Measurement of Helium Isotopes on the U.S. GEOTRACES Alaska-Tahiti Section (GP15)

美国 GEOTRACES 阿拉斯加-塔希提段 (GP15) 的氦同位素测量

• 批准号: 1756138
• 负责人: Chris German
• 金额: $ 78.05万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-01 至 2024-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1756138&HistoricalAwards=false
• 关键词: Measurement; Helium; Isotopes; U.S.; GEOTRACES

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. An essential part of this effort is determining the sources of trace elements to the oceans. One important such source comes from seafloor hydrothermal venting. This project will support the measurement of helium isotopes on the 2018 U.S. GEOTRACES expedition in the Pacific Ocean, running south from Alaska to Tahiti. Helium isotopes provide important information on the presence and dispersion of hydrothermal plumes. On a larger scale, they can also be used to calculate global-scale inputs of hydrothermally-sourced trace elements and isotopes. Thus, the proposed work is closely tied to many other projects associated with this expedition. The measurement of helium isotopes will also allow enable the investigation of physical mixing rates within the upper ocean to help interpret the fate of other trace elements. At the northern end of the section, this approach will also be used to investigate the rate at which other trace elements and isotopes from seafloor hydrothermal venting are delivered to the more biologically productive surface ocean. In addition to supporting the GEOTRACES effort and participating in community-scale outreach efforts associated with the expedition, the investigators will also work with a visual artist to communicate their science to the public in new ways.The U.S. GEOTRACES Pacific Meridional Transect (56°N to 20°S, along 152°W) in late 2018 will intercept: strong margin fluxes, sub-Arctic high-nutrient, low-chlorophyll waters, the oldest deep waters in the world's oceans, the distal ends of multiple hydrothermal plumes, oxygen minimum zones, subpolar and equatorial upwelling, and, in the South Pacific near 20°S, some of the most oligotrophic waters known. This section, together with the US GEOTRACES East Pacific Zonal Transect (EPZT) conducted in 2013, will also close off a large volume of the Pacific Ocean. Consequently, this work will facilitate new, improved evaluations of regional-scale fluxes of hydrothermally-sourced trace elements and isotopes (TEIs) to the oceans. Because the 2018 expedition will intercept multiple hydrothermal plumes, this project will also allow the investigation of three key questions emerging from the larger U.S. and international GEOTRACES programs: 1) Is there a significant source of hydrothermally-sourced Fe and other TEIs to the euphotic zone in the North Pacific, through upwelling, as was demonstrated for the Southern Ocean from the 2013 EPZT results? 2) How do TEI:He-3 ratios in hydrothermal plumes vary with different geologic settings of their vent-sources? 3) How do the TEI:He-3 ratios imparted to hydrothermal plumes vary along the thermohaline conveyor as a function of varying water column chemistry? Throughout the section the investigators will also combine upper-water column helium-3 measurements with water column tritium concentrations (extrapolated from data collected on past expeditions) to estimate water column ventilation time scales that can be used to quantify rates of TEI transformation across the wide range of biogeochemical regimes to be intercepted (tropical, subtropical, subpolar). In regions characterized by upwelling, precise measurements of helium isotopes can be combined with canonical gas-exchange rate estimates to make flux-gauge determinations of upwelling rates for some key TEIs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

国际地学研究计划的目标是了解海洋中痕量化学元素及其同位素的分布。这项工作的一个重要部分是确定海洋中微量元素的来源。其中一个重要的来源来自海底的热液喷发。该项目将支持2018年美国地理轨迹探险队在太平洋从阿拉斯加向南到塔希提岛的氦同位素测量。氦同位素提供了有关热液羽流的存在和扩散的重要信息。在更大的范围内，它们还可用于计算热液来源的痕量元素和同位素的全球范围的输入。因此，拟议的工作与与这次探险相关的许多其他项目密切相关。氦同位素的测量还将使研究上层海洋内的物理混合速率成为可能，以帮助解释其他微量元素的命运。在该部分的北端，这一方法还将用于调查海底热液喷发产生的其他微量元素和同位素向更具生物生产力的表层海洋输送的速度。除了支持GEOTRACES的努力和参与与这次探险相关的社区规模的推广工作外，调查人员还将与一名视觉艺术家合作，以新的方式向公众传播他们的科学。2018年底的美国地理追踪太平洋子午线(56°N到20°S，沿152°W)将截获：强大的边缘通量，亚北极高营养，低叶绿素水域，世界上最古老的深水，多个热液羽流的远端，氧气最少的地带，亚极点和赤道上涌，以及在南太平洋20°S附近的一些已知最少营养的水域。这一部分与2013年进行的美国地球物理观测系统东太平洋纬向断面(EPZT)一起，也将关闭太平洋的大片区域。因此，这项工作将有助于对热液来源的痕量元素和同位素流入海洋的区域尺度通量进行新的、改进的评估。由于2018年的探险将拦截多个热液羽流，该项目还将允许调查美国和国际上更大的GEOTRACES计划中出现的三个关键问题：1)是否存在水热来源的铁和其他TEI的重要来源，通过上升流进入北太平洋的真光层带，就像2013年EPZT结果在南大洋所展示的那样？2)热液羽流中的TEI：He-3比率如何随其喷口来源的不同地质环境而变化？3)作为不同水柱化学的函数，热液羽流中的TEI：He-3比率如何随温盐传送器的变化而变化？在整个部分中，研究人员还将结合上层水柱氦-3测量和水柱氚浓度(根据以往考察收集的数据外推)来估计水柱通风时间尺度，该时间尺度可用于量化将被截获的广泛的生物地球化学系统(热带、亚热带、亚极地)的TEI转化速率。在以上升流为特征的地区，氦同位素的精确测量可以与规范的气体交换率估计相结合，以流量计确定一些关键TEI的上升率。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Noble gas evidence of a millennial-scale deep North Pacific palaeo-barometric anomaly

北太平洋深部千年古气压异常的稀有气体证据

• DOI: 10.1038/s41561-023-01368-z
• 发表时间: 2024
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: Jenkins, W. J.;Seltzer, A. M.;Gebbie, G.;German, C. R.
• 通讯作者: German, C. R.

Using Excess 3 He to Estimate Southern Ocean Upwelling Time Scales

使用过量 3 He 估算南大洋上升流时间尺度

• DOI: 10.1029/2020gl087266
• 发表时间: 2020
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Jenkins, William J.