Antarctic Intermediate Water (AAIW) is an essential component of the Atlantic meridional overturning circulation (AMOC) contributing to balance the southward flow of North Atlantic Deep Water (NADW). However, the role of AAIW in Holocene abrupt climate changes remains poorly understood. Here we reconstruct changes in the flow strength of AAIW based on a high temporal resolution paleocurrent record from the Southwest Atlantic. Superimposed on a slight increase in AAIW strength at ~ 7 ka BP, a succession of millennial-scale AAIW variations is recognized in our paleocurrent records indicating a highly variable intermediate water circulation throughout the Holocene. Although variations in the strength and position of the Southern Westerlies Winds (SWW) are proposed to greatly influence the formation and circulation of AAIW, we cannot confirm such a potential SWW-AAIW linkage since our records of AAIW flow strength do not correlate to Holocene shifts of the SWW across the Atlantic. However, our data shows a good correspondence with abrupt variations in the AMOC with enhanced (reduced) northward advection of AAIW during periods of reduced (enhanced) NADW circulation. These results provide evidence for a Holocene AAIW-NADW see-saw. Thus, although the exact forcing mechanism remains unresolved, we suggest that Holocene perturbations in AAIW exerted a significant impact on the AMOC.

We applied sortable silt paleo-current flow proxies (i.e., sortable silt mean size and percentage) to reconstruct relative changes in intermediate-depth contour current strength, i.e., the Antarctic Intermediate Water flow strength. Both parameters refer to the fraction of the sediment (i.e., terrigenous 10-63 µm) whose size sorting varies in response to hydrodynamic processes, where higher values reflect stronger near-bottom flow and vice versa. Grain-size distributions of the terrigenous fraction were measured with a LS 13320 Laser Diffraction Particle Size Analyzers, resulting in 116 size classes from 0.04 to 2000 µm.

Supplement to: Voigt, Ines; Chiessi, Cristiano Mazur; Piola, Alberto R; Henrich, Rüdiger (2016): Holocene changes in Antarctic Intermediate Water flow strength in the Southwest Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology, 463, 60-67