Chlorophyll Concentration Response to the Typhoon Wind-Pump Induced Upper Ocean Processes Considering Air–Sea Heat Exchange

Abstract

The typhoon Wind-Pump induced upwelling and cold eddy often promote the significant growth of phytoplankton after the typhoon. However, the importance of eddy-pumping and wind-driven upwelling on the sea surface chlorophyll a concentration (Chl-a) during the typhoon are still not clearly distinguished. In addition, the air-sea heat flux exchange is closely related to the upper ocean processes, but few studies have discussed its role in the sea surface Chl-a variations under typhoon conditions. Based on the cruise data, remote sensing data, and model data, this paper analyzes the contribution of the vertical motion caused by the eddy-pumping upwelling and Ekman pumping upwelling on the surface Chl-a, and quantitatively analyzes the influence of air-sea heat exchange on the surface Chl-a after the typhoon Linfa over the northeastern South China Sea (NSCS) in 2009. The results reveal the Wind Pump impacts on upper ocean processes: (1) The euphotic layer-integrated Chl-a increased after the typhoon, and the increasing of the surface Chl-a was not only the uplift of the deeper waters with high Chl-a but also the growth of the phytoplankton; (2) The Net Heat Flux (air-sea heat exchange) played a major role in controlling the upper ocean physical processes through cooling the SST and indirectly increased the surface Chl-a until two weeks after the typhoon; (3) the typhoon-induced cyclonic eddy was the most important physical process in increasing the surface Chl-a rather than the Ekman pumping and wind-stirring mixing after typhoon; (4) the spatial shift between the surface Chl-a blooms and the typhoon-induced cyclonic eddy could be due to the Ekman transport; (5) nutrients uplifting and adequate light were two major biochemical elements supplying for the growth of surface phytoplankton. tropical cyclones during the summer time [4]. Tropical cyclones have important "Wind Pump" impact on transporting and increasing the surface and subsurface Chl-a in oligotrophic ocean waters [5][6][7][8] through uplifting the nutrients by strong vertical mixing, upwelling, entrainment, as well as near inertial wave on the upper ocean layer, especially on the right-hand side of the storm track in the Northern Hemisphere [2,9,10]. Typhoons with slower translation speeds and stronger wind speeds have greater impact on Chl-a and the translation speeds play the more crucial role [4,11]. Tropical cyclones can also induce cyclone eddies (or reduce anti-cyclone eddies), and these eddy-pumping upwelling can further increase the surface and subsurface Chl-a [4,12]. These typhoon wind-driven physical processes and air-sea exchanges that subsequently affect the ocean's ecological status is defined as the "Wind Pump" [2,4,7,8,10,11].Biochemical conditions are essential in affecting the Chl-a through affecting its carbon/chlorophyll ratios [1,13]. Upwelling of the nutrient-rich waters from the deeper layer is the principal source of nutrients fueling the phytoplankton especially over the oligotrophic ocean like the NSCS [1,4]. The nitrogen is the maj...

Modulation Effect of Mesoscale Eddies on Sequential Typhoon-Induced Oceanic Responses in the South China Sea

“…On the other hand, convergence inhibits upwelling within anticyclonic eddies such that subsurface water outcrops to the surface only when a typhoon initiates intensive mixing (Figure 6), while the water column is restratified rapidly after a typhoon (Figure 6b,d). Liu and Tang [59] consistently found that the typhoon-induced CHL increase differs greatly among pre-existing oceanic conditions, with cyclonic and anticyclonic eddies increasing the CHL by approximately 35% and 6%, respectively. Furthermore, the magnitude of SST cooling varies only weakly between the two types of eddies (Figure 5) because typhoon-induced mixing is dominant, while upwelling within cyclonic eddies adds to the typhoon's impact and results in greater cooling at the surface than that within anticyclonic eddies [37].…”

Satellite Observations of Wind Wake and Associated Oceanic Thermal Responses: A Case Study of Hainan Island Wind Wake

“…However, the weak background stratification condition could prohibit the wake-induced upwelling to generate strong surface thermal response [17]. In contrast, the wake-induced upwelling could still bring nutrients upward, and might enhance the primary production in the upper ocean [58,63,64]. Thus the identification of the suction/pumping process on the sub-mesoscale is meaningful to regional ecosystem dynamic studies.…”

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“…After the passage of typhoon Halong, the chl-a concentration in CE increased significantly with a maximum chl-a concentration of over 0.4 mg/m 3 . the usually sufficient sunshine and strong photosynthesis after the passing of a typhoon, there can be a marked increase in the surface chl-a concentration [12,58,59]. Figure 3i shows that typhoon Neoguri increased the chl-a concentration weakly in CE and caused no changes in AE.…”

“…In the tropical oceans, limited nutrient concentrations in the upper ocean are not conducive to enhancing primary productivity, which can be indicated by the variations in chl-a concentrations in phytoplankton [56,57]. Typhoon-induced upwelling and vertical mixing, which can be indicated by strong SST cooling, will bring relatively more phytoplankton and richer nutrients from the subsurface to the sea surface layer, and together with the usually sufficient sunshine and strong photosynthesis after the passing of a typhoon, there can be a marked increase in the surface chl-a concentration [12,58,59]. Figure 3i shows that typhoon Neoguri increased the chl-a concentration weakly in CE and caused no changes in AE.…”