Status: this discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.
Feasibility for detection of ecosystem response to disturbance by atmospheric carbon dioxide
Bjorn-Gustaf J. Brooks,Ankur R. Desai,Britton B. Stephens,Anna M. Michalak,and Jakob Zscheischler
Abstract. Monitoring the terrestrial carbon cycle for responses to disturbances, caused for example by extreme climate events and insect outbreaks, has the potential to provide early warnings about ecosystem change. However, our capability to detect these carbon balance responses by atmospheric CO2 monitoring remains unknown despite sub-ppm comparability of many well-calibrated CO2 measurement sites. Here, this study explores how accurately atmospheric CO2 and transport models can detect imposed carbon flux anomalies against a background terrestrial flux. Air mass back trajectories from three CO2 monitoring stations in the central U.S. Rocky Mountains for one year (2008) were computationally simulated. To simulate reduced CO2 uptake, a constant +0.2 µmol C m−1 s−2 anomaly was added to all surface fluxes within perturbation domains of varying size. A spatially and temporally uniform 10°×10° +0.2 µmol C m−2 s−1 flux anomaly (+6 Tg C m−1) was detectable above a comprehensive model-data mismatch detection threshold in a large majority of months at each site, but only when the perturbation was located in the central Mountain West. The intensity of the perturbation and its area were important to detection, but the effect of area declined exponentially with increasing source-to-station distance. To further evaluate response, a more realistic spatiotemporally varying drought extracted from a dynamic global vegetation model with a monthly varying perturbation area (1°×1° to 5°×5°) and higher peak intensity (+0.8 µmol C m−2 s−1) was applied. Detectability of excess CO2 from this experiment by the nearest CO2 site (Utah) was similar to detectability of the largest (10°×10°) uniform perturbation. These experiments demonstrate disturbance and drought related carbon-cycle perturbations do create a discernible impact on the composite signal of atmospheric CO2 if sufficiently proximal to a measurement station.
How to cite. Brooks, B.-G. J., Desai, A. R., Stephens, B. B., Michalak, A. M., and Zscheischler, J.: Feasibility for detection of ecosystem response to disturbance by atmospheric carbon dioxide, Biogeosciences Discuss. [preprint], https://doi.org/10.5194/bg-2016-223, 2016.
Received: 24 May 2016 – Discussion started: 20 Jun 2016
CO2 is the primary greenhouse gas, and its abundance in the atmosphere tends to increase during disturbances like drought. This paper demonstrates how CO2 measurements are combined with models to determine not only how strongly different locations influence CO2 measurement stations, but also the capacity of those measurement stations to detect drought effects. Understanding detection sensitivity will help assess what kinds of changes and turnings points can be monitored using atmospheric CO2.
CO2 is the primary greenhouse gas, and its abundance in the atmosphere tends to increase during...