The 1991-1992 atmospheric methane anomaly: Southern Hemisphere super(1) super(3) C decrease and growth rate fluctuations

• Published in: Geophysical research letters Vol. 24; no. 8; pp. 857 - 860
• Main Authors: Lowe, David C, Manning, Martin R, Brailsford, G W, Bromley, A M
• Format: Journal Article
• Language: English
• Published: 01.01.1997
• Subjects: Scott Base, Antarctica; Baring Head, New Zealand
• ISSN: 0094-8276

Measurements of atmospheric methane from 1989-1996 at Baring Head, New Zealand, and at Scott Base, Antarctica show a seasonal cycle in the mixing ratio with a peak to peak amplitude of 28 ppb. This is superposed on a trend varying between 16 ppb yr super(-) super(1) and near zero. delta super(1) super(3) C values also show a seasonal cycle, with an amplitude of 0.1-0.30/00, approximately 6 months out of phase with the mixing ratio cycle. A pronounced negative anomaly in delta super(1) super(3) C occurred in 1992 with annual average values dropping from -47.080/00 to -47.280/00. From 1992 to 1996, average delta super(1) super(3) C values recovered slowly at an average rate of about 0.040/00 yr super(-) super(1) . The simultaneous changes in the mixing ratio growth rate and delta super(1) super(3) C together with the rapid drop and slow recovery in the latter provide a stringent test of possible causes. Although a combination of causes cannot be ruled out, decreased emissions from an isotopically heavy source such as biomass burning best meet the constraints of the data.