Imagine trying to understand how Earth learned to breathe. Not metaphorically, but literally: how did our planet's oceans and atmosphere accumulate the oxygen that complex life, including us, desperately needs? Scientists have been piecing together this puzzle for decades, but they've been missing a crucial tool. Now, researchers from Germany have discovered that a little-known element called tungsten might hold the key to reading Earth's ancient oxygen levels, locked away in seafloor sediments like messages in bottles sent from the distant past.

This matters more than you might think. Understanding when and how Earth's oceans became oxygenated helps us grasp not just our own origins, but also guides our search for life on other planets and helps us predict how ocean chemistry might respond to modern climate change.

The Detective Element Nobody Expected

Tungsten doesn't get much attention. It's best known for light bulb filaments and industrial tools. But in ocean chemistry, tungsten behaves like a highly sensitive recorder, documenting oxygen levels with remarkable precision.

Here's how it works. Tungsten dissolved in seawater gets trapped by manganese oxide minerals that form on the seafloor, but only when oxygen is present. Think of manganese oxides as sticky traps that only work when the ocean has enough oxygen. When oxygen disappears, these traps dissolve and tungsten escapes back into the water. Even more remarkably, tungsten comes in different isotopic flavors (slightly different atomic weights), and the seafloor sediments preferentially capture certain isotopes depending on the chemical conditions.

The research team, working primarily from institutions in Cologne, Kiel, Hamburg, and Münster, analyzed sediment cores from locations ranging from the oxygen-starved depths of the Gulf of California to well-oxygenated basins across the Pacific, Atlantic, and Indian Oceans. What they found was surprising and elegant.

Following Tungsten From Rivers to the Deep

Every year, rivers carry about 17 million moles of tungsten from weathered rocks into the ocean. That might sound like a lot, but dissolved in the entire ocean, tungsten exists in vanishingly small concentrations, measured in picomoles (trillionths of a mole per liter). Yet this scarcity makes tungsten an even better detective. Small changes in its behavior reveal large changes in ocean chemistry.

The team discovered that tungsten's fate in the ocean is almost entirely controlled by manganese. Where manganese oxide minerals accumulate on the seafloor (which only happens in oxygenated conditions), tungsten gets locked away. Where oxygen vanishes, both manganese and tungsten stay dissolved in the water.

This relationship is remarkably specific. The researchers found virtually no correlation between tungsten burial and organic matter, iron minerals, or other common sediment components. Only manganese mattered. This exclusivity makes tungsten uniquely useful as an oxygen indicator.

Tales From Three Sediment Cores

The study examined three sediment cores from the Guaymas Basin in the Gulf of California, each telling a different story about oxygen and tungsten.

The first core came from an oxygenated basin floor about 2,000 meters deep, where manganese-rich sediments had accumulated. Here, tungsten concentrations were elevated near the surface but decreased with depth. The pattern revealed a dynamic process: as sediments were buried and oxygen levels changed within the seafloor layers, tungsten moved around, eventually settling into stable patterns that recorded the burial history.

The second core came from the oxygen minimum zone, a region between 500 and 1,000 meters deep where oxygen is nearly absent. Here, despite high concentrations of iron, tungsten showed no enrichment at all. The sediments contained only the tungsten that came from eroded continental rocks, with no additional accumulation from seawater. This confirmed that without oxygen to form manganese oxides, tungsten simply doesn't get trapped.

The third core came from near hydrothermal vents, where hot, mineral-rich fluids seep from the seafloor. These environments are rich in iron and other metals. Yet even here, tungsten concentrations were actually lower than in normal sediments. Hydrothermal systems, despite their chemical intensity, don't trap tungsten effectively.

The Global Picture Emerges

Expanding beyond the Gulf of California, the researchers analyzed 47 surface sediment samples from ocean basins around the world. The global survey revealed a consistent pattern: deep-ocean sediments rich in manganese showed substantial tungsten enrichment, while sediments from oxygen-poor environments like the Black Sea showed none.

Pacific Ocean sediments exhibited the highest tungsten enrichment, reaching up to 425 times the concentration found in continental rocks at one North Pacific site. This makes sense because the Pacific has vast fields of manganese nodules, potato-sized lumps of manganese and iron oxides that carpet huge areas of the seafloor.

The isotopic composition of tungsten in these sediments also told a story. The researchers measured tungsten isotope ratios (specifically, the ratio of tungsten-186 to tungsten-184) and found that sediments showed heavier isotopic signatures than would be expected from simple adsorption onto manganese oxides. This suggests that after tungsten initially sticks to manganese minerals, it undergoes further processing within the sediment, exchanging between dissolved and solid forms, with heavier isotopes preferentially remaining in the solid phase.

Revising the Ocean's Tungsten Budget

Armed with these new data, the team recalculated the ocean's tungsten budget. Here's what flows in and out of the ocean each year:

Inputs: Rivers contribute about 17 million moles of tungsten annually. Smaller amounts come from hydrothermal vents and from tungsten recycling out of seafloor sediments.

Outputs: The team calculated that manganese-oxide-rich sediments bury approximately 22 million moles of tungsten per year. Of this, manganese nodules and crusts account for about 2.6 million moles, while dispersed manganese oxide particles in regular seafloor sediments bury about 19.6 million moles.

These numbers reveal a problem. The known inputs don't quite balance the outputs. This suggests that scientists have been underestimating how much tungsten gets recycled from sediments back into the ocean. As manganese oxides dissolve and reform in the upper layers of sediment, they release tungsten back into bottom waters, creating an additional source that previous studies hadn't fully accounted for.

Why Manganese Matters for Earth's Oxygen History

Manganese plays a starring role in this story because it's exquisitely sensitive to oxygen. Manganese dissolves easily when oxygen is absent but rapidly oxidizes and precipitates when even small amounts of oxygen appear. This sensitivity makes manganese accumulation in ancient sediments a classic indicator that oxygen was present.

But there's a limitation. Manganese has only one stable isotope, so there's no manganese isotope system to track how much manganese was being buried globally at different times in Earth's history. This is where tungsten becomes invaluable.

Because tungsten burial is so tightly coupled to manganese burial, and because tungsten has multiple isotopes that fractionate in predictable ways, the tungsten isotope system can potentially track ancient manganese burial rates. And since manganese burial tracks ocean oxygenation, tungsten isotopes become an indirect but powerful proxy for ancient oxygen levels.

A Window Into Deep Time

The implications extend far beyond the modern ocean. Earth's oxygen levels have changed dramatically over geological time. The atmosphere was nearly oxygen-free for the first two billion years of Earth's history. Then, in a series of "oxygenation events," oxygen levels rose episodically, eventually reaching modern levels that sustain complex animal life.

These oxygenation events left chemical fingerprints in sedimentary rocks. Scientists study these fingerprints using various geochemical proxies, each with strengths and limitations. Molybdenum isotopes, for example, are widely used but complicated by the fact that molybdenum gets trapped by both manganese oxides (under oxic conditions) and sulfide minerals (under oxygen-poor but sulfide-rich conditions).

Tungsten is simpler. It couples almost exclusively with manganese, avoiding the complications that affect other elements. This simplicity could make tungsten isotopes especially useful for studying oxygenation events in Earth's early history, when ocean chemistry was very different from today.

The research team notes that previous studies have already begun exploring tungsten isotopes in ancient rocks spanning from the Archean Eon (over 2.5 billion years ago) to the late Miocene (about 5 million years ago). These pioneering efforts showed promise, but a comprehensive understanding of how tungsten behaves in modern oceans was needed to properly interpret the ancient signals. This study provides that foundation.

The Path Forward

While the findings are compelling, the researchers emphasize that more work is needed before tungsten isotopes can become a routine tool for paleoceanography (the study of ancient oceans).

First, scientists need to better understand how tungsten isotopes fractionate across different types of iron and manganese oxide minerals. The study revealed that tungsten isotope ratios in sediments differ from what laboratory experiments predict for simple adsorption. This suggests that mineral transformations during sediment burial alter the isotope signal. Understanding these processes in detail will improve interpretations of ancient records.

Second, more studies of sediment cores from the deep ocean are needed, particularly from locations with high manganese accumulation. The Gulf of California cores provided crucial insights into continental margin environments, but open-ocean settings where manganese nodules form may show different patterns.

Third, researchers need to identify which ancient sedimentary rocks best preserve the seawater tungsten isotope signal. Some rocks may have had their original signal altered by heat, pressure, or chemical reactions long after they formed.

Why This Matters Today

You might wonder why reconstructing ancient ocean oxygen levels matters for our modern world. The reasons are both scientific and practical.

Scientifically, understanding Earth's oxygenation history addresses fundamental questions about life's evolution. Complex animals require oxygen. When did oxygen levels rise high enough to support animal life? How stable were those oxygen levels? Did oxygen crashes contribute to mass extinctions? Tungsten isotopes could help answer these questions.

Practically, modern oceans are experiencing expanding oxygen minimum zones due to climate change and nutrient pollution. As waters warm, they hold less oxygen, and as excess nutrients fuel algal blooms, decomposing organic matter consumes oxygen. Understanding how manganese and associated elements behaved during past oxygenation changes could help predict how ocean chemistry will respond to ongoing deoxygenation.

Additionally, the search for life beyond Earth focuses heavily on oxygen as a biosignature. Telescopes are being designed to detect oxygen in the atmospheres of distant planets. But how much oxygen is necessary for complex life? How quickly can oxygen levels change? Earth's oxygenation history, revealed partly through proxies like tungsten isotopes, provides the only empirical data set we have to answer these questions.

An Element Reveals Its Secrets

What makes this research particularly elegant is how an element previously overlooked in oceanography turns out to be one of the most specific recorders of ocean oxygenation. While other elements provide valuable information, they often respond to multiple environmental factors simultaneously, making their signals difficult to interpret. Tungsten's tight coupling with manganese, and only manganese, gives it unusual clarity.

The research also highlights how scientific understanding progresses through systematic observation. By analyzing sediments from environments ranging from oxygen-rich to oxygen-free, from hydrothermal vents to quiet abyssal plains, from coastal margins to mid-ocean basins, the team built a comprehensive picture of tungsten behavior that no single location could provide.

The samples themselves tell stories. Each sediment core is a archive of environmental conditions, with layers representing years, decades, or longer periods of accumulation. Reading these archives requires patience, precision, and sophisticated analytical techniques. The researchers used mass spectrometers that can detect isotopic differences of a few parts per thousand, separating tungsten from interfering elements through multiple chemical purification steps.

Looking Ahead

The tungsten isotope system joins a growing toolkit of geochemical proxies for reconstructing Earth's environmental history. Each proxy has its niche. Together, they allow scientists to cross-check interpretations and build robust reconstructions of past conditions.

For tungsten, the next steps are clear but challenging. Researchers need to find sedimentary archives that span major events in Earth's oxygenation history and are well preserved enough to retain original tungsten isotope signals. They need to continue refining their understanding of how tungsten isotopes fractionate during sediment formation and burial. And they need to build comprehensive models of the global tungsten cycle in different ocean states.

The payoff could be substantial: a new window into one of Earth's most important transitions, from a nearly oxygen-free world to one where oxygen enabled the explosion of complex life forms. That transformation, written in isotopes of an obscure element trapped in manganese minerals on the seafloor, might finally yield its secrets.

In the meantime, every time you see tungsten mentioned—perhaps in reference to light bulbs or drill bits—you might remember that this tough, high-melting-point metal is also telling us, in whispers measured in isotopic ratios, about the very air we breathe and how Earth learned to make it.

Publication Details

Published online: April 7, 2025
Journal: Earth and Planetary Science Letters
Publisher: Elsevier B.V.
DOI: https://doi.org/10.1016/j.epsl.2025.119346

Credit and Disclaimer

This article is based on original research published in Earth and Planetary Science Letters by scientists from the University of Cologne, GEOMAR Helmholtz Centre for Ocean Research Kiel, University of Hamburg, and University of Münster in Germany. The content has been adapted for general audiences while maintaining complete scientific accuracy. Readers are encouraged to consult the full research article for comprehensive technical details, complete data tables, analytical methods, and supplementary information via the DOI link provided above. All scientific findings, data, and conclusions presented here are derived directly from the original publication, and full credit belongs to the research team and their institutions.