Barium and cadmium stable isotopes as tracers for carbon export, remineralization strength and post-deposition diagenesis in the Peruvian oxygen minimum zone

钡和镉稳定同位素作为秘鲁最低氧带碳输出、再矿化强度和沉积后成岩作用的示踪剂

• 批准号: 432469432
• 负责人: Dr. Ruifang Xie, Ph.D.
• 金额: --
• 依托单位: Shanghai Jiao Tong University (SJTU)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/432469432?language=en
• 关键词: Barium; cadmium; stable; isotopes; tracers

Oxygen minimum zones (OMZs) associated with eastern boundary upwelling systems are important economic areas where intense upwelling of nutrient-rich waters to the surface ocean sustains high marine primary production and supports >50% global fisheries. Vertical expansion and intensification of OMZs is predicted as a consequence of climate change because less oxygen dissolves in warmer waters and strengthened ocean stratification reduces oxygen supply to the ocean interior. These changes of OMZs directly restrict fish habitats to the surface, increase the risk of over-fishing, and may lead to future mass extinctions in coastal marine ecosystems. Variabilities of OMZs will also affect nutrient availability to the surface ocean and the marine carbon cycle it supports, but the exact mechanisms are not fully understood. Understanding how nutrient supply and marine biota responded to past changes of OMZ intensities will provide important insights on how marine biogeochemical and carbon cycles respond to future ocean deoxygenation. In this proposed research, I will use two novel proxies, stable cadmium (Cd) and barium (Ba) isotopes, from the Peruvian OMZ to 1) constrain processes that affect surface ocean productivity and subsurface remineralization in OMZs, and 2) assess how future ocean deoxygenation may impact the global carbon cycle. Both dissolved Cd and Ba isotopes in seawater are tightly coupled to biological processes and water mass mixing. In marine sediments, Cd and Ba isotopes are also affected by authigenic precipitation of these elements and post-depositional diagenesis, whereas the extent of isotope fractionation among these processes are poorly quantified. I will measure Cd and Ba isotope ratios in seawater, marine sinking particulates, sediments and pore waters to constrain their isotope fractionation effects during different biological, chemical and physical processes. With these results, I will quantify the sources and sinks that fractionate both isotope systems in the modern ocean and assess how post-depositional diagenesis affects Cd and Ba isotope fractionation. The ultimate goal of this proposed work is to develop sedimentary Cd and Ba isotopes as reliable proxies for past changes in export production and remineralization strength.

与东部边界上升流系统相关的最低含氧区是重要的经济区，营养丰富的水域向表层海洋的强烈上升流维持了海洋初级生产力的高水平，并支持了50%的全球渔业。OMZ的垂直扩展和加强预计是气候变化的结果，因为在较温暖的水域中溶解的氧气减少，海洋层化的加强减少了对海洋内部的氧气供应。海洋保护区的这些变化直接将鱼类栖息地限制在海面上，增加了过度捕捞的风险，并可能导致未来沿海海洋生态系统的大规模灭绝。OMZ的多样性也将影响表层海洋的营养物质供应及其支持的海洋碳循环，但确切的机制尚不完全清楚。了解营养供应和海洋生物群如何响应过去OMZ强度的变化，将为海洋生物地球化学和碳循环如何响应未来的海洋脱氧提供重要的见解。在这项拟议的研究中，我将使用来自秘鲁OMZ的两种新的替代物--稳定的镉(Cd)和钡(BA)同位素，以1)限制影响表层海洋生产力和OMZ次表层再矿化的过程，以及2)评估未来海洋脱氧可能如何影响全球碳循环。海水中溶解的Cd和Ba同位素与生物过程和水团混合密切耦合。在海洋沉积物中，Cd和Ba同位素也受到这些元素的自生降水和沉积后成岩作用的影响，但这些过程之间的同位素分馏程度很难量化。我将测量海水、海洋下沉颗粒物、沉积物和孔隙水中的Cd和Ba同位素比率，以限制它们在不同生物、化学和物理过程中的同位素分馏效应。根据这些结果，我将量化现代海洋中使这两个同位素系统分馏的源和汇，并评估沉积后成岩作用如何影响Cd和Ba同位素分馏。这项拟议工作的最终目标是开发沉积Cd和Ba同位素，作为过去出口产量和再矿化强度变化的可靠指标。