Green Sahara

Green Sahara
Name	Green Sahara
Other names	African Humid Period, Neolithic Subpluvial
Location	Sahara
Epoch	Holocene
Notable sites	Tassili n'Ajjer, Chad Basin, Nile River

Green Sahara The term describes a series of intervals during the Holocene when parts of the Sahara Desert supported extensive lakes, rivers, grasslands, and human populations, transforming landscapes between the Atlas Mountains and the Sahel. Evidence for these humid phases derives from sediment cores, cave speleothems, lacustrine deposits, and rock art found across regions such as the Tassili n'Ajjer, Ténéré, and the Chad Basin. Research on the phenomenon engages disciplines and institutions including teams from Max Planck Society, NASA, University of Cambridge, and the French National Centre for Scientific Research.

Overview and Terminology

Researchers commonly use names such as the African Humid Period and Neolithic Subpluvial to describe the humid intervals that affected the Sahara and adjacent regions during the early to mid-Holocene. Publications from groups at ETH Zurich, Columbia University, University of Oxford, and Sorbonne University employ varying chronologies and criteria tied to proxies from the Nile River, Lake Chad, and the Mediterranean Sea. Debates involve chronostratigraphic correlations among records from Tassili n'Ajjer, the Hoggar Mountains, and the Ahaggar highlands.

Paleoclimatic History

Paleoclimate reconstructions show humid conditions beginning around 14,800–5,500 years before present, with peak wetness between roughly 9,000–6,000 years ago, as documented in cores from Lake Yoa, the Mediterranean Sea sapropels correlated to uprisings in the Nile River discharge, and speleothem records from Höhlen von Hegau. Marine records near Cape Verde and the Gulf of Guinea indicate strengthened monsoon winds that shifted the Intertropical Convergence Zone northward, affecting rainfall over the Sahara and influencing populations linked to sites like Gobero and the Saharan rock art panels.

Causes and Mechanisms

Mechanisms invoked include orbital forcing tied to variations in Earth's precession documented in studies from Woods Hole Oceanographic Institution, ocean–atmosphere interactions demonstrated in work by NOAA, and vegetation–albedo feedbacks explored by Princeton University modelers. Teleconnections with the Atlantic Meridional Overturning Circulation, sea-surface temperature patterns near Gulf of Guinea, and atmospheric dynamics involving the Intertropical Convergence Zone contributed to increased precipitation. Human-induced landscape changes, debated by teams at Max Planck Institute for the Science of Human History and University College London, may have modulated local feedbacks through pastoralism and fire management.

Archaeology and Human Occupation

Archaeological evidence from Tassili n'Ajjer, Gobero, Niger, Nubia, and the Chad Basin reveals settlements, burial grounds, and rock art styles depicting cattle, fish, and boats, indicating exploitation of lacustrine and riverine resources. Cultural sequences connect to groups studied by archaeologists at British Museum, National Museums of World Culture, and Institut de Recherche pour le Développement, with artifacts including ceramics, lithic assemblages, and domesticated fauna linked to migrations toward the Nile River and the Saharan trade routes. Genetic studies from teams at Harvard Medical School and University of Tübingen trace population movements concurrent with humid-to-arid transitions.

Flora, Fauna, and Ecosystems

Paleoecological records indicate expansion of grasslands, savanna trees such as Acacia species referenced in palynological records, abundant fish taxa in ancient lakes like Lake Mega-Chad, and megafauna documented in rock art that included antelope and elephant populations known from comparisons with contemporary faunas in Niger River floodplains and the Sahel. Vegetation and animal assemblages reconstructed by researchers at Smithsonian Institution and Natural History Museum, London imply complex ecosystems with wetlands, gallery forests, and seasonal floodplains supporting hunter-gatherer and early pastoralist lifeways.

Evidence and Proxy Records

Multiproxy evidence comes from lacustrine sediments in Lake Yoa and cores from the Chad Basin, marine sediments off North Africa featuring sapropel layers, speleothem isotopes from caves studied by teams at University of Innsbruck, pollen records held at Royal Botanic Gardens, Kew, and geomorphological mapping of palaeodrainage by researchers at UNESCO and US Geological Survey. Radiocarbon chronologies calibrated by laboratories at Oxford Radiocarbon Accelerator Unit and dendrochronological comparisons provide age control used alongside oxygen isotope sequences produced by Max Planck Institute for Chemistry.

Modern Implications and Research

Contemporary research addresses desertification, climate model evaluation by groups at IPCC, Met Office Hadley Centre, and National Center for Atmospheric Research, and implications for modern water resource management in countries such as Mali, Niger, Chad, and Algeria. Ongoing projects combine remote sensing from Landsat, paleoclimate modeling at California Institute of Technology, and archaeological surveys coordinated with local institutions like Université d'Abomey-Calavi and University of Algiers to better understand human–environment interactions and inform resilience strategies in the face of ongoing climatic change.

Category:Holocene paleoclimate