[A-CG36] 中緯度大気海洋相互作用

[ACG36-05] 北太平洋におけるサブダクション及びオブダクション率のトレンド

*川合 義美¹、木戸 晶一郎² (1.国立研究開発法人海洋研究開発機構　地球環境部門　海洋観測研究センター、2.国立研究開発法人海洋研究開発機構　付加価値情報創生部門　アプリケーションラボ)

キーワード：北太平洋、サブダクション、中規模渦、海洋温暖化

Subduction and obduction are water mass exchanges between the mixed layer and the permanent pycnocline, and it is of great importance for material circulation and biogeochemistry to know how they change under the warming climate. The authors investigated temporal variations of annual subduction and obduction rates (S_ann and O_ann) over the North Pacific Ocean using an eddy-resolving ocean reanalysis. Both S_ann and O_ann integrated over the basin exhibited increasing trends with a decadal-scale variation in the recent decades. The volume of subducted and obducted water parcels increased in most of the potential density range and regions of the large volumes shifted northward after 2004. These increases of S_ann and O_ann were especially large north of the Kuroshio Extension (KE), despite decreasing potential density of the wintertime mixed layer. On the contrary, they decreased south of the KE. The increasing trends did not appear in either S_ann or O_ann when meso-scale spatial variations were filtered out, which is consistent with calculations using gridded data produced from in situ observations. This fact indicated that eddy activity was responsible for the trends. The variations of S_ann and O_ann well corresponded to that of eddy kinetic energy north of the KE. It can be inferred that northward migration of the KE increased available potential energy, leading to the elevation of eddy kinetic energy through baroclinic conversion. The enhancement of eddy activity reinforced subduction and obduction. Our results suggest that these processes activate vertical exchanges of water masses and materials, overcoming the opposite effect of the upper-ocean warming.