Julie M. Palais

Inter‐hemispheric Transport of Volcanic Ash from a 1259 A.D. Volcanic Eruption to the Greenland and Antarctic Ice Sheets

A strong volcanic sulfuric acid signal corresponding to an age of 1259 A.D. has been reported in ice cores from Greenland, Antarctica, and Arctic Canada. Tiny (< 5 μm) volcanic glass shards were reported previously in samples from this layer in an ice core from the South Pole. Here we report the discovery of volcanic glass shards from a contemporaneous layer in an ice core from Summit, Greenland. The major element composition of the glass shards in the Greenland sample are identical to those from the South Pole, confirming the assumption that has been made previously that the sulfuric acid signal in the ice cores is an inter-hemispheric time stratigraphic marker. The composition of these glass shards is similar to those produced by a 550–700 yrs. B.P. eruption of El Chichon volcano in Mexico, suggesting that it may be the source of the widely dispersed material.

Identification of Some Global Volcanic Horizons by Major Element Analysis of Fine Ash in Antarctic Ice

Acid fallout from volcanic eruptions is well documented in the Greenland and Antarctic ice sheets (Hammer and others, 1980; Hammer, 1984; Legrand and Delmas, 1987). However, to date, no volcanic ash (tephra) layers have been positively identified in association with any of the high electrical conductivity layers that mark the volcanic acid deposition. In this paper we report the results of a study of the chemical compositIOn of insoluble microparticles filtered from five intervals of a core from the South Pole. These five intervals were identified by Kirchner (1988) as being due to volcanic fallout, on the basis of electrical conductivity and sulfuric acid measurements. The major element composition of tiny «5 /lm) glass shards found in these layers was determined and compared with analyses of volcanic ash from known eruptions or from volcanic sources suspected of having produced the fallout. Glass shards from volcanic eruptions of both local (Antarctic and sub-Antarctic) and of global (Indonesian/ South American) importance have been identified in this study.

Changing sources of impurities to the Greenland ice sheet over the last 250 years

Abstract Because the composition of precipitation reflects the composition of the atmosphere, polar ice cores provide a useful way of investigating past and present atmospheres. We have measured concentrations of major ions in nine sections of a central Greenland ice core and we found that concentrations of both SO 4 2− and NO 3 − have increased dramatically over the last 250 years, up to three to four times the 18th century levels. Large changes have also occurred in the average concentrations of several other chemical species, such as NH 4 + , excess Cl, and Ca 2+ . We used a principal-component analysis to characterize variations of the season of maximum deposition rate of HNO 3 and H 2 SO 4 to the snow. We found that source fluctuations of H 2 SO 4 are faithfully recorded in the Greenland snow and appear to switch their preferential time of deposition in the snow from summer to winter early in the 20th century. On the other hand, HNO 3 is deposited preferentially during summer throughout the core, emphasizing the role of photochemistry in understanding nitrogen cycling in the Arctic. Anthropogenic inputs have clearly modified the behavior of several chemical compounds in the atmosphere.

Emission of elemental gold particles from Mount Erebus, Ross Island, Antarctica

Volcanoes are an important source of gases and aerosols in the atmosphere. Significant quantities of trace elements are emitted as vapor species [Nriagu, 1989; Symonds et al., 1987] and are strongly enriched in the gas relative to the magma [Tazieff and Sabroux, 1983; Crowe et al., 1987]. After eruption the trace elements condense on ash and other particles or they form sublimates and agglomerates. Here we report on the emission of gold (Au) from Mount Erebus, Antarctica. Although the flux of emitted Au is low compared to other volcanoes, crystalline particulate Au has been found in the plume near the crater, in ambient air up to 1000 km from the volcano and in near surface samples. Vapor phase transport of Au may occur as a chloride species and could be an important transport mechanism in crystallizing magmatic intrusions.

The Volcanic Record of Antarctic Ice Cores: Preliminary Results and Potential for Future Investigations

Occurrences of tephra layers in four ice cores from Antarctica are reviewed. A new tephra, informally named the Vostok tephra, is described from a depth of 100.85 m in an ice core from Vostok station. Ice associated with four tephra layers at depths between 1390 and 1450 m in the Byrd station ice core shows increased levels of sulfate and nitrate which correlate well with peaks in particle concentrations. High levels of sulfate and nitrate are also associated with the Vostok tephra. Tephra offer great potential as strati graphic markers and should be useful in providing time planes as well as assisting in correlation between widely spaced ice cores. INTRODUCTION Tephrochronology is a relatively new field which is concerned with the establishment of time-related sequences of geological events based on the characterization of tephra layers (Westgate and Gold 1974). The term tephra was initially defined by Thorarinsson (1944) and is now used as a collective term for all airborne volcanic ejectamenta. Interest in volcanism has increased with the realization that volcanic eruptions may affect the global climate (Lamb 1970, Pollack and others 1976). Therefore, the identification and characterization of tephra in ice cores offer a method of studying the relationship between volcanism and climate during the late Pleistocene and Recent times. Ice cores are also useful for such a climatic interpretation since t hey preserve information on past temperature variations, as recorded by fluctuations in stable isotope ratios. In addition to the insoluble particulate record, the record of soluble aerosols, such as sulfate and nitrate, is preserved in ice cores. Secondary aerosols formed from volcanic gases when injected into the stratosphere in large quantities may have an important role in modifying the Earths climate following a major volcanic eruption (Pollack and others 1976). In Antarctica, numerous studies (Thompson 1977, r~osl ey-Thompson 1980, Thompson and others 1981) have shown that good microparticle records can be obtained. Tentative correlations with major eruptive events have been suggested. A combination of static electrical conductivity (Hammer 1980), to locate layers, followed by analyses of the soluble impurity and microparticle concentrations offer great potential for evaluating the southern hemisphere volcanic record. In this paper we review the known occurrences of tephra layers in Antarctic ice cores (Fig.l). We also present preliminary grain-size analyses of tephra layers and values for the concentrations of soluble impurities (S042and N03-) of the associated ice from several Antarctic ice cores. The potential for future studies is discussed. TEPHRA IN ANTARCTIC ICE CORES Byrd station ice core (BSIC) The 2 164 m deep B5!C (Gow and others 1968) contains 25 distinct dirt layers and an estimated 2 000 cloudy layers. The cloudy layers contain increased levels of particulate material and have been referred to as dust layers by Gow and Williamson (1971). Preliminary size analyses suggest that there is a graduation in the number and size of particles between the dirt and dust layers so we refer to them all collectively as dust layers. Once the particles from the layers have been examined and shown to be composed of airfall volcanic material, they are termed tephra layers. To date, all dust layers have been shown to *Ohio State IJ niversity. Institute of Polar Studies. Contribution No.416.

Modified HNO3 seasonality in volcanic layers of a polar ice core - Snow-pack effect or photochemical perturbation?

Using the chemical composition of snow and ice of a central Greenland ice core, we have investigated changes in atmospheric HNO3 chemistry following the large volcanic eruptions of Laki (1783), Tambora (1815) and Katmai (1912). The concentration of several cations and anions, including SO42− and NO3−, were measured using ion chromatography. We found that following those eruptions, the ratio of the concentration of NO3− deposited during winter to that deposited during summer was significantly higher than during nonvolcanic periods. Although we cannot rule out that this pattern originates from snow pack effects, we propose that increased concentrations of volcanic H2SO4 particles in the stratosphere may have favored condensation and removal of HNO3 from the stratosphere during Arctic winter. In addition, this pattern might have been enhanced by slower formation of HNO3 during summer, caused by direct consumption of OH through oxidation of volcanic SO2.