Atlantic Cruise 09: Lisa's Inhibitor Experiments

Part of my reason for participating in the cruise is to collect samples for my Master's thesis project. It is hypothesized that bacteria are responsible for methylating mercury, or converting it from its inorganic form to its toxic form, MMHg. The current paradigm is that sulfate-reducing bacteria (i.e., bacteria that use sulfate to obtain their energy and live in hypoxic or anoxic sediments, such as sediments at the bottom of the ocean which have little or no oxygen and are disturbed rarely) are the primary functional group of bacteria methylating mercury to MMHg. However, recent studies have shown that other groups may be responsible (such as iron-reducers). The purpose of my thesis work is to figure out who is methylating mercury in various environments. I do this by adding inhibitor or promoter solutions to my samples to try and target specific groups. I also add stable enriched isotopes (not radioactive ones!) that allow me to track how much mercury is methylated and how much MMHg is demethylated (which, in combination, tell me what net methylation is like). Basically, I am seeking to answer the question, "Who is primarily responsible for converting mercury to its toxic form in the oceans?"

I start by collecting sediments as a part of the box coring team (first photo). Then, I homogenize my sediment by mixing it well in a nitrogen filled glove-box (second photo). I feel like a kid playing with mud! (third photo). Meanwhile, I make my inhibitor and promoter solutions (fourth photo). I add the sediment to my sample bottles (fifth photo), add 25 mL of a solution to each bottle, cap them, and flush the headspace with nitrogen gas to get rid of oxygen (sixth photo).