Iodine-129, 137Cs, and CFC-11 tracer transit time distributions in the Arctic Ocean

Time series measurements of the nuclear fuel reprocessing tracers, I-129 and Cs-137, and ventilation tracer, CFC-11, were used to determine circulation time scales for Atlantic Water (AW) in the Arctic Ocean. Measurements in surface water are consistent with an advection model and transit times from the North Sea of 1-4 years to the Barents Sea, 3-6 years to the Kara Sea, and 9-12 years to the North Pole. Tracer ages for intermediate waters do not support an advection model because they vary with time. The tracer relationships were employed to determine transit time distributions (TTD), using inverse Gaussian functions, that implicitly incorporate the effects of mixing in simulating fluid flow. Tracer concentrations were used to constrain the ratio of the width, Delta, of the TTD to the mean age, Gamma, a measure of the relative importance of mixing, giving values for most intermediate water regimes of Delta/Gamma <= 1. These results are in contrast to values, Delta/Gamma congruent to 1 typical of the North Atlantic, indicating the greater relative importance of advection compared to mixing in the Arctic Ocean. Mean ages for AW increase from 12-20 years in the southern Makarov Basin to 30-40 years near the Arctic outflow north of Greenland. A decline in Delta/Gamma with distance along the direction of AW boundary flow from the Makarov into the Canada Basin may indicate relatively stronger mixing in regimes upstream of the Makarov Basin but also implies that TTDs may differ from inverse Gaussian functions for flow in the Arctic domain.