Drivers of Phytoplankton Variability in and Near the Pearl River Estuary, South China Sea During Typhoon Hato (2017): A Numerical Study. Issue 10 (10th October 2022)

• Record Type: Journal Article
• Authors: Feng, Yang; Huang, Jingwen; Du, Yan; Balaguru, Karthik; Ma, Weiwei; Feng, Qingyu; Wan, Xiuquan; Zheng, Youchang; Guo, Xianghui; Cai, Shuqun
• Is Part Of: Journal of geophysical research. Volume 127:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-10-10
• Subjects: Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2022JG006924
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: The Pearl River Estuary and adjacent seas in South China Sea are frequently affected by tropical cyclones (TCs). Previous in situ and remote sensing studies have found that typhoons can enhance phytoplankton biomass and induce blooms in this region. However, the mechanistic links between phytoplankton blooms and typhoons have not been well understood due to the interplay of multiple complex processes along the land‐ocean‐atmosphere interface. Here, we constructed an integrated modeling system with the marine ecosystem and sediment components for the China Great Bay Area. By using the integrated modeling system, we quantitatively investigated the phytoplankton response to hydrological conditions variations under Typhoon Hato (2017), a strong typhoon case. Passive tracer experiments showed that with high river discharge induced by heavy rainfall, the residence time within Lingding Bay is as short as 15 days, less than half of that under the climatological discharge. The increase in freshwater pulse washes out the phytoplankton biomass within Lingding Bay. While for the offshore region, the analysis of various source and sink terms for the offshore region's post‐typhoon response showed that the increase of phytoplankton biomass in the first week was because of the uplift of nutrient‐rich subsurface water, while in the second week, it was due to the seaward propagation of nearshore high phytoplankton biomass water. While riverine nutrients support phytoplankton growth in the third week, a large part of phytoplankton biomass was lost to zooplankton grazing, showing the system shifted from the bottom‐up control to the top‐down control. Plain Language Summary: Several previous satellite‐based studies observed phytoplankton blooms within the Pearl River estuary‐coastal system after the passage of Typhoons. However, the mechanisms controlling the occurrence of the bloom are not very well known. Here, we introduce a comprehensive modeling system to quantitatively diagnose the relative importance of multiple processes in regulating the phytoplankton bloom from the inner bay to the outer shelf. By taking a strong typhoon case, Hato (2017), as an example, we found that much of the phytoplankton was washed out of the Lingding Bay after Hato. The nearshore phytoplankton bloom occurred 2 weeks after Hato's arrival due to the increased terrestrial runoff after heavy rainfall. For the offshore region, storm‐induced upwelling also played a role in increasing the phytoplankton biomass, in addition to the impact from the river discharge. However, the offshore bloom did not occur due to the high grazing impact from the zooplankton. Key Points: An integrated modeling system was constructed for the Pearl River Estuary to diagnose the phytoplankton response after Typhoon Hato The increased discharge after Hato halved the residence time and doubled the decay rate of the water mass within Lingding Bay The uplifted nutrient‐rich subsurface water and the riverine nutrient export jointly support the offshore phytoplankton bloom