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.

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.