Collaborative Research: Forced drivers of trends in ocean biogeochemistry: Volcanos and atmospheric carbon dioxide

世界海洋在全球碳和氧循环中发挥着重要作用。除了在碳的自然循环中发挥重要作用外，海洋还吸收了化石燃料燃烧所排放的大约40%的二氧化碳。了解导致海洋碳和氧浓度时空变化的过程对于预测这些海洋循环将如何发展到未来至关重要。最近基于测量的估计和计算机模型一致认为，海洋碳吸收量在20世纪90年代初显著增加，然后在20世纪90年代的剩余时间里放缓。观测和模式也表明了显著的氧变化。这些模式的一个可能的驱动因素尚未被探索是大型火山爆发的影响，特别是1991年的皮纳图博火山。随着火山喷发，小颗粒被逼到很高的高度，在那里它们通过高层大气扩散，将阳光反射回太空，导致全球气候暂时降温。该项目将通过比较包含和不包含皮纳图博火山喷发影响的地球系统模型模拟，探索这种暂时的降温是如何影响海洋环流和海气碳氧交换的。在NCAR的社区地球系统模型大集合（CESM-LE）努力的框架内，该团队将完成一个明确排除皮纳图博山（CESM-LE- novolc）强迫的新实验。与现有的包括所有强迫的CESM-LE不同，研究人员将直接确定皮纳图博山的影响，并将这些影响与观测到的碳和氧变化联系起来。具体来说，他们提出了两个假设：假设1：自20世纪90年代以来，人为碳和氧的地表通量和内部分布趋势受到皮纳图博山的显著影响。假设2：在皮纳图博山引起的初始吸收异常之后，温度较低且示踪剂异常高的温跃层异常返回地表。这些异常现象抑制了火山爆发后长达10年的海气通量。最近的研究还表明，大气二氧化碳增长率的变异性对海洋碳吸收的变异性具有一级效应。研究人员还将利用CESM海冰预报的一次新运行和CMIP6模式的分层分析进行初步分析，以进一步探讨这一问题。具体地说，他们提出了第三个假设：假设3：通过在模拟中包括大气二氧化碳的季节循环和纬度分布，全球综合海气碳通量的变异性增加，并与基于观测的估计值更具可比性。通过创建CESM-LE-NoVolc，这项工作将允许调查皮纳图博山对广泛的海洋生物地球化学和物理过程的强迫影响。在CESM-LE项目的保护伞下，模型运行将很容易获得。在这个研究项目下，研究生和本科生的研究将得到支持。该团队将继续我们长期以来的努力，吸引代表性不足的学生参与科学，并向公众和K-12学生解释海洋和碳循环科学。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。

The world’s oceans play an important role in the global carbon and oxygen cycles. In addition to their importance in the natural cycling of carbon, the oceans have absorbed approximately 40% of the carbon dioxide that has been emitted by fossil fuel burning. Understanding the processes that cause spatial and temporal variations of ocean carbon and oxygen concentrations is critical to predicting how these ocean cycles will develop into the future. Recent measurement-based estimates and computer models agree that ocean carbon uptake increased significantly in the early 1990s and then slowed over the rest of the decade. Observations and models also indicate significant oxygen variations. One possible driver of these patterns that has not been explored is the influence of large volcanic eruptions, specifically Mount Pinatubo in 1991. With the eruption, small particles were forced to great altitude where they spread through the upper atmosphere, reflected sunlight back to space, and led to a temporary cooling of global climate. This project will explore how this temporary cooling influenced ocean circulation, and air-sea carbon and oxygen exchange, by comparing Earth system model simulations that do and do not include the effects of Mt. Pinatubo’s eruption. Within the framework of NCAR’s Community Earth System Model Large Ensemble (CESM-LE) effort, the team will complete a new experiment that explicitly excludes forcing from Mt. Pinatubo (CESM-LE-NoVolc). By difference from the existing CESM-LE that includes all forcing, the investigators will directly identify the effects of Mt. Pinatubo and put these effects in context with observed carbon and oxygen change. Specifically, they propose to address two hypotheses: Hypothesis 1: Trends in surface fluxes and interior distributions of anthropogenic carbon and oxygen since the 1990s have been significantly impacted by Mt. Pinatubo.Hypothesis 2: After the initial uptake anomaly due to Mt. Pinatubo, thermocline anomalies that are cool and anomalously high in tracers return to the surface. These anomalies suppress air- to-sea fluxes for up to a decade after the eruption. Recent work has also indicated that variability in the growth rate of atmospheric carbon dioxide has a first-order effect on variability of ocean carbon uptake. The investigators will also do preliminary analysis using one new run of the CESM ocean-ice hindcast and a stratified analysis of CMIP6 models to further explore this issue. Specifically, they propose a third hypothesis: Hypothesis 3: By including the seasonal cycle and latitudinal distribution of atmospheric carbon dioxide in simulations, variability of the globally integrated air-sea carbon flux is increased and becomes more comparable to observationally-based estimates. By creating CESM-LE-NoVolc, this work will allow for investigation of the forced impact of Mt. Pinatubo on a wide range of ocean biogeochemical and physical processes. Model runs will be made easily available under the CESM-LE project umbrella. Under this research project, graduate and undergraduate research will be supported. The team will continue to our long-standing efforts to attract underrepresented students to science, and to explain ocean and carbon cycle science to the general public and K-12 students.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.