The Copernicus Sentinel-2 mission showed blooming algae in the Pacific Ocean off the coast of Japan. The picture was taken by a satellite of the European Space Agency (ESA).

Algae bloom is a sign of the rapid proliferation of phytoplankton. These are microscopic marine plants that drift on or near the sea surface. An overgrowth or bloom of algae can become visible to the naked eye and collectively stain ocean waters, allowing these tiny organisms to be detected even from space.

Although algal blooms are a natural and important part of life at sea, it is believed that human activities increase the number of annual blooms. Harmful algal blooms can be caused by environmental factors such as light, higher water temperatures, and excess nutrients.

The ESA satellite image shows high algae concentrations about 130 km from Hokkaido, Japan’s second-largest island. The size of this particular algal bloom was over 500 km across and 200 km wide. The photograph shows only a small part of the bloom, about 100 km from north to south and about 110 km from east to west.

During the spring flowering period, nutrients such as nitrates and phosphates are abundant in surface waters. Without direct measurements on-site, it is difficult to determine which algae are covering the ocean here.

Phytoplankton play an important role in the food chain, but they also affect the global carbon cycle by absorbing greenhouse gases on a scale equivalent to that of terrestrial plants.