deglaciation and holocene climate change in the western peruvian andes pollen charcoal magnetic susceptibility and bulk density data provide the first paleoecological record spanning the last 33 000 years from the western cordillera of the peruvian andes sparse super puna vegetation existed before 30 000 cal yr b p around lake compuerta 3950 m elevation prior to a sedimentary hiatus that lasted until c 16 200 cal yr b p when sedimentation resumed a glacial foreland or super puna flora is represented in which polylepis was a significant element glacial outwash marked by high sedimentary magnetic susceptibility increased from c 16 200 cal yr b p and reached a peak at c 13 200 cal yr b p between c 12 500 cal yr b p and 10 000 cal yr b p magnetic susceptibility was reduced vegetation shifts suggest a cool dry time consistent with regional descriptions of the younger dryas event deglaciation resumes by 10 000 cal yr b p and the last ice is lost from the catchment at 7500 cal yr b p during the early holocene warm and dry period between 10 000 and 5500 cal yr b p alnus expanded in downslope forests alnus declined in abundance at 5500 cal yr b p when wetter and cooler conditions returned and human activity intensified maize zea mays pollen first occurred in the core at 2600 cal yr b p indicating a minimum age for local agriculture an increase in alnus pollen abundance at 1000 cal yr b p could be due to human activity or perhaps due to a regional climate change associated with cultural turnover elsewhere in the andes at this time

chemistry and mineralogy of outcrops at meridiani planum analyses of outcrops created by the impact craters endurance fram and eagle reveal the broad lateral continuity of chemical sediments at the meridiani planum exploration site on mars approximately ten mineralogical components are implied in these salt rich silicic sediments from measurements by instruments on the opportunity rover compositional trends in an apparently intact vertical stratigraphic sequence at the karatepe west ingress point at endurance crater are consistent with non uniform deposition or with subsequent migration of mobile salt components dominated by sulfates of magnesium striking variations in cl and enrichments of br combined with diversity in sulfate species provide further evidence of episodes during which temperatures ph and water to rock ratios underwent significant change to first order the sedimentary sequence examined to date is consistent with a uniform reference composition modified by movement of major sulfates upward and of minor chlorides downward this reference composition has similarities to martian soils supplemented by sulfate anion and the alteration products of mafic igneous minerals lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the rock abrasion tool survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid h2o in this region since the time of crater formation

rock spectral classes observed by the spirit rover s pancam on the gusev crater plains and in the columbia hills 1 this paper examines the ferrous and ferric iron mineralogy of rocks inferred from 246 visible near infrared 430 1010 nm multispectral observations made by the mars exploration rover spirit s pancam on its traverse from its landing site to its second winter haven location principal component correspondence analyses and a sequential maximum angle convex cone technique were used to identify 14 candidate classes spectra from the west spur of husband hill and the watchtower area had the highest 535 and 601 nm band depths indicating that these areas were more oxidized differences in the depth and band center of a near infrared nir absorption feature were observed using 904 nm band depth and 803 904 nm ratio and parameters gauging the 754 864 and 754 1009 nm slopes spectra of rocks from the southern flank of husband hill had negative 754 1009 nm slopes and a broad nir absorption consistent with high olivine abundances rocks observed on the lower west spur at the cumberland ridge locale at the husband hill summit and at the haskin ridge locale had deep 904 nm band depths and steep 754 864 nm slopes consistent with greater pyroxene abundances these observations are consistent with results on iron bearing mineralogy from spirit s mossbauer spectrometer comparisons of these rock spectral classes with a set of terrestrial analog samples found similarities between the west spur and watchtower classes and red hematite bearing impact melts fewer similarities were found in comparisons of the columbia hills classes with basaltic hydrovolcanic tephras

late pleistocene and holocene environmental change inferred from the cocha caranga sediment and soil records in the southeastern ecuadorian andes abstract late pleistocene and holocene vegetation climate and fire dynamics of mountain forest and paramo ecosystems as well as human impact are presented from the cocha caranga area at 2710 m elevation in the podocarpus national park southeastern ecuadorian andes palaeoenvironmental changes inferred from two sediment cores and a soil core were investigated by pollen spore algae and charcoal analyses during the transition from late pleistocene to early holocene between ca 14 500 to 9700 cal yr bp upper mountain forest vegetation expanded suggesting increasing temperature and moisture this expansion abruptly stopped with increasing fires at ca 9700 cal yr bp and open grassy vegetation became established the period from ca 9700 to 1300 cal yr bp of strong fire intensity indicate that vegetation components mainly weinmannia and myrica react sensitively to past probably human caused fires during the last few centuries modern vegetation established characterised by open grassy areas with forest patches and small mires the green algae botryococcus braunii isoetes and cyperaceae were used to identify lake level fluctuation to reconstruct holocene wet dry phases drier climatic conditions occurred from ca 9700 to 6900 cal yr bp and from ca 4200 to 1300 cal yr bp from ca 6900 to 4200 cal yr bp and from ca 1300 cal yr bp to modern times wetter climatic conditions occurred

giant landslide triggerings and paleoprecipitations in the central western andes the aricota rockslide dam south peru abstract the central part of the western andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material v km3 while those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the andes relief formation and tectonic activity the question of their triggering mechanisms remains enigmatic to clarify the respective roles of climatic versus seismic forcing on the andean landslides new temporal constraints on paleo movements are essential here we focus on one of those giant slope failures the aricota giant rockslide that damned the locumba valley in southern peru we conducted fieldwork high resolution dem analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms our results point to the occurrence of two successive events a giant failure mobilizing a rock volume of ca 2 km3 first produced a dam at 17 9 0 7 ka considering its height of ca 600 m the aricota rockslide dam is one of the three largest landslide dams worldwide at 12 1 0 2 ka a second event produced ca 0 2 km3 of material and the rock avalanche debris spread out over the dam as the chronology of those two events is pointing to the two main paleoclimatic pluvial periods in this region heinrich stadial 1a and younger dryas we favor the interpretation of a climatic forcing at a regional scale the concomitant aggradation of alluvial terraces and fan systems along the nearby valleys highlights higher regional erosion sediments supply and mass wasting events during those paleoprecipitation events and strengthens this conclusion

field reconnaissance geologic mapping of the columbia hills mars based on mars exploration rover spirit and mro hirise observations chemical mineralogic and lithologic ground truth was acquired for the first time on mars in terrain units mapped using orbital mars reconnaissance orbiter s high resolution imaging science experiment mro hirise image data examination of several dozen outcrops shows that mars is geologically complex at meter length scales the record of its geologic history is well exposed stratigraphic units may be identified and correlated across significant areas on the ground and outcrops and geologic relationships between materials may be analyzed with techniques commonly employed in terrestrial field geology despite their burial during the course of martian geologic time by widespread epiclastic materials mobile fines and fall deposits the selective exhumation of deep and well preserved geologic units has exposed undisturbed outcrops stratigraphic sections and structural information much as they are preserved and exposed on earth a rich geologic record awaits skilled future field investigators on mars the correlation of ground observations and orbital images enables construction of a corresponding geologic reconnaissance map most of the outcrops visited are interpreted to be pyroclastic impactite and epiclastic deposits overlying an unexposed substrate probably related to a modified gusev crater central peak fluids have altered chemistry and mineralogy of these protoliths in degrees that vary substantially within the same map unit examination of the rocks exposed above and below the major unconformity between the plains lavas and the columbia hills directly confirms the general conclusion from remote sensing in previous studies over past years that the early history of mars was a time of more intense deposition and modification of the surface although the availability of fluids and the chemical and mineral activity declined from this early period significant later volcanism and fluid convection enabled additional if localized chemical activity

constraints on ripple migration at meridiani planum from opportunity and hirise observations of fresh craters 1 observations of fresh impact craters by the opportunity rover and in high resolution orbital images constrain the latest phase of granule ripple migration at meridiani planum to have occurred between 50 ka and 200 ka opportunity explored the fresh resolution crater cluster and concepcion crater that are superposed on and thus younger than the ripples these fresh craters have small dark pebbles scattered across their surfaces which are most likely fragments of the impactor suggesting that the dark pebbles and cobbles observed by opportunity at meridiani planum are a lag of impactor derived material either meteoritic or secondary impactors from elsewhere on mars two larger fresh rayed craters in meridiani planum bracket ripple migration secondaries from ada crater are clearly superposed on and secondaries from an unnamed 0 84 km diameter crater have been modified and overprinted by the ripples three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred the inactivity of the ripples over the past 50 ka at meridiani is also consistent with other evidence for the stability of the ripples the lack of observed eolian bed forms in craters that formed in the past 20 years and little evidence for much dune motion in the past 30 yr on mars observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in meridiani planum over the past million years

lower lithospheric structure beneath the trans european suture zone from polonaise 97 seismic profiles abstract the large scale polonaise 97 seismic experiment investigated the velocity structure of the lithosphere in the trans european suture zone tesz region between the precambrian east european craton eec and palaeozoic platform pp in the area of the polish basin the p wave velocity is very low vp 8 25 km s in the palaeozoic platform and 8 1 km s in the precambrian platform good quality record sections were obtained to the longest offsets of about 600 km from the shot points with clear first arrivals and later phases of waves reflected refracted in the lower lithosphere two dimensional interpretation of the reversed system of travel times constrains a series of reflectors in the depth range of 50 90 km a seismic reflector appears as a general feature at around 10 km depth below moho in the area independent of the actual depth to the moho and sub moho seismic velocity ringing reflections are explained by relatively small scale heterogeneities beneath the depth interval from 90 to 110 km qualitative interpretation of the observed wave field shows a differentiation of the reflectivity in the lower lithosphere the seismic reflectivity of the uppermost mantle is stronger beneath the palaeozoic platform and tesz than the east european platform the deepest interpreted seismic reflector with zone of high reflectivity may mark a change in upper mantle structure from an upper zone characterised by seismic scatterers of small vertical dimension to a lower zone with vertically larger seismic scatterers possible caused by inclusions of partial melt

athena microscopic imager investigation 1 the athena science payload on the mars exploration rovers mer includes the microscopic imager mi the mi is a fixed focus camera mounted on the end of an extendable instrument arm the instrument deployment device idd the mi was designed to acquire images at a spatial resolution of 30 microns pixel over a broad spectral range 400 700 nm the mi uses the same electronics design as the other mer cameras but has optics that yield a field of view of 31 31 mm across a 1024 1024 pixel ccd image the mi acquires images using only solar or skylight illumination of the target surface a contact sensor is used to place the mi slightly closer to the target surface than its best focus distance about 66 mm allowing concave surfaces to be imaged in good focus coarse focusing 2 mm precision is achieved by moving the idd away from a rock target after the contact sensor has been activated the mi optics are protected from the martian environment by a retractable dust cover the dust cover includes a kapton window that is tinted orange to restrict the spectral bandpass to 500 700 nm allowing color information to be obtained by taking images with the dust cover open and closed mi data will be used to place other mer instrument data in context and to aid in petrologic and geologic interpretations of rocks and soils on mars

seismic models of the lower lithosphere beneath the southern baltic sea between sweden and poland abstract based on recordings from the northern part of the baltic sea black sea profile and eugeno s profile 4 2 d seismic models have been constructed for a profile across the southwestern part of the east european platform from southern sweden to northern poland the thickness of the crust along the profile varies from 33 to 47 km the moho p wave velocity is 8 0 8 3 km s the uppermost mantle has a fine structure with alternating layers of higher and lower velocities down to a depth of about 120 km three alternating high and low velocity layers have been modelled the velocities vary between 8 2 and 8 7 km s in the high velocity layers and 8 0 and 8 5 km s in the low velocity layers a tendency of the depth of the moho and the depth of the uppermost mantle seismic boundaries to increase towards the southeast is observed

a perched high elevation wetland complex in the atacama desert northern chile and its implications for past human settlement a previously undocumented type of wetland is described from the atacama desert in northern chile 3000 m above sea level sustained exclusively by direct precipitation and perched above the regional water table geomorphological mapping pedostratigraphy geochemistry and analysis of contemporary vegetation is used to understand wetland formation and dynamics during historical and present time periods the paleowetland deposits overlie a miocene tuff that acts as an impermeable barrier to water transfer and creates conditions for local shallow ground water these deposits include several paleosols that were formed during periods when precipitation increased regionally at 7755 7300 1270 545 and 400 300 cal yr bp the similarity in timing with other palaeohydrological records for the atacama implies that paleosols from this wetland are proxies for reconstructing past changes in local and regional hydrological cycle archaeological investigations have revealed the presence of two small farms from the late intermediate period i e during the earliest wetter phase represented by the paleosols both farms are located near the paleowetland deposits which suggests that local inhabitants exploited these water sources during late pre hispanic times results of this study improve knowledge of settlement patterns during this and earlier cultural periods

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

a 12 700 year history of paleolimnological change from an andean microrefugium we present a 12 6700 yr limnological history of lake miski a high elevation lake in a wet section of the peruvian andes while many shallow andean lakes dried up during the mid holocene loss on i

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

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

athena mars rover science investigation 1 each mars exploration rover carries an integrated suite of scientific instruments and tools called the athena science payload the primary objective of the athena science investigation is to explore two sites on the martian surface where water may once have been present and to assess past environmental conditions at those sites and their suitability for life the remote sensing portion of the payload uses a mast called the pancam mast assembly pma that provides pointing for two instruments the panoramic camera pancam and the miniature thermal emission spectrometer mini tes pancam provides high resolution color stereo imaging while mini tes provides spectral cubes at mid infrared wavelengths for in situ study a five degree of freedom arm called the instrument deployment device idd carries four more tools a microscopic imager mi for close up imaging an alpha particle x ray spectrometer apxs for elemental chemistry a mossbauer spectrometer mb for the mineralogy of fe bearing materials and a rock abrasion tool rat for removing dusty and weathered surfaces and exposing fresh rock underneath the payload also includes magnets that allow the instruments to study the composition of magnetic martian materials all of the athena instruments have undergone extensive calibration both individually and using a set of geologic reference materials that are being measured with all the instruments using a mer like rover and payload in a number of field settings we have devised operations processes that will enable us to use the mer rovers to formulate and test scientific hypotheses concerning past environmental conditions and habitability at the landing sites

geochemical and mineralogical indicators for aqueous processes in the columbia hills of gusev crater mars 1 water played a major role in the formation and alteration of rocks and soils in the columbia hills the extent of alteration ranges from moderate to extensive five distinct rock compositional classes were identified the order for degree of alteration is watchtower clovis wishstone peace backstay the rover s wheels uncovered one unusual soil paso robles that is the most s rich material encountered clovis class rocks have compositions similar to gusev plains soil but with higher mg cl and br and lower ca and zn watchtower and wishstone classes have high al ti and p and low cr and ni peace has high mg and s and low al na and k backstay basalts have high na and k compared to plains adirondack basalts and paso robles soil has high s and p some rocks are corundum normative indicating that their primary compositions were changed by loss and or gain of rock forming elements clovis materials consist of magnetite nanophase ferric oxides npox hematite goethite ca phosphates ca and mg sulfates pyroxene and secondary aluminosilicates wishstone and watchtower rocks consist of fe oxides oxyhydroxides ilmenite ca phosphate pyroxene feldspar mg sulfates and secondary aluminosilicates peace consists of magnetite npox mg and ca sulfates pyroxene olivine feldspar apatite halides and secondary aluminosilicates paso robles consists of fe3 mg ca and other sulfates ca phosphates hematite halite allophane and amorphous silica columbia hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks volcaniclastic materials and or impact ejecta by solutions that were rich in acid volatile elements

holocene climate variability and vegetation dynamics inferred from the 11700 cal yr bp laguna rabadilla de vaca sediment record southeastern ecuadorian andes palaeoenvironmental changes inferred from a 492 cm long lake sediment core from laguna rabadilla de vaca 3312 m in podocarpus national park southeastern ecuadorian andes were investigated usin

lithospheric structure in southern sweden results from fennolora abstract the major objective of fennolora the fennoscandian long range seismic project of 1979 was the determination of lower lithospheric and upper mantle structure down to depths in excess of 400 km below the fennoscandian shield in the component represented by this study data recorded at stations in southern sweden from three shotpoints one in northern germany profile wn and two separated by 300 km in southern sweden profiles bn and cs are used to derive a two dimensional lithosphere structure model extending over 600 km from north to south the profile crosses the svecofennides the smaland varmland granite belt paleozoic cover rocks lying unconformably on the fennoscandian shield the baltic sea where there were no stations and into the caledonian tectonic province of northern germany where one shotpoint but no stations were located interpretation of the three record sections was based on a two dimensional ray tracing procedure which included the calculation of asymptotic ray theory synthetic seismograms lack of data from 0 150 km for the shotpoint in germany to the first station in southern sweden precluded derivation of any detailed crustal structure for this region crustal thickness was determined to be 32 km a rapid increase in velocity from 8 0 to 8 35 km s at about a depth of 50 km is underlain by a low velocity zone extending to a depth of 70 km the reversed profiles bn and cs in southern sweden are fundamentally different interpretation shows a difference in crustal thickness of about 12 km with the northern segment having a deeper moho a feature resulting from a thicker lower crust and a crust mantle transition zone rather than a rapid increase in velocity in the southern segment of the reversed profile a crustal low velocity zone of limited extent is indicated the most significant aspect of the interpretation is the suggestion that the change in crustal structure between the two shotpoints in southern sweden occurs within a transition zone of limited lateral extent less than a few tens of kilometers we suggest that the model transition zone is a fundamental lithosphere boundary associated with the juxtaposition of the smaland varmland granite belt and the svecofennides

ancient aqueous environments at endeavour crater mars opportunity has investigated in detail rocks on the rim of the noachian age endeavour crater where orbital spectral reflectance signatures indicate the presence of fe 3 rich smectites the signatures are associated with fine grained layered rocks containing spherules of diagenetic or impact origin the layered rocks are overlain by breccias and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the endeavour impact compositional data for fractures in the layered rocks suggest formation of al rich smectites by aqueous leaching evidence is thus preserved for water rock interactions before and after the impact with aqueous environments of slightly acidic to circum neutral ph that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate rich rocks at meridiani planum

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

vnir multispectral observations of rocks at cape york endeavour crater mars by the opportunity rover s pancam from its arrival at the portion of the rim of endeavour crater known informally as cape york the mars exploration rover opportunity has made numerous visible and near infrared vnir multispectral observations of rock surfaces this paper describes multispectral observations from opportunity s arrival at cape york to its winter over location at greeley haven averages of pixels from the pancam s left and right eyes were joined to form 11 point spectra from numerous observations and were examined via a number of techniques these included principal components analysis a sequential maximum angle convex cone approach examination of spectral parameters and a hierarchical clustering approach the end result of these analyses was the determination of six primary spectral ps classes describing spectrally unique materials observed on cape york these classes consisted of a standard outcrop spectrum that was observed on the clasts and matrix comprising the upper unit of the shoemaker formation a class representing rock surfaces exposed around odyssey crater and typified by the rocks of the tisdale series pebbles occurring in and weathered out of the upper unit of the shoemaker formation that appear red in 1009 904 754 nm color composites patches on tisdale rocks exhibiting a 864 nm band minimum that were spectrally anomalous in root mean square error images derived from spectral mixture analyses clasts with a high 904 nm band depth occurring in the greeley haven location and gypsum veins typified by the vein homestake comparisons of three of these classes that had well defined band minima between 800 and 1009 nm with spectral library spectra of ferrous silicates and ferric oxide oxyhydroxide and ferric sulfate minerals indicated tentative matches of the red pebbles with orthopyroxenes of the spectrally anomalous 864 nm band minimum material with hematite or ferric sulfates and of the high 904 nm band depth material with an orthopyroxene clinopyroxene mixture the spectral properties of rock surfaces on cape york are distinct from those of burns formation outcrops observed on the meridiani plains the cape york outcrop is noachian in age and study of these materials provides insight into less acidic environmental conditions extant before the formation of the burns formation

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

crater geometry and ejecta thickness of the martian impact crater tooting we use mars orbiter laser altimeter mola topographic data and thermal emission imaging system themis visible vis images to study the cavity and the ejecta blanket of a very fresh martian impact crater 29 km in diameter with the provisional international astronomical union iau name tooting crater this crater is very young as demonstrated by the large depth diameter ratio 0 065 impact melt preserved on the walls and floor an extensive secondary crater field and only 13 superposed impact craters all 54 to 234 meters in diameter on the 8120 km 2 ejecta blanket because the pre impact terrain was essentially flat we can measure the volume of the crater cavity and ejecta deposits tooting crater has a rim height that has 500 m variation around the rim crest and a very large central peak 1052 m high and 9 km wide crater cavity volume i e volume below the pre impact terrain is 380 km 3 and the volume of materials above the pre impact terrain is 425 km 3 the ejecta thickness is often very thin 20 m throughout much of the ejecta blanket there is a pronounced asymmetry in the ejecta blanket suggestive of an oblique impact which has resulted in up to 100 m of additional ejecta thickness being deposited down range compared to the up range value at the same radial distance from the rim crest distal ramparts are 60 to 125 m high comparable to the heights of ramparts measured at other multi layered ejecta craters tooting crater serves as a fresh end member for the large impact craters on mars formed in volcanic materials and as such may be useful for comparison to fresh craters in other target materials

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

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

holocene vegetation history from fossil rodent middens near arequipa peru rodent abrocoma lagidium phyllotis middens collected from 2350 to 2750 m elevation near arequipa peru 16 s provide an 9600 yr vegetation history of the northern atacama desert based on identification of 50 species of plant macrofossils these midden floras show considerable stability throughout the holocene with slightly more mesophytic plant assemblages in the middle holocene unlike the southwestern united states rodent middens of mid holocene age are common in the arequipa area the midden record does not reflect any effects of a mid holocene mega drought proposed from the extreme lowstand 100 m below modern levels 6000 to 3500 yr b p of lake titicaca only 200 km east of arequipa this is perhaps not surprising given other evidence for wetter summers on the pacific slope of the andes during the middle holocene as well as the poor correlation of summer rainfall among modern weather stations in the central andes atacama desert the apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the holocene to changes in el nino southern oscillation modes

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

the age of the medusae fossae formation evidence of hesperian emplacement from crater morphology stratigraphy and ancient lava contacts abstract the medusae fossae formation mff covering about 2 1 10 6 km 2 with an estimated volume of 1 4 10 6 km 3 and straddling the equatorial region of mars east of tharsis has historically been mapped and dated as amazonian in age analysis of the mff using a range of new observations from recent mission data at multiple resolutions reveals evidence that the formation is older than previously hypothesized with parts of the mff having formed in the hesperian and parts having been reworked and reformed throughout the amazonian up to the present ancient outcroppings of the mff edged with jagged yardangs became a mold for embaying hesperian aged lavas the erosion of the mff left solidified lava casts in the embaying lava unit this lava edge morphology permits the identification of ancient contacts between the mff and hesperian aged lava terrain additionally the flanking fan of the hesperian aged apollinaris patera volcano embays the formation at its foot indicating that parts of the mff were formed in the hesperian erosion has erased and inverted many of the superposed craters in the region showing that very young amazonian ages derived from impact crater size frequency distributions are resurfacing ages and not emplacement ages we find abundant evidence that the formation is extremely mobile and continuously reworked we conclude that a significant part of the mff may have originally been emplaced in the hesperian these observations place new constraints on the mode of origin of the mff

seismic model of the earth s crust and upper mantle for the east european platform a model is presented of the p wave velocity distribution for the east european platform from the sedimentary layer through the crystalline complex of the earth s crust the lower lithosphere and the asthenosphere down to a depth of 900 km in the upper mantle the structure of the earth s crust for the east european platform is complex and heterogeneous the crystalline basement usually lies at a depth of 2 3 kin outcropping in the area of the baltic and ukrainian shields a characteristic of the marginal zones of the precambrian platform is the existence of large sedimentary basins where the thickness of the sediments exceeds 10 km e g p o l i s h g e r m a n d a n i s h trough donbass basin pre caspian foredeep pechora basin and barents sea depression for the sedimentary cover we have determined the dependences of the velocities on depth from the results obtained from 261 boreholes in the polish part of the east european platform in the sediments a distinct increase in velocity with increasing depth is observed and there is also a large velocity differentiation from about 1 8 km s 1 for the tertiary and quaternary to about 5 0 5 5 km s a for permian devonian and cambrian formations the j ump in velocity at the boundary of the cenozoic mesozoic cover and the permian exceeds 1 0 km s i and consequently it is the most distinct seismic discontinuity in the sedimentary layer for the cenozoic mesozoic cover and for the whole sedimentary complex we determined the dependences of the mean velocities on thickness to determine the dependence of the mean velocity on the thickness of the whole sedimentary layer we used data from 71 boreholes which reached the crystalline basement for these data up to a depth of 5 6 km we obtained the linear dependence vsed z 2 13 0 34 z for a greater depth for which there are no data from direct measurements in boreholes we used the results of interpretation and modelling of shallow refraction seismic data with the formula obtained from these data vsed z 2 35 1 0 227 z we can estimate the mean velocity of sediments for thicknesses up to 10 km in the polish part of the east european platform the thickness of the earth s crust is 42 47 kin and the boundary velocity of pn waves at the moho is 8 1 8 3 km s 1 the crystalline complex of the crust consists of three parts with velocities of 6 1 6 3 6 7 6 9 and 7 2 7 3 km s a grad 1986 in the other regions of the platform the earth s crust thickness varies over a wide range from 35 to 55 km the mean crust thickness is 40 45 kin in the crystalline complex we can distinguish three different parts in the layer velocity and the velocity gradient the first upper part is characterized by velocities of 5 8 6 4 km s a corresponding to acid rocks in this part there are zones of low velocities horizontal heterogeneities and also fractures and tectonic disturbances the second transition part is characterized by velocities of 6 3 6 6 km s 1 corresponding to basic rocks with an admixture of acid rocks the lower part with velocities of 6 8 7 5 km s 1 is built from basic rocks with the addition of ultrabasic rocks pavlenkova 1984 the mean velocity of the whole crystalline complex is 6 4 6 5 km s 1 and the velocity beneath the moho is 8 1 8 3 km s 1 over the last decade within the east european platform a number of long range seismic profiles were made fig 1 their purpose was to study the earth s crust and the lower lithosphere in this study we have determined one dimensional seismic models of the lithosphere for two travel time branches for the shot point p4 on the baltic sea black sea profile we used ukrainiaja and polish recordings from the distance intervals 0 400 and 600 900 kin respectively refracted pn waves from the moho occur as the first arrivals beginning at a distance of 220 km and are

a 350014c yr high resolution record of water level changes in lake titicaca bolivia peru abstract sediment cores collected from the southern basin of lake titicaca bolivia peru on a transect from 4 6 m above overflow level to 15 1 m below overflow level are used to identify a new century scale chronology of holocene lake level variations the results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century scale lake level changes detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores a chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water level fluctuations two methods were used to estimate the14c reservoir age both indicate that it has remained nearly constant at 25014c yr during the late holocene core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level implying negative moisture balance for the northern andean altiplano over the last 3500 cal yr between 3500 and 3350 cal yr b p a transition from massive inorganic clay facies to laminated organic matter rich silts in each of the four cores signals a water level rise after a prolonged mid holocene dry phase evidence of other significant low lake levels occurs 2900 2800 2400 2200 2000 1700 and 900 500 cal yr b p several of the low lake levels coincided with cultural changes in the region including the collapse of the tiwanaku civilization

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

soil grain analyses at meridiani planum mars 1 grain size analyses of the soils at meridiani planum have been used to identify rock sources for the grains and provide information about depositional processes under past and current conditions basaltic sand dust millimeter size hematite rich spherules interpreted as concretions spherule fragments coated partially buried spherules basalt fragments sedimentary outcrop fragments and centimeter size cobbles are concentrated on the upper surfaces of the soils as a lag deposit while finer basaltic sands and dust dominate the underlying soils there is a bimodal distribution of soil grain sizes with one population representing grains 125 m and the other falling between 1 4 5 mm soils within craters like eagle and endurance show a much greater diversity of grain morphologies compared to the plains the spherules found in the plains soils are approximately 1 2 mm smaller in size than those seen embedded in the outcrop rocks of eagle and endurance craters the average major axis for all unfractured spherules measured in the soils and outcrop rocks is 2 87 1 18 mm with a trend toward decreasing spherule sizes in both the soils and outcrop rocks as the rover drove southward wind ripples seen across the plains of meridiani are dominated by similar size 1 3 1 7 mm hematite rich grains and they match in size the larger grains on plains ripples at gusev crater larger clasts and centimeter size cobbles that are scattered on the soils have several spectral and compositional types reflecting multiple origins the cobbles tend to concentrate within ripple troughs along the plains and in association with outcrop exposures

ancient impact and aqueous processes at endeavour crater mars the rover opportunity has investigated the rim of endeavour crater a large ancient impact crater on mars basaltic breccias produced by the impact form the rim deposits with stratigraphy similar to that observed at similar sized craters on earth highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits gypsum rich veins cut sedimentary rocks adjacent to the crater rim the gypsum was precipitated from low temperature aqueous fluids flowing upward from the ancient materials of the rim leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate rich sandstones of the meridiani region

holocene palaeohydrology of lake titicaca estimated from an ostracod based transfer function lacustrine deposits of holocene age 8000 14c yr bp present were studied in lake titicaca bolivia ostracod assemblages were identified in six cores taken in the three basins which today form lake titicaca factorial correspondence and multiple linear regression analysis of the ostracods have permitted the reconstruction of 1 lake level 2 water salinity and 3 water mg ca ratio variations palaeolake levels indicate a complex evolution of the three basins with some major phases after a flooding at about 8000 yr 14c bp the lake level fluctuated around a mean position until 3900 14c yr bp when a second rise took place it seems however that the present day lake level was not reached until after 680 yr 14c bp some major dry events are also recorded at about 5300 14c yr bp and 2300 14c yr bp the lake titicaca data are consistent with other records from south america and also seem to reflect some world wide events

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

studies of mantle structure of u s s r territory on long range seismic profiles long range seismic sounding carried out during the last few years on the territory of the u s s r has shown a basic inhomogeneity of the uppermost mantle as well as evidence of regularities in the distribution of its seismic parameters the following data were used times and apparent velocities of p and s waves for investigation of mantle velocities converted waves for seismic discontinuity model studies and wave attenuation for q factor estimation strong regularities were distinguished in the distribution of average seismic velocities for the uppermost mantle in their dependence on the age and type of geostructure and on their position relative to the central part of the continent old platforms and the inner part of the continent are marked by velocities under the mohorovicic discontinuity of more than 8 2 8 3 km s 1 young platforms and outer parts of the continent by 8 0 8 2 km s 1 and orogenic and rift zones by 7 8 8 0 km s 1 the difference becomes more pronounced at a depth of about 100 200 km for the old platform mantle velocities of 8 5 8 6 km s 1 are typical beneath the orogenic and rift areas inversion zones with velocities less than 7 8 km s 1 are observed the converted waves show fine inhomogeneities of the crust and uppermost mantle the presence of many discontinuities with positive and negative changes of velocity and anisotropy of seismic waves in some of the layers wave attenuation allowed the determination of the q factor in the mantle it varied from one region to another but a close relation between q and p wave velocity is the main cause of its variation

context of ancient aqueous environments on mars from in situ geologic mapping at endeavour crater using the mars exploration rover opportunity we have compiled one of the first field geologic maps on mars while traversing the noachian terrain along the rim of the 22 km diameter endeavour crater latitude 2 16 33 longitude 5 10 51 in situ mapping of the petrographic elemental structural and stratigraphic characteristics of outcrops and rocks distinguishes four mappable bedrock lithologic units three of these rock units predate the surrounding burns formation sulfate rich sandstones and one the matijevic formation represents conditions on early mars predating the formation of endeavour crater the stratigraphy assembled from these observations includes several geologic unconformities the differences in lithologic units across these unconformities record changes in the character and intensity of the martian aqueous environment over geologic time water circulated through fractures in the oldest rocks over periods long enough that texturally and elementally significant alteration occurred in fracture walls these oldest pre endeavour rocks and their network of mineralized and altered fractures were preserved by burial beneath impact ejecta and were subsequently exhumed and exposed the alteration along joints in the oldest rocks and the mineralized veins and concentrations of trace metals in overlying lithologic units is direct evidence that copious volumes of mineralized and or hydrothermal fluids circulated through the early martian crust the wide range in intensity of structural and chemical modification from outcrop to outcrop along the crater rim shows that the ejecta of large 8 km in diameter impact craters is complex these results imply that geologic complexity is to be anticipated in other areas of mars where cratering has been a fundamental process in the local and regional geology and mineralogy

fibrous gypsum and fibrous anhydrite in veins fibrous calcium sulphate occurs in nature mainly as gypsum satinspar in extensional veins several mechanisms have been put forward to account for these veins and their fillings but a number of features remain unexplained or are not in accord with the interpretation s given this paper describes anhydrite as a fibrous vein precipitate which shows most features typical of satinspar subhorizontal attitude of the vein s vertical fibres a parting separating a lower from an upper seam and incorporated wall rock fragments new observations include the stacked nature of the fibres pressure shadows next to wall rock fragments and parabolic alignment of the latter these features suggest that the veins opened due to vertically oriented tensile stress the vein filling crystals grew centrifugally outwards from the initial plane of rupture which now forms the parting keeping pace with the dilation the mode of incorporation of wall rock fragments in the fibres requires repeated differential opening of the fissure thereby either wall rock fibre interface ruptured at a time and statistically the ruptures alternated so that trace element trends across the vein s are roughly symmetrical to the parting the source of the calcium and sulphate ions may have been adjacent evaporite beds but an external source is indicated where no evaporite beds are present in contrast to previous interpretations hydration of anhydrite to gypsum in the host rocks is not a prerequisite for the formation of satinspar veins the exact causes for the vertical dilation remain somewhat speculative and may have been different in various locations the vertically oriented tensile stress may have resulted from lateral tectonic compression or hydraulic overpressure or a combination of the two

a late quaternary diatom record of tropical climatic history from lake titicaca peru and bolivia abstract a composite high resolution diatom stratigraphy from three piston cores and one box core in the deep sub basin of lake titicaca reveals large moisture variations during the past 30 kyr in the altiplano region diatom sequences indicate orbital and millennial scale variability in water level and salinity the pelagic freshwater diatom species cyclotella andina and cyclotella stelligera dominate glacial age sediments suggesting that the lake was above its present outlet generally wet conditions continued until 11 000 cal yr bp as indicated by high percentages of freshwater planktonic diatoms large pulses of benthic diatom species between about 11 000 and 10 000 cal yr bp suggest brief intervals of large amplitude declines in lake level during the early holocene 10 000 8500 cal yr bp a freshwater diatom assemblage suggests overflowing conditions pelagic freshwater diatoms are replaced ca 8500 cal yr bp by the salinity indifferent species cyclotella meneghiniana and by benthic taxa indicating the beginning of lake regression during the mid holocene 6000 3500 cal yr bp the abundance of the saline taxon chaetoceros muelleri coupled with high abundances of epiphytic and epipelic diatoms indicates maximum salinity and lowest lake levels in the entire 30 000 year record lake transgression began ca 4000 cal yr bp and the lake achieved modern levels by about 1500 cal yr bp these water level changes imply changes in effective moisture most likely resulting from large precipitation changes precipitation was high throughout the last glacial maximum 21 000 18 000 cal yr bp likely due to an enhanced south american summer monsoon during peak summer insolation in the southern hemisphere in contrast the mid holocene transition was dryer than today in association with an austral summer insolation minimum and the subsequent weakening of the summer monsoon

estimating rock compressive strength from rock abrasion tool rat grinds 1 each mars exploration rover carries a rock abrasion tool rat whose intended use was to abrade the outer surfaces of rocks to expose more pristine material motor currents drawn by the rat motors are related to the strength and hardness of rock surfaces undergoing abrasion and these data can be used to infer more about a target rock s physical properties however no calibration of the rat exists here we attempt to derive an empirical correlation using an assemblage of terrestrial rocks and apply this correlation to data returned by the rover spirit the results demonstrate a positive correlation between rock strength and rat grind energy for rocks with compressive strengths less than about 150 mpa a category that includes all but the strongest intact rocks applying this correlation to rocks abraded by spirit s rat the results indicate a large divide in strength between more competent basaltic rocks encountered in the plains of gusev crater adirondack class rocks and the weaker variety of rock types measured in the columbia hills adirondack class rocks have estimated compressive strengths in the range of 70 130 mpa and are significantly less strong than fresh terrestrial basalts this may be indicative of a degree of weathering induced weakening rock types in the columbia hills wishstone watchtower clovis and peace class all have compressive strengths 50 mpa and are consistent with impactites or volcanoclastic materials in general when considered alongside chemical spectral and rock textural data these inferred compressive strength results help inform our understanding of rock origins and modification history

summertime precipitation variability over south america role of the large scale circulation abstract the observed large scale circulation mechanisms associated with summertime precipitation variability over south america are investigated particular attention is paid to the altiplano where a close relationship has been observed between rainfall and the position and intensity of the bolivian high empirical orthogonal function eof correlation and composite analyses suggest that on intraseasonal timescales typically 5 20 days rainy periods on the altiplano are associated with at least three types of circulation anomalies involving either extratropical cyclones cold core lows or the westward enhancement of the south atlantic high in each instance the primary support for high rainfall rates is a moist poleward flow at low levels along the eastern flank of the central andes in association with the south atlantic convergence zone sacz the warm low level flow along the sacz also inflates the overlying atmospheric column resulting in an intensification and southward shift of the bolivi

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

silica rich deposits and hydrated minerals at gusev crater mars vis nir spectral characterization and regional mapping abstract the mars exploration rover mer spirit has discovered surprisingly high concentrations of amorphous silica in soil and nodular outcrops in the inner basin of the columbia hills in pancam multispectral observations we find that an absorption feature at the longest pancam wavelength 1009 nm appears to be characteristic of these silica rich materials however spectral analyses of amorphous silica suggest that the 1009 nm spectral feature is not a direct reflection of their silica rich nature based on comparisons with spectral databases we hypothesize that the presence of h 2 o or oh either free as water ice adsorbed or bound in a mineral structure is responsible for the spectral feature observed by pancam the gertrude weise soil which is nearly pure opaline silica may have adsorbed water cold trapped on mineral grains the origin of the 1009 nm pancam feature observed in the silica rich nodular outcrops may result from the presence of additional hydrated minerals specific sulfates halides chlorides sodium silicates carbonates or borates using the 1009 nm feature with other spectral parameters as a hydration signature we have mapped the occurrence of hydrated materials along the extent of spirit s traverse across the columbia hills from west spur to home plate sols 155 1696 we have also mapped this hydration signature across large panoramic images to understand the regional distribution of materials that are spectrally similar to the silica rich soil and nodular outcrops our results suggest that hydrated materials are common in the columbia hills

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

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

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

veneers rinds and fracture fills relatively late alteration of sedimentary rocks at meridiani planum mars veneers and thicker rinds that coat outcrop surfaces and partially cemented fracture fills formed perpendicular to bedding document relatively late stage alteration of ancient sedimentary rocks at meridiani planum mars the chemistry of submillimeter thick buff colored veneers reflects multiple processes at work since the establishment of the current plains surface veneer composition is dominated by the mixing of silicate rich dust and sulfate rich outcrop surface but it has also been influenced by mineral precipitation including nacl and possibly by limited physical or chemical weathering of sulfate minerals competing processes of chemical alteration perhaps mediated by thin films of water or water vapor beneath blanketing soils and sandblasting of exposed outcrop surfaces determine the current distribution of veneers dark toned rinds several millimeters thick reflect more extensive surface alteration but also indicate combined dust admixture halite precipitation and possible minor sulfate removal cemented fracture fills that are differentially resistant to erosion occur along the margins of linear fracture systems possibly related to impact these appear to reflect limited groundwater activity along the margins of fractures cementing mechanically introduced fill derived principally from outcrop rocks the limited thickness and spatial distribution of these three features suggest that aqueous activity has been rare and transient or has operated at exceedingly low rates during the protracted interval since outcropping meridiani strata were exposed on the plains surface

holocene environments from stable isotope stratigraphy of ostracods and authigenic carbonate in chilean altiplano lakes abstract sediment cores from three shallow 4000 m a s l paleoclimatic profiles show coherency within tropical subtropical circulation patterns climatic signals however are partially masked by local environmental systems results suggest similar arid mid holocene to less arid late holocene trends in the three lakes although each lake shows distinct response characteristics linked to differences in regional moisture balance isotopic signatures for each lake group in discrete 18o vs 13c populations high isotopic variability results from episodic flooding and brine evolution in the shallow lakes laguna seca 18 11 s 69 14 w 4500 m a s l is characterized by a diverse ostracod assemblage of at least 8 species indicating highest moisture levels among the three sites high 13c values are the result of continuous evasion of co2 derived from volcanically charged groundwaters and springs plus the formation of travertine and photosynthetic activity in the lake a 3 decrease in 18o about 4 7 m suggests an abrupt shift to wetter conditions at the transition from mid to late holocene lagunas miscanti 23 44 s 67 46 w 4140 m a s l and del negro francisco 27 28 s 69 14 w 4125 m a s l each contain only one ostracod species limnocythere sappaensis attesting to higher salinities although sediment facies and ostracod continuity and abundances imply a history of higher effective moisture at laguna del negro francisco sediment cores from each lake document more arid conditions in the lower sections with a sharp shift to wetter conditions in the upper sections highly variable isotope values at the transition from mid to late holocene suggest rapid short term climate shifts during this transition this overall trend can be correlated from laguna seca laguna miscanti and laguna del negro francisco to lago titicaca implying climatic coherency along the altiplano isotopic profiles show second order fluctuations and drought events that suggest short term variability along the transect in order to explain differences in the effective moisture among the three sites we postulate interactions of regional air masses in the north convective tropical precipitation dominates laguna seca as for lakes in the titicaca region effective moisture for lagunas del negro francisco and miscanti follows a south to north gradient generated by cold air masses from cut offs of pacific westerlies colliding with moist tropical air masses coherent shifts in the past therefore imply changes in available tropical air mass moisture

medusae fossae formation new perspectives from mars global surveyor 1 the nature and origin of the medusae fossae formation mff on mars has been debated since the return of the first viking images the mff s young age distinctive surface texture and lack of obvious source have prompted multiple hypotheses for its origin this study uses data from the mars global surveyor mgs mission to examine the mff at all available scales we discuss and quantify observations from mars orbiter laser altimeter mola topography and mars orbiter camera moc images to better constrain the origin of the mff topographic grid estimates yield a present extent of 2 1 106 km2 and a volume of 1 4 106 km3 however remnant yardang deposits observed far from the thicker lobes of mff material suggest that it may have once covered up to 5 106 km2 we do not find compelling evidence for extensive fluvial reworking of the mff however in several regions buried channels are apparent in the mff because the formation is draped over underlying topography layering is apparent at all scales from submeter to hundreds of meters with variable resistance to weathering continuity of layers appears to be local to regional but not likely formation wide yardangs form both parallel and bidirectional patterns with resistant layers and jointing probably influencing their orientations a comparative study of mff regional topography and surface expression indicates that the mff is quantitatively dissimilar to martian polar layered deposits the material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin

p wave velocity features of the lithosphere under the eromanga basin eastern australia including a prominent mid crustal conrad discontinuity abstract the crustal structure of the central eromanga basin in the northern part of the australian tasman geosyncline revealed by coincident seismic reflection and refraction shooting contrasts with some neighbouring regions of the continent the depth to the crust mantle boundary moho of 36 41 km is much less than that under the north australian craton to the northwest 50 55 km and the lachlan fold belt to the southeast 43 51 km but is similar to that under the drummond and bowen basins to the east the seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the north australian and lachlan provinces in particular there is a sharp velocity increase at mid crustal depths 21 24 km which has not been observed with such clarity elsewhere in australia the conrad discontinuity in the lower crust the many discontinuous sub horizontal reflections are in marked contrast to lack of reflecting horizons in the upper crust further emphasising the differences between the upper and lower crust the crust mantle boundary moho is characterised by an increase in velocity from 7 1 7 7 km s to a value of 8 15 0 04 km s the depth to the moho under the canaway ridge a prominent basement high is shallower by about 5 km than the regional moho depth there is also no mid crustal horizon under the canaway ridge but there is a very sharp velocity increase at the moho depth of 34 km the ridge could be interpreted as a horst structure extending to at least moho depths but it could also have a different intra crustal structure from the surrounding area the sub crustal lithosphere has features which have been interpreted from limited data as being caused by a velocity gradient at 56 57 km depth with a low velocity zone above it because of the contrasting crustal thicknesses and velocity gradients the lithosphere of the central eromanga basin cannot be considered as an extension of the exposed lachlan fold belt or the north australian craton the lack of seismic reflections from the upper crust indicates no coherent accoustic impedance pattern at wavelengths greater than 100 m consistent with an upper crustal basement of tightly folded meta sedimentary and meta volcanic rocks the crustal structure is consistent with a pericratonic or arc back arc basin being cratonised in an episode of convergent tectonics in the early palaeozoic the seismic reflections from the lower crust indicate that it could have developed in a different tectonic environment

holocene lake level fluctuations of lake aricota southern peru lacustrine deposits exposed around lake aricota peru 17 22 s a 7 5 km2 lake dammed by debris flows provide a middle to late holocene record of lake level fluctuations chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14c reservoir effects 350 yr diatomites associated with highstands several meters above the modern lake level indicate wet episodes maximum holocene lake level was attained before 6100 14c yr b p and ended 2700 14c yr b p moderately high lake levels occurred at 1700 and 1300 14c yr b p the highstand at lake aricota during the middle holocene is coeval with a major lowstand at lake titicaca 16 s which is only 130 km to the northeast and shares a similar climatology comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid holocene climate in the central andes

fluidization and hydrothermal alteration of the suevite deposit at the ries crater west germany and implications for mars the formation cooling and alteration of the impact ejecta deposits at the ries crater are an analog for impact processes and the formation of regoliths and soils on mars we have studied the suevite deposit an impact melt bearing breccia found outside of the crater rim this suevite contains large numbers of chimney like degassing pipes apparently formed by high gas pressures in the hot 500 c fluidized suevite immediately after deposition of the suevite the likely sources of the gas are volatiles from the melted and shocked basement inclusions the suevite outside of the crater rim contains about 15 wt clay indicating a large amount of alteration of the suevite the clay is an fe rich montmorillonite with less than 5 interstratified illite indicating that the temperature at which most of the alteration occurred was less than 100 130 c the duration of this low temperature period may have been extended by additional heating from the exothermal alteration reactions the surfaces of the degassing pipes are not altered to clays however but have a thin fe rich oxide or hydroxide coating the absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions such that the walls of the pipes were dry suevite deposits are likely to exist on mars because of the presence of volatile rich target rock martian suevites may have also been fluidized and hydrothermally altered contributing significantly to the formation of the clay like phases inferred to exist in the martian soil

visible and near infrared multispectral analysis of rocks at meridiani planum mars by the mars exploration rover opportunity multispectral measurements in the visible and near infrared of rocks at meridiani planum by the mars exploration rover opportunity s pancam are described the pancam multispectral data show that the outcrops of the burns formation consist of two main spectral units which in stretched 673 535 432 nm color composites appear buff and purple colored these units are referred to as the hfs and lfs spectral units based on higher and lower values of 482 to 535 nm slope spectral characteristics are consistent with the lfs outcrop consisting of less oxidized and the hfs outcrop consisting of more oxidized iron bearing minerals the lfs surfaces are not as common and appear primarily at the distal ends of outcrop layers and on steep more massive surfaces locations that are subject to greater eolian erosion consequently the hfs surfaces are interpreted as a weathering rind further inherent spectral differences between layers and between different outcrop map units both untouched and patches abraded by the rover s rock abrasion tool are also described comparisons of the spectral parameters of the meridiani outcrop with a set of laboratory reflectance measurements of fe 3 bearing minerals show that the field of outcrop measurements plots near the fields of hematite ferrihydrite poorly crystalline goethite and schwertmannite rind and fracture fill materials observed intermittently at outcrop exposures are intermediate in their spectral character between both the hfs and lfs spectral classes and other less oxidized surface materials basaltic sands spherules and cobbles

high resolution seismic reflection profiles from lake titicaca peru bolivia evidence for holocene aridity in the tropical andes high resolution seismic reflection profiles of the sediments of lake titicaca peru bolivia suggest that lake levels in the recent past were considerably lower than today incised channels on the major deltas extend to depths of 85 m below modern lake level erosional truncation of onlapping seismic reflectors is found at similar depths this interpretation of the seismic data is supported by analyses of sediment cores from the lake which indicate that there was a significant drop in lake level during the early to mid holocene

reconstructing past upwelling intensity and the seasonal dynamics of primary productivity along the peruvian coastline from mollusk shell stable isotopes 1 we present here a potential new method to evaluate past variations of the mean intensity of peruvian coastal upwelling and of the seasonal timing of phytoplankton blooms this method uses a combination of the monthly carbon and oxygen isotopic signals preserved in fossil mollusk shells and a series of corrections to extract the variations of the dissolved inorganic carbon dic 13c based on the analysis of five shell samples 85 shells in total from the southern peruvian coast we suggest that the mean coastal upwelling intensity can be determined from a linear relationship between average values of corrected shell 13c and 18o this new potential proxy would bring additional independent information valuable to interpret paleoproductivity changes reconstructed from marine sediment of the nearby continental shelf results obtained on fossil samples from the middle holocene show an increase in upwelling intensity during this period associated to a spatial reorganization of upwelling centers along the south peruvian coast at the seasonal scale corrected shell 13c enrichment indicates a phytoplankton bloom seasonal timing of phytoplankton blooms can be estimated by the lag with the annual temperature cycle reproduced by shell 18o monthly variations the results obtained with two modern shell samples indicate phytoplankton blooms occurring during summer and fall consistently with in situ productivity observations our method relies on revisited assumptions about the influence of temperature and metabolism in mollusk shell 13c we further discussed the validity of these assumptions and the potential implications for the interpretation of similar data sets

origin of the medusae fossae formation mars insights from a synoptic approach 1 the geologic origin of the medusae fossae formation mff has remained a mystery despite three decades of research to better constrain its formation an in depth analysis of observations made in the literature was combined with a new survey of over 700 mars orbiter camera narrow angle images of the mff to identify morphologic characteristics and material properties that define this formation as a whole while previous work has identified clear agreement on some characteristics our analysis identifies yardangs collapse features and layering as pervasive features of the mff whereas collapse features and layering may implicate several different physical and chemical processes yardangs provide vital information on material properties that inform about mechanical properties of the mff lithology aspect ratios of megayardangs range from 3 1 to 50 1 and slope analyses reveal heights of up to 200 m with cliffs that are almost vertical other yardangs show lower aspect ratios and topographic profiles these characteristics coupled to the presence of serrated margins suggest that mff lithology must be of weakly to heavily indurated material that lends itself to jointing the characteristics and properties of the mff are inconsistent with those of terrestrial pyroclastic fall deposits or loess but are in common with large terrestrial ignimbrites a hypothesis that explains all key observations with a single mechanism yardang fields developed in regionally extensive ignimbrite sheets in the central andes display morphologic characteristics that correlate with degree of induration of the host lithology and suggest an origin by pyroclastic flow for the mff

el nino variability in the coastal desert of southern peru during the mid holocene abstract fourteen organic rich sedimentary layers in the deposits at quebrada de los burros in coastal southern peru tacna department lie between two debris flow units interpreted to result from el nino events at 8980 cal yr b p and after 3380 cal yr b p respectively the accumulation of the fine grained and low energy sediments of this deposit during the mid holocene is incompatible with the occurrence of el nino events in this region as these would produce catastrophic flood deposits the occurrence of organic rich sediments and evidence of an enhancement of upwelling strength at this time imply the existence of a permanent water supply resulting from an increased condensation of fog at mid altitudes these results suggest a lower intensity and perhaps a lower frequency of occurrence of the el nino phenomenon during the mid holocene it is precisely during this period that the most important human settlements are found at this site probably indicating the presence of reliable supply of fresh water the chronologies for wetlands in the central south altiplano are out of phase with those indicating increased soil moisture episodes on the coast implying a long term difference in climate between these two regions

holocene paleohydrology and glacial history of the central andes using multiproxy lake sediment studies here we document at century to millennial scale the regional changes of precipitation evaporation from the late pleistocene to present with multiproxy methods on a north south transect of lake sites across the eastern cordillera of the central andes the transect of study sites covers the area from v14 s to 20 s and includes core studies from seven lakes and modern calibration water samples from twenty three watersheds analyzed to constrain the down core interpretations of stable isotopes and diatoms we selected lakes in different hydrologic settings spanning a range of sensitivity to changes in the moisture balance these include 1 lakes directly receiving glacial meltwater 2 overflowing lakes in glaciated watersheds 3 overflowing lakes in watersheds without active glaciers and 4 lakes that become closed basins during the dry season the results of our current work on multiple lakes in the bolivian andes show that while the overall pattern of holocene environmental change is consistent within the region conditions were not always stable over centennial to over millennial timescales and considerable decadal to centuryscale climate variability is evident abbott et al quat res 47 1997 70 80 quat res 47 1997 169 180 quat sci rev 19 2000 1801 1820 polissar master s thesis university of massachusetts 1999 comparison of the paleoclimate record from one well studied site lago taypi chaka kkota ltck with others within the region illustrates a consistent overall pattern of aridity from the late glacial through the middle holocene previous work noted a difference between the timing of water level rise in lake titicaca v5 0 3 5 ka b p abbott et al quat res 47 1997 169 180 cross et al holocene 10 2000 21 32 rowe et al clim change 52 2002 175 199 and the onset of wetter conditions at 2 3 ka b p in ltck a lake that drains into the southern end of lake titicaca abbott et al quat res 47 1997 70 80 sedimentary and oxygen isotope evidence from paco cocha 13 54ps located in the northern reaches of the expansive 57 000 km 2 titicaca watershed which spans v14 s to 17 s indicates that

radiocarbon reservoir effect and the timing of the late glacial early holocene humid phase in the atacama desert northern chile we revise substantially the regional chronology of lake level fluctuations from the late glacial early holocene humid phase along a high altitude transect 3500 to 4500 m between 18 s and 28 s in the southwestern altiplano of northern chile radiocarbon dates and 210pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14c dates our chronology suggests that the latest pleistocene early holocene humid phase started between 13 000 and 12 000 14c yr b p and that maximum lake levels were reached between 10 800 and 9200 14c yr b p this is significantly younger than what has been established so far for the titicaca uyuni basin in bolivia the paleolakes disappeared sometime between 8400 and 8000 14c yr b p our revised chronology agrees with the regional history of human occupation and is broadly synchronous with vegetation changes in subtropical continental south america and with the onset of wetland expansion in the northern hemisphere tropics

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

gusev crater wind related features and processes observed by the mars exploration rover spirit 1 wind related features observed by the rover spirit in gusev crater mars include patches of soil on the surface some of which are organized into bed forms windblown grains include dust inferred to be 2 mm in diameter microscopic imager data show the sands and granules to be rounded and relatively spherical typical of grains transported long distances by the wind the interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains indicating that these sands are not currently experiencing saltation orientations of 1520 features such as bed forms and ventifacts along spirit s traverse from the landing site the columbia memorial station to west spur in the columbia hills suggest primary formative winds from the north northwest which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models a secondary wind from the southeast is also suggested which correlates with predictions for nighttime early morning winds wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks the orientations of which also indicate prevailing winds from the north northwest orientations of many aeolian features in the west spur area however have more scatter than elsewhere along the traverse which is attributed to the influence of local topography on the patterns of wind active dust devils observed on the floor of gusev from the columbia hills demonstrate that dust is currently mobile sequential images of some dust devils show movement as rapid as 3 8 m s consistent with wind velocities predicted by atmospheric models for the afternoon when most of the dust devils were observed sands accumulated on the rover deck in the same period suggest that some sands in the columbia hills experience active saltation two toned rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure while perched rocks could represent materials lowered onto other rocks by deflation of supporting soils measurements of the heights of the light bands and the perched rocks range from 1 cm to 27 cm indicating local deflation by as much as 27 cm

climate in the western cordillera of the central andes over the last 4300 years abstract the distichia peat core obtained in the carhuasanta valley near nevado mismi cordillera chila provides information on climatic and environmental conditions over the last 4300 years the relative changes in the stable carbon isotope composition of plant remains preserved in the core reflect major temperature fluctuations in the western cordillera of the southern peruvian andes these temperature variations can be additionally linked with the changes in precipitation patterns by analysing c and c n ratio in the core relatively warm and moist conditions prevailed from 4280 to 3040 cal yrs bp bc 2330 1090 with a short colder dry episode around 3850 cal yrs bp bc 1900 the most prominent climate changes recorded in the peat occurred between 3040 and 2750 cal yrs bp bc 1090 800 when the initial warming turned to a rapid cooling to temperatures at least 2 c lower than the mean for the late holocene initially drier conditions within this event turned to a short wet phase after 2780 cal yrs bp bc 830 when the temperature increased again this event coincides with significant changes in peat and ice core records in the central andes matching the timing of the global climate event around 2 8 cal ka bp climatic conditions in the study area became relatively dry and stable after the event for about 800 years highly variable temperatures and humidity prevailed during the last 2000 years when an extended warm and relatively humid period occurred between 640 and 155 cal yrs bp ad 1310 1795 followed by predominantly colder and drier conditions the established 13 c peat record represents the first continuous proxy for the temperature in the southern peruvian andes dated by the ams 14 c distichia peat is wide spread in the andes and the proposed approach can be applied elsewhere in high altitudes where no other traditional climate proxies are available

seismic model of the lithosphere of the east european platform beneath the baltic sea black sea profile abstract this paper presents the results of seismic measurements along the baltic sea black sea profile the basic wave groups recorded up to distances of 900 km are characterized the main elements of a lithospheric model of the southwestern part of the precambrian east european platform are given the thickness of the earth s crust is about 45 km and the mean velocity of the crust is about 6 3 km s at a depth of 65 km the velocity increases from 8 2 to 8 5 km s in the depth interval 110 to 135 km there is a series of layers with low and high velocities the lower boundary of the lithosphere is probably defined by the boundary at a depth of 110 km

modeling climate shift of el nino variability in the holocene a coupled ocean atmosphere general circulation model is used to investigate climatic shift of el nino in the holocene the model simulates a reduced enso intensity in the early and mid holocene in agreement with paleoclimate record the enso reduction is proposed to be caused by both an intensified asian summer monsoon and a warm water subduction from the south pacific into the equatorial thermocline

upper lithospheric seismic velocity structure across the pripyat trough and the ukrainian shield along the eurobridge 97 profile abstract we present new results on the structure resulting from palaeoproterozoic terrane accretion and later formation of one of the aulacogens in the east european platform seismic data has been acquired along the 530 km long n s striking eurobridge 97 traverse across sarmatia a major crustal segment of the east european craton the profile extends across the ukrainian shield from the devonian pripyat trough across the palaeoproterozoic volyn block and the korosten pluton into the archaean podolian block seismic waves from chemical explosions at 18 shot points at approximately 30 km intervals were recorded in two deployments by 120 mobile three component seismographs at 3 4 km nominal station spacing the data has been interpreted by use of two dimensional tomographic travel time inversion and ray trace modelling the high data quality allows modelling of the p and s wave velocity structure along the profile there are pronounced differences in seismic velocity structure of the crust and uppermost mantle between the three main tectonic provinces traversed by the profile i the pripyat trough is a ca 4 km deep sedimentary basin fully located in the osnitsk mikashevichi igneous belt in the northern part of the profile the velocity structure is typical for a precambrian craton but is underlain by a ca 5 km thick lowest crustal layer of high velocity the development of the pripyat trough appears to have only affected the upper crust without noticeable thinning of the whole crust this may be explained by a rheologically strong lithosphere at the time of formation of the trough ii very high seismic velocity and vp vs ratio characterise the volyn block and korosten pluton to a depth of 15 km and probably also the lowest crust the values are consistent with an intrusive body of mafic composition in the upper crust that formed from bimodal melts derived from the mantle and the lower crust iii the podolian block is close to a typical cratonic velocity structure although it is characterised by relatively low seismic velocity and vp vs ratio a pronounced sw dipping mantle reflector from moho to at least 70 km depth may represent the proterozoic suture between sarmatia and volgo uralia the structure from terrane accretion or a later shear zone in the upper mantle the sub moho p wave seismic velocity is high everywhere along the profile with the exception of the area above the dipping reflector this velocity change further supports a plate tectonic origin of the dipping mantle reflector the profile demonstrates that structure from palaeoproterozoic plate tectonic processes are still identifiable in the lithosphere even where younger metamorphic equilibration of the crust has taken place

seismic structure of the sub crustal continental lithosphere abstract seismic models of the continental lower lithosphere obtained from interpretation of body p waves in various regions of the earth are discussed the models differ in the character of velocity distribution the number of layers and the presence of the lower velocity layers this is the consequence of inhomogeneity of the lower lithosphere but it also follows from the differing accuracy and quality of seismic data the differences in models resulting from the use of seismological methods based on earthquake observations and experiments on long range profiles are pointed out the results of surveys into the lower lithosphere of the east european platform are analysed in greater detail

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

distichia peat a new stable isotope paleoclimate proxy for the andes article i nfo global climate variability is a well documented fact however the human contribution to climate change is now being vigorously debated therefore a better understanding of past natural climate variability may help to establish the actual anthropogenic contribution to the observed climatic trend a variety of high resolution proxies now exist for documenting climate variability that has occurred in the northern hemisphere over the last 10 ka in contrast high resolution paleoclimate records are more limited for regions such as high altitudes in the andes south america however many regions of the andes contain a rich but as yet overlooked paleoclimate archive in the form of thick peat deposited in situ by the distichia plant in our study based on altitudinal transect from the peruvian andes we found a statistically significant and strong relationship between the stable carbon isotope composition of distichia and air temperature r 0 92 pb0 01 we also confirmed good preservation of relative differences in the original stable carbon isotope composition in peat derived from this plant our calibration showed that a decrease of 0 97 0 23 in the stable carbon isotope composition of distichia peat reflects a 1 c increase in mean air temperature of the growing seasons this relationship can be used as a new high resolution proxy for reconstruction of paleotemperature variations over the past several thousand years in the andes mountains based on distichia peat cores

an ice core pollen record showing vegetation response to late glacial and holocene climate changes at nevado sajama bolivia we present the results of pollen analysis performed on an ice core recovered from nevado sajama bolivia dated to 25 ka bp low pollen concentrations from 25 to 15 ka bp are consistent with the scenario of an expanded ice cap surrounded by sparse vegetation and cold conditions on the altiplano during the last glacial maximum after 15 ka bp more pollen is present and percentages show vegetation response to climate fluctuations during the late pleistocene initially high concentrations of poaceae pollen are replaced by asteraceae pollen suggesting the occurrence of dry conditions towards the end of the bolling allerod guantiva interstadial a deglacial climatic reversal is registered in the pollen record by an abrupt decline in asteraceae and maximum percentages of poaceae indicating wet conditions during 14 12 ka bp the climate changed abruptly to warm and dry after 12 ka bp but vegetation remained in disequilibrium with climate until 10 ka bp pollen results indicate dry conditions at the beginning of the holocene with humidity increasing steadily until 8 5 ka bp decreased pollen concentration values used as a moisture availability proxy place the mid holocene dry period between 8 and 5 ka bp this was followed by wetter conditions to the present day

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

terminal pleistocene through mid holocene archaeological sites as paleoclimatic archives for the peruvian coast abstract along the peruvian coast standard paleoclimatic archives such as pollen cores or corals are absent or undeveloped however anthropogenic deposits offer paleoclimatic information for the last 13 000 years at temporal scales ranging from centennial for long term records to seasonal for short term records this paper summarizes archaeologically based paleoclimatic data for the peruvian coast from the terminal pleistocene through the middle holocene south of 12 s coastal waters have been cool temperate and terrestrial conditions have been hyperarid for the entire period between 8000 and 3600 cal bp the highland precipitation supplying runoff to the south coast may have diminished sufficiently to restrict human occupation of ephemeral streams north of 10 s sea surface temperatures were warmer and seasonal precipitation may have been greater from prior to 13 000 to 5800 cal bp from 9000 to 5800 cal bp el nino was absent or very infrequent after 5800 cal bp the northern coastal waters cooled and el nino was present but with a lower frequency than seen in the historical and instrumental record el nino frequencies in the modern and historical range were established 3000 cal bp cultural changes correlate temporally with these major climatic transitions

late quaternary hydroclimatology of a hyper arid andean watershed climate change floods and hydrologic responses to the el nino southern oscillation in the atacama desert abstract although certain characteristics of the el nino southern oscillation enso are well known on contemporary timescales less is known about the magnitude frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding especially in its core zone along the sub tropical andes where la nina or el nino episodes control regional hydroclimatology using a combination of stratigraphic evidence geochronologic dating 14c and osl stable isotope analyses and water geochemistry along the rio moquegua in the northern fringes of the atacama desert we assemble a paleoflood chronology for mainstem and tributary sections for the past ca 20 ka and ascertain the variation in enso frequency and magnitude because of the inherent watershed structure and regional hydroclimatology mid valley tributaries of the rio moquegua only flood during el nino episodes and thus provide an important proxy of extreme el ninos while mainstem stratigraphy records both la nina and el nino episodes el nino floods appear to have been pronounced during the late pleistocene and up to at least the younger dryas 12 000 cal yr bp while stratigraphic evidence of large el nino floods is lacking in tributary systems during the mid holocene flood stratigraphy in a 2 ka 7 m high terrace along the mainstem indicates an increased frequency and magnitude of large floods between ca 700 and 1610 ad as compared to the period from ca 160 bce to 700 ad with mega ninos occurring ca 1330 ad and ca 1650 ad water geochemistry and radiocarbon dating indicate that at least two major aquifers exist with wells and springs in the mid valley dating to 710 and 3100 14c yr bp respectively while water from a spring in the headwaters dates to 10 320 14c yr bp this range in dates suggests that groundwater flow in the mid valley is neither fossil water nor exclusively recharged from local precipitation while the older date for headwater sections suggests a more fossil groundwater source and lack of contemporary recharge the 18o similarity between groundwater in the mid valley and the regional meteoric water line mwl suggests a pacific moisture source and the role of el nino precipitation in recharging local aquifers thus el ninos and pacific sourced moisture are an important component of the regional hydroclimatology and the variation in enso frequency and intensity has significant social and hydrologic repercussions in these hyper arid settings

inhomogeneities of the eurasian mantle structure from the traveltimes of the nuclear explosions recorded by the finnish seismic network during 1961 1985 summary during the period 1961 1985 hundreds of nuclear explosions from the area of the soviet union and china were well recorded at finnish seismological stations the seismic waves recorded on the baltic fennoscandian shield penetrated through the mantle of the siberian platform the ural mountains and the east european platform from the known crustal models the functions describing the increase of the average velocities of sedimentary cover and crystalline complex of the crust with thickness were found the corrections for sedimentary cover and crustal thickness were included the large amount of data permitted the calculation of traveltimes of p waves for three sectors up to distances of about 5000 km in all mantle models the boundaries 400 and 700 km were found comparison of the results shows a difference in the traveltimes of the order of 5 s at a distance of about 4000 km which reflects the mantle structure differentiation for depths greater than 700 km lowest velocities for latitudinal direction and highest velocities for longitudinal direction the average s wave velocity model of the mantle was obtained using the traveltimes of s wave first arrivals high values of the vp vs ratio were found in the depth interval 200 400 km while in other depth intervals they were close to 1 73 our 1 d models are compared with and discussed in connection with other models of the east european and siberian platforms as well as with global tomographic solutions

equatorial and midlatitude distribution of chlorine measured by mars odyssey grs 1 the 2001 mars odyssey gamma ray spectrometer grs has made the first measurement of the equatorial and midlatitude distribution of cl at the near surface of mars a mean concentration value of 0 49 wt cl has been determined from a grand sum of grs spectra collected over the planet excluding high latitude regions cl is significantly enriched within the upper few tens of centimeters of the surface relative to the martian meteorites and estimates for the bulk composition of the planet however cl is not homogeneously distributed and varies by a factor of 4 even after smoothing of data with a 10 arc radius filter several contiguous geographically large 20 regions of high and low cl concentrations are present in particular a region centered over the medusae fossae formation west of tharsis shows significantly elevated cl a large region north of syrtis major extending into utopia planitia in the northern hemisphere shows the lowest cl concentrations on the basis of hierarchical multivariate correlations cl is positively associated with h while negatively associated with si and thermal inertia we discuss four possible geologic mechanisms aeolian volcanic aqueous and hydrothermal that may have affected the cl distribution seen by grs while some of the distribution may be due to cl rich dust deposits transported by aeolian processes this mechanism does not appear to account for all of the observed variability we propose that reactions with volcanic exhalations may have been important for enriching cl in medusae fossae formation material

isotopic evidence for late quaternary climatic change in tropical south america the tropical hydrologic cycle affects atmospheric trace gases and global climate change and thus records of hydrologic change encompassing a variety of time scales from the low latitudes are important in paleoclimatology isotopic analysis of calcite from lake junin peru provides a record of hydrologic variability that spans the last glacial interglacial transition in the southern tropics the record reveals a 6 enrichment in 18 o calcite during the late glacial followed by a gradual depletion during the holocene which can be interpreted as a decrease followed by a long term increase in effective moisture close agreement between 18 o calcite and rainy season insolation indicates that long term changes in tropical hydrology were linked to orbital variations furthermore hydrologic change was out of phase in the northern and southern tropics over this time period

overview of the opportunity mars exploration rover mission to meridiani planum eagle crater to purgatory ripple the mars exploration rover opportunity touched down at meridiani planum in january 2004 and since then has been conducting observations with the athena science payload the rover has traversed more than 5 km carrying out the first outcrop scale investigation of sedimentary rocks on mars the rocks of meridiani planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine grained siliciclastics and sulfates the siliciclastic fraction was produced by chemical alteration of a precursor basalt the sulfates are dominantly mg sulfates and also include ca sulfates and jarosite the stratigraphic section observed to date is dominated by eolian bedforms with subaqueous current ripples exposed near the top of the section after deposition interaction with groundwater produced a range of diagenetic features notably the hematite rich concretions known as blueberries the bedrock at meridiani is highly friable and has undergone substantial erosion by wind transported basaltic sand this sand along with concretions and concretion fragments eroded from the rock makes up a soil cover that thinly and discontinuously buries the bedrock the soil surface exhibits both ancient and active wind ripples that record past and present wind directions loose rocks on the soil surface are rare and include both impact ejecta and meteorites while opportunity s results show that liquid water was once present at meridiani planum below and occasionally at the surface the environmental conditions recorded were dominantly arid acidic and oxidizing and would have posed some significant challenges to the origin of life copyright 2006 by the american geophysical union

spectral variability among rocks in visible and near infrared multispectral pancam data collected at gusev crater examinations using spectral mixture analysis and related techniques 1 visible and near infrared vnir multispectral observations of rocks made by the mars exploration rover spirit s panoramic camera pancam have been analyzed using a spectral mixture analysis sma methodology scenes have been examined from the gusev crater plains into the columbia hills most scenes on the plains and in the columbia hills could be modeled as three end member mixtures of a bright material rock and shade scenes of rocks disturbed by the rover s rock abrasion tool rat required additional end members in the columbia hills there were a number of scenes in which additional rock end members were required the sma methodology identified relatively dust free areas on undisturbed rock surfaces as well as spectrally unique areas on rat abraded rocks spectral parameters from these areas were examined and six spectral classes were identified these classes are named after a type rock or area and are adirondack lower west spur clovis wishstone peace and watchtower these classes are discriminable based primarily on near infrared nir spectral parameters clovis and watchtower class rocks appear more oxidized than wishstone class rocks and adirondack basalts based on their having higher 535 nm band depths comparison of the spectral parameters of these gusev crater rocks to parameters of glass dominated basaltic tuffs indicates correspondence between measurements of clovis and watchtower classes but divergence for the wishstone class rocks which appear to have a higher fraction of crystalline ferrous iron bearing phases despite a high sulfur content the rock peace has nir properties resembling plains basalts

surface geology from viking landers on mars a second look aside from reddish dust products of martian weathering are not abundantly obvious on viking lander images surface stones appear sound spalls and disintegration fragments are largely lacking pitting of stones is probably not due to differential weathering and reddish stone colors more likely result from adhered dust than from patination judging from wind scoured drifts deflated ground rippled bed forms lee side tails basal scours fretted rocks and ubiquitous dust wind is currently the most effective transportive and erosive agent the dogma that martian eolian material is almost exclusively of 10 100 size is challenged by granule ripples and the possibility that wind drifted deposits consist largely of sand sized particles fretting is more common than faceting on martian ventifacts crusts on martian surface fines are more akin to case hardened rinds than to true duricrust crusting a possibly continuing process may be the product of atmospheric breathing of the regolith pits on surfaces of many martian stones are probably vesicles modified by eolian erosion pits on nonvesicular rocks may be solely the product of wind blasting vesicular lava dense lava and breccias are the most likely rocks among surface stones around the landers the bedrock outcrops near vl 1 may be large boulders embedded in a breccia substrate pyroclastics seem a likely constituent of surface deposits