Fate of pelagic organic carbon and importance of pelagic-benthic coupling in a shallow cove in Disko Bay, West Greenland

Abstract

Biomass and production of phytoplankton, bacteria, proto- and mesozooplankton together with vertical flux of particulate organic carbon, sediment oxygen demand and biomass of macrozoobenthos were estimated over 2 wk in spring and 2 wk in autumn 2003 in a shallow cove in Disko Bay, West Greenland. In spring, bloom conditions were encountered with high phytoplankton concentrations of 20 to 30 mg chlorophyll a m-3. The zooplankton community associated with the spring bloom could not control the developing bloom, which resulted in high sedimentation rates of 1438 mg C m-2 d-1, of which 518 mg C m-2 d-1 could be related to chlorophyll a (chl a). The settling phytoplankton was ingested by filter-feeding as well as deposit-feeding bivalves. In autumn, the water column was stratified and nutrient levels reduced, resulting in a phytoplankton biomass below 0.5 mg chl a m-3. The vertical flux of particulate carbon was reduced to 235 mg C m-2 d-1. Compared to spring, benthic mineralisation rates had increased. Ingestion of chl a was reduced in filter-feeding and in deposit-feeding bivalves. The pronounced seasonal shift in production and mineralisation pathways clearly highlights the importance of the spring bloom in the costal waters of subarctic Greenland. Analysis of local sea ice conditions from 1979 to 2003 suggests that the mismatch between primary producers and copepods observed during 2 wk in spring could be related to an earlier than usual break-up of sea ice in 2003, which illustrates how climate can influence pelagic-benthic coupling. © Inter-Research 2007.