Graduation date: 1995

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.

Tephrochronology is a powerful tool to correlate and improve the chronology of sedimentaryarchives in the Arctic Ocean. The Aniakchak Caldera Forming Eruption (CFE) in Alaska at3.6 cal kyr BP ejected ash that were found in a widespread layer in Alaska, and as cryptotephrain the Chukchi Sea, Newfoundland, and Greenland. This study presents data from the coreSWERUS-L2-4-PC1 (4PC) taken at a water depth of 120 m in the Chukchi Sea. The sharp peakin tephra shards concentration permitted to clearly place the isochron. Unfortunately, the microprobeanalyses were unsuccessful, however measurements of trace elements were performedwith Laser Ablated-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). The geochemicalsignature of the Aniakchak 3.6 eruption was ensured with significant trace elementratios. The isochron of the eruption combined with the radiocarbon dates from 4PC permittedto calculate the local marine radiocarbon reservoir age offset DR=36446 years. This value isrelatively low compared to recent estimates in the Chukchi Sea, especially to the neighbouringcore SWERUS-L2-2-PC1 were DR=47760. The DR value of this study is explained by theinfluence of the "young" Atlantic water mixing with the "old" Pacific water at the depth wherethe core was taken.