Abstract Detail

Beringia!: Current Insights on the Geology, Climate, Paleontology, Floristic Assembly, and Biodiversity of a Subcontinent that is Central to Northern Hemisphere Biogeography

Fowell, Sarah J [1].

Palynological Evidence for Coastal Refugia in Central Beringia.

Palynological assemblages from Integrated Ocean Drilling Program (IODP) Expedition 323 site U1343, in the Bering Sea, record the vegetation of the southern coast of Central Beringian during Marine Isotope Stages (MIS) 1-6, 8, 10, 12, 14 and 15. Samples analyzed at ~10 kyr intervals between ~11 kya and ~150 kya, and samples ranging in age from ~258 kya to ~615 kya, are all dominated by grass (Poaceae) and sedge (Cyperaceae). Boreal forest taxa, including birch (Betula), alder (Alnus), and relatively sparse grains of spruce (Picea) are present throughout the record, revealing little difference between glacial and interglacial assemblages. Interglacial pollen spectra from stage 15 differ from glacial assemblages only in that they contain slightly higher percentages of Poaceae and lower percentages of tree and shrub taxa such as Alnus and Betula.
Canonical correspondence analysis clusters glacial and interglacial assemblages together within a quadrant defined by high percentages of Poaceae pollen. Comparison with 220 modern pollen spectra from lakes and bogs throughout Alaskan indicate that the closest modern analogs are sites proximal to the Yukon/Kuskokwim Delta, where the vegetation consists of herbaceous tundra with isolated stands of trees.
During glacial stages, falling sea levels exposed interglacial sediment deposited on the Bering Sea shelf to fluvial erosion and reworking. It is therefore conceivable that the similarity between glacial and interglacial assemblages from IODP site U1343 is the result of reworking by fluvial systems on the emergent Bering Land Bridge. However, minimal damage to pollen from boreal taxa in assemblages from glacial stages 2-14 argues against long distance transport by rivers to the shelf edge. Analogs from the modern coastal tundra suggest an alternative: Vegetation migrated with the coastline during glacial/interglacial cycles, and maritime conditions on the southern margin of Central Beringia supported a belt of herbaceous tundra with stands of boreal trees and shrubs throughout MIS 2-14. To test this hypothesis, samples from lakes or bogs on the lowlands of the Bering Land Bridge are required. These can be obtained by coring sedimentary basins on the submerged Bering Sea shelf.

1 - University of Alaska Fairbanks, Department of Geosciences, 1930 Yukon Drive, Fairbanks, AK, 99775-5780, USA

Keywords:
Pollen analysis.

Presentation Type: Symposium Presentation
Number: S1004
Abstract ID:903
Candidate for Awards:None