Disturbing new research suggests warm water is pouring into the world's largest ice sheet in Antarctica

Warmer water is flowing toward the East Antarctic ice sheet, according to our alarming new research that reveals new potential drivers of global sea level rise.

Author

• 
  Laura Herraiz Borreguero
  

  Physical oceanographer, CSIRO

• 
  Alberto Naveira Garabato
  

  Professor, National Center for Oceanography, University of Southampton

• 
  Jess Melbourne-Thomas
  

  Transdisciplinary Researcher & Knowledge Broker, CSIRO

The research, published today in Nature Climate Change, suggests changes in water circulation in the Southern Ocean could jeopardize the stability of the East Antarctic ice sheet. The ice sheet, the size of the United States, is the largest in the world.

Changes in water circulation are caused by shifting wind patterns, and are linked to factors including climate change. Warmer waters and rising sea levels can damage marine life and threaten human coastal settlements.

Our findings underscore the urgency of limiting global warming to below 1.5℃, to prevent the most catastrophic climate damage.

Ice sheets and climate change

The ice sheet consists of glacial ice that has accumulated from precipitation over land. Where the sheets extend from the ground and float on the sea, 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, far less was known about his eastern counterpart.

Our research focuses off the coast of a region known as the Aurora Subglacial Basin in the Indian Ocean. This area of ​​frozen sea ice is part of the East Antarctic ice sheet.

How the basin will respond to climate change is one of the biggest uncertainties in projected sea level rise this century. If the basin melted completely, global sea levels would rise by 5.1 meters.

Most of the basin is below sea level, so it is very sensitive to sea melting. That’s because deep ocean water requires a lower temperature to freeze than shallower ocean water.

What we found

We examine 90 years of oceanographic observations of the Aurora Subglacial Basin. We find marked ocean warming at rates 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 levels of 0.3℃ to 0.9℃ every decade.

So how is this warming related to climate change? The answer has to do with the belt of strong westerly winds over the Southern Ocean. Since the 1960s, these winds have been moving south toward Antarctica for years when the Southern Annular Mode, a climate driver, was in a positive phase.

This phenomenon is partly attributed to the increase in greenhouse gases in the atmosphere. As a result, westerly winds move closer to Antarctica in summer, bringing warm water.

The East Antarctic ice sheet was once thought to be relatively stable and protected from warming oceans. That’s partly because it’s surrounded by very cold water known as “solid shelf water”.

Part of our research focuses on the Vanderford Glacier in East Antarctica. There, we observed warm water displacing cooler solid shelf water.

The movement of warm water towards East Antarctica is expected to worsen throughout the 21st century, further threatening the stability of the ice sheet.

Why is it important for marine life

Previous work on the effects of climate change in East Antarctica generally assumed that warming first occurred in the sea surface. Our finding – that the deeper water warms up first – points to the need to rethink the potential impact on marine life.

Strong assessment work is needed, including investments in monitoring and modeling that can link physical changes to complex ecosystem responses. This should include the possible effects of very rapid changes, known as tipping points, which may mean the oceans are changing much faster than marine life can adapt.

The marine ecosystems of East Antarctica tend to be particularly vulnerable to warming waters. Antarctic krill, for example, reproduce by sinking eggs into the depths of the deep ocean. Warming of deeper waters can affect the development of eggs and larvae. This in turn affects krill populations and dependent predators such as penguins, seals and whales.

Limiting global warming to below 1.5℃

We hope our results will inspire global efforts to limit global warming to below 1.5℃. To achieve this, global greenhouse gas emissions need to fall by about 43% by 2030 and to near zero by 2050.

Heating above 1.5℃. greatly increases the risk of destabilization of the Antarctic ice sheet, leading to substantial sea level rise.

But staying below 1.5℃ will make sea level rise no more than an additional 0.5 meters by 2100. This will allow greater opportunities for humans and ecosystems to adapt.

Laura Herraiz Borreguero received funding from the European Research Council Horizon 2020 Marie Skłodowska-Curie Individual Fellowship, through grant number 661015, and the Center for Southern Hemisphere Oceans Research (CSHOR, Hobart, Australia); He receives funding from the Australian government through CSIRO and the Australian Antarctic Partnership Program (AAPP). He is affiliated with CSIRO, AAPP.

Alberto Naveira Garabato received funding from the Royal Society through the Wolfson Research Merit Award.

Jess Melbourne-Thomas receives funding from the Climate Systems Hub of the Australian Government’s National Environmental Science Program, Fisheries Research and Development Corporation and The Pew Charitable Trusts.

/Courtesy of The Conversation. Material from this original organization/author may be timely, edited for clarity, style and length. The views and opinions expressed are those of the author.

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