COASTAL RESPONSE TO LATE HOLOCENE CLIMATE AND SEA LEVEL CHANGE IN NORTHWEST ALASKA

Quaternary stratigraphy exposed in coastal bluffs of the Chukchi and Beaufort Seas provided a window through which Dave Hopkins led a generation of researchers into the world of Beringian history and paleogeography. The threshold of that view lay solidly in the Holocene, however, and Dave frequently paused there, inspiring curiosity and nurturing research into the dynamic “recent.” During the past 30 years several communities in which he developed lifelong attachments have experienced substantial damage to infrastructure and homes due to storm-related erosion and rapid coastal retreat. Despite a tendency to view this transgression as unique, coastal deposits in the region record similar periods of shoreline erosion during the Holocene. Our ability to anticipate coastal behavior and to assess the vulnerability of habitats and communities to environmental change in the intertidal zone requires an understanding of the factors that control shorezone dynamics. These factors include sedimentary geology and cryology, tectonics, environmental forcing from marine and terrestrial climate, and sea level change.

This paper integrates geological, archaeological, historical climate and shoreline erosion data to provide a coastal geomorphic classification and a model of dynamic coastal oceanographic processes and erosion potential for the southern Chukchi Sea. These data sets record annual to millennial scale environmental changes that must be understood for effective coastal management. Eustatic sea level has risen slowly during the past 5000 years, while climatic variability over this period has resulted in fluctuating relative sea levels. Climatic warming during recent decades has forced longer open water periods and storm seasons, permafrost degradation, accelerated erosion and sedimentation, and increased rates of organic carbon release into the coastal zone. While sea level trend during the late Holocene plays an important role in coastal evolution, decadal-scale shifts in marine and atmospheric climate play a more critical role in controlling coastal morphodynamics and exposing communities to changes in the coastal environment.