台湾海峡陆源沉积碳汇的有机分子记录及其对极端气候事件的响应

Chinese marginal seas play a significant role in the global and regional organic carbon cycle, which are strongly influenced by the Yangtze River, Yellow River, Pearl River and Taiwan mountainous rivers. Both human activities and climate changes can effect the mobilization of terrigenous organic matter (TOM) delivered from the continental to marine environment, eventually influencing the capacity of carbon sink in marginal seas. In addition of marine source material interference, the inherent complexity and heterogeneity of TOM make it difficult to evaluate the atmospheric carbon dioxide sequestration ability in these sedimentary systems and interpret implications for paleo-climate and paleo-environment reconstructions from marginal sea sediment records. In the past decades, extreme climate events (e.g. floods and typhoons) show a frequency decrease but increase in intensity. Highly terrigenous materials input always associated with hyperpycnal discharge caused by extreme climate events. Here, we propose to carry out multiple organic geochemistry proxies based on bulk (TOC and black carbon) and biomarker characteristics (e.g., content and carbon isotopic compositions) to develop a more complete view of the compositions, sources and ages of organic matter delivery in the climatically sensitive Taiwan Strait where underlying highly frequent hyperpycnal events and terrestrial clastic sediment loading. These would enable us to understand various carbon sink for atmospheric carbon dioxide associated with various OM pool derived from different origins (marine vs. terrestrial biosphere vs. fossil). Moreover, we attempt to reconstruct the history of hyperpycnal events through molecular-level records over the past 2,000 years in Taiwan Strait. Our data can provide long-term historical material for model the future trends of extreme climate change in the global and regional scale.

近海埋藏的陆源物质的多源性、异质性及其在海源基质上的叠加，不仅增加了边缘海沉积碳汇评估的难度，还给海洋沉积物中陆源信号记录的解读带来了挑战。受长江、黄河和珠江以及台湾高山河流物质输运的贡献，我国边缘海是一个重要的陆源有机碳汇。近几十年来我国洪水和台风事件频发，虽然频率降低但强度增强，导致极端气候条件影响下的径流输入边缘海的陆源物质仍明显增加。本研究拟采用多种陆源有机质示踪手段（生物标志物法及总有机碳/有机分子单体13C、14C同位素法），系统地研究既受到台风影响且高陆源输入的台湾海峡陆源沉积有机质的来源、迁移及其所蕴含的古环境重建意义，估算沉积有机质中海源、陆地生源和化石源的埋藏贡献，为深入了解边缘海碳汇提供科学依据。在此基础上，重建过去2000年台湾海峡陆源有机质埋藏变化的沉积记录，反演气候变化和人类活动影响下的台风事件高频信号，为未来极端气候变化预测模型建立提供长期连续的历史观测资料。

近海埋藏的陆源物质的多源性和异质性对海洋沉积物中陆源信号记录的解读带来了巨大的挑战。至今对于陆源有机质在我国河流-海洋跨系统传输中的生物地球化学循环过程及定性定量的综合研究仍然十分缺乏。本项目选取既受到台风影响且高陆源输入的台湾海峡为研究区，1）首先，通过研究多种来源典型性有机分子含量和碳同位素空间分布特征定性地揭示不同来源有机质向海洋的输送和埋藏行为，确证沉积柱中有机分子记录的古环境重建意义。2）其次，利用多种有机地球化学指标（生物标志物指标和13C、14C同位素指标）定量地估算该区域沉积有机质的来源（海源vs陆地生源vs化石源）。 3）最后，通过重建过去4000年来台湾海峡有机分子的沉积记录，认识气候变化和极端事件对地壳（沉积岩和土壤）物理侵蚀过程和边缘海不同来源有机碳埋藏的影响，为深入了解我国边缘海碳汇提供科学依据。