Assessment of the High-Resolution Sediment Gravity Flow Record in Prince William Sound, Alaska
Master of Science (M.Sc.)
Virginia Institute of Marine Science
Steven A. Kuehl
Joshua R. Williams
Christopher J. Hein
James E. Perry
Courtney K. Harris
South-Central Alaska is one of the most seismically active and climatologically sensitive places in the world. Within this region, Prince William Sound (PWS) receives abundant sediment from multiple sources, potentially housing a high-resolution environmental record spanning the past 4,000 years. Inputs to PWS are derived from local rivers and glaciers, and may include earthquake- and glacial-outburst-triggered sediment gravity flows. Therefore, this is an ideal location to investigate the long-term record of seismic, glacial, and riverine activity. This study examines the elemental, grain size, and stable isotope signatures in PWS to identify gravity flow deposits and the potential paleoseismic and paleoclimate record. Previous sediment core studies have focused on central and southern PWS, and this study fills a knowledge gap on sediment characteristics in northern PWS. Shelf sediments are transported into PWS via Hinchinbrook Inlet during winter storms, and the Copper River plume is advected into PWS during summer months. Local sources in PWS and the Copper River/Shelf sediments in southern PWS have unique signatures of Sr/Pb, Cu/Pb, K/Ca, Rb/Sr, and Rb/Ca. as a result, sediment gravity flows originating from different locations have distinct provenance signatures and can be distinguished from locally emplaced sediment. Six cores in central and northern PWS were collected and sedimentation rates were determined by 210Pb, 137Cs, and 239,240Pu geochronology. The cores were assessed for elemental content and grain size patterns to identify gravity flow deposits. Deposits, sedimentation rates, and provenance were correlated with five previously collected cores in southern and central PWS. The stable isotopic content of 13C and 15N were assessed across all eleven cores. The sedimentation rates, mean grain size, Sr/Pb and Cu/Pb all decrease moving northward through PWS, and sediments derived in northern PWS have the lowest Sr/Pb, Cu/Pb, δ13C, δ15N, and C/N and highest K/Ca, Rb/Sr, and Rb/Ca values observed. This trend is due to decreasing influence from the Copper River and shelf sediments in the south and increasing influence of local PWS sources in the north. Using these distinct provenances, several earthquake deposits were identified. Earthquakes of magnitudes 6.0 < Mw < 7.0 produced deposits in the central channel, and those of Mw ≥ 7.0 with epicenters in PWS had distinctly mixed signatures from generating numerous flows throughout the region. We also identified a flow sourced near the Columbia Glacier region which may have derived from earthquake activity or the glacier’s rapid retreat. Based on spatial analysis of the eleven gravity cores, the most robust gravity flow records are captured within deep ponded sediment basins and the area spanning the southern end of the channel to the northern ponded sediment basin.
© The Author
Clyne, Elisabeth Rose, "Assessment of the High-Resolution Sediment Gravity Flow Record in Prince William Sound, Alaska" (2017). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1516639590.