Development of a Novel Deep-Sea in situ Bubble Sampling Instrument: SeaBAT

Methane (CH
₄
) is a greenhouse gas that is often found in a solid hydrate clathrate form in marine sediments along continental margins. Under certain conditions, CH
₄
can escape from the seafloor as free gas bubbles and rise in the water column. Traditional methods of determining CH4 flux from the seafloor into the shallow ocean often rely on determining the rise height of the bubble plume, but cannot identify how much CH4 is left in the bubbles at the terminus of their rise. Here we describe the development of the Deep-Sea Bubble Acquisition Tool (SeaBAT), a novel bubble capture system for determining the composition of these bubbles in situ. The SeaBAT was deployed at the Cascadia Margin - an area well known for its active CH
₄
bubble seeps - where over 90 bubble samples were collected and analyzed for composition. Most bubbles contained over 90% CH
₄
with trace amounts of Nitrogen (N
₂
), Oxygen (O
₂
), and Carbon Dioxide (CO
₂
).