Why Is the Ocean Different Colors?

Ocean water can appear many dazzling shades of blue and green depending on where you are. Learn why in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,
Lauren Vogal Bomb. Here, someone gazing out at the ocean
from the main coast sees very different hues than someone
squinting at the sea from a sunny beach on a
Greek island. But why does the ocean come in so
many shades of blue? Of course, ocean water isn't inherently blue.

(00:23):
It's clear the colors that we see on the surface
are the result of light being absorbed and reflected by
the water itself, whatever is floating and living in it,
and the surface of the ocean floor below it. A
glass of water will of course appear clear as visible
light passes through it with little to no obstruction. But
if a body of water is deep enough that light
isn't reflected off the bottom, it appears blue. Basic physics

(00:47):
explains why light from the sun is made up of
a spectrum of different wavelengths. The longer wavelengths appear to
our eyes as the reds and oranges, while the shorter
ones appear blue and green. When the Sun's strikes the ocean,
it interacts with water molecules and can be either absorbed
or scattered. If nothing is in the water except water.

(01:08):
The longer red portions of the spectrum tend to be
absorbed by the water molecules, whereas the light of those
shorter wavelengths is more likely to go deep, hit water
molecules there, and scatter back up towards our eyes, making
the ocean appear blue. Depth and the ocean bottom also
influence whether the surface appears a dusky dark blue, as
in parts of the Atlantic, or casts a sapphire like shiver,

(01:30):
as in many tropical locations. We spoke with NASA oceanographer
Jeane carl Feldman. He said, in Greece, the water is
this beautiful turquoise color because the bottom is either white
sand or white rocks. What happens is the light comes
down and blue light gets down, hits the bottom, and
then reflects back up, So you make this beautiful light

(01:51):
blue color in the water. Darker sand rocks or other
formations mean darker water. The color is further complicated by
the fact that the ocean is rarely just water, but
is instead teeming with tiny plant and animal life, plus
suspended sediment or other natural or band made contaminants. Oceanographers
monitor the ocean's color the way that doctors read vital

(02:14):
signs of their patients. Colors seen on the ocean's surface
reflect what's going on in its vast depths. Feldman, who
is based at the NASA Goddard Space Flight Center in Maryland,
studies images taken by the sea viewing wide field of
view since her satellite launched in from its perch more
than four hundred miles above Earth or nearly six hundred

(02:35):
fifty kilometers, The satellite captures van go like swirls with
the ocean's colors. The patterns are not only mesmerizing, but
they also reflect where sediment and runoff may make water
appear a dull brown, and where microscopic plants called phytoplankton
collect in nutrient rich waters, often tinting it green. Phytoplankton
used chlorophyll to capture energy from the sun to convert

(02:58):
water and carbon dioxide into energy and then waste. Through
this process called photosynthesis, phytoplankton generate about half of the
oxygen we breathe. Oceans with high concentrations of phytoplankton can
appear blue green to green, depending on the density. Some
lend the water a yellow, reddish or brown tint. Phytoplankton

(03:18):
serve as the base of the food web and primary
source of food for zooplankton, which are tiny animals eaten
by fish. The fish are then eaten by bigger animals
like whales and sharks. It's when oceans become polluted with
runoff that the amount of phytoplankton can escalate to unhealthy levels.
Phytoplankton feed on the pollutants, flourish, and then die, sinking

(03:39):
to the bottom to decompose in a process that depletes
oxygen from the water. Over the past fifty years, ocean
zones with depleted oxygen have more than quadrupled to an
area roughly the size of the European Union. Part of
the cause may be an increase in ocean temperature due
to climate change, since warmer water supports less oxygen. In

(04:00):
still areas, phytoplankton blooms are suspected to be the cause.
Phytoplankton may serve as the base of the ocean food chain,
but as Feldman says, too much of a good thing
is not a good thing. On a map on Feldman's
office wall is a marker showing where there's little human
interference and ocean water is perhaps the clearest on the planet.
In this region, off the coast of Eastern Island in

(04:20):
the Southeast Pacific Ocean. The water is deep and remarkably
clear due to its location in the middle of a
giant oceanic eye, which is a large circular current. Its
central location means there's minimal mixing of ocean layers and
nutrients aren't pushed up from the deep bottom. The purity
of the water they're coupled with the depth make the
ocean appear a deeper indigo than perhaps anywhere else. Feldman said,

(04:44):
the light just keeps going down, down, down. There's nothing
that bounces it back. Here is the deepest blue you'll
ever see. Today's episode writtain by Amanda Onion and produced
by Tyler Clang. Brain Stuff is a production of I
Heart Radio's How Stuff Works. For more in this and
lots of other topics is our Home Planet has to

(05:05):
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