CTD rosette instrument being deployed off the fantail of the Wecoma.

Teacher Logbook - R/V Wecoma

Missy Holzer 's Sealog:
CTD Cruise Day 3
Weather at 1630 hours PST: Overcast sky with winds of 16 knots out of the Northwest. Barometric pressure is 1023.2 mb, and the temperature is 57 degrees Farenheit. Ocean swells are 6-8 feet out of the Northwest.

It's only the second day and it feels like business as usually already. When I started my "watch" (work period) at 0600 hours, the ship's crew and science staff was totally immersed in the work of the cruise, which is to gather ocean water samples in and around Axial Volcano crater. The science lab works around the clock, so when 0600 hours came along, a "tow-yo" was already in progress.

The object in tow was a rosette frame that contained a CTD that continuously records conductivity, temperature, and depth, a nepholometer for measuring the scattering of light, and over 20 Nisken bottles (each has a 19 liter capacity) that can each be electronically "fired" to collect water samples at various locations during the tow. The whole unit is collectively nicknamed a "fish." The formal name of the tow is called a "tow-yo," and it samples the water column by continually raising and lowering the fish through the water while steaming ahead at about 3 km/hour. Communication is maintained among the crew on the bridge, the crew working the winch that controls the placement of the "fish," and the scientsts monitoring the movement of the "fish." The oceanographer radios the crew member controlling the winch and says when to raise or lower the fish while the crew on the bridge maintains a steady speed along a predetermined transect. This morning our tow-yo went a total of 12 nautical miles over about 7 hours, and collected water samples in 17 of the Nisken bottles as well as a continuous set of CTD data for the entire tow. It was exciting to see the monitors in the lab recording the data because right before our eyes we saw a spike in the nepholometer data that signaled that we were moving through a hydrothermal plume. It should be interesting to see what the water samples show from this plume.

The second mission of the day was to perform a few "casts" which used the same above described fish, except it was lowered in one location through the water column instead of being towed over a distance. The fish gathers CTD data on the way down and back up, and collects water samples on the way back up. As the fish is lowered, the data is displayed on a monitor in the lab so that the oceanographer can watch for the any abnormalities in the water column that could signal the presence of a hydrothermal plume. If the signals are present then the oceanographer knows where to take the water samples in the water column. Today's samples were gathered at about 1500 meters below the surface of the water while the fish was moving up through a hydrothermal plume. The selection of a place to lower the cast has been set by the chief scientist whose goal is to maintain a continuous set of data over a number of years.

The next phase is for the chemists on board to analyze the samples from the tow-yo and casts to determine the presence and concentration of various elements that are known to be associated with hydrothermal activity. Stay tuned for further developments in the quest to gather information about Axial Volcano.