Alison Ballance eavesdrops on the songs of the world's southern-most mammal, the Weddell seal, and finds out about sea ice.

Weddell seals are large blobs when they are ashore sleeping, but underwater they transform into the most graceful dancers and the most incredible songsters.

Seal song is a mixture of space sounds, jungle noises and even construction noises, which carries for many kilometres in the almost freezing water under the sea ice.

Dive into the underwater song world of the Weddell seal

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Weddell seals near Scott Base are being studied by a NIWA-led Ross Sea research and monitoring programme, known as Ross RAMP. The programme is monitoring the effectiveness of the very large Ross Sea marine protected area.

Weddell seals are the southern-most living and breeding mammal in the world.

Females give birth on the sea ice in late spring. They feed their pups a rich milk that sees them gain two kilograms a day and be weaned within just a few weeks. Female Weddell seals lose up to 40 percent of their body weight while they are feeding their pups

In 2019, about 20 Weddell seals gave birth in the pressure ridges in front of Scott Base. It is the first time in more than 50 years that such numbers have bred there.

Following the establishment of Scott Base, seals were killed to feed the huskies and the breeding seals moved away, although individuals continued to use the breathing holes in the pressure ridges and haul out to rest.

The research team are putting data loggers and video cameras on females with pups to find out what they eat and where they go.

Sea ice

Greg Leonard and Maren Richter, from the University of Otago, spent several weeks in November 2019 driving skidoos around on the sea ice in McMurdo Sound.

They were towing a system that could measure the thickness of the sea ice below, identifying not just the solid sea ice but also the less dense layer of platelet ice crystals that grows under the sea ice here. Platelet ice can be up to seven metres thick in parts of the Sound, as a result of the proximity of the enormous Ross Ice Shelf.

The annual land-fast sea ice in McMurdo Sound, which forms each winter and breaks up in summer, averages 1.6 to 2 metres thick.

Voices from Antarctica - listen to the full series

Voices from Antarctica 1: Ice Flight

Voices from Antarctica 2: Scott Base

Voices from Antarctica 3: Flags to physics

Voices from Antarctica 4: best journey in the world

Voices from Antarctica 5: Waiting for Emperors

Voices from Antarctica 6: Seal songs

Voices from Antarctica 7: What the ice is saying…

Go to this episode on rnz.co.nz for more details