Phytoplanktonic DOC and POC production in the Bransfield and Gerlache Straits as derived from kinetic experiments of ¹⁴C incorporation

The production rates of DOC and POC by phytoplankton during the FRUELA 95 cruise were estimated by means of time-course experiments of ¹⁴C-bicarbonate incorporation. A three-compartment carbon exchange model was used to avoid the artifacts that may appear in end-point experiments due to heterotrophic removal of recently released DOC. The study area was classified into three regions with different ecological characteristics: Bransfield Strait, Gerlache Strait and the Gerlache-Bransfield Confluence (GB Confluence). Percent extracellular release (PER) for all stations ranged from 3% to 47%, with an average of 24%. In surface (5 m depth) waters, POC and DOC production rates were higher in Gerlache Strait than in the GB Confluence and Bransfield Strait. PER values followed an opposite trend, with an average of 26% in Bransfield Strait, 17% in the GB Confluence and 13% in Gerlache Strait. In Gerlache Strait, PER at 10 m depth was significantly higher than at the surface. With pooled data from all experiments, there was a positive relationship between DOC and POC production rates (log-log), but the slope significantly smaller than 1.0 indicated an inverse trend between PER and primary production rate. Phytoplanktonically produced DOC appeared to meet carbon requirements of heterotrophic prokaryotes in the whole area. A positive relationship between prokaryotic heterotrophic production and DOC production rate was found only in Bransfield Strait. These differences are discussed in relationship with the ecological characteristics of the different regions.