the mera site revisited ice age amazon in the light of new evidence abstract the mera site is the only fossil pollen and forest bed radiocarbon dated 33 26 ka bp in tropical lowland amazonia here i conclude from the study of the geology geomorphology and paleopedology of the mera site area as well as from new 14c and u th age determination of the organic layers that the pollen sections are not of last glacial age but of middle pleistocene age at least no evidence of last glacial age has been found for the mera fossil forest beds the data from the mera sites therefore should neither be used for climate reconstructions of the last glacial maximum nor for disputing the refugial theories

delta progradation and neoglaciation laguna paron cordillera blanca peru the history of holocene glaciation serves as an important record of glacier mass balance and therefore of climatic change the moraine record of holocene glaciation in the tropical andes however is fragmentary and poorly dated in contrast increases in the rate of accumulation of inorganic sediment in glacier fed lakes have been linked to periods of neoglaciation in many mountain regions the interpretation of such a record of neoglaciation from sediment cores in glacier fed lakes in the tropical andes can provide the continuity and chronologic control that is lacking in the existing moraine record unusual exposures of glacial lacustrine sediment in the cordillera blanca peru provide a rare opportunity to assess the link between climatic change glaciation and lacustrine sedimentation intentional lowering of water levels in laguna paron 9 s 77 44 w 4200 m a s l in 1985 resulted in the incision and exposure of at least 20 m of deltaic deposits at the eastern end of the lake three deltaic units can be identified horizontal topset beds steeply dipping and deformed foreset beds and horizontally laminated fine grained sediment six radiocarbon ages ranging from 1800 210 to 465 95 14c yr bp on wood indicate that the average rate of delta progradation in the late holocene has been approximately 290 m per 1000 yr the lake formed during deglaciation at least 10 000 yr ago and if such a rate of progradation of the delta had prevailed over the entire holocene then the delta would be at least three times as extensive as it is today thus the rate of delta progradation has varied significantly over the holocene we suggest that the rate of delta progradation was at least three times greater when glaciers were in advanced positions these positions are clearly delimited by neoglacial moraines which are within 1 2 km of the exposures studied and within 1 km of modern ice limits the most recent increase in the rate of delta progradation is evidenced by an increase in sedimentation rate ca 575 90 14c yr bp coincident with the onset of the little ice age copyright 2005 john wiley sons ltd

radiocarbon dates on deglaciation cordillera central northern peruvian andes abstract three radiocarbon dates along with relative dating criteria place limits on the deglaciation history of manachaque valley cordillera central ice retreated from the late glacial maximum by at least 12 100 yr b p during ice retreat numerous moraines were deposited throughout the valley glacier cover was reduced to about half that of the last glacial maximum by at least 9700 yr b p and to less than a tenth by at least 6450 yr b p because all dates are minimum the dates and field data are consistent with little or no ice remaining by early holocene no unambiguous younger dryas moraines are present

millennial scale climate variability during the last glacial period in the tropical andes millennial scale climate variation during the last glacial period is evident in many locations worldwide but it is unclear if such variation occurred in the interior of tropical south america and if so how the low latitude variation was related to its high latitude counterpart a high resolution record derived from the deep drilling of sediments on the floor of lake titicaca in the southern tropical andes is presented that shows clear evidence of millennial scale climate variation between 60 and 20 ka bp this variation is manifested by alternations of two interbedded sedimentary units the two units have distinctive sedimentary geochemical and paleobiotic properties that are controlled by the relative abundance of terrigenous or nearshore components versus pelagic components the sediments of more terrigenous or nearshore nature likely were deposited during regionally wetter climates when river transport of water and sediment was higher whereas the sediments of more pelagic character were deposited during somewhat drier climates regionally the majority of the wet periods inferred from the lake titicaca sediment record are correlated with the cold events in the greenland ice cores and north atlantic sediment cores indicating that increased intensity of the south american summer monsoon was part of near global scale climate excursions

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

lichenometric and radiocarbon dating of holocene glaciation cordillera blanca peru hfeasurements of rliizocurpoii subgenus rliizocurpo r thalli on moraines the ages of which are constrained by six radiocarbon dates two pre colombian structures and one historically dated flood dep6sit indicate that lichenometry can be used to estimate the age of stabilization of glacial deposits that date to the last c 7 ka on the west side of the cordillera blanca perlj 8 40 9040 s 77 00 77 40 w the preliminary growth curve for subgenus rtiizocurpan resembles those derived for alpine areas in alaska and colorado and can be subdivided into an initial rapid phase of growth c 0 4 mm yr that lasts c 100 years a c 500 to 1000 year long phase of decelerating growth and a period of slow linear growth 0 016 mm yr that commences after c loo0 years size clustering of subgenus riiizocurpoir thalli supports a four fold subdivision of cirque moraines at altitudes between 4200 and 4650 m the oldest moraines stabilized between c 7000 and 6ooo bp and the three younger groups between c 3350 and 1600 bp between c 1250 and 400 bp and within the last 100 years this subdivision is supported by limiting radiocarbon dates from the cordillera blanca and from several cordilleras in southern peni and indicates that the holocene glacial chronology of the cordillera blanca is the most complete heretofore recognized in the tropical andes

broad synchrony of a late glacial glacier advance and the highstand of palaeolake tauca in the bolivian altiplano the morphology and sedimentology of glacially influenced fan deltas on massifs at the margin of the southern altiplano bolivia suggest a broadly synchronous expansion of glaciers and palaeolake tauca during the late glacial interval this is shown by sedimentary successions of glacigenic glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake tauca on the flanks of cerro azanaques and cerro tunupa at altitudes of 3770 3720 m radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca 13 300 14 c yr bp glacifluvial fan deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake tauca radiocarbon dated to the interval ca 13 500 11 500 yr bp modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer wet season moisture possibly amounting to 600 mm above the modern values of 200 400 mm greater cloud cover probably depressed local temperatures and reduced the evaporation rate the consequent rise in effective annual moisture p e comfortably accommodates a palaeolake 48 50 10 3 km 2 in area and up to 100 m deep in the southern altiplano because the palaeoglacier equilibrium line altitudes rose toward the south and west like the gradient of modern precipitation totals we conclude that the increased late glacial moisture was brought by weather systems similar to those of the present but that atmospheric conditions were cloudier and cooler 1997 john wiley sons ltd

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

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

snowline depression in the tropics during the last glaciation five primary methods have been used to reconstruct pleistocene snowlines or equilibrium line altitudes elas in the tropics 23 53n 23 53s during the last glaciation but each has inherent errors that limit the accuracy of the results additional potential errorsin determiningela depression involveestimates of modernsnowline altitude datingresolution topographicreconstructionof former glaciers orographic e ects the presence of rockfall debris on glaciers and calculation of regional ela gradients eustatic sea level lowering during the last glaciation is an additional factor in uencing estimates of ela depression ela in cases where modern snowline lies above a mountain summit only a minimum value for ela can be obtained at 12 tropical sites in africa the americas to 103s latitude and paci c islands estimates of average ela range from 440 to 1400m but most fall in the range of 800 1000m mean 1 900 135m in a regional study of ela depression in the southern tropical andes 8 223s an average ela of ca 920 250m has been reported based on the assumption that glacier mass balance was controlled solely by ablation season temperature and assuming a full glacial temperature lapse rate of 63c km depression of mean annual temperature in glaciated alpine areas was ca 5 4 0 83c if adjusted for a sea level fall of 120m at the glacial maximum this value is reduced to 4 7 0 83c the gure is based on the unlikely assumption that accumulation on alpine glaciers has been invariant nevertheless it is similar to values of temperaturedepresson 5 6 43c for the last glaciationobtainedfrom variousterrestrial sites but contrasts with tropical sea surface temperature estimates that are only 1 33c cooler than present 2001 elsevier science ltd all rights reserved

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

palaeoclimates in central and south america since 18 000 bp based on pollen and lake level records abstract the last 18 ka of palaeoclimates are discussed at 3 ka intervals based on palaeoenvironmental changes shown in pollen and lake level records from central and south america a total of 61 pollen records fulfill the requirements of continuity and chronology to be used in this synthesis 8 records from tropical and subtropical lowlands in central and south america 7 records from the central american highlands 26 records from the high andes north and south of the equator 2 records from the southern subtropics and 18 from the southern andes and subantarctic islands palaeoclimatic interpretation of the pollen records is semiquantitative based on bioclimatic parameters such as e g elevational temperature gradients or latitudinal precipitation gradients that can be related to vegetation zonation additional palaeoclimatic information is obtained from lake level records derived either from dated shorelines or from the limnological history of lake sediment sections large scale palaeoclimatic comparison of the proxy data records indicates that full and late glacial climates throughout central and south america were cooler than today by about 4 to 5 c but that moisture patterns showed regional differentiation thus in both the southern subtropics and high latitudes in southern chile conditions were substantially moister than today during full and late glacial times whereas everywhere else conditions were far drier than today in terms of palaeocirculation this scenario can be interpreted as a poleward shift of the subtropical as well as the westerly circulation a scenario that has been suggested by palaeoclimatic simulations from general circulation models gcm another major palaeoclimatic aspect predicted by the gcm simulations is the suppressed early holocene summer monsoon in the southern subtropics although proxy records are few from this zone their palaeoenvironmental history during that time shows a period of aridity that would support the model one of the most controversial aspects of south american palaeoclimates concerns the existence of a younger dryas equivalent a cold period between 11 and 10 ka bp based on the existing data from south america that show a great diversity of palaeoclimatic trends the concept of an interval that is characterized by the same climatic signal as documented for the north atlantic seems too simplistic moreover at this point only very few records have been analysed in sufficient detail to yield unambiguous climatic information for the interval in question the principal outcome of this palaeoenvironmental and palaeoclimatic synthesis is the better understanding of the type and quality of data available at present and the realization of regions and periods where much more and concerted effort is needed to address problems of intra and interhemispheric palaeoclimatic correlations only then can questions concerning the mechanism of climatic change be tackled successfully

evidence of an lgm cooling in nw argentina 22 s derived from a glacier climate model abstract a climate glacier model is used to interpret late pleistocene maximum glaciations in the nw argentinan andes 22 s according to the model massive cooling combined with a moderate precipitation increase is necessary to explain maximum glacier extension even given a factor of 2 4 precipitation increase the model indicates that temperatures must have been lowered by 4 5 8 c suggesting that maximum glaciation probably occurred during full glacial times of mis 2 25 18 ka this conclusion is supported by dated proglacial lake sediments and evidence of past glacial geometry the extremely long tongues and low accumulation area ratios indicate that ablation was reduced during cold periods in agreement with the model a strong relationship exists between glacier geometry and prevailing climate contrary to the precipitation controlled late glacial 12 10 ka maximum glaciation of the arid central andes in southern peru and northern chile the glaciations on the much more humid eastern andean slope are mainly controlled by temperature and therefore reached their maximum extent during the mis 2 cold conditions

glacier recession on cerro charquini 16 s bolivia since the maximum of the little ice age 17th century cerro charquini bolivia cordillera real 5392 m a s l was selected as a site to reconstruct glacier recession since the maximum of the little ice age lia in the central andes five glaciers located on differently exposed slopes present comprehensive and well preserved morainic systems attributed to former centuries the moraines were dated by lichenometry and show a consistent organization on the different slopes the past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry lichenometric dating shows that the lia maximum occurred in the second half of the 17th century after which the glaciers have receded nearly continuously over the last decades of the 20th century 1983 97 recession rates increased by a factor of four on the northern and western slopes glaciers receded more than on the southern and eastern slopes by 78 and 65 of their lia maximum area respectively the mean equilibrium line altitude ela rose by about 160 m between the lia maximum and 1997 recession rates were analysed in terms of climatic signal suggesting that glacier recession since the lia maximum was mainly due to a change in precipitation and that the 19th century may have been drier for the 20th century a temperature rise of about 0 68c appears to be the main cause of glacier recession recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1 36 m w e a 1 if such conditions persist the small glaciers below 5300 m a s l in the cordillera real should disappear completely in the near future

late pleistocene climate conditions in the north chilean andes drawn from a climate glacier model a climate glacier model was used to reconstruct late glacial climate conditions from two case study glaciers at 18 and 22 s in the arid sub tropical western andes of northern chile the model uses i the geometry of the late glacial maximum glaciation ii modern diurnal and annual cycles amplitudes and lapse rates of the climate iii empirical statistical sublimation melt and accumulation models developed for this area and iv dynamic ice flow through two known cross sections for steady state conditions the model is validated with modern conditions and compares favorably with the glaciological features of today the mass balance model calculates the modern equilibrium line altitude at 18 s as high as 5850 m field data 5800 m whereas no glaciers exist in the fully arid southern area at 22 s despite altitudes above 6000 m and continuous permafrost for late glacial times the model results suggest a substantial increase in tropical summer precipitation ap 840 50 10 mm a 1 for the northern test area 1000 10 30 mm a 1 for the southern test area and a moderate temperature depression t 4 4 0 1 0 2 c at 18 s 3 2 0 1 c at 22 s extratropical frontal winter precipitation june september was 15 of the total annual precipitation a scenario with higher winter precipitation from the westerlies circulation belt does not yield a numerical solution which matches the observed geometry of the glaciers therefore we conclude that an equatorward displacement of the westerlies must be discarded as a possible explanation for the late pleistocene glaciation in the andes of northern chile

comment on pleistocene glaciation of volcano ajusco central mexico and comparison with the standard mexican glacial sequence by sidney e white and salvatore valastro jr

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

proglacial lake sediment records of holocene climate change in the western cordillera of peru abstract sediment records from proglacial lakes between 9 and 10 s in the western cordillera of the peruvian andes document the waxing and waning of alpine glaciers since the end of the lateglacial stage these records from the southern tropical andes provide supporting evidence that the early holocene between 12 and 8 ka was relatively warm and dry and the middle holocene between 8 and 4 ka was marked by a shift to cooler and possibly wetter conditions in certain regions leading to glacial advances although there were multiple periods of brief ice advances that interrupted the overall trend glaciers in multiple valleys generally retreated from 4 0 ka through the medieval climate anomaly 1 0 0 7 ka this late holocene pattern of ice retreat occurred during a period when lake level studies and both lacustrine and speleothem stable isotopic records indicate wetter conditions relative to the middle holocene suggesting that higher temperatures contributed to the pattern of ice retreat following this period of glacial retreat multiple proxy records suggest that the start of the little ice age 0 6 0 1 ka was a colder and wetter time throughout much of the tropical andes there appear to be two primary synoptic scale climatic controls on temperature and precipitation linked to insolation dynamics that drive changes in ice cover in the southern tropical andes during the holocene 1 the strength of the south america summer monsoon which is linked to northern hemisphere temperatures and the mean position of the intertropical convergence zone over the atlantic and 2 sea surface temperature distributions in the tropical pacific ocean and its influence on atmospheric temperature precipitation and circulation patterns

unlined trench as a falling head permeameter analytic and hydrus2d modeling versus sandbox experiment abstract an isosceles triangle in a vertical cross section of a trench is considered as a boundary from which free water in the trench seeps into a porous bed a finite initially impounded water volume vanishes from the channel and soil moisture moves in conjugation with surface water in a transient 2 d saturated unsaturated regime if capillarity is ignored and the subjacent soil is assumed to be dry before filling the channel then a wetting front propagates as a sharp interface mated with drawdown of the channel free water a lembke method of consecutive steady states is used to model the interface as a rotating straight line a zone of darcian seepage is a triangle three sides of which at each time instance are a streamline a constant piezometric head line and isobar the instantaneous hinge point of the interface demarcates a zone of imbibition from a zone of drainage of this saturated triangle mathematically a green ampt type nonlinear first order ode is obtained and explicitly integrated by separation of variables and the drawdown time t is explicitly expressed through the water depth h in the trench in a sandbox with a dune sand an experimental h t is measured in a trench having mild and steep bank slopes when h t 0 the drawdown rate increases that is attributed to an increase of the effect of capillarity for this stage riesenkampf s analytical solution for steady 2d tension saturated flow with a capillary fringe is used the analytical and experimental results are compared with those obtained by hydrus 2d numerical modeling involving a reservoir boundary condition introduced for furrow irrigation applications model performance parameters including the root mean squared error rmse mean absolute error mae coefficient of determination r2 and nash sutcliffe efficiency e showed a good agreement between the measured and simulated values of drawdown time results of the t test between the measured and simulated drawdown time showed insignificant differences at a 5 confidence interval for all the trenches p 0 05 hydrus simulations quantified the dynamics of a sinking saturated bubble under the trench isobars isotachs streamlines and loci of the stagnation points are plotted we illustrate how to use a drawdown curve h t for determination of saturated hydraulic conductivity and air entrance pressure in the vedernikov bouwer model

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

holocene hydrological reconstructions from stable isotopes and paleolimnology cordillera real bolivia multiproxy analyses of sediment cores from lago taypi chaka kkota ltck cordillera real bolivia provide a record of drier conditions following late pleistocene deglaciation culminating in pronounced aridity between 6 2 and 2 3 ka b p today ltck is a glacial fed lake that is relatively insensitive to changes in p e because it is largely bu ered from dry season draw down through the year round supply of glacial meltwater this was not the case during the middle to late holocene when glaciers were absent from the watershed lake water d18o values inferred from d18o analysis of sediment cellulose range from 12 9 to 5 3 and average 8 7 between 6 2 and 2 3 ka b p modern lake water d18o from ltck averages 14 8 which is compatible with the d18o 8 value of 14 3 for the surface sediment cellulose analyses of d18o from modern surface waters in 23 lakes that span the range from glacial fed to closed basin vary from 16 6 to 2 5 this approximates the magnitude of the down core shift in d18o 8 values in ltck during the middle to late holocene from 12 9 to 5 3 strong paleohydrologic change during the middle holocene is also evident in diatom assemblages that consist of shallow water non glacial periphytic taxa and bulk organic d13c and d15n that show increases likely resulting from degradation of lacustrine organic matter periodically exposed to subaerial conditions neoglaciation began after 2 3 ka b p as indicated by changes in the composition of the sediments lower d18o values and a return to diatom assemblages characteristic of the glacial sediments that formed during the late pleistocene collectively these data indicate that the past 2 3 ka b p have been the wettest interval during the holocene millennial scale shifts in the paleohydrologic record of ltck during the early to middle holocene conform to other regional paleoclimatic time series including lake titicaca and nevado sajama and may be driven by insolation and resultant changes in atmospheric circulation and moisture supply in contrast an apparent 1200 year lag in the onset of wetter conditions at ltck 2 3 ka b p compared to lake titicaca 3 5 ka b p provides evidence for variable sub regional hydrologic response to climate change during the middle to late holocene 2000 elsevier science ltd all rights reserved

mechanisms and variations of the paleoproductivity off northern chile 24 s 33 s during the last 40 000 years 1 a multiparameter investigation including organic carbon carbonate opal and planktic foraminifera was carried out on five sediment cores from the coastal upwelling area between 24 s and 33 s along the peru chile current to reconstruct the history of the paleoproductivity and its driving mechanisms during the last 40 000 years inferred from our data we conclude that the antarctic circumpolar current as the main nutrient source in this region mainly drives the productivity by its latitudinal shifts associated with climate change simplified its northerly position during the last glacial led to enhanced productivities and its southerly position during the holocene caused lower productivities at 33 s the paleoproductivity was additionally affected by the southern westerlies and records highest levels during the last glacial maximum lgm north of 33 s several factors e g position and strength of the south pacific anticyclone wind stress continental runoff and el nino southern oscillation events supplementary influenced upwelling and paleoproductivity where maximum values occurred prior to the lgm and during the deglaciation

comparison of terrestrial and marine temperature estimates for the past 135 kyr off southeast africa a test for gcm simulations of palaeoclimate a combined oxygen isotope planktonic foraminiferal and pollen record from the southwestern indian ocean makes possible a comparison between estimated lowland terrestrial temperatures and isotope and faunal sea surface temperatures the estimates of land and sea mean temperatures over the past 135 kyr are consistent to within 0 5 c and in all three records the maximum temperature changes between glacial and interglacial times are about 3 4 c

late quaternary glacier response to humidity changes in the arid andes of chile 18 29 s abstract today no glaciers exist between 18 30 s and 27 s even on mountains much higher than 6000 m these dry high mountain environments are very sensitive to changes in climatic boundary conditions particularly humidity since temperatures are far below freezing here we present a reconstruction of climatic changes since the last glacial maximum for the chilean dry andes of the southern hemisphere we reconstructed regional equilibrium line altitudes ela for three different moraine stages representing extensive past glaciations in this currently unglaciated region comparison of the regional pattern of the ela with modern climate conditions allows us to draw implications about the paleoclimatic conditions during the best preserved moraine stage ii glaciations in the northern as well as in the southern part of the research area our results suggest humid conditions in the northern part 18 24 s during late glacial times with strongly increased convective precipitation during austral summer the temporal coincidence of glaciers in the mountains and high lake levels on the altiplano tauca phase is evident to the south no simple shift of the westerlies is implied by our glacier reconstructions the northern limit of effective moisture for glacier formation did not shift significantly but stayed in the area of the present day northernmost glaciers of the westerlies at about 27 s but further south precipitation increased significantly accompanied by at least 2 3 c colder conditions the age of this glaciation is uncertain but probably of late glacial or last glacial maximum lgm times overall glaciers in the dry andes of south america clearly responded to large changes in the humidity not primarily the temperature regime with all its consequences on the environment hydrology vegetation etc illustrating the different regional responses to global climatic change

holocene pedogenesis along a chronotoposequence of soils from the altiplano to the cordillera real bolivian andes abstract the high mountains of central andean represents one of the most diverse and heterogeneous landscape of south america with very contrasting climates across an east west gradient that remains poorly investigated in terms of late quaternary soil formation climatic forces within a diverse pedogeomorphological framework generates a complex geoenvironmental scenario extremely susceptible to climatic changes from the high aridic bolivian altiplano to moist periglacial regions at high mountain and from these to the tropical rainforest downslope one finds soil chronosequences and different ecosystems the objective of this work was to describe and interpret chronological morphological physical chemical and mineralogical attributes of 18 profiles along a long and representative east west transect through the cordillera real at altitudes varying between 1800 and 5030 m a s l the parent material is lithologically diverse ranging from till fluvio glacial talus and loess sediments most soils show a sequence of o a c and c r with high organic carbon contents at surface and subsurface forming umbric horizons buried polycyclic organic layers are common and the 14c dating reveals a sequence of processes as one moves away from the glaciated peaks varying from 1500 to 6000 years bp the occurrence of paleo peatlands and past and present day hydromorphic areas bofedales result in widespread melanization trend with histic horizons and histosols formation in the bottomlands the relict degraded state of bofedales indicates a reduction of waterlogging in the altiplano in the late holocene resulting in increasing water shortage inceptisols occur at the high mountain sector under periglacial conditions and high slope instability and solifluxion in general soils are acid or high acid with low base saturation and high al saturation high mountain tundra soils at 5020 m are exclusively developed on moraines of resistant granodiorite and have low clay content and less mineralogical diversity soils at the western slope were affected by the last glaciation and show more diverse mineralogy with cryogenic features under dry open vegetation puna on the other hand soils at the eastern slope are associated with a greater climatic variation varying mineralogical attributes greater organic carbon mineralization and formation of organometallic complexes although most soils show influence of non crystalline minerals such as allophanes and amorphous fe oxides andic soil properties were apparently absent

late quaternary glacial chronology on nevado illimani bolivia and the implications for paleoclimatic reconstructions across the andes 10be terrestrial cosmogenic nuclide surface exposure ages from moraines on nevado illimani cordillera real bolivia suggest that glaciers retreated from moraines during the periods 15 5 13 0 ka 10 0 8 5 ka and 3 5 2 0 ka late glacial moraines at illimani are associated with an ela depression of 400 600 m which is consistent with other local reconstructions of late glacial elas in the eastern cordillera of the central andes a comparison of late glacial elas between the eastern cordillera and western cordillera indicates a marked change toward flattening of the east to west regional ela gradient this flattening is consistent with increased precipitation from the pacific during the late glacial period

late pleistocene climate and water budget of the south american altiplano abstract geomorphic evidence from the peruvian bolivian altiplano indicates that during episodes prior to 28 000 and around 12 500 11 000 yr b p lakes covered an area about six and four times as large as at present respectively within the constraints of the heat and water budget model calculations are used to estimate the precipitation rate that would allow hydrologic equilibrium on this basis it is suggested that rainfall on the altiplano during the episodes of enlarged lakes was respectively some 300 and 200 mm annum 1 larger than at present representing increases of about 75 and 50 respectively field evidence suggests that the episodes of enlarged lakes on the altiplano may have preceded or coincided with periods of maximum glaciation in the neigh boring andes in this region with high elevation of the ice equilibrium line increased precipitation is particularly conducive to glaciation

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

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

albedo changes milankovitch forcing and late quaternary climate changes in the central andes late quaternary humidity changes resulted in substantial modifications of the land surface characteristics in the altiplano of the atacama desert central andes reconstructions of surface albedo top of atmosphere toa albedo and short wave net radiation in the andes of northern chile for 20 14 10 7 and 0 ka suggest that surface and toa albedo increased substantially during periods of relatively humid environmental conditions i e with large palaeolakes glaciers and dense vegetation the decrease of summer shortwave net radiation and seasonality during the late glacial early holocene humid phase 14 to 10 ka due to earth s surface and atmospheric characteristics added to the effect of orbitally driven negative deviations of southern hemisphere austral summer insolation and minimum seasonality at 20 s therefore in situ radiative forcing is in contrast to the northern hemisphere tropics not a suitable explanation for enhanced convective precipitation and ultimately humid climatic conditions our results suggest that late quaternary humidity changes on the altiplano reflect a collective response to 1 environmental changes in the source area of the moisture e g re expansion of the rain forest and increased release of latent heat over amazonia and the chaco warm sea surface temperatures in the e pacific and 2 large scale circulation patterns and wave structures in the upper troposphere strength and position of the bolivian high divergent flow stimulating convection over the altiplano or that they even reflect a response to 3 interhemispherical teleconnections

late glacial and late holocene moraines in the cerros cuchpanga central peru abstract small ice fields on the western cordillera northeast of lima were expanded to three times their present size in the recent past and the regional snow line was probably about 100 m lower than it is today outwash from the expanded glaciers formed deltas of silt in valley bottom lakes when the ice lobes retreated the reduced outwash was trapped behind recessional moraines and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools the delta surfaces then became covered with peat and radiocarbon dates for the base of the peat 1100 70 and 430 70 yr b p for two different deltas indicate that the maximum ice advance was older than those dates and thus older than the little ice age of many north temperate regions much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys which had previously been inundated by the cordilleran ice field the cordilleran deglaciation and this expansion of local glaciers probably occurred between 12 000 and 10 000 yr ago on the basis of slightly contradictory radiocarbon dates

reconstruction of glacier equilibrium line altitudes for the last glacial maximum on the high plain of bogota eastern cordillera colombia climatic and topographic implications the high plain of bogotain the andes of colombia provides an exceptionally detailed record of glaciation a two stage last glacial maximum lgm is noted in bogota the older stage max presents an opportunity to reconstruct individual valley glaciers and explore spatial patterns well mapped geomorphic features on topographic base maps permit the reconstruction of 23 palaeo glacier surfaces glacier extent varies across the region with lower altitudes reached farther to the east equilibrium line altitudes elas are reconstructed using the area altitude balance ratio aabr method with brs in three groups reflecting the w e gradient in glacier extent and selected by mini mising variation from group means average lgm ela for all palaeoglaciers is 3488 m with a stan dard deviation of 182 m the average lowering in ela from lgm to modern of ca 1300 m is best explained by a considerable drop in temperature significant intra regional variance in lgm ela can be ascribed to topography and its influence on precipitation and or glacier form with lower headwall elevations being correlated to larger accumulation areas copyright 2005 john wiley sons ltd

glacier readvances in the andes at 12 500 10 000 yr bp implications for mechanism of late glacial climatic change radiocarbon dates from two sites in the andes ecuador and peru confirm that glaciers culminated a readvance after 11 000 yr bp a moraine stage equivalent in altitude and position relative to existing glaciers is present in most glacierized ranges but its age is equivocal broadly limiting dates from colombia and peru suggest that the stage may be late glacial as it is younger than 12100 yr bp but formed before the early holocene in southern chile a comparable moraine stage is older than ca 9100 yr bp andean glaciers appear to have advanced at least twice during the late glacial interval glacier reconstruction from these moraine limits suggests depression of the equilibrium line altitude by at least 300 400 m in the northern and north central andes and possibly less than this farther south late glacial climatic change occurred globally and possibly reflects north atlantic temperature and circulation changes forced by deglaciation of the northern ice sheets migrations north and south of the atlantic polar front and the switching off and on of a dust pump in low midlatitudes

quantifying denudation rates and sediment storage on the eastern altiplano bolivia using cosmogenic 10be 26al and in situ 14c abstract denudation processes and sediment transfer are investigated in a high elevation low relief environment eastern altiplano bolivia using 10be 26al and in situ 14c analysis in fluvial sediments concentrations of the long lived nuclides 10be and 26al yield consistently low catchment wide denudation rates of 3 29 mm ky 1 integrating over 21 194 ky which reflect the low geomorphic gradients and the discontinuity of fluvial transport along the eastern altiplano margin no significant correlation is recorded between denudation rates of individual catchments and morphological basin parameters slope area elevation this is attributed to the overall little variability in morphology the agreement between the denudation rates and published modern sediment discharge data suggests steady landscape evolution of the eastern altiplano from the latest pleistocene until today while 10be and 26al provide long term estimates on sediment production in situ cosmogenic 14c is used to trace short term sediment storage in situ 14c concentrations are comparatively low indicating that 14c decayed during alluvial storage over at least the past 11 20 ky we assume storage at shallow depth 2 m and consider the influence of soil mantled hillslopes on the in situ 14c concentration our results illustrate the importance of sediment storage even over short distances and demonstrate the potential of in situ 14c to study sediment routing and transfer times within drainage systems however this study also demonstrates that the long lived 10be and 26al nuclides can provide adequate estimates on long term denudation rates even if sediment transport is not fast but interrupted by several thousands of years of storage

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

a late holocene 2600 bp glacial advance in the south central andes 29 s northern chile radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late holocene 2600 bp readvance of glaciers in the western part of the arid andes at 29 s the glacier in the encierro valley northern chile reached about 60 of its late pleistocene extent the equilibrium line altitude ela during this advance remained between 4250 and 4500 m which is above the modern 0 c isotherm of the free atmosphere during summer it is suggested that given the specific climate at high elevations in the extremely arid andes a substantial increase in effective moisture is sufficient to explain this advance whereas no significant temperature depression was needed this compares favourably with the regional late holocene climatic history when lake levels were higher and effective moisture greater than today between 3000 and 1800 bp judging from regional palaeodata we suggest that this late holocene humid spell was most likely related to increased westerly moisture sources from the pacific

palaeomagnetic stratigraphy of pliocene continental deposits of the bolivian altiplano abstract fluvio lacustrine post miocene deposits of the bolivian altiplano have been sampled in 400 m of section in the la paz and avo avo basins in order to provide a magnetostratigraphic scheme for chronostratigraphic interpretations stable characteristics components were isolated after stepwise af or thermal demagnetizations the directions of cleaned magnetization were compared to the normal and reverse dipole field directions at the site the plot of the mean directions calculated for each stratigraphic level define successive magnetozones which can be identified on the standard geomagnetic polarity scale with the help of the k ar ages obtained on tuff layers the deposition of the middle and upper part of the la paz formation covers the gauss epoch the gauss matuyama 2 48 ma and the gilbert gauss 3 4 ma limits are located in the top and the middle of the formation the occurrence of the first glacial interglacial oscillation can be placed in the early matuyama ca 2 2 ma in agreement with the oxygen isotopic record from the equatorial ocean

holocene paleohydrology of the tropical andes from lake records two century scale time series in northern bolivia constrain the ages of abrupt changes in the physical geochemical and biological characteristics of sediments obtained from lakes that formed during deglaciation from the late pleistocene glacial maximum the watersheds of laguna viscachani 16 12 s 68 07 w 3780 m and lago taypi chaka kkota 16 13 s 68 21 w 4300 m located on the eastern and western slopes of the cordillera real respectively contain small cirque glaciers a high resolution chronology of the lake sediments is provided by 23 ams14c dates of discrete macrofossils late pleistocene glaciers retreated rapidly exposing the lake basins between 10 700 and 970014c yr b p the sedimentary facies suggest that after 890014c yr b p glaciers were absent from the watersheds and remained so during the middle holocene an increase in the precipitation evaporation balance is indicated above unconformities dated to 230014c yr b p in both lago taypi chaka kkota and laguna viscachani an abrupt increase in sediment accumulation rates after 140014c yr b p signals the onset of neoglaciation a possible link exists between the observed millennial scale shifts in the regional precipitation evaporation balance and seasonal shifts in tropical insolation

subdivision of glacial deposits in southeastern peru based on pedogenic development and radiometric ages the cordillera vilcanota and quelccaya ice cap region of southern peru 13 30 14 00 s 70 40 71 25 w contains a detailed record of late quaternary glaciation in the tropical andes quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history secondary iron and clay increase linearly in quelccaya soils and clay accumulates at a linear rate in vilcanota soils which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils in contrast logarithmic rates of iron buildup in soils in the cordillera vilcanota reflect chemical weathering high concentrations of secondary iron in vilcanota tills may mask the role of eolian input to these soils soil age estimates from extrapolation of field and laboratory data suggest that the most extensive late quaternary glaciation occurred 70 000 yr b p this provides one of the first semiquantitative age estimates for maximum ice extent in southern peru and is supported by a minimum limiting age of 41 520 14c yr b p a late glacial readvance culminated 16 650 cal yr b p in the cordillera vilcanota following rapid deglaciation of unknown extent an advance of the quelccaya ice cap occurred between 13 090 and 12 800 cal yr b p which coincides approximately with the onset of the younger dryas cooling in the north atlantic region moraines deposited 394 cal yr b p in the cordillera vilcanota and 300 cal yr b p on the west side of the quelccaya ice cap correlate with little ice age moraines of other regions

early warming of tropical south america at the last glacial interglacial transition glaciation in the humid tropical andes is a sensitive indicator of mean annual temperature here we present sedimentological data from lakes beyond the glacial limit in the tropical andes indicating that deglaciation from the last glacial maximum led substantial warming at high northern latitudes deglaciation from glacial maximum positions at lake titicaca peru bolivia 16 s and lake junin peru 11 s occurred 22 000 to 19 500 calendar years before the present several thousand years before the bolling allerod warming of the northern hemisphere and deglaciation of the sierra nevada united states 36 5 to 38 n the tropical andes deglaciated while climatic conditions remained regionally wet which reflects the dominant control of mean annual temperature on tropical glaciation

late quaternary paleosol sediment sequences and landscape evolution along the andean piedmont bolivian chaco abstract as part of the bolivian chaco the andean piedmont is situated in the transitional zone between the tropical humid climate regime to the north amazonia and the subtropical semiarid regime to the south gran chaco in this zone which is sensitive to climatic changes late quaternary landscape and climate history was reconstructed based on detailed sedimentological pedological and geochemical analyses of paleosol sediment sequences along the andean piedmont the determination of characteristic lithofacies allowed correlation between the investigated profiles and their interpretation in terms of paleoenvironmental conditions i e geomorphic stability soil formation or geomorphic activity fluvial or fluvio aeolian sedimentation erosion etc coarse fluvial deposits gravels sands form the base of the investigated profiles and have likely been deposited in a braided river environment with low vegetation cover and intensive discharge events before and during the last glacial maximum well developed paleosols formed in the upper part of these sediments during the lateglacial documenting geomorphic stability high vegetation cover and wet conditions overlying palustrine sediments dated to the early holocene indicate a dramatic change in seasonality i e increased winter precipitation and decreased summer precipitation subsequent erosion followed by accumulation of fluvial and fluvio aeolian sands points to much drier conditions during the mid holocene since 2 9 cal ka bp soil formation indicates a return to geomorphic stability and wetter conditions characteristic of the present day climate interrupted by short arid intervals

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

late quaternary climate history of the bolivian altiplano abstract sediment cores and outcrops from the bolivian altiplano are used to interpret late pleistocene holocene paleoclimates and lake evolution based on a multi proxy approach ostracod content palynology sedimentology and radiocarbon dating despite the different sensitivity of the lacustrine basins to environmental changes interpreting the records in terms of paleohydrology climate and more especially timing of events is difficult notwithstanding these problems lake titicaca in the north and lake pocoyu lake poopo salars of coipasa and uyuni in the south reveal a similar evolution in general trends through the course of time during the minchin phase until 30 26 kyr bp the altiplano was wetter than present the last glacial maximum ca 26 14 kyr bp marked by cooler drier conditions was followed by a return to a wetter climate interrupted by short arid events between ca 14 and 10 5 kyr bp another cycle of aridity between 10 5 and 8 kyr bp took place abruptly just after the humid tauca phase the mid holocene is interpreted as climatically unstable with an alternation of humid and dry episodes since 3 9 kyr bp wetter conditions have persisted and intensified to the present the data are interpreted in terms of changes in inter tropical convergence zone extension summer precipitation and in polar air mass intensity winter precipitation

paleoenvironments and human occupation in late glacial panama the first pollen and phytolith data covering the entire pleistocene holocene transition from the lowlands of the central american isthmus indicate that the forests of late glacial panama at an altitude of 650 m resembled those currently found at ca 1500 1800 m a temperature depression of ca 5 c and reduced precipitation evaporation ratios in the late glacial period are suggested forest composition from ca 14 000 to 10 500 yr b p although primarily montane in character contained a low biomass of species today segregated in lowland forests and hence a floral assemblage with no modern analog the sudden appearance of carbon and burnt weedy plant material at ca 11 000 yr b p is attributed to the earliest human impact yet recorded from tropical america and may perhaps have been associated with the first human occupation of the region

comparing reconstructed pleistocene equilibrium line altitudes in the tropical andes of central peru glacier equilibrium line altitude ela and the difference between modern and palaeo ela can be interpreted as a proxy for climate change one issue in ela reconstruction is that different methods of ela reconstruction may produce a range of results for the same palaeoglacier when a range of methods is used to reconstruct elas across a region resulting variations may be related to the method rather than the past climate palaeoclimatic interpretation of elas that were reconstructed by different methods may prompt spurious inferences if the ela range is the result of methodological differences rather than climatic variation we address the relationship and degree of variation between methods by comparing terminus to headwall altitude ratio thar accumulation area ratio aar and accumulation area balance ratio aabr methods for palaeoglaciers in four valleys in the tropical andes valleys in the eastern cordillera of the peruvian andes bordering the junin plain 11 s 76 w ca 4100 m a s l are presently ice free but were glaciated repeatedly during the pleistocene we use a combination of 90 m shuttle radar topography mission srtm data 15 m advanced spaceborne thermal emission and reflection radiometer aster data and 1 25 000 topographic maps to reconstruct elas within each of three groups of moraines map based thar and aabr estimates of ela tend to be highest followed by dem derived thar elas with aar reconstructed elas somewhat lower in this region ela estimates for the local last glacial max imum llgm range from ca 4250 to 4570 m a s l with elas of ca 220 to 550 m depending on valley and method used within individual valleys elas for the same palaeoglaciers calculated by different methods vary by 100 m elas of the llgm glaciers and those of the largest glaciers to occupy the junin valleys 65 ka are not markedly different from each other regardless of the method used in their calculation which is largely a reflection of the valley hypsometry in the region our analysis suggests relatively low decreases in temperature during glacial periods in the region ca 2 5 1 c copyright 2005 john wiley sons ltd

comparison of late pleistocene and modern glacier extents in central nepal based on digital elevation data and satellite imagery abstract late pleistocene and modern ice extents in central nepal are compared to estimate equilibrium line altitude ela depressions new techniques are used for determining the former extent of glaciers based on quantitative objective geomorphic analyses of a 90 m resolution digital elevation model dem for every link of the drainage network valley form is classified as glacial or fluvial based on cross valley shape and slope statistics down valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley landsat multispectral scanner imagery for the same region is used to map current glacier extents for both full glacial and modern cases elas are computed from the glacier limits using the dem and a toe to headwall altitude ratio of 0 5 computed ela depressions range from 100 900 m with a modal value of 650 m and a mean of 500 m values consistent with previously published estimates for the central himalaya but markedly smaller than estimates for many other regions we suggest that this reflects reduced precipitation rather than a small temperature depression consistent with other evidence for a weaker monsoon under full glacial conditions

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

late pleistocene snowline fluctuations at nevado coropuna 15 s southern peruvian andes deposits preserved on peaks in the southern peruvian andes are evidence for past glacial fluctuations and therefore serve as a record of both the timing and magnitude of past climate change moraines corresponding to the last major expansion of ice on nevado coropuna date to 20 25 ka during the last glacial maximum we reconstructed the snowline at coropuna for this period using a combined geomorphic numeric approach to provide a first order estimate of the magnitude of late pleistocene climate change our reconstructions show that snowline was approximately 550 770m lower during the last glacial maximum than during the late holocene maximum which ended in the 19 th century and 750m lower than today while these values are similar to data from nearby nevado solimana reconstructions from the neighbouring peak of nevado firura reveal a smaller snowline depression suggesting the glacial response to climate forcing in the tropics is strongly influenced by non climatic factors these data constitute some of the first directly dated palaeo snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical andes was similar to late pleistocene events at higher latitudes copyright 2011 john wiley sons ltd

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

recent glacial history and paleoclimate of the peruvian bolivian andes abstract radiocarbon dates of glacial deposits in the peruvian bolivian andes are used to place the observed phases of glaciation in a common chronological framework the climatic conditions that may determine modern snowline are examined in order to understand the types of climatic forcing to which glaciers may have been sensitive in the past also considered are independent proxies of climatic change including pollen sequences lake level history and ice core data late pleistocene glaciation in central peru between 24 ka and 12 ka bp appears to have occurred during colder and perhaps drier conditions in bolivia a glacial maximum is dated to phases of late holocene glaciation in peru that correspond in part to the little ice age in the northern hemisphere appear to have been caused by a combination of colder and wetter conditions an overall warming trend may be the cause for the retreat of many glaciers in the region since the mid 19th century

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of

regional synthesis of last glacial maximum snowlines in the tropical andes south america the modern glaciers of the tropical andes are a small remnant of the ice that occupied the mountain chain during past glacial periods estimates of local last glacial maximum lgm snowline depression range from low e g 200 300 m in the junin region peru through intermediate 600 m at laguna kollpa kkota in bolivia to high e g 1100 1350 m in the cordillera oriental peru although a considerable body of work on paleosnowlines exists for the tropical andes absolute dating is lacking for most sites moraines that have been reliably dated to 21 cal kyr bp have been identified at few locations in the tropical andes more commonly but still rarely moraines can be bracketed between about 10 14 c kyr 11 5 cal kyr bp and 30 14 c kyr bp typically only minimum limiting ages for glacial retreat are available cosmogenic dating of erratics on moraines may be able to provide absolute dating with sufficient accuracy to identify deposits of the local lgm ongoing work using cosmogenic 10 be and 26 al in peru and bolivia suggests that the local lgm may have occurred prior to 21 cal kyr bp r 2005 elsevier ltd and inqua all rights reserved

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

reflections on cohmap cohmap cooperative holocene mapping project had its start in the 1970s with the intent to compare atmospheric general circulation models with quantitative palaeoclimatic reconstructions based on stratigraphic pollen analysis as the sophistication of the models increased and as additional palaeoclimatic indicators lake levels marine microfossils were incorporated in the reconstructions the programme expanded to global coverage through the participation of numerous collaborators the carefully nurtured dual approach of modelling and data analysis was strengthened by continued testing of one against the other with emphasis on interdisciplinary understanding fostered by workshops with the development of new computer models that have higher spatial resolution and improved boundary conditions and with diversification and enlargement of the geographic and temporal coverage of field and analytical data substantial refinements can be anticipated in the understanding of global climatic changes since the

fluctuations of glaciers in the tropical andes over the last millennium and palaeoclimatic implications a review abstract the aim of this paper is to document the evolution of glaciers in the tropical andes between 10 n and 16 s for the last millennium based on moraines dated by lichenometry and radiocarbon lake sediment records and historical documents viewed collectively several glacial advances occurred synchronously the first advance is dated around ad 1200 1350 the maximum glacial extent mge defined as the furthest down valley extent recorded synchronously by the majority of glaciers occurred around 1630 1680 in bolivia and peru the outer tropics and around ad 1730 in ecuador colombia and venezuela the inner tropics subsequently during the 18th and 19th centuries glaciers retreated continuously with only minor synchronous readvances in the outer tropics minor glacial advances occurred around 1730 1760 1800 1850 and 1870 in the inner tropics synchronous minor advances occurred around 1760 1820 and 1880 between the mge and the early 20th century glaciers lost about 30 of their total length the retreat was slow between the 17th and 18th centuries but then became more marked use of the accumulation area ratio aar method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude ela of about 300 m from the mge onward palaeoclimatic hypotheses based on glaciological models run in different countries suggest a cool and humid period in the 16 18th centuries followed by a colder and drier period in the 19th century the reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before here quantitative estimates are proposed to explain the evolution of the glaciers in venezuela results indicate for the period 1250 1820 that mean air temperatures were 3 2 1 4 c cooler and precipitation was about 22 higher than at present in ecuador temperatures of between 0 8 and 1 1 c lower than today and between 25 and 35 higher accumulation than today appear to have occurred in the 18th century followed by a short drier but colder period at the beginning of the 19th century in bolivia the mge could be a consequence of a decrease in temperature of 1 1 to 1 2 c and a 20 to 30 increase in accumulation or an increase in cloudiness of about 1 2 10 we discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance dating uncertainties however have made the role of volcanism in glacier fluctuations impossible to determine finally we discuss the relationships between enso and glacier fluctuations in recent centuries which do not match directly with current knowledge of modern teleconnections between tropical pacific ssts and variations in glacier mass balance

rates of deglaciation during the last glaciation and holocene in the cordillera vilcanota quelccaya ice cap region southeastern peru abstract moraine chronology is combined with digital topography to model deglacial rates of paleoglacier volumes in both the huancane valley on the west side of the quelccaya ice cap and the upismayo valley on the northwest side of the cordillera vilcanota the fastest rates of deglaciation 39 10 5 to 114 10 5 km3 yr 1 and 112 10 5 to 247 10 5 km3 yr 1 for each valley respectively were calculated for the most recent paleoglaciers corresponding to the last few centuries these results are consistent with observations in the venezuelan andes showing high rates of deglaciation since the little ice age these rates also fall within the range of 20th century rates of deglaciation measured on the quelccaya ice cap 29 10 5 to 220 10 5 km3 yr 1 brecher and thompson 1993 thompson 2000 these results imply that rates of deglaciation may fluctuate significantly over time and that high rates of deglaciation may not be exclusive to the late 20th century equilibrium line altitude ela depressions for the ice volumes of the last glaciation modeled here were computed as 230 m for the quelccaya ice cap and 170 m for the cordillera vilcanota maximum ela depressions are lower than previously published

petrogenesis of mid proterozoic granitic magmas examples from central and west texas abstract circa 1 1 ga granitic magmatism in texas was manifested as two compositional groups 1 the 1 12 ga red bluff granitic suite in west texas and 2 1 12 1 07 ga granites of the llano uplift of central texas both suites share some characteristics typical of anorogenic granites e g potassium and iron rich bulk compositions fe rich hydrous silicates emplacement conditions involving low oxygen fugacities and water contents and exhibit similar isotopic characteristics however rock associations mineral chemistries and trace element compositions of the two suites are distinct and no single petrogenetic model for the two suites is possible the red bluff granitic suite includes cogenetic syenites quartz syenites and granites transitional ferrobasaltic dikes are also present in contrast syenitic and mafic rocks are not associated with the llano granites the llano granites contain biotite and calcic amphibole with lower fe fe mg ratios compared to those occurring in the red bluff rocks alkali amphiboles e g arfvedsonite occur in the red bluff granites but not in the llano granites the red bluff granitoids are characterized by high feo t mgo ratios high na2o k2o high concentrations of hfse and rare earth elements ree and other features typical of a type within plate granites e g the pikes peak batholith ppb the llano granites are geochemically distinct with generally higher p2o5 and sr lower na2o feo t mgo zr y and ree and much lower ta and nb nd isotopic data overlap between the two granite suites and have juvenile signatures however trace element data suggest different petrogeneses for the two suites the red bluff suite is interpreted as having a direct derivation from mantle sources via extended fractional crystallization of basaltic parental magmas with minor crustal assimilation the llano granites appear to represent anatectic melts derived from slightly older juvenile crustal sources some melts underwent fractional crystallization controlled by feldspar and accessory minerals the petrology and geochemistry of 1 1 ga granites in texas indicate that they should not be considered as part of a single anorogenic magmatic event the red bluff granitic suite was emplaced into a shelf sequence north of the grenville front within a broad zone characterized by mild extension in contrast llano granites are late stage intrusions emplaced into multiply deformed and metamorphosed crust south of the grenville front during or after waning stages of grenville orogenesis

glaciation in the andes during the lateglacial and holocene this review updates the chronology of andean glaciation during the lateglacial and the holocene from the numerous articles and reviews published over the past three decades the andes which include some of the world s wettest and driest mountainous regions offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68 degree meridional transect the geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad scale atmospheric circulation and consequent regional moisture patterns glaciers in the tropical andes and in the mid latitude andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical andes broad scale temporal and spatial patterns of glaciation during the lateglacial are apparent in the southernmost andes the lateglacial chronology appears to have a strong antarctic signature with the best dated moraines correlating closely with the antarctic cold reversal the southernmost andes do not appear to have experienced a significant ice advance coeval with the younger dryas yd climatic reversal at the other end of the andes from w 0t o 9 n a stronger yd connection may exist but critical stratigraphic and geochronologic work is required before a yd ice advance can be fully demonstrated in the central andes of peru well dated moraines record a significant ice readvance at the onset of the yd but ice was retreating during much of the remaining yd interval the spatial temporal pattern of holocene glaciation exhibits tantalizing but incomplete evidence for an early to mid holocene ice advance s in many regions but not in the arid subtropical andes where moraines deposited during or slightly prior to the little ice age lia record the most extensive advance of the holocene in many regions there is strong evidence for neoglacial advances in the interval between 1 0 and 2 5 ka moraines that correlate with the lia of the northern hemisphere are seen in all presently glacierized mountain ranges most of these date to within the past 450 years outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the lia priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies for the lateglacial these gaps include the arid regions of northern chile and argentina the southern peruvian andes between 11 5 and 13 5 s and the andes of northern peru and

moraine preservation and boulder erosion in the tropical andes interpreting old surface exposure ages in glaciated valleys cosmogenic dating provides a long awaited means of directly dating glacial deposits that pre date the last glacial cycle although the potential benefits of longer chronologies are obvious the greater uncertainty associated with older cosmogenic ages may be less readily apparent we illus trate the challenges of developing and interpreting a long chronology using our data from the peruvian andes we used surface exposure dating with cosmogenic radionuclides crns 10 be and 26 al to date 140 boulders on moraines in valleys bordering the junin plain 11 s 76 w in central peru our chronology spans multiple glacial cycles and includes exposure ages greater than 1 million years which indicate that long term rates of boulder erosion have been very low interpreting the chronology of moraines for glaciations that predate the last glacial cycle is complicated by the need to consider boulder erosion and exhumation surface uplift and inheritance of crns from pre vious exposure intervals as an example we recalculate exposure ages using our boulder erosion rates 0 3 0 5 metres per million years and estimated surface uplift rates to emphasise both the chal lenges involved in interpreting old surface exposure ages and the value of chronological data even with large uncertainties when reconstructing the palaeoclimate of a region copyright 2005 john wiley sons ltd

late quaternary glacier advances and palaeolake highstands in the bolivian altiplano abstract recent study of late quaternary moraines and pluvio lacustrine features around the southern altiplano of bolivia suggests they developed more or less synchronously during the last glacial cycle the stratigraphy of lacustrine and deltaic sediments can be linked to outwash and moraines on glaciated massifs e g cerro condor iquina cerro azanaques and cerro tunupa which border the poopo uyuni and coipasa salt basins uranium series and radiometric dating of lake carbonates by previous workers suggests that major palaeolakes developed during the intervals 72 68 ka bp 44 34 ka bp and 15 4 9 5 ka bp radiocarbon dating of peat associated with glacifluvial and glacial sediments indicates that the most extensive glacier advance of the later part of the last glacial cycle culminated after 13 3 ka bp and that a smaller readvance may have occurred between 12 and 10 ka bp as the highest palaeolake stand the tauca phase has been dated to ca 13 8 ka bp it is concluded that increased effective moisture and cool climatic conditions during the interval ca 14 13 ka bp forced the simultaneous expansion of glaciers and lakes in and around the southern altiplano a palaeolake may have been present on the southern altiplano for much of the interval ca 15 4 9 5 ka bp its surface reaching different levels at different times

late quaternary lowstands of lake titicaca evidence from high resolution seismic data abstract approximately 600 km of high resolution seismic reflection data were collected to investigate the late quaternary stratigraphic development of lake titicaca the focus of this report is on two seismic sequence boundaries which are interpreted as erosional surfaces formed at times of low lake level the younger erosional surface occurs as much as 90 m below the present lake level and up to 8 m below the present sediment water interface this erosional surface is interpreted to be coeval with a well documented early to mid holocene lowstand dated between 8000 and 3600 cal yr bp an earlier and previously unknown erosional surface occurs at a sub bottom depth of approximately 30 m and as much as 240 m below the present lake level which implies a major late pleistocene lowstand of lake titicaca by extrapolation of sedimentation rates from the upper 14 m of sediment we estimate the age of this older lowstand at 90 000 cal yr bp both lowstands of lake titicaca indicated by the seismic data are likely to have been a response to climatic change in the region

climate variation and the rise and fall of an andean civilization paleolimnological and archaeological records that span 3500 years from lake titicaca and the surrounding bolivian peruvian altiplano demonstrate that the emergence of agriculture ca 1500 b c and the collapse of the tiwanaku civilization ca a d 1100 coincided with periods of abrupt profound climate change the timing and magnitude of climate changes are inferred from stratigraphic evidence of lake level variation recorded in14c dated lake sediment cores paleo lake levels provide estimates of drainage basin water balance archaeological evidence establishes spatial and temporal patterns of agricultural field use and abandonment prior to 1500 b c aridity in the altiplano precluded intensive agriculture during a wetter period from 1500 b c to a d 1100 the tiwanaku civilization and its immediate predecessors developed specialized agricultural methods that stimulated population growth and sustained large human settlements a prolonged drier period ca a d 1100 1400 caused declining agricultural production field abandonment and cultural collapse