Why are only certain parts of the moon lit up at different times?

Depends on the way the moon is facing the sun

Explanation: The moon is lit up by the way the moon is facing the sun. So, for example, when there is a full moon, the earth ius facing the sun compleatly. When there is a half, half of the moon is facing the sun.

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answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c