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Bubble‐plumes are commonly used in lake restoration to alleviate problems associated with hypolimnetic hypoxia. In lakes with multiple basins separated by sills, bubble‐plumes have been used locally to boost oxygen levels in individual basins. However, they have the potential to affect inter‐basin exchange leading to unexpected results. Our goal is to assess the relative importance of natural versus plume forcing as drivers of exchange. This is critical to evaluate the field‐scale performance of bubble‐plume systems. We hypothesize that the contribution of bubble‐plumes as drivers of inter‐basin oxygen transport depends on the depths of detrainment and maximum plume rise relative to sill level (plume geometry). To test this hypothesis, 1D integral bubble‐plume models coupled to a 3D‐hydrodynamic model are applied to simulate the performance of an oxygenation system installed in 1990 in the north basin of Amisk Lake, Canada. Sources of uncertainty in bubble‐plume modeling, associated with model assumptions and parameter values (structural and parametric uncertainty), are systematically analyzed, and their effect on plume‐structure and inter‐basin exchange predictions are quantified. The effects of plume forcing on exchange rates and patterns are only significant as the equilibrium depth rises above the sill. For the prevailing conditions in the study case and the most widely accepted plume model, this occurs with low probability. More plausibly (for most parameter combinations), the plume injects oxygen below the sill, the oxygenated water being transported by internal waves between basins. Solid conclusions on the dominant drivers of large‐scale transport arise in attribution studies accounting for model uncertainty.

The causes and global distribution of intraplate volcanism remain poorly understood, particularly the occurrence of scattered magmatism unrelated to large igneous provinces (LIPs). In this study, high‐resolution numerical simulations are employed to examine the interaction between deep thermochemical mantle plumes and the mantle transition zone (MTZ) to clarify its role in plume ascent and surface magmatism. Results demonstrate that the MTZ exerts a significant control on plume behavior, with some plumes ascending directly while others stall and generate secondary upwellings (“baby plumes”), which may contribute to scattered, localized magmatism. The transition from direct ascent to stagnation of the primary (“parent”) thermochemical plume is influenced by temperature, plume volume, Clapeyron slopes, and compositional heterogeneities. Our results highlight the crucial role of the MTZ in how mantle plumes evolve and drive surface magmatism. This provides new insights into why some deep mantle plumes fail to generate LIPs, instead producing widely scattered volcanism.

In this study, we propose a method to predict the classification of the eruption plume types: “strong plumes” and “weak plumes”. Our method reproduces the general features that the eruption plume types depend on, both the meteorological conditions and eruption conditions, and successfully reproduces the classification of the plume types for historical eruption events. Application of the method to Monte Carlo simulations revealed that eruption plumes at a low latitude tend to form strong plumes due to weak ambient winds, whereas eruption plumes at a mid latitude tend to form weak plumes due to the strong ambient winds associated with the jet stream. The simulation also revealed that mid‐latitude eruption plumes tend to be strong plumes in the summer when ambient winds are lowered by a weakening and poleward movement of the jet stream. Plain Language Summary When an explosive volcanic eruption occurs, an eruption plume rises up to a few kilometers or tens of kilometers while incorporating ambient air. After the plume density equals to that of the atmosphere, the plume intrudes horizontally into the stratified atmosphere. This intrusion is classified into mainly two types: a radial spreading type (i.e., strong plume, often called an “umbrella cloud”) and a downwind spreading type (i.e., weak plume). Estimation of the intrusion type is vital to forecast ash dispersal, because an input parameter for ash dispersal calculation depends on the intrusion type. In this study, we introduce a method to predict the plume intrusion type, and we validated the method for 14 historical eruptions. In addition, to investigate the relationship between the intrusion type and meteorological conditions at the volcano's location, we conducted Monte Carlo simulations with random eruption intensities and actual long‐term meteorological data. The simulation results revealed the following trends: (a) eruption plumes at a low latitude tend to be a radial spreading type, and (b) eruption plumes at mid latitudes tend to be a downwind spreading type except during the summer. These features can be understood from the meteorological conditions at the volcano's location. Key Points A method to predict an eruption plume type (“strong plume” or “weak plume”) is introduced Eruption plumes at low‐latitudes tend to be strong plumes, because ambient winds at high altitude are weak Strong wind associated with jet stream at mid latitude affects eruption plumes, favoring weak plumes in all seasons except summer

A whole-mantle seismic imaging technique, combining accurate wavefield computations with information contained in whole seismic waveforms, is used to reveal the presence of broad conduits beneath many of Earth’s surface hotspots, supporting the idea that these conduits are the source of hotspot volcanoes. Plume-like conduits beneath surface hotspots Scott French and Barbara Romanowicz use a whole-mantle seismic imaging technique, combining accurate wavefield computations with information contained in whole seismic waveforms, to reveal the presence of wide, quasi-vertical conduits beneath many of the Earth's surface hotspots. The conduits they image extend from the core–mantle boundary, where they are rooted in patches of strongly reduced shear velocity, and correspond to known locations of large ultralow-velocity zones beneath Hawaii, Iceland and Samoa, in support of the idea that they may be the source of hotspot volcanoes. As the conduits are broader than classical thermal plume tails, the authors suggest that they are long lived and may have a thermochemical origin. Plumes of hot upwelling rock rooted in the deep mantle have been proposed as a possible origin of hotspot volcanoes, but this idea is the subject of vigorous debate 1 , 2 . On the basis of geodynamic computations, plumes of purely thermal origin should comprise thin tails, only several hundred kilometres wide 3 , and be difficult to detect using standard seismic tomography techniques. Here we describe the use of a whole-mantle seismic imaging technique—combining accurate wavefield computations with information contained in whole seismic waveforms 4 —that reveals the presence of broad (not thin), quasi-vertical conduits beneath many prominent hotspots. These conduits extend from the core–mantle boundary to about 1,000 kilometres below Earth’s surface, where some are deflected horizontally, as though entrained into more vigorous upper-mantle circulation. At the base of the mantle, these conduits are rooted in patches of greatly reduced shear velocity that, in the case of Hawaii, Iceland and Samoa, correspond to the locations of known large ultralow-velocity zones 5 , 6 , 7 . This correspondence clearly establishes a continuous connection between such zones and mantle plumes. We also show that the imaged conduits are robustly broader than classical thermal plume tails, suggesting that they are long-lived 8 , and may have a thermochemical origin 9 , 10 , 11 . Their vertical orientation suggests very sluggish background circulation below depths of 1,000 kilometres. Our results should provide constraints on studies of viscosity layering of Earth’s mantle and guide further research into thermochemical convection.

Volcanic eruption columns typically have unsteady source conditions, where mass and heat fluxes from the vent evolve or fluctuate on time scales from seconds to hours. However, integral plume models routinely assume source conditions that are statistically stationary, and the degree to which source unsteadiness influences the mechanics of column rise and air entrainment has not been established with quantitative predictions. We address this knowledge gap by examining eruptions with varying unsteady character at Sabancaya Volcano, Peru. Using a novel tracking algorithm based on spectral clustering, we track the spatiotemporal evolution of coherent turbulent structures in columns using ground‐based, thermal infrared imagery. For turbulent structures tracked in time and space, we calculate the power law decay exponent of excess temperature with height. In general, the starting pulses of transient events are characterized by power law exponents matching theoretical predictions for an instantaneous point release of buoyancy (i.e., a thermal), which evolve with sustained emissions to values consistent with steady plumes. Our results support previous findings from field evidence and laboratory experiments that entrainment and gravitational stability in unsteady volcanic columns are inadequately captured by time‐averaging or constant entrainment coefficients. We propose a quantitative definition for column source unsteadiness which captures the timing and magnitude of source fluctuations on time scales that influence entrainment mechanics, and which provisionally predicts our observed differences in power law behavior. We argue for systematic experimental and numerical studies of the relationship between source unsteadiness and entrainment to implement unsteady entrainment parameterizations for integral plume models. Plain Language Summary Volcanic eruptions are routinely simulated as sustained, jet‐like flows of gas and ash. However, most eruptions in nature are unsteady at the source vent, meaning the flow rate and heat content of erupted material varies substantially over time scales ranging from seconds to hours. This variation impacts mixing of eruption plumes with the background atmosphere (a process called entrainment), ultimately affecting how high plumes rise and where they disperse hazardous ash. To better understand how unsteady conditions influence eruption behavior and hazard, we analyzEd infrared camera imagery of eruption plumes at Amancaya Volcano, Peru. By developing a new algorithm which tracks individual turbulent eddies in the rising plume, we measure how the heat content in the plumes evolve with entrainment of atmosphere. Our measurements show the plume mixing process evolving between theoretical predictions for sustained, jet‐like flows and single, brief pulses, as a result of unsteady, evolving conditions at the plume source. We use our measurements to propose a mathematical framework for quantifying unsteadiness in volcanic plumes, enabling future experiments and computer simulations that include unsteady effects. Ultimately, this will lead to improved forecasts of ash dispersal and resulting hazards for unsteady eruptions. Key Points Unsupervised machine learning algorithm tracks evolving plume structures in thermal imagery at Sabancaya Volcano Temperature evolution in both space and time reflects unsteady transitions between steady plume and discrete thermal regimes We propose a quantitative unsteadiness metric for the prediction of entrainment regimes as a function of eruption source unsteadiness

The widespread High Arctic Large Igneous Province (HALIP) exhibits prolonged melting over more than 50 Myr, an observation that is difficult to reconcile with the classic view that large igneous provinces (LIPs) originate from melting in plume heads. Hence, the suggested plume‐related origin and classification of HALIP as a LIP have been questioned. Here, we use numerical models that include melting and melt migration to investigate a rising plume interacting with lithosphere of variable thickness, that is, a basin‐to‐craton setting applicable to the Arctic. Models reveal that melt migration introduces significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30–40 Myr, because of the dynamic feedback between migrating melt and local lithosphere thinning. For HALIP, plume material deflected from underneath the Greenland craton can re‐activate melting zones below the previously plume‐influenced Sverdrup Basin after a melt‐free period of about 10–15 Myr, even though the plume is already ∼500 km away. Hence, actively melting zones do not necessarily represent the location of the deeper plume stem at a given time, especially for secondary pulses. Additional processes such as (minor) plume flux variations or local lithospheric extension may alter the timing and volume of HALIP pulses, but are to first order not required to reproduce the long‐lived and multi‐pulse magmatism of HALIP. Since melting zones are always plume‐fed, we would expect HALIP magmatism to exhibit plume‐related trace element signatures throughout time, potentially shifting from mostly tholeiitic toward more alkalic compositions. Plain Language Summary Typically, the arrival of a large mantle upwelling (“mantle plume”) is expected to cause catastrophic large‐scale volcanism that lasts a few million years. However, a massive past volcanic event now distributed onshore and offshore across the Arctic (the High Arctic Large Igneous Province—HALIP) defies this definition. This wide‐spread magmatism exhibits dates spanning more than 50 Myr, with several pulses of activity. Based on this prolonged magmatism, it has been questioned whether all of it can be attributed to a mantle plume, despite the geochemistry of basalts indicating a plume source. Here, we show that a plume can cause prolonged and multi‐pulse magmatism if it interacts with an increase in lithosphere thickness. Once the plume moves below the thicker lithosphere, hot plume material is channeled along the base of the lithosphere toward the adjacent thinner part, where it can reactivate previous melting regions. At this time, the active plume can be about 500 km away from the melting region, hence plume‐related melt cannot be used as a proxy for the plume position at the given time. Based on the models, we suggest that the prolonged HALIP magmatism was caused by a plume interacting with the edge of a craton. Key Points Mantle plumes interacting with changes in lithosphere thickness at craton edges can cause prolonged melting with pulses in the same region Rejuvenated melting happens underneath previously melt‐affected thinned lithosphere several hundred km downstream of the plume stem The timing and duration of rejuvenated melting in models correspond to and therefore may explain observations of magmatic pulses from High Arctic Large Igneous Province

Deciphering the Earth's deep carbon cycle, from mantle plumes to mid‐ocean ridges, remains incompletely understood. In this study, we analyze the magnesium isotope composition of basalts collected from the South Mid‐Atlantic Ridge (SMAR), which have been influenced by the off‐axis Saint Helena plume originating from the core‐mantle boundary. The magnesium isotope composition of SMAR basalts falls within a similar range (−0.22 to −0.32‰; average −0.25‰ ± 0.03‰) to that of known global oceanic basalts. However, isotope mixing calculations suggest that the lighter magnesium isotope composition in the SMAR basalts is due to the incorporation of approximately 5%–10% recycled carbonate material carried by the Saint Helena plume into the SMAR asthenosphere. This finding not only highlights the interaction between ridges and off‐axis plumes but also proposes a comprehensive model for the Earth's deep carbon cycle, spanning from the subduction zone through the core‐mantle boundary to the mid‐ocean ridge system. Plain Language Summary The investigation of the Earth's deep carbon cycle is crucial for elucidating the processes of material transport within the Earth's interior and mantle convection. Despite significant advancements, understanding the complete carbon cycle still presents challenges, particularly in relation to the process of carbon transfer from subducted ancient oceanic crust to the generation of new oceanic crust. By exploring the interaction between mantle plumes and mid‐ocean ridges (MORs), it is possible to achieve a more comprehensive understanding of the intricate Earth's deep carbon cycle. In this study, we present precise Mg isotopic data obtained from mid‐ocean ridge basalts (MORBs) in the South Atlantic region. By integrating the Mg isotope and radiogenic isotopic compositions of basalts from the South Mid‐Atlantic Ridge (SMAR) and Saint Helena Island, we have determined that approximately 5%–10% of recycled carbonate material carried by the Saint Helena mantle plume has been transported into the asthenosphere beneath the SMAR system. Our findings contribute to the development of a coherent model of the Earth's deep carbon cycle, tracing the pathway from subduction zones to the core‐mantle boundary and ultimately return to MOR systems. This model provides valuable insights for geologists seeking to comprehend the material cycle of the Earth. Key Points The composition of Mg isotope in basalts suggests interaction of the Saint Helena plume and South Mid‐Atlantic Ridge system Subducted carbon from the Saint Helena plume has been transported to the South Mid‐Atlantic Ridge system Carbon derived from the subduction zone has the potential to transport to the core‐mantle boundary and return to the mid‐ocean ridge system

Open biomass burning contributes significantly to air quality degradation and associated human health impacts over large areas. It is one of the largest sources of reactive trace gases and fine particles to Earth’s atmosphere and consequently a major source of cloud condensation nuclei on a global scale. However, there is a large uncertainty in the climate effect of open biomass burning aerosols due to the complexity of their constituents. Here, we present an exceptionally large dataset on southern African savannah and grassland fire plumes and their atmospheric evolution, based on 5.5 years of continuous measurements from 2010 to 2015. We find that the mass of submicrometre aerosols more than doubles on average, in only three hours of daytime ageing. We also evaluate biomass burning aerosol particle size distributions and find a large discrepancy between the observations and current model parameterizations, especially in the 30–100 nm range. We conclude that accounting for near-source secondary organic aerosol formation and using measurement-based size distribution parameterizations in smoke plumes is essential to better constrain the climate and air quality effects of savannah and grassland fires.

Aerosol absorption of visible light has an important impact on global radiative forcing. Wildfires are one of the major sources of light-absorbing aerosol, but there remains significant uncertainty about the magnitude, wavelength dependence, and bleaching of absorption from biomass burning aerosol. We collected and analyzed data from 21 western US wildfire smoke plumes during the 2018 Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen (WE-CAN) airborne measurement campaign to determine the contribution of black carbon (BC), brown carbon (BrC), and lensing to the aerosol mass absorption cross section (MAC). Comparison to commonly used parameterizations and modeling studies suggests that model overestimation of absorption is likely due to incorrect BrC refractive indices. Modelers (Wang et al., 2018; Carter et al., 2021) invoke a bleaching process that decreases the MAC of organic aerosol (OA) to offset the overestimation of absorption in models. However, no evidence of a decreasing MAC is observed in individual WE-CAN fire plumes or in aged plumes from multiple fires. A decrease in OA mass and water-soluble organic carbon (WSOC), both normalized by carbon monoxide (CO) to correct for dilution, is observed with an increasing oxygen-to-carbon (O : C) ratio and a decreasing gas-phase toluene : benzene ratio, when data from all fires are combined in half of the individual fire plumes. This results in a strong decrease in total absorption at 405 nm and a slight decrease at 660 nm with these chemical markers. These results demonstrate that changes in absorption with chemical markers of plume age are the result of decreasing OA rather than changes in the MAC of the organic material itself. While decreasing MAC or OA mass with aging could both be called bleaching and can both correct overestimation of absorption in models, it is important to distinguish between these two effects because decreasing OA mass will also decrease scattering, which will cause a significantly different net radiative effect. We also find that an average of 54 % of non-BC absorption (23 % total absorption) at 660 nm is from water-soluble BrC, confirming that BrC absorption is important across the visible spectrum. Quantification of significant BrC at red wavelengths and observation of bleaching being caused by changes in OA with O : C and toluene : benzene markers of plume age provide important improvements to our understanding of BrC and critical constraints on aerosol absorption in regional and global climate models.