A considerable fraction of soil-respired CO is not emitted directly to the atmosphere.

Soil CO efflux (F) is commonly considered equal to soil CO production (R), and both terms are used interchangeably. However, a non-negligible fraction of R can be consumed in the subsurface due to a host of disparate, yet simultaneous processes. The ratio between CO efflux/O influx, known as the apparent respiratory quotient (ARQ), enables new insights into CO losses from R not previously captured by F. We present the first study using continuous ARQ estimates to evaluate annual CO losses of carbon produced from R. We found that up to 1/3 of R was emitted directly to the atmosphere, whereas 2/3 of R was removed by subsurface processes. These subsurface losses are attributable to dissolution in water, biological activities and chemical reactions. Having better estimates of R is key to understanding the true influence of ecosystem production on R, as well as the role of soil CO production in other connected processes within the critical zone.