variable parent magmas and recharge regimes of the parinacota magma system n chile revealed by fe mg and sr zoning in plagioclase abstract zoning patterns of an content and fe mg and sr concentrations in plagioclase phenocrysts in andesites from parinacota volcano n chile reflect alternating recharge events with two chemically distinct mafic magmas these magmas are characterized by low and high sr contents similar to two recent mafic flank eruptions one end member basaltic andesite shows large sr enrichment and heavy rare earth depletions and thus equilibrated with lower crustal rocks at depth where plagioclase high sr is unstable and garnet high hree y is stable a second end member magma is lower in sr ba contents and has ree patterns typical for parent magmas elsewhere in the central andes the number of recorded recharge events increases after a catastrophic sector collapse and during the subsequent rebuilding of the stratocone variations of an fe and mg contents and morphology of zones suggest also changes in water pressure including decompression under water under saturated and water saturated conditions evidence for decompression is more present in post collapse samples suggesting that the change in the volcano dynamics involves changes in magma chamber location this shows the importance of the cone collapse event in the volcano s magmatic evolution we propose that both end members are only seen at the surface of parinacota volcano because of the particular dynamics of this volcanic system and that similar processes might occur in other volcanic centres of the central volcanic zone

a study of oxygen isotopic fractionation during bio induced calcite precipitation in eutrophic baldeggersee switzerland in order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences we undertook an extensive one year study march 1995 to february 1996 of water column chemistry and daily sediment trap material from a small lake in central switzerland comparisons between calculated equilibrium isotope values using the fractionation equation of friedman and o neil 1977 and measured oxygen isotope ratios of calcite in the sediment traps reveal that oxygen isotopic values of autochthonous calcite 18o are in isotopic equilibrium with ambient water during most of the spring and summer when the majority of the calcite precipitates in contrast small amounts of calcite precipitated in early spring and again in late autumn are isotopically depleted in 18o relative to the calculated equilibrium values by as much as 0 8 this seasonally occurring apparent isotopic nonequilibrium is associated with times of high phosphorous concentrations elevated ph 8 6 and increased co32 50 mol l in the surface waters the resulting weighted average 18o value for the studied period is 9 6 compared with a calculated equilibrium 18o value of 9 4 these data convincingly demonstrate that 18o of calcite are for the most part a very reliable proxy for temperature and 18o of the water

middle to late holocene palaeoenvironmental study of gialova lagoon sw peloponnese greece abstract the coastal areas of eastern mediterranean have long been the subject of research due to their rapid geomorphological changes but also because of their archaeological interest our study is focused on a shallow coastal lagoon of peloponnese gialova lagoon which for several years has attracted the scientific interest of archaeologists geomorphologists as well as sedimentologists gialova lagoon is located near the ancient city of pylos the kingdom of king nestor during the mycenaean period 1600 1100 bc the objectives of this study are a to reconstruct the middle to late holocene depositional environments of the lagoon and b to correlate our data to already existing publications in order to shed new light on the holocene evolution of the lagoon and the associated coastal palaeoenvironmental changes an 8 m deep vibracore was drilled and a multi proxy analysis was carried out on the sediment sequence including sedimentological grain size analysis and moment measures total organic carbon toc total nitrogen tn and total phosphorus tp high resolution geochemical xrf scanning and palaeontological micro and macro faunal analysis the chronological framework is based on five 14c datings forming the basis for an age depth model calculated using the oxcal software the radiocarbon dates from previous studies 6 cores 20 dates were also taken into account the data synthesis and interpretation provided robust and coherent indications regarding the palaeoenvironment shoreline changes and the rate of geomorphological changes of the coastal area of gialova lagoon as well as useful information about the palaeonvironmental and palaeoclimatic conditions that prevailed during the mycenaean period the interpretation reveal a transition from a shallow marine environment 6500 5800 yr b p to a brackish lagoonal 5800 3300 yr b p followed by a shift towards a freshwater marsh environment 3300 yr b p to present

the transition of the monsoonal and the n atlantic climate system off nw africa during the holocene 1 the northward extent of the influence of the w african monsoon during humid periods of interglacials is subject to investigations highlighting feedback mechanisms such as vegetation to detect this regional variation and the climate system acting farther to the north will be the aim of this paper focussing on the holocene we present two very high resolution holocene sediment records off nw africa located at 31 n and 27 n the well known mid holocene climate change from the african humid period to present arid conditions is well reflected by the terrigenous input in the southern core in contrast in the northern core spectral and wavelet analyses indicate a periodic oscillation of about 900 years of the terrigenous input throughout the last 9000 years b p we conclude that the w african monsoonal influence characterized by the abrupt climatic change at 5000 years b p can be separated from the influence of the n atlantic climate system reflected by a periodic oscillation throughout the holocene

a vegetation and fire history of lake titicaca since the last glacial maximum fine resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding lake titicaca 3810 m peru bolivia since ca 27 500 cal yr bp hereafter bp time control was based on 26 accelerator mass spectrometer ams radiocarbon dates seventeen ams dates and 155 pollen and charcoal samples between ca 17 500 bp and ca 3100 bp allow a centennial scale reconstruction of deglacial and early to mid holocene events local and regional fire signals were based on the separation of two charcoal size fractions 180 m and 179 65 m charcoal abundance correlated closely with the proportion of woody taxa present in the pollen spectra little or no pollen was detected in the sedimentary record prior to ca 21 000 bp very cold climatic conditions prevailed with temperatures suggested to be at least 5 8 c cooler than present increases in pollen concentration suggest initial warming at ca 21 000 bp with a more significant transition toward deglaciation ca 17 700 bp between 17 700 bp and 13 700 bp puna brava is progressively replaced by puna and sub puna elements the most significant changes between the pleistocene and the holocene floras were largely complete by 13 700 bp providing an effective onset of near modern conditions markedly earlier than in other andean records fire first occurs in the catchment at ca 17 700 bp and becomes progressively more important as fuel loads increase no evidence is found of a rapid cooling and warming coincident with the younger dryas chron a dry event between ca 9000 bp and 3100 bp with a peak between 6000 and 4000 bp is inferred from changes in the composition of aquatics and the marsh community as pollen of cyperaceae is replaced by poaceae apiaceae plantago and the shrub polylepis human disturbance of the landscape is evident in the pollen spectra after ca 3100 bp with the appearance of weed species

the hydrological and environmental evolution of shallow lake melincue central argentinean pampas during the last millennium summary lake melincue located in the central pampean plains of argentina is a shallow 4 m subsaline lake tds 2000 ppm highly sensitive to hydrological changes the modern shallow lake system is composed of a a supralittoral area which includes a narrow mudflat a vegetated mudflat and wetlands subenvironments and b the main water body comprising lacustrine marginal and inner areas the development and extension of these subenvironments are strongly conditioned upon lake surface fluctuations past environmental changes were reconstructed through sedimentological physical and geochemical proxy analyses of two short sedimentary cores 127 cm well constrained 210 pb ages profiles were modeled and radiocarbon chronologies were determined covering a period from ad 800 to the present the analyzed sedimentary cores from lake melincue allowed for the reconstruction of past hydrological scenarios and associated environmental variability ranging from extremely low lake levels during dry phases to pronounced highstands at wet periods the paleohydrological reconstruction revealed very shallow conditions in the period between ad 806 and ad 1880 which was registered by massive deposits with low organic matter relatively wetter phases disrupting this dry period were represented by organic matter increases a major wet phase was registered by ad 1454 after the end of the medieval climate anomaly a subsequent abrupt shift from this wet phase to drier conditions could be matching the transition between the end of the medieval climatic anomaly and the beginning of the little ice age the occurrence of sedimentary hiatuses between ad 1492 and ad 1880 in melincue sequence could correspond to intensive droughts during the little ice age after ad 1880 banded and laminated autochthonous organic matter rich sediments registered an important lacustrine transgression and the onset of a permanent shallow lake corresponding to the beginning of the current warm period the uppermost recent fine grained low salinity organic sediments represent a lake transgression occurred in the 1970s coeval with a general increase in precipitation across southeastern south america this transgression is registered regionally in other pampean lakes and in the 20th century instrumental records of lake melincue this paleoenvironmental reconstruction provides a new high resolution record that registers striking hydroclimatic changes occurred at a regional scale across the pampean plains during the last millennium and it contributes to understand the past climatic history in southeastern south america

a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years the quaternary paleoclimate of the central andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region the exact timing duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another and there have been few opportunities to compare climatic records from the same proxy along environmental gradients vegetation histories from fossil rodent middens provide one such opportunity on the pacific slope of the andes we previously reported a vegetation history from the upper margin 2400 3000 m of the absolute desert in the central atacama desert of northern chile that record identified a distinct wet phase that peaked between 11 8 and 10 5 ka when steppe grasses and other upland elements expanded as much as 1000 m downslope and a secondary wet period during the middle to late holocene 7 1 3 5 ka the latter wet phase remains controversial and is not as readily apparent in our lowelevation midden record we thus sought to replicate both phases in a midden record from the mid elevations 3100 3300 m of the arid prepuna where slight precipitation increases would be amplified midden records from these elevations identify conditions wetter than today at 13 5 9 6 7 6 6 3 4 4 3 2 and possibly 1 8 1 2 ka dry phases occurred at 9 4 8 4 ka and possibly at ca 5 1 ka present floras and modern hyperarid conditions were established after 3 2 ka the records from the two elevational bands generally match with some important differences these differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert 2003 elsevier science b v all rights reserved

pronounced occurrence of long chain alkenones and dinosterol in a 25 000 year lipid molecular fossil record from lake titicaca south america abstract our analysis of lipid molecular fossils from a lake titicaca 16 s 69 w sediment core reveals distinct changes in the ecology of the lake over an 25 000 yr period spanning latest pleistocene to late holocene time previous investigations have shown that over this time period lake titicaca was subject to large changes in lake level in response to regional climatic variability our results indicate that lake algal populations were greatly affected by the changing physical and chemical conditions in lake titicaca hydrocarbons are characterized by a combination of odd numbered mid to long chain c 21 c 31 normal alkanes and alkenes during periods when lake level was higher latest pleistocene early holocene and late holocene the c 21 n alkane and the c 25 and c 27 alkenes dominate hydrocarbon distributions and indicate contribution from an algal source potentially the freshwater alga botryococcus braunii the c 30 4 methyl sterol dinosterol increases sharply during the mid holocene suggesting a greatly increased dinoflagellate presence at that time long chain alkenones lcas become significant during the early holocene and are highly abundant in mid holocene samples there are relatively few published records of lca detection in lake sediments but their occurrence is geographically widespread antarctica asia europe north america lake titicaca represents the first south american lake and the first low latitude lake in which lcas have been reported lca abundance and distribution may be related to the temperature dependent response of an unidentified algal precursor although the lca unsaturation indices cannot be used to determine absolute lake titicaca temperatures we suspect that the published lca u 37 k unsaturation calibrations can be applied to infer relative temperatures for early to mid holocene time when lca concentrations are high using these criteria the u 37 k unsaturation indices suggest relatively warmer temperatures in the mid holocene in contrast to previous speculation lipid analysis provides little evidence of a greatly increased presence of aquatic plants during the mid holocene instead it appears that a few algal species were dominant in the lake based on the dramatic rise in abundances of lcas and dinosterol during the early to mid holocene we suspect that the algal producers of these compounds rose in response to a combination of physical and chemical changes in the lake these include temperature salinity and alkalinity changes that occurred as lake level dropped sharply during a multi millennial drought affecting the central andean altiplano

holocene environments from stable isotope stratigraphy of ostracods and authigenic carbonate in chilean altiplano lakes abstract sediment cores from three shallow 4000 m a s l paleoclimatic profiles show coherency within tropical subtropical circulation patterns climatic signals however are partially masked by local environmental systems results suggest similar arid mid holocene to less arid late holocene trends in the three lakes although each lake shows distinct response characteristics linked to differences in regional moisture balance isotopic signatures for each lake group in discrete 18o vs 13c populations high isotopic variability results from episodic flooding and brine evolution in the shallow lakes laguna seca 18 11 s 69 14 w 4500 m a s l is characterized by a diverse ostracod assemblage of at least 8 species indicating highest moisture levels among the three sites high 13c values are the result of continuous evasion of co2 derived from volcanically charged groundwaters and springs plus the formation of travertine and photosynthetic activity in the lake a 3 decrease in 18o about 4 7 m suggests an abrupt shift to wetter conditions at the transition from mid to late holocene lagunas miscanti 23 44 s 67 46 w 4140 m a s l and del negro francisco 27 28 s 69 14 w 4125 m a s l each contain only one ostracod species limnocythere sappaensis attesting to higher salinities although sediment facies and ostracod continuity and abundances imply a history of higher effective moisture at laguna del negro francisco sediment cores from each lake document more arid conditions in the lower sections with a sharp shift to wetter conditions in the upper sections highly variable isotope values at the transition from mid to late holocene suggest rapid short term climate shifts during this transition this overall trend can be correlated from laguna seca laguna miscanti and laguna del negro francisco to lago titicaca implying climatic coherency along the altiplano isotopic profiles show second order fluctuations and drought events that suggest short term variability along the transect in order to explain differences in the effective moisture among the three sites we postulate interactions of regional air masses in the north convective tropical precipitation dominates laguna seca as for lakes in the titicaca region effective moisture for lagunas del negro francisco and miscanti follows a south to north gradient generated by cold air masses from cut offs of pacific westerlies colliding with moist tropical air masses coherent shifts in the past therefore imply changes in available tropical air mass moisture

holocene precipitation and atmospheric changes inferred from river paleowetlands in the bolivian andes abstract in the southern tropical andes previous studies performed on lacustrine basins display large water level fluctuations due to changes in the precipitation minus evaporation balance during the holocene significant changes in groundwater levels were also inferred from river paleowetland deposits in northern chile and the northern bolivian altiplano but the discrepancies which appeared in the data from paleolakes and paleowetlands are still not understood in this paper we present stratigraphy and diatom analyses in new paleowetland records from non glacial valleys these data compared with previous results show that non stormy precipitation recorded by fine and or organic sedimentation dominated continuously from 11 200 to 1500 cal yr bp and that convective rainfall recorded by strong erosion occurred only episodically in the northern altiplano convective rainfall was similar to the type of precipitation which nowadays occurs during the rainy season austral summer when the tropical easterlies from the atlantic reach the bolivian andes non stormy precipitation is interpreted as a result of an intensification of cold air incursions from southern polar regions in good agreement with data from brazil the maximum intensity in cold air incursions occurred during the early holocene and coincided with a climatic optimum in antarctica and a considerably reduced el nino southern oscillation enso during the middle and late holocene cold air incursions decreased and the enso frequency increased we suggest that the interactions between the southern high and low latitudes by means of cold air incursions and associated changes in the west wind flow have been the main mechanisms involved in climatic changes at the latitudes of bolivia

late glacial to mid holocene palaeoclimate development of southern greece inferred from the sediment sequence of lake stymphalia ne peloponnese abstract the sedimentary sequence of lake stymphalia ne peloponnese for the first time sheds light on the palaeoclimate development of southern greece from 15 to 5 ka bp new geochemical data based on high resolution x ray fluorescence scanning provide in situ and continuous analysis of predefined element suites on split core surfaces variations of elements over time were assessed constructing correlation matrices based on the calculation of pearson correlation coefficients the element suite includes al si k ca ti mn fe zn rb sr and zr a major result includes that changes in element behaviour are related to hydrological changes in the catchment precipitation lake level status and evaporation insolation solar activity and are ultimately driven by climate major trends shifts in elemental ratios correspond to the climate development in the eastern mediterranean region based on correlation of rb sr reflecting wet dry climates with foraminiferal proxies of marine core lc21 from the southern aegean sea and the stable oxygen isotope record of soreq cave israel the bolling allerod the younger dryas and the 8 2 ka cold event were identified

holocene lacustrine deposition in the atacama altiplano facies models climate and tectonic forcing abstract we investigate the holocene sedimentary infilling of two high altitude 4000 m a s l lacustrine basins in the subtropical regions of the atacama altiplano central andes northern chile that today contain permanent shallow saline lakes laguna del negro francisco 27 s and laguna miscanti 23 s laguna miscanti was surveyed with multi frequency high resolution seismic techniques and sediment cores were retrieved from offshore areas of both lakes because of the geological location of these lacustrine basins within the active andean convergent margin and the presence of present and past climatic gradients in the altiplano our detailed sedimentologic mineralogic and geochemical study evaluates tectonic volcanic and climatic controls on lacustrine sedimentation in an arid environment both lakes originated by tectonic and volcanic activity during the pleistocene tectonic control of basin dynamics was clearly exerted during the early stages increased subsidence was responsible for alluvial fan activity in the laguna miscanti basin prior to the establishment of the lake and the negro francisco basin changed from exorheic to endorheic hydrogeologic conditions needed to maintain the two perennial saline lakes are largely controlled by the basins tectonic history the evolution of laguna del negro francisco comprises four successive stages 1 perennial saline carbonate sulfate lake 2 saline pan saline lake complex with a carbonate sulfate brine 3 a perennial brackish stage with high macrophyte chara productivity and mostly calcite formation and 4 a residual stage with halite precipitation the depositional history recorded in the miscanti core illustrates the evolution from an aragonite producing ephemeral saline lake to a macrophyte dominated perennial brackish lake with an aragonite saline pan saline lake complex and a calcite producing perennial brackish lake as intermediate stages the hydrologic budget of the lakes is a direct response to effective moisture precipitation evaporation fluctuations and therefore climate variability has played a major role in chemical composition and lake level changes climate forcing has controlled the depositional history of the lakes during the holocene our study illustrates different responses of lake systems to external climatic forcing especially with respect to cyclicity threshold dynamics and the importance of sedimentary recycling the main sedimentary sequences in both lakes correspond to cycles of increasing and decreasing effective moisture however this cyclicity is characterized by abrupt change rather than gradual evolution threshold dynamics modulated limnogeological changes and caused a stepwise evolution of the lacustrine systems laguna miscanti and laguna del negro francisco sedimentary sequences provide depositional models for small topographically closed brackish to saline lakes that developed on active margins and evolved under fluctuating but generally arid climatic conditions

the palaeohydrological evolution of lago chungara andean altiplano northern chile during the lateglacial and early holocene using oxygen isotopes in diatom silica oxygen isotopes of diatom silica and petrographical characterisation of diatomaceous laminated sediments of lago chungara northern chilean altiplano have allowed us to establish its palaeohydrological evolution during the lateglacial early holocene ca 12 000 9400 cal yr bp these laminated sediments are composed of light and dark pluriannual couplets of diatomaceous ooze formed by different processes light sediment laminae accumulated during short term diatom blooms whereas dark sediment laminae represent the baseline limnological conditions during several years of deposition oxygen isotope analysis of the dark diatom laminae show a general 18o enrichment trend during the studied period comparison of these 18odiatom values with the previously published lake level evolution suggests a correlation between 18odiatom and the precipitation evaporation ratio but also with the evolution of other local hydrological factors as changes in the groundwater outflow as well as shifts in the surface volume ratio of lago chungara the lake expanded probably increasing this ratio during the rising lake level trend due to changes in its morphology enhancing evaporation furthermore the lake s hydrology was probably modified as the groundwater outflow became sealed by sediments increasing lake water residence time and potential evaporation both factors could cause isotope enrichment natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical andean lake abstract the coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia yet little is known on the impacts of the morphometry of lakes throughout their ontogeny as lake chungara central andean altiplano northern chile experienced long term lake level fluctuations that strongly modified its area volume ratio it is an ideal system for exploring the relative roles that long term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity in this paper we review previous data on the percent contents of total organic carbon total inorganic carbon total nitrogen total biogenic silica isotopic composition of organic matter carbonates and diatom frustules as well as data on the abundance of the chlorophycean botryococcus braunii in this lake for the period 12 400 1300 cal yr bp we also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14 c and u th biosiliceous productivity in lake chungara was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation humid phases dated at approx 12 400 to 10 000 and 9600 to 7400 cal yr bp coincide with periods of elevated productivity whereas decreases in productivity were recorded during arid phases dated at approx 10 000 to 9600 and 7400 to 3550 cal yr bp andean mid holocene aridity period however morphometry related in lake controls led to a lack of a linear response of productivity to precipitation variability during the late glacial to early holocene lowstands facilitated complete water column mixing prompting episodic massive blooms of a large centric diatom cyclostephanos cf andinus thus moderate productivity could be maintained regardless of aridity by this phenomenon of morphometric eutrophy during the early history of the lake the subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion preventing complete overturn surpassing a certain depth threshold at approx 8300 cal yr bp caused cessation of the morphometric eutrophy conditions associated with cyclostephanos cf andinus superblooms after 7300 cal yr bp the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability with a lesser contribution of diatoms to the total primary productivity our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogeny

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

a 14kyr record of the tropical andes the lago chungara sequence 18 s northern chilean altiplano abstract high resolution geochemical analyses obtained using an x ray fluorescence xrf core scanner as well as mineralogical data from the lago chungara sedimentary sequence in the northern andean chilean altiplano 18 s provided a detailed reconstruction of the lacustrine sedimentary evolution during the last 14 000 cal yr bp the high resolution analyses attained in this study allowed to distinguish abrupt periods identify the complex structures of the early and mid holocene arid intervals and to compare their timing with titicaca lake and sajama ice records three main components in the lake sediments have been identified a biogenic component mainly from diatoms b volcanics ash layers from the nearby parinacota volcano and c endogenic carbonates the correlation between volcanic input in lago chungara and the total particles deposited in the nevado sajama ice core suggests the parinacota volcano as the common source the geochemical record of lago chungara indicates an increase in siliceous productivity during the early holocene lagging behind the rise in temperatures inferred from the nevado sajama ice core the regional mid holocene aridity crisis can be characterized as a number of short events with calcite and aragonite precipitation in the offshore lake zones

a 7000 year high resolution lake sediment record from coastal central chile lago vichuquen 34 s implications for past sea level and environmental variability we present a 7 ka environmental reconstruction based on sedimentological and geochemical data from lago vichuquen a coastal eutrophic lake in central chile 34 48 s 72 03 w 4 m a s l a relatively shallow and restricted marine environment with low productivity high detrital input and dominant anoxic conditions in the vichuquen basin occurred from 7 0 to 6 5 cal ka bp rapid onset of a holocene marine transgression at 6 5 cal ka bp favoured deeper and more biologically productive environments that existed until 2 8 cal ka bp bioproductivity changes during the mid holocene 6 5 4 2 cal ka bp were related to upwelling dynamics controlled by the intensity of the south east pacific anticyclone spa periods with lower organic productivity and dominant anoxic conditions reflect an increased intensity of spa increased upwelling and decreased precipitation a shift at 4 0 cal ka bp reflects the onset of modern southern westerly winds and el nino southern oscillation patterns tectonic uplifting and geormorphological activity dune advancement are possible reasons behind the vichuquen basin closure at 1 2 cal ka bp leading to a low bioproductivity lacustrine environment which has developed until the present

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

timing of wet episodes in atacama desert over the last 15 ka the groundwater discharge deposits gwd from domeyko range at 25 s abstract a chronologically robust reconstruction of timing and dynamics of millennial time scale wet episodes encompassing the entire atacama desert during the last 15 ka has been constructed to accomplish this a new composite paleoclimatic record from groundwater discharge deposits gwd in the sierra de varas domeyko range southern atacama in chile at 25 s has been compiled and compared with other published paleohydrologic records from the atacama region in sierra de varas sv three millennial timescale wet climate phases have been characterized around 14 5 ka cal bp 12 2 9 8 ka cal bp and 4 7 ka cal bp to the present day these wet phases are interpreted from intervals of gwd facies formed during periods when the springs were active gwd facies include 1 black organic peat rooted mudstones and sandstones formed in local wetland environments and 2 gypsum carbonate rich layers formed by interstitial growth gwd intervals alternate with gravelly alluvial material deposited during arid phases a trend towards less humid conditions during the late holocene wet episode characterizes gwd sedimentary series in sierra the varas suggesting the onset of a dry episode over the last few centuries around 0 7 ka bp a very short wet episode is recorded in the central part of the desert suggesting this was the time of maximum humidity for the entire late holocene wet period a brief arid phase occurred between 1 5 and 2 0 ka bp indicated by the absence of gwd in the domeyko range the paleoclimatic reconstruction encompassing the entire atacama region shows that both the intensity and occurrence of wetter conditions were governed mainly by the distance to the source of moisture and secondarily by the elevation of the sites in the northern atacama 16 20 s four wet phases fed by n ne summer monsoon precipitations have been proposed tauca phase 18 14 ka cal bp and coipasa phase 13 10 ka cal bp during the late glacial followed by early holocene and late holocene phases in contrast southern atacama records 23 28 s display only three pluvial periods which result from se summer monsoon precipitation and outbreaks from the westerlies during wintertime the early holocene in the southern atacama was a period of aridity generating important landscape differences to those in the northern atacama where conditions were wetter the core of atacama 20 23 s is the overall driest part of the desert because it is located in the distal limits of both n ne and se sources of moisture the amazon basin and gran chaco areas respectively

paleoenvironment changes in juag lagoon philippines based on sedimentology bulk geochemistry and stable isotopes and their implication to nutrification in recent decades eutrophication has been identified as a major problem in coastal and estuarine systems eutrophication can be due to cultural activities but can also be due to natural factors this study explores the possible role of geomorphic change in the eutrophication history of juag lagoon which is one of the sites with harmful algal blooms in the philippines surface and sediment cores were acquired for this study to trace the paleoenvironmental changes that brought about the present day lagoon radiocarbon dates and 210pb based estimates of sedimentation rates provided age control sedimentological indicators and stable isotope signatures of organic matter were utilized to assess changes in the source of organic matter deposited in the lagoon whereas xrf derived bulk sediment geochemistry was used as proxy for sediment input three phases of geomorphic state were identified over the lagoon history prior to 700 a d bulk geochemistry and isotopic measurements indicate a pre lagoon environment subsequent drop in sea level led to the development of the lagoon which persisted until 1100 a d the lagoonal condition transitioned to increased marine influence towards 1200 a d through several sandbar breaching events that may have persisted in recent years the present day lagoon maintains a continuous water exchange through a small tidal channel the closing of the lagoon and the limited flushing of lagoon waters could have led to the nutrification of the lagoon moreover anthropogenic impact through forest denudation mariculture and fertilizer use in the neighboring islands is reflected which could have also affected the nutrification of the lagoon in the last 100 years

a continuous record of vegetation fire regime and climatic changes in northwestern patagonia spanning the last 25 000 years abstract we present a high resolution precisely dated terrestrial paleovegetation paleoclimate record from lago pichilaguna northwestern patagonia 40 44 s which spans continuously from the last glacial maximum lgm to the present we find abundant and continuous presence of arboreal pollen chiefly nothofagus during the lgm accompanied by other trees shrubs and alpine herbs these results suggest subantarctic parkland and or scattered woodlands under a cold and hyperhumid climate during the lgm 25 000 17 800 cal yr bp with expansion of nothofagus under relatively warm interstadial conditions between 25 000 and 19 200 cal yr bp this was followed by cooling and a precipitation increase between 19 200 and 17 800 cal yr bp which was contemporaneous with the youngest lgm advance of andean glaciers in the region and maximum influence of the southern westerly wind sww the last glacial termination t1 started at 17 800 cal yr bp and featured the spread of thermophilous trees and ferns characteristic of north patagonian rainforests along with lake level lowering these results suggest a warm pulse and southward shift of the sww concurrent with a rapid collapse of andean glacier lobes subsequent changes led to the establishment of closed canopy rainforests under peak interstadial warmth between 16 000 and 15 000 cal yr bp we detect a shift to cold wet conditions during the antarctic cold reversal 14 800 12 700 cal yr bp and a precipitation decline during younger dryas time followed by maximum temperature relatively lower lake level and minimum sww influence between 11 300 and 7700 cal yr bp precipitation then rose punctuated by centennial scale variations since 6200 cal yr bp chilean european deforestation and spread of invasive exotic species started at 350 cal yr bp aided by fire we conclude that temperate rainforests have persisted with little interruption since t1 with major changes in floristic composition driven by climate change and fires rainforest composition and heterogeneity declined in response to chilean european disturbance during the 1600s and intensified since the 1800s these events constitute the fastest largest magnitude vegetation changes of the last 25 000 years

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

last glacial maximum in an andean cloud forest environment eastern cordillera bolivia climatically sensitive tropical ecosystems provide important information that may help us to fill the gaps in our knowledge concerning the evolution of rainforests during periods of full glaciation small changes in precipitation in the amazon basin have immediate consequences for the survival of the andean cloud forest because its dominant source of moisture today is the atlantic ocean a 40 k y lacustrine record from the eastern cordillera in bolivia in an endemic species rich and ecologically threatened region shows a dry last glacial maximum indicating a drastic decrease of the amazonian moisture source to explain this aridity we infer steep temperature gradients between the pole and equator in both hemispheres that would have reduced considerably the size and displacement of the intertropical convergence zone and the austral summer precipitation this major change in water supply induced a dramatic reduction in species diversity and suggests that the andean cloud forest did not provide refugia for tropical lowland taxa during full glacial times

a perched high elevation wetland complex in the atacama desert northern chile and its implications for past human settlement a previously undocumented type of wetland is described from the atacama desert in northern chile 3000 m above sea level sustained exclusively by direct precipitation and perched above the regional water table geomorphological mapping pedostratigraphy geochemistry and analysis of contemporary vegetation is used to understand wetland formation and dynamics during historical and present time periods the paleowetland deposits overlie a miocene tuff that acts as an impermeable barrier to water transfer and creates conditions for local shallow ground water these deposits include several paleosols that were formed during periods when precipitation increased regionally at 7755 7300 1270 545 and 400 300 cal yr bp the similarity in timing with other palaeohydrological records for the atacama implies that paleosols from this wetland are proxies for reconstructing past changes in local and regional hydrological cycle archaeological investigations have revealed the presence of two small farms from the late intermediate period i e during the earliest wetter phase represented by the paleosols both farms are located near the paleowetland deposits which suggests that local inhabitants exploited these water sources during late pre hispanic times results of this study improve knowledge of settlement patterns during this and earlier cultural periods

rapid development of an unusual peat accumulating ecosystem in the chilean altiplano stratigraphic relationships radiocarbon dating sediment and peat characteristics and rates of peat and carbon accumulation from a soligenous peatland or bofedal in the chilean altiplano shows the peatland to be unusually young dynamic and sensitive to environmental changes the site lies in the national park nevado de tres cruces in the puna desert grassland at an elevation of 4300 m a s l eight peat cores were extracted from a 1 75 km transect yielding a maximum of 3 6 m of organic sediment organic matter began to accumulate 1700 1100 cal yr b p under a progressively arid local climate after a period when regional climate is believed to have been more humid than at present areas of greater relief and better drainage in the valley bottom eventually fostered the growth of a riparian cushion plant community after water flowing down the valley began to diminish this led to rapid lateral expansion of the riparian peatland communities over open water in topographic depressions at a rate heretofore unprecedented in the peatland literature it appears that development of the peatland has been encouraged by autoregulation of internal hydrology the drainage impediment created by organic mass accumulation in lower relief areas probably reduced the amount of water arriving at the lower reaches of the peatland these areas have become progressively drier and have since died and oxidized through endogenous peat accumulation and a concomitant drainage impediment the ecosystem has been migrating upstream over the past 50 years

isolation and water level fluctuations of lake kachishayoot northern quebec canada this study combines different methods including grain size macrofossil and pollen analyses to reconstruct paleogeographical and paleoclimatological conditions for periods before during and after the isolation of a small lake lake kachishayoot in northern quebec after the retreat of the laurentide ice sheet around 8000 14c yr b p the area was submerged by the tyrrell sea the transition from marine to lacustrine environment occurred about 5400 yr b p two major periods of water level fluctuations were inferred from organic and mineral sediments a high water level that occurred after 3200 yr b p and a low water level that started before 2200 yr b p our chronological data for the first period are consistent with those from nearby lac des pluviers and from other lakes in east central canada and in the northeastern united states during the low water level period however there is no evidence for minor fluctuations whereas other lakes in northern quebec and east central canada underwent several brief lowerings long term changes in atmospheric circulation caused by changing global boundary conditions likely explained long term water level fluctuations of lake kachishayoot

the nevados de payachata volcanic region 18 s 69 w n chile subduction related volcanism in the nevados de payachata region of the central andes at 18 s comprises two temporally and geochemically distinct phases an older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late miocene age the pleistocene to recent phase 0 3 ma includes the twin stratovolcanoes volcan pomerape and volcan parinacota the nevados de payachata volcanic group and two small centers to the west i e caquena and vilacollo both stratovolcanoes consist of an older dome and flow series capped by an andesitic cone the younger cone i e v parinacota suffered a postglacial cone collapse producing a widespread debris avalanche deposit subsequently the cone reformed during a brief second volcanic episode a number of small relatively mafic satellitic cinder cones and associated flows were produced during the most recent activity at v parinacota at the older cone i e v pomerape an early dome sequence with an overlying isolated mafic spatter cone and the cone forming andesitic dacitic phase mostly flows have been recognized the two nevados de payachata stratovolcanoes display continuous major and trace element trends from high k2o basaltic andesites through rhyolites 53 76 sio2 that are well defined and distinct from those of the older volcanic centers petrography chemical composition and eruptive styles at v parinacota differ between pre and post debris avalanche lavas precollapse flows have abundant amphibole at sio2 59 wt and lower mg numbers than postcollapse lavas which are generally less silicic and more restricted in composition compositional variations indicate that the magmas of the nevados de payachata volcanic group evolved through a combination of fractional crystallization crustal assimilation and intratrend magma mixing isotope compositions exhibit only minor variations pb isotope ratios are relatively low 206pb 204pb 17 95 18 20 and208pb 204pb 38 2 38 5 87sr 86sr ratios range 0 70612 0 70707 143nd 144nd ratios range 0 51238 0 51230 and 18osmow values range from 6 8 o to 7 6 o smow a comparison with other central volcanic zone centers shows that the nevados de payachata magmas are unusually rich in ba up to 1800 ppm and sr up to 1700 ppm and thus represent an unusual chemical signature in the andean arc these chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components primary mantle derived melts which are similar to those generated by subduction processes throughout the andean arc are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface these magmas subsequently evolve at shallower levels through assimilation crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast

identification of arid phases during the last 50 cal ka bp from the fuentillejo maar lacustrine record campo de calatrava volcanic field spain geochemical element analysis molecular analysis of organic compounds physical palynological mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in fuentillejo maar lake in the central spanish volcanic field of campo de calatrava in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies the upper 20 m of core fuent 1 show variations in clastic input water chemistry vegetation and organic fraction sources in the lake throughout the late pleistocene and holocene the temporal framework provided by 14c accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal ka bp arid phases identified in the fuent 1 sequence are correlated to heinrich events he and to stadials of the dansgaard oeschger d o cycles siliciclastic facies with high magnetic susceptibility values high juniperus pollen content a low paq index aquatic macrophysics proxy index a decrease in the relative percentage of the n c27 and an increase in the n c31 alkanes are indicative of arid and colder climatic events related to he 2 he 1 and the younger dryas yd similar short cold and arid phases during the holocene were identified at 9 2 8 6 7 5 7 and 5 5 5 cal ka bp in dolomite mud facies the pollen data show an increase in the herbs component mainly chenopodiaceae artemisia and ephedra steppe taxa a low paq index a decrease in the relative percentage of the n c27 alkane and an increase in the n c31 alkane are also observed this facies was probably the result of lower lake levels and more saline alkaline conditions which can be interpreted as linked to arid warm periods these warm and arid phases were more frequent during marine isotope stage mis 3 and the interstadials of mis 2 he 4 he 2 he 1 and the yd in core fuent 1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the d o cycles but do not imply increasing humidity in the area fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the north atlantic region at millennial scale during the last 50 cal ka bp copyright 2009 john wiley sons ltd

geological constraints on the emplacement mechanism of the parinacota debris avalanche northern chile the holocene parinacota volcanic debris avalanche ca 8 000 years b p is located in the central andes of northern chile the avalanche formed by the sector collapse of a major stratovolcano adjacent to a lake basin in a single catastrophic event the deposit has an estimated volume of ca 6 km3 a run out of over 22 km and covers more than 140 km2 of the surrounding terrain the values of the heim coefficient 0 08 and the ratio a v 2 3 ca 50 where a is the area covered and v the volume of the deposit indicate high mobility of the avalanche debris in transport two avalanche units can be distinguished the lower unit consists mainly of blocks of rhyodacitic lavas and domes and pyroclastic flow deposits and glacial fluvial and lacustrine sediments the upper unit consists of a coarse grained breccia with little matrix largely composed of andesite blocks which are angular with little or no rounding by abrasion the avalanche displays pronounced hummocky topography in which hummock volume and amplitude as well as maximum block size within individual hummocks tends to decrease with transport distance and towards the lateral margins of the avalanche deposit some surfaces of individual breccia blocks are covered by tens to thousands of small scale impact marks indicating that neighbouring blocks were vibrating and colliding without significant shearing motion most of the deformation and shearing was instead accommodated in a basal layer of wet structureless sediments incorporated into the avalanche debris from the inundated lake basin we propose that the ancestral parinacota stratovolcano collapsed because of loading of underlying fluvioglacial and lacustrine sediments the edifice disintegrated during collapse along existing fractures into large rock domains volumes from 10 to greater than 1 106 m3 which were transported with little internal deformation and then fragmented into hummocks of breccia as they were deposited the decrease of hummock volume with distance suggests that material that travelled further broke up and had an initial greater kinetic energy

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

an ice core pollen record showing vegetation response to late glacial and holocene climate changes at nevado sajama bolivia we present the results of pollen analysis performed on an ice core recovered from nevado sajama bolivia dated to 25 ka bp low pollen concentrations from 25 to 15 ka bp are consistent with the scenario of an expanded ice cap surrounded by sparse vegetation and cold conditions on the altiplano during the last glacial maximum after 15 ka bp more pollen is present and percentages show vegetation response to climate fluctuations during the late pleistocene initially high concentrations of poaceae pollen are replaced by asteraceae pollen suggesting the occurrence of dry conditions towards the end of the bolling allerod guantiva interstadial a deglacial climatic reversal is registered in the pollen record by an abrupt decline in asteraceae and maximum percentages of poaceae indicating wet conditions during 14 12 ka bp the climate changed abruptly to warm and dry after 12 ka bp but vegetation remained in disequilibrium with climate until 10 ka bp pollen results indicate dry conditions at the beginning of the holocene with humidity increasing steadily until 8 5 ka bp decreased pollen concentration values used as a moisture availability proxy place the mid holocene dry period between 8 and 5 ka bp this was followed by wetter conditions to the present day

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

holocene vegetation history from fossil rodent middens near arequipa peru rodent abrocoma lagidium phyllotis middens collected from 2350 to 2750 m elevation near arequipa peru 16 s provide an 9600 yr vegetation history of the northern atacama desert based on identification of 50 species of plant macrofossils these midden floras show considerable stability throughout the holocene with slightly more mesophytic plant assemblages in the middle holocene unlike the southwestern united states rodent middens of mid holocene age are common in the arequipa area the midden record does not reflect any effects of a mid holocene mega drought proposed from the extreme lowstand 100 m below modern levels 6000 to 3500 yr b p of lake titicaca only 200 km east of arequipa this is perhaps not surprising given other evidence for wetter summers on the pacific slope of the andes during the middle holocene as well as the poor correlation of summer rainfall among modern weather stations in the central andes atacama desert the apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the holocene to changes in el nino southern oscillation modes

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

the origin of brines and salts in chilean salars a hydrochemical review abstract northern chile is characterized by a succession of north south trending ranges and basins occupied by numerous saline lakes and salt crusts collectively called salars fossil salt crusts are found to the west in the extremely arid central valley while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid cordillera sea salts and desert dust are blown eastward over the cordillera where they constitute an appreciable fraction of the solute load of very dilute waters salt content evaporative concentration of inflow waters leads to sulfate rich or calcium rich near neutral brines alkaline brines are almost completely lacking the alkalinity calcium ratio of inflow waters is lowered by the oxidation of native sulfur reducing alkalinity and the deposition of eolian gypsum increasing ca concentration theoretically so4 rich inflow waters and their derived so4 rich brines should be found in the intravolcanic basins of the cordillera because of the ubiquity of native sulfur while ca rich brines should prevail in sedimentary basins where ca rich minerals are abundant this relation is perfectly observed in the salar de atacama the largest in chile however several salars located within the volcanic cordillera belong to the ca rich group inflows and brines may have acquired their ca rich composition in pleistocene time when their drainage basins were mainly sedimentary later on recent lava flows and ignimbrites covered the sedimentary formations underground waters may have kept their early sedimentary signature by continuous recycling however the weathering of volcanic rocks tend to slowly shift the water compositions from the ca rich to the so4 rich type

early holocene collapse of volcan parinacota central andes chile volcanological and paleohydrological consequences the catastrophic gravitational collapse of the old cone of volcan parinacota produced a 6 km 3 debris avalanche that traveled 22 km and covered more than 150 km 2 the upper lauca drainage a broad high altitude basin in the chilean altiplano was permanently altered by the collapse although the eruptive history of parinacota before and after the debris avalanche is well known from petrologic and geochronologic studies previous age limits on the debris avalanche based on multiple chronometers span ca 8 20 ka new cosmogenic surface exposure ages from boulders atop the deposit are based on a regionally calibrated production rate of in situ 10 be and indicate that the avalanche occurred at 8 8 0 5 ka these data demonstrate that cosmogenic 10 be surface exposure dating can be successfully applied to quartz bearing volcanic debris avalanche deposits and that this method offers a distinct advantage over 14 c chronologies that provide only minimum or maximum age limits the 8 8 ka exposure age for the debris avalanche 1 agrees with 14 c age limits of paleosol material incorporated in the debris avalanche 2 requires a voluminous initial phase of postcollapse volcanism with an eruptive rate exceeding that of recent cone building episodes at most continental arc volcanoes and 3 suggests that volcano collapse did not result in the formation of lago chungara but instead led to a major expansion of a preexisting closed basin

dating of paleolakes in the central altiplano of bolivia abstract the deposits of the extensive paleolakes of the bolivian altiplano correspond to an alternation of lacustrine episodes and dry periods a phenomenon commonly explained by climatic changes the lack of precise dating of the deposits has prevented detailed reconstruction of the evolution of paleolakes that would allow a determination of the relative influence of interconnections between neighboring basins and local climatic conditions among the five paleolakes of the northern altiplano titicaca basin and the three of the central altiplano poopo coipasa and uyuni basins only the two most recent paleolakes have been dated a 121 m long sediment core recovered from the salar de uyuni contained 11 lacustrine layers l1 l11 separated by 12 salt crusts radiocarbon dating shows that the younger layers l1 and l2 are related to the tauca lacustrine phase 12 000 16 000 cal yr bp and layers l3 and l4 to the minchin lacustrine phase 30 000 73 000 cal yr bp layer l5 located at 46 m below the surface contains a volcanic ash with well preserved biotites is here dated by the 40 ar 39 ar method the measured age of 191 000 5000 y is the first date ever obtained from a pre minchin paleolake lake escara this result combined with 14 c and u th data obtained on lakes tauca and minchin from various authors suggests that the duration of the lacustrine events increased regularly during the pleistocene in contrast paleolake levels in the northern altiplano decreased from the oldest known lake mataro 3950 m to the present titicaca level 3806 m a progressive erosion of the threshold between the northern and central altiplano may have allowed important volumes of water to overflow from the northern basin into the central altiplano the existence of large paleolakes in the central altiplano was thus not only dependent on local climatic conditions but also on additional inputs from the north where climatic conditions could have been quite different from those prevailing in the south

patterns of regional hydrological variability in central southern altiplano 18 26 s lakes during the last 500 years abstract paleohydrological reconstructions based on sedimentological geochemical and isotopic records from a lake transect in the central southern altiplano 18 26 s indicate abrupt moisture fluctuations during the last 500 years a change to modern conditions occurred in the late 19th century in all the records from northern chile lago chungara 18 15 s and the atacama laguna miscanti 23 45 s to the southern tip of the altiplano laguna el peinado nw argentina 26 30 s a previous drier period shows different patterns of timing duration and intensity in chungara the arid period was shorter and occurred during the late 19th and early 20th centuries while in miscanti it occurred earlier and ended at the beginning of the 20th century in el peinado conditions were wetter during the 17 19th centuries and the arid period occurred prior to the 17th century other records from the region show abrupt paleohydrological and paleoclimatic changes synchronous with the termination of the little ice age despite local differences and dating uncertainties the little ice age stands out as a significant though complex climatic event in the andean altiplano the discrepancies between the northern and southern altiplano records during the last few centuries may reflect contrasting responses to external forcing in two areas with different climatic regimes

holocene paleohydrology and glacial history of the central andes using multiproxy lake sediment studies here we document at century to millennial scale the regional changes of precipitation evaporation from the late pleistocene to present with multiproxy methods on a north south transect of lake sites across the eastern cordillera of the central andes the transect of study sites covers the area from v14 s to 20 s and includes core studies from seven lakes and modern calibration water samples from twenty three watersheds analyzed to constrain the down core interpretations of stable isotopes and diatoms we selected lakes in different hydrologic settings spanning a range of sensitivity to changes in the moisture balance these include 1 lakes directly receiving glacial meltwater 2 overflowing lakes in glaciated watersheds 3 overflowing lakes in watersheds without active glaciers and 4 lakes that become closed basins during the dry season the results of our current work on multiple lakes in the bolivian andes show that while the overall pattern of holocene environmental change is consistent within the region conditions were not always stable over centennial to over millennial timescales and considerable decadal to centuryscale climate variability is evident abbott et al quat res 47 1997 70 80 quat res 47 1997 169 180 quat sci rev 19 2000 1801 1820 polissar master s thesis university of massachusetts 1999 comparison of the paleoclimate record from one well studied site lago taypi chaka kkota ltck with others within the region illustrates a consistent overall pattern of aridity from the late glacial through the middle holocene previous work noted a difference between the timing of water level rise in lake titicaca v5 0 3 5 ka b p abbott et al quat res 47 1997 169 180 cross et al holocene 10 2000 21 32 rowe et al clim change 52 2002 175 199 and the onset of wetter conditions at 2 3 ka b p in ltck a lake that drains into the southern end of lake titicaca abbott et al quat res 47 1997 70 80 sedimentary and oxygen isotope evidence from paco cocha 13 54ps located in the northern reaches of the expansive 57 000 km 2 titicaca watershed which spans v14 s to 17 s indicates that

holocene paleohydrology of the tropical andes from lake records two century scale time series in northern bolivia constrain the ages of abrupt changes in the physical geochemical and biological characteristics of sediments obtained from lakes that formed during deglaciation from the late pleistocene glacial maximum the watersheds of laguna viscachani 16 12 s 68 07 w 3780 m and lago taypi chaka kkota 16 13 s 68 21 w 4300 m located on the eastern and western slopes of the cordillera real respectively contain small cirque glaciers a high resolution chronology of the lake sediments is provided by 23 ams14c dates of discrete macrofossils late pleistocene glaciers retreated rapidly exposing the lake basins between 10 700 and 970014c yr b p the sedimentary facies suggest that after 890014c yr b p glaciers were absent from the watersheds and remained so during the middle holocene an increase in the precipitation evaporation balance is indicated above unconformities dated to 230014c yr b p in both lago taypi chaka kkota and laguna viscachani an abrupt increase in sediment accumulation rates after 140014c yr b p signals the onset of neoglaciation a possible link exists between the observed millennial scale shifts in the regional precipitation evaporation balance and seasonal shifts in tropical insolation

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

climate change and human occupation in the northernmost chilean altiplano over the last ca 11 500 cal a bp this interdisciplinary study represents an approximation towards understanding how regional human cultural systems may have been affected by climate change in the northernmost chilean altiplano 3600 m over the last ca 11 500 cal a bp we compare the archaeological record from hakenasa cave with the lake record from lago chungarasediment cores located 50 km to the south by integrating both of these archives in conjunction with regional palaeoclimate and archae ological data we provide new evidence for the role of changing environmental and climatic conditions in human settlement patterns the first human occupation of the entire altiplano occurs at hakenasa and is dated to 9980 40 14 c a bp 11 265 11 619 cal a bp and took place under wetter regional climate conditions an archaeologically sterile deposit occurs at hakenasa between 7870 and 6890 cal a bp constituted by sands and gravels these sediments are interpreted as a flood event this time period is synchronous with alternating short dry and wet events recorded in the lake chungara sedimentary sequence human activity resumes and increases in importance at hakenasa by ca 6000 cal a bp this corresponds to wetter conditions indicated by the chungararecord even though the lake record indicates intense volcanic activity over the last 6000 cal a bp this had little or no impact on the human population present at hakenasa this study shows that even in this extreme environment human settlement patterns do not always respond in a linear fashion to environmental change copyright 2008 john wiley sons ltd

climate catchment runoff and limnological drivers of carbon and oxygen isotope composition of diatom frustules from the central andean altiplano during the lateglacial and early holocene diatom based carbon and oxygen isotope analyses 13cdiatom and 18odiatom were performed on diatom rich laminated sediments of lake chungara andean altiplano northern chile deposited during the lateglacial and early holocene 12 400 8300 cal years bp to reconstruct climate change and environmental response across this major climate transition the 13cdiatom data show both centennial to millennial scale changes related to fluctuations in lake productivity and co2 concentration in the lake water and variations in carbon sources to the lake through time the 18odiatom data reflect changes in lake hydrology and climate the combination of 13cdiatom and 18odiatom data reveals interactions between the internal lake processes and its catchment runoff during wet periods low 18odiatom values 13cdiatom indicates an enhanced contribution of allochthonous carbon whereas during dry periods high 18odiatom 13cdiatom values suggest more autochthonous carbon production and recycling these decadal to centennial oscillations are not recognized after 10 000 cal years bp possibly as a result of enso like phenomenon weakening humid conditions during the lateglacial early holocene transition 12 400 10 100 cal years bp were possibly due to the establishment of la nina like conditions in the tropical south pacific whereas dry conditions in the early holocene 10 100 9100 cal years bp may be caused by the northward migration of the itcz due to both enso like weakening and an insolation minimum finally a return to humid conditions at the end of the early holocene 9100 8300 cal years bp is coincident with an increase in summer insolation

a late quaternary diatom record of tropical climatic history from lake titicaca peru and bolivia abstract a composite high resolution diatom stratigraphy from three piston cores and one box core in the deep sub basin of lake titicaca reveals large moisture variations during the past 30 kyr in the altiplano region diatom sequences indicate orbital and millennial scale variability in water level and salinity the pelagic freshwater diatom species cyclotella andina and cyclotella stelligera dominate glacial age sediments suggesting that the lake was above its present outlet generally wet conditions continued until 11 000 cal yr bp as indicated by high percentages of freshwater planktonic diatoms large pulses of benthic diatom species between about 11 000 and 10 000 cal yr bp suggest brief intervals of large amplitude declines in lake level during the early holocene 10 000 8500 cal yr bp a freshwater diatom assemblage suggests overflowing conditions pelagic freshwater diatoms are replaced ca 8500 cal yr bp by the salinity indifferent species cyclotella meneghiniana and by benthic taxa indicating the beginning of lake regression during the mid holocene 6000 3500 cal yr bp the abundance of the saline taxon chaetoceros muelleri coupled with high abundances of epiphytic and epipelic diatoms indicates maximum salinity and lowest lake levels in the entire 30 000 year record lake transgression began ca 4000 cal yr bp and the lake achieved modern levels by about 1500 cal yr bp these water level changes imply changes in effective moisture most likely resulting from large precipitation changes precipitation was high throughout the last glacial maximum 21 000 18 000 cal yr bp likely due to an enhanced south american summer monsoon during peak summer insolation in the southern hemisphere in contrast the mid holocene transition was dryer than today in association with an austral summer insolation minimum and the subsequent weakening of the summer monsoon

late quaternary climate history of the bolivian altiplano abstract sediment cores and outcrops from the bolivian altiplano are used to interpret late pleistocene holocene paleoclimates and lake evolution based on a multi proxy approach ostracod content palynology sedimentology and radiocarbon dating despite the different sensitivity of the lacustrine basins to environmental changes interpreting the records in terms of paleohydrology climate and more especially timing of events is difficult notwithstanding these problems lake titicaca in the north and lake pocoyu lake poopo salars of coipasa and uyuni in the south reveal a similar evolution in general trends through the course of time during the minchin phase until 30 26 kyr bp the altiplano was wetter than present the last glacial maximum ca 26 14 kyr bp marked by cooler drier conditions was followed by a return to a wetter climate interrupted by short arid events between ca 14 and 10 5 kyr bp another cycle of aridity between 10 5 and 8 kyr bp took place abruptly just after the humid tauca phase the mid holocene is interpreted as climatically unstable with an alternation of humid and dry episodes since 3 9 kyr bp wetter conditions have persisted and intensified to the present the data are interpreted in terms of changes in inter tropical convergence zone extension summer precipitation and in polar air mass intensity winter precipitation

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

mid holocene paleoenvironments in northwestern argentina main patterns and discrepancies abstract this paper summarizes the available paleoenvironmental information for the mid holocene in northwestern argentina in order to systematize a multi scale scenario for human adaptation in the area the main results of the studies carried out by several research teams that have studied the conditions during this period in the tropical andean region are described and compared taking into account their geographical setting the proxies involved and their particular space time resolution the paleoenvironmental situation prior to the onset of mid holocene conditions i e starting at the late glacial maximum is summarized to estimate the nature and extent of the changes occurred during this period paleoenvironmental results their characteristics and interpretation are also considered a general trend towards an aridization process that fostered a hydrologic stress process is traceable along the mid holocene in northwestern argentina and the tropical andes however several localities seem to have retained wetter conditions increasing the contrast between highly productive environments and the generally dry landscape this paper is only a first step towards a full understanding of the diversity and complexity of the mid holocene in different space time scales but a necessary one in order to start to model the resources structure available for human groups in the past in the andes

carbonate and organic matter sedimentation and isotopic signatures in lake chungara chilean altiplano during the last 12 3 kyr abstract sediments in lakes in the andean volcanic setting are often made up of diatomaceous ooze together with volcaniclastics and small amounts of carbonates despite their scarcity carbonates along with organic matter provide significant paleoenvironmental information about lake systems this study focuses on the carbonates in lake chungara their morphologies distribution and origin deduced from the isotopic markers these markers reflected changes in the water and the biomass between the onset of the holocene and around 9 6 cal kyr bp these changes are marked by general increases in toc tn and tn 15nair and by fluctuating values of toc 13cvpdb in its sediments and are probably related to major shifts in the lake surface volume associated with rises in lake level an increase in salinity around 10 cal kyr bp is thought to be linked to a short dry period giving rise to the onset of carbonate production the mid holocene arid period between 7 3 and 3 5 cal ka bp with a maximum of aridity around 6 0 cal kyr bp was deduced from 18ovpdb values in the endogenic carbonates these results match the reconstructions in lake titicaca based on benthic diatoms and paleoshore levels offshore sediments mainly consist of a diatomaceous ooze laminated in the lower half unit 1 and banded massive with tephra layers in the upper half of the sequence unit 2 toc 13cvpdb and the c n ratio confirm that phytoplankton was the main source of organic matter in these sediments shallower sediments units 3 to 5 developed in platform and littoral settings providing evidence of subaqueous macrophytes and to a lesser extent land plants carbonate content ranges between 0 1 and 6 wt in offshore settings 30 to 40 m water depth and reaches the maximum values in the lower part of unit 2 carbonate minerals low magnesium calcite and minor amounts of high magnesium calcite and aragonite are scarce and are arranged in mm thick layers commonly forming cm thick levels or bioclasts carbonate layers are made up of euhedral to subhedral spindle shaped calcite crystals and to a lesser extent aragonite needles all in the m range aragonite spheroids coexist in littoral sediments with other carbonate shapes and charophyte remains where carbonate reaches locally up to 20 wt co2 photosynthetic depletions related to seasonal phytoplankton blooms were responsible for the high frequency deposition of mm thick carbonate layers the average values for 13cvpdb in lake water plankton and sediments of lake chungara as organic matter or as carbonate are around 15 higher than commonly reported values in other lakes this 13c enrichment is attributed to carbon assimilation from a dic affected by methanogenesis in which hco3 is the dominant species the 13cvpdb and 18ovpdb variations and their covariation in endogenic carbonates suggest that lake water volume and lake level increased along the holocene

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

from proxy data to paleoclimate interpretation the mid holocene paradox of the atacama desert northern chile abstract the question whether the mid holocene climate between ca 9 and 4 cal kyr b p in the atacama desert and the central andes in general was humid or dry has wide implications with regard to the understanding of long term climate variability in south america paleosols regional groundwater tables abiotic proxy data and pollen of aquatic plants in lake sediments show a marked and rapid shift from very humid late glacial early holocene climatic conditions between ca 14 and 9 5 kyr b p to extremely dry mid holocene conditions more arid than today between ca 9 and 4 kyr b p an exception during this hyperarid period is a century scale more humid interval around ca 5 5 6 kyr b p that appears systematically in lake sediment archives in contrast pollen for most terrestrial plants preserved in lake sediments do not show major changes during the holocene whereas more humid mid holocene conditions compared with late holocene conditions were inferred from plant macrofossils in rodent middens is the reason for this disagreement to be attributed to misinterpretation of the paleoenvironments or of the proxy records themselves or to incomplete paleoclimatic interpretation of the paleoenvironments we argue that these different paleoclimate archives record different aspects and facets of climate while paleosols and groundwater in the atacama desert record low frequency climate variability at century to millennium scales lake sediments on the altiplano record decade to century scale variability terrestrial vegetation responds to shorter high frequency climate variability at seasonal to inter annual scales and preferably to humid years vegetation remains in hibernation or does not germinate during arid years thus information from these three types of archives is not a priori comparable and requires careful site specific archive specific and time scale specific evaluation what is natural in modern climatology is also true for paleoclimatology a comprehensive assessment must account for the complex daily and seasonal cycles for the range of climate variability and trends at different scales in space and time for impacts of short term extreme events and for specific often non linear responses of individual bio geo physical archives to any of the numerous aspects of climate

recommendations for using xrf core scanning as a tool in tephrochronology x ray fluorescence xrf core scanning is a relatively new arrangement of a classic analytical technique which allows for non destructive in situ xrf analysis of sediment cores from submillimetre

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

radiocarbon reservoir effect and the timing of the late glacial early holocene humid phase in the atacama desert northern chile we revise substantially the regional chronology of lake level fluctuations from the late glacial early holocene humid phase along a high altitude transect 3500 to 4500 m between 18 s and 28 s in the southwestern altiplano of northern chile radiocarbon dates and 210pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14c dates our chronology suggests that the latest pleistocene early holocene humid phase started between 13 000 and 12 000 14c yr b p and that maximum lake levels were reached between 10 800 and 9200 14c yr b p this is significantly younger than what has been established so far for the titicaca uyuni basin in bolivia the paleolakes disappeared sometime between 8400 and 8000 14c yr b p our revised chronology agrees with the regional history of human occupation and is broadly synchronous with vegetation changes in subtropical continental south america and with the onset of wetland expansion in the northern hemisphere tropics

the last deglaciation in the picos de europa national park cantabrian mountains northern spain a sedimentological and geochemical study of the lago enol sequence cantabrian mountains northern spain together with detailed geomorphological mapping provides a first record of glacier evolution and climate change over the last 40 ka in the picos de europa national park the enol glacier retreated from its maximum extent prior to 40 ka bp as demonstrated by the onset of proglacial lacustrine sedimentation in two glaciated depressions the comella hollow to the north before 40 ka bp and the lago enol before 38 ka bp these results support previous evidence that the maximum extent of southern european glaciers occurred earlier than in northern europe alternation of homogeneous and laminated proglacial sediments during the glacier retreat illustrate a dynamic glacial evolution during the marine isotope stage mis 3 40 26 ka bp a slight warming is detected at 26 ka ago with the change from proglacial sediments in a lake located in contact to the glacier to glaciolacustrine sedimentation in a non contact or distal lake finally the onset of organic rich sediments took place at 18 ka ago this last transition occurred in two phases similarly to the north atlantic last termination suggesting a link between north atlantic deep water formation oscillations and palaeohydrological variability in the cantabrian mountains copyright 2009 john wiley sons ltd

lacustrine radiocarbon reservoir ages in co ngoin and zige tangco central tibetan plateau abstract a series of 14 c ages were made in two lake sediment cores from co ngoin and zige tangco central tibetan plateau china using bulk organic carbon plant remains chitin of cladocera and carbonates the old 14 c ages of the surface sediments in both cores suggests that there is a significant reservoir effect in these lakes the magnitude of the reservoir age of different material is variable authigenic carbonate has the largest reservoir age while plant remains and chitin show smaller deviations due to a lack of terrestrial macrofossils at most depths a regression approach was used to obtain the approximate 14 c reservoir correction for bulk organic matter which is 3260 14 c bp and 2010 14 c bp for co ngoin and zige tangco respectively

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

geochemical investigation of the south wellesley island wetlands insight into wetland development during the holocene in tropical northern australia the south wellesley islands in the gulf of carpentaria northern australia were the recent focus of a palynological investigation which found vegetation change during the holocene was driven by coastal progradation and regional climate here we present new elemental data from x ray fluorescence core scanning which provides non destructive continuous and high resolution analysis from three wetlands across bentinck island the largest of the south wellesley islands elemental data and grain size analyses are combined with lead 210 210pb and accelerator mass spectrometry ams carbon 14 14c dates an open coastal environment was present 1250 cal a bp on the south east coast of bentinck island with sediment supply incorporating fluvial deposition and detrital input of titanium and iron from eroding lateritic bedrock prograding shorelines dune development and river diversion formed a series of swales parallel to the coast by 800 cal a bp forming the marralda wetlands wetlands developed at sites

u th pb isotope chronology of sulfide ores and rocks in the early proterozoic metavolcanic belt of northern wisconsin lead was probably derived from 3 7 b y old source material about 1 8 to 1 9 b y ago data on metavolcanic and granitic rocks from the belt show that the u th pb systems in most were reset about 1 6 b y ago a time of shearing and retrogressive metamorphism a concordia plot of the whole rock lead data shows that many of the rocks lost lead relative to uranium and thorium during the interval 200 to 400 m y ago similar ores might be sought between the northern wisconsin metavolcanic belt and the upper mississippi valley because the lead lost from the basement there might be available for ore formation in overlying units the lead in the early proterozoic metavolcanic belt of northern wisconsin seems to have been derived from the same mantle parent as the late archean metavolcanic belts of northeastern minnesota and southern ontario modified journal abstract

biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in late glacial to holocene lacustrine rhythmites biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes changes in the isotopic composition of the diatom frustules 18odiatom and 13cdiatom in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes the lago chungara andean altiplano 18 15 s 69 10 w 4520 masl diatomaceous laminated sediments are made up of white and green multiannual rhythmites white laminae were formed during short term diatom super blooms and are composed almost exclusively of large sized cyclostephanos andinus these diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and or when nutrients are introduced from the catchment during periods of strong runoff conversely the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms mainly smaller valves of c andinus and discostella stelligera and organic matter these green laminae reflect the lake s hydrological recovery from a status favouring the diatom super blooms white laminae towards baseline conditions 18odiatom and 13cdiatom from 11 990 to 11 530 cal years bp allow us to reconstruct shifts in the precipitation evaporation ratio and changes in the lake water dissolved carbon concentration respectively 18odiatom values indicate that white laminae formation occurred mainly during low lake level stages whereas green laminae formation generally occurred during high lake level stages the isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events el nino southern oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events favouring hydrological changes at interannual to decadal scale this study demonstrates the potential for laminated lake sediments to document extreme pluriannual events

holocene indian summer monsoon variation inferred from geochemical and grain size records from lake ximenglongtan southwestern china abstract identifying holocene indian summer monsoon ism variability and its possible mechanism is critical for predicting future environmental changes in this study we present a well dated ca 9 4 kyr geochemical and grain size record derived from lake ximenglongtan southwestern china the record depicts the holocene ism evolution and multi decadal to centennial abrupt precipitation change events superimposed on the long term climate changes the results indicate that precipitation was high during the first half of the holocene from ca 9 4 to 4 5 cal kyr b p but decreased over the later holocene on the multi decadal to centennial time scale our results show that a pronounced and prolonged drought event occurred between 7 6 and 7 0 cal kyr b p in addition several other low precipitation events occurred at about 8 9 6 3 5 2 4 2 3 7 2 5 and 1 7 cal kyr b p which correspond well with reported intervals of abrupt ism weakening events our findings suggest that changes in solar activity may have primarily controlled the fluctuations of ism intensity on the multi decadal to centennial time scale cooling of the north atlantic climate and the interactions between tropical ocean and atmosphere may have amplified the solar signal

mid holocene climate in the south central andes humid or dry have concluded thatgenerally drier conditions prevailed we argue that wet conditions result in high er river discharge and erosion whereas accu mulation of fine materials in a steep valleyrequires overall decreased river flow and a low energy environment with dry conditions fine grained but permeable sediments that accumu late in the valley bottom may form local aqui fers and raise the groundwater table despite alarger cross section in the valley and reduceddischarge overall modern analogs show thatgroundwater tables in such wetlands are oftenself sustained very local and disconnectedfrom their surroundings and are thus difficult tointerpret in terms of climate conditions today the rivers in both the tula n and puripica valleysare erosive and have dissected the mid holo cene sediments down to bedrock typically sediments from between 14 and 9 ky b p aperiod of well documented extreme humidity are missing in these valleys because of strongerosion whereas as expected sediments fromthis humid period are present in fossil springcomplexes tilomonte springs figure 4 in