Fig.1. Aqueduct of Segovia, a Roman aqueduct in modern-day Spain (Credit: Arian Zwegers, 2013, via Flickr).
At the height of the Roman Empire, aqueducts stretched across Europe and helped sustain a population of one million people in Rome alone. As water rushed through these engineering marvels, it often left behind layers of sediment along the walls, which built up for hundreds of years. A recent study has found that the sediment, often deposits of calcium carbonate, may provide a highly nuanced and localized picture of the climate during ancient times. Such a specific record of temperatures or precipitation, along with historical and cultural accounts, would shed light on how human societies adapt to climate change.
Many reliable Roman aqueduct sources were limestone cave springs, which are rich with dissolved calcium carbonate. When the water is exposed to air, this compound starts to fall out of the water and lines aqueduct walls in layers of deposit called calcareous sinter. The sinter was the object of interest for Gül Sürmelihindi and Cees Passchier, of the Johannes Gütenberg University of Mainz, who took samples from aqueducts in southern Europe and Turkey. They found that sinter built up in dark and light stripes with specific chemical compositions.
Sürmelihindi and Passchier tested each layer for the abundance of oxygen-18 (18O), a chemical isotope that contains more neutrons than the more common form of oxygen. In the darker stripes, they found a higher ratio of the heavier 18O, whereas the lighter stripes contained less of this heavy oxygen isotope. The difference could reflect changes in temperature. Calcium carbonate more readily stays dissolved in colder water, so any sinter accumulating during winter is more likely to contain 18O, which precipitates out of water faster than the less heavy and more common oxygen form. Sürmelihindi and Passchier believe that the darker layers of deposit correspond to a cooler environment, and the lighter layers show warmer temperatures.
Even though the isotope analysis supports the color gradation, the researchers acknowledged that other causes could underlie the layers’ chemical composition. Varied precipitation, the presence of biological material, or even human activity might affect isotopic ratios. Sürmelihindi and Passchier need to accurately date each layer, but such depositions could represent hundreds of years of local climate change and therefore a valuable resource.
Fig.2. Calcified remains of Eifel aqueduct near Euskirchen-Kreuzweingarten, Germany. The calcareous sinter has built up significantly along the inside walls of the aqueduct (Credit: Putput, 2006)
Recording the climate’s history
This study is not the first to examine the effect of climate change on ancient societies. Researchers have used ancient Roman trade routes to model how temperature affects human populations, whereas other projects linked the fall of the Mayan empire to drought after analyzing cave deposits. In order to study ancient climate, paleoclimatologists normally examine polar ice cores, deep ocean sediments, tree rings, or even pollen records. The advent of certain chemical techniques, however, opened the field to the study of stalactites and stalagmites, which can date as far back as 500,000 years.
Although Sürmelihindi and Passchier are still researching sinter, this new record of ancient climate variation offers an important addition to stalactite and stalagmite records. Such deposit records offer a much more localized view of ancient climate change and show nuances that ice or sediment cores are unable to capture. Furthermore, chemical changes in sinter can be compared to historical records of Roman culture, creating a picture of how they adapted to regional changes in the environment. These records are vital not only to track the rise and fall of ancient civilizations, but also to predict how modern day society might adjust to climate change.
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NOVA (2000, February 22), Watering Ancient Rome. Retrieved from http://www.pbs.org/wgbh/nova/ancient/roman-aqueducts.html.
Wendel, J. (2015, March 19), Ancient Roman aqueducts could spill climate secrets. Eos, 96, doi:10.1029/2015EO026629.