Sensitivity of the global carbonate weathering carbon-sink flux to climate and land-use changes

Abstract

The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is still not well understood on the global scale. This hinders understanding of the terrestrial carbon cycle. Here, we show that there is likely to be a widespread and consistent increase in the global CCSF (ranging from + 9.8% (RCP4.5) to + 17.1% (RCP8.5)) over the period 1950-2100. In the coming years the increasing temperature might be expected to have a negative impact on carbonate weathering. However, the increasing rainfall and anticipated land-use changes will counteract this, leading to a greater CCSF. This finding has been obtained by using long-term historical (1950-2005) and modeled future (2006-2100) data for two scenarios (RCP4.5 and RCP8.5) for climate and land-use change in our CCSF equilibrium model. This study stresses the potential role that carbonate weathering may play in the evolution of the global carbon cycle over this century.

Fig. 1. Interannual changes in relevant variables.

a [HCO₃⁻]_eq, b R (runoff), and c CCSF (carbonate weathering carbon-sink flux) on global carbonate rock outcrops during the historical period (1950–2005) and the two future (2006–2100) scenarios (RCP4.5 and RCP8.5). All the variables display increasing trends. The historical period (black line) has the lowest CCSF variation and RCP8.5 (purple line) has the highest, indicating the substantial response of CCSF to dramatic climate change and land-use conversion.

Fig. 2. Spatial distribution of CCSF and its changes.

a Annual average CCSF (carbonate weathering carbon-sink flux) in carbonate rock outcrops for the historical period (1950–2005) and its changes for the two differing climate and land-use change scenarios, b RCP4.5, and c RCP8.5. Note: nearly 72% of carbonate rock outcrop is distributed in the mid and high latitudes (30°–90°) and less in the low latitudes (0°–30°).

Fig. 3. Latitudinal distribution of relevant variable trends.

a Soil pCO₂, b [HCO₃⁻]_eq, c R (runoff), and d CCSF trends for three cases (the historical period, and the future period for RCP4.5 and RCP8.5). The shaded areas are the northern high latitudes (60°N–90°N, light gray) and the low latitudes (30°S–30°N, light pink).

Fig. 4. Latitudinal variations of relevant variables.

[HCO₃⁻]_eq (dark-shaded area in a–d) and R (runoff, light-shaded area in e–g) in relation with mean temperature (black line in a and e), mean precipitation (blue line in b and f), land-use type (multicolor lines in c and g), and soil pCO₂ (purple lines in d) in the historical period (1950–2005). Three [HCO₃⁻]_eq peaks occur in three latitudinal zones (50–70 °N, 0–10 °S, and 40–50 S°). The dashed line in a is the upper temperature limit (15 °C) for maximum carbonate dissolution. The highest runoff (R) can be found in the tropical zone and the area close to 40 °S.

Fig. 5. Latitudinal CCSF variation with relevant variables.

CCSF (carbonate weathering carbon-sink flux, blue line in a and b) in relation to a [HCO₃⁻]_eq (dark grey-shaded area) and b R (runoff, light-gray shaded area) in the historical period (1950–2005). CCSF shows a significant positive relationship to runoff (R) across all latitudes.

Fig. 6. Relationship between CCSF and relevant variables.

a CCSF (carbonate weathering carbon-sink flux) and [HCO₃⁻]_eq, and b CCSF and R (runoff) in the historical period (1950–2005), normalized into three global latitudinal zones. Runoff dominates the CCSF variation across different latitudinal zones. [HCO₃⁻]_eq shows a high (R² = 0.86) positive relation with CCSF only in high latitudes (60°–90°), where runoff is low.