Background, aim, and scope Significant spatial differences of (paleo-) climate change on the Tibetan Plateau (TP) has been revealed by researches. However, there are scarcer paleoclimate records in the northern than the southern and eastern regions, which hinders our fully understanding of the regional differences in climatic change on the TP. Little Kalakul Lake (LKL, 38°27.67' 38°28.62'N, 75°01.77' 75°03.02'E, 3661 m.a.s.l) is located in the Muztag Ata region. LKL is a hydrologically open freshwater lake mainly fed by rainfall, connects to the upstream lake in the southwest, and has a lake outlet in the northeast. The area is dominated by westerly winds and has a dry and cold climate. Owing to be sensitive response to climate changes and little human activity, lake sediment in Little Kalakul Lake is ideal for reconstructing regional climate and environment change. To fill the gap about temperature change in northwestern TP, we reconstructed a temperature-proxy record with ~3-year resolution during AD 18122012, based on the total organic carbon (TOC) variation of lake sediment from Little Kalakul Lake in the Muztag Ata. Materials and methods In June 2013, a lake sediment core (6.28 m long) was collected from the eastern basin of LKL. The water depth of the sampling site was about 22 m. The core was sliced in the field at intervals of 1 cm. In this study, we analyzed samples of the upper 77 cm. Meanwhile, we collected 7 dominant terrestrial plant species, 7 submerged plant species, 1 emergent plant species and 1 algae sample (all above plant were unidentified species). The sediment chronology was constructed by measuring radionuclides (210Pb and 137Cs). The contents of TOC were obtained through total carbon contents subtract inorganic carbon contents, and Kjeldahl method was employed to determine the contents of TN. Results According to the results of 210Pb and 137Cs specific activity measurement, the average sedimentation rate of the upper 77 cm samples is 0.38 cm · a-1, and the sediment record covers about 200 years, reaching back to AD 1812. TOC contents of LKL sediment vary between 5.1% and 12.2% with an average of 7.4%. TN contents range from 0.4% to 1.8% with an average of 0.8%. In addition, the average C/N ratios of sediment samples, terrestrial plants, aquatic plants and algae are 9.1, 29.4, 14.3 and 1.9, respectively. Over the past 200 years, TOC contents of sediment increased generally in fluctuation, but grew remarkably during AD 1980 2004 and AD 1864 1914 (to 12.2% from 6.2% and to 8.9% from 5.1%the lowest, respectively), and decreased during AD 1812 1864, AD 1914 1980 and since 2004. TN contents had a consistent trend with TOC contents while smaller amplitude, resulting in the decreasing C/N ratios. Discussion C/N ratio has been commonly used to identify the source of organic matter. Normally, C/N ratios in algae are less than 10; C/N ratios in terrestrial plants are more than 20. The results showed that the C/N ratios of terrestrial plants were much higher than those of aquatic plants (P = 0.009), C/N ratios of sediment were lower than those of terrestrial plants and similar to those of aquatic plants, which indicated that TOC of LKL sediment mainly originated from aquatic organisms. This coincided with LKL catchment conditions such as cold and dry climate, poor development of terrestrial plants. The growth of aquatic organisms in lakes is mainly controlled by the lake nutrient conditions and temperature changes.