Reconciling carbon exchange efficiency from ecosystem to global scales
Abstract
One of the greatest challenges for earth system scientists (ESMs) is improving important carbon cycle processes, so that more reliable climate predictions can be provided to society. However, part of the challenge of benchmarking carbon cycle observations with model simulations is that estimates of important C cycle processes, such as gross primary productivity (GPP) and net ecosystem exchange (NEE), are inconsistent at ecosystem and global scales and difficult to reconcile due to units of flux that vary by 12 orders of magnitude. Here we present a carbon exchange (CEE=NEE/GPP) framework to estimate the fraction of atmospheric CO 2 fixed through photosynthesis that remains in the biosphere and can be used to test hypotheses to explain differences across scales. At the global scale, we estimate that less than 2% of CO 2 fixed annually actually remains in the terrestrial biosphere (120.8/2.5 PgC/yr). In contrast, across ecosystems we estimate a wide range of CEE from 2% at some grassland sites to as much as 25% at some deciduous forest sites. We hypothesize that this scale mis-match in CEE is either due to biases in eddy covariance network measurements, or due to carbon loss pathways leading to C oxidation. Our preliminary results do not indicate that the scale mismatch in CEE is due to measurement or network bias, but rather due to C loss pathways, such as the oxidation of volatile organics, evasion from aquatic ecosystems, and harvest. Our results imply that there is considerable lateral transport and transformation of C among ecosystems and that ecosystems are more leaky than previously thought. Furthermore, ESMs do not often simulate this myriad of C oxidation loss pathways and thus overestimate total respiration in order to conserve the mass balance of atmospheric CO 2 .
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A53Q3127B
- Keywords:
-
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0480 Remote sensing;
- BIOGEOSCIENCES