Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden
Pandey, Sudhanshu ; Houweling, Sander ; Krol, Maarten ; Aben, Ilse ; Nechita-Banda, Narcisa ; Thoning, Kirk ; Röckmann, Thomas ; Yin, Yi ; Segers, Arjo ; Dlugokencky, Edward J. - \ 2019
Geophysical Research Letters 46 (2019)4. - ISSN 0094-8276 - p. 2302 - 2311.
atmospheric burden - atmospheric transport - CH emissions - interhemispheric difference - methane - TM5
We quantify the impact of atmospheric transport and limited marine boundary layer sampling on changes in global and regional methane burdens estimate using tracer transport model simulations with annually repeating methane emissions and sinks but varying atmospheric transport patterns. We find the 1σ error due to this transport and sampling effect on annual global methane increases to be 1.11 ppb/year and on zonal growth rates to be 3.8 ppb/year, indicating that it becomes more critical at smaller spatiotemporal scales. We also find that the trends in inter-hemispheric and inter-polar difference of methane are significantly influenced by the effect. Contrary to a negligible trend in the inter-hemispheric difference of measurements, we find, after adjusting for the transport and sampling, a trend of 0.37 ± 0.06 ppb/year. This is consistent with the emission trend from a 3-D inversion of the measurements, suggesting a faster increase in emissions in the Northern Hemisphere than in the Southern Hemisphere.
Atmospheric measurements of Δ17O in CO2 in Göttingen, Germany reveal a seasonal cycle driven by biospheric uptake
Hofmann, M.E.G. ; Horváth, B. ; Schneider, L. ; Peters, W. ; Schützenmeister, K. ; Pack, A. - \ 2017
Geochimica et Cosmochimica Acta 199 (2017). - ISSN 0016-7037 - p. 143 - 163.
3D transport model - O - Carbon dioxide - Terrestrial gross primary production - TM5 - Triple oxygen isotopes - Troposphere - ΔO
The triple oxygen isotope composition of tropospheric CO2 might be a promising new tracer for terrestrial gross carbon fluxes. This notion is based on global box modeling of its abundance, and on highly challenging and therefore very sparse measurements of 16O, 17O and 18O in CO2 in the lower atmosphere. Here, we present additional high-precision triple oxygen isotope measurements of ambient air CO2 sampled in Göttingen (NW Germany) over the course of 2 years and of two air samples taken on top of the Brocken Mountain (1140 m, NW Germany). Göttingen differs from other locations where Δ17O was measured by its proximity to both urban sources of CO2, and to extensive uptake of CO2 by vegetation. In our analysis, we specifically try to discern this latter influence on our measurements, and to distinguish it from other known sources of variation in Δ17O. Our triple oxygen isotope data are reported as Δ17O values relative to a CO2-water equilibration line with Δ17O = ln (δ17O + 1) − 0.5229 × ln (δ18O + 1). We report an average of -0.02 ± 0.05‰ (SD) in the first year and -0.12 ± 0.04‰ (SD) in the second year of our measurements. This year-to-year difference is higher than expected based on other available Δ17O records, but careful scrutiny of our measurement approach did not reveal obvious analytical biases, leaving this aspect of our record unexplained. After removing the year-to-year trend, our time series shows a statistically robust seasonal cycle with maximum values in June/July and an amplitude (peak-to-trough) of 0.13 ± 0.02‰. We compare our observational data to a revised triple oxygen isotope mass balance “box” model of tropospheric CO2 where we reconcile both 18O/16O and 17O/16O fractionation processes. We also compare them to Göttingen-specific output from a three-dimensional transport model simulation of Δ17O in CO2 performed with the Tracer Model 5 (TM5). Both the modeled isofluxes at the surface, and the modeled stratospheric, fossil, and biospheric Δ17O components in the atmosphere at Göttingen confirm that the observed seasonal cycle in Δ17O is driven primarily by the seasonal cycle of gross primary productivity (GPP), and that the seasonal variations in both stratospheric transport and fossil fuel emissions play a minor role at our location. Our results therefore strengthen earlier suggestions that GPP is reflected in Δ17O, and call for more seasonally resolved measurements at continental locations like Göttingen.