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

Measurements of concurrent changes in both the atmospheric O₂ and CO₂ mixing ratios have been proven to be useful independent information for the partitioning of anthropogenic CO₂ into its different sinks [e.g. Keeling et al., 1996]. This information is used along with the “classical” partitioning models that make use of CO₂ concentration and (radioactive as well as stable) isotopic composition information [e.g. Keeling et al., 1995]. Global carbon budget reconstruction needs long time series observations of global means. Downscaling to a more regional assessment introduces a closer relation to possible annual and regional variations in prescribed oxidative ratios of biospheric and combustion processes. With the goal of improving the knowledge on the temporal and local variability of the O₂/ CO₂ signal, we present the results of the analysis on an extended data set from the remote station of Lutjewad (The Netherlands) and compare them with the findings of different other sampling stations in Europe, starting from 2001 till present.

First atmospheric δO₂/N₂, CO₂ and δ¹³C flask measurements from vertical aircraft sampling in the lower troposphere above Griffin Forest (GRI), Perthshire, UK, (56°37’N, 3°47’W) and from ground based flask sampling at the high altitude site Jungfraujoch (JFJ), Switzerland (3580m above sea level (a.s.l.), 46°33’N, 7°59’E), and the mountain site Puy de Dôme (PUY), France (1480m a.s.l., 45°46’N, 2°58’E) are presented.

We use the theoretically ideal tracer ¹⁴CO₂ to estimate the fossil fuel CO₂ enhancement in boundary layer air at two sites in New England and Colorado. Improved D¹⁴C measurement precision of 1.6-2.6‰ provides fossil fuel CO₂detection capability of 0.8-1.5 ppm. Using the tracers CO and SF₆, we obtain two additional independent estimates of the fossil fuel CO₂ component, and we assess the biases in these methods by comparison with the ¹⁴CO₂-based estimates. Large differences are observed between the SF₆-based estimates and those from the ¹⁴CO₂ and CO methods. The CO-based estimates show seasonally coherent biases, underestimating fossil fuel CO₂ in winter and overestimating in summer.

Air-water CO₂ fluxes were up-scaled to take into account the latitudinal and ecosystem diversity of the coastal ocean, based on an exhaustive literature survey. Marginal seas at high and temperate latitudes act as sinks of CO₂ from the atmosphere, in contrast to subtropical and tropical marginal seas that act as sources of CO₂ to the atmosphere. Overall, marginal seas act as a strong sink of CO₂ of about -0.45 Pg C yr^-1. This sink could be almost fully compensated by the emission of CO₂ from the ensemble of near-shore coastal ecosystems of about 0.40 Pg C yr^-1.

Spatial and temporal characteristics of land and ocean sources and sinks of carbon remain elusive. Better understanding of the anthropogenic influences on these carbon cycle dynamics is a common goal. This experiment is one of the efforts to reach a middle ground of flux estimates for regions larger than experimental plots and flux tower footprints, but smaller than continents and ocean basins. This work tests the hypothesis that including well-calibrated continuous North American continental CO₂ measurements in the observation data used in a global inversion will provide a constraint that improves inversion estimates of the source and sink regions within North America. These continuous data are collected at tall towers and flux towers. The experiment follows the TransCom 3 synthesis inversion framework, using the NASA Goddard Space Flight Center Parameterized Chemistry and Transport Model (PCTM) with Goddard Earth Observing System, version 4 (GEOS-4) meteorological data. Seasonal fluxes are estimated for a recent year for sub-regions within North America and at continent and basin scale globally. Methods of preparing the continental continuous CO₂ measurements for the inversion will be tested. Initial inversion results will be presented along with recommendations for applicability to other global regions and use of the method to evaluate additional sites for the measurement network.

Satellite measurements of total column CO₂ can be used in inverse models to help isolate sources and sinks; however, using satellite concentrations in inversions may introduce spatial, temporal, and clear-sky errors. Using a coupled ecosystem-atmosphere model, we found that using satellite measurements to represent temporal averages will introduce large errors into the inversion and that inverse models must sample the concentrations at the same time as they are measured.  Spatial and local clear-sky errors are much smaller than the instrumental errors, although they increase with domain heterogeneity. Inverse models can minimize sampling errors by using homogenous regions and sampling the CO₂ concentrations at the same time as the satellite.

The remote sensing of CO₂ from satellites is an exciting new and rapidly developing field in carbon cycle research. Satellite sensors have the potential to provide a wealth of information on atmospheric CO₂, covering many regions that are scarsely monitored the ground based observational networks. Satellite measurements could significantly strengthen the power of inverse modelling computations in tracing sources and sinks of CO₂. The main challenge, however, is to reach the measurement accuracy needed to resolve the important CO₂ concentration gradients. The current generation of satellite instruments from which CO₂ can be retrieved is expected to meet the requirements only partly, as the instruments were not originally designed to measure CO₂. Nevertheless interesting results come out as we will show for the Sciamachy instrument. A particularly difficult aspect is the determination of the airmass factor, which is needed to translate the observed optical thickness into a column averaged dry air mixing ratio. The airmass factor is influenced by e.g. clouds, aerosols, air pressure, and orography. So far the uncertainty assessments have mainly relied on theoretical investigations and ground-based measurements. The measurements from Sciamachy allow us to verify these studies, and some of the methods that have been proposed to reduce or eliminate the errors. We will demonstrate this with the main focus on aerosols. Error assessments using in-flight data will be indispensable for improving future instruments.

The air-sea gas exchange rate is important for modeling and verifying ocean CO₂ uptake, but remains subject to considerable uncertainty. The widely assumed quadratic or cubic dependence of the exchange rate on windspeed together with the latitudinal pattern of mean windspeed implies that exchange is much faster at high compared with low latitudes. This should affect the pattern of ocean uptake of bomb carbon-14 as well as the rate of decline of and latitudinal gradients in atmospheric Δ¹⁴CO₂. We evaluate the constraints on the windspeed dependence of the exchange rate offered by available isotopic measurements, discuss the major uncertainties, and suggest observational strategies to reduce these uncertainties.

We report on the set-up of and first experiences with a medium-precision CO₂ concentration monitoring network in Europe, linked to existing flux towers. The system is to be embedded in an integral GHG monitoring system to be developed for the Netherlands and into the CABOEUROPE effort to quantify the European carbon balance. The proof of concept has not been fully satisfactory as yet, but work continues.