late miocene holocene canyon incision in the western altiplano northern chile tectonic or climatic forcing abstract major fluvial incision 600 1000 m affecting the coastal cordillera and central depression of northern chile is analysed to evaluate supposed coeval uplift of the altiplano and or climatic changes in the atacama desert the timing of the beginning of incision is constrained by the age of deposition of the central depression top in the north 18 19 s this top corresponds to fluvial gravels accumulated between 11 9 0 6 ma and 8 3 0 5 ma which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15 0 0 6 and 11 2 0 6 ma thus gravel deposition ended at 11 9 11 2 ma to the south 19 20 s the central depression top corresponds to c 6 ma alluvial deposits stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and or developed under a regime of lower erosion capacity owing to drier climate vertical incision rate evolution is compatible with eastward knickzone migration dissection required a considerable altitude difference between ancient and present day river base levels which was achieved predominantly by basin infill on an already partially elevated bedrock therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift exoreic canyons occur when climatic conditions in the catchments are arid semiarid whereas endoreism is developed when these conditions in catchments are hyperarid

erosional processes topographic length scales and geomorphic evolution in arid climatic environments the lluta collapse northern chile the lluta collapse of northern chile is one of the oldest recognizable landslides 2 5 ma in a hyperarid continental setting this paper develops a conceptual landscape evolution model of the lluta collapse and analyzes the controls of mass wasting and erosion sediment transport in channels on the topographic development the data presented here imply that high relief along a topographic scarp surface fracturing elevated groundwater table during a more humid climate and an aquitard underlying permeable ignimbrites are preparatory causal factors for landsliding 2 5 ma ago a strong seismic event then possibly resulted in the displacement of ca 26 km3 of mass subsequent modification of the landslide scar occurred by backward erosion resulting in the establishment of a dendritic drainage network and the removal of an additional ca 24 km3 of material it appears that this mass was produced by mass wasting in the headwaters and exported by high concentrated debris flows in channels in addition morphometric information suggest that whereas the geometrical development of the lluta collapse has been controlled by gravitational mass wasting the rates of the development of this geomorphic unit have been limited by the export rates of mass and hence by the transport capacity of the flows

anti cyclonic eddies northwest of luzon in summer fall observed by satellite altimeters anti cyclonic eddies northwest of luzon of the philippines in summer fall are identified in the merged data products of satellite altimeters of topex poseidon jason 1 and european research satellites the generation and propagation of the anti cyclonic eddies which are confirmed by satellite ocean color data are found to be a seasonal phenomenon that is phase locked to the onset of the southwesterly monsoon and the relaxation of the cyclonic wind curl in the northeastern south china sea the eddies originate from northwest of luzon in summer move across the northeastern south china sea to reach the china continental slope in fall and propagate southwestward along the continental slope in fall winter inducing shelfbreak current variations in the western south china sea in fall winter the anti cyclonic eddy discovered by li et al 1998 in the northern south china sea is found to originate from northwest of luzon and carry primarily the south china sea waters it does not appear to be an eddy shed from the kuroshio in the luzon strait area as alluded by li et al 1998 and others

denudation rates and a topography driven rainfall threshold in northern chile multiple cosmogenic nuclide data and sediment yield budgets abstract the quantification of geomorphic process rates on the outcrop and the orogen scale is important to describe accurately the interaction between the relative effects of erosion tectonics and climate on landscape evolution we report single and paired cosmogenic nuclide 10 be 26 al and 21 ne derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central andes that show a distinct spatial variation a positive correlation of erosion rates with elevation and present day rainfall rates is observed erosion rates at lower altitudes the hyperarid coastal cordillera and the western escarpment with the northern part of the atacama desert are extremely low and of the order of 10 100 cm my nominal exposure ages 1 6 my in contrast erosion rates at higher altitudes the semiarid western cordillera range up to 4600 cm my nominal exposure ages 0 02 0 1 my this latter average long term bedrock erosion rate record suggested to be coupled to an orographically controlled pattern of rainfall is also reflected in the pattern of denudation rates derived from a short term decadal record of limited sediment yield data specifically denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long lived cosmogenic nuclides from bedrock hillslope interfluves of the western cordillera nevertheless the production and the supply of sediment from the western andean slope are very limited analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non bedrock samples such as boulders or amalgamated clast samples notably this study shows that saturation of nuclides usually assumed in studies where only a single nuclide is analyzed is rather the exception than the rule as revealed by erosion island plots constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non steady state concentrations and more complicated exposure scenarios furthermore the use of multiple nuclides with different half lives allowed us to infer that no significant variations in long term erosion rates have occurred and that at the western escarpment erosion rates have been low and constant for most of the late neogene nevertheless the time intervals necessary to reach steady state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state

palaeo geoecological significance of pleistocene trees in the lluta valley atacama desert in the lluta valley northern chile climate is hyperarid and vegetation is restricted to the valley floors and lowermost footslopes fossil tree trunks and leaves of predominantly escallonia angustifolia however are abundant up to 15 m above the present valley floor where they are intercalated with slope deposits reflecting higher water levels in the past a total of 17 samples have been radiocarbon dated yielding ages between 38 and 15k cal a bp the youngest ages of 15 4k cal a bp are interpreted as reflecting the beginning of river incision and lowering of the valley floor impeding the further growth of trees at higher parts of the slopes the most plausible scenario for this observation is intensified river incision after 15 4k cal a bp due to increased stream power and runoff from the rio lluta headwaters in the western cordillera and altiplano corresponding to the highstand of the tauca and central andean pluvial event cape wet phase

a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years the quaternary paleoclimate of the central andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region the exact timing duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another and there have been few opportunities to compare climatic records from the same proxy along environmental gradients vegetation histories from fossil rodent middens provide one such opportunity on the pacific slope of the andes we previously reported a vegetation history from the upper margin 2400 3000 m of the absolute desert in the central atacama desert of northern chile that record identified a distinct wet phase that peaked between 11 8 and 10 5 ka when steppe grasses and other upland elements expanded as much as 1000 m downslope and a secondary wet period during the middle to late holocene 7 1 3 5 ka the latter wet phase remains controversial and is not as readily apparent in our lowelevation midden record we thus sought to replicate both phases in a midden record from the mid elevations 3100 3300 m of the arid prepuna where slight precipitation increases would be amplified midden records from these elevations identify conditions wetter than today at 13 5 9 6 7 6 6 3 4 4 3 2 and possibly 1 8 1 2 ka dry phases occurred at 9 4 8 4 ka and possibly at ca 5 1 ka present floras and modern hyperarid conditions were established after 3 2 ka the records from the two elevational bands generally match with some important differences these differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert 2003 elsevier science b v all rights reserved

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

review of erosion dynamics along the major n s climatic gradient in chile and perspectives abstract chile is an elongated country running in a north south direction for more than 30 along a subduction zone its climate is progressively wetter and colder from north to south this particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate land use slope tectonics volcanism etc here we review the erosion rates factors and dynamics over millennial to daily periods reported in the literature in addition 21 new catchment mean erosion rates suspended sediment and 10be are provided and previous suspended sediment derived erosion rates are updated a total of 485 local and catchment mean erosion rates are reported erosion rates vary between some of the smallest values on earth 10 5 mm a to moderate values 0 5 mm a compared to other active ranges this review highlights strong limitations concerning the quantification of local erosion factors because of uncertainties in sampling point location slope and rainfall data for the mean erosion rates e for the millennial and decennial catchments a model of the form e s 1 s 0 6 2 r with 0 3 0 8 accounts for 40 to 70 of the erosion variance confirming a primary role of slope s compared to precipitation rate r over this time scale over the long term this review points to the long 5 to 10 ma response time of rivers to surface uplift in north central arid chile over millennia data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates as well as the link between glacier erosion and glacier sliding velocity in this period of time a discrepancy exists between the long term offshore sedimentological record and continental decennial or millennial erosion data for which no single explanation appears still little information is available concerning the magnitude of variation of millennial erosion rates over centuries data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years probably associated with historical harvesting

monsoon surges trigger oceanic eddy formation and propagation in the lee of the philippine islands 1 two winter monsoon surge events northerly and easterly of january 2005 are captured in a one way coupled atmosphere 8 km resolution and ocean 3 km resolution simulation of the philippines region intensified wind jets and wakes in the lee of mindoro and luzon islands induce the generation and migration of a pair of counter rotating oceanic eddies in the model with propagation direction related to the orientation of the winds during each of the surges features shared by the eddies include size 100 200 km depth 300 m and propagation speed 0 1 0 15 m s 1 for cyclones mean wintertime model wind stress positive negative curl coincides with the climatological cyclone anticyclone distribution from a prior 8 year altimetry based census of eddies in the southeast quadrant of the south china sea during the winter monsoon moreover the simulation results agree with contemporaneous satellite and historical in situ data characterizing regional oceanic eddy and atmospheric surface jet properties

seasonal thermal fronts on the northern south china sea shelf satellite measurements and three repeated field surveys seasonal thermal fronts associated with wind driven coastal downwelling upwelling in the northern south china sea are investigated using satellite measurements and three repeated fine resolution mapping surveys in winter spring and summer the results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons which tend to be approximately aligned with the 20 100 m isobaths driven by the prevailing winter summer monsoon the band shaped fronts were observed with a magnitude exceeding 0 1 degrees c km in the subsurface and accompanied by energetic coastal downwelling upwelling due to shoreward offshore ekman transport the downward upward tilting of seasonal thermoclines across the shelf exceeds 20 m significantly contributing to the development of thermal fronts over the shelf in addition the diagnostic analysis of potential vorticity pv suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling favorable monsoon forcing this is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing at the same time the coastal currents are substantially regulated by the seasonal winds an expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region these results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf

landscape modification in response to repeated onset of hyperarid paleoclimate states since 14 ma atacama desert chile the landscape of the hyperarid atacama desert in northern chile records extremely slow change on earth s surface disputed ages for the onset of hyperaridity range from the late paleogene through the pleistocene a long term paleoclimate record is recorded in a nonmarine basin whose fill is primarily alluvial strata for this setting the primary proxies for climate state are the mineralogical and chemical composition of soil which varies across a precipitation gradient and the landforms and deposits of alluvial fans during the most recent 15 million years five climate related landscape stages are resolved for the pampa del tamarugal sedimentary basin with each successively younger stage inset lower in the local topography than its predecessor the earliest landscape stage is expressed as a set of alluvial strata inherited from a time of arid or semi arid climate ca 14 12 ma the younger four landscape stages generated a composite long lasting exposure surface predominantly hyperarid conditions have persisted since ca 12 1 ma during which four intervals of arid to semi arid climate occurred each wet interval was short lived a million years or less whereas some of the hyperarid periods were lengthy 1 5 m y the hyperarid intervals were roughly 11 5 5 ma 4 5 4 ma 3 6 2 6 ma 2 2 1 ma and repeated intervals during the last 1 m y the onset of hyperaridity ca 12 ma likely reflects the growth of the andes mountains above a climate threshold in contrast sea surface temperature variability likely has controlled atacama paleoclimate changes since the late miocene

fault related folding drainage network evolution and valley incision during the neogene in the andean precordillera of northern chile abstract we describe neogene drainage network development before during and after regional folding in the precordillera of the andes of northern chile 18 19 s the drainage network developed on an extensive regular erosional surface formed on oligocene miocene ignimbrites oxaya formation the folding affecting the rocks of the precordillera is represented by the oxaya anticline oa which trends n to nw is 50 km long and 30 km wide the fold is gentle west vergent and has resulted in an uplift of the hinge zone by up to 850 m it formed by the propagation on its western border of a subvertical east dipping blind reverse fault ausipar fault af the folding occurred in the middle late miocene essentially between 11 7 0 7 and 10 7 0 3 ma its maximum duration was 2 my two phases of drainage development are recognised in the precordillera an initial lower middle miocene 19 12 ma parallel drainage network is well preserved and synchronous with fluvial and lacustrine sedimentation in the central depression the network was poorly structured and attained maximum incision of to 250 50 m the minimum long term rate of incision was 36 7 m my folding generated the progressive abandonment and fossilisation of the initial parallel drainage network which became trellissed and concentrated in a few deeply incised valleys in the anticline hinge the lluta and azapa main valleys present a total incision of 1650 50 and 1605 50 m respectively whereas the cardones valley presents 595 50 m during folding river incision at the fold hinge was equal to or greater than the amplitude of the folding which is 790 50 m in the lluta valley and 715 50 m in the azapa valley consequently the long term rate of synfolding incision was much greater than 395 25 lluta valley and 358 25 m my azapa valley the cardones valley was fossilised approximately in the middle of the folding after folding 11 to 0 ma the incision in the lluta and azapa rivers was 610 100 and 640 100 m and with a rate of 56 9 and 58 9 m my respectively the postfolding incision rate is approximately twice than of the prefolding incision rate this implies an acceleration of valley incision since the late miocene which is considered as consequence of regional uplift of the andean forearc

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

geochronologic and stratigraphic constraints on canyon incision and miocene uplift of the central andes in peru the deepest valleys of the andes have been cut in southern peru by the rios cotahuasi ocona and colca majes these canyons are late miocene landforms based on a new ignimbrite stratigraphy supported by 42 new 40ar 39ar age determinations obtained on plateau forming and valley filling ignimbrites between 19 and 13 ma a gently sloping surface bevelling the clastic wedge southeast of the developing mountain front was mantled by widespread ignimbrites after 13 ma this paleosurface was tilted up from 2 2 km a s l at the mountain front to 4 3 km a s l at the base of the pliocene and pleistocene volcanoes that crown the southwestern edge of the altiplano the canyons incised this topography after 9 ma while the dated base of younger ignimbrite valley fills suggests that these canyons had been cut down to near their present depths as early as 3 8 ma by 1 4 ma however the canyons had been almost completely refilled by 1 3 km thick unwelded pyroclastic deposits which were subsequently eroded valley incision since 9 ma at an average rate of 0 2 mm yr 1 is the response to topographic uplift after 13 ma combined with increasing runoff due to a wetter climate recorded after 7 ma although long term aridity generated an imbalance between high long term uplift rates and low plateau denudation rates the combination of aridity and volcanism still promoted canyon incision because episodic volcanic fills maintained a cycle of catastrophic debris avalanches and subsequent dam breakouts

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

re evaluation of mid holocene deposits at quebrada puripica northern chile duringthe middle holocene 8 3 ka wetland deposits accumulated in areas with emerg ent water tables in the central atacama desert 22 24 s producinga stratig raphic unit unit c that can be mapped and correlated across different basins and geomorphic settings wherever mapped unit c is located between 6 and 30 m above modern wetlands and includes thick sequences of diatomite and organic mats the origin depositional environment and paleoclimatic significance of unit c is controversial and currently under debate grosjean science 292 2001 2391a suggests the unit developed under a regime of falling lake and ground water levels whereas evidence presented here suggests that unit c formed during a period of rising ground water levels and increased vegetation cover the debate is embedded in broader discussions about geomorphic processes in ground water fed streams as well as the history and forcingof climate variability in the central andes the central atacama and andes are remote with few opportunities for different researchers to examine the same site one exception is a sequence of mid holocene deposits at the confluence of quebrada seca and r o puripica in northern chile 23 s grosjean et al quat res 48 1997 239 246 initially suggested the deposits accumulated in temporary lake basins which formed when recurringdebris flows from a side canyon quebrada seca dammed the main channel r o puripica duringa period of drought and reduced stream flow upon our visit to the site we found evidence that clearly demonstrates the deposits were not formed in temporary lakes but rather were deposited in a wetland environment disagreement remains about the climatic interpretation of wetland deposits grosjean science 292 2001 2391a now suggests that local ground water levels rise and wetland deposits aggrade in deep canyon systems such as r o puripica when stream power and channel erosion is reduced duringprolong ed dry spells however sedimentological evidence and the presence of unit c in many depositional environments not just deep canyons indicate that it formed during a period of higher regional ground water levels that were sustained by enhanced precipitation and recharge in the high andes 2003 elsevier science b v all rights reserved

late quaternary hydrological and ecological changes in the hyperarid core of the northern atacama desert 21 s abstract the hyperarid core of the atacama desert possesses important reserves of fossil or ancient groundwater yet the extent and timing of past hydrologic change during the late quaternary is largely unknown in situ and or short distance transported leaf litter deposits abound along relict fluvial terraces inserted within four dry and unvegetated valleys that drain into the endorheic basin of pampa del tamarugal pdt 21 s 900 1000 m one of the largest and economically important aquifers in northern chile our exceptional archive offers the opportunity to evaluate the response of low elevation desert ecological and hydrological systems to late quaternary climate variability three repeated expansions of riparian wetland ecosystems and perennial rivers occurred along the southernmost pdt basin between 17 6 14 2 ka 12 1 11 4 ka and from 1 01 0 71 ka both early and late archaic archaeological artefact are present in clear association with our fossil riparian wetland assemblages which suggests that these palaeoenvironmental changes facilitated past human occupations in the hyperarid core of the atacama desert using modern analogues we estimate that these ecological and hydrological changes were triggered by a threefold increase in rainfall along the headwaters of what are presently inactive canyons comparisons with other regional palaeoclimatic records from the central andes indicate that these changes were synchronous with the widespread pluvial stages now termed the central andean pluvial event cape 17 5 14 2 ka and 13 8 9 7 ka in addition we summarize new evidence for perennial runoff riparian ecosystems and a major human settlement during the latest holocene our findings clearly show that local hydrological changes in the pdt were coupled with precipitation variability in the adjacent eastern highlands during the late quaternary the long term dynamics of low elevation desert ecological and hydrological systems are likely driven by changes in moisture sources with one source tied to the amazon region n ne mode and the other to the gran chaco region se mode we conclude by linking enso like variability and moisture variations over the gran chaco to the three major regional scale recharge events over the last 18 ka in the pdt basin we conclude by asserting that an important portion of the groundwater resources in the pdt is indeed fossil inherited from past pluvial events we recommend that the relationship between ancient recharge together with palaeoclimate records of past headwater rainfall fluctuations should be incorporated into future water balance models and evaluation of groundwater potential in northern chile

upper layer circulation in the south china sea abstract upper layer circulation is investigated by using all available historical temperature profiles combined with climatological temperature salinity relationships in the south china sea two cyclonic eddies are revealed one is located east of vietnam called the east vietnam eddy and the other is off northwest luzon called the west luzon eddy both local ekman pumping and remotely forced basin scale circulation are important mechanisms controlling these two eddies the luzon strait transport relative to 400 db is estimated to be of the order 3 0 sv 1 sv 1 106 m3 s 1 in the mean and has a seasonal cycle dominated by the annual signal with a maximum 5 3 sv in january february and a minimum 0 2 sv in june july pressure gradients are also examined to explore the dynamics of the intrusion of waters from the pacific into the south china sea through the luzon strait

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

renewed uplift of the central andes forearc revealed by coastal evolution during the quaternary most of the pacific coast of the central andes between 15 s and 30 s displays a wide a couple of kilometres planar feature gently dipping oceanwards and backed by a cliff this morphology usually of marine orgin is called rasa and argues for a recent and spatially continuous uplift of the margin over the 1 500 km long coastal region we describe the cliff foot is found at a similar elevation 110 m amsl all over the studied area with the exception of peninsulas such as the mejillones peninsula the compilation of published chronological data and the extrapolation of re appraised uplift rates provide evidence for a common cliff foot age of around 400 ka i e marine isotopic stage mis 11 this together with other geological constraints indicates a quaternary renewal of uplift in the central andes forearc after a late pliocene quiescence or subsidence

neogene climate change and uplift in the atacama desert chile the relationship between andean uplift and extreme desiccation of the west coast of south america is important for understanding the interplay between climate and tectonics in the central andes yet it is poorly understood here we use soil morphological char acteristics salt chemistry and mass independent fractionation anomalies 17 o values in dated paleosols to reconstruct a middle miocene climatic transition from semiaridity to extreme hyperaridity in the atacama desert paleosols along the southeastern margin of the calama basin change from calcic vertisols with root traces slickensides and gleyed horizons to an extremely mature salic gypsisol with pedogenic nitrate we interpret this transition which occurred between 19 and 13 ma to represent a change in precipitation from 200 mm yr to 20 mm yr this drastic reduction in precipitation likely resulted from uplift of the central andes to elevations 2 km the uplift blocked moisture from the south american summer monsoon from entering the atacama the mid miocene gyp sisol with pedogenic nitrate is located at elevations between 2900 and 3400 m in the cal ama basin significantly higher than modern nitrate soils which occur below 2500 m modern and quaternary soils in this elevation zone contain soil carbonate and lack ped ogenic gypsum and nitrate we infer that 900 m of local surface uplift over the past 10 m y displaced these nitrate paleosols relative to modern nitrate soils and caused a return to wetter conditions in the calama basin by decreasing local air temperatures and creating an orographic barrier to pacific air masses

chronology of alluvial terrace sediment accumulation and incision in the pativilca valley western peruvian andes abstract the incision and aggradation of the pativilca alluvial fan delta system in the western peruvian andes through quaternary time can be traced in detail using well exposed fill terraces studied by a combination of cosmogenic nuclide dating terrace mapping and paleo erosion rate calculations two alluvial terraces have been dated through depth profile exposure dating using in situ 10be the dating results return an age for the abandonment of the terrace at 200 90 ka in pativilca and 1 2 ma 0 3 ma in barranca these new ages complete the database of previously dated terrace fills in the valley together with the results of the terrace mapping and the absolute ages of the terraces we show that the valley fills are made up of at least four terraces two terraces near the city of pativilca and two terraces in the city of barranca while previous studies have shown two periods of sediment aggradation one period around 100 ka barranca and another period around 30 ka pativilca our new results show two additional periods of sediment aggradation and subsequent incision that have not been reported before finally paleo erosion rates at the time of the deposition of the terrace material were calculated and compared to the available modern estimates the paleo erosion rates vary from 140 12 m ma 1 to 390 40 m ma 1 the period of sediment accumulation prior to the abandonment of the terrace at 200 ka corresponds to a wet phase and a pulse of erosion in contrast the period of sediment accumulation prior to the abandonment of the terrace at 1 2 ma does not correspond to a pulse of erosion and could rather correspond to a change of the base level possibly induced by a sea level rise

eddy heat and salt transports in the south china sea and their seasonal modulations this study describes characteristics of eddy turbulent heat and salt transports in the basin scale circulation as well as in the embedded mesoscale eddy found in the south china sea scs we first showed the features of turbulent heat and salt transports in mesoscale eddies using sea level anomaly sla data in situ hydrographic data and 375 argo profiles we found that the transports were horizontally variable due to asymmetric distributions of temperature and salinity anomalies and that they were vertically correlated with the thermocline and halocline depths in the eddies an existing barrier layer caused the halocline and eddy salt transport to be relatively shallow we then analyzed the transports in the basin scale circulation using an eddy diffusivity method and the sea surface height data the argo profiles and the climatological hydrographic data we found that relatively large poleward eddy heat transports occurred to the east of vietnam eov in summer and to the west of the luzon islands wol in winter while a large equatorward heat transport was located to the west of the luzon strait wls in winter the eddy salt transports were mostly similar to the heat transports but in the equatorward direction due to the fact that the mean salinity in the upper layer in the scs tended to decrease toward the equator using a 21 2 layer reduced gravity model we conducted a baroclinic instability study and showed that the baroclinic instability was critical to the seasonal variation of eddy kinetic energy eke and thus the eddy transports eov wls and wol were regions with strong baroclinic instability and thus with intensified eddy transports in the scs the combined effects of vertical velocity shear latitude and stratification determined the intensity of the baroclinic instability which intensified the eddy transports eov during summer and wls and wol during winter

three long lived anticyclonic eddies in the northern south china sea 1 in august 2007 three long lived anticyclonic eddies ace1 ace2 and ace3 were detected by both satellite sea level anomaly sla map and in situ measurements in the northern south china sea scs ace3 had a two core ace3 1 and ace3 2 structure in situ stations along 18 degrees n almost cut through the centers of ace2 and ace3 2 near the centers of ace2 and ace3 2 mean temperature and sound velocity are similar to 0 65 degrees c and similar to 2 m s 1 larger than those in their surrounding areas respectively while mean salinity and density are similar to 0 02 psu and similar to 0 15 m 3 s 1 smaller than those in their surrounding areas due to downwelling near the eddy cores the depths of maximum and minimum salinity near the eddy cores are similar to 65 m and similar to 35 m larger than those in their surrounding areas the vertical depth with current speed larger than 0 05 m s 1 can reach similar to 900 m their detailed evolutionary processes were depicted based on the variation of geostrophic currents and the trajectories of five drifting buoys ace1 lasted 147 days while ace2 and ace3 lasted 168 days and 210 days respectively ace1 had a smaller mean sla 18 8 cm in its lifetime than ace2 21 8 cm and ace3 25 3 cm but had a larger negative mean vorticity 7 7 x 10 6 s 1 than ace2 7 0 x 10 6 s 1 and ace3 7 0 x 10 6 s 1 one short lived anticyclonic eddy that split from ace2 and another one that merged with ace3 both had a smaller sla negative vorticity and diameter than ace2 and ace3 respectively

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

uplift of the western margin of the andean plateau revealed from canyon incision history southern peru we explore canyon incision history of the western margin of the andean altiplano puna plateau in the central andes as a proxy for surface uplift u th he apatite data show rapid cooling beginning at ca 9 ma and continuing to ca 5 1 ma in response to incision a minimum of 1 0 km of incision took place during that interval the youngest apatite date and a volcanic fl ow perched 125 m above the present valley fl oor dated at 2 261 0 046 ma 40 ar 39 ar show that an additional 1 4 km of incision occurred between ca 5 1 and 2 3 ma thus we infer that a total of at least 2 4 km or 75 of the present canyon depth was incised after ca 9 ma u th he zircon data collected along the same transect imply that the western margin of the plateau was warped upward into its present monoclinal form rather than uplift being accommodated on major surface breaking faults

kuroshio intrusion and the circulation in the south china sea 1 the princeton ocean model is used to study the circulation in the south china sea scs and its seasonal transition kuroshio enters leaves the scs through the southern northern portion of the luzon strait the annually averaged net volume flux through the luzon strait is 2 sv into the scs with seasonal reversals the inflow season is from may to january with the maximum intrusion of kuroshio water reaching the western scs during fall in compensation of summertime surface offshore transport associated with coastal upwelling from february to april the net transport reverses from the scs to the pacific the intruded kuroshio often forms an anticyclonic current loop west of the luzon strait the current loop separates near the dongsha islands with the northward branch continuously feeding the south china sea warm current scswc near the shelf break and the westward branch becoming the south china sea branch of kuroshio on the slope which is most apparent in the fall the scswc appears from december to february on the seaward side of the shelf break flowing eastward against the prevailing wind diagnosis shows that the onshore ekman transport due to northeasterly monsoon generates upwelling when moving upslope and the particular distributions of the density and sea level associated with the cross shelf motion supports the scswc

winter eddy genesis in the eastern south china sea due to orographic wind jets abstract generation of mesoscale eddies in the eastern south china sea scs in winters during august 1999 to july 2002 is studied with a reduced gravity model it is found that the orographic wind jets associated with the northeast winter monsoon and the gaps in the mountainous island chain along the eastern boundary of the scs can spin up cyclonic and anticyclonic eddies over the scs results suggest that direct wind forcing could be an important generation mechanism for the rich eddy activity in the scs and that to simulate this mechanism the resolution of the wind forcing has to be high enough to resolve the local wind jets induced by orographic effects

geochronology and stratigraphy of late pleistocene lake cycles on the southern bolivian altiplano implications for causes of tropical climate change large paleolakes 33 000 60 000 km2 that once occupied the high altitude poopo coipasa and uyuni basins in southern bolivia 18 22 s provide evidence of major changes in low latitude moisture in these now dry or oligosaline basins extensive natural exposure reveals evidence for two deep lake and several minor lake cycles over the past 120 k y fifty three new u th and 87 new 14c dates provide a chronologic framework for changes in lake level deposits from the ouki deep lake cycle are extensively exposed in the poopo basin but no deep lakes are apparent in the record between 98 and 18 1 ka the ouki lake cycle was 80 m deep and nineteen u th dates place this deep lake cycle between 120 and 98 ka shallow lakes were present in the terminal uyuni basin between 95 and 80 ka salinas lake cycle at ca 46 inca huasi lake cycle and between 24 and 20 5 ka sajsi lake cycle the tauca deep lake cycle occurred between 18 1 and 14 1 ka resulting in the deepest 140 m and largest lake in the basin over the past 120 ka multiple 14c and u th dates constrain the highest stand of lake tauca along a topographically conspicuous shoreline between 16 4 and 14 1 ka a probable post tauca lake cycle the coipasa produced a 55 m deep lake that is tentatively dated between 13 and 11 ka we suggest that paleolakes on the bolivian altiplano expanded in response to increased moisture in the amazon and enhanced transport of that moisture onto the altiplano by strengthened trade winds or southward displacement of the intertropical convergence zone itcz pole to equator sea surface temperature sst and atmospheric gradients may have influenced the position of the itcz affecting moisture balance over the altiplano and at other locations in the amazon basin links between the position of the itcz and the ca 23 ka precessional solar cycle have been postulated march insolation over the altiplano is a relatively good fit to our lake record but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire amazon basin temperature may influence altiplano lake levels indirectly as potentially dry glacial periods in the amazon basin are linked to dry conditions on the altiplano intensification of the trade winds associated with la nina like conditions currently brings increased precipitation on the altiplano and deep lake development during the tauca lake cycle coincided with apparently intense and persistent la nina like conditions in the central pacific this suggests that sst gradients in the pacific are also a major influence on deep lake development on the altiplano

perennial stream discharge in the hyperarid atacama desert of northern chile during the latest pleistocene abstract a large fraction of the vital groundwater in the atacama desert of northern chile is likely composed of fossil or ancient reserves that receive little or no recharge in today s hyperarid climate here we present evidence for latest pleistocene perennial streamflow in canyons from the hyperarid core of the atacama desert in northern chile fluvial terraces in the pampa del tamarugal pdt basin 21 s contain widespread fossil wood in situ roots and well preserved leaf litter deposits indicative of perennial surface flow currently absent in these channels nineteen radiocarbon dates on these deposits from four separate drainages within this endorheic basin indicate ages from 16 380 to 13 740 cal yr bp synchronous with paleolake tauca on the bolivian altiplano and other regional evidence for wetter conditions during the latest pleistocene groundwater fed riparian ecosystems and associated fluvial deposits abound today in the absence of direct rainfall in northern atacama canyons with perennial discharge our relict riparian ecosystems from the pdt basin are indicative of conditions similar to these northern canyons given that discharge was higher than present during this time we propose that these deposits represent the most important groundwater recharge events of the last 18 000 years a lesser recharge event occurred during the holocene when phreatophytic trees also grew in these drainages between 1 070 and 700 cal yr bp during the medieval climatic anomaly taken together our evidence lends further support for gradient changes in the equatorial pacific as a major driver of hydrologic change in the atacama on both centennial and millennial time scales central andes hyperaridity riparian ecosystems late quaternary fluvial terraces

late quaternary vegetation and climate history of a perennial river canyon in the rio salado basin 22 s of northern chile abstract plant macrofossils from 33 rodent middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the rio salado northern chile yield a unique record of vegetation and climate over the past 22 000 cal yr bp presence of low elevation prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5 c and may have been near modern at 16 270 cal yr bp displacements in the lower limits of andean steppe and puna taxa indicate that mean annual rainfall was twice modern at 17 520 16 270 cal yr bp this pluvial event coincides with infilling of paleolake tauca on the bolivian altiplano increased enso activity inferred from a marine core near lima abrupt deglaciation in southern chile and heinrich event 1 moderate to large increases in precipitation also occurred at 11 770 9550 central atacama pluvial event 7330 6720 3490 2320 and at 800 cal yr bp desiccation occurred at 14 180 8910 8640 and 4865 cal yr bp compared to other midden sites in the region early holocene desiccation seems to have happened progressively earlier farther south emerging trends from the cumulative midden record in the central atacama agree at millennial timescales with improved paleolake chronologies for the bolivian altiplano implying common forcing through changes in equatorial pacific sea surface temperature gradients

climate controlled shifts in sediment provenance inferred from detrital zircon ages western peruvian andes provenance analysis of pleistocene terrace deposits together with modern sediments from the same streams from four catchments draining the western margin of the andes in peru is used to infer changes in erosion patterns between the past and the present period by matching detrital zircon ages with crystallization ages of source rocks age populations suggest major changes in sediment provenance through the past 100 k y at present sediment sources are mainly located along the steep middle reaches of the rivers whereas during the pleistocene sources were additionally located in the low relief headwaters of these catchments these shifts in the loci of erosion are interpreted to reflect changes in precipitation patterns where periods of stronger precipitation on the altiplano allowed the entrainment of material from the low relief plateau in the past in contrast modern precipitation patterns result in negligible erosion rates on the altiplano and the site of material entrainment shifts to the knickzone reaches where steeper slopes and higher stream power promote erosion in that sense this work illustrates that terrace aggradation is associated with major shifts in provenance sources

mesoscale eddies in the northern south china sea a fine grid resolution model with realistic bathymetry and forcing has been developed to study the characteristics of the mesoscale eddies for the northern south china sea scs the scs model derives its open boundary conditions from a larger scale model which minimizes errors related to the uncertainty of the kuroshio intrusion at the open boundaries the model results are consistent with previous observations model sea surface height anomaly demonstrates that the hydrography and circulation in the northern scs are modulated by westward propagating mesoscale eddies originating in the vicinity of the luzon strait this explains the observed intra seasonal fluctuations at the southeast asian time series study seats station the mesoscale eddies have the same propagation speed as baroclinic rossby waves 0 1 ms 1 the periods of eddy shedding estimated from strouhal number are around 40 50 days in december and 80 120 days in august respectively the seasonal variability of the kuroshio intrusion results in more eddies in winter than in summer r 2007 elsevier ltd all rights reserved

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

generation and life cycle of the dipole in the south china sea summer circulation 1 the south china sea scs summer circulation often has a dipole structure associated with an eastward jet appearing off central vietnam the dipole has an anticyclonic eddy ae south of the jet and a cyclonic eddy ce north of it the life cycle of the dipole structure is analyzed using satellite altimetry data and a reduced gravity model on average the dipole structure begins in june peaks in strength in august or september and disappears in october the dipole evolution lags behind the basin scale wind by about 40 days and 40 days are exactly what it takes for baroclinic planetary waves to cross the southern scs our results show that the vorticity transports from the nonlinear effect of the western boundary currents are crucial for the generation of the dipole structure in addition the strength and direction of the offshore wind jet also play a significant role in determining the magnitudes and the core positions of the two concomitant eddies

lateglacial and early holocene glaciation in the tropical andes caused by la nina like conditions the response of the tropics to north atlantic cold events such as heinrich event i h i 17 15 ka and the younger dryas yd 12 7 11 5 ka is still one of the most tantalizing yet unresolved issues in paleoclimatology the advent of surface exposure dating has therefore instigated the establishment of glacial chronologies in the tropical andes to investigate potential climate teleconnections here we present new exposure ages from the cordillera cochabamba 17 17 s bolivia that reveal glacial advances during h i and yd as well as during the early holocene our chronology correlates well with cold sea surface temperatures in the eastern tropical pacific which indicates that la nina like conditions i e forcings intrinsic to the tropics played a key role for moisture advection and glaciation in the tropical andes

circulations and eddies over the south china sea derived from topex poseidon altimetry topex poseidon t p altimeter data were used to derive time varying circulation and eddies over the south china sea scs for 1993 1999 large variabilities of sea surface heights and dense distribution of eddies were found to occur along a band across the scs basin a cross over method is introduced to compute pointwise velocity components the t p derived circula tions and eddies are consistent with the drifter results from the world ocean circulation experi ment data center 1 because of monsoons the scs circulation is largely cyclonic in winter is largely anticyclonic in summer and is modulated interannually by el nifio southern oscillation 2 both cold and warm core eddies were found in the waters east of vietnam west of luzon and west of the luzon strait but their times of occurrence and the way they evolved vary interannually 3 the reversal of the alongshore currents east of vietnam was in complete accordance with wind stress the locations and kinematic properties of eddies over scs were estimated by the least squares method the averaged vorticities of the cold and warm core eddies are 1 684x 10 6 and 1 738x l0 6 tad s respectively and the shearing and stretching deformations are one thousandth of the vorticities the angular velocity of eddy decreases with increasing radius coherence analy sis suggests that the interannual and seasonal variations of circulation are largely due to wind stress and the semi annual variation is largely due to wind stress curl the angular velocities of eddies over the central scs basin are coherent with the magnitudes and signs of wind stress curl the seasonal steric anomaly was also computed and its spatial pattern and scale are quite different from those of circulation and eddy

timing and nature of alluvial fan development along the chajnantor plateau northern chile abstract alluvial systems in the atacama desert provide a unique opportunity to elucidate the sedimentary response to climate variability particularly changes in precipitation in hyperarid environments alluvial fans along the eastern margin of the salar de atacama adjacent to the chajnantor plateau in the atacama desert of northern chile provide an archive of climate modulated sediment transfer and erosion at an extreme of earth s climate three regional alluvial fan surfaces qf1 oldest to qf3 youngest were mapped along the western flank of the chajnantor plateau the alluvial fans were examined with geomorphic and terrestrial cosmogenic 36 cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment alluvial fans in the study area are comprised of hyperconcentrated flow and boulder rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes alluvial fan surfaces yield exposure ages that range from 49 6 4 4 to 194 12 ka while debris flow boulders yield exposure ages ranging from 12 4 2 1 to 229 53 ka cosmogenic 36 cl exposure ages indicate that abandonment of alluvial fan surfaces qf1 qf2 and qf3 date to 175 22 6 ka mis 6 134 5 9 18 ka mis 6 and 20 07 6 26 ka mis 2 respectively a 36 cl concentration depth profile through alluvial fan qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation 6 m in ca 25 kyr followed by surface abandonment ca 180 200 ka our data support a strong climatic control on alluvial fan evolution in the region and we propose that the alluvial fans along the margins of the salar de atacama form according to the humid model of fan formation

the vertical structure of eddy heat transport simulated by an eddy resolving ogcm abstract the vertical structure of meridional eddy heat transport eht of the north pacific was investigated by analyzing the results from an eddy resolving ocean general circulation model ogcm with a horizontal resolution of while comparing with previous simulation results and observation data in particular the spatial and temporal variation of the effective depth of eht he was investigated which is defined by the depth integrated eht d eht divided by eht at the surface it was found that the annual mean value of he is proportional to the eddy kinetic energy eke level at the surface in general however its seasonal variation is controlled by the mixed layer depth mld in the extratropical ocean 20 n examination of the simulated eddy structures reveals that the temperature associated with mesoscale eddies is radically modified by the surface forcing in the mixed layer while the velocity field is not and the consequent enhanced misalignment of temperature and velocity anomalies leads to

the seasonal variation of the intrusion of the philippine sea water into the south china sea the seasonal variation of the intrusion of the philippine sea water into the south china sea was studied by analyzing the historical hydrographic station data in the northern south china sea and the philippine sea water masses at 150 200 and 250 m were classified by discriminant analysis according to their temperature salinity characteristics at each depth most water in the study region was classified into two groups representing the philippine sea water and the south china sea water respectively the geographic distribution of water masses in the south china sea shows that the philippine sea water was present along the continental margin south of china between october and january a westward current in the northern south china sea in winter was inferred from the distribution of the intrusion water

scale of relief growth in the forearc of the andes of northern chile arica latitude 18 s the stream profiles of rivers of northern chile reveal two graded segments separated by 20 km long knickzones their formation was initiated in the late miocene in response to surface uplift of the western flank of the altiplano this phase of uplift that was coeval with the shift of deformation from the altiplano to the sub andean zone caused relief to grow at the scale of the whole drainage basin above and beneath these knickzones the presence of braided channels and the absence of erosion on adjacent pediplains suggest no substantial modification in the local relief the knickzones however show bedrock channels and fluvial dissection rates have exceeded erosion rates on adjacent pediplains by two orders of magnitudes hence the data imply that the only geomorphic recorders of relief growth are the knickzones that currently transpose the effects of the late miocene phase of surface uplift from the coast to the altiplano

timing of the late quaternary glaciation in the andes from 15 to 40 s the central andes play a pivotal role for glacier and climate reconstruction along the american pole equator pole transect nevertheless knowledge about late quaternary palaeoenvir onmental changes in this region is extremely limited with the advent and application of surface exposure dating during the last few years the establishment of more detailed glacial chronologies could provide important insights into forcings and mechanisms of glaciation and climate change this paper reviews previously published exposure ages and compares them with independent age control on glacial chronologies and with information about the palaeohydrological conditions although available data are still very limited and there are remaining systematic uncertainties related to surface exposure dating the following simplified palaeoglacial palaeoclimate model is presented to serve as a testable hypothesis for future studies i glaciers in the humid tropical andes were mainly temperature sensitive and therefore advanced during temperature minima advances are dated to 20 25 ka 15 ka and 11 13 ka i e synchronous to the global last glacial maximum lgm the heinrich event 1 and the younger dryas antarctic cold reversal ii further south and west precipitation decreases and glaciers therefore become more precipitation sensitive maximum or at least prominent glacial advances as far south as 308 s are dated into the lateglacial i e synchronous with lake transgression phases tauca 14 18 ka and coipasa 11 13 ka iii between 30 and 408 s glaciers reached their maximum extent much earlier during the pre lgm 35 40 ka this is attributed to a northward shift and or intensification of the westerlies whereas conditions during the global lgm were too dry to allow for significant glacial advances iv south of 408 glaciers become temperature sensitive again and reached their maximum accordingly synchronous to the global lgm copyright 2008 john wiley sons ltd

invited review paper neogene to quaternary tectonics of the coastal cordillera northern chile abstract the extreme aridity of the northern chilean coastal cordillera enables the complete preservation of permanent deformation related to the coupling between nazca and south america the region between antofagasta and arica is characterized by four types of late cenozoic structures ew striking reverse faults ns striking normal faults sparse wnw and nnw striking right lateral strike slip faults and unimodal and bimodal populations of surface cracks the ew reverse faults occur only between 19 and 21 40 s latitude and have been active since at least 6 ma to present a march 2007 earthquake demonstrates that this deformation can occur during the interseismic phase of the plate boundary seismic cycle the ns normal faults are most abundant near antofagasta and mejillones and diminish in significance northward several of these faults in both the antofagasta and the salar grande area have been reactivated as reverse faults causing minor topographic inversion we suggest that normal faults move during both interseismic and coseismic deformation and are fundamentally very weak surface cracks are ubiquitous throughout the region and form by both non tectonic and tectonic mechanisms a significant proportion forms during coseismic deformation and thus may be used to identify long lived rupture segments on the plate boundary overall forearc deformation is very slow with permanent strain rates of 1 5 nstrain year and fault slip rates less than 0 5 mm year

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

mesoscale eddies in the northwestern subtropical pacific ocean statistical characteristics and three dimensional structures mesoscale eddy properties in the northwestern subtropical pacific ocean are investigated by analyzing 22 567 cyclonic eddies ces and 26 365 anticyclonic eddies aes detected from 19 year altimetric sea level records eddy occurrence frequency and kinetic energy are prevailingly high in the subtropical countercurrent zonal band between 19 degrees n and 26 degrees n and further elevated near the luzon taiwan coast a general superiority of aes is observed at most latitudes except between 19 degrees n and 22 degrees n where the ce number is larger the modal radius and mean lifespan of the ces aes are 134km and 11 2weeks 121km and 10 9weeks respectively after generation most eddies propagate westward with a mean speed of 7 2cms 1 and deflect northward following the kuroshio along the luzon taiwan coast three dimensional eddy structures are further explored with composite eddy images in five subregions constructed by surfacing argo temperature salinity data into altimeter detected eddy areas due to the existence of mode waters in the main thermocline eddy induced temperature anomaly exhibits a double core vertical structure which is especially evident in ce images because of the vertical water mass distribution salinity anomaly features a sandwich like pattern which is more evident in ae images also revealed is the significant structure difference in these five subregions eddies are greatly intensified as they approach the western boundary inducing larger temperature and salinity anomalies and influencing deeper ocean along the luzon taiwan coast aes are preferentially strengthened by the northward background flow

mesoscale dongsha cyclonic eddy in the northern south china sea by drifter and satellite observations 1 near the center of the northern south china sea nscs the dongsha atoll is situated on the continental slope that runs from taiwan to hainan a mesoscale cyclonic eddy south or southwest of dongsha seems to appear annually and has been identified as the dongsha cyclonic eddy dce historical drifter 1988 2005 and satellite altimeter 2000 2005 data were adopted to study the variations to and characteristics of the dce some typical features were derived such as mean tangential speed of 20 cm s moving speed of 8 km d i e 9 cm s eddy size of 22 103 km2 center sea surface lowering height difference dif of 6 cm and angular velocity of 9 d mean tangential speeds of 12 16 cm s in late spring and summer are slower than those of 16 31 cm s in winter and early spring moving speeds are of the order of the rossby wave at nscs latitudes variations in the time series of eddy size and dif are generally similar and show a positive linear relation between them the dce starts near dongsha and moves southwestward along the continental slope at a depth of 1000 2000 m the eddy peaks with maximum eddy size and dif when reaching 114 e and then diminishes south of hainan because of trapping of the underwater bay formed by the continental slope the dce typically exists 1 2 times per year and lasts 1 3 months roughly 90 of observed dces formed in winter or spring a unique dce was identified in the summer of 2000 and lasted for over 4 months its birth was associated with typhoon kai tak the positive linear relationship between eddy size and dif in this case was unique before reaching 114 e and then returned to the typical relationship of other dces the dif of this unique dce attained the highest of 24 cm right at the climax longitude according to avhhr and seawifs images such a dce is associated with a core of which sea surface temperature is 2 c lower and chlorophyll a concentration is 0 1 mg m3 higher than those of surrounding seas migration of the dce may be linked to tuna fish farms in the nscs

late quaternary paleohydrology of the central atacama desert lat 22 24 s chile in northern chile precipitation in the high andes 3500 m recharges groundwater systems that flow down the pacific slope and feed large aquifers in the hyperarid atacama desert wetlands which are often found along the base of the andes mark locations where the water table intersects the land surface at these locations paleo wetland deposits which are present as terraces between 3 and 20 m above modern wetlands record past water table heights along the andean front and are used to reconstruct changes in groundwater discharge paleo wetland deposits in the central atacama desert lat 22 24 s record an episode 15 4 9 ka of high water tables followed by an episode 8 3 ka of moderately high water tables elevated water tables result from increased groundwater discharge and ultimately from enhanced recharge in the andes the concordance of results from three separate hydrologic systems suggests that changes in groundwater discharge and recharge are regional and reflect climatic fluctuations this interpretation is supported by close agreement with other paleoclimatic records in the region the periods of greater groundwater discharge were separated by episodes 9 8 and 3 0 ka of significant groundwater lowering and stream incision implying greatly diminished discharge the central atacama and andes lat 22 24 s receive precipitation mainly from moist air masses transported from the amazon basin by the south american summer monsoon sasm increases in groundwater recharge are therefore thought to reflect an increase in the frequency and or moisture content of sasm air masses crossing the andes fluctuations in sasm precipitation have previously been linked to summer insolation in the southern hemisphere the wettest period in the central atacama 15 4 9 ka however coincides with a minimum in austral summer insolation at 10 ka suggesting that regional summer insolation is not a dominant influence on the sasm instead intensification of the sasm may be linked to extraregional forcings such as the walker circulation

canyon incision and knickpoint propagation recorded by apatite 4he 3he thermochronometry abstract in many regions of the world deeply incised canyons demonstrate the net effects of physical processes active at earth s surface in response to surface uplift low temperature thermochronometry can constrain the timing and rates of bedrock incision which is necessary for relating canyon incision to surface uplift over geological timescales we analyzed four samples from the cotahuasi ocona canyon system in southwest peru using 4 he 3 he thermochronometry and we present a new inversion model to identify continuous low temperature cooling histories that are consistent with the observed data derived cooling histories limit the onset of fluvial incision to 13 to 8 ma this is in agreement with previously reported interpretations based on a three dimensional thermal model interpolation to a much larger set of conventional apatite u th he ages however because 4 he 3 he thermochronometry constrains an independent cooling history for each sample the results also permit testing of landscape evolution models with greater spatial variability in exhumation compared to those models that can be tested by a geographically scattered set of conventional u th he ages the different cooling histories of the four samples require asynchronous incision along at least part of the canyon system that is best explained by headward propagation of fluvial incision by knickpoint migration

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

drainage basin response to climate change in the pisco valley peru the quaternary development of the pisco valley in central peru has been characterized by multiple phases of sediment accumulation and erosion that formed distinct levels of cut and fill terraces and alluvial fans luminescence dating shows that they formed in response to at least two different stages of sediment accumulation and erosion during the past 60 ka the main phase of sediment aggradation occurring between ca 54 and 38 ka ago the ages show that sediment accumulation was contemporaneous with the time intervals of the minchin 47 8 36 ka ago with enhanced precipitation beginning ca 54 8 ka ago and tauca 26 14 9 ka ago paleolakes on the altiplano where the headwaters of the pisco river are located we conclude that sediment accumulation was triggered by shifts toward a more humid climate whereas erosion is the response of the fluvial system to the depletion of the hillslope sediment reservoirs

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

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

on the origin of the bolivian high and related circulation features of the south american climate abstract the climatological structure in the upper tropospheric summertime circulation over south america is diagnosed using a gcm with and without south american topography a linear model and observational data emphasis is placed on understanding the origin of observed features such as the bolivian high and the accompanying nordeste low to the east results from the linear model indicate that these two features are generated in response to precipitation over the amazon basin central andes and south atlantic convergence zone with african precipitation also playing a crucial role in the formation of the nordeste low the direct mechanical and sensible heating effects of the andes are minimal acting only to induce a weak lee trough in midlatitudes and a shallow monsoonal circulation over the central andes in the gcm the effects of the andes include a strengthening of the bolivian high and northward shift of the nordeste low primarily through changes in the precipitation field the position of

oligocene miocene age of aridity in the atacama desert revealed by exposure dating of erosion sensitive landforms the age of onset of hyperaridity in the atacama desert chile which is needed to validate geological and climatological concepts has been heretofore uncertain measurement of cosmogenic 21 ne in clasts from erosion sensitive sediment surfaces in northern chile shows that these surfaces have been barely affected by erosion since 25 ma surface exposure ages of sediment clasts give replicate values at 25 20 and 14 ma and individual values at 37 and 9 ma predominantly hyperarid conditions are required to preserve these oldest continuously exposed surfaces on earth our findings are compatible with the hypothesis that the onset of aridity in the atacama desert could be the reason for rather than the consequence of uplift of the high andes

eddy effects on sea surface temperature and sea surface wind in the continental slope region of the northern south china sea 1 warm and cold sea surface temperature sst tongues on weather timescales are detected in the continental slope region of the northern south china sea nscs and their effects on sea surface wind are studied using satellite observations crossing the basin scale sst front geostrophic currents between cyclonic and anticyclonic eddies induce the warm and cold sst tongues during the northeast monsoon corresponding to the warm and cold sst tongues the sea surface wind is highly uneven in spatial distribution its speed is faster slower over the warm cold sst tongues than the surrounding areas the sst and sea surface wind non uniformity in space shifts southwestward with eddy motion along the continental slope these new findings from satellite observations give us an opportunity to study oceanic eddy s roles in ocean atmosphere interaction on weather timescales

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

mesoscale eddies in the south china sea observed with altimeter data 1 a composite time series 1993 2000 of sea surface height anomaly from several satellites is used to identify eddies in the south china sea scs the eddy lifetime radius strength and straight line travel distance are estimated altogether 58 anticyclonic eddies and 28 cyclonic eddies are identified for this period they are grouped into four geographical zones according to known eddy generation mechanisms and their statistics are discussed accordingly our geographical classification is a useful first step in gaining an overview of their generation

apparent enhancement of 234th based particle export associated with anticyclonic eddies national basic research program of china 973 program 2009cb421200 national natural science foundation of china nsfc 41121091 41130857

paleowetlands and regional climate change in the central atacama desert northern chile abstract widespread organic rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central atacama desert one of the driest places on earth today we mapped and dated these paleowetland deposits at three presently waterless locations near salar de punta negra 24 5 s on the western slope of the andes elevated groundwater levels supported phreatic discharge into wetlands during two periods 15 900 to 13 800 and 12 700 to 9700 cal yr bp dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase 11 000 9700 cal yr bp water tables dropped below the surface before 15 900 and since 8100 cal yr bp and briefly between 13 800 and 12 700 cal yr bp this temporal pattern is repeated with some slight differences in rodent middens from the study area in both paleowetland and rodent midden deposits north and south of the study area and in lake level fluctuations on the adjacent bolivian altiplano the regional synchroneity of these changes points to a strengthening of the south american monsoon which we term the central andean pluvial event in two distinct intervals 15 900 13 800 and 12 700 9700 cal yr bp probably induced by steepened sst gradients across the tropical pacific i e la nina like conditions

the dry puna as an ecological megapatch and the peopling of south america technology mobility and the development of a late pleistocene early holocene andean hunter gatherer tradition in northern chile abstract current scientific evidence shows that humans colonized south america at least 15 000 years ago but there are still many unknown aspects of this process including the major and minor migratory routes involved and the pattern of successive occupation of a diverse continental mosaic of ecosystems in this context the role of the andean highlands 3400 meters above sea level has been neglected because of the supposedly harsh conditions for humans including hypoxia and cold climate nevertheless the environmental and cultural resources available in the high andes constitutes an important megapatch that should be assessed in terms of human settlement patterns we review the evidence for late pleistocene early holocene hunter gatherer occupation of one part of this megapatch the northern chilean dry puna in its palaeoecological context we focus on lithic technology faunal remains radiocarbon dates and other archaeological materials related to different social activities which allow us to suggest that groups of hunter gatherers organized and adapted their way of life to highland ecosystems through logistical mobility and curatorial strategies for lithic tool kits that included projectile points and other formalized tools the morphology and technological processes involved are recognized over vast territories along the high andes we identify this material expression as the high south central andean archaic hunter gatherer tradition which also featured long distance mobile settlement systems and communication processes over this broad and distinct megapatch more speculatively we outline the hypothesis that these highland ecosystems constituted a suitable migratory route that may have been key for the early peopling of the continent and contrast it with the alternative hypothesis of the initially secondary and seasonally intermittent exploitation of this habitat by hunter gatherers dispersing along the pacific coastal corridor