Sinking rates of phytoplankton assemblages in the Weddell Sea marginal ice zone

Abstract

Sinking rates of phytoplankton assemblages from the Weddell Sea marginal ice zone were measured during a cruise in November-December 1983. A homogeneous sample method (SETCOL) was used to measure sinking rates which permitted rates of various parameters of particulate matter to be determined simultaneously. Parameters assayed in this study included chlorophyll a. phaeophytin, biogenic silica, particulate carbon, particulate nitrogen, and for certain stations, numbers of diatoms. Sinking rates varied within each measurement but exhibited the following trends: phaeophytin > biogenic silica > particulate carbon > diatoms > particulate nitrogen > chlorophyll a. Sinking rates as determined by chlorophyll a ranged from 0 to 2.73 m d-' (Y = 0.89), i.e. are similar to those reported for temperate and subpolar regions of the ocean. Phytoplankton assemblages from pycnoclines generally sank slower than those from the surface; differences in seawater density and viscosity between the 2 depths could account for no more than 5 '10 of the observed differences. Samples placed in the dark tended to sink faster than those placed in surface light. The reported rates represent the settling of suspended microparticulates within the upper water column in the absence of turbulence and should not be extrapolated to estimate the vertical flux of particulates from the euphotic zone.