The imprint of Pacific SST low- and high-frequency modes of variability on the South American Summer Monsoon precipitation through the lens of stable oxygen isotopes

Abstract

The summertime rainfall associated with the South American monsoon is important for the hydropower and agricultural sectors in South America as well as to the traditions of many Amazonian indigenous cultures. The amount and spatial extent of the monsoon rainfall patterns are influenced by a variety of factors, including changes in Pacific Ocean sea surface temperatures. While evaluating this link has been mostly limited to meteorological observations, the analysis of heavy and light oxygen atoms, called isotopes, in natural archives such as cave deposits, lake sediments, glacier ice, and tree rings, can help extend this relationship further back in time. In combination with climate models, the ratio between heavy and light isotopes can provide insight for the link between the Pacific Ocean and South American water cycle changes on interannual to multidecadal timescales. This allows us to better understand how the Pacific has influenced the South American monsoon in the past. It also allows us to better define the range of natural climate variability against which future changes can be compared.

Key Findings

South American summer monsoon variability is influenced by multidecadal and interannual variability of Pacific sea surface temperatures
Paleoclimate records combined with climate model synthesis enhance the interpretation of Pacific Ocean–South America teleconnections
The development of new paleoclimate records in South America can be informed by the archived signals of Pacific multidecadal variability

SASM (DJF) &\delta;¹⁸O_p climatology and its response to Pacific Ocean modes. &\delta;¹⁸O_p data are from the iCAM5 model (shading), terrestrial proxy records (circles), and IAEA station observations (squares). (a) DJF precipitation‐weighted average of &\delta;¹⁸O_p (1880–1999 CE). Composites of positive–negative phase years for (b) IPO and (c) ENSO. Reference period for iCAM5 and proxy data cover the full study period of 1880–1999 CE and IAEA data are available from 1965–1986 CE. Statistical significance at p < 0.05 is indicated with a black cross for proxy records and IAEA stations and with black stippling for model simulations. Pumacocha, P00‐H1 and CR1 records are shifted slightly for visibility.

SASM (DJF) δ¹⁸O_p climatology and its response to Pacific Ocean modes. δ¹⁸O_p data are from the iCAM5 model (shading), terrestrial proxy records (circles), and IAEA station observations (squares). (a) DJF precipitation‐weighted average of δ¹⁸O_p (1880–1999 CE). Composites of positive–negative phase years for (b) IPO and (c) ENSO. Reference period for iCAM5 and proxy data cover the full study period of 1880–1999 CE and IAEA data are available from 1965–1986 CE. Statistical significance at p < 0.05 is indicated with a black cross for proxy records and IAEA stations and with black stippling for model simulations. Pumacocha, P00‐H1 and CR1 records are shifted slightly for visibility.

Project products:

This researched was published in the Journal of Geophysical Reseaerch: Atmospheres and the code is available from Zenodo:

Orrison, R., Vuille, M., Cauhy Rodrigues, J., Strı́kis, N., Cruz, F., Andreu-Hayles, L., Rodriguez-Caton, M., (2024), Pacific Multidecadal and Interannual Variability influences on South American Monsoon δ¹⁸O, Journal of Geophysical Research: Atmospheres, 129(17), e2024JD040999.
Orrison, R., Pacific influence on d18o in South American Monsoon precipitation (v1.0.1). Zenodo.