AR-News: Toxic brew engulfs Namibia's fisheries
unclewolf at olypen.com
Sun Feb 8 15:22:06 EST 2004
Toxic brew engulfs Namibia's fisheries
New Scientist vol 181 issue 2433 - 07 February 2004, page 16
UNDERSEA eruptions of noxious hydrogen sulphide are having a major impact on one of the world's richest fisheries. Satellite images show that toxic eruptions off the coast of Namibia are more frequent and widespread than anyone realised.
The world's most productive fisheries are found in upwelling regions of ocean, where wind-driven currents fertilise surface waters with nutrients from the deep. The Benguela upwelling along Namibia's coast has the strongest such currents in the world. The area supports a fishery that was worth around US$400 million in 1998, providing Namibia with its second largest source of revenue after mining.
But trouble bubbles beneath these productive waters. Microscopic algae called diatoms grow where upwelling is most intense. These are grazed by plankton, but any that aren't eaten sink when they die, forming beds of sediment on the seafloor. Bacteria in the sediments break down the diatoms and produce hydrogen sulphide in the process. The sulphide builds up in gas pockets that eventually erupt into the ocean, poisoning marine life and stripping oxygen from the water.
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