organic carbon δ13c variations in sedimentary rocks as chemostratigraphic and paleoenvironmental tools abstract carbon isotopic variations in marine carbonate rocks and organic matter can provide important information on stratigraphic correlations and paleoenvironments in particular carbon isotopic variations in marine organic materials may yield information about the concentration of oceanic dissolved co 2 and or the physiology of the microalgal community this paper reviews evidence from laboratory experiments and oceanographic studies aimed at understanding controls on carbon isotopic fractionation by marine phytoplankton we also review factors affecting carbon isotopic compositions of bulk sedimentary organic matter and individual biomarker compounds guidelines for analysis of isotopic compositions of organic materials and interpretations of these results for use as chemostratigraphic and paleoenvironmental tools are presented we recommend caution in interpreting carbon isotopic variations of sedimentary organic matter because no environmental factor explains adequately variations in the carbon isotopic composition of modern phytoplankton studies of ancient materials should include compound specific isotopic analyses of known phytoplankton biomarkers or organism specific isotopic analyses with bulk isotopic results to assess the proportions of allochthonous organic materials the degree of reworking and the extent of thermal degradation to confirm any trends present in values of bulk sedimentary organic matter

some forms of mountain peaks in the canadian rockies controlled by their rock structure abstract different mountain shapes in sedimentary sequences in the canadian rockies were enhanced by glacial erosion and have been modified post glacially by gravity driven slope processes slope modification by both glacial erosion and post glaciation landslides is related to slope geometry and rock structure particularly bedding dip five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips 1 castellate and 2 matterhorn mountains occur in sub horizontal beds and their slopes are generally 35 65 and oblique to both bedding and joints 3 cuestas develop in gently to moderately dipping beds dip slopes and steeper normal escarpments form their cataclinal and anaclinal sides respectively with the dihedral angle between them about 90 4 hogbacks in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments the dihedral angle between the slopes is usually slope gradients on a sample of 34 peaks are closely related to landslides particularly rock slides and rock topples these landslide modes are controlled by bedding dips

wind direction and equilibrium mixed layer depth general theory abstract a usually neglected coriolis term in the turbulent kinetic energy budget of the ocean surface mixed layer is examined for the special case of a steady state mixed layer depth with no entrainment in this term the reynolds stresses interact with the northward component of planetary rotation to exchange turbulent kinetic energy between horizontal and vertical components the direction of the exchange depends upon the sign of east west component of the wind stress a vertically integrated or bulk theory is derived for a non entraining mixed layer in equilibrium the results show that the vertical turbulent kinetic energy and hence the vertical mixing and mixed layer depth will be reduced for westerly winds fasterly winds will increase vertical mixing and mixed layer depth

effects of rotation on convective plumes from line segment sources abstract effects of rotation on finite length line plumes are studied with a three dimensional nonhydrostatic numerical model geophysical convection with this source geometry occurs for example as the result of fissure releases of hot hydrothermal fluids at the seafloor from terrestrial release of hot gases and ash during volcanic activity along fissures and in the descent from the sea surface of brines formed during freezing of ice leads at high latitudes here the model treats the case of a starting plume of dense fluid descending into a rotating environment results are compared with laboratory experiments so that the validity of the model particularly the nonlinear subgrid scale mixing formulation might first be established differences in plumes caused by varying rotation rate ohm and buoyancy flux b0 are the primary focus with experiments in fluid of depth h spanning a convective rossby number b01 3 2 h of 0 01 1 0 rotation initiates spiraling of the descending plumes but it has litt

middepth flow near hydrothermal venting sites on the southern juan de fuca ridge long term moored current measurements around the southern end of the juan de fuca ridge show that flow parallels the ridge and may be intensified by its presence the mean flow is northward on the west side and southward on the east thus plumes emanating from the ridge probably are advected along the ridge before flowing away from the ridge other topographic features may be responsible for westward or eastward turning along the west side of the ridge we hypothesize a regional flow pattern with southward flow north of axial seamount northward flow south of axial and a convergence somewhere south of axial resulting in westward flow along the east side the flow may be southward everywhere above the ridge crest the long term mean flow is weaker and more variable and it includes tidal inertial and a dominant broadband 4 day oscillation this 4 day energy is maximum in the rift valley where the inertial is least decreases upward and away from the ridge and is more energetic in winter this oscillation is predominately a clockwise rotating feature which along with the presence of inertial oscillations suggests that it may be storm induced from the sea surface these observations along with those by cannon and pashinski 1990 suggest northward propagation flow variations across the ridge lasting one to a few months have mean speeds of 1 3 cm s and are capable of transporting plumes off axis to the west or east into the northerly or southerly flows respectively

numerical simulations of rotating bubble plumes in stratified environments the effects of system rotation on the turbulent dynamics of bubble plumes evolving in stratified environments are numerically investigated by considering variations in both the system rotation rate and the gas phase slip velocity the turbulent dispersion of a passive scalar injected at the source of a buoyant plume is strongly altered by the rotation of the system and the nature of the buoyancy at the source when the plume is driven by the density defect associated with the presence of slipping gas bubbles the location of the main lateral intrusion decreases with respect to the single phase case with identical inlet volume momentum and buoyancy fluxes enhanced downdrafts of carrier phase fluid result in increased turbulent mixing and short circuiting of detraining plume water that elevate near field effluent concentrations similarly rotation fundamentally alters dynamic balances within the plume leading to the encroachment of the trapping height on the source and an increase in turbulent dispersion in the near field system rotation even at modest rossby numbers produces a sustained robust anticyclonic precession of the plume core the effects of rotation and the presence of bubbles are cumulative the vertical encroachment of the primary intrusion and the overall dispersion of effluent are greatest at smallest rossby numbers and largest slip velocities the main characteristic feature in rotating single phase plumes namely the robust anticyclonic precession persists in bubble plumes analysis of the momentum budgets reveal that the mechanism responsible for the organized precession i e the establishment of an unstable vertical hydrostatic equilibrium related to radial cyclostrophic balance does not differ from the single phase case

geology of a vigorous hydrothermal system on the endeavour segment juan de fuca ridge a high precision high resolution geologic map explicitly documents relationships between tectonic features and large steep sided sulfide sulfate silica deposits in the vigorously venting endeavour hydrothermal field near the northern end of the juan de fuca ridge water depth in the vent field varies from 2220 to 2200 m location of the most massive sulfide structures appears to be controlled by intersections of ridge parallel normal faults and other fracture fissure sets that trend oblique to and perpendicular to the overall structural fabric of the axial valley the fractured basaltic substrate is primarily composed of well weathered pillow and lobate flows as presently mapped the field is about 200 by 400 m on a side and contains at least 15 large 1000 m3 sulfide edifices and many tens of smaller commonly inactive sulfide structures the larger sulfide structures are also the most vigorously venting features in the field they are commonly more than 30 m in diameter and up to 20 m in height actively venting sulfide structures in the northern portion of the field stand higher and are more massive than active structures in the southern portion of the field which tend to be slightly to distinctly smaller maximum venting temperatures of 375 c are associated with the smaller structures in the southeastern portion of the field highest temperature venting fluids from the more massive structures in the northern portion of the field are consistently 20 30 c lower hydrothermal output from individual active sulfide features varies from no flow in the lower third of the edifice to vigorous output from fracture controlled black smoker activity near the top of the structures a different type of high temperature venting takes place from the upper sides of the structures in the form of overflow from fully exposed quiescent pools of buoyant 350 c vent water trapped beneath overhanging sulfide sulfate silica ledges or flanges these flanges are attached to the upper outer walls of the large sulfide edifices two types of diffuse venting in the endeavour field include a lower temperature 8 15 c output through colonies of large tubeworms and 25 50 c vent fluid that seems to percolate through the tops of overhanging flanges the large size and steep walled nature of the these structures evidently results from sustained venting in a mature hydrothermal system coupled with dual mineral depositional mechanisms involving vertical growth by accumulation of chimney sulfide debris and lateral growth by means of flange development

effluent from diffuse hydrothermal venting 2 measurement of plumes from diffuse hydrothermal vents at the southern juan de fuca ridge an array of temperature and velocity sensors was deployed for two weeks in the bottom boundary layer at the southern juan de fuca ridge during the national oceanic and atmospheric administration vents 90 field experiment the instruments were placed close to the seafloor to detect effluent from diffuse hydrothermal sources located 1 2 km distant over the duration of the field deployment we detected effluent from two vent sources the plume from the larger of the two sources was sensed at all of the instrument locations permitting estimates of dilution based on the field measurements our data also permitted estimation of energy flux from diffuse vents approximately 125 75 mw from a source to the north of the instrument array and 12 8 mw from a small source to the east the largest source of error in the data was estimation of the plume width we have described a sensor array that would reduce this error in future work such an array would be suitable for a long term vent activity monitor

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

reconnaissance of rockslide hazards in kananaskis country alberta kananaskis country is situated in the front ranges of the canadian rockies in southwestern alberta sedimentary rock thrust northeastwards forms mountain ridges that trend northwest southeast parallel to the major thrust faults older palaeozoic rocks mainly limestone and dolomite form the ridges and peaks younger mesozoic rocks sandstones quartzites siltstones shales conglomerates and coals are more easily eroded and form mountain passes and valleys a reconnaissance mapped 228 rockslides 8 km2 of rockslide debris and 96 km2 of talus the largest rockslide exceeds 50 106 m3 rockslides are most probable in the devonian palliser formation then in the permo pennsylvanian rocky mountain group mississippian rundle group devonian fairholme group mississippian banff formation and the younger detrital rocks rockslides are most probable on dip and overdip slopes followed by reverse dip slopes oblique and strike dip slopes and underdip slopes large rock masses have not slid on slopes below the

postglacial topographic evolution of glaciated valleys a stochastic landscape evolution model the retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime we have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model the model incorporates a stochastic process to represent deepseated landsliding non linear diffusion to represent shallow landsliding and an approximation of the bagnold relation to represent fluvial sediment transport it was calibrated using field data from several recent surveys within british columbia canada we present ensemble model results and compare them with results from a deterministic linear diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline similar to that inferred for holocene time we also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse

the relationship between δ13c of organic matter and co2 aq in ocean surface water data from a jgofs site in the northeast atlantic ocean and a model the 13c of suspended particulate organic matter spom in surface waters increased from 22 9 to 18 1 during april 25 may 31 1989 at the jgofs north atlantic bloom experiment site nabe site 47 n 20 w during the same period nearly parallel increases in sinking pom 13c were also found although these values were usually lower than those of the corresponding spom consistent with the hypothesis that plankton 13c and co2 aq are inversely related the increases in both sinking and suspended pom 13c were highly negatively correlated with mixed layer co2 aq that generally decreased from 10 1 13 2 moles kg during the five weeks the change in spom 13c per change in co2 aq however appears to be somewhat greater than that expected from previous though less direct ocean and laboratory evidence by adapting a model of plant 13c by farquhar et al 1982 it is shown that under a constant phytoplankton demand for co2 an inverse nonlinear spom 13c response to ambient co2 aq is expected such trends are unlike the negative linear relationships indicated by data from the nabe site and or from southern hemisphere waters such differences between predicted and observed spom 13c vs co2 aq trends and among observed relationships can be reconciled however if biological co2 demand is allowed to vary this has significant implications for the use of the 13c of plankton or their organic subfractions or sedimentary remains as a proxy for past or present ocean co2 concentrations and biological productivity

a numerical study of local convection in the benthic ocean induced by episodic hydrothermal discharges a nonhydrostatic primitive equation model is used to investigate motions and water column property distributions accompanying the rise of hot hydrothermal fluids into a rotating water column stratified in temperature and salinity after preliminary model experiments used to fix the level of turbulent mixing the model is applied to a megaplume event the release of a large amount of hydrothermal heat into the benthic ocean over a period of several days events of this kind have produced water masses with anomalous temperature and salinity distributions 20 km in diameter 800 m thick centered vertically 700 1000 m off the seafloor the model allows the study of the initial time development and maturation of the plume from such an event preliminary experiments demonstrate the sensitivity of plume rise to the level of turbulent mixing and to the ratio of turbulence viscosity to turbulence diffusivity i e prandtl number rise to maximum plume height occurs in 4 6 n 1 where n is buoyancy frequency consequences of a megaplume sized release of heat are examined over an initial 30 day period vertical circulation accompanying a hydrothermal event leads to a slight negative salinity anomaly below the plume s temperature anomaly core the plume s heat potential temperature anomaly is shown to be a composite of hydrothermal heat and ambient heat that has been redistributed by the same vertical circulation cell horizontal circulation is dominated by an anticyclonic flow vortex centered just above the temperature anomaly maximum at 800 m above bottom and a cyclonic flow vortex at the seafloor azimuthal flow accounts for the largest fraction of kinetic energy within 4 5 hours 1 7 1 after the start of heat release azimuthal velocities reach maximum values of 70 cm s 1 90 of which is attained within the initial 10 hours even as much as 4 weeks past cessation of heat release maximum azimuthal velocities are of the order of 10 cm s 1 the balance of vertical forces is hydrostatic by 12 hours save for near bottom frictional effects during plume formation the radial force balance is primarily cyclostrophic near axis and geostrophic at a distance

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

deep sea hydrothermal plumes and their interaction with oscillatory flows 1 the acoustic scintillation method is applied to the investigation and monitoring of a vigorous hydrothermal plume from dante within the main endeavour vent field mef in the endeavour ridge segment a 40 day time series of the plume s vertical velocity and temperature fluctuations provides a unique opportunity to study deep sea plume dynamics in a tidally varying horizontal cross flow an integral plume model that takes into account ambient stratification and horizontal cross flows is established from the conservation equations of mass momentum and density deficit using a linear additive entrainment velocity in the model e um u that is a function of both the plume relative axial velocity um and the relative ambient flow perpendicular to the plume u gives consistent results to the experimental data suggesting entrainment coefficients 0 1 and 0 6 also from the integral model the plume height in a horizontal cross flow ua is shown to scale as 1 8b1 3ua 1 3n 2 3 for 0 01 ua 0 1 m s where b is the initial buoyancy transport and n is the ambient stratification both of which are assumed constant

rock topples in the highway cut west of clairvaux creek jasper alberta the topples exposed in the road cut along highway 16 17 km west of jasper alberta were caused by slope steepening by both glaciation and excavation the toppling of layers that underdip the cut slope was initiated by water pressure ice pressure and loose materials in the cracks of rock masses with large block ratios toppling formed well exposed sliding surfaces on steep slopes and rupture surfaces on shallower slopes key words rock slopes rock cuts rockies toppling sliding underdip slopes

exhaustion and steady state models for predicting landslide hazards in the canadian rocky mountains abstract the temporal distribution of landslides can be evaluated by steady state and exhaustion models the probability of landsliding remains constant through time in the steady state model but the probability decreases in the exhaustion model as more slopes fail rock sliding down bedding surfaces on overdip slopes exhausts hazardous sites to leave stable dipslope landforms in kananaskis country in the canadian rocky mountains the distribution of rock slides in this area can be better explained by the exhaustion model than by the steady state model

the relationship between near axis hydrothermal cooling and the spreading rate of mid ocean ridges recent seismic observations and new crustal thermal models suggest that near axis 1 km from the spreading axis hydrothermal cooling increases linearly with increasing spreading rate we present here the first corroborating evidence from near axis hydrothermal plume observations comprehensive surveys of plume distributions have now been conducted on multi segment portions of ridge crest with full spreading rates from 20 to 150 km myr these surveys find thatph the fraction of ridge crest length overlain by hydrothermal plumes and full spreading rate us are related byph us where 0 004 myr km we recast this large scale spatial variability into long term temporal variability by postulating that any vent field site is hydrothermally active for an us fraction of geologic time we then use this relationship and the mean of eight studies that have determined instantaneous heat flux ha at vent field scales 75 45 mw km to estimate the time averaged heat flux ha asha us applying these scaled values ofha to the distribution of mid ocean ridge spreading rates yields a global near axis heat flux ha of 8 8 1011 w this value is 10 of the total oceanic hydrothermal heat flux and agrees with a crustal cooling model derived value of ha of 9 1011 w our estimate of ha implies a mean global3he heat ratio of 2 4 8 3 10 13 cm3 j stp and high temperature hydrothermal fluid flow of 1 8 1013 kg yr

the palliser rockslide canadian rocky mountains characterization and modeling of a stepped failure surface abstract this paper presents the results of an investigation of the prehistoric palliser rockslide rocky mountains canada conventional aerial photograph interpretation and field mapping are complemented by terrestrial digital photogrammetry these techniques allow quantification of the rockslide debris volume and reconstruction of the pre slide topography it has been estimated that the volume of rock involved in the most recent large rockslide is 8 mm 3 terrestrial digital photogrammetry is used in the characterization of the failure surface morphology which is subdivided into four types of step path geometry comprising both pre existing discontinuities and intact rock fractures incorporation of these data into various rock slope stability numerical modeling methods highlights a complex failure mechanism which includes sliding along a large scale curved failure surface intact rock bridge fracturing and lateral confinement a preliminary quantification of the contribution of intact rock bridges to the shear strength of the failure surface is presented in terms of the apparent cohesion apparent tensile strength and cumulative length of the intact rock segments

the shapes of cold high mountains in sedimentary rocks abstract terzaghi geotechnique 12 1962 251 and young young a 1972 slopes oliver and boyd edinburgh 288 pp described the stable forms of slopes in sedimentary rock masses assuming penetrative discontinuities which are parallel to bedding and joints which are perpendicular to bedding the only movements considered were slides along bedding experience in the canadian rockies indicates that the cohesionless rock masses that exist at or above tree line may also move by toppling buckling and sliding along joints these processes also act to limit the inclinations of stable slopes rock strength is a factor in the critical height of a slope that buckles the processes can be represented as fields on a process diagram a plot of slope inclination against bedding dip using the basic friction angles of the rocks present the process diagram also separates five common mountain peak shapes which form on homoclinal sequences of beds castellate and matterhorn mountains occur in sub horizontal beds cuestas develop in gently to moderately dipping beds hogbacks formed in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes dogtooth mountains occur in steeply dipping sub vertical beds

redox dependent distribution of early macro organisms evidence from the terminal ediacaran khatyspyt formation in arctic siberia abstract the ediacaran period witnessed the first appearance of macroscopic animal life in earth s history however the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain in part due to the dearth of integrated paleobiological and chemostratigraphic datasets in this study a comprehensive geochemical analysis was conducted on the fossiliferous khatyspyt formation in arctic siberia in order to gain insights into the ediacaran paleoenvironments this study was designed to specifically address the relationship between paleoredox conditions and ediacaran fossil occurrences in the khatyspyt formation our data reveal a dramatic shift in pyrite sulfur isotope compositions 34 s pyrite from ca 20 to ca 55 and this shift is intriguingly associated with the first occurrence of ediacara type macrofossils at the studied section suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms based on multiple lines of sedimentological and geochemical evidence we propose that the development of oceanic euxinia which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal ediacaran period may have locally prohibited the colonization of ediacara type organisms and resulted in low 34 s pyrite values in the lower khatyspyt formation in the middle and upper khatyspyt formation progressive secular transition from euxinic to non euxinic and more habitable conditions may have allowed for the colonization of ediacara type and other macro organisms

buoyancy driven plumes in rotating stratified cross flows plume dependence on rotation turbulent mixing and cross flow strength a three dimensional time dependent convection model is used to describe circulation and property fields in rotating stratified and moving fluids near a point source of heat the study context and consequently model scales are those of chronically discharging hydrothermal vent fields found at submarine ridge crests hydrothermal plumes having distinctive thermal and chemical anomalies have been observed to rise several hundreds of meters above the deep sea floor before being advected away by background cross flows typically of magnitude 1 4 cm s 1 the model is used to study effects of rotation and indicate differences in plumes with respect to variation of subgrid scale turbulence intensity and cross flow strength counterrotating vorticity couplets in all three coordinate directions develop in the lower plume stem at startup and follow the plume to the level of neutral buoyancy for a nonrotational case 0 patterns resemble those previously found for jets injected into homogenous cross flow ambient fluid entrainment into the convecting column is primarily from the upstream side but deflection of background flow around both sides of the rising column is the root of the relative vorticity z couplet in the lower plume turbulence intensity within the buoyant region of the plume and or globally controls smoothness and temporal variability of distal nonbuoyant plume distributions allowing or preventing oscillations of potential temperature for example at background buoyancy frequency n over the range of turbulent mixing studied rise height of plumes did not change appreciably but breadth of plumes counterintuitively increased for decreasing turbulent mixing strength increasing cross flow strength u0 bends model plumes such that rise height u0 0 4 for the two largest values of cross flow for which r the ratio of maximum vertical velocity to u0 took values of 2 8 and 1 0 plumes showed evidence of bifurcation

signature of rhine valley sturzstrom dam failures in holocene sediments of lake constance germany abstract landslide dammed lakes that form upstream of large scale rockslide avalanches sturzstroms present an enormous potential hazard to downstream areas such failures are recorded in the early holocene sediments of upper lake constance germany by the presence of two clastic layers that were emplaced around 9400 cal ybp the sedimentology of these layers contrasts sharply with the typical late glacial and holocene lacustrine sediments present beneath the floor of the lake sedimentary structures and the magnetic fabric of these clastic deposits strongly suggest that they were emplaced by hyperpycnal underflows related to catastrophic floods that entered the lake from the rhine river from stratigraphic and geologic data it is inferred that the hyperpycnite deposits are directly related to the failure of two sturzstrom dams and the draining of the dammed lakes that developed upstream from them these lakes were dammed by the flims and the tamins sturzstrom deposits respectively sedimentologic data from lake constance indicate that the two successive events occurred within a very short time interval probably not exceeding several years consequently these lacustrine deposits provide essential information about the morphogenic evolution of the rhine river valley during the early holocene and about the sturzstrom events that occurred during the same time interval

diffuse venting and background contributions to chemical anomalies in a neutrally buoyant ocean hydrothermal plume plumes originating in high temperature hydrothermal discharges entrain background water and often entrain diffuse source fluids during convective ascent the mixing of fluid from those three different sources determines the chemical composition of the ensuing neutrally buoyant plumes here convection models and aluminum data from the trans atlantic geotraverse tag site are used to examine relative contributions of focused diffuse and background sources to anomalies in the plume our analysis shows that anomalously high al values observed just above the seafloor at tag which we assume stem from diffuse flows can contribute as much as 50 to the al anomaly in the neutrally buoyant plume found 350 m above bottom background water contributes nearly an equal fraction of al to the anomaly more generally entrained contributions depend on gradients in profiles external to the rising plume entrainment also depends on effective source area distributed high temperature vents entrain more fluid than a single composite high temperature vent larger effective source area is particularly significant for entrainment of diffuse source or other tracers trapped within a few tens of meters of the seafloor downstream cross stream and temporal variabilities exhibited in the three dimensional model plume also underscore problems of sampling and interpreting actual plume data

the path to covis a review of acoustic imaging of hydrothermal flow regimes abstract acoustic imaging of hydrothermal flow regimes started with the incidental recognition of a plume on a routine sonar scan for obstacles in the path of the human occupied submersible alvin developments in sonar engineering acoustic data processing and scientific visualization have been combined to develop technology which can effectively capture the behavior of focused and diffuse hydrothermal discharge this paper traces the development of these acoustic imaging techniques for hydrothermal flow regimes from their conception through to the development of the cabled observatory vent imaging sonar covis covis has monitored such flow eight times a day for several years successful acoustic techniques for estimating plume entrainment bending vertical rise volume flux and heat flux are presented as is the state of the art in diffuse flow detection

manganese and methane in hydrothermal plumes along the east pacific rise 8 40 to 11 50 n abstract in november 1991 we surveyed the water column for hydrothermal plumes along 350 km of the east pacific rise axis from 8 40 to 11 50 n using a combination of physical and chemical measurements our survey included the two major ridge segments north and south of the clipperton transform fault at about 10 10 n both limbs of the overlapping spreading centers osc s at 9 03 n and 11 45 n and a 30 km section of the next ridge segment to the south we found vigorous plumes along most of this ridge axis in keeping with its magmatically robust cross section axial summit caldera and shallow magma related seismic reflector these plumes were detectable by both physical temperature and light attenuation and chemical dissolved mn and ch4 measurements although the chemical measurements were more sensitive the least active sections were the southern third of the northern segment from 10 20 to 52 n and the oscs especially the osc at 11 45 n plumes there had weak mn and ch4 signals and were barely detectable by physical methods these axial sections were the only ones surveyed that lie deeper than 2600 m and appear to be magma starved the most active sections on the northern segment gave stronger signals for mn and temperature than for ch4 and light attenuation whereas the opposite was true on the southern segment which was the site of a volcanic eruption at 9 45 52 n only seven months prior to our cruise on the northern segment the four physical and chemical plume tracers correlated positively and linearly with one another suggesting that the segment was fed by relatively uniform end member fluids with a mean ch 4 mn molar ratio of 0 075 the southernmost section surveyed from 8 42 to 9 08 n closely resembled the northern segment the rest of the southern segment fell into three sections with different ch 4 mn ratios 9 39 to 53 n with ch 4 mn as high as 10 9 08 to 39 n with ch 4 mn of 0 51 and 9 53 to 10 07 n with ch 4 mn of 0 85 the section with the highest ch 4 mn was the site of the volcanic eruption which produced high temperature low salinity gas rich vent fluids carrying abundant bacterial particles the high ch4 concentrations are clearly associated with the volcanic eruption but the origin of the ch4 is unclear

an integrated biomarker isotopic and palaeoenvironmental study through the late permian event at lusitaniadalen spitsbergen abstract the largest extinction of the phanerozoic occurred near the permian triassic p tr boundary some 252 ma ago several scenarios and drivers have been proposed for this event here we report for the first time an integrated study comprising sedimentological data biomarker distributions abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes 34spyrite 13ccarb 13corg for a late permian section from lusitaniadalen spitsbergen norway sedimentological and geochemical data support a marine transgression and collapse of the marine ecosystem in the late permian strong evidence for waxing and waning of photic zone euxinia throughout the late permian is provided by chlorobiaceae derived biomarkers including 13c data and 34spyrite implying multiple phases of h2s outgassing and potentially several pulses of extinction a rapid decrease in abundance of various land plant biomarkers prior to the marine collapse event indicates a dramatic decline of land plants during the late permian and or increasing distance from palaeoshoreline as a consequence of sea level rise changes in d of selected biomarkers also suggest a change in source of organic matter om or sea level rise we also found biomarker and isotopic evidence for a phytoplanktonic bloom triggered by eutrophication as a consequence of the marine collapse compound specific isotope analyses csia of algal and land plant derived biomarkers as well as 13c of carbonate and bulk om provide strong evidence for synchronous changes in 13c of marine and atmospheric co2 attributed to a 13c depleted source the source could be associated with isotopically depleted methane released from the melting of gas clathrates and or from respired om due to collapse of the marine ecosystem

correlating terrestrial signatures from biomarker distributions δ13c and palynology in fluvio deltaic deposits from nw australia triassic jurassic abstract a multidisciplinary study using molecular and organic isotope geochemistry petrology and palynology has been used to establish palaeoenvironmental conditions of fluvio deltaic deposits from the delambre 1 well western australia triassic jurassic changes in higher plant biomarker distributions correlate with 1 brackish water environments 2 major changes in composition of spore and pollen assemblages 3 variations in types of sedimentary facies and 4 stable carbon isotopic composition of higher plant biomarkers these changes are all consistent with the occurrence of climatic shifts in northwestern australia during triassic jurassic periods established by parrish j t bradshaw m t brakel a t mulholland s m totterdell j m yeates a n 1996 palaeoclimatology of australia during the pangean interval palaeoclimates 1 241 281 the combustion marker benzo e pyrene is abundant in samples that contain pollen from falcisporites australis the decline of f australis and the rapid emergence of assemblages dominated by corollina spp at the end of the triassic marks a rapid pollen spore extinction event at the triassic jurassic boundary there is an increase in relative abundance of the higher plant biomarkers cadalene and simonellite in a prodeltaic facies the 13 c values of between 26 9 and 24 9 for retene are consistent with a source from class i conifer resinites and relate to samples abundant in araucariacian conifers in the early middle jurassic where facies are characterized as pro distal deltaic

organic rich sedimentation in the south pacific ocean associated with late paleocene climatic cooling abstract a distinctive organic rich marine mudstone of late paleocene age occurs in most of new zealand s sedimentary basins and has been identified as a potential source rock for oil and gas identified as the waipawa formation in the east coast basin and the tartan formation in the great south and canterbury basins the unit is a relatively uniform massive mudstone that varies greatly in thickness 2 70 m and grades laterally into distinctive facies equivalents notably greensand and a thin bedded siliceous mudstone all these facies are characterised by relatively high toc 0 5 10 wt and 13 c enrichment 13 c toc 24 and we refer to them collectively as waipawa organofacies our detailed stratigraphic and geochemical studies refine the age 58 7 to 59 4 ma distribution and nature of the waipawa organofacies we have determined that deposition occurred in continental margin settings throughout much of the southwest pacific under cool dysoxic conditions associated with a significant influx of terrestrial organic matter high marine productivity a global fall in sea level and a regional unconformity across shallow and deep marine settings the combination of cool temperatures lowered sea level and bathyal erosion suggests that deposition was linked to short lived growth of an antarctic ice sheet in the earliest late paleocene 59 ma

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

bifurcation of volcanic plumes in a crosswind bent over buoyant jets distorted by a crosscurrent develop a vortex pair structure and can bifurcate to produce two distinct lobes which diverge from one another downwind the region downwind of the source between the lobes has relatively low proportions of discharged fluid factors invoked by previous workers to cause or enhance bifurcation include buoyancy release of latent heat at the plume edge by evaporating water droplets geometry and orientation of the source and the encounter with a density interface on the rising path of the plume we suggest that the pressure distribution around the vortex pair of a rising plume may initially trigger bifurcation we also report new experimental observations confirming that bifurcation becomes stronger for stronger bent over plumes identifying that bifurcation can also occur for straight edged plumes but gradually disappears for stronger plumes which form a gravity current at their final level and spread for a significant distance against the current observations from satellites and the ground are reviewed and confirm that volcanic plumes can show bifurcation and a large range of bifurcation angles many of the bifurcating plumes spread out at the tropopause level and suggest the tropopause may act on the plumes as a density interface enhancing bifurcation even for quite moderate bifurcation angles the two plume lobes become rapidly separated downwind by distances of tens of kilometers such bifurcating plumes drifting apart can only result in bilobate tephra fall deposits the tephra fall deposit from the 16 km elevation se spreading bifurcating volcanic plume erupted on 15 may 1981 from mt pagan was sampled by previous workers and clearly displayed bilobate characteristics examples of bilobate tephra fall deposits are reviewed and their origin briefly discussed bilobate deposits are common and may result from many causes plume bifurcation should be considered one of the possible mechanisms which can account for come examples of bilobate tephra fall deposits

deepwater mantle 3he plumes over the northern mid atlantic ridge 36 n 40 n and the azores platform as part of a multidisciplinary project aimed at studying mid ocean ridge processes near the azores fifty water column profiles were analysed for 3he 4he ratios in dissolved helium a well known hydrothermal tracer from 36 n to 40 n along the mid atlantic ridge mar and over the azores plateau as expected large 3he anomalies could be observed over the rainbow lucky strike and menez gwen hydrothermal sites the main finding of the present study is the discovery of a large hydrothermal 3he plume north of the acor fracture zone north afz site with a ch4 3he ratio indicative of a basaltic hosted hydrothermal system clear 3he and ch4 anomalies likely corresponding to unknown venting sites too were also detected in the amar minor segment and south of the kurchatov fracture zone evidence for substantial mantle helium degassing was also observed in the deep nodal basins along the terceira rift based on 3he plumes over the total length of the surveyed segments the distribution of hydrothermal sites corresponds to a site frequency of 1 3 0 2 site 100 km in good agreement with the global vent field statistics of baker and german 2004 for the rainbow lucky strike and menez gwen sites the application of a plume model based on the conservation of mass heat and momemtum shows that the heat output computed by the model is only an estimation of the heat released by the focused part of the flow imputable to one single vent applied to the north afz venting site for which the height of the plume is not known precisely the model does not allow to discriminate between a menez gwen rainbow type of venting or a more focused vent complex as the one observed at the tag site 26 n

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

changes in the trophic state of lake erie discordance between molecular δ13c and bulk δ13c sedimentary records abstract prior to 1980 anthropogenic phosporus p loadings resulted in increased algal productivity and the deterioration of water quality within lake erie we measured c and n elemental compositions geolipid concentrations and 13 c values for bulk organic material and individual alkanes in samples taken from a 40 cm sediment core from the eastern basin of lake erie to infer recent trends in primary productivity and diagenesis the predominance of autochthonous algal derived c throughout the core is evidenced by low c n values 9 10 and the persistent abundance of n c 15 to n c 17 alkanes throughout the core the 13 c values of bulk organic c from lake erie vary between 25 9 and 24 9 with a maximum corresponding to the period of elevated historical p loading within lake erie 13 c values of short chained algal derived alkanes n c 18 are lower approximately 1 0 than their terrestrial derived homologs n c 25 down core variations in the 13 c composition of algal derived short chained alkanes do not exhibit the same trend as that observed for bulk organic c down core variation in 13 c values of individual alkanes likely reflect multiple diagenetic effects including kinetic fractionation effects variations in the relative contributions of isotopically unique n alkanes to the sediments and or temporal changes in 13 c enrichments of n alkanes associated with a single source high sedimentation rates characteristic of this core emphasize temporal variations in molecular 13 c values that might not otherwise be observed whereas 13 c data for bulk sedimentary organic c appear to reflect variation in trophic state the isotopic record for algal derived n alkanes e g n c 17 and pristane from lake erie must be considered from the perspective of molecular transformations

hydrothermal fluid migration and brine pool formation in the red sea the atlantis ii deep numerical heat and fluid flow simulations of the atlantis ii deep in the red sea were conducted to investigate the development migration and discharge of hydrothermal fluids into a submarine depression and determine the conditions necessary to form a brine pool high salinity fluids are predicted to form by leaching miocene evaporates migrate and convect within young oceanic crust and discharge onto the seafloor predicted fluid discharge temperatures t max 301 c discharge fluid velocities v max 0 09 m s and salinities s max 21 wt increase over time and reach values comparable to modern seafloor observations established convection patterns and discharge behavior are robust and are not greatly affected by geometry of rock property changes modeling results were used to calculate the minimum conditions for hydrothermal fluids from a developing hydrothermal system to mix with seawater reverse buoyancy and begin to form a brine pool in a submarine depression under conditions encountered on the seafloor t 25 300 c s 5 25 wt fluid mixtures predicted to pond on the seafloor range from late in the mixing process 99 at low temperatures t 26 c to much earlier 36 mixing at higher temperatures t 94 c a model of brine pool evolution is proposed that describes the processes and conditions necessary to initiate brine pool formation and compares formation conditions with accumulated ore material in the atlantis ii deep and other locations

dispersal of hydrothermal vent larvae at east pacific rise 9 10 n segment author posting american geophysical union 2018 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 123 11 2018 7877 7895 doi 10 1029 2018jc014290

evidence for a weakly stratified europan ocean sustained by seafloor heat flux we interpret chaos type features on the surface of europa as melt through structures formed by rotationally confined steady and or episodic oceanic plumes that rise to the base of the ice shell from magmatically heated regions of the seafloor smaller lenticular features in the vicinity of chaos type regions might be formed by baroclinically unstable vortices that spin off the main convective plume or by persistent heating from localized hydrothermal venting sites the ocean is assumed to be weakly stratified because of turbulent convection generated by heating from below and cooling from above seafloor heating maintained by tidal dissipation in the rocky interior generates an estimated global heat flux of 8 7 1012 w and limits the mean ice thickness to 2 5 km for seafloor heat sources with radii r that are less than the ocean s deformation radius rd nd n is the brunt vaisala frequency d is the water depth and is the coriolis parameter the diameters of chaos type regions are expected to diminish from o 100 km within equatorial regions to o 10 km at high latitudes assuming spatially uniform water depth and density structure where r rd the scale of the source region determines the scale of the melt through features provided there is sufficient time before refreezing ice rafts in large melt through regions are imbedded in episodes of preferentially anticyclonic circulation corresponding to clockwise counterclockwise motions in the northern southern hemisphere we calculate that 1021 j were required to melt the ice in the 100 km diameter conamara chaos region and that for a steady localized heat flux f 1011 w 1 of the global heat flux it took 1000 years for the initial melt through to occur assuming that ice raft displacements in conamara chaos occurred during a major melt through event maximum current speeds in the region were o 10 cm s 1 and refreezing occurred within 20 hours a lack of well defined ice drift in other major melt through regions suggests that these regions formed through episodes of melting and refreezing that modified the existing structure but left little time for the establishment of organized advective motion

rock slope movements in the canadian cordillera some recent work on natural rock slope movements in the cordillera is reviewed climate geology and seismicity combine to produce rockslides in the mackenzies and rockies slower more complex be

acoustic detection of a seafloor spreading episode on the juan de fuca ridge using military hydrophone arrays until recently no practical method has been available to continuously monitor seismicity of seafloor spreading centers the availability of the u s navy s sound surveillance system sosus for environmental research has allowed the continuous monitoring of low level seismicity of the juan de fuca ridge in the northeast pacific on june 22 1993 noaa installed a prototype system at u s naval facility whidbey island to allow real time acoustic monitoring of the juan de fuca ridge using sosus on june 26 2145 gmt a burst of low level seismic activity with accompanying harmonic tremor was observed and subsequently located near 46 15 n 129 53 w on the spreading axis of the juan de fuca ridge over the following 2 days the activity migrated to the nne along the spreading axis with the final locus of activity near 46 31 5 n 129 35 w the nature of the seismicity was interpreted to represent a lateral dike injection with the possibility of eruption on the seafloor based on this interpretation a response effort was initiated by u s and canadian research vessels and both warm water plumes and fresh lavas were subsequently identified at the site

late pleistocene debris flow deposits in large glacial lakes in british columbia and alaska the movement of late wisconsin 30 000 b p ice sheet lobes counter to the direction of regional drainage ponded large lakes up to 5000 km2 in both the upper fraser river valley in british columbia and the cooper river valley in alaska along the fraser river near quesnel glaciolacustrine sediment gravity flow complexes contain thick up to 10 m and laterally extensive up to 3 km diamict units containing large rafts of poorly lithified tertiary rocks diamicts offlap and thin away from tertiary bedrock highs and were emplaced by subaqueous debris flows these flows probably evolved from slumps and slides associated with the downslope failure of unstable tertiary bedrock slopes triggered by rising lake levels a process akin to first filling slope failures around the margins of man made lakes in alaska along the copper river valley massive and stratified diamicts were also deposited by debris flows and are interbedded with thin bedded turbidites poorly sorted gravels and normally graded diamicts debris flow deposits show basal grooves internal compressional structures and rafted clasts that protrude from bed tops flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock observations in both british columbia and alaska stress the significance of sediment gravity flow processes acting to deposit glacial sedimentary successions in large ice contact lake basins

photosynthetic fractionation of 13c and concentrations of dissolved co2 in the central equatorial pacific during the last 255 000 years carbon isotopically based estimates of co2 levels have been generated from a record of the photosynthetic fractionation of 13c is equivalent to epsilon p in a central equatorial pacific sediment core that spans the last approximately 255 ka contents of 13c in phytoplanktonic biomass were determined by analysis of c37 alkadienones these compounds are exclusive products of prymnesiophyte algae which at present grow most abundantly at depths of 70 90 m in the central equatorial pacific a record of the isotopic composition of dissolved co2 was constructed from isotopic analyses of the planktonic foraminifera neogloboquadrina dutertrei which calcifies at 70 90 m in the same region values of epsilon p derived by comparison of the organic and inorganic delta values were transformed to yield concentrations of dissolved co2 is equivalent to c e based on a new site specific calibration of the relationship between epsilon p and c e the calibration was based on reassessment of existing epsilon p versus c e data which support a physiologically based model in which epsilon p is inversely related to c e values of pco2 the partial pressure of co2 that would be in equilibrium with the estimated concentrations of dissolved co2 were calculated using henry s law and the temperature determined from the alkenone unsaturation index u k 37 uncertainties in these values arise mainly from uncertainties about the appropriateness particularly over time of the site specific relationship between epsilon p and 1 c e these are discussed in detail and it is concluded that the observed record of epsilon p most probably reflects significant variations in delta pco2 the ocean atmosphere disequilibrium which appears to have ranged from approximately 110 microatmospheres during glacial intervals ocean atmosphere to approximately 60 microatmospheres during interglacials fluxes of co2 to the atmosphere would thus have been significantly larger during glacial intervals if this were characteristic of large areas of the equatorial pacific then greater glacial sinks for the equatorially evaded co2 must have existed elsewhere statistical analysis of air sea pco2 differences and other parameters revealed significant p 0 01 inverse correlations of delta pco2 with sea surface temperature and with the mass accumulation rate of opal the former suggests response to the strength of upwelling the latter may indicate either drawdown of co2 by siliceous phytoplankton or variation of co2 si oh 4 ratios in upwelling waters

hydrocarbon biomarkers in the topla mežica zinc lead deposits northern karavanke drau range slovenia paleoenvironment at the site of ore formation the mississippi valley type zinc and lead deposits at topla 250 150 metric tons t of ore grading 10 wt zn and 3 3 wt pb and me ica 19 million metric tons mt of ore grading 5 3 wt pb and 2 7 wt zn occur within the middle to upper triassic platform carbonate rocks of the northern karavanke drau range geotectonic units of the eastern alps slovenia the ore and host rocks of these deposits have been investigated by a combination of inorganic and organic geochemical methods to determine major trace and rare earth element ree concentrations hydrocarbon distribution and stable isotope ratios of carbonates kerogen extractable organic matter and individual hydrocarbons these data combined with sedimentological evidence provide insight into the paleoenvironmental conditions at the site of ore formation the carbonate isotope composition the ree patterns and the distribution of hydrocarbon biomarkers normal alkanes and steranes suggest a marine depositional environment at topla a relatively high concentration of redox sensitive trace elements v mo u in the host dolostones and ree patterns parallel to that of the north american shale composite suggest that sediments were deposited in a reducing environment anoxic conditions enhanced the preservation of organic matter and resulted in relatively higher total organic carbon contents up to 0 4 wt the isotopic composition of the kerogen 13 c kerogen 29 4 to 25 0 15 n kerogen 13 6 to 6 8 suggests that marine algae and or bacteria were the main source of organic carbon with a very minor contribution from detrital continental plants and a varying degree of alteration extractable organic matter from topla ore is generally depleted in 13 c compared to the associated kerogen which is consistent with an indigenous source of the bitumens the mineralization correlates with 15 n kerogen values around 0 per mil 13c depleted kerogen 13c enriched n heptadecane and relatively high concentrations of bacterial hydrocarbon biomarkers indicating a high cyanobacterial biomass at the site of ore formation abundant dissimilatory sulfate reducing bacteria feeding on the cyanobacterial remains led to accumulation of biogenic h 2 s in the pore water of the sediments this biogenic h 2 s was mainly incorporated into sedimentary organic matter and diagenetic pyrite higher bacterial activity at the ore site also is indicated by specific concentration ratios of hydrocarbons which are roughly correlated with total pb plus zn contents this correlation is consistent with mixing of hydrothermal metal rich fluids and local bacteriogenic sulfide sulfur the new geochemical data provide supporting evidence that topla is a low temperature mississippi valley type deposit formed in an anoxic supratidal saline to hypersaline environment a laminated cyanobacterial mat with abundant sulfate reducing bacteria was the main site of sulfate reduction

a turbulent convection model with an observational context for a deep sea hydrothermal plume in a time variable cross flow 1 a turbulent convection model for a hydrothermal fluid discharging into a tidally modulated stratified cross flow is used to investigate time variable conditions in plumes such as the one rising from dante a sulfide mound at 2175 m depth on the endeavour segment of the juan de fuca ridge that plume is the consequence of the coalescence of 10 or more small individual plumes from chimneys discharging hot salt diminished fluid into the near bottom ocean at dante the discharge encounters ambient horizontal currents with speeds oscillating from near zero to a maximum of 7 cm s 1 speeds which can bend a plume more than 45 from the vertical model results are compatible with field measurements of the plume footprint size and vertical velocity both 20 m above the source when earlier estimates for dante s heat flux of 50 mw drive the convection the small scale short period variability of velocities and properties distributions observed in the field is mimicked in model results plumes pool above a source during periods of weak cross flows but stream away from the source with more diluted concentrations and lower rise heights at other times plume distributions at identical cross flow speeds differ whether the flow is accelerating or decelerating small changes in background hydrographic profiles create differences in rise heights comparable to those caused by large changes in source buoyancy flux if put into an entrainment context results suggest an entrainment coefficient eff that varies from 0 11 to 0 025 with increasing height 2 76 m above the source

magnitude and variance of near bottom horizontal heat flux at the main endeavour hydrothermal vent field 1 we characterize hydrothermal plumes and hydrography within the axial valley of the endeavour segment juan de fuca ridge northeast pacific using data from an autonomous underwater vehicle a lowered ctd and two current meter moorings our survey of the main endeavour hydrothermal vent field mef shows hydrographic variability on scales as short as 20 m and 10 min within the 100 m deep axial valley the mean flow is 1 5 cm s to the north and tidal oscillations have 5 cm s amplitude combining the mean flow with an estimate of the difference in average temperature observed north and south of mef we find that the net along axis horizontal heat flux has a mean magnitude of 8 42 mw an advection diffusion model forced by local current records explains the observed temporal hydrographic variability and shows that mean horizontal flux variance is correspondingly high standard deviation 63 mw a steady state mef heat budget constrained by the observed horizontal flux and measurements of vertical fluxes from other studies has two implications the mef heat flux is partitioned about equally between diffuse and focused vents and about 85 of the flux from diffuse plumes is entrained by focused plumes

factors controlling 13c contents of sedimentary organic compounds principles and evidence the carbon isotopic composition of any naturally synthesized organic compound depends on 1 the carbon source utilized 2 isotope effects associated with assimilation of carbon by the producing organism 3 isotope effects associated with metabolism and biosynthesis and 4 cellular carbon budgets these factors are reviewed and quantitative considerations summarized particularly with regard to active and passive modes of carbon assimilation by phytoplankton and the existence of discernible regularities in isotope effects associated with lipid biosynthesis it is concluded that n alkyl lipids are in general depleted in 13c by about 1 5 relative to polyisoprenoid lipids produced by the same organism the effects of biological reworking on isotopic compositions of organic carbon are examined and it is suggested that enrichment of 13c in sedimentary organic carbon may result from loss of ch4 from zooplanktonic gut communities isotopic methods for estimation of ancient co2 levels are considered and a hyperbolic form favored for the relationship between concentrations of dissolved co2 and isotopic fractionation

vertical and lateral splitting of a hydrothermal plume at steinaholl reykjanes ridge iceland abstract the generation of multiple neutrally buoyant intrusions by a single bubble rich plume asaeda and imberger j fluid mech 249 1993 35 57 and plume bifurcation ernst et al bull volcanol 56 1994 159 169 lavelle j geophys res 102 1997 3405 3420 are predicted from theory and experiments but have yet to be documented for hydrothermal plumes in contrast bifurcation of volcanic plumes which are dynamically analogous to hydrothermal plumes is very common ernst et al bull volcanol 56 1994 159 169 and thus bifurcation of hydrothermal plumes should be expected lavelle j geophys res 102 1997 3405 3420 ernst et al bridge newslett 10 1996 76 77 recent 38 khz echo sounder and water column chemical tracer studies near the steinaholl vent site reykjanes ridge iceland identified a bubble rich hydrothermal plume intruding at three levels two main ones and a subsidiary one before reaching the sea surface and spreading there ernst et al bridge newslett 10 1996 76 77 olafsson et al ridge events 2 1991 35 38 german et al earth planet sci lett 121 1994 647 654 the two main intrusions ca 100 and 200 m above the vent show lateral development of two lobes away from the vent and are consistent with the 350 m rise of a bubble plume yielding seafloor and surface gas fluxes of 2 5 10 3 and 0 75 10 1 m3 s respectively the bubble rich core of the hydrothermal plume also penetrates the 150 m deep thermocline and generates an intrusion visible at the sea surface although bifurcation of the bent over plume could have been initiated by crossflow alone ernst et al bull volcanol 56 1994 159 169 several other processes may also have enhanced plume bifurcation including interaction with the thermocline and entrainment of the plume lobes by horseshoe eddies in the lee of a 150 m high hill on the seafloor

the formation and impact of landslide dams state of the art abstract the blocking of river courses by mass movements is very common in mountainous areas with deep and narrow valleys landslide dams may pose serious threats to people and their livelihoods downstream in the case of abrupt dam failure since the publication of benchmark reviews of costa and schuster 1988 and korup 2002 there is a growing number of studies focusing on the formation stability and short term impacts of landslide dams this review combines the insights of all these studies builds on current concepts of landslide dams and suggests ways to unify terminologies and classifications we furthermore present a new worldwide database compiled from literature data it contains 410 landslide dams 1 million m3 in volume that were formed since 1900 since these have the most complete data entries these data show that dam longevity is among other factors correlated with the type of landslide forming the dam those formed by rock debris avalanches and rockslides have longest lifespans however the influence of landslide type or material on dam longevity decreases with time after dam formation to ensure consistency in the next database generation we suggest guidelines for data collection to provide a solid basis for evaluating dam stability and governing factors a preliminary classification matrix for landslide dam stability that combines topographic setting and the internal structure of the dam body is another outcome of our review furthermore an evaluation of the various geomorphic stability indices proposed in the literature regarding their suitability and limitations in assessing dam formation and stability shows that they predict the probability of dam formation reasonably well but that their application to longevity estimates requires further assessment the geomorphic impacts of landslide dams in the short medium and long term are summarized and illustrated with key examples finally for a better understanding of the factors controlling dam stability we recommend to 1 include dam composition and sedimentary structures in future case studies 2 maintain and update the worldwide database for sound statistical analyses 3 refine landslide dam stability indices and test them for different landslide types and 4 study hazard cascades related to multiple dams in one watershed for long term landscape evolution studies we suggest to 5 quantify terrestrial sediment flux related to landslide dams 6 detect ancient landslide dams in river profiles and 7 further exploit the sediment archives in former impoundment areas

observations of manganese and iron at the coaxial seafloor eruption site juan de fuca ridge magmatic injection during june july 1993 on the coaxial segment of the juan de fuca ridge resulted in an axial lava eruption an overlying chronic style hydrothermal plume and at least three megaplume like event plumes a comprehensive view of mn and fe liberated as hydrothermal discharge during this volcano hydrothermal event was obtained as part of a rapid field response that included continuous in situ measurements of mn and fe distribution maps for mn fe and temperature anomaly within the chronic and event plumes reveal significant thermochemical diversity that we ascribe to variable extraction efficiencies for heat and metals by source fluids and to plume age differences the mn heat data suggest that diffuse fluids could be the primary source of the chronic plume at northern coaxial segment but make only a minor contribution to event plumes measurements of ephemeral fe ii were used to estimate that the event plumes were 2 4 and 6 8 days old when first sampled corresponding to formation times during peak seismic activity the inventories of mn and fe within the three coaxial event plumes were similar to values previously reported for megaplumes

opening the carbon isotope vital effect black box 2 quantitative model for interpreting foraminiferal carbon isotope data interpretation of carbon isotope records from late quaternary planktonic foraminifers are confounded due to the presence of a significant physiological component in the carbon isotopic signal a quantitative carbon isotope qc model is presented which relates the carbon isotopic composition of a foraminiferal shell to the physiological processes of respiration and symbiont photosynthesis and to the 13c value of seawater co2 the qc model is calibrated with physiological and stable isotopic data from laboratory experiments with living planktonic foraminifers model simulations of chamber and shell 13c values with the symbiont bearing foraminifers orbulina universa and globigerinoides sacculifer suggest 1 variations in symbiont density and photosynthetic rate light level or habitat depth are the primary physiological parameters controlling intraspecific carbon isotopic variability in these species 2 respiration has little effect on the 13c of o universa and 3 each chamber in a multichambered foraminiferal test will have a distinct 13c value depending on its position in the test whorl size 13c value relationships reported for g sacculifer from fossil assemblages can be explained as a function of increasing symbiont density during ontogenetic development

a forced baroclinic vortex around a hydrothermal plume a steady frictional flow around a hydrothermal plume is described which is forced by the entrainment of water into the buoyant part of the plume as it rises above its source the circulation is anticyclonic clockwise in the northern hemisphere near the equilibrium density level or spreading level of the plume and cyclonic below this level the strength of this flow is adequate to trap anomalous properties from the hydrothermal fluid near the source in the presence of weak background flow some observational support for such a flow is presented

an isotopic biogeochemical assessment of shifts in organic matter input to holocene sediments from mud lake florida abstract a molecular and isotopic study of sediment cores from a sinkhole lake mud lake florida usa was performed in order to relate documented changes in the regional terrestrial vegetation and water table over the last 5500 years to molecular and isotopic proxies for biological sources of organic matter to the lake sediments temporal shifts in the source of organic matter to the sediment as determined by the stable carbon isotope composition of bulk organic matter and biomarkers correspond with previously defined regional scale transitions in forest ecosystems quercus to pinus at 5500 14 c yr bp and taxodium expansion at 2500 14 c yr bp and coincident increases in the floridan water table the 13 c values for total sedimentary organic carbon showed a shift from terrestrial and aquatic macrophyte sources 27 8 in sediments dated at 5400 14 c yr bp within the basal peat to a cyanobacterial dominated sapropel 18 1 at the surface a comparison of the 13 c values of bulk sediment and biomarkers representative of cyanobacterial and algal input e g 7 and 8 methylheptadecane and the n alkane c 17 indicates that the present shallow lake was fully developed by 2400 14 c yr bp differences among the 13 c values of specific biomarkers derived from vascular plants c 29 and c 31 n alkanes and cuo lignin oxidation products and from cyanobacteria and algae are nearly equivalent in magnitude to the shift recorded in 13 c of toc indicating their effective use as source proxies in this system

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

3d numerical modeling of circulations associated with a submerged buoyant jet in a shallow coastal environment abstract a three dimensional 3d numerical model was applied to examine the buoyant jet driven circulation in port moody arm canada the arm which has a relatively shallow water environment of 5 30 m depth receives considerable cooling water from burrard thermal generating station the cooling water behaves as a typical submerged buoyant jet and has significant impact on the natural circulation of the receiving water in order to resolve the sharp gradients in the hydrothermal field and overcome the scale barrier between the far field and near field zones of the submerged buoyant jet a newly developed embedded grid scheme was incorporated into the model which solves the complete field with a single modeling procedure using a pre conditioned conjugate gradient approach special care was taken with the turbulence diffusion and jet entrainment by using a second order turbulence closure model and the smagorinsky formula the simulated buoyant jet was calibrated using an integral model matched to empirical jet data modeled velocity and temperature profiles were quantitatively verified as being in good agreement with the available observations after the modeled flow pattern was qualitatively verified with data from historical dye tracing surveys extensive simulations were carried out to examine circulation behavior under the impact of the buoyant jet

the shapes of some mountain peaks in the canadian rockies different mountain shapes in sedimentary sequences in the canadian rockies were enhanced by glacial erosion and have been modified postglacially by gravity driven slope processes slope modification by both glacial erosion and postglaciation landslides is related to rock structure particularly bedding dip rock mass strength and slope geometry five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips castellate 1 and matterhorn 2 mountains occur in sub horizontal beds and their slopes on all sides follow combinations of bedding planes and joints the overall slopes are generally 37 to 65 and oblique to both bedding and joints slopes in sub horizontal beds may be controlled by their rock mass strength cuestas 3 develop in gently to moderately dipping beds dip slopes and steeper normal escarpments form their cataclinal and anaclinal sides respectively with the dihedral angle between them about 90 hogbacks 4 in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments the dihedral angle between the slopes is usually less than 90 dogtooth 5 mountains occur in steeply dipping to sub vertical beds and the dihedral angle can be as low as 60 slope gradients in inclined beds are closely related to landslides whose modes are controlled by bedding dips copyright 1999 john wiley sons ltd

deep ocean circulation and transport where the east pacific rise at 9 10 n meets the lamont seamount chain 1 we report the first 3 d numerical model study of abyssal ocean circulation and transport over the steep topography of the east pacific rise epr and adjoining lamont seamount chain in the eastern tropical pacific we begin by comparing results of hydrodynamical model calculations with observations of currents hydrography and sf6 tracer dispersion taken during larval dispersal on the deep east pacific rise ladder field expeditions in 2006 2007 model results are then used to extend observations in time and space regional patterns are pronounced in their temporal variability at m2 tidal and subinertial periods mean velocities show ridge trapped current jets flowing poleward west and equatorward east of the ridge with time varying magnitudes weekly average maximum of 10 cm s 1 that make the jets important features with regard to ridge originating particle larval transport isotherms bow upward over the ridge and plunge downward into seamount flanks below ridge crest depth the passage p1 between the epr and the first lamont seamount to the west is a choke point for northward flux at ridge crest depths and below weekly averaged velocities show times of anticyclonic flow around the lamont seamount chain as a whole and anticyclonic flow around individual seamounts results show that during the ladder tracer experiment sf6 reached p1 from the south in the western flank jet a short lived change in regional flow direction just at the time of sf6 arrival at p1 started the transport of sf6 to the west on a course south of the seamounts as field observations suggest approximately 20 days later a longer lasting shift in regional flow from west to sse returned a small fraction of the tracer to the epr ridge crest

methane in the upper water column of the northwestern gulf of mexico shallow subsurface dissolved methane maxima were commonly observed in the northwestern gulf of mexico during a series of cruises between 1975 and 1977 although there were often several methane maxima at various depths at any one particular station the most prevalent and widespread occurred over a narrow band of t in a range from 24 to 26 and could be traced as layers extending along and outward from the continental shelf these layers generally followed the local stratification and were associated with the upper part of the pycnocline advection was undoubtedly of importance in determining the extent and distribution of these methane maxima layers but in situ production appears to have supported them some vertical profiles revealed associations between methane atp and suspended matter maxima it is postulated that methane forms in situ in reducing microenvironments associated with suspended participates which are advected from the shelf or which have accumulated in the upper pycnocline due to increase in buoyancy forces

hydrothermal plume dynamics on europa implications for chaos formation 1 hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from europa s rocky interior through a liquid ocean to the base of its ice shell this process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer in contrast to earlier work we argue that europa s ocean should be treated as an unstratified fluid we have adapted and expanded upon existing work describing buoyant plumes in a rotating unstratified environment we discuss the scaling laws governing the flow and geometry of plumes on europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a europa like parameter regime we predict that hydrothermal plumes on europa are of a lateral scale at least 25 50 km comparable to large chaos regions they are too broad to be responsible for the formation of individual lenticulae plume heat fluxes 0 1 10 w m 2 are too weak to allow complete melt through of the ice layer current speeds in the plume 3 8 mm s are much slower than indicated by previous studies the observed movement of ice blocks in the conamara chaos region is unlikely to be driven by such weak flow index terms 6218 planetology solar system objects jovian satellites 5418 planetology solid surface planets heat flow 5430 planetology solid surface planets interiors 8147 4540 oceanography physical ice mechanics and air sea ice exchange processes 4568 oceanography physical turbulence diffusion and mixing processes keywords chaos europa hydrothermal plumes

hydrography and high temperature heat flux of the rainbow hydrothermal site 36 14 n mid atlantic ridge on the basis of an extensive set of conductivity temperature depth lowered acoustic doppler current profiler ladcp and nephelometry profiles and tow yos the hydrography flow field and particle plume of the rainbow hydrothermal site on the mid atlantic ridge are analyzed in the rift valley the water column is less dense and stratified than both eastern and western off ridge water with t s characteristics consistent with inflow across a sill from the east the buoyant hydrothermal plumes rise into a strong boundary current flowing along the slope of a topographic high which partially blocks the rift valley below 1950 m the bulk of the neutrally buoyant plume is advected across a sill which forms both the narrowest and the shallowest part of the valley and acts as a hydraulic control point for the flow below 2000 m large amplitude internal waves consistent with tidal forcing are observed near the sill but ladcp measurements suggest that the tidal signal is not strong enough to lead to flow reversal at plume depth above 2000 m the mean current across the topography generates lee waves which radiate energy upward and downstream density averaged light scattering profiles show the hydrothermal particle plume to be gaussian in depth even in the near field where many of the individual profiles are characterized by multiple peaks and the horizontal variability is highest the temperature anomalies associated with the mean near source particle plume are of order 5 10 3 c that is the plume is cold fresh as expected from the background hydrography of the deep atlantic using the flow field light scattering and hydrographic anomaly observations the heat flux associated with the hydrothermal particle plume at rainbow is estimated to lie between 1 and 5 gw

heat flux from black smokers on the endeavour and cleft segments juan de fuca ridge we have estimated the heat flux from black smoker vents on the juan de fuca ridge to evaluate their importance for heat transfer from young oceanic crust the velocity and temperature of smoker effluent were measured from the manned submersible alvin within a few centimeters of vent orifices using a turbine flowmeter with an attached temperature probe exit velocity was calculated from a simple plume model and vent orifices were measured in photographs and video records the estimated power output from smokers alone is 49 13 mw for the plume site vent 1 and vent 3 on the southern cleft segment near 45 n 364 73 mw for the main vent field on the endeavour segment near 48 n and 122 61 mw for the tubeworm field 2 km north the estimates for the cleft and tubeworm fields could be too low because of undiscovered vents these values constitute only 4 to 14 of the total advective heat flux estimated for these vent fields from measurements in the nonbuoyant plume and of diffuse flow at the seafloor indicating that most of the heat advected at these hydrothermal vent sites is carried by diffuse rather than focused flow values for individual smokers vary from 0 1 to 94 mw with an average of 6 2 mw at the endeavour field and 3 1 mw at the cleft field our estimates agree well at all scales with those of bemis et al 1993 based on measurements made during the same dives in some cases simultaneously up to 50 m high in the buoyant plume the good agreement between the two techniques implies that little diffuse flow at either high or low temperature is incorporated into the buoyant plumes generated by smokers at these sites velocity temperature measurements at vents excavated by alvin could not be modeled successfully suggesting that vent structures may grow in equilibrium with the force of the exiting water such that orifice size is determined by volume flux at the endeavour field the heat flux is focused by faults

severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting a possible mechanism for gustiness abstract the clark nonhydrostatic anelastic code is extended to allow for interactive grid nesting in both two and three spatial dimensions tests are presented which investigate the accuracy of three different quadratic interpolation formulae which are used to derive boundary conditions for the fine mesh model application of the conservation condition of kurihara and others is shown to result in significant improvements in the treatment of interactive nesting a significant improvement in the solutions for interactive versus parasitic nesting is also shown in the context of forced gravity wave flow this result for the anelastic system is in agreement with the earlier results of phillips and shukla who considered the hydrostatic shallow water system of equations the interactive nesting model is applied to the simulation of the severe downslope windstorm of 11 january 1972 in boulder using both two and three spatial dimensions the three dimensional simulation results in a gustiness signature in the

vertical and temporal vorticity observations at juan de fuca ridge hydrothermal signatures moored current measurements made from april 1994 to june 1995 reveal the vertical and temporal structure of the vorticity over the northern segment of the juan de fuca ridge at a depth of 2100m near the thermal and particle maximum associated with the neutrally buoyant hydrothermal plume the relative vorticity is anticyclonic with a mean value of nearly 0 09f with variability of the same magnitude this arises from cross ridge shear in the horizontal currents at this level in the vertical the anticyclonic shear has a peak value at plume level decreasing in magnitude both upward and downward from depths of 2100 2150m as the bottom is approached the transverse shear changes sign with cyclonic values of up to 0 09f below 2250m depth this vorticity signature is suggestive of dynamics of a line source of buoyant fluid entering the plume at its neutral density horizon and not due to individual point sources

catastrophic landslides and their effects on the upper indus streams karakoram himalaya northern pakistan abstract the paper examines the nature and geomorphic influences of deposits from rock avalanches that obstruct rivers most of the 115 rockslide rock avalanche events identified in the karakoram himalaya straddled one or more stream valleys at least 73 of these landslides formerly dammed the indus or its tributaries upstream of the barriers remnants exist of once very extensive lacustrine deposits the stability and long term survival of dams from large rock avalanches is addressed and the reasons for the gradual or phased rather than catastrophic and sudden breaching case histories emphasise the erosional and depositional forms associated with the barriers they are reconstructed in terms of the emplacement and properties of the deposits from rock avalanches and the response of the river to interruption by them these barriers have exerted a substantial control over stream response and development for most of the holocene at least today they are associated with distinctive features of channel form and thalweg river terrace systems intermontane sediment sinks and sources and local erosional forms in bedrock more broadly the landslide barriers have created a naturally fragmented river system deposition and erosion in the lower few tens or hundreds of meters of the upper indus stream valleys have been dominated by epicycles of aggradation trenching and downcutting that mainly reflect the scale timing and history of each barrier the landforms involved are only indirectly related to the late glacial and paraglacial conditions that have hitherto been regarded as the main explanation

convection waves observations of gravity wave systems over convectively active boundary layers widespread gravity wave systems have been found to exist over convectively active boundary layers cbls in the presence of vertical wind shear in contrast to mountain waves these convection waves occur over flat terrain and are ubiquitous over fields of shallow fair weather cumuli or clear air thermals they extend vertically to at least 9km a m s l probably to the tropopause first discovered by glider pilots as thermal waves they have now been systematically investigated by research aircraft during the ncar convection wave project which also incorporates an effort in numerical simulation the flight results are reported in this paper while the numerical simulations are described in a companion paper typical wavelengths of convection waves were found to range from 5 to 15 km average 9 km and typical vertical motion amplitudes from 1 to 3 m s 1 in all cases vertical wind shear exceeded 3 10 3s 1 under these conditions cloud tops were measured to move with relative velocities of 8 to 10 m s 1 against their environment hence they present an obstacle to the surrounding airflow the analogy to mountainous obstacles launching gravity waves into the atmosphere is suggestive and borne out by the aforementioned numerical simulations which describe this process step by step the interaction between the cbl and the overlying stable layers is studied by spectral and cross spectral analysis of aircraft data including coherence and phase relations between wave motions and cloud population underneath consideration is given to other potential sources of the observed gravity waves at this stage the conclusions of our pilot study may be considered tentative some implications for further research are also discussed

origins of etioporphyrins in sediments evidence from stable carbon isotopes abstract in samples of the julia creek and condor oil shales australia albian and early tertiary respectively etioporphyrin iii is significantly depleted in 13 c 4 relative to porphyrins derived from chlorophylls this isotopic difference suggests a large contribution from some independent source the haem group found in cytochromes derived from microbial sources is the most likely candidate

effects of rotation on turbulent buoyant plumes in stratified environments we numerically investigate the effects of rotation on the turbulent dynamics of thermally driven buoyant plumes in stratified environments at the large rossby numbers characteristic of deep oceanic releases when compared to nonrotating environments rotating plumes are distinguished by a significant decrease in vertical buoyancy and momentum fluxes leading to lower and thicker neutrally buoyant intrusion layers the primary dynamic effect of background rotation is the concentration of entraining fluid into a strong cyclonic flow at the base of the plume resulting in cyclogeostrophic balance in the radial momentum equation the structure of this cyclogeostrophic balance moving upward from the well head is associated with a net adverse vertical pressure gradient producing an inverted hydrostatic balance in the mean vertical momentum budgets the present simulations reveal that the primary response to the adverse pressure gradient is an off axis deflection of the plume that evolves into a robust organized anticyclonic radial precession about the buoyancy source the off axis evolution is responsible for the weaker inertial overshoots the increased thickness of lateral intrusion layers and the overall decrease in the vertical extent of rotating plumes at intermediate rossby numbers compared to the nonrotating case for inlet buoyancy forcings and environmental rossby numbers consistent with those expected in deepwater blowout plumes the speed of the organized precession is found to be as large as typical oceanic cross flow speeds

large eddy simulation of the convective atmospheric boundary layer abstract large eddy simulations of a free convective atmospheric boundary layer with an overlying capping inversion are considered attention is given to the dependence of the results upon the various factors influencing the simulation the subgrid model the domain size and the mesh resolution by providing artificial constraints upon the convection the results also provide extra insight into the underlying dynamics the gross features of the boundary layer such as the overall energy budget are not sensitive to the details of the simulations but a number of important factors are revealed it has been found that near the surface the subgrid diffusivity must be larger than is usually supposed in order for the vertical velocity skewness to have the correct sign this region of the flow has a significant subgrid scale heat flux and it seems that the subgrid model requires improvement in such cases a revised model which under statically unstable conditions allows the mixing length of the subgrid scale tu

geothermal heat flux from hydrothermal plumes on the juan de fuca ridge thesis m s massachusetts institute of technology dept of ocean engineering and woods hole oceanographic institution 1991

multiple plant wax compounds record differential sources and ecosystem structure in large river catchments abstract the concentrations distributions and stable carbon isotopes 13c of plant waxes carried by fluvial suspended sediments contain valuable information about terrestrial ecosystem characteristics to properly interpret past changes recorded in sedimentary archives it is crucial to understand the sources and variability of exported plant waxes in modern systems on seasonal to inter annual timescales to determine such variability we present concentrations and 13c compositions of three compound classes n alkanes n alcohols n alkanoic acids in a 34 month time series of suspended sediments from the outflow of the congo river we show that exported plant dominated n alkanes c25 c35 represent a mixture of c3 and c4 end members each with distinct molecular distributions as evidenced by an 8 1 0 7 1 standard deviation spread in 13c values across chain lengths and weak correlations between individual homologue concentrations r 0 52 0 94 in contrast plant dominated n alcohols c26 c36 and n alkanoic acids c26 c36 exhibit stronger positive correlations r 0 70 0 99 between homologue concentrations and depleted 13c values individual homologues average 31 3 and 30 8 respectively with lower 13c variability across chain lengths 2 6 0 6 and 2 0 1 1 respectively all individual plant wax lipids show little temporal 13c variability throughout the time series 1 0 9 indicating that their stable carbon isotopes are not a sensitive tracer for temporal changes in plant wax source in the congo basin on seasonal to inter annual timescales carbon normalized concentrations and relative abundances of n alcohols 19 58 of total plant wax lipids and n alkanoic acids 26 76 respond rapidly to seasonal changes in runoff indicating that they are mostly derived from a recently entrained local source in contrast a lack of correlation with discharge and low stable relative abundances 5 16 indicate that n alkanes better represent a catchment integrated signal with minimal response to discharge seasonality comparison to published data on other large watersheds indicates that this phenomenon is not limited to the congo river and that analysis of multiple plant wax lipid classes and chain lengths can be used to better resolve local vs distal ecosystem structure in river catchments

tracking the dispersal of hydrothermal plumes from the juan de fuca ridge using suspended matter compositions in 1988 and 1989 particles from on and off axis neutrally buoyant plumes over the juan de fuca ridge were sampled to study their changing composition with distance from the ridge crest plume depth and particle composition in off axis hydrothermal plumes were used to identify plume sources and trajectories iron and phosphorus concentrations and in particular p fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter phosphorus vanadium and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer sized particles of fe oxyhydroxide the p fe molar ratio 0 23 is essentially the same for vent fields along cleft and endeavour segments indicating that the scavenging processes are the same for both regions high p fe ratios are observed over the south and north cleft segment vent fields and to the west along the vance seamount chain the seamounts evidently function as a barrier bathymetrically steering the hydrothermal plumes to the west away from the ridge crest since particles from the endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the juan de fuca ridge copper concentrations in the plumes can be used to distinguish plume sources based on water column depth and elemental composition hydrothermal plume particles from specific vent fields on the juan de fuca ridge may be tracked as much as several tens of kilometers from their source using particle compositions