What interrupted monomictic mixing in Lake Biwa? Heat budget analysis using a circulation model

Abstract

ABSTRACTEcosystems in deep lakes are vulnerable to mixing regime alterations induced by global warming. Detection of mixing regime shifts contributes to a better understanding of the changes that occur in lake ecosystems due to climate change. In the winter of 2018/2019, the monomictic mixing in Lake Biwa, Japan, was partially incomplete. To identify the determining factor, our study reproduced this interruption in monomictic mixing using a realistic three-dimensional lake circulation model and heat budget analysis. The results revealed that weak surface cooling was primarily caused by a decrease in wind speed during the winter rather than by an increase in the air/water temperature, leading to the weak overturn and interruption in monomictic mixing. The results outlined that the mixing regime in Lake Biwa may be shifting from a monomictic to an oligomictic system because of atmospheric stilling or wind speed reductions affected by global warming.