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Volcanic stratospheric sulfur injections and aerosol optical depth during the Holocene (past 11 500 years) from a bipolar ice-core arrayAbstract. The injection of sulfur into the stratosphere by volcanic eruptions is thedominant driver of natural climate variability oninterannual to multidecadal timescales. Based on a set of continuous sulfateand sulfur records from a suite of ice cores from Greenland and Antarctica,the HolVol v.1.0 database includes estimates of the magnitudes andapproximate source latitudes of major volcanic stratospheric sulfurinjection (VSSI) events for the Holocene (from 9500 BCE or 11 500 years BP to1900 CE), constituting an extension of the previous record by 7000 years.The database incorporates new-generation ice-core aerosol records with asub-annual temporal resolution and a demonstrated sub-decadal dating accuracyand precision. By tightly aligning and stacking the ice-core records on theWD2014 chronology from Antarctica, we resolve long-standing inconsistenciesin the dating of ancient volcanic eruptions that arise from biased (i.e.,dated too old) ice-core chronologies over the Holocene for Greenland. Wereconstruct a total of 850 volcanic eruptions with injections in excess of 1 teragram of sulfur (Tg S); of these eruptions, 329 (39 %) are located in the low latitudes with bipolarsulfate deposition, 426 (50 %) are located in the Northern Hemisphere extratropics (NHET) and 88 (10 %) are located in the Southern Hemisphere extratropics (SHET). The spatial distribution of the reconstructed eruption locationsis in agreement with prior reconstructions for the past 2500 years. Intotal,more »
No evidence for tephra in Greenland from the historic eruption of Vesuvius in 79 CE: implications for geochronology and paleoclimatologyAbstract. Volcanic fallout in polar ice sheets provides important opportunities to date and correlate ice-core records as well as to investigate theenvironmental impacts of eruptions. Only the geochemical characterization of volcanic ash (tephra) embedded in the ice strata can confirm the sourceof the eruption, however, and is a requisite if historical eruption ages are to be used as valid chronological checks on annual ice layercounting. Here we report the investigation of ash particles in a Greenland ice core that are associated with a volcanic sulfuric acid layer previouslyattributed to the 79 CE eruption of Vesuvius. Major and trace element composition of the particles indicates that the tephra does not derive fromVesuvius but most likely originates from an unidentified eruption in the Aleutian arc. Using ash dispersal modeling, we find that only an eruptionlarge enough to include stratospheric injection is likely to account for the sizable (24–85 µm) ash particles observed in the Greenlandice at this time. Despite its likely explosivity, this event does not appear to have triggered significant climate perturbations, unlike some otherlarge extratropical eruptions. In light of a recent re-evaluation of the Greenland ice-core chronologies, our findings further challenge the previousassignation of this volcanic event to 79 CE. We highlight themore »
The Circulation Response to Volcanic Eruptions: The Key Roles of Stratospheric Warming and Eddy Interactions
Proxy data and observations suggest that large tropical volcanic eruptions induce a poleward shift of the North Atlantic jet stream in boreal winter. However, there is far from universal agreement in models on this effect and its mechanism, and the possibilities of a corresponding jet shift in the Southern Hemisphere or the summer season have received little attention. Using a hierarchy of simplified atmospheric models, this study examines the impact of stratospheric aerosol on the extratropical circulation over the annual cycle. In particular, the models allow the separation of the dominant shortwave (surface cooling) and longwave (stratospheric warming) impacts of volcanic aerosol. It is found that stratospheric warming shifts the jet poleward in both the summer and winter hemispheres. The experiments cannot definitively rule out the role of surface cooling, but they provide no evidence that it shifts the jet poleward. Further study with simplified models demonstrates that the response to stratospheric warming is remarkably generic and does not depend critically on the boundary conditions (e.g., the planetary wave forcing) or the atmospheric physics (e.g., the treatment of radiative transfer and moist processes). It does, however, fundamentally involve both zonal-mean and eddy circulation feedbacks. The time scales, seasonality, and structuremore »