Eddy-mediated aggregation of mesopelagic organisms in the North Atlantic

Mesoscale eddies, dynamic oceanic features that span tens to hundreds of kilometers, influence the distribution and behavior of mesopelagic organisms by modulating nutrient fluxes and primary productivity. These organisms play a key role in trophic interactions and biogeochemical cycles but remain understudied in the context of eddies. This study investigates the aggregation patterns and diurnal migration behaviors of mesopelagic organisms within CE and AE cores in the North Atlantic using advanced BGC-Argo backscatter data extraction techniques. Our results reveal distinct aggregation patterns and diurnal migration behaviors of mesopelagic organisms within eddies: in the North Atlantic Current region, mesopelagic organisms exhibit clear habitat partitioning. At AE cores and CE peripheries aggregation intensity shows a negative association with dissolved oxygen concentration, indicating that organisms tend to occupy relatively low-oxygen, stratified layers within the eddy environment. These layers are also generally warmer, suggesting that fine-scale hydrographic and biogeochemical gradients jointly structure habitat use. Diel vertical migration amplitudes are greater in eddy cores than in peripheries, with AE cores showing 1.13 times the range of CE cores. Aggregation tends to be stronger during the mature–decay phases compared with the formation stage, consistent with variations in the amplitude-to-radius ratio. Overall, these findings suggest that mesoscale eddies play a role in shaping the spatial distribution and vertical migration behavior of mesopelagic organisms through coupled physical and biogeochemical mechanisms, and by influencing habitat selection and behavioral patterns, eddies are likely to affect trophic coupling and midwater ecosystem dynamics, with implications for carbon transport and fisheries management.