Cross-shelf overturning in geostrophic-stress-dominant coastal fronts

• Published in: Journal of Oceanography
• Main Authors: Yuan, Nan, Mitsudera, Humio
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer
• Subjects: Coastal mixing; Front; Downwelling-favorable wind; Reverse Ekman overturning; 452; Okhotsk; Pacific; Sakhalin
• Online Access: http://hdl.handle.net/2115/87130; https://doi.org/10.1007/s10872-022-00661-6

Compared to the dynamics of the predominantly geostrophic along-shelf current, our understanding of the cross-shelf dynamics in the Sea of Okhotsk is inadequate despite their importance in water mixing and nutrient entrainment. We investigated the cross-shelf overturning circulation along the East Sakhalin Current, which is a source of nutrients such as iron for the western North Pacific. Here, we reveal that the cross-shelf circulation during winter is characterised by a nearshore upwelling and a shelf-break downwelling under a downwelling-favourable monsoon wind, contrary to a classical Ekman overturning (EOT). This reverse EOT is driven by the internal water stress, which is caused by intensive vertical mixing and geostrophic vertical shear in the shelf-break front produced by riverine discharges from the far-eastern Eurasian Continent. The EOT blocks the Ekman onshore transport from the open ocean, thereby producing a deep mixed layer at the shelf break. Scaling analyses indicate the applicability of this mechanism to various other shelf-break fronts.