unprecedented erosion of the upper texas coast response to accelerated sea level rise and hurricane impacts the upper texas coast is an ideal location to examine coastal response to global change over geologic and historic time here we quantify the long term sequestration for sand eroded from an island into two main sinks offshore galveston island and san luis pass tidal delta in order to compare long term and short term erosion we determine the average storm related offshore sand fl ux for the middle part of the holocene ca 5240 5040 2 cal yr b p to present to be 4200 4400 670 m 3 yr with a decrease in the offshore sand fl ux to 920 970 270 m 3 yr during the latter part of the holocene ca 2730 2610 2 cal yr b p to present the tidal delta initially formed ca 2100 1 median cal yr b p when the rate of sealevel rise slowed from 2 0 mm yr to 0 60 mm yr we calculate the sand fl ux from galveston island into san luis pass from ca 2100 1 median cal yr b p to 200 yr ago to be 4700 m 3

meso scale transfer of sand during and after storms implications for prediction of shoreline movement abstract monitoring beach volume changes of the texas coast following a major hurricane reveals the impact of storms on sand dispersal and shoreline movement at spatial and temporal scales encompassing tens of kilometers and decades beach volume histories at profile sites show the interdependence of sand exchange among adjacent sites and the spatial autocorrelation of sand movement beach volume histories also indicate periods when either longshore or cross shore transport predominate and illustrate the long term effects of coastal structures on beach mobility this study confirms that net losses of sand from updrift barriers may not be directly linked with net gains of sand on adjacent downdrift barriers instead sand dispersal within a coastal compartment may depend partly on the dynamics of shoals and temporary sand storage at the intervening tidal inlet in our study sand eroded from the updrift barrier galveston island is deposited in a terminal sand flat of the barrier whereas sand accreted to the downdrift barrier follets island is derived from the intermediate ebb tidal delta san luis pass unlike continuous sand bypassing on some microtidal wave dominated coasts sand bypassing at san luis pass is episodic event driven and inefficient and sand is not transferred directly from one barrier to the next p because storms rapidly redistribute beach sediment they can be the most important factor controlling short term

influence of a spatially complex framework geology on barrier island geomorphology abstract barrier island response and recovery to storms and island transgression with relative sea level rise can be influenced by the framework geology the influence of framework geology on barrier island geomorphology has previously been examined in areas where the framework is rhythmic alongshore or consists of an isolated paleo channel or headland the purpose of this paper is to examine the influence of framework geology on beach and dune geomorphology at padre island national seashore pais texas usa where the framework geology is variable alongshore alongshore beach and dune morphometrics and offshore bathymetric profiles were extracted from a combined topography and bathymetry digital elevation model dem using an automated approach along the 100 km study area and an electromagnetic induction emi survey was used to map the subsurface framework geology wavelet decomposition global wavelet gw and bicoherence analyses were used to test for spatial relationships between and within the extracted alongshore metrics gw trendlines demonstrate that beach and dune morphometrics are structurally controlled hotspots in wavelet coherence plots between framework geology and alongshore island morphometrics indicate that the paleo channels dissecting the island influence beach and dune morphology with large dunes found in the area directly landward of the paleochannels bicoherence analysis of alongshore beach and dune morphometrics indicates that low frequency oscillations due to framework geology interact with higher frequency oscillations with greater small scale variability in the dune line directly landward of the paleo channels these results suggest that the paleo channels of pais non linearly influence beach and dune morphology which in turn alters the response of the island to storms and sea level rise it is argued that an understanding of the framework geology is key to predicting island response to sea level rise and framework geology needs to be included in barrier island models this paper demonstrates that an irregular framework geology influences small scale coastal processes and creates interactions across scales that influence beach and dune morphology and affects barrier island response to storms and sea level rise

iron spin state and site distribution in fealo 3 bearing bridgmanite abstract dft at the gga gga u and hybrid functional levels were used to investigate thousands of different al and fe3 configurations of mgsio3 fealo3 ms fa and mgsio3 fealo3 al2o3 bridgmanite at deep mantle conditions comparison of the different functionals and atomic charge analysis suggests that gga frequently used to explain high to low spin transitions observed in several mossbauer and x ray emission spectroscopy experiments is hampered by spurious self interaction errors in the exchange correlation energy configurational boltzmann averaging shows that the b site is thermally inaccessible to fe3 at the gga u and hybrid levels and we find no evidence for a spin pairing transition in fully thermodynamically equilibrated samples of bridgmanite even at the lowermost mantle conditions the comparison of the cation radii of fe3 and mg supports a spin transition accompanied by a site exchange but the flexibility of fe o bonds to locally adapt promotes the incorporation of iron in the irregularly coordinated a site the concept of ionic radii is therefore unsuitable for analysis of spin state and site exchange in bridgmanite at these conditions consistent with previous computational work and experimental studies with glass and gel as starting material we find that ferric iron kinetically trapped at the b site undergoes a spin transition under lowermost mantle conditions in bridgmanite with mole fraction of fe 3 al a charge balancing amount of low spin fe3 will be thermodynamically stable at the b site but because bridgmanite in peridotitic and basaltic lithologies mostly has al fetotal above unity fa with high spin fe3 in the a site will be the dominant iron component the lack of a fe3 spin transition in the fa component has important implications for bridgmanite ferropericlase partitioning of iron and magnesium and the mineral physics of the lowermost mantle

kinematic constraints on glacier contributions to 21st century sea level rise on the basis of climate modeling and analogies with past conditions the potential for multimeter increases in sea level by the end of the 21st century has been proposed we consider glaciological conditions required for large sea level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable we find that a total sea level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits more plausible but still accelerated conditions lead to total sea level rise by 2100 of about 0 8 meter these roughly constrained scenarios provide a most likely starting point for refinements in sea level forecasts that include ice flow dynamics

tracking the sea level signature of the 8 2 ka cooling event new constraints from the mississippi delta 1 the ever increasing need for accurate predictions of global environmental change under greenhouse conditions has sparked immense interest in an abrupt century scale cooling around 8200 years ago with a focal point in the north atlantic and with hemispheric teleconnections despite considerable progress in the unraveling of this striking feature including a conceivable driving mechanism rapid drainage of proglacial lake agassiz ojibway and a resulting reduced strength of north atlantic thermohaline circulation several key questions remain unanswered one salient aspect concerns the total amount of freshwater released during this catastrophic event likely echoed by a near instantaneous eustatic sea level rise so far no attempts have been made to perform high resolution sea level studies that explicitly focus on this critical time interval here we present new data from the mississippi delta suggestive of abrupt sea level rise associated with the 8 2 ka event however the amount of sea level rise was likely less than 1 2 m corresponding to a meltwater volume of less than 4 3 1014 m3 values lower than estimates used by several recent studies

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

spin state of ferric iron in mgsio3 perovskite and its effect on elastic properties abstract recent studies have indicated that a significant amount of iron in mgsio 3 perovskite pv is fe 3 fe 3 fe 10 60 due to crystal chemistry effects at high pressure p and that fe 3 is more likely than fe 2 to undergo a high spin hs to low spin ls transition in pv in the mantle we have measured synchrotron mossbauer spectroscopy sms x ray emission spectroscopy xes and x ray diffraction xrd of pv with all iron in fe 3 in the laser heated diamond anvil cell to over 100 gpa fe 3 increases the anisotropy of the pv unit cell whereas fe 2 decreases it in pv synthesized above 50 gpa fe 3 enters into both the dodecahedral a and octahedral b sites approximately equally suggesting charge coupled substitution combining sms and xes we found that the ls population in the b site gradually increases with pressure up to 50 60 gpa where all fe 3 in the b site becomes ls while fe 3 in the a site remains hs to at least 136 gpa fe 3 makes pv more compressible than mg endmember below 50 gpa because of the gradual spin transition in the b site together with lattice compression the completion of the spin transition at 50 60 gpa increases bulk modulus with no associated change in density this elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with fe 3

initial results from the mini tes experiment in gusev crater from the spirit rover the miniature thermal emission spectrometer mini tes on spirit has studied the mineralogy and thermophysical properties at gusev crater undisturbed soil spectra show evidence for minor carbonates and bound water rocks are olivinerich basalts with varying degrees of dust and other coatings dark toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy 5 to 10 of 45 pyroxene 20 ca rich pyroxene and 25 pigeonite 40 sodic to intermediate plagioclase and 15 olivine forsterite 45 5 to 10 two spectrally distinct coatings are observed on rocks a possible indicator of the interaction of water rock and airfall dust diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0 5 to 3 mm in soils

paleoclimatic evidence for future ice sheet instability and rapid sea level rise sea level rise from melting of polar ice sheets is one of the largest potential threats of future climate change polar warming by the year 2100 may reach levels similar to those of 130 000 to 127 000 years ago that were associated with sea levels several meters above modern levels both the greenland ice sheet and portions of the antarctic ice sheet may be vulnerable the record of past ice sheet melting indicates that the rate of future melting and related sea level rise could be faster than widely thought

response of a vulnerable barrier island to multi year storm impacts lidar data inferred morphodynamic changes on ship island mississippi usa barrier systems around the world are experiencing accelerated sea level rise reduced sediment supply and frequent hurricane impacts however detailed quantitative field based studies concerning the response to these external forcing mechanisms are scarce particularly on the scale of entire islands the mississippi alabama barrier island chain located along the u s gulf of mexico coastline has lost land on the order of hectares per year since records began in the 1840s putting mainland coastal communities and important ecosystems at risk here we present an analysis of light detection and ranging lidar digital elevation models revealing erosional depositional patterns and geomorphologic changes around the most vulnerable of these islands ship island four lidar datasets 2004 2007 2010 and 2012 capturing the complete topography of the island and some bathymetry in the inlet and surrounding shallows to depths of up to 8 m are used to investigate subaerial and subaqueous sediment volume changes between these years the impact of hurricane katrina which produced the highest storm surge ever recorded in the united states is captured in the 2004 2007 dataset during this time sediment comparable to 1 5 times the 2004 subaerial island volume was lost from the area included in the topographic bathymetric dataset only 1 5 of this volume was recovered to this area between 2007 and 2010 the island returned to a state of sediment loss between 2010 and 2012 albeit within the error bounds while the areal extent of the islands continued to increase this study examines the impact severe storm events can have on vulnerable barrier islands it highlights the importance of utilizing 3d datasets that include both topographic and bathymetric data for morphodynamic analyses of barrier island systems

is low spin fe2 present in earth s mantle abstract recently x ray spectroscopy indicated that the low spin ls electronic configuration of fe 2 and fe 3 ions substituting in silicate perovskite of various compositions and also in magnesiowustite is stable at room temperature above pressures of 49 to 120 gpa j badro g fiquet f guyot j p rueff v v struzhkin g vanko g monaco iron partitioning in earth s mantle toward a deep lower mantle discontinuity science 300 2003 789 791 j badro j p rueff g vanko g monaco g figuet f guyot electronic transition in perovskite possible non convecting layers in the lower mantle science 305 2004 383 386 j li v v struzhkin h k mao j shu r j hemley y fei b mysen p dera v prakapenka g shen electronic spin state of iron in lower mantle perovskite proc natl acad sci 101 2004 14027 14030 j m jackson w sturhahn g shen j zhao m y hu d errandonea j d bass y fei a synchrotron mossbauer study of mg fe sio 3 perovskite up to 120 gpa am mineral 90 2005 199 205 j f lin v v struzhkin s d jacobsen m y hu p chow j kung h liu h k mao r j hemley spin transition of iron in magnesiowustite in the earth s lower mantle nature 436 2005 377 380 simple thermodynamic relationships combined with crystal field theory provide a minimum clausius clapeyron slope of 0 23 to 0 4 gpa k for the high spin hs to low spin transition of fe ions in perovskite consistent with lower mantle temperatures stabilizing the disordered hs state this computation of p t utilizes experimentally determined parameters only p and t at the transition and is supported by microstructural analysis of the change in volume and entropy considerations similarly p t min 0 18 to 0 31 gpa k for magnesiowustite high spin fe 2 should be stable in silicates throughout earth s mantle for compositions of fe mg fe 0 1 consistent with disorder prevailing at high temperature although partial conversion of octahedral fe 3 to ls may occur similarly partial conversion of octahedral fe 2 in magnesiowustite to the ls is possible for fe rich compositions which transform at relatively low pressures

a sedimentologic description of a microtidal flood tidal delta san luis pass texas abstract san luis pass is a microtidal tidal inlet located at the southwest end of galveston island texas continuous cores taken with a portable vibracoring rig and surface grab samples provide data for constructing vertical sequences and three dimensional sedimentologic descriptions of the flood tidal delta complex these descriptions are based on the type and vertical and lateral distribution of lithofacies sedimentary structures textures and trace fossils a vertical sequence through the flood tidal delta complex consists from base to top of highly bioturbated bay muds and associated oyster reefs highly bioturbated clayey sand sandy clay of the tidal delta margin burrowed sand and shelly sand of the tidal delta and rooted or burrowed mud of the marsh or mud flat washover shell hash deposits may occur at random intervals throughout this sequence a vertical sequence in the vicinity of san luis pass consists of a basal tidal inlet deposit of graded layers of sand and shell overlain by burrowed to shelly sand of the barrier spit this description of a microtidal flood tidal delta differs significantly from descriptions presented for mesotidal flood tidal delta systems in the 1 general lack of large scale high angle sedimentary s ructures 2 presence of intense bioturbation 3 presence of washover deposits and 4 general coarsening upward nature of the vertical sequence

how stable is the mississippi delta large deltas are commonly believed to exhibit rapid rates of tectonic subsidence largely due to sediment loading of the lithosphere as a result deltaic plains are prone to accelerated relative sea level rise coastal erosion and wetland loss hurricane katrina s devastation testifies to the severe threat that these processes pose to the mississippi delta but the relative role of tectonics versus other mechanisms causing land subsidence remains elusive relative sea level records derived from basal peat have the potential to quantify differential crustal movements over holocene time scales with exceptionally high accuracy and precision here we present new sea level index points from two study areas in the southwestern mississippi delta that essentially coincide with a recently published detailed relative sea level record from the eastern part of the delta our results show that differential vertical movements among the three study areas have been only 0 1 mm yr 1 w e compare our evidence with a recent sea level compilation from the caribbean to a large extent based on data from areas that are tectonically stable our sea level index points nearly coincide with the caribbean data showing surprising tectonic stability for considerable sections of the mississippi delta however the well documented high subsidence rates in and near the birdfoot of the mississippi delta indicate that different conditions prevail there the rapid wetland loss in coastal louisiana is likely due to a considerable extent to the compaction of holocene strata

effects of the fe3 spin transition on the properties of aluminous perovskite new insights for lower mantle seismic heterogeneities abstract we have measured the effects of the coupled substitution of fe3 and al on the density and compressibility of mantle silicate perovskite pv up to 95 gpa x ray emission spectroscopy and synchrotron mossbauer spectroscopy reveal a rapid increase in the population of low spin fe3 in fe3 al bearing pv over a narrow pressure range near 70 gpa which is in sharp contrast with al free fe3 bearing pv where fe3 undergoes a gradual spin transition and with al free fe2 bearing pv where fe2 does not become low spin at low pressure fe3 and al expand the perovskite lattice however near the pressure range of the abrupt increase in the low spin population the unit cell volume of fe3 al bearing pv becomes similar to that of mg endmember pv while those of al free fe3 bearing pv and al free fe2 bearing pv remain larger throughout the lower mantle consequently pv in al rich systems should have lower density in the shallow lower mantle but similar or greater density than pv in pyrolite in the deep lower mantle affecting the buoyancy and mechanical stability of heterogeneities although the fe3 spin transition in pv is unlikely to cause a seismic discontinuity at mantle temperatures it may result in a large change in bulk sound speed at 1200 1800 km depth such that a vertically extending structure with an elevated amount of fe3 would generate slower and faster anomalies above and below the depth of the spin transition respectively relative to the surrounding mantle this may have important implications for bulk sound speed anomalies observed at similar depths in seismic tomography studies

evidence of similar probablility of intense hurricane strikes for the gulf of mexico over the late holocene hurricane magnitude and frequency have been linked to numerous mechanisms including the steady rise in annual sea surface temperatures el nino southern oscillation enso variations and atmospheric changes in order to better understand those factors that control hurricane magnitude and frequency a long term record spanning the entire gulf of mexico coast is needed here we present a detailed record from ca 5300 900 yr b p of past intense hurricane impacts for cores collected from laguna madre texas united states relative storm intensities were calculated for each event and the average intense storm impact probability for south texas was determined to be 0 46 annual landfall probability previous field studies in western lake florida and lake shelby alabama reveal similar probability intense hurricane strikes of 0 39 although high frequency oscillations between warm and dry and cool and wet climate conditions have occurred in texas through the late holocene there has been no notable variation in intense storm impacts across the northwestern gulf of mexico coast during this time interval implying no direct link between these changing climate conditions and annual hurricane impact probability in addition there have been no significant differences in the landfall probabilities of storms between the eastern and western gulf of mexico during the late holocene suggesting that storm steering mechanisms have not varied during this time

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

coordinated analyses of orbital and spirit rover data to characterize surface materials on the cratered plains of gusev crater mars 1 comparison of the mars exploration rover spirit s pancam 0 4 to 1 0 m and mars express observatoire pour la mineralogie l eau les glaces et l activite omega 0 4 to 2 5 m spectral reflectance data over spirit s traverses shows that gusev cratered plains are dominated by nanophase ferric oxide rich dust covering weakly altered basaltic sands this interpretation is also consistent with both observations from omega data covering plains beyond the traverse region and interpretations of data from the other payload instruments on the spirit rover omega observations of relatively low albedo regions where dust has presumably been stripped by dust devils show negative spectral reflectance slopes from 1 5 to 2 5 m and moderately masked spectral features which are indicative of olivine or pyroxene high albedo regions north and south of the spirit landing site have flat spectral reflectance slopes and few spectral features although all spectra have a nanophase ferric oxide absorption edge between 0 4 and 0 75 m comparison of themis derived thermal inertia values with omega derived spectral parameters shows that although the dust cover can be optically thick 0 4 to 2 5 m wavelength region in some areas it is not thick enough 1 cm to mask the thermal inertia of the underlying substrate for areas included in this study

rock abundance on mars from the thermal emission spectrometer 1 nighttime infrared spectral observations returned from the mars global surveyor thermal emission spectrometer tes are well suited for determining the subpixel abundance of rocks on the surface of mars the algorithm used here determines both the areal fraction of rocky material and the thermal inertia of the fine grained nonrock component present on the surface rock is defined as any surface material that has a thermal inertia 1250 j m 2 k 1 s 1 2 this can be bedrock boulders indurated sediments or a combination of these on a surface mixed with finer grained materials over 4 9 million observations were compiled to produce the 8 pixels per degree global rock abundance and fine component inertia maps total coverage is 45 of the planet between latitudes 60 and 60 less than 1 of the planet has rock abundances greater than 50 and 7 of the mapped surface has greater than 30 rocks rocky regions on mars correspond primarily to the high inertia surfaces observed in thermal inertia data sets the fine component inertia data set is used to identify high inertia exposures that contain few rocks and more homogeneous materials

subsidence of the texas coast inferences from historical and late pleistocene sea levels abstract changes in sea level observed at tide gauges are caused by actual changes in water level and by changes in elevation at the observing station recent research has focused on the relationship between climatic change and sea level but vertical land movement can be just as important particularly in subsiding sedimentary basins the purpose of this study is to compare long term rates of subsidence estimated from upper pleistocene strata along the central texas coast with historical subsidence rates from the same area obtained from geodetic surveys and tide gauge data this comparison shows that historical subsidence rates are much greater than long term averages and are equal or greater than actual sea level change along the texas coast south of galveston bay long term 10 5 yr subsidence rates were estimated by establishing the extent of marine marine influenced and nonmarine strata within the upper pleistocene beaumont formation in the copano bay area of the central texas coast and comparing the maximum elevation of in place marine influenced deposits with published maximum sea level estimates of 5 8 m above mean sea level msl from correlative well dated coral terraces from stable and uplifted areas in place shell bearing horizons deposited at or below sea level occur no higher than 2 m msl in the copano bay area suggesting that there has been no more than 6 m of subsidence since the probable time of deposition during the sangamon interglacial at 120 ka the long term average subsidence rate for this part of the texas coast is thus 0 05 mm yr or less historical subsidence rates were obtained by 1 1 calculating relative elevation changes between national geodetic survey first order leveling surveys conducted in the early 1950s with those conducted in the late 1970s to early 1980s 2 2 normalizing the relative elevation differences between surveys to annual rates of change relative to an arbitrarily chosen benchmark 3 3 referencing these lines to sea level at three tide gauges and 4 4 comparing calculated rates of relative sea level rsl rise along the lines with estimates of eustatic sea level esl rise rates of rsl rise for the texas coast south of galveston bay were generally 4 8 mm yr locally rates were as high as 23 mm yr these rates are significantly higher than global averages of 1 mm yr much of the difference is probably caused by subsidence of the texas coastal zone at rates of 1 22 mm yr or 20 440 times the long term average of 0 05 mm yr the highest subsidence rates were found locally where there has been historical water level decline in shallow aquifers lower subsidence rates of 3 7 mm yr occur regionally where groundwater decline is minimal or nonexistent increased subsidence over the long term average in these areas may be caused by pressure decline in underlying oil and gas reseivoirs

breaching of mustang island in response to the 8 2 ka sea level event and impact on corpus christi bay gulf of mexico implications for future coastal change the results from an investigation of the coupled mustang island corpus christi bay complex gulf of mexico shows that the island was eliminated as an effective salinity barrier between 8 86 and 8

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

physical properties of the mars exploration rover landing sites as inferred from mini tes derived thermal inertia 1 the miniature thermal emission spectrometer mini tes on board the two mars exploration rovers provides the first opportunity to observe thermal properties from the martian surface relate these properties to orbital data and perform soil conductivity experiments under martian conditions the thermal inertias of soils bedforms and rock at each landing site were derived to quantify the physical properties of these features and understand geologic processes occurring at these localities the thermal inertia for the gusev plains rock target bonneville beacon 1200 j m 2 k 1 s 1 2 is consistent with a dense basaltic rock but the rocks at the columbia hills have a lower thermal inertia 620 j m 2 k 1 s 1 2 suggesting that they have a volcaniclasic origin bedforms on the floors of craters at both landing sites have thermal inertias of 200 j m 2 k 1 s 1 2 consistent with a particle diameter of 160 m this diameter is comparable to the most easily moved grain size in the current atmosphere on mars suggesting that these bedforms may have formed under current atmospheric conditions along the meridiani plains the thermal inertia is lower than that derived from tes and thermal emission imaging system themis orbital data this discrepancy is not well understood mini tes derived thermal inertias at gusev along a 2 5 km traverse follow trends in thermal inertia measured from orbit with tes and themis however along the traverse there are variability and mixing of particle sizes that are not resolved in the orbital thermal inertia data due to meter scale processes that are not identifiable at larger scales

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

holocene evolution of the east texas coast and inner continental shelf along strike variability in coastal retreat rates abstract the low gradient east texas coast and inner continental shelf from sabine lake at the texas louisiana border to the western end of galveston island experienced extreme along strike variations in rates of holocene coastal retreat around 7 7 ka a barrier shoreline was located approximately 55 km offshore toward the western end of galveston island the shoreline retreated 55 km occupying a position on the lagoon side of the island by about 5 3 ka toward the texas louisiana border the shoreline retreated more gradually occupying a position seaward of sabine bank by 5 3 ka between 4 7 ka and 2 8 ka the shoreline at sabine bank retreated 30 km while galveston island prograded seaward bolivar peninsula began to accrete around 1 5 ka heald and sabine banks located on the inner continental shelf above terraced fluvial deposits of the trinity sabine incised valley are the only preserved remnants of these former shoreline positions fluctuating rates of sea level rise were not the forcing mechanism behind episodes of rapid shoreline retreat because these events were localized rather along strike variations in the rate of transgression were caused by the variable inner shelf gradients which increase towards the west and the orientation of the sabine incised valley and associated terraced fluvial deposits which trend northeast southwest parallel to shore as shorelines retreated over fluvial deposits these served as local sand sources that enabled barrier islands to persist figure 1 map of the east texas inner shelf showing locations of sabine heald and shepard banks paleotopographic map of the pleistocene surface thin contours siringan 1993 delineates the trinity sabine incised valley which formed during the last lowstand of sea level thomas and anderson 1994 bathymetric contours are shown as thick lines with bold numbers dots are core locations end page 405 offshore out of equilibrium with sea level once these sand sources became depleted and or sea level reached some critical threshold barrier shorelines became stranded offshore as banks and new shorelines formed landward the geologic setting of coastal areas specifically antecedent topography plays a primary role in controlling coastal evolution to accurately forecast long term centennial to millennial coastal evolution it is essential that impacts associated with variations in the underlying geology of coastal areas be incorporated into coastal forecasting models

variable response of coastal environments of the northwestern gulf of mexico to sea level rise and climate change implications for future change the results from nearly three decades of marine geological research in the northwestern gulf of mexico are compiled in an effort to understand those factors e g sea level rise sediment supply subsidence antecedent topography that influenced coastal evolution during the last eustatic cycle 120 ka to present armed with this information we evaluate coastal response to variable sea level rise of the holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes the early holocene evolution of northwestern gulf of mexico bays was punctuated by rapid and possibly synchronous flooding events that are interpreted as resulting from episodes of rapid sea level rise two of these events one between 8 4 and 8 0 ka and the other between 7 4 and 6 8 ka were associated with known episodes of ice sheet retreat in north america and antarctica respectively during the middle and late holocene the east texas and western louisiana coasts experienced episodes of stability and growth followed by rapid shoreline retreat while the central texas coast remained relatively stable this variability in coastal response to sea level rise resulted mainly from differences in sediment supply and the highly irregular antecedent topography on which coastal environments formed sand that nourished the evolving east and south texas as well as westernmost louisiana coasts was derived mainly from transgressive ravinement of deltas that were formed during the falling stage of sea level mis5e mis2 the loci of these deltas controlled the spatial variability of this offshore sand supply sand supply to the central texas coast has been dominated by converging longshore currents and throughout the middle to late holocene was large enough to keep pace with sea level rise moreover sand supply from rivers has varied considerably in response to climate change during the early holocene when the average rate of linear sea level rise was 4 2 mm yr the brazos colorado and rio grande rivers all formed deltas on the inner continental shelf today only the brazos contributes enough sediment to the gulf of mexico to form a delta but its sand delivery is minimal a reversal from late holocene growth of western louisiana east texas and south texas barrier islands and peninsulas to erosion occurred during the last 2 0 ka after the rate of sea level rise began to decelerate the actual timing of this reversal was diachronous across the coast and was caused by a decrease in sediment supply once offshore sand sources were bypassed by the landward advancing shoreface transgressive ravinement differences in the exact timing and rate of retreat also reflect variability in the offshore profiles of these barriers and their thickness which results from the underlying relief on the pleistocene surface the late holocene was also the time of chenier plain development in western louisiana and east texas that was marked by localized differences in growth and retreat the current rate of eustatic sea level rise in the northern gulf of mexico is in the range of 2 0 and 3 0 mm yr and is approaching rates of the early holocene this is on average about five times the long term rate of the past 4 0 ka this larger rate is associated with an increase in coastal erosion in historical time relative to long term rates current rates of gulf shoreline erosion are approaching rates of the early to mid holocene and the rate of retreat of some barriers is not sustainable core transects off central texas reflect a late holocene history of shoreface progradation but the modern shoreline is currently eroding albeit at slower rates than elsewhere along the coast overall the sand supply needed to sustain the gulf shoreline is lacking likewise baylines are experiencing erosion rates that are faster than the late holocene average and bayhead deltas are at the tipping point of catastrophic retreat spatial variability in erosion rates highlights the importance of factors such as sediment supply subsidence and anthropogenic influences on coastal evolution tropical storms and hurricanes while exerting the most noticeable coastal change merely exacerbate overall shoreline retreat and migration along the entire northwestern gulf coast the impact of human intervention to natural processes is particularly evident primarily due to alterations in river discharge and sediment supply to the coast interruptions in along shore and cross shore sand transport and increases in rates of subsidence through fluid withdrawal compared to natural changes that took place during the holocene the impacts of human activity have been virtually instantaneous the geological record indicates that the ongoing increase in the rate of sea level rise coupled with diminished sediment supply and human intervention will continue to severely impact the low gradient coastal environments of the northwestern gulf of mexico

coastal barriers northern gulf last eustatic cycle genetic categories and development contrasts a review abstract a large body of chronologically well constrained and detailed quaternary data accumulated in the last decades from the coastal shelf region of the northern gulf of mexico consequently a preliminary synthesis of major aspects of the late quaternary barrier and mainland coastal development on the northern gulf of mexico is timely several major factors account for the striking differences between barrier size and development styles in the three northern gulf coast regions barriers are nearly continuous in the nw where they dominate by the greatest dimensions and continuity sand supply from shelf and mainland sources continued at variable rates throughout six stages of the last eustatic cycle lec differences in antecedent topography in fluvial runoff volumes and relative sea level rise including rapid overstepping flooding events were critical in the regional distinctions leaving fewer and smaller relict fluvial delta behind drowned shore and nearshore landforms on the shelf only two large fluvial systems impacted the ne the nw shelf and nearshore received abundant sediment supply from the mississippi and lesser streams indirectly by ravinement erosion of relict landforms and landward directed cross shelf sediment transfer sands originated mainly in relict deltas fluvial tidal channel and inlet fill as well as from submerged shore ridge remnants on the continental shelf shelf margin deltas represented major secondary sources barrier formation categories and their respective importance in specific areas represent critical aspects of coastal development the authorship of various formation concepts e g penck gilbert mcgee haage ganong and keilhack often is still miscredited or remains unrecognized in the literature recognition of the stratigraphic and sedimentological diagnostic characteristics of the basic genetic barrier categories plays a key role in testing the validity of barrier evolution models closely knit process form relationships prevail between hydrodynamic sea level change storm tidal current overwash sedimentary shoal and island aggradation rollover and eolian accumulation processes and the resulting landform morphology the most detailed accounts that deal with the development of the alabama louisiana and apalachicola barrier chains are particularly instructive almost all modern gulf barriers with identifiable genetic background formed by shoal aggradation between 5 5 and 2 0 ka during a marked deceleration in sea level rise concurrently a sizable mainland strand plain complex extended the ne coastal plain tide and storm driven sediment transport to the large mobile bay ebb delta the focal role of composite east dauphin island in establishing the ms la island chain and the island blocking role of mississippi delta advance were prime factors in a complex barrier history migration paradoxically may also occur by transgressive rollover concurrently with regressive landward progradation of island strand plains stream discharge and sand reworked from relict lithosomes on the shelf were insufficient in compensating for wave and tide related sediment loss gulf levels stayed below the present throughout the mid and late holocene

spin crossover of iron in aluminous mgsio3 perovskite and post perovskite using density functional theory hubbard u dft u calculations we investigate how aluminum affects the spin crossover of iron in mgsio3 perovskite pv and post perovskite ppv the major mineral phases in the earth s lower mantle we find that the presence of aluminum does not change the response of iron spin state to pressure only ferric iron fe3 in the octahedral b site undergoes a crossover from high spin hs to low spin ls state while fe3 in the dodecahedral a site remains in the hs state same as in al free cases however aluminum does significantly affect the placement of fe3 in these mineral phases the most stable atomic configuration has all al3 in the b site and all fe3 in the a site thus in the hs state metastable configurations with ls fe3 in the b site can happen only at high pressures and high temperatures therefore experimental observations of ls fe3 at high pressures in al bearing pv require diffusion of iron from the a site to the b site and should be sensitive to the annealing temperature and schedule in the earth s lower mantle the elastic anomalies accompanying the b site hs ls crossover exhibited in al free pv are likely to be considerably reduced according to the b site fe3 population

offshore transport of sediment during cyclonic storms hurricane ike 2008 texas gulf coast usa extreme storms can have a large impact on coastal sediment budgets and the character of strata preserved in the geologic record here we investigate the impact of a cyclonic storm surge flood and ebb on sediment transport in a microtidal beach barrier shelf system hurricane ike made landfall on the texas united states coast on 13 september 2008 the accompanying storm surge flooded galveston bay with up to 5 m of water above sea level the surge flood and ebb preferentially flowed over a low elevation bay fronting spit known as the bolivar peninsula destroying buildings and eroding sediments surge waters also flowed through bolivar roads tidal inlet the main passageway through the barrier system that separates the gulf and the bay bathymetry chirp data and samples were collected in bolivar roads tidal inlet 9 to 10 d after the storm and we compare them here to data collected 4 mo prior additional data were collected offshore of bolivar peninsula in october 2008 our results document the dominance of the storm surge ebb in forcing sediment transport through the inlet which is not considered in models of beach barrier evolution shoreface sands appear to have been incised by the storm and advected with beach barrier sediments sufficiently offshore by the storm surge ebb that they cannot be reincorporated indicating a significant loss to the barrier system9s sediment budget as a result of a single storm

variations in shoreface progradation and ravinement along the texas coast gulf of mexico shoreface architecture evolution mid holocene to present and depths of transgressive ravinement were examined from sabine pass at the texas louisiana border to south padre island near the texas mexico border using 30 shoreface transects shoreface transects extend out to 16 m water depth each created from an echo sounding profile and on average seven sediment cores the shoreface is composed of three broad sedimentological facies the upper shoreface composed almost entirely of sand the proximal lower shoreface composed of sand with thickly to medium bedded 50 10 cm mud and the distal lower shoreface composed dominantly of mud with medium to thinly bedded 20 3 cm sand shoreface architecture and evolution is extremely variable along the texas coast shoreface gradients increase from 2 25 m km 1 in east texas to 3 50 m km 1 in south texas shoreface sands coarsen towards south texas east and south texas shoreface deposits are thin and retrograding whereas central texas shoreface deposits are thicker and prograding central texas is characterized by stacked shoreface successions whereas in east texas lower shoreface sands are preserved only in offshore banks preservation of shoreface deposits is low in south texas although eustatic fluctuations and accommodation space have a strong impact on overall mid holocene to present shoreface evolution and preservation potential along strike variations in sediment supply and wave energy are the main factors controlling shoreface architecture the transgressive ravinement surface varies from 6 to 15 m along the texas coast

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

modern shoreface and inner shelf storm deposits off the east texas coast gulf of mexico abstract the modern shoreface and inner shelf sediments off the east texas coast on the gulf of mexico were examined using sediment cores and high resolution seismic data low sediment input and low effective accommodation space resulted in the overall thinness of the modern marine sediment cover in the region erosion on the inner shelf during historic 100 yr times produced patches of sand in a predominantly mud dominated environment storm beds are scarce on the inner shelf the shoreface succession off galveston island is characterized by offshore directed crosscutting storm channels of varying sizes the existence of these channels and the relatively high frequency of storms and hurricanes that have affected the region during historical imes are inconsistent with the paucity of storm deposits on the inner shelf the offshore directed channelized flows may have been prevented from going beyond the shoreface by strong along shelf storm currents that impinged on the shoreface in contrast to the storm record on the east texas shelf the central texas shelf shows a greater frequency of and more laterally persistent storm sand beds due to greater effective accommodation space and higher sediment supply there

coastal response to late stage transgression and sea level highstand coastal morphologic features associated with past shoreline transgressions and sealevel highstands can provide insight into the rates and processes associated with coastal response to the modern global rise in sea level along the eastern and southern brazilian coasts of south america 6000 years of sea level fall have preserved late stage transgressive and sea level highstand features 1 4 m above present mean sea level and several kilome ters landward of modern shorelines gps with real time kinematics data ground penetrating radar stratigraphy and radiocarbon dating within a 2 3 km wide river associated strandplain in central santa catarina southern brazil uncovered a diverse set of late stage transgressive and highstand deposits here the highstand took the forms of 1 an exposed bedrock coast in areas of high wave energy and low sediment supply 2 a 3 8 m high transgressive barrier ridge where landward barrier migration was prohibited by the presence of shallow bedrock and 3 a complete barrier island complex containing a 5 2 m high barrier ridge washover deposits a paleo inlet and a backbarrier lowland formed in a protected cove with ample sediment supply from small local streams and the erosion of upland sediments similar signatures of the mid holocene highstand can be traced across all coastal brazilian states this study presents the fi rst complete compilation of the diversity of these sedimentary sequences they are broadly classifi ed here as exposed bedrock coasts type a back barrier deposits type b transgressive barrier ridges type c and barrier island complexes type d according to localized conditions of upland migration potential wave exposure and sediment supply these brazilian systems present a paradigm for understanding future coastal response to climate change and accelerated sea level rise the recognition of a minimum threshold sea level rise rate of 2 mm yr 1 above which transgression proceeded too rapidly for the formation of these stable accretionary shoreline features demonstrates the nonlinearity of coastal response to sea level change and the site specifi city of conditions associated with the formation of each highstand deposit type even within a single small embayment demonstrates the non uniformity of that response

shoreface ravinement evolution tracked by repeat geophysical surveys following hurricane ike bolivar peninsula texas 2008 2013 we have investigated the impact of hurricane ike on the shoreface of the bolivar peninsula texas using three nearsurface marine geophysical surveys during a five year span following the storm which made landfall in september of 2008 multibeam bathymetry sidescan backscatter and chirp subbottom reflection data were collected during each survey the first survey in november 2008 discovered the presence of an erosional landward facing scarp across a broad of the barrier spit shoreface at approximately 3 5 m water depth the erosion incised into a shallow reflection horizon interpreted as the holocene shoreface ravinement exposing lag deposits that were truncated at the scarp and forming a thin high backscatter anomaly up to 1 0 m of material was excavated shoreward of the scarp including up to 0 5 m of shoreface sand above the shoreface ravinement and another 0 5 m of indeterminate

mgs tes thermal inertia study of the arsia mons caldera 1 temperatures of the arsia mons caldera floor and two nearby control areas were obtained by the mars global surveyor mgs thermal emission spectrometer tes these observations revealed that the arsia mons caldera floor exhibits thermal behavior different from the surrounding tharsis region when compared with thermal models our technique compares modeled and observed data to determine best fit values of thermal inertia layer depth and albedo best fit modeled values are accurate in the two control regions but those in the arsia mons caldera are consistently either up to 15 k warmer than afternoon observations or have albedo values that are more than two standard deviations higher than the observed mean models of both homogeneous and layered such as dust over bedrock cases were compared with layered cases indicating a surface layer at least thick enough to insulate itself from diurnal effects of an underlying substrate material because best fit models of the caldera floor poorly match observations it is likely that the caldera floor experiences some physical process not incorporated into our thermal model even on mars arsia mons is an extreme environment where co2 condenses upon the caldera floor every night diurnal temperatures range each day by a factor of nearly 2 and annual average atmospheric pressure is only around one millibar here we explore several possibilities that may explain the poor modeled fits to caldera floor and conclude that temperature dependent thermal conductivity may cause thermal inertia to vary diurnally and this effect may be exaggerated by presence of water ice clouds which occur frequently above arsia mons

themis high resolution digital terrain topographic and thermophysical mapping of gusev crater mars 1 we discuss a new technique to generate high resolution digital terrain models dtms and to quantitatively derive and map slope corrected thermophysical properties such as albedo thermal inertia and surface temperatures this investigation is a continuation of work started by kirk et al 2005 who empirically deconvolved thermal emission imaging system themis visible and thermal infrared data of this area isolating topographic information that produced an accurate dtm surface temperatures change as a function of many variables such as slope albedo thermal inertia time season and atmospheric opacity we constrain each of these variables to construct a dtm and maps of slope corrected albedo slope and albedo corrected thermal inertia and surface temperatures across the scene for any time of day or year and at any atmospheric opacity dtms greatly facilitate analyses of the martian surface and the mola global data set is not finely scaled enough 128 pixels per degree 0 5 km per pixel near the equator to be combined with newer data sets e g high resolution imaging science experiment context camera and compact reconnaissance imaging spectrometer for mars at 0 25 6 and 20 m per pixel respectively so new techniques to derive high resolution dtms are always being explored this paper discusses our technique of combining a set of themis visible and thermal infrared observations such that albedo and thermal inertia variations within the scene are eliminated and only topographic variations remain this enables us to produce a high resolution dtm via photoclinometry techniques that are largely free of albedo induced errors with this dtm themis observations and a subsurface thermal diffusion model we generate slope corrected maps of albedo thermal inertia and surface temperatures in addition to greater accuracy these products allow thermophysical properties to be directly compared with topography

elasticity of mg fe si al o 3 perovskite at high pressure the most abundant mineral on earth has a perovskite crystal structure and a chemistry that is dominated by mgsio3 with the next most abundant cations probably being aluminum and ferric iron the dearth of experimental elasticity data for this chemically complex mineral limits our ability to calculate model seismic velocities for the lower mantle we have calculated the single crystal elastic moduli c ij for mg fe3 si al o 3 perovskite using density functional theory in order to investigate the effect of chemical variations and spin state transitions of the fe3 ions considering the favored coupled substitution of mg2 si4 by fe3 al3 we find that the effect of ferric iron on seismic properties is comparable with the same amount of ferrous iron ferric iron lowers the elastic moduli relative to the al charge coupled substitution substitution of fe3 for al3 giving rise to an fe mg ratio of 6 causes 1 8 lower longitudinal velocity and 2 5 lower shear velocity at ambient pressure and 1 1 lower longitudinal velocity and 1 8 lower shear velocity at 142 gpa the spin state of the iron for this composition has a relatively small effect 0 5 variation on both bulk modulus and shear modulus c 2005 elsevier b v all rights reserved

palaeohurricane reconstructions from sedimentary archives along the gulf of mexico caribbean sea and western north atlantic ocean margins hurricanes annually threaten the atlantic ocean margins historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity here we review palaeo trends in hurricane activity elucidated from sedimentary archives we discuss dating methods site selection and stat istics associated with previously published records these archives have been useful for under standing the long term evolution of coastal systems and the response of intense hurricane activity to climatic changes regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability including el nino southern oscillation and the north atlantic oscillation but could also reflect regional scale controls on hurricane activity

electronic spin transitions in iron bearing mgsio3 perovskite the electronic spin state of iron in perovskites with the chemical composition mg0 9375fe0 0625sio3 mg0 8750fe0 1250sio3 and mg0 9375fe0 0625si0 9375fe0 0625o3 have been determined at 0 k and various pressures between 40 160 gpa using ab initio methods the results indicate that ferric iron exhibits a wide range of spin transition pressures between about 60 160 gpa while ferrous iron has a much narrower span between about 130 145 gpa in general the lowest spin transition pressures are associated with the most energetically favorable substitution configurations where iron atoms are closest together the effect of spin state on calculated elastic properties is found to be small c 2006 elsevier b v all rights reserved

mars exploration rover candidate landing sites as viewed by themis the analysis of six landing sites that were candidates for the two nasa mars exploration rovers mer benefited from recently available image data from the thermal emission imaging spectrometer themis onboard the 2001 mars odyssey spacecraft the combination of daytime and nighttime thermal infrared images from themis supplemented by additional data sets has lead to new or expanded insights into the nature of each landing site in meridiani planum a layer of lighter toned higher thermal inertia material is observable just below the hematite bearing layer gusev crater displays a more complex stratigraphy than previously observed including an upper layer with lobate margins the highest inertia unit of southern isidis planitia is confined to topographic lows in the rim basin margin and does not appear to be due to highland material transported onto the basin floor the enigmatic ovoid blocky terrain on the floor of melas chasma displays higher thermal inertia than its surroundings an indication that it contains coarser or more indurated material than the adjacent aeolian bedforms the myriad channels of athabasca valles display distinctive thermal signatures despite the presence of a bright layer of dust covering the region the presence of alluvial fans produced from spur and gulley erosion of the walls of eos chasma demonstrates that mass movements have occurred following the canyon scouring floods

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

thermal behavior of horizontally mixed surfaces on mars abstract current methods for deriving thermal inertia from spacecraft observations of planetary brightness temperature generally assume that surface properties are uniform for any given observation or co located set of observations as a result of this assumption and the nonlinear relationship between temperature and thermal inertia sub pixel horizontal heterogeneity may yield different apparent thermal inertia at different times of day or seasons we examine the effects of horizontal heterogeneity on mars by modeling the thermal behavior of various idealized mixed surfaces containing differing proportions of either dust sand duricrust and rock or slope facets at different angles and azimuths latitudinal effects on mixed surface thermal behavior are also investigated we find large several 100 j m 2 k 1 s 1 2 diurnal and seasonal variations in apparent thermal inertia even for small 10 admixtures of materials with moderately contrasting thermal properties or slope angles together with similar results for layered surfaces mellon m t putzig n e 2007 lunar planet sci xxxviii abstract 2184 this work shows that the effects of heterogeneity on the thermal behavior of the martian surface are substantial and may be expected to result in large variations in apparent thermal inertia as derived from spacecraft instruments while our results caution against the over interpretation of thermal inertia taken from median or average maps or derived from single temperature measurements they also suggest the possibility of using a suite of apparent thermal inertia values derived from single observations over a range of times of day and seasons to constrain the heterogeneity of the martian surface

timing and magnitude of recent accelerated sea level rise north carolina united states we provide records of relative sea level since a d 1500 from two salt marshes in north carolina to complement existing tide gauge records and to determine when recent rates of accelerated sea level rise commenced reconstructions were developed using foraminifera based transfer functions and composite chronologies which were validated against regional twentieth century tide gauge records the measured rate of relative sea level rise in north carolina during the twentieth century was 3 0 3 3 mm a consisting of a background rate of 1 mm a plus an abrupt increase of 2 2 mm a which began between a d 1879 and 1915 this acceleration is broadly synchronous with other studies from the atlantic coast the magnitude of the acceleration at both sites is larger than at sites farther north along the u s and canadian atlantic coast and may be indicative of a latitudinal trend

high spin fe2 and fe3 in single crystal aluminous bridgmanite in the lower mantle spin and valence states of iron in single crystal bridgmanite mg0 89fe0 12al0 11si0 89o3 are investigated using x ray emission and mossbauer spectroscopies with laser annealing up to 115 gpa the results show that fe predominantly substitutes for mg2 in the pseudo dodecahedral a site in which 80 of the iron is fe3 that enters the lattice via the charge coupled substitution with al3 in the octahedral b site the total spin momentum and hyperfine parameters indicate that these ions remain in the high spin state with fe2 having extremely high quadrupole splitting due to lattice distortion al fe bearing bridgmanite is expected to contain mostly high spin a site fe3 together with a smaller amount of a site fe2 that remains stable throughout the region even though the spin transition of b site fe3 in bridgmanite was reported to cause changes in its elasticity at high pressures fe al bearing bridgmanite with predominantly a site fe will not exhibit elastic anomalies associated with the spin transition

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

accelerated sea level rise from west antarctica recent aircraft and satellite laser altimeter surveys of the amundsen sea sector of west antarctica show that local glaciers are discharging about 250 cubic kilometers of ice per year to the ocean almost 60 more than is accumulated within their catchment basins this discharge is sufficient to raise sea level by more than 0 2 millimeters per year glacier thinning rates near the coast during 2002 2003 are much larger than those observed during the 1990s most of these glaciers flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates providing exit routes for ice from further inland if ice sheet collapse is under way

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

optical signatures of low spin fe3 in nal at high pressure the iron spin transition directly affects properties of lower mantle minerals and can thus alter geophysical and geochemical characteristics of the deep earth while the spin transition in ferropericlase has been documented at p 60 gpa and 300 k experimental evidence for spin transitions in other rock forming minerals such as bridgmanite and post perovskite remains controversial multiple valence spin and coordination states of iron in bridgmanite and post perovskite are difficult to resolve with conventional spin probing techniques optical spectroscopy on the other hand can discriminate between high and low spin and between ferrous and ferric iron at different sites here we establish the optical signature of low spin fe3 o6 a plausible low spin unit in bridgmanite and post perovskite by optical absorption experiments in diamond anvil cells we show that the optical absorption of fe3 o6 in new aluminous phase nal is very sensitive to the iron spin state and may represent a model behavior of bridgmanite and post perovskite across the spin transition specifically an absorption band centered at 19 000 cm 1 is characteristic of the 2t2g 2t1g 2a2g transition in low spin fe3 in nal at 40 gpa constraining the crystal field splitting energy of low spin fe3 to 22 200 cm 1 which we independently confirm by first principles calculations together with available information on the electronic structure of fe3 o6 compounds we show that the spin pairing energy of fe3 in an octahedral field is 20 000 23 000 cm 1 this implies that octahedrally coordinated fe3 in bridgmanite is low spin at p 40 gpa

recycling sediments between source and sink during a eustatic cycle systems of late quaternary northwestern gulf of mexico basin abstract the northwestern gulf of mexico basin is an ideal natural laboratory to study and understand source to sink systems an extensive grid of high resolution seismic data hundreds of sediment cores and borings and a robust chronostratigraphic framework were used to examine the evolution of late quaternary depositional systems of the northwestern gulf of mexico throughout the last eustatic cycle 125 ka to present the study area includes fluvial systems with a wide range of drainage basin sizes climate settings and water and sediment discharges detailed paleogeographic reconstructions are used to derive volumetric estimates of sediment fluxes volume accumulation rates the results show that the response of rivers to sea level rise and fall varied across the region larger rivers including the former mississippi western louisiana presumably the ancestral red river brazos colorado and rio grande rivers constructed deltas that advanced across the shelf in step wise fashion during marine isotope stages mis 5 2 sediment delivery to these deltas increased during the overall sea level fall due to increases in drainage basin area and erosion of sediment on the inner shelf where subsidence is minimal and transport of that sediment to the more rapidly subsiding outer shelf the sediment supply from the brazos river to its delta increased at least 3 fold and the supply of the colorado river increased at least 6 fold by the late stages of sea level fall through the lowstand repeated filling and purging of fluvial valleys from 119 22 ka contributed to the episodic growth of falling stage deltas during the mis 2 lowstand 22 17 ka the mississippi river abandoned its falling stage fluvial deltaic complex on the western louisiana shelf and drained to the mississippi canyon likewise the western louisiana delta was abandoned presumably due to merger of the red river with the mississippi river terminating growth of the western louisiana delta the brazos river abandoned its mis 3 shelf margin delta to merge with the trinity sabine and calcasieu rivers and together these rivers nourished a lowstand delta and slope fan complex the colorado and rio grande rivers behaved more as point sources of sediment to thick lowstand delta fan complexes lowstand incised valleys exhibit variable morphologies that mainly reflect differences in onshore and offshore relief and the time intervals these valleys were occupied they are deeper and wider than falling stage channel belts and are associated with a shelf wide surface of erosion sequence boundary during the early mis 1 17 ka to 10 ka sea level rise the offshore incised valleys of the calcasieu sabine trinity brazos colorado and rio grande rivers were filled with sediment the offshore valleys of smaller rivers of central texas would not be filled until the late holocene mainly by highstand mud the lower onshore portions of east texas incised valleys were filled with sediment mainly during the holocene with rates of aggradation in the larger brazos and colorado valleys being in step with sea level rise smaller rivers filled their valleys with back stepping fluvial estuarine and tidal delta deposits that were offset by flooding surfaces in general the sediment trapping capacity of bays increased as evolving barrier islands and peninsulas slowly restricted tidal exchange with the gulf and valley filling led to more shallow wider bays a widespread period of increased riverine sediment flux and delta growth is attributed to climate change during mis 1 between 11 5 and 8 0 ka and occurred mainly under cool wet climate conditions relatively small sea level oscillations during the mis 1 transgression 17 ka to 4 0 ka profoundly influenced coastal evolution as manifested by landward stepping shorelines on the order of tens of kilometers within a few thousand years the current barriers strand plains and chenier plains of the study area formed at different times over the past 8 ka due mainly to differences in sand supply and the highly variable relief on the mis 2 surface on which these systems formed modern highstand deposition on the continental shelf formed the texas mud blanket which occurs on the central texas shelf and records a remarkable increase in fine grained sediment supply this increase is attributed to greater delivery of sediments from the colorado and brazos rivers which had filled their lower valleys and abandoned their transgressive deltas by late holocene time and to an increase in westward directed winds and surface currents that delivered suspended sediments from the mississippi river to the texas shelf collectively our results demonstrate that source to sink analyses in low gradient basin settings requires a long term perspective ideally a complete eustatic cycle because most of the sediment that was delivered to the basin by rivers underwent more than one cycle of erosion transport and sedimentation that was regulated by sea level rise and fall climate was a secondary control the export of sediments from the hinterland to the continental shelf was not directly in step with temperature change but rather varied between different fluvial deltaic systems

spirit rover localization and topographic mapping at the landing site of gusev crater mars 1 by sol 440 the spirit rover has traversed a distance of 3 76 km actual distance traveled instead of odometry localization of the lander and the rover along the traverse has been successfully performed at the gusev crater landing site we localized the lander in the gusev crater using two way doppler radio positioning and cartographic triangulations through landmarks visible in both orbital and ground images additional high resolution orbital images were used to verify the determined lander position visual odometry and bundle adjustment technologies were applied to compensate for wheel slippage azimuthal angle drift and other navigation errors which were as large as 10 5 in the husband hill area we generated topographic products including 72 ortho maps and three dimensional 3 d digital terrain models 11 horizontal and vertical traverse profiles and one 3 d crater model up to sol 440 also discussed in this paper are uses of the data for science operations planning geological traverse surveys surveys of wind related features and other science applications

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

surface albedo observations at gusev crater and meridiani planum mars 1 during the mars exploration rover mission the pancam instrument has periodically acquired large scale panoramic images with its broadband 739 338 nm filter in order to estimate the lambert bolometric albedo of the surface along each rover s traverse in this work we present the full suite of such estimated albedo values measured to date by the spirit and opportunity rovers along their traverses in gusev crater and meridiani planum respectively we include estimated bolometric albedo values of individual surface features e g outcrops dusty plains aeolian bed forms wheel tracks light toned soils and crater walls as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date we also present comparisons to estimated lambert albedo values taken from the mars global surveyor mars orbiter camera moc along the rovers traverses and to the large scale bolometric albedos of the sites from the viking orbiter infrared thermal mapper irtm and mars global surveyor thermal emission spectrometer tes the ranges of pancam derived albedos at gusev crater 0 14 to 0 25 and in meridiani planum 0 10 to 0 18 are in good agreement with irtm tes and moc orbital measurements these data sets will be a useful tool and benchmark for future investigations of albedo variations with time including measurements from orbital instruments like the context camera and high resolution imaging science experiment on mars reconnaissance orbiter long term accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes

oxidation state of the lower mantle in situ observations of the iron electronic configuration in bridgmanite at extreme conditions abstract we have investigated the electronic configuration of iron in fe al containing magnesium silicate perovskite i e bridgmanite the main component of the lower mantle at conditions of the deep earth s interior using the energy domain synchrotron mossbauer source technique we show that the high ferric iron content observed previously in quenched samples is preserved at high temperatures and high pressures our data are consistent with high spin to intermediate spin hs is crossover in fe2 at high pressures and ambient temperature we see no evidence of spin crossover in fe3 occupying the a position of bridgmanite on laser heating at pressures above 40 gpa we observe a new doublet with relative area below 5 which is assigned to fe3 in the octahedral b site position in bridgmanite we conclude that at lower mantle conditions fe3 remains predominantly in the hs state while fe2 occurs solely in the is state

seismic facies architecture and evolution of the bolivar roads tidal inlet delta complex east texas gulf coast abstract the seismic facies facies architecture and stratigraphy of tidal inlet and tidal delta deposits and their relation to the development of adjacent coastal lithosomes are examined using high resolution seismic profiles vibracores and borehole descriptions the bolivar roads tidal inlet delta complex along the east texas gulf coast was formed 3 3 ka by spit accretion across a baymouth following a rapid sea level rise 4 ka an increase in the tidal prism through time and entrenchment of the tidal inlet over the trinity river incised valley stabilized the inlet and intensified tidal processes on the tidal inlet delta complex the tidal inlet facies show channel stacking and cut and fill structures stacked clinoforms dip westward across the inlet the spit facies is characterized by oblique tangential clinoforms that build outward and deepen from the edge toward the center of the valley the flood tidal delta facies has a base that shallows abruptly bayward as the flood tidal delta facies thins bayward it interfingers with bay sediments near the inlet the flood tidal delta shows channel cut and fill with an overall channel stacking pattern on the seaward side the channels have a trough like geometry bayward the channels broaden and shallow the channels show a prograded fill pattern the ebb tidal delta facies exhibits gently inclined clinoforms prograding over a ravinement surface tidal inlet deposits are composed of sand shell and mud interbeds sand and clay interlaminae are ubiquitous in the tidal deltas and sand and shell beds are common near the inlet overall the bolivar roads tidal inlet delta complex is mud dominated as a result of high influx of fine sediment into the bay

2500 year paleotempestological record of intense storms for the northern gulf of mexico united states abstract the northern gulf of mexico has been devastated by recent intense storms camille 1969 and katrina 2005 are two notable hurricanes that made landfall in nearly the same location in mississippi fully understanding the risks and processes associated with hurricane impacts are impeded by a short and fragmented instrumental record however paleotempestology has the potential to employ modern analogues from intense storms in this region to extend the hurricane record beyond pre observational time existing empirically based models can back calculate surge heights over coastal systems as a function of transport distance particle settling velocity and gravitational acceleration we collected sediment cores in a pond 3 and adjacent beach 1 in hancock county mississippi grain size loss on ignition and microfossil analyses were conducted on cores in the context of a bayesian statistical age model using 137cs and 14c dating using hurricane camille to calibrate the archive similar coarse grained deposits were identified and inverse sediment transport models calculated paleosurge intensities similar in magnitude to camille over the 2500 yr record our multi millennial annual average landfall probability 0 48 closely matches previously published studies from the gulf of mexico indicating that intense hurricanes have not varied over these timescales over centennial timescales active intervals occurred between 900 to 600 and 2200 to 1900 yr bp with relative quiescence between 1900 to 900 yr bp comparisons with other published sites support the notion that southerly shifts in the loop current may be responsible for the decline in activity around 600 yr bp