Palaeoenvironmental changes in the southwestern Mediterranean (ODP site 976, Alboran sea) during the MIS 12/11 transition and the MIS 11 interglacial and implications for hominin populations

Abstract

The transition from the Marine Isotope Stage (MIS) 12 glacial (ca. 478–424 ka BP) to the MIS 11 interglacial (ca. 424–365 ka BP) is one of the most remarkable climatic shifts of the Middle Pleistocene and is regarded as a phase of major behavioural innovation for hominins. However, many of the available pollen records for this period are of low resolution or fragmented, limiting our understanding of millennial-scale climatic variability. We present a high-temporal resolution pollen record that encompasses the period between MIS 12 and MIS 10 (434–356 ka BP), recovered from the Ocean Drilling Program (ODP) Site 976 in the Alboran Sea. This study aims to provide new insights into the response of vegetation during the transition and to highlight patterns of climatic variability during MIS 11.The ODP Site 976 pollen record shows the shift from glacial to interglacial at 426 ka BP, highlighted by the transition from Pinus, herbaceous and steppic taxa to temperate and Mediterranean taxa. A climatic optimum for temperate and Mediterranean taxa is identified around 426–400 ka BP, equivalent to substage MIS 11c and synchronous with the maxima in SSTs, greenhouse gas concentrations and insolation. A phase with increased Pinus and Cedrus indicates the return to colder and more arid conditions during substage MIS 11b (400–390 ka BP). Substage MIS 11a (390–367 ka BP) is marked by a period of short-term warming followed by gradual cooling, until the return of glacial conditions during MIS 10. Forest contractions have been linked with high- and moderate-intensity climate events also observed in other pollen records and proxies from the Mediterranean and North Atlantic.Our results confirm the intense shift during the MIS 12/11 transition and show that this region is sensitive to millennial-scale climatic variation during MIS 11. The forest contractions observed in our record during events of millennial-scale variability appear to be less intense than in the central and eastern Mediterranean. This suggests that the southwestern Mediterranean may have been less variable during periods of climatic deterioration, thereby representing a possible ecological niche for vegetation. This may have provided a source of subsistence for hominins during harsher conditions, thus contributing to their demographic expansion and technological innovations.