A new study led by UCLA reinforces the importance of collaboration in assessing the effects of climate change.
The research, published today in the journal Proceedings of the National Academy of Sciences offers new insights into previously unknown factors affecting Greenland's melting ice sheet, and could help scientists predict more precisely how the Greenland phenomenon is the largest melting ice layer in terms of meltwater spills that contribute to sea level rise, and at least half of Greenland's sea level rise comes from ice melted, said Laurence C. Smith, a geography professor at UCLA. (That's even more than the amount caused by ice-breaking, when large blocks of ice separate from the ice sheet, forming icebergs that eventually melt in the sea.)
Since 2012, a team led by Smith has visited the Greenland ice sheet several times, using satellites, drones and sophisticated sensors to track the flow rates of rivers melting water on glaciers, and map their watersheds, which include the surface areas between the rivers.
In 2015, Smith and a group of UCLA graduate students and collaborators focused on a 27-square-mile watershed, and discovered an important process that had previously been left out of the climate model calculations. Part of the meltwater from the lakes and rivers in the region's glaciers, which ends in large sinkholes called "moulins" and barrels through the glacier, is stored and trapped in the upper part of the glacier inside a rotten porous ice of low density. "
" Ours is the first independent data collection effort to directly measure the rates of meltwater runoff from the top of the ice, "said Smith, whose research was funded by NASA. researchers, including us, have tried to gather information using flows from the edge of the ice, but those measurements are problematic for testing climate models. "
Smith's team found a discrepancy between their data and the water runoff calculations of A fusion of five climate models, estimates of those models were between 21 and 58 percent higher than those that Smith's team measured on ice.
Smith invited the scientists who created those models to collaborate with him Together, they checked the real-time statistics of the weather stations on the ice to confirm that the data in the climate models were correct, and They found that the calculations of the models were accurate. Which meant that the meltwater trip on the surface of the ice was more complex than previously imagined: the scientists recognized that before the water crosses the ice through moulins, it can clump together, sit indefinitely or return to Freeze on porous ice on the surface. 19659011] "After eliminating all other possibilities, we inferred that the disagreement in our data is due to sunlight penetrating the ice, causing subsurface melting and storage of fusion water," said Dirk van As, co-author of the study. Principal investigator in the Geological Survey of Denmark and Greenland. "And now we know that this is happening in the higher reaches of the bare ice zone that cover large regions of the ice sheet.
" Now we know that the calculation of meltwater retention in porous ice should be included in some way, "he said.
To measure the discharge of the rivers in the ice, Smith and his team adapted a technique normally used on land, working in shifts, collecting data every hour, throughout the day, for three days. in July 2015, defying the cold, the wind and the wind, the team used safety equipment to anchor in the ice and protect themselves from the fast flowing water in dangerous moulins, where the surface water falls in a dive inside the layer of ice.
Among the many logistical challenges I was determining how to set up the equipment to measure the flow of the river so that researchers would not need to be placed on either side of a river.
"Unless you have a helicopter, you can not place people on either side of a large river on the top of the ice," said Lincoln Pitcher, a UCLA geography student who discovered a way to keep the sensors on track. place after trial and error on land and ice. They needed to find a stable and strong system that would stay in place even though the ice surface around them was melting.
Study co-author Asa Rennermalm, a geography professor at Rutgers-New Brunswick University, was part of the field team.
"We use a device called Acoustic Doppler Current Profiler, which tracks the download based on the sound". she said. "We connected it to a floating platform, and then we connected it to ropes, which were attached to poles on both sides of the ice river." We moved the platform from one side to the other across the river every hour for 72 hours. never before in the Greenland ice sheet. "
Van As said that the project demonstrated that combining the experience of multiple disciplines, including meteorology, oceanography and hydrology (the study of the properties and movement of water above ground) is essential for understanding how glaciers and ice sheets respond to the climate system.
"It is important that hydrologists like Larry contribute their extensive knowledge in the field of glaciology, using approaches that are new to our discipline," he said.
In general, glaciologists are not used to thinking about watersheds on ice, said Smith. The irregularities that these basins impart to the timing and amount of meltwater entering the ice are not currently considered in the geophysical models of "ice dynamics," that is, the velocity and spatial pattern of glacial ice sliding. To the sea.
& # 39; Taking the very mature field of the hydrology of the earth's surface, which deals with the flow of the river and the watersheds in the earth, and its application to the ice sheet, which has typically been the domain Scientist of solid ice geophysics, "he said." We have to borrow from hydrology because the surface of the ice is becoming a hydrological phenomenon. And we can take these tools from another discipline and apply them and really have a conceptual breakthrough. "
Smith and his team are now working on a study based on data from a trip to Greenland in 2016, when they spent a week tracing river basins and digging In the rotten ice.
Led by UCLA graduate student Matthew Cooper, researchers try to better explain how rotten ice traps water.They have tracked rotten ice to a depth of almost 3 feet below the surface, a finding that could help scientists developing climate models better understand how ice sheets are losing mass.
Part of Smith's mission in Greenland is to empower a new generation of hydrologists who are eager to join the monitoring front of global climate change.
"Climate change is no longer remote news for me," said Kang Yang, a former Fellow postdoctoral river of UCLA, who was part of the field team of this study. Now a professor at Nanjing University in China, Yang will continue to work with Smith on mapping the rivers in the Greenland ice sheet.
A study shows how meltwater in the Greenland ice sheet contributes to sea level rise
Laurence C. Smith et al. Direct measurements of meltwater runoff on the surface of the Greenland ice sheet, Procedures of the National Academy of Sciences (2017). DOI: 10.1073 / pnas.1707743114