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

[摘要] Rivers carry large amounts of freshwater and terrestrialmaterial into shelf seas, which is an important part of the global water andbiogeochemical cycles. The earth system model or climate model is animportant instrument for simulating and projecting the global water cycleand climate change, in which tides however are commonly removed. For abetter understanding of the potential effect of the absence of tides in thesimulation of the water cycle, this study compared the results of a regionalmodel with and without considering tides, and evaluated the effect of tideson the behavior of three major rivers (i.e., the Yellow, Yalujiang, andChangjiang rivers) water in the eastern shelf seas of China from theperspectives of transport pathways, timescales, and water concentration. Theresults showed that the tides induced more dispersed transport for the waterof the Yellow and Yalujiang rivers, but more concentrated transport for theChangjiang River water. The effect of tides on the transit areas of theYellow, Yalujiang, and Changjiang rivers was 13 %, 40 %, and 21 %,respectively. The annual mean water age and transit time of the three riversin the model with tides were several ( ∼  2–10) times higherthan those in the no-tide model, suggesting that tides dramatically slow theriver water transport and export rate over the shelf. By slowing the riverwater export, tides induced a three-fold increase in river waterconcentration and a decrease in shelf seawater salinity by  >  1.Moreover, the effect of tides on river behavior was stronger in relativelyenclosed 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 bytides is the main cause of the difference in the river water behaviorbetween the two model runs. Tides can increase bottom stress and thus weakenshelf currents and decrease the water transport timescales. The improvementin tidal parameterization in the no-tide model in the simulation of riverwater behavior was very limited. Given the important role of river runoff onthe global water cycle and the effect of changes in river water behavior onocean carbon cycling, it is important to include the tidal effect in earthsystem models to improve their projection accuracy.

[学科分类] 妇产科学