South Atlantic circulation in a world ocean model

The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW) at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC) through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current) and fresher Subantarctic surface water (originating in the ACC). The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor). Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW) equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model’s rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of thermocline, intermediate and deep waters are constructed from an analysis of flows bound between isothermal and isobaric surfaces. This analysis shows how the return path of NADW is partitioned between a cold water route through the Drake Passage (6.5 Sv), a warm water route involving the Agulhas Current sheeding thermocline water westward (2.5 Sv), and a recirculation of intermediate water originating in the Indian Ocean (1.6 Sv).     

Mercury content of shark from south-Western Australian waters

Muscle samples from four species of commercially sought shark have been analysed for total mercury and the mercury concentration related to the size of the fish.     

Petroleum hydrocarbons in the arctic ocean surface water

The concentration of petroleum hydrocarbons in Arctic surface water under the ice north of Svalbard has been determined by fluorescence spectrofluorometry using three different excitation/emission wavelength combinations. With Kuwait crude oil as a reference, the concentration range is 0.1–0.6 μg l^?1 crude oil equivalents with respect to light molecular weight components and 0.05–0.2 μg l^?1 heavy molecular weight components.     

Rare anthropogenic and natural particles suspended in deep ocean waters

Four hundred membrane filters from the Atlantic and Pacific deep waters have been scanned for coloured and opaque particles by a method integrating the light and the scanning electron microscopes, the electron microprobe and the micro-X-ray diffraction camera. About 40 different types of particles have been found. A tentative classification of the particles and of their morphological and chemical varieties is presented, according to their anthropogenic or natural origins. From this point of view, the particles fall into five groups: (1) particle species exclusively produced by man's activities (like brass, cobalt aluminate); (2) particles exclusively produced by natural processes (like amphibole, ilmenite); (3) particles rarely produced by natural processes, but massively so by man (like metallic copper, chromium oxide); (4) a large group of particles massively produced by nature and by man (like magnetite spherules, malachite); (5) a very small group of particles whose origin could not be attributed at present. Very few entirely new compounds from the point of view of continental mineralogy have been encountered.     

Mercury,organic-mercury and selenium in small cetaceans in Taiwanese waters

Total Hg (∑Hg), organic-Hg (O-Hg) and Se bioaccumulations in small cetaceans distributed in Taiwanese waters of the Taiwan Strait and the southwestern Pacific have been investigated for the first time. The results could represent the baseline metal concentrations of marine mammals in the southwestern Pacific, where volcanic activities are possibly the major source of mercury to the environments. Muscle samples of four species of small cetaceans were collected from animals accidentally caught by tuna-longline fisheries from 1994 through 1995. In total, 53 pantropical spotted dolphins, Stenella attenuata, nine spinner dolphins, S. longirostris, five bottlenose dolphins, Turiops truncatus and four Risso's dolphins, Grampus giseus were analyzed. In addition, two stranded pantropical spotted dolphins were investigated. Cold vapour AAS and ICP-MS were used in the analysis of Hg and Se, respectively. Significant species difference was found in the four species of small cetaceans. Among them, the pantropical spotted dolphin showed the highest mean concentration (mg/kg wet wt.) of both ∑Hg (3.64±2.19) and O-Hg (2.79±1.23), whereas the Risso's dolphin had the highest mean concentrations of Se (1.77±1.29). There was no significant sex difference with respect to metal bioaccumulation in the samples of S. attenuata. Significant correlations between body length (BL) and ∑Hg, as well as O-Hg concentrations were observed in pantropical spotted (Sa) and spinner dolphins (Sl). The linear relationships were Sa: ∑Hg=−8.290+0.066BL, r=0.421; Sl: ∑Hg=−2.735+0.025BL, r=0.875; Sa: O-Hg=−3.723+0.036BL, r=0.408; and Sl: O-Hg=−3.017+0.025BL, r=0.870. However, a demethylation phenomenon that decreasing the percentage of O-Hg coupled with increasing levels of Se was observed when the ∑Hg concentrations in the muscle tissues of dolphins reached 4 mg/kg wet wt.     

The diurnalK 1 tide in the world ocean — A numerical investigation

Summary Based on a special numerical method (HN method) hydrodynamical processes in the sea were studied with an aim at their prediction. Within this framework, constantly checking the reliability of the numerical models, tides and wind driven motions have been investigated in estuaries, in marginal and adjacent seas, and in the oceans (seeH. Friedrich [1], W. Hansen [2–4], H. P. Schmitz [5]). Encouraged by the promising results, these numerical investigations have been extended by the author to the world ocean, initially to the semi-diurnalM ₂ tide ([8]) and now to theK ₁ tide. Results of computations carried out for theK ₁ tide are given in this paper.     

On the surface temperature of Greek waters

Summary This study deals with the surface temperature of Greek seas. The general distribution of this element for the months February, May, August and November is given and the factors controlling the sea-surface temperature are examined. In addition the annual variation and the monthly variability of the sea surface temperature are studied, as well as the difference between the sea-surface and air temperature in three different regions of Greek waters.

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Résumé Cette étude concerne la température de la surface des mers de la Grèce. La distribution générale de cet élément pour les mois de Février, Mai, Août et November est donnée et les facteurs qui contrôlent la température de la mer sont examinés. De plus la variabilité mensuelle de la température de la surface de la mer ainsi que la différence qui existe entre la température de la surface de la mer et la température de l'air dans trois différentes régions des mers Grecques.

     

Dissolved petroleum hydrocarbons in some regions of the northern Indian ocean

Dissolved petroleum hydrocarbons were measured in some parts of the Northern Indian Ocean using UV absorbance technique with a clean up step. The concentration of oil ranged from 0.6 to 26.5 μg l^?1. Higher values were recorded along the oil tanker route compared with the coastal region From surface to about 10 m depth the oil appeared to be well mixed with water.     

Spatial characteristics of ocean surface waves

The spatial variability of open ocean wave fields on scales of O (10km) is assessed from four different data sources: TerraSAR-X SAR imagery, four drifting SWIFT buoys, a moored waverider buoy, and WAVEWATCH III^? model runs. Two examples from the open north-east Pacific, comprising of a pure wind sea and a mixed sea with swell, are given. Wave parameters attained from observations have a natural variability, which decreases with increasing record length or acquisition area. The retrieval of dominant wave scales from point observations and model output are inherently different to dominant scales retrieved from spatial observations. This can lead to significant differences in the dominant steepness associated with a given wave field. These uncertainties have to be taken into account when models are assessed against observations or when new wave retrieval algorithms from spatial or temporal data are tested. However, there is evidence of abrupt changes in wave field characteristics that are larger than the expected methodological uncertainties.     

Plastic debris in the surface waters of the South Atlantic

Polyethylene and polypropylene pellets, together with tarballs, were found to be the most common contaminates of the sea surface in the Cape Basin area of the South Atlantic Ocean. This is an area far removed from any obvious source of such materials.     

Prospects of magnetotelluric sounding in some large structures in the Arctic ocean

In the work, the results of modeling of electric resistivity distribution at the Gakkel and Alpha-Mendeleev underwater ridges are given. Based on the seismostratigraphic models, the apparent resistivity curves at a few points of the profile at the crossing of the ridge were constructed. The advantages and disad-vantages of the MT sounding method are presented. The results obtained can be used for future experiments.     

Radium-barium-silica correlations and a two-dimensional radium model for the world ocean

Radium-barium-silica relationships are examined in various regions of the Pacific. Ra, Ba and Si are not linearly correlated except in the Circumpolar region. From surface water to the intermediate water, Ra usually increases linearly with Ba and Si. In the North Pacific where there is a Ra excess in the deep water, both the Ra-Ba and Ra-Si diagrams show curves concave upward with an increasing slope. The relationships are further complicated by a deep gentle Ba maximum and a broad mid-depth Si maximum.In the western boundary where the Antarctic Bottom Water and Pacific Deep Water are separated by the benthic front, the Ra-Ba and Ra-Si plots show “hooks” of various size and shape caused by a discordance in the depths of the Ra, Ba and Si maxima. The hook becomes smaller toward the south and flips from counterclockwise to clockwise in the southern basin.A two-dimensional horizontal model with a geostrophic circulation pattern is employed to calculate Ra distribution in the deep water with a constant upwelling rate but a variable mean input rate for Ra. The mean input rate or fluxF is the sum of the in-situ production rateJ by particulate dissolution in the water column and the bottom fluxQ_b. The global mean fluxF needed to balance the radiodecay in a steady-state distribution is used as a reference for discussion. It is found that anF value set at1.5 ×F fits the observed data in the deep Atlantic. TheF value needs to be about2.7 ×F in order to produce a comparable distribution in the deep Pacific. These model calculations indicate that a Ra source is required in the northeast Pacific. It appears that no uniqueF can produce a global Ra distribution in deep water comparable to both the Atlantic and Pacific observations. This is also true within the Pacific Ocean itself because of the large Ra excess observed in the northeast Pacific. Thus the Ra input rate is quite variable and increases by a factor of two from the Atlantic to the Pacific. This probably reflects the non-uniformity of the bottom fluxQ_b rather than that of the in-situ productionJ in the world oceans.     

On the computation of the barotropic mode of a free-surface world ocean model

The free-surface formulation of the equations of our world ocean model is briefly described. The barotropic mode equations are solved according to the split-explicit method, using different time steps for the external and internal modes. Because the numerical algorithm is implemented on the B-grid, a spurious, free-surface, two-grid interval mode may develop. This mode must be filtered out. The properties of two filters are theoretically investigated and their actual performance is tested in a series of numerical experiments. It is seen that one of these filters may severely perturb the local mass conservation, rendering it impossible to enforce the impermeability of the surface or the bottom of the ocean. The dynamics of the external mode is also examined, by studying the depth-integrated momentum equations. The depth-integral of the pressure force due to the slope of the ocean surface is approximately balanced by the depth-integral of the force ensuing from the horizontal variations of the density. The depth-integral of the Coriolis force is an order of magnitude smaller, except in the Southern Ocean. Two variational principles are resorted to for computing the fictitious ocean surface elevation corresponding to the approximate equilibrium between the dominant forces of the barotropic momentum equations.     

Solar activity and dynamic processes in the atmosphere and world ocean heat content

The scenario of climatic changes in the 20th century has been presented in the scope of the developed model concerning the effect of solar activity on the parameters of the climatic system governing the energy flux, outgoing from the Earth into space in the high-latitude regions. The regularities of changes in the circulation in the atmosphere and ocean are discussed. Specific attention is paid to the causes of a “cold snap” in 1940–1976 in the Northern Hemisphere and the nature of an anomalous increase in the heat content in the Earth climatic system (ocean) in 1969–1980. It has been indicated that these phenomena result from changes in the circulation in the atmosphere and ocean (specifically, a change in the thermohaline circulation in the Northern Atlantic), heat exchange between the ocean and the atmosphere and cryosphere.     

Mercury pollution in the waters around Harboøre Tange and Limfjord,Denmark

High concentrations of mercury have been measured in mussels (Mytilus edulis) collected in two ‘hot spot’ areas: (1) near a closed-down chemical factory on the west coast of the Limfjord, and (2) on groynes in the immediate vicinity of a chemical deposit in the dunes on the Danish west coast. By collecting comparable samples of mussels from chains of buoys, the mercury pollution in the western Limfjord could be traced 50–100 km into the central and innermost parts of the Limfjord as a gradual decreasing mercury concentration gradient. By collecting mussels from groynes north and south of the chemical deposit, it was possible to monitor the relative extent of the mercury leakage to the North Sea before and after the excavation of the deposit. The investigations have demonstrated the applicability of M. edulis as a monitoring organism for mercury when importance is attached to concentration gradients and distribution patterns in well defined and homogeneous samples of mussels collected from natural populations.     

Nitrogen compounds in the surface and subsurface waters of Karelia

Materials of long-term studies of the concentration and distribution of N forms (NH₄⁺, NO₃⁻, NO₂⁻, N_org) in precipitation, surface water and groundwater are generalized. Precipitation was found to be the main source of N compounds input into these waters. The effect of anthropogenic factors is local and does not influence the concentration and distribution of N forms in most water bodies that serve as wastewater recipients. The N forms dominating in precipitation are NO₃⁻ and N H₄⁺; N_org dominates in most surface water bodies, and NO₃⁻ dominates in groundwater. The median concentrations of N_tot in clear surface and subsurface waters are similar. The obtained characteristics of the concentrations and distribution of N forms in natural waters of Karelia can be used for other water bodies in the humid zone.     

Penetrative convection in the upper ocean due to surface cooling

Abstract

A new non-linear model of mixing and convection based on a modelling of two buoyant interacting fluids is applied to penetrative convection in the upper ocean due to surface cooling. In view of simple algebra, the model is one-dimensional. Dissipation is included, but no mean shear is present. A non-similar analytical solution is found in the case of a well-mixed layer bounded below by a sharp thermocline treated as a boundary layer. This solution is valid if the Richardson number, R _i , defined as the ratio of the total mixed-layer buoyancy to a characteristic rms vertical velocity, is much greater than unity. The model predicts a deepening rate proportional to R _i ^?3/4. The thermocline remains of constant thickness, and the ratio thermocline thickness to mixed-layer depth decreases as R _i ^?3/4 as the mixed layer deepens. If the surface flux is constant, the mixed-layer depth increases with time as t ^½. The vertical structure throughout the mixed layer and thermocline is given by the analytical solution, and vertical profiles of mean temperature and vertical fluxes are plotted. Computed profiles and available laboratory data agree remarkably well. Moreover, the accuracy of the simple analytical results presented here is comparable to that of sophisticated turbulence numerical models.     

Dissolved trace metals in the surface waters of Puget Sound

Employing clean and quantitative techniques, a marine monitoring programme succeeded in detecting large surface elevations in the concentrations of dissolved Cu, Zn and Pb in the marine surface waters of Puget Sound adjacent to Seattle and Tacoma, Washington. Physical mixing with cleaner waters was the controlling factor in reducing the dissolved concentrations of Cu downstream of these contaminated regions. Comparisons between Puget Sound waters and coastal waters adjacent to Puget Sound suggest that a portion of this Cu, Zn and Pb pollution is being advected out of Puget Sound. The low Ni and Cd concentrations found in this study indicate that these trace metals are not a significant pollution problem in the main basin of Puget Sound.     

Sampling for isotopic responses in surface waters

This paper considers situations in which stable isotopes may be used as natural tracers of precipitation through to surface waters. Two aspects affecting the applicability of the technique are highlighted: first, the variance through time of isotope concentrations in precipitation, i.e. the isotope input signal, and second, the attenuation or damping of this signal during the transmission of water downwards through the hydrological system. Both factors affect the likelihood of obtaining an isotope response, i.e. a variation of isotope concentrations in a surface water which may be related to variations in the precipitation input. Analysis of precipitation over the Malham area, U.K., reveals large isotopic variations through time. These variations, however, are only poorly correlated with meteorological variables (temperature, precipitation amount, and air mass type). Snowmelt and occluded frontal rainfall are suggested as providing the most reliable ‘spikes’ for an isotopic response at the output in tracing studies. In most hydrological systems, a high degree of signal attenuation is noted. In the Malham area of karst, 57 per cent of the total range of input variation was lost in surface waters, whilst 74 per cent was lost in mobile soil moisture. An isotopic response can only reasonably be expected in a system with rapid throughput, where there is little opportunity for mixing and storage of waters.