English: The Shetland Islands, an archipelago in the Northern Isles of Scotland, are featured in this Copernicus Sentinel-2 image.

Zoom in to see this image at its full 10 m resolution or click on the circles to learn more about the features in it. Lying roughly 100 km north of the Scottish mainland, the Shetland Islands separate the Atlantic Ocean on the west from the North Sea to the east. The archipelago comprises around 100 islands and islets, with fewer than 20 of them inhabited. The islands cover an area of around 1468 sq km and have a rugged coastline approximately 2700 sq km long. The largest island, known as the Mainland, has an area of around 900 sq km, making it the third-largest Scottish island. The next largest are Yell, Unst and Fetlar, which lie in the north, as well as Bressay and Whalsay, which lie to the east. Lerwick, located on Mainland, is the capital and largest settlement of the archipelago. The most striking feature in this week’s image, captured on 1 July 2021, is the vivid, turquoise-coloured bloom visible to the east of the islands. This type of bloom is slightly different to the harmful cyanobacteria often visible around the Baltic Sea. In the absence of any known samples being analysed, it is assumed that it is a coccolithophore bloom – a type of microscopic marine algae living in the upper layer of the sea. Like all phytoplankton, coccolithophores contain chlorophyll and have the tendency to multiply rapidly near the surface.

In large numbers, coccolithophores periodically shed their tiny scales called ‘coccoliths’ into the surrounding waters. These calcium-rich coccoliths turn the normally dark water a bright, milky-turquoise colour. Although invisible to the eye, in large quantities, they are easy to spot in satellite imagery. These types of algae play a huge role in the ocean uptake of atmospheric carbon dioxide, as their shells sink to deeper ocean depths after they die, storing carbon in the process.