Numerical Studies of Tritium and Helium-3 in the Thermocline

Abstract

The effects of circulation and lateral mixing on the distributions of tritium and heliurn-3 in the thermocline are investigated using a two-dimensional numerical model. The gyre circulation was approximated by a steady flow with closed streamlines and a western boundary current. Variations of the strength of the circulation and mixing showed that for either very high or very low mixing (relative to the strength of the circulations the distributions are analogous to a one-dimensional model. For very low mixing, the single dimension corresponds to the cross-stream dimension of the gyre. Mixing in the western boundary current increases the rate at which a tracer moves from the exterior streamlines the center of the circulation. The distributions and inventories of tritium and helium-3 are sensitive to the overall ventilation of the gyre and cannot easily resolve diffusive ventilation from direct ventilation. The results of simulations in a small parameter range are consistent with mappings of the distributions of tritium in 1972 and 1981.