Evidence for the presence of mesic herbaceous shrub tundra with isolated stands of trees in south central Beringia during glacial stages 2 - 16

Abstract

Palynological analysis of assemblages from the Integrated Ocean Drilling Program (IODP) Expedition 323, Bering Sea Expedition, site U1343, located in deep water adjacent to the Bering Sea shelf edge, permit reconstruction of the terrestrial vegetation of the southern margin of central Beringia. Previous research done by Rachel Westbrook on marine isotope stages (MIS) 1-6 indicates that the southern coast of central Beringia was a glacial refugium for boreal forest vegetation. This study extends and augments Westbrook's research by analyzing additional samples from IODP site U1343 spanning the last 258 - 615.3 kya, during glacial stages 8, 10, 12, 14, and 16. Grass (Poaceae) and sedge (Cyperaceae) pollen dominate the assemblages with small but persistent amounts of boreal forest taxa, such as alder (Alnus), birch and dwarf birch (Betula and Betula nana), and spruce (Picea). A set of modern surface samples forming a transect from the southwestern margin of the Bering Sea shelf to Nome, AK were obtained and analyzed as potential modern analogs for the palynofloral assemblages from site U1343. Low percentages of boreal forest taxa in nearshore samples from this Bering Sea shelf transect reflect the vegetation of the coastal Seward Peninsula and the Yukon/Kuskoskim delta, regions dominated by herbaceous tundra with isolated stands of trees. Comparison of modern and fossil assemblages via canonical community ordination indicates that the IODP samples from site U1343 and modern samples from the Bering Sea shelf are most similar to surface samples from lakes and bogs surrounded by moist herbaceous/shrub tundra. These data suggest that boreal forest taxa persisted throughout MIS 8, 10, 12, 14, and 16 on the southcentral Beringian coast, where the vegetation was primarily moist herbaceous/shrub tundra with intermittent stands of trees.