Nepheloid layers and bottom currents in the Arctic Ocean

Abstract

Between 1965 and 1969, fifty-one profiles of light scattering were made in the central Arctic Ocean from Fletcher's Ice Island (T-3). The profiles, taken with an in situ photographic nephelometer extend from just below the surface to the bottom. Two distinctly different types of profiles were observed. At all stations the strongest scattering occurs near the surface, decreasing with depth in the upper layers. Over the Canada abyssal plain, light scattering is almost constant below 2000 meters, decreasing slightly with depth all the way to the bottom so that the bottom water is the clearest. Over the ridges and rises surrounding the Canada basin, however, scattering increases with depth below an intermediate scattering minimum. The zone of deep light scattering on the ridges and rises is called the bottom nepheloid layer. The bottom nepheloid layer is evidently caused by fine material that is maintained in suspension by the turbulent flow. Four spot measurements of bottom currents on the Mendeleyev ridge gave speeds of 4 to 6 cm/sec. One spot measurement over the Canada abyssal plain gave a speed of less than 1 cm/sec. This indication of swifter current speeds over the ridges is supported by bottom photographs in which animal tracks are much less evident on the ridges than on the Canada abyssal plain in spite of a greater abundance of life on the ridges. This is attributed to the higher current speeds, which obliterate the tracks. The observations suggest a counterclockwise deep circulation in the Canada basin with the currents confined primarily to the sloping margins of the basin. This pattern of deep circulation is in agreement with ideas and experiments on deep circulation with a concentrated source and distributed surface sink. Deep water enters the basin over a sill and leaves by upward diffusion through the halocline into the surface water, which then flows out of the basin.

Patterns of suspended particulate matter across the continental margin in the Canadian Beaufort Sea

“…Past the shelfbreak, the SPM at specific depths generally decreased with distance from the shelfbreak and with increasing depth. The c p (660) profiles in Canada Basin waters agree with the two types of profiles described in Hunkins et al (1969), first, in waters with bottom depths less than about 3000 m the SPM had minimum values roughly at mid-depths of 25 the water column and then increased towards the bottom forming a c-shaped profile, and second, in waters exceeding the 3000 m depth the SPM reached minimum values near the bottom. The deepest INL (below which no INLs were seen) extending to the Canada Basin abyssal plain was observed at the 2500-2600 m depth at the top of the adiabatic Canada Basin bottom water layer (Timmermans et al, 2003).…”

“…12). Past the 3000 m bottom depth, BNLs were essentially absent with the clearest waters found close to the bottom as may also be the case for the Canada Basin abyssal plain (Hunkins et al, 1969). Near-bottom SPM values based on c p (660) were ∼2×10 −3 g m-3 at the station A notable INL at stations CB-23, CB-27, and CB-21 was spreading in the layer immediately below the isopycnal surface where the potential density anomaly σ θ reached 28.096 kg m −3 or the salinity reached 34.956 (Fig.…”

A submarine fan in the Amundsen Basin, Arctic Ocean

“…1). The most important sediment transport in this part of the basin probably occurs in a near bottom nepheloid layer (Hunkins et al, 1969) and as the vertical £ux from fallout of biogenic matter and ice transported lithic material (Clark and Hanson, 1983;Reimnitz et al, 1994).…”

Light scattering properties of marine particles in coastal and open ocean waters asrelated to the particle mass concentration

“…Spectral slope of the exponential fit applied to the nonalgal particle absorption spectrum (nm Ϫ1 ) (Eq. 14) layers and other hydrodynamical features, as well as for monitoring particulate matter in the open ocean (e.g., Jerlov 1955;Pickard and Giovando 1960;Hunkins et al 1969;Pak et al 1970b;Carder and Schlemmer 1973;Baker 1976;Pak and Zaneveld 1977;Kitchen et al 1978;Zaneveld and Pak 1979;Eggimann et al 1980;Spinrad and Zaneveld 1982;Baker et al 1983;McCave 1983).…”