stratigraphy and radiocarbon chronology of a subaerially exposed holocene coral reef dominican republic a subaerially exposed coral reef records a period of marine conditions following earliest holocene transgression into the technically active subsea level enriquillo valley dominican republic field mapping detailed leveling of reef elevations and i4c dating of fossil corals and mollusks reveal the following chronology of reef development in an unusual geologic and tectonic environment 1 earliest holocene 9760 pm 100 yr b p marine transgression and growth of oysters on an alluvial fan surface approximately 33 m below sea level bsl 2 colonization of reef corals at approximately 34 m bsl on the oyster shell deposits 8990 pm 60 yr b p 3 middle holocene development of a typical caribbean fringing reef in a protected environment 6200 pm 80 to 4760 pm 90 yr b p 4 late holocene sedimentation over the reef with fossil bivalves 5710 pm 90 to 2820 pm 40 yr b p that record a gradual change from marine to brackish water that accompanied growth of shoreline th

drivers of holocene sea level change in the caribbean abstract we present a holocene relative sea level rsl database for the caribbean region 5 n to 25 n and 55 w to 90 w that consists of 499 sea level index points and 238 limiting dates the database was compiled from multiple sea level indicators mangrove peat microbial mats beach rock and acroporid and massive corals we subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on rsl we account for the local scale processes of sediment compaction and tidal range change using the stratigraphic position overburden thickness of index points and paleotidal modeling respectively we use a spatio temporal empirical hierarchical model to estimate rsl position and its rates of change in the caribbean over 1 ka time slices because of meltwater input the rates of rsl change were highest during the early holocene with a maximum of 10 9 0 6 m ka in suriname and guyana and minimum of 7 4 0 7 m ka in south florida from 12 to 8 ka following complete deglaciation of the laurentide ice sheet lis by 7 ka mid to late holocene rates slowed to

tracer transport within abyssal mixing layers abstractmixing layers near sloped topography in the abyss are thought to play a critical role in the global overturning circulation yet the behavior of passive tracers within sloping boundary laye

terrestrial shallow water hydrothermal outflow characterized from out of space abstract we investigate the potential of satellite imagery to map and monitor the activity of shallow water hydrothermal systems which are often found around volcanic islands for this study we used publicly available data and proprietary worldview 2 satellites images with spectral bands that can penetrate up to water depths of 30 m shallow water hydrothermal sites are visible on satellite imagery primarily with publicly available data demonstrating the potential of satellite imagery to study and monitor shallow water hydrothermal activity we focus our work on volcanic islands showing intense near shore shallow water hydrothermal activity and distinct styles of hydrothermal venting satellite imagery constrains regional outflow geometry and the temporal variability or stability of these systems milos island shows hydrothermal outflow associated with reflective mineral precipitates and or bacterial mats which are stable over time 2010 2014 these outflows locally define polygonal patterns likely associated with hydrothermal convection in porous media in kueishantao island individual hydrothermal plumes charged with particles are visible at the sea surface and display great variability in intensity and distribution of plume sources 2002 2019 worldwide we have identified 15 shallow water hydrothermal sites with satellite imagery that are similar to either the milos system e g vulcano and panarea italy or the kueishantao system numerous sites in pacific volcanic islands this study demonstrates that satellite imagery can be used to map and monitor different types of shallow water hydrothermal systems at regional scale and monitor their evolution satellite data provide not only regional and temporal information on these systems unavailable to date but also the regional context for follow up in situ field data and observations e g instrumental monitoring sampling observations and mapping with divers or auvs to understand both the nature and dynamics of these systems and ultimately the associated fluxes

mechanisms controlling the sensitivity of the atlantic thermohaline circulation to the parameterization of eddy transports in ocean gcms abstract the authors identify and describe the important dynamical mechanisms that explain the significant sensitivity of the atlantic thermohaline circulation to the parameterization of heat and salt transports by mesoscale eddies in numerical models in particular the effects of the gent mcwilliams gm scheme which has a strong flattening effect on isopycnals and a simple horizontal diffusion scheme are considered and compared two control runs one with each scheme exhibit very different circulations and density structures to analyze the dynamical reasons for the differences between the control runs a number of numerical experiments with regionally varying diffusion coefficients are carried out emphasizing the effects of different schemes in key regions the main effect of eddies in the southern ocean in nature is to shoal the subsurface isopycnal surfaces thus increasing the density of the northward inflow of relatively dense intermediate waters into the atlantic as will be seen this is more

sensitivity of the ocean state to lee wave driven mixing abstractdiapycnal mixing plays a key role in maintaining the ocean stratification and the meridional overturning circulation moc in the ocean interior it is mainly sustained by breaking internal waves two important classes of internal waves are internal tides and lee waves generated by barotropic tides and geostrophic flows interacting with rough topography respectively currently regarding internal wave driven mixing most climate models only explicitly parameterize the local dissipation of internal tides in this study the authors explore the combined effects of internal tide and lee wave driven mixing on the ocean state a series of sensitivity experiments using the geophysical fluid dynamics laboratory cm2g ocean ice atmosphere coupled model are performed including a parameterization of lee wave driven mixing using a recent estimate for the global map of energy conversion into lee waves in addition to the tidal mixing parameterization it is shown that although the global energy input in

abyssal circulation driven by near boundary mixing water mass transformations and interior stratification the emerging view of the abyssal circulation is that it is associated with bottom enhanced mixing which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor in the limit of slowly varying vertical stratification and topography however boundary layer theory predicts that these upslope and downslope flows largely compensate such that net water mass transformations along the slope are vanishingly small using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large scale overturning in an idealized basin with bottom enhanced mixing along a midocean ridge we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks the resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge these results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation requiring a revision of abyssal ocean theories

the relationship between current and paleo groundwater base levels abstract base levels are basically divided into two categories oceanic and marine base levels and continental terminal endorheic ones the marine domain serves as the ultimate base level for both surface and groundwater drainage systems continental inland depressions very often serve as terminal endorheic base levels to both surface drainage and groundwater systems many of the current both marine and inland base levels served also in the past as paleo base levels fluctuations of base level elevations affect the adjoined groundwater system in several ways such as changes in groundwater levels location of divides depths of fresh saline water interfaces and the amount of flow to the base levels this paper provides examples from many different parts of the world that describe the relationship between current and paleo base levels the examples include marine base levels as well as inland endorheic ones both currently above and below sea level close to and distant from the sea

topographic advection of dense bottom water the time development of a dense eddy placed on a varying topography in a rotating system is the subject of this paper it is shown that if the bathymetric variations are comparable with the thickness of the eddy these will induce a first order time development in the water mass large amplitude geostrophic theory shows that the water is advected along the depth contours with a speed that is proportional to the slope of the bottom the results are applied to a laboratory experiment with a rotating parabolic channel according to theory an initially circular eddy placed in the centre of the channel becomes elliptical while shifting its axis along the channel the outcome of the experiment is in accordance with theory and the importance of topographic advection in the ocean is discussed it is suggested that the mechanism may be important for moving water from deep water formation sites and into the global deep water circulation

the exhaust valve of the north atlantic during glacial periods climate records are marked by large amplitude oscillations believed to be a result of north atlantic na freshwater anomalies which weakened the thermohaline circulation thc and introduced instabilities such oscillations are absent from the present interglacial period with the aid of a semiglobal analytical model it is proposed that the bering strait bs acts like an exhaust valve for the above na freshwater anomalies specifically it is suggested that large instabilities in the thc are only possible during glacial periods because during these periods the bs is closed during interglacial periods when the bs the exhaust valve is open low salinity anomalies are quickly flushed out of the north atlantic by the strong southern ocean winds

decadal response of global circulation to southern ocean zonal wind stress perturbation abstract a substantial component of north atlantic deep water formation may be driven by westerly wind stress over the southern ocean variability of this wind stress on decadal time scales may lead to circulation variability far from the forcing region the hybrid coordinate ocean model hycom a numerical ocean model is used to investigate the spatial patterns and the time scales associated with such wind variability the evolution of circulation and density anomalies is observed by comparing one 80 yr simulation forced in part by relatively strong southern hemisphere westerlies with a simulation driven by climatological wind the volume transport anomaly takes about 10 yr to reach near full strength in the entire southern hemisphere however in the northern hemisphere it grows for the duration of the run the southern hemisphere indo pacific volume transport anomaly is about twice the strength of that found in the atlantic in the thermocline water exits the southern westerlies belt in a broad f

quaternary reef response to sea level and environmental change in the western atlantic the tropical subtropical western atlantic realm harbours abundant fringing reefs two major barrier reefs belize florida several atolls and large reef fringed carbonate platforms bahamas data from belize and south florida indicate that major barrier reefs were established during the high sea levels of the long and warm marine isotope stage 11 reefs formed during pleistocene sea level highstands whereas erosion non deposition and the formation of subaerial exposure surfaces prevailed during lowstands of sea level florida bahamas exposed reefs and platforms with siliciclastic hinterlands were characterized by deposition of clays and sands on fluvial plains belize elevated terraces and outcrops of reefs of the last interglacial of marine isotope stage 5e are evidence of higher than present sea level and temperature that sustained large reef fringed carbonate platforms and ramps in the florida bahamas region and central america belize mexico including ooid deposition in warm and shallow waters during the highstands of marine isotope stages 5c and 5a at sea levels several metres lower than today fringing reefs developed in parts of the caribbean for example in south florida outlier reefs data from the island of barbados support the contention that the postglacial sea level rise from about 120 m was rapid and punctuated by two meltwater pulses ia and ib which bracket the beginning and end of the younger dryas respectively after reflooding of shelves in the early holocene reefs developed preferentially on highs of the underlying karstified pleistocene limestone surface and on former river channel bars many reefs in the western atlantic region kept pace with holocene sea level rise whereas some were drowned reasons for reef drowning are debated and include sea level rise elevation of antecedent topography and deterioration of environmental conditions such as high nutrient input apart from sea level and antecedent topography factors such as exposure to waves and currents storms and sedimentation have controlled reef development the historical decline of acroporid corals in the caribbean realm has been attributed to cooling following the holocene thermal optimum however historical die offs of reef building corals and other reef organisms suggest that some if not all recent declines were unprecedented during the holocene rising temperatures decreasing carbonate saturation increased frequency of major storms high nutrient concentrations and sedimentation overfishing and disease certainly played a role in decline but systematic studies relating these environmental factors to holocene reef building are only in the early stages

mixing at the head of a canyon a laboratory investigation of fluid exchanges in a rotating stratified basin 1 observations indicate that oceanic mixing is intensified near the head of submarine canyons how the presence of canyon walls affects the local production and distribution of mixed fluid is an open question these dynamics are addressed through rotating tank experiments which impose mixing at middepth at the closed end of a channel open to a larger body of water turbulence is generated in a linearly stratified fluid with initial buoyancy frequency n by means of a single bar oscillated with frequency the mixed fluid quickly reaches a steady state height h n 1 2 independent of the coriolis frequency f and collapses into the channel interior a small percentage of the fluid exported from the turbulent zone enters a boundary current the bulk forms a cyclonic circulation in front of the bar as the recirculation cell expands to fill the channel it restricts horizontal entrainment into the turbulent zone mixed fluid flux decays with time as t and is dependent on the size of the mixing zone and the balance between turbulence rotation and stratification the recirculation cell is confined within the channel and export of mixed fluid into the basin is restricted to the weak boundary current as horizontal entrainment is shut down long term production of mixed fluid relies more on vertical entrainment however the scalings indicate that short term dynamics are the most applicable to oceanic conditions

anatomy of turbulence in thermally stratified lakes turbulence within the thermocline of two thermally stratified lakes lake biwa japan and lake kinneret israel was investigated using a portable flux profiler this instrument provided high resolution profiles of temperature conductivity and two components of velocity within a measuring volume of approximately 8 mm 3 each data profile was segmented into statistically stationary segments a range of properties of the turbulence including direct estimates of the vertical mass flux were then calculated for each segment it was found that turbulence in the thermocline was generally patchy but within a patch dissipation levels were relatively high the turbulent motions were found to be fine grained with small thorpe scales and a large skewness of the distribution of the displacement scale this is distinct to that found in the ocean where shear instability produces large overturns the measurement showed that the net vertical mass flux in the thermocline was negligible and less than that predicted by osborn 1980 this is explained by noting that the net buoyancy flux consisted of two opposing parts a down gradient irreversible flux due to turbulent mixing and an up gradient reversible flux due to restratification that often cancel each other within a segment the low measured net buoyancy flux within the interior of the lakes suggested that other processes such as gravitational adjustments and benthic boundary layer processes should be responsible for the basin averaged vertical transport in these lakes

comparison of shear measurements and mixing predictions with a direct observation of diapycnal mixing in the atlantic thermocline four sets of velocity and density profiles have been measured with an autonomous profiler during an upper ocean intentional tracer sf6 diapycnal diffusivity measurement the north atlantic tracer release experiment natre the tracer was injected near 310 m depth in the canary basin two profile sets were collected 6 months after tracer release and two were collected i year after release all within the horizontal boundaries of the sf6 patch shear and strain can be combined with turbulent kinetic energy dissipation and diffusivity measurements published elsewhere to test existing expressions for dissipation and diffusivity due to shear induced turbulence these expressions arise from internal wave decay modeling one expression of dissipation parameterized in terms of shear based on stochastic nonlinear internal wave interaction has fared well empirically its extension to estimate diffusivity is evaluated shear variance of the first two data sets was about 1 6 times gm76 and 2 5 to 3 0 times gm76 in the later sets the average parameterized mixing estimate computed using all of the temporally limited shear measurements overestimates annual mean natre diffusivity 1 5 x 10 m 2 s by a factor of 1 2 a modified parameterization gives an underestimate to first order this supports the present understanding of open ocean diffusivity in terms of fine scale shear and internal wave decay that is the slow diapycnal mixing was not a consequence of unusually low shear adjustment of the shear induced mixing models to better fit the data is not warranted because of the lack of direct comparability between the various measurements the expected natural variability of the shear and sampling errors

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

mapping seagrass and colonized hard bottom in springs coast florida using worldview 2 satellite imagery abstract the offshore extent of seagrass habitat along the west florida usa coast represents an important corridor for inshore offshore migration of economically important fish and shellfish surviving at the fringe of light requirements offshore seagrass beds are sensitive to changes in water clarity beyond and intermingled with the offshore seagrass areas are large swaths of colonized hard bottom these offshore habitats of the west florida coast have lacked mapping efforts needed for status and trends monitoring the objective of this study was to propose an object based classification method for mapping offshore habitats and to compare results to traditional photo interpreted maps benthic maps were created from worldview 2 satellite imagery using an object based image analysis obia method and a visual photo interpretation method a logistic regression analysis identified depth and distance from shore as significant parameters for discriminating spectrally similar seagrass and colonized hard bottom features seagrass colonized hard bottom and unconsolidated sediment sand were mapped with 78 overall accuracy using the obia method compared to 71 overall accuracy using the photo interpretation method this study suggests an alternative for mapping deeper offshore habitats capable of producing higher thematic and spatial resolution maps compared to those created with the traditional photo interpretation method

boundary mixing in a rotating stratified fluid extension d une experience de laboratoire sur le melange en couche limite dans un fluide stratifie pour inclure les effets de rotation la combinaison du melange vertical a la frontiere et du melange horizontal par des tourbillons d echelle moyenne conduit a l affaiblissement du gradient de densite interieur

neotectonics of hispaniola plate motion sedimentation and seismicity at a restraining bend abstract the pattern of neogene faulting volcanism and sedimentation in hispaniola helps to resolve a problem that arises in attempting to determine the direction of caribbean plate motion from earthquakes alone namely how well do earthquake mechanisms define plate motion hispaniola occupies a compressional north step or restraining bend in the generally east west trending motagua cayman trough puerto rico trench fault system which marks an active plate boundary zone pbz of left lateral strike slip motion between the north america and caribbean plates four areas are distinguishable in hispaniola from field mapping and from the interpretation of satellite imagery and conventional aerial photographs two of these areas consist of active left lateral strike slip fault systems that roughly define the northern and southern coasts of the island the structure of both fault systems suggest a roughly east west trending direction of relative plate motion consistent with previous findings the intervening area consists of en echelon mountain ranges thrust up at the restraining bend from the early miocene a pleistocene volcanic province within this area is interpreted as defining a diffuse extensional fault termination of the southern strike slip fault zone the fourth area in eastern hispaniola is interpreted as being underthrust by discontinuous fragments of lithosphere in response to convergence at the restraining bend it appears possible that thinner young island arc lithosphere may be more prone to subduction than to escape or flaking processes that are more important in older more buoyant lithosphere

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

comparison of deep ocean finescale shear at two sites along the mid atlantic ridge abstract four drifting floats were used to measure the magnitude of the vertical derivative of horizontal velocity in waters above the rough bathymetry of the mid atlantic ridge this derivative is typically the dominant component of the velocity gradient the shear two floats were at the site of the brazil basin tracer release experiment bbtre in the south atlantic and two were near the site of the guiana abyssal gyre experiment gage in the north atlantic floats operated for 1 year except for one bbtre float which operated for 100 days shear was measured over a vertical span of 9 5 m using drag elements that caused the floats to rotate slowly in response to shear for each float the first second and fourth moments of shear were elevated above levels associated with the garrett munk model internal wave spectrum three of the four floats were tracked as they moved over mountainous terrain allowing shear intensity to be measured as a function of height above the bottom a deep bbtre float showed enhancement of rms shear near the bottom floats at both areas provided measurements at 2000 m above the bottom with differing results the gage site had a lower fourth moment of shear diapycnal diffusivity proxy than the bbtre site however application of normalization factors accounting for differences between the sites in bottom roughness latitude dependent internal wave dynamics and tidal current speeds brings the results into agreement

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

an experiment on boundary mixing part 2 the slope dependence at small angles experiments of the type described by phillips et at 1986 were performed using different slopes with the aim of examining the slope dependence of the buoyancy and volume transports particularly at small slopes

the effect of localized mixing on the ocean circulation and time dependent climate change observations indicate that intense mixing in the ocean is localized above complex topography and near the boundaries model experiments presented here illustrate that accounting for this fact can be important in particular it is found that in the case of localized mixing the rate of overturning circulation is proportional to the net rate of generation of potential energy by the vertical mixing linked to the net downward heat diffusion rather than to the value of the mean vertical diffusivity coefficient furthermore it is shown that two climate models having the same vertical profile of diffusivity but differing in their distribution horizontally uniform versus topography boundary intensified can simulate significantly different meridional oceanic circulations vertical heat transfers and responses of simulated climate to atmospheric co2 increase this is found for relatively large o 1 0 cm 2 s 1 horizontal mean values of vertical diffusivity in the pycnocline however in cases of relatively small o 0 1 cm 2 s 1 mean diffusivity in the pycnocline the simulated integral quantities such as meridional mass and heat transports do not depend much on the details of the mixing distribution even so it is found that the deep western boundary currents are more localized near the boundaries in the case of topography boundary intensified mixing also the stratification in the deep ocean is set through the localized regions of intense vertical mixing in addition it is shown that reconciling the observed basin mean values of diffusivity in the abyssal ocean of o 10 cm 2 s 1 with realistic stratification can be problematic unless the regions of enhanced vertical mixing are localized

a 4000 year record of fire and forest history from valle de bao cordillera central dominican republic we examined evidence of past vegetation climate and disturbance history in a sediment core from a bog on the windward slope of the cordillera central in the dominican republic the sediments revealed a continuous 4000 cal yr history of pine pinus occidentalis dominance and fire bog formation may have been linked with a regional shift toward wetter conditions seen at other highland sites around 4000 cal yr bp low pollen influx low organic content and poor pollen preservation suggested periodic drying of the bog surface between 3700 and 1200 cal yr bp and the loss of sediments to either deflation or erosion spikes in pollen of broadleaf trees and shrubs mainly before 2500 cal yr bp may indicate warmer or wetter intervals remobilized old charcoal along with peaks in poaceae cyathea and lophosoria indicate a possible large tropical storm event around 2900 cal yr bp transported clasts of peat and soil in the core signal other high precipitation events we found no clear evidence of prehistoric human activity d 2005 elsevier b v all rights reserved

finescale shear at 1660 and 2850 dbar over the mid atlantic ridge in the eastern brazil basin abstract two drifting shearmeter instruments have provided records of the magnitude of shear the magnitude of the vertical derivative of horizontal velocity measured over a 10 m aperture in the vicinity of the brazil basin tracer release experiment the floats drifted at roughly 1660 and 2850 dbar where the buoyancy frequencies were n 1 1 and 0 5 cph respectively two additional floats provided deep trajectories but no shear data the records of hourly mean values of shear magnitude with mean values denoted sh exhibit strong temporal variability with time scales comparable to those of fortnightly tidal modulation the deep record exhibits stronger mean sh near the seafloor than above with the exception of the bin closest to the seafloor sh from neither float correlates strictly with tidal forcing shallow sh varies in apparent response to atmospheric forcing the mean squared shear of the shallow record is 4 times the n dependent value associated with the garrett munk spectral model and that

differential mixing in a stratified fluid we present an experimental and theoretical study of the effects of localized mixing on a stratified fluid contained in a reservoir in the experiments mixing is accomplished by means of a vertically oscillating horizontal grid located near the water surface at one end of the reservoir once the grid is set in motion a mixed layer forms immediately beneath it as this layer deepens a horizontal pressure gradient builds up which drives an outflow of mixed fluid into the unmixed interior of the reservoir this outflow slows and eventually brings to a halt mixed layer deepening under the grid at this equilibrium depth the vertical velocity of the entrainment interface induced by the outflow exactly equals the velocity at which the entrainment interface would move downwards because of mixing this equilibrium state persists until the outflow intrusion is blocked by the far wall of the reservoir at which time deepening resumes under the grid asymptotically the fluid reaches a state in which mixed layer deepening is independent of position

biogeochemical cycling in the global ocean 1 a new analytical model with continuous vertical resolution and high latitude dynamics a new simple analytical model of ocean chemistry is presented which includes continuous vertical resolution high latitude dynamics air sea exchange and sea ice cover in this high latitude exchange interior diffusion advection hilda model ocean physics are represented by four parameters k and w an eddy diffusion coefficient and a deep upwelling velocity in the stratified interior q a rate of lateral exchange between the interior and a well mixed deep polar ocean and u an exchange velocity between surface and deep layers in the polar ocean first estimates are made of ice free and ice covered areas at high latitudes surface temperatures and air sea exchange velocities from available data then values of the physical parameters are estimated from simultaneous least mean square fits of model solutions for temperature t and abiotic carbon 14 14c to interior profiles of t and 14c and surface layer 14c values all derived from available data best fit values for k w q and u are 3 2 10 5 m2 s 1 2 0 10 8 m s 1 7 5 10 11 s 1 and 1 9 10 6 m s 1 respectively these results are interpreted in terms of modes of ocean circulation and mixing and compared with results from other simplier and more complex models in parts 2 and 3 of this series these values for k w q and u are taken as inputs for studying phosphorus oxygen and carbon cycling in the global ocean with the hilda model

vertical mixing and cabbeling in layered models abstract a consistent scheme for vertical mixing in layered numerical models is derived in this paper the fact that the vertical coordinate density depends on the properties being transported namely salinity and potential temperature renders the inclusion of vertical mixing in layered models a subtle problem the approach the authors have taken is based upon the entrainment into a layer being proportional to the turbulent activity in that layer across each interface there are then two entrainment velocities one upward velocity that is the entrainment of fluid into the layer above the interface and one downward velocity being the entrainment velocity into the layer below the interface this double entrainment accounts for both the diffusive and the advective consequences of turbulent mixing the proposed scheme works without approximation for a nonlinear equation of state and can readily handle the production of density caused by cabbeling several examples are given

subaerially exposed holocene coral reef enriquillo valley dominican republic an extremely well preserved holocene fringing coral reef occurs at an average elevation of 5 m below sea level around the margins of the central enriquillo valley dominican republic the reef records the latest marine incursion from the east into an 85 km long 12 km wide tectonic depression and appears to represent a unique preservation excellent cross sections of the reef exposed in erosional gullies reveal a composition and zonation typical of modern caribbean reefs that are found in offshore low energy environments radiocarbon age determinations 2 indicate that reef growth coincided with sea level rise following the last ice age 5 930 100 to 4 760 90 yr b p deltaic deposition and possible vertical movements on active fault scarps dammed the eastern mouth of the valley and created lago enriquillo the level of which was then rapidly lowered by evaporation in an arid climate to produce a saline lake 40 m below sea level stratigraphic studies of rocks along the valley edge and data from drill holes in the basin center indicate that there were earlier post miocene marine incursions similar to that described here

the role of boundary mixing in the deep ocean recent laboratory studies demonstrate that mixing at the boundaries of stratified and rotating fluids can be described by a relatively simple parameterization these results are applied to the deep ocean and by using available field observations it is argued that mixing at the boundaries can lead to an apparent diapycnal diffusivity in the interior of the deep ocean whose magnitude has an upper bound of 3 10 5 m2 s 1

atlantic pycnocline theory scrutinized using a coupled climate model simulations with changed southern ocean wind stress oceanic vertical mixing surface freshwater forcing and global warming confirm the basic equations of gnanadesikan s 1999 theory for the atlantic one vertical scale the pycnocline depth d contributes inversely proportional to low latitudinal upwelling and linearly to southern ocean eddy transport the maximum atlantic overturning is confirmed to be quadratic in d but is also shown to be linear in a meridional density difference our simulations strongly suggest that the theory needs to be complemented by a dynamical equation for since changes in both d and are significant and mutually independent while under global warming d varies strongly and is practically constant the situation is reversed for altered surface freshwater fluxes similarly variations in the meridional length scale of southern ocean outcropping require a dynamical equation in order to capture the fundamental behavior of the atlantic meridional overturning circulation

a 10 300 14c yr record of climate and vegetation change from haiti abstract pleistocene and holocene vegetation dynamics in the american tropics are inferred largely from pollen in continental lake sediments maritime influences may have moderated climate and vegetation changes on caribbean islands stable isotope 18 o study of a 7 6 m core from lake miragoane haiti provided a high resolution record of changing evaporation precipitation e p since 10 300 14 c yr b p the miragoane pollen record documents climate influences and human impacts on vegetation in hispaniola the 18 o and pollen data near the base of the core indicate cool dry conditions before 10 000 14 c yr b p lake miragoane filled with water in the early holocene as e p declined and the freshwater aquifer rose despite increasing early holocene moisture shrubby xeric vegetation persisted forest expanded 7000 14 c yr b p in response to greater effective moisture and warming the middle holocene 7000 3200 14 c yr b p was characterized by high lake levels and greatest relative abundance of pollen from moist forest taxa climatic drying that began 3200 14 c yr b p may have driven some mesophilic animal species to extinction the pollen record of the last millennium reflects pre columbian taino and european deforestation long term holocene vegetation trends in southern haiti are comparable to trends from continental lowland circum caribbean sites suggesting a common response to regional climate change

layers and internal waves in uniformly stratified fluids stirred by vertical grids laboratory experiments in which uniformly stratified fluids are stirred by horizontally moving vertical grids or arrays of vertical rods are reviewed to examine their consistency and to compare their findings particularly those relating to the generation of layers selected experiments are of three types those in which a turbulence spreads from a horizontally confined region where it is continuously generated by an oscillating grid b grid stirring is maintained throughout a rectangular tank or c a cloud of turbulence decays after a short period of horizontally localized grid mixing in all the experiments turbulence is generated over the full vertical extent of the tank in the experiments of types a and c layers of comparable scale are observed to intrude into the ambient fluid from the turbulent region in the type b experiments layers form only when the time interval between the passage of the grid through the stratified fluid is sufficiently long allowing turbulence to decay substantially between grid strokes two mechanisms are found to be dominant in the production of layers in experiments of type a and c overturning eddies in the turbulent region of scale significantly larger than the ozmidov length scale collapse and spread intruding and forming layers in the adjoining laminar region internal shear waves propagating ahead of the intrusions have a vertical wavelength that is approximately twice the layer height in type b experiments layers are formed through a process described by holford linden dyn atmos oceans vol 30 1999 a pp 173 198 the bending of vortices shed by the grid bars the height of the layers is approximately half the vertical wavelength of internal shear waves that travel at the speed of the grid it is proposed that the flow field of the shear waves bends the vortices resulting in diapycnal mixing that forms the layers the relationship of layers and internal shear waves in the experiments is therefore as follows in type a and c experiments internal waves are generated by layers intruding from the turbulent region into the quiescent stratified region but in experiments of type b internal waves drive and dictate the height of the layers layers are generated as a consequence of vortex bending by internal waves there is insufficient evidence to establish whether zigzag instability either of vortex pairs or of vortex streets shed by a moving grid accounts for the layers in any of the three types of grid experiments the phillips and posmentier instability may reinforce layers formed by other processes the generation of pancake vortices or vortical mode motion is left for later review

radon 222 in the benthic boundary layer a detailed survey of radon 222 and temperature profiles of the benthic boundary layer in the hatteras abyssal plain shows a strong correlation between the structure of both the apparent vertical diffusivities estimated from radon 222 are of the order of 50 cm2 s 1 in the mixed layer and of the order of 1 cm 2 s 1 above it one profile appears to have been taken in a frontal zone where isotherms dip sharply into the sediments this is the only profile where there is significant penetration of radon above the mixed layer several other profiles suggest that the temperature may take longer than several radon half lives to adjust to new mixing and advection regimes in such cases one often sees considerable structure in the radon profile within the region where the potential temperature is well mixed

sediment resuspension and mixing by resonantly generated internal solitary waves the observation of internal solitary waves isws propagating upstream along a strongly stratified bottom layer on the california shelf is reported an increased concentration of particulates in the water column accompanies the passage of these isw packets the estimated local richardson number in the bottom vicinity is around 1 4 and a vertical coefficient of eddy diffusivity of order 1022 m2 s21 is associated with the upstream propagating leading isw the leading isw gave rise to reversed flow in an 8 m layer above the bottom it is argued that the upstream propagating isws were generated by resonant flow over bottom topography internal waves generated in this way seem to be frequent in the record of a month long experiment model results suggest that the isws can carry up to 73 of such generated long wave energy the ocean conditions at the site are similar to those of other coastal sites which suggests that the phenomenon described here may be common

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

how vulnerable is acropora cervicornis to environmental change lessons from the early to middle holocene the coral acropora cervicornis is considered a modern environmental indicator species vulnerable to anthropogenic stress and rapidly disappearing throughout the caribbean causes for its decline have been attributed to both natural and anthropogenic factors physical and geochemical data are used to explore conditions under which this species thrived in early to middle holocene reef deposits ca 9 4 5 4 ka of the enriquillo valley southwestern dominican republic this study shows that a cervicornis fl ourished during a 4000 yr period spanning the holocene thermal maximum and high resolution radiocarbon dating reveals continuous growth for at least 2000 yr holocene a cervicornis survived large scale climate and environmental changes that included high temperatures variable salinity hurricanes and rapid sea level rise with remarkable resilience our data suggest that the recent decline in a cervicornis is anomalous and likely tied to ecosystem change beyond natural causes

a study of the bottom boundary layer over the eastward scarp of the bermuda rise velocity and temperature measurements from the bottom boundary layer bbl over the eastward scarp of the bermuda rise in water depth of 4620 m show little variability over an 8 month period the free stream flow 62 m above the bottom was south southeasterly following the isobaths in the region with an average speed of 22 cm s the current vector in the bbl rotated an average of 5 in a counterclockwise sense between 62 and 0 8 m above the bottom the thickness of the bbl was 40 m and the average magnitude of the bottom stress was 0 7 dynes cm2 mean speed profiles height of the bbl and the magnitude of the bottom stress predicted by a model compare favorably with the observations but the model predicts a rotation of the current vector between 62 and 0 8 m more than twice that measured the time dependent nature of the flow field is also reproduced by the model the bermuda rise data and speed profile measurements at the base of the scotian rise show that the m2 clockwise polarized tide is damped more than the mean current as the bottom is approached in the bbl this phenomenon is reproduced by the model and can be explained by differing effective ekman layer thicknesses associated with tidal and steady components of the flow

boundary versus internal diapycnal mixing in stratified natural waters using the fluorescent dye uranin tracer release experiments to study the contribution of bottom boundary mixing to diapycnal transport in stratified natural waters were performed in lake alpnach central switzerland during 1992 1995 a first experiment involved injecting the tracer from a point source into the center of the hypolimnion that part of the lake below the surface mixed layer an in situ fluorometer was then employed to detect the horizontal and vertical spreading of the tracer cloud allowing rates of diapycnal diffusivity to be determined as long as the tracer was confined to the interior water region the diapycnal diffusivity was relatively small however after the tracer cloud had reached the lake boundary the diapycnal diffusivity increased by approximately one order of magnitude in a second experiment the tracer was released near the sediment water interface in this case the dynamics of vertical tracer spreading were opposite during the first few hours after tracer release diapycnal diffusivities were large subsequently decreasing as the tracer cloud drifted away from the lake boundary basin wide diapycnal diffusivities calculated from heat flux measurements based on temperature profiles obtained from thermistor chains or conductivity temperature depth casts agreed well with the values obtained from the vertical tracer diffusion after horizontal homogenization the results of the tracer experiments corroborate the hypothesis that diapycnal fluxes are determined predominantly by mixing in the bottom boundary region

internal wave induced dispersion and mixing on a sloping boundary 1 a fluorescent dye tracer was released in a stratified water column above a sloping boundary revealing profound dispersive asymmetry initially the dye spread symmetrically in the vertical until the deeper portion became influenced by the bottom boundary layer bbl the shallower portion then spread rapidly up slope in a thin boundary layer influenced by highly non linear isopycnal distortions the deeper down slope portion of dye subsequently became detached from the boundary and intruded into the basin interior in three distinct layers along isopycnal surfaces the intrusions result from the gravitational collapse of mixing patches created by baroclinic flow over an irregular boundary the vertical separation of the layers matches the inverse topographic wavenumber up slope displacement of the dye is consistent with an advective diffusive balance near the sloping boundary controlled by slope angle and roughness horizontal diffusivities increased from 1 4 m2s 1 to 18 4 m2s 1 during the 4 day experiment

robustness of multiple equilibria in the global ocean circulation 1 in an idealized atlantic pacific ocean model we study the steady state solutions versus freshwater input in the northern north atlantic we find that four different states the conveyor c the southern sinking ss the northern sinking ns and the inverse conveyor ic appear as two disconnected branches of solutions where the c is connected with the ss and the ns with the ic we argue that the latter has the intriguing consequence that the parameter volume for which multiple steady states exist is greatly increased

oceanography of the black sea a review of some recent results abstract a new synthesis of the black sea oceanography is presented primarily based on studies carried out in the southern black sea as well as on some recent work covering the entire basin obtained in a new era of increasing cooperation between the riparian countries a review of the physical environment is given seasonal and interannual climatic variability of the system are discussed in relation to its hydrology water mass variability and formation are studied with emphasis on the inflow of mediterranean waters pycnocline variability shelf and internal mixing and double diffusive convection the general circulation of the basin and the roles of stratification topography and coastline variations in determining the behaviour of the rapid unstable boundary currents and upwelling along the coast are discussed based on hydrographic data and satellite observations impacts of the physical processes on the ecosystem are discussed

the behavior of a turbulent front in a stratified fluid experiments with an oscillating grid a simple laboratory model utilizes an oscillating grid to produce a turbulent front in a linearly stratified fluid the motion of the front is studied visually using laser fluorescence and neutrally buoyant tracer particles when the turbulence is vigorous near the grid stratification has no effect as the front propagates away vertical scales become limited by stratification as postulated by ozmidov the break up of the front can be identified at the nondimensional time nt 10 here a series of layers are formed which intrude into the surrounding nonturbulent fluid the vertical scale of these layers is also predicted using ozmidov s postulate it is approximately 7 times the estimated ozmidov scale at nt 10 the advance of individual intrusions comprising the front is characterized by a local froude number which decreases as the intrusions lengthen the mechanism of advance is intimately connected with wave motions produced at the turbulent end of the intrusions

multidecadal variability of the overturning circulation in presence of eddy turbulence at low resolution idealized ocean circulation models forced by prescribed differential surface heat fluxes show spontaneous multidecadal variability depending critically on eddy diffusivity coefficients the existence of this critical threshold in the range of observational estimates legitimates some doubt on the relevance of such intrinsic oscillations in the real ocean through a series of numerical simulations with increasing resolution up to eddy resolving ones 10 km and various diapycnal diffusivities this multidecadal variability proves a generic ubiquitous feature at least in model versions with a flat bottom the mean circulation largely changes in the process of refining the horizontal grid along with the associated implicit viscosity and diffusivity and the spatial structure of the variability is largely modified but there is no clear influence of the resolution on the main oscillation period the interdecadal variability appears even more robust to low vertical diffusivity and overturning when mesoscale eddies are resolved the mechanism previously proposed for these oscillations involving westward propagating baroclinically unstable rossby waves in the subpolar region and its feedback on the mean circulation appears unaffected by mesoscale turbulence and is simply displaced following the polar front

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

a thermal oscillation under a restorative forcing summary the authors report an interdecadal oscillation in a wind and thermally driven ocean general circulation model ogcm the oscillation is tantalizing in that it occursunder a relatively strong thermal damping 26 3 w m 2k examinations involving a two dimensional ogcm a simple thermal flip flop model and a three dimensional ogcm with and without the nonlinear effect of temperature in the state equation of sea water demonstrate that the oscillation is not driven by mechanisms such as the so called convective oscillator or the advective overshooting oscillator instead the oscillation is associated with the propagation of modelled long rossby waves with westward phase velocity it is found that the north south basin extent of the ogcm is an important factor a larger northsouth basin extent is conducive to the generation of thermal wind flows crucial for initiating the propagation of disturbances the geophysical relevance of these results is discussed

sea surface correction of high spatial resolution ikonos images to improve bottom mapping in near shore environments a significant number of high spatial resolution 4 m ikonos images acquired over shallow coastal environments present quasi stochastic sea surface effects that seriously compromise reconnaissance of bottom features this problem is common in wide field of view images where there is limited control on acquisition conditions other than cloud cover to eliminate most of these wave and glint patterns we use the near infrared band which exhibits maximum absorption and minimal water leaving radiance over clear waters to characterize the spatial distribution of relative glint intensity which is then scaled by absolute glint intensities in each of the visible bands the result is subtracted from the visible bands thus filtering out glint effects corrected visible bands clearly reveal seabed structural features obscured in the original data before and after correction classifications of an ikonos image of lee stocking island bahamas reveal an improvement of user s accuracies for critical benthic habitat classes such as coral dominated habitat 46 8 versus 60 5 or dense seagrass beds 31 7 versus 52 1 this technique offers potential to use previously discarded sections of high spatial resolution airborne or satellite images of optically shallow water for mapping substrate features

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

inner shelf hardbottom areas northeastern gulf of mexico abstract indurated sediments are common on the seafloor of offshore alabama and nw florida in water depths of 60 to 130 ft 18 to 40 m hardbottom areas include reef like outcrops with up to 6 5 ft 2 m of relief above the surrounding seafloor moderately sloping ridges of rock rubble and shell hash and also areas of surficial rock and shell rubble with little or no relief although most of these hardbottoms are classified as live i e they support a diverse encrusting epifauna their composition and texture indicate formation prior to growth of the epifauna four types of hardbottom rock are identified 1 massive to nodular sideritic sandstones and mudstones are widely distributed in the central and western portions of the area 2 slabby aragonite cemented coquina and sandstone occur in the central part of the area mostly as rubble associated with storm related ridges of shell and sand 3 dolomitic sandstone occurs in small irregular outcrops and is compositionally related to 2 4 calcite cemented algal calcirudite occurs in reef like knobs in the southeastern portion of the area in all but 4 mineralogy and isotope ratios suggest that cementation took place via marine rather than fresh waters and that methane and plant detritus served as carbon sources most mappable hardbottom areas are rubble zones on northeast facing slopes of gentle low relief shore oblique ridges thus present day extent of hardbottoms is a function not only of original depositional and cementational patterns but also a response to modern shelf processes such as energetic storm events

turning ocean mixing upside down abstractit is generally understood that small scale mixing such as is caused by breaking internal waves drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes however the observational evidence that the strong turbulent fluxes generated by small scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small scale mixing converts light waters into denser ones thus driving a net sinking of abyssal waters using a combination of theoretical ideas and numerical models it is argued that abyssal waters upwell along weakly stratified boundary layers where small scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom the abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters driven by small scale mixing in the stratified interior above the bottom boundary layers and a slightly larger net upwelling driven b

a two dimensional model of boundary mixing the steady flow in and near a turbulent boundary layer on a sloping boundary is considered for a nonrotating stratified fluid it is shown that the effect of nonuniform stratification in the interior i e away from the turbulent layer is to induce a convergent divergent flow in the boundary layer which results in an inflow or outflow to the interior this inflow outflow acts in a divergent convergent manner on the interior isopycnals use of a filling box argument for the slow time variation of the interior then produces an approximate expression for an effective interior vertical diffusivity the parameter dependence of this diffusivity is very strong however with realistic geophysical values subject to the omission of rotation e g a mixed layer depth of 50 m munk s canonical value of 10 4 m2 s 1 can easily be achieved this work thus supports the view that boundary mixing is likely to be an important process in setting the vertical density profile in the ocean

a laboratory simulation of mixing across tidal fronts a laboratory study which simulates the dynamics of shallow sea fronts and the mixing across a tidal front is described the experiments show for the first time that it is possible to simulate a stationary tidal front with the inclusion of buoyancy effects coriolis effects and turbulence in the laboratory experimental data obtained for the cross front mixing rate are presented the data analysis shows that the mixing rate increases with stratification and decreases with rotation a theoretical model of the flow which collapses the experimental data is developed which shows that the cross front mixing is controlled by baroclinic processes the model enables an extrapolation of the laboratory results to oceanographic conditions estimates of the cross front mixing velocity for oceanographic conditions give values consistent with estimates obtained from north sea data

internal waves and tides in the western weddell sea observations from ice station weddell the upper ocean current and temperature fields in the western weddell sea were measured from the drifting pack ice at ice station weddell 1 isw and nearby sites using a vertical profiler and an array of moored sensors in january june 1992 these data document the structure and variability of the internal gravity wave field and tidal currents in this remote region the variance of the internal wave continuum frequency n at isw was 0 2 0 6 of the garrett munk gm universal level for the first 60 days increasing to near gm levels during the final 10 days of the deployment in contrast the energy density at site c 50 km west of isw and farther up the continental slope was always near gm levels variations may be due to a combination of spatial and temporal gradients of the internal wave field at isw coherence between vertically separated sensors was used to estimate vertical wave number bandwidth energy and bandwidth estimates are compared with previous studies in both ice covered and temperate oceans using our measurements of the internal wave field and existing parameterizations of mixing we estimate the vertical heat flux from the warm deep water toward the surface at isw the upward heat flux due to mixing associated with the internal waves was about 1 w m 2 much less than the 20 w m 2 average flux required to balance the heat budget for the weddell gyre tidal currents contributed significantly to the total measured horizontal velocity variance the tides were primarily barotropic and increased toward the west in both the semidiurnal and diurnal frequency bands it is suggested that the stronger tidal currents to the west over the shallower water of the upper continental slope are indirectly responsible for the higher internal wave energy at site c relative to isw

isolating the role of mesoscale eddies in mixing of a passive tracer in an eddy resolving model 1 this study examines the role of mesoscale eddies in distribution of chlorofluorocarbon cfc in a numerical model of the north atlantic our main conclusions are based on a comparison of two eddy resolving experiments one with and one without eddy advection of cfc the cfc distributions in these two experiments exhibit substantial differences within the subpolar gyre in particular in the presence of eddies the horizontal distribution of cfc in the upper 1000 m is more uniform and the cfc concentration is lower in the lower 1500 m our analysis demonstrates that these basin wide differences are caused by the interactions of eddy advection with convection and mean advection in several isolated locations the corresponding eddy flux divergence terms are spatially non uniform in magnitude their effects are often nonlocal and sometimes work against the spreading of cfc being carried out by the mean advection these conclusions are further confirmed by a third experiment in which the eddy advection was replaced by a down gradient diffusive parameterization our results demonstrate that advection by mesoscale eddies is crucial to the mixing of atmospheric gasses into the ocean and outline difficulties in representing eddies by the down gradient diffusion

an isopycnal view of near boundary mixing and associated flows abstract the effectiveness of mixing near a sloping boundary is reduced not just by the ratio of the stratification there to that in the interior but by the square of this ratio this result has previously been derived and interpreted by invoking the upgradient vertical buoyancy flux associated with secondary circulation as this opposes the downgradient vertical diffusive flux here it is shown that the result may be derived very simply by considering the diffusive flux across an isopycnal rather than a horizontal surface the reduction in the buoyancy flux comes from the increased isopycnal spacing and the reduced distance to the boundary derivation of the secondary circulation in the isopycnal diapycnal framework is more subtle however as it involves allowing for the curvilinear nature of the coordinates

stirring by small scale vortices caused by patchy mixing evidence is presented that lateral dispersion on scales of 1 10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small scale geostrophic motions caused by patches of mixed fluid adjusting in the aftermath of diapycnal mixing events dye release experiments conducted during the recent coastal mixing and optics cmo experiment provide estimates of diapycnal and lateral dispersion microstructure observations made during these experiments showed patchy turbulence on vertical scales of 1 10 m and horizontal scales of a few hundred meters to a few kilometers momentum scaling and a simple random walk formulation were used to estimate the effective lateral dispersion caused by motions resulting from lateral adjustment following episodic mixing events it is predicted that lateral dispersion is largest when the scale of mixed patches is on the order of the internal rossby radius of deformation which seems to have been the case for cmo for parameter values relevant to cmo lower bound estimates of the effective lateral diffusivity by this mechanism ranged from 0 1 to 1 m 2 s 1 revised estimates after accounting for the possibility of long lived motions were an order of magnitude larger and ranged from 1 to 10 m 2 s 1 the predicted dispersion is large enough to explain the observed lateral dispersion in all four cmo dye release experiments examined

mixing in the main thermocline abstract a series of profiles of velocity microstructure along 152 e in the western north pacific ocean were collected in may june 1982 large averaged turbulent dissipation rates found in the main thermocline 400 to 1000 m were determined by a combination of large independent estimates of and a greater rate of occurrence of turbulent events in the main thermocline than elsewhere concurrently we find that averaged values of exhibit a positive dependence on the buoyancy frequency n and that form an is best fit by 1 when only the data below 400 m are considered of the more than 5000 m of data collected below 1000 m depth 12 showed measurable turbulence and dominated the depth averages a deep ocean estimate of an upper bound to the eddy coefficient for vertical diffusion k is 10 4 m2 s 1 and not significantly different from the value estimated by munk the inferred dependence of the mass flux with depth indicates the relative significance of vertical mixing in the main thermocli

coastal boundary layer characteristics during summer stratification in lake ontario abstract simultaneous measurements of eulerian and lagrangian currents along the north shore of lake ontario are analyzed to provide the mean flow properties and horizontal turbulent exchange characteristics in the coastal boundary layer cbl the summer coastal boundary layer is characterized by a frictional boundary layer fbl of a width of 3 km in which shore and bottom friction affects the flow in this regime the currents are predominantly shore parallel and persistent the outer boundary layer also called an inertial boundary layer ibl typically of the order of 5 6 km wide is a consequence of the adjustment of inertial oscillations to the lateral boundary during the summer season within the cbl the current motions are associated with thermocline displacements the eastward westward wind stress causes thermocline elevation depression causing upwelling downwelling the mean subsurface westward currents associated with downwelling events are typically stronger in comparison to weak east

a basinwide estimate of vertical mixing in the upper pycnocline spreading of bomb tritium in the north pacific ocean abstract the vertical diffusivity kv in the upper half kilometer of the north pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium the calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s the data coverage does not permit detailed mapping of tritium penetration especially in the sparsely sampled western pacific for this reason and to minimize advective effects the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning 5 n to 40 n the result kv 1 5 0 7 10 5 m2 s 1 is consistent with inferences from microstructure and purposefully released tracer measurements in the north atlantic confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical munk estimate for the lower pycnocline

parameter sensitivity of primitive equation ocean general circulation models abstract experiments with a low resolution primitive equation ocean general circulation model with idealized basin geometry and surface forcing have been carried out in order to identify the processes controlling the climatically important aspects of the circulation emphasis was placed on the sensitivity of the model solutions to the magnitude of the vertical diffusivity scaling arguments suggest and the numerical experiments confirm that the solutions are most sensitive to the magnitudes of the wind stress curl and the vertical diffusivity for small vertical diffusivity wind forcing dominates the solution the vertical scale of the thermocline is set by the strength of the ekman pumping and there is a multiple gyre circulation in the upper layers for large vertical diffusivity diabatic surface forcing dominates the solution vertical diffusion controls the vertical scale of the thermocline and there is a single large anticyclonic gyre in the upper layers both the meridionally and zonally inte