Can I spot a thermocline layer using the Deeper?

Yes, Deeper PRO, PRO+ and CHIRP+ models are sensitive enough to spot the thermocline layer. In case you discover it, it will be shown on the sonar screen as a faint horizontal line of noise, and clutter of small dots beneath the line.

If you are using Deeper PRO or PRO+, use Narrow beam setting and >75% sensitivity if you're specifically looking for the thermocline. Your smart imaging setting must also be set to Detailed. Here's how a thermocline layer looks like on a PRO/PRO+ sonar (Classic color mode):

 

If you are using Deeper CHIRP+, use High or Mid CHIRP beam and 75% sensitivity. Here's how a thermocline layer looks like on a CHIRP sonar (Day color mode):