GEOTRACES Arctic Section: Diagnosing the unique silicon isotope composition of the Arctic Ocean

一名调查人员将参加2015年美国GEOTRACES北冰洋考察队，测量海水样本中硅酸的硅同位素组成，以及硅藻和海冰。与国际GEOTRACES计划中的其他多国倡议一样，美国北极考察的目标是确定控制海洋中关键微量元素和同位素分布的过程和量化通量，并确定这些分布对不断变化的环境条件的敏感性。有些微量元素是生命所必需的，有些是已知的生物毒素，还有一些很重要，因为它们可以用作海洋中各种物理、化学和生物过程的示踪剂。由于硅是硅藻壳的关键组成部分，因此在本研究中对其浓度的测量可以为当今以及过去海洋的初级生产力提供重要指标。该项目将为硅化学领域的本科生和博士后研究员提供培训，并向K-12学生提供服务。硅同位素代用物越来越多地被用于评估硅藻和硅酸供应在过去海洋生产力变化中的作用及其在地球气候中的作用。代理的应用需要了解通风水团的硅同位素组成。这些值的不确定性直接转化为代理所暗示的生产率水平的不确定性。不断增长的全球海水硅同位素数据集表明，地下水中的硅同位素不是均匀的，而是在硅同位素分异、生物泵和热盐环流之间的相互作用下系统地变化。此外，在模式预测和观测之间存在显著的异常。在这项研究中，研究人员将通过大大扩展该地区的硅同位素数据集来验证有关该信号起源的假设以及控制北冰洋内硅同位素分布的机制。要验证的总体假设是，硅同位素分布受硅生产和硅溶解过程中硅分馏与生物泵和经向翻转环流耦合的控制。

An investigator will participate in the 2015 U.S. GEOTRACES Arctic Ocean expedition and measure silicon isotopes composition of silicic acid in seawater samples, as well as diatoms and sea ice. In common with other multinational initiatives in the International GEOTRACES program, the goals of the U.S. Arctic expedition are to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions. Some trace elements are essential to life, others are known biological toxins, and still others are important because they can be used as tracers of a variety of physical, chemical, and biological processes in the sea. As silicon is a key component of diatom shells, the measurement of their concentrations in this study can provide an important indicator of primary productivity, both in the present day, as well as past oceans. The project will provide training for undergraduate students and a post-doctoral researcher in silicon chemistry, as well as include outreach to K-12 students.The silicon isotope proxy is increasingly being used to assess the role of diatoms and silicic acid supply to past shifts in ocean productivity and their role in Earth's climate. Application of the proxy requires knowledge of the silicon isotopic composition of ventilating water masses. Uncertainty in these values translates directly into uncertainty in the level of productivity implied by the proxy. The growing global data set of silicon isotopes in marine waters suggest that silicon isotopes in subsurface waters are not uniform, but vary systematically driven by interactions between silicon isotope fractionation, the biological pump and thermohaline circulation. In addition, significant anomalies exist between model predictions and observations. In this study, researchers will test hypotheses regarding the origin of this signal and the mechanisms controlling silicon isotope distributions within the Arctic Ocean by greatly expanding the silicon isotope data set for this region. The overarching hypothesis to be tested is that silicon isotope distributions are controlled by the coupling of silicon fractionation during silica production and during silica dissolution to the biological pump and to the meridional overturning circulation.