Earlier ice melt increases hypolimnetic oxygen despite regional warming in small Arctic lakes

Although trends toward earlier ice-out have been documented globally, the links between ice-out timing and lake thermal and biogeochemical structure vary spatially. In high-latitude lakes where ice-out occurs close to peak intensity of solar radiation, these links remain unclear. Using a long-term dataset from 13 lakes in West Greenland, we investigated how changing ice-out and weather conditions affect lake thermal structure and oxygen concentrations. In early ice-out years, lakes reach higher temperatures across the water column and have deeper epilimnia. Summer hypolimnia are the warmest (~ 11°C) in years when cooler air temperatures follow early ice-out, allowing full lake turnover. Due to the higher potential for substantive spring mixing in early ice-out years, a warmer hypolimnion is associated with higher dissolved oxygen concentrations. By affecting variability in spring mixing, the consequences of shifts in ice phenology for lakes at high latitudes differ from expectations based on temperate regions.