Montreal

Astrophysicists working on an Antarctic particle-physics experiment have serendipitously created a device that can track ancient climate trends.

The researchers say that initial results from the probe, to be published in the next few weeks, could provide the most accurate record yet of global temperature change over the past million years. Climatologists think that average global temperature is closely correlated with levels of volcanic dust in the atmosphere — something they can track by careful examination of the polar ice caps.

The ‘Dust Logger’ arose from work in the 1980s by researchers interested in using polar ice in detecting subatomic particles called neutrinos. These stream in from space and occasionally collide with protons or neutrons in Earth, creating a shower of secondary particles. Researchers can identify the path of neutrinos by tracking light emitted when the new particles are formed.

The Antarctic Muon and Neutrino Detector Array (AMANDA) used this technique to spot its first neutrino in 2001. But to calibrate the detector, Buford Price, an astrophysicist at the University of California, Berkeley, had to read up on how the movement of light through ice is affected by dust trapped within it.

Price, together with his graduate student Ryan Bay, soon realized that they could generate data on dust levels in the ancient atmosphere by measuring the optical properties of ice below the Antarctic surface.

The first tests of the Dust Logger took place in 2001, using holes drilled to extract cores of ice for other palaeoclimate experiments. The logger sends out bursts of light that last a nanosecond, and by recording how long it takes for the light to be reflected back to the logger, Price and Bay can estimate the dust content at different depths.

The results were discussed at the March meeting of the American Physical Society in Montreal, Canada, and are due to appear in the Proceedings of the National Academy of Sciences. They track levels in an Antarctic bore hole 1 kilometre deep, which is the equivalent to looking back on about a million years of climate history. The logger revealed 60–70 peaks in dust levels thought to be caused by volcanic eruptions. Less than 20 such peaks had been identified from direct examination of the ice core, says Price.