Final answer:
Fjords are narrow, deep inlets of the sea that are surrounded by steep cliffs or mountains. They often have very little mixing between their deep and shallow layers of water.
Step-by-step explanation:
Fjords are narrow, deep inlets of the sea that are surrounded by steep cliffs or mountains. They are typically found in areas where glaciers have carved out valleys and then filled with water. Due to their unique characteristics, fjords often have very little mixing between their deep and shallow layers of water. This is because the cold, dense, and nutrient-rich water from the bottom of the fjord doesn't easily mix with the warmer and less dense water near the surface.