Constraining the EvoLution of the southern Ocean-carbon Sink (CELOS)

南大洋（SO）对气候和气候变化起着关键作用。它是最大的人为二氧化碳海洋汇，每年吸收全球人类活动排放的5%到10%的二氧化碳。因此，本世纪南大洋二氧化碳汇的演变将在调节气候变化的速度方面发挥重要作用。有几个因素可以影响南大洋二氧化碳汇的效率。这些变化包括大气中二氧化碳变化的速度和水平，包括变暖和风在内的相关气候变化，以及海洋生态系统和生物地球化学因人为驱动因素而发生的变化。CELOS有助于了解这些过程中的每一组将如何影响南大洋二氧化碳汇，并确定如何用指标跟踪其演变。特别是，在过去50年中，观测到南大洋的风有所增加。这种增加与平流层臭氧的变化有关，但预测气候变化的模型也将风的增加归因于温室气体的增加。因此，温室气体和臭氧恢复的相对演变在本世纪可能是重要的，而这一点尚未得到探讨。CELOS以一组有限的模型模拟的形式提出了一项独特的贡献，这些模拟超出了已经完成的工作，并以一种前所未有的方式探索了科学界限。新的模拟详细探讨了三个要素。首先，将用NEMO全球海洋模型在两种配置下进行模拟，一种是低物理分辨率（2度），另一种是相对高分辨率（0.25度）。这两项决议主要不同于它们对涡流的表示。在低分辨率中，涡旋被参数化，并且假设这种参数化抑制了南大洋二氧化碳汇的变异性。在高分辨率下，漩涡的参数化被去除，漩涡活动明显响应海洋密度梯度的变化。这使得对风的变化作出更机械的反应成为可能。其次，在未来的预测中，臭氧的作用将被孤立。UKESM将继续他们已经做过的模拟，直到2015年，到本世纪末，关闭交互臭氧。他们还将做一个进一步的模拟，将交互臭氧固定在1985年的水平，假设臭氧不会恢复。因此，我们将有三组强迫，一组没有臭氧，一组有臭氧但没有臭氧恢复，一组有最佳估计臭氧恢复。这一组将很好地描述本世纪臭氧可能的演变。第三，模拟将对CUSTARD和PICCOLO中确定的生态系统和生物地球化学过程进行测试。最初提出了五种变体，包括铁的可用性以及地表生态系统的变化如何转化为向深海输出碳的变化。然而，在年度会议期间，通过与RoSES和ORCHESTRA社区的互动，有可能进行额外的模拟。使用这些新的模拟和来自UKESM的现有模型结果，我们将继续进行度量的开发，以跟踪未来的变化。计量工作将以碳汇率为基础，作为未来碳汇效率的衡量标准。它将利用变化的指纹识别来确定如何跟踪本世纪特定过程的演变。它将特别注意碳汇的总体效率，以及由海洋生态系统和由此产生的碳输出所介导的变化。最后，CELOS的新见解将用于为UKESM的未来发展、使用和分析提出建议。

The Southern Ocean (SO) plays a key role for climate and climate change. It is the largest oceanic sink of anthropogenic CO2, absorbing each year between 5 and 10 percent of the global CO2 emissions from human activities. The evolution of the Southern Ocean CO2 sink this century will therefore play an important role for modulating the pace of climate change. Several factors can influence the efficiency of the Southern Ocean CO2 sink. These include the rate and level of change of CO2 in the atmosphere, the associated changes in climate including warming and winds, and the changes in marine ecosystems and biogeochemistry that occur within the ocean in response to anthropogenic drivers. CELOS contribute to understanding how each of these sets of processes will impact the Southern Ocean CO2 sinks, and to determine how to keep track of its evolution with metrics. In particular, winds in the Southern Ocean have been observed to increase in the past 50 years. This increase has been linked to the change of stratospheric ozone, but models that project climate change also attribute the increase in winds to the increase in greenhouse gases. The relative evolution of greenhouse gases and ozone recovery could therefore be important this century, and this has not yet been explored. CELOS proposes a unique contribution in the form of a limited set of model simulations that go beyond what is already done, and an analysis that explores scientific boundaries in a way never done before. The new simulations explore three elements in detail.First, simulations will be done with the NEMO global ocean model in two configurations, one of low physical resolution (2 degrees) and one of relatively high resolution (0.25 degrees). The two resolutions mostly differ in their representation of eddies. In the low resolution, eddies are parameterised, and it is hypothesised that this parameterisation dampens the variability of the Southern Ocean CO2 sink. In the high resolution, the parameterisation of eddies is removed, and eddy activity responds explicitly to changes in ocean density gradients. This enables more mechanistic responses to changes in winds. Second, the role of ozone will be isolated in future projections. The UKESM will pursue simulations that they have already done, turning off interactive ozone up to year 2015, to the end of this century. They will also do one further simulation, fixing interactive ozone at its 1985 level, which assumes no recovery in ozone. Therefore, we will have three set of forcing, one with no ozone, one with ozone but no ozone recovery, and one with best estimated ozone recovery. This set will nicely border the possible evolution of ozone this century. Third, simulations will be done to test the ecosystem and biogeochemical processes identified in CUSTARD and PICCOLO. Five variants are proposed initially, covering iron availability and how changes in surface ecosystems translate into changes in carbon export to the deep ocean. However, there is potential for additional simulations through the interactions with the RoSES and ORCHESTRA communities during annual meetings. Using these new simulations and existing model results from the UKESM, we will then proceed into the development of metrics to keep track of future changes. The metrics work will build on the sink rate as a measure of the efficiency of the carbon sinks in the future. It will use the identification of fingerprints of changes to identify how to keep track of the evolution of specific processes this century. It will pay particular attention to the overall efficiency of the sink and to the changes mediated by marine ecosystems and resulting carbon export. Finally, the new insights of CELOS will be used to make recommendations for future developments, use and analysis of the UKESM.