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Simmonds, PG, Derwent RG, Manning AJ, Fraser PJ, Krummel PB, O'Doherty S, Prinn RG, Cunnold DM, Miller BR, Wang HJ, Ryall DB, Porter LW, Weiss RF, Salameh PK.  2004.  AGAGE observations of methyl bromide and methyl chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998-2001. Journal of Atmospheric Chemistry. 47:243-269.   10.1023/B:JOCH.0000021136.52340.9c   AbstractWebsite

In situ AGAGE GC-MS measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998-2001) reveal a complex pattern of sources. At Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr(-1) (CH3Br) and 2.6% yr(-1) (CH3Cl), and mean northern hemisphere baseline mole fractions of 10.37 +/- 0.05 ppt and 535.7 +/- 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH3Br and CH3Cl also show annual decreases in their baseline mixing ratios of 2.5% yr(-1) and 1.5% yr(-1), respectively. Mean baseline mole fractions were 7.94 +/- 0.03 ppt (CH3Br) and 541.3 +/- 1.1 ppt (CH3Cl). Although CH3Cl has a strong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH3Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).

Klatt, O, Roether W, Hoppema M, Bulsiewicz K, Fleischmann U, Rodehacke C, Fahrbach E, Weiss RF, Bullister JL.  2002.  Repeated CFC sections at the Greenwich Meridian in the Weddell Sea. Journal of Geophysical Research-Oceans. 107   10.1029/2000jc000731   AbstractWebsite

[1] Repeated observations of the tracer chlorofluorocarbon-11 (CFC-11) for a section along the Greenwich Meridian from Antarctica (70degreesS) to about 50 S are presented for the period 1984-1998. The CFC sections display a highly persistent pattern. A middepth CFC minimum in the central Weddell Sea is bounded laterally by elevated levels of dissolved CFCs at the southern margin of the Weddell Basin and by a column of elevated CFC concentrations around 55degreesS near to the northern margin. Part of the latter column covers waters of the Antarctic Circumpolar Current, which indicates that a moderate portion of these waters was ventilated in the Weddell Sea. Deep CFC maxima adjoining the southern and northern margins of the Weddell Basin indicate advective cores of recently ventilated waters. The southern core supports previous notions of deep water import into the Weddell Sea from the east. For all deep and bottom waters, the portions ventilated on the CFC timescale (similar to50 years) are small. Effective initial CFC saturations for these portions are estimated to be between 60 and 70%, using in part new data from off the Filchner-Ronne Ice Shelf. For various CFC features along the section (mostly advective cores), ventilated fractions and mean ages of these fractions were obtained (with error limits). The procedure was to fit an age distribution of a prescribed form to CFC-11 time series for these features, constructed from the various realizations of the CFC section. The ages are between 3 and 19 years, and the ventilated fractions range between 6 and 23%, indicating a rather limited ventilation of the interior Weddell Sea subsurface layer waters on the CFC timescale. It is shown that the concurrent CFC-12 data provide little additional information. The work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions.