AGU Advances最新文献

Rocky coast morphology is shaped by interactions between wave action, sea level, and tectonics over millennial time scales. However, a clear and quantifiable signature of tectonic uplift on decadal to centennial shoreline retreat rates is outstanding. We isolate the contribution of tectonic uplift to setting shoreline retreat and shore platform morphology from other marine and geologic drivers across the West Coast of the USA. Specifically, we find that decadal-scale tectonic uplift, derived from tide gauge records, exerts a significant and measurable control on shoreline retreat rates. Additional influences from wave action, shore platform morphology, and tidal range further contribute to the regional patterns in coastal erosion, and together these factors enable accurate prediction of retreat rates using a multivariate model. Our analysis also reveals robust, time-scale dependent relationships between uplift rate, shore platform morphology, and shoreline retreat. On decadal time scales, rapid tectonic uplift acts as a buffer, shielding the shore from wave action, slowing retreat, and corresponding with narrow shore platforms. On millennial time scales, higher uplift rates relate to wider shore platforms, reflecting greater cumulative shoreline retreat. These observations likely reflect the effects of episodic, seismically driven subsidence, which shifts wave action landward, enhancing wave-driven erosion. Through repeated cycles of uplift and subsidence, the seismic cycle amplifies both shore platform development and long-term retreat. Together, these findings highlight the critical role of tectonics in shaping shoreline retreat and driving landscape evolution timescales on active margins.

Carbonate mineral production and dissolution regulate atmospheric carbon dioxide (CO₂) concentrations via modulation of the ocean alkalinity content. The anthropogenic rise in atmospheric CO₂ reduces calcification rates and enhances calcium carbonate dissolution, which increases ocean alkalinity, counteracts acidification, and stimulates ocean CO₂ uptake. However, carbonate dissolution takes place primarily in the deep ocean, so this feedback is slow, maintaining ocean CO₂ uptake over millennial timescales. Here, we present evidence that seawater alkalinity on the continental shelf is increasing on annual-decadal timescales, at a rate that is orders of magnitude faster than the deep ocean feedback. Biogeochemical model analyses suggest this fast feedback results from calcium carbonate dissolution in the shelf seafloor driven by increasing atmospheric CO₂ concentrations. Extrapolating these results to the global continental shelf suggests that shelf carbonate dissolution has been accelerating since the 1800s and may account for up to 10% of the missing ∼0.3 Pg C yr⁻¹ in ocean model carbon budgets.

Energetic electron precipitation plays a pivotal role in shaping Earth's radiation belt dynamics and drives significant physical and chemical changes in the upper atmosphere. However, the detailed mechanisms governing the loss of relativistic electrons have remained unclear, largely due to the limited energy coverage and coarse resolution of previous measurements. Here we report high-resolution observations of bursty electron precipitation across a broad energy range (0.3–2.3 MeV), obtained by the Relativistic Electron and Proton Telescope integrated little experiment-2 (REPTile-2) onboard the Colorado Inner Radiation Belt Experiment (CIRBE) CubeSat. REPTile-2 employs a novel instrument design that minimizes background to enable clean spectral measurements with the highest energy resolution achieved to date in low-Earth orbit for this energy range. During the conjunction events when CIRBE was close to the same field line with Arase satellite at higher altitudes, our analysis shows that pitch angle diffusion driven by chorus waves can fully account for the observed three bursty precipitation events over the entire energy range. These results provide the definitive evidence for a unified chorus-driven electron loss process acting across a wide energy range and underscore the critical importance of high-resolution measurements in resolving long-standing uncertainties in radiation belt dynamics. Furthermore, they offer new insight into the energy-dependent atmospheric impacts of electron precipitation, with broad implications for space weather forecasting and upper atmospheric chemistry.

The continuous increase in atmospheric methane (CH₄) concentrations over the past few decades has become a major concern due to its strong role as a greenhouse gas contributing to climate change. In this work, we investigate the changes in the global methane budget using a global chemistry-climate model constrained with methane and its isotopic observations. We apply spatially-resolved isotopic signatures to better constrain the methane sources and include methane-hydroxyl radical (OH) feedback to better represent methane sinks and lifetime in the model. While anthropogenic activities are found to be mainly responsible for the methane increase since the 1980s, the increasing OH trend simulated by the model plays a critical role in the global methane evolution. We find the observed post-2006 shift of δ¹³CH₄ can be explained by increases in ¹³C-depleted agricultural and waste emissions in the tropics, coupled with decreasing ¹³C-enriched biomass burning emissions and an increasing OH trend. We also find post-2006 emission increases in energy and agriculture sectors are large enough to offset the increasing sinks (due to increasing OH), and therefore are shown to contribute to the post-2006 renewed methane growth. With CH₄-OH feedback included in the model, the results show an increasing sensitivity to emission increases on methane concentrations and lifetime. Our study underscores the importance of OH in the global methane evolution. Neglecting changes in OH could potentially lead to misinterpreting emission changes with respect to the long-term observations of methane and δ¹³CH₄.

Anthropogenic climate change affects regional hydrological cycles and poses significant challenges to the sustainable supply of freshwater. The Central China water tower (CCWT) is the key source region feeding the Yangtze and Yellow Rivers, and its runoff is indispensable for the surrounding mega-city clusters. Here we present a reconstruction of CCWT runoff depth (RD) back to 1595 CE, based on a new dendrochronological network including 100 tree-ring sampling sites and an ensemble averaging approach that combines multiple regression models. Comparison of this reconstruction with similar records from six water tower regions along the Pacific Rim (Mongolian Plateau, Tibetan Plateau TP, Great Dividing Range, Southern and Northern Rocky Mountains, Andes Mountains) revealed that the CCWT provide the most stable water supply, while the TP to be most susceptible to extreme runoff events. Twenty-first century projections indicate generally increasing runoff across most Pacific Rim water towers, whereas the Northern Rocky Mountains are projected to decline substantially. We attribute the differences in runoff variability and projected trends across Pacific Rim water towers to their distinct geographies and synoptic climatic conditions. The long-term runoff reconstructions and projected changes highlighted in this study provide insights for adaptive management strategies in China and all other regions relying on supply from mountain water towers.

Earth observation (EO) technologies are increasingly driving parametric insurance and risk financing for climate disasters, yet few operational programs demonstrate effective integration within national government systems. Uganda's Disaster Risk Financing Program (2016–2020) provides a rare example of satellite-triggered financing operating at scale. Using MODIS vegetation indices to trigger drought response, the $14 million program supported over 452,000 people. It generated $11.1 million in immediate emergency aid savings, achieving a total return on investment of approximately 2.9 and an Internal Economic Rate of Return of 28.2%. This commentary synthesizes lessons from program implementation, highlighting that institutional and financial barriers, rather than technical limitations, now constrain the scaling of this EO-driven climate resilience mechanism. While the program successfully integrated satellite data with transparent triggers and financial instruments, its sustainability depended on financial commitment extending beyond experimental phases. As climate risks intensify globally, Uganda's experience demonstrates that data-triggered financing can operate within government institutions, but successful replication requires prioritizing institutional architecture and sustained financing over technical perfection.

Cratonic lithospheres carry a long history of tectonic modifications that result in heterogeneous structures, as revealed by an increasing number of geophysical observations. The existence of cratonic basins indicates protracted periods of tectonic modification, causing subsidence within global continental interiors. An enigmatic aspect of this process is the cessation of subsidence in cratonic basins with unclear mechanisms. Here, using full-wave ambient noise tomography, we reveal distinct seismic low-velocity anomalies below 60 km beneath the Illinois and Michigan Basins, where subsidence terminated in the late Paleozoic to the early Mesozoic. These low-velocity volumes, surrounded by distinctly higher velocities, are attributed to asthenospheric materials upwelling to shallow mantle depths during lithospheric foundering or delamination. This lithospheric modification may be associated with a major regional tectonic exhumation in the early Mesozoic that could have terminated basin subsidence and unroofed upper portions of basin stratigraphy. This timing coincides with the passage of this region over mantle plumes, which likely triggered lithospheric delamination and asthenospheric upwelling. Geodynamic modeling shows that the emplacement of these buoyant asthenospheric materials would lead to an uplift of about 3.5 km, sufficient to terminate the subsidence in the cratonic basins within this region. These findings document evidence of lithospheric delamination in the North American midcontinent and present important links between geodynamic drivers and geological records of the evolution of the cratonic lithosphere in North America and beyond. They also offer broader implications for understanding how deep Earth processes shape surface environments, influencing resource distribution and long-term landscape evolution.

Geomorphic and stratigraphic studies of Mars prove that extensive liquid water flowed and pooled on the surface early in Mars' history. Martian paleoclimate models, however, have difficulty simulating climate conditions warm enough to maintain liquid water on early Mars. Reconciling the geologic record and paleoclimatic simulations of Mars is critical to understanding Mars' early history, atmospheric conditions, and paleoclimate. This study uses an adapted lake energy balance model to investigate the connections between Martian geology and climate. The Lake Modeling on Mars for Atmospheric Reconstructions and Simulations (LakeM²ARS) model is modified from an Earth-based lake model to function in Martian conditions. We use LakeM²ARS to investigate the conditions necessary to simulate a lake in Gale crater. Working at a localized scale, we combine climate input from the Mars Weather Research & Forecasting general circulation model with geologic constraints from Curiosity rover observations to identify potential climatic conditions required to maintain a seasonally ice-free lake. Our results show that an initially small lake system (10 m deep) with ∼50 mm monthly water input and seasonal ice cover would retain seasonal liquid water for over 100 years, demonstrating conditions close to long-term lake survivability. These results are an important step in resolving the historic disconnect between climate and geology on Mars. Continued use and iteration of LakeM²ARS will strengthen connections between Mars' paleoclimate and geology to inform climate models and enhance our understanding of conditions on early Mars.

Root distributions are typically based on root mass per soil volume. This plant-focused approach masks the biogeochemical influence of fine roots, which weigh little. We assert that centimeter-scale root presence-absence data from soil profiles provide a more soil-focused approach for probing depth distributions of root-regolith interfaces, where microsite-scale processes drive whole-ecosystem functioning. In 75 soil pits across the continental USA, Puerto Rico, and the Alps, we quantified fine and coarse root presence as deep as 2 m. In 70 of these pits we estimated root mass and created standardized metrics of both data sets to compare their depth distributions. We addressed whether: (a) depth distributions of root presence-absence data differ from root mass data, thus implying different degrees of root-regolith interactions with depth; and (b) if root presence or any depth-dependent differences between these data sets vary predictably with environmental conditions. Presence of fine roots exhibited diverse depth-dependent patterns; root mass generally declined with depth. In B and C horizons, standardized root presence was greater than standardized root mass; random forest analyses suggest these discrepancies are greater in B horizons with increasing mean annual precipitation and in C horizons with increasing mean annual temperature. Our work suggests that deep in the subsurface, biogeochemical and reactive transport processes result from more numerous root-regolith interfaces than mass data suggest. We present a new paradigm for discerning patterns in depth distributions of root-regolith interfaces across multiple biomes and land uses that promotes understanding of the roles of those interfaces in driving key critical zone processes.