Beneath Antarctica’s Ross Ice Shelf lies one of the least measured oceans on Earth – a vast, dark cavity roughly twice the volume of the North Sea.

This hidden ocean matters because it is the ice sheet’s Achilles heel. The ice sheet is the continent’s enormous, kilometres-thick mass of land-based ice, while the ice shelf is the floating platform that fringes it.

If warmer water reaches the underside of the shelf, it can melt the ice that holds back millions of cubic kilometres of Antarctic ice, with consequences for global sea levels.

Yet almost everything we know about this cavity has come from brief snapshots at its edges. Until now, no one had captured a long, continuous record from its central heart. Our newly published study set out to change that.

Ice shelves act as buttresses for Antarctica’s 30 million cubic kilometres of ice, built up over millions of years. The Ross Ice Shelf is the largest, among the coldest and most southerly, and perhaps the most sheltered from a warming ocean.

It spans both West and East Antarctica, where dozens of giant glaciers merge to form a wedge of ice 300 to 700 metres thick that flows northward, melting from below and calving the world’s largest icebergs.

When studying the ocean, snapshots are useful, but long time series are far more powerful. They........

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