Impact of Typhoon Morakot (2009) on the compositions and distributions of sedimentary organic matter in the Mud Depo-center of Zhejiang-Fujian Coast

Typhoons are one of the most significant ocean-atmosphere interaction processes at the weather scale, exerting a large impact on the marine environment (including the deposition of organic matter) within a short period. The effects of Typhoon Morakot (2009) on the compositions and distributions of sedimentary organic matter (SOM) were analyzed. The distinct influence of typhoons following different paths on SOM was compared, and their mechanisms were discussed based on the analysis on grain size, total organic carbon (TOC), total nitrogen (TN), and carbon isotope composition (δ¹³C) of sediments collected in the Mud Depo-center of the Zhejiang-Fujian Coast before and after Typhoon Morakot (2009). Results indicate that Typhoon Morakot (2009) significantly affected the compositions and distributions of TOC in the study area. The findings from a three end-member mixing model revealed that the sedimentary organic carbon in the study area originated primarily from the sediments of the Yangtze River Delta and marine phytoplankton. The influence of Typhoon Morakot led to an increase in primary productivity in the study area, resulting in a higher proportion of marine-sourced organic carbon in the sediments. Additionally, nearshore sediments experienced significant erosion and re-transport due to the dynamic effects of Typhoon Morakot, leading to a reduction in TOC content in the sediment. The differential response of sediment dynamics caused by the asymmetric wind field of typhoons with varying paths led to distinct impacts on material sources, marine biogeochemical processes, and sediment transport and modification processes within the same study area and thus had different impacts on the compositions and distributions of SOM. These findings provide a scientific basis for the comprehensive understanding of carbon burial in the coast and shelf under the influence of extreme marine dynamics.