limnologic analysis of gusev crater paleolake mars abstract the survey of the hydrogeologic system formed by gusev crater and ma adim vallis aeolis subquadrangle of mars points out evidence for the existence of an ice covered lake in gusev crater a first lake was formed by the drainage of the aquifer in the region surrounding gusev before the entry of ma adim vallis in the crater the existence of a former lake in gusev is deduced from the morphology of the ma adim delta its comparison with terrestrial antarctic analogs argues for the presence of an ice covered lake in gusev at the time that the southern part of the crater s rampart was breached by ma adim first release and for a subice lacustrine construction of the valley s delta our survey shows that ma adim vallis may have entered gusev crater as late as late hesperian early amazonian as part of a second lake episode the relationship between the variation of the gusev lake water level the volume of the lake and the surface of the lake bed is established by our bathymetric model the elevation of the former lake is deduced from the elevation of the mesa like structures in the delta of ma adim vallis furthermore the correlation of the crater frequency of gusev rampart with mars stratigraphic age shows that lakes may have occupied gusev crater over a period of time covering 2 gyrs from the formation of the crater to the last episode of water release from ma adim vallis though it is most likely that the lake was episodical the recurrence of abundant water in gusev crater makes this site a high priority for missions either for martian resource exploration or for the search of life

diatom response to the holocene climatic optimum on the north icelandic shelf abstract a diatom record from core md992275 on the north icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal year bp the study period includes the holocene climate optimum hco as widely known in the north atlantic region a comparison with data for the last 2000 years and with the present day surface sediment diatom assemblages shows that there was considerably stronger influence of atlantic water masses in the area during the hco than in the late holocene and today the results of cluster analysis and principal component analysis divide the studied period into three intervals each characterised by a specific diatom assemblage the assemblages indicate changes in the interaction of the relatively warm irminger current ic and the cold east greenland current egc and east icelandic current eic the north icelandic shelf was strongly affected by the ic during the interval 8000 6800 cal year bp which may be the warmest period of the holocene during the intervals 9000 8000 and 6800 5600 cal year bp the influence of the ic was relatively weak and that of the egc and eic increased correspondingly the well known 8200 cal year bp cooling event shown in many records from the north atlantic is reflected by a relatively strong influence of the egc and eic between about 8300 and 8100 cal year bp in our record however the diatom assemblages show that the inferred circulation change did not bring the strength of the ic down to the levels seen at present and during the last two millennia

hydrothermally altered impact melt rock and breccia contributions to the soil of mars samples of melt rock and breccia from 12 terrestrial impact craters were examined to identify alteration minerals and their conditions of formation the dominant assemblage in most cases is clay silica k feldspar zeolite indicating hydrothermal alteration at low pressures and temperatures of 100 300 c the clays are predominantly fe chlorites and smectites in most cases depleted in al and enriched in fe and mg relative to their source rocks alteration of impact glass is often complete while alteration of crystalling melt rock is limited to a few percent of the rock volume impact breccia is altered to only a small extent compared to the alteration of glass impact induced hydrothermal alteration is to be expected at martian impact sites if significant quantities of ground ice and or water are present the alteration products are likely to resemble the clays found at terrestrial craters al fe fractionation similar to that observed on earth is strongly suggested by the viking soil analyses the quantitative contribution of hydrothermal clays to the soil of mars is estimated based on a model which predicts the generation of the equivalent of a 61 m thick blanket of impact melt planet wide the inefficiency of melt production in small craters and the inefficiency of alteration in large craters limit the expected production of clay to a few percent of this figure clays produced by impact induced hydrothermal alteration may be expected to contribute to the fines on mars but this contribution is probably not dominant relative to other suggested sources

wind related features in gusev crater mars 1 gusev crater has a complex history beginning with its formation by an impact in the noachian period and subsequent evolution including erosion and deposition associated with ma adim vallis which cut through gusev crater from the south various wind related features are found on the crater floor including albedo patterns bedforms such as barchan dunes and elongated hills possibly reflecting erosion by the wind comparisons of the orientations of these features with predictions from global and atmospheric models show wind patterns as functions of season and time of day strongest global winds occur out of the southeast in the late fall and early winter and appear to be responsible for the formation of a large dark streak that drapes 100 km across the crater floor on an intermediate scale bright wind streaks correlate with nighttime winds that flow into the crater from the rim and outlying high areas these streaks are interpreted to be deposits of dust settled from the atmosphere during times of positive atmospheric static stability smaller features include various dark streaks and duneforms the orientations of which are inferred to represent local zones of high wind shear surface stress these features also tend to correlate with strong afternoon upslope winds caused by the uneven heating of the atmosphere across the crater thus the large dark streak reflects global scale wind patterns the smaller dark features and duneforms represent flow of strong winds out of the crater in the afternoon and the small bright streaks represent deposition of dust associated with nighttime flow of wind into the crater the correlation between the wind regime predicted by the models and the orientations of the aeolian features gives confidence that the models are essentially correct because gusev is a prime candidate landing site for landers including the mars exploration rovers understanding the interplay of the atmosphere and the surface including the erosion and deposition of windblown particles is important in assessments of the science potential for these missions despite the abundance of wind related features on the floor of gusev only about 1 2 of the proposed landing ellipse area is covered with organized bedforms e g dunes although mantles of sand and dust are also likely to be present on the basis of an analysis of random landing points within the ellipse traverse distances to ridges ejecta from small craters and other potential sources of rocks are within 150 m traverse distance for 95 of the touchdown points

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

a high resolution opal and radiolarian record from the subpolar north atlantic during the mid pleistocene transition 1069 779ka palaeoceanographic implications abstract a high resolution record of radiolarian assemblages from site u1314 was studied to reconstruct hydrographic and climatic changes in the north atlantic ocean during the mid pleistocene transition period 1069 779 ka besides the faunal record absolute accumulation of radiolarians and total biogenic opal are used to determine changes in surface water productivity results show that the north atlantic arctic front shifted back and forth repeatedly at a glacial interglacial timescale bringing the site under the influence of both cold arctic glacial and much warmer atlantic interglacial waters during glacial intervals and ice rafted debris ird events the deep dwelling taxon cycladophora davisiana was the greatest contributor of the radiolarian assemblage suggesting cold surface conditions melt water discharge and changes in deep and intermediate circulation interglacial intervals were characterized by abundant shallow dwelling taxa like pseudodyctiophimus gracilipes and lithomelissa setosa increased opal accumulation and higher radiolarian diversities indicating a northward flow of warm atlantic surface waters to the site u1314 area a marked change in the structure of the radiolarian assemblage occurred after mis 22 860 ka with large taxa differences between warm and cold periods probably in response to changing ocean conditions due to the higher amplitude of glacial interglacial changes as the dominant periodicity of high latitude climate oscillations shifted from 41 kyr to 100 kyr thus we conclude that the radiolarian assemblage from the north atlantic have changed drastically along with variations in ocean circulation in response to orbital and millennial scale climatic variations that occurred in the early and mid pleistocene

the micromorphology of gypsum and halite in reg soils the negev desert israel gypsum and halite are the most common salts in reg soils developed on alluvial parent material under extremely arid conditions in the negev desert israel the aim of this paper is to document the changes in the micromorphology of these salts at different stages of reg soil development on two alluvial fan chronosequences the micromorphological analyses included thin section observations and scanning electron microscope and electron microprobe analyses in this arid soil environment gypsum and halite possess a variety of crystal forms which may change with depth in a single profile and or between profiles of different ages the variety of crystal forms results from changes in the microenvironmental conditions that occur in desert reg soils over time poikilitic lenticular gypsum is found in all reg soils and is distributed throughout the profiles the conditions needed for such crystals to form are high ionic impurities and deposition in a void system where space is not limiting microcrystalline alabastrine gypsum is only found in mature reg soils and is crystallized when the profile has high amounts of fine material and a well developed desert pavement in a well developed reg soil profile indicators such as a well developed desert pavement and high amounts of fine earth limit the leaching depth and cause gypsum deposition from supersaturated soil solutions under high evaporation rates close to the surface prismatic and fibrous gypsum are less common low amounts of prismatic gypsum are found in young and mature soils while fibrous gypsum is found only in mature soils in re cemented shattered gravel the halite crystal form is mainly cubic with low amounts of host material incorporated into the crystal it occurs predominantly in mature reg soil profiles through the crystallization from supersaturated soil solutions at the depth of maximum water penetration although the alabastrine prismatic and fibrous gypsum and cubic halite are deposited in a displacive manner no correlation was found between their occurrence and the distribution of shattered gravel in the soil profile

a model for formation of dust soil and rock coatings on mars physical and chemical processes on the martian surface 1 a model is presented here to explain the generation of surface material on mars using chemical magnetic and spectroscopic data from mars and geologic analogs from terrestrial sites one basic premise is that the dust soil units are not derived exclusively from local rocks but are rather a product of global and possibly remote weathering processes another assumption in this model is that there are both physical and chemical interactions of the atmosphere with dust particles and that these two processes create distinctly different products physical processes distribute dust particles on rocks and drift units forming physically aggregated layers these are reversible processes chemical reactions of the dust soil particles create alteration rinds on rock surfaces and cohesive crusted surface units between rocks both of which are relatively permanent materials according to this model the dominant components of the dust soil particles are derived from alteration of volcanic ash and tephra and contain primarily nanophase and poorly crystalline ferric oxide oxyhydroxide phases as well as silicates these phases are the alteration products that formed in a low moisture environment these dust soil particles also contain a smaller amount of material that was exposed to more water and contains crystalline ferric oxides oxyhydroxides sulfates and clay silicates these components could have formed through hydrothermal alteration at steam vents or fumeroles thermal fluids or through evaporite deposits wet dry cycling experiments are presented here on mars soil analogue mixtures containing poorly crystalline and crystalline components dominated by nanophase to 2 m diameter particles cemented products of these soil mixtures are formed in these experiments and variation in the surface texture was observed for samples containing smectites nonhydrated silicates or sulfates reflectance spectra were measured of the initial particulate mixtures the cemented products and ground versions of the cemented material the spectral contrast in the visible near infrared and midinfrared regions is significantly reduced for the cemented material compared to the initial soil and somewhat reduced for the ground cemented soil compared to the initial soil the results of this study suggest that transient fluvial activity on mars will have a profound effect on the texture and spectral properties of the dust soil particles on the surface the model developed in this study provides an explanation for the generation of cemented or crusted soil units and rock coatings on mars and may explain albedo variations on the surface observed near large rocks or crater rims

late holocene summer sea surface temperatures based on a diatom record from the north icelandic shelf diatom assemblages from a high resolution core on the north icelandic shelf reveal a general late holocene cooling trend which is interrupted by three relatively warm periods diatom data from sur

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

thermophiles early biosphere evolution and the origin of life on earth implications for the exobiological exploration of mars mars holds great interest for exobiology and presently stands center stage in our plans to explore the inner solar system for signs of past or present life with the spectacular success of the pathfinder mission golombek 1997 and upcoming mapping efforts by the mars global surveyor orbiter albee et al 1998 it is an especially appropriate time to revisit some important issues in mars exobiology the papers making up this journal of geophysical research planets special issue on mars were the outgrowth of an american geophysical union special session entitled exploring for a martian biosphere which was presented at the fall meeting in san francisco in 1995 farmer 1995a together these papers provide a context for evaluating some fundamental issues in the exobiological exploration of mars topics covered fall into the following broad categories 1 environments and conditions required for the origin of life hydrothermal environments as sites for prebiotic chemical synthesis shock and schulte this issue 2 early martian environments as a context for the evolution and diversification of life on mars early impact hazards sleep and zahnle this issue early volatile and climate history of mars haberle this issue and ice covered lakes as habitats for early life doran et al this issue 3 exploring for extant martian life results of the viking missions klein this issue environmental extremes for martian life clark this issue and planetary protection and mars sample return devincenzi et al this issue and 4 exploration strategies phosphate minerals as targets for chemofossils mojzsis and arrhenius this issue and the role of robotic surface missions stoker this issue

mixed hydrothermal fluids and the origin of the martian soil the martian soil consists mainly of weathered basaltic rock and a salt component enriched in volatile and mobile elements primarily sulfur chlorine sodium and potassium since the discovery of this mobile element component by the viking x ray fluorescence spectrometer volcanic aerosols have been considered a likely source for these enrichments alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism we show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil this model is constructed using terrestrial analogs constrained by the viking and pathfinder measurements of the martian soil chemistry the potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant the two end member types of hydrothermal fluids considered in the model are the neutral chloride and the acid sulfate type the neutral chloride fluids have high cl and na contents and a significant amount of k but their s abundance relative to cl s cl ratio is too low to match the martian soil however acid sulfate hydrothermal systems characterized by substantial vapor transport and high s cl ratios are likely on mars due to the low abundance of water indeed as the availability of water declines in a hydrothermal system the neutral chloride system can evolve to a vapor dominated acid sulfate system a combination of the two types of fluids can quantitatively explain the s and cl abundance in the soil and provide reasonable abundances of other mobile elements including na k and br without predicting an excess of any element measured in the soil however the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the fe contents of the fluids are too low although the acid sulfate fluids have fe concentrations a factor of 100 larger than the neutral chloride fluids the acid sulfate fluids would contribute less than 1 of the total fe in the soil the volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable therefore while volcanic aerosols can explain the mobile element component of the soil significant contributions from other sources cannot be excluded determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the martian soil of trace elements that provide signatures of the hydrothermal fluids such as high lithium contents that are associated with neutral chloride fluids

thermal inertia of crater related wind streaks on mars data from the thermal emission spectrometer tes on board the mars global surveyor spacecraft are used to analyze the structure of and materials comprising crater related wind streaks comparisons of high resolution tes albedo and tes based thermal inertia values within and adjacent to the streaks allow us to constrain the properties of the streaks and gain insight into their physical structure the majority of the analyzed type i bright depositional streaks are distinct from the surrounding terrain in albedo but not in thermal inertia we conclude that these streaks consist of thin deposits of bright material greater than 1 pm thick but less than 1 3 mm thick the majority of the analyzed type i dark erosional streaks identified from viking images are now indistinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks have been covered by a thin deposit of bright material greater than 1 m thick but less than 1 3 mm thick all of the analyzed type ii dark depositional streaks are distinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks consist of deposits greater than a few centimeters thick in this case we were also able to use the thermal inertia values to estimate the particle sizes of the deposited material the values correspond to a broad range of sand sized particles easily mobilized by wind supporting the deflation deposition theory of type ii streak formation

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

duration of the ma adim vallis gusev crater hydrogeologic system mars abstract ma adim vallis and gusev crater aeolis subquadrangle of mars formed a complex hydrogeologic system through time crater statistics over five geologic units coupled with morphologic and geologic observations show that this system was active over a period ranging from 0 7 to about 2 billion years these results make the floor of gusev crater one of the most prominent martian depositional features the last aqueous sedimentary deposition could have occurred during early amazonian

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

alteration of basaltic glasses from north central british columbia canada abstract evidence of palagonitization glass replacement by poorly crystallized clay like material is seen on all glasses studied from three pleistocene subglacial volcanoes in north central british columbia canada samples from foreset breccias of tuya butte are more highly palagonitized than those from the tephra cones of ash mountain and southern tuya extensive palagonitization is generally associated with authigenic mineralization clays zeolites palagonite composition varies widely relative to glass composition and palagonite can be broadly categorized as either high al or low al depending on whether al was retained or lost to aqueous solutions during palagonitization the lowest al palagonites are those from the foreset breccias of tuya butte loss of al during palagonitization is related to closed system alteration including precipitation of aluminosilicate authigenic cements low initial ph is suggested for al depletion consistent with the behavior of ni co and cr which are retained in high al and depleted in low al palagonite microenvironment appears to be more influential than macroenvironment in determining the composition of palagonite palagonite rinds are compositionally zoned generally becoming progressively higher in al and ca and lower in fe and mg towards the innermost later formed portions of the rinds this apparently reflects changing solution composition increasing ph with time compositional zoning does not change the overall stoichiometry of palagonite which resembles smectite clay mineral paragenesis is related to the ca content of the palagonite with partial replacement of palagonite by smectite fe saponite occurring when ca is retained in the rind this replacement phenomenon occurs prior to zeolitization no such replacement clay occurs with low ca palagonite but a late stage nontronite film overgrows zeolite phillipsite is the first zeolite formed followed by chabazite analcime and calcite occur in the most highly palagonitized samples mass balance considerations indicate higher mass loss where palagonitization has not proceeded to the point where zeolite solubility limits were attained in the local solution zeolites occur in closed system conditions low flow rates where little net system mass loss or gain has occurred the colloidal nature of palagonite allows the effective adsorption of rb cs sr ba and rees

a search for nitrates in martian meteorites martian atmospheric nitrogen is highly enriched in n 15 nitrates formed by interaction of the atmosphere with the martian regolith should therefore also be characterized by an elevated delta 15 n value a search has been made for nitrates in two martian meteorites in order to determine the extent of possible regolith atmosphere interaction shock produced glass from the elephant moraine eet a79001 shergottite e1 149 and a water soluble extract from nakhla were analyzed by fourier transform infrared ftir spectroscopy and stepped combustion stable isotope mass spectrometry ftir of both meteorites had features at 1375 cm 1 and 1630 cm 1 consistent with nitrates on account of their low thermal stability nitrates break down at temperatures below 600 degrees c in this temperature range e1 149 yielded similar to 1250 ppb nitrogen with delta 15 n 8 5 parts per thousand if this nitrogen is from a nitrate then it cannot be distinguished from terrestrial salts by its isotopic composition the water soluble extract from nakhla also released nitrogen at low temperatures approximately 17 ppb with delta 15 n approximately 11 4 parts per thousand since nakhla is an observed fall this is unlikely to be a terrestrial weathering product nitrates apparently occur in e1 149 and nakhla but in very low abundance and their origin is unclear the isotopic composition of the salts which is within the range of that proposed for martian magmatic volatiles is far removed from that of nitrogen in the present day martian atmosphere if the nitrates are martian in origin they did not form in recent times from reactions involving atmospheric gases rather the nitrates could be the result of an earlier episode of atmospheric interaction with the regolith or with implantation of magmatic volatiles introduced during degassing

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

late holocene glacial advance and ice shelf growth in barilari bay graham land west antarctic peninsula three marine sediment cores were collected along the length of the fjord axis of barilari bay graham land west antarctic peninsula 65 55 s 64 43 w multi proxy analytical results constrained by high resolution geochronological methods 210 pb radiocarbon 137 cs in concert with historical observations capture a record of holocene paleoenvironmental variability our results suggest early and middle holocene 7022 2815 cal calibrated yr b p retreated glacial positions and seasonally open marine conditions with increased primary productivity climatic cooling increased sea ice coverage and decreased primary productivity during the neoglacial 2815 to cal 730 cal yr b p this climatic cooling culminated with glacial advance to maximum holocene positions and expansion of a fjord wide ice shelf during the little ice age lia ca 730 82 cal yr b p seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming 82 cal yr b p to present our findings agree with previously observed late holocene cooling and glacial advance across the antarctic peninsula suggesting that the lia was a regionally significant event with few disparities in timing and magnitude comparison of the lia antarctic peninsula record to the rest of the southern hemisphere demonstrates close synchronicity in the southeast pacific and southern most atlantic region but less coherence for the southwest pacific and indian oceans comparisons with the northern hemisphere demonstrate that the lia antarctic peninsula record was contemporaneous with pre lia cooling and sea ice expansion in the north atlantic arctic suggesting a global reach for these events

ma adim vallis evolution geometry and models of discharge rate abstract episodes of confined flows in ma adim vallis are reconstructed by surveying the terraces in the valley three major levels and their associated tributary systems are identified and mapped this study points out the evidence of the cessation of the valley activity between the formation of levels 1 and 2 characterized by degraded and large perched valleys which floor are not adjusted to the following flow episode level a strong asymmetry in the tributary distribution points toward a groundwater supplied water origin of the valley potential source areas are demonstrated to be in volcano tectonic regions implying a hydrothermal origin of the water that may include melted permafrost calculation of hydraulic radii valley sections and models of discharge rates associated with the morphologic and geologic survey shows that ma adim vallis was an episodic channel the lifetime of which spanned between the noachian and amazonian

the imager for mars pathfinder experiment the imager for mars pathfinder imp a stereoscopic multispectral camera is described in terms of its capabilities for studying the martian environment the camera s two eyes separated by 15 0 cm provide the camera with range finding ability each eye illuminates half of a single ccd detector with a field of view of 14 4 14 0 and has 12 selectable filters the 18 optics have a large depth of field and no focussing mechanism is required a mechanical shutter is avoided by using the frame transfer capability of the 512 512 ccd the resolving power of the camera 0 98 mrad pixel is approximately the same as the viking lander cameras however the signal to noise ratio for imp greatly exceeds viking approaching 350 this feature along with the stable calibration of the filters between 440 and 1000 nm distinguishes imp from viking specially designed targets are positioned on the lander they provide information on the magnetic properties of wind blown dust measure the wind vectors and provide radiometric standard reflectors for calibration also eight low transmission filters are included for imaging the sun directly at multiple wavelengths giving imp the ability to measure dust opacity and potentially the water vapor content several experiments beyond the requisite color panorama are described in detail contour mapping of the local terrain multispectral imaging of the surrounding rock and soil to study local mineralogy viewing of three wind socks measuring atmospheric opacity and water vapor content and estimating the magnetic properties of wind blown dust this paper is intended to serve as a guide to understanding the scientific integrity of the imp data that will be returned from mars starting on july 4 1997

chronology eruption duration and atmospheric contribution of the martian volcano apollinaris patera geologic mapping thermal inertia measurements and an analysis of the color visual wavelengths of the martian volcano apollinaris patera indicate the existence of two different surface materials comprising an early easily eroded edifice and a more recent competent fan on the southern flank a chronology of six major events that is consistent with the present morphology of the volcano has been identified we propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on earth a basal escarpment typically 500 m in relief and morphologically similar to the one surrounding olympus mons was produced between the formation of the main edifice and the fan indicating multistage eruptions over a protracted period of time contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed apollinaris patera stereophotogrammetric measurements permit the volume of the volcano to be estimated at 105 km3 from this volume measurement and an inferred eruption rate 1 5 10 2 km3 yr 1 we estimate the total eruption duration for the main edifice to be 107 yrs plausible estimates of the exsolved volatile content of the parent magma imply that greater than 1015 kg of water vapor was released into the atmosphere as a consequence of this activity this large amount of water vapor as well as other exsolved gases must have had a significant impact on local and possibly global climatic conditions

clay mineral assemblages in weathered basalt profiles from central and southern portugal climatic significance abstract mineralogical and chemical changes during weathering of basalts from central and southern portugal were studied both regions have a temperate mediterranean type climate the algarve being more arid the areas concerned are the lisbon 72 ma and the runa volcanic complexes 100 70 ma and rio maior 160 130 ma in central portugal and budens 170 180 ma in the south the basalts are generally rich in olivine phenocrysts clay minerals are in general well crystallised and comprise smectites associated with 1 1 minerals principally halloysite illite and palygorskite kaolin minerals prevail in topographic highs whilst smectites predominate in lower areas smectites were analysed from the

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

soil like deposits observed by sojourner the pathfinder rover most of the soil like materials at the pathfinder landing site behave like moderately dense soils on earth with friction angles near 34 39 and are called cloddy deposits cloddy deposits appear to be poorly sorted with dust sized to granule sized mineral or rock grains they may contain pebbles small rock fragments and clods thin deposits of porous compressible drifts with friction angles near 26 28 are also present drifts are fine grained cohesions of both types of deposits are small there may be indurated soil like deposits and or coated or crusted rocks cloddy deposits may be fluvial sediments of the ares tiu floods but other origins such as ejecta from nearby impact craters should be considered drifts are probably dusts that settled from the martian atmosphere remote sensing signatures of the deposits inferred from rover observations are consistent with those observed from orbit and earth

mediterranean coccolith ecobiostratigraphy since the penultimate glacial the last 145 000 years and ecobioevent traceability abstract the mediterranean sea is a miniature ocean ideal to test the response of marine ecosystems to amplified orbital and suborbital climate changes here we present coccolith data from a sardinia channel gravity core arcose c 33 analysed over the last 145 000 years with a mean resolution of about 900 years the study highlights that regional phytoplankton assemblages underwent significant modifications between the penultimate glacial and the last interglacial as well as between the last glacial and the holocene the n ratio palaeoproductivity index suggests reduced productivity levels and the development of a deep nutricline during the last interglacial and the holocene within the last glacial period many taxa exhibit abundance fluctuations that parallel oscillations in 18 o values of globigerina bulloides tests heinrich events and stadials seem to be associated with drops in primary productivity levels as already observed in the alboran sea and the sicily channel a total of 19 ecobioevents were identified in the sardinia channel sediments including abundance fluctuations of emiliania huxleyi 4 m florisphaera profunda and gephyrocapsa oceanica the comparison of events across the mediterranean sea suggests that traceability applies to the sicily channel balearic and tyrrhenian seas supporting the adoption of a common ecobiostratigraphic scheme less certain is the correlation with the alboran sea although peaks of helicosphaera carteri and syracosphaera histrica during heinrich events and stadials suggest similar nutrient dynamics in response to suborbital climatic variations in the sicily channel southern tyrrhenian and alboran seas the traceability of events within eastern mediterranean cores is strongly limited possibly due to different physico chemical properties and nutrient dynamics

the circum chryse region as a possible example of a hydrologic cycle on mars geologic observations and theoretical evaluation the transection and superposition relationships among channels chaos surface materials units and other features in the circum chryse region of mars were used to evaluate relative age relationships and evolution of flood events channels and chaos in contact with one another were treated as single discrete flood carved systems some outflow channel systems form networks and are inferred to have been created by multiple flood events within some outflow channel networks several separate individual channel systems can be traced to a specific chaos which acted as flood source area to that specific flood channel individual flood carved systems were related to widespread materials units or other surface features that served as stratigraphic horizons chryse outflow channels are inferred to have formed over most of the perceivable history of mars outflow channels are inferred to become younger with increasing proximity to the chryse basin in addition outflow channels closer to the basin show a greater diversity in age the relationship of subsequent outflow channel sources to the sources of earlier floods is inferred to disfavor episodic flooding due to the progressive tapping of a juvenile near surface water supply instead we propose the circum chryse region as a candidate site of past hydrological recycling the discharge rates necessary to carve the circum chryse outflow channels would have inevitably formed temporary standing bodies of h2o on the martian surface where the flood waters stagnated and pooled the chryse basin is topographically enclosed these observations and inferences have led us to formulate and evaluate two hypotheses 1 large amounts of the sublimated h2o off the chryse basin flood lakes precipitated snowed onto the flood source highlands and this h2o was incorporated into the near surface recharging the h2o sources making possible subsequent deluges and 2 ponded flood water in chryse basin drained back down an anti basinward dipping subsurface layer accessed long the southern edge of the lake recharging the flood source aquifers h2o not redeposited in the flood source region was largely lost to the hydrologic cycle this loss progressively lowered the vitality of the cycle probably by now killing it our numerical evaluations indicate that of the two hypotheses we formulated the groundwater seep cycle seems by far the more viable optimally approximately 3 4 of the original mass of an ice covered cylindrical lake albedo 0 5 1 km deep 100 km radius draining along its rim for one quarter of its circumference into substrata with a permeability of 3000 darcies can be modeled to have moved underground on timescales of the order of 10 3 years before the competing mechanisms of sublimation and freeze down choked off further water removal once underground this water can travel distances equal to the separation between chryse basin and flood source sites in geologically short approximately 10 6 year scale times conversely we calculate that optimally only approximately 40 of the h2o carried from chryse can condense at the highlands and most of the precipitate would either collect at the base of the highlands lowlands scarp or sublimate at rates greater than it would accumulate over the flood source sites further observations from forthcoming missions may permit the determination of which mechanisms may have operated to recycle the chryse flood waters

reliability of a fjord glacier s fluctuations for paleoclimatic reconstructions abstract historical observations of fjord glaciers in southern alaska suggest that their fluctuations may be asynchronous with one another and with climate possible causes for anomalous fjord glacier response to climatic changes involve the instabilities inherent in a calving terminus the interaction of fjord geometry with the extent of the calving terminus and the intersection of low lying snow line by a thickening glacier the lituya glacier system in southeast alaska is analyzed with reference to these phenomena to test the reliability of its holocene glacial deposits as paleoclimatic records this fjord glacier is shown to have been probably free of major nonclimatic responses during the holocene except for an insensitive period of up to 1000 yr that followed calving retreats the insensitive period has no functional effect on how the relatively coarse geologic record is interpreted in terms of paleoclimate however it makes impossible any inference of climatic trends from this glacier s behavior in historical times fjord glacier deposits can be dependable records of paleoclimate but each glacier requires careful scrutiny anomalous glacier responses to climate are most likely to occur in fjords of complex geometry in regions of relatively low snow line and where glaciers terminate at fjord mouths bordering the open sea

millennial scale variability in western subtropical north atlantic surface and deep water circulation during marine isotope stages 11 and 12 1 marine isotope stages miss 11 and 12 460 380 ka contain what may be the most extreme climate conditions of the last 500 000 years and occurred at a time when earth received a similar amount of solar insolation as the most recent glacial interglacial cycle two high deposition rate sediment cores ocean drilling program sites 1059 31 6 n 75 4 w 2985 m and 1055 32 6 n 76 2 w 1799 m from the western north atlantic were studied in order to examine the nature of millennial scale variability in north atlantic surface and thermohaline circulation during this time interval detailed records of 18o and 13c in the benthic foraminifera species cibicidoides wuellerstorfi and the planktonic species globigerinoides ruber white as well as detailed records of carbonate content were generated for both sites these records suggest rapid variability in the strength of north atlantic deep water production throughout miss 11 and 12 most of the observed changes in deep water circulation appear to be associated with or coupled to changes in sea surface hydrography the duration of interglacial conditions during mis 11 20 000 30 000 years is much longer than subsequent interglacial stages combined 18o measurements and mg ca based temperature estimates from g ruber suggest sea surface temperatures increased 2 3 c across the mis 12 mis 11 transition

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

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

millennial climate oscillations over the course of the ice ages the climate oscillated with a period of about 20 000 to 100 000 years superimposed on these variations were millennial oscillations of 1000 to 2000 years these oscillations also occurred in the holocene which began 11 000 years ago and has been thought to be a time of a relatively stable climate as shown on p 1257 of this issue by bond et al the perspective by oppo discusses these results obtained from marine sediments and the possible mechanisms underlying these relatively rapid changes in climate

sea surface temperature variability and deep water reorganisation in the subtropical north atlantic during isotope stage 2 4 abstract two sediment cores from a high accumulation sediment drift at 3000 m water depth in the western north atlantic are investigated in order to examine possible linkages between subtropical surface and bottom water properties and global climate oscillations during the last glacial interglacial cycle planktonic foraminiferal assemblages and the 18 o of globigerinoides ruber both document large sea surface temperature oscillations 3 4 c that appear to co vary with greenland ice core records short episodes of sea surface cooling as far south as the blake outer ridge at 33 n are inferred from increased abundance of the polar species neogloboquadrina pachyderma sinistral during the ice core stadials events nutrient proxy records suggest that the deep waters flooding the site alternated between a northern north atlantic deep water and a southern southern ocean water source in most cases warm surface water conditions interstadials were accompanied by a strong north atlantic deep water component in the bottom water circulation however the transitions into interstadial 14 and 12 seem to be marked by a 1500 yr lag between surface water warming and the deep water circulation shift as recorded by caco 3 and 13 c of benthonic foraminifera

geology and geochemistry of paleosols developed on the hekpoort basalt pretoria group south africa the hekpoort paleosols comprise a regional paleoweathering horizon developed on 2 224 0 021 ga basaltic andesite lavas at the top of the hekpoort formation of the pretoria group transvaal supergroup south africa in five separate profiles from outcrops along road cuts near waterval onder and the daspoort tunnel and in three drill cores from the bank break area bb3 bb8 and bb14 the top of the paleosol is a sericite rich zone the sericite zone grades downward into a chlorite rich zone in core bb8 and in the road cut at the daspoort tunnel we sampled the underlying or parent basaltic andesite into which the chlorite zone grades we did not obtain samples of the parent material at waterval onder and in cores bb3 and bb14 but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core bb8 and at the daspoort tunnel the presence of apparent rip up clasts of the paleosol in the overlying ironstones of the strubenkop formation in the cores from bank break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at waterval onder point to a subaerial weathering origin very little if any al ti zr v or cr moved a discernible distance during weathering of any of the five profiles the vertical distribution of fe mg mn ni and co indicates that these elements were largely removed from the top of the soil during weathering the overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an fe 2 rich smectite the loss of fe from the top of the soil during weathering of the hekpoort paleosols indicates that atmospheric p o 2 was less than 8 x 10 4 atm about 2 22 ga fe 2 rich smectite should only precipitate during soil formation if atmospheric p co 2 is less than or equal to 2 x 10 2 atm rye kuo and holland 1995 ca and na were largely lost during weathering some na was apparently added to the sericite zone in cores bb3 bb8 and bb14 after weathering all five profiles are enriched in k and rb and most are enriched in ba the distribution of these elements indicates that they all were added during post weathering hydrothermal metasomatism rb sr analysis of the paleosol at the daspoort tunnel indicates that metasomatism last affected that profile 1 925 0 032 ga macfarlane and holland 1991

acidic volatiles and the mars soil large portions of mars surface are covered with deposits of fine homogeneous weathered dusty soil material nanophase iron oxides silicate mineraloids and salts prevail in the soil the mode of formation of this somewhat peculiar type of soil is still far from being clear one scenario suggests that weathering took place during early epochs when mars may have been warm and wet the properties of the soil are not easily reconciled with this scenario we propose another possible scenario that attributes in part the peculiar nature of the martian dust and soil to a relatively young weathering product formed during the last few hundreds of millions of years in a process that involves acidic volatiles we tested this hypothesis in an experimental study of the first step of acidolytic weathering of a partly palagonitized volcanic tephra of hawaiitic lava origin using sulfuric hydrochloric and nitric acids and their mixtures the tephra effectively neutralize the added acidity the protonic acidity added to the tephra attacks the primary minerals releasing fe al and mg which control the ph acting as lewis acid species of varying acid strengths the full amount of acidity added to the tephra is stored in it but only a very small fraction is preserved as the original protonic acidity the majority of the added sulfate and chloride were present as salts and easily solubilized minerals well crystallized sulfate salt minerals of aluminum and calcium were detected by powder x ray diffractometry whereas secondary magnesium and iron minerals were not detected due probably to lack of crystallinity the presence of gypsum caso4 2 h2o and alunogen al2 so4 3 17 h2o is probably responsible for the observed increased hygroscopicity of the acidified tephra and their tendency to form hardened crusts we suggest that if this mechanism is of importance on mars then the chemically weathered component of the martian soil consists of a salt rich mineral mixture containing the salts of the anionicligands so4 and cl resulting from volatiles emitted from volcanoes during more recent eruptions up to 109 years b p the lack of liquid water on mars surface during that time slowed or halted mineralogical evolution into highly crystallized minerals having large mineral grains the chemically weathered components are mixed with the products of physical weathering the recently formed soil may cover and coat more evolved hydrothermally modified mineral deposits formed in earlier epochs of mars

a 100 ka record of water tables and paleoclimates from salt cores death valley california abstract sedimentary and petrographic features of evaporites and associated sediments from a 185 m deep core taken in death valley ca together with uranium series dating have been used to reconstruct the history of water table fluctuations and climate changes in death valley for the past 100 ka death valley has been arid during the holocene 0 10 ka with predominantly mudflat and saline pan subenvironments a perennial lake up to 90 m deep existed in death valley from 10 to 35 ka saline pan and mudflat subenvironments dominated death valley from 35 to 100 ka the chronology of changing subenvironments and water table fluctuations in death valley generally correlates with other climate records in the western us owens lake and searles lake ca browns room cave calcite nv the marine oxygen isotope record and the vostok ice core record core intervals through saline pan sediments are composed of interbedded halite chaotic muddy halite and mud the halite contains abundant vertical dissolution pipes cemented with clear halite these sediments record repeated flooding by dilute waters dissolution of subaerially exposed surface salt crusts deposition of mud from suspension precipitation of halite during the saline lake phase and cementation by diagenetic halite mudflat sediments consist of clayey silt with sand patches and mud cracks which document long periods of desiccation and the formation of efflorescent salt crusts from the evaporation of groundwater brines saline pan and mudflat deposits formed during periods when death valley was relatively arid similar to the modern climate lacustrine deposits consist of mudhalite cycles accumulated during the early lake stage bedded thenardite na 2 so 4 and mud above and a cap of massive halite formed during the latest lake stage all of which record fluctuating salinities and lake levels in a perennial system such deposits document a relatively wet climate with a high ratio of water inflow to evaporation ostracodes in mud layers represent the least saline deepest lake phases halite layers are made of fine grained cumulates and clear vertically oriented crystals precipitated during shallower perennial lake stages of significance is the nearly complete absence of syndepositional dissolution of saline minerals in the lacustrine interval indicating that accumulated salts were permanently protected from dissolution by saline lake waters such evidence strongly suggests that lakes existed continually without desiccating for 25 ka between 10 and 35 ka b p

holocene glacial history of the lituya district southeast alaska radiocarbon dates from the lituya district of southeast alaska indicate the occurrence of at least four glacial periods during the past 10 000 years further detail is added to the record by a relative age chronology for moraines based on cross cutting relationships as well as soil vegetation and boulder weathering characteristics the most recent deglaciation occurred approximately 350 500 years bp ending advances begun shortly after 1500 years bp the relative age chronology for moraines indicates that at least three episodes of moraine building occurred during this period dates on logs in outwash and organic deposits in a moraine pond indicate glacial recession 1500 1900 years bp this recession was preceded by advances beginning sometime after 3600 years bp and including several periods of moraine construction radiocarbon dated basal organics in moraine ponds buried soils and overridden forest beds delimit a mid holocene advance ending before 5000 years bp and probably starting around 6000 yea

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

a chronostratigraphy of mid and late holocene slope evolution creagan a chaorainn northern highlands scotland unusual exposure of the drift stratigraphy of a typical vegetated hillslope in the northern highlands of scotland has allowed reconstruction of its holocene history graphic logging of palaeogully fill sediment analysis radiocarbon dating and microscopic investigation of horizon boundaries link periodic slope instability to changes in hydrology and vegetation cover the oldest preserved organic matter dates from about 7 5 cal ka bp several millennia of subsequent stability were followed at about 4 3 cal ka bp by destabilization whose magnitude and frequency markedly increased after about 2 7 cal ka bp precipitation driven weathering and erosion offer the best explanation for late holocene slope rejuvenation at this site with change effected through long lasting shifts in system equilibria as well as high magnitude inputs anthropogenic impacts on slope stability are apparently restricted to the last few hundred years the timing and episodicity of slope evolution suggests climate forcing resu

a volcanic interpretation of gusev crater surface materials from thermophysical spectral and morphological evidence 1 gusev crater the mars exploration rover spirit landing site 160 km diameter 14 5 s 184 5 w has been identified in previous studies as a prime site of geological and exobiological interest on the basis of its potential for having hosted a fluviolacustrine environment such environment may have been favorable for the development of biological activity the origin and nature of the materials present at the surface of gusev crater are still being debated in previous studies based on geomorphological and thermophysical data surface materials in the crater have been interpreted as originating from fluviolacustrine volcanic or aeolian processes or combinations thereof we present results from the analysis of newly compiled thermophysical thermal emission spectrometer tes and thermal emission imaging system themis spectroscopic tes and visible themis and mars observer camera data for the gusev region these data were analyzed using a new mosaicking technique developed to match the values of contiguous scenes and to produce seamless mosaics apt for geological interpretation thermophysical spectroscopic and morphological evidence point to the presence of local outcrops of lava flows of basaltic composition materials consistent with a regolith developed from basaltic materials fine grained deposits of basaltic composition strongly modified by wind erosion and wind deposits according to these findings we conclude that most of the materials occupying the present surface of gusev have characteristics consistent with those of volcanic and aeolian deposits fluviolacustrine deposits proposed by other authors may exist under the volcanic materials and may be exposed in impact craters

modelling teleconnections between the north atlantic and north pacific during the younger dryas evidence for a cooling event synchronous with the younger dryas 12 000 calendar years before present has been found in the north pacific ocean north of 30 n in records of surface1 5 and subsurface water properties6 7 these changes may be related to a temporary shut down of north atlantic deep water formation and associated surface cooling over the north atlantic it has remained unclear however whether this north atlantic cooling was communicated to the north pacific ocean through the atmosphere or the ocean here we report results of a sensitivity experiment with a coupled ocean atmosphere general circulation model that support a primarily atmospheric forcing of north pacific climate variations changes in wind strongly affect coastal upwelling at the north american west coast and surface cooling by the atmosphere causes better ventilation of the thermocline waters of the northeast pacific this effect is amplified by oceanic progagation to the pacific of the signal arising from collapse of north atlantic deep water formation these teleconnections may also explain earlier north pacific and western north american millenial scale cooling events of a similar nature8 12

geochemical and mineralogical analyses of palagonitic tuffs and altered rinds of pillow basalts in iceland and applications to mars samples of altered pillow lavas and hyalotuffs were collected from a volcanic tuya and hyaloclastite ridge in western iceland altered basaltic material from regions such as hloudufell tuya and thorolfsfell ridge may be similar to the surface fines on mars which are thought to contain altered basaltic components as well geochemical and mineralogical analyses have been performed on the icelandic samples in order to characterize the properties that distinguish palagonitization from other forms of low temperature alteration in this environment major elements were measured using an electron microprobe and mineralogy was determined through x ray diffraction and visible infrared reflectance spectroscopy the primary focus in this study was on the less than 2 microns size fractions of the hloudufell altered pillow and thorolfsfell palagonitic tuff samples the palagonitic tuff contained more crystalline clay minerals and has a higher al fe ratio the altered pillow lava contained higher abundances of nanophase iron oxides oxyhydroxides the extended visible region spectra of the less than 2 microns fractions of both icelandic samples are similar to bright martian soils measured by pathfinder

aeolian features and processes at the mars pathfinder landing site the mars pathfinder landing site contains abundant features attributed to aeolian or wind processes these include wind tails drift deposits duneforms of various types ripplelike features and ventifacts the first clearly seen on mars many of these features are consistant with formation involving sand size particles although some features such as dunes could develop from saltating sand size aggregates of finer grains the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline rather than aggregates excluding the ventifacts the orientations of the wind related features correlate well with the orientations of bright wind steaks seen on viking orbiter images in the general area they also correlate with wind direction predictions from the nasa ames general circulation model gcm which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209

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

examining the sediments and soils of gusev crater with the athena science payload 1 gusev crater has been proposed to contain lacustrine and or fluvial sediments however eolian or volcanic sediments global dust and locally produced soils may also be present this work describes the use of the athena instrument package to evaluate the environment in which sampled materials were deposited in gusev crater sedimentary or soil deposits can be sampled by examining materials that were 1 excavated by impact events 2 revealed by wind deflation or 3 exposed by spinning the rover wheels specific observations can be diagnostic of a depositional environment for instance pancam images of thin e g 5 cm planar layers of phyllosilicates and or evaporites as determined by mini tes would suggest lacustrine sediments layered sediments e g trough cross bed with rounded particles 4 mm would suggest fluvial activity eolian sediments may have planar or cross planar layers of well sorted grains 200 m parallel bed deposits consisting of glass observable by microscopic imager would indicate volcanic ash soil bulk chemistry reported by alpha particle x ray spectrometer that is similar to the viking and mars pathfinder soils would indicate global dust mini tes should only detect primary mineralogies in physically weathered soils whereas chemically weathered soils may contain carbonates sulfates and or phyllosilicates although some characteristics are unique to a sediment or soil deposit different deposit types can have similar characteristics e g planar layering determining the depositional history of material in gusev will require the integration of measurements from several instruments and careful geologic reasoning by the investigators

a large paleolake basin at the head of ma adim vallis mars at 8 to 15 kilometers wide ma9adim vallis is one of the largest valleys in the martian highlands although a groundwater source was previously suggested the channel originates at a spillway in the divide of a 3 000 000 square kilometer closed drainage basin the interior morphology of this source basin including likely shoreline features following topographic contours suggests that ma9adim vallis was created through catastrophic overflow of a 1 100 000 square kilometer highland lake the size constant levels and interior morphology of three regional paleolake basins require a warmer paleoclimate and a long term recharged stable highland water table more than 3 5 billion years ago

exploring gusev crater with spirit review of science objectives and testable hypotheses 1 gusev crater was selected as the landing site for the mars exploration rover mer spirit mission located at the outlet of ma adim vallis and 250 km south of the volcano apollinaris patera gusev is an outstanding site to achieve the goals of the mer mission the crater could have collected sediments from a variety of sources during its 3 9 ga history including fluvial lacustrine volcanic glacial impact regional and local aeolian and global air falls it is a unique site to investigate the past history of water on mars climate and geological changes and the potential habitability of the planet which are central science objectives of the mer mission because of its complex history and potential diversity gusev will allow the testing of a large spectrum of hypotheses with the complete suite of mer instruments evidence consistent with long lived lake episodes exist in the landing ellipse area they might offer a unique opportunity to study for the first time martian aqueous sediments and minerals formed in situ in their geological context we review the geological history and diversity of the landing site the science hypotheses that can be tested during the mer mission and the relevance of gusev to the mer mission objectives and payload

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

ma adim vallis revisited through new topographic data evidence for an ancient intravalley lake abstract based on a comprehensive study of the recent topographic map usgs mc 23 se i 2119 usgs 1991 topographical map of aeolis plus geomorphic and digital elevation we have constructed a geometric model of ma adim vallis the sedimentary history of the valley was determined by the damming of the valley by two impact craters one by the southern crater over gusev rim and the second located 120 km upstream the presence of an intravalley lake system is inferred from independent sedimentary analysis and from geomorphic evidence for valley benches peripheral and parallel topographic contour intervals of the putative intravalley lake shores suggest that the lake was covered by a thick ice sheet the longitudinal profile of the valley floor shows a peculiar reverse slope located 300 km upstream from the southern gusev crater rim we conclude that this is an accumulation of sedimentary deposits adjacent to the crater rampart which defined the northern boundary of the lake when the water level reached the lowest point of the west bank which is 0 4 km below the top of the rim of gusev crater it began to floor the surrounding plateau as the intravalley lake level raised its ice cover formed a wide lateral bench later this ponded water was funneled into gusev crater through the breaching of the southern gusev rampart by an impact crater the paleolacustrine sediments transported by the lake water that channeled through the rampart debris slope mantled the floor of gusev crater the sublacustrine sediments are promising targets for future missions and of high priority in the search for past life

thermal emission spectra of mars 5 4 10 5 μm evidence for sulfates carbonates and hydrates we have obtained spectra of the thermal emission from mars in the 5 4 10 5 m wavelength domain at a resolving power of about 60 from the kuiper airborne observatory spectra were obtained for several large spots on mars whose ground temperatures and air masses through the martian atmosphere differed significantly these data were taken at two times during the flight by taking the ratio of the spectral flux from one spot to that of a second spot we obtained results that were independent of uncertainties in the instrument s spectral response and the transmission of the earth s atmosphere these data as well as spectral fluxes of single spots based using the star tau as a calibration standard show a number of emission and absorption features they are present in sets of spectra taken at two different times some of the absorption features are due to gaseous co2 in the martian atmosphere the remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface comparison of the strength of features seen at similar times but with three different air masses and ground temperatures suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere based on comparisons of the observed features with laboratory data for a broad ensemble of minerals spectra of other solar system bodies and relevant compositional information about mars we have made the following tentative identifications of the observed features emission features at 7 8 and 9 7 m are attributed to surface silicates an emission feature at 6 1 m is attributed to a molecular water component of the surface material an absorption band at 8 7 m as well as possibly one at 9 8 m is ascribed to sulfate or bisulfate anions probably located in a distorted crystalline site and an absorption band at 6 7 m is attributed to carbonate or bicarbonate anions located in a distorted crystalline site although we cannot totally rule out a nitrate origin for this feature we have simulated these spectra with radiative transfer programs for the atmosphere and surface these simulations indicate that the sulfate and carbonate bearing minerals are contained in the same particles of the airborne dust as the dominant silicate minerals that the dust optical depth was about 0 6 at a reference wavelength of 0 3 m over the area of the observed spots and that sulfates and carbonates constitute about 10 15 and 1 3 by volume of the airborne dust respectively these results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current mars

a chemical model for evaporites on early mars possible sedimentary tracers of the early climate and implications for exploration martian geomorphology seems to indicate extensive hydrological activity during the noachian era liquid water at the surface would require a large greenhouse effect that is widely hypothesized to have been caused by a high partial pressure of atmospheric carbon dioxide pco2 a sedimentation model driven by sequential evaporation is used to calculate the evaporite mineral sequence in a closed basin lake subject to high pco2 the initial fluid is derived from weathered igneous rock similar to martian meteorite basalts siderite feco3 is always the first major carbonate to precipitate thus siderite is predicted to be an important fades component in ancient martian sediments along with silica which is also an early precipitate these would form varves in lakes that undergo cycles of evaporation and water recharge after silica and siderite the sequence is magnesian calcite nearly pure hydromagnesite and gypsum followed by highly soluble salts like nacl the presence of siderite sediments generally requires an atmospheric pco2 level in excess of 0 1 bar otherwise iron silicates such as greenalite would form this may be used in exploration as an observational test on the past atmospheric composition of mars subject to consideration of the depositional environment at pco2 of approximately several bar gypsum precipitation could occur before calcite upon evaporation if the initial so42 ca2 ratio is high and there is no water recharge the predicted carbonate sequence upon evaporation is generally consistent with recent hypotheses suggesting traces of evaporite carbonates in some martian meteorites several mechanisms destroy or obscure carbonates at the martian surface consequently in situ analysis of the interior of ejecta from recent impact craters lying within sedimentary basins may offer the most practical approach to future exploration of ancient carbonate sediments

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

a holocene climatic record from arid northwestern china abstract the history of climatic changes during the interval 8500 3000 cal yr b p has been reconstructed from stratigraphical and chronological studies and the results of total organic carbon toc total inorganic carbon tic element composition pollen and stable isotope analyses of a section along the hongshui river in the southern tengger desert nw china the record suggests that from 8450 bottom of the studied section to 7500 yr b p the climate was characterized by instability from 7500 to 5070 yr b p the climatic conditions improved and can be divided into two parts a warm humid spell between 7290 and 6380 yr b p during which the average temperature was 3 4 c higher than that of today and a warm dry spell lasting from 5950 to 5720 yr b p the climate deteriorated between 6380 and 5950 yr b p from 5720 to 5070 yr b p the temperature decreased but humidity increased an abrupt temperature drop occurred between 5340 and 5290 yr b p that indicated the decline of the warmer and humid mid holocene climate from 5070 yr b p onward the climate oscillated significantly and there were three large temperature decreases coinciding with high mountain glacier advances between 5070 4670 yr b p 4300 3740 yr b p and 3410 3230 yr b p top of the section respectively the climatic fluctuations recorded in the southern tengger desert appear in phase with climatic changes recognized in the tibetan plateau suggesting that the period between 7290 and 6380 yr b p was the most warm humid spell one extremely dry event occurred at ca 3000 yr b p and subsequently the fluvial lacustrine depositional process terminated and wind action prevailed in the area both of these features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation which are closely connected with global changes

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

mineralogic and compositional properties of martian soil and dust results from mars pathfinder mars pathfinder obtained multispectral elemental magnetic and physical measurements of soil and dust at the sagan memorial station during the course of its 83 sol mission we describe initial results from these measurements concentrating on multispectral and elemental data and use these data along with previous viking snc meteorite and telescopic results to help constrain the origin and evolution of martian soil and dust we find that soils and dust can be divided into at least eight distinct spectral units based on parameterization of imager for mars pathfinder imp 400 to 1000 nm multispectral images the most distinctive spectral parameters for soils and dust are the reflectivity in the red the red blue reflectivity ratio the near ir spectral slope and the strength of the 800 to 1000 nm absorption feature most of the pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide s sometimes mixed with small but varying degrees of well crystalline ferric and ferrous phases darker soil units appear to be coarser grained compacted and or mixed with a larger amount of dark ferrous materials relative to bright soils nanophase goethite akaganeite schwertmannite and maghemite are leading candidates for the origin of the absorption centered near 900 nm in imp spectra the ferrous component in the soil cannot be well constrained based on imp data alpha proton x ray spectrometer apxs measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average viking derived soil elemental composition differences exist between viking and pathfinder soils however including significantly higher s and cl abundances and lower si abundances in viking soils and the lack of a correlation between ti and fe in pathfinder soils no significant linear correlations were observed between imp spectral properties and apxs elemental chemistry attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions we attempted to use the pathfinder results to constrain a number of putative soil and dust formation scenarios including palagonitization and acid fog weathering while the pathfinder soils cannot be chemically linked to the pathfinder rocks by palagonitization this study and mcsween et al 1999 suggest that palagonitic alteration of a martian basaltic rock plus mixture with a minor component of locally derived andesitic rock fragments could be consistent with the observed soil apxs and imp properties

dansgaard oeschger oscillations in a coupled atmosphere ocean climate model abstract a reduced model of the global thermohaline circulation has been asynchronously coupled to a simple energy balance climate model in order to investigate the natural variability of the overturning circulation that may have been characteristic of late glacial conditions previous analyses with the ocean only component of the model have suggested that the nature of the internal variability of the thermohaline circulation was a strong function of the surface boundary conditions on temperature and salinity flux when the boundary conditions were altered from those corresponding to modern conditions to those appropriate to full glacial conditions then the internal variability was shown to be radically transformed under modern conditions the ocean only version of the model delivered an overturning circulation that was only weakly time dependent with a characteristic period of centuries under full glacial boundary conditions however the circulation became strongly time dependent with a characteristic

themis characterization of the mer gusev crater landing site 1 gusev crater previously interpreted as the depocenter for the gusev ma adim vallis fluvio lacustrine system is a proposed landing site for one of the mars exploration rovers mer here we use new remote sensing data from the thermal emission imaging system themis supplemented by data from the thermal emission spectrometer tes mars orbiter camera moc and mars orbiter laser altimeter mola to characterize the geology of gusev crater thermal infrared data from themis and tes were used to map thermophysical units on the basis of relative albedos and diurnal temperature variations themis and moc visible images were used to map unit morphologies and to estimate crater density ages mola data were used to identify unit contacts and stratigraphic relationships various data were then combined to construct a new surface unit map and stratigraphy for units on the floor of gusev seven surface units were identified in gusev mostly hesperian in age but with two showing evidence of later modification and redistribution five or more surface units and layering are present within the mer a landing ellipse attesting to the geologic diversity of this site surface units show features that could be consistent with fluvio lacustrine aeolian and or volcanoclastic deposition but the spatial resolution of visible infrared data does not allow for the identification of unambiguous volcanic or fluvio lacustrine textures however a mer landing in gusev may provide the opportunity to analyze multiple units distinguish rock types examine stratigraphic relationships and shed light on the ancient depositional environment

holocene centennial to millennial scale climatic variability evidence from high resolution magnetic analyses of the last 10 cal kyr off north iceland core md99 2275 abstract high resolution magnetic analysis has been performed on the top 25 m of core md99 2275 66 33 06 n 17 41 59 w 440 m water depth from the mid outer shelf off north iceland this is a key boundary region for climate changes related to atmospheric and oceanographic variations influenced by the moving limit between the cold and warm water masses at the polar front and the low depression track with its associated westerlies situated across iceland an age model based on tephrochronology was previously reported for this core and has allowed precise timing of significant variations in the magnetic mineral concentration and grain size over the last 10 cal kyr the holocene climatic optimum identified in north iceland between 10 and 6 cal kyr bp is characterized by minor variations in the magnetic record while there is a clear increase in oceanographic instability from 6 cal kyr bp to the present at large scale a decreasing trend in the magnetic mineral content toward the present is presumably associated with a change in the circulation pattern and coincides in time with decreasing north atlantic deep water formation short term intervals of decreased magnetic mineral content are also identified at 5 2 4 9 3 77 3 41 3 01 2 7 and 0 93 0 62 cal kyr bp the youngest one ad 1020 to 1330 corresponding in time to the medieval warm period these events are interpreted to reflect periods of increased activity of the relatively warm high salinity surface irminger current related to stronger input of north atlantic waters into the nordic seas in addition spectral analysis of selected magnetic parameters demonstrates centennial scale periodicities of 715 240 170 and 100 yr which are more clearly expressed in the last 6 cal kyr bp than in the previous period these periodicities might be attributed to intervals of persistence in the north atlantic oscillation nao mode at centennial timescales this record therefore indicates that the holocene climate was more unstable than is often assumed and it demonstrates the importance of high resolution climatic studies for this recent time period to improve climate model predictions

changes in sea surface hydrology associated with heinrich event 4 in the north atlantic ocean between 40 and 60 n abstract the changes in distribution of sea surface temperature and salinity in the north atlantic between 40 and 60 n were reconstructed for the time interval between 40 and 30 kyr bp which includes the large iceberg discharge event associated with the deposition of heinrich layer 4 we found that the meltwater input during deposition of heinrich layer 4 resulted in a 1 2 kyr temperature decrease of about 2 c and a salinity decrease in the range of 1 5 3 5 between 40 and 50 n sites above 50 n did not experience significant salinity variations a much larger area was affected by the reduction in sea surface temperature the amplitude of the sea surface temperature shift was however much smaller than the atmospheric temperature changes over greenland at gisp and grip sites

evidence for martian electrostatic charging and abrasive wheel wear from the wheel abrasion experiment on the pathfinder sojourner rover the wheel abrasion experiment wae on the mars pathfinder rover was designed to find out how abrasive the martian dust would be on strips of pure metals attached to one of the wheels a specially modified wheel with 15 thin film samples five each of three different metals specularly reflected sunlight to a photovoltaic sensor when the wheel was rotated to present the different sample surfaces to the sensor the resulting signal was interpreted in terms of dust adhesion and abrasive wear many data sequences were obtained ground tests of similar wheels in a simulated martian environment showed that static charging levels of 100 300 v could be expected to prevent the possibility of paschen discharge in the low pressure martian atmosphere charge dissipation points were added to the sojourner rover and were shown in ground tests to keep charging levels at 80 v or less nevertheless significant dust accumulations on sojourner s wheels may be interpreted as evidence for electrostatic charging simple considerations of the expected maximum level of charging and electrostatic dust adhesion lead to an estimate for the size of the adhering dust grains from the wae data it is hypothesized that the photoelectric effect is the most important mechanism for slow discharge in martian daylight sensor signals obtained late in the pathfinder mission show that significant wheel wear was seen on the metal wheel strips with the most wear on the thinnest aluminum samples and the least on the thickest nickel and platinum samples an estimate is made of the reflectance of the adhering martian dust the depth of dig of the wae wheel shows that the dust is in some places very loose and in others tightly packed finally comparison of the wae results with ground test results makes possible a comparison of the martian soil with mineral grain types and sizes found on earth and show that the martian dust is fine grained and of limited hardness

holocene history of hubbard glacier in yakutat bay and russell fiord southern alaska stratigraphic and geomorphic data defined by radiocarbon ages tree ring dates and historical observations provide evidence of three major holocene expansions of hubbard glacier early in each advance the hubbard glacier margin blocked russell fiord to create russell lake raising base level and causing stream beds and fan deltas throughout the russell drainage basin to aggrade each hubbard glacier expansion continued with an ice lobe advancing through disenchantment and yakutat bays in the west and an eastern lobe advancing into russell fiord the earlier two holocene expansions were respectively under way at 7690 and 5600 calibrated yr b p and each advance culminated more than 1 k y later the late holocene advance was under way by 3100 yr ago and reached 13 km farther south in russell fiord than the preceding two expansions late holocene deglaciation of yakutat and disenchantment bays was complete before a d 1791 nunatak glacier flowing from neves east of russell fiord became the primary ice source to the russell fiord lobe at or before this date ice retreat from the southern end of russell fiord began in the late eighteenth century and the penultimate russell lake drained ca a d 1860 the relatively slow advances and more rapid retreats of hubbard glacier are consistent with the model of the iceberg calving glacier cycle hubbard glacier is currently advancing and will likely reestablish russell lake in the near future affecting local fisheries however glacier lobes are unlikely to reach the area of the town of yakutat built on late holocene glacial deposits in the next 1 k y