Abstract
AbstractPrecipitation extremes with devastating socioeconomic consequences within the South American Monsoon System (SAMS) are expected to become more frequent in the near future. The complexity in SAMS behavior, however, poses severe challenges for reliable future projections. Thus, robust paleomonsoon records are needed to constrain the high spatiotemporal variability in the response of SAMS rainfall to different climatic drivers. This study uses Ti/Ca ratios from X‐ray fluorescence scanning of a sediment core retrieved off eastern Brazilian to trace precipitation changes over the past 322 Kyr. The results indicate that despite the spatiotemporal complexity of the SAMS, insolation forcing is the primary pacemaker of variations in the monsoonal system. Additional modulation by atmospheric pCO2 suggests that SAMS intensity over eastern Brazil will be suppressed by rising CO2 emissions in the future. Lastly, our record reveals an unprecedented strong and persistent wet period during Marine Isotope Stage 6 driven by anomalously strong trade winds.
Highlights
Over a broad region of South America, low‐level atmospheric circulation and convective precipitation during austral summer are governed by the South American Monsoon System (SAMS) (Liebmann & Mechoso, 2011; Zhou & Lau, 1998)
This moist air mass is deflected by the Andes and heads southeastward toward the South Atlantic Convergence Zone (SACZ) (Gan et al, 2004; Zhou & Lau, 1998), a convective belt that extends from the western Amazon basin toward southeastern (SE) South America and into the western South Atlantic Ocean (Carvalho et al, 2002, 2004) (Figure 1)
We present the longest record of the SAMS yet published by using Ti/Ca ratios from a marine sediment core retrieved off the coast of tropical eastern Brazil, coupled with planktic foraminiferal stable isotopes to reconstruct changes in monsoonal precipitation intensity across three glacial‐interglacial cycles
Summary
Over a broad region of South America, low‐level atmospheric circulation and convective precipitation during austral summer are governed by the South American Monsoon System (SAMS) (Liebmann & Mechoso, 2011; Zhou & Lau, 1998). The onset of peak SAMS activity occurs during austral summer when strong heating over central South America enhances the prevailing northeast (NE) trade winds which transport moist air from the tropical North Atlantic Ocean toward the continent (Silva & Kousky, 2012; Zhou & Lau, 1998). This moist air mass is deflected by the Andes and heads southeastward toward the South Atlantic Convergence Zone (SACZ) (Gan et al, 2004; Zhou & Lau, 1998), a convective belt that extends from the western Amazon basin toward southeastern (SE) South America and into the western South Atlantic Ocean (Carvalho et al, 2002, 2004) (Figure 1). Across much of tropical South America, over 40% of the total annual precipitation occurs during the mature SAMS phase (Figure 1)
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