3.3.1 Water Temperature, Stratification, and DO Concentrations
DO concentrations, water temperature, and Schmidt stability varied considerably over the course of the Turnover Deployment (Figures 4A-C). Prior to turnover, DO concentrations were strongly stratified by depth and exhibited large sub-daily fluctuations in the epilimnion and metalimnion (Figure 4C). Hypolimnetic DO concentrations were stable around 2 mg/L during the pre-turnover period, due to the HOx system operation (Figure 4C). A sharp temperature gradient (4-7°C) between the epilimnion and hypolimnion existed until approximately 3 days prior to turnover (Figure 4B). However, the water temperature profile equalized periodically between the metalimnion and hypolimnion prior to turnover, indicating ephemeral periods of mixing between those layers (Figure 4B). Starting on 29 October 2020, the temperature gradient decreased progressively until the full water column temperature profile equalized on 02 November 2020, meeting our criteria for turnover.