Iceberg A-23A has had a more eventful run than most of the large Antarctic icebergs that have calved from the continent’s ice shelves in recent decades. Over its winding, forty-plus-year journey, the “megaberg” spent decades grounded in the Weddell Sea before drifting north, twirling in an ocean vortex for months, and nearly colliding with an island in 2025.
By 2026, the iconic iceberg, sopping with meltwater and shedding smaller bergs as it moved into warmer ocean waters, put on one more show. The chunks of ice and frigid glacial meltwater left in its wake appear to have fueled a surge in phytoplankton abundance, known as a bloom, observed in surface waters by NASA satellites.
Phytoplankton, which harvest sunlight to carry out photosynthesis, form the base of the marine food web. They also produce up to half of the oxygen on Earth and serve as part of the ocean’s “biological carbon pump,” which transfers carbon dioxide from the atmosphere to the deep ocean.
The VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite captured this image (left) of the splintering tabular berg on January 25, 2026. The image was acquired after several large pieces had drifted northwestward and then curled toward the northeast following the iceberg breaking apart on January 9. A debris field full of brash ice, small icebergs, and bergy bits was visible east of the largest remaining pieces. Also on January 25, the OCI (Ocean Color Instrument) on NASA’s PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) satellite detected plumes of chlorophyll-a (right) drifting around the remaining bergs and debris field. Researchers use chlorophyll concentrations as a marker of phytoplankton abundance.
“This bloom is too big and too clearly spreading from the icebergs not to be strongly linked to them,” said Grant Bigg, an emeritus oceanographer at the University of Sheffield. Bigg, who has studied how large icebergs have enhanced phytoplankton activity in this region, noted that while blooms unconnected to icebergs do occur regularly here, satellite imagery shows a connection that has persisted for weeks—increasing his confidence that the iceberg and phytoplankton bloom are related.
The primary factors that limit phytoplankton in th …