[A-OS16] [EE] 地球規模環境変化に関する分野横断の海洋研究

[AOS16-P02] Multi-year estimate of the air-sea CO2 flux in the Arctic with the use of the chlorophyll-a concentration

*安中 さやか¹、Siswanto Eko¹、Olsen Are^2,7、Hoppema Mario³、渡邉 英嗣¹、Fransson Agneta⁵、Chierici Melissa⁴、村田 昌彦¹、小杉 如央⁶、Lauvset Siv⁷、Mathis Jeremy⁸ (1.海洋研究開発機構、2.University of Bergen、3.Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research、4.Institute of Marine Research、5.Norwegian Polar Institute、6.気象研究所、7.Bjerknes Centre for Climate Research、8.NOAA Arctic Research Program)

キーワード：CO2 flux, Arctic, chlorophyll-a, SOCAT

We examined the relationship between partial pressure of CO₂ in the surface water (pCO_2w) and chlorophyll-a concentration (Chl-a) in the Arctic. The relationship between pCO_2w and Chl-a is negative where Chl-a < 1 mg m^-3, but there is no significant relationship where Chl-a > 1 mg m^-3. In the Greenland/Norwegian Seas, a relationship between pCO_2w and Chl-a is strongly negative in spring and weakly negative in summer. Chl-a is higher in summer than in spring, while nutrient concentration is high in spring and low in summer there. A positive relationship between pCO_2w and Chl-a is found in the Barents Sea in summer when Chl-a values decline while pCO_2w remains at a relatively constant low level. In the Kara and East Siberian Seas and the Bering Strait, the relationships are positive because of high pCO_2w and Chl-a water in the coastal region.
We estimated monthly air–sea CO₂ flux in the Arctic north of 60°N from 1997 to 2014 by applying a self-organizing map technique with Chl-a, SST, SSS, SIC, xCO_2a, and geographical positions. The addition of Chl-a as a training parameter enables us to improve the estimate of pCO_2w through reproducing its decline in spring by biological production. A significant CO₂ uptake of 180 ± 130 TgC yr^–1 in the Arctic Ocean was obtained. This estimate has been much improved compared to a previous estimate thanks to the use of Chl-a, but to some extent also due to a higher number of CO₂ data.