Visible Stratigraphic Dating, Siple Dome and Upstream C Cores

Summary

This data set is part of the West Antarctic Ice Sheet cores (WAISCORES) project, an NSF-funded project to understand the influence of the West Antarctic Ice Sheet on climate and sea level change. WAISCORES researchers acquired and analyzed ice cores from the Siple Dome, in the Siple Coast region, West Antarctica.

This data set includes melt layers and annual layer data for Siple Dome cores A through J, and upstream core C (UpC). Cores were examined on a light table after the core had been sectioned longitudinally and samples removed for isotopic, chemical, and other analyses, and after the surface had been smoothed using a planer. Major stratigraphic features were noted, such as coarse-grained and fine-grained firn at shallow depths, and coarse-bubbled and fine-bubbled ice at greater depth. Melt layers were identified as bubble-free or nearly-bubble-free zones. Core lengths ranged from 30 to 133 meters.

Data in this collection were obtained in the summer of 1997. The data set is available via FTP as ACSII data (.dat), metadata (.meta) and text (.txt) files.

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Alley, R. B. , 1997. Visible Stratigraphic Dating, Siple Dome and Upstream C Cores. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N53F4MHS.

Overview Table

Category	Description
Data format	ACSII data (.dat), metadata (.meta), and text (.txt)
Spatial coverage and resolution	Southernmost Latitude: -81° Northernmost Latitude: -81° Westernmost Longitude: -149° Easternmost Longitude: -149°
Temporal coverage and resolution	Data were collected in 1997
Tools for accessing data	Data are available via FTP.
File naming convention	psumeltb.dat psumelti.dat psuvise.dat
File size	Files in this data set range in size from 1KB to 194 KB. Total file size is less than 500 KB
Parameter(s)	Bottom age and depth Melt layer year and depth Confidence

Table of Contents

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(s)

Richard Alley
Pennsylvania State University
306 Deike Building City:
University Park Province, PA 16802

Technical Contact

Acknowledgements

This research was supported by NSF OPP grant 9526374.

2. Detailed Data Description

Format

The data set is available via FTP as data (.dat), metadata (.meta), and text (.txt) files

File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/waiscores/alley/ directory. Within this directory, there are a total of 21 files. Nineteen data files contain melt data and visible stratigraphic data information for Siple Dome ice cores A through J and Upstream core C (UpC). Two metadata files, psuvis.meta and psumelt.meta, contain researcher's notes on data processing for the two layer dating techniques.

File Naming Convention

Files are named according to the following convention and as described in Table 1:
Note. Melt layer data for Siple Dome ice core A is listed in the file sdma_years.txt.

Example: psumeltb.dat, psuvisb.dat,

where:

Table 1. File Naming Convention

Variable	Description
psu	Pennsylvania State University
melt	Melt data
vis	Visual stratigraphy data
b	Siple Dome ice core identification, in this case Siple Dome ice core B
.dat	File extension

 

File Size

Files in this data set range in size from 1KB to 194 KB.

Spatial Coverage

Southernmost Latitude: -81°
Northernmost Latitude: -81°
Westernmost Longitude: -149°
Easternmost Longitude: -149°

Temporal Coverage

The data in this collection were collected and analyzed in 1997.

Parameter or Variable

Parameter Description

This data set contains files with melt layer data and visual stratigraphy data for Siple Dome ice cores A-J and the Upstream C (UpC) Core.

Melt layer files, such as psumeltb.dat, include bottom age and depth, listed in the heading, and a list containing the following parameters:

Table 2. Melt Layer Data Parameters

Parameter	Description
melt layer year	Layer age in years counted from the surface
confidence	0.5: Possible melt, but not both convincing and likely to be recognizable after >50% strain thinning; 0.75: Probable melt, count in most applications; 1: Melt, little or no doubt.
depth	Meters from surface

 

Visual stratigraphy files, for example psuvisb.dat, contain two columns, described in Table 3:

Table 3. Visual Stratigraphy Data Parameters

Parameter	Description
depth of annual layer	Depth of layer in meters from surface
confidence	3: Clear indication 2: Fair indication 1: Poor indication 0.5: Something present, but not picked as a summer 0: Interpolated where visible examination too difficult for choices, as in badly fractured or wafered core

 

Sample Data Records

Melt layer:

Melt Layer Year	Confidence	Depth
19	1	5.065

Visual stratigraphy:

Depth of annual layer (m)	Confidence
0.200	1

Error Sources

Based on independent layer counts, the researchers estimated accuracy at 10 percent or better. For more information on the intercomparisons attempted by Penn State researchers, please see the metadata file, psuvis.meta, available via FTP.

3. Data Access and Tools

Data Access

Data is available via FTP.

Volume

The entire data set is less than 500 KB.

Software and Tools

Data can be accessed using standard spreadsheet software.

Related Data Collections

• Antarctic Glaciological Data Center (AGDC)
• WAISCORES

4. Data Acquisition and Processing

Data Acquisition Methods

Melt Layers

Melt layers were identified as bubble-free or nearly-bubble-free zones. Ambiguity is introduced by thin crusts, which are approximately 1 mm thick, typically nearly uniform in thickness, and may result from multiple factors, including sun, drizzle, and wind packing. Crusts may occur in non-summer snow. To avoid counting crusts as melt layers, the researchers required that melt features be at least 2 mm thick. Ideally, melt features also show irregularity in thickness; in practice, thick features almost always do. Confidence levels were assigned as described in Table 2. For more information on melt layer data acquisition methods, see the researchers' notes in the file psumelt.meta, available via FTP.

Visual Stratigraphy

Ice cores were examined on a light table over fluorescent tubes. Visible examination occurred after the core had been sectioned longitudinally and samples removed for isotopic, chemical, and other analyses, and after the surface had been smoothed using a planer and then sampled electrically by Kendrick Taylor and other scientists. All core sections were transferred to core trays of clear plastic designed and built by the National Ice Core Laboratory (NICL), which has a curved cross-sectional aspect that conforms closely to the exterior of the core. For more information on visual stratigraphy data acquisition methods, see the researchers' notes in the file psuvis.meta, available via FTP.

 

5. References and Related Publications

Alley, R. B. 2000. The Younger Dryas cold interval as viewed from central Greenland. Quaternary Science Reviews 19, 213-226.

Alley, R. B. and P. U. Clark. 1999. The deglaciation of the northern hemisphere: a global perspective. Annual Reviews of Earth and Planetary Sciences 27, 149-182.

Alley, R. B. and K. M. Cuffey. 2001. Oxygen- and hydrogen-isotopic ratios of water in precipitation: Beyond paleothermometry. In J.W. Valley and D. Cole, eds., Stable Isotope Geochemistry, Reviews in Mineralogy and Geochemistry, v. 43, Mineralogical Society of America.

Alley, R. B. and J. J. Fitzpatrick. 1999. Conditions for bubble elongation in cold ice-sheet ice. Journal of Glaciology 45, 147-154.

Alley, R. B., A. M. Agustsdottir and P. J. Fawcett. 1999. Ice-core evidence of Late-Holocene reduction in north Atlantic ocean heat transport, in Clark, P. U., R. S. Webb and L. D. Keigwin, eds., Mechanisms of Global Climate Change at Millennial Time Scales, Geophysical Monograph 112, American Geophysical Union, Washington, DC, 301-312.

Alley, R. B., S. Anandakrishnan and P. Jung. 2001. Stochastic resonance in the North Atlantic. Paleoceanography 16, 190-198.

Alley, R. B., S. Anandakrishnan, P. Jung and A. Clough. 2001 Stochastic resonance in the north Atlantic: Further Insights. In D. Seidov, B. J. Haupt and M. Maslin, eds., The Oceans and Rapid Climate Change: Past, Present and Future, Geophysical Monograph 126, p. 57-68.

Alley, R. B., E. J. Brook and S. Anandakrishnan. 2002. A northern lead in the orbital band: North-south phasing of ice-age events. Quaternary Science Reviews, 21, 431-441.

Alley, R. B., P. U. Clark, L. D. Keigwin and R. S. Webb. 1999. Making sense of millennial-scale climate change, in Clark, P. U., R. S. Webb and L. D. Keigwin, eds., Mechanisms of Global Climate Change at Millennial Time Scales, Geophysical Monograph 112, American Geophysical Union, Washington, DC, 385-394.

Clark, P. U., R. B. Alley and D. Pollard. 1999. Northern hemisphere ice-sheet influences on global climate change. Science 286, 1103-1111.

Spencer, M., R. B. Alley, and T. T. Creyts. 2001. Firn densification: an empirical model. Journal of Glaciology 47(159) 671-676.

Steig, E. J. and R. B. Alley. 2002. Phase relationships between Antarctic and Greenland climate records. Annals of Glaciology 35(1), 451-456.

The following related documents are available on NSIDC's Web site.

Table 4. Related Documents

Document	Description	URL
WAISCORES Major Findings: Richard Alley	Project report by Alley, et. al.	http://nsidc.org/data/waiscores/findings/alley_findings.html
WAISCORES	Project Web site	http://nsidc.org/data/waiscores/data.html
Antarctic Glaciological Data Center	Data center Web site	http://nsidc.org/agdc/

6. Document Information

Acronyms

The following acronyms are used in this document.

Table 5. Acronyms a

Acronym	Description
.DAT	Data file extension
FTP	File Transfer Protocol
NICL	National Ice Core Laboratory
NSIDC	National Snow and Ice Data Center
URL	Uniform Resource Locator
WAISCORES	Western Divide West Antarctic Ice Cores

Document Creation Date

11 March 2009

Document URL

http://nsidc.org/data/docs/agdc/nsidc0121_alley/index.html