Whales and the carbon cycle

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In addition to being amazing creatures, whales play important roles in ocean processes, and some of these roles influence how much carbon dioxide is removed from the atmosphere and eventually moved to and stored in the deep sea.

Whales carbon cycle diagram article 2

It all starts with creatures that you can only see properly with a microscope. The top, sunlit layer of the ocean is full of floating microscopic marine algae, which are tiny single-celled plants that – like plants on land – take up carbon dioxide from the atmosphere through a process called photosynthesis, to live and grow. These plants are fed upon by tiny animals collectively called zooplankton, and it is these animals that whales with baleen (bristles) eat.

Because whales live for a long time, many decades and perhaps even up to 200 years in the case of bowhead whales, this carbon that was taken up by the phytoplankton gets stored in their bodies. When whales eventually die, their bodies will sink into the deep sea, taking that carbon with them.

Whale fall NOAA

Whales’ bodies are very important in supporting deep sea ecosystems and the carbon is eventually incorporated into marine sediments. The image above is taken from a video shot by NOAA at the Davidson Seamount off the coast of California in the USA (Pacific Ocean) at a depth of about 3,000 metres. It is possible to make out the baleen is visible, the thin filter-like structures at the front of the skeleton. The whole skeleton is about 4 to 5 metres long and could be a young blue or humpback or grey whale, or adult minke.

All the octopus, fish (eelpouts) and worms (the red fuzz on the ribs are bone-eating worms called Osedax) show how important a food source dead whales are in the deep sea.

As whales have declined so much, these whale falls are far fewer than historically.

Whales carbon cycle diagram article 3

Whales do not just contribute to carbon storage when they eat and when they die, they also have an impact when they poo. Whales eat an enormous amount of food. For example, blue whales can eat up to two tonnes of krill (a small prawn-like creature found in the Southern Ocean) in a single day. This produces a lot of poo. Whales always poo near the surface of the ocean, and their poo contains important nutrients such as iron that help phytoplankton to grow. Essentially, whales help to fertilise the oceans.

Whale poo

The clip above shows a humpback whale pooing near the surface. You can see this is quite liquid and floats. This means that the poo stays near the surface and provides important nutrients for marine algae. More algae allow more carbon dioxide to be removed from the atmosphere, and so the cycle continues.