The team took a holistic, ocean-basin-scale approach to the problem, analyzing the distributions of eight dissolved trace metals across the Atlantic. Rather than treating each metal as a unique geochemical puzzle governed by its own idiosyncratic chemistry, they asked how much of the observed variability could be explained by the large-scale movement of water masses, the vast parcels of water that form in high latitudes, sink, and spread through the deep ocean over centuries. Their conclusion: transport through water masses formed in high latitudes can explain between 60 and 90 percent of dissolved trace metal distributions throughout the Atlantic interior, and more than 75 percent of the total metal inventories held within the ocean interior.

This finding reframes how scientists think about marine metal cycling. Trace metals behave very differently from one another in seawater. Iron is notoriously scarce at the surface and rapidly scavenged onto sinking particles. Manganese is sensitive to redox conditions and oxidation. Cadmium tracks phosphate-like nutrient cycling, while lead carries the historical fingerprint of industrial pollution. Given these distinctive geochemical behaviors, one might expect each metal to be controlled by a unique combination of local sources and sinks. Instead, the study demonstrates that once the starting concentrations of these metals are set at their formation regions, the grand conveyor of oceanic circulation does most of the work of distributing them across the basin.

The methodology behind this result is as important as the finding itself. The researchers used water mass analysis, a technique that decomposes any sample of seawater into contributions from its source water masses, each identified by characteristic temperature and salinity signatures formed at the ocean surface in high latitudes. By combining these fractional contributions with the metal concentrations measured in each endmember, they could predict the baseline distribution of each trace metal throughout the Atlantic at high spatial resolution. The agreement between these predictions and observed concentrations allowed them to quantify, for the first time on an ocean scale, exactly how much of the metal distribution is inherited from circulation and how much is added or removed by processes acting along the way.

That residual signal, the gap between what circulation alone predicts and what is actually measured, tells its own story. The team found that the water mass signatures of trace metals are only slightly modified during their journey through the Atlantic interior, but the modifications that do occur are chemically meaningful and metal-specific. Sinking organic matter, the steady snow of biological particles descending from the sunlit surface, remineralizes at depth and releases certain metals back into solution. This process mainly affects iron, cobalt, nickel, and cadmium, which are incorporated into biological material in the upper ocean and returned to the dissolved pool as the particles decay.

A second process, scavenging, works in the opposite direction. Reactive particle surfaces adsorb dissolved metals and carry them downward, removing them from solution. The study identified scavenging removal as a significant modifier for iron, manganese, cobalt, and lead, the metals with the strongest particle affinity. This loss term partially counteracts the internal source supplied by remineralization, and for iron in particular, the balance between the two processes has long been recognized as one of the central tensions in marine geochemistry. The new quantification places these competing effects in a basin-wide, circulation-based framework, showing that they act as refinements on a distribution that is fundamentally set by water mass transport.

A third driver leaves its mark in specific locations: hydrothermal inputs. Where seawater circulates through the hot basalt of mid-ocean ridge systems and re-emerges through hydrothermal vents, it carries dissolved metals picked up from the crust. The study found that these inputs measurably modify the distributions of iron and manganese, adding localized enrichment to the baseline pattern predicted by circulation alone. While hydrothermal venting has often been discussed as a potentially major source of iron to the deep ocean, the new analysis places it in context as a secondary modifier rather than the dominant control on basin-scale distributions.

The implications of this work extend well beyond descriptive oceanography. Trace metals, especially iron, limit phytoplankton growth across vast regions of the ocean, and phytoplankton absorb carbon dioxide as they photosynthesize, forming the biological pump that transfers carbon from the atmosphere into the deep sea. If the distribution of metals is largely dictated by circulation and the concentrations established in high-latitude source regions, then any climate-driven change to those endmembers or to the relative contributions of different water masses could ripple through the entire system. Warming, altered sea ice cover, and changing ventilation patterns in the North Atlantic and Southern Ocean could therefore perturb downstream metal inventories across the basin, with consequences for ocean productivity and the efficiency of the ocean carbon pump.

This sensitivity makes the study’s predictive framework particularly timely. Because the approach can generate baseline trace metal distributions at high spatial resolution from water mass data, it offers a way to identify where observed metal concentrations deviate from expectations, flagging regions where unusual sources or removal processes are at work. It also provides a benchmark against which ocean models can be tested, helping to improve the representation of metal cycling in Earth system simulations used to project future climate. As observational programs such as GEOTRACES have built up a global picture of marine metal distributions, the challenge has shifted from describing patterns to explaining and predicting them, and this study represents a significant step in that direction.

What emerges from the analysis is a picture of the Atlantic’s trace metal inventory as a system with a dominant engine and a set of fine-tuning mechanisms. The engine is the global overturning circulation, which stamps the chemical signature of high-latitude surface waters onto the deep ocean and carries it across the basin. The fine-tuning comes from remineralization, scavenging, and hydrothermal venting, each leaving its characteristic imprint on particular metals. The authors emphasize that despite the distinctive geochemical behaviors of the eight metals assessed, large-scale oceanic circulation plays the decisive role in determining global distributions once water mass endmember concentrations are set. In an ocean facing rapid environmental change, understanding which levers move these essential micronutrients, and how strongly, has never mattered more for anticipating the future of marine life and the carbon cycle it sustains.

Subject of Research: Controls on dissolved trace metal distributions in the Atlantic Ocean

Article Title: Distinct drivers control trace metal distributions through the Atlantic Ocean

Article References: Chen, X.-G., Tagliabue, A., & Achterberg, E. P. (2026). Distinct drivers control trace metal distributions through the Atlantic Ocean. Communications Earth & Environment. https://doi.org/10.1038/s43247-026-04145-z

Image Credits: AI Generated

DOI: 10.1038/s43247-026-04145-z

Keywords: trace metals, Atlantic Ocean, ocean circulation, water masses, iron, marine biogeochemistry, scavenging, remineralization, hydrothermal vents, ocean carbon pump, phytoplankton, climate change

Central to the significance of this research is the concept of biomass – the cumulative mass of living organisms within an ecosystem – which encapsulates essential ecological traits not readily deduced from biodiversity counts alone. While past studies have meticulously chronicled species richness and niche diversity, the quantification of biomass over geological time had remained an elusive, unmet challenge despite its crucial role as an indicator of ecosystem productivity and ecological energy flow. Pulkit Singh, lead author and postdoctoral scholar in Earth and Planetary Sciences at Stanford’s Doerr School of Sustainability, undertook this enormous endeavor to fill this knowledge gap, painstakingly compiling data from thousands of marine rock samples that preserve skeletal remnants, acting as a tangible proxy for marine life’s historical abundance.

The methodology depended primarily on petrographic point-counting, a painstaking lab technique involving the preparation of ultra-thin slices of limestone that allow scientists to peer through and quantify the proportion of shell material under a microscope. This technique, although time-consuming, is vital for accurately documenting the percentage of skeletal content within rock layers formed over disparate geologic periods. The researchers’ database encompasses over 7,700 samples drawn from global marine limestone outcrops, allowing a statistically robust reconstruction of biomass fluctuations across diverse paleoenvironments spanning the Phanerozoic eon.

The fossil record from the Cambrian period, which marks the dawn of modern animal life approximately 540 million years ago, indicates a modest presence of skeletal material, with less than 10 percent of rock samples comprising shells. This coincides with the explosive Cambrian diversification event, a biological renaissance during which marine ecosystems became increasingly complex and varied. Over the ensuing Ordovician Period, shell biomass experienced a marked increase, paralleled by the emergence and radiation of calcifying sponges, echinoderms—including precursors of starfish—and a myriad of arthropods such as trilobites. This evolution of shell-producing taxa reflects not only an increase in diversity but also a rising contribution to ecosystem biomass.

For nearly 230 million years following these early Cambrian and Ordovician blooms, marine shelly biomass remained robust, often exceeding 20 percent by volume in the rock record. Yet this sustained abundance was punctuated by profound declines linked to the planet’s major extinction pulses. The Late Devonian extinction events brought a significant reduction in shell prevalence about 375 to 360 million years ago, an ecological wrench that dramatically rearranged marine communities and diminished their biomass. The most severe decimation, however, occurred during the Permian-Triassic “Great Dying” roughly 250 million years ago, a cataclysmic extinction episode that caused skeletal abundance to nosedive to a mere 3 percent of rock volume, reflecting near-total system collapse in marine ecosystems.

Remarkably, post-extinction recovery phases revealed a resilience in oceanic life. During the Mesozoic and Cenozoic eras, marine biomass rebounded vigorously, with the rock record showing shell content climbing to over 40 percent, particularly fueled by the evolutionary success of mollusks and reef-building corals. Notably, secondary mass extinctions—such as the end-Triassic and end-Cretaceous events—caused sharp but transient drops in marine biomass that quickly rebounded. These patterns illustrate a general trend of biomass expansion, reinforcing the interconnectedness of evolutionary innovation, ecological energy utilization, and ecosystem productivity.

Crucially, the researchers addressed pivotal methodological concerns that could confound interpretations of shifting skeletal content. They rigorously tested whether observed biomass increases were artifacts of sampling biases or ecological factors like predator-prey dynamics. By stratifying data across environmental gradients such as water depth, paleolatitude, and continental configurations, the team demonstrated consistent biomass trends irrespective of these variables. This meticulous cross-validation confirms that the long-term patterns identified are genuine biological signals, rather than noise introduced by geological or sampling variability.

The evolutionary drivers underlying this biomass rise lie in the increasing complexity and specialization of marine life forms over geological time. Specialized species exploit ecological niches more effectively, enabling more efficient energy capture and nutrient cycling within marine food webs. Phytoplankton serve as primary producers, transforming solar energy into organic matter, while diverse decomposers recycle nutrients back into the system, sustaining higher trophic levels. This enhanced ecosystem efficiency translates into larger, more productive biological communities capable of sustaining greater biomass and indicative of healthy ocean systems.

While the fossil record extends this hopeful narrative over deep time, the present and near future paint a more cautionary picture. The Anthropocene epoch, defined by rapid and widespread human impact, is marked by events such as fertilizer runoff, overfishing, ocean acidification, and habitat destruction that pose severe threats to marine biodiversity. Scientists widely recognize this as a sixth mass extinction, driven by anthropogenic forces operating on a scale and pace unmatched in geological history. This contemporary loss of biodiversity carries the ominous potential to erode marine biomass in real time, with cascading effects on ocean productivity and planetary health.

The Stanford team emphasizes the critical linkage demonstrated between biodiversity and biomass, highlighting that reductions in species richness may suppress productivity over geological timescales. This insight underscores the broader implications of biodiversity conservation, as maintaining species diversity is foundational not only to ecological resilience but also to sustaining the flow of ecosystem services upon which humanity depends. As Jonathan Payne, senior author and esteemed professor at Stanford, notes, understanding these macroevolutionary relationships helps inform strategies to safeguard ecosystem function amid accelerating environmental change.

By bridging paleobiology, geology, and ecology, this research offers a transformative lens on Earth’s marine biosphere, revealing how the intertwined evolution of biomass and biodiversity has shaped ocean life through epochs of triumph and tragedy. It invites us to consider how current human actions will be recorded—and felt—across future chapters of Earth’s biological history, while reinforcing the imperative of stewardship in preserving the ocean’s ancient and vital legacy.

Subject of Research: Marine biomass and biodiversity changes across the Phanerozoic eon
Article Title: Macroevolutionary coupling of marine biomass and biodiversity across the Phanerozoic
News Publication Date: 25-Jun-2025
Web References: http://dx.doi.org/10.1016/j.cub.2025.06.006
Keywords: Marine biology, Earth sciences, Evolution, Fossils, Paleobiology, Geologic periods