The color of the ocean can vary significantly depending on location, time of day, weather, and other factors. While the deep open ocean typically appears deep blue, ocean waters closer to shore can range from green to blue to brown. Understanding what causes these color differences can provide insight into the ocean’s ecology and chemistry.
What Makes Ocean Water Blue?
The deep, open ocean commonly appears deep blue, which is caused by the way sunlight interacts with the water molecules. Pure water molecules alone absorb almost all sunlight except for the blue wavelengths, which are reflected back to our eyes. This causes the deep ocean to take on a deep blue appearance.
Additional factors that contribute to the deep blue color include:
- Water depth – the deeper the water, the more blue it appears.
- Fewer suspended particles – clear ocean water allows blue wavelengths to penetrate deeper.
- Fewer phytoplankton – these microscopic plant-like organisms reflect green/brown colors.
Therefore, the deep open ocean far from land generally appears blue because of its depth, clarity, and lack of phytoplankton.
What Makes Ocean Water Green?
In contrast to the blue ocean, coastal waters can often take on greenish hues. This is generally caused by higher levels of phytoplankton and sediment near shorelines. The main factors causing green ocean water include:
- Phytoplankton – These tiny plant-like organisms contain chlorophyll which reflects green wavelengths of sunlight. Blooms of phytoplankton can turn waters green.
- Sediments – Particles from land runoff can add a cloudy, greenish color to coastal waters.
- Shallow depths – In shallower water, there is less blue wavelength absorption so more green is reflected.
Phytoplankton thrive in nutrient-rich waters near coasts and rivers. Their concentrations are highest in areas of upwelling, where cold, nutrient-rich waters rise from the deep. Large phytoplankton blooms are commonly seen in coastal zones, estuaries, and near the equator, turning these waters green.
| Location | Phytoplankton Level | Water Color |
|---|---|---|
| Open ocean | Low | Blue |
| Coastal waters | High | Greenish |
| Estuaries | Very high | Green/brown |
This table shows how phytoplankton levels correlate with ocean color in different marine environments.
Other Factors Affecting Ocean Color
In addition to phytoplankton and sediments, other factors can also influence the color of ocean waters:
- Sun angle – Lower sun angles scatter more blue light, enhancing the water’s blue color.
- Cloud cover – Clouds can block certain wavelengths, impacting water color.
- Time of day – In the evening, more red wavelengths are scattered, making water appear more purple.
- Water salinity – Higher salinity absorbs more red/yellow light, making water appear more blue.
- Surface films – Oil slicks and floating debris can create prismatic color bands.
In some rare cases, unusual phytoplankton species can dramatically shift ocean color. Red tides caused by some algae can turn waters brick red. In Antarctica, blooms of cryptophyte algae occasionally turn waters a vivid green.
Using Remote Sensing to Study Ocean Color
Scientists use satellite remote sensing to measure subtle variations in ocean color on a global scale. By analyzing these measurements, they can detect phytoplankton concentrations, identify nutrient upwelling, and study impacts of climate change:
- Detect algal blooms and red tides
- Model primary productivity and carbon fixation
- Identify regions of upwelling
- Study sediment transport and land runoff
- Monitor impacts of warming, acidification, pollution
Some of the key ocean color satellites used for this purpose include SeaWiFS, MODIS, VIIRS, and OLCI. The data collected provides insights into ocean health and ecology.
Conclusion
In summary, the blue ocean primarily represents the deep open waters, where less phytoplankton and clearer water allows blue wavelengths to dominate. In contrast, green coastal waters contain more phytoplankton, sediments, and shallower depths that reflect greener shades. Ocean color varies across locations and seasons based on changes in phytoplankton, sediments, and other factors. Analyzing subtle color changes using satellites provides scientists with insights into ocean processes and change.
