Methane Hydrates at Glendhu and Honeycomb Ridges

Gas hydrates are solidified masses of natural gas - commonly methane! But what is methane? Methane is a light natural gas, similar to the stuff that comes out of your stove, and the back of a cow. Methane forms from the decay of organic things - in this case it’s dead sea life (plants and plankton) on the Pacific tectonic plate sliding underneath the Australian plate, where it breaks down into chemical parts such as natural gas. As a light gas, methane works its way up into cracks or space between grains of rock (pore space). When these cracks reach the sea floor, methane is released as a stream of bubbles - sometimes called a ‘cold seep!’

What about those white bits? If gas and water meet under high pressure and at low temperatures, they can join together. The mass of the ocean applies a lot of pressure (~200 atmospheres), and being so deep it gets pretty chilly (~4°C). The water molecules form a ice-like cage around a gas molecule, resulting in the white gas hydrate solids! As they contain natural gas, these solids are also flammable.

So, why do we care about ‘frozen’ gas and bubbles? They support unique oases of life. Not many things can survive the deepest darkest depths of the ocean, but methane seeps feed tiny microbes, in turn feeding mussels and tube worms, which support the fish and crustaceans living in these inhospitable areas.

When in their solid form, scientists think gas hydrates may act like cement within the ocean floor. As oceans warm up, hydrates could break down and release their greenhouse gasses into the ocean (furthering acidification). This breakdown of the cementing solids may also reduce slope stability, possibly causing underwater landslides which could harm the unique ecosystems at these seeps.

These future impacts and unique biodiversity make gas hydrate research both very important and also very exciting!

How do we find things under the ocean floor from the water’s surface 2km above? Research vessels can release sound waves into the water and learn what’s down there by how much is reflected back to the receivers. Methane hydrates are only stable (solid, instead of going back to gas bubbles and water) under specific conditions below, so reflections that indicate the same shape as the sea floor but a little below are often strong indicators of hydrates (called bottom simulating reflectors)! They can then drop a deep ocean Remotely Operated Vehicle to look around and take samples - ours are called ROPOS and JASON!