Abstract
The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.
Highlights
The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established
There is, an ongoing discussion about several critical aspects. These include (1) the timing of the monsoon intensification, which has been placed at ~7 to 8 Ma1 or at ~28.7–22 Ma2–5, and its relation to the high topographic relief linked to the uplift of the Tibetian-Himalayan orogeny[2,6]; (2) the linkage between the monsoon and the evolution of global cooling[7]; and (3) the interpretation of the establishment and fluctuations of the oxygen minimum zone (OMZ), as triggered by atmospheric circulation linked to the summer monsoon winds[1]
Data collected during IODP Expediton 359 pertinent to the discussion of the SAM include stratigraphical, geophysical, and geochemical data that are displayed in Figs 2–4 and Tables 1 and 2
Summary
The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. New data acquired during IODP Expedition 359 from the Inner Sea of the Maldives provide a previously unread archive that reveals an abrupt onset of the SAM-linked circulation pattern and its relationship to the long term Neogene climate cooling. In particular it registers ocean current fluctuations and changes of intermediate water mass properties for the last 25 myrs that are directly related to the monsoon. Data reveal how the Maldives carbonate platform responded to the Early and early Middle Miocene sea level fluctuations through changes of the platform growth pattern and growth interruptions
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