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

Abstract

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.

The Seasonal Effect of Coastal Current and Upwelling on the Dynamics of Dissolved Organic Matter in the Northwestern South China Sea

“…Winter was less influenced by upwelling and showed removal of some DOM (a CDOM (325), C1, C3, and C4; Tables 3 and 4). The vertical uniformity of temperature and salinity in winter (Figures 2k and 2v), which indicated enhanced vertical water mixing, contributed to microbial decomposition (Lu et al, 2024). Additionally, when comparing ΔDOM values between spring and winter, it was found that ΔDOM values in winter were higher than those in spring (Tables 3 and 4).…”

“…In addition, the positive values of Δa CDOM (254), Δa CDOM (325), ΔC1, ΔC2, ΔC3, and ΔC4 were observed in the nearshore during the three seasons (Tables 3 and 4). Such high positive values indicated the pronounced addition of DOM in the nearshore area during these seasons, most likely resulting from microbial-mediated decomposition of particulate organic matter (POM), particle desorption, or biological production (Guo et al, 2014;Lu et al, 2024). The dominant process for the addition of DOM can be identified by observing a significant negative correlation between POM and DOM as well as a positive correlation between TSM and DOM (Guo et al, 2007;Li et al, 2015Li et al, , 2020.…”