03 Jan 2022

03 Jan 2022

Review status: this preprint is currently under review for the journal BG.

Contrasting responses of phytoplankton productivity between coastal and offshore surface waters in the Taiwan Strait and the South China Sea to future CO2-induced acidification

Guang Gao1, Tifeng Wang1, Jiazhen Sun1, Xin Zhao1, Lifang Wang1, Xianghui Guo1, and Kunshan Gao1,2 Guang Gao et al.
  • 1State Key Laboratory of Marine Environmental Science & College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China
  • 2Co-Innovation Center of Jiangsu Marine Bio industry Technology, Jiangsu Ocean University, Lianyungang 222005, China

Abstract. Future CO2-induced ocean acidification (OA) has been documented to either inhibit or enhance or result in no effect on marine primary productivity (PP). In order to examine effects of OA under multiple drivers, we investigated the influences of OA (a decrease of 0.4 pHtotal units with corresponding CO2 concentrations ranged 22.0–39.7 µM) on PP through deck-incubation experiments at 101 stations in the Taiwan Strait and the South China Sea (SCS), including the coastal zone, the continental shelf and slope, as well as deep-water basin. The daily net primary productivities in surface seawater under incident solar radiation ranged from 17–306 µg C (µg Chl a)−1 d−1, with the responses of PP to OA being region-dependent and the OA-induced changes varying from −88.03 % (inhibition) to 56.87 % (enhancement). The OA-treatment stimulated PP in surface waters of coastal, estuarine and shelf waters, but suppressed it in the South China Sea basin. Such OA-induced changes in PP were significantly related to NOX (the sum of NO3 and NO2) availability, in situ pH and solar radiation in surface seawater, but negatively related to salinity changes. Our results indicate that phytoplankton cells are more vulnerable to pH drop in oligotrophic waters. Considering high nutrient and low salinity in coastal waters and reduced nutrient availability in pelagic zones with the progressive stratification associated with ocean warming, our results imply that future OA will enhance PP in coastal waters but decrease it in pelagic oligotrophic zones.

Guang Gao et al.

Status: open (until 14 Feb 2022)

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Guang Gao et al.


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Short summary
After conducting a large-scale deck-incubation experiments, we found that ocean acidification (OA) increased primary production (PP) in coastal waters but reduced it in pelagic zones, which is mainly regulated by nutirent availability, local pH and community structure. OA cominbed with eutrophication may lead to higher frequency of harmful algal blooms in future coastal oceans.