Deep Sea Research and Oceanographic Abstracts最新文献

Over 5500 km of sounding lines were used to construct a detailed bathymetric chart of the sea floor between Honduras and the southern Cayman Trough. The submarine morphology is related clearly to the tectonic setting. Complex transform faulting has ruptured the crust seaward of the Honduras continental margin into a series of deep grabens separated by irregular submarine ridges. Because of the proximity of the Cayman Trough, the western continental margin is a faulted platform characterized by an irregular shelf as narrow as 10 km and a steeply dipping slope; both shelf and slope have been modified substantially by the growth of thick reef masses. Further east, tectonism is reduced as a result of the divergent trends of the Cayman Trough and the Honduras continental margin. Consequently, the eastern margin sector is a depositional platform consisting mostly of a broad, smooth shelf and gentle slopes. Submarine erosion and local slumping have steepened the slope throughout the area.

The authors conducted a detailed quantitative analysis of dissolved and particulate hydrocarbons in the surface microlayer of the oceans, sampled by a metallic screen, with respect to the underlying water. The n-alkane content varies from 0.11 to 5.66 μg 1⁻¹ in the underlying water: much higher concentrations are encountered in the microlayer, reaching as high as 1200 μg 1⁻¹. On the average, the n-alkanes account for 10% of total hydrocarbons in the underlying water and 15% of these in the surface microlayer. The hydrocarbons are in general of biological origin (distribution of n-alkanes centred around n C₂₇ to n C₂₉, approaching that of algae). Of note is the contribution of petroleum pollution. The remarkable fact is the accumulation of hydrocarbons in the surface microlayer, with an enrichment factor averaging 50.

Acoustic observations of a low-density sediment flow originating from a dredge operating in the main Miami shipping channel have been made. The flow proceeded seaward along layered thermal gradients at the top of the shallow thermocline and at greater depths. Acoustic, thermal, salinity, chemical, and transmissivity measurements were made during summer and winter in 1974.

Measurements at 12 kHz indicate that there are at least three regions in the eastern tropical Pacific that can be distinguished by volume sound scattering profiles. These regions are consistent with the known distribution of midwater fishes.

The Airborne Expendable Bathythermograph (AXBT) system is described. Results of extensive calibrations and field tests are presented. It is shown that with proper calibration these devices are a useful oceanographic research tool with temperature accuracies of a few tenths of a degree Celsius.

Gulf Stream cold core rings are major oceanographic features in the northwestern Atlantic Ocean. During formation, cold water of Slope origin and the associated flora and fauna are entrapped within a ring of Gulf Stream water. These systems generally move southwesterly into the Sargasso Sea and are of biological interest because they offer a unique opportunity to assess the relative importance of physical and biotic factors in determining the distribution and abundance of plankton organisms. In effect, the formation and consequent decay of a cold core ring represents a large-scale ecological field experiment wherein major environmental changes are gradually imposed on a plankton community.

Four cruises have been made to sample Gulf Stream rings and the surrounding Sargasso Sea. Biomass has been estimated and selected species of Zooplankton, phytoplankton, and midwater fish populations have been assessed. Concurrent hydrocasts have yielded physical-chemical data.

Although a ring may remain physically identifiable for as long as two years, decay of the initially distinct biological community appears to be more rapid. A Zooplankton assemblage appears to persist longer than a phytoplankton assemblage. The season of formation appears to be critical in determining the biological changes of a Gulf Stream ring. The rapid demise of the Slope Water species assemblages in the rings may be the result of biological interactions with the Sargasso Sea assemblage initiated by the rapid modification of physical and chemical properties of ring surface waters.