Geoscience: Giant icebergs regularly slow deep water formation

The protruding tongue of the Mertz Glacier in the East Antarctic may have snapped off at regular intervals over the past 250 years according to a study published in Nature Communications. The findings suggest that the periodic calving generated giant icebergs every 70 years and these clogged up the local environment, reduced sea-ice production and slowed deep ocean circulation, which may have affected the global climate.

The Mertz Glacier Tongue protrudes tens of kilometres into the Southern Ocean and shelters a highly productive sea-ice environment on its leeward side. As the sea-ice is formed, large quantities of salt are expelled into the ocean, generating approximately 25% of the dense Antarctic bottom waters, which are responsible for driving heat and salt around the planet. In February 2010, a huge iceberg collided with the Mertz Glacier Tongue, breaking it off from the rest of the glacier, creating an 80 kilometre-long iceberg in the process, which inhibited local sea-ice formation. Whether this calving represents an isolated event or is part of a longer-term regime remains unclear.

Xavier Crosta and colleagues analyse fossilized plankton and chemical compounds - indicators of past changes in sea-ice production and deep water formation - from a 250-year long sediment core retrieved from the sea floor downstream of the Mertz Glacier. The authors reveal that sea-ice conditions and bottom water production varied at a periodicity of 70 years over the past two and a half centuries, suggesting a longer-term regime is in place.

Given the local dominance of the Mertz Glacier it is likely that these 70 year cycles are set by the glacier's calving dynamics, however, icebergs released from other nearby glaciers, in addition to regional patterns of atmospheric variability may also play a role.

doi: 10.1038/ncomms7642

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