The tip of the iceberg

August 21, 2014

MBARI’s long-term investment in ships, robotic vehicles, and a wide range of instruments regularly reap advances in science. Likewise, groundwork laid when working on one ship close to home in Monterey Bay can set the stage for further research on distant expeditions. Case in point, today’s science work aboard the R/V Western Flyer validated a controlled experiment conducted several years ago close to home using the R/V Point Lobos.

Knowing they would only have a couple of hours on the seafloor because the ship had to start sailing toward port, the science team went straight to the large chunk of hydrate marked during yesterday’s dive. This time, rather than collecting a sample to be evaluated, the tip of a short laser Raman probe was placed directly onto the surface of the exposed hydrate surface. After days of collecting oil, melting hydrate, and contorting the cumbersome tripod, this process was much easier and quicker.

short tip laser probe

The short tip laser probe is placed against an exposed section of hydrate on the seafloor at a depth of about 1,600 meters.

laser raman system

The laser is used to interrogate the solid hydrate to learn what gases are present within. All other lights on the remotely operated vehicle are turned off (at right) to be sure the external lights don’t contaminate the signal from the laser Raman system.

The hydrates are made up of a cluster of “cages” that form around some gases under the pressure and temperatures of the deep sea. The Raman spectrometer records the wavelength of the light bouncing back from the hydrate, and the scientists then interpret those data to tell what gases are present within the hydrate. Today they saw signs of several hydrocarbons, including methane, ethane, carbon dioxide, and hydrogen sulfide. This composition tells us quite a lot about where these deep sea gases come from and their value as a possible energy resource.

Chemists know the presence of different gases indicate which types of hydrates they are looking at—“structure one” or “structure two”, which relate to their composition at the molecular level. Today they found both within a very small area—perhaps just a meter wide—indicating these two different types of hydrate form naturally in close proximity to each other. This validated in the natural environment what had been determined several years ago when Brewer’s team and their former postdoctoral fellow Keith Hester performed controlled experiments in Monterey Bay.

Although it was a relatively short expedition, the Brewer team efficiently managed to test deep-sea gas composition and behavior using a variety of tools and methods. As the world ocean becomes warmer and more acidic, so too might we see changes in the behavior of these deep-sea gases. Results from this expedition will build on what has been learned before, both in terms of the science and in terms of developing better tools and methods to study deep-sea chemistry.

—Nancy Barr