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AGS Meeting (November 5): Reconstruction of Holocene coupling between the South America Monsoon System and local moisture variability from speleothem δ18O and 87Sr/86Sr records

Reconstruction of Holocene coupling between the South America Monsoon System and local moisture variability from speleothem δ18O and 87Sr/86Sr records

Dr. Corinne Wong

Brittany M. Ward, Corinne I. Wong, Valdir F. Novello, David McGee, Roberto V. Santos, Xianfeng Wang, Lawrence R. Edwards, Lucas C.R. Silva, Hai Cheng


Investigating past variability in South American hydroclimate is pertinent to understanding how hydroclimate might respond to global climate change. δ18O records from South America provide insight into past variability of the South American Monsoon System (SAMS). Precipitation δ18O values, however, can be decoupled from local moisture conditions at a given site and, thereby, limit ability to reconstruct local moisture conditions. In this study, we investigate the coherence of Holocene δ18O records from across tropical and subtropical South America using a principal components analysis and assess the co-variability of reconstructed SAMS variability with local moisture conditions reconstructed from speleothem 87Sr/86Sr values. The main mode of variability across Holocene δ18O records (PC1) closely tracks changes in austral summertime insolation, consistent with existing work. Sites towards the periphery of the continent are heavily weighted on PC1, whereas interior sites as not. Further δ18O variability at interior sites bear little similarity to each other and implicate controls, beyond monsoon intensity, on these δ18O records. Further, we develop speleothem 87Sr/86Sr records spanning the Holocene from Tamboril Cave (Brazilian Highlands), Paraíso Cave (eastern Amazon Basin), Jaraguá Cave (Mato Grosso do Sol Plateau), and Botuverá Cave (Atlantic coastal plain) to investigate coupling between reconstructed monsoon variability (reflected by PC1) and local moisture conditions (interpreted from 87Sr/86Sr records). Speleothem 87Sr/86Sr variability is interpreted as a proxy of local moisture conditions, reflecting the degree of water-rock interaction with the cave host rock as driven by variations in water residence time. Speleothem 87Sr/86Sr records from all the sites, except Botuverá cave, do not co-vary with PC1, suggesting that local moisture conditions do not necessary follow variations in monsoon intensity at these interior sites. These speleothem 87Sr/86Sr records, however, generally suggest dry mid-Holocene conditions relative to the early- and late-Holocene, consistent with interpretations of other paleo-moisture records in the region. These results highlight that controls, in addition to SAMS variability, might influence δ18O variability as well as local moisture conditions at interior sites, and stress the need for δ18O-independent reconstructions of moisture conditions.

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Dr. Corinne Wong is an environmental isotope geochemist who studies modern cave environments to understand how past climate can be interpreted from speleothem cave deposits and reconstructs past hydroclimate from speleothem isotopic and geochemical variability in the western United States and the region of the South American Monsoon System. Corinne was an Environmental Protection Agency STAR Graduate Fellow at The University of Texas at Austin, a University of California Chancellor’s Postdoctoral Fellow in Davis, California, an Assistant Professor at Boston College, and Research Associate at The University of Texas at Austin.