Ocean's vibrant secret: How phytoplankton's bloom impacts climate

New Delhi (The Uttam Hindu): Whether it's the ocean or the mountains, every corner of the Earth holds a mystery. One such mystery is the phytoplankton bloom, which displays a unique play of colors in the ocean.

In June 2025, the waters of the North Sea near the Shetland Islands in Scotland suddenly turned colorful. This stunning display of green and blue hues was caused by a massive bloom of microscopic organisms called phytoplankton. These organisms are so small that they are invisible to the naked eye, but when their numbers suddenly increase, they become clearly visible even from satellites.

The OLI-2 camera on NASA's Landsat-9 satellite captured an image on June 13, 2025, showing a portion of the bloom, approximately 160 kilometers wide. The satellite image showed the water as green, with some areas appearing bluish and white.

According to scientists, the green hues were mostly due to phytoplankton called diatoms. Diatoms have silica shells and are rich in chlorophyll. They thrive in spring, but are sometimes seen in summer as well. The bloom also included phytoplankton called coccolithophores, whose shells have tiny plates of shiny calcium carbonate that give the water a milky or turquoise blue hue. This species is common in the North Sea and a similar phenomenon was previously observed off the coast of Scotland in 2021.

First, we need to understand simply what phytoplankton are. This name, derived from the Greek words "phyto" (plant) and "plankton" (wanderer), refers to microscopic organisms that live in both saltwater and freshwater. These include cyanobacteria, diatoms, dinoflagellates, green algae, and coccolithophores. Most are unicellular. Like terrestrial plants, they produce energy from sunlight through photosynthesis. They absorb carbon dioxide and release oxygen. Their growth requires sunlight, carbon dioxide, and nutrients such as nitrates, phosphates, and silicates. Some species can also fix nitrogen. During favorable weather, their numbers increase explosively, creating a bloom called a bloom. This bloom can cover hundreds of square kilometers and last for several weeks, although the lifespan of each individual is only a few days.

Phytoplankton are the foundation of the marine food chain. They are primary producers, providing food for all life forms, from tiny zooplankton to giant whales. Small fish eat them, and then larger fish eat the smaller ones. They are also vital to the environment. They absorb carbon dioxide through photosynthesis.

Dead phytoplankton sink to the deep ocean, storing carbon there for long periods of time. This way, they help regulate climate. However, along with these advantages, there are also disadvantages. Some species produce toxic substances, known as "red tides," which can be dangerous to fish and humans. After large blooms, the decay of dead organisms depletes oxygen in the water, creating "dead zones" where other organisms cannot survive.