five years of florida current structure and transport from the royal caribbean cruise ship explorer of the seas 1 using ship of opportunity platform explorer of the seas five years of full depth velocity data have been collected across the florida straits at 26 n between may 2001 and may 2006 the mean transport of the florida current was 31 0 4 0 sv this compares to a mean transport of 32 4 3 2 sv inferred from cable voltages at 27 n over the same period implying an average 1 4 sv transport into the straits through the northwest providence channel the climatological core of the florida current is 170 cms 1 and is positioned at 79 8 w about 10 km east of the shelf break the largest variability in velocity occurs over the shelf and shelf break and is likely related to shelf waves a secondary maximum occurs across much of the straits over the top 100 m of the water column and may be associated with wind events the annual cycle of florida current transports has a range of 4 7 sv with a maximum in may june july and a minimum in january the difference between the summer and winter current structure appears as a first baroclinic mode with zero crossing at 150 m the maximum difference is about 15 cms 1 at the surface and is centered just offshore of the mean current core on interannual timescales low pass filtered explorer and cable transports show similar downward trends between 2002 and 2005 but diverge over the last year or so of the record

influence of porewater advection on denitrification in carbonate sands evidence from repacked sediment column experiments abstract porewater flow enhances mineralization rates in organic poor permeable sands here a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from heron island great barrier reef experimental conditions flow path length advection rate and temperature were manipulated to represent conditions similar to near shore tropical environments hgcl2 poisoned controls were used to assess whether reactions were microbially mediated overall significant correlations were found between oxygen consumption and n2 production the n o2 slope of 0 114 implied that about 75 of all the nitrogen mineralized was denitrified a 4 fold increase in sediment column length from 10 to 40 cm resulted in an overall increase in oxygen consumption 1 6 fold tco2 production 1 8 fold and denitrification 1 9 fold oxic respiration increased quickly until advection reached 80 l m 2 h 1 and then plateaued at higher advection rates interestingly denitrification peaked up to 336 mol n2 m 2 h 1 at intermediate advection rates 30 80 l m 2 h 1 we speculate that intermediate advection rates enhance the development of microniches i e steep oxygen gradients within porous carbonate sands perhaps providing optimum conditions for denitrification the denitrification peak fell within the broad range of advection rates often on scales of 1 100 l m 2 h 1 typically found on continental shelves implying that carbonate sands may play a major but as yet unquantified role in oceanic nitrogen budgets

the importance and challenge of hyporheic mixing the hyporheic zone is the interface beneath and adjacent to streams and rivers where surface water and groundwater interact the hyporheic zone presents unique conditions for reaction of solutes from both surface water and groundwater including reactions which depend upon mixing of source waters some models assume that hyporheic zones are well mixed and conceptualize the hyporheic zone as a surface water groundwater mixing zone but what are the controls on and effects of hyporheic mixing what specific mechanisms cause the relatively large 1m mixing zones suggested by subsurface solute measurements in this commentary we explore the various processes that might enhance mixing in the hyporheic zone relative to deeper groundwater and pose the question whether the substantial mixing suggested by field studies may be due to the combination of fluctuating boundary conditions and multi scale physical and chemical spatial heterogeneity we encourage investigation of hyporheic mixing using numerical modeling and laboratory experiments to ultimately inform field investigations

current variability on a narrow shelf with large ambient vorticity signals respectively and with corresponding phase speeds of 0 85 and 1 7 m s 1 the phase trend in east west direction of the 10 hour signal is consistent with unstable growing waves the 10 and 27 hour signals appear dominantly barotropic near the coast out to depths of at least 50 m but the 10 hour signal displayed a 180 phase change between surface and bottom farther away from the shelf break at 160 m depth the two dominant signals cannot be attributed to barotropic instability index terms 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4572 oceanography physical upper ocean processes keywords shelf circulation florida current vorticity flow instability surface doppler radar

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

stochastic boundary conditions for coastal flow modeling 1 recent high resolution radar data of surface velocity between the florida current and the coast allow us for the first time to deduce coastal boundary conditions for ocean models based on observations a stochastic model is found to be a better choice for simulating properties of the observed vorticity than a model with deterministic boundary conditions a stochastic model parameterizing boundary conditions is developed and embedded in a simple quasigeostrophic ocean model comparison of numerical simulations of western boundary flow with stochastic boundary conditions against simulations with traditional no slip and free slip conditions reveals significant differences in the formation of coherent mesoscale structures and the energetics of the western boundary current coherent structures such as dipoles and submesoscale vortices can be generated using stochastic boundary conditions the boundary current variability becomes more energetic and episodic than quasi periodic circulation features in the simulations using the conventional boundary conditions

a multi proxy palaeolimnological study to reconstruct the evolution of a coastal brackish lake lough furnace ireland during the late holocene abstract this study examines the evolution of lough furnace a coastal brackish lake in the west of ireland using high resolution sensors in the water column and palaeolimnological examination of the sediment archive palaeoenvironmental reconstructions suggest that meromixis formed as a result of sea level rise prior to ca 4000 cal yr bp increased seawater inflow has progressively led to permanent water stratification which caused the onset of anoxia making the monimolimnion a harsh environment for biological life diatom floristic interpretations suggest a progressive upcore increase in salinity which is paralleled by a reduction in cladocera remains diagenetic processes have not altered the sediment organic matter signature organic matter mainly derives from freshwater doc and appears to be linked to the presence of peat bogs in the catchment as confirmed by the c n ratio upcore variations in the c n ratio with a ca 800 year periodicity have been interpreted as the result of alternating dry and wet climatic phases during the late holocene which appear synchronous with the nao and long term solar cycles the current hydrology is largely controlled by freshwater inflow which determines permanent meromictic conditions overturns are rare requiring a specific combination of factors such as exceptionally dry and warm summers followed by cool autumns according to the climate projections for the next century in ireland permanent meromictic conditions will probably continue

hydrochemical water evolution in the aral sea basin part i unconfined groundwater of the amu darya delta interactions with surface waters summary the aral sea which has been affected by lake level lowering of approximately 25 m and a salinity increase from 10 to 100 g l since 1963 represents along with the amu dary delta a dynamic hydrological system under an arid climate regime the system receives river water inflow at high seasonal and inter annual variability from remote alpine source areas in the amu darya delta there is a distinct salinity contrast between the low salinity river water 1 g l and the salinity of the unconfined gw gw unconf 10 95 g l the gw unconf levels are predominantly controlled by the seepage of the river water inflow and gw discharge into the shrinking aral sea in june 2009 and august 2009 we sampled water from various sources including surface waters gw unconf lake water and soil leachates for chemical analyses evaporative enrichment precipitation dissolution of gypsum and precipitation of calcite drive the gw unconf to an nacl so 4 water type presenting a positive correlation between na and so 4 we model the hydrochemical evolution of the gw unconf in a box model which considers the capillary rise of near surface gw the precipitation of minerals in the unsaturated horizon and the seasonal re flushing of adhesive residual brines and soluble salts the model documents a rapid increase in salinity over a few annual cycles furthermore the model simulations demonstrate the importance of the aeolian redistribution of soluble salts on the hydrochemical gw evolution in a lab experiment halite hexahydrite and starkeyite are precipitated during the late stages of evaporative enrichment from a representative local brine processes specific to different water compartments plausibly explain the variations of selected element ratios for example the precipitation of low sr calcite in irrigation canals and natural river branches of the delta lowers ca sr the dissolution of gypsum in soils ca sr mole ratio 150 and the possible precipitation of srso 4 associated with sr depletion in adhesive residual brines increases ca sr in seepage and re increases ca sr in the unconfined gw aral sea water which receives high ca sr surface and groundwater inflow developed due to continued precipitation of high ca sr calcite the almost lowest ca sr ratio 25 over time we observed spatial variations in the gw unconf composition i ammonium levels increase strongly due to interaction with lake sediments rich in organic matter and ii distinct increases in levels of nitrate u mo and se locally reflect oxygenation when gw levels decrease the amu darya delta acts as a sink for boron uptake via terrestrial vegetation and a source for bromide release by degradation of organically bound br our results concerning the hydrochemical evolution of the gw unconf and additional data from the aral sea constrain the parameter gw discharge in water budget models of the lake and improve the basis for palaeoclimatic interpretations of sediment records from the aral sea

influence of sediment permeability and mineral composition on organic matter degradation in three sediments from the gulf of aqaba red sea abstract in order to investigate the influence of sediment physical and chemical characteristics on the degradation of deposited organic matter decomposition in three sediments from the gulf of aqaba red sea that differ in permeability and mineral composition were compared freeze dried spirulina was added to coarse carbonate and silicate sands from a shallow nearshore region and silt clay sediment from the deeper center region of the gulf incubated in laboratory chambers the stirring in the chambers caused higher solute exchange in the coarse permeable sands relative to the fine less permeable silt due to the generation of advective fluid exchange between the sediment and overlying water this enhanced exchange increased the decomposition rates of organic matter in the incubated sands the decomposition rates of total organic carbon in the permeable carbonate 3 0 mg c m 2 d 1 and silicate sands 2 0 mg c m 2 d 1 exceeded that in the fine grained sediment 1 4 mg c m 2 d 1 oxygen consumption in the coarse sands was 3 fold higher than in the silt clay sediment with highest rates in the carbonate sand in carbonate and silicate sands of the same grain size the carbonate sediment was more permeable than the silicate resulting in 1 4 fold higher fluid exchange rates and 1 4 fold larger sedimentary organic matter mineralization rates an in situ experiment comparing trapping efficiencies in carbonate and silicate sands showed that the higher fluid exchange rate in the carbonate sand results in larger filtration rates and a faster accumulation of particulate organic matter from the boundary layer these experiments demonstrate that with respect to sedimentary mineralization rates higher transport rates in permeable coarse sediments can outweigh the effect of a higher specific surface area in fine grained silt sediments in permeable sands however the higher specific surface area and fluid exchange in biogenic carbonate sands result in higher mineralization rates than in silicate sands of the same grain size

advective transport affecting metal and nutrient distributions and interfacial fluxes in permeable sediments abstract our laboratory flume experiments demonstrate that advective porewater flows produce biogeochemical reaction zones in permeable sediments leading to specific and reproducible complex patterns of fe mn and nutrients oxygenated water forced into the sediment when boundary flows were deflected by protruding sediment structures generated distinct zones of nitrification and ferric iron precipitation this inflow was balanced by ammonium rich porewater ascending from deeper sediment layers thereby creating an anoxic channel where dissolved fe2 and mn2 could reach the surface between the zones of ferric iron precipitation and fe2 upwelling a layer with increased manganese oxide and solid phase fe ii concentrations formed indicating redox reaction between these components the establishment of topography on the previously smooth sediment surface reversed the net interfacial flux of solutes while the smooth control core was found to be a sink for metals and nutrients the sediment with mounds acted as a source for these substances our experiments show that in sandy sediment with an oxidised surface layer reduced metal species can be released to the water column by flow topography interactions we conclude that advective transport processes constitute an important process controlling biogeochemical zonations and fluxes in permeable sea beds

the negligible effect of bed form migration on denitrification in hyporheic zones of permeable sediments bed form celerity the migration rate of ripples along a sediment bed has previously been shown to have dramatic effects on oxygen distribution and transport within the hyporheic zone of permeable sediments this has the potential to influence denitrification rates in particular by increasing the coupling of nitrification and denitrification to further understand this we numerically modeled nitrogen cycling under migrating ripples while the simulated oxygen profiles match with expected behavior almost no effect on denitrification or coupled nitrification denitrification was observed with increasing celerity instead denitrification rates were dominantly controlled by the flow velocity of water overlying the sediment

benthic photosynthesis and oxygen consumption in permeable carbonate sediments at heron island great barrier reef australia abstract in order to investigate benthic photosynthesis and oxygen demand in permeable carbonate sands and the impact of benthic boundary layer flow on sedimentary oxygen consumption in situ and laboratory chamber experiments were carried out at heron island great barrier reef australia total photosynthesis net primary production and respiration were estimated to be 162 9 43 4 98 0 40 7 and 64 9 15 0 mmol c m 2 d 1 respectively din and dip fluxes for these sands reached 0 34 and 0 06 mmol m 2 d 1 respectively advective pore water exchange had a strong impact on oxygen consumption in the permeable sands consumption rates in the chamber with larger pressure gradient 20 rpm 1 2 pa between centre and rim simulating a friction velocity of 0 6 cm s 1 were approximately two fold higher than in the chambers with slow stirring 10 rpm 0 2 pa between centre and rim friction velocity of 0 3 cm s 1 in the laboratory chamber experiments with stagnant water column oxygen consumption was eight times lower than in the chamber with fast stirring laboratory chamber experiments with br tracer revealed solute exchange rates of 2 6 2 2 0 7 ml cm 2 d 1 at stirring rates of 20 10 and 0 rpm respectively in a laboratory experiment investigating the effect of sediment permeability on oxygen and dic fluxes a three fold higher permeability resulted in two to three fold higher oxygen consumption and dic release rates these experiments demonstrate the importance of boundary flow induced flushing of the upper layer of permeable carbonate sediment on oxygen uptake in the coral sands the high filtration and oxidation rates in the sub tropical permeable carbonate sediments and the subsequent release of nutrients and dic reveal the importance of these sands for the recycling of matter in this oligotrophic environment

effects of western boundary current dynamics on the internal wave field of the southeast florida shelf 1 shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces however this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate during the summers of 2003 and 2004 observational studies were conducted to examine the effects of a western boundary current the florida current tides and wind on the mean currents and internal wave field on the outer southeast florida shelf wavelet analyses of nonstationary shelf currents coupled with altimetry images of the straits of florida reveal the strong influence of florida current fluctuations on outer shelf flows local winds were found to be a small factor in flows on the outer shelf region and tidal forcing diurnal and semidiurnal accounted for less than a third of the total barotropic variance high frequency internal waves dominate the internal wave field and result in bottom intensified currents and strong shoreward mass transport we present evidence that suggests that the florida current plays as large a role in the determination of the high frequency internal wave field as tidal forces these observations and analyses show that it is necessary to include the forcing from the florida current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the southeast florida shelf

denitrification in shallow sublittoral gulf of mexico permeable sediments we examined nitrogen cycling over a 1 yr period in shallow sandy sediments at two contrasting sites near a barrier island in the northeastern gulf of mexico and we provide here the direct determination of dinitrogen gas n2 production at ambient nitrate concentrations in permeable marine sediments nitrogen stable isotope tracer techniques were used to quantify n2 production rates and pathways in sediment cores and slurries to simulate pore water advection the dominant transport process in the upper layer of the permeable sand beds intact sediment cores were perfused with aerated seawater this perfusion increased denitrification rates up to 2 fold in apalachicola bay sands and up to 17 fold in gulf of mexico sublittoral sands respectively relative to static cores seasonal n2 production rates were highest in spring and fall denitrified nitrate originated almost entirely from benthic nitrification at the exposed gulf site whereas water column nitrate dominated sedimentary denitrification at the sheltered bay site sediment incubations in stirred chambers were used to determine net fluxes of oxygen o2 n2 nitrate and ammonium across the sediment water interface during varied degrees of continuous pore water exchange rates of n2 efflux correlated with rates of pore water flow increasing from 0 12 mmol n m22 d21 under diffusion limited transport conditions up to 0 87 mmol n m22 d21 with pore water advection mineralized nitrogen was completely converted to n2 gas in gulf of mexico sediments our results demonstrate that advective pore water circulation will accelerate benthic n2 production by coupled nitrification denitrification and that substantial nitrogen loss occurs from coastal permeable sediments

breathing of a coral cay tracing tidally driven seawater recirculation in permeable coral reef sediments 1 coral reefs are characterized by high gross productivity in spite of low nutrient concentrations this apparent paradox may be partially reconciled if seawater recirculation in permeable sediments over large meters and long hours to days scales is an important source of recycled nitrogen and phosphorus to coral reefs in this paper we use radon 222rn a natural tracer to quantify tidally driven pore water or groundwater exchange between 1 an offshore coral cay island and its fringing reef lagoon and 2 a reef lagoon and the surrounding ocean as seawater infiltrates heron island at high tide it acquires a radon signal that can be detected when pore waters emerge from carbonate sands at low tide a nonsteady state model indicated that vertical pore water upwelling rates or saline submarine groundwater discharge were 40 cm d within the reef lagoon and 100 cm d outside the lagoon at low tide within the lagoon tidal pumping and temperature driven convection were the main driving forces of pore water advection at low tide the reef lagoon level is about 1 m higher than the surrounding ocean as a result a steep hydraulic gradient develops at the reef edge driving unidirectional filtration through the reef framework groundwaters were highly enriched in nitrate average of 530 mol likely influenced by bird guano relative to lagoon waters 1 9 mol rough but conservative estimates indicated that groundwater derived nitrate fluxes 7 9 mmol m2 d can replace the entire lagoon nitrate inventory every 19 days we speculate that as offshore coral islands breath inhale seawater at high tide and exhale groundwater at low tide they release nutrients that lead to sustained productivity within coral reefs

enhancement of denitrification in permeable carbonate sediment due to intra granular porosity a multi scale modelling analysis abstract it has recently been hypothesized that bulk denitrification rates in carbonate sands may be enhanced by reactions occurring in the intra granular pores cracks and crevices we tested this hypothesis using a series of flow and reactive transport models spanning from the pore scale mm to the continuum scales 10 cm bedforms pore scale simulations solved the coupled navier stokes and brinkman equations and represented flow through reactor experiments previously performed on coral reef sands the results revealed that intra granular transport and reactions can explain over all denitrification enhancement a sensitivity study with a single grain diffusive transport model showed that in the majority of cases the resultant increase in denitrification was not coupled to nitrification within a single grain only for large grain diameters of 2 and 4 mm was coupled nitrification denitrification important in most cases coupled nitrification denitrification instead arose as conditions became more reducing along a flow path as is the case in quartz sands without intragranular pores an intra granular reaction rate based on a single grain model was incorporated into a continuum scale darcy flow and reactive transport model for a rippled sand bed where porewater flow is driven by the turbulent current over the ripple the results of the darcy scale model suggest that intra granular pores increase the amount of slow flowing areas within which coupled nitrification denitrification can occur we conclude that the complex advective flow field does not strongly inhibit denitrification enhancement by carbonate sand grains as it does in silica sands thus intra granular reactions may enhance bulk denitrification in carbonate sediment with porous grains under natural advective conditions

pore water advection and solute fluxes in permeable marine sediments ii benthic respiration at three sandy sites with different permeabilities german bight north sea this contribution presents total oxygen uptake tou rates and nutrient fluxes of organically poor permeable shelf sands of the german bight measurements have been made in situ with the novel autonomous benthic chamber system sandy under controlled conditions of advective pore water exchange average oxygen consumption rates of 31 3 18 2 mmol m 2 d 1 measured in this study were relatively high as compared with rates reported from shelf sediments with much higher organic contents tou of highly permeable medium and coarse grained sands was substantially enhanced in the presence of advection this indicates that advective oxygen supply contributed significantly to respiration in these sediments and that advection has to be considered when assessing oxygen consumption and organic matter mineralization in shelf areas in fine grained less permeable sands no effect of advection could be measured a lower advective oxygen supply in these sediments is in agreement with a release of ammonium instead of nitrate and a shallower oxygen penetration depth scaled up to the entire german bight the results imply that in 40 of the area an effect of advection on benthic oxygen uptake and other advectionrelated processes can be largely excluded while in the remaining 60 significant pore water advection potentially takes place however because permeabilities of the sediments investigated in this study were widely spaced a significant effect on oxygen supply was only verified for highly permeable sands that are likely to cover approximately 3 of the area

mudflow gully characteristics formation and impact on reservoir heterogeneity a gas field in the yinggehai basin south china sea abstract mudflow gullies are well developed in offshore areas and on the upper deepwater slope in this paper we discuss the formation and characteristics of mudflow gullies in a gas field in the yinggehai basin along the northwestern south china sea margin and address their impacts on sand body distribution reservoir heterogeneity and hydrocarbon accumulation the geological setting and sedimentary characteristics indicate that the sedimentary environment of the study intervals is located in an area between lower shore face and offshore the gullies are several meters to a few tens of meters wide and are filled mainly with thick mudstones interbedded with thin siltstones gully fills show an overall fining upward depositional trend and exhibit a high value low amplitude linear gr wireline log shape mudflow gullies always incise the underlying sand bars or sand sheets are overlain by offshore shales and are therefore considered to have developed in a transgressive setting they are of three basic types i e deep moderate and shallow classes according to the incision depth the mudflows developed in offshore environment with rapidly varying topography and deeply cut the underlying sand bars in lower shore face environment influenced by diapiric events plastic mud rich sediments were apt to slump yielding the studied gullies gullies can converge to generate a lobe at front of them in particular during marine transgression due to the high depositional rate of muddy sediments and tectonic activity marine transgression offered the most favorable scenario for the development of these gullies the mudflows also slumped down the slope into the deep water areas of the basin because of the incision of mudflow gullies and transgressive wave ravinement from the southeast the pre existing sand bars on the lower shore face were reworked by waves and oriented in a ne sw direction perpendicular to the east shoreline to hainan island the sand bars were affected by the mudflow gullies and diapir faults often isolated from each other resulting in a weak sand connectivity vertically and laterally the degree of erosion of the sand bodies by mudflows decreases with depth in addition diapiric activity not only induces the formation of mudflow but also causes co2 in the deep buried intervals to migrate into gas reservoir attached by faults the mudflow gullies are important causes of gas reservoir compartmentalization co2 filling process and gully development in the area resulted in more heterogeneity than the areas without them therefore mudflow gullies control not only the reservoir compartments but also the gas content in the reservoir

quantifying denitrification in rippled permeable sands through combined flume experiments and modeling we measured denitrification in permeable sediments in a sealed flume tank with environmentally representative fluid flow and solute transport behavior using novel measurements numerical flow and reactive transport models representing the flume experiments were implemented to provide mechanistic insight into the coupled hydrodynamic and biogeochemical processes there was broad agreement between the model results and experimental data the model showed that the coupling between nitrification and denitrification was relatively weak in comparison to that in cohesive sediments this was due to the direct advective transport between anoxic pore water and the overlying water column and little interaction between the mostly oxic advective region and the underlying anoxic region denitrification was therefore mainly fueled by nitrate supplied from the water column this suggests that the capacity of permeable sediments with nonmigratory ripples to remove bioavailable nitrogen from coastal ecosystems is lower than that of cohesive sediments we conclude that while experimental measurements provide a good starting point for constraining key parameters reactive transport models with realistic kinetic and transport parameters provide critical insight into biogeochemical processes in permeable sediment that are difficult to experimentally evaluate

small scale permeability heterogeneity has negligible effects on nutrient cycling in streambeds 1 aquatic sediment hosts coupled pore water flow and biogeochemical reactions that mediate water quality across the fluvial corridor including adjacent alluvial aquifers however the effect of small scale variations in sediment hydraulic properties on nutrient transformation occurring within the sediment is poorly understood we show through numerical flow and transport simulations for two realistic heterogeneous permeability cases typical of lowland rivers and two idealized homogeneous ones that there is little difference in the reactive transport fields the bulk reaction rates and nutrient sink source function despite stark differences in flow fields this is because the reactions are ultimately controlled by characteristic or bulk residence times that are similar for the heterogeneous and homogeneous cases this is a promising result for predictive models based solely on relative ratios of residence times and reactive time scales

the role of eddies inside pores in the transition from darcy to forchheimer flows 1 we studied the role of intra pore eddies from viscous to inertial flows in modifying continuum scale flow inside pores flow regimes spanning reynolds numberre 0 to 1350 are divided into three zones one zone follows darcy flow and the other two zones describe non darcy or forchheimer flow during viscous flows i e re 1 and their growth leads to the deviation from darcy s law and the emergence of forchheimer flow manifested as a characteristic reduction in the apparent hydraulic conductivity ka the reduction in ka is due to the narrowing of the flow channel which is a consequence of the growth in eddies the two zones of forchheimer flow correspond to the changes in rate of reduction in ka which in turn are due to the changes in eddy growth rate since the characteristics of forchheimer flow are specific to pore geometry our results partly explain why a variety of forchheimer models are expected and needed for different porous media

energetic baroclinic super tidal oscillations on the southeast florida shelf 1 historical and recent data reveal a very energetic regime on the shelf off southeast florida in addition to spin off eddies large amplitude tidal velocity fluctuations with amplitudes exceeding 0 5 ms 1 are observed recent exploratory measurements conducted as a part of the south florida ocean measurement center sfomc show that the time scale of these oscillations is about 10 hrs this period does not coincide either with the inertial period 27 hrs or with the semidiurnal m2 12 42 hrs or s2 12 hrs tidal constituents in addition these internal oscillations appear to be modulated seasonally a possible explanation is that these oscillations are near resonant internal seiches generated by barotropic tidal wave in the channel between florida and bahamas

spatial and temporal variability of internal wave forcing on a coral reef the deployment of a dense spatial array of temperature sensors on a coral reef in the florida keys provided a unique view of the interaction of cool water incursions generated by internal waves with the three dimensional reef bathymetry water temperature on the reef surface was sampled every 5 s at 100 points on a 100 m by 150 m grid with concomitant measurements of water column velocity and temperature from mid may through mid august 2003 episodic incursions of cool subsurface water were driven by periods of strong semidiurnal internal tide and higher frequency internal wave activity for every time step in the data record the mean profile of temperature as a function of depth is calculated with a 3 m vertical averaging length scale subtracting this mean profile from the raw record yields a within depth horizontal temperature anomaly visualization through time of the anomaly mapped onto the measured reef bathymetry reveals episodic variability of thermal patchiness across the reef as well as persistent features associated with reef bathymetry variation in the nature of the cooling and resulting thermal heterogeneity among events and seasons suggests multiple modes of cool water incursion ranging from unbroken tidal period internal waves to packets of higher frequency energetic broken internal bores

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter