Paris | Sunday
BELCHES of hydrogen sulphide gas from the seabed off the Namibian coast, until now thought to be a smelly bit of local folklore, have been found to be a massive phenomenon that can affect thousands of square kilometres of ocean.
The gas is released from the remains of microscopic creatures called diatoms, which comprise a decaying carpet of ooze several metres thick on the seabed off the Namib Desert coast.
The ”rotten egg” smell is well familiar to local inhabitants, who also harvest rock lobsters that flee ashore from the noxious conditions in the water.
Seabirds are also beneficiaries of the gas, gorging on the floating bodies of fish which are killed in the immediate vicinity when the toxic bubble is released from the ocean floor.
Oceanographers from the University of Cape Town and the National Marine Research and Information Centre at Swakopmund, Namibia, say new satellite pictures show that the gas emissions are far bigger, more frequent and last longer than previously thought.
Images taken by the OrbView-2 SeaWIFS satellite on March 18 last year showed a 200-km patch of sea that had been turned a milky turquoise by billions of microgranules of sulphur.
The patch drifted for several weeks, eventually covering more than 20 000 square kms of sea. Another big emission, detected on May 17, was still plainly visible on June 6.
”These naturally occurring events are much more extensive and longer-lasting than previously suspected, and… the resultant hypoxia [oxygen starvation of the surrounding water] may last for much longer,” the researchers reported in Nature, the British scientific weekly.
”The effects on the marine ecology and valuable coastal fisheries of this region are likely to be important.” – Sapa-AFP