Radiocarbon age dating of biological material from cores collected off British Columbia, Canada and southeastern Alaska, U.S. along the Queen Charlotte-Fairweather fault zone

Piston cores, trigger weight cores, and IKU grab samples were collected by personnel from the Pacific Geoscience Centre of the Geological Survey of Canada (PGC) on two cruises (in 2015 and 2017) while onboard the CCGS John P. Tully as part of joint operations by the PGC and the USGS (personnel from Santa Cruz, California and Menlo Park, California). Cores and grab samples were taken in the Northeastern Pacific Ocean off Canada and Alaska along the Queen Charlotte/Fairweather Fault. The cores and grab samples were returned to the PCG facility in Sidney, British Columbia, Canada and placed in a core refrigerator.

Samples for radiocarbon analysis were measured by accelerator mass spectrometry (AMS) at the National Ocean Sciences AMS (NOSAMS) facility of Woods Hole Oceanographic Institution and the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry facility (UCIAMS) at the University of California Irvine. The radiocarbon ages were obtained by a ratio of 14C to 12C using a 14C half-life of 5568 years (Stuiver and Polach, 1977) and then were converted to calibrated calendar ages (cal years BP), with BP (Before Present) equal to 1950, using the CALIB 8.2 program (Stuiver and Reimer, 1993; website accessed in 2022 and 2023) and the Marine20 calibration curve (Heaton and others, 2020). The calibrated ages are reported as the minimum, maximum, and median probability ages at the 95 percent confidence level. The regional marine radiocarbon reservoir correction as defined by Ingram and Southon (1996), using the Marine20 calibration curve (delta R20) for the planktic foraminiferal samples, varied depending upon the age of the sample. The following were used: in the Bolling-Allerod interstade (dates older than 10,700 14C year BP, ca. 14,700-12,900 cal yr BP), delta R20 equal to 575 plus or minus 165 years; in the Younger Dryas stade (10,700-10,000 14C year BP, ca. 12,900-11,700 cal yr BP), delta R20 equal to negative 55 plus or minus 110 years; in the Early Holocene (10,000-8,000 14C year BP, 11,700-9000 cal yr BP), delta R20 equal to 245 plus or minus 200 years; in the Middle Holocene (8,000-2,000 14C year BP, 9000-2000 cal yr BP), delta R20 equal to 145 plus or minus 165 years; in the Late Holocene (2,000-200 14C year BP, 2000 cal yr BP to AD 1850), delta R20 equal to 140 plus or minus 110 years; and the Historic period (ages less than 200 14C year BP, ages less than AD 1850),delta R20 equal to 235 plus or minus 95 years (Schmuck and others, 2021). The pelecypods were considered to have lived at shallow depths and so the delta R20 values for the planktic foraminifera was applied to the dating of their shell fragments as well. For the benthic foraminiferal samples, a delta R20 equal to 860 plus or minus 330 years was used for samples less than 42,000 years (Walczak and others, 2020).