why is the atlantic ocean brown

Why is the Atlantic Ocean brown? It can surely make you put your thinking cap on because the answer seems a bit tricky. Or is it?

The Atlantic Ocean is the world’s second-largest, and it is responsible for our weather patterns and is home to a wide variety of marine life.

Yes, it is important, but why is the Atlantic Ocean water brown and Caribbean water so clear?

The Atlantic Ocean looks brown because of microscopic particles (CDOM), which are suspended in it. 

The Grandeur of the Atlantic Ocean

atlantic ocean wave beating against rocks

The Atlantic is a vast ocean containing some of the deepest waters on the earth.

It lies between North and South America on the west and Europe and Africa to the east.

To the north, the Atlantic connects with the colder waters of the Arctic and the Southern Ocean to the south.

The Atlantic Ocean receives water from some of the greatest rivers in the world.

Some of these include:

  • The Amazon River
  • The Mississippi River
  • The Niger River
  • The Congo River

All these rivers drain into either the Baltic or Mediterranean Seas, and all these seas ultimately drain into the Atlantic Ocean. 

Why is the Atlantic Ocean Brown?

When the waters of any of the world’s oceans are generally considered to be blue, you might have wondered why is the Atlantic Ocean so dark. Could it be because of its size?

The Atlantic covers such a huge area that for convenience scientists often divide it into the North and South Atlantic.

But, when we ask why is the Atlantic Ocean brown, it has little to do with its overall size.

In fact, the Atlantic is brown because of the microscopic matter it has floating in it.

Fact: The name of the Atlantic Ocean comes from Greek mythology, as Herodotus used it in his writings in 450 BC. 

An Atlantic Soup Responsible for Darker Water

Usually, in clear water, light bounces off and passes through, reflecting the color blue back to our eyes. But, that is certainly not the case with the Atlantic Ocean.

globe showing atlantic ocean

This is when you have to understand the concept of CDOM. These are microscopic particles, collectively known as CDOM, and suspended in Atlantic water.

They block the blue wavelength resulting in green, red, and brown water instead. 

Understanding the Concept of CDOM

CDOM, colored or chromophoric dissolved organic matter, is a complex mixture of dissolved material that creates a nutrient-rich soup.

This is what makes the Atlantic Ocean black, yet a highly productive ecosystem.

CDOM typically contains:

  • Single-cell organisms such as algae, phytoplankton and plankton
  • Small crustaceans, eggs and larvae
  • Dissolved organic carbon matter
  • Sediments
  • Chemical molecules as a result of land runoff 

CDOM and the Color of Atlantic Water

blue empty sea

The amount of CDOM in any body of water obstructs the amount of blue light that can be reflected back.

This means scientists can use this property as a measure to determine the health of the water. In water that has little or no CDOM the water is clear blue.

It is important to understand that measuring surface temperature across an entire ocean is difficult, even impossible.

Therefore, scientists have developed equations that relate color to temperature, a reliable indicator of oceanic health. 

It implies that understanding what drives ocean color can help better understand the condition of the world’s oceans.

Fact: The Atlantic Ocean is the resting place of the RMS Titanic, which was destroyed when it collided with a huge iceberg.

Factors Contributing to CDOM and Brown Atlantic Water

CDOM basically refers to organic matter found in the water, but it could be divided into different categories.

To understand how CDOM contributes to brown Atlantic water, you need to know about those other organisms as well. 

phytoplankton micrograph


Multitudes of single cell organisms called phytoplankton and plankton are suspended in the water as CDOM.

Although microscopic in size, these planktons are essential for healthy marine ecosystems. Planktons do not swim or stay in one place like coral.

They drift suspended in the upper layers of the water. And where they end up is usually dependent on currents, tides, and many other factors.   

Living Organisms

plankton drifting in ocean

Within the plankton are living plant organisms called phytoplankton.

They contain the green pigment chlorophyll and use it to photosynthesize the energy from sunlight into carbohydrates for food.

Like all other green plants, phytoplankton takes in CO2 and releases oxygen. 

One of the most significant contributors to the world’s oxygen supply, phytoplankton are responsible for roughly half of all photosynthesis.

They subsist on food sources naturally present in their environment, such as:

  • Phosphate
  • Nitrate
  • Calcium

Phytoplankton are essential for a healthy marine ecosystem and form the base of the entire marine food web. 

An Important Consideration

Zooplankton and other small marine creatures, also part of the plankton and eat phytoplankton and then become food for fish, crustaceans, and other larger species. 

Dangerous Blooms

It is worth mentioning that plankton populations, including microscopic algae, are essential for healthy marine ecosystems.

But, an excess of them in a given location can have disastrous effects on that ecosystem.

blooming blue-green algae

In these large dense populations, known as ‘blooms’, the algae overload the area with dangerous toxins that contaminate the water and the environment locally.

Blooms occur when the environmental conditions are optimal for abundant growth.

For example when there is,

  • An increase in nutrients.
  • An increased temperature.
  • An abundance of sunlight.
  • Low wind conditions. 

Role of Blooms in Dictating the Atlantic Water Color

Since the color of the organisms dictates watercolor in it, the color of the water containing the bloom may appear brown, yellow, green or red.

It is worth mentioning that plankton and phytoplankton are the producers at the base of the food web. And when fish and other marine life eat them, they can be sufficiently contaminated to severely threaten life.

It is possible to divide blooms into three different types that contribute to making phytoplankton harmful for living organisms.

For instance:

  • Cyanobacteria or blue-green algae
  • Dinoflagellates or red tide
  • Diatoms or microalgae

Keeping these microscopic plants and animals healthy and in check is crucial to the aquatic food chain as a whole.

The plankton population faces grave threats from global warming and rising water temperatures.

Fact: The Bermuda triangle is in the Atlantic Ocean, as Florida's southernmost city of Bermuda, Miami, and the Caribbean Island of Puerto Rico all border it.

The Atlantic Ocean as The Global Ocean Conveyor

greenish color sea

Plankton and phytoplankton form only a part of the CDOM that make the Atlantic appear brown in color.

Another factor is how the deep waters of the oceans create strong circulating currents that churn up and move sediment.

One such circulating current is the global oceanic conveyor. It is a system that helps regulate climate on a global scale. 

Sediments and Thermohaline Circulation 

The global ocean conveyor is an example of thermohaline circulation.  

It describes the movement of ocean currents due to differences in temperature and salinity in different regions of water such as the oceans. 

Any current of moving water gathers up both organic and non-organic sediments as it creates turbulence.

All these clouds color the water. 

How Does It Work?

endless patterns caused by ocean currents

Thermohaline circulation happens when water is frozen into sea ice or evaporated leaving its salt content behind in the water.

As the salinity increases the salty water increases in density until eventually, it sinks.

This dumping of warmer water into the deep ocean cold forces a current that moves horizontally returning to close the loop as it rises in warmer water. 

How Does It Affect the Color of the Water?

Particles are carried by the current until conditions change and they drop out and are deposited when the current slows down.

Such movement of water allows energy rich nutrients to be spread and dispersed over thousands of miles. And as it increases in quantity, it directly affects the color of the water.

Fact: Researchers have found that the Atlantic Ocean is only about 150 years old. 


beach sunset

Why is the Atlantic Ocean brown? The color blue is reflected back to us from water as light travels through it.

But, the presence of tiny particles and microscopic algae known as CDOM can make it harder for the light to bounce back.

And when this happens, the oceans appear red, green, or brown. And the presence of so many organisms, algae, and tiny particles in the Atlantic Ocean is the reason why it seems brown or even darker.