Deep Sea Research (1953)最新文献

The quantitative distribution of heterotrophs in the water column of the Atlantic Ocean between Greenland and the Tropic of Capricorn (along 30°W), in the Norwegian, and in the Greenland Seas was studied. In the tropics the abundance of micro-organisms which assimilate slightly decomposed, non-humus organic matter is great, while in the subarctic and arctic areas it is low.

Equatorial-tropical water, rich in heterotrophs, was identified in the subatropic and subantarctic zones of the Atlantic Ocean, in the Norwegian and in the Greenland Seas at various depths. It occurred not only down to 1000 m but also much deeper at 2000–2500–3000 m.

Judging by the finding of equatorial-tropical water layers or ‘islands’ in the Atlantic Ocean, in the western Norwegian Sea and in the Greenland Sea at the same levels, it may be supposed that the circulation of these waters at certain depths is stable over extensive areas.

Most of the Atlantic Water (along 30 °W) from Denmark Strait to the Tropic of Cancer, is of arctic origin, i.e., water with few heterotrophs. These waters penetrate into the tropics and cross the equator. However, in the equatorial-tropical zone they do not form as thick a layer as Defant (1957) estimates.

Microbiological data indicate that waters in the equatorial-tropical zone of the Atlantic are significantly enriched by slightly decomposed, non-humus organic matter. In this respect they are similar to the Equatorial Water Masses of the Indian and Pacific Oceans. They, therefore, cannot be considered as merely transitional between the Central Water Masses of the northern and southern Atlantic.

Mass spectrometric measurements of nitrogen/argon and nitrogen isotope ratios have been used to examine the fate of nitrogen arising from the decomposition of organic matter in two anaerobic marine environments, the Cariaco Trench in the Caribbean Sea and the Dramsfjord in Norway.

Values of N₂/A in these waters are larger than would be expected from dissolved atmospheric gases. By assumingthat the A concentration is biologically unaffected, the excess quantities of N₂ can be calculated. These are in good agreement with the amounts of nitrogen which would be expected to arise from the decomposition of organic matter. The latter values are computed from the observed concentrations of nitrogen compounds and either the observed concentrations of inorganic phosphate or the amounts of oxygen (either free or bound in the sulphate ion) consumed from the water.

It is shown that nitrogen isotope ratios are markedly different in the nitrogen of biogenic origin from those in nitrogen dissolved from the atmosphere.

It is shown that it is probable that free nitrogen can be formed from organic matter only through the denitrification of nitrate, formed as an intermediate.

Various factors which influence the concentrations of gases dissolved in sea water are discussed. A surface equilibrium model is proposed, and results presented to test the model and to ascertain whether or not nitrogen dissolved in sea water is biologically and chemically inert. The method utilized argon as a reference gas, with a mass spectrometer as the primary analytical tool. The conclusion is reached that within ± 1 per cent the model is applicable and nitrogen is ‘conservative.’ The possible implications of apparent small differences between the predictions of the model and the experimental results are discussed. There is some evidence that the nitrogen 29/28 relative abundance in the dissolved gas may be greater than that in the atmosphere by approximately one part in 10,000.

The surface of the Pacific Ocean stands about 40 cm higher than the Atlantic Ocean with respect to the 1000-decibar surface, and the North Atlantic and North Pacific stand respectively about 14 and 17 cm higher than the South Atlantic and Pacific. The North Atlantic is warmest and saltiest, the South Atlantic is coldest and densest, and the North Pacific is least dense and least salty.

The extreme values in temperature and salinity of the North Atlantic are probably related to the formation of the deep water there, which carries away from the upper layer the cold water of relatively low salinity. If this water spreads into the South Atlantic at depth and is replaced with warm saline surface water from the South Atlantic via the South Equatorial Current and the Gulf Stream, then the South Atlantic should be substantially cooler and less salty.

The difference in density and sea level of the Atlantic and Pacific oceans may stem from the difference in latitude of the southern tips of America, Africa, and Australia, and the constriction of the west wind drift at Drake Strait. Only the densest surface waters of the Pacific pass through to the Atlantic, while lighter waters from lower latitudes of the South Atlantic pass eastward south of Africa. Further, the constriction of the flow by Drake Strait may result in a higher sea level on the Pacific side through the effect of Windstau (Montgomery, 1938).

The density difference between the southern and northern oceans may be partly a consequence of the west wind drift around Antarctica. This is the greatest current of all oceans. Its flow is approximately geostrophically balanced and the surface slopes down to the south. The northern west wind drifts are not so strong, are at lower latitudes, and the high latitude flow is westward with slope upward to the north.

These differences are not confined to the upper thousand metres. The average density difference between the Atlantic and the Pacific from the surface to the bottom is about 17 × 10⁻⁵ g/cm³. Referred to some deep surface such as 4000 decibars, the Pacific stands about 68 cm higher than the Atlantic.

Benthic animals are essentially absent at the deepest part of Santa Barbara Basin where the oxygen content of the bottom water is very low and where hydrogen sulphide is present in surface layers of the sediments. Past periods of similarly barren seafloor in the area are recorded by the presence of laminated sediments in cores. These periods are alternated with others when benthic megafauna was sufficiently abundant to mix and homogenize the sediments. The presence or absence of benthic megafauna in the basin appears to be controlled by small differences in the content of oxygen in bottom waters. It is inferred that periodically oxygen contents greater than 0·1 ml/l result from the inflow of larger than ordinary quantities of new basin water, which in turn is permitted by greater than normal mixing of basin waters by standing internal waves.