A New Palaeo-environmental Proxy from Roman Aqueducts: What Can We Learn from Calcareous Sinter?
Thursday, 18 December 2014
Roman aqueducts belong to the greatest engineering structures of the ancient world. Recently, carbonate deposits in the remains of aqueduct bridges and channels were recognized as a new proxy for palaeo-environmental changes. These deposits show similar fabric and lamination characteristics as other types of terrestrial carbonates from caves and rivers such as freshwater tufa, and hot spring deposits like travertine.
We present a multi-disciplinary study on calcium carbonate deposits from aqueduct sites in Southern France and Turkey, assisted by monitoring studies at aqueduct water sources in Italy of water composition and recent carbonate growth. The microstructure of the deposits shows considerable variation, even along a single aqueduct, mainly due to different climatic regimes, variations in channel type, aqueduct gradient and water velocity. However, downstream samples of several aqueducts show regular laminations associated with a strong δ18O cyclicity that can be interpreted as an effect of seasonal warming and cooling of water in the aqueduct channel. δ13C isotope curves are more complicated but commonly show antithetic cyclicity to δ18O. Deposits from aqueducts in the eastern Mediterranean, at Aspendos and Patara (Southern Turkey), typically show a regular layering of alternating sparite and micrite, which coincides with δ18O cyclicity. This reflects extreme seasonal cyclicity in temperature and rainfall in southern Turkey. However, deposits from the aqueduct of Cahors (Southern France), have cyclicity in δ18O that shows poor correlation with the microstructure and δ13C. This is probably due to the more variable, less seasonal rainfall patterns in southern France.
Carbonate deposits from ancient aqueducts can serve as a high-resolution data source of palaeoclimate, and to determine the number of years the aqueducts functioned. Besides a regular lamination, most deposits also show single, distinct layers that can be a proxy for extreme weather events or earthquakes.