Microplastics, severe deglaciation observed in Antarctica

Most people see Antarctica as a pristine, relatively untouched place, but a newly published study has revealed the presence of microplastics in freshly fallen Antarctic snow. These findings, published in the journal The Cryosphere, bring to light a serious threat to the Antarctic.

University of Canterbury PhD student Alex Aves collected snow samples from the Ross Ice Shelf in Antarctica in late 2019. At the time, there had been few studies investigating the presence of microplastics in the air, and it was unknown how widespread this problem was. Indeed, it was assumed that Aves wouldn’t find any microplastics in such a remote location, so she was asked to collect additional snow off the Scott Base and McMurdo Station roadways so she’d have at least some microplastics to study.

Once back in the lab, it quickly became obvious there were plastic particles in every sample. According to Aves, “We collected snow samples from 19 sites across the Ross Island region of Antarctica and found microplastics in all of these.”

Aves analysed snow samples using micro-Fourier transform infrared spectroscopy to identify the type of plastic particles present; the plastic particles were also looked at under a microscope to identify their colour, size and shape. She found an average of 29 microplastic particles per litre of melted snow, which is higher than marine concentrations reported previously from the surrounding Ross Sea and in Antarctic sea ice.

Next to Scott Base and McMurdo Station, the density of microplastics was nearly three times higher, with similar concentrations to those found in Italian glacier debris. There were 13 different types of plastic found, with the most common being PET, commonly used to make soft drink bottles and clothing. Atmospheric modelling suggested the microplastics may have travelled thousands of kilometres through the air; however, it is equally likely that the presence of humans in Antarctica has established a microplastic ‘footprint’, the researchers said.

Antarctica New Zealand Environmental Adviser Natasha Gardiner said the research is of huge value, improving our understanding of the extent of plastic pollution near Scott Base and where it’s coming from.

“We can use this information to reduce plastic pollution at its source and inform our broader environmental management practices,” Gardiner said.

Research has found that microplastics have negative impacts on environmental health (limiting growth, reproduction and general biological functions in organisms, as well as having negative implications for humans). On a wider scale, the presence of microplastic particles in the air has the potential to influence the climate by accelerating melting of snow and ice. Indeed, a recent study by US and UK researchers has found that two major glaciers in West Antarctica may be losing ice faster than they have in at least the last 5000 years, with their results published in the journal Nature Geoscience.

Over the past few decades, the West Antarctic Ice Sheet has retreated and thinned at accelerated rates. The Thwaites and Pine Island glaciers that extend deep into the heart of the ice sheet are particularly susceptible to rapid melting because they sit on an inland-sloping bed where warm ocean water can flow underneath floating parts of the glacier tongues and erode the ice sheet from its base, which can lead to runaway ice loss. Runaway retreat of these two glaciers could reduce the size of the West Antarctic Ice Sheet, potentially contributing as much as 3.4 m to global sea level rise over the next several centuries.

It is however hypothesised that the glaciers may have been much smaller in the geologically recent past — namely, during the mid-Holocene, an era over 5000 years ago that was even warmer than the present day. If they were smaller, they must have subsequently regrown, raising the hope that they could do this again in the future. The research team looked at the relative sea-level change close to the glaciers during the past 5000 years as an indirect way of determining whether they were substantially smaller than present in the mid-Holocene and then re-expanded.

Relative sea level at a location depends on the amount of water in the ocean but also, importantly, on local changes in the shape of the Earth’s crust due to loading and unloading of glacier ice; thus, reconstructions of relative sea level over time can be used to identify large-scale changes in glacier advance and retreat. The team used radiocarbon dating of shells from ancient beaches that are now elevated above modern sea level to reconstruct changes in relative sea level over time — the shape of the resulting curve is related to the growth and retreat of the glaciers.

The results showed a steady fall in relative sea level over the last 5000 years, which suggests relatively stable glacier behaviour with no evidence of large-scale glacier retreat or advance. Moreover, the researchers found that the rate of relative sea-level fall recorded by the shells was almost five times lower than that measured today. The most likely reason for such a large difference is recent rapid ice loss in the region.

“Our work suggests that these vulnerable glaciers were relatively stable during the past millennia, yet their current rate of melting is accelerating and raising global sea level,” said study co-author Dylan Rood, from Imperial College London. “These currently elevated rates of ice melting may signal that those vital arteries from the heart of [the] West Antarctic Ice Sheet have burst, leading to accelerating flow into the ocean that is potentially disastrous for future global sea level in a warming world.”

The researchers also compared their results to existing models of the dynamics between ice and the Earth’s crust. They found that the models did not accurately represent the sea-level history revealed by their data. Their study thus helps to paint a more accurate picture of the history of the region and suggests that the models need refining.

Although the new evidence does not exclude the possibility of minor fluctuations of the Thwaites and Pine Island glaciers over the past 5000 or so years, the researchers concluded that the simplest interpretation of their data is that these glaciers have been relatively stable since the mid-Holocene until recent times — and that the present-day rate of glacier retreat may be unprecedented over the last 5000 years. The possibility thus remains that the present accelerating retreat of these glaciers could lead to ever-increasing ice recession into the heart of the West Antarctic Ice Sheet, with consequent implications for global sea level.

Image caption: View from Castle Rock, Ross Island across to the Transantarctic Mountains, taken in 2019. Image credit: Alex Aves.

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