Signature of Recent Sediment Accumulating in Prince William Sound, Alaska: A Record of Storms, Earthquakes, and Seasonal Inputs

This study focuses on the development o f provenance signatures for sediments accumulating in Prince William Sound, with an emphasis on interpreting mechanisms of sediment deposition using historical earthquake, wave, river discharge, and glacial outburst flood records. A highresolution sedimentary sequence in Prince William Sound, Alaska contains sediments sourced from local watersheds as a result of seasonal and event-driven sedimentation. This study contributes to the development of paleo-proxies for sediment provenance, earthquakes, shelf sediment resuspension, and Copper River discharge. Geochemical studies of sediment cores and end-member samples using X-ray fluorescence and inductively coupled plasma mass spectrometry allows for the development of elemental proxies for sediment provenance during the past ~ 100 years. Seasonal sedimentation is resolved at Hinchinbrook Entrance as a result of high sediment accumulation rates and distinct textural and geochemical changes. Sediments deposited during the winter are derived from shelf sediment resuspension and sediments deposited during the summers are sourced from a complex mixture of the Copper River plume and direct discharge within Prince William Sound. Analyses of a continuous 18-year (1995—2013) wave record reveal that shelf sediment resuspension has a strong seasonality with large waves in the winters compared to the summers. More than 65 % of the sediments at Hinchinbrook Entrance accumulate during the winters, and those sediments are sourced from the shelf with distinct provenance signatures from the Copper River Basin. A north-south transect of sediment cores in Prince William Sound reveal that provenance signatures can be used to identify deposits in the Sound that were initiated by different mechanisms. Deposits in northern Prince William Sound that correspond to large earthquakes occurred in 1912, 1964, and 1983. A similar deposit from ~ 1895 in northern Prince William Sound, prior to historical earthquake records, may also have been initiated from a large earthquake in the 1890’s. Additional deposits in southern Prince William Sound from 1977 and 1992 were likely formed due to an increase in Copper River discharge. The 1977 deposit occurred during a shift to abruptly warmer climate conditions in Alaska that resulted from the well-documented climate regime shift in the North Pacific in 1976—1977. The most recent identifiable deposit in the north-south transect has an age of 2001 with sediments that contain distinct Prince William Sound provenance signatures. Relative to any other season in the 18-year record, the winter of 2001 experienced the highest bottom wave orbital velocity on the Gulf of Alaska continental shelf, the largest area of the shelf with sediment in resuspension, and the shortest time between resuspension events. During a time of minimal seismicity, slope failure within the southern portion of the central channel in Prince William Sound may have occurred due to the extreme waves in the winter of 2001 and could explain the occurrence of this deposit in southern Prince William Sound