The North Atlantic region is a complex geodynamic setting that comprises multiple continental blocks, sedimentary basins, mid-ocean ridge systems and prominent hotspots. Recent geophysical surveys of the near-surface have enhanced our understanding of crustal elements and the shallow lithosphere. However, our knowledge of the deep lithospheric structure and the physical state and dynamics of the upper mantle is still limited. Here, we exploit the combined sensitivity of surface-wave data, geoid anomalies, absolute topography and surface heat flow to obtain full thermochemical models of the region from the surface down to 350 km. We jointly invert these data sets using a simulation-based, multi-observable probabilistic framework. We validate our results with independent thermobarometric and chemical information from mantle xenoliths and test the effects of using different seismic models on the inversion results. Our model reveals an intricate sublithospheric flow system, driven by the interaction of deep upwellings with the highly irregular lithospheric structure. We corroborate that the main thermal anomaly in the sublithospheric mantle shows a tilted geometry, moving toward Greenland with depth. We reveal that this large-scale anomaly transition into a more complex pattern once it reaches depths of 

∼150 km beneath the North Atlantic. Small-scale downwellings originate from the margins of continental domains, resulting in a complex circulation pattern that limits the radial spread of the deep upwellings and preferentially focuses them within regions of thin lithosphere along a N–S direction. Distinct compositional anomalies in the Greenland lithosphere delineate the North Atlantic Craton, the Nagssugtoqidian mobile belt, and the covered remnants of the Disko Craton. In continental Europe, the East European Craton shows clear indications of depletion in incompatible elements, with the Kola-Karelian cratonic region showing the highest levels of depletion. Our model serves as a base to make interpretations on the enigmatic paleotectonic history of the North-Atlantic region.

Markov chain Monte Carlo (MCMC) methods have become standard in Bayesian inference and multi-observable inversions in almost every discipline of the Earth sciences. In the case of geodynamic and/or coupled geophysical-geodynamic inverse problems, however, the computational cost associated with the solution of large-scale 3-D Stokes forward problems has rendered probabilistic formulations impractical. Here we present a novel and extremely efficient method to produce ultrafast solutions of the 3-D Stokes problem for MCMC simulations. Our approach combines the individual benefits of Reduced Basis techniques, goal-oriented error formulations, and MCMC algorithms to produce an accurate and computationally efficient surrogate for the forward problem. Importantly, the surrogate adapts itself during the MCMC simulation according to the history of the chain and the goals of the inversion. This maximizes the efficiency of the forward problem and removes the need for preinversion off-line computations to build a surrogate. We demonstrate the benefits and limitations of the method with several numerical examples and show that in all cases the computational cost is of the order of <1% compared to a traditional MCMC approach. The method is general enough to be applied to a range of problems, including uncertainty quantification/propagation, adjoint-based geodynamic inversions, sensitivity analyses in mantle convection problems, and in the creating surrogate models for complex forward problems (e.g., heat transfer, seismic tomography, and magnetotellurics).

The evaluation of peripheral dose has become a relevant issue recently, in particular, the contribution of secondary neutrons. However, after the revision of the Recommendations of the International Commission on Radiological Protection, there has been a lack of experimental procedure for its evaluation. Specifically, the problem comes from the replacement of organ dose equivalent by the organ-equivalent dose, being the latter “immeasurable” by definition. Therefore, dose equivalent has to be still used although it needs the calculation of the radiation quality factor Q, which depends on the unrestricted linear energy transfer, for the specific neutron irradiation conditions. On the other hand, equivalent dose is computed through the radiation weighting factor wR, which can be easily calculated using the continuous function provided by the recommendations. The aim of the paper is to compare the dose equivalent evaluated following the definition, that is, using Q, with the values obtained by replacing the quality factor with wR.