Tidal Effect on Water Export Rate in the Eastern Shelf Seas of China. Issue 5 (27th April 2020)

• Record Type: Journal Article
• Authors: Lin, Lei; Liu, Dongyan; Guo, Xinyu; Luo, Chongxin; Cheng, Yao
• Is Part Of: Journal of geophysical research. Volume 125:Issue 5(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-27
• Subjects: Tides -- Water exchange -- Residence time -- Adjiont method -- Shelf seas of China -- Hydrodynamic modelling; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015863
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Water export rate of shelf seas is a pivotal factor impacting the global carbon cycle. Tides have important impacts on shelf hydrodynamics but are excluded in many climate models. To assess the effect of tides on export rates of shelf water, this study used a regional hydrodynamic model and a water residence time (WRT) adjoint model and examined model runs with and without tides for the eastern shelf seas of China. The results show that the average WRTs in the Bohai, Yellow, and East China seas were 11.60, 4.95, and 0.39 years, respectively. When tides were excluded, the WRTs decreased by >70% in the Bohai and Yellow seas and by ~10% in the East China Sea, indicating a significant acceleration in the shelf water export due to the absence of tides. The tidal effect has spatial variability associated with the water depth. Sensitivity experiments suggest that the tidal effect on the mean WRT was stronger than the effect of other dynamical factors (winds, rivers, and boundary currents). In the model with tides, tides weakened the wind‐driven coastal current by intensifying the bottom resistance and thus slowed water export in the inner and middle portions of the shelf, compared to the model without tides. Parameterization of the tidal bottom friction in the model without tides could significantly improve the WRT result. This study highlights the crucial role of tides on the long‐term transport of shelf seas and the significance of parameterizing the effect of tidal friction in climate models. Plain Language Summary: The export of water with a high carbon content to the deep oceans from shelf seas is a pivotal process impacting the global carbon cycle. Tides play an important role in the hydrodynamics of shelf seas and thus influence the water export. Hence, a quantitative assessment of the tidal effect on the water export rate is essential, in order to understand the role of tides in the global carbon cycle. Using water residence time (WRT) as an indicator and numerical modeling, this study finds that the model without tides decreased the WRT of the eastern shelf seas of China (ESSC) to ~1/3 compared to the model with tides, indicating a significant effect of tides on the water export from shelf seas. Meanwhile, the tidal effect on the water export in the ESSC was much stronger in the inner and middle shelves compared with that in the outer shelf. The findings of this study highlight the crucial impact of tides on the water exchange between shelf seas and deep oceans, which implies that small timescale and space‐scale processes should be simulated or effectively parameterized in climate models in order to accurately predict the ocean and climate change. Key Points: The tidal effect on the water export rate in the eastern shelf seas of China (ESSC) is assessed from a timescale perspective Average water residence time in the ESSC is 2.12 years and reduces to 0.64 year if tides are excluded in the hydrodynamic model There is a high spatial variability of the tidal effect on the water export rate, which is associated with the water depth