Desert Dust Storms May Impact the World's Oceans with More Nutrients

It turns out that dust storms in the desert may also impact the world's oceans. Scientists have found that particles from these storms that escape into the atmosphere blow to the Pacific where they then seed the water for phytoplankton.

"If there are changes to the sizes of the deserts in Asia, or changes in the way people are using land, there could be a larger source of dust to the ocean," said Chris Hayes, one of the researchers, in a news release. "It's difficult to predict how the whole ecosystem will change, but because the residence time [of iron] is very short, year-to-year changes in dust will definitely have an impact on phytoplankton."

Certain species of phytoplankton, such as cyanobacteria, require iron as a main nutrient to fuel nitrogen fixation and other growth-related processes. The researchers estimate that up to 40 percent of the ocean contains phytoplankton species whose growth is limited by the amount of iron available.

Desert dust, though, is one source of oceanic iron. That's why researchers decided to see what extent changing levels of dust would have on iron concentrations in seawater.

The researchers traveled to Hawaii to collect ocean samples at a station called ALOHA, which was the site of a long-term oceanography program. The researchers took a cruise into the open ocean and then spent two weeks collecting samples at varying depths.

The researchers then analyzed the samples for both iron and thorium, a chemical element that's found in dust alongside iron. Since it's difficult to determine the rate at which iron sinks from the ocean's surface to deep waters, the researchers believed that thorium might be a reasonable proxy.

So what did they find? The iron tends to stay within 150 meters of the ocean's surface for about six months before accumulating on larger particles and sinking to the deep ocean. This residence time leaves a relatively short period for phytoplankton to absorb the iron, which makes the organisms sensitive to the dust.

"Dust can change a lot from season to season-by an order of magnitude," said Hayes. "From satellite images, you can see big pulses of dust coming from these deserts. That could change with climate change, and different precipitation patterns. So we're trying to keep track: if it does change, will it have an impact?"

The findings are published in the journal Geochimica et Cosmochimica Acta.

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