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Throughout the last cold stage, the North Atlantic region was punctuated by abrupt climate shifts and atmospheric processes propagated their effects to adjacent continents. During Heinrich Stadials, the ocean was chilled by icebergs calved from the great ice sheets. The impact of multiple temperature and precipitation regime changes on Late Pleistocene mountain glaciers and landscape development is poorly understood. Here we analyse 1,118 cosmogenic exposure ages—spanning the last 100,000 years—from glacial landforms on three continents across the Mediterranean. We evaluate their geomorphological context and stratify the record by depositional setting and geographical region. The database includes 300 dated moraines. We show that, despite cold temperatures, Heinrich Stadial aridity caused negative glacier mass balance and repeatedly stalled glacier growth across the Mediterranean. In contrast, relatively warm and humid climates between Heinrich Stadials favoured positive glacier mass balance, resulting in region-wide glacier growth and moraine formation. Our analysis supports climate model simulations of repeated and widespread Heinrich Stadial aridity in the Mediterranean basin during the last cold stage. Heinrich Stadials also saw enhanced supply of coarse debris from valley sides. The cumulative geomorphological impact of these climate shifts saw the largest moraines form at the culmination of the glacial cycle. Mountain glacier growth around the Mediterranean repeatedly stalled during cold, dry Heinrich Stadials, according to an analysis of cosmogenic isotope-dated glacial landforms from across the region.

The timing and extent of mountain glaciation during the Late Pleistocene shows considerable variability around the world. Identifying the nature and timing of glaciation is important for understanding landscape evolution and changing climatic conditions (precipitation and temperature). In the Balkans, glaciers were actually larger during the Middle Pleistocene when large ice caps formed in several mountain ranges including the Dinaric Alps, Montenegro, and the Pindus Mountains, Greece. Glaciations younger than Marine Isotope Stage 6 were characterised by smaller ice masses with glaciers mainly restricted to the highest mountains. The behaviour of Late Pleistocene glaciers in this region influenced the timing of sediment and meltwater delivery to river systems; the migration of modern humans across Europe; and the dynamics of biological refugia. However, dating control is limited for Late Pleistocene glaciers in the Balkans.Here we report new in-situ 36Cl terrestrial cosmogenic nuclide exposure ages from moraine boulders sampled in the Velika Kalica valley, in the Durmitor massif, Montenegro. This valley was targeted because it contains the Debeli Namet glacier - the last remaining glacier in Montenegro. We have sampled 25 limestone boulders from 5 moraines situated down-valley of the current glacier at altitudes between 1650–2000 m. AgCl targets for 36Cl assay were prepared at The University of Manchester and 36Cl concentrations were measured on the SIRIUS 6MV accelerator at the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation. At the last local glacial maximum, the Debeli Namet glacier extended almost 3 km beyond its current position. These 36Cl analyses are part of a wider regional Mediterranean study, totalling >50 new exposure ages, which also includes Mount Tymphi in the Pindus Mountains, NW Greece. The project will address both a significant spatial and temporal gap in Mediterranean glacial chronologies by targeting the hitherto undated Late Pleistocene glacial record. The work in Montenegro will also shed light on the nature of Holocene glaciation in the Balkans.

Large glaciers and ice caps formed in the Mediterranean mountains during the cold stages of the Pleistocene and some small glaciers remain today. Here we review 157 outputs that include radiometric dates on glacial deposits or outwash in the Mediterranean published between 1975 and 2020. The last decade has seen a striking increase in the use of terrestrial cosmogenic nuclide (TCN) dating and this has revolutionised our understanding of the Late Pleistocene glacial record. Our meta-analysis of 1663 radiometric ages highlights much greater complexity in the timing of Pleistocene glaciation across the region than hitherto recognised. Evidence from multiple dating methods, in a range of depositional settings, confirms that the Mediterranean glacial record extends through all of the Late Pleistocene and deep into the Middle Pleistocene. Evidence of Early Pleistocene glacial activity has been recognised from outwash deposits in the Julian Alps of Slovenia. The most extensive glaciations occurred during the Middle Pleistocene: their ages have been established primarily by using 40Ar/39Ar in the Italian Apennines and U-series dating in the glaciokarst of the Balkans. The Late Pleistocene glacial geochronologies are based on optically stimulated luminescence (OSL), radiocarbon and TCN dating. TCN dating is now the dominant method for dating Late Pleistocene glacial landforms. It is now clear that glaciers were present throughout the Late Pleistocene and, in most parts of the Mediterranean, they were at or near their maximum extent before the global last glacier maximum (27.5–23.3 ka). The outwash record in river valleys downstream of the glaciated terrains confirms that glaciers were important agents of landscape change throughout this period. Deglaciation in the Mediterranean mountains was punctuated by glacier stabilisations as well as some readvances towards the very end of the Pleistocene. The deglacial trend has continued throughout the Holocene with rapid change in recent decades due to rising global temperatures. Some small glaciers remain today due to the influence of locally favourable topoclimatic factors. For much of the Quaternary Period conditions in the Mediterranean mountains involved much more extensive glaciation than recorded at any time in the Holocene.

Terrestrial cosmogenic nuclide dating of ice-marginal moraines can provide unique insights into Quaternary glacial history. However, pre- and post-depositional exposure histories of moraine boulders can introduce geologic uncertainty to numerical landform ages. To avoid geologic outliers, boulders are typically selected based on their depositional context and individual characteristics but while these criteria have good qualitative reasoning, many have not been tested quantitatively. Of these, boulder location is critical, as boulders located on moraine crests are prioritised, while those on moraine slopes are typically rejected. This study provides the first quantitative assessment of the relative utility of moraine crest and moraine slope sampling using new and published 10Be and 36Cl ages (n = 19) and Schmidt hammer sampling (SH; n = 635 moraine boulders, ∼19,050 SH R-values) in the northern and southern Pyrenees. These data show that for many of the studied moraines, the spatial distribution of “good” boulders is effectively random, with no consistent clustering on moraine crests, ice-proximal or -distal slopes. In turn, and in contrast to prior work, there is no clear penalty to either moraine crest or moraine slope sampling. Instead, we argue that landform stability exerts a greater influence on exposure age distributions than the characteristics of individual boulders. For the studied landforms, post-depositional stability is strongly influenced by sedimentology, with prolonged degradation of matrix-rich unconsolidated moraines while boulder-rich, matrix-poor moraines stabilised rapidly after deposition. While this pattern is unlikely to hold true in all settings, these data indicate that differences between landforms can be more significant than differences at the intra-landform scale. As ad hoc assessment of landform stability is extremely challenging based on geomorphological evidence alone, preliminary SH sampling, as utilised here, is a useful method to assess the temporal distribution of boulder exposure ages and to prioritise individual boulders for subsequent analysis.