evidence of bottom trapped currents in the kuroshio extension region as partof thekuroshioextensionsystemstudy observations fromfivecurrentmetermoorings revealthat the abyssal currents are weakly bottom intensified in the framework of linear quasigeostrophic flow the best fittedverticaltrappingdepthsrangefrom8to15 kmintheabsenceofsteeptopography butonemooringnear an isolated seamount exhibited vertical trapping that was more pronounced and energetic with a vertical trapping depth of 5 km the ratios of current speeds and geostrophic pressure streamfunctions at the sea surface compared to the bottom are 88 in the absence of steep topography 63 near an isolated seamount and overall on average 83 of their value at a reference depth of 5300 m it is hypothesized that weakly depth dependent eddies impinging upon topographic features introduce to the flow the horizontal length scales of the topography and these smaller lateral scales are subject to bottom intensification

mechanics of upward propagation of cover collapse sinkholes cover collapse sinkholes occur by failure of the walls of a soil void above cavernous bedrock i examine conditions for failure in compression by crack propagation and coalescence and for failure by sloughing in which pore water pressure produces a net tension perpendicular to the wall of the void compressive failure without relaxation of stress does not explain observed long term stability of thick soils nor failures in thin residual soils if stress relaxation occurs with compressive failure soil voids tend to stabilize and sinkholes are not predicted sloughing failure is not predicted for steady state pore pressure fields even for a perched water table at the surface over a drained void transient pore pressure conditions that could produce sloughing may result from 1 rapid drawdown causing soil consolidation and transient high pore pressure gradients 2 approach of a wetting front in unsaturated soil with high permeability behind the front 3 dissolution of air from bubbles in the soil and exsolution near the void producing a low permeability zone near the void

coupling of the surface and near bottom currents in the gulf of mexico coupling between the surface and near bottom currents in the gulf of mexico gom has been reported in many case studies however geographical variations of this coupling need more examination in this study surface geostrophic currents derived from satellite observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the gom the short period 30 90 days fluctuations generated by the loop current lc and the lc eddies lces have a more vertically coherent structure and stronger deep ocean expressions than the long period fluctuations 90 days in addition the strength of the coupling is modulated by the long period variations of the lc and lce sheddings moreover the surface and bottom coupling varies geographically in the lc region the surface fluctuations along the eastern side of the lc are important in causing the bottom current fluctuations through baroclinic instability under the lc and through traveling topographic rossby waves trws north of the lc in the central deep gom the bottom currents are affected by the upper fluctuations of the northern lc through both local baroclinic instability and remote trw propagation in the northwestern gom the bottom current fluctuations are largely related to the remote surface variability from the west side of the lc by trws propagating northwestward this study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties

a numerical study of the propagation of topographic rossby waves abstract the propagation of linear barotropic rossby waves is investiaged numerically over a one dimensional topography similar to the continental rise and slope a point source is used to generate waves with periods from 4 to 36 days the resulting distribution of streamfunction and kinetic energy density is examined the result show that the propagating of tropographic rossby waves depends on the wave period over the continental rise waves are generated mainly by low frequency disturbances at periods of about a month in addition the continental slope is a good insulator to these waves therefore deep ocean circulation will not influence motions on the continental shelf at 36 and 15 days the steep continental slope is a wave guide and regions of high energy density generated by local sources may be found energy of 36 day waves over the continental shelf cannot penetrate the steep slope although waves of periods shorter than a week may reach the lower slope these waves are trapped by the coast

barium partitioning during the transformation of corals from aragonite to calcite examination of fresh aragonite and altered calcite corals from the pleistocene reef terraces exposed on barbados west indies reveals the natural partitioning of ba2 during the aragonite calcite transformation the ba2 decreased from typical values of 8 15 ppm in the aragonites to 1 3 ppm in the calcites a finding consistent with the experimentally determined partition coefficient of ba2 into calcite 0 06 0 02 at 25 c quantitatively the degree of partitioning of ba2 in these samples was compatible with the simultaneous partitioning of sr2

loop current frontal eddies formation along the campeche bank and impact of coastally trapped waves abstractvelocity data from a mooring array deployed northeast of the campeche bank cb show the presence of subinertial high frequency below 15 days velocity fluctuations within the core of the northward flowing loop current these fluctuations are associated with the presence of surface intensified loop current frontal eddies lcfes with cyclonic vorticity and diameter 30 days that have been linked to caribbean eddies and the lc separation process model results show that wind variability associated with winter cold surges are responsible for the emergence

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

mechanical behavior of groundwater seepage in karst collapse pillars abstract groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars kcps which are widely distributed in north china in order to study the mechanism of groundwater inrush from coal seam floor the variable mass dynamics and nonlinear dynamics were introduced a mechanical model plug model is established to describe the behavior of water seepage flow in coal seam floor containing kcp the study shows that 1 if the mass of the kcp keeps steady the water seepage velocity in the kcp and the surrounding rocks will reach a constant value soon 2 if the mass of the kcp and the surrounding rocks increases by grouting etc the seepage velocity in the kcp and the surrounding rocks will reach its minimum value gradually and 3 if the mass of the kcp and the surrounding rocks decreases by scouring the flow velocity in the kcp and the surrounding rocks shows a monotone increase the water flow may change into pipe flow especially when a large number of the mass of the kcp and the surrounding rocks enters into goaf road which may lead to instable flow and cause groundwater inrush

loop current and deep eddies abstract in contrast to the loop current and rings much less is known about deep eddies deeper than 1000 m of the gulf of mexico in this paper results from a high resolution numerical model of the gulf are analyzed to explain their origin and how they excite topographic rossby waves trws that disperse energy to the northern slopes of the gulf it is shown that north of campeche bank is a fertile ground for the growth of deep cyclones by baroclinic instability of the loop current the cyclones have horizontal vertical scales of about 100 km 1000 2000 m and swirl speeds 0 3 m s 1 the subsequent development of these cyclones consists of two modes a and b mode a cyclones evolve into the relatively well known frontal eddies that propagate around the loop current mode a cyclone can amplify off the west florida slope and cause the loop current to develop a neck that sometimes leads to shedding of a ring this process is shown to be the loop current s dominant mode of upper to deep variability

near inertial ocean current response to hurricane frederic abstract hurricane frederic passed with 80 to 130 km of the u s naval oceanographic office current meter arrays in water depths ranging from 100 to 470 m near the desoto canyon region and within 150 km of an ocean thermal energy conversion otec mooring in 1050 m of water excitation of near inertial waves by the moving hurricane was observed throughout the water column along the canyon walls and at the otec site the frequencies of the waves were blue shifted between 1 to 6 above the local inertial frequency the horizontal wavelength of 250 km is consistent with an energetic first baroclinic mode response but is considerably below the linear theory prediction of 550 km the inferred vertical wavelengths of the immediate response exceeded 1000 m along the northern and eastern sides of the canyon since the currents throughout the water column increased within hours of the hurricane passage later the vertical wavelengths were about equal to the water depth the vertical group velocities associated

models and mechanisms of drilling induced sinkhole in china the present paper distinguishes the four general types of collapsed sinkholes induced by drilling in regions where non indurated sediments clay silt and sand overlie unknown caves or open voids in underlying lithified karst rocks these sinkhole models are classified into balance arch hourglass vibration and subjacent drilling induced erosion forms a mechanical model was built for each type to assess the collapse probability drilling operations using boreholes facilitate rapid turbulent and erosive flow these activities resulted in the 26 sinkholes that have been attributed to constructions in china in the last several years awareness of potential collapse conditions should allow construction projects to avoid high risk settings that result in economic losses environmental concerns and life threatening accidents caused by such rapid collapse of the land surface awareness and close monitoring of high risk conditions during borehole monitoring should minimize the hazard

observations of the response of thermocline currents to a hurricane abstract in september 1985 the eye of hurricane gloria passed within about 100 km of a current meter mooring in the western north atlantic data from this mooring provide a clear view of the vertical structure of the near inertial wake in the main thermocline the response at 159 m was strong 25 cm s 1 amplitude and lasted about 18 days at greater depths the response was weaker and more irregular the phase of the near inertial currents increased with depth consistent with the downward spreading of enemy the total phase change across the thermocline reached about a half cycle seven days after the hurricane s passage indicating a large vertical scale of the response the observations are briefly compared with other time series measurements on the continental margin and with models

radium isotopes alkaline earth diagenesis and age determination of travertine from mammoth hot springs wyoming u s a abstract travertine from active springs former vents and drill core from mammoth hot springs wyoming was analyzed for ra isotopes 226 ra 228 ra other alkaline earth elements mg sr ba and mineralogical composition thermal water also was analyzed travertine presently being deposited contains 3 0 15 3 pci g 226 ra and has a 228 ra 226 ra ratio identical to that in thermal water travertine precipitates mostly as aragonite and experiences a complete diagenetic transformation to calcite within 9 a estimated from 228 ra 226 ra value of youngest completely calcite travertine systematic compositional changes associated with this diagenetic transformation are enrichment of mg and depletion of sr ba and ra apparent mineral water distribution coefficients for mg sr and ba in aragonite and calcite are within the range of those determined experimentally implying near equilibrium conditions and high water rock ratios during travertine diagenesis impure travertine from near the base of the travertine section in the u s geological survey y 10 drill hole at 72 9 m depth has a 230 th 234 u isochron age of 7700 440a the content of 226 ra in normal subhorizontally layered porous travertine decreases with depth in y 10 the observed 226 ra vs depth relation is consistent with continuous deposition of travertine at the y 10 site from 7700 a bp to near present at a mean rate of 1 0 cm a and indicates minimal exchange of ra between travertine and pore water after the early diagenetic transformation of aragonite to calcite these data imply that under favorable conditions 226 ra measurements may be useful in determining ages and deposition rates for other travertines

observations of high speed deep currents in the northern gulf of mexico recent measurements in water depths of 2000 m in the vicinity of the sigsbee escarpment south of new orleans show the presence of recurring high speed current episodes some of which had velocities greater than 85 cm s only 10 m above the local bottom in the gulf of mexico currents above about 1000 m are not locally coupled with the relatively depth independent currents in the deeper layers topographic rossby waves with periods of approximately 10 to 14 days appear to control the dynamics of the lower water column

forced stage response to a moving hurricane abstract the upper ocean s response to three hurricanes norbert 1984 josephine 1984 and gloria 1985 is examined using field observations and a numerical ocean model our goal is to describe the physical processes that determine the structure and amplitude of hurricane driven upper ocean currents all three of these northern hemisphere hurricanes produced a rightward biased response of the mixed layer current and transport this asymmetry arises because the wind stress vector rotates clockwise on the right side of the track and remains nearly parallel with the inertially rotating mixed layer current during most of the hurricane passage the maximum observed mixed layer current varied from 0 8 m s 1 in response to josephine which was a large but comparatively weak hurricane to 1 7 m s 1 in response to gloria which was very large and also intense these cases have been simulated with a three dimensional numerical model that includes a treatment of wind driven vertical mixing within the primitive

hurricane generated currents on the outer continental shelf 1 model formulation and verification a numerical model is developed to simulate currents generated by hurricanes on the outer continental shelf and slope emphasis is on the mixed layer response within a few hours of storm passage however some attention is given to the lower layer and shelf wave responses the model is based on a layered explicit finite difference formulation using the nonlinear primitive equations including conservation of heat the problem of topography intersecting the model layer is resolved by introducing artificial steps of the order of 100 m where the layer intersects the slope model comparisons are presented for three gulf of mexico hurricanes using a 0 2 grid for two of the storms the model reproduces better than 80 of the observed velocity variance with correlation coefficients of greater than 0 8 for the mixed layer discrepancies in the comparisons are traced to unresolved local topography and nonstorm forcing such as warm core rings further model simulations reveal that 1 substantial shelf waves were generated with phase speeds of 4 to 10 m s 1 2 the response is primarily baroclinic even in water as shallow as 200 m 3 an entrainment law which scales with the velocity difference between the mixed layer and upper thermocline yields markedly better comparisons than one which scales with the wind stress and 4 deviations from a straight line storm path can significantly alter the response

rotary empirical orthogonal function analysis of currents near the oregon coast abstract empirical orthogonal function eof analysis in the frequency domain is extended to complex time series eofs are calculated from the eigenvectors of the band averaged rotary cross spectral matrix this gives eof amplitude and phase for negative and positive frequencies corresponding to clockwise and anticlockwise rotation for the hodograph model rotary eof analysis is applied to velocity and temperature measurements from the coastal upwelling experiment cue ii during july and august 1973 on the continental shelf off oregon rotary eofs for horizontal velocities are computed for the diurnal near inertial and semidiurnal frequency bands approximately 1 0 1 5 and 2 0 cycles per day respectively and for frequency bands below 0 3 cycles per day in addition single sided frequency space eofs for vertical displacement are calculated from temperature measurements the first mode velocity eof for the semidiurnal frequency band shows baroclinic structure for clockwise rotation and barotropic str

evaluation of the effect of diagenetic cements on element ca ratios in aragonitic early miocene 16ma caribbean corals implications for deep time palaeo environmental reconstructions abstract early miocene corals siderastrea conferta and montastraea limbata from the paraguana peninsula venezuela and a modern coral s radians from bermuda were examined in order to quantitatively assess the effect of skeletal preservation on element ca proxies used for palaeo environmental reconstructions the biostratigraphic age burdigalian of the corals was confirmed via sr isotope stratigraphy to 16 5 0 4 ma light and scanning electron microscopy revealed the presence of aragonite and calcite cements in both fossil and modern corals but brucite cements were found only in the modern coral cement distribution is very heterogeneous resulting in zones of excellent preservation juxtaposed with less well preserved regions in both modern and fossil coral oil filled pore spaces were noted in the fossil specimens targeted la icpms depth profile analyses showed significant differences in sr ca mg ca b ca ba ca and u ca in aragonite and calcite cements compared to primary skeletal aragonite increased sr ca and decreased mg ca ratios were found in aragonite cements compared to skeletal aragonite whereas in calcite cements these trends were reversed b ca ratios were lower in both aragonite and calcite cements compared to primary aragonite estimates of the effect of 1 contamination by aragonite cements on coral sr ca mg ca b ca and u ca palaeo sea surface temperature reconstructions for the fossil corals produced anomalies of 1 2 c 0 2 c 0 3 c and 0 1 c respectively similar percentage calcite cement contamination produced temperature anomalies of 1 7 c 2 7 c 0 3 c and 0 1 c because of both highly elevated and depleted ba ca signatures in aragonite and calcite cements respectively care has to be exercised when reconstructing past flood or upwelling events from fossil corals when using targeted spatially resolved analysis well preserved early miocene corals may overall yield reliable deep time palaeo proxy information in much the same way as commonly utilised holo pleistocene corals

the generation of internal waves on the continental shelf by hurricane andrew observed currents temperature and salinity from moored instruments on the louisiana continental slope and shelf reveal multiple baroclinic oscillations during hurricane andrew in august 1992 these measurements are supplemented by numerical models in order to identify possible internal wave generation mechanisms the princeton ocean model is run with realistic topography stratification and wind forcing to extend the observations to mississippi canyon and other areas on the shelf a two layer isopycnal model is used with idealized topography and spatially uniform winds to isolate internal waves generated in and around the canyon the combination of the observations and the results from the numerical models indicates several possible mechanisms for generating long internal waves 1 near inertial internal waves were generated across the slope and shelf by dislocation of the thermocline by the wind stress 2 interaction of inertial flow with topography generated internal waves along the shelf break which bifurcated into landward and seaward propagating phases 3 downwelling along the coast depressed the thermocline after downwelling relaxes an internal wave front propagates as a kelvin wave and 4 poincare waves generated within mississippi canyon propagate seaward while being advected westward over the continental slope these processes interact to produce a three dimensional internal wave field which was only partly captured by the observations

a puzzling disagreement between observations and numerical models in the central gulf of mexico abstracttwo large independent sets of direct observations in the central gulf of mexico show a mean near surface flow of 10 cm s 1 to the west concentrated in the northern and southern gulf numerical models that the authors have examined do not produce this mean westward flow the observed speeds appear to be almost an order of magnitude larger than the estimated errors this paper studies the observations to estimate carefully the possible errors involved and compares the observations with model results the flow to the west in the southern gulf is presumably wind driven on the shallow parts of the shelf and in slightly deeper water at the outer edges of the shelf is possibly the result of southward sverdrup interior flow driven by the negative curl of the wind stress in another possibly related issue long term deep current meter observations in the northern gulf at 1000 m and below find flow to the west whereas some models find flow to the east the flow proposed here assumes a mean flow to t

the effect of a bottom shelf front upon the generation and propagation of near inertial internal waves in the coastal ocean abstract a three dimensional nonlinear baroclinic model in cross sectional form is used to study the generation and propagation of wind forced near inertial internal waves in a coastal region in the presence of a bottom front initially calculations are performed with the front in an infinite domain region by this means coastal effects are removed the initial response is in terms of inertial oscillations in the surface layer however in the frontal area these are modified by interaction through the nonlinear momentum terms with regions of positive and negative vorticity associated with the alongfront flow this leads to a change in amplitude phase and frequency of the inertial current and a resulting ekman pumping that drives near inertial internal waves in the frontal region on the positive vorticity side of the front these waves are at the superinertial frequency and rapidly propagate away on the negative side they are at the subinertial frequency and are trapped and inertial energy leaks to dep

ocean response to a hurricane part i observations abstract the response of the ocean to hurricanes was investigated using aircraft deployable expendable current profilers axcp the goals were to observe and separate the surface wave and surface mixed layer sml velocities under the storms and to map the across track and along track velocity and temperature response in the mixed layer and thermocline custom instrumentation was prepared including slower failing axcps and the axcp equipment was installed on noaa wp 3d aircraft research flights were made into two 1984 hurricanes norbert in the eastern pacific off baja california 19 n 109 w and josephine off the east coast of the united states 29 n 72 w thirty one probes were deployed in each hurricane and about half the axcps provided temperature and velocity profiles most velocity profiles exhibited strong surface wave contributions slablike velocities in the sml strong shears beneath the sml and only weak flows in the upper thermocline separation of the surface gravity wave velociti

paleocene eocene thermal maximum environmental change in the new jersey coastal plain benthic foraminiferal biotic events abstract the environmental impact of the paleocene eocene thermal maximum petm has been intensively studied in the new jersey coastal plain but the benthic foraminiferal response reflecting bottom water conditions has not been documented at high resolution we use benthic foraminiferal data across the paleocene eocene boundary in cores from wilson lake wl and bass river br to recognize 5 foraminiferal associations based on species clusters their varying abundances allow the identification of a stratigraphic succession of 8 distinct biofacies across the studied interval uppermost paleocene biofacies 1 corresponds to the glauconitic sands of the vincentown formation and contains rare small planktic foraminifera and a diverse benthic fauna sediments accumulated slowly in a sufficiently oxygenated outer neritic setting depth 100 110 m at wl 140 150 m at br under fairly oligotrophic conditions the embayment was storm dominated and influenced by strong currents inhibiting deposition of suspended fine particles e g planktic foraminifera clay and enhancing re suspension no significant pre petm environmental changes are detected in the benthic foraminiferal assemblages deposition of the fine grained silty clays of the marlboro clay started at the onset of the petm with transitional lithology present at wilson lake gavelinella beccariiformis common at deep shelfal to bathyal abyssal depths is the only taxon to become extinct at this level water depth increased during the petm to a maximum of 130 150 m at wl planktic foraminifera increased strongly in abundance while the benthic foraminiferal assemblage changed to a more opportunistic less diverse assemblage dominated by stress tolerant taxa tappanina selmensis pulsiphonina prima and anomalinoides acutus biofacies 2 increased riverine influence may have reduced vertical mixing initiating stratification of the water column and establishment of a continuously dysoxic mud belt benthic diversity then gradually increased indicating environmental recovery biofacies 3 and 4 40 95 kyr post petm onset riverine influence probably became more variable generating peak abundances of specialized taxa in a mud belt system with increased accumulation rates the latest petm biofacies 5 95 kyr post onset contains a poorly diverse bulimina callahani assemblage indicative of reoxygenated but still eutrophic bottom water conditions with renewed vertical mixing the lower eocene glauconitic sandy clays of the manasquan formation contain an outer neritic benthic fauna biofacies 6 8 depth 100 135 m at wl indicative of persistent high primary production with return of more vigorous currents higher abundances of buliminids may have been triggered by upwelling along frontal zones our environmental interpretations indicate relatively stable benthic foraminiferal ecosystems at persistently outer neritic water depths 100 150 m despite distinct temporary changes during the petm including eustatic sea level rise of up to 30 m and widespread establishment of dysoxic conditions

deep cyclonic circulation in the gulf of mexico abstract the anticyclonic loop current dominates the upper layer flow in the eastern gulf of mexico with a weaker mean anticyclonic pattern in the western gulf there are reasons however to suspect that the deep mean flow should actually be cyclonic topographic wave rectification and vortex stretching contribute to this cyclonic tendency as will the supply of cold incoming deep water at the edges of the basin the authors find that the deep mean flow is cyclonic both in the eastern and western gulf with speeds on the order of 1 2 cm s 1 at 2000 m historical current meter mooring data as well as profiling autonomous lagrangian circulation explorer palace floats at 900 m suggest that vertical geostrophic shear relative to 1000 m gives a surprisingly accurate result in the interior of the basin the temperature around the edges of the basin at 2000 m is coldest near the yucatan channel where caribbean sea water is colder by 0 1 c the temperature increases steadily with distance in the counter

bottom scour observed under hurricane ivan 1 observations that extensive bottom scour along the outer continental shelf under hurricane ivan resulted in the displacement of more than 100 million cubic meters of sediment from a 35 15 km region directly under the storm s path are presented sediment resuspension was accomplished by the extreme waves generated by ivan and transported by strong near bottom wind driven currents the sediment transport was primarily westward along the shelf but also contained a significant offshore component suggesting sediment was transported toward the mississippi delta and that it may have accumulated near the shelf break and on the upper continental slope the maximum observed scour of about 32 and 36 cm took place at two locations approximately 17 km apart along the 60 m isobath over which the maximum wind stress occurred

observed oceanic response over the upper continental slope and outer shelf during hurricane ivan abstract hurricane ivan passed directly over an array of 14 acoustic doppler current profilers deployed along the outer continental shelf and upper slope in the northeastern gulf of mexico currents in excess of 200 cm s 1 were generated during this hurricane shelf currents followed ekman dynamics with overlapping surface and bottom layers during ivan s approach and transitioned to a dominant surface boundary layer as the wind stress peaked slope currents at the onset of ivan were wind driven near the surface but deeper in the water column they were dominated during and after the passage of ivan by subinertial waves with a period of 2 5 days that had several characteristics of topographic rossby waves currents on the slope at 50 m and greater depths commonly exceeded 50 cm s 1 surprisingly the strongest currents were present to the left of the storm track on the shelf while more energetic currents were to the right of the hurricane path on the slope during the forced stage near inertial motion last

surface to subsurface velocity projection for shallow water currents sea surface currents in coastal oceans are accessible to continuous direct observations by shore based high frequency doppler radar systems inferring current structure in shallow water from such surface current observations is attempted the approach assumes frictionally dominated flow and vertically varying current velocity on the scale of the ekman boundary layer the approximation of the velocity variation with depth is consequently derivable in terms of orthogonal basis functions from the sea surface kinematic and dynamic boundary conditions specifically the viscous momentum and shear equations evaluated at the sea surface the inference procedure developed is demonstrated with sea surface data obtained in the coastal high resolution remote sensing experiment on the continental shelf off cape hatteras despite uncertainties in the surface measurements qualitative agreement is obtained between the inferred subsurface current and the current measured in situ the sensitivity of the inference to the measurement uncertainties as well as to the model assumptions is investigated and the inferred result is found to be generally robust

temporal and spatial variations in the diagenetic fabrics and stable isotopes of pleistocene corals from the ironshore formation of grand cayman british west indies abstract on grand cayman the unconformity bounded units a to f in the ironshore formation represent repeated cycles of deposition and subaerial exposure that were associated with the dramatic oscillations in sea levels that characterized the middle to late pleistocene montastrea annularis and acropora palmata the dominant corals found in units a to f in the rogers wreck point area and offshore george town area reflect these changes with their complex mosaics of marine aragonite cements bioerosion internal sediments and meteoric calcitization of coral skeleton dissolution diagenetic features the distribution of the diagenetic fabrics throughout this sequence however is not predictable the randomness in the degree of skeletal calcitization is shown by the lack of systematic variation in calcitization from units a to f and the fact that the degree of skeletal calcification in m annularis is higher than that in a palmata in the rogers wreck point area but less than in a palmata in the george town cores the stable isotope compositions 13c 18o of the corals from units a to f plot along the same trend line with their positions on that trend reflecting the amount of meteoric diagenesis they have undergone the variable styles and degrees of diagenesis evident in the corals from the ironshore formation reflect 1 the variable impact of intrinsic e g skeletal architecture porosity of coral and extrinsic e g sea level climate factors during each phase of diagenesis and 2 temporal effects associated with the diagenetic overprinting that took place during each successive phase of diagenesis this means that the diagenetic fabrics are not stratigraphically ordered and that it is impossible to correlate specific diagenetic phases with specific sea level lowstands or highstands

simulation of mesoscale variability in the gulf of mexico sensitivity studies comparison with observations and trapped wave propagation abstract a primitive equation gulf of mexico model was used to examine variability of the loop current lc and loop current eddies lce realistic results were obtained for a certain range of values of the horizontal mixing coefficient eddy paths were west and southwestward eddy propagation speeds from 3 to 5 km day 1 the ratio of minor to major eddy axes about 0 8 eddy shedding periods from 200 to 500 days eddy lifetimes from 100 to 200 days eddy sizes from 200 to 400 km and eddy swirl transports as fractions of the specified inflow of 30 sv were from 0 55 to 0 85 on the other hand the maximum vertical deepening of the 20 c isotherm was 15 to 50 less than that observed resulting in weaker near surface currents of about 0 65 m s 1 in comparison to observed values of 0 88 to 1 7 m s 1 a strong correlation between eddy shedding and decreasing or reversing lower layer below 750 m transport in the yucatan channel is found in the western gulf current variability is produced by eddy arriva

deep currents in the gulf of mexico abstract direct current measurements using moored arrays have been made below 1000 m in the eastern central and western gulf of mexico basin the major low frequency velocity fluctuations in the lower 1000 to 2000 m of the water column in the three regions have the characteristics of topographic rossby waves trws spectral peaks are observed at periods of about 25 days and 40 to 100 days motions are highly coherent with depth variances increase toward the bottom despite the very weak stratification of the deep waters of the gulf wave lengths are about 150 250 km and phase propagation is offshore with energy propagation westward a group velocity of about 9 km day 1 could be directly estimated from significantly coherent signals between eastern and western arrays this value is consistent with estimates derived from the dispersion relation and is higher than the westward translation speed of 3 to 6 km day 1 of the large anticyclonic eddies shed from the loop current it appears that a major source of

the wake of hurricane allen in the western gulf of mexico abstract in august 1980 hurricane allen passed over a moored array of instruments recording current temperature and conductivity in the western gulf of mexico an alongshore surge occurred during the storm passage with the horizontal current speed reaching 91 cm s 1 in the thermocline 200 m and diminishing to 15 cm s 1 32 m above the bottom 732 m a wake of near inertial frequency internal waves commenced after the storm passed the array the alongshore current oscillation reached a maximum range of 50 cm s 1 within 3 days and decayed thereafter with a time scale of about 5 days the current oscillations were clockwise polarized and slightly elliptical with a period of 22 23 h or about 85 of the local inertial period near uniform upwelling of 20 m occurred in the thermocline region 200 300 m during the most intense part of the wake depth leading phases of the horizontal current and temperature oscillations indicated downward radiation of wake energy the wake oscillations were highly coheren

relationship between hydraulic conductivity of karst collapse column and its surrounding lithology groundwater inrush from karst collapse column kcc is a serious water hazard in north china the factors determining the hydraulic conductivity of kcc remain unclear this study analyzes the hydraulic conductivity of two kccs from the same coal mine region and one kcc from different strata and statistically compares lithology related data for kccs from 11 coal mines in north china finally we calculated the probability of the hydraulic conductivity of kcc and compared these calculations with field data the results indicate that the hydraulic conductivity of kcc is mostly affected by surrounding lithology formation and closely correlated with mudstone content when the thickness ratio of mudstone in the surrounding strata is less than 0 5 the hydraulic conductivity of kcc is more likely to be permeable this observation of the mudstone thickness ratio provided here can be used as a criterion to qualitatively assess the hydraulic conductivity of kccs

minor and trace elements in sclerosponge ceratoporella nicholsoni biogenic aragonite near the inorganic endmember abstract the trace and minor element composition have been investigated in the accretionary skeletons of two specimens of the caribbean sclerosponge species ceratoporella nicholsoni one from tongue of the ocean bahamas toto and the other from pear tree bottom jamaica ptb both sclerosponges were analyzed at high resolution using laser ablation icp ms la icp ms and verified using wet chemical methods icp oes the shallow ptb sclerosponge 25 m was analyzed for a short temperature calibrated record of trace and minor elements while the toto sclerosponge 146 m was analyzed for a century long record from subsurface waters the resulting ba ca mg ca pb ca and u ca ratios were compared with sr ca ratios which have been shown to reliably record seasonal scale temperature change in sclerosponges close to equilibrium precipitation of inorganic aragonite sclerosponge aragonite incorporates minor and trace elements according to general mineralogic constraints with less vital effects than other calcium carbonate secreting organisms this is perhaps most obvious in the behavior of mg ca ratios which show an inverse correlation to temperature unlike any other calcite or aragonite organism despite having mg concentrations 1 mmol mol within published estimates of equilibrium aragonite ratios of mg ca and ba ca show a strong positive correlation despite large differences in ionic radii and u ca values 3 15 mol mol are 2 5 higher in sclerosponge aragonite than in aragonite from corals supporting earlier work ratios of u ca show an insignificant correlation with temperature dependent sr ca ratios r 2 0 05 supporting existing theories that temperature signals recorded by u ca ratios can be convolved with ph co 3 2 and phosphate signals differences between sclerosponge aragonite and other calcium carbonate arising from siliceous spicule contamination are unlikely because of the small mole percent of silicon in the aragonite small differences between the two sclerosponges were noticed in pb ca and sr ca because of the average ages of the sampled material and average temperatures of the ambient environment respectively anomalies between la icp ms and icp oes were noticed in measurements of ba ca and pb ca due to standardization differences for la icp ms ba ca and measurements close to the instrument detection limits of pb icp oes

observation of tropical cyclone induced shallow water currents in taiwan strait the data from three stations equipped with acoustic doppler current profilers adcps deployed in the shallow water of the taiwan strait tws were used to study the shallow coastal ocean response to five quasi continuous tropical cyclone tc events in the late summer 2006 we revealed that in the forced stage when the large and strong tc bilis transited the geostrophic currents were formed which dominated the whole event while the strong but relatively small one saomai or the weak one bopha primarily leaded to the generation of ekman currents in the relaxation stage the barotropic subinertial waves and or the baroclinic near inertial oscillations nios were triggered typically during the transit of the saomai subinertial waves were induced which demonstrated a period of 2 8 4 1 days and a mean alongshore phase velocity of 14 9 3 2 m s in the form of free barotropic continental shelf waves however the nios are only notable in the area in which the water column is stably stratified and also where the wind stress is dominated by the clockwise component and accompanied by high frequency near inertial variations we also demonstrated that due to the damping effects the nonlinear wave wave interaction e g between nio and semidiurnal tide in our case together with the well known bottom friction led to the rapid decay of the observed tc induced near inertial currents giving a typical e folding time scale of 1 3 inertial periods moreover such nonlinear wave wave interaction was even found to play a major role during the spring tide in tws

deep eddy energy and topographic rossby waves in the gulf of mexico abstract observations suggest the hypothesis that deep eddy kinetic energy eke in the gulf of mexico can be accounted for by topographic rossby waves trws it is presumed that the trws are forced by loop current lc pulsation loop current eddy lce shedding and perhaps also by lce itself although the hypothesis is supported by model results such as those presented in oey the existence of trws in the model and how they can be forced by larger scale lc and lces with longer period vacillations have not been clarified in this paper results from a 10 yr simulation of lc and lces with double the resolution of that used by oey are analyzed to isolate the trws it is shown that along an east to west band across the gulf approximately over the 3000 m isobath significant eke that accounts for over one half of the total spectrum is contained in the 20 100 day periods bottom energy intensification exists in this east west band with vertical decay scales of about 600 300 m decreasing westward the de

on the response of the ocean to a moving storm parameters and scales abstract this paper has two purposes one is to present a new and efficient multilevel numerical model for calculating the response of the ocean to a moving storm the second is to show how on a time scale of a few inertial periods following the arrival of the storm the maximum horizontal and vertical velocities found in the wake can be calculated using a linear ekman model and a knowledge of that part of the change in the depth of the wind mixed layer due to entrainment this is demonstrated over a range of experiments with the multilevel numerical model these integrate the full nonlinear equations of motion with realistic ocean stratification and involve substantial entrainment of water into the wind mixed layer it is also shown that on this time scale the horizontal currents are confined near the surface but that the vertical velocity field extends throughout the depth of the ocean it is shown in appendix b that the wind forcing need only be large or fast for the forced response not to feel t

deep currents in the bay of campeche abstractdata from five moorings deployed in the bay of campeche during november 2007 july 2008 are used to analyze subinertial motions of waters below 1000 m depth to the authors knowledge this is the first time such a comprehensive observational program of direct deep current measurements has been carried out in the region the mean currents are in agreement with a cyclonic circulation at 1000 m depth however this cyclonic pattern is not so clearly defined at deeper levels only at the deepest mooring located at 3500 m depth are the mean currents uniform all the way to the bottom over the bay of campeche s smooth western slope currents show features compatible with topographic rossby waves having vertical trapping scales thicker than 700 m periods between 5 and 60 days and horizontal wavelengths of 90 140 km in contrast the eastern slopes are characterized by rough topography and motions with periods longer than 28 days decrease toward the bottom suggesting a substantial reduction in the l

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

topographic rossby waves in the gulf of mexico abstract observations of topographic rossby waves trw using moored current meters bottom pressure gauges and lagrangian rafos floats are investigated for the deep basin of the gulf of mexico recent extensive measurement programs in many parts of the deep gulf which were inspired by oil and gas industry explorations into ever deeper water allow more comprehensive analyses of the propagation and dissipation of these deep planetary waves the gulf of mexico circulation can be divided into two layers with the 800 1200 m upper layer being dominated by the loop current lc pulsations and shedding of large diameters 300 400 km anticyclonic eddies in the east and the translation of these lc eddies across the basin to the west these processes spawn smaller eddies of both signs through instabilities and interactions with topography and other eddies to produce energetic surface layer flows that have a rich spectrum of orbit periods and diameters in contrast current variability below 1000 m often has the characteristics of trws with periods ranging from 10 100 days and wavelengths of 50 200 km showing almost depth independent or slightly bottom intensified currents through the weakly stratified lower water column these fluctuations are largely uncorrelated with simultaneous upper layer eddy flows trws must be generated through energy transfer from the upper layer eddies to the lower layer by potential vorticity adjustments to changing depths of the bottom and the interface between the layers therefore the lc and lc eddies are prime candidates as has been suggested by some model studies model simulations have also indicated that deep lower layer eddies may be generated by the lc and lc eddy shedding processes in the eastern gulf the highest observed lower layer kinetic energy was north of the campeche bank under the lc in a region that models have identified as having strong baroclinic instabilities part of the 60 day trw signal propagates towards the sigsbee escarpment a steep slope at the base of the northern continental slope and the rest into the southern part of the eastern basin higher energy is observed along the escarpment between 89 w and 92 w than either under the northern part of the lc or further south in the deep basin because of radiating trws from the western side of the lc in the northern part of the lc evidence was found in the observations that 20 30 day trws were connected with the upper layer through coherent signals of relative vorticity the 90 phase lead of the lower over the upper layer relative vorticity was consistent with baroclinic instability along the sigsbee escarpment the trws are refracted and reflected so that little energy reaches the lower continental slope and a substantial mean flow is generated above the steepest part of the escarpment rafos float tracks show that this mean flow continues along the escarpment to the west and into mexican waters this seems to be a principal pathway for deepwater parcels to be transported westward away from the slope rafos floats tend to oscillate in the same general area as if primarily responding to the deep wave field little evidence of westward translating lower layer eddies was found in both the float tracks and the moored currents in the western gulf the highest deep energy levels are much less than in the central gulf and are found seaward of the base of the slope otherwise the situation is similar with trws propagating towards the slope probably generated by the local upper layer complex eddy field being reflected and forcing a southward mean flow along the base of the mexican slope amplitudes of the lower layer fluctuations decay from the northwest corner towards the south

high resolution reconstruction of a holocene coastal sequence nw germany using inorganic geochemical data and diatom inventories abstract holocene deposits of the nw german coastal plain consist of many different lithological facies for example tidal flats brackish water sediments and peat beds the effects of the holocene sea level rise on palaeoenvironmental conditions of this coastal sequence were studied by inorganic geochemical methods in conjunction with diatom analyses three hundred samples from two parallel sediment cores which cover the entire nw german holocene were taken at high resolution and were examined for major and minor elements and bulk parameters selected samples were analysed for redox sensitive trace elements and ree distribution reactive iron and bulk sediment 34 s 32 s ratios chemical parameters for example si al and ca sr ratios and total organic carbon toc contents correlate with depositional factors such as wave energy and lithofacies changes which allow a detailed reconstruction of the palaeoenvironment diatom analyses reveal information about changes between marine brackish and limnic conditions and serve to reconstruct palaeosalinity early diagenetic effects are evident in the toc rich intervals most peat layers are affected by sulphate reduction and resulting pyrite formation as well as by enrichments in redox sensitive trace elements the highest enrichments are seen for as mo re and u indicating a distinct seawater influence s isotope ratios of peat samples are compatible with pyrite formation under both open and closed system conditions depending on exposition to seawater the inorganic geochemical and diatom data suggest limnic conditions at the base of the sequence and repeated changes towards marine conditions within the overlying clastic units on the other hand data obtained from the clastic units yield evidence of a recurrent succession from open to restricted marine brackish lagoonal and finally fen environments clastic sediments overlying peat layers correlate with the increase of marine derived geochemical signatures and pelagic diatoms attest transgressive overlaps the analyses suggest that major controls on the palaeoenvironments were i climate related oscillations of the coast line and ii the morphology of the coastal region allowing marine incursions even into distal semi terrestrial lowlands

eddy statistics from lagrangian drifters and hydrography for the northern gulf of mexico slope 1 cyclones and anticyclones on the northern gulf of mexico slope have been statistically characterized using upper layer drifter orbits and repeated hydrographic surveys a total of 243 slope eddy drifter orbits 151 cyclones and 92 anticyclones were analyzed in terms of size mean radius and eccentricity and rotation period orbits in large loop current anticyclones were excluded eddies of both signs scale approximately as the baroclinic radius of deformation with relatively smaller radii on the upper slope where water depths are less than 1000 m the median radius for all eddies was 30 km and median periods were 12 and 13 5 days for cyclones and anticyclones respectively anticyclones also tend to be more circular than cyclones relative vorticity maps were constructed for seven hydrographic surveys which mapped the slope at 4 5 month intervals a total of 26 cyclones and 15 anticyclones had statistics that were consistent with drifter orbit analyses the surveys indicate that at any one time between 2 and 5 cyclones and 1 and 3 anticyclones may be present both drifters and surveys indicate that cyclones have a slight numerical dominance

resonance of long waves generated by storms obliquely crossing shelf topography in a rotating ocean the oceanic forced wave beneath a moving atmospheric disturbance is amplified by proudman resonance when modified by the earth s rotation this classical resonance only occurs if the disturbance time scale is smaller than the inertial period with or without coriolis effects free transients generated by storm forced waves obliquely crossing step changes in water depth at particular angles are shown to resonate by exciting a range of barotropic free waves rotationally influenced slow atmospherically forced waves crossing a vertical coast at a critical angle lead to a form of sub critical resonance which occurs only when the component of the disturbances phase velocities along the coast matches that of a free kelvin wave kw in a rotating ocean transients generated by disturbances crossing a step at a particular angle are shown to excite a free double kelvin wave dkw this new type of resonance only occurs for sufficiently large steps and disturbances with time scale greater than the inertial period a storm crossing a step shelf can result in the excitation of an infinite set of edge waves a single kw a unique dkw and a first mode continental shelf wave depending on the topography and the disturbance time scale translation speed and incident angle the study of resonances and wave mode excitations generated by storms crossing a coast or a continental shelf may contribute to understanding how a particular combination of the storm characteristics can result in destructive coastal events with time scales encompassing the typical meteotsunami period band tens of minutes and storm surges with periods of several hours or days

current and density observations across the wake of hurricane gay abstract ctd and acoustic doppler current profiler data are analyzed for the response of the upper ocean to rapidly moving hurricane gay currents were observed within about two days of the hurricane passage and were dominated by a blue shifted inertial oscillation confined largely to the mixed layer the amplitude of the current was strongly asymmetric about the track with the largest amplitude 1 m s 1 about 80 km to the right of the track there was also an asymmetry of the mixed layer depth and temperature with deeper and cooler values to the right of the track the gradient richardson number was found to have low values in some places less than 1 4 in a layer from 10 to 30 m thick below the base of the surface mixed layer this suggests that shear flow instability played an important role in the vertical mixing that occurred within the mixed layer and upper thermocline

shallow water currents during hurricane andrew oceanographic measurements are used in combination with a numerical model to examine the influence of stratification on shallow water currents during the directly forced stage of a tropical cyclone hurricane andrew on the continental shelf the following stratification dependent coastal processes are examined 1 turbulent mixing 2 coastally trapped waves 3 near inertial oscillations and 4 upwelling and downwelling turbulent mixing was strong within 1 rw radius of maximum winds of the storm track and stratification was nearly destroyed turbulent mixing was weak at distances greater than 2 rw the dominant coastal wave was a barotropic kelvin wave generated as the storm surge relaxed after landfall baroclinic near inertial oscillations were dominant at the shelf break and occurred along with a barotropic response on the middle shelf downwelling favorable flow developed east of the track prior to the storm peak and upwelling favorable flow evolved west of the track as the eye crossed the shelf the idealized storm flow was modified by local barotropic and baroclinic pressure gradients on the shelf ocean circulation during hurricane andrew was hindcast using both stratified and unstratified three dimensional numerical models for areas within 1 rw of the storm track the unstratified model matched the observed currents better than the stratified model partly because of errors in the initial stratification at distances greater than 2 rw the influence of stratification increases and the unstratified model does not reproduce the observed upwelling favorable flow

biweekly periodic deep flow variability on the slope inshore of the kuril kamchatka trench abstract five long term current records are analyzed to investigate the temporal variability for deep flows from a single mooring fitted with two current meters on the slope inshore of the southern end of the kuril kamchatka trench southeast of cape erimo where the oyashio and a deep western boundary current are considered to flow southwestward together at 3000 m the spectral peaks of eddy kinetic energy were found at about 2 weeks in all current records the flow variability with period of 2 weeks at 3000 m was more energetic than that at 1000 m by applying topographic rossby wave theory this variability is thought to be due to bottom trapped topographic rossby waves

on the behavior of internal waves in the wakes of storms abstract the rossby adjustment process in the wake of a storm is studied with a view to finding within the context of linear theory how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer comparisons are made between three cases 1 a periodic storm on the f plane where dispersion is purely vertical 2 a bounded storm on the f plane and 3 a bounded storm centered 2700 km from the equator on an equatorial beta plane particular attention is paid to the initial rate of loss of energy from the mixed layer and some simple formulas which work very well in the cases studied are derived these show that the rate of loss goes up when the mixed layer depth is increased and also that the rate scales as the square of the wavenumber values of the rates are sufficient to provide a major source of energy for internal waves below the mixed layer the often observed tendency for phase lines to propagate upward is found in all case

deep current variability near the sigsbee escarpment in the gulf of mexico abstract observations of deep currents from a closely spaced array deployed at the base of the sigsbee escarpment south of the mississippi delta are dominated by energetic short period 10 days topographic rossby waves over a 2 yr interval distinct trains of waves occurred with differing characteristic periods wavelengths and horizontal energy distribution usually initiated with a burst of large amplitude current fluctuations that slowly decay over the next 2 3 months two of the wave trains were associated with the shedding and westward passage of major loop current anticyclones however one event occurred when upper layer currents were quiescent this latter wave train showed that bottom trapped topographic wave motions can be traced to within 300 m of the surface in a 2000 m water column ray tracing showed that a likely source region of the short period waves was the west side of an extended loop current the data and ray paths suggest that through refraction and reflection the steep es

hydrography of the gulf of mexico using autonomous floats abstractfourteen autonomous profiling floats equipped with ctds were deployed in the deep eastern and western basins of the gulf of mexico over a four year interval july 2011 august 2015 produ

compaction and seepage properties of crushed limestone particle mixture an experimental investigation for ordovician karst collapse pillar groundwater inrush as mining activity rapidly develops to deeper and deeper ground there have been an increasing number of groundwater inrush events occurring in china the ordovician limestone karst collapse pillar kcp which contains a lot of crushed rocks usually functions as a channel for groundwater inrush the factors such as the geological conditions groundwater flow and extraction percentage of coal seam in underground mines are the main causes of recompaction and permeability change of crushed rock particles in kcp the high permeability of rock will cause large volumes of groundwater flow thus posing a great threat of loss of lives in the mines it is important to take into account the compaction and seepage behaviors of the crushed rocks in ordovician limestone kcp the mts815 02 system and a self designed water flow apparatus were used to investigate the effect of particle size distribution on compaction and seepage behavior of crushed limestone particle mixture the reynolds number calculation of particle mixture shows that the seepage has been influenced by non darcy flow testing results indicate that the effective porosity of crushed limestone sample is strongly influenced by compaction and particle size distribution the effective porosity decreases with the increase in compaction and decrease in larger particle size respectively particle crushing during compaction is a main cause of size 0 2 5 mm materials whereas some fine particles are washed away due to the effect of water seepage which is a main cause of weight loss non darcy seepage properties of the crushed limestone are strongly influenced by compaction and particle size distribution in general during the compaction the permeability decreases while the non darcy coefficient increases with the decreasing of effective porosity the effective porosity particle crushing and seepage properties of crushed limestone are not only related to compaction levels and mixture sizes but also to style of arrangement and initial pore structure

assessment of numerical simulations of deep circulation and variability in the gulf of mexico using recent observations abstractthree simulations of the circulation in the gulf of mexico the gulf using different numerical general circulation models are compared with results of recent large scale observational ca

the loop current observations of deep eddies and topographic waves abstracta set of float trajectories deployed at 1500 and 2500 m depths throughout the deep gulf of mexico from 2011 to 2015 are analyzed for mesoscale processes under the loop current lc in t

major and minor effects of holocene sea level rise recorded from microfossils and ca sr ratios in coastal sequences of nw germany to study responses of the depositional environments to holocene sea level rise high resolution analyses of diatoms foraminifera and ca sr ratios of two boreholes were performed the diatoms were differentiated according to pelagic and littoral benthic lifestyles and classified following oligohalobous mesohalobous or polyhalobous attributes the foraminifera were grouped into brackish water and euryhaline tidal flat species the sedimentary successions include marine and non marine facies marine facies is characteristic of channels and tidal flats non marine facies units include deposits of a low lying lagoonary and swampy hinterland natural and fluvial levees and finally fen reed complexes in the boreholes studied polyhalobous marine pelagic diatoms exceed marine facies boundaries and even occur in peat layers the occurrence of marine allogenes in non marine strata suggest an origin from minor sea level undulations since the hinterland was a lowland area it was easily accessible by landward directed pulses of the sea minor sea level variations were short enough to not change the environment which remained semi terrestrial this is different to the transgress ive onlaps

subinertial slope trapped waves in the northeastern gulf of mexico abstract current velocity from moored arrays of acoustic doppler current profilers adcps deployed on the outer shelf and slope south of mobile bay in the northeastern gulf of mexico shows evidence of alongslope generally westward propagating subinertial baroclinic kelvin waves with periods of about 16 and 21 days amplitudes of 5 10 cm s 1 and wavelengths of about 500 km the observed waves were highly coherent over the slope between about 200 and 500 m and accounted for a significant amount of the current variability below 200 m the source of the waves could be attributed to effects of the loop current on the west florida slope but is more likely due to direct forcing by loop current generated eddies impacting the experimental area

gulf stream generated topographic rossby waves abstract an inverse ray tracing model is applied to observations of 40 day topographic rossby waves on the continental slope off of cape hatteras north carolina to determine their origin the rays are traced seaward and extend into the deep gulf stream where the bottom slope remains strong enough that topographic dominates planetary this enable coupling to occur between eastward propagating gulf stream meanders and topographic waves with eastward phase speed and matching zonal wavelength previous satellite observations indicate that the most frequently occurring gulf stream meanders have a period of 40 days and the model reveals that as these meanders pass a topographic bend near 71 72 w they are able to couple to the observed topographic waves traced back from cape hatteras the 40 day gulf stream meanders occur in bursts which leads to associated bursts of the topographic waves

near surface currents in desoto canyon 1997 99 comparison of current meters satellite observation and model simulation this study evaluates a data assimilated model simulation of near surface circulation in desoto canyon dsc gulf of mexico with emphasis on analyzing moored current meter observations and comparing them with satellite data and model results the study period is for two years from april 1997 to april 1999 the model results are from a high resolution gulf of mexico model forced by analyzed wind and surface heat flux two types of data are used to deduce near surface circulation moored current meters at 13 locations in the dsc and satellite sea level anomaly the moored currents are mapped through multivariate objective analysis to produce surface currents and surface geopotentials against which satellite and model derived sea surface heights and geostrophic currents are compared coupled patterns between the observations model results and satellite data are obtained using the singular value decomposition svd analysis there are two dominant modes a single eddy mode in which currents are concentrated at the foot of the canyon and an eddy pair mode in which one eddy is at the foot of the canyon and the other a counterrotating eddy is over the head of canyon mode 1 appears to be associated with the mesoscale eddy traveling around the loop current crest and trough and mode 2 is associated with the intrusion of loop current crest and trough over the west florida shelf the observed and model currents are in good agreement about the means and variances the model currents also appear to be well constrained by the steep topography however the model velocity field contains only the first mode the satellite derived velocity field on the other hand contains both the first and second modes though the satellite field does not adequately resolve the velocity structures over the slope

evaluation of susceptibility for terrain collapse and subsidence in karst areas municipality of iraquara chapada diamantina ba brazil the morphological evolution of the karstic systems is associated with a set of physical and chemical processes triggered by the dissolution of the rocks related to percolation of groundwater and surface water which consequently open underground voids and carve out peculiar forms of relief due to environmental and geotechnical aspects this system is naturally more fragile and vulnerable than other natural systems and therefore has increasingly received the attention of the scientific community over the past decades the objective of the study was to delimit zones with varying degrees of susceptibility for collapses and subsidence of sinkholes in the municipality of iraquara chapada diamantina ba brazil and to understand their geological and morphological determinant factors geological data karst phenomenon map and visual analysis in the field were used to categorize zones with different types of susceptibilities to the nucleation of new sinkholes based on a hazard index this index was defined from the sum of geological hazard factors lineament density and sinkhole density the areas that presented the highest susceptibility for terrain collapse and subsidence corresponded to regions where carbonate rocks outcrop with high density of photolineaments and 2 62 sinkholes km2 processes associated with terrain collapse and subsidence in karst areas consisted of a combination of various factors hindering precise predictions however zones of different types of susceptibilities to terrain collapse and subsidence can be delimited when the relationships between these processes and their factors are understood the hazard index proposed does not provide quantitative values for the probability of hazard susceptibility but rather indicates areas that are more susceptible to terrain subsidence and collapse

geochemical and microfacies characterization of a holocene depositional sequence in northwest germany abstract holocene depositional sequences in the coastal zone of the north sea reflect climate driven sea level changes that led to lateral interfingering of marine brackish lagoonal and limnic sediments and peat layers this succession is reflected in an 18 m sediment core drilled in the marsh lands of the river weser the core spanning the entire holocene was analyzed at high stratigraphic resolution for major and minor elements bulk and molecular constituents and microfacies characteristics abundant triterpenoids in sediments of the basal organic unit indicate nutrient rich limnic paleoconditions not yet influenced by the rising sea level lithological description of several sedimentary units overlying the basal sequence initially suggested a mainly lagoonal setting with occasional influence by tidal channel activities geochemical and microfacies analyses confirmed repeated marine ingression marine conditions are indicated by pyrite enrichment the presence of sterathiols formed by the reaction of sterols with reduced sulfur species and the occurrence of marine pelagic diatoms towards the top of the sedimentary sequence estuarine conditions become more and more pronounced as the river weser established its modern course whereas it had been quite variable previously estuarine conditions are reflected by sterol and amino acid distributions and by limnic diatom species that are mixed with marine pelagic forms although the majority of the clastic units consist of silty to clayey sediments some intercalated quartz sand layers reflect the increase of hydrodynamic energy characteristic of lower tidal flats and channels lumps of reworked peat within fine clastic deposits also reflect high energy events even a dark layer within the upper clastic unit formerly considered a fossil soil horizon is not the direct result of regression induced soil development but originates mainly from eroded fossil organic material from the basal unit this interpretation was established by biomarker analysis and radiocarbon dating

topographic and inertial waves on the continental rise of the mid atlantic bight analysis of an array of four closely spaced moorings 2800 m water depth instrumented by near bottom current meters has been performed with a view to isolating coherent wave motions in the low frequency and inertial bands the low frequency motions are dominated by topographic rossby waves similar to the results of previous studies of deep currents on the continental rise of the mid atlantic bight estimated wave parameters show good agreement with the linear topographic rossby wave theory of rhines 1970 inertial oscillations are shown to be coherent over the array horizontal separations 15 20 km the peak frequency and phase and group velocity estimates are consistent with surface layer generation at a site north of the array the relative vorticity of the mean currents and the low frequency wave motions do not account for the observed shift of the near inertial peak to frequencies 7 above f an event of strong near bottom inertial currents amplitudes 10 cm s 1 appears to be attributable to the passage of hurricane belle august 9 10 1976 24 days earlier primarily because the vertical travel times are consistent with the estimates of vertical group velocity strong ringing inertial currents north of the array amplitude 40 cm s 1 due to hurricane belle were observed at the shelf edge mayer et al 1981 with peak frequencies comparable to the near inertial frequencies observed at the array on the rise

structure of the circulation induced by a shoaling topographic wave abstract the structure of the potential vorticity flux and a mean flow induced by a topographic wave incident over a bottom slope are investigated analytically and numerically with focus on the case that bottom friction is the dominant dissipation process in this case it is shown that the topographic wave cannot be a steady source of the potential vorticity outside the bottom ekman layer instead the distribution of potential vorticity is determined from the initial transient of the topographic wave this potential vorticity and the heat flux by the topographic wave at the bottom determine the mean flow and give a relation between the horizontal and vertical scales of the mean flow when the horizontal scale of the mean flow is larger than the internal deformation radius and the potential vorticity is not so large the mean flow is almost constant with depth independent of whether the topographic wave is bottom intensified then the mean flow is proportional to the divergence of the vertically integrat

high sea floor stress induced by extreme hurricane waves 1 strong surface waves and currents generated by major hurricanes can produce extreme forces at the seabed that scour the seafloor and cause massive underwater mudslides our understanding of these forces is poor due to lack of concurrent measurements of waves and currents under these storms using unique observations collected during the passage of a category 4 hurricane ivan bottom stress due to currents and waves over the outer continental shelf in the gulf of mexico was examined during the passage of ivan the bottom stress was highly correlated with the wind with a maximum of about 40 of the wind stress the bottom stress was dominated by the wave induced stresses and exceeded critical levels at depths as large as 90 m surprisingly the bottom damaging stress persisted after the passage of ivan for about a week and was modulated by near inertial waves

observed currents over the outer continental shelf during hurricane ivan 1 hurricane ivan crossed the gulf of mexico as a category 4 5 storm before making landfall in alabama here we show in unprecedented detail the oceanic response generated by ivan as it crossed the outer continental shelf the current structure was found to be frictionally dominated with overlapping surface and bottom boundary layers as ivan approached before transitioning to a dominant surface boundary layer as the wind stress peaked the strongest currents largest temperature fluctuations and greatest transports were generated left of the storm track

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

energetic topographic rossby waves in the northern south china sea abstracttopographic rossby waves trws are reported to make a significant contribution to the deep ocean current variability on the northern south china sea nscs continental slope trws with pe

palaeo karst collapse pillars in northern china and their damage to the geological environments according to statistics there are a total of 39 sites of palaeo karst collapse pillars in northern china as well as 3 650 palaeo karst collapse pillars through an overall survey and analysis of the distribution regularities and formation mechanisms of palaeo karst collapse pillars in the northern coal mine regions this paper found that the rock formation structures geological structures karst characters underground hydrodynamic conditions of karst and neotectonic movement conditions are basic geological bases for the formation of karst collapse pillars and rule the distribution of them karst collapse pillars apparently have three south north regularities in terms of distribution and they have resulted in severe damages to geological resources and environment in their distribution areas mine water inrush causing and coal resources damage and influencing the impounding of reservoirs as well as the stability of dam sites based on the basic geological features of palaeo karst collapse pillars in northern china this paper also introduces the new methods of integrated prospecting of successive approximation to determine hydraulic conductivity of palaeo karst collapse pillars

sustained in situ measurements of dissolved oxygen methane and water transport processes in the benthic boundary layer at mc118 northern gulf of mexico abstract within months of the bp macondo wellhead blowout elevated methane concentrations within the water column revealed a significant retention of light hydrocarbons in deep waters plus corresponding dissolved oxygen do deficits however chemical plume tracking efforts were hindered by a lack of in situ monitoring capabilities here we describe results from in situ time series lander based investigations of physical and biogeochemical processes controlling dissolved oxygen and methane at mississippi canyon lease block 118 18 km from the oil spill conducted shortly after the blowout through april 2012 multiple sensor arrays plus open cylinder flux chambers chimneys deployed from a benthic lander collected oxygen methane pressure and current speed and direction data within one meter of the seafloor the rovard lander system was deployed for an initial 21 day test experiment 9 13 2010 10 04 2010 at 882 m depth before a longer 160 day deployment 10 24 2011 4 01 2012 at 884 m depth temporal variability in current directions and velocities and water temperatures revealed strong influences of bathymetrically steered currents and overlying along shelf flows on local and regional water transport processes do concentrations and temperature were inversely correlated as a result of water mass mixing processes flux chamber measurements during the 160 day deployment revealed total oxygen utilization tou averaging 11 6 mmol m2 day chimney do concentrations measured during the 21 day deployment exhibited quasi daily variations apparently resulting from an interaction between near inertial waves and the steep topography of an elevated scarp immediately adjacent to the 21 day deployment site that modulated currents at the top of the chimney variability in dissolved methane concentrations suggested significant temporal variability in gas release from nearby hydrocarbon seeps and or delivery by local water transport processes free vehicle lander monitoring over time scales of months to years utilizing in situ sensors can provide an understanding of processes controlling water transport respiration and the fate and impacts of accidental and natural gas and oil releases

impact of particle transfer on flow properties of crushed mudstones karst collapse pillar kcp is widespread in north china coalfields where coal extraction above the ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure kcp is composed of rock skeleton and fine fillings which can be transferred under the effect of water flow thus kcp usually functions as a channel for groundwater inrush in order to investigate the mechanism of mining induced groundwater inrush of kcp which was caused by fine fillings transfer a self designed particle transfer permeability testing system was used to test the crushed mudstones flow properties which included fine filling particle transfer rate porosity increase rate and permeability under the conditions of varying pore pressure particle size mixture and compaction level initial porosity the tests indicate fine fillings transfer is the essential reason for mining induced groundwater inrush flow instability of kcp the flow properties changeability during fine particle transfer could be divided into four stages i e initial flow stage flow inrush stage continued particle flow stage and stable flow stage and flow inrush stage which is the key point to cause water inrush due to the crushing of edges and corners and the adjustment of the structure the fluctuation of permeability time relationship mainly distributed in the first two stages which make a change to flow channel moreover with the increasing of pore pressure particle size mixture and initial porosity the water inrush time and stable seepage time decreased more rapidly the fine fillings porosity and permeability increased gradually the efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well and not all of the pore structures were in flow this means there was a part of pores that were invalid but the effective porosity in flow can be treated as calculation value approximately

cyclonic eddies northeast of the campeche bank from altimetry data eight cyclonic eddies were identified near the western edge of the loop current at the northeast shelf break of the campeche bank through topex poseidon sea surface height anomaly data from january 1993 through march 2000 the eddies migration and their lifecycle are described the formation of the eddies appears to be related to the dynamics of the loop current because the timing of their generation corresponds to the last stage of the anticyclone shedding from the loop current the cyclones intensify while moving slightly to the northwest along the shelf break of the campeche bank later some cyclones are observed to move northward toward the mississippi shelf break the cyclones remain next to the campeche bank south of 268n from 1 3 to 9 6 months later some of them move northward and strengthen by merging with other eddies extending their life span the eddies vertical structure is analyzed with hydrographic data and the connection between the formation of the cyclones and the evolution of the loop current is further described using sea surface temperature images

subinertial response of the gulf stream system to hurricane fran of 1996 the evidence of subinertial frequency with peri ods from 2 days to 2 weeks oceanic response to hurricane fran of 1996 is documented hurricane fran traveled northward across the gulf stream and then over a cool core trough known as the charleston trough due east of charleston sc and in the lee of the charleston bump during the period 4 5 september 1996 during the passage of the storm the trough closed into a gyre to form an intense cool core cyclonic eddy this cool core eddy had an initial size of approximately 130 km by 170 km and drifted northeastward along the gulf stream front at a speed of 13 to 15 krn day as a subinertial baroclinic wave superimposed on this subinertial frequency wave were near inertial frequency internal inertia gravity waves formed in the stratified mixed layer base after the passage of the storm the results from a three dimensional numerical ocean model confirm the existence of both near inertial and subinertial frequency waves in the gulf stream system during and after the passage of hurricane fran model results also showed that hurricane

extreme waves under hurricane ivan hurricane ivan a category 4 storm passed directly over six wave tide gauges deployed by the naval research laboratory on the outer continental shelf in the northeastern gulf of mexico waves were observed with significant wave heights reaching 17 9 meters and maximum crest to trough individual wave heights of 27 7 meters 91 feet analysis suggests that significant wave heights likely surpassed 21 meters 69 feet and that maximum crest to trough individual wave heights exceeded 40 meters 132 feet near the eyewall

data and numerical analysis of astronomic tides wind waves and hurricane storm surge along the northern gulf of mexico the northern gulf of mexico ngom is a unique geophysical setting for complex tropical storm induced hydrodynamic processes that occur across a variety of spatial and temporal scales each hurricane includes its own distinctive characteristics and can cause unique and devastating storm surge when it strikes within the intricate geometric setting of the ngom while a number of studies have explored hurricane storm surge in the ngom few have attempted to describe storm surge and coastal inundation using observed data in conjunction with a single large domain high resolution numerical model to better understand the oceanic and nearshore response to these tropical cyclones we provide a detailed assessment based on field measurements and numerical simulation of the evolution of wind waves water levels and currents for hurricanes ivan 2004 dennis 2005 katrina 2005 and isaac 2012 with focus on mississippi alabama and the florida panhandle coasts the developed ngom3 computational model describes the hydraulic connectivity among the various inlet and bay systems gulf intracoastal waterway coastal rivers and adjacent marsh and built infrastructure along the coastal floodplain the outcome is a better understanding of the storm surge generating mechanisms and interactions among hurricane characteristics and the ngom s geophysical configuration the numerical analysis and observed data explain the 2 m s hurricane induced geostrophic currents across the continental shelf a 6 m s outflow current during ivan the hurricane induced coastal kelvin wave along the shelf and for the first time a wealth of measured data and a detailed numerical simulation was performed and was presented for isaac

vertical structure of the ocean current response to a hurricane abstract during the passage of hurricane norbert in 1984 the hurricane research division of noaa conducted a planetary boundary layer experiment that included the deployment of airborne expendable current profilers axcp a total of 16 axcps provided for the fist time high resolution vertical profiles of currents and temperatures in hurricane wind conditions this study focuses on the vertical structure of the near inertial baroclinic current excited by the passage of this hurricane the transient hurricane induced currents are isolated from the axcp profiles in norbert by subtracting a spatially averaged current near the center of hurricane norbert the wkbj scaled vertical wavenumber spectra are a decade greater than the garrett munk spectra gm75 the fist ten linear baroclinic free modes are calculated from the spatially averaged brunt vaisala frequency to allow a more direct comparison with the axcp observations in the current wind regime the near inertial response for the three dimensional v

subsidence and sinkhole hazard assessment in the southern dead sea area jordan the dead sea area is increasingly facing serious subsidence and sinkhole hazards on march 22 2000 the dyke of a two month old major salt evaporation pond located along the shore of the lisan peninsula jordan collapsed over almost two kilometers the pond was set up over unstable new lands that have been progressively emerging during the last three decades in one hour 56 millions m 3 of brine poured out into the northern natural part of the sea here we present data suggesting that the drop of the water level in conjunction with the particular tectonic setting of this area is at least one of the factors that led to the disaster we focused our study over the northern part of the lisan peninsula and ghor al haditha which are two places undergoing the most intense deformations along the jordanian dead sea coast we used the results of a static high precision gravimetric survey to detect subsurface cavities in ghor al haditha we analyzed a interferometric digital terrain model of the recent emerged platform of the lisan peninsula and interpreted radar differential interferograms contemporary with gravity measurements for the peninsula we discuss the possibilities to detect assess and monitor areas prone to collapse on the jordanian side of the southern dead sea coast

observations of intermittent deep currents and eddies in the gulf of mexico 1 intense currents having speeds between 10 and 40 cm s 1from 1000 m below the surface to the bottom have been measured in the loop current lc region and in the western gulf of mexico wgm the observations come from moored current meters sampling from the near surface to the bottom at 3300 3500 m and from august 2008 to august 2010 ten intermittent intensified currents are documented these events last 10 to 30 days and take place in the region just between the surface intensified anticyclonic cyclonic features as deduced from altimetry and measured currents in the wgm they occur between the cores of anticyclone cyclone pairs in the eastern gulf of mexico egm they occur in the loop current edge between its anticyclonic circulation and a neighboring cyclone during each event the analysis shows an increase in the barotropic contribution to the current in the loop current region these events are often associated with intensification of cyclonic vorticity in the deep layer