Description: The transitional regions between the low and high latitudes of the Northern Hemisphere are highly vulnerable to future climate change yet most of the current climate models usually diverge in their projections. To better understand the dynamics in these regions, the reconstruction of past hydrological fluctuations and precipitation patterns is of paramount importance to accurately constrain present and future climate scenarios. In this study, we investigated paleohydrological dynamics in the western Mediterranean region, a transitional zone between low-mid latitudes and Atlantic - Mediterranean realms. We reconstruct precipitation and moisture source changes during the last ~35 ka in order to propose the potential mechanisms driving these oscillations. To do so, we use hydrogen isotopes from sedimentary leaf waxes, more specifically the C31 n-alkane homologue, and a precipitation proxy based on previously published pollen data from a sedimentary core (Padul-15-05) in southern Iberia (Padul wetland ~37° N). With this combination we disentangle the coupled effect of precipitation amount and source on the hydrogen isotopic signature of the studied C31 n-alkane record. Our results show three main periods characterized by different precipitation patterns. Low precipitation, mainly linked to a significant contribution from an isotopically-enriched Mediterranean precipitation source, occurred from ~30 to ~15.5 ka BP and during the last ~5 ka, whereas enhanced precipitation with a predominant isotopically-depleted Atlantic precipitation source prevailed from ~15.5 to ~5 ka BP. This latter stage is here defined as the Western Mediterranean Humid Period (WMHP). In addition, some occasional millennial-scale opposite precipitation patterns can be observed during these climatically distinct periods. These changes in the source of precipitation were likely coupled to a shift in the main rainy season from winter, when Atlantic precipitation prevailed, to late winter-early spring, when the contribution of Mediterranean moisture is higher. Comparison between the studied mid-latitude terrestrial Padul-15-05 core and a low-latitude marine record offshore of northwestern Africa shows clear long-term synchronous responses of both western Mediterranean precipitation and western African monsoon systems to northern Hemisphere atmospheric dynamics, ultimately controlled by orbital forcing and ice-sheets fluctuations.

Description: Quantitative continental climate reconstructions covering the last glacial cycle from the Iberian Peninsula are scarce. In order to fill this gap, we obtained for the first time a high-resolution mean annual air temperature (MAAT) record based on the distribution of specific bacterial membrane lipids (i.e., branched glycerol dialkyl glycerol tetraethers; brGDGTs) from the last 36.0–4.7 kyr palaeolake record recovered by the Padul-15-05 sedimentary core (Padul, Sierra Nevada, southern Iberia). The fractional abundance of the three major groups of GDGTs present in the Padul sediments, GDGT-0, crenarchaeol and the summed brGDGTs, is comparable with that of other shallow and small (〈10 km2) European lakes. Despite variations in the lithology in the studied section, the GDGT composition remains relatively stable, except for the uppermost 116 cm of the record, representing the ephemeral/emerged lake stage, which is characterized by higher crenarchaeol fractional abundances. The identification of a specific brGDGT that has only been detected in anoxic lakes provides evidence for in-situ brGDGT production in the water column and/or sediments in the Padul palaeolake. Its presence/absence probably denotes a succession of periods with a variable oxygen content in the bottom waters of the palaeolake. MAAT was reconstructed based on the distribution of brGDGTs using an African lake calibration and ranged between 12 and 20 °C. A new Bayesian calibration to mean temperature of Months Above Freezing (MAF) depicts similar temperature variations with a mean absolute difference of 0.7 °C. The MAAT reconstruction in the Padul palaeolake for the 36.0–4.7 kyr period reveals similarities with climate variability described at high-latitudes and in the westernmost Mediterranean area during this interval, showing cold conditions during the last three Heinrich Stadials and the Younger Dryas and warm conditions during the Dansgaard–Oeschger interstadials (7–1) and the Bölling-Alleröd period. Despite the more stable and warm general climate conditions during the Early and Mid-Holocene, rapid centennial-scale temperature changes are registered in the Padul palaeolake in good agreement with variations observed in the Mediterranean forest record.