glacial stage ice core records from the subtropical dunde ice cap china the first ice core record of both the holocene and wisconsin wiirm late glacial stage lgs from the subtropics has been extracted from three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau ice thicknesses at the ice cap summit average 138 m the bedrock surface is relatively flat surface and basal temperatures are 7 3 and 4 7 c respectively and the ice cap exhibits radial flow away from the summit dome these records reveal a major change in the climate of the plateau 10 000 years ago and suggest that lgs conditions were colder wetter and dustier than holocene conditions this is inferred from the more negative 6180 ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes which characterize the lgs part of the cores total b radioactivity from shallow ice cores indicates that over the last 24 years the average accumulation rate has been 400 mm a 1 at the summit the ice cores have been dated using a combination of annual layers in the insoluble dust and 6180 in the upper sections of core visible dust layers which are annual and ice flow modeling the oxygen isotope record which serves as a temperature proxy indicates that the last 60 years have been the warmest in the entire record

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

a 350014c yr high resolution record of water level changes in lake titicaca bolivia peru abstract sediment cores collected from the southern basin of lake titicaca bolivia peru on a transect from 4 6 m above overflow level to 15 1 m below overflow level are used to identify a new century scale chronology of holocene lake level variations the results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century scale lake level changes detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores a chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water level fluctuations two methods were used to estimate the14c reservoir age both indicate that it has remained nearly constant at 25014c yr during the late holocene core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level implying negative moisture balance for the northern andean altiplano over the last 3500 cal yr between 3500 and 3350 cal yr b p a transition from massive inorganic clay facies to laminated organic matter rich silts in each of the four cores signals a water level rise after a prolonged mid holocene dry phase evidence of other significant low lake levels occurs 2900 2800 2400 2200 2000 1700 and 900 500 cal yr b p several of the low lake levels coincided with cultural changes in the region including the collapse of the tiwanaku civilization

tropical glaciers potential for ice core paleoclimatic reconstructions the objective of this work is to evaluate the potential of tropical glaciers and ice caps for the reconstruction of past climatic conditions by the analysis of firn and ice cores samples were collected in pits and from cores retrieved on three snow fields in the south american andes quelccaya ice cap and huascaran in peru and chimborazo in ecuador these are compared with results from west africa and indonesia measurements include the microparticle concentration oxygen isotopic abundance ratios and total beta radioactivity which in polar regions often exhibit seasonal depositional cycles annual variations in these three parameters are fairly well defined on quelccaya and huascaran and are apparently absent on chimborazo the quelccaya ice cap contains the best preserved annual signal for all three parameters and although in some instances the annual cycle is difficult to distinguish the measurement of more than one stratigraphic parameter aids in the interpretation of the firn core records the relatively flat bottom topography under quelccaya suggests a simple ice flow regime and depth age calculations indicate that an ice core to bedrock should contain a record of 600 to 1300 years this inference was confirmed by drilling to bedrock in 1983 this investigation of tropical glaciers indicates that the quelccaya ice cap on the eastern edge of the peruvian andes has excellent potential to contain a lengthy and interpretable record of climatic conditions within the tropics of south america

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

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

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

pre incan agricultural activity recorded in dust layers in two tropical ice cores in south america no documentary records survive from before the incursion of the spaniards in the mid sixteenth century knowledge of pre hispanic civilizations in this region comes largely from archaeological excavations which may now be supplemented by information recorded in two ice cores drilled in the quelccaya ice cap in southern peru fig 1 1 2 a 1 500 year record of particle concentrations and conductivity in these cores shows two major dust episodes each lasting about 130 years centred at ad 920 and 600 here we examine these dust events in the light of oxygen isotope and net accumulation records and suggest a correlation with pre incan agricultural activity the annual net accumulation record for ad 1915 1984 compares well with annual changes in lake titicaca water levels and with annual precipitation at el alto lapaz bolivia suggesting that the 1 500 year net accumulation record from quelccaya may serve as a proxy for water level changes in lake titicaca the ice core record suggests that climatic variability reflected in lake level changes has strongly influenced fluctuations in agricultural activity in southern peru

el nino southern oscillation events recorded in the stratigraphy of the tropical quelccaya ice cap peru snow accumulation measured during 1982 1983 on the quelccaya ice cap peru was 70 percent of the average from 1975 through 1983 inspection of 19 years 1964 through 1983 of accumulation measured near the summit of quelccaya reveals a substantial decrease 30 percent in association with the last five el nino southern oscillation enso occurrences in the equatorial pacific the enso phenomenon is now recognized as a global event arising from large scale interactions between the ocean and the atmosphere understanding this extreme event with the goal of prediction requires a record of past occurrences the quelccaya ice cap which contains 1500 years of annually accumulated ice layers may provide a long and detailed record of the most extreme enso events

late pleistocene climate and water budget of the south american altiplano abstract geomorphic evidence from the peruvian bolivian altiplano indicates that during episodes prior to 28 000 and around 12 500 11 000 yr b p lakes covered an area about six and four times as large as at present respectively within the constraints of the heat and water budget model calculations are used to estimate the precipitation rate that would allow hydrologic equilibrium on this basis it is suggested that rainfall on the altiplano during the episodes of enlarged lakes was respectively some 300 and 200 mm annum 1 larger than at present representing increases of about 75 and 50 respectively field evidence suggests that the episodes of enlarged lakes on the altiplano may have preceded or coincided with periods of maximum glaciation in the neigh boring andes in this region with high elevation of the ice equilibrium line increased precipitation is particularly conducive to glaciation

surface and subsurface expressions of gas seepage to the seabed examples from the southern north sea expressions of gas seepage observable within north sea seismic and acoustic data include seabed pockmarks seepage plumes in the water column acoustic blanking shallow enhanced reflectors and shallow seismic chimneys three areas were selected for a marine survey in

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

an evaporite based high resolution sulfur isotope record of late permian and triassic seawater sulfate abstract variations in the sulfur isotope composition of dissolved marine sulfate through time reflect changes in the global sulfur cycle and are intimately related to changes in the carbon and oxygen cycles a large shift in the sulfur isotope composition of sulfate at the permian triassic boundary has been recognized for long time and a number of studies were carried out to understand the causes and significance of this shift however data for the middle and late triassic are very sparse and the stratigraphic evolution of the sulfur isotope composition of seawater is poorly constrained due to the small number of samples analyzed and or due to the limited stratigraphic intervals studied moreover in the last few years the triassic timescale has significantly changed due to a wealth of new radiometric and stratigraphic data in this study we show that for the late permian and the triassic it is possible to obtain a precise reconstruction of the evolution of the sulfur cycle for parts of it at sub million year resolution by analyzing exclusively gypsum and anhydrite deposits we base our reconstruction on new data from the middle and late triassic evaporites of northern switzerland and literature data from evaporites from germany austria italy and the middle east we propose a revised correlation between the well dated marine tethyan sections in northern italy and the evaporites from northern switzerland and from the germanic basin calibrated to the newest radiometric absolute age scale this new correlation allows for a precise dating of the evaporites and constructing a composite sulfur isotope evolution of seawater sulfate from the latest permian lopingian epoch to the norian we show that a rapid positive shift of approximately 24 at the permian triassic boundary can be used to constrain seawater sulfate concentrations in the range of 2 6 mm thus higher than previous estimates but with less rapid changes finally we discuss two possible evolution scenarios for the middle triassic negative shift to values of 15 that subsequently remain constant during the late triassic

recording of el nino in ice core δ18o records from nevado huascaran peru the 68 year monthly resolved time series of 18 o from ice cores retrieved from the glaciated col of nevado huascaran peru 9 s 77 w 6050 m reflects climate variability over amazonia and the western tropical atlantic over the 25 year period 1968 1993 of midtroposphere observations the interannual variations in huascaran 18 o relate closely with the zonal wind variations over tropical south america at the 500 hpa level additionally there is some evidence that the spatial distribution of temperature anomalies in the western tropical atlantic has influence on the 500 hpa circulation and hence the isotopic fractionation of moisture advected across amazonia during el nino warming the moisture convergence axis over the atlantic ocean is commonly diverted northward leading to unusual warm and dry conditions over northeast brazil and 18 o enriched snowfall at huascaran this enrichment phase is enhanced when the peak pacific warming occurs during the first half of the calendar year coincident with the wet season over amazonia approximately 12 months later the el nino demise is affiliated with a reprisal of strong trade wind circulation and the resultant cool pluvial environment over amazonia triggers a reversal to strongly depleted isotope anomalies

glacier readvances in the andes at 12 500 10 000 yr bp implications for mechanism of late glacial climatic change radiocarbon dates from two sites in the andes ecuador and peru confirm that glaciers culminated a readvance after 11 000 yr bp a moraine stage equivalent in altitude and position relative to existing glaciers is present in most glacierized ranges but its age is equivocal broadly limiting dates from colombia and peru suggest that the stage may be late glacial as it is younger than 12100 yr bp but formed before the early holocene in southern chile a comparable moraine stage is older than ca 9100 yr bp andean glaciers appear to have advanced at least twice during the late glacial interval glacier reconstruction from these moraine limits suggests depression of the equilibrium line altitude by at least 300 400 m in the northern and north central andes and possibly less than this farther south late glacial climatic change occurred globally and possibly reflects north atlantic temperature and circulation changes forced by deglaciation of the northern ice sheets migrations north and south of the atlantic polar front and the switching off and on of a dust pump in low midlatitudes

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

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

isotopic tracers in polar seas and glacier ice the relationship between isotope concentration and salinity provides important evidence on the origin of water masses in polar regions it can be used to deduce the isotopic composition of melting ice we discuss a source of error implicit in the use of isotope salinity diagrams for this purpose we argue that conventional 18o and d salinity diagrams should be abandoned in favor of 1 s 18o and 1 s d salinity diagrams which are physically more meaningful and which introduce no significant error

timing is everything in a game of two hemispheres what causes ice ages and other episodes of violent climate change one clue comes from a new study of ice cores which unexpectedly seems to show rapid warming events happening first in the southern hemisphere

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

late quaternary vegetation and climate change in the amazon basin based on a 50 000 year pollen record from the amazon fan odp site 932 hemipelagic sediments from the amazon deep sea fan odp site 932 5 12 7 n 47 1 8 w and continental shelf provide a 50 000 yr long pollen record of amazon basin vegetation the age model for hole 932a is constrained by eight magnetic remanence intensity features one paleomagnetic excursion and three ams14c dates alchornea melastomataceae myrtaceae and moraceae urticaceae are dominant taxa in the pollen record between 40 200 and 19 800 cal yr b p andean taxa such aspodocarpusandhedyosmum increase in abundance between 19 800 and 11 000 cal yr b p and prior to 40 200 cal yr b p the holocene pollen assemblage derived from amazon river and continental shelf sediments is dominated by secondary growth taxa such ascecropia climatic factors influencing the development of glacial and interglacial tropical vegetation are considered by comparing marine with terrestrial records of vegetation change this comparison shows that the amazon basin forests were not extensively replaced by savanna vegetation during the glacial period contradicting the refugia hypothesis

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

late quaternary glacier advances and palaeolake highstands in the bolivian altiplano abstract recent study of late quaternary moraines and pluvio lacustrine features around the southern altiplano of bolivia suggests they developed more or less synchronously during the last glacial cycle the stratigraphy of lacustrine and deltaic sediments can be linked to outwash and moraines on glaciated massifs e g cerro condor iquina cerro azanaques and cerro tunupa which border the poopo uyuni and coipasa salt basins uranium series and radiometric dating of lake carbonates by previous workers suggests that major palaeolakes developed during the intervals 72 68 ka bp 44 34 ka bp and 15 4 9 5 ka bp radiocarbon dating of peat associated with glacifluvial and glacial sediments indicates that the most extensive glacier advance of the later part of the last glacial cycle culminated after 13 3 ka bp and that a smaller readvance may have occurred between 12 and 10 ka bp as the highest palaeolake stand the tauca phase has been dated to ca 13 8 ka bp it is concluded that increased effective moisture and cool climatic conditions during the interval ca 14 13 ka bp forced the simultaneous expansion of glaciers and lakes in and around the southern altiplano a palaeolake may have been present on the southern altiplano for much of the interval ca 15 4 9 5 ka bp its surface reaching different levels at different times