The South American Monsoon System (SAMS) is generally considered to be highly sensitive to Northern Hemisphere (NH) temperature variations on multi-centennial timescales. The direct influence of solar forcing on moisture convergence in global monsoon systems on the other hand, while well explored in modeling studies, has hitherto not been documented in proxy data from the SAMS region. Hence little is known about the sensitivity of the SAMS to solar forcing over the past millennium and how it might compete or constructively interfere with NH temperature variations that occurred primarily in response to volcanic forcing. Here we present a new annually-resolved oxygen isotope record from a 1500-year long stalagmite recording past changes in precipitation in the hitherto unsampled core region of the SAMS. This record details how solar variability consistently modulated the strength of the SAMS on centennial time scales during the past 1500 years. Solar forcing, besides the previously recognized influence from NH temperature changes and associated Intertropical Convergence Zone (ITCZ) shifts, appears as a major driver affecting SAMS intensity at centennial time scales.
Bibliographical noteFunding Information:
This work was supported by the Fundacao de Amparo a Pesquisa do Estado de Sao Paulo, Brazil (FAPESP grants 2012/01187-4 to I.K., 2009/12902-3 fellowship to M.S.P, 2012/03942-4, 2014/10095-1 and 2015/08351-2 fellowships to V.F.N.), NASA/FAPESP through the Dimensions of Biodiversity Program grants 2012/50260-6 and 2013/50297, INCLINE/USP and PRIMO cooperative project (CNPq-IRD) to F.W.C, and the US National Science Foundation NSF grants AGS-1303828 to MV and 1103403 to R.L.E and H.C.