Primary productivity and photosynthetic products around the Kuroshio warm-core ring

Abstract

¹³C uptake experiments were carried out in the Kuroshio warm-core ring and adjacent waters during the cruise of R.V. Hakuho-Maru. The depth-integrated primary productivity at the warm-core center ranged from 840 to 1200 mgC m⁻² day⁻¹. These rates were higher than those obtained in the surrounding water and the warm streamer existing in the southern part of the warm-core ring, and lower than that in the cold Oyashio water.

Production rates of 13 amino acids and eight monosaccharides at six stations were determined after hydrolysis of particulate matter by the ¹³C−GC−MS method. Protein and free amino acid (sum of 13 amino acids) carbon production rate accounted for 20–39% of organic carbon production at 10 m, whereas carbohydrate (sum of eight monosaccharides) was responsible for 11–21%. Composition of photosynthetic products and the spectrum of specific production rate (SPR) of organic compounds indicate that phytoplankton population in and around the warm-core ring was in a generally healthy state.