CTD data were collected with a Seabird 911 plus CTD (AOML CTD #1 S/N 50619). This instrument provided pressure, temperature, conductivity and dissolved O2 channels, and additionally measured secondary temperature, conductivity and oxygen sensors as a calibration check. Inlet ports for the sensor pairs including temperature, conductivity and oxygen are at the same depth, located 6 inches apart. The secondary temperature sensor is used to calibrate the secondary conductivity sensor.
Standard CTD maintenance procedures included soaking the conductivity and O2 sensors in distilled water between casts to maintain sensor stability, and protecting the CTD from exposure to direct sunlight or wind to maintain an equilibrated internal temperature. The Seabird SBE 24-place pylon provided generally reliable operation and positive confirmation of all bottle trip attempts. The SEWARD JOHNSON Seabird CTD acquisition PC, deck unit and external power supply were employed.