Can I spot a thermocline layer using the Deeper?

Yes, Deeper 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):