Analysis of CO<sub>2</sub> mole fraction data: first evidence of large-scale changes in CO<sub>2</sub> uptake at high northern latitudes

Abstract

Abstract. Atmospheric variations of carbon dioxide (CO 2 ) mole fraction reflect changes in atmospheric transport and regional patterns of surface emission and uptake. Here we present a study of changes in the observed high northern latitude CO 2 seasonal cycle. We report new estimates for changes in the phase and amplitude of the seasonal variations, indicative of biospheric changes, by spectrally decomposing multi-decadal records of surface CO 2 mole fraction using a wavelet transform to isolate the changes in the observed seasonal cycle. We also perform similar analysis of the first derivative of CO 2 mole fraction, t CO 2 , that is a crude proxy for changes in CO 2 flux. Using numerical experiments, we quantify the aliasing error associated with independently identifying trends in phase and peak uptake and release to be 10-25 %, with the smallest biases in phase associated with the analysis of t CO 2 . We report our analysis from Barrow, Alaska (BRW), during 1973-2013, which is representative of the broader Arctic region. We determine an amplitude trend of 0.09 ± 0.02 ppm yr −1 , which is consistent with previous work. Using t CO 2 we determine estimates for the timing of the onset of net uptake and release of CO 2 of −0.14±0.14 and −0.25±0.08 days yr −1 respectively and a corresponding net uptake period of −0.11±0.16 days yr −1 , which are significantly different to previously reported estimates. We find that the wavelet transform method has significant skill in characterizing changes in the peak uptake and release. We find a trend of 0.65±0.34 % yr −1 (p < 0.01) and 0.42 ± 0.34 % yr −1 (p < 0.05) for rates of peak uptake and release respectively. Our analysis does not provide direct evidence about the balance between uptake and release of carbon when integrated throughout the year, but the increase in the seasonal amplitude of CO 2 together with an invariant net carbon uptake period provides evidence that high northern latitude ecosystems are progressively taking up more carbon during spring and early summer.

Atmospheric radiocarbon measurements to quantify CO&lt;sub&gt;2&lt;/sub&gt; emissions in the UK from 2014 to 2015

“…The background concentration can be determined by applying statistical methods to high-frequency observations (Barlow et al, 2015;Ruckstuhl et al, 2012) or estimated by models (Balzani Lööv et al, 2008;Lunt et al, 2016). In this work, high-frequency data existed only for 12 CO 2 but not its isotopes and there was no model-derived background available for the isotopes; therefore, MHD data were used as background for the simulation of all CO 2 isotopes.…”

“…This has motivated researchers to combine 14 CO 2 observations with other tracers, such as carbon monoxide (CO), to improve temporal coverage (Gamnitzer et al, 2006;Levin and Karstens, 2007;Lopez et al, 2013;Miller et al, 2012;Turnbull et al, 2006Turnbull et al, , 2011. For example, high-frequency CO data have been used with 14 CO 2 measurements to regularly calibrate the CO enh (enhancement of CO from background concentration) to ffCO 2 ratio, based on weekly 14 C measurements in Europe (Berhanu et al, 2017;Levin and Karstens, 2007). However, using a CO enh : ffCO 2 ratio to estimate higherfrequency ffCO 2 can be challenging to implement even when using a well-calibrated ratio because the ratios of different sources and sinks impacting each measurement can vary considerably as each source emits with its own CO : ffCO 2 ratio (Adams et al, 2016).…”

Increasing boreal wetland emissions inferred from reductions in atmospheric CH&lt;sub&gt;4&lt;/sub&gt; seasonal cycle

“…We use a wavelet transform, described in detail in Appendix B (Torrence and Compo, 1998; 50 Barlow et al, 2015;Mackie et al, 2016), to spectrally decompose the flask CH 4 mole fraction data collected at seven high northern latitude sites ( Figure 1). The wavelet transform decomposes a time series into time-frequency space, allowing us to investigate the dominant modes of variability and how they change with time.…”

“…Here, we show that observed changes in the peak-to-peak amplitude of the seasonal cycle of atmospheric CH 4 , isolated using a wavelet transform (Barlow et al, 2015) provide additional information about changes in high northern latitude fluxes of CH 4 .…”

Atmospheric radiocarbon measurements to quantify CO&lt;sub&gt;2&lt;/sub&gt; emissions in the UK from 2014 to 2015

“…The background concentration can be determined by applying statistical methods to high-frequency observations (Barlow et al, 2015;Ruckstuhl et al, 2012) or estimated by models (Balzani Lööv et al, 2008;Lunt et al, 2016). In this work, highfrequency data existed only for 12 CO2 but not its isotopes and there was no model-derived background available for the isotopes, therefore, MHD data was used as background for the simulation of all CO 2 isotopes.…”