Preprints
https://doi.org/10.5194/hess-2022-247
https://doi.org/10.5194/hess-2022-247
 
25 Jul 2022
25 Jul 2022
Status: this preprint is currently under review for the journal HESS.

Effect of tides on river water behavior over the eastern shelf seas of China

Lei Lin1,2, Hao Liu1, Xiaomeng Huang2, Qingjun Fu1, and Xinyu Guo3 Lei Lin et al.
  • 1College of Ocean Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
  • 2Ministry of Education Key Laboratory for Earth System Modeling, Department of Earth System Science, Tsinghua University, Beijing 100084, China
  • 3Center for Marine Environmental Study, Ehime University, Matsuyama 790-8577, Japan

Abstract. Rivers carry large amounts of freshwater and terrestrial material into shelf seas, which is an important part of the global water and biogeochemical cycles. The earth system model or climate model is an important instrument for simulating and projecting the global water cycle and climate change, in which tides however are commonly removed. For a better understanding of the potential effect of the absence of tides in the simulation of the water cycle, this study compared the results of a regional model with and without considering tides, and evaluated the effect of tides on the behavior of three major rivers (i.e., the Yellow, Yalujiang, and Changjiang Rivers) water in the eastern shelf seas of China from the perspectives of transport pathways, timescales, and water concentration. The results showed that the tides induced more dispersed transport for the water of the Yellow and Yalujiang rivers, but more concentrated transport for the Changjiang River water. The effect of tides on the transit areas of the Yellow, Yalujiang, and Changjiang Rivers was 13, 40, and 21 %, respectively. The annual mean water age and transit time of the three rivers in the model with tides were several (~2–10) times higher than those in the no-tide model, suggesting that tides dramatically slow the river water transport and export rate over the shelf. By slowing the river water export, tides induced a three-fold increase in river water concentration and a decrease in shelf seawater salinity by >1. Moreover, the effect of tides on river behavior was stronger in relatively enclosed seas (i.e., the Bohai and Yellow Seas) than in relatively open seas (i.e., the East China Sea). The change in the shelf currents induced by tides is the main cause of the difference in the river water behavior between the two model runs. Tides can increase bottom stress and thus weaken shelf currents and decrease the water transport timescales. The improvement in tidal parameterization in the no-tide model in the simulation of river water behavior was very limited. Given the important role of river runoff on the global water cycle and the effect of changes in river water behavior on ocean carbon cycling, it is important to include the tidal effect in earth system models to improve their projection accuracy.

Lei Lin et al.

Status: open (until 19 Sep 2022)

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Lei Lin et al.

Lei Lin et al.

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Short summary
Earth system (climate) model is an important instrument for projecting the global water cycle and climate change, in which tides are commonly excluded due to the much small timescales compared to the climate. However, we found that tides significantly impact the river water transport pathways, transport timescales, and concentrations in shelf seas. Thus, the tidal effect should be carefully considered in earth system models to accurately project the global water and biogeochemical cycle.