Relationship between net and gross primary production in the Sagami Bay, Japan

Hashimoto, S., N. Horimoto, Y. Yamaguchi, T. Ishimaru, T. Saino

Limnol. Oceanogr., 50(6), 2005, 1830-1835 | DOI: 10.4319/lo.2005.50.6.1830

ABSTRACT: Net and gross primary production (GPP), based on the incorporation of 13C-labeled inorganic carbon into particulate carbon and O2 production, were compared from September 2001 to July 2003 in Sagami Bay, Japan. Euphotic zone integrated GPP, 13C uptake, and their ratio (13C uptake : GPP) ranged from 40 to 331, 14 to 163 mmol C m-2 d-1, and 0.34 to 0.69, respectively. The 13C uptake :GPP ratios were relatively lower in summer (low nutrient, LN) than from fall to spring (high nutrient, HN), with a mean value (±standard error) of 0.52 ± 0.03 during the study period. The mean value of the ratio in the upper water column above which 20% of surface light penetrates was higher during HN than during LN periods. On the contrary, no significant differences were observed between HN and LN periods in the depths at which <10% light penetrates. Algal respiration was 36% of GPP in the study periods. The sum of 13C uptake and algal respiration accounted for 58-100% of GPP, with a mean value of 80%. This implies that about 20% of GPP might have been excreted as dissolved organic cargon and/or mineralized as light respiration.

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