Increased atmospheric dust transport to the Bahamas during early Marine Isotope Stage 8

Abstract

<p>Long-range atmospheric dust transport affects the climate by impacting radiative transfer, cloud formation and the global carbon cycle. Furthermore, dust plays an important role in pedogenesis, whereas Fe-rich dust in particular influences the primary productivity of the ocean. Transport of Saharan dust via the westerlies to the Caribbean is well recorded, even under present conditions, however, its variability over Quaternary glacial-interglacial cycles is less well understood. Here, we present initial investigations into the speleothem record of long-range Saharan dust transport to the Bahamas. A stalagmite collected from -25.6 m below sea level from Abaco Island, Bahamas, macroscopically displays a tripartite structure beginning and ending with opaque crystalline calcite, but with a middle section containing striking insoluble Fe-rich layers several mm thick that alternate with finer opaque layers. The red layers are interpreted to be formed under vadose conditions and not due to precipitation of an Fe-rich crust in an unsaturated mixing zone. U-Th dating reveals that the opaque calcite sections were deposited during Marine Isotope Stage (MIS) 10 and late MIS 8, with the intervening Fe-rich section being deposited during early MIS 8. Dripstone speleothem deposition during MIS 10 and 8 therefore places an upper constraint on relative sea-level elevation of -25.6 m during those glacial periods, with the interglacial MIS 9 hiatus considered to be sea-level controlled. The Fe-rich section indicates atmospheric dust transport to Abaco Island increased during early MIS 8 synchronous with an episode of cooler sea surface temperatures in the sub-tropical Atlantic. On the other hand, the decline in dust transport during late MIS 8 is associated with higher sea surface temperatures.</p>