The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

Despite a global decline in marine cold spells (MCSs) under ongoing warming, the Taiwan Strait has experienced a pronounced increase in wintertime MCS frequency and persistence since ~2011, causing large-scale coral bleaching and fishery losses. This study investigates the interdecadal change and physical mechanisms of wintertime MCSs in the Taiwan Strait from 1985 to 2025 using satellite observations and reanalysis data. Results reveal a clear regime shift  around 2011. Before 2011, MCSs occurred ~0.5 events per year and lasted ~33 days on average. After 2011, both metrics nearly doubled to 1.1 events per year and ~55 days. Mixed‑layer heat budget analysis reveals a systematic transition across three hotspots: the northwestern strait (R1), the southwestern strait (R2), and mid-to-northern coast of Taiwan Island (R3). Surface heat flux contributions declined from 64%-75% in R1-R3 regions pre‑2011 to 24%-56% post‑2011, while advective contributions rose from 26%-35% to 42%-79%, particularly becoming dominant in R3. This shift from a surface‑flux–dominated to a dynamically reinforced cold regime is driven by the intensified East Asian winter monsoon, expressed via stronger mean northerlies and more frequent cold surges. The enhanced wind forcing amplifies southward cold advection by the China Coastal Current, while increased oceanic memory delays seasonal warming. This monsoon intensification is linked to a post-2011 reorganization of large-scale atmospheric circulation over the North Pacific. Under this reorganized background, a multi‑modal state integrating tropical and enhanced extratropical variabilities emerges, favoring persistent northerly wind forcing and contributing to the prolonged duration of MCS in the Taiwan Strait.