Articles | Volume 18, issue 9
Clim. Past, 18, 2045–2062, 2022
Clim. Past, 18, 2045–2062, 2022
Research article
 | Highlight paper
02 Sep 2022
Research article  | Highlight paper | 02 Sep 2022

South American Summer Monsoon variability over the last millennium in paleoclimate records and isotope-enabled climate models

Rebecca Orrison et al.

Data sets

Global Historical Climatology Network daily (GHCNd) NOAA NCEI

NOAA Extended Reconstructed Sea Surface Temperature (SST) V3b NOAA PSL

NOAA Interpolated Outgoing Longwave Radiation (OLR) NOAA PSL

Last Millennium δ¹⁸O, δ¹³C, and U/Th ages of MV1 and MV30 stalagmite records from Mata Virgem cave (central Brazil) Rebecca Orrison, Mathias Vuille, Jason E. Smerdon, James Apaéstegui, Vitor Azevedo, Jose Leandro P S Campos, Francisco William Cruz, Marcela Eduarda Della Libera, and Nicolás Misailidis Stríkis

Model code and software

SASM-MCEOF-v1.1.0 Rebecca Orrison

This study presents a novel Monte Carlo Empirical Orthogonal Function analysis that combines a dense isotopic proxy network with isotope-enabled climate models to study dynamics and variability of South American Monsoon System (SAMS) over past millennium. This analysis reveals that the leading modes of SAMS variability over the past millennium are regionally stable, arising independently of external forcing (solar, volcanic, orbital). Significant enhancement of the SAMS is accompanied by southward displacement of the South Atlantic Convergence Zone during the Little Ice Age, giving rise to a strengthened South American precipitation dipole. Proxy-model comparison demonstrates outstanding mismatches in centennial-scale hydroclimate departures during the Medieval Climate Anomaly and Little Ice Age from the last millennium mean state. The results of last millennium SASM variability contextualizes modern variability of SASM. The identified proxy data-model mismatch raises a key question to climate simulations of SASM variability, which may attract broad attention from paleoclimate modeling community. Moreover, the reported methodology can be applied to paleoclimate problems of various spatial and temporal scales and is of relevance for the broader geoscience community.
Short summary
We evaluated the South American Summer Monsoon over the last millennium and dynamically interpreted the principal modes of variability. We find the spatial patterns of the monsoon are an intrinsic feature of the climate modulated by external forcings. Multi-centennial mean state departures during the Medieval Climate Anomaly and Little Ice Age show regionally coherent patterns of hydroclimatic change in both a multi-archive network of oxygen isotope records and isotope-enabled climate models.