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CO2海洋汇，每年吸收人类活动产生的全球CO2排放量的5%至10%。因此，本世纪南大洋CO2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CO2汇的效率。这些因素包括大气中二氧化碳的变化速率和水平、气候的相关变化，包括变暖和风，以及海洋生态系统和海洋内因人为驱动因素而发生的生物地球化学变化。CELOS有助于了解这些过程中的每一组将如何影响南大洋CO2汇，并确定如何用指标跟踪其演变。特别是，在过去50年中，观察到南大洋的风在增加。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很重要，但这一点尚未得到探讨。CELOS提出了一个独特的贡献，其形式是一组有限的模型模拟，超越了已经完成的工作，并以前所未有的方式探索科学边界。新的模拟详细探讨了三个要素：首先，将使用NEMO全球海洋模式在两种配置下进行模拟，一种是低物理分辨率（2度），另一种是相对较高的分辨率（0.25度）。这两种分辨率的主要区别在于它们对涡旋的表示。在低分辨率，涡旋参数化，它是假设，这种参数化抑制南大洋CO2汇的变化。在高分辨率，参数化的涡旋被删除，和涡旋活动明确地响应海洋密度梯度的变化。这使得能够对风的变化做出更机械的响应。第二，臭氧的作用将在今后的预测中单独列出。联合王国环境与安全管理局将继续进行他们已经进行的模拟，在2015年之前，即本世纪结束之前，关闭相互作用的臭氧。他们还将做进一步的模拟，将臭氧相互作用固定在1985年的水平上，假设臭氧没有恢复。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，一组有最佳估计的臭氧恢复。这一组将很好地边界臭氧可能演变本世纪。第三，将进行模拟，以测试CUSTARD和PICCOLO中确定的生态系统和生物地球化学过程。初步提出了五个变量，涵盖铁的可用性以及表层生态系统的变化如何转化为向深海输出碳的变化。然而，有可能通过与玫瑰和交响乐团社区在年度会议期间的互动进行额外的模拟。使用这些新的模拟和来自UKESM的现有模型结果，我们将继续开发指标，以跟踪未来的变化。计量工作将以汇率为基础，作为未来衡量碳汇效率的一个指标。它将利用指纹识别的变化来识别如何跟踪本世纪的具体演变过程。它将特别注意汇的总体效率以及海洋生态系统引起的变化和由此产生的碳输出。最后，CELOS的新见解将被用来为未来的发展，使用和分析的UKESM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.