the mass balance history 1980 2010 of a monsoon dominated glacier in the southeast tibetan plateau is reconstructed using an energy balance model and later interpreted with regard to macroscale atmospheric variables the results show that this glacier is characterized by significant interannual mass fluctuations over the past three decades with a remarkably high mass loss during the recent period of 2003 2010 analysis of the relationships between glacier mass balance and climatic variables shows that interannual temperature variability in the monsoonal season june september is a primary driver of its mass balance fluctuations but monsoonal precipitation tends to play an accentuated role for driving the observed glacier mass changes due to their covariation concurrence of warm dry and cold wet climates in the monsoon influenced southeast tibetan plateau analysis of the atmospheric circulation pattern reveals that the predominance of anticyclonic cyclonic circulations prevailing in the southeastern northern tibetan plateau during 2003 2010 contributes to increased air temperature and decreased precipitation in the southeast tibetan plateau regionally contrasting atmospheric circulations explain the distinct mass changes between in the monsoon influenced southeast tibetan plateau and in the north tibetan plateau tien shan mountains during 2003 2010 the macroscale climate change seems to be linked with the europe asia teleconnection

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

relative and radiocarbon chronology of two former glaciers in the chilean lake district this paper investigates the relative importance of climatic and topographic factors on the fluctuations of two adjacent palaeoglaciers in the chilean lake district geomorphological mapping of the landforms around two lakes occupied by the palaeoglaciers has identified a series of intersecting moraine limits and ice marginal meltwater channels which allow the relative timing of glacier fluctuations to be established the broad pattern of advance and retreat is the same in the two basins with at least one synchronous major advance sometime after 19 500 yr bp but there is also evidence of discordant behaviour with one glacier advancing less often and lagging the other glacier during retreat seventeen radiocarbon dates suggest a similar chronology to other palaeoglaciers in the chilean lake district but the advance after 19 500 yr bp may have been 1500 14c yr later than major advances of palaeoglaciers situated immediately south the empirical evidence of differential behaviour can be simulated by a glaciological model which suggests that the differences in glacier response are due to contrasts in basin topography contrasts of this magnitude between the timing of some glacier advances has important implications for regional and interhemispheric correlation of chilean lake district glacier chronologies to other climate proxy records 1997 by john wiley sons ltd

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

an assessment of iron isotope fractionation during core formation abstract iron is a ubiquitous element in terrestrial and extra terrestrial settings and can provide clues as to the conditions during which planetary scale processes occurred one example of this is determining the conditions accompanying metal core formation in rocky planets and planetesimals for at least two decades there has been a growing database of experimental and natural data aimed at understanding whether iron isotopes fractionate during the separation of silicate and metal while it has been argued that the data are not in agreement with one another it is apparent that once criteria are established that prove equilibrated samples there is good agreement amongst the different studies when looked at as a function of the metallic composition proving equilibrium is critical in these types of experiments the three isotope experimental technique for establishing equilibrium is found to be both mathematically and fundamentally sound further it is clear that the question of whether there is an equilibrium iron isotope fractionation between metal and silicate is not straightforward and that it can vary significantly as a function of temperature pressure metallic composition oxygen fugacity and silicate composition

evidence of neogene wildfires in central chile charcoal records from the navidad formation abstract mediterranean type climate mtc ecosystems are characterized by recurrent wildfires although the majority of wildfires are human ignited non anthropogenic i e natural wildfires are common in all mtc regions except central chile the low frequency of natural wildfires in this chilean region is explained by the scarcity of non anthropogenic ignition sources basically thunderstorm induced lightning and volcanic activity however from a geological perspective the current relative absence of non anthropogenic wildfires in central chile is a recent phenomenon in the transition from the early to middle miocene the climate in the region was likely warm and seasonally dry such climate conditions would allow the growth of fuel during the spring becoming flammable during the dry season this fire prone landscape would likely have been ignited by the high volcanic activity that concomitantly occurred with the orogeny of the andes to evaluate this hypothesis we sampled rocks from the three locations at the navidad formation considering the fossil plant evidence deposited during this warm and seasonally dry period we found a high concentration of charcoal in playa navidad coinciding with the global warming event reported between 17 and 15 ma the predominance of microscopic charcoal particles between 125 and 250 m only allows us to infer the occurrence of neogene fires at a regional scale the fused cell walls preserved in the charcoal anatomy likely suggest that such fire events were highly severe the presence of pumice associated with the high charcoal concentrations supports the hypothesis of volcanic ignition sources very little charcoal was found in punta perro late oligocene early miocene or in cerro los pololos late middle miocene where fire may have been limited by fuel humidity and ignition sources respectively although changes in the depositional environment would also help explain differences in the fire record throughout the navidad formation in conclusion our results provide the first quantitative neogene charcoal record for south america the evidence of fire occurrence in central chile during the neogene will contribute to understanding the evolution of the mediterranean type flora

the last glacial maximum climatic conditions on easter island abstract the aim of this paper is to refine previous estimates of last glacial maximum lgm climatic conditions for easter island samples were analysed for fossil pollen from the lower half of a 13 40 m sediment core rra5 this part of the core includes a time span from ca 28 000 10 000 14 c bp the results show that during this period there were three different climatic conditions first a time span from ca 28 000 23 200 14 c bp with slightly cooler and probably drier conditions relative to present day second a more cool and dry climatic condition from ca 23 200 14 700 14 c bp the second time span had two peak points at ca 22 100 and 17 150 14 c bp it seems that the coolest and driest conditions occurred at 17 150 14 c bp third a warm and wet climate started at ca 15 000 14 c bp and continued until the end of the period studied 10 000 14 c bp in all the time covered in this study there was an inverse relationship between values of palmae and poaceae while poaceae and tubuliflorae shrubs show similar variations the temperature estimations that are presented by different authors based on oxygen isotopes are for approximately 4 c cooling at the lgm however the empirical values derived from the pollen evidence suggest only ca 1 9 c cooling this is in agreement with recently obtained values from tropical lowlands

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

nature of environmental changes in south america at the last glacial maximum abstract a review is given of geomorphological evidence suggesting the nature of environmental changes in south america during the last glaciation maximum lgm the data are from glacial geocryogenic alluvial colluvial and aeolian systems and span 68 of latitude making the most complete land transect of major climatic systems in the southern hemisphere glaciers in the northern and central andes may have reached their maximal extent by 27 000 yr b p reduced precipitation at the lgm caused by lower temperatures and lower atmospheric humidity probably led to slight glacier recession in the tropical andes icefields in the southern andes were most expansive when global temperature and sea level were lowest because pacific westerlies supplied abundant moisture and western outlets advancing across the continental shelf were constrained by sea level low gradient river networks became incised by at least 100 m into narrow channels as global sea level fell by 120 m during the lgm draw down of water tables possibly impacted the forest cover enhancing the drying influence of reduced sea surface temperature and atmospheric humidity as forest and grass covers diminished in extent effecting greater atmospheric cooling because of reduced evapotranspiration and convective condensation colluvial and aeolian processes became more active and widespread almost 25 of the continent is covered with palaeo aeolian features presumed to have been active when airflow was stronger due to steeper atmospheric pressure and temperature gradients at the lgm substantial changes in precipitation totals and incidence and in ground water availability probably eliminated modern type tropical rainforest except in areas currently receiving ca 5000 mm of annual rainfall equivalent changes in vegetation cover spread across much of the guyana and brazilian highlands and throughout the southern temperate regions

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

complex pedogenesis related to differential aeolian sedimentation in microenvironments of the southern part of the semiarid region of argentina abstract the aim of this paper is to explain soil genesis and spatial variability in the soil cover of a flat landscape in the southern part of argentina s semiarid region soil survey data indicate random differences in the properties of soils lying within a few hundred meters of one another as reflected in an intricate distribution pattern which cannot be explained by the climatic theory of soil genesis in a single pedogenetic cycle this pattern is unrelated to the actual vegetation cover the soil parent materials consist of a

polar perspective of late quaternary climates in the southern hemisphere abstract late quaternary paleoecological and glacial evidence from the higher latitudes of the southern hemisphere implies overall uniformity of large scale glacial and interglacial climatic fluctuations for the past 40 000 yr climate of the last glacial maximum variously dated between 30 000 and 11 000 yr b p was relatively cold and dry compared with the warmer more humid climate of the holocene and the interstade preceding the last glacial maximum conditions were apparently coldest during millennia centered around 20 000 yr b p and warmest in the early holocene recorded small scale fluctuations frequently variable for any given time interval are less consistent a cold late glacial episode estimated as occurring between ca 13 000 and 11 000 yr b p in antarctica possibly was coeval with the younger dryas stade in northwestern europe and may be correlative with a climatic episode in southern south america and perhaps in new zealand and south georgia however there is no evidence for the event in tasmania general atmospheric circulation models for the polar latitudes at the time of the last glacial maximum show an intensification of the southern westerlies apparently a result of the expansion of ice cover in antarctica and of sea ice in the southern ocean

late glacial holocene climate of the lake district of chile pollen evidence from a 350 cm section of a fen in a moraine belt at rucanancu 39 33 s 72 18 w bears on the controversy regarding interpretation of late glacial and holocene climate in midlatitude chile earlier pollen studies indicating a cooling trend between approximately 11 000 and 10 000 yr b p disagreed with observations of glacier fluctuations which show continuous glacier wastage and by inference warming after 12 500 yr b p and possibly earlier up until neoglaciation beginning after 6850 yr b p fossil beetle assemblage data in this time range support the interpretation of climate made from the observed glacier behavior at rucanancu a pollen assemblage containing upper montane podocarp podocarpus andinus in quantities reaching 34 and dating between 10 440 and 10 000 yr b p implies a cold climate with summer temperatures possibly 5 8 c lower than today s holocene warming began afterward later than the glacier and beetle records indicate and continued until at least 8350 yr b p as suggested by the sequence of assemblages dominated by myrtaceae by aextoxicon punctatum and by gramineae a subsequent assemblage of nothofagus obliqua type implies an increase of moisture until 6960 yr b p following which n dombeyi type under a cool and humid neoglacial climate became dominant

palynology of cushion bogs of the cordillera pelada province of valdivia chile abstract fossil pollen identified in the earliest sediments of three cushion bogs in the cordillera pelada 40 10 s 73 30 w dated 10 425 14 c yr b p includes the subantarctic species dacrydium fonckii tetroncium magellanicum astelia pumila gaimardia australis donatia fascicularis and drosera uniflora all grow today in the cordillera pelada and range poleward to the southernmost province of magallanes one species drapetes muscosa included with the pollen of these plants in the earliest record is no longer a constituent of the flora but is limited only to subantarctic chile available evidence indicates that plants survived the last glaciation north of the glacial border with the course of postglacial migration southward following the wastage of the glacier complex holocene climatic and vegetational changes in the cordillera pelada are interpreted in the context of regional reconstructions which show maximum warmth about 9000 yr ago with a pronounced dry period lasting from 9000 to 6500 yr b p maximum precipitation was later reached around 4000 yr ago but has decreased overall since then the regional decline of the endemic gymnosperm fitzroya cupressoides which today is extensively destroyed in the cordillera pelada follows this decrease in precipitation these climatic data suggest a net south ward shift in the zone of westerly winds that bring rainfall to the region over the past 4000 yr

mechanisms and variations of the paleoproductivity off northern chile 24 s 33 s during the last 40 000 years 1 a multiparameter investigation including organic carbon carbonate opal and planktic foraminifera was carried out on five sediment cores from the coastal upwelling area between 24 s and 33 s along the peru chile current to reconstruct the history of the paleoproductivity and its driving mechanisms during the last 40 000 years inferred from our data we conclude that the antarctic circumpolar current as the main nutrient source in this region mainly drives the productivity by its latitudinal shifts associated with climate change simplified its northerly position during the last glacial led to enhanced productivities and its southerly position during the holocene caused lower productivities at 33 s the paleoproductivity was additionally affected by the southern westerlies and records highest levels during the last glacial maximum lgm north of 33 s several factors e g position and strength of the south pacific anticyclone wind stress continental runoff and el nino southern oscillation events supplementary influenced upwelling and paleoproductivity where maximum values occurred prior to the lgm and during the deglaciation

changing fire regimes in the temperate rainforest region of southern chile over the last 16 000 yr abstract a high resolution macroscopic charcoal record from lago melli 42 46 s 73 33 w documents the occurrence of forest fires in the lowlands of isla grande de chiloe southern chile over the last 16 000 yr our data suggest that fire activity in this region was largely modulated by the position intensity of the southern westerlies at multi millennial time scales fire activity was infrequent or absent between 16 000 11 000 and 8500 7000 cal yr bp and was maximal between 11 000 8500 and 3000 0 cal yr bp a mosaic of valdivian north patagonian rainforest species started at 6000 cal yr bp along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr bp the modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability suggesting the onset of high frequency variability in summer precipitation regimes starting at 5500 cal yr bp because negative anomalies in summer precipitation in this region are teleconnected with modern el nino events we propose that the onset of el nino like variability at 5700 6200 cal yr bp led to a reshuffling of rainforest communities in the lowlands of isla grande de chiloe and an increase in fire activity

enso tropical extratropical climate teleconnections and mechanisms for holocene debris flows along the hyperarid coast of western south america 17 24 s abstract el nino the warm phase of the enso cycle involves ocean climate anomalies in the tropical pacific ocean and in the extratropics which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western south america here we investigate meteorological mechanisms producing heavy rains floods and debris flows along the less known hyperarid coasts of southern peru and northern chile to evaluate the paleoclimate significance of holocene debris flow deposits our results reveal that heavy rainfall over the coast of southernmost peru occurs either during austral summer at the mature stage of el nino in connection with warmer sea surface temperatures and anomalous jet streams off northern chile or during the previous austral winter spring associated with equatorward shifted pacific south america psa atmospheric teleconnection patterns at antofagasta in northern chile such events occur almost exclusively in the latter season when deeper psa related anomaly poles extend their influence equatorwards beyond central chile during non el nino conditions short lived heavy rainfall episodes in southernmost peru can be associated with similar albeit weaker or less persistent circulation anomalies in addition to that a seasonally enhanced low level southerly flow provides orographic uplift rainfall favourable conditions by the andes at the 18 s coastal bend ultimately the trigger for rainfall events in all seasons and phases of the enso cycle was invariably connected with mid troposphere wave disturbances from mid latitudes the chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at the western side of the andes suggests that the enso related teleconnection patterns operated only during the second half of the holocene supporting an onset of modern el nino manifestations at 5300 5500 cal bp and increased frequency of major events during recent times we suggest that several debris flows dated between 12 900 and 8400 cal bp in southernmost peru previously interpreted as an indication of strong el nino events were associated with short and intense heavy rainfall episodes similar to those described here during the late winter spring season in non el nino conditions concomitant with stronger low level southerlies strengthened south eastern pacific subtropical anticyclone and intensified coastal upwelling

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

southern hemisphere westerly wind changes during the last glacial maximum model data comparison the southern hemisphere sh westerly winds are thought to be critical to global ocean circulation productivity and carbon storage for example an equatorward shift in the winds though its affect on the southern ocean circulation has been suggested as the leading cause for the reduction in atmospheric co2 during the last glacial period despite the importance of the winds it is currently not clear from observations or model results how they behave during the last glacial here an atmospheric modelling study is performed to help determine likely changes in the sh westerly winds during the last glacial maximum lgm using lgm boundary conditions the maximum in sh westerlies is strengthened by 1 m s 1 and moved southward by 2 at the 850 hpa pressure level boundary layer stabilisation effects over equatorward extended lgm sea ice can lead to a small apparent equatorward shift in the wind band at the surface further sensitivity analysis with individual boundary condition changes indicate that changes in sea surface temperatures are the strongest factor behind the wind change the hadam3 atmospheric simulations along with published pmip2 coupled climate model simulations are then assessed against the newly synthesised database of moisture observations for the lgm although the moisture data is the most commonly cited evidence in support of a large equatorward shift in the sh winds during the lgm none of the models that produce realistic lgm precipitation changes show such a large equatorward shift in fact the model which best simulates the moisture proxy data is the hadam3 lgm simulation which shows a small poleward wind shift while we cannot prove here that a large equatorward shift would not be able to reproduce the moisture data as well we show that the moisture proxies do not provide an observational evidence base for it

reconstructed droughts for the southeastern tibetan plateau over the past 568 years and its linkages to the pacific and atlantic ocean climate variability we present a palmer drought severity index reconstruction r 0 61 p 0 01 from 1440 to 2007 for the southeastern tibetan plateau based on tree rings of the forest fir abies forrestii persistent decadal dry intervals were found in the 1440s 1460s 1560s 1580s 1700s 1770s 1810s 1860s and 1980s and the extreme wet epochs were the 1480s 1490s 1510s 1520s 1590s 1610s 1630s 1720s 1730s 1800s 1830s 1870s 1930s 1950s and after the 1990s comparisons of our record with those identified in other moisture related reconstructions for nearby regions showed that our reconstructed droughts were relatively consistent with those found in other regions of indochina suggesting similar drought regimes spectral peaks of 2 3 5 5 years may be indicative of enso activity as also suggested by negative correlations with ssts in the eastern equatorial and southeastern pacific ocean significant multidecadal spectral peaks of 29 2 40 9 and 56 8 60 2 years were identified as indicated by the spatial correlation patterns the decadal scale variability may be linked to sst variations in the northern pacific and atlantic oceans

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

large rockslides in the southern central andes of chile 32 34 5 s tectonic control and significance for quaternary landscape evolution abstract the distribution and age of large 0 1 km2 pliocene to recent rockslides in the chilean cordillera principal 32 34 5 s the southern central andes has been analyzed to determine the rockslide triggering mechanisms and impact on regional landscape evolution most of the rockslides appear in the western cordillera principal and cluster along major geological structures variographic analyses show spatial correlation between rockslides geological structures and shallow seismicity a relative chronosequence was calibrated with existing 14c and 40ar 39ar dates and new cosmogenic nuclide exposure ages for selected rockslides rockslide induced sediment yield was estimated with empirical relations for rockslide area distributions throughout the quaternary rockslides have delivered sediment to streams at rates equivalent to denudation rates of 0 10 0 06 mm a 1 while estimates using short term 20 a seismicity records are 0 3 0 2 0 6 mm a 1 the estimates of sediment transfer and the spatial distribution of rockslides reflect a landscape in which tectonic and geological controls on denudation are more significant than climate

late quaternary vegetation and climate history of a perennial river canyon in the rio salado basin 22 s of northern chile abstract plant macrofossils from 33 rodent middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the rio salado northern chile yield a unique record of vegetation and climate over the past 22 000 cal yr bp presence of low elevation prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5 c and may have been near modern at 16 270 cal yr bp displacements in the lower limits of andean steppe and puna taxa indicate that mean annual rainfall was twice modern at 17 520 16 270 cal yr bp this pluvial event coincides with infilling of paleolake tauca on the bolivian altiplano increased enso activity inferred from a marine core near lima abrupt deglaciation in southern chile and heinrich event 1 moderate to large increases in precipitation also occurred at 11 770 9550 central atacama pluvial event 7330 6720 3490 2320 and at 800 cal yr bp desiccation occurred at 14 180 8910 8640 and 4865 cal yr bp compared to other midden sites in the region early holocene desiccation seems to have happened progressively earlier farther south emerging trends from the cumulative midden record in the central atacama agree at millennial timescales with improved paleolake chronologies for the bolivian altiplano implying common forcing through changes in equatorial pacific sea surface temperature gradients

chilean and southeast pacific paleoclimate variations during the last glacial cycle directly correlated pollen and δ18o records from odp site 1234 abstract joint pollen and oxygen isotope data from ocean drilling program site 1234 in the southeast pacific provide the first continuous record of temperate south american vegetation and climate from the last 140 ka located at 36 s 65 km offshore of concepcion chile site 1234 monitors the climatic transition zone between northern semi arid summer dry winter wet climate and southern year round rainy cool temperate climate dominance of onshore winds suggests that pollen preserved here reflects transport to the ocean via rivers that drain the region and integrate conditions from the coastal mountains to the andean foothills down hole changes in diagnostic pollen assemblages from xeric lowland deciduous forest characterized by grasses herbs ferns and trees such as deciduous beech nothofagus obliqua mesic valdivian evergreen forest including conifers such as the endangered prumnopitys andina and subantarctic evergreen rainforest comprised primarily of southern beech n dombeyi reveal large rapid shifts that likely reflect latitudinal movements in atmospheric circulation and storm tracks associated with the southern westerly winds during glacial intervals mis 2 4 and 6 rainforests and parkland dominated by nothofagus moved northward into the region at the mis 6 5e transition coeval with the rapid shift to lower isotopic values rainforest vegetation was rapidly replaced by xeric plant communities associated with mediterranean type climate an increased prominence of halophytic vegetation suggests that mis 5e was more arid and possibly warmer than mis 1 although rainforest pollen rises again at the end of mis 5e lowland deciduous forest pollen persists through mis 5d and 5c into mis 5b substantial millennial scale variations occur in both interglacial and glacial regimes attesting to the sensitivity of the southern westerly belt to climate change comparison of the cool mesic n dombeyi rainforest assemblage from site 1234 with 18 o in the byrd ice core shows that on time scales longer than 10 ka cool moist conditions in central chile were coherent with and occurred in phase with antarctic cooling this is also likely at millennial scales although rainforest pollen lags antarctic cooling with exponential response times of about 1000 years which plausibly reflects the ecological response time to regional climate change

deglacial and postglacial climate history in east central isla grande de chiloe southern chile 43 s abstract palynologic and stratigraphic data from laguna tahui 42 50 s 73 30 w indicate cool temperate and humid conditions there between 14 000 and 10 000 14c yr b p followed by warmer and drier than present conditions between 10 000 and 7000 14c yr b p and subsequent cooling and rise in precipitation over the last 5800 14c yr the thermophilous valdivian trees eucryphia cordifolia and caldcluvia paniculata reached their maximum abundance during the early holocene warm dry phase 10 000 7000 14c yr b p followed by a rise in lake levels and reexpansion of north patagonian conifers starting at 7000 and 5800 14c yr b p respectively variations in the stratigraphic and geographic distribution of temperate rainforests in southern chile suggest multimillennial trends in temperature and westerly activity which are spatially and temporally coherent with paleoclimate records from neighboring regions climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine scale mosaics of valdivian and north patagonian rainforest species in low to mid elevation communities since 5800 14c yr b p

deglacial palaeoclimate at puerto del hambre subantarctic patagonia chile the primary objective of this study is to further substantiate multistep climatic forcing of late glacial vegetation in southern south america a secondary objective is to establish the age of deglaciation in estrecho de magallanes bahia inutil pollen assemblages at 2 cm intervals in a core of the mire at puerto del hambre 53 36 21 s 70 55 53 w provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic patagonia chronology over the 262 cm length of core is regulated by 20 ams radiocarbon dates between 14 455 and 10 089 14c yr bp of 13 pollen assemblage zones the earliest representing the oldest dryas chronozone 14 455 13 000 14c yr bp records impoverished steppe with decreasing frequencies and loss of southern beech nothofagus successive 100 yr long episodes of grass herbs and of heath empetrum ericaceae before 14 000 14c yr bp infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass dominated steppe the bolling allerod 13 000 11 000 14c yr bp is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14c yr bp was warmer and not as humid at the time of the younger dryas 11 000 10 000 14c yr bp grass steppe expanded with a return of colder more humid climate later with gradual warming communities were invaded by southern beech the puerto del hambre record parallels multistep deglacial palaeoclimatic sequences reported elsewhere in the southern andes and at taylor dome in antarctica deglaciation of estrecho de magallanes bahia inutil is dated close to 14 455 14c yr bp invalidating earlier dates of between 15 800 and 16 590 14c yr bp copyright 2000 john wiley sons ltd

the glacial geomorphology and pleistocene history of south america between 38 s and 56 s abstract this paper presents new mapping of the glacial geomorphology of southern south america between latitudes 38 s and 56 s approximately the area covered by the former patagonian ice sheets glacial geomorphological features including glacial lineations moraines meltwater channels trimlines sandur and cirques were mapped from remotely sensed images landsat 7 etm pan sharpened landsat 7 and aster the landform record indicates that the patagonian ice sheets consisted of 66 main outlet glaciers together with numerous local cirque glaciers and independent ice domes in the surrounding mountains in the northern part of the mapped area in the chilean lake district 38 42 s large piedmont glaciers developed on the western side of the andes and the maximum positions of these outlet glaciers are in general marked by arcuate terminal moraines to the east of the andes between 38 s and 42 s outlet glaciers were more restricted in extent and formed alpine style valley glaciers along the eastern flank of the andes south of 45 s a series of large fast flowing outlet glaciers drained the ice sheet the location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes west of the andes at this latitude there is geomorphological evidence for an independent ice cap close to sea level on the taitao peninsula the age of this ice cap is unclear but it may represent evidence of glacier growth during the antarctic cold reversal and or younger dryas chronozone maximum glacier positions are difficult to determine along much of the western side of the andes south of 42 s because of the limited land there and it is assumed that most of these glaciers had marine termini in the south east of the mapped area in the fuegan andes cordillera darwin the landform record provides evidence of ice sheet initiation by adding published dates for glacier advances from the literature we present maps of pre last glacial maximum lgm glacier extent lgm extent and the positions of other large mapped moraines younger than lgm in age a number of large moraines occur within the known lgm limits the age of these moraines is unknown but since many of them lie well outside the established maximum neoglacial positions the possibility that they reflect a return to glacial climates during the younger dryas chronozone or antarctic cold reversal cannot be discounted

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

the pleistocene holocene transition and human occupation in the central andes of argentina agua de la cueva locality in the central andes of argentina evidences of early human occupations come from the precordillera a low mountain system which was under periglacial conditions prior to 14 000 14c yr bp when the cordillera principal and cordillera frontal were glaciated the corridors for human migration across the andes may have opened before 13 000 14c yr bp the pleistocene holocene transition gave rise to a substantial variability of environments and consequently of natural resources for early people who found in the precordillera new ecosystems with suitable conditions for living the first human groups arrived ca 11 000 14c yr bp at agua de la cueva rockshelter located at 2900 m above sea level in the western flank of the precordillera the occurrence of raw material outcrops close to the site and the archaeofaunistic record indicate a local and likely seasonal exploitation of mountain resources these early people lived in a shrub steppe environment under cooler and probably wetter conditions in which camelids were the most important food resource since 9000 14c yr bp warmer and drier conditions were dominant except for a lower intensity of human occupations the site function of agua de la cueva seems to have remained the same

glacial to holocene changes in sea surface temperature and coastal vegetation in north central chile high versus low latitude forcing abstract north central chile is located at an important climatic transition zone between humid conditions under the influence of the southern hemisphere westerly winds in the south and the extremely dry climate of the atacama desert in the north offshore equatorward flowing cold waters of the peru chile current converge with relatively warmer waters coming from the low latitudes based on terrestrial and marine proxies from the same archive geob 7139 2 30 12 s 71 59 w we show that during the glacial between 33 and 19 kyr cold sea surface temperatures paralleled enhanced humidity with high terrestrial input and abundant vegetation on the adjacent land suggesting a stronger influence of cold waters from the antarctic circumpolar current and the westerly winds while the deglacial sea surface temperature warming started at 19 kyr the humidity decrease occurred around 17 16 kyr bp the early to mid holocene is characterized by extremely warm and dry conditions we suggest that climate changes were driven by fluctuations in antarctic sea ice extent and the circulation of the hadley cell both ultimately linked to insolation changes our records further imply warm and dry conditions in north central chile during the northern hemisphere heinrich events

high precision iron isotope measurements of terrestrial and lunar materials we present the analytical methods that have been developed for the first high precision fe isotope analyses that clearly identify naturally occurring mass dependent isotope fractionation a double spike approach is used which allows rigorous correction of instrumental mass fractionation based on 21 analyses of an ultra pure fe standard the external precision 1 sd for measuring the isotopic composition of fe is 0 14 mass for demonstrated reproducibility on samples this precision exceeds by at least an order of magnitude that of previous attempts to empirically control instrumentally produced mass fractionation dixon et al 1993 using the double spike method 15 terrestrial igneous rocks that range in composition from peridotite to rhyolite 5 high ti lunar basalts 5 fe mn nodules and a banded iron formation have been analyzed for their iron isotopic composition the terrestrial and lunar igneous rocks have the same isotopic compositions as the ultra pure fe standard providing a reference fe isotope composition for the earth and moon in contrast fe mn nodules and a sample of a banded iron formation have iron isotope compositions that vary over a relatively wide range from 56fe 0 9 to 1 2 this range is 15 times the analytical errors of our technique these natural isotopic fractionations are interpreted to reflect biological vital effects and illustrate the great potential fe isotope studies have for studying modern and ancient biological processes

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

southern westerlies during the holocene deduced from geomorphological and pedological studies in the norte chico northern chile 27 33 s abstract in the norte chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation the holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations in comparison to modern climatic conditions increased influence of the westerlies is deduced for the time periods prior to 7300 yr b p between 5000 3700 yr b p 3000 1800 yr b p and around 270 yr b p it remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole of a meridional expansion of the westerly belt or only of intensity changes of the atmospheric dynamics almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated probably due to a weakened upwelling and warmer water conditions in the eastern pacific in general the climate of the norte chico has become more variable since 5000 yr b p especially since 3000 yr b p with frequent changes of the geoecological conditions

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

palaeohydrology of laguna de tagua tagua 34 30 s and moisture fluctuations in central chile for the last 46 000 yr central chile 32 35 s lies at the northern border of the strong influence of the westerly circulation belt and thus exhibits a steep rainfall gradient a new core from laguna de tagua tagua 34 30 0 s provides a sedimentologic geochemical and palynological record of regional hydrologic balance for the last 46 000 cal yr bp according to our age model relatively humid conditions occurred during glacial times before 43 500 cal yr bp and from 40 000 to 21 500 cal yr bp reduced moisture conditions and likely lower temperatures occurred from 42 400 40 100 cal yr bp higher lake levels and pollen assemblages with valdivian rainforest taxa imply much higher precipitation during glacial times 40 100 21 000 cal yr bp compared to today and therefore enhanced westerly activity in northern central chile afterwards the general decrease in moisture was punctuated by two abrupt arid periods at 21 000 19 500 cal yr bp and 17 000 15 000 cal yr bp and two more humid intervals 19 500 17 000 almost coincident with the global last glacial maximum lgm and 13 500 11 500 cal yr bp the early and mid holocene were the most arid periods in central chile for the studied time interval millennial scale palaeohydrological reconstructions from tagua tagua are consistent with regional climatic records copyright 2005 john wiley sons ltd

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

expansion of magellanic moorland during the late pleistocene palynological evidence from northern isla de chiloe chile the late quaternary vegetation of northern isla de chiloe is inferred from palynological analysis of a section in the rio negro drainage 42 03 s 73 50 w at ca 30 500 yr b p maxima of astelia and donatia occurred suggesting wetland development from that time until ca 27 000 yr b p steppe indicators such as compositae gramineae dominated suggesting drier conditions after 27 000 yr b p the moorland shrub dacrydium gradually increased reaching a maximum by 18 000 yr b p at this time astelia increased again suggesting development of cushion bog during cold and wet conditions the glacial postglacial transition is characterized by a marked change from peaty sediments to clays a decrease in the cushion bog flora and the prevalence of gramineae compositae and swamp taxa this vegetation prevailed until ca 7000 yr b p when forest taxa became dominant the floristic pattern inferred from the pollen spectra of the rio negro section suggests that the late pleistocene vegetation of chiloe resembled modern magellanic moorland vegetation 52 56 lat s based on climatic conditions presently associated with magellanic moorland its occurrence in chiloe at low elevations during the late pleistocene implies a decrease in average temperature of at least 4 c and an increase in annual precipitation of at least 1500 mm

late pleistocene ecological environmental and climatic reconstruction based on megafauna stable isotopes from northwestern chilean patagonia abstract stable isotope analyses have been performed on the bioapatite 13 c 18 o and collagen 13 c 15 n of four late pleistocene south american megafaunal taxa notiomastodon platensis equus andium cf hemiauchenia paradoxa and xenarthra indet to evaluate paleoclimatic and paleoenvironmental conditions as well as paleoecological features of this time period the analyzed megafauna was found at several locations in the northwestern chilean patagonia 38 42 s 74 71 w the bioapatite 13 c values indicated the presence of c 3 vegetation ranging from forestal to woodland areas the collagen 15 n values pointed to temperate and humid ecosystems and to the consumption of shrubs trees grasses and sedges mean annual temperatures estimated from bioapatite 18 o po4 values show a similarity to modern temperatures and suggested that the megafauna under study may have lived during warm stages interstadials of the late pleistocene when comparing our results with those obtained from other south american regions we find that the diet of this particular chilean megafauna appears to have been more influenced by resource availability than by the potential dietary range of the taxa

a review of tertiary climate changes in southern south america and the antarctic peninsula part 2 continental conditions abstract climate changes in southern south america and the antarctic peninsula during the tertiary show a strong correlation with ocean warming and cooling events which are in turn related to tectonic processes during periods of accelerated sea floor spreading and mid ocean ridge activity sea levels rose so that parts of the continents were flooded and forests were destroyed however this was balanced by the large scale release of co2 during volcanic outgassing and carbonate precipitation on the continental shelves which caused rising air temperatures and the poleward expansion of sub tropical and temperate forests cooling episodes generally caused an increase in the north south thermal gradient because of an equatorward shift in climate belts so that the westerly winds intensified and brought higher rainfall to the lower latitudes an increase in wind blown dust caused temperatures to drop further by reflecting sunlight back into space the rising andes range had a marked influence on climate patterns up to the middle miocene it was still low enough to allow summer rainfall to reach central and north central chile but after about 14 ma it rose rapidly and effectively blocked the spill over of moisture from the atlantic ocean and amazon basin at this time the cold humboldt current was also established which together with the andes helped to create the arid diagonal of southern south america stretching from the atacama desert to the dry steppes of patagonia this caused the withdrawal of subtropical forests to south central chile and the expansion of sclerophytic vegetation to central chile however at the same time it intercepted more rain from the northeast causing the effect of the south american monsoon to intensify in northwestern argentina and southern bolivia where forest communities presently occur in patagonia glaciation started as early as 10 5 ma but by 7 ma had become a prominent feature of the landscape and continued apparently uninterruptedly into the pleistocene the antarctic peninsula saw its first mountain glaciation between 45 and 41 ma with major ice sheet expansion commencing at about 34 ma isolated stands of nothofagus forests were still present in low lying areas suggesting that the glaciers were initially wet based but dry based glaciers were established at around 8 ma although temperatures rose briefly during the messinian pliocene transition causing sub antarctic flora to retreat to higher elevations of the transantarctic mountains the present cold polar conditions were finally established by about 3 ma

southern hemisphere westerly wind changes during the last glacial maximum paleo data synthesis changes in the strength and position of southern hemisphere westerly winds during the last glacial cycle have been invoked to explain both millennial and glacial interglacial climate fluctuations however neither paleo models nor paleodata agree on the magnitude or even the sign of the change in wind strength and latitude during the most studied glacial period the last glacial maximum lgm compared to the recent past this paper synthesizes paleo environmental data that have been used to infer changes in lgm winds data compilations are provided for changes in terrestrial moisture dust deposition sea surface temperatures and ocean fronts and ocean productivity and existing data on southern hemisphere ocean circulation changes during the lgm are summarized we find that any hypothesis of lgm wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents cooler temperatures and higher productivity in the subantarctic zone and reductions in agulhas leakage around southern africa our comparison suggests that an overall strengthening an equatorward displacement or no change at all in winds could all be interpreted as consistent with observations if a single cause related to the southern westerlies is sought for all the evidence presented then an equatorward displacement or strengthening of the winds would be consistent with the largest proportion of the observations however other processes such as weakening or poleward shifts in winds a weakened hydrological cycle extended sea ice cover and changed buoyancy fluxes cannot be ruled out as potential explanations of observed changes in moisture surface temperature and productivity we contend that resolving the position and strength of westerly winds during the lgm remains elusive based on data reconstructions alone however we believe that these data reconstructions of environmental conditions can be used in conjunction with model simulations to identify which processes best represent westerly wind conditions during the lgm

late quaternary environmental dynamics in the atacama desert reconstructed from rodent midden pollen records in the past two decades much has been learned about the late quaternary climate history of the atacama desert with some details still unclear about the seasonality timing and extent of wet and dry phases modern climate studies reveal that far from exhibiting a unique pattern seasonal precipitation originates from many sources and mechanisms for the last 16 ka we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22 25 s in northern chile widespread wet conditions prevailed during the late pleistocene and early holocene particularly between 13 and 9 ka evidenced by 400 m lowering of pollen zones plant communities compared to today regional differences in the timing and magnitude of this displacement may be related to the prevailing source tropical extra tropical or mode nnw se of tropical precipitation through time wet conditions persisted well into the early holocene lasting 1 1 5 ka longer than previously suggested the pollen record suggests extreme drying 8 ka possibly associated with a northward shift of the inter tropical convergence zone tracking minimum insolation values at subtropical latitudes during the austral summer the establishment of conditions similar to today happened 4 ka copyright 2017 john wiley sons ltd

the southern westerlies in central chile holocene precipitation estimates based on a water balance model for laguna aculeo 33 50 s central chile 32 35 s lies at the northern border of strong influence of the westerly circulation belt westerlies and is therefore characterized by a steep precipitation gradient in this region quantitative reconstructions of holocene precipitation are scarce hence the present study estimates precipitation changes based on lake level fluctuations of laguna aculeo 33 50 s 70 54 w the lake level curve has been reconstructed using a multi proxy study of lake sediments lake level changes have been simulated using a simple water balance model as a result palaeo precipitation could be estimated uncertainties concerning the input parameters and past conditions have limitated the precision of precipitation estimates the results suggest that during the beginning of the holocene when the lake level 1 5 m was low precipitation was 200 mm year before 8000 cal yr bp the lake frequently dried out between 8000 and 6000 cal yr bp precipitation appeared to be higher 150 300 mm year and after about 6000 cal yr bp precipitation increased dramatically 350 450 mm year around 3000 cal yr bp modern lake level and precipitation 450 550 mm year were generally established the dry conditions during the early and mid holocene are in good agreement with other records from central chile and northern patagonia the westerlies were probably deflected southward by the southeast pacific subtropical high pressure cell during the mid and early holocene subsequently the increase in moisture in central chile during the late holocene appears to be strongly related to intensified westerly activity and probably also to increased el nino activity

turbidite paleoseismology along the active continental margin of chile feasible or not abstract much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial lacustrine and marine paleoseismic archives recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events turbidite paleoseismic archives may potentially extend past earthquake records to the pleistocene and can thus complement commonly shorter term terrestrial archives however in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents synchronous deposition of turbidites in widely spaced isolated depocenters has to be ascertained furthermore characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account here we analyze 8 marine sediment cores along 950 km of the chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites our results suggest that the deposition of areally widespread synchronous turbidites triggered by seismicity is largely controlled by sediment supply and hence the climatic and geomorphic conditions of the adjacent subaerial setting the feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high resolution radiocarbon dating we conclude that offshore northern central chile 29 32 5 s holocene turbidite paleoseismology is not feasible because sediment supply from the semi arid mainland is low and almost no holocene turbidity current deposits are found in the cores in contrast in the humid region between 36 and 38 s frequent holocene turbidite deposition may generally correspond to paleoseismic events however high terrigenous sedimentation rates prevent high resolution radiocarbon dating the climatic transition region between 32 5 and 36 s appears to be best suited for turbidite paleoseismology

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