Abstract. Atmospheric methane mixing ratios from 1000 A.D. to present are measured in three Antarctic ice cores, two Greenland ice cores, the Antarctic firn layer, and archived air from Tasmania

We present measurements of the stable carbon isotope ratio in air extracted from Antarctic ice core and firn samples. The same samples were previously used by Etheridge and co-workers to construct a high precision 1000-year record of atmospheric CO 2 concentration, featuring a close link between the ice and modern records and high-time resolution. Here, we start by confirming the trend in the Cape Grim in situ d13C record from 1982 to 1996, and extend it back to 1978 using the Cape Grim Air Archive. The firn air d13C agrees with the Cape Grim record, but only after correction for gravitational separation at depth, for diffusion effects associated with disequilibrium between the atmosphere and firm, and allowance for a latidudinal gradient in d13C between Cape Grim and the Antarctic coast. Complex calibration strategies are required to cope with several additional systematic influences on the ice core d13C record. Errors are assigned to each ice core value to reflect statistical and systematic biases (between ±0.025‰ and ±0.07‰); uncertainties (of up to ±0.05‰) between core-versus-core, ice-versus-firn and firn-versus-troposphere are described separately. An almost continuous atmospheric history of d13C over 1000 years results, exhibiting significant decadal-to-century scale variability unlike that from earlier proxy records. The decrease in d13C from 1860 to 1960 involves a series of steps confirming enhanced sensitivity of d13C to decadal timescale-forcing, compared to the CO 2 record. Synchronous with a ''Little Ice Age'' CO 2 decrease, an enhancement of d13C implies a terrestrial response to cooler temperatures. Between 1200 AD and 1600 AD, the atmospheric d13C appear stable.

We present measurements of the stable carbon isotope ratio in air extracted from Antarctic ice core and firn samples. The same samples were previously used by Etheridge and co‐workers to construct a high precision 1000‐year record of atmospheric CO2 concentration, featuring a close link between the ice and modern records and high‐time resolution. Here, we start by confirming the trend in the Cape Grim in situ δ13C record from 1982 to 1996, and extend it back to 1978 using the Cape Grim Air Archive. The firn air δ13C agrees with the Cape Grim record, but only after correction for gravitational separation at depth, for diffusion effects associated with disequilibrium between the atmosphere and firm, and allowance for a latidudinal gradient in δ13C between Cape Grim and the Antarctic coast. Complex calibration strategies are required to cope with several additional systematic influences on the ice core δ13C record. Errors are assigned to each ice core value to reflect statistical and systematic biases (between ± 0.025‰ and ± 0.07‰); uncertainties (of up to ± 0.05‰) between core‐versus‐core, ice‐versus‐firn and firn‐versus‐troposphere are described separately. An almost continuous atmospheric history of δ13C over 1000 years results, exhibiting significant decadal‐to‐century scale variability unlike that from earlier proxy records. The decrease in δ13C from 1860 to 1960 involves a series of steps confirming enhanced sensitivity of δ13C to decadal timescale‐forcing, compared to the CO2 record. Synchronous with a ‘‘Little Ice Age’′ CO2 decrease, an enhancement of δ13C implies a terrestrial response to cooler temperatures. Between 1200 AD and 1600 AD, the atmospheric δ13C appear stable.

This paper presents an attempt to recover the space-time structure of fluxes of CO 2 to the atmosphere over the period 1980-1995 from atmospheric concentration and isotopic composition measurements. The technique used is Bayesian synthesis inversion in which sources are aggregated into large regions and their strengths adjusted to match observed concentrations. The sources are constrained by prior estimates based on a priori knowledge. The input data are atmospheric CO 2 concentration measurements from the NOAA/CMDL network, 13CO 2 composition and O 2 /N 2 ratios measured at Cape Grim, Tasmania by CSIRO Atmospheric Research. The primary findings are a relatively large long-term mean ocean uptake of CO 2 , and seasonal fluxes over land with similar integrated magnitude, but smaller peak amplitude, compared with those derived by Fung and co-workers. Predicted interannual variability is smaller than reported in previous studies. The largest contributor is the oceanic tropics where fluxes vary on the time scale of the southern oscillation. There is evidence of longer time-scale variation in land uptake. Increases in ocean uptake and northern land uptake in the early 1990s are consistent with a response to the Mt. Pinatubo eruption.

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