Melt water cascading from the top of one of the icebergs
Icebergs drifting around Antarctica are 鈥渆cological hotspots鈥� that trigger blooms of carbon dioxide-absorbing phytoplankton, researchers say.
Far from being sterile chunks of floating ice, icebergs attract thriving communities of seabirds above the waterline, and a web of algae, krill and fish below, say researchers, who examined two large ice 鈥渋slands鈥� in the Weddell Sea.
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Algae in these mini marine ecosystems draw CO2 from the atmosphere for photosynthesis, and a portion of this is then sequestered in deep ocean waters.
鈥淲hile the melting of Antarctic ice shelves is contributing to rising sea levels and other climate change dynamics in complex ways, this additional role of removing carbon from the atmosphere may have implications for global climate models that need to be further studied,鈥� says Ken Smith, at the Monterey Bay Aquarium Research Institute (MBARI) in California, US, who carried out the study with colleagues.
Increased productivity
It is too early to say exactly how this phenomenon could affect the efficiency of the Southern Ocean carbon sink, Smith says. But, based on the new findings and satellite imagery, the Smith鈥檚 team estimates that icebergs may increase the biological productivity of the Weddell Sea by close to 40%.
Smith and his team examined the two icebergs in the Weddell Sea in early 2005, using a remotely operated underwater vehicle equipped with cameras. The frozen structures were up to 20 kilometres long, more than 40 metres high, and extended to 300 metres beneath the surface.
The researchers found increased concentrations of marine and bird life, in the form of phytoplankton, krill and seabirds (such as Cape petrels and Antarctic fulmars) around the icy platforms and for a radius of two miles.
鈥淗alo effect鈥�
They attribute this 鈥渉alo effect鈥� to a shedding of accumulated terrestrial material that fertilises the surrounding waters as the icebergs melt. The run-off appears to be rich in iron, which stimulates the growth of phytoplankton, the critical building block for the whole food chain.
鈥淭he Southern Ocean lacks a major source for terrestrial material due to the absence of major rivers. The icebergs constitute a moving estuary, distributing terrestrially-derived nutrients that are typically supplied by rivers in other areas of the oceans,鈥� said Timothy Shaw at the University of South Carolina, US, who was involved in the study.
The number of Southern Ocean icebergs has increased in the last decade as global warming has caused ice shelves to shrink and split apart.
Journal reference: Science (DOI: 10.1126/science.1142834)
