Intermittent migration of mixing front driven by typhoon events on the inner shelf of the East China Sea: A FVCOM modeling study

Abstract

Mixing fronts on the inner shelf of the East China Sea (ECS) are common under normal summer conditions, yet its migration during extreme weather events, such as typhoons, has been poorly understood due to limited availability of observational data. In this study, we used a well-validated Finite-Volume Community Ocean Model (FVCOM) to investigate the intermittent migration of mixing fronts on the inner shelf of the ECS during the passage of Typhoon Chan-hom in July 2015. The sedimentary and ecological effects of the front migration were also revealed. Results suggested that the potential energy anomaly (PEA) of 10 J/m3 could be a critical value to determine the location of the mixing front, which was consistent with that derived from the Simpson-Hunter (SH) parameter. Accordingly, the mixing front showed a rapid seaward migration from 15-m isobaths to 60-m isobaths under the drastic ocean turbulence during the typhoon and recovered shortly after its passage. This intermittent migration of the mixing front had the potential to facilitate cross-shelf material transport during the typhoon. On the one hand, the front migration could not only open the access for the seaward transport of nearshore resuspended sediments but also trap them within a certain area, causing an offshore deposition between 20 and 60 m isobaths south of the typhoon track. The mixing fronts had a boundary effect constraining the typhoon-induced sedimentation. On the other hand, unlike sediments that would settle down with weakened ocean dynamics, the offshore movement of coastal diluted water triggered by the typhoon remained after the front recovery. These nutrient-rich waters could be transported to the middle or even outer shelf of the ECS by the subsequent southwest summer monsoon, enhancing local primary production and potentially trigering significant algal blooms.