Huge Antarctic icebergs may slow global warming, study suggests

The biggest icebergs breaking offAntarctica unexpectedly help to slow global warming as they meltaway into the chill Southern Ocean, scientists say.

The rare Manhattan-sized icebergs, which may become morefrequent in coming decades because of climate change, release avast trail of iron and other nutrients that act as fertilizersfor algae and other tiny plant-like organisms in the ocean.

These extract carbon dioxide from the atmosphere as theygrow, a natural ally for human efforts to limit the pace of
climate change blamed on man-made greenhouse gas emissions.

Ocean blooms in the wake of giant icebergs off Antarcticaabsorbed 10 to 40 million tonnes of carbon a year, the studyestimated, roughly equivalent to annual man-made greenhouse gasemissions of countries such as Sweden or New Zealand.

Until now, the impact of ocean fertilization from the demiseof giant icebergs, defined as floating chunks of ice longer than18 kilometresor almost the length of Manhattan,had been judged small and localized.

"We were very surprised to find that the impact can extendup to 1,000 kilometres," (625 miles) from the icebergs, Prof.GrantBigg of the University of Sheffield, an author of the studypublished in the journal Nature Geoscience, told Reuters.

• Grant Bigg talks to Quirks & Quarks Jan. 16 at noon on CBC Radio One

Greener waters

The scientists studied satellite images of 17 giant icebergsoff Antarctica from 2003-2013 and found that algae could turnthe water greener for hundreds of kilometresaround theicebergs, with nutrients spread by winds and currents.

There are typically 30 giant icebergs floating offAntarctica at any one time they can linger for years. The
study said the giant icebergs had an outsized impact inpromoting ocean fertilization when compared with small icebergs.

Bigg noted that global man-made greenhouse gas emissions hadbeen growing at about two per cent a year. "If the giant icebergsweren't there, it would be 2.1 to 2.2 per cent," he said.

Ken Smith, an expert at the Monterey Bay Aquarium ResearchInstitute in California who reviewed Monday's study, said in anemail he found the new findings "convincing."

The Sheffield University scientists noted other estimatesthat the amount of ice breaking off Antarctica had gained byfive per cent in the past two decades and that it was likely torise in future with warming. That in turn could spur more oceanfertilization.

• Massive Antarctic iceberg heads for open ocean
• Antarctic iceberg break-off captured in NASA images