Five specialist NIWA divers were left ‘gasping’ during their recent plunge under the ice near Scott Base.

The researchers were working with Antarctica New Zealand to set up experiments and equipment to monitor coastal currents and the marine environment.

Full dry suits are mandatory in such icy waters, and you know it’s a cold day at work when your dive mouthpiece sticks to your lips. But it wasn’t the cold that really took their breath away – the team say it was the clarity of the water and the rich diversity of marine life under the Antarctic ice.

Photography by Peter Marriott

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Small blue octopus.

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Some species have antifreeze glycoproteins in their blood to enable life amongst the anchor ice, pictured here is an isopod.

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Emerald rock cod.

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Scientific dive specialist David Bremner descends through a 2m thick hole in the ice to begin work. Water temperatures of below minus 1°C cause plate-like ice crystals – known as anchor ice – to form along the seabed.

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Antarctic creatures often provide vital habitat for others. This large spiky sponge (Rosella racovitzae) is both a platform for a hitchhiking 1m ribbon worm and a hiding place for fish.

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More than 20m under the ice, a large orange sea spider negotiates the delicate thecate hydroid branches attached to a sea squirt (Cnemidocarpa verrucosa). The sea squirts open siphon filters plankton and bacteria from the rich Antarctic waters.

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A delicate spiral egg case – probably deposited by a nudibranch – decorates the outer coating of a large sea squirt. Brittle stars, sponges, soft corals and bryozoans dominate the background.

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Dark patches of algae grow on the sea ice above. Algae are an important food source for seafloor dwellers such as these anemones, finger-like “bush” sponges and fan worm polychaetes.

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Part of the mission was to investigate the strength and direction of underwater currents near Scott Base. This Acoustic Doppler Current Profiler was one of two deployed under the sea ice.

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Sitting on the sea floor 12m below, this 0.5m tall sponge (Rossella racovitzae) is fully encased by anchor ice, yet the aperture which expels filtered water remains free.

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Sea urchin


This article forms part of Water & Atmosphere July 2020, read more stories from this series.