[L]ife can multiply until all the phosphorus is gone, and then there is an inexorable halt which nothing can prevent…

—Isaac Asimov, "Life’s Bottleneck"

Sea life reduced to flotsam is a hint at the surface of a suffocated sea. The Gulf of Gabès in Southern Tunisia, like five hundred other sites across our oceans, is starved of most life. The candid “dead zone” occurs in coastal waters when an excess of phosphorous and nitrogen causes algal blooms, robbing the water of oxygen. The Gulf of Gabès is mostly devoid of animal life; the fishermen are out of work. Home to the phosphate industry, Gabès doesn’t just suffer this calamity but exports it, as phosphate and nitrogen fertilizer are the main culprits for coastal dead zones across the world. Globally, the biochemical flow of phosphorous is nearing its “planetary boundary,” a threshold that when crossed, “will trigger non-linear, abrupt environmental change” (Rockström et al. 2009). Hypoxic ocean zones, which have quadrupled since the 1950s, might become unbound. But the deadzone is not the limiting factor of life, the “inexorable halt” that Asimov (1974, 140) described in the quote above. It is rather the removal of life’s limiting factor in some places—the bottleneck turned floodgate in the Anthropocene.

As organic chemist Justus von Liebig noted in 1840, a population’s growth is not governed by the net nutrients available, but by the essential nutrient in shortest supply. Among the six elemental building blocks of life—carbon, hydrogen, nitrogen, phosphorous, and sulfur—phosphorus is life’s limiting factor. In its compound organophosphate form, it is a vital component of cell membranes, DNA, RNA, and ATP, a molecule that provides cells with energy. But for any one of the ten thousand atoms of phosphorus in living systems, there is only one in the rest of the universe. Phosphorous therefore regulates the growth of the biosphere like no other element. Its scarcity is exacerbated by an extremely slow biogeochemical cycle, which in theory transfers each phosphorus atom from soil, to plant, to animal, and back to the soil as excrement. But with the onset of industrial agriculture, we unhinged this cycle.

In eighteenth-century Europe, agriculture coupled with urbanization saw plant nutrients transferred from the fields to the city, where they became unavailable for crop growth. Resultant soil erosion and discoveries in plant nutrient cycling led to a global onslaught on phosphorus reserves (Marx 1981, 949–50). Resources were robbed from the colonies and transferred to the newly bottomless soils of urbanizing Europe. First guano droppings were stolen from Peru’s Quechua communities and stripped from Pacific islands like Nauru and Banabu (Clark and Foster 2009). Then, the recognition that phosphoric acid could be produced from phosphate rock led to the establishment of mines in North Africa, where the majority of global deposits lie.

Today, phosphate rock reserves underpin world food security and concerns over peak phosphate conjure up neo-Malthusian nightmares. Phosphorous is still bound up with colonialism in North Africa, where it limits life chemically and socially to make soils abroad more fertile. “We Want to Live” (nheb na’ish) was a 2013 grassroots campaign against pollution from phosphate refineries in Gabès. As a bold activist known as Gabès Girl explained to me, “The Gulf of Gabes was known for its wealth in fish. The seaside oasis is the only of its kind in the world. Now the only thing we’re known for is yellow air and a sea full of wastes.”

The Gulf of Gabès is not just a dead zone but a "dumping ground for Tunisia's chemical industry.” Here, as in the phosphate mining towns of Gafsa and Metlaoui, in Tunisia’s interior, mountains of powdered phosphate rock lie dormant, waiting for the wind to be dispersed. From there, phosphate bonding with industrial chemicals seeps into ground and seawater and eventually the bodies of plants, animals, and humans, where they bring about mostly undocumented disease. Knowing that only one-fifth of the phosphorus mined and refined here will eventually feed crops, while the rest will feed the planet’s deadzones, makes this violence even harder to accept. The slow death of the oasis—the ultimate symbol of life surviving in the desert against its limiting factor, water—is particularly demoralizing to Gabèsians. Under assault from pollution, in Gabès it is involuntary and embodied knowledge that the sea, the oasis, the people, the refineries, and the minerals beneath your feet are ultimately connected through their chemical cycles.

There used to be a reductive certainty in the chemical symbols C, H, N, O, P, S, which form the covalent bonds of 98 percent of life. They link algae, fish, palms, and humans in a 4.5-billion-year history, and extend that history through geochemical cycles into our oceans and deserts. Yet in the geological age of humankind, life has fallen into renewed disarray. As Stefan Helmreich (2016) writes, this destabilization brings about an intrinsic concern with the extremes and limits of life. Essential, finite, limiting, and squandered with detrimental effects, phosphorus, life’s limiting factor, is a chemical prism onto life in the Anthropocene.

At least since Justus von Liebig’s times, the limiting factor has been in the service of growth, an impediment that required removal for development to continue. Yet at a time when the ultimate limiting factor to life is the underbelly of growth, excessive waste, and the inability of our ecosystems to absorb it, the elemental limiting factor can attune us to the fragility and connectedness of all socio-natural assemblages. Here the bottleneck offers an opportunity for conscious restraint, redistribution, and sustainable management of resources. With the dictatorship gone, Gabès is slowly being remediated, but, globally, phosphorous is washed into our water systems at an unprecedented speed. Escalated by warming oceans, deadzones are spreading. In their expansion, they exemplify that life in the anthropocene is no longer only limited by its chemical bottleneck, phosphorous, but by chemical excess.