Response Process of Coastal Hypoxia to a Passing Typhoon in the East China Sea

Abstract

Details of the development of coastal hypoxia in response to the passage of Typhoon Bavi (2020) in the East China Sea were reconstructed by numerical modeling using a three-dimensional coupled physical–biogeochemical model. The model was validated via repeated surveys along a transect across a submerged river valley off the Changjiang Estuary before and after the passage of Typhoon Bavi. Before Bavi’s arrival, survey data indicated that the coastal hypoxia had formed off the Changjiang Estuary. However, the hypoxia was not eliminated but instead migrated and aggravated along the observed transect after the typhoon passage. This phenomenon cannot be attributed to the typhoon-induced mixing. Simulation results reveal that the observed development and spatial migration of hypoxia was mainly controlled by typhoon-induced oceanic advection. Results show that Bavi stimulated a regional quasi-barotropic cyclonic loop circulation and coastal downwelling reversing general summer circulation patterns. The onshore transport of the warmer shelf water and subsequent downwelling resulted in a warming of coastal water. The southward coastal current and downwelling induced by the typhoon also led to a migration of the hypoxic zone. Meanwhile, a massive transport of resuspended planktonic detritus from the steep inner shelf and the shallow Changjiang bank toward the submerged river valley occurred. This study reveals that the typhoon-driven currents can play an important role in the development of hypoxia and redistribution of deposited organic matter in coastal shelf seas, which may have both short- and long-term effects on the regional marine biogeochemical environment.

Biogeochemical dynamics in a marine storm demonstrates differences between natural and anthropogenic impacts

“…Nevertheless, the capacity for storms to transport fresh OM and nutrients into a system can trigger longer-term changes to dissolved oxygen levels. Following the initial increase of oxygen from wave mixing, local biogeochemistry may be stimulated by the storm-induced arrival of fresh OM 11 , 20 , 25 leading to reductions in dissolved oxygen 21 , 26 , 27 . Coastal areas with high anthropogenic influence are particularly vulnerable to storm-induced hypoxia after an initial spike in primary production 19 , 20 .…”

“…Particle transport and vertical mixing driven by storm-induced currents can stimulate biogeochemical cycling in the water column after receiving an influx of OM and nutrients 11 , 20 , 24 , 25 . Oxygen-consuming OM mineralization has been documented to be a prominent biogeochemical process taking place in the water column after storm disturbance 11 , 21 , 26 , 27 , although, storms have also been linked with reduced sedimentary OM and lower fluxes of dissolved inorganic carbon from the seafloor 28 .…”

Using Stable Isotopes and Spectral Properties of Particulate and Dissolved Organic Matter to Quantify Typhoon‐Induced Organic Matter Decomposition

“…Thus, in recent years, despite the dangerous and challenging of field observations before and after typhoons, some field observations have been conducted to explore the characteristics and mechanisms of decomposition. Recent studies based on field observations of typhoons have reported that typhoon processes cause strong decomposition of OM in coastal areas (Lao, Chen, et al., 2023; Meng et al., 2022; Wang et al., 2017; Zhou et al., 2021). In the Yangtze Estuary, a large amount of terrestrial OM is imported into the coastal area due to the significant rainfall during typhoons, resulting in decomposition of OM and expansion of the anoxic area (Meng et al., 2022).…”

“…Recent studies based on field observations of typhoons have reported that typhoon processes cause strong decomposition of OM in coastal areas (Lao, Chen, et al., 2023; Meng et al., 2022; Wang et al., 2017; Zhou et al., 2021). In the Yangtze Estuary, a large amount of terrestrial OM is imported into the coastal area due to the significant rainfall during typhoons, resulting in decomposition of OM and expansion of the anoxic area (Meng et al., 2022). In addition, field observations from our previous studies have found that regardless of whether phytoplankton blooms occur after a typhoon, the enhanced water mixing caused by the typhoon leads to an increase decomposition of OM, resulting in intense oxygen depletion in the water column (Lao, Chen, et al., 2023; Lu et al., 2022; Zhou et al., 2021).…”

Changes in hydrodynamics and nutrient load of the coastal bay induced by Typhoon Talim (2023)

“…Particularly in the coastal waters, typhoons can increase the input of massive terrestrial nutrients, and can enhance water mixing to carry the deeper eutrophic water to the upper layer (Lao et al, 2023b;2023c;Chen et al, 2024). These processes will lead to a series of marine ecological problems, such as algal blooms (Wang et al, 2016;Jiang et al, 2022;Li et al, 2022), decomposition of organic matter (Zhou et al, 2021;Lu et al, 2022;Lao et al, 2023a), hypoxia (Wang et al, 2017;Li et al, 2019;Zhao et al, 2021;Meng et al, 2022). Therefore, studying the changes in ocean hydrodynamic processes and nutrient supplies caused by typhoons will be beneficial for us in gaining a deeper understanding of their impact on the marine eco-environment.…”