Large blooms of tiny marine plants called phytoplankton are flourishing in areas of open water left exposed by the recent and rapid melting of ice shelves and glaciers around the Antarctic Peninsula. This remarkable colonisation is having a beneficial impact on climate change. As the blooms die back phytoplankton sinks to the sea-bed where it can store carbon for thousands or millions of years.
Reporting recently in the journal Global Change Biology, scientists from British Antarctic Survey (BAS) estimate that this new natural 'sink' is taking an estimated 3.5 million tonnes* of carbon from the ocean and atmosphere each year.
Lead author, Professor Lloyd Peck from BAS says, "Although this is a small amount of carbon compared to global emissions of greenhouse gases in the atmosphere it is nevertheless an important discovery. 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."
Professor Peck and his colleagues compared records of coastal glacial retreat with records of the amount of chlorophyll (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 km2 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).
Professor Peck continues, "Elsewhere in the world human activity is undermining the ability of oceans and marine ecosystems to capture and store carbon. 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."
Phytoplankton use chlorophyll and other pigments to absorb sunlight for photosynthesis, and when they grow in large numbers, they change the way the ocean surface reflects sunlight. They are eaten by krill and are the foundation of the ocean food web. Animals such as sponges and corals also consume phytoplankton. They can live for decades to hundreds of years and when they die they form mats on the seabed that are buried under sedimentation.
*The 3.5 million tonnes of carbon taken from the ocean and atmosphere is equivalent to 12.8 million tonnes of CO2.
Global carbon dioxide emissions from fossil fuel combustion and land use change reached 8.7 billion tonnes of carbon in 2007.
Sea ice loss and retreat of coastal glaciers on the Antarctic Peninsula were studied using historical accounts, aerial photographs and satellite images. This shows that seven of the major ice shelves and 87% of the 244 marine glaciers have retreated over the past 50 years.
The 24,000 km2 of new open water is approximately the size of Vermont, New Hampshire, New Jersey, Belize or Israel.
A glacier -- is a 'river of ice' that is fed by the accumulation of snow. Glaciers drain ice from the mountains to lower levels, where the ice either melts, breaks away into the sea as icebergs, or feeds into an ice shelf.
Ice sheet -- is the huge mass of ice, up to 4km thick that covers bedrock in Antarctica or Greenland. It flows from the centre of the continent towards the coast where it feeds ice shelves.
Ice shelf -- is the floating extension of the grounded ice sheet. It is composed of freshwater ice that originally fell as snow, either in situ or inland and brought to the ice shelf by glaciers. As they are already floating, any disintegration will have no impact on sea level. Sea level will rise only if the ice held back by the ice shelf flows more quickly onto the sea.
- Peck et al. Negative feedback in the cold: ice retreat produces new carbon sinks in Antarctica. Global Change Biology, 2009; DOI: 10.1111/j.1365-2486.2009.02071.x
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