Massive iceberg breaks off from Antarctica

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In early July 2017, a massive section of ice split off from Antarctica’s Larsen C ice shelf.

Massive Iceberg breaks off from Antarctica
Date & Time
12/13/14 July 2017
Infrared Channel, Day-Night Band (DNB)

By William Straka III (CIMSS)

The Larsen C was the fourth largest ice shelf in Antarctica, with an area of about 44,200 km2. In August 2016, Project MIDAS, a UK-based Antarctic research project, noted the significant growth of a rift on the Larsen C ice shelf, which they had been monitoring using the MODIS instruments on the NASA Terra and Aqua satellites, plus the ESA Sentinel-1 satellite.

This rift continued to grow until sometime between 10 July and the morning of 12 July, 2017, when an iceberg finally calved from the ice shelf and was captured by the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the NOAA/NASA Suomi National Polar-orbiting Partnership (NPP) satellite. The US National Ice Center (USNIC) confirmed a new iceberg, using both VIIRS and Sentinel-1 imagery, and named it A-68.

A-68 measures 5,800 km2, or more than three times the size of the Greater London area. It weighs more than 1.1 trillion tons, or about twice the volume of Lake Erie, in Midwest America, and represents more than 10% of the Larsen C ice self.

Figure 2
Figure 2: Animated gif of VIIRS IR imagery showing breakage and movement of iceberg 12-14 July

Visible imagery from the Day-Night Band (DNB) on VIIRS, due to the fact that the moon at the time was a waning gibbous moon providing light, showed both the movement of A-68 after it fractured completely from the Larsen C ice shelf, as well as the calving of two smaller icebergs off A-68 (Figure 2).

The clear water between A-68 and the Larsen C ice shelf can be seen in both the infrared and DNB visible imagery of the fracture (Figure 3). In the case of the DNB imagery, the sea water can be seen as the dark area between the iceberg and the ice shelf. In the case of the infrared imagery, the open sea water appears as warmer (white) temperatures.

Image comparison
Day-Night Band, 14 July 04:30 UTC Infrared, 14 July 04:30 UTC
Figure 3: VIIRS I-band 5, 11 µm and Day-Night Band imagery.

Such breakoffs from the ice shelf are normal. However, this is one of the largest icebergs to have broken off the ice shelf. Because of a lack of measurements over the Larsen C ice shelf, there is much debate about if this event can be attributed in any way to climate change. In this case, A68 will not raise global sea levels, as it was already afloat in the Weddell Sea. Research will need to be done in order to see if the loss of this iceberg will speed up the collapse of the Larsen C ice shelf.

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