Collaborative Research: Quantifying the atmospheric flux of bio-active trace elements to the southwestern Indian Ocean

海洋浮游植物（微小的光合藻类）产生了我们呼吸的大约一半的氧气，每年从大气中清除数十亿吨的二氧化碳。这种初级生产力在控制大气二氧化碳水平和全球气候方面起着核心作用。然而，浮游植物的生产力受到全球约40%海洋中缺乏铁（一种必需的微量元素）的限制。虽然浮游植物的生产力有助于从大气中去除二氧化碳，但它也从上层海洋中去除铁和其他必需的微量元素（如锰、钴、铜和锌）。一个关键的问题是，“这些必需的微量元素的来源是什么？这些微量元素需要取代浮游植物所移除的元素，以保持每年的生产力循环？”这在南极洲周围的南大洋水域尤其重要，那里的海洋环流将深水带到海面；富含硝酸盐和磷酸盐等营养物质但缺乏必需微量元素的水。公海中铁的主要来源是沙漠尘埃沉积。在这个项目中，科学家们将收集南大洋上空的气溶胶（空气中的细颗粒）和雨水样本，以测量有多少铁（以及其他必需的微量元素）沉积到地表水中。其他科学家将测量浮游植物的生长速度，我们将一起了解灰尘中微量元素的输入如何帮助去除大气中的二氧化碳。这些信息可以用来帮助预测地球气候的未来。科学家们将通过各自校园的开放日活动以及在线论坛向公众传播他们的研究结果。来自佛罗里达国际大学的一名本科生将作为该项目的一部分得到支持和培训。佛罗里达国际大学是一所主要的少数民族大学。该项目将测量生物必需微量元素的气溶胶溶解度和大气沉积，作为研究南大洋印度洋部分微量元素来源、转化和汇的多学科项目的一部分。研究巡航路线将穿越洋流和海洋锋，这是该地区环流的主要路径，我们预计在那里可以找到多种可能的气溶胶来源，预计气溶胶铁沉积和降雨率的范围超过1-2个数量级。每天收集气溶胶样本（散装和分级大小），并分析基于事件的降雨样本，以分析总和可溶性主要和微量元素，包括硝酸盐，磷酸盐，硅酸盐，氯化物，硫酸盐，Na, Mg, Al， V, Mn, Fe, Co, Ni, Cu， Zn和Cd。此外，科学家将分析气溶胶中的水溶性有机化合物，重点关注草酸盐和甲烷磺酸（MSA）等化合物，这些化合物增强了气溶胶中微量元素的溶解度。科学家将使用气溶胶和上层水柱中的be -7浓度来计算气溶胶的总体沉降速度，并测试我们之前发表的降雨率和总体沉降速度之间的关系是否可以应用于更广泛的全球基础。此外，科学家将利用微量元素浓度数据以及空气质量反轨迹分析来分配人为和自然来源之间的气溶胶，并研究气溶胶来源如何影响分数溶解度。气溶胶和雨水亚样本将提供给合作者在巡航中分析其他重要参数。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Marine phytoplankton (microscopic photosynthetic algae) produce about half of the oxygen we breath and remove billions of tons of carbon dioxide from the atmosphere each year. This primary productivity plays a central role in controlling atmospheric carbon dioxide (pCO2) levels and the global climate. Yet, phytoplankton productivity is limited by lack of iron (an essential trace element) in about 40% of the global ocean. While phytoplankton productivity helps remove carbon dioxide from the atmosphere, it also removes iron and other essential trace elements (like manganese, cobalt, copper, and zinc) from the upper ocean. One critical issue is, “What are the sources for these essential trace elements that are needed to replace those removed by phytoplankton to keep the annual productivity cycles going?” This is especially important in the waters of the Southern Ocean around Antarctica, where ocean circulation brings deep water to the surface; water that is enriched in nutrients like nitrate and phosphate but depleted in essential trace elements. The main source for iron in the open ocean is from desert dust deposition. In this project, scientists will collect aerosols (fine particles in the air) and rain samples over the Southern Ocean to measure how much iron (and the other essential trace elements) is depositing to surface waters. Other scientists will be measuring how fast phytoplankton are growing, and together we will learn how the input of trace elements from dust helps to remove carbon dioxide from the atmosphere. This information can then be used to help predict the future of Earth’s climate. The scientists will communicate results of their study to the public via open house events at their respective campuses, as well as through online forums. One undergraduate student from Florida International University, a leading minority serving university, would be supported and trained as part of this project. The project will measure the aerosol fractional solubility and atmospheric deposition of bio-essential trace elements as part of a multidisciplinary project studying trace element sources, transformations and sinks in the Indian Ocean sector of the Southern Ocean. The research cruise track will cross the currents and oceanographic fronts that are major pathways of the general circulation in the region where we expect to find multiple possible aerosol sources, and where aerosol Fe deposition and rainfall rates are predicted to range over 1-2 orders of magnitude. Aerosol samples (bulk and size-fractionated) will be collected on a daily basis and event-based rain samples to be analyzed for total and soluble major and trace elements including nitrate, phosphate, silicate, chloride, sulfate, Na, Mg, Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Cd. In addition, scientists will analyze the water-soluble organic compounds in aerosols, focusing on compounds such as oxalate and methane-sulfonic acid (MSA) that enhance aerosol trace element solubility. Scientists will use Be-7 concentrations in aerosols and the upper water column to calculate aerosol bulk deposition velocities and test whether the relationship between rainfall rate and bulk deposition velocity that we have previously published can be applied on a more global basis. Further, scientists will use the trace element concentration data along with air-mass back trajectory analysis to apportion the aerosols between anthropogenic and natural sources, and study how aerosol sources affect the fractional solubility. Aerosol and rain subsamples will be provided to collaborators on the cruise for the analysis of additional important parameters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.