Contributing Monkie Sarah Backhouse
Published on June 2, 2008
photo by AriaFotografia cc
There’s more grim news for fish and other marine life as scientists uncover oxygen deprived “dead zones” — also known as “hypoxic zones” — in the Pacific and Atlantic Oceans. Once again, it appears that global warming is the main culprit.
A study by a team of scientists, led by Lothar Stramma of the University of Kiel in Germany, published in the journal Science, shows that oxygen depleted zones have been expanding over the past 50 years. They warn that the oxygen levels in these zones have reached critical levels and that the “continued expansion of these zones could have dramatic consequences for both sea life and coastal economies.”
The science behind the phenomena is fairly simple: “Warmer water simply cannot absorb as much oxygen as colder water,” explained co-author Gregory C. Johnson of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory in Seattle.
Research oceanographer at the National Oceanic and Atmospheric Administration’s Environmental Research Division in Pacific Grove, California, Steven J. Bograd, had similar findings while studying trends in dissolved oxygen in the waters off California. Bograd explains that oxygen decreases will result in marine life suffering or being compelled to move to other areas. Johnson further explains: “The general pattern is for the colder ocean waters in the north and south to absorb oxygen, cool and sink below the surface to then flow toward the equator.” However, rising temperatures can prevent oxygen-rich water from reaching lower depths, as warmer water is less dense.
Says Stramma: “Hypoxic zones severely reduce overall biological productivity, which reverberates throughout the food chain.” An ominous warning for commercial fisheries. What’s not entirely clear is whether global warming alone is to blame. Agricultural fertilizers, sewage and algae blooms may also be contributing factors.