Simulation of CFCs in the North Atlantic Ocean using an adiabatically corrected ocean circulation model

Abstract

A three‐dimensional ocean circulation model is used to examine the uptake, spreading and interannual variability of chlorofluorocarbons (CFCs) in the North Atlantic Ocean during the 50‐year period from 1948 to 1997. The model is forced by climatological and North Atlantic Oscillation (NAO) related monthly mean surface forcing, and a realistic, time‐varying air‐sea flux of CFCs. Different from previous studies, the model uses the modified semiprognostic method to correct for systematic bias, leading to improvements in the modeled ocean circulation near the western boundary. Comparisons are made between simulated concentrations and observations made along three World Ocean Circulation Experiment transects, and between the simulated inventory of CFCs in the Labrador Sea and estimates based on observations. The model reproduces the general structure of the observed concentrations, including the concentration maxima associated with Labrador Sea Water (LSW) near the western boundary, although quantitative comparisons indicate that the model CFC concentrations associated with LSW are generally too high. The equatorward spreading rate of LSW is estimated from CFC effective age and found to be about 1.3 cm s−1, in agreement with observational estimates. We also discuss the close relationship between the NAO and interannual variability in the uptake and inventory of CFCs in the Labrador Sea, and the spreading of CFCs along the western boundary.