6500 YEARS OF CLIMATE CHANGE IN SOUTH GREENLAND INFERRED FROM INSECT (DIPTERA: CHIRONOMIDAE) ASSEMBLAGES

Paleoclimate records from non-glacial areas of Greenland are necessary to provide context for ongoing climate-driven dynamics and to assess the role of climate in past human migrations. However, high-resolution temperature reconstructions from Greenland, especially beyond the ice sheet, are sparse. We reconstruct chironomid assemblages over the past 6500 years (mean sampling interval = 104 yr.) from a small, high-elevation non-glacial lake in South Greenland (Scoop Lake, N 60.697°, W 45.419°, 500 m asl). We interpret assemblages in the context of lake-sediment geochemistry from X-ray fluorescence and past lake-water isotopic composition from δ¹⁸O of chironomid headcapsules.

Scoop Lake chironomid assemblages were dominated by Micropsectra (40-60% abundance) and taxa indicative of cool, oligotrophic conditions throughout the past 6500 years. Principal component analysis reveals a marked shift in assemblages ~2500 years ago, driven by increased abundances of cold-tolerant Heterotrissocladius after 2500 cal BP. Additional taxa with cooler temperature optima (e.g., Eukiefferiella, Corynoneura) were also abundant after 2500 cal BP, compared to higher percentages of warm-dwelling Psectrocladius and Dicrotendipes 6500-2500 cal BP. These assemblage shifts pre-date possible influences from nearby low-elevation Norse settlements, established ~960 cal BP, and are concurrent with decreased sedimentary Si:Al, suggesting both chironomids and primary production responded to cooler late-Holocene temperatures. Abundances of Procladius and Limnophyes, associated with enhanced lake productivity and aquatic macrophytes, respectively, increased as Heterotrissocladius decreased ~1150-450 cal BP, coincident with elevated chironomid δ¹⁸O values that suggest warm summers overlapped with Norse settlement. Fossil chironomid assemblages have good analogues with modern assemblages from North America. However, attempts to apply published training sets to model fossil-based paleotemperatures yielded mixed results. We will evaluate the roles of taxonomic resolution and biogeography in explaining issues with these quantitative reconstructions. Meanwhile, our qualitative interpretation of the Scoop Lake dataset provides preliminary insight into South Greenland climate over the past 6500 years.