Ocean fronts are ubiquitous physical features that play a critical role in regulating marine biogeochemical cycles and climate. However, how frontal activity influences nitrogen cycles remains poorly quantified, particularly under varying frontal intensities and interannual climate variability. Based on five cruises covering seasonal and interannual scales (2018–2023) in the Beibu Gulf, we integrated satellite remote sensing data with in situ physical, chemical, and stable isotopic measurements, to investigate frontal‑driven nitrogen cycling. Our results show that nearshore nitrate dynamics are dominated by external inputs (mainly from sewage and manure, accounting for 63–70%), whereas offshore areas exhibit a distinct seasonal shift from assimilation dominance under stratified non‑frontal periods to concurrent assimilation and nitrification during winter frontal periods. Interannual comparisons reveal a strong positive correlation between frontal intensity and regenerated nitrogen contribution, with highest contribution (55%) during the strongest frontal activities in 2019, demonstrating that stronger fronts drive greater organic matter degradation and nitrogen regeneration. This relationship is modulated by ENSO activity, which influences frontal intensity through its effects on the intrusion of coastal currents. This study suggests that frontal intensity serves as a primary regulator of regenerated nitrogen production through enhanced degradation of organic matter, which may reduce carbon export and burial in coastal waters, particularly under future climate warming. These findings highlight the critical role of frontal activity in coastal nitrogen and carbon cycling, with implications for understanding how intensifying coastal fronts under global warming may alter nitrogen recycling and carbon export in coastal seas.
 

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