South America Last Millennium Precipitation Variability in the Little Ice Age and in the Medieval Climate Anomaly Periods Through Speleothems

In the last decades across the South America the number of last millennia paleoclimatic studies and isotopic time series rose substantially allowing the study of the paleo-precipitation on different sites along the Tropical South America or on the monsoon region. However, most of previous works studied the South American Monsoon System (SAMS) in a punctual or very localized region, just assessing the precipitation variability on the records’ site. In this work a new approach is applied to eleven δ¹⁸O isotopic and one Sr/Ca trace element paleoclimatic time series using Monte-Carlo Principal Component Analysis, accounting the uncertainty of the individual records. This approach allows us to reduce the set of 12 time series into a set of fewer physically significant variables. Just the two leading Principal Component Loadings were found physically and statistically significant. The 1st Principal Component mode representing 30±2% of the data variability, depicts the monsoon intensity variability, presenting a dipole between the South Atlantic Convergence Zone (SACZ) and the Andes region to the Northeast of Brazil (NEB) and Northern of Brazil. The 2nd Principal Component mode representing 13±1% of the data variability shows the South American Monsoon shape parameter, presenting a tripole between the Southeast south America (SESA), the SACZ domain and the NEB regions, coherent with the footprint of extreme South American Low Level Jets (SALLJ) episodes. Composite analysis based on a regime shift test based on sample means, reveals an enhanced monsoon during the early Little Ice Age (LIA) period with a monsoon axis or SACZ wider than in the Current Warm Period (CWP) and Mediaeval Climate Anomaly (MCA), rather than a southward SACZ displacement, contrasting to previous interpretations. The MCA period is found the driest period in all the South America domain except Eastern Amazonia region. Time series analysis suggest coupled behaviour between the 2nd Principal Component mode and the Atlantic Multidecadal Oscillation 
(AMO) during the MCA period and the Southern Annular Mode (SAM) during the Transitional Period (TRANS) between the MCA and LIA. Future efforts to sample paleoclimatic data over the continent, particularly over the Amazonia and the La Plata basin as well as over the ocean, where reliable paleoclimatic proxy time series is still scarce, is urgently needed to improve the South America last millennium climate variability understanding. A climate without anthropic forcings.