Deep Sea Research and Oceanographic Abstracts最新文献

The clay mineralogy of 235 surface sediment samples from the western Indian Ocean reveals many sedimentary sources and processes: (1) some areas, mainly in the central Indian Ocean, where very little sediment transport is involved, have smectite-rich clays derived from the alteration of in situ submarine basalts. (2) In many other areas, the mineralogy is significantly influenced by several modes of long-distance sediment transport, and the continental climate or the southern ocean volcanism. These areas consist of: (a) smectite-rich sediments in the Crozet and Madagascar basins and in the eastern Arabian Sea; (b) illite-rich sediments in the Indus Cone, the Agulhas Basin, and the ocean adjacent to Africa west of the Agulhas Plateau; (c) illite-palygorskite-rich sediments in the Carlsberg Ridge, Owen Ridge and in the westernmost Arabian Sea; (d) illite-kaolinite-rich sediments in the Mozambique Basin and in the regions between Madagascar and Africa; (e) kaolinite-rich sediments adjacent to central Africa and Madagascar. (3) A third category of areas has mixed type sediments with no specific mineral in characteristically high amounts. Mixing of sediments derived from the alteration of in situ submarine basalts and/or from other areas rich in different minerals resulted in this group.

The mineral distributions suggest that the Antarctic Bottom Water circulation is responsible for the sediment dispersal in the Crozet, Madagascar, Agulhas and Mozambique basins. Although the aeolian process could be effective throughout the Arabian Sea, it is dominant only in the western Arabian Sea.

Maps of the stream function field at 4 depths in the ‘MODE region’ of the North Atlantic Ocean are presented. The maps are of variable quality. The maps at 500 and 1500 m serve to show the sense of rotation of eddies throughout the period described and the shapes of eddies for a substantial part of this time. At the two lower levels, 3000 and 4000 m, the shapes of eddies are not defined. Maps of the stream function field in the time-longitude plane show unmistakable evidence of westward propagation of the eddy field. The speed of westward pattern propagation is 5 cm s⁻¹ below the thermocline and 2 cm s⁻¹ above the thermocline.

Measures of the diversity and relative abundance of gastropod predators are positively and significantly correlated with overall gastropod diversity in 15 epibenthic sled samples collected from 478 to 4862 m along the Gay Head-Bermuda transect. Predator diversity is lowest on the abyssal plain, highest on the lower continental slope and abyssal rise, and relatively low on the upper continental slope. The variation of gastropod predator diversity with depth is similar to those of their most probable prey, the polychaetes and protobranch bivalves. Predator diversity and overall diversity were also related to variation in faunal density with depth. Density decreases exponentially with depth and reflects the average rate of production reaching the deep-sea benthos. Relationships among diversity, predation, and production are consistent with the theory that predators exert a diversifying influence on communities and that the degree to which they are able to do this depends on the rate and stability of production. The results suggest that both predation and productivity are important to biological accomodation in deep-sea communities and that their relative contributions to maintaining diversity vary considerably with depth.

A simple, inexpensive and effective system for collecting faecal pellet material from marine zooplankton is described. With euphausiids, about 750mg wet weight of faecal material of excellent consistency can be recovered from about 1000 euphausiids within 12 h of shipboard collection of the animals.

The formation of layered structure by the imposition of an unstable buoyancy flux on a region containing opposing, uniform gradients of two components is examined. Turner (Journal of Fluid Mechanics, 33, 183–200, 1968) investigated the formation of layers when a stable salinity gradient is heated from below. The present work is an extension of his, allowing for the presence of a destabilizing temperature gradient in the interior of the fluid. Experiments were carried out using two solutes (sugar and salt) as the components contributing to the density field. It is found theoretically, and confirmed by experiment, that the scale of the layers depends on the ratio of the two density gradients in the interior Gϱ. The layers were observed to form sequentially with increasing distance from the boundary across which the buoyancy flux was applied. The relative contributions of the energy provided by the boundary flux and that stored in the destabilizing component during the formation of the first layer are found to depend on Gϱ but not on the magnitude of the boundary flux. When Gϱ=0, and there is no destabilizing density gradient, all the energy comes from the imposed flux. As Gϱ→1, the energy from the destabilizing component becomes more important, providing all the energy in the limit. Some observations of destruction of fine-structure are reported. Two kinds were observed. One type was characterized by the vertical migration of an interface to an adjacent one thereby destroying the layer in between. The other kind was identified by a breakdown of an interface in situ, apparently resulting from an equalization of the density of the two layers on either side. Finally some brief comparisons with oceanic fine-structure are made.

A meandering zonal jet was found in the winter circulation through the region between New Zealand and Norfolk Island. This current is marked at the surface by a temperature and salinity front, the Mid Tasman Convergence. It is suggested that the zonal jet connects the East Australian Current System with the weaker western boundary currents found off the New Zealand coast. The effects of bottom topography on the flow appear to be small except near the shallowest part of the Norfolk Ridge. Observed movements in the front were consistent with the westward propagation predicted by planetary wave theory.