Deep-sea study reveals iron limitations in ocean's twilight zone
by Clarence Oxford
Los Angeles CA (SPX) Sep 26, 2024

New research has shed light on the ocean's twilight zone, a region between 200 to 1,000 meters below the surface where iron deficiency limits the growth of bacteria. These microorganisms compensate by producing siderophores - molecules that help them scavenge trace amounts of iron from seawater.

"Understanding the organisms that facilitate carbon uptake in the ocean is important for understanding the impacts of climate change," explained Tim Conway, associate professor of chemical oceanography at the USF College of Marine Science. Conway, a co-author of the study, noted that organic matter sinking from the surface ocean acts as a biological pump, removing carbon from the atmosphere and storing it in the deep ocean.

During a recent expedition across the eastern Pacific Ocean from Alaska to Tahiti, researchers collected water samples from the upper 1,000 meters of the water column. They were surprised to find elevated concentrations of siderophores not only in surface waters but also between 200 and 400 meters deep, where bacterial growth was previously thought to be less affected by nutrient and iron levels.

"Unlike in surface waters, we did not expect to find siderophores in the ocean's twilight zone," said Conway. "Our study shows that iron deficiency is widespread for bacteria in the twilight zone, and that the bacteria use siderophores to increase their uptake of iron. This has a knock-on effect on the biological carbon pump, because these bacteria are responsible for the breakdown of organic matter as it sinks through the twilight zone."

This finding is part of the GEOTRACES program, an international initiative aimed at providing high-quality data to understand climate-driven changes in ocean biogeochemistry. Although research into siderophores is still in its early stages, this study highlights their role in nutrient movement within the ocean's twilight zone.

"For a full picture of how nutrients shape marine biogeochemical cycles, future studies will need to take these findings into account," said Daniel Repeta, senior scientist at Woods Hole Oceanographic Institution and co-author of the research. Repeta stressed that experiments should expand beyond surface waters to include the twilight zone.

Research Report:Microbial iron limitation in the ocean's twilight zone
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