The Neogene Indian Ocean Record of Asian monsoon Driven Ocean Currents
and Winds from the Maldives (IODP Exp. 359)
Abstract
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.