Origin of Deposited Material Sedimented in a Marine Bay

Abstract

Suspended and sedimented particulate carbon, nitrogen, chlorophyll a, and phaeophytin were measured at various depths throughout the year in a small marine bay. Seasonal and vertical differences in sedimentation rates were not simply related to changes in concentration of suspended particulate matter. Chlorophyll a/total pigment, carbon/nitrogen, and carbon/chlorophyll a ratios in suspended and sedimented material were usually different. Sedimentation rates generally increased with depth with greatest increases during periods of low stratification. Resuspension and horizontal transport of sedimenting material was implied by discontinuities in sedimentation at particular depths. Annual sedimentation of particulate carbon at 20 m depth (below the seasonal thermocline) was equivalent to 15% of the estimated supply from photosynthetic and chemosynthetic production, river discharge, and sewage input. Material deposited during periods of stratification, however, which coincided with high rates of primary production and increased zooplankton biomass during the summer, contained high amounts of carbon and chlorophyll a with a low carbon/nitrogen ratio indicative of a supply from biological production. Thus, although a small fraction of the total suspended particulate matter annually available was deposited, large differences in the quantity and quality of sedimented material occurred seasonally. Key words: sedimentation, resuspension, suspended particulate matter, biological production, organic supply, coastal embayment