Speed changes of the continental slope currents in the SW atlantic in the last 45,000 years

Abstract

The Intermediate Western Boundary Current (IWBC) is a critical component of the large-scale South Atlantic circulation, functioning as a northward carrier of the Antarctic Intermediate Water (AAIW) along the upper limb of the Atlantic Meridional Overturning Circulation (AMOC). This study examines the IWBC's flow speed variations over the last 45,000 years by analyzing four sediment cores from the Southwest Atlantic continental slope, focusing on the Sortable Silt proxy $\left(\overline{SS}\right)$ as an estimator for paleocurrent speeds. The cores, retrieved from depths between 840 m and 1558 m, reveal distinct sedimentation rates and grain-size distributions reflecting the hydrodynamic conditions associated with the IWBC and Deep Western Boundary Current (DWBC). Notably, the core located at 840 m exhibited the highest flow speeds, decreasing from 22 cm s⁻¹ at its base to 18 cm s⁻¹ at around 23,000 cal BP, while cores at 1343 and 1558 m maintained lower, stable speeds (3–7 cm s⁻¹). The core at 1469 m presented higher sedimentation rates and demonstrated more variability, with periods of increased flow speeds coinciding with significant climatic events (Heinrich 1, 3, and 4 and the Younger Dryas). Our results confirm the suitability of using $\overline{SS}$ as a reliable indicator of past flow speeds, highlighting the complex interactions between the IWBC and regional oceanographic processes. This study contributes to understanding past SW Atlantic slope dynamics and their influence on sedimentary processes within the Santos Basin. It also elucidates their role in the broader context of the Atlantic circulation.