Physically modulated phytoplankton production and export at submesoscales in the oligotrophic South China Sea Basin

Zhonghua ZHAO ¹Mengdi XU ¹Bangqin HUANG ²Wenfang LU ³Hongshuai QI ⁴Feng CAI ⁴Yuwu JIANG⁵

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作者信息

1. State Key Laboratory of Marine Environmental Science,Xiamen University,Xiamen 361102,China;College of Ocean and Earth Sciences,Xiamen University,Xiamen 361102,China
2. State Key Laboratory of Marine Environmental Science,Xiamen University,Xiamen 361102,China;Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies,Xiamen University,Xiamen 361102,China;National Observation and Research Station for the Taiwan Strait Marine Ecosystem,Xiamen University,Xiamen 361102,China
3. School of Marine Sciences,Sun Yat-Sen University/Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519000,China
4. Laboratory of Ocean and Coast Geology,Third Institute of Oceanography,Ministry of Natural Resources,Xiamen 361005,China
5. State Key Laboratory of Marine Environmental Science,Xiamen University,Xiamen 361102,China;College of Ocean and Earth Sciences,Xiamen University Xiamen 361102,China;National Observation and Research Station for the Taiwan Strait Marine Ecosystem,Xiamen University,Xiamen 361102,China
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Abstract

Oceanic submesoscales can significantly influence phytoplankton production and export owing to their similar timescales of days.Based on two-year Biogeochemical Argo(BGC-Argo)observations,this study investigated the development of submesoscale instabilities,particularly symmetric and mixed-layer baroclinic instabilities,and their impacts on biological production and export in the oligotrophic South China Sea basin.In the northern basin,near-surface winter blooms consistently cooccurred with seasonally deepened mixed layers.However,significantly stronger and weaker winter blooms were observed over two consecutive winters within the BGC-Argo observation period.During the first winter,symmetric-instability-induced upward nutrient entrainment played a crucial role in initiating the strong winter bloom in early December,when the mixed layer was approximately 20-30 m shallower than the nutricline.This bloom occurred approximately 20-30 days earlier than that anticipated owing to the contact between the seasonally deepened mixed layer and mesoscale-cyclone-induced uplifted nutri-cline.The symmetric instability also facilitated the export of fixed phytoplankton carbon from the surface to deeper layers.Conversely,during the second winter,remarkably intense mixed-layer baroclinic instability associated with an intense mesoscale anticyclone led to more significant shoaling of the mixed layer compared to the nutricline,thus increasing the vertical distance between the two layers.Under this condition,upward nutrient injection,phytoplankton bloom,and carbon export were sup-pressed.In contrast,the BGC-Argo float in the central basin revealed significantly inhibited seasonality of phytoplankton biomass and submesoscale instabilities compared to those in the northern basin,primarily owing to the significantly shallower winter mixed layer.

Key words

Submesoscale instability/Phytoplankton/Nutrient transport/BGC-Argo/South China Sea

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基金项目

National Key Research and Development Program of China(2022YFA1004404)

National Natural Science Foundation of China(U22A20579)

National Natural Science Foundation of China(42306006 & 41876004)

出版年

2024

中国科学:地球科学(英文版)

中国科学院

中国科学:地球科学(英文版)

影响因子：1.002

ISSN：1674-7313

参考文献量1

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