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).