Saturday, June 23, 2007

Icebergs sink lower productivity claims of Southern Ocean

Due to the lack of rivers and little glacial runoff, there are limitations for nutrient runoff in the waters of the Southern Ocean surrounding Antarctica. The various biogeochemical trace elements, that is necessary for productivity within the ecological Antarctic systems.

According to a new study in this week’s journal Science these floating islands of ice – some as large as a dozen miles across – are having a major impact on the ecology of the ocean around them, serving as “hotspots” for ocean life, with thriving communities of seabirds above and a web of phytoplankton, krill, and fish below.

The icebergs hold trapped terrestrial material, which they release far out at sea as they melt. The researchers discovered that this process produces a “halo effect” with significantly increased phytoplankton, krill and seabirds out to a radius of more than two miles around the icebergs. They may also play a surprising role in global climate change.

“One important consequence of the increased biological productivity is that free-floating icebergs can serve as a route for carbon dioxide drawdown and sequestration of particulate carbon as it sinks into the deep sea,” said oceanographer Ken Smith of the Monterey Bay Aquarium Research Institute (MBARI), first author and principal investigator for the research.

“While 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,” added Smith.

“Phytoplankton around the icebergs was enriched with large diatom cells, known for their role in productive systems such as upwelling areas of the west coast of the U.S. or ice-edge communities in polar oceans. As diatoms are the preferred food for krill, we expect the changes in phytoplankton community composition to favor grazing as a key biological process involved in carbon sequestration around free-floating icebergs,” said oceanographer Maria Vernet from Scripps Institution of Oceanography at UC San Diego, one of the members of the research team.


This is of course important as the constraints on productivity is the limitation of the scarcest resource ie the Lieberg's Law of the Minimum: at any given instant, any metabolic process is limited by only one factor at a time; the nutrient in shortest supply relative to demand.

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