Maëlis Arnould

Over roughly the last decade, a visible, community-led Diamond Open Access (OA) ecosystem has emerged in the Earth sciences, not as a departure from tradition, but as the latest expression of a long-standing culture of open, society-supported scholarly communication. While free-to-read, fee-free publishing initiatives have deep roots in the field, predating the Diamond terminology by decades and encompassing regional infrastructures and institutional serial publishing by geological surveys and learned societies, the period since the mid-2010s has brought a new wave of explicitly Diamond-identified, community-governed disciplinary journals that have transformed the visibility and ambition of this model. This article analyzes that transition through a field-specific lens, taking journals such as Volcanica, Seismica, Tektonika, Geomorphica, Geodynamica, Sedimentologika, Advances in Geochemistry and Cosmochemistry, Open Paleontology, Planetary Research, and Journal of Studies of Earth’s Deep Interior as emblematic of a broader shift in scholarly communication. Building on current Diamond OA debates, we argue that Earth sciences Diamond journals are not merely “no-fee” outlets but sociotechnical experiments in reclaiming agency, redistributing publishing labor, and redefining value away from commercial metrics. This article develops three claims. First, the Earth sciences Diamond turn has been enabled by existing community infrastructures and high levels of volunteer coordination, but it remains uneven and fragile. Second, Diamond models strengthen equity for authors and readers while exposing unresolved tensions around labor sustainability, institutional support, and recognition regimes still structured by prestige metrics. Third, Earth sciences offer a strategically important testbed for a wider transition towards commons-based scholarly communication, especially where global fieldwork, data justice, and decolonizing commitments demand alternatives to the pay-to-read and pay-to-publish systems. We conclude that the next decade should prioritize durable funding compacts, shared technical infrastructure, and reform of research assessment so that Diamond OA can scale without reproducing extractive or technocratic governance.

Many intraplate volcanic chains are explained as hotspot trails formed by plate motion over mantle plumes, yet some deviate from this model. The Rodrigues Ridge, a volcanic lineament extending eastward from the Réunion hotspot track toward the Central Indian Ridge (CIR), is one such case. To assess its origin, we integrated field studies with zircon U‐Pb and (U‐Th)/He geo‐/thermochronology, groundmass K‐Ar dating, and major and trace element analyses of volcanic rocks from Rodrigues Island. Our results reveal that Rodrigues Island experienced a prolonged subaerial volcanic history from 4.1 to 1.1 Ma, 2.7 million years longer than previously thought. This history shows two episodes of volcanic construction: (a) a circular ‐volcano construction between 4.1 and 2.5 Ma, followed by erosion, subsidence, and coral reef development and (b) fissural volcanism from 2.3 to 1.1 Ma, which shaped the island's elongated morphology. Subaerial lavas are more alkalic and enriched in incompatible elements than older submarine ridge lavas. This geochemical evolution suggests an eastward migration of partial melting degree, with oceanic accretion driving magmatism along the Rodrigues Ridge. Combined with magnetic anomalies of the oceanic lithosphere, the chronology points to at least two propagation episodes toward the CIR (≥9.9–7.9 Ma and 4.1–0.4 Ma). We conclude that the Rodrigues Ridge originated as a fracture in the oceanic lithosphere, driven by plume‐related buoyancy forces and asthenospheric flow beneath the CIR, without any direct contribution from the Réunion plume to the partial melting degree. These findings emphasize the role of lithospheric stresses and oceanic accretion in shaping off‐axis volcanic chains.

Etude de l'expression de surface d'instabilités convectives mantelliques: Constituant la couche limite supérieure de la convection mantellique, la lithosphère terrestre est à l'interface entre les enveloppes externes et internes de notre Planète. Les interactions multiples entre celle-ci et le manteau sont à l'origine de déformations latérales (tectonique des plaques) et verticales (topographie dynamique) de la surface terrestre. Comprendre comment la formation et l'évolution d'instabilités convectives mantelliques renouvellent sans-cesse la surface est donc primordial pour améliorer nos interprétations d'un grand nombre d'observations de surface, telles que la formation de bassins sédimentaires, le mouvement des continents, la localisation des points chauds, la formation d'anomalies gravimétriques ou encore les variations du niveau marin.Cette thèse propose de développer des modèles numériques de convection mantellique générant defaçon auto-organisée de la tectonique des plaques en surface an d'étudier la façon dont le développement et la dynamique d'instabilités convectives telles que les panneaux de subduction ou les panaches mantelliques modifient la surface, dans un contexte de tectonique de surface approchant le régime terrestre.Dans une première partie, je m'intéresse à l'influence du couplage des mouvements de convection mantellique et de tectonique des plaques sur le développement de topographie dynamique (i.e. les mouvements verticaux de la lithosphère induits par la convection mantellique) à différentes échelles spatio-temporelles. Mes résultats suggèrent que la surface terrestre peut se déformer à toutes les échelles spatiales, du fait de mouvements convectifs de grande ampleur faisant intervenir le manteau entier (> 104 km) ou encore de convection à petite échelle sub-lithosphérique (< 500 km). Les variations temporelles de topographie dynamique s‘étendent de cinq à plusieurs centaines de millions d'années selon la nature des processus convectifs dont elles dérivent. En particulier, la dynamique d'initiation ou d'arrêt des zones de subduction contrôle l'existence d'échelles intermédiaires de topographie dynamique (longueurs d'onde variant entre 500 et 104 km). Ces résultats montrent donc que les interactions entre la dynamique de la lithosphère et la convection mantellique génèrent des motifs spatio-temporels de topographie dynamique complexes et cohérents par rapport aux observations terrestres.Dans un deuxième temps, cette thèse se focalise sur la dynamique des panaches mantelliques, et leurs interactions avec la surface. Je caractérise d'abord précisement le comportement des panaches générés dans nos modèles de convection à la lumière d'observations de surface. Puis, j'étudie la façon dont leurs interactions avec la tectonique de surface et les différentes échelles convectives modifient leurs mouvements latéraux. Enfin, la compréhension de la signature thermique des interactions entre panaches et rides océaniques me permet de proposer une reconstitution des mouvements relatifs entre le panache des Açores et la ride médio-Atlantique.

Many hotspots worldwide display evidence of fluctuating magmatic activities that may be linked to time-dependent variations in melt production within mantle plumes. These periodicities are observed globally on Earth, ranging from 1 Myr to 20 Myr [Morrow and Mittelstaedt, 2021 ; Sokolov et al., 2025]. Remarkably, the Réunion hotspot exhibits short magmatic pulsations with a periodicity of ~400 kyr [Famin et al., in rev.]. Given the ~230 km separation between La Réunion and Mauritius, the synchronous short-period pulsations observed at the Réunion hotspot imply that they originate from deeper plume dynamics. Understanding the physical controls behind these pulsations could establish links between mantle convection, plume dynamics, and surface volcanism. Previous studies suggest that plume behavior is sensitive to mantle rheology. Plume pulsations with periods of ~1-10 Myr have indeed been reported in numerical experiments and can stem from thermochemical instabilities due to the interaction of plumes with small-scale convection in the asthenosphere [Ballmer et al., 2009], thermal instabilities in sufficiently vigorous convection (Rayleigh number > 5×10⁶), buoyancy changes due to mineralogical phase transitions [Trubitsyn and Evseev, 2018], horizontal shearing caused by plate motions over an asthenosphere dominated by dislocation creep, leading to unstable tilted plume conduits [Neuharth and Mittelstaedt, 2023]. Here, we seek to investigate how mantle rheology can favour short-period pulses of plume activity and aim to identify the core physical mechanisms that control plume dynamics. We thus run 3D regional convection models in spherical cap geometry with plate-like behavior (viscoplastic rheology) at the surface using the StagYY code [Tackley, 2000]. We developed an automated algorithm to detect and track plumes in space and time, by defining plumes as the highest percentiles of the upwards vertical advective heat transport . The morphology and dynamics of plumes are then quantified using various parameters such as the buoyancy flux, heat flux, angle of inclination, along with their associated uncertainties. Our study explores the effects of surface yield stress (ranging 10-100 MPa), radiogenic heat production (3-15 pW/kg), a 30 to 100 fold viscosity jump at the transition zone, and of compressibility and phase transitions (especially the post-spinel transition at ~660 km depth that works as an accelerator of upwellings plumes and thus favors dynamic instabilities [Faccenda and Dal ZIlio 2016]) on plume dynamics as well as on plate tectonics. We aim to understand how these parameters control the generation of periodic activity and short-period term plume pulses and ultimately to estimate melt production variations at the surface in order to compare it with geological observations of magmatic products at the Réunion hotspot. Preliminary results indicate that surface yield stress and radiogenic heat production primarily affect plate tectonics, whereas a viscosity jump across the transition zone promotes periodic (~2 Myr) plume behavior.

One efficient driver for atmospheric CO2 removal over 10-100 Ma timescales is silicate-rich rock weathering, which is notably favored in the context of arc magmatism (Gernon et al., 2021). The modeling of the past evolution of atmospheric CO2 therefore requires to finely reconstruct the evolution of past subduction zones, which is challenging due to the permanent recycling of oceanic lithosphere. One difficulty notably resides in the reconstruction of intra-oceanic arcs, which leave almost no direct imprints in the geological record, although they could significantly contribute to the atmospheric CO2 removal through silicate weathering, especially in the tropics (Gaillardet et al., 2011).We propose to test how the variability of intra-oceanic arcs can affect the amount of CO2 removed from the atmosphere through supercontinent cycles. To do so, we use 3D numerical models of whole-mantle convection self-generating Earth-like plate tectonics in order to quantify the temporal evolution of the number and length of intra-oceanic arcs, in a fully-dynamic context, independent of any plate reconstructions. We use the automatic plate tessellation algorithm MAPT3 based on the open-source library Topology ToolKit (Janin et al., 2025) to detect intra-oceanic subduction zones. We show that the total length of intra-oceanic arcs varies significantly depending on the continental configuration in the models. We then test the sensitivity of atmospheric CO2 absorption level through silicate weathering to mantle convective parameters, to the latitudinal distribution of the intra-oceanic arcs, their width and fraction above sea-level, and the potential effect of True Polar Wander. We show that in a fully-dynamic model, it is possible to reach the amount of extra-weathering required to possibly explain the atmospheric CO2 and temperature drops observed, especially during periods of continental aggregation. Nevertheless, the amount of intra-oceanic subduction zones in the geodynamic models varies over longer timescales than in the plate reconstruction, and cannot explain alone, rapid cooling events, such as during the Hirnantian (Marcilly et al., 2022).

Earth’s interior plays a fundamental role in the long-term evolution of the surface, climate, and biosphere. However, Earth's mantle evolution remains largely ambiguous, as imaging techniques are limited to present-day observations and geochemical or geological constraints apply to a non-global scale. Plate tectonic reconstructions coupled with convection models could provide constraints on the evolution of mantle structure. In this study, we employ both fully self-consistent and kinematically constrained mantle convection models[1]. The mantle rheology is temperature-, pressure-, phase-, and stress-dependent, with the latter represented through pseudo-plasticity. The novelty of this work lies in employing a composite rheology with “realistic” rheological parameters[2] in a fully three-dimensional geometry. By using both fully self-consistent models and plate-driven models, we aim to address the discrepancies in terms of long-term convective and tectonic behaviour that arise when forcing plate velocities onto the surface. The latter is done by imposing time-dependent surface velocity boundary conditions provided by a plate tectonic reconstruction[3].To evaluate the extent to which the models reproduce plate-like tectonics, we explore several independent constraints. In particular, we compute slab sinking rates and compare them to estimates inferred from seismic tomography[4]. Slab sinking rates in self-consistent models provide insight into the mantle’s rheology. For example, sinking rates that are lower than those based on tomographic and geological data may indicate an overly viscous mantle. Our results show that the slab sinking rate is generally higher in models with imposed plate velocities compared to fully self-consistent models. Furthermore, a tessellation algorithm[5] will be applied to the surface of the models to detect plates in the self-consistent models with plate-like behaviour. Based on these results, a plate-size frequency distribution can be calculated and compared to present-day Earth[6]. Results show that low yield stresses generate too many small plates, and too few large plates [Fig. 1]. In order to generate Earth-like plate tectonics, yield stress needs to be sufficiently high to reproduce the plate-size frequency distribution of present-day Earth, but also sufficiently low to facilitate a long-term mobile lid regime.[1] Tackley, P. J. (2008). Phys. Earth Planet. Inter. 171, 1–4.[2] Tackley, P. J., Ammann, M., Brodholt, J. P., Dobson, D. P., & Valencia, D. (2013). Icarus 225, 50–61.[3] Merdith, A. S., Williams, S. E., Collins, A. S., et al. (2021). Earth-Sci. Rev. 214, 103477.[4] Van der Meer, D. G., van Hinsbergen, D. J. J., & Spakman, W. (2018). Tectonophysics 723, 309–448.[5] Janin, A., Coltice, N., Chamot-Rooke, N., & Tierny, J. (2025). Nat. Geosci. 18, 1041–1047.[6] Bird, P. (2003). Geochem. Geophys. Geosyst. 4, 2001GC000252.

Intra-plate volcanism is commonly attributed to mantle plumes originating from deep-seated therm0-chemical anomalies that rise buoyantly through the mantle and puncture the overlying lithosphere. These long-lived magmatic systems can persist for tens of millions of years, producing age-progressive volcanic chains and, in some cases, interacting with mid-ocean ridges to generate off-axis volcanism. The Rodrigues Ridge, and more generally the Mascarene Islands in the Indian Ocean have traditionally been interpreted within this framework as the result of interaction between the Central Indian Ridge and the Réunion hotspot. Here, we present a new geochemical and geochronological investigation of volcanic rocks from Rodrigues Island, the subaerial expression of the Rodrigues Ridge, which challenges this classical model. Compared with published data from the Mascarene islands, our major, trace element and Sr-Nd-Pb isotopic analyses reveal systematic deviations from compositions expected for simple mixing between depleted mid-ocean ridge mantle and Réunion plume-derived melts. Instead, Rodrigues subaerial lavas, along with the intermediate and younger volcanic series of Mauritius Island; record the contribution of a third, geochemically distinct mantle source whose signature lies in the focus zone (FOZO) of Ocean Island Basalts isotopic compositions. This additional component requires the involvement of material derived from another deep mantle source. The most suitable candidate providing this plume-related material is the Mascarene Basin asthenospheric reservoir (MBAR), a low shear velocity zone in the asthenosphere beneath the Mascarene Basin identified by seismic tomographies described in Barruol et al. (2019). Moreover, on-axis volcanism in the Central Indian Ridge —and thus recent— have already been linked to the influence of the MBAR (Vincent et al., 2024). K-Ar geochronology combined with geochemistry allows us to constrain the timing of its contribution to the magmatism of the western Indian Ocean to the last ~4 million years. These results highlight the complexity of mantle plume–ridge interactions and suggest that the Indian Ocean upper mantle is fed by multiple plume sources whose contributions may overlap in space and time. Our study emphasizes the need to reconsider the upper mantle architecture beneath off-axis volcanic ridges and sheds light on the dynamics of plume dispersal within the asthenosphere.

The number of geophysics students is rapidly declining across Europe, despite the great demand for geophysicists. Many students are interested in quantitative sciences with Earth science applications, but they are often not aware of geophysics as a career option as it is not typically taught in school (Jenkins et al., 2024). Furthermore, the spread of misinformation, conspiracy theories, and anti-scientific movements across Europe have highlighted the need for scientific literacy (Siarova et al., 2019 European Parliament). Now more than ever, there is a need to introduce the general public to the basics of the scientific method and what it means to do research, particularly in geosciences (EGU Barcelona Manifesto for the Teaching of Geosciences, 2023). We are therefore developing materials for Science Storytellers: scientists who go into their community to engage with students and the general public. Our curiosity-driven teaching materials are based around well-known tales and incorporate elements of narrative, performance, and play. Through this original framework, we provide scientists and teachers with the tools to effectively engage students. This year, we focus on the classic tale of “The House At Pooh Corner” by A. A. Milne (1928). In this novel, Eeyore is relieved that there has not been an earthquake lately. The book takes place in Sussex (UK), where earthquakes are not typical. Why then, is Eeyore talking about them? We present the science case behind this story in the General Seismology session (SM1.1) and here we show how we developed this research into teaching and outreach material. We developed a set of different questions around the research-project, which naturally arise from the Winnie-the-Pooh premise to encourage children to follow their own curiosity to discover why Eeyore is worried about earthquakes. With this abstract, we seek feedback from fellow science communicators and teachers and invite everyone along to the try-out of the corresponding "The Science Storyteller" theatre show, which will make its debut on the Friday afternoon of EGU in a dedicated splinter meeting. We hope to reach even more young people and curious minds through this interactive, musical journey through the science story behind Winnie-the-Pooh. References Jenkins, J., Gilligan, A., & Bie, L. (2024). Who wants to be a geophysicist?. Astronomy & Geophysics, 65(5). Siarova, H., Sternadel, D., & Szőnyi, E. (2019). Research for CULT committee–Science and scientific literacy as an educational challenge.

Over geological timescales climate is regulated by the long carbon cycle, in which a balance is struck between CO2 degassing from the solid Earth and CO2 consumption by continental silicate weathering stabilizing atmospheric CO2 levels and maintain habitable conditions. Geodynamic processes regulate both CO2 degassing rates as well as the distribution and elevation of continents, thereby controlling continental weatherability and, ultimately, atmospheric CO2 and long-term climate.However, long-term carbon cycle models are often limited by their definition of degassing independently of geodynamics evolution and their inevitable attribution of continental weatherability as the primary driver of long-term climate. Furthermore, the sparsity of the geological record means that models often rely on observations of present-day Earth to simulate past Earth states. All these constrains provide limited insight into how geodynamics interacts with climate, and surface processes to regulate atmospheric CO2 over geological timescales.To address these limitations, we use fully integrated "digital siblings” of the Earth: 3D fully virtual planets designed to simulate internally consistent evolution of habitable planets over a several 100~Myr timescales, not necessarily aiming to replicate Earth. We integrate three numerical models in a dynamically interdependent framework: the geodynamic model StagYY (Coltice et al., 2019), the climate model PLASIM-GENIE (Holden et al., 2016), and the surface processes model goSPL (Salles et al., 2023).From these simulations, we compute time-dependent CO2 degassing rates, using geodynamic outputs, and weathering fluxes, using the formulation of West (2012). Our results reveal fluctuations in degassing rate over a factor of about three, consistent with reconstruction of Earth (Müller et al., 2024) and correlated with seafloor production rate. Weatherability strongly depends on True Polar Wander during supercontinent aggregation, and on sea level fluctuations controlled by seafloor production. Together, these results highlight how geodynamic evolution may regulate the long-term carbon cycle through its interdependent effects on degassing and continental weatherability.

How the formation and breakup of supercontinents drive environmental shifts remains a fundamental question, but piecemeal deep-time records prevent an answer based on observations. Here we present the first simulation of an Earth-like planet integrating geodynamics, climate, and surface processes to assess how solid Earth dynamics regulate environmental change. We show that mantle flow governs surface conditions through two coupled pathways: true polar wander (TPW) and seafloor spreading rate. During supercontinent assembly, a large-scale mantle flow draws continents together and, through TPW, aggregates the landmasses toward the equator, while seafloor production decreases and the seafloor ages. The larger tropical land area increases planetary albedo and continental weatherability, while reduced seafloor spreading lowers mantle degassing; together these effects suggest a cooling of the atmosphere while the mantle warms. During breakup, the switch to smaller-scale mantle flow reverses both pathways: continents drift as seafloor rejuvenates, lowering tropical albedo and weatherability while increasing degassing and sea level, which together warm the atmosphere as the mantle cools. These internally generated, mantle-driven shifts reproduce key features of Pangea on Earth, providing a mechanistic framework linking deep Earth dynamics to climate and, ultimately, to conditions for life.