Where is the massive deep water reservoir primarily located within the mantle layers?

Answer

The transition zone (between 250 and 410 miles deep)

The key location confirmed for the water saturation is the mantle's transition zone, situated roughly between 250 miles and 410 miles beneath the surface. This contrasts with the upper and lower mantles, which are generally considered dry.

Where is the massive deep water reservoir primarily located within the mantle layers?
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