An Antarctic lake suddenly disappears


Landsat 8 images over the South Amery Ice Shelf show the lake covered before and after

Landsat 8 images over the South Amery Ice Shelf show the lake covered before and after
EP

A large, deep, ice-covered lake has rapidly disappeared on the surface of an Antarctic ice shelf, probably due to the water’s own weight.

East rare event, narrated in a study published in the journal Geophysical Research Letters, occurred during the Antarctic winter of 2019 on the Amery Ice Shelf in East Antarctica, and an estimated 600-750 million cubic meters of water, roughly double the volume from San Diego Bay, they were lost in the ocean.

The study authors – including several from the Scripps Institute of Oceanography at the University of California, San Diego – used images from a radar satellite that can “see” during polar night to time the event to a week or less in June. . After the drainage, instead of the lake, there was a crater-shaped depression in the surface of the ice shelf, covering about eleven square kilometers. This depression on the surface, known as the ice “sinkhole,” contained the fractured remains of the ice sheet.

We believe that the weight of the accumulated water in this deep lake opened a fissure in the ice shelf below the lake., a process known as hydrofracturing, which causes water to drain into the ocean below, “said lead study author Roland Warner, a glaciologist with the Australian Antarctic Program at the University of Tasmania.

The hydrofracture process has been implicated in the collapse of smaller ice shelves in the Antarctic Peninsula, where meltwater forms on the surface of ice shelves during the austral summer, but is not often seen breaking through 1,400 meter thick ice at this location on the Amery Ice Shelf.

The southern winter event was also captured by a green light laser instrument on the ICESat-2 of the POT. This satellite transmits pulses of photons and precisely locates the point of reflection of each photon it receives from Earth.

Repeating orbits of ICESat-2 on the exact ground tracks before and after the lake’s drainage revealed the vertical scale of the disruption. The ice surface fell up to 80 meters into the sinkhole, even though the loss of water load caused the floating ice shelf to become lighter and the pressure of the ocean caused it to flex upward, and the immediate surroundings of the lake rose as much as 36 meters.

In recent decades, with rising air temperatures, some ice shelves have experienced greater surface melt, and the most recent model projections for future warming show that this trend continues and creates more melting lakes. This increases the risk of widespread hydrofracture, which could cause ice shelves to collapse, allowing more rapid discharge of ice from grounded ice sheets and rising sea levels. Now, potential increased flows into deep, ice-covered lakes and hydrofracturing of thick ice shelves should also be considered in projections for future warming, the researchers said.

The team also used surface elevation maps generated by the Polar Geospatial Center (PGC) at the University of Minnesota. to show that the disruption modified the regional landscape by 60 square kilometers.

The amount of water lost to the ocean was calculated using the volume of the cavity and the extent of the uplift. While the Amery Ice Shelf has many melt lakes and streams in the austral summer, the amount of water lost when the lake drained was many times greater than the annual meltwater inflow.

The elevation of the lake created a new lake from a shallow arm of the original. During the following thaw season, this lake filled in a few days to more than a million cubic meters per day and overflowed into the cavity of the sinkholes. When ICESat-2 re-crossed the sinkhole a few days later, the team was able to measure a 20-meter wide meltwater channel, freshly cut into the sinkhole, detecting the surface of the water at a depth of three meters and scattered photons from the sinkhole. creek bed another three meters below.

The authors say that it is too early to conclude that the drainage of this meltwater lake was related to broader trends such as climate warming around Antarctica.

“This abrupt event was apparently the culmination of decades of accumulation and storage of melt water under that insulating cap of ice,” said co-author Jonathan Kingslake, a professor at the Lamont Doherty Earth Observatory at Columbia University.

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