Spatial variations in time-integrated plankton metabolic rates in Sagami Bay using triple oxygen isotopes and O2:Ar ratios

Abstract

Plankton metabolic rates, such as rates of gross, net community production and community respiration, were measured in the surface waters using triple oxygen isotopes and O2 : Ar ratios. The 17 delta anomaly showed clear coastal and offshore gradients that were consistent with the distribution of chlorophyll a and oxygen saturation. Gross primary production (GPP) rates in coastal regions were several times higher than offshore regions, and the net-to-gross production ratio (N : G) indicated that coastal regions were net autotrophic, whereas offshore regions were net heterotrophic. On a seasonal scale, about 73% of the phytoplankton-produced carbon was respired. Based on floating-sediment-trap data, export production to the aphotic zone was about 12-20% of the GPP; the rest accumulated as dissolved organic carbon (DOC) or was respired