A 40,000-yr record of environmental change from Burial Lake in Northwest Alaska

Burial Lake in northwest Alaska records changes in water level and regional vegetation since ?39,000 cal yrBP based on terrestrial macrofossil AMS radiocarbon dates. A sedimentary unconformity is dated between34,800 and 23,200 cal yr BP. During all or some of this period there was a hiatus in deposition indicating amajor drop in lake level and deflation of lacustrine sediments. MIS 3 vegetation was herb-shrub tundra;more xeric graminoid-herb tundra developed after 23,200 cal yr BP. The tundra gradually became moremesic after 17,000 cal yr BP. Expansions of Salix then Betula, at 15,000 and 14,000 cal yr BP, respectively, arecoincident with a major rise in lake level marked by increasing fine-grained sediment and higher organicmatter content. Several sites in the region display disrupted sedimentation and probable hiatuses during thelast glacial maximum (LGM); together regional data indicate an arid interval prior to and during the LGMand continued low moisture levels until ?15,000 cal yr BP. AMS 14C dates from Burial Lake are approximatelysynchronous with AMS 14C dates reported for the Betula expansion at nearby sites and sites across northernAlaska, but 1000–2000 yr younger than bulk-sediment dates