Ted Ozersky, Amanda Poste, Milla Rautio, Eva Leu

Climate warming is especially pronounced in winter and at high latitudes. Warming winters are leading to loss of lake ice and changing snow cover on seasonally freezing lakes. Past neglect of the ice cover period by lake scientists has resulted in critical data and theory gaps about the role of winter conditions in lake ecosystem function and the effects of changing winters on aquatic systems. Here we use simple models to show that the latitudinal interaction between ice cover duration and light flux seasonality has profound and underappreciated implications for lake ecosystems. Our models focus on light and temperature, two paramount drivers of ecosystem processes. We show that the amount of light arriving in lakes while they are ice covered increases non-linearly with latitude and that light climate of high latitude lakes is much more sensitive to changing winter conditions than that of lower latitude lakes. We also demonstrate that the synchronicity between light flux (a key controller of primary production) and temperature (which controls invertebrate production) decreases with latitude. Our results indicate that ice loss will lead to greater change to the productivity and nature of biotic interactions in higher latitude aquatic ecosystems and make several testable predictions for understanding the consequences of climate-induced changes across latitudinal gradients.