Dissolved organic carbon distributions in the Bransfield and Gerlache Straits, Antarctica

Abstract

Abstract During FRUELA’95 cruise, seawater samples were collected at the Bransfield and Gerlache Straits for the analysis of dissolved organic carbon (DOC) profiles throughout the water column. An excess of DOC probably derived from phytogenic material was observed in the upper mixed layer (UML; average: +22±13 μmol C l−1), compared to the constant concentration of refractory DOC below 400 m (44±4 μmol C l−1). The average excess DOC concentration was higher than the particulate organic carbon concentration indicating the major contribution of DOC to carbon export in this area. However, large spatial variability of DOC in the upper mixed layer (52–102 μmol C l−1) was observed: excess DOC contributed from 15% to 57% to the actual DOC concentration. Maximum average DOC concentrations in the UML were recorded in the Gerlache Strait (71 μmol C l−1) and in the Gerlache–Bransfield confluence (80 μmol C l−1), whereas minimum values were recorded in the Bransfield Strait (61 μmol C l−1). Several shelf and slope stations showed a slight increase of DOC (5–10 μmol C l−1) in the deep layer which might be related to organic matter release from the underlying sediments. Considering the net DOC release from phytoplankton, the low bacterial biomass and the reduced vertical DOC export, the DOC excess could build up in about 6 days for most of the sampling stations. The probable fate of the DOC excess is the eastwards horizontal transport by the Bransfield Current out of the study area.