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Prof. Zhang Brings New Perspective to River Plume Dynamics over Estuary

November 04, 2020      Author:

Recently, a research paper titled "Spatial Variations of Phytoplankton Biomass Controlled by River Plume Dynamics Over the Lower Changjiang Estuary and Adjacent Shelf Based on High-Resolution Observations" was published on the website of Frontiers in Marine Science, an internationally renowned journal in the field of oceanography. The paper was completed by Associate Prof. Zhang Zhaoru, Prof. Zhou Meng from School of Oceanography, Shanghai Jiao Tong University and other collaborators. The article proposes that meso- to sub-mesoscale dynamical processes of freshwater plumes are the key mechanism in regulating the spatial and temporal variations of algal biomass in the Yangtze River Estuary and adjacent continental shelf regions, providing a new perspective and inspiration for us to examine the dynamics of the coastal ecosystem of the estuary. The article has been viewed 595 times since it was published.

The first author of this article is Zhang Zhaoru, tenure-track associate professorfrom School of Oceanography, SJTU, and the corresponding authors are Prof. Zhou Meng and Associate Prof. Zhang Zhaoru from SJTU. The collaborators include Mr.Zhong Yisen, Associate Prof. Gao Yonghui, Associate Researcher Zhang Ruifeng, and Prof. Smith from SJTU, as well as Dr. Zhang Guosen and Dr. Jiang Shan from East China Normal University. The research was funded by "Integrated Process of Convection, Diffusion, and Material Transformation of Diluted Water in the Yangtze River Estuary" (41530960), a key project supported by the National Natural Science Foundation of China.

 

ABSTRACT:

Phytoplankton biomass in estuarine and continental shelf regions are regulated and modified by physical processes, but these interactions have mostly been investigated at a scale of tens of kilometers, and the role of meso- to sub-mesoscale dynamical processes of freshwater plumes in regulating the spatial and temporal variations of algal biomass is largely unknown. To assess the importance of features at these scales, high-resolution (horizontal spacing < 1 km) cross-sectional profiles of hydrographic and biogeochemical variables were collected in the lower Changjiang Estuary and adjacent continental shelf with a towed, undulating vehicle equipped with sensors measuring fluorescence, turbidity and irradiance. Discrete stations were also occupied to allow for the characterization of nutrients. Multiple physical features at different scales regulated the spatial variation of phytoplankton biomass. Phytoplankton biomass was initialized by an improved irradiance field driven by reduced turbidity together with a rapid development of subsurface stratification at the main plume front (isohaline of 23) downstream from the turbidity maximum zone. Phytoplankton blooms did not occur until outcrops located within the main front that were characterized by surface convergence and downwelling, which contributed to large algal biomass by mass trapping and enhanced light penetration. Wave-like features were detected seaward of the main front, coinciding with deacceleration of currents, indicating that they are front-released internal waves that increase algal retention time. This study revealed the critical role of small-scale processes near the plume front in triggering phytoplankton blooms under the large-scale context of improved light conditions, coastal upwelling and nutrient additions from intruding oceanic waters.

 

Author: Xie Anqi

Affiliation: School of Oceanography, SJTU