Do Trees or the Ocean Make More Oxygen?

In 1904, whalers killed 195 whales in the Antarctic waters. In 1931, this figure rose to 37,000, a majority of which comprised blue whales. The Antarctic blue whale, the largest animal known to have lived, is estimated to have fallen from 200,000 to 300,000 individuals to fewer than 400. These figures carry significance not only as an indicator of changes in marine life, but they also impact our breath.

Phytoplankton, the microscopic marine life drifters of the sunlit ocean, produce roughly half of the oxygen that photosynthesis releases each year. Blue whales feed deep, surface and leave waste so rich in iron that it fertilises the phytoplankton. Therefore, saving whales impacts our breath. Additionally, according to widely circulated figures, phytoplankton also captures the carbon production of four Amazon forests. However, this explanation also carries inconsistencies.

Roughly half of Earth’s photosynthesis occurs on land and half in the ocean. Most of the oxygen produced in the ocean is consumed by marine life. Researchers at Sorbonne University put the ocean’s net oxygen production close to zero. The ocean contains less than one percent of the oxygen stored in the air. And this oxygen we breathe built up over millennia from organic matter buried. Therefore, irrespective of whether trees or marine plants produce more oxygen, our consumption is based on centuries of accumulation.

However, this does not change the fact that the open ocean lost 0.5 to 3.3 per cent of its oxygen in the top 1,000 metres between 1970 and 2010. Ocean water is stratified. As the density of water changes from layer to layer, so does its oxygen content. As the planet warms, the surface layer grows warmer, increasing the density contrast between the layers, making it difficult for oxygen to mix and reach to the deeper, denser ocean water. Global warming exacerbates this density contrast, risking oxygen supply to marine life.

Secondly, Baleen whales feed at depth and return to the surface, releasing waste into the light. In the Southern Ocean, iron limits phytoplankton growth. A 2010 study of 27 faecal samples from four baleen species found iron at roughly ten million times the concentration of Antarctic seawater. The effect of the iron-rich waste on the Southern Ocean, before whaling, was published in Nature in 2021.

A team led by Matthew Savoca tagged seven baleen whale species and calculated that whales in the Southern Ocean once consumed 430 million tonnes of krill a year, twice the number that exists now. They estimated that before whaling, whales recycled close to 12,000 tonnes of iron annually, compared with 1,200 today. However, there’s a paradox. For krill, whaling should have meant fewer predators and more prey. Yet, the krill have reduced too. The authors of the research suggest that larger whale populations have supported higher productivity as a result of nutrient recycling. Thus, the whales farmed their own food. This reveals that the most visible impact of whaling has not been on oxygen but on the food chain.

In 2019, economist Ralph Chami and his colleagues published an article in the IMF’s Finance & Development stating that phytoplankton capture an estimated 37 billion tonnes of carbon dioxide in a year, the equivalent of four Amazon forests. The same article cites the whale’s share as hypothetical. It states that if whale activity raised phytoplankton productivity by even one per cent, the extra carbon dioxide captured would equal the sudden appearance of two billion mature trees. Joe Roman of the University of Vermont has studied the phenomenon for years. According to him, how much whale waste boosts phytoplankton growth globally is unknown. However, a 2010 study on sperm whales in the Southern Ocean found that approximately 12,000 sperm whales fuel extra phytoplankton growth to carry close to 200,000 tonnes of carbon dioxide annually.

In 1995, fisheries scientist Daniel Pauly explained why the numbers are unsettled. He described it as the shifting baseline syndrome. Each generation of researchers accepts the state of the fishery at the start of its career as normal, judging a depleted ocean against an already depleted past. The whale pump proves it. No survey measured a Southern Ocean with all its blue whales intact. The IMF’s figure is a hypothesis and the 12,000 tonnes of iron is a reconstruction. This is not a criticism of the scientists or science but rather the conditions of nature. Pauly also offered a remedy. He suggested that old accounts be treated as data rather than anecdote.

The authors of the IMF article estimated that a great whale is worth about $2 million over its lifetime, concluding that “one whale is worth thousands of trees”. Chami hoped that the figure would reach policymakers who do not buy into saving species for their own sake. However, Steven Lutz of GRID-Arendal also cautions: “It’s not like we save the whales, and we save the climate.” Even the economists' most optimistic scenario, a recovery from about 1.3 million great whales to four or five million, would capture about 1.7 billion tonnes of carbon dioxide a year, a few per cent of the roughly 40 billion tonnes humanity emits.

Thus, the impact of whales on human oxygen consumption, after testing, remains smaller. This leaves us with Chami’s pricing of whales as a possible reason for saving them. But this too poses a question. What happens when someone quotes a better price for not saving them or when the price is revised?

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