US GEOTRACES PMT: Shipboard determination of key dissolved trace elements

该项目将在阿拉斯加至塔希提岛的邮轮上对溶解的痕量元素铝(Al)、铁(Fe)和锰(Mn)进行船上测量，该邮轮将作为美国地质调查局太平洋子午线(PMT)的一部分航行。PMT探险是国际GEOTRACES计划的一部分，旨在提高对全球海洋生物地球化学循环的了解。微小海洋植物在表层水中的生长取决于某些微量元素(特别是溶解的铁)的可用性。此外，这种元素和其他微量元素的分布记录了海洋中当前和过去的化学和生物过程。PMT巡航轨道包括多种独特的海洋条件，因此这项工作的结果将为了解不同的全球海洋过程提供重要的见解。为了产生更广泛的科学影响，结果将被纳入解决海洋目前和未来在全球进程中的作用的模型。评估沿巡航路线的克拉里昂-克利珀顿断裂带中的微量元素分布，也将为计划进行海底锰结核开采的这一区域提供一个重要的基线。将在夏威夷希洛的一个中途邮轮停靠站进行教育推广，吸引当地学生参观这艘船。直接接触工作中的海洋研究船，以及邮轮后的后续访问，将为学生提供一个独特的机会，直接与参与该项目的科学家讨论考察结果。为了开发所需的数据集，以新的理解微量元素输入过程在建立海洋化学分布方面的相对重要性，将在62天的邮轮期间，使用定制设计的采样包在41个地点收集整个水柱的海水样本。邮轮航道的北部起源于一个地表水中极低浓度的溶解铁限制植物生长的地区。再往南，将通过测量地表水中溶解的铝浓度来追踪从大陆吹来的矿物粉尘在大气中沉积的增加。这种粉尘的加入也增加了溶解的铁。来自沿海地区的潜在额外铁输入将通过溶解锰浓度的一致增加来确定。该项目将比较和关联铝、铁和锰的变化，以量化和识别沿巡航轨道的不同添加过程。通过使用船上流动注射分析为这些痕量元素提供近乎实时的测量，存在修改采样策略以获得最大科学回报的可能性。船上的结果还将有助于识别任何采样污染问题，这些问题在收集这些低水平痕量元素时是一个持续的风险。总之，船上对这些基本要素的分析是确保GEOTRACES PMT成功的一项基本活动。

This project will provide shipboard measurements of the dissolved trace elements aluminum (Al), iron (Fe), and manganese (Mn) during an Alaska to Tahiti cruise that will sail as part of the US GEOTRACES Pacific Meridional Transect (PMT). The PMT expedition is part of the international GEOTRACES program designed to improve understanding of global ocean biogeochemical cycles. The growth of microscopic oceanic plants in surface waters depends on the availability of certain trace elements (particularly dissolved Fe). In addition, the distribution of this and other trace elements record current and past chemical and biological processes in the ocean. The PMT cruise track includes multiple unique oceanic conditions and thus the results of the work will provide important insight into diverse global ocean processes. For broader scientific impact, results will be incorporated into models that address the current and future role of the ocean in global processes. Assessing the distribution of trace elements in the Clarion-Clipperton Fracture Zone, along the cruise track, will also provide an important baseline for this region where seabed mining of manganese nodules is planned. Educational outreach will take place with a mid-cruise stop in Hilo, Hawaii to engage local students with visits to the ship. Direct exposure to a working oceanographic research vessel together with a post-cruise follow up visit will provide students with a unique opportunity to discuss the findings from the expedition directly with the scientists engaged in the project.To develop the data sets required for new understanding of the relative importance of trace element input processes in establishing oceanic chemical distributions, seawater samples from the entire water column will be collected using a custom designed sampling package at 41 locations during the 62-day cruise. The northern part of the cruise track originates in a region where very low concentrations of dissolved Fe in surface waters limit plant growth. Further to the south, increased atmospheric deposition of mineral dust blown from the continents will be traced by measuring the dissolved Al concentration in surface waters. The addition of this dust also adds dissolved Fe. Potential additional inputs of Fe from coastal regions will be identified by coincident increases in dissolved Mn concentrations. The project will compare and correlate variations in Al, Fe, and Mn to quantify and identify distinct addition processes along the cruise track. By using shipboard flow injection analysis to provide near real-time measurements for these trace elements, the potential exists to modify sampling strategies for maximum scientific return. The shipboard results will also help identify any sampling contamination problems that are a constant risk when collecting these low-level trace elements. Altogether, the shipboard analysis of these essential elements is an essential activity to ensure success of the GEOTRACES PMT.