Data selection
Growth interval-I (GI-I) is the most recent period of stalagmite
deposition recorded in stalagmite Y99 (Fleitmann et al., 2011; Nicholson
et al., 2020). Previous 230Th dating analyses have
shown that the 15.3 cm (composite depth of two growth axes: Fig. S1)
period of stalagmite deposition falls within the Last Interglacial (MIS
5e), with ages ranging 132-117 ka BP (Fleitmann et al., 2011; Nicholson
et al., 2020). GI-I can be visually and isotopically distinguished from
GI-II (MIS 7a) and GI-III (MIS 7e), which are separated by clear growth
discontinuities (Fig. S1) and abrupt shifts in
δ18Oca values (Nicholson et al.,
2020).
For this study, we selected only the more recent 230Th
age determinations (Nicholson et al., 2020) obtained using a refined
methodology, smaller chronological uncertainties and revised U and Th
decay constants (Cheng et al., 2013). Prior to age-depth modelling, one
age (Y99-E-5; Fig. S1) was removed from consideration. This sample was
collected from the top of the stalagmite, in which there is evidence of
condensation corrosion. Such corrosion can cause localised open-system
behaviour through post-depositional mobilisation of U and Th (Borsato et
al., 2003; Scholz et al., 2014; Bajo et al., 2016). Whereas
post-depositional leaching of U can lead to older ages, re-precipitation
of calcite or incorporation of Th can cause younger ages. While no major
period of growth following MIS 5e is observed in Y99, other stalagmites
from Mukallah Cave (Y97-4 and Y97-5) indicate that drips were activated
during the subsequent wet phases of MIS 5c and the Holocene (Fleitmann
et al., 2011; Nicholson et al., 2020). These increase the likelihood
that any minor activations of the Y99 drip following MIS 5e may have
altered U or Th in the corroded area of GI-I, as supported by the
relatively high 232Th content compared to the rest of
our sample. Due to these uncertainties, we excluded Y99-E-5 from our
analyses. We proceeded with six previously published ages (Nicholson et
al., 2020).