Geochemistry of surface sediment and sediment cores in Bellingham Bay, Whatcom County, Washington, in February 2020

Process duplicates for carbon analyses were run for every sample and were within 15 percent. For stable isotope analyses, long-term internal reference materials were included in every run. For short-lived radionuclides, sample activities were calculated by comparison to reference standards with the same geometry and counting time; reported uncertainties include 1 standard deviation counting errors, detector efficiency, and background corrections. Detector efficiency for Cesium-137 was determined using National Institute of Standards and Technology (NIST) Standard Reference Material 4350B (at the Menlo Park Gamma Counting Lab) and International Atomic Energy Agency (IAEA) Standard Reference Material 300 (at Pacific Coastal and Marine Science Center Radiochemistry Lab). Detector efficiency for Lead-210 was determined using IAEA standards RGU-1 and RGTh-1. Detector efficiency for Beryllium-7 was calculated by interpolation between the efficiencies of Lead-214 at 351.9 keV and Bismuth-214 peak at 609.3 keV. For sediment grain size analyses (GSA), the laser particle counter was calibrated with three manufacturer-provided standards every day. Process duplicates for GSA were analyzed every 20 samples and were within 15 percent. For elemental chemistry determinations, long-term internal reference materials were used to standardize the data. The percent recovery for all elements was within 15 percent of reference values for concentrations that were not less than five times the limit of detection.