The late Holoce ¹⁴C reservoir age in the Chukchi Sea as inferred from tephra in marine sediments

Abstract:

Volcanic ash, or tephra, blankets the local and regional landscape following a volcanic eruption. If this ash layer is preserved and identified, it can act as a time synchronous marker bed (isochron) for correlation between marine, terrestrial, glacial and lacustrine deposits. This can be a powerful tool when attempting to determine the true age of a marine sample (e.g. clam or mollusk), affected by the marine reservoir effect (MRE). The MRE causes dated radiocarbon to appear the age that carbon was last in equilibrium with the atmosphere rather than the time that a dated material was deposited. The offset (in years) caused by the MRE is referred to as ΔR. Presented in this study is new data on the lowermost part of SWERUS-L2-2-PC1 (2PC), a marine sedimentary core retrieved from the Chukchi shelf north of Siberia. By using quantification of rhyolitic tephra to locate tephra-rich layers for further study, results show a thick layer that is interpreted to have originated from the caldera-forming eruption of Aniakchak (Aniakchak II). The geochemical identification of the tephra was done using electron probe micro-analysis. A grain size analysis was also conducted to learn more about the sedimentology of 2PC and the possible proxies that can be used when trying to determine where to place the isochron. The isochron was finally placed with the help of relevant literature and the results from this study. That position shifted the previous age model of 2PC at a position to yield a ΔR of 482 years for the Chukchi Sea during this time period.