Beach ridge geomorphology of Kotzebue Sound: Implications for paleoclimatology and archaeology

Abstract

Beach ridges occur on all continents and record the horizontal addition of shoreface beyond the reach of storms. Improved cartographic methods in the nineteenth century allowed British historians to link shoreline changes with abandoned villages. This scientific trajectory was paralleled in the Bering Strait region from the 1880's to the 1930's. In the 1950's J. L. Giddings formalized "beach ridge archaeology" as a survey strategem using relative position to infer relative cultural chronology in northwest Alaska. Modern researchers use archaeological dates and data to document past climates or environments. At Cape Espenberg, on Seward Peninsula, my use of archaeological, stratigraphic, pedological, granulometric and photogrammetric data allows the delineation of 4000 years of coastal evolution. Four chronostratigraphic units are distinguished, using archaeological dates as minimum age assignments. Dune ridges formed in discrete intervals: 3300 to 2000 BP and from 1200 BP to the present; while low, berm ridges are predominant 4000-3300 and from 2000-1200 BP. The two different types of ridges correspond to variable climatic conditions: dune ridges formed after higher storm surges and winter winds while the lower berm ridges are related to less intense storm surges. Coastal dunes at Cape Espenberg are soon altered by plant succession processes with distance from the beach. As primary dunes are eroded, a complex blowout topography results. Erosional processes in blowouts were monitored during 1987-1989, revealing substantial vertical changes, up to 10 cm of erosion per yr. These rapid changes have considerable influence on archaeological site stability. Studies of the gravel ridge systems confirm the proxy storm record apparent in the coastal dunes atop the beach ridges on the Seward Peninsula. The geoarchaeological methodology allows correlations between depositional units within nine of the principal beach ridge and chenier complexes of northwest Alaska. The onset of deposition was at 4000-3500 BP. The complexes at Cape Espenberg and Choris Peninsula contain elevated, broader transgressive ridge sets 3300-2000 BP and from 1100-200 BP, connected with increased storm activity in the North Pacific. Erosional disconformities between successive sets of beach ridges occur at Cape Krusenstern at ca. 3000 BP and before 2000 BP. Between 2000-1000 BP extensive progradation occurred at nearly all complexes, indicating that less stormy conditions predominated.