Changes in the South American Monsoon System since the Last Glacial Maximum

Abstract

Abstract The main objective of this study is to investigate the spatial-temporal variability and the climate forcing influence during the last 21,000 years of the South American Monsoon System (SAMS). TraCE-21k simulations Full and Single Forcings experiments were used. The identification of spatial variability patterns associated to the core of monsoon region and the South Atlantic Convergence Zone (SACZ) patterns are based on multivariate EOF analysis (precipitation, humidity, zonal and meridional wind) which produces two main modes: the South American Large Scale Monsoon Index (LISAM) and the SACZ mode. The LISAM and SACZ modes show that the TraCE-21k represents the SAMS and SACZ patterns and the comparison to the 20th Century reanalysis EOF analysis show significant agreement. LISAM time series proved to be an important instrument to identify monsoon precipitation variability, consistent with the regime changes registered in climatic proxies. The freshwater pulses forcing in TraCE-21k is a determining factor for the observed changes in the precipitation regime, mainly for the periods between the Heinrich Stadial 1 and the Younger Dryas. The results show that the observed and modeled SACZ southward shift in the Late Holocene is mainly modulated by insolation changes, with stronger correlation observed since the Mid-Holocene period. Through wavelet analysis, it was noted that energy was transferred from low frequencies to high frequencies during Bolling Allerod for the full forcing and freshwater pulse experiments in the Northern Hemisphere, with the SAMS multidecadal variability increasing from the early Holocene with direct influences of orbital forcing and ice cover.