The radium isotope quartet as tracers of sediment-water interaction and cross-shelf transport in the Chukchi and Beaufort Seas during autumn freeze-up

Previous observations of shelf-basin interactions in the Chukchi and Beaufort Seas have shown highly patchy timescales of halocline ventilation [1], indicating the importance of time-dependent, mesoscale processes that allow for cross-shelf transport [2, 3]. Further, sea ice characteristics are changing over shelves due to climate warming [4] that further warrant observations in seasons other than summer to establish baselines and understand the impact of sea ice changes on these processes. In October-November 2018 we measured the quartet of radium isotopes on a series of shelf/slope transects in the Chukchi and Beaufort Seas – the first such radium measurements during freeze-up. Long-lived isotopes indicate increased sediment-water interaction and further penetration of Chukchi shelf waters into the Canada Basin than during spring or summer. A unique approach of this study is the use of short-lived isotopes in shelf bottom waters to model shelf water ages and transport times from the inner shelf to the shelf-break. Cross-stream fluxes were spatially variable. Sediments collected from the Chukchi and Beaufort Shelves were used in lab experiments to characterize radium isotope production ratios at high spatial resolution, improving the future use of radium as a tracer in the western Arctic.

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