North Pond - Mid-Atlantic Ridge Microbiology

Microbiology of a sediment pond and the underlying young, cold, hydrologically active ridge flank

IODP Expedition 336 co-chief scientists: Katrina Edwards (University of Southern California) and Wolfgang Bach (Bremen University)

The Mid-Atlantic Ridge Microbiology IODP Expedition 336 in the fall of 2011 drilled a site known as North Pond, a shallow sediment pond on the western flank of the mid-Atlantic ridge. Prior expeditions to North Pond have set the stage, young oceanic crust (7-8 m.y.) with active, low temperature, oxygenated (?) fluids that vigorously advect through basaltic basement. Such a thermal and hydrologic setting are characteristic of large portions of the global ridge flank system, where a significant fraction of lithospheric heat is lost via hydrothermal processes, and the associated fluid-microbe-rock reactions significantly alter the composition of the oceans and crust. The role that microbes play in altering the physical and chemical characteristics of the crust in ridge flank settings may be substantial, and quantifying this alteration is a fundamental goal of IODP in general. Evidence for microbial alteration exists, yet we lack robust molecular, biochemical, or physiological data so that we can understand the very nature of microbial processes in the oceanic lithosphere.

Map of North Pond showing the heat flow survey of Langseth et al. (1992). Bathymetry is shown in meters, with contour intervals of 100 m except for the deepest contour at 4440 m.

To address this lack of knowledge related to this fundamental crustal process, the Mid-Atlantic Microbial Expeditions strive to answer three fundamental questions:

1. What is the nature of microbial communities harbored in young ridge flanks and what is their role in ocean crust alteration?
2. Are these communities unique, particularly in comparison with seafloor and sedimentary communities?
3. Where do deep-seated microbial communities come from (sediment, rock, seawater, other)?

To address these questions the expedition has two major thrusts. The first is to recover materials (sediment and basalt) for extensive chemical, microbial, and physical testing. Samples will be collected during the drilling expedition, but most of the analysis will occur ashore, providing numerous opportunities for graduate students and post doctoral fellows to work on these samples with partners in the United States, Europe, and Japan. The second thrust of the expedition is to deploy three borehole observatories, allowing one to place experiments within the borehole and also at the seafloor where plumbing systems pump fluids from within the basaltic crust to experiments on the seafloor. Several experiments and sampling protocols will be deployed providing a foundation of information, but a variety of additional experiments and samplers can be accommodated both during the initial deployment on the drilling expedition for downhole experiments and during the first submersible cruise, which will occur four months after drilling ceases, for seafloor-based experiments. Experiments and sampling opportunities are not limited by these expeditions; additional opportunities will exist for decades. The basic design of these observatories makes the subseafloor assessable to a plethora of researchers for a variety of activities that are only limited by one's imagination.

To get involved with samples from the drilling expedition and future observatory operations, please contact one of the two co-chief scientists: Katrina Edwards or Wolfgang Bach.

Learn more about the science and outreach associated with our North Pond expedtions from the links below.

> See the North Pond IODP Drilling Proposal [PDF]
> About our major programs
> Our expedition schedule