Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra)

High-resolution oxygen isotope (δ¹⁸O) profiles of Holocene stalagmites from four caves in Northern and Southern Oman and Yemen (Socotra) provide detailed information on fluctuations in precipitation along a latitudinal transect from 12°N to 23°N. δ¹⁸O values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the ITCZ and dynamics of the Indian summer monsoon (ISM). During the early Holocene rapidly decreasing δ¹⁸O values indicate a rapid northward displacement in the mean latitudinal position of the summer ITCZ and the associated ISM rainfall belt, with decadal- to centennial-scale changes in monsoon precipitation correlating well with high-latitude temperature variations recorded in Greenland ice cores. During the middle to late Holocene the summer ITCZ continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation, a trend, which is also recorded in other monsoon records from the Indian and East Asian monsoon domains. Importantly, there is no evidence for an abrupt middle Holocene weakening in monsoon precipitation. Although abrupt monsoon events are apparent in all monsoon records, they are short-lived and clearly superimposed on the long-term trend of decreasing monsoon precipitation. For the late Holocene there is an anti-correlation between ISM precipitation in Oman and inter-monsoon (spring/autumn) precipitation on Socotra, revealing a possible long-term change in the duration of the summer monsoon season since at least 4.5 ka BP. Together with the progressive shortening of the ISM season, gradual southward retreat of the mean summer ITCZ and weakening of the ISM, the total amount of precipitation decreased in those areas located at the northern fringe of the Indian and Asian monsoon domains, but increased in areas closer to the equator.