Half-precession modulation of the West African Monsoon and possible links to continental hydroclimate records since the Mid-Pleistocene Transition.

Half-precession cycles (HPs), first identified in the 1980s, have been increasingly recognized as an important driver of tropical hydroclimate variability during the Quaternary. However, continuous long-term proxy records capturing their imprint on monsoon systems remain scarce. Here, we investigate the presence and evolution of HPs signals in a high-resolution inorganic geochemical record from ODP Site 663 (Eastern Equatorial Atlantic). This record provides a continuous perspective on West African Monsoon (WAM) variability over the last 1.2 Myr, spanning the Mid-Pleistocene Transition (MPT). Our results indicate that WAM variability during the MPT does not exhibit clear glacial–interglacial pacing. While this contrasts contemporaneous records from the Mediterranean and North Africa, the influence of the WAM becomes more pronounced after ~600 kyr, with intensified interglacial conditions and weaker glacial phases. In contrast, HPs show a stronger imprint on monsoon variability after the MPT, particularly during interglacial intervals. These findings are consistent with runoff records from the tropical American ICDP sites, suggesting a coherent low-latitude hydroclimate response. We propose that modulation of the Atlantic Meridional Overturning Circulation may provide a mechanistic link between HPs forcing, West African Monsoon variability, and tropical American precipitation.