WOODS HOLE, Mass. — Some of the ocean’s tiniest organisms get swept into underwater currents that act as a conduit, shuttling them from the sunny surface to darker depths, where they play an important role in carbon cycling and other ecosystem dynamics, according to new research.
Published this week in Proceedings of the National Academy of Sciences and based on fieldwork during three research cruises spanning 2017 to 2019, the study focuses on subtropical regions in the Mediterranean Sea. It uncovered how some microscopic single-celled organisms that are too light to sink beyond 100 meters or so — like phytoplankton and bacteria — end up going deeper into the ocean, where there's not enough sunlight for these photosynthetic organisms to live.
Lead author Mara Freilich on a research vessel during a sampling trip. Credit: Amala Mahadevan"It's often a one-way trip for these organisms, but by taking this trip, they play a critical role in connecting different parts of the ocean,” said first author Mara Freilich, who is now an assistant professor in Brown University’s Division of Applied Mathematics and Department of Earth, Environmental and Planetary Sciences.
Freilich conducted the research during her Ph.D. in the joint MIT-Woods Hole Oceanographic Institution (WHOI) doctoral program with Amala Mahadevan, senior scientist at WHOI, in a close collaboration with Alexandra Z. Worden, senior scientist at the Marine Biological Laboratory, and her team.
The currents the team found are called intrusions. By sweeping up tiny organisms, they help change the types of food available in the deeper layers of the ocean while also transporting a significant amount of carbon from the water surface. This helps feed other organisms in the ocean’s food chain and increases the complexity of the ecosystem at deeper depths, influencing how life and chemistry work underwater.