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

一名研究人员将参加2015年美国GEOTRACES北冰洋考察，并测量海水样本中草酸的硅同位素组成，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，并确定这些分布对环境条件变化的敏感性。一些微量元素是生命所必需的，另一些是已知的生物毒素，还有一些是重要的，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，在这项研究中测量其浓度可以提供当今和过去海洋初级生产力的重要指标。该项目将为本科生和一名博士后研究员提供硅化学方面的培训，并包括对幼儿园至12年级学生的外联活动，硅同位素代用品正越来越多地用于评估硅藻和藻酸供应对过去海洋生产力变化的作用及其在地球气候中的作用。代理的应用需要通风水体的硅同位素组成的知识。这些价值的不确定性直接转化为代理所暗示的生产力水平的不确定性。全球海洋沃茨中硅同位素数据集的不断增加表明，地下沃茨中的硅同位素并不均匀，而是在硅同位素分馏、生物泵和温盐循环之间的相互作用的驱动下系统地变化。此外，模型预测和观测之间存在显著的异常。在这项研究中，研究人员将通过极大地扩展该地区的硅同位素数据集来测试有关该信号起源和控制北冰洋内硅同位素分布的机制的假设。要测试的首要假设是，硅同位素分布控制的耦合过程中的硅分馏二氧化硅生产和二氧化硅溶解的生物泵和反相翻转循环。

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.