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

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

concretion morphologies reflecting diagenetic and epigenetic pathways abstract due to complex physicochemical processes concretions develop variable but distinctive morphologies reflecting the state of the sediment in subsequent stages of diagenesis and epigenesis they deserve a study and systematization in their own right at the same time concretional morphologies illustrate the effect of hierarchic self organization which is a basic element also in biological evolution

a record from lake cardiel of climate change in southern south america southern south america the only continental land mass lying between 38 s and the antarctic circle presents a rare opportunity to reconstruct terrestrial records of palaeoclimate in an area that is subject to shifts of polar and mid latitude wind and pressure belts in the bulk of this region patagonia are many hydrographically closed lakes which despite the palaeoclimatic significance of the region and the proven utility of lake level records in reconstructing past climates1 2 have escaped detailed study using sedimentary and geomorphic evidence together with 14c dating we present here a detailed lake level record for lake cardiel fig 1 the highest level of the past 21 000 years occurred at about 9 780 bp reminiscent of tropical lakes rather than those in northern mid latitudes1 2 the lake cardiel record corroborates and clarifies the timing of the wetness record inferred from pollen studies in patagonia

holocene explosive activity of hudson volcano southern andes fallout deposits in the vicinity of the southern andean hudson volcano record at least 12 explosive holocene eruptions including that of august 1991 which produced 4 km3 of pyroclastic material medial isopachs of compacted fallout deposits for two of the prehistoric hudson eruptions dated at approximately 3600 and 6700 bp enclose areas at least twice that of equivalent isopachs for both the 1991 hudson and the 1932 quizapu eruptions the two largest in the andes this century however lack of information for either the proximal or distal tephra deposits from these two prehistoric eruptions of hudson precludes accurate volume estimates andesitic pyroclastic material produced by the 6700 bp event including a 1 10 cm thick layer of compacted tephra that constitutes a secondary thickness maximum over 900 km to the south in tierra del fuego was dispersed in a more southerly direction than that of the 1991 hudson eruption the products of the 6700 bp event consist of a large proportion of fine pumiceous ash and accretionary lapilli indicating a violent phreatomagmatic eruption this eruption which is considered to be the largest for hudson and possibly for any volcano in the southern andes during the holocene may have created hudson s 10 km diameter summit caldera but the age of the caldera has not been dated independently

precise radiocarbon dating of late glacial cooling in mid latitude south america abstract variability of atmospheric 14c content often complicates radiocarbon based chronologies however specific features such as periods of constant 14c age or steep changes in radiocarbon ages can be useful stratigraphic markers the younger dryas event in the northern hemisphere is one of those periods showing conspicuous 14c wiggles although the origin of those variations is not fully understood we can make practical use of them and determine i whether the younger dryas was global in extent if so ii were the initial cooling and the final warming synchronous worldwide and iii what are the implications of these similarities differences here we report high resolution ams 14c chronologies from the mid latitudes of south america that pinpoint a cool episode between 11 400 and 10 20014c yr b p the onset of the final cool episode of the late glacial in the southern mid latitudes i e the huelmo mascardi cold reversal preceded the onset of the younger dryas cold event by 550 calendar years both events ended during a radiocarbon age plateau at 10 20014c yr b p thus the huelmo mascardi cold reversal encompasses the younger dryas as well as a couple of short term cool warm oscillations that immediately preceded its onset in the north atlantic region

mid holocene climatic variability reconstruction from pollen records 32 52 s argentina abstract this study reviews 42 published pollen records to gain a better understanding of holocene climate variability especially of the past displacement and location of the arid semiarid region asr between 32 and 52 s in argentina at present the asr is delimited approximately between the 500 mm isohyet in the pampa region and the 300 mm isohyet in the andean sector south of 37 s represented by arid and semiarid climate types where precipitation can be as low as 200 mm mid holocene climatic variability affected the regional vegetation patterns and the borders of the asr paleoenvironmental reconstruction is based on comparison of fossil pollen records from different depositional environments maps of distribution patterns of plant formations are reconstructed at 2000 500 year intervals from 8000 to 4000 14 c years bp vegetation changes are mainly explained by changes in the position and the seasonal amplitude of latitudinal shifts of the pacific and atlantic anticyclones and of the westerlies from 8000 to 4000 bp the eastern limit of the asr was displaced eastward the western limit reached the maximum eastward displacement in the southern extreme of patagonia at 6000 years bp at this time at the center of asr shrub steppes and the monte developed suggesting maximum dry conditions and the establishment of the arid diagonal north of 42 s while the present day espinal dry pampa ecotone became established at 4000 years bp paleodata suggest a transitional stage towards the present situation of the asr

palaeoenvironmental changes in southern patagonia during the last millennium recorded in lake sediments from laguna azul argentina marked environmental changes in the southern patagonian steppe during the last 1100 years are detected by a multi proxy study of radiocarbon dated sediment cores from the crater lake laguna azul 52805vs 69835vw a prominent shift in carbon isotope records occurred between ad 1670 and ad 1890 induced by a change to cooler climate conditions with a concurrent lake level rise a second perturbation of the lake ecosystem started with a fire event around ad 1830 the fire event triggered increased soil erosion initiating a change of the diatom assemblages this shift in diatom assemblages may have been enhanced by shrinkage of littoral habitats and higher nutrient supply in the course of permanent european settlement at the end of the 19th century the introduction of neophytes by european sheep farmers is confirmed by the permanent occurrence of rumex pollen in the sediment record since the beginning of the 20th century d 2005 elsevier b v all rights reserved

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

where have all the craters gone earth s bombardment history and the expected terrestrial cratering record here we make the first quantitative estimates of the maximum total number of large terrestrial impact craters that can survive until the current era on earth our estimates of crater survival are made using the age of earth s crust and the expected flux of large extraterrestrial bodies striking earth this analysis neglects effects such as weathering and burial which tend to preferentially erase smaller craters thus our results represent the maximum number of craters we expect to exist on earth today although the constant recycling of crustal material creates a strong bias toward younger ages our model suggests that the terrestrial cratering record can be used to determine the size frequency distribution of the impactors that bombarded earth over the past 3 5 g y however our model suggests that the cratering record cannot be used to distinguish between scenarios with a constant flux of impactors over time and scenarios where the bombardment rate was considerably higher in earth s ancient history luckily layers of distal impact ejecta may act as records of impacts even when the source craters have been tectonically recycled we suggest that searches for these distal impact ejecta layers will be more fruitful for constraining the bombardment history of earth than searches for large craters

cold climatic episode of younger dryas age in tierra del fuego pronounced climatic change during the last glacial maximum is recognized as global in extent and has been attributed to orbital forcing1 not readily explained in a global context because of the equivocal nature of the evidence are the late glacial climatic events of short 100 1 000 yr duration the cold climate of the younger dryas chron 11 000 10 000 yr bp for example is known to have been particularly pronounced over the north atlantic and parts of europe and north america2 3 whereas in the southern hemisphere cold conditions for that time are not well established here we present evidence for late glacial climatic cooling in southernmost south america from studies of radiocarbon dated glacial and pollen stratigraphy at sites along the beagle channel in tierra del fuego where a forest tundra tension zone in the region is especially sensitive to shifting climate we conclude that the cold episode corresponds with the time of the younger dryas in europe when a drop in temperature ascribed most recently to colder sea surface temperatures and production rate of deep water in the north atlantic4 5 apparently occurred worldwide

holocene climate evolution in the high latitude southern hemisphere simulated by a coupled atmosphere sea ice ocean vegetation model the holocene climate is simulated in a 9000 yr long transient experiment performed with the ecbilt clio vecode coupled atmosphere sea ice ocean vegetation model this experiment is forced with annually varying orbital parameters and atmospheric concentrations of co2 and ch4 the objective is to study the impact of these long term forcings on the surface temperature evolution during different seasons in the high latitude southern hemisphere we find in summer a thermal optimum in the mid holocene 6 3 ka bp with temperatures locally 3 degrees c above the preindustrial mean in autumn the temperatures experienced a long term increase particularly during the first few thousand years the opposite trend was simulated for winter and spring with a relatively warm southern ocean at 9 ka bp in inter up to 3 5 degrees c above the preindustrial mean and a warm continent in spring 3 degrees c followed by a gradual cooling towards the present these long term temperature trends can be explained by a combination of 1 a delayed response to orbital forcing with temperatures lagging insolation by i to months owing to the thermal inertia of the system and 2 the long memory of the southern ocean this long memory is related to the storage of the warm late winter spring anomaly below the shallower summer mixed layer until next winter sea ice plays an important role as an amplifying factor through the ice albedo and ice insulation feedbacks our experiments can help to improve our understanding of the holocene signal in proxies for instance the results suggest that in contrast to recent propositions teleconnections to the northern hemisphere appear not necessarily to explain the history of southern hemisphere temperature changes during the holocene

climate and chronology of antarctica and adjacent south america over the past 30 000 yr abstract well dated records of paleoclimate essential for developing general circulation models of the atmosphere during the quaternary are limited in the subpolar southern hemisphere for antarctica where dating is particularly restricted records from distal south america provide a measure to assess antarctic ice sheet chronology and to establish the timing of past climatic events of the continental and insular land masses in the middle latitudes south america lies closest to antarctica and most reflects conditions in the polar region close interval dating of a pollen record at harberton 54 52 s 67 53 w in southern tierra del fuego strengthens implications drawn from paleoecological data and from fluctuations of glaciers to show a climatic parallel with isotope temperature climate data developed from antarctic ice cores over the time span of approximately 30 000 yr since before the full glacial coldest conditions both in antarctica and south america appear centered at 20 000 yr b p warming of climate occurred in the late glacial after 15 000 yr b p interrupted by a cold episode between about 13 000 and 10 500 yr b p with maximum warmth at 9000 yr b p in the early holocene after which temperatures were lower varying only moderately until the present this deglacial pattern although inconsistent in other southern hemisphere records is reproducible on a global scale

paleoenvironments and paleoclimates in tierra del fuego and southernmost patagonia south america abstract a continuous paleoclimatic history for the past 14 000 years is presented based on palynological records from south of latitude 50 s in south america prior to 12 500 yr b p dry empetrum heathlands not mesic tundra dominated throughout the high southern latitudes indicating high winds annual precipitation of less than 300 mm and freezing temperatures year round after 12 500 yr b p steppe replaced the heathlands suggesting decrease in wind intensity increase in effective moisture and increase in temperatures when forests expanded at 9000 yr b p along the rainward side and at 8000 yr b p in the rainshadow side of the andes precipitation reached holocene levels judging from the greater openness of the early holocene forests including those in the rainward part of the region precipitation levels probably ranged between 500 and 800 mm comparable to those from today s forest steppe transition after a pronounced mid holocene dry event the late holocene forests appeared more closed than the early holocene forests suggesting greater effective moisture probably related to cooler temperatures the high latitude paleoclimatic history differs from that of lower latitudes as far as the actual amplitude of change and the climatic signal is concerned low moisture levels prior to 12 500 yr b p between latitudes 45 and 55 c suggest that the westerly stormtracks responsible for precipitation patterns in southern south america may have been located year round closer to the equator than today the precipitation increase at 12 500 yr b p that extended only as far south as 50 s indicates that the stormtracks had shifted poleward but did not reach tierra del fuego by 9000 yr b p the stormtracks had shifted to the high southern latitudes but the large seasonal latitudinal shift comparable to the modern situation equatorwards in winter and polewards in summer did not develop until after 4500 yr b p

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

seismic stratigraphy buried beach ridges and contourite drifts the late quaternary history of the closed lago cardiel basin argentina 49 s the results of a seismic stratigraphic analysis of a closed lake basin lago cardiel in southernmost south america are reported very few high resolution continental records spanning the late quaternary have been obtained from this region seismic sequence stratigraphic analysis allows a reconstruction of lake level variations two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period following the development of a relatively shallow lake during the late pleistocene and a short desiccation pulse around 11 220 14c yr bp a transgression of over 135 m occurred at the beginning of the holocene the transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern lago cardiel at four different elevations the preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level there is no seismic evidence of a major lowering of the lake below modern level during the entire holocene deposition since the mid holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution seismic reflection geometries as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80 100 km2 as lago cardiel is under the influence of westerly winds these most likely drove lake circulation the identification of drowned beach ridges and of contourite drifts illustrates that high resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins but it can also provide information about the rate of lake level changes and the presence and strength of lake currents

southern ocean deglacial record supports global younger dryas abstract in northern hemisphere deglaciation records the transition from the last glacial to the holocene indicates a rapid return to near glacial conditions during the younger dryas whereas their southern hemisphere ice core counterparts record two separate cooling events the antarctic cold reversal and the oceanic cold reversal spatial distribution and relative timing of these events in both hemispheres are central for our understanding of causes and mechanisms of abrupt climate change to date no marine record from the southern mid latitudes conclusively demonstrates that the younger dryas was a significant event in the southern ocean here we present high resolution oxygen isotope and iron content records of a radiocarbon dated sedimentary sequence from the great australian bight which constrains oceanic and atmospheric changes during the last deglaciation oxygen isotopes from planktonic foraminifera indicate two rapid cold reversals between 13 1 and 11 1 kyr bp separated by a brief warming the sedimentary iron content interpreted as a proxy for wind strength indicates a simultaneous change in atmospheric circulation pattern both records demonstrate the existence of cooling events in the southern hemisphere which are synchronous with the northern hemisphere younger dryas cold reversal between 12 9 and 11 5 kyr bp such evidence for the spatial distribution and timing of abrupt climatic fluctuations is essential data for groundtruthing results derived from global climate models

the occurrence of calcified planktonic green algae in freshwater carbonates phacotus and coccomonas two carbonate secreting non marine planktonic chlorophyte genera are important sediment contributors mainly in hard water lakes the calcite loricae of these flagellate algae exhibit characteristic features easily recognizable under the microscope making phacotus and coccomonas important facies fossils for the recognition of ancient non marine environments the fossil record of phacotus can be traced back to the miocene and it is probable that further research could extend this record into pre tertiary periods

younger dryas in southernmost south america an update abstract high resolution pollen data from a peat section in southern tierra del fuego documents high paleoenvironmental variability between 11 ka and 9 ka detailed analysis of plant macro remains in the same section showed that the repeated high amplitude changes in pollen taxa were related to repeated fire disturbance burning at least once even the surface of the mire in many peat sections from southernmost patagonia and tierra del fuego charcoal particles have been found intermittently since about 13 ka and in great abundance especially after 11 ka this suggests that the environmental changes previously interpreted to imply a return to colder climates comparable to the north atlantic younger dryas event instead are in response to local and regional disturbances by fires

hydrological variability in southeastern patagonia and explosive volcanic activity in the southern andean cordillera during oxygen isotope stage 3 and the holocene inferred from lake sediments of laguna potrok aike argentina abstract seismic reflection studies in the maar lake laguna potrok aike 51 58 s 70 23 w revealed an erosional unconformity associated with a sub aquatic lake level terrace at a water depth of 30m radiocarbon dated multi proxy sediment studies of a piston core from this location indicate that the sediment below this discontinuity has an age of 45kyr bp oxygen isotope stage 3 and was deposited during an interval of high lake level in comparison to the holocene section geochemical indicators of this older part of the record either point towards a different sediment source or to a different transport mechanism for oxygen isotope stage 3 sediments holocene sedimentation started again before 6790cal yr bp providing a sediment record of hydrological variability until the present geochemical and isotopic data indicate a fluctuating lake level until 5310cal yr bp during the late holocene the lake level shows a receding tendency nevertheless the lake level did not drop below the 30m terrace to create another unconformity the geochemical characterization of volcanic ashes reveals evidence for previously unknown explosive activity of the reclus and mt burney volcanoes during oxygen isotope stage 3

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

deglacial paleoclimate of the american sector of the southern ocean late glacial holocene records from the latitude of canal beagle 55 s argentine tierra del fuego abstract paleoclimate at the time of deglaciation 14 000 10 000 14 c yr b p in different sectors of the southern ocean has followed a continuous warming trend but also warming broken by a transitory episode the younger dryas stadial event during which on the order of a millennium colder conditions prevailed evidence is from antarctic ice cores deep sea cores glacier fluctuations and pollen and beetle records reasons for the apparent nonuniformity include differential sensitivity of each sector to climatic change uneven dating control and the variable forcing response nature of biota used as climatic indicators establishing the late glacial paleoclimate of the southern ocean is of significance as it bears on comprehending the character of deglaciation in a global context with the object of investigating further the sequence of deglacial climatic events pollen stratigraphic studies at canal beagle at the southern extremity of south america were extended westward to the vicinity of ushuaia and lapataia supplementing work done previously at caleta robalo puerto harberton and bahia moat at ushuaia pollen frequency and influx records of the late glacial as well as the holocene chronologically controlled by 25 14 c age determinations are from four sphagnum empetrum mires results obtained at sites dating from 12 500 to 12 000 yr b p show late glacial climatic variability most indicative among tundra communities of grass and dwarf shrub heath is a drop both in frequency and influx of the singular arboreal component nothofagus at the time of the younger dryas when estimated summer january temperature was 3 c lower than at present at ushuaia in general terms the late glacial pattern is not unlike the northwestern european sequence sensu walker 1995 which exhibits a late glacial interstadial 13 000 11 000 yr b p followed by a younger dryas stadial 11 000 10 000 yr b p within limits of the chronology in the american sector there is no indication as shown by marine cores from the southern ocean and by antarctic ice cores that deglacial climatic events at higher latitudes of the southern hemisphere exemplified by the younger dryas lead similar events in the northern hemisphere uninterrupted warming evident in the marine and ice cores occurred after 11 600 11 500 yr b p at canal beagle in contrast the trend toward steadily milder climate indicated by continuous expansion of nothofagus frequency followed in the early holocene after 10 000 yr b p early holocene nothofagus woodland containing grass and composites replaced tundra under a warmer and drier set of conditions coupled with burning estimated summer temperature averaged 1 c higher than today and annual precipitation 100 mm less pollen influx remained generally low until about 5000 yr b p when the rate of nothofagus greatly increased together with increase in the rate of empetrum a characteristic mire component the implication is of late holocene spread of both closed forest and mire the result of greater precipitation and lower temperatures while burning abated summer temperatures evidently varied within about 0 5 c and precipitation by 100 mm compared with the present renewed albeit fluctuating glacial activity is recorded after 5000 yr b p under a variable cooler and more humid late holocene climatic regime

early diagenetic influences on iron transformations in a freshwater lake sediment abstract iron transformations in a calcium carbonate rich fresh water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter analysis of interstitial water shows that the observed redox sequence no 3 nh 4 mno 2 mn ii feooh fe ii so 2 4 s ii is roughly in agreement with that predicted by the gibbs free energy for the corresponding reactions in contrast to marine sediments these redox transitions occur in the uppermost sediments i e at depths of 0 4 cm deeper in the sedimentary sequence the depth profile for dissolved iron exhibits a steady non linear increase up to 400 mol dm 3 in this anoxic zone according to thermodynamic predictions iron ii minerals such as iron sulfide siderite and vivianite should precipitate while fe iii oxides should be completely dissolved however microscopic analysis showed that fe iii oxides were present throughout the studied sediment furthermore scanning electron microscope energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite these observations indicate kinetic control of iron transformations we have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron ii a rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions using the calculated rate constant we established that more than 1000 years would be required for the complete dissolution of fe iii oxides which is agreement with our observations and experimental data from the literature calculated precipitation rates of fe ii for a given mineral phase such as siderite yield a maximum value of 3 g feco3 g 1 dry sediment yr 1 such low rates would explain the absence of siderite and vivianite finally it can be inferred from the mn t fe t ratio in the sediments that this ratio depends on the redox conditions of the sediment water interface at the time of deposition thus this ratio can be used as paleo redox indicator in lacustrine sediments

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

an inter laboratory comparison of the electron probe microanalysis of glass geochemistry abstract tephrochronology commonly relies upon grain discrete analysis of glass shards to reveal the subtle geochemical differences between tephras from past explosive volcanic eruptions the use of electron probe microanalysis for this purpose is widely accepted by tephrochronologists it is widely recognised that both precision and accuracy must be maximised and that rigorous standardisation procedures must be followed in this paper the performances of seven northern european electron microprobe centres are compared using a geochemically homogeneous obsidian secondary standard the results reveal that a number of tephra oriented probe centres could benefit from exercises similar to the programme outlined within in particular it is evident that a number of these centres undertaking tephrochronological investigations have generated geochemical data that may be inadequate in terms of distinguishing between tephras inaccuracy in the determination of sodium is seen to be the main difficulty in recent years the application of distal tephrochronology to stratigraphical problems in the northern european quaternary record has become increasingly common geochemical standardisation is essential at an early stage in the development of a regional tephrochronological framework and we hope exercises such as presented here will encourage the production of reliable tephra geochemical data

late pleistocene and holocene palaeoenvironments in golfo san jorge patagonia molluscan evidence palaeoenvironments suggested by molluscan assemblages preserved in late pleistocene and holocene raised marine terraces along the golfo san jorge central patagonia coastline argentina are reviewed in this work a better precision of the stratigraphical and geographical ranges of the molluscs through their systematic review shows that all taxa have living representatives mostly within the argentine and or magellanean zoogeographical provinces in general no significant taxonomic appearances or disappearances are evident along this coastal area since the last pleistocene highstand reinforcing that the modern palaeoceanographical pattern dominated by the cool malvinas falkland current has not been substantially modified and that the magellanean malacological province has lasted at least since the pleistocene although with varying boundaries the so called marine terrace v recently assigned to the last interglacial highstand oxygen isotope substage 5e showed in this area a molluscan assemblage characterised by very low diversity dominantly large shells of mulinia edulis and by cold water taxa in disagreement with higher sea surface temperatures within oxygen isotope substage 5e last interglacial maximum and suggesting softer substrates than in the modern adjacent littoral zone

geochemical response on redox fluctuations in holocene lake sediments lake steisslingen southern germany abstract holocene sediments of lake steisslingen record sedimentation under different redox conditions this is proven by the changing depth of the chemocline and the resulting varying extension of laminated sediments from the deepest part of the lake to shallower water depths redox fluctuations are additionally reflected by colour changes between red and green and the quality of the nonglacial varves major and trace elements were analysed on bulk sediment samples period between 8200 6200 and 2650 2000 cal a bp to test their response to the observed changes in past depositional environments mn mo u fe and s were found to be redox sensitive elements in lake steisslingen fe and s are almost entirely fixed in pyrite because pyrite formation is limited by fe availability a parallel distribution of mo u fe and s between 8200 7200 cal a bp is interpreted as a signal for syngenetic pyrite formation from anoxic and sulfidic hypolimnetic waters since bioproductivity was low this must have been caused by conditions favouring a longterm stable stratification of the lake i e high water level high summer temperatures ice cover wind protection and or low storm activity between 6000 2000 cal a bp frequently changing redox conditions from anoxic to dysoxic are assumed mo and u curves are mirror images of the fe s and mn variations this is interpreted as showing diagenetic pyrite formation from pore waters which is enhanced during times of high fe availability under rather oxygenated conditions i e when high input of fe oxy hydroxides is possible but when u and mo cannot necessarily be fixed in the sediments changes from slightly disturbed lamination dysoxic restricted mixis to homogenous sediments oxic conditions holomixis cannot be traced within the geochemical record the observed redox fluctuations between 6000 and 2000 cal a bp are not correlated to changes in bioproductivity detrital input or cultural influences and must therefore be of a natural probably climatic origin the north atlantic oscillation is discussed as a possible cause

the dynamics of chironomid assemblages and vegetation during the late quaternary at laguna facil chonos archipelago southern chile abstract we compare high resolution pollen and chironomid records from the last 15 000 yr in laguna facil southern chile major vegetation and chironomid changes are recorded between ca 14 900 and 14 700 cal yr bp during the lateglacial changes in the chironomid stratigraphy lag behind changes in the pollen stratigraphy suggesting that the chironomids are responding to changes in the tree canopy or in soil chemistry brought about by vegetational development at about 7200 cal yr bp there is a change in the chironomid stratigraphy in advance of changes in the vegetation this suggests that the response is to regional climatic change the relatively close correlation of the chironomid and pollen stratigraphies with changes in charcoal concentrations also implicates the importance of fire and or vulcanism in influencing the dynamics of forest and limnological systems there is no clear evidence of cooling during the younger dryas chronozone in laguna facil

quaternary of tierra del fuego southernmost south america an updated review abstract the quaternary of tierra del fuego is represented by glacial glaciofluvial glaciolacustrine marine and aeolian deposits six drift units have been described the oldest dating from the late pliocene these are starting from the oldest the rio grande sierra de los frailes cabo virgenes punta delgada primera angostura and segunda angostura drifts neoglacial and little ice age events are represented in cirques and higher mountain valleys marine deposits and raised beaches were formed during middle pleistocene late pleistocene and holocene interglacial stages after the definitive ice retreat 10 ka ago vegetation changed from tundra and cold steppe to subantarctic forest environments marine deposits reflect also colder conditions than the present ones aeolian processes prevailed in northern tierra del fuego where semiarid conditions and the frequent westerlies favoured the retransportation of finer materials coming from pre existing deposits before the opening of the magellan straits earliest human colonization occurred in northern tierra del fuego ca 11 ka bp in tundra like environmental conditions pedestrian hunters of camelids and foxes co existed with pleistocene fauna that became extinct during late glacial earliest holocene times the steppe area inland and atlantic coast was successively occupied since then until recent times on the other hand the beagle channel coasts were occupied since 6 ka bp by hunter gatherer groups adapted to maritime littoral conditions finally the easternmost area of the island was inhabited at least since 1 5 ka bp the human settlements in these latter areas occurred under environmental conditions similar to the present ones when the fuegian forest was definitively established

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

holocene palaeoclimates of southern patagonia limnological and environmental history of lago cardiel argentina multiproxy palaeoenvironmental and palaeolimnological analyses of two holocene age sediment cores from the margin of lago cardiel a 76 m deep closed basin lake in southern patagonia latitude 49 s provide information on lake level changes that can be related to regional palaeoclimate scenarios sedimentol ogic magnetic susceptibility organic and inorganic carbon content and environmental indicators pollen dia toms ostracodes and stable isotopes on ostracodes show lake levels markedly higher than today during the early holocene following a rapid lake level rise after a desiccation phase prior to 11 000 bp after about 6000 bp lake levels were generally lower but underwent repeated e uctuations these inferred changes support the previously proposed view that the southern westerly stormtracks were focused zonal north of latitude 50 s during the early holocene allowing for antarctic cold fronts to bring easterly moisture to southern patagonia whereas during the late holocene the stormtracks shifted seasonally with an overall more meridional behaviour resulting in less and more variable moisture at these latitudes

late glacial and holocene palaeoenvironmental change in the central strait of magellan southern patagonia abstract high resolution palaeoenvironmental data for the wisconsin late glacial and early holocene is provided from two sites puerto del hambre and estancia esmeralda ii in the central section of the strait of magellan southern chile palaeoecological and lithostratigraphical evidence is correlated with other palaeoenvironmental data from the magellan region using 14 c dating and tephrochronology the oldest record from puerto del hambre commences at 14 470 14 c yr bp 17 330 cal yr bp following retreat of the magellan glacier climatic warming after that time is indicated by ice retreat from the central section of the strait of magellan and palynological evidence however mean annual temperature continued to be cooler than present until c 10 300 14 c yr bp 12 270 12 110 cal yr bp the magellan environment was relatively humid between c 14 100 and c 12 550 14 c yr bp 16 910 and 15 170 14 410 cal yr bp at c 12 550 14 c yr bp there was a sharp decrease in effective moisture levels of humidity fluctuated but remained relatively low until c 10 300 14 c yr bp this period of cool and drier climate is contemporary with a significant glacier advance dated to between c 12 700 and 10 300 14 c yr bp 15 330 and 12 270 12 110 cal yr bp which would have produced an enhanced rainshadow effect around 10 300 14 c yr bp a shift to warmer conditions occurred between c 10 300 and 8550 14 c yr bp 12 270 12 110 and 9530 cal yr bp an extreme arid phase is recorded which led to an increase in fires at c 8550 14 c yr bp an increase in available moisture allowed the eastward spread of nothofagus forest at 8265 14 c yr bp 9270 9160 cal yr bp there was a relative rise in sea level in the strait of magellan this marine incursion lasted until 3970 14 c yr bp 4420 cal yr bp reaching its maximum around c 6450 14 c yr bp 7420 7340 cal yr bp

lateglacial and holocene wet dry cycles in southern patagonia chronology sedimentology and geochemistry of a lacustrine record from laguna potrok aike argentina a high resolution multiproxy geochemical approach was applied to the sediments of laguna potrok aike in an attempt to reconstruct moist and dry periods during the past 16 000 years in south eastern patagonia the age depth model is inferred from ams 14 c dates and tephrochronology and suggests moist conditions during the lateglacial and early holocene 16 000 8700 cal bp interrupted by drier conditions before the beginning of the holocene 13 200 11 400 cal bp data also imply that this period was a major warm phase in southeastern patagonia and was approximately contemporane ous with the younger dryas chronozone in the northern hemisphere 12 700 11 500 cal bp after 8650 cal bp a major drought may have caused the lowest lake level of the record since 7300 cal bp the lake level rose and was variable until the little ice age which was the dominant humid period after 8650 cal bp

fluctuations of outlet and valley glaciers in the southern andes argentina during the past 13 000 years abstract in the southern argentine andes ten advances of valley glaciers were used to reconstruct the late glacial and holocene glacier history the accumulation areas of these glaciers lie in the precordillera and are thus independent of fluctuations of the south patagonian icefield like the viedma outlet glacier the valley glaciers advanced three times during late glacial time 14 000 10 000 yr b p the youngest advance correlates with the younger dryas stade based on two minimum ams 14 c dates of 9588 and 9482 yr b p the second oldest advance occurred before 11 800 yr b p during the first half of the holocene ca 10 000 5000 yr b p advances culminated about 8500 8000 7500 and 5800 5500 yr b p during the second half of the holocene advances occurred between ca 4500 and 4200 yr b p as well as between 3600 and 3300 yr b p in the rio condor valley three subsequent advances have been identified