The influence of gas hydrate cyclicity on global and regional gas hydrate inventories

Abstract

Gas hydrate (GH) formation and dissociation in natural systems is a complex, multi-process phenomenon controlled by local pressure-temperature-salinity (p-T-s) conditions and availability of methane gas. Our recent findings based on detailed analyses of GH systems using high fidelity multi-physics numerical model suggest that the long-term stability of the natural gas hydrate systems is not straightforward. On time scales ranging from hundreds to hundred of thousands of years, natural gas hydrate systems are able to develop, so-called, periodic steady-states characterized by a cyclic growth and dissolution of gas hydrate layers as well as a free gas migration through the gas hydrate stability zone (GHSZ). In this presentation, we show how these new results directly affect the estimates of global GH inventories and how they can be used to investigate the development of multiple bottom simulating reflectors (BSRs), slope failures, pockmarks, and gas migration pathways observed in the geological records that may have occurred spontaneously due to the internal system dynamics (i.e. gas hydrate cyclicity). On a global scale, we have quantified the potential effect of the periodic states expressed as a new uncertainty measure that sets the hard limits on the predictability of present-day gas hydrate inventories through steady-state analysis. On a regional scale, focused on high-latitude locations, we present a combination of system parameters leading to periodic states and provide uncertainty quantifications on the gas hydrate system stability and faith. In that context, we discuss the relation between the time-periods of the cyclic states and the external triggers affecting gas hydrate systems in the Arctic (e.g. anthropogenic warming, sea level changes, glacial- interglacial cycles, etc.). Keywords: methane cycle, global carbon budget, natural gas hydrate systems, periodic steady-states