González, Rodrigo R., and Renato A. Quiñones

Centro COPAS, Departamento de Oceanografía, Universidad de Concepción, Casilla 160-C, Concepción, Chile, Tel: +56 41 204239, Fax: +56 41 256571, E-mail: rogonzal@udec.cl

Catabolic carbon demand of microplankton communities inhabiting the oxygen minimum zone (OMZ) of the Humboldt Current System (HCS)

The presence of the subsurface OMZ in extensive areas of the HCS has important effects on the metabolism of the organisms inhabiting this environment. The catabolic demand of the microplankton community (<100um) living in the OMZ and its impact on carbon biogeochemistry remains unknown. Here we characterize, the potential enzymatic activities involved in catabolic pathways of this microplanktonic community. A specific index was estimated for catabolic energetic demand in carbon units. The following enzymes were analyzed: Pyruvate oxidoreductases (LDH, OPDH, ALPDH and STRDH), Ethanol dehydrogenase, Malate dehydrogenase (MDH), Citrate synthase, and Nitrate reductase. Electron transport system activity was also estimated. Microplankton biomass was determined as particulate ATP.

Our results demonstrate the existence of significant potential catabolic activity in the OMZ implying that this zone is biogeochemically active. Inside the OMZ, MDH presents the highest apparent specific catabolism and the highest correlation with microplanktonic biomass (R² = 0.8; p < 0.00001). The catabolic demand of the microplankton cells in the OMZ corresponds to 4.5 ng C day^-1 pgATP^-1. Based on estimates of (i) the extension of the OMZ in the HCS, (ii) the average microplanktonic biomass in the OMZ and (iii) microplanktonic catabolism; we have roughly estimated that the total flux of carbon used in this OMZ as metabolic fuel is about 4.1 Pg C y^-1. We discuss the relevance of the OMZ of the HCS in the context of global carbon fluxes.