Northern 2014 Expedition

Deep-Sea Chemistry

August 16-22, 2014

Natural hydrocarbon seeps provide an opportunity to apply MBARI tools and techniques to study the chemical and physical behavior of small quantities of oil as they move from the seafloor to overlying water. During this cruise, the deep-sea chemistry group is revisiting sites near the Eel River Canyon Slump off Northern California, where gas and oil are released naturally.

The research group will complete studies of the chemistry of the pore water—water that occupies the space between seafloor sediment particles—in sediments that surround a site of active natural seepage of oil and gas from the seafloor. They will also continue investigating the composition of the gas and oil as they seep from the seafloor and how they change as they rise toward the surface of the ocean.

Chief Scientist Peter Brewer and his group will also investigate the composition and chemical structure of any gas hydrate deposits that they might find exposed in the areas surrounding the gas vents and oil seeps.

Pacnw-2013-hydrates-wide

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These gas and oil vents were first discovered by University of New Hampshire and National Oceanographic and Atmospheric Administration (NOAA) scientists in May and June of 2009 during cruises onboard the NOAA research vessel Okeanos Explorer (Gardner, Malik, and Walker, 2009. Plume 1, 400 meters high discovered at the seafloor off the Northern California margin. Eos Vol. 90, No. 32, p.275.). The natural seeps appeared as large plumes rising from the seafloor in their multibeam echo sounder display. In 2011, these sites were mapped in very high resolution by a team from MBARI by Dave Caress using the D. Allan B., a Dorado-class autonomous underwater vehicle (AUV) equipped for seafloor mapping. Later that same year, another team of MBARI scientists, led by Charlie Paull and aided by the high-resolution maps, explored the seafloor using the remotely operated vehicle (ROV) Doc Ricketts onboard the R/V Western Flyer to locate the source of these plumes, and discovered oil seeps in addition to the natural gas vents that were already expected.

The deep-sea chemistry group will use as their primary tool a laser Raman spectrometer, which can bounce a specially-tuned laser beam off many objects and substances, and receive back a signal that provides information about that object’s chemical composition and molecular structure. This tool will allow the team to get chemical data back from the seafloor in real time. They will use the high-resolution seafloor maps produced by MBARI’s mapping AUV to plan and conduct their dives around these natural vents and seeps. This work can be applied towards improving our understanding of the chemical and physical consequences associated with deep-sea oil spills.

Logbook

short tip laser probe

The tip of the "iceberg"

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.
In the year since this polypropylene rope and marker were placed on the seafloor, a snail laid a large deposit of eggs.

An intern's eye view of science at sea

After flying between “Marker 1” and “Marker 2” over the past couple dives, today the Peter Brewer team marked new territory as a research site. “Marker 3” signifies the location of a five-meter hunk of hydrate.
stream of gas bubbles and funnel

Bringing a heater to the deep

We have seen how chemists use a probe to learn about gases in the water within the seafloor sediments, and how they bring oil samples close to the surface to test the gases that were dissolved in the oil. Today the Brewer team used another tool in its arsenal—the heated gas funnel.
oil sample

Validation

One goal of this expedition is to repeat an experiment first performed last year to determine what gases are dissolved in oil that emanates from the deep seafloor. By repeating experiments, scientists further validate their results, add more data points, and refine the methods used to perform the experiments. By any measure, today’s oil and gas experiment was a successful repeat.
a tube held above a bubble stream

Revisiting a field of bubbles

The initial dive of this expedition gave Chief Scientist Peter Brewer and his team a chance to get reacquainted with the dive sites they first visited a year ago, scoping out locations to continue their studies of deep-sea chemistry processes.