Two million year history of the Indian Monsoon
Final Report Abstract
The aim of the project was to produce the first long orbital resolution records of precipitation in the core convective region of the Indian Monsoon. To this end we have generated proxy records of river runoff, salinity and weathering in the Andaman Sea and surrounding watersheds. These data have revealed; 1. A relatively stable source of clay minerals transported by the monsoon to the Andaman Sea over the last 60 kyrs. 2. A weak monsoon during the last glacial maximum and strong middle Holocene monsoon river runoff. 3. Regional patchiness within South Asia in the timing of deglacial monsoon strengthening. 4. The orbital resolution record of mixed layer seawater δ18O for the last 1 million years exhibits only 30% of the variance in the precession band and the phasing is similar to that observed in the Arabian Sea, and most importantly, NOT like the paradigmatic Chinese speleothem records. 5. The orbital resolution record of mixed layer seawater δ18O for the last 1 million years exhibits a significant variance in the obliquity band, suggesting cross hemisphere process are important, and various heterodyne frequencies that highlight the importance of internal feedbacks on monsoon precipitation dynamics. 6. Orbital scale variability of the thermocline layer is primarily governed by similar processes driving mixed layer changes in the Andaman Sea. Thermocline and mixed layer seawater d18O document very similar spectral peaks and provide clear evidence that freshening of the mixed layer and the thermocline waters is controlled by a common monsoonal forcing. 7. The 1cm resolution record of sediment elemental composition generated by XRF core scanning to cover the last 2 million years reveals the important role that sea level has played in the transport of terrigenous material to the Andaman Sea sites. 8. The lack of millennial scale variability in the 1cm resolution record of Andaman Sea sediment elemental composition generated by XRF core scanning contrasts to records in the Bay of Bengal and Arabian Sea.
Publications
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(2014). History of theIndian Monsoon recorded in Andaman Sea sediments. In: IODP conference 2014, Erlangen, 17.03. -19.03.2014
Gebregiorgis, D., Hathorne, E., Giosan, L., Collett, T.S, and Frank, M.
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(2014). Pleistocene Indian Monsoon rainfall variability dominated by Obliquity. In: AGU conference 2015, San Francisco, 15.12. - 19.12.2014
Gebregiorgis, D., Hathorne, E., Giosan, L., Collett, T.S, Nürnberg, D., and Frank, M.
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(2015), South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea, Geochem. Geophys. Geosyst., 16, 505–521
Ali, S., E. C. Hathorne, M. Frank, D. Gebregiorgis, K. Stattegger, R. Stumpf, S. Kutterolf, J. E. Johnson, and L. Giosan
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(2016), South Asian summer monsoon variability during the last ∼54 kyrs inferred from surface water salinity and river runoff proxies, Quaternary Science Reviews, Volume 138, 6-15
Gebregiorgis, D., E.C. Hathorne, A.V. Sijinkumar, B. Nagender Nath, D. Nürnberg, M. Frank
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(2016). Astronomical forcing of South Asian Monsoon precipitation over the past ~1 million years. In: ICP conference 2016, Utrecht, 29.08.-02.09.2016
Gebregiorgis, D., Hathorne, E., Giosan, L., Clemens, S., Nürnberg, D., and Frank, M.
