Mineral dust as a forcing factor behind primary productivity in the northwestern Arabian Sea since the Last Glacial Maximum

Located in the northwestern part of the Indian Ocean, the Arabian Sea (AS) is under the influence of Indian monsoon surface winds that create a coastal upwelling off Somalia and Oman during summer and a convective mixing north of 15°N during winter. It is also surrounded by vast arid regions regularly swept by regional winds, namely the Shamal and the Levar, that supply mineral dust to the sea surface. Coastal upwelling, convective mixing and mineral dust bring significant amount of nutrients to the euphotic zone, making the AS one of the most productive oceanic regions in the world. Since the Last Glacial Maximum (LGM), many studies attribute changes in western AS primary productivity (PP) to variations in coastal upwelling and summer monsoon dynamics. However, it has been recently demonstrated that convective mixing was a significant contributor in the northwestern part of the AS, while mineral dust may have also played a role. No high-resolution mineral dust records are available in the literature, nor are any linked to reconstructed PP signals, limiting our understanding of the relationship between mineral dust and PP in this region since the LGM. In this study, we provide sub-millennial scale records of detrital fraction grain-size distribution and clay mineralogy composition of sediment core MD00-2354 (21°02.55′N, 61°28.51′E, 2740 mbsl), located in the northwestern AS, and that benefits from a centennial PP signal previously obtained based on a micropaleontological approach (Zhou et al., 2022). Together with high-resolution geochemical X-ray fluorescence (XRF) data from the studied site as well as geochemical data from literature, these records enable us to reconstruct changes in regional wind dynamics and link them to PP patterns since the LGM. During the LGM and the near-glacial Henrich Stadial 1 (HS1; 17–14.7 ka) and Younger Dryas (YD; 12.9–11.7 ka), stronger Levar and Shamal together with stronger aridity in the source areas associated to more extended ice sheet in the Northern Hemisphere, weaker Atlantic Meridional Overturning Circulation (AMOC), and stronger winter monsoon, seem to be responsible for the higher dust inputs and PP signals recorded in the northwestern AS. During the Holocene and the mild interstadial Bølling-Allerød (B-A; 14.7–12.9 ka), weaker regional winds together with stronger humidity in the source area due to reduced ice sheet extension, stronger AMOC, and stronger summer monsoon, seem to diminish mineral dust inputs and hence lower PP. In such scenarios, convective mixing and mineral dust appear to be the main nutrient sources for PP in the northwestern AS, questioning the influence of the coastal upwelling system in that area.