科研动态 Research Highlight

台风结合海底峡谷对生源有机碳来源及其向深海传输行为的影响
Isotopic evidence for the influence of typhoons and submarine canyons on the sourcing and transport behavior of biospheric organic carbon to the deep sea
发布日期:2017-5-27      浏览次数:613

分布在西太平洋的高山岛屿由于活跃的地质构造以及受频繁台风袭扰带来的高物理侵蚀,使其成为陆海界面碳输出的热点研究区域。这些区域狭窄的陆架及广泛分布的地形陡峭的海底峡谷系统是河流沉积物和陆地有机物向深海输送的主要通道,然而目前对海底峡谷有机质的来源、组成及其传输行为尚不清楚。

高树基教授课题组以碳同位素(δ13C14C)为手段,分析了高屏海底峡谷沉降颗粒,并结合潜在的有机碳来源(高屏河流悬浮物、陆架沉积物),从源到汇的视角揭示了高山流域与海底峡谷的耦合对有机物的迁移转化的影响。

结果表明,河流悬浮物及其周边海域沉积物中老化的有机物质主要源自对古代台风/地震引发的古滑坡形成的冲积扇和堆积扇的侵蚀。在非台风期间,河流传输能力较弱,海底峡谷的沉降颗粒主要来自浅层陆架沉积物的再悬浮。在台风期间,河流与海底峡谷直接连接,海底峡谷的沉降颗粒主要来自河流输入。在台风引发的洪峰期间,在深层水中发现新鲜的植物残体(属于现代碳汇),表明异重流的高夹带效率可以将轻密度的植物碎屑有效地运输到深水中。因此,台风事件结合海底峡谷地形有利于陆地有机物向深海传输,从而是大气二氧化碳重要的汇。此外,由于植物碎屑被认为是石油和天然气的重要来源,因此这种高效的有机质搬运方式对海底形成地质资源有重要的影响。该团队推测,在全球变暖背景下,降雨强度及随之而来的洪水的增强使得这一途径对气候的效应变得更为重要。

该研究成果于20175月发表于地学领域权威期刊Earth and Planetary Science Letters上(2015年影响因子4.326)。论文第一作者是博士研究生郑立伟,通讯作者为 “千人计划特聘教授高树基。

Abstract: Export of biospheric organic carbon from land masses to the ocean plays an important role in regulating the global carbon cycle. High-relief islands in the western Pacific are hotspots for such land-to-ocean carbon transport due to frequent floods and active tectonics. Submarine canyon systems serve as a major conduit to convey terrestrial organics into the deep sea, particularly during episodic floods, though the nature of ephemeral sediment transportation through such canyons remains unclear. In this study, we deployed a sediment trap in southwestern Taiwan's Gaoping submarine canyon during summer 2008, during which Typhoon Kalmaegi impacted the study area. We investigated sources of particulate organic carbon and quantified the content of fossil organic carbon (OCf) and biospheric non-fossil carbon (OCnf) during typhoon and non-typhoon periods, based on relations between total organic carbon (TOC), isotopic composition (δ13C, 14C), and nitrogen to carbon ratios (N/C) of newly and previously reported source materials. During typhoons, flooding connected terrestrial rivers to the submarine canyon. Fresh plant debris was not found in the trap except in the hyperpycnal layer, suggesting that only hyperpycnal flow is capable of entraining plant debris, while segregation had occurred during non-hyperpycnal periods. The OCnf components in typhoon flood and trapped samples were likely sourced from aged organics buried in ancient landslides. During non-typhoon periods, the canyon is more connected to the shelf, where waves and tides cause reworking, thus allowing abiotic and biotic processes to generate isotopically uniform and similarly aged OCnf for transport into the canyon. Therefore, extreme events coupled with the submarine canyon system created an efficient method for deep-sea burial of freshly produced organic-rich material. Our results shed light on the ephemeral transport of organics within a submarine canyon system on an active tectonic margin.

Citation: Li-Wei Zheng, Xiaodong Ding, James T. Liu, Dawei Li, Tsung-Yu Lee, Xufeng Zheng, Zhenzhen Zheng, Min Nina Xu, Minhan Dai, Shuh-Ji Kao. Isotopic evidence for the influence of typhoons and submarine canyons on the sourcing and transport behavior of biospheric organic carbon to the deep sea. Earth and Planetary Science Letters 2017, 465: 103-111, doi: 10.1016/j.epsl.2017.02.037.

论文链接http://www.sciencedirect.com/science/article/pii/S0012821X1730105X