Synoptic I-129 and CFC-SF6 Transit Time Distribution (TTD) Sections Across the Central Arctic Ocean From the 2015 GEOTRACES Cruises

Measurements of the tracers, I-129, CFC-11, and SF6 on water samples collected in the Arctic Ocean in 2015 have been used to calculate mean ages, Gamma and mixing, Delta parameters using transit time distributions (TTDs) to constrain water circulation and mixing time scales. Values of Gamma and Delta determined separately using the two tracer pairs, SF6-CFC-11, and I-129-CFC-11 are in good agreement for gas solubilities estimated for saturation levels of 0.90, but agreement decreases for other gas saturation levels. Both Gamma and Delta increase rapidly with increasing depth below the base of the intermediate water layer (ca. 1,000 m), but maintaining a value of Delta/Gamma approximately equal to 1 supporting the use of this proportionality in applications of TTDs to deep ocean transport of substances such as anthropogenic carbon. Isolines of Gamma = 20 years deepening to depths below 1,000 m over the flank of the Mendeleyev Ridge near the North Pole outline the bathymetrically steered, return flow of recently ventilated Atlantic Water toward Fram Strait. Basin interior waters are significantly older with the Gamma = 25 years mean age isoline shallowing upward to depths above 500 m in the Makarov, Canada, and Eurasian Basins. Values of Delta remain relatively constant in the 6-10 years range in upper intermediate water across all three basins indicating that flow is principally advective and that the mixing specified by Delta likely occurs upstream of the central basins in regions proximal to the outflow from the Santa Anna Trough.