Molecular microbial ecology and biogeochemistry of gassy and oily cold seeps

This project is a collaborative effort between Dr. Joye and Dr. Antje Boetius(Max Planck Institute for Marine Microbiology, Bremen, Germany), Dr. Peter Girguis (Monterey Bay Aquarium Research Institute and Harvard Univeristy), Dr. Ian MacDonald (Texas A&M University at Corpus Christi), Dr. Joe Montoya (Georgia Institute of Technology) and Dr. Heide Schulz (Institute for Microbiology, Hannover, Germany). We are working at sites in the Northern and Southern Gulf of Mexico, at Hydrate Ridge, offshore Oregon (as part of ODP Leg 204), and in Monterey Bay, California (in collaboration with Dr. Girgus). Researchers in the Joye group quantify rates of microbial processes, like anaerobic oxidation of methane, methanogenesis, and sulfate reduction, study the controls on cold seep microbe metabolism, and use molecular ecological techniques to determine which microbes are involved in key biogeochemical processes. We have examined a suite of ancillary geochemical parameters in water, sediment and vent gas samples (gases only), including, nutrient concentrations, redox species (e.g., H₂S, Fe²⁺, dissolved inorganic carbon, etc.), organic matter (e.g., DOC, volatile fatty acids) and dissolved gas (e.g., CH₄, C₂H₆, C₃H₈, H₂) concentrations.

Gulf of Mexico Project

The study area is in the Gulf of Mexico, along the Louisiana and Texas continental shelf and slope (500-1000m water depth). We are working at four stations, green canyon 234 (GC 234), GC 185, GC 233 and Garden Banks 425 (GB 425). Gas hydrate mounds (left) are abundant and this portion of the Gulf of Mexico is a rich petroluem basin and oil and gas harvesting platforms (right) are common.

Using Submersibles

To obtain access to cold seep habitats, we conduct research cruises using the mother ship R/V Seward Johnson II and the research submersible, the Johnson Sea Link (JSL), which are operated by the Harbor Branch Oceanographic Institute. The JSL is launched from the Seward Johnson II, as seen here from inside the submersible (left), twice per day. Two scientists accompany a pilot and engineer on each dive. Dr. Joye (right) enjoys being in the "sphere", i.e., the front compartment, of the submersible because the view on the bottom is amazing.

Gas Hydrates

Methane hydratesrepresent one of the most important reservoirs of organic carbon on Earth. Methane hydrates are found along continental margins around the world. Hydrates represent a unique extreme environment that could serve as a novel niche for microbial life. The picture on the left shows a hydrate breaching the surface of the sediment. The picture at the right shows a close up view of the hydrate surface. Hydrates are either white or orange in color. The surface is very uneven because the hydrate is somewhat unstable and dissolution may cause pitting on the surface. The orange coloration results from the incorporation of oil in the ice lattice. These structure II gas hydrates are rich C2-C6 alkanes and hydrogen sulfide and carbon dioxide.

Microbial Mats

Beggiatoa is a chemoautotrophic (=uses inorganic CO₂ as structural carbon source) bacteria that makes a living by coupling sulfur oxidation with nitrate reduction to ammonium (or possibly N₂). Beggiatoa comes in white and orange varieties. Beggiatoa mats are a common feature observed around hydrate and brine sites. Beggiatoa is present on the sediment surface but is also observed deep in the sedimnet. Orange Beggiatoa is often found adjacent to white Beggiatoa (left). Note that the bottom water temperature on the figure is incorrect. The actual temperature is around 6-7 ºC on the bottom. Other bacteria, including sulfur-oxidizing bacteria related to Thiomargarita namibiensis (right) are also common (note white "spheres"). The cores are taken back up to the surface and in the shipboard lab, they are used to examine rates of processes and to obtain pore water profiles of chemical species.

Additional information about the new Thiomargarita-like microorganism is provided here.

Brine Pools

Hypersaline brine pools are another feature of the Gulf of Mexico petroleum basin. Brine pools form when warm, salty fluids migrate through the sediments through fissures in the sediment. The brine is more dense than sea water, so it pools on the surface after cooling to ambient temperature. To date, we have examined two brine pools, one stable brine pool with apparently lower rates of fluid flow (GC233 brine). This brine pool has been stable long enough for a dense community of methanotrophic mussels to develop around the pools edge (A). Such chemoautotrophic symbiotic associations are common at sites of fluid and gas seepage, as seen in the Gulf of Mexico, along the Florida Escarpment and along the Cascadia margin. The other brine site is an active mud volcano that is known for high rates of fluid flow (GB425, B). The GB425 brine has frequent eruptions of warmer (10 or more ºC warmer than bottom waters) fluid (B) and macrofaunal communities are not common here. We sample the brines using a novel device called the 'brine trapper' (C, 3-m long gray PVC device in lower part of figure), which is deployed from the side of the submersible. A photo of the brine trapper deployed in the GB425 brine pool is shown in panel (D). The brine is sediment is particle rich (E), as noted by the change in color deeper in the brine (from L to R in the image). A unique feature of the mud volcano site is the abundance of barite (Barium-Sulfate) chimneys (F). Barium originating from the brine precipitates when it comes into contact with sulfate-rich seawater.

A		B
C		D
E		F

We thank the National Science Foundation's Life in Extreme Environment's program for supporting this work.

**Disclaimer** The content of this page is based in part on work supported by the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed here are those of the author (Mandy Joye) and do not necessarily reflect the views of the National Science Foundation.