Edward M. Thorndike

Suspended Matter in Deep Ocean Water

A nepheloid layer has been observed by optical means in the lower part of the water column on the continental slope and rise. By sampling it has been found to be a suspension of lutite, apparently in sufficient quantity to induce downslope flow. Sediment transported in the nepheloid layer may be a major component of deep-sea sediment bodies.

Suspended matter along the continental margin of the North American Basin

Abstract Vertical profiles of light scattering at 31 stations along the western margin of the North American Basin establish the bottom nepheloid layer as a permanent (non-seasonal) feature of the bottom waters of this region in depths greater than 3000 m. Its thickness ranges from 300 to 2400 m, the greatest thickness occurring toward the south off the Blake Plateau and Bahama Islands. Scattering intensities are greatest on the lower continental rise and abyssal plain north of Cape Hatteras. This layer represents sediment in suspension in the southerly bottom current along the western margin. Frequently near the outer ridges, the water is relatively clear adjacent to the bottom under the main nepheloid layer. In the Gulf Stream at about 500 m, the approximate depth of a high gradient in horizontal velocity, a marked increase in light scattering may mark the Sargasso Sea Water-Slope Water boundary.

Turbidity distribution in the Atlantic Ocean

Abstract The regional coverage of Lamont nephelometer data in the North and South Atlantic can be used to map seawater turbidity at all depths. At the level of the clearest water, in the mid-depth regions, the turbidity distribution primarily reflects the pattern of productivity in the surface waters. This suggests that the ‘background’ turbidity level in the oceans is largely a function of biogenic fallout. The bottom waters of the western Atlantic generally exhibit large increases in turbidity. The most intense benthic nepheloid layers are in the southwestern Argentine basin and northern North American basin; the lowest bottom water turbidity in the western Atlantic is in the equatorial regions. Both the Argentine and North American basin bottom waters appear to derive their high turbidity largely from local resuspension of terrigenous input in these basins. In contrast to the west, the eastern Atlantic basins show very low turbidities with the exception of three regions: the Mediterranean outflow area, the Cape basin, and the West European basin.

Long-term photographic, current, and nephelometer observations of manganese nodule environments in the Pacific

Long-term measurements on and near the seafloor were made at five locations in the Pacific as part of the Manganese Nodule Project (MANOP). Bottom Ocean Monitor (BOM) tripods deployed at each site contained a time-lapse camera, nephelometer, and current meter. From nearly three years of photographs of the seafloor, there was no evidence that benthic organisms turned over, rotated, or moved nodules. There were indications, however, that benthic organims cleaned sediment from the tops of nodules and in some cases deposited sediment underneath nodules. Currents never exceeded the expected threshold for sediment resuspension of nodule movement. Particle concentrations in the water remained uniformly low throughout the deployments. Degredation of fecal pellets and organic matter proceeded more rapidly than expected. All changes of the seafloor morphology were attributable to the activity of organisms as opposed to currents. The occurrence in one photo sequence of dark, fluffy globs may be related to phytoplankton blooms in the region of equatorial upwelling.

Fish, Crustaceans, and the Sea Floor Under the Ross Ice Shelf

Baited traps and a camera lowered through the Ross Ice Shelf, Antarctica, at a point 475 kilometers from the open Ross Sea and to 597 meters below sea level revealed the presence of fish, many amphipods, and one isopod. Biological or current markings were not evident on a soft bottom littered with subangular lumps. A fish was caught through a crevasse 80 kilometers from the shelf edge.

Suspended Matter in the Red Sea Brines and Its Detection by Light Scattering

A dense layer of suspended particulate matter exists below a depth of 1,900m in the Atlantis II Deep in the Red Sea. This layer was detected with a light scattering meter (nephelometer) at two locations within this deep and was found to conform generally to the zone of hot brines. The nepheloid layer scatters light with a constant intensity except for a few very thin internal layers of greater light scattering which correlate with the interface between the different temperature and salinity brines. The intensity of light scattering is found to increase gradually over an interval of eighty meters in the transition zone between the hot brine and the normal Red Sea deep water. The particles which produce the light scattering are interpreted as the colloidal suspensions and mineral precipitates created by the interaction of the reducing, acidic, and metal-containing hot brine with the oxidizing and alkaline overlying normal Red Sea deep water.

A comparison of suspended particulate matter from nepheloid and clear water

Abstract Particulate matter from the nepheloid layer and from regions of clearer water have been examined under the light microscope to determine particle concentration, size and composition. The total count of suspended particles is a basic difference between water samples from nepheloid layers of the North American and Brazil basins, and samples from the clearer water over the Mid-Atlantic Ridge in both the North and South Atlantic. The nepheloid layer of the North American Basin has four times, and the Brazil Basin three times the particle density of clearer water over the mid-ocean ridge. A greater percentage of particles of μ size prevails in nepheloid water ranging from 85–96% as compared to a range of 76–87% in the clear water. Non-opaque mineral grains form the major constituent.

A suspended-drop current meter

Abstract : A simple and direct method for measuring ocean currents is given by providing an identifiable point in the water and determining its displacement in a known time interval. The speed is obtained by dividing the displacement by the time, and the direction of the velocity is the direction of the displacement. The method is capable of measuring very small velocities and also rather large ones. An identifiable point can be provided by a small drop of colored liquid having approximately the same density as sea water but being immiscible with it. Positions can be obtained from photographs of the drop. Knowledge of the time intervals between photographs can be provided by a motor-driven timer or by a watch. A magnetic compass in the field of view of the camera that photographs the drop can provide the direction. (Author)

Corehead camera for measurement of currents and core orientation

Abstract The corehead camera is an instrument designed for use with the piston coring apparatus. It has been used for determining the direction and strength of the bottom currents and for core orientation. Results from the central North Pacific indicate that bottom current velocities are of the order of 1–2 cm/sec. Manganese nodules were photographed on the bottom and have been disturbed by the coring operation. Other transient bottom effects can be monitored.

Light Scattering In The Sea

Nephelometers for making in situ measurements of light scattering at all depths from the surface to the bottom of the ocean are described. Preliminary results in the Atlantic, Pacific, and Arctic oceans and in the Bering and Caribbean seas are summarized.