Abstract Marine Isotope Stage (MIS) 13, ∼533–478 ka, has received particular attention due to the unexpected enhancement of monsoon systems under a cool climate characterized by lower atmospheric CO2 and larger ice volume than many other interglacials. Key questions remain about its regional expression (intensity, climate variability, length), and underlying forcing factors, in particular at the mid-latitudes. Here we examine the SW Iberian vegetation, terrestrial climate and sea surface temperature (SST) variability during MIS 13 by combining pollen and biomarker data from IODP Site U1385 with climate-model experiments. We show, for the first time, that despite strong precessional forcing, MIS 13 stands out for its large forest expansions with a reduced Mediterranean character alternating with muted forest contractions, indicating that this stage is marked by a cool-temperate climate regime with high levels of humidity. Results of our data-model comparison reveal that MIS 13 orbitally driven SW Iberian climate and vegetation changes are modulated by the relatively strong ice-sheet forcing. We find that the Northern Hemisphere ice-sheets prescribed at the MIS 13 climate optimum reinforce the insolation effect by increasing the tree fraction and both winter and summer precipitation. We propose that the interactions between ice-sheets and major atmospheric circulation systems may have resulted in the persistent influence of the mid-latitude cells over the SW Iberian region, which led to intensified moisture availability and reduced seasonality, and, in turn, to a pronounced expansion of the temperate forest.

中文翻译：

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MIS 13 期间日照和冰盖强迫的结合驱动了北亚热带地区湿度的增加

摘要 海洋同位素阶段 (MIS) 13，∼533–478 ka，由于季风系统在凉爽气候下意外增强，其特征是大气 CO2 较低，冰体积比许多其他间冰期大，因此受到了特别关注。关键问题仍然在于其区域表现（强度、气候变率、长度）和潜在的强迫因素，特别是在中纬度地区。在这里，我们通过将来自 IODP 站点 U1385​​ 的花粉和生物标志物数据与气候模型实验相结合，研究了 MIS 13 期间伊比利亚西南部的植被、陆地气候和海面温度 (SST) 的变化。我们第一次表明，尽管有强大的岁差强迫，但 MIS 13 因其大面积的森林扩张而脱颖而出，地中海特征减弱，森林收缩减弱，表明这一阶段的特点是具有高湿度的凉爽温带气候体系。我们的数据模型比较结果表明，MIS 13 轨道驱动的西南伊比利亚气候和植被变化受到相对较强的冰盖强迫的调节。我们发现，在 MIS 13 气候最佳条件下规定的北半球冰盖通过增加树木比例以及冬季和夏季降水来加强日照效应。我们提出，冰盖和主要大气环流系统之间的相互作用可能导致中纬度细胞对伊比利亚西南部地区的持续影响，从而导致水分可用性增强和季节性降低，进而导致温带森林明显扩张。