Spatially variable warming of the Laurentian Great Lakes: an interaction of bathymetry and climate

Previous research has identified significant and highly variable summertime (July–August–September) warming trends across the Great Lakes, with critical implications for aquatic ecosystems. However, these analyses of long-term warming trends have generally been constrained by the short duration or coarse spatial resolution of available observational datasets. Here, we integrate two existing datasets of Great Lakes surface temperature (LSWT) to evaluate long-term warming trends during 1982–2012 at fine spatial scales and understand the roles of lake bathymetry and climatic factors in regulating the spatially heterogeneous warming rates with the aid of regional climate modeling. Our results show amplified warming in Lake Superior, central-northern Lake Michigan, and central Lake Huron, and muted lake warming elsewhere. This spatial heterogeneity in summertime lake warming is primarily ascribed to the interplay of lake bathymetry and climatological springtime (April–May–June) air temperature. The climatological air temperature strongly influences the relationship between lake warming rates and bathymetry, as the summertime warming rates increase markedly with greater lake depth in the relatively cold environment of Lake Superior but change little in the warmer environment of Lake Ontario. This conditional dependence on background temperature has important implications for understanding and predicting global lake temperature trends.