Climatic and environmental variability of the Early–Middle Pleistocene transition in the western Mediterranean

The transition between the Early and Middle Pleistocene (1400-400 ka) represents a key phase of climatic system reorganization, marked by the shift in dominant orbital periodicity from 41 kyr to 100 kyr cycles. In the Mediterranean region, this transition is associated with a trend toward increasing aridity. A multi-proxy analysis was conducted on the continuous marine sediment sequence from ODP Leg 161- Site 976, in the Alboran Sea. The study integrates pollen, isotopic, and clay mineral data together with a multi-method pollen-based climate-reconstruction approach (CAM, MAT, WA-PLS, RF and BRT) and reveals contrasting dynamics among the different indicators. The isotopic records, pollen assemblages, and quantitative climate reconstructions all display variability structured by glacial–interglacial alternation. These proxies show progressive yet well-defined transitions between open cold and dry phases and warmer and more humid conditions. Between 1100 and 870 ka, the record shows a decrease in the amplitude of temperate deciduous forest development. In contrast, the clay mineral composition exhibits a distinct cyclicity that diverges from the classical glacial–interglacial rhythm, and is characterized by a series of abrupt changes, particularly pronounced between 1235 and 870 ka. These mineralogical disruptions suggest rapid reorganizations of hydro-sedimentary conditions, potentially linked to regional modifications in ocean and/or sea circulation and aeolian inputs. Altogether, the results highlight the complexity of the Early–Middle Pleistocene transition in the western Mediterranean, shaped by the superposition of global climatic forcing and regionally specific responses.