Icebergs the size of Singapore could be playing a bigger role in how much carbon the Southern Ocean absorbs than previously thought, a new study says.
Icebergs that break off Antarctica could
account for twice as much carbon dioxide stored in the Southern Ocean than previously believed, the study suggested. The findings were published this week in Nature Geoscience.
Pioneering research from the University of Sheffield’s Department of Geography discovered melting water from giant icebergs, which contains iron and other nutrients, supports hitherto unexpectedly high levels of phytoplankton growth.
These plankton blooms - which can stretch for hundreds of miles - then absorb a substantial amount of carbon dioxide from the atmosphere and lock it into the ocean depths.
Researchers examined 175 satellite photos of giant icebergs in the Southern Ocean which surrounds Antarctica and discovered green plumes stretching up to 1,000km behind them.
The surprise findings could have major implications for climate change predictions, as more carbon is 'sequestered' or locked away by the phytoplankton. This activity, known as carbon sequestration, contributes to the long-term storage of atmospheric carbon dioxide, therefore helping to slow global warming.
“If giant iceberg calving increases this century as expected, this negative feedback on the carbon cycle may become more important than we previously thought,” said Professor Grant Bigg at the University of Sheffield, who led the study published in the journal Nature Geoscience
Giant icebergs, defined as greater than 18km in length, make up half the ice floating in the Southern Ocean, with dozens present at any one time. The researchers calculated that the fertilisation effect of the icebergs in the normally iron-poor waters contributes up to 20% of all the carbon buried in the Southern Ocean, which itself contributes about 10% of the global total.
However, there is no salvation here — although it seems to be real, the iceberg feedback is relatively small in the grand scheme of things. The Southern Ocean overall sequesters about 0.2 gigatons of carbon every year, according to Bigg, out of about 10 gigatons emitted annually. And the large iceberg process may enhance this sequestration by 10 to 20 percent, the research suggested.