Champagne and ice

September 5, 2013

sketch of Peter Brewer

We are lucky to have science illustrator Kelly Lance with us on this expedition. Her sketches capture the team at work and her illustrations will help explain the science. Here, Kelly shows Peter Brewer in the chief scientist’s chair, where he mans the controls for the main camera and directs the sampling of the gas caught in the glass tube.

The ocean chemistry group had an advantage going into today’s remotely operated vehicle dive—our geologist colleagues have already been to this area and pointed us to some target dive sites. Researcher Charlie Paull’s team had seen both solid methane hydrate and venting gas in the Eel River Canyon area, off the coast of Eureka California. Chemist Peter Brewer and his group went to some of these sites today to continue their investigations into the composition and behavior of oil and gas emanating from the seafloor in this area.

solid ice-like methane

A close-up of the solid ice-like methane hydrate poking out from just under the seafloor sediment. Some sections were very hard and resistant to poking with the ROV’s robotic arm, while other sections were so soft they crumbled on touch.

This expedition builds on the Brewer group’s years of work into the ocean chemistry of greenhouse gases. Each research effort adds to the body of knowledge about what gases are emanating from the seafloor, how they behave, and how they may impact the health of the ocean and the life within. Do they bubble up to the surface and enter the atmosphere? Do they dissipate within the water column as they rise toward the surface? What happens when a plume of oil escapes the seafloor, whether by natural means or as a result of human intervention?

natural gases streaming up into the deep sea

The favorite frame grab of the day evokes an image of champagne bubbles and methane “ice”. Of course, this “bubbly” was actually composed of natural gases streaming up into the deep sea at Eel River Canyon. The ROV pilot held a glass tube above the stream to collect the gas. As the gas was caught in the confined space, a hydrate “skin” formed around it. The laser Raman spectrometer’s beam was then trained on the collected substance. The signal returned from this test indicated a high level of methane, but also indicated other chemicals were present. When the core was later brought to the surface, it had an obvious odor of oil; further analysis of the data will determine what kind of oil was present.

Today, the group used the remotely operated vehicle to visit two sites with solid ice-like methane hydrate—under the cold temperatures and high pressure of the deep sea, a cage-like skin forms around the gas, making for the white solid structure that looks like ice. We also investigated plumes of gas bubbling up from the seafloor. The team then used the laser Raman spectrometer to interrogate these materials to determine their composition. A green laser is aimed at the material in question; the light signal that bounces back can help identify their makeup. In all the tests done today, a strong methane signal was detected, although there were signs that there may be other substances included as well, probably ethane and propane, and also sulfide. The data returned from the spectrometer will quickly be processed and analyzed to determine the exact chemicals present.

crab trying to eat methane-laden bubbles

This crab is trying to eat the methane-laden bubbles streaming out of the seafloor, only to have the gas turn to a solid on its claws. See the MBARI video showing this phenomenon.

— Nancy Barr