Like many plants, phytoplankton bloom in the springtime. The microscopic photosynthesing organisms are at the foundation of the oceanic food web, providing nourishment for the likes of the tiny krill that themselves sustain larger sea creatures up to and including the leviathan blue whale.
But the phytoplankton need sunlight, and they need iron. In the Gulf of Alaska, glacier melt releases ‘glacial flour’, a fine sediment of glacier-ground bedrock rich in iron, into the water where it mixes with existing nitrates to make the perfect conditions for a phytoplankton bloom.
In the image above, captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite in April, the opaque turquoise swirls are plumes of glacial flour while the bright green is the phytoplankton itself.