Melting ice shelves give way to carbon-trapping plankton blooms

The rapid melting of Antarctic ice shelves and glaciers might be a worrisome indicator of climate change, but it’s also produced an unexpected upside: large blooms of phytoplankton that could end up storing lots of carbon on the seafloor.

Researchers with the British Antarctic Survey (BAS) have found that phytoplankton, tiny marine plants, are flourishing in areas of open water left exposed by melting ice around the Antarctic Peninsula. As those blooms die back, the phytoplankton will likely sink to the sea-bed, where their absorbed carbon could be stored for thousands or millions of years.

Reporting this week in the journal Global Change Biology, the BAS scientists estimate this new natural carbon sink is taking up about 3.5 million tonnes of carbon from the ocean and atmosphere each year. That’s the equivalent of 12.8 million tonnes of carbon dioxide.

For comparison’s sake, global carbon dioxide emissions from fossil fuel combustion and land use change reached 8.7 billion tonnes of carbon in 2007.

“Although this is a small amount of carbon compared to global emissions of greenhouse gases in the atmosphere it is nevertheless an important discovery,” said Lloyd Peck, lead author of the study. “It shows nature’s ability to thrive in the face of adversity. We need to factor this natural carbon-absorption into our calculations and models to predict future climate change. So far we don’t know if we will see more events like this around the rest of Antarctica’s coast but it’s something we’ll be keeping a close eye on.”

Peck and his colleagues compared records of coastal glacial retreat with records of the amount of chlorophyll (the green plant pigment essential for photosynthesis) in the ocean. They found that, over the past 50 years, melting ice has opened up at least 24,000 square kilometres of new open water (an area similar to the size of Wales) — and this has been colonised by carbon-absorbing phytoplankton.

According to the authors, this new bloom is the second-largest factor acting against climate change so far discovered on Earth (the largest is new forest growth on land in the Arctic).

“Elsewhere in the world human activity is undermining the ability of oceans and marine ecosystems to capture and store carbon,” Peck said. “At present, there is little change in ice shelves and coastal glaciers away from the Antarctic Peninsula, but if more Antarctic ice is lost as a result of climate change then these new blooms have the potential to be a significant biological sink for carbon.”