Lachniet et al. (2004) intend to illustrate in their paper a climate shift at low latitude, marked by a change in the monsoon regime recorded by oxygen isotopes of a stalagmite, that would correlate with the so-called “8.2 ka event” (de Vernal et al., 1997; Alley et al., 1997). Although the title includes a question mark, the reader of the paper is still led to the conclusion that, despite some uncertainties, the studied time series does provide a record of the critical period (i.e., ca 8.2 ka, assigned here to a layer ~40 mm above the base of the stalagmite, as suggested by Figure 1 in Lachniet et al., 2004).
Unfortunately, the U-series data used to establish a chronology may be interpreted in a different way. Although relatively low, the 232Th-contents of the carbonate layers, especially between 12 and 87 mm, still indicate significant mixing between a detrital phase and an authigenic phase. When plotted as a classical Rosholt isochron (e.g., Rosholt, 1976; Luo and Ku, 1991; Ludwig and Titterington, 1994), the corresponding data fit quite well on the isochron defined by subsamples A–C (Table 1 in Lachniet et al., 2004), from the base of the stalagmite, as illustrated in Figure 1. This suggests that most of the stalagmite was deposited during two short phases of precipitation dated 8.8 and 4.9 ka, respectively, possibly separated by a ~4 k.y. gap. In this scenario, the stable isotope excursion observed at a distance of ~40 mm above the base of the stalagmite (this is unclear in the paper) and attributed to a dry event would date from the early phase of precipitation (i.e., ~8.8 ka). Therefore, it cannot be linked with certainty to any more recent climate excursions that would correlate with the 8.2 ka event. Furthermore, the δ13C and δ18O records of the studied stalagmite depict a relatively high correlation coefficient (r2 = 0.48), which raises concerns about the possibility that at least part of the data sets would not pass a Hendy test (Hendy, 1971) and would thus be more difficult to interpret in terms of a general change in climate. This also needs to be further documented by the authors to permit an unequivocal interpretation of the isotopic shift in their record.