Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity

Abstract

Lead pollution in Arctic ice reflects midlatitude emissions from ancient lead-silver mining and smelting. The few reported measurements have been extrapolated to infer the performance of ancient economies, including comparisons of economic productivity and growth during the Roman Republican and Imperial periods. These studies were based on sparse sampling and inaccurate dating, limiting understanding of trends and specific linkages. Here we show, using a precisely dated record of estimated lead emissions between 1100 BCE and 800 CE derived from subannually resolved measurements in Greenland ice and detailed atmospheric transport modeling, that annual European lead emissions closely varied with historical events, including imperial expansion, wars, and major plagues. Emissions rose coeval with Phoenician expansion, accelerated during expanded Carthaginian and Roman mining primarily in the Iberian Peninsula, and reached a maximum under the Roman Empire. Emissions fluctuated synchronously with wars and political instability particularly during the Roman Republic, and plunged coincident with two major plagues in the second and third centuries, remaining low for >500 years. Bullion in silver coinage declined in parallel, reflecting the importance of lead-silver mining in ancient economies. Our results indicate sustained economic growth during the first two centuries of the Roman Empire, terminated by the second-century Antonine plague.

Keywords: antiquity; ice core; lead pollution; plague; war.

Fig. 1.

Sensitivity (23) of the NGRIP2 ice-core record to Northern Hemisphere atmospheric lead emissions from FLEXPART (20) transport model simulations. Also shown are locations of the NGRIP2 and GRIP ice cores (green), three peat bog coring sites (cyan), where historical lead records were evaluated, and Roman-era mine sites (blue) including Rio Tinto (red).

Fig. 2.

Lead measurements in Greenland ice. (A) Nearly contiguous 1000 BCE to 800 CE annual average lead measured in the NGRIP2 ice core compared with the 18 previously reported discrete lead measurements from the GRIP core (red squares) (2) on the new DRI_NGRIP2 chronology with an estimated overall uncertainty of 1 to 2 y during antiquity (Materials and Methods). (B) Typical high-resolution lead measurements in depth with the non–sea-salt sulfur/sea-salt sodium (nssS/ssNa) ratio that was one of several parameters used for annual-layer counting. Midwinter depths assigned to years 4–10 CE are shown. The discrete lead measurements in the GRIP core (2) each represented 2 y of snowfall.

Fig. 3.

Nonbackground lead deposition in Greenland ice and estimated European lead emissions, silver bullion content in coinage, and selected historical events during antiquity. Gray shading indicates 22% uncertainty (1 σ) in estimated annual emissions after 11-y median filtering based on year-to-year variability in FLEXPART-simulated atmospheric transport (Materials and Methods). We estimate a factor of two uncertainty in the overall magnitude of lead emissions. Estimated annual emissions derived from the measured annual lead deposition record ranged from 0.3 to 3.8 kt/a and averaged 1.1 kt/a during the first-century apogee of the Roman Empire, comparable to previous, less quantitative peak emissions estimates during this period of 4 kt/a, based only on historical and archeological evidence and a roughly estimated 5% emissions factor (3). Also shown are the changing silver bullion content of Roman denarius coins (31), periods of major wars and plagues thought to have affected mining regions of southern Spain (Table S1), and selected historical events (A: Punic Wars, B: Sertorian War, C: Civil Wars, D: Final pacification of Gaul and Spain, E: Antonine plague, F: Plague of Cyprian, G: Roman abandonment of Britain, H: Collapse of the Western Roman Empire).