As a member of the Seep Team, I help take samples of the seafloor mud at locations where methane gas concentrations are relatively high (in some places, you can actually see methane gas bubbling out of seafloor). We are interested in the mud for two sample types.
First, we collect the microorganisms – mostly bacteria, but also some called archaea – living in the mud. We want to determine which species are living in the mud, and the relative abundance of those species compared to one another. This is because the microbes are actively regulating the chemistry of the water portion of the mud, called pore water (mud is just a mixture of tiny rocks and pore water). Some of the archaea in the mud are known to eat methane, and for every methane molecule the archaea eat there is one fewer methane molecule which can escape into the ocean and, ultimately, into the atmosphere. In fact, if it weren’t for seafloor archaea ocean sediments would contribute much more methane to the oceans than they already do. We care about methane escaping from ocean sediments into the ocean because methane is a strong greenhouse gas and thus can dramatically affect our climate.
The second sample type we collect from the seafloor mud is the pore water itself. In the water, we measure the concentrations of a variety of chemical compounds. It is important for us to learn as much as possible about the pore water because it is the environment in which the microorganisms are living. If we want to truly understand microbial seafloor populations, it isn’t sufficient to simply ascertain which species are present and in what abundance (even though that information is important). We also need to know which species prefer which environmental conditions, for example whether the microbial community is different in more or less acidic water, or if the amount of methane available affects the microbial community.
Extracting some mud from a sediment core taken in the OMZ.
Besides my science commitments on the R/V Melville, I’m also looking forward to getting to know all the other scientists onboard. The large number of graduate students on our cruise makes it a unique opportunity to meet and get to know other young scientists doing different work in similar ecosystems to those which I study. I appreciate the opportunity to participate in this cruise, and would like to thank Ben Grupe for his generosity in inviting me and hard work in putting the cruise together!
- David Case, PhD student at California Institute of Technology