Scientists have found what may be the world’s largest undersea “pockmarks” in the Chatham Rise, about 500 kilometres east of the South Island city of Christchurch, according to the New Zealand research institute GNS Science.
The pockmarks are crater-like structures on the seabed caused by fluids and gases erupting through sediments into the ocean. Three giant pockmarks have been identified, the largest of which, at 11 kilometres by 6 kilometres in diameter and 100 metres deep, could be twice the size of the largest such features recorded in scientific literature.
New Zealand, German and U.S. scientists, investigating the pockmarks on board the German research ship, the Sonne, believe they are the ancient remnants of a vigorous “de-gassing” from under the seafloor into the ocean, caused either by volcanic activity or by the release of hydrocarbon gas from gas hydrate deposits.
Impact on climate change
The escape of such large volumes of gas could have significant implications for climate change and ocean acidification.
Survey leader on the Sonne, Joerg Bialas, from GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, said there were clear indications of gas pockets and fluid flow structures in the deeper sediments under the pockmarks.
“Gas release from the larger pockmarks may have been sudden and possibly even violent, with a massive volume being expelled into the ocean and atmosphere within hours or days.”
Gas hydrate scientist Ingo Pecher of the University of Auckland said that while there was no sign of active gas systems in the larger pockmarks, the smaller ones in shallower water appeared to have been sporadically active.
“Gas escape could be occurring from the smaller pockmarks during glacial intervals every 20,000 or 100,000 years,” he said.