Quantifying mechanisms of variability in ocean CO2 uptake 1980-present

随着时间的推移，由于化石燃料燃烧和森林砍伐，海洋吸收了大约三分之一的人类二氧化碳(CO2)排放。然而，观测表明，海洋从大气中吸收二氧化碳的速度每年都会有很大的不同，甚至在更长的时间尺度上也会有很大差异。这些变化是自然和人为气候变化的某种组合造成的，但我们对这种变化的原因的理解仍然不完整，这阻碍了我们对全球碳预算的理解，并阻碍了我们做出准确气候预测的能力。在这个项目中，我们将使用几种不同的最先进的海洋碳循环模型进行有针对性的实验，以确定哪些因素导致过去40年海洋吸收二氧化碳的速率发生变化。这些实验将确定哪些模型最能代表驱动海洋二氧化碳吸收可变性的重要气候过程，并将确定模型可以改进的领域，这将导致对海洋碳吸收的气候敏感性进行更好的约束，并导致更好的气候预测。这项工作还将有助于确定模型中二氧化碳吸收的可变性如何以及为什么与观测结果不同，并有助于解决全球碳预算中的不平衡问题。最后，这将改善对二氧化碳排放的限制，以限制全球变暖的破坏性影响。这项工作的更广泛影响包括对一名海洋碳循环模型研究生的培训，以及对两名来自历史上黑人院校的本科生的培训。海洋是人为二氧化碳排放的两个主要汇之一(陆地生物圈是另一个)，吸收了目前大约25%的人为二氧化碳排放。最近的研究表明，在十年的时间尺度上，海洋二氧化碳汇的可变性与陆地二氧化碳汇的可变性不相上下，但驱动这种可变性的机制尚不清楚。确定海洋二氧化碳汇变化的驱动因素对于了解海洋碳汇将如何应对未来的气候变化、开发更准确的预测气候模型以及协调全球碳预算中的十年不平衡具有重要意义。该项目将利用海洋生物地球化学模型和海洋逆模型进行有针对性的模拟，以回答一个重要的科学问题：在过去40年里，海洋二氧化碳汇年际到年代际变化的驱动因素是什么？为了回答这个问题，这项工作侧重于三个主要目标：(1)用一套海洋生物地球化学模型和一个海洋环流逆模型量化过去40年海洋二氧化碳吸收的可变性机制；(2)比较各种模型和方法，以确定在全球和区域范围内驱动海洋二氧化碳吸收可变性的最可靠机制；(3)比较生物地球化学模型和海洋逆模型中海洋二氧化碳吸收的可变性，以确定哪些模型和机制最符合观测结果。这项工作将确定哪些模型最能代表驱动海洋二氧化碳吸收可变性的重要过程，并将确定模型可以改进的领域。这项工作还将有助于确定模型中二氧化碳吸收的可变性如何以及为什么与观测结果不同，并有助于解决全球碳预算中的不平衡问题。最后，我们的结果将导致对海洋碳汇变异性的更好的机械理解，这将导致对海洋碳吸收的气候敏感性的更好限制，以及更好的气候项目。这一奖项反映了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。

Over time, the ocean has absorbed roughly one third of all human carbon dioxide (CO2) emissions due to fossil fuel burning and deforestation. However, observations show that the rate at which the ocean absorbs CO2 from the atmosphere can vary greatly from one year to the next, and on even longer timescales. These variations result from some combination of natural and human-caused climate variability, but our understanding of the reasons for this variability remains incomplete, which hampers our understanding of the global carbon budget and hinders our ability to make accurate climate forecasts. In this project, we will perform targeted experiments with several different state-of-the-art models of the ocean carbon cycle to determine what factors are responsible for variability in the rate of CO2 uptake by the ocean over the past four decades. These experiments will determine which models best represent the important climate processes driving variability in ocean CO2 uptake, and will identify areas where the models can be improved, which will lead to better constraints on the climate sensitivity of ocean carbon uptake, and lead to better climate projections. This work will also help to identify how and why the variability of CO2 uptake in models differs from the observations and help to resolve imbalances in the global carbon budget. Finally, this will lead to improved constraints on CO2 emissions to limit the damaging effects of global warming. The broader impacts of this work include the training of a graduate student in ocean carbon cycle modeling, and training of two undergraduate students from historically black colleges and universities.The ocean is one of the two main sinks for anthropogenic CO2 emissions (the terrestrial biosphere being the other) and absorbs roughly 25% of current anthropogenic CO2 emissions. Recent work has shown that the variability of the ocean CO2 sink rivals that of the terrestrial CO2 sink on decadal timescales, but the mechanisms driving this variability remain unclear. Identifying the drivers of variability in the ocean CO2 sink is important for understanding how the ocean carbon sink will respond to future climate changes, for developing more accurate prognostic climate models, and for reconciling decadal imbalances in the global carbon budget. This project will undertake targeted simulations with ocean biogeochemical models and ocean inverse models to answer the overarching science question: “What are the drivers of interannual to decadal variability in the ocean CO2 sink over the past four decades?” To answer this question this work focusses on three main objectives: (i) quantifying mechanisms of variability in ocean CO2 uptake over the past four decades in a suite of ocean biogeochemical models and an ocean circulation inverse model, (ii) comparing across models and methods to determine the most robust mechanisms driving variability in ocean CO2 uptake at both global and regional scales, and (iii) comparing the variability of ocean CO2 uptake in biogeochemical models and ocean inverse models to determine which models and mechanisms best agree with the observations. This work will determine which models best represent the important processes driving variability in ocean CO2 uptake and will identify areas where the models can be improved. This work will also help to identify how and why the variability of CO2 uptake in models differs from the observations, and help to resolve imbalances in the global carbon budget. Last, our results will lead to an improved mechanistic understanding of variability in the ocean carbon sink, which will lead to better constraints on the climate sensitivity of ocean carbon uptake, and to better climate projections.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.