particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump a synthesis of global sediment trap programs since 1983 particulate organic carbon poc is vertically transported to the oceanic interior by aggregates and their ballasts mainly caco3 and biogenic opal with a smaller role for lithogenic aerosols through the mesopelagic zone diel migrating zooplankton communities effect vertical transport and remineralization of poc in the upper layers of the ocean below 1 5 km the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport we normalized the fluxes of poc caco3 and biogenic opal from data published on samples collected at 134 globally distributed bottom tethered time series sediment trap ts trap stations to annual mole fluxes at the mesopelagic bathypelagic boundary m b at 2 km and defined them as fm bcorg fm bcinorg and fm bsibio using this global data set we investigated 1 the geographic contrasts of poc export at m b and 2 the supply rate of co2 to the world mesopelagic water column fm bcorg varies from 25 pacific warm pool to 605 divergent arabian sea mmolc m 2 yr 1 fm bcinorg varies from 8 high latitude polar oceans or 15 pacific warm pool to 459 divergent arabian sea mmolc m 2 yr 1 and fm bsibio the most spatially temporally variable flux ranges from 6 north atlantic drift to 1118 pacific subarctic gyre mmolsi m 2 yr 1 the oceanic region exhibiting the highest poc flux over a significantly large region is the area of the north pacific boreal gyres where the average fm bcorg 213 fm bcinorg 126 and fm bsibio 578 mmol m 2 yr 1 fm bcorg and fm bcinorg are particularly high in large upwelling margins including the divergent arabian sea and off cape verde one of the data sets showing the lowest flux over a significant region basin is fm bcorg 39 fm bcinorg 69 and fm bsibio 22 mmol m 2 yr 1 in the north pacific subtropical tropical gyres pan atlantic average fluxes are similar except fm bsibio fluxes are even lower where corg cinorg and sibio cinorg are 1 defines the carbonate ocean and where these ratios are 1 defines the silica ocean the carbonate ocean occupies about 80 of the present world pelagic ocean between the two major oceanographic fronts the north pacific polar front and the antarctic polar front and the silica ocean is found on the polar sides of these fronts the total global annual fluxes of fm bcorg fm bcinorg and fm bsibio at m b calculated by parameterizations of the export flux data from 134 stations are surprisingly similar 36 2 33 8 and 34 6 teramol yr 1 120 112 and 114 mmol m 2 yr 1 respectively resulting in a near uniform binary ratio between the above three elements of about one the global ternary ratios estimated from 152 ts trap samples of the three elements are 35 32 33 from our global fm bcorg and a published model estimate of the global export production we estimate the regeneration rate of co2 through the mesopelagic zone by the biological pump is 441 teramolc yr 1 based on our global fm bcinorg and recently estimated global primary production of pic 36 86 teramolc yr 1 of pic is assumed to be dissolved within the upper 2 km of the water column

influence of oxygen on heterotrophic reworking of sedimentary lipids at the pakistan margin abstract oceanic oxygen minimum zones omzs are thought to be regions of enhanced organic carbon burial with high organic matter om quality preservation resulting from low oxygen concentrations and faunal biomass both in the water column and at the seafloor here we use the pakistan continental margin to assess the controls on om deposition and quality along a transect through the omz from water depths of 140 1850 m we sampled five sites spanning the omz during the inter and late monsoon seasons to address the role of a oxygen b the benthic fauna and c seasonality on the composition and quality of om using lipid biomarkers organic carbon concentrations were highest within the omz and lipid biomarkers revealed that om at the pakistan margin was primarily of marine origin oxygen concentrations in bottom waters played an indirect role in controlling om quality by influencing faunal community composition and biomass both in the water column and at the seafloor benthic fauna appear to influence om quality via molecular filtration of certain compounds lipid biomarkers for example foraminifera that peak in the omz core 300 m 122 individuals 10 cm 2 0 11 ml l 1 4 91 m efficiently removed polyunsaturated fatty acids from the sediments whilst at the lower omz boundary suspension feeding pennatulids 1200 m 108 individuals hm 2 0 35 ml l 1 15 62 m stripped labile lipids from the water column particulates leading to the deposition of lipid poor om in the surficial sediments low infaunal and epifaunal biomass at the fully oxygenated deep site led to the persistence of phytodetritus and subsequently labile lipids in the sediments seasonal changes in om quality and composition were noted at 140 300 and 1850 m and were attributed to both particulate fluxes and faunal feeding patterns finally lipid biomarker indices demonstrated that the om at the pakistan margin was of low quality when compared to other similar environments

seismic hazard assessment for mymensingh bangladesh mymensingh municipality lies in one of the most earthquake prone areas of bangladesh the town was completely destroyed during the great indian earthquake of 12 june 1897 for which the surface wave magnitude was 8 1 in this study the 1897 great indian earthquake was used as a scenario event for developing seismic microzonation maps for mymensingh for microzonation purposes spt data from 87 boreholes were collected from different relevant organizations to verify those data ten boreholes of depth up to 30 m were drilled intensity values obtained for different events were calibrated against attenuation laws to check applicability to the study area vibration characteristics at diverse points of the study area were estimated by employing the one dimensional wave propagation software shake shake discretizes the soil profile into several layers and uses an iterative technique to represent the non linear behavior of the soil by adjusting the material properties at each iteration step the required input information includes depth shear wave velocity damping factor and unit weight of each soil layer the liquefaction resistance factor and the resulting liquefaction potential were estimated to quantify the severity of liquefaction quantification of secondary site effects and the weighting scheme for combining the various seismic hazards were heuristic based on judgment and expert opinion

new evidence for global tectonic zones on venus venera 15 and 16 spacecraft images show clear evidence of major crustal disruptions on venus which have been interpreted to indicate crustal divergence complementary to the divergent zones are mountain belts that border the continent like high terrains the requisite transcurrent motions appear to be manifested as diffuse shear zones the rift zones form an interconnected transpolar system which ties in with previously recognized equatorial disruption zones suggesting a global tectonic network several independent lines of evidence suggest that the tectonism may be geologically young

epibenthic megacrustaceans from the continental margin slope and abyssal plain of the southwestern gulf of mexico factors responsible for variability in species composition and diversity abstract the community structure of megacrustaceans orders lophogastrida isopoda and decapoda collected in trawls on the continental margin upper slope and abyssal plain of the southern gulf of mexico was studied to determine to what extent broad scale variation in community composition and diversity was influenced by geographic regions environmental variability and depth trawls were collected in the mexican ridges the campeche bank and the sigsbee abyssal plain there was variability in species composition density and diversity among geographic regions and along the depth gradient a total of 106 species were identified and grouped in three orders five infraorders 40 families and 70 genera this study extends the known geographic ranges of the species homolodromia monstrosa and ephyrina benedicti the largest number of species was recorded in the mexican ridges and on the upper continental shelf lower values were found on the continental margin and in the abyssal plain the largest densities were recorded on the continental margin in the mexican ridges megacrustaceans show in general low frequencies and low abundances in trawls characterizing them as rare components of benthic assemblages contrary to an accepted paradigm about deep sea biodiversity the highest h diversity values were recorded in the sigsbee abyssal plain followed by values from the upper continental slope diversity values were correlated with evenness canonical redundancy analysis results showed a significant affinity to regions for 18 crustacean species 33 species showed a significant affinity to both regions and depth zones within regions

tectonics and evolution of venus the global tectonics of venus differs significantly from that of earth most markedly in that the surface is covered predominately by gently rolling terrain there apparently are no features like ocean rises the gravity is positively correlated with topography at all wavelengths and the few highlands are estimated to be supported or compensated at a depth of approximately 100 kilometers the surface of venus appears to be covered mainly by an ancient crust the high surface temperature making subduction difficult it seems likely that well over 1 billion years ago water was destabilized at the surface and soon after plate tectonics ceased the highlands appear to be actively supported presumably as manifestations of long enduring hot spots

volcanic hazard communication using maps an evaluation of their effectiveness hazard maps are considered essential tools in the communication of volcanic risk between scientists the local authorities and the public this study investigates the efficacy of such maps for the volcanic island of montserrat in the west indies using both quantitative and qualitative research techniques normal plan view maps which have been used on the island over the last 10 years of the crisis are evaluated against specially produced three dimensional 3d maps and perspective photographs thirty two demographically representative respondents of mixed backgrounds sex education and location were interviewed and asked to complete a range of tasks and identification on the maps and photographs the overall results show that ordinary people have problems interpreting their environment as a mapped representation we found respondents ability to locate and orientate themselves as well as convey information relating to volcanic hazards was improved when using aerial photographs rather than traditional plan view contour maps there was a slight improvement in the use of the 3d maps especially in terms of topographic recognition however the most striking increase in effectiveness was found with the perspective photographs which enabled people to identify features and their orientation much more readily for montserrat it appears that well labelled aerial and perspective photographs are the most effective geo spatial method of communicating volcanic risks

on the possibility of plate tectonics on venus abstract several arguments have been put forward suggesting that venus has no place tectonics we examine some of these arguments and suggest that because conditions on the surface of venus are very different from those on earth the arguments should be reconsidered we show that in the absence of an ocean the differential hypsographic curve of earth would probably have only one mode like that for venus we show that the atmosphere of venus is quite capable of erosion provided that near surface velocities are about 1 m sec 1 or more and that therefore the oceanic areas on venus should they exist are probably covered with some thickness of sediment if sedimentation on venus is at all rapid it is likely that subduction zones could be filled up and made unrecognizable topographically because venus does not have an ocean and because its surface temperature is much greater than that on earth ridge crests on venus have a much smaller topographic expression than those on earth if significant sedimentation occurs they would be completely unrecognizable topographically

sea level variations global sedimentation rates and the hypsographic curve sea level changes during the neozoic have been estimated by two different methods the first involves measuring the amount of present day land area which was flooded during the past and using the present day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding the second involves the estimation of the changing volume of mid oceanic ridges through time and estimating sea level changes after having allowed for isostatic adjustment a difference in sea level of 170 m is obtained from the two methods for the cretaceous 80 100 m y b p this is equivalent to a difference in continental flooding of 24 mm 2 using the present day hypsographic curve we attempt to explain this difference firstly by allowing for the fact that the present day ocean basins have more sediment in them than did the cretaceous ocean basins this produces a sea level change in the opposite direction to that produced by the reduction in mid ocean ridge volume since the cretaceous secondly we suggest another large factor in producing the difference is that the present day hypsographic curve is not the correct one to use when studying sea level stands in the cretaceous present day average continental heights are closely related to continental areas accepting this principle if continents are joined together in the past their average height must be greater and so their hypsographic curve must be steeper a given sea level rise would produce less continental flooding during times of continental aggregation than it would today

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

evolution of oceanographic conditions off baja california 1997 1999 abstract this paper examines the oceanic response off baja california mexico to the 1997 1998 el nino and the transition to la nina conditions the data presented were gathered during seven cruises over a grid based on the calcofi station plan from lines 100 130 out to station 80 t s diagrams with data obtained during the peak phase of el nino demonstrate that warmer and saltier spicier than normal conditions prevailed in the upper 600 m over this region temperature and salinity anomalies calculated for calcofi line 120 revealed waters near the coast at 50 m depth to be up to 8 7 c warmer and s 0 8 saltier than the climatology during october 1997 these large anomalies persisted through january 1998 with some slight diminution in the magnitudes near the surface this study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest identified as subtropical surface water stsw and that low salinity tropical surface waters tsw were blocked to the southeast in the vicinity of the tip of the peninsula subsurface waters associated with the california undercurrent cu fed from the eastern tropical pacific etp were also warmer and saltier than normal and indicate a significant expansion in volume of the cu presumably a result of intensification of poleward flow at depth we postulate that the well defined near surface and deep poleward flows in the study area reflect anomalous large scale cyclonic circulation affecting the flow in the southeastern region of the north pacific subtropical gyre east of 125 w following the el nino event warm and salty upper waters retreated to latitudes south of punta eugenia with the return to normal and cooler conditions equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity transition to la nina conditions would have been associated with re establishment of normal anticyclonic flow in the southeastern quadrant of the pacific subtropical gyre

planetary radar astronomy planetary radar research reported during 1979 1982 was highlighted by radar observations of venus by the pioneer venus spacecraft earth based high resolution imaging of venus and the moon construction of accurate topographic profiles for martian tropical regions observational and theoretical advances in relating the radar signatures of mars and the moon to surface characteristics and the initial radar detections of echoes from a comet and a mainbelt asteroid this review begins with a brief synopsis of radar definitions and technical terminology and then summarizes recent results for individual targets readers interested in radar astronomy prior to the current quadrennium are directed to excellent reviews by jurgens 1982a pettengill 1978 evans 1969 muhleman 1966 and pettengill and shapiro 1965 detailed descriptions of planetary radar techniques include pettengill 1970 and evans and hagfors 1968

megafaunal responses to strong oxygen gradients on the pakistan margin of the arabian sea the arabian sea oxygen minimum zone omz which intersects the continental margin between approximately 100 and 1200 m is one of the world s largest deep water oxygen deficient water masses we analysed megafaunal organisms seen in images obtained using a wide angle survey photographic wasp system at nine sites 140 1850 m water depth across the omz on the pakistan margin during the late monsoon period august september 2003 the visible megafauna comprised 1 the megabenthos sensu strictu s s 2 large polychaetes and 3 the benthopelagic megafauna fish natant decapods and octopods large protozoans mainly the foraminiferan pelosina sp were counted but not included in the megafauna the megabenthos s s were rare at the seasonally hypoxic 140 m site o2 0 11 ml l 1 entirely absent in the omz core and most of the lower transition zone 300 900 m o2 0 12 0 15 ml l 1 but peaked in abundance 27 94 indiv m 2 at 1000 m o2 0 16 ml l 1 densities were much lower at 1100 and 1200 m 0 52 0 69 indiv m 2 o2 0 25 0 38 ml l 1 and declined to minimal values 0 01 indiv m 2 at 1850 m o2 1 68 ml l 1 there was no correlation with depth dissolved oxygen concentration or sediment organic chemistry variables corg total n c n 13c 15n pelosina sp was the only strictly benthic organism visible at 400 and 700 m fish and natant decapods were fairly common at 300 m and fish were the only metazoans seen in photographs from 700 m large polychaetes almost certainly linopherus sp were very abundant in photographs from 900 m where megabenthos s s were absent and somewhat less abundant at 1000 m suspension feeding cnidarians and tunicates were abundant at 1100 and 1200 m respectively the number of megabenthos s s species visible at each site ranged from six 1000 and 1850 m to 11 1100 and 1200 m diversity h loge was the lowest at 1000 and 1850 m and the highest at 1100 m with intermediate values at 140 and 1200 m dominance was the highest 99 at 1000 m high 87 at 1200 m and lower 32 50 at 140 1100 and 1850 m benthopelagic megafauna appeared more tolerant of dysoxia than the megabenthos s s although densities peaked at 1100 m slightly deeper than for the megabenthos s s the presence of uneaten carrion dead fish and natant decapods between 300 and 900 m suggests that scavengers were either not active or not present within the omz the megabenthos s s appeared to respond to oxygen concentrations above a threshold value 0 15 0 16 ml l 1 the ophiuroid dominated abundance peak at 1000 m and the abrupt changes in megabenthic assemblage composition between 1000 and 1200 m were probably expressions of an edge effect known from other omzs and believed to reflect a threshold release from physiological oxygen limitation accompanied by an abundant food supply

organic content and preservational controls in surficial shelf and slope sediments from the arabian sea pakistan margin abstract in the arabian sea organic rich deposits occur on the continental slope at depths roughly coincident with the impingement of an intense water column oxygen minimum zone omz this relationship has often been taken as causal and such deposits are often proposed as modern analogues of organic rich facies from the palaeorecord however there are numerous other potential preservational controls on continental margins and their relative importance remains unclear and much debated we report the results of organic inorganic and stable c isotope analyses on surficial sediments from three transects of the pakistan margin ranging in depth from well above to well below the omz organic carbon c org and total nitrogen n total contents show expected mid slope maxima although these do not mirror bottom water dissolved o 2 profiles maximal values are observed near the lower boundary of the omz or even in homogenous sediments below it together lignin yields and 13 c org values indicate a general paucity of terrigenous organic matter om this information combined with c org n total relationships suggests that the om contents of all sediments are dictated by differing accumulation of a predominant marine fraction while there are no obvious redox related differences in c org n total or om hydrogen richness across the margin there are clear minima in 13 c org within the omz in apparent contradiction with maximal accumulation of marine om the latter phenomenon is ascribed either to local source effects such as variable algal isotopic signatures or to differences in om preservation state possibly linked to bottom water redox conditions this remains to be clarified but along with the rough correspondence between mid slope sedimentary c org maxima and bottom water o 2 minima may indicate that o 2 availability is an important factor in determining sedimentary om content on this margin however evidence from redox sensitive indicators i c org mn al for persistent accumulation of om rich deposits under oxidizing conditions in homogeneous sediments below the omz clearly indicates that o 2 availability is not the sole or over riding control on om distributions

characterization of venera 15 16 geologic units from pioneer venus reflectivity and roughness data abstract geologic units have been defined for the surface of venus from venera 15 16 image data a characterization of these geologic units is carried out using information on surface properties derived from pioneer venus pv reflectivity and rms slope data the geologic context provided by venera 15 16 units allows additional more specific interpretations of surface radar properties to be made characterization of venera units results in the definition of four groups of venera units i smooth rocky units ii rough rocky units iii rough high dielectric units and iv diffusely scattering units on the basis of correlations of surface morphology to spatial and statistical distributions in rms slope and reflectivity data we test models for the origin of the surface properties of some units we conclude that plains and tectonic units can be contrasted in terms of the average roughness of the surface and that tectonic deformation appears to roughen the surface at 0 5 to 10 m and 5 to 50 cm scales this tectonic weathering process appears to dominate the erosional regime of venus unlike earth or mars production and transport of soils dominates only a small portion 5 of the surface some of the venera units display distinctive spatial and statistical distributions of pv radar data in particular apparent low reflectivity in the tesserae appears to be caused by small 5 50 cm rock fragments on the surface which cause diffuse scattering at pioneer venus wavelenghts analysis of models for the formation of these fragments suggests that they are due to the pervasive deformation undergone by the tesserae finally aspects of this study have been used to extend results of venera image data analysis southward of 30 n lat resulting in a prediction of the distribution of tessera such results can aid in magellan investigations

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

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

role of the oxygen deficient zone in transfer of organic carbon to the deep ocean 5 0 77 off mexico the rain rates estimated from sedimentary parameters were corroborated by values determined directly from sediment trap deployments the generally smaller rain rates off mexico are probably due to the lower primary production hence lower initial supply the lower attenuation rate however is hypothesized to result from a decreased oxidation rate of the sinking flux within the oxygen deficient zone relative to a more typical oxic water column the transition from the last glacial to the present interglacial was accompanied by an 85 ppm increase in the co2 content of the atmosphere it is currently thought that much of this change was due to movement of co2 between the deep ocean and the atmosphere although the exact mechanism is still under debate see broecker and henderson 1998 for discussion three important carbon cycle processes that determine co2 uptake from the atmosphere and subsequent transfer and storage in the ocean interior are 1 photosynthetic carbon fixation in the euphotic zone 2 transfer of some fraction of this fixed carbon out of the euphotic zone as export production and 3 permanent carbon burial in marine sediments as the export flux falls through the oceans it is biologically oxidized such that the sinking flux of organic matter decreases progressively with increasing depth leaving only a small fraction available for burial the manner in which the export flux or carbon rain rate decreases with depth is important for two reasons first it determines the quantity and time scale at which carbon is sequestered as co2 in the deep ocean i e the shallower the regeneration depth the shorter in general the sequestration time second greater attenuation rates result in proportionally less of the initial carbon flux reaching the sediments which has attendant implications for benthic ecology and

relations between density of earthquake damaged trace and environmental factors in seismic intensity a case study in wenchuan county china many studies have been designed to assess seismic hazard and to improve post earthquake damage evaluation models compared with previous studies the research attempted to solve the problems of the effectiveness differences of seismic intensity on density of earthquake damaged trace de and established the appropriate models for de in different scale of seismic intensity de as a relative value reduced the influence of area on earthquake damaged trace the research will provide the necessary scientific support to fast post earthquake damage assessment and modeling by utilizing gis rs and field investigation data the spatial distribution characteristic of earthquake damaged traces was analyzed effective factors including seismic intensity distance to rivers and slope were identified through pca specifically seismic intensity was identified as the key factor the inherent relations between de and seismic intensity de and distance to rivers in seismic intensity and de and slope in seismic intensity were modeled by regression analysis the results demonstrated that both earthquake energy and de have attenuation characteristics there is a significant positive correlation between de and seismic intensity the pearson correlation is 0 917 that is the higher the seismic intensity the greater the de was the erosion of river leads to steep slope which is in favor of the formation of mountain hazards de showed the decreasing tendency with the increasing distance to river with the increase of slope the de gradually became stronger for distance to river the largest changing rate of de appeared on seismic intensity xi but for slope the largest changing rate of de appeared on seismic intensity x

oxygen minimum zones omzs in the modern ocean in the modern ocean oxygen minimum zones omzs are potential traces of a primitive ocean in which archean bacteria lived and reduced chemical anomalies occurred but omzs are also keys to understanding the present unbalanced nitrogen cycle and the oceans role on atmospheric greenhouse control omzs are the main areas of nitrogen loss as n2 n2o to the atmosphere through denitrification and anammox and could even indirectly mitigate the oceanic biological sequestration of co2 it was recently hypothesized that omzs are going to spread in the coming decades as a consequence of global climate change despite an important omz role for the origin of marine life and for the biogeochemical cycles of carbon and nitrogen there are some key questions on the structure of omzs at a global scale there is no agreement concerning the threshold in oxygen that defines an omz and the extent of an omz is often evaluated by denitrification criteria which at the same time are o2 dependent our work deals with the identification of each omz the evaluation of its extent volume and vertical structure the determination of its seasonality or permanence and the comparison between omzs and denitrification zones at a global scale the co existence in the omz of oxic in its boundaries and suboxic even anoxic in its core conditions involves rather complex biogeochemical processes such as strong remineralization of the organic matter removal of nitrate and release of nitrite the quantitative omz analysis is focused on taking into account the whole water volume under the influence of an omz and adapted to the study of the specific low oxygen biogeochemical processes a characterization of the entire structure for the main and most intense omzs o2 10 mu m maximum zone the larger omz relative to the extent of denitrification zone suggests that the unbalanced nitrogen cycle on the global scale could be more intense than previously recognized and that evaluation of the omz from denitrification could underestimate their extent

macrofaunal communities and sediment structure across the pakistan margin oxygen minimum zone north east arabian sea abstract benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect depths 140 300 940 1200 1850 m through the pakistan margin oxygen minimum zone omz during the 2003 intermonsoon march may and late post monsoon august october periods objectives were to compare patterns with those described from other omzs particularly the oman margin of the arabian sea in order to assess the relative influence of bottom water oxygenation and sediment organic content on macrofaunal standing stock and community structure macrofaunal density was highest at the 140 m station subject to monsoon driven shoaling of the omz but there was no elevation of density at the lower omz boundary 1200 m numbers was extremely low in the omz core 300 m and were not readily explicable from the environmental data there was no consistent depth related trend in macrofaunal biomass macrofaunal densities were consistently lower than found off oman but there was less contrast in biomass a significant post monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from oman cirratulidae and spionidae were major components of the polychaete fauna at most stations but acrocirridae ampharetidae amphinomidae and cossuridae were more important at 940 m polychaete assemblages at each station were almost completely distinct at the species level polychaete species richness was positively correlated with bottom water dissolved oxygen and negatively correlated with sediment toc c n ratio and total phytopigments community dominance showed the opposite pattern the strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects the strongly laminated sediments in the omz core contrasted with the homogeneous heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition in general data from the oman margin were weak predictors of patterns seen off pakistan and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in omzs

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

plate tectonics on venus the high surface temperature of venus implies a permanently buoyant lithosphere and a thick basaltic crust terrestrial style tectonics with deep subduction and crustal recycling is not possible overthickened basaltic crust partially melts instead of converting to eclogite because mantle magmas do not have convenient access to the surface the 40 ar abundance in the atmosphere should be low venus may provide an analog to archean tectonics on the earth

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

mechanisms for lithospheric heat transport on venus implications for tectonic style and volcanism the tectonic and volcanic characteristics of the surface of venus are poorly known but these characteristics must be closely related to the mechanism by which venus rids itself of internal heat on the other solid planets and satellites of the solar system lithospheric heat transport is dominated by one of three mechanisms 1 plate recycling 2 lithospheric conduction and 3 hot spot volcanism we evaluate each mechanism as a candidate for the dominant mode of lithospheric heat transfer on venus and we explore the implications of each mechanism for the interpretation of venus surface features despite claims made to the contrary in the literature plate recycling on venus cannot be excluded on the basis of either theoretical arguments or present observations on topography and radar backscatter landforms resulting from plate convergence and divergence on venus would differ substantially from those on the earth because of the high surface temperature and the absence of oceans on venus the lack of free or hydrated water in subducted material the possibility that subduction would more commonly be accompanied by lithospheric delamination and the rapid spreading rates that would be required if plate recycling removes a significant fraction of the internal heat if plate recycling occurs on venus the rolling plains and lowlands provinces would be approximate analogs to terrestrial ocean basins in terms of age igneous rock type and formative process highlands on venus would be roughly analogous to terrestrial continents the hypothesis that lithospheric conduction dominates shallow heat transfer on venus leads to the prediction that the lithosphere is thin if venus has a global heat loss per mass equal to that for earth then temperatures marking the base of the thermal lithosphere on earth would be reached on venus at an average depth of about 40 km unless the mantle convective planform can maintain lithospheric regions of persistently low heat flow or unless the present atmospheric greenhouse on venus is geologically recent then such a lithospheric thickness leads to the conclusion that the topographic features contributing to the 13 km of relief on the planet must be geologically young the hypothesis that hot spot volcanism dominates lithospheric heat transfer on venus leads to the prediction that the surface must be covered with numerous active volcanic sources in particular if a typical venus hot spot has a volcanic flux equal to the average flux for the hawaiian hot spot for the last 40 m y then 104 such hot spots are necessary to remove the venus internal heat by volcanism such a number would produce enough volcanic material to resurface the entire planet to a depth of 1 km every 2 m y few areas of the planet would escape resurfacing for geologically long periods of time we find that none of the mechanisms for lithospheric heat transfer on venus can be excluded as unimportant at present it is likely that as on earth a combination of mechanisms operates on venus the strongest conclusion to emerge from this evaluation is that most of the major topographic features and probably many of the surface geological units on venus are young by comparison with the surfaces of the smaller terrestrial planets

rates of continental erosion and mountain building the first objective of this work was to obtain values for the rates at which continental erosion can smooth out or remove the topographic expression produced by orogeny the dominant part is played by mechanical erosion which acts most strongly in regions of large topographic expression chemical erosion depends strongly on precipitation or runoff in individual river drainage basins but because most continents have very similar average rainfall chemical erosion is fairly uniform for continental sized areas and will succeed in planing down all continents to a level peneplain if given enough time the exception to this rule is australia which has a very low chemical erosion rate because of its dryness the time constants for mechanical and chemical erosion so obtained vary between about 30 and 300 my depending on the continent and the assumptions made mountain building occurs throughout the geological time scale but at a non uniform rate although there will not be a balance between erosion and mountain building over a short time scale due to the non uniform rate of mountain building the long term situation must be that the two phenomena should balance out it is shown that the freeboard of continents will respond to the long term balance between mountain building and erosion an expression has been derived for the average continental elevation in which the rate of mountain building depends on the rate of radiogenic heat production within the earth it is shown that relatively small changes in average elevation above sea level of a few hundred metres are predicted to have occurred since the beginning of the proterozoic as mountain building is predicted to decrease on average with time because of the reduction in internal heat generation and as erosion is dependent on the average elevation this average elevation will decrease slowly through time the opposite of what some workers have predicted a more complicated model of mountain building is then investigated in which one component of mountain building has a sinusoidal signal the oscillations in average elevation depend on the period of the sinusoid being smaller for shorter periods finally an average continental elevation is derived using a list of real orogenic events although this list of orogenies is incomplete there is some indication that the actual continental elevation as seen in the flooding history of the continents is similar to that derived in this paper

effects of latitudinal changes in the oxygen minimum zone of the northeast pacific on the distribution of bathyal benthic decapod crustaceans abstract the presence of an oxygen minimum zone omz is one of the major characteristics of the eastern pacific the omz changes strongly adjacent to mexico in its thickness and intensity the ecological impacts of those changes were studied by examining the community structures of bathyal benthic and bentho pelagic decapod crustaceans and their oceanographic contexts on the mexican pacific slope along a wide latitudinal range 16 32 n decapod crustaceans were collected with a benthic sledge from 48 stations between 865 and 2165 m in three main areas offshore of northern baja california nbc off southern baja california sbc and in the southern mexican pacific smp physical chemical parameters were measured in the water column and sediment composition was analyzed for each station the narrowing and weakening of the omz north of ca 26 n was confirmed water with dissolved oxygen

seasonality of the transitional region of the california current system off baja california hydrographic data collected over the period 1997 2013 are analyzed to investigate the seasonality of hydrographic features and associated geostrophic flows off the baja california peninsula the upper ocean in the region was found to be homogeneous in winter and spring but subdivided into two regions in the summer and autumn in the first case the system typically shows relatively low temperature and salinity waters which give it a subarctic character in the second only the region north of punta eugenia 28 n maintains subarctic characteristics while the southern region receives an inflow of tropical and subtropical waters that results from the weakening of northwesterly winds which allows the poleward advection of surface waters also during this period a positive wind stress curl promotes the zonal advection of north pacific s eastern edge waters into the coast and to the north as a surface coastal flow average seasonal patterns of geostrophic flow at 200 dbar revealed that the differentiation into provinces is also evident at that depth with two clearly defined cyclonic structures in summer and autumn both separated at the latitude of punta eugenia the analyses conducted also showed a clear continuity of the california undercurrent along the shelf break with more diffuse currents in the winter poleward flows were observed throughout the water column especially in summer and autumn although the origin of the surface flow does not necessarily involve a surfacing of the california undercurrent

benthic megafaunal and demersal fish assemblages on the chilean continental margin the influence of the oxygen minimum zone on bathymetric distribution abstract benthic megafaunal and demersal fish assemblages were sampled in three areas off chile during the german chilean expedition puck so 156 onboard the r v sonne from march to may 2001 at depths ranging from 120 to 2201 m these samples taken with an agassiz trawl are among the deepest ever taken in chilean waters a total of 147 species were recorded mainly decapod crustaceans galatheidae pandalidae crangonidae gastropods trochidae muricidae volutidae ophiuroids asteronychidae gorgonocephalidae ophiolepididae ophiurinae asteroids pterasteridae solasteridae goniopectinidae polychaetes onuphidae aphroditidae maldanidae and demersal fish macrouridae ipnopidae squalidae species richness and rarefaction analyses suggest that the fauna was undersampled from the 147 species identified in this study 36 species 24 5 occurred only once and another 24 species occurred only twice 16 3 depth and dissolved oxygen levels were found to be the main factors influencing megafaunal changes along the continental shelf and in bathyal areas as indicated by principal component and pearson s correlation analyses some species appear to be limited to distinct areas in the upper and lower bathyal zones whereas other species have a wider range extending from the continental shelf to lower bathyal zones biogeographic relations exist with the pacific south atlantic and southern oceans but the latter seem to be weaker than would be expected considering the connection by antarctic intermediate water