Coastal dissolved organic matter (DOM), with mixed allochthonous and autochthonous sources, is the dominant reduced carbon pool and thus the key modulator of coastal carbon cycle. Coastal DOM can undergo a variety of biogeochemical processing (e.g. production, transformation and degradation) which are strongly shaped by river plumes, coastal upwelling and their interactions. To quantitatively determining the long-term DOM variations by these processing is very important for better defining the storage potential of DOM in coastal carbon budget. However, this remains a big challenge as coastal physical dynamics are highly changing in spatial and temporal scales due to hydroclimatic change, e.g. El Niño Southern Oscillation (ENSO) perturbations. In this study, we conducted seven high-resolution observations for DOC, colored and fluorescent DOM (CDOM/FDOM) along three sections of the southern Taiwan Strait during fifteen-year period (2010-2025), fully covering two upwelling systems (the coastal southwest upwelling, SWU; the Taiwan Bank upwelling, TBU) and the Pearl River Plume system (PRP). The coupling between ENSO index, upwelling intensity, and addition of humic-like FDOM (FDOMH), and its implication for refractory carbon storage in the coastal region will be presented.