Toolik Lake: A 40-year record of geochemical change in the absence of trends in thaw depth, precipitation, and air and water temperatures

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The alkalinity of Toolik Lake on the North Slope of Alaska (ARC LTER) has consistently increased and doubled in the last 40 years.  This doubling has occurred mainly due to inputs of alkalinity from the surrounding catchment rather than from in-lake redox reactions.  However, while deep (20 m) permafrost temperatures in nearby boreholes have increased, there has been no thawing and no increase in the measured summer thaw depth of tundra at Toolik in the last 25 years.  In addition, there has been no significant warming of annual air temperatures or increases in precipitation at Toolik over the last 25 years, and there has been no warming of Toolik Lake water temperatures over the last 40 years.  Thus, given the lack of change over four decades in these fundamental meteorological and mineral weathering drivers or corollary effects (e.g., thaw depth), we would not have predicted this dramatic geochemical change in the catchment and the lake.  Clearly this ecosystem is vulnerable to change, and apparently the ecosystem stressors causing the change are either hidden from our observational capabilities or as yet undiscovered.  It is possible that this arctic system is extremely vulnerable to small variations in a combination of drivers, and similar geochemical changes may be occurring in other parts of the Arctic with or without documented trends in climate.