🌊 Iceberg melting is not at all producing what was expected

How is it that iron, normally essential for marine life, does not stimulate algae growth when it comes from West Antarctic icebergs? This intriguing question emerges from new research, published in Nature Geoscience, which challenges our ideas about the ocean's capacity to absorb carbon dioxide.

By analyzing sediment cores taken from the Southern Ocean, a team of researchers uncovered an unexpected link between ice sheet dynamics and biological activity. Their work shows that during warm periods of the past, the iron delivered by icebergs did not increase algae production as anticipated. This finding contradicts the hypothesis that an increased supply of this nutrient systematically promotes phytoplankton growth.


The team discovered that the iron transported by icebergs was frequently in a chemically altered form, made poorly soluble by prolonged weathering processes. Torben Struve, lead author of the study, indicates that this configuration of the iron makes it difficult for algae to use. Consequently, even in large quantities, biological productivity did not increase in the waters south of the Antarctic Polar Front.

This observation has direct implications for the Southern Ocean's capacity to capture carbon dioxide. Normally, increased algae growth leads to greater absorption of this greenhouse gas. Yet, the link appears to be broken here, a mechanism that could influence the future climate if the West Antarctic Ice Sheet continues its retreat.

The sensitivity of this ice sheet to high temperatures is illustrated by the sediment data. This data indicates that during the last interglacial period, approximately 130,000 years ago, a significant loss of ice generated many icebergs. These icebergs transported iron-rich sediments to the ocean, without however stimulating marine life.

Gisela Winckler, co-author of the publication, specifies that the chemical configuration of the iron is decisive, and not just its quantity. These results change our perception of the carbon pump in this region, where natural inputs may prove less effective than assumed.

With current global warming, increased thinning of Antarctic ice could reproduce these past conditions. Such a situation could reduce the absorption of carbon dioxide in the South Pacific, creating a mechanism likely to intensify climate changes. Scientists are closely monitoring this trend to better anticipate the interactions between the cryosphere and the ocean.