Deep Sea Research and Oceanographic Abstracts最新文献

Sonobuoy modified to receive low (< 100 Hz) frequency sounds in the deep ocean were deployed from the R.V. Yaquina on the Rivera fracture zone and 4·3 kmoff San Benedicto Island. An array of at least two operating sonobuoys was maintained for 24 h at each station. Calculated earthquake magnitudes were 2·2 to 3·7 on the Richter scale. Most of the acoustic energy in the signals was below 40 Hz and recorded well on the modified sonobuoys but poorly on simultaneously monitored unmodified buoys. A swarm of microearthquakes following a magnitude 4·3 earthquake was recorded on the Rivera fracture zone site while seismic activity at the San Benedicto Island was more sporadic. Epicentral distance from the sonobuoys, calculated from the T-P interval (when present), ranged from 10 to 120 km, most less than 20 km. The earthquake magnitude versus occurrence rate curve for the Rivera fracture zone events has b value of 0·6, indicating that the earthquakes were associated with the fracture zone rather than the median rift of the East Pacific Rise.

Time series of chlorophyll a fluorescence and temperature have been obtained at a number of depths, from two widely separated areas of the North Atlantic. These data strengthen the view of Platt and his co-workers that, over space scales between 40 m and 1 km, phytoplankton behaves as a passive contaminant of fluid motion. It was found that the observed high coherence between chlorophyll a and temperature extended to longer wavelengths for stations observed in temperature spring bloom conditions, than for stations observed in tropical summer conditions.

Certain features of the temperature and chlorophyll a power spectra are discussed which suggest that, at frequencies less than the Brunt-Va¨isa¨la¨frequency, internal waves make a significant con-contribution to the spectrum. This implies that, for space scales between tens of meters and a few kilometres, improved sampling methods will be required to separate the effect of internal waves from the real spatial heterogeneity of the phytoplankton.

On a cruise of the R.V. Meiring Naude´, wave records wer taken in and ou the Agulhas Current. These have been analysed using the standards methods of spectral analysis and the energy increase in a frequency band from 0.067 to 0.02 Hz determined. Rough agreemeent with theory is found up to maximum current speeds of 1.6 m s⁻¹.

Series of chlorophyll a and temperature obtained from multiple-depth horizontal tows have been treated by spectral analysis. Composite power or variance spectra show the chlorophyll spectra to be similar but not identical in shape to the temperature spectra. Temperature and chlorophyll at the same depth usually were significantly coherent at wavelengths greater than 100 m. Parameters measured 4 to 5 m apart in depth showed no significant coherence.

In general, for runs with low chlorophyll variance and high coherence with temperature, most of the observed variance in the chlorophyll is attributed to internal wave and vertical mixing effects. However, in several runs with high chlorophyll variance, the observed variance is more than 10 times that which could be accounted for by internal wave effects. Such ‘patchy’ observations are believed to indicate regimes of greater biological activity, as characterized by higher growth rates.

Foraminifera from 54 cores from the surface and slopes of the Ontong Java Plateau were used to identify Tertiary outcrops as old as Late Eocene on some of the slopes. Using the direct relationship between radiolarian concentrations and bathymetry, it was determined that the Tertiary deposits from the slopes accumulated in deeper water than the synchronous deposits sampled through the plateau surface (Deep Sea Drilling Project, Site 64), indicating that the topographic high has existed at least since early Tertiary time. Comparison of assemblages from several foraminiferal zones of the plateau and certain of the adjacent Solomon Islands supports the conclusion of a genetic connection between those islands and the plateau.