The Secret Life of Bubbles

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GEOMAR experts Jens Greinert and Tim Weiss provide a more complete picture of undersea bubbles than you ever thought possible.

“Wait, stop, back up! There were bubbles back there!”

With a cry and dramatic gesture to the screen, GEOMAR scientist and shipboard bubble expert Jens Greinert grabbed all of our attention.

Image shows several people sitting in front of computer screens

GEOMAR scientist Jens Greinert (pointing) directs the ROV SuBastian team to investigate a new source of methane bubbling up from the seafloor.

(Credit: Shelton Du Preez, Schmidt Ocean Institute. Courtesy of Schmidt Ocean Institute)

“Trust me, I’ve got a sixth sense for bubbles,” Jens assured us, or more specifically, the operator of ROV SuBastian. And sure enough, after we performed the delicate navigation involved to make the ROV do a u-turn 1,500 feet below the surface, there they were ---a silvery stream of bubbles wobbling up from the seafloor.

In a real sense, this is what we came for: These bubbles contain the methane coming from the seafloor at those seep environments. They’re the base of the food webs that Jennie and Amanda described, and they’re the foundation of the geology that we’ll cover in future blogs. And at the moment, they’re the target of one of the critical pieces of equipment on this cruise, the BubbleBox.

Image shows two men in hard hats examining an ROV

GEOMAR engineer Tim Weiss (left) and GEOMAR scientist Jens Greinert fine-tune the Bubble Box on ROV SuBastian before it deploys to Grays Canyon.

(Credit: Shelton Du Preez, Schmidt Ocean Institute. Courtesy of Schmidt Ocean Institute)

The BubbleBox is a tool developed by Jens and his colleagues at GEOMAR to measure both how much gas is coming out of the seep and what the shape, size and rising speeds of these bubbles are. GEOMAR engineer Tim Weiss explains how it works:

“First, the ROV locates a seep area with active gas release, then maneuvers the BubbleBox over the bubbling vent and either places it on the seafloor or holds it just above it. As the bubbles move through the Bubble Box, twinned high-resolution cameras take rapid-fire pictures (80 per second) of the bubbles. Then, a computer algorithm processes the images, removing the background and identifying, measuring and counting the bubbles. By using paired cameras, we can create three-dimensional, high-resolution images of these bubbles and model their shapes as they move through the water inside the BubbleBox.”

Image shows a technical box being placed on the ocean floor

ROV SuBastian deploys the Bubble Box on top of methane bubbling up from a seep on the seafloor of Grays Canyon.

(Credit: Shelton Du Preez, Schmidt Ocean Institute. Courtesy of Schmidt Ocean Institute)

Sizing Things Up

So why are we looking at bubbles in such detail?

“The biggest reason is to help figure out how much gas is coming out of the seeps,” said Tim. “That’s one of the main goals of this cruise.”

Image shows animated gif of bubbles rising through Bubble Box

Footage from the Bubble Box. The paired cameras allow for a three-dimensional analysis of the bubbles.

(Credit: Tim Weiss, GEOMAR. Courtesy of GEOMAR)

By getting an idea of how large the bubbles are and how many of them are coming out, we can estimate the volume of gas escaping the seafloor at this particular site. And that helps determine how much food is available to the creatures living here and how much methane carbon is leaking into the ocean.

The information from the Bubble Box will then be paired with hydroacoustic data from an echosounder on board R/V Falkor to give an idea how much gas is coming out, not just at a particular moment but also over time. The hydroacoustic data gives us the information on the stream of bubbles, and the Bubble Box gives us the particulars on the bubbles within the stream.

But the Bubble Box also sheds light on a whole host of other fascinating aspects of bubbles that Jens was only too happy to describe.

Scientists in hard hats load equipment onto an ROV

GEOMAR engineer Tim Weiss (right) and GEOMAR scientist Jens Greinert recover the Bubble Box from ROV SuBastian after deployment into Astoria Canyon.

(Credit: Shelton Du Preez, Schmidt Ocean Institute. Courtesy of Schmidt Ocean Institute)

How Long Does a Bubble “Live?”

When you blow a bubble under the pool, how long does it last? Until it reaches the surface and pops, right? What if the source of the bubble isn’t just a few feet below the surface, but instead hundreds or even thousands of feet down?

“The general rule is that if a methane bubble starts more than 100 meters (328 feet) below the water surface, its chances of making it to the surface are very slim,” said Jens. “So down here, at four hundred, five hundred meters, or eight hundred meters even, there’s almost no chance the bubble will make it to the surface.”

Image shows bubbles moving upward against a white background

Bubbles move up through the Bubble Box where paired cameras provide a stereoscopic view.

(Credit: Tim Weiss, GEOMAR. Courtesy of GEOMAR)

But what happens to it? Mostly, the gas of the bubble dissolves into the water. As the methane bubble pops out of the seafloor, it represents a super-high concentration of methane close to the seafloor, while the surrounding ocean water has a much lower concentration of methane.

“The water and bubble methane concentrations are not in a chemical equilibrium,” explains Jens. “Immediately, the ocean starts trying to rectify this imbalance by dissolving the methane bubble into the ocean water.”

There are factors that can change how long the bubble dissolution takes. The larger the bubble, the longer it lasts. Another factor that can change how fast bubbles dissolve is a protective barrier around the bubble.

Image shows a bubble hovering in front of laboratory instruments

A bubble wrapped in xenon-hydrate floats in the laboratory. Gas hydrate is a naturally-occurring, ice-like form of a gas and water that is stable within a narrow range of pressure and temperature conditions. The hydrate makes the bubble more rigid, and it does not undulate as much as a non-hydrate-encased bubble does.

(Credit: William Waite, USGS. Public domain.)

For methane bubbles emitted from the seafloor more than about 500 to 600 meters in depth, one common armor is gas hydrate. Gas hydrate is an ice-like crystalline substance composed of water and gas molecules arranged in a specific way. A thin gas hydrate coating can enclose the bubble and trap the methane inside.  As long as the bubble stays within the pressure and temperature zone where hydrate can exist, the bubble will last much longer.

A Deeper Concern

Determining the fate of the methane that comes out of these seeps is one of the primary goals of this research cruise. Not only do seafloor organisms depend on methane for food, but methane also fuels bacterial processes in the water column. 

And so Jens and Tim will take their BubbleBox to each of the seeps we visit and capture every angle of these silvery orbs as they rise from the seafloor.

Image shows two men working on a computer in a machine shop

GEOMAR engineer Tim Weiss (left) and GEOMAR scientist Jens Greinert program the Bubble Box for an upcoming dive.

(Credit: Shelton Du Preez, Schmidt Ocean Institute. Courtesy of Schmidt Ocean Institute)