In recent years there has been a surge in the recovery of ancient organic molecules from archaeological contexts. These analyses are yielding unprecedented insights into human evolution and cultural practices, and are providing valuable data for reconstructing paleoenvironments. However, contamination of archaeological sediments by microorganisms can alter ancient biomolecular data. Furthermore, the extent to which microbes can penetrate ancient archaeological sediments once these are exposed by excavation is unknown. We tested this question at Crvena Stijena, a rock shelter in the Dinaric alps in Montenegro that contains archaeological deposits spanning more than 80,000 years. Excavations in the early 1960s exposed these profiles, which have been cleaned several times to permit sampling for archaeological, geological, and biomolecular analyses. The growth of green biofilms on the exposed profiles after cleaning has prompted the question of whether this surface contamination extends into the profile. To test this question, we examined five different geological layers by sampling sediments from the exposed surface and at 1 cm intervals horizontally into the profile. Results from 16S rRNA gene sequencing show that samples from sediment surfaces have distinct microbial communities from most samples collected more than 1 cm deep, and microbial biomass from the deeper samples is very low. Together, this evidence strongly indicates that microbial contamination is limited to the profile surfaces. This lowers the likelihood that ancient biomolecules in these sediments have been altered by recent changes to the in situ microbial community, and that cleaning of the profiles before sampling may not need to exceed 2 cm in depth. These results lend further support to the research utility of limited vertical sampling along archaeological profiles and witness sections, a strategy which conserves rare and limited archaeological deposits while helping to tackle key questions about the past.

近年来，从考古环境中恢复古代有机分子的浪潮激增。这些分析为人类进化和文化实践提供了空前的见识，并为重建古环境提供了有价值的数据。但是，微生物对考古沉积物的污染会改变古老的生物分子数据。此外，一旦这些微生物通过挖掘而暴露出来，微生物能够穿透古代考古沉积物的程度是未知的。我们在黑山迪纳里克阿尔卑斯山的岩石避难所Crvena Stijena中测试了这个问题，该避难所内藏有八万多年的考古沉积物。1960年代初期的发掘工作暴露了这些轮廓，这些轮廓已被清洗了数次，以便可以进行考古，地质和生物分子分析的采样。清洁后裸露的轮廓上绿色生物膜的生长引发了这样的问题，即该表面污染是否扩展到轮廓中。为了测试该问题，我们通过从裸露的表面以1 cm的间隔水平取样到剖面中的沉积物来检查五个不同的地质层。16S rRNA基因测序的结果表明，沉积物表面的样品与大多数超过1 cm深的样品具有明显的微生物群落，而较深样品的微生物生物量非常低。总之，这一证据强烈表明微生物污染仅限于型材表面。这降低了这些沉积物中古代生物分子因原位微生物群落的最新变化而改变的可能性，并且采样前清洁型材的深度可能不需要超过2厘米。这些结果进一步为沿考古剖面和目击者部分进行有限垂直采样的研究效用提供了支持，该策略在保留宝贵且有限的考古存量的同时，还有助于解决有关过去的关键问题。