B51E-01
Constraining the North American Carbon Sink with CO2 measurements from the NOAA/ESRL Aircraft Program
Profiles of CO2 mixing ratios collected from the NOAA/ESRL Aircraft Program are unique in their ability to constrain estimates of the North American carbon sink. This three dimensional dataset which reaches as far north as 65°N and as far south as 27°N between 500m above the ground and 8000m altitude provides a valuable picture of the seasonal changes in CO2 mixing ratios over North America which does not depend on 3-D transport models. The timing, amplitude and spatial distribution of CO2 mixing ratios at 19 aircraft profiles sites throughout North American not only provides an excellent benchmark for inverse flux estimates but also provides the opportunity for independent estimates of the North American carbon sink. Here we present a novel budgeting approach to estimate land-to-atmosphere fluxes, by relying mostly on CO2 vertical data and a climatological wind distribution. We find a sink of 0.51±0.39 GtC yr-1, moderate compared to other estimates for the period 2004-2006, with the highest uptake occurring in the South-East deciduous region, the agricultural Mid-West states and the Southern Boreal region.
B51E-02
Variability in the Mass and Stable Carbon Isotopic Composition of Fossil-Fuel-Derived Carbon Dioxide Emissions for the Countries of the North American Carbon Program
As we focus more intently on the carbon cycle in North America, the spatial and temporal scales of our observations become more important. The carbon dioxide released from fossil fuel consumption can show large variability in both spatial and temporal scales. This presentation will focus on this variability. We have compiled a data set that contains the monthly emissions of carbon dioxide released from fossil-fuel consumption for the countries of the North American Carbon Program. These data are consistent with the annual emissions as reported by CDIAC. As an example of spatial variability, in August 2000, emissions from Idaho (356 Gg C) and Texas (19,051 Gg C) differed by a factor of 53. As an example of temporal variability, in 1999, emissions from Texas differed by 31% between the months of February (13,807 Gg C) and August (18,107 Gg C). When looking at the stable carbon isotopic composition (del 13 C), variability also exists at these spatial and temporal scales. As an example of spatial variability, in April 1984, emissions from Louisiana (-36.32 per mil) and North Dakota (-25.23 per mil) differed by 11.09 per mil. As an example of temporal variability, in 2002, emissions from Montana differed by 5.22 per mil between the months of July (-28.38 per mil) and December (- 33.60 per mil). Finally, this presentation will also include analysis of the uncertainty associated with these time series. Variations in data collection are such that the uncertainty varies among the three countries of North America and uncertainty increases as the spatial and temporal scales decrease. http://cdiac.esd.ornl.gov/
B51E-03
Constraining Regional Fossil Fuel CO2 Emissions and Choosing an Optimal Measurement Network Using 14C Observations, Modeling, and Inversions.
We are developing a capability to separately retrieve regional fossil fuel and biospheric CO2 sources, using a combination of high resolution global modeling of CO2 tracers, highly accurate 14C measurements, and TransCom style direct inversions. Our primary data-set is a suite of 7 Scripps clean air sites that construct a trans Pacific latitudinal profile, and existing published data. In these initial experiments we have retrieved the fossil fuel emissions from 3-5 regions, and are selecting additional measurement locations to optimize our retrievals for the 22 TransCom regions. In the future we will build on this work to separately retrieve regional fossil-fuel and biospheric CO2 emissions for each region using C-12,13,14 measurements from all potential sites. We use the LLNL global atmospheric chemical transport model, IMPACT, at 2x2.5 degree resolution and GEOS4 meteorological data to perform a TransCom 3 style forward simulation using 22 separate tracers (11 land regions and 11 ocean regions) to form 22 basis functions. Using this forward simulation and a limited number of both conventional 14CO2 measurements and more recent AMS 14C measurements, we estimate the fraction of the CO2 which is from fossil fuel emissions. Model results and measurements are then used in an inversion algorithm to retrieve regional fossil fuel emissions from each geographical region. We are using a linear inversion algorithm based on single value decomposition. This formulation of linear inversion allows us to investigate retrievable degrees of freedom, the information retrievable from measurements for particular regions, and the marginal contributions from particular measurement sites. With initial data only available at 7 sites, we have combined the 22 regions into 3 or 5 latitude bands. Then using the model results and the inversion we can select the site for an additional measurement which will maximally reduce the retrieval error. In this way we can design an optimal observation network by adding one site at a time.
B51E-04
New Observations of Regional Variability in Delta-14C of Background CO2 from the Scripps CO2 Program
We present new records of Δ14C in CO2 from a set of 7 sites in the Scripps CO2 flask sampling program. The monthly records span 2 years at Palmer Station, 5 years at Mauna Loa, Kumukahi and Samoa, 7 years at Pt Barrow and South Pole, and 15 years at La Jolla. The long time series were made possible by the archiving of extracted CO2 samples. The samples were analyzed by Accelerator Mass Spectrometry (AMS) at the Lawrence Livermore National Laboratory, where an initiative to support high precision Δ14C analysis in CO2 with improved analytical methodology has been ongoing since 2003. The new records build on previous work by I. Levin, M. Manning, R. Nydal and others to characterize atmospheric Δ14C levels following nuclear weapons testing. Our time series reveal changes in the latitudinal profile of Δ14C that reflect shifting regional 14C fluxes. As 14C fluxes depend on the source of CO2 to the atmosphere, atmospheric 14C measurements improve our understanding of regional oceanic, biospheric and industrial CO2 exchanges and provide important constraints on carbon cycle models. The new records will additionally serve as a background definition for studies utilizing Δ14C measurements to identify local fossil fuel-derived CO2.
B51E-05
Seasonal Rectifier Effects in Atmospheric Potential Oxygen (APO) and CO2
The CO2 seasonal rectifier contributes to the latitudinal gradient in atmospheric CO2 predicted by forward transport models and influences atmospheric CO2 inversions accordingly. The actual strength of the CO2 rectifier can not be directly observed due to uncertainties in terrestrial CO2 sinks. Forward transport model simulations also produce a seasonal rectifier in the complementary tracer atmospheric potential oxygen (APO = O2/N2 + 1.1 CO2). Since APO in principle is free from terrestrial influences, comparison of a model-derived rectifier to observations should be more straightforward for APO than for CO2. This presentation will discuss the seasonal rectifier in APO and its relation to the CO2 rectifier based on forward simulations of the MATCH atmospheric transport model and archived results from the Transcom 3 and APO Transcom experiments.
B51E-06
Natural Variation in the Carbon Oxidation State and Oxidative Ratio of a Deciduous Forest
Here we report natural variability in the oxidative ratio (OR) and carbon oxidation state (Cox) of a temperate, deciduous forest measured on an annual basis via elemental analysis of leaf litter. The OR of the terrestrial biosphere is a key component in O2 -based calculations of the biosphere's uptake of fossil fuel CO2 (eg [ Keeling, et al., 1996]). Ecosystem OR has been assumed to be invariant; however, small OR variations may cause significant shifts in the calculated size of the terrestrial biospheric C sink [ Randerson, et al., 2006]. Accurate measurements of OR are necessary for the accurate apportionment of fossil fuel CO2 between the atmosphere, oceans, and terrestrial biosphere. Ecosystem OR is linearly related to Cox, a parameter which can be easily measured via elemental analysis, calorimetry, or solid state nuclear magnetic resonance [ Masiello, et al., 2007]. We are measuring Cox and OR at the three deciduous forest sites within the Kellogg Biological Station NSF LTER (lter.kbs.msu.edu). We report OR from litter collected from three forest sites from 1998-2003, a time series which covers periods of both normal and low precipitation. We also report error introduced in the Cox to OR conversion via a range of plausible assumptions about ecosystem N cycling. Keeling, R. F., et al. (1996), Global and hemispheric CO2 sinks deduced from changes in atmospheric O2 concentration, Nature, 381, 218-221. Masiello, C.A. et al. (in review 2007) Two new approaches for measuring ecosystem carbon oxidation state and oxidative ratio. J.G.R. Biogeosciences. Randerson, J. T., et al. (2006), Is carbon within the global terrestrial biosphere becoming more oxidized? Implications for trends in atmospheric O2, Global Change Biology, 12, 260-271.
B51E-07
Canopy Nitrogen, Carbon Assimilation and the Albedo of North American Forest Ecosystems
Terrestrial ecosystems can influence the Earth's climate through exchanges of carbon with the atmosphere and through their influence on land surface albedo. We present evidence from an ongoing NACP study suggesting that these two mechanisms are related and that linkages between them are moderated by the nitrogen status of plant canopies. Across a diverse series of forested AmeriFlux sites, ecosystem photosynthetic capacity was positively correlated with canopy N concentrations as estimated from air and space-borne imaging spectroscopy. Although canopy N detection has traditionally focused on narrow-band spectral features, we also found strong correlations with simpler and widely available reflectance properties and with albedo estimates from the MODIS satellite sensor. Our findings indicate that high nitrogen ecosystems have more reflective canopies, absorb less radiant energy and fix more carbon than their low N counterparts. If these patterns can be shown to exist more broadly, our results suggest a previously unrecognized feedback in the Earth's climate system involving the nitrogen cycle as a moderator of carbon cycling and surface energy exchange under changing environmental conditions.
B51E-08
Relationship of photosynthesis to atmospheric carbonyl sulfide for the North American growing season
Projected changes in climate may reduce the uptake of atmospheric CO2 by terrestrial plants, creating a positive carbon-climate feedback. Our understanding of this feedback is primarily based on global photosynthesis models that were derived from leaf-scale models. It is difficult to validate photosynthesis models with atmospheric CO2 measurements because air depleted of CO2 by photosynthesis mixes with air enriched in CO2 by respiration. It was recently hypothesized that an independent assessment of photosynthesis models could be developed using atmospheric carbonyl sulfide (COS) which is closely related to photosynthesis by COS plant uptake but only has small terrestrial ecosystem sources. Here we report a COS model-observation analysis that is supportive of modeled photosynthesis estimates for the North American growing season. We compared airborne measurements with an atmospheric model driven by COS plant uptake, soil sinks, ocean sources, and anthropogenic sources. The COS plant uptake was calculated by scaling modeled photosynthesis by the plant chamber-derived ratio of photosynthesis to COS plant uptake. Observed and simulated COS concentrations along the flightpaths showed remarkable agreement, both indicating a 13 percent tropospheric drawdown. Modeled COS concentrations were dominated by plant uptake, unlike previous COS models that did not account for the COS-photosynthesis relationship. The model-observation agreement for this plant dominated system corroborates the modeled photosynthesis estimates and the extrapolation of the photosynthesis-COS relationship from plant chamber experiments to our regional atmospheric analysis. We anticipate that our model- observation analysis will be a starting point for using the global observation network9 in a data assimilation framework to constrain climate-photosynthesis sensitivities. http://www.stanford.edu/~campbell/