Nature Geoscience最新文献

The rheology of the lower crust and upper mantle influences Earth’s plate tectonic style of mantle convection, yet its spatial variability is poorly resolved, particularly in continental interiors. Here we use satellite radar interferometry to map the delayed uplift resulting from the desiccation of the Aral Sea, which has lost ~1,000 km³ of water since 1960. From this we constrain the rheology of the underlying upper mantle by elastic and viscoelastic modelling. We find a long-wavelength uplift of up to ~7 mm yr^–1 between 2016 and 2020 that decays radially from the Aral Sea. This uplift pattern is best explained by viscoelastic relaxation of the asthenosphere below a strong lithospheric mantle. We estimate that the asthenosphere has an effective viscosity of 4–7 × 10¹⁹ Pa s below 130–190 km depth, slightly larger than the values inferred from post-seismic deformation at subduction zones, but 1–2 orders of magnitude smaller than estimates from glacial isostatic adjustment in other tectonically stable regions. Such uplift highlights the potential for human activities to influence deep-Earth dynamics and the interconnectedness of surface and mantle processes.

Mesoscale convective systems are a class of storm linked to extensive flooding and other destructive hazards in many regions globally. In West Africa, soil moisture impacts provide a valuable source of predictability for mature storm hazards, but little is known about mature storm sensitivity to soil moisture in other climatic regions. Here we use a storm track dataset, satellite observations and reanalysis fields to investigate the response of mature storms to soil moisture in seven global storm hotspots—West Africa, India, South America, South Africa, Australia and the United States Great Plains. We demonstrate that mesoscale soil moisture gradients (~500 km) can enhance storms by driving increased vertical wind shear conditions, a crucial ingredient for storm organization, through the strengthening of atmospheric temperature gradients. This is evidenced by a 10–30% increase in precipitation feature size and rainfall for the largest storms on days with favourable soil moisture gradients compared with unfavourable gradients. Global simulations confirm that soil moisture gradients influence wind shear. The results demonstrate the importance of soil moisture feedbacks for accurate forecasting of mesoscale convective systems and future projections of extreme events under climate change.

Ice-sheet mass loss is one of the clearest manifestations of climate change, with Antarctica discharging mass into the ocean via melting or through calving. The latter produces icebergs that can modify ocean water properties, often at great distances from source. This affects upper-ocean physics and primary productivity, with implications for atmospheric carbon drawdown. A detailed understanding of iceberg modification of ocean waters has hitherto been hindered by a lack of proximal measurements. Here unique measurements of a giant iceberg from an underwater glider enable quantification of meltwater effects on the physical and biological processes in the upper layers of the Southern Ocean, a region disproportionately important for global heat and carbon sequestration. Iceberg basal melting erodes seasonally produced winter water layer stratification, normally forming a strong potential energy barrier to vertical exchange of surface and deep waters, while freshwater run-off increases and shoals near-surface stratification. Nutrient-rich deeper waters, incorporating meltwater loaded with terrigenous material, are ventilated to below this stratification maxima, providing a potential mechanism for alleviating critical phytoplankton-limiting components. Regional historical hydrographic data demonstrate similar stratification changes during the passage of another large iceberg, suggesting that they may be an important pathway of aseasonal winter water modification.

The susceptibility of cloud droplet number to cloud condensation nuclei number is one of the major factors controlling the highly uncertain change in the amount of solar radiation reflected by clouds when aerosol emissions are perturbed (the radiative forcing due to aerosol–cloud interactions). We investigate this susceptibility in low-level stratiform clouds using long-term (3–10-yr) in situ observations of aerosols and clouds at three high-latitude locations. The in situ observations show higher susceptibility for low-level stratiform clouds than values reported for satellite data. We estimate −1.16 W m⁻² for the aerosol indirect radiative forcing on the basis of our observations, which is at the higher end of satellite-derived forcing estimates and the uncertainty range of the most recent Intergovernmental Panel on Climate Change report. We evaluate four Earth system models against the observations and find large inter-model variability in the susceptibility. Our results demonstrate that, even if the susceptibility in some of the models is relatively close to observations, the underlying physics in the models is unrealistic when compared with observations. We show that the inter-model variability is driven by differences in sub-grid-scale updraught velocities and aerosol size distributions, raising a need to improve these aspects in models.

Precipitation over East Asia and the western United States is projected to increase as a result of global warming, although substantial uncertainties persist regarding the magnitude. A key factor driving these uncertainties is the tropical surface warming pattern, yet the mechanisms behind both this warming pattern and the resulting regional precipitation changes remain elusive. Here we use a set of climate model experiments to argue that these changes are partly driven by global teleconnection from the Southern Ocean, which rapidly absorbs anthropogenic heat but releases it with a delay of decades to a century. We show that the delayed Southern Ocean warming contributes to broad tropical ocean warming with an El Niño-like pattern, enhancing precipitation during summer in East Asia and winter in the western United States. The atmospheric teleconnections from the tropical ocean link the Southern Ocean warming to the Northern Hemisphere regional wetting. Southern Hemisphere low clouds are a key regulator of this teleconnection, partly explaining the projected uncertainty of regional precipitation. The documented teleconnection has practical implications: even if climate mitigation reduces carbon dioxide levels, the delayed Southern Ocean warming will sustain a wetter East Asia and western United States for decades to centuries.

The Meng Xiang (‘Dream’ in Chinese) is a recently commissioned vessel that was specifically designed to drill through intact ocean crust into the mantle¹⁰. Able to operate in rough seas with a dynamic stabilization system (pictured), it can drill down up to 11 kilometres using a variety of modes — including both riser and riserless systems — optimized for settings from the tropics to the poles. The titanium alloy drill rod and the diamond bit enable reliable drilling in the high-temperature and high-pressure environment. Rapid processing and analysis of core material will take place in a floating laboratory that can operate continuously for months. But we must be patient, allowing enough time for the process of trial and error. For any chosen site, we must be prepared for multiple entries, multiple expeditions, and perhaps multiple years to reach the Moho. Beyond targeting the Moho, the ship has the capability to carry on the legacy of the JOIDES Resolution — a drilling vessel that was operated by the International Ocean Discovery Program until 2024 — by addressing the full range of scientific questions identified by the international ocean drilling community⁸.

The first scientific drilling expeditions by the Meng Xiang are expected to begin next year and plans are being developed to carry out full-scale drilling to the Moho beneath the Pacific or Indian seafloor before 2030. The oceanic crust is thin in each region, though sites can be chosen to focus on differences in crust formed from both fast- and slow-spreading ridges. The drill core samples will give scientists an unprecedented opportunity for understanding the architecture and formation of the ocean crust as well as the petrological nature of the oceanic Moho — which will help ground truth many important aspects of plate tectonics theory. Alongside this, the samples will also be used to explore the bottom limit of Earth life among other research interests. With this long-sought goal to sample the boundary between crust and mantle within reach with the Meng Xiang, we advocate for the development of an international collaboration⁶ around this shared goal in the spirit of ‘mission Moho’. International scientists will be welcome to join the drilling expeditions and to share the samples for their research following a moratorium similar to the Integrated Ocean Drilling Program (IODP).