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

Typhoons exert a profound impact on marine biogeochemical processes, with organic matter (OM) decomposition serving as a key biogeochemical process in coastal waters after typhoons. Despite its significance, the specific contributions of particulate organic matter (POM) and dissolved organic matter (DOM) to OM decomposition triggered by typhoons remains unclear. In this study, stable isotopes of POM and spectral properties of DOM were investigated before and after Typhoon "Barija" in Zhanjiang Bay, northwestern South China Sea. The typhoon-induced intrusion of high-salinity seawater from the lower bay to the upper bay, driven by the external clockwise wind stress, led to the formation of an ocean front in the middle bay during the typhoon. Notably, the POM decomposition induced by the typhoon in the upper bay (72%) significantly surpassed that in the lower bay (5%), attributed to the barrier effect of the ocean front and increased vertical mixing in the upper bay. In contrast, the decomposition removed only 29% DOM in the upper bay, and a net addition of DOM occurred in the lower bay due to phytoplankton growth and POM decomposition. More importantly, despite the overall larger DOM in the water column, the POM inventory in the upper bay removed by typhoon-induced decomposition (20.19 g m(-2)) exceeded that of DOM (16.08 g m(-2)). Overall, our study suggests that POM decomposition is more critical than DOM decomposition after typhoons, primarily influenced by the ocean front and vertical mixing. These findings contribute to a clearer understanding of the post-typhoon biogeochemical dynamics in coastal waters.