Drake Passage Radiocarbon (Δ¹⁴C) of Dissolved Inorganic Carbon (DIC)

Measurements from R/V Laurence M. Gould Transects

T. P. Guilderson^1,2, C. Sweeney^3,4, P. D. Quay⁵, T. Newberger³, and J. Stutsman⁵

¹Center for Accelerator Mass Spectrometry, LLNL
²Institute of Marine Sciences, University of California ‐ Santa Cruz CA
³Earth System Research Laboratory, NOAA, Boulder CO
⁴Cooperative Institute for Research in Environmental Sciences, University of Colorado ‐ Boulder CO
⁵School of Oceanography, University of Washington, Seattle WA

Data and Documentation Files      &nbsp

The following radiocarbon (¹⁴C) of dissolved inorganic carbon (ΣCO₂) has been determined on samples collected during hydrographic and transect cruises of the L. M. Gould (see map of the measurement locations).

All samples were prepared and analyzed at the Center for Accelerator Mass Spectrometry (CAMS), Lawrence Livermore National Laboratory. Radiocarbon results are reported according to the internationally standardized nomenclature put forth in Stuiver and Polach [1977]. Results presented as fraction modern contain corrections for both background subtraction (using ¹⁴C-free calcite) and δ¹³C on splits of the same extracted CO₂ used for ¹⁴C analyses and are equivalent to "F14C" [Reimer et al., 2004]. Conventional radiocarbon age (years BP) utilize the Libby half-life. Age-corrected Δ¹⁴C (‰) has been determined using the date of collection. Reproducibility of the Δ¹⁴C results is ±2.2‰ (1-sigma sd) based on random replicate analyses (n=30). It is this error that is reported.

Shipboard Sample Collection Methods

Samples (underway and from niskin bottles) are collected in pre-washed and baked (450°C) 250 or 500 ml ground glass- stoppered bottles using the following method. A length of Tygon tubing is attached to the Niskin bottle or seawater line and flushed for a few seconds. The end of the tubing is then placed at the bottom of the upright sample bottle and the bottle is filled, then overflowed with an amount equal to its volume if Niskin water volume permits, otherwise with at least half its volume. Flow is stopped as the Tygon tubing is removed from the top of the bottle to avoid any splashing in the top.

Using a syringe or turkey baster, 10 to 20cc are withdrawn off the top of the sample to lower the water level to approximately 1 cm below the neck of the bottle, avoiding backwash of water from the turkey baster into the sample. The ground glass joint of the bottle is wiped dry with Kimwipes. Then 100 µL of a saturated HgCl₂ solution (per 250 mL of seawater) is injected beneath the surface of the sample using an Eppendorf pipette. The ground-glass stopper, which has been pre-greased with Apiezon^® M grease, is then inserted straight into the bottle without twisting. If any air streaks in the grease seal are visible, the stopper is removed, cleaned, and regreased, then the bottle is resealed. Clips (if required for the neck-type of bottle) are placed on the necks of the bottles, and two heavy rubber bands are placed around the stopper and bottle to prevent leakage. The sample bottle is then inverted a couple of times to mix the HgCl₂ throughout the sample.

Laboratory Methods (Extraction, δ¹³C, Δ¹⁴C)

CO₂ is extracted from the DIC seawater sample using a modification of the helium stripping technique described by Kroopnick [1974] as described in Quay et al [1992]. The stripper is comprised of a glass tube with a stainless steel fitting and silicone-greased glass stopcock at the bottom (which connects to the He line), a glass frit which the He passes through, and a stainless steel fitting containing a 3-layer silicone rubber septum at the top. Approximately 1 mL phosphoric acid is injected into the stripper and bubbled with He for 10 minutes. The gas is then evacuated out of the stripper and the stripper is weighed. Then 80 to 125 mL of the sample is drawn into the stripper and it is weighed again to calculate the weight of water analyzed. A stainless steel needle pierces the septum and connects the stripper to the extraction line which has been evacuated and filled with helium. The sample is stripped with 99.997% pure He at a flow rate of about 200 mls/min for 20 minutes. Water is trapped out in two glass traps submerged in dewars containing a slush mixture of dry ice and isopropanol at -70°C. CO₂ is collected at -196°C in glass loop traps submerged in liquid N2. The δ¹³C is then measured on a Finnigan MAT 251 mass spectrometer at the University of Washington's School of Oceanography.

The efficiency of the extraction method is 100 ± 0.5 percent based on gravimetrically prepared Na₂CO₃ standards. The precision of the δ¹³C analysis is ± 0.02 ‰ based on a replicate analysis of standards and seawater samples.

Ampoules of CO₂ (sample splits) collected during stripping of DIC were shipped to the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory. CO₂ was, with an optimized carbon:catalyst ratio [Graven et al., 2007], quantitatively reduced to graphite in the presence of a metal catalyst [Vogel et al., 1987] and pressed into individual aluminum target holders. The ¹⁴C/¹³C ratio of each target was determined following the description presented in Guilderson et al., [2006]. Individual replicate DIC samples were not available for ¹⁴C analyses. Thus, to assess analytical reproducibility and on the assumption that extraction of ΣCO₂ is 100% quantitative and no additional uncertainty was introduced (consistent with the quality of the δ¹³C analyses), random ampoules of CO₂ were carefully split into two different graphite reduction reactors and processed/analyzed independently. Reproducibility of the Δ¹⁴C results is ±2.2‰ (1- sigma sd) based on random replicate analyses (n=30). It is this error that is reported.

Acknowledgements

Radiocarbon analyses were funded by the NSF Office of Polar Programs (ANT-0636905). Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48 and in part under Contract DEAC52- 07NA27344.

Please cite this dataset as:
Guilderson, T. P., C. Sweeney, P. D. Quay, T. Newberger, and J. Stutsman. 2012. Drake Passage Radiocarbon (Δ¹⁴C) of Dissolved Inorganic Carbon (DIC): Measurements from R/V Laurence M. Gould Transects. http://cdiac.ornl.gov/ftp/oceans/Drake_C14_data/. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/OTG.DRAKE_C14

References

• Graven, H. D., T.P. Guilderson, and R.F. Keeling, 2007. Methods for high precision measurements of atmospheric CO₂ at LLNL. Radiocarbon, 49, 349-356.


• Guilderson, T.P., E.B. Roark, S.R. Flood Page, C. Moy, and P.D. Quay, 2006. Sea Water Radiocarbon Evolution in the Gulf of Alaska: 2002 Observations. Radiocarbon, 48, 1-15.


• Kroopnick, P. The dissolved O₂-CO₂-¹³C system in the eastern equatorial Pacific. Deep-Sea Research, 21, 211-227.


• Quay, P. D., B. Tilbrook, and C. S. Wong, 1992. Oceanic uptake of fossil fuel CO₂: C-13 Evidence. Science, 256, 74-79.


• Reimer, P. J., Brown, T. A., & Reimer, R. W. 2004. Discussion: Reporting and calibration of postbomb C-14 data. Radiocarbon, 46(3), 1299-1304.


• Stuiver, M., and H. A. Polach, 1977. Discussion and reporting of ¹⁴C data, Radiocarbon, 19, 355- 363.


• Vogel, J. S., J. R. Southon, and D. E. Nelson, 1987. Catalyst and binder effects in the use of filamentous graphite for AMS. Nuclear Instruments and Methods In Physics, B29, 50-56.