This summer CAGE scientists picked up methane-derived rocks from the ocean floor, using a remotely operating vehicle (ROV). The rocks prove past and present methane seeps in Vesterålen, Norway.
Text: Maja Sojtaric. Photo/video: Jochen Knies
CAGE scientists employed Research Vessel G.O Sars this summer for a cruise to Hola, Vesterålen. Hola-region is known to be an area of active methane seepage, with flares observed in the water column. Methane is a highly potent greenhouse gas and thus important to understand in a world of climate change.
To be able to collect specific samples, the scientists used a remotely operated vehicle (ROV). Contrary to what one may believe, the marine geologist seldom gets to visit vast expanses of the ocean floor. An ROV is often the closest they may get to actually being there. ROVs are often equipped with high definition underwater cameras, and are controlled from the ship. The scientists get to use ROVs superb camera vision to twist and turn them so that they can pick up the samples of interest.
A striking phenomenon
Jochen Knies, a CAGE research leader from NGU in Trondheim, and his colleagues were able to collect carbonate crust from targets on the ocean floor, indicating also past major releases of methane off the Vesterålen coast.
“Methane-derived carbonate crust formation is a striking phenomenon that occurs in places where methane seeps from the ocean floor. We call these crusts authigenic which means that they are formed in the place where they are found. This means that they can tell us a story about past and current methane leakage at the floor of the ocean”, says Knies.
What happens, in essence, is a chemical reaction involving microbes that thrive in methane rich environments under the ocean floor. To make it simple, we may say that the microbes eat methane and sulphate and produce among others bicarbonate which increases alkalinity in the pore water. This causes a chemical reaction to occur, called precipitation. This means that solid matter is created in the porewater of the sediment and forms carbonate nodules. Methane seepage has consequences for the chemistry of, and life in, the ocean. Often, these locations are oasis for life that does not need light to thrive.
“The typical carbonate species at sites of methane seepage, so called cold seeps, are magnesium calcite, aragonite and dolomite”, says Knies.
A succesfull cruise
The PhD work of Simone Sauer, also CAGE, is to find out where, why and when methane seepage occurred.
She will use the carbonate crusts for studying past seepage activity in the area. Is their formation related to fault re-activitation, or retreat of the ice sheet during the last deglaciation? Or maybe a combination?
“We will use geochemistry to measure stable isotope of the carbonates, such as carbon. In this way we can find out the sources of carbon. We can also use isotopes to date the carbonate and find out when it was formed” says Knies.
In addition to the crusts, CAGE scientists have taken gravity cores during the cruise to study the sediments of the ocean floor deposited nearby. They also mapped the area of crust formation by multibeam echosounder and TOPAS sub bottom profiler (shallow seismics).
The cruise was a collaborative effort with another centre of excellence, The Centre for Geobiology at University of Bergen. Their primary research focus is the extreme environments found in the deep seafloor, the deep biosphere and remnants of ancient crust, which were formed in deep time.
