Reconstruction of decadal to centennial Holocene variability of the North Atlantic Oscillation using speleothems from Morocco

北大西洋涛动（North Atlantic Oscillation， NAO）是北大西洋地区主要的气压模态，它通过影响北半球的海洋和大陆冬季气候而对生态和社会经济产生巨大影响。因此，了解影响NAO的机制及其与其他气候参数的关系是非常重要的。有人提出了NAO、太阳活动和海洋-大气-海冰系统之间的联系。由于仪器气候数据集不能追溯到人类世以后，因此NAO的自然变率只能通过古气候重建来评估。然而，目前只有少数的大陆NAO重建超出了仪器数据期。因此，全新世的演化和北大西洋涛动的强迫因素是科学界争论的一个问题。在其博士论文的框架内，研究人员利用摩洛哥西北部阿特拉斯中部洞穴中的石笋重建了全新世的降雨变异性。摩洛哥西北部对北大西洋涛动状态的变化非常敏感，洞穴数据表明过去北大西洋涛动在百年时间尺度上具有显著的变率。然而，关于十年至百年时间尺度的信息需要（近）年分辨率的气候重建。目前还没有这些功能。拟议中的项目重点关注摩洛哥两个洞穴中的石笋，这些洞穴提供了与NAO有关的气候记录。研究的目的是：(1)基于同一洞穴不同石笋记录的共同降雨信号构建一个主记录；(2)提供具有年分辨率的全新世有效降雨量重建。频率分析用于检测重要的周期分量。以特定的年代际至百年频率或NAO持续正/负状态为主导的时间间隔将与潜在的NAO强迫因子（即太阳活动、海洋参数、海冰扩展）进行比较。

The North Atlantic Oscillation (NAO; the dominating atmospheric pressure mode in the North Atlantic region) has large ecological and socio-economical impact by affecting both marine and continental winter climate in the Northern Hemisphere. Understanding the mechanisms influencing the NAO as well as its relationship to other climate parameters is, thus, of great importance. Links between the NAO, solar activity and the ocean-atmosphere-sea ice system have been proposed. Since instrumental climate datasets do not extend back beyond the Anthropocene, the natural variability of the NAO can only be assessed by paleoclimate reconstructions. However, only a few continental NAO reconstructions extending beyond the instrumental data period are currently available. The Holocene evolution and forcing factors of the NAO are, thus, a matter of debate in the scientific community. In the framework of the proponents PhD thesis, stalagmites from caves in the Middle Atlas, NW Morocco, were used to reconstruct rainfall variability during the Holocene. NW Morocco is very sensitive to changes in the state of the NAO, and the speleothem data indicated significant past variability of the NAO on multi-centennial timescales. However, information on decadal to centennial timescales requires (near-) annual resolution climate reconstructions. At present these are not available. The proposed project focuses on stalagmites from two caves in Morocco, which have provided climate records with a relationship to the NAO. The aims are (i) to construct one master record based on the common rainfall signals of different stalagmite records from the same cave, and (ii) to provide a Holocene reconstruction of effective rainfall with annual resolution. Frequency analysis is employed to detect significant periodic components. Time intervals dominated by specific decadal to centennial frequencies or a persistent positive/negative state of the NAO will be compared with potential NAO forcing factors (i.e. solar activity, oceanic parameters, sea ice extension).