US GEOTRACES PMT: Rare earth elements, gallium, barium, and methane as indicators of internal cycling and input processes

该项目包括参加计划于2018年年中从大溪地到阿拉斯加的海洋研究邮轮，该邮轮将沿着太平洋中的152°W到达阿拉斯加。这一巡航横断面将允许在各种环境中对海水进行采样。这些环境包括阿留申边缘(那里有大量的大陆物质输入)、亚北极北太平洋(那里的植物生产力可能受到铁可获得性的限制)、北太平洋的深水(这是海洋中最古老的深水)、以及氧气最少的地带、热液羽流和受上升流影响的赤道水域。调查人员将确定钡(Ba)、镓(Ga)、稀土元素(Rees)和甲烷的溶解浓度。这些研究与重要的海洋问题有关，包括矿物粉尘和营养铁向表层海洋(Ga)的输送、微量元素(Ba、Rees)的清除和内部循环、过去海洋过程的示踪剂的开发以及物质(Ga、Ba、Rees、甲烷)的追踪来源，包括边缘来源(Ba、Rees、甲烷)。参与这次巡航的其他研究人员将确定其他元素和同位素，包括铁(Fe)、铝(Al)和镭同位素(Ra)。比较这些化学物质的分布是所有相关研究小组测试元素输入、移除和海洋循环的假设机制的关键。这些机制反过来又与理解海洋-S生物生产力及其在全球气候中的作用有关。从这个项目中获得的知识和经验将被纳入首席调查员S的海洋学课程。作为该项目的一部分，一名研究生也将得到支持和培训。来自南密西西比大学的一名研究人员将参加2018年美国地质调查局太平洋子午线断面(PMT)，该断面沿152°W从塔希提岛延伸到阿留申群岛。在这次航行中，样本将从边缘通量强的地区采集，亚北极HNLC水域，世界上最古老的深水？S海洋，胡安德富卡海脊和东太平洋海隆的热液羽流的远端，以及氧气最少的地带，赤道上升流，以及世界上营养最少的一些水域-南太平洋环流20°的S海洋。样本将被分析溶解的镓(Ga)，钡(Ba)，稀土元素(REE)和溶解的甲烷。这些研究涉及重要问题，包括矿物粉尘和营养铁向表层海洋(Ga)的输送，微量元素(Ba，Rees)的迁移和内循环，古海洋示踪剂(BA)的开发，追踪物质来源(Ga，Ba，Rees，甲烷)，包括边缘来源(Ba，Rees，甲烷)，以及对示踪剂分布(BA，Rees)保守和非保守变化的理解。总体而言，PMT中的尘埃输送、生产力、深水年龄和最低含氧区范围中的梯度提供了比较这些梯度如何影响微量元素分布的机会，从而为对分布的解释提供了信息。PMT还将提供机会，在一个水团较少、盆地混合时间尺度比大西洋更长的盆地中，研究深水和底层水中化学信号的演变。因此，这些数据可能提供一个机会，将保守的混合与非保守的生物地球化学区分开来，并将包括使用水团反褶积来估计微量元素分布的保守成分、元素-AOU图以及偏离全球元素-营养相关性的分布。巡航还允许与其他调查人员进行广泛合作。因此，溶解的Ga数据将与同事获得的铝(Al)和钍-232等其他成岩快速清除元素的分布数据进行比较；溶解的Ba数据将与那些确定Re和Ba同位素的人共享；REE数据将提供给那些检查钕(ND)同位素的人，以及与其他清除示踪剂(如Sc)进行比较的数据。将我们的化学分布与其他人确定的化学分布进行比较，是所有相关研究小组测试元素输入、移除和海洋循环的假设机制的关键。这些机制反过来又与理解海洋-S生物生产力及其在全球气候中的作用有关。

This project involves participation in an oceanographic research cruise scheduled for mid-2018 and going from Tahiti to Alaska along 152° W in the Pacific Ocean. This cruise transect will allow for sampling of ocean waters in a wide variety of environments. These environments include the Aleutian margin (where there is significant input of continental materials), the subarctic North Pacific (where plant productivity may be limited by iron availability), deep waters of the North Pacific (which are the oldest deep waters of the ocean), as well as oxygen minimum zones, hydrothermal plumes, and equatorial waters subject to upwelling. The investigators will determine dissolved concentrations of barium (Ba), gallium (Ga), rare earth elements (REEs), and methane. These studies are pertinent to important oceanic issues including delivery of mineral dust and nutrient iron to the surface ocean (Ga), removal and internal cycling of trace elements (Ba, REEs), development of tracers of past ocean processes (Ba), and tracing sources of material (Ga, Ba, REEs, methane) including margin sources (Ba, REEs, methane). Other researchers involved in the cruise will determine additional elements and isotopes including iron (Fe), aluminum (Al), and radium isotopes (Ra). Comparing these chemical distributions is key for all of the involved research groups to test hypothesized mechanisms of element input, removal, and cycling through the ocean. These mechanisms, in turn, are pertinent to understanding the ocean?s biological productivity and its role in global climate. The knowledge and experience gained from this project will be incorporated into the principle investigator?s courses in oceanography. A graduate student will also be supported and trained as part of this project. A researcher from the University of Southern Mississippi will participate in the 2018 US GEOTRACES Pacific Meridional Transect (PMT) going from Tahiti to the Aleutians along 152° W. During the cruise, samples will be collected from regions exhibiting strong margin fluxes, the subarctic HNLC waters, the oldest deep water in the world?s oceans, the distal ends of hydrothermal plumes from the Juan de Fuca Ridge and East Pacific Rise as well as oxygen minimum zones, equatorial upwelling, and some of the most oligotrophic waters in the world?s oceans in the South Pacific gyre at 20°S. The samples will be analyzed for dissolved gallium (Ga), barium (Ba), rare earth elements (REEs) along with dissolved methane. These studies are pertinent to important issues including delivery of mineral dust and nutrient iron to the surface ocean (Ga), removal and internal cycling of trace elements (Ba, REEs), development of paleoceanographic tracers (Ba), tracing sources of material (Ga, Ba, REEs, methane) including margin sources (Ba, REEs, methane), and understanding of conservative vs non-conservative changes in tracer distributions (Ba, REEs). Overall, the gradients in dust delivery, productivity, age of deep waters, and extent of oxygen minimum zones in the PMT provide opportunities to compare how trace element distributions are affected by these gradients and hence inform the interpretation of the distributions. The PMT will also provide the opportunity to examine evolution of chemical signals in deep and bottom waters in a basin with fewer water masses and a longer timescale of basin mixing than the Atlantic. As such, this data may provide an opportunity to tease apart conservative mixing from non-conservative biogeochemistry and will include using water mass deconvolution to estimate the conservative component of trace element distributions, element-AOU plots, and distributions of the deviations from global element-nutrient correlations. The cruise also allows extensive collaboration with other investigators. Thus, the dissolved Ga data will be compared with data obtained by colleagues on distributions of other lithogenic, rapidly-scavenged elements like aluminum (Al) and thorium-232; the dissolved Ba data will be shared with those determining radium and Ba isotopes; and, the REE data will be made available to those examining neodymium (Nd) isotopes as well as compared with other scavenging tracers such as scandium (Sc). Comparing our chemical distributions with those determined by others is key for all of the involved research groups to test hypothesized mechanisms of element input, removal, and cycling through the ocean. These mechanisms, in turn, are pertinent to understanding the ocean?s biological productivity and its role in global climate.