NOAA/WDS Paleoclimatology - Bay of Bengal U1446 Benthic and Leaf Wax Isotopes during the Last 640 kyr

Orbital-scale Indian Summer Monsoon variability is often interpreted as a direct response to northern hemisphere summer insolation. Here we present a continuous (0-640 kyr) orbital scale precipitation isotope (dDprecip) record using leaf wax dD from the core monsoon zone of India. The dDprecip record is quantitatively coherent with, and dDprecip minima in phase with, greenhouses gas maxima, and ice volume minima across all orbital bands. The dDprecip record is also coherent and in phase with the two existing orbital-scale Indian speleothem d18O records, demonstrating a consistent regional response among independent proxies. These findings preclude interpretation of Indian precipitation isotope records as a direct response to northern hemisphere summer insolation. Rather, they dominantly reflect changes in moisture source and transport paths associated with changes in greenhouse gases and ice volume. The orbital-scale precipitation isotope responses of the Indian and East Asian monsoon systems are uncoupled and are driven by different forcings.