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https://doi.org/10.5194/os-2020-82
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2020-82
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 Aug 2020

25 Aug 2020

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This preprint is currently under review for the journal OS.

Circulation timescales of Atlantic Waters in the Arctic Ocean determined from anthropogenic radionuclides

Anne-Marie Wefing1,2, Núria Casacuberta1,2, Marcus Christl1, Nicolas Gruber2, and John N. Smith3 Anne-Marie Wefing et al.
  • 1Laboratory of Ion Beam Physics, Institute for Particle Physics and Astrophysics, ETH Zürich, Switzerland
  • 2Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Switzerland
  • 3Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS, Canada

Abstract. The inflow of Atlantic Waters to the Arctic Ocean is a crucial determinant for the future trajectory of this ocean basin with regard to warming, loss of sea-ice and ocean acidification. Yet many details of the fate and circulation of these waters within the Arctic remain unclear. Here, we use the two long-lived artificial radionuclides 129I and 236U together with two tracer age models to constrain the pathways and circulation times of Atlantic waters in the surface and in the mid-depth Atlantic layer (250–800 m depth). We thereby benefit from the unique time-dependent tagging of Atlantic waters by these two isotopes. In the surface layer, a binary mixing model yields tracer ages of Atlantic Waters between 9–16 years in the Amundsen Basin, 12–17 years in the Fram Strait (East Greenland Current) and up to 20 years in the Canada Basin, reflecting the pathways of Atlantic Waters through the Arctic and their exiting through Fram Strait. In the mid-depth Atlantic layer (250 to 800 m), the transit time distribution (TTD) model yields mean ages in the central Arctic ranging between 15 and 65 years, while the mode ages representing the most probable ages of the TTD range between 2 and 30 years. The estimated mean ages are overall in good agreement with previous studies using artificial radionuclides or ventilation tracers. Although we find the overall flow to be dominated by advection, the shift of the mode age towards a younger age compared to the mean age reflects also the presence of a substantial amount of lateral mixing. For applications interested in how fast signals are transported into the Arctic's interior, the mode age appears to be a suitable measure. The short mode ages obtained in this study suggest that changes in the properties of Atlantic Waters will quickly spread through the Arctic Ocean and can lead to relatively rapid changes throughout the upper water column in future years.

Anne-Marie Wefing et al.

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Anne-Marie Wefing et al.

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Short summary
Atlantic Waters that carry heat and anthropogenic Carbon into the Arctic Ocean play an important role in the Arctic sea-ice cover decline, but their pathways and travel times remain unclear. Here we used two radionuclides of anthropogenic origin (129I and 236U) to track Atlantic-derived waters along their way through the Arctic Ocean, estimating their travel times and mixing properties. Results help to understand how future changes in Atlantic Water properties will spread through the Arctic.
Atlantic Waters that carry heat and anthropogenic Carbon into the Arctic Ocean play an important...
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