THE INFLUENCE OF ANTICYCLONIC EDDIES ON THE VERTICAL DISTRIBUTION OF THE COLD INTERMEDIATE LAYER IN AVACHA BAY BASED ON OBSERVATIONAL DATA FROM THE SUMMER SEASONS OF 2024–2025

Abstract

Of particular interest in Avacha Bay, as a significant fishing area in the northwestern Pacific Ocean, are cold-core anticyclonic eddies that are rarely encountered elsewhere in the ocean. In this regard, the aim of the present study is to assess the nature of their influence on the vertical distribution of the Cold Intermediate Layer (CIL) in the bay during the summer period. Satellite altimetry data and shipboard CTD measurements collected during two expeditions in 2024 and 2025 were used. It was established that in both years anticyclonic eddies were present in the water area, forming near Cape Shipunsky and propagating southward into the bay; however, their positions during the expedition periods differed: in 2024 the eddy was displaced into the deepwater region, whereas in 2025 it was localized over the continental slope. In 2024, maximum expansion of the CIL was recorded in the zone distant from the shelf (a 30 m shoaling of the upper boundary and a 50 m deepening of the lower boundary relative to climatological values). In 2025, the greatest anomalies were observed over the continental slope (deepening of the lower boundary by more than 60 m), with cold waters pressed against the shelf; a transformation of the CIL in the coastal zone was also noted, most likely attributable to advection of waters from the eddy. It is concluded that the spatial localization of anticyclonic eddies is an important factor governing the interannual variability of the vertical structure of the CIL, with the depth of its lower boundary undergoing the most pronounced changes.