Articles | Volume 15, issue 21
Biogeosciences, 15, 6559–6572, 2018
Biogeosciences, 15, 6559–6572, 2018

Research article 07 Nov 2018

Research article | 07 Nov 2018

Ecosystem carbon transit versus turnover times in response to climate warming and rising atmospheric CO2 concentration

Xingjie Lu1,2,3, Ying-Ping Wang3, Yiqi Luo2,4, and Lifen Jiang2 Xingjie Lu et al.
  • 1School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou 510275, China
  • 2Center for Ecosystem Science and Society, Department of Biological Sciences, Northern Arizona University, Flagstaff 86011, USA
  • 3CSIRO Oceans and Atmosphere, Aspendale 3195, Australia
  • 4Department for Earth System Science, Tsinghua University, Beijing 100084, China

Abstract. Ecosystem carbon (C) transit time is a critical diagnostic parameter to characterize land C sequestration. This parameter has different variants in the literature, including a commonly used turnover time. However, we know little about how different transit time and turnover time are in representing carbon cycling through multiple compartments under a non-steady state. In this study, we estimate both C turnover time as defined by the conventional stock over flux and mean C transit time as defined by the mean age of C mass leaving the system. We incorporate them into the Community Atmosphere Biosphere Land Exchange (CABLE) model to estimate C turnover time and transit time in response to climate warming and rising atmospheric [CO2]. Modelling analysis shows that both C turnover time and transit time increase with climate warming but decrease with rising atmospheric [CO2]. Warming increases C turnover time by 2.4 years and transit time by 11.8 years in 2100 relative to that at steady state in 1901. During the same period, rising atmospheric [CO2] decreases C turnover time by 3.8 years and transit time by 5.5 years. Our analysis shows that 65 % of the increase in global mean C transit time with climate warming results from the depletion of fast-turnover C pool. The remaining 35 % increase results from accompanied changes in compartment C age structures. Similarly, the decrease in mean C transit time with rising atmospheric [CO2] results approximately equally from replenishment of C into fast-turnover C pool and subsequent decrease in compartment C age structure. Greatly different from the transit time, the turnover time, which does not account for changes in either C age structure or composition of respired C, underestimated impacts of warming and rising atmospheric [CO2] on C diagnostic time and potentially led to deviations in estimating land C sequestration in multi-compartmental ecosystems.

Short summary
How long does C cycle through terrestrial ecosystems is a critical question for understanding land C sequestration capacity under future rising atmosphere [CO2] and climate warming. Under climate change, previous conventional concepts with a steady-state assumption will no longer be suitable for a non-steady state. Our results using the new concept, C transit time, suggest more significant responses in terrestrial C cycle under rising [CO2] and climate warming.
Final-revised paper