New paper: how do bubbles escape deep seafloor?

In the last decades, persistent seepage of methane gas at the seafloor has been widely observed in marine environments. In order to understand where, when and how much methane bubbles into the ocean, and how this persistent injection of greenhouse gas into the world's ocean may impact the global climate, scientists have spent months of time out at the sea to observe the bubble seepage in-situ using remotely operated vehicles (ROV). These amazing video footages taken as deep as ~1000m beneath the water surface have provided us a rare glimpse of just how complicated bubble escape can be, and an opportunity to understand the physics better.

In this paper, we harness the information from several deep seafloor videos from around the coast of America to understand better the fluid mechanics of methane bubble detachment from the seafloor. In deep marine environment where pressure is high, methane hydrate, a solid mixture of methane and water, could readily form on the bubble surface. It has been puzzling to many scientists why some bubbles acquire a hydrate shell while others do not at these deep methane seeps. After carefully analyzing these videos, our study concludes that there might be a simple explanation. We find that, on average, bubbles that take longer than 5 ~10s to detach will become hydrate-coated at the seafloor. Fast-released (<2s) bubbles tend to be hydrate-free at the seafloor, but will likely acquire a hydrate shell within the subsequent 1.5m of rise. We apply these observed rules to a simple bubble dissolution model to estimate the impact of hydrate shell on the vertical transport of methane through bubbles. We find that bubbles that become shelled at the seafloor carry ~5% more methane than bubbles that detach without any hydrate covering.

This work is a collaborative effort with Dr. Bill Waite and Dr. Carolyn Rupple from USGS Woods Hole. You can read it here (open access!).