The most important thing to remember about NASA’s Oceans Melting Greenland mission, which ends December 31, 2021, may be what the name implies: OMG has demonstrated that ocean water is melting Greenland’s glaciers at least It’s like warm air is melting them from above. Because ice loss from the Greenland ice sheet is now contributing more to the global rise of the oceans than any other single source, this discovery has revolutionized scientists’ understanding. study on the rate of sea level rise in the coming decades.
These new, unique measurements shed light on the likely course of future ice loss in a place where glaciers today are melting six or seven times faster than they were just 25 years ago. If all of Greenland’s ice sheet melted, global sea levels would rise by about 24 feet (7.4 meters).
But that’s just the tip of the iceberg in the story of this plane and small boat mission. In six years of operation, OMG made the first scientific measurements along many miles of the most remote coastline in the Northern Hemisphere. The mission performed the most complete survey of the seafloor around the coast of Greenland, including dozens of previously unexplored fjords (cliffy intakes clogged with icebergs caused by icebergs). glaciers are disintegrating), and measure how ocean temperatures change from place to place, year to year, and from top to bottom. To obtain this unique data set, the mission planes logged enough miles to fly around and over Greenland to orbit the globe more than 13 times.
More than 220 glaciers flow from Greenland into the ocean. Before OMG, scientists had shown that ocean water swirling around and below these glaciers must have contributed to their loss of ice. But how much?
Satellite observations of sea surface temperatures don’t do much to answer that question. Around Greenland, the top layer of the ocean is extremely cold and not very salty, containing a lot of water from the Arctic, the freshest of the oceans. A shallow glacier that only touches this layer will melt slowly. But at depths hundreds of feet below, the ocean is warmer and saltier. Deeper glaciers are eroded by warmer water, losing ice four or five times faster than shallow rivers.
The only way to find out any glacial risk is to go to Greenland and measure the glacier, seafloor and water in front of it. Scientists have studied each glacier that way for years, but Josh Willis, principal investigator for OMG at NASA’s Jet Propulsion Laboratory in Southern California, wants to get the complete picture: measurement all over 220 glaciers in 5 years – the time period to be ready for missions funded by NASA’s Earth Ventures airborne research program.
“When we started designing the OMG, we asked ourselves, ‘Can we do a five-year trial to tell us about the next 50 years? ”” Willis said. The results proved that they can. NASA even allowed them to do field surveys for a sixth year to observe sudden, rapid changes in water temperature off the west coast of Greenland.
The mission’s first job was to map the seafloor around the island to see where warm, deep water could reach the glaciers. A contractor completed most of the mapping by research boat, and OMG Deputy Principal Investigator Eric Rignot of JPL and the University of California, Irvine led smaller surveys in the following years to Fill in the missing parts.
To measure seawater temperature and seafloor salinity, Willis conducts an aerial campaign over the summer, dropping about 250 probes a year into the ocean at strategic locations around the entire coastline. . Six summers flying over the far North Pole sounds like more of an adventure than a research project, but Willis says, “It was just an adventure in retrospect. When you’re in it, you have to keep your head down and you’re working as hard as you can. “For scientists, the transmission of data to their computers from the probes was exciting enough.
The detailed map and temperature data collected by OMG shows that two to four times more than glaciers sitting in water several degrees warmer than previously thought and, therefore, at higher risk of disease than anyone has ever known. The researchers understand that about a third of Greenland’s glaciers account for half of the ice loss; OMG found that all of these culprits go into warm water. Climate models do not take into account the effect of warm water underestimate the ice loss of the ice by at least a factor of two – in other words, less than half of sea level rise comes from this source.
OMG’s groundbreaking data has influenced many types of Arctic research beyond oceanography. For example, Kristin Laidre of the University of Washington is a world-renowned expert on narwhals, arctic whales with protruding tusk-like teeth. She and Ian Fenty, an OMG co-investigator at JPL, developed plan that benefits both marine biologists and oceanographers: a research cruise to place OMG probes and acoustic transmitters that record the presence of narwhals in front of glaciers West Greenland.
The probe data provides a close-up look at how ocean conditions change over a small area, and Laidre hopes that, combined with the hearing aid data, it will help explain why some oceans are not. Glacier money is particularly attractive to narwhal. “Our biologists can better understand animals and populations by working with physical scientists,” she said, referring to the OMG team. “Having a group of scientists who want to collaborate is really cool.”
The end of the mission does not mean the end of all new data from the Greenland ocean. In 2021, the team has launched a few longer-life probes in areas where changes in ocean temperature or circulation are not well understood. These probes “winter” below the surface, continuing to bobble up and down in the water to collect data that will be read from a distance when the ice melts next summer.
And scientists in many fields will continue to rely on OMG’s observations for their research. To date, about half of peer-reviewed journal articles use data written by researchers outside of the mission’s science team — an unusually large share. “We are seeing more science than we originally planned,” said Willis. “Those papers won’t stop.”
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.