To know regional-to-continental scale CO₂ fluxes between atmosphere and terrestrial biosphere using an inverse model, the CO₂ measurements on plural towers situated in a thousand square kilometer area of West Siberia have been carried out since 2002. The CO₂ concentrations at 80m of the tower during daytime afternoon well represents those of PBL with its difference in ±3 ppm, and 90% of them in ±2 ppm, in clear sky day, when no strong inversion is occurred in winter. The tower observation expands to five sites to date, and additional four sites will be established in a year.

Existing instruments for measuring atmospheric profiles of carbon dioxide can be very sensitive, but are all large and bulky and must be flown using aircraft or large, research gondolas.  This work reports on the development of a stand-alone, lightweight CO₂ sensor for use on balloon sondes.  This device will have sub part-per-million (ppm) sensitivity and weigh less than 1 kg.

This presentation describes in-situ atmospheric CO₂ measurements at Waliguan Observatory (WLG, 36°17'N, 100°54'E, 3816m asl) since 1994, together with 5-day isobaric back trajectory analysis.  We also use the Hybrid Single-Particle Lagrangian Integrated Trajectory (Hysplit-4) transport/diffusion model to simulate the CO₂ variation at WLG in January 1999 and compared with observations. A case study for polluted air mass transport event with a short-term elevated CO₂ has been conducted to further investigate the impact of source, sink and long-range transport of atmospheric CO₂.

The oxygen isotopic composition of atmospheric CO₂ can help constrain local- to global-scale biophysical processes and partition measured net ecosystem CO₂ fluxes into gross fluxes. Although current models still lack key features controlling gross ecosystem CO¹⁸O fluxes, considerable improvements have been achieved in the last four years. In this study we examine the influence on atmospheric CO¹⁸O of 1) a delayed seasonal cycle in soil water isotopes (relative to rain water) and 2) a new one-way flux model of night-time leaf respiration [Cernusak et al., 2004]. The latter covaries with enhanced night-time stomatal conductance, for which evidence arose recently [e.g. Snyder et al., 2003].

To understand the difference in CO₂ behavior between planetary boundary layer (PBL) and free troposphere (FT), we conduct CO₂ measurements using a small aircraft and a tower at the forest area in West Siberia. More than 120 vertical CO₂ profiles were observed by newly developed small CO₂ measurement device. Seasonal amplitude in PBL (36.9 ppm) is two times larger than that in FT (15.7 ppm). Diurnal variation in CO₂ profile is affected not only by PBL growth but also by horizontal advection and entrainment flux from FT to PBL.

We quantify atmosphere-biosphere carbon exchange at the continental scale across North America during the summers of 2003 and 2004. The 2003 campaign features continental transects across the northern portion of North America with significant influence from biomass burning, while the 2004 study focuses on the greater New England and Quebec region. We use a Lagrangian, adjoint atmospheric model [Gerbig et al. 2003a,b; Lin et al. 2003] coupled to a biosphere model derived from the Vegetation Photosynthesis Model [Xiao et al., 2004]. Our analysis of the 2004 airborne data demonstrates the progression of increasing carbon uptake through the boreal zone during the seasonal transition from early spring to late summer. Data from the coast-to-coast transects of the 2003 campaign allow us to quantify large scale carbon exchange across the continent.

Since 1993, regular seasonal water sampling has been conducted along a ship-track between Island and Newfoundland in the open ocean of the North Atlantic subpolar gyre in the frame of the long-term SURATLANT program. In this study, we analyse the interannual variation of the carbon dioxide system, including seawater fugacity (fCO₂) and air-sea CO₂ fluxes for the period 1993-2004. During 1993-1997, the data present a clear seasonality in this region marked by a strong CO₂ sink in summer and near-equilibrium in winter. For recent years, 2001-2004, we observed a dramatic change of the source/sink seasonality. An extreme case was observed in 2003 when oceanic fCO₂ was above equilibrium during all seasons. This strong anomaly was driven by ocean warming.

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 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.

The Orbiting Carbon Observatory is a NASA ESSP mission that is scheduled for launch in September 2008 [Crisp et al., 2004]. The space-based observatory will sample the dry air, column averaged mole fraction of CO₂ (X_CO2) based on analysis of reflected solar radiation, between ~0.78 and 2.0 microns, acquired by three grating spectrometers. To fulfill the mission’s science objectives, the OCO validation activities are focused on demonstrating that space-based retrievals of X_CO2 have random errors no larger than 0.3% (1 ppm) over a network of ground based validation sites on monthly time scales [Miller et al., 2005]. Furthermore, space-based retrievals of X_CO2 will be compared to measurements from this network of ground-based stations to detect and mitigate geographically coherent biases on regional to continental scales. We describe plans and progress to date of the OCO validation program, which consists primarily of a series of ground-based, Fourier Transform Spectrometers (FTS), that measure X_CO2 in the same spectral regions as the space-based spectrometers.