Trend Ocean losing dissolved oxygen

Summary

Over the past five decades the global ocean has lost roughly 0.5 to 3 percent of its dissolved oxygen. Deoxygenation enlarges the volume of water that is critically low in oxygen or entirely without it, expanding oxygen minimum zones that can shoal upward from mid-depths. Most marine animals cannot survive long in such water, so they suffocate or move to oxygen-rich areas, shifting species distributions and impairing ecosystem function. Low oxygen also slows decomposition of sinking organic matter, burying more carbon on the seafloor, and promotes microbial processes that turn usable nitrogen into inert nitrogen gas and the potent greenhouse gas nitrous oxide, with long-term effects on climate. Geological records show that past mass extinctions coincided with expanded ocean anoxia. The report is examining hypoxic water volume as a candidate control variable for bringing deoxygenation into the boundary framework.