Our Changing World: New Antarctic methane seeps

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The bright green Hägglund, a staple of Antarctic transport, is pulled up alongside a crack in the sea ice. The crack runs for hundreds of metres, pointing towards Mount Erebus in the distance.

Nearby a group of Weddell seals are hanging out on the ice – mostly mums with pups taking advantage of the crack to gain access to the sea below.

A group of NIWA scientists are also taking advantage. They’ve used a pit saw to make a rectangular hole out of the crack, just large enough for a remotely operated vehicle (ROV) to fit neatly into.

A thin yellow tether is all that’s visible of the ROV right now. It leads to a large spool holding the rest, and from there a wire runs to the Hägglund, where NIWA molecular ecologist Dr Leigh Tait sits, a monitor and controls set up in front of him.

On the screen: a startling long white streak against the dark volcanic soil background, like a narrow roll of fluffy carpet laid out on the seafloor.

Methane seeps and microbes

This streak is actually a mat of white microbes.

When methane gas or fluid emerges from below the seafloor through cracks or fissures – what’s known as a methane seep – a host of microbes show up, attracted by the altered chemistry.

It’s a telltale sign that Dr Sarah Seabrook, her NIWA colleagues, and her collaborators in the US Antarctic Programme are becoming more and more familiar with.

The first active methane seep was found in Antarctica in 2012 by a team led by Dr Andrew Thurber of Oregon State University. The seep was discovered at a site called Cinder Cones, in the shallows of McMurdo Sound beside Ross Island.

Sarah completed her PhD under the supervision of Dr Thurber, and dove at the site in 2016 as part of her research. That’s when they found a second seep, quite close by.

This finding was the catalyst for the questions that have been driving Sarah’s research ever since: How many seeps are there? Are they all connected? And why are new ones emerging now?

The number of active Antarctic seeps keeps increasing, with new discoveries from ship expeditions along the Northern Victoria Land Coast, as well as reports from divers and from ROV footage.

Sarah has just returned from a trip to Antarctica in which she and her colleagues further explored sites where seeps had been recently reported. Using divers and an ROV they’ve been able to sample the soil, water and gases at these sites, and in some areas have left instruments on the seafloor that will monitor the gas coming out for the full year.

Strange new findings

But as well as the ‘classic’ white microbial mats indicating of the presence of a seep, the team have been finding some things they can’t explain.

An area they dubbed ‘the pit of death’ full of sea creatures fleeing or dying is perhaps the early days of a seep, before the microbes move in. A shimmering fluid caught on camera, and a ‘lake of mist’ at a site with microbial mats also go in the unexplained column.

“We’re just making so many discoveries of things that we’re still trying to understand as we’re finding them, things that haven’t really been seen before.” says Sarah.

It’s scientific discovery right at the edge of our understanding, which, for any scientist, is extremely exciting. But for Sarah, this excitement is balanced by the potential implications for our climate change present and future.

The key questions

With findings so new, and so strange, there are more questions than answers right now.

Sarah and the team are keen to jump on the key ones straight away. First: are these seeps all connected and being fed from the same reservoir of methane?

Samples taken from the sites will allow them to analyse the chemical signatures of the methane. Isotopic analysis will help Sarah understand if it’s one source, or several, and will give clues as to how the methane formed.

Second: is the methane coming from these seeps making its way from the sea and into the air, where it would contribute to warming?

The seeps are being found at quite shallow depths, and while the microbes ‘mop up’ some of the gas, they don’t get it all. The team have seen bubbles rise through the water to stick to the underside of the sea ice.

Plus, in July the British Antarctic Survey published a report where they had driven ships over seeps and found sea to air movement of methane.

But perhaps the main question is: why now? Why are these seeps suddenly emerging in some places that have been visited for many years, where divers could not have failed to notice the white microbial mats now clearly visible?

The main hypothesis that Sarah is investigating is whether this is due to warming-induced changes in Antarctica.

The methane under Antarctica would have started life as carbon buried millions of years ago, when Antarctica was a continent lush with life. The carbon can be converted to methane by certain microbes. One hypothesis suggests that for a long time methane has been essentially trapped by the weight and pressure of the ice sheets.

But ice loss due to warming could be changing the game. Satellite measurements by NASA indicate that between 2002 and 2023, Antarctica shed an average of 150 billion tonnes of ice per year. Sarah wants to know whether this ice loss is correlated with the emergence of the seeps, something that geological evidence indicates has happened in the past.

Listen to the episode to take a trip to the site where the first active methane seep was found, and to learn more about Sarah and the team’s brand-new findings.

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