polar vortices on earth and mars a comparative study of the climatology and variability from reanalyses polar vortices on mars provide case studies to aid understanding of geophysical vortex dynamics and may help to resolve long standing issues regarding polar vortices on earth due to the recent development of the first publicly available martian reanalysis dataset macda for the first time we are able to characterise thoroughly the structure and evolution of the martian polar vortices and hence perform a systematic comparison with the polar vortices on earth the winter atmospheric circulations of the two planets are compared with a specific focus on the structure and evolution of the polar vortices the martian residual meridional overturning circulation is found to be very similar to the stratospheric residual circulation on earth during winter while on earth this residual circulation is very different from the eulerian circulation on mars it is found to be very similar unlike on earth it is found that the martian polar vortices are annular and that the northern hemisphere vortex is far stronger than its southern counterpart while winter hemisphere differences in vortex strength are also reported on earth the contrast is not as large distinctions between the two planets are also apparent in terms of the climatological vertical structure of the vortices in that the martian polar vortices are observed to decrease in size at higher altitudes whereas on earth the opposite is observed finally it is found that the martian vortices are less variable through the winter than on earth especially in terms of the vortex geometry during one particular major regional dust storm on mars martian year 26 an equatorward displacement of the vortex is observed sharing some qualitative characteristics of sudden stratospheric warmings on earth

geochemistry of interstitial gases in quaternary sediments of the gulf of california abstract interstitial gases from the deep sea drilling project dsdp ipod leg 64 sites 474 477 479 and 481 in the gulf of california have been analyzed by gas chromatography and stable isotope mass spectrometry in order to evaluate their compositions in terms of biogenic and thermogenic sources the hydrocarbon gas c 1 c 5 concentrations were comparable to the shipboard data and no olefins could be detected the 13 c data for the ch 4 confirmed the effects of the thermal stress on the sedimentary organic matter in that the values were typically biogenic near the surface and become more depleted in 12 c vs depth at sites 474 478 and 481 the ch 4 at site 477 was the heaviest in 13 c and at site 479 it did not show a predominant high termperature component the co 2 at depth from most sites was of a primarily thermogenic origin from carbonate decomposition

possible effects of breaking gravity waves on the circulation of the middle atmosphere of mars a simplified quasi geostrophic beta plane dynamical model of the zonal mean flow is used to investigate the possible effects of breaking internal gravity waves on the circulation in the middle atmospheric region 10 100 km altitude of mars the gravity wave parameterization employed is basically the saturation parameterization of lindzen 1981 which has been utilized in several terrestrial modeling studies numerical simulations are performed for a range of plausible values of the gravity wave parameters and for different representations of the mean flow thermal forcing with a focus on the effects of topographically forced stationary gravity waves on the winter hemisphere circulation the results of the model simulations show that breaking gravity waves of intermediate horizontal scales 100 1000 km wavelengths could act to close off the winter westerly circumpolar jet in the 40 80 km altitude region and induce strong high latitude warming at these levels the latter could explain recent thermal measurements indicating that martian winter polar latitudes may be very warm far above radiative equilibrium in this middle atmospheric region deming et al 1986 for the most plausible range of parameter values breaking gravity waves do not induce much warming below 40 km consistent with available data showing that winter high latitudes are normally very cold at lower levels several dust storm cases indicate that breaking gravity waves possibly could act to induce a very large polar warming at relatively low altitudes such as was observed during the 1977 winter solstice dust storm however quite large gravity wave amplitudes and or relatively long horizontal wavelengths are required for such strong low level effects thermal forcing associated with dust heating might be a source for such anomalous gravity wave activity during a global dust storm summer simulations indicate that breaking gravity waves might alter the mean flow at somewhat higher levels than in the winter hemisphere as a consequence of the presence of westerlies in the lower atmosphere this could explain the presence of a warm summer pole in the recent 50 80 km thermal measurements of deming et al several aspects of the results relating to the middle atmospheric circulation and the polar warming phenomenon are discussed the possible importance of breaking gravity waves for constituent transports in the middle atmosphere of mars is also briefly considered

mars atmospheric dynamics as simulated by the nasa ames general circulation model 3 winter quasi stationary eddies a set of simulations with the nasa ames mars general circulation model gcm has been analyzed to define the basic properties and dynamics of quasi stationary eddy circulations in the winter hemisphere these circulations differing substantially from those in low latitudes and the summer hemisphere extend from the surface to the model top at 47 km typically the largest geopotential and wind perturbations are found at the highest model level near the surface the eddies are of largest amplitude in lower latitudes but above 5 10 km the amplitudes are a maximum in middle and high latitudes the vertical structure of the eddies is nearly equivalent barotropic the phase variation in latitude is also relatively small zonal wavenumbers 1 and 2 dominate the stationary circulations with wave 3 being of significance only at low levels below 10 km the quasi stationary eddies differ substantially in northern and southern winters and undergo considerable changes with increasing dustiness in northern winter the southern winter eddy circulation is dominated by zonal wavenumber 1 while the northern eddies have a strong wavenumber 2 component at low levels of dust loading at high dust levels wavenumber 1 becomes dominant this change may be at least partly the result of the dusty zonal mean state becoming more responsive to wave 1 forcing the standing eddies in a gcm simulation for ls 0 exhibit considerable similarity in basic structure and amplitude to those revealed by an recent analysis of viking irtm data banfield et al 1996 though there are differences in the phases of the eddy patterns

sublimation and transport of water from the north residual polar cap on mars several features of the viking mars atmospheric water detection observations have suggested that the residual north polar cap on mars is a major source of atmospheric water during northern summer and that the water it supplies to the atmosphere is transported equatorward to low northern latitudes by summer s end we have explored the role of the north residual cap in the current martian water cycle by constructing models to assess the ability of the cap to supply water to the atmosphere and the ability of the atmosphere to transport it out of the polar regions from our sublimation model we conclude that the residual cap can sublime the 7 1014 g of water that appears in the atmosphere after ls 80 provided surface winds are high 10 m s the cap emissivity is low 0 9 or the exposed soil in polar regions contains ice that is accessible to the atmosphere in our view these requirements seem unlikely and we are drawn to the conclusion that other sources of water exist this conclusion is further supported by the results of two dimensional transport simulations which show that most of the water sublimed from the cap remains at high latitudes the polar circulation simply lacks the intensity and scale to move water very far from the cap a weak circulation places additional constraints on cap sublimation rates since abundant clouds and significant ice deposits would form just equatorward of the cap edge according to the model if the cap is allowed to sublime 7 1014 g of water such predictions are inconsistent with available data we suggest that the nature of the additional source is water desorbing from the nonpolar regolith

hurricane records on the south carolina coast can they be detected in the sediment record abstract more than 40 short cores were collected from 10 localities in the myrtle beach to mcclellandville coastline of south carolina the localities were selected on the basis of whether or not they should have a well preserved record of recent hurricanes most notably hugo which occurred in september 1989 of the 40 cores collected results from two sites are presented here as examples price s inlet a non tidal intra beach ridge area which was directly in the path of the eyewall of hugo and sandpiper pond which is a coastal non tidal pond near murrells inlet about 50 75 km north of where the main landfall of hurricane hugo but still in the area of high storm surge these cores were analyzed for percentage organic carbon visual observations x rays and microfossils the microfossils were used to differentiate marine non marine sequences in the non tidal inlets and identify reworked sediments by means of displaced benthic foraminifera cores were dated using pb 210 techniques that provide resolution for the last 100 yr in price s inlet the hugo effect was most pronounced with an 8 cm thick sand layer containing many nearshore foraminifera showing transport from offshore in sandpiper pond we could see the trace of hugo from the offshore foraminifera contained in sediments sandwiched between the freshwater intervals both before and after hugo however there was little detectable trace in the x rays or sedimentology of this core to indicate a storm event hence we can recognize a range of responses for hurricanes in the form of different types of sediment layers and microfossil assemblages in these non tidal areas depending on where the impact point is on the coast here we are able to distinguish at least two types of signals from the same storm which has significant implications for detecting these events in the pre historic record and determining their paleo periodicity

isotope techniques for tracing migration of gases in sedimentary basins the isotopic composition of methane is primarily dependent on the stage of maturation of organic matter present in the hydrocarbon source rocks and is not changed during migration the isotopic composition of in situ methane can be estimated from the maturity of the source organic matter migrated methane from deeper more mature sources is recognized by its relative 13 c enrichment compared to indigenous methane examples are presented in this paper to evaluate the migration pattern of gases in sedimentary basins

role of minerals in thermal alteration of organic matter ii a material balance pyrolysis experiments were performed on green river and monterey formation kerogens types i and ii respectively with and without calcite illite or montmorillonite at 300 c for 2 to 1 000 hours under dry and hydrous conditions pyrolysis products were identified and quantified and a material balance of product and reactants resulted significant differences were found in the products generated by pyrolysis of kerogens with and without minerals both illite and montmorillonite adsorb a considerable portion up to 80 of the generated bitumen the adsorbed bitumen is almost exclusively composed of polar compounds and asphaltenes that crack to yield low molecular weight compounds and insoluble pyrobitumen during prolonged heating montmorillonite shows the most pronounced adsorptive and catalytic effects with calcite however the pyrolysis products are similar to those from kerogen heated alone and bitumen adsorption is negligible applying these results to maturation of organic matter in natural environments we suggest that a given type of organic matter associated with different minerals in source rocks will yield different products furthermore the different adsorption capacities of minerals exert a significant influence on the migration of polar and high molecular weight compounds generated from the breakdown of kerogen therefore the overall accumulated products from carbonate source rocks are mainly heavy oils with some gas whereas light oils and gases are the main products from source rocks that contain expandable clays with catalytic and adsorptive properties

linear baroclinic instability in the martian atmosphere abstract the linear baroclinic instability of zonal mean flows like those in the wintertime martian atmosphere under both relatively nondusty and highly dusty conditions is examined using a spherical quasi geostrophic model the basic states are idealized but based closely upon mariner 9 and viking observations zonal wavenumbers 3 and 4 are found to be most unstable and phase speeds are 10 20 m s 1 in middle latitudes generally consistent with observations as well as with previous results obtained with simpler models growth rates are not greatly reduced by the rapid martian radiative relaxation though the growth at higher wavenumbers is significantly inhibited by ekman friction even with this dissipation minimum e folding times of 2 days are obtained for a dust storm basic state characterized by enhanced static stability growth rates are substantially decreased but the most unstable wavenumber is essentially not altered this behavior differs from that found in simple models but is consistent wi

winter polar warmings and the meridional transport on mars simulated with a general circulation model abstract winter polar warmings in the middle atmosphere of mars occur due to the adiabatic heating associated with the downward branch of the cross equatorial meridional circulation thus they are the manifestation of the global meridional transport rather than of local radiative effects we report on a series of numerical experiments with a recently developed general circulation model of the martian atmosphere to examine the relative roles of the mechanical and thermal forcing in the meridional transport the experiments were focused on answering the question of whether the martian circulation is consistent with the thermally driven nearly inviscid hadley cell as was pointed out by some previous studies or it is forced mainly by zonally asymmetric eddies it is demonstrated that under realistic conditions in the middle atmosphere the meridional transport is maintained primarily by dissipating large scale planetary waves and solar tides this mechanism is similar to the extratropical pump in the middle atmosphere on earth only in the run with artificially weak zonal disturbances was the circulation reminiscent of thermally induced hadley cells in the experiment with an imposed dust storm the modified atmospheric refraction changes the vertical propagation of the eddies as the result the eliassen palm fluxes convergence increases in high winter latitudes of the middle atmosphere the meridional transport gets stronger and the polar temperature rises additional numerical experiments demonstrated that insufficient model resolution increased numerical dissipation and especially neglect of non lte effects for the 15 m co2 band could weaken the meridional transport and the magnitude of polar warmings in gcms

lake sediment record of late holocene hurricane activities from coastal alabama coastal lake sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene time frederic a category 3 hurricane that struck the alabama coast on the gulf of mexico in 1979 left a distinct sand layer in the nearshore sediments of lake shelby as a result of storm tide overwash of beaches and dunes sediment cores taken from the center of lake shelby contain multiple sand layers suggesting that major hurricanes of category 4 or 5 intensity directly struck the alabama coast at ca 3 2 3 0 2 6 2 2 1 4 and 0 8 ka 14 c yr with an average recurrence interval of 600 yr the alabama coast is likely to be struck by a category 4 or 5 hurricane within the next century

spatio lateral continuity of hurricane deposits in back barrier marshes sedimentological and micropaleontological analysis of fifteen 3 m gouge auger cores revealed a lack of spatio lateral continuity for paleohurricane deposits from the back barrier marshes of folly island south carolina the offshore indicative calcareous microfossil content of some storm deposits was taphonomically altered or destroyed and in many cases cores taken 10 m apart provided significantly different storm records in several low marsh cores where bioturbation is more intense storm deposits were completely unrecognizable using foraminifer or sedimentological analyses in nearly all cores the sedimentary record of storm deposits was more extensive than the record produced using foraminifers and as a result the sedimentary proxy produced shorter hurricane return periods while offshore indicative foraminifers in the salt marshes behind folly island are good indicators of their original source and mode of deposition storm current transport from the shelf by overwash storm inlet or via lighthouse inlet their susceptibility to destruction from bioturbation and dissolution suggests that they provide a less accurate or less complete record of storm frequency than previously thought

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

hydrocarbon gas seeps of the convergent hikurangi margin north island new zealand abstract two hydrocarbon gas seeps located about 13 km apart have distinctive molecular and isotopic compositions these seeps occur within separate tectonic melange units of narrow parallel trending and structurally complex zones with incorporated upper cretaceous and palaeogene passive continental margin deposits which are now compressively deformed and imbricated along the convergent hikurangi margin of north island new zealand at brookby station within the coastal high the seeping hydrocarbon gas has a methane ethane ratio of 48 and 13 c and d values of methane of 45 7 and 188 respectively relative to the pdb and smow standards within the complex core of the elsthorpe anticline at campbell station seep gas has a methane ethane ratio of about 12000 and the methane has 13 c and d values of 37 4 and 170 respectively the source of the gases cannot be positively identified but the gases probably originate from the thermal decomposition of organic matter in tectonically disturbed upper cretaceous and or lower tertiary sedimentary rocks of passive margin affinity and reach the surface by migration along thrust faults associated with tectonic melange the geochemical differences between the two gases may result from differences in burial depths of similar source sediment

geochemical characterization of natural gas a physical multivariable approach and its applications in maturity and migration estimates gas geochemistry has recently been shown to enhance information regarding the geological history of hydrocarbons in this paper graphical representations of physico chemical processes affecting the chemical and isotopic signatures of natural gases are exemplified these diagrams are based on experimental studies and the use of basic statistics to extract significant and synthetic parameters from the geochemical data from 11 chemical and isotopic ratios a statistical analysis pca yields two very important parameters the first parameter using mainly the c2 fraction of the gas relates to maturity and the second parameter involving the proportions and d13c values of methane indicates mainly segregative migration positive values of the second parameter indicate that gases accumulated far from their source whereas negative values correspond to residual gas pools after leakage of a part of the fluids a tentative reconstruction of the gas history has been performed in two brazilian basins the espirito santo basin and part of the reconcavo basin the espirito santo basin is located on the passive continental margin of the atlantic ocean and the reconcavo basin corresponds to an intracontinental aborted rift in both cases the source rocks are mainly lacustrine with thermal maturities ranging between the oil window and the beginning of the gas window results show that in the reconcavo basin a major fault the mata catu fault acts as a drain for hydrocarbon migration at the basin scale associating a major isotopic fractionation to the gas migration with a clear correlation between isotope fractionation and the distance of migration in the espirito santo basin this segregation appears in the platform sediments to a lesser extent and is absent in the gas pools located in the paleocanyons filled with turbidites this long distance migration in the platform sediments suggests that a hydrocarbon kitchen is located offshore

foraminifera as an indicator of overwash deposits barrier island sediment supply and barrier island evolution folly island south carolina abstract micropaleontological analysis of four vibracores from back barrier marshes of folly island south carolina detected intervals of storm deposited sediment individual washover intervals were not detectable from lithology alone but only in conjunction with associated foraminifera washovers contained more modern offshore and oligo miocene genera and total calcareous foraminifera than background marsh samples the presence of tertiary foraminifera in the back barrier cores from folly island supports the hypothesis that much of the sediment for barrier island migration is derived from offshore foraminiferal analyses of back barrier cores were also used to calculate relative bioturbation rates by the method of officer and lynch officer c b lynch d r 1983 mixing sedimentation rates and age dating for sediment cores mar geol 46 261 278 eqs 10 14 in all cores the current depositional environment correlated well with the expected mixing parameter g the highest mixing parameter greatest signal attenuation was recorded in a core from a low marsh creek side environment whereas the lowest mixing parameter least smearing of signal was recorded in a high marsh core

mars atmospheric dynamics as simulated by the nasa ames general circulation model 2 transient baroclinic eddies a large set of experiments performed with the nasa ames mars general circulation model gcm have been analyzed to determine the properties structure and dynamics of the simulated transient baroclinic eddies the mars gcm simulations span a wide range of seasonal dates and dust loadings and include a number of special sensitivity experiments e g with flat topography there is strong transient baroclinic eddy activity in the extratropics of the northern hemisphere during the northern autumn winter and spring seasons the eddy activity remains strong for very large dust loadings though it shifts northward the eastward propagating eddies are characterized by zonal wavenumbers of 1 4 and periods of 2 10 days in several simulations the eddy variance is dominated by a single zonal wavenumber and a narrow range of periods the longer wavenumbers 1 and 2 transient eddies have a very deep vertical structure exhibiting a maximum kinetic energy density at the model top 45 50 km in many of the simulations in a simulation for early northern spring the eddies are quite shallow however the transient eddies generate the bulk of their energy baroclincally via large meridional and vertical heat fluxes at both lower and upper levels this is despite the fact that their vertical structure is typically close to equivalent barotropic above the lowest 10 km the eddies also appear to generate a substantial amount of energy barotropically via large meridional momentum fluxes at both lower and upper levels in the tropics and northern subtropics at upper levels 25 50 km there are strong transient eddy motions with structures resembling those characteristic of inertially unstable modes this eddy activity appears to be a response to the forcing of a region of marginal inertial stability by the extratropical transient baroclinic eddies as the wavenumbers and periods are the same as those in the extratropics a major surprise is the presence of very weak transient eddy activity in a number of the southern winter simulations it appears that this is partly a consequence of the stabilizing effects of the zonally symmetric topography in the gcm but it also must be associated with certain aspects of the zonal mean circulation in southern winter this is indicated by the presence of relatively large amplitude eddies in simulations for early southern autumn and spring and in a southern winter solstice simulation incorporating a different topography derived from the mars digital terrain model this topography differs from that used in most of the gcm simulations in not being characterized by steep symmetric slopes which are stabilizing to baroclinic instability in southern high latitudes it is hypothesized that the very large extent of the southern seasonal polar cap and high elevations in the south both might contribute to weakening the transient eddy activity large zonally symmetric topography in the northern hemisphere of the mars gcm also appears to have a strong impact on the transient eddies acting to increase the dominant zonal wavenumbers and phase speeds the properties of the gcm baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from viking lander meteorology observations the gcm eddies are found to be very similar to those observed in most respects a notable exception is that the eddy amplitudes in the highly dusty gcm simulations are much larger than those observed by viking during the 1977 winter solstice dust storm this is almost certainly at least partly due to the relatively small latitudinal expansion of the hadley circulation in the highly dusty gcm experiments

geochemical surface exploration for hydrocarbons in north sea approximately 350 sediment samples were taken in the central part of the north sea and hydrocarbon composition methane c1 and ethane c2 yields and carbon isotope composition of the methane dgr13c1 adsorbed in the sediment were determined methane generation or oxidation by bacterial activity can not be deduced from the analytical data this fact is explained by the assumption of a threshold of methane concentration in sediments below which methane oxidizing bacteria are inactive and that this threshold was not reached in the area investigated background gases in the surface sediments characterized by low c1 yields and dgr13c1 37 ppt can be distinguished from thermal sediment g ses which are obviously derived from a hydrocarbon generating source rock in the subsurface source rock data obtained from several wells situated on a cross section through the investigated area were compared to the geochemical patterns of the sediment gases and used to define profile sections with good dgr13c1 approx 40 ppt yield c1 approx 217 ppb and poor source rock properties dgr13c1 approx 33 ppt yield c1 approx 24 ppb an assessment of the source rock potential of the whole area under investigation has been carried out using the geochemical data of the surface sediment gases and taking into account that the c1 and c2 yields are generally higher in clay sediments than in sand samples the number of producing wells was related to the number of all wells 271 in the areas characterized by surface geochemistry as good or poor source rock areas the comparison showed that the relative number of producing wells is higher in areas geochemically characterized as good hydrocarbons in surface sediments of good north sea areas are not generated by bacteria at shallow depth they are formed thermally from the organic carbon of deep source rocks and migrate to the surface therefore they are indicative of thermal hydrocarbon generation in the subsurface

sedimentary evidence of intense hurricane strikes from new jersey nine vibracores from the backbarrier marsh at whale beach new jersey reveal three large scale overwash deposits associated with historic and prehistoric storms the uppermost and smallest overwash fan was deposited in the ash wednesday northeaster of march 5 8 1962 a second more substantial overwash fan between 100 and 35 cm depth dates to the late eighteenth or early nineteenth century this fan was most likely deposited during the 1821 hurricane the only intense hurricane to make landfall in new jersey in the past 350 yr a third larger overwash fan between 200 and 300 cm depth was deposited between a d 1278 and 1438 and is likely the result of a prehistoric intense hurricane strike the combination of historical and stratigraphic evidence indicates that two intense hurricanes winds 50 ms 21 have likely made landfall on the southern new jersey coast in the past 700 yr resulting in an annual landfall probability of 0 3

atmospheric tidal forcing of the zonal mean circulation the martian dusty atmosphere abstract classical atmospheric tidal theory has been used to compute the bilinear tidal zonal mean forcing per unit mass of the zonal mean meridional and zonal winds together with the tidal zonal mean heating per unit mass for the dusty martian atmosphere the convergences of the tidal eliassen palm ep flux have been computed for both clear and dusty atmospheric conditions including the special case of a dusty corridor in the summer southern subtropics that is meant to simulate the early stages of a planetary scale martian dust storm the calculation of the tidal ep zonal forcing differs from hamilton in that more realistic thermotidal forcings and basic state temperatures are used the zonal mean convergences of the tidal fluxes of heat and momentum are large during a martian great dust storm and should alter significantly the zonal mean circulation and its residual component driven by the zonal mean heating in particular the tidal forcing of the meridional wind which is an order of magnitude gr

spatial variations in major u s hurricane activity statistics and a physical mechanism abstract the authors provide a statistical and physical basis for understanding regional variations in major hurricane activity along the u s coastline on long timescales current statistical models of hurricane activity are focused on the frequency of events over the entire north atlantic basin the exception is the lead author s previous work which models the occurrence of hurricanes over the caribbean sea gulf of mexico and the southeast u s coast separately here the authors use statistics to analyze data from historical and paleoclimatic records to expand this work in particular an inverse correlation in major hurricane activity across latitudes at various timescales is articulated when activity is above normal at high latitudes it tends to be below normal at low latitudes and vice versa past research paleoclimatic records and historical data hint at the potential of using the north atlantic oscillation nao as an indicator of where storms will likely track over long timescales an excite

reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern florida from lake sediment records abstract sediment cores from western lake provide a 7000 yr record of coastal environmental changes and catastrophic hurricane landfalls along the gulf coast of the florida panhandle using hurricane opal as a modern analog we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity few catastrophic hurricanes struck the western lake area during two quiescent periods 3400 5000 and 0 1000 14 c yr b p the landfall probabilities increased dramatically to ca 0 5 per yr during an hyperactive period from 1000 3400 14 c yr b p especially in the first millennium a d the millennial scale variability in catastrophic hurricane landfalls along the gulf coast is probably controlled by shifts in the position of the jet stream and the bermuda high

bedform and stratification characteristics of some modern small scale washover sand bodies washover sand bodies commonly develop along microtidal coastlines in beach barrier island or spit settings wave runup usually in conjunction with an abnormally high water level may overtop the most landward berm of the beach and the foredune crest if one exists to produce overwash and subsequent runoff across the more landward subaerial surface two main elements of the resulting deposit are the washover fan and runoff channel newly formed small scale washover deposits were examined along the outer banks north carolina near pt mugu california and at presque isle lake erie pennsylvania the fans were formed in response to unidirectional landward transport and the runoff channels in response to unidirectional flow usually in a landward direction but sometimes in shore parallel then seaward direction where overwash carried across the fan surface and entered a pond or lagoon a small scale delta microdelta developed in this case the washover fan consisted of two subfacies the wetted but subaerial part of the fan and the subaqueous washover delta flow associated with the development of the fan and runoff channel produced distinctive sets of bedforms and internal stratification high velocity discontinuous surges moving across the fan surface resulted in the development of a plane bed and subhorizontal to low angle landward dipping planar stratification which comprised the major part of the fan similarly rhomboid forms were produced by high velocity sheet flow across the fan surface where flow carried into a standing body of water delta type foreset strata developed for this case the lateral structural sequence was subhorizontal planar stratification merging landward into landward dipping delta tabular foreset strata in the runoff setting where flow became channelized and continuous both upper flow and lower flow regime currents were typical upper flow regime bedforms included antidunes standing waves and plane beds the most commonly observed lower flow regime bedforms included microdelta like bars low amplitude bars linguoid ripples and sinuous crested current ripple trains the sets of sedimentary structures comprising modern washover sand bodies provide criteria for the identification of similar deposits in ancient sediments and for more specific interpretation of the environment

dynamical modeling of a planetary wave mechanism for a martian polar warming abstract a dynamical mechanism for the martian atmospheric polar warming observed by the viking irtm during the 1977 winter solstice dust storm and a similar one possibly observed by mariner 9 in 1971 is proposed and investigated using a simplified nonlinear model the model is of a type previously used to successfully simulate the essential aspects of terrestrial sudden stratospheric warmings the dynamical mechanism is in part very similar fundamentally to that responsible for these warmings involving planetary scale waves a number of numerical experiments have been conducted to assess the basic viability of such a mechanism for the martian polar warming and to examine its sensitivity to several factors these experiments demonstrate that a planetary wave mechanism can produce a polar warming with the magnitude and suddenness of that observed a planetary wave mechanism must primarily involve wavenumber 1 as wavenumber 2 is too strongly vertically trapped to produce a warming like that observed the necessary wave forcing in the present model can be topographic mechanical or thermal and nonstationary and is relatively large but certainly plausible the strong radiative damping in the mars atmosphere acts to substantially inhibit a warming through its effects on both the zonal flow and the wave dissipation plays a greater role relative to transience in a model martian warming of the type studied here than in a sudden stratospheric warming increasing radiative damping during a warming due to higher temperatures and greater dust loading may play a role in yielding a relatively rapid cooling phase for the mars warming event the residual mean meridional circulation during a model warming entails strong poleward and downward flow into high northern latitudes throughout a very deep region this probably indicates similar transport of atmospheric dust as well as water such transports are of considerable potential significance for both the dust and water cycles on mars

700 yr sedimentary record of intense hurricane landfalls in southern new england five intense category 3 or greater hurricanes occurring in 1635 1638 1815 1869 and 1938 have made landfall on the new england coast since european settlement historical records indicate that four of these hurricanes 1635 1638 1815 and 1938 and hurricane carol a strong category 2 storm in 1954 produced significant storm surges 3 m in southern rhode island storm surges of this magnitude can overtop barrier islands removing sediments from the beach and nearshore environment and depositing overwash fans across back barrier marshes lakes and lagoons in a regime of rising sea level accumulation of marsh lake or lagoon sediments on top of overwash deposits will preserve a record of overwash deposition we examined the record of overwash deposition at succotash salt marsh in east matunuck rhode island and tested the correlation with historical records of intense storms aerial photographs taken after hurricanes in 1954 and 1938 show overwash fans deposited at the site analysis of 14 sediment cores from the back barrier marsh confirmed the presence of these fans and revealed that 4 additional large scale overwash fans were deposited within the marsh sediments the four overwash fans deposited since the early seventeenth century at succotash marsh matches the historical record of significant hurricane induced storm surge these fans were most likely deposited by hurricanes in 1954 1938 1815 and either 1638 or 1635 radiocarbon dating of two prehistoric overwash fans indicated that these were deposited between a d 1295 1407 and 1404 1446 and probably represent intense hurricane strikes in the past 700 yr at least 7 intense hurricanes struck the southern rhode island coast and produced a storm surge that overtopped the barrier at succotash marsh

planetary scale wave structure in the martian atmosphere abstract wave like perturbations are found in the mariner 9 iris atmospheric temperature data during late northern hemisphere winter in a latitude band between 45 n and 65 n the nature of the data base prevents a unique separation of spatial and temporal behavior but fourier analysis of the data constrains the waves to discrete combinations of planetary wavenumber and period one major spectral component possesses a meridional amplitude cross section with a maximum near the 1 mbar level at 60 n and is strongly correlated with the circumpolar jet observed in thermal winds calculated from the mean meridional temperature cross section this feature is consistent with the low wavenumber baroclinic waves observed in viking lander data and the vertical structure reflects the behavior anticipated for a vertically penetrating quasi geostrophic disturbance other possible origins for the wave cannotbe ruled out however among these is a stationary wave forced by wavenumber 2 topographic relief

a 1200 year proxy record of hurricanes and fires from the gulf of mexico coast testing the hypothesis of hurricane fire interactions abstract we present here the first high resolution pollen record of vegetation response to interactions of hurricane and fire disturbances over the past 1200 yr from a small lake in alabama on the gulf of mexico coast the paleotempestological record inferred from the overwash sand layers suggests that the alabama coast was directly struck by saffir simpson category 4 or 5 hurricanes twice during the last 1200 yr around 1170 and 860 cal yr bp suggesting an annual landfall probability of 0 17 for these intense hurricanes the charcoal data suggest that intense fires occurred after each of these hurricanes the pollen data suggest that populations of halophytic plants chenopodiaceae and heliophytic shrubs myrica expanded after the hurricane strikes probably due to saltwater intrusion into the marshes and soil salinization caused by overwash processes populations of pines pinus sp decreased significantly after each intense hurricane and the ensuing intense fire suggesting that repeated hurricane fire interactions resulted in high tree mortality and probably impeded recruitment and recovery our data support the hypothesis that the likelihood and intensity of fire increased significantly after a major hurricane producing responses by vegetation that are more complex and unpredictable than if the disturbance agents were acting singly and independently

stratigraphy of washover deposits in florida implications for recognition in the stratigraphic record abstract twelve washover deposits were cored on the west central gulf coast of florida to provide data to permit development of a model to help identify washover facies in the stratigraphic record typical modern washover stratigraphy displays landward dipping plane beds comprised of well sorted sand with distinct laminae of shells and heavy minerals five subfacies are delineated which show variations in composition texture and bioturbation throughout the washover facies these subfacies represent differences in flow conditions during overwash position relative to sea level and variable degrees of reworking after deposition three shell assemblages aid in identification of washover deposits backbarrier sediments composed of shoreface open water species or mixed shoreface backbarrier species may potentially be washover in origin sediments with purely backbarrier quiet water shell species are likely to have been deposited independently of washover activity examination of washover deposits of differing ages reveals that preservation of washover stratigraphy is not exclusively a function of time reworking of small scale stratification can occur in as short as a decade however this same stratification was found to be preserved in deposits several hundred years old destruction of original washover signatures is related to the position of the deposits relative to sea level and the rate and depth of burial even after the destruction of small scale stratigraphic features washover deposits may still be identified as such due to their texture composition and shell assemblages key features in recognizing the facies after bioturbation and reworking are 1 the presence of clean sand in otherwise muddy backbarrier sediments 2 the landward thinning of the facies and 3 the presence of shoreface shells or mixed shoreface backbarrier shells on landward portions of the barrier island system if reworking is severe and or there are limited subsurface data distinguishing washovers from genetically similar deposits e g flood tidal deltas and spillover deposits in the stratigraphic record is difficult and when considered out of stratigraphic context may not be recognizable

source and migration of light hydrocarbons indicated by carbon isotopic ratios carbon isotopic ratios can distinguish among different sources of methane and can be used to correlate maturity of sediments with the methane this technique has been applied to several wells and the isotopic values have been used to suggest the sources of the methane and whether the methane migrated into the area comparison of the isotopic ratio changes in ethane propane and butanes indicated that isotopic fractionation of methane by migration is not a major factor the significant changes in methane isotopic ratio and the small changes in the isotopic ratios of these heavier hydrocarbons suggest that although diffusion is not the sole process in migration the time for migration is moderate

model for hydrocarbon microseepage and related near surface alterations despite recent advances in surface and near surface geochemical methods there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits we have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man years of our experience to contribute to that end evidence indicates that hydrocarbon micro seepage from reservoirs most probably involves buoyant colloidal size microbubbles of light hydrocarbons principally methane through the butanes ascending relatively rapidly through a water filled network of fractures joints and bedding planes bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide which may alter sediments producing detectable modifications in geomorphic seismic magnetic and radiometric properties we have used combinations of 1 airborne microwave sensing and laboratory analyses of soil gas hydrocarbons 2 shallow source aeromagnetic and soil magnetic susceptibility measurements 3 aerial and surface gamma ray measurements and 4 geomorphology to find productive oil and gas deposits results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings however these surface methods cannot reveal depth size or quality of reservoirs or even if producible hydrocarbons will be found

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present

origin and development of anclote key west peninsular florida abstract the morphology of barrier system elements on the west coast of peninsular florida is atypical for microtidal coasts because it includes numerous drumstick shaped barriers and large ebb tidal deltas anclote key in pinellas county is the most northern island of the system it was investigated in detail in order to determine its origin and developmental history extensive vibracoring and shallow seismic sub bottom profiling demonstrate that a miocene limestone platform underlies the area and is covered by only a few meters of pleistocene and holocene strata shoreward of anclote key the irregular limestone surface slopes very gradually toward the gulf whereas the gradient on the gulf side is two to three times greater a subtle but well defined limestone ridge with relief of approximately 1 m is present beneath anclote key stratigraphic analysis of 24 vibracores has identified nine quaternary facies above the miocene limestone a pleistocene muddy sand unconformably overlies the limestone and is unconformably overlain by holocene units as sea level rose to within a few meters of its present position beginning about 4200 yrs b p extensive shallow sub tidal grass flats and inter tidal to supratidal mangrove swamp and salt marsh environments were present in this area wave action near the break in slope of the limestone surface caused concentration of sand and shell to be deposited as a shallow subtidal shoal continued wave and tidal action accompanied by slowly rising sea level caused vertical accretion and spillover as the shoal became intertidal and eventually supratidal once the sand body became subaerially exposed as a barrier island processes typical of such environments gave rise to the deposition of well defined beach dune and mangrove covered washover facies the configuration of the shallow limestone platform was instrumental in controlling the location of anclote key as it developed during the late holocene

records of prehistoric hurricanes on the south carolina coast based on micropaleontological and sedimentological evidence with comparison to other atlantic coast records singleton swash on the south carolina coast provides an extended record of storm events for this coast we used experience gained by looking at storm traces detected as layers of offshore foraminifera intercalated with marsh sediments from a known storm in the area hugo which occurred in 1989 to detect storm horizons from the sediments that have been accumulating in singleton swash since 5700 yr b p we suggest here that the most intense storm activity occurred in the 0 1000 yr b p interval six storms only three occurred in the 1000 2000 yr b p interval and two in the 2000 3000 yr b p time interval calibrated radiocarbon years there was one giant storm in the pre 5000 yr b p interval a sea level oscillation in the 3500 5000 yr b p interval appears to have destroyed most records during that period previous work suggests that the position of the bermuda or azores high influences the direction of general storm paths for major north atlantic hurricanes a position of the bermuda high farther to the south tends to force storms into the gulf of mexico whereas a northern position allows them to track up the atlantic coast results here combined with results of other workers on the gulf coast suggest a more southern position for the bermuda high causing more storms on the gulf coast in the interval of 1000 3400 yr b p conversely a more northern position during the past 1000 yr is suggested to have contributed to higher frequencies of storms on the atlantic coast in that period to test this hypothesis modern records of the movement of the north atlantic oscillation nao which controls the position of the bermuda high have been compared with historical records of hurricane tracks over the twentieth century there does appear to be a strong correlation between the position of the nao and the track the storms have pursued in modern times

radio science investigations with mars observer mars observer radio science investigations focus on two major areas of study the gravity field and the atmosphere of mars measurement accuracies expressed as an equivalent spacecraft velocity are expected to be of the order of 100 m s for both types of investigations from use of an improved radio transponder for two way spacecraft tracking and a highly stable on board oscillator for atmospheric occultation measurements planned gravity investigations include a combination of classical and modern elements a spherical harmonic or equivalent field model of degree and order in the range 30 50 will be obtained while interpretation will be in terms of internal stress and density models for the planet using the topography to be obtained from the mars observer laser altimeter atmospheric investigations will emphasize precision measurement of the thermal structure and dynamics in the polar regions which are regularly accessible as a result of the highly inclined orbit studies based on the measurements will include polar processes cycling of the atmosphere between the poles traveling baroclinic disturbances small scale waves and turbulence the planetary boundary layer and possibly the variability and altitude of the ionosphere as the radio occultation is insensitive to dust in the atmosphere per se and measures only the resulting change in thermal structure it is expected that the radio technique can contribute to understanding of dust storm phenomena mutual observations of the atmosphere by means of radio occultation and by the pressure modulator infrared radiometer and the thermal emission spectrometer are expected to strengthen the reliability and accuracy of all three investigations