Iceberg A-23A, which has been trapped on the ocean floor for decades, is now free to drift north, toward warmer, iceberg-destroying waters. For decades, the A-23A iceberg has sat quietly off the coast of Antarctica, hidden from view. But in November 2023, attention was raised as the icebergs drifted north across the Weddell Sea - closer to shipping lanes, wildlife-inhabited islands and the warmer, iceberg-damaged waters of the Southern Ocean.
The MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite acquired this image of the iceberg on November 28, 2023, 37 years after the iceberg broke off from the Filchner Ice Shelf (located east of the larger Ronn Ice Shelf). On this day, the iceberg drifted near several islands at the tip of the Antarctic Peninsula, about 1,700 kilometers (1,000 miles) from its birthplace.
The iceberg broke off the Filchner continental shelf in 1986 and soon became stuck on the bottom of the southern Weddell Sea. For decades, the iceberg has been anchored about 200 kilometers (120 miles) from the ice shelf. The image above shows the path of the iceberg mapped using data provided by the National Snow and Ice Center since 2011. Notice that the initial trajectory of the iceberg is like a ball, driven by ocean currents and winds. Despite the impact of these forces, the A-23A basically stayed in place.
In the early 2020s, the iceberg began to break away from the seafloor, possibly due to melting below the waterline. By March 2023, it was floating freely alongside other large icebergs. Since then, it has drifted along the Weddell Sea Gyre (a clockwise rotating ocean current that pushes icebergs in the western Weddell Sea north) during the warmer months of the year.
Data from the U.S. National Snow and Ice Center shows that as of November 24, 2023, the iceberg covers an area of approximately 4,300 square kilometers (1,700 square miles). This makes it currently the largest iceberg in the world's oceans. Bigger icebergs come and go. For example, icebergs A-68 and A-76 briefly held the title of largest iceberg in 2017 and 2021 respectively, and then broke apart.
Past icebergs in the area, such as A-68A and A-76A, eventually broke free of the eddy's clockwise circulation and entered the Drake Passage, a body of turbulent water between South America's Cape Horn and Antarctica's South Shetland Islands. From there, they typically move north to the South Atlantic and melt rapidly in the region's warmer waters.
Picture of NASA Earth Observatory, author: Liang Wanmei, using MODIS data from NASA EOSDISLANCE and GIBS/Worldview as well as data from the Antarctic Iceberg Tracking Database. NASA/JPL - Worldview animation created by Caltech's Karin Kirk using MODIS imagery provided by NASA's Aqua and Terra satellites. Kathryn Hansen wrote the story, and Christopher Shuman of NASA/UMBC provided image interpretation.
Compiled source: ScitechDaily