Boundary Phosphate Transport of the East China Sea and Its Influence on Biological Process

Zhijian Lin,Fei Chai,Peng Xiu,Xiaochun Wang,Qiong Wu

doi:10.4236/gep.2019.79007

Abstract

The East China Sea (ECS) is one of the largest marginal seas in the Northwest Pacific, and also one of the most productive regions of the global ocean. Using a three-dimensional Pacific physical-biological model, we investigate the interannual variation of phosphate transport via Kuroshio intrusion (KIPT) in the eastern boundary of the East China Sea (ECS) and its influence on the ECS biological process during 1997 to 2016. The KIPT into the ECS mainly occurs in the northeast of Taiwan and southwest of Kyushu, with stronger interannual variability in the northeast of Taiwan. The variation of the KIPT is more significant in the near-bottom water, and is dominated by volume transport. On the interannual timescale, the KIPT changes in response to the shift of the Kuroshio axis and to the bottom upwelling in the ECS eastern boundary. When the Kuroshio axis is closer to (farther away from) the ECS shelf, the strength of the bottom upwelling increases (decreases). This process induces more (less) significant topographic beta spiral, which causes an anticyclonic (cyclonic) eddy-like bottom velocity feature in the northeast of Taiwan. Eventually, more phosphate is transported to the ECS inner shelf, which increases chlorophyll concentration around the Zhoushan Islands and Yangtze Estuary but reduces chlorophyll concentration in the ECS outer shelf. Conversely, the chlorophyll increases in the ECS outer shelf but decreases around the Zhoushan Islands and Yangtze Estuary when there is less phosphate transport. This study highlights the importance of Kuroshio intrusion in connecting the inner and outer shelves of the ECS on the interannual timescale. Phosphate transport into the East China Sea via Kuroshio intrusion shows great interannual variability in the northeast of Taiwan. On the interannual timescale, the variation of phosphate transport into the East China Sea via Kuroshio intrusion is dominated by volume transport. When the Kuroshio axis is closer to the East China Sea shelf, there is more phosphate transport into the East China Sea, and chlorophyll increases around the Zhoushan Islands and Yangtze Estuary.

Highlights

The East China Sea (ECS) is one of the largest marginal seas in the Northwest Pacific
Using the three-dimensional Pacific physical-biological model of Regional Ocean Modeling System (ROMS)-CoSiNE, we investigated the variation of nutrient transport via Kuroshio intrusion and chlorophyll in the ECS
The model simulation shows that the total phosphate transport across the eastern boundary of the ECS enters the ECS, and the major intrusion regions are the northeast of Taiwan and southwest of Kyushu; the total phosphate transport across the eastern boundary of the ECS is similar to the Kuroshio intrusion volume transport

Summary

Introduction

The East China Sea (ECS) is one of the largest marginal seas in the Northwest Pacific. The ECS meets the Ryukyu Islands chain and Kyushu Island of Japan, which are along the flow direction of the Kuroshio. Based on observed and estimated data, Chen (2008) demonstrated that the nutrients of the Kuroshio water contribute 49% (4.69 kmol/s) of the externally sourced nitrogen and 71% (0.34 kmol/s) of the phosphorous for the ECS. This indicated that the phosphorous from the Kuroshio water might play a more important role in the ECS biological process. The variation of phosphate transport via Kuroshio intrusion (KIPT) into the ECS is a crucial factor that influences the change of the ECS biological process, especially for the area of phosphorous limitation

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Results

Conclusion