Diatom-inferred Holocene climatic and environmental changes in an unusually subsaline high Arctic nunatak pond on Ellesmere Island (Nunavut, Canada)

Abstract

Stygge Nunatak Pond is a small, shallow, closed-basin pond situated on a nunatak in Stygge Glacier at the head of Jokel Fiord, east-central Ellesmere Island, Nunavut, Canada. Its ionic concentration is unusually high by inland Arctic standards, with specific conductivity measured at up to 1,090 μS/cm, making this site a rare example of a subsaline athalassic Arctic pond. Small, closed-basin lakes and ponds are particularly sensitive to changes in the balance between precipitation and evaporation (P–E), which affect the site’s chemical, physical and biological characteristics. Such lakes and ponds therefore have the potential to serve as sensitive archives of past environmental change, which can be reconstructed using paleolimnological techniques. Diatom assemblages from two sediment cores (a short gravity core [21.5 cm] and a long core of frozen material [387 cm]) were examined so as to reconstruct regional environmental changes. Basal radiocarbon dating of the long core suggests that the pond has existed since before 10,500 cal. year BP. The diatom assemblages from both cores record similar ecological changes since approximately 2,200 cal. year BP, with a stable, coldwater assemblage dominated by Fragilaria construens var. venter. This assemblage was replaced in the early- to mid-20th century by dramatic, unprecedented expansion in periphytic taxa with more complex life forms, especially Cymbella descripta, Navicula halophila and Achnanthes minutissima. These assemblage shifts are indicative of recent warming, with a longer open-water period, expanded littoral substrates, and increased ionic concentration, as would be expected with enhanced evaporation relative to precipitation. Between ~10,500 and ~6,200 cal. year BP, the diatom assemblages underwent a shift from a near monoculture of F. construens var. venter to a more complex, epiphytic assemblage, which then reverted back to the former virtual monoculture. These shifts may provide further evidence for an early Holocene thermal maximum in this region of the Arctic, followed by Neoglacial cooling. However, interpretation of assemblages before ~6,200 cal. year BP is complicated by the fact that the sediment beneath 47 cm depth is unconsolidated and embedded within a core of solid ice, a feature that has not been reported in any other Arctic paleolimnological study to date. Superficial examination of the contact surfaces of the ice, and the fact that radiocarbon ages obtained from entrained sediment are chronologically consistent with those from the sediment above, suggest that the ice might be intrasedimental segregation ice.