Radioisotope and grain-size data from sediment cores collected in Harrison Bay (Beaufort Sea continental shelf), Alaska 2021-2022

Seabed sediment cores were collected from 13 sites across Harrison Bay on the Alaskan Beaufort Shelf between Cape Halkett and Oliktok Point. Sediment cores were collected aboard the Research Vessel Ukpik in the summers of 2021 and 2022 for NSF project 1913195: “Arctic Shelf sediment fate – an observational and modeling study of sediment pathways and morphodynamic feedbacks in a changing polar environment.” Core sites included the subaqueous Colville River Delta, inner shelf, and middle shelf. The dataset consists of Lead-210 (Pb-210) activities by alpha and gamma spectroscopy, Lead-214 (Pb-214) activities by gamma spectroscopy, Cesium-137 (Cs-137) by gamma spectroscopy, grain-size distributions, organic matter, dry bulk density, and porosities. Sediment cores were collected using an 8-centimeter (cm) diameter gravity corer, and cores were sliced in 1-cm intervals and bagged in the field before being returned to labs for analyses. At the University of North Carolina at Chapel Hill and Oregon State University, samples were weighed, dried, and reweighed in the laboratory to determine the porosity and dry bulk density before other lab analyses. Samples were measured for Pb-210 activities using an acid digestion procedure and alpha spectroscopy developed from the Nittrouer et al. (1979) Po-210 detection methods. Alpha energy emissions were counted in a Mirion© Alpha Analyst Integrated Alpha Spectrometer. Samples were also analyzed for Pb-210, Pb-214, and Cs-137 activities by gamma-ray spectroscopy by counting for greater than or equal to 24 hours in a Canberra GL2020RS LEGe planar gamma-ray spectrometer. Samples were sonicated for two minutes prior to grain-size distribution analysis, which was performed using an Escitec Bettersizer S3Plus laser diffraction sensor. Samples were analyzed for percent organic matter (OM) by a loss-on-ignition (LOI) procedure that combusted samples at 550 degrees Celcius (ºC) for five hours in a muffle furnace to volatize organics. No regions of decay were observed in Pb-210 activity profiles, and Pb-210 activities were generally low, ranging from 0.90 ±0.05 to 5.09 ±0.13. Most samples did not contain detectable Cs-137 activities. Grain-size distributions varied considerably among the 13 sediment cores, with samples ranging from unimodal muds to unimodal sands to bimodal sands and muds. Porosity profiles were linear in most sediment cores; however, there was some variability among linear profiles. Down-core OM were mostly linear and trended with porosity profiles.