Phytoplankton size class in the East China Sea derived from MODIS satellite data

Abstract. The distribution of the phytoplankton size class (PSC) and the variations in the size classes are key to understanding ocean biogeochemical processes and ecosystem. Remote sensing of the PSC in the East China Sea (ECS) remains a challenge, although many PSC algorithms have been developed. Here based on a local dataset from the ECS, a regional model was tuned to infer the PSC from the spectral features of normalized phytoplankton absorption (αph) using a principal component analysis approach. Before applying the refined model to the real MODIS (Moderate Resolution Imaging Spectroradiometer) data, reconstructing satellite Rrs at 412 and 443 nm becomes critical through modeling them from Rrs between 469 and 555 nm using multiple regression analyses. Satellite-derived PSC values compare well with those derived from pigment composition, which demonstrates the potential of satellite ocean color data to estimate PSC distributions in the ECS from space. The refined model was applied to αph derived from Rrs observations collected by MODIS over the ECS from 2003 to 2016. Seasonal images show that the PSC distribution was heterogeneous in both temporal and spatial scales. Seasonal variations of the PSC in the ECS were probably affected by a combination of the water column stability, upwelling, sea surface temperature, and the Kuroshio Current. Additionally, human activity and riverine discharge may also influence the PSC distributions in the ECS, especially in coastal regions.

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Phytoplankton size class in the East China Sea derived from MODIS satellite data

Biogeosciences ◽

10.5194/bg-15-4271-2018 ◽

2018 ◽

Vol 15 (13) ◽

pp. 4271-4289 ◽

Cited By ~ 8

Author(s):

Hailong Zhang ◽

Shengqiang Wang ◽

Zhongfeng Qiu ◽

Deyong Sun ◽

Joji Ishizaka ◽

...

Keyword(s):

Remote Sensing ◽

East China Sea ◽

Spatial Scales ◽

Size Class ◽

East China ◽

The East China Sea ◽

China Sea ◽

Water Column Stability ◽

Phytoplankton Size ◽

The Kuroshio

Abstract. The distribution and variation of phytoplankton size class (PSC) are key to understanding ocean biogeochemical processes and ecosystems. Remote sensing of the PSC in the East China Sea (ECS) remains a challenge, although many algorithms have been developed to estimate PSC. Here based on a local dataset from the ECS, a regional model was tuned to estimate the PSC from the spectral features of normalized phytoplankton absorption (aph) using a principal component analysis approach. Before applying the refined PSC model to MODIS (Moderate Resolution Imaging Spectroradiometer) data, reconstructing satellite remote sensing reflectance (Rrs) at 412 and 443 nm was critical through modeling them from Rrs between 469 and 555 nm using multiple regression analysis. Satellite-derived PSC results compared well with those derived from pigment composition, which demonstrated the potential of satellite ocean color data to estimate PSC distributions in the ECS from space. Application of the refined PSC model to the reconstructed MODIS data from 2003 to 2016 yielded the seasonal distributions of the PSC in the ECS, suggesting that the PSC distributions were heterogeneous in both temporal and spatial scales. Micro-phytoplankton were dominant in coastal waters throughout the year, especially in the Changjiang estuary. For the middle shelf region, the seasonal shifts from the dominance of micro- and nano-phytoplankton in the winter and spring to the dominance of nano- and pico-phytoplankton in the summer and autumn were observed. Pico-phytoplankton were especially dominant in the Kuroshio region in the spring, summer, and autumn. The seasonal variations of the PSC in the ECS were probably affected by a combination of the water column stability, upwelling, sea surface temperature, and the Kuroshio. Additionally, human activity and riverine discharge might also influence the PSC distribution in the ECS, especially in the coastal region.

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Review report for "Phytoplankton size class in the East China Sea derived from MODIS satellite data" by Zhang et al.

10.5194/bg-2017-508-rc2 ◽

2018 ◽

Author(s):

Anonymous

Keyword(s):

East China Sea ◽

Satellite Data ◽

Size Class ◽

East China ◽

The East China Sea ◽

China Sea ◽

Phytoplankton Size

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

Biogeosciences ◽

10.5194/bg-11-1759-2014 ◽

2014 ◽

Vol 11 (7) ◽

pp. 1759-1773 ◽

Cited By ~ 21

Author(s):

S. Q. Wang ◽

J. Ishizaka ◽

H. Yamaguchi ◽

S. C. Tripathy ◽

M. Hayashi ◽

...

Keyword(s):

Chlorophyll A ◽

East China Sea ◽

Light Absorption ◽

Size Fraction ◽

East China ◽

The East China Sea ◽

Absorption Properties ◽

China Sea ◽

Fraction Versus ◽

Phytoplankton Size

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&ast;(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&ast;(λ) in ECS than in TS. Within SCM, average aph&ast;(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&ast;(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&ast;(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&ast;(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&ast;(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.

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