Deglacial and Holocene variability of intermediate water masses in the Ligurian Sea based on a multi-proxy approach

Abstract

In this study, we combine analyses of benthic foraminiferal assemblages, grain-size distributions, and elemental composition (X-ray fluorescence) with geochemical measurements of foraminiferal coatings (U/Mnfc) and stable oxygen isotopes (δ18O) from sediment core NDT_22_2016 (432 m water depth) to reconstruct oceanographic variability over the past ∼18 kyr. Our findings reveal a significant influx of shelf-derived benthic foraminiferal assemblages during Heinrich Stadial 1 (HS1), which we attribute to enhanced melting of Northern Apennines glaciers, particularly during HS1b (∼17-16 kyr). These observations support the occurrence of warm summers despite the overall regional cooling linked to HS1. At the same time, micropaleontological and geochemical data record an abrupt decline in mid-depth oxygen conditions, potentially reflecting HS1-driven changes in the properties of intermediate waters originating from the eastern Mediterranean Sea. During the formation of Sapropel 1 (S1) in the eastern basin, the presence of well-oxygenated waters and the formation of a sandy condensed layer are interpreted to reflect intense sediment winnowing associated with episodes of dense shelf-water formation in the study region. We argue that these conditions may have facilitated the development of a western-sourced intermediate water mass, which would have occupied the pathway of weakened eastern-sourced Mediterranean waters during S1 deposition. We further propose that the modern Mediterranean circulation pattern was established at ∼6 kyr, marked by notable changes in both sedimentary and benthic ecosystem records. Lastly, a significant shift in sediment supply over the last ∼2 kyr is linked to pronounced anthropogenic impacts.