Equatorial Pacific forcing of western Amazonian precipitation during Heinrich Stadial 1

Yancheng Zhang (1) , Xu Zhang (2) , Cristiano M Chiessi (3) , Stefan Mulitza (1) , Xiao Zhang (4, 1) , Gerrit Lohmann (1) , Matthias Prange (1) , Hermann Behling (5) , Matthias Zabel (1) , Aline Govin (6, 7) , André O Sawakuchi (3) , Francisco W Cruz (3) , Gerold Wefer (1)

1 MARUM - Center for Marine Environmental Sciences [Bremen]
2 AWI - Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung = Alfred Wegener Institute for Polar and Marine Research = Institut Alfred-Wegener pour la recherche polaire et marine
3 USP - Universidade de São Paulo = University of São Paulo
4 NUIST - Nanjing University of Information Science and Technology
5 Albrecht-von-Haller Institut für Pflanzenwissenschaften
6 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
7 CLIMAG - Climat et Magnétisme

Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18-15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5-1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.

Domaines: Climatologie; Hydrologie

Yancheng Zhang, Xu Zhang, Cristiano M Chiessi, Stefan Mulitza, Xiao Zhang, et al.. Equatorial Pacific forcing of western Amazonian precipitation during Heinrich Stadial 1. Scientific Reports, 2016, 6, pp.35866. ⟨10.1038/srep35866⟩. ⟨hal-02180994⟩