Around the clock CTDs began last night and will continue through the morning. We are currently at station 22. The image shows a CTD rosette. The frame holds 24 of the 12 liter grey Niskin bottles. Below the bottles, on the inside of the frame, are the many sensors connected to the CTD. This particular CTD has 2 temperature sensors, 2 conductivity sensors that are used to calculate salinity, a pressure sensor that calculates depth, an altimeter showing elevation off of the bottom and an Eh sensor that measures a change in the chemical composition of the water. There are also a few optical sensors, 2 turbidity sensors and a transmissometer on the rosette. They give an indication of the amount of matter in the water or in other words, water clarity. The data from these sensors is viewed in real time in the lab from a signal carried through the wire being used to raise or lower the CTD. On this cruise we are closely watching the optical and Eh sensors to try and identify hydrothermal plumes. The bottles can be closed, or fired, at any desired depth while the CTD is ascending through the water column. This is the water that the scientists later sample and analyze. Some of the water samples are run through a gas chromatograph in the ship's main lab. Other samples are saved for later analysis on shore. An orange cylinder can be seen on the top center of the image. This USBL beacon relays the position of the CTD, relative to the ship, to a computer in the main lab and the bridge aft steering station. This allows the scientist to know the exact position of the CTD as they are taking their water samples. There's also a USBL beacon inside Nereus. Weather: clear, 84 degrees, winds east 2 knots, seas 1 foot