Salinity Spikes: Sensor or Environment?

Answer: This CTD’s pump was not functioning properly, resulting in a poor response from the conductivity and oxygen sensors. This problem is most pronounced while travelling through gradients or during times of significant ship heave.

These data originated from the secondary temperature/conductivity/oxygen channels on a 9plus CTD. The figure above shows data from the primary sensors superimposed over the secondary sensor data (red is primary salinity, green is primary oxygen). The primary sensors had a fully functional pump, so the data are much cleaner, with tighter grouping between samples and greater similarity in the upcast and downcast.

Repairing the pump associated with the secondary Temperature/Conductivity/Oxygen plumbing on the 9plus fixed the problem, and data from the secondary sensors matched nicely with data from the primary sensors.