Predictions of Water-Column Properties under Widespread Artificial Upwelling Scenarios in the North Pacific Subtropical Gyre using an Ocean General Circulation Model.

The physical evolution of water-column stratification following the implementation of widespread artificial upwelling across the North Pacific Subtropical Gyre (NPSG) is examined in a numerical experiment using the ocean general circulation model MIT-gcm. The upwelling process is represented by distributed pairs of fluid sinks and sources located at different depths to mimic the withdrawal of cool nutrient-rich water at about 400 m below the surface and its discharge in the upper water column. The overarching conclusion from the simulations is that within the NPSG, the upwelling process as modeled appears to enhance relatively strong stratification and to weaken relatively weak stratification. This generally holds for the short term as well as when a new steady-state is reached after a few decades. In the latter case, it applies temporally, with deeper mixed layers in the winter and shallower ones in the summer, as well as geographically with a broad separation between less stratified northern regions and more stratified southern regions within the NPSG. The global model allows an estimation of possible unintended consequences well outside the upwelling implementation area. It is predicted, for example, that surface cooling in the NPSG allows heat to penetrate the ocean interior until the overall oceanic surface heat flux is restored to zero (in a yearly averaged sense). As a result, changes in the thermal structure of the water column occur. Regions with a net surface warming develop outside the NPSG, most notably along the East coast of Japan and the West coasts of the Americas. [ABSTRACT FROM AUTHOR]