No abstract

The dynamics of carbon dioxide fluxes in the high-altitude Alpine Critical Zone is only partially understood. The complex geomorphology induces significant spatial heterogeneity, and a strong interannual variability is present in the often-extreme climatic and environmental conditions of Alpine ecosystems. To explore the relative importance of the spatial and temporal variability of CO2 fluxes, we analysed a set of in-situ measurements obtained during the summers from 2018 to 2021 in four sampling plots, characterised by soils with different underlying bedrock within the same watershed in the Nivolet plain, in the Gran Paradiso National Park, western Italian Alps. Multi-regression models of CO2 emission and uptake were built using measured meteo-climatic and environmental variables considering either individual years (aggregating over plots) or individual plots (aggregating over years). We observed a significant variability of the model parameters across the different years, while such variability was much smaller across different plots. Significant changes between the different years mainly concerned the temperature dependence of respiration (CO2 emission) and the light dependence of photosynthesis (CO2 uptake). These results suggest that spatial upscaling can be obtained from site measurements, but long-term flux monitoring is required to properly capture the temporal variability at interannual scales.

Abstract. We developed a new fluid-dynamical numerical model, which we call convectiveFoam, designed to simulate fluids with very large Prandtl number. First we implemented the high-Pr case, in which advection still acts explicitly, and then the Pr → ∞ version, where the momentum equation becomes diagnostic (that is, without time derivatives) and it is formalized as an elliptic problem. The new solver, based on a finite volume integration method, is developed on the OpenFOAM platform and it exhibits a good performance in terms of computational costs and accuracy of the results. Scaling properties show a maximum performance around 16000 cells/core, in agreement with other works developed on the same platform. A systematic validation of the solver was performed for both 2D and 3D geometries, showing that convectiveFoam is able to reproduce the main results of several iso-viscous cases. This new solver can thus simulate idealized configurations of natural geophysical convection, such as in the Earth Mantle where Pr = 1023. This solver represents a starting point for general exploration of the behaviour and parameter dependence of several fluid systems of geological interest.