The whale pump: how the great whales fertilize our oceans

The snow falling at the bottom of the sea, Picture from Marine madness

We all know and love whales, whether it is for their serenity, impressive size or acrobatic behaviour. There is, however, a whole different aspect for which these gentle giants deserve to be appreciated, namely their inexhaustible efforts towards the welfare of our oceans and our climate. Whales are what we call “ecosystem engineers”. This term refers to organisms that shape our ecosystems either directly and/or indirectly by inducing physical or chemical changes to the abiotic environment. The great whales specifically, are essential for the nutrient cycling in our oceans. The process through which cetaceans do so is called the “whale pump”.  

Left - Humpback whale fluke diving and leaving a fecal plume behind, Picture by Eline, Right - fecal plume from a sperm whale, Picture by Blue Planet Archive

The general rule in the ocean is that the majority of nutrients move down in the water column, whether it is through the food web or as the result of particles ending up on the ocean floor in the form of “marine snow”. Theoretically this means that over time all nutrients in the ocean would end up on the ocean floor, leaving the water column completely depleted. But in reality, this does not happen. Dust storms, river sediments and upwelling from wind and waves are the main providers of nutrients in the ocean, while hydrothermal vents and certain foodchains cause nutrients to go upwards. Next to this, whales also play an essential role in recycling the nutrients that already have made their way down into the water column. Whales often dive deep to find their favorite snack. (Sperm whales (Physeter macrocephalus), for example, can swim over 2000 meters deep to find a savoury giant squid while the absolute record holder, the Cuvier’s beaked whale (Ziphius cavirostris), reaches staggering depths of around 3000 meters. Of course, whales still need air to breathe so they do spend a lot of time at the ocean’s surface to catch their breath, rest, or travel. A healthy, well-digesting whale might then go on and release its faeces in the form of large liquid plumes often containing some solid, indigestible parts. One such example is ambergris; a grey waxy lump often containing squid beaks secreted by sperm whales, these are well sought after by perfume makers. 

Coincidentally, these fecal plumes are extremely rich in the essential nutrients required for photosynthesis. On land plants are the main photosynthesisers, whereas phytoplankton (microscopic algae) mainly fulfill this role in our oceans. Just like plants, phytoplankton are at the very bottom of the food chain, providing the necessary nutrition for nearly all marine life, either directly or indirectly. Since whales locally provide a large amount of nutrients that stimulate phytoplankton growth, they are essentially providing the fuel needed to keep our oceanic food webs alive.  Simultaneously, they close the marine nutrient cycle by bringing these nutrients back again from deep down towards the surface. 

Infografic visualising the whale pump process, By Whale and Dolphin Conservation

Just like any other photosynthesizing organism, phytoplankton uses CO2 from its environment. Due to the massive scale at which they do so, phytoplankton globally accounts for about half of all carbon captured from the atmosphere. This makes them even more important for reducing atmospheric CO2 than trees. Phytoplankton growth is, however, often limited by the availability of nutrients in its environment. Nitrogen and phosphorus tend to be the main limiting factors in warmer waters while in colder regions the limiting mineral tends to be iron. 

Thankfully, whales are capable of stepping in and are an important mitigator for these shortages. Not only do whales help in controlling the climate by stimulating phytoplankton growth, but the whale pump also aids in taking carbon out of the atmosphere and storing it long-term at the ocean floor. It’s hypothesized that when phytoplankton consumes carbon dioxide, much of the unused carbon is stored within their bodies. Phytoplankton then gets eaten by zooplankton such as krill and they in turn serve as food for the great whales. Each animal storing the carbon of their food source into their bodies. Due to their size, whale bodies hold a vast amount of carbon and due to their longevity, whales store carbon in their tissues much longer than most other animals. Eventually, when a whale passes away, it sinks to the bottom of the ocean. This is often referred to as a "whale fall". Whale falls are truly a feast for an abundance of ocean floor dwelling creatures providing a temporary food source and habitat often for decades. The whales´ stored carbon will be transferred into their scavengers’ and so eventually the carbon will end up in the seabed as these creatures´ lives come to an inevitable end. This way, each single great whale has the potential to store multiple tons of carbon down into the depths of the ocean and store it for hundreds of years.  

Sadly, it is estimated that overall whale populations decreased to about a quarter of their original size. Some species have been hit harder than others and while some species (e.g. humpback whales) are recovering at remarkable rates, others, like the blue whales (Balaenoptera musculus), have barely shown any improvement in population size. Today a global estimate of around 1,3 million whales roam our ocean, which is a great step back from the 4-5 million whales that swam freely merely decades ago. Among other threats like heavy shipping, overfishing, plastic pollution and climate change, commercial whaling has played a major role in this. Luckily, most countries imposed a moratorium on whaling in the 1980's (except Iceland, Faroe Islands, Norway and Japan). Ever since whale numbers have been increasing ever so slowly. Supporting a healthy whale population could potentially have a major positive impact on our climate. If we would allow the great whales to recover to their pre-whaling numbers, it could add significantly to the amount of phytoplankton and to the carbon being captured each year. Even still today, the great whales are responsible for an estimated 200,000 metric tons of carbon to be drawn from the atmosphere each year, which is about the same as 400,000 acres of forest. Over its lifetime, each great whale individually is estimated to help draw an average of 33 tons of CO2 out of the atmosphere, meaning it performs roughly the same amount of carbon sequestration as 2000 trees! 

This infographic depicts the economic values of whales in different sectors, including fisheries, tourism and climate change mitigation. (source:  GRID Arendal)

At this point it is clear that whales are a key player in our fight against climate change. In modern times however, the economic value of things is often a key factor taken into consideration by legislators when it comes to policy-making. Luckily, a monetary value can now also be used to highlight the importance of our great whales in combatting climate change. A study was conducted to estimate the value of an average great whale by calculating the current worth of the carbon it sequesters over its lifetime while also taking into account the value of the whale’s other economic contributions, such as boosting fisheries and supporting ecotourism. The study´s most conservative estimate places the value of a single great whale at over $2 million, with the total value of the current great whale population exceeding $1 trillion. 

To conclude, the great whales, often unknowingly, serve as incredibly important caretakers of our ocean, thanks to their enormous appetite (and subsequent flatulence). They play a major role in keeping the marine foodweb and nutrient cycle alive while at the same time tempering our planet’s climate by naturally storing carbon. This makes them equally impressive contributors to nature’s health as they are charismatic and enchanting to observe. In the end, this makes us appreciate these majestic animals even more!

Milan Vansteelandt