Anthrobiogeochemical Cycles

Biogeochemical cycles concern the distinct pathways of chemical substances through the Earth’s surface reservoirs, that make up a global flow across the biosphere, the hydrosphere, the atmosphere, the cryosphere, and the uppermost part of the lithosphere. Over the course of the last century, human activities have started to exert a tremendous influence on these chemical fluxes, such that they would now be more accurately called anthrobiogeochemical cycles. Indeed, this term has been used before, but in the more limited context of describing only the human modification of metal cycles through mining and manufacturing.

But today, we face changes whose origins and effects do not seem so neatly limited to any single domain of human craft or trade. A prominent example of anthropogenic disruption of geochemical cycles is the alteration of the nitrogen and phosphorous cycles. With the invention of the Haber-Bosch process in the early twentieth century, the artificial fixation of atmospheric nitrogen to synthesize ammonia on an industrial scale has led to an entirely new fertilization regime in agricultural production, which in turn has contributed to the exponential growth of the world’s population ever since.

Or take instead the global carbon cycle, whose alteration through the burning of fossil fuels, land use change, and cement production is causing the atmosphere to warm, ice sheets to melt, sea levels to rise, and oceans to acidify. The carbon cycle holds special importance for designating a clear-cut Anthropocene signal. Direct analyses of the air trapped in polar ice reveal a rise in CO₂ concentration already in the late eighteenth century, coinciding with some decisive improvements made to the steam engine. The combustion of coal to power these engines—the very engines, in the common metaphor, of the industrial revolution—has already released detectable quantities of fossil carbon. Increases in the atmospheric accumulation of carbon dioxide and methane, however, have been dramatically accelerating since around the mid-twentieth century with the onset of the “Great Acceleration” and the tapping into ever more reservoirs of coal, oil, and gas.

Not coincidentally, the scientific conceptualization and study of the carbon cycle followed these developments. Fossil carbon has an isotopic fingerprint of the long-dead plants and animals that these fuels originally derive from (the so-called Suess effect). Elaborating and quantifying this fingerprint was part of the scientific proof, and in that way part of the growing “self-awareness,” of the planetary impact that an industrialized humanity has on the Earth system. Another example for a more comprehensive understanding of the system-wide disruption of human powers was the research undertaken in the 1980s on the global effects of a thermonuclear war. It triggered a more substantial engagement with global change studies that from the assessment of atmospheric consequences of nuclear detonations extended to research on the whole biosphere and the functioning of the Earth system.

As this dossier makes clear, the onset of the Anthropocene did more or less co-evolve with the emergence of the epistemic and technical means of registering and understanding it. Isotope chemistry and nuclear science, (paleo)climate science and the study of biogeochemical cycles across the Earth—now viewed as a system—all belong to a converging field of modern geoscience whose methods and explanatory rigor directly fed into today’s toolbox of chronostratigraphy.

The human alteration of biogeochemical cycles through the mobilization of chemical elements for the purpose of generating and powering the technosphere’s industrial and agro-industrial mode of operation is, in fact, key to understanding the geohistorical importance of the current situation. The study of these cycles answers fundamental questions of the current geohistorical crisis: where it all started, where it is leading to, and what the strategies are to revert the dangerous march of the Great Acceleration by actively closing the anthrobiogeochemical cycles.