US GEOTRACES GP17-OCE: Measurements of the trace gases chlorofluorocarbons and sulfur hexafluoride

US GEOTRACES GP17-OCE：痕量气体氯氟烃和六氟化硫的测量

• 批准号: 2048995
• 负责人: James Happell
• 金额: $ 55万
• 依托单位: University of Miami
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-10-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2048995&HistoricalAwards=false
• 关键词: US; GEOTRACES; GP17; OCE; Measurements

The goal of the international GEOTRACES program is to understand the distributions in the ocean of trace chemical elements and their isotopes (TEIs), which are different forms of the same element. Many of the TEIs are essential for phytoplankton growth (e.g., iron) and are micronutrients. Yet, other TEIs are pollutants (e.g., lead). The U.S. GEOTRACES GP17-OCE expedition will occur in the South Pacific and Pacific sector of the Southern Ocean. Essential to understanding how TEIs change, e.g., scavenging and regeneration, and for estimating rates of biochemical processes is to identify water masses that are newly ventilated with atmospheric gases. These are waters that have been in contact with the atmosphere in the past few decades. The main objective of this project will be to measure the concentration of three man-made tracers of ocean ventilation that can be used to determine how long since a water mass was at the ocean surface in contact with the atmosphere. The tracers are particularly useful for following water masses along pathways as they age and estimating rates of effective spreading and dilution. An analogy would be adding a colored dye in the surface ocean, with a bit more dye added each year, and then measuring the concentration of this dye as surface water moves into the interior ocean. The three tracers that will be measured are Chlorofluorocarbon-11 (CFC-11), Chlorofluorocarbon-12 (CFC-12) and Sulfur Hexafluoride (SF6). The trace gas concentrations, ventilation ages, and rate data will all be made available to other investigators within six months of collection, forming an important foundation for the broader GEOTRACES program. The project team will measure CFC-11, CFC-12, and SF6 concentrations at sea aboard the GP17-OCE expedition. In addition to conducting these measurements, the specific objectives are: 1) Calculate tracer ages and identify the relative extent of ventilation and dilution of thermocline, intermediate and bottom waters within which TEIs reside - from the end member sources to downstream locations as waters age, and put the GEOTRACES data in the historical context of changing ventilation due to natural and anthropogenic climate change. The age data will be available for PIs to evaluate how scavenging and regeneration are affected as TEIs are transported downstream. 2) Using tracer ages, calculate rates of biochemically important processes - e.g., apparent oxygen utilization rates, and help to distinguish between contributions from physical and biochemical processes across the different circulation regimes. Tracer ages will be calculated, from the ratio of SF6 to CFCs, and for oldest waters the ratio of CFCs to each other. The most robust tracer combination for ocean processes on time scales of less than 35 years is obtained using the SF6/CFC ratios.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GEOTRACES计划的目标是了解海洋中微量化学元素及其同位素(TEI)的分布，这些元素是同一元素的不同形式。许多TEI对浮游植物的生长(如铁)是必不可少的，并且是微量营养素。然而，其他TEI是污染物(例如，铅)。美国地理跟踪公司的GP17-OCE探险队将在南太平洋和南大洋的太平洋区域进行考察。要了解TEI如何变化，例如，清除和再生，以及估计生化过程的速率，关键是识别新通风的大气气体的水团。在过去的几十年里，这些水域一直与大气层接触。该项目的主要目标将是测量海洋通风的三种人造示踪剂的浓度，这些示踪剂可用来确定水团距离海洋表面与大气接触有多长时间。示踪剂对于跟踪水团随着水团老化和估计有效扩散和稀释的速度特别有用。一个类比是在表层海洋中加入一种有色染料，每年增加一点染料，然后在地表水进入海洋内部时测量这种染料的浓度。将被测量的三种示踪剂分别是氯氟烃-11(CFC-11)、氯氟烃-12(CFC-12)和六氟化硫(SF6)。示踪气体浓度、通风年龄和速率数据将在收集后六个月内全部提供给其他调查人员，为更广泛的GEOTRACES计划奠定重要基础。该项目团队将在GP17-OCE探险队上测量海上氟氯化碳-11、氟氯化碳-12和SF6的浓度。除进行这些测量外，具体目标是：1)计算示踪年龄并确定温跃层、TEI所在的中间和底层水域--从末端成员来源到下游地点--随着水域年龄的变化--的相对通风和稀释程度，并将GEOTRACES数据置于自然和人为气候变化导致通风变化的历史背景下。随着TEI向下游输送，PIS将获得年龄数据，以评估清扫和再生受到的影响。2)使用示踪年龄，计算具有生物化学重要性的过程的速率--例如，表观氧利用率，并帮助区分不同循环系统中物理和生化过程的贡献。示踪年龄将根据SF6与CFCs的比率计算，对于最古老的水域，将根据CFCs彼此的比率进行计算。在不到35年的时间尺度上，使用SF6/CFC比率获得了最可靠的海洋过程示踪剂组合。该奖项反映了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。