Day 39 The Thrill of Discovery, Part II

Hydrothermal vent communities were first studied in detail in the spreading center east of the Galapagos Islands in 1977 by a group of scientists exploring the area with the submersible Alvin. Alvin can go several miles below the surface and holds a pilot and 2 observers. My fascination with the deep sea grew when I first heard of Alvin and escalated after the discovery of the first hydrothermal vent communities.

Alvin is limited to a 9-hour working day because launch and recovery are restricted to daylight hours. There is little working space so the pilot and observers are scrunched in close quarters, looking out little port holes and it gets really cold as the metal sphere takes on the temperature of the deep sea. On this trip, with Jason, we can work uninterrupted for days on end. The Jason pilot, copilot, navigator and observers sit in the control van in real chairs and in air-conditioned comfort. There are normally 6 people in the control van, but when things get exciting it can turn into standing-room only.

Today was one of those days. At one point I counted 13 of us in the control van.

We arrived at the Malaguana-Gadao spreading center and launched Jason at 0000. No one was interested in sleep because we fully expected to find hydrothermal vents and their associated vent communities. No one had ever looked for vent communities in this location before but the NOAA expedition in February found evidence in the water column indicating the possibility. Although we expected vents, we were amazed when we found them just 82 minutes after reaching the seafloor. It’s 0300 and the van is packed as we watch in awe. The hot water seeping from the vents is obvious from the shimmering heat waves visible in the water. Called schlieren, the shimmering occurs because the hot water has a different density than the surrounding sea water. We used a temperature probe in many areas and found water temperatures as high at 247 degrees Celsius coming up from the vents. When the hot water from below mixes with the cold water of the sea floor, chemicals precipitate forming chimneys. On the mud volcanoes of the Mariana forearc chimneys form because of differences in the chemistry of the water—here chimneys form because of differences in temperature.

The vent areas are small but swarming with life. Snails larger than golf balls are piled up several layers deep. Crabs and shrimp are darting about but concentrated in the area of warm water. All 3 species are animals found only in hydrothermal vent communities of the deep sea. Their food source is the chemosynthetic microbes I mentioned yesterday. In some places these microbes are so thick they cover the volcanic rocks like carpets up to 4 inches thick called bacterial mats, or more correctly microbial mats (microbial because the organisms are both bacteria and archaea).

Archaea refers to a kingdom of single-cell organisms that can survive in extreme habitats and have chemical pathways that bacteria don’t have. The bacteria and archaea of the microbial mats are extremophiles which translates to mean “lovers of extreme.” The environment of the vents is certainly extreme: high temperatures, extreme pressure, toxic chemicals and the absence of sunlight.

Science Summary - Day 39, April 30th

Science Objectives, Day 39:

The thirty-ninth day of the cruise, Apr. 30, we will dive with Jason2/Medea on the spreading center of the Mariana backarc basin with the expectation that we will examine end-member subduction-factory-related fluids to compare with forearc fluid emanations recovered as pore waters in the mud volcanoes. We will collect rock samples, hydrothermal and biological materials if present, take temperature measurements, and water samples.