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https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL103334 *Authors* Ally Peccia, Yves Moussallam, Terry Plank, Kevin DallaSanta, Lorenzo Polvani, Alain Burgisser, Jessica Larsen, Janet Schaefer *First published: 28 October 2023* https://doi.org/10.1029/2023GL103334 *Abstract* The 43 BCE eruption of Okmok Volcano has been proposed to have had a significant climate cooling impact in the Northern Hemisphere. In this study, we quantify the climate cooling potential of the Okmok II eruption by measuring sulfur concentration in melt inclusions (up to 1,606 ppm) and matrix glasses and estimate a total of 62 ± 16 Tg S released. The proportion reaching the stratosphere (2.5%–25%, i.e., 1.5–15.5 Tg S) was constrained by physical modeling of the caldera-collapse eruption. Using the NASA Goddard Institute for Space Studies E2.2 climate model we found a linear response between cooling and stratospheric sulfur load (0.05–0.08°C/Tg S). Thus, the 1–2°C of cooling derived from proxy records would require 16–32 Tg sulfur injection. This study underscores the importance of combining approaches to estimate stratospheric S load. For Okmok II, we find all methods are consistent with a range of 15–16 Tg S. *Key Points* Petrologic evidence suggests a total of 62 Tg S was released in the caldera-forming eruption of Okmok Volcano in 43 BCE Climate models respond linearly to stratospheric sulfur loads. 1–2°C cooling from proxy records suggests 16–32 Tg S injection A physical model constrains the proportion of stratospheric sulfur to 2.5%–25%; thus we find a common range for all methods of 15–16 Tg S *Plain Language Summary* Gaseous sulfur released in explosive volcanic eruptions can reflect incoming solar radiation in the stratosphere and cool the Earth's surface. Here, we calculate the total amount of sulfur released in the 43 BCE caldera-forming eruption of Okmok Volcano, Alaska by measuring the concentration of sulfur dissolved in magma prior to the eruption. We find that the total sulfur load from the Okmok II eruption is one of the largest in the last 2,500 years, and we use climate models to simulate cooling and precipitation anomalies associated with total or partial injection of volcanic sulfur into the stratosphere. However, the estimated sulfur load is larger than that predicted by sulfur signals preserved in ice cores, and physical modeling of the eruption suggests that only a proportion of the sulfur released reached stratospheric altitudes. Further, comparison of temperature reconstructions from tree ring and cave deposit proxies with climate model results show the cooling associated with the eruption requires only a fraction of the total sulfur load. Thus, we propose that only a quarter of the total sulfur released in the eruption made it to the stratosphere, responsible for 1–2°C of cooling in the year following the eruption. *Source: AGU* -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAHJsh99xn%3D5xK9yCbg4UERwrm%3DmzAKaca9hPLPVu1GpRRGmCbA%40mail.gmail.com.
