Indian subcontinent hydroclimate and vegetation changes during the last ~75 kyr reconstructed from terrestrial leaf wax stable isotope data obtained from IODP Site U1446

Understanding past variability and forcing of the Indian Summer Monsoon (ISM) is essential for better anticipating its behaviour under future climate change scenarios and the resulting consequences for the subsistence of a large part of the world’s population. However, long-term high-resolution proxy records of terrestrial hydroclimate variability from the ISM core zone are still relatively scarce. To reconstruct ISM variability and associated vegetation changes in northern India during the last ~75 kyr, we analysed the stable hydrogen and carbon isotope composition (δD, δ13C) of long-chain n-alkanes (n-C29, n-C31) from higher terrestrial plants that are preserved in marine sediments from IODP Site U1446 in the northwestern Bay of Bengal. Being located within the reach of several large rivers, this site is characterized by high riverine input of terrestrial organic matter and thus ideal for establishing representative records of past hydroclimate and vegetation changes on the northern Indian subcontinent. The obtained δD data reveal a stepwise ISM intensification at the last glacial-interglacial transition but also several distinct centennial- to millennial-scale reductions in ISM intensity during the last glacial period. These so-called Weak Monsoon Intervals (WMIs) occurred parallel to cold events in the North Atlantic realm, e.g. during Heinrich events H1, H2, H4, H5 and H6, pointing at a close hemisphere-scale climatic teleconnection between the North Atlantic and Asia. In contrast, hydroclimate-driven changes in vegetation composition during the WMIs – reflected by the δ13C data – were only very subtle, possibly reflecting a partial resilience of the vegetation during the last glacial period.