Bat guano deposits are increasingly used as records of past environmental changes, an approach that requires a precise chronology of the guano layers. This paper presents a comparison between the well-established ¹⁴C dating method and methods based on natural ²¹⁰Pb excesses, (²¹⁰Pb)_ex, and artificial radionuclides ¹³⁷Cs and ²⁴¹Am. The studied example is a bat guano deposit from a cave in SW France (the Brantites III cave), which is currently investigated for paleo-environmental reconstructions using stable isotopes. ¹⁴C data show that the upper part of the guano deposit accumulated during the last 150 years with a marked increase in accumulation rates after around 1960 AD. While the incorporation of atmospheric ¹⁴C in guano is a well-understood process, the origin of ²¹⁰Pb excesses is more complex. Based on consideration of ¹³⁷Cs and (²¹⁰Pb)_ex inventories recorded in undisturbed soils in France, and the measured inventories in the guano deposit, we suggest that most of the ²¹⁰Pb excess is produced by ²²²Rn decay in the cave air and then adsorbed onto the guano. As Radon concentrations in caves can vary significantly on both short and long-term timescales, one needs to be cautious before applying the often-used CRS (constant rate of supply of ²¹⁰Pb excess) model to guano dating. Our (²¹⁰Pb)_ex data are best interpreted by two successive periods of roughly constant, but widely different accumulation rates (0.3 cm/y and 2.6 cm/y before and after 1960, respectively) and (²¹⁰Pb)_ex fluxes. We suggest that these relatively abrupt variations result from a change in cave ventilation leading to a more favourable shelter for bats after 1960. The upper 40 cm of the deposit shows evidence of ²¹⁰Pb mobility, adding a further complexity to the interpretation of (²¹⁰Pb)_ex profiles in guano deposits. However, the existence of well-defined ¹³⁷Cs and ²⁴¹Am peaks allows a precise identification of the year of maximum atmospheric fallouts (∼1963–1964). When the ages provided by artificial radionuclides are combined with the ²¹⁰Pb-derived accumulation rates, an age model can be built, which is in good agreement with the ¹⁴C age model. This example shows that the (²¹⁰Pb)_ex method, when associated with ¹³⁷Cs (²⁴¹Am) data, can be used to date recent guano deposit, although its application is not as straightforward as the ¹⁴C method.

蝙蝠鸟粪沉积物越来越多地被用作过去环境变化的记录，这种方法需要精确的鸟粪层年表。本文介绍了成熟的¹⁴ C 测年方法与基于天然²¹⁰ Pb 过量、( ²¹⁰ Pb) _ex和人工放射性核素¹³⁷ Cs 和²⁴¹ Am 的方法之间的比较。研究的例子是来自法国西南部一个洞穴（Brantites III 洞穴）的蝙蝠鸟粪沉积物，目前正在研究使用稳定同位素重建古环境。¹⁴C 数据显示，鸟粪矿床的上部在过去 150 年中积累，在公元 1960 年左右之后积累率显着增加。虽然在鸟粪中加入大气¹⁴ C 是一个众所周知的过程，但²¹⁰ Pb 过量的起源更为复杂。考虑到法国原状土壤中记录的¹³⁷ Cs 和 ( ²¹⁰ Pb) _ex库存量以及鸟粪沉积物中的实测库存量，我们建议大部分²¹⁰ Pb 过剩是由²²²Rn 在洞穴空气中衰变，然后吸附到鸟粪上。由于洞穴中的氡浓度在短期和长期时间尺度上可能存在显着差异，因此在将常用的 CRS（²¹⁰ Pb 过量供应的恒定速率）模型应用于鸟粪测年之前需要谨慎。我们的 ( ²¹⁰ Pb) _ex数据最好通过两个连续的大致恒定但差异很大的积累速率（1960 年前后分别为 0.3 cm/y 和 2.6 cm/y）和 ( ²¹⁰ Pb) _ex通量来解释。我们认为，这些相对突然的变化是由于洞穴通风的变化导致 1960 年后蝙蝠更有利的庇护所造成的。沉积物的上部 40 厘米显示了²¹⁰Pb 流动性，进一步增加了鸟粪矿床( ²¹⁰ Pb) _ex剖面解释的复杂性。然而，明确定义的¹³⁷ Cs 和²⁴¹ Am 峰的存在允许精确识别最大大气沉降的年份（~1963-1964）。将人工放射性核素提供的年龄与²¹⁰ Pb衍生的积累率相结合，可以建立年龄模型，与¹⁴ C年龄模型吻合较好。此示例显示 ( ²¹⁰ Pb) _ex方法与¹³⁷ Cs ( ²⁴¹Am) 数据，可用于确定近期鸟粪矿床的日期，尽管其应用不如¹⁴ C 方法那么简单。