Geochronological implications of 210Pb and 137Cs mobility in cave guano deposits

Some recent publications on the paleo- and historical environmental interpretation of bat guano sequences have relied on ²¹⁰Pb and ¹³⁷Cs distribution to establish age-depth models, even when these are at odds with radiocarbon models in the lower parts of the sequence. Here, we present both field and laboratory evidence for the unpredictable mobility of lead and cesium in decomposing bat guano deposits. We suggest that ²¹⁰Pb- and ¹³⁷Cs-based chronologies of bat guano deposits should only be used when independently supported, for example, by a robust radiocarbon age-depth model.