Lead Isotopes in North American Precipitation Record the Presence of Saharan Dust

Abstract

Atmospheric dust is an important mass transfer and nutrient supply process in Earth surface ecosystems. For decades, Saharan dust has been hypothesized as a supplier of nutrients to the Amazon rainforest and eastern North America. However, isotope studies aimed at detecting Saharan dust in the American sedimentary record have been ambiguous. A large Saharan dust storm emerged off the coast of Africa in June 2020 and extended into the southeastern United States. This storm provided a means to evaluate the influence of Saharan dust in North America confirmed by independent satellite and ground observations. Precipitation samples from 17 sites within the National Atmospheric Deposition Program (NADP) were obtained from throughout the southeastern United States prior to, during, and after the arrival of Saharan dust. Precipitation samples were measured for their lead (Pb) isotopic composition, total Pb content, and 210Pb activity using multicollector inductively coupled plasma mass spectrometry. We measured a significant isotopic shift (approximately 0.7% in the 208Pb/206Pb relative to the 207Pb/206Pb) in precipitation that peaked in late June 2020 when the dust blanketed the southeastern United States. However, the magnitude and short time period of the isotopic shift would make it difficult to detect in sedimentary records.