evidence for the episodic erosion of the medusae fossae formation preserved within the youngest volcanic province on mars we use orbital shallow radar sharad sounder data to three dimensionally visualize the subsurface structure of elysium planitia the youngest volcanic province on mars our results reveal an emplacement history consisting of multiple groups of overlapping lava flow units originating from different sources the uniquely complex radar stratigraphy of elysium planitia relative to other volcanic regions requires a distinct mechanism to generate the numerous reflectors observed in sharad data sedimentary deposits interbedded with successive batches of lava flows could account for the elaborate pattern of reflectors we infer that widespread rapidly emplaced material sourced from the enigmatic medusae fossae formation mff creates these sedimentary layers this implies that episodes of atmospheric activity perhaps linked with the obliquity of mars periodically erode and redeposit material from the mff across a large region

a 100 kyr periodicity in the flux of extraterrestrial 3he to the sea floor most of the helium 3 in oceanic sediments comes from interplanetary dust particles idps and can therefore be used to infer the accretion rate of dust to the earth through time 3he records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of years probably owing to cometary and asteroidal break up events muller and macdonald have proposed that periodic changes in this accretion rate due to a previously unrecognized 100 kyr periodicity in the earth s orbital inclination might account for the prominence of this frequency in climate records of the past million years here we report variations in the 3 he flux to the sea floor that support this idea we find that the flux recorded in rapidly accumulating quaternary sediments from the mid atlantic ridge oscillates with a period of about 100 kyr we cannot yet say however whether the 100 kyr climate cycle is a consequence of a cause of or an effect independent of these periodic changes

sharad radar sounding of the vastitas borealis formation in amazonis planitia 1 amazonis planitia has undergone alternating episodes of sedimentary and volcanic infilling forming an interleaved sequence with an upper surface that is very smooth at the kilometer scale earlier work interprets the near surface materials as either young rough lava flows or ice rich sediment layers overlying a basement comprising the vastitas borealis formation and earlier hesperian plains sounding radar profiles across amazonis planitia from the shallow radar sharad instrument on the mars reconnaissance orbiter reveal a subsurface dielectric interface that increases in depth toward the north along most orbital tracks the maximum depth of detection is 100 170 m depending upon the real dielectric permittivity of the materials but the interface may persist at greater depth to the north if the reflected energy is attenuated below the sharad noise floor the dielectric horizon likely marks the boundary between sedimentary material of the vastitas borealis formation and underlying hesperian volcanic plains the sharad detected interface follows the surface topography across at least one of the large wrinkle ridges in north central amazonis planitia this conformality suggests that vastitas borealis sediments at least in this region were emplaced prior to compressional tectonic deformation the change in radar echo strength with time delay is consistent with a loss tangent of 0 005 0 012 for the column of material between the surface and the reflector these values are consistent with dry moderate density sediments or the lower end of the range of values measured for basalts while a component of distributed ice in a higher loss matrix cannot be ruled out we do not find evidence for a dielectric horizon within the vastitas borealis formation that might suggest an abrupt change from an upper dry layer to an ice rich lower deposit

flux and size fractionation of 3he in interplanetary dust from antarctic ice core samples article i nfo accretion of extraterrestrial material to earth is of interest for a variety of reasons including as a possible driver of long or short term climate change and as a record of solar system events preserved in the geological record 3 he is highly enriched in extraterrestrial material and provides a useful tracer of its input into sedimentary archives previous work showed that polar ice could be a suitable archive for studying variations in extraterrestrial input additional measurements reported here confirm that the late quaternary 3 he flux derived from antarctic ice samples is similar to 3 he fluxes determined from marine sediments the mean flux from nine replicate 1 kg ice samples from the vostok ice core site 112 115 m depth age of 3800 years is 1 25 0 37 10 12 cm 3 stp cm 2 ka 1 mean 2se the large range for the 9 replicates is probably due to the small number of interplanetary dust particles idps present and illustrates that large ice samples are required for precise constraints on temporal variations in the 3 he flux size fraction experiments show that the majority of the 3 he flux is delivered by particles in the 5 10 m size range consistent with the hypothesis

replacement of primary monazite by apatite allanite epidote coronas in an amphibolite facies granite gneiss from the eastern alps accessory monazite crystals in granites are commonly unstable during amphibolite facies regional metamorphism and typically become mantled by newly formed apatite allanite epidote coronas this distinct textural feature of altered monazite and its growth mechanism were studied in detail using backscattered electron imaging in a sample of metagranite from the tauern window in the eastern alps it appears that the outer rims of the former monazites were replaced directly by an apatite ring with tiny thorite intergrowths in connection with ca supply through metamorphic fluid around the apatite zone a proximal allanite ring and a distal epidote ring developed this concentric corona structure with the monazite core regularly preserved in the center shows that the reaction kinetics were diffusion controlled and relatively slow quantitative electron microprobe analyses suggest that the elements released from monazite breakdown p ree y th u were diluted and redistributed in the newly formed apatite allanite and epidote overgrowth rings and were unable to leave the corona this supports the common hypothesis that these trace elements are highly immobile during metamorphism furthermore microprobe data suggest that the preserved monazite cores lost little possibly none of their radiogenic lead during metamorphism thus metastable monazite grains from orthogneisses appear to be very useful for constraining u th pb protolith ages on the basis of these findings and a review of literature data it seems that monazite stability in amphibolite facies metamorphic rocks depends strongly on lithologic composition while breaking down in granitoids monazite may grow during prograde metamorphism in other rocks such as metapelites

accretion rate of cosmic spherules measured at the south pole micrometeorites are terrestrially collected extraterrestrial particles smaller than about 1 mm which account for most of the mass being accreted to the earth1 2 compared with meteorites micrometeorites more completely represent the earth crossing meteoroid complex3 4 and should include fragments of asteroids comets mars and our moon as well as pre solar and interstellar grains3 6 previous measurements of the flux of micrometeoroids that survive to the earth s surface have large uncertainties owing to the destruction of particles by weathering7 8 9 inefficiencies in magnetic collection or separation techniques7 8 9 low particle counts10 11 poor age constraint7 8 9 12 13 or highly variable concentrating processes12 13 here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the south pole water well which supplies drinking water for the scott amundsen station using this collection we have determined precise estimates of the flux and mass distribution for 50 700 m cosmic spherules melted micrometeorites allowing for the expected abundance of unmelted micrometeorites14 in the samples our results indicate that about 90 of the incoming mass of submillimetre particles evaporates during atmospheric entry our data indicate the loss of glass rich and small stony spherules from deep sea deposits7 8 and they provide constraints for models describing the survival probability of micrometeoroids15 16

on the fluxes and fates of 3he accreted by the earth with extraterrestrial particles abstract the influx of extraterrestrial et matter on the earth results in appreciable fluxes of 3 he originating from several different processes we have analyzed the published data on the observed concentrations of 3 he in interplanetary dust particles idps sampled in the stratosphere in polar ice samples and in meteorites this information considered together with production of secondary fragments during the atmospheric entry of meteoroids allows us to make plausible estimates of fluxes of the extra terrestrial fluxes of the two principal 3 he types accreted along with the extraterrestrial materials i solar wind sw and solar energetic particle sep 3 he implanted in et particles and ii 3 he produced in the et matrix by interactions of galactic cosmic ray gcr particles an appreciable fraction of 3 he brought to the earth by et particles is expected to be lost from the particles during ablation and fragmentation of the particles during their transit through the atmosphere by comparing the measured 3 he fluxes in two terrestrial archives polar ice and marine sediments and based on supplementary data 3 he 4 he and 20 ne 22 ne ratios we have attempted to determine the relative fluxes of solar sw and sep and gcr 3 he that are preserved in them our analyses establish the fact that the reported 3 he concentrations in particles in relatively small size polar ice samples from greenland and antarctica are primarily due to the solar 3 he accreted via idps of 2 5 m radii scavenged in the polar ice we predict that if larger ice samples were analyzed greater contributions would be found from gcr 3 he present in fragments of meteoroids produced during their entry through the atmosphere it follows therefore that long term fluxes of idps can be estimated from studies of 3 he in relatively small samples of polar ice sheets one observes appreciable concentrations of 3 he in marine sediments extensive observational data are available for sediments in the atlantic and pacific oceans we show that besides idps there is an important source which is an important contributor to the flux of 3 he in marine sediments this is the gcr produced 3 he in meteoroids of sizes up to 1 m we compare the measured 3 he fluxes in marine sediments with those predicted from solar 3 he in idps and from gcr produced 3 he in secondary fragments of meteoroids of sizes up to 1 m produced during their transit through the atmosphere our studies allow us to reach plausible conclusions regarding the predominant source of 3 he in marine sediments

new insights into the carrier phase s of extraterrestrial 3he in geologically old sediments to better understand the composition characteristics of helium diffusion and size distribution of interplanetary dust particles idps responsible for the long term retention of extraterrestrial 3he we carried out leaching stepped heating and sieving experiments on pelagic clays that varied in age from 0 5 ma to 90 myr the leaching experiments suggest that the host phase s of 3he in geologically old sediments are neither organic matter nor refractory phases such as diamond graphite al2o3 and sic but are consistent with extraterrestrial silicates fe ni sulfides and possibly magnetite stepped heating experiments demonstrate that the 3he release profiles from the magnetic and non magnetic components of the pelagic clays are remarkably similar because helium diffusion is likely to be controlled by mineral chemistry and structure the stepped heating results suggest a single carrier that may be magnetite or more probably a phase associated with magnetite furthermore the stepped outgassing experiments indicate that about 20 of the 3he will be lost through diffusion at seafloor temperatures after 50 myrs while sedimentary rocks exposed on the earth s surface for the same amount of time would lose up to 60 the absolute magnitude of the 3he loss is however likely to depend upon the 3he concentration profile within the idps which is not well known contrary to previous suggestions that micrometeorites in the size range of 50 100 m in diameter are responsible for the extraterrestrial 3he in geologically old sediments stuart f m harrop p j knott s turner g 1999 laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he flux to earth geochim cosmochim acta63 2653 2665 our sieving experiment demonstrates that at most 20 of the 3he is carried by particles greater than 50 m in diameter the size distribution of the 3he bearing particles implies that extraterrestrial 3he in sediments record the idp flux rather than the micrometeorite flux

size fractionation reproducibility and provenance of helium isotopes in north equatorial pacific pelagic clays helium isotope compositions were measured in late quaternary pelagic clays from the north equatorial pacific where terrestrial and extra terrestrial end member components are identified and quantified in different grain size populations the results provide important constraints on the nature of interplanetary dust particles idps in sedimentary environments and on their application as constant flux proxies in paleoceanographic studies approximately 92 95 of the extra terrestrial 3 he 3 heet is concentrated in particles smaller than 20 mm within this grain size group 44 of 3 heet is concentrated in the 20 10 and 10 2 mm fractions while more than 50 of the total 3 heet is found in fine particles smaller than 2 mm the peak concentration of 3 heet in the very fine particle size population explains a consistently better reproducibility of 3 heet in sediments compared to model predictions that is related to the relatively homogenous distribution of clay size particles in sediments compared to coarser particles especially in deep sea sediments and ice cores the 3 he 4 he ratios are highest in the coarser than 20 mm fractions peaking between 63 and 38 mm 1 7871 13 10 4 compared to the bulk and the o20 mm fractions 3 2072 62 10 5 and 2 1170 88 10 5 respectively the isotopic composition of helium in each of the size fractions reflects a mixture between a pure extraterrestrial end member and a terrigenous component which is itself comprised of varying mixtures of volcanic material and eolian material associated with the fine grain size fraction of loess deposits in south east asia poor 3 heet reproducibility observed here and elsewhere inhibiting its application as a constant flux proxy stems from the presence of a small number of aliquots displaying significantly higher 3 heet contents compared to the average of their reference group these helium rich particles hrps are probably characterized by a o20 mm diameter and carry significant amounts of extraterrestrial 3 he and 4 he careful rejection of such aliquots improves the signal reproducibility by more than two fold

francoisite ce a new mineral species from la creusaz uranium deposit valais switzerland and from radium ridge flinders ranges south australia description and genesis the new mineral francoisite ce ce nd ca uo 2 3 o oh po 4 2 6h 2 o is the ce analog of francoisite nd it has been discovered simultaneously at the la creusaz uranium deposit near les marecottes in valais switzerland and at the number 2 uranium workings radium ridge near mt painter arkaroola area northern flinders ranges in south australia francoisite ce is a uranyl bearing supergene mineral that results from the alteration under oxidative conditions of ree and u 4 bearing hypogene minerals allanite ce monazite ce uraninite at les marecottes monazite ce ishikawaite samarskite and an unknown primary u mineral at radium ridge the ree composition of francoisite ce results from a short aqueous transport of ree leached out of primary minerals most likely monazite ce at radium ridge and allanite ce at la creusaz with fractionation among ree resulting mainly from aqueous transport with only limited ce loss due to oxidation to ce 4 during transport

a magmatic hydrothermal transition in arkaroola northern flinders ranges south australia from diopside titanite pegmatites to hematite quartz growth a set of palaeozoic diopside titanite veins are present in mesoproterozoic metagranites and metasediments that constitute the basement mt painter inlier of the adelaide fold belt south aus tralia these massive veins up to 1 m of pegmatitic nature contain large crystals of diopside lree y enriched titanite up to 40 cm in length and minor amounts of quartz they can be used to trace the sys tem s development from a high temperature magmatic stage through to a massive hydrothermal event the pegmatitic origin of these veins is evident from a complex fluid melt inclusion assemblage consisting of a highly saline inhomogeneous fluid and relicts of melt immiscibility of melt and heterogeneous highly saline fluids exceeding 61 eq mass nacl is preserved in primary inclusions in diopside and secondary inclusions in titanite indicating relatively shallow conditions of formation 510 20 c and 130 10 mpa graphic intergrowth of diopside and albite occurs at the contact with granitic pegmatites the system evolved into hydrothermal conditions which can be deduced from a later population of only fluid inclusions homogeneous and less saline 40 eq mass nacl trapped around 350 20 c and 80 10 mpa during quartz crystallization the conditions moved across the halite liquidus resulting in a heterogeneous mixture of brine and halite crystals which were trapped at 200 20 c and 50 10 mpa brecciation and a palaeo geother mal system overprinted the pegmatitic veins with an epithermal hematite quartz assemblage and lesser amounts of bladed calcite and fluorite in an intermit tently boiling hydrothermal system of fairly pure h2o at 100 140 c and 1 5 mpa remobilization of lrees and y from titanite and or the granitic host rock is evidenced by precipitation of apatite allanite and wakefieldite in an intermediate stage occasional incorporation of radioactive elements or minerals presumably u rich in the fluorite is responsible for radiolysis of h2 ot o h 2

extraterrestrial 3he in seafloor sediments evidence for correlated 100 kyr periodicity in the accretion rate of interplanetary dust orbital parameters and quaternary climate we have determined the helium abundance and isotopic composition of seafloor carbonate sediments from the flanks of the ontong java plateau western equatorial pacific ocean odp site 806 these results provide a two million year record of the burial flux of extraterrestrial 3he which we believe is a proxy for the terrestrial accretion rate of interplanetary dust particles the 3he burial flux prior to 700 ka was relatively low 0 5 pcc cm 2 kyr 1 but from 700 ka to the present the burial flux gradually increased to a value of 1 0 pcc cm 2 kyr 1 100 kyr periodicity in the 3he burial flux is apparent over the last 700 kyr and correlates with the oxygen isotope record of global climate with high 3he burial fluxes associated with interglacial periods this periodicity and phase are consistent with previous 3he measurements in north atlantic sediments although 100 kyr periodicity in 3he burial flux is in agreement with recent predictions of the accretion rate of interplanetary dust based on a model of the orbital evolution of asteroidal debris the measurements and predictions differ by one half cycle in phase nevertheless our observations suggest the terrestrial accretion rate of interplanetary dust is controlled by orbital eccentricity and or inclination relative to the solar system invariable plane such control is a necessary but not sufficient condition for the hypothesis of muller and macdonald 1995 that variations in extraterrestrial dust accretion modulates terrestrial climate with a 100 kyr period we also identify several brief 25 kyr intervals of strongly enhanced 3he burial possibly related to random and transient fluctuations in the accretion rate of asteroidal or cometary dust particles

3d structure of the gusev crater region abstract gusev crater lies within the aeolis quadrangle of mars at the boundary between the northern lowlands and southern highlands the ancient valley ma adim vallis dissects the highlands south of gusev crater and is thought to have fed the crater with sediments high resolution stereo camera data and digital elevation models were used to construct a geologic geomorphic map 173 5 178 5 e 10 18 s and cross sections complemented by data from mars orbiter camera mars orbiter laser altimeter and thermal emission imaging system three geologic domains are recognised the highlands in the south gusev crater and lowlands in the north twelve units are mapped with thicknesses ranging from hundred meters to several kilometres thicknesses of units and their bedding attitude are estimated combining the geologic map and topographic information relative ages are determined from crater counts ranging from early noachian for highland units to middle amazonian for units in gusev crater and in lowlands episodes of intense geologic activity deposition volcanism deformation occur at around 4 0 ga 3 7 ga and 3 5 ga comparing the geometry of the gusev crater with similar sized filled and un filled martian craters suggests that the columbia hills are relics of the original central peak of gusev crater

antarctic and global climate history viewed from ice cores a growing network of ice cores reveals the past 800 000 years of antarctic climate and atmospheric composition the data show tight links among greenhouse gases aerosols and global climate on many timescales demonstrate connections between antarctica and distant locations and reveal the extraordinary differences between the composition of our present atmosphere and its natural range of variability as revealed in the ice core record further coring in extremely challenging locations is now being planned with the goal of finding older ice and resolving the mechanisms underlying the shift of glacial cycles from 40 000 year to 100 000 year cycles about a million years ago one of the great mysteries of climate science a discussion of past antarctic and global climate history as seen from antarctic ice cores with an outlook on future goals and drilling priorities

direct observation of tetravalent cerium in ferromanganese nodules and crusts by x ray absorption near edge structure xanes abstract x ray absorption near edge structure xanes was successfully applied for the direct determination of ce valence in hydrogenetic ferromanganese nodules two samples and crust one sample rare earth element ree patterns of the hydrogenetic ferromanganese nodules and crust recovered from the pacific ocean show large positive ce anomalies especially when normalized to seawater despite some disadvantages in the spectroscopic analysis of ce in natural samples e g low concentration and interference from other elements intense synchrotron radiation and measurement of fluorescent xanes with semiconductor detectors having high energy resolution enabled us to detect xanes at ce l iii edge in the ferromanganese nodule or crust in the xanes spectra of the nodule or crust large double peaks were observed showing that the oxidation state of ce in the nodule or crust is predominantly tetravalent with little contribution from ce iii this is the first in situ quantitative analysis of ce iv among total ce in natural samples as a trace element as far as we know the results obtained by xanes seem to be consistent with the percentage of ce iv estimated from seawater normalized ree patterns suggesting that seawater is a precursor of ree in the marine deposits the present results also confirm that ce enrichment relative to other rees in hydrogenetic ferromanganese deposits is due to oxidative removal of ce from seawater to the ferromanganese nodules and crust in the marine environment comparison of xanes spectra of ce sorbed on synthetic manganese oxide and ceo 2 vs those of the ferromanganese nodules and crust suggests that the initial reaction of ce with the ferromanganese nodules and crust is the sorption of dissolved ce iii to the manganese oxide surface

meteoric smoke fallout over the holocene epoch revealed by iridium and platinum in greenland ice an iridium anomaly at the cretaceous tertiary boundary layer has been attributed to an extraterrestrial body that struck the earth some 65 million years ago1 it has been suggested that during this event the carrier of iridium was probably a micrometre sized silicate enclosed aggregate2 or the nanophase material of the vaporized impactor3 but the fate of platinum group elements such as iridium that regularly enter the atmosphere via ablating meteoroids remains largely unknown here we report a record of iridium and platinum fluxes on a climatic cycle timescale back to 128 000 years ago from a greenland ice core4 we find that unexpectedly constant fallout of extraterrestrial matter to greenland occurred during the holocene whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust laden atmosphere of the last glacial age we suggest that nanometre sized meteoric smoke particles5 6 formed from the recondensation of ablated meteoroids in the atmosphere at altitudes 70 kilometres are transported into the winter polar vortices by the mesospheric meridional circulation7 and are preferentially deposited in the polar ice caps this implies an average global fallout of 14 5 kilotons per year of meteoric smoke during the holocene

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

helium and thorium isotope constraints on african dust transport to the bahamas over recent millennia abstract despite its potential linkages with north atlantic climate the variability in saharan dust transport to the western north atlantic over the past two millennia has not been well characterized a factor of 4 increase in dust production in sub saharan africa has been attributed to the onset of sahelian agriculture 200 yr ago the regional extent of this anthropogenic dust increase however remains uncertain additionally while millennial scale cold periods of the last deglaciation have been associated with strong increases in north african dust emissions few adequate records exist to observe dustiness during the little ice age a century scale cooling of the north atlantic ad 1400 1800 in this study we develop a new technique for the paired use of 230 th normalized 232 th fluxes and 3 he normalized 4 he fluxes in bahamian tidal flat sediments after justifying the fact that 230 th and 3 he have had relatively constant sources to tidal flat and banktop waters and accounting for the smoothing effect of bioturbation a factor of 4 change in far field dust transport to the western north atlantic between the pre industrial and modern era is not supported by our dust proxies over the past 2000 yr furthermore we speculate why the response of western north atlantic dust deposition associated with the little ice age climate anomalies may have been modest compared to prior climatic events of the early holocene or the last deglaciation

absorption and scattering in ground penetrating radar analysis of the bishop tuff 1 ground penetrating radar gpr signals are attenuated by both absorption and scattering we performed low frequency 100 mhz gpr surveys at the volcanic tableland of the bishop california tuff to evaluate the factors that control gpr depth of investigation and to develop insight into the capabilities of such radars for mars the subsurface reflection character was very different for two different commercial systems used together they revealed both internal welding contacts in the tuff and an abundance of discrete scatterers attenuation coefficients were computed from profiles that showed distributed scattering the semilogarithmic signal decay is directly analogous to seismic coda the absorption intrinsic loss was determined to be 1 db m from low frequency vertical electric soundings the residual attenuation that is the attenuation in the absence of absorption is attributed to scattering scattering attenuation of 1 db m at 25 50 mhz corresponds to mean free paths as short as 4 m a fraction of the two way propagation distances of 20 40 m therefore the bishop tuff is formally a strong scatterer to gpr the mean free path is also comparable to the subsurface radar wavelength in this case maximizing scattering loss the scatterers themselves likely originate as welding heterogeneities contrasts in dielectric constant due to density differences may be supplemented by moisture variations on mars scattering is likely to contribute significant losses to gpr signals in all but the most uniform materials and unfrozen thin films of water in the lower cryosphere could influence both absorption and scattering

comparison between greenland ice margin an ice core oxygen 18 records old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice sheet margins the d18o content of the surface ice was studied at 15 different greenland ice margin locations at some locations two or more records were obtained along closely spaced parallel sampling profiles showing good reproducibility of the records we present ice margin d18o records reaching back into the pleistocene many of the characteristic d18o variations known from greenland deep ice cores can be recognized allowing an approximate time scale to be established along the ice margin records a flow line model is used to determine the location on the ice sheet where the margin ice was originally deposited as snow the pleistocene holocene d18o change at the deposition sites is determined by comparing the d18o values in the ice margin record to the present 18o values of the surface snow at the deposition sites on the northern slope of the greenland ice sheet the pleistocene holocene d18o change is c 10 per mil in contrast to a change of 6 7 per mil at locations near the central ice divide this is in accordance with deep ice core results we conclude that d18o records measured on ice from the greenland ice sheet margin provide useful information about past climate and dynamics of the ice sheet and thus are important and cheap supplements to deep ice core records

gas records from the west greenland ice margin covering the last glacial termination a horizontal ice core abstract certain sites along ice sheet margins provide an easily accessible and almost unlimited supply of ancient ice at the surface measurements of gases in trapped air from ice outcropping at pakitsoq west greenland demonstrate that ancient air is mostly well preserved no alterations in 18 o atm and 15 n of n 2 are apparent and alterations in methane are found in only a few ice sections using measurements of these gases we have unambiguously identified a stratigraphic section containing ice from the end of last glacial period as well as bolling allerod younger dryas and preboreal intervals extensive sections of ice from the holocene and most ages within the last glacial period are probably also present very accurate dating has been possible in the ice section containing the younger dryas preboreal abrupt climate transition signal the ice at pakitsoq is folded and non uniformly thinned with many cross cutting bands of bubble free ice and dust the cross cutting features are associated with anomalies in both the gas and the ice records with careful sampling to avoid these the ice at pakitsoq is suitable for recovery of large volume samples of the ancient atmosphere for analysis of trace constituents such as 14 ch 4

a 135 000 year vostok specmap common temporal framework the object of the present study is to introduce a means of comparing the vostok and marine chronologies our strategy has been to use the 18o of atmospheric o2 denoted 18oatm from the vostok ice core as a proxy for the 18o of seawater denoted 18osw our underlying premise in using 18oatm as a proxy for 18osw is that past variations in 18osw an indicator of continental ice volume have been transmitted to the atmospheric o2 reservoir by photosynthesizing organisms in the surface waters of the world s oceans we compare our record of 18oatm to the 18osw record which has been developed from studies of the isotopic composition of biogenic calcite 18oforam in deep sea cores we have tied our 18oatm record from vostok to the specmap timescale throughout the last 135 kyr by correlating 18oatm with a 18osw record from v19 30 results of the correlation indicate that 77 of the variance is shared between these two records we observed differences between the 18oatm and the 18osw records during the coldest periods which indicate that there have been subtle changes in the factors which regulate 18oatm other than 18osw our use of 18oatm as a proxy for 18osw must therefore be considered tentative especially during these periods by correlating 18oatm with 18osw we provide a common temporal framework for comparing phase relationships between atmospheric records from ice cores and oceanographic records constructed from deep sea cores our correlated age depth relation for the vostok core should not be considered an absolute vostok timescale we consider it to be the preferred timescale for comparing vostok climate records with marine climate records which have been placed on the specmap timescale we have examined the fidelity of this common temporal framework by comparing sea surface temperature sst records from sediment cores with an antarctic temperature record from the vostok ice core we have demonstrated that when the southern ocean sst and antarctic temperature records are compared on this common temporal framework they show a high degree of similarity we interpret this result as supporting our use of the common temporal framework for comparing other climate records from the vostok ice core with any climate record that has been correlated into the specmap chronology

evaluating the accretion of meteoritic debris and interplanetary dust particles in the gpc 3 sediment core using noble gas and mineralogical tracers abstract extraterrestrial et noble gases helium and neon in 35 sediment samples from central pacific core ll 44 gpc 3 demonstrate the variable flux of interplanetary dust particles idps and major meteorite impacts over the past 70 ma 21 72 ma spinel mineralogical and chemical compositions clearly distinguish major impact events from the continuous flux of idps including the well established cretaceous tertiary k t and late eocene e o impact boundaries no spinel grains with chemical or mineralogical evidence of a distinctly et origin were found in an extensive survey of background samples i e non e o or k t boundary suggesting that either the carrier grains for et noble gas occur within the fe ti oxide mineral fraction observed in this study found to include ilmenite and ulvospinel or are too small for identification by sem the presence of ilmenite and ulvospinel suggest lunar regolith is a potential source for et noble gas rich particles noble gas analysis on both the emf extractable magnetic fraction and the bulk minus emf bulk emf show that the he and ne compositions are consistent with partially degassed noble gas signatures of zero age magnetic grains z mag and stratospheric interplanetary dust particles idps conclusive evidence for a planetary ne a noble gas signature is found only in the bulk sediments at the k t boundary although all gpc 3 k t fractions bulk emf and hf digestion plot along a mixing line between planetary ne a and solar wind sw spinels from major impact boundaries k t e o exhibit dendritic texture and elevated ni consistent with previous reports in contrast to the otherwise consistent 3he signal from idps the 3he at the known impact boundaries k t and e o actually decreases these anomalously low 3he are accompanied by significantly elevated ne and significantly lower 3he 20ne solar ratios 10 lower produced by both preferentially degassing of he relative to ne at times of increased flux of larger et material degassed degassed he enriched ne profile noble gas characteristics occur in two sample intervals that do not correspond to any known impact events 47 and 71 ma explained by an influx of larger particles sem analysis of the 47 ma sample shows spinels with dendritic textures but without distinctive markers of large meteorite impacts e g elevated ni particle size increases and degassed signatures may be caused by major bolides micrometeorites comet showers or simply a flux of larger idps potentially with a different source

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

geology of quartz and hydrated silica bearing deposits near antoniadi crater mars 1 the only area on mars where crystalline quartz has been identified from orbit is near antoniadi crater on the northern edge of the syrtis major shield volcano however the method of quartz formation has remained unknown in this study we use high resolution satellite imagery as well as thermal and near infrared spectroscopy to construct a geologic history of these deposits and their local context we find that the quartz bearing deposits are consistently co located with hydrated silica this spatial coherence suggests that the quartz formed as a diagenetic product of amorphous silica rather than as a primary igneous mineral diagenetic quartz is a mature alteration product of hydrated amorphous silica and indicates more persistent water and or higher temperatures at this site beneath the silica bearing rocks we also find spectral evidence for smectites in the lowermost exposed noachian aged breccia a similar stratigraphic sequence smectite bearing breccias beneath deposits containing minerals suggesting a greater degree of alteration has also been found at nearby exposures at nili fossae and toro crater suggesting a widespread sequence of alteration by merging the mineral detections of thermal infrared quartz feldspar and near infrared spectroscopy hydrated silica smectite clays we are able to construct a more complete geologic history from orbit

tracking eolian dust with helium and thorium impacts of grain size and provenance reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples more recently dust fluxes have been estimated from measurements of helium and thorium as rare isotopes of these elements he 3 and th 230 allow estimates of sediment flux and the dominant isotopes he 4 and th 232 are uniquely associated with the lithogenic fraction of marine sediments in order to improve the fidelity of dust flux reconstructions based on he and th we present a survey of he and th concentrations in sediments from dust source areas in east asia australia and south america our data show systematic relationships between he and th concentrations and grain size with he concentrations decreasing and th concentrations increasing with decreasing grain size we find consistent he and th concentrations in the fine fraction 5 m of samples from east asia australia and central south america puna central west argentina with th concentrations averaging 14 g g and he concentrations averaging 2 cc stp g we recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine grained and suggest that previous studies may have systematically overestimated th based dust fluxes by 30 source areas in patagonia appear to have lower he and th contents than other regions as fine fraction concentrations average 0 8 cc stp g and 9 g g for 4he and 232th respectively the impact of grain size on lithogenic he and th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably our data also have important implications for the hosts of he in long traveled dust and for the 3he 4he ratio used for terrigenous he in studies of extraterrestrial he in sediments and ice we also investigate the use of he th ratios as a provenance tracer our results suggest differences in fine fraction he th ratios between east asia australia central south america and patagonia with ratios showing a positive relationship with the geological age of source rocks he th ratios may thus provide useful provenance information for example allowing separation of patagonian sources from puna central west argentina or australian dust sources he th ratios in open ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas he th ratios in mid latitude south atlantic sediments suggest that dust in this region primarily derives from the puna central west argentina region 23 32 s rather than patagonia 38 s in the equatorial pacific he th ratios are much lower than in extratropical pacific sediments or potential source areas measured as a part of this study east asia south america australia for reasons that are at present unclear complicating their use as provenance tracers in this region

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

sediment focusing creates 100 ka cycles in interplanetary dust accumulation on the ontong java plateau the accumulation of extraterrestrial 3 he a tracer for interplanetary dust particles idps in sediments from the ontong java plateau ojp western equatorial pacific ocean has been shown previously to exhibit a regular cyclicity during the late pleistocene with a period of v100 ka those results have been interpreted to reflect periodic variability in the global accretion of idps that in turn has been linked to changes in the inclination of earth s orbit with respect to the invariable plane of the solar system here we show that the accumulation in ojp sediments of authigenic 230 th produced by radioactive decay of 234 u in seawater exhibits a 100 ka cyclicity similar in phase and amplitude to that evident in the 3 he record we interpret the similar patterns of 230 th and 3 he accumulation to reflect a common origin within the ocean climate system comparing spatial and temporal patterns of sediment accumulation against regional patterns of biological productivity and against the well established pattern of caco3 dissolution in the deep pacific ocean leads to the further conclusion that a common 100 ka cycle in accumulation of biogenic authigenic and extraterrestrial constituents in ojp sediments reflects the influence of climate related changes in sediment focusing rather than changes in the rate of production or supply of sedimentary constituents 7 2002 elsevier science b v all rights reserved

gasparite la la aso4 a new mineral from mn ores of the ushkatyn iii deposit central kazakhstan and metamorphic rocks of the wanni glacier switzerland

geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at bangombe gabon to study geochemical processes for migration and fixation of fissiogenic rare earth elements ree in association with uranium dissolution in situ isotopic analyses using an ion microprobe were performed on u and ree bearing secondary minerals such as coffinite francoisite uraniferous goethite and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at bangombe gabon phosphate minerals such as phosphatian coffinite and francoisite with depleted 235u 235u 238u 0 00609 to 0 00638 contained large amount of fissiogenic light ree while micro sized uraninite grains in a solid bitumen aggregate have normal u isotopic values 235u 238u 0 00725 and small amount of fissiogenic ree components the proportions of fissiogenic and non fissiogenic ree components in four samples from the core of bax03 vary in depth ranging from 30 cm to 130 cm beneath the reactor which suggests mixing between fissiogenic isotopes from the reactor and non fissiogenic isotopes from original minerals in the sandstone significant chemical fractionation was observed between ce and the other ree in the secondary minerals which shows evidence of an oxidizing atmosphere during their formation pb isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of u pb decay system due to recent geologic alteration however systematic pb isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes pb and u from the reactor in association with dolerite dyke intrusion 0 798 ga ago and the formation of the secondary minerals by mixing event between 2 05 ga old original minerals and reactor materials due to recent alteration

extraterrestrial accretion from the gisp2 ice core the rate of extraterrestrial accretion for particles in the size range 0 45 m to 20 m was determined from dust concentrates extracted from greenland ice sheet project 2 gisp2 ice core samples using instrumental neutron activation analysis inaa we determined the iridium ir content of the dust following a core specific correction for terrestrial ir and assuming a chondritic ir abundance of 500 ppb we measure an average accretion rate for 0 45 m to 20 m particles over the entire earth of 0 22 0 11 109 g yr kton yr for 317 years of ice through the interval 6 to 20 ka this is consistent with the interplanetary dust accretion rate of 0 17 0 08 x 109 g yr that we derive from published 3he data for the gisp2 core accounting for particles that are larger and smaller than those detected by or experiment our best estimate of the total accretion rate including particle sizes up to about 4 cm in diameter is 2 5 109 g yr the uncertainty in this estimate is dominated by statistical fluctuations in the number of particles expected to end up in the ice core and not by measurement error based on monte carlo simulations we estimate the upper limit for total extraterrestrial accretion to earth of 6 25 109 g yr 95 confidence level this accretion rate is consistent with some estimates from micrometeorite concentrations in polar ice estimates from ground based radar studies and with accretion estimates of 3he bearing interplanetary dust particles assuming that 3he is correlated with particle surface area it is however lower than estimates based on platinum group element studies of marine sediments the conflict may indicate systematic errors with either the marine or the non marine samples departures from the assumed particle spectrum of grun and coauthors or time variable accretion rates with the early holocene period being characterized by low levels of accretion

laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he to earth helium isotopes have been measured in 45 putative micrometeorites in the size range 50 to 400 m that were extracted from antarctic ice forty of the antarctic micrometeorites amms are irregular in shape and display varying degrees of partial melting whereas five are spherical and thought to represent completely melted particles of the 30 50 to 100 m suspected micrometeorites only 8 released neither 3he or 4he sixteen released 3he and 4he 0 004 3 5 10 3 cm3 stp g having 3he 4he in the range 1 5 10 4 to 4 1 10 4 six particles released only 3he yielding minimum 3he 4he of 1 6 to 10 6 10 4 5 of which fall in the range of values for amms that had measurable 3he and 4he only 2 of the 15 100 to 400 m amms released measurable 4he 4 44 10 7 cc g 1 these have 3he 4he of 6 10 4 and 20 10 4 respectively significantly higher than the majority of the ratios of 50 to 100 m amms implanted solar energetic particles are the dominant source of he in the 50 to 100 m amms with small contributions of solar wind and or spallogenic he present in 10 particles the absence of sw he is likely due to the loss of the outermost layers of the micrometeorites by ablation during atmospheric entry and abrasion during residence in ice and sampling spallation he is most important in the 100 to 400 m amms consistent with their smaller surface area to volume ratio maximum spallation 3he exposure ages of six particles are close to that predicted from poynting robertson spiral in times of asteroidal micrometeorites the two terrestrial particles identified by chemical composition and mineralogy released only 4he yielding radiogenic he isotope compositions an inverse relationship between particle sizes and solar he abundance is explained by he loss during entry helium loss is likely controlled by phyllosilicate breakdown where present and diffusion controlled bubble growth and rupture rather than melting the 50 to 100 m micrometeorites deliver 8 10 8 cm3 stp 3he g to earth this is more than 100 times less than transported by 20 m particles 2 10 5 cm3 stp 3he g but because 50 to 100 m micrometeorites deliver approximately 20 times more extraterrestrial matter to earth than 20 m particles the larger particles may contribute 5 of the total flux of extraterrestrial 3he to terrestrial sediments the mean he concentrations of the 50 to 100 m amms antarctic micrometeorites and the five spherules 2 1 10 9 cm3 stp 3he g 1 overlap those of the magnetic fraction of deep sea sediments 0 8 68 10 9 cm3 stp g a combination of this material could provide the extraterrestrial 3he measured in ancient deep sea sediments without calling upon the survival of friable 20 m chondritic interplanetary dust particles for tens of millions of years

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

accretion of interplanetary dust in polar ice measurements of helium isotopes in particles separated from polar ice demonstrate that extraterrestrial he dominates the he flux at the gisp2 greenland and vostok antarctica ice core sites replicate measurements of late holocene ice samples yield he fluxes of 0 62 0 27 10 12 cm stp cm 2 ka 1 gisp2 and 0 77 0 25 10 12 cm stp cm 2 ka 1 vostok similar to results from marine sediments these are the first detailed measurements of he in particles from ice core samples and they demonstrate the utility of the ice core record for evaluating the temporal history of the extraterrestrial dust flux results from vostok samples from 1096 1403 m depth 75 97 ka b p are similar to the late holocene data with the exception of two highly anomalous results from 1307 m the latter probably indicate the presence of rare large or gas rich extraterrestrial particles

does interplanetary dust control 100 kyr glacial cycles the cause of the 100 kyr glacial interglacial cycles during the past 800 kyr is one of the fundamental puzzles in paleoclimatology the widely accepted milankovitch theory relating earth s climate cycles to variations in insolation caused by periodic changes in orbital parameters has difficulties to explain the predominant 100 kyr rhythm although earth s eccentricity varies with a period of 100 kyr the resulting change in insolation is too small to produce the corresponding climate cycle by direct forcing imbrie et al paleoceanography 8 1993 699 in order to solve the 100 kyr problem muller and macdonald nature 377 1995 107 science 277 1997a 215 proc nat acad sci usa 94 1997b 8329 proposed an alternative orbital but non milankovitch mechanism attributing the glacial cycles to regular variations in the accretion of interplanetary dust particles idp caused by 100 kyr cycles in the orbital inclination of the earth to test this controversial hypothesis we study the idp accumulation in deep sea sediments from a period in the early pleistocene we find apparent 41 kyr cycles but no 100 kyr periodicity in the idp accumulation rate as there is no known mechanism to produce 41 kyr cycles in idp supply from space we conclude that the 41 kyr cycles are caused by the dynamics of sediment accumulation and that changes in the idp flux do not drive the pleistocene glacial cycles r 2004 elsevier ltd all rights reserved

an analysis of open basin lake deposits on mars evidence for the nature of associated lacustrine deposits and post lacustrine modification processes abstract a large number of candidate open basin lakes low lying regions with both inlet valleys and an outlet valley have been identified and mapped on mars and are fed by valley network systems that were active near the noachian hesperian boundary the nature of processes that modified the open basin lake interiors subsequent to lacustrine activity and how frequently sedimentary deposits related to lacustrine activity remain exposed has not been extensively examined an analysis of 226 open basin lakes was undertaken to identify evidence for 1 exposed deposits of possible lacustrine origin and 2 post lacustrine activity processes that may have modified or resurfaced open basin lakes spectroscopic data from the compact reconnaissance imaging spectrometer for mars crism instrument were analyzed over identified exposed open basin lake deposits to assess the mineralogy of these deposits particular attention was paid to the possible detection of any component of aqueous alteration minerals e g phyllosilicates hydrated silica zeolites or evaporites e g carbonates sulfates chlorides associated with these exposed deposits the aim of this paper is to act as a broad survey and cataloguing of the types of lacustrine and post lacustrine deposits that are present within these 226 paleolake basins results of the morphologic classification indicate that 79 open basin lakes 35 of the population contain exposed deposits of possible lacustrine origin identified on the basis of fan delta deposits layered deposits and or exposed floor material of apparent lacustrine origin additionally all 226 open basin lakes examined appear to have been at least partially resurfaced subsequent to their formation by several processes including volcanism glacial and periglacial activity impact cratering and aeolian activity results from the analysis of crism data show that only 10 29 of the 34 deposits with crism coverage of the exposed open basin lake deposits contain positively identified aqueous alteration minerals with one deposit also containing evaporites the identified hydrated and evaporite minerals include fe mg smectite kaolinite hydrated silica and carbonate with fe mg smectite the most commonly identified mineral these results indicate that hydrated and evaporite minerals are not as commonly associated with lacustrine deposits on mars as they are on earth this suggests in situ alteration and mineral precipitation a common source of such minerals in terrestrial lakes was not a major process occurring in these paleo lacustrine systems and that the observed minerals are likely to be present as transported material within the lacustrine deposits the lack of widespread in situ alteration also suggests that either the water chemistry in these paleolake systems was not conducive to aqueous alteration and mineral precipitation or that the open basin lake systems were relatively short lived

discontinuous drainage systems formed by highland precipitation and ground water outflow in the navua valles and southwest hadriacus mons regions mars abstract the navua valles are systems of paleodrainages located north of dao vallis which empty into hellas planitia the largest impact basin on mars in this study we mapped and characterized the navua valles region s individual drainage systems including drainages along the southwestern flank of hadriacus mons and one valley network from the same source as navua valles but flowing in the opposite direction the major drainage systems share morphological characteristics common to both outflow channels and valley networks the slopes in this region are dissected by two major navua drainage systems here navua a and b and several shorter sub parallel valleys formed on the highest gradient approximately 20 m km 1 15 slopes at the lowest part of hellas basin s rim the two major drainage systems originate in the highlands and empty into the basin our mapping suggests that water in navua valles reached the basin floor in a complicated descent and included several episodes of surface ponding surface runoff infiltration subsurface flow and subsequent outflow the most prominent channel system navua a forms a repetitive sequence of deep incision into bedrock followed by a transition into broad channels in erodible materials and then into unconfined deposits this successive erosion transport deposition sequence continues to repeat along the valley s entire length forming a discontinuous pattern that is consistent with classical fluvial process models the channels cut into volcanic plains likely emplaced from the formation of tyrrhenus and hadriacus montes the dendritic source valleys of navua a originate from the rim of a highland crater while the rest of this subsystem consists of a single discontinuous channel which is consistent with a single water source zone that likely supplied water for all channels downslope these drainages may have formed as discontinuous channels revealing the potential existence of subsurface drainage pathways located within an approximately 1 5 10 5 km 2 area water transported underground emerged in segments that are either isolated or aligned downslope from each other we have identified several causes of discontinuities located the zones of potential ground water discharge and recharge and a site of localized precipitation at the headwaters of navua a

30 000 years of cosmic dust in antarctic ice polar ice provides an archive for the influx of cosmic dust here we present a high resolution glacial to interglacial record of cosmic dust using helium isotope analysis of the european project for ice coring in antarctica epica ice core drilled in dronning maud land we obtained a relatively constant 3he flux over the past 30 000 years this finding excludes 3he as a pacemaker of late pleistocene glacial cycles rather it supports 3he as a constant flux parameter in paleoclimatic studies a last glacial to holocene shift of the 4he non sea salt ca2 ratio appears to indicate a glacial to interglacial change in the terrestrial dust source

the response of excess 230th and extraterrestrial 3he to sediment redistribution at the blake ridge western north atlantic the constant flux proxies excess 230th 230thxs and extraterrestrial 3he 3heet are commonly used to calculate sedimentary mass accumulation rates and to quantify lateral advection of sediment at core sites in settings with significant lateral input or removal of sediment these calculations depend on the assumption that concentrations of 230thxs and 3heet are the same in both advected sediment and sediment falling through the water column above the core site sediment redistribution is known to fractionate grain sizes preferentially transporting fine grains though relatively few studies have examined the grain size distribution of 230thxs and 3heet presently available data indicate that both are concentrated in fine grains suggesting that fractionation during advection may bias accumulation rate and lateral advection estimates based on these proxies in this study we evaluate the behavior of 230thxs and 3heet in holocene and last glacial samples from two cores from the blake ridge a drift deposit in the western north atlantic at the end of the last glacial period both cores received large amounts of laterally transported sediment enriched in fine grained material we find that accumulation rates calculated by normalization to 230th and 3he are internally consistent despite large spatial and temporal differences in sediment advection our analyses of grain size fractions indicate that 70 of 3heet bearing grains are in the 20 m fraction with roughly equal amounts in the 4 and 4 20 m fractions 230thxs is concentrated in 4 m grains relative to 4 to 20 m grains by approximately a factor of 2 in holocene samples and by a much larger factor averaging a factor of 10 in glacial samples despite these enrichments of both constant flux proxies in fine particles the fidelity of 230th and 3he based accumulation rate estimates appears to be preserved even in settings with extreme sediment redistribution perhaps due to the cohesive behavior of fine particles in marine settings

the accretion rate of extraterrestrial 3he based on oceanic 230th flux and the relation to os isotope variation over the past 200 000 years in an indian ocean core abstract in the eastern equatorial indian ocean the flux of extraterrestrial 3 he a proxy of interplanetary dust particles idps has been relatively constant over the past 200 ka the flux is equal to 1 1 0 4 10 12 cm 3 stp cm 2 ka 1 a value obtained using the xs 230 th profiling method variations in mass accumulation rates mars derived assuming a constant extraterrestrial 3 he flux have a 40 ka periodicity similar to that observed in the 18 o derived mars this frequency is similar to that of the earth s obliquity measured 187 os 188 os ratios are less radiogenic than present day seawater 0 49 0 98 reflecting the mixing of os derived from extraterrestrial terrigenous and hydrogenous sources when coupled with he data measured on the same samples os isotope data yield important information about the terrigenous component supplied to the eastern equatorial indian ocean the amount of os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics once corrected for the extraterrestrial component of os os isotope signatures in conjunction with the 4 he concentrations suggest a supply of terrigenous material from indonesian ultramafic and himalayan crustal sources that clearly varies through time

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

microbial controls on phosphate and lanthanide distributions during granite weathering and soil formation abstract both microbial and geochemical factors control the form distribution and abundance of lanthanides during weathering and soil formation in a profile in the bemboka granodiorite from southern new south wales australia during the initial stages of weathering hydrous ce bearing lanthanide and lanthanide aluminum phosphates including rhabdophane and florencite crystallize on etched apatite surfaces throughout the profile however their fate depends greatly on their location within the profile in rocks weathered 5 6 m below the soil zone the lower profile secondary lanthanide phosphates persist long after all apatite has been dissolved however in rocks weathered within 2 m of the soil zone the upper profile secondary phosphates are dissolved and lanthanides other than ce are removed bacteria and fungal hyphae are localized on secondary phosphate surfaces suggesting that rhabdophane and florencite are solubilized in the upper profile due to organic complexation of dissolved lanthanides and or uptake of phosphate by cells in the soils defined by loss of granitic texture secondary phosphates are replaced by ce oxides lanthanides other than ce removed in solution from the upper profile precipitate as ce poor phosphates in the lower profile when the solubility product is exceeded due to high dissolved phosphate concentrations in proximity to apatite thus the upper profile is the source of lanthanides added to the lower profile in both the lower and upper weathered granite the degree to which weight based ce abundances increase with increasing weathering is consistent with ce immobility on the centimeter scale we attribute the very high weight based ce abundances up to 12 concentrations in fresh rock to extensive leaching and compaction during transformation of weathered rock to soil

the spirit rover s athena science investigation at gusev crater mars the mars exploration rover spirit and its athena science payload have been used to investigate a landing site in gusev crater gusev is hypothesized to be the site of a former lake but no clear evidence for lacustrine sedimentation has been found to date instead the dominant lithology is basalt and the dominant geologic processes are impact events and eolian transport many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration any lacustrine sediments that may exist at this location within gusev apparently have been buried by lavas that have undergone subsequent impact disruption

roughness and near surface density of mars from sharad radar echoes 1 we present a technique for estimating mars topographic roughness on horizontal scales from about 10 m to 100 m using shallow radar sharad sounding data our results offer a view of surface properties complementary to mars orbiter laser altimeter mola pulse width or baseline roughness maps and can be compared to sharad peak echo properties to infer deviations from the average near surface density latitudinal averaging of sharad derived roughness over arabia and noachis terrae shows good agreement with mola derived roughness and provides clear evidence for latitude dependent mantling deposits previously inferred from image data in northwestern gordii dorsum we find that bulk density in at least the upper few meters is significantly lower than in other units of the medusae fossae formation we observe the same behavior indicative of low near surface density in wind eroded crater fill in the southern highlands combining surface properties analysis subsurface sounding and high resolution optical images we show that the pavonis mons fan shaped deposit differs significantly from lobate debris aprons which sharad has shown to be ice cored there are no internal radar reflections from the smooth facies portion of the pavonis mons fan shaped deposit and we suggest that these deposits are either quite thin or have little dielectric i e density contrast with the underlying terrain future application of these techniques can identify other low density units across mars assist in the mapping of regional volatile rich mantling units and provide new constraints on the physical properties of the polar layered terrain

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

glacial cycles and astronomical forcing narrow spectral features in ocean sediment records offer strong evidence that the cycles of glaciation were driven by astronomical forces two million years ago the cycles match the 41 000 year period of earth s obliquity this supports the croll milankovitch theory which attributes the cycles to variations in insolation but for the past million years the spectrum is dominated by a single 100 000 year feature and is a poor match to the predictions of insolation models the spectrum can be accounted for by a theory that derives the cycles of glaciation from variations in the inclination of earth s orbital plane

constraints on the history of open basin lakes on mars from the composition and timing of volcanic resurfacing 1 abundant evidence exists for valley network related fluvial activity near the noachian hesperian transition on mars and areally significant quantities of volcanic ridged plains were emplaced during this period as well thus it is worthwhile to explore the hypothesis that lava water interaction occurred on the surface of mars at this time we analyzed the morphology physical properties composition and surface ages of thirty open basin lakes topographic lows with both an inlet valley and an outlet valley that were also resurfaced by volcanic flows hyperspectral imaging data from the compact reconnaissance imaging spectrometer for mars crism and observatoire pour la mineralogie l eau les glaces et l activite omega instruments indicate that of the 30 basins 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine high calcium pyroxene and low calcium pyroxene an olivine high calcium pyroxene mixture is the most commonly identified mineral assemblage consistent with other hesperian aged volcanic units therefore our mineralogical results for over a third of the open basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties e g surface roughness thermal inertia of the resurfaced open basin lake floors in these 30 examples however no evidence was found for lava water interaction the ages of emplacement derived through counts of superposed craters of all 30 of the open basin lake volcanic resurfacing units show that resurfacing began in the late noachian near the noachian hesperian boundary was concentrated in the hesperian and continued into the early amazonian the lack of geologic features indicative of lava water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing we conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units several of which date to the late noachian early hesperian

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

noble gas compositions of antarctic micrometeorites collected at the dome fuji station in 1996 and 1997 the noble gases he ne ar kr and xe were measured in 27 individual antarctic micrometeorites amms in the size range 60 to 250 m that were collected at the dome fuji station eleven of the amms were collected in 1996 f96 series and 16 were collected in 1997 f97 series one of the f97 amms is a totally melted spherule whereas all other particles are irregular in shape noble gases were extracted using a nd yag continuous wave laser with an output power of 2 5 3 5 w for 5 min most particles released measurable amounts of noble gases 3he 4he ratios are determined for 26 amms 0 85 9 65 10 4 solar energetic particles sep are the dominant source of helium in most amms rather than solar wind sw and cosmogenic he three samples had higher 3he 4he ratios compared to that of sw showing the presence of spallogenic 3he the ne isotopic composition of most amms resembled that of sep as in the case of helium spallogenic 21ne was detected in three samples two of which had extremely long cosmic ray exposure ages 100 ma calculated by assuming solar cosmic ray scr galactic cosmic ray gcr production these two particles may have come to earth directly from the kuiper belt most amms had negligible amounts of cosmogenic 21 ne and exposure ages of 1 ma 40ar 36ar ratios for all particles 3 9 289 were lower than that of the terrestrial atmosphere 296 indicating an extraterrestrial origin of part of the ar with a very low 40ar 36ar ratio plus some atmospheric contamination indeed 40ar 36ar ratios for the amms are higher than sw sep and q ar values which is explained by the presence of atmospheric 40ar the average 38ar 36ar ratio of 24 amms 0 194 is slightly higher than the value of atmospheric or q ar suggesting the presence of sep ar which has a relatively high 38ar 36ar ratio according to the elemental compositions of the heavy noble gases dome fuji amms can be classified into three groups chondritic eight particles air affected nine particles and solar affected eight particles the eight amms classified as chondritic preserve the heavy noble gas composition of primordial trapped component due to lack of atmospheric adsorption and solar implantation the average of 129xe 132xe ratio for the 16 amms not affected by atmospheric contamination 1 05 corresponds to the values in matrices of carbonaceous chondrites 1 04 one amm f96dk038 has high 129xe 132xe in excess of this ratio our results imply that most dome fuji amms originally had chondritic heavy noble gas compositions and carbonaceous chondrite like objects are appropriate candidate sources for most amms

oxidation state of europium in scheelite tracking fluid rock interaction in gold deposits abstract we used xanes spectroscopy to measure the oxidation state of europium in situ at near m resolution in hydrothermal scheelite from the giant archean gold deposits of kalgoorlie western australia by combining these measurements with xrf imaging it is possible to distinguish inhomogeneities in eu2 eu3 ratios that developed during mineral precipitation from the effects of subsequent hydrothermal alteration and weathering thermodynamic analysis reveals that under the conditions typical of the formation of many au deposits the eu2 eu3 ratio in the hydrothermal fluid is highly sensitive to ph the range in ph calculated from the eu2 eu3 ratios in the analyzed scheelite corresponds to a maximum in au solubility under the ore forming conditions and suggests buffering of ph by the co2 aq rich fluid the primary heterogeneity of the karlgoorlie scheelite most likely results from ph oscillating between fluid and rock buffered conditions and reflects the dynamics of the hydrothermal system

echo source discrimination in single pass airborne radar sounding data from the dry valleys antarctica implications for orbital sounding of mars the interpretation of radar sounding data from mars where significant topographic relief occurs will require echo source discrimination to avoid the misinterpretation of surface echoes as arising from the subsurface this can be accomplished through the identification of all radar returns from the surface in order to positively identify subsurface echoes we have developed general techniques for this using airborne radar data from the dry valleys of antarctica these data were collected in a single pass including taylor glacier ice covered lake bonney and an ice free area of taylor valley the pulsed radar 52 5 67 5 mhz was coherently recorded our echo discrimination techniques included a radar simulator using a digital elevation model dem to predict the location and shape of surface echoes in the radar data real and simulated echo strengths were used to calculate a signal to clutter ratio this was complemented by the cross track migration of radar echoes onto the surface these migrated echoes were superimposed on the dem and imagery in order to correlate with surface features using these techniques enabled us to identify a number of echoes in the radar data as arising from the surface and to identify subsurface echoes including a continuous reflector under the main trunk of taylor glacier and multiple reflectors beneath the terminus of taylor glacier surface based radar confirms the thickness of the glacier at three crossing points the results illustrate the importance of using complementary techniques the usefulness of a dem and the limitations of single pass radar sounding data

a climatic control on the accretion of meteoric and super chondritic iridium platinum to the antarctic ice cap meteoric smoke particles msps form through the vaporization of meteoroids and the subsequent re condensation of metallic species in the mesosphere recently iridium and platinum enrichments have been identified in greenland ice layers and attributed to the fallout of msps supplying polar latitudes with cosmic matter during the holocene however the msp fallout to antarctica during the earth s climatic history remains essentially unknown we have determined iridium and platinum in deep antarctic ice from dome c and vostok dated back to 240 kyrs bp we find high super chondritic fluxes during warm periods and low meteoric accretion during glacial times a pattern that is opposite to any known climatic variation in dust fallout to polar regions the proposed explanation of this accretion regime is a weaker polar vortex during warm periods allowing peripheral air masses enriched in volcanic iridium and platinum to penetrate inland to antarctica the msp signal emerges only during cold phases and is four times lower than in the greenland ice cap where more snow accumulates this suggests that wet deposition is an important route of cosmic material to the earth s surface

a record of the extraterrestrial 3he flux through the late cretaceous abstract late cretaceous 100 73 ma pelagic limestones were measured for helium concentration and isotopic composition to characterize the interplanetary dust flux using 3he as a tracer in the bottaccione section near gubbio italy three intervals of elevated 3he concentration were detected k1 in the campanian stage at 79 ma k2 in the santonian stage at 85 ma and k3 in the turonian stage at 91 ma all three of these episodes are associated with high 3he 4he and 3he non carbonate ratios consistent with their derivation from an enhanced extraterrestrial 3he flux rather than decreased carbonate sedimentation or dissolution while k2 is modest in magnitude and duration and thus is of limited significance k1 and k3 are each identified by a few myr interval with an 4 fold enhancement in mean 3he flux compared with pre event levels samples from odp hole 762c in the indian ocean spanning both k2 and k3 93 83 ma confirm the presence of a peak in the turonian stage suggesting that k3 is a global event the k1 and k3 3he events are similar in most respects to the two peaks previously detected in the cenozoic suggesting a similar origin these have been attributed to a major asteroid collision in the late miocene and to a shower of either comets or asteroids in the late eocene based on the age and temporal evolution of k1 we suggest that it most likely records the collision which produced the baptistina asteroid family independently dated at 80 ma the k3 event is less easily explained it is characterized by an unusually spiky and erratic temporal progression suggesting an unusual abundance of very 3he rich particles not previously seen in the sedimentary 3he record we suggest this episode arises either from a comet shower or from an asteroid shower possibly associated with dust producing lunar impacts

high geothermal gradient metamorphism during thermal subsidence the burial of a basement sequence enriched in heat producing elements during thermal subsidence following rifting produces two concomitant changes in the thermal structure of the crust firstly the burial of the enriched layer produces high geothermal gradients in the overlying sedimentary succession with the high gradients propagating down into but not through the enriched basement sequence secondly the lithospheric thickening that drives thermal subsidence reduces the heat flowing into the deeper crust from the mantle because the process of thermal subsidence promotes burial it naturally increases the depth extent of the high geothermal gradients in the upper crust potentially inducing significant temperature increases in the mid upper crust during burial the lowering of the thermal gradients in the deep crust accompanying burial severely limits the temperature changes affecting the moho potentially allowing moho cooling while the mid upper crust heats these effects can promote high geothermal gradient 40 c km metamorphism in the mid upper crust without inducing significant melting in the lower crust providing the basement heat production contributes 70 mw m 2 to the surface heat flow and that the horizontal length scale for the basement heat production anomaly is 50 km these conditions appear to be met in several australian intermediate to high temperature low pressure metamorphic terranes where the thermal causes of metamorphism have hitherto remained enigmatic one of these terrains the mt painter province in the northern flinders ranges south australia is used to illustrate some of the attributes of the model

estimation of the extraterrestrial 3 he and 20 ne fluxes on earth from he and ne systematics in marine sediments abstract sediments contain interplanetary dust particles idps carrying extraterrestrial noble gases such as 3 he which have previously been used to estimate the idp accretion flux over time and the duration of past environmental events however due to its high diffusivity he can be lost by diffusion either due to frictional heating during entry in the atmosphere or once it has been incorporated in the sediments therefore the absolute values of 3 he idp fluxes cannot be known due to its lower diffusivity ne is less likely to be lost by diffusion than he and can potentially provide an absolute idp flux value here we studied the ne and he isotopic composition of 21 sediments of different ages 3 to 38 myr 56 myr and 183 myr in order to better constrain the retention of 3 he in such deposits the samples are carbonates from 2 sites of the integrated ocean drilling program iodp which previously showed evidence of detectable extraterrestrial 3 he and from the sancerre core in the paris basin the 3 he 4 he 20 ne 22 ne and 21 ne 22 ne ratios of decarbonated residues vary respectively from 0 09 10 6 to 76 5 10 6 9 54 0 08 to 11 30 0 60 and from 0 0295 0 0001 to 0 0344 0 0003 these isotopic compositions can be explained by a mixing between two terrestrial components atmosphere and radiogenic he and nucleogenic ne present in the terrigenous fractions and an extraterrestrial component the linear relationship between 20 ne 22 ne and 3 he 22 ne ratios shows that the extraterrestrial component has a unique composition and is similar to the he and ne composition of implanted solar wind this composition is different from the individual stratospheric idps for which the ne and he isotopic compositions have been measured we suggest that this difference is due to a bias in the sampling of the individual idps previously analyzed toward the largest ones that are more likely to lose he during entry in the atmosphere our data further constrains the size of the majority of the idps to be less than 10 m in diameter in addition the constant 3 he 22 ne ratio of the extraterrestrial component present in the samples which is similar to the implanted solar wind composition suggests that no diffusive loss of 3 he occurred in the atmosphere or on the seafloor thus neglecting any non fractionating he and ne loss by weathering and or alteration of the host phases on the seafloor the extraterrestrial 3 he and 20 ne fluxes between 3 to 38 myr ago are respectively 0 2 0 1 10 12 cm 3 cm 2 kyr 1 and 0 2 0 1 10 11 cm 3 cm 2 kyr 1 during the sharp increases of the late eocene and late miocene the idp 3 he and 20 ne fluxes reach values up to five times higher

sharad soundings and surface roughness at past present and proposed landing sites on mars reflections at phoenix may be attributable to deep ground ice we use the shallow radar sharad on the mars reconnaissance orbiter to search for subsurface interfaces and characterize surface roughness at the landing sites of viking landers 1 and 2 mars pathfinder the mars exploration rovers spirit and opportunity the phoenix mars lander the mars science laboratory curiosity rover and three other sites proposed for curiosity only at the phoenix site do we find clear evidence of subsurface radar returns mapping out an interface that may be the base of ground ice at depths of 15 66 m across 2900 km2 in the depression where the lander resides at the opportunity spirit and candidate curiosity sites images and altimetry show layered materials tens to hundreds of meters thick extending tens to hundreds of kilometers laterally these scales are well within sharad s resolution limits so the lack of detections is attributable either to low density contrasts in layers of similar composition and internal structure or to signal attenuation within the shallowest layers at each site we use the radar return power to estimate surface roughness at scales of 10 100 m a measure that is important for assessing physical properties landing safety and site trafficability the strongest returns are found at the opportunity site indicating that meridiani planum is exceptionally smooth returns of moderate strength at the spirit site reflect roughness more typical of mars gale crater curiosity s ultimate destination is the smoothest of the four proposed sites we examined with holden crater eberswalde crater and mawrth vallis exhibiting progressively greater roughness