Circulation Timescales and Pathways of Atlantic Water in the Canada Basin: Insights From Transient Tracers 129I and 236U.

Anthropogenic radionuclides 129I and 236U are used to investigate pathways of the Atlantic Water flow in the Canada Basin, estimate transport timescales, and investigate mixing dynamics within the Atlantic Water layer and the overlying Pacific Water. Transit Time Distribution (TTD) model mean ages indicate water takes 25–35 years to reach the Canada Basin from the entrance of the Arctic, with limited lateral and vertical mixing along the core of the Arctic Ocean Boundary Current. Mode ages obtained from the model yield shorter transport times of 20–32 years. These age estimates agree with previous studies using these radionuclides and ventilation tracers in this region, indicating a steady‐state flow of Atlantic Water for the last 15 years. The distribution of the isotopes in the Atlantic layer indicates two pathways Atlantic Water may take into the basin, supported by the distribution of ages in the TTD model. End‐member mixing models indicate that the Pacific Winter water acquires a 20%–40% Atlantic Water signal of the radionuclides, upwelled over short periods, most likely along the shelf and Barrow Canyon region. Plain Language Summary: Man‐made nuclear products are used to trace the path of Atlantic water from the Atlantic Ocean to the Canada Basin in the Arctic, determine its transit time, and how it interacts with itself and Pacific Water that enters through the Bering Strait. The model suggests water takes 25–35 years to flow from the entrance of the Arctic to the Canada Basin, while a second estimate of age suggests slightly shorter transit times. The results of this study show that Atlantic Water flow has not changed significantly in the last 15 years. The distribution of the isotopes and ages also indicates two possible pathways water may take to the basin. An additional finding is that Pacific Winter Water carries a tracer concentration of 20%–40% of Atlantic Water, probably from Atlantic Water upwelling along the shelf, and in the Barrow Canyon region. Key Points: 129I and 236U trace Atlantic sourced water in the Canada BasinUpwelling of tracer labeled Atlantic Water into the Pacific Winter Water distinguishes the layer from Pacific Summer WaterTransit time distributions yield ages of 25–35 years for the core Atlantic Water [ABSTRACT FROM AUTHOR]