Late-glacial vegetational, tephra, and climatic history of southwestern Kodiak Island, Alaska

Abstract

Late-glacial vegetational, tephra, and climatic history of western Kodiak Island is developed based upon detailed palynological, macrofossil, and AMS ¹⁴C stratigraphy. A series of distinctive Purple, White, and Grey tephras allows correlation amongst several sections along the southwestern Kodiak coastline. Changes in loss-on-ignition within these sections support our interpretation of climatic change since deglaciation. The macrofossil component of the sedimentary record provides insight for late-glacial plant diversity. Earliest vegetation after glacial recession 14 000 years BP is composed of a diverse array of moist herbaceous species, along with a dominance of Empetrum nigrum (heath). As climate became warmer and moister after 13 000 BP, Polypodiaceae (ferns) spread over the landscape. A dramatic reversal in vegetation and climate to colder, drier conditions is indicated from 10 800 to 10 000 years BP, which we term the “Fern Gap”. We interpret this oscillation as a high-latitude Pacific expression of the Younger Dryas event, well-known from Greenland and continental regions surrounding the North Atlantic. The subsequent Holocene warming at 10 000 years BP is quite abrupt, as shown by the section lithostratigraphy, palynological and macrofossil records, and percent loss on ignition. This late-glacial series of events indicates a high correlation between paleoclimate on Kodiak Island and the North Atlantic region, suggesting comparable climatic forcing in both regions.