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.

Deep-Water Circulation over the Last Two Glacial Cycles Reconstructed from Authigenic Neodymium Isotopes in the Equatorial Indian Ocean (Core HI1808-GPC04)

“…It is also interesting that the maximum aeolian grain size record from a nearby site in the Maldives (IODP Exp. 359 site U1467; Lindhorst et al 2019;Fig. 5f) does not bear many similarities to the Chinese loess grain size record.…”

Weakening of the South Asian summer monsoon linked to interhemispheric ice-sheet growth since 12 Ma

“…Therefore, the Maldives Inner Sea acts as a natural sediment trap best suited for dust deposition 7 . Evidence of sedimentology, geochemistry and morphology of sediment grains from Site U1467 all suggest that the lithogenic fraction is primarily dominated by eolian materials 25,26 . Consequently, the lithogenic fraction at Site U1467 is of eolian origin, and the contribution of fluvially-derived material supplied by currents from the Arabian Sea and the Bay of Bengal can be neglected [24][25][26] .…”

“…Evidence of sedimentology, geochemistry and morphology of sediment grains from Site U1467 all suggest that the lithogenic fraction is primarily dominated by eolian materials 25,26 . Consequently, the lithogenic fraction at Site U1467 is of eolian origin, and the contribution of fluvially-derived material supplied by currents from the Arabian Sea and the Bay of Bengal can be neglected [24][25][26] . Previous studies have demonstrated that the input of eolian dust to the Arabian Sea is primarily linked to the southwesterly monsoonal winds and subordinated northwesterly Shamal winds, both during the summer monsoon season [26][27][28][29] .…”

Variability of indian monsoon and its forcing mechanisms since late quaternary

“…The influence of Earth orbital forcing on the long-term evolution of Indian monsoon has been recorded in deep-sea cores, lake sediments and stalagmites (Ziegler et al, 2010a;Cai et al, 2010;An et al, 2011). Previous researches demonstrated that the climate evolution of Indian monsoon is dominated by precession (~23 ka), obliquity (~41 ka) and eccentricity (~100 ka) cycles (e.g., Clemens et al, 1996;Clemens and Prell, 2003;Kelly et al, 2005;Kunkelova et al, 2018;Lindhorst et al, 2019;Lu et al, 2020). Previous orbital-scale studies of the ISM mainly used proxies of phytoplankton (G. bulloides) from the northern Arabian Sea (Prell et al, 1984;Prell and Van Campo, 1986;, grain size (Clemens and Prell, 1990;Krissek and Clemens, 1992), Ti/Al and excess Ba MAR (Shimmield et al, 1990), biogenic opal and organic carbon MAR (Murray and Prell, 1991).…”