Sediment structure and deposition rates in the Yukon coast

The aim of this project was to investigate nearshore depositional processes in the Arctic within the last century. For this study sediment cores were retrieved from lagoon and marine sites at Kanivaliuraq – Ptarmigan Bay (lagoon) and Herschel Basin (marine). The lagoon (YC18-PB-SC01, 64 cm length) and two marine (YC18-HB-GC01, 40 cm length; and PG2303-1, 20 cm length) sediment cores, were collected at 3, 18 and 43 m water depth, respectively. Sampling missions took place in April 2016 and August 2018 in the nearshore areas of the southern Beaufort Sea along the Yukon North Slope in the western Canadian Arctic. Lagoon core YC18-PB-SC01 was taken with a percussion corer and marine cores with an UWITEC gravity corer. The cores were kept cool and dark until further analysis in the laboratories. Mineralogy composition was obtained by X-ray diffraction (XRD) of bulk sediment (well ground and mixed) through a Siemens D500 X-Ray diffractometer and the spectra were resolved with EVA Bruker-AXS software. The grain size analysis results are presented in three groups, particles between 2 mm and 63 µm, 63 µm and 2 µm and smaller than 2 µm. All samples were treated with peroxide (30%) before laser diffraction to remove organic matter particles. Grain size analysis was performed using a Microtrac MRB's Bluewave and a Partica HORIBA laser diffraction device. The 210Pb activities were obtained by assuming a secular equilibrium with 210Po and using a spike of 209Po. Samples were digested by acid solutions (HNO3, HCl, HF and HNO3+H2O2). Both polonium radionuclides were deposited on a silver disk and measured by alpha spectrometry using ORTEC detectors coupled to MaestroTM data acquisition software. 226Ra and 137Cs activity were assessed by high-resolution gamma spectrometry through a germanium detector (ORTEC). The ages, mass and sediment accumulation rates (MAR and SAR, respectively) were inferred by a Constant Flux model also known as Constant Rate of Supply model. All uncertainties were calculated by Monte Carlo method.