A team of researchers at Caltech has discovered new pathways of seawater around Antarctica that are accelerating the melting of the floating ice shelves ringing Antarctica, already underway as a consequence of climate change. The findings, made possible by data from autonomous underwater vehicles and sensor-equipped seals, help explain the complex system of ocean currents driving the melting processes at work across the continent.
Climate change is causing the Antarctic ice shelves to melt at an unprecedented rate. Much of this melt comes from the undersides of the ice shelves, where warm water is flowing under them. But that is not all. The resulting meltwater, once it reaches the ocean, plays a role in driving additional melt along the coast of Antarctica as it’s carried along by ocean currents to ice shelves farther downstream. This understanding of the meltwater pathways is thus critical in predicting future sea level rise.
“We used to think about ice shelves as isolated systems, but we now understand that multiple ice shelves are connected by currents along the Antarctic coast,” said Andy Thompson, John S. and Sherry Chen Professor of Environmental Science and Engineering at Caltech. He put more emphasis on one ice shelf change impacting processes at another, which creates something like a domino effect. Such changes are now possible to predict with a high level of accuracy since researchers have started to understand these connected systems properly.
For more than a decade, Thompson’s lab has taken a multifaceted approach to studying the seas around Antarctica. Led by senior research scientist Mar Flexas, the new research analyzed data from both an underwater autonomous vehicle and from sensors fixed to the heads of seals. They found a new current that meltwater follows through the Bellingshausen Sea, a region on the side of Antarctica nearest South America.
“The Bellingshausen Sea is not a well-studied region, but it’s the first place where warm water from the Atlantic and Pacific oceans reaches the ice shelves,” Thompson said. That warm water, in melting the ice shelves, cools and becomes fresher; its capacity to melt more is then decreased.
It was also based on a collaboration lasting several decades by researchers at several institutions, equipping seals with small sensors that measure oceanic properties the animals travel and dive through the seas in search of food. This program, called Marine Mammals Exploring the Oceans Pole to Pole, or MEOP, makes its data openly available to other researchers.
Using information from undersea ocean gliders operated by the Thompson lab, combined with data obtained by Flexas and colleagues on the temperature, salinity, oxygen content, and particle concentration in the water column throughout the Bellinghausen and Amundsen seas, the authors found two separated meltwater pathways associated with flow from different ice shelves. One pathway flows along the coast and may raise the melting at downstream ice shelves because of the deep trapping of warm waters; the other returns to the open ocean.
An interesting thing in the seal data was that the scientists found a previously unknown trough, or canyon, in the seafloor, which they called the Seal Trough. Underwater topographic features like Seal Troughs influence the flow of currents much in the same way canyons on dry land guide the flow of rivers.
It is the first step in understanding how melting at individual ice shelves has an impact on the larger Antarctic circulation and ice shelf melting around the entire continent. Understanding the processes that occur near the Antarctic coast is critical for predicting global sea level rise in the near and far future as the oceans continue to warm due to a changing climate.
Results are described in a paper entitled, “Pathways of Inter-Basin Exchange from the Bellingshausen Sea to the Amundsen Sea,” published in the journal JGR Oceans. The co-authors were Caltech undergraduate Megan Robertson; Kevin Speer of Florida State University; and Peter Sheehan and Karen Heywood of the University of East Anglia. Funding was provided by the National Science Foundation, NASA, the Internal Research and Technology Development program at JPL-Caltech, and the European Research Council.