A 4 kyr stalagmite oxygen isotopic record of the past Indian Summer Monsoon in the Andaman Islands

In order to reconstruct the activity of the Indian Summer Monsoon (ISM) during the last ∼4 kyr, two stalagmites from Baratang cave in Andaman Islands have been investigated for their temporal variations in δ 18 O. The chronology is provided by radiocarbon ages on the stalagmites. During 1800–2100 cal yr BP, we observed a significant increase in stalagmite δ 18 O that we infer is caused by the amount effect. This increase implies a strong reduction in the strength of the ISM that is correlated with the Roman Warm Period. Other proxy records in the region confirm a reduction in ISM activity during this time. Reduction in the ISM is also observed around 1500 and 400–800 cal yr BP; the latter period is the transition from the Medieval Warm Period to the Little Ice Age. The strongest monsoon in the last ∼4 kyr is observed during 800–1200 cal yr BP, the Medieval Warm Period.