US GEOTRACES Pacific Meridional Transect (GP-15): Resolving Silicon Isotope Anomalies in the Northeast Pacific

美国地理追踪太平洋经线横断面 (GP-15)：解决东北太平洋硅同位素异常问题

• 批准号: 1732139
• 负责人: Mark Brzezinski
• 金额: $ 65.8万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-10-01 至 2022-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1732139&HistoricalAwards=false
• 关键词: US; GEOTRACES; Pacific; Meridional; Transect

This project will examine the distribution of isotopes of the element silicon in the Pacific Ocean to gain insights into processes that control the movement of silicon through the global ocean. Such studies are motivated by the fact that the silicon that is dissolved in seawater supports the growth of diatoms. Diatoms are microscopic algae that use silicon to produce ornately sculpted shells called frustules. Diatoms are unique in that they are the only major group of marine photosynthetic microbes that need silicon in order to grow. Diatoms are responsible for 20% of the total photosynthesis on Earth so we can each thank a diatom for every fifth breath of oxygen that we breathe. The sheer scale of their contribution makes understanding what controls their distribution and abundance important for the ecology and chemistry of the oceans and for society. Their need for silicon means that the amount of silicon dissolved in seawater can control where diatoms grow and how many are produced. Diatoms obtain silicon, and other nutrient fertilizer, when currents bring deep waters that are rich in these nutrients to the surface ocean. This project will investigate how the stable isotopic composition of dissolved silicon varies in the Pacific Ocean. Why bother with isotopes? It turns out that diatoms preferentially use lighter isotopes of silicon when building their frustules. This produces signals in diatom frustules and in the dissolved silicon in the sea that allows isotopes to be used to reconstruct diatom productivity in the past. The isotopic composition of the dissolved silicon in deep ocean waters is different in different ocean basins. These differences in isotopes of silicon in deep waters appear to be systematic and are tied to the movement of currents in the deep sea. Once these patterns are understood evaluations of diatom productivity based on isotopes will improve enormously. Testing the relationship between isotopes of silicon and the water masses that comprise the deep circulation of the global ocean is a major goal of this study.This study will take place as part of the 2018 GEOTRACES expedition from Alaska to Tahiti. This expedition will sample several important water masses. The deep waters of the northeast Pacific are among the most puzzling relative to current understanding of the processes controlling Si isotope distributions. Deep waters of the north Pacific possess the highest concentration of dissolved silicon and oldest waters at the "end" of the global deep water circulation. Moreover, the northeast Pacific is of particular interest as it contains what could be the largest silicon isotope anomaly in the global ocean, known as the North Pacific Silicic Acid Plume. The plume, as its name implies, consists of a tongue of elevate dissolved silicon that extends from the Cascadia Basin off North America nearly to Japan. The limited data available so far implies that isotope patterns across the plume are the opposite of model predictions challenging our current understanding of controls on Si isotope distributions. Elsewhere, the planned expedition will intersect key water masses including surface waters, North Pacific Intermediate Water, North Pacific Deep Water, and at the southern extreme of the section, Antarctic Intermediate Water and Circumpolar Deep Water allowing tests of hypotheses on how silicon isotope relate to the distribution of deep water masses in the Pacific. Examining these features will involve sampling seawater using the logistical support from the GEOTRACES management team. Seawater will be collected from the surface to near ocean bottom at twelve stations between Tahiti and Alaska targeting key water masses and the North Pacific Plume. Samples of diatom frustules from throughout the water column will be collected at three stations to explore fractionation of silicon during the dissolution of diatoms frustules. This project will also provide partial support for a postdoctoral scholar who will both participate in the science and also collaborate with the principal investigator on disseminating the discoveries to the public.

该项目将检查太平洋元素硅的同位素分布，以了解控制硅通过全球海洋的流动的过程。这样的研究是由于溶解在海水中的硅支持硅藻的生长以下事实。硅藻是微观藻类，使用硅生产雕塑壳，称为浮雕。 硅藻是独一无二的，因为它们是唯一需要硅才能生长的海洋光合微生物。硅藻是地球上光合作用总计的20％，因此我们每个人都可以感谢我们呼吸的每第五次氧气。 他们的贡献规模的范围使得了解什么控制了他们的分布和丰度对于海洋和社会的生态和化学重要。它们对硅的需求意味着溶解在海水中的硅数量可以控制硅藻生长的位置以及产生多少硅。当电流带来富含这些养分的深水时，硅藻获得了硅和其他营养肥料。该项目将研究溶解硅的稳定同位素组成在太平洋中如何变化。为什么要去同位素呢？事实证明，硅藻在构建硅质时优先使用硅的较轻同位素。这会在硅藻瓣中产生信号，并在海洋中的溶解硅中产生信号，从而使同位素用于重建过去的硅藻生产率。 在深海水域中溶解的硅的同位素组成在不同的海盆中不同。 深水中硅同位素的这些差异似乎是系统性的，并且与深海的电流运动有关。一旦理解了这些模式的评估，对基于同位素的硅藻生产力的评估将大大提高。 测试硅的同位素与构成全球海洋深层循环的水块之间的关系是这项研究的主要目标。这项研究将作为2018年从阿拉斯加到大溪地的2018 Geotraces Expedition进行。这次探险将品尝几个重要的水质量。相对于当前对控制SI同位素分布的过程的理解，东北太平洋的深水是最令人困惑的。 在全球深水循环的“末端”，北太平洋的深水具有最高的溶解硅和最古老的水。 此外，东北太平洋特别令人感兴趣，因为它包含了全球海洋中可能是最大的硅同位素异常，称为北太平洋硅酸羽流。 该羽流的名字暗示，该羽流包括一条高架溶解的硅的舌头，该硅从北美的卡斯卡迪亚盆地延伸到日本。到目前为止，可用的有限数据意味着整个羽流的同位素模式与模型预测相反，这挑战了我们当前对SI同位素分布的控制的理解。 在其他地方，计划中的探险将与包括地表水，北太平洋中级水，北太平洋深水在内的关键水块相交，在该部分的南部极端，南极中间水和圆形深水测试允许对硅同位素与太平洋地区深水分布相关的假设测试。 检查这些功能将涉及使用GeoTraces管理团队的后勤支持对海水进行采样。海水将从塔希提岛和阿拉斯加之间的十二个站点的海底收集到靠近海底的海水，以钥匙水块和北太平洋羽流。整个水柱中的硅藻样品样品将在三个站点收集，以探索硅胶溶解期间硅的分馏。该项目还将为博士后学者提供部分支持，该学者将参与科学，并与主要研究人员合作，将发现传播给公众。