Assessing the potential role of vegetation and fire drivers of woolly mammoth extinction on St. Paul Island, a Holocene refugium

Background/Question/Methods

In North America, more than 50% of mammal species > 32kg and all species > 1000kg were extirpated during the last deglaciation, with the latest mammoths on the mainland dating to 12,291 years BP. Hypothesized extinction drivers include climate change, vegetation change and human hunting. However, woolly mammoth (Mammuthus primigenius) survived into the middle Holocene on St. Paul Island, AK, an isolated island refugia in the Bering Land Bridge, with fossils dating to 6,480 years BP. The mechanisms enabling survival and eventual extinction of woolly mammoth on the island are enigmatic because the environmental history is poorly known. A pollen record collected by Paul Colinvaux (1981) indicates vegetation transitions from herb tundra without shrubs to forest community dominated by Picea, Alnus and Betula then to modern herb tundra, but requires redating. There is no evidence of human presence on St. Paul prior to Russian arrival in the 1780s. This project aims to explore the possible drivers of megafauna extinction in Arctic islands by reconstructing vegetation, megafaunu population and fire history from pollen, Sporormiella spore and charcoal records from Lake Hill, St. Paul, AK. Other paleoenvironmental proxies and sea-level models will also be used to analyze the influence of climate and environment changes on St. Paul.

Results/Conclusions

A 13.5m composite core was retrieved from Lake Hill in March, 2013. Initial radiocarbon dates indicate the oldest date at 7.2m is 11,390 years BP and there is a lithological transition around 5,500 years BP at 5m from silts and sands below to organic rich sediments above. Initial counts of Sporormiella indicate it is consistently present in low abundances (2%, around 700 grains/cm²/yr) in the lower records until it decreases at 558cm (6,788 yr BP). The timing of the Sporormiella decline matches to the youngest mammoth bone date on St. Paul. Major pollen types include Apiaceae, Poaceae, Cyperaceae, Artemisia, and Salix, with lower abundances of Betula, Alnus and Ericaceae, consistent with herbaceous tundra with some shrubs. Declines in Apiaceae and Poaceae and increases in Artemisia and Salix between 606 and 590cm (8014 to 7605 yr BP) suggest an increased prevalence of shrub tundra, preceding the Sporormiella decline. No Picea pollen has been found so far, contrasting with prior reports from Colinvaux. Sedimentary charcoal is extremely rare in initial surveys, suggesting fires are rare to absent. More pollen and charcoal samples will be counted in the next several months to reconstruct and compare the vegetation, megafauna population and fire history since deglaciation.