CAPE GRIM

Period of Record

Trends

In the ALE/GAGE program, the site in the middle-latitude of the Southern Hemisphere is at Cape Grim, on the northwest coast of Tasmania, Australia. The site is 80 m from the shoreline and 93 m above mean sea level. (From 1980 through 1982 the station was temporarily moved 165 m north of the previous site to a location ~35 m from the shoreline and 80 m above mean sea level.) The site generally receives unpolluted oceanic air from the southwest, with rare but increasingly frequent instances of pollution originating in Tasmania or the Australian mainland. The site at Cape Grim was initially supervised jointly by R.A. Rasmussen and A.J. Crawford of the Oregon Graduate Institute and by P.J. Fraser of the Commonwealth Scientific and Industrial Research Organisation's (CSIRO's) Division of Atmospheric Research. Currently, P.J. Fraser supervises the measurements here. Measurements at Cape Grim began in July 1978 and continued as part of ALE through June 1985. Since December 1981, measurements were also collected as part of GAGE. Following the termination of ALE, measurements at Cape Grim continued as part of GAGE for the remainder of the record period (Fraser and Derek 1992).

The monthly mean mixing ratio of CFC-11 increased from 134.9 parts per trillion (ppt) in July 1978 to 256.6 ppt in December 1991. Cunnold et al. (1994) reported that the average rate of increase was 9.0±0.1 ppt/year from July 1978 to June 1988 but dropped to 7.8±0.2 from July 1988 to June 1991. From July 1978 to December 1991, the mixing ratio of CFC-12 increased from 251.3 to 490.3 ppt. For CFC-12, Cunnold et al. (1994) determined that the average rate of increase was 17.4±0.1 ppt/year from July 1978 to June 1988 and 16.8±0.4 from July 1988 to June 1991. For both CFC-11 and CFC-12, these trends are highly significant (P < 0.0001). According to Cunnold et al. (1994), the data from Cape Grim also show a consistent seasonal cycle for CFC-11 and CFC-12.

The time series of the monthly mean mixing ratios of N₂O is generally linear, and the values show a highly significant (P < 0.0001) trend during the period of record. The monthly mixing ratio increased from 297.7 parts per billion (ppb) in July 1978 to 308.4 ppb in December 1991. For the 10-year period July 1978 to June 1988, Prinn et al. (1990) calculated that the mixing ratio of N2O increased by an average of 0.90±0.05 ppb/year. In addition, the data were found to exhibit a statistically significant quasi-biennial (tau = 2.25 years) oscillation with an amplitude of 0.28 ppb.

Cape Grim
Tasmania, Australia
Promontory seashore
40° 41' S, 144° 41' E
93 m above MSL

Cape Grim Mixing Ratios Graph

• Monthly average CFC-11, CFC-12, and N₂O mixing ratios at Cape Grim