Journal of Tropical Oceanography ›› 2023, Vol. 42 ›› Issue (1): 43-55.doi: 10.11978/2022019CSTR: 32234.14.2022019

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A study of the regional size-fractionated primary production algorithm based on phytoplankton absorption coefficient and photosynthetically active radiation in the South China Sea

ZHAO Hongwuyi1,2(), ZHOU Wen1,3(), ZENG Kai1,2, DENG Lin4, LIAO Jianzu5, CAO Wenxi1,3()   

  1. 1. State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
    2. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
    3. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
    4. School of Marine Sciences, Sun Yat-sen University, Guangzhou 519082, China
    5. School of Chemistry and Environmental Sciences, Guangdong Ocean University, Zhanjiang 524088, China
  • Received:2022-01-29 Revised:2022-05-29 Online:2023-01-10 Published:2022-05-31
  • Contact: ZHOU Wen, email: wenzhou@scsio.ac.cn;CAO Wenxi, wxcao@scsio.ac.cn
  • Supported by:
    Major Special Innovation Team Project of Guangdong Provincial Laboratory of Southern Ocean Science and Engineering(Guangzhou)(GML2019ZD0305); Major Special Innovation Team Project of Guangdong Provincial Laboratory of Southern Ocean Science and Engineering(Guangzhou)(GML2019ZD0602); National Natural Science Foundation of China(41976170); National Natural Science Foundation of China(41976172); National Natural Science Foundation of China(42276181); National Natural Science Foundation of China(41976181)

Abstract:

Marine primary production is an important part of the ocean carbon cycle, affecting biogeochemical cycles and global climate change. Phytoplankton, as the main contributor to marine primary production, can be classified as micro- (>20μm), nano- (2~20μm), and pico- (<2μm) phytoplankton depending on particle size. Different phytoplankton size classes contribute differently to primary production (PPsize) and thus play different roles in the oceanic circulation of matter or energy and ocean carbon cycle. Based on the bio-optical dataset collected at 12 stations in the western South China Sea in 2019, this study presented the spatial variability of size-fractionated primary production and chlorophyll a concentration of phytoplankton and their percentage contribution. The size-fractionated primary productivity of phytoplankton was well estimated from the product of size-fractionated phytoplankton absorption coefficient at 670nm [aph-size(670)] and photosynthetically active radiation (PAR) [aph-size(670)×PAR]. The coefficients of determination R2 between log[aph-size(670)×PAR] and log(PPsize) were 0.64, 0.76, and 0.67 for the micro-, nano-, and pico-phytoplankton dataset, respectively. The cross-validation of the algorithm based on the size-fractionated phytoplankton absorption coefficient and PAR has shown a good generalization performance. This algorithm could better predict the size-fractionated primary productivity compared to the size-fractionated phytoplankton absorption coefficient as the only input. This result indicates that PAR is one of the important factors to estimate the size-fractionated primary productivity. Meanwhile, the performance of the chlorophyll a concentration-based algorithm for estimating primary productivity at each size was closer to that of the algorithm constructed in this paper for both micro- and pico- phytoplankton dataset, but significantly lower for the nano-phytoplankton, probably due to the weak correlation between the absorption coefficients and chlorophyll a concentration of nano-phytoplankton.

Key words: size-fractionated phytoplankton absorption coefficient, size-fractionated primary production, photosynthetically active radiation, size-fractionated chlorophyll a