Glacier melt may play a role in reducing atmospheric carbon dioxide

Giant melting icebergs may be nutrient factories that are helping to slow the rate of climate change even as warmer weather melts them, a new study suggests.

The study, published in Nature Geoscience, found that the icebergs leave plumes of nutrient-rich waters in their wake – sometimes stretching for 1,000 kilometres behind them. These feed blooms of phytoplankton that thrive on the iron and other nutrients shed by the bergs.

These tiny algae or the animals that eat them die, they fall to the bottom of the ocean taking with the the carbon dioxide they have absorbed, reducing the amount of the gas in the atmosphere.

“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.

Giant icebergs, more than 18 kilometres in length, make up half the ice floating in the Southern Ocean.

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.

“We detected substantially enhanced chlorophyll levels, typically over a radius of at least four to 10 times the iceberg’s length,” said Bigg.

Back in 2014 Cosmos reported on a similar phenomenon in Greenland where glacier melt was providing a similar fertilisation service for the waters there (see There may be a bright side to glacier melt).

In that case, Jon Hawkings from Bristol University found high concentrations of iron beneath west Greenland’s glaciers. Iron is the fourth most abundant element in the Earth’s crust, and plenty accumulates in glaciers (where the Southern Ocean’s icebergs come from, too)  as they gouge their way across the landscape.