Influence of mixing on CFC uptake and CFC ages in the North Pacific thermocline
Warner, Mark J.
Greene, Catherine E.
Hautala, Susan L.
Sonnerup, Rolf E.
MetadataShow full item record
A diagnostic, isopycnal advection-diffusion model based on a climatological, geostrophic flow field is used to study the uptake of chlorofluorocarbons (CFCs) into the portion of the thermocline that outcrops in the open North Pacific (σ θ ≤ 26.6 kg m−3). In addition to advection, isopycnal diffusion is required to match the CFC data collected during the World Ocean Circulation Experiment (WOCE) in the early 1990s. Using reduced outcrop saturations of 80–95% for isopycnals outcropping in the northwestern North Pacific (σ θ ≥ 25.4 kg m−3), together with an isopcynal interior diffusivity of 2000 m2 s−1 and enhanced diffusion (5000 m2 s−1) in the Kuroshio Extension region, further improves the model-data agreement. Along-isopycnal diffusion is particularly important for isopycnals with shadow zones/pool regions in the western subtropical North Pacific that are isolated from direct advective ventilation. The isopycnal mixing causes an estimated increase in CFC-12 inventories on these isopycnals, compared to advection only, ranging from 10–20% (σ θ = 25.6 kg m−3) to 50–130% (σ θ = 26.6 kg m−3) over the subtropics in 1993. This contribution has important consequences for subduction rate estimates derived from CFC inventories and for the location of the subsurface CFC maxima. When tracer ages are derived from the modeled CFC distributions, time-evolving mixing biases become apparent that reflect the nonlinearities in the atmospheric CFC time histories. Comparison with model-calculated ideal ages suggests that during the time of WOCE (∼1993), ventilation ages based on CFC-12 were biased young by as much as 16–24 years for pCFC-12 ages of 25 years, underestimating ideal ages by as much as 40–50%.
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C07014, doi:10.1029/2003JC001988.
Showing items related by title, author, creator and subject.
Holbrook, W. Steven; Fer, Ilker; Schmitt, Raymond W.; Lizarralde, Daniel; Klymak, Jody M.; Helfrich, L. Cody; Kubichek, Robert (American Meteorological Society, 2013-08)Seismic images of oceanic thermohaline finestructure record vertical displacements from internal waves and turbulence over large sections at unprecedented horizontal resolution. Where reflections follow isopycnals, their ...
Huang, Rui Xin (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1984-05)Part one of this thesis discusses the structure of the thermocline and the current pattern within a two-layer model. The corresponding flow field is explored as the amount of water in the upper layer is gradually reduced ...
Farrar, J. Thomas (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2003-09)In this thesis I have endeavored to determine the factors and physical processes that controlled SST and thermocline depth at 10°N, 125°W during the Pan American Climate Study (PACS) field program. Analysis based on the ...