ARCUS | Arctic Research Consortium of the United States

7th Annual ARCUS Award for Arctic Research Excellence

Honorable Mention Interdisciplinary Research
Submitted by   W. Wyatt Oswald
Authors   W. Wyatt Oswald, L. Brubaker, F. Sheng Hu, and G. Kling
Category   Interdisciplinary Research
Title   Holocene Pollen Records from the Central Arctic Foothills, Northern Alaska: Testing the Role of Substrate in the Response of Tundra to Climate Change
Affiliation   College of Forest Resources, University of Washington, Seattle , WA, USA

Abstract

To explore the role of edaphic controls in the response of arctic tundra to climate change, we analyzed Holocene pollen records from lakes in northern Alaska located on glaciated surfaces (Sagavanirktok and Itkillik II) with contrasting soil texture (fine versus coarse), topography (smooth versus irregular), and tundra (dwarf-shrub versus prostrate-shrub). Using indicator taxa, pollen accumulation rates (PARs), and multivariate (Canberra metric distance) comparison of fossil and modern pollen assemblages, we reconstructed the vegetational changes at Upper Capsule Lake (Sagavanirktok surface) and Red Green Lake (Itkillik II surface) in response to increased effective moisture between the early and middle Holocene. In the Red Green record, low PARs and the continuous presence of taxa indicative of prostrate-shrub tundra (PST; Equisetum, Polypodiaceae, Thalictrum, and Rosaceae) indicate that the vegetation of the Itkillik II surface resembled PST throughout the Holocene. During the warm, dry early Holocene (11,300 to 10,000 cal years BP), PST also occurred on Sagavanirktok surfaces, as evidenced by PST indicators (Bryidae, Polypodiaceae, Equisetum, and Rosaceae) in this interval of the Upper Capsule record. However, PST taxa declined, PARs increased, and taxa indicative of dwarf-shrub tundra (DST; Rubus chamaemorus and Lycopodium annotinum) increased between 10,000 and 7500 cal years BP, suggesting increased vegetation cover and a transition from PST to DST. As climate changed during this interval, we hypothesize that the Sagavanirktok surface experienced increased soil moisture because of its fine-textured soils and smooth topography. This would have led to a series of positive feedbacks involving greater vegetation cover, permafrost aggradation, anoxic and acidic soil conditions, slower decomposition, and the development of a thick organic layer. In contrast, soil moisture remained low on the better-drained Itkillik II surface, and as a result only minor vegetational changes occurred between the early and middle Holocene. These findings indicate that landscape-scale substrate variations have an important effect on how tundra responds to climate change, which suggests that the response of arctic ecosystems to future climatic variability may be spatially heterogeneous.