What is the metabolic state of the oligotrophic ocean? A debate.

For more than a decade there has been controversy in oceanography regarding the metabolic state of the oligotrophic subtropical gyres of the open ocean. Here we review the background of this controversy, commenting on several issues to set the context for a moderated debate between two groups of scientists. In one of the two companion articles, Williams et al. (2013) take the view that these gyres exhibit a state of net autotrophy-that is, their gross primary production (GPP) exceeds community respiration (R) when averaged over some suitably extensive region and over a long duration. In the other companion article, Duarte et al. (2013) take the opposite view, that these gyres are net heterotrophic, with R exceeding the GPP. This idea-that large, remote areas of the upper ocean could be net heterotrophic-raises a host of fundamental scientific questions about the metabolic processes of photosynthesis and respiration that underlie ocean ecology and global biogeochemistry. The question remains unresolved in part because the net state is finely balanced between large opposing fluxes and most current measurements have large uncertainties. This challenging question must be studied against the background of large, anthropogenically driven changes in ocean ecology and biogeochemistry. Current trends of anthropogenic change make it an urgent problem to solve and also greatly complicate finding that solution.