Periodic Reporting for period 1 - WarmArctic (Impacts of Changing Climate on Arctic Shelf Hydrogeology)
Periodo di rendicontazione: 2023-05-01 al 2025-10-31
Arctic shelves are critical regions in terms of fluid dynamics due to high organic matter and fluid fluxes, thin permafrost, and shallow gas hydrate stability zones. Complex multi-physics processes and critical data sparsity make predictive modelling of Arctic shelves extremely challenging. The goal of WarmArctic project was to develop, using advanced multiphysics and multidomain models, a detailed process-level understanding of the state and responses of the subsurface fluids and sediment in the Arctic continental shelves and their influence on seafloor morphologies under rapid past and ongoing environmental changes.
Theoretical analyses of the mathematical properties of our high-fidelity multiphysics model led to the discovery that the gas hydrate systems show extremely rich internal dynamics where the long-term (i.e. steady-state) behaviour is characterized by bifurcations in a high- dimensional parameter space. This means that besides the commonly known fixed-point steady state solutions, for some combinations of parameters, the GH systems exhibit the more exotic periodic steady-state solutions, and even chaotic solutions. The periodic steady state solutions are characterized by a closed-loop trajectory in the phase-space, which implies that even in the most idealized geological settings where there is a continuous sediment burial at a constant rate and absolutely no external environmental triggers or other perturbations, the GH system will exhibit a fully self-sustaining internal dynamics where multiple GH layers will form and dissolve ad infinitum, and cause sudden spontaneous release of pore-pressure (several bars) at regular time-intervals. This means that in some geological settings, observations of landslides, gas venting from chimneys and pockmarks, and multiple BSRs may not necessarily be related to changes in external environmental conditions like sea-level changes, glacial-interglacial cycles, changes in bottom-water conditions, etc.
Our numerical results showed that the chaotic states in the GH dynamics appear to be clustered in the geological settings with shallow water-column depths (<=1000m), low thermal gradients (<=35°C/km), and relatively low to moderate sediment burial rates (0.02
The existence of periodic and chaotic states is particularly important for predicting the climate change impacts due to rapid anthropogenic environmental forcings. It is well known that if a dynamical system shows bifurcations, it is highly sensitive to perturbations. Formerly stable states of the system can become periodic (which means that the model predictions will have an irreducible, but bounded, uncertainty), or the formerly periodic states can become chaotic (which means that the model predictions will have an unbounded uncertainty, and future projections can not be deterministic, only stochastic). The implications of these findings are profound for the Arctic regions, which are already susceptible to chaos and are warming at a much larger rate than the global average.
Our numerical results showed that the chaotic states in the GH dynamics appear to be clustered in the geological settings with shallow water-column depths (<=1000m), low thermal gradients (<=35°C/km), and relatively low to moderate sediment burial rates (0.02
The existence of periodic and chaotic states is particularly important for predicting the climate change impacts due to rapid anthropogenic environmental forcings. It is well known that if a dynamical system shows bifurcations, it is highly sensitive to perturbations. Formerly stable states of the system can become periodic (which means that the model predictions will have an irreducible, but bounded, uncertainty), or the formerly periodic states can become chaotic (which means that the model predictions will have an unbounded uncertainty, and future projections can not be deterministic, only stochastic). The implications of these findings are profound for the Arctic regions, which are already susceptible to chaos and are warming at a much larger rate than the global average.
These results are first of their kind, and have generated much debate and discussion in the gas hydrate and carbon cycling communities. These results have profound implications for natural systems as they strongly challenge the conventional and generally accepted notion of “causality” in nature where every observation of an out-of-equilibrium system is a direct result of some external environmental changes in its history. Our results show, with mathematical proof, that under certain conditions the Earth systems can show completely spontaneous and self-sustained dynamics which is independent of any past environmental changes. This result has the potential to disrupt and transform our understanding of the geological history of Earth’s subsurface and our estimates of their fate under future changes.