Documentation: Blue Ice Tephra II - Mt. DeWitt (N. Dunbar)

Blue Ice Tephra II - Mt. Dewitt

Data Set Summary

This data set is the result of a study of volcanic ash and rock fragment (tephra) layers in exposed bare blue ice areas on Mt. DeWitt, Antarctica (77.12°S, 159.51° E). Tephra samples were collected between 15 November 1996 and 15 January 1997.

Data include the following information for each sample site: a general description, electron microprobe analysis, GPS location, neutron activation analysis, and a visual description of the petrography. Data are provided as an Excel 97 data file (this file is also divided into various text files) and TIF images. Data are available via ftp.

The Antarctic ice sheets preserve a record of the volcanic ash layers and chemical aerosol signatures of local and distant volcanic eruptions. Correlation of individual tephra layers, or sets of layers, in blue ice areas will allow a better understanding of the geometry of ice flow in these areas. Tephra layers in deep ice cores can also provide unique time-stratigraphic markers in cores that are difficult to date.

Citing These Data:

Please cite these data as follows:

Dunbar, N. 2002. Blue Ice Tephra II - Mt. DeWitt. Boulder, CO, USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5GQ6VPV.

Overview Table

Category	Description
Parameter(s)	Backscattered electron images and GPS locations of blue ice tephra samples
Spatial coverage	Mt. Dewitt, Antarctica (77.12°S, 159.51°E)
Temporal coverage	Data were collected between 15 November 1996 and 15 January 1997.
Data format	Backscattered electron (BSE) images of blue ice tephra samples: TIF format Differential GPS locations Excel 97 (.xls)file Text (.txt) files (contain same information as the Excel file)
File sizes	Excel file: 140 KB Text files: 51 KB TIF files: 18 MB combined
Procedures for obtaining data	Data are available via ftp.

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments:

Investigator Name(s) and Affiliation(s):

Nelia Dunbar
New Mexico Bureau of Mines & Mineral Resources
Earth and Environmental Science Department
New Mexico Institute of Mining and Technology
Socorro, NM, USA

Technical Contact:

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgements:

This research was supported by NSF grant OPP-9527373 ("Collaborative Research: Volcanic Record in Antarctic Ice: Implications for Climatic and Eruptive History and Ice Sheet Dynamics of the South Polar Region").

2. Detailed Data Description:

Format and File Sizes:

bit*.tif: Backscattered electron images of blue ice tephra samples (TIF format, 771 KB each, 18 MB combined)
dewitt.xls: Includes worksheets for general field descriptions, GPS locations, and analyses for chemical composition, electron microprobe, neutron activation, and petrography of the tephra layers. (Excel 97 format, 140 KB). Columns include:
- Sample number
- Location (DeWitt)
- Station number
- Latitude (degrees South)
- Longitude (degrees East)
- Elevation (m)
Text files (derived from the Excel file):
- chem.txt - Chemical composition of tephra layers
- gps.txt - Differential GPS locations of tephra layers
- elect_micro.txt - Electron microprobe analyses of individual tephra shards
- petrography.txt - Petrography of the tephra samples
- neutron.txt - Neutron activation analyses of tephra
- general.txt - General field descriptions, plus strikes and dips of tephra layers
Reference_map.gif and GPS_tephra_map.gif: Maps of sampling locations (GIF format, 136 KB combined)

Spatial Coverage:

Blue ice tephra samples were collected from Mt. DeWitt, Antarctica (77.12°S, 159.51°E).

Study Area Location Map:

Mt. Dewitt

See Dunbar's Maps: Blue Ice Tephra II - GPS and Reference Maps sampling location maps.

Temporal Coverage:

Data were collected between 15 November 1996 and 15 January 1997.

3. Data Access:

Data are available via ftp.

Related Data Collections:

Tephra in Siple and Taylor Dome Ice Cores

Blue Ice Tephra II: Brimstone Peak

4. Data Acquisition and Processing:

Because of their ease of access and sampling, blue ice areas offer an alternative to deep ice cores in the reconstruction of regional and possible global volcanic records. Dunbar sampled and mapped volcanic ash (tephra) layers in exposed bare blue ice areas on Mt. Dewitt, Antarctica. She processed backscatter electron images of tephra samples with a Cameca SX-100 microprobe.

Notes on the neutron activation analysis:

INAA was performed on separated samples at New Mexico Institute of Mining and Technology after having undergone irradiation at the University of Missouri Research Reactor.
Irradiation took place for approximately 40 hours at a flux of 2.5x1013N cm-2 s-1.
Analytical errors, based on replicate analysis of samples, to 1 sigma, are as follows for major element: FeO ± 0.01 wt%; Na2O ± 0.04 wt%, and for trace elements (in ppm), Sc±0.04, Cr±12, Co±0.13, Ni±1, Zn±1, As±0.7, Br±0.07, Rb±0.8, Sr±0.7, Sb±0.1, Cs±1.4, Ba±10, La±1.8, Ce±1.4, Nd±0.7, Sm±0.07, Eu±0.14, Tb±0.02, Yb±0.07, Lu±0.01, Hf±0.12, Ta±0.04, Ta±0.04, W±0.05, U±0.02, Th±1.

Notes on the electron microprobe analysis:

Analyses are made using a Cameca SX-100 electron microprobe. Geochemical quantities are in weight %. Analyses are normalized to 100 wt.%, and Na2O is normalized to the value obtained by neutron activation analysis. Analytical precision, based on replicate analyses of standard reference materials of similar composition to the unknowns, are as follows (all in wt.%): SiO2±0.47, TiO2±0.03, FeO±0.06, MnO±0.06, MgO±0.07, CaO±0.02, Na2O±0.55, K2O±0.27, P2O5±0.02, Cl±0.07.

5. References and Related Publications:

Dunbar, N., G. Zielinski, and D. Voisins, D. 2002. Tephra layers in the Siple and Taylor Dome Ice Cores, Antarctica: Sources and Correlations. Journal of Geophysical Research 108 (B8).

Dunbar, N., R. Esser, and W. McIntosh. 1998. Englacial tephra layers in West Antarctica: Implications for the history of the West Antarctic Ice Sheet. Antarctic Journal of the U.S. XXXIII.

Dunbar, N., R. Esser, W. McIntosh, P. Kyle, and G. Zielinski. 1997. Englacial tephra layers in the East and West Antarctic ice sheets: Indicators of glacial flow patterns on ice sheet margins. EOS 78: F250.

Dunbar, N., R. Esser, W. McIntosh, G. Zielinski, and P. Kyle. 1997. Englacial tephra layers in West Antarctica: Implications for the history of the West Antarctic Ice Sheet. 4th Annual West Antarctic Ice Sheet workshop.

Dunbar, N., W. McIntosh, R. Esser, T. Wilch, and G. Zielinski. 1998. Direct dating and geochemical correlations of englacial tephra layers at two sites in West Antarctica, in Proceedings of the West Antarctic Ice Sheet Meeting Chapman Conference, Sept. 13-18, 1998, Orono, Maine, p. 18-19.

Dunbar, N., W. McIntosh, R. Esser, T. Wilch, and G. Zielinski. 1999. Englacial tephrochronology in West Antarctica: Constraints on ice sheet history, and potential longer ice records, in 8th International Symposium on Antarctic Earth Science, Victoria University of Wellington, New Zealand, p. 95.

Esser, R., P. Kyle, and N. Dunbar. 1999. 40Ar/39Ar chronology of the Pleiades Volcanic Centre, Northern Victoria Land, Antarctica: A potential source of late-pleistocene englacial tephra layers, in 8th International Symposium on Antarctic Earth Science, Victoria University of Wellington, New Zealand, p. 100.

Licht, K., N. Dunbar, A. Jennings, and J. Andrews. 1999. Sedimentological evidence for the maximum extent of grounded ice in the western Ross Sea, Antarctica during the last glacial maximum. Geological Society of America Bulletin 111(1): 91-103.

Wilch, T. 1998. Volcanic record of the West Antarctic ice sheet in Marie Byrd Land [PhD thesis]: New Mexico Institute of Mining and Technology. 160 pp.

Wilch, T., W. McIntosh, and N. Dunbar. 1999. Late quaternary volcanic activity in Marie Byrd Land: Potential 40Ar/39Ar dated time horizons in West Antarctic ice and marine cores. Geological Society of America Bulletin 111: 1563-1580.

6. Document Information:

Terms and Abbreviations

anorth - anorthite
BIT - blue ice tephra
BSE - backscattered electron (images)
bw - bubble wall
contam - contaminants
cpx - clinopyroxene
frag - fragments
ksp - potassium feldspar
low RI - low refractive index
mod - moderate
ol - olivine
pl - plagioclase feldspar
plag - plagioclase feldspar
pum - pumice
pyx - pyroxene
san - sanidine
Station - the name of the location data file for a GPS sample
vesic or ves - vesicular
xtals - crystals

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National Snow and Ice Data Center

Blue Ice Tephra II - Mt. Dewitt

Data Set Summary

Citing These Data:

Overview Table

Table of Contents

1. Contacts and Acknowledgments:

Investigator Name(s) and Affiliation(s):

Technical Contact:

Acknowledgements:

2. Detailed Data Description:

Format and File Sizes:

Spatial Coverage:

Study Area Location Map:

Temporal Coverage:

3. Data Access:

Related Data Collections:

4. Data Acquisition and Processing:

5. References and Related Publications:

6. Document Information:

Terms and Abbreviations

Document Creation Date:

Document Revision Date:

Document Curator:

Document URL:

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