Holocene Records of Rainfall Variation and Associated ITCZ Migration from Stalagmites from Northern and Southern Oman

Abstract

Oxygen isotope ($δ$18O) profiles of uranium-series-dated stalagmites from Oman provide a record of Holocene Indian Ocean monsoon intensity at sub-decadal resolution over the past 10,000 years. The $δ$18O values are a proxy for the amount of monsoon precipitation, which is controlled by the mean summer latitudinal position and convection intensity of the Intertropical Convergence Zone (ITCZ). The longest stalagmite record, derived from a stalagmite (Q5) from southern Oman, continuously covers the period from 10,300 to 2,700 BP (before present) with an average temporal resolution of 4 to 5 years. Additional contemporaneously deposited stalagmites from northern and southern Oman are used to confirm the results obtained from Q5 time series. All stalagmite records indicate that changes in monsoon precipitation between 10,300 and 8,000 BP are in phase with high-latitude temperature fluctuations recorded in Greenland ice cores during the glacial-to-interglacial transition; this result indicates that late glacial and early Holocene monsoon precipitation and tropical convection are largely controlled by glacial boundary conditions. After the final melting of Northern Hemisphere ice sheets, monsoon precipitation decreases gradually in near linear response to changing Northern Hemisphere summer solar insolation. Comparison with the Cariaco Basin precipitation record, off the Venezuelan coast, indicates that post-glacial to modern precipitation patterns in the northern tropics are controlled on a global scale by the gradual southward migration of the ITCZ due to orbitally induced changes in insolation. At the decadal and centennial scales, fluctuations in monsoon rainfall appear to be driven primarily by variations in solar irradiance, with higher solar irradiance being correlated with higher monsoon rainfall.