The role of subtropical mode water transportation in redistributing anthropogenic CO2

What is it about?

Oceanic uptake and storage of anthropogenic CO2 (C_ANT) are regulated by ocean circulation and ventilation. To decipher the storage and redistribution of C_ANT in the western North Pacific, where a major C_ANT sink develops, we investigated the water column carbonate system, dissolved inorganic radiocarbon and ancillary parameters in May and August 2018, spanning the Kuroshio Extension (KE, 35–39 °N), Kuroshio Recirculation (KR, 27–35 °N) and subtropical (21–27 °N) zones.

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Why is it important?

Water column C_ANT inventories were estimated to be 40.5 ± 1.1 mol m−2 in the KR zone and 37.2 ± 0.9 mol m−2 in the subtropical zone. In comparison with historical data obtained in 2005, relatively high rates of increase of the C_ANT inventory of 1.05 ± 0.20 and 1.03 ± 0.12 mol m−2 yr−1 in the recent decade were obtained in the KR and subtropical zones, respectively. Our water-mass-based analyses suggest that formation and transport of subtropical mode water dominate the deep penetration, storage, and redistribution of C_ANT in those two regions. In the KE zone, however, both the water column C_ANT inventory and the decadal C_ANT accumulation rate were small and uncertain owing to the dynamic hydrology, where the naturally uplifting isopycnal surfaces make C_ANT penetration relatively shallow. The findings of this study improve the understanding of the spatiotemporal variations of C_ANT distribution, storage, and transport in the western North Pacific.

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