Collaborative Research: Evaluating the use of Se/S in marine barite as a tracer of ocean nutrients

硝酸盐在许多海洋环境中是一种关键的限制性营养物质，因此硝酸盐浓度的代用物对于理解过去驱动碳输出通量的机制将是非常宝贵的。硒酸盐（SeO4=）是微量元素硒的溶解化学种之一，与硝酸盐具有良好的相关性，具有地表水耗竭和深水富集的特点。在这方面，硒的生物地球化学循环与氮的类似。此外，硒酸盐在化学上几乎与硫酸盐相同，因此被纳入重晶石中，重晶石是一种在水柱中无机形成的成岩稳定矿物。来自老道明大学和斯坦福大学的研究人员将测试海洋自生重晶石中Se/S比率作为上层海洋硝酸盐浓度代表的适用性。为了实现这一目标，他们将评估和量化导致硒酸盐掺入海洋重晶石的过程，并开发一种经验岩心顶部校准，以便该代理的应用尽可能准确。他们基于实验室的方法将包括：(1)在不同环境条件和硒酸盐/硫酸盐比例下的实验室无机/非生物重晶石沉淀，并测量所得重晶石中的Se/S；(2)在腐烂的海洋颗粒（浮游植物）和变化的硒酸盐/硫酸盐存在下的重晶石沉淀，以模拟实际水柱过程；(3)在1000 m以上2 ~ 3深度的沉积物捕集器样品中分离重晶石并测定Se/S；(4)测定从世界各地海洋岩心顶部样品中分离的重晶石中的硒/硫，这些样品有相应的硒酸盐和营养物质数据。就更广泛的影响而言，拟议的研究将直接涉及研究生研究助理，作为博士论文的一部分。少数族裔学生也将有机会通过老道明大学（ODU）少数族裔本科生奖学金和培训REU计划，以及奥德明大学-汉普顿大学-弗吉尼亚海洋科学研究所大厅-邦纳海洋科学少数族裔博士学者计划参与并为拟议的研究做出贡献。pi还将保留其大学网站，展示当前的研究成果，旨在供公众浏览，而不仅仅是内部科学交流。

Nitrate is a key limiting nutrient in many oceanic environments, and so a proxy for nitrate concentration would be invaluable for understanding mechanisms driving C export fluxes in the past. Selenate (SeO4=), one of the dissolved chemical species of the trace element selenium, shows an excellent correlation with nitrate, having surface water depletion and deep-water enrichment. In this respect, the biogeochemical cycle of selenium is analogous to that of nitrogen. Furthermore, selenate is almost chemically identical to sulfate and as such is incorporated into barite, a diagenetically stable mineral that is formed inorganically in the water column. Investigators from Old Dominion University and Stanford University will test the suitability of the Se/S ratio in marine authigenic barite as a proxy for upper ocean nitrate concentrations. To achieve this goal, they will evaluate and quantify the processes leading to the incorporation of selenate into marine barite, and develop an empirical core top calibration so that the application of this proxy is as accurate as possible. Their laboratory based approach will include: (1) inorganic/abiotic barite precipitations in the laboratory under varying environmental conditions and selenate/sulfate ratios, and measurements of the Se/S in the resulting barite; (2) barite precipitation in the presence of decaying marine particles (phytoplankton) and varying selenate/sulfate to simulate actual water column processes; (3) isolation of barite and determination of Se/S from available sediment trap samples taken at 2-3 depths in the upper 1000 m; and (4) determinations of Se/S in barites isolated from core-top samples from throughout the world's oceans where there are corresponding selenate and nutrient data. In terms of broader impacts, the proposed research will directly involve a graduate research assistant as part of a Ph.D. dissertation. There will also be opportunities for underrepresented minority students to participate and contribute to the proposed research through Old Dominion University's (ODU) Minority Undergraduate Scholarship and Training REU program, and the joint ODU-Hampton University-Virginia Institute of Marine Sciences Hall- Bonner Program for Minority Doctoral Scholars in Ocean Sciences. The PIs will also maintain their university web sites featuring current research endeavors that are designed for public viewing rather than just internal scientific communication.