It is not a revelation that the sea level is rising. Rising temperatures caused by human-caused climate change are melting ice sheets and expanding ocean water. What happens inside the Earth will also shape future coastlines. Jacky Austermann is trying to understand those internal dynamics.
As a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory, Austermann didn’t always know she would end up studying climate. Her fascination with mathematics from a young age, coupled with her love of nature and the outdoors (she grew up hiking in the Alps), led her to study physics as a student and then geophysics.
As Austermann delved into Earth’s geosystems, he learned to what extent the movement of hot rocks in the mantle influences life on the surface. “I was very interested in all this interaction of the solid earth, the oceans and the climate,” he says.
Much of Austermann’s work focuses on how that interaction influences changes in sea level. The global mean sea level has risen more than 20 centimeters since 1880, and the annual rise is increasing. But changes in local sea level can vary, with those levels rising or falling along different coastlines, Austermann says, and solid land plays a role.
“We think of sea level change in general as ‘the ice is melting, so the sea level is rising.’ But there are so many more nuances,” she says. “Much of the change in sea level is driven by the movement of the land.”
Understanding that nuance could lead to more accurate climate models for predicting future sea level rise. Such work should help inform practical solutions for communities in coastal areas at risk.
So Austermann is building computer models that reconstruct changes in sea level over the last few million years. His models incorporate data on how progressive mantle upheaval and other geological phenomena have altered the elevation of land and sea, particularly during interglacial periods when Earth’s temperatures were a few degrees warmer than they are today. .
Previous studies had suggested that this upheaval, known as mantle convection, sculpted Earth’s surface millions of years ago. “It pushes the surface up where the hot material gushes out,” says Austermann. And it also drags [the surface] below, where the cold material sinks back into the mantle.”
In 2015, Austermann and colleagues were the first to show that mantle-induced topographic changes influenced the melting of Antarctic ice during the last 3 million years. Near the edges of the ice sheet, the ice retreated faster in areas where the land surface was lower due to convection.
Furthermore, mantle convection is affecting Earth’s surfaces even on relatively short time scales. Since the last interglacial period, about 130,000 to 115,000 years ago, mantle convection has deformed ancient shores as much as several meters, his team reported in Progress of science in 2017.
the the growth and melting of ice sheets can also deform solid earthAusterman says. As the land sinks under the weight of the ice pack, the local sea level rises. And when the land rises where the ice melts, the water falls. This effect, as well as the way the ice sheet pulls on the water around it, is changing local sea levels around the world today, he says, making it highly relevant for coastal areas planning their defenses in the current climate crisis.
Understanding these geological processes can help improve models of past sea level rise. Austermann’s team is collecting more data from the field, scouring the coasts of Caribbean islands for clues about which areas were once near or below sea level. Such clues include fossilized corals and ripples of water etched in stone, as well as tiny conduits in rocks that indicate air bubbles once burst through the sand on ancient beaches. The work is “really fun,” says Austermann. “It’s essentially like a scavenger hunt.”
Their efforts put solid Earth at the forefront of studying sea level changes, says Douglas Wiens, a seismologist at Washington University in St. Louis. Before, “many of these factors were ignored.” What is most remarkable is his ability “to take what we normally think of as several different disciplines and bring them together to solve the sea level problem,” he says.
Austermann says the most enjoyable part of her job is working with her students and postdocs. More than writing the next big article, she wants to cultivate a happy, healthy, and motivated research group. “It’s really rewarding to see them grow academically and scientifically, come up with their own ideas… and also help each other.”
Roger Creel, a Ph.D. A student in Austermann’s group and the first to join his lab, she treasures Austermann’s mentorship. She offers clear and fluid realistic expectations, provides quick and thoughtful feedback, and meets for regular check-ins, she says. “Sometimes I think it’s like water skiing, and Jacky is the boat.”
For Oana Dumitru, a postdoc in the group, one aspect of that valuable mentorship came in the form of a gentle push to write and submit a grant proposal on her own. “I thought she wasn’t ready for it, but she said, you have to try it,” says Dumitru.
Austermann prioritizes the well-being of his group, which encourages collaboration, Creel and Dumitru say. That sense of inclusion, support and community “is the foundation for having an environment where great ideas can flourish,” says Austermann.
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