Why is deep ocean water generally high in nutrients?

When surface water is warm, cooler, nutrient-rich water is trapped below. Because the vertical layers of the ocean aren't mixing, nutrients that have built up in deep waters can't reach the surface. ... The rising, or upwelling water carries iron and other nutrients from the ocean floor

Ibelieve the answer is relative humidity  because it makes more sense that way. solar flares usually occur in space it doesn't affect the earth, well it could but it wont make a significant damage.  latitude is land it doesnt do anything. prevailing winds, i dont know the correct meaning for this but i doubt that affects the land so it has to be relative humidity.