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Dust from Asia fertilizes the North Pacific Ocean

Large systems of ocean currents called gyres cover 40 percent of the Earth’s surface and are comprised mainly of nutrient-poor waters.

However, the North Pacific Subtropical Gyre is an anomaly when compared to other nutrient-poor gyres. Oceanographers have recorded inconsistent spikes in iron and phosphorous levels, which in turn impacts biological productivity in the region.

These chemical spikes impact the overall nutrient composition by turning the typically nutrient-poor waters to a nutrient-rich oasis. Now, researchers have finally tracked the source of this sporadic “fertilization” of the North Pacific Subtropical Gyre.

Researchers from Oregon State University and the University of Hawaii reviewed 30 years of data from the from Station ALOHA, a six-mile portion of the Pacific Ocean that is used in many ocean monitoring projects and research.

The North Pacific Subtropical Gyre is made up of clear waters that allow sunlight to reach deep below the surface.

Marine organisms take advantage of what little nutrients there are to be had in these upper ocean layers, and thousands of feet below life is sustained by the decaying and dead organisms that sink from the surface.

The researchers found that wind patterns carrying dust from Asia occasionally fertilize the North Pacific Gyre, which increases nutrient levels at the surface.

Asian dust transport over the North Pacific. Image Credit: Robert Simmon/NASA

“We now know that these areas that were thought to be barren and stable are actually quite dynamic,” said Ricardo Letelier, a leader of the study. “Since these areas cover so much of the Earth’s surface, we need to know more about how they work in order to better predict how the system will respond to climate variations in the future.”

Iron and phosphorus are key nutrients in marine ecosystems, supporting life at the surface and deep below. Both phosphorus and iron levels changed drastically throughout the years reviewed for the study.

The researchers linked these changes in nutrient levels to iron deposited in the ocean, which was carried from Asia with other dust particles. Desertification, wildfires, and industrial activity all contribute to the varied nutrient levels in the North Pacific Gyre.

The Pacific Decadal Oscillation also plays a role in this relationship, the researchers found. During years with low atmospheric pressure over the northeast Pacific, winds are stronger and carry more dust.

“Sometimes there are periods of 5-6 years of phosphorus enrichment, and then there are periods when it switches over,” said Letelier. “From 2000 to 2007, there was almost no phosphorus. We have seen some changes in the function of the ecosystem, but we haven’t yet seen significant changes in the biological composition. They may be coming; it’s too early to tell.”

Climate change and pollution could impact wind patterns and dust deposits in the North Pacific Gyre, which could threaten the marine organisms that feed on nutrients at the surface.

The researchers published their findings in the journal Proceedings of the National Academy of Sciences.

By Kay Vandette, Staff Writer

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Image Credit: Shutterstock/DiegoMariottini

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