Stable isotoper tracer method for gross fluxes

How much of the “missing source” can be attributed to an overestimated sink?

We have developed a stable isotope tracer technique using 13C labeled methyl halides to quantify gross emission and consumption fluxes, not just in laboratory incubations but also in field flux studies. This allowed us to simultaneously search for new plant sources while quantifying the soil sink in situ. Soil uptake estimates for Kansas tallgrass prairie (Rhew, 2011), peatland pastures (Khan, Whelan and Rhew, 2012; Khan et al, 2013), and coastal salt marshes in northern California (Rhew and Mazeas, 2010) were combined with our earlier work on boreal forest (Rhew, Aydin, and Saltzman, 2003), tundra (Teh et al., 2009), shortgrass steppe (Teh et al., 2008), annual grasslands (Rhew and Abel, 2007) and oak-savannah woodland (Rhew et al. 2010). These provided an estimate the soil sink that was 10-70% lower (i.e., longer partial lifetime) than the prior ranges, resolving a portion of the missing source problem and reducing the soil sink uncertainty (Montzka et al., 2011). Our work also demonstrated that there was a corresponding soil sink for CH3Cl, slightly exacerbating the imbalance for that compound (e.g., Rhew et al., 2010).