subsurface gas offshore of northern california and its link to submarine geomorphology abstract the northern california continental margin contains evidence of abundant subsurface gas and numerous seafloor features that suggest a causative link between gas expulsion and geomorphology analyses of seismic reflection sidescan sonar and high resolution multibeam bathymetric data show that the occurrence of subbottom gas and the migration processes beneath the shelf differ from those beneath the slope subsurface gas inferred from enhanced reflectors and other geophysical indicators is spatially variable and related more to total depth and stratigraphy than to underlying structure with the exception of one band of gas that follows the regional structural trend shallow depressions on the seafloor pockmarks are used to infer expulsion sites the largest zone of acoustically impenetrable subsurface gas occurs between water depths of 100 m and 300 m where expulsion features are rare the upper slope water depths 400 600 m has a high concentration of pockmarks diameter 10 20 m in contrast to a near absence of pockmarks at water depths shallower than 400 m of nearly 4000 pockmarks observed on sidescan sonar records more than 95 are located in water depths deeper than 400 m bottom simulating reflectors bsrs on some seismic reflection profiles indicate the possible presence of gas hydrate we find that gas and pore fluid migration in the offshore eel river basin is 1 correlated to surface morphology 2 a contributor to seabed roughness 3 a significant mode of sediment redistribution on the upper slope and 4 potentially a factor in large slope failures

flux and fate of small mountainous rivers derived sediments into the taiwan strait article i nfo high resolution chirp sonar profiles across the taiwan strait reveal a large silt sand dominated deltaic clinoform up to 50 m thick overlying the postglacial transgressive sea floor across the southeastern central and northern strait delta like configuration and internal depositional sequences indicate a northwestward progradation from western taiwan primarily from the choshui zhuoshui river grain size and mineral data confirm the sediment s taiwanese derivation the chirp profiles together with existing radiocarbon and geomagnetic dates suggest that the clinoform has formed over the past 10 kyr the estimated volume of 375 km 3 of sediment mainly sand and silt suggests a mean annual accumulation of 60 10 6 t yr presumably much of fine mud delivered by taiwanese rivers has been washed away by the local currents and escaped either northeastward into the southern okinawa trough or southward into the south china sea numerous shallow borings onshore over the central western taiwan coastal plain reveal an additional 350 km 3

deposition and modification of a flood layer on the northern california shelf lessons from and about the fate of terrestrial particulate organic carbon the 1995 flood of the eel river in northern california provided an opportunity to follow the short term history of riverine particulate matter on a continental shelf particulate organic carbon including both vascular plant debris and soil carbon was utilized as a tracer of the distribution and modification of the shelf flood deposit these components were sorted during initial emplacement of the deposit both in the river plume and in the benthic boundary layer during the 8 months following the flood lateral transport shallow burial and bioturbation contributed to spatial changes in the amount and character of carbon in the flood deposit study of the deposit suggests that this and previous flood layers may be preserved in the shelf and upper slope stratigraphic record as clay rich beds with relatively high carbon to nitrogen ratios and more negative 13c values than background non flood sediment concentrations of vascular plant debris are locally characteristic of such layers and may serve as distinctive stratigraphic markers investigation of organic carbon in the 1995 flood layer on the eel river shelf provides insight into the fate of terrestrial particulate carbon on continental margins in general flooding of the eel river and of similar river systems draining mountainous terrains introduces large quantities of terrestrial carbon to the marine environment and may favor the preservation of both terrestrial and marine carbon the abundant woody vascular plant debris discharged during floods is especially likely to survive oxidation and sulfate reduction in the shallower zones of the seabed this study reveals the dominant role that physical and biological processes may play in attenuating the terrestrial organic carbon signal on shelves over monthly to yearly time scales

matrix association effects on hydrodynamic sorting and degradation of terrestrial organic matter during cross shelf transport in the laptev and east siberian shelf seas this study seeks an improved understanding of how matrix association affects the redistribution and degradation of terrigenous organic carbon terroc during cross shelf transport in the siberian m

changes in the composition of organic matter from prodeltaic sediments after a large flood event po river italy abstract the po river italy experienced a 100 year flood in october 2000 surface sediments 0 1 cm from cross shelf transects were collected in the po prodelta area adriatic sea in december 2000 in order to describe the distribution of organic matter om along the main sediment dispersal system immediately after the flood event stations were subsequently reoccupied in october 2001 and april 2002 this sampling program provided a special opportunity to characterize the initial surficial flood deposit and the evolution of its associated om over the course of 2 years cuo oxidation elemental 13 c 14 c and grain size analyses were carried out to characterize the source age and spatial variability of sedimentary om statistical analysis permanova was then applied to investigate temporal changes in different portions of the po prodelta area isotopic and biomarker data suggest that the sedimentary om in the flood deposit was initially dominated by aged 14 c dec 00 298 7 56 3 lignin poor om dec 00 1 96 0 33 mg 100 mg oc adsorbed on the fine material clay dec 00 72 1 4 8 delivered by the flood in the 2 years following the flood post depositional processes significantly increased the content of lignin oct 01 2 19 0 51 mg 100 mg oc apr 02 2 61 0 63 mg 100 mg oc and coarse material silt and sand while decreasing the contributions from aged oc 14 c oct 01 255 7 32 8 14 c apr 02 213 2 30 4 and fine fraction clay oct 01 54 8 9 5 clay apr 02 44 6 13 3 the major changes were observed in the northern and central portions of the prodelta

response of moist convection to multi scale surface flux heterogeneity we investigate the response of moist convection to the spatial variation of surface sensible heat flux shf in a mesoscale domain during the evolution of the afternoon convective boundary layer cbl using large eddy simulation the surface shf heterogeneity in the domain is analytically created as a function of the spectral slope in the wavelength range from a few tens of kilometres to a few hundreds of metres in the shf spectrum on a log log scale assuming surface energy balance and spatially uniform available energy the prescribed shf has a phase lag of 180 with respect to the latent heat flux lhf in the domain two sets of three simulations are forced by heterogeneous surface shf fields which are characterized by similar statistics one set however is created with a spectral slope of k 3 where k is wave number and the other with a slope of k 2 all of the simulations are integrated with the same observation based initial sounding favourable for moist convection in all of the k 3 slope cases early non precipitating shallow clouds further develop into deep thunderstorms but in all of the k 2 slope cases only shallow clouds develop a key process in the transition to deep convection is the formation of a mesoscale pool of cool and moist air just above the top of the cbl this high relative humidity rh pool is formed by repeated deep penetrations of turbulent plumes into the free atmosphere over a mesoscale surface of high shf these cross scale fluxes the vertical transports of mesoscale moisture and heat fluctuations by turbulent updraughts are critical for the formation of the mesoscale pool of high rh however these cross scale fluxes are cancelled out in the process of averaging and thus appear negligible in the vertical profiles of domain averaged moisture and heat fluxes

across shelf variations in bed roughness bed stress and sediment suspension on the northern california shelf abstract field measurements of bed micromorphology roughness benthic flow bed stress and suspended sediment flux were made on the northern california continental shelf in connection with the strataform program a sediment profiling camera and side scan sonar were used to observe bed features in december 1995 biogenic roughness with 2 cm relief prevailed at both sites bottom boundary layer tripods were deployed on the 60 m and 70 m isobaths over the period 5 january to 7 march 1996 during which time two high energy events occurred skin friction shear stresses were subcritical under average conditions but appreciably exceeded the threshold for sediment suspension during storms for those high energy events near bed suspended sediment concentrations reached 2 g l at 60 m 15 cm above bed and 1g l at 70 m 27 cm above bed and suspended sediment induced stratification significantly affected bed stress estimates at those times increases in current shear were accompanied by increases in suspended sediment concentration gradients causing the gradient richardson number within the log layer to remain near the critical value of 1 4 this suggests suppression of turbulence by sediment induced stratification the abundance of under consolidated fine sediment on the shelf to the north of the eel river mouth presumably allows increases in stress to be accompanied by progressive increases in suspended sediment concentration within the log layer to maintain the critical richardson number this contrasts to situations where bed armoring limits the total amount of fine sediment in suspension applications of a wave current boundary layer model with stratification effects included reduces estimates of current friction velocities by u c about 24 relative to results from fitting the von karman prantdl equation without stratification the model suggests that the total wave current friction velocity u cw reached 3 0 cm s at 70 m and 3 5 cm s at 60 m depth integrated across shelf suspended sediment fluxes were seaward at the 60 m isobath and near zero to weakly landward at the 70 m isobath during high energy periods implying flux convergence this is consistent with the conclusions of other strataform investigators that rapid long term accumulation of mud is occurring on the mid shelf

dispersal and transformation of organic carbon across an episodic high sediment discharge continental margin waipaoa sedimentary system new zealand abstract the rivers that drain active collisional margins of the southwest pacific deliver up to 35 of particulate organic carbon poc to the world ocean and are a key component of the global organic carbon flux however knowledge of the fate of terrestrial poc in the ocean is both limited and necessary for quantifying terrestrial and coastal ocean carbon budgets here the fate of terrestrial poc is determined off the high discharge waipaoa river sediment yield 15 mt y 1 based on a transect of seven cores from the river floodplain to the adjacent continental shelf and slope total organic carbon toc 13 c 14 c c n ratios and lipid biomarker compounds were used to determine biogeochemical characteristics of surface sediments from terrestrial source to marine sink and how these characteristics vary with river discharge complementary to surface sediments down core characteristics of three multi cores covering the shelf and slope regions were used to identify perturbations in sediment supply via major floods the presence of flood deposits allows us to compare their oc characteristics with non flood sediment thereby helping address the question of how flood events in the river catchment affect the transfer and fate of terrestrial oc through the marine environment results from this study show that as surface sediments are physically and biologically processed across the continental margin they gain a marine signature biomarker analyses of surface samples show decreases in terrigenous vascular plant sources with increasing distance offshore biomarkers also demonstrate that terrestrial oc is being transferred across the continental margin with plant sterols long chain alcohols and long chain fatty acids biomarkers indicative of vascular plants persisting as far offshore as the mid continental slope in contrast to ambient conditions represented by surface sediments rapid delivery by floods allows for more complete transfer of terrestrial carbon to the marine environment a 1 10 cm thick flood layer preserved from cyclone bola march 1988 contains a significant amount of terrestrially sourced oc which subsequently was rapidly buried by sediments delivered during less extreme conditions

effects of triple junction migration and glacioeustatic cyclicity on evolution of upper slope morphologies offshore eel river basin northern california abstract the upper continental slope of the eel river basin is affected both by uplift and seismicity associated with the northward migrating mendocino triple junction mtj and by glacioeustatic fluctuations as a result seismically imaged slope sequences vary dramatically along strike the southern slope is dominated by the humboldt slide a stack of nine deformed sequences older undeformed sequences thicken landward while slide sequences maintain a constant travel time thickness onset of deformation was abrupt within the slide reflector amplitudes alternate high amplitude reflectors are wavy to shingled and suggest increasing deformation with depth low amplitude reflectors are sub parallel to wavy throughout high and low amplitude sequence couplets suggest repetitive deposition of contrasting lithologies a response we ascribe to late pleistocene glacioeustatic cyclicity if each couplet represents a 100 kyr late pleistocene sea level cycle then humboldt slide deformation began 450 ka this is approximately coeval with onset of deformation on the adjacent shelf 500 ka previously attributed to uplift and seismicity associated with northward encroachment of the mtj we believe migration of the mtj triggered the slide and is the cause for continuing deformation today by sediment creep along internal glide planes north of the humboldt slide we interpret an upper slope anticline as a seaward extension of the little salmon fault zone lsfz previously identified landward both faulting and folding extend to the seafloor indicating that deformation continues an adjacent buried anticline suggests that deformation has also jumped northward within the lsfz on some parts of the upper slope north of the lsfz the slope is dominated by downslope trending channels and gullies these features are v shaped vertically stacked and increase in depth downslope they are mostly infilled their physiographic expression is generally subdued by sediment draping channel fills generally consist of basal high amplitude reflectors overlain by reflectors of lower amplitudes several large channels on older surfaces are concentrated near the northern end of the seismic coverage smaller channels are more evenly distributed along the margin on younger surfaces channels also extend increasingly landward on progressively younger surfaces indicating migration in that direction with time these incisions are clearly inactive during highstands as at present slope deposition today is dominated by draping of hemipelagic sediments channels form and migrate landward through headward erosion during base level changes when both shoreface and fluvial sediment sources are more proximal to the upper slope the increasing lateral distribution of channels through time supports an increase in shoreface erosion north of the lsfz a possible explanation is a known decrease in fluvial sediment input from the north combined with mtj related uplift in the south along strike contrasts in upper slope sequence morphology in the southern eel river basin are clearly a function of both regional tectonism and proximity to sediment sources influenced by base level changes humboldt slide sequences while deformed are continuously influenced by systematic lithological variations occurring as a result of glacioeustatic cycles effects of base level changes similarly control the distribution and fill of incisions on the northern slope all of these observations reinforce previous seismic investigations of the offshore eel river basin shelf and confirm that the competing effects of tectonism and glacioeustacy on the preservation of continental margin stratigraphy can be differentiated

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

sensitivity of deep convection to terrain forcing over mediterranean islands the influence of mountainous islands on the initiation of deep convection is investigated using the consortium for small scale modeling cosmo model a case study and sensitivity analysis is performed for 26 august 2009 when moist convection occurred over both corsica and sardinia islands in the western mediterranean sea sensitivity runs with systematically modified topography are explored to evaluate the relative importance of the land sea contrast and the terrain height for convection initiation whereas no island precipitation is simulated when the islands are completely removed all simulations that represent these land surfaces develop convective precipitation although convection initiates progressively earlier in the day over taller islands the precipitation rates and accumulations do not show a fixed relationship with terrain height this is due to the competing effects of different physical processes firstly whereas the forcing for low level ascent increases over taller islands the boundary layer moisture supply decreases which diminishes the conditional instability and precipitable water secondly whereas taller islands enhance the inland propagation speeds of sea breeze fronts they also block these fronts mechanically and prevent them from reaching the island interior as a result the island precipitation is rather insensitive to island terrain height except for one particular case in which the island precipitation increases considerably due to an optimal superposition of the sea breeze and upslope flow comparing the two islands convective precipitation develops earlier over corsica due to its increased terrain height and reduced convective inhibition however precipitation amounts are substantially larger over sardinia where a stronger land sea contrast gives rise to a more intense and organized line of sea breeze convergence these results demonstrate the complexity of interactions between sea breezes and orography and reinforce that an adequate representation of detailed topographic features is necessary to account for thermally induced wind systems that initiate deep convection

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

rapid and widespread dispersal of flood sediment on the northern california margin the dispersal of flood sediment from small river systems is a poorly studied yet potentially important aspect of active continental margin sedimentation in january 1995 during a flood with a 30 yr return period the eel river northern california delivered an estimated 25 3 106 t metric tons of fine grained 62 m sediment to the ocean the flood formed a distinct layer on the sea bed that was centered on the 70 m isobath extended for 30 km along shelf and 8 km across shelf and was as thick as 8 5 cm but contained only 6 106 t of sediment thus 75 of the flood derived sediment did not form a recognizable deposit but was instead rapidly and widely dispersed over the continental margin stratigraphic models of and compilations of sediment flux to active continental margins need to take the dispersive nature of small river systems into account

influence of the wind profile on the initiation of convection in mountainous terrain a number of days with small precipitating convective cells were investigated using weather radars during the cops convective and orographically induced precipitation study field campaign in the region of the vosges and the rhine valley in central europe depending on the weather situation two distinct mechanisms could be identified for the initiation of convection on some days cells were initiated over the ridge of the vosges whereas on other days cells were initiated in the lee of the vosges the initiation of convection appeared to be concentrated in a few favourable locations using the froude number it was possible to describe the two distinct mechanisms when the froude number was low the flow was diverted around the vosges and thermally driven convergence at the ridge initiated convection whereas when the froude number was high the flow passed through mountain gaps and then converged on the lee side with the flow in the rhine valley the convergence on the lee side was enhanced at locations where the outflows through valleys converged low froude numbers were accompanied by weak winds varying with height whereas high froude numbers were observed during situations with stronger southwesterly winds increasing with height

ecogeochemical fate of coarse organic particles in sediments of the rhone river prodelta coarse particulate organic matter cpom represents a small portion of the inner shelf sediments but occurs across all river outlets to consider the ecogeochemical fate of cpom in such an environment we examined both the infauna community and secondary evidence of geochemical reactions preserved in the surface sediments of the rhone prodelta icp aes scanning electron microscopy and energy dispersive x ray spectrometry of the cpom showed that the fate of organic matter in this environment is driven by sulphate reduction and geochemical reactions resulting from the precipitation of sulfide due to the presence of large amounts of iron bearing minerals leaf litter debris contained such high quantities of iron that after dry ashing the remaining material is easily attracted by a magnet the observed geochemical trade off was proposed as a mechanism that helps to maintain a bioturbating animal community that in turn contributes to the mineralization of organic matter within this suboxic environment this study showed that the accumulation of refractory organic carbon in sediments was intimately associated with the sequestering of iron and sulphur by providing a nucleation point for mineral deposition and also that the extent of decomposition of the organic materials did not necessarily increase progressively from coarser to finer particles

flow over heated terrain part ii generation of convective precipitation previous studies have shown that thunderstorms in the rocky mountain region have preferred areas in which to form there has been some indication that these areas depend on the midtropospheric wind direction a nonhydrostatic model with a terrain following horizontal grid is employed to investigate the initiation of precipitating convection over heated topography horizontally homogeneous meteorological conditions with no directional shear in the vertical wind profile are used the numerical simulations indicate that precipitating convection was more likely to be generated downwind of ridges than upwind of them initiation of these storms was more likely downwind of ridges with their long axis parallel to the wind direction than downwind of ridges with their long axis perpendicular to the wind direction in part i of this study it was shown that heating induced convergence is larger downwind of a ridge with its longer axis parallel to the wind direction for the orographic configuration of the rocky mountains total precipitation is maximized for southerly and northwesterly winds slower wind speeds are more likely and faster wind speeds are less likely to produce convective storms soundings with larger instability are more likely to produce convection the soundings with a greater temperature lapse rate produce more initiation locations and soundings with greater moisture produce greater amounts of precipitation even though a number of assumptions were made for this study the authors believe the results explain a significant amount of the observed variability in the initiation locations of precipitating convection in the rocky mountains during the summer because of the theoretical basis for this work detailed in part i of this study the authors believe it should explain convective initiation in other mountainous areas that are subject to strong solar heating

reponse aux commentaires de lattanzi et al au sujet des articles sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie

temporal and spatial variability of the sediment grain size distribution on the eel shelf the flood layer of 1995 abstract sediment grain size characteristics observed on the eel shelf have been analyzed using a wet sieving technique that minimizes breakage of aggregates at several sites on the 70 m isobath north of the river where a 1995 flood layer attained a maximum thickness of about 9 cm replicate box cores were collected on seven cruises during february 1995 to january 1997 these samples provide a unique opportunity to follow the evolution of a flood layer over a two year period as it was modified and gradually buried one month after the flood a layer of tan colored high porosity sediment with up to 96 of its particles in the size range of 0 20 m had accumulated on the central part of the shelf 7 30 km north of the river and principally between the 50 m and 90 m isobaths substantial coarsening of this layer occurred between february 1995 and may 1995 particularly along the southern and the landward edge of the deposit in water depths of

composition and provenance of terrigenous organic matter transported along submarine canyons in the gulf of lion nw mediterranean sea abstract previous projects in the gulf of lion have investigated the path of terrigenous material in the rhone deltaic system the continental shelf and the nearby canyon heads this study focuses on the slope region of the gulf of lion to further describe particulate exchanges with ocean s interior through submarine canyons and atmospheric inputs nine sediment traps were deployed from the heads to the mouths of lacaze duthiers and cap de creus submarine canyons and on the southern open slope from october 2005 to october 2006 sediment trap samples were analyzed by cuo oxidation to investigate spatial and temporal variability in the yields and compositional characteristics of terrigenous biomarkers such as lignin derived phenols and cutin acids sediment trap data show that the dense shelf water cascading event that took place in the months of winter 2006 january february and march had a profound impact on particle fluxes in both canyons this event was responsible for the majority of lignin phenol 55 4 and cutin acid 42 8 inputs to submarine canyons with lignin compositions similar to those measured along the mid and outer continental shelf which is consistent with the resuspension and lateral transfer of unconsolidated shelf sediment to the canyons the highest lithogenic normalized lignin derived phenols contents in sediment trap samples were found during late spring and summer at all stations i e 193 46 g vp g 1 lithogenic at deep slope station when river flow wave energy and total particle fluxes were relatively low during this period lignin compositions were characterized by elevated cinnamyl to vanillyl phenol ratios 3 at almost all stations high p coumaric to ferulic acid ratios 3 and high yields of cutin acids relative to vanillyl phenols 1 all trends that are consistent with high pollen inputs our results suggest marked differences in the sources and transport processes responsible for terrigenous material export along submarine canyons mainly consisting of fluvial and shelf sediments during winter and atmospheric dust inputs during spring and summer

on thermally forced circulations over heated terrain abstracta combination of analytical and numerical models is used to gain insight into the dynamics of thermally forced circulations over diurnally heated terrain solutions are obtained for two layer flows representing the boundary layer and the overlying free troposphere over an isolated mountainlike heat source a scaling based on the linearized boussinesq system of equations is developed to quantify the strength of thermally forced updrafts and to identify three flow regimes each with distinct dynamics and parameter sensitivities this scaling closely matches corresponding numerical simulations in two of these regimes the first characterized by a weakly stable boundary layer and significant background winds and the second by a strongly stable boundary layer in the third regime characterized by weak winds and weak boundary layer stability this scaling is outperformed by a fundamentally different scaling based on thermodynamic heat engines within this regime the inability of wind ventilation or

idealized large eddy and convection resolving simulations of moist convection over mountainous terrain abstracton summertime fair weather days thermally driven wind systems play an important role in determining the initiation of convection and the occurrence of localized precipitation episodes over mountainous terrain this study compares the mechanisms of convection initiation and precipitation development within a thermally driven flow over an idealized double ridge system in large eddy less and convection resolving crm simulations first les at a horizontal grid spacing of 200 m is employed to analyze the developing circulations and associated clouds and precipitation second crm simulations at horizontal grid length of 1 km are conducted to evaluate the performance of a kilometer scale model in reproducing the discussed mechanisms mass convergence and a weaker inhibition over the two ridges flanking the valley combine with water vapor advection by upslope winds to initiate deep convection in the crm simulations the spatial distribution of clouds and precipitation is generally well captured ho

depositional processes on an ancient and modern muddy shelf northern california the modern eel river shelf and analogous pleistocene rio dell formation in northern california provide an ideal opportunity to combine the advantages of studying a modern environment with those of studying an ancient sequence and thereby enables further understanding of muddy shelf processes the modern shelf is the site of accumulation of a thick deposit of holocene mud both large scale sediment distribution patterns and small scale stratigraphy on the shelf indicate that river floods play an important role in sediment accumulation even on a high energy storm dominated coast the major factors in preservation of this flood signature are the cohesive behaviour of fine grained sediments and episodically rapid rates of sediment input the rio dell formation includes approximately 400 m of mostly fine grained shelf deposits that accumulated offshore from a palaeo eel river mouth the shelf sediments comprise four depositional sequences sequence 1 records progradation from outer to inner shelf depths facies trends closely resemble across shelf trends on the modern shelf suggesting that processes were similar detailed examination of these deposits provides insight into the nature and role of various processes on both the ancient and modern shelf muddy facies of the rio dell sequence are characterized by bioturbated clayey silts interbedded with event layers of several types clay rich silt layers are interpreted as flood deposits and physically stratified coarse silt layers are interpreted to record transport and deposition of coarse silt on the midshelf during storms sediment transport calculations and consideration of grain size distributions of bioturbated sediments which form the bulk of the rio dell sequence suggest that these sediments are the result of biological homogenization of the fine grained flood deposits and of the coarser grained storm deposits the results of this study in general indicate that fine grained shelf deposits do preserve a distinguishable if subtle record of depositional processes

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

river plume sedimentation modeling for sequence stratigraphy application to the eel margin northern california abstract sediment deposition in the coastal zone from riverine input is of key importance in understanding the construction of sediment sequences through time a turbulent jet model is used to simulate sediment input to the continental margin from a riverine source turbulent jet models track the momentum which is the first order force carrying most of the sediment flowing into the ocean the froude number at the river mouth remains supercritical during floods of the eel river justifying the use of a jet model for the initial dispersion of the sediment laden plume sediment is deposited from the plume prior to the centerline froude number decreasing to its critical value empirically derived first order removal rate constants are used for each grain size in an advection diffusion equation to predict the areal extent of sediment deposition one strength of using a jet model is its ability to simulate deposits on a daily time step over intermediate time scales thousands of years using a limited number of input parameters a number of simulations of the eel river plume are shown for conditions of the present day and 18 000 yr bp during the last glacial maximum the model results for modern conditions show that a majority of the deposition occurs within 20 km north of the river mouth and is typically confined to within 10 km of the coastline corresponding well with the shelf sands on the eel margin however the initial mud deposit from a 1995 flood was farther offshore and northward additional advection of the mud fraction must occur after it leaves the surficial plume and prior to its initial deposition the model runs of 18 000 yr bp with 100 m lower sea level wetter and colder climate and the river mouth assumed to be at the canyon show that the plume is able to transport sand silt and clay out of the canyon and onto the continental slope

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

orographic precipitation and air mass transformation an alpine example a case of orographic precipitation in the alps on 20 september 1999 was studied using several models along with rain gauge and radar data the objective of the study is to describe the orographic transformation of an air mass including multi scale aspects several new and some conventional diagnostic quantities are estimated including drying ratio precipitation efficiency buoyancy work condensed water residence time parcel changes in heat moisture and altitude and dominant space and time scales for the case considered the drying ratio was about 35 precipitation efficiency values are ambiguous due to repeated ascent and descent over small scale terrain the sign of buoyancy work changed during the event indicating a shift from stratiform orographic to weak convective clouds cloud water residence times are different for the two mesoscale models 400 compared to 1000 s due to different cloud physical formulations the two mesoscale models agree that the dominant spatial scale of lifting and precipitation is about 10 km smaller than the scale of the main alpine massif trajectory analysis of air crossing the alps casts doubt on the classic model of fohn few parcels exhibit classic pattern of moist ascent followed by dry descent parcels that gain latent heat descend only briefly before rising into the middle troposphere parcels that descend along the lee slope originate in the middle troposphere and gain little or even lose latent heat during the transit as parcels seek their proper buoyancy level downstream a surprising scrambling of the air mass occurs radar data confirm the model prediction that the rainfall field is tightly controlled by local terrain on scales as small as 10 km rather than the full 100 km cross alpine scale a curious pulsing of the precipitation is seen indicating either drifting moisture anomalies or weak convection copyright 2003 royal meteorological society

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

boundary layer energy transport and cumulus development over a heated mountain an observational study abstract aircraft and surface measurements of the boundary layer transport of mass and moisture toward an isolated heated mountain are presented the data were collected around the santa catalina mountains in arizona 20 30 km in diameter during the north american monsoon on days with weak winds and cumulus congestus to cumulonimbus development over the mountain flights in the boundary layer around the mountain and surface station data indicate that mountain scale anabatic surface wind generally develops shortly after sunrise peaking at 1 m s 1 in strength close to solar noon there is some evidence for a toroidal heat island circulation with divergence in the upper boundary layer the aircraft data and mainly the diurnal surface temperature and pressure patterns confirm that this circulation is driven by surface heating over the mountain three case studies suggest that growth spurts of orographic cumulus and cumulonimbus are not preceded by enhanced mountain scale mass convergence near the surfac

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

isotopic evidence for chemosynthesis based nutrition of macrobenthos the lightness of being at pacific methane seeps the importance of chemosynthetic nutritional pathways was examined for macrofaunal invertebrates 300 mm from methane seeps in the gulf of alaska 4 413 4 443 m on the oregon margin 590 m and on the northern california slope eel river margin 520 m by use of natural abundance stable isotopic data seep macrofauna exhibited lighter d 13 c and d 15 n values than those in nonseep sediments but isotopic signatures varied among seep sites macrofaunal isotopic signatures indicated chemosynthetically fixed carbon sources with a significant contribution from methane derived carbon mdc in macrofauna from sediments of pogonophoran fields averaged 13

application of theory to simulations of observed cases of orographically forced convective rainfall abstractin two recent papers the authors reported on numerical simulations of conditionally unstable flows past an idealized mesoscale mountain ridge these idealized simulations which were performed with a three dimensional explicitly cloud resolving model allowed the investigation of simulated precipitation characteristics as a function of the prescribed environment the numerical solutions were carried out for a uniform wind flowing past a bell shaped ridge and using an idealized unstable sounding with prescribed values of the relevant parameters in the present work the application of these theoretical results to observed cases of orographically forced convective rainfall including the big thompson flood 1976 colorado the oahu flood 1974 hawaii and the gard flood 2002 france is reported specifically numerical simulations have been carried out using observed and idealized soundings relevant to these cases but with idealized topography it is found that using the observed soundings but

the evolution of convective storms initiated by an isolated mountain ridge abstractthe evolution of convective storms over the black hills an isolated mountain ridge in south dakota and wyoming and a regional convection hotspot is investigated using a 10 yr observational climatology and quasi idealized numerical simulations radar observed diurnally forced mountain convection events are classified according to their maximum cell track length and duration which are quantified using an automated cell tracking algorithm environmental conditions during these events are obtained from operational radiosonde and model analysis data these data suggest that mountain forced convective cells generally struggle to survive in the convectively inhibited flow downwind of the black hills those cells that do survive downwind prefer environments with strong bulk vertical shear over the 0 6 km layer which favors organized multicellular or supercellular convection under slightly weaker shear the cells tend to dissipate rapidly as they propagate downwind relatively weak winds aloft when c

source to sink sedimentary systems and global carbon burial a river runs through it abstract source to sink sedimentary systems are important settings of carbon cycling serving as sites of carbon transfer between terrestrial and marine reservoirs and as the primary locations for organic carbon burial on earth the age and character of the carbon that is buried at the terminal ends of these systems reflects the sources and transformations of the organic carbon oc throughout their linked terrestrial and marine segments profound differences are observed between large passive and small active margin systems large passive margin systems are characterized by large floodplains and relatively broad shelves where oc has protracted exposure to oxidants rapid burial in prograding subaqueous deltaic clinoforms or bypass to submarine fans however leads to high burial efficiency of terrestrial biospheric oc in some passive margin settings the oc in small active margin systems in contrast follows relatively short pathways from headwaters to seabed this rapid transit facilitated by the important role of storm driven transport in such settings can lead to high oc burial efficiencies the study of oc sources and transformations in contemporaneous source to sink sedimentary systems informs interpretations about the systems in which oc was buried in the geologic past their stratigraphic records of environmental change and their potential to produce petroleum resources

comments on the paper of r dechomets sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie

rainfall occurrence in the u s warm season the diurnal cycle the diurnal occurrence of warm season rainfall over the u s mainland is examined particularly in light of forcings at multiple scales the analysis is based on a radar dataset of 12 seasons duration covering the u s mainland from the continental divide eastward the dataset resolves 2 km features at 15 min intervals thus providing a detailed view of both large and regional scale diurnal patterns as well as the statistics of events underlying these patterns the results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain between the rockies and the appalachians 60 of midsummer rainfall occurs in this manner most rainfall in the central united states is nocturnal and may be attributed to the following three main forcings 1 the passage of eastward propagating rainfall systems with origins near the continental divide at 105 w 2 a nocturnal reversal of the mountain plains solenoid which is associated with widespread ascent over the plains and 3 the transport of energetic air and moisture convergence by the great plains low level jet other features of interest include effects of the appalachians semidiurnal signals of regional significance and the impact of breezes along the gulf of mexico a modest effort was put forth to discern signals associated with el nino and the southern oscillation while tendencies in precipitation patterns are observed the record is too short to draw conclusions of general significance

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

a sulfur isotope study on pyrite deposits of southern tuscany italy the s isotope composition 34scdt of 213 samples of sulfides sulfates and native sulfur from the pyrite mineralizations of southern tuscany and associated country rocks were determined the sulfur isotopic composition of pyrite is quite homogeneous and similar for all studied ore bodies with an average 34s value near 9 5 pyrite disseminated within the filladi di boccheggiano formation and thought to be authigenic shows a much larger range of 34s values 13 1 to 14 5 the isotopic compositions of other sulfides associated with pyrite in the deposits show that isotopic equilibrium among sulfides was approached on a regional scale but seldom fully attained isotopic data suggest that sedimentary marine sulfate was the ultimate source of sulfur in ores

mountain volume control on deep convective rain amount during episodes of weak synoptic forcing abstractthermally driven upslope flows in mountainous areas provide favorable conditions for diurnal deep moist convection especially during episodes of weak synoptic forcing the present study inv

a fractal interpretation of topography and geoid spectra on the earth moon venus and mars global spectra are available for topography and geoid on the earth venus mars and the moon if the spectral energy density has a power law dependence on wave number a fractal is defined the topography spectrum for the earth is a well defined fractal with d 1 5 this corresponds to brown noise with the amplitude proportional to the wave length although there is more scatter for the other planetary bodies the data for mars and the moon correlate well with the data for the earth venus topography also exhibits a brown noise behavior but with a smaller amplitude the power law dependence of the earth s geoid is known as kaula s law we show that uncompensated brown topography gives a geoid with a power law dependence that is in quite good agreement with kaula s law however the required amplitude is only 8 of the observed topography a similar result is found for the other bodies with the ratio of the amplitude of topography required to explain the geoid to the observed topography increasing to 72 for the moon

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

a new look at old carbon in active margin sediments recent studies suggest that as much as half of the organic carbon oc undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering these estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils freshwater sediments and river deltas and thus only minimally contributes to the extraneously old 14c ages of total organic matter often observed on adjacent shelves here we test this paradigm by measuring the 14c and 13c values of individual higher plant wax fatty acids as well as the 13c values of extractable alkanes isolated from the eel river margin california the isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition a coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated with pre aged terrestrial material instead composing a considerable proportion of all organic matter if these findings are characteristic of other continental margins proximal to small mountainous rivers then the importance of petrogenic oc burial in marine sediments may need to be reevaluated 2009 the geological society of america

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

sediment accumulation in a modern epicontinental shelf setting the yellow sea sediment accumulation in the yellow sea epicontinental shelf environment is investigated on 100 yr and 1000 yr time scales using 210pb and 14c geochronologies the distribution of modern 210pb accumulation rates in the yellow sea reveals that the loci of modern huanghe sediment accumulation are the topset 1 2 mm yr foreset 4 9 mm yr and proximal bottomset deposits 2 4 mm yr of the shandong subaqueous delta which extends south from the shandong peninsula 210pb rates in the distal bottomset deposits of the subaqueous delta in the central and southern yellow sea are generally low 0 3 0 9 mm yr a sediment budget demonstrates that between 9 15 of the annual huanghe discharge is accumulating in the yellow sea about two thirds of this sediment is accumulating in the topset foreset and proximal bottomset deposits of the shandong subaqueous delta with the remaining third accumulating as widespread distal bottomset deposits 14c age dates of subaqueous delta sediments indicate that the thick 40m clinoform structure formed predominantly between 6200 and 4060 yrs b p at rates approaching 20 mm yr observations in the yellow sea as well as on the amazon and ganges brahmaputra shelves demonstrate that subaqueous deltaic stratigraphy is the general rule where major rivers enter energetic shelves whether epicontinental or pericontinental the development of extensive bottomset deposits may be restricted to epicontinental shelf environments and may be diagnostic of sedimentation in this type of setting

sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie l etude detaillee du gisement de niccioleta revele les reactions metasomatiques ayant transforme l anhydrite en grenatite la dolomie en pyroxenite et les micaschistes en epidotite et celles qui ont entraine la reduction du sulfate en pyrite les solutions ferriferes ont lessive na k co2 et partiellement ca mg et s l inertie de al et ti et les deplacements de ca si s et sr precisent les modalites des transformations dont on a evalue les bilans pour un volume restant constant le comportement de s est complexe lessive lors de la grenatisation il est apporte lors de la cristallisation de la pyrite sans que le bilan global soit equilibre l origine de ce s est discutee en liaison avec le contexte evaporitique et un systeme geothermique regional tertiaire en l absence de preuve d eventuelles preconcentrations sulfurees syn sedimentaires le gisement parait resulter d une metasomatose de l anhydrite dans un systeme geothermique semblable a celui de larderello mais a alimentation marine

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie physico chimie de la mtallogense nature et origine des fluides hydrothermaux systme gothermal

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

cloud resolving simulations of deep convection over a heated mountain abstract cloud resolving numerical simulations of airflow over a diurnally heated mountain ridge are conducted to explore the mechanisms and sensitivities of convective initiation under high pressure conditions the simulations are based on a well observed convection event from the convective and orographically induced precipitation study cops during summer 2007 where an isolated afternoon thunderstorm developed over the black forest mountains of central europe but they are idealized to facilitate understanding and reduce computational expense in the conditionally unstable but strongly inhibited flow under consideration sharp horizontal convergence over the mountain acts to locally weaken the inhibition and moisten the dry midtroposphere through shallow cumulus detrainment the onset of deep convection occurs not through the deep ascent of a single updraft but rather through a rapid succession of thermals that are vented through the mountain convergence zone into the deepening cloud mass emerging t

numerical simulations of conditionally unstable flows over a mountain ridge abstractin two recent papers the authors performed numerical simulations with a three dimensional explicitly cloud resolving model for a uniform wind flowing past a bell shaped ridge and using an idealized unstable weisman klemp sounding with prescribed values of the relevant parameters more recently some observed cases of orographically forced wind profiles were analyzed showing that in order to reproduce larger rainfall rates it was necessary to initialize the sounding with low level flow toward the mountain with weak flow aloft as observed additional experiments using the weisman klemp sounding but with nonuniform wind profiles are performed here to identify the conditions in which the presence of a low level cross mountain flow together with calm flow aloft may increase the rain rates in conditionally unstable flows over the orography the sensitivity of the solutions to the wind speed at the bottom and the top of a shear layer and the effect of different mountain widths and heights are

the mississippi valley convection minimum on summer afternoons observations and numerical simulations abstractanalysis of 15 years of composite radar images over the continental united states reveals a distinct minimum of deep convection occurrence over the interior lower mississippi valley on summer afternoons relative to surrounding areas to understand the mechanisms behind this convection signature quasi idealized numerical simulations with the weather research and forecasting wrf model are performed the simulations which broadly reproduce the valley convection minimum suggest that convective inhibition is maximized and low level ascent minimized over the flat valley terrain by contrast weaker inhibition and stronger mechanically forced ascent over the hills flanking the valley combine to initiate convection more readily although the orography of the region is unremarkable it has a stronger influence on the regional convection pattern than do variations in land use

sediment transport events on the northern california continental shelf abstract a long term monitoring tripod has been maintained in 60 m water depth at the northern end of the strataform study site on the northern california continental shelf as part of this ongoing study tripod data for 1 year beginning 24 september 1995 are used to provide a sediment transport analysis on an event by event basis the objective of this paper is to highlight the energetic nature of this shelf region in terms of the frequency duration and magnitude of sediment suspension events and the associated particle flux analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed data from these instruments and a pressure sensor were averaged over 7 5 min every hour during the year of record 41 distinct sediment suspension events occurred i e sustained suspended sediment concentrations greater than 20 mg l above background level at 100 cm above bed suspended sediment events were associated with significant wave activity tidal currents and river discharge the average duration of a sediment suspension event was 3 1 days and varied from 0 7 to 8 days during events mean suspended sediment concentrations of 110 mg l were observed with peak hourly observations exceeding 1000 mg l concentrations between events averaged 35 mg l the overall sediment flux for the period of record was directed seaward and southward the distribution and magnitude of sediment suspension events and particle flux showed a strong seasonality for example of the sediment transport during events 98 of the net along shelf and 73 of the net across shelf sediment transport occurred in the winter three major winter storms could account for 72 of the total along shelf transport but only 10 of the across shelf transport the across shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low frequency seaward flows associated with mesoscale circulation patterns

three dimensional evolution of simulated long lived squall lines abstract simulations of squall lines using nonhydrostatic convection resolving models have been limited to two dimensions or three dimensions with the assumption of along line periodicity the authors present 3d nonhydrostatic convection resolving simulations produced using an adaptive grid model where the lines are finite in length and the restriction to along line periodicity is removed the base state for the simulations is characterized by weak shallow shear and high convective available potential energy cape an environment in which longlived midlatitude mesoscale convective systems mcss are observed the simulated systems bear strong resemblance to many observed systems suggesting that large scale forcing absent in the horizontally homogeneous environment is not needed to produce many of the distinguishing features of midlatitude mcss in simulations without coriolis forcing the presence of line ends leads to mature symmetric systems characterized by a central region of strong convectio

estimates of suspended sediment flux and bedform activity on the inner portion of the eel continental shelf energetic waves strong bottom currents and relatively high rates of sediment discharge from the eel river combined to produce large amounts of suspended sediment transport on the inner continental shelf near the eel river during the winter of 1995 1996 bottom boundary layer bbl measurements at a depth of 50 m using the geoprobe tripod showed that the strongest near bottom flows combined wave and current speeds of over 1 m s and highest sediment concentrations exceeding 2 g l at 1 2 m above the bed occurred during two storms one in december 1995 and the other in february 1996 discharge from the eel river during these storms was estimated at between 2 and 4 103 m3 s suspended sediment flux ssf was measured 1 2 m above the bed and calculated throughout the bbl by applying the tripod data to a shelf sediment transport model these results showed initially northward along shelf ssf during the storms followed by abrupt and persistent southward reversals along shelf flux was more pronounced during and after the december storm than in february across shelf ssf over the entire measurement period was decidedly seaward this seaward transport could be responsible for surficial deposits of recent sediment on the outer shelf and upper continental slope in this region sediment ripples and larger bedforms were observed in the very fine to fine sand at 50 m depth using a sector scanning sonar mounted on the tripod ripple wavelengths estimated from the sonar images were about 9 cm which compared favorably with photographs of the bottom taken with a camera mounted on the tripod the ripple patterns were stable during periods of low combined wave current bottom stresses but changed significantly during high stress events such as the february storm two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement these changes are thought to have been caused principally by the migration of low amplitude long wavelength sand waves into the measurement area

impact of storm induced remobilization on grain size distribution and organic carbon content in sediments from the blanes canyon area nw mediterranean sea abstract interactions between organic carbon and mineral particles are known to play a key role for the preservation of organic carbon in marine sediments in this study we combine meteorological hydrological and oceanographic information with grain size and geochemical analyses organic carbon oc its stable isotope 13 c and the nitrogen to oc ratio in different grain size fractions of surface sediments to determine the impact of a major storm on organic matter redistribution in a deep continental margin of the nw mediterranean sea sediment cores were obtained from the continental shelf along the axis of the blanes submarine canyon bc and in the adjacent southern open slope before november 2008 and after february and may 2009 the occurrence of one of the most severe coastal storms recorded in the last century in the study area the storm occurred the 26 of december 2008 and dramatically impacted the north catalan coast and its offshore area the high shear stress produced by this event on the shelf floor led to sediment erosion and subsequently to its transport and deposition into bc while sand and gravel sized particles up to 2500 m in diameter were deposited at 300 m of water depth in the canyon head the finer particles the results obtained show that the hydrodynamic processes that controlled the sorting and differential deposition of particles according to their grain size also controlled the redistribution of particles with different loads of oc thus whereas coarse particles transported to the canyon head were poorly loaded with oc fine particles reaching greater depths were relatively rich in oc a significant proportion of which was of marine origin i e derived from marine primary production this adds to evidence that the physical action of waves and currents during storms plays a key role in determining the amount of oc stored in surface sediments not only in the shelf but also in the deep margin and possibly deeper

formation of authigenic minerals and their use as indicators of the physicochemical parameters of the fluid in the larderello travale geothermal field different authigenic mineral assemblages and mineral compositions have been found in different areas of the larderello travale geothermal field in the peripheral areas the most abundant authigenic minerals are quartz calcite chlorite and sulfides they formed in a temperature range of 150 sup 0 to 250 sup 0 c and with a p sub co2 range of 0 1 to 1 0 atm in a hotter part of the field at depths between 200 and 1 300 m where the main productive fractures are located the most important authigenic minerals are quartz chlorite calcite k feldspar and k bearing mica with which wairakite hematite anhydrite and barite are sometimes associated deposition of all these minerals occurs in a temperature range of 200 sup 0 to 300 sup 0 c under p sub co2 of about 1 atm and relatively high p sub o2 in fluids sometimes characterized by silica oversaturation below the 1 300 m depth in the hottest part of the field k feldspar chlorite epidote sulfides with minor sphene prehnite clinopyroxene and clinoamphibole are present these minerals form in a temperature range of 250 sup 0 to 350 sup 0 c under a p sub co2 of less than 1 atm and a p sub o2 ranging from 10 sup 40 to 10 sup 33 atm and reasonablymore reflect the physicochemical parameters of the geothermal fluid before exploitation evidence of an earlier hydrothermal stage characterized by higher temperatures can be seen in the occurrence of relic wollastonite and andradite less

loss of organic matter from riverine particles in deltas abstract in order to examine the transport and burial of terrigenous organic matter along the coastal zones of large river systems we assessed organic matter dynamics in coupled river delta systems using mineral surface area as a conservative tracer for discharged riverine particulate organic matter pom most pom in the rivers studied n 6 is tightly associated with suspended mineral material e g it is sorbed to mineral surfaces average organic loadings in the amazon river 0 67 0 14 mg c m 2 the river for which we have the largest dataset are approximately twice that of sedimentary minerals from the amazon delta 0 35 mg c m 2 stable carbon isotope analysis indicate that approximately two thirds of the total carbon on the deltaic particles is terrestrial the combined surface normalized isotope distinguished estimate is that 70 of the amazon fluvial pom is not buried in the delta consistent with other independent evidence aller et al 1996 losses of terrestrial pom have also been quantified for the river delta systems of columbia in the usa fly in new guinea and huange he in china if the losses of riverine pom observed in these river delta systems are representative of rivers worldwide then the surface constrained analyses point toward a global loss of fluvial pom in delta regions of 0 1 x 1015 g c y 1

relationships between mineral surfaces and organic carbon concentrations in soils and sediments abstract relationships between mineral specific surface area and organic carbon oc concentration are examined for sediments and soil a horizons from throughout the world i found published elsewhere that continental shelf sediments from many different regions exhibit downcore loss of oc to a refractory background level which shows a consistent relationship with mineral surface area slope 0 86 mg m 2 oc this trend is equivalent to a monolayer of organic matter over all surfaces and is termed the monolayer equivalent me level sediments and soils from other environments are compared to this empirically derived relationship several continental slope areas show extension of this relationship to considerable depth marked excesses of oc above this trend which persist downcore were found in sediments with high carbonate mineral content or slope sediments with low dissolved oxygen concentrations in the overlying water column about half of the soils examined also adhered to this relationship while soils with high carbonate content low ph or poor drainage showed oc concentrations higher than the me level oc concentrations below the me level are found in deltaic regions and areas with low organic matter delivery such as the deep sea or arid soils the nature of mineral surfaces was examined using n2 adsorption desorption isotherms and most surface area was found to be present as pores with