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The end of the Middle Pleistocene Transition (MPT, ~ 800-670 thousand years before present, ka) was characterised by the emergence of large glacial ice-sheets associated with anomalously warm North Atlantic sea surface temperatures enhancing moisture production. Still, the direction and intensity of moisture transport across Eurasia towards potential ice-sheets is poorly constrained. To reconstruct late MPT moisture production and dispersal, we combine records of upper ocean temperature and pollen-based Mediterranean forest cover, a tracer of westerlies and precipitation, from a subtropical drill-core collected off South-West Iberia, with records of East Asia summer monsoon (EASM) strength and West Pacific surface temperatures, and model simulations. Here we show that south-western European winter precipitation and EASM strength reached high levels during the Marine Isotope Stage 18 glacial. This anomalous situation was caused by nearly-continuous moisture supply from both oceans and its transport to higher latitudes through the westerlies, likely fuelling the accelerated expansion of northern hemisphere ice-sheets during the late MPT. © 2023, The Author(s).

The MIS 17 interglacial, ~715 675 ka, marks the end of the Mid-Pleistocene Transition as intensified, long and asymmetrical 100-kyr ice age cycles became eminently established. Increasing arrival of moisture to the Northern Hemisphere high latitudes, resulting from the northwestward migration of the Subpolar Front and the intensification of the Norwegian Greenland Seas (NGS) convection, has been put forward to explain the emergence of this quasi-periodic 100-kyr cycle. However, testing this hypothesis is problematic with the available North Atlantic precipitation data. Here we present new pollen-based quantitative seasonal climate reconstructions from the southwestern Iberian margin that track changes in the position and intensity of the westerlies. Our data compared to changes in North Atlantic deep and surface water conditions show that MIS 17 interglacial was marked by three major changes in the direction and strength of the westerlies tightly linked to oceanographic changes. In particular, we report here for the first time a drastic two-steps northward shift of the westerlies centered at ~693 ka that ended up with the sustained precipitation over southern European. This atmospheric reorganization was associated with northwestward migration of the Subpolar Front, strengthening of the NGS deep water formation and cooling of the western North Atlantic region. This finding points to the substantial arrival of moisture to the Northern Hemisphere high latitudes at the time of the decrease in summer energy and insolation contributing to the establishment of strong 100-kyr cycles. © 2019 Elsevier B.V.

Intensity and regional expression of past interglacial periods are among the challenging questions on natural interglacial variability. Model experiments show that some interglacials of the last 800 kyr, such as MIS 9 and 5 interglacials, stand out by the strongest warming at high latitudes resulting from important insolation and greenhouse gas forcing while weak or no temperature difference with other interglacials is simulated at mid-latitudes. Processes leading to glacial inceptions are also debated. Millennialscale climate variability during ice volume minima was proposed to play a predominant role in prescribing interglacial duration. A major evidence of that process was given by the pollen record from the SW Iberian margin MD01-2443 showing an early collapse of the Mediterranean forest in SW Europe during MIS 9e likely due to an abrupt climate change. This terrestrial interglacial appears however anomalously short-lasting as compared to other records from the southern Europe and North Atlantic. The IODP site U1385 from the SW Iberian margin enables to revisit the regional signature of the MIS 9 interglacial in southwestern Europe. We will present new pollen data to characterize the Iberian vegetation and climate changes during MIS9e. Our results display, in agreement with the MD01-2443 pollen record, a short-lasting maximal forest expansion during the early MIS9e but a persisting forest over the entire MIS9e. Comparisons with MIS 5 pollen data from the Iberian margin and model simulations confirm that in contrast to high latitudes, interglacial climate in southern Europe, in particular precipitation, mainly result from the contribution of insolation.

An atypical short-lived terrestrial interglacial in SW Iberia during MIS 9e due to a millennial-scale climatic change is not confirmed. High latitude warming induced by both strong GHG and insolation forcing may be associated with a different regional climatic expression in regions sensitive to climate change in terms of water availablity. Difference in forest expansion and precipitation in SW Iberia between MIS9 and MIS 5 mainly result from the contribution of insolation.

The spatial-temporal landscape dynamics through the Eemian interglacial (including preceding and succeeding transitional phases) have been examined along a latitudinal transect (50–55 °N). Three Eemian pollen diagrams are presented. As follows from comparison of the data from Central and Eastern Europe, changes of environment and climate became more contrasting from west to east. At the same time, the main phases in the evolution of vegetation appear to be similar throughout the latitudinal belt. The interglacial optimum was characterised by an essential similarity of vegetation all over the region investigated. Plant communities of the cooler intervals (at the beginning and closer to the end of the interglacial) differed noticeably from west to east. Significant contrasts in environmental and climatic fluctuations mark the Saalian/Eemian boundary (transition from MIS 6 to MIS 5e). Vegetation dynamics at this boundary resemble those detected at the transition from Weichselian to Holocene (Alleröd and Younger Dryas).

The last four interglacials (intervals during which global ice volume was similar to, or less than, that of our current warm stage) correspond to the warmest parts of the marine oxygen isotope stages marine isotopic age (MIS) 5, 7, 9, and 11. These interglacials followed the 100-kyr rhythm of eccentricity, but each had different insolation regimes, different durations, different ice volumes, and different sea-level heights. However, atmospheric greenhouse gas concentrations were similar and reached values, which, largely, were close to those of the current interglacial (Holocene or MIS 1) before the industrial revolution led to the artificial enrichment of the atmosphere's greenhouse gas concentrations via the burning of fossil fuels. This chapter summarizes the state of knowledge on each of the climatic warm intervals.