Salt‐Fingering in Seasonally Ice‐Covered Lakes

When ice forms on lakes, dissolved salts are rejected, which can lead to under‐ice salt finger formation. We performed a series of laboratory experiments to visualize these fingers. While we detected salt fingers in our camera recordings, the signal of these fingers is nearly absent in the temperature record. We quantify the velocity of the salt‐plumes and measure the bottom salinity increase from these fingers. Further, we estimate that the salinity is often distributed evenly with depth. Comparing the salt fluxes in our experiments with a typical salt flux in lakes, we suggest that conditions are favorable for salt fingering in most seasonally ice‐covered lakes. Plain Language Summary When ice forms on the surface of lakes, dissolved salts are expelled from the ice into the liquid water below. If enough salt is rejected from the ice, the excess weight of the salt can lead to long “fingers” of salty fluid moving from the ice into the water below. We ran a series of experiments to investigate these “fingers”, and conclude that this process likely occurs in most freshwater lakes that freeze annually. This process is important for the evolution of lakes and will change as fewer lakes freeze. Key Points Cryoconcentration produces gradients in solutes under the ice in freshwater lakes Laboratory experiments indicate that salt fingers, enabled by contrasting gradients in solutes and temperature, may be common in ice‐covered lakes Salt fingers may not obviously perturb the temperature stratification