Tiny animals migrating from the ocean's surface to the sunlit depths release ammonia, the equivalent of our urine, that plays a significant role in marine chemistry, particularly in low-oxygen zones. One might not think that peeing into the vastness of the oceans could have an effect. But the animals -- which include tiny zooplankton, crustaceans such as krill, and fish such as lanternfish up to a few inches long -- compensate for their small size with huge abundance throughout the world's oceans. The ocean's low-oxygen zones are projected to expand under climate change, as warmer waters hold less oxygen and decrease oxygen content below the surface. Understanding these zones is thus important for predicting what might happen to the oceans under climate change.