Wind variability over the northern Indian Ocean during the past 4 million years – Insights from coarse aeolian dust (IODP exp. 359, site U1467, Maldives)

Abstract

The lithogenic fraction of carbonate drift sediments from IODP Exp. 359 Site U1467 (Maldives) provides a unique record of atmospheric dust transport over the northern Indian Ocean during the past 4 Myr. Grain-size data provide proxies for dust flux (controlled by source area aridity) as well as wind transport capacity (wind speed). 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. There is no clear trend in dust flux between 3.3 and 1.6 Ma, whereas wind transport capacity decreased. Between 1.6 Ma and the Recent, dust flux increased and shows higher variability, especially during the last 500 kyr. Transport capacity increased between 1.2 and 0.5 Ma and slightly decreased since then. Frequency analysis shows that 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 more pronounced in wind transport capacity than in the amount of dust. This indicates that the amount of coarse dust in sediments from the Maldives as a far-field site is more prone to changes in transport mechanisms than to changes in dust source-area aridity.