Cyclonic circulation and upwelling in Lake Baikal

摘要

We investigated upwelling events in the pelagic area of Lake Baikal that developed during summer stratification (July-November) using a combination of in situ and satellite observations. These upwellings appear in the centres of local cyclonic macrovortices with compensatory downwelling located on their periphery in coastal areas. The average duration of upwelling events was 5 weeks, with an observed maximum of 16 weeks. The most stable upwellings in Southern Baikal and over the Academician Ridge covered areas of up to 4,400 km~2 (59 % of Southern Baikal's surface) and 1,550 km~2, respectively. Water was ascending in the upwelling zones at velocities of 1 × 10~(-4) to 1.2 × 10~(-2) cm s~(-1). Temperature differences of 1-4 ℃ and 2-13 ℃ were observed between the downwelling and upwelling zones in the epi-limnion and metalimnion, respectively. On the surface of the lake, water temperature can drop 4-7 ℃ for water ascending from depths of 10-75 m, but the observed thickness of the layer within which water was ascending reached a depth of 280 m in August-September and 380 m in October; i.e. the ascending water included the entire upper layer (0-300 m). Geostrophic currents reached up to 24-38 cm s~(-1) on the boundary between up- and downwelling zones (usually 5-7 km offshore), but did not exceed 6-10 cm s~(-1) in the centres of upwelling zones. Comparison with other large lakes of the world is carried. This study is important for understanding the upwelling process that develops in Lake Baikal during summer stratification and can influence the heterogeneity of nutrients and primary production.