Millennial and orbital-scale variability of Amazon Basin precipitation over the last 200 kyr

The Amazon rainforest is a key component of the South American climate system, with strong vegetation-convection feedback and a tight coupling with large-scale atmospheric circulation. However, the relative roles of abrupt millennial-scale climate events and orbital forcing in modulating Amazon Basin hydroclimate remain incompletely understood over long timescales. Indeed, most available records either cover short time windows or come from distal sites where Amazonian signals may be diluted by non-local influences. Here, we reconstruct precipitation variability over the Amazon Basin during the last 200 kyr using the composite marine sediment core MD23-3652Q-53, recovered from the mid-depth western equatorial Atlantic and directly influenced by Amazon River discharge. First, we produced a detailed age model for the composite core based on nine calibrated radiocarbon ages and 511 benthic foraminifera stable oxygen isotope values. Second, we assessed changes in continental runoff and precipitation based on X-ray fluorescence elemental ratios and sediment reflectance data. Third, we determined the timing of millennial-scale changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) based on benthic foraminifera stable carbon isotope (d¹³C). Lower δ¹³C values during millennial-scale events coincide with increased ln(Ti/Ca) ratios and higher L* reflectance, indicating a reduction in North Atlantic Deep-Water ventilation and enhanced terrigenous sediment supply to the western equatorial Atlantic. These hydroclimate changes are consistent with a weakened AMOC, which promoted interhemispheric temperature asymmetry, a southward displacement of the Intertropical Convergence Zone, and strengthened of Amazonian precipitation. In contrast, higher a* reflectance values could be associated with periods of increased austral summer insolation, likely reflecting orbitally-driven changes in terrigenous sediment composition, primarily linked to enhanced precipitation over the Andean headwaters. These findings highlight the response of the Amazon hydrological system to distinct modes of climate forcing and provide important constraints on the sensitivity of tropical South American precipitation to future changes in the AMOC.