How Far North Did the African Monsoon Fringe Expand During the African Humid Period? Insights From Southwest Moroccan Speleothems

We present new high-resolution oxygen isotope (δ¹⁸O) records from three NW African speleothems located at ~31°N. The present-day rainfall patterns at 31°N in NW Africa are linked to negative winter North Atlantic Oscillation phases. However, on multimillennial time scales, our δ¹⁸O records, together with other hydroclimate records, provide new evidence of humid conditions during the mid-Holocene, a period that was presumably characterized by arid climate. Thus, the apparent increase in moisture during the mid-Holocene is interpreted better as an increase in summer rainfall. This is most likely linked to the expansion of the West African summer monsoon fringe during the African Humid Period, which terminated in our record abruptly around 4 Kyr BP. The temporospatial difference with speleothem records from N Morocco suggests that the High-Atlas Mountains might have been a topographic barrier to further expansion of the West African summer monsoon fringe into higher latitudes.