Hydrographic Distributions Research Articles

A general unit hydrograph distribution and its application on the marginal distribution of global wind speed

We here introduce a simple, general, and analytical method based on the general unit hydrograph (GUH) theory proposed by Guo (2022a, 2022b, 2022c) to describe wind speed marginal distribution. Wind speed probability is generally described by the Weibull distribution; however, its accuracy depends on the contribution made by null wind speed (owing to its zero initial condition). To overcome this disadvantage, we propose a three-parameter GUH distribution with significant flexibility in modeling symmetric heavy-tailed distributions as well as skewed distributions. We show that our proposed GUH distribution corresponds to a generalized logistic distribution that contains both type I and type II generalized logistic distributions. The shape properties of the GUH distribution are discussed along with a simple method for estimating parameters by means of least squares methods. The flexibility of the proposed GUH distribution was assessed by applying it to a well reconstructed global gridded wind speed dataset. Subsequently, we quantify the changes caused by a reversal in global surface wind speed stilling using our GUH distribution. Finally, we confirm that our proposed GUH model agrees with reconstructed wind speed data better than conventional Weibull distribution models, which suggests that the new distribution can be a useful tool for sustainable development of wind energy.

Estudio hidromorfológico de la cuenca efímera Maconta con relación al riesgo de inundaciones repentinas.

Es importante dar a conocer que la presente investigación comprende analizar las características morfométricas e hidrológicas de la cuenca efímera de Maconta, a través de parámetros generales, de forma, relieve y red de drenaje con el software (QGIS). Es importante también evaluar mediante una modelación cuya interpretación será con periodos de retorno (tr), los cuales se realizará con datos de precipitación del (INAMHI), realizando un modelo de simulación hidrológica con datos periodicos se obtendrá resultados en el que se logra determinar el comportamiento del cauce fluvial. Con la ayuda del programa de modelo hidrológico HEC-HMS, está herramienta es utilizada para la gestión y manejo de los recursos hídricos, que en sus resultados busca representar los procesos de distribución hidrológica, hidrográfica.

Territorialização do agronegócio no estuário amazônico e re-existência camponesa: estudo de caso na Ilha do Capim, Abaetetuba/PA

Na região do Baixo Tocantins, especificamente no Município de Barcarena/PA, o agronegócio vem se territorializando de forma a criar um centro hidroviário de distribuição de commodities para o mundo. Este trabalho tem como objetivo pautar quais são as ações do agronegócio na Ilha do Capim e seus arredores e demonstrar quais as estratégias de luta dos ribeirinhos. Foram utilizados os seguintes métodos: entrevistas históricas, observação participante e oficina para análise de conflitos socioambientais. Verificou-se que, na percepção dos ribeirinhos, a principal estratégia utilizada pelo grupo do agronegócio é fundamentada na propagação do discurso de desenvolvimento. Outras estratégias utilizadas foram a tentativa de compra de terra na Ilha do Capim, o que é ilegal, segundo o § 2º do Art. 59. da instrução normativa Nº 97 de 17 de dezembro de 2018, e o não reconhecimento, por parte das empresas, dos ribeirinhos como sendo povos e comunidades tradicionais. Consideramos que os ribeirinhos percebem as estratégias do agronegócio como um jogo de ações articuladas, com diversos sujeitos institucionais ou individuais para efetivar a territorialização desse modelo econômico na região. Por sua vez, os povos e comunidades tradicionais promovem iniciativas que afirmam o direito de permanência em seus territórios, como que esses territórios tenham capacidade de promover suas funções para quem nele se territorializa.

The impact of monsoon winds and mesoscale eddies on thermohaline structures and circulation patterns in the northern South China Sea

We deployed 5 pressure-recording inverted echo sounders (PIES) along a section in the northern South China Sea (NSCS), and estimated well the distributions of temperature, salinity and velocity across the section. Applying the empirical orthogonal function (EOF) method, we found that variability of the estimates is dominated by two modes: one named the seasonal mode affecting strongly on the hydrographic distribution with explained variability of temperature/salinity by 62.9/72.2%; the other named the eddy mode, corresponding to the arrival of mesoscale eddies, affecting strongly on the circulation pattern with explained variability of velocity by 63.2%. Temporal variation of the seasonal mode is highly correlated with the monsoon winds southeast of Vietnam, suggesting a nonlocal forcing mechanism. Case studies looking at the structures and evolutions of three captured eddies, whose impacts were well quantified by the eddy mode. The monsoon (eddies) significantly affects temperature, salinity and velocity shallower than 635m (860m), 160m (150m) and 1055m (920m), respectively. The monsoon (eddies) can induce maximum temperature, salinity and velocity anomalies up to −1.6 to 2.1°C (−2.5 to 2.2°C), −0.11 to 0.14psu (−0.13 to 0.27psu) and −0.31 to 0.46m/s (−0.40 to 0.38m/s), respectively. Mean volume transport (VT) across the section is 1.0Sv (1Sv=1×106m3s−1, positive to the northeast). Seasonal VT (with eddy impacts removed) is −4.6Sv, 11.4Sv, −5.1Sv and −4.1Sv for spring, summer, autumn and winter, respectively.

Controlling factors of summer phytoplankton community in the Changjiang (Yangtze River) Estuary and adjacent East China Sea shelf

We analyzed the composition and distribution of phytoplankton in relation to physicochemical factors in the Changjiang (Yangtze River) Estuary and adjacent East China Sea shelf in June and August 2009. Diatoms and dinoflagellates dominated the community, particularly in eutrophic inshore waters controlled by the Changjiang Diluted Water (CDW), coastal current, and upwelling. However, high densities of cyanobacteria and cryptophytes were observed in the oligotrophic offshore waters influenced by the Taiwan Warm Current (TWC) and Kuroshio. In June, the northeastward CDW plume combined with the Yellow Sea Coastal Current induced algal bloom in the northern part of the CE. In August, the enhanced CDW formed two narrow, low-salinity tongues that extended eastward and southward (associated with the upwelling and coastal current), resulting in phytoplankton blooms off the CE and in the Zhejiang coastal waters, respectively. Phytoplankton abundance in August was considerably higher than in June, with increased solar radiation, CDW, and upwelling. The maximum abundance occurred on the surface in inshore turbid waters and on the subsurface (5–30m) in offshore clear waters with increased stratification. Based on multidimensional scaling and cluster analysis, we found appreciable spatio-temporal variations in algal community composition. Different ecological groups corresponded with hydrographic distributions. Canonical correspondence analysis showed that nutrients, salinity, temperature, and suspended particulate matter were the main variables associated with community distribution. We suggest that the variations in summer phytoplankton community are highly correlated with the significant monthly and spatial variability in physicochemical properties, which are primarily controlled by the CDW and TWC.

A high-resolution modeling study of the Western Iberian Margin mean and seasonal upper ocean circulation

The mean seasonal hydrography and circulation of the Western Iberian Margin (WIM) are studied by means of a high-resolution configuration of the Regional Oceanic Modeling System. A comparison of 5-year model averages for January and July with climatological datasets shows a general good agreement in the reproduction of the mean water mass properties and hydrographic distribution. We find that there is a prevailing tendency for slope poleward flow at about 80–100 km offshore at all latitudes from the surface to 1,500 m with strong vertical coupling. This northward flow, which is mainly along slope and amounts up to 8–10 cm s−1, exhibits several mean flow recirculation regions on its way and evidences of an offshore pathway of poleward flow. Transports at different zonal sections further confirm the poleward flow tendency with two peaks of poleward transport in summer (3–10 Sv) and winter (2–7 Sv). The transport time series emphasize the seasonal character of the alongshore circulation and the interannual intrinsic variability of the circulation, since the forcing fields are climatological. As a conceptual essay with the purpose of assessing the Mediterranean Water flow influence on the WIM mean circulation, a second model configuration is setup, where the Mediterranean outflow into the study domain is removed. We find that there is an attenuation of the mesoscale field, but the slope poleward flow intensifies and remains as a mean dynamical feature closer to the upper slope.

Storm-induced circulation in the Pearl River Estuary of China during super Typhoon Koryn

This study presents a numerical investigation of storm-induced circulation and hydrographic distributions over the Pearl River Estuary (PRE) in South China's Guangdong Province during super Typhoon Koryn in June 1993. The nested-grid modelling system used in this study has three downscaling subcomponents: an outer-most sub-model with a coarse horizontal resolution of ∼7 km for simulating surface elevations and depth-mean currents forced by wind and tides over China Seas from Bohai Sea to the northern South China Sea; and an inner-most sub-model with a fine resolution of ∼1.2 km for simulating the three-dimensional estuarine circulation and hydrographic distributions in the PRE and adjacent waters. A parametric vortex is inserted into the coarse-resolution (0.5°) numerical weather forecast products to better represent the atmospheric pressure and wind stress associated with Koryn. Model results demonstrate that large surface elevations and intense surface currents are generated over the area of influence of the storm. Lagrange velocities of near-surface particles are also used to examine the effect of the storm on the movements and dispersion of near-surface particles over the study region.

Biogeo-optical modeling of SPM in the St. Lawrence Estuary

Optical and chemical measurements were obtained in the St. Lawrence Estuary during spring of 2000 and 2001 to develop three biogeo-optical models for estimating concentration of suspended particulates (SPM) in optically complex waters where light absorption in the visible range is dominated by coloured dissolved organic matter (CDOM). SPM was computed from remote sensing reflectance (Rrs) calculated at 670 and 550 nm (SPM = 50.35 [Rrs(670)/ Rrs(555)]2.03) and corrected using a linear function related to the absorption coefficient of CDOM measured at a wavelength of 412 nm (aCDOM(412)). The resulting CDOM-unbiased estimates of SPM had an uncertainty of ± 40%, a major improvement with respect to uncorrected measurements (relative error up to 85%) or theoretical calculations assuming a constant SPM and a variable aCDOM(412) (up to 400%). Spatial patterns of unbiased SPM derived from SeaWiFS (Sea-viewing Wide Field-of-view Sensor) during spring 1998 were consistent with general trends previously described based on shipboard data. Satellite observations also highlighted the important association between hydrographic features and horizontal distribution of suspended solids in surface waters of the Estuary.

Investigation of three-dimensional circulation and hydrography over the Pearl River Estuary of China using a nested-grid coastal circulation model

The Pearl River Estuary (PRE) in South China's Guangdong Province is a subtropical estuary with highly irregular topography and dynamically complicated circulations. A nested-grid coastal circulation modelling system is used in this study to examine dynamic responses of the PRE to tides, meteorological forcing and buoyancy forcing. The nested-grid modelling system is based on the Princeton Ocean Model and consists of three downscaling subcomponents: including an outer-most model with a coarse horizontal resolution of ~7 km for simulating tidally forced and wind-driven surface elevations and depth-mean currents over the China Seas from Bohai Sea to the northern South China Sea and an innermost model with a fine resolution of ~1.2 km for simulating the 3D coastal circulation and hydrography over the PRE and adjacent coastal waters. Model results during the winter northeast monsoon surge in January and super typhoon Koryn in June of 1993 are used to demonstrate that the 3D coastal circulation and hydrographic distributions in the PRE are affected by tides, winds and buoyancy forcing associated with river discharge from the Pearl River with significant seasonal and synoptic variabilities.

High-resolution surveys of the biogeochemistry of the New England shelfbreak front during Summer, 2002

We present the observations from a pair of field experiments at the New England shelfbreak front in June and August of 2002, each consisting of 14 cross-frontal surveys using the Lamont Pumping SeaSoar. Measurements of the front's physical, chemical, and bio-optical characteristics were made at high spatial and temporal resolution. The front, based on water-column hydrographic distributions, was found within a few km of the 200 m isobath during both cruises. We present here composite sections, based on averages of individual sections shifted in space to a common frontal location, of the cross-frontal distributions of these properties as a measure of the mean state of the front in both June and August. The observations show the familiar temperature, salinity, and density distributions of the summertime front, dominated by surface thermal heating. Nutrient and bio-optical distributions show the combined effects of water-mass exchange and biological processes. T, S, silicate, and phosphate distributions are suggestive of cross-frontal exchange of slope- and shelf waters, although transport mechanisms and pathways are not apparent. These properties, along with nitrate and optical measures of the suspended particle distributions, show vertical displacements of isopleths as the front is approached: property contours slope upwards toward the front from the shoreward side, and downwards toward the front from the seaward side. Again, actual water-movement pathways are not constrained by these suggestive patterns. Bio-optical distributions show elevated indicators of photosynthetic efficiency both seaward and shoreward of the front, but the front itself is a minimum in biomass. Accumulation of photosynthetic biomass appears to be controlled primarily by nitrate scarcity in waters within and above the pycnocline. At the base of the pycnocline, light limitation appears to be the controlling factor, although the base of the euphotic zone is deeper than the biomass maxima and the base of the pycnocline. Mechanisms explaining this phenomenon are unclear, but tenuous evidence suggests low stratification at the depth of the 1% light level may not allow phytoplankton to optimize for the low-light, high-nutrient conditions at depth. Cross-frontal differences in nutrient and bio-optical parameters, particularly in August, suggest distinct phytoplankton assemblages, and the presence of calcite-forming or nitrogen fixing groups to the community structure, especially in very shallow waters across the front and in pycnocline waters seaward of the front.

Process study of coastal circulation over the inner Scotian Shelf using a nested-grid ocean circulation model, with a special emphasis on the storm-induced circulation during tropical storm Alberto in 2006

This study examines main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the inner Scotian Shelf (ISS) in June and July 2006 using a nested-grid coastal ocean circulation modeling system known as the NCOPS-LB. The nested-grid system has five relocatable downscaling submodels, with the outermost submodel of a coarse horizontal resolution of (1/12)° for simulating storm surges and barotropic shelf waves over the Eastern Canadian shelf and the innermost submodel of a fine resolution of ∼180 m for simulating the 3D coastal circulation and hydrography over Lunenburg Bay of Nova Scotia in the default setup. The NCOPS-LB is driven by meteorological and astronomical forcing and used to study the storm-induced circulation over the ISS during tropical storm Alberto. Model results demonstrate that the coastal circulation and hydrographic distributions over the ISS are affected significantly by tides, local wind forcing, and remotely generated coastal waves during the study period.

Reverse vertical migration and hydrographic distribution of Anomalocera ornata (Copepoda: Pontellidae) in the US South Atlantic Bight

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 268:195-204 (2004) - doi:10.3354/meps268195 Reverse vertical migration and hydrographic distribution of Anomalocera ornata (Copepoda: Pontellidae) in the US South Atlantic Bight Patricia A. Tester1, Jonathan H. Cohen2, Guillermo Cervetto1 1Center for Coastal Fisheries and Habitat Research, National Ocean Service, NOAA, 101 Pivers Island Road, Beaufort, North Carolina 28516, USA 2Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, North Carolina 28516, USA *Email: pat.tester@noaa.gov ABSTRACT: The vertical and horizontal abundance of juvenile and adult stages of the pontellid copepod Anomalocera ornata was determined on cruises of the ŒOregon II¹ during February 1991 and 1994 at coastal, shelf and Gulf Stream-influenced stations in Onslow Bay, North Carolina, USA. The presence and patterns of diel vertical migration (DVM) in this species, as well as its hydrographic habitat, were inferred from these data. Juveniles exhibited twilight vertical migration with residence in the upper water column at night, whereas adults had a reverse vertical migration pattern with residence in surface water during the day. The hydrographic distribution of A. ornata is primarily limited to the colder waters of coastal and shelf regions, with very few copepods present in warmer water influenced by the Gulf Stream. Given the hydrographic structure of Onslow Bay during the winter months, undergoing any DVM pattern could aid in retaining this species inshore. KEY WORDS: Diel migration · Frontal zone · Horizontal and vertical abundance Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 268. Online publication date: March 09, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

A mid-twentieth century reduction in tropical upwelling inferred from coralline trace element proxies

The Cariaco Basin is an important archive of past climate variability given its response to inter- and extratropical climate forcing and the accumulation of annually laminated sediments within an anoxic water column. This study presents high-resolution surface coral trace element records ( Montastrea annularis and Siderastrea siderea) from Isla Tortuga, Venezuela, located within the upwelling center of this region. A two-fold reduction in Cd/Ca ratios (3.5–1.7 nmol/mol) is observed from 1946 to 1952 with no concurrent shift in Ba/Ca ratios. This reduction agrees with the hydrographic distribution of dissolved cadmium and barium and their expected response to upwelling. Significant anthropogenic variability is also observed from Pb/Ca analysis, observing three lead maxima since 1920. Kinetic control of trace element ratios is inferred from an interspecies comparison of Cd/Ca and Ba/Ca ratios (consistent with the Sr/Ca kinetic artifact), but these artifacts are smaller than the environmental signal and do not explain the Cd/Ca transition. The trace element records agree with historical climate data and differ from sedimentary faunal abundance records, suggesting a linear response to North Atlantic extratropical forcing cannot account for the observed historical variability in this region.

Ecology Ditch: A Best Management Practice for Storm Water Runoff Mitigation

A full-scale physical model of a modified infiltration trench was constructed to test a new storm water best management practice called an ecology ditch. The ditch was constructed using compost, sand, and gravel, and a perforated drain pipe. A series of 14 tests were conducted on the physical model. The tests controlled rainfall application and overland roadway runoff amounts and monitored outflow from the discharge pipe. The objectives were to increase the time to peak and reduce the peak discharge coming out of the pipe. The results were also used to calibrate a modified existing unsaturated two-dimensional groundwater flow code. After the code was calibrated, computer simulations were performed to determine the effects of storm size, rainfall distribution, constant rainfall application, media type, initial conditions, and the physical size of the ecology ditch. The simulations used 24-hour duration storm sizes of 0.64, 1.27, 2.54, 3.81, 5.08, and 6.35 cm (0.25 to 2.5 in.). Peak reduction was found to depend greatly on input hydrograph distribution and the ability of the soil to store water. In turn, the storage in the soil was found to be dependent on the intensities of the input hydrograph. The peak delay time for larger storms was quantifiable since it depended on the saturated hydraulic conductivity and the distance of the flow path. For larger storms, the ecology ditch managed a peak reduction in the range of 10 to 50%.

On subinertial oscillations trapped by the Juan de Fuca Ridge, northeast Pacific

Spectra of currents measured along the 2100 m deep Juan de Fuca Ridge in the northeast Pacific have prominent tidal, inertial, and weather‐band (3–7 day period) spectral peaks. The weather‐band peak, in particular, has a number of interesting features. It is strongest in close lateral proximity to the ridge and strongest near ridge depth; intensification near the ridge is characteristic of trapped motion. Spectral peak intensities vary seasonally, with largest amplitudes occurring in autumn and winter; seasonal variation suggests that surface weather is forcing flow at depth. Together, trapping and seasonality indicate opportunistic amplification of oscillatory motion at the ridge. At all frequencies, forcing, topography, and stratification together shape current and hydrographic distributions near the ridge. Effects of those interactions for subinertial motion are quantified here using a primitive equation numerical model. Forcing period (1–10 days) and friction are the principal dependencies examined. Results show that flow over the Juan de Fuca Ridge can be amplified by factors of 3–4 for diurnal and up to a factor of 7 for weather‐band frequencies. Amplification is ridge trapped, with effects extending many hundreds of meters upward and extending 5–10 km laterally for 5‐day‐period flow; the strength and area of amplification increase with increasing period over the 1‐ to 10‐day‐period band. Oscillatory weather‐band flow leads to vertical velocities on the order of 0.3 cm s−1 on ridge flanks, which in turn cause periodic temperature (T) and salinity (S) variations with amplitudes of as much as 0.05°C and 0.01 practical salinity units, respectively. The vertical motion and consequent vertical displacement (>100 m) lead to isotherms that plunge below the crest alternately each side of the ridge, a distribution observed in conductivity‐temperature‐depth transect data. Near the ridge crest, cross‐ridge baroclinic pressure gradients caused by cyclically plunging isopycnals are in near‐geostrophic balance with the Coriolis force associated with along‐ridge flow. Along‐ridge current amplification is therefore closely tied to isopycnal movement up and down ridge flanks. Since weather‐band oscillations lead to much larger cross‐ridge baroclinic pressure gradients than do diurnal motions of the same amplitude, weather‐band forcing causes greater along‐ridge current amplification. Results vary strongly with forcing period and direction of forcing with respect to the ridge but depend only moderately on friction and turbulent mixing coefficients.

Predation risk on larval gadids by pelagic fish in the Georges Bank ecosystem. I. Spatial overlap associated with hydrographic features

We investigated the relationship between hydrographic variables on Georges Bank and the spatial distribution of larval Atlantic cod (Gadus morhua), larval haddock (Melanogrammus aeglefinus), and two planktivorous fish, Atlantic herring (Clupea harengus) and Atlantic mackerel (Scomber scombrus). We conducted cruises during April-May of 1990, 1994, and 1995 to document spatial distributions and employed logistic regression and a spatial-overlap index to assess relationships between hydrographic variables, spatial distributions and spatial overlap between gadid larvae and planktivorous fish. Cod larvae were more abundant in shallow well-mixed areas, while both haddock larvae and herring were more abundant in stratified areas. Atlantic mackerel occurred in deeper water and had little spatial overlap with the other species. In 1995, the presence of Scotian Shelf water and an intrusion of continental slope water altered temperature and salinity distributions and increased spatial overlap between cod larvae and herring. The stratified areas offer a higher concentration of prey for larval haddock, however there is increased exposure to planktivorous fish predators, creating a potential trade-off between predation and starvation. Due to the high abundance of planktivorous fish and high spatial and temporal overlap, predation is likely an important factor influencing survival of gadid larvae on Georges Bank.

The US Southern Ocean Joint Global Ocean Flux Study: an introduction to AESOPS

The United States Southern Ocean Joint Global Ocean Flux Study (JGOFS), also known as AESOPS (Antarctic Environment and Southern Ocean Process Study), focused on two distinct regions. The first was the Ross-Sea continental shelf, where a series of six cruises collected a variety of data from October 1996 through February 1998. The second area was the southwest Pacific sector of the Southern Ocean, spanning the Antarctic Circumpolar Current (ACC) at ∼170°W. Data were collected within this region during five cruises from September 1996 through March 1998, as well as during selected transits between New Zealand and the Ross Sea. The first results of these cruses are described in this issue. The Ross-Sea investigation extensively sampled the area along 76°30′S to elucidate the temporal patterns and processes that contribute to making this one of the Antarctic's most productive seas. Hydrographic distributions confirm that stratification is initiated early in October within the polynya, generating an environment that is favorable for phytoplankton growth. Significant spatial variations in mixed-layer depths, the timing of the onset of stratification, and the strength of the stratification existed throughout the growing season. Nutrient concentrations reflected phytoplankton uptake, and reached their seasonal minimal in early February. Chlorophyll concentrations were maximal in early January, whereas productivity was maximal in late November, which reflects the temporal uncoupling between growth and biomass accumulation in the region. Independent estimates of biogenic export suggest that majority of the flux occurred in late summer and was strongly uncoupled from phytoplankton growth. The ACC region exhibited seasonal changes that in some cases were greater than those observed in the Ross Sea. Sea ice covered much of the region south of the Polar Front in winter, and retreated rapidly in late spring and early summer. Mixed layers throughout the region shoaled in summer due to surface heating, while the addition of freshwater from melting sea ice enhanced stratification in the Seasonal Ice Zone, creating conditions favorable for phytoplankton growth. For example, silicic acid concentrations decreased from initial values as high as 65 to less than 2 μM within approximately 100 km (from 65.7 to 64.8°S). Fluorescence values, however, showed less than a two-fold variation over the same distance. The vertical flux of carbon in the Polar Front area is substantial, and marked variations in the composition of exported material exited over the region. The results provide a means whereby the controls of phytoplankton growth and organic matter flux and remineralization can be analyzed in great detail. Additional results of the AESOPS project are discussed.

On the Hydrographic Distribution in the Source Region of the Delaware Coastal Current

The buoyant discharge from Delaware Bay forms two separate branches of residual outflow near the bay mouth, one along each shore. Upon exiting the bay, the branch along the Delaware shore turns right to form the southward flowing Delaware coastal current along the inner continental shelf off the Delaware, Maryland, and Virginia coasts. CTD and thermosalinograph, data collected at the mouth of Delaware Bay over two semidiurnal tidal cycles are used to examine the hydrographic distribution at the source region of the Delaware coastal current. In this region the buoyant source water of the coastal current, is largely detached from the shoreline and confined to the top 15 m of the water column over much of the tidal cycles. The core of the coastal current's source water, as defined by the point of salinity minimum, is located over the deep channel well offshore of the Delaware coast. The separation between this buoyant water and the more saline waters right along the Delaware coast and that in the central part of the bay mouth are marked by regions of high horizontal salinity gradients. The horizontal salinity gradients around the inshore and offshore boundaries of the source water of the coastal current are intensified during the flood tide, and clearly defined fronts (with a change of 3‰ over a distance of 150 m) are present at the offshore boundary near the end of the flood tide. The structure of the mean flow and the distribution of the brackish coastal current on the inner continental shelf contribute to the persistence of stratification in the source region off the Delaware shore throughout the ebb and flood tides. In contrast, the ebb-induced stratification in the region off the New Jersey shore is quickly destroyed with the onset of the flood current.

Convection in the Greenland Sea, 1982–1993

Convection in the Greenland Sea is studied, using chlorofluorocarbons (CFCs, components F11, F12) and hydrographic distributions taken in spring 1993. A comparison with CFC data in the Greenland Sea Deep Water taken in 1989 shows that the CFC concentrations increased ony slightly, that is, the deep convection activity below 2200 m depth remained on the very low level of the previous years 1982–1989. A simple convection model shows that in the depth range 550–2250 m the mean annual convection rate ceased significantly in the period from 1989 to 1993 compared to the previous years 1982–1989. For the upper 500 m, the modeled tracer concentrations deviate from the observations, most likely due to horizontal advection, neglected in the model.

The Atlantic Deep Western Boundary Current: Water masses and transports near the equator

The distributions and transports of deepwater masses at the western boundary in the tropical Atlantic off Brazil have been studied on three surveys along 35°W and 5°S and one at 10°S. Transports are obtained from direct measurements of the velocity fields (Pegasus profiling system and lowered acoustic Doppler current profiler) and from geostrophic computations. Using chlorofluoromethane (CFM) and hydrographic distributions, four water masses could be identified forming the North Atlantic Deep Water (NADW) system. Two of these have a high CFM content, the “shallow upper NADW” (SUNADW) and the “overflow lower NADW” (OLNADW). These exhibit the highest velocity signals at 35°W, where distinct flow cores seem to exist; most of the southeastward flow of the SUNADW (centered around 1600 m) occurs 320 km offshore between 3°09′S and 1°50′S (9.7±3.3 Sv); farther north in that section, a highly variable reversing flow is found in a second velocity maximum. The transport of OLNADW (centered around 3800 m) of 4.6±2.6 Sv is guided by the Parnaiba Ridge at 1°45′S, 35°W. The water masses located between the two CFM maxima, the Labrador Sea Water (LSW) and the LNADW old water mass (LNADW‐old), did not show any persistent flow features, however, a rather constant transport of 11.1±2.6 Sv was observed for these two layers. The total southeastward flow of the NADW at 35°W showed a transport of 26.8±7.0 Sv, if one neglects the reversing SUNADW north of 1°50′S. At 5°S the flow of all deepwater masses shows vertically aligned cores; the main southward transport occurred near the coast (19.5±5.3 Sv). The boundary current is limited offshore by a flow reversal, present in all three surveys, but located at different longitudes. At 10°S a southward transport of 4.7 Sv was observed in November 1992. However, the section extended only to 32°30′W, so that probably a significant part of the flow has been missed. An important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35°W, which could lead to large uncertainties in the interpretation of single cruise observations. Despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations.