New research from the Amundsen Sea is reshaping scientists’ understanding of how key nutrients reach one of the planet’s most important marine ecosystems.
Scientists have long assumed that melting Antarctic ice shelves would release iron trapped in the ice, fertilizing surface waters and boosting phytoplankton growth. But a recent study focused on the Dotson Ice Shelf shows that meltwater contributes far less dissolved iron than previously thought.
(Figure: Chinni et al. 2026, Communications Earth and Environment)
Instead, most of this essential nutrient comes from deep ocean waters and seafloor sediments. The team compared water flowing into and out of the ice shelf cavity and used iron isotopes to trace its origin.
Iron limits biological productivity across much of the Southern Ocean, where phytoplankton form the base of the food web and help absorb atmospheric carbon dioxide. For years, increasing ice melt was expected to directly fertilize these surface waters.
The new findings challenge that view. Meltwater accounts for only about 10% of dissolved iron in waters flowing out from beneath the ice shelf. Around 62% is supplied by relatively warm Circumpolar Deep Water, while a further 28% comes from sediments as this water moves across the continental shelf.
(Figure: Chinni et al. 2026, Communications Earth and Environment)
Rather than acting as a major source, melting ice plays a more indirect role. Fresh meltwater adds buoyancy, helping lift iron rich deep water toward the surface in a process known as the meltwater pump.
The study also highlights a hidden source beneath the ice sheet. Chemical evidence points to subglacial systems as an important contributor of iron, released in low oxygen environments beneath grounded ice. The researchers note that meltwater itself carries relatively little iron, with much of its contribution linked to these subglacial processes.
As climate change accelerates ice loss in West Antarctica, the results suggest that future ocean productivity will depend less on meltwater itself and more on how melting influences ocean circulation and the movement of nutrients from the deep ocean. The findings could lead to revisions in climate and ecosystem models, which often overestimate the role of meltwater as a direct iron source.
Léa Zinsli, PolarJournal