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A warm climate is putting a strain on the glaciers of Greenland and Antarctica, melting them from above and below. The more they melt, the higher the sea level.
When an ice cube is exposed to a heat source, such as hot water or air, it melts. Hence, it is not surprising that a warm climate is melting our glaciers and ice sheets. However, predicting how much glaciers and ice sheets will melt and how quickly – key components of sea level rise – is not that simple.
Greenland and Antarctica are home to most of the world’s glacial ice, including its only two ice caps, making them areas of particular interest to scientists. Combined, the two regions also contain enough ice, that if it all melted at once, it would raise sea levels by nearly 215 feet (65 meters), making studying and understanding them not only interesting, but crucial to our next one. long-term adaptability and our long-term survival in a changing world. Credit: NASA
Glaciers and ice caps are much more complex structures than ice cubes. They form when snow accumulates and is compressed into ice by fresh snow for many years. As they grow, they begin to move slowly under the pressure of their own weight, dragging smaller rocks and debris with them across the earth. Glacial ice that extends to cover vast continental masses, such as in Antarctica and Greenland, is considered an ice sheet.
The processes that cause glaciers and ice sheets to lose mass are also more complex. The surface of an ice cube melts when it is exposed to ambient (warm) air. And while warm air certainly melts the surface of glaciers and ice caps, they are also significantly affected by other factors, including the ocean water that surrounds them, the terrain (both land and ocean) on which they move and even their own meltwater.
Greenland and Antarctica are home to most of the world’s glacial ice, including its only two ice sheets. These thick sheets of ice, approximately 10,000 feet (3,000 meters) and 15,000 feet (4,500 meters) respectively, contain most of the fresh water stored on Earth, making them of particular interest to scientists. Combined, the two regions also contain enough ice, that if it all melted at once, it would raise sea levels by nearly 215 feet (65 meters), making studying and understanding them not only interesting, but crucial to our next one. long-term adaptability and our long-term survival in a changing world.
Ice loss in Greenland
A glacier is considered to be in equilibrium when the amount of snow that falls and accumulates on its surface (the accumulation zone) equals the amount of ice lost through melting, evaporation, calving and other processes.
But with annual air temperatures in the Arctic rising faster than anywhere else in the world, that balance is no longer achievable in Greenland. The warmer ocean waters surrounding the island’s glaciers are also problematic.
“It’s basically like pointing a hair dryer at an ice cube while the ice cube is also sitting in a pot of hot water,” said Josh Willis, principal investigator at NASA’s Ocean’s Melting Greenland (OMG), a project that is studying the effects of ocean water temperature on melting ice in the region. “Glaciers are melted by heat from above and below simultaneously.”
Although warm air and warm water contribute to melting individually, the interaction between glacier melt water and warm ocean water also plays a significant role.
When hot summer air melts the surface of a glacier, meltwater makes holes in the ice. It makes its way to the bottom of the glacier where it runs between the ice and the glacier bed, and eventually shoots into a plume at the base of the glacier and the surrounding ocean. The meltwater plume is lighter than the surrounding ocean water because it contains no salt. It then rises to the surface, mixing warm ocean water upward in the process. The hot water then rubs against the bottom of the glacier, causing even more of the glacier to melt. This often leads to childbirth – ice breaking and breaking into large chunks of ice (icebergs) – at the front or end of the glacier. Credit: NASA
When hot summer air melts the surface of a glacier, meltwater makes holes in the ice. It makes its way to the bottom of the glacier where it runs between the ice and the glacier bed, and eventually shoots into a plume at the base of the glacier and the surrounding ocean.
The meltwater plume is lighter than the surrounding ocean water because it contains no salt. It then rises to the surface, mixing warm ocean water upward in the process. The hot water then rubs against the bottom of the glacier, causing even more of the glacier to melt. This often leads to childbirth – ice breaking and breaking into large chunks of ice (icebergs) – at the front or end of the glacier.
The complicated shape of the sea floor surrounding Greenland affects how quickly this warm water melt can occur. It provides a barrier in some areas, preventing the deep, warmer waters of the Atlantic Ocean from reaching the glacier fronts. However, underwater terrain, just like above-water terrain, includes other features such as deep canyons. The canyons cut the continental shelf, allowing the waters of the Atlantic to enter. Glaciers found in these waters will melt faster than those where hot water is blocked by submarine ridges or sills.
Ice loss in Antarctica
In Antarctica, where similar surface and ocean melting processes occur, the topography and bedrock on which the ice sheet is located significantly affect the stability of the ice sheet and its contribution to sea level rise. .
Researchers separate Antarctica into two regions based on the relationship between the ice and the underlying bedrock. East Antarctica, the area east of the Transantarctic Mountains, is extremely high in elevation and has the thickest ice on the planet. The bedrock below the ice sheet is also mostly above sea level. These features help keep the east side relatively stable. West Antarctica, on the other hand, is lower in elevation and most of the ice sheet is thinner. Unlike in the east, the ice sheet in West Antarctica is located on a bedrock below sea level.
“In West Antarctica, we have these glaciers resting on a bedrock underwater. As in Greenland, there is a warmer ocean water layer underneath the cold surface layer. So this warm water is able to flow over the surface. continental shelf, and then down to below the ice shelves – the floating ice that extends from glaciers and the ice sheet, ”said NASA Jet Propulsion Laboratory scientist Helene Seroussi. “The water melts the ice shelves from below, which can cause them to thin and crack.”
The visualization shows how ocean currents flow around and under the Pine Island Glacier in Antarctica. As the water makes its way under the ice shelf, it erodes the ice shelf from the bottom making it thinner. The visualization was produced using the V3 ocean circulation model “Stimating the Circulation and Climate of the Ocean” (ECCO), the “Reference Elevation Model of Antarctica” (REMA) surface elevation of 100 meters and the bed topography of 450 meters and the thickness of the ice BedMachine Antarctica Data set V1. The surface is mapped with scenes from NASA’s LandSat 8 satellite. For greater clarity, exaggeration factors of 4 and 15 were used, respectively above and below sea level. Credit: NASA / Cindy Starr
This is important because ice shelves act like corks. They hold back the ice flowing from the mountain, slowing its approach to the ocean, where it raises the sea level. When the ice shelves break off, the plug is essentially removed, allowing more internal ice to flow freely into the ocean. Furthermore, this leads to the retreat of the foundation zone, the area where the ice separates from the bedrock and begins to float.
“The ground zone delineates the floating ice, which is already accounted for in the sea level balance from the ground ice which is not accounted for in the balance,” said ICESat-2 scientist Kelly Brunt of the Goddard Space Flight Center of NASA and the University of Maryland. “Floating ice is like an ice cube floating in a glass. It doesn’t overflow from the glass when it melts. But when you add non-floating ice to the ocean, it’s like adding more ice cubes to the glass, which will cause the level some water to go up. “
The bedrock in West Antarctica is also in reverse slope, meaning it is higher at the edges and gradually gets deeper inland. Then, whenever the land area retreats inland, thicker ice is exposed to ocean water and the glacier or ice sheet takes root in deeper water. This allows even more ice to flow upstream into the ocean.
“It’s concerning in West Antarctica, because as we push back the grounding zones, the downward and reverse slope means there’s really no backstop, nothing to interrupt this cycle of melting and retreat,” Brunt said. . “Our maps of the bedrock beneath the ice sheet are not as complete as in Greenland, partly because Antarctica is much less accessible. For this reason, we don’t really know if there are any small bumps or peaks down there that could help slow down. retreat. “
West Antarctic glaciers like Thwaites and Pine Island are already retreating faster than they were in the past. This is problematic because they provide a main path for ice from the West Antarctic ice sheet to enter the Amundsen Sea and raise sea level.
Overall, melting and ice loss have accelerated at both poles in recent years. The more we learn about the processes and interactions that cause it, some of which have been discussed here, the better we will be able to accurately and accurately predict sea level rise in the distant future.
Media contact
Ian J. O’Neill / Jane J. Lee
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-2649 / 818-354-0307
[email protected] / [email protected]
Written by NASA’s Esprit Smith / Earth Science News Team
2020-209
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