Stable nitrogen isotopic ratios of sediments from the Arabian Sea: Influences of water column oxygenation sedimentation rates, and diagenesis

阿拉伯海沉积物的稳定氮同位素比：水柱充氧沉积速率和成岩作用的影响

• 批准号: 12795331
• 负责人: Professor Dr. Kay-Christian Emeis
• 金额: --
• 依托单位: Institut für Geologie
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 财政年份: 2005
• 资助国家: 德国
• 起止时间: 2004-12-31 至 2006-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/12795331?language=en
• 关键词: Stable; nitrogen; isotopic; ratios; sediments

Nitrogen is a key element in regulating biological processes in the ocean. The ratio of the two stable N-isotopes (expressed as ol5N) in sinking particles and surface sediments reflects Nsources, biogeochemical processes, and nutrient regime in the overlying water. The ratio is commonly used as a proxy to reconstruct marine nutrient cycles in the geological past, and is gaining importance for the detection of global changes in the cycling in an essential nutrient forced by climatic and oceanographic change. Possible biases on the use of 15N/I4N ratios as a proxy are sedimentation rates and diagenesis under either oxic, suboxic, or anoxic conditions. Differential degradation of biological products under oxic and anoxic conditions has been postulated from several studies on Sl5N of bulk nitrogen in suspended matter and in sediments. We propose to explore these possible biases in a key region for the global nitrogen cycle, the Arabian Sea (Leg 117, Sites 722 and 724); the region also experienced significant changes in sedimentation rates under glacial and interglacial conditions. To elucidate possible diagenetic effects and effects of sedimentation rates requires that we determine 6I5N in conjunction with an index of organic matter quality, i.e., the state of degradation, which is affected by oxygen content at the sediment water interface and by sedimentation rate. A suitable index is a degradation index based on the ratios of amino acids. This coupled analysis of stable N-isotope ratio and its dominant molecular source (amino acids) will permit an assessment of the value of nitrogen isotope ratios for reconstructions of past biogeochemical cycles in the ocean.

氮是调节海洋生物过程的关键元素。沉积物和沉降颗粒中两种稳定氮同位素比值（以δ 15 N表示）反映了上覆水体中氮的来源、地球化学过程和营养状况。这一比率通常被用作重建地质学历史中海洋营养循环的替代指标，对于探测气候和海洋变化所导致的一种基本营养循环的全球变化越来越重要。使用15 N/I4 N比值作为替代可能存在的偏差是在好氧、亚氧或缺氧条件下的沉积速率和成岩作用。根据对悬浮物和沉积物中大量氮的S15 N的几项研究，已经假定在好氧和缺氧条件下生物产物的不同降解。我们建议在全球氮循环的一个关键区域，阿拉伯海（腿117，网站722和724），探索这些可能的偏见，该地区也经历了重大变化，在冰川和间冰期条件下的沉积速率。为了阐明可能的成岩作用和沉积速率的影响，我们需要结合有机质质量指数，即，降解状态，受沉积物-水界面氧含量和沉积速率的影响。合适的指数是基于氨基酸比率的降解指数。这种稳定的N-同位素比值及其主要分子源（氨基酸）的耦合分析将允许在过去的海洋地球化学循环重建的氮同位素比值的价值进行评估。