Summer Wind-driven Upwelling and Tidal Mixing on the Western Kamchatka Shelf in the Sea of Okhotsk

Abstract

The response of the thermohaline structure of water off the western Kamchatka shelf of the Sea of Okhotsk to the wind-driven upwelling and tidal mixing is analyzed, and the results are presented. The upwelling intensity was estimated based on the offshore Ekman mass transport (the upwelling index). The mean position of the tidal mixing front was determined using the spatial distribution of the Simpson-Hunter stratification parameter. The hydrographic observations and the results of the upwelling index calculation revealed the occurrence of the summer transient upwelling on the western Kamchatka shelf under certain synoptic conditions. The favorable meteorological conditions for the upwelling development were associated with the propagation of atmospheric cyclones to the Kamchatka Peninsula. The zone of intensive tidal mixing is located in the northwestern part of the Kamchatka shelf in the open part of the Shelikhov Bay. The western Kamchatka tidal mixing front which separates tidally mixed coastal water from stratified open shelf water emerges in May during the period of seasonal thermocline formation and disappears in July due to enhanced thermal stratification. The wind-driven coastal upwelling and the tidal mixing might support the high biological productivity of the western Kamchatka shelf.