Radiocarbon dating of silicified wood from around Steamboat Geyser in Norris Geyser Basin, Yellowstone National Park, 2021-2022

In the past century, eruptions of Steamboat Geyser in Yellowstone’s Norris Geyser Basin were mainly clustered in three episodes: between 1961 and 1969, between 1982 and 1984, and in a sequence of eruptions that began in 2018 (Reed et al., 2021) and resulted in extensive damage to, and mortality of the surrounding trees. To characterize tree response to geyser activity over time, and the response of geyser activity to climate variability, aerial and ground imagery were analyzed to document changes in tree coverage around the geyser since 1954. Twenty samples of silicified tree remnants were collected from near the geyser vent for radiocarbon (14C) dating to determine if trees grew during periods when the geyser was not erupting because of prolonged droughts in the Yellowstone Region in past centuries. Samples were collected on September 30, 2021, and on April 27, 2022, under the National Park Service Geology Programs Milestones Permit 2016-9. Radiocarbon (14C) dating of the mineralized wood and stable carbon isotope analyses (δ13C) were performed at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution. Measurement and calculation methods are described in the laboratory’s web page. The Bayesian software package Bchron (Haslett and Parnell, 2008) was used with the measured radiocarbon ages and the IntCal20 calibration curve (Reimer et al., 2020) to calculate age probability density functions for the most probable ages of tree growth. Two samples that yielded modern ages were excluded from the calculations. The Bchron software package uses a continuous Markov monotone stochastic process to make inference on a partially observed monotone stochastic process. The probability density functions were generated by randomly calibrating the radiocarbon date of each sample against the IntCal20 curve 10,000 times. References Cited Haslett, J. and Parnell, A., 2008. A simple monotone process with application to radiocarbon?dated depth chronologies. Journal of the Royal Statistical Society: Series C, 57, 399-418. https://doi.org/10.1111/j.1467-9876.2008.00623.x Reed, M.H., Munoz-Saez, C., Hajimirza, S., Wu, S.M., Barth, A., Girona, T., Rasht-Behesht, M., White, E.B., Karplus, M.S., Hurwitz, S. and Manga, M., 2021, The 2018 reawakening and eruption dynamics of Steamboat Geyser, the world’s tallest active geyser: Proceedings of the National Academy of Sciences 118, p.e2020943118. https://doi.org/10.1073/pnas.2020943118 Reimer, P.J., Austin, W.E., Bard, E., Bayliss, A., Blackwell, P.G., Ramsey, C.B., Butzin, M., Cheng, H., Edwards, R.L., Friedrich, M. and Grootes, P.M., 2020. The IntCal20 Northern Hemisphere radiocarbon age calibration curve (0–55 cal kBP). Radiocarbon, 62, 725-757. https://doi.org/10.1017/RDC.2020.41