Using the geochemical fingerprint of cryptotephra we pinpointed major eruptions from Iceland, New Zealand, Asia and North America as well as tropcal eruptions from Mesoamerica. Global climate effects were studied using model simulations and climate proxies following the 43 BCE Okmok eruption (Alaska). Exceptional strong sulfur burden in the Northern Hemisphere resulted in extreme weather in 43 BCE affecting the Nile River flow with economic impacts during late Roman Republic. Since the eruption date and climatic effects coincided with the civil war unfolding following the murder of Julius Caesar in 44 BCE, this study has sparked global interest far beyond the geosciences, prominently covered by leading media outlets (e.g. NYT, CNN, FOX News, FAZ).
Based on a set of continuous sulphate records from a suite of ice cores from Greenland and Antarctica, the HolVol v.1.0 volcanic eruption catalogue was developed and includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulphur injection (VSSI) events for the Holocene (9500 BCE-1900 CE). This new long-term reconstruction of past VSSI variability confirms evidence from regional volcanic eruption chronologies by showing that the early Holocene experienced a higher number of volcanic eruptions and cumulative VSSI compared to the past 2,500 years. This increase coincided with the rapid retreat of ice sheets during deglaciation, providing an analogy for the future if volcanic activity increased in regions under projected glacier melting in the 21st century.
Cryptotephra and heavy metals in ice cores from Greenland showed that volcanic activity in Iceland can persist for up to decades-to-centuries, providing context to the possible durations and associated risks of the recent volcanic activity in Iceland. Such a magnitude, duration and frequency of volcanic ash, sulfur, metal, and halogen emissions from Iceland is unprecedented within the Common Era. While this is the youngest long-lasting eruptive episode from Iceland, similar periods were more frequent and extensive during the early Holocene. This type of activity is comparable to the anthropogenic release of sulfur peaking in the 20th century and it will require additional efforts to understand its role in the climate system.
Results:
1) We reconstructed sulfur injection, atmospheric aerosol properties and their climate forcing potential for close to 1000 eruptions over the past 12,000 years and analyzed long-term trends of volcanic activity and changes in climate forcing.
2) For key eruptions we used the geochemical composition of ash to identify source volcanos and discriminated the sulfate contributions transported via the stratosphere and troposphere to improve our estimates of climate forcing.
3) Tropospheric sulfur emitted from long-lasting eruptive episodes over decades to centuries emerged as potentially important new climate forcing agent.
4) Proxy records and output from fully coupled Earth System Climate Model simulations show diverse effects of volcanic eruptions on global climate parameters.
We disseminated the project results in the science community through hosting three topical international workshops at the University of Bern. We engaged with the media and the general public through press releases, interviews on television, radio and in newspapers, social media and other outreach activities.
