Friday, May 23, 2014

Melting Ice Sheets Are Dumping Nutritious Iron into Earth's Oceans


It sure doesn't sound very much like a hidden benefit, but the large volumes of dissolved iron currently being released into the oceans from melting ice sheets might help take some of the hit out of global warming. This is according to a study out this week in the journal Nature Communications describing a feedback mechanism in which melting ice releases bioavailable iron, promoting the growth of phytoplankton (that are way into iron as a nutrient), which in turn act to capture atmospheric carbon while serving as a food source for seagoing animals.

Needless to say, capturing atmospheric carbon is a highly desirable thing within the general goal of keeping climate change in check. The researchers, concentrated around the UK's National Oceanography Centre, note that this particular iron source has been so far unconsidered. "The Greenland and Antarctic Ice Sheets cover around 10 percent of global land surface," says the study's lead author, Jon Hawkins, in a statement. "Iron exported in icebergs from these ice sheets have been recognised as a source of iron to the oceans for some time. Our finding that there is also significant iron discharged in runoff from large ice sheet catchments is new."

Note that there's a difference between the iron you might commonly think of and the stuff that's available as a nutrient. While iron is the fourth most-common element found in Earth's crust, it's usually found as one of the iron oxide minerals, which are unreactive and so limited in their usefulness for biological processes. They're just stupid rocks, in other words.

The good stuff, the highly bioavailable iron, is typically in short supply in Earth's oceans, at least from the perspective of phytoplankton. It's poorly soluble in water, and its main sources for ocean life include upwellings from deep, nutrient-rich water or places where deep water suddenly runs into a beach or shoal, thus eroding away solid material and the nutrients contained within. Places like these are where you find the oceans' largest marine habitats. Iron also winds up in our oceans via dust blown offshore from land masses and from icebergs, glaciers, and, indeed, melting ice sheets.

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