September 7, 2017

UCI, JPL investigators find direct evidence of sea level ‘fingerprints’

Indicators of global climate change are detected in tropical oceans

“I am proud to have been selected by NASA to become a member of this team with a vitally important mission,” said Isabella Velicogna, UCI Earth system science professor, shown here on a Greenland expedition. Maria Stenzel / For UCI

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Irvine, Calif., Sept. 7, 2017 – Researchers from the University of California, Irvine and NASA’s Jet Propulsion Laboratory have reported the first observation of sea level “fingerprints,” tell-tale differences in sea level rise around the world in response to changes in continental water and ice sheet mass. The team’s findings were published today in the American Geophysical Union journal Geophysical Research Letters.

“Scientists have a solid understanding of the physics of sea level fingerprints, but we’ve never had a direct detection of the phenomenon until now,” said co-author Isabella Velicogna, UCI professor of Earth system science and JPL research scientist.

Cumulative sea level fingerprints calculated from observations of Greenland, Antarctica, glaciers and ice caps and land water storage mass changes observed with the GRACE satellites for the time period January 2003 to April 2014. Isabella Velicogna & Chia-Wei Hsu / UCI

As ice sheets and glaciers undergo climate-related melting, they alter Earth’s gravity field, which causes nonuniform sea level change. Certain regions, particularly in the middle latitudes, are harder hit. For instance, Antarctica-generated sea level rise in California and Florida is as much as 52 percent greater than what’s average in the rest of the world.

The team calculated sea level fingerprints using time-variable gravity data collected by the twin satellites of NASA’s Gravity Recovery & Climate Experiment between April 2002 and October 2014. During that time, according to the study, the global mean sea level grew by about 1.8 millimeters per year, with 43 percent of the increased water mass coming from Greenland, 16 percent from Antarctica, and 30 percent from mountain glaciers. The scientists verified their calculations of sea level fingerprints associated with these mass variations via ocean-bottom pressure readings from stations in the tropics.

“It was very exciting to observe the sea level fingerprints in the tropics, where they were not expected to be detectable,” said lead author Chia-Wei Hsu, a graduate student researcher at UCI. “In the tropics, sea level fingerprint values are very close to global average sea level values, making them harder to detect.”

Velicogna added: “We know that sea levels climb faster in the middle to low latitudes versus the high latitudes and that Greenland and Antarctica contribute differently to the process. With our improved understanding through GRACE data and other techniques, we’re now able to take any point on the global ocean and determine how much the sea level there will rise as a result of glacier ice melt.”

Sea level fingerprints in millimeters per year calculated from observations of the mass loss of Greenland, Antarctica, glaciers and ice caps and changes in land water storage using time-variable gravity data collected by the twin satellites of the U.S./German Gravity Recovery and Climate Experiment mission between April 2002 and October 2014. The blue contour (1.8 mm/year) is the average sea level rise if the total addition of mass of water to the ocean was spread uniformly over the world’s oceans. The SLF are not uniform and bulge around the equatorial regions. Isabella Velicogna & Chia-Wei Hsu / UCI

This research project was supported by UCI and NASA’s Cryospheric Sciences Program.

About the University of California, Irvine: Founded in 1965, UCI is the youngest member of the prestigious Association of American Universities. The campus has produced three Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UCI has more than 30,000 students and offers 192 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $5 billion annually to the local economy. For more on UCI, visit www.uci.edu.

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