Western Mediterranean vegetation and climate responses to MIS 14-12 glacial-interglacial variability: new insights from ODP Site 976 (Alboran Sea)

Marine Isotope Stages (MIS) 14 to 12 (~563-424 ka) precede the Mid-Brunhes Event (~424 ka, MIS 12/11 transition), which marks a significant shift in the amplitude of glacial-interglacial cycles, and an increase in interglacial temperatures. This interval would also encompass the end of the Early-Middle Pleistocene transition (EMPT; 1.4-0.4 Ma) as defined by Head & Gibbard (2015). Despite ongoing debate regarding the precise EMPT boundaries, the MIS 14-12 interval remains crucial for understanding Pleistocene climate dynamics; particularly MIS 12 (~478–424 ka), one of the Pleistocene’s most intense Northern Hemisphere glaciations. The climatic oscillations during MIS14-12 profoundly influenced environmental conditions, potentially creating areas that were more or less favourable for human settlements in southern Spain. Archaeological data indeed show an absence of sites south of Spain during MIS 14-12 period, a pattern that could be interpreted as a possible response to environmental and climatic constraints. However, vegetation dynamics in the region during this key interval are still poorly understood due to the scarcity of available records.

Here, we present a new, continuous and regional pollen record from marine ODP Site 976 in the Alboran Sea, located south of the Iberian Peninsula. This record covers MIS 14 to MIS 12. to document the vegetation response in a climatically sensitive region. A multi-method approach, combining modern analogues, regression models and machine-learning techniques (e.g., Modern Analogue Technique (MAT), Weighted Average Partial Least Squares (WAPLS), Boosted Regression Trees (BRT), Random Forest (RF) & Climatic Amplitude Method (CAM)), are applied to the pollen data to reconstruct annual and seasonal temperature and precipitation. These results are compared with those from other western Mediterranean pollen records, as well as with the timing of human occupations recorded in an archaeological database to strengthen our understanding of settlement dynamics and their relationship with environmental changes.

The pollen data and climate reconstructions reveal significant shifts in vegetation and climate: a steppe-dominated landscape under less severe conditions during MIS 14, two phases of temperate forest expansion during MIS 13; and an enhanced steppe development under the very cold MIS 12 climate. Additionally, this study reveals three distinct climatic phases in southern Spain during MIS 13 and MIS 12, which are also recorded in several marine, pollen and Chinese loess archives. Although these archives were able to distinguish several phases within MIS 14, the resolution of our pollen record is insufficient to detect them.