thermocline

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Given that terms like "transcending thermoclines" are not defined in class, I'm so glad I am learning in a way that lets me stop and go look them up!

The problem is "Diving deep means dealing with big temperature changes -- an issue for critters who make their livings doing those deep dives."

According to Wikipedia:  A thermocline is a thin but distinct layer in a large body of fluid in which temperature changes more rapidly with depth than it does in the layers above or below.

I'm assuming that "transcending thermoclines" means diving deep enough to go through the thermocline into the deep (cold) water.

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