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Plankton bloom, glacial meltwater link more complex than thought

"The fertilizing effect of the upwelling works only for a certain depth range of the glaciers terminating in the sea," researcher Mark Hopwood said.

By Brooks Hays
The research of Mark Hopwood showed meltwater from Greenland glaciers doesn't always fuel plankton blooms. Photo by Thomas Juul-Pedersen/GCRC
The research of Mark Hopwood showed meltwater from Greenland glaciers doesn't always fuel plankton blooms. Photo by Thomas Juul-Pedersen/GCRC

Aug. 14 (UPI) -- Glacial meltwater can fuel plankton blooms, but new research suggests the link between ice loss and algae isn't as straightforward as scientists previously thought.

According to a new study published in the journal Nature Communications, the depth of the glacier from which the meltwater originates determines whether the runoff will encourage or curb plankton blooms.

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Algal blooms off the coast of Greenland peak during the summer months, when meltwater rates increase. And previous studies have suggested the latter accelerates the former.

During recent surveys, however, scientists found evidence that inland glacial retreat precipitated decreases in plankton blooms -- the inverse of what many scientists expected.

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When researchers reexamined the relationship between meltwater and plankton, they realized they dynamic was more complex than they had realized.

"The main nutrient that plankton lack around Greenland is nitrate, while glacier meltwater contains mostly iron and silicon," Mark Hopwood, chemical eceanographer at the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany, said in a news release.

To understand the meltwater-plankton relationship, scientists looked to more accurately characterize the impact of meltwater on nutrients in Greenland's coastal waters.

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Many glaciers extend several hundred feet below the ocean surface. Meltwater enters the ocean at the bottom of glaciers, and because it is less dense than sea water, it rises to the surface. This process causes upwelling, which brings deep-lying water, rich in nitrates, to the surface.

But not all meltwater enters at the same depth. Some glaciers terminate at shallower depths than others. Only meltwater flowing under sufficiently deep glaciers trigger upwelling, while meltwater entering at shallower depths may prevent sufficient upwelling.

"The fertilizing effect of the upwelling works only for a certain depth range of the glaciers terminating in the sea," Hopwood said. "This depth is likely to vary regionally but is generally between about 700 and 500 meters."

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The researcher's investigation of the meltwater-plankton relationship helped them build more accurate models to describe the dynamic and predict the role different factors sources play in fueling plankton blooms. The latest data suggest upwelling is responsible for 90 percent of plankton bloom growth, while the nutrients provided by meltwater account for only 10 percent of the growth.

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