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Anatomy of Glacial ice loss




The warming climate is affecting glaciers in Greenland and Antarctica, melting them from above and below the surface. The more it melts, the higher the sea level rises.


When an ice cube comes into contact with a heat source, such as warm water or air, it melts. So it’s no surprise that warming climate is causing our glaciers and ice sheets to melt. However, predicting how much glaciers and ice sheets will melt and the speed – a key component of sea level rise – is not nearly as simple.

Greenland and Antarctica are home to most of the world’s ice – including its only two icebergs – making them areas of particular interest to scientists. Combined, the two areas also contain enough ice that, if melted at once, will raise sea levels by almost 215 feet (65 meters) – making it not only interesting to study and learn about them, but also very exciting. important to our resilience and our long-term survival in a changing world. Vendor: NASA

Glaciers and ice sheets are much more complex structures than ice cubes. They form when snow accumulates and is compressed into ice by new snow over the years. As they get older, they begin to move slowly under the pressure of their own weight, pulling smaller boulders and debris on the ground. The expansive frost covering large lands, like those in Antarctica and Greenland, is considered an iceberg.

The processes that cause glaciers and ice sheets to lose mass are also more complex. The surface of an ice cube melts when it comes into contact with (warm) ambient air. And while warm air definitely melts the surface of glaciers and ice sheets, they are also significantly affected by other factors, including the oceanic water that surrounds them, the topography (both land and ocean) by which they move, and even their melted water.

Greenland and Antarctica are home to much of the world’s ice, including its only two ice sheets. These thick slabs of ice – about 10,000 feet (3,000 meters) and 15,000 feet (4,500 meters) thick 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 melted at once, will raise sea levels by almost 215 feet (65 meters) – making it not only interesting to study and learn about them, but also very much important to our long-term resilience and ability to survive in a changing world.

Ice loss in Greenland

Glaciers are considered to be in equilibrium when the amount of snow that falls and accumulates on its surface (accumulation zone) is equal to the amount of ice lost through melting, evaporation, formation, and other processes.

But with the annual Arctic air temperatures rising faster than anywhere else in the world, that balance is no longer achievable in Greenland. Warmer seawater surrounding the island’s tidewater glaciers is also a problem.

“It’s basically like directing a hairdryer at a block of ice while the block,” said Josh Willis, principal investigator at NASA’s Ocean’s Melting Greenland (OMG), a project that is studying the effects of the ocean. Ice is also located in a pot of warm water. “Glaciers are being melted by heat from above and below simultaneously.”

Although warm air and warm water contribute to individual melting, the interaction between meltwater from glaciers and warm ocean water also plays an important role.

When the warm summer air melts the surface of the glacier, flowing water pierces the ice. It goes down to the bottom of the glacier, where it runs between the ice and the bottom of the glacier, and eventually shoots out in a cluster at the bottom of the glacier and into the surrounding ocean. The water flow is lighter than the surrounding ocean water because it does not contain salt. So it rises towards the surface, mixing the warmer seawater in the process. The warm water will then rub against the glacier bottom, causing more of the ice to melt. This often results in birth – the ice cracks and breaks into large chunks of ice (icebergs) – at the anterior end, or terminal, of a glacier. Vendor: NASA

When the warm summer air melts the surface of the glacier, flowing water punches holes through the ice. It goes down to the bottom of the glacier, where it runs between the ice and the bottom of the glacier, and eventually shoots out in a cluster at the bottom of the glacier and into the surrounding ocean.

The flow is lighter than the surrounding seawater because it contains no salt. So it rises towards the surface, mixing the warmer seawater in the process. The warm water then rubs against the glacier bottom, causing more of the ice to melt. This often results in birth – the ice cracks and breaks into large chunks of ice (icebergs) – at the anterior end, or terminal, of a glacier.

The complex shape of the seabed around Greenland affects how easily this warm water melts. It provides a barrier in some areas – preventing deeper and warmer water from the Atlantic from reaching the glacial facades. However, underwater terrain, like that above water, includes other features such as deep canyons. The gorges cut into the continental shelf, allowing Atlantic water to enter. Glaciers in these waters will melt faster than those where warm water is blocked by underwater burrs or thresholds.

Ice loss in Antarctica

In Antarctica, where similar surface and ocean melting processes occur, the topography and foundation on which the ice is located significantly affects the stability of the iceberg and its contribution to water. sea ​​rise.

The researchers split the Antarctic into two regions based on the relationship between the ice and the substrate below it. East Antarctica, the eastern region of the Transantarctic Mountains, is extremely high altitude and has the thickest ice sheet on the planet. The foundation below the ice sheet is also mostly above sea level. These features provide a relatively stable handlebar. On the other hand, West Antarctica has a lower elevation, and much of the ice there is thinner. Unlike the east, the West Antarctic ice sheet is located on rocky ground below sea level.

“In the West Antarctic, we have glaciers on underwater rocks. Like in Greenland, there is a warmer layer of seawater under the icy surface. So this warm water can flow into the shelf.” Continent, and later NASA Jet Propulsion Laboratory scientist Helene Seroussi said it all the way underneath the ice shelves – floating ice extending from glaciers and ice sheets. “The water melted. The ice from below can cause them to thin and break. “

The visualization shows how ocean currents flow around and under the Pine Island glacier in Antarctica. As water moves below the ice shelf, it erodes the ice shelf from below, making it thinner. Image created using ocean circulation model V3 “Estimation of ocean flow and climate” (ECCO), a surface elevation of 100 meters “Antarctic Reference Altitude Model” ( REMA) and 450 meter bottom topography and BedMachine Antarctic ice thickness Data set V1. The surface was mapped with views from NASA’s LandSat 8 satellite. Magnification factors 4 and 15 – above and below sea level respectively – are used for clarification. Image provider: NASA / Cindy Starr

That’s important because the ice racks act like a cork. They keep ice flowing from upstream again, slowing down access to the ocean, where it raises sea levels. When the ice shelves settle, the cork is essentially removed, allowing more inland ice to flow freely into the ocean. Furthermore, this leads to a retreat of the landing zone – the area where the ice separates from the platform and begins to float.

“The ground area delineates the floating ice, which is already included in the sea level budget from the ice above,” said ICESat-2 scientist Kelly Brunt of NASA’s Goddard Space Flight Center and the University of Maryland. ground without being included in the budget. “Floating ice is like a floating ice cube in a glass. It doesn’t overflow the glass when it melts. But when adding non-floating ice into the ocean, it’s like adding more ice cubes to a glass, this will cause the squid. water rises. “

The rock in the West Antarctic is also steep – that is, it is higher at the edge and gradually becomes deeper inland. So each time the land recesses to land, the thicker layer of ice comes into contact with ocean water and glaciers or ice sheets become grounded in deeper waters. This allows more ice to flow from upstream into the ocean.

“It is of interest to West Antarctica,” Brunt said, because when we push the grounding areas back, the slope goes down, the opposite means there is really no stop, nothing to do. interrupt this cycle of melt and retreat ”. “Our map of the foundation under the ice is not as comprehensive as in Greenland, partly because Antarctica has less people coming. So we really don’t know if there are any small protrusions or crests there. Couldn’t help slow the retreat process. “

Glaciers in the West Antarctic like Thwaites and Pine Island are receding faster than they used to. This is a problem because they provide a major pathway for ice from the West Antarctic ice sheet into the Amundsen Sea and raise the sea level.

Overall, melting and ice loss have increased rapidly 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 more we can accurately and accurately predict future sea level rise.

Contact Media News

Ian J. O’Neill / Jane J. Lee
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-2649 / 818-354-0307
ian.j.oneill@jpl.nasa.gov / jane.j.lee@jpl.nasa.gov

Written by Esprit Smith / NASA Earth Science News Group

2020-209


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