shear induced convective mixing in bottom boundary layers on slopes field data from a stratified lake demonstrate that buoyancy driven convective mixing can be an important mechanism for the formation of well mixed bottom boundary layers bbls on slopes convective turbulence is caused by differential transport of stratified water masses along the slope of a basin because the current velocity usually decreases toward the sediment water at some distance from the bottom is transported faster than is water below during upslope flow this process leads to transport of heavier water on top of lighter water and hence to unstable stratification within the bbls analogously strong bbl stratification occurs during downslope flow high frequency acoustic doppler current profiler adcp and temperature measurements in the bbls of a lake revealed the cyclic occurrence of convective turbulence driven by periodic across slope currents of internal seiching the estimated maximum buoyancy flux within the bbls was in good agreement with the highest observed dissipation rates of turbulent kinetic energy this suggests that in our specific case classical bottom shear production and the mentioned buoyancy driven convective production contributed by similar amounts to the turbulent kinetic energy

the galapagos rift at 86 w 5 variations in volcanism structure and hydrothermal activity along a 30 kilometer segment of the rift valley a 30 km segment of the galapagos rift near 86 w has been mapped in detail using the angus towed camera system the submersible alvin and multi narrowbeam sonar data recent volcanic activity and active hydrothermal circulation are evident along the entire length of the segment mapped there are however clear along strike variations in these processes which render previous two dimensional models obsolete although alternate explanations are possible eruptive sequences appear to begin with the outpouring of surface fed sheet flows and end with more channelized pillow flows in the western portion of the rift studied sheet flows dominate with the entire valley floor covered by recent flows associated with a broad shield volcano the eastern portion on the other hand is narrower consisting primarily of less voluminous pillow flows of apparently the same youthful age three possible models for the volcanic evolution of this rift segment are presented according to the first model the extrusive portion of the crust is formed by a distinct volcanic episode followed by a long period of volcanic quiescence the volcanic phase begins with voluminous sheet flows emerging from numerous eruptive fissures which in time evolve into a narrow pillow ridge farther along strike where the flows are smaller and the extrusive zone narrow the marginal portions undergo continued fissuring and subsequent uplift to form marginal highs and lows this deformational activity also affects the extrusive zone once volcanic activity ends converting the distinctly lobate topography of the active period into highly lineated fault controlled terrain according to the second model extension and voleanism can be viewed as a continuous process without major periods of volcanic quiescence the initial lava flows of a new eruptive sequence fill low areas frequently spilling over local sills and flooding much of the rift valley these sheet flows are then capped by pillow ridges but from an areal view sheet flows dominate since they can flow over much greater distances in the third model along strike differences in flow type arise from ephemeral differences in spreading rate along adjacent segments of the rift separated by transient transform faults or adjacent segments of en echelon spreading segments in this third model eruptions dominated by sheet flows are associated with a faster spreading element than eruptions dominated by pillow flows active hydrothermal vent fields were found throughout the study area as well as numerous yellow and ocher accumulations of what appear to be massive sulfide deposits these latter deposits are not associated with active venting apparently reflecting previous active hydrothermal phases when the exiting temperatures were sufficently high to permit surficial sulfide deposition the active vent fields exhibit along strike variations in their exiting temperatures either due to ephemeral differences in spreading rate or variations in the volcanic flow sequences

a simple magma driven thermal balance model for the formation of volcanogenic massive sulphides abstract a simple model is used to examine the balance of heat water flow and temperature in a long lived single pass hydrothermal system heated by magmatic heat the geometry of the system is based on mid ocean ridge observations cold water percolates downward to the top of a shallow magma chamber is heated by conduction through a thin boundary layer and discharges through a permeable fault zone modelled as a bundle of narrow rough pipes as heat input is increased the model shows a catastrophic temperature transition at an exit water temperature of between 340 and 410 c depending on seafloor pressure which in nature would probably be represented by surging flow and sudden changes in the specific volume of the circulating fluids to generate a 3 million tonne sulphide deposit with 70 efficiency of deposition from water at 350 c within 4000 years would require a heat flux of 110 w m 2 from the magma chamber for a mass flow rate of 140 kg s 1 if the plan area of the reacting part of the system is 2 km 2 the total heat input would be 3 10 19 j under these conditions the thickness of the solid boundary layer between liquid magma and circulating water will be about 10 m and the integrated reactive water rock ratio over the lifetime of the system will be about 30 decreasing the water temperature to 250 c would require a heat flux of only 60 w m 2 but the time to form a 3 million tonne deposit is increased to 33 000 years and the overall heat requirement is more than quadrupled

development of partial rock veneers by root throw in a subalpine setting rock veneers stabilize hillslope surfaces occur especially in areas of immature soil and form through a variety of process sets that includes root throw near westcliffe colorado usa data were collected from a 20 500 m transect on the east slope of the sangre de cristo mountains ages of pit mound complexes with rock fragments exposed at the surface by root throw ranged from recent freshly toppled tree to unknown complete tree decay calculations based on dimensions of the pit mound complexes estimated time of tree toppling sizes of exposed rock fragments and percentage rock covers at pit mound complexes as well as within the transect area indicate that recent rates of root throw have resulted in only partial rock veneering since late pleistocene deglaciation weathering of rock fragments prevents development of an extensive rock veneer and causes a balance achieved within an estimated 700 years between the rates of rock fragment exposure by root throw and clast disintegration by chemical reduction the estimated rate of rock fragment reduction accounts for part of the fluvial sediment yields observed for forested subalpine areas of western north america copyright 2005 john wiley sons ltd

assimilation of moored velocity data in a model of coastal wind driven circulation off oregon multivariate capabilities 1 horizontal current measurements from an array of moored acoustic doppler profilers are assimilated sequentially into a model of coastal wind driven circulation off oregon during the upwelling season of may august 2001 model results are compared against independent moored and ship survey data to document a positive effect of velocity data assimilation da on other oceanic variables of interest such as the sea surface height ssh temperature potential density surface salinity and near bottom turbulence parameters significant improvement is achieved for the nearshore ssh even when data are assimilated from only two moorings at an alongshore distance of 50 km from the ssh verification site at 45 n in an area of simple shelf bathymetry with relatively small alongshore variations the model even without da provides a good description of the isopycnal structure on a cross shore section at 44 2 n over complicated bathymetry velocity da may improve the slope of isopycnals but at the same time not necessarily the density values themselves data assimilation based on a time invariant representation of the forecast error covariance may inhibit spatial variability on horizontal scales smaller than the assumed forecast error decorrelation scale an experiment involving assimilation of both velocity and moored salinity measurements demonstrates that moored velocity da improves transport of buoyant surface water the level of improvement in the near bottom turbulent dissipation and bottom stress found with the da model indicates that it is suitable for future studies of spatial and temporal variability in the bottom boundary layer off oregon

energetics of bottom ekman layers during buoyancy arrest abstractturbulent bottom ekman layers are among the most important energy conversion sites in the ocean their energetics are notoriously complex in particular near sloping topography where the feedback between cross slope ekman transports buoyancy forcing and mixing affects the energy budget in ways that are not well understood here the authors attempt to clarify the energy pathways and different routes to mixing using a combined theoretical and modeling approach the analysis is based on a newly developed energy flux diagram for turbulent ekman layers near sloping topography that allows for an exact definition of the different energy reservoirs and energy pathways using a second moment turbulence model it is shown that mixing efficiencies increase for increasing slope angle and interior stratification but do not exceed the threshold of 5 except for very steep slopes where the canonical value of 20 may be reached available potential energy generated by cross slope advection may equal up to

hydrothermal activity at the trans atlantic geotraverse hydrothermal field mid atlantic ridge crest at 26 n the first submersible observations of the only known active submarine hydrothermal field on a slow spreading oceanic ridge are incorporated with results of 10 prior years of investigation to derive an understanding of periodicity duration and varying intensity of hydrothermal activity at the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge crest near latitude 26 n hydrothermal activity has persisted at this location for at least 1 106 years based on the distribution of hydrothermal and hydrogenous mineralization with respect to crustal age the hydrothermal activity has been cyclic multistage and episodic prior high temperature hydrothermal venting stages with a periodicity of the order of 1 104 years and duration of the order of 101 years are deduced from the estimated ages of discrete sedimentary layers anomalously enriched in cu fe and zn and correspond with the independently determined periodicity of volcanic eruptive cycles on the mid atlantic ridge the most recent episode of high temperature venting is inferred to have ceased in the recent past based on metal enrichment cu fe zn in the surficial sediment layer low temperature hydrothermal venting stages with a duration of the order of 1 104 years intervene between the short high temperature stages and produce stratiform deposits of layered and earthy manganese oxide iron oxide hydroxide and silicate bivalve like forms with the characteristics of vent clams in various stages of dissolution are identified on bottom photographs the fresh appearance of intact tubules composed of iron hydroxide that acted as vents on relict deposits conductive heat flow anomalies in the sediment column and the record of temperature anomalies and excess 3he in the near bottom water column suggest that the low temperature hydrothermal discharge is intermittent at individual vents on a time scale of years

the distribution of geothermal fields on the juan de fuca ridge near bottom water temperatures were mapped along 400 km of the strike of the juan de fuca ridge as part of a combined sea marc seabeam experiment to image the variability of morphology and structure along a spreading center segment the water temperature data collected by a continuously towed thermistor chain in addition to salinity data indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the cobb propagator and one field just to the north of the propagator on the endeavor ridge segment each thermal region is located above a morphological dome on the spreading center these domes are an average of 100 200 m shallower than the rest of the axis the structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0 06 sup 0 c up to 300 m above the bottom two simple models are used to estimate the heat flux associated with these features

geomorphology and ecosystems challenges and keys for success in bridging disciplines geomorphology plays a fundamental role in controlling many ecosystem processes and in turn ecosystems can have a profound influence on many geomorphic forms and processes over the past few decades a proliferation of research has developed at the interface of geomorphology and ecosystems ecology the 2005 binghamton symposium brought together some of the leading researchers from both communities to address these critical interfaces between the disciplines this paper reviews some of the aspects of the disciplines of geomorphology and ecosystems ecology and the papers presented at the symposium the papers in this volume illustrate the current status of the disciplines the difficulties in bridging the disciplines and the issues that are emerging as research priorities

statistics of microstructure patchiness in a stratified lake 1 statistics of microstructure patches in a sheared strongly stratified metalimnion of lake banyoles catalonia spain which occupied 40 of the total lake depth of 12 m are analyzed light winds 0 25 m the ratio ltp hp depends on the patch richardson and mixing reynolds numbers following the parameterization of lozovatsky and fernando 2002 analysis of the dynamics of mixing reveals that averaged vertical diffusivities ranged between 1 10 4 m2 s 1 and 5 10 5 m2 s 1 depending on the phase of the internal waves episodic wind gusts wind speed above 6 m s 1 transfer 1 6 of the wind energy to the metalimnion and 0 7 to the hypolimnion generating large microstructure patches with hp of several meters

biogeomorphology and landscape evolution the problem of scale abstract vegetation may vary continuously and rapidly while landforms sometimes vary episodically and relatively slowly this disparity in temporal scales creates scale linkage problems in dealing with landform vegetation interactions four theoretical approaches for coping with these issues are outlined and illustrated via applications to problems arising from fieldwork on the coastal plain of north carolina the first approach the transient form ratio is used to determine whether ecosystems and geomorphic environments preserved in pleistocene stratigraphy represent stable landform ecosystem combinations which should reflect landform and vegetation responses to sea level rise the second the information criterion is applied to estimate the appropriate time steps for simulation modelling and appropriate spatial resolutions for field studies of vegetation effects on soil thickness in coastal plain uplands the abstracted systems argument the third approach is used to show that alluvial sedimentation and floodplain ecological dynamics cannot be considered independently in studies of floodplain system response to post european settlement finally ratios of relaxation times and durations suggest that changes in upland erosion regimes associated with historical devegetation are best treated as a singular perturbation in the context of quaternary landscape evolution

tidal current effects on temperature in diffuse hydrothermal flow guaymas basin a twelve day record of temperature collected from the diffuse flow area of a guaymas basin hydrothermal site exhibits variations from a minimum of 3 05 c to a maximum of 4 87 c whose periodicity is correlated with tides measured at the nearby town of guaymas a simple model based on the hypothesis that temperature variations result as changes in tidal bottom currents induce changes in the height of the thermal boundary layer is in good quantitative agreement with observed temperatures for most of the record the success of this model illustrates that the effects of tidal currents can be strong enough to dominate the time variability of a temperature signal at a fixed point in hydrothermal flow therefore tidal currents must be taken into account when using temperature measurements to estimate time varying heat fluxes from hydrothermal diffuse flow regions

a search for hydroacoustic signals associated with the 2 june 1988 temperature anomaly at axial seamount data from the wake island hydrophone array is examined for signals possibly associated with sudden decreases in bottom temperature at axial seamount which is located on the juan de fuca ridge in spite of the extreme sensitivity of the wake hydrophones to small explosive charges and unreported shallow focus earthquakes along the juan de fuca ridge and to unreported episodes of submarine volcanism no sustained signals were found which appear to be related to the observed temperature anomalies because of intermittent recording problems some hydroacoustic signals of extremely short duration possibly associated with the temperature anomalies could have escaped detection in the eight hours subsequent to the occurrence of these anomalies however no such signals could have escaped detection during an eight hour period prior to the onset of the observed anomalies since the recording system was working properly the absence of signals indicates that sustained teleacoustically detectable submarine volcanism was not associated with the 2 june 1988 temperature anomaly

convectively driven mixing in the bottom boundary layer closely spaced vertical profiles through the bottom boundary layer over a sloping continental shelf during relaxation from coastal upwelling reveal structure that is consistent with convectively driven mixing parcels of fluid were observed adjacent to the bottom that were warm by several millikelvin relative to fluid immediately above on average the vertical gradient of potential temperature in the superadiabatic statically unstable bottom layer was found to be 21 7 3 1024 km 21 or 6 0 3 1025 kg m24 in potential density turbulent dissipation rates increased toward the bottom but were relatively constant over the dimensionless depth range 0 4 1 0z d where d is the mixed layer height the rayleigh number ra associated with buoyancy anomalies in the bottom mixed layer is estimated to be approximately 1011 much larger than the value of approximately 10 3 required to initiate convection in simple laboratory or numerical experiments an evaluation of the data in which the bottom boundary layer was unstably stratified indicates that the greater the buoyancy anomaly is the greater the turbulent dissipation rate in the neutral layer away from the bottom will be the vertical structures of averaged profiles of potential density potential temperature and turbulent dissipation rate versus nondimensional depth are similar to their distinctive structure in the upper ocean during convection nearby moored observations indicate that periods of static instability near the bottom follow events of northward flow and local fluid warming by lateral advection the rate of local fluid warming is consistent with several estimates of offshore buoyancy transport near the bottom it is suggested that the concentration of offshore ekman transport near the bottom of the ekman layer when the flow atop the layer is northward can provide the differential transport of buoyant bottom fluid when the density in the bottom boundary layer decreases up the slope

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

pedologic and geomorphic impacts of a tornado blowdown event in a mixed pine hardwood forest abstract biomechanical effects of trees on soils and surface processes may be extensive in forest environments two blowdown sites caused by a november 2005 tornado in the ouachita national forest arkansas allowed a case study examination of bioturbation associated with a specific forest blowdown event as well as detailed examination of relationships between tree root systems soils and underlying bedrock the sites occur within mixed shortleaf pine and hardwood forests more than 95 of trees in the severe blowdown areas were either uprooted or suffered trunk break with uprooting more common than breakage within the most heavily damaged areas all uprooted trees were pines while all trees left standing were hardwoods root wads of uprooted trees had a mean surface area of about 3 m 2 and volume of about 2 m 3 though individual sizes were quite variable nearly 4 of the ground surface area was affected by uprootings with a soil volume equivalent to a disturbance of the entire surface area to a depth of 2 4 cm tree size as measured by diameter at breast height was significantly related to the area and volume of root wads r 2 0 55 0 71 respectively with volume of uprooted soil varying as diameter to the 3 power suggesting that the timing of blowdown events relative to tree age or growth stage significantly influences the area of disturbance and the mass and volume of material involved in 93 of cases the roots of the uprooted trees contacted or penetrated the underlying bedrock and in all those cases bedrock was quarried by uprooting only 11 of the tree throws showed evidence of general lateral root turning at the soil bedrock interface in most cases roots penetrated bedrock along joints the propensity for tree roots to penetrate bedrock joints facilitate weathering and excavate bedrock during uprooting supports the idea that tree roots play a predominant role in locally deepening soils

observation of pressure change associated with hydrothermal upwelling at a seamount in the south mariana trough using an ocean bottom seismometer an obsh ocean bottom seismometer with hydrophone was deployed just 1 m from a hot thermal vent on the summit region of a seamount located 18 km east of the south mariana trough axis to record continuous data on hydrothermal activity although the seismicity beneath the seamount was very weak numerous pulse shape pressure events showing sudden pressure decrease were observed on the hydrophone channel the characteristic period of the pressure events varied from 20 seconds to 1 minute after the submersible shinkai 6500 relocated the obsh 10 m south of the vent where no thermal vents existed the number and amplitude of pressure events drastically decreased this suggests that pressure events were generated by the hot water upwelling from the thermal vent the pressure events appear to be related to the ocean tide this experiment indicates that observations using obshs are an effective means of monitoring hydrothermal activity

tide related variability of tag hydrothermal activity observed by deep sea monitoring system and obsh abstract hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone obsh and a composite measuring system manatee including ctd current meter transmission meter and cameras at a small depression on the tag hydrothermal mound in the mid atlantic ridge low frequency pressure pulses detected by the hydrophone with semi diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short lived smoker vent close to the observing site the peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting temporal variations in bottom water temperature also have semi diurnal periodicity but are more complicated than the pressure events temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

cover beds as soil parent materials in midlatitude regions abstract in parts of southern france the russian plain south central turkey the western usa and in germany slopes are covered by deposits cover beds formed by geomorphic processes not limited to linear discharges often loess material is mixed into them cover beds usually form sequences of two or more distinct layers and their distribution depends on the geomorphic climate driven processes of their formation as they influence pedogenesis they contribute to the understanding of soil properties and soil distribution horizon boundaries occur at depths where cover bed properties change where aeolian matter is mixed in podzolisation is buffered but depletion of clay may occur loess rich cover beds may entirely decouple pedogenesis from bedrock influence in humid areas soil water stagnation is often associated with varying cover bed bulk densities particularly upon flat relief in semiarid areas deep soil profiles consist of multiple layer sequences often with argillic and calcic properties within the same horizons they reflect several cycles of cover bed deposition and incorporation of loess alternating with decalcification accompanied and followed by clay translocation this led to the overprinting of buried soils by pedogenic carbonate leached from younger sediments synchronous sediment and or airborne carbonate accretion and pedogenesis which is usually invoked to explain soil profiles with several calcic horizons cannot apply to cover beds

boundary mixing in lakes 1 modeling the effect of shear induced convection 1 recent studies in lakes have shown evidence for a strong influence of shear induced stratification on mixing in turbulent bottom boundary layers bbls on sloping topography these observations suggest that the periodic near bottom shear resulting from internal wave motions may lead to alternating periods of gravitationally stable and unstable stratification in the bbl with relevant implications for turbulence and mixing in the entire basin the impact of these processes for basin scale mixing is investigated here in a three dimensional processes oriented modeling study using a well investigated system lake alpnach switzerland as an example consistent with available observations our results indicate that the bbl becomes gravitationally unstable in areas with upslope flow covering a substantial fraction of the total bottom area of the lake while near bottom convection associated with the unstable stratification in these areas results in strong turbulence its contribution to net mixing is negligible since the bbl is already well mixed conversely in areas with downslope flow the near bottom shear generates stable stratification leading to a suppression of turbulence but also to larger mixing rates due to an enhanced mixing efficiency overall bbl mixing is found to dominate basin scale mixing these mechanisms are likely to be important for a large class of stratified natural waters in which boundary layer mixing is energized by periodic internal waves or basin scale motions

organization of stratification turbulence and veering in bottom ekman layers 1 detailed observations of the ekman spiral in the stratified bottom boundary layer during a 3 month period in an upwelling season over the oregon shelf suggest a systematic organization counter clockwise veering in the bottom boundary layer is constrained to the weakly stratified layer below the pycnocline and its height is nearly identical to the turbulent boundary layer height veering reaches 13 4 degrees near the bottom and exhibits a very weak dependence on the speed and direction of the interior flow and the thickness of the veering layer a simple ekman balance model with turbulent viscosity consistent with the law of the wall parameterization modified to account for stratification at the top of the mixed layer is used to demonstrate the importance of stratification on the ekman veering the model agrees reasonably well with observations in the lower 60 70 of the bottom mixed layer above which it diverges from the data due to the unaccounted physics in the interior neglect of stratification in an otherwise identical model results in far worse agreement with the data yielding veering in the bottom ekman layer which is much smaller than measured but distributed over a much thicker layer

east pacific rise at 21 n the volcanic tectonic and hydrothermal processes of the central axis abstract photographs obtained by the angus survey system at 21 n reveal many similarities to the geological processes delineated at other spreading centers and in particular those observed in the galapagos rift at 86 w the region of recent volcanism is restricted to a narrow zone zone 1 approximately 1 km wide this suggests that the width of the magma chamber feeding these flows is also narrow at the top variations in sediment cover are used to subdivide the flows within zone 1 into three sheet flow pillow flow pairs the youngest pair appears to have erupted form a linear fissure 8 km long running parallel to the valley axis this fissure is part of a larger en echelon pattern of eruptive fissures active hydrothermal vents associated with the youngest flows are situated directly above the apparent eruptive fissure the high 350 c temperature for some of the fluids exiting from the vents suggests a highly restricted circulation system involving at times little to no mixing with cold seawater the lava terrain in the remainder of zone 1 and bordering regions is characterized by extensive fracturing further suggesting a narrow upper dimension to the magma chamber and also that subsurface hydrothermal deposition of massive sulfides may lead to a reduction in the mixing processes

modeling bottom mixed layer variability on the mid oregon shelf during summer upwelling abstract results from a model of wind driven circulation are analyzed to study spatial and temporal variability in the bottom mixed layer bml on the mid oregon shelf in summer 2001 the model assimilates acoustic doppler profiler velocities from two cross shore lines of moorings 90 km apart to provide improved accuracy of near bottom velocities and turbulence variables in the area between the mooring lines model results suggest that the response of the bml thickness to upwelling and downwelling favorable winds differs qualitatively between an area of simple bathymetric slope at 45 n and a wider shelf area east of stonewall bank 44 5 n at 45 n the bml grows in response to downwelling favorable conditions in agreement with known theories east of stonewall bank the bml thickness is increased following upwelling events in this area the southward upwelling jet detaches from the coast and flows over a wider part of the oregon shelf creating conditions for ekman pumping near the bottom based on

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

acoustic noise measurements on axial seamount juan de fuca ridge anomalously high ambient acoustic noise was observed within the caldera of axial seamount located on the juan de fuca ridge at 46 n noise spectra from 2 to 30 hz were calculated from hydrophone signals from four separate seismic recording systems noise levels varied up to 25 db over 6 km this observation suggests the noise source is at or near the sea floor by assuming spherical spreading we estimate the source of the noise to be within 400 m of one of the instruments a low temperature hydrothermal vent field located within 600 m of this instrument has been previously mapped with submersibles and is likely the source of the anomalous noise a high temperature black smoker vent field also located within the caldera shows no evidence of anomalous acoustic noise

transient convection in upper lake sediments produced by internal seiching 1 we present the first evidence of free convection development in lake sediments caused by seiche oscillations appearance of the pore water convection is manifested by increase in the upward heat flux during periodical seiche driven upwelling of cold deep water over the bottom slope the dimensionless convective heat flux scales favorably with the square root of the rayleigh number suggesting an intermediate character of the convective flow between the rayleigh benard free convection in fluid and the horton rogers lapwood convection in porous media according to the scaling analysis the seiche induced pore water convection could intensify up to 1000 times the dissolved matter exchange between lake sediment and water column among lake processes that can be significantly affected by the transient convection in sediments are the nutrients cycle the water sediments exchange of dissolved gases and the benthic microbial activity

bottom stress estimates from vertical dissipation rate profiles on the continental shelf abstract measurements of the near bottom distribution of the turbulent dissipation rate on the continental shelf west of vancouver island are used to calculate bottom stress a free failing vertical profiler with microstructure shear probes was used to measure the dissipation rate from near the surface to within 0 15 m of the bottom the shear probes measure velocity gradients at scales within the viscous subrange of the turbulence and therefore directly measure the rate at which kinetic energy is dissipated by viscosity friction velocities are computed from the formula uast z where the dissipation rate is measured in the constant stress layer the technique is more reliable than estimates of the dissipation rate obtained by fitting spectral slopes to velocity spectra at scales in the inertial subrange near bottom current measurements indicate that the bottom stress values obtained from the turbulent measurements are well correlated with the current magnitude an estimate of the drag coeff

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

convectively driven turbulent mixing in the upper ocean abstract two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper ocean in the first a diurnal convective mixed layer developed in the bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling the mixed layer reached as deep as 100 m each night and restratified each day in the second the mixed layer of a warm core gulf stream ring deepened from less than 50 m to more than 150 m in a little more than a day when subjected to rapid cooling during a cold air outbreak although individual profiles of the rate of viscous dissipation of turbulent kinetic energy had considerable spatial and temporal variability the mean dissipation profiles were similar to those in convecting atmospheric boundary layers the is established by the surface buoyancy flux jb0 jb0 0 61 and 0 72 in the bahamas and ring data respectively compared with 0 64 in convecting atmospheric mixed layers the mean profiles decre

breaking ground pedological geological and ecological implications of soil bioturbation abstract soil and its biota are fundamental components of the critical zone earth s living skin that most directly sustains life within that zone geologically rapid soil and saprolite displacement by biota particularly invertebrate meso and macrofauna affects a large proportion of earth s soils this was first recognised by late 19th century observers on both sides of the atlantic ocean who regarded bioturbation as fundamental to soil formation throughout much of the 20th century however the agronomical focus of soil scientists and the dominant paradigm of landscape evolution relegated bioturbation as a result many aspects of bioturbation are still not widely appreciated only in the last few decades has a re evaluation commenced in a range of disciplines primary effects of bioturbation which we quantify herein include soil production from saprolite the formation of surface mounds soil burial and downslope transport rates of bioturbation can be as rapid as sustained maximum rates of tectonic uplift in concert with surface geomorphic processes bioturbation alters fundamental properties of soil including particle size distribution porosity the content of carbon and other nutrients and creep flux rate the precise influence of biotic mixing is regulated by its depth function earth s incredibly diverse soil biota also perform a number of functions at a range of spatial and temporal scales that extend beyond soil to landscape evolution ecosystem engineering niche construction and carbon cycling understanding these linkages which have operated since the evolution of trees in the devonian period is of growing importance as we seek a fuller picture of earth s history to predict and manage its future

surface processes and interactions with forest vegetation on a steep mudstone slope stolowe mountains sw poland abstract in this study we recognize complex physical biotic abiotic interactions on a steep forested slope in the moderately elevated mountain terrain of the sudetes central europe using geomorphological pedological and dendrochronological methods on the forested hillslopes of mt rogowa kopa the evidence of disturbance in natural systems is widespread in the geomorphic subsystem its most obvious manifestation is the origin and disappearance of pit and mound microtopography resulting from tree uprooting 82 pit and mound associations have been mapped on a test slope providing quantitative data for calculating sediment flux the flux is around 2 10 4 m 3 m 1 year 1 hence less than suggested in the literature but within the same order of magnitude nevertheless in the long term such a transport rate is comparable with the one typical for creep while it affects a greater thickness of hillslope regolith tree bending and abrupt changes in tree ring width are indicators of disturbed tree growth causally linked to soil creep of mudstone derived regolith eccentric growth is best recorded in wet years and in younger trees which have to adapt to the pre existing pit and mound surface topography we offer a conceptual model that links biotic and abiotic factors and discuss implications of the widespread tree uprooting we suggest that veneers of angular clasts and occasional larger boulders are not necessarily residuals of washed pleistocene solifluction mantles but may result from root plate degradation after uprooting recent catastrophic wind events may through tree uprooting lead to structural changes in cover deposits so that they lose their inherited periglacial signatures

the sound field near hydrothermal vents on axial seamount juan de fuca ridge high quality acoustic noise measurements were obtained by two hydrophones located 3 m and 40 m from an active hydrothermal vent on axial seamount juan de fuca ridge in an effort to determine the feasibility of monitoring hydrothermal vent activity through flow noise generation most of the measured noise field could be attributed to ambient ocean noise sources of microseisms distant shipping and weather punctuated by local ships and biological sources long period low velocity water rock interface waves were detected with high amplitudes which rapidly decayed with distance from the seafloor detection of vent signals was hampered by unexpected spatial nonstationarity due to the shadowing effects of the caldera wall no continuous vent signals were deemed significant based on a criterion of 90 probability of detection and 5 probability of false alarm however a small signal near 40 hz with a power level of 10 4pa2 hz was noticed on two records taken within 3 m of the inferno black smoker hie frequency of this signal is consistent with predictions and the power level suggests the occurrence of jet noise amplification due to convected density inhomogeneities

drilling the snake pit hydrothermal sulfide deposit on the mid atlantic ridge lat 23 sup 0 22 n a major high temperature hydrothermal area has been discovered in the mid atlantic ridge rift valley about 25 km south of the kane fracture zone the vent field consists of a wide area 40 000 m sup 2 of dark hydrothermal deposits numerous sulfide chimneys and mounds some up to 11 m high and high temperature black smoker vents ten shallow holes the first ever drilled in an active submarine hydrothermal area recovered friable unconsolidated fe cu fe and zn sulfides and several large fragments of massive sulfide mainly chalcopyrite from the locally thick 13 m hydrothermal deposits the vents are also associated with an unusual biological community of smaller more mobile organisms than reported from the east pacific rise

geologic form and setting of a hydrothermal vent field at lat 10 56 n east pacific rise a detailed study using angus and alvin a hydrothermal vent field here called the feather duster site occurs on the eastern marginal high near the edge of a narrow 95 m and shallow 15 20 m axial graben within an area dominated by sheet flows and collapse features the sheet flows are intermediate in relative age between younger fluid flow lavas on the floor of the axial graben and older pillow constructional lavas on the marginal highs hydrothermal activity occurs in two zones within a 65 by 45 m area the main zone is located where a fissure system and sulfide sulfate chimneys vent warm 9 47 sup 0 c and hot 347 sup 0 c hydrothermal fluids here two mounds of massive sulfide totaling about 200 t are forming one occurs at the base of a 3 m high scarp which is the wall of a drained lava lake the other is perched on top of the scarp 19 references 4 figures

internal hydraulic flows on the continental shelf high drag states over a small bank observations of currents hydrography and turbulence provide unambiguous evidence for hydraulic control of flow over an isolated three dimensional topographic feature on oregon s continental shelf the flow becomes critical at the crest of the bank forming a strong supercritical downslope flow in the lower layer farther downstream internal hydraulic jumps form as the bottom flow becomes subcritical as a consequence turbulence is greatly enhanced in the bottom boundary layer in the sheared interface above the swiftly flowing bottom current and in the internal hydraulic jump the dissipation rate of turbulent energy is consistent with the mean energy removal rate for a hydraulic jump in an idealized two layer flow this enhanced turbulence constitutes a high drag state of the flow in which the form drag introduced by the topography exerts significant influence on the flow around it and mixing is increased 102 103 times the background values

geological setting of hydrothermal activity at 12 50 n on the east pacific rise a submersible study abstract a detailed submersible investigation of a 20 km segment of the east pacific rise near 12 50 n between the orozco and clipperton fracture zones has resulted in the localization of 24 active hydrothermal vent fields and over 80 sites of sulfide accumulations the active vents range from low temperature vents characterized by exotic benthic communities to high temperature black smokers and the deposition of polymetallic sulfides the study is based upon a combination of fine scale topography obtained using the seabeam sonar system on n o jean charcot camera lowerings along the axis using the raie vehicle and 32 dives by the submersible cyana operating from n o le suroit the observations made between the orozco and clipperton fracture zones show topographic highs situated along the strike of the accreting plate segment separated by a small ridge offset at 11 49 n this offset divides this portion of the ridge into two separate spreading segments each of which has a primary topographic high along strike secondary highs are associated with each segment of the ridge separated by either small offsets or relay zones or in some cases zones where spreading centers overlap dives made on the tops of both primary highs 12 50 n and 11 30 n confirm the presence inferred from previous surface work of high temperature vent fields while one reconnaissance dive 14 20 n near the orozco fracture zone ridge axis intersection reveals the absence of any hydrothermal activity in the present or recent past the vast majority of vent fields investigated were found at the topographic high near 12 50 n are associated with the most recent period of volcanism and are confined to lava ponds situated within the axial graben

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

the baltic sea tracer release experiment 2 mixing processes 1 deep water mixing processes in the largest basin of the baltic sea gotland basin are investigated here with the help of long term moored instrumentation and turbulence microstructure measurements budgets for heat and salinity reveal a strong temporal variability in the deep water mixing coefficients that is shown to be coupled to the wind forcing down to time scales of individual wind events consistent with the results from a simultaneously conducted tracer release experiment near boundary turbulence was identified as the key processes for basin scale mixing turbulent bottom boundary layers were found to be thick and stable in the flat deep part of the basin where highest dissipation rates were observed and comparatively thin less energetic and highly variable on the slopes due to a permanent tendency for boundary layer restratification in the absence of internal tides strongly damped basin scale topographic waves with periods of a few days a deep rim current and to a smaller extent near inertial waves were identified as the main energy sources for boundary mixing these results are likely to be relevant also for other medium sized stratified basins

gravity current dynamics and entrainment a process study based on observations in the arkona basin abstract a 19 h time series of dissipation stratification and horizontal velocities has been obtained for a dense gravity current flowing into the arkona basin in the western baltic sea the observations are compared with one dimensional quasi steady theory in which the gravity component in the flow direction is balanced by bottom friction while that in the cross flow direction is balanced by the coriolis force the observations deviate from the theory in that the bottom shear stress is more than 2 times as large as that required to balance the gravity several reasons for this discrepancy are discussed a 1d turbulence model is also compared with the observations profiles of velocity stratification and dissipation rates generally show similar variations with depth as the observations although the observed dissipation rates are somewhat larger than the modeled and the modeled transverse velocities are much larger than the observed subsequently the model is used to investigate the variation of t

microearthquakes in the black smoker hydrothermal field east pacific rise at 21 n in july and august 1980 an array of five ocean bottom seismographs was deployed within 3 km of the 350 c hydrothermal vents at the rivera submersible experiment rise site at 21 n on the east pacific rise two of these instruments were placed within 600 m of the vents using a transponder navigation network the array detected four basic types of events the first type consisted of local very small microearthquakes locations obtained for 11 of these events place three within 1 km of the vents with the others elsewhere along the rise crest they appear to originate either from movement on the faults in the area or from the hydrothermal system beneath this area a study of the s p times of this type indicates a maximum hypocentral depth of 2 3 km implying a similar limit to the depth of hydrothermal circulation and brittle fracturing in the vicinity of the vents the second type of event found consisted of emergent earthquakes that have many of the characteristics of volcanic harmonic tremor the frequency of these events falls in the 1 5 hz range and are similar in appearance to those seen at mount st helens prior to and during its may 1980 eruption they may be either hydrothermal or volcanic in origin the third type of event produced a very monochromatic high frequency seismogram with the energy concentrated at 20 hz these events also appear to have a local origin the particle motion of these earthquakes shows almost pure stonely wave propagation and they appear to originate from a regularly oscillating dilatational source the nature of the source of event types two and three is clearly not the usual sort of motion on a fault and is still not understood the fourth type of earthquake recordings were regional events apparently from the nearby rivera and tamayo fracture zones the low frequency acoustic noise in the water was 16 64 times higher within 300 m of the vents than it was 2 km away this implies that the black smoker vents may be generating a large acoustical disturbance as the 350 c water pours into the ocean the observations are among the first of seismicity on moderate to fast spreading ridges and many of the events appear to be related to the hydrothermal activity found there

active hydrothermal vents and sulfide deposits on the southern juan de fuca ridge massive sulfide deposits rich in zinc and silver were recovered from the juan de fuca ridge 500 km west of oregon in september 1981 the samples recovered are composed largely of zinc sulfide with lesser amounts of iron lead and copper sulfide most of the deposits occur at a series of hydrothermal vents within a relatively continuous depression in the center of a smooth 1 km wide valley along the ridge axis the depression appears to be formed by collapse of a lava lake possibly modified by extensional faulting the axial valley floor outside the depression is underlain by fresh glassy ferrobasalt sheet and lobate flows two types of sulfide mineral deposits were dredged from one of the hydrothermal vents 1 angular slabs of dark gray zinc sulfide and 2 subrounded fragments of porous light gray zinc sulfide the samples contain fresh sphalerite zoned wurtzite pyrite and minor amounts of marcasite galena and chalcopyrite cubanite the spreading rate of the juan de fuca ridge and the composition of the sulfide samples are generally similar to the east pacific rise lat 21 n site however the texture and geologic setting of the sulfide deposits are significantly different

observations of tidal straining within two different ocean environments in the east china sea stratification and near bottom turbulence tidal straining describes the straining effect induced by the vertical shear of oscillatory tidal currents that act on horizontal density gradients it tends to create tidal periodic stratification and modulate the turbulence in the bottom boundary layer bbl here we present observations of current hydrology and turbulence obtained at two mooring stations that are characterized by two typical hydrological environments in the east china sea ecs one is located adjacent to the changjiang river s mouth and the other is located over a sloping shelf which is far from the freshwater sources tidal straining induces a semidiurnal switching between stable and unstable stratification at both stations near bottom high frequency velocity measurements further reveal that the dissipation rate of turbulent kinetic energy tke is highly elevated during periods when unstable stratification occurs a comparison between the tke dissipation rate e and the shear production p further reveals that the near bottom mixing is locally shear induced most of the time except during the unstable stratification period within this period the magnitude of dissipation exceeds the expected value based on the law of the wall by an order of magnitude the buoyancy flux that calculated by the balance method is too small to compensate for the existing discrepancy between the dissipation and shear production another plausible candidate is the advection of tke which may play an important role in the tke budget during the unstable stratification period

geothermal heating in the panama basin part ii abyssal water mass transformation diabatic upwelling of abyssal waters is investigated in the panama basin employing the water mass transformation framework of walin 1982 we find that in large areas of the basin the bottom boundary layer is very weakly stratified and extends hundreds of meters above the sea floor within the weakly stratified bottom boundary layer wsbbl neutral density layers intercept the bottom of the basin the area of these density layer incrops increases gradually as the abyssal waters become lighter large incrop areas are associated with strong diabatic upwelling of abyssal water geothermal heating being the largest buoyancy source while a significant amount of water mass transformation is due to extreme turbulence downstream of the ecuador trench the only abyssal water inflow passage water mass transformation across the upper boundary of abyssal water layer is accomplished almost entirely by geothermal heating

rock fragment distributions and regolith evolution in the ouachita mountains arkansas usa rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls erosion deposition bioturbation and weathering the distribution of rock fragments in regoliths of the ouachita mountains arkansas shows that sandstone fragments are common in all layers even if sandstone is absent in parent material shale and sandstone fragments are produced at the bedrock weathering front but the shale weathers rapidly and intact fragments are rare in the solum sandstone is weathered from ridgetop outcrops and transported downslope some of these fragments are moved downward by faunalturbation and by transport into pits associated with rotting tree stumps upward movement by treethrow is common resulting in a net concentration of rocks near the surface however the highest fragment concentrations are in the lower regolith indicating active production at the weathering front the regolith is a dynamic feature reflecting the influences of vertical and horizontal processes of active weathering at the bedrock interface and of surficial sediment movements the role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities and that forest soils have likely been extensively mixed within holocene and historic time copyright 2005 john wiley sons ltd

the concept of the pleistocene periglacial cover beds in central europe a review in low mountain areas of central europe pleistocene periglacial conditions and relevant processes have led to the formation of cover beds in general holocene soils are not developed in bedrock but they have formed in periglacial cover beds their occurrence and characteristics control the spatial distribution of soils and thus periglacial sediments are a useful tool for soil mapping and soil survey the concept of periglacial cover beds distinguishes four main layers topmost upper middle and basal periglacial cover bed the upper and middle layers contain loess whereas the basal one consists entirely of bedrock the loess content causes an increase of site specific soil ecological quality in comparison to soils formed directly on bedrock the occurrence and characteristics of the cover beds is reviewed summarizing the present state of the art

similarity structure in the convective boundary layer of a lake natural convection influences a variety of geophysical phenomena including daily mixing cycles in the atmosphere and in surface waters the seasonal overturn of lakes and global climate variability conceptual models of convection in water are primitive and based on very limited data particularly at small dissipative scales here i present an analysis of microscale data from the convective boundary layer of a lake indicating a complex depth dependence in the rate at which temperature fluctuations are dissipated suitably scaled this vertical structure is remarkably similar to that found in the atmospheric convective boundary layer1 2 stirred by rising thermals of buoyant air heated at the earth s surface this comparison consistent with recent documentation of similarity in the more uniform vertical structure of energy dissipation3 5 suggests another unifying link in the structure and dynamics of convection in boundary layers of lakes oceans and the atmosphere6

stratification and mixing on sloping boundaries 1 in lakes as well as in the ocean vertical transport is to a large extent controlled by localized mixing along the boundaries of the respective basin direct measurements of turbulent mixing and density stratification in the bottom boundary layer of a large and deep lake reveal the importance of cross slope advection near sloping boundaries for local and basin scale vertical transport the periodic internal wave driven occurrence of up and downslope directed currents results in periodic heating and cooling of the boundary layer cooling of the boundary layer during periods of up slope flow is associated with unstable stratification and turbulent diffusivities exceed those observed during periods of down slope flow by almost one order of magnitude the periodic replacement of water in this layer with water from the interior of the basin maintains vertical density gradients and thus enhances the overall efficiency of the boundary mixing

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

hydroacoustic noise precursors of the 1990 eruption of kelut volcano indonesia abstract the results of a hydroacoustic monitoring experiment in the kelut crater lake indonesia prior to its 1990 eruption are presented with the benefit of hindsight indeed the underwater noise levels in three widely separated frequency bands together with the lake water temperature was radio transmitted and almost continuously recorded from a period of quiescence of the volcano till the onset of its 10 february 1990 eruption which destroyed the monitoring buoy the comparative analysis of the noise variations in the three bands together with seismic and temperature data have shed light on the mechanisms underlying the pre eruptive activity the three acoustic levels had shown conspicuous yet distinctive changes prior to the eruption acoustic level in the low frequency 1 50 hz band which increased one year before the resumption of seismic activity and the lake warming up is interpreted as the result of boiling at depth the source of high acoustic level in the audiometric 500 5000 hz range is clearly the bubbling of volcanic gases occurring as a strong convective column in the middle of the lake from the variations of this audiometric level we have estimated that the degassing rate in the lake increased by a hundred fold during the pre eruptive period variations of ultrasonic 20 100 khz frequency acoustic level seem to be related with pressure and thermal changes within the hydrothermal system and its rock matrix beneath the lake in conclusion this experiment demonstrates the potential of hydroacoustic monitoring as an early warning system at crater lake volcanoes

bedrock erosion by root fracture and tree throw a coupled biogeomorphic model to explore the humped soil production function and the persistence of hillslope soils 1 in 1877 g k gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker subsequent analyses of this humped functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil to explore this issue we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw the coupled biogeomorphic model combines data on conifer population dynamics rootwad volumes tree throw frequency and soil creep from the pacific northwest usa although not hardwired into the model a humped relationship emerges between bedrock erosion and soil thickness the magnitudes of the predicted bedrock erosion rates and their functional dependency on soil thickness are consistent with independent field measurements from a coniferous landscape in the region imposed perturbations of soil erosion during model runs demonstrate that where bedrock weathering is episodic and localized hillslope soils do not exhibit runaway thinning or thickening the pit and mound topography created by tree throw produces an uneven distribution of soil thicknesses across a hillslope thus although episodes of increased erosion can lead to temporary soil thinning and even the exposure of bedrock patches local areas of thick soils remain these soil patches provide habitat for trees and serve as nucleation points for renewed bedrock erosion and soil production model results also suggest that where tree throw is a dominant weathering process the initial mantling of bedrock is not only a vertical process but also a lateral process soil mounds created by tree throw flatten over time spreading soil over bedrock surfaces

black smokers fuelled by freezing magma if ocean floor hot spring activity is to continue long enough to produce a large massive sulphide deposit heat must be stripped by the circulating water from a store within the ocean crust we argue here that this heat store can only be a magma chamber and that production of a large sulphide deposit requires very rapid crystallization of large volumes of magma 1 km3 per 100 yr for several hundred years the effects of such rapid solidification should be apparent in the gabbroic components of ophiolite complexes as well as in plutons in other environments where large high temperature massive sulphides are formed

implications for the thermal regime of acoustic noise measurements in crater lake mount ruapehu new zealand hydrophone measurements of acoustic noise levels in the crater lake of mount ruapehu new zealand were made on 18 january 1991 from an inflatable rubber boat on the lake the greatest sound pressures were recorded in the 1 10 hz band with sound levels generally decreasing about 20 db per decade from 10 hz to 80 khz the low frequency noise did not have an obvious relationship to the tremor observed at a seismic station within 1 km of the lake the comparatively low levels of middle and high frequency sound meant that at the time of measurement direct steam input did not make a significant contribution to the heating of crater lake this is consistent with the earlier conclusion that during the last decade a major part of the heat input of crater lake has come from lake water that was heated below the lake and recycled back into the lake

irreversible nitrate fluxes due to turbulent mixing in a coastal upwelling system 1 detailed and repeated measurements of nitrate across the oregon shelf made coincident with turbulence measurements reveal the importance of cross isopycnal mixing via turbulence in providing nitrate to the upper water column spatial distributions of vertical gradients and turbulent fluxes in the oregon coastal ocean reveal variability that could not have been resolved with traditional sampling approaches nitrate rich near bottom waters are drawn up the shelf during upwelling and back down the shelf during downwelling continuous turbulent mixing in the bottom boundary layer increases nitrate on intermediate isopycnals by several m toward the shelf this increased nitrate is consistent with measured turbulent flux of nitrate of o 0 1 mol m 2 s 1 for a period of 3 days roughly the timescale for changes in the wind and hence to the upwelling circulation our flux estimates are consistent with high biomass nutrient replete incubation based primary productivity estimates in this area and suggest that turbulent vertical nitrate transport plays a significant role in supporting the high productivity seen here offshore of 30 m depth we estimate the irreversible transport of nitrate from nitrate rich near bottom waters to be about 25 of the rate at which it is provided by upwelling the total irreversible transport is greater by some unknown amount when we consider the transport inshore of 30 m depth we suggest that the onshore transport of offshore water whether deep water during upwelling or surface water during relaxation forces the juxtaposition of strong gradients and mixing regimes such that turbulent vertical fluxes are consistently elevated in the shoreward reaches of the coastal ocean

prescriptions for heat flux and entrainment rates in the upper ocean during convection abstract a detailed investigation of the upper ocean during convection reveals the vertical structure of potential temperature to be steady in time and the current shear to vanish in the bulk of the mixed layer these imply that a slab type model may be an adequate representation of the convective ocean boundary layer obl in contrast when convection is not the dominant forcing mechanism the obl is stratified and can support a significant current shear this indicates the inadequacy of slab models for the nonconvective obl two independent estimates of the vertical heat flux profile in the convective obl were made the first estimate results from heat conservation and the steadiness of the vertical structure of potential temperature the second estimate is based on the turbulent kinetic energy tke balance and the vertical profiles of tke dissipation rate the estimates are consistent and suggest that the nondimensional vertical heat flux due to turbulence has a linear depth dependence o

boundary mixing in lakes 2 combined effects of shear and convectively induced turbulence on basin scale mixing a detailed comparison of results from a numerical three dimensional hydrostatic lake model with high resolution observations of the vertical structure of the turbulent bottom boundary layer bbl in a medium size lake lake alpnach switzerland is provided the focus of this study is on the shear induced generation and destruction of stratification in the bbl that may ultimately lead to unstable layers convection the model was shown to provide a reliable description of the internal seiching dynamics as well as the local bbl properties including the generation of shear induced convection in two data sets from 2003 and 2007 basin scale mixing parameters inferred from the simulations are closely connected to the seiching motions with the hypolimnetic mixing reacting almost immediately to the variable wind forcing and seiching activity during upslope flow the bbl becomes convectively turbulent causing low mixing efficiency on a basin scale whereas during downslope flow the bbl is restratifying and shear induced turbulence is weak but leads to a higher mixing efficiency the overall deep water mixing efficiency varied in the range of 5 to 10 in this system dominated by turbulent boundary processes

geomorphology and vegetation on hillslopes interactions dependencies and feedback loops article i nfo the linkages between vegetation and hillslope geomorphology have been the subject of serious study for years but traditionally ecologists and geomorphologists have viewed these interactions as unidirectional on the one hand botanists and landscape ecologists have examined the effects of hillslope features processes and materials on vegetation structure composition and dynamics focus has been placed on the effects of topography elevation slope angle slope aspect edaphic factors rock type and geomorphic disturbance mass movement snow avalanches land surface erosion on the other hand geomorphologists have traditionally treated vegetation as an independent variable that affects landforms and sediment routing at limited spatial temporal scales hillslope vegetation and landforms however co evolve one key is to understand the role of time disturbances and feedbacks that link vegetation and geomorphology on hillslopes the effects of vegetation on mass movement and landscape evolution are being studied in new ways many regional studies claim that vegetation becomes less relevant as one moves to larger and larger watershed scales but ecoregion analysis offers a contrasting view whereas these efforts have produced vehicles of understanding that are simple ordered unified and harmonious they often do not reflect the complexity that leads to multiple possible outcomes place dependent results recent perspectives focus on the two way interplay between vegetation and hillslope geomorphology where establishing cause and effect linkages is made difficult by confounding factors spatial temporal scale location convergence divergence nonlinearity thresholds feedbacks vegetation and geomorphology interactions are controlled by a combination of global factors independent of time and place and the local environmental history continued refinement of fine scale deterministic models should be encouraged but the ability to translate these results to larger scales needs to be explored at large scales future research especially those with predictive modeling as the goal should concentrate on how to increase the generality of concepts and models and should seek to reduce the number of variables and factors considered

submesoscale baroclinic instability in the bottom boundary layer abstractweakly stratified layers over sloping topography can support a submesoscale baroclinic instability mode a bottom boundary layer counterpart to surface mixed layer instabilities the instab

reconstruction of quaternary landscape formation as a tool to understand present geomorphological processes in the eastern prealps austria abstract the rhenodanubian flysch of the n vienna forest is composed of various layers of sandstones marly shales calcareous marls and clay schists covered by quaternary periglacial cover beds and loess deposits there is a characteristic sequence of slope evolution during the quaternary seven main phases are related to pleistocene processes and two stages reflect the most recent geomorphodynamic processes phases of erosion redeposition sedimentation and soil formation demonstrate stages of activity and stability under varying climatic conditions on the basis of pedological and geomorphological investigations it is possible to differentiate pleistocene and holocene sediments and processes in particular the distribution of periglacial cover beds loess and modern soils allows the reconstruction of the undisturbed pleistocene slope and sediments the sequence of slope formation causes a distinct spatial distribution of quaternary sediments and solid rock at the present land surface in consequence the influence of quaternary landscape formation significantly influences slope stability conditions in the study area this applies to the specific composition of the basal periglacial cover bed in the study area it often consists of densely bedded marls and sandstone and is therefore impermeable which can induce mass movements in the study area loess deposits frequently slide on top of the basal periglacial cover bed and form a susceptible pre requisite for the occurrence of landslides in the study area

measurements of plume flow from a hydrothermal vent field simultaneous velocity temperature and conductivity data were taken in the convective flow emanating from a hydrothermal vent field located at 10 56 n 103 41 w on the east pacific rise the horizontal profiles obtained indicate that the flow field approaches an ideal plume in the temperature and velocity distribution such parameters as total heat flow and maximum plume height can be estimated using either the velocity or the temperature information the results of these independent calculations are in close agreement yielding a total heat flow from this vent site of 3 7 0 8 mw and a maximum height of 150 10 m the nonlinear effects of large temperature variations on heat capacity and volume changes slightly alter the calculations applied to obtain these values

temperature statistics above a deep ocean sloping boundary we present a detailed analysis of temperature statistics in an oceanographic observational dataset the data are collected using a moored array of thermistors 100 text m 100 m tall and starting 5 text m 5 m above the bottom deployed during four months above the slopes of a seamount in the north eastern atlantic ocean turbulence at this location is strongly affected by the semidiurnal tidal wave mean stratification is stable in the entire dataset we compute structure functions of order up to 10 of the distributions of temperature increments strong intermittency is observed in particular during the downslope phase of the tide and farther from the solid bottom in the lower half of the mooring during the upslope phase the temperature statistics are consistent with those of a passive scalar in the upper half of the mooring the temperature statistics deviate from those of a passive scalar and evidence of turbulent convective activity is found the downslope phase is generally thought to be more shear dominated but our results suggest on the other hand that convective activity is present high order moments also show that the turbulence scaling behaviour breaks at a well defined scale of the order of the buoyancy length scale which is however dependent on the flow state tidal phase height above the bottom at larger scales wave motions are dominant we suggest that our results could provide an important reference for laboratory and numerical studies of mixing in geophysical flows

direct breaking of the internal tide near topography kaena ridge hawaii abstract barotropic to baroclinic conversion and attendant phenomena were recently examined at the kaena ridge as an aspect of the hawaii ocean mixing experiment two distinct mixing processes appear to be at work in the waters above the 1100 m deep ridge crest at middepths above 400 m mixing events resemble their open ocean counterparts there is no apparent modulation of mixing rates with the fortnightly cycle and they are well modeled by standard open ocean parameterizations nearer to the topography there is quasi deterministic breaking associated with each baroclinic crest passage large amplitude small scale internal waves are triggered by tidal forcing consistent with lee wave formation at the ridge break these waves have vertical wavelengths on the order of 400 m during spring tides the waves are nonlinear and exhibit convective instabilities on their leading edge dissipation rates exceed those predicted by the open ocean parameterizations by up to a factor of 100 with the disparity in

time series measurements of hydrothermal activity on northern juan de fuca ridge during august september 1984 the submersible alvin visited a large active hydrothermal system on the juan de fuca ridge a time lapse camera taking photographs every 42 minutes for six days was deployed at an active vent to characterize the dynamic nature of this system this report documents the growth rate of a low temperature measured at 56 c hydrothermal deposit and establishes that this growth is not constant periods of substantial erosion are superimposed upon the general growth pattern quantitative photographic interpretation of the suspended particulate load suggests a strong diurnal component to these fluctuations water flow manifest by the movement of attached worm tubes also shows strong variations but on a semi diurnal basis correlated to tidal motions