Award: OCE-2023621

Overview:

This NSF-funded project investigated the functioning of the Biological Carbon pump, the sum of all biological processes that result in the sinking of organic matter to the deep ocean.  This mostly happens in the form of tiny sinking particles that transport organic carbon to depth and with it, contribute to removing CO₂ from the atmosphere. We specifically studied how the formation, transformation and sinking of these particles are influenced by small ocean animals called zooplankton. Some of these planktonic animals carry out vertical migrations many hundred meters deep during the day, only to return to the surface waters during the night to feed on their planktonic prey. But not all of the zooplankton migrate, some stay at a depth in the twilight zone of the water column and collect the sinking particles falling past them from above. These are called resident zooplankton.

Intellectual Merit:

Our project has uniquely contributed to the knowledge not only of these zooplankton, but also to the importance of individual groups and even species. We collected these animals during a total of 6 cruises from July 2021 till March 2023 in finely resolved depth layers in the upper 600 m at the Bermuda Atlantic Time-series Study (BATS) site in the Sargasso Sea south of Bermuda. This is a time-series station where since 1988 researchers have studied in monthly intervals the biology, physics and chemistry of this open ocean region. We participated in 6 of these regular cruises on the research vessel Atlantic Explorer (RVAE), spread out over two years, covering the spring, summer and fall seasons.   We combined the collection and identification of the zooplankton with the collection of sinking particles in three depths (150 m, 200m, 300 m) using the Particle Interceptor Traps (PITs) that are routinely deployed at BATS. We added special tubes to these traps that contained a gel that allowed us to collect,  identify and quantify  individual particles that sank into the traps.  We also collected live zooplankton and held them in the onboard laboratory on the Atlantic Explorer to be able to quantify the production of fecal pellets. Combined with their abundance in the different depth layers, this allowed us to quantify their combined fecal pellet production rate during the day and night.

 Some key findings:

• Species-specific vertical distributions of three main zooplankton groups, the abundant copepods Pleuromamma xiphias, planktonic snails (pteropods) and different krill species, revealed clear differences between migratory and resident taxa. This distinction allowed us for the first time to identify how behavior influences particle mediation and to quantify the role of individual zooplankton species in carbon flux.
• Fecal pellet production rates were significantly higher during nighttime periods compared to daytime.
• Zooplankton collected from 150 m depth and above produced the highest number of fecal pellets during the 8-hour incubation period across all taxa.
• Zooplankton fecal pellet production and flux were higher in spring and summer compared to fall.
• Distinct zooplankton taxa exhibited significant differences in both fecal pellet production rates and the carbon content of their pellets.
• Fecal aggregates and fecal pellets were the main contributors to carbon flux at most depths and seasons, except at 150m in spring and summer, where phytoplankton aggregates were predominant.

 This project successfully characterized the dynamics of sinking particles and carbon flux at the BATS site, a key location in the open Atlantic Ocean, and revealed significant seasonal and depth-related variations. We showed how zooplankton communities influence the formation, modification, and flux of these sinking particles and how the resident zooplankton communities influence particle transformations. Our findings highlight their importance in the ocean's carbon cycle and the biological carbon pump.

 Broader Impacts:

 A key broader impact was the creation of Keys to the Ocean, an interactive marine science learning game hosted on the widely accessed Ask A Biologist platform at Arizona State University. Purposefully designed for open access, the tool runs directly in a web browser—eliminating login or software barriers—and offers a flexible, engaging way for learners to explore ocean science. Since going live, the platform has attracted over 22,000 unique visits and recorded more than 14,000 active game sessions.

The project produced a virtual tour of the R/V Atlantic Explorer—a browser-based experience that introduces users to the ship’s layout and research capabilities. Developed by a Ph.D. student supported by the project, the tour reflects graduate student leadership in public-facing science communication and contributes to broader participation in STEM outreach.

The project also provided hands-on research experience to undergraduate and graduate students, who participated in field sampling, laboratory analyses, and data processing. These students gained valuable skills and knowledge that will benefit their future scientific careers.

We acknowledge the support of the ASU-Bermuda Institute of Ocean Sciences and the National Science Foundation for funding this research.

Last Modified: 08/15/2025
Modified by: Susanne Neuer