Investigation of the Kuroshio-coastal current interaction and marine heatwave trends in the coral habitats of Northeastern Taiwan

Highlights

• The Kuroshio branch exhibits a northwestward intrusion trend into the ECS shelf.
• The coral habitats experienced over 400 days of marine heatwaves from 2020 to 2022.
• The coral habitats reached the bleaching alert level 2 for the first time in 2020.
• The PDO negative phase and La Niña occurrence have increased MHW days.
• The lack of periodic cooling is harmful to this area’s coral habitats.

Abstract

The continually rising concentration of the surface aqueous partial pressure of carbon dioxide has led to sustained ocean acidification and increased sea surface temperature (SST) in the coral habitats of northeastern Taiwan. Since 2016, this region has been experiencing intense marine heatwave (MHW) events, with the accumulated thermal stress reaching its peak between 2020 and 2022. Apart from the attributing factor of the increasing atmospheric carbon dioxide concentration, the Kuroshio (KC) path along the eastern coast of Taiwan has exhibited a westward tendency towards the coast of Taiwan from October to April. The westward and northward components of the KC’s branch into the East China Sea (ECS) shelf have rapidly increased. The interplay between the KC and the northeastern Taiwan coastal countercurrent (NETCC) near the coral habitats has formed a counterclockwise circulation, which continues to show a westward trend. This has resulted in the influx of warmer waters into northeastern Taiwan. On another note, the pronounced negative phase of the Pacific decadal oscillation (PDO) and La Niña conditions from 2020 to 2022 have further contributed to the increased SST, with the average MHW event accumulating to 172 days annually. The coral bleaching index, degree heating week (DHW), indicates that 2020 was historically the first year for this region to experience a DHW exceeding 8°C-weeks, reaching an Alert Level 2 for bleaching, and 2022 saw even more severe conditions with an average of 12 days at this level. With a reduced number of typhoon incursions in recent years in northeastern Taiwan, and the absence of periodic cold waters to mitigate the heat, the future marine environment of the coral habitats in this region is of significant concern.

Hsu P.-H., Tabanao Macagga R. A., Lu C.-Y. & Yuan-Jane Lo D., 2024. Investigation of the Kuroshio-coastal current interaction and marine heatwave trends in the coral habitats of Northeastern Taiwan. Regional Studies in Marine Science 71: 103431. doi: 10.1016/j.rsma.2024.103431. Article (subscription required).

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