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.

北半球低纬度和高纬度之间的过渡地区极易受到未来气候变化的影响，但目前大多数气候模型的预测通常存在分歧。为了更好地了解这些地区的动态，重建过去的水文波动和降水模式对于准确限制当前和未来的气候情景至关重要。在这项研究中，我们调查了地中海西部地区的古水文动力学，该地区是中低纬度和大西洋 - 地中海地区之间的过渡带。我们重建了过去~35 ka 期间降水和水分源的变化，以提出驱动这些振荡的潜在机制。为此，我们使用来自沉积叶蜡的氢同位素，更具体地说是 C₃₁ 正构烷烃同系物，以及基于先前公布的来自伊比利亚南部（Padul 湿地 ~37° N）沉积岩心 (Padul-15-05) 的花粉数据的降水代理。通过这种组合，我们解开了沉淀量和来源对所研究 C ₃₁ n的氢同位素特征的耦合影响-烷烃记录。我们的结果显示了以不同降水模式为特征的三个主要时期。低降水，主要与同位素富集的地中海降水源的显着贡献有关，发生在~30 至~15.5 ka BP 和最后~5 ka，而增强的降水与主要的同位素贫化大西洋降水源来自~ 15.5 至 ~5 ka BP。后一阶段在此定义为西地中海湿润时期（WMHP）。此外，在这些气候不同的时期，偶尔可以观察到一些与千年尺度相反的降水模式。降水来源的这些变化可能与主要雨季从冬季（大西洋降水盛行时）到晚冬至早春的转变有关。当地中海水分的贡献较高时。研究的中纬度陆地 Padul-15-05 核心与非洲西北部近海低纬度海洋记录的比较表明，西地中海降水和西非季风系统对北半球大气动力学的长期同步响应明显，最终得到控制通过轨道强迫和冰盖波动。