NeMO September 6, 2003

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Aug/Sep 2003

Logbook: September 6, 2003

45° 56.0' N, 128° 58.9' W
Air temperature 62°F, 1830 PST

One of the five extensometers placed at the northern rim of the caldera on Dive 742.

During dive R742 all 5 extensometers were placed on the bottom at the north rim of the caldera, and pressure measurements were performed at each. Then, for the first time on this expedition the weather became an issue, with winds gusting to over 30 knots. The decision was made to end the dive at that point. While waiting for the winds to die down, 2 sub-surface moorings were deployed. The moorings have several instruments attached, which measure a variety of physical oceanographic parameters including currents, temperature and optical backscatter. The ocean bottom hydrophone, deployed at the beginning of the expedition, was recovered. Bathymetry data around Axial Volcano were also collected with the Thompson=92s EM300 multibeam system. The winds have calmed down a bit allowing ROPOS to go back in the water at 1600 PST. Dive R743 has begun at Marker-33 vent. The plan is for ROPOS to remain on the bottom until 0730 tomorrow.

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Teacher's Report
Bill Hanshumaker, Educator at Sea

A spider crab hangs from an arch between two lava pillars.

In addition to being posted on the NeMO website, these journal entries are being used in auditorium presentations conducted daily at the Hatfield Marine Science Center (HMSC) in Newport, Oregon. HMSC's Visitor Center informs and educates over 130,000 people annually about the research conducted by Oregon State University and other state and federal agencies such as NOAA's EOI Program. Participants in the auditorium presentations are offered the opportunity to direct questions to the researchers and educators at sea. Here are some of the questions:

Does the hydrothermal plume reach the surface?
A hydrothermal plume is produced by volcanic activity on the ocean bottom. These events range in magnitude from the venting of hot water heated by the magma beneath the surface, to an eruption of an undersea volcano. Currents, the depth of the ocean, and the magnitude of the volcanic event can all effect how rapidly this heated water disperses. Generally, as long as there is a temperature difference between the hydrothermal plume and the surrounding ocean, the hydrothermal plume will rise. Because of the depth of the ocean, the hydrothermal plumes usually do not reach the surface.

Healthy tubeworms and palmworms near Marker-33 vent.

How are these undersea volcanoes related to Mt. St. Helens?
Axial Volcano, the site we are studying, is at a spreading center where the giant Pacific plate and smaller Juan de Fuca plate are moving apart. The Juan de Fuca plate is moving east and subducting, or moving under, the North American plate. As this material moves deeper beneath the crust, some of it melts. This molten material then rises to the surface and forms the volcanic Cascade Range, where Mt. St. Helens is located.

How far offshore is the subduction zone?
The subduction zone is at the base of the continental slope, approximately 60 miles (100 kilometers) off the coast of Oregon and Washington.

Are most of the volcanoes on earth underwater?
Most of the volcanoes on earth are found at the mid-oceanic ridge that girdles the globe like the seams of a baseball.

So, in addition to shaking, can the ground drop in an earthquake?
Yes, especially in subduction zones, and we can see this evidence in different ways. Direct evidence of ground movement was immediately visible after the Alaskan earthquake in 1964. Offshore, tsunamis are sometimes generated by submarine landslides, which create large waves as they approach the shore. Indirect evidence includes groves of dead Sitka spruce that are still standing in water on the Oregon coastline. Recent beach erosion there has also uncovered stumps of trees that were buried by subsidence during earthquakes thousands of years ago.

How does the sulfide get into the tubeworm if it has no mouth?
Hydrothermal vent tubeworms have neither a mouth nor anus. Rather than a digestive track, these amazing animals rely on bacteria living inside a specialized organ called a trophosome to produce the nutrients necessary for life. The bacteria use the hydrogen sulfide found in the hydrothermal vent waters. Hydrogen sulfide yields considerable energy when oxidized by the bacteria. Hydrogen sulfide is taken up by the worm's gill-like red plume and is transported to the bacteria via hemoglobin in its blood. This mutualistic type of symbiosis benefits both the bacteria (they get a place to live) and the tubeworm.

Are the bacteria in the tubeworms aerobic or anaerobic?
Aerobic animals require oxygen for respiration, while anaerobic animals do not. The bacteria that live inside of hydrothermal tubeworms are aerobic and require oxygen. The tubeworm provides the oxygen, using hemoglobin to transport it from its gills where it is extracted from the surrounding seawater. Tubeworm hemoglobin is unique as it can simultaneously transport both hydrogen sulfide and oxygen. Humans are poisoned by hydrogen sulfide since it binds to our hemoglobin and renders it incapable of transporting oxygen.

How do the worms get bacteria inside?
There are two possibilities. Either the symbiont acquisition is passed from generation to generation (vertical) or the bacteria are acquired from the external environment (horizontal). In vent clams (Calyptogena magnifica) molecular techniques revealed that the symbiotic bacteria is passed vertically from the mother via the egg. Though the results are still controversial, juvenile tubeworms most likely acquire their symbiotic bacteria directly from the environment.