Climate: Antarctic icebergs seen as key carbon sinks

Southern Ocean sequesters up to 10 percent of global carbon

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Giant Southern Ocean icebergs are key links in the carbon cycle, according to a new study. @bberwyn photo.

Staff Report

A new study by the University of Sheffield’s Department of Geography helps confirm the importance of giant Antarctic icebergs as key pieces in the global carbon cycle. The findings were published this week in Nature Geoscience.

The trails of fresh water from the melting slabs of ice contain iron and other nutrients, supporting unexpectedly high levels of phytoplankton growth, the study found.That biological activity, known as carbon sequestration, contributes to the long-term storage of atmospheric carbon dioxide, helping to slow global warming. In all, icebergs may responsible for storing up to 20 percent of carbon in the Southern Ocean, the researchers concluded.

Led by Professor Grant Bigg, the research team analyzed 175 satellite images of ocean color ā€” which is an indicator of phytoplankton productivity at the ocean’s surface ā€” from a range of icebergs in the Southern Ocean which were at least 18 km in length.

The images from 2003-2013 showed that enhanced phytoplankton productivity, which has a direct impact on carbon storage in the ocean, extends hundreds of kilometres from giant icebergs, and persists for at least one month after the iceberg passes.

“This new analysis reveals that giant icebergs may play a major role in the Southern Ocean carbon cycle,” Biggs said. “We detected substantially enhanced chlorophyll levels, typically over a radius of at least four-10 times the iceberg’s length.

“If giant iceberg calving increases this century as expected, this negative feedback on the carbon cycle may become more important than we previously thought,” he added.

The Southern Ocean plays a significant part in the global carbon cycle, and is responsible for approximately 10 percent of the ocean’s total carbon sequestration through a mixture of biologically driven and chemical processes, including phytoplankton growth.

Previous studies have suggested that ocean fertilization from icebergs makes relatively minor contributions to phytoplankton uptake of CO2.

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