NASA's Ocean Melt greenland (OMG) mission found that, like the Apusiaajik Glacier shown in the figure, Greenland glaciers face greater risk of glacial ablation than previously anticipated.
Source: NASA/Jet Propulsion Laboratory - California Institute of Technology (JPL-Caltech)
To understand the role of the ocean in greenland's glacier melting, NASA's OMG mission conducted an extensive survey of Greenland's coastline, the world's largest island.
NASA's OMG mission, which ended on December 31, 2021, found that glaciers melt at least as much as those caused by warm air due to seawater. With melting Greenland's ice currently contributing more to global sea-level rise than any other single source, the discovery has revolutionized scientists' understanding of how fast sea-level rise will be in the coming decades.
These unique new measurements identify potential progress in future glacier melting, which in Greenland is currently six to seven times faster than it was 25 years ago. If all of Greenland's ice melts, global sea levels would rise by about 24 feet (about 7.4 meters).
The OMG mission's six-year fieldwork in Greenland has changed scientists' understanding of how fast global sea levels will rise in the coming decades.
Source: NASA/JPL-Caltech
But that's just the tip of the iceberg for this small mission based on airplanes and boats. Over a six-year period, the OMG mission made the first scientific measurements along the northern hemisphere's most remote miles of coastline. The mission conducted a comprehensive and detailed survey of the seafloor around Greenland's coastline, including dozens of previously unknown fjords, and measured the temperature change of the seawater from top to bottom at different locations and in different years. In order to obtain this unique data set, the aircraft on the mission flew more than 13 times around and over Greenland, recording a large amount of data.
Preparations
There are more than 220 glaciers on Greenland that blend into the ocean. Prior to the OMG mission, scientists thought that the currents around and below these glaciers must have played a role in the melting of the glaciers. But to what extent has it had an impact?
Satellite-observed sea-level temperatures don't help much to answer that question. Around Greenland, ocean surface water is very low in temperature and salinity, contains large amounts of meltwater from the Arctic, and is the largest source of freshwater shelf ice. Shallow glaciers at the bottom that only touch the surface water of the ocean melt more slowly. But hundreds of feet below sea level, the sea temperature gradually rises and the salinity gradually increases. As a result, deep glaciers are eroded by warmer waters and melt four to five times faster than shallow glaciers.
The only way to determine the risk of any glacier is to travel to Greenland to make measurements of the seafloor and seawater in the area where the glacier is located. Scientists have been studying individual glaciers this way for years, but Josh Willis, principal investigator of the OMG mission from NASA's Jet Propulsion Laboratory, wants to get the big picture: a five-year measurement of all 220 or so glaciers, which is also the time frame for a mission funded by NASA's Earth Risk Level Project.
"When we started designing OMG missions, we asked ourselves, 'Can we run an experiment in five years to predict what will happen over the next 50 years?'" said Willis. As it turns out, they did. NASA even approved a six-year field survey aimed at observing unexpected rapid fluctuations in water temperatures off Greenland's west coast.
NASA's Gulfstream III aircraft is one of several research aircraft used in OMG missions. Airports in Greenland, Iceland and Norway are base for study flights.
implement
The first job of the mission was to map the seafloor around Greenland to understand where the warm deep ocean waters could reach the glacier. The contractor completed most of the mapping work through a research vessel, and Eric Rignot from UC Irvine and NASA's Jet Propulsion Laboratory spearheaded several small surveys over the next few years to fill in the missing parts of the previous mapping effort.
To measure the temperature and salinity of seawater from the surface to the seabed, Willis conducted a summer airborne observation campaign that launched about 250 probes into the ocean each year at strategic locations along the entire coastline. Flying over the distant North Pole for six summers may sound more like an adventure than a research effort. But Willis said: "Looking back now, it can be said that it is an event of the rest. But when you're in it, everyone is working hard and working with all your might. For scientists, seeing the data collected from the detector flow into the computer is enough to make them happy.
Detailed maps from the OMG mission and temperature data collected show that two to four times the glaciers are located in seawater several degrees higher than previously predicted, so the risk of glacier ablation is higher than anyone expected. The researchers learned that 50 percent of Greenland's glaciers melt from 1/3 of its glaciers; OMG mission observations showed that the bottoms of these glaciers were deep into the warm deep ocean water. Climate models that do not take into account the effects of warm seawater underestimate at least twice the loss of glaciers, in other words, miss the 50% sea-level rise caused by this cause.
cooperate
The groundbreaking data from the OMG mission has influenced arctic research of several kinds, including oceanography. For example, Kristin Laidre from the University of Washington, an internationally renowned narwhal expert, and Ledall and co-lead investigator Ian Fenty from the Jet Propulsion Laboratory OMG mission created a project that would benefit both marine biologists and oceanographers: a research cruise to document the presence of narwhals by placing OMG detectors and acoustic detectors in front of West Greenland glaciers.
The probe data provides a close-up view of the magnitude of changes in ocean conditions over a small area, and Leder hopes that combined with the data from the soundsin, will help explain why certain glacial fronts are unique to narwhals. "Biologists can better understand animals and populations by working with physical scientists, and it's really great to have a group of scientists who want to collaborate [referring to the OMG mission team]," she said. ”
continuation
The end of this mission does not mean the end of all new data from Greenland's oceans. In 2021, the mission team dropped some longer-lived probes in areas where seawater temperature or circulation changes were not yet fully understood. The probes "overwinter" beneath the surface of the sea and continue to float up and down in the ocean to collect data that will be remotely read as the ice melts next summer.
In addition, scientists in many fields will continue to use observational data from OMG missions for research. To date, about 50 percent of peer-reviewed journal articles using this data have been written by researchers outside the mission science team, a very large percentage. Willis said: "We are actually seeing a lot more scientific results than we initially expected, and these scientific papers will be endless." ”
source:
https://www.nasa.gov/feature/jpl/nasa-greenland-mission-completes-six-years-of-mapping-unknown-terrain