orbital observations of contemporary dune activity in endeavor crater meridiani planum mars 1 although aeolian landforms are pervasive on mars evidence for contemporary activity has been limited the next major campaign for the mars exploration rover opportunity is the investigation of the 20 km diameter endeavor crater 6 km to southeast of the rover s position as of december 2010 we present evidence from orbital imagery that eight aeolian bed forms 14 000 m2 in endeavor crater have been active within the past decade 2001 2009 at a spatial scale that should be directly observable by opportunity from the crater rim two dunes appear to show translational migration 10 20 m but all dunes indicate erosion to be the dominant process with up to 100 sediment removal thermophysical properties of these dunes are consistent with very fine to fine sand sizes the particle sizes most easily moved by the martian atmosphere the dunes that show the most surface change have a rippled appearance without well defined slip faces based on their morphology elliptical shape we classify them as dome dunes mesoscale atmospheric modeling is employed to provide insight into the atmospheric forcing of this aeolian system the major wind regimes from modeling are consistent with observations of wind streaks sand streamers ripples and slip faces of regional dune fields although modeled wind speeds are insufficient to move sand the translation and erosion of these dunes constitutes the largest contemporary movement of sand sized sediment reported on mars to date and demonstrates that endeavor crater has been subject to wind profiles exceeding the threshold velocity at the surface daily seasonally and or episodically in the recent past

observations of a cyclonic ring gulf stream coalescence event over the blake plateau hydrographic data collected in september 1980 over the blake plateau were analyzed using a combination of empirical search and inverse techniques five sections extending from the continental shelf break eastward across the blake plateau were positioned at approximately 1 intervals between 28 and 32 n the empirical search procedure was applied to four closed regions boxes constructed from adjacent sections where each region was assumed to consist of two conservative layers five geostrophic velocity sections were obtained using the average optimum reference level for the four boxes the inverse technique provided barotropic correction velocities that caused all layers to conserve mass the sections and the resulting transport streamline fields revealed the presence of a cyclonic feature whose meridional and zonal extent was about 200 km in both directions this feature was shown to be a coalescing gulf stream ring in a late stage of decay water mass analyses current meter data and earlier studies were used to support this hypothesis the cyclonic advection of gulf stream water around the ring formed a meander in the eastern gulf stream wall topography appeared to be affecting this flow suggesting that other rings entering the region would be similarly influenced evidence of recurring rings at or near this location and hence meanders of the eastern gulf stream wall was found in hydrographic data collected by noaa over a 12 month period from 1965 to 1966 these data suggested that two such events lasting about 4 weeks each occurred during this period the frequency of these events was in agreement with earlier findings while the duration of these events was supported by current meter observations

variations in relative abundances of goethite and hematite in bengal fan sediments climatic vs diagenetic signals abstract relative abundances of goethite and hematite in marine sediments have been increasingly used in reflectance spectrometry studies to infer the precipitation regime at the source area of detrital sediments this interpretation is contingent on the assumption that the ratio of these minerals is not modified by diagenetic processes our rock magnetic study of the 10 5 4 0 ma interval of the bengal fan sedimentary sequence indicates that this is not always the case we demonstrate that a statistical analysis of isothermal remanent magnetization acquisition curves provides an adequate estimate of the content of goethite and hematite in sediments we also identified distinctive biogenic and detrital components likely titano magnetite or maghemite in the studied samples the sediments of the bengal fan contain a significant change in relative abundance of goethite and hematite at 7 ma which is approximately coeval with a postulated climatic turnover in the sediment source region however systematic variations in the detrital and biogenic components as well as an increase in the total organic carbon content and the appearance of pyrite concretions at the same stratigraphic level suggest that this change in magnetic mineral content reflects a change in the degree of diagenetic alteration of the initial detrital assemblage rather than a climatic signal when assigning climatic interpretations to changes in the relative abundance of goethite and hematite in marine sediments in future studies the possibility of diagenetic modification should be evaluated with rock magnetic methods alteration of ancient sediments can be detected and the severity of alteration can be estimated based on the presence and grain size variation of the ferrimagnetic fraction magnetite maghemite which is more sensitive to early reductive dissolution than high coercivity minerals goethite and hematite

brittle star distribution patterns and population densities on the continental slope off central california echinodermata ophiuroidea abstract the ophiuroid communities on the continental slope off central california were examined using box cores and trawls box cores were taken between 550 and 3085 m at sites southwest of the farallon islands and otter and beam trawls were used below 2300 m at three sites between the farallon islands and point sur eighteen ophiuroid species from six families were identified eighty percent of the individuals collected with box cores belonged to two species ophiura leptoctenia and ophiacantha normani which were dominant between 1000 and 2000 m the largest ophiuroid faunal break occurred at around 2000 m and was associated with elevated dissolved oxygen levels decreasing sediment grain size and increasing sediment organic content a comparison of box core and trawl data from below 2300 m showed that box cores undersampled the ophiuroid community on the continental slope missing almost 50 of the species collected by trawls within the same area whereas trawls underestimated ophiuroid densities reporting on average 243 times fewer ophiuroids per m2 than did box cores there was a change in species relative abundance patterns between sampling locations ophiuroids exhibited patchy spatial distribution patterns on both a small scale of around 0 1 m2 and a large scale on the order of 100 1000 s of square meters

geochemical and sedimentological control of the magnetic properties of hemipelagic sediments owing to their high sedimentation rates and wide areal extent hemipelagic sediments along continental borderlands are potentially important high resolution recorders of geomagnetic secular variation to assess this possibility we studied suboxic hemipelagic muds from the oregon continental slope and anoxic laminated diatomaceous oozes from the gulf of california these sediments were rapidly deposited with average sedimentation rates of 121 and 135 cm kyr respectively bulk sediment sedimentological and geochemical analyses indicate that the two areas represent contrasting depositional regimes the remanence in both environments resides in fine grained magnetite particles although minor amounts of hematite were observed in the topmost gulf of california sediments despite first order differences the sediments from both areas show similar downcore patterns of systematic increases in solid sulfur mainly as pyrite dramatic decreases in natural nrm anhysteretic and isothermal remanent magnetization intensities and accompanying shifts in the magnetic stabilities these changes are consistent with reduction and dissolution of the ferrimagnetic iron oxides with depth due to early diagenesis of organic matter the magnetic grain size distribution first appears to rapidly coarsen downcore as the smallest and most abundant grains are removed then slowly grows finer as the remaining particles dissolve no evidence was observed for authigenic formation of magnetite provided sufficient concentration and stability of the detrital magnetic particles paleomagnetic directions can survive this dissolution diagenesis however relative paleointensity determinations based on normalization of nrm by concentration in related parameters will give erroneous estimates of paleofield behavior in such diagenetically altered sediments

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

role of bacterial mats in oxygen deficient marine basins and coastal upwelling regimes preliminary report bacterial mats play an important role in the sedimentation history of many marine biogenic regimes observations of the living mats suggest that in shallow waters they are dominated by photosynthetic cyanobacteria while in deeper waters the mats are dominated by nonphotosynthetic sulfur oxidizing bacteria fossilized remains of analogous mat structures from the miocene monterey formation are commonly associated with oil producing and phosphate rich zones preliminary observations suggest that bacterial mats may be a source of the organic matter that in time is thermally altered to hydrocarbons

biogenic magnetite as a primary remanence carrier in limestone deposits abstract studies on the microbial communities and magnetic phases of samples collected from carbonate oozes at sugarloaf key fl u s a and calcareous laminated sediments from laguna figueroa baja california mexico have revealed the existence of magnetotactic bacteria and ultrafine grained single domain magnetite in both environments magnetotactic bacteria were identified by light and electron microscopy the single domain magnetite was detected by coercivity spectra analysis with a squid magnetometer and examined under the transmission electron microscope the similarity in terms of size and shape between the single domain magnetite found in these sediments and the magnetite observed in the bacterial magnetosome from enriched cultures indicates the ultrafine grained magnetite in these two marine environments was biologically formed these results combined with the common occurrences of ultrafine grained magnetite in limestone deposits detected rock magnetically suggest biogenic magnetite may be present and contribute to the magnetic remanence in these rocks several cambrian limestone samples separately collected from siberia china and kazakhstan were examined for the presence of bacterial magnetite samples from the lower cambrian sinskian formation at siberia platform were found to contain both a large amount of apparently bacterial magnetite particles and a very stable primary magnetic component post cambrian diagenesis does not seem to affect the microgranulometry of these apparently bacterial magnetite crystals or the magnetic remanence carried by them assessing the potential role of biogenic magnetite as a primary remanence carrier in other phanerozoic limestone deposits ought to be further pursued

early diagenesis in an organic rich turbidite and pelagic clay sequence from the cape verde abyssal plain ne atlantic magnetic and geochemical signals abstract processes of early diagenesis in sediments from the cape verde abyssal plain are investigated using the complimentary techniques of environmental magnetism and solid phase geochemistry the sequence captured by a 2 m long box core comprises an organic rich turbidite derived from the nw african continental margin emplaced ca 330 ka bp overlain by brown pelagic clay diagenesis in the pelagic clay mainly involves slow in situ oxidation of the iron oxide phases present which mossbauer effect data suggest are detrital haematite and magnetite possibly maghaemitised in the turbidite diagenesis has proceeded in two stages the first involving suboxic reductive processes following depletion of porewater o2 and the second involving oxidative processes associated with the slow descent of an oxidation front through the bed due to diffusion of o2 from the overlying seawater carbonate free magnetic parameters interparametric quotients and remanence acquisition demagnetisation and coercivity measurements of the core reveal that significant depletion of detrital ferrimagnetic iron fe2 fe3 oxide grains like titano magnetite has occurred within the turbidite during suboxic diagenesis and confirm previous suggestions that reductive dissolution of such components is a grain size selective process however the higher oxidation state fe3 canted antiferromagnetic iron oxide grains like haematite and goethite are much less susceptible to reductive diagenesis remobilisation of transition metal ions from below the oxidation front in the turbidite has led to authigenic precipitation of ferrimagnetic fe mn micronodules in a distinct layer immediately overlying the front and above this a further interval of mn enriched diagenetic laminae however within the suboxic organic rich zone of the turbidite well below the oxidation front there is clear evidence for the presence of a significant concentration of fine single domain ferrimagnetic iron oxide grains which are most probably associated with a population of live magnetotactic bacteria between this zone and the oxidation front there is a transitional interval in which the number of live magnetotactic bacteria declines rapidly and fossil magnetosomes in the sediment are being reductively dissolved progressively up sequence these results are broadly similar though differing in some respects to magnetic and geochemical studies of hemipelagic and high productivity pelagic sediments in which mn and fe redox boundaries have been recognised and further illustrate the value of environmental magnetic parameters for characterising early diagenetic processes in sediments of this kind

rock magnetic characterization of early redoxomorphic diagenesis in turbiditic sediments from the madeira abyssal plain rock magnetic measurements of two sediment cores from the madeira abyssal plain map north atlantic are used to investigate post depositional changes in the concentration grain size and composition of magnetic minerals in the sediments that have occurred within organic rich turbidite horizons the changes are associated with an initial stage of suboxic reductive diagenesis following depletion of porewater o2 and a later stage of oxidative diagenesis associated with the slow descent of an oxidation front through the sediment as a result of diffusion of o2 from the overlying sea water the turbidites are of late quaternary age 18o stages 1 3 and derive both from different sites on the nw african continental margin and from the flanks of the canary islands thus the turbidites are variable compositionally especially in terms of carbonate detrital magnetic mineral and organic carbon content diagenetic changes in these sediments have been identified using solid phase geochemical data u mn corg and caco3 reported previously in more than one study rock magnetic parameters of the sediments when expressed on a carbonate free basis reveal that significant depletion of detrital ferrimagnetic iron fe2 fe3 oxide grains has occurred within organic rich turbidites during redoxomorphic diagenesis normalized quotients of magnetic parameters also show that reductive diagenesis is a ferrimagnetic grain size selective process but it has a minimal effect on the canted antiferromagnetic fe3 oxides in the sediment such components if present therefore become relatively enriched in magnetic assemblages as the ferrimagnetic grains are dissolved progressively and bulk magnetic concentration is thus depleted there is clear evidence in both cores for the existence of ultrafine ferrimagnetic grains at depth within the suboxic zone of the organic rich turbidites beneath both active and fossil oxidation fronts these grains are most probably associated with populations of live magnetotactic bacteria which commonly inhabit such organic rich horizons and play a part in the chain of bacterially mediated reactions normally associated with suboxic diagenesis these results show that simple and rapid rock magnetic techniques can be used to characterize early diagenetic processes involving iron phases in deep sea sediments at least as effectively as more laborious time consuming and sample destructive geochemical measurements

early diagenesis in north atlantic abyssal plain sediments characterized by rock magnetic and geochemical indices processes of early diagenesis are investigated in a sequence of late quaternary turbiditic sediments from the madeira abyssal plain map west of the nw african continental margin in three sediment cores from this region solid phase geochemical indices of redox sensitive ion mobilization are compared with rock magnetic parameters as proxies for diagenesis characterization the mud dominated distal turbidites are emplaced mainly as a result of glacio eustatic changes in sea level and derive both from different sites on the nw african margin and from the flanks of the canary islands thus the turbidites are of variable composition especially in terms of carbonate detrital magnetic mineral and organic carbon content within organic rich 0 5 corg turbidite horizons remineralization of organic detritus proceeds in two stages the initial stage involves suboxic reductive diagenesis following depletion of pore water o2 while the later stage involves oxidative diagenesis associated with the slow descent of an oxidation front through the sediment due to diffusion of o2 from the overlying seawater rock magnetic parameters of these sediments when expressed on a carbonate free basis reveal that significant depletion of detrital ferrimagnetic iron fe2 fe3 oxide grains has occurred within the organic rich turbidites during suboxic diagenesis normalized quotients of magnetic parameters and remanence coercivity profiles of selected samples also show that reductive diagenesis is a ferrimagnetic grain size selective process but it has a minimal effect on the canted antiferromagnetic fe3 oxides in the sediment such components if present therefore become relatively enriched in magnetic assemblages as the ferrimagnetic grains are progressively dissolved in all three cores studied however there is clear evidence for the presence of ultrafine ferrimagnetic iron oxide grains at depth within the suboxic zones of organic rich turbidites beneath both active and fossil oxidation fronts these grains are probably associated with populations of live magnetotactic bacteria which inhabit such organic rich horizons and which form a link in the chain of bacterially mediated reactions normally associated with suboxic diagenesis these results comply with previous observations made in studies of suboxic diagenesis in hemipelagic sediments and demonstrate the value of rapid and non destructive rock magnetic measurements for illuminating redoxomorphic processes of diagenesis involving transformation of iron phases in deep sea sediments

oxygen and organic matter thresholds for benthic faunal activity on the pakistan margin oxygen minimum zone 700 1100 m abstract a transition from fully laminated to highly bioturbated sediments on continental margins is thought to derive from increased animal activity associated with increasing bottom water oxygen concentration we examined faunal community responses to oxygen and organic matter gradients across the lower oxygen minimum zone omz on the bathyal pakistan margin where sediments grade from fully laminated sediment at 700 m 0 12 ml l 1 o 2 5 m to highly bioturbated sediment at 1100 m 0 23 ml l 1 o 2 10 m high resolution sampling of the seafloor every 50 m water depth was conducted along a single transect during inter and post monsoon periods in 2003 to address a the existence of oxygen thresholds regulating macrofaunal abundance composition diversity and lifestyles b the interactive effects of organic matter quantity and quality c associated community effects on sediment structure and d potential seasonality in these processes macrofaunal biomass and bioturbation depth were positively correlated with organic matter availability which peaked at 850 950 m 3 39 3 53 org c in contrast macrofaunal diversity h dominance r1d and burrow number exhibited threshold responses at oxygen concentrations of 0 12 0 20 ml l 1 5 9 m with few animals and highly laminated sediments present below this concentration and most taxa present in fully bioturbated sediments above it the highly mobile burrowing amphinomid polychaete linopherus sp exhibited almost complete dominance and high density at 750 850 m 0 12 0 14 ml l 1 o 2 5 6 m but despite its activity sediment laminae remained faintly visible formation of permanent burrows and detritivory were dominant macrofaunal lifestyles within the omz allowing laminae to persist at surprisingly high animal density and biomass results reflect a shift from organic matter to oxygen regulation of body size and biogenic structures following the monsoon this study suggests that for assemblages evolving under permanent severe hypoxia food availability remains a significant determinant of animal abundance and biogenic structure depth oxygen influences patterns of diversity and dominance and interacts with organic matter to generate abrupt faunal transitions on the pakistan margin

an investigation of the circulation of the gulf of mexico empirical search and inverse techniques were used to reanalyze historical hydrographic data obtained in the gulf of mexico february 12 to march 31 1962 from these data eight transects which provide basin wide coverage of the gulf were constructed on the basis of water properties the circulation of the gulf of mexico was characterized as a three layer mass conservative system along most sections an empirical search in density coordinates was sufficient to obtain an optimum reference level that balanced the transport in the three layers an inverse correction was necessary to obtain a mass balance for those sections that crossed the loop current and mesoscale eddies the density of the optimum reference level 1 32 17 obtained from this analysis corresponds approximately to the bottom of the antarctic intermediate water layer that exists in the gulf of mexico by using this optimum reference level total velocity profiles at specific locations in the gulf of mexico were obtained taken together these yielded a description of the winter circulation of this region in general the large scale circulation consists of a clockwise anticyclonic gyre which is most prominent in the upper 500 m eastward and westward transports associated with the gyre are approximately equal at about 5 106 m3 s 1 variations to this flow are provided by the loop current in the eastern gulf and a cyclonic eddy in the northwestern gulf transports obtained for these circulation features are approximately 30 106 and 8 106 m3 s 1 respectively which are in agreement with values obtained from other hydrographic surveys in the gulf of mexico

magnetotactic bacteria and single domain magnetite in hemipelagic sediments remanent magnetism in marine sediments has been used extensively over the past twenty years to calibrate the geological time scale study geomagnetic reversals and secular variation and measure the rates of seafloor spreading although these sediments may contain different magnetic minerals magnetite is the most commonly observed and magnetically stable phase and its size shape and post depositional fate affect the magnetic remanence of the sediments biogenic magnetites are single domain with a high natural magnetic remanence nrm and have been suggested as a significant source of magnetic remanence in marine sediments we have studied surface sediments from the santa barbara basin and report the occurrence of living magnetotactic bacteria and the deposition of biogenic ultra fine grained single domain magnetite using a novel extraction technique transmission electron microscopy and squid magnetometry we show that these bacteria and the magnetite they produce are the major source of stable remanent magnetism in these sediments

electron optical characterization of bacterial magnetite abstract magnetic grains isolated from magnetococcoid bacterial cells were studied by means of transmission electron microscopy electron diffraction and electron microprobe analysis observed in situ the magnetic grains are each surrounded by an organic membrane and are usually found in a random array although chains are also seen electron diffraction confirms the magnetite mineralogy and provides additional evidence in favor of vacancies in the structure electron microprobe analysis shows the magnetite to be slightly titaniferous electron microscopy indicates that the grains rather than being flake shaped are parallelepiped crystals with a mean length of 99 3 8 7nm a mean width of 62 3 6 1nm yielding a width to length ratio of 0 63 these data support the contention that the magnetic bacterial grains are single domain crystals capable of producing a natural remanent magnetization in sediments

active aeolian processes on mars a regional study in arabia and meridiani terrae 1 we present evidence of widespread aeolian activity in the arabia terra meridiani region mars where different kinds of aeolian modifications have been detected and classified passing from the regional to the local scale we describe one particular dune field in meridiani planum where two ripple populations are distinguished by means of different migration rates moreover a consistent change in the ripple pattern is accompanied by significant dune advancement between 0 4 1 meter in one martian year that is locally triggered by large avalanche features this suggests that dune advancement may be common throughout the martian tropics

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

oxygen minimum zone edge effects evidence from the central california coastal upwelling system geologic and biological data from box cores gravity cores and bottom photographs across the modern coastal upwelling system of central california reveal that biogeochemical activity increases along the edges of the oxygen minimum zone omz 0 5 ml 1 o2 macrofauna and benthic foraminifers as well as relative concentrations of calcium carbonate glauconite and fecal pellets all display edge effects the major controls appear to be a combination of dissolved oxygen concentration of near bottom waters bottom currents and possibly bacterially mediated nutrient recycling as well as food supplies omz edge effects should be recognizable in the rock record and may prove to be powerful paleoenvironmental paleoecological indicators

the exaerobic zone a new oxygen deficient marine biofacies classical biofacies models1 2 for reconstructing palaeoenvironments of strata deposited in oxygen deficient marine settings define three principal facies aerobic 1 0 ml 1 1 o2 dysaerobic 1 0 to 0 1 ml 1 1 o2 and anaerobic 0 1 ml 1 1 o2 zones these models have postulated a decrease in organism size and degree of calcification as well as a drastic reduction in the relative percentage of fauna possessing calcified skeletons as the dysaerobic anaerobic boundary is approached through use of evidence independent of that provided by body fossils we demonstrate here that in portions of the monterey formation miocene california the bivalve anadara montereyana occurs in situ almost exclusively in strata deposited at the dysaerobic anaerobic boundary the occurrence of fossils of large well calcified benthic macroinvertebrates at this redox boundary contradicts classical biofacies models1 2 and there fore provides the basis for definition of a new oxygen related biofacies the exaerobic zone the exaerobic zone concept when adjusted for differences in basin configuration and palaeoceano graphic conditions provides a potentially useful model for explain ing occurrences of shelly benthic fossils within laminated organic rich strata of other phanerozoic marine sequences

lift off parameters of saltating particles on mars abstract the aeolian events are frequent on mars however we have very limited understanding of aeolian process because we cannot conduct experiments as we did on earth on martian surface directly right now in this paper we studied the lift off parameters of saltating particles in wind blown sand on mars systematically through a numerical way the main findings are shown as follows 1 the lift off speeds of martian particles increase linearly with wind shear velocities 2 the lift off speeds of particles on mars have the same order of magnitude as but a little smaller than those on earth at the same shear velocity 3 the lift off angles on mars are almost equal to those on earth and have weak dependence on shear velocities 4 the lift off parameters both speeds and angles are influenced by particle diameters

biogenic magnetite and the magnetization of sediments biogenic magnetites are produced through the reduction of ferric iron by both biologically induced extracellular and biologically controlled intracellular processes with few exceptions all are ultra fine grained single domain magnetite biogenic magnetites formed by magnetotactic bacteria biologically controlled have been shown to contribute significantly to the natural remanent magnetization of carbonates and limestones hemipelagic and deep sea marine sediments the input into sediments of ultra fine grained magnetite produced by dissimilatory iron reducing bacteria biologically induced has yet to be firmly established but may be even more significant whether either type of authigenic biomagnetite is preserved is determined by postdepositional factors including oxidation reduction by substitution and dissolution unconsolidated and lithified sediments can be screened for putative biogenic magnetite by rock magnetic techniques it is not generally appreciated that magnetotactic bacteria and their magnetofossils can be identified by the unusual and in some cases unique morphologies size range and composition of the magnetite crystals magnetite produced by dissimilatory iron reducing bacteria have a distinctive morphology and size range but it is currently controversial as to whether these can be distinguished from certain chemically precipitated magnetites the presence of dissimilatory iron reducing bacteria however can be detected using microbiological techniques and sediment geochemistry biogenic magnetites are trace fossils and potentially useful environmental indicators and are considered to have significant input to the magnetization of most sediments both modern and ancient

observations of collisions of saltating grains with a granular bed from high speed cine film high speed photography was used to record saltating sand grains colliding with a horizontal noncohesive bed of similarly sized grains impacting grain bed interaction is discussed in general the process as observed from the films is then described in terms of the apparent bed contact length abcl and various parameters of the impacting grains and any ejected grains examples are given of typical behaviour of bed grains in response to impacting grains of different sizes saltating grains that are large in comparison to the bed grains they encounter at collision can churn up the surface layers of soils and sediments so that previously buried grains become available for entrainment this process is discussed in relation to the potential release of dust particles into the airflow

circulation and heat flux in the bermuda triangle abstract data from the atlantis 215 cruise from cape henry to bermuda to fort pierce is analyzed to determine absolute geostrophic velocities in the region the search procedure that fiadeiro and veronis 1982 proposed for finding an empirical level of no motion is used to obtain 3500 m as the average level which satisfies mass balance for the bottom three of the five layers that appeared to be conservative ones mass in the two upper layers is not conserved for any choice of a reference level since those two layers contain the gulf stream which is known to have finite velocities near the bottom an inverse calculation is used to provide a velocity correction in the boundary region so that all layers satisfy mass conservation an improved method summarized in the appendix is used to carry out the inverse calculation the results include mass transports of 31 sverdrups sv through fort pierce 64 sv past cape romain and 91 sv past cape hatteras in agreement with direct determination of transports al

planet wide sand motion on mars prior to mars reconnaissance orbiter data images of mars showed no direct evidence for dune and ripple motion this was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low density atmosphere we show that many sand ripples and dunes across mars exhibit movement of as much as a few meters per year demonstrating that martian sand migrates under current conditions in diverse areas of the planet most motion is probably driven by wind gusts that are not resolved in global circulation models a past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

magnetostratigraphic dating of shallow water carbonates from san salvador bahamas magnetostratigraphic results are reported here from a sequence of late neogene quaternary shallow water carbonate sediments from a continuous core drilled on the island of san salvador bahamas on the basis of the remanent magnetism of 136 samples from a 91 m measured section of core the polarity sequence can be correlated with the magnetic polarity time scale from the gilbert chron early pliocene through the late brunhes chron late pleistocene holocene magnetic polarities were determined on the basis of relative up down direction in the unoriented core extraction studies of the magnetic particles reveal the presence of single domain crystals of magnetite resembling those produced by the magnetotactic bacteria and algae the sequence of reversals provides a minimum of six new major chronostratigraphic markers for the pliocene pleistocene of the bahamas it confirms and refines the local timing of both the lithologic change from skeletal to nonskeletal sediments and the disappearance of coral and molluscan species from the bahamas as upper late pliocene between 2 6 and 2 7 ma that the primary magnetic remanence is preserved in shallow water carbonates including replacement dolomites suggests that this technique could be used to date similar tertiary and possibly even older carbonate sequences the establishment of a reliable magnetostratigraphy provides refined dating of shallow water carbonates and regional faunal appearances or disappearances sediment accumulation rates subsidence and depositional events

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

chemosymbiont dominated seafloor communities in modern and cretaceous upwelling systems support a new high productivity variant of standard low oxygen models faunal analysis of modern benguela upwelling system namibia and ancient upper cretaceous israel sedimentary records rich in organic matter biogenic silica carbonate and phosphate indicates that contrary to stereotypes of upwelling systems as dead zones macrobenthic communities are present but highly variable biofacies vary with distance from the upwelling core and as a function of both the supply of food to the seafloor and the oxygen demand it creates there under a high organic supply large bodied chemosymbiotic bivalves dominate exaerobic and lower dysaerobic seafloors and deposit feeders are abundant in upper dysaerobic and aerobic zones macrobenthic biofacies under upwelling thus contrast strongly with the overwhelmingly filter feeder dominated biofacies encountered in the dark siliciclastic shales on which standard oxygen restricted biofacies models have been based and argue that mechanistically the low oxygen conditions characterizing those shales reflect ordinary levels of water column productivity and arise largely from water column stratification our biofacies model requires testing in other upwelling records however we expect it to be robust and useful given the long evolutionary histories of the chemosymbiotic and deposit feeding guilds providing a new means for discriminating the relative roles of high organic flux and low ventilation in creating low oxygen conditions at the seafloor

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

biogenic magnetite in stromatolites ii occurrence in ancient sedimentary environments abstract in this paper we report the discovery of fossil bacterial single domain magnetite particles in ancient stromatolites the biogenicity of the crystals was determined by the following criteria 1 distinctive morphology and habit 2 composition and 3 environment of deposition stromatolites ranging in age from the middle archean to pleistocene composed of both carbonate and chert were analyzed for the presence of single domain magnetite using rock magnetic methods the granulometry and composition of the ultra fine grained magnetite crystals extracted were determined by transmission electron microscopy and electron diffraction the oldest magnetofossils were extracted from stromatolitic chert of the gunflint iron formation which is approximately 2000 ma old the implications of these findings and the potential uses of fossil bacterial magnetite in studies of the evolution of biomineralization and prokaryotic metabolic processes paleomagnetism and as an indicator of ancient oxygen levels are discussed bacterial magnetite represents the oldest evidence of biomineralization yet discovered in the fossil record

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

paleoenvironmental conditions in a travertine complex deduced from rock magnetism we present a rock magnetic study on ca 100 specimens from a 7 5 m travertine section bmh and a parallel 1 0 m profile bmp to evaluate vertical and lateral variations concentration dependent parameters and inter parametric ratios point to varying redox conditions through time and space suggesting local paleoenvironmental rather than paleoclimatic control of the rock magnetic properties

aeolian vertical mass flux profiles above dry and moist sandy beach surfaces abstract the vertical distribution of aeolian mass flux was investigated in a natural beach environment field experiments conducted on the beach of the eba barrier southern baltic coast poland measured the sand transport rate and the vertical mass flux distribution above dry rippled sand and a moist flat sandy surface the experiments were intended to show the changes in the vertical distribution of sand with changing wind speed all the data represent saturated flux conditions sand transport was measured using 0 5 m high vertically segmented passive sand traps while the wind speed and direction were monitored at 1 m elevation the obtained dataset comprises 65 measurements on dry surfaces and 51 measurements on moist sandy surfaces the sand transport rate above the moist surface was up to 90 higher than above the dry surface for wind speeds of 7 11 m s but higher velocities gave smaller differences between the surfaces the saltation layer was thicker above the moist surface than above the dry surface all the vertical sand flux profiles are best described by exponential decay functions analysis of the normalised flux profiles grouped by wind velocity shows that the fitted curves are less inclined for moist surfaces than dry surfaces moreover the regression coefficients depict a marked trend in which the intercept decreases and the slope increases with increasing wind speed this indicates that more sand is transported at higher elevations above the bed and less at lower elevations the proportion of total transport seems to be independent of wind speed at elevations of approximately 35 mm and 50 mm above the dry and moist surfaces respectively differences between the measured and exponential fit values of mass flux are particularly distinct close to the bed where the exponential fit either over or under predicts the measured values over predictions occur in weaker winds up to 6 7 m s whereas under predictions become more pronounced as the wind becomes stronger and when the layer in which the under prediction occurs thickens the under predictions are particularly obvious above the moist surface it is not clear whether this phenomenon is due to technique measurement error or to another source the proportion of creep is often considered to be responsible for the difference from the exponential fit which represents the saltation mode of aeolian transport this proportion is difficult to determine because the mass flux measured by the lowermost chamber of the sand trap used in the experiments represents sand transported in both saltation and creep or and reptation

ultrafine grained magnetite in deep sea sediments possible bacterial magnetofossils a new extraction technique now permits ultrafine magnetite crystals to be separated from a variety of deep sea sediments morphologic characterization of these particles with transmission electron microscopy reveals the presence of several distinct crystal types some of which closely resemble those formed by the magnetotactic bacteria the apparently biogenic magnetite particles are of single domain size and dominate the population in calcareous deep sea sediments bacterially precipitated magnetite may therefore be a major source of the stable magnetic remanence in some marine sediments these objects possibly constitute the smallest mineral fossils yet recovered from the sedimentary record

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

high resolution geochemistry and sequence stratigraphy of the hushpuckney shale swope formation eastern kansas implications for climato environmental dynamics of the late pennsylvanian midcontinent seaway abstract the hushpuckney shale member of the swope formation missourian stage eastern kansas is the core shale of a kansas type cyclothem formed during the late transgressive to early regressive phases of a late pennsylvanian glacio eustatic cycle coeval high frequency climato environmental dynamics of the midcontinent seaway are preserved in the kgs orville edmonds no 1a study core as centimeter scale variation in major components organic carbon authigenic sulfides and phosphate detrital siliciclastics organic macerals trace element redox proxies mo u v zn and ichnofabric features benthic o 2 levels declined sharply from the base of the black shale 0 cm went sulfidic at 4 cm and reached a redox minimum at 21 cm above this level redox potential gradually rose fluctuating between sulfidic and nonsulfidic conditions from 35 cm to the black shale gray shale contact at 52 cm onset of dysoxic conditions at that contact allowed establishment of a benthic community of soft bodied organisms comprised of deep tiered tracemakers tolerant of low o 2 conditions trichichnus and shallow tiered tracemakers favoring soupground helminthopsis or firmground substrates the zoophycos phycosiphon schaubcylindrichnus planolites association most geochemical records exhibit a low order cycle spanning the full 52 cm thickness of the black shale submember reflecting a dominant glacio eustatic control the base and top of the black shale submember record lateral migration of the pycnocline across the midcontinent shelf during the transgressive and regressive phases respectively the maximum flooding surface mfs is at 17 23 cm an interval containing the euxinic peak and characterized by high concentrations of illite representing a cratonic siliciclastic flux and terrestrial organic macerals the product of transient increases in humidity weathering rates and the export of coal swamp vegetation associated with the interglacial highstand of the swope cyclothem although a transgressive surface of maximum starvation sms cannot be confidently identified a phosphate rich regressive condensation surface at 28 34 cm records pycnoclinal weakening due to increased aridity associated with renewed southern hemisphere icesheet growth a correlative shift in dominance from terrestrial to marine derived organic macerals reflects increased upwelling of nutrient rich deepwaters and enhanced primary productivity penecontemporaneous paleogeographic and climatic factors e g semirestricted circulation monsoonal precipitation predisposed the midcontinent seaway toward sensitivity to high frequency climato environmental fluctuations which are preserved as 2 to 7 cm thick cycles in the study core the 52 cm thick black shale submember contains 12 such high order cycles which have an estimated average duration of 2 to 9 kyr implying a sub milankovitch band i e millennial scale climatic control the results of this study are relevant to the sequence stratigraphic interpretation of kansas type cyclothems the dynamics of gondwanan ice age glacio eustatic cycles and the development of boundary conditions for late pennsylvanian paleoclimate models