Figure 9-11 (right): High pressure systems with anticyclonic circulation (Northern Hemisphere) cause downwelling. Downwelling can limit phytoplankton productivity by shutting off the deepwater supply of nutrients. It has been suggested that regions where high pressure systems persist, such as Bermuda and Hawaii, are oligotrophic because of depression of the thermocline and limitation of nutrient supply.

Exploring the World Ocean: Sean Chamberlin, Tommy Dickey, 2008 http://www.oceansonline.com/