the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Nov 2024
Two different phytoplankton blooming mechanisms over the East China Sea during El-Niño decaying summers
Abstract. During an El Niño-decaying summer, the East China Sea (ECS) has experienced anomalous phytoplankton blooming, but the understanding of associated generating mechanisms remains limited. Here, we analyzed observational (25 years) and long-term simulation data (1,000 years) to investigate the underlying mechanisms for the anomalous phytoplankton blooming in ECS. Results highlight two mechanisms associated with enhanced phytoplankton blooming in ECS during El Niño-decaying summers: inland runoff-driven and oceanic sub-surface upwelling-driven blooming mechanisms. Firstly, increased river discharge from the Yangtze River (YR) induces phytoplankton blooms. Secondly, wind-driven Ekman upwelling in ECS provides nutrients for phytoplankton from the sub-surface to the surface water layer. Rossby wave propagations from Western North Pacific Anti-Cyclone (WNPAC) cause a distinctive cyclonic atmospheric circulation over ECS that induces Ekman upwelling. The climate model simulation supports these two mechanisms, and thus our results suggest that both mechanisms contribute to the phytoplankton bloom concurrently.
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RC1: 'Comment on egusphere-2024-3406', Anonymous Referee #1, 16 Nov 2024
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This manuscript discusses an important issue of international interest. However, it is premature because of major flaws.
The major flaw is the erroneous assumption that riverine input is the primary source of nutrients(line 27). Much of the Introduction and Methods concerns river input. However, the Kuroshio Intermediate Water is the primary source of nutrients for the East China Sea shelf. Many papers substantiated this notion. The authors used the results presented in Figs. 2 and 3 to prove the importance of riverine inputs of nutrients. Yet, Figs. 2 and 3 only provided a good correlation between chlorophyll and nutrients that mostly did not come from rivers. Instead, the upwelling of nutrient-rich Kuroshio subsurface waters provided most of the nutrients. Of course, upwelling could be induced by the buoyance effect caused by the river water(e.g., Chen 2008, Acta Oceanologica Sinica, 27,133, 2008). To summarize, the so-called runoff-driven blooming mechanism is not caused by riverine nutrients. Instead, it is caused by buoyancy-driven upwelling and vertical mixing. BTW, validation is needed to substantiate the modeled results presented in these two figures.
Another factor worth mentioning is that the outflow of the South China Sea is the primary source of Kuroshio waters entering the East China Sea. During El Nino years, there is a more substantial outflow of the more nutrient-rich SCS water(e.g., Chen et al., Deep-Sea Res. I, 103,13, 2015), which may enhance productivity on the ECS shelf.
As a final note, many of the figures are not labeled correctly. Figures 1, 2, 3, 4, 5, 6, 9, and 10 are all related to anomalies, not the actual values. The "p" values should also be provided.
Citation: https://doi.org/10.5194/egusphere-2024-3406-RC1
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