Collaborative Research: Microparticle/tephra analysis of the WAIS Divide ice coreEntry ID: dunbar_0636767
Abstract: Visible tephra layers were found in the Byrd Station ice core, the first deep core drilled in Antarctica. Since then, tephra have been found in many other Antarctic ice cores. Tephra layers in ice cores range from sub-centimeter thick, visible layers to cryptotephra consisting of sparse, fine-grained (~10 micron) glass particles. Detection of tephra particles has improved with advances in methods ... of detecting cryptotephra in ice cores. Identification of tephra layers traditionally relied on physical properties or association with sulfate aerosols, but is now supplemented by downhole optical logging (Bay et al., 2001). Improved analytical techniques for glass characterization, such as high quality quantitative electron microprobe analysis, and more complete information on source eruptions has allowed development of a regional database of volcanic eruptions, which can be used to identify tephra horizons in ice cores.
Two deep ice cores drilled in West Antarctica (Siple Dome and WAIS Divide) contain rich tephra records, with the former containing 37 tephra layers and the latter containing several hundred distinct, visible layers, many of which are likely to be tephra. Most of the tephra layers with strong correlations are derived from Antarctic volcanoes, many from two large West Antarctic stratovolcanoes Mt. Berlin and Mt. Takahe, tephra from which have also been recognized in the marine record (Hillenbrand et al., 1988). A well-defined ash layer was recognized at a depth of between 190.37-190.39 m depth in the WAIS Divide core, which contains 20 um ash shards, and was chemically characterized as being derived from the Pleaides volcanoes, located in northern Victoria Land. This tephra layer correlates to one found in a Siple Dome (B) ice core (97.2 to 97.7 m depth) and in the Taylor Dome ice core (79.2 m depth). Deeper parts of the WAIS Divide ice core represent a time interval of abundant regional volcanism. 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 Ky BP preliminary 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 preliminary 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 segment of WAIS Divide ice core, between 2251 and 2557 m depth (15.2 to 20.6 preliminary age), numerous dust bands and cloudy layers are reported in the ice. 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 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 WAIS Divide and SDMA cores, but once made, will allow one additional tool to tie the records in these two cores together.
Purpose: The main purpose of this research was to address the following question: What is the detailed chronology of volcanic eruptions producing atmospheric microparticles (tephra), the possible climatic impact of such eruptions, and can these tephra layers be used to chronostratigraphically link the WAIS Divide ice core with other paleoclimate records?
The location and identification of tephra adds ... valuable information to the ice core volcanic record. Determining the source volcano of the tephra, using geochemistry of the volcanic glass found in the ice core with that from the particular eruption (e.g., Palais et al., 1992; Grönvold et al., 1995; Wilch et al.,1999; Dunbar et al., 2003b), can pinpoint the specific eruption responsible for the observed volcanic aerosol signal. For instance, the presence of two distinct glass populations can indicate the presence of aerosols from multiple eruptions or provide evidence of the eruptive processes for a known eruption (e.g., Zielinski et al., 1995). The ability to reliably identify the eruption(s) responsible for a particular signal provides the information needed to clearly assess the climatic forcing capability of a particular eruption/volcano and the particular type of eruption (e.g., a plinian versus fissure type of eruption). Further, if the presence of tephra that can be correlated to a known, dated, eruption, the layer provides an absolute time line for developing the depth/age scale of the ice core. Even if the source eruption is not known, volcanic glass in an ice core can allow for correlation among ice cores (Hawley et al., 2002; Dunbar et al., 2003b), as well as, in some cases, direct correlation of the ice core paleoclimatic records with those available in deep sea sediment cores (Grönvold et al., 1995) and terrestrial records (especially continuous lake and bog records) containing the same tephra.
In the case of Antarctica, local volcanism has the potential to swamp the ice core signal (Dunbar et al., 2003b; Kurbatov et al, 2006). Although we do not have a complete record of explosive volcanism in Antarctica, recent work at blue ice areas such as Mt. Moulton and Mt. Waesche, in West Antarctica
(Dunbar et al., 1999, Wilch et al., 1999) provides a substantial record. Ground-based field work on a number of West Antarctic volcanoes also has provided information about the chemical signature of West Antarctic volcanism (Panter et al., 1994; 1997; 2000; Wilch et al., 1999; Wilch and McIntosh, 2000).
Furthermore, recent tephra analyses from Antarctica ice cores have improved on the record of Antarctic volcanism for the past 100,000 yrs (Dunbar et al, 2003a; Kurbatov et al., 2006).
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Start Date: 2007-07-01Stop Date: 2012-06-30
CRYOSPHERE > GLACIERS/ICE SHEETS
CRYOSPHERE > GLACIERS/ICE SHEETS > ICE SHEETS
CRYOSPHERE > SNOW/ICE
PALEOCLIMATE > ICE CORE RECORDS
SOLID EARTH > TECTONICS > VOLCANIC ACTIVITY
SOLID EARTH > TECTONICS > VOLCANIC ACTIVITY > ERUPTION DYNAMICS
SOLID EARTH > TECTONICS > VOLCANIC ACTIVITY > ERUPTION DYNAMICS > PYROCLASTICS COMPOSITION/TEXTURE
SOLID EARTH > TECTONICS > VOLCANIC ACTIVITY > ERUPTION DYNAMICS > ASH/DUST COMPOSITION
ISO Topic Category
Data Set Progress
Phone: (505) 835-5783
Email: nelia at nmt.edu
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Province or State: NM
Postal Code: 87801-4796
Dunbar, NW; Mcintosh, WC; Kurbatov, AV. "Integrated tephrochronology of the West Antarctic region - Implications for a potential tephra record in the West Antarctic Ice Sheet (WAIS) divide ice core," in 8th Annual V M Goldschmidt Conference., v.72, 2008, p. A232-A232.
Dunbar, N.W., Kurbatov, A.V., and McIntosh, W.C., 2011, A Rich Tephra Record in the WAIS Divide (WDC06A) Ice Core: WAIS Divide ... Science Meeting, Sept. 28-29, 2011, La Jolla, CA, p. 21.
Dunbar, N.W., Kurbatov, A.V., and McIntosh, W.C., 2011, A Maturing Tephra Record in the West Antarctic Ice Sheet: Abstract presented at 2011 Fall Meeting, AGU, San Francisco, Calif, 5-9 Dec., v. V11D-2538 p. V11D-2538.
Dunbar, N.W., Kurbatov, A.V., McIntosh, W., and Koffman, B.G., 2011, Antarctic tephrochronology: From visible layers to cryptotephra: 11th International Symposium on Antarctic Earth Sciences, 10-16 July, Edinburgh, Scotland, p. PS5.12.
Dunbar, N.W., Kurbatov, A.V., Koffman, B.G., and Kreutz, K.J., 2010, Tephra Record of Local and Distal Volcanism in the WAIS Divide Ice Core, 2010 WAIS Divide Science Meeting: La Jolla, CA.
Dunbar, N.W., and McIntosh, W.C., 2009, Tephra as an absolute dating and correlation tool for Antarctic ice cores: Geochimica Et Cosmochimica Acta, v. 73, p. A312-A312.
Dunbar, N.W., McIntosh, W.C., and Kurbatov, A.V., 2008, Integrated tephrochronology of the West Antarctic region - Implications for a potential tephra record in the West Antarctic Ice Sheet (WAIS) divide ice core: Geochemica cosmochimica acta, v. 72 (supplement- abstract volume), p. A232-A232.
Dunbar, N.W., McIntosh, W.C., Kurbatov, A.V., and Wilch, T.I., 2007, Integrated tephrochronology of the West Antarctic region; implications for a potential tephra record in the West Antarctic ice sheet (WAIS) Divide ice core (peer reviewed extended abstract), in Cooper, A., Raymond, Carol, and the 10th ISAES Editorial Team, ed., Antarctica; A Keystone in a Changing World--Online Proceedings for the 10th International Symposium on Antarctic Earth Sciences, Volume U.S. Geological Survey Open-File Report 2007-1047: United States, U. S. Geological Survey : Reston, VA, United States.
Dunbar, N.W., McIntosh, W.C., Kurbatov, A.V., and Wilch, T.I., 2007, Integrated Tephrochronology of the West Antarctic Region- Implications for a potential tephra record in the West Antarctic Ice Sheet (WAIS) Divide Ice Core: 2007 WAIS Divide Science Meeting.
Creation and Review Dates
DIF Creation Date: 2012-06-19
Last DIF Revision Date: 2012-08-01