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 p rimary production across a wide spectrum of marine ecosystems. However, tot al utilization rates are poorly constrained due to a lack of data on conver sion efficiencies and/or bacterial respiration rates. We estimated total co mmunity dark respiration rates (DCR) from in vitro oxygen utilization and e stimated bacterial production from H-3-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, an d by choosing values for the bacterial growth efficiency. By comparing thes e derived bacterial respiration rates with the DCR we were able to constrai n conversion efficiency and bacterial production within various bounds. Bac terial biomass was 10% of phytoplankton stocks, and we considered that bact erial respiration was a similar fraction of the total respiration. To meet this constraint bacterial production rates likely averaged about 5-10% of t he net community production, and conversion efficiencies had to be in the r ange of 35-45%, similar to independent discrete measurements made during th e summer season on this cruise. Dark respiration rates are an absolute cons traint on the estimates of bacterial carbon demand. A low value of the leuc ine conversion factor (1.5 kgC mol(-1)) was required to meet this strong co nstraint. (C) 2000 Elsevier Science Ltd. All rights reserved.