Icebergs typically get a bad rap (see: Titanic), but new research shows that giant icebergs — chunks that are more than 11 miles long — may increase oceans' ability to pull carbon from the atmosphere.
The Southern Ocean encircles Antarctica and acts as a carbon sink, accounting for roughly 10 percent of all the carbon drawn out of the atmosphere by oceans around the globe. But the Southern Ocean is low on iron, a nutrient that bumps up the growth of tiny marine organisms, called phytoplankton, that take in carbon from the atmosphere. When icebergs calve away from the Antarctic Ice Sheet, they drift through the ocean, leaving behind a trail of iron-packed melt in their wake that can seed phytoplankton growth. The largest icebergs can survive for years before completely melting.
In a new study published in Nature Geoscience, researchers from the United Kingdom sought to quantify the effect of melting icebergs on phytoplankton growth, and thus the carbon cycle. Over a 10-year period, the team measured chlorophyll levels — a common proxy for the photosynthetic phytoplankton — around giant icebergs that had broken away from Antarctica.
The researchers found that the water around the icebergs had 10 times the normal amount of chlorophyll, and those levels remained high up to a month after the iceberg had passed through. Researchers have long known that nutrient-packed icebergs could fertilize phytoplankton growth as they melt, but the new study shows the peak growth actually occurs anywhere from 30 to 600-plus miles away from the melting icebergs. So previous field campaigns that measured carbon drawdown near the massive chunks of melting ice were likely underestimating their effects, the authors note.
Several dozen giant icebergs are floating around the Southern Ocean at any given moment, and the authors estimate they could account for up to a fifth of all the carbon drawdown in the entire ocean.
As our warming climate melts the ice sheets and makes calving events more likely, the Southern Ocean may become an even greater carbon sink, and could in turn help to slow down climate change in the future.
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