Bongo nets deployed by divers to collect marine snow. Photo Credit: J. Morin / NOAA
During the height of the COVID-19 pandemic, an international team of scientists launched an ambitious expedition to the North Atlantic to investigate how the ocean regulates Earth’s carbon cycle. The mission unfolded amid severe storms and unprecedented logistical hurdles that at times threatened to derail the effort entirely. Despite these challenges, the expedition yielded major scientific advances.
The resulting study, led by David Siegel — Distinguished Professor in UC Santa Barbara’s Department of Geography and principal investigator at UCSB’s Marine Science Institute — was published in Global Biogeochemical Cycles. The research deepens understanding of the ocean’s biological carbon pump, the process that moves organic carbon from surface waters into the deep ocean, where it can be stored for long periods. Importantly, the work goes beyond observation to predict carbon fluxes into the deep sea.
Central to this process is marine snow, aggregates of organic material that sink through the water column. Foundational research on marine snow was conducted in the 1980s by oceanographers Alice Alldredge of UC Santa Barbara and Mary Silver of UC Santa Cruz. Alldredge is Professor Emeritus in UCSB’s Department of Ecology, Evolution, and Marine Biology and is affiliated with the Marine Science Institute. Their work established how marine snow forms, sinks and breaks apart, revealing its critical role in exporting carbon from the ocean’s surface.
The EXPORTS (Export Processes in the Ocean from RemoTe Sensing) mission was designed to build on this legacy by connecting satellite measurements of ocean productivity with direct observations of what happens to that carbon below the surface. After a successful North Pacific campaign in 2018, the North Atlantic expedition was delayed by the pandemic and ultimately launched in April 2021 aboard three research vessels. Extensive coordination, vaccination efforts and continuous testing allowed the mission to proceed without a single COVID-19 case onboard. Reflecting on the effort, Siegel said, “It’s a friggin’ miracle that we pulled this off.”
Powerful storms during the cruise proved scientifically revealing. Turbulence broke marine snow into smaller fragments that sank more slowly, temporarily reducing carbon export. When conditions calmed, particles below the mixed surface layer recombined and descended, producing pulses of sinking material. As marine snow traveled deeper into the ocean, the team examined how it was broken down biologically.
UCSB Professor Alyson Santoro, a faculty member in the Department of Ecology, Evolution, and Marine Biology and part of the Marine Science Institute, along with her doctoral student Nicola Paul, analyzed observations showing that microbes accounted for less than half of the consumed marine snow. Their findings indicate that zooplankton are responsible for most of the breakdown — a process not yet fully represented in climate models.
It’s a friggin’ miracle that we pulled this off.
By capturing how marine snow responds to both physical forces and biological activity in the open ocean, the study helps explain persistent uncertainty in estimates of oceanic carbon storage. The next phase of EXPORTS will integrate these findings into global carbon-cycle and climate models, improving predictions of the ocean’s role in a changing climate.
Adapted from original reporting by Harrison Tasoff, “A stormy ocean voyage yields insights on the global carbon cycle,” The Current, UC Santa Barbara, 2025.