The Atlantic Ocean stretches over 41 million square miles, making it the second largest ocean in the world. While most people imagine crystal clear blue waters when thinking of the ocean, the Atlantic often takes on greenish hues in certain areas and seasons. The green coloration has long fascinated sailors, scientists, and beachgoers alike. After centuries of speculation, modern oceanographers have determined several main factors that contribute to the Atlantic’s green waters.
Phytoplankton Cause Greenness
The prevalence of phytoplankton is the primary reason why parts of the Atlantic Ocean appear green. Phytoplankton are microscopic marine plants that contain chlorophyll, giving them a green pigmentation. Just like plants on land, phytoplankton require sunlight to grow via photosynthesis. They thrive in sunlit surface waters.
Phytoplankton populations bloom seasonally when conditions are optimal for growth. In the spring and summer months, strengthened sunlight and upwelling currents bring nutrients to the ocean’s upper layers. With sufficient light and nutrients available, phytoplankton can reproduce exponentially into massive blooms that turn the seawater green.
| Month | Bloom Status |
|---|---|
| January | Minimal |
| February | Building |
| March | Moderate |
| April | Abundant |
| May | Peak |
| June | Peak |
| July | Declining |
| August | Minimal |
| September | Minimal |
| October | Building |
| November | Moderate |
| December | Minimal |
As illustrated in the table above, phytoplankton blooms in the Atlantic peak in the spring and summer when conditions are ideal. The blooms fade during the winter when decreased light and mixing of the water column become less favorable for growth. Localized seasonal upwelling of nutrients can also lead to green patches in the ocean.
Shallow Waters Appear Greener
In addition to blooms, shallow waters often take on a greenish hue in the Atlantic. Shallow areas receive more direct sunlight, fueling increased phytoplankton growth. The shallower depth also allows the green pigmentation to be viewed more easily. Deep ocean waters further offshore appear darker blue since blue light penetrates to greater depths.
Several wide, shallow regions of the Atlantic promote very green waters. The largest is the North Sea between the United Kingdom and Scandinavia. Other shallow zones along the Atlantic coasts of Europe, Africa, North America, South America, and the Caribbean Sea also appear green due to proliferous phytoplankton.
Sediments Cause Greenish Tints
In some areas along the Atlantic coast, sediments can influence the ocean’s color. Particles like eroded cliff material and organic matter from rivers and wetlands get suspended in the ocean. These particles help scatter and absorb light, tinting the waters. Sediments near large rivers and wetlands often lend a greenish-brown cast.
One example is the Chesapeake Bay along the United States’ mid-Atlantic coast. It receives high sediment loads from the Susquehanna River. The particle-dense outflow creates murky green-brown waters in the bay. Coastal areas near large river deltas like the Mississippi and Amazon also take on greenish hues from sediment particles.
Algae Blooms Appear Green
In addition to phytoplankton, blooms of larger marine algae can contribute to patches of green in the Atlantic. Green macroalgae species like sea lettuce, ulva, and enteromorpha proliferate in nutrient-rich waters. When conditions are right, they can bloom into thick green mats on the ocean surface.
Green algal blooms typically occur in constrained, nutrient-rich waters. Prime examples include algae overgrowth in estuaries, bays, harbors, and fjords enriched by agricultural and urban runoff. Toxic green algae blooms that kill fish and mammals occasionally occur in polluted waters as well.
Conclusion
The Atlantic Ocean derives its green color from a variety of factors. Phytoplankton blooms, shallow depths, sediment loads, and green macroalgae growth can all contribute to the Atlantic’s greenish tints depending on the location and season. While the open ocean usually appears blue, the Atlantic’s coastal fringes shift from blue to green. The green waters ultimately result from the abundance of life that teems in the Atlantic to create one of the most productive ocean ecosystems on Earth.