Measurements of stable carbon isotopes on board GO-SHIP cruises in the South Atlantic Ocean to enhance our ability to quantify anthropogenic CO2 uptake rates by the ocean

大气中二氧化碳浓度的上升、全球气候变化以及地球生物圈的可持续性都是重大的科学和社会问题。每年排放的化石燃料排放的二氧化碳中，约有四分之一被海洋吸收，了解这一过程发生的地点和速度非常重要。碳的稳定同位素可以作为识别大气和海洋中化石燃料来源的二氧化碳的“标志”。研究人员开发了一种新的方法，可以在海上快速准确地测量溶解的二氧化碳的稳定碳同位素组成。他们将对南大西洋的两次研究探险中的数千个样本进行测量。他们将把他们的测量结果与大约十年前在相同地点进行的测量结果进行比较，并确定在这段时间内吸收的二氧化碳数量。拟议的研究将加强海洋碳研究基础设施、普通科学教育以及公众对气候变化和环境问题的认识。研究人员计划通过招募少数族裔学生参与研究来增强地球科学的多样性，并让一名毕业生和一名本科生参与该项目的所有阶段。该小组，包括学生，将在国际、国家、区域、地方教育和外联活动以及同行评议期刊上积极传播研究成果。在南大西洋，人为的二氧化碳吸收速率很高，并且随着模式和中间水域的形成而变化，对气候变化很敏感。13C-Suess效应使大气中的Delta13C-CO2成为明确定义的端元，而海洋中的Delta13C-DIC成为独立估计海洋人为二氧化碳吸收和储存的强大示踪剂。该团队开发了一种精确、快速和出海的方法，通过将二氧化碳提取设备与腔环形光谱分析(CRDS)同位素分析仪相结合，同时测量溶解无机碳(DIC)浓度(每公斤正负2微摩尔)和稳定碳同位素组成(Delta13C-DIC)(正负0.03permil)。他们将在A13.5和A16S邮轮上使用这种方法来分析船上的大约1000个样本和每次巡航的陆地上的2000个样本。该方法将与传统的基于同位素比质谱仪(IRMS)的方法进行广泛的评估和比较。PI假设模式和中间水的形成和强度对人为碳的横向输送有很大的影响，从而影响水柱人为碳储量变化的年代际变化。因此，库存的变化既有经向趋势，也有纬向趋势，因此A13.5和A16S的组合将更好地代表整个盆地的变化。在检验这一假设时将实现两个目标：(1)证明可以通过基于CRDS的方法收集在质量上可与IRMS数据相媲美的精确和准确的delta13C-DIC数据，并且可以在船上和国内以与DIC等其他GO-SHIP一级参数相媲美的高空间分辨率分析大量样本；(2)评估南大西洋人为碳吸收和储存速率的空间变化和时间变化。特别是，独立于三角洲13C-DIC和DIC观测的东部盆地A13.5样带(2022年与2010年及更早的数据)和西部盆地A16S样带(2024年与2013年及更早的数据)的估计人为碳储量将进行比较。他们还将比较盆地范围的水柱人为13C-DIC清单与根据海-气碳同位素不平衡估计的表层海洋人为13CO2吸收通量，两者之间的差异是通过横向输送携带的人为碳。这一裁决反映了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。

Rising carbon dioxide concentrations in the atmosphere, global climate change, and the sustainability of the Earth’s biosphere are of great scientific and societal concern. Approximately one-quarter of fossil fuel emissions of carbon dioxide emitted each year are absorbed by the oceans, and it is important to understand where and how fast this process occurs. Stable isotopes of carbon can be used as a “signature” to identify fossil fuel-derived carbon dioxide in the atmosphere and ocean. The investigators have developed a new method for measuring the stable carbon isotope composition of dissolved carbon dioxide rapidly and precisely while at sea. They will measure several thousand samples on two research expeditions to the South Atlantic Ocean. They will compare their measurements to ones made in the same locations approximately ten years earlier, and determine the amount of carbon dioxide absorbed over that time period. The proposed research will enhance ocean carbon research infrastructure, general science education, and public awareness of climate change and environmental issues. The investigators plan to enhance diversity in earth sciences by recruiting underrepresented minority students in the research and have a graduate and an undergraduate student involved in all phases of this project. The team, including the students, will actively disseminate the research results in international, national, regional, local education and outreach activities, and in peer-review journals. In the South Atlantic Ocean, anthropogenic CO2 uptake rates are high and variable as mode and intermediate waters are formed and are sensitive to climate changes. The carbon-13 Suess effect makes delta13C-CO2 in the atmosphere a clearly defined endmember and delta13C-DIC in the ocean a powerful tracer to independently estimate anthropogenic CO2 uptake and storage in the ocean. The team has developed a precise, rapid, and sea-going method to simultaneously measure dissolved inorganic carbon (DIC) concentration (to plus or minus 2 micromol per kilogram) and stable carbon isotope composition (delta13C-DIC) (to plus or minus 0.03 permil) by combining a CO2 extraction device with a Cavity Ring-Down Spectroscopy (CRDS) isotope analyzer. They will use this method aboard GO-SHIP cruises A13.5 and A16S to analyze about 1000 samples onboard the ship and 2000 samples on land for each cruise. Extensive evaluation and comparison of this method with the traditional isotope ratio mass spectrometry (IRMS)-based method will be done. The PIs hypothesize that the formation and the strength of mode and intermediate waters have a strong influence on the lateral transport of anthropogenic carbon and thus the decadal variability of the water column anthropogenic carbon inventory change. As a result, the change in inventory has both meridional and zonal trends, and therefore a combination of A13.5 and A16S will better represent the basin-wide changes. Two objectives will be achieved in testing this hypothesis: (1) Demonstrate that precise and accurate delta13C-DIC data, comparable in quality to IRMS-based data, can be collected via the CRDS-based method, and that large numbers of samples can be analyzed onboard ships and back home with high spatial resolution comparable to other GO-SHIP level 1 parameters such as DIC; (2) Assess the spatial variations and temporal changes of the anthropogenic carbon uptake and storage rates in the South Atlantic Ocean. In particular, the PIs will compare estimated anthropogenic carbon inventories independently from delta13C-DIC and DIC observations from transect A13.5 (2022 vs. 2010 and earlier data) in the eastern basin with those of transect A16S (2024 vs. 2013 and earlier data) in the western basin. They will also compare the basin-wide water column anthropogenic 13C-DIC inventory with the surface ocean anthropogenic 13CO2 uptake flux estimated from air-sea carbon isotope disequilibrium, the difference being anthropogenic carbon carried by lateral transport.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.