Surprising Research: How Melting Antarctic Ice Might Reduce an Ocean Carbon Sink

A new study reveals a surprising and worrying connection between melting Antarctic ice and the ocean's ability to absorb carbon dioxide. Published in the journal Nature Geoscience, the research suggests that iron released from breaking icebergs may not help algae grow as much as scientists previously believed. This could mean that as the planet gets warmer, a major natural carbon sink becomes weaker.

Scientists have discovered that historical changes in the West Antarctic Ice Sheet (WAIS) closely matched changes in algae growth in the Southern Ocean. However, this connection worked in an unexpected way. The key lies in the sediment carried into the ocean by icebergs that break off from West Antarctica. This sediment is rich in iron.

Iron is a vital nutrient that helps microscopic algae, known as phytoplankton, grow. These tiny organisms take in carbon dioxide from the air when they perform photosynthesis. For a long time, scientists believed that more iron from melting ice would lead to more algae and, consequently, more carbon being removed from the atmosphere.

However, when researchers analyzed a long cylinder of sediment, known as a core, taken from deep in the Pacific section of the Southern Ocean in 2001, they made a surprising discovery. They found that times with more iron did not align with faster algae growth. "Normally, more iron in the Southern Ocean would cause algae to grow more, which increases the ocean's intake of carbon dioxide," said lead author Torben Struve, who conducted the research at Columbia University. "But we found that wasn't the case in this area."

Why didn't the extra iron boost algae growth? The research team traced the answer to the chemical nature of the sediment carried by icebergs. Their analysis shows that much of the iron was highly "weathered." This means it had been chemically changed over very long periods of time, turning it into a form that does not dissolve easily in water.