Poo-nami: How Whale Poo Can Combat Climate Change
Guest post by marine biologist and The Conservation Project International community member Felicity Johnson
Figure 1 - Feeding humpback, Antarctic
Research now indicates more clearly than ever that our carbon footprint threatens our finite ecosystems and our way of life. This climate catastrophe demands urgent and life-saving intervention before we reach the critical point of no return.
Efforts to mitigate climate change face two significant challenges; firstly, we need to find effective ways to reduce the amount of carbon dioxide (CO2) in the atmosphere; secondly, there need to be sufficient funds to implement these technologies. This article will focus specifically on the former challenge. Many of the proposed solutions to combat climate change are complex, untested and expensive. But what if there were a low-tech solution that is not only effective and economical, but also has a successful model?
The importance of forests in removing CO2 from the atmosphere is well recognised, however the oceans are by far the largest carbon sink in the world. Roman et al. (2014) found that whales, in particular the great whales, play a significant role in capturing carbon from the atmosphere. Over the course of their life, a great whale can accumulate, on average, 33 tonnes of carbon in their bodies, whereas a tree can only absorb upwards of 48lbs of CO2 per year, meaning even if a tree lives to 100 years old, it would still absorb just 4.2 tonnes compared to the whales 33 tonnes.
Wherever the largest living animals are found, so too are the populations of some of the smallest. Phytoplankton are microscopic, plant-like organisms that form the base of the entire marine ecosystem. Phytoplankton contribute more than 50% of all oxygen in our atmosphere by capturing nearly one third of all CO2 produced (Basu and Mackey 2018), approximately equivalent to 1.7 trillion trees, or 4 amazon rainforests.
Antarctic krill (Euphausia superba), once thought to live mostly in surface waters, regularly feed on fragments of decaying organisms on the sea floor, ingesting iron-rich particles. When the iron-rich krill return to the surface, they in turn will become prey for the filter-feeding baleen whales, who can swallow almost two tonnes of Antarctic krill every day (figure 1). When the whales are at the surface, they release gigantic plumes (up to 200 litres) of nutrient-rich faeces, nicknamed a poo-nami. The iron is then freed metabolically from the ingested krill and recycled back into the euphotic zone (the upper 200m of the ocean). Baleen whales are a part of a positive feedback loop, the ‘whale pump’ (Nicol, et al. 2010), in which the release of nutrient-rich whale faeces, leads to greater primary productivity and uptake of CO2 from the atmosphere (figure 2).
Figure 2 - Whale pump illustration
In the Southern Ocean, iron is a limiting nutrient, without which the phytoplankton cannot reproduce and grow, leading to less CO2 removal from the atmosphere. Whilst other oceans receive a steady stream of these trace metals from continental runoff and dust, in the remote Southern Ocean, animal faecal matter may be the critical source. The concentration of iron in whale faeces is on average, 10 million times higher than the concentration of iron found in the Southern Ocean (Nicol, et al. 2010).
Additionally, a whale’s seasonal migration allows transportation of consumed or captured nutrients from cold to warmer waters, where there is lower nutrient availability. Thus, the whale-pump mechanism creates a system of nutrient transport both vertically, between depth and surface, and horizontally, across oceans, thereby boosting ecosystem productivity.
A terminal contribution from the whale also occurs at its death. A whale’s carcass sinks rapidly to the seabed and provide an important additional concentrated, small scale ecosystem. Known as whale falls, the carcass is vital for deep-sea biodiversity as they support rich communities for years. The carcass will pass through three stages. The first stage is the mobile scavenger stage, lasting months to years, where soft tissue will be consumed by scavengers. The second stage, known as the enrichment opportunist stage, also lasting months to years, is where the skeleton is surrounded by dense aggregations of polychaete worms and crustaceans. Finally, the third stage is the sulfophilic stage, lasting for decades, where microbes live off the organic compounds from the decaying skeleton (Smith and Baco 2003).
The reason whales were hunted is precisely the reason they are so valuable now: Carbon-dense whale oil was a useful fuel. If whales were allowed to return to their pre-whaling number of 4 to 5 million from a slight 1.3 million today, it could add significantly to the number of phytoplankton in the oceans and to the carbon captured each year. Even a slight increase of 1% of phytoplankton productivity due to whale activity, would capture hundreds of millions of additional tonnes of CO2 per year, the equivalent to the sudden appearance of 2 billion trees.
Despite the drastic reduction in commercial whaling, whales still face significant anthropogenic (man-made) threats, including ship strikes, entanglement in fishing nets, plastic and noise pollution. Whilst the recovery of the South Atlantic Humpback population is a story of conservation success, many other species of whales are still struggling to recover. Enhancing the protection of whales from man-made threats would deliver lifelong benefits to ourselves, the planet and of course, the whales. Nature has had millions of years to perfect the whale-based carbon sink technology, all we need to do is let the whales live, so enabling our continued existence.