A picture straight from the CTD's operating computer showing the data transmitted back up through its cable to the computer. 4 different characteristics are graphed against water depth (0-500 meters). The blue line represents O2 (oxygen) concentrations, the white line = seawater temperature, the red line = salinity and the green line represents chlorophyll (phytoplankton) levels. As you can see from the graph, water temperature and salinity tend to be higher near the surface, while O2 levels increase with depth. Phytoplankton concentrations increase with depth as nutrient levels increase with water depth. However, it eventually reaches a depth where the sunlight is too low for the phytoplankton to live and their concentrations fall off rapidly below that depth.