Tephra Record of Local and Distal Volcanism in the WAIS Divide
Ice Core


Nelia W. Dunbar1, Andrei V. Kurbatov2, Bess G. Koffman2 and Karl J. Kreutz2
1 NMBG/EES Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA
2 Climate Change Institute, 236 Sawyer Hall, University of Maine, Orono, Maine 04469, USA


The climate impact of volcanic eruptions is related to the complex impact of non-silicate aerosols and
silicate ash (tephra) particles on Earth's radiative balance. Complex transport mechanism of
different volcanic products from the eruptive site to polar regions complicates identification of the
eruption magnitude and sources. The aerosol component of an eruption is manifest in ice cores as an
increase in acidity or several chemical species (Bi, As, SO4), and is typically assigned to a source volcano
based on the depth, and therefore the age, of the signal within the ice core, and/or the distinctive size of
the chemical signal. However, these features cannot tie the chemical signal to the source eruption as
directly as can be done with tephra geochemistry, because tephra composition is typically diagnostic of
the source eruption (Lemieux-Dudon et al., 2010). In the upper 600 m of the WDC06A ice core, a
single, well-defined ash layer was recognized at a depth of between 190.37-190.39 m (Fig. 1a). This
tephra contains 20 um size shards, and the chemical composition of the glass fragments in this layer is
statistically indistinguishable from a tephra layer found in the WDC05A at between 190.81-190.86 m
depth (Fig. 1b), in the Siple Dome B ice core (97.2 to 97.7 m depth, corresponding to an age of 705-710
yrs before 1950) and in the Taylor Dome ice core (79.2 m depth, corresponding to an age of 675 yrs
before 1996 (Hawley et al., 2002)). These tephra layers are interpreted to all be related to the same, shortduration
eruptive event, from the Pleaides volcanoes located in northern Victoria Land, so should have
been deposited very close in time, suggesting some chronological discrepancy in the older ice cores.
Figure 1. Backscattered electron images of tephra shards in WDC06A (A) and WDC05A (B). Scale bars on both
images are 0.5 mm.
Five intervals of the WCD06A core, corresponding to eruptions of Agung (1963), Krakatau/Tarawera
(1883/1886), Coseguina (1835), Tambora (1815) and an unknown eruption (1809) were chosen to search
for tephra shards from large, equatorial eruptions. Segments of ice corresponding to sulfate peaks in areas
of the core with ages thought to correspond to the eruptions listed above (based on unpublished data of J.
Cole-Dai, J. McConnell and K. Taylor) were sampled, melted and filtered. Material from the filters was
mounted in epoxy, polished and examined using the electron microprobe. Although abundant silicate
dust particles were found to be present on the filters, no population of tephra shards with chemical
compositions corresponding to the known eruptions was found. We suggest that the silicate component
from these eruptions is not arriving in Antarctica to be deposited on the Antarctic ice sheets. This
conclusion is consistent with the lack of anomalous particle signals observed in some of these intervals
(Koffman et al., this meeting). However, Koffman et al., (this meeting) have observed possible
anomalous dust concentrations associated with core depths that may correspond to some other large
eruptions nearer to Antarctica. We plan to examine these parts of the core in detail, using a modified
sample preparation technique that allows morphological examination of particles prior to polishing for
quantitative analysis.
The part of the WDC06A drilled during the 2009/10 field season represents a time interval of abundant
regional volcanism in West Antarctica. This activity is reflected in the large number of visible dust bands
and cloudy layers that were observed in the core (A. Orsi, pers. comm., 2010). Although no chemical
analyses have been made, a distinct "visible brown layer" at a depth of 1586.363 m. (8.279 KyBP
Neumann age) is very likely to be from a major eruption of the West Antarctic volcano Mt. Takahe. This
eruption is dated at 8.2±5.4 using 40Ar/39Ar geochronology (Wilch et al., 1999) and is observed at a depth
of between 503.58 and 503.87 m in the Siple Dome A core (SMDA) corresponding to ages between 8.167
and 8.181 Ky before 1950. A layer almost certainly corresponding to this one was identified and
analyzed in the Byrd ice core at a depth of 788 m (Palais et al., 1988). A visible double layer at 1741.246
m (9.57 KyBP Neumann age) may correspond to a very distinct tephra layer in the SDMA core at a depth
of around 550 m (corresponding to an age of around 9.7 Ky before 1950). This layer is derived from
West Antarctic stratovolcano, Mt. Berlin. In the next interval of WDC06A ice core, between 2251 and
2557 m depth (15.2 to 20.6 KyBP Neumann age), numerous dust bands and cloudy layers are reported in
the ice (A. Orsi, pers. comm., 2010). This corresponds to the age of ice in the Byrd Core that contained
many volcanic layers (Gow and Williamson, 1971), and also an interval in the SDMA where numerous
distinct tephra layers mainly associated with highly explosive eruptions of Mt. Berlin. Detailed
quantitative chemical analyses will be required to make one-to-one correlations between tephra layers in
the WDC06A and SDMA cores, but once made, will allow one additional tool to tie the records in these
two cores together.


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