oxygen and carbon isotopes in modern fresh water ostracod valves assessing vital offsets and autecological effects of interest for palaeoclimate studies abstract the isotopic composition of modern benthic ostracod and mollusc carbonate the oxygen isotope composition of lake water 18ow the carbon isotope composition of dissolved inorganic carbon 13cdic and water temperatures were monitored during a year at different water depths in two lakes ammersee and starnberger see southern germany the aim was to test whether the valves are built in isotopic equilibrium and how seasonal water temperatures are recorded in the shells we find systematic offsets between 18o of valve carbonate compared to 18o expected for a theoretical calcite formed in isotopic equilibrium offsets are higher than 2 for different species of the candona group 1 5 for cytherissa lacustris and around 0 8 for limnocythere inopinata and darwinula stevensoni they seem to be constant for all instars of a species and temperature independent mean water temperatures of the calcification period are readily reflected in the valve 18o if corrected for the offsets 13c of valve carbonate is mainly controlled by 13c of the dissolved carbonate in ambient lake water but seems to be biased by micro habitat effects and vital offsets the study provides information on the seasonality of valve formation thus potentially allowing the quantification of temporal and spatial water temperature gradients from specific 18o records

from catastrophic collapse to multi phase deposition flow transformation seafloor interaction and triggered eruption following a volcanic island landslide abstract the current understanding of tsunamis generated by volcanic island landslides is reliant on numerical models benchmarked against reconstructions of past events as the largest historical event with timed tsunami observations the 1888 sector collapse of ritter island papua new guinea provides an outstanding opportunity to better understand the linked process of landslide emplacement and tsunami generation here we use a combination of geophysical imaging bathymetric mapping seafloor observations and sampling to demonstrate that the ritter landslide deposits are spatially and stratigraphically heterogeneous reflecting a complex evolution of mass flow processes the primary landslide mass was dominated by well bedded scoriaceous deposits which rapidly disintegrated to form an erosive volcaniclastic flow that incised the substrate over much of its pathway the major proportion of this initial flow is inferred to have been deposited up to 80 km from ritter the initial flow was followed by secondary failure of seafloor sediment over 40 km from ritter the most distal part of the 1888 deposit has parallel internal boundaries suggesting that multiple discrete units were deposited by a series of mass flow processes initiated by the primary collapse the last of these flows was derived from a submarine eruption triggered by the collapse this syn collapse eruption deposit is compositionally distinct from pre and post collapse eruptive products suggesting that the collapse immediately destabilised the underlying magma reservoir subsequent eruptions have been fed by a modified plumbing system constructing a submarine volcanic cone within the collapse scar through at least six post collapse eruptions our results show that the initial tsunami generating landslide at ritter generated a stratigraphically complex set of deposits with a total volume that is several times larger than the initial failure given the potential for such complexity there is no simple relationship between the volume of the tsunamigenic phase of a volcanic island landslide and the final deposit volume and deposit area or run out cannot be used to infer primary landslide magnitude the tsunamigenic potential of prehistoric sector collapse deposits cannot therefore be assessed simply from surface mapping but requires internal geophysical imaging and direct sampling to reconstruct the event

postglacial vegetation fire and climate dynamics at central chilean patagonia lake shaman 44 s a 19 cal ka bp pollen and charcoal record from lake shaman 44 s 71 w chile was analyzed to establish vegetation fire and climate dynamics of the forest steppe ecotone in central chilean patagonia lake shaman record indicates that the upper rio cisnes valley was free of ice at around 19 cal ka bp from this date and until 14 8 cal ka bp a grass steppe with high proportions of shrubs associated to colder and drier conditions than present developed in this area a continuous increase of nothofagus accompanied by a decline in the steppe shrubs and sudden dominance of paludal over aquatic plants from 11 cal ka bp was associated to effective moisture increase but still under modern values the replacement of the cold dry grass shrub steppe by a similar than present forest steppe ecotone suggests an increase in temperature indicating the onset of the holocene at the same time moderate fire activity suggested by the charcoal record could be related to major fuel availability as consequence of nothofagus forest expansion between 8 and 3 cal ka bp the record indicates the easternmost position of the forest steppe ecotone suggesting the highest effective moisture with the establishment of seasonality between 5 and 3 cal ka bp from 3 cal ka bp the record indicates a retraction of the forest steppe ecotone accompanied by a high pollen record variability and an increased fire activity these late changes suggest decreased effective moisture associated with a high climatic variability at regional and extra regional scale climatic changes at lake shaman s record are mostly associated to changes latitudinal shifts and or strengthening weakening of past southern westerlies that were previously recorded along patagonia from the lateglacial to the mid holocene during the late holocene a regional pattern characterized by high record variability emerges throughout central chilean patagonia this variability would be related to 1 low magnitude southern westerlies changes probably associated to enso and or sam or 2 the complex relationships between vegetation fire and human occupations during the last 3 cal ka

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

sea level pressure variability around antarctica since a d 1750 inferred from subantarctic tree ring records a tree ring chronology network recently developed from the subantarctic forests provides an opportunity to study long term climatic variability at higher latitudes in the southern hemisphere fifty long 1911 1985 homogeneous records of monthly mean sea level pressure mslp from the southern latitudes 15 65 s were intercorrelated on a seasonal basis to establish the most consistent long term trans polar teleconnections during this century variations in summer mslp between the south america antarctic peninsula and the new zealand sectors of the southern ocean are significantly correlated in a negative sense r 0 53 p 0 001 climatically sensitive chronologies from tierra del fuego 54 55 and new zealand 39 47 were used to develop verifiable reconstructions of summer november to february mslp for both sectors of the southern ocean these reconstructions which explain between 37 and 43 of the instrumentally recorded pressure variance indicate that inverse trends in mslp from diametrically opposite sides of antarctica have prevailed during the past two centuries however the strength of this relationship varies over time differences in normalized mslp between the new zealand and the south america antarctic peninsula sectors were used to develop a summer trans polar index stpi which represents an index of sea level pressure wavenumber one in the southern hemisphere higher latitudes tree ring based reconstructions of stpi show significant differences in large scale atmospheric circulation between the nineteenth and the twentieth centuries predominantly negative stpi values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the new zealand sector during the 1800s in contrast cyclonic activity appears to have been stronger in the mid twentieth than previously for the south american sector of the southern ocean recent variations in mslp in both regions are seen as part of the long term dynamics of the atmosphere connecting opposite sides of antarctica a detailed analysis of the mslp and stpi reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3 3 3 6 y cross spectral analysis between the stpi reconstruction and the southern oscillation index suggests that teleconnections between the tropical ocean and extra tropical mslp variations may be influencing climate fluctuations at southern latitudes

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

refining the late quaternary tephrochronology for southern south america using the laguna potrok aike sedimentary record abstract this paper presents a detailed record of volcanism extending back to 80 kyr bp for southern south america using the sediments of laguna potrok aike icdp expedition 5022 potrok aike maar lake sediment archive drilling project pasado our analysis of tephra includes the morphology of glass the mineral componentry the abundance of glass shards lithics and minerals and the composition of glass shards in relation to the stratigraphy firstly a reference database of glass compositions of known eruptions in the region was created to enable robust tephra correlations this includes data published elsewhere in addition to new glass shard analyses of proximal tephra deposits from hudson eruption units h 1 and h 2 aguilera a 1 reclus r 1 r 2 3 mt burney mb 1 mb 2 mb x mb 1910 and historical lautaro viedma deposits the analysis of the ninety four tephra layers observed in the laguna potrok aike sedimentary sequence reveals that twenty five tephra deposits in the record are the result of primary fallout and are sourced from at least three different volcanoes in the austral andean volcanic zone mt burney reclus lautaro viedma and one in the southernmost southern volcanic zone hudson one new correlation to the widespread h 1 eruption from hudson volcano at 8 7 8 6 9 0 cal ka bp during the quaternary is identified the identification of sixty five discrete deposits that were predominantly volcanic ashes glass and minerals with subtle characteristics of reworking in addition to three likely reworked tephra and one unknown layer indicates that care must be taken in the analysis of both visible and invisible tephra layers to decipher their emplacement mechanisms

microsedimentological characterization using image analysis and μ xrf as indicators of sedimentary processes and climate changes during lateglacial at laguna potrok aike santa cruz argentina palaeoclimatic and paleoenvironmental high latitude records in the southern hemisphere are scarce compared to the northern counterpart however understanding global evolution of environmental systems during sudden climate changes is inseparable from an equivalent knowledge of both hemispheres in this context a high resolution study of lacustrine sediments from laguna potrok aike santa cruz province patagonia argentina was conducted for the lateglacial period using concurrent x ray fluorescence xrf and scanning electron microscope analyses peaks of ca si and mn and occurrences of the green alga phacotus lenticularis have been interpreted as variations in ventilation of the water column from 13 6 to 11 1 ka cal bp during this interval mild climate conditions during the younger dryas are characterized by relatively weak westerlies favouring the formation of a stratified water body as indicated by preserved manganese and ca si peaks and high total organic carbon toc values in this environment water in the epilimnion can reach sufficiently high temperature to allow p lenticularis to grow colder conditions are marked by peaks in ca without p lenticularis and occur during the antarctic cold reversal acr in this lateglacial interval micropumices were also detected in large amount image analysis of thin sections allowed the counting and size measurement of detrital particles and micropumices separately micropumices significantly influence the iron and titanium content hence preventing to use them as proxies of detrital input in this interval

millennial scale variability in southern hemisphere westerly wind activity over the last 5000 years in sw patagonia abstract here we report results from a high resolution palynological record and stratigraphic geochronologic data related to a neoglacial event in torres del paine national park southern chile 51 s 71 w to investigate climatic variations in southwest patagonia during the last 5000 years the record reveals a stepwise expansion of nothofagus dominated woodlands and forests with discrete pulses at 4400 2900 1300 and 570 cal yr bp superimposed upon this trend we identify a relative opening of the woodlands between 4100 2900 and 2300 1300 cal yr bp closed canopy forests dominated the landscape between 570 60 cal yr bp followed by a rapid decline at the end of the 19th century that coincided with intense fire activity and the appearance of rumex cf acetocella an exotic species introduced by european settlers we interpret these changes as variations in the intensity and or position of the southern margin of the westerly winds which culminated with a net eastward shift of the forest steppe ecotone during the little ice age we propose that millennial scale changes in either the latitudinal position and or the overall strength of the southern westerlies may be responsible for vegetation changes fire occurrence and the dynamic behavior of patagonian glaciers during the last 5000 years because the modern maximum in near surface wind velocities and precipitation is located between 48 and 50 s we suggest that the core of the southern westerlies may have achieved this modern position 570 years ago

assemblage diversity and isotopic signals of modern ostracodes and host waters from patagonia argentina abstract ostracode species assemblages and stable oxygen and carbon isotope ratios of living and recent ostracodes together with 18 o and 13 c dic dic dissolved inorganic carbon values of host water samples provide a first data set that characterizes a wide range of modern aquatic environments in the laguna cari laufquen 41 s 68 69 w and the lago cardiel area 48 49 s 70 71 w in patagonia argentina this data set will ultimately be used to interpret and calibrate data acquired from lake sediment cores with the goal of reconstructing past climate species assemblages and isotope values can be assigned to three groups 1 springs seeps and streams 2 permanent ponds and lakes and 3 ephemeral ponds and lakes springs seeps and streams are characterized by darwinula sp heterocypris incongruens eucypris fontana amphicypris nobilis and ilyocypris ramirezi ostracode and water isotope values range between 13 and 5 for oxygen and between 15 and 3 for carbon they are the most negative of the entire sample set reflecting ground water input with little or no evaporative enrichment limnocythere patagonica eucypris labyrinthica limnocythere sp and eucypris aff fontana are typical species of permanent ponds and lakes isotope values indicate high degree of evaporation of lake waters relative to feeder springs and streams and range between 7 and 5 for oxygen and 5 and 4 for carbon limnocythere rionegroensis is the dominant species in ephemeral ponds and lakes these systems display the most enriched isotope values in both ostracodes and host waters extending from 5 to 7 for oxygen and from 5 to 6 for carbon living ostracodes show a positive offset from equilibrium values of up to 2 for oxygen carbon isotope values are up to 6 more negative than equilibrium values in highly productive pools comparison of ostracode and host water isotope signals permits assessment of the life span of the aquatic environments valves from dead ostracodes collected from ephemeral ponds and lakes show a wide scatter with each sample providing a snapshot of the seasonal history of the host water the presence of the stream species i ramirezi and a wide range of ostracode isotope values suggest that ephemeral ponds and lakes are fed by streams during spring run off and seasonally dry a temporary character of waters is also indicated by h incongruens a drought resistant species that occupies most springs and seeps in addition l rionegroensis has adjusted its reproduction strategies to its environment whereas only females were collected in fresh host waters males were found in ephemeral ponds and lakes with higher solute content sexual reproduction seems to be the more successful reproduction strategy in waters with high and variable salinities and affected by seasonal droughts the temporary character of the aquatic environments shows that the availability of meteoric water controls the life span of host waters and underlines the sensitivity of the area to changes in precipitation

giant landslides in the foreland of the patagonian ice sheet abstract quaternary glaciations have repeatedly shaped large tracts of the andean foreland its spectacular large glacial lakes staircases of moraine ridges and extensive outwash plains have inspired generations of scientists to reconstruct the processes magnitude and timing of ice build up and decay at the mountain front surprisingly few of these studies noticed many dozens of giant 108 m3 mass wasting deposits in the foreland we report some of the world s largest terrestrial landslides in the eastern piedmont of the patagonian ice sheet pis along the traces of the former lago buenos aires and lago puyerredon glacier lobes and lakes more than 283 large rotational slides and lateral spreads followed by debris slides earthflows rotational and translational rockslides complex slides and few large rock avalanches detached some 164 56 km3 of material from the slopes of volcanic mesetas lake bounding moraines and river gorge walls many of these landslide deposits intersect with well dated moraine ridges or former glacial lake shorelines and offer opportunities for relative dating of slope failure we estimate that 60 of the landslide volume 96 km3 detached after the last glacial maximum lgm giant slope failures cross cutting shorelines of a large late glacial to early holocene lake glacial lake pis likely occurred during successive lake level drop between 11 5 and 8 ka and some of them are the largest hitherto documented landslides in moraines we conclude that 1 large portions of terminal moraines can fail catastrophically several thousand years after emplacement 2 slopes formed by weak bedrock or unconsolidated glacial deposits bordering glacial lakes can release extremely large landslides and 3 landslides still occur in the piedmont particularly along postglacial gorges cut in response to falling lake levels

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

patagonian glacier response during the late glacial holocene transition whether cooling occurred in the southern hemisphere during the younger dryas yd is key to understanding mechanisms of millennial climate change although southern hemisphere records do not reveal a distinct climate reversal during the late glacial period many mountain glaciers readvanced we show that the puerto bandera moraine 50 s which records a readvance of the southern patagonian icefield spi formed at or shortly after the end of the yd the exposure age 10 8 0 5 thousand years ago is contemporaneous with the highest shoreline of lago cardiel 49 s which records peak precipitation east of the andes since 13 thousand years ago absent similar moraines west of the andes these data indicate an spi response to increased amounts of easterly sourced precipitation reflecting changes in the southern westerly circulation rather than regional cooling

late pleistocene dust deposition in the patagonian steppe extending and refining the paleoenvironmental and tephrochronological record from laguna potrok aike back to 55 ka abstract paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern south america here we present a continuous record for the past 55 ka from the maar lake laguna potrok aike 51 58 s 70 23 w southern patagonia argentina previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of oxygen isotope stage ois 3 59 29 ka whereas a second core from the centre of the basin comprised the last 16 ka tephrostratigraphical constraints and osl ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites high resolution xrf and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in antarctica this is therefore the first evidence for contemporaneity of aeolian deposition in both the target area antarctica and in the major source area of patagonia during the holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times the identification of a minor lake level lowering at approximately 4 cal ka bp allows to refine earlier paleoenvironmental reconstructions for the holocene within error margins the osl ages are consistent with published radiocarbon dated records offering hence a valuable tool for further studies of the sediments from laguna potrok aike the new chronology confirms the age of three tephra layers up to now only found in laguna potrok aike sediments and ascribed to ois 3

late holocene hydrology inferred from lacustrine sediments of laguna chaltel southeastern argentina abstract hydrological changes that occurred during the last 4700 years have been reconstructed using multi proxy analyses of sediment cores from the volcanic crater lake of laguna chaltel 50 s 71 w the chronology is based on ams 14 c age modeling constrained by paleomagnetic secular variations chemical and physical properties of the lake water together with results of lake water surface temperature monitoring as well as sediment characteristics reveal conspicuous features archived as different sedimentary carbonate phases and morphologies which are attributed to lake level changes sedimentological geochemical and biological proxies together suggest the development from an initial playa lake phase towards a system with progressively rising lake level in detail proxies indicate the existence of an ephemeral lake since 4700 cal bp until a glauberite bearing carbonate crust formed around 4040 cal bp which probably is associated to the globally recognized 4 2 ka event this crust is interpreted as a desiccation event terminating the ephemeral lake phase following this desiccation a shift towards conditions with a positive hydrological balance of laguna chaltel occurs which leads to the development of a saline lake with ooid formation between 4040 and 3200 cal bp further lake level increase with initially high minerogenic input until 2700 cal bp resulted in a lake freshening which allowed the preservation of diatoms sigmoidal and star shaped carbonate crystals occurred until 1720 cal bp indicating a syn or post depositional formation of ikaite anoxic conditions and increased deposition of clay and sand through fluvial and eolian input are interpreted as a further lake level rise and or a prolonged winter ice cover culminating during the little ice age the highest lake level was probably reached at that time and since then dropped to its present day height previous studies have shown that the southern hemisphere westerly winds sww exert an oppositional control on hydrological regimes at the eastern and the western sides of the patagonian andes at laguna chaltel sww forcing is changing evaporation rates by varying wind intensities air temperatures and lake ice coverages as well as by precipitation rates easterly vs westerly sources of moisture our data suggests that the lake level history of laguna chaltel reflects changes in the sww during the last 4 7 ka on the eastern side of the andes however the elevated location of laguna chaltel on an 800 m high plateau at the leeward side of the andes potentially leads to a local overprint of the sww influence on the hydrological balance

late quaternary chronology of the taitao peninsula southern chile six new radiocarbon ages and a pollen sequence are provided for laguna stibnite a small lake on the taitao peninsula chile latitude 46 25 s longitude 74 24 w the sediments record a late glacial to present sequence with a basal age of 14 335 145 yr bp q 2840 the radiocarbon ages provide the basis for a sound chronology in a region of chile where few palynological studies have been made and where previous radiocarbon ages are ambiguous the chronology from laguna stibnite supports the acceptance of a radiocarbon chronology based on wood fragments rather than bulk analysis at a site near puerto eden further south in the chilean channels 49 08 s these data from laguna stibnite provide evidence for an early deglaciation before 14 000 yr bp in this region of southern chile the sequence provides no evidence for a climatic reversal between 11 000 yr bp and 10 000 yr bp the so called younger dryas chron

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

the last glacial holocene transition in southern chile warming at the last glacial termination in the north atlantic region was interrupted by a period of renewed glacial activity during the younger dryas chronozone ydc the underlying mechanism of this cooling remains elusive but hypotheses turn on whether it was a global or a north atlantic phenomenon chronological sedimentological and palaeoecological records from sediments of small lakes in oceanic southern chile demonstrate that there was no ydc cooling in southern chile it is therefore likely that there was little or no cooling in southern pacific surface waters and hence that ydc cooling in the north atlantic was a regional rather than global phenomenon

tracking abrupt climate change in the southern hemisphere a seismic stratigraphic study of lago cardiel argentina 49os lake sediments from a closed basin in southern patagonia argentina provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events high resolution sub bottom seismic profiles of lago cardiel indicate substantial lake level changes since the late pleistocene which were identified and dated in a series of long piston cores these data allow the reconstruction of the regional water balance at 49 s since the late glacial the seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr bp 14 c lake level rapidly increased by 135 m at the holocene transition following the early holocene highstand at 55 m lake level never dropped significantly below modern level the palaeoclimate changes implied by the lago cardiel record are out of phase with those implied by records from tropical south america and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent

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

late holocene intensification of colds fronts in southern brazil as indicated by dune development and provenance changes in the sao francisco do sul coastal barrier abstract holocene coastal barriers from southern brazil present great geomorphological changes during their late stages of development in this study we investigate the holocene evolution of the sao francisco do sul sfs barrier through geomorphological heavy minerals and grain size analyses constrained by optically stimulated luminescence osl dating the sfs barrier stands out among the southern brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion the progradation of the sfs barrier started at least 4914 478 years ago and had a pronounced morphodynamic shift around 1891 155 years ago this shift is characterized by episodic development of parabolic dunes migrating to nnw associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the sfs barrier this morphodynamic provenance shift resulted from the strengthening of sse winds and associated wave systems responsible for the northward alongshore drift implying intensification of cold fronts coupled with higher precipitation since 1891 155 years ago osl dating combined with grain size heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the late holocene reconstruction of the late holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

17 000 years of vegetation fire and climate change in the eastern foothills of the andes lat 44 s abstract paleoenvironmental records from patagonia reveal the importance of latitude longitude and elevation in shaping the response of vegetation to climate change we examined the vegetation fire and watershed history from two sites at lat 44 s as inferred from pollen charcoal and lithologic data these reconstructions were compared with independent paleoenvironmental records to better understand ecosystem dynamics along the southeastern andes lat 41 50 s our results show that at lat 44 s late glacial heath steppe was colonized by trees at 14 200 cal yr bp and forests became more closed at 11 500 cal yr bp differences in forest cover between the two sites were likely due to elevation dependent disparities in humidity and fire north of lat 44 s increasing precipitation favored initial forest development at 16 500 cal yr bp while dry conditions restricted tree expansion in the south until 7000 cal yr bp the time transgressive pattern is attributed to a gradual southward shift in the southern westerlies resulting from deglaciation and increasing annual insoltion present day vegetation developed at all latitudes during the middle to late holocene when the core of the southern westerlies reached its modern position 50 s asynchronous forest expansions north and south of lat 45 s between 5000 and 3000 cal yr bp are ascribed to centennial cycles of contraction and expansion of the southern westerlies which led to seasonal variations in precipitation at the core and northern border of the wind belt synchronous oscillations in tree abundance along the eastern andes prevailed during the last 3000 years decreased forest cover at all latitudes between 2500 and 1500 cal yr bp is concurrent with la nina like conditions and high solar irradiance these climate drivers likely decreased effective moisture and favored fires at all latitudes

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

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

holocene tephrochronology record of large explosive eruptions in the southernmost patagonian andes for regionally widespread holocene tephra layers in southernmost patagonia correlations based on both chemical and chronological data indicate their derivation from five large volume 1 km3 explosive eruptions of four different volcanoes in the southernmost andes bulk tephra and tephra glass major and trace element chemistry and sr isotopic ratios unambiguously distinguish different source volcanoes and imply that two of the regionally widespread tephra mb1 and mb2 were derived from mt burney 52 s one r1 from reclus 51 s one a1 from aguilera 50 s and one h1 from hudson volcano 46 s the h1 tephra derived from the hudson volcano which is located at the southern end of the andean southern volcanic zone svz 33 46 s contains distinctive greenish andesitic glass with feo 4 5 wt and tio2 1 2 wt in contrast rhyolitic glass in tephra derived from the eruptions of mt burney reclus and aguilera volcanoes which are located in the andean austral volcanic zone avz 49 55 s is clear and transparent and has significantly lower feo and tio2 tephra derived from these three avz volcanoes all contain plagioclase orthopyroxene minor clinopyroxene and amphibole biotite occurs only in the aguilera a1 tephra which also has the highest bulk tephra and tephra glass k2o and rb contents averages of new and published 14c ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated 14c age of the r1 eruption of reclus volcano to 12 685 260 years bp the mb1 and mb2 eruptions of mt burney to 8 425 500 and 3 830 390 years bp the hudson h1 eruption to 6 850 160 years bp and the a1 eruption of aguilera volcano to 3 000 100 years bp the volume of the largest of these eruptions h1 of the hudson volcano is estimated as 18 km3 the volume of the reclus r1 eruption is estimated at 10 km3 the aguilera a1 eruption at between 4 and 9 km3 and the younger mt burney mb2 eruption at 2 8 km3 the volume of the older mb1 mt burney eruption is the least well constrained but must have been larger than the younger mb2 eruption the data indicate that the frequency of explosive activity of volcanic centers in the avz is lower than in the southern svz

limits on conservative behavior of nd isotopes in seawater assessed from analysis of fish teeth from pacific core tops abstract neodymium nd isotopes have become an accepted water mass tracer for paleoceanographic reconstructions however high rates of radiogenic nd input from volcanic islands arcs in the western equatorial pacific wep and the subarctic north pacific sanp can significantly alter the isotopic composition of ambient seawaters leading to questions about the conservative nature of nd isotopes in the pacific here we present the first comprehensive study of nd isotopes preserved in core top fossil fish teeth debris from 31 sites in the pacific to define the vertical and horizontal distributions of seawater nd isotopes and to test the reliability of nd isotopes as a water mass tracer in the pacific we found that nd isotopic values of northward flowing lower circumpolar deep water lcdw are significantly modified in the western central equatorial pacific and the sanp as a result of local radiogenic inputs from young circum pacific island arcs consequently modified lcdw with 5 end is created in the central equatorial pacific while recirculated north pacific deep water npdw acquires a radiogenic nd isotope value 2 end in the sanp nd isotopic ratios of fish teeth debris in the central north pacific plotted against salinity or phosphate concentration from the overlying bottom water produce a mixing envelope between modified lcdw and npdw indicating that these nd isotopic values represent the southern and northern sourced end member values for the central north pacific and that mixing of these water masses defines vertical profiles of nd isotopes in this region in the eastern equatorial pacific eep three water masses modified lcdw npdwsanp and npdwwestern pacific combine to produce nd isotopic values that reflect this conservative mixture therefore nd isotopes behave as a conservative water mass tracer in the central north pacific and the eep but high rates of lithogenic inputs from young circum pacific island arcs compromise the conservative behavior of nd isotopes in the wep and sanp

changes in holocene climate and the intensity of southern hemisphere westerly winds based on a high resolution palynological record from sub antarctic south georgia sub antarctic south georgia is a key region for studying climate variability in the southern hemisphere because of its position at the core of the southern hemisphere westerly wind belt and between the antarctic circumpolar current and the polar frontal zone here we present a 5 8 m long high resolution pollen record from fan lake on annenkov island dominated by local sub polar vegetation with acaena and poaceae being present throughout the last 7000 years palynological and sedimentological analyses revealed a warm late holocene climate optimum between 3790 and 2750 cal yr bp which was followed by a gradual transition to cool and wet conditions this cooling was interrupted by slightly warmer environmental conditions between 1670 and 710 cal yr bp that partly overlap with the northern hemisphere medieval climate anomaly increases in non native and long distance pollen grains transported from south america e g nothofagus podocarpus indicate that stronger southern hemisphere westerly winds over south georgia possibly occurred during some colder phases of the late holocene most notably between c 2210 and 1670 cal yr bp and after 710 cal yr bp

palaeoenvironment and early human occupation of southernmost south america south patagonia argentina abstract pollen and archaeological records from two areas of southern patagonia one in the southern part of the deseado massif the other south of lago argentino suggest an important influence of climate on human movements into new areas pollen spectra record a significant dry climate throughout the region prior to ca 12 900 cal bp that may correlate with the antarctic cold reversal acr from ca 14 500 to 12 700 cal bp the earliest archaeological sites date the initial exploration sensu borrero 1994 95 of the deseado massif between 13 081 and 12 141 cal bp at the time of the northern hemisphere younger dryas yd cold interval ca 12 700 11 500 cal bp which in the southern hemisphere was a time of gradually increasing temperatures when humans set foot into the deseado massif vegetation was grass steppe indicating that conditions were wetter than during the acr the area south of lago argentino was occupied somewhat later around 11 000 cal bp also when the vegetation changed to grass steppe as temperatures increased during the early holocene forest replaced grass steppe in southwest santa cruz a mix of forest and grass steppe persisted until ca 9400 cal bp when there was a return to drier conditions as those of today in the deseado massif

late quaternary climatic history of the chilean channels based on fossil pollen and beetle analyses with an analysis of the modern vegetation and pollen rain fossil beetles and pollen were examined from an intermorainal bog at puerto eden isla wellington chile latitude 49 08 s longitude 74 25 w wood from near the base of the section has an age of 12 960 150 yr bp occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia the assumption that the chilean channels were entirely ice covered is incorrect plants and insects that invaded the deglaciated terrain were those of an empetrum heathland in which patches of nothofagus forest were restricted to sheltered locations the climate supporting the heathland is inferred to have been windier and probably drier than that of the present day from 13 000 yr bp to 9500 yr bp nothofagus forest expanded possibly in response to less windiness and more available moisture neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr bp at the time of the younger dryas stade from 9500 to 5500 yr bp the climate was as wet as that of the present day based on an increased representation of the pollen of moorland plants and of aquatic beetle species from 5500 to 3000 yr bp the climate was drier as indicated by the expansion of empetrum heath and the reduction in mesic habitats from 3000 yr bp to the present day mesic habitats dominated as the climate returned to a wetter mode the alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of southern westerlies

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

sinking of volcanic ash in uncompacted sediment in williams lake washington volcanic ash from the eruption of mount st helens on 18 may 1980 fell into williams lake in eastern washington and was temporarily suspended at the sediment water interface after several months of compaction the ash layer broke up and sank into lower density uncompacted lake sediment stratigraphic time displacements of several hundred years and a failure to recognize discontinuous ash layers in sediment cores are possible consequences of this process

new insights into paleoenvironmental changes in laguna potrok aike southern patagonia since the late pleistocene the pasado multiproxy record a series of long sediment cores was retrieved from laguna potrok aike southern patagonia within the framework of pasado potrok aike maar lake sediment archive drilling project an icdp interna