New research led by scientists at Rutgers University suggests that meltwater flowing from West Antarctica’s ice shelves delivers far less iron to the Southern Ocean than previously believed undermining the idea that glacier melt could naturally boost the ocean’s ability to absorb carbon dioxide.
The study, published in Communications Earth & Environment, challenges the popular “iron fertilization” hypothesis. That theory proposed that as Antarctica warms and glaciers melt, iron trapped in the ice would be released into surrounding waters, fueling blooms of phytoplankton microscopic marine plants that absorb heat-trapping carbon dioxide through photosynthesis.
But direct field measurements tell a different story.
Testing a Climate Assumption in the Field
In 2022, researchers traveled aboard the U.S. icebreaker RV Nathaniel B. Palmer to the Dotson Ice Shelf in the Amundsen Sea a region responsible for much of Antarctica’s contribution to rising sea levels. Their mission: to measure iron levels in meltwater at its source beneath the ice shelf.
By sampling seawater flowing into and out of the cavity beneath the ice shelf, the team calculated how much iron was added through glacial melting. The findings were striking.
Meltwater accounted for only about 10% of the dissolved iron leaving the cavity. The majority roughly 62% originated from deep ocean water, while another 28% came from sediments on the continental shelf.
In other words, nearly 90% of the dissolved iron flowing from beneath the ice shelf did not come from the melting ice itself.
Rethinking Antarctica’s Role in Climate Regulation
Iron plays an outsized role in the Southern Ocean ecosystem. Though sunlight is limited for much of the year, Antarctic waters support vast blooms of phytoplankton. These organisms form the base of the marine food web, sustaining krill, penguins, seals and whales. More importantly for the climate, they help remove enormous quantities of carbon dioxide from the atmosphere, making the Southern Ocean the world’s largest oceanic carbon sink.
Until now, much of what scientists believed about iron supply in the region was based on computer simulations. This study relied instead on direct sampling and chemical fingerprinting techniques to trace iron’s origins.
The results suggest that most iron in these waters is delivered by deep ocean currents specifically circumpolar deep water and from subglacial processes involving bedrock and sediments, rather than from the melting ice that contributes to sea-level rise.
Researchers also found evidence that oxygen-poor meltwater beneath glaciers may dissolve iron-rich minerals from bedrock more readily than previously understood, offering another potential source that is largely independent of ice shelf melting.
Implications for Climate Models
The findings complicate earlier assumptions that accelerated glacier melt could create a natural feedback mechanism to offset warming by stimulating carbon-absorbing algae blooms.
Instead, the study suggests Antarctica’s melting ice may not provide the climate benefit some researchers had hoped for. Scientists say the results could influence how future climate models account for iron cycling and carbon uptake in polar oceans.
As global temperatures continue to rise, understanding the precise mechanisms that regulate carbon in the world’s oceans is becoming increasingly urgent. This latest research underscores that Antarctica’s influence on climate is more complex and less forgiving than once believed.