Global patterns in oceanic planktonic metabolism

Rates of gross primary production (GPP) and respiration (CR) of plankton communities in the upper ocean were evaluated on the basis of a data set comprising 3149 paired light and dark bottle measurements of volumetric GPP-CR of euphotic zone plankton communities. The data were from 72 published and unpublished reports of measurements made between 1981 and 2011 from the open ocean and the Mediterranean Sea. The data set is dominated by measurements in chlorophyll a (Chl a)-rich oceans and North Atlantic waters, with a paucity of measurements in the Indian Ocean and South Pacific Ocean. CR scaled as the 3/4 power of GPP with a power slope of 0.79 ± 0.01, implying that the threshold GPP separating heterotrophic from autotrophic plankton communities is 1.26 mmol O₂ m^-3 d^-1. Plankton communities with Chl a < 0.35 mg m^-3 tend to be heterotrophic. Both GPP and CR declined exponentially with depth, but the GPP declined faster, at 42% ± 7% m^-1, than CR (29% 6 8% m^-1), so that CR increases relative to GPP with depth.