Dominance of inorganic carbon burial in a closed-basin lake under arid climate

Understanding carbon burial in lake sediments is essential for evaluating long-term carbon sinks, particularly in closed-basin saline lakes of arid and semi-arid regions. This study analyzes 5 sediment cores from Lake Daihai, a terminal saline lake in Inner Mongolia, to investigate the temporal and spatial variations of organic (TOC) and inorganic carbon (TIC) concentrations and burial rates over the past century. Sediment chronologies based on the CRS model and ¹³⁷Cs markers confirm continuous accumulation. Results show that TIC dominates the total sedimentary carbon pool, contributing 61 % of total burial, with a mean ICAR (from 58.4 g C m^-2 yr^-1 in 1950s to 104.9 g C m^-2 yr^-1 in 2020s) significantly exceeding OCAR (from 84.9 in 1950s to 172.7 g C m^-2 yr^-1 in 2020s). Source apportionment suggests that TOC primarily originates from soil (25.5 %), sewage (24.4 %), and phytoplankton (16.3 %), reflecting both anthropogenic and autochthonous contributions. Since the early 2000s, both TOC and TIC concentrations and burial rates have increased sharply, coinciding with accelerated GDP growth, peak population, and substantial lake surface shrinkage (reduced by 58.4 %). Partial Least Squares Path Modeling analysis reveals that lake trophic status positively influences both TOC (R = 0.48) and TIC (R = 0.78), while land use has contrasting effects TOC (R = -0.34) but positively influencing TIC (R = 0.53) through enhanced carbonate delivery. The land use reduces TOC may though limiting organic matter retention but increases TIC via enhanced carbonate input and precipitation. These results provide a framework for understanding carbon cycling in closed-basin lakes of arid regions subject to increasing human and climatic pressures.