Deploying the CTD off the fantail of the Wecoma.

R/V Wecoma - CTD Cruise
Science News

Science Report - Thursday, July 19, 2001
Position: 45 55.85' N /129 59.09' W
Chief Scientist Ed Baker

Part of the excitement of going to sea is discovering what's going on in the hidden world below. Last year we left five moorings on the seafloor here to monitor hydrothermal plumes, and today we'll recover them to see what secrets they hold. Since we can only visit Axial once a year, we must depend on instruments to provide information on changing hydrothermal conditions between cruises. The moorings are lengths of special line, 200 to 500 m long, anchored at the bottom with a heavy weight--often an old railroad wheel--and held upright in the water by floats attached along the line. At the bottom of each mooring is an acoustic release. When it's time to recover the mooring we send a coded acoustic signal from the ship to the release, which trips a lever that disengages it from the weight and allows the entire mooring to float to the surface. Our acoustic signals sound like a rapid series of high-pitched "pings." We can't use radio or light to communicate because these electromagnetic waves can only travel a short way through water, while sound waves can be heard for great distances.

On the moorings we have three kinds of sensors. Temperature sensors monitor the changing temperature of the seawater. Optical sensors monitor the amount of tiny particles in the water by shining a light into the water and measuring how much is reflected back to the sensor. Current meters measure both the speed and direction of water movements. By combining all three of these measurements we try and reconstruct the movement of hydrothermal plumes during the time the moorings were on the seafloor.

Our recoveries this year were highly successful. All five moorings returned to the surface with all instruments intact and functioning. The ship's crew did a great job in grappling the moorings and hauling them onboard. After the cruise, back at PMEL, we will interrogate each instrument and recover the data stored inside. Tomorrow we will start our water sampling in earnest, looking to see how the Axial Volcano vent fields have changed over the last year.