Modeling Phytoplankton New Production in the Peru Upwelling from Nitrate Reductase Activity and Light.

Abstract

Oceanic New Production is limited by nitrate (NO3-), ammonium (NH4+), and light. Measuring it by 15NO3- incubations is the current gold-standard, but the data acquisition rate is slow. Calculating it from plankton nitrate reductase activity (NR) is an inexpensive alternative with a higher data acquisition rate. Here, we calculate phytoplankton new production for the Peru upwelling ecosystem from measurements of NR activity using an enzyme kinetic model based on light-limitation. Calculations for the C-Line section at 15°S find new production ranging from 0.1 to 0.4 micro M N h-1 at the shelf edge and compares well to gross primary productivity when Redfield equivalents are used for N-C conversion. JASON-CUEA expedition data for September 1976 were used.