Space-for-time proxy for climate change in deep lakes in the Canadian cordillera: Seasonality along a latitudinal climate gradient

A comparison of the annual thermal histories in seven deep, intermontane lakes in western Canada along a north-south transect from 49.67° to 61.25° N reveals latitudinal trends in thermal structure; specifically: 1) summer maximum and winter minimum mean temperatures decrease ~  0.2°C per degree latitude, 2) the dates of maximum and minimum heat content lag ~ 1 and ~  6 days per degree latitude, respectively, 3) the lengths of summer and winter stratification lag ~  8 days per degree latitude, 4) the timing of the spring and autumn turnovers lags ~  4 days per degree latitude, 5) the timing of the onset and break-up of ice cover lags ~ 6 days per degree latitude, and 6) the rate of response to atmospheric heating and cooling is ~  1MJ m− 2 day− 1 per degree latitude. We propose that insight into the response of a lake at a specific latitude to climate change can be acquired by examining the present conditions of a morphologically and dynamically similar lake at an appropriate latitude and altitude further south. Of interest is the potential transition of a lake from one mictic state to another, with consequences to the resupply of nutrients to the euphotic zone and to the phenology of spring and fall phytoplankton blooms. The absence or presence of ice cover and timing of freeze-up and break-up also affect a lake's heat budget and thermal history. The full interpretation of climate signals in lake systems requires an understanding of lake-specific physical forcing and response mechanisms.