Abstract Oceanic internal waves are often thought to be ineffective in stirring and mixing tracer fields such as heat, salt, carbon, and other nutrients. Due to their oscillatory nature, waves are expected to merely displace tracers periodically around their mean position. However, observations of enhanced lateral tracer dispersion at submesoscales (<10 km), where energetic internal waves are abundant, urge better understanding of the role of waves in dispersing oceanic tracers. Using theoretical and numerical methods, this study examines the impact of waves and their amplitudes on the lateral dispersion of passive tracers. We show that two or more waves can irreversibly stir and mix tracers. A broadband spectrum of waves further enhances stirring and mixing. Tracer dispersion in general is seen to become more efficient with increasing amplitude of waves. These findings stem from kinematic non‐interacting waves and dynamic nonlinearly interacting waves. Our results highlight the effectiveness of finite‐amplitude internal waves in tracer stirring and underscore the need to resolve or parameterize wave‐induced lateral mixing in large‐scale ocean models.
Abstract While climate‐driven increases in wildfires are altering the composition and function of Arctic ecosystems, the impact of burn severity on longer‐term changes in community composition and ecosystem fluxes remains less understood, creating uncertainty in estimates of the biome's carbon storage capacity. Here, we used field and remote sensing observations from the 2007 Anaktuvuk River Fire on Alaska's North Slope to explore post‐fire changes in gross primary production (GPP) and solar‐induced fluorescence (SIF). A key goal was to develop a mechanistic understanding of the relationships between burn severity, active layer thickness, post‐fire plant functional type composition, and GPP, using SIF to explore these linkages at a landscape scale. We measured GPP using eddy covariance flux towers at sites with high and moderate burn severity and at a nearby unburned control site. In high burn severity areas, GPP increased by 38 ± 19% and SIF increased by 48 ± 34% 11–15 years after the fire compared to unburned controls. A positive correlation across space between SIF and post‐fire shrub cover within the fire perimeter ( r = 0.38, p < 0.01) suggests that shrub expansion (43 ± 22%) was a key driver of the observed pattern of SIF enhancement. Post‐fire shrub cover, in turn, was positively correlated to active layer thickness ( r = 0.33, p < 0.01) and burn severity ( r = 0.76, p < 0.01). Our findings suggest that more frequent and severe Arctic wildfires could accelerate shrub dominance and increases in photosynthesis, trends that are already being driven by climate warming.
Abstract Space weather poses an important but under‐quantified threat to society. While severe geomagnetic storms are recognized as potential global catastrophes, their socio‐economic impacts remain poorly quantified. We present a novel physics‐engineering‐economic framework that links geophysical drivers to power grid geoelectric fields, transformer vulnerability, and macroeconomic consequences. Using the United States as an example, we estimate daily economic losses for a 250‐year geomagnetic storm from transformer thermal heating of 1.81 billion USD (95 percent confidence interval: 1.65 to 1.96 billion USD), disrupting power for approximately 5.1 million people and 135,000 businesses. These estimates are conservative lower bounds, reflecting only transformer thermal heating effects and excluding voltage collapse, cascading failures, and restoration costs. The true societal risk could be substantially higher. Nonetheless, this contribution provides the first nationwide end‐to‐end coupling from space physics to potential macroeconomic loss, with quantified uncertainties. Our results demonstrate that coupled socio‐economic modeling of space weather is feasible and essential, and the framework is scalable and transferable, offering a template for assessing space weather risk to critical infrastructure in other countries.
Abstract The geomagnetic superstorm in May 2024 represents the most extreme space weather event over the past two decades, offering a unique opportunity to investigate radiation belt electron dynamics under exceptionally strong solar wind driving conditions. Observations from the Arase satellite show that relativistic electron fluxes dropped by several orders of magnitude during the storm main phase. Although magnetopause shadowing and wave‐driven losses are established mechanisms, the response of radiation belt electrons to superstorm‐level solar wind driving remains poorly constrained. Using the Versatile Electron Radiation Belt model, we present the first physics‐based simulation of the May 2024 electron dropout. Utilizing multi‐satellite and ground‐based observations, we show that the decades‐long, widely adopted Kp‐driven radial diffusion parameterization fails to represent radial transport under superstorm conditions, substantially misrepresenting both the timing and magnitude of enhanced diffusion relative to observed ultra‐low‐frequency wave activity. Accurate modeling of the observed extreme dropout requires precise specification of the onset of enhanced radial diffusion, which should coincide with the nearly simultaneous storm‐time magnetopause compression. These coupled processes drive the dramatic depletion, followed by scattering from whistler‐mode plasma waves.
Abstract We report the discovery of an extinct deep‐sea brine pool in the Red Sea's Hume Deep, providing evidence that rift‐shoulder pools are ephemeral on millennial timescales, and that the microbially‐enriched metalliferous deposits produced during the pool's active phase persist into the stratigraphic record. Now devoid of brine, the Hume Deep retains signatures of activity, including a well‐preserved Lagerstätte death assemblage, seafloor staining consistent with past inhabitation by extremophile microbes, and enrichment of metals associated with their metabolisms. Elemental analyses of seafloor sediments demonstrate that the high metal concentrations in the Hume Deep match those of the active NEOM brine pool, situated 90 km north. In the NEOM pool, metagenomics and metatranscriptomics, coupled with scanning electron microscopy and energy‐dispersive spectroscopy, suggest that microbes drive metal enrichment via microbe‐mineral interactions up to 117× higher than background values. These results suggest a role for microbial processes in metalliferous sediment formation in deep‐sea brine pools. Uranium‐thorium dating suggests the Hume pool was last active between two and 16 thousand years ago. We propose that rift‐shoulder brine pools fill and drain in response to tectonically controlled hydrothermal circulation. Our findings suggest that: (a) microbes inhabiting ancient Red Sea brine pools radically enhanced the metalliferous content of the stratigraphy within and above the basin's Miocene evaporites, and (b) that the elemental composition of other salt giant basins might have been similarly microbially mediated. With implications for understanding early life on Earth, our results provide a framework for interpreting deep‐sea metal enrichments in modern and ancient extremophile environments.
Abstract The January 2025 Los Angeles County wildfires burned more than 50,000 acres, destroyed more than 16,000 structures, and caused 31 deaths. This Commentary examines how NASA's Disasters Program coordinated with response organizations to deliver 22 satellite and airborne products during the fires, even as the Eaton Fire forced the Jet Propulsion Laboratory (JPL) to close and displaced many employees. No single sensor met all operational needs. Airborne Visible Infrared Imaging Spectrometer 3 (AVIRIS‐3) observations supported methane screening and detailed mapping of burn severity and relative char and ash abundance. Sentinel‐1 synthetic aperture radar provided damage information through smoke and clouds, while thermal, optical, and nighttime‐lights sensors contributed active‐fire, power‐outage, surface‐temperature, and burn‐scar observations. The combined products supported situational awareness, damage assessment, air quality monitoring, infrastructure evaluation, and debris‐flow planning. Their operational value, however, depended on whether observations were delivered within the relevant decision window and at a spatial scale suited to agency needs. The response exposed persistent limitations associated with data latency, uneven spatial resolution, manual processing, and the difficulty of quantifying how individual products influenced decisions. Priorities for future events include automated and cloud‐based processing, higher‐resolution commercial and airborne observations, cross‐center continuity planning, and sustained training and exercises with response agencies. The recently launched NASA‐ISRO Synthetic Aperture Radar (NISAR) mission and the future Explorer for Artemis Geology Lunar and Earth (EAGLE) missions can expand these capabilities when paired with the processing systems and partnerships needed to convert observations into actionable products.
Abstract Numerical simulations play an essential role in the study of ionospheric irregularities. In the past few decades, electrostatic simulations have successfully simulated the nonlinear evolution of terrestrial ionospheric irregularities. However, the Mars Atmosphere and Volatile EvolutioN (MAVEN) observations reveal that the Martian ionospheric irregularities are electromagnetic in nature, in contrast to the electrostatic nature of terrestrial ionosphere. In this study, we develop a non‐electrostatic model to investigate the evolution of Martian ionospheric irregularities under nighttime conditions and predominantly horizontal magnetic fields. Our simulation results indicate that electromagnetic Rayleigh‐Taylor instability (RTI) can induce the formation of Martian ionospheric irregularities. Consistent with MAVEN observations, the simulated Martian ionospheric irregularities exhibit plasma density variations of approximately 10%–70% relative to the background ionospheric density, with maximum magnetic field variations reaching about 2 nT.
Abstract The Ross Sea continental shelf plays a key role in the global carbon cycle. However, the sources and cycling of dissolved organic carbon (DOC) in the region are poorly understood. Here, we determined the radiocarbon (14C) and stable carbon isotope (13C) contents of DOC in addition to those of dissolved inorganic carbon (DIC) in the Little America Basin, eastern Ross Sea. Carbon isotope values of DIC indicate rapid vertical mixing across the continental shelf, along with high surface primary productivity near the ice shelf. Despite the supply of freshly produced DOC from high primary productivity, the 14C age of the DOC throughout the water column was unexpectedly old (5,100–7,400 years), with surface DOC being older than that in deeper waters, in contrast to the typical oceanic distribution. A Keeling plot of the relationship between DOC 14C contents and the inverse of the DOC concentrations exhibits a positive linear correlation, which is the opposite trend to that of the global ocean. This demonstrates the presence of DOC with a 14C age of >10,000 years in the surface waters. Although the exact source of this aged DOC remains uncertain, we suggest that DOC from subglacial lake discharge is the likely source.
The carbon sequestration capacity of the biological carbon pump (BCP) is determined by surface ocean carbon fixation and the transportation of fixed carbon to the ocean interior, which is closely linked to the trophic structure of planktonic ecosystem. However, previous biogeochemical reconstructions focused mostly on primary productivity, overlooking changes in community structure (e.g., ratio of primary producers to consumers). In this study, we investigate the late Quaternary history of planktonic trophic structure in the western equatorial Pacific by generating sedimentary amino acid δ 15 N record of Site MD10‐3340. Our results demonstrate well‐preserved amino acid δ 15 N signatures. Using the δ 15 N gradients between trophic and source amino acids, we calculate the average sedimentary trophic position and design an idealized ecosystem model to quasi‐quantitively estimate changes in grazing proportion (the proportion of primary production consumed by zooplanktons). Notably, lower trophic position and smaller grazing proportion point to a decline of zooplankton grazing during precession maxima, which is primarily attributed to enhanced nutrient availability in the western equatorial Pacific during El Niño‐like mean‐states. Moreover, average grazing proportion is slightly lower during Interglacial warmth than the last glacial period, implying a secondary control of sea level change. Furthermore, our ocean‐biogeochemical simulations show that a halved grazing proportion could cause pronounced decrease in Pacific carbon storage and a remarkable increase in atmospheric p CO 2 , due to a shallower remineralization depth. We thus highlight the necessity to incorporate varying marine grazing proportions into future proxy reconstructions and model simulations to facilitate a more comprehensive understanding of the BCP.
A more “efficient” biological pump is thought to have played a key role in glacial CO 2 drawdown, with two principal mechanisms invoked to stem the CO 2 “leak” from the modern Southern Ocean. The first sees a strengthened soft tissue pump, associated with a reduction in the ocean's “preformed” nutrient inventory. The second sees an increase in air‐sea CO 2 disequilibrium (termed the disequilibrium pump). We use an Earth system model (CM2Mc) to show the tracers radiocarbon (Δ 14 C) and oxygen (O 2 ) exhibit distinct sensitivities to these two pumps within the deep ocean: Δ 14 C is more sensitive to disequilibrium pump changes, whereas O 2 is more sensitive to soft tissue pump changes, as expected from the underlying processes. We apply these pump‐specific tracer stoichiometries to available deep ocean Δ 14 C and O 2 proxy data from the Last Glacial Maximum (LGM). Despite the sparsity of O 2 data, the results show a consistent increase in soft tissue and disequilibrium DIC within the deep ocean of ∼135 μmol/kg, with broadly comparable contributions from the two pumps. Our results imply a reduction in air‐sea gas exchange (likely linked to expansion and/or increased isolation of Antarctic Bottom Water), as well as a slowdown of deep ocean overturning and Southern Ocean upwelling at the LGM. Notably, current ocean models struggle to simulate both of these changes simultaneously under glacial forcings. The combined changes in the soft tissue and disequilibrium DIC are of sufficient magnitude to explain the glacial reduction in atmospheric CO 2 once a whole ocean alkalinity increase is accounted for.
Abstract Atmospheric winds play a key role in shaping climate, ecosystems, and infrastructure. The energy that drives the winds is generated by the atmospheric heat engine. However, traditional entropy‐budget descriptions of this heat engine rely on poorly constrained microscale processes, limiting their predictive power. To address this, we introduce a framework to compute the wind work from only two climate‐dependent quantities: the height‐weighted integrated radiative‐cooling profile and a bulk Bowen ratio. Our results show that moderate global warming leads to only weak changes in wind work (and hence weak changes in global wind energy dissipation), due to a balance between increased height‐weighted radiative cooling and decreased bulk Bowen ratio. This result is in line with the relatively weak and inconsistent trends in wind energy dissipation found in comprehensive climate models and reanalyses. However, this balance is not predicted to hold over a wider range of climates, consistent with a much less energetic circulation in simulations of past Snowball Earth climates.
Abstract Uranus possesses the most extreme magnetic and rotational geometry in the solar system, resulting in a uniquely dynamic and asymmetric interaction between its magnetosphere and the solar wind. Here we investigate the diurnal evolution of the Uranian bow shock (BS) at equinox using global multifluid magnetohydrodynamic simulations constrained by Voyager 2 observations. The BS structure and variability are quantified using the stand‐off distance, terminator distance, flaring parameter, and BS parameter, enabling a systematic assessment of its global asymmetry over one planetary rotation. Our results show that the BS exhibits pronounced diurnal asymmetry that is primarily controlled by planetary rotation. Even under steady upstream solar wind conditions, the BS undergoes periodic expansion and contraction, reflecting rotation‐driven reconfiguration of the planetary magnetospheric topology. This diurnal modulation represents a remarkably large asymmetry in planetary BS geometry within the solar system. These results establish planetary rotation as the intrinsic primary driver of Uranus' BS dynamics at equinox and provide essential constraints for the design and formulation of future space missions to the ice giants. These findings also offer a unique framework for understanding shock physics in the abundant population of ice‐giant exoplanets.
Tidal rivers are defined as the tide-influenced, salinity-free inland reaches of estuaries. Understanding the occurrence of peak water levels (PWLs) is critical for flood risk management, yet the timing and magnitude of PWLs in tidal rivers have been little studied. We address this gap by investigating PWLs during two catastrophic floods (1954 and 2020) in the tidal Yangtze River, which reveals that PWLs are higher during perigean spring tides under intermediate discharges following peak flow. Three factors modulate the PWLs in tidal rivers: river-enhanced tidal damping, flow-elevation hysteresis that raises the falling flow limb of the hydrograph, and low-frequency subharmonics. The latter, arising from nonlinear river-tide interactions, are distinct in tidal rivers and culminate under intermediate river flow as a result of the balance between tidal energy dissipation and the spectral energy transfer to subharmonics. They elevate PWLs by up to 0.3 m during perigean spring tides in the Yangtze case and amplify compound flood risk. Channel degradation has reduced tidal damping compared with circumstances in the 1950s, resulting in larger tidal ranges and record-breaking PWLs during the 2020 flood despite a smaller peak discharge. We identify tidal rivers spanning over 3,380 km in worldwide estuaries and deltas, where prevalent subharmonics like MSf are up to 0.65 m in amplitude. Many of those experience even larger tidal amplification due to channel deepening, implying escalating flooding risk under sea-level rise and human impact. These findings underscore a need to include nonlinear river-tide interactions in flood risk assessment for river-coast transition zones.
Abstract Hillslopes in arctic regions commonly display large‐scale features—known as solifluction patterns—that form due to the exceedingly slow downhill movement of frost‐heaved soil. Here we use a combination of remote sensing data, linear stability analysis, numerical modeling, and review of a wide range of literature to evaluate several working hypotheses for the necessary and sufficient conditions needed to form solifluction patterns. We find that despite striking visual similarity, fluid buckling, wrinkling, dripping, and roll wave patterns are not directly analogous to solifluction patterns. However, broadly inspired by non‐inertial instabilities observed in shear‐thickening oobleck (cornstarch mixed with water), we propose a conceptual framework for the formation of solifluction instabilities that relies on spatial heterogeneity of soil velocities in the presence of random frost heave‐induced topographic bumps. More broadly, this study illustrates both caveats and the potential for success in drawing inspiration from diverse fields to understand pattern formation in the complex granular and fluid materials on Earth's surface.
While several hypotheses exist to explain the development of large-scale perennial Northern Hemisphere ice sheets in the late Pliocene and early Pleistocene, the prevailing view is that a decline in atmospheric carbon dioxide (CO2) drove this substantial change in late Neogene climate. However, the primary mechanism responsible for this reduction in CO2 has yet to be fully explored. Mineral dust-derived iron enhancement of ocean organic carbon production and export to the deep ocean and marine sediments has previously been invoked to explain reductions in atmospheric CO2 on multiple timescales. Here we test the hypothesis that iron fertilization of the Pliocene subarctic North Pacific affected atmospheric CO2, and in turn drove the formation of Northern Hemisphere ice sheets. By compiling Pliocene dust and export productivity proxy data sets from across the North Pacific and then progressively filtering for the most reliable records, we find that there is no relationship between North Pacific dust inputs and export production in the Pliocene. Finally, we apply these new composites to broadly assess previously proposed drivers of Pliocene Asian dust dynamics as well as North Pacific Ocean circulation and biogeochemistry.
The accumulation of organic matter (OM) near shorelines, known as blue carbon, is a key sink in the global carbon cycle. This accumulation is influenced by elevation relative to sea level of the delta-top, which changes through the movement of shorelines with time. The influence of internally generated, or autogenic, delta dynamics on meso-timescale (<10(5) yr) OM preservation in river deltas is unknown. We develop a framework that links local autogenic shoreline migration to the spatial extent of preserved organic-rich strata, which we term paleo-blue carbon, and validate this against observations from a physical experiment that couples a clastic delta to a coastal wetland environment. We show that autogenic processes exert a control on shoreline migration and preservation of organic material: the longitudinal subsurface extent of paleo-blue carbon is approximately seven times larger than the wetland accumulation zone on the surface at any given period. Further, autogenic processes enhance carbon burial rates, which are fast enough to be preserved prior to degradation. Given that autogenic processes operate in sedimentary environments that accumulate appreciable quantities of OM, we recommend incorporation of this framework into any predictions of the spatial extent of paleo-blue carbon stored in strata.
Abstract The afternoon detached auroral arc is an important phenomenon in the subauroral region, reflecting coupling processes between the Earth's magnetosphere and ionosphere. Previous studies have not identified fine‐scale structures in such arcs, leaving the dynamics underlying their formation poorly understood. Here we report an afternoon detached auroral arc event on 13 September 2017 during the recovery phase of a storm. For the first time, the sawtooth‐like undulations were observed along the equatorward boundary of the afternoon detached arc in the Lyman‐Birge‐Hopfield Long (LBHL) wavelength band of Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager (DMSP/SSUSI). This auroral structure is accompanied by >10 keV ion precipitation and by tens to hundreds of eV electron precipitation at higher latitudes. Detailed analyses based on coordinated observations from the Arase satellite indicate that the structure is associated with a plasmaspheric plume, with surface waves occurring along its boundary. Joint observations from ground‐based magnetometer stations indicate that magnetic pulsations in the Pc1‐2 band were also distinctly detected. We suggest that surface waves perturb the cold plasma density within the plume, thereby modulating Electromagnetic Ion Cyclotron (EMIC) waves. The modulated EMIC waves resonate with energetic ions, producing precipitation that contributes to the formation of the sawtooth‐like undulations in afternoon detached auroral arc.
