Abstract
Typhoon events have large impacts on marginal seas’ environmental conditions with implications for biological processes and carbon cycling. However, little is known about the responses of phytoplankton and particulate organic carbon (POC) to typhoon events in the Yellow-Bohai Sea (YBS). In this study, we utilized satellite-derived datasets of chlorophyll-a (Chl-a) and POC, together with key physical parameters, to analyze their responses to the Typhoon Lekima event induced heavy rainfall and strong winds. Overall, there were enhanced upwelling, strengthened currents, and increased terrestrial runoff during weakened Typhoon Lekima in the YBS. The basin-scale response of Chl-a showed large differences post the Typhoon Lekima event, with a decrease in the Bohai Sea (BS, 0.34 ± 3.0 mg m−3) but an increase in Yellow Sea (YS, 0.23 ± 1.7 mg m−3 in the south YS and 0.54 ± 0.8 mg m−3 in the north YS). The increase of Chl-a in the YS was attributed to increased nutrients, whereas the reduction of Chl-a in the BS was caused by dilution and water exchange with the North Yellow Sea. However, there was an overall increase in POC post-Typhoon Lekima in both BS and YS. The increase of POC in the majority of BS resulted largely from enhanced sediment resuspension and terrigenous input. The increase of POC in the nearshore waters of YS was attributable to enhanced biological production, sediment resuspension, and terrigenous input of POC, whereas the increase of POC in the central YS was partly due to transportation of high-POC waters from nearshore to offshore via strengthened current. Our study highlights the complex impacts of typhoon events on the carbon cycle in marginal seas.
Highlights
Typhoons are one of the most intensive meteorological activities on earth and can impose significant impacts on the marine environment
The decrease (0.34 ± 3.0 mg m−3) of chlo‐ rophyll-a (Chl-a) in the Bohai Sea (BS) was mainly caused by dilution due to freshwater inputs from heavy rainfall and water exchange with North Yellow Sea (NYS), whereas the increase (0.23–0.54 mg m−3) of Chl-a in the Yellow Sea (YS) was largely attributable to the increase of nutrients caused by enhanced upwelling and terrestrial inputs
There was a basin-scale increase in particulate organic car‐ bon (POC) post the typhoon event in the Yellow-Bohai Sea (YBS), i.e., mg m−3 or 24% in the BS, mg m−3 or 46% in NYS, and 41 mg m−3 or 22% in the South Yellow Sea (SYS), which were much greater than the increases of 9–45 mg m−3 or 4–16% over the same period in non-typhoon years
Summary
Typhoons are one of the most intensive meteorological activities on earth and can impose significant impacts on the marine environment. Typhoon-induced strong wind can cause significant entrainment and upwelling in the ocean, which uplifts nutrient-rich subsurface water to the surface layer of water column (Liu et al 2019; Pan et al 2018). Nutrient concentration in surface water often increases during/after the passage of typhoon, which stimulates phytoplankton growth and. There is evidence of high frequency of typhoon passages in marginal seas, and great impacts of typhooninduced strong wind on its biogeochemistry because of the marginal seas’ shallow stratification that is broken (Chen et al 2017). In addition to the enhanced nutrient supply from subsurface of the ocean, typhooninduced heavy rainfall could increase runoff, delivering more nutrients from adjacent lands (Shiah et al 2000).
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