ocean dead zone

Syllable breakdown

Dictionary meaning

a coastal or open-ocean region where dissolved oxygen concentrations have fallen below the threshold of approximately two milligrams per litre necessary to support most aerobic marine life, creating a hypoxic or anoxic environment in which fish, crustaceans, and other mobile organisms flee or die while sessile organisms suffocate in place; dead zones are primarily caused by eutrophication, the excessive enrichment of coastal waters with nitrogen and phosphorus from agricultural fertiliser runoff and sewage effluent, which stimulates algal blooms whose decomposition by bacteria consumes oxygen faster than it can be replenished by mixing with surface air; the number of documented oceanic dead zones has grown from fewer than fifty in the 1960s to over five hundred today, representing one of the most significant human impacts on coastal marine ecosystems