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).