Spice, internal waves, and sound speed in the upper ocean

Sound‐speed variations in the upper ocean may be caused by spice fluctuations or isopycnal tilt associated with internal waves. Given finely resolved fields of temperature and salinity, the relative effects of spice and tilt on sound‐speed can be ascertained. For example, in a 1000‐km section in the North Pacific thermocline, root‐mean‐square sound‐speed variability in the horizontal caused by spice is roughly one‐half that caused by tilt. Sound‐speed variability is almost exclusively caused by spice in the nearly unstratified mixed layer. During the June 2004 North Pacific Acoustics Laboratory (NPAL) Spice04 mooring deployment cruise, fine‐scale hydrographic observations were made with the newly developed Underway CTD. Observations on a horizontal scale of 10 km and a vertical scale of 5 m show strong spice‐caused sound‐speed variability in the remnant of the winter‐mixed layer. The largest sound‐speed changes were greater than 6 m/s in a horizontal distance of tens of kilometers. The effect of these cha...