Bacterial pathogens in coastal sediments may pose a health risk to users of beaches. Although recent work shows that beach sands harbor both indicator bacteria and potential pathogens, it is not known how deep within beach sands the organisms may persist nor if they may be exposed during natural physical processes. In this study, sand cores of approximately 1 m depth were collected at three sites across the beach face in Kitty Hawk, North Carolina before, during and after large waves from an offshore hurricane. The presence of DNA from the fecal indicator bacterium Enterococci was detected in subsamples at different depths within the cores by PCR amplification. Erosion and accretion of beach sand at the three sites also was determined for each sampling day. The results indicate that ocean beach sands with persisting enterococci signals could be exposed and redistributed when wind, waves, and currents cause beach erosion or accretion.
Field observations of flow and sediment transport in a tributary channel through intertidal mudflats indicate that suspended sediment was closely linked to advection and dispersion of a tidal salinity front. During calm weather when tidal forcing was dominant, high concentrations of suspended sediment advected up the mudflat channel in the narrow region between salty water from San Francisco Bay and much fresher runoff from the small local watershed. Salinity and suspended sediment dispersed at similar rates through each tidal inundation, such that during receding ebbs the sediment pulse had spread spatially and maximum concentrations had decreased. Net sediment transport was moderately onshore during the calm weather, as asymmetries in stratification due to tidal straining of the salinity front enhanced deposition, particularly during weaker neap tidal forcing. Sediment transport by tidal forcing was periodically altered by winter storms. During storms, strong winds from the south generated wind waves and temporarily increased suspended sediment concentrations. Increased discharge down the tributary channels due to precipitation had more lasting impact on sediment transport, supplying both buoyancy and fine sediment to the system. Net sediment transport depended on the balance between calm weather tidal forcing and perturbations by episodic storms. Net transport in the tributary channel was generally off-shore during storms and during calm weather spring tides, and on-shore during calm weather neap tides.
Here we present observations of the hydrography of the Patagonian Shelf, shelf break and offshore waters, with reference to the environmental conditions present during the period of peak coccolithophore abundance. Analysis of a hydrographic dataset collected in December 2008 (austral spring/summer), as part of the Coccolithophores of the Patagonian Shelf (COPAS) research cruise, identified 5 distinct surface water masses in the region between 37°S and 55°S. These water masses, identified through salinity gradients, displayed varying mixed layer depths, macronutrient inventories and chlorophyll-a fluorescence. Subantarctic Shelf Water (SSW), located to the north of the Falkland Islands and extending north along the shelf break, was also host to a large coccolithophore bloom. The similarities between the distribution of calcite, as seen in remote sensing data, and SSW indicate that the coccolithophore bloom encountered conditions conducive to bloom development within this water mass. Analysis of chemical and environmental data also collected during the COPAS cruise revealed that many of the commonly cited conditions for coccolithophore bloom development were present within SSW (e.g. low N:P ratio, high N:Si ratio, shallow mixed layer depth). In the other water masses present on the Patagonian Shelf greater variability in these same parameters may explain the more diffuse concentration of calcite, and the smaller size of possible coccolithophore blooms. The distribution of SSW is strongly influenced by the latitudinal variation in shelf break frontal width, which varies from 20 to 200 km, and consequently strong hydrographic controls underlie the position of the coccolithophore bloom during austral summer.
Intertidal marine systems are highly dynamic systems which are characterized by periodic fluctuations in environmental parameters. Microbial processes play critical roles in the remineralization of nutrients and primary production in intertidal systems. Many of the geochemical and biological processes which are mediated by microorganisms occur within microenvironments which can be measured over micrometer spatial scales. These processes are localized by cells within a matrix of extracellular polymeric secretions (EPS), collectively called a “microbial biofilm”. Recent examinations of intertidal systems by a range of investigators using new approaches show an abundance of biofilm communities. The purpose of this overview is to examine recent information concerning the roles of microbial biofilms in intertidal systems. The microbial biofilm is a common adaptation of natural bacteria and other microorganisms. In the fluctuating environments of intertidal systems, biofilms form protective microenvironments and may structure a range of microbial processes. The EPS matrix of biofilm forms sticky coatings on individual sediment particles and detrital surfaces, which act as a stabilizing anchor to buffer cells and their extracellular processes during the frequent physical stresses (e.g., changes in salinity and temperature, UV irradiation, dessication). EPS is an operational definition designed to encompass a range of large microbially-secreted molecules having widely varying physical and chemical properties, and a range of biological roles. Examinations of EPS using Raman and Fourier-transform infared spectroscopy, and atomic-force microscopy suggest that some EPS gels possess physical and chemical properties which may hasten the development of sharp geochemical gradients, and contribute a protective effect to cells. Biofilm polymers act as a sorptive sponge which binds and concentrates organic molecules and ions close to cells. Concurrently, the EPS appear to localize extracellular enzyme activities of bacteria, and hence contribute to the efficient biomineralization of organics. At larger spatial scales, the copious secretion of specific types of EPS by diatoms on the surfaces of intertidal mudflats may stabilize sediments against resuspension. Biofilms exert important roles in environmental- and public health processes occurring within intertidal systems. The sorptive properties of EPS effectively chelate toxic metals and other contaminants, which then act as an efficient trophic-transfer vehicle for the entry of contaminants into food webs. In the water column, biofilm microenvironments in suspended flocs may form a stabilizing refugia that enhances the survival and propagation of pathogenic (i.e., disease-causing) bacteria entering coastal waters from terrestrial and freshwater sources. The EPS matrix affords microbial cells a tremendous potential for resiliency during periods of stress, and may enhance the overall physiological activities of bacteria. It is emphasized here that the influences of small-scale microbial biofilms must be addressed in understanding larger-scale processes within intertidal systems.
A secondary depression crossing southern Wales and England on the 13 December 1981 resulted in the highest water levels experienced in the Bristol Channel this century and severe flooding along the north Somerset coast. Both a numerical model-based prediction scheme and theLennon (1963,Quarterly Journal of the Royal Meteorological Society,89, 381–394) criteria for west coast storm surges failed to provide adequate warning of the expected levels. A numerical reconstruction of the event shows that the failure of the surge model forecast was due to an incorrect prediction by the atmospheric model used to provide the meteorological input to the sea model. The fallibility of the Lennon criteria suggests their reappraisal, particularly in the light of a subsequent failure in November 1984. Some of the difficulties in the identification of storm surge residuals within the Bristol Channel are shown to be associated with tidal measurement and prediction problems which are, as yet, unresolved.
Data on the temporal and spatial variations of 99Tc and 137Cs in UK coastal waters are provided from surveys carried out over the period 1993–1998; prior to and post the discharge of elevated quantities of 99Tc from the nuclear fuel reprocessing plant at Sellafield (Cumbria, UK). 99Tc seawater concentrations in the Irish Sea increased by more than an order of magnitude within the study period concomitant with the increase in discharges. 137Cs discharges were relatively low (∼0.3% of their peak values in the 1970s). Simplistically, the 137Cs distribution reflected varying hydrographic conditions superimposed upon the residual concentrations of a system approaching steady state. Differences between the 137Cs/99Tc ratio in Sellafield discharges and seawater indicate that 137Cs remobilisation, from sediments contaminated by large discharges in the 1970s, is presently the predominant (∼90%) source term to the water column. The 137Cs/99Tc ratio in the Irish Sea decreased significantly within the period of these surveys (e.g. reduced from ∼14 in 1993 to 0.4 in 1996, within the vicinity of Sellafield). However, it is difficult to extrapolate this information to assess the contribution from Sellafield in distant waters because the low levels of 137Cs are continuously perturbed by additional inputs during transit (e.g. remobilisation from sediments outside the Irish Sea). Examination of 99Tc data for the North Sea indicates that the leading edge of the first EARP pulse, entering via the Scottish coastal current, may have migrated to the limit of the current flowing south along the British coastal margin within 9 months. The estimated transfer factor (TF) for Sellafield discharges in this current is 52 Bq m−3/PBq annum−1 with transit times from Sellafield to the Pentland Firth and Lowestoft of ∼9 and ∼24 months, respectively. These transit times, derived from the 99Tc data, are significantly shorter than previous estimates based on 137Cs and 90Sr data from the 1970s and 1980s.
Vertical profiles of and have been collected at micro-, meso- and macrotidal mudflats in order to calculate present accumulation rates. Sediment cores were taken at the mudflat at Kongsmark in the microtidal Lister Dyb tidal area (Denmark), at the BOA bridge in the mesotidal Dollard estuary (Netherlands), and at the Skeffling mudflat in the macrotidal Humber estuary (UK). Except for the Kongsmark site and site A in the Humber estuary, no accurate calculation of accumulation rates was possible for the investigated sites. The accumulation rate obtained for the Kongsmark site is confirmed by other independent data and shows that the accumulation is not supply limited at this site at present. For site A in the Humber estuary a modified CIC method was applied to the -profile and the result agrees with results from the nearby Welwick Marsh. The salt marsh at Skeffling is advancing out onto the fringing mudflat with accumulation at the innermost part of the mudflat but with erosion taking place further offshore. The reasons for the generally poor dating results seems to be either erosion (two Humber sites) or postdepositional reworking of the deposited material (bioturbation and continued resuspension) and the data set suggests that the mixing depth may increase with tidal range and thereby hydrodynamic forcing.
Dating techniques based on the natural and anthropogenic radionuclides 210Pb and 137Cs were applied to the study of the sedimentation regime in Cienfuegos Bay, Cuba. Core samples were collected from different locations in the bay and analysed to evalute the accumulation rate. Results evidenced significant changes in the sedimentation rate during the last 40 years: the recent sediment accumulation rates (0.47–0.50 g cm−2 yr−1) in the Northen basin are almost double those estimated before 1965 (0.30 g cm−2 yr−1). The 210Pb profiles show significant deviations from a simple exponential decline and abrupt variations between 1966 and 1970. These irregularities match closely periods of changes in land use (intense de-forestation and regimentation of the Arimao and Caonao rivers in the late 1960s and early 1970s) and exceptional natural events (Hurricane “Camille” in 1969 and the intense rainfall of 1988) which occurred in Cienfuegos. The 137Cs and chlorite minerals profiles validate the results obtained from 210Pb dating and confirm the effect of exceptional events and changes in the natural hydrological regime of the bay during the past 40 years.
The deposition record of 137Cs was traced in the SE Black Sea sediments adjacent to the Coruh river mouth in comparison with the earlier studied chronology of 137Cs deposition in front of the Danube delta (NW Black Sea). In both cases, the 137Cs profiles showed two subsurface peaks attributable to maximum fallout of ‘bomb’ and Chernobyl radionuclides. The Coruh profile revealed a larger contribution of ‘bomb’ 137Cs in comparison with the Chernobyl input, suggesting different coverage of NW and SE Black Sea regions with the Chernobyl fallout. The 137Cs-derived dating showed that maximum deposition of particulate bound 137Cs in sediments adjacent to the Coruh river mouth was delayed for ∼14 yr relative to date of Chernobyl accident, reflecting a buffer effect of the watershed soils. This transit time is 3 times longer than in the Danube catchment area, indicating a difference in retention processes in these mountainous (Coruh) and lowland (Danube) river basins. The 137Cs profile in Coruh sediments showed penetration of 137Cs to much greater depth than would be expected from 137Cs fallout chronology, suggesting the sediment mixing rate of 1.3 cm2 yr−1. This value was used to evaluate deposition chronology of 137Cs, applying the model developed for pulse fallout case. Comparing the measured and modelled data has allowed differentiation of the flood-induced discharge of the 137Cs-containing suspended matter and the slower transit of eroded soil particles from the contaminated catchment areas. The obtained results may be used for the prediction of period when the pollutants, deposited over the river basins, can reach the Black Sea.
The net storage of the radionuclides 238Pu (2.8 TBq), 239, 240Pu (75 TBq), 137Cs (730 TBq), 241Am (40 TBq) and 210Pbxs (2700 TBq) in North Sea sediments has been estimated from their concentrations in 40 boxcores. From comparison of 238Pu/239, 240Pu ratios between those found in the sediments and those in atmospheric fallout and discharges from the nuclear fuel reprocessing plants at Sellafield (UK) and la Hague (France), it is concluded that the latter is the main supplier of plutonium to the Southern Bight, while the former is dominant in the remainder of the North Sea. About 7% of all Sellafield plutonium discharge is stored in North Sea sediments. The German Bight receives and stores plutonium and fine particulate matter mainly from the Elbe estuary. Of all 137Cs transported through the North Sea, about 2% is stored in the sediment. 241Am is scavenged faster than plutonium and is probably transported from Sellafield to the North Sea as 241Pu.
A model for radionuclide transport in the marine environment is described and applied, in the Irish Sea, to the movement of caesium (137Cs) and plutonium (239/240Pu) discharged from Sellafield. The model resolves processes operating on tidal time scales, whilst being simple enough to run over decadal time periods. Modelled processes include transport in the water column, exchange of contaminants between dissolved and particulate phases, wave–current sediment resuspension, sediment transport and mixing of material within the seabed. Transport in the water column is by a combination of tide, wind and density-driven flows. Sediment transport is based on the erosion, advection and deposition of three sediment classes representing sand, flocculated mud/silt and fine background components. Transfer of radionuclides between the dissolved and sediment phases is implemented using rate equations. A layered seabed is incorporated with transfers between layers representing biological and physical mixing processes. We demonstrate that the model is able to reproduce observed concentrations of 137Cs and 239/240Pu in the water column, the build-up of 239/240Pu in the seabed over a 30-year time span, including recent changes in seabed inventory distributions. The model is used to identify and quantify the mechanisms responsible for this recent redistribution of 239/240Pu in the region. The results suggest that whilst sediment transport plays a role in redistributing contaminated sediment in the eastern Irish Sea, desorption, followed by transport in the dissolved phase and reabsorption onto particulate material, is the primary mechanism for redistribution of 239/240Pu.
The Camamu Bay (CMB) is located on the narrowest shelf along the South American coastline and close to the formation of two major Western Boundary Currents (WBC), the Brazil/North Brazil Current (BC/NBC). These WBC flow close to the shelf break/slope region and are expected to interact with the shelf currents due to the narrowness of the shelf. The shelf circulation is investigated in terms of current variability based on an original data set covering the 2002–2003 austral summer and the 2003 austral autumn. The Results show that the currents at the shelf are mainly wind driven, experiencing a complete reversal between seasons due to a similar change in the wind field. Currents at the inner-shelf have a polarized nature, with the alongshore velocity mostly driven by forcings at the sub-inertial frequency band and the cross-shore velocity mainly supra-inertially forced, with the tidal currents playing an important role at this direction. The contribution of the forcing mechanisms at the mid-shelf changes between seasons. During the summer, forcings in the two frequency bands are important to drive the currents with a similar contribution of the tidal currents. On the other hand, during the autumn season, the alongshore velocity is mostly driven by sub-inertial forcings and tidally driven currents still remain important in both directions. Moreover, during the autumn when the stratification is weaker, the response of the shelf currents to the wind forcing presents a barotropic signature. The meso-scale processes related to the WBC flowing at the shelf/slope region also affect the circulation within the shelf, which contribute to cause significant current reversals during the autumn season. Currents at the shelf-estuary connection are clearly supra-inertially forced with the tidal currents playing a key role in the generation of the along-channel velocities. The sub-inertial forcings at this location act mainly to drive the weak ebb currents which were highly correlated with both local and remote wind forcing during the summer season.
We evaluated changes in siliceous export production and the source of organic matter preserved in sediment core MD07-3109H recovered from the Gulf of Ancud, Chiloé Inner Sea (42°S, 72°W, water column depth: 328 m), southern Chile. We analyzed the abundance of siliceous microfossils (diatoms, silicoflagellates, sponge spicules, Chrysophyte cysts, phytoliths), geochemical proxies (weight percent silicon %SiOPAL, organic carbon, total nitrogen, C/N molar), and sediment stable isotopes (δ13Corg, δ15N). Chronology based on 210Pb and 14C provided an accumulated age of 144 years at the base of the core.Sediments of core MD07-3109H are predominantly marine in origin, averaging δ13Corg=–20.75‰±0.82, δ15N=8.7±0.35‰, and C/N=8.76±0.36. Marine diatoms compose 94% of the total assemblage of siliceous microfossils. Our record of productivity based on the mass accumulation rates of organic carbon, total nitrogen, SiOPAL, and total diatoms showed high values between 1863 and 1869 AD followed by a declining trend until 1921 AD, a transition period from 1921 to 1959 AD with fluctuating values, and a clear decreasing pattern from 1960 AD to the present. This marked reduction in productivity was associated with decreased precipitation and Puelo River streamflow (41°S), as well as a warmer and more stratified water column, especially since the 1980s.
We have evaluated the feasibility of using the terminal restriction fragment length polymorphism (T-RFLP) pattern of polymerase chain reaction (PCR) amplified 16S rRNA sequences to track the changes of the free-living bacterial community for the Pearl River Estuary surface waters. The suitability of specific PCR primers, PCR bias induced by thermal cycles, and field-sampling volumes were critically evaluated in laboratory tests. We established a workable protocol and obtained TRF patterns that reflected the changes in the bacterial population. The temporal dynamics over a 24 h period were examined at one anchored station, as well as the spatial distribution pattern of the bacterial community at several stations, covering the transects along the river discharge direction and across the river plume. The TRF pattern revealed 9 dominant bacterial groups. Changes in their relative abundance reflecting the changes in the bacterial community composition were documented. Many culturable species were isolated from each field sample and a portion of the 16S rRNA gene for each species was sequenced. The species was identified based on sequence data comparison. In this region, the dominant species belong to the γ-subdivision of proteobacteria and the Bacillus/Clostridium group of Firmicutes. We also detected the wide spread distribution of Acinetobacter spp.; many of these species are known nosocomial pathogen for humans.
Part of the Northeast Atlantic mackerel population migrates towards the southern spawning area (Cantábrian Sea) at the end of winter. In this seasonal handline fishery targeting mackerel, the most important in the study area that targets this species, the timing of the peak of catches has shifted forward (later) in recent years. This paper presents results pointing to the likelihood that this shift is due to a change in the timing of the spawning migration to the southern area of the Northeast Atlantic mackerel population. Three types of fleet have been identified within this fishery, and in all of them there is a forward shift in time in effort exerted. Moreover, a new model has been defined for the standardization of catch per unit effort (CPUE). The fishing season appears to have shifted forward by 29 days between 2000 and 2006. Nevertheless, changes have been detected neither in the exploitation pattern nor in the duration of the fishing season during the period studied. A shift on this scale has important consequences for the management of the resource, the fleets that exploit it and the resource assessment survey designs that will have to be adapted to this new scenario.
Kraternaya Bight (Yankich Island, the Kuril Islands) is a submerged crater of the active Ushishir Volcano characterized by terrestrial and underwater gasohydrothermal activity. The gasohydrothermal activity of the volcano produces a great influence on the physico-chemical characteristics of water column, as well as planktonic and bottom communities of marine organisms of the bight. The bivalve mollusks Macoma golikovi and Macoma calcarea are dominant macrobenthos species of Kraternaya Bight, which inhabit all the zones of underwater volcanic activity. Macoma golikovi occurs at a depth of 1–45 m. This species forms the densest aggregations (with an average biomass of 500–800 g m−2 and a population density of 500–700 ind. m−2) at a depth of 3–15 m, on steep underwater crater slopes (40–45°), on slightly silted gravel. The majority of gasohydrothermal vents are located at that depth. Macoma calcarea occurs at a depth of 5–55 m. In contrast to Macoma golikovi, this species is dominant at a depth of 25–40 m, on gentle slopes of the crater (to 20°), on silt and silty sand. That depth is less subjected to the influence of volcanic products. Its average biomass is 450–750 g m−2 with a population density of 200–450 ind. m−2 there. It is assumed that the differences in the distribution are due the fact that Macoma golikovi is mainly a suspension-feeder in Kraternaya Bight, and Macoma calcarea is a deposit-feeder. The studies conducted between 1987 and 1997 on the quantitative distribution of Macoma golikovi and Macoma calcarea in four areas of the bight, which had different intensity, temperature and chemical composition of gasohydrothermal vents and volcanic water seeping showed that both species formed settlements with lesser density in the area of the gasohydrothermal vents containing hydrogen sulfide. Beyond the area of volcanic activity, these species were most abundant. In 1993 and 1995, the mortality of the populations of the bivalve mollusks was observed in the areas of hydrogen sulfide gasohydrothermal vents and volcanic water seeping. In other areas of the bight, their abundance decreased sharply suggesting a relationship to the gasohydrothermal activity of the volcano in those years. Circumstantial evidence for this suggestion was that in 1993, the maximal concentrations of Fe, Zn, Cd, and Mn were observed in the tissues of both species. Macoma golikovi accumulated 5–10 times more Zn than Macoma calcarea. The concentration of Zn in the tissues of Macoma golikovi reached 2000 μg g−1.
A hand-operated, rotating-scoop sediment sampler (HORS) has been developed for coarse-grained, shallow-marine sediment. Design of the 10 kg HORS was inspired by the 60 kg, winch-operated Shipek sampler which also has a 180° rotating scoop. At one-sixth of the Shipek mass, the HORS typically collects about one-sixth as much sediment. The HORS is recommended only if a winch is unavailable for a Shipek grab sampler.Grab samplers without a 180° rotating scoop rely on one or two pairs of jaws which close toward the center along arcs of 90°. These center-closing devices commonly fail to sample coarse sediment because a large grain, e.g. a shell fragment, impedes closure and allows the sample to escape during ascent. Center-closing jaws which meet rather than overlap eventually fail to meet completely because of wear along the jaw edge or misalignment. All grab samplers, including rotating-scoop types, may induce some loss of the finest fraction and so are best reserved for reconnaissance work. The sampler described herein has facilitated reconnaissance of the modern equivalent of oolitic ironstone in the southeastern Caribbean.
A recently extended and spatially rich English Channel sea level dataset has been used to evaluate changes in extreme still water levels throughout the 20th century. Sea level records from 18 tide gauges have been rigorously checked for errors and split into mean sea level, tidal and non-tidal components. These components and the interaction between surge and tide have been analysed separately for significant trends before determining changes in extreme sea level. Mean sea level is rising at 0.8–2.3 mm/year, depending on location. There is a small increase (0.1–0.3 mm/year) in the annual mean high water of astronomical tidal origin, relative to mean sea level, and an increase (0.2–0.6 mm/year) in annual mean tidal range. There is considerable intra- and inter-decadal variability in surge intensity with the strongest intensity in the late 1950s. Storm surges show a statistically significant weak negative correlation to the winter North Atlantic Oscillation index throughout the Channel and a stronger significant positive correlation at the boundary with the southern North Sea. Tide–surge interactions increase eastward along the English Channel, but no significant long-term changes in the distribution of tide–surge interaction are evident. In conclusion, extreme sea levels increased at all of the 18 sites, but at rates not statistically different from that observed in mean sea level.
This paper presents an overview of the significant research on morphodynamics and sediment dynamics on intertidal mudflats in China (1961–1994), particularly in the past 15 years (1980–1994). Development of intertidal mudflats has long been regarded as the response of the intertidal profile to tides, waves and storms. It has been found that there were long-term and short-term cyclic developments of intertidal mudflats in China. Three sedimentological zones have generally been identified from land to sea within the intertidal zone: high mudflat, middle mudflat and low mudflat. In addition, the sediments in the middle mudflat are relatively coarser than those in the high mudflat and low mudflat. Storms have great impacts on the intertidal morphology, sediment textures and sedimentary structures. Based on field investigations of intertidal sedimentary processes, many researchers have found that “settling and scour lags” were only applicable to intertidal cohesive sediment transport during periods of weak waves, but not during storms. In fact, flood fronts, waves, storm surges and longshore drift play important roles in suspended sediment transport on open intertidal mudflats in China. Despite of these extensive studies in the past several decades, there is still a need for an improved understanding of fundamental physical and biological processes governing erosion and deposition of cohesive fine sediment within the intertidal zone in China.
Monthly time series of nutrient pools and transport in the Baltic Entrance were computed for the period 1974–1999 from a combination of hydrodynamic model results and observational data obtained in national monitoring programmes. Significant seasonal variations in both nutrient pools and transport were found. For example, inflowing dense nutrient-rich Skagerrak water causes net transport of dissolved inorganic phosphorus (DIP) and inorganic nitrogen (DIN) towards the Baltic during summer where surface concentrations are low. Surface-water concentrations of DIN and DIP increase during winter and the net transport may reverse. The computations indicated that the pools of dissolved inorganic phosphorus and total phosphorus (TP) were larger in the 1980s than in previous and following decades. Variations in pools of dissolved inorganic nitrogen (DIN) and total nitrogen (TN) were more irregular throughout the period. Computed nutrient transports likewise exhibited long-term variations. Net transport of DIN and DIP was southward, from the Skagerrak to the Kattegat and further into the Belt Sea, during the 1970s. In the same period, the transport of DIN and DIP from the Baltic Sea to the Baltic entrance was below average. In both the Kattegat and the Belt Sea transports reversed during the 1980s. In the 1990s the southward transport of DIP was restored, but the transport of DIN was not restored to the same extent. Between the Kattegat and the Skagerrak the transport diminished while the Belt Sea continued to export DIN to the Kattegat. Northward transports of TN and TP persisted throughout the period. A notable maximum TP transport was found to have taken place during the 1980s.
Temperatures recorded over the Georgia shelf and at near-bottom locations on the slope are compared with records of thermocline elevation from inverted echo sounders on the slope and with shore wind observations, for the period January to April 1978.Both upwelling and downwelling events are observed. Upwelling events are associated with upwelling-favorable wind and/or Gulf stream frontal eddies. Strong upwellings are accompanied by risings of the thermocline over the slope, but some weaker eddies occur without noticeable thermocline disturbance. Downwelling events are associated with onshore meander crests of the Gulf Stream, and sometimes with downwelling-favorable wind. The influence of downwelling does not extend seaward of the upper slope.A long-term (1 month) variation of the thermal structure is observed at the shelf break and under the Gulf Stream. It is related to a filament of cold water on the slope, varying in path and size. This cold filament appears to be Antarctic Intermediate Water which is variably advected through the Straits of Florida. Theory suggest that the variability may be caused by changes in the thermocline depth and tilt across the Gulf Stream in response to transport fluctuations.
Previous work concerning Gulf Stream warm-core rings (WCRs) and their associated shelf water entrainments have been based upon single surveys or time series from individual WCRs. To date, estimates of annual shelf water volume entrained into the Slope Sea by WCRs and its interannual variability have not been made. Using a long time series of satellite-derived sea surface temperature (SST) observations of Slope Sea WCRs, we have completed an analysis of 22 years of WCR data (1978–1999) between 75°W and 50°W to understand the interannual variability of WCRs and their role in entraining shelf water. Satellite-derived SST data digitized at Bedford Institute of Oceanography are analyzed using an ellipse-fitting feature model to determine key WCR characteristics including WCR center position, radius and orientation. Key characteristics are then used to compute WCR swirl velocity by finite-differencing WCR orientations (θ) obtained from the feature model time series. Global mean WCR-edge swirl velocity calculated from all observations is 105.72±10.7 km day−1 (122.36±12.4 cm s−1), and global mean WCR radius is 64.8±6.2 km. Primary and derived WCR data are incorporated into a two-dimensional ring entrainment model (RM) using the quasi-geostrophic approximation of the potential vorticity equation. The RM defines ambient water as entrained by a WCR only if the gradient of relative vorticity term (horizontal shear) dominates the potential vorticity. Proximity of a WCR to the position of the shelf-slope front (SSF) is then used to determine whether the ambient water is entrained from the outer continental shelf. WCR-induced shelf entrainment derived from the RM displays considerable spatial variability, with maximum entrainment occurring offshore of Georges Bank, advecting a mean total annual shelf water volume of 7500 km3 year−1 from the region. Estimates of shelf water fluxes display significant interannual variability, which may be in part due to the observed covariance between WCR occurrences and the state of the North Atlantic Oscillation (NAO). Increased (decreased) occurrences of WCRs are evidenced during positive (negative) phases of the NAO. The total mean annual shelf-wide WCR-induced shelf water transport is estimated to be 23,700 km3 year−1 (0.75 Sv), accounting for nearly 25% of the total transport in the Slope Sea region neighboring the outer continental shelf.
The subinertial circulation within 2 to 12 km of the Long Island coast is described from a set of observations of the velocity and density fields during August 1978. The flow was characteristically to the southwest, increasing offshore and decreasing with depth. This southwest flow was driven by an externally imposed shoreward rising sea level which was modified at the coast by local wind-driven divergences and convergences. Upwelling and downwelling circulations maintained isopycnal tilts which in turn geostrophically sheared the flow. Nearly complete compensation was observed during steady periods, reducing the near-bottom flow to within ∼80% of its barotropic magnitude. This decreased the effectiveness of bottom stress on the subinertial flow. Even with fairly uniform alongshore bathymetry, the flow was substantially not two-dimensional, because of bathymetric divergences, bottom slope interaction, and bottom stress variations. These effects, in addition to the greater responsiveness of the shallower water columns, tend to define a nearshore regime partially uncoupled from a midshelf regime. The boundary in this case was often observed between 25- and 30-m contours (4 to 8 km offshore).
Based on two years (July 1978–June 1980) of current meter array measurements and bimonthly STD/XBT transects over the continental margin off central California, the mean California Undercurrent has a jet-like core in excess of 15 cm s−1 which is generally confined to the upper 300 m of the water column and to within 30 km of the coast. A comparison of measured current velocities with relative geostrophic velocities suggests, on average, a poleward flow of 10 cm s−1 at the reference level, 450 db. The variability is predominantly annual with a maximum poleward flow in May–June. Equatorward flow was suprisingly weak and infrequent in the transect studied. The alongshore flow has characteristic fluctuations of 15 cm s−1 on time scales of a few days to weeks. The strongest and most coherent element of variation is the “spring transition”, which had different manifestations in the two years observed, perhaps due to differences in the combination of local and remote forcing. The spring transition is characterized by an abrupt decrease in subsurface temperature which is well-correlated with a coastal sea surface temperature (SST) decrease, an upwelling index increase, and a transient reduction or reversal of the poleward flow. The subsurface current and temperature fluctuations are associated with coastal SST and wind fluctuations, and with satellite infra-red imagery patterns and changes.
Currents, coastal winds, coastal sea level, and coastal ocean temperatures were observed at a number of northern Baja California Pacific sites between October 1978 and October 1979. Coastal winds were weakly southward on average and fluctuated north-south throughout the year. Fluctuations were uncorrelated over alongshore separations of 200 km. Coastal winds differed considerably from the large-scale offshore wind estimate (Bakun's Index) both in strength and in variability. At 30°50′N the mean currents were weakly equatorward at 25 m depth and weakly poleward at 42 and 60 m in a water depth of 75 m. The seasonal mean flow was equatorward from October to April and poleward from April to October at the shallower level but poleward all year near bottom. The fluctuations on a time scale of days to weeks were about an order of magnitude stronger than the seasonal variation, were oriented predominantly alongshore, and were quasi-barotropic in nature. Empirical orthogonal analyses showed that almost 90% of the variability could be represented by a single empirical mode. The alongshore fluctuations were significantly correlated with coastal sea level from October to July but during the rest of the year correlation was insignificant, possibly as a result of offshore eddies approaching the shelf.