Six Decades of Thermal Change in a Pristine Lake Situated North of the
Arctic Circle
Abstract
The majority of lake temperature studies have investigated
climate-induced changes occurring at the lake surface, primarily by
analyzing detailed satellite images of surface water temperature. Whilst
essential to observe long-term change, satellite images do not provide
information on the thermal environment at depth, thus limiting our
understanding of lake thermal responses to a warming world. Long-term
in-situ observational data can fill some of the information gap, with
depth-resolved field measurements providing a detailed view of thermal
change throughout the water column. However, previous studies that have
investigated multi-decadal changes in lake temperature, both at the
surface and at depth, have typically focused on north temperate lakes.
Relatively few studies have investigated temperature variations in lakes
situated north of the Arctic circle, which is one of the most rapidly
warming regions globally. Here, using a sixty-year (1961-2020)
observational dataset of summer water temperature from Lake Inari
(Finland), we investigate changes in the thermal environment of this
pristine lake. Our analysis suggests a significant summer warming trend
at the lake surface (+0.247 °C decade-1) and a
marginal cooling trend (–0.027 °C decade-1) at depth.
The contrasting thermal response of surface and bottom water
temperatures to climatic warming has likewise resulted in a
strengthening of summer stratification in this high latitude lake.
Implications of the observed change in both temperature and
stratification on the lake ecosystem will likely be extensive, including
impacts on aquatic organisms in which this lake supports. Our work
builds on ever-growing literature regarding lake thermal responses to
climate change.