Teacher Logbook - NOAA Ship Ron Brown

Iron oxide "cabbage patch type" mounds at FeHyde vent, southern ASHES vent field. This is a "flange pool" where hot buoyant vent fluid is trapped beneath a part of the sulfide chimney that is protuding outward (toward the camera). The bottom surface of the hot fluid looks like a horizontal mirrored surface because its properties are dramatically different from the surrounding seawater.

Jeff Goodrich's Sealog:
Axial Volcano: Western part of caldera at ASHES vent field
July 22, 2001

297, 298, 299, 299.9 degrees Celsius.......(a quiet pause)....... We just couldn't break 300. A hydrothermal playground, the ASHES vent field has black smokers, diffuse vents, tube worms, and everything else that excites scientists about these submarine hot springs. Looking at the monitor I asked, "What are all those orangish mounds?" "Talk to Chris Kennedy. He's the Iron-oxide guy" someone exclaimed. A few minutes later Chris entered the hydro lab and gave me the rundown on what they were. Here's what he had to say.......

Iron oxide deposits are found extensively at Mid Ocean Ridges (MOR) around the globe including Axial Volcano. On the sea floor they look like "cabbage patches" or "blankets" covering large areas (100's of meters2) near low temperature diffuse vents. What makes them unique and interesting is the large component of iron oxidizing bacteria within them that holds many possibilities for understanding past environmental conditions on Earth, and may serve as evidence for life on other planets. The composition and structure of these deposits may also contribute to the regulation of trace elements in the oceans and may be an excellent material to aid in remediation of polluted terrestrial watersheds. The structure of a bacterial cell wall is intrinsically negatively charged and able to attract a variety of positive ions such as iron. In some ways it's similar to seeding a cloud for rain. Normally, soft-bodied organisms degrade quickly after death. In this case the bacteria's morphology is preserved by an "encasing" of iron. Vent bacteria are likely increasing the rate of iron mineralization in the oceans.

Bacteria similar to those seen here at Axial Volcano, have been noted in ancient terrestrial deposits. It is entirely possible that these mineralized bacteria are surviving the test of geologic time by becoming fossils. By discovering bacterial fossils on land, many inferences to past environmental conditions (paleoenvironments) can be made. Bacterial fossils may not be restricted to Earth. There is increasing evidence of iron oxides on Mars that may harbor bacterial fossils. Early Mars may have had similar MOR geologic activity to that seen here today on Earth. Evidence is also mounting for geologic activity on Jupiter's moon Europa, which may provide a favorable environment for iron oxidizers.

Sea floor iron oxides, which have been identified as the iron oxide phase ferrihydrite [Fe(OOH) or Fe(OH3)], may play a significant role in the cycling
of trace elements in the world's oceans. Mid-ocean ridges form a planetary "seam" extending approximately 80,000 km around the globe, with ferrihydrite likely present over much of the area. The combination of the large surface area of ferrihydrite, its chemical structure and composition, provides it with the ability to adsorb (i.e. "suck up") many trace elements to concentrations
much higher than normal seawater. Understanding how ferrihydrite is able to "suck up" metals makes it a useful agent in potentially cleaning up polluted watersheds, acting locally as the "paper towel" of the vent systems and global oceans.