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Aridification of the Indian Subcontinent During the Holocene: Implications for Landscape Evolution, Sedimentation, Carbon Cycle and Human Civilizations

Camilo Ponton, Ph.D., 2012
Timothy Eglinton and Liviu Giosan, Advisors

Despite the importance of climate to society, knowledge of long-term monsoon variability is limited. This thesis provides Holocene records of monsoon variability on the Indian subcontinent, using sediment cores from river-dominated margins of (1) the Bay of Bengal and (2) the Arabian Sea. Carbon isotopes of terrestrial plant leaf waxes (d13Cwax) preserved in sediment provide records of flora for both sites. For Site 1 the d13Cwax record shows gradual increase in aridity-adapted vegetation from ~4,000 until 1,700 years ago followed by persistence of aridity-adapted plants to the present. This aridity record allowed examination of relationships between hydroclimate and terrestrial carbon discharge to the ocean. Comparison of radiocarbon measurements of sedimentary plant waxes with planktonic foraminifera reveal increasing age offsets starting ~4,000 yrs BP, suggesting that increased aridity slows carbon cycling and/or transport rates. For Site 2 the d13Cwax record shows a stable arid climate over the dry regions of the Indus plain and a terrestrial biome dominated by C4 vegetation for the last 6,000 years. This thesis integrates marine and continental records to create regionally extensive paleoenvironmental reconstructions with implications for landscape evolution, sedimentation, the terrestrial organic carbon cycle, and prehistoric human civilizations.