Land–sea Decoupling During Termination Ii and Its Implications for the Upper Pleistocene GSSP: Insights from a Western Mediterranean Marine Core

During past glacial Terminations, the climate system underwent deep reorganization globally, representing potential major milestones for refining regional and global stratigraphic frameworks. This potential is, however, fraught with major challenges linked to our understanding of the complex terrestrial and marine environmental dynamics at times of important climatic feedbacks and millennial climatic oscillations. The case study of Termination II (TII, ~136-129 ka) provides a critical example of these difficulties. The onset of the MIS 5 interglacial is widely used to mark the base of the Upper Pleistocene, yet precisely correlating this boundary across different depositional contexts remains challenging, mainly due to temporal offsets between marine and terrestrial records and the occurrence of a major millennial-scale climatic event (known as Heinrich Stadial 11) at the transition between MIS 6 and MIS 5. For these reasons, the formal definition of a GSSP for the Upper Pleistocene boundary remains unresolved. Among the available records, ODP Site 976 (Alboran Sea) is located in a key position for understanding the connection between North Atlantic, Saharan, and Mediterranean dynamics. The high-resolution palynological study recently carried out on this core, coupled with pollen-based climatic reconstructions and clay mineralogical data, complements previous isotope and SST reconstructions, leading to a complete and detailed record of changes occurring on land and in the sea between 140 and 120 ka. In parallel, several marine sedimentary cores from the Iberian Margin, tuned to speleothem records, now provide multi-proxy reconstructions for TII. Speleothems offer the crucial advantage of high-quality radiometric dating, although the interpretation of their environmental significance can sometimes be complex. Comparison with high-quality global and regional records, including Antarctic ice-cores and speleothems, helps to refine the scenario for the MIS 6 to MIS 5 transition and the structure of the HS11 complex. The apparent lag between marine and terrestrial responses to interglacial warming seems strongly linked to the rapid melting of Northern Hemisphere ice sheet at the end of the penultimate glacial and the subsequent North Atlantic freshening and cooling events, to which the Mediterranean marine and continental ecosystems have been very sensitive. In addition to oceanic changes, major shifts in atmospheric circulation possibly linked to migrations of the Intertropical Convergence Zone are well established in the paleo-dust record from the southwestern Mediterranean. These results highlight the need to integrate high- and low-latitude processes when defining a future GSSP for the Upper Pleistocene.