Leg 4: March 17, 2012
Day 4: Bacteria heaven on the seafloor
Persistence paid off today from searching an unexplored area of the sea floor with a beautiful outcrop covered with large patches of yellow bacteria-an indication of sulfur-laden water rising up from below.
Returning today to the valley where we had seen the big yellow mass of pulsating bacteria two days ago, several more small vents were discovered. After several hours of exploring the slopes, Peter Brewer directed the pilots to fly the remotely operated vehicle a little further afield, to a spot where an old map showed a hint of a ridge. It took a while to get there, but we came upon the best discovery of the expedition so far.
A ridge of rocks and rubble was covered with yellow bacteria surrounding holes and cracks all throughout the ridge and along its base. Each of these holes was surrounded by mats of bacteria that thrive on the sulfur. The sulfur vents are an external sign of the volcanic activity below the seafloor. The valley we traversed beneath the Gulf of California is slowly spreading apart. As it does, cracks open up in the seafloor and cold seawater seeps in, reaching the hot volcanic activity below. The water comes back out of the same cracks hotter and carrying some of the chemicals present in the volcanic emissions below.
To check just how hot the venting fluids were, a thermistor was inserted into several of the crevices where shimmering water was visible. While the ambient seawater was about 2.5 degrees Celsius (37 degrees Fahrenheit), the venting fluids were as much as 5.9 degrees Celsius (42.6 degrees Fahrenheit). Not very hot, but certainly enough to indicate the volcanic activity below.
While we may have hoped for bigger, hotter, denser fields of vents, the day’s discoveries were certainly rewards after exploring this seafloor valley northeast of La Paz.