Comment on egusphere-2026-3334

Le résumé fourni par la source

Abstract. Understanding the evolution of deep ocean circulation and chemistry over the last glacial cycle is key for elucidating the ocean’s role in modulating atmospheric CO2 changes on millennial and orbital timescales. Marine Isotope Stage (MIS) 4 is a key paleoclimatic interval of the last glacial inception for assessing the role of the deep-ocean carbon storage in driving atmospheric CO2 levels, because it is characterized by a large decrease of air temperature and a rapid atmospheric CO2 drop of ~40 ppmv, likely linked to changes in ocean circulation, and includes several millennial climatic events, for example Heinrich Stadial (HS) 6. Although previous proxy-based studies have suggested a weakened Atlantic overturning during MIS 4, and particularly HS 6, basin wide changes in circulation remain poorly constrained. Here, we present high-resolution deep-water hydrography reconstructions from the mid-depth Iberian Margin (core MD01-2444, ~2.65 km water depth), based on benthic foraminiferal Mg/Ca-derived deep-water temperature (Tdw), benthic δ18O, and associated δ18Odw records, alongside SS- based flow-speed record. Our data reveal three distinct deep-water hydrographic ‘regimes’ at the Iberian Margin: 1) warm “interglacial-like” mode during MIS 5a (including Greenland stadials C19 and C20); 2) a colder glacial circulation mode during early MIS 4 (pre- HS 6); and 3) a “Heinrich” circulation mode during HS 6. A stronger influence of colder southern-sourced waters is inferred at the Iberian Margin throughout MIS 4 and intensifies during HS 6, whereas MIS 5a stadials are characterised by a pronounced subsurface warming. The warm stadials C19 and C20 were likely driven by a southward displacement of convection sites in the North Atlantic and appear to be unique to MIS 5a as they are not observed during MIS 3 Dansgaard-Oeschger events at this site. We also find evidence of “millennial-type” variability and, similar to recent studies for MIS 2, a persistent contribution of northern sourced waters during MIS 4 (pre- HS 6). The contrasting impacts of similar millennial-scale DO-type variability on North Atlantic deep-water hydrography and circulation strength during MIS 3, 4, and 5 highlight the strong dependence on the background climate state.

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