Southern Ocean carbon indices and metrics (SARDINE)

南大洋提供了一个主要窗口，通过这个窗口，大气可以影响内部海洋的特性，反过来，也可以了解深海如何影响大气。这里形成的地表水在全球海洋深处被转移，而深水又返回海面。全球海洋在碳循环中的作用受到这两种活动的强烈控制：离开南大洋的地表水减少了大气中的二氧化碳，而深水富含碳，因此当深水返回海面时，二氧化碳被释放到大气中。南大洋模态水域的体积正在发生变化，预估其随不同排放情景以非线性方式变化，此外还有与南极洲上空大气变化有关的翻转环流的变化。目前尚不清楚的是，南大洋海洋碳吸收的相关变化，以及对全球碳和气候指标的更广泛影响。例如，如果南大洋的分层加强而通风减弱，那么对碳和气候系统的最终影响是什么？我们需要知道南大洋是如何吸收热量和碳的，以及这种吸收会如何随着气候变化而改变。通过利用通风和主要物理程序（ORCHESTRA）的颠覆性诊断，我们将确定不同水团中吸收了多少碳，并确定与不同物理、生物和化学过程相对应的碳库的变化。我们需要知道南大洋是如何改变全球气候系统中的碳反馈的。通过确定地球系统模式预测中海洋碳储量的变化，我们将揭示南大洋对全球碳循环反馈的影响，并确定其成分如何随着物理、化学和生物过程的变化而变化。同样，我们需要知道南大洋是如何影响全球气候指标的，包括在给定的累积碳排放下，预计地表会变暖多少，为了避免超过变暖目标可能会排放多少碳，以及在停止排放后延迟达到变暖峰值的程度。通过采用代表性浓度路径的地球系统模型的热和碳诊断，我们将确定南大洋对全球地表变暖对碳排放的响应的影响，避免变暖目标的最大允许碳排放以及在排放停止后可能发生的全球地表变暖程度。如果我们要了解在一个变暖的世界中，南大洋环流和通风变化如何影响全球碳和气候指标，这项工作至关重要。南大洋主导着全球海洋热量和碳吸收，但在全球气候模型中代表性不足。目前的地球系统模式对最近过去的海洋物理和生物地球化学的描述存在广泛的差异，而且模式之间对气候强迫下的未来的预测往往存在巨大差异。这项研究将使我们第一次将南大洋的物理、生物和化学过程的贡献归因于各种关键的全球气候指标。通过将这些气候指标与正在进行的ORCHESTRA和RoSES项目揭示的对南大洋物理和生物地球化学特性的新理解进行综合，我们将能够对预测的气候未来的传播产生新的解释，并确定南大洋对不确定性的影响。

The Southern Ocean provides the primary window by which the atmosphere affects the properties of the interior ocean and, in turn, how the deep ocean affects the atmosphere. Surface waters formed here are transferred at depth over the global ocean and deep waters are returned to the sea surface. The role of the global ocean in the carbon cycle is strongly controlled by this dual activity: surface waters leaving the Southern Ocean act to drawdown atmospheric carbon dioxide, while deep waters are carbon rich and so when deep waters return to the sea surface carbon dioxide is outgassed to the atmosphere.There are ongoing changes in the volume of Southern Ocean mode waters, which are projected to vary in a nonlinear manner with different emission scenarios, together with changes in the overturning circulation associated with atmospheric changes over Antarctica. What is unclear are the associated changes in ocean carbon uptake in the Southern Ocean together with the wider effects on global carbon and climate metrics. For example, if the stratification strengthens and ventilation weakens in the Southern Ocean, what then are the resulting effects for the carbon and climate system?We need to know how the Southern Ocean is sequestering heat and carbon, and how that uptake is likely to alter with climate change. By drawing upon ventilation and overturning diagnostics from a mainly physical programme (ORCHESTRA), we will identify how much carbon is taken up in different water masses and identify the changes in carbon pools corresponding to different physical, biological and chemical processes.We need to know how the Southern Ocean alters global carbon feedbacks in the climate system. By identifying the changes in ocean carbon inventories in Earth system model projections for 1% annual rise in CO2, we will reveal the effect of the Southern Ocean on global carbon-cycle feedbacks, as well as identify how their components alter with changes in physical, chemical and biological processes.Similarly, we need to know how the Southern Ocean affects global climate metrics, including how much surface warming is expected for a given cumulative carbon emission, how much carbon may be emitted to avoid exceeding warming targets and the extent of delayed peak warming after emissions cease. Through combined heat and carbon diagnostics of Earth system models following Representative Concentration Pathways, we will identify the effect of the Southern Ocean on the global surface warming response to carbon emissions, the maximum permitted carbon emission to avoid warming targets and how much global surface warming might occur after emissions cease.This work is crucial if we are to understand how Southern Ocean circulation and ventilation changes affect global carbon and climate metrics in a warming world. The Southern Ocean dominates global ocean heat and carbon uptake, but is poorly represented in global climate models. There is a wide spread across current Earth system models in their ocean physical and biogeochemical representation of the recent past, and often dramatic differences between models in their projections for the future under climate forcing. This study will allow us to attribute for the first time the contribution of the physical, biological and chemical processes in the Southern Ocean to various critical global climate metrics. Through a synthesis of these climate metrics with new understanding of the physical and biogeochemical properties of the Southern Ocean revealed by ongoing projects ORCHESTRA and RoSES, we will be able to produce new interpretations of the spread in projected climate futures and identify the effect of the Southern Ocean on the uncertainty.