Changing climate in northern regions is causing permafrost to thaw with major implications for the global mercury (Hg) cycle. We estimated Hg in permafrost regions based on in situ measurements of sediment total mercury (STHg), soil organic carbon (SOC), and the Hg to carbon ratio (R_HgC) combined with maps of soil carbon. We measured a median STHg of 43 ± 30 ng Hg g soil⁻¹ and a median R_HgC of 1.6 ± 0.9 μg Hg g C⁻¹, consistent with published results of STHg for tundra soils and 11,000 measurements from 4,926 temperate, nonpermafrost sites in North America and Eurasia. We estimate that the Northern Hemisphere permafrost regions contain 1,656 ± 962 Gg Hg, of which 793 ± 461 Gg Hg is frozen in permafrost. Permafrost soils store nearly twice as much Hg as all other soils, the ocean, and the atmosphere combined, and this Hg is vulnerable to release as permafrost thaws over the next century. Existing estimates greatly underestimate Hg in permafrost soils, indicating a need to reevaluate the role of the Arctic regions in the global Hg cycle.

Global warming has led to permafrost degradation worldwide. The Qinghai‐Tibet Plateau (QTP) hosts most of the world's alpine permafrost, yet its impending changes remain largely unclear, thereby affecting regional hydrological and ecological processes and the global carbon budget. By employing a land surface model adapted to simulate frozen ground, and using state‐of‐the‐art multi‐model and multi‐scenario data from the Coupled Model Intercomparison Project Phase 6, changes in permafrost distribution and its thermal regimes on the QTP are systematically predicted under various shared socioeconomic pathways (SSPs). Projections for SSP2‐4.5, SSP3‐7.0, and SSP5‐8.5 show that most of the continuous permafrost region of the QTP will persist through 2050. Much of the permafrost is likely to degrade in the late 21st century, with projected area losses of 44 ± 4%, 59 ± 5%, and 71 ± 7%, respectively, by 2100. In particular, the Three Rivers Source region in the central eastern part of the QTP is a key area of permafrost degradation, where permafrost is most vulnerable and degradation occurs earliest. The mean annual ground temperature of QTP permafrost will increase by 0.8 ± 0.2°C, 2.0 ± 0.3°C, and 2.6 ± 0.3°C under SSP2‐4.5, SSP3‐7.0, and SSP5‐8.5, respectively, and the active layer thickness will increase by 0.7 ± 0.1 m, 1.5 ± 0.3 m, and 3.0 ± 1.0 m, respectively. The surviving permafrost under SSP3‐7.0 and SSP5‐8.5 will be thermally unstable, which is a clear warning sign of complete disappearance. The analysis of permafrost sensitivity to climate change signifies that alpine permafrost on the QTP has low resilience to climate change, in contrast to permafrost in pan‐Artic high latitudes.

The current Northern Circumpolar Soil Carbon Database did not include organic carbon storage in permafrost regions on the Qinghai–Xizang (Tibetan) Plateau (QXP). In this study, we reported a new estimation of soil organic carbon (SOC) pools in the permafrost regions on the QXP up to 25 m depth using a total of 190 soil profiles. The SOC pools were estimated to be 17.3 ± 5.3 Pg for the 0–1 m depth, 10.6 ± 2.7 Pg for the 1–2 m depth, 5.1 ± 1.4 Pg for the 2–3 m depth and 127.2 ± 37.3 Pg for the layer of 3–25 m depth. The percentage of SOC storage in deep layers (3–25 m) on the QXP (80%) was higher than that (39%) in the yedoma and thermokarst deposits in arctic regions. In total, permafrost regions on the QXP contain approximately 160 ± 87 Pg SOC, of which approximately 132 ± 77 Pg (83%) stores in perennially frozen soils and deposits. Total organic carbon pools in permafrost regions on the QXP was approximately 8.7% of that in northern circumpolar permafrost region. The present study demonstrates that the total organic carbon storage is about 1832 Pg in permafrost regions on northern hemisphere.

To investigate the thermal characteristics and dynamics of permafrost as well as seasonally frozen ground over the upper reaches of the Heihe River Basin (URHR), an observation network with 14 boreholes was established during 2011–2014. The in situ measurements indicated mean annual air temperature that ranged from −5.2 to −2.3°C at the monitored elevation range of ∼3,600–4,150 m, and mean annual ground surface temperature that ranged from −1.3 to 1.7°C during 2013–2017. The mean annual ground temperature at 16‐ to 18‐m depth ranged from −1.71°C on the high (>4,000 m above sea level) north facing slope to about 0‐C around areas near the lower limit of permafrost. Active layer thickness at the monitored sites varied significantly with the range of 0.77–4.90 m during 2011–2017, and maximum frozen depth in seasonally frozen ground was about 5 m. Permafrost thickness was between ∼136 m and less than 10 m. Both permafrost and seasonally frozen ground were found to be subject to serious warming during the measured period in the URHR. This study provides new quantitative insights for permafrost and seasonally frozen ground in the URHR.