B21E-01 INVITED 08:00h
Regional-Scale Carbon Flux Estimates Over Complex Terrain and the Airborne Carbon in the Mountains Experiment
Mountain forests represent a large portion of gross primary productivity within the United States and a significant potential net CO2 sink. Because of their importance to current and future national carbon budgets, the complexity of their controlling processes, and their sensitivity to land-use practices and climate change, NACP strategies must be devised to address how to distinguish and partition carbon fluxes in montane regions. We conducted the first Airborne Carbon in the Mountains Experiment (ACME I) in May and July of this year to explore methods for constraining regional-scale CO2 fluxes over complex terrain and to collect measurements useful for devising and testing strategies for long-term monitoring of these fluxes. We flew a total of 54 hours on the NCAR C-130 aircraft over large regions of the Colorado Rocky Mountains, making continuous measurements of CO2, CO, O3, and water vapor concentrations, and collecting discrete flask samples for 13C and 18O isotope ratios in CO2. In addition to these primary measurements, we also flew a scanning radiometer with thermal and vegetation channels, collected flask samples for radiocarbon measurements and for verification of our in situ CO2 and CO measurements, and collected high rate CO2, CO, O3, and water vapor data for direct eddy-correlation flux estimates. Our airborne measurements will be compared to and integrated with the extensive ongoing carbon and ecosystem measurements at Niwot Ridge and an enhanced network of ground-based measurements deployed as part of the broader Carbon in the Mountains Experiment. The flights were conducted according to a combination of experimental designs, including morning to afternoon Lagrangian flux measurements, regional survey measurements for assimilation into a high-resolution ecosystem-atmosphere model, morning sampling of nocturnally respired CO2 and its concentration by topography and dispersion by turbulence, flask sampling to resolve elevation gradients in isotope signatures, and direct flux measurements. During the Lagrangian experiments and regional surveys, we observed CO2 drawdowns of several ppm in boundary-layer CO2, representing significant CO2 uptake by the forests and strong signals for use in our analyses. Also, in large mountain valleys we observed on the order of 30 ppm of respired CO2 pooling as deep as 1000 ft. and persisting until 10 AM, which may suggest techniques for making respiration estimates on relatively large scales. We will present results of our preliminary analyses and discuss strategies the NACP should consider to improve constraints on mountain carbon fluxes.
B21E-02 08:20h
The Orbiting Carbon Observatory (OCO) Mission
The Orbiting Carbon Observatory (OCO) mission will make the first global, space-based measurements of atmospheric carbon dioxide (CO$_2$) with the precision, resolution, and coverage needed to characterize CO$_2$ sources and sinks on regional scales. The measurement approach and instrument specifications were determined through an analysis of existing carbon cycle data and a series of observing system simulation experiments. During its 2-year mission, OCO will fly in a 1315 LST sun-synchronous orbit with a 16-day ground-track repeat time, 15 minutes ahead of the EOS Aqua platform and the A-train constellation. OCO will carry a single instrument that incorporates three bore-sighted high-resolution spectrometers designed to measure reflected sunlight in the 0.76 $\mu$m O$_2$ A-band and in the CO$_2$ bands at 1.61 and 2.06 $\mu$m. Soundings recorded in these three bands will be used to retrieve the column-averaged CO$_2$ dry air mole fraction (\ital{X$_{CO2}$}). A comprehensive validation program was included in the mission to ensure that the space-based \ital{X$_{CO2}$} retrievals have precisions approaching 0.3$%$ (1 ppm) on regional scales. OCO data products will be used in global synthesis inversion and data assimilation models to quantify CO$_2$ sources and sinks. While OCO will have a nominal lifetime of only 2 years, it will serve as a pathfinder for future long-term CO$_2$ monitoring missions.
http://oco.jpl.nasa.gov
B21E-03 08:35h
Carbon Dioxide and Methane Column Abundances Retrieved from Ground-Based Near-Infrared Solar Spectra and Comparison with In Situ Aircraft Profiles
We have developed an automated observatory for measuring ground-based column abundances of CO$_{2}$, CH$_{4}$, CO, N$_{2}$O, O$_{2}$, H$_{2}$O, and HF. Near-infrared spectra of the direct sun are measured between 3,900 - 15,600 cm$^{-1}$ (0.67 - 2.56 $\mu$m) by a Bruker 125HR Fourier Transform Spectrometer. This is the first laboratory in a proposed network of ground-based solar observatories that will be used for carbon cycle studies and validation of spaceborne column measurements of greenhouse gases. The laboratory was assembled in Pasadena, California and then permanently deployed to northern Wisconsin during May 2004. It is located in the heavily forested Chequamegon National Forest at the WLEF Tall Tower site, 14 km east of Park Falls, Wisconsin. This site was chosen because NOAA CMDL and other groups conduct intensive measurements in the area, including continuous monitoring of CO$_{2}$ at six heights on the 447-m tall tower. CO$_{2}$ and CH$_{4}$ column abundances for May - November 2004 demonstrate $\sim$0.1% precision. The seasonal drawdown of CO$_{2}$ is recognizable within the late-May column abundances. As part of the INTEX and COBRA campaigns, the DC-8 or King Air recorded in situ measurements during profiles over the WLEF site during five dates in July and August 2004. We will compare the column abundances of CO$_{2}$, CH$_{4}$, and CO with these in situ aircraft measurements.
B21E-04 08:50h
Can Carbonyl Sulfide Help Constrain Gross Vegetative Fluxes of Carbon Dioxide?
Uptake by vegetation represents an important loss mechanism for atmospheric carbonyl sulfide (COS). COS undergoes rapid reaction by carbonic anhydrase and Rubisco, the same enzymes involved in the initial stages of carbon assimilation by vegetation. Measurements of COS during multiple years show large seasonal variations in the northern hemispheric atmosphere that are strongly related to those observed for CO$_{2}$; the seasonal changes observed for COS, however, are about eight times larger on a relative basis. Our current understanding of sources and sinks of COS and CO$_{2}$ suggests that this amplified seasonality arises for COS because its uptake flux is not diminished, as is the case for CO$_{2}$, by emissive fluxes associated with respiration and retro-diffusion of unassimilated CO$_{2}$ from leaf stomata. These results imply that the large-scale variations observed for COS in the northern hemispheric atmosphere reflect primarily the magnitude of gross vegetative uptake fluxes. They further suggest the possibility that COS could provide unique constraints on gross vegetative uptake fluxes of CO$_{2}$.
B21E-05 09:05h
Full-waveform, Laser Altimeter Measurements of Vegetation Vertical Structure and Sub-Canopy Topography in Support of the North American Carbon Program
Full-waveform, scanning laser altimeters (i.e. lidar) provide a unique and precise view of the vertical and horizontal structure of vegetation across wide swaths. These unique laser altimeters systems are able to simultaneously image sub-canopy topography and the vertical structure of any overlying vegetation. These data reveal the true 3-D distribution of vegetation in leaf-on conditions enabling important biophysical parameters such as canopy height and aboveground biomass to be estimated with unprecedented accuracy. An airborne lidar mission was conducted in the summer of 2003 in support of preliminary studies for the North America Carbon Program. NASA's Laser Vegetation Imaging Sensor (LVIS) was used to image approximately 2,000 km$^2$ in Maine, New Hampshire, Massachusetts and Maryland. Areas with available ground and other data were included (e.g., experimental forests, FLUXNET sites) in order to facilitate numerous bio- and geophysical investigations. Data collected included ground elevation and canopy height measurements for each laser footprint, as well as the vertical distribution of intercepted surfaces (i.e. the return waveform). Data are currently available at the LVIS website (http://lvis.gsfc.nasa.gov/). Further details of the mission, including the lidar system technology, the locations of the mapped areas, and examples of the numerous data products that can be derived from the return waveform data products are available on the website and will be presented. Future applications including potential fusion with other remote sensing data sets and a spaceborne implementation of wide-swath, full-waveform imaging lidar will also be discussed.
http://lvis.gsfc.nasa.gov/
B21E-06 09:20h
Photochemical Production of Dissolved Inorganic Carbon from Oceanic Colored Dissolved Organic Matter: a Gentle Approach to Measuring a new "Wild Card" Carbon Cycle Term
BACKGROUND: Massive oceanic photochemical remineralization (termed "photo-CO2") has been reported[1-3]: CDOM + hv -----$<$ CO2 (DIC) CDOM = Colored Dissolved Organic Matter. DIC = Dissolved Inorganic Carbon. The oceanic carbon cycle cannot be understood without quantifying photo-CO2 fluxes and their sensitivity to environmental variables. The optical model of Johannessen implies a global marine photo-CO2 of $\sim$1015 mol C or 12 Gt C a-1[4]; Kieber and Mopper find photo-CO2 formation rates in the NW Sargasso Sea of $\sim$20 nmol kg-1 hr-1, extrapolating to $\sim$1.3 Gt C a-1[5-7; D. Kieber pers. comm, 2003]. CURRENT METHOD: To achieve essential sensitivity, $<$1 micromole CO2 per day, prior workers remove 99.9+%\ of the DIC (Pool Depletion method - PD). PD users acidify, strip CO2 out by bubbling, readjust pH, irradiate, and analyze. PD's chemically rough sample-handling might give rise to impossible-to-evaluate artifacts. NEW APPROACH: We designed and are implementing a gentle Pool Isotope Exchange (PIE) method, that retains the seawater carbonate system and avoids bubbling. At pH$\sim$8, we exchange[8] the natural DI12C pool (98.9% 12C) with $\sim$400 ppm 13CO2 ($<$1.5% 13\2C) to minimize the DI12C pool that dilutes new-formed photo-12CO2 (from DOM carbon, $\sim$98.9%12C). Rates of DI12C formation in incubations are then measured by isotope ratio mass spectrometry (IRMS). The PIE procedure's steps are: Sample and sterile filter seawater; Exchange DIC to near-completion; Seal incubation aliquots in quartz tubes; Irradiate aliquots with dark controls; Convert aliquots DIC to CO2; Trap and purify; Measure 13/12C ratios. Calculate fluxes from isotope ratios, their rates of change, and [DIC]. PIE STATUS: all but the first and last Steps are novel and have required extensive development. Present progress, sensitivity, and prospects for improvement will be summarized. PIE currently gives detectable, moderately reproducible signals in non-estuarine coastal (East-Coast US) seawater. Many coastal water samples will likely be quantitatively assessable by PIE. BLUE-WATER PROSPECTS: assessing the global photo-CO2 flux requires open ocean data, since CDOM there likely differs chemically from coastal CDOM[9]. However, currently no method is sensitive enough to measure it. An estimate of the requirements for future blue water photo-CO2 work will be presented, based on Nelson et al.'s blue water model of microbial CDOM production and CDOM loss by photobleaching, constrained with seasonally-cycle data at BATS[9]. REFERENCES: 1. Johannessen, S.C., W.L. Miller and J.J. Cullen (1999). Eos, Trans. Am. Geophys. Un., 80:0S63, Abstract OS 12M-02 (2000 AGU-ASLO Ocean Sciences Meeting. January 24-28, 2000, San Antonio, TX). 2. Johannessen, S., L. Ziolkowski and W. Miller (2000). (Abstracts of Pacifichem 2000, Vol. 1, ENVR-332). 3. Miller, W.L. and S.C. Johannessen (1999). Eos, Trans. Am. Geophys. Un., 80:0S93, Abstract 0521K-09 (2000 AGU-ASLO Ocean Sciences Meeting, January 24-28, 2000. 4. Johannessen, S. C.H. A photochemical sink for dissolved organic carbon in the ocean. Ph.D Thesis, Dalhousie University, CA. 179pp May, 2000. 5. Kieber, D. J., K. Mopper and J.G. Qian (1999). Trans. Am. Geophys. Un. 80: OS 128, Abstract #0522J-01 6. Kieber, D., K. Mopper and J. Qian (2000). Abstracts of Pacifichem 2000, Vol. 1, ENVR-28). 7. Kieber, D.J., K. Mopper, J. Qian and O.C. Zafiriou 8. Zeebe, R.E., D.B. Wolf-Gladrow and H. Jansen (1999). Mar.Chem. 65, 135-153. 9. Nelson, N.B, D. A. Siegel, and A.F. Michaels (1998) Deep-Sea Res. 45, 931-957.
B21E-07 09:35h
Preliminary Constraints on Fossil-fuel CO$_{2}$: Comparison of Tracers CO and SF$_{6}$ With Measurements of $^{14}$CO$_{2}$
CO$_{2}$ derived from the combustion of fossil fuels is a significant component of the carbon balance of North America. However, on the sub-continental spatial scales and sub-annual time scales relevant to the objectives of the North American Carbon Program, estimates of combustion CO$_{2}$ from traditional economic inventories are unlikely to be accurate, and may contribute to biases in the interpretation of atmospheric CO$_{2}$ measurements. Indirect estimates of the combustion CO$_{2}$ component can also be obtained from measured CO:CO$_{2}$ ratios and SF$_{6}$:CO$_{2}$ ratios. The low cost and ease of measurement allow the application of these methods in intensive measurement campaigns. However, the accuracy of the combustion CO$_{2}$ detection capability relies on accurately determining the emission ratio of CO:CO$_{2}$ or SF$_{6}$:CO$_{2}$ at relevant time and space scales. In the case of CO, atmospheric chemical biases and non fossil fuel sources must also be understood. CO$_{2}$ derived from fossil fuels contains no $^{14}$C, whereas other sources have a $^{14}$C content close to that of ambient air. Measurement of the $^{14}$C content in CO$_{2}$ thus provides a direct tracer for fossil fuel derived CO$_{2}$, without the biases associated with the indirect tracer methods. We used high-precision accelerator mass spectrometry to determine the $^{14}$C content of CO$_{2}$ at several North American sites (Niwot Ridge, CO, Harvard Forest, MA and New Hampshire) during 2003 and 2004, and calculate the fossil fuel CO$_{2}$ contribution in each case. We compare these results with CO:CO$_{2}$ and SF$_{6}$:CO$_{2}$ measurements on the same samples to evaluate the indirect tracer methods at these sites. Preliminary results for wintertime measurements (when biological CO$_{2}$ exchange fluxes are small) support the accuracy of the $^{14}$C method. The back-calculated emission ratios for SF$_{6}$:CO$_{2}$ vary significantly and consistently underestimate the global average. While the back-calculated CO:CO$_{2}$ ratios are more consistent, they also underestimate the predicted values from emissions inventories.