Researchers discover first definitive evidence of elusive fingerprints at sea level

When ice sheets melt, something strange and highly contradictory happens to sea levels.

It basically works like a seesaw. Near where these glacial masses melt, the sea level falls. But thousands of miles away they are actually rising. This is mainly due to the loss of gravitational pull on the ice sheet, causing the water to evaporate. The patterns have become known as sea level fingerprints because each melting glacier or ice sheet affects sea level in a unique way. Elements of the concept – which lies at the core of the understanding that global sea level is not rising uniformly – have been around for over a century, and modern sea level science has been built on it. But there has long been a catch to the widely accepted theory. A sea level fingerprint has never been definitively proven by researchers.

A team of scientists — led by Harvard graduate Sophie Coulson and with Harvard geophysicist Jerry X. Mitrovica — think they’ve spotted the first one. The findings are described in a new study published in Thursday Science. The work validates nearly a century of sea-level research and helps build confidence in models that predict future sea-level rise.

“Sea-level projections, urban and coastal planning — all of that — was built on the idea of ​​fingerprints,” said Mitrovica, Frank B. Baird Jr. Professor of Science in the Department of Earth and Planetary Sciences. “That’s why fingerprints are so important. They allow you to estimate what the geometry of sea level changes will be like… so now we have a lot more confidence in how sea level changes will evolve… If the physics of fingerprints weren’t true, we would need the entire rethink modern sea level research.”

Sea level fingerprints are notoriously difficult to detect due to the large fluctuations in sea level caused by changing tides, currents and winds. What makes it such a mystery is that researchers are trying to detect millimeter-scale movements in the water and link them to melting glaciers thousands of miles away.

Mitrovica compared the search to the search for the subatomic particle Higgs boson.

“Almost all physicists thought Higgs existed, but it was nonetheless a transformative achievement when it was unequivocally proven,” Mitrovica said. “In sea level physics, almost everyone assumed the fingerprints existed, but they have never been discovered with a comparable level of confidence.”

The new study uses newly released satellite data from a European marine surveillance agency, which collects over 30 years of observations near the Greenland ice sheet and much of the ocean near central Greenland, to fingerprint sea level fluctuations.

The satellite data caught the attention of Mitrovica and his colleague David Sandwell of the Scripps Institute of Oceanography. Typically, satellite records from this region had only extended to the southern tip of Greenland, but in this new release, the data reached a latitude ten degrees higher, allowing them to spot a possible indication of the see-saw caused by the fingerprinting.

Mitrovica quickly reached out to Coulson, a former Ph.D. Student in Mitrovica’s lab and now a postdoctoral fellow at Los Alamos National Laboratory to verify that this is really the fingerprint signal that sea-level scientists have been chasing for decades.

“She was the best person to … model exactly what the fingerprint would look like, given our understanding of how the Greenland ice sheet was losing mass, and was able to determine whether that prediction matched the satellite observation,” Mitrovica said.

Coulson, an expert in modeling sea level change and crustal deformation associated with melting ice sheets and glaciers, was visiting her family in the UK when the datasets hit her inbox. She recognized the potential immediately, she said.

Coulson quickly amassed the best three decades of observations she could find of changes in ice height in the Greenland ice sheet, as well as reconstructions of changes in glacier height in the Canadian Arctic and Iceland. She combined these different datasets to create sea level change predictions in the region from 1993 to 2019, which she then compared to the new satellite data. The fit was perfect. A one-to-one match showing with more than 99.9% confidence that the sea level change pattern revealed by the satellites is a fingerprint of the melting ice sheet.

“I was absolutely amazed, there it was — a fingerprint at sea level, proof of their existence,” Coulson said. “It was a really, really exciting moment for all of us. There are very few moments in science that provide such simple, remarkable clarity about complex Earth processes.”

“This work, so remarkably led by Sophie, is one of the highlights of my career, a book end to all the theoretical and computational work we have built with a community of international colleagues,” added Mitrovica, whose group was the first to present They model and predict what sea-level fingerprints should look like.

Scientific research usually takes years to develop the results and then put them into a publication, but here the researchers were able to act quickly. Overall, the process from viewing the satellite data to submitting the article took just a few months.

That’s because most of the legwork was already done. Much of the theory, technology, and methods were already well developed and advanced since Mitrovica and his team presented their work on sea-level fingerprinting about 20 years ago—calculations that have been widely accepted and incorporated into almost all models used to predict sea-level rise .

“This was high-risk, high-reward science, and no one expected such a rapid discovery. We’ve benefited incredibly from the groups that have supported us, particularly the Star Friedman Challenge,” Mitrovica said.

Now that the first fingerprint has been discovered at sea level, the question with the biggest global impact is where it is all going.

“There are more discoveries to come,” Mitrovica said. “Soon the full power of fingerprint physics will be available to project sea level changes into the next decade, century and beyond.”