Chapter 3 Simulated In Situ Measurements of Primary Production in Japanese Waters

Abstract

Abstract In the global carbon cycle and related mapping based on satellite imagery program (GCMAPS), daily primary production, integrated over the euphotic zone (IPP), was measured around Japan for the validation of algorithms to estimate primary productivity derived from satellite observations. A total of 176 measurements were made by simulated in situ deck-incubations and a small number of in situ incubations, with inoculation of stable isotope 13C-bicarbonate, essentially according to the JGOFS protocol. IPP ranged from 30 mgC/m2/day in March in Oyashio-transition waters (subarctic) to 3,980 mgC/m2/day in May in continental shelf waters of the East China Sea (ECS, subtropic Case II). IPP varied seasonally in Oyashio-transition waters, with high values from April to August, and very low values from September to March. In contrast, seasonal variations in IPP in other areas were not marked, with a slight increase in May in Kuroshio waters (subtropic) and Tosa Bay (subtropic inshore), and in both May and August in ECS continental shelf waters. We estimated annual primary production (gC/m2/year) to be 340 in ECS continental shelf waters, 280 in Tosa Bay, 200 in Oyashio-transition waters, and 110 in Kuroshio waters. Maximum primary production per unit of chlorophyll a ( P opt B ) tended to increase with temperature where sea surface temperature (SST) was between 0 and 30°C, but varied largely above about 16°C in the subtropics including Kuroshio waters, Tosa Bay, and ECS continental shelf waters. The water-column light-utilization efficiency index increased as photosynthetically available radiation (PAR) on the surface decreased in Oyashio-transition waters, Kuroshio waters, and ECS continental shelf waters. We propose preliminary empirical relationships for estimating IPP from standing stock of chlorophyll a (IPP) and surface PAR (integrated over a day), for these three waters around Japan.