Clinton Phillips Conrad

• Kierulf, Halfdan Pascal; Maria, Kern, Lisa; Conrad, Clinton Phillips; Kirkvik, Ann-Silje; Hana, Krásná, & Moholdt, Geir [Show all 7 contributors for this article] (2026). Effects of glacial loading in Svalbard on the VLBI scale realisation. Journal of Geodesy. ISSN 0949-7714. 100. doi: 10.1007/s00190-026-02121-1. Full text in Research Archive Show summary

  In the realisation of the International Terrestrial Reference System in 2000, and in the realisations since 2008, the scale of the International Terrestrial Reference Frame (ITRF) has been defined based on Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) solutions, whereas ITRF2005 relied solely on VLBI. In the latest ITRF realisation, i.e. ITRF2020 with its first and second updates, VLBI sessions after September 2013 are excluded from the ITRF scale definition due to a detected drift in the VLBI solution with respect to the average scale trend computed from September 1997 until September 2013. Ny-Ålesund station in Svalbard, the northernmost fundamental geodetic station hosting all major techniques, plays a key role in ITRS realisation due to its location. Crustal motion measurements at Ny-Ålesund reveal nonlinear vertical motion, largely explained by elastic deformation caused by thinning glaciers. In the ITRF2020 updates (u2023 and u2024), a discontinuity in August 2016 was introduced for the VLBI station to account for the increasing uplift, reducing the detected scale drift relative to ITRF2020 by approximately 50%. In this study, we analyse the nonlinear vertical motion at Ny-Ålesund, compare it with predicted elastic loading signals arising from glacier thinning, and assess its impact on the VLBI scale estimates. Over the past 25 years, the land uplift rate increased from about 6 mm/year to 14 mm/year, indicating that the vertical displacement through time is not well described by a constant-rate model. The record also shows substantial interannual variability, of which the glacier loading model explains only about 50%. Including a nonlinear station motion model—based on Global Navigation Satellite System (GNSS) observations or loading predictions—for the VLBI station in Ny-Ålesund reduces the relative scale drift by 30–60%. Finally, we discuss alternative approaches to mitigate the negative effects of nonlinearity, such as modelling the elastic glacier signal or better integrating VLBI station motion with GNSS-derived displacement.

• Király, Ágnes; Wang, Yijun; Conrad, Clinton P; Hansen, Lars N & Mather, Ben (2026). CPO2Hill: An Efficient Parametrisation to Infer Anisotropic Viscous Behaviour Directly from Olivine Texture Parameters. Geodynamica. 1(1). doi: 10.5070/f3.49008. Full text in Research Archive Show summary

  Anisotropic viscosity is likely prevalent within the upper mantle, but is usually disregarded in geodynamics models. On a crystal scale, olivine’s intrinsic properties are such that dislocation creep occurs over an order of magnitude more easily along olivine’s [100] symmetry axis than along its [001] axis. However, deforming olivine aggregates generate crystallographic preferred orientations (CPO) with their own macroscopically effective anisotropic viscosities that have proven difficult to estimate from the microscopic anisotropies of individual olivine crystals. Here we present a simple method to derive anisotropic viscosity parameters directly from the CPO mean orientation tensors. To calibrate the method, we created a large database of textures likely to occur in geodynamic simulations. We tested our method within numerical simulations of simple shear with both constant and varying shear directions. Finally, we integrated our method into the geodynamic code ASPECT, where it can be used to explore the geodynamic importance of anisotropic viscosity.

• Conrad, Clinton Phillips & Domeier, Mathew Michael (2026). Seamount volcanism associated with Earth’s basal mantle structures | Nature Geoscience. Nature Geoscience. ISSN 1752-0894. 19(7), p. 822–827. doi: 10.1038/s41561-026-02007-z. Full text in Research Archive Show summary

  While seafloor spreading and subduction explain much of the volcanic activity in Earth’s oceans, magmatism occurring within tectonic plate interiors requires a deeper mantle explanation. Various types of oceanic intraplate volcanism, including oceanic plateaus and hotspot-associated seamount chains, have been attributed to plumes rising from the margins of two continent-sized structures termed large low-shear-velocity provinces (LLSVPs) in the lowermost mantle beneath Africa and the Pacific Ocean. Here we analyse seamount catalogues and show that seamount volcanism is more voluminous on seafloor that has passed above a LLSVP. We find that this volcanic enhancement is evident above both LLSVPs, but is greater above the Pacific one and has declined since the mid-Cretaceous. We suggest that weak plumes rising from both LLSVPs interact with oceanic lithosphere to promote seamount volcanism. This process may be enhanced for the Pacific because of elevated mantle temperature, transition zone hydration and/or convective vigour in the Pacific hemisphere. Our findings provide additional support for the hypothesis that plumes carrying heat from the LLSVPs are responsible for most oceanic intraplate volcanism, including dispersed seamounts. This deep mantle connection means that seamount volcanism is sensitive to, and thus may constrain, the time-dependent dynamics of Earth’s deepest mantle. Seamount volcanism is more voluminous where seafloor has passed above a large low-shear-velocity province, consistent with mantle plumes being responsible for most oceanic intraplate volcanism, according to an analysis of seamount catalogues.

• Törnqvist, Torbjörn E.; Conrad, Clinton Phillips; Dangendorf, Sönke & Hamlington, Benjamin D. (2025). Evaluating IPCC Projections of Global Sea‐Level Change From the Pre‐Satellite Era. Earth's Future. 13(8). doi: 10.1029/2025ef006533. Full text in Research Archive Show summary

  Abstract With an acceleration of global sea‐level rise during the satellite altimetry era (since 1993) firmly established, it is now appropriate to examine sea‐level projections made around the onset of this time period. Here we show that the mid‐range projection from the Second Assessment Report of the IPCC (1995/1996) was strikingly close to what transpired over the next 30 years, with the magnitude of sea‐level rise underestimated by only ∼1 cm. Projections of contributions from individual components were more variable, with a notable underestimation of dynamic mass loss from ice sheets. Nevertheless—and in view of the comparatively limited process understanding, modeling capabilities, and computational resources available three decades ago—these early attempts should inspire confidence in presently available global sea‐level projections. Such multidecadal evaluations of past climate projections, as presented here for sea‐level change, offer useful tests of past climate forecasts, and highlight the essential importance of continued climate monitoring.

• Wang, Zhirui Ray; Conrad, Clinton Phillips; Lebedev, Sergei; Iaffaldano, Giampiero & Hopper, John R. (2025). Depth-dependent azimuthal seismic anisotropy governed by Couette/Poiseuille flow partitioning in the asthenosphere. Earth and Planetary Science Letters. ISSN 0012-821X. 667. doi: 10.1016/j.epsl.2025.119527. Full text in Research Archive Show summary

  Azimuthal seismic anisotropy provides crucial knowledge on spatial patterns of past and present upper mantle deformation. Origins of this deformation were traditionally tied to relative shear between surface plates and mantle, and in turn a constant orientation of anisotropy azimuths with depth. However, observations of azimuthal seismic anisotropy based on surface-wave tomography often feature depth-dependent azimuths in the upper mantle. This is consistent with the existence of low-viscosity, thin asthenosphere that facilitates the channelization of both plate-driven Couette flow and pressure-driven Poiseuille flow. If the two flows are not aligned, their combination yields depth rotations of asthenospheric shear, giving rise to depth dependence of azimuthal seismic anisotropy. In this study, we utilize publicly available azimuthal seismic anisotropy together with predictions from a global mantle flow model that incorporates Couette/Poiseuille flow. We find that Poiseuille flow has significant influence on depth rotations of seismically inferred azimuthal anisotropy. Depth rotations are prominent under the Atlantic basin and the Nazca plate, where modeled asthenospheric flow regimes are dominated by Poiseuille flow. Significant Poiseuille flow may exist beneath the Indian basin, but its depth rotations are small, probably because subduction zones to the north align Couette and Poiseuille flows into the same direction. Our results indicate that interpretation of azimuthal seismic anisotropy cannot be simply associated with relative shearing between plates and mantle. Instead, the relative importance of Couette and Poiseuille flows must be considered to account its depth dependence.

• Ebbing, Jörg; Hopper, John R.; Conrad, Clinton Phillips; Milne, Glenn; Steffen, Rebekka & Afonso, Juan Carlos [Show all 16 contributors for this article] (2025). Importance of solid earth structure for understanding the evolution of the Greenland ice sheet. Journal of the Geological Society. ISSN 0016-7649. 182(5). doi: 10.1144/jgs2024-291. Full text in Research Archive Show summary

  The solid earth structure beneath Greenland, meaning the rocky part of Earth from the ice-bed interface to depth, has gained increased interest in recent years as it provides a critical boundary condition for the dynamic evolution of the Greenland ice sheet (GrIS), one of the largest sources of sea-level rise contributions since the early 2000s. However, no consensus has been reached regarding the key internal or surface earth properties influencing this boundary condition and thus GrIS behaviour. One important surface property is the subglacial heat flow, which affects sliding conditions of the ice sheet including the onset of major ice streams and is related to subglacial geology. Lithospheric architecture and mantle viscosity structure are internal properties that influence ice sheet evolution through changes in the height and slope of the ice-bed interface caused by glacial isostatic adjustment. Because there is no general agreement regarding crustal and lithospheric structures, some glaciological studies use an ensemble of solid earth models to incorporate uncertainties into their GrIS predictions, but it is unclear how these variations ultimately affect estimates of future sea-level rise. Here we describe the main solid earth properties that are important for GrIS evolution (heat flow, temperature, viscosity), from the base of the ice sheet to the upper mantle, and we provide some perspectives on how future collaborative efforts and integrated studies could lead to better agreement regarding these key characteristics.

• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips & Maupin, Valerie (2025). Mantle Flow and Anisotropy in Subduction Zones: Modeling and Clustering of Olivine Textures. Geochemistry Geophysics Geosystems. 26(7). doi: 10.1029/2025gc012160. Full text in Research Archive Show summary

  The mantle near Earth's subduction zones endures intense deformation that generates anisotropic rock textures. These textures can be observed seismically and modeled geodynamically, but the complexity of this deformation makes analyses of these textures difficult. In this study, we apply time‐series clustering analysis to tracers within subduction models, allowing for the identification of regions in the subduction zone with common deformation histories and olivine crystallographic‐preferred orientation development. We compare olivine texture evolution predicted using different methods in both retreating and stationary‐trench settings. Our results reveal distinct variations in olivine texture, indicating that both seismic and viscous anisotropy can exhibit substantial heterogeneity within the mantle wedge, sub‐slab, and subducting plate regions. For retreating trenches, olivine textures are strongest in the mid‐depth mantle wedge region about 200 km away from the trench between 100 and 300 km depth. Our study shows that trench‐normal olivine a ‐axis orientations dominate in the center of subduction zones. Toroidal flow around slab edges generates a mix of trench‐normal, trench‐parallel, and oblique fast seismic directions. Textures and anisotropy are stronger for the retreating trench model than for the stationary trench model since more deformation has been accumulated due to trench motion. These findings provide insights for interpreting seismic anisotropy in subduction zones and highlight the importance of considering texture heterogeneity, as characterized by clustering algorithms, when analyzing both geodynamic models and seismic observations of subduction zones.

• Mohn, Chris Erik; Caracas, Razvan & Conrad, Clinton Phillips (2025). Lower mantle water distribution from ab initio proton diffusivity in bridgmanite. Earth and Planetary Science Letters. ISSN 0012-821X. 649. doi: 10.1016/j.epsl.2024.119095. Full text in Research Archive Show summary

  Proton self diffusion coefficients for bridgmanite at lower mantle conditions are calculated from ab initio molecular dynamics simulations. We find that the proton self diffusion coefficient, is nearly constant ∼ 10−8 m2 s−1 along the lower mantle geotherm but increases by nearly one order of magnitude from ∼10−10 m2 s−1 to ∼ 10−9 m2 s−1 along a cold slab geotherm to about 1800 km depth. These rates imply that the proton diffusion length scale is less than 10 km in lower mantle peridotite in the 150-200 million years timescale for slab material to sink through the lower mantle. Cold wet slabs probably lose less than one percent of their total water content to the ambient mantle on their journey through the lower mantle, indicating that recycled water is far from homogeneously distributed since slab delivery is highly heterogeneous. We estimate that 0.1 to 0.3 ocean masses (<100 ppm wt%) of recycled water may be currently stored in slab remnant materials within the lower mantle. This water is likely not entrained by plumes but is instead captured by background mantle flow before returning to the mid-ocean ridges. By contrast, deep-rooted mantle plumes may entrain materials containing primordial-like water from the lowermost mantle or the core, and preserve these anomalies in fairly small-scale heterogeneities. Over the age of the Earth, the proton diffusion length scale is a few tens of km, which places constraints on the size of possible primordial water reservoirs isolated from convective mixing, and indicates little flux of water across the core-mantle boundary.

• Wang, Helene; Magni, Valentina; Conrad, Clinton Phillips & Domeier, Mathew Michael (2025). Hydrous Regions of the Mantle Transition Zone Lie Beneath Areas of Continental Intraplate Volcanism. Geochemistry Geophysics Geosystems. 26(3). doi: 10.1029/2024GC011901. Full text in Research Archive Show summary

  Great volumes of water are carried downward into the mantle transition zone (MTZ, 410–670 km depth) by subducting slabs. If this water is later drawn upward, the resulting mantle melting may generate continental intraplate volcanism (IPV). Despite water's importance, its amount and spatial distribution within the MTZ, and its impact on IPV, are poorly constrained. Here we use plate tectonic reconstructions to estimate the rates and positions of water injection into the MTZ by subducted slabs during the past 400 Myr. This allows us to construct global maps of heterogeneous MTZ hydration, which we then compare to IPV eruption locations from the past 200 Myr. We detect a statistically significant correlation between wet MTZ regions and IPV locations at the surface, but only if slabs sink faster than 1 cm/yr, water remains stored in the MTZ for periods of 30–100 Myr, and IPV eruptions occur 10–30 Myr later. We find that 42%–68% of continental IPV is underlain by wet MTZ, with greater fractions associated with longer MTZ residence time. Hydrous underpinning of continental IPV was highest during the Jurassic, when more extensive slab interaction with the MTZ hydrated a wider area of the MTZ. Since the Cretaceous, continents have been moving over the wet MTZ, increasing IPV possibilities. MTZ regions near the northern Pacific, southern Africa, and western Europe have remained dry by avoiding wet slabs. We suggest that subducted water shapes global patterns of intraplate volcanism, with hydrous upwellings rising from the MTZ to generate continental IPV above wet MTZ regions.

• Weerdesteijn, Maaike Francine Maria & Conrad, Clinton Phillips (2024). Recent ice melt above a mantle plume track is accelerating the uplift of Southeast Greenland. Communications Earth & Environment. 5. doi: 10.1038/s43247-024-01968-6. Full text in Research Archive Show summary

  Around the periphery of the Greenland ice sheet, satellite-based observations of ground uplift record Earth’s response to past and recent unloading of Greenland’s ice mass. On the southeast coast, near the Kangerlussuaq glacier, rapid uplift exceeding 12 mm/yr cannot be explained using current layered Earth deformation models. Here we find that 3D models with a weakened Earth structure, consistent with the passage of Greenland over the Iceland plume, can explain the rapid uplift of Southeast Greenland. This uplift is dominated by a viscous response that is accelerated by the low viscosities of the hot plume track. Recent mass loss, occurring during the last millennium and especially within the past few decades, drives most of the uplift. Holocene indicators recorded similarly rapid uplift following deglaciation that ended the last ice age. Such rapid uplift, occurring beneath marine terminating glaciers, can affect the future stability of entire ice catchment areas and will become increasingly important in the near future as deglaciation accelerates.

• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Fraters, Menno (2024). The Importance of Anisotropic Viscosity in Numerical Models, for Olivine Textures in Shear and Subduction Deformations. Tektonika. 2(1), p. 157–173. doi: 10.55575/tektonika2024.2.1.67. Full text in Research Archive Show summary

  Olivine lattice preferred orientation (LPO), or texture, forms in relation to deformation mechanisms such as dislocation creep and can be observed in the upper mantle as seismic anisotropy. Olivine is also mechanically anisotropic, meaning that it responds to stresses differently depending on the direction of the stress. Understanding the interplay between anisotropic viscosity (AV) and LPO, and their role in deformation, is necessary for relating seismic anisotropy to mantle flow patterns. In this study, we employ three methods to predict olivine texture (D-Rex, MDM, and MDM+AV) in a shear box model and a subduction model. D-Rex and MDM are two representative texture development methods that have been compared before, and our results are in line with previous studies showing that textures computed by D-Rex develop faster and are stronger and more point-like than textures calculated with MDM. MDM+AV uses the same isotropic mantle stresses and particle paths as D-Rex and MDM but includes the effect of AV for texture predictions. MDM+AV predicts a texture similar to MDM with a distinct girdle-like orientation for simple shear deformation or at low strain in the subduction model. At larger strains, MDM+AV’s textures are more point-like and stronger compared to the other two methods. The effective viscosity for MDM+AV drops by up to 60% in a shear box model and can be either strengthened or weakened relative to isotropic viscosity for different regions of the subduction model experiencing different patterns of deformation. Our results emphasize the significant role of AV in olivine texture development, which could substantially affect geodynamic processes in the upper mantle.

• Ramirez, Florence; Selway, Katherine; Conrad, Clinton Phillips; Maupin, Valerie & Smirnov, Maxim (2024). Lateral and radial viscosity structure beneath Fennoscandia inferred from seismic and magnetotelluric observations. Physics of the Earth and Planetary Interiors. ISSN 0031-9201. 351. doi: 10.1016/j.pepi.2024.107178. Full text in Research Archive Show summary

  Fennoscandia is continuously uplifting in response to past deglaciation, termed glacial isostatic adjustment or GIA, and its mantle viscosity is well constrained from ice sheet and sea level data. Here, we compare those GIA-constrained viscosities for the Fennoscandian upper mantle with geophysically-constrained viscosities. We construct the upper mantle viscosity structure of Fennoscandia by inferring temperature and water content from seismic and magnetotelluric (MT) data. Using a 1-D MT model for Fennoscandian cratons together with a global seismic model, we infer an upper mantle viscosity (below 250 km) of ∼1021±2 Pa·s, which encompasses the GIA-constrained viscosities of 1020 − 1021 Pa·s. The GIA viscosities are better matched if the Fennoscandian upper mantle is a wet harzburgite or a dry pyrolite, where pyrolite is ∼10 times more viscous than harzburgite. Using the average temperatures and water contents for harzburgitic upper mantle, the GIA viscosities require 1–4 mm grain sizes indicating a diffusion creep regime. In northwestern Fennoscandia, where a high-resolution 2-D resistivity model is available, greater inferred mantle water content implies viscosities that are 10–100 times lower than those for the Fennoscandian Craton. Our work suggests that the combination of seismic and MT observations can improve upper mantle viscosity estimates, especially for regions with laterally-varying viscosity structures or where GIA constraints are not available. Although our method represents an important step forward, viscosity uncertainty can be further reduced by incorporating additional constraints on rock composition, grain size and mantle stress, as well as more accurate geophysical data, into the viscosity calculation.

• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2024). Prolonged Multi-Phase Magmatism Due To Plume-Lithosphere Interaction as Applied to the High Arctic Large Igneous Province. Geochemistry Geophysics Geosystems. 25(6). doi: 10.1029/2023GC011380. Full text in Research Archive Show summary

  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.

• Weerdesteijn, Maaike Francine Maria; Naliboff, John B.; Conrad, Clinton Phillips; Reusen, Jesse M.; Steffen, Rebekka & Heister, Timo [Show all 7 contributors for this article] (2023). Modeling Viscoelastic Solid Earth Deformation Due To Ice Age and Contemporary Glacial Mass Changes in ASPECT. Geochemistry Geophysics Geosystems. 24(3). doi: 10.1029/2022GC010813. Full text in Research Archive Show summary

  Abstract The redistribution of past and present ice and ocean loading on Earth's surface causes solid Earth deformation and geoid changes, known as glacial isostatic adjustment. The deformation is controlled by elastic and viscous material parameters, which are inhomogeneous in the Earth. We present a new viscoelastic solid Earth deformation model in ASPECT (Advanced Solver for Problems in Earth's ConvecTion): a modern, massively parallel, open‐source finite element code originally designed to simulate convection in the Earth's mantle. We show the performance of solid Earth deformation in ASPECT and compare solutions to TABOO, a semianalytical code, and Abaqus, a commercial finite element code. The maximum deformation and deformation rates using ASPECT agree within 2.6% for the average percentage difference with TABOO and Abaqus on glacial cycle (∼100 kyr) and contemporary ice melt (∼100 years) timescales. This gives confidence in the performance of our new solid Earth deformation model. We also demonstrate the computational efficiency of using adaptively refined meshes, which is a great advantage for solid Earth deformation modeling. Furthermore, we demonstrate the model performance in the presence of lateral viscosity variations in the upper mantle and report on parallel scalability of the code. This benchmarked code can now be used to investigate regional solid Earth deformation rates from ice age and contemporary ice melt. This is especially interesting for low‐viscosity regions in the upper mantle beneath Antarctica and Greenland, where it is not fully understood how ice age and contemporary ice melting contribute to geodetic measurements of solid Earth deformation.

• Ramirez, Florence Dela Cruz; Conrad, Clinton Phillips & Selway, Katherine (2023). Grain size reduction by plug flow in the wet oceanic upper mantle explains the asthenosphere's low seismic Q zone. Earth and Planetary Science Letters. ISSN 0012-821X. 616. doi: 10.1016/j.epsl.2023.118232. Full text in Research Archive Show summary

  The prominent seismic low-velocity zone (LVZ) in the oceanic low-viscosity asthenosphere is approximately coincident with the low seismic Q zone (LQZ; a zone of high seismic attenuation). Small olivine grain sizes could link these seismic and rheological properties because they reduce viscosity, seismic velocity and seismic Q. Because rock deformation reduces grain sizes, the asthenosphere's seismic properties can place constraints on asthenospheric flow. To determine dominant flow patterns, we develop a self-consistent analytical 1-D channel flow model that accounts for upper mantle rheology and its dependence on flow-modified grain-sizes, water content, and melt fraction, for flow driven by both surface plate motions (Couette flow) and/or horizontal pressure gradients (Poiseuille flow). We find that Couette flow dominates if the upper mantle is dry, and plug flow (a Poiseuille flow for power law rheology) dominates if it is weakened by wet conditions. A plug flow configuration spanning the upper 670 km of the mantle best explains the LQZ in the asthenosphere, and can be attributed to significant grain-size reduction due to extensive shearing across the asthenosphere. This flow configuration also explains high seismic Q values below the asthenosphere associated with minimal shear deformation and large grain sizes above the mantle transition zone. We suggest that the asthenospheric LQZ and LVZ seismic anomalies can be largely explained by grain-size variations associated with plug flow in the wet upper mantle.

• Paul, Jyotirmoy; Conrad, Clinton Phillips; Becker, Thorsten W. & Ghosh, Attreyee (2023). Convective Self-Compression of Cratons and the Stabilization of Old Lithosphere. Geophysical Research Letters. ISSN 0094-8276. 50(4). doi: 10.1029/2022GL101842. Full text in Research Archive Show summary

  Abstract Despite being exposed to convective stresses for much of the Earth's history, cratonic roots appear capable of resisting mantle shearing. This tectonic stability can be attributed to the neutral density and higher strength of cratons. However, the excess thickness of cratons and their higher viscosity amplify coupling to underlying mantle flow, which could be destabilizing. To investigate the stresses that a convecting mantle exerts on cratons that are both strong and thick, we developed instantaneous global spherical numerical models that incorporate present‐day geoemetry of cratons within active mantle flow. Our results show that mantle flow is diverted downward beneath thick and viscous cratonic roots, giving rise to a ring of elevated and inwardly‐convergent tractions along a craton's periphery. These tractions induce regional compressive stress regimes within cratonic interiors. Such compression could serve to stabilize older continental lithosphere against mantle shearing, thus adding an additional factor that promotes cratonic longevity.

• Weerdesteijn, Maaike Francine Maria; Conrad, Clinton Phillips & Naliboff, John B. (2022). Solid Earth Uplift Due To Contemporary Ice Melt Above Low-Viscosity Regions of the Upper Mantle. Geophysical Research Letters. ISSN 0094-8276. 49(17). doi: 10.1029/2022GL099731. Full text in Research Archive Show summary

  Glacial isostatic adjustment explains topographic change in formerly and currently glaciated regions, but the role of small (∼100s km) regions of unusually low-viscosity mantle is poorly understood. We developed viscoelastic models with low-viscosity regions in the upper mantle, and measured the effect of these regions on solid earth uplift resulting from contemporary surface ice melt. We found viscous uplift occurring on decadal timescales above the low-viscosity region, at rates comparable to or larger than those from elastic uplift or the viscous response to ice age melting. We find that uplift rates are sensitive to the location, dimensions, and viscosity of the low-viscosity region, and that the largest uncertainty in uplift rates likely comes from the low-viscosity region's horizontal extent. Rapid viscous ground uplift can impact ice dynamics if the low-viscosity region is located close to an ice sheet margin, as for Antarctica and Greenland.

• Heyn, Björn Holger & Conrad, Clinton Phillips (2022). On the Relation Between Basal Erosion of the Lithosphere and Surface Heat Flux for Continental Plume Tracks. Geophysical Research Letters. ISSN 0094-8276. 49(7). doi: 10.1029/2022GL098003. Full text in Research Archive Show summary

  While hotspot tracks beneath thin oceanic lithosphere are visible as volcanic island chains, the plume-lithosphere interaction for thick continental or cratonic lithosphere often remains hidden due to the lack of volcanism. To identify plume tracks with missing volcanism, we characterize the amplitude and timing of surface heat flux anomalies following a plume-lithosphere interaction using mantle convection models. Our numerical results confirm an analytical relationship in which surface heat flux increases with the extent of lithosphere thinning, which is primarily controlled by the viscosity structure of the lower lithosphere and the asthenosphere. We find that lithosphere thinning is greatest when the plate is above the plume conduit, while the maximum heat flux anomaly occurs about 40-140 Myr later. Therefore, younger continental and cratonic plume tracks can be identified by observed lithosphere thinning, and older tracks by an increased surface heat flux, even if they lack extrusive magmatism.

• Ramirez, Florence Dela Cruz; Selway, Katherine; Conrad, Clinton Phillips & Lithgow-Bertelloni, C. (2022). Constraining Upper Mantle Viscosity Using Temperature and Water Content Inferred From Seismic and Magnetotelluric Data. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 127(8). doi: 10.1029/2021JB023824. Full text in Research Archive Show summary

  Mantle viscosity controls a variety of geodynamic processes such as glacial isostatic adjustment (GIA), but it is poorly constrained because it cannot be measured directly from geophysical measurements. Here we develop a method that calculates viscosity using empirical viscosity flow laws coupled with mantle parameters (temperature and water content) inferred from seismic and magnetotelluric (MT) observations. We find that combining geophysical constraints allows us to place significantly tighter bounds on viscosity estimates compared to using seismic or MT observations alone. In particular, electrical conductivity inferred from MT data can determine whether upper mantle minerals are hydrated, which is important for viscosity reduction. Additionally, we show that rock composition should be considered when estimating viscosity from geophysical data because composition directly affects seismic velocity and electrical conductivity. Therefore, unknown composition increases uncertainty in temperature and water content, and makes viscosity more uncertain. Furthermore, calculations that assume pure thermal control of seismic velocity may misinterpret compositional variations as temperature, producing erroneous interpretations of mantle temperature and viscosity. Stress and grain size also affect the viscosity and its associated uncertainty, particularly via their controls on deformation regime. Dislocation creep is associated with larger viscosity uncertainties than diffusion creep. Overall, mantle viscosity can be estimated best when both seismic and MT data are available and the mantle composition, grain size and stress can be estimated. Collecting additional MT data probably offers the greatest opportunity to improve geodynamic or GIA models that rely on viscosity estimates.

• Marcilly, Chloe M.; Torsvik, Trond Helge & Conrad, Clinton Phillips (2022). Global Phanerozoic sea levels from paleogeographic flooding maps. Gondwana Research. ISSN 1342-937X. 110, p. 128–142. doi: 10.1016/j.gr.2022.05.011. Full text in Research Archive Show summary

  The validity of sea level estimates based on stratigraphic correlations has been debated since the 1990 s as relative sea level curves differ between sites due to local tectonics, different deposition rates and changes in dynamic topography. Here, we offer a new eustatic (global) sea level curve for the past 520 million years (Myrs) based on observations of global flooding. We use paleogeographic reconstructions to measure the area of today’s exposed land that was flooded in the past (modern-land flooding). We then apply the modern global hypsometric slope to reconstruct the sea level history. We find minimum sea levels (comparable to today’s level) towards the end of Pangea (210 Ma) and peak levels (∼280 m higher than today) at 80 Ma when Pangea was widely dispersed. A first-order “supercontinent” cycle of 250 million years (Myrs) is recognized but we also document a second-order cycle of 37 Myrs that was previously thought to be undetectable using the hypsometric method. The hypsometric slope is critical for reconstructing past sea levels, and steepening the hypsometric slope during Pangea assembly implies dramatically larger sea level fluctuations. Our new sea level curve shares strong similarities with stratigraphic constraints and correlates with seafloor production proxies throughout the Phanerozoic. Measurements of global flooding represent averages across great continental extents, making them less sensitive than stratigraphic analyses to regional-scale vertical land motion, such as from dynamic topography and hence more reliable for estimating eustatic sea level. This method can also help to identify local deviations caused by regional uplift or subsidence and serves to constrain geodynamic mechanisms for sea level change. Our new sea level reconstruction usefully tracks global variations in Phanerozoic eustatic sea level, but also opens opportunities to estimate such variations in deeper time.

• Karlsen, Krister Stræte; Conrad, Clinton Phillips; Domeier, Mathew & Trønnes, Reidar G (2021). Spatiotemporal Variations in Surface Heat Loss Imply a Heterogeneous Mantle Cooling History. Geophysical Research Letters. ISSN 0094-8276. 48(6). doi: 10.1029/2020GL092119. Full text in Research Archive Show summary

  Earth's heat budget is strongly influenced by spatial and temporal variations in surface heat flow caused by plate tectonic cycles. Here, we use a novel set of paleo‐seafloor age grids extending back to the mid‐Paleozoic to infer spatiotemporal variations in surface heat loss. The time‐averaged oceanic heat flow is 36.6 TW, or ∼25% greater than at present‐day. Our thermal budget for the mantle indicates that 149 K/Gyr of cooling occurred over this period, consistent with geochemical estimates of mantle cooling for the past 1 Gyr. Our analysis also suggests sustained rapid cooling of the Pacific mantle hemisphere, which may have cooled ∼50 K more than its African counterpart since 400 Ma. The extra heat released from the Pacific mantle may have been trapped there by the earlier long‐lived supercontinent Rodinia (∼1.1–0.7 Ga), and the Pacific mantle may still be hotter than the African mantle today.

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• Conrad, Clinton Phillips (2025). Seasons and Sea-Levels from a Year in Iceland. Full text in Research Archive
• Paul, Jyotirmoy & Conrad, Clinton Phillips (2025). Craton thickening controls the onset and frequency of kimberlite volcanism. Full text in Research Archive
• Lundmark, Anders Mattias; Bakken, Kristian Bjelbøle; Anell, Ingrid; Augland, Lars Eivind; Conrad, Clinton Phillips & Dunkel, Kristina G [Show all 10 contributors for this article] (2025). Why don’t my students come to class? Full text in Research Archive
• Thieulot, Cedric; Ortega-Gelabert, O.; Root, Bart & Conrad, Clinton Phillips (2025). Benchmarking dynamic topography across codes. Full text in Research Archive
• Robert, Boris; Conrad, Clinton Phillips; Steinberger, Bernhard & Domeier, Mathew Michael (2025). Linking plate tectonics and true polar wander over the last 250 Myrs. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence (2025). Sensitivity of dynamic topography and gravity anomalies to lateral variations in mantle viscosity. Full text in Research Archive
• Conrad, Clinton Phillips (2025). Patterns of uplift around Greenland’s periphery during the Early Holocene. Full text in Research Archive
• Weerdesteijn, Maaike Francine Maria & Conrad, Clinton Phillips (2025). Rapid Earth uplift in Southeast Greenland driven by deglaciation above the weakened rocks of the Iceland Plume Track. Full text in Research Archive
• Conrad, Clinton Phillips (2025). Rapid Ground Motion Driven by Deglaciation above the Iceland Plume Track. Full text in Research Archive
• Steffen, Rebekka; Conrad, Clinton Phillips; Diego, Fernandez Prieto,; Ola, Grabak,; Larisa, Lorinczi, & Martin, Wearing, (2025). The role of the solid earth for the evolution of the polar ice sheets. doi: 10.5281/zenodo.15017317. Full text in Research Archive Show summary

  The 2nd European Polar Science Week is an important milestone in the cooperation between the European Commission and the European Space Agency. The event took place from 3 to 6 September 2024, in Copenhagen, at the Black Diamond, Royal Danish Library.The overall objective of the European Polar Science Week has been to bring together the European polar science community and reinforce European cooperation for polar science. During this week, key scientists and stakeholders of polar science have had the opportunity to discuss the major challenges and opportunities in front of us, promote networking and collaboration across projects and activities advancing the EC-ESA Polar research cooperation. The scientific advancements, identified research gaps, and recommendations are highlighted in the body of this report.

• Conrad, Clinton Phillips (2025). Three Magmatic Pulses Helped Rifting Transform into Seafloor Spreading - Eos. EOS. ISSN 0096-3941. Full text in Research Archive Show summary

  A new geochronology of Mesozoic magmatism along the eastern margin of North America shows that continental breakup involved three distinct pulses of magmatism that localized extensional deformation.

• Conrad, Clinton Phillips (2025). Impact of Rheology on Glacial Isostatic Adjustment (GIA) Processes in Greenland. Full text in Research Archive
• Paul, Jyotirmoy & Conrad, Clinton Phillips (2025). Slow Thickening of Cratons Has Increased Kimberlite Frequency Over Time. Full text in Research Archive
• Tjoflot, Gunn Kristin & Conrad, Clinton Phillips (2025). New research explains rapid ground uplift in Southeast Greenland. Phys.org. Full text in Research Archive Show summary

  The coastline of Southeast Greenland is uplifting more rapidly than other parts of the island. This is caused by weak rocks beneath this part of Greenland, combined with the melting of the ice sheet, according to researchers.

• Lundmark, Anders Mattias; Bakken, Kristian Bjelbøle; Anell, Ingrid; Augland, Lars Eivind; Conrad, Clinton Phillips & Dunkel, Kristina G [Show all 10 contributors for this article] (2025). “Why don’t my students come to class?”. Full text in Research Archive
• Lundmark, Anders Mattias; Bakken, Kristian Bjelbøle; Anell, Ingrid; Augland, Lars Eivind; Conrad, Clinton Phillips & Dunkel, Kristina G [Show all 10 contributors for this article] (2025). “Why don’t my students come to class?”. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips & Maupin, Valerie (2025). Subduction dynamics and mantle anisotropy: modeling and clustering of olivine textures. Full text in Research Archive Show summary

  The mantle near Earth's subduction zones experiences significant deformation, forming anisotropic rock textures. These textures can be detected using seismic methods and simulated in geodynamic models. This study employs time-series clustering to examine tracers in subduction models, identifying regions with similar deformation histories, olivine crystallographic-preferred orientation (CPO) development, and CPO-induced anisotropic viscosity. We compare the evolution of olivine textures predicted by various numerical methods (e.g. D-Rex, MDM, and MDM+AV) for both retreating and stationary trench subduction settings. Our modeling shows notable variations in olivine texture around the slab and as a function of subduction dynamics. These variations, which are illuminated by the clustering analysis, show that texture, seismic, and viscous anisotropy can vary greatly within the mantle wedge, sub-slab, and subducting plate regions of the upper mantle. In the retreating-trench model, the strongest textures are observed in the mid-depth mantle wedge region and beneath the slab at the 660 km transition zone. Trench-normal olivine a-axis orientations are predominant in the center of subduction zones, while toroidal flow around slab edges produces a mix of trench-normal, trench-parallel, and oblique fast seismic directions. On the other hand, in the stationary-trench model, the trench-normal signal in front of the slab is weaker while there are stronger trench-normal signals behind the slab at shallow depths between 100 and 300 km. At the edge of the slab, weak toroidal flow produces trench-oblique orientations while trench-parallel and trench-normal orientations are missing. In general, the retreating trench model exhibits stronger textures and anisotropy due to increased deformation from trench motion. These results provide valuable insights into seismic anisotropy in subduction zones and underscore the importance of considering texture heterogeneity when interpreting geodynamic models and seismic data. The use of time-series clustering algorithms highlights the intricate pattern of evolution and the relationship between deformation history, CPO, and CPO-induced viscous anisotropy occurring within subduction zones.

• Kiraly, Agnes; Wang, Yijun; Conrad, Clinton Phillips; Dannberg, Juliane; Fraters, Menno & Gassmoeller, Rene [Show all 7 contributors for this article] (2025). ANIMA the journey: how we model olivine CPO-related anisotropic viscosity. Full text in Research Archive Show summary

  The long-term fluid-like movements in the Earth’s mantle largely depend on the rheological behaviour of olivine, the main rock-forming mineral in the upper mantle. Although the average viscosity of the mantle can be estimated from post-glacial rebound or geoid anomalies, the micromechanical mechanisms that facilitate the deformation of the solid mantle have been identified from rock mechanics experiments. Dislocation creep emerges as the predominant deformation mechanism in the uppermost mantle, aligning olivine crystals into a crystallographic preferred orientation (CPO) parallel to the flow, while this alignment of crystals also results in anisotropic viscous behaviour. Thus, anisotropic viscosity and CPO evolve hand in hand, and this interaction may impact many geodynamic processes. For example, beneath tectonic plates CPO evolves parallel to the plate motion direction, weakening the asthenosphere in that direction. However, if the plate motion direction changes, the asthenosphere will resist this change, leading to smaller velocities, less deformation and therefore a slow evolution of the CPO towards the new plate motion direction. In the ANIMA project, we aimed to find an efficient way of modelling CPO evolution and the related anisotropic viscosity in a fully coupled way within a geodynamic simulation. We developed a method that tracks CPO evolution on advected particles based on the D-REX method and utilizes the eigenvalues of the mean CPO orientation matrices to predict the anisotropic viscous parameters. These parameters allow us to calculate a tensor form of the viscosity, which we then feed back into our model solution. This method can be applied in combination with other rheologies, although with a cost of having to represent the viscosity as a tensor in the entire model domain, regardless of the dominant deformation mechanism. Despite an estimated increase in computational cost by up to an order of magnitude, incorporating anisotropic viscosity coupled to CPO evolution stands feasible for regional geodynamic models. This development will facilitate the study of a broad new range of geodynamics problems that involve olivine texture and anisotropic viscosity.

• Conrad, Clinton Phillips; Ito, Garrett; Smith, Walter & Bercovici, David (2024). Pål Wessel (1959 – 2024). IASPEI Newsletter. June 2024, p. 9–10. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes & Conrad, Clinton Phillips (2024). Implementation of anisotropic viscosity in ASPECT. Full text in Research Archive
• Weerdesteijn, Maaike Francine Maria & Conrad, Clinton Phillips (2024). Rapid Earth uplift in Southeast Greenland driven by deglaciation above the Iceland Plume Track. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2024). Sensitivity of dynamic Earth. Full text in Research Archive
• Rychert, Catherine A.; Dai, Yuhang; Ozaydin, Sinan; Debayle, Eric; Harmon, Nicholas & Chin, Emily [Show all 11 contributors for this article] (2024). A global and interdisciplinary perspective on variations and dynamics of the lithosphere-asthenosphere boundary. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2024). Sensitivity of Long-Wavelength Dynamic Topography and Free-Air Gravity to Lateral Variations in Lower Mantle Viscosity. Full text in Research Archive
• Weerdesteijn, Maaike Francine Maria & Conrad, Clinton Phillips (2024). Rapid Earth uplift in southeast Greenland driven by recent ice melt above low-viscosity upper mantle. Full text in Research Archive
• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2024). Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars; Wang, Yijun & Mather, Ben (2024). Direct estimation of anisotropic viscosity parameters using texture scores of olivine polycrystals. Full text in Research Archive
• Conrad, Clinton Phillips; Weerdesteijn, Maaike Francine Maria; Ramirez, Florence Dela Cruz & Selway, Kate (2024). Rapid Earth uplift where the Iceland Plume Track Crosses Greenland: GIA modelling and MT Constraints. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2024). Sensitivity of long-wavelength dynamic topography and free-air gravity to lateral variations in lower mantle viscosity. Full text in Research Archive
• Jaah, Ilyas; Kiraly, Agnes; Shephard, Grace; Conrad, Clinton Phillips & Domeier, Mathew Michael (2024). On the Role of Anisotropic Viscosity on the Motion of the Pacific Plate. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2024). Admittance and dynamic topography: Effect of lateral variations in viscosity. Full text in Research Archive
• Conrad, Clinton Phillips (2024). Mantle Heterogeneity Beneath Greenland: Importance for Uplift and Deglaciation. Full text in Research Archive
• Conrad, Clinton Phillips (2024). Rapid Earth Uplift in Greenland above the Iceland Plume Track. Full text in Research Archive
• Conrad, Clinton Phillips (2024). Geodynamic implications of lateral viscosity variations in the mantle. Full text in Research Archive
• Marcilly, Chloe M.; Torsvik, Trond Helge & Conrad, Clinton Phillips (2024). Corrigendum to “Global Phanerozoic sea levels from paleogeographic flooding maps” [Gondwana Res. 110 (2022) 128–142, (S1342937X22001563), (10.1016/j.gr.2022.05.011)]. Gondwana Research. ISSN 1342-937X. 129, p. 367–368. doi: 10.1016/j.gr.2024.01.006. Full text in Research Archive
• Etzelmüller, Bernd; Lilleøren, Karianne Staalesen; Conrad, Clinton Phillips; Åkesson, Henning & Lund, Martin (2023). GeoOnsdag Spesial "Arven etter Esmark" - Sjå opptak frå foredraget. [Internet]. https://www.mn.uio.no/geo/om/organisasjon/geohyd/aktuelt/geo. Full text in Research Archive
• Ramirez, Florence Dela Cruz; Conrad, Clinton Phillips & Selway, Kate (2023). Plug flow and its associated grain-size variation in the oceanic asthenosphere explain the low seismic Q zone. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Wang, Yijun (2023). Deriving anisotropic viscosity parameters directly from texture scores of olivine polycrystals. Full text in Research Archive
• Ramirez, Florence Dela Cruz & Conrad, Clinton Phillips (2023). Long wavelength topography: Effect of lateral and radial viscosity variations in the mantle. Full text in Research Archive
• Shephard, Grace; Heyn, Björn Holger & Conrad, Clinton Phillips (2023). Prolonged multi-phase magmatism due to plume-lithosphere interaction as applied to the High Arctic Large Igneous Province. Full text in Research Archive
• Ramirez, Florence Dela Cruz; Selway, Kate; Conrad, Clinton Phillips; Smirnov, Maxim & Maupin, Valerie (2023). Lateral and radial viscosity variations beneath Fennoscandia inferred from seismic and MT observations. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Fraters, Menno & Hansen, Lars (2023). Anisotropic Viscosity in Subduction Models. Full text in Research Archive
• Weerdesteijn, Maaike Francine Maria & Conrad, Clinton Phillips (2023). Rapid Earth uplift in southeast Greenland driven by recent ice melt above low-viscosity upper mantle. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2023). Dynamic topography and admittance. Full text in Research Archive
• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2023). Locally amplified plume-lithosphere interaction and multiple melting events for 2-phase flow models. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2023). Effect of Lateral Viscosity Variations in the Mantle on Earth’s Long-Wavelength Dynamic Topography and Free-Air Gravity. Full text in Research Archive
• Conrad, Clinton Phillips & Ramirez, Florence Dela Cruz (2023). Long wavelength dynamic topography. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Shephard, Grace (2023). Plume-lithosphere interaction and continental plume tracks. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2023). Development and implications of a free base for numerical models. Full text in Research Archive
• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2023). Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction. Full text in Research Archive
• Shephard, Grace; Heyn, Björn Holger & Conrad, Clinton Phillips (2023). Large-scale volcanism at the top of the world; plume and melt modelling of the High Arctic Large Igneous Province (HALIP). Full text in Research Archive
• Åkesson, Henning; Etzelmüller, Bernd; Lund, Erik Martin; Conrad, Clinton Phillips & Lilleøren, Karianne Staalesen (2023). Arven etter Esmark - GeoOnsdag Spesial. Full text in Research Archive Show summary

  Arven etter Esmark, Bernd Etzelmüller/Karianne Lilleøren Imagining Esmark’s Lost Scandinavian Ice, Clint Conrad Gårsdagens is - fremtidens fasit, Henning Åkesson Wind of change, Martin Lund

• Conrad, Clinton Phillips (2023). Sea Level and the Solid Earth. Full text in Research Archive
• Conrad, Clinton Phillips (2023). Imagining Esmark's Lost Scandinavian Ice. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Fraters, Menno (2023). Effect of olivine anisotropic viscosity in advancing and retreating subduction settings. Full text in Research Archive Show summary

  Lattice preferred orientation (LPO) of olivine crystals occurs due to deformation in the mantle. Different parts of the upper mantle can undergo a large variety of deformation paths. During simple processes, such as simple shearing below oceans due to the movement of tectonic plates, the LPO will reflect the direction of the movement of tectonic plates. On the other hand, in areas, such as around subduction zones, the mantle undergoes more complex deformation paths, resulting in a less easily predictable LPO. Seismic anisotropy has been used as a proxy for mantle flows and the LPO formed in the mantle. To interpret the seismic anisotropy observations more accurately, we need to understand how LPO forms in different regions of subduction. LPO has been implemented in many numerical modelling tools to predict seismic anisotropy, which places constraints on mantle dynamics. However, a few recent studies have linked olivine texture development to viscous anisotropy, resulted from the summed effect of individual crystals that are deforming anisotropically. Anisotropic viscosity can affect deformation and in turn the resulting LPO. To study the effect of anisotropic viscosity (AV) and LPO evolution in geodynamics processes, it is important to know the role of AV on LPO and the differences between the numerical methods that calculate them. We choose three methods of olivine texture development to examine in this study. D-Rex is a polycrystal LPO model that is relatively balanced in computational efficiency and accuracy. From previous studies, D-Rex has been shown to produce faster texture development and stronger texture compared to other methods, including our second choice, the modified director method (MDM). The MDM parameterizes the olivine LPO formation as relative rotation rates along the slip systems that participate in the rotation of olivine grains due to finite deformation. We also couple the MDM with a micromechanical model for olivine AV (which makes our third choice MDM+AV), to allow the anisotropic texture to modify the viscosity and in turn affect the formation of LPO. Here we compare the LPO evolution under subduction settings with a slowly advancing trench and a retreating trench, with and without the effect of AV. Since the mantle flow pattern in subduction zones is not homogeneous, different particles experience a variety of deformation paths. We place 60 particles in each subduction model around the slab to track the deformation and resulting olivine texture. We compute olivine texture using the above-mentioned three different methods (D-Rex, MDM, MDM+AV). With the particles, we can identify characteristic textures developed in key regions such as the mantle wedge, sub-slab area, and lateral slab edge. We then run a statistical analysis on the texture parameter and anisotropic properties of the particles from both retreating and advancing subduction models, to study where anisotropic viscosity has the largest effect on the mantle flow. We expect AV to have a larger effect in a retreating slab setting since the mantle flows feeding material to the sub-slab region is more intensive.

• Kiraly, Agnes; Wang, Yijun; Conrad, Clinton Phillips; Hansen, Lars N. & Mather, Ben (2023). Modelling anisotropic viscosity. Full text in Research Archive Show summary

  Many of Earth’s layers – from the crust to the inner core – are mechanically anisotropic. Anisotropic (i.e. direction-dependent) behaviour of rocks can derive from intrinsic properties of rock forming minerals or from microscopic or macroscopic layering of rocks and/or melts with different composition (extrinsic anisotropy). The Earth Science community often discusses the phenomena of seismic anisotropy, which results from the direction dependent propagation of seismic waves. However, materials that are characterized by elastic (seismic) anisotropy often exhibit viscous anisotropy as well, which is less explored. In geodynamics we are primarily interested in anisotropic viscosity in the crust and the mantle, where both intrinsic and extrinsic anisotropy are present. To model anisotropic viscous behaviour, we have to handle the viscosity as a 4th order tensor while also thinking about the re-orientation of anisotropy (or evolution of texture) in time. In the upper mantle the main source of anisotropy derives from the lattice preferred orientation (LPO) of olivine. Under deformation olivine grains rotate into the deformation direction (we often refer to this as texture evolution), resulting in a texture where some – or many – olivine grains are aligned with each other. Furthermore, because single olivine crystals are mechanically anisotropic – which means they deform more easily along some slip systems than others – then LPO that is developed in the upper mantle will yield anisotropic viscosity on a macroscopic scale. The foundation of our modelling approach is the Modified Director Method, which includes texture evolution and micromechanical models, both deriving from rock mechanic laboratory experiments on olivine aggregates (Hansen et al., 2016a, 2016b). The micromechanical model allows us to calculate the stress needed to achieve a certain strain rate on an aggregate, while the texture evolution model calculates the rotation of grains under a given deformation. To integrate these models into a geodynamic code, or use it to model the evolution of texture and anisotropic viscosity under specific deformation paths, we have to characterize our texture with a rank 4 viscosity or fluidity tensor (Király et al., 2020). It has been shown that the anisotropy related to olivine textures can be characterized by the Hill coefficients (Hill, 1948; Signorelli et al., 2021). Here we show that by building a large database of different textures derived from geodynamic models, we can define a linear model between simple texture parameters and the Hill coefficients with a reasonable cost. This is advantageous for integrating anisotropic viscosity into 4D geodynamic models because it allows for a direct determination of the viscosity tensor from the evolving rock texture, saving a large amount of computational time.

• Shephard, Grace; Gaina, Carmen; Heyn, Björn Holger; Conrad, Clinton Phillips; Anfinson, Owen & Schaeffer, Andrew [Show all 7 contributors for this article] (2022). Exploring potential lower mantle structures and interactions for the origins of HALIP. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2022). Basal erosion and surface heat flux anomalies associated with plume-lithosphere interaction beneath continents. Full text in Research Archive
• Conrad, Clinton Phillips (2022). Deep down temperature shifts give rise to eruptions. [Journal]. https://www.esa.int/Applications/Observing_the_Earth/FutureE. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars N. & Fraters, Menno (2022). Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity. Full text in Research Archive Show summary

  The development of olivine texture, or lattice preferred orientation (LPO), has been implemented in many numerical modelling tools to predict seismic anisotropy, which places constraints on mantle dynamics. However, a few recent studies have linked olivine texture development to its mechanical anisotropy, which in turn can affect deformation rates and also the resulting texture. To study the effect of anisotropic viscosity (AV) and LPO evolution in geodynamics processes, it is important to know the role of AV and LPO and the differences between the numerical methods that calculate them. The modified director method parameterizes the olivine LPO formation as relative rotation rates along the slip systems that participate in the rotation of olivine grains due to finite deformation. When it is coupled with a micromechanical model for olivine AV, it allows the anisotropic texture to modify the viscosity. We compare the olivine textures predicted by the modified director method both with and without a coupled micromechanical model and textures predicted by the D-Rex LPO evolution model. To do this, we recalculate the texture observed in simple 3D models such as a shear box model and two other well-understood models: a corner flow model and a subduction model. In general, we observed that the D-Rex models predict a stronger anisotropic texture compared to the texture predicted by the modified director method both with and without the micromechanical model, in agreement with previous studies. When including the micromechanical model, the anisotropic texture changes the observed strain rates, which allows for a slightly faster texture evolution that is more similar to the D-Rex predictions than it is to those produced by the modified director method alone. We found that even for the simplest settings there is an increase of 10~15% in strain rate during deformation until a strain of 2.5. When shearing the asthenosphere over ~10 Myr, such anisotropy could modify the effective viscosity of the mantle,causing an up to 40% increase in plate velocity for the same applied stress. The anisotropy can also induce deformation in planes other than the initial shear plane, which can change the direction of the primary deformation. Our ultimate goal is to understand the role of AV and LPO evolution in geodynamic processes by looking at deformation paths predicted by geodynamic models in ASPECTWith this initial test, we will gain a basic understanding of olivine AV behavior and LPO evolution under different deformation settings calculated with different numerical methods, which we will carry onto our next step of implementing anisotropic viscosity of olivine in 3D into ASPECT. How to cite: Wang, Y., Király, Á., Conrad, C. P., Hansen, L., and Fraters, M.: Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7201, https://doi.org/10.5194/egusphere-egu22-7201, 2022.

• Root, B.; Conrad, Clinton Phillips; Ebbing, J.; Fullea, J. & Lebedev, S. (2022). 4D Deep Dynamic Earth project: Recommendations for future research. Full text in Research Archive
• Ramirez, Florence Dela Cruz; Selway, Kate; Conrad, Clinton Phillips & Lithgow-Bertelloni, C. (2022). Constraining Upper Mantle Viscosity Using Temperature and Water Content Inferred from Seismic and Mag-netotelluric Data. Full text in Research Archive
• Ebbing, J.; Fullea, J.; Root, B.; Conrad, Clinton Phillips & Team, The 3D Earth Study (2022). 3D Earth – Towards a digital twin for the geosphere. Full text in Research Archive
• Wessel, Paul; Chase, Andrew; Frazer, L.N. & Conrad, Clinton Phillips (2022). A method for examining recent drifts of Pacific hotspots. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Fraters, Menno; Gassmoeller, Rene; Dannberg, Juliane & Hansen, Lars [Show all 7 contributors for this article] (2022). Olivine texture evolution under a simple deformation scheme: Comparing different numerical methods of LPO calculations. Full text in Research Archive
• Robert, Boris; Conrad, Clinton Phillips; Steinberger, Bernhard & Domeier, Mathew Michael (2022). Linking plate kinematics and true polar wander over the last 250 Myrs. Full text in Research Archive
• Paul, Jyotirmoy; Conrad, Clinton Phillips; Becker, Thorsten W. & Ghosh, Attreyee (2022). Self-induced craton compression: Potential implications for craton stability. Full text in Research Archive
• Kiraly, Agnes; Wang, Yijun; Fraters, Menno; Gassmoeller, Rene; Dannberg, Juliane & Hansen, Lars [Show all 7 contributors for this article] (2022). Incorporating olivine CPO-related anisotropic viscosity into 3D geodynamics simulations. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Fraters, Menno & Hansen, Lars (2022). Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity. Full text in Research Archive
• Conrad, Clinton Phillips (2021). Tectonic Reconstructions of Past Sea Level, Dynamic Topography and the Deep Water Cycle. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2021). Plume-induced heat flux anomalies and the associated thinning of the continental lithosphere. Full text in Research Archive
• Weerdesteijn, Maaike Francine Maria; Conrad, Clinton Phillips; Reusen, J.M.; Steffen, R. & Naliboff, J. (2021). Solid earth uplift due to contemporary ice melting above low-viscosity regions of Greenland’s upper mantle. Full text in Research Archive
• Conrad, Clinton Phillips (2021). Earth’s History of Changing Sea Level: Billions of Years to Decades. Full text in Research Archive
• Weerdesteijn, Maaike Francine Maria; Conrad, Clinton Phillips; Hollyday, A.; Austermann, J. & Gassmöller, R. (2021). Extending the open-source code ASPECT to solve the sea level equation on a heterogeneous Earth. Full text in Research Archive
• Conrad, Clinton Phillips (2021). Global Mantle Flow Patterns and the Time Dependence Dynamic Topography at Earth’s Surface and CMB. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes & Conrad, Clinton Phillips (2025). Texture evolution in subduction models, influenced by anisotropic viscosity. Simple tests, cluster analysis, and numerical implementation. Universitetet i Oslo. Full text in Research Archive Show summary

  The anisotropic viscosity of olivine plays a crucial role in mantle dynamics, influencing both large-scale geodynamic processes and texture evolution, and thus the resulting seismic anisotropy. While experimental studies have characterized the directional dependence in the viscosity of olivine, its integration into numerical geodynamic models remains limited. This thesis systematically investigates the effects of anisotropic viscosity during simple shear and during complex deformations in subduction zones, using a series of numerical methods implemented outside and within the geodynamic modeling software, ASPECT. As an initial step to estimate the effect of anisotropic viscosity, we compute olivine textures and texture-induced anisotropic viscosity as postprocessors based on deformation paths obtained from geodynamic models run in ASPECT. In these models, textures and Associated anisotropic viscosity do not modify deformations directly. We demonstrate that anisotropic viscosity has a limited impact during simple shear with a constant imposed velocity but can significantly alter texture development and the effective viscosity in a more dynamic subduction model. This is particularly the case in regions where accumulated strain is large, for example, in the mantle wedge region. Using time-series cluster analysis, we expand the analysis in subduction models to include more than 1000 particles located throughout the subduction zone covering the mantle wedge, sub-slab, and slab areas. We identify the spatial variability of mantle deformation, olivine texture, and anisotropic direction and strength, which are particularly pronounced in the retreating-trench model with large deformation. The clusters characterize the trench-normal orientations above and beneath the slab, as well as the trench-parallel orientations between 300 and 400 km depth behind the slab. These directions have also also observed in seismic anisotropy studies near subduction systems. To describe texture-induced anisotropic viscosity, we establish a quantitative relationship between olivine texture and anisotropic viscosity parameters, expressed as the Hill coefficients. This relationship is validated with textures both from experiments and numerical models. We then integrate this relationship into ASPECT, representing anisotropic viscosity with a tensor composed of the Hill coefficients and a stress-dependent scalar component. This implementation is tested under simple shear deformation, providing a framework for incorporating anisotropic viscosity into large-scale geodynamic simulations. Collectively, this research advances our understanding of how anisotropic viscosity influences olivine textures and mantle Dynamics and provides a computational methodology for integrating anisotropic viscosity into geodynamic models. The results emphasize the necessity of considering anisotropic viscosity in subduction zone modeling and offer new insights into the interpretation of seismic anisotropy in complex mantle flow environments.

• Weerdesteijn, Maaike Francine Maria & Conrad, Clinton Phillips (2023). Solid earth deformation due to glacial mass changes above low-viscosity upper mantle: Model development, importance of contemporary ice melt, and an application to southeast Greenland. Universitetet i Oslo. Full text in Research Archive Show summary

  Changes to Earth’s climate redistribute masses of ice and water on Earth's surface. These loads cause the solid earth to deform, and it is commonly thought that this happens in two ways: ice age ice melting caused a long-term viscous flow that is still occurring, and modern ice melting drives an instantaneous elastic deformation. However, regions in West Antarctica and southeast Greenland are currently uplifting so rapidly that another deformation mechanism must be important. Here we study how confined regions of unusually weak rocks within Earth’s upper mantle can deform viscously, generating rapid surface uplift. This doctoral thesis presents a new viscoelastic earth deformation model that can accommodate large lateral variations in Earth structure. We benchmark this code and use it to investigate the poorly understood role of small (~100s km) regions of unusually low-viscosity mantle beneath rapidly melting ice. We then apply our code to southeast Greenland, a region likely weakened by the Iceland plume ~40 Ma ago. We show that the uplift here is dominated by a viscous response to recent and rapid deglaciation, occurring within the past few decades. This viscous contribution is not usually considered, but will become increasingly important in the future as deglaciation accelerates.

• Ramirez, Florence Dela Cruz & Conrad, Clinton Phillips (2022). Improving upper mantle viscosity estimates: Constraints from seismic and magnetotelluric data, and impacts on asthenospheric flow. Universitetet i Oslo. Full text in Research Archive Show summary

  A simplified Earth’s structure consists of three geological layers: a stiff lithosphere (plates), a mantle and a core. Like for an example your favorite yogurt, the rock in the solid mantle can be flowing, but it requires an enormous amount of force to deform it and a time scale over thousands to millions of years! To quantify how fast the deformation process would be for a certain applied force, the physical quantity “viscosity” is used. For instance, water has lower viscosity than yogurt, which enables you to stir the water faster than the yogurt. For the mantle, viscosity affects how fast the plates can move laterally and vertically. An example for this is Scandinavia (including Norway), which is continuously uplifting as a response to melting of past ice sheet from “siste istid” with up to 3000 meters ice caps, thereby influencing climate and sea level. Unfortunately, mantle viscosity cannot be measured directly, but is commonly estimated from surface deformations. This doctoral study introduces a method for estimating viscosity using geophysical observations (seismic and magnetotelluric), which reflect realistic mantle conditions such as temperature, water content, and partial melt that control viscosity. The method provides useful results for Scandinavia and can be applied in other places as well. Resulting viscosity models can aid in geodynamic studies such as modelling flow patterns below the moving oceanic plates.

• Wang, Helene; Magni, Valentina & Conrad, Clinton Phillips (2022). Hydrous Regions of the Mantle Transition Zone Affect Patterns of Intraplate Volcanism. Universitetet i Oslo. Full text in Research Archive Show summary

  The Earth’s mantle transition zone (MTZ), located between approximately 410-660 km depth, can store an amount of water equivalent to 2-10 oceans of water, which is transported into the deep mantle by subducting oceanic lithosphere. The presence of water is likely to reduce the viscosity of mantle rocks and has the potential to generate melting in the upper mantle that could promote the occurrence of intraplate volcanism (IPV). Therefore, water within the Earth’s interior impacts mantle convection dynamics, plate tectonics and could alter the chemical and thermal evolution of the planet. Despite its importance, the amount and spatial distribution of water within the mantle, and its effect on the origin of volcanism far from plate boundaries, are poorly constrained. Previous modeling studies have estimated rates and volumes of water subducted into the deep mantle based on plate tectonic reconstructions that track the history of subduction through time. In this work, I extend this approach to model the spatial and temporal heterogeneity of water in the MTZ during the past 400 million years (Myr) and compare the predicted regions of wet and dry MTZ with the locations of past and present IPV. I conduct a parametric study where I vary the residence time of water in the MTZ, the slab sinking rate, and the delay period between water in the MTZ and IPV occurrence. Despite the uncertainties associated with the plate tectonic reconstructions and IPV dataset, my models show a remarkable agreement between the hydrated regions of the MTZ and locations of IPV. I find a statistically significant correlation at the 95% confidence level for models where 60-89% of IPV locations occur above wet regions of the MTZ during the past 250 Myr. This confirms the hypothesis that water is transported to the MTZ by subducting slabs and, consequently, causes spatial and temporal mantle heterogeneities. Furthermore, my results show that the MTZ water residence time significantly impacts the distribution of water, with the best fits obtained for residence times of 100 Myr or longer. This implies that MTZ water reservoirs caused by the dehydration of stagnating slabs can remain stable for time periods much longer than the sinking time of a slab. In contrast, the effect of varying the vertical descent rate of slabs and the IPV delay period is modest. However, a delay of 10-50 Myr between water in the MTZ and intraplate eruptions better predicts IPV locations than accounting for no delay. Overall, these findings suggest a link between the formation of volcanism far from plate boundaries and water within the MTZ.

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