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

大气中不断上升的二氧化碳浓度、全球气候变化以及地球生物圈的可持续性都是科学界和社会关注的问题。每年大约四分之一的化石燃料排放的二氧化碳被海洋吸收，了解这一过程发生的地点和速度是很重要的。碳的稳定同位素可以作为识别大气和海洋中化石燃料产生的二氧化碳的“标志”。研究人员开发了一种新方法，可以在海上快速准确地测量溶解二氧化碳的稳定碳同位素组成。他们将在两次前往南大西洋的研究探险中测量数千个样本。他们将把他们的测量结果与大约十年前在同一地点进行的测量结果进行比较，并确定那段时间内吸收的二氧化碳量。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未被充分代表的少数民族学生参与研究，并让一名研究生和一名本科生参与该项目的所有阶段，以增强地球科学的多样性。包括学生在内的团队将积极在国际、国家、区域、地方教育和推广活动以及同行评审期刊上传播研究成果。在南大西洋，人为CO2吸收率很高，并且随着模态和中间水的形成而变化，并且对气候变化敏感。碳- 13ess效应使大气中的delta13C-CO2成为一个明确定义的端元，而海洋中的delta13C-DIC则是一个强大的示踪剂，可以独立估计海洋中人为二氧化碳的吸收和储存。该团队开发了一种精确、快速和航海的方法，可以同时测量溶解的无机碳（DIC）浓度（每公斤±2微摩尔）和稳定的碳同位素组成（delta13C-DIC）（±0.03 permil），方法是将二氧化碳提取装置与腔衰荡光谱（CRDS）同位素分析仪相结合。他们将在GO-SHIP邮轮A13.5和A16S上使用这种方法，每次邮轮上分析大约1000个船上样本和2000个陆地样本。将对该方法与传统的同位素比质谱（IRMS）方法进行广泛的评估和比较。PIs假设模式水和中间水的形成和强度对人为碳的横向输送产生强烈影响，从而影响水柱人为碳储量变化的年代际变化。因此，库存量变化具有经向和纬向两种趋势，因此A13.5和A16S的组合将更好地代表全流域的变化。验证这一假设将实现两个目标：(1)证明通过基于crds的方法可以收集精确和准确的delta13C-DIC数据，其质量可与基于irms的数据相媲美，并且可以在船上和国内以与其他GO-SHIP一级参数（如DIC）相当的高空间分辨率对大量样本进行分析；(2)评估南大西洋人为碳吸收和碳储存速率的时空变化。特别是，pi将比较东部盆地A13.5样带的delta13C-DIC和DIC观测数据（2022年与2010年及更早的数据）与西部盆地A16S样带的观测数据（2024年与2013年及更早的数据）独立估算的人为碳库存。他们还将比较全流域水柱人为13C-DIC清单与海气碳同位素不平衡估算的表层海洋人为13CO2吸收通量，差异在于人为碳通过横向运输携带。该奖项反映了美国国家科学基金会的法定使命，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。

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.