Interpreting Climate and Water Management Limestone Archives in Rome's Aqueducts - Dr Keenan-Jones

Archaeological travertine deposits show great promise as a record of the environmental and climate conditions under which they formed. Dark-coloured layers are present in these travertine deposits on multiple scales down to the micron-scale. Here, we present a new 55-cm-long core procured from the complete travertine deposit of ancient Rome’s Anio Novus aqueduct in November 2019. We are using this new core to test the hypothesis that aqueduct travertine dark layering is a high-resolution record of rainfall patterns. Advanced fluorescence imaging and lipid biomarker analysis, interpreted using isotopic analyses and Principal Component Analysis, estimate the relative contribution of rainfall runoff and microbial communities by differentiating between different carbon compounds introduced by each, which has been very effective in similar deposits such as stalagmites. If the hypothesis is correct, dark layering in archaeological travertines from river-fed aqueducts would be a proxy of rainfall distribution at a sub-annual (likely even daily) resolution, due to the practically instantaneous response of the upper Aniene river to rainfall events. Stable isotope analyses reveal the impact of the building of a dam on the Aniene River, upstream of the aqueduct intake. Dating has been a recurrent problem with these deposits, but C14 dating of both carbonate and trapped organics, coupled with dating from Latin texts and isotopic investigation of potential annual cycles, is underway to resolve this problem.