Tracer ages along a section between Ellesmere Island and the North Pole: Implications for circulation and mean residence times of the upper water colum

We present age tracer distributions (Tritium/He-3 and SF6) from a section between Ellesmere Island and the North Pole as part of the Switchyard project. The sections cover the period between 2008 and 2013. The tracers are interpreted in the context of circulation patterns and mean residence times of the main water masses. Mixed layer tracer ages range from close to zero to ca. 5 years with most of the ages grouping around 2.5 years. The tracer ages increase rapidly through the halocline waters (roughly 10 years at about 100 and 20 years close to 200 meters depth, respectively) and typically reach their maximum values close to the depth of the core of the Atlantic Water (up to 35 years). Within the AW there are large lateral gradients with higher ages found in the boundary current along the slope of the Canadian Archipelago, and lower ages prevalent close to the North Pole. We also observe temporal variability in the age tracer distributions, mainly in the lateral gradient of the ages in the AW layer. We discuss the age tracer results in the context of the circulation and mean residence times of waters in the Switchyard region of the Arctic Ocean and their variability. We also discuss possible systematic differences between the Tritium/He-3 and SF6 ages and their relevance for our main conclusions.