pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

late quaternary vegetation and climate of southern tierra del fuego vegetation and climate over approximately the past 13 000 yr are reconstructed from fossil pollen in a 9 4 m mire section at caleta robalo on beagle channel isla navarino 54 56 s 67 38 w southern tierra del fuego fifty surface samples reflecting modern pollen dispersal serve to interpret the record chronologically controlled by nine radiocarbon dates fossil pollen assemblages are empetrum gramineae gunnera tubuliflorae zone 3b 13 000 11 850 yr b p gramineae empetrum assorted minor taxa zone 3a 11 850 10 000 yr b p nothofagus gramineae tubuliflorae polypodiaceae zone 2 10 000 5000 yr b p nothofagus empetrum zone 1b 5000 3000 yr b p and empetrum nothofagus zone 1a 3000 0 yr b p assemblages show tundra under a cold dry climate zone 3 followed by open woodland zone 2 as conditions became warmer and less dry and later with greater humidity and lower temperatures by closed forest and the spread of mires zone 1 comparisons drawn with records from antarctica new zealand tasmania and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar southern hemisphere the influences of continental and maritime antarctic air masses were apparently considerable in tierra del fuego during cold late glacial time whereas holocene climate was largely regulated by interplay between maritime polar and maritime tropical air

3d aquifer characterization of the hermalle sous argenteau test site using crosshole ground penetrating radar amplitude analysis and full waveform inversion to improve the understanding of flow and transport processes in the critical zone high resolution and accurate estimation of the small scale heterogeneity is essential preferential flow paths related to high porosity layers and clay lenses in gravel aquifers greatly affect flow and transport processes in the subsurface and their high electrical contrast to their surrounding matrix and limited extent can act as low velocity electromagnetic waveguides in the past decade time domain full waveform inversion fwi of crosshole ground penetrating radar gpr data has shown to provide 2d decimeter scale resolution images of relative permittivity and electrical conductivity of the subsurface which can be related to porosity and soil texture most studies using crosshole gpr fwi resolved high porosity zones that were identified by an amplitude analysis approach but clay lenses or zones with higher electrical conductivity that act as low velocity waveguides are hard to distinguish in the measured data and amplitude analysis because of the absence of characteristic wave propagation features we have investigated a set of nine crosshole gpr data sets from a test site in hermalle sous argenteau near the meuse river in belgium to characterize the aquifer within a decimeter scale resolution and to improve the understanding of a previously performed heat tracer experiment thereby we extend the amplitude analysis to identify two different types of low velocity waveguides either caused by an increased porosity or a higher electrical conductivity and higher porosity combining the gpr amplitude analysis for low velocity waveguide zones with the standard fwi results provided information on waveguide zones which modified the starting models and further improved the fwi results moreover an updated effective source wavelet is estimated based on the updated permittivity starting models in comparison with the traditional fwi results the updated fwi results present smaller gradient of the medium properties and smaller root mean squared error values in the final inversion results the nine crosshole sections are used to generate a 3d image of the aquifer and allowed a detailed analysis of the porosity distribution along the different sections consistent structures of the permittivity and electrical conductivity show the robustness of the updated fwi results the aquifer structures obtained by the fwi results agree with those results of the heat tracer experiment

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

multiproxy record of late pleistocene holocene climate and vegetation changes from a peat bog in patagonia abstract pollen assemblage changes and stable hydrogen isotope analysis of mosses sphagnum magellanicum and drepanocladus s l from a bog in tierra del fuego argentina provided independent proxies for reconstructing changes in effective moisture and temperature over the past 16 000 cal yr b p a deterministic model was used to reconstruct the stable hydrogen isotope composition of meteoric water from the d h ratios of bog mosses over the last 16 000 years abrupt changes in temperature as recorded in d h ratios of moss cellulose were accompanied by synchronous changes in vegetation composition during the late pleistocene and early and middle holocene when moisture levels were lower than today in contrast temperature variability during the late holocene was not accompanied by comparable vegetation changes in particular grass pollen poaceae increased during periodic cold spells between 15 000 and 11 000 cal yr b p but a cold spell of similar magnitude ca 2000 cal yr b p did not appear to affect vegetation during the late pleistocene the isotopic record from the peat core shows variations similar to the d h ratios in the antarctic taylor dome ice core however the timing of the changes in the harberton record is more in line with the timing of other southern hemisphere records

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

quaternary glaciations of the southern andes abstract the southern andes comprise the southernmost portion of the andean cordillera beginning at the edge of the puna altiplano lat 27 s and ending at isla de los estados lat 55 s the late cainozoic glacial record of these mountains spans the interval from the late miocene to the present and is one of the most complete to be found anywhere in the world this has arisen for several reasons i the conterminous mountain ice cap extended to the piedmont zone on both flanks of the range where the sedimentary and morphological record has been well preserved ii periodic volcanism mainly from monogenetic fissure eruptions of basalt east of the range and from central tephra producing cones along the mountain crest has provided opportunity for the preservation and radiometric dating of interbedded glacial deposits iii a tectonically induced interval of stream incision in the mid pleistocene and simultaneous uplift has preserved glacial sediments on interfluves iv in the chilean lakes region west of the mountains late quaternary glaciers terminated in a well vegetated landscape thus creating scope for radiocarbon dating of interbedded and incorporated organic materials consequently the last glaciation in the llanquihue area of chile is one of the best dated sequences in south america thus the llanquihue glaciation is proposed as the south american equivalent of the wisconsin and weichsel glaciations of north america and north west europe respectively

integrated reconstruction of holocene millennial scale environmental changes in tierra del fuego southernmost south america abstract this study presents new paleoenvironmental data obtained from sedimentary cores from lago fagnano an elongated lake located at 54 s in southernmost south america data from palynomorphs pollen spores and algae and associated palynofacies as well as from diatom taxa retrieved from these cores compared with other regional proxies contribute to evaluate the similarities and differences in the climate patterns based on different proxies from southernmost patagonia the pollen analysis reveals that a grass steppe environment existed during the early holocene 11 300 8000 cal a bp followed by a major vegetation change characterized by development of forest steppe ecotone communities between 8000 and 6500 cal a bp under more humid conditions between 6500 and 4000 cal a bp expansion and colonization by nothofagus forests reflect an increase in effective moisture levels while openness in the forest communities characterizes the region after 1100 cal a bp the palynological organic matter combined with the algal content reflects hydrological changes occurring in the lake and its nutrient status probably in close relation with past climate oscillations all these past ecological changes are closely related to oscillations in precipitation and temperature as a response to the variations in the latitudinal position and or strength of the southern westerlies wind belt during the holocene

holocene climatic fluctuations and positioning of the southern hemisphere westerlies in tierra del fuego 54 s patagonia recent advances in the chronology and the palaeoclimatic understanding of antarctic ice core records point towards a larger heterogeneity of latitudinal climate fluctuations than previously thought thus realistic palaeoclimate reconstructions rely in the development of a tight array of well constrained records with a dense latitudinal coverage climatic records from southernmost south america are critical cornerstones to link these antarctic palaeoclimatic archives with their south american counterparts at 548s on the island of tierra del fuego lago fagnanois located in one of the most substantially and extensively glaciated regions of southernmost south america during the late pleistocene this elongated lake is the largest 110km long and non ice covered lake at high southern latitudes a multi proxy study of selected cores allows the characterisation of a holocene sedimentary record detailed petrophysical sedimentological and geochemical studies of a complete lacustrine laminated sequence reveal variations in major and trace elements as well as organic content suggesting high variability in environmental conditions comparison of these results with other regional records allows the identification of major known late holocene climatic intervals and the proposal for a time for the onset of the southern westerlies in tierra del fuego these results improve our understanding of the forcing mechanisms behind climate change in southernmost patagonia copyright 2009 john wiley sons ltd

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

globally synchronous climate change 2800 years ago proxy data from peat in south america initial findings from high latitude ice cores implied a relatively unvarying holocene climate in contrast to the major climate swings in the preceding late pleistocene however several climate archives from low latitudes imply a less than equable holocene climate as do recent studies on peat bogs in mainland north west europe which indicate an abrupt climate cooling 2800 years ago with parallels claimed in a range of climate archives elsewhere a hypothesis that this claimed climate shift was global and caused by reduced solar activity has recently been disputed until now no directly comparable data were available from the southern hemisphere to help resolve the dispute building on investigations of the vegetation history of an extensive mire in the valle de andorra tierra del fuego we took a further peat core from the bog to generate a high resolution climate history through the use of determination of peat humification and quantitative leaf count plant macrofossil analysis here we present the new proxy climate data from the bog in south america the data are directly comparable with those in europe as they were produced using identical laboratory methods they show that there was a major climate perturbation at the same time as in northwest european bogs its timing nature and apparent global synchronicity lend support to the notion of solar forcing of past climate change amplified by oceanic circulation this finding of a similar response simultaneously in both hemispheres may help validate and improve global climate models that reduced solar activity might cause a global climatic change suggests that attention be paid also to consideration of any global climate response to increases in solar activity this has implications for interpreting the relative contribution of climate drivers of recent global warming

new directional archeomagnetic data of burned cave sediments from switzerland and geomagnetic field variations in central europe this paper presents new directional archeomagnetic data from nine meso neolithic fireplaces sampled in a cave shelter at arconciel in western switzerland rock magnetic measurements indicate a homogenous magnetic mineralogy in all fireplaces with magnetite as the main magnetic carrier the remanent magnetization is stable and generally shows one characteristic directional component nine new directions which were obtained from arconciel are combined with 356 other archeomagnetic data from a circular area with a radius of 700 km around this site to obtain a penalized least square spline fit for the past 9000 yr we found in general good agreement with other local compilations such as the balkan curve the regional scha dif 8k model and with lake sediments from uk fennoscandia and switzerland nevertheless a time lag of several centuries is observed for a declination maximum between the archeomagnetic spline fit and the other european data records around 5900 bc this time lag is also observed in the swiss lake sediment record therefore we interpret this shift as a local feature of the earth s magnetic field

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

geomorphological evidence of different glacial stages in the martial cirque fuegian andes southernmost south america abstract the geomorphological features of a cirque partially occupied by receding ice bodies are presented as evidences of different glacial stages in the fuegian andes summits since the last glaciation ios 2 a glacierization scheme involving i regional glacier accumulation basin ii glacier individualization from a main regional ii a stillstand during the general retreat and iii two advancing stages are suggested geomorphic and sedimentary units named martial i ii iii and iv have been distinguished as a consequence of the glacial scheme unfortunately the lack of datable materials has impeded establishment of an absolute chronology recognized glacier advances in the region are discussed the palaeoclimatic framework for the surroundings based on previous studies is presented

isotopic evidence for hydrologic change related to the westerlies in sw patagonia chile during the last millennium abstract the southern hemisphere westerly winds influence the spatial distribution of precipitation in southern south america and play a significant role in the global carbon cycle yet little is known about how this important atmospheric circulation feature has varied in the past here we present a sediment core record of late holocene variability from lago guanaco a small closed basin lake located in torres del paine national park chilean patagonia the park is located in the core of the modern wind field and variations in the intensity of the atmospheric circulation directly influence the hydrology of this region we combine stable isotopic measurements of biogenic carbonate and bulk organic matter to identify two periods of increased evaporation between 900 550 and 400 50 calendar years before present cal yr bp the first interval is coincident with the medieval climate anomaly mca while the more recent period is broadly coincident with the timing of the little ice age lia during the lia interval we observe simultaneous monotonic increases in the 18 o of biogenic carbonate and nothofagus dombeyi type pollen which we interpret as indicative of significant changes in the intensity of the southern westerlies during the last millennium the isotopic and palynological variations in the guanaco record are coincident with geochemical variations found in an antarctic ice core record from siple dome suggesting that the signal preserved in lago guanaco is regional rather than local and that the lia intensification was accompanied by a poleward shift in the southern margin of the westerlies in addition we interpret four periods of increased lake productivity centered on 900 650 500 and 200 cal yr bp from simultaneous increases in the 13 c of bulk organic material and biogenic carbonate these increases in lake productivity are most likely tied to increases in summer temperatures

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

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

past human populations and landscapes in the fuegian archipelago southernmost south america this contribution discusses possible relationships between human populations and holocene environmental deterioration phenomena cold arid pulses and volcanic eruptions in the fuegian archipelago south america based on summed probability distributions of archaeological dates paleoenvironmental information geospatial data and archaeological evidence during the first millennia after peopling only the hudson ca 7700 cal yr bp and the first monte burney ca 8600 cal yr bp eruptions might have played a role in human dispersion particularly a more intense human occupation around the beagle channel and long distance interactions are proposed as risk buffer strategies related to the hudson eruption a cooling phase and a demographic growth at ca 5500 cal yr bp might have favored more dispersed spatial occupations and a subsistence diversification in the beagle channel in the northern steppes the second monte burney eruption ca 4300 cal yr bp and an arid episode ca 2600 cal yr bp are proposed as the main triggers for changes in land use patterns long network interactions and subsistence strategies even though occupation changes in the fuegian archipelago coexist with environmental deterioration episodes after 1500 cal yr bp demographic processes and the european colonization most likely explain this trend similarities between the steppe ecotone and forest occupation curves suggest common behavioral patterns across the holocene

late holocene climatic changes in tierra del fuego based on multiproxy analyses of peat deposits a ca 1400 yr record from a raised bog in isla grande tierra del fuego argentina registers climate fluctuations including a medieval warm period although evidence for the little ice age is less clear changes in temperature and or precipitation were inferred from plant macrofossils pollen fungal spores testate amebae and peat humification the chronology was established using a 14c wiggle matching technique that provides improved age control for at least part of the record compared to other sites these new data are presented and compared with other lines of evidence from the southern and northern hemispheres a period of low local water tables occurred in the bog between a d 960 1020 which may correspond to the medieval warm period date range of a d 950 1045 generated from northern hemisphere tree ring data a period of cooler and or wetter conditions was detected between ca a d 1030 and 1100 and a later period of cooler wetter conditions estimated at ca cal a d 1800 1930 which may correspond to a cooling episode inferred from law dome antarctica

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

late holocene glacier variations in the cordillera darwin tierra del fuego chile radiocarbon dates obtained on peat and macrofossils sampled both proximally and distally of a terminal moraine in the bahia pia area cordillera darwin tierra del fuego chile indicate that the glacier system reached maxima sometime before 3060 bp prior to 940 bp and between 940 bp and 675 bp the glacier retreated 4 km to a pinning point position where it dammed a lake before 2605 80 bp between 1950 75 and 1790 75 bp and some time shortly after 1790 75 bp by 250 bp the glacier system had receded more than 15 km towards the fjord head and probably reached close to its present position thus we obtained no evidence from bahia pia of any glacial advance occurring during the global little ice age maximum seventeenth to nineteenth centuries

extraterrestrial chromite in middle ordovician marine limestone at kinnekulle southern sweden traces of a major asteroid breakup event the distribution of sediment dispersed extraterrestrial chromite grains and other cr rich spinels 63 mu m has been studied in middle ordovician orthoceratite limestone from two quarries at kinnekulle southern sweden in the thorsberg quarry all similar to 3 2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment dispersed extraterrestrial chromite grains typically 1 3 grains are found per kilogram of limestone in the nearby hallekis quarry the same beds show similarly high concentrations of extraterrestrial chromite grains but in samples representing the 9 m downward continuation of the section exposed at this site only 5 such grains were found in a total of 379 kg of limestone the extraterrestrial equilibrated ordinary chondritic chromite grains call be readily distinguished by a homogeneous and characteristic major element chemistry including 2 0 3 5 wt tio2 and stable v2o3 concentrations close to 0 7 wt terrestrial cr rich spinels have a wide compositional range and co exist with extraterrestrial chromite in some beds these grains may be derived for example from mafic dykes exposed and weathered at the sea floor considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied instead the difference may be primarily related to all increase in the ancient flux or extraterrestrial matter to earth in connection with the disruption of the l chondrite parent body in the asteroid belt at about this time the coexistence in some beds of high concentrations of chondritic chromite and terrestrial cr rich spinels however indicates that redistribution of heavy minerals on the sea floor related to changes in sea level and sea floor erosion and currents must also be considered less

multiproxy record of holocene paleoenvironmental change tierra del fuego argentina abstract we interpret holocene environmental conditions in a subantarctic high andean valley from palynological and diatom analysis peat stratigraphy and local geomorphology the multiproxy data from las cotorras mire 54 41 13 s 68 02 51 w 420 m a s l indicate the development of a soligenous mire as a result of a fine grained tephra layer deposition over the mineral soils sometime prior to 8000 cal yr bp the paleoecological conditions in the mire after 8000 cal yr bp show a rapid succession from a limnic to a telmatic stage as the mire is colonized by sedges cyperaceae and herbaceous communities the upland vegetation changed from cushion and shrub heaths to an expansion of nothofagus forest at high altitudes after 6500 cal yr bp the peat is interbedded with clastic sediment that originates from mass wasting events or floods these depositional changes affected the mire ecosystem water table level and nutrient status oligotrophic and or eutrophic conditions maxima in total pollen influx at about 2800 1100 and 700 cal yr bp coincide with heightened mineral flux and these changes are related to precipitation and slope processes the major vegetational change registered in the pollen record is the decline of nothofagus pollen after 1000 cal yr bp which reaches a minimum between ca 680 and 300 cal yr bp this minimum was likely caused by cool wet conditions that coincided with the little ice age lia in the southern hemisphere our results indicate the sensitivity of subantarctic nothofagus forest and mire ecosystems to changes during the holocene