The Arctic can seem like a barren landscape but huge numbers of “slimeballs” are lurking beneath the sea ice. As Antje Boetius of the Alfred Wegener Institute (AWI) Helmholtz Center for Polar and Marine Research, Germany, explained at an AGU Fall Meeting press conference, she discovered these larvaceans, as they are more correctly known, during a July 2014 test run of the brand new Nereid Under Ice (NUI) remotely operated vehicle. “It was the first time we could see such an abundance of life under the ice,” she said.
The larvaceans, first named because scientists thought they must be the larval stage of a creature that would later become more beautiful, feed on the algae growing beneath the sea-ice. And they’re gelatinous so they look pretty slimy. Copepods and ctenophores (comb jellyfish) were also in evidence, with the jellyfish feeding on the copepods. What’s not clear, according to Boetius, is which animals are feeding on the jellyfish and acting in turn as food for the seals, and ultimately the polar bears, also spotted during the tests.
NUI was ideal for this task because its fibreoptic link to the Polarstern icebreaker means it can stray further from the ship than a conventional tether would allow, reaching undisturbed ice or even beneath glacial ice tongues or ice shelves. The tethering system for NUI was originally developed for the Nereus deep-sea robot which explored the Mariana Trench in 2009 but was lost in May 2014.
Although polar explorer Nansen was first to describe, in Boetius’ words, the “brownish greenish mass of ice algae”, scientists hadn’t been able to map the algae until now. “People still assume zero production under the ice but that is wrong,” said Boetius. Previously, scientists were only able to observe algae underneath ice broken up as their research ships passed through it. Even buoys can’t reach the top two metres of the ocean beneath sea-ice – they’re at risk of damage from ice projecting below the surface.
Boetius first included NUI in a research cruise proposal five years ago, even though it didn’t then exist. “The biggest fun is when someone tells you that you can’t do something and you go ahead and do it anyway,” she said. “It was a real joy to be able to work with it.” The researcher was confident that Woods Hole Oceanographic Institution (WHOI), US, could develop such a vehicle in time for an Arctic research cruise by AWI’s icebreaker Polarstern. And the organization came up trumps. As well as the fibre-optic link, the $3 million vehicle incorporates under-ice and seafloor landing skids and an acoustic communication system in case the fibre breaks. “Usually ROVs are constrained to stay below the ship,” said Michael Jakuba, WHOI’s lead project engineer for NUI. “This one can be further away.”
This summer NUI made four dives in the Arctic, reaching up to 800 m away from the ship and to a maximum depth of 45 m. Now Boetius and colleague Christopher German of WHOI have 16 hours of video to examine in detail.