Factors contributing to spatial–temporal variations of observed oxygen concentration over the Qinghai-Tibetan Plateau

Abstract

Oxygen (O2) is the most abundant molecule in the atmosphere after nitrogen. Previous studies have documented that oxygen concentration remains nearly constant (20.946%) at all altitudes. Here we show for the first time that oxygen concentration varies significantly from earlier consensus and shows strong spatial and seasonal differences. Field observations on the Qinghai-Tibetan Plateau (QTP) indicate oxygen concentration of 19.94–20.66% (2018, n = 80), 19.98–20.78% (2019, n = 166) and 19.97–20.73% (2020, n = 176), all statistically different from earlier reports (p < 0.001) and are lower than the nearly constant. The mean oxygen concentration in summer (20.47%) is 0.31% higher than that of winter (20.16%) (n = 53) at identical locations in 2019, sampled in the Qilian Mountains, northwest QTP. We used LMG (The Lindeman, Merenda and Gold) method to estimate the relative contributions of altitude, air temperature and vegetation index (Fractional Vegetation Cover, FVC and Leaf Area Index, LAI) to oxygen concentration, which are 47%, 32% and 3% (FVC, R2 = 82%); 45%, 30% and 7% (LAI, R2 = 82%), respectively. These findings provide a new perspective for in-depth understanding on population risk in high altitude regions in the context of global climate change, to ensure the health and safety of residents and tourists in high altitude regions and promoting the stability, prosperity and sustainable development of high-altitude regions worldwide.

Environmental Factors Affecting Near-Surface Oxygen Content Vary in Typical Regions of the Qinghai-Tibet Plateau

“…In our study, vegetation (i.e., NPP, LAI, FVC) factors were significantly correlated with oxygen content in the Qilian Mountains and Three-River Headwater Area (northern QTP), while in the Hengduan Mountains (southern QTP), oxygen content was mainly related to altitude (Table 1). Similar results were reported by Shi et al (2021b), suggesting that changes in oxygen content over the northern QTP will be more sensitive under future climate change scenarios (Guo et al, 2022). Therefore, more research on changes in oxygen content in the region is strongly needed to ensure the sustainable development of high-altitude regions under global climate change.…”

“…During July and August from 2017 to 2020, several field investigations were conducted along sample lines on the QTP and its vicinities (Figure 1). The altitude, geographical location, and near-surface oxygen content were recorded from 487 sites, of which 214 samples were selected in the present study (more details in Shi et al, 2021b). Each site's geographical location and altitude were recorded using an Oregon 450 Satellite Navigation device (Garmin., Schaffhausen, Switzerland).…”

“…In the modern atmosphere, primary production in terrestrial and marine ecosystems is the main source of atmospheric oxygen (Keeling et al, 1993;Huang et al, 2021). Altitude, through its effect on microclimate shaping and a range of biological and physical processes, such as the weathering of organic matter, microbial activity (Battle et al, 2019;Cao et al, 2020;Shi et al, 2021b), and vegetation NPP (Chen S.-t. et al, 2021), may diminish the effect of vegetation on atmospheric oxygen. These findings jointly highlight the non-negligible role of altitude on oxygen flux estimates in highland ecosystems.…”

“…However, climate change and intensified human activities have caused a steady decline in oxygen content (Liu et al, 2020). For high-altitude areas (≥2,500 m above sea level), the total area of which is 7.7% of the Earth's land area and is home to 1.5% of the world's total population, such subtle changes have posed challenges to economic, social, and environmental sustainability (Shi et al, 2021b). Chronic mountain sickness caused by hypoxia severely limits the use of resources and survival of the sedentary population in these areas (Vingrys and Garner, 1987;Hobkirk et al, 2013).…”

“Urban Respiration” Revealed by Atmospheric O2 Measurements in an Industrial Metropolis

“…The longest record of direct atmospheric O 2 measurements in the modern atmosphere shows a steady decline of approximately 4 ppm/yr since the late 1980s, which is generally attributable to fossil fuel combustion and anthropogenic modifications to the land surface including deforestation. , The aggressive urban expansion has not only substantially boosted anthropogenic fossil fuel and O 2 consumption but also deprived the ecosystem of biological O 2 production and CO 2 fixation, breaking the atmospheric O 2 balance. , A recent ice-core-based study attributed a decline in atmospheric O 2 since the Mid–Pleistocene transition (1.2–0.7 million years ago) to glacial weathering . Shi et al and Chen et al measured O 2 content over the Tibetan Plateau and implied reduced hypoxia risk on the Tibetan Plateau in a warming climate.…”