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HYPOTHESIS AND THEORY article

Front. Mar. Sci.
Sec. Ocean Observation
Volume 12 - 2025 | doi: 10.3389/fmars.2025.1523434
This article is part of the Research Topic Advances in Remote Sensing Technologies for Ocean Ecology and Carbon Cycle View all 4 articles

Impacts of IOD and ENSO on the Phytoplankton's Vertical Variability in the Northern Indian Ocean

Provisionally accepted
Qiwei Hu Qiwei Hu 1*Xiaoyan Chen Xiaoyan Chen 2*Xianqiang He Xianqiang He 2Yan Bai Yan Bai 2Tingchen Jiang Tingchen Jiang 1Yu Huan Yu Huan 1Zhanlin Liang Zhanlin Liang 3
  • 1 School of Marine Technology and Geomatics, Jiangsu Ocean University, Lianyungang, China
  • 2 Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, Zhejiang Province, China
  • 3 State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences (CAS), Guangzhou, China

The final, formatted version of the article will be published soon.

    The Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) are the primary climatic modes that profoundly impact physical and biological processes in the Northern Indian Ocean (NIO). IOD-and ENSO-related vertical phytoplankton anomalies, however, remain poorly understood. Using the three-dimensional Chlorophyll a concentration dataset generated by a machine learning model, this study examines IOD-and ENSO-linked vertical phytoplankton anomalies over the entire euphotic layer (0-100 m) in the NIO during 2000-2019. Results reveal that IOD and ENSO trigger significant opposite changes in phytoplankton at 0-50 m and 50-100 m. The effects of IOD and ENSO on the vertical structure of phytoplankton are generally asymmetric, with anomalies at 0-50 m being significantly larger than that at 50-100 m. During summer and fall, the significant vertical phytoplankton anomalies in the Central Arabian Sea (CAS), Southern Tip of India (STI), and the Eastern Equatorial Indian Ocean (EEIO), are primarily related to IOD forcing. IOD-linked negative (positive) phytoplankton anomalies at 0-50 m (50-100 m) are driven by the westward propagating downwelling Rossby waves. During winter and spring, due to the local wind anomalies and shallower thermocline, the Seychelles-Chagos Thermocline Ridge (SCTR) is the only region where ENSO exhibits greater positive effects on phytoplankton at 50-100 m than IOD. Different from IOD, the ENSO-related wind reversal impedes subsurface upwelling in the STI and EEIO, thereby constraining vertical biological activity. These findings could shed light on how phytoplankton will respond to changing ocean dynamics under global warming.

    Keywords: IOD, Enso, Phytoplankton, Vertical structure, the northern Indian Ocean

    Received: 06 Nov 2024; Accepted: 15 Jan 2025.

    Copyright: © 2025 Hu, Chen, He, Bai, Jiang, Huan and Liang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence:
    Qiwei Hu, School of Marine Technology and Geomatics, Jiangsu Ocean University, Lianyungang, China
    Xiaoyan Chen, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, 310012, Zhejiang Province, China

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