Permafrost degradation related to global warming has been widespread in the Tibetan Plateau (TP), manifesting prominently as variations in the soil thermal regime, an essential characteristic of permafrost. Altered soil thermal conditions can influence the energy and water balance between the atmosphere and land, leading to the release of stored carbon dioxide and methane. In this study, reanalysis and observed soil temperature data were combined to analyse the long-term changes in the thermal regime of the uppermost soil layer at six sites in the central TP. MERRA2 and ERA5-Land had the highest quality in matching the observed data at each site. The mean annual soil temperature ranged from -0.11 degrees C to 4.75 degrees C (averaging 1.73 degrees C) and warms at 0.059 degrees C a(-1). The mean annual first dates of freezing and thawing and the mean duration of freezing were 123.23 +/- 10.85 d, 285.67 +/- 10.34 d, and 161.44 +/- 20.54 d, respectively, indicating lagged, advanced, and shortened trends with 0.54 +/- 0.49 d a(-1), 0.50 +/- 1.06 d a(-1), and 1.05 +/- 1.16 d a(-1), respectively. The mean annual freezing and thawing N-factors were 0.53 +/- 0.13 and 2.43 +/- 2.09, respectively. The maximum and minimum monthly average soil temperatures were 11.81 +/- 2.17 degrees C in July and-9.54 +/- 3.24 degrees C in January, respectively. Partial correlation analysis was used to quantify the influences of factors (including surface air temperature, snow depth, rainfall, normalised difference vegetation index [NDVI], shortwave radiation, and soil moisture) on soil temperature implicated surface air temperature as the most significant influencing factor in the increased soil temperature. Rainfall and NDVI were implicated as being likely to suppress the soil temperature warming. This study provides detailed information about the thermal regime of the uppermost soil in the central TP and facilitates validation of the land surface model.

The influence of the Indian summer monsoon (ISM) and mid-latitude westerlies on the central Tibetan Plateau (TP) during the Holocene, particularly during the mid-Holocene, is still unclear, limiting our understanding of past climate change in this region. Cuona Lake, located on the central TP, is a transitional zone of atmospheric circulation that is well situated for investigations on the interplay between the ISM and mid-latitude westerlies. In this study, multiple proxies of lacustrine sediments from Cuona Lake were measured, including total organic carbon (TOC), total nitrogen (TN), delta C-13(org), n-alkanes, and their hydrogen isotopes, to reconstruct the evolution of climate on the central TP over the past 13 cal kyr BP. Decreased TOC/TN ratios, dominant short-chain n-alkanes/alkanoic acid C-15/16/17, and lower values of n-alkane indicator ratios (carbon preference index and average chain length) throughout the investigated period suggest that the organic matter of the lake essentially originated from aquatic algae, and was weakly affected by terrestrial input. The historic variations in the delta D, TOC, and delta C-13(org) values revealed cold-wet conditions during 12.4-11.4 cal kyr BP, warm-wettest environments during the early Holocene (from 11.4 to 8.2 cal kyr BP), cool-wet conditions in the mid-late Holocene (from 5 to 3 cal kyr BP), and warm-dry conditions since 3 cal kyr BP. The reconstructed climatic variability in the Cuona area agrees well with previous indexes in south-central TP, indicating that the climatic pattern of the studied area is basically controlled by the monsoonal circulation from the late part of the last deglaciation to the early Holocene, with the ISM reaching the north-central TP at similar to 11 cal kyr BP. During the mid-late Holocene, the humid conditions coincided with an enhanced influence of westerlies, providing strong evidence for the contribution of westerlies-delivered moisture to the central TP. Based on a comparison of paleoclimate records, the Cuona region displays a transitional phase between monsoon circulation and westerly jets during the Holocene.

Permafrost degradation related to global warming has been widespread in the Tibetan Plateau (TP), manifesting prominently as variations in the soil thermal regime, an essential characteristic of permafrost. Altered soil thermal conditions can influence the energy and water balance between the atmosphere and land, leading to the release of stored carbon dioxide and methane. In this study, reanalysis and observed soil temperature data were combined to analyse the long-term changes in the thermal regime of the uppermost soil layer at six sites in the central TP. MERRA2 and ERA5-Land had the highest quality in matching the observed data at each site. The mean annual soil temperature ranged from -0.11 degrees C to 4.75 degrees C (averaging 1.73 degrees C) and warms at 0.059 degrees C a(-1). The mean annual first dates of freezing and thawing and the mean duration of freezing were 123.23 +/- 10.85 d, 285.67 +/- 10.34 d, and 161.44 +/- 20.54 d, respectively, indicating lagged, advanced, and shortened trends with 0.54 +/- 0.49 d a(-1), 0.50 +/- 1.06 d a(-1), and 1.05 +/- 1.16 d a(-1), respectively. The mean annual freezing and thawing N-factors were 0.53 +/- 0.13 and 2.43 +/- 2.09, respectively. The maximum and minimum monthly average soil temperatures were 11.81 +/- 2.17 degrees C in July and-9.54 +/- 3.24 degrees C in January, respectively. Partial correlation analysis was used to quantify the influences of factors (including surface air temperature, snow depth, rainfall, normalised difference vegetation index [NDVI], shortwave radiation, and soil moisture) on soil temperature implicated surface air temperature as the most significant influencing factor in the increased soil temperature. Rainfall and NDVI were implicated as being likely to suppress the soil temperature warming. This study provides detailed information about the thermal regime of the uppermost soil in the central TP and facilitates validation of the land surface model.