Net Community Production Variability in Response to Changing Upwelling Intensity Before and After a Typhoon in the Southern East China Sea

Abstract

Continental shelves contribute approximately 30% of the ocean's net community production (NCP), significantly influencing the global oceanic carbon cycle. However, the regulation of NCP variability on continental shelves by physical processes, such as upwelling remains poorly understood. High spatial resolution mixed-layer O₂/Ar-NCP measurements were conducted using equilibrator inlet mass spectrometry in the southern East China Sea (ECS) before (6–9 July 2018) and after (13–17 July 2018) Typhoon “Maria.” The relationship between biological N₂O and O₂ in the water column was used to correct for the impact of upwelling and vertical mixing on O₂/Ar-NCP measurements (refined NCP, RNCP). Our study revealed that the periodic upwelling in the southern ECS relaxed before the typhoon and intensified afterward. This change in upwelling conditions corresponded to an increase in RNCP at the southern ECS from an average of 17 ± 11 mmol C m⁻² d⁻¹ to 99 ± 25 mmol C m⁻² d⁻¹. The N₂O-based correction improved the estimation of O₂/Ar-NCP measurements in upwelling regions. Without this correction, NCP values were underestimated, with the degree of underestimation increasing from 18 ± 9 to 80 ± 17 mmol C m⁻² d⁻¹ as upwelling intensified during our study period. We suggest that the upwelling regions within the mixed layer were net autotrophic before and after the typhoon, yielding valuable information for refining fishery models.