The EXPORTS program is a large-scale multi-institutional effort led by NASA that brings together a variety of disciplines and perspectives—including ocean optics, remote sensing, and molecular biology—to deploy diverse state-of-the-art technologies to understand the transport of carbon from the surface ocean to the deep sea.

Kramer and Durkin joined EXPORTS field campaigns in the North Atlantic and North Pacific. With a team of researchers from MBARI, the University of Rhode Island, the University of Maine, and the University of California, Santa Barbara, they meticulously sorted the individual sinking particles sampled by sediment traps deployed at five depths between 100 to 500 meters (330 to 1,640 feet). Previous studies have typically examined bulk-filtered biomass, not individual particles. The team’s novel approach allowed them to compare finer details of how carbon was packaged and transported to the information contained in bulk particles. They then examined 18S rRNA gene sequences from phytoplankton sampled in surface seawater, bulk-filtered particles, and 800 individual particles of marine snow. These genetic tags allowed researchers to detect specific phytoplankton groups in the surface ocean and follow their transport into deeper waters where their carbon is sequestered.

Pairing the relative abundance of genetic sequences with chemical measurements of sinking carbon allowed the team to identify predictive relationships between the export of specific phytoplankton taxa and the magnitude of carbon flux with depth. They found that two key groups of phytoplankton—diatoms and photosynthetic Hacrobia—can be used to predict the magnitude of carbon export into the deep ocean.

The relationships found in this study expand the utility of satellite observations of the ocean. Satellites are the most powerful tool for visualizing marine processes on a global scale. New ocean color satellites, like NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) mission, are providing a fresh perspective on the ocean from space. PACE is equipped with a hyperspectral Ocean Color Instrument—a radiometer that allows scientists to quantify the pigments in different taxonomic groups of phytoplankton in the surface ocean. Scientists can now look for blooms of diatoms and Hacrobia, specifically, to develop better models that estimate carbon export to the ocean’s depths at a global scale.

Since both of the key phytoplankton groups identified here can be reliably detected with DNA sequencing and satellite observations, the relationship with carbon export can be tested in other regions and ecosystems. 

“Responding to the climate crisis will require major leaps forward in our ability to monitor the ocean ecosystem. We must find new ways to observe the processes occurring on the microscopic scale and integrate that perspective with the climate drivers occurring on the global scale,” said Durkin. “This work demonstrates the value of translating across scientific disciplines and physical scales. By identifying the tiny microbes inside marine snow particles, we can propose strategic use of our global observing technologies that may improve monitoring of the ocean carbon cycle.”

This research was funded by a Simons Foundation Postdoctoral Fellowship in Marine Microbial Ecology (Award #986836), NASA (grants 80NSSC21K0015, 80NSSC18K1431, and 80NSSC17K0716), and the David and Lucile Packard Foundation.

Research Publication:

Kramer, S.J., E.L. Jones, M.L. Estapa, N.L. Paul, T.A. Rynearson, A.E. Santoro, S. Sudek, C.A. Durkin. 2025. Sinking particles exporting diatoms and Hacrobia predict the magnitude of oceanic POC flux. The ISME Journal, 19(1): wraf105. https://doi.org/10.1093/ismejo/wraf105 

Story by Senior Science Communication and Media Relations Specialist Raúl Nava

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