Productivity diagnosed from the diel cycle of particulate carbon in the North Pacific Subtropical Gyre

Abstract

The rate of primary production (PP) in the ocean is a critical ecosystem function that contributes to the regulation of air-sea CO2 exchange. Historically, oceanographers have relied primarily on in vitro measurements of 14C uptake (14C-PP) as a proxy for PP. Yet it can be difficult to reconcile PP rates measured in vitro with in situ rates such as those based on oxygen. Here we present diel cycles of optically derived particulate organic carbon (POC) measured in the North Pacific Subtropical Gyre. We have calculated gross production (OPTGP) from the daytime increase and nighttime decrease of optically derived POC, assuming that the observed change in POC represents the sum of PP and community losses. We have compared these estimates to parallel 14C-PP incubations and considered sources of difference. We find that OPTGP is strongly related to 14C-PP in this region and that growth and loss rates of POC are tightly coupled.