multiproxy analysis of a lateglacial holocene sedimentary section in the fuegian steppe northern tierra del fuego argentina implications for coastal landscape evolution in relation to climatic variability and sea level fluctuations abstract we report the sedimentology palynology geochemistry and diatom assemblages of a well dated succession at laguna las vueltas lv on the atlantic coast of the fuegian steppe in southern argentina the multiproxy analysis offers a unique opportunity to study the evolution of this coastal landscape in relation to past sea level and climate changes in the southern high latitudes after ca 19 000 cal yr bp the sediments were subjected to subaerial exposure and oxidation linked to a low sea level the sr ba ratio a paleosalinity geochemical parameter indicates variations in the water body level and diatoms imply the existence of an ephemeral and brackish freshwater body subject to desiccation under arid conditions between ca 11 600 and 8500 cal yr bp a shrubby steppe vegetation mainly composed of asteraceae subf asteroideae spread over the coastal area associated with a shallow freshwater body and the deposition of fine grained sediments in low energy environments all indicative of low effective moisture and warm climate conditions between ca 8500 and 8100 cal yr bp salt carpet vegetation dominated by chenopodiaceae developed around a coastal lagoon in response to the holocene marine transgression the record of dinocysts and geochemical data indicate marine influence at this time between ca 8100 and 7000 cal yr bp salt marshes colonized the coastal area a coastal lagoon with a more restricted connection to the sea and minor freshwater input are inferred linked to the beginning of a regressive phase after ca 7000 cal yr bp grassland vegetation and an open shrub stratum developed along with a shallow lake pan that was disconnected from the sea following a fall in the sea level and regression fluctuations in the water level of the pan and changes in the physical chemical conditions as indicated by fluctuations in mn fe ti ca rb sr ca tic and toc suggest abrupt events of desiccation and flooding between ca 4500 and 2000 cal yr bp a drier phase is indicated by changes in vegetation algal content and geochemistry of the pan a grassland vegetation and a shallow lake with seasonal water level variations characterized the last 2000 years our results from llv area match well with andean forest fluctuations and regional climatic conditions recorded from tierra del fuego and chilean southwest

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

submarine landforms in the fjords of southern chile implications for glacimarine processes and sedimentation in a mild glacier influenced environment abstract chilean fjords are the lowest latitude at which glaciers reach the sea today high accumulation and mass throughput sustain tidewater glacier margins in this relatively mild climatic and oceanographic setting 27 000 km 2 of swath bathymetry allow mapping of sea floor landforms and inferences on glacimarine sediments and sedimentation tidewater glaciers are present in several fjords beyond retreating tempano glacier a terminal moraine marks the limit of probable little ice age advance with smaller transverse ridges closer to the glacier beyond advancing pio xi glacier there are few signs of organised submarine landforms older moraine ridges along several fjords formed at still stands during deglaciation elsewhere meltwater fed braided rivers connect the glacial and marine sedimentary systems swath imagery shows glacifluvial and fluvial deltas with small channels and chutes that develop into long and sinuous turbidity current channels few iceberg ploughmarks and submarine slope failures were observed but several fields of pockmarks were present the fjords of chile are dominated by sediment delivery from turbid meltwater which distributes fine grained debris widely producing sorted and laminated fine grained ice proximal wedges and draping ice distal seismic architecture to give a predominantly smooth sea floor turbidity currents also transfer sediments to some ice distal environments the chilean fjordlands represent the mildest climatic and oceanographic end member of a continuum of glacier influenced marine settings similar to south east alaska in the northern hemisphere components of a landform assemblage model for climatically mild meltwater dominated fjords include ice contact moraine ridges glacifluvial and fluvial deltas and turbidity current channels full glacial and deglacial streamlined subglacial landforms are likely to have been buried in many areas by subsequent glacimarine sedimentation

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

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

late holocene covariability of the southern westerlies and sea surface temperature in northern chilean patagonia abstract the climate of chilean patagonia is strongly influenced by the southern westerlies which control the amount and latitudinal distribution of precipitation in the southern andes in austral summer the southern westerly wind belt swwb is restricted to the high latitudes it expands northward in winter which results in a strong precipitation seasonality between 35 and 45 s here we present a new precipitation seasonality proxy record from quitralco fjord 46 s where relatively small latitudinal shifts of the swwb result in large changes in precipitation seasonality our 1400 yr record is based on sedimentological and geochemical data obtained on a sediment core collected in front of a small river that drains the patagonian andes which makes this site particularly sensitive to changes in river discharge our results indicate fe al and ti al values that are low between 600 and 1200 ce increasing at 1200 1500 ce and high between 1500 and 1950 ce increasing fe al and ti al values reflect a decrease in mean sediment grain size from 30 to 20 m which is interpreted as a decrease in seasonal floods resulting from an equatorward shift of the swwb our results suggest that compared to present day conditions the swwb was located in a more poleward position before 1200 ce it gradually shifted towards the equator in 1200 1500 ce where it remained in a sustained position until 1950 ce this pattern is consistent with most precipitation records from central and southern chile the comparison of our record with published regional sea surface temperature sst reconstructions for the late holocene shows that equatorward shifts of the swwb are systematically coeval with decreasing ssts and vice versa which resembles fluctuations over glacial interglacial timescales we argue that the synchronicity between sst and swwb changes during the last 1400 years represents the response of the swwb to temperature changes in the southern hemisphere

deglacial environmental changes on isla de los estados 54 4 s southeastern tierra del fuego the island of isla de los estados is situated at 54 5 degrees s 64 degrees w east of argentinian tierra del fuego and is located in a sensitive geographic position in relation to the zonal circulation between antarctica and south america its terrestrial records of the last deglaciation recording atmospheric conditions but within an oceanic setting can help to clarify changes of regional circulation patterns both atmospheric and marine here we present geochemical analyses from 16 10 ka cal bp of a peat core from lago galvarne bog at the northern coast of the island and a lake sediment core from laguna cascada 3 kin further south the data comprise tc tn loss on ignition analyses and continuous xrf scanning on both cores as well as age depth modeling based on ams c 14 dating deglaciation and onset of peat formation in the coastal areas began before 16 ka cal bp followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland data suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14 5 ka cal bp the warming trend slows down until ca 13 5 ka cal bp followed by arid conditions culminating around 12 8 ka cal bp our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10 6 ka cal bp contemporaneous with the onset of the antarctic thermal optimum this indicates large scale shifts in the placement of zonal flow and the westerlies at the beginning of the holocene c 2008 elsevier ltd all rights reserved

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

relationships between terrestrial animal exploitation marine hunter gatherers and palaeoenvironmental conditions during the middle late holocene in the beagle channel region tierra del fuego abstract palaeoenvironmental information collected from zooarchaeological guanaco exploitation and palynological pollen and fungal remains records from tierra del fuego and isla de los estados allowed us to reconstruct the natural scenarios during the holocene to better understand the human behavioral patterns and cultural changes we have seen that changes in subsistence and guanaco exploitation would not have necessarily been synchronous with climatic variations however there is evidence of great climatic and environmental variability in the fuegian archipelago during the last 6000 years that would have influenced the distribution of the hunter gatherer societies in particular the little ice age lia event could have caused a reorganization of subsistence activities of the hunter gatherer societies the stress caused by this severe climatic episode might have changed the availability of the guanaco population over the inland and coastal areas along the beagle channel indeed the colder conditions would have significantly impacted on both the animal population and the availability of their food sources in summary the guanaco availability decreased under those colder and intense winters which is clearly reflected in the substantial drop in the zooarchaeological record

a holocene pollen record of persistent droughts from pyramid lake nevada usa pollen and algae microfossils preserved in sediments from pyramid lake nevada provide evidence for periods of persistent drought during the holocene age we analyzed one hundred nineteen 1 cm thick samples for pollen and algae from a set of cores that span the past 7630 years the early middle holocene 7600 to 6300 cal yr b p was found to be the driest period although it included one short but intense wet phase we suggest that lake tahoe was below its rim for most of this period greatly reducing the volume and depth of pyramid lake middle holocene aridity eased between 5000 and 3500 cal yr b p and climate became variable with distinct wet and dry phases lake tahoe probably spilled intermittently during this time no core was recovered that represented the period between 3500 and 2600 cal yr b p the past 2500 years appear to have had recurrent persistent droughts the timing and magnitude of droughts identified in the pollen record compares favorably with previously published y 18 o data from pyramid lake the timing of these droughts also agrees with the ages of submerged rooted stumps in the eastern sierra nevada and woodrat midden data from central nevada prolonged drought episodes appear to correspond with the timing of ice drift minima solar maxima identified from north atlantic marine sediments suggesting that changes in solar irradiance may be a possible mechanism influencing century scale drought in the western great basin d 2004 university of washington all rights reserved

late quaternary palaeoenvironmental change in western staaten island 54 5 s 64 w fuegian archipelago abstract late glacial holocene environmental conditions were interpreted in western isla de los estados staaten island from geomorphological and palynological analysis the geomorphological data from caleta lacroix 54 50 s 64 40 w indicate the presence of a fossil dune field that suggest exposition of a larger land surface and stronger wind intensity predominantly from sw and w probably during late glacial times when sea level was lower than today deglaciation and onset of peat formation in the western coastal area began prior to 12 600 cal bp in response to warmer conditions the pollen data indicates initial treeless herbaceous and paludal vegetation with scarce empetrum ericaceae type heaths and scrubs as a result of plant invasion and short term succession vegetal communities spreading over the shoreline areas under locally more humid conditions the vegetation between 10 300 and 8300 cal bp included dwarf shrub heaths scrubs cushion plants and grasses with scattered trees under warmer and drier climate conditions than today after 8300 cal bp more humid conditions allowed the expansion of an open nothofagus forest associated with dwarf shrub heath communities it was followed at 6700 cal bp by a gradual closed forest development in association with drimys winteri and shrub and herb vegetation indicative of subantarctic evergreen forest magellanic moorland vegetation transition under cold and wet conditions after 5500 cal bp the rate of evergreen beech forest greatly increased with the development of almost pure subantarctic evergreen forest communities these vegetation changes accompanied a modification of the climate toward colder and wetter conditions after 2700 cal bp the closed forest was replaced by an open nothofagus forest indicative of warm and dry conditions the minimum of nothofagus pollen registered between 1000 and 500 cal bp may correspond to the medieval climate anomaly mca period all these vegetation changes are in turn related to the positioning and intensity of the southern westerlies wind belt sea ice antarctic extent and changes in the sea level

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

quantitative reconstruction of holocene precipitation changes in southern patagonia abstract holocene variations in annual precipitation p ann were reconstructed from pollen data from southern argentinian patagonia using a transfer function developed based on a weighted averaging partial least squares wa pls regression the pollen climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units and modern precipitation values obtained from a global climate database the performance r 2 0 517 rmsep 126 mm of the model was comparable or slightly lower than in other comparable pollen climate models fossil pollen data were obtained from a sediment core from cerro frias site 50 24 s 72 42 w located at the forest steppe ecotone reconstructed p ann values of about 200 mm suggest dry conditions during the pleistocene holocene transition 12 500 10 500 cal yr bp p ann values were about 300 350 mm from 10 500 to 8000 cal yr bp and increased to 400 500 mm between 8000 and 1000 cal yr bp an abrupt decrease in p ann at about 1000 cal yr bp was associated with a nothofagus decline the reconstructed p ann suggests a weakening and southward shift of the westerlies during the early holocene and intensification with no major latitudinal shifts during the mid holocene at high latitudes in southern patagonia

clockwise rotation of the brahmaputra valley relative to india tectonic convergence in the eastern himalaya naga hills and shillong plateau gps data reveal that the brahmaputra valley has broken from the indian plate and rotates clockwise relative to india about a point a few hundred kilometers west of the shillong plateau the gps velocity vectors define two distinct blocks separated by the kopili fault upon which 2 3 mm yr of dextral slip is observed the shillong block between longitudes 89 and 93 e rotating clockwise at 1 15 myr and the assam block from 93 5 e to 97 e rotating at 1 13 myr these two blocks are more than 120 km wide in a north south sense but they extend locally a similar distance beneath the himalaya and tibet a result of these rotations is that convergence across the himalaya east of sikkim decreases in velocity eastward from 18 to 12 mm yr and convergence between the shillong plateau and bangladesh across the dauki fault increases from 3 mm yr in the west to 8 mm yr in the east this fast convergence rate is inconsistent with inferred geological uplift rates on the plateau if a 45 n dip is assumed for the dauki fault unless clockwise rotation of the shillong block has increased substantially in the past 4 8 myr such acceleration is consistent with the reported recent slowing in the convergence rate across the bhutan himalaya the current slip potential near bhutan based on present day convergence rates and assuming no great earthquake since 1713 a d is now 5 4 m similar to the slip reported from alluvial terraces that offsets across the main himalayan thrust and sufficient to sustain a mw 8 0 earthquake in this area

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

palaeoenvironmental change in southern patagonia during the lateglacial and holocene implications for forest refugia and climate reconstructions abstract a high resolution palynological record from punta yartou fuego patagonia 53 51 s 70 08 w supported by lithostratigraphy radiocarbon dating and tephrochronology was examined to reconstruct the vegetation changes during the last glacial interglacial transition and the holocene following deglaciation from the last glacial maximum sometime before c 23 070 cal yr bp the vegetation was initially dominated by ericaceous shrubs and following modest climate amelioration between c 20 480 and 14 820 cal yr bp the environment favoured the spread of acaena the trend to a warmer and more humid climate was interrupted between c 14 820 and 13 560 cal yr bp when the vegetation community was dominated by cold tolerant herbs such as poaceae and asteraceae subfamily asteroideae suggesting an open treeless landscape with colder climatic conditions coeval with the antarctic cold reversal after c 13 560 cal yr bp a gradual rise in temperature and humidity is inferred from the colonisation of nothofagus a further warming and increase is inferred from the establishment of the forest steppe ecotone by c 12 900 cal yr bp the early holocene was then characterised by increasing development of nothofagus open canopy forest however between c 8080 and 5060 cal yr bp there was a significant reduction in the forest cover and high values of charcoal which suggest an intense arid phase leading to increased availability of dry fuel between c 5060 and 2170 cal yr bp there were centennial scale periods of increased wetter and colder climatic conditions the punta yartou record demonstrates the sensitivity of fuego patagonian forest to changes in the proximity and intensity of the southern westerly winds

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

paleobathymetric implications of microborings in tertiary strata of alaska usa abstract microboring algae bacteria and fungi that lived under non tropical conditions are abundantly present in four richly fossiliferous marine strata of paleocene to miocene age in alaska by comparing their boring trace communities with endolithic guide ichnocoenoses characterizing various photic zones which have been previously defined mainly in tropical and subtropical environments the alaska strata can be placed in bathymetric zones as follows the lower upper paleocene prince creek formation in the dysphotic zone the lower oligocene stepovak formation in the shallow euphotic zone shallow euphotic zone iii and the upper miocene tachilni formation in the deep euphotic zone these interpretations agree very well with bathymetric reconstructions inferred from other criteria a fourth formation the lower middle miocene narrow cape formation contains only heterotrophic microborers as if it had been deposited in the aphotic zone in contrast to previous reconstructions in this formation the periostracum of the mollusc shells is exceptionally well preserved this may explain the absence of boring algae because only heterotrophs can penetrate through organic shell layers the absolute depth ranges of these ichnocoenoses zones are inferred from their ranges in comparable latitudes of the modern north atlantic the most important features of bathymetrically controlled tropical and subtropical guide ichnocoenoses are also present at the non tropical alaskan sites although some boring algae that are widespread in tropical realms are absent

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

seismic structure of the underthrusting indian crust in sikkim himalaya 1 this study presents the first results of the seismic character of the underthrusting indian crust in the sikkim himalaya deduced through an analysis of 3600 receiver functions rfs abstracted from waveforms registered at 11 broadband stations spanning a 110 km long n s profile from the foothills to the higher himalaya common conversion point stacks of receiver functions prominently trace the northward dipping geometry of the indian moho beneath the himalaya monte carlo inversion of the azimuthal variations of the rfs at individual stations adopting the nearest neighborhood algorithm approach reveals that the crustal thickness varies from 40 km to 61 km from south to north with a dip varying between 4 and 10 among stations a moho doublet prominently seen at a depth of 40 km in the higher himalaya to the north of main boundary thrust has been interpreted in terms of possible partial eclogitization of a granulitic indian lower crust akin to the finding just north of the study region beneath southern tibet a strong layer of anisotropy 17 localized within a low velocity layer between 20 and 30 km has a nw se oriented fast polarization direction counterintuitive to the convergence parallel and range perpendicular alignment expected in a convergent setting due to shear processes midcrustal transcurrent deformation in sikkim and bhutan evidenced by a conjugate system of strike slip faulting with nw to ne trending p axis orientations is the most feasible mechanism for causing a near strike parallel oriented fast axis of anisotropy in this segment of himalaya

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

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

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

crustal structure and tectonics of bangladesh new constraints from inversion of receiver functions abstract an understanding of the sedimentary and crustal structure of the bengal basin and of the tectonics deforming it remains elusive due to lack of seismic data from bangladesh taking advantage of recently available data from 11 seismic stations deployed over bangladesh we determine the crustal structure beneath each station using 2768 high quality receiver functions rfs inversion of the rfs reveals a highly variable thickness of the overlying sediments beneath the bengal basin the thickness of the sediments increases dramatically across the hinge zone of the early cretaceous passive margin from 3 to 17 km the thick sediments partly represent progradation of the continental margin due to the influx of clastic sediments from the himalayas the moho shallows across the region this reflects thinning of the crystalline crust from 38 km in the indian craton to 34 km at the hinge zone to 4 0 km s at lower crustal levels supports an influence of the kerguelen plume igneous activity during rifting we invert data for a station near the dauki fault which marks the southern boundary of the uplifted shillong plateau for dip and anisotropic effects our results show the dauki as a north dipping thrust fault at jaflong with a dip angle of 32 and strike 110 close to its surficial expression a strong anisotropy 15 and the sense of shear plunge 24 trend 79 compliment the dipping geometry and deformation seems to be related to the initiation of the dauki fault

the significance of chemical isotopic and detrital components in three coeval stalagmites from the superhumid southernmost andes 53 s as high resolution palaeo climate proxies abstract stalagmites are important palaeo climatic archives since their chemical and isotopic signatures have the potential to record high resolution changes in temperature and precipitation over thousands of years we present three u th dated records of stalagmites ma1 ma3 in the superhumid southern andes chile 53 s they grew simultaneously during the last five thousand years ka bp in a cave that developed in schist and granodiorite major and trace elements as well as the c and o isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo temperature and palaeo precipitation calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records water insoluble elements such as y and hree in the stalagmites indicate the amount of incorporated siliciclastic detritus monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded in general drip rate variations of the stalagmites depend on the amount of rainfall however different drip water pathways above each drip location gave rise to individual drip rate levels only one of the three stalagmites ma1 had sufficiently high drip rates to record detrital proxies over its complete length carbonate compatible element contents e g u sr mg which were measured up to sub annual resolution document changes in meteoric precipitation and related drip water dilution in addition these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the ph of acidic pore waters in the peaty soils of the cave s catchment area in general higher rainfall resulted in a lower concentration of these elements and vice versa the mg ca record of stalagmite ma1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations carbonate compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa 13c and 18o values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and or outgassing only c and o isotopes from stalagmite ma1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate compatible elements a temperature related change in rainwater isotope values modified the ma1 record during the little ice age 0 7 0 1 ka bp that was 1 5 c colder than today the isotopic composition of the stalagmites ma2 and ma3 that formed at lower drip rates shows a poor correlation with stalagmite ma1 and all other chemical proxies of ma1 hendy tests indicate that the degassing controlled isotope fractionation of ma2 and ma3 had already started at the cave roof especially when drip rates were low changing pathways and residence times of the seepage water caused a non climatically controlled isotope fractionation which may be generally important in ventilated caves during phases of low drip rates our proxies indicate that the neoglacial cold phases from 3 5 to 2 5 and from 0 7 to 0 1 ka bp were characterised by 30 lower precipitation compared with the medieval warm period from 1 2 to 0 8 ka bp which was extremely humid in this region

a geochemical and sedimentary record of high southern latitude holocene climate evolution from lago fagnano tierra del fuego abstract situated at the southern margin of the hemispheric westerly wind belt and immediately north of the antarctic polar frontal zone tierra del fuego is well positioned to monitor coupled changes in the ocean atmosphere system of the high southern latitudes here we describe a holocene paleoclimate record from sediment cores obtained from lago fagnano a large lake in southern tierra del fuego at 55 s to investigate past changes in climate related to these two important features of the global climate system we use an ams radiocarbon chronology for the last 8000 yr based on pollen concentrates thereby avoiding contamination from bedrock derived lignite our chronology is consistent with a tephrochronologic age date for deposits from the middle holocene volcan hudson eruption combining bulk organic isotopic 13 c and 15 n and elemental c and n parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret holocene climate and tectonic change during the last 8000 yr co variability and long term trends in c n ratio carbon accumulation rate and magnetic susceptibility reflect an overall holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin we attribute this variability to westerly wind derived precipitation increased wind strength and precipitation in the late holocene drives the nothofagus forest eastward and enhances run off and terrigenous inputs to the lake superimposed on the long term trend are a series of abrupt 9 negative departures in c n ratio which constrain the presence of seismically driven mass flow events in the record we identify an increase in bulk 13 c between 7000 and 5000 cal yr bp that we attribute to enhanced aquatic productivity driven by warmer summer temperatures the lago fagnano 13 c record shows similarities with holocene records of sea surface temperature from the mid latitude chilean continental shelf and antarctic air temperatures from the taylor dome ice core record in east antarctica mid holocene warming occurred simultaneously across the antarctic frontal zone and in particular in locations currently influenced by the antarctic circumpolar current

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

diatoms as indicators of hydrological and climatic changes in laguna potrok aike patagonia since the late pleistocene abstract southern south america is a key site to study climate variability in the southern hemisphere allowing for a wide variety of climatic archives recently several investigations using lacustrine sediments have provided an enormous amount of information to reconstruct past environmental changes in the framework of the potrok aike maar lake sediment archive drilling project pasado more than 500 m of sediment cores were retrieved from the center of this lake this contribution is centered in the diatom record of a core covering over the last 50 cal ka bp nine statistically significant zones were determined based on changes in the assemblages of more than 200 species of diatoms showing changes in productivity throughout time although it appears that the presence of mass waste events may have triggered some peaks in productivity large fluctuations in diatom abundance and changes in species assemblages coincide with distinctive antarctic warm events a2 and a1 described for antarctic ice cores at around 44 5 and 38 5 kyr bp respectively blunier and brook 2001 furthermore a smaller diatom peak may account for the a3 event compatible with a new osl based chronological model up to now they have only been described for antarctica but the fact that these events are recorded in southern patagonia indicates their magnitude and importance for climate in the southern hemisphere

geophysical evidence of multiple glacier advances in lago fagnano 54 s southernmost patagonia the island of tierra del fuego at the southernmost extreme of patagonia is located in one of the most extensively glaciated areas of the southern hemisphere outside antarctica during the late pleistocene the lago fagnano region at w54 30 0 s and w68 w has experienced several phases of glacier growth and retreat since the last glacial maximum lgm we illustrate these phases using combined geomorphological geophysical and coring surveys in lago fagnano itself a w105 km long e w oriented glaciotectonic basin we identify and map a complex set of submerged frontal central and lateral moraines covered by lacustrine sediments using seismic stratigraphic analysis of multi channel profiles imaging the sub lake floor we then combine these geophysical data with field observations and regional maps of similar structures around the lake to reconstruct the spatial behavior of the fagnano paleo glacier since the lgm we interpret the preserved frontal moraines as having formed during at least 20 re advance stages of the glacier within a long term deglaciation interval post lgm preliminary tephrochronological dating of a w7 5 m long core indicates a step wise deglaciation pattern comprising a final glacier re advance stage at w11 2 ka bp

middle late holocene palynology and marine mollusks from archipielago cormoranes area beagle channel southern tierra del fuego argentina abstract the palynology and marine mollusks of a marine sequence from rio ovando 54 51 s 68 35 w archipielago cormoranes beagle channel has been studied in order to reconstruct paleoenvironmental conditions during the middle late holocene the dinoflagellate cyst assemblages from rio ovando sequence reflect fjord estuarine environments close to terrestrial ice field affected by glacier meltwater discharge and characterized by short term oscillations of sea surface water parameters the base of the section which is dated at about ca 4160 14 c yr b p 4736 cal yr b p palynological subzone ro 2c is characterized by a high species diversity of dinocyst and mollusks and it is immediately followed by an interval palynological subzone ro 2b characterized by the presence of the echinidinium islandinium complex and the monospecific mytilus mollusk assemblage this subzone registers an inverse correlation between nothofagus dombeyi type and echinidinium islandinium complex concentration values during ca 4160 14 c yr b p 4736 cal yr b p 4064 14 c yr b p 4540 cal yr b p suggesting a variable climatic condition probably related to neoglacial episodes occurred in the southern patagonia andes during this interval the pollen assemblages permit direct correlations with the onshore palynostratigraphy from southern of tierra del fuego the high percentages of nothofagus dombeyi type recorded throughout most of the profile strongly suggest the presence of a closed forest confirming the existence of a variable cool and wet climate for the archipielago cormoranes area during the middle late holocene

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

late and postglacial vegetation and fire history in southern patagonia and tierra del fuego abstract two 17 000 yr old peat bog records from low elevation sites in tierra del fuego harberton 54 54 s and southern patagonia rio rubens 52 4 48 s and one c 14 000 cal yr bp record from the upper treeline in tierra del fuego paso garibaldi 54 43 s were analyzed for pollen charcoal and plant macrofossils to reconstruct changes in regional and local vegetation fire frequency and bog hydrology respectively past environmental changes in both lowland records and in the upper treeline record are interpreted in terms of variations in effective moisture during the late glacial period effective moisture changes at both low and high elevation sites were interpreted from comparable shifts between mesic herb rich grasslands and arid empetrum heath or shrub grassland with abundant disturbance indicators the late glacial effective moisture changes were primarily driven by temperature changes during the early holocene expansion of open nothofagus woodlands in the lowlands in present day areas of dense forest was related to a marked precipitation increase however precipitation must have remained highly variable with century long periods of increased summer drought as evidenced by repeated intervals when bogs dried out and fire frequency was high up slope shifts of the nothofagus forest andean tundra ecotone at 11 000 and 9000 cal yr bp also appear to reflect precipitation increases precipitation variability however must not have affected the upper treeline environments as no fires were recorded and the present day nothofagus forest had become established after 9000 cal yr bp upper treeline apparently was below present from 8000 to 7000 and 2500 to c 400 cal yr bp during those times low elevation environments did not register change which suggests that the upper treeline may have been affected by lower temperatures after c 5000 cal yr bp fires became rare in the lowlands suggesting a shift to an equable precipitation regime with only minor intervals of summer drought no simultaneous change was recorded at the upper treeline thus for the late glacial and early holocene the upper and lower treeline environments apparently responded similarly to primarily moisture changes only during the mid and late holocene environmental changes at high and low elevations differed suggesting responses to different climate signals precipitation in the lowlands and temperature at high elevation

temporal scaling of groundwater discharge in dual and multicontinuum catchment models this paper presents a multicontinuum approach to model fractal temporal scaling of catchment response in hydrological systems the temporal scaling of discharge is quantified in frequency domain by the transfer function h x which is defined as the ratio between the spectra of catchment response and recharge time series the transfer function may scale with frequency x as h x x2b while the classical linear and dupuit models predict exponents of b52 and b51 observations indicate scalings with noninteger exponents b such behaviors have been described by multifractal models which however often lack a relation to the medium characteristics we revisit and extend the classical linear dupuit aquifer models and discuss their physical meanings in the light of the resulting aquifer dynamics on the basis of these classical models we derive a multicontinuum approach that provides physical recharge models which are able to explain fractal behaviors with exponents 1 2 b 2 furthermore this approach allows to link the fractal dynamics of the discharge process to the physical aquifer characteristics as reflected in the distribution of storage time scales we systematically analyze the catchment responses in the proposed multicontinuum models and identify and quantify the time scales which characterize the dynamics of the catchment response to recharge

covariability of the southern westerlies and atmospheric co2 during the holocene a suite of mechanisms has been proposed to account for natural variations in atmospheric co 2 during the holocene all of which have achieved limited success in reproducing the timing direction and magnitude of change recent modeling studies propose that changes in the latitudinal position and strength of the southern hemisphere westerly winds sww can greatly influence large scale ocean circulation and degassing of the deep ocean via changes in wind driven upwelling in the southern ocean the extent to which the hypothesized sww southern ocean coupled system could account for changes in atmospheric co 2 is uncertain because of a lack of observations on the behavior of the sww in the past the paucity of appropriate records of productivity changes in the southern ocean and our limited understanding of the sensitivity of the southern ocean biological and or physical system to sww forcing here we report a reconstruction of the behavior of the sww during the past 14 k y based on terrestrial ecosystem proxies from western patagonia south america the reconstructed variations in the intensity of zonal flow correspond to the timing and structure of atmospheric co 2 changes and are consistent with the modeled magnitude of co 2 changes induced by varying strengths of the sww the close match between data and models supports the view that the sww southern ocean coupled system underpins multimillennial co 2 variations during the current interglacial and possibly during glacial cycles over the past 800 k y

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

multi proxy analyses of a peat bog on isla de los estados easternmost tierra del fuego a unique record of the variable southern hemisphere westerlies since the last deglaciation we have analyzed an almost 14 000 year old peat sequence on the island of isla de los estados 55 degrees s 64 degrees w east of tierra del fuego in the core of the southern hemisphere westerlies a multitude of methods have been used high resolution c 14 dating detailed lithologic descriptions including humification degree loss on ignition magnetic susceptibility bulk density pollen and spore analysis and determination of aeolian sand influx by combining proxies for wind and precipitation we have been able to reconstruct how the westerlies have varied over time in the atlantic sector of the southern ocean it shows that this westerly wind belt was most intense at the onset of the record 13 600 13 200 cal bp coinciding with the mid to late part of the antarctic cold reversal followed by a gradual decline at 12 200 cal bp the westerlies seem to have shifted to a position south of tierra del fuego and this phase the calmest and driest period on the island throughout the sequence ended at 10 000 cal bp when the westerlies moved equatorward again since then the westerlies have been present but with a variable impact on the 55 degrees s latitude of the atlantic mostly conditions have been fairly similar to today but occasionally with a wider or narrower and or weaker or stronger wind belt at 7200 cal bp wind intensity began to increase and between 4500 and 3500 cal bp these southern latitudes experienced a distinct wind and precipitation maximum both in terms of perseverance and intensity our results show a both wide and strong wind belt with possible niveo aeolian activity in tierra del fuego in winter and possibly creating milder summers around the antarctic peninsula in the later part of the holocene expansion contraction phases of the wind belt especially in winter seem to have been a common phenomenon c 2012 elsevier ltd all rights reserved

late holocene wet dry intervals from fuegian steppe at laguna carmen southern argentina based on a multiproxy record abstract late holocene environmental conditions are reconstructed from a sedimentary core lctf2 retrieved from laguna carmen 53 40 60 s 68 18 0 w 29 m a s l in the fuegian steppe northern tierra del fuego southern argentina the multiproxy study utilizes pollen spores algae ostracods palynofacies total organic carbon toc carbonate content and lithology findings show that grass communities developed over the landscape from 4200 to 1400 cal yr bp after that the plant communities fluctuated between grasses to scrubland vegetation changes in the lake level as indicated by the halophytes algal content and ostracod associations revealed alternation of wet and dry intervals the palynofacies indicate environments close to the terrestrial source with a great input of terrigenous organic matter into the lake in agreement with the sedimentary environment by comparison with other sites from tierra del fuego and southwestern patagonia the record of wind carried nothofagus pollen is consistent with variations in the andean forest communities as a consequence of shifts in the latitudinal position and or strength of the westerlies the short term wet dry intervals seem to be associated with climate events of local occurrence on the other hand some wet intervals have been reported in lacustrine records from southern patagonia the last millennium showed high environmental variability humid conditions characterized the medieval climate anomaly mca event while dryness conditions were related to the little ice age lia event in particular this latter interval has been related to a northward migration of the westerlies from their present day focus

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

glacial geomorphology of the pleistocene lake fagnano ice lobe tierra del fuego southern south america abstract a regional geomorphological study is presented of the southern and eastern coast of lake fagnano one of the most extensive glacial areas of tierra del fuego island at the southernmost tip of south america a palaeoglacial reconstruction is made based on the location of erosional and depositional glacial landforms the outlet glacier flowing eastwards from the darwin cordillera fuegian andes chile had more than 50 tributary glaciers an alpine type landscape including aretes cirques truncated spurs and hanging valleys developed in the western region of the present lake whereas a piedmont type landscape including lateral moraines glaciofluvial and glaciolacustrine terraces and an ice disintegration landscape developed in the eastern region the glacier spread over the low ranges and lowlands through three different lobes and was drained by four main outwash basins directly into the atlantic ocean the ice covered area is estimated at 4000 km 2 the maximum length of the main lobe at 132 km and the general slope at 8 four terminal positions of the glacier were recognized and related to the inutil bay and beagle channel glacial areas located to the north and south respectively 14 c dates from basal peats show that most of the area especially the easternmost part and the southern coast were free of ice by 12 300 years b p fossil peat contained in the lower basal till deposits yield 14 c dates of 31 000 48 200 years b p indicating that a glacial advance occurred in the area prior to the last glacial maximum ca 25 000 23 000 cal years b p