What is bottom water? Where and how does bottom water form?
What will be an ideal response?
Bottom water constitutes the densest water produced in the oceans. Near the poles, the surface waters are cooled below the normal freezing point (~1.9°C in some areas) by contact with the cold overlying atmosphere. (The freezing point is lower than that of pure water because of the presence of salt.) When that water freezes, it forms a layer of sea ice several meters thick that floats on the surface of the polar oceans. When the ocean surface freezes, most of the sea salt is excluded, because the salt does not fit into the crystal structure of the ice. As a result, the water just beneath the sea ice becomes saltier, and an underlayer of very cold, highly saline water forms. The combination of low temperatures and high salinities results in very dense water that sinks and flows down the slope of the basin and spreads toward the equator as the bottom layer of water in the deep-ocean basins.
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