The Impact of Typhoon “Mangkhut” on Surface Water Nutrient and Chlorophyll Inventories of the South China Sea in September 2018

Abstract

The influence of the exceptionally strong typhoon Mangkhut on the availability of nutrients and changes in primary production were studied in the northern South China Sea in September 2018. A tight station grid was sampled to analyze major nutrients, chlorophyll_a, particulate and dissolved organic carbon and nitrogen. Based on interpolated profiles, nutrients and organic matter budgets were determined for the upper 100 m of the water column prior to and after Mangkhut's passage. An upper layer of 100 m was found to reflect the important changes by the typhoon. Considerable differences between the on‐shelf, shelf edge and the deep‐sea stations were determined. Nitrate and phosphate increased by about 80% and 36% on the shelf, respectively, and both by almost 40% at the shelf edge. The open deep‐sea part of the study area reflects some deviating results that may be caused by just displacement of water or by mixing water of different origin. However, right on Mangkhut's track on the shelf even contact between surface waters and bottom waters was enabled, increasing phosphate and silicate, but declining nitrate. The inventory of organic carbon of the upper 100 m of the study area (138,000 km2) of 92 Gmol had increased within a few days after the typhoon's passage by 5 Gmol on the shelf and about 2 Gmol in the shelf edge area. Chlorophyll_a doubled during our stay and might have reached a factor of 3 increase in the subsequent time by nitrate supply and excess phosphate.

Typhoon Effects on the Vertical Chlorophyll Distribution on the Northern Shelf of the South China Sea

“…In the offshore region away from the river plume, the Chla change was attributed to advection and vertical mixing, which was consistent with the findings of previous studies (Liu et al., 2013; S. Pan et al., 2017; Zhao et al., 2009). In response to typhoons, both nutrients and sediments have been suggested to change (Kuss et al., 2021; Li et al., 2021), which may lead to delayed Chla changes. This study showed that the biological process in response to typhoon‐perturbed nutrients was generally stronger in the nearshore region than in the offshore region.…”

“…Pan et al, 2017;Zhao et al, 2009). In response to typhoons, both nutrients and sediments have been suggested to change (Kuss et al, 2021;Li et al, 2021), which may lead to delayed Chla changes. This study showed that the biological process in response to typhoon-perturbed nutrients was generally stronger in the nearshore region than in the offshore region.…”

Tropical cyclone Wind Pump induced chlorophyll-a enhancement in the South China Sea: A comparison of the open sea and continental shelf

“…In the SCS, the nutricline and the chlorophyll maximum layer are always below the mixed layer (Kuss et al, 2021). When the mixed layer after a TC is deeper than the chlorophyll maximum layer, a high Chl-a concentration can be transmitted to the sea surface (Wang et al, 2010); when the mixed layer is deeper than the nutricline, more nutrients are transported to the euphoric layer, which promotes the growth of phytoplankton (Palter, 2015).…”