When the atmospheric turbulent flux of a minor constituent such as CO, (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived.If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre-dried and brought to a common temperature, then again no correction is required: while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required.If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are requirea.These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In C02 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per Cent but will sometimes exceed 10 per cent. heat flux, by Bakan (1978)* and by Jones and Smith (1978), came to our notice respectively shortly before and shortly after submission of the present paper. We are not aware of any other previous treatments in either meteorology or physical chemistry (cf. Bird et al. 1960; Hirschfelder et al. 1964) which deal with the density effects in turbulent transfer in the way required here. We note that the molecular 'thermal diffusion' process in gases, with which corresponds the 'Soret effect' in liquids, and which is discussed by Grew and Ibbs (1952), Monchick and Mason (1967), and Grew (1969), is quite different in nature from (and more complicated than) the effect of a mean temperature gradient on the transfer relationship for a constituent as discussed in the present paper.Our initial motivation in this topic arose in the evaluation of CO, flux from the fluxgradient relationship, with the mean CO, concentration at different heights measured by use of an infrared gas analyser (IRGA). It is common practice (Monteith and Szeicz 1960; Denmead 1969; Uchijima 1970;Pearman and Garratt 1973) to pre-dry the air, in order to avoid the difficulty of infrared absorption by the water vapour bands. Since the volume of any sample of air is reduced by drying, the density of the CO, component is increased, ...

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To determine in detail how the concentration of tropospheric methane has changed from preindustrial until recent times, an ice core with remarkably fine air-age resolution was investigated. The core, called DE08, contains air from as recent as 1978 with an age resolution (80% air-age distribution width) of about 14 years. It was drilled from a region of Law Dome, Antarctica with extremely high snow-accumulation rate ( 1160 kg m -2 yr-1 ). The ice chronology was determined from the observed chemical and isotopic seasonal variations, verified against a volcanic horizon. The calculated air-age includes the effects of bubble close-off, sealing of the firn and diffusive mixing of air in the firn. The mean air-age was 35 years younger than the host ice except for air in summer ice layers which was 37 years younger than the host ice. The extracted ice-core air was analysed for methane using gas chromatography with flame-ionisation detection.Adjustments of -6 ppbv and + 0.3 % were made to the measured concentrations to allow for the effects of the extraction process and gravitational fractionation respectively. Methane concentrations in the DE08 record increased from 823 parts per billion by volume (ppbv, in dry air) in 1841 to 1481 ppbv in 1978. The measurement precision was ± 22 ppbv ( 1u ). The similarity of the methane records from the DE08 ice core and from Cape Grim, Tasmania implies that there was insignificant modification during the enclosure of air in the ice or during its recovery and analysis. Methane concentrations in the period from 1951 to 1978, which were previously estimated from sporadic and inferred data, are particularly well defined in this core. The DE08 record shows that methane growth rates have generally increased since the onset of the industrial revolution to a level of 14 ppbv year-1 (about 1 % per year) by the 1970s. The exception was between about 1920-1945 when the growth rate stabilised at about 5 ppbv year-1 .

A technique for extracting and analysing large air samples from bubbles occluded in an Antarctic ice core is discussed . Core samples of up to 1400 g were milled to release approximately 120 cm s of air, which was dried, collected in a cold finger and then analysed by gas chromatography. The concentrations of atmospheric carbon dioxide (C0 2 ), methane (CH.) and nitrous oxide (N 2 0) over the past 450 years have thus been revealed. Measurements of a chlorofluorocarbon (CCI 2 F 2 ) in the ice-core air were used to check core quality and the air-occlusion process.The ice core, designated BHD, was thermally drilled from the summit of Law Dome, Antarctica, where the average accumulation rate is 0.65 m a-I water equivalent and the annual average temperature is -22 ·C. Ice dating was achieved by counting annual cycles of oxygen -isotope ratio and d.c. conductivity, and air dating was deduced from the density profile.The results show the pre-industrial concentrations of the gases to be 288 ± 5 ppm volume for CO 2 , 800 ± 50 ppb volume for CH. and 285 ± 10 ppb volume for N 2 0.

A two-dimensional global atmospheric diffusion simulation model is used to establish zonal and monthly average net surface fluxes of carbon dioxide (CO2) which are consistent with the variations in CO,. concentration observed at six monitoring stations distributed globally. These fluxes represent the zonally averaged net ecosystem production of primarily terrestrial biosphere. Annually, the global net ecosystem production during the photosynthetically more active season removed 6.8 x 1012 kg of carbon from the atmosphere, returning it during the less active winter months. This turnover represents about 14% of the annual continental net primary production of carbon and 0.8% of the total terrestrial biomass. During the growing season, net ecosystem production appears to be relatively independent of latitude in the northern hemisphere (-6 x 10 -9 kg carbon m -•-s-X). The model indicates that time correlations between the CO2 concentration at different altitudes of the northern hemisphere with the interhemispheric advection of air results in a net interhemispheric CO•. flux which becomes zero when the South Pole COe concentration is on average 0.92 ppmv above that at Mauna Loa, Hawaii. The influence of both the net and the gross atmospheric biospheric exchange of carbon on the atmospheric stable carbon isotope ratio is modeled. On time scales of a year the gross turnover of carbon has an insignificant effect, and all isotopic effects can be related to the net exchanges. It is argued that as with concentration, long-term trends in isotopic composition will be best observed in the southern hemisphere.It was argued that the seasonality of CO,. concentration is well known, at least for a small number of background locations, and given an adequate model of the atmospheric mixing, it should be possible to generate a set of global surface exchange rates consistent with the observations. In this paper we report Copyright ¸ !980 by the American Geophysical Union.Paper number 80C0348. 0148-0227/80/080C.034850 ! .00 preliminary attempts at such a simulation. The surface exchange rates generated are used to calculate the net ecosystem production of latitude zones for comparison with the net primary production of those zones. The significance of simultaneous observations of the stable carbon isotopic composition of atmospheric CO,. is discussed. MODELThe model used in this study has been developed for use in a number of projects concerned with the global distribution of atmospheric constituents [e.g., Hyson et al., !980], and it will be described in detail elsewhere. Briefly, it is a two-dimensional zonally averaged multiple-box model in which vertical and horizontal transport is assumed to occur via Fickian diffusion and advection. While the number of boxes in the