A recent study has the potential to alter scientists’ perspectives on microbial activities in the deep ocean. These surprising results enhance our comprehension of climate change effects, particularly regarding the ocean’s carbon storage capabilities.
The ocean’s twilight zone is a vast, dark expanse and, as recent research reveals, it suffers from a lack of iron.
This area, situated 200 to 1,000 meters beneath the ocean surface, receives no sunlight, resulting in extremely low iron levels, a crucial micronutrient, that limit bacterial growth. To adapt to these conditions, bacteria produce molecules known as siderophores, which enable them to capture small quantities of iron from the surrounding seawater.
The findings could significantly alter the scientific understanding of microbial dynamics in the deep ocean while providing fresh insights into the ocean’s role in carbon absorption.
“Grasping the functions of organisms that aid in oceanic carbon absorption is vital for comprehending the effects of climate change,” explained Tim Conway, an associate professor of chemical oceanography at the USF College of Marine Science, who co-authored the study. “As organic material from the surface sinks to the depths, it acts like a biological pump, extracting carbon from the atmosphere and sequestering it in seawater and sediments. Analyzing the rates and mechanisms that affect this pump grants us a better understanding of how and where the ocean retains carbon.”
For their research, scientists gathered water samples from the top 1,000 meters of the ocean during a voyage across the eastern Pacific Ocean, traveling from Alaska to Tahiti. The results from these samples were unexpected. They found high levels of siderophores not only in surface waters, where iron is commonly low but also in the depths of 200 to 400 meters, an area previously thought to have minimal impact from iron and nutrient levels on bacterial growth.
“We didn’t anticipate finding siderophores in the ocean’s twilight zone like we did in the surface waters,” Conway remarked. “This study illustrates that iron deficiency is pervasive for bacteria in this area of the eastern Pacific Ocean and that these bacteria rely on siderophores to boost their iron absorption. This has a cascading effect on the biological carbon pump since these bacteria play a key role in decomposing organic matter as it descends through the twilight zone.”
This remarkable finding is part of the GEOTRACES project, an international initiative aimed at gathering high-quality data regarding climate-induced changes in ocean biogeochemistry.
The exploration of siderophores is still in its nascent phase. Researchers involved with GEOTRACES have only recently developed effective techniques for measuring these molecules in water, and they continue to investigate when and where microbes utilize siderophores for iron acquisition.
Despite being a new area of research, this study clearly illustrates the significant role that siderophores play in nutrient dynamics within the ocean’s twilight zone.
“To fully understand how nutrients influence marine biogeochemical cycles, future research will need to incorporate these findings,” noted Daniel Repeta, a senior scientist at the Woods Hole Oceanographic Institution and co-author of the study. “In essence, experiments conducted in surface waters should expand to include analyses within the twilight zone.”
This research received funding from the National Science Foundation and the Simons Foundation, while the U.S. segment of GEOTRACES is also supported by the National Science Foundation.
