Today we did a different kind of CTD cast, a tow-yo. The CTD was put over the side and descended in the water column while the ship traveled at around 1.5 knots. Once the CTD got to 4500 meters it was brought back up to 3900 meters, then back down to 4500m and back up to 3900m. This was done consecutively for 10 hours while the ship traveled a 7 mile track across a section that a Nereus dive found anomalies in its optical and Eh sensors last week. At around the same spot Nereus found evidence of hydrothermal activity the CTD's optical and Eh sensors found similar data. Another CTD tow-yo will be done tonight to try and narrow down where the hydrothermal activity is originating. Weather: overcast, 82 degrees, winds NE at 25 knots, seas 6 feet