Desert Abiotic Carbon Sequestration Weakening by Precipitation.

Desert carbon sequestration plays an active role in promoting carbon neutralization. However, the current understanding of the effect of hydrothermal interactions and soil properties on desert carbon sequestration after precipitation remains unclear. Based on the experiment in the hinterland of the Taklimakan Desert, we found that the heavy precipitation will accelerate the weakening of abiotic carbon sequestration in deserts under the background of global warming and intensified water cycle. The high soil moisture can significantly stimulate sand to release CO2 at an incredible speed by rapidly increasing microbial activity and organic matter diffusion. At this time, the CO2 flux in the shifting sand was synergistically affected by soil temperature and soil moisture. As far as soil properties are concerned, with less organic carbon substrate and stronger soil alkalinity, the carbon sequestration of shifting sand is gradually highlighted and strengthened at low temperature. On the contrary, the carbon sequestration of shifting sand is gradually weakened. Our study provides a new way to assess the contribution of desert to the global carbon cycle and improve the accuracy and scope of application.

Evolution law of atmospheric boundary layer in Gurbantünggüt Desert based on reanalysis dataset and in situ observation data.

As a special geographical unit on the earth, deserts have certain differences in planetary boundary layer (PBL) characteristics from other surface types. In order to find out the long-term evolution law of the Gurbantünggüt Desert, on the basis of evaluating the availability of reanalysis data, using the most effective reanalysis data and situ measured data in this area, the evolution law of the atmospheric boundary layer in the desert area was studied. The results show that among the ERA5, MERRA2, JRA-55 and NCEP-FNL reanalysis data, the ERA5 data has the smallest error with the measured data in the comparison of ground elements or high-altitude meteorology parameters, and can be used for the long-term evolution of the atmospheric boundary layer in desert areas. Based on the ERA5 dataset, the annual planetary boundary layer height (PBLH) of the desert fluctuated between 1979 and 1985, but showed a downward trend overall. From 1986 to 2019, the PBLH generally shows an upward trend, and by 2020, the PBLH decreases again. The PBLH in the summer of the desert was contrary to the inter-annual change trend of the PBLH throughout the year. The spatial distribution shows that the PBLH has the characteristics of north-south anisotropy. The characteristics of the ABL in the Gurbantünggüt Desert in different thermal states in summer vary greatly. Based on the sounding observational data, the average PBLH of the stable boundary layer in the Gurbantünggüt Desert in summer is 496 m, the average PBLH of the convective boundary layer is 1693 m, and the average PBLH of the neutral boundary layer is 1208 m. The ABL in desert areas from 02:00 to 08:00 and 23:00 is dominated by stable boundary layers, of which the proportion of stable boundary layers at 05:00 is as high as 67%. During the day, the boundary layer from 14:00 to 17:00 is mainly the convective boundary layer, accounting for more than 50%, and the boundary layer at 20:00 is mainly a neutral boundary layer, accounting for 55%.

Evaluation of carbon sink in the Taklimakan Desert based on correction of abnormal negative CO2 flux of IRGASON.

Studies showing that deserts can sequester CO2 through non-photosynthetic processes have contributed to locating missing carbon sinks. However, the contradiction between the desert CO2 flux obtained by different observation methods leads to uncertainty in evaluating desert carbon sequestration. This has caused scepticism regarding desert carbon sequestration after years of research. Through a comparative experiment in the non-vegetated shifting sand of the Taklimakan Desert (TD), it was found that if the abnormal negative CO2 flux observed by IRGASON during the day was not corrected, the carbon sequestration of the TD would be overestimated. The CO2 flux observed by EC155 is highly consistent with that of LI-COR8100A and can reflect the real CO2 exchange in the desert. The CO2 flux observed by EC155 was used to correct the results of IRGASON. Results show that the expansion/contraction of soil air containing CO2 caused by the change in the daily average soil temperature difference (T0-10cm) drives CO2 exchange in shifting sand. This results in diurnal variation of CO2 release caused by shifting sand during the day and CO2 absorption at night, and a unimodal distribution of CO2 exchange caused by shifting sand throughout the year. From April to September (T0-10cm > 2 °C), the shifting sand releases CO2 as a carbon source. In the other months (T0-10cm < 2 °C), the shifting sand absorbs CO2 as a carbon sink. The stronger absorption shows that the shifting sand in the TD provides carbon sequestration, with a CO2 uptake rate of ~148.85 × 104 tons a-1. This suggests that deserts play an active role in locating the missing carbon sinks and mitigating climate change, and that the status of deserts in the global carbon cycle cannot be ignored.

Characteristics of land-atmosphere interaction parameters in hinterland of the Taklimakan Desert.

The importance of the energy exchange between the land surface and the atmosphere can be characterized by bulk transfer coefficients for momentum, Cd, and heat, Ch. The diurnal and monthly variations of both bulk transfer coefficients and lengths of surface roughness are analyzed. Based on observed data from January to December 2009 in hinterland of the Taklimakan Desert, the characteristics of aerodynamic roughness length, z0m, and thermal roughness length, z0h, are discussed. It should be noted that the diurnal and monthly variations of the parameters are fundamentally different from those reported in vegetated areas. Specifically, four unique features can be identified in the surface layer. First, in Taklimakan Desert, z0m does not vary with seasons; however, it significantly depends on wind speed. Second, z0h is higher in the daytime and lower at night, showing obvious diurnal characteristics. The high values appear at sunrise and sunset. Third, both Cd and Ch have two peaks, one peak at sunrise, and another one at noon. Fourth, both Cd and Ch have larger values in winter season and smaller values in summer season.

Coefficients optimization of the GLASS broadband emissivity based on FTIR and MODIS data over the Taklimakan Desert.

In this paper, the Taklimakan Desert land surface emissivity measured by portable Fourier Transform thermal InfraRed spectroscopy (FTIR) was used to re-estimate Global LAnd Surface Satellite (GLASS) BroadBand Emissivity (BBE) and Moderate Resolution Imaging Spectroradiometer (MODIS) BBE optimal coefficients equations. In addition, the revised BBE equations of both GLASS and MODIS with the optimized coefficients were obtained. Comparing the FTIR and MODIS BBE data with the values retrieved before and after the revised GLASS BBE equation, it was found that the revised GLASS BBE equation is more accurate than the original one. First, according to the error analysis with FTIR data, the value of R2 is increased from 0.4 to 0.9, and the Root Mean Square Error (RMSE) and Bias are reduced by 1 and 3 magnitude orders, respectively. Second, with MODIS BBE data, the value of R2 is increased from 0.6 to 0.9, the RMSE and Bias are reduced by 1 and 2 magnitude orders, respectively. Finally, the Taklimakan Desert BBE was calculated using the revised GLASS BBE equation. The results showed that the BBE values are between 0.890 and 0.920 in the desert center, between 0.920 and 0.950 in the sparse vegetation areas, and between 0.950 and 0.980 in the oasis edges.