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

Abstract

Abstract The rate of primary production (PP) in the ocean is a critical ecosystem function that contributes to the regulation of air‐sea CO 2 exchange. Historically, oceanographers have relied primarily on in vitro measurements of 14 C uptake ( 14 C‐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 ( OPT GP) 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 14 C‐PP incubations and considered sources of difference. We find that OPT GP is strongly related to 14 C‐PP in this region and that growth and loss rates of POC are tightly coupled.