iron and oxygen isotope fractionation during iron uv photo oxidation implications for early earth and mars abstract banded iron formations bifs contain appreciable amounts of ferric iron fe 3 the mechanism by which ferrous iron fe 2 was oxidized into fe 3 in an atmosphere that was globally anoxic is highly debated of the three scenarios that have been proposed to explain bif formation photo oxidation by uv photons is the only one that does not involve life the other two are oxidation by o 2 produced by photosynthesis and anoxygenic photosynthesis whereby fe 2 is directly used as electron donor in place of water we experimentally investigated iron and oxygen isotope fractionation imparted by iron photo oxidation at a ph of 7 3 the iron isotope fractionation between precipitated fe 3 bearing lepidocrocite and dissolved fe 2 follows a rayleigh distillation with an instantaneous 56 fe 54 fe fractionation factor of 1 2 such enrichment in the heavy isotopes of iron is consistent with the values measured in bifs we also investigated the nature of the mass fractionation law that governs iron isotope fractionation in the photo oxidation experiments i e the slope of the 56 fe 57 fe relationship the experimental run products follow a mass dependent law corresponding to the high t equilibrium limit the fact that a 3 8 gyr old bif sample if g from isua greenland falls on the same fractionation line confirms that iron photo oxidation in the surface layers of the oceans was a viable pathway to bif formation in the archean when the atmosphere was largely transparent to uv photons our experiments allow us to estimate the quantum yield of the photo oxidation process 0 07 iron atom oxidized per photon absorbed this yield is used to model iron oxidation on early mars as the photo oxidation proceeds the aqueous medium becomes more acidic which slows down the reaction by changing the speciation of iron to species that are less efficient at absorbing uv photons iron photo oxidation in centimeter to meter deep water ponds would take months to years to complete oxidation by o 2 in acidic conditions would be slower iron photo oxidation is thus likely responsible for the formation of jarosite hematite deposits on mars provided that shallow standing water bodies could persist for extended periods of time the oxygen isotopic composition of lepidocrocite precipitated from the photo oxidation experiment was measured and it is related to the composition of water by mass dependent fractionation the precipitate fluid 18 o 16 o isotope fractionation of 6 is consistent with previous determinations of oxygen equilibrium fraction factors between iron oxyhydroxides and water

rise of the ellsworth mountains and parts of the east antarctic coast observed with gps 1 using gps observations from 1996 to 2011 we constrain postglacial rebound in antarctica sites in the ellsworth mountains west antarctica are rising at 5 4 mm yr 95 confidence limits as in the postglacial rebound model of peltier but 10 mm yr slower than in the model of ivins and james therefore significant ice loss from the ellsworth mountains ended by 4 ka and current ice loss there is less than inferred from grace gravity observations in studies assuming the model of ivins and james three sites along the coast of east antarctica are rising at 3 to 4 2 mm yr in viscous response to holocene unloading of ice along the queen maud land coast and elsewhere kerguelen island and seven sites along the coast of east antarctic are part of a rigid antarctica plate o higgins northern antarctic peninsula is moving southeast at 2 3 0 6 mm yr relative to the antarctic plate

phyllosilicate poor palagonitic dust from mauna kea volcano hawaii a mineralogical analogue for magnetic martian dust the mineralogical and elemental composition of dust size fractions 2 and 5 m of eight samples of phyllosilicate poor palagonitic tephra from the upper slopes of mauna kea volcano hawaii were studied by x ray diffraction xrd x ray fluorescence xrf visible and near ir reflectance spectroscopy mossbauer spectroscopy magnetic properties methods and transmission electron microscopy tem the palagonitic dust samples are spectral analogues of martian bright regions at visible and near ir wavelengths the crystalline phases in the palagonitic dust are in variable proportions plagioclase feldspar ti containing magnetite minor pyroxene and trace hematite no basal reflections resulting from crystalline phyllosilicates were detected in xrd data weak broad xrd peaks corresponding to x ray amorphous phases allophane nanophase ferric oxide possibly ferrihydrite and for two samples hisingerite were detected as oxidative alteration products of the glass residual unaltered glass was also present mossbauer spectroscopy showed that the iron bearing phases are nanophase ferric oxide magnetite titanomagnetite hematite and minor glass and ferrous silicates direct observation by tem showed that the crystalline and x ray amorphous phases observed by xrd and mossbauer are normally present together in composite particles and not normally present as discrete single phase particles ti bearing magnetite occurs predominantly as 5 150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass rare spheroidal halloysite was observed in the two samples that also had xrd evidence for hisingerite the saturation magnetization js and low field magnetic susceptibility for bulk dust range from 0 19 to 0 68 am2 kg and 3 4 10 6 to 15 5 10 6 m3 kg at 293 k respectively simulation of the mars pathfinder magnet array ma experiment was performed on mauna kea volcano in areas with phyllosilicate poor palagonitic dust and with copies of the pathfinder ma on the basis of the magnetic properties of dust collected by all five ma magnets and the observation that the pathfinder mas collected dust on the four strongest magnets the value for the saturation magnetization of martian dust collected in the ma experiments is revised downward from 4 2 am2 kg to 2 5 1 5 am2 kg the revised value corresponds to 2 7 1 6 wt magnetite if the magnetic mineral is magnetite using js 92 am2 kg for pure magnetite fe3o4 or to 5 0 3 0 to 3 4 2 0 wt maghemite if the magnetic mineral is pure maghemite using js 50 to 74 am2 kg for pure maghemite fe2o3 comparison of the magnetic properties of bulk mauna kea palagonitic dust to those for dust collected by ma magnets shows that the ma magnets extracted culled a subset 25 34 wt of composite magnetic particles from bulk dust the extent of culling of martian dust is not well constrained because the mauna kea palagonitic dust satisfies the essential constraints of the pathfinder magnetic properties experiment composite and magnetic particles capable of being collected by five ma magnets a working hypothesis for the strongly magnetic mineral present in martian dust and soil is magnetite possibly ti bearing formed by rapid crystallization from silicate liquids having volcanic and or impact origins subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of martian bright regions at visible and near ir wavelengths magnetic and phyllosilicate poor palagonitic dust from mauna kea volcano is thus a spectral and magnetic analogue for magnetic martian dust

iron isotope constraints on fe cycling and mass balance in oxygenated earth oceans the fe isotope composition of proterozoic to modern clastic sedimentary rocks and aerosols defines a range ind 56 fe values that is only slightly more variable than the range of fe isotope com positions measured in terrestrial igneous rocks indicating that chemical weathering sedimentary transport and diagenesis play only a minor role in producing fe isotope variations in environ ments where fe redox conditions have been controlled by current levels of atmospheric oxygen in contrast the fe isotope composi tions of hot fluids 300 8c from mid ocean ridge mor spread ing centers define a narrow range that is shifted to lower d 56 fe values by 0 2 0 5 as compared to igneous rocks these new data allow a conceptual model for the fe isotope composition of the oxic oceans that predicts large ranges in fe isotope composition under conditions of changing aerosol and mor fe fluxes such as during periods of major worldwide glaciation

iron isotope fractionation during oceanic crust alteration abstract the purpose of this work is to study the mobility and budget of fe isotopes in the oceanic crust and in particular during low temperature interaction of seawater with oceanic basalt we carried out this investigation using samples from ocean drilling program odp site 801c drilled during leg 129 and leg 185 in jurassic pacific oceanic crust seaward of the mariana trench the site comprises approximately 450 m of sediment overlying a section of 500 m of basalt which includes intercalated pelagic and chemical sediments in the upper basaltic units and two low temperature 10 30 c ocherous si fe hydrothermal deposits fe was chemically separated from 70 selected samples and 57fe 54fe ratios were measured by mc icp ms isoprobe the isotopic ratios were measured relative to an internal standard solution and are reported relative to the international fe standard irmm 14 based on duplicate measurements of natural samples an external precision of 0 2 2 has been obtained the results indicate that the deep sea sediment section has a restricted range of 57fe which is close to the igneous rock value in contrast large variations are observed in the basaltic section with positive 57fe values up to 2 05 for highly altered basalts and negative values down to 2 49 for the associated alteration products and hydrothermal deposits secondary fe minerals such as fe oxyhydroxides or fe bearing clays celadonite and saponite have highly variable 57fe values that have been interpreted as resulting from the partial oxidation of fe2 leached during basalt alteration and precipitated as fe3 rich minerals in contrast altered basalts at site 801c which are depleted in fe up to 80 display an increase in 57fe values relative to fresh values which suggest a preferential leaching of light iron during alteration the apparent fractionation factor between dissolved fe2 and fe remaining in the mineral is from 0 5 to 1 3 and may be consistent with a kinetic isotope fractionation where light fe is stripped from the minerals alternatively the formation of secondary clays minerals such as celadonite during basalt alteration may incorporate preferentially the heavy fe isotopes resulting in the loss of light fe isotopes in the fluids because microbial processes within the oceanic crust are of potential importance in controlling rates of chemical reactions fe redox state and fe isotope fractionation we evaluated the possible effect of this deep biosphere on fe isotope signatures the fe isotope systematics presented in this study suggest that even though iron behavior during seafloor weathering may be mediated by microbes such as iron oxidizers 57fe variations of more than 4 may also be explained by abiotic processes further laboratory experiments are now required to distinguish between various processes of fe isotope fractionation during seafloor weathering

depositional setting of the late archean fe oxide and sulfide bearing chert and graphitic argillite in the shaw dome abitibi greenstone belt canada abstract interbedded chert rich exhalite and graphitic argillite are the only sedimentary rocks deposited in deep water settings during long lived hiatuses in mafic to ultramafic volcanism within the hart area of the shaw dome in the late archean abitibi greenstone belt in canada the fe oxide and sulfide bearing but predominantly cherty exhalite lithological unit in the hart area can be traced laterally to iron formation elsewhere in the shaw dome whole rock as well as fe and s isotope geochemistry suggest that the exhalite unit was formed as a result of direct precipitation from seawater distally from hydrothermal centres fractionation of fe isotopes through the precipitation of iron oxyhydroxides in a neutrally buoyant hydrothermal plume removed the heavier isotopes of fe resulting in the negative 56fe values observed in the exhalite in the hart area archean seawater is generally considered to be anoxic but moderate mn enrichments up to 1 87 wt mno in exhalite along with negative fe isotope values resulting from partial fe ii oxidation suggest the presence of oxygen in the upper part of the water column along the pathway of hydrothermal plumes from their source to the depositional site in the abitibi greenstone belt in contrast the graphitic argillite contains abundant pyrite nodules and bands that exhibit systematic negative fe isotope values but does not show mn enrichment this unit likely formed in a zone of upwelling of nutrient rich waters from deeper parts of the basin resulting in high organic productivity both exhalite and graphitic argillite have negative 33s values suggesting that sulfur was derived from seawater sulfate which is consistent with an anoxic atmosphere with sulfate aerosols produced by photochemical reactions combined our data indicates disequilibrium between anoxic atmosphere and partially oxygenated upper part of the water column during periods of volcanic quiescence in the 2 7 ga abitibi greenstone belt supporting the existence of oxidized oases within the archean ocean

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

mineralogy of three slightly palagonitized basaltic tephra samples from the summit of mauna kea hawaii certain palagonites from hawaii are considered to be among the best analogs for martian fines based upon similar spectral properties for this study three distinctly colored layers were sampled from slightly palagonitized basaltic tephra just below the summit of mauna kea at 4145 m elevation the mineralogy of size fractions of these samples was examined by diffuse reflectance visible and near ir and far ir spectroscopy optical microscopy x ray diffraction mossbauer spectroscopy magnetic analysis electron microprobe analysis empa and transmission and scanning electron microscopy for the 20 1000 m size fraction sample hwmk11 red is essentially completely oxidized and has a hematite ti hematite pigment dispersed throughout the silicate matrix the alteration is present throughout particle volumes and only a trace amount of glass is present no palagonitic rinds were detected in addition to ferric fe ti oxides other phases detected were plagioclase feldspar and a trace of olivine sample hwmk12 black has the lowest proportion of ferric bearing phases and is thus least weathered it consists mostly of unaltered glass with embedded plagioclase and minor amounts of pyroxene olivine and ti magnetite in some grains a thin palagonitic rind is visible indicating some surface alteration the mineralogy for sample hwmk13 yellow is the same as that for hwmk12 except that it has distinct well developed palagonitic rinds consisting of erionite and smectite for all samples the amount of glass and plagioclase decreases and the amount of smectite increases with decreasing particle size for size fractions 20 m for hwmk11 the amount of hematite is essentially constant and mica is present only in the coarse clay sized fraction smectites are low in structural fe for hwmk12 and hwmk13 the zeolite erionite is present along with smectites and nanophase ferric oxides np ox erionite abundance decreases and np ox abundance increases with decreasing particle size the smectite in both black and yellow samples contains some fe3 in octahedral layers there were only two mineral phases containing iron in the fine clay fraction namely smectites and iron oxides for hwmk11 relatively large iron oxide particles 0 1 to 0 4 m were dispersed on clay surfaces for hwmk12 and hwmk13 much finer np ox particles were present in lesser concentrations formation of the zeolite erionite is consistent with the arid climate zone where these samples were collected however transient hydrothermal processes that occurred during the eruption of mauna kea volcano under its permanent ice cap during the pleistocene may have resulted in minerals such as zeolites and smectites which may persist as relicts over a long period of time most of the iron released during weathering of basaltic tephra precipitated as poorly crystalline iron oxides and some of the fe has substituted for the octahedral cations in the structure of authigenic smectites the ti hematite in hwmk11 however is the result of high temperature oxidation of ti magnetite and exsolution from ironbearing silicate phases visible and near ir reflectivity spectra for the 20 m size fraction of hwmk11 is dominated by well crystalline ti hematite corresponding spectra for hwmk12 and hwmk13 whose ferric mineralogy is dominated by np ox particles are more similar to martian bright region spectra

fe oxidation processes at meridiani planum and implications for secondary fe mineralogy on mars fe oxidation processes may have occurred during groundwater mediated diagenesis in meridiani planum sediments to address this question melanterite oxidation experiments were conducted at epsomite saturation as a function of ph results show that schwertmannite is initially formed from acidic fe oxidation and that its formation and aging to mixtures of jarosite and nanocrystalline goethite is strongly controlled by ph over the range b 2 0 4 0 the ph is controlled in turn by fe oxidation and fe3 hydrolysis in one 77 d oxidation experiment nanocrystalline hematite was tentatively identified by mc6ssbauer spectroscopy accordingly aging experiments with synthetic nanocrystalline goethite were conducted 1 to further resolve the formation mechanisms of fe phases identified from oxidation experiments and 2 to test whether low water activity aw controls the thermodynamically favored goethite to hematite transition at low temperature mc6ssbauer spectroscopy and total x ray scattering show no observable changes after 4 months of aging and instead these results point to a jarosite precursor for the tentatively identified hematite on the basis of these results we suggest that the oxidation and maturation of initially formed fe2 bearing saline minerals may account in large part for the distribution of secondary fe minerals at the martian surface contributing to the association of fe oxides and mg ca sulfates observed from orbital surface analyses we hypothesize that oxidation of fe2 sulfates at low temperature could account for sustained diagenetic acidity in addition to much of the observed fe mineralogy in meridiani planum outcrop rocks the origin of the gray crystalline hematite at meridiani however is deserving of further experimental work to test this mechanism copyright 2008 by the american geophysical union

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

low temperature reflectivity spectra of red hematite and the color of mars reflectivity spectra visible and near ir were measured near 141 210 and 300 k for four red and well crystalline powders of hematite red hematite used as commercial pigments two samples of volcanic tephra from mauna kea volcano that contain red hematite as their dominant pigment three samples of palagonitic tephra from the same location that contain nanophase ferric oxide as their dominant pigment and two mixtures of the two types of pigmenting phases relative proportions of red hematite and nanophase ferric oxide were determined by mossbauer spectroscopy for samples containing red hematite as the dominant pigment the positions of the ferric electronic transitions near 430 500 630 and 860 nm are essentially independent of temperature but their widths decrease with decreasing temperature this decrease results in a well defined minimum for the band at 630 nm at low temperatures and in significant increases in reflectivity in spectral regions near 1050 and 600 nm for example the reflectivity ratios r 600 r 530 and r 600 r 860 both increase by a factor as large as l 4 between 300 and 140 k the spectral features from nanophase ferric oxide in samples of palagonitic tephra are nearly independent of temperature spectral data of martian bright regions that are characterized by a shallow band minimum near 860 nm a reflectivity maximum near 740 nm a distinct bend near 600 nm and a shallow absorption edge from 400 to 740 nm are attributed to the presence of nanophase ferric oxide plus subordinate amounts of red hematite the 600 740 and 860 nm features are associated with red hematite because the reflectivity of red hematite at 600 nm is strongly dependent on temperature and because this wavelength is in the red part of the visible spectrum the color of the martian surface may vary as a function of its temperature a conservative upper limit for the red hematite content of the optical surface of mars is 5

routine isotopic analysis of iron by hr mc icpms how precise and how accurate abstract high temperature isotopic variations documented in natural materials span a narrow range and call for precise and accurate isotopic analyses precisions better than 0 03 95 confidence interval for 56 fe have been obtained by high resolution multi collector inductively coupled plasma mass spectrometry hr mc icpms whether these uncertainties encompass all sources of error has not been carefully evaluated the current study examines all parameters that can affect accuracy and precision of fe isotopic measurements by hr mc icpms it is demonstrated that accurate 56 fe measurements can be routinely achieved within the quoted uncertainties

visible near infrared and middle infrared spectroscopy of altered basaltic tephras spectral signatures of phyllosilicates sulfates and other aqueous alteration products with application to the mineralogy of the columbia hills of gusev crater mars 1 we studied visible to near infrared vnir 0 35 2 5 m and middle infrared mir 1800 250 cm 1 also called thermal infrared and vibrational spectra of basaltic tephras from mauna kea volcano that were altered under ambient hydrothermal hydrolytic and acid sulfate and dry heat conditions although models of mir spectra of altered tephras generally produce fits whose quality is reduced compared to deconvolutions of primary lithologies they successfully identify major alteration phases cristobalite oxide phyllosilicate and sulfate except in palagonites mir spectra of the 1 in spectra of the 500 1000 m fraction only if phyllosilicates are present although mauna kea palagonitic tephra is considered a vnir analog to martian dust comparison of mir altered tephra spectra 45 m fraction to dust spectra retrieved from mars global surveyor and mars exploration rover instruments do not provide good spectral matches the best mir match is a tephra that has a strong plagioclase feldspar transparency feature and was altered under dry high temperature oxidizing conditions this sample is not a vnir analog and is not a process analog but it emphasizes the mineralogical importance of plagioclase feldspar in martian dust no single tephra is a good spectral analog across the vnir and mir we found no evidence for substantial sulfates or phyllosilicates in mini thermal emission spectrometer mini tes spectra from gusev crater

the origin of certain wide valleys in the canary islands abstract the present work addresses a long term controversy concerning the origin of orotava valley one of the most peculiar valleys in the island of tenerife the canary islands spain this valley is characterized by its great width its flat floors gently inclined towards the sea its parallel and almost vertical lateral slopes and its equally steep but irregular valley head where there are recent volcanic cones the source of the lava flows that have covered the valley floor several different theories were formulated since the last century for the formation of orotava valley examination of other wide volcanic valleys and gorges in tenerife whose origin may be similar to orotava valley indicate an alternation of erosion volcanism analysis of the key features of orotava valley itself leads to formulation of an hypothesis which could be applicable to numerous volcanic areas such valleys are developed as volcanic valleys undergo lateral expansion due to repeated alternations of processes initial erosion of the gorges by streams the burial of the gorges by lava flows and the inversion of the relief by erosion at the base of valley walls the continued occurrence of this mechanism causes the side walls of the valley to retreat progressively giving a configuration similar to that of orotava valley

the last deglacial history of lutzow holm bay east antarctica past fluctuations of the antarctic ice sheet are poorly understood because of a lack of datable materials radiocarbon reservoir ages and severe environments direct evidence of the timing of ice retreat is important in order to understand the antarctic contribution to global sea level rise since the last glacial maximum here we report the first exposure ages constraining the timing of the last deglaciation from lutzow holm bay east antarctica our data suggest that the final retreat of the ice sheet in the region occurred rapidly in the early holocene and the reduction of the ice thickness in the region was at least 350 m this occurred after the major northern hemisphere deglaciation copyright 2011 john wiley sons ltd

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

hematite spherules in basaltic tephra altered under aqueous acid sulfate conditions on mauna kea volcano hawaii possible clues for the occurrence of hematite rich spherules in the burns formation at meridiani planum mars abstract iron rich spherules 90 fe2o3 from electron microprobe analyses 10 100 m in diameter are found within sulfate rich rocks formed by aqueous acid sulfate alteration of basaltic tephra on mauna kea volcano hawaii although some spherules are nearly pure fe most have two concentric compositional zones with the core having a higher fe al ratio than the rim oxide totals less than 100 93 99 suggest structural h2o and or oh 1 the transmission mossbauer spectrum of a spherule rich separate is dominated by a hematite fe2o3 sextet whose peaks are skewed toward zero velocity skewing is consistent with al3 for fe3 substitution and structural h2o and or oh 1 the grey color of the spherules implies specular hematite whole rock powder x ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra whether spherule formation proceeded directly from basaltic material in one event dissolution of basaltic material and precipitation of hematite spherules or whether spherule formation required more than one event formation of fe bearing sulfate rock and subsequent hydrolysis to hematite is not currently constrained by analogy a formation pathway for the hematite spherules in sulfate rich outcrops at meridiani planum on mars the burns formation is aqueous alteration of basaltic precursor material under acid sulfate conditions although hydrothermal conditions are present on mauna kea such conditions may not be required for spherule formation on mars if the time interval for hydrolysis at lower temperatures is sufficiently long

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

late quaternary evolution of reedy glacier antarctica abstract fresh deposits above the margins of reedy glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present day surface at the head of the glacier exposure ages of samples from five sites along its margin show that reedy glacier and its tributaries thickened asynchronously between 17 and 7 kyr bp at the quartz hills located midway along the glacier maximum ice levels were reached during the period 17 14 kyr bp farther up glacier the ice surface reached its maximum elevation more recently 14 7 10 2 kyr bp at the caloplaca hills 9 1 7 7 kyr bp at mims spur and around 7 kyr bp at hatcher bluffs we attribute this time transgressive behavior to two different processes at the glacier mouth growth of grounded ice and subsequent deglaciation in the ross sea embayment caused a wave of thickening and then thinning to propagate up glacier during the lateglacial and holocene increased snow accumulation on the east antarctic ice sheet caused transient thickening at the head of the glacier an important result of this work is that moraines deposited along reedy glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile the profile steepened during deglaciation of the ross sea thinning at the quartz hills after 13 kyr bp while thickening upstream near its confluence with mercer ice stream rapid thinning beginning prior to 7 8 kyr bp reduced the level of reedy glacier to close to its present level thinning over the past 1000 years has lowered the glacier by less than 20 m

first exposure ages from the amundsen sea embayment west antarctica the late quaternary context for recent thinning of pine island smith and pope glaciers dramatic changes acceleration thinning and grounding line retreat of major ice streams in the amundsen sea sector of the west antarctic ice sheet wais have been observed during the past two decades but the millennial scale context for these changes is not yet known we present the first surface exposure ages recording thinning of pine island smith and pope glaciers which all drain into the amundsen sea from these we infer progressive thinning of pine island glacier at an average rate of 3 8 0 3 cm yr 1 for at least the past 4 7 k y and of smith and pope glaciers at 2 3 0 2 cm yr 1 over the past 14 5 k y these rates are more than an order of magnitude lower than the similar to 1 6 m yr 1 recorded by satellite altimetry for pine island glacier in the period 1992 1996 similarly low long term rates 2 5 9 ern yr 1 since 10 ka have been reported farther west in the ford ranges marie byrd land but in that area the same rates of thinning continue to the present day our data provide the first evidence that puts into context recent rates of thinning of the wais in the amundsen sea embayment and demonstrates that these are unusually rapid the data also provide much needed constraints for ice sheet models which are the primary tool for predicting the future behavior of the wais and its likely contribution to sea level rise

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

dynamics of oceanic iron prior to the great oxygenation event abstract we report fe isotope compositions in banded iron formations bif from three cores from the pre goe transvaal supergroup south africa and one core from the pre goe joffre member of the hamersley group australia the low abundances of detrital elements such as al ti sc and v suggest that these bif were deposited in distal positions with respect to precambrian continents while the very low p abundances are incompatible with strong biological productivity at these localities a combination of u pb chronology and cobalt accumulation rates is used to establish a high resolution time scale and deduce chemical fluxes the e folding time of 56 fe variations up stratigraphy is used to determine fe oceanic residence times and fe concentrations as well as the dissolved carbonate content of early proterozoic seas iron oceanic residence times increased from 0 2 to 2 3 ma during the time interval between 2521 and 2394 ma covered by the present cores translating into ocean fe concentrations increasing from 6 4 to 37 mmol kg 1 massive bif precipitation was triggered by release of co2 into the atmosphere and subsequent surges of alkalinity into the ocean due to the weathering of large subaerial volcanic systems we argue that a suitable electron acceptor for fe2 oxidation to magnetite is the inorganic conversion of co2 or dissolved inorganic carbon to ch4 in the process h is produced which is reinjected into oceanic hydrothermal systems liberating fe2 the couple fe2 magnetite may in the archean have played the same buffering role as the couple ca2 calcite plays today massive injection of methane into the atmosphere would accompany bif deposition and make the early earth similar to modern titan therefore although biological processes may have assisted iron oxidation and precipitation they are not a prerequisite for bif deposition

absolute gravity calibration of gps velocities and glacial isostatic adjustment in mid continent north america 1 we examine absolute gravity ag and vertical global positioning system gps time series between 1995 and 2010 at eight collocated sites in mid continent north america the comparison of ag and gps rates aligned to itrf2005 yields a gravity uplift ratio of 0 17 0 01 gal mm 1 1 gal 10 nm s 2 and an intercept of 0 1 0 5 mm yr 1 in contrast aligning the gps velocities to itrf2000 results in a gravity uplift intercept of 1 3 0 5 mm yr 1 the near zero gravity uplift offset for the itrf2005 or itrf2008 results shows a good alignment of the gps vertical velocities to earth s center of mass and confirms that gps velocities in this reference frame can be compared to predictions of geodynamic processes such as glacial isostatic adjustment gia or sea level rise the observed gravity uplift ratio is consistent with gia model predictions the ratio remains constant in regions of fast and slow uplift indicating that gia is the primary driving process and that additional processes such as local hydrology have a limited impact on a decadal time scale combining ag and gps measurements can provide significant constraints for geodetic geodynamic and hydrological studies

marine geological constraints for the grounding line position of the antarctic ice sheet on the southern weddell sea shelf at the last glacial maximum abstract the history of grounded ice sheet extent on the southern weddell sea shelf during the last glacial maximum lgm and the timing of post lgm ice sheet retreat are poorly constrained several glaciological models reconstructed widespread grounding and major thickening of the antarctic ice sheet in the weddell sea sector at the lgm in contrast recently published onshore data and modelling results concluded only very limited lgm thickening of glaciers and ice streams feeding into the modern filchner and ronne ice shelves these studies concluded that during the lgm ice shelves rather than grounded ice covered the filchner and ronne troughs two deep palaeo ice stream troughs eroded into the southern weddell sea shelf here we review previously published and unpublished marine geophysical and geological data from the southern weddell sea shelf the stratigraphy and geometry of reflectors in acoustic sub bottom profiles are similar to those from other west antarctic palaeo ice stream troughs where grounded ice had advanced to the shelf break at the lgm numerous cores from the southern weddell sea shelf recovered sequences with properties typical for subglacially deposited tills or subglacially compacted sediments these data sets give evidence that grounded ice had advanced across the shelf during the past thereby grounding in even the deepest parts of the filchner and ronne troughs radiocarbon dates from glaciomarine sediments overlying the subglacial deposits are limited but indicate that the ice grounding occurred at the lgm and that ice retreat started before 15 1 corrected 14c kyrs before present bp on the outer shelf and before 7 7 corrected 14c kyrs bp on the inner shelf which is broadly synchronous with ice retreat in other antarctic sectors the apparent mismatch between the ice sheet reconstructions from marine and terrestrial data can be attributed to ice streams with very low surface profiles similar to those of ice plains that had advanced through filchner trough and ronne trough at the lgm considering the global sea level low stand of 130 m below present a low surface slope of the expanded lgm ice sheet in the southern weddell sea can reconcile grounding line advance to the shelf break with limited thickening of glaciers and ice streams in the hinterland this scenario implies that ice sheet growth in the weddell sea sector during the lgm and ice sheet drawdown throughout the last deglaciation could only have made minor contributions to the major global sea level fluctuations during these times

the rocks of gusev crater as viewed by the mini tes instrument 1 the miniature thermal emission spectrometer mini tes on board the mars exploration rover spirit is part of a payload designed to investigate whether a lake once existed in gusev crater mini tes has observed hundreds of rocks along the rover s traverse into the columbia hills yielding information on their distribution bulk mineralogy and the potential role of water at the site although dust in various forms produces contributions to the spectra we have established techniques for dealing with it all of the rocks encountered on the plains traverse from the lander to the base of the columbia hills share common spectral features consistent with an olivine rich basaltic rock known as adirondack class beginning at the base of the west spur of the columbia hills and across its length the rocks are spectrally distinct from the plains but can be grouped into a common type called clovis class these rocks some of which appear as in place outcrop are dominated by a component whose spectral character is consistent with unaltered basaltic glass despite evidence from other rover instruments for significant alteration the northwest flank of husband hill is covered in float rocks known as wishstone class with spectral features that can be attributed uniquely to plagioclase feldspar a phase that represents more than half of the bulk mineralogy rare exceptions are three classes of basaltic exotics found scattered across husband hill that may represent impact ejecta and or float derived from local intrusions within the hills the rare outcrops observed on husband hill display distinctive spectral characteristics the outcrop called peace shows a feature attributable to molecular bound water and the outcrop that hosts the rock called watchtower displays a dominant basaltic glass component despite evidence from the rover s payload for significant alteration of some of the rocks no unambiguous detection of crystalline phyllosilicates or other secondary silicates has been observed by mini tes the mineralogical results supplied by mini tes provide no clear evidence that a lake once existed in gusev crater

antarctic contribution to sea level rise observed by grace with improved gia correction antarctic volume changes during the past 21 thousand years are smaller than previously thought and here we construct an ice sheet history that drives a forward model prediction of the glacial isostatic adjustment gia gravity signal the new model in turn should give predictions that are constrained with recent uplift data the impact of the gia signal on a gravity recovery and climate experiment grace antarctic mass balance estimate depends on the specific grace analysis method used for the method described in this paper the gia contribution to the apparent surface mass change is re evaluated to be 55 13 gt yr by considering a revised ice history model and a parameter search for vertical motion predictions that best fit the gps observations at 18 high quality stations although the gia model spans a range of possible earth rheological structure values the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity nor for a preferred lithospheric thickness grace monthly solutions from the center for space research release 04 csr rl04 release time series from january 2003 to the beginning of january 2012 uncorrected for gia yield an ice mass rate of 2 9 29 gt yr the new gia correction increases the solved for ice mass imbalance of antarctica to 57 34 gt yr the revised gia correction is smaller than past grace estimates by about 50 to 90 gt yr the new upper bound to the sea level rise from the antarctic ice sheet averaged over the time span 2003 0 2012 0 is about 0 16 0 09 mm yr

hydrothermal synthesis of hematite spherules and jarosite implications for diagenesis and hematite spherule formation in sulfate outcrops at meridiani planum mars we synthesized hematite spherules whose mineralogic chemical and crystallographic properties are strikingly similar to those for the hematite rich spherules in lag deposits on the surface and embedded in outcrops at meridiani planum mars the spherules were synthesized in the laboratory along with hydronium jarosite and minor hydronium alunite from fe al mg s cl acid sulfate solutions under hydrothermal conditions the reaction sequence was 1 precipitation of hydronium jarosite 2 jarosite dissolution and precipitation of hematite spherules and 3 precipitation of hydronium alunite upon depletion of hydronium jarosite the spherules exhibit a radial growth texture with the crystallographic c axis aligned along the radial direction so that thermal emission spectra have no hematite emissivity minimum at 390 cm 1 our experiments show that hydrothermal acid sulfate solutions are a pathway for formation of jarosite and the hematite spherules at meridiani planum mars

deceleration in the earth s oblateness 1 for over three decades satellite laser ranging slr has recorded the global nature of the long wavelength mass change within the earth system analysis of the most recent time series of 30 day slr based estimates of earth s dynamical oblateness characterized by the gravitational degree 2 zonal spherical harmonic j2 indicates that the long term variation of j2 appears to be more quadratic than linear in nature the superposition of a quadratic and an 18 6 year variation leads to the unknown decadal variation reported by cheng and tapley 2004 although the primary trend is expected to be linear due to global isostatic adjustment there is an evident deceleration j 2 18 1 10 13 yr2 in the rate of the decrease in j2 during the last few decades likely due to changes in the rate of the global mass redistribution from melting of the glaciers and ice sheets as well as mass changes in the atmosphere and ocean

timing of the most recent neoglacial advance and retreat in the south shetland islands antarctic peninsula insights from raised beaches and holocene uplift rates abstract the timing of the most recent neoglacial advance in the antarctic peninsula is important for establishing global climate teleconnections and providing important post glacial rebound corrections to gravity based satellite measurements of ice loss however obtaining accurate ages from terrestrial geomorphic and sedimentary indicators of the most recent neoglacial advance in antarctica has been hampered by the lack of historical records and the difficulty of dating materials in antarctica here we use a new approach to dating flights of raised beaches in the south shetland islands of the northern antarctic peninsula to bracket the age of a neoglacial advance that occurred between 1500 and 1700 ad broadly synchronous with compilations for the timing of the little ice age in the northern hemisphere our approach is based on optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent neoglacial advance in addition these beaches mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the south shetland islands we use a maxwell viscoelastic model of glacial isostatic adjustment gia to determine whether the rates of uplift calculated from the raised beaches are realistic given the limited constraints on the ice advance during this most recent neoglacial advance our rebound model suggests that the subsequent melting of an additional 16 22 increase in the volume of ice within the south shetland islands would result in a subsequent uplift rate of 12 5 mm yr that lasted until 1840 ad resulting in a cumulative uplift of 2 5 m this uplift rate and magnitude are in close agreement with observed rates and magnitudes calculated from the raised beaches since the most recent neoglacial advance along the south shetland islands and falls within the range of uplift rates from similar settings such as alaska

oxidation of manganese in an ancient aquifer kimberley formation gale crater mars the curiosity rover observed high mn abundances 25 wt mno in fracture filling materials that crosscut sandstones in the kimberley region of gale crater mars the correlation between mn and trace metal abundances plus the lack of correlation between mn and elements such as s cl and c reveals that these deposits are mn oxides rather than evaporites or other salts on earth environments that concentrate mn and deposit mn minerals require water and highly oxidizing conditions hence these findings suggest that similar processes occurred on mars based on the strong association between mn oxide deposition and evolving atmospheric dioxygen levels on earth the presence of these mn phases on mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient mars than in the present day

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

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

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

iron isotopic and chemical tracing of basalt alteration and hematite spherule formation in hawaii a prospective study for mars abstract hematite spherules from mauna kea volcano hawaii resemble martian hematite spherules at meridiani planum in morphology mineralogy and geochemistry and they both formed in association with acid sulfate alteration of basalt to gain insights into the processes involved in the formation of these spherules we have measured the fe isotopic compositions of unaltered basalts and tephras as well as a variety of weathering alteration products including altered basalts hematite rich breccia and individual hematite spherules jarosite bearing tephras palagonitic tephras calcined tephras high t dry oxidation and steam vent tephras compared to other alteration processes that induce little fe mobility acid sulfate alteration produces large fe isotopic variations 56 fe values ranging from 0 15 to 0 94 we used rock slabs from a variably altered basaltic rock to constrain the fe isotope fractionation factor during acid sulfate alteration of basaltic rocks we found that the process followed a rayleigh distillation with an instantaneous fractionation factor of 0 24 between the fluid and the residue for 56 fe resulting in a heavy fe isotope enrichment in the alteration residue however the constant mn fe ratios of the slabs suggest that acid sulfate leaching does not significantly fractionate mn fe ratios in basalts which is consistent with the mobilization of iron as fe ii we also measured the fe isotopic compositions and mn fe ratios using nanosims of individual hematite spherules from a spherule rich breccia hwmk745r the spherules show heavy fe isotopic enrichments and low mn fe ratios compared to unaltered samples which is similar to the fractionations encountered in iron formations a rayleigh fractionation model suggests that both fe isotopic compositions and mn fe ratios of the spherules are consistent with 80 fe oxidation and precipitation from an acid sulfate fluid therefore direct fe precipitation from a fluid can readily explain the hematite spherule formation and a more complex scenario involving jarosite precipitation followed by conversion to hematite is not needed combined thermodynamic and kinetic constraints also suggest that precipitation of jarosite would be hindered the study presents a roadmap for studying future returned martian samples in the laboratory

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment