Prolonged Ice Cover Dampens Diatom Community Responses to Recent Climatic Change in High Arctic Lakes

ABSTRACT

Numerous paleolimnological studies of Arctic lakes and ponds have shown marked shifts in both algal and invertebrate taxa within the past ∼150 years that are consistent with recent climatic warming. However, the magnitude and timing of changes are often non-uniform, with large, deep lakes frequently exhibiting muted assemblage shifts relative to smaller ponds. The hypothesis that duration and extent of ice cover exerts an overriding influence on habitat availability for biota has been commonly invoked to explain these differences, and many studies indicate that changes in ice cover are important drivers of recent biological changes. However, a detailed paleolimnological comparison of two lakes from the same region that have similar water chemistry but different ice cover regimes has not yet been attempted. Here we examine the influence of prolonged ice cover on the rate, magnitude, and direction of fossil diatom species shifts over time in two remarkably similar and adjacent Ellesmere Island lakes that mainly differ in their periods of ice cover. These two lakes exhibit strikingly different paleolimnological diatom profiles, despite their physical proximity, similar depths, and nearly identical water chemistry. In the lake characterized by prolonged ice cover, we find little evidence of diatom-inferred environmental change over its recent history, while diatom assemblages have undergone dramatic changes in the lake with the shorter duration of ice cover. This study supports the general hypothesis that changes in ice cover are a principle determinant of shifting diatom assemblages in High Arctic lakes.

Acknowledgments

Funding for this project came from Natural Sciences and Engineering Research Council of Canada (NSERC) grants to Keatley, Douglas, and Smol, and from a Northern Scientific Training Program (NSTP) grant to Keatley. We would also like to thank the Polar Continental Shelf Project and Parks Canada for logistical support. We are grateful to the National Laboratory for Environmental Testing (NLET) at Environmental Canada for water chemistry analysis, S. Arnott and J. Glew for assistance in the field, and J. R. Glew for drafting the detailed inset map. Many thanks to D. Antoniades, N. Michelutti, and the anonymous journal reviewers for constructive comments on the manuscript, and to one of the journal reviewers for suggesting Figure 7. This is PCSP contribution number 010-07.