Carbonate drift deposits in the Santaren Channel, on the Marion Plateau and in the Inner Sea of the Maldives were cored and dated by ODP and IODP expeditions. The ages based on biostratigraphy of these drifts are 11.4 Ma (Marion Drift), 12.3 Ma (Santaren Drift) and 12.9 Ma (Maldives Inner Sea), indicating a near simultaneous onset of the Florida, East Australia and Indian Ocean Currents that are all part of the global ocean current system. The Himalayan tectonics started with the collision of the Indian continent with Asia about ~50 Ma ago and continues today. The uplift of the Himalaya and Tibetan Plateau was not steady and not consistent across the mountain belt. The uplift of the southern and central Tibetan Plateau occurred from 40–35 Ma, at the northern Tibetan plateau at approximately 25–20 Ma, and at the northeastern to eastern Tibetan plateau at ~15 Ma. Significant increases in altitude of the entire Tibetan plateau are thought to have occurred about 10–8 Ma agoor more recently, some 3 myrs after the onset of the modern Indian Ocean monsoon-driven circulation system that is dated at 12.9 Ma. This sudden onset or intensification is puzzling in light of the continuous uplift of the Himalaya and Tibetan Plateau. If a linkage between tectonics and climate exists, the uplift must have stepped over a threshold that caused the climate to change dramatically. The near simultaneous onset of the global ocean circulation and the intensification of the monsoon is strong evidence that a combination of factors caused the sudden climate change. It is likely that onset of the intense monsoon is the combined result of the tectonic configuration, consisting of the Himalayan uplift but also the closing of the Tethyan seaway, and progressive glaciation on Antarctica.
The Maldives archipelago acts for over 25 myrs as a giant natural sediment trap in the eastern Arabian Sea. Drifts and periplatform deposits bear the record of environmental changes such as sea-level fluctuations but also of monsoon-driven changes of the surface and intermediate water mass current regime, and of wind-driven dust influx. Carbonate drifts in the Inner Sea indicate the establishment of a strong wind-driven current regime in the Maldives at 12.9 – 13 Ma. Ten unconformities, dissecting the Miocene to Recent drift sequences, attest to changes in current strength or direction. A major shift in the drift packages is dated at 3.8 Ma that coincides with the end of stepwise platform drowning and a reduction of the OMZ in the Inner Sea. The lithogenic fraction of the Maldives carbonate drifts provides a unique record of atmospheric dust transport during the past 4 myrs as grain size provides proxies for dust flux as well as wind transport capacity. Entrainment and long-range transport of dust in the medium to coarse silt size range is linked to the strength of the Arabian Shamal winds and the occurrence of convective storms which prolong dust transport. Dust flux and the size of dust particles increased between 4.0 and 3.3 Ma, corresponding to the closure of the Indonesian seaway and the intensification of the South Asian Monsoon. Between 1.6 Ma and the Recent, dust flux again increased and shows higher variability, especially during the last 500 kyr. Transport capacity increased between 1.2 and 0.5 Ma but slightly decreased since then. Dust transport varies on orbital timescales, with eccentricity control being the most prominent (400 kyr throughout the record, 100 kyr between 2.0 and 1.3 Ma, and since 1.0 Ma). Higher frequency cycles (obliquity and precession) are most pronounced in wind transport capacity. The published and ongoing studies of IODP Expedition 359 cores show that deposits surrounding carbonate platforms, i.e. carbonate drifts, bear a previously underestimated potential to add substantial knowledge for the understanding of the monsoon evolution on million-year, but also on shorter time scales. Potential targets for further research and drilling are for example the Laccadives, the Mascarene Plateau or the South China Sea platforms.