US GEOTRACES GP17-OCE and GP17-ANT: Mapping zinc speciation in the Southern Ocean overturning circulation to test the zinc scavenging hypothesis

南大洋在全球碳循环中扮演着重要的角色，因为富含二氧化碳的深海水被带到表层，可以与大气交换。浮游植物的生长通过将二氧化碳固定在生物质中来抵消这种碳源，这些生物质可以沉回深海。虽然南大洋富含支持浮游植物生长的大量营养素，但铁、锰和锌等关键微量营养素的丰度非常低。在这些金属中，只有铁被发现大规模地限制浮游植物的生产力，但对锌和锰的观察很少。该提案旨在绘制从南太平洋到阿蒙森海的海洋样带的生物可利用锌浓度。在低丰度时，锌的缺乏会限制浮游植物，但锌也会影响其他稀有金属的吸收，尤其是锰。作为该项目的一部分进行的测量将确定在这一关键但采样不足的海洋区域Zn的极限和有毒水平的程度。这些限制对于模拟过去和未来气候情景下海洋锌循环的变化及其对浮游植物活动的影响是必要的。作为GEOTRACES GP17 OCE和ANT考察的一部分，控制Zn反应性的参数将以高垂直和纬度分辨率测量，横跨数千公里的样带，穿越全球重要水团的形成区域。伏安法技术将用于测定数百个样品中溶解在海水中的游离锌（Zn '）和锌结合有机配体的浓度。与GEOTRACES计划的其他研究人员一起，这些测量将限制深海中Zn ‘的反应性，并确定Zn ’与浮游植物金属摄取之间的经验关系。这对于了解锌和其他微量营养素在海洋中的全球分布及其对初级生产的潜在影响至关重要。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。

The Southern Ocean plays a significant role in the global carbon cycle because deep ocean waters rich in CO2 are brought into the surface layer and can exchange with the atmosphere. The growth of phytoplankton counteracts this carbon source by fixing CO2 into biomass, which can sink back to the deep sea. While the Southern Ocean is rich in macronutrients that support phytoplankton growth, key micronutrients such as iron, manganese and zinc are at very low abundance. Of these metals, only iron has been found to limit phytoplankton productivity on a large scale, but few observations of Zn and Mn have been made. This proposal seeks to map bioavailable Zn concentrations across an oceanographic transect from the South Pacific Ocean to the Amundsen Sea. At low abundance, Zn scarcity can limit phytoplankton, but Zn can also affect the uptake of other scarce metals, especially Mn. Measurements made as part of this project will determine the extent of limiting and toxic levels of Zn in this critical but undersampled region of the oceans. Such constraints are necessary for modelling changes to the oceanic Zn cycle – and its effect on phytoplankton activity – under past and future climate scenarios. As part of the GEOTRACES GP17 OCE and ANT expeditions, parameters governing the reactivity of Zn will be measured in high vertical and latitudinal resolution across a transect extending several thousand kilometers and crossing formation regions of globally important water masses. Voltammetry techniques will be used to determine the concentrations of free zinc (Zn’) and Zn-binding organic ligands dissolved in seawater for hundreds of samples. Together with other investigators in the GEOTRACES program, these measurements will constrain the reactivity of Zn’ in the deep ocean and define empirical relationships between Zn’ and phytoplankton metal uptake. This is essential for understanding the global distribution of Zn and other micronutrients in the oceans and their potential to affect primary production.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.