During 2005, 2008 and 2009, researchers from more than a dozen institutions tracked individual icebergs in the Weddell Sea using satellite and GPS tracking devices dropped onto individual icebergs using a radio-controlled aeroplane. They also used a newly developed robotic instrument known as a Lagrangian sediment trap to collect particles of sediment, bits of dead algae, and other debris that drifted down from the waters under and around the iceberg. The trap was programmed to sink 600 meters below the ocean surface while a iceberg drifted overhead then rise back to the surface after it had passed. This allowed scientists to measure, for the first time, the amount of organic carbon sinking into the deep sea beneath large free-floating icebergs.

When they compared the amount of carbon sinking beneath the iceberg with the amount of carbon sinking in the open ocean nearby, the researchers found that about twice as much carbon sank into the deep sea within a 30-kilometre radius of the iceberg, compared with an open-ocean ‘control’ area.

The fertilising effect is due to iron-rich sediment that has eroded from the Antarctic continent and become trapped within the icebergs. As the icebergs melt, some of the iron dissolves in the sea water, creating a trail of iron-rich water that can be up to 19 kilometres long.

July 2011