ALBERT

Description: Thaw slumps can lead to considerable carbon loss in permafrost regions, while the loss of components from two major origins, i.e., microbial and plant-derived carbon, during this process remains poorly understood. Here, we provide direct evidence that microbial necromass carbon is a major component of lost carbon in a retrogressive permafrost thaw slump by analyzing soil organic carbon (SOC), biomarkers (amino sugars and lignin phenols), and soil environmental variables in a typical permafrost thaw slump in the Tibetan Plateau. The retrogressive thaw slump led to a ∼61% decrease in SOC and a ∼25% SOC stock loss. As evident in the levels of amino sugars (average of 55.92 ± 18.79 mg g–1 of organic carbon, OC) and lignin phenols (average of 15.00 ± 8.05 mg g–1 OC), microbial-derived carbon (microbial necromass carbon) was the major component of the SOC loss, accounting for ∼54% of the SOC loss in the permafrost thaw slump. The variation of amino sugars was mainly related to the changes in soil moisture, pH, and plant input, while changes in lignin phenols were mainly related to the changes in soil moisture and soil bulk density.

Description: This study aims to better understand the ENSO impacts on climate anomalies over East Asia in early winter (November–December) and late winter (January–February). In particular, the possible mechanisms during early winter are investigated. The results show that ENSO is associated with a Rossby wave train emanating from the tropical Indian Ocean toward East Asia (denoted as tIO-EA) in early winter. This tIO–EA wave train in El Niño (La Niña) is closely related to a weakening (strengthening) of the East Asian trough, and thereby a weakened (strengthened) East Asian winter monsoon and warm (cold) temperature anomalies over northeastern China and Japan. By using partial regression analysis and numerical experiments, we identify that the formation of tIO–EA wave train is related to precipitation anomaly in the tropical eastern Indian Ocean/ western Pacific (denoted as eIO/wP). In addition, the ENSO-induced North Atlantic anomalies may also contribute to formation of the tIO-EA wave train in conjunction with the eIO/wP precipitation. The response of eIO/wP precipitation to ENSO is stronger in early winter than in late winter. This can be attributed to the stronger anomalous Walker circulation over the Indian Ocean, which in turn is caused by higher climatological SST and stronger mean precipitation state in the Indian Ocean during early winter.

Description: This study investigates the impact of boreal spring tropical South Atlantic surface sea temperature anomalies (TSA-SSTA) on the anticyclone over the western North Pacific (WNPAC) and the Meiyu onset date (MOD) based on reanalysis data and numerical experiments. The results indicate an intimate linkage between the MOD and TSA-SSTA, in which warmer spring TSA-SSTA are associated with an earlier MOD and vice versa, and the underlying mechanism is identified. Warm TSA-SSTA can trigger a Gill-type response and anomalous equatorial Walker circulation, which leads to anomalous upward motion and latent heating over the Maritime Continent. This anomalous condition over the Maritime Continent strengthens local Hadley circulation accordingly accompanied by anomalous descending motion over the western North Pacific. This descending motion reduces the local rainfall and enhances the equatorward northerly wind at a low level. Further analysis reveals that local Sverdrup positive feedback between the anomalous diabatic cooling owing to reduced rainfall and the lower-level equatorward northerly wind are critical for sustaining the well-developed anomalous WNPAC. The abundant water vapor transport embedded in the northwestern flank of the anomalous WNPAC eventually favors an earlier MOD. Atmospheric conditions corresponding to cold TSA-SSTA produce the opposite effect. The spring TSA-SSTA can therefore prominently communicate with the subsequent East Asian MOD via the aforementioned mechanism, and the spring TSA-SSTA can be interpreted as a precursor signal of the East Asian MOD.

Description: Excessive precipitation was observed throughout the Yangtze River Valley during the 2020 Meiyu season. However, the mechanism of extreme precipitation over the upper reaches of the Yangtze River remains unclear. Our results show that the activities of high potential vorticity (PV) systems are responsible for the above-normal rainfall over both western and eastern China. The activity of high-PV systems is characterized by a prominent diurnal cycle, and their formation is closely related to the thermal contrast between the near-surface and lower atmosphere. In the morning, surface sensible heating increases sharply after sunrise, leading to a decrease in diabatic heating with height and weakened PV in the lower atmosphere. An increase in turbulence increases near-surface evaporation and reduces surface diabatic heating. At the same time, cloud formation increases diabatic heating at approximately 400 hPa. Consequently, the thermal contrast below 400 hPa leads to an increase in diabatic heating with height, favoring the generation of high-PV systems. Compared with the climatology, an excessive water vapor supply from the anomalous anticyclone forced by the Indian Ocean warming in 2020, contributes to a stronger thermal contrast and enhanced activity of high-PV systems over the TP. The arrival timing of high-PV systems at the eastern flank of the TP plays an important role in the subsequent development of these systems. Early arrival in the afternoon or evening is generally accompanied by air convergence and sufficient water vapor supply downstream of the TP, which favors the systems moving off the TP and influencing precipitation downstream.

Description: Super typhoons (SuperTYs) generated in the Northwest Pacific (WNP) constantly undergo a sharp weakening after crossing the Philippines-Taiwan into the South China Sea (SCS), thus acting as a natural “buffer” to protect the south-eastern coast of China from severe typhoons due to the blockage of the mountains and the unique atmospheric and oceanic environmental fields. This study examines the determinants of this buffer zone and speculates on the response of this part of the SuperTYs in future climate change. Here, we show that the strong vertical wind shear accompanying the South China Sea summer monsoon is a determining factor in the weakening of SuperTYs into the buffer zone, with a linear correlation up to 0.71. Although most studies suggest that the risk of severe typhoons will increase with global warming, our diagnosis of the latest Sixth Coupled Model Intercomparison Project (CMIP6) multi-model ensemble shows that the decisive factor, vertical wind shear, will not change in trend even in the worst scenario. Therefore, the risk of a severe typhoon making landfall off the southeast coast of China is not getting any worse in future global warming.

Description: The balance between alkalinity generation by carbonate and silicate weathering and sulfuric acid generation by sulfide weathering controls the effect of weathering on atmospheric pCO2 over geologic timescales. How this balance varies across environmental gradients remains poorly constrained. Here, we analyze this balance across an erosional gradient of two orders of magnitude in the Three Rivers (Yangtze, Mekong, and Salween Rivers) Headwater Region (TRHR), eastern Qinghai-Tibet Plateau (QTP). By employing major element chemistry and multiple isotopes (δ34SSO4, δ18OSO4, and δ18OH2O) coupled with forward and inverse approaches, we unmix contributions of silicates, carbonates, evaporites, and sulfides to the total weathering budget. Across the TRHR, riverine SO42– is derived mainly from a mixture of an evaporite source with uniform values of δ34SSO4 and δ18OSO4, and a sulfide source that contributes highly variable values of δ34S (−12.2 ‰ to +4.1 ‰) and δ18O (−17.7 ‰ to −1.6 ‰). Contributions of sulfide oxidation to riverine SO42– vary from 16 % to 94 %, and sulfuric acid consumes 6 % to 63 % of the alkalinity produced by weathering. The fractions of weathering alkalinity derived from carbonate weathering range from 36 % to 98 % relative to silicate weathering. The combination of silicate, carbonate, and sulfide weathering suggests that the instantaneous weathering fluxes of most sampled catchments in the TRHR act as a sink of atmospheric CO2 over timescales shorter than marine carbonate burial (∼104 years), but as a carbon source over timescales longer than carbonate burial and shorter than sulfide burial (∼107 years). The spatial variability of the balance between alkalinity and acid generation, and, thus, the relationship between chemical weathering and atmospheric pCO2, are largely dependent on lithology. However, within comparable lithologic settings, sulfide and carbonate weathering rates rise with increasing erosion, whereas silicate weathering rates remain constant. Consequently, plateau weathering shifts from a sink to a source of atmospheric CO2 with increasing erosion. These findings suggest that sulfide weathering is more sensitive to erosion than carbonate and silicate weathering, and that it could play an important role in the long-term carbon cycle during mountain building.