Our understanding of biogeochemical and physical processes in the Southern Ocean, which are critically important to future anthropogenic CO₂ uptake and global climate, is limited by the sparse spatial and temporal coverage of existing oceanographic and atmospheric measurements. We will present high-precision horizontal atmospheric O₂ and CO₂ concentration gradients over the Southern Ocean from three independent observing networks. These measurements reveal that, relative to southern mid-latitudes and Antarctica, CO₂ concentrations over the Southern Ocean are high during winter and low during summer (Fig. 1). This suggests a seasonal variation between net CO₂ summertime uptake and wintertime release that is in disagreement with the T99 [Takahashi et al., 2002] dissolved pCO₂ climatology, which predicts year‑round CO₂ uptake, and with the OCMIP‑2 biological ocean general circulation models [BOGCMs, Doney et al., 2004], which either predict year-round CO₂ uptake or opposite seasonality with wintertime uptake and summertime release.

Variations in atmospheric oxygen (O₂) are a sensitive indicator of biogeochemical processes involved in the global carbon cycle.  To improve our understanding of these processes, we developed a system for continuous high precision measurements of atmospheric O₂ and CO₂ that is suitable for shipboard use.  This system was employed on two voyages in the Western Pacific sector of the Southern Ocean, in February 2003 and April 2004.  Elevated O₂ concentrations were observed south of New Zealand and across the Chatham Rise suggesting that these regions of ocean are outgassing O₂ in late summer to autumn.

The CARBOOCEAN consortium aims at an accurate scientific assessment of the marine carbon sources and sinks within space and time. It will determine the ocean’s quantitative role for uptake of atmospheric carbon dioxide (CO₂), the most important manageable driving agent for climate change. Since the ocean has the most significant overall potential as a sink for anthropogenic CO2, the correct quantification of this sink is a fundamental necessary condition for all realistic prognostic climate simulations. Target is to reduce the present uncertainties in the quantification of net annual air-sea CO₂ fluxes by a factor of 2 for the world ocean and by a factor of 4 for the Atlantic Ocean.

With the increasing temporal and spatial density of CO₂ flux and concentration observations from worldwide tower networks, the importance of interpreting the data is becoming more conspicuous. Previous work shows that tower observations might be able to catch synoptic, regional, and local signals of CO₂ simultaneously. Thus a study that can explain CO₂ transport and the response of the ecosystem to the weather change simultaneously is necessary and will help the development of the regional inverse modeling technique in the future.

Greenhouse gases Observing SATellite (GOSAT) of Japan is planned to be launched in 2008. GOSAT will be equipped with a FTS to monitor CO₂ column density globally. The FTS has three near infrared bands which cover 0.76 µm, 1.6 µm, and 2.0 µm spectral regions, respectively. Retrieval algorithms to estimate CO₂ and CH₄ column densities from these bands data are now being developed. We have investigated retrieval algorithms under the non-clear sky conditions. As one of these cases, a cirrus cloud parameter estimation was researched. The cirrus vertical profile (i.e., existing height) is estimated from the 0.76 µm band data. Strong water vapor absorption area is included in the 2.0 µm spectral band, so that the reflected radiance from a ground surface is absorbed completely by H₂O in this area. Thus the signal in this area is considered as path radiance caused by the cirrus clouds reflection, because there is little water vapor above the cirrus cloud top. By using this signal, the cirrus optical depth can be estimated, and then column densities of CO₂, CH₄ and H₂O are retrieved precisely.

The current WMO CO₂ Mole Fraction Scale consists of a set of fifteen CO₂ –in-air primary standard calibration gases ranging in CO₂ mole fraction from 250 to 520 micromol/mol. Since the WMO CO₂ Expert Group transferred responsibility for maintaining the WMO Scale from the Scripps Institute of Oceanography (SIO) to the Climate Monitoring and Diagnostics Laboratory (CMDL) in 1995, the fifteen WMO primary standards have been calibrated at regular interval, between one and two years, by the CMDL manometric system. From mid-1996 to 2001, the assigned CO₂ values of the WMO Primaries have been jointly based on the SIO and CMDL manometric measurements, and completely on the CMDL manometric measurements alone from 2001 to present. The uncertainty of the 15 primary standards is estimated to be 0.07 micromol/mol in the one-sigma absolute scale. Manometric calibration results indicated that there is no evidence of overall drift of the Primaries from 1996 to 2004. In order to lengthen the useful life of the Primary standards, CMDL has always transferred the WMO Scale to the Secondaries via NDIR analyzers. The uncertainties arising from the analyzer random error and the propagation error due to the uncertainty of the reference gas concentration are discussed. Precision of NDIR transfer calibrations is about 0.01 micromol/mol from 1979 to present. Propagation of the uncertainty is calculated theoretically. In the case of interpolation, the propagation error is estimated to be between 0.05 and 0.07 micromol/mol when the Primaries are used as the reference gases via NDIR transfer calibrations.

We present here a test of convection uncertainty within a single model framework driven by the same meteorological fields. Our primary goal is to explore to what extent do convection schemes impact atmospheric CO₂ distribution, by testing three referred cloud convection schemes ranging from a very simple to a relatively complex form [Table 1]. Our second goal is to examine the sensitivity of atmospheric CO₂ to its regional emission/sink uncertainty [Fig. 1] constrained by IPCC 2001 at a “fixed” convection scheme to clarify the pros and cons of the convection schemes.

An inverse modeling system has been developed based on the Bayesian principle for estimating the carbon fluxes of the 48 regions globally and 28 regions over North America in monthly steps for 2003 using CO₂ concentration measurements at 95 atmospheric baseline stations and with regularization using remote sensing-based surface flux field. Preliminary inversion results of global carbon flux and a carbon flux field over North America have been obtained.

Measurements of the radiocarbon content of atmospheric carbon dioxide are a potentially powerful, yet relatively unexplored method of improving the understanding of natural carbon dynamics and verifying fossil fuel emissions. Development of ¹⁴CO₂ as a tracer has been limited by measurement capabilities given that seasonal and spatial variation in D¹⁴C is currently of the same order as traditional instrument precision: 3-5 per mil. We have demonstrated 1-2 per mil reproducible measurement precision at the Center for Accelerator Mass Spectrometry of Lawrence Livermore National Laboratory. Here we present preliminary measurements of the natural variability of ¹⁴CO₂ from the SIO network of background air sampling stations.

We examine the growth-rate of atmospheric CO₂ in 2002 and 2003. Observations show consecutive increases of greater than 2 ppmv per year for the first time on the Mauna Loa record. We use a statistical regression to show that increasing anthropogenic emissions and ENSO activity are unable to account for the CO₂ growth-rates of 1992 and 1993 following the Pinatubo volcanic eruption, or the anomalously high growth-rate of 2003. Increased forest fires in the northern hemisphere, consistent with remote-sensing and carbon monoxide measurements, seem likely to have contributed significantly to the 2003 anomaly. We hypothesise that the hot and dry Eurasian summer of 2003 led to an increase in forest fire emissions from Siberia, and may also have directly suppressed land-carbon uptake. Model results lead us to expect a steady increase in airborne fraction as climate change weakens the natural carbon sink and accelerates CO₂ rise.