台风“莫拉克”(2009)对浙闽沿岸泥质中心沉积有机质组成与分布的影响

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

  • 摘要: 台风是天气尺度上对海洋环境影响最大的海气相互作用过程之一,在短时间内会对影响海域的海洋环境(包括沉积有机质等)产生巨大的影响。本文基于夏季台风前、后采集的浙闽沿岸泥质中心沉积物的粒度、总有机碳(TOC)、总氮(TN)以及碳同位素组成(δ13C)的测试结果,分析了台风“莫拉克”(2009)对研究区沉积有机质来源及分布的影响,对比了台风“莫拉克”与其他不同路径的台风对沉积有机质分布影响的差异,探讨了影响差异的机制。结果显示,台风“莫拉克”(2009)对浙闽沿岸泥质区沉积物中TOC的来源和分布产生了显著影响。端元分析结果表明,浙闽沿岸泥质中心沉积物中有机碳主要来源于长江三角洲沉积物以及海洋自生有机质,在台风的影响下,浙闽沿岸泥质中心的初级生产力升高,进而增加了沉积物中海源有机碳的比例。同时,在台风的动力作用下,近岸沉积物发生了明显的侵蚀与再搬运,导致近岸沉积物中TOC的含量显著降低。受控于台风不对称风场造成的沉积动力差异,不同路径的台风会对研究区的物源输入、海洋生物地球化学以及沉积物的搬运改造等产生不同的影响,进而影响到沉积有机质的组成和分布。研究结果为全面认识极端海况影响下近岸陆架“碳埋藏”提供了科学依据。

     

    Abstract: 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.

     

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