A Model of CFC-11 Invading the North Atlantic Ocean

1. A Model of CFC-11 Invading the North Atlantic Ocean Chlorofluorocarbons (CFCs) are of entirely industrial origin. They are used in aerosol cans and as refrigerants and have been escaping into the atmosphere in increasing amounts since the 1930s. A very small fraction of the atmospheric CFCs dissolves in the ocean. Because they are totally inert, once dissolved they act as tracers of ocean circulation and mixing processes - like a plume of dye spreading in a stream. Developed by Mick Follows, Chris Hill and John Marshall Simulated 1983 CFC-11 distribution at -2000m Observed 1983 CFC-11 distribution at -2000m Since the 1970s oceanographers have been measuring the concentration of CFCs in the oceans. The picture on the right shows the observed CFC-11 distribution at 2000m depth in the North Atlantic (Weiss et al, Nature, 314, 608, 1985). At the depth shown here, a strong boundary current flows southward creating an elongated tongue of CFC rich waters. Using numerical models of the ocean we simulate the invasion of CFCs. By this process we learn about the paths of ocean currents. The animation shows a simulation of CFC-11 concentration at about 2000m depth in the North Atlantic ocean between 1955 and 1983. The pink colors indicate the waters which are “dyed” with CFC-11. Darker pinks indicate higher concentrations. The high latitude oceans are strongly cooled at the surface and deep convective mixing occurs, bringing dissolved CFCs rapidly to depth. From here they are transported by currents into the ocean interior. MITgcm surface currents About the authors The CFC model is driven by the flow field from a global ocean simulation using the MIT General Circulation Model (MITgcm). The picture on the right shows one of the monthly mean surface current fields from that simulation. The simulation is driven with wind and surface heat fluxes taken from meteorological observations. Mick Follows is a postdoctoral researcher at MIT specializing in the study of biogeochemical cycles in the ocean. He can be contacted via e-mail as mick@plume.mit.edu Chris Hill is a researcher at MIT. His work focuses on developing “usable” models that help bring supercomputing power nearer to the desktops of everyday researchers and engineers. He can be contacted by e-mail as cnh@plume.mit.edu. John Marshall is a Professor in the Department of Earth, Atmospheric and Planetary Sciences at MIT. His research focuses on understanding the dynamics which govern the large-scale circulation of the ocean and atmosphere. He can be contacted via e-mail as marshall@gulf.mit.edu Further information can be found at http://pleiades.lcs.mit.edu and http://geoid.mit.edu/climatemodel/climatemodel.htm