Temporal Change of Dissolved Inorganic Carbon in the Subsurface Water at Station KNOT (44°N, 155°E) in the Western North Pacific Subpolar Region

• Published in: Journal of oceanography 2005-02, Vol.61 (1), p.129-139
• Main Authors: Wakita, Masahide, Watanabe, Shuichi, Watanabe, Yutaka W, Ono, Tsuneo, Tsurushima, Nobuo, Tsunogai, Shizuo
• Format: Article
• Language: English
• Subjects: Alkalinity; Anthropogenic factors; Chemical speciation; Decomposition; Dissolved inorganic carbon; Intermediate water; Marine; Oceanography; Organic matter; Subsurface water; Water exchange
• ISSN: 0916-8370; 1573-868X
• DOI: 10.1007/s10872-005-0026-2

The dissolved inorganic carbon (DIC) and related chemical species have been measured from 1992 to 2001 at Station KNOT (44°N, 155°E) in the western North Pacific subpolar region. DIC (1.32.3 µ mol/kg/yr) and apparent oxygen utilization (AOU, 0.71.8 µmol/kg/yr) have increased while total alkalinity remained constant in the intermediate water (26.927.3σ^sub [theta]^). The increases of DIC in the upper intermediate water (26.927.1σ^sub [theta]^) were higher than those in the lower one (27.2 27.3σ^sub [theta]^). The temporal change of DIC would be controlled by the increase of anthropogenic CO^sub 2^, the decomposition of organic matter and the non-anthropogenic CO^sub 2^ absorbed at the region of intermediate water formation. We estimated the increase of anthropogenic CO^sub 2^ to be only 0.50.7 µmol/kg/yr under equilibrium with the atmospheric CO^sub 2^ content. The effect of decomposition was estimated to be 0.8 ± 0.7 µmol/kg/yr from AOU increase. The remainder of non-anthropogenic CO^sub 2^ had increased by 0.6 ± 1.1 µmol/kg/yr. We suggest that the non-anthropogenic CO^sub 2^ increase is controlled by the accumulation of CO^sub 2^ liberated back to atmosphere at the region of intermediate water formation due to the decrease of difference between DIC in the winter mixed layer and DIC under equilibrium with the atmospheric CO^sub 2^ content, and the reduction of diapycnal vertical water exchange between mixed layer and pycnocline waters. In future, more accurate and longer time series data will be required to confirm our results.[PUBLICATION ABSTRACT]