Full-glacial upland tundra vegetation preserved under tephra in the Beringia National Park, Seward Peninsula, Alaska

Abstract

The nature of the full-glacial vegetation of Beringia has been the subject of a great deal of investigation and debate. Here we present a reconstruction of an intact example of the full-glacial upland vegetation of part of the northern Seward Peninsula at one point in time. The area was blanketed by more than 1 m of tephra ca. 18,000 14C BP (ca. 21,500 cal. BP), and the former land-surface was preserved in the permafrost. The discovery of the land-surface provides a unique opportunity to study a fossil ecosystem preserved in situ. Macrofossils were used to reconstruct the vegetation growing at several sites on the buried land-surface. The macrofossil assemblages indicate a vegetation characterized by graminoids and forbs, with the occasional occurrence of Salix arctica. The vegetation was dominated by Kobresia myosuroides, other sedges ( Carex), and grasses, with a fine-scale mosaic related to snow accumulation and moisture availability. Overall, the vegetation was a closed, dry, herb-rich tundra-grassland with a continuous moss layer, growing on calcareous soil that was continuously supplied with loess. Nutrient renewal by loess deposition was probably responsible for the relatively fertile vegetation, and the occurrence of a continuous mat of acrocarpous mosses. Good physiognomic analogues can be suggested, but no exact modern vegetational analogues have been found, probably because the full-glacial environment and climate with loess deposition do not occur today.