by Laura Herraiz Borreguero, Alberto Naveira Doodle and Jess Melbourne-Thomas, The Conversation
Credit: Shutterstock
Warmer waters are flowing into the East Antarctic ice sheet, according to our alarming new research that reveals a potential new driver of global sea level rise.
The research, published today in Nature Climate Change, shows that the changing circulation of water in the Southern Ocean may compromise the stability of the East Antarctic ice sheet. The ice sheet, roughly the size of the United States, is the largest in the world.
Changes in water circulation are caused by changes in wind patterns and are related to factors such as climate change. Warmer waters and resulting sea level rise can harm marine life and threaten coastal human settlements.
Our findings underscore the urgency of limiting global warming below 1.5℃, to avoid the most catastrophic climate damage.
Ice sheets and climate change
Ice sheets comprise glacial ice that has accumulated from precipitation on land. Where sheets extend from land and float into the ocean, they are known as ice shelves.
It is well known that the West Antarctic ice sheet is melting and contributing to sea level rise. But until now, much less was known about its eastern counterpart.
Our research focused on the coast of a region known as the Aurora Subglacial Basin in the Indian Ocean. This frozen sea ice area is part of the East Antarctic Ice Sheet.
How this basin will respond to climate change is one of the biggest uncertainties in sea level rise projections this century. If the basin were to melt completely, global sea levels would rise 5.1 meters.
Much of the basin is below sea level, making it particularly sensitive to ocean melting. This is because deep sea water requires lower temperatures to freeze than shallow sea water.
What we found
We examined 90 years of oceanographic observations in the Aurora subglacial basin. We found unequivocal ocean warming at a rate of up to 2℃ to 3℃ since the first half of the 20th century. This equates to 0.1℃ to 0.4℃ per decade.
The warming trend has tripled since the 1990s, reaching a rate of 0.3℃ to 0.9℃ per decade.
So how does this warming relate to climate change? The answer refers to a belt of strong westerly winds over the Southern Ocean. Since the 1960s, these winds have been moving south toward Antarctica during years when the Southern Annular Mode, a climate driver, is in a positive phase.
The phenomenon has been attributed in part to the increase in greenhouse gases in the atmosphere. As a result, westerly winds are approaching Antarctica in summer, bringing warm water with them.
Where ice sheets extend from land and float into the ocean, they are known as ice shelves. Pictured: Iceberg Alley in East Antarctica. Credit: Dr Joel B Pedro, contributing author
The East Antarctic ice sheet was previously thought to be relatively stable and protected from warming oceans. This is partly because it is surrounded by very cold water known as “dense shelf water”.
Part of our research focused on the Vanderford Glacier in East Antarctica. There, we observed warm water replacing the cooler, denser water on the shelf.
The movement of warm waters into East Antarctica is expected to worsen throughout the 21st century, further threatening the stability of the ice sheet.
Why is this important to marine life?
Previous work on the effects of climate change in East Antarctica has generally assumed that warming occurs first in the surface layers of the ocean. Our findings, that deeper water warms first, suggests a need to rethink potential impacts on marine life.
Robust assessment work is required, including investment in monitoring and modeling that can link physical change to complex ecosystem responses. This should include the potential effects of very rapid change, known as tipping points, which can mean the ocean is changing much faster than marine life can adapt.
Marine ecosystems in East Antarctica are likely to be highly vulnerable to warming waters. Antarctic krill, for example, reproduce by sinking eggs into the ocean depths. Warming of deeper waters may affect egg and larval development. This in turn would affect krill populations and dependent predators such as penguins, seals and whales.
The minke whale emerges through the ice in Antarctica, where warming water will affect marine ecosystems. Credit: Jess Melourne-Thomas
Limit global warming below 1.5 ℃
We hope our results will inspire global efforts to limit global warming below 1.5℃. To achieve this, global greenhouse gas emissions must be reduced by around 43% by 2030 and almost zero by 2050.
Warming above 1.5 ℃. greatly increases the risk of destabilizing the Antarctic ice sheet, causing a substantial rise in sea level.
But staying below 1.5℃ would keep sea level rise to no more than an additional 0.5 meters by 2100. This would allow more opportunities for people and ecosystems to adapt.
Research into the drivers of Antarctic ice retreat provided by The Conversation
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