In 2008, PISCO researchers documented the rise of anoxic waters caused by upwelling currents. Upwelling currents typically support extremely productive ecosystems (20% of global fishery yield are taken from upwelling areas) because they transport nutrient-rich water from the deep to surface waters where they can be used by photosynthetic organisms. Because upwelling currents transport nutrient-rich but oxygen-depleted water onto shallow seas, large expanses of productive continental shelves can be vulnerable to the risk of extreme low-oxygen events.
This research documents the novel rise of water-column shelf anoxia in the northern California Current system, a large marine ecosystem with no previous record of such extreme oxygen deficits. These findings are particularly alarming as large scale changes in productive ecosystem, such as the expansion of anoxia could severely impact a major portion of the world's fisheries.
Chan, F., J. A. Barth, et al. (2008). "Emergence of Anoxia in the California Current Large Marine Ecosystem." Science 319(5865): 920. http://dx.doi.org/10.1126/science.1149016