Japan Geoscience Union Meeting 2025

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[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG36] Extratropical oceans and atmosphere

Mon. May 26, 2025 10:45 AM - 12:15 PM 101 (International Conference Hall, Makuhari Messe)

convener:Yuta Ando(Department of Earth and Planetary Sciences, Kyushu University), Tong Wang(Japan Agency for Marine-Earth Science and Technology), Kenta Tamura(National Research Institute for Earth Science and Disaster Resilience), Shota Katsura(Department of Geophysics, Graduate School of Science, Tohoku University), Chairperson:Tong Wang(Japan Agency for Marine-Earth Science and Technology), Shota Katsura(Department of Geophysics, Graduate School of Science, Tohoku University)


11:45 AM - 12:00 PM

[ACG36-05] Trends of subduction and obduction rates in the North Pacific

*Yoshimi Kawai1, Shoichiro Kido2 (1.Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2.Application Laboratory, Japan Agency for Marine-Earth Science and Technology)

Keywords:North Pacific Ocean, Subduction, Mesoscale eddy, Ocean warming

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 (Sann and Oann) over the North Pacific Ocean using an eddy-resolving ocean reanalysis. Both Sann and Oann 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 Sann and Oann 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 Sann or Oann 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 Sann and Oann 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.