The German research vessel Sonne. (Photo: RF Forschungsschifffahrt, Bremen, Germany)

An overview of the area investigated during New Vents.

Images taken by OFOS (Ocean Floor Observations System), a towed camera platform. (Photos: David Bowden, SO191-NZ New Vents)

Clockwise from above:
Ruth Martin ‘slaughtering’ a sample from the multicorer to see what macrofauna it holds.
‘Stefan’s worm’ (not yet identified).
Specimens brought up by the TV grab. (Photos: Ruth Martin, University of Washington, and Andrew Thurber, Scripps Institution of Oceanography (Stefan’s worm))

Deploying the TV grab from the stern deck of RV Sonne. (Photo: Ruth Martin)

Kerstin Kröger and David Bowden have been to sea for a closer look at what’s bubbling up from below.

Methane (natural gas) comes out of bogs, sheep, cows, and cookers, right? Strange then that NIWA and co-researchers have recently been searching for it a thousand metres down on the seabed of the Hikurangi Margin off New Zealand’s east coast.

From January to March 2007, a multinational crew of research scientists aboard the German research vessel Sonne studied Hikurangi Margin ‘cold seeps’, where methane emerges from the seabed. Many of these sites were first discovered the previous year by NIWA and US scientists using circumstantial data from fishermen compiled in the 1990s by NIWA and Te Papa. The three legs of Sonne voyage SO191 enabled much more detailed investigations of the sites. For their part in the New Vents voyages, NIWA scientists worked on broad-scale geophysical surveys of the area, remote camera deployments, and biological sampling of seep sites.

Work at sea

Following seismic and multibeam surveys of the area, the team used side-scan sonar, towed cameras, and an ROV (remotely operated vehicle) to create accurate maps of the seep sites. Then TV-guided equipment, including a massive benthic (seafloor) grab, was used for precise sampling of minerals and biology. The Sonne’s live-camera capability on these tools puts an end to the usual ‘fishing in the dark’ when taking samples from many hundreds of metres below the ship. This is especially important on cold seep sites, which may be only a few metres across. Seabed signs of seeps include white bacterial mats, patches ofblack anoxic sediment with a characteristic ‘raindrop’ texture caused by an unidentified species of polychaete worm from the Ampharetidae family, empty white shells of the seep clam Calyptogena sp., and dense populations of bizarre Siboglinid tube worms that live only at seeps and hydrothermal vents.

Back on shore

The overall goals of the multinational New Vents programme are to describe the geological setting in which seeps occur, to quantify the flux of methane through the seafloor, and to understand the bio-geochemical processes that maintain the distinctive biological communities of the seep sites. Post-voyageanalyses are now underway in several institutes around the world, with NIWA scientists working on geological data from seismic surveys and on the identification of animals recovered from the seeps. When results from all these analyses are combined, we will have a much more comprehensive picture of where cold seeps occur on the Hikurangi Margin, how they form, the processes that govern energy flow through them, and the feeding relationships, diversity, and evolutionary history of organisms that live in them.

Dr Kerstin Kröger is a benthic ecologist working on soft-bottom invertebrate communities and Dr David Bowden is a specialist in capturing images of life on the ocean floor. They both work at NIWA in Wellington.