Ice coverage in the Arctic sea is rapidly declining, which causes the remaining ice to melt faster and alters nutrient availability. In a University of Washington-led study, researchers show how particles from space can help recreate ice conditions over the past 30,000 years. Credit: Bonnie Light/ University of Washington. CC BY.

New research has found that space dust can reveal Arctic ice conditions before the age of satellite imaging began in 1979.

Arctic sea ice has declined by more than 42% since 1979, when regular satellite monitoring began.

As the ice grows thinner and recedes, more water is exposed to sunlight. Ice reflects sunlight but dark water absorbs it, advancing warming and accelerating ice loss.

Climate models indicate that the Arctic will see ice-free summers within the coming decades, and scientists still aren’t sure what this will mean for life on Earth. 

Researchers have known for some time that fine-grained dust from space blankets the surface of Earth, falling from the cosmos at a constant rate and settling into ocean sediments.

A new study shows that tracking where cosmic dust has fallen — and where it hasn’t – can reveal how sea ice coverage has changed over millennia. 

Study lead Frankie Pavia, a University of Washington assistant professor of oceanography, said: “If we can project the timing and spatial patterns of ice coverage decline in the future, it will help us understand warming, predict changes to food webs and fishing, and prepare for geopolitical shifts.”

Credit: Bonnie Light/ University of Washington. CC BY.

The absence of cosmic dust

Cosmic dust swirls through space after stars explode and comets collide.

Passing the Sun, cosmic dust is implanted with a rare form of helium — helium-3. Scientists measure helium-3 to distinguish cosmic dust from earthly debris.

Pavia said: “It’s like looking for a needle in a haystack. You’ve got this small amount of cosmic dust raining down everywhere, but you’ve also got Earth sediments accumulating pretty fast.”

In this study, Pavia was more interested in the absence of cosmic dust: “During the last ice age, there was almost no cosmic dust in the Arctic sediments.”

The researchers hypothesised that cosmic dust could stand as a proxy for ice before there were satellites to monitor changes in coverage.

Ice at the sea surface blocks cosmic dust from reaching the seafloor, while open water allows cosmic dust to settle into sediment.

By analysing the amount of cosmic dust in sediment cores from three sites, researchers reconstructed the history of sea ice for the past 30,000 years.

The three sites featured in the study “span a gradient of modern ice coverage,” Pavia said.

The first, located near the North Pole, is covered year-round. The second borders the edge of the ice during its annual low in September, and the third was ice-bound in 1980 but is now seasonally ice-free. 

The researchers found that year-round ice coverage corresponded with less cosmic dust in the sediment.

This was also observed during the last ice age, around 20,000 years ago. As Earth began to thaw, cosmic dust once again appeared in samples.

The researchers then matched ice coverage to nutrient availability, showing that nutrient consumption peaked when sea ice was low and decreased as ice built up. 

Credit: Bonnie Light/ University of Washington. CC BY.

Additional research

The data on nutrient cycling comes from tiny shells once occupied by nitrogen digesters called foraminifera.

Chemical analysis of these organisms’ shells shows what percentage of the total available nutrients were consumed when they were alive.

Pavia said: “As ice decreases in the future, we expect to see increased consumption of nutrients by phytoplankton in the Arctic, which has consequences for the food web.” 

Additional research is needed to show what is driving changes in nutrient availability.

One hypothesis suggests that sea ice decline increases the amount of nutrients used by surface organisms because there is more photosynthesis, but another argues that nutrients are diluted by ice melting.

Both scenarios present as more consumption, but only the first indicates an increase in marine productivity. 

The study is published in Science.