Deep Sea Research and Oceanographic Abstracts最新文献

The metabolism of entire clumps of Sargassum collected from the Florida Straits in February was measured in a flow-through system with and without the addition of arsenic. Net production and respiration ranged from 0.14 to 0.76 mg C g⁻¹ h⁻¹ and 0.22 to 0.86 ml O₂ g⁻¹ h⁻¹, respectively. Net production of the community over 24 h exceeded respiration by 1.3 times. Respiration values varied with time of night; maximum respiration occurred shortly after sunset. Arsenic additions had no measurable effect upon the metabolism of the community, but when the ‘steadystate’ distribution of arsenic species was altered, there was a rapid response to re-establish the ambient As (III)/As (V) ratio.

Measurements of currents, temperatures and salinities were made in March 1970 and 1971 on the north side of the Gulf of Cadiz in the Mediterranean undercurrent. Observations were concentrated in two areas. In the first the undercurrent is free from the sea bed and flows as a free jet although in contact with the continental slope on its northerly side, whilst in the second it is in direct contact with the sea bed and influenced by the topography of a submarine valley. These measurements demonstrate the mesoscale variability of the undercurrent, and the interruption of the flow in the first area by the arrival of denser near-bottom water and an eddy-like motion in the overlying water.

The interaction between temporally varying currents and the bottom topography of the ocean is investigated by the numerical and analytic examination of the following simple model. The flow of an inviscid, stratified fluid is initiated from relative rest in a uniformly rotating system containing an isolated topographic feature. The evolution of the flow redistributes vorticity and temperature in such a way that relatively cold water with anticyclonic vorticity exists over the topographic feature, while water shed from above the topographic feature sinks, thereby inducing a warm anomaly with cyclonic vorticity. For sufficiently strong oncoming flows, the shed fluid continually drifts downstream in the form of a relatively warm eddy. If the oncoming flow is relatively weak, the interaction between the anticyclonic and cyclonic vorticity distributions traps the warm eddy and it remains in the vicinity of the topographic feature.

We suggest that recent observations of an eddy in the vicinity of the Atlantis II Seamount and the existence of the large amount of high frequency energy near the bottom of the ocean measured by the MODE experiment may be partly explained in terms of the above mechanism. We conclude by speculating that vorticity redistribution by topography may be a contributing factor to cyclogenesis in the atmosphere.

Data from 86 detailed Zooplankton profiles taken during the EASTROPAC cruises of 1967 to 1968 have enabled a first-order description to be made of Zooplankton distribution in the upper 1000 m of the water column in relation to density, light, oxygen, and phytoplankton. A layer of abundant epiplankton contains a subsurface maximum that tends to coincide with the bottom of the mixed layer and with the depth of maximum carbon fixation, but lies above the chlorophyll-a maximum. Zooplankton abundance declines sharply downwards across the pycnocline, forming a discontinuity between the epiplankton and the low-biomass plankton below. Coincident with the deep sonic scattering layers are diurnal layers of migrant interzonal species which rise at night into the epiplankton. Major regional differences are caused by the shoaling of the pycnocline at the equatorial divergence, and the very deep pycnocline of the southern gyral region. An hypothesis, based upon the EASTROPAC data, is stated: that the form of phytoplankton profiles, in periods or regions of stable production, may be primarily determined by a depth-differential in herbivore grazing pressure, rather than by differential cell-sinking rates as is suggested in classical production models.

In four sedimentary environments off North Carolina 209 species of free-living marine nematodes were identified. Of these, 106 were restricted to one of four habitats. Clayey-silts (800 to 2500 m) contained the most stenotopic species (49). Quartz-algal sands (50 to 100 m) contained 35, foraminiferan sands (250 to 500 m) 17, and sandy silts (500 to 800 m) only 5 stenotopic species.

A sand zone (50 to 500 m) and a clayey-silt faunistic zone (800 to 2500 m) are recognized, separated by a transition zone (500 to 800 m) characterized by little endemism. There may be zonation of the fauna within these major zones.

Species diversity decreased with increasing water depth, attributable to the decreased number of microhabitats available in the clayey-silts. Diversity is largely a function of species richness. Withinhabitat diversity in the North Carolina sediments is higher than in Long Island Sound (a shallower, temperate body of water).

In a search for a natural occurrence of Taylor-column effects, salinity-temperature-depth (STD) observations were made in the Gulf Stream as it passed over Atlantis II Seamount. Although the stream path changed markedly during the course of the observations, one 5-day set of stations seems to provide a quasi-synoptic picture of the flow. Maps, based on this subset, of potential temperature at eight levels between 200 and 3500 m show deflections and distortions of isotherms near the seamount, and warm-core and cold-core eddies in its lee. The eddies are probably a consequence of the recent incursion of the Stream onto the seamount, while the other features seem qualitatively intelligible in terms of existing Taylor-column theory. From the data available, however, it is not possible to tell with certainty if there was a region of closed streamlines just above the seamount.

A simple linear model is used to investigate the possibility of baroclinic instability in the Arctic. The basic state consists of a barotropic flow directed along depth contours, a baroclinic component uniform in horizontal directions which decreases exponentially with depth, and an exponentially decaying stratification. With no β-effect there is always a shortwave cutoff for wavelengths shorter than the radius of deformation based on the surface N² and total depth. With β there appears to be no shortwave cutoff but the growth rate peaks near the same values of wavelength. The results suggest that the 10- to 20-km eddies observed in the Arctic are probably not generated by baroclinic instability in the open ocean but may arise from instability in the shallow regions.

Current-meter observations near 39°N, 70°W, on the continental rise, provide evidence that the motions with periods of 1 to 2 weeks are dominated by baroclinic topographic Rossby waves which decay upward from the bottom. Temperature and up-slope velocity are coherent and in quadrature at these frequencies, as predicted. The kinetic energy structure versus depth is consistent with horizontal wavelengths of 100 to 200 km. The spectra drop abruptly for periods shorter than a week, the shortest period the model says the slope and stratification around Site D can maintain. The principal axis of the velocity shifts from nearly perpendicular to the isobaths at 1-week period to nearly along the isobaths at long periods, in satisfactory quantitative agreement with the model.

The compressions of distilled water and of seawater of approximately 31, 35, and 39% salinity were measured at 10°C for pressures up to 1000 bars. The data were summarized by a ‘best’ least-square fit polynomial in pressure and salinity. The summary formula was combined withBryden's (Deep-Sea Research,20, 401–408, 1973) similar type fit to our earlier thermal expansion data (Bradshaw andSchleicher, Deep-Sea Research,17, 691–706, 1970) andFofonoff andBryden's (Journal of Marine Research, in press) recent empirical formula for sigma-0 of seawater to give an expression for the specific volume of seawater as a function of temperature, pressure and salinity in the salinity range 31 to 39%. At 35% specific volumes from this expression in the oceanographic range of temperature and pressure agree within 15 × 10⁻⁶cm³g⁻¹ with those computed using sound velocities (Wang andMillero, Journal of Geophysical and Research,78, 7122–7128, 1973). Our mean compressibilities for distilled water at 10°C also agree with those from sound velocities (to within 0·05%) but disagree with those ofKell andWhalley (Philosophical Transactions of the Royal Society of London, A,258, 565–614, 1965) by about 0·3%.