MEPS 249:53-67 (2003)  -  doi:10.3354/meps249053

Rates of dissolved organic carbon production and bacterial activity in the eastern North Atlantic Subtropical Gyre during summer

E. Teira1,5,*, M. J. Pazó1, M. Quevedo2, M. V. Fuentes3, F. X. Niell4, E. Fernández1

1Departamento de Ecología y Biología Animal, Universidad de Vigo, 36200 Vigo, Spain
2Departamento de Biología de Organismos y Sistemas, Universidad de Oviedo, 33071 Oviedo, Spain
3Departamento de Microbiología, and
4Departamento de Ecología, Universidad de Málaga, 29071 Málaga, Spain
5Present address: Royal Netherlands Institute for Sea Research (NIOZ), Department of Biological Oceanography, PO Box 59, 1790 AB Den Burg, The Netherlands

ABSTRACT: Rates of particulate organic carbon (POC) production, dissolved organic carbon (DOC) production and bacterial production were measured at 8 stations in the eastern North Atlantic Subtropical Gyre during August 1998. The euphotic-depth-integrated POC rate was on average 27 mgC m-2 h-1. The corresponding averaged integrated DOC production rate was 5 mgC m-2 h-1, i.e. about 20% of the total primary production. No statistically significant relationship was found between the rates of POC and DOC production, suggesting that other processes besides phytoplankton exudation, such as cell lysis or protist grazing, could be implied in the release of dissolved organic materials to the oceanic environment. Euphotic-depth-integrated bacterial biomass and production were on average 214 mgC m-2 and 1.4 mgC m-2 h-1, respectively. The lack of correlation between the rates of DOC release and bacterial activity and a bacterial carbon demand (BCD, calculated using an estimated bacterial growth efficiency ranging from 11 to 18%) in excess of DOC production suggested the existence of additional organic carbon sources (both allochthonous and/or autochthonous reservoirs), apart from in situ phytoplankton-derived DOC production, for the maintenance of bacterial activity in this region during summer 1998. This uncoupling between phytoplankton and bacterioplankton could partially explain the heterotrophic metabolic balance in this oligotrophic region during summer 1998.

KEY WORDS: Phytoplankton · Bacteria · Primary production · DOC production · Bacterial activity · Coupling · North Atlantic Subtropical Gyre

Full text in pdf format