evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater 1 a single scoop of the rocknest aeolian deposit was sieved 150 m and four separate sample portions each with a mass of 50mg were delivered to individual cups inside the sample analysis at mars sam instrument by the mars science laboratory rover ss ample acquisition system the samples were analyzed separately by the sam pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes several chlorinated hydrocarbons including chloromethane dichloromethane trichloromethane a chloromethylpropene and chlorobenzene were identified by sam above background levels with abundances of 0 01 to 2 3nmol the evolution of the chloromethanes observed during pyrolysis is coincident with the increase in o2 released from the rocknest sample and the decomposition of a product of n methyl n tert butyldimethylsilyl trifluoroacetamide mtbstfa a chemical whose vapors were released from a derivatization cup inside sam the best candidate for the oxychlorine compounds in rocknest is a hydrated calcium perchlorate ca clo4 2 nh2o based on the temperature release of o2 that correlates with the release of the chlorinated hydrocarbons measured by sam although other chlorine bearing phases are being considered laboratory analog experiments suggest that the reaction of martian chlorine from perchlorate decomposition with terrestrial organic carbon from mtbstfa during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by sam chlorobenzene may be attributed to reactionsofmartian chlorine released during pyrolysiswith terrestrial benzene or toluene derived from 2 6 diphenylphenylene oxide tenax on the sam hydrocarbon trap at this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons nor do we exclude the possibility that future sam analyses will reveal the presence of organic compounds native to the martian regolith

metal accumulation rates in northwest atlantic pelagic sediments measurements of 230th 87sr86sr and twenty four metals were made on cores from the nares abyssal plain the sediment is characterized by slowly accumulating 0 3 0 7 g cm2 103 yr pelagic red clays and rapidly deposited grey clays transported by turbidity currents despite their colour differences and the enrichment of mn fe cu co ni zn v and to a lesser degree the rare earths in the red clays sr isotope evidence demonstrates that the clays have the same terrigenous origin the excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated the fluxes obtained are in the ranges 20 50 mol cm2 103 yr for mn and fe 0 1 0 4 mol cm2 103 yr for cu co ni zn v sr and ce 10 20 nmol cm2 103 yr for la and nd and 0 5 3 nmol cm2 103 yr for sm eu gd dy er and yb authigenic fluxes of y nb cr zr rb u and th were not resolvable fluxes appear to be near constant on the plain but comparison with other areas shows that they are quite variable both between and within ocean basins the chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter element comparisons and from differences in fluxes between atlantic and pacific red clays corresponding to the oceanic reactivities of the elements

the mathematics of early diagenesis from worms to waves the changes that sediments undergo after deposition are collectively known as diagenesis diagenesis is not widely recognized as a source for mathematical ideas however the myriad processes responsible for these changes lead to a wide variety of mathematical models in fact most of the classical models and methods of applied mathematics emerge naturally from quantification of diagenesis for example small scale sediment mixing by bottom dwelling animals can be described by the diffusion equation the dissolution of biogenic opal in sediments leads to sets of coupled nonlinear ordinary differential equations and modeling organisms that eat at depth in the sediment and defecate at the surface suggests the one dimensional wave equation while the effect of waves on pore waters is governed by the two or three dimensional wave equation diagenetic modeling however is not restricted to classical methods diagenetic problems of concern to modern mathematics exist in abundance these include free boundary problems that predict the depth of biological mixing or the penetration of o2 into sediments algebraic differential equations that result from the fast reversible reactions that regulate ph in pore waters inverse calculations of input functions histories and the determination of the optimum choice in a hierarchy of possible diagenetic models this review highlights and explores these topics with the hope of encouraging further modeling and analysis of diagenetic phenomena

control of manganese and iron in skagerrak sediments northeastern north sea three cores with variable physicochemical characteristics from different areas of the skagerrak northeastern north sea have been studied to understand the processes such as redox conditions caco3 bioturbation etc controlling the fe and mn abundance in sediments sequential extraction was performed to identify the partitioning patterns of these elements into sorbed and carbonate mn fe oxyhydroxide fe oxyhydroxide residual leachable and residual non leachable phases pore water fe and mn contents in the central skagerrak increase up to 100 mm depth while they reach maximum concentrations around 50 mm depth in the southern skagerrak sediments the fe redox boundary lies below the mn redox boundary whereas the latter coincides with the level of oxygen penetration extractable mn in the upper layers of the central basin sediments is 10 times higher than that present in sediments of the southern part 30 mmol kg 1 fe is present in all fractions extracted but mn occurs mainly in carbonate and fe mn oxyhydroxide phases total extractable fe is about three times less than that of total fe in all cores whereas total mn is nearly equivalent to the total extractable mn mn in sediments showed two peaks the surficial one due to precipitation of oxyhydroxides from the diagenetically upwelled and sedimented mn from overlying waters and the deeper one associated with diagenetically formed carbonate phase the substitution approach has been used to explain the presence of significant quantities of mn and fe in the carbonate phase the computed observed partition coefficients decrease with depth in general but increase with corresponding decrease in ca substantiating the ionic replacement reactions mn in the carbonate phase is negatively related to caco3 suggesting possible rhodochrosite formation evaluated observed and thermodynamic partition coefficients revealed the likelihood of siderite formation solutions to diagenetic equations showed contrasting behaviour of mn and fe in skagerrak sediments increased reduction of mn oxyhydroxides in the central parts compared to that in the southern skagerrak results in the significant enrichment rate of mn in pore water 1365 mol m 3 yr 1 in sediments of the former area large amounts of fe oxyhydroxides are reduced in southern parts compared to the skagerrak basin itself mn and fe fluxes from reducing to oxidizing zones are larger in the southern skagerrak 8 8 and 9 0 m mol m 2 yr 1 respectively than in central parts 5 3 and 4 6 m mol m 2 yr 1 respectively mn and fe also exhibit contradicting sedimentation patterns where the former has high deposition fluxes in the central skagerrak while the latter is deposited more in the southern skagerrak mn seems to be internally cycled within the skagerrak

an ams radiocarbon method to determine the emplacement time of recent deep sea turbidites abstract this paper reports the evaluation of a novel method based on accelerator mass spectrometer ams radiocarbon dating of planktonic foraminifera to evaluate the times of emplacement of recent deep sea turbidites it assumes that the standing stock of relatively large 150 m planktonic foraminifera in the bioturbated surface mixed layer of box cores represents an integration of the flux from the water column since the turbidite was emplaced and exploits the potential of the ams method to analyse the resultant small samples which can be readily separated the method is evaluated by application to three atlantic turbidites which form the present day sediment surfaces on the horseshoe madeira and tagus abyssal plains the time of emplacement of madeira abyssal plain turbidite is estimated at 1120 730 and 870 years before present each 120 140 years in three different cores the resultant weighted mean emplacement time 930 76 years before present is somewhat older than previous estimates by geochemical methods the times of emplacement for the horseshoe 240 and 140 years before present each 120 years and tagus 300 120 years before present abyssal plains are both consistent with initiation by the lisbon earthquake of 1755

laboratory studies of perchlorate phase transitions support for metastable aqueous perchlorate solutions on mars abstract perchlorate salts recently discovered on mars are known to readily absorb water vapor from the atmosphere and deliquesce into the aqueous phase at room temperature here we study the deliquescence crystalline solid to liquid transition and efflorescence liquid to crystalline solid transition of perchlorate salts at low temperatures relevant to mars a raman microscope and environmental cell were used to determine the deliquescence relative humidity drh and efflorescence relative humidity erh of naclo 4 and mg clo 4 2 as a function of temperature and hydration state we find that the deliquescence of anhydrous naclo 4 is only slightly dependent on temperature and occurs at 38 rh the drh of naclo 4 h 2 o increases with decreasing temperature from 51 at 273 k to 64 at 228 k the drh of mg clo 4 2 6h 2 o also increases with decreasing temperature from 42 at 273 k to 64 at 223 k the efflorescence of both naclo 4 and mg clo 4 2 salt solutions occurs at a lower rh than deliquescence due to the kinetic inhibition of crystallization for all temperatures studied the erh values of naclo 4 and mg clo 4 2 are 13 and 19 respectively these results indicate perchlorate salts can exist as metastable supersaturated solutions over a wide range of rh and temperature conditions summer diurnal temperature and relative humidity cycles at low latitudes on mars could allow the surface salts to be aqueous for several hours per day

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

characterization and comparison of structural and compositional features of planetary quadrilateral pyroxenes by raman spectroscopy this study reports the use of raman spectral features to characterize the structural and compositional characteristics of different types of pyroxene from rocks as might be carried out using a portable field spectrometer or by planetary on surface exploration samples studied include lunar rocks martian meteorites and terrestrial rocks the major structural types of quadrilateral pyroxene can be identified using their raman spectral pattern and peak positions values of mg mg fe ca of pyroxene in the mg fe ca quadrilateral can be determined within an accuracy of 0 1 the precision for ca mg fe ca values derived from raman data is about the same except that corrections must be made for very low ca and very high ca samples pyroxenes from basalts can be distinguished from those in plutonic equivalents from the distribution of their mg mg mg fe and wo values and this can be readily done using point counting raman measurements on unprepared rock samples the correlation of raman peak positions and spectral pattern provides criteria to distinguish pyroxenes with high proportions of non quadrilateral components from mg fe ca quadrilateral pyroxenes

mixing sedimentation rates and age dating for sediment cores abstract analytic solutions to the advection diffusion equation useful as a guide for the interpretation of mixing sedimentation rate and age dating effects in sediment cores have been derived various simplified mixing models appropriate to 14 c and 210 pb measurements have been considered the emphasis has been on a discussion of the various interrelations and dependencies among the mixing coefficient sedimentation rate and radioactive decay constant parameters in determining the 14 c and 210 pb concentrations as a function of depth porosity variations within the sediment column are also considered and the transformed advection diffusion equation including porosity effects is derived

rates of sediment reworking at the hebble site based on measurements of th 234 cs 137 and pb 210 abstract th 234 cs 137 and pb 210 measurements have been made on ten cores from the hebble site on the nova scotian continental rise th 234 mixing coefficients from hebble sediments show substantial lateral variability with values ranging from 1 to 33 cm 2 yr 1 these mixing coefficients are one to two orders of magnitude greater than values from typical continental rise and abyssal sediments because of high densities of benthic macrofauna th 234 data from hebble cores indicate that particles at the sediment water interface are mixed to depths of 1 5 cm on a 100 day time scale cs 137 and pb 210 data indicate that on time scales of 30 100 yrs surface sediments are reworked to depths ranging from 1 to 12 cm based on th 234 profiles from two hebble cores collected less than 200 m apart during consecutive years no temporal variability in mixing rate could be resolved in some hebble sediments there is good agreement between the th 234 mixing coefficient 100 day time scale and the pb 210 mixing coefficient 100 yr time scale in other hebble cores however th 234 data indicate that the pb 210 profile has not reached steady state if steady state solutions are used to model these non steady state profiles the calculated pb 210 mixing coefficient may underestimate the true mixing coefficient by as much as an order of magnitude

constraining the characteristics of tsunami waves from deformable submarine slides as a marine hazard submarine slope failures have the potential to directly destroy offshore infrastructure and if a tsunami is generated it also endangers the life of those who live and work at the coastline the hazard and risk from tsunamis generated by submarine mass failure is difficult to quantify and evaluate due to the problems to constrain the characteristics of the triggered submarine landslide which introduces unquantifiable uncertainty to hazard assessments based on numerical modelling to lower the uncertainty we present a method that determines material parameters for the slide body to constrain the generated tsunami waves our method employs the distribution of landslide run out masses and their comparison with simulations it assumes that the slide material can be approximated by bulk values during the slide motion to demonstrate our method we make use of valdes slide run out masses off the chilean coast

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

forming perchlorates on mars through plasma chemistry during dust events abstract we report experimental evidences to support a new formation mechanism multiphase redox plasma chemistry for perchlorate on mars observed during the phoenix mission whose high concentrations and high clo4 cl ratio cannot be fully interpreted by photochemistry this chemical reaction occurs between cl bearing minerals on the mars surface and free radicals generated by electrostatic discharge esd during mars dust events dust storms dust devils and grain saltation we conducted simulated esd experiments in a mars chamber with pure co2 co2 h2o g and mars simulate gas mixture at martian atmospheric pressure we directly observed 1 the instantaneous generation of atmospheric free radicals co 2 co oi hiii hii oh ari n2 and n 2 in normal glow discharge ngd detected by in situ plasma emission spectroscopy and o3 by uv and mid ir spectroscopy 2 the fast transformation of nacl to naclo3 and naclo4 detected by laser raman spectroscopy with oxychlorine enrichment at the sample surfaces confirmed by ion chromatography through two sets of experimental comparison we found that the oxidation power of esd electron is three orders of magnitude higher than that of uvc photon we scaled our experimental results to the modeled esd in mars dust events and mars surface uv radiation level and concluded that plasma chemistry occurred during mars dust events can be an additional important formation mechanism for the large amounts of perchlorates observed during various missions to mars

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

the origins of perchlorate in the martian soil perchlorate clo4 has been detected on mars but its production and distribution are unclear mechanisms requiring atmospheric chlorine are insufficient for measured concentrations we conducted studies under mars conditions using halite nacl alone soil simulants consisting of silica sio2 fe2o3 al2o3 and tio2 after 170 h irradiation samples analyzed by ion chromatography ic showed clo4 and clo3 present in all samples when sio2 was added yield increased from 2 to 42 nmol and 0 4 to 2 6 nmol respectively we attribute this to sio2 and metal oxides acting as photocatalysts generating o2 radicals from o2 which react with chloride results show clo4 and clo3 can be produced photochemically on cl minerals without atmospheric chlorine or aqueous conditions and explain high concentration of clo4 and clo4 cl ratios detected by phoenix they provide evidence that its distribution on mars is dictated by distribution of chlorine and provide insight into the oxidizing nature of the soil and its potential effects on organics

uranium series tracers of mudwave migration in the argentine basin abstract large wave like sediment structures are formed in the argentine basin where active bottom currents carry a heavy load of suspended sediments a model previously developed to explain the formation and migration of these mudwaves predicts that sediment deposition occurs on the upstream face of the wave while the downstream face experiences reduced deposition or erosion depending on the current velocity two mudwaves on the zapiola sediment drift in the argentine basin were cored to evaluate the relationship between present day currents and the migration of these particular structures 210 pb and 230 th were measured in sediments from upstream and downstream faces of each mudwave 210 pb inventories ranged from 33 to 118 dpm cm 2 among the various locations cored the general tendency is for higher inventories of 210 pb to occur on upstream faces indicating higher rates of sediment deposition there as predicted by the model over the time scale reflected by the 210 pb inventories sediments have accumulated on the downstream faces at rates at least one third to one half as high as on the upstream faces which rules out complete non deposition on the downstream faces unsupported 230 th activities of upstreamface sediments are a factor of 3 4 higher than activities of sediments on downstream faces indicating that late pleistocene sediments are being exposed by erosion on the downstream faces taken together these results suggest a situation on the downstream face of each mudwave where fresh particulate matter deposited from the water column is being worked into mixed layer sediments under conditions of net sediment erosion

bioturbation into a recently emplaced deep sea turbidite surface as revealed by210pbexcess 230thexcess and planktonic foraminifera distributions abstract this study concerns the surface of a single distal turbidite emplaced on the madeira abyssal plain a few hundred years ago the vertical and horizontal homogeneity of the unit and the low pelagic sediment accumulation rate enable a ready identification of the post emplacement signals of near surface bioturbation data have been gathered to define 210 pb excess 230 th excess and pelagic foraminifera profiles with depth these are used as constant input flux tracers and treated by models conventionally used to determine bioturbation parameters the mixed layer depths 7 11 cm bioturbation coefficients 0 08 0 18 cm 2 y 1 and inventory data 10 23 dpm cm 2 derived from the 210 pb excess data in five out of six cores are similar to those previously observed elsewhere with the same model in the deep sea under steady state sediment accumulation conditions although the mixed layer depths are similar for all three tracers the 210 pb excess bioturbation intensities are larger by a factor of 3 than those estimated from 230 th excess profiles and about an order of magnitude larger than those from the foraminifera profiles it is suggested that the conventional 210 pb excess model and those for other short lived tracers probably over estimate the intensity of biomixing of foraminifera for palaeontological and related geochemical purposes

estimates of particle flux and reworking at the deep sea floor using234th 238u disequilibrium abstract because of high specific activities of excess234th t1 2 24 1 days on suspended particles in the deep sea this nuclide is potentially an extremely sensitive indicator of particle inputs and dynamics at the seafloor measurements were made at two deep sea sites in order to examine this potential inventories of excess234th at a low current hemipelagic mud site 3990 m in the panama basin were 1 5 september 81 and 2 5 june 82 dpm cm2 the steady state fluxes to the seafloor calculated from these inventories are in rough agreement with radionuclide fluxes measured in sediment traps small scale 100m spatial variability in inventories implies biologically significant heterogeneity in particle inputs sediment from the continental rise site in the northwest atlantic 2800 m a site with higher current velocities than the panama basin had an inventory of 1 9dpm cm2 this inventory is also in rough agreement with predictions made on the basis of nearby sediment trap data particle mixing coefficients of 30cm2 yr calculated at the pacific and atlantic sites are similar to those in shallow water deposits but could reflect disturbance during handling based on210pb data from the panama basin sediment from below 6cm is mixed at a rate 10 slower than the near surface sediment to a depth of at least 20 cm agreement between234th predicted mixing rates at the panama basin site with210pb profiles and in situ experiments with glass bead tracers implies that these rates are real although the diffusion of dissolved234th into deep sea sediments complicates interpretations 234thxs distributions in bottom sediments offer a useful adjunct to sediment traps for investigation of particle dynamics near the deep sea floor

extracting olivine fo fa compositions from raman spectral peak positions the dominant feature of the olivine raman spectrum is a doublet that occurs in the spectral region of 815 825 cm 1 db1 and 838 857 cm 1 db2 these features arise from coupled symmetric and asymmetric stretching vibrational modes of the constituent sio4 tetrahedra the frequencies of both peaks show monotonic shifts following cation substitution between forsterite and fayalite we present a calibration for extracting olivine fo contents fo mg mg fe molar ratio fo0 100 from the peak positions of this doublet permitting estimates of chemical composition from raman spectra acquired in the laboratory or field as well as providing information on crystal structure distinction of polymorphs eight samples spanning the compositional range from forsterite to fayalite were used to develop the calibration equations for the db1 and db2 peaks individually and together the data indicate that the db1 peak is more reliable for calculating the compositions of fe rich olivine but that the db2 peak is better for magnesian compositions the two peak calibration overcomes the limitations of the single peak calibrations and is capable of calculating olivine compositions to within 10 fo units

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

origin sedimentary processes and depositional evolution of the agadir turbidite system central eastern atlantic the oligocene to recent agadir turbidite system occurs in the agadir basin abutting against the continental margin off south morocco central eastern atlantic this system is part of the submarine drainage system linking back to the anti and high atlas mountains through the agadir canyon and its sedimentary evolution is shown to comprise lateral shifts of canyon channel overbank and lobe deposits governed by local topography draped palaeorelief seamounts and a contourite ridge and channel avulsions in addition the turbidite system shows an overall retrogradational stacking migrating about 60 km upslope this probably reflects a decrease in gradient on the continental margin gradual basin filling and or a progressive decrease in energy and load of the sediment gravity flows that fed the system the latter change in sediment flux could result from the interplay between the progressive denudation of the source areas together with the climatic change which led to the present arid desertic conditions in the hinterland the seismic features observed with new ultra high resolution seismic tools allow the recognition of the present day sedimentary activity within the agadir turbidite system and this is related among other factors to the active seismicity of the area

spectral evidence for hydrated salts in recurring slope lineae on mars transient streaks that appear seasonally on martian slopes are consistent with brine flows but evidence of water or salts has been lacking analysis of spectral data reveals hydrated salts associated with the streaks confirming a briny origin

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

the rate of dissolution of calcium carbonate from the surface of deep ocean turbidite sediments it is known that past periods of high atmospheric carbon dioxide concentration are associated with poor carbonate preservation in the deep ocean sedimentary record bottom water can become more aggressive towards carbonate sediments during such periods to interpret the sedimentary record more exactly and to predict future atmospheric carbon dioxide levels it is necessary to know the rate of solution of carbonate for a given degree of bottom water undersaturation in parts of the atlantic ocean turbidite sedimentation mechanisms have emplaced carbonate rich material in contact with undersaturated bottom water the time of the emplacement event can be determined from natural radionuclide distributions and the degree of carbonate dissolution in this time can be measured this provides a direct measurement of dissolution rate from a natural sediment surface at a known degree of undersaturation the range of applicability of the method is explored with a mathematical model and field data from a 5430 m depth atlantic site are presented

effect of benthic mixing on the information content of deep sea stratigraphical signals benthic mixing or bioturbation affects sediments in various ways including 1 the production of trace fossils 2 mechanical and or chemical alteration of the sediment and 3 filtering or smearing stratigraphical signals1 because mixing alters both the slopes and amplitudes of any recorded events some knowledge of the process is essential for the correct interpretation of the signals in view of recent trends towards high resolution stratigraphy2 3 and signal unmixing4 6 the frequency characteristics of the benthic mixing filter must be understood to determine which types of signals can be detected after mixing analyses of ash and tektite profiles in deep sea cores from various geographical regions indicate that even signals from cores having sedimentation rates as high as 7 cm kyr 1 will show severe attenuation of frequencies higher than 0 35 cycles kyr 1 periods shorter than 2 9 kyr resulting in loss of ability to resolve closely spaced events most signals will experience much more serious high frequency attenuation however the severity of high frequency loss is directly related to sedimentation rate r 0 97 for the cores examined suggesting that this is the most important variable to take into account when considering a core for palaeoceanographic or palaeoclimatic study

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

experimental evidence for the formation of liquid saline water on mars evidence for deliquescence of perchlorate salts has been discovered in the martian polar region while possible brine flows have been observed in the equatorial region this appears to contradict the idea that bulk deliquescence is too slow to occur during the short periods of the martian diurnal cycle during which conditions are favorable for it we conduct laboratory experiments to study the formation of liquid brines at mars environmental conditions we find that when water vapor is the only source of water bulk deliquescence of perchlorates is not rapid enough to occur during the short periods of the day during which the temperature is above the salts eutectic value and the humidity is above the salts deliquescence value however when the salts are in contact with water ice liquid brine forms in minutes indicating that aqueous solutions could form temporarily where salts and ice coexist on the martian surface and in the shallow subsurface

stability of phases in the mg clo4 2 nh2o system and implications for perchlorate occurrences on mars 1 salt hydrates have been identified on the martian surface and in some instances can affect or be affected by the h2o flux between the atmosphere and regolith recently perchlorates were identified in the northern plains of mars by the phoenix lander in association with ca2 mg2 and na cations solid perchlorates are rare on earth and the stability of perchlorate phases at low temperatures and relative humidities is poorly constrained we have examined the stability of hydrated phases in the magnesium perchlorate system mg clo4 2 nh2o using thermogravimetric and controlled temperature and humidity x ray diffraction experiments from 253 to 523 k our data revealed the existence of three distinct hydrate phases and an anhydrous phase and the data suggest that the stable form on mars would be mg clo4 2 6h2o rehydration experiments on the anhydrous form at 263 k and 0 5 relative humidity rh show complete hydration to the hexahydrate after 12 h given the hygroscopic nature of this material and its resistance to dehydration we conclude that mg clo4 2 6h2o will not undergo dehydration rehydration related phase changes on diurnal or seasonal cycles on mars recent evidence suggests a more widespread distribution of perchlorate in the martian regolith than previously thought and mg clo4 2 6h2o could thus represent another potential reservoir for h2o

radionuclides as indicators of sedimentary processes in abyssal caribbean sediments li w q guinasso jr n l cole k h richardson m d johnson j w and schink d r 1985 radionuclides as indicators of sedimentary processes in abyssal caribbean sediments in d k young and m d richardson editors benthic ecology and sedimentary processes of the venezuela basin past and present mar geol 68 187 204 concentrations of 2 pb and 23 24 pu were measured in triplicate sub cores from three different sedimentary environments of the venezuela basin 239 24 pu profiles gave bioturbation rate coefficients from 500 to 900 cm ka bioturbation rate coefficients determined from 239 240pu distributions were not consistent with those derived from a two layer mixing model applied to the 2 pb concentration data a four layer mixing model established that at two of the sites mixing was most rapid from 2 to 7 cm indicating that macrofauna at these depths are more effective bioturbators these findings are discussed with reference to the animals found at each site approximately 20 of the 239 24 pu that has fallen to the surface of caribbean sea is present in the sediments excess 2 0pb inventories varied from 30 to 110 of the estimated pb in the overlying water column sediments from the hemipelagic turbidite and pelagic carbonate sites contained 121 108 and 40 of the estimated flux of 2 pb to the sea floor higher 2 pb inventories at the hemipelagic and turbidite sites could have resulted from the recent incorporation of shelf sediments rich in 21 pb alternatively high inventories may indicate that 21 pb produced in deep waters is effectively scavenged by the cycling of reduced metals near the sediment seawater interface iron and manganese are found in reduced forms near the sediment seawater interface at these sites

variability of natural and bomb produced radionuclide distributions in abyssal red clay sediments the nature of sedimentation and mixing are examined in abyssal red clay sediments from the north central pacific using three types of indicators 23 th 232th organic 14c and 137cs and 239 24 pu 23 th 232th analysed revealed that the clay sedimentation rate in three box cores collected within a 50 km radius was less than 1 0 ram 10 3 yr however analyses of the organic carbon in thin layers of sediment revealed that radiocarbon was present much deeper in the cores down to 20 cm than was expected from the 23 th 232th distribution in addition both the stratigraphy and inventory of radiocarbon was significantly different between box cores the distributions and inventories of 137cs and 239 24 pu were similar to that found for radiocarbon further illustrating the spatial variability of radionuclides in oligotrophic north pacific red clays these data suggest that bioturbational processes are important for transporting organic carbon down into the sediment column

evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater evidence for perchlorates at rocknest

statistical re analysis for size dependency in deep sea mixing using the data of ruddiman et al we tested the implicit assumption that biogenic mixing intensity dbslb within a deposit is independent of particle size a conservative friedman rank sums test and the multiple comparison test for it were used to compare the downcore dispersion of several size fractions 11 500 m of volcanic ash in three of the seven cores analyzed the null hypothesis of size independent mixing was rejected fisher s method of compounding independent probabilities forced rejection of the hypothesis of size independent mixing overall p 0 001 i e when all the data for the seven cores were considered together mixing is size dependent with finer fractions being more intensely mixed the likely cause is size selective feeding by infauna the importance of the observed differences in stratigraphy among size fractions must be evaluated against the resolution required to address the problem at hand

fine scale distributions of porosity and particulate excess210pb organic carbon and caco3 in surface sediments of the deep equatorial pacific abstract sediment samples were recovered from the central equatorial pacific ocean sectioned at 1 mm intervals and analyzed for porosity organic carbon excess210pb and caco3 steep porosity gradients were measured in the upper 1 cm of the sediment column with extremely high values observed near the sediment surface similarly particulate organic carbon contents are highest at the sediment surface decrease sharply in the upper 1 cm and are relatively constant between 1 and 5 cm caco3 values on the other hand are lowest at the sediment surface and increase to a constant value below 5 10 mm depth at the carbonate ooze sites excess210pb is present throughout the upper 5 cm of the sediments suggesting relatively rapid particle mixing rates however extremely high excess210pb activities 100 dpm g are observed at the sediment surface with sharp gradients present in the upper 1 cm which would suggest slow rates of mixing this apparent contradiction along with the major features of the caco3 and particulate organic carbon profiles can be explained by a particle selective feeding mechanism in which organic carbon excess210pb enriched particles are preferentially maintained at the sediment surface via ingestion and defecation by benthic organisms

spectroscopic study of perchlorates and other oxygen chlorides in a martian environmental chamber abstract we report a study where the molecular spectral features of nine anhydrous and hydrous oxygen chlorides were analyzed both under mars atmospheric pressure and temperature conditions in a planetary environment and analysis chamber peach and for comparison under ambient laboratory conditions the goal is to understand the effect of mars environmental conditions mainly temperature t and co 2 pressure p on their spectral features as determined by both raman and nir spectroscopy these results will be used for in situ simultaneous identification of the cl o 4 and other intermediate oxygen chloride products generated during a dynamic electrostatic discharge esd experiment we have three major findings from the first phase of this study 1 the 1 raman peak position is the most sensitive parameter for identifying the cation speciation in perchlorates e g na mg ca the hydration state of magnesium perchlorate e g mg clo 4 2 x h 2 o x 0 2 4 6 and the degree of oxidation of sodium oxygen chlorides e g naclo y y 1 2 3 4 2 1 raman peak positions of most tested hydrous and anhydrous oxygen chlorides show no detectable changes within the tested t and p ranges relevant to the environmental conditions at mars surface and shallow subsurface but water raman peaks of the hydrated salts change following t decreases 3 under the p t conditions relevant to current surface and shallow subsurface at mars mid latitude regions both mg clo 4 2 6h 2 o and ca clo 4 2 2h 2 o are stable against dehydration while naclo 4 h 2 o dehydrates with a dehydration rate that is a function of t which was quantified by in situ nir spectroscopy these results are useful for the interpretations of the data from current orbital remote sensing vis nir spectra and from future landed missions raman spectra furthermore we have designed a set of systematic esd experiments to be conducted in peach for studying the pathways and the rates of oxygen chloride generation from chloride salts as a potential mechanism to form oxygen chlorides during martian dust storm the results of the current study will be used for in situ simultaneous identification of the cl o 4 and other intermediate oxygen chloride products generated during a dynamic esd experiment

239 240pu and excess210pb inventories along the shelf and slope of the northeast u s a abstract sedimentary pu and excess 210 pb inventory data are examined from a large number of sites along the u s north atlantic shelf and slope from these data an estimate can be made of the magnitude and location of pu and 210 pb accumulation in this region a major feature of the data is a decrease in the pu and 210 pb inventories with water depth which appears to reflect a decrease in the net scavenging of these elements off shore when pu and 210 pb inventories are summed over water depths less than 4000 m in the north atlantic shelf and slope region the sediments can account for 24 8 of the expected pu and 83 15 of the expected 210 pb inputs at water depths greater than 4000 m in this region we find a greater deficiency in the measured inventories of both 210 pb and pu which cannot be accounted for in the shallower sediments this suggests that the northwest atlantic continental margin is not a major site of pu or 210 pb removal and storage when compared to atmospheric in situ and lateral inputs of these radionuclides