fifty thousand year vegetation and climate history of noel kempff mercado national park bolivian amazon abstract pollen and charcoal records from two large shallow lakes reveal that throughout most of the past 50 000 yr noel kempff mercado national park in northeastern lowland bolivia southwestern amazon basin was predominantly covered by savannas and seasonally dry semideciduous forests lowered atmospheric co 2 concentrations in combination with a longer dry season caused expansion of dry forests and savannas during the last glacial period especially at the last glacial maximum these ecosystems persisted until the mid holocene although they underwent significant species reassortment forest communities containing a mixture of evergreen and semideciduous species began to expand between 6000 and 3000 14 c yr b p humid evergreen rain forests expanded to cover most of the area within the past 2000 14 c yr b p coincident with a reduction in fire frequencies comparisons between modern pollen spectra and vegetation reveal that the moraceae dominated rain forest pollen spectra likely have a regional source area at least 2 3 km beyond the lake shore whereas the grass and sedge dominated savanna pollen spectra likely have a predominantly local source area the holocene vegetation changes are consistent with independent paleoprecipitation records from the bolivian altiplano and paleovegetation records from other parts of southwestern amazonia the progressive expansion in rain forests through the holocene can be largely attributed to enhanced convective activity over amazonia due to greater seasonality of insolation in the southern hemisphere tropics driven by the precession cycle according to the milankovitch astronomical theory

impact of tropical sst on stratospheric planetary waves in the southern hemisphere abstractthe impact of tropical sea surface temperature sst on stratospheric planetary waves in the southern hemisphere sh is investigated in austral spring using observed sst and reanalysis data for the past three decades maximum covariance analysis indicates that the tropical sst and the sh stratospheric planetary wave activity are primarily coupled through two modes the leading two modes show the la nina like and the central pacific el nino like sst anomalies in their positive polarities respectively which each are related to enhanced stratospheric planetary wave activity these two modes also introduce phase shifts to the stratospheric stationary planetary waves a westward shift is seen for la nina and an eastward shift for warm sst anomalies is seen in the central pacific the eliassen palm fluxes associated with the two modes indicate that the anomalous stratospheric wave activity originates in the troposphere and propagates upward over the mid high latitudes so that the linkages between tr

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

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

a reevaluation of the evidence for a younger dryas climatic reversal in the tropical andes abstract a review of the evidence for a younger dryas equivalent climatic reversal in the tropical andes shows that a number of hypotheses need to be reassessed assumptions of the el abra cold and humid phase in colombia are compromised by insufficient dating control periods of glacier advance in peru and bolivia lack sufficient dating control to be correlated with the european younger dryas only glaciers on the quelccaya ice cap in peru may have advanced shortly before the onset of the european climatic reversal but even there a correlation is questionable a late glacial advance in the chimborazo area in ecuador is considerably older than previously suggested the same glacier advance has been dated to earlier than 12 000 bp in other areas of ecuador the emerging picture suggests two phases of glacier advances in the tropical andes 13 000 12 000 bp and 9000 10 000 bp both may have been caused by increasing precipitation unequivocal evidence for a cold younger dryas event in the tropical andes has yet to emerge

ion microprobe analysis of oxygen isotope ratios in quartz from skye granite healed micro cracks fluid flow and hydrothermal exchange quartz grains in hydrothermally altered granites from the isle of skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 m scale ion microprobe analysis of one grain shows a gradient of 13 over 400 m and a greater range in 18o than all quartz previously analyzed on the isle of skye other crystals from the same outcrop are homogeneous digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable the ion probe analysis correlates low 18o values on a micro scale to one set of healed cracks thus quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures in contrast to more reactive feldspar that appears to exchange from the grain boundary inward macroscopic models of isotope exchange are not realistic for these rocks the flow of hydrothermal fluids was heterogeneous anisotropic and crack controlled

lake level chronology on the southern bolivian altiplano 18 23 s during late glacial time and the early holocene stratigraphic analyses of outcrops shorelines and diatoms from the southern bolivian altiplano uyuni coipasa basin reveal two major lacustrine phases during the late glacial period and the early holocene based on a chronology established by radiocarbon and u th control a comparison of14c and230th 234u ages shows that during times of high lake level radiocarbon ages are valid however during low water periods 14c ages must be corrected for a reservoir effect the lacustrine tauca phase started a little before 16 00014c yr b p and the lake level reached its maximum between 13 000 and 12 00014c yr b p a dry event ticana occurred after ca 12 000 and before 950014c yr b p a moderate lacustrine oscillation coipasa event occurred between ca 9500 and 850014c yr b p using a reservoir corrected conventional14c chronology comparisons between the lake level chronology in the uyuni coipasa basin and data from other southern tropical areas of south america suggest that the lacustrine evolution may reflect large scale climatic changes

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

the origin of brines and salts in chilean salars a hydrochemical review abstract northern chile is characterized by a succession of north south trending ranges and basins occupied by numerous saline lakes and salt crusts collectively called salars fossil salt crusts are found to the west in the extremely arid central valley while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid cordillera sea salts and desert dust are blown eastward over the cordillera where they constitute an appreciable fraction of the solute load of very dilute waters salt content evaporative concentration of inflow waters leads to sulfate rich or calcium rich near neutral brines alkaline brines are almost completely lacking the alkalinity calcium ratio of inflow waters is lowered by the oxidation of native sulfur reducing alkalinity and the deposition of eolian gypsum increasing ca concentration theoretically so4 rich inflow waters and their derived so4 rich brines should be found in the intravolcanic basins of the cordillera because of the ubiquity of native sulfur while ca rich brines should prevail in sedimentary basins where ca rich minerals are abundant this relation is perfectly observed in the salar de atacama the largest in chile however several salars located within the volcanic cordillera belong to the ca rich group inflows and brines may have acquired their ca rich composition in pleistocene time when their drainage basins were mainly sedimentary later on recent lava flows and ignimbrites covered the sedimentary formations underground waters may have kept their early sedimentary signature by continuous recycling however the weathering of volcanic rocks tend to slowly shift the water compositions from the ca rich to the so4 rich type

late local glacial maximum in the central altiplano triggered by cold and locally wet conditions during the paleolake tauca episode 17 15 ka heinrich 1 the timing and causes of the last deglaciation in the southern tropical andes is poorly known in the central altiplano recent studies have focused on whether this tropical highland was deglaciated before synchronously or after the global last glacial maximum 21 ka bp in this study we present a new chronology based on cosmogenic 3he 3he c dating of moraines on cerro tunupa a volcano that is located in the centre of the now vanished lake tauca 19 9 s 67 6 w these new 3he c ages suggest that the tunupa glaciers remained close to their maximum extent until 15 ka bp synchronous with the lake tauca highstand 17 15 ka bp glacial retreat and the demise of lake tauca seem to have occurred rapidly and synchronously within dating uncertainties at 15 ka bp we took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the lake tauca highstand this new approach indicates that during the tauca highstand 17 15 ka bp the centre of the altiplano was characterized by temperature 6 5 c cooler and average precipitation higher by a factor ranging between 1 6 and 3 compared to the present cold and wet conditions thus persisted in a significant part of the southern tropical andes during the heinrich 1 event 17 15 ka bp this study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions

a 370 000 year record of vegetation and fire history around lake titicaca bolivia peru fossil pollen and charcoal analyses of sediments from lake titicaca peru bolivia provide a record of palaeoclimatic variation spanning four full glacial cycles pollen aquatic microfossils and charcoal as well as previously published data including diatom assemblages carbonate content and stable carbon isotopic ratios of organic carbon indicate that interglacials were warm and dry whereas the peaks of glacials were cold and wet each of the interglacials documented in the record are somewhat different with those of mis 5e and mis 9 inducing lower lake levels and a drier vegetation signature than those of mis 7 and 1 the presence of charcoal particles in sediments deposited during previous interglacials provides evidence of the long term role of fire in shaping andean ecosystems

modulations of the phase speed of convectively coupled kelvin waves by the itcz abstracta number of studies suggest a two way feedback between convectively coupled kelvin waves cckws and the intertropical convergence zone itcz viewed here as a proxy for deep convection analysis of brightness temperature data reveals several aspects of these interdependencies a wavenumber frequency spectral analysis is applied to the satellite data in order to filter cckws the itcz is characterized by a region of low brightness temperature and a proxy for both the itcz location and width are defined the phase speed of cckw data is determined using the radon transform method linear regression techniques and probability density analysis are consistent with previous theoretical predictions and observational results in particular the fastest waves are found when the itcz is the farthest from the equator and the narrowest conversely the slowest waves coincide with broad itczs that are located near the equator

a new look at the midlatitude mjo teleconnection in the northern hemisphere winter the midlatitude to madden julian mjo teleconnection in the northern hemisphere wintertime was investigated using twenty years of outgoing long wave radiation and national center for atmospheric research national centers for environmental prediction re analysis data it is revealed through empirical orthogonal functions and regression analyses that the tropical upper level divergence convergence associated with enhanced reduced tropical convection has a subtropical counterpart of upper level convergence divergence as the convective region of mjo moves eastward from the indian ocean to the western pacific the divergent circulation connecting the tropics and subtropics moves eastward from an analysis of vertical motion diagnosed by the generalized omega equation it was revealed that the position of the subtropical rossby gyres of the mjo with respect to the asian pacific jet was the most important factor affecting the existence of the localized divergence convergence and associated lower level vertical motion in the subtropics as the subtropical rossby gyres pass by the longitudinal position of the asian pacific jet vertical motion occurs to meet the balance required by quasi geostrophic theory since this anomalous vertical motion is large enough to cause convection at that region the diabatic heating process reinforces the vertical motion furthermore other dynamical processes neglected in quasi geostrophic theory are activated and contribute to the vertical motion balancing the diabatic heating as a result of the vertical motion near the jet entrance region in the subtropics the vorticity advection by vertical wind and the tilting of vorticity become important since these two terms are similar in shape and magnitude they reinforce each other during the development phase of the midlatitude mjo teleconnection combining these two terms we define the baroclinic jet source bjs in order to evaluate the bjs as a source for the midlatitude mjo teleconnection a numerical experiment is carried out the linear barotropic model is forced by only two terms yet the model captured clearly the main feature of the midlatitude mjo teleconnection copyright 2006 royal meteorological society

lateglacial and holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold based glaciers at nevado sajama bolivia comparisons of palaeo equilibrium line altitudes between the western and eastern cordilleras in the central andes are commonly based on the assumption that the tall outermost moraines visible in remotely sensed images of the western cordillera date to the last glacial maximum lgm however field investigation and geomorphic mapping at nevado sajama bolivia indicates the tall moraines are relic features with shorter moraines overlying and in some cases extending beyond them 36cl exposure ages from the shorter moraines suggest that they date to lateglacial times ca 16 9 10 2 ka although lateglacial deposits have been found throughout the central andes the extent of these deposits relative to lgm deposits varies both between the western and eastern cordilleras and north to south along the western cordillera in the western cordillera in the zone of easterly winds the lateglacial appears to be the most extensive glacial advance of the last glacial cycle geomorphic evidence also suggests that some lateglacial moraines were deposited by cold based ice a previously unreported finding in the tropical andes retreat from other glacial features occurred at about 7 0 4 4 ka and 4 7 3 3 ka these are the first directly dated holocene glacial deposits in the western cordillera of bolivia and their presence suggests that the mid holocene may not have been as warm and dry as previously thought copyright 2008 john wiley sons ltd

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

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

late quaternary palaeolakes rivers and wetlands on the bolivian altiplano and their palaeoclimatic implications drill cores of sediments from the rio desaguadero valley bolivia provide new information about the climate of tropical south america over the past 50 000 years the modern rio desaguadero is fed by lake titicaca overflow and by local tributaries in the wetter northern altiplano and discharges into lake poopo in the more arid central altiplano during the late quaternary the rio desaguadero valley was the site of several generations of palaeolakes and wetlands that formed during periods of increased precipitation and local runoff augmented by increased overflow from lake titicaca sediments recovered by drilling in eight localities along the 390 km long valley of the rio desaguadero yield a regional history of lacustrine sedimentation and effective precipitation lacustrine strata in the drill cores record 12 distinct wet periods in the past 50 000 years four of these wet periods resulted in the formation of major palaeolakes in the rio desaguadero valley during the last glacial maximum from before 20 000 to 16 000 cal yr bp during the late glacial from about 14 000 to 12 000 cal yr bp in the early holocene from about 10 000 to 7900 cal yr bp and in the late holocene from 4500 cal yr bp to present the period that appears to have been most arid was between 7900 and 4500 cal yr bp the altiplano wet periods were generally synchronous with north atlantic cold events respectively the last glacial maximum the younger dryas the 8200 cal yr bp event and the neoglacial implying a relationship between past precipitation variability in tropical south america and north atlantic sea surface temperature copyright 2005 john wiley sons ltd

late glacial and holocene avulsions of the rio pastaza megafan ecuador peru frequency and controlling factors the geomorphological study by means of remote sensing imagery of the rio pastaza megafan ecuador and northern peru reveals the traces of numerous avulsions one hundred and eight avulsion sites have been defined the location of these sites the available radiocarbon ages as well as historical maps of the seventeenth century enable us to propose an evolution history of the migration and avulsions of the rio pastaza since the last glacial maximum the first avulsions of the rio pastaza occurred after the lgm in a zone close to and roughly parallel to the sudandean front where the developed avulsion gave a distributive pattern to the ancient stream of the rio pastaza in an area located between the modern rio morona and pastaza where they caused the rio pastaza to develop a fan like distributary pattern this is interpreted as a response to thrust related forelimb tilt progressively shifting eastward the rio pastaza and the apex of the megafan this sequence of events ended with the great diversion of the rio pastaza towards the modern rios corrientes and tigre avulsions occurred in the tigre corrientes area between 9200 and 8 500 years cal bp afterwards the rio pastaza was diverted to its present day north south course this last significant avulsion occurred before ad 1691 in the area located between the modern rio morona and pastaza avulsion frequency probably overestimated ranges between 100 and 200 years in the rios tigre and corrientes area avulsion frequency probably underestimated ranges from 300 to 400 years regional tectonics is likely to have triggered most of the avulsions in the morona pastaza area but its influence is restricted to this area the factors controlling the avulsions in the tigre corrientes area are less clear because the frequently described hydrologic driven avulsion as observed in areas characterized by contrasted hydrologic cycles are inconsistent with the characteristics of the hydrologic cycles of the rio pastaza

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

the southern westerlies in central chile holocene precipitation estimates based on a water balance model for laguna aculeo 33 50 s central chile 32 35 s lies at the northern border of strong influence of the westerly circulation belt westerlies and is therefore characterized by a steep precipitation gradient in this region quantitative reconstructions of holocene precipitation are scarce hence the present study estimates precipitation changes based on lake level fluctuations of laguna aculeo 33 50 s 70 54 w the lake level curve has been reconstructed using a multi proxy study of lake sediments lake level changes have been simulated using a simple water balance model as a result palaeo precipitation could be estimated uncertainties concerning the input parameters and past conditions have limitated the precision of precipitation estimates the results suggest that during the beginning of the holocene when the lake level 1 5 m was low precipitation was 200 mm year before 8000 cal yr bp the lake frequently dried out between 8000 and 6000 cal yr bp precipitation appeared to be higher 150 300 mm year and after about 6000 cal yr bp precipitation increased dramatically 350 450 mm year around 3000 cal yr bp modern lake level and precipitation 450 550 mm year were generally established the dry conditions during the early and mid holocene are in good agreement with other records from central chile and northern patagonia the westerlies were probably deflected southward by the southeast pacific subtropical high pressure cell during the mid and early holocene subsequently the increase in moisture in central chile during the late holocene appears to be strongly related to intensified westerly activity and probably also to increased el nino activity

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

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

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

pronounced occurrence of long chain alkenones and dinosterol in a 25 000 year lipid molecular fossil record from lake titicaca south america abstract our analysis of lipid molecular fossils from a lake titicaca 16 s 69 w sediment core reveals distinct changes in the ecology of the lake over an 25 000 yr period spanning latest pleistocene to late holocene time previous investigations have shown that over this time period lake titicaca was subject to large changes in lake level in response to regional climatic variability our results indicate that lake algal populations were greatly affected by the changing physical and chemical conditions in lake titicaca hydrocarbons are characterized by a combination of odd numbered mid to long chain c 21 c 31 normal alkanes and alkenes during periods when lake level was higher latest pleistocene early holocene and late holocene the c 21 n alkane and the c 25 and c 27 alkenes dominate hydrocarbon distributions and indicate contribution from an algal source potentially the freshwater alga botryococcus braunii the c 30 4 methyl sterol dinosterol increases sharply during the mid holocene suggesting a greatly increased dinoflagellate presence at that time long chain alkenones lcas become significant during the early holocene and are highly abundant in mid holocene samples there are relatively few published records of lca detection in lake sediments but their occurrence is geographically widespread antarctica asia europe north america lake titicaca represents the first south american lake and the first low latitude lake in which lcas have been reported lca abundance and distribution may be related to the temperature dependent response of an unidentified algal precursor although the lca unsaturation indices cannot be used to determine absolute lake titicaca temperatures we suspect that the published lca u 37 k unsaturation calibrations can be applied to infer relative temperatures for early to mid holocene time when lca concentrations are high using these criteria the u 37 k unsaturation indices suggest relatively warmer temperatures in the mid holocene in contrast to previous speculation lipid analysis provides little evidence of a greatly increased presence of aquatic plants during the mid holocene instead it appears that a few algal species were dominant in the lake based on the dramatic rise in abundances of lcas and dinosterol during the early to mid holocene we suspect that the algal producers of these compounds rose in response to a combination of physical and chemical changes in the lake these include temperature salinity and alkalinity changes that occurred as lake level dropped sharply during a multi millennial drought affecting the central andean altiplano

application of strontium isotopes to understanding the hydrology and paleohydrology of the altiplano bolivia peru abstract strontium concentrations and strontium isotopic ratios were measured in natural waters and carbonate sediments from throughout the bolivian and peruvian altiplano in order to improve hydrologic and paleohydrologic mass balances with the ultimate goal of better understanding the paleoclimatic history of the central andes rivers flowing into lake titicaca have a wide range of strontium isotopic ratios that exhibit spatial patterns consistent with the lithologies of the different drainage basins because of the limited exchange of water between the two main sub basins of lake titicaca lago grande and lago huinaimarca and between the sub basins of lago huinaimarca there are significant differences in strontium isotopic ratios between the sub basins calculated elemental balances of strontium in lake titicaca are in reasonable agreement with previously published budgets of water and major elements however the strontium isotopic budget indicates that the lake is not in isotopic steady state this also implies that the major element budgets are unlikely to be in steady state lake titicaca had a higher than modern strontium isotopic ratio during the early and middle holocene elevated values persisted in lago grande until at least 2000 cal yr bp consistent with other evidence that modern hydrologic conditions namely overflow were not established until that time an isotopic budget calculated for late pleistocene paleolake tauca in the central altiplano suggests that between 70 and 83 of its riverine inputs were derived from lake titicaca overflow this calculated flow represents about a 30 fold increase over the average discharge of the modern rio desaguadero at desaguadero or a seven fold increase over its average discharge into lago poopo the strontium isotopic budget if complete precludes the possibility that decreased evaporation alone could have accounted for the existence of paleolake tauca

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

nature of environmental changes in south america at the last glacial maximum abstract a review is given of geomorphological evidence suggesting the nature of environmental changes in south america during the last glaciation maximum lgm the data are from glacial geocryogenic alluvial colluvial and aeolian systems and span 68 of latitude making the most complete land transect of major climatic systems in the southern hemisphere glaciers in the northern and central andes may have reached their maximal extent by 27 000 yr b p reduced precipitation at the lgm caused by lower temperatures and lower atmospheric humidity probably led to slight glacier recession in the tropical andes icefields in the southern andes were most expansive when global temperature and sea level were lowest because pacific westerlies supplied abundant moisture and western outlets advancing across the continental shelf were constrained by sea level low gradient river networks became incised by at least 100 m into narrow channels as global sea level fell by 120 m during the lgm draw down of water tables possibly impacted the forest cover enhancing the drying influence of reduced sea surface temperature and atmospheric humidity as forest and grass covers diminished in extent effecting greater atmospheric cooling because of reduced evapotranspiration and convective condensation colluvial and aeolian processes became more active and widespread almost 25 of the continent is covered with palaeo aeolian features presumed to have been active when airflow was stronger due to steeper atmospheric pressure and temperature gradients at the lgm substantial changes in precipitation totals and incidence and in ground water availability probably eliminated modern type tropical rainforest except in areas currently receiving ca 5000 mm of annual rainfall equivalent changes in vegetation cover spread across much of the guyana and brazilian highlands and throughout the southern temperate regions

rapid development of an unusual peat accumulating ecosystem in the chilean altiplano stratigraphic relationships radiocarbon dating sediment and peat characteristics and rates of peat and carbon accumulation from a soligenous peatland or bofedal in the chilean altiplano shows the peatland to be unusually young dynamic and sensitive to environmental changes the site lies in the national park nevado de tres cruces in the puna desert grassland at an elevation of 4300 m a s l eight peat cores were extracted from a 1 75 km transect yielding a maximum of 3 6 m of organic sediment organic matter began to accumulate 1700 1100 cal yr b p under a progressively arid local climate after a period when regional climate is believed to have been more humid than at present areas of greater relief and better drainage in the valley bottom eventually fostered the growth of a riparian cushion plant community after water flowing down the valley began to diminish this led to rapid lateral expansion of the riparian peatland communities over open water in topographic depressions at a rate heretofore unprecedented in the peatland literature it appears that development of the peatland has been encouraged by autoregulation of internal hydrology the drainage impediment created by organic mass accumulation in lower relief areas probably reduced the amount of water arriving at the lower reaches of the peatland these areas have become progressively drier and have since died and oxidized through endogenous peat accumulation and a concomitant drainage impediment the ecosystem has been migrating upstream over the past 50 years

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

paleoevaporation and paleoprecipitation in the tanganyika basin at 18 000 years b p inferred from hydrologic and vegetation proxies abstract paleo hydrologic and vegetation proxy data from the tanganyika basin are integrated in energy and water balance equations to infer past evaporation and precipitation during the last glacial maximum lgm our approach is first validated on the modern system large variations are assigned to input variables to simulate the interannual precipitation variability equations are then applied to the lgm we first change those input parameters inferred from proxies basin and lake surfaces temperature and land albedo our lgm simulation suggests in percent of modern mean values decreases in evaporation from the lake el 5 between 13 and 3 and land ec 8 19 5 bodies in precipitation p 11 21 0 and p ec 42 44 40 decreases in p and e are amplified el 8 16 0 ec 14 24 2 p 17 26 6 when including empirical changes in atmospheric transmission coefficient and bowen ratio sensitivity runs suggest that even large changes in cloud cover and air humidity should not modify these trends the results suggest that the earth s glacial interglacial boundary conditions play a significant role on climate of subequatorial southern africa

geomorphic evidence of active deformation and uplift in a modern continental wedge top foredeep transition example of the eastern ecuadorian andes abstract the eastern ecuadorian andes appear as a fold and thrust belt adjacent to a continental foredeep represented by one of the world s largest tropical alluvial megafans the pastaza megafan debouching into the amazonian lowland the apex of the pliocene pleistocene megafan situated in the present day wedge top subandean zone has been cut by an erosion surface the western part of which has been uplifted of 500 m along the frontal thrust forming a poorly dissected plateau the mera plateau this erosion surface erased most of the previous fluvial landscape but preserved a large thrust related anticlinal hinge deforming less erodible underlying strata the mirador fold and smaller sized anticlines this surface has been then incised by two antecedent major rivers the pastaza and the napo and few tributaries the plateau edge is marked by a series of large scale gently sloping landslides clustered along a 70 km long concave eastward line associated with the frontal thrust fault the newly formed immature rivers issued from the landslides or sourced within east dipping remnants of the erosion surface downstream of the landslide line constitute the greatest part of the streams feeding the ecuadorian amazonian basin at 70 to 100 km from the landslide line the drainage abruptly changes from highly immature to mature with a well defined hinge line representing the outer limit of landslide and tectonic control the diversions of the pastaza river indicate ongoing fold growth since at least the late pleistocene in the eastern cordillera and the early holocene in the mera plateau the preserved terraces of the pastaza valley are all degradational and are ascribed to periods of tectonic seismic activity alternating with periods of tectonic quiescence or decreased seismic activity rather than to climatic events 14c dating of the plateau erosion surface and of the upper pastaza terraces indicates that the minimum average incision rate since 18 000 years bp varies locally in the upper pastaza valley from 0 5 to 0 67 cm year 1 increasing from 18 000 years bp to now a comparison of these incision rates with fold and thrust fault uplift rates indicates that incision in the upper pastaza valley was a result of rapid uplift up to 1 cm year 1 along the mirador fold and thrust which caused a restoration of the local equilibrium profile of the upper reach combined with smaller local fault uplift along the westernmost thrust faults the uplift of the whole mera plateau with respect to the upper amazonian basin gives a minimum average uplift rate of 2 8 cm year 1 since 18 000 years bp the overall uplift of the mera plateau and the eastern cordillera is likely to have been caused by a regional scale low angle thrust ramp emerging as the frontal thrust fault

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

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

response of planetary waves to stationary tropical heating in a global atmosphere with meridional and vertical shear abstract the response of planetary waves to stationary tropical heating in a stratified global atmosphere linearized with respect to a basic zonal mean flow is investigated the basic zonal wind has meridional and vertical shear the basic equations are solved by using the method of three dimensional normal mode expansion forced solutions to a prescribed tropospheric equatorial heating distribution with a specific wavenumber in longitude are examined without the basic zonal flow the internal vertical modes whose equivalent depths are on the order of a few hundred meters are favorably excited but the response of the external mode barotropic mode is relatively small with the inclusion of a zonal flow the vertical shear of the zonal wind permits the coupling of the external mode with the internal vertical modes as a result of the coupling a significant response occurs in the external mode due to the excitation of the baroclinic internal modes by tropical heating the meridional structures of in

low holocene level 7700 to 3650 years ago of lake titicaca bolivia abstract preliminary results of sedimentological and paleontological analysis of two cores taken in lake titicaca bolivia indicate that between 7700 and 3650 yr b p the lake level was up to 50 m lower than at present evaporitic deposits occurred at the maximum low lake level

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

mechanisms of meridional teleconnection observed between a summer monsoon system and a subtropical anticyclone part i the pacific japan pattern abstract summertime atmospheric circulation over the midlatitude western north pacific wnp is influenced by anomalous convective activity near the philippines this meridional teleconnection observed in monthly anomalies and known as the pacific japan pj pattern is characterized by zonally elongated cyclonic and anticyclonic anomalies around the enhanced convection center and to its northeast respectively in the lower troposphere with an apparent poleward phase tilt with height the authors idealized two layer linear model whose basic state consists of a zonal subtropical jet and a pair of a monsoon system and a subtropical anticyclone can simulate a pj like response against diabatic heating located between the pair each of the observed and simulated patterns can gain energy through barotropic and baroclinic conversions from the zonally varying baroclinic mean flow in an efficiency comparable with that of energy generation due to the anomalous diabatic heating indicating a characteristic of

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

extensive carbonate algal bioherms in upper pleistocene saline lakes of the central altiplano of bolivia during the upper pleistocene the central altiplano of bolivia was repeatedly flooded by deep and extensive saline lakes in response to climatic fluctuations development of carbonate algal bioherms took place during at least three major periods of lacustrine highstands discontinuously covering the 300 km long and 100 km wide lacustrine slopes and terraces up to an elevation of 100 m above the surface of the modern halite crust of uyuni distribution size and shape of the bioherms are diverse due to various factors e g the nature and morphology of the substrate and the hydrodynamic conditions that prevailed during growth on larger palaeoterraces the build ups coalesced to form platform like carbonate accumulations although the morphologies closely resemble those induced by cyanobacteria they were predominantly constructed by other plant communities probably dominated by filamentous green algae cyanobacterial communities flourished in association with these plants but they did not contribute significantly to the architecture of the bioherms they participated to encrust the plant stems and algal bushes or to form thin laminated layers covering the build ups a prominent feature of some bioherms is their composite structure due to repeated algal growth during successive lacustrine episodes that were separated by subaerial exposures with moderate erosional effects the build ups located between 3660 and 3680 m elevation display up to three major parts 1 a massive inner core formed during an early minchin highstand before 40 ka 2 a large peripheral envelope deposited at about 40 ka late minchin and 3 a thinner outermost crust formed during a late glacial event lake level dropped during interlacustrine stages sometimes leading to desiccation and deposition of salt layers in the deepest parts of the system i e the present day salar of uyuni

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

the different configurations of the east asian polar front jet and subtropical jet and the associated rainfall anomalies over eastern china in summer abstractto investigate the concurrent impacts of the east asian polar front jet eapj and subtropical jet easj on the summer rainfall over eastern china positive strengthened eapj with weakened easj and negative weakened eapj with strengthened easj configurations are identified in the positive configuration rainfall decreases in the northern part of eastern china and increases in the southern part vice versa in the negative configuration the possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature sst and synoptic scale transient eddy activities stea in the positive configuration meridional distributed cold warm sst anomalies over the eastern north pacific may induce regional circulation and meridional temperature gradient anomalies which can strengthen the eapj and weaken the easj the central pacific la nina like sst anomalies are related with the arctic vortexlike anomalies in the stratosphere which may strength

mechanisms of global teleconnections associated with the asian summer monsoon an intermediate model analysis the indian summer monsoon ism and western north pacific summer monsoon wnpsm are two subsystems of the asian summer monsoon and they exhibit different global teleconnection patterns the enhanced ism strengthens the south asian high and mascarene high and the wnpsm excites a meridional tripolar wave train in the northern hemisphere and affects the australian high in the southern hemisphere to understand the dynamics behind these global teleconnections especially the processes responsible for the cross equatorial teleconnection an intermediate model describing a two level troposphere and a steady planetary boundary layer pbl is linearized from the background horizontal wind field the model results indicate that the ism heating located under the strong easterly vertical shear vs and close to the westerly jet in the northern hemisphere can excite a barotropic rossby wave that emanates northwestward and then propagates downstream along the westerly jet since the wnpsm heating is far away from the westerly jet over the north pacific it only excites a weak rossby wave train which cannot explain the meridional tripolar teleconnection associated with the wnpsm it is found that both the ism and wnpsm heating excite strong teleconnections in the southernhemisphere via an advectionmechanism that is the background upper level northerly winds can transport energy across the equator from the northern hemisphere summer monsoon to the southern hemisphere westerly jet in addition the pbl enhances monsoon teleconnections by trapping more energy in the upper troposphere the elevated maximum monsoon heating also reinforces upper level perturbations and enhances the teleconnection pattern

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

structure and dynamics of the summertime pacific japan teleconnection pattern convective activity over the tropical western pacific is known to influence the extratropical circulation over east asia in the boreal summer in the form of teleconnection called the pacific japan pj pattern but its structure and dynamics have not yet been studied in depth in this study a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the philippines the composited monthly mean vorticity anomalies associated with the pj pattern are elongated zonally with a distinct poleward tilt with height this structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes as has widely been accepted as a conceptual model of the pj pattern a wave activity flux points polewards only in the lower troposphere indicating that rossby wave teleconnection occurs primarily through a low level south westerly jet those tilted anomalies over the western pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy ape in the presence of the vertically sheared jets the enhanced convection can generate ape effectively and the associated low level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre warmed ocean surface it is thus hypothesized that the pj pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the asian summer monsoon with an efficient self sustaining mechanism through moist processes copyright 2006 royal meteorological society

dating of paleolakes in the central altiplano of bolivia abstract the deposits of the extensive paleolakes of the bolivian altiplano correspond to an alternation of lacustrine episodes and dry periods a phenomenon commonly explained by climatic changes the lack of precise dating of the deposits has prevented detailed reconstruction of the evolution of paleolakes that would allow a determination of the relative influence of interconnections between neighboring basins and local climatic conditions among the five paleolakes of the northern altiplano titicaca basin and the three of the central altiplano poopo coipasa and uyuni basins only the two most recent paleolakes have been dated a 121 m long sediment core recovered from the salar de uyuni contained 11 lacustrine layers l1 l11 separated by 12 salt crusts radiocarbon dating shows that the younger layers l1 and l2 are related to the tauca lacustrine phase 12 000 16 000 cal yr bp and layers l3 and l4 to the minchin lacustrine phase 30 000 73 000 cal yr bp layer l5 located at 46 m below the surface contains a volcanic ash with well preserved biotites is here dated by the 40 ar 39 ar method the measured age of 191 000 5000 y is the first date ever obtained from a pre minchin paleolake lake escara this result combined with 14 c and u th data obtained on lakes tauca and minchin from various authors suggests that the duration of the lacustrine events increased regularly during the pleistocene in contrast paleolake levels in the northern altiplano decreased from the oldest known lake mataro 3950 m to the present titicaca level 3806 m a progressive erosion of the threshold between the northern and central altiplano may have allowed important volumes of water to overflow from the northern basin into the central altiplano the existence of large paleolakes in the central altiplano was thus not only dependent on local climatic conditions but also on additional inputs from the north where climatic conditions could have been quite different from those prevailing in the south

record of redox status in laminated sediments from lake titicaca a sulfur k edge x ray absorption near edge structure xanes study abstract laminated sediments are commonly used to examine limnological and ecological processes on short time scales here we examine changes in sulfur speciation of lamination couplets from lake titicaca south america using x ray absorption near edge structure xanes spectroscopy the dark colored layer of each lamination couplet contains a significant fraction of reduced organic sulfides with smaller fractions of iron sulfides and sulfate in contrast the light colored layer of each couplet is primarily composed of sulfate in all laminae the sulfate is present as inorganic sulfate substituted in calcite the differences in speciation likely reflect changes in productivity during sediment deposition during the warm productive summer months micritic calcite precipitation was induced in oxidized surface waters due to ph changes induced by consumption of dissolved co 2 this calcite incorporates dissolved sulfate and forms the light colored layers this pulse of productivity creates organic matter that partially decomposes during the austral winter months consuming oxygen and delivering organic rich sediment to the lake bottom this decomposition and the possible presence of a halocline kept bottom waters low in oxygen and lead to the production of organic matter rich in reduced sulfur these data suggest that these laminations are deposited annually and illustrate the utility of s k edge xanes for the analysis of laminated sediments

the equivalent barotropic structure of waves in the tropical atmosphere in the western hemisphere abstracttropical waves are generally considered to have a baroclinic structure however analysis of era interim and noaa olr data for the period 1979 2010 shows that in the equatorial and northern hemisphere near equatorial regions in the tropical western hemisphere wh westward and eastward moving transients with zonal wavenumbers 2 10 and periods of 2 30 days have little tilt in the vertical and can be said to be equivalent barotropic the westward moving transients in the equatorial region have large projections onto the westward mixed rossby gravity wmrg wave and those in the near equatorial region project onto the gravest rossby wave and also the wmrg the eastward moving transients have large projections onto the doppler shifted eastward moving versions of these waves to examine how such equivalent barotropic structures are possible in the tropics terms in the vorticity equation are analyzed it is deduced that waves must have westward intrinsic phase speeds and can exist in the wh with its

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

multidecadal to century scale arid episodes on the northern altiplano during the middle holocene abstract we present reconstructions of multidecadal to centennial scale shifts in the hydrologic balance of the northern altiplano during the middle holocene using stable isotopic geochemical and sedimentologic evidence from lake titicaca sediments large downcore changes in the 13corg of bulk organic matter previously shown to be a site specific lake level proxy indicate that extended periods of lake level regression occurred in response to sustained reductions in mean annual precipitation and or increases in air temperature supporting evidence from a floating interval of finely laminated sediments indicates that salinity and stratification were enhanced at lake titicaca during the middle holocene the age model used in this study is based on 7 ams 14c age dates estimated from bulk decalcified sediment from a 60 cm sequence spanning 7200 5600 14c cal yr bp simulations from a hydrological energy balance model of the titicaca basin indicate that the 38 m drop in lake level that preceded the maximum lowstand at 6200 yr bp would require a significant decrease in mean annual precipitation of up to 50 and or a significant increase in mean annual temperature of up to 8 c today the altiplano is often affected by drought during periods of enhanced summertime westerly wind flow which reduces the delivery of moisture from the east this investigation supports the idea of sustained periods of enhanced westerly air flow during the mid holocene and provides additional submillennial scale information about the timing and magnitude of regional drought results of our frequency domain analysis of the floating lamination interval indicate significant power at a decadal periodicity 10 12 yr associated with the schwabe cycle of solar activity frequency domain analysis also reveals power in a 75 year time series of modern lake level we suspect that solar influence on large scale atmospheric circulation features results in changes to the moisture balance in the titicaca basin over decadal and possibly century scale time periods

influence of the basic state zonal flow on convectively coupled equatorial waves observational data are used to test the hypothesis that the basic state modulates the dispersion properties of convectively coupled equatorial waves ccews this hypothesis is based on shallow water theory which predicts that the zonal speed of propagation of such tropospheric equatorial modes is altered by the equivalent depth and the basic zonal flow localized space time spectra are calculated to investigate how ccew spectral peaks vary across the tropics and how they are affected by the variations in zonal wind observed geographically and by season doppler shifting by the basic state barotropic zonal flow is readily identified once this doppler shifting is taken into account the equivalent depths of ccews inferred from global power spectra are surprisingly uniform both geographically and temporally however there are also detectable modulations that appear consistent with changes in vertical shear of the zonal flow along with other shifts that are not as easily explained

hydrologic variation during the last 170 000 years in the southern hemisphere tropics of south america despite the hypothesized importance of the tropics in the global climate system few tropical paleoclimatic records extend to periods earlier than the last glacial maximum lgm about 20 000 years before present we present a well dated 170 000 year time series of hydrologic variation from the southern hemisphere tropics of south america that extends from modern times through most of the penultimate glacial period alternating mud and salt units in a core from salar de uyuni bolivia reflect alternations between wet and dry periods the most striking feature of the sequence is that the duration of paleolakes increased in the late quaternary this change may reflect increased precipitation geomorphic or tectonic processes that affected basin hydrology or some combination of both the dominance of salt between 170 000 and 140 000 yr ago indicates that much of the penultimate glacial period was dry in contrast to wet conditions in the lgm our analyses also suggest that the relative influence of insolation forcing on regional moisture budgets may have been stronger during the past 50 000 years than in earlier times d 2003 university of washington all rights reserved

remotely sensed evapotranspiration estimates for an improved hydrological modeling of the early holocene mega lake suguta northern kenya rift abstract the actual evapotranspiration is an important but difficult to determine element in the water balance of lakes and their catchment areas reliable data on evapotranspiration are not available for most lake basins for which paleoclimate reconstructions and modeling have been performed particularly those in remote parts of africa we have used thermal infrared multispectral data for 14 aster scenes from the terra satellite to estimate the actual evapotranspiration in the 12 800 km2 catchment of the suguta valley northern kenya rift evidence from sediments and paleo shorelines indicates that during the african humid period ahp 14 8 to 5 5 kyrs bp this valley contained a large lake 280 m deep and covering 2200 km2 which has now virtually disappeared evapotranspiration estimates for the suguta basin were generated using the surface energy balance algorithm for land sebal climate data required for the model were extracted from a high resolution gridded dataset obtained from the climatic research unit east anglia uk results suggest significant spatial variations in evapotranspiration within the catchment area ranging from 450 mm yr in the basin to the north to 2000 mm yr in more elevated areas and precipitation that was 20 higher during the ahp than in recent times these results are in agreement with other estimates of paleo precipitation in east africa the extreme response of the lake system 280 m greater water depth than today and a lake surface area of 2200 km2 to only moderately higher precipitation illustrates the possible sensitivity of this area to future climate change

temperature and precipitation in the southern central andes during the last glacial maximum heinrich stadial 1 and the younger dryas abstract recent developments in terrestrial cosmogenic nuclide tcn exposure dating and the reinterpretation of tcn boulder ages from moraines have improved our understanding of the glacial chronology in the central andes according to these records glacial advances throughout the region correlate with insolation driven changes in the intensity of the south american summer monsoon and millennial scale climate events such as heinrich stadials and the younger dryas quantifying the temperature and precipitation shifts during these events helps to constrain past moisture pathways and associated changes in atmospheric circulation patterns yet particularly in the southern central andes where a wealth of glacigenic landforms attests to formerly cooler and or wetter conditions the magnitudes of past temperature and precipitation changes are only loosely constrained at a few sites here we present results from tcn dated moraines combined with the reconstruction of former glaciers and paleolakes within the eastern sector of the southern central andes 24 27 s for the last glacial maximum lgm heinrich stadial 1 hs1 and the younger dryas yd we performed monte carlo simulations with 2 dimensional models of ice flow and lake hydrology that are forced by a spatially distributed surface energy balance model our results indicate that temperatures were 3 0 4 2 c 2 0 3 3 c and 1 3 2 5 c cooler during the lgm hs1 and yd respectively in agreement with previous estimates elsewhere in the central andes we find that temperature changes during the late glacial are compatible with sea surface temperature anomalies derived from the tropical atlantic precipitation was only 5 27 greater than today which contrasts with larger anomalies reconstructed for the bolivian part of the andean plateau altiplano we attribute this discrepancy to the southerly position of our study region with respect to the bolivian high supporting the hypothesis that this atmospheric pressure system played a prominent role for south american summer monsoon dynamics during glacial episodes

contrasting types of late archean plutonic rocks in northwestern ontario implications for crustal evolution in the superior province abstract the late archean aulneau and lount lake batholiths have contrasting geochemical characteristics that are interpreted to be a consequence of derivation from different sources the aulneau batholith which was intruded into low grade metavolcanic rocks of the wabigoon subprovince is characterized by high na2o and low k2o rb and y together with enriched light rare earth elements lree near chondritic heavy rare earth elements hree negligible eu anomalies and mantle type initial sr and nd isotopic compositions these geochemical characteristics are consistent with derivation from the partial melting of metamorphosed tholeiitic basalt in contrast the lount lake batholith which was intruded into older 2 83 3 17 ga tonalitic plutonic rocks of the winnipeg river subprovince has relatively high k2o rb y and ree low na2o and prominent eu anomalies the initial sr and nd isotopic compositions of the lount lake batholith are consistent with a crustal source at least 200 400 ma older than the crystallization age of the batholith these geochemical characteristics indicate that the lount lake batholith originated from the partial melting of deeper level equivalents of the tonalitic metaplutonic rocks 2 83 3 17 ga which they intrude these results suggest that reworked 3 0 ga crust may be extensive in the winnipeg river subprovince and that the geochemical and isotopic signature of late archean plutonic rocks may be a useful reconnaissance tool in the identification of areas of extensive older crust the results can be interpreted within a uniformitarian model diachronous ensimatic magmatic arcs represented by the winnipeg river and western wabigoon subprovinces developed independently collision of these arcs at 2707 8 ma marks the cessation of subduction and related magmatic activity and the initiation of high grade metamorphism and melting in tectonically thickened portions of the crust

late quaternary climate and hydrology of tropical south america inferred from an isotopic and chemical model of lake titicaca bolivia and peru abstract a simple mass balance model provides insight into the hydrologic isotopic and chemical responses of lake titicaca to past climatic changes latest pleistocene climate of the altiplano is assumed to have been 20 wetter and 5 c colder than today based on previous modeling our simulation of lacustrine change since 15 000 cal yr b p is forced by these modeled climate changes the latest pleistocene lake titicaca was deep fresh and overflowing the latest pleistocene riverine discharge from the lake was about 8 times greater than the modern average sufficient to allow the expansion of the great paleolake tauca on the central altiplano the lake 18o value averaged about 13 smow the modern value is about 4 2 the early holocene decrease in precipitation caused lake titicaca to fall below its outlet and contributed to a rapid desiccation of paleolake tauca continued evaporation caused the 100 m drop in lake level but only a slight 1 2 increase relative to modern in 18o of early holocene lake waters this holocene lowstand level of nearly 100 m was most likely produced by a precipitation decrease relative to modern of about 40 the lake was saline as recently as 2000 cal yr b p the timing of these hydrologic changes is in general agreement with calculated changes of insolation forcing of the south american summer monsoon

impact of tropical heat sources on the south american tropospheric upper circulation and subsidence the nonlinear adjustment of the wind and mass fields to idealized tropical heat sources is studied with a simple nonlinear primitive equation model with emphasis on the upper level circulation over south america and neighboring oceanic regions during the austral summer numerical experiments are performed with 1 an idealized symmetrical heat source in the amazon region 2 the asymmetry induced in source 1 by the sacz 3 the effect of the atlantic itcz off the amazon mouth 4 the african heat source 5 the west pacific source and 6 the central pacific source during the warm phase of enso the linear response is obtained through the reduction of the heat source by a factor of 10 and subsequent multiplication of the results by the same factor two basic questions are discussed 1 are localized heat sources important for the development of the observed cyclonic flow in the midequatorial atlantic and 2 where is the compensating subsidence associated with the amazon heat source located the nonlinearity helps organizing a weak cyclonic curvature in the midequatorial atlantic with the inclusion of source 2 the basic state generated by the west pacific source and primarily by the central pacific source has a large impact on the cyclonic curvature on the equatorial atlantic the compensating subsidence associated with the amazon source is concentrated on the southwest side of the source the sacz extension helps to enhance the subsidence over the northern argentina and the atlantic itcz enhances the subsidence over northeast brazil and central equatorial atlantic nonlinearity weakens the subsidence at the 500 hpa level inducing a more barotropic structure in the dynamical response to the heating

hydrological modelling of a pleistocene landslide dammed lake in the santa maria basin nw argentina abstract around 30 000 14 c yr bp multiple landslides in the quebrada de cafayate 26 s 66 w dammed the rio de las conchas and caused a lake in the santa maria basin nw argentina since climate could have played a major role in landslide generation we used a lake balance model to compare the present day climate with the conditions during landsliding this model reveals that a hypothetical present day lake would stabilize around 70 m below the reconstructed paleolake level the volume of the water body would be one third of the corresponding paleolake volume however a minimum 10 15 increase in mean annual precipitation accompanied by at least a 3 4 c drop in temperature would result in a stable lake level at the reconstructed elevation this result implies wetter and cooler conditions at 30 000 14 c yr bp as compared to the present wetter climate in turn could help to explain enhanced landsliding in the quebrada de cafayate during this time

changes in the influence of the western pacific subtropical high on asian summer monsoon rainfall in the late 1990s the year to year variability of the western pacific subtropical high wpsh is primarily controlled by atmosphere ocean interaction aoi between the wpsh and the indo pacific warm pool dipole sst anomalies aoi mode and the anomalous sst forcing from the equatorial central pacific the cp forcing mode in this study we show that the impacts of the wpsh variability on asian summer monsoon rainfall have changed after the late 1990s before the late 1990s the pre epoch the wpsh primarily affects east asian summer monsoon easm and had little influence on indian summer monsoon ism whereas after the late 1990s the post epoch the wpsh has strengthened its linkage to the ism while weakened its relationship with the easm this epochal change is associated with a change in the leading circulation mode in the asia wp region during the pre post epoch the wpsh variation is mainly controlled by the aoi cp forcing that mainly affects easm ism the epochal change of the leading mode may be attributed to the change of the enso properties in late 1990s the cp types of el nino become a leading enso mode in the post epoch this work provides a new perspective for understanding decadal changes of the enso monsoon relationship through subtropical dynamics

isotopic tracers of paleohydrologic change in large lakes of the bolivian altiplano we have developed an 87sr 86sr 234u 238u and 18o data set from carbonates associated with late quaternary paleolake cycles on the southern bolivian altiplano as a tool for tracking and understanding the causes of lake level fluctuations distinctive groupings of 87sr 86sr ratios are observed ratios are highest for the ouki lake cycle 120 95 ka at 0 70932 lowest for coipasa lake cycle 12 8 11 4 ka at 0 70853 and intermediate at 0 70881 to 0 70884 for the salinas 95 80 ka inca huasi 45 ka sajsi 24 20 5 ka and tauca 18 1 14 1 ka lake cycles these sr ratios reflect variable contributions from the eastern and western cordilleras the laca hydrologic divide exerts a primary influence on modern and paleolake 87sr 86sr ratios waters show higher 87sr 86sr ratios north of this divide most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from lake titicaca the coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide in contrast the ouki lake cycle was an expansive lake deepest in the northern poopo basin and spilling southward these results indicate that regional variability in central andean wet events can be reconstructed using geochemical patterns from this lake system

late quaternary glacial history in the encierro valley northern chile 29 s deduced from 10be surface exposure dating abstract the late pleistocene glacial and climate history in the dry central andes is not well known so far mainly because of the lack of suitable material for radiocarbon dating in order to establish a glacial chronology we applied surface exposure dating using in situ produced cosmogenic 10be for 11 boulders from moraines in the encierro valley 29 s northern chile we discuss sample specific effects topographic shielding sample geometry rock surface erosion inheritance and post depositional geomorphological instability and systematic uncertainties production rate of 10be latitude and altitude scaling minor glacial advances probably occurred around 11 6 1 2 ka bp whereas major advances are recorded at 14 0 1 4 ka bp and eventually at 24 1 2 4 ka bp this may indicate synchrony of some late pleistocene glacial advances south and north of the so called arid diagonal 25 s increased precipitation plays a dominant role for the observed late pleistocene glacial advances in the absence of further glacial chronologies south and north of the research area it remains difficult to disentangle the influence of the complex and in space and time variable westerlies and the tropical summer precipitation regime

the initial value problem for tropical perturbations to a baroclinic atmosphere large scale wave propagation ideas have proved extremely valuable in interpreting real and model data these ideas have been developed in the context of barotropic models and here the extension to baroclinic atmospheres is investigated the dispersion of waves from an initial large scale tropical perturbation to a baroclinic basic flow is studied using a direct approach a 15 level spectral primitive equation model is integrated forward in time even in baroclinically unstable flows it is found that for a period normally of order 12 days the model yields what can be considered to be the direct response to the tropical perturbations after this time baroclinic instability dominates the basic flows are a resting atmosphere a climatological westerly an equatorial longitudinal modification to this and a 3 d climatological december february state for the perturbations used here equatorial kelvin waves play only a very small role the large scale equatorial rossby wave shows only small dispersion and tends to move with a doppler shifted phase speed which allows it to accumulate to the east of an equatorial maximum of 10 ms 1 or more rossby wavetrains propagate into the middle and high latitude westerly regions with the climatological flow perturbations in the indian ocean west pacific sector trigger a modal structure in the north pacific and wavetrain across north america very much as barotropic theory would suggest and similar to observed pacific north america pna patterns in such a flow the middle latitude waves tend to extend to the equator in the westerly regions of the east pacific and atlantic in agreement with observed behaviour

oxygen isotope perspective on precambrian crustal growth and maturation in this study the authors contrast insights on precambrian crustal growth and maturation from radiogenic and oxygen isotope systematics in the superior 3 0 2 7 ga and grenville 1 3 1 0 ga provinces of the canadian shield oxygen isotope ratios in zircon provide the best evidence of supracrustal input into ancient orogens archean superior province zircons have relatively low delta sup 18 o values and a limited range 5 7 per thousand 0 6 per thousand while proterozoic grenville province zircons have elevated delta sup 18 o values and a wider range 8 2 per thousand 1 7 per thousand these data reflect fundamental differences in crustal evolution and maturation between the superior and the grenville provinces in the grenville province radiogenically juvenile supracrustal material with high delta sup 18 o values was buried or subducted to the base of the crust within 150 m y of initial crust production causing high magmatic delta sup 18 o values delta sup 18 o zircon ge 8 per thousand in anorthosite suite and subsequent plutons information about large volumes and rapid recycling of grenville crust is not accessible from radiogenic isotope data alone the grenville data contrast with the restricted delta sup 18 o values of superior province magmatism where subtle approximately 1 per thousand elevation in delta sup 18 o occurs only in volumetrically minor late to postorogenic sanukitoid plutons differences in sediment delta sup 18 omore values between the superior and grenville provinces are predominantly a function of the delta sup 18 o of source materials rather than differences in chemical maturity or erosion styles this study shows that zircon is a robust reference mineral to compare igneous processes in rocks that have undergone radically different histories less

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

parabolic halite dunes on the salar de uyuni bolivia abstract palaeoenvironmental interpretation in desert and evaporitic sediments is often ambiguous consequently the recognition of primary sedimentary structures that indicate subaerial exposure or shallow marine conditions are therefore of crucial importance when interpreting marginal sedimentary evaporite facies parabolic halite dunes described here for the first time are observed on the salt crust of the largest salt flat in the world the salar de uyuni in bolivia the halite dunes are relatively small 0 7 1 3 m in width and length well defined lobate to hemicyclic parabolic dunes and are formed directly on the salt crust a model describing the formation and migration of the dunes in relation to brine level and climatic conditions is presented

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

lake highstands on the altiplano tropical andes contemporaneous with heinrich 1 and the younger dryas new insights from 14 c u th dating and δ 18 o of carbonates this study provides new geochronological and stable isotope constraints on late pleistocene fluctuations in lake level that occurred in the closed watershed of the central altiplano between 25 and 12 ka u series isochrons and 14 c ages from carbonates are used to confirm and refine the previous chronology published placzek et al 2006b our new data support three successive lake highstands during the late pleistocene i the lake sajsi cycle from 25 to 19 ka that culminated at 3670 m at about 22 ka almost synchronously with the global last glacial maximum ii the lake tauca cycle that lasted from 18 to 14 5 ka and was characterized by the highest water level reached at least 3770 m from 16 5 to 15 ka iii the lake coipasa cycle from 12 5 to 11 9 ka that reached an elevation of 3700 m 42 m above the elevation of the salar de uyuni 3658 m these high amplitude lake level fluctuations are in phase with the cold warm oscillations that occurred in the north atlantic and greenland during the late pleistocene heinrich 1 bolling allerod younger dryas such temporal coincidence supports the hypothesis that wet events recorded in the central altiplano are controlled by the northesouth displacement of the inter tropical convergence zone resulting from changes in the meridional temperature gradient finally the oxygen isotope ratios measured in these lacustrine carbonates allows for calculation of the 18 o value of paleolake waters estimates of water 18 o v smow are 2 8 0 7 for lake tauca and 1 6 0 9 for lake coipasa these data are used to constrain changes in lake hydrology and can be interpreted to indicate that the proportion of precipitation arising from local water recycling was less than 50

astronomical forcing of contrasting rainfall changes in tropical south america between 12 400 and 8800 cal yr b p abstract today precipitation over tropical south america is largely controlled by the seasonal movements of the inter tropical convergence zone itcz during the summer the itcz is shifted southward due to the warming of the continent paleoclimate data from southeastern amazonia and the central andes indicate that these two areas evolved similarly during the last 30 000 yr however between 12 400 and 8800 cal yr b p eastern amazonia received substantial moisture whereas the bolivian altiplano was arid this suggests that the itcz during summer was then farther north than it is today

a simple atmospheric model of the local and teleconnection responses to tropical heating anomalies abstract a minimal complexity model of both the local and remote stationary responses of the atmosphere to tropical heating anomalies is described and demonstrated two levels are recast as baroclinic and barotropic components with thermal advection in the tropics neglected the model is linearized about some idealized and realistic background wind fields and forced with a localized heating for illustration in the tropics the baroclinic responses are familiar from the matsuno gill model these excite barotropic responses by advective interactions with vertical background wind shear the barotropic signals are in turn transmitted to high latitudes only in the presence of barotropic background westerly winds for an el nino like equatorial heating the barotropic response has anticyclones to the north and south of the heating reinforcing opposing the anticyclonic cyclonic baroclinic gyres in the upper lower troposphere with realistic background flows the model reproduces the hemispheric asymmetry

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

paleohydrology of the laguna lejia north chilean altiplano and climatic implications for late glacial times paleoenvironmental and sedimentological data from laguna lejia 23 30 s 67 42 w 4325 m in the high altiplano of the chilean atacama desert indicate that climatic conditions during late glacial times were significantly wetter than today a water and energy budget model was used to simulate climatic scenarios that would have resulted in the observed changes in the water levels water surfaces water volumes and salinity during the time interval different climatic scenarios for the laguna lejia catchment include precipitation increases of over 100 up to 400 500 mm yr today 200 mm yr to account for the late glacial lake levels with shorelines 15 25 m higher than at present and a lake surface of 9 11 km2 compared to the present 2 km2 during the lake maximum about 13 500 11 300 yr b p finely laminated sediments consisting of mg calcite diatoms and sometimes gypsum were deposited the paleoenvironmental evidence indicates that north easterly wind direction prevailed and the summer rainfall resulted from a seasonal poleward shift of the tropical circulation the lake history of laguna lejia is representative for the altiplano area between 21 and 24 s

tropical south america during the last glacial maximum evidence from glacial periglacial and fluvial records abstract the records of the lgm climates of tropical south america are still sparse compared to the vast region under consideration nevertheless a number of records hold up to critical evaluation early attempts to reconstruct the lgm temperature and precipitation conditions for the lgm around 21 14 c ka bp have suggested that relative to present lowland temperatures were on average only a few c cooler whereas in the andes the temperature depression was in the range of 6 8 c these reconstructions further suggested that tropical precipitation was more limited in both the lowlands and in the andes although recent pollen evidence supports significantly cooler tropical lowland temperatures during the lgm additional alkenone evidence from sea surface temperatures and model analysis are contradictory the data from tropical south america suggest that the late quaternary climatic changes of the lowlands as well as of the andean mountains reflect a response 1 to environmental changes in the source area of the moisture and 2 to global temperature fluctuations based on glacial periglacial and pollen evidence a lgm temperature depression of 5 6 c can be assumed for both tropical lowland south america and the andes these lgm values for the cooling correspond with recent coral records from barbados and the southwestern pacific ice core records from peru noble gas measurements in brazil and ocean core records from the western equatorial atlantic no difference in the value of lgm cooling can be recognised between the tropical lowlands and the high mountains of south america furthermore in all regions the lgm climates were more arid than the present day climates terrestrial records have not yet yielded records of younger dryas age apart from the tropical andes of ecuador where the younger dryas time is characterised by a cooler and drier climate pollen evidence for cooler younger dryas conditions comes from the bolivian andes

climate change in the circum north atlantic region during the last deglaciation a survey of new and published palaeoclimate data indicates that both the high and low latitude north atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial to interglacial transi tion climate model results suggest that changes in the melting history of the laurentide ice sheet may explain much of this nonlinear response of the climate system to astronomical milankovitch forcing

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

iod influence on the early winter tibetan plateau snow cover diagnostic analyses and an agcm simulation using diagnostic analyses and an agcm simulation the detailed mechanism of indian ocean dipole iod influence on the early winter tibetan plateau snow cover ewtpsc is clarified in early winter of pure positive iod years with no co occurrence of el nino the anomalous dipole diabatic heating over the tropical indian ocean excites the baroclinic response in the tropics since both baroclinic and barotropic components of the basic zonal wind over the arabian peninsula increase dramatically in early winter due to the equatorward retreat of the westerly jet the baroclinic mode excites the barotropic rossby wave that propagates northeastward and induces a barotropic cyclonic anomaly north of india this enables the moisture transport cyclonically from the northern indian ocean toward the tibetan plateau the convergence of moisture over the plateau explains the positive influence of iod on the ewtpsc in contrast the basic zonal wind over the arabian peninsula is weak in autumn this is not favorable for excitation of the barotropic rossby wave and teleconnection even though the iod related diabatic heating anomaly in autumn similar to that in early winter exists this result explains the insignificant significant positive partial correlation between iod and the autumn early winter tibetan plateau snow cover after excluding the influence of enso the sensitivity experiment forced by the iod related sst anomaly within the tropical indian ocean well reproduces the baroclinic response in the tropics the teleconnection from the arabian peninsula and the increased moisture supply to the tibetan plateau also the seasonality of the atmospheric response to the iod is simulated

systematic multiscale models for the tropics systematic multi scale perturbation theory is utilized to develop self consistent simplified model equations for the interaction across multiple spatial and or temporal scales in the tropics one of these models involves simplified equations for intraseasonal planetary equatorial synoptic scale dynamics ipesd this model includes the self consistent quasi linear interaction of synoptic scale generalized steady matsuno webster gill models with planetary scale dynamics of equatorial long waves these new models have the potential for providing self consistent prognostic and diagnostic models for the intraseasonal tropical oscillation other applications of the systematic approach reveal three different balanced weak temperature gradient wtg approximations for the tropics with different regimes of validity in space and time a synoptic equatorial scale wtg sewtg a mesoscale equatorial wtg mewtg which reduces to the classical models treated by others and a new seasonal planetary equatorial wtg spewtg both the spewtg and mewtg model equations have solutions with general vertical structure yet have the linearized dispersion relation of barotropic rossby waves thus these models can play an important role in theories for midlatitude connections with the tropics the models are derived both from the equatorial shallow water equations in a simplified context and also as distinguished limits from the compressible primitive equations in general

a late glacial holocene pollen record from the eastern andes of northern peru abstract a pollen and sediment record of a core 4 2 m long from laguna baja 7 42 s 77 32 w 3575 m in the cordillera oriental of northern peru suggests several episodes of major vegetational and climatic change over the past 13 000 yr the oldest pollen assemblage consists of a mixture of paramo elements tropical alpine vegetation including high percentages of poaceae 40 that decline upward moist montane forest compositae and polylepis and wet montane forest e g hedyosmum and podocarpaceae organic carbon content range from 60 with high percentages of jamesonia a fern characteristic of paramo and decreasing values of plantago tubulosa and the wet montane forest elements hedyosmum and podocarpaceae charcoal percentages are at a maximum during this period magnetic susceptibility and sand percentages are high and percentages of organic matter are low several explanations for these changes are possible including a reduction in temperature and moisture more frequent periods of aridity with increased fires or natural succession the holocene record begins with pronounced increases in organic carbon and pollen of wet montane forest primarily hedyosmum podacarpaceae and urticales high values of podocarpaceae pollen 35 and a decline in charcoal suggest temperature and moisture levels above modern day values wet montane forest pollen remain high and charcoal values are low from about 10 000 to 6000 yr b p suggesting that warm and moist conditions prevailed for about 4000 yr subsequently podocarpaceae and urticales decline and for a brief time alnus is prominent in the pollen record following the alnus maximum at about 5000 yr b p poaceae ambrosia and chenopodiaceae amaranthaceae become frequent increased paramo and disturbance indicator pollen suggest increased anthropogenic activities in this region from the middle holocene to the present