Constraining bacterial production, conversion efficiency and respiration in the Ross Sea, Antarctica, January–February, 1997

Bacteria consume dissolved organic carbon at rates averaging about 50% of primary production across a wide spectrum of marine ecosystems. However, total utilization rates are poorly constrained due to a lack of data on conversion efficiencies and/or bacterial respiration rates. We estimated total community dark respiration rates (DCR) from in vitro oxygen utilization and estimated bacterial production from 3H-leucine incorporation during January–February 1997 in the Ross Sea, Antarctica. Bacterial respiration rates (BR) were estimated by assuming that BR was less than some fraction of DCR, and by choosing values for the bacterial growth efficiency. By comparing these derived bacterial respiration rates with the DCR we were able to constrain conversion efficiency and bacterial production within various bounds. Bacterial biomass was 10% of phytoplankton stocks, and we considered that bacterial respiration was a similar fraction of the total respiration. To meet this constraint bacterial production rates likely averaged about 5–10% of the net community production, and conversion efficiencies had to be in the range of 35–45%, similar to independent discrete measurements made during the summer season on this cruise. Dark respiration rates are an absolute constraint on the estimates of bacterial carbon demand. A low value of the leucine conversion factor (1.5 kgC mol−1) was required to meet this strong constraint.