Manuscripts by MRI/JMA Group

Seasonal variation in total inorganic carbon and its controlling processes in surface waters of the western North Pacific subtropical gyre

Masao Ishii ^a,*, Hisayuki Y. Inoue ^a, Hidekazu Matsueda ^a, Shu Saito ^a, Katsuhiko Fushimi ^a, Kazuhiro Nemoto ^a, Toshihiko Yano ^b, Hideki Nagai ^b, Takashi Midorikawa ^b,1

^a Geochemical Research Department, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
^b Climate and Marine Department, Japan Meteorological Agency, Tokyo 100-8122, Japan
¹ Present address: Hakodate Marine Observatory, Hakodate 041-0806, Japan.

Marine Chemistry 75 2001 17-32
Received 15 June 2000; received in revised form 28 February 2001; accepted 7 March 2001

^*Corresponding author address: Masao Ishii, Geochemical Research Department, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan.
E-mail: mishii@mri-jma.go.jp

Abstract

Seasonal variation in total inorganic carbon (TCO₂) in surface waters of the western North Pacific (137°-152°E) subtropical gyre was analyzed on the basis of measurements of TCO₂ and partial pressure of CO₂ (pCO₂^sw) . The controlling processes including vertical mixing, horizontal advection, and net air-sea CO₂ transport, as well as biological activity, were quantified. The seasonal increase in normalized TCO₂ (NTCO₂) from autumn to winter, ranging from 19 to 37 µmol kg^-1 in the northern part of the subtropical gyre between 24°N and 30°N, was predominantly accounted for by the upward supply of TCO₂ due to enhanced vertical mixing. The contribution of horizontal advection, estimated from monthly meridional NTCO₂ distributions and the monthly advection field of the Meteorological Research Institute (MRI)'s 3D-ocean general circulation model, was insignificant. Analyses of the mixed-layer NTCO₂ budget revealed that biological activity was playing an important role in the decrease in surface NTCO₂ from winter to summer. Annual net community production reached 48±19 gC m^-2 between 24°N and 30°N, and 19±16 gC m^-2 between 15°N and 23°N. ©2001 Elsevier Science B.V. All rights reserved.