TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 63 (No. 6), pp. 1009-1020, 2007

Indian Summer Monsoon Variability during the Holocene as Recorded in Sediments of the Arabian Sea: Timing and Implications

Meloth Thamban1*, Hodaka Kawahata2 and Venigalla Purnachandra Rao3

1National Centre for Antarctic and Ocean Research, Headland Sada, Goa 403 804, India
2Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan
3National Institute of Oceanography, Dona Paula, Goa 403 004, India

(Received 24 April 2007; in revised form 3 July 2007; accepted 5 August 2007)

Abstract: Indian monsoon precipitation fluctuated significantly during the Holocene and a reliable reconstruction of the timing of the events and their implications is of great benefit to our understanding of the effect and response of low latitude climate systems to the forcing factors. We have carried out high-resolution terrigenous proxy studies on a laminated sediment core from the Oxygen Minimum Zone of the eastern Arabian Sea margin to reconstruct the summer monsoon-controlled precipitation changes during the Holocene. The temporal variation in the terrigenous proxy indicators of this core, in combination with other high-quality cores from the Arabian Sea, suggests several abrupt events in monsoon precipitation throughout the Holocene. The early Holocene monsoon intensification occurred in two abrupt steps at 9500 and 9100 years BP and weakened gradually thereafter, starting at 8500 years BP. A weakening in precipitation recorded at ~7000 years BP, synchronous with similar conditions in India. One of the most significant weak monsoon periods recorded in our studies lies between 6000 and 5500 years BP. Spectral analysis of the precipitation records reveals statistically significant periodicities at 2200, 1350, 950, 750, 470, 320, 220, 156, 126, 113, 104 and 92 years. Most of these millennial-to-centennial cycles exist in various monsoon records as well as the tree ring Δ14C data and/or other solar proxy records. We suggest that throughout the Holocene, externally, small changes in solar activity controlled the Indian monsoon to a large extent, whereas internally, non-solar causes could have influenced the amplitude of decadal-to-centennial oscillations.

*Corresponding author E-mail: meloth@ncaor.org

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