Much attention has been given to the hypoxic zone (zone deficient of dissolved oxygen) in the Gulf of Mexico presumably caused in large measure by nutrient runoff from agricultural lands in the US Midwest. But Grantham et al. (2004) report changes in the natural hypoxic region that develops seasonally in the Northeast Pacific Ocean caused by ocean circulation in open coast systems that bring oxygen-depleted and nutrient-rich deep water into coastal areas through upwelling. They found that in 2002 the hypoxic zone was particularly severe and led to mass die-offs of fish and invertebrates off the California coast. The authors conclude that a better understanding of ocean control of coastal upwelling and its associated oxygen-depleted water is needed. Any link of ocean-controlled upwelling to global warming would have significant impacts on coastal ecosysems.
Reference
Grantham, B.A., F. Chan, K.J. Nielsen, D.S. Fox, J.A. Barth, A, Huyer, J. Lubchenco, and B.A. Menge, 2004: Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific. Nature, 429, 749-754.