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

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 (T_1/2 = 5730 y) and ²³⁹Pu (T_1/2 = 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 (T_1/2 = 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.