Regional Studies in Marine Science 39 (2020) 101394 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Impacts of the unique landfall Typhoons Damrey on chlorophyll-a in the Yellow Sea off Jiangsu Province, China Haibin Lü a,b,d , Xiao Ma c , Yuntao Wang c ,∗ , Huijie Xue d , Fei Chai c a Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang 222005, China b Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang 222005, China c State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China d State Key Laboratory of Oceanography in the Tropics, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China article info Article history: Received 27 February 2020 Received in revised form 30 May 2020 Accepted 10 August 2020 Available online 12 August 2020 Keywords: Coast of Jiangsu Typhoon Suspended sediment concentration Upwelling Chlorophyll-a abstract Typhoon Damrey was the rare typhoon to make a straight landfall in northern Jiangsu Province (35 ◦ N), China. The unique influence of typhoon Damrey and the following typhoons Haikui on the phytoplankton bloom and related dynamic mechanisms were fully investigated. Because of the complex regional features, e.g., nutrient distribution, stratification and sediment concentration, it induced different responses to the ocean along its track. In the near shore region, the Chlorophyll- a (Chl_a) concentration dropped prominently during typhoon, associating with strong wind events, because of the onshore advection of water with a low amount of Chl_a and coastal downwelling. For the shelf regions, no significant blooms were identified and the Chl_a values after typhoon were less than the preceding maximum values. Although a large amount of mixing happened in the water column, insufficient sunshine for photosynthesis caused by a high suspended sediment concentration (SSC) (10.8 g m −3 ) near the shore and a lack of nutrients in the bottom boundary of the open sea resulted in no Chl_a bloom in these two areas. For the open ocean area off the Yangtze River estuary, where subsurface nitrate concentration was high, the formation of a Chl_a bloom after strong winds was mainly determined by the intensity of the stratification in the upper ocean. The enhancement of nutrients from the subsurface layer became stronger (weaker) when the pycnocline was weakened (strengthened). As the pycnocline and stratification weakened, the Chl_a concentration was significantly higher than that on August 7 because of the intensified upward transport of nutrients from the deep layer. This study offers a comparison of the different mechanisms by which typhoons can impact Chl_a in mid-latitude regions and will be helpful for evaluating typhoon-induced biological responses in future. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Typhoons, which are also known as hurricanes or tropical cyclones, can induce strong ocean mixing and upwelling (Price, 1981; Sanford et al., 2011) and trigger conspicuous upper ocean biological and physical responses (Xiu et al., 2016; He et al., 2017). The typhoons in the Northwestern Pacific (NWP) Ocean are the highest, both in number and intensity (Lin et al., 2009), and can uplift deeper ocean nutrients to the euphotic zone to trigger upper ocean biogeochemical responses and increase primary pro- ductivity (Babin et al., 2004; Zheng and Tang, 2007; Shang et al., 2008). ∗ Corresponding author. E-mail address: yuntao.wang@sio.org.cn (Y. Wang). Over the last eighteen years, Typhoon Damrey was the rare typhoon to make straight landfall in Haizhou Bay, in northern Jiangsu Province. The track of typhoons in August 2012 was shown in Fig. 1, and it is interesting to notice Typhoons Damrey is followed by typhoon Haikui, which landed south of Jiangsu Province. The unique landfall patterns could have induced com- plex dynamical processes, but the associated biological responses have not been investigated. Many phytoplankton blooms caused by population explosions have been reported in the Yellow Sea since 2000 (Tang et al., 2006; Son et al., 2012; Jin et al., 2013). The green tides in the Yellow Sea immediately before the 2008 Olympic Sailing Competition in China were identified as one of the world’s largest macroalgal blooms (Liu et al., 2009, 2016). Therefore, it is important to study the impacts of typhoons on the upper ocean and Chl_a blooms in the region, particularly during the passage of the unique landfall Typhoons Damrey. https://doi.org/10.1016/j.rsma.2020.101394 2352-4855/© 2020 Elsevier B.V. All rights reserved.