Towards detecting and attributing long-term changes in CO2 outgassing in the equatorial Pacific

海洋中二氧化碳（CO2）源和汇的变化具有高度不确定性，因此可能对未来大气CO2水平产生重大影响。热带太平洋的二氧化碳释放是这种强大的温室气体进入大气的最大自然来源。该项目将结合使用现有的和新的地球系统模型（ESM）模拟来研究热带太平洋海-气CO2交换的持续和未来变化。研究方法将侧重于强大的机制，在赤道出气的变化，在21世纪世纪的气候和海洋地球化学模拟。这里提出的研究可以提供关于热带海洋继续减缓二氧化碳释放的能力的答案，从而有助于减缓大气二氧化碳的增加。此外，拟议的取样偏差分析是了解今后在热带海洋扩大海洋碳观测系统的要求的第一步。最后，该项目将支持一名早期职业研究人员和一名博士后学者，他们将接受气候动力学和海洋地球化学的跨学科培训。 先进的诊断和新的模拟相结合，将被用来确定和理解强大的机制，即那些可以链接到简单的动态和物理过程，因此是独立的参数化过程的动态和物理。将进行新的模拟，目的是隔离二氧化碳增加、海洋环流和温度升高对赤道释气的影响。将使用多模式集合的现有输出探索结果的模式依赖性。该项目还将探索这些机制在随后的几个世纪中如何运作，因为大气中的二氧化碳稳定下来，碳循环接近新的平衡。将考虑使用1984 - 2012年期间观察到的变化评估模拟机制的策略。重点将放在减少由于对赤道太平洋上空pCO2的空间和时间变异性取样有限而造成的不确定性。还将使用新的仅限于海洋的模拟来研究太平洋气候持续数十年变化的影响，这些模拟旨在将二氧化碳增加的影响与环流变化分开。这项工作的成果是多方面的，包括：（1）研究模式预测的可靠机制;（2）评价2100年以后赤道放气的长期反应;（3）系统评价热带太平洋现有的观测系统;（4）评价太平洋气候的几十年变化对热带碳循环观测变化的影响。

Changes in carbon dioxide (CO2) sources and sinks in the ocean are highly uncertain, and could therefore have a significant influence on future atmospheric CO2 levels. Outgassing of CO2 in the tropical Pacific is the largest natural source of this powerful greenhouse gas to the atmosphere. This project will use a combination of existing and new Earth System Model (ESM) simulations to study ongoing and future changes in sea-air CO2 exchange over the tropical Pacific. The research approach will focus on robust mechanisms governing changes in equatorial outgassing in 21th Century simulations of climate and ocean biogeochemistry. The research proposed here could provide answers regarding the ability of the tropical oceans to continue to slow their outgassing of CO2, thus contributing to moderating the increase of atmospheric CO2. In addition, the proposed analysis of sampling biases is a first step towards understanding the requirements of future expansions of the ocean carbon observing system in the tropical oceans. Last, this project will support one early career researcher and one post-doctoral scholar, who will receive cross-disciplinary training in climate dynamics and ocean biogeochemistry. A combination of advanced diagnostics and new simulations will be used to identify and understand the dynamics and physics of the robust mechanisms, i.e. those that can be linked to simple dynamical and physical processes and therefore are independent of parameterized processes. New simulations will be performed with the objective of isolating the effects of increasing CO2, ocean circulation, and warmer temperatures on equatorial outgassing. Model dependence of the results will be explored using existing output from a multi-model ensemble. The project will also explore how these mechanisms operate in subsequent centuries as atmospheric CO2 stabilizes and the carbon cycle approaches a new equilibrium. Strategies for evaluating the simulated mechanisms using observed changes during the 1984-2012 period will be considered. Emphasis will be placed on reducing uncertainty due to limited sampling of spatial and temporal variability of pCO2 over the equatorial Pacific. The effect of ongoing multi-decadal changes in Pacific climate will also be studied using new ocean-only simulations designed to isolate the effect of increasing CO2 from changes in circulation. The outcomes of this work are manifold, including 1) study of robust mechanisms in model projections; 2) evaluation of the long-term response of equatorial outgassing beyond year 2100; 3) a systematic evaluation of the existing observing system in the tropical Pacific; and 4) evaluation of the effect of multi-decadal changes in Pacific climate on the observed changes in the tropical carbon cycle.