Join us for the next BPE Seminar
Speleothems Reveal Amplification of the Indian Monsoon at the Onset of Industrial Warming
with Aniket Dhar, Ph.D. Candidate, University of Arizona.
We investigate how natural variability and anthropogenic forcing have influenced the strength of the Indian Summer Monsoon (ISM) from the pre-industrial period into the modern era. To address this, we integrate speleothem δ¹⁸O records, used as a proxy for monsoon convection, within a statistical framework, including a newly developed high-resolution δ¹⁸O record from Kona Cave in southeastern India.
Using Monte Carlo Principal Component Analysis (MC-PCA), we reconstruct ISM variability over the past six centuries. The leading mode of variability (ISM MC-PC1) exhibits a significant negative correlation with instrumental rainfall over the Core Monsoon Zone (CMZ). Both proxy-based and instrumental datasets display nearly identical, though inverse, spatial relationships with sea surface temperature fields, underscoring the reconstruction's robustness in capturing CMZ convection.
To explore the influence of regional and remote drivers, MC-PCA was further applied to tropical and boreal extratropical proxy datasets. ISM MC-PC1 shows pronounced multidecadal-to-centennial variability, with a notable phase shift during the mid-Little Ice Age between ISM variability and these dynamical modes. By the late 19th century, ISM MC-PC1 reached its lowest values, consistent with widespread drought conditions documented in historical records. Following this prolonged weakening, both proxy reconstructions and instrumental observations indicate a two-step intensification of ISM convection and precipitation between 1900 and 1960 C.E. This recovery occurs in the absence of corresponding changes in solar, volcanic, or large-scale dynamical forcing. This recent intensification aligns with rising global temperatures associated with increased greenhouse gas concentrations, suggesting that industrial-era warming has already exerted a thermodynamic influence on the ISM, enhancing atmospheric moisture availability and amplifying monsoon convection.
Zoom info:
https://columbiauniversity.zoom.us/j/95332400100?
Meeting ID: 953 3240 0100
Passcode: 504872
