A new study reveals that the flux of bioavailable iron from wind-blown dust of the Saharan desert is enriching the Western Atlantic regions, including the Amazon rain forest and coral reefs in the Caribbean, by enhancing their long-term productivity.
Over the past few decades, scientists have been observing natural ocean fertilization occurrences, like, plumes of volcanic ash, wildfire soot, and specifically desert dust. The sudden influx of these factors onto the sea surface spurs massive phytoplankton blooms. Apart from these events, the long-distance traveling of dust has steadily stimulated phytoplankton growth all year and in every basin.
While Iron is the most crucial micronutrient serving as a catalyst in ocean productivity, it is a limiting factor. This means that despite its importance, iron is relatively scarce in many parts of the ocean, hindering the growth of phytoplankton.
Interestingly, the study found that iron becomes more bioavailable the farther it travels through the atmosphere. The study also discovered that once the desert dust deposited on the ocean surface, Fe was lost, indicating its utilization by marine organisms.
“Our results suggest that during long-distance atmospheric transport, the mineral properties of originally non-bioreactive dust-bound iron change, making it more bioreactive. This iron then gets taken up by phytoplankton, before it can reach the bottom,” said Dr Timothy Lyons, a professor at the University of California.
“The transported iron seems to be stimulating biological processes much in the same way that iron fertilization can impact life in the oceans and on continents. This study is a proof of concept confirming that iron-bound dust can have a major impact on life at vast distances from its source.”
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This increase in iron bioavailability directly impacts phytoplankton, which thrive near the ocean surface by absorbing sunlight and nutrients. Researchers believe that these areas with enhanced iron bioavailability may be a factor in determining the loci of strong primary production.
To better understand the characterization, spatial trends, and grain size relationships, researchers selected the four key sites in the Northern Atlantic to track dust’s journey. Researchers used iron isotopes to identify the sources of these sites and examined the grain size to assess how bioavailable iron becomes over long distances. Researchers documented that dust-borne Fe at distant sites experiences enhanced atmospheric processing, like acid production due to interaction with light, which leads to increasing iron solubility.
These sites are located near the Cape Verde Plateau near the northwest African continental margin. The reason to select these sites is their proximity to the Northern Atlantic Ocean.
“We conclude that dust that reaches regions like the Amazonian basin and the Bahamas may contain iron that is particularly soluble and available to life, thanks to the great distance from North Africa, and thus a longer exposure to atmospheric chemical processes,” said Lyons.
Moreover, the research found no correlation between grain size and iron bioavailability, and not all dust-borne iron is bioavailable. The study also implies that bioavailable signatures of iron are yet to be explored systematically.
Journal Reference:
Kenlee, B., Owens, J. D., Raiswell, R., Poulton, S. W., Severmann, S., Sadler, P. M., & Lyons, T. W. (2024). Long-range transport of dust enhances oceanic iron bioavailability. Frontiers in Marine Science, 11, 1428621. DOI: 10.3389/fmars.2024.1428621