variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

holocene fire related alluvial fan deposition and climate in ponderosa pine and mixed conifer forests sacramento mountains new mexico usa we employed 14c dating of alluvial fan deposits in ponderosa pine and mixed conifer forests of the sacramento mountains new mexico to document holocene fires and related geomorphic impacts rapid aggradation by charcoal rich debris flows occurred in the middle holocene 5800 4200 cal yr bp indicating episodic sedimentation following severe fires fire related deposition virtually ceased 4200 cal yr bp with most fan deposits indicating slower aggradation with cumulic soil development until 1800 cal yr bp from 1800 to 500 cal yr bp fire related sedimentation increased again although not to middle holocene levels a peak in fire related sedimentation c 650 cal yr bp corresponds to widespread severe drought in the southwestern usa limited fire related sedimentation is evident from 500 to 100 cal yr bp consistent with little ice age climate and tree ring records indicating frequent low severity fires although at least one severe fire burned in this interval increased fire related sediment

curiosity at gale crater mars characterization and analysis of the rocknest sand shadow the rocknest aeolian deposit is similar to aeolian features analyzed by the mars exploration rovers mers spirit and opportunity the fraction of sand 150 micrometers in size contains 55 crystalline material consistent with a basaltic heritage and 45 x ray amorphous material the amorphous component of rocknest is iron rich and silicon poor and is the host of the volatiles water oxygen sulfur dioxide carbon dioxide and chlorine detected by the sample analysis at mars instrument and of the fine grained nanophase oxide component first described from basaltic soils analyzed by mers the similarity between soils and aeolian materials analyzed at gusev crater meridiani planum and gale crater implies locally sourced globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations

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

chemistry mineralogy and grain properties at namib and high dunes bagnold dune field gale crater mars a synthesis of curiosity rover observations the mars science laboratory curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active bagnold dune field the bagnold sands are rounded to subrounded very fine to medium sized 45 500 m with 6 distinct grain colors in contrast to sands examined by curiosity in a dust covered inactive bedform called rocknest and soils at other landing sites bagnold sands are darker less red better sorted have fewer silt sized or smaller grains and show no evidence for cohesion nevertheless bagnold mineralogy and rocknest mineralogy are similar with plagioclase olivine and pyroxenes in similar proportions comprising 90 of crystalline phases along with a substantial amorphous component 35 15 yet bagnold and rocknest bulk chemistry differ bagnold sands are si enriched relative to other soils at gale crater and h 2o s and cl are lower relative to all previously measured martian soils and most gale crater rocks mg ni fe and mn are enriched in the coarse sieved fraction of bagnold sands corroborated by visible near infrared spectra that suggest enrichment of olivine collectively patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils 1 amorphous components in the sand sized fraction represented by bagnold that are si enriched hydroxylated alteration products and or h 2o or oh bearing impact or volcanic glasses and 2 amorphous components in the fine fraction 40 m represented by rocknest and other bright soils that are fe s and cl enriched with low si and adsorbed and structural h 2o

hydraulics morphology and energy dissipation in an alpine step pool channel 1 to investigate the relationship between hydraulics and channel morphology in step pool channels we combined three dimensional velocity measurements with an acoustic doppler velocimeter and topographic surveys in a steep step pool channel the rio cordon italy measurements were organized around step pool and tread units and occurred within a range of 36 57 of bankfull discharges as flow moved from steps to their downstream pools in our study reach an average of approximately two thirds of the total energy was dissipated as measured by relative head loss through step pool sequences much of this head loss was achieved by elevation potential energy loss rather than velocity reductions although an overall expected pattern of flow acceleration toward step crests and deceleration in pools was present pool velocities were high especially where upstream step crests were irregular and where residual pool depths were low many steps were porous or leaky with irregular cross channel bed and water surface topography producing high velocity jets and less flow resistance than channel spanning dammed steps longitudinal variations in hydraulics are thus often overshadowed by lateral variations arising from morphologic complexities velocity and turbulence characteristics in the rio cordon show marked differences from data we have collected in a more stable and wood rich channel in the colorado rockies in which ponded steps are more prevalent and pools are slower and more turbulent comparison of these channels illustrates that step pool structure and hydraulics are strongly influenced by flow regime sediment supply lithology time since the last step forming flood and availability of in stream wood

how do sediment yields from post wildfire debris laden flows depend on terrain slope soil burn severity class and drainage basin area insights from airborne lidar change detection we derived a high resolution spatially continuous map of erosion and deposition associated with the debris laden flows triggered by the 2011 las conchas wildfire and subsequent rainstorms over a 197 km2 area in new mexico usa this map was produced using airborne lidar derived bare earth digital elevation models dems acquired approximately one year before and one year after the wildfire differencing of the pre wildfire and post wildfire and rainstorm bare earth dems yielded a dem of difference dod map that quantifies the magnitude of ground surface elevation changes due to erosion deposition within each 1 m2 pixel we applied a 0 3 m threshold filter to our dod to remove changes that could have been due to artifacts and or imperfect georeferencing the 0 3 m value for the threshold filter was chosen based on the stated accuracy of the lidar as well as a comparison of areas of significant topographic change mapped in aerial photographs with those predicted using a range of candidate threshold values for the dod filter we developed an automated procedure that accepts the dod map as input and computes for every pixel in the dem the net sediment volume exported through each pixel by colluvial and or fluvial processes using a digital routing algorithm an analysis of the resulting sediment volume map for the las conchas fire demonstrates that sediment volume is proportional to upstream contributing area after normalized by contributing area the average sediment yield defined as the sediment volume divided by the contributing area increases as a power law functions of the average terrain slope and soil burn severity class sbsc with exponents equal to approximately 1 5 our analysis quantifies the relationships among sediment yield average terrain slope and average soil burn severity class at the watershed scale and should prove useful for predicting the geomorphic response of wildfire affected drainage basins copyright 2014 john wiley sons ltd

stability and fate of ferrihydrite during episodes of water rock interactions on early mars an experimental approach the presence on the surface of mars of ferrihydrite a nanocrystalline iron oxide species has long been suspected from spectroscopic observations and is further suggested by recent results from the mer mars exploration rovers and msl mars science laboratory robotic missions however because ferrihydrite is a metastable species in terrestrial environments it is unclear what would have been its fate during episodes of water rock interactions that are known to have occurred at the landing sites of the above mentioned robotic missions accordingly the laboratory experiments presented in this paper investigate the recrystallization of ferrihydrite under various conditions applicable to early mars these included low temperature experiments one month at 40 c at ph ranging from circum neutral to strongly acidic and high temperature experiments 8 days at 150 c at circum neutral ph the effect of mixtures with other mineral phases namely amorphous silica and olivine was also tested results obtained at low temperature are at odds with some earlier studies and suggest that ferrihydrite behaves differently in rock dominated conditions compared to water dominated conditions the co existence of amorphous silica favored the formation of jarosite under low temperature acidic conditions whereas a sample of pure ferrihydrite produced only goethite under the same conditions at high temperature ferrihydrite converted into hematite in all samples but the ferrihydrite silica mixture led to hematite with much broader diffraction peaks than other experiments indicating an inhibiting effect of dissolved silica on the recrystallization process the implications of these results for the aqueous history of early mars are discussed

a global mars dust composition refined by the alpha particle x ray spectrometer in gale crater modern martian dust is similar in composition to the global soil unit and bulk basaltic mars crust but it is enriched in s and cl the alpha particle x ray spectrometer apxs on the mars science laboratory curiosity rover analyzed air fall dust on the science observation tray o tray in gale crater to determine dust oxide compositions the o tray dust has the highest concentrations of so3 and cl measured in mars dust so3 8 3 cl 1 1 wt the molar s cl in the dust 3 35 0 34 is consistent with previous studies of martian dust and soils s cl 3 7 0 7 fe is also elevated 25 over average mars soils and the bulk crust these enrichments link air fall dust with the s cl and fe rich x ray amorphous component of gale crater soil dust and soil have the same s cl constraining the surface concentrations of s and cl on a global scale

el nino variability off peru during the last 20 000 years here we present a high resolution marine sediment record from the el nino region off the coast of peru spanning the last 20 000 years sea surface temperature photosynthetic pigments and a lithic proxy for el nino flood events on the continent are used as paleo el nino southern oscillation proxy data the onset of stronger el nino activity in peru started around 17 000 calibrated years before the present which is later than modeling experiments show but contemporaneous with the heinrich event 1 maximum el nino activity occurred during the early and late holocene especially during the second and third millennium b p the recurrence period of very strong el nino events is 60 80 years el nino events were weak before and during the beginning of the younger dryas during the middle of the holocene and during medieval times the strength of el nino flood events during the last millennium has positive and negative relationships to global and northern hemisphere temperature reconstructions

wishstone to watchtower amorphous alteration of plagioclase rich rocks in gusev crater mars previous observations by the spirit rover in gusev crater revealed a suite of rocks dubbed wishstone and watchtower class in which the parent lithology and daughter products of a distinctive style of aqueous alteration are evident results from spirit s miniature thermal emission spectrometer mini tes 2000 340 cm 1 were compromised by dust contamination of one of the instrument s mirrors for which a correction has since been developed now we have documented nearly 200 examples of rocks encompassing the span of alteration from wishstone class which spectrally resemble minimally altered plagioclase phyric basalt to the most altered watchtower class among them is a rock dubbed bruce that may be a previously unrecognized alteration spectral end member we employed factor analysis target transformation and linear least squares modeling to investigate the spectral characteristics and mineralogy of these rocks our results amplify those of a prior preliminary analysis showing that alteration produced a material resembling basaltic glass that masks the spectral features of plagioclase the association of this amorphous silicate component with a ferric iron nanophase oxide phase identified via spirit s mossbauer spectrometer is now clearly shown by our data further characterizing the distinctive mineralogic expression of the alteration these components and the absence of any recognizable secondary silicates or opaline silica may be an expression of alteration in the extreme aridity and cold of the martian environment similar mineralogic characteristics of soil measured with the chemin x ray diffraction instrument on the curiosity rover in gale crater may be an indication that this alteration process is widespread on mars

calcium sulfate veins characterized by chemcam curiosity at gale crater mars the curiosity rover has analyzed abundant light toned fracture fill material within the yellowknife bay sedimentary deposits the chemcam instrument coupled with mastcam and chemcam remote micro imager images was able to demonstrate that these fracture fills consist of calcium sulfate veins many of which appear to be hydrated at a level expected for gypsum and bassanite anhydrite is locally present and is found in a location characterized by a nodular texture an intricate assemblage of veins crosses the sediments which were likely formed by precipitation from fluids circulating through fractures the presence of veins throughout the entire similar to 5 m thick yellowknife bay sediments suggests that this process occurred well after sedimentation and cementation lithification of those sediments the sulfur rich fluids may have originated in previously precipitated sulfate rich layers either before the deposition of the sheepbed mudstones or from unrelated units such as the sulfates at the base of mount sharp the occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions

a comparison and integration of tree ring and alluvial records of fire history at the missionary ridge fire durango colorado usa we used tree ring and alluvial sediment methods to reconstruct past fire regimes for a mixed conifer forest within a 1 km2 drainage basin which was severely burned by a wildfire near durango color

ferrian saponite from the santa monica mountains california u s a earth characterization as an analog for clay minerals on mars with application to yellowknife bay in gale crater ferrian saponite from the eastern santa monica mountain near griffith park los angeles california was investigated as a mineralogical analog to smectites discovered on mars by the chemin x ray diffraction instrument onboard the mars science laboratory msl rover the martian clay minerals occur in sediment of basaltic composition and have 02 l diffraction bands peaking at 4 59 a consistent with tri octahedral smectites the griffith saponite occurs in basalts as pseudomorphs after olivine and mesostasis glass and as fillings of vesicles and cracks and has 02 l diffraction bands at that same position we obtained chemical compositions by electron microprobe x ray diffraction patterns with a lab version of the chemin instrument mossbauer spectra and visible and near ir reflectance vnir spectra on several samples from that locality the griffith saponite is magnesian mg mg fe 65 70 lacks tetrahedral fe 3 and octahedral al 3 and has fe 3 fe from 64 to 93 its chemical composition is consistent with a fully tri octahedral smectite but the abundance of fe 3 gives a nominal excess charge of 1 to 2 per formula unit the excess charge is likely compensated by substitution of o 2 for oh causing distortion of octahedral sites as inferred from mossbauer spectra we hypothesize that the griffith saponite was initially deposited with all its iron as fe 2 and was oxidized later x ray diffraction shows a sharp 001 peak at 15 a 00 l peaks and a 02 l diffraction band at the same position 4 59 a and shape as those of the martian samples indicating that the martian saponite is not fully oxidized vnir spectra of the griffith saponite show distinct absorptions at 1 40 1 90 2 30 2 32 and 2 40 m arising from h 2 o and hydroxyl groups in various settings the position of the 2 31 m spectral feature varies systematically with the redox state of the octahedrally coordinated fe this correlation may permit surface oxidation state to be inferred in some cases from vnir spectra of mars obtained from orbit and in any case ferrian saponite is a viable assignment for spectral detections in the range 2 30 2 32 m

occurrence and scale of compositional heterogeneity in martian dune fields toward understanding the effects of aeolian sorting on martian sediment compositions abstract aeolian transport and hydrodynamic sorting have been proposed to be a significant influence on martian sediment bulk compositions through laboratory experiments modeling and terrestrial analogies but to date few studies have directly examined compositional grain size relationships within sediment fields on mars thus the prevalence of hydrodynamic sorting as well as the scales at which sorting is important remain poorly understood to that end we assessed the degree and occurrence of thermophysical and compositional heterogeneity for 25 dune fields within a 42 000 000 km2 area on mars among these only four exhibit spatial heterogeneity in spectral properties and composition two of these four sites show a strong positive relationship between particle size and olivine abundance the rarity of compositional heterogeneity within dune fields in our study region 5 185 e 45 n 20 s may indicate phenocryst poor source rocks alternatively sorting within individual bedforms may be present but not at the scale of the full dune field 10 20 km compositional segregation correlated with grain size due to hydrodynamic sorting has been observed by rovers at scales much smaller than themis ground resolution 100 m pixel thus these small scales might be the operable relevant ones of hydrodynamic compositional sorting prevailing most commonly in martian dune fields

a two step k ar experiment on mars dating the diagenetic formation of jarosite from amazonian groundwaters following k ar dating of a mudstone and a sandstone a third sample has been dated by the curiosity rover exploring gale crater the mojave 2 mudstone which contains relatively abundant jarosite yielded a young k ar bulk age of 2 57 0 39 ga 1 precision a two step heating experiment was implemented in an effort to resolve the k ar ages of primary and secondary mineralogical components within the sample this technique involves measurement of 40 ar released in low temperature 500 c and high temperature 930 c steps and a model of the potassium distribution within the mineralogical components of the sample using this method the high temperature step yields a k ar model age of 4 07 0 63 ga associated with detrital plagioclase compatible with the age obtained on the cumberland mudstone by curiosity the low temperature step associated with jarosite mixed with k bearing evaporites and or phyllosilicates gave a youthful k ar model age of 2 12 0 36 ga the interpretation of this result is complicated by the potential for argon loss after mineral formation comparison with the results on cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials correcting for plausible extents of argon loss is still less than 3 ga suggesting post 3 ga aqueous processes occurred in the sediments in gale crater such a result is inconsistent with k bearing mineral formation in gale lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on mars is thought to have largely ceased

constraining ancient magmatic evolution on mars using crystal chemistry of detrital igneous minerals in the sedimentary bradbury group gale crater mars

jet and hydraulic jump near bed stresses below a horseshoe waterfall 1 horseshoe waterfalls are a common but unexplained feature of bedrock rivers as a step toward understanding their geomorphology a six component force torque sensor was used to evaluate clear water scour mechanisms in a 0 91 m broad crested horseshoe waterfall built into a 2 75 m wide flume to measure longitudinal lateral and temporal profiles of the near bed spatially averaged stress vector jet impact caused moderate near bed stress downstream of the impact point the stress vector shifted into a much more forceful upthrust with peak stress beyond the boil crest instantaneous fluctuations in near bed lift exceeded drag by 5 10 times and occurred over a wider range of frequencies suggesting a larger role for particle entrainment predictions of bed stress significantly underestimated actual conditions these results show that horseshoe waterfalls have an extended region of high scour along their centerline corresponding with the three dimensional convergent dynamics associated with both jet impact and jump enhanced lift fluctuations

evidence for pacific modulated precipitation variability during the late holocene from the southwestern usa 1 the mechanisms driving late holocene drought cycles in the western united states are not well known due to the general scarcity of long term high resolution absolutely dateable proxies for precipitation in continental interiors here we show that late holocene precipitation variability in the southwestern united states has been caused by changes in the pacific ocean we present a stalagmite based annually resolved moisture record that indicates large shifts from pluvial to drought conditions alternating with periods of dampened near average precipitation over the last 3000 years significant spectral peaks at decadal scale 20 50 70 80 year frequencies likely correspond to modern frequencies of the pacific decadal oscillation or a low frequency component of the el nino southern oscillation and are dominant during episodes of large precipitation shifts overall pluvial conditions punctuated by severe droughts may have challenged the adaptive capacities of emerging agrarian communities of ancestral americans

the predominance of post wildfire erosion in the long term denudation of the valles caldera new mexico nsf ear 0724958 ear 1331408 valles caldera national preserve gsa graduate student research grant

redox stratification of an ancient lake in gale crater mars introduction the primary goal of nasa s curiosity rover mission is to explore and quantitatively assess a local region on mars surface as a potential habitat for past or present life a necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient mars gale crater was selected as the landing site for curiosity it hosts a 5 km tall mountain of layered sedimentary rock the rocks of mount sharp preserve a long duration record of martian environmental conditions geological reconstructions from curiosity rover data have revealed an ancient habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater rationale we seek to constrain the chemical environment within the lake in gale crater as well as short and long term climate variations in and around gale crater we focus on fine grained sedimentary rocks that carry information about sediment provenance the environment of deposition the conversion of sediment to rock during burial i e lithification and the chemical conditions of later modification i e diagenesis these were investigated during the first 1300 martian solar days sols of rover operations in gale crater using bulk geochemical and mineralogical analysis techniques combined with high resolution color imagery at a variety of scales results two mudstone units have been recognized both deposited in lakes the sheepbed member of the yellowknife bay formation an older set of strata defining the base of the stratigraphic section and the murray formation of relatively younger age and positioned higher in the stratigraphic section the chemical index of alteration cia paleoclimate proxy increases by up to 10 to 20 cia units expressed in from the sheepbed member to the murray formation on the basis of mineralogy geochemistry textural properties and stratigraphic relationships the murray formation can be subdivided into two sedimentary associations or facies the hematite phyllosilicate hp facies and the magnetite silica ms facies the hp facies is characterized by abundant fe 3 oxides accompanied by phyllosilicates as well as indications of mn oxidation and trace metal concentration these properties are consistent with deposition in an oxidizing environment the ms facies is recognized by a near complete absence of pure fe 3 minerals and high concentrations of silica accompanied by magnetite consistent with deposition in an anoxic environment both facies were affected by a saline overprint after burial and lithification conclusion the observed variations in cia are consistent with modest short term fluctuations in the ancient climate between cold dry conditions and relatively warmer wetter conditions these changes occurred during the deposition of lake bed mudstones in an environment that was conducive to the presence of a long lived lake in gale crater we propose that the distinct properties of the two murray facies were developed as a result of i fractionation of river borne detritus into coarser denser materials in shallow water close to shore and finer lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake and ii redox stratification of the lake water body caused by depth dependent variations in the concentration of atmospheric oxidants and dissolved groundwater derived solutes resulting in oxidizing conditions in shallow water and anoxia in deeper water the addition of saline minerals during a later phase of brine migration through the section records longer term changes in martian climate at gale crater perhaps driven by global atmospheric escape processes the recognition of redox stratification in the lake in gale crater adds new detail to our understanding of ancient martian aquatic environments previously reported detections of organic carbon compounds nitrogen phosphate minerals and fe and s minerals in a variety of redox states combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state provide compelling evidence that all of the physical chemical and energetic conditions necessary to establish a habitable environment were present on mars between 3 8 billion and 3 1 billion years ago

vegetative and climatic controls on holocene wildfire and erosion recorded in alluvial fans of the middle fork salmon river idaho the middle fork salmon river watershed spans high elevation mixed conifer forests to lower elevation shrub steppe in recent decades runoff from severely burned hillslopes has generated large debris flows in steep tributary drainages these flows incised alluvial fans along the mainstem river where charcoal rich debris flow and sheetflood deposits preserve a record of latest pleistocene to holocene fires and geomorphic response through deposit sedimentology and 14c dating of charcoal we evaluate the processes and timing of fire related sedimentation and the role of climate and vegetation change fire related deposits compose 66 of the total measured fan deposit thickness in more densely forested upper basins versus 33 in shrub steppe dominated lower basins fires during the middle holocene 8000 5000 cal yr bp mostly resulted in sheetflood deposition similar to modern events in lower basins decreased vegetation density during this generally warmer and drier period likely resulted in lower sev

solar forcing of holocene climate new insights from a speleothem record southwestern united states holocene climate change has likely had a profound infl uence on ecosystems and culture a link between solar forcing and holocene climate such as the asian monsoon has been shown for some regions although no mechanism for this relationship has been suggested here we present the fi rst high resolution complete holocene climate record for the north american monsoon region of the southwestern united states southwest in order to address the nature and causes of holocene climate change we show that periods of increased solar radiation correlate with decreased rainfall the opposite to that observed in the asian monsoon and suggest that a solar link to holocene climate is through changes in the walker circulation and the pacifi c decadal oscillation and el nino southern oscillation systems of the tropical pacifi c ocean given the link between increased warming and aridity in the southwest additional warming due to greenhouse forcing could potentially lead to persistent hyperarid conditions similar to those seen in our record during periods of high solar activity

the origin and implications of clay minerals from yellowknife bay gale crater mars the mars science laboratory msl rover curiosity has documented a section of fluvio lacustrine strata at yellowknife bay ykb an embayment on the floor of gale crater approximately 500 m east of the bradbury landing site x ray diffraction xrd data and evolved gas analysis ega data from the chemin and sam instruments show that two powdered mudstone samples named john klein and cumberland drilled from the sheepbed member of this succession contain up to 20 wt clay minerals a trioctahedral smectite likely a ferrian saponite is the only clay mineral phase detected in these samples smectites of the two samples exhibit different 001 spacing under the low partial pressures of h2o inside the chemin instrument relative humidity 1 smectite interlayers in john klein collapsed sometime between clay mineral formation and the time of analysis to a basal spacing of 10 a but largely remain open in the cumberland sample with a basal spacing of 13 2 a partial intercalation of cumberland smectites by metal hydroxyl groups a common process in certain pedogenic and lacustrine settings on earth is our favored explanation for these differences the relatively low abundances of olivine and enriched levels of magnetite in the sheepbed mudstone when compared with regional basalt compositions derived from orbital data suggest that clay minerals formed with magnetite in situ via aqueous alteration of olivine mass balance calculations are permissive of such a reaction moreover the sheepbed mudstone mineral assemblage is consistent with minimal inputs of detrital clay minerals from the crater walls and rim early diagenetic fabrics suggest clay mineral formation prior to lithification thermodynamic modeling indicates that the production of authigenic magnetite and saponite at surficial temperatures requires a moderate supply of oxidants allowing circum neutral ph the kinetics of olivine alteration suggest the presence of fluids for thousands to hundreds of thousands of years mineralogical evidence of the persistence of benign aqueous conditions at ykb for extended periods indicates a potentially habitable environment where life could establish itself mediated oxidation of fe 2 in olivine to fe 3 in mag

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

effect of surface roughness on runoff and erosion in a mediterranean ecosystem the role of fire mechanisms at the micro patch scale influencing runoff and erosion processes following a forest fire were investigated the study was conducted in a mediterranean mountainous region with a mean annual rainfall of 690 mm terra rossa soil and vegetation composed of a dense shrubland of pinus halepensis and quercus calliprinos simulated rainfall experiments were carried out on plots representing different intervals of time elapsed since a fire i e immediately after fire two weeks after fire one year after fire unburned plots were also used for comparison at a local scale great variability was found whereby some patches produced high runoff and sediment yields following fire while others did not the conclusion is that the main effect of fires of low to moderate intensity is to produce a mosaic like surface containing both rough patches in which there is almost no chance for runoff generation and relatively smooth patches in which fire can subsequently lead to higher runoff and erosion rates

a holocene climatic record for the sonoran desert from pollen analysis of montezuma well arizona usa abstract pollen and macrofossil analyses of a radiocarbon dated core 1125 cm long from montezuma well elev 1125 m yavapai county arizona provide a record of summer precipitation similar to that of other monsoonal regions of the world precipitation was least from 4000 to 5000 yr b p and generally was greater than today before 8400 yr b p during the early holocene moist period oak and grass pollen are abundant and the best modern analogs are within the arizona monsoon boundary so increased summer precipitation is indicated climatic parameters are estimated with the technique of best modern analogs for fossil samples temperature was highest ca 3400 and 5700 yr b p and generally was cooler than today before 6800 yr b p brief cold intervals in the holocene match periods of global cooling and of positive 14 c and 10 be anomalies

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

experimental reproduction of the martian weathering profiles argues for a dense noachian co2 atmosphere abstract on mars mineral sequences have been detected and they are composed of a top layer of al rich clay minerals then al fe rich clay minerals and a bottom layer composed of mg fe rich clay minerals by analogy with earth such sequences are interpreted as weathering profiles formed by the interaction of acidic solutions in equilibrium with the atmosphere and the parent rock thus understanding of the aqueous solution composition leading to the above mineral description allows deciphering the atmosphere composition we designed an experimental column system with three levels containing powdered basaltic rock to test the influence of different acidic fluids on the mineralogical formation five solutions were used h 2 so 4 and hcl at ph 3 in equilibrium with n 2 atmosphere pure water in equilibrium with 0 1 and 1 atmospheric pressure co 2 leading to ph values of 3 9 and 4 4 respectively and a h 2 so 4 solution at ph 3 in equilibrium with 0 1 atmospheric pressure co 2 leading to a ph value of 2 98 the results obtained show that the content of al rich clay minerals and the evolution from al al fe to fe mg rich clay minerals formed are better reproduced with an originally high pco 2 hence we suggest that acidic alteration driven by a dense co 2 atmosphere reproduced better the observed martian weathering profiles the experiments involving co 2 led to the formation of carbonates their identification by near infrared nir detection methods is challenged because even the laboratory nir spectra acquired on the experimental products show that i the absorption bands related to carbonates are very weak and ii the strongest feature at 3 95 m is beyond the crism nir range such carbonate formation is consistent with the recent carbonate detection at a planetary scale in weathering profiles which goes toward that the weathering profiles could have been formed under a dense co 2 rich atmosphere as suggested also by climatic models

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

quantifying the time scale of elevated geomorphic response following wildfires using multi temporal lidar data an example from the las conchas fire jemez mountains new mexico abstract sediment yields commonly increase following wildfires in mountainous landscapes quantifying the magnitude and duration of elevated sediment yields following wildfires is important for quantifying the relative importance of wildfire affected versus non wildfire affected erosion in the long term evolution of landscapes and for understanding the processes of post wildfire erosion in this study we use bi annual terrestrial laser scanning tls surveys conducted over a 2 yr period together with repeat airborne laser scanning als surveys conducted over a 1 yr period to estimate the dependence of sediment yield on time following the high severity las conchas fire of 2011 within two small approximately 1 3 km 2 watersheds the dependence of sediment yield on time since the wildfire was quantified using dems of difference dods of the upland watersheds to measure erosion and of the adjacent piedmonts to measure the deposition of eroded sediment over the 2 yr study period sediment volume decreased linearly with time and sediment yield decreased exponentially with time in one watershed while the other watershed showed a more complex relationship with time influenced by the specific sequence of rainstorms that impacted that watershed both watersheds had a recovery time of approximately 1 yr suggesting that vegetation regrowth and the stabilization of incised valley bottoms were primarily responsible for the decline in sediment yield versus time following the wildfire multi temporal dods of the piedmonts show how they responded to the delivery of elevated sediment yields from the upland watersheds i e by 1 incision of the proximal portion of the piedmont triggering distal deposition 2 infilling of the incised channel and avulsion and 3 incision of the distal portion creating an incised channel connecting the proximal and distal ends of the piedmont the dynamic nature of incision aggradation and channel shifting on piedmonts following wildfires has important implications for post wildfire flood hazard assessments

mineralogy provenance and diagenesis of a potassic basaltic sandstone on mars chemin x ray diffraction of the windjana sample kimberley area gale crater the windjana drill sample a sandstone of the dillinger member kimberley formation gale crater mars was analyzed by chemin x ray diffraction xrd in the msl curiosity rover from rietveld refinements of its xrd pattern windjana contains the following sanidine 21 weight or95 augite 20 magnetite 12 pigeonite olivine plagioclase amorphous and smectitic material 25 and percent levels of others including ilmenite fluorapatite and bassanite from mass balance on the alpha proton x ray spectrometer apxs chemical analysis the amorphous material is fe rich with nearly no other cations like ferrihydrite the windjana sample shows little alteration and was likely cemented by its magnetite and ferrihydrite from chemcam laser induced breakdown spectrometer libs chemical analyses windjana is representative of the dillinger and mount remarkable members of the kimberley formation libs data suggest that the kimberley sediments include at least three chemical components the most k rich targets have 5 6 k2o 1 8 times that of windjana implying a sediment component with 40 sanidine e g a trachyte a second component is rich in mafic minerals with little feldspar like a shergottite a third component is richer in plagioclase and in na2o and is likely to be basaltic the k rich sediment component is consistent with apxs and chemcam observations of k rich rocks elsewhere in gale crater the source of this sediment component was likely volcanic the presence of sediment from many igneous sources in concert with curiosity s identifications of other igneous materials e g mugearite implies that the northern rim of gale crater exposes a diverse igneous complex at least as diverse as that found in similar age terranes on earth

fire related sedimentation events on alluvial fans yellowstone national park u s a abstract we document initiation and flow processes deposit facies and geomorphic effects of forest fire related sedimentation on small alluvial fans in yellowstone national park brief intense convective storm precipitation on steep basins burned in the 1988 fires produced sedimentation events involving a variety of depositional processes on fans over the course of all documented events flows on fans progressed from higher to lower sediment concentration events were often dominated by either debris flows or relatively sediment poor streamflow processes in some events however flows ranging a over wide spectrum of sediment concentration produced significant fan deposits debris flows were generated by progressive sediment bulking involving pervasive surface runoff and rill erosion on st ep upper basin slopes followed by deep incision as flows progressed down channels debris flow deposits show a marked decline in thickness and coarse gravel content downfan often with extensive distal gravel poor facies we recognized a relatively minor percentage of noncohesive debris flow and hyperconcentrated flow facies with sorting and stratification intermediate between muddy debris flow and streamflow facies these were deposited where dilute flows bulked with coarse sediment by eroding channel alluvium or earlier deposits of the event below incised fan channels streamflows expanded as sheetfloods which prograded lower fans with distally fining deposits basins 3 km2 typically produced streamflow events on fans but sediment texture and availability on slopes and in channels are primary factors determining flow processes on fans of smaller basins burned soil surfaces provided abundant silt and clay for debris flow generation but because soil surface sediment was stripped and or compacted over time the lack of available fines resulted in dominance of streamflow processes in later events

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

encounters with an unearthly mudstone understanding the first mudstone found on mars the sheepbed mudstone forms the base of the strata examined by the curiosity rover in gale crater on mars and is the first bona fide mudstone known on another planet from images and associated data this contribution proposes a holistic interpretation of depositional regime diagenesis and burial history a lake basin probably received sediment pulses from alluvial fans bed cross sections show millimetre to centimetre scale layering due to distal pulses of fluvial sediment injections fine grained hyperpycnites fall out from river plumes and some aeolian supply diagenetic features include mineralized synaeresis cracks and millimetre scale nodules as well as stratiform cementation clay minerals were initially considered due to in situ alteration but bulk rock chemistry and mineralogy suggests that sediments were derived from variably weathered source rocks that likely contained pre existing clay minerals x ray diffraction analyses show contrasting clay mineralogy in closely spaced samples consistent with at least partial detrital supply of clay minerals a significant 30 wt amorphous component is consistent with little post depositional alteration theoretical modelling of diagenetic reactions as well as kinetic considerations suggest that the bulk of diagenetic clay mineral formation occurred comparatively late in diagenesis diagenetic features synaeresis cracks and nodules were previously thought to reflect early diagenetic gas formation but an alternative scenario of synaeresis crack formation via fabric collapse of flocculated clays appears more likely the observed diagenetic features such as solid nodules hollow nodules matrix cement and raised ridges synaeresis cracks can be explained with progressive alteration of olivine glass in conjunction with centrifugal and counter diffusion of reactive species anhydrite filled fractures in the sheepbed mudstone occurred late in diagenesis when fluid pressures built up to exceed lithostatic pressure generating fluid overpressure by burial to facilitate hydraulic fracturing suggests a burial depth of at least 1000 m for the underlying strata that supplied these fluids this article is protected by copyright all rights reserved

aspect related microclimatic influences on slope forms and processes northeastern arizona 1 climate is a major control on geomorphology yet the effects of aspect related differences in microclimate have been little studied we examined several 60 100 m deep canyons in semiarid northeastern arizona where rock type and structure are essentially constant but where field data and a high resolution digital elevation model reveal consistent morphologic and microclimatic differences between asymmetric north and south facing sideslopes cliffs account for 29 of the vertical relief of south facing slopes but only 2 5 of north facing slopes excluding cliffs south facing slopes are 1 3 steeper than north facing slopes and have significantly less weathered bedrock we monitored air surface and subsurface temperatures and soil moisture at 0 5 h intervals at four locations over 1 year south facing slopes were 1 4 5 6 c warmer and soil moisture tension at 10 cm depth averages at least 78 kpa lower drier than on north facing slopes the dominant rock type in the study area morrison formation sandstone weathers primarily by clay hydration these sandstones form disaggregated mantles where weathering exceeds erosion but also maintain steep slopes and cliffs where little weathered south facing slopes were too dry during most of the instrumented year for significant clay expansion whereas the north facing bedrock slope was moist all year cliff growth thus occurs preferentially on warmer and drier slopes where weathering is reduced small north facing cliffs typically 3 m could have formed during the holocene but cliffs up to 70 m high on southerly aspects require more time to form and likely persisted or expanded under cooler and wetter late pleistocene climates

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

silicate mineralogy of martian meteorites abstract basalts and basaltic cumulates from mars delivered to earth as meteorites carry a record of the history of that planet from accretion to initial differentiation and subsequent volcanism up to recent times we provide new microprobe data for plagioclase olivine and pyroxene from 19 of the martian meteorites that are representative of the six types of martian rocks we also provide a comprehensive wds map dataset for each sample studied collected at a common magnification for easy comparison of composition and texture the silicate data shows that plagioclase from each of the rock types shares similar trends in ca na k and that k2o na2o wt of plagioclase multiplied by the al content of the bulk rock can be used to determine whether a rock is enriched or depleted in nature olivine data show that meteorite y 980459 is a primitive melt from the martian mantle as its olivine crystals are in equilibrium with its bulk rock composition all other olivine bearing shergottites have been affected by fractional crystallization pyroxene quadrilateral compositions can be used to isolate the type of melt from which the grains crystallized and minor element concentrations in pyroxene can lend insight into parent melt compositions in a comparative planetary mineralogy context plagioclase from mars is richer in na than terrestrial and lunar plagioclase the two most important factors contributing to this are the low activity of al in martian melts and the resulting delayed nucleation of plagioclase in the crystallizing rock olivine from martian rocks shows distinct trends in ni co and cr systematics compared with olivine from earth and moon the trends are due to several factors including oxygen fugacity melt compositions and melt structures properties which show variability among the planets finally fe mn ratios in both olivine and pyroxene can be used as a fingerprint of planetary parentage where minerals show distinct planetary trends that may have been set at the time of planetary accretion although the silicate mineralogical data alone cannot support one specific model of martian magmatism over another the data does support the basic igneous reservoirs proposed for mars and may also be used to constrain some aspects of specific petrogenetic models examples include enriched and depleted reservoirs that can be identified by plagioclase k na and al composition multivalent element partitioning in olivine and pyroxene v cr elucidates oxygen fugacity conditions of the reservoirs and minor element concentrations i e cr in pyx show that proposed fractional crystallization models linking y 980459 to que 94201 will not work

temporal and spatial climatic controls on holocene fire related erosion and sedimentation jemez mountains new mexico in the jemez mountains tree ring data indicate that low severity fires characterized the 400 yr before euro american settlement and that subsequent fire suppression promoted denser forests recent severe fires and erosion over longer timescales climate change may alter fire regimes thus we used fire related alluvial deposits to assess the timing of moderate to high severity fires their geomorphic impact and relation to climate over the last 4000 yr fire related sedimentation does not clearly follow millennial scale climatic changes but probability peaks commonly correspond with severe drought e g within the interval 1700 1400 cal yr bp and ca 650 and ca 410 cal yr bp the latter episodes were preceded by prolonged wet intervals that could promote dense stands estimated recurrence intervals for fire related sedimentation are 250 400 yr climatic differences with aspect influenced holocene post fire response fire related deposits constitute 77 of fan sediments from north facing basins but only 39 of deposits from drier southerly aspects with sparser vegetation and exposed bedrock south aspects can generate runoff and sediment when unburned whereas soil mantled north aspects produce minor sediment unless severely burned recent channel incision appears unprecedented over the last 2300 yr suggesting that fuel loading and extreme drought produced an anomalously severe burn in 2002

ferric sulfates on mars a combined mission data analysis of salty soils at gusev crater and laboratory experimental investigations 1 a temporal visible near infrared vis nir spectral variation was observed from tyrone yellowish salty soils based on seven periodic pancam 13 filter observations made by the spirit rover the major change was the reduction of spectral slope from 434 nm to 753 nm based on the results from a set of systematic laboratory experiments on the stability field and phase transition pathway of typical ferric sulfates we suggest that the strong dehydration processes of ferricopiapite either through amorphization or chemical alteration could be the reasons for the spectral changes of tyrone yellowish salty soils excavated from a deep trench the change of soil property suggests that they were originally not in equilibrium with the surface atmospheric conditions that there is a relative humidity rh gradient existing in the upper few tens of centimeters depth below the surface a layer of salt rich regolith beneath the surface will change the underground temperature profile especially to keep a low temperature zone with a small temperature oscillation than diurnal cycle at surface in a salt enriched regolith layer this temperature profile will provide a relatively high rh and small rh variation and thus will facilitate the preservation of hydrous sulfates with high degree of hydration during the moderate obliquity period on mars additionally the sulfates with high degrees of hydration are excellent rh buffers in a local environment the subsurface hydrous sulfates can be the sources for high level of water equivalent hydrogen found at two large equatorial regions on mars by neutron spectrometer on mars odyssey orbiter

analyses of high iron sedimentary bedrock and diagenetic features observed with chemcam at vera rubin ridge gale crater mars calibration and characterization curiosity investigated a topographic rise named vera rubin ridge vrr in gale crater for which a distinct hematite like signature was observed from orbit however the chemcam and apxs instruments on board the rover did not record any significant iron enrichment in the bulk of the ridge compared to previous terrains for this study we have re verified chemcam iron calibration at moderate abundances and developed more accurate calibrations at high iron abundances using iron oxide mixtures in a basaltic matrix in order to complete the chemcam calibration database the high iron calibration was first applied to the analysis of dark toned diagenetic features encountered at several locations on vrr which showed that their chemical compositions are close to pure anhydrous iron oxides then we tracked iron abundances in the vrr bedrock and demonstrated that although there is no overall iron enrichment in the bulk of the ridge 21 2 1 8 wt feo t compared to underlying terrains the iron content is more variable in its upper section with areas of enhanced iron abundances in the bedrock up to 26 6 0 85 wt feo t since the observed variability in iron abundances does not conform to the stratigraphy the involvement of diagenetic fluid circulation was likely an in depth chemical study of these fe rich rocks reveals that spatial gradients in redox potential eh may have driven iron mobility and reactions that precipitated and accumulated iron oxides we hypothesize that slightly reducing fluids were probably involved in transporting ferrous iron mobile fe could have precipitated as iron oxides in more oxidizing conditions

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

constraints on abundance composition and nature of x ray amorphous components of soils and rocks at gale crater mars x ray diffraction patterns of the three samples analyzed by curiosity s chemistry and mineralogy chemin instrument during the first year of the mars science laboratory mission the rocknest sand and the john klein and cumberland drill fines both extracted from the sheepbed mudstone show evidence for a significant amorphous component of unclear origin we developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from chemin data in turn the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions all oxides 0 wt 21 22 wt for rocknest and 15 20 wt for cumberland in good agreement with estimates derived from the diffraction patterns 27 and 31 wt respectively despite obvious differences between the rocknest sand and the sheepbed mudstone the amorphous components of the two sites are chemically very similar having comparable concentrations of sio2 tio2 al2o3 cr2o3 feot cao na2o k2o and p2o5 mgo tends to be lower in rocknest although it may also be comparable between the two samples depending on the exact composition of the smectite in sheepbed the only unambiguous difference is the so3 content which is always higher in rocknest the observed similarity suggests that the two amorphous components share a common origin or formation process the individual phases possibly present within the amorphous components include volcanic or impact glass hisingerite or silica ferrihydrite amorphous sulfates or adsorbed so42 and nanophase ferric oxides

mossbauer mineralogy of rock soil and dust at meridiani planum mars opportunity s journey across sulfate rich outcrop basaltic sand and dust and hematite lag deposits additonal co authors p gutlich e kankeleit t mccoy dw mittlefehldt f renz me schmidt b zubkov sw squyres re arvidson

weathering of olivine under co2 atmosphere a martian perspective abstract recent analyses from the curiosity rover at yellowknife bay gale crater mars show sedimentary rocks deposited in a lacustrine environment and containing smectite clays thought to derive from the alteration of olivine however little is known about the weathering processes of olivine under early martian conditions and about the stability of smectite clays in particular here we present a 3 month experiment investigating the weathering of forsteritic olivine powders fo 90 under a dense co 2 atmosphere and under present day terrestrial conditions for comparison the experiment also evaluates the potential effects of hydrogen peroxide h 2 o 2 as a representation of the highly oxidizing compounds produced by photochemical reactions throughout martian history the weathered samples were characterized by means of near infrared spectroscopy nir x ray diffraction xrd transmission electron microscopy with energy dispersive x ray spectrometry tem edx mossbauer spectroscopy and thermogravimetry the results show that a mg rich smectite phase formed from the weathering of olivine under co 2 conditions although in lower abundance than under terrestrial conditions the main secondary phase formed under co 2 turns out to be a silica rich phase possibly acting as a passivating layer with a non diagnostic near infrared spectral signature the use of h 2 o 2 highlights the critical importance of both the redox conditions and fe content of the initial olivine on the nature of the secondary phases

hillslope asymmetry maps reveal widespread multi scale organization 1 hillslope asymmetry is the condition in which oppositely facing hillslopes within an area have differing average slope angles and indicates aspect related variability in hillslope evolution as such the presence orientation and magnitude of asymmetry may be a useful diagnostic for understanding process dominance we present a new method for quantifying and mapping the spatial distribution of hillslope asymmetry across large areas resulting maps for the american cordillera of the western hemisphere and the western united states reveal that hillslope asymmetry is widespread with distinct trends at continental to drainage scales spatial patterns of asymmetry correlate with latitude along the american cordillera mountain range orientation for many ranges in the western united states and elevation in the idaho batholith of the northern rocky mountains spatial organization suggests that non stochastic process driven controls cause these patterns the hillslope asymmetry metric objectively captures previously documented extents and frequencies of valley asymmetry for the gabilan mesa of the central california coast range broad scale maps of hillslope asymmetry are of interest to a wide range of disciplines as spatial patterns may reflect the influence of tectonics atmospheric circulation topoclimate geomorphology hydrology soils and ecology on landscape evolution these maps identify trends and regions of hillslope asymmetry allow possible drivers to be spatially constrained and facilitate the extrapolation of site specific results to broader regions

cool and warm season precipitation reconstructions over western new mexico precipitation over the southwestern united states exhibits distinctive seasonality and contrasting ocean atmospheric dynamics are involved in the interannual variability of cool and warm season totals tree ring chronologies based on annual ring widths of conifers in the southwestern united states are well correlated with accumulated precipitation and have previously been used to reconstruct cool season and annual precipitation totals however annual ring width chronologies cannot typically be used to derive a specific record of summer monsoon season precipitation some southwestern conifers exhibit a clear anatomical transition from the earlywood and latewood components of the annual ring and these exactly dated subannual ring components can be measured separately and used as unique proxies of cool and warm season precipitation and their associated large scale ocean atmospheric dynamics two 2139 yr long reconstructions of cool november may and early warm season july precipitation have been developed from ancient conifers and relict wood at el malpais national monument new mexico both reconstructions have been verified on independent precipitation data and reproduce the spatial correlation patterns detected in the large scale sst and 500 mb height fields using instrumental precipitation data from new mexico above

sulfur bearing phases detected by evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument suite detected so2 h2s ocs and cs2 from 450 to 800 c during evolved gas analysis ega of materials from the rocknest aeolian deposit in gale crater mars this was the first detection of evolved sulfur species from a martian surface sample during in situ ega so2 3 22 mol is consistent with the thermal decomposition of fe sulfates or ca sulfites or evolution desorption from sulfur bearing amorphous phases reactions between reduced sulfur phases such as sulfides and evolved o2 or h2o in the sam oven are another candidate so2 source h2s 41 109 nmol is consistent with interactions of h2o h2 and or hcl with reduced sulfur phases and or so2 in the sam oven ocs 1 5 nmol and cs2 0 2 1 nmol are likely derived from reactions between carbon bearing compounds and reduced sulfur sulfates and sulfites indicate some aqueous interactions although not necessarily at the rocknest site fe sulfates imply interaction with acid solutions whereas ca sulfites can form from acidic to near neutral solutions sulfides in the rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source the presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering the possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage understanding the sulfur mineralogy in rocknest materials which exhibit chemical similarities to basaltic fines analyzed elsewhere on mars can provide insight in to the origin and alteration history of martian surface materials

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

a process for fire related debris flow initiation cerro grande fire new mexico in this study we examine factors that pertain to the generation of debris flows from a basin recently burned by wildfire throughout the summer 2000 thunderstorm season we monitored rain gauges channel cross sections hillslope transects and nine sediment runoff traps deployed in a steep 0 15 km 2 basin burned by the may 2000 cerro grande fire in new mexico debris flows were triggered in the monitored basin during a rainstorm on july 16 2000 in response to a maximum 30 min rainfall intensity of 31 mm h 1 return period of approximately 2 years eleven other storms occurred before and after the july storm these storms resulted in significant runoff but did not generate debris flows the debris flows generated by the july 16 storm initiated on a broad open hillslope as levee lined rills the levees were composed of gravel and cobble sized material supported by an abundant fine grained matrix debris flow deposits were observed only on the hillslopes and in the first and second order drainages of the monitored basin no significant amounts of channel incision were measured following the passage of the debris flows indicating that most of the material in the flows originated from the hillslopes sediment runoff concentrations of between 0 23 and 0 81 kg l 1 with a mean of 0 42 kg l 1 were measured from the hillslope traps following the debris flow producing storm these concentrations however were not unique to the july 16 storm the materials entrained by the july 16 storm contained a higher proportion of silt plus clay sized materials in the 2 mm fraction than the materials collected from storms that produced comparable sediment runoff concentrations but not debris flows the difference in materials demonstrates the critical role of the availability of fine grained wood ash mantling the hillslopes in the runoff dominated generation of post wildfire debris flows the highest sediment runoff concentrations again not unique to debris flow production were produced from maximum 30 min rainfall intensities greater than 20 mm h 1

holocene flood histories in south western usa harden t macklin m g baker v r 2010 holocene flood histories in south western usa earth surface processes and landforms 35 6 707 716 sponsorship aberystwyth university university of arizona

msl apxs titanium observation tray measurements laboratory experiments and results for the rocknest fines at the curiosity field site in gale crater mars the mars science laboratory msl rover curiosity has a titanium science observation tray o tray upon which portions from drilled and scooped martian samples can be delivered for analyses by the alpha particle x ray spectrometer apxs the standard apxs calibration approach to derive elemental concentrations cannot be applied to samples on the o tray because they 1 have a nonuniform three dimensional distribution within the apxs field of view and 2 are thin 90 m to develop techniques for interpreting msl apxs o tray measurements we conducted laboratory measurements of thin particulate basalt samples on ti metal with the flight equivalent apxs unit the experiments demonstrate that relative to an infinitely thick sample increasing areal coverage of particulates on a ti metal substrate results in a proportional decrease in the ti signal and increase in the sample signal count rates for heavier elements mn and fe drop with decreasing sample thickness because the mean thickness is smaller than the apxs information depth similar effects were seen in the msl apxs o tray measurement of rocknest fines on martian solar day 95 an aliquot of material delivered to sample analysis at mars and chemistry and mineralogy the thin layer effect caused a drop in mn and fe signals which cannot be quantitatively compared to the in situ rocknest target portage because sample thickness was unknown otherwise rocknest fines on the o tray had no significant compositional differences from portage except for slight increases in s and cl

elemental geochemistry of sedimentary rocks at yellowknife bay gale crater mars sedimentary rocks examined by the curiosity rover at yellowknife bay mars were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts no evidence of chemical weathering is preserved indicating arid possibly cold paleoclimates and rapid erosion and deposition the absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature circumneutral ph rock dominated aqueous conditions analyses of diagenetic features including concretions raised ridges and fractures at high spatial resolution indicate that they are composed of iron and halogen rich components magnesium iron chlorine rich components and hydrated calcium sulfates respectively composition of a cross cutting dike like feature is consistent with sedimentary intrusion the geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of mars

chemical alteration of fine grained sedimentary rocks at gale crater abstract from sol 750 to 1550 the curiosity rover documented 100 m thick stack of fine grained sedimentary rocks making up part of the murray formation at the base of mt sharp gale crater here we use data collected by the chemcam instrument to estimate the level of chemical weathering in these sedimentary rocks both the chemical index of alteration cia and the weathering index scale wis indicate a progressive increase in alteration up section reaching values of cia of 63 and wis of 25 the increase in cia and wis values is coupled with a decrease in calcium abundance suggesting partial dissolution of ca bearing minerals clinopyroxene and plagioclase mineralogy from the chemin x ray diffraction instrument indicates a decrease in mafic minerals compared with previously analyzed strata and a significant proportion of phyllosilicates consistent with this interpretation these observations suggest that the sediments were predominantly altered in an open system before or during their emplacement contrasting with the rock dominated conditions inferred in sedimentary deposits analyzed at yellowknife bay

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

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

the little ice age in the canadian rockies abstract this paper reviews the evidence and history of glacier fluctuations during the little ice age lia in the canadian rockies episodes of synchronous glacier advance occurred in the 12th 13th early 18th and throughout the 19th centuries regional ice cover was probably greatest in the mid 19th century although in places the early 18th century advance was more extensive glaciers have lost over 25 of their area in the 20th century selective preservation of the glacier record furnishes an incomplete chronology of events through the 14th 17th centuries in contrast varve sequences provide continuous annually resolved records of sediments for at least the last millennium in some highly glacierized catchments such records have been used to infer glacier fluctuations evaluation of recent proxy climate reconstructions derived from tree rings provides independent evidence of climate fluctuations over the last millennium most regional glacier advances follow periods of reduced summer temperatures reconstructed from tree rings particularly ca 1190 1250 1280 1340 1690s and the 1800s reconstructed periods of higher precipitation at banff alberta since 1500 are 1515 1550 1585 1610 1660 1680 and the 1880s glacier advances in the early 1700s the late 1800s and in places the 1950 1970s reflect both increased precipitation and reduced summer temperatures negative glacier mass balances from 1976 to 1995 were caused by decreased winter balances the glacier fluctuation record does not contain a simple climate signal it is a complex response to several interacting factors that operate at different timescales evaluation of climate proxies over the last millennium indicates continuous variability at several superimposed timescales dominated by decade century patterns only the 19th century shows a long interval of sustained cold summers this suggests that simplistic concepts of climate over this period should be abandoned and replaced with more realistic records based on continuous proxy data series the use of the term lia should be restricted to describing a period of extended glacier cover rather than being used to define a period with specific climate conditions

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

large holocene lakes and climate change in the chihuahuan desert lake level variations preserved as beach ridges in the laguna el fresnal and laguna santa maria subbasins northern mexico record millennially spaced episodes of increased precipitation during the holocene epoch we find that the early middle and late holocene were punctuated by periods wet enough to establish large pluvial lakes in currently dry basins in the chihuahuan desert the largest dated pluvial lake covered 5650 km2 during the early holocene constructional beach ridges in these subbasins are 221 33 14c yr b p little ice age equivalent 3815 52 to 4251 59 14c yr b p early neoglacial 6110 80 to 6721 68 14c yr b p mid holocene and 8269 64 to 8456 97 14c yr b p early holocene dates that correlate with other millennially spaced wet or cold events in the northern hemisphere we attribute these wet episodes to increased precipitation cooler temperatures and reduced evaporation following southward shifts in winter storm tracks which are related to long term el nino southern oscillation variability during the holocene

athena mimos ii mossbauer spectrometer investigation 1 mossbauer spectroscopy is a powerful tool for quantitative mineralogical analysis of fe bearing materials the miniature mossbauer spectrometer mimos ii is a component of the athena science payload launched to mars in 2003 on both mars exploration rover missions the instrument has two major components 1 a rover based electronics board that contains power supplies a dedicated central processing unit memory and associated support electronics and 2 a sensor head that is mounted at the end of the instrument deployment device idd for placement of the instrument in physical contact with soil and rock the velocity transducer operates at a nominal frequency of 25 hz and is equipped with two 57co rh mossbauer sources the reference source 5 mci landed intensity reference target fe2o3 plus fe0 and pin diode detector are configured in transmission geometry and are internal to the instrument and used for its calibration the analysis mossbauer source 150 mci landed intensity irradiates martian surface materials with a beam diameter of 1 4 cm the backscatter radiation is measured by four pin diode detectors physical contact with surface materials is sensed with a switch activated contact plate the contact plate and reference target are instrumented with temperature sensors assuming 18 fe for martian surface materials experiment time is 6 12 hours during the night for quality spectra i e good counting statistics 1 2 hours is sufficient to identify and quantify the most abundant fe bearing phases data stored internal to the instrument for selectable return to earth include mossbauer and pulse height analysis spectra 512 and 256 channels respectively for each of the five detectors in up to 13 temperature intervals 65 mossbauer spectra engineering data for the velocity transducer and temperature measurements the total data volume is 150 kb the mass and power consumption are 500 g 400 g for the sensor head and 2 w respectively the scientific measurement objectives of the mossbauer investigation are to obtain for rock soil and dust 1 the mineralogical identification of iron bearing phases e g oxides silicates sulfides sulfates and carbonates 2 the quantitative measurement of the distribution of iron among these iron bearing phases e g the relative proportions of iron in olivine pyroxenes ilmenite and magnetite in a basalt 3 the quantitative measurement of the distribution of iron among its oxidation states e g fe2 fe3 and fe6 and 4 the characterization of the size distribution of magnetic particles special geologic targets of the mossbauer investigation are dust collected by the athena magnets and interior rock and soil surfaces exposed by the athena rock abrasion tool and by trenching with rover wheels

surface mineralogy of martian low albedo regions from mgs tes data implications for upper crustal evolution and surface alteration 1 mars global surveyor thermal emission spectrometer mgs tes data are used to derive the modal mineralogy of spectrally distinct martian low albedo regions and to identify spatial trends in mineralogic assemblages results from this work are consistent with the major results of previous spectroscopic studies 1 plagioclase and clinopyroxene are the dominant minerals of most southern highlands regions 2 the northern plains exhibit the lowest pyroxene abundance within martian low albedo regions and 3 the highest concentrations of high silica phase s are found in the northern plains solis planum and a few southern high latitude regions low albedo regions may be classified into four units on the basis of relative abundances of plagioclase pyroxene and high silica phase s unit distributions between 45 latitude exhibit moderate correlation with distinct provinces e g syrtis major aonium sinus defined by large scale morphology elevation and to some extent surface age suggesting that the spectral and compositional differences between these units are more strongly controlled by original bedrock mineralogy than by surface atmosphere interactions and alteration syrtis major exhibits a difference in mineralogy from the surrounding highlands suggesting a differing degree of fractional crystallization assimilation or source region composition areas with thick crust near the tharsis plateau exhibit lower abundances of olivine and greater plagioclase pyroxene ratios than surrounding highland terrains suggesting that magmas in this region may have undergone increased olivine fractionation regions where surface alteration is more likely to be the primary control on observed spectral signatures are the high latitude areas 45 where globally surfaces dominated by high silica phase s are most commonly found

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

light and variable 37 cl 35 cl ratios in rocks from gale crater mars possible signature of perchlorate cl isotope ratios measured on hcl thermally evolved from as yet unknown phases in sedimentary rocks and sand in gale crater provide unexpected insights to the martian surficial cl cycle the seven samples yield 37 cl values ranging from 1 25 to 51 5 five analyses from two samples of the sheepbed mudstone yellowknife bay study area are analytically indistinguishable with a mean 37 cl of 11 7 1 in contrast four mudstones sandstones from the kimberley and pahrump study areas also yielded indistinguishable ratios but with a mean 37 cl of 43 6 the rocknest sand deposit gave a highly uncertain 37 cl value of 7 44 these light and highly variable 37 cl values are unique among known solar system materials two endmember models are offered to account for these observations and in both perchlorate with its extreme ability to fractionate cl isotopes is critical in the first model sam is detecting hcl from an oxychlorine compound e g perchlorate produced from volcanic gas emissions by atmospheric chemical reactions similar reactions in earth s atmosphere may be responsible for the isotopically lightest known cl outside of this study in perchlorate from the atacama desert some of the gale crater 37 cl values are more negative than those in atacama perchlorate but because reaction mechanisms and associated fractionation factors are unknown it is impossible to assess whether this difference is prohibitive if the negative 37 cl signal is produced in this fashion the isotopic variability among samples could arise either from variations in the relative size of the reactant chloride and product perchlorate reservoirs or from variations in the fraction of perchlorate reduced back to chloride after deposition such reduction strongly enriches 37 cl in the residual perchlorate perchlorate reduction alone offers an alternative endmember model that can explain the observed data if sam measured hcl derived from chloride in this model isotopically normal perchlorate produced by an unspecified mechanism is reduced to chloride depending on the relative size of the reduced reservoir the integrated product chloride can vary in isotopic composition from 70 in the first increment all the way to the starting composition if the perchlorate is fully reduced thus variable degrees of perchlorate reduction can produce chloride with the appropriate 37 cl range combination of the two endmember models in which the perchlorate subject to post deposition reduction is isotopically negative from atmospheric reactions is also possible determination of the phase hosting the cl measured by sam an oxychlorine compound or chloride is critical for selecting between these models and for developing implications of the results for the mars surficial cl cycle at present it is not possible to conclusively establish which phase is responsible possibly both but limited evidence favors the conclusion that the measured cl derives mostly from an oxychlorine compound

transition from hydraulic jump to open channel flow this technical note presents the results of a laboratory study of the transition region from the end of a hydraulic jump to fully developed open channel flow the velocity profile changes from that of a wall jet to the semilogarithmic form of open channel flow in this region the bed shear stress continues to decrease rapidly to eventually become constant the intensity of flow on the centerplane decreases continuously to attain the relevant open channel value the length of this transition region was found to be approximately equal to 10 times the tailwater depth for the range of froude numbers studied which varied from 3 87 to 10 48

composition of conglomerates analyzed by the curiosity rover implications for gale crater crust and sediment sources the curiosity rover has analyzed various detrital sedimentary rocks at gale crater among which fluvial and lacustrine rocks are predominant conglomerates correspond both to the coarsest sediments analyzed and the least modified by chemical alteration enabling us to link their chemistry to that of source rocks on the gale crater rims in this study we report the results of six conglomerate targets analyzed by alpha particle x ray spectrometer and 40 analyzed by chemcam the bulk chemistry derived by both instruments suggests two distinct end members for the conglomerate compositions the first group darwin type is typical of conglomerates analyzed before sol 540 it has a felsic alkali rich composition with a na2o k2o 5 the second group kimberley type is typical of conglomerates analyzed between sols 540 and 670 in the vicinity of the kimberley waypoint it has an alkali rich potassic composition with na2o k2o 2 the variety of chemistry and igneous textures when identifiable of individual clasts suggest that each conglomerate type is a mixture of multiple source rocks conglomerate compositions are in agreement with most of the felsic alkali rich float rock compositions analyzed in the hummocky plains the average composition of conglomerates can be taken as a proxy of the average igneous crust composition at gale crater differences between the composition of conglomerates and that of finer grained detrital sediments analyzed by the rover suggest modifications by diagenetic processes especially for mg enrichments in fine grained rocks physical sorting and mixing with finer grained material of different composition

millennial and centennial scale vegetation and climate changes during the late pleistocene and holocene from northern new mexico usa abstract high resolution pollen and magnetic susceptibility ms data from a sediment core from an alpine bog 3100 m in the sangre de cristo mountains new mexico record variations in treeline elevation and in sedimentation for the last 14 ka cal yr bp strong correspondence between the paleovegetation and the ms profile suggests that both records can be used to reconstruct past climatic conditions the coldest conditions in this area occurred at the end of the late pleistocene during the pinedale glaciation and the younger dryas chron a general warming trend took place during the early holocene lasting until 5 6 ka when the warmest conditions occurred a progressive climate cooling is then observed until today millennial and centennial scale changes are also observed throughout the vegetation and ms records the higher amplitude millennial scale cold events appear to correlate with the timing and duration of episodes of enhanced sea ice drift in the north atlantic and the lower amplitude centennial scale cold events may correlate with periods of lower solar activity a solar climate connection is suggested from these records by a prominent ca 200 yr cycle in tree pollen abundance which may correlate with the 208 yr suess solar cycle this study shows an immediate response of the vegetation treeline to climate change at millennial and centennial scales probably related to variations in summer insolation and solar activity during the late pleistocene and holocene such high resolution studies are very important in order to predict future climate change and particularly in very arid areas where human activity and economies are strongly influenced by climate

effect of solution ph and chloride concentration on akaganeite precipitation implications for akaganeite formation on mars akaganeite beta feooh chloride containing fe iii hydr oxide has been recently discovered on the surface of mars by the mars science laboratory curiosity rover in yellowknife bay gale crater mars 1 and from orbit by the mars reconnaissance orbiter in robert sharp crater and antoniadi basin 2 however the mechanism and aqueous environmental conditions of akaganeite formation e g ph and chloride concentration remain unknown we have investigated formation of akaganeite through fe iii hydrolysis at variable initial ph and chloride concentrations the formed fe iii precipitates were characterized by instruments similar to instruments on mars robotic spacecraft syntheses were performed through hydrolysis of fe iii perchlorate with addition of na cloride fe cl ratio between 0 5 and 5 and at initial ph of 1 5 2 4 6 and 8 at 90degc x ray diffraction analysis revealed formation of akaganeite alone or in mixture with goethite hematite and ferrihydrite at all initial phs and fe cl ratio between 0 5 and 2 while akaganeite precipitated only at ph 1 5 and fe cl greater than2 chloride content of akaganeite was affected by initial ph and decreased from 20 60 mg g at ph 1 5 to less than 0 1 mg g at ph 8 the synthesized akaganeite samples were also characterized by mssbauer and infrared spectroscopy and volatiles were analysed by thermal and evolved gas analysis the obtained characterization data will be compared to published data from rover and orbital missions 1 3 to determine martian akaganeite composition crystallinity and formation conditions