3.1 Timing and Duration of SAHP 4 (MIS 5e)
The chronology of the MIS 5e section of stalagmite Y99 is based on seven230Th ages. Two ages were discarded: one230Th age at the top was not included as it is most likely influenced by condensation corrosion and one age appears to be an outlier for unknown reasons (Extended methods; Fig. S1 and S2). Importantly, the onset of stalagmite growth is determined by two230Th ages of 127.634 ± 0.557 ka BP and 127.811 ± 0.626 ka BP; whereas the StalAge model places the onset of growth at 127.725 +/- 0.448/0.374 ka BP. Stalagmite growth ceased at around 121.170 ± 0.500 ka BP (Fig. 2A). As ~300 mm yr-1 of rainfall are mostly likely required to trigger large speleothem growth in desert caves (Vaks et al., 2010), onset of stalagmite growth reveals that monsoonal rainfall during MIS 5e (SAHP 4) was at least twice as high as today. Considering the height and diameter of stalagmite Y99 and contemporaneously deposited speleothems in Hoti Cave in Northern Oman (Burns et al., 2001; Fleitmann et al., 2011), ASM and ISM rainfall must have been considerably higher than 300 mm yr-1 (Burns et al., 2001). This assumption is also supported by model-based estimates of rainfall over Arabia during MIS 5e (Otto-Bliesner, 2006; Herold and Lohmann, 2009; Jennings et al., 2015; Gierz et al., 2017). Based on the age model for stalagmite Y99, SAHP 4 lasted for ~6.5 kyrs, which is slightly longer than the 4.3 kyr-long Holocene Humid period in Southern Arabia (Fleitmann et al., 2007) (Fig. 3).
Additional evidences support the timing and duration of SAHP 4. The onset of the MIS 5e growth interval (SAHP 4) of stalagmite Y99 at 127.725 +/- 0.448/0.374 ka BP is synchronous with the onset of sapropel S5 at ~128.3 ± 2 ka BP (Grant et al., 2017) and associated negative shifts in speleothem δ18Oca records from Soreq and Peqiin Caves in Israel (Bar-Matthews et al., 2003). In both caves, speleothem δ18Oca values are influenced by the “source effect” as δ18O of (palaeo)precipitation in the Levant is directly linked to δ18O of surface water in the Eastern Mediterranean. During interglacial periods, increased monsoon precipitation in the Ethiopian Highlands and higher discharge of low-δ18O freshwater runoff from the Nile and North African wadi systems (Grant et al., 2012) into the Mediterranean lead to more negative δ18O and sapropel formation (Rohling et al., 2015). Thus, the sharp decrease in δ18Oca at ~128.3 ± 1.2 ka BP in the Soreq and Peqiin Cave records (Fig. 3) is caused by an up to ~8 times higher Nile flow (compared to the pre-Aswan period; Amies et al., 2019) during MIS 5e. Taken together, the Soreq and Peqiin Cave records are in line with marked increase in ASM and ISM rainfall at onset of SAHP 4 at 127.725 +/- 0.448/0.374 ka BP in stalagmite Y99, supporting the accuracy of its chronology. The termination of SAHP 4 at 121.170 ± 0.500 ka BP is also concurrent with the independently derived age estimate for the termination of sapropel S5 at ~121.5 ± 2 ka BP (Grant et al., 2016, 2017) and the distinct positive shift in δ18Ocain the Soreq and Peqiin Cave records (Bar-Matthews et al., 2003). Such a close correspondence between sapropel deposition in the Eastern Mediterranean and the timing of peak rainfall in Southern Arabia is also observed for other SAHPs (Nicholson et al., 2020) and (SAHP 1) between 10.5 and 6.2 ka BP (Fleitmann et al., 2007; Grant et al., 2017). The timing of SAHP 4 also conforms with significantly higher ASM/ISM rainfall in other – albeit less precisely-dated – monsoon records (Weldeab et al., 2007; Grant et al., 2017; Tierney et al., 2017; Fig. 4).