Decadal Changes in the Pathways of the Atlantic Water Core in the Arctic Ocean Inferred From Transient Tracers

Abstract

The Atlantic Water plays a major and increasing role in the heat budget of the Arctic Ocean (Atlantification). The pathways of Atlantic Water within the Arctic Ocean, and in particular their sensitivities to large-scale atmospheric patterns such as the Arctic Oscillation, remain unclear. In this study, we used the trace gases CFC-12 and ${\text{SF}}_6$ to investigate the Atlantic Water pathways during different phases of the Arctic Oscillation. We calculated tracer ages for the temperature maximum of the Atlantic Water, focusing on repeated transects (1994, 2005, 2015) in the Amerasian Basin of the Arctic Ocean. During a positive phase of the Arctic Oscillation in 1994, tracer ages were low along the Chukchi shelf due to a strong coherent boundary current. In contrast, the ages were up to 10 years higher in 2015 without this coherent current during a mixed phase of the Arctic Oscillation. Further, we identified a discontinuity in the inflow between the Makarov Basin and the Canada Basin during this phase. Tracer ages were 10 years higher in the Canada Basin, suggesting a closed circulation without direct inflow in this region. Our tracer ages generally align with previously proposed circulation schemes and water ages, with major exceptions in 2015. We have shown that the tracer ages are applicable to identify decadal changes in the Atlantic Water core pathways in the central Arctic Ocean.