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Newswise — Submesoscale eddies serve as vital connectors within ocean circulation. Despite their significance, traditional satellite sensors have struggled to capture them due to their minuscule size. Prior studies have largely depended on computational models, leaving significant gaps in empirical observations. This limitation has driven the urgent need for high-resolution satellite data capable of accurately capturing SE distribution and their role in ocean dynamics.

on March 28, 2025, in , this pioneering research was conducted by scientists from the First Institute of Oceanography and the China Academy of Aerospace Science and Innovation. Utilizing data from the Interferometric Imaging Radar Altimeter (InIRA), the team examined SEs in the South China Sea from September 2016 to April 2018, unveiling their seasonal patterns and vertical heat transfer properties. By overcoming long-standing observational challenges, the study marks a milestone in understanding how these small-scale oceanic features influence global climate systems and marine ecosystems.

The study analyzed 264 swaths of InIRA data, revealing distinct characteristics of SEs. The study found that the numbers of cyclonic eddies (SCEs) and anticyclonic eddies (SAEs) are quite similar. However, according to the statistics, the former is larger in size. The average radii of the two types of eddies are 1.92 kilometers and 1.68 kilometers respectively. The findings indicated that SEs peak in summer and decline in autumn, coinciding with seasonal shifts in the South China Sea’s frontal systems. Notably, SEs were predominantly located at the peripheries of mesoscale eddies and oceanic fronts, where intense horizontal shear fosters their formation. The study further revealed that SEs contribute to substantial vertical heat flux, reaching up to 0.55°C—comparable to the impact of larger mesoscale eddies—suggesting their critical role in regulating oceanic heat transport and potentially influencing global climate patterns.

Employing high-resolution InIRA data with a spatial resolution of 40 meters, the researchers successfully detected SEs as small as 1 km in radius. A spatial bandpass filter was applied to isolate SEs within the 2-10 km range, ensuring precise identification. Additionally, surface drifting buoy data was incorporated to validate temperature fluctuations induced by SE activity, confirming their significant influence on surface heat budgets. Spectral analysis further reinforced these findings, identifying distinct temperature fluctuation patterns that aligned with SE occurrences, underscoring their role in oceanic heat dynamics.

Dr. Zexun Wei, the corresponding author of the study, emphasized the breakthrough nature of the research: "Our findings provide an unprecedented look into the role of submesoscale eddies in ocean dynamics. The high-resolution InIRA data has enabled us to observe these small but influential features in remarkable detail, revealing their substantial contributions to vertical heat transfer and marine ecosystems."

The study’s findings hold profound implications for climate modeling and marine resource management. By enhancing our understanding of SE behavior, the research supports improved predictions of oceanic heat transport—critical for climate change assessments. Furthermore, the role of SEs in nutrient distribution underscores their significance for marine biodiversity and fisheries sustainability. Future research could extend these methodologies to other oceanic regions, deepening our understanding of global ocean circulation. Integrating multiple satellite data sources will be crucial for advancing the study of submesoscale phenomena and their interactions with larger-scale oceanic processes.

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Funding information

This study is supported by the National Natural Science Foundation of China under grant 42006032, 42376034, Qian Xuesen Laboratory of Space Technology, CAST under grant GZZKFJJ2020005, CAS Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology under grant KLOCW2005.

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