Atmospheric δ¹⁴C Record from Wellington

Graphics    Digital Data

Investigators

M.R. Manning, W.H. Melhuish
National Institute of Water and Atmospheric Research, Ltd.,
Climate Division,
Gracefield Road, Gracefield,
P.O. Box 31-311,
Lower Hutt, New Zealand

Period of Record

1954-93

Methods

Trays containing ~2 L of 5 normal NaOH carbonate-free solution are typically exposed for intervals of 1-2 weeks, and the atmospheric CO₂ absorbed during that time is recovered by acid evolution. Considerable fractionation occurs during absorption into the NaOH solution, and the standard fractionation correction (Stuiver and Polach 1977) is used to determine a δ ¹⁴C value corrected to δ ¹³C = -25 per mil.

Some samples reported here were taken using BaOH solution or with extended tray exposure times. These variations in procedure do not appear to affect the results (Manning et al. 1990). A few early measurements were made by bubbling air through columns of NaOH for several hours. These samples have higher δ ¹³C values. Greater details on the sampling methods are provided in Manning et al. (1990) and Rafter and Fergusson (1959).

Wellington, New Zealand
41°18' S, 174°48' E

Trends

These measurements of ¹⁴C in atmospheric CO₂ at Wellington constitute one of the longest isotopic records available, particularly for the Southern Hemisphere, and support the overall decline in atmospheric ¹⁴CO₂ reported by others. The ¹⁴C record for Wellington in 1965 shows a peak occurring roughly 1 year later than that observed in the Northern Hemisphere (Nydal and Lovseth 1983; Levin et al. 1985).

Manning et al. (1990) reported a seasonal component for the Wellington record and a cycle of decreasing amplitude for the seasonal component. Manning et al. (1990) reported that up to 1980, the cycle had a maximum in March and a minimum in August along with a negative anomaly in December. The amplitude of the cycle for this period decreased steadily from a peak-to-peak range of 20 per mil in 1966 to 3 per mil in 1980. From 1980 onwards, Manning et al. (1990) found that a different cycle emerged: the new cycle had an amplitude of ~5 per mil, a maximum in July-August, and a minimum in January.

References

• Levin, I., B. Kromer, H. Schoch-Fischer, M. Bruns, M. Münnich, D. Berdau, J.C. Vogel, and K.O. Münnich. 1985. 25 years of tropospheric ¹⁴C observations in central Europe. Radiocarbon 27(1):1-19.
• Manning, M.R., D.C. Lowe, W.H. Melhuish, R.J. Sparks, G. Wallace, C.A.M. Brennninkmeijer, and R.C. McGill. 1990. The use of radiocarbon measurements in atmospheric studies. Radiocarbon 32:37-58.
• Nydal, R., and K. Lovseth. 1983. Tracing bomb ¹⁴C in the atmosphere 1962-1980. Journal of Geophysical Research 88:3621-42.
• Rafter, T.A., and G.J. Fergusson. 1959. Atmospheric radiocarbon as a tracer in geophysical circulation problems. In United Nations Peaceful Uses of Atomic Energy, Pergamon Press, London.
• Stuiver, M., and H.A. Polach. 1977. Discussion: Reporting of ¹⁴C data. Radiocarbon 19(3):355-63.

11/26/97