Analysis of spatio-temporal variability of Pacific water distribution in the Sea of Okhotsk based on Lagrangian approach

The aim of this work is characteristic of spatio-temporal variability of Pacific water distribution in the Sea of Okhotsk based on Lagrangian approach and spatial analysis.

Materials and methods. The study is based on geostrophic current data product from satellite altimetry. The dataset has resolution of 0,25° × 0,25° × 1 day. This data is used for calculation of approximately 100000 water parcels trajectories during 400 days back in time for every day from 31st of January 1997 to 17th of April 2022. For each date in this interval, those parcels which intersected the conditional Kuril transect were determined, as well as region and date of transect intersection. Those two parameters were used in cluster analysis with DBSCAN method in order to distinguish individual Pacific intrusions. Position, shape, and size of each intrusion were investigated.

Results allowed to suggest two types of indexes describing distribution of Pacific-origin water in the Sea of Okhotsk. First, centroid of particles of Pacific origin with residence time between 1 and 6 months is calculated. Variability of centroid position showed northward displacement of Pacific waters in spring-summer and south[1]ward displacement in autumn-winter. Eastward displacement towards Kamchatka coast usually occurs during winters and opposite westward displacement is usual for summers. In 1998, 2003, 2010, 2013, 2017, and 2019 waters of Pacific origin had the most northern location. Second type of indexes is based on location and shape characteristics of Pacific water intrusions. The fractal dimensionality and convexity measure of intrusions are rapidly decreasing after the intrusion reaches its maximum area. Centroids of the most prominent intrusions follow the path along 152–154 °E. Both types of indices showed intensification of Pacific inflow since 2010.

Practical value. The time-series of resulted indexes are suggested to be implemented in integrated ecosystem assessments of the eastern Sea of Okhotsk.

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