No changes in overall AMOC strength in interglacial PMIP4 time slices
No changes in overall AMOC strength in interglacial PMIP4 time slices
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DOI：
10.5194/cp-19-107-2023
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发表时间：
2023-01
影响因子：
4.3
通讯作者：
Zhiyi Jiang;C. Brierley;D. Thornalley;Sophie E. Sax
中科院分区：
文献类型：
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作者：
Zhiyi Jiang;C. Brierley;D. Thornalley;Sophie E. Sax
抽象的。大西洋经向翻转环流（AMOC）是向极热量输送的重要机制，也是全球气候系统的重要组成部分。它如何响应过去的强迫变化，如在第四纪间冰期经历的变化，是一个有趣的和开放的问题。以前的建模研究表明，在全新世中期相比，工业化前时期的AMOC增强。在古气候模拟相互比较项目（PMIP）的早期模拟中，这是由海冰和AMOC变化之间的反馈引起的，这取决于分辨率。在这里，我们提出了一个初步的分析，最近可用的PMIP 4模拟三个实验，代表不同的间冰期条件-一个127 000年前在末次间冰期（127 ka，称为lig 127 k），一个在全新世中期（中全新世，6 ka），和前工业控制模拟（piControl，1850 CE）。与piControl相比，lig 127 k和中全新世都改变了轨道配置。PMIP 4模式的集合平均值表明，AMOC的强度在中全新世和piControl实验之间或在lig 127 k和piControl实验之间没有明显变化。因此，轨道强迫本身似乎并不改变整个AMOC。我们进一步调查的一致性的强迫响应在AMOC在两个间冰期，沿着与信号的强度，使用8个PMIP 4模型，进行两个间冰期实验。只有两个模型显示了更强的强迫下更强的变化，但这些模型对变化的方向不一致。我们认为，这两个模式中的强信号是由强迫和内部变率的组合引起的。在考察了间冰期AMOC变化的基础上，进一步探讨了AMOC对气候系统的影响，特别是对模拟地表温度和降水变化的影响。在识别了AMOC在地表温度和降雨量上的指纹之后，我们证明了只有一小部分模拟的地表气候变化可以归因于AMOC。两个间冰期的沉积Pa/Th比值的代用记录都显示出与工业化前相似的AMOC强度，这与模拟结果吻合得很好。尽管AMOC的总体强度变化很小，但未来的工作需要探索这是否是通过补偿AMOC不同组成部分（如冰岛-苏格兰溢流水）的变化而发生的。这一系列的证据告诫我们不要将过去间冰期气候的重建解释为受AMOC驱动，而不是突发事件。
Abstract. The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism of poleward heat transport and an important part of the global climate system. How it responded to past changes in forcing, such as those experienced during Quaternary interglacials, is an intriguing and open question. Previous modelling studies suggest an enhanced AMOC in the mid-Holocene compared to the preindustrial period. In earlier simulations from the Palaeoclimate Modelling Intercomparison Project (PMIP), this arose from feedbacks between sea ice and AMOC changes, which were dependent on resolution. Here we present an initial analysis of recently available PMIP4 simulations for three experiments representing different interglacial conditions – one 127 000 years ago within the Last Interglacial (127 ka, called lig127k), one in the middle of the Holocene (midHolocene, 6 ka), and a preindustrial control simulation (piControl, 1850 CE). Both lig127k and midHolocene have altered orbital configurations compared to piControl. The ensemble mean of the PMIP4 models shows the strength of the AMOC does not markedly change between the midHolocene and piControl experiments or between the lig127k and piControl experiments. Therefore, it appears orbital forcing itself does not alter the overall AMOC. We further investigate the coherency of the forced response in AMOC across the two interglacials, along with the strength of the signal, using eight PMIP4 models which performed both interglacial experiments. Only two models show a stronger change with the stronger forcing, but those models disagree on the direction of the change. We propose that the strong signals in these two models are caused by a combination of forcing and the internal variability. After investigating the AMOC changes in the interglacials, we further explored the impact of AMOC on the climate system, especially on the changes in the simulated surface temperature and precipitation. After identifying the AMOC's fingerprint on the surface temperature and rainfall, we demonstrate that only a small percentage of the simulated surface climate changes could be attributed to the AMOC. Proxy records of sedimentary Pa/Th ratio during the two interglacial periods both show a similar AMOC strength compared to the preindustrial, which fits nicely with the simulated results. Although the overall AMOC strength shows minimal changes, future work is required to explore whether this occurs through compensating variations in the different components of AMOC (such as Iceland–Scotland overflow water). This line of evidence cautions against interpreting reconstructions of past interglacial climate as being driven by AMOC, outside of abrupt events.