Eddy generation in a large, deep dimictic freshwater lake in ice-free period

Abstract

We address eddy generation in the middle part of Lake Baikal—a large freshwater dimictic lake in Siberia, where river discharge, wind influence and coastline shape impact horizontal water exchange. We use satellite remote sensing, historical observations and in situ data to follow the different stages of warm and cold anticyclonic eddy generation before and after vertical overturn; an aspect that has received little attention in previous works. Thermal satellite images for 1998–2022 indicate a stable repeating seasonal pattern which is classified into stage of eddy generation and development. Field observations complement satellite imagery to characterize the vertical structure of the eddies. The main source of eddy generation is the outflow from Barguzin Bay which interacts with the coastline. Subsequent eddy generation is driven by density gradients and geostrophic adjustment. In summer, this outflow is dominated by river inflow and lead to the formation of warm anticyclonic eddies. After autumnal vertical overturn, the outflow is forced by the wind bringing cold water from the bay to Middle Baikal and creating cold anticyclonic eddies. We suggest that in the autumn, when the surrounding water cools to a temperature below about 4°C, these cold eddies sink and transform into intrathermocline lens-like eddies that persist under ice and can later create giant ice rings on the Baikal ice cover.