地球科学最新文献

The absence of reliable paleomagnetic constraints from the Lhasa Block has led to alternative interpretations of its late Paleozoic position and timing of rifting from Gondwana, reflecting uncertainties in early Neo-Tethyan paleogeography. This study presents paleomagnetic and geochronological data from the middle Permian Luobadui Formation, providing a new paleogeographic constraint on the Lhasa Block. Despite possible remagnetization, the dual-polarity magnetization, hosted in different minerals and lithologies, likely represents a middle Permian remanence. This constraint implies the Lhasa Block was located at 16.7 ± 5.3°S at 267.8 ± 5 Ma, following its rifting from Gondwana. New U-Pb detrital zircon ages from sandstones further suggest the Lhasa Block was located along the northwestern margin of Australia prior to rifting. Integrating other geological evidence, we propose that the Bangong Co-Nujiang and Yarlung-Zangbo oceans, now preserved as sutures flanking the Lhasa Block, both opened before the middle Permian, potentially representing branches of the same nascent oceanic corridor (Neo-Tethys).

Alkaline lakes are among the most bioproductive aquatic ecosystems on Earth. The factors that ultimately limit productivity in these systems can vary, but nitrogen (N) cycling in particular has been shown to be adversely affected by high salinity, evidently due to the inhibition of nitrifying bacteria (i.e., those that convert ammonic species to nitrogen oxides). The coastal plain of Coorong National Park in South Australia, which hosts several alkaline lakes along 130 km of coastline, provides an ideal natural laboratory for examining how fine-scale differences in the geochemistry of such environments can lead to broad variations in nitrogen cycling through time, as manifest in sedimentary δ¹⁵N. Moreover, the lakes provide a gradient of aqueous conditions that allows us to assess the effects of pH, salinity, and carbonate chemistry on the sedimentary record. We report a wide range of δ¹⁵N values (3.8‰–18.6‰) measured in the sediments (0–35 cm depth) of five lakes of the Coorong region. Additional data include major element abundances, carbonate δ¹³C and δ¹⁸O values, and the results of principal component analyses. Stable nitrogen isotopes and wt% sodium (Na) display positive correlation (R² = 0.59, p < 0.001) across all lake systems. Principal component analyses further support the notion that salinity has historically impacted nitrogen cycling. We propose that the inhibition of nitrification at elevated salinity may lead to the accumulation of ammonic species, which, when exposed to the water column, are prone to ammonia volatilization facilitated by intervals of elevated pH. This process is accompanied by a significant isotope fractionation effect, isotopically enriching the nitrogen that remains in the lake water. This nitrogen is eventually buried in the sediments, preserving a record of these combined processes. Analogous enrichments in the rock record may provide important constraints on past chemical conditions and their associated microbial ecologies. Specifically, ancient terrestrial aquatic systems with high δ¹⁵N values attributed to denitrification and thus oxygen deficiency may warrant re-evaluation within the framework of this alternative. Constraints on pH as provided by elevated δ¹⁵N via ammonia volatilization may also inform critical aspects of closed-basin paleoenvironments and their suitability for a de novo origin of life.

Understanding and mapping seabed sediment distribution in shelf seas is essential for effective coastal management, offshore developments, and for blue carbon stock assessments and conservation. Fine-grained marine sediments, particularly muds, play a key role in long-term organic carbon sequestration, so knowledge of the spatial extent of these carbon-rich deposits is important. Here, we consider how changes in shelf sea tidal dynamics since the Last Glacial Maximum have influenced the development of three mud depocenters in the northwest European shelf seas: the Fladen Ground, the Celtic Deep, and the Western Irish Sea Mud Belt. Using a new high-resolution paleotidal model, we demonstrate how the evolution of simulated tidal parameters, including bed shear stress and bottom boundary layer thickness, differ across these sites. Geological data support our findings, indicating that long-term mud sedimentation continues to the present in the Celtic Deep and Western Irish Sea Mud Belt, while in the Fladen Ground, accumulation cannot be fully explained by contemporary hydrodynamics. In the latter, mud deposition is relict, deposited during quiescent tidal conditions between 17,000 and 5,000 years ago. We suggest that simulating paleoceanographic conditions can contribute to understanding first-order sediment dynamics over large spatial and temporal scales, a key input for predictive mapping and regional blue carbon inventories. This approach is a valuable first step in data-poor regions to identify potential fine sediment deposits. By illustrating the temporal evolution of organic carbon-rich deposits, we provide a broader context for managing organic carbon storage in shelf sea sedimentary environments.

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.

Landslide assessments typically focus on the mechanical properties of the basal shear zone, but lateral faults are frequently overlooked, possibly due to their lower normal stresses and variably saturated conditions. Using double-cylinder shear experiments on wet granular systems as analogs for landslide lateral faults, we observe anomalous shear stress variations with fluid volume fractions, defying an expected unimodal relationship associated with capillary cohesion. At low fluid volume fractions, shear strength weakens as the wet grain assembly experiences reduced lateral pressure and increased boundary slip. This boundary slip subsequently vanishes, with an abrupt strengthening due to the dilation of the grain assembly against fluid surface tension as saturation approaches. Strike-slip motion and confinement in this system explain the strength anomaly, highlighting a critical role of lateral faults in landslide stability, particularly in cases where dynamics cannot be adequately explained by monitored pore-water pressure or basal friction.

Satellite Traces (STs) are the important ionogram signatures for the presence of upwellings in the bottom-side ionosphere, which provide the necessary seed perturbation for the development of equatorial plasma bubbles (EPBs). In this study, a virtual ionosonde experiment is simulated to investigate the various ST signatures under the presence of shallow, deep, overhead, and off-centered upwellings in the bottom-side ionosphere. It is shown that STs occur at higher and lower virtual heights than the main ionogram trace for the off-centered and overhead upwellings, respectively. The height separation between the main trace and STs increases with the deepening of overhead upwellings. Further, a proof-of-concept is demonstrated that multiple STs from ionograms can be used to reconstruct the spatial structure of bottom-side upwellings, if the precise Angle-of-Arrival information can be resolved from the wide beam Ionosonde systems, and can have potential applications in predicting the occurrence of EPBs.

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.