Great question! You’re right, when we look at
deep parts of the ocean, the water appears blue or
very dark, and we can’t actually see the seafloor.
This is because water absorbs sunlight before
it can reach the bottom of the ocean. Almost
all of the visible light from the sun gets
absorbed in the upper 200 meters (~650 feet) of
ocean waters. We could only see the seafloor if
light traveled down that far, reflected off the
seafloor, and returned to our eyes (or cameras).
The average depth of the seafloor is about 4,250
meters (14,000 feet), and the deepest part of the
ocean is about 11,000 meters deep (36,200 feet).
Visible light can’t penetrate that deep, and so we
cannot see the bottom of the deep oceans.
I have included a couple diagrams that illustrate
how light is absorbed by ocean waters. Both of the
diagrams are from the U.S. National Oceanic and
Atmospheric Administration (NOAA).
diagram, light depth
diagram, light in ocean
Most violet and red light is absorbed in the
upper 50 meters of ocean water. Blue light
penetrates the farthest, but only to about 200
meters in the open ocean. Notice that light
penetrates much deeper in open ocean waters than
in waters near the coasts of continents. Why do
you think that is?
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