Spatio-temporal Distribution of Carbon Source/Sink and Carbon Surplus/Deficit in Northeast China

The carbon cycle is a key component influencing climate change. Existing studies have primarily focused on natural carbon sink or social carbon emission, whereas integrated assessments of regional natural-social carbon surplus/deficit within a unified spatiotemporal context remain relatively scarce. Taking Northeast China as the study area, this study estimated net ecosystem productivity (NEP) during 2000–2020 using the Carnegie-Ames-Stanford Approach (CASA) model combined with soil microbial respiration, projected land-cover distribution and associated carbon sink capacity for 2025, 2030, and 2035 using the CA-Markov model, and analysed social carbon emissions using the STIRPAT framework and ridge regression. Scenario analysis was further applied to project future carbon emission and regional carbon surplus/deficit. The results showed that: 1) NEP in Northeast China exhibited a fluctuating upward trend during 2000–2020, with a net increase of 4.34 Tg C, and the projected total carbon sink was 267.32, 266.28 and 266.82 Tg C/yr in 2025, 2030, and 2035, respectively. 2) Future scenario simulations revealed marked inter-provincial and pathway differences, with Z1 representing the optimal pathway balancing development and emission reduction and Z6 showing the highest mitigation efficiency. 3) Northeast China shifted from a carbon surplus to a carbon deficit during 2000–2020, with the turning point occurring in 2005, and the region is expected to remain in carbon deficit during 2025–2035. However, the deficit gap is expected to gradually narrow, from 106.27 to 84.64 Tg C/yr under Z1 and from 99.99 to 72.17 Tg C/yr under Z6. These findings highlight the importance of coordinating natural carbon sink enhancement with social emission reduction and provide scientific support for regionally differentiated strategies for carbon peaking and carbon neutrality.