Silt the cold sea


Greenland’s glaciers work like bulldozers, crushing and pulverizing rocks along the earth’s surface as they creep through valleys into coastal waters. The process produces a fine-grained powder of silt and clay called glacial flour that accumulates under and around glaciers. This powder often accumulates in deltas and in the meltwater lakes and streams that form along the edges of these slow-flowing rivers of ice. Because the particles are so fine, they are slow to sink and often stay suspended in water longer than other types of sediment.

The presence of silt can dramatically change the appearance of water. When sunlight hits water rich in silt, the particles absorb the shortest wavelengths: purples and indigos. Water absorbs the longer wavelengths: reds, oranges and yellows. This mostly leaves blues and greens scattering around our eyes, often giving the silty water a striking turquoise color. Water filled with glacial flour may also appear milky green or brown depending on lightning conditions and silt concentration.

The Operational terrestrial imager (OLI) on Satellite 8 acquired this image of glacial meltwater flowing from FrederikshÃ¥b Isblink and mixing with the darker waters of the Labrador Sea. FrederikshÃ¥b is a lobe piedmont glacier in southwest Greenland which descends from the Greenland ice sheet, winds through a series of valleys and nunataks, then flattens out into a delta along the coast. FrederikshÃ¥b’s ice dammed several adjacent valleys, turning them into large meltwater lakes filled with milky green water and glacial flour.

Ocean currents had carried two silt plumes about 40 kilometers (25 miles) to the south when Landsat 8 acquired this image on November 15, 2021. However, this was not the only day the satellites captured striking images of silty plumes extending into Labrador. Sea. November 10, an unusually narrow plume of sediment stretched over 180 kilometers (120 miles) to the east.

Silt plumes from FrederikshÃ¥b and other Greenland glaciers are actually quite common. According to satellite data analysis, Greenland delivers about 8 percent of all sediment deposited in the oceans each year, even though it provides only 1 percent of total freshwater. About 15 percent of Greenland’s glaciers, including FrederikshÃ¥b, provide more than 80 percent of all sediment on the island. Researchers also found evidence that the volume of suspended sediment delivered to the ocean by glaciers in this part of Greenland has increased dramatically in recent decades as the rate of retreat has accelerated.

While increasing rates of ice loss in Greenland are a worrying sign for future sea levels on Earth, some scientists believe that a growing abundance of glacial sand and flour deposited along Greenland’s coasts may have practical uses for Greenlanders. Sediment could be collected to help relieve global sand shortage, according to some researchers. Other scientists are investigating whether Glacial Flour from Greenland could be used as fertilizer for crops.

Image from NASA’s Earth Observatory by Joshua Stevens, using Landsat data from the United States Geological Survey. Story of Adam Voiland.


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