Articles | Volume 11, issue 7
Biogeosciences, 11, 1759–1773, 2014
Biogeosciences, 11, 1759–1773, 2014

Research article 03 Apr 2014

Research article | 03 Apr 2014

Influence of the Changjiang River on the light absorption properties of phytoplankton from the East China Sea

S. Q. Wang1, J. Ishizaka2, H. Yamaguchi3, S. C. Tripathy4, M. Hayashi1, Y. J. Xu2, Y. Mino2, T. Matsuno5, Y. Watanabe6, and S. J. Yoo7 S. Q. Wang et al.
  • 1Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 2Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya, Japan
  • 3Earth Observation Research Center, Japan Aerospace Exploration Agency, Tsukuba, Japan
  • 4National Centre for Antarctic and Ocean Research, Goa, India
  • 5Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan
  • 6The General Environmental Technos Co., LTD, Osaka, Japan
  • 7Korea Institute of Ocean Science and Technology, Ansan, Korea

Abstract. Phytoplankton light absorption properties were investigated at the surface and subsurface chlorophyll a maximum (SCM) layer in the East China Sea (ECS), a marginal sea which is strongly influenced by the Changjiang discharge in summer. Results from ECS were compared with those from the Tsushima Strait (TS) where the influence of Changjiang discharge is less. The probable controlling factors, packaging effect (cell size) and pigment composition of total chlorophyll a (Tchl a)-specific absorption coefficient (aph*(λ)) were examined by the corresponding measurements of pigments identified by high-performance liquid chromatography. We observed distinct phytoplankton size structure and thereby absorption properties between ECS and TS. At the surface, mixed populations of micro-, nano- and pico-phytoplankton were recorded in ECS while pico-phytoplankton dominated in TS, generating a lower average aph*(λ) in ECS than in TS. Within SCM, average aph*(λ) was higher in ECS than in TS because of the dominance of nano- and micro-phytoplankton in ECS and TS, respectively. By pooling surface and SCM samples, we found regular trends in phytoplankton size-fraction versus Tchl a; and correlations between aph*(λ) and Tchl a consistent with previous observations for the global ocean in TS but not in ECS. In ECS phytoplankton size-fraction was not correlated with Tchl a, which consequently caused poor relationships between aph*(λ) and Tchl a. The abnormal values mainly originated from the surface low-salinity waters and SCM waters beneath them. At high Tchl a, aph*(λ) of these samples was substantially higher compared to the values in TS and from the global regressions, which was attributable to the lower micro-phytoplankton fraction, and higher nano- and/or pico-phytoplankton fractions in ECS. These observations indicated that the distinct light absorption properties of phytoplankton in ECS were possibly influenced by the Changjiang discharge. Our findings imply that general bio-optical algorithms proposed based on the correlations between aph*(λ) and Tchl a or the patterns in size-fraction versus Tchl a are not applicable in ECS, and need to be carefully considered when using these general algorithms in river-influenced regions.

Final-revised paper