Dead Zones in the Oceans

As this chapter shows, the open oceans are also running out of dissolved oxygen as seen at Station Papa in the subarctic Pacific Ocean, thanks to work done on Canadian weather ships starting in the 1950s. Not only are areas of severe hypoxia, or oxygen minimum zones, expanding, but the level of dissolved oxygen in all oceans is decreasing. The open oceans are losing oxygen because of climate change. The warming of the oceans reduces the solubility of oxygen in water and stimulates oxygen use by respiring organisms. This chapter explores how climate change is also altering circulation and the mixing of oxygen into oxygen-poor waters. Even where oxygen remains above dead-zone levels, its depletion is another sign of how climate change is reshaping the biosphere. The expansion of low-oxygen water has shifted the habitats of fish and invertebrates, such as the giant squid, over thousands of miles, and has disrupted the nitrogen cycle of the entire biosphere. The chapter explains that because of oxygen depletion, biological production of the oceans may decline due to the loss of nitrogen, while release of a potent greenhouse gas (nitrous oxide) may increase.