Respiratory electron transport activity and adenosine triphosphate in the oxygen minimum of the eastern tropical North Pacific

The vertical distribution of respiratory electron transport system (ETS) activity has been determined through the oxygen-deficient zone of the eastern tropical North Pacific. Adenosine triphosphate (ATP) concentration has also determined in the Costa Rica Dome area. There is a distinct, local ETS activity maximum associated with the oxygen minimum but no corresponding ATP increase. It is suggested that the ETS activity maximum results from intracellular biochemical modifications of the ETS system in response to the stress imposed by the low oxygen concentrations, because it is not associated with an increase in ATP biomass. These distributions are also discussed in light of recent suggestions of a mid-depth bacterioplankton maximum.