MIT researchers reveal how ocean eddies shape chlorophyll patterns across seasons and regions.
Reporting by Helen Hill for CBIOMES
A new study led by Alexandra Jones-Kellett and Michael Follows in the MIT CBIOMES Group sheds light on how swirling ocean eddies influence satellite-detected chlorophyll concentrations—and how these effects vary dramatically across space and time. Published in Ocean Sciences, the research offers a nuanced view of biological productivity in the subtropical gyres, one of the ocean’s largest and least understood ecosystems.
Subtropical gyres, vast rotating systems of ocean currents, are often perceived as biological deserts. Yet within these gyres, mesoscale eddies—circular currents spanning tens to hundreds of kilometers—can trap and transport nutrients and plankton, creating hotspots of biological activity. Understanding how these eddies affect chlorophyll, a proxy for phytoplankton biomass, is crucial for interpreting satellite data and modeling ocean carbon cycles.
Using a Lagrangian framework, which tracks water parcels as they move through the ocean, Jones-Kellett and Follows analyzed how eddy trapping influences chlorophyll signatures across the North Pacific Subtropical Gyre. Their approach allowed them to isolate the biological signal associated with water that remains inside eddies for extended periods, rather than simply comparing eddy centers to surrounding waters.
“By following water parcels within eddies, we can better understand the true biological impact of these features,” said Jones-Kellett. “It’s not the instantaneous plankton concentration in eddies that matters —it’s about how much is retained and for how long.”
The pair combined satellite chlorophyll data with eddy trajectories derived from sea surface height anomalies. They found that the chlorophyll signature of eddy trapping is highly variable, depending on both the region within the gyre and the season. In some areas, eddies consistently enhance chlorophyll concentrations, while in others, they suppress them or show no clear effect.
Seasonal differences were particularly striking. During winter and spring, when nutrient availability is higher, eddies tended to amplify chlorophyll signals. In contrast, during summer and fall, the biological response was muted or even negative, likely due to stratification and nutrient limitation.
The study also revealed that eddy polarity—whether an eddy rotates clockwise (anticyclonic) or counterclockwise (cyclonic)—plays a role, but not in a uniform way. While cyclonic eddies are traditionally associated with upwelling and nutrient enrichment, their impact varied depending on local conditions and the duration of water parcel trapping. In fact, the highest chlorophyll concentrations were observed in wintertime anticyclonic eddies generated in the Lee of the Hawaiian Islands.
“These findings challenge the idea of a one-size-fits-all view of eddy effects on productivity and chlorophyll” said Follows. “We need to account for regional and seasonal context to accurately interpret satellite observations and predict biological responses.”
The implications extend beyond academic modeling. Satellite chlorophyll data are widely used in climate studies, fisheries management, and carbon budget assessments. Misinterpreting the biological effects of eddies could lead to errors in estimating ocean productivity and carbon sequestration.
Jones-Kellett and Follows emphasize the importance of integrating Lagrangian perspectives into remote sensing and biogeochemical modeling. Their work highlights the dynamic nature of ocean ecosystems and the need for tools that capture the complexity of physical-biological interactions.
Publication
Jones-Kellett, A. E. and Follows, M. J. (2025), The satellite chlorophyll signature of Lagrangian eddy trapping varies regionally and seasonally within a subtropical gyre, Ocean Sci., doi: 10.5194/os-21-1141-2025