late quaternary climate change from δ18o records of multiple species of planktonic foraminifera high resolution records from the anoxic cariaco basin venezuela seasonal trade wind induced upwelling along the southern margin of the caribbean sea occurs in response to the annual migration of the intertropical convergence zone laminated high deposition rate sediments of the cariaco basin a small anoxic basin on the venezuelan continental shelf clearly record large changes in the past intensity of this upwelling because sediments of the cariaco basin are largely unbioturbated they offer a natural opportunity to study the stable isotopic records of multiple planktonic foraminiferal taxa and to evaluate their sensitivity to both the modern hydrography and temporal changes in upwelling intensity and climate oxygen isotope data 18o from four dominant foraminiferal taxa are presented for the time period covering the last 28 kyr the 18o data from globigerina bulloides after correction for nonequilibrium precipitation are used as a monitor of sea surface conditions during the winter spring upwelling season the 18o data from white globigerinoides ruber are used as a measure of annual average conditions in the near surface while pink g ruber data are consistent with use as an index of endmember conditions during the summer fall nonupwelling season data from the deeper dwelling neogloboquadrina dutertrei yield information on conditions near the base of the local thermocline during the last glacial 18o data from g ruber and generally reduced interspecific differences indicate cooling of surface waters over the cariaco basin by up to 4 c this longer term cooling does not appear to be related to changes in upwelling intensity along the coast but may instead reflect more regional cooling of the larger caribbean superimposed on this pattern between 12 6 and 10 ka is a convergence of 18o data between g bulloides and n dutertrei implying much stronger upwelling during the last deglaciation this scenario is consistent with other evidence for high productivity at this time at 14 ka a sharp 18o depletion event observed in all taxa seems to have been produced by increased freshwater discharge to the southern caribbean suggesting either higher regional rainfall or the influence of glacial melting in the andes minimum 18o values of pink g ruber around 6 7 ka record warmer summer sea surface temperatures and or decreased salinity in the mid holocene

interhemispheric climate links revealed by a late glacial cooling episode in southern chile understanding the relative timings of climate events in the northern and southern hemispheres is a prerequisite for determining the causes of abrupt climate changes but climate records from the patagonian andes1 2 3 4 and new zealand5 6 7 8 for the period of transition from glacial to interglacial conditions about 14 6 10 kyr before present as determined by radiocarbon dating show varying degrees of correlation with similar records from the northern hemisphere it is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of northern hemisphere ice sheets and oceanic atmospheric and astronomical influences in initiating climate change in the late glacial period here we report pollen records from three sites in the lake district of southern chile 41 s from which we infer conditions similar to modern climate between about 13 and 12 2 14c kyr before present bp followed by cooling events at about 12 2 and 11 4 14c kyr bp and then by a warming at about 9 8 14c kyr bp these events were nearly synchronous with important palaeoclimate changes recorded in the north atlantic region9 supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation in other regions of the southern hemisphere where climate events are not in phase with those in the northern hemisphere local oceanic influences may have counteracted the effects that propagated through the atmosphere

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

late pleistocene glacial sequence in the area of the high plain of bogota eastern cordillera colombia abstract four main glacial events could be reconstructed on the basis of morphologic and 14c evidence in the parano regions surrounding the high plain of bogota eastern cordillera colombia in the area four distinct morainic levels were recognized between ca 2750 3000 m and ca 3750 m radiocarbon dates in combination with climatological data derived from palynological evidence indicate that morainic complex 4 was formed between ca 13 000 12 400 yr b p complex 3 between ca 18 000 14 000 yr b p complex 2 between ca 22 500 19 500 yr b p whereas complex 1 may be of middle last glacial age or of penultimate glacial age the spatial distribution of moraines throughout the area clearly shows that limits of former glacier systems were strongly influenced by local climatological conditions

quaternary glaciations in the northern andes venezuela colombia and ecuador abstract the nature and distribution of glacial drift in the high andes of venezuela colombia and ecuador suggest that deposits of only the last two quaternary glaciations isotope stages 6 and 4 2 are present the penultimate glaciation in ecuador may be represented by deeply weathered drift that is beyond the range of radiocarbon dating in colombia and venezuela subdued moraines covered with loess may be of equivalent age in places this drift extends 1000 m lower in altitude than the limits of the last glaciation which comonly reach 3400 3600 m radiocarbon dated organic deposits 33 43 ka bp lying between tills composing superposed terminal moraines suggest that andean glaciers may have been as extensive during isotope stage 4 as during isotope stage 2 a relatively long interstadial from 43 33 ka bp preceded the glacier advance that culminated during the interval ca 28 15 ka bp two late glacial stadials are marked by moraine complexes at 3900 4200 m altitude they are partly constrained by radiocarbon ages of 12 9 ka bp and 12 10 ka bp moraines apparently deposited during neoglacial advances of the last ca 5 ka lie in front of most of the glaciers remaining in the northern andes

late holocene hydroclimate variability in costa rica signature of the terminal classic drought and the medieval climate anomaly in the northern tropical americas abstract in the northern tropical americas neotropics notable hydrological variability has been documented in multi proxy paleoclimate records between 600 and 1200 ce this interval generally overlaps with the maya terminal classic drought tcd 770 1100 ce and the medieval climate anomaly mca 950 1250 ce there is however limited paleoclimate data that provide reliable estimates of terrestrial thermal variability in southern central america during this time in this study we present chironomid based temperature reconstructions developed from sediment cores from two lakes 1 lago morrenas 3c a high elevation glacial lake located on the crest of the atlantic slope of the cordillera talamanca costa rica and 2 laguna zoncho a mid elevation lake located on the pacific slope in southern costa rica distinctive shifts in the chironomid assemblages occurred at both sites between 610 and 1230 ce these changes are inferred to reflect an 600 year interval characterized by depressed mean annual temperatures at lago morrenas 3c and dry conditions and lake level decline at laguna zoncho taken together the multi proxy paleoclimate records from these two lakes including stable carbon isotope 13c and charcoal data suggest that middle elevations on the pacific slope and high elevations on the atlantic slope of costa rica experienced sustained drought and possible cooling coeval with the tcd mca interval the timing of hydroclimate variability in these records provides support for the hypothesis that cooling and drought in the northern tropical americas during the tcd and early mca were linked to thermal changes in the tropical north atlantic

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

modern and last local glacial maximum snowlines in the central andes of peru bolivia and northern chile late pleistocene snowlines in the central andes were 500 1200 m lower than at present radiocarbon dates imply that the late pleistocene glacial maximum in the region occurred prior to 20 14c ka but lack of maximum limiting ages adds considerable uncertainty to the exact timing snowline modeling demonstrates that snowlines in the eastern and western cordilleras of the central andes respond differently to temperature and precipitation changes in the eastern cordillera the snowline is near the level of the annual 0 c isotherm and melting occurs throughout the year here snowlines are sensitive to temperature changes but relatively insensitive to accumulation changes in the western cordillera the snowline rises 1000 higher owing to increasing aridity and the snowline exhibits a much stronger sensitivity to accumulation changes the consistent 1200 m snowline depression along the eastern cordilleras of the central andes can be modeled by a mean annual cooling of 5 9 c this is inconsistent with the 2 c cooling in tropical sea surface temperatures suggested by climap reconstructions the 800 1000 m snowline depression in the western cordillera cannot be accounted for solely by cooling but also requires an increase in precipitation

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

evolution of fluid geochemistry at the turrialba volcano costa rica from 1998 to 2008 turrialba 10 02 n 83 45 w is a 3 349 m high stratovolcano belonging to the holocene cordillera central volcanic belt of costa rica the summit consists of three ew oriented craters east central and west since its last eruptive phase 1864 1866 the central and west craters have displayed modest fumarolic activity with outlet temperatures clustering around 90 c in 2001 seismic swarms ground deformation and increasing fumarolic activity occurred from 2005 to 2008 new fumarolic vents opened between and within the central and west craters and along the western and southwestern outer flanks of the volcanic edifice these physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages 1 hydrothermal from 1998 to autumn 2001 characterized by the presence of h2o co2 h2s and to a very minor extent hcl and hf 2 hydrothermal magmatic autumn 2001 2007 with the appearance of so2 and a significant increase of hcl and hf and 3 magmatic dominated 2007 2008 characterized by increased so2 content so2 h2s 100 and temperatures up to 282 c accordingly gas equilibrium in the co2 ch4 h2 system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions the chemical physical modifications of turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems nevertheless the risk of rejuvenation of the volcanic activity cannot be excluded and an appropriate seismic ground deformation and geochemical monitoring program is highly recommended turrialba lies at a distance of 35 and 15 km from san jose and cartago respectively the two largest cities in costa rica

deglacial and postglacial vegetation changes on the eastern slopes of the central patagonian andes 47 s abstract we report pollen spore and charcoal records from lago augusta 47 05 s 72 23 w 440 m a s l a small closed basin lake located near the modern forest steppe ecotone east of the andes in central patagonia chile the record shows local ice free conditions through the last glacial termination in the rio chacabuco valley and flooding by an ice dammed lake once this proglacial lake ceased to inundate areas above 450 m a s l the valley was colonized by herbs shrubs and evergreen rainforest taxa between 15 600 and 16 000 cal yr bp indicating an open landscape under cold wet conditions millennial scale fluctuations in the hygrophilous conifer fitzroya pilgerodendron suggest precipitation variations within a cool wet climate between 11 800 and 13 400 cal yr bp followed by the establishment of dense nothofagus forests between 9800 and 11 800 cal yr bp and declines in hygrophilous and cold resistant trees herbs and shrubs this interval coincided with peak fire activity and laminated carbonate deposition nothofagus forests have persisted with little variation since 9800 cal yr bp except for a sudden decline associated with a rapid increase in rumex cf acetosella an exotic weed introduced by europeans our results and interpretations are best explained by changes in the strength position of the southern westerly winds at millennial and multi millennial timescales since the last glaciation contrary to previous interpretations we propose increased precipitation of westerly origin in the andean sector of central east patagonia between 11 800 and 16 000 cal yr bp followed by a decline between 9800 and 11 800 cal yr bp and an increase thereafter these trends are coherent with variations of the southern westerly winds identified in other terrestrial mid latitude records suggesting zonally symmetric changes in atmospheric circulation since the last glaciation

past glaciation in the tropics abstract tropical glaciers are considered along three meridional profiles for the australasian sector africa and the americas evaluated are the annual mean freezing level 0 c modern equilibrium line altitude mel and past equilibrium line altitude pel the calculation of 0 c is based on a 1958 1997 global data set mel refers to estimates concerning the first half of the 20th century and the timing of the pel is not generally known 0 c stands around 4000 5000 m with lower levels in the outer tropics mel is reached in the australasian sector on four mountains and in africa on three mountains near the equator near or above 0 c in the american cordilleras many peaks are still glaciated above 0 c but in the arid southern tropical andes even summits above 6000 m do not reach mel the pel stands between 3000 m and 5000 m high in the equatorial zone but highest in the arid southern tropical andes the height difference between mel and pel is of order 1000 m with regional differences deglaciation dates range between 15 000 and 8000 years bp with later timing towards the higher elevations this synopsis suggests priority targets for further research morphological mapping and age determination in the high atlas of morocco timing of deglaciation in the high semyen of ethiopia and the altos de cuchumatanes of guatemala exploration in the highlands of lesotho and of the dominican republic and glaciation in the arid southern tropical andes

quaternary glacial stratigraphy and chronology of mexico the volcano iztaccihuatl in central mexico was glaciated twice during the middle pleistocene once probably in pre illinoian or pre bull lake time and once in late illinoian or bull lake time glaciation during the late pleistocene was restricted to the late wisconsin or pinedale a maximum advance and one readvance are recorded in the early part and one readvance in the latter part three or four small neoglacial advances occurred during the holocene two other volcanoes nearby ajusco and malinche have a partial record of late pleistocene and holocene glaciations three others popocatepetl pico de orizaba and nevado de toluca have a full holocene record of three to five glacial advances during neoglaciation

on the interaction between bathymetry and climate in the system dynamics and preferred levels of the great salt lake 1 the great salt lake is a terminal lake whose level is determined by the balance between inflows and outflows we examine the causes for multimodality in the distributions of lake level and hence volume and area that have previously been examined from a system dynamics perspective we focus on the role of bathymetry in the dynamics of this system and show that some of the modes that are observed and that represent preferred system states are attributable to features of the bathymetry described using the topographic area volume relationship being a terminal lake the only outflow is evaporation which depends directly on lake area which adjusts with stochastic fluctuations to balance inflows where the topographic side slopes are relatively flat and the lake goes through a large change in area for a given increase in level the outflux evaporation will go through a corresponding large change tending to stabilize the lake at that point conversely where topographic side slopes are relatively steep the stabilizing effect is diminished this effect was quantified using the derivative of the lake area lake volume function determined from u s geological survey topographic and bathymetric surveys we show how some of the observed modes that represent preferred lake volume states are attributable to peaks in this area volume derivative while a complete description of the observed distribution of lake volume requires combining the bathymetry represented by the area volume derivative with a multimodal lake area distribution that may be connected to multimodality in the aggregate hydrological forcing

quaternary glaciers and climate on cerro chirripo costa rica abstract glacial lake sediments and glacial geomorphology in valle de las morrenas a glacial trough on the north face of cerro chirripo costa rica provide evidence on high altitude pleistocene conditions in central america the most recent glacier in the valley chirripo stage i receded very rapidly near the end of the younger dryas chronozone radiocarbon dates on basal organic sediments from lakes beneath upper middle and lower limits of that glacier fall close together and two sigma calibrated ages overlap for the period 9700 9600 cal yr b p earliest datable transition sediments from the central lake date to 12 360 11 230 cal yr b p larger older moraines and associated trimlines allowed reconstruction of three paleoglaciers chirripo stages ii iii and iv computer analysis of hypsometry using published tropical glacier vertical mass balance profiles yields elas of 3506 3523 3515 3537 and 3418 3509 m respectively chirripo ii ela estimate positions applied to chirripo i yield an ela of 3538 3546 m we infer minimal temperature depressions of 7 4 8 0 c for the chirripo i iv stages modeling the behavior of modern tropical glaciers yields basinwide net accumulation estimates of 440 620 550 830 and 960 1760 mm yr 1 for the chirripo ii iii and iv stages

climate and local controls of long term vegetation dynamics in northern patagonia lat 41 s abstract patagonian vegetation has dramatically changed in composition and distribution over the last 16 000 yr although patterns of vegetation change are relatively clear our understanding of the processes that produce them is limited high resolution pollen and charcoal records from two lakes located at lat 41 s provide new information on the postglacial history of vegetation and fire activity at the forest steppe ecotone and help clarify the relative importance of local and regional drivers of late holocene ecological change our results suggest that late glacial parkland was colonized by shrubs at ca 11 200 cal yr bp and this vegetation persisted until 4900 cal yr bp when increased humidity allowed for the establishment of nothofagus forest the late holocene is characterized by oscillations in forest dominance largely driven by changes in humidity possibly associated with the onset or strengthening of enso in the last 4900 yr humid periods 4900 3800 and 2850 1350 cal yr bp have promoted nothofagus forest whereas drier times 3800 2850 and 1350 450 cal yr bp have favored austrocedrus expansion at intermediate moisture levels however the lower forest supported both taxa and fire became an important control of community composition with severe infrequent fires facilitating nothofagus regeneration and high fire frequency and intensity supporting austrocedrus

abrupt vegetation changes during the last glacial to holocene transition in mid latitude south america a pollen record from the huelmo site ca 41 30 s shows that vegetation and climate changed at millennial time scales during the last glacial to holocene transition in the mid latitude region of western south america the record shows that a nothofagus parkland dominated the landscape between 16 400 and 14 600 14c yr bp along with magellanic moorland and cupressaceous conifers evergreen north patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14c yr bp following a prominent rise in nothofagus at 14 600 14c yr bp highly diverse closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14c yr bp followed by the expansion of cold resistant podocarps and nothofagus at ca 12 500 and 11 500 14c yr bp local disturbance by fire favoured the expansion of shade intolerant opportunistic taxa between 10 900 and 10 200 14c yr bp subsequent warming pulses at 10 200 and 9100 14c yr bp led to the expansion of thermophilous summer drought resistant valdivian rainforest trees until 6900 14c yr bp our results suggest that cold and hyperhumid conditions characterised the final phase of the last glacial maximum lgm between 16 400 and 14 600 14c yr bp the last ice age termination commenced with a prominent warming event that led to a rapid expansion of north patagonian trees and the abrupt withdrawal of andean ice lobes from their lgm positon at ca 147 000 14c yr bp hyperhumid conditions prevailed between 16 400 and 13 000 14c yr bp what we term the extreme glacial mode of westerly activity this condition was brought about by a northward shift and or intensification of the southern westerlies the warmest driest conditions of the last glacial interglacial transition occurred between 9100 and 6900 14c yr bp during this period the westerlies shifted to an extreme interglacial mode of activity via a poleward migration of stormtracks our results indicate that a highly variable climatic interval lasting 5500 14c years separate the opposite extremes of vegetation and climate during the last glacial interglacial cycle i e the end of the lgm and the onset of the early holocene warm and dry period copyright 2003 john wiley sons ltd

late quaternary deglacial history of the merida andes venezuela radiocarbon dated sediment cores from seven lakes and two bogs spanning the cordillera de merida in the venezuelan andes were used to identify and date the regional history of late pleistocene and holocene glacial activity coring sites were selected at different elevations across a pronounced rain shadow from southeast wet to northwest dry sediment lithostratigraphy and magnetic susceptibility in conjunction with ams radiocarbon dates on macrofossils and char coal were used to constrain deglaciation the local expression of the last glacial maximum occurred between 22 750 and 19 960 cal yr bp on the wetter southeastern side of the cordillera de merida glaciers had significantly retreated by 15 700 cal yr bp followed by several minor glacial advances and retreats between 14 850 and 13 830 cal yr bp at least one major glacial readvance occurred between 13 830 and 10 000 cal yr bp in the wetter southeastern sector of the region the drier northwest side of the cordillera de merida records initial glacial retreat by 14 240 cal yr bp multiple sites on both sides of the merida andes record a further phase of extensive deglaciation approximately 10 000 cal yr bp however the north northwest facing mucubajo catchment remained partially glaciated until ca 6000 cal yr bp deglacial ages from the venezuelan andes are consistently younger than those reported from the southern hemisphere andes suggesting an inter hemispheric deglacial lag in the northern tropics of the order of two thousand years copyright 2005 john wiley sons ltd

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

climatic interpretation of alpine snowline variations on millennial time scales abstract the depression of snowlines or equilibrium line altitudes of alpine glaciers is often used by glacial geologists to infer variations in mass balance the climatic interpretation of snowline depression however is complicated by the number of factors that control glacier mass balance the simple lapse rate method of temperature interpretation ignores the effects of changes in radiation and snow accumulation the statistical approach to temperature interpretation which regresses precipitation and temperature against snowline altitude neglects the effect of radiation the most comprehensive approach for the climatic interpretation of snowline depression couples the heat and mass balances of a glacier surface a sensitivity analysis that utilizes the coupled heat and mass balance approach indicates that the 1000 m variation in snowline of alpine glaciers on glacial to interglacial time scales could be a result of significant changes in temperature and to a lesser extent changes in insolation snowline variations are sensitive only to relatively large changes in annual accumulation which should also be evident in other proxy records of moisture change the approaches outlined here provide glacial geologists with a summary of how various climatic forcings associated with glaciation may be quantified from snowline data

late quaternary vegetation of southern isla grande de chiloe chile late glacial holocene forest history of southern isla chiloe latitude 43 10 s was reconstructed on the basis of pollen analysis in three profiles laguna soledad laguna chaiguata puerto carmen prior to 12 500 yr b p pollen records are dominated by plant taxa characteristic of open habitats zone i from 12 500 yr b p to the present tree species predominate in the pollen records zones ii v between 12 500 and 9500 yr b p ombrophyllous taxa nothofagus podocarpus nubigena myrtaceae fitzroya pilgerodendron and drimys are frequent in all pollen diagrams suggesting a wetter and colder climate than the present between 9000 and 5500 yr b p valdivian forest elements such as nothofagus dombeyi type weinmannia and eucryphia caldcluvia dominate indicating a period of drier and warmer climate from 5500 yr b p onward the expansion of mixed north patagonian subantarctic forest elements and the increased frequence of tepualia suggest increased rainfall and temperatures oscillating around the modern values the change from open to forest vegetation ca 12 500 yr b p probably represents the most pronounced climatic change in the record and can be interpreted as the glacial postglacial transition in the study area

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

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

new excavations at the late pleistocene site of chinchihuapi i chile this paper presents new excavation data on the chinchihuapi i ch i locality within the monte verde site complex located along chinchihuapi creek in the cool temperate valdivian rain forest of south central chile the 2017 and 2018 archaeological excavations carried out in this open air locality reveal further that ch i is an intermittently occupied site dating from the early holocene 10 000 cal yr bp to the late pleistocene at least 14 500 cal yr bp and probably earlier a new series of radiocarbon dates refines the chronology of human use of the site during this period in this paper we describe the archaeological and stratigraphic contexts of the recent excavations and analyze the recovered artifact assemblages a fragmented monte verde ii point type on an exotic quartz newly recovered from excavations at ch i indicates that this biface design existed in at least two areas of the wider site complex 14 500 cal yr bp in addition associated with the early holocene component at ch i are later paijan like points recovered with lithic tools and debris and other materials we discuss the geographic distribution of diagnostic artifacts from the site and their probable relationship to other early sites in south america

geomorphic and exhumational response of the central american volcanic arc to cocos ridge subduction 1 the timing of collision of the cocos ridge at the middle america trench remains one of the outstanding questions in the tectonic evolution of the central american convergent margin new analyses of the tectonic geomorphology of the cordillera de talamanca the extinct volcanic arc inboard of the cocos ridge coupled with low temperature thermochronometry data provide insight into the cooling and erosional history of the arc from late miocene to present we identify a low relief surface at high elevation along the northeastern flanks of the range which represents a relict erosional landscape cut across shallow plutonic rocks of the arc edifice longitudinal profiles of rivers on this surface are isolated from steep downstream sections by prominent knickzones that are interpreted to reflect a migrating wave of transient incision generated during differential rock uplift of the range reconstruction of pre incision profiles suggests that rock uplift during the growth of the cordillera de talamanca is no greater than 2 km this inference is corroborated by results from our apatite u th he and apatite fission track analyses along an elevation transect on mt chirripo the highest mountain in the cordillera de talamanca low temperature cooling ages overlap significantly with published high temperature40ar 39ar ages the combined results imply that rapid cooling in the late miocene was related to secular cooling of a shallow pluton rather than exhumation our results imply that rapid incision along downstream channel segments differential rock uplift and growth of the talamanca as a bivergent orogenic wedge associated with the onset of cocos ridge subduction are relatively young characteristics of the range a review of previously published radiometric ages and revised plate reconstructions for the late miocene further suggest that the cessation of arc volcanism in both the cordillera de talamanca and the cordillera central of western panama was coeval with the initiation of oblique subduction of the nazca plate during the late miocene thus we conclude that the cessation of arc volcanism in the late miocene 5 8 ma and the onset of cocos ridge collision 3 ma are separate events that reflect recent changes in the configuration of the plate boundary system

cosmogenic 36cl and 10be ages of quaternary glacial and fluvial deposits of the wind river range wyoming we measured cosmogenic 36 cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the wind river range wyoming we also measured 10 be in 10 of the same samples most of the 10 be ages were in good agreement with the 36 cl ages indicating that rock surface erosion rates were very low the oldest moraine investigated the type sacagewea ridge site yielded only a limiting minimum age of 232 ka the oldest moraines in the type bull lake complex also could be constrained only to 130 ka the main sequence of type bull lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka the best estimates are closer to the upper limits of these ranges and associated uncertainties are in the range of 10 to 15 these uncertainties could permit deposition in either marine isotope stage 6 or stage 5d we found no evidence of glacial deposits dating to marine isotope stage 4 both bull lake age moraines from fremont lake on the opposite side of the wind river range and boulders on a fluvial terrace above the wind river gave age distributions very similar to that of the second oldest bull lake advance ca 130 to 100 ka the distribution of boulder ages for pinedale moraines at bull lake indicated deposition between 23 and 16 ka nearly identical to the distribution of 10 be ages previously reported for the type pinedale moraines at fremont lake

paleosol evidence for quaternary uplift and for climate and ecosystem changes in the cordillera de talamanca costa rica abstract a noncalcareous volcanic paleosol succession from the upper montane rain forest of the cordillera de talamanca costa rica lat 9 41 03 3 n long 83 53 45 9 w 2507 m elev provides evidence for changing quaternary elevation climate and ecosystems basal deposits crb horizons are saprolitized porphyritic andesite enriched in si al and fe and depleted in base cations which record an earliest period of very intense weathering forming a leached residuum of smectite kaolinite and fe oxides or oxyhydroxides on a mature paleolandscape probably in tropical lowlands paleo saprolite deposits are sharply overlain by interbedded lapilli tuffs and two paleosols with dark colored organic c rich 2 3 wt ab horizons one containing abundant grass pollen interpreted as mollic epipedons of grassland soils andic mollisol like paleosols with 13c values 24 5 pdb that record a former c3 grassland ecosystem possible pedogenic carbonate btkb horizons with all carbonate removed by overprinting by younger pedogenic processes provide evidence of former drier and drained conditions uppermost buried soils mainly btb horizons are non calcareous clay rich andic ultisol like paleosols that record pedogenesis under climates similar to current conditions with highly weathered clay mineral suites ams dating of charcoal from the upper btb paleosol constrains a latest glacial age 36 640 650 14c yr bp ages for two additional deeper samples were 43 48 ka for the 2btb paleosol uplift rates of the cordillera de talamanca are estimated as 1 km 1 ma consequently the described paleosols provide evidence for 1 initial lowland pedogenesis perhaps at 2 3 ma 2 regional uplift and major unconformity volcanism and development of a grassland ecosystem that has 13c values similar to those measured in modern high elevation paramo sites in the cordillera 24 4 to 26 3 pdb but formed mollic epipedons and pedogenic carbonates which do not characterize modern paramo soils followed by 3 continued late pleistocene volcanism and pedogenesis in environments similar to current oak dominated montane rain forest conditions the paleosol succession provides a valuable record of dynamic climate ecosystem change and uplift history in the cordillera de talamanca that can complement and extend existing bog and lake sediment records

changing fire regimes in the temperate rainforest region of southern chile over the last 16 000 yr abstract a high resolution macroscopic charcoal record from lago melli 42 46 s 73 33 w documents the occurrence of forest fires in the lowlands of isla grande de chiloe southern chile over the last 16 000 yr our data suggest that fire activity in this region was largely modulated by the position intensity of the southern westerlies at multi millennial time scales fire activity was infrequent or absent between 16 000 11 000 and 8500 7000 cal yr bp and was maximal between 11 000 8500 and 3000 0 cal yr bp a mosaic of valdivian north patagonian rainforest species started at 6000 cal yr bp along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr bp the modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability suggesting the onset of high frequency variability in summer precipitation regimes starting at 5500 cal yr bp because negative anomalies in summer precipitation in this region are teleconnected with modern el nino events we propose that the onset of el nino like variability at 5700 6200 cal yr bp led to a reshuffling of rainforest communities in the lowlands of isla grande de chiloe and an increase in fire activity

nonlinear dynamics of the great salt lake dimension estimation we study the possibility that variations in the volume of the great salt lake gsl a large closed basin lake may be described as a low dimensional nonlinear dynamical system there is growing evidence for structure in the recurrence patterns of climatic fluctuations that drive western united states hydrology moreover the time behavior of such lakes is generally more regular than that of the climatic forcing this suggests the possibility that an analysis of the 144 year biweekly time series of the gsl volume may shed some light on the underlying dynamics of lake variations three methods correlation dimension nearest neighbor dimension and false neighbor dimension of estimating attractor dimension are applied and compared the analysis suggests that the gsl dynamics may be described by a dimension of about four implications of such analyses relative to low frequency variations and colored noise and limitations of such analyses are discussed

asynchronous maximum advances of mountain and continental glaciers the last maximum glacier advance in many mountain ranges appears to have predated the last maximum advance of the wisconsinan continental ice sheets 20 000 years b p published evidence from widely spaced localities in north and south america europe asia and hawai i suggests that some mountain glaciers extended farther during one or more stades early in the last glaciation roughly 115 000 30 000 years b p than at its end when low global temperature and high precipitation presumably were most favorable for the growth of glaciers variations in the timing of glacier advances in different mountain ranges suggest that alpine glaciers are dependent on regional climate as well as global conditions their study might provide sensitive tests for theories of global climate change glacial deposits are often used as time markers in neotectonic and geomorphic studies and their ages sometimes are inferred from distant measurements or from proxy histories of global climate change undated geomorphic features such as moraines sharply incised streams and river terraces which commonly have been associated with the last maximum glacier advance 20 000 years b p or last deglaciation 13 000 years b p may actually be older by a factor of 2 to 4 or more conversely deposits assigned to the maximum advances of the penultimate global glaciation 130 000 years b p may actually date from early in the most recent glacial cycle and be younger by a comparable factor rates of faulting or folding estimated from displacements or deformation and the assumed ages of such geomorphic features might be too great or too small by corresponding factors

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

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

last glacial maximum equilibrium line altitude and paleo temperature reconstructions for the cordillera de merida venezuelan andes abstract the pattern and magnitude of glacier equilibrium line altitude ela lowerings in the tropics during the last glacial maximum lgm are topics of current debate in the northern tropics paleo ela data are particularly limited inhibiting the ability to make regional and large scale paleoclimatic inferences to improve these records nine paleo glaciers in the venezuelan andes were reconstructed based on field observations aerial photographs satellite imagery and high resolution digital topographic data paleo glacier equilibrium line altitudes elas were estimated using the accumulation area ratio aar and the area altitude balance ratio aabr methods during the local lgm in venezuela 22 750 to 19 960 cal yr bp elas were 850 to 1420 m lower than present local lgm temperatures were are at least 8 8 2 c cooler than today based on a combined energy and mass balance equation to account for an ela lowering this is greater than estimates using an atmospheric lapse rate calculation which yields a value of 6 4 1 c cooler the paleo glacial data from the venezuelan andes support other published records that indicate the northern tropics experienced a greater ela lowering and possibly a greater cooling than the southern hemisphere tropics during the lgm

deglacial and postglacial climate history in east central isla grande de chiloe southern chile 43 s abstract palynologic and stratigraphic data from laguna tahui 42 50 s 73 30 w indicate cool temperate and humid conditions there between 14 000 and 10 000 14c yr b p followed by warmer and drier than present conditions between 10 000 and 7000 14c yr b p and subsequent cooling and rise in precipitation over the last 5800 14c yr the thermophilous valdivian trees eucryphia cordifolia and caldcluvia paniculata reached their maximum abundance during the early holocene warm dry phase 10 000 7000 14c yr b p followed by a rise in lake levels and reexpansion of north patagonian conifers starting at 7000 and 5800 14c yr b p respectively variations in the stratigraphic and geographic distribution of temperate rainforests in southern chile suggest multimillennial trends in temperature and westerly activity which are spatially and temporally coherent with paleoclimate records from neighboring regions climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine scale mosaics of valdivian and north patagonian rainforest species in low to mid elevation communities since 5800 14c yr b p

fire and vegetation history from the coastal rain forest of the western oregon coast range high resolution charcoal and pollen analyses were used to reconstruct a 4600 yr long history of fire and vegetation near taylor lake in the wettest forests of coastal oregon today fires in these forests are rare because the season of ignition does not coincide with months of dry fuels from ca 4600 to 2700 cal yr b p fire episodes occurred at intervals of 140 30 yr while forest vegetation was dominated by disturbance adapted taxa such as alnus rubra from ca 2700 cal yr b p to the present fire episodes have become less common occurring at intervals of 240 30 yr and firesensitive forest taxa such as tsuga heterophylla and picea sitchensis have become more prominent fire occurrence during the midholocene was similar to that of the more xeric forests in the eastern coast range and suggests that summer drought was widespread after ca 2700 cal yr b p a decrease in fire episode frequency suggests that cooler conditions and possibly increased summer fog allowed the establishment of present day picea sitchensis forests within the watershed these results provide evidence that fire has been an important disturbance agent in the coast range of oregon and variations in fire frequency and climate have led to the establishment of present day forests c 2002 university of washington

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

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

coherence between the great salt lake level and the pacific quasi decadal oscillation the lake level elevation of the great salt lake gsl a large closed basin lake in the arid western united states is characterized by a pronounced quasi decadal oscillation qdo the variation of the gsl elevation is very coherent with the qdo of sea surface temperature anomalies in the tropical central pacific also known as the pacific qdo however such coherence denies any direct association between the precipitation in the gsl watershed and the pacific qdo because in a given frequency the precipitation variation always leads the gsl elevation variation therefore the precipitation variation is phase shifted from the pacific qdo this study investigates the physical mechanism forming the coherence between the gsl elevation and the pacific qdo pronounced and coherent quasi decadal signals in precipitation streamflow water vapor flux and drought conditions are found throughout the great basin recurrent atmospheric circulation patterns develop over the gulf of alaska during the warm to cool and cool to warm transition phases of the pacific qdo these circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western united states and in turn lead to the qdo in the hydrological cycle of the great basin as the gsl integrates the hydrological responses in the great basin the hydrological qdo is then transferred to the gsl elevation because the gsl elevation consistently lags the precipitation by a quarter phase about 3 yr in the quasidecadal time scale these processes take an average of 6 yr for the gsl elevation to eventually respond to the pacific qdo this creates a half phase delay of the gsl elevation from the pacific qdo thereby forming the inverse yet coherent relationship between them tree ring reconstructed precipitation records confirm that the quasi decadal signal in precipitation is a prominent feature in this region

late quaternary glaciation and equilibrium line altitudes of the mayan ice cap guatemala central america abstract the sierra los cuchumatanes 3837 m guatemala supported a plateau ice cap and valley glaciers around montana san juan 3784 m that totaled 43 km 2 in area during the last local glacial maximum former ice limits are defined by sharp crested lateral and terminal moraines that extend to elevations of 3450 m along the ice cap margin and to ca 3000 3300 m for the valley glaciers equilibrium line altitudes elas estimated using the area altitude balance ratio method for the maximum late quaternary glaciation reached as low as 3470 m for the valley glaciers and 3670 m for the mayan ice cap relative to the modern altitude of the 0 c isotherm of 4840 m we determined ela depressions of 1110 1436 m if interpreted in terms of a depression of the freezing level during maximal glaciation along the modern lapse rate of 5 3 c km 1 this ela indicates tropical highland cooling of 5 9 to 7 6 1 2 c our data support greater glacial highland cooling than at sea level implying a high tropical sensitivity to global climate changes the large magnitude of ela depression in guatemala may have been partially forced by enhanced wetness associated with southward excursions of the boreal winter polar air mass

tropical snowline changes at the last glacial maximum a global assessment snowline reconstructions from the tropics and subtropics 33 s 33 n at the last glacial maximum lgm have been extracted from a new database which provides information on glacier equilibrium line altitudes elas for over 350 glacier valley localities during the late quaternary about 60 of the intra regional variability observed change in ela ela between the lgm and today is related to headwall altitude reflecting the influence of basin morphometry e g catchment size glacier slope on the response to climate change glacier valley aspect which influences the local patterns of radiation and precipitation also causes intra regional variability in ela although this influence varies greatly between regions overall reconstructed elas are smallest in the himalayas relatively small in the southern central andes and east africa and largest in the northern andes mexico and papua new guinea estimates of the temperature change implied by the range of ela within any one region calculated using the cru 10 modern climate database are consistent with high altitude temperature changes projected from reconstructions of temperature changes at lower altitude sites based in vegetation and geochemical data in the 21 ka tropics data set farrera et al 1999 climate dynamics 15 823 856

vegetation fire and climate change in central east isla grande de chiloe 43 s since the last glacial maximum northwestern patagonia abstract we present a detailed record from lago lepue to examine vegetation climate and fire regime changes since the last glacial maximum lgm in central east isla grande de chiloe 43 s northwestern patagonia precipitation in this region correlates with the intensity of the southern westerly winds sww allowing reconstruction of past sww behavior through precipitation sensitive sensors recession from the lgm glacier margins exposed the central east sector of isla grande de chiloe by 17 800 cal yr bp followed by the immediate colonization of pioneer cold resistant herbs shrubs and rapid establishment of closed canopy nothofagus forests by 17 000 cal yr bp broad leaved temperate rainforests have persisted since then with compositional changes driven by changes in temperature hydrologic balance and disturbance regimes we detect low lake levels and enhanced fire activity between 800 2000 4000 4300 8000 11 000 and 16 100 17 800 cal yr bp implying southward shifts and or weaker sww flow that alternated with cold humid phases with muted fire activity covariation in paleoclimate trends revealed by the lago lepue record with tropical and antarctic records since the lgm suggests that the sww have been a highly dynamic component of the climate system capable of linking climate changes from low and high southern latitudes during the last glacial termination and the current interglacial

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

climate fire and vegetation between about 13 000 and 9200 14c yr b p in the chilean lake district abstract a pollen record from lago condorito 41 45 s 73 07 w shows that north patagonian rain forest taxa predominated between about 13 000 and 12 200 14c yr b p in the lowlands of southern chile near the city of puerto montt this was followed by the expansion and persistence of the conifer podocarpus nubigena between 12 200 and 9900 14c yr b p trees favored by disturbance expanded between 11 200 and 9900 14c yr b p concurrent with sharp and sustained increases of microscopic charcoal particles taxa of low elevation rain forests expanded and became more diverse in pulses centered at 9900 and 9000 14c yr b p following the disappearance of p nubigena these data suggest conditions approaching modern climate between about 13 000 and 12 200 14c yr b p the climate cooled between 12 200 and 9900 14c yr b p then quickly warmed to interglacial conditions stand replacing fires occurred near lago condorito between 11 200 and 9900 14c yr b p under cool temperate humid conditions the proximity and reported antiquity of the monte verde archeological site raise the possibility that these fires were set by human activities

late quaternary glaciation of costa rica the highest peaks of costa rica 9 15 9 36 n were glaciated during the late quaternary attesting to a significantly cooler climate in central america than today during the last local glacial maximum llgm an ice cap 35 km2 in extent covered the highest peaks of the cordillera de talamanca around cerro chirripo and around cerros de la muerte and kamuk 5 and 2 km2 of ice existed respectively in chirripo national park three moraine groups define three glacial stages the talamanca stage extends to 3040 m and represents the last local glacial maximum chirripo stage moraines reach elevations of 3300 m and talari stage moraines formed at 3300 and 3420 m former equilibrium line altitudes elas were 3500 m 3600 m and 3620 m respectively cirque floor elevations of 3260 m at cerro kamuk suggest a lower pre llgm ela radiosonde data from san jose place the modern 0 c isotherm at 5000 m which suggests a late quaternary ela depression of 1500 m which is consistent with a temperature reduction at chirripo of 8 9 c during the llgm some of this cooling may be attributable to a steeper lapse rate associated with a drier atmosphere possibly due to a more restricted position of the intertropical convergence zone decreased yearly convection or more frequent incursion of polar air masses

postglacial vegetation and fire history in the chirripo paramo of costa rica abstract pollen and charcoal analysis of a 5 6 m sediment core from lago de las morrenas 9 29 n 83 29 w 3480 m provides evidence of postglacial vegetation and fire history in the highlands of the cordillera de talamanca costa rica the site is presently surrounded by treeless paramo vegetation and apparently has been so since deglaciation about 10 000 yr b p pollen spectra suggest no pronounced changes in vegetation since ice retreat fires set by people or lightning have burned the paramo repeatedly with fire activity probably highest during the late holocene but these fires have not carved paramo from forest pollen percentages for gramineae and other paramo taxa decline upward whereas percentages for certain subalpine lower montane and lowland forest taxa increase slightly these changes may reflect the impact of prehistoric human activity or slight upslope migrations of forest taxa owing to climatic warming there is no clear evidence of higher timberlines during the mid holocene

ice age vegetation and climate of subtropical chile abstract vegetation and climate of subtropical chile over the past 50 000 yr are reconstructed from pollen spores and other microfossils contained in a 10 7 m section of lacustrine deposits of laguna de tagua tagua 34 30 s 71 10 w controlled by 14 radiocarbon age determinations five pollen assemblages covering stratigraphic zones in the section represent plants on the upland and species inhabiting the lake basin surface pollen spectra from 58 stations approximately 30 40 s form an adjunct for interpreting past vegetation and climate from the fossil record temperature semi humid woodland of southern beech nothofagus dombeyi type and podocarp prumnopitys andina was apparently established about laguna de tagua tagua during the pleistocene contrasting existing semi arid broad sclerophyllous vegetation the woodland was extensive about the lake at the time of the last glacial maximum 25 000 14 000 yr b p and earlier 43 000 34 000 yr b p pollen from the families chenopodiaceae and amaranthaceae which characterize intervals of the pleistocene centered around 33 000 and 43 000 yr b p and the holocene suggests intervening episodes of relative aridity lake level fluctuations appear to follow the late quaternary climatic pattern implied by pollen assemblage data water in the lake was relatively high during development of southern beech podocarp woodland whereas during intervals of chenopod amaranth dominance lake levels were comparatively low excess precipitation over evaporation which during the pleistocene favored development of woodland of beech and podocarp is attributed to greater storm frequency conditions were apparently governed by strengthening of atmospheric circulation in the belt of southern westerly winds in the late glacial the temperate and more humid ice age climate with limited seasonality underwent transition to a subtropical semi arid mediterranean type that identifies the postglacial fluctuations in intensity of the southern westerlies marked by latitudinal movement of the polar front can account for past vegetation changes at laguna de tagua tagua

the amplifying effects of humans on fire regimes in temperate rainforests in western patagonia abstract during european colonization and settlement of southern hemisphere temperate ecosystems historical fire regimes were often dramatically altered by either burning vast areas to create farmland or reducing fire frequencies by suppressing fires or by eliminating aboriginal populations that formerly set fires to determine the historical range of variability of wildfire and the potential human influences on wildfire activity in temperate rainforests of western patagonia we used tree rings to reconstruct fire history over the past ca 400 years over a 6 latitudinal range we examined spatiotemporal changes in fire history and compared it to ethnohistorical evidence of human activities time series of fire years were developed from fire scars at 27 sites for comparison with a priori defined periods of land use in each of six areas of homogeneous land use history we also examined the influence of climate variability to discriminate the relative roles of human ignitions and decadal scale climate variability on fire activity fires were relatively common in the forest bog habitats sampled in our study at least two centuries prior to any likely impact from euro chilean settlers implying that fires set by the indigenous peoples in this rainforest climate were much more common and sometimes even widespread than previously known our results also show that coincident with euro chilean settlement fire regimes shifted into long lasting regimes of substantially higher fire frequency however decadal scale climate variability also clearly was a driver of shifts in fire regimes and the second half of the 20th century has been a time of increased temperatures and drought throughout the region overall our findings indicate that although in both pre historic and modern times climate variability is the dominant control on years of widespread fires aboriginals and euro chilean settlers have amplified fire activity particularly during the 20th 21st centuries and shifted the region s fire regimes to new behaviors

variation in holocene el nino frequencies climate records and cultural consequences in ancient peru analysis of mollusks from archaeological sites on the north and central coasts of peru indicates that between ca 5800 and 3200 2800 cal yr b p el nino events were less frequent than today with modern rapid recurrence intervals achieved only after that time for several millennia prior to 5 8 ka el nino events had been absent or very different from today the phenomena called el nino have had severe consequences for the modern and colonial historically recorded inhabitants of peru and el nino events also influenced prehistoric cultural development the onset of el nino events at 5 8 ka correlates temporally with the beginning of monumental temple construction on the peruvian coast and the increase in el nino frequency after 3 2 2 8 ka correlates with the abandonment of monumental temples in the same region

evidence of deterministic chaos in the pulse of storm rainfall abstract rainfall data obtained by a highly sensitive raingage have been analyzed for the presence of strange attractors analysis of three storms that occurred in cambridge massachusetts revealed for each storm the presence of a low dimensional strange attractor with correlation dimension that was less than 4 the datasets consist of the discrete time series of the interarrival times of one hundredth of a millimeter rainfall amounts in all cases the number of data points in the datasets was at least 3300 which makes the evidence of determinism in storm rainfall strong

pleistocene glaciation of volcano ajusco central mexico and comparison with the standard mexican glacial sequence abstract three pleistocene glaciations and two holocene neoglacial advances occurred on volcano ajusco in central mexico lateral moraines of the oldest glaciation the marques above 3250 m are made of light gray indurated till and are extensively modified by erosion below 3200 m the till is dark red decomposed and buried beneath volcanic colluvium and tephra very strongly to strongly developed soil profiles inceptisols have formed in the marques till and in overlying colluvia and tephra large sharp crested moraines of the second glaciation the santo tomas above 3300 m are composed of pale brown firm till and are somewhat eroded by gullies below 3250 m the till is light reddish brown cemented and weathered less strongly developed soil profiles inceptisols have formed in the santo tomas till and in overlying colluvia and tephra narrow crested moraines of yellowish brown loose till of the third glaciation the albergue are uneroded weakly developed soil profiles inceptisols in the albergue till have black ash in the upper horizon two small neoglacial moraines of yellowish brown bouldery till on the cirque floor of the largest valley support weakly developed soil profiles with only a and cox horizons and no ash in the upper soil horizons radiocarbon dating of organic matter of the b horizons developed in tills volcanic ash and colluvial volcanic sand includes ages for both the soil organic residue and the humic acid fraction with differences from 140 to 660 yr the dating provides minimum ages of about 27 000 yr for the marques glaciation and about 25 000 yr for the santo tomas glaciation dates for the overlying tephra indicate a complex volcanic history for at least another 15 000 yr comparison of the ajusco glacial sequence with that on iztaccihuatl to the east suggests that the marques and santo tomas glaciations may be equivalent to the diamantes glaciation first and second advances the albergue to the alcalican glaciations and the neoglacial to the ayolotepito advances

temperate rainforest response to climate change and disturbance agents in northwestern patagonia 41 s over the last 2600 years abstract we present detailed pollen and charcoal records from lago pichilafquen 41 s to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the andean foothills of northwestern patagonia during the last 2600 yr here temperate rainforests have dominated the landscape since 2600 cal yr bp with variations ranging from cool temperate and wet north patagonian rainforests to relatively warm and summer drought resistant valdivian rainforests we interpret relatively warm dry conditions between 1900 2600 690 750 and 320 430 cal yr bp alternating with cold wet conditions between 1500 1900 750 1100 and 430 690 cal yr bp rapid deforestation and spread of plants introduced by europeans occurred at 320 and 140 cal yr bp the record includes five tephras with ages of 2130 1460 1310 1210 and 340 cal yr bp all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr we conclude that centennial scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern patagonia over the last 2600 yr within this interval local disturbance regimes altered the structure composition and dynamics of the lowland rainforest vegetation during several discrete short lived episodes

late pleistocene ecological environmental and climatic reconstruction based on megafauna stable isotopes from northwestern chilean patagonia abstract stable isotope analyses have been performed on the bioapatite 13 c 18 o and collagen 13 c 15 n of four late pleistocene south american megafaunal taxa notiomastodon platensis equus andium cf hemiauchenia paradoxa and xenarthra indet to evaluate paleoclimatic and paleoenvironmental conditions as well as paleoecological features of this time period the analyzed megafauna was found at several locations in the northwestern chilean patagonia 38 42 s 74 71 w the bioapatite 13 c values indicated the presence of c 3 vegetation ranging from forestal to woodland areas the collagen 15 n values pointed to temperate and humid ecosystems and to the consumption of shrubs trees grasses and sedges mean annual temperatures estimated from bioapatite 18 o po4 values show a similarity to modern temperatures and suggested that the megafauna under study may have lived during warm stages interstadials of the late pleistocene when comparing our results with those obtained from other south american regions we find that the diet of this particular chilean megafauna appears to have been more influenced by resource availability than by the potential dietary range of the taxa

late pleistocene climate inferred from the reconstruction of the taylor river glacier complex southern sawatch range colorado abstract ice surface topography of a late pleistocene glacier complex herein named the taylor river glacier complex trgc was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps during the last glacial maximum lgm the trgc covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and or upland ice fields equilibrium line altitudes elas for the glaciers of the trgc were estimated using the accumulation area ratio method assuming that ratio to be 0 65 0 05 elas thus derived ranged from about 3275 to 3400 m with a mean of 3340 60 m a degree day model ddm was used to infer the climatic significance of the lgm ela with no appreciable differences in precipitation with respect to modern climate the ela implies that mean summer temperatures during the lgm were 7 6 c cooler than today the ddm was also used to determine the temperatures required to maintain steady state mass balances for each of the reconstructed glaciers the required reductions in summer temperature vary little about a mean of 7 1 c the sensitivity of these results to slight 25 changes assumed for lgm precipitation are less than 0 5 c even under an lgm climate in which precipitation is assumed to be substantially different 50 than the present mean summer temperatures must be on the order of 7 0 to 8 5 c lower to depress equilibrium lines to lgm altitudes the greater sensitivity of the ela to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation

radiocarbon chronology of the last glacial maximum and its termination in northwestern patagonia abstract we examine the timing and magnitude of the last glacial maximum lgm and the last glacial termination lgt in northwestern patagonia situated in the middle latitudes of south america our data indicate that the main phase of the lgt began with abrupt warm pulses at 17 800 and 17 100 cal yrs bp accompanied by rapid establishment of evergreen temperate rainforests and extensive deglaciation of the andes within 1000 years this response shows that south american middle latitude temperatures had approached average interglacial values by 16 800 cal yrs bp the temperature rise in northwestern patagonia coincides with the beginning of major warming and glacier recession in the southern alps of new zealand at southern mid latitudes on the opposite side of the pacific ocean from this correspondence the warming that began at 17 800 cal yrs bp appears to have been widespread in middle latitudes of the southern hemisphere accounting for at least 75 of the total temperature recovery from the lgm to the holocene moreover this warming pulse is coeval with the first half of the heinrich stadial 1 hs1 in the north atlantic region hs1 featured a decline of north atlantic meridional overturning circulation a southward shift of the westerly wind belt in both hemispheres and of the intertropical convergence zone as well as a weakening of the asian monsoon along with the initiating trigger identifying the mechanisms whereby these opposing climate signals in the two polar hemispheres interacted whether through an oceanic or an atmospheric bipolar seesaw or both lies at the heart of understanding the lgt

upper quaternary vegetation dynamics and palaeoclimatology of the la chonta bog area cordillera de talamanca costa rica two pollen records from la chonta bog 2310 m altitude and one pollen record of a soil profile 2430 m altitude at a short distance from the bog permit the reconstruction of the vegetational history and climatic sequence of probably the last ca 80 000 yr of the cordillera de talamanca costa rica the three pollen records can be correlated on the basis of three radiocarbon dated horizons 39 900 yr bp 34 850 yr bp and 1390 yr bp and palynostratigraphy pollen concentration data provide indirect time control between radiocarbon dated horizons of the la chonta 2 core during the early glacial successive fluctuations of the upper forest line occurred between ca 2300 m and 2800 m altitude and the bog is alternately situated close to the subalpine rainforest belt and in the uppermontane rainforest belt during the pleniglacial ca 50 000 13 000 yr bp the forest line fell to ca 2000 m altitude and paramo vegetation surrounded the la chonta site during the late glacial the forest line shifted rapidly in ca 270 yr to 2700 2800 m altitude and the lake became surrounded by quercus dominated upper montane rainforest during a period of ca 1655 yr a distinct climate cooling by 2 2 5 c followed during ca 580 yr and the upper forest line dropped to ca 2400 m altitude this temperature rebound is probably equivalent to the younger dryas event in the depression extensive alnus carr and swamp vegetation developed finally during the holocene the forest line shifted to 3300 3500 m elevation and the lower montane rainforest reached close to ca 2300 m altitude in the later part of the holocene subparamo scrub with hypericum puya compositae escallonia and ericaceae largely replaced alnus carr and the regional and local vegetation closely resembles the presentday composition during the last glacial to holocene transition a shift of the upper forest line of ca 1400 m is inferred corresponding to a glacial temperature depression at 2300 m altitude of ca 8 c

a cooling event during the younger dryas chron in costa rica abstract a fossil pollen record from the costa rican cordillera de talamanca presents the first ams radiocarbon dated evidence of a temperature decrease during the younger dryas chron this cooling event is named la chonta stadial after the bog at 2310 m altitude located at the actual lower to upper montane forest boundary high resolution pollen analysis revealed that between 11 070 130 ams 14c age and 10 400 yr b p interpolated age vegetation comparable to present day subalpine forest occurred about 300 400 m lower than in the previous warmer interval and 600 to 700 m lower than at present time the radiocarbon dates are close to the earlier estimated ages of 11 080 10 500 yr b p for this interval based on interpolation and pollen concentration rates hooghiemstra et al 1992 the downslope shift of the upper forest line indicates an estimated temperature drop of 2 3 c during the la chonta stadial the local vegetation development is indicative of a drier climate from 10 400 to 9800 120 yr b p ams 14c age subalpine rain forest was replaced by upper montane forest a transitional period to holocene environmental conditions

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

uranium thorium chronometry of weathering rinds rock alteration rate and paleo isotopic record of weathering fluids abstract the potential of 238u 234u 230th chronometry for constraining the formation rate of weathering rinds developed on fresh rocks is assessed by analyzing a weathering rind on a basaltic clast from a 125 kyr old costa rican alluvial terrace eighteen subsamples were collected from one section of the clast by drilling cores 4 mm in diameter and 5 mm depth along two transects straddling the core rind boundary variations of major and trace element concentrations along the two transects point out a intense loss of alkaline and alkaline earth elements b conservative behaviour of elements such as zr hf and th and c external input of u into the rind without any evidence of u loss during basalt weathering in addition variations in u concentrations along the transects show that the main u th fractionation process associated with the weathering of the basaltic clast is an external input of u without addition nor loss of th in the basalt rind transition zone and that once deposited u is immobile in the weathering rind in the frame of this interpretation scheme a weathering rate of 0 5 0 2 mm kyr can be calculated for the studied clast which is consistent with geological and isotopic evidence constraining the depositional ages of the terraces in addition the variations in the 234u 238u ratio along the analysed transects as well as the increase in sr isotopic ratios within the weathering rind are best explained by temporal variation of the u activity ratios and sr isotope ratios of the soil solutions brought into the rind this work highlights how well detailed u th chronological studies of weathering rinds can 1 constrain the formation rates of weathering systems and 2 record the time variation of isotopic composition of weathering fluids

chronological database for southern chile 35 30 42 s 33000 bp to present human implications and archaeological biases abstract a chronological database of 398 dates 247 14 c dates 148 thermoluminescence dates and 3 obsidian hydration dates covering the early peopling period up to the present is presented for southern chile this information is used to assess both the paleodemography understood as human population dynamics in the past and the archaeo demography understood as the research dynamics of archaeologists in the present of that region from the early peopling up to the late archaic information is geographically and chronologically scarce and scattered the exception being the coast for this latter area it is possible to posit the existence of an occupation hiatus extending from at least around 3400 cal bp to around 2350 cal bp after this latter date a regional incremental trend is evident along with the earliest presence of ceramics as well as evidence of probable horticultural practices on the other hand the coast compared to the valley and cordillera has been the most active area for archaeological research and dating since the 1990s this database as a whole helps to expose research biases and current gaps in order to improve and expand our knowledge of the long history of southern chile s human occupation

seasonality of the enso related rainfall variability in central chile and associated circulation anomalies the seasonality of the enso rainfall relationship in central chile 308 418s and associated circulation anomalies are studied using correlation and compositing techniques during el nino episodes there is a tendency for the occurrence of above average precipitation between 308 and 358s in winter june july august jja and from 358 to 388s in late spring october november on while rainfall deficit is typically observed from around 388 to 418s during the following summer january february march jfm when el nino reaches its maximum development opposite rainfall anomalies are characteristic during la nina events this study confirms results from previous investigations indicating that enhanced blocking activity over the amundsen bellings hausen seas area in the southeastern se pacific during el nino is a key feature explaining the wet conditions in winter it is also shown that the same circulation anomaly explains the relatively wet conditions in late spring in the 358 388s region during el nino episodes furthermore the southward displacement from winter to late spring of the area with significant enso related rainfall anomalies seems associated with the seasonal migration of the boundary separating the region under the influence of the subtropical domain from the extratropical domain where the westerly regime and associated disturbances prevail blocking episodes in the se pacific during el nino seem to be part of a wave structure particularly intense during spring characterized by a sequence of positive and negative quasi barotropic height anomalies stretching southeastward from the equator toward the se pacific and back to the southwestern atlantic on the other hand anomalously dry conditions in winter and late spring during la nina are favored by long lasting and intense ridges at subtropical latitudes over the se pacific and south america resulting in a southward migration of the midlatitude storm tracks in summer a higher frequency of ridges in the southern tip of the south america during el nino episodes presumably contributes to reinforcement of the southern edge of the subtropical anticyclone in the se pacific which at this time of the year reaches its southernmost position resulting in the annual rainfall minimum on the other hand an increased frequency of cyclonic circulation anomalies crossing the southern tip of the continent is associated with relatively wet conditions in southern central chile particularly during la nina events