Documentation for High-resolution Atmospheric CO2 during 7.4-9.0 ka, Version 1

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This data set provides a CO2 record from the Siple Dome ice core, Antarctica, that covers 7.4-9.0 ka (thousand years) with an 8- to 16-year resolution.

Detailed Data Description

This data set provides a carbon dioxide (CO2) record from the Siple Dome ice core, Antarctica, that covers 7.4-9.0 ka (thousand years) with an 8- to 16-year resolution. A small, about 1-2 ppm, increase of atmospheric CO2 during the 8200 years ago event (8.2 ka event) was observed. The increase is not significant when compared to other centennial variations in the Holocene that are not linked to large temperature changes. The results do not agree with leaf stomata records that suggest a CO2 decrease of up to ~25 ppm and imply that the sensitivity of atmospheric CO2 to the primarily Northern Hemisphere cooling of the 8.2 ka event was limited (Ahn et al. 2014).

We analyzed Siple Dome ice samples from 107 depth intervals that correspond to ages including the 8.2 ka event. For most depth intervals, we analyzed two samples from a mean depth range of 7 cm (corresponding to 2.6 years), and we report the mean depths of the replicates. Refer to Figure 1. The CO2 mixing ratios follow the NOAA WMOX2007 CO2 mole fraction scale (Ahn et al. 2014).

The timing of the 8.2 ka event in our Siple Dome gas records is well constrained by comparison of our new Siple Dome methane (CH4) record with the North Greenland Ice Core Project's (NGRIP) ice core δ18Oice record, which is a proxy for Greenlandic climate (North Greenland Ice Core Project Members 2004) because the abrupt cooling event in Greenland is essentially synchronous with a sharp CH4 decrease within ±4 years (Kobashi et al. 2007). Refer to Figure 1. The synchronized ages are on the GICC05 time scale (Greenland Ice Core Chronology 2005), which is constructed by annual layer counting and has been widely used for paleoproxy data (Rasmussen et al. 2006). Refer to Figure 1. We also utilized a high-resolution CH4 record from the Greenland Ice Sheet Project 2 (GISP2) ice core and correlated it with the Siple Dome record. Refer to Figure 1. We find that the CH4 change in the Siple Dome ice is similar to that of the GISP2 ice with an almost constant offset, supporting the contention that Siple Dome gas records are well preserved and have experienced only minimal firn smoothing. The offset in CH4 between the GISP2 and Siple Dome records is attributed to the inter hemispheric CH4 gradient caused by the predominance of Northern Hemisphere CH4 sources, for example, Etheridge et al. 1998 and Dlugokencky et al. 2005 (Ahn et al. 2014).

Note: Refer to Table 1 for a legend describing the letters A through C, the Yellow Box, and the Red Triangles in Figure 1.

atmospherice CO2 from Siple Dome Ice Core for 9.0 - 7.3 k.a.
Figure 1. Atmospheric CO2 from Siple Dome Ice Core for 9.0 - 7.3 k.a.Caption

Table 1. Legend for Figure 1
Letter Reference
Greenlandic temperature proxy, δ18Oice from NGRIP ice core (North Greenland Ice Core Project Members 2004).
Atmospheric CH4 records obtained from GISP2, Greenlandic (blue), and Siple Dome, Antarctic (red), ice cores (this study).
Atmospheric CO2 record from Siple Dome ice core, Antarctica (this study).
Yellow Box
Indicates the timing of the 8.2 ka event.
Red Triangles
Represent age tie points.
Note: To obtain the GICC05 time scale for Siple Dome ice records, we adjusted the existing chronology for synchronization at the age tie points (red triangles) (Severinghaus et al. 2009).

Figure 2 is an illustration of the effect of smoothing in the firn on Siple Dome ice core CO2 record. Three gray lines indicate imaginary atmospheric CO2 peak lasting (top) 200, (middle) 100, and (bottom) 50 years, respectively. The orange and blue curves represent the effect of firn smoothing on Siple Dome (EDC) ice core record.

Illustration of the Effect of Smoothing in the Firn on Siple Dome Ice Core
Figure 2. Illustration of the Effect of Smoothing in the Firn on Siple Dome Ice Core CO2 Record

Figure 3 is a comparison of CO2 records from leaf stomata and ice core records. Note: Refer to Table 2 for a legend describing the letters A through C in Figure 3.

Comparison of CO2 Records from Leaf Stomata and Ice Core Records
Figure 3. Comparison of CO2 Records from Leaf Stomata and Ice Core Records

Table 2. Legend for Figure 3
Letter Reference
Atmospheric CH4 from Siple Dome ice core, Antarctica (this study). The timing of the 8.2 ka event is indicated with the yellow box. The atmospheric CH4 decrease is essentially synchronous with the abrupt cooling in Greenland at the 8.2ka event (Kobashi et al. 2007).
Reconstructed atmospheric CO2 records from leaf stomata (Wagner et al. 2002). Black solid line and dashed gray lines indicate the mean CO2concentration and uncertainty range, respectively. The orange curve represents the stomata CO2 record convolved with the gas age distribution of Siple Dome ice core.
Ice core CO2 records from Siple Dome (red, this study), Taylor Dome (green), and Dome C (brown), Antarctica. We added an interlaboratory offset of 1.5ppm CO2 on the Taylor Dome and Dome C records.

Data are provided in Microsoft Excel (.xlsx) format.

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File and Directory Structure

Data are available on the FTP site in the directory. Within this directory, there is one file: Siple_Dome_CO2_7.4_9.0ka.xlsx.

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File Size

19 KB

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Spatial Coverage

Siple Dome Ice Core:
Southernmost Latitude: -81.66°
Northernmost Latitude: -81.66°
Westernmost Longitude: -148.82°
Easternmost Longitude: -148.82°

Spatial Resolution

Siple Dome Ice Core:
Min Depth: 490.19 m
Max Depth: 538.52 m

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Temporal Coverage

Paleo Temporal Coverage: 7.4 ka to 9.0 ka

Temporal Coverage: The data were collected between 1997 and 1999.

Temporal Resolution

An 8- to 16-year resolution.

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Parameter or Variable

Ice Core Depth
Ice Core Gas Age
CO2 concentration
CO2 Uncertainty
Number of Sample Replicates

Sample Data Record

The following Sample Data Record is of the Siple_Dome_CO2_7.4_9.0ka.xlsx data file.

sample data
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Software and Tools

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Data Acquisition and Processing

Replicate measurements were typically done on different days within three months. Each ice sample weighed about 8 - 9 g after trimming >0.5 cm from all surfaces. The analytical methods were greatly improved from the previous ones (Ahn et al. 2004) and the details are reported in (Ahn et al. 2009). Briefly, samples were placed in a double-walled stainless steel vacuum chamber at -35°C, cooled using cold ethanol circulation between the walls, and then crushed with steel pins, affixed to a pneumatically actuated linear motion feedthrough. Air liberated from the ice was dried in a cold stainless steel coil at -85°C and then cryotrapped in ~6 cm3 stainless steel sample tubes at -262°C. After warming the trapped air to room temperature and expanding to a 5 cm3 stainless steel sample loop, the CO2 mixing ratio was measured with an Agilent 6890N Gas Chromatograph (GC) with flame ionization detector, with nickel catalyst conversion of CO2 to CH4 prior to measurement.

The pressure in the loop was measured with an MKS Baratron® Capacitance Manometer (accuracy better than 0.15 percent). CO2 peak area was divided by the sample pressure and the results quantified with similar measurements of standard air. Daily calibration curves used several measurements of standard air with 291.13 ppm CO2(WMOX2007 CO2 mole fraction scale). Each air sample was measured twice. Daily corrections for the dry extraction and GC analysis were done using several air standards (291.13 ppm) that were introduced over the ice samples and transported to sample tubes mimicking the procedure of the air samples from ice.

Data reproducibility for the same depth intervals measured 1-3 months apart shows a pooled standard deviation of 0.5 ppm. We also analyzed Taylor Dome samples and compared our results with those previously analyzed at the University of Bern (Indermühle et al. 1999). We find that our results are 1.5 ppm higher than those from the University of Bern. Assuming the difference is an inter-laboratory offset, we find that our Siple Dome CO2 record agrees well with those from Taylor Dome and Dome C within 4 ppm, part of which could be attributed to the relative age uncertainty on multi-centennial to millennial timescales and aliasing of the atmospheric signal in the low resolution Dome C and Taylor Dome.

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References and Related Publications

Contacts and Acknowledgments

Edward J. Brook
Oregon State University
Department of Geosciences
104 Wilkinson Hall
Corvallis, OR 97331-5506

Jinho Ahn
School of Earth and Environmental Sciences
Seoul National University
599 Kwanak-ro, Kwanak-gu, Seoul 151742, South Korea


This research was supported by NSF OPP Grant Number 0944764-ANT.

Document Information

Document Creation Date

June 2014