129I in the SE-Dome ice core, Greenland: A new candidate golden spike for the Anthropocene

Abstract

The Anthropocene is a proposed geological epoch that will mark the time when humans have irreversibly affected the Earth. One of the primary requirements to formally establish this is a Global Boundary Stratotype Section and Point or “golden spike” – a record of a planetary signal marking the new epoch's beginning. The leading candidates for the Anthropocene's golden spike are the fallout peaks of 14C (T1/2 = 5730 y) and 239Pu (T1/2 = 24,110 y) from nuclear weapons testing in the 1960s. However, these radionuclides' half-lives may not be long enough for their signals to be observable in the far future and are, thus, not durable. In this regard, here we show the 129I time series record (1957–2007) of the SE-Dome ice core, Greenland. We find that 129I in SE-Dome records almost the entire history of the nuclear age in excellent detail at a time resolution of about four months. More specifically, 129I in SE-Dome reflects signals from nuclear weapons testing in 1958, 1961, and 1962, the Chernobyl Accident in 1986, and various signals from nuclear fuel reprocessing within the same year or a year after. The quantitative relationships between 129I in SE-Dome and these human nuclear activities were established using a numerical model. Similar signals are observed in other records from various environments worldwide, such as sediments, tree rings, and corals. This global ubiquity and synchronicity are comparable to those of the 14C and 239Pu bomb signals, but the much longer half-life of 129I (T1/2 = 15.7 My) makes it a more durable golden spike. For these reasons, the 129I record of the SE-Dome ice core can be considered an excellent candidate for the Anthropocene golden spike.