Organic Carbon Deposition in Gyre Versus Eddy Oceans

William W. Hay
University of Colorado - Emeritus, Estes Park, CO

Today's ocean is characterized by shallow anticyclonic gyres that extend from the equatorial region to 45 N and S, and deeply convecting cyclonic gyres in the polar regions. These gyre systems are separated by fronts where water enters the ocean interior to form the thermocline and intermediate water masses that floor the anticyclonic gyres. This ocean structure depends on steady westerly winds centered on 45 latitude induced by persistent high polar atmospheric pressure forced by the presence of polar ice. This gyre ocean is well ventilated and organic carbon deposition is limited to upwelling regions along the equator and low to mid-latitude eastern margins of the ocean basins.

Without ice there would be no persistent polar atmospheric highs. The westerly winds would not be constant but would be replaced by light and variable winds during much of the year. The structure of the ocean would be very different. The oceanic large gyres and frontal systems would be replaced by an array of mesoscale eddies pumping water upward and downward according to their rotation. The ocean interior would become relatively unstructured and poorly ventilated, with nutrients more widely distributed. High productivity, anoxic conditions, and organic carbon deposition could occur throughout the ocean. Moving eddies would be steered by bottom topography as in the Circum-Antarctic Current today. Other eddies would be relatively stable, like the Socotra Gyre and Great Whirl in the western Indian Ocean today. Stable cyclonic eddy sites and tracks would become loci of organic carbon deposition.