Evidence for a glacial refugium in south-central Beringia using modern analogs: a 152.2 kyr palynological record from IODP Expedition 323 sediment

Abstract

Palynological assemblages from Integrated Ocean Drilling Program (IODP) Expedition 323 (Bering Sea Expedition) site U1343, on the edge of the Bering Sea Shelf, permit reconstruction of the terrestrial vegetation of the southern margin of central Beringia. Previous research indicates that central Beringia was a glacial refugium for boreal vegetation, which expanded into eastern and western Beringia as glaciers retreated. This hypothesis has been difficult to test because sampling has been largely restricted to eastern and western Beringia and islands in the Bering Sea. Pollen grains and spores preserved in core samples from site U1343 provide a record of central Beringian vegetation over the past 152.2 kyr at a resolution of ~10 kyr. Grass (Poaceae ≥ 17.4%) and sedge (Cyperaceae ≥ 17.1%) pollen dominate the assemblages, indicating the presence of graminoid tundra. Lower abundances of spruce (Picea ≤ 8.5%), birch (Betula ≤ 19.9%), and alder (Alnus ≤ 27.7%) pollen are consistently present throughout glacial/interglacial cycles, suggesting that trees and shrubs remained in central Beringia during glacial maxima. Sphagnum spores (3.4-10.9%) in all samples indicate locally or regionally mesic conditions during marine oxygen isotope stages (MIS) 1-6. Minimum site paludification during MIS 2, indicated by high ratios of angiosperm pollen to Sphagnum spores, coincides with the lowest shrub/herb ratios in our record, suggesting that conditions were drier and woody plants were sparse during the last glacial maximum.