Deep Water Renewal in the Amerasian Basin Derived From Natural and Anthropogenic Tracer Data Sets

Abstract The deep waters of the Amerasian Basin in the Arctic Ocean are among the most isolated in the modern Arctic Mediterranean Sea (e.g., Schlosser et al., 1997, https://doi.org/10.1016/s0168‐583x(96)00677‐5 ). In this study, we use a suite of tracers spanning a range of timescales—including chlorofluorocarbons (CFCs), SF 6 , radiocarbon ( 14 C), and the radioactive noble gas argon‐39 ( 39 Ar)—to assess the mean age and renewal rates of deep and bottom waters in the Canada and Makarov basins. Measurements from the 2015 US Arctic GEOTRACES expedition (GN01), combined with data from samples collected since 1979, reveal a homogeneous deep layer below ca. 2,500 m depth characterized by limited ventilation and gradual warming, consistent with estimates of geothermal heat fluxes. Apparent tracer ages in this layer average ca. 450 years, with a standard deviation of about ±40 years. Sparse but detectable CFC maxima in bottom waters observed at several stations suggest episodic inputs of dense, shelf‐derived waters, likely resulting from the downslope cascading of brine‐enriched plumes. Salinity and oxygen isotope analyses indicate that these inputs originate primarily from the Chukchi Borderland and Beaufort Sea shelf. Time‐dependent mass balance calculations show that present‐day 14 C and 39 Ar concentrations can be explained by radioactive decay since a single deep water renewal event. These results indicate that the most recent basin‐wide deep water renewal occurred approximately 450 years ago and constrain present deep ventilation rates to no more than approximately 0.01 Sv.