Venus’ light slab hinders its development of planetary-scale subduction and habitability

Terrestrial planets Venus and Earth have similar sizes, masses, and bulk compositions, but only Earth developed planetary-scale plate tectonics. Plate tectonics generates weatherable fresh rocks and transfers surface carbon back to Earth’s interior, which provides a long-term climate feedback, serving as a thermostat to keep Earth a habitable planet. Yet Venus shares a few common features with early Earth, such as stagnant-lid tectonics and the possible early development of a liquid ocean. Given all these similarities with early Earth, why would Venus fail to develop global-scale plate tectonics? In this study, we explore solutions to this problem by examining Venus’ slab densities under hypothesized subduction-zone conditions. Our petrologic simulations show that eclogite facies may be reached at greater depths on Venus than on Earth, and Venus’ slab densities are consistently lower than Earth’s. We suggest that the lack of sufficient density contrast between the high-pressure metamorphosed slab and mantle rocks may have impeded self-sustaining subduction. Although plume-induced crustal downwelling exists on Venus, the dipping of Venus’ crustal rocks to mantle depth fails to transition into subduction tectonics. As a consequence, the supply of fresh silicate rocks to the surface has been limited. This missing carbon sink eventually diverged the evolution of Venus’ surface environment from that of Earth.

Large invisible carbon sink potential of global clay minerals to mitigate climate change

The chemical weathering of clay minerals widely distributed in the soil have great potential of carbon sink (CS), but the magnitude and influence mechanisms of this CS are unclear. Here we analyse recent changes in five major clay minerals (chlorite, smectite, mica, illite, and vermiculite) carbon sink and its driving factors, using a process-based model (PROFILE) and satellite data assimilation. We show that magnitude of CS in five major clay minerals is about 0.11 Pg C yr-1 from 0 to 2m depth of soil, which is one third of CS in rocks and also may be mainly responsible for the world's missing carbon sink. According to our simulations, the linear trend of CS during 1970-2018 showing that CS in 56% of the world increasing significantly, although the intensification of CS cannot be explained by soil moisture (SM) or soil temperature (STMP) alone, they are the dominant cause of the intensification of CS in the high latitude area and the decrease of CS in parts of the tropics, while in areas where SM is drier, STMP may weaken the former’s negative effect on CS. Besides, simulation results based on medium emission scenarios indicating that CS may increase by about 36% by the end of this century. These results highlight that a more comprehensive understanding of the magnitude and driving mechanism of the soil minerals’ CS is the key to realizing their potential as a nature-based climate solution.

Increasing Autochthonous Production in Inland Waters as a Contributor to the Missing Carbon Sink

Accounting for the residual land sink (or missing carbon sink) has become a major budget focus for global carbon cycle modelers. If we are not able to account for the past and current sources and sinks, we cannot make accurate predictions about future storage of fossil fuel combustion emissions of carbon in the terrestrial biosphere. Here, we show that the autochthonous production (AP) in inland waters appears to have been strengthening in response to changes in climate and land use, as evidenced by decreasing CO2 emissions from and increasing dissolved organic carbon storage and/or organic carbon burial in inland waters during recent decades. The increasing AP may be due chiefly to increasing aquatic photosynthesis caused by global warming and intensifying human activities. We estimate that the missing carbon sink associated with the strengthening AP in inland waters may range from 0.38 to 1.8 Gt C yr-1 with large uncertainties. Our study stresses the potential role that AP may play in the further evolution of the global carbon cycle. Quantitative estimates of future freshwater AP effects on the carbon cycle may also help to guide the action needed to reduce carbon emissions, and increase carbon sinks in terrestrial aquatic ecosystems.

Remote Sensing of CO2Absorption by Saline-Alkali Soils: Potentials and Constraints

CO2absorption by saline-alkali soils was recently demonstrated in the measurements of soil respiration fluxes in arid and semiarid ecosystems and hypothetically contributed to the long-thought “missing carbon sink.” This paper is aimed to develop the preliminary theory and methodology for the quantitative analysis of CO2absorption by saline-alkali soils on regional and global scales. Both the technological progress of multispectral remote sensing over the past decades and the conjectures of mechanisms and controls of CO2absorption by saline-alkali soils are advantageous for remote sensing of such absorption. At the end of this paper, the scheme for remote sensing is presented and some unresolved issues related to the scheme are also proposed for further investigations.