US GEOTRACES GP17-OCE: Evaluating Southern Ocean Control of Global Marine Si Isotope Distribution

美国 GEOTRACES GP17-OCE：评估南大洋对全球海洋硅同位素分布的控制

• 批准号: 2048998
• 负责人: Mark Brzezinski
• 金额: $ 68.1万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2048998&HistoricalAwards=false
• 关键词: US; GEOTRACES; GP17; OCE; Evaluating

The Southern Ocean around Antarctica is connected to the rest of the global ocean through the meridional overturning circulation. That circulation moves water from the Southern Ocean through the tropics and all the way into the northern hemisphere. Those waters carry nutrient chemicals that fuel the growth of phytoplankton throughout the global ocean whose photosynthetic carbon fixation is a major factor in setting how much atmospheric carbon dioxide is removed by ocean biology. Diatoms are a key group of phytoplankton involved in this process of carbon uptake and they are especially abundant in the Southern Ocean. Diatoms are unique among the phytoplankton because they need the element silicon to grow. They take the silicon (Si) that is dissolved in seawater and use it to produce a shell made of opal called a frustule. In this project we are interested in how the availability of dissolved Si, as set by the Southern Ocean, controls the distribution and abundance of diatoms in the sea and their contribution to ocean biogeochemistry such as the uptake and removal of carbon. We will use a relatively new tool to trace diatom dynamics – silicon isotopes. Variations in silicon isotopes in the dissolved Si in seawater and in diatom frustules can inform the level of diatom growth that has occurred in ocean waters and how diatom growth is coupled to ocean circulation and nutrient transport. The distribution of isotopes of silicon between Tahiti in the tropics to the Southern Ocean will allow us to better understand how the physics, chemistry and biology of the Southern Ocean controls diatom activity at global scales. The research will involve an early career scientist and undergraduate students at UCSB. The PIs will also reach out to regional K-12 schools through UCSB’s Research and Education Experience Facility (REEF) by developing curricula on Southern Ocean biogeochemistry and the GEOTRACES program.Silicon isotopes will be measured in full ocean depth profiles along US GEOTRACES GP17OCE from Tahiti, French Polynesia to Punta Arenas, Chile. It is now clear that successful application of the Si isotope proxy in the modern ocean and for paleoclimate reconstructions requires a mechanistic understanding of how the silicon isotopic composition of ventilating waters masses varies in time and space. Our goal is to test hypotheses related to predictions from models that processes in the Southern Ocean dictate silicon isotopes distributions throughout the global ocean. That prediction arises because the Southern Ocean is the central hub of the meridional overturning circulation. The interplay between silica production in Southern Ocean surface waters, opal export and the Southern Ocean counter current meridional circulation traps silicic acid in the Southern Ocean while partitioning and redistributing Si isotopes between mode and deep waters. Heavy Si isotopes are distilled out of the Southern Ocean in relatively shallow mode waters while light isotopes ride the northward flow of deep waters. Individual aspects of these predictions have been examined previously; however, measurements of Si isotopes in GP17OCE will provide the first section that samples all relevant water masses synoptically. Those distributions together with other data collected on GP17OCE will allow a more comprehensive evaluation of these mechanisms partitioning Si isotopes in the Southern Ocean and their redistribution in the overturning circulation more globally.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.

南极洲周围的南大洋通过纬向翻转环流与全球海洋的其他部分相连。 这种环流将南大洋的水通过热带地区一直输送到北方。 这些沃茨携带营养化学物质，为全球海洋中浮游植物的生长提供燃料，浮游植物的光合固碳作用是确定海洋生物清除大气中二氧化碳的主要因素。硅藻是参与这一碳吸收过程的浮游植物的一个关键群体，它们在南大洋特别丰富。硅藻在浮游植物中是独一无二的，因为它们需要硅元素来生长。他们将溶解在海水中的硅（Si）用于生产由蛋白石制成的壳，称为硅藻壳。在这个项目中，我们感兴趣的是南大洋溶解硅的可用性如何控制海洋中硅藻的分布和丰度，以及它们对海洋地球化学的贡献，如碳的吸收和去除。 我们将使用一种相对较新的工具来追踪硅藻动力学-硅同位素。海水中溶解的硅和硅藻硅藻壳中硅同位素的变化可以告知海洋沃茨中发生的硅藻生长水平以及硅藻生长如何与海洋环流和营养物运输相耦合。硅同位素在热带塔希提岛和南大洋之间的分布将使我们能够更好地了解南大洋的物理，化学和生物学如何在全球范围内控制硅藻活动。这项研究将涉及一名早期职业科学家和UCSB的本科生。PI还将通过UCSB的研究和教育体验设施（REEF），通过开发南大洋地球化学和GEOTRACES计划的课程，接触到区域K-12学校。硅同位素将在从法属波利尼西亚塔希提岛到智利蓬塔阿雷纳斯的沿着US GEOTRACES GP 17 OCE的全海洋深度剖面中进行测量。现在很清楚，硅同位素代用品在现代海洋和古气候重建的成功应用，需要一个机械的理解，如何通风沃茨质量的硅同位素组成在时间和空间上的变化。我们的目标是测试与模型预测相关的假设，该模型预测南大洋的过程决定了整个全球海洋的硅同位素分布。这一预测的出现是因为南大洋是纬向翻转环流的中心枢纽。在南大洋表层沃茨的二氧化硅生产，蛋白石出口和南大洋逆流三角洲环流之间的相互作用，在南大洋的捕集硅酸，同时分区和重新分配模式和深沃茨之间的硅同位素。重硅同位素是在相对较浅的模式沃茨中从南大洋中蒸馏出来的，而轻同位素则是在较深的沃茨中向北流动。这些预测的各个方面以前已经检查过，但是，在GP 17 OCE的硅同位素的测量将提供第一部分，样品所有相关的水团天气。这些分布与GP 17 OCE上收集的其他数据一起将允许对这些机制进行更全面的评估，这些机制将南大洋中的硅同位素分开，并在翻转环流中进行更全球性的重新分布。该奖项反映了NSF的法定使命，并被认为值得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来支持。