We estimated the production of bomb radiocarbon using available information on atmospheric nuclear bomb tests, the simple (radio-)carbon cycle model GRACE (Global RadioCarbon Exploration Model) and atmospheric observations as constraints. Subsequent forward simulations of the bomb radiocarbon inventory in the different carbon reservoirs turned out to be in very good agreement with recent observation-based estimates, therewith for the very first time allowing to close the global bomb radiocarbon budget. Besides confirming original stratospheric bomb ¹⁴C data published in the reports of the Health and Safety Laboratories [Telegadas, 1971, and references therein], our results confirm recent observation-based ocean bomb radiocarbon inventory estimates for the time of GEOSECS (1970s) and WOCE (1990s) from Peacock [2004] and Key et al. [2004], but refute the GEOSECS ocean inventory estimates from Broecker et al. [1985, 1995].

In order to elucidate seasonal and interannual variations of oceanic CO₂ uptake in the Greenland Sea and the Barents Sea, partial pressures of CO₂ in the surface ocean (pCO₂^sea) were measured from 1992 to 2001. The values of pCO₂^sea were lower than the partial CO₂ pressures in the atmosphere (pCO₂^air) throughout the year, and the annual net air-sea CO₂ fluxes in the Greenland Sea and the Barents Sea were evaluated to be 52 ± 31 and 46 ± 27 gC m^-2 yr^-1, respectively, yielding a total oceanic CO₂ uptake of 0.050 ± 0.030 GtC yr^-1. We also found that the annual mean CO₂ uptake was positively correlated with the North Atlantic Oscillation Index (NAOI) via wind strength, but was negatively correlated with DpCO₂ (pCO₂^air-pCO₂^sea) and the sea ice coverage. The results also indicate that the wind speed and sea ice coverage play a major role in determining the interannual variation of CO₂ uptake, with DpCO₂ playing a minor role.

Exchange rates within the Global Carbon Cycle, between oceans, atmosphere and terrestrial biosphere – including the anthropogenic CO₂ production – are being traced by concentration and isotope ratio measurements of atmospheric CO₂. The background value of the stable isotope ratio of oxygen in atmospheric CO₂ is determined by oxygen exchange with the ocean surface waters. During contact with leaf water, the signature of this then evaporation-enriched groundwater (the extent still being dependent on plant physiological and environmental parameters), will be imprinted on CO₂ diffusing back out of the leaf stomata. From water cycle studies the continental effect (Rayleigh-distillation) is known, leading to precipitation strongly depleted in d¹⁸O over e.g. Siberia. This signal is also transferred into plant material. These main mechanisms within the ¹⁸O-cycle are known or under investigation. The d¹⁸O source term for atmospheric CO₂ derived from biomass burning and anthropogenic fossil fuel combustion, however, is less well-known.

We have carried out the tank experiment in the low-temperature room to clarify the CO₂ gas exchange mechanism between the sea and the overlying air during the sea-ice formation process. The air CO₂ concentration in the headspace of the tank began to increase simultaneously with the sea-ice formation and growth. The CO₂ flux was with in the range from 2.1x10^-4 to 4.5x10^-4 g-C m^-2 hour^-1 at ice thickness of 5cm. The CO₂ flux was mainly dependent on the brine salinity in the upper layer of sea-ice, which suggests that CO₂ was released from the brine in the sea-ice, and transported to the atmosphere.

The formation of Antarctic Intermediate Water is investigated in a state of the art numerical model. Results are compared with a previous, lower resolution version of the model, and with data from the World Ocean Circulation Experiment.

This paper presents estimates of the ¹³C Suess effect and anthropogenic carbon concentration increase in the Nordic Seas since 1981.

We present a new version of the global atmospheric tracer transport model driven by analyzed meteorology with diurnally varying mixing in the boundary layer capable of running globally at resolutions up to quarter degree longitude-latitude or higher. The impact of the higher resolution model can be visible in resolving city plumes, airmass boundaries, diurnal cycle, fronts and synoptic scale events often observed in continuous CO₂ monitoring site data.

The inventory of nuclear bomb produced ¹⁴C (bomb ¹⁴C) in the ocean is a major constraint of CO₂ exchange between the atmosphere and ocean in numerical models and analytical estimates of gas exchange. New ¹⁴C data in the ocean, improved methods of separating the bomb ¹⁴C from the natural background of ¹⁴C in the ocean, and reassessment of previous inventories are challenging the canonical estimates of the air-sea gas transfer. An improved method of separating natural ¹⁴C from the observed ¹⁴C distribution is being used to estimate the bomb ¹⁴C distribution and inventory. We use GEOSECS ¹⁴C data to represent the global distribution in 1975, and the new WOCE dataset for 1995 to get two time representations of inventory. To reduce the bias error for averaging zonal bomb ¹⁴C inventories from limited observation stations during the GEOSECS times, we use zonal averages given by Peacock [2004] for re-evaluation of 1975 air-sea CO₂ exchange rates. Zonal inventories for 1995 will be from GLODAP mapping results using WOCE data [Key et al. 2004]. Lateral transport models developed by Broecker et al. [1985] are used to assess the regional air-sea CO₂ exchange rates as well as an appropriately weighted global mean. Four independent methods of estimating bomb ¹⁴C inventory in the ocean show that the original estimate by Broecker et al. [1995] could be about 25% too high, the air-sea CO₂ exchange rates derived from this original bomb ¹⁴C inventory could also be too high by a similar amount. Results of this assessment will be presented.

We present an analysis of terrestrial net CO₂ fluxes from North America for the period 2000-2004. These fluxes consist of hourly maps at ~70km×100km resolution that are consistent with observed atmospheric CO₂ mixing ratios, as well as with varying climatic conditions across different ecosystems as observed from space. The flux maps are created in a newly developed ensemble data assimilation system that consists of the atmospheric Transport Model v5 (TM5), the Vegetation Photosynthesis Respiration Model (VPRM), and an efficient Bayesian least-squares algorithm to optimize the fluxes from different biomes in VPRM against CO₂ mixing ratios from the NOAA-CMDL observing network. The stochastic nature of the ensemble data assimilation system allows us to consistently include uncertainty on net CO₂ fluxes from the neighboring oceans and more distant continents in the flux estimates for North America.

We present preliminary results of a modeling experiment that compares observed vertical profiles of CO₂ with those generated by an atmospheric transport model (ATM). The ATM is driven by CO₂ flux fields generated from the inversion of monthly averaged CO₂ surface data (GLOBALVIEW). We note large differences between the best fit to the observations produced in the inversion and the same quantity simulated by the forward model. This difference arises from the nonlinearity of the advection scheme used in the transport model. When comparing with vertical profiles, we note that much of the difference between simulated and observed concentration has the same structure as the impact of this nonlinearity. Inversion schemes must therefore take nonlinearity into account. Despite these differences, the profiles are able to distinguish among inversions that fit subsets of the surface data, suggesting they are a useful validation dataset.