Sarah Bedolfe
Phytoplankton – the base of the marine food chain – depend on polar sea ice.

A weekly dose of education in the ocean. 

In the polar regions winter has always meant the arrival of sea ice – a vast expanse of ice that acts like a lid on the ocean. It is important for many reasons. Sea ice provides habitat for polar bears and other critters. It also reflects the sun’s rays keeping the planet cool.  

Photo of the Arctic sea ice by NASA Goddard Photo and Video, Flickr, Creative Commons License

A perhaps less-known benefit of sea ice is its important place in the foodweb, supporting an entire ecosystem. It is the habitat for a special community of tiny organisms that live underneath a ceiling of ice: phytoplankton. These microscopic algae and bacteria, which form the basis of the marine food web in the Arctic and Antarctic, depend on the sea ice. 

Ice has little salt content and when it melts, the freshwater floats above the salty ocean water. When sea ice starts to melt from underneath, pools of freshwater form under the ice. Eventually when the ice is all gone, a layer of nutrient-rich freshwater remains on the surface. Together with sunlight, it provides the right conditions for phytoplankton blooms – the sudden growth of large amounts of phytoplankton.

Photo of phytoplankton bloom in the Ross Sea by NASA Goddard Photo and Video, Flickr, Creative Commons License

The phytoplankton are at the lowest trophic level in the marine environment. As primary producers they perform photosynthesis, making food that will pass energy on as it is eaten by zooplankton (tiny animals), which are food for small fish, which are food for larger fish… and so forth. This high productivity at the base of the food web – thanks to the sea ice – supports the rich biodiversity found at both poles. 

Photo by NSF/USAP Steve Clabuesch, Wikimedia Commons, Creative Commons License



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