Tracking the Green Sahara: Assessing periods of humidity in North-West Africa using speleothem geochemistry

横跨北非的干旱撒哈拉地带是当今气候系统的重要组成部分。然而，过去气候的变化和未来的潜在变化目前知之甚少。这主要是由于该地区缺乏年代准确的古气候记录和历史仪器数据。最近的研究为全新世期间西撒哈拉的潮湿时期以及晚更新世期间北非的反复潮湿时期和“绿化”提供了证据。然而，在这些时期为该地区提供水分的过程还没有得到很好的理解。过去的湿度变化被认为对非洲的早期人类迁徙有重要影响，未来的变化可能对生活在该地区的现代人口产生社会影响。该项目将评估过去湿润期相对于其他气候变化的时间，以及这些时期的水分来源。石笋是强大的、高分辨率的古气候档案，它可以确定绝对的年代，从而产生每年解决的区域气候变化记录。该项目将有助于弥补目前在西北非洲缺乏洞穴记录的地理空间覆盖，补充其他陆地古气候档案，如湖泊沉积物。还将对先前从摩洛哥南部收集的样本进行额外的工作，以进一步了解全新世（如非洲湿润期）重要气候事件期间气候变化的程度。这些样品是从以前的旅行中收集的，可供部门进一步分析。考虑到英国外交部对这些国家的旅行建议，将在摩洛哥、西撒哈拉和阿尔及利亚开展收集石笋的实地工作。然后将在实验室中利用稳定同位素比率、微量元素浓度和样品岩石学，从石笋的地球化学特征中建立古气候记录。洞穴怪的生长是由于水进入碳酸盐岩溶系统的结果。因此，对石笋生长期到非生长期的分析以及生长速度的变化是区域湿度变化的一个有价值的指标。通过对整个北非石笋稳定同位素比率的变化和生长期的时间进行整体解释，可以观察到极度干旱的撒哈拉带的迁移和湿度周期的发生。对记录的个别分析也有助于以前对气候的解释。例如，观察石笋18O的地理空间变化将推断过去和现在可能的水汽来源和在西北非洲的输送。了解北非气候变化的控制和程度对于限制区域水文与全球气候变化之间的关系非常重要。该项目旨在利用洞穴主题重建阿特拉斯山脉和撒哈拉沙漠之间的气候变化，以提高我们对该地区的了解。

The arid Saharan belt running across North Africa is an important part of today's climate system. However, changes in past climate and potential future variations are currently poorly understood. This is largely due to the lack of well-dated paleoclimate records and historical instrumental data from the region. Recent work has given evidence for a period of humidity in Western Sahara during the Holocene as well as recurrent moist periods and 'greening' of North Africa during the late Pleistocene. However, the processes which provided moisture to the region at these times are not well understood. Past variations in humidity are thought to have had important influences on early human migration within Africa and future changes may have societal implications for modern populations living in the area. This project will assess the timing of past humid periods relative to other climatic changes, and the sources of the moisture during these periods. Stalagmites are powerful, high-resolution paleoclimate archives which can be absolute dated to produce annually resolved records of regional climate change. This project will contribute to the currently lacking geospatial coverage of speleothem records in NW Africa, complementing other terrestrial paleoclimate archives such as lake deposits. Additional work will also be undertaken on previously collected samples from southern Morocco to further understand the extent of climate change during important climate events within the Holocene, such as the African Humid Period. These samples were collected from a previous excursion and are available for further analysis in department. Fieldwork to collect stalagmites will be undertaken in Morocco and potentially in Western Sahara and Algeria, taking into account FCO travel advice to these countries. A record of paleoclimate will then be constructed in the lab from the geochemistry of stalagmites, using stable isotope ratios, trace element concentrations and sample petrography. Speleothems grow as a consequence of the input of water into a carbonate karst system. Analysis of growth to non-growth periods in stalagmites, as well as changes in growth speed, are therefore a valuable indicator of changes in regional humidity. By performing a holistic interpretation of changes in stable isotope ratios and the timing of growth periods in stalagmites across North Africa, the migration of the hyper-arid Saharan belt and the occurrence of periods of humidity may be observed. Individual analysis of records would also contribute to previous interpretations of climate. For example, observing geospatial changes in stalagmite 18O would infer possible moisture sources and transport across NW Africa both in the past and towards the present. An understanding of the controls and extent of climate change in North Africa are important for constraining the relationship between regional hydrology and global climate variations. This project will aim to reconstruct climate change between the Atlas Mountains and Sahara Desert using speleothems to advance our understanding of the region.