The Early-Middle Pleistocene Transition, or EMPT, is one of the great unsolved puzzles of Quaternary science. Between about 1.4 and 0.4 million years ago, glacial cycles lengthened and became asymmetric, with gradual ice build-up and abrupt terminations. Scientists attribute this shift to a combination of orbital forcing and internal feedbacks, including long-term cooling, declining atmospheric carbon dioxide, the stripping away of soft regolith beneath ice sheets and the resulting dynamics of thicker, more persistent ice. Crucially, the start of this transition coincides with the first known hominin occupations in Western Europe, at sites in Italy and the Iberian Peninsula dated to around 1.4 to 1.2 million years ago. Understanding the environmental backdrop against which the earliest Europeans lived makes the Mediterranean, a corridor for dispersal and a region exquisitely sensitive to climate change, an indispensable natural archive.

The team, led by Maé Catrain of the Muséum National d’Histoire Naturelle in Paris, focused on a depth interval of the ODP 976 core spanning 281.23 to 256.53 metres composite depth, with an age model anchored by nannofossil events, sapropel layers and correlation with global benthic oxygen isotope stacks. The pollen record, previously established by the same group, captures 31 plant families and 72 genera distributed across the classic altitudinal belts of Mediterranean vegetation, from thermo-Mediterranean olive and pistachio woodlands to supra-Mediterranean pine and fir forests. Alternations between temperate taxa such as deciduous oak and steppe indicators like Artemisia, Amaranthaceae and Ephedra trace the rhythm of warm-humid interglacials and cold-dry glacials across the studied interval.

To translate vegetation into numbers, the researchers applied five independent climate reconstruction methods to the pollen data: the modern analogue technique, weighted averaging partial least-squares regression, random forest, boosted regression trees and the climatic amplitude method. Each rests on a different mathematical foundation, from machine learning bootstrapping and boosting to the overlap of climatic tolerances of around 135 taxa calibrated on thousands of modern pollen spectra. Importantly, the climatic amplitude method can incorporate relict taxa that have since vanished from the Mediterranean, such as Tsuga, Zelkova and Cathaya, a decisive advantage for a period as ancient as the late Early Pleistocene. A non-parametric PERMANOVA test confirmed that, for most stages, the methods produced statistically consistent reconstructions of mean annual air temperature and precipitation, lending confidence to the overall picture.

The results reveal that MIS 37, between about 1245 and 1215 thousand years ago, was the warmest interval of the entire study period, with temperate forests reaching roughly 35 percent representation, steppes shrinking to about 10 percent, warm-water foraminifera peaking and sea surface temperatures climbing to around 16.5 degrees Celsius. This finding challenges the conventional view of MIS 31, often dubbed the super interglacial, as the warmest stage of the era. While MIS 31 is associated with maxima in obliquity, eccentricity and insolation and has been linked to unusual warmth at high latitudes, the Alboran record shows it as comparatively modest, closer to MIS 33 and MIS 35 than to the pronounced warmth of MIS 37. The result echoes earlier observations from Iberian margin cores U1385 and U1387, suggesting that the Atlantic exerted a moderating influence on the western basin.

On the glacial side of the ledger, MIS 34, from roughly 1141 to 1114 thousand years ago, emerges as the most severe cold phase, with steppe expansion to about 28 percent, forest regression to 10 percent, peaks of the polar-affinity foraminifera Neogloboquadrina pachyderma reaching 40 to 70 percent, and reconstructed annual air temperatures near 9 degrees Celsius, corroborated by heavy oxygen isotope values of up to 1.62 per mille. Sea surface temperatures in the glacial stages fell as low as 9.5 degrees, far below the modern value of 17.7 degrees for the region. The synchrony between steppe pollen and cold-water foraminifera indicates that Iberian steppe landscapes were driven not only by aridity but also by low temperatures, a subtle but important distinction for interpreting early hom habitats.

Perhaps the most striking discovery comes from the clay mineralogy. Analysed by X-ray diffraction on oriented slides, the clay assemblages are dominated by illite and smectite, with chlorite, kaolinite and minor palygorskite. Around 1140 thousand years ago, at the transition between MIS 35 and MIS 34, the record shows an abrupt shift: smectite rises sharply to average values near 42 percent while illite, kaolinite and chlorite decline, and the illite-to-kaolinite ratio climbs. Because illite dominates dust from the northern Sahara while kaolinite becomes prevalent toward the Sahel, the rising ratio points to intensified Saharan dust supply and developing aridity in North Africa. The simultaneous smectite shift, which cannot be explained by local rivers or sea-level changes, points to a reorganisation of oceanic advection, likely involving smectite-rich sediments recirculated through the Strait of Gibraltar by the Mediterranean outflow and the Western Alboran Gyre. Notably, this signal fades eastward and is absent from Ionian and Levantine records, suggesting the change is tied to Atlantic circulation and attenuates into the central Mediterranean.

The land-sea comparison across basins reveals a Mediterranean that was climatically fragmented. At Montalbano Jonico in southern Italy, interglacial forest development peaked in MIS 31 and 35 rather than MIS 37, and the foraminiferal assemblages are dominated by the cold-water, productivity-loving Turborotalita quinqueloba, indicating warmer but still cool central Mediterranean waters less influenced by cold Atlantic inflow. Within the Western Mediterranean itself, the marine ODP 976 record, the continental Palominas section in southern Spain and Monte San Giorgio in Sicily show broadly consistent temperature oscillations, but precipitation patterns diverge: MIS 34 was wet at Monte San Giorgio, MIS 36 wet at Palominas, while the Alboran record shows dry glacials throughout. These contrasts paint a picture of steep regional gradients shaped by the interplay of Atlantic, monsoonal and Mediterranean circulation systems.

One of the study’s most consequential conclusions concerns the relative roles of temperature and rainfall. Pollen-based temperature reconstructions systematically run colder than estimates derived from faunal assemblages at early hominin sites in southern Spain, such as Barranco León, Fuente Nueva 3, Quibas and Cueva Victoria, a discrepancy the authors attribute partly to the regional averaging inherent in marine pollen records, which integrate vegetation from coasts to mountains across both Spain and Morocco, and partly to methodological limitations when deciduous oak dominates the assemblage. Precipitation reconstructions, by contrast, align remarkably well between pollen and faunal archives, converging around 700 to 750 millimetres per year at several sites. This consistency suggests that vegetation and climate in the southwestern Mediterranean were governed more by variations in rainfall and drought than by temperature, a finding with clear implications for modelling the environments encountered by the first hominins to venture into Western Europe.

The team emphasises that this window, spanning MIS 37 to 31, captures only the opening act of the Early-Middle Pleistocene Transition, including the exceptionally long 75,000-year MIS 36-35 cycle that foreshadowed the coming 100,000-year world. Extending this kind of integrated, multi-method analysis across the full transition is the declared next step, both to disentangle the mechanisms behind the lengthening of climate cycles and to reconstruct the environmental stage on which early humans expanded into Europe. For now, the Alboran mud has delivered a rare, precisely dated snapshot of a world in climatic flux, where a sudden shift in dust and ocean circulation at 1140 thousand years ago marks the moment the Western Mediterranean began its long march toward the ice ages of the later Pleistocene.

Subject of Research: Paleoclimate and paleoenvironmental reconstruction in the Western Mediterranean during the late Early Pleistocene

Article Title: Paleoenvironmental and paleoclimatic reconstruction in the Western Mediterranean during the Late Early Pleistocene

Article References: Catrain, M., Fauquette, S., Peyron, O., Combourieu-Nebout, N., Lebreton, V., Fischer-Fries, M., Robles, M., Bout-Roumazeilles, V., Richard, P., Delattre, M., Dubost, L., Joannin, S., Viala, A., Altolaguirre, Y., Suc, J.-P., Lepelletier, J., & Moncel, M.-H. (2026). Paleoenvironmental and paleoclimatic reconstruction in the Western Mediterranean during the Late Early Pleistocene. Climate of the Past, 22(9), 1631-1653. https://doi.org/10.5194/cp-22-1631-2026

Image Credits: AI Generated

DOI: 10.5194/cp-22-1631-2026

Keywords: Mediterranean climate, Early-Middle Pleistocene Transition, ODP Site 976, Alboran Sea, pollen analysis, planktonic foraminifera, clay mineralogy, paleoclimate reconstruction, Marine Isotope Stage 31, Saharan dust, hominin dispersal, Climate of the Past