Late Holocene dynamics of the south American summer monsoon: New insights from the Andes of northern Chile (21°S)

The South American summer monsoon (SASM) is the most important climate system of tropical South America, transporting moisture from the tropical Atlantic Ocean to the core of the continent during the austral summer. Recent paleoclimate studies suggest that past variability of the SASM has been more heterogenous in space and time than previously thought, implying that different atmospheric drivers controlled its long-term evolution. Unfortunately, past SASM reconstructions are largely limited to the last 2000 years and mainly focused on the core of the monsoon domain where precipitation does not fall exclusively during the monsoon season, thereby limiting our understanding of its long-term changes, drivers and mechanisms. Here we present a new 4000-year SASM precipitation reconstruction based on a high-resolution pollen sequence from a mountain lake in the dry Andes of northern Chile (21°S). We provide evidence for two centennial-scale intervals of enhanced SASM precipitation between 4000–3400 and 2300-1900 cal yr BP. These intervals are replicated in records from the southern portion of the central Andes (>18°S) but not clearly detected further north, suggesting the existence of a monsoon dynamics largely decoupled from latitudinal shifts of the Intertropical Convergence Zone. A comparison with precipitation reconstructions from the entire SASM domain and modern climate datasets suggests a teleconnection with the Southern Hemisphere circulation through the intensification of the South Atlantic Convergence Zone and/or the intrusion of extra-tropical Atlantic moisture. Our results highlight that significant spatial and temporal variability of the SASM occurred during the most recent millennia, and therefore social and environmental forecast should consider that similar variations will likely occur in the future.