EGU2020-9472
https://doi.org/10.5194/egusphere-egu2020-9472
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Orbitally-paced South American Summer Monsoon variability during the mid- to late-Pleistocene

Alicia Meng Xiao Hou1, André Bahr1, Jacek Raddatz2, Silke Voigt2, Ana Luiza Albuquerque3, Cristiano M. Chiessi4, and Oliver Friedrich1
Alicia Meng Xiao Hou et al.
  • 1Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany (alicia.hou@geow.uni-heidelberg.de)
  • 2Institute of Geosciences, Goethe University Frankfurt, Frankfurt, Germany
  • 3Programa de Geociências (Geoquímica), Universidade Federal Fluminense, Niterói, Brazil
  • 4School of Arts, Sciences and Humanities, University of São Paulo, São Paolo, Brazil

Hydrological extremes related to the South American Summer Monsoon (SASM) are expected to become more frequent in the near future and might have devastating socioeconomic consequences for the densely populated region of eastern Brazil. Given the complexity in SASM behaviour in space and time, a dense coverage of monsoonal precipitation records, particular those spanning multiple glacial-interglacial cycles, are urgently needed to constrain this high spatial-temporal variability. This information is necessary to reduce the uncertainty associated with projections of SASM precipitation in response to rising anthropogenic greenhouse gas (GHG) emissions. Here we use elemental ratios from X-ray fluorescence scanning of two sediment cores retrieved off the eastern Brazil margin to reconstruct long-term rainfall changes in the hinterland. Our findings from core M125-55-7 (offshore the Doce River, 20°S) reveal that during the past ~320 kyr, precession-paced insolation forcing is the primary pacemaker of variations in SASM precipitation over the Doce basin. We also determined an anomalous interval of weak monsoonal response to insolation forcing during Marine Isotope Stage 6, which we attribute to enhanced wintertime precipitation due to exceptionally strong southeast trade winds created by a steep South Atlantic latitudinal temperature gradient. Moreover, our results suggest that albeit predominantly driven by insolation forcing, the intensity of SASM rainfall responds negatively to GHG forcing, most likely through indirect feedbacks. We propose that GHG forcing directly influences the magnitude of both the inter- and intrahemispheric latitudinal temperature gradients, which in turn modify the strength of atmospheric circulation and precipitation in the tropics. Thus, we suggest that SASM rainfall intensity over tropical eastern Brazil will likely be suppressed by rising CO2 emissions in the future. Our preliminary analysis of core M125-73-3 (off the Contas River; 12°S) reveals regional differences in monsoonal precipitation between the more northerly Contas basin and the more southerly Doce basin. Most notably, unlike the insolation-paced continental rainfall variability recorded at site M125-55-7, SASM rainfall intensity over the Contas basin appears to be more sensitive to glacial-interglacial scale pacing over the past ~800 kyr. Taken together, our records reveal both the high spatial variability in SASM precipitation over eastern Brazil and the dominant influence of orbital forcing on monsoonal rainfall intensity.

How to cite: Hou, A. M. X., Bahr, A., Raddatz, J., Voigt, S., Albuquerque, A. L., Chiessi, C. M., and Friedrich, O.: Orbitally-paced South American Summer Monsoon variability during the mid- to late-Pleistocene , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9472, https://doi.org/10.5194/egusphere-egu2020-9472, 2020

Comments on the presentation

AC: Author Comment | CC: Community Comment | Report abuse

Presentation version 1 – uploaded on 03 May 2020 , no comments