Using 226 Ra and 228 Ra isotopes to distinguish water mass distribution in the Canadian Arctic Archipelago

Chantal Mears, Helmuth Thomas, Paul B. Henderson, Mathew A. Charette, Hugh MacIntyre, Frank Dehairs, Christophe Monin, Alfonso Mucci

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5 Citations (Scopus)
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As a shelf-dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (226Ra, 228Ra, 224Ra, and 223Ra), are transferred from the sediments to seawater, making them ideal tracers of sediment-water exchange processes and ocean mixing. As the two long-lived isotopes of the radium quartet, 226Ra and 228Ra (226Ra with a t1=2 of 1600 years and 228Ra with a t1=2 of 5.8 years) can provide insight into the water mass compositions, distribution patterns, as well as mixing processes and their associated timescales throughout the Canadian Arctic Archipelago (CAA). The wide range of 226Ra and 228Ra activities, as well as of the 228Ra=226Ra, measured in water samples collected during the 2015 GEOTRACES cruise, complemented by additional chemical tracers - dissolved inorganic carbon (DIC), total alkalinity (AT), barium (Ba), and the stable oxygen isotope composition of water (18O) - highlight the dominant biogeochemical, hydrographic, and bathymetric features of the CAA. Bathymetric features, such as the continental shelf and shallow coastal sills, are critical in modulating circulation patterns within the CAA, including the bulk flow of Pacific waters and the inhibited eastward flow of denser Atlantic waters through the CAA. Using a principal component analysis, we unravel the dominant mechanisms and apparent water mass end-members that shape the tracer distributions. We identify two distinct water masses located above and below the upper halocline layer throughout the CAA and distinctly differentiate surface waters in the eastern and western CAA. Furthermore, we highlight water exchange across 80W, inferring a draw of Atlantic water (originating from Baffin Bay) into the CAA. This underscores the presence of an Atlantic water "U-turn" located at Barrow Strait, where the same water mass is seen along the northernmost edge at 80W as well as along the southeasternmost confines of Lancaster Sound. Overall, this study provides a stepping stone for future research initiatives within the Canadian Arctic Archipelago, revealing how quantifying disparities in the distributions of radioactive tracers can provide valuable information on water mass distributions, flow patterns, and mixing within vulnerable areas such as the CAA.

Original languageEnglish
Pages (from-to)4937–4959
Number of pages52
Issue number20
Publication statusPublished - 16 Oct 2020

Bibliographical note

Funding Information:
Financial support. This research has been supported by Canadian

Funding Information:
Acknowledgements. We wish to express our sincere gratitude to Michiel Rutgers van der Loeff, Michael E. Böttcher, and Amber Annett, whose constructive reviews greatly helped to improve our paper. Furthermore, we wish to thank the captains and crew of the icebreaker CCGS Amundsen as well as the chief scientist, Roger Francois and his team for their support at sea. We would also like to extend our appreciation to Jacoba Mol and colleagues on the ship for their collaboration. This study was financially supported by the Canadian GEOTRACES program, as part of the NSERC-CCAR initiative. Matthew A. Charette and Paul B. Hen-derson were supported by U.S. GEOTRACES via the NSF Chemical Oceanography program (grant no. OCE-1458305). Frank De-hairs is grateful to Jacques Navez, Martine Leermakers, Kokuhen-nadige Hashan Niroshana for assistance during the Ba analyses in Brussels. Helmuth Thomas acknowledges support from the German Academic Exchange service (DAAD, MOPGA-GRI, grant no. 57429828), which received funds from the German Federal Ministry of Education and Research (BMBF).

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