Climate Change: Desert Dust Storms Affect Phytoplankton Growth in the Pacific
Dust particles from the deserts of Mongolia and northern China are blown eastward to the Pacific during strong storms, where they then settle in the ocean for phytoplankton to feed on. These dust particles contain many valuable minerals, including nutrient-rich iron.
Phytoplankton species, such as cyanobacteria, require iron as a main nutrient to fuel nitrogen fixation and other growth-related processes. So, altering the amount of dust that is deposited throughout ocean waters could have a vast impact on phytoplankton, according to a news release.
"If there are changes to the sizes of deserts in Asia, or changes in the way people are using land, there could be a larger source of dust to the ocean," Chris Hayes, a postdoc in MIT's Department of Earth, Atmospheric, and Planetary Sciences (EAPS), said in a statement. "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."
The researchers estimate that up to 40 percent of the ocean contains phytoplankton species whose growth is limited by the amount of iron available. So they decided to test how changing the amount of dust deposited would affect the amount of iron available in ocean waters.
To do this, the team of researchers traveled to a station in Hawaii called ALOHA, where they collected ocean samples from varying depths for two weeks. So what did they discover?
After analyzing the samples for iron and thorium, a chemical element that's found in dust alongside iron, the researchers found that iron tends to stay within 150 meters of the ocean's surface for about six months before sinking deeper into the ocean.
According to their study, this is also the layer where phytoplankton resides. However, this amount of time does not give phytoplankton enough time to absorb it all, making them sensitive to any changes.
"Dust can change a lot from season to season -- by an order of magnitude," Hayes said. "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?"
Since phytoplankton naturally remove carbon dioxide from the atmosphere, monitoring iron deposits more closely could help scientists further understand the species' role in helping the fight against climate change.
"It's a very small part that we're getting more quantitative about," Hayes explained. "It's one piece that adds to trying to make the prediction: If there's more dust, will the ocean take up more carbon? That's a big-picture question that we can't totally answer with this, but we have one piece on the way to answering that."
This study was recently published in the journal Geochimica et Cosmochimica Acta.
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