A study of North Atlantic ventilation using transient tracers

• Main Author: Doney, Scott C.
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution 1991
• Subjects: Ocean circulation; Tritium; Chlorofluorocarbons; Oceanus (Ship : 1975-) Cruise OC134; Oceanus (Ship : 1975-) Cruise OC202; Arctic; Nordic Seas; North Atlantic
• Online Access: https://hdl.handle.net/1912/5474

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1991 The oceanic distributions of tritium 3H), 3He, and the chlorofluorocarbons (CFCs) can be used to constrain the time-scales of the major ventilation pathways for an ocean basin such as the North Atlantic. I present a new global model function, developed from a factor analysis of the WMO/IAEA data set, for predicting the spatial and temporal variability of bomb-tritium in precipitation. Model estimates for the atmospheric 3H delivery to the North Atlantic are recomputed and combined with advective 3H input estimates in a budget for the North Atlantic Basin. Key features of the model budget include refined estimates of the 3H vapor flux and southward advection of 3H in the low salinity, surface flow from the Arctic. Arctic tritium sources contribute about half of the observed increase (40%) in the decay corrected tritium inventory from the 1972 GEOSECS program and the 1981 TTO/NAS program. The 3H concentration in the intermediate and deep waters for the sub-polar North Atlantic increased substantially between 1972 and 1981. A time dependent model for the 3H and 3He inflow to the abyssal Atlantic from the Nordic Seas is developed. The 3H and 3He distributions in the abyssal North Atlantic and Deep Western Boundary Current (DWBC) are also presented. A simple model of abyssal circulation is constructed using the model Nordic Seas overflow curves, the observed tracer gradients in the DWBC, and the GEOSECS and TTO tracer inventories for the deep basins. Although the tracer concentrations in the boundary current are rather insensitive to the velocity of the boundary current, they do place bounds on the magnitude of recirculation between the boundary current and the interior. On average, a volume equal to the boundary current transport is entrained/detrained over a length scale of about 5000 km. About half of the overflow water ...