Wednesday, October 17, 2018

As Arctic Sea Ice Declines, Phytoplankton Spreads North

A study released by the American Geophysical Union confirms that as Arctic sea ice declines phytoplankton blooms are expanding northward into ice-free waters. The big question is how this expansion will impact marine ecosystems in coming years.

The study, based on satellite imagery of ocean color, shows phytoplankton spring blooms in the Arctic Ocean’s central basin at low biomass, where none were found before, and expanding northward at a rate of one degree of attitude per decade.

Phytoplankton are microscopic organisms that form the base of the marine food web, indirectly feeding everything from small fish to whales. They live in water, consume carbon dioxide and release oxygen through photosynthesis, converting sunlight into chemical energy.

Decline in Arctic sea ice over the past several decades has resulted in areas of open water where phytoplankton can thrive. Researchers are not sure how the expansion of phytoplankton will impact the food web, but their results suggest the decline of ice cover is already impacting marine ecosystems in unforeseen ways, and that as phytoplankton spring blooms move north these changes could affect the fate of the Arctic Ocean as a carbon source or a carbon sink.

“If the ice pack totally disappear in summer, there will be consequences for the phytoplankton spring bloom,” said Sophie Renaut, a doctoral student at Laval University in Quebec City, Canada, and lead author of the study. “We cannot exactly predict how it will evolve, but we’re pretty sure there are going to be drastic consequences for the entire ecosystem.”

Phytoplankton growth is dependent on availability of carbon dioxide, sunlight, nutrients, water temperature and salinity, water depth and grazing animals, according to the NASA Earth Observatory. Phytoplankton in the Arctic Ocean typically bloom every spring. In the past, such blooms have not been found in the highest Arctic latitudes, because they were usually covered by sea ice.

To learn if sea ice declines had any effect on spring phytoplankton blooms, researchers used satellite observations of ocean color to track changes of blooms each spring from 2003 to 2013. They found that in spring and summer months, net primary productivity in the Arctic Ocean increased by 31 percent between 2003 and 2013, and that these blooms in the Barents and Kara seas north of Russia are expanding north at a rate of one degree of latitude per decade.

The research was shared by the American Geophysical Union via EurekAlert, the online publication of the American Association for the Advancement of Science. It was first published in Geophysical Research letters, a journal of the American Geophysical Union.

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