Part 1 of this study examined the ability of the Geophysical Fluid Dynamics Laboratory (GFDL) primitive equation ocean general circulation model to simulate the steady state distribution of naturally produced 14C in the ocean prior to the nuclear bomb tests of the 1950's and early 1960's. In part 2 begin with the steady state distributions of part 1 and subject the model to the pulse of elevated atmospheric 14C concentrations observed since the 1950's.

This study focuses on the processes and time scales which govern the transient distributions of bomb 14C in the upper kilometer of the ocean. Model projections through 1990 are compared with observations compiled by the Geochemical Ocean Sections Study (GEOSECS) in 1972, 1974, and 1978; the Transient Tracers in the Ocean (TTO) expedition in 1981, and the French INDIGO expeditions in 1985--1987. In their analysis of the GEOSECS 14C observations, Broecker et al. (1985) noted that much of the bomb 14C which entered the ocean's equatorial belts prior to GEOSECS accumulated in the adjacent subtropical zones. Broecker et al. argued that this displacement of bomb 14C inventories was caused by the wind-driven upwelling and surface divergence in the tropics combined with convergent flow and downwelling in the subtropics. Similar displacements were invoked to shift bomb 14C from the Antarctic circumpolar region into the southern temperate zone. The GFDL model successfully reproduces the observed GEOSECS inventories, but then predicts a significantly different pattern of bomb 14C uptake in the decade following GEOSECS. The post-GEOSECS buildup of bomb 14C inventories is largely confined to the subthermocline layers of the North Atlantic, the lower thermocline of the southern hemisphere, and down to 2000 m in the circumpolar region. A great deal of attention is devoted to detailed comparisons between the model and the available radiocarbon data. A number of flaws in the model are highlighted by this analysis. The Subantarctic Mode Waters forming along the northern edge of the circumpolar current are identified as a very important process for carring bomb 14C into the thermocline of the southern hemisphere.

The model concentrates its mode water formation in a single sector of the circumpolar region and consequently fails to form its mode waters with the correct T-S properties. The model also moves bomb 14C into the deep North Atlantic and deep circumpolar region much too slowly. ¿ American Geophysical Union 1989