What hormone produced by the pineal gland regulates the biological clock and is linked to the onset of puberty?

The hormone produced by the pineal gland that regulates the biological clock is melatonin. Melatonin helps regulate sleep-wake cycles and circadian rhythms. Its levels fluctuate in response to light exposure, and it is also linked to the timing of puberty by influencing reproductive hormone release. As melatonin levels decrease, particularly during the onset of puberty, this can trigger the activation of reproductive hormones.