Discoloured surface waters off Namibia attributed to toxic hydrogen sulphide. (Photo: J. Descloitres/NASA)

Sulphur-eating bacteria clean ocean depths

GERMANY
Wednesday, December 17, 2008, 16:50 (GMT + 9)

Researchers from the Max Planck Institute (MPI) for Marine Microbiology discovered that hydrogen sulphide, which is toxic to many living beings, is ‘cleaned' by certain bacterial blooms found in deep oceanic water.

"Hydrogen sulphide is toxic, even in low concentrations, and can instantly kill fish, molluscs and shellfish. The good news is, it seems, the discovered bacteria consume hydrogen sulphide before it reaches superficial waters, where fish live," explained lead researcher Marcel Kuypers.

The discovery of a gigantic bacterial bloom in the Benguela water system located in the continental African shelf off the coast of Namibia "that has eliminated hydrogen sulphide is very good news, but also worryisome at the same time," the researcher warned.

Dolphins swimming in the upper surface layer. (Photo: Max Planck)

"What concerns us is the discovery of a sea extension the size of the Irish Sea or the Wadden sea with deep sulphidic waters, which is not evident in satellite photos nor detectable by control posts located close to shore," he added.

According to the scientists, the discoveries published in Nature have implications for the management of contaminants of agricultural origin in coastal waters.

"Coastal waters source 90 per cent of the world’s fisheries, which constitutes a crucial food source for our planet," highlighted the study's authors.

The international group took samples at various depths in the area chosen and discovered that the toxic compound covers an extension of 7,000 sqkm, despite the fact that its surface water did not present any anomalies.

The scientists tracked this phenomenon over time and observed that the sulphur would disappear at certain depths and even shift to a deeper point in some areas to a suboxic zone where oxygen is lacking.

"The existence of this apparent sulphur sinkhole in the suboxic zone strongly indicates that sulphur had been oxidised anaerobically in the water column," the researchers stated in their report.

As the nitrate can oxidise sulphur in the absence of oxygen, and in the suboxic zone, at around 90 metres in depth, there was as much nitrate as sulphur, the experts found. The team deduced that some significant interaction must be taking place.

In deep sea water they found similar concentrations of ammonia and sulphur, but the researchers also found that the ammonia disappeared (or was oxidised anaerobically) right on top of the sulphur.

"There are many bacteria that do not need oxygen to breathe, but rather make use of nitrate for that. And in effect we found a stratum of water that contains as much hydrogen sulphide as nitrate," said team scientist Torben Stuhrmann.

"Now we can deduce the presence of sulphidic waters under certain environmental conditions, which offers us a certain ability to foresee these phenomena in the future," added Gaute Lavik, another scientist at Max Planck Institute.

By Analia Murias
editorial@fis.com
www.fis.com

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