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

国际GEOTRACES计划的目标是了解微量化学元素及其同位素（TEI）在海洋中的分布，这些元素是同一元素的不同形式。许多TEI对浮游植物生长至关重要（例如，铁）和微量营养素。然而，其他TEI是污染物（例如，铅）。美国GEOTRACES GP 17-OCE考察将在南太平洋和南大洋的太平洋部分进行。对于理解TEI如何变化至关重要，例如，清除和再生，并估计生化过程的速率是确定水团是新通风与大气气体。这些沃茨在过去几十年里一直与大气层接触。该项目的主要目标是测量海洋通风的三种人造示踪剂的浓度，这些示踪剂可用于确定水团在海洋表面与大气接触的时间。示踪剂是特别有用的以下水团沿着路径，因为他们的年龄和估计有效的扩散和稀释率。一个类比是在海洋表面添加一种有色染料，每年添加更多的染料，然后测量这种染料的浓度，因为表面水进入海洋内部。将测量的三种示踪剂是氯氟烃-11（CFC-11）、氯氟烃-12（CFC-12）和六氟化硫（SF6）。 痕量气体浓度、通风年龄和速率数据都将在收集后的六个月内提供给其他调查人员，为更广泛的GEOTRACES计划奠定重要基础。项目小组将在GP 17-OCE考察队上测量海上CFC-11、CFC-12和SF6的浓度。除了进行这些测量外，具体目标是：1）计算示踪剂年龄，确定温跃层、中间层和底层沃茨（TEI位于其中）的通风和稀释的相对程度--从端元源到下游位置，作为沃茨年龄，并将GEOTRACES数据置于自然和人为气候变化导致的通风变化的历史背景下。年龄数据将可用于PI，以评估TEI向下游运输时如何影响清除和再生。2)使用示踪剂年龄，计算生物化学重要过程的速率-例如，表观氧利用率，并有助于区分不同循环体系中物理和生物化学过程的贡献。将根据SF6与CFCs的比率计算示踪剂年龄，对于最古老的沃茨，将根据CFCs之间的比率计算示踪剂年龄。使用SF6/CFC比率获得了时间尺度小于35年的海洋过程的最稳健的示踪剂组合。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.