Lake-Level Reconstructions and Paleohydrology of Birch Lake, Central Alaska, Based on Seismic Reflection Profiles and Core Transects

Lake-level history for Birch Lake, Alaska, was reconstructed using seismic profiles and multiproxy sedimentary analyses including sedimentology, geochemistry, magnetic susceptibility, and palynology. Twenty-two seismic profiles (18 km total) and eight sediment cores taken from the lake margin to its depocenter at 13.5 m provide evidence for low lake stands during the late Pleistocene and Holocene. Thirty-one AMS radiocarbon dates of macrofossils and pollen provide a century-scale chronology. Prior to 12,700 C yr B.P., the lake, which now overflows, was either seasonally dry or desiccated for prolonged periods, indicating a severe period of aridity. Lake level rose more than 18 m between 12,700 and 12,200 C yr B.P. before falling to 17 m below the level of overflow. Between 11,600 and 10,600 C yr B.P. the water remained between 14 and 17 m below the overflow level. Onlap sedimentary sequences were formed during a transgression phase between 10,600 and 10,000 C yr B.P. Between 10,000 and about 8800 C yr B.P. the lake was between 6 and 9 m below the overflow level. Lake level again rose, approaching the overflow level, between 8800 and 8000 C yr B.P. Seismic and core evidence of minor erosional events suggest lowstands of 2– 6 m until 4800 C yr B.P. There ave been no prolonged periods of lake-level depression since hat time. The major restructuring of the climate system during eglaciation evidently generated a complex set of fluctuations n effective moisture in interior Alaska, which likely affected olian processes and vegetation development, as well as lake evels. © 2000 University of Washington.