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

与东部边界上升流系统相关的最小含氧区（OMZ）是重要的经济区，在那里，营养丰富的沃茨向表层海洋的强烈上升流维持了较高的海洋初级生产力，并支持了全球50%以上的渔业。据预测，有机隔离带的垂直扩展和加强是气候变化的结果，因为溶解在较温暖的沃茨中的氧气减少，海洋分层的加强减少了海洋内部的氧气供应。这些有机开放区的变化直接将鱼类栖息地限制在表面，增加了过度捕捞的风险，并可能导致沿海海洋生态系统未来的大规模捕捞。有机磁区的变化也会影响表层海洋的营养物质供应及其支持的海洋碳循环，但确切的机制尚未完全了解。了解营养供应和海洋生物群如何响应OMZ强度的过去变化将提供重要的见解如何海洋生物地球化学和碳循环响应未来的海洋脱氧。在这项拟议的研究中，我将使用两个新的代理，稳定的镉（Cd）和钡（Ba）同位素，从秘鲁OMZ 1）限制影响表层海洋生产力和OMZ地下矿化的过程，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体混合密切相关。在海洋沉积物中，Cd和Ba同位素也受到这些元素的自生沉淀和沉积后成岩作用的影响，而这些过程之间的同位素分馏程度很难量化。本研究将测量海水、海洋沉降颗粒物、沉积物和孔隙沃茨中Cd和Ba的同位素比值，以限制其在不同生物、化学和物理过程中的同位素分馏效应。有了这些结果，我将量化的源和汇，fractionated两个同位素系统在现代海洋和评估沉积后成岩作用如何影响镉和钡同位素分馏。这项拟议工作的最终目标是开发沉积镉和钡同位素作为可靠的代理过去的变化，出口生产和矿化强度。

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.