Upwelling of high-nutrient waters in the equatorial Pacific gives rise to a band of enhanced primary production around the equator that stretches from Peru almost to Indonesia. It has been suggested that this oceanic region accounts for a large part of global net production. The equatorial Pacific is also thought to be the largest oceanic CO₂ source and makes an important contribution to the atmospheric CO₂ budget.

Based on simulations with high-resolution transport models we investigate the detectability of surface flux signals in the atmospheric CO₂ concentration and infer some general guidelines for the sampling of the continental troposphere for the purpose of constraining mid-latitude land carbon sinks.

Simulations with a regional transport model are evaluated in order to determine to which extend the indirect fossil fuel combustion tracer CO or the purely anthropogenic tracer SF₆ can be used to retrieve the contribution of fossil fuel emissions in the atmospheric CO₂ signal.

The results of atmospheric CO₂, CH₄ and CO measurements are presented. The measurements were made in air samples collected at heights of 4, 25, 100, 200 and 300 m above ground, and in the atmospheric column in Obninsk, Russia (55.11 N, 36.57  E, 183 m asl).

Measurements of atmospheric CO₂ began in 1957-1958 at a wide range of locations, including at fixed stations, on ice floes, on oceanic expeditions, and on aircraft flights, with logistical and financial support provided by the International Geophysical Year (IGY) program. Although the measurement effort was reduced in scope immediately following the IGY, today, measurements are made at more than 100 locations.  Over this same time interval, emissions of CO₂ from fossil fuel combustion increased from 2.3 thousand million metric tons per year (GtC/yr) in 1958 to 7.1 GtC/yr in 2003 [Marland et al., 2005, and personal communication].  More than 90% of this CO₂ was released into the northern hemisphere where it lingered before mixing fully world-wide.  The atmospheric CO₂ concentration, in response, rose faster in the northern hemisphere than in the southern, the interhemispheric difference increasing from near zero during the IGY to about 3 parts per million (ppm) in 2003. For all northern hemisphere stations where our program has measured CO₂, the gradient changes relative to the South Pole are generally proportional to the rate of fossil fuel CO₂ emissions, disregarding seasonal and short term interannual variability in the CO₂ data.  Here, we use this fact to diagnose how the carbon cycle has evolved over the past half century.

Measurements of atmospheric O₂/N₂ ratio and CO₂ concentration are presented over the period 1989 to present from the Scripps Institution of Oceanography global flask sampling network. The data are used to make estimates of land and ocean sinks over various time scales. The oceanic and land biotic sinks are estimated to be 1.9±0.6 (ocean) and 1.2±0.8 Pg C/yr (land) over the period Jan. 1990-Jan. 2000 and 2.2±0.5 (ocean) and 0.5±0.7 Pg C/yr (land) over the period Jan. 1993-Jan. 2003. These estimates make allowance for oceanic O₂ and N₂ outgassing based on observed changes in ocean heat content and estimates of the relative outgassing per unit warming. The recent ocean sink is consistent, to within the uncertainties, with estimates of the accumulation of anthropogenic CO₂ in the ocean since 1800, assuming the oceanic sink varied over time as predicted by a box-diffusion model. The possibility that the ocean sink is being reduced slightly by climate feedbacks, as predicted by some models, is not ruled out, however.

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.

Over the last decade the TransCom group has coordinated a number of intercomparisons. The latest project focuses on the diurnal and synoptic behaviour of transport models.  The poster will describe the experiment, introduce the participating models and present a sample of preliminary results.