Phytoplankton swim near the ocean surface, feeding mainly on sunlight and mineral nutrients floating from the depths or dumped into the sea by coastal current. But mineral-rich desert dust carried by strong winds and deposited in the ocean also plays an important role in the health and abundance of phytoplankton.

Dust accumulation in the ocean accounts for about 4.5% of annual global exports – a measure of how much carbon is absorbed by phytoplankton that descends into the ocean during photosynthesis, according to a new study. However, in some parts of the ocean at mid and high latitudes, this contribution approaches 20-40%.

Phytoplankton play an important role in the Earth’s climate and carbon cycle. Like land plants, they contain chlorophyll and obtain energy from sunlight through photosynthesis. In the process, they produce oxygen and capture large amounts of carbon dioxide, potentially on a scale comparable to that of rainforests. And they’re at the bottom of the ocean’s food hierarchy, from tiny zooplankton to fish and whales.

Co-author Lorraine Refer, a research professor at the University of Maryland in Baltimore County, said dust particles can travel thousands of miles before falling into the ocean, where they feed on phytoplankton at great distances from the dust source. “We knew that the atmospheric transport of desert dust was part of what ‘clicks’ the ocean, but we didn’t know how to find it,” he said.

The color of the ocean tells a story

How do you monitor ocean biology from 400 miles above the Earth’s surface? Follow the green trail of chlorophyll. Study authors Toby Westberry and remote sensing oceanographers Michael Berenfeld at Oregon State University analyzed 14 years of ocean color measurements collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite from 2003 to 2016. they were able to determine not only when and where the phytoplankton explosion occurred, but also how healthy and abundant it was (in terms of chlorophyll concentration).

To determine whether phytoplankton is responding to desert dust, the team compared their findings on ocean color with data from NASA’s Goddard Earth Observation System (GEOS) model from dust deposition events over the same time period. The intensity of these events ranged from powerful dust storms in the Sahara to relatively weak clouds off the US West Coast. They found that even small amounts of desert dust increased the mass and health of phytoplankton blooms almost everywhere they looked.

Previous research has focused on major local events (volcanic eruptions, forest fires, extreme dust storms) that release large amounts of organic and mineral particles into the air. In other studies, researchers have deliberately encouraged phytoplankton growth by “seeding” iron, an important but often limited nutrient in the ocean, into seawater.

“We realized that the phytoplankton response is not limited to iron-poor regions of the ocean,” said co-author Hongbin Yu, a scientist at NASA’s Goddard Space Flight Center. “Reactions came from all over the world. Add some nutrients and something happens to the water.”

According to scientists, the beneficial properties of desert dust are not limited to iron. Dust particles contain other nutrients that plants need, especially phosphorus and nitrogen. More research is needed as climate change affects atmospheric conditions, soil moisture and other factors that affect the way dust enters the ocean, Roemer said.

“For me,” he added, “the most interesting thing about what we’re doing here is that oceanographers and atmospheric scientists sit at the same table.”