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The distribution and movement of chloropigments (chlorophylls and associated degradation products) in the bottom boundary layer near Duck, North Carolina, were examined during July and August 1994. Time series of chloropigment fluorescence, current velocity, and surface wave properties were acquired from instruments mounted on a bottom tripod set at 20 m depth. These data were combined with moored current meter measurements, meteorological data, and shipboard surveys in a comparative assessment of physical processes and chloropigment distribution over a wide range of temporal and spatial scales. Two dominant scales of chloropigment variation were observed. On numerous occasions, small-scale (order m) structure in the near-bottom fluorescence field was observed, even in the absence of identifiable structure in the temperature and salinity fields. Over larger time-scales and space scales, variations in fluorescence were related to changes in water mass properties that could be attributed to alternating events of upwelling and downwelling. This view was reinforced by shipboard measurements that revealed correlations between fluorescence and hydrographic fields, both of which were modified by wind-forced upwelling and downwelling and by the advection of low-salinity water from Chesapeake Bay. Local resuspension of sediments did not contribute appreciably to the near-bottom pigment load seen at the tripod, because of low bottom stress. Estimates of chloropigment flux indicated a net shoreward transport of chloropigments in the lower boundary layer. However, the rapid fluctuations of currents and pigment concentrations gave rise to large and frequent variations in chloropigment fluxes, generating uncertainty in extrapolations of this finding to longer timescales.

This study was motivated by the need to understand dispersion processes which affect the redistribution of nuclear wastes in the Arctic from dump sites in the Kara Sea and in the rivers which flow into the Kara Sea. We focus on vertical profiles of light beam transmission and fluorometry made over the delta region fronting the Ob and Yenisey Rivers and over the East Novaya Zemlya Trough (ENZT). The delta region fronting the Ob River Estuary contains a large repository of particles in a dense bottom nepheloid layer with a maximum centered ∼100 km in front of the estuary entrance and covering an area of roughly 200 km diameter. This suspended particle mass repository appears to contain both sediments and detritus and lends credence to the Lisitsyn [1995] concept of the marginal filter zone. In the deep water of the ENZT we found a strong increase of beam attenuation with depth, indicating a relatively large increase of particle mass concentration from ∼50 m to the bottom (depths in excess of 300 m). The strongest concentration was adjacent to the southeast coast of Novaya Zemlya. We suggest that a type of hyperpycnical flow occurs from accumulation of sediments in the bottom waters of Novaya Zemlya fjords which then cascades down the steep slopes adjacent to the island, producing the particle mass distribution as observed by the transmissometer. The accumulation of these repositories of high particle mass concentrations in suspension would suggest that the residence time is high but that storm-driven events could act to disperse the material.

The flux of particles from the euphotic zone through 200 m was investigated on the Ross Sea continental shelf during two cruises, the first in November-December 1994 and the second in December 1995 and January 1996. An assessment of surface layer phytoplankton biomass and productivity was made simultaneously. Particle flux was measured using floating sediment traps whose collection efficiency was assessed rigorously. Phytoplankton biomass and productivity increased rapidly in November-December, and biomass was maximal in mid-December. Thereafter productivity appeared to decline substantially. Biomass declined as well, but not as rapidly as productivity. Vertical flux rates were low early in the bloom period, averaging 457 mg m−2 d−1, but increased markedly in late December and January (mean = 1160 mg m−2 d−1). Daily losses due to vertical flux represented only 2.3% of the surface layer particulate organic carbon standing stock. Measured particle fluxes were greater than those observed previously, and this is attributed to the period and depths sampled as well as to the care taken to ensure accuracy of sample collection. As in other regions, vertical flux of biogenic material is coupled with surface layer production and biomass. In our study area, however, a distinct temporal lag is introduced between surface production and flux at depth as a result of the temporal characteristics of the dominant mechanism generating large particles (aggregation) as well as the characteristic species of the region (Phaeocystis antarctica).