Abstract
Abstract. We estimated monthly air–sea CO2 fluxes in the Arctic Ocean and its adjacent seas north of 60∘ N from 1997 to 2014. This was done by mapping partial pressure of CO2 in the surface water (pCO2w) using a self-organizing map (SOM) technique incorporating chlorophyll a concentration (Chl a), sea surface temperature, sea surface salinity, sea ice concentration, atmospheric CO2 mixing ratio, and geographical position. We applied new algorithms for extracting Chl a from satellite remote sensing reflectance with close examination of uncertainty of the obtained Chl a values. The overall relationship between pCO2w and Chl a was negative, whereas the relationship varied among seasons and regions. The addition of Chl a as a parameter in the SOM process enabled us to improve the estimate of pCO2w, particularly via better representation of its decline in spring, which resulted from biologically mediated pCO2w reduction. As a result of the inclusion of Chl a, the uncertainty in the CO2 flux estimate was reduced, with a net annual Arctic Ocean CO2 uptake of 180 ± 130 Tg C yr−1. Seasonal to interannual variation in the CO2 influx was also calculated.
Highlights
The Arctic Ocean and its adjacent seas (Fig. 1) generally act as a sink for atmospheric CO2 because of the high solubility of CO2 in their low-temperature waters, combined with extensive primary production during the summer season (Bates and Mathis, 2009)
We examined the relationship between pressure of CO2 in the surface water (pCO2w) and Chl a in the Arctic Ocean and its adjacent seas and computed monthly air–sea CO2 flux maps for regions north of 60◦ N using a self-organizing map (SOM) technique similar to that of Yasunaka et al (2016) and with Chl a added to the SOM process
In summer, when the ice cover is less extensive, Chl a is high in the Chukchi Sea, the Kara Sea, the Laptev Sea, and the East Siberian Sea (> 1 mg m−3) and especially high in the coastal regions of the two latter (> 2 mg m−3). pCO2w is high in the Norwegian Sea in spring, and in the Kara Sea, the Laptev Sea, and the Canada Basin during summer (> 300 μatm)
Summary
The Arctic Ocean and its adjacent seas (Fig. 1) generally act as a sink for atmospheric CO2 because of the high solubility of CO2 in their low-temperature waters, combined with extensive primary production during the summer season (Bates and Mathis, 2009). The Arctic Ocean and its adjacent seas consist of complicated subregions that include continental. S. Yasunaka et al.: Arctic Ocean CO2 uptake. Subpolar North Atlantic Norwegian Sea. Kara Eurasian Sea Basin Canadian Archipelago Laptev Sea East
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