Abrupt weakening of the Indian summer monsoon at 8.2 kyr B.P.

- Early to middle Holocene history of Indian Summer Monsoon (ISM) is presented.
- We used oxygen isotopes of biogenic carbonate from the paleolake Riwasa in NW India.
- An abrupt desiccation event at ∼8.2 ka B.P. formed a hardground in the region
- The desiccation provides evidence of an abrupt monsoon weakening at ∼8.2 ka B.P.
- The 8.2 ka drying coincides with North Atlantic cooling suggesting teleconnection.

An oxygen isotope record of biogenic carbonate from paleolake Riwasa in northwestern (NW) India provides a history of the Indian Summer Monsoon (ISM) from ∼11 to 6 kyr B.P. The lake was dry throughout the Late Glacial period when aeolian sands were deposited. Lacustrine sedimentation commenced in the early Holocene and the lake deepened significantly at ∼9.4 kyr B.P., indicating a strengthening of the ISM in response to summer insolation forcing. This high lake stand was interrupted by an abrupt desiccation, which is marked by a 12-cm limestone hardground that formed during a period of sub-aerial exposure after ∼8.3 kyr B.P. The base of the hardground surface coincides with the beginning of the '8.2-kyr B.P. cooling event' in the North Atlantic that has been associated with a glacial outburst flood and slowdown of Atlantic meridional overturning circulation. The hardground provides robust evidence of a weakening of the ISM on the Indian subcontinent at ∼8.2 kyr B.P., and supports previous results of a strong teleconnection between monsoon Asia and North Atlantic climate. Lacustrine sedimentation resumed at ∼7.9 kyr B.P. suggesting the 8.2-kyr desiccation of paleolake Riwasa represented an abrupt response of the ISM to forcing from the North Atlantic.