Particle fluxes during austral spring and summer in the southern Ross Sea,Antarctica

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 Novembe r-December 1994 and the second in December 1995 and January 1996. An assess ment of surface layer phytoplankton biomass and productivity was made simul taneously. Particle flux was measured using floating sediment traps whose c ollection efficiency was assessed rigorously. Phytoplankton biomass and pro ductivity increased rapidly in November-December, and biomass was maximal i n mid-December. Thereafter productivity appeared to decline substantially. Biomass declined as well, but mot as rapidly as productivity. Vertical flux rates were low early in the bloom period, averaging 457 mg m(-2) d(-1), bu t 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 o f sample collection. As in other regions, vertical flux of biogenic materia l is coupled with surface layer production and biomass. In our study area, however, a distinct temporal lag is introduced between surface production a nd flux at depth as a result of the temporal characteristics of the dominan t mechanism generating large particles (aggregation) as well as the charact eristic species of the region (Phaeocystis antarctica).