Hidden periodic states in gas hydrate systems causing spontaneous gas release without external triggers

Natural marine gas hydrate deposits are one of the largest solid carbon-sequestrated reservoirs on Earth. Here we show that, remarkably, over 80 percent of all natural hydrate-bearing systems exhibit stable periodicity (i.e. periodic growth and dissolution of massive gas hydrate layers) without any external forcing such as the bottom water warming or sea level fluctuations. This stable periodicity is the manifest of the intrinsic gas hydrate system dynamics related to a complex, kinetically controlled   interplay between three phases, e.g. the free gas, solid gas hydrate, and methane-saturated pore fluids. Our results state that, globally, periodic (cyclic) states are present for wide range of marine sediment type and sedimentation regimes and the length of each cycle can last from tens to hundreds of thousands of years with cyclic variations in gas hydrate concentration from 20 vol. % to 60 vol. %. Each cycle is also associated with periodic release of the free methane gas in large quantities without the presence of any external forcing. The apparent existence of the periodic states has profound implications setting hard limits on hydrate predictability and implies a systematic source of uncertainty embedded within hydrate dynamics. Moreover, the anthropogenic climate perturbations may overprint the natural gas hydrate cycle and push formerly stable hydrate reservoirs to new periodic states with large p-T-s fluctuations, thereby significantly increasing the risks of uncontrolled gas escape and geomechanical failures, or formerly periodic states towards chaotic states, making long-term predictions extremely challenging.