Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 3
Biogeosciences, 15, 749–765, 2018
https://doi.org/10.5194/bg-15-749-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 15, 749–765, 2018
https://doi.org/10.5194/bg-15-749-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Feb 2018

Research article | 07 Feb 2018

Phytoplankton growth response to Asian dust addition in the northwest Pacific Ocean versus the Yellow Sea

Chao Zhang1, Huiwang Gao1,2, Xiaohong Yao1, Zongbo Shi3, Jinhui Shi1, Yang Yu1, Ling Meng1, and Xinyu Guo4 Chao Zhang et al.
  • 1Key Laboratory of Marine Environment and Ecology, Ministry of Education of China, Ocean University of China, Qingdao, China
  • 2Laboratory for Marine Ecology and Environmental Sciences, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
  • 3School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
  • 4Center for Marine Environmental Studies, Ehime University, Matsuyama, Japan

Abstract. In this study, five on-board microcosm experiments were performed in the subtropical gyre, the Kuroshio Extension region of the northwest Pacific Ocean (NWPO), and the Yellow Sea (YS) in order to investigate phytoplankton growth following the addition of artificially modified mineral dust (AM dust) and various nutrients (nitrogen (N), phosphorus (P), iron (Fe), N + P, and N + P + Fe). The two experiments carried out with AM-dust addition in the subtropical gyre showed a maximum chlorophyll a (Chl a) concentration increase of 1.7- and 2.8-fold, while the cell abundance of large-sized phytoplankton ( >  5 µm) showed a 1.8- and 3.9-fold increase, respectively, relative to the controls. However, in the Kuroshio Extension region and the YS, the increases in maximum Chl a and cell abundance of large-sized phytoplankton following AM-dust addition were at most 1.3-fold and 1.7-fold larger than those in the controls, respectively. A net conversion efficiency index (NCEI) newly proposed in this study, size-fractionated Chl a, and the abundance of large-sized phytoplankton were analysed to determine which nutrients contribute to supporting phytoplankton growth. Our results demonstrate that a combination of nutrients, N–P or N + P + Fe, is responsible for phytoplankton growth in the subtropical gyre following AM-dust addition. Single nutrient addition, i.e., N in the Kuroshio Extension region and P or N in the YS, controls the phytoplankton growth following AM-dust addition. In the AM-dust-addition experiments, in which the increased N–P or P was identified to determine phytoplankton growth, the dissolved inorganic P from AM dust (8.6 nmol L−1) was much lower than the theoretically estimated minimum P demand (∼ 20 nmol L−1) for phytoplankton growth. These observations suggest that additional supply augments the bioavailable P stock in incubated seawater with AM-dust addition, most likely due to an enhanced solubility of P from AM dust or the remineralization of the dissolved organic P.

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This study compares the response of phytoplankton growth in the northwest Pacific to those in the Yellow Sea. In general, larger positive responses of phytoplankton induced by combined nutrients (in the subtropical gyre of the northwest Pacific) than those induced by a single nutrient (in the Kuroshio Extension and the Yellow Sea) from the dust are observed. We also emphasize the importance of an increase in bioavailable P stock for phytoplankton growth following dust addition.
This study compares the response of phytoplankton growth in the northwest Pacific to those in...
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