How do you measure temperature under Arctic ice? Sound carried the answer 2,500 km

The challenge of ice-covered seas

We want to know Arctic ocean temperatures. But the surface is locked under thick ice. Satellites cannot help. They cannot see water temperatures from space. Icebreakers offer a partial solution, but tracking a vast ocean year-round is simply not practical.

The link between sound speed and temperature

Matthew Dzieciuch and colleagues at Scripps Institution of Oceanography turned to sound. The warmer the water, the faster sound travels. By measuring how long a signal takes to arrive, you can work out the average temperature along its path.

The principle had been known for decades. But in the Arctic, ice scatters acoustic signals. Long-range propagation was thought to be impossible.

CAATEX — sending sound across 2,600 km

The team launched CAATEX in 2019–2020. The distance: 2,600 kilometres. Six moorings were deployed from north of Alaska to north of Svalbard. Signals were transmitted every three days.

The results exceeded expectations. Signals propagated over 2,500 kilometres. Seasonal temperature patterns came through clearly.

What the researcher says

The sea-ice has dramatically thinned over the past forty years and its roughness has also decreased. We wanted to see if scattering losses have now decreased enough to enable acoustic propagation.

— Matthew Dzieciuch (Scripps Institution of Oceanography, physical oceanographer)

Thinner ice opened the door

Climate change thinned the Arctic ice, and ironically that is what made this technique viable. When the ice was thick and rough, sound scattered and the experiment could not have worked.

The experiment also involved Woods Hole Oceanographic Institution and Norway's Nansen Center. Arctic observation cannot be done by one country alone.

For more on Scripps observation technology, see 'SWOT satellite captures Kamchatka tsunami.'

A note from the author: The fact that 'thinner ice lets sound through' stuck with me. It is ironic that warming produced a new observation tool, but the researchers turned that irony into results.

Alaska to Svalbard is farther than Tokyo to Bangkok. The idea that sound can travel that far underwater still does not feel quite real.