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It is said that the Amazon rainforest receives up to half of its nutrients via mineral dust from the Sahara desert. But a few thousand years ago, the Sahara desert was much more fertile, having a savannah-like environment.
Did this mean that the nutrient transfer to the Amazon did not take place during this time? If so, what did the Amazon look like?
According to the article Africa: Greening of the Sahara (Claussen et al.), the 'Green Sahara, occurred during the Holocene climatic optimum, occurring at the same time as the "African Humid Period", also similar ages to the events mentioned in your 3rd link. All occurring during the mid Holocene
At the same time in the Amazon region, according to the article Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum (Mayle et al. 2004), was
reduced precipitation in the Early–Mid-Holocene (ca. 8000–3600 years ago) caused widespread, frequent fires in seasonal southern Amazonia, causing increased abundance of drought-tolerant dry forest taxa and savannahs in ecotonal areas.
Although, this effect was not uniform over the entire Amazonian Basin, the authors conclude from pollen, charcoal and other samples, that the Amazon Basin had far less precipitation (up to 40 less in places), which caused
increased fires and consequently greater ecosystem disturbance, which would be expected to have caused structural as well as compositional changes to plant communities, such as expansion of drought-tolerant lianas and semi-deciduous taxa within forests and expansion of savannahs at forest–savannah ecotones. Populations of coldadapted species (e.g. Podocarpus) were largely eliminated from the Amazon lowlands during this interval, and cloud forests on the eastern flanks of the Bolivian Andes diminished while open, grass-dominated ecosystems expanded.
Here is a brand new (January 2021) study from Nature.
It proposes that the Sahara has not been the main source of dust for the Amazon for the past 7,500 years of Holocene, but rather dust from North and South Africa, the Andes, and Southern South America.
