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It's 10pm at night in one of the labs at Scott Base, New Zealand's Antarctic research station. Elsewhere people are winding down - reading books or watching a movie, getting ready to head to bed.
But not Dr Jürgen Laudien. He's too excited about what tomorrow will bring: another chance to dive under the sea ice and unravel some of the mysteries of the giant glass sponges found on the seafloor.
A deep dive into the life of a sponge
Jürgen explains tomorrow's experiment: they will pump a non-toxic green dye into the sponges' barrel-like opening, so that they can visualise how the sponges move water around.
A senior scientist at the German Alfred Wegener Institute for Polar and Marine research, Jürgen is one of the principal investigators on a project called SpongeScan. In collaboration with international colleagues, including Professor Ian Hawes of the University of Waikato, the aim is to learn more about the mysterious glass sponges which are key to this cold-water seafloor ecosystem.
The SpongeScan team, from left to right: Andreas Schmider Martínez, Ian Hawes, Erik Wurz, Kat Rowe and Jürgen Laudien. Photo: Claire Concannon / RNZ
Glass sponges can be found around the world. But they often live in quite deep water, which makes it tricky to investigate them, says Ian.
In McMurdo Sound - the patch of ocean next to Scott Base - they can be found at shallower depths, which means scientists can dive here and study them in detail.
Diving under the ice
From Scott Base, the team's dive site is a short 20-minute Hägglund drive across the sea ice.
The dive camp on the sea ice. Photo: Claire Concannon / RNZ
The camp is small: a large, rounded, solid-framed yellow dive tent, a green shipping container kitted out with a door and heater, a small polar tent serving as a bathroom, and on either side of these, black flags marking holes in the ice.
These holes - rectangles chainsawed through the ice - serve as the back-up exits for the divers, just in case their main entrance gets occupied by a Weddell seal when they need to surface.
The divers' main entry way to the watery world below is in the large dive tent, a heated area big enough to hold the team and their dive equipment.
When kitted out, the only parts of the researchers exposed are lower face and lips, which, Dr Erik Wurz says, go completely numb.
Ian Hawes and Andreas Schmider Martínez prep for diving while Erik Wurz is on standby as safety diver. Photo: Claire Concannon / RNZ
Erik works at the Wageningen University & Research in the Netherlands. This is not his first time to Antarctica, but it is his first experience of diving in the -2 °C water under the sea ice.
"It's pretty scary the first time to be honest, because you're under two metres of thick ice, it's like a cave," he says. But he's been captivated by the experience, and how busy it is down there.
"It's full of life, I was really surprised," he says. "You don't see the seafloor, actually, because there are sponges growing on top of each other, anemones, worms crawling around... it's really like a rainforest, in minus-two-degree water."
Sponge secrets
While the Antarctic glass sponges take on a tree-like role in this underwater rainforest - providing structure and food - they are actually animals.
They grow very slowly, feeding on bacteria and viruses and taking silica from the water around them to create their glass 'bodies'.
Some can grow to quite large, up to two metres in height. And previous investigations have estimated that some glass sponge species can live as long as 15,000 years, though this involved moving the sponges into an aquarium to study them.
Using an aluminium lander that they can set up over individual sponges, Jürgen and the team have been doing detailed investigations of these animals in their natural habitat.
The lander in position over a sponge. Photo: Ian Hawes
Cameras, sensors and methods to sample water both in and outside the sponge are being used to help them understand which bacteria they might be feeding on, how much oxygen they are respiring, how much water they are moving around, and the nutrients they are taking in and excreting.
The species these researchers are focused on is called Anoxycalyx joubini, a large white barrel-shaped animal also known as the giant volcano sponge. Biopsies for viewing under an electron microscope will help them confirm this identity, as each sponge species has a unique design in the needle-like structures that make up their skeletons, called spicules.
Plus, coupled with 3D models of the sponges reconstructed from hundreds of images, the biopsy will help them to calculate the biomass, or weight, of the sponges without having to lift them off the seabed floor. This is key to figuring out their growth rate, and how long they might live.
Fluorescin dye experiment to investigate sponge pumping and flow. Photo: Erik Wurz
The overall objective is to understand how these sponges interact with the environment.
"They are providing the structure for the community, and that's why they are really important," says Jürgen. "But we don't know even what they are feeding on, and how fast they are growing."
He and the team are hoping to change that.
Reporting on this episode was supported by Antarctica New Zealand's community engagement programme.
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