Iceberg due to collide with island splits in 2

Satellite image cloud-covered sea, island visible, and large white area with one small piece separate.
A December 17, 2020, image shows iceberg A-68A after a piece broke from it. Experts with the European Space Agency said the split is likely due to a collision with shallow seabed off the shore of remote South Georgia Island. The berg is on a collision course with the island. Image via ESA.

The European Space Agency (ESA) reported on December 18, 2020, that giant iceberg A-68A has now broken into two pieces. One piece is city-sized (about 12 miles or 18 km long), and the other is much bigger (about 80 miles, or 135 km, long). The iceberg was previously Earth’s biggest iceberg, but is now second-biggest. It’s apparently still moving toward South Georgia Island, a remote, mostly uninhabited island in the South Atlantic, populated by seals and penguins. Scientists said the giant berg might or might not collide with the island this month, wreaking havoc near the island’s waters. ESA said:

New satellite images revealed yesterday that the iceberg has spun around in a clockwise direction, moving one end of the berg closer to the shelf and into shallow waters. In doing so, the berg could have scraped the seafloor, measuring less than 200 meters [650 feet] deep, causing an enormous block of ice to snap off the iceberg’s northern tip.

The new chunk of ice is around 18 km [11 miles] long and approximately 140 sq km [54 sq mi], around the same size as Seville, Spain, and can be seen detached from the main A-68A iceberg in the images. Despite its small appearance in the images, the new piece of ice is so large it will most likely be named A-68D by the U.S. National Ice Center in the coming days. Two other chunks of ice that previously broke off were named A-68B and A-68C.

The main A-68A iceberg is now approximately 3700 sq km [1400 sq mi] with a length of around 135 km [84 mi]. Having lost many other pieces of ice over the past weeks, A-68A has now lost its title as the world’s largest iceberg.

First place now passes onto the A-23A iceberg, which is currently stuck in the Weddell Sea, with a size of almost 4000 sq km [1500 sq mi].

Klaus Strübing, a scientist with the International Ice Charting Group, who’s been using satellite data to track the berg, thinks the iceberg might already be grounded on the land shelf surrounding South Georgia. He reported that as of December 13, part of the iceberg was in waters just 245 feet (76 meters) deep.

Time will tell if A-68A will stall on the shelf, or if the region’s complex ocean currents will carry the berg back out to sea and around the island, ESA said.

Illustration showing the island, its surrounding shallows and the iceberg's two parts near them.
A-68A’s position on December 17, 2020. Image via ESA.

The iceberg first broke from Antarctica’s Larsen C Ice Shelf in July 2017. Since then, it has traveled thousands of miles, and on December 14 lay around 75 miles (120 km) from South Georgia Island. If it stays on its current path, the iceberg – which is about the same size as the island itself – could ground in the shallow waters offshore this month, and cause real problems for the island wildlife and seafloor-dwelling life.

South Georgia Island is a British Overseas Territory in the South Atlantic. It’s part of a chain of smaller islands, known as the South Sandwich Islands.

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Map of iceberg's path, 2017 to 2020.
The map shows the different positions of iceberg A68-A over the course of its 3-year journey. The map also includes historic iceberg tracks, based on data from a number of satellites as part of the Antarctic Iceberg Tracking Database. The map shows that A-68A is following a well-trodden path for icebergs released from Antarctica. Image via ESA.

As the berg drifts menacingly close to South Georgia Island, scientists around the world are watching to see what the berg will do next. According to NASA’s Earth Observatory:

The concern is that the iceberg has approached the edge of the island’s submarine shelf, an area where waters become relatively shallow, measuring less than 200 meters (650 feet) deep. Scientists think the iceberg extends about that far below the water line, meaning it has the potential to snag the seafloor and become “grounded.” Biologists worry about the potential effect a grounded iceberg could have on the island’s wildlife, such as the ability for penguins to access food.

Penguins and seals need access to the sea to feed so the iceberg could easily block their foraging routes and life on the seafloor could be crushed if the berg grounds. The fear, according to ESA scientists, is that if the berg does anchor against the South Georgia coast, it could remain there for up to 10 years.

In just over three years at sea, Iceberg A-68A has moved generally northward, passing the tip of the Antarctic Peninsula and floating into what’s called “Iceberg Alley.” David Long, a remote sensing and polar ice scientist at Brigham Young University, has been tracking A-68A’s journey. He said that although more than 90% of all Antarctic icebergs are swept along this path from the Weddell Sea toward the South Atlantic Ocean, most just don’t survive the journey from the Weddell to South Georgia Island. But A-68A’s huge size has helped it survive the relatively warm, iceberg-killing waters of the South Atlantic that shrink and break up lesser bergs.

Diagram: iceberg with world-wide islands to scale.
The size of A-68A compared to islands from around the world. Image via Reuters.

Bottom line: Antarctic iceberg A-68A, formerly the biggest iceberg on Earth, has now split into two parts. The bergs are moving toward South Georgia Island, a remote, mostly uninhabited south Atlantic island populated by seals and penguins. Scientists think the smaller – but still city-sized – part might have struck the shallow seafloor around the island. The bergs could wreak havoc for living ecosystems near the island’s waters.

Via NASA Earth Observatory


December 20, 2020

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