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

• Main Authors: Wefing, Anne-Marie, Casacuberta, Núria, Christl, Marcus, Gruber, Nicolas, Smith, John N.
• Format: Report
• Language: English
• Published: Copernicus 2020
• Subjects: Amundsen Basin; Arctic; Arctic Ocean; Canada; Greenland; amundsen basin; canada basin; Central Arctic; East Greenland; east greenland current; Fram Strait; Ocean acidification; Sea ice
• Online Access: https://hdl.handle.net/20.500.11850/445773; https://doi.org/10.3929/ethz-b-000445773

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. ISSN:1812-0806 ISSN:1812-0822