Long-Lived Iceberg Sails Away

An enormous iceberg located off the Antarctic coast for more than two decades finally started moving out to sea in late 2022. With the longtime nearshore feature now gone, scientists are waiting to see if the change will affect nearby Thwaites Glacier—one of the largest contributors to global sea level rise from the West Antarctic Ice Sheet.

The iceberg on the move is known as B-22A. Measuring more than 3,000 square kilometers as of March 2023, it is the largest-remaining piece of the Rhode-Island-sized berg that broke from Thwaites Glacier in early 2002. In the decades since being set adrift in the Amundsen Sea, B-22A has stayed relatively close to Thwaites Glacier. It became stuck (grounded) by 2012, and has remained parked in a relatively shallow part of the sea just 100 kilometers (60 miles) from its birthplace; that is, until recently.

In autumn 2022, Iceberg B-22A broke from the seafloor and started to drift northwest. The movement is visible in this animation, made with images from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA’s Terra and Aqua satellites. It shows the berg sailing away from the continent between October 24, 2022, and March 26, 2023. During this time, B-22A drifted about 175 kilometers (110 miles). (Thwaites Glacier is located off the top of these images.)

It is uncommon—but not unheard of—for an iceberg to persist for so long. “Twenty-plus years is a long-lived iceberg, generally speaking,” said Christopher Shuman, a University of Maryland, Baltimore County, glaciologist based at NASA’s Goddard Space Flight Center. Its unmooring is also notable because of what it might mean for the future of Thwaites Glacier. Grounded icebergs play an important role in stabilizing the area’s sea ice, which in turn helps to buttress glacial ice onshore and slow its flow into the sea. While icebergs do not contribute to sea level rise (because they are already floating in the ocean), land ice from glaciers does contribute.

Several factors likely helped the iceberg get moving again. Shuman said that warm waters reaching into the Amundsen Sea Embayment have likely been thinning the berg from below since it broke free from Thwaites. Such thinning could have helped it lose contact with the shallow seafloor and allow it to be carried away by wind, waves, and tides.

By mid-April, the polar darkness of Antarctica’s austral winter had almost fully engulfed this part of Antarctica. Several satellite instruments can still “see” the berg even in the dark, but new natural-color images will have to wait until sunlight starts to return in late August.

NASA Earth Observatory video by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Kathryn Hansen.

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