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Logbook
July 8, 1999

Contents:

• News from Thompson
• Participant Perspective
• Logbook from Teacher at Sea
• Question/Answer from shore to sea

Science Report - Thursday, July 8
Ships Location: 46 03.8/129 57.7

CASM vent with lush tubeworms and hydrothermal fluid venting from a chimney.

Dive 497 visited the CASM vent site to collect biological, sulfide, microbial mat, and vent fluid samples. The CASM site is located at the northern end of Axial's caldera where its north rift zone intersects the caldera. High temperature vent fluids have produced a line of sulfide chimneys in the bottom of a 10-meter wide fissure. Surrounding these chimneys are extensive areas of diffuse venting where tens of thousands of tubeworms grow in lush colonies that at times extend as far as you can see. This makes CASM a rather spectacular site for the biologists on board. CASM was the first high-temperature vent site visited by submersible on the Juan de Fuca Ridge back in 1983, and although it has not been visited many times since then, it appeared to be rejuvenated when ROPOS visited it last year. This site is of interest since the focus of the NeMO project is how hydrothermal venting and their biological communities change in response to volcanic events.

Later in dive 497, ROPOS moved further north along Axials north rift zone to where four extensometer instruments were deployed last year. (photo left) These instruments have measured the distance across the rift zone once a day since then to look for changes related to magma movements under the volcano. ROPOS had to return to the surface briefly during this operation, but then returned to finish the job on dive 498. ROPOS found each instrument on the bottom and moved each one to the elevator mooring, then released the mooring from its anchor so that it could recovered at the surface by the ship. We plan to download the data from the instruments, refurbish them, and then deploy them again for another year deployment.

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Leigh Evans
OSU/NOAA Vents Program

I'm on this expedition to sample the fluids which emerge from vents and separate the gases from them. These gases are sealed in glass ampoules for a number of chemical analyses which will be done in laboratories on land. Aside from that I test variations in the methods of sampling the vents.

One of the analyses which I will be personally involved in performing is that of the helium isotopes, He3 and He4, in vent fluids. This is a gauge of the input of gases from the earth's magma into the vent system. The data are also used in comparison to other analyses of the vents such as the concentrations of iron or the amount of heat present. Sampling over a variation in geography and over time might tell us about increases or decreases in the volcano's activity, or its activity in a particular location. Other labs will analyze these samples for hydrogen and methane.

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Thompson Teacher at Sea Log

Teachers Log #18 7/8/99

Octopus and rattail fish at the CASM vent site.

It is a beautiful day out here today. Blue sky, no breeze, and the water is smooth. Last night ROPOS had a busy night surveying and sampling a vent site known as CASM. This is an awe inspiring lush environemnt filled with sulphide chimneys and an abundance of colorful life. It's amazing that so much can be found in such a small area. (photo left)

When hydrothermal vents were first discovered in the late 70s near the Galapagos Islands, the deep ocean floor was believed to be desert-like. We now know that there is a wide diversity of life in these areas and have gained a better understanding of the interactions between the geology, chemistry and biology in deepsea environemnts, including hydrothermal vents.

Life at the vent site is intimately connected to the vent fluid. (see diagram below, click for full size) As seawater seeps through the porous crust of the seafloor, it is heated and reacts with the chemicals in the rock. The heat is believed to come from a magma chamber within the ocean crust. This superheated water rises rapidly through the crust, seeking a way to the surface. This is what we refer to as hydrothermal vent fluid.

Most of the microbes (bacteria and archea) that exist here are referred to as hyperthermophiles because they exist in an environment that is above 80 degrees Celsius (about 180 degrees Farenheit) and probably anoxic (without oxygen). Factors such as space, nutrients and temperature are important limiting factors of this area, but have yet to be specifically determined. Within the vents and under the seafloor surface, it is possible that subsurface microenvironments exist. How many, what kind and how deep they go is still a mystery. As with all vent microbes, they rely on chemosynthesis as their source of energy rather than photosynthesis (remember, no sunlight - no photosynthesis). (Chemosynthesis uses the oxidation of sulphide from the vents rather than sunlight to create energy.) It is unknown just what role the subsurface plays in the development of the surface ecosystem. Many believe there is a definite connection. But we do know that the microbes are the basis for the food web in this mysterious ecosystem.

Tomorrow we'll finish this discussion on the hydrothermal vent ecosystem with special attention on the macrofauna (multicellular animals).
Bye for now.

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