The confusion stems from the fact that ‘groundwater age’ is not one quantity but three. The first is the Peak Age, sometimes called the piston-flow or advective age, which describes how long it takes the centre of a concentration front — the peak of a tracer pulse — to travel a given distance. The second is the Mean Residence Time, the average age of all the water molecules in a sample, equivalent to the centre of mass of the age distribution. The third is the Tracer Age, the number actually calculated from a measured tracer concentration using standard formulas such as the conventional radiocarbon age or the tritium–helium age. In a perfectly ordered, dispersion-free aquifer these three values coincide. In the real world, where groundwater always undergoes at least some dispersive mixing, they diverge — sometimes dramatically.

Suckow’s analysis rests on the one-dimensional advection–dispersion equation, the workhorse model of solute transport, in which the balance between advective flow and dispersive spreading is captured by a single dimensionless quantity: the Peclet number. A high Peclet number means advection dominates and the water moves like a piston; a low Peclet number means dispersion smears everything extensively. Drawing on the classic field-data review by Gelhar and colleagues, the study notes that Peclet numbers observed in aquifers span an enormous range, from about 0.1 to 1000, with a best estimate near 10. When Suckow computed tracer output concentrations across that range, the consequences were sobering. For a Peclet number of 0.1, the Mean Residence Time exceeds the Peak Age by a factor of sixty; even at a Peclet number of 1, the gap is still a factor of six.

The behaviour of individual tracers adds further layers of complexity. For radioactive tracers with a constant atmospheric input — a reasonable approximation for argon-39, carbon-14 and krypton-81 — the calculated Tracer Age starts out equal to the Mean Residence Time and only gradually approaches the Peak Age as the water ages toward the tracer’s detection limit. For helium-4, a stable isotope produced underground at a roughly constant rate by the decay of uranium and thorium, the situation is different again: because helium mixes linearly rather than exponentially, its Tracer Age always reflects the Mean Residence Time and never the advective velocity. The practical result is that a single water sample, measured with a suite of modern tracers, will yield systematically different ages that increase in the order of tracer half-life: tritium, then argon-39, then carbon-14, then krypton-81, then helium-4.

Some of these discrepancies are large enough to rewrite interpretations of published datasets. The study highlights that reported contradictions between carbon-14 ages and helium-4 ages in major aquifers — differences previously explained by invoking a mysterious ‘crustal flux’ of helium rising from deep strata — may simply reflect low Peclet numbers. In the Great Artesian Basin of Australia, Torgersen and Clarke reported in 1985 that helium-based ages exceeded hydrologic age estimates by a factor of seventy-four, remarkably close to the factor of sixty that pure dispersion produces at a Peclet number of 0.1. Suckow is careful not to dismiss crustal degassing as a real phenomenon, but points out that such an external flux could only be quantified once the Peclet number is known — and under low-Peclet conditions the inferred flux would be substantially smaller than previously claimed.

The timing of this theoretical advance is no accident. For decades, the tracers needed to test these ideas simultaneously simply could not be measured on the same sample. That changed with the advent of Atom Trap Trace Analysis, or ATTA, a laser-based technique developed for krypton-81 and argon-39 that has turned isotopes once considered unmeasurable into routine tools. Before ATTA, only around 300 argon-39 groundwater measurements existed worldwide; today the two ATTA laboratories, in Hefei, China and Heidelberg, Germany, each process on the order of a hundred samples per year. Combined with the established workhorses tritium–helium, radiocarbon and chlorine-36, and supplemented by new stable noble-gas methods, researchers can now assemble continuous groundwater dating records spanning from a few decades to more than a million years — precisely the range needed to exploit Suckow’s framework.

The practical payoff is a new method for determining Peclet numbers on time scales of centuries to many millennia, something field tracer tests and contaminant plume studies — typically confined to transport distances of tens to hundreds of metres — have never been able to deliver. The logic is elegant: because each tracer’s age responds differently to dispersion depending on its half-life, the spread of Tracer Ages measured along a flow path encodes the Peclet number itself. For Peclet numbers below about 2, the differences between tracers become large and systematic; above 2, all tracers converge on the same age. By fitting the advection–dispersion equation directly to multi-tracer data from a series of wells, both the advective velocity and the Peclet number can be recovered simultaneously. Suckow demonstrates the approach on two published datasets — the Guarani aquifer in South America and the western Great Artesian Basin in Australia — deriving Peclet numbers of roughly 0.2 and 0.1, and correspondingly higher flow velocities than the original studies had estimated, a result with direct consequences for groundwater resource management in arid regions.

The findings also cast new light on palaeoclimate records preserved in groundwater. Noble-gas palaeotemperatures dissolved in recharging water have long been used to reconstruct past climates, and multiple studies report that land temperatures during the Last Glacial Maximum were about six degrees Celsius cooler than today. But dispersion acts as a low-pass filter on any signal carried by groundwater. Suckow’s calculations show that at Peclet numbers of 10 or less, temporal variations in the palaeotemperature record are progressively ironed out, and the reconstructed glacial cooling becomes biased warm — by nearly a degree at a Peclet number of 10, and potentially by several degrees at lower values. The widespread six-degree figure, in other words, may partly be an artefact of dispersive smoothing, and the true Last Glacial Maximum cooling on land could have been colder than commonly stated. The study also suggests that groundwater realistically preserves climate signals only up to about 100,000 years, even under favourable transport conditions.

For practitioners, the message is a call to methodological reform. Tracer Ages, the study concludes, should only be interpreted as advective or piston-flow ages when the Peclet number is known to exceed 2 — a condition rarely demonstrated in historical studies. Tritium–helium ages deserve particular caution: for all realistic dispersive conditions with Peclet numbers below 10, they do not represent the movement of a concentration front, as generally assumed, but instead follow or exceed the Mean Residence Time before levelling off with distance. The strongest recommendation is to measure as many tracers with different time scales as possible on every sample along a flow path, since no single tracer can disentangle velocity from dispersion. In an era when aquifers supply drinking water to billions and host critical infrastructure from nuclear waste repositories to carbon storage sites, knowing how water — and whatever it carries — actually moves underground has never mattered more. What was once dismissed as pedantic quibbling over definitions now looks like the key to one of hydrogeology’s oldest unsolved problems.

Subject of Research: The effect of dispersion on tracer-derived groundwater ages and its use for deriving Peclet numbers in large-scale groundwater transport

Article Title: The effect of dispersion on the “age” of groundwater calculated from environmental tracers allows a novel way to derive Peclet numbers for large-scale groundwater transport

Article References: Suckow, A. (2026). The effect of dispersion on the “age” of groundwater calculated from environmental tracers allows a novel way to derive Peclet numbers for large-scale groundwater transport. Hydrogeology Journal. https://doi.org/10.1007/s10040-026-03156-6

Image Credits: AI Generated

DOI: 10.1007/s10040-026-03156-6

Keywords: groundwater, environmental tracers, dispersion, Peclet number, hydrogeology, radiocarbon dating, krypton-81, argon-39, helium-4, advection, Mean Residence Time, paleoclimate

The research, published in the journal Society and Animals under the title The Origins of Bear Baiting: Evidence from Medieval England and France, represents the first detailed synthesis of archaeological and documentary evidence for bears in medieval Britain. Its central conclusion is striking: the practice of importing live bears and exhibiting them in fights with dogs appears to have intensified dramatically in the wake of the Norman Conquest of 1066. Before that date, the archaeological record for live bears in England is essentially empty. Immediately afterwards, bear remains begin to appear at sites in London and North Yorkshire, suggesting that the new Norman elite brought with them both the animals and the appetite for spectacle that had characterised aristocratic entertainments on the continent.

Brown bears were once native to Great Britain, but the species had already disappeared from the island by the Roman period. Every bear that appeared in a medieval English arena, market square or royal court therefore had to be transported from continental Europe, at considerable expense. The logistics alone are remarkable. Captured animals would have needed to be moved across hundreds of kilometres, ferried across the Channel, and then sustained on journeys that could take them as far as Colchester in the south of England or Carlisle near the Scottish border, both of which have yielded confirmed medieval bear remains. The costs of importation, travel and ongoing sustenance imply that bears were valuable commodities, owned and displayed by people with significant resources.

Dr Liam Lewis of Cardiff University’s School of Global Humanities, who led the research, explained that the convergence of different strands of evidence is what makes the new findings so conclusive. The combination of literary, archival, archaeological and visual analysis allows researchers to state definitively that bear baiting was an established activity in England by the twelfth century. Lewis noted that the absence of bear remains from live animals in England prior to the Norman Conquest, and their sudden appearance in London and North Yorkshire in its immediate aftermath, points to a real increase in the importation of live bears following the conquest. The timing is too consistent to be coincidental, and it reframes the blood sport not as a Tudor novelty but as a Norman import that took root and spread.

What emerges from the study is a picture of bears circulating widely through medieval English society. Literary works, sermons and chronicles frequently mention baiting in connection with marriages, aristocratic pastimes and rowdy public festivities, and historians had generally assumed these references described elite entertainments or literary conveniences. The archaeological evidence tells a different story. Bear bones indicative of live animals have been recovered from a number of English towns, indicating that ordinary townspeople encountered bears regularly and that baiting functioned as popular entertainment for the general public, not merely as a diversion of the nobility. For a town to host a bear, someone had to pay for the animal’s transport, feeding and upkeep, and someone had to profit from exhibiting it, a commercial dynamic that anticipates the professional bear gardens of the later middle ages.

Material evidence for the earliest phase of this trade comes from a network of ten sites across England and France where bear bones from the medieval period have been identified. Among the most significant new results is a radiocarbon date obtained on a bear shoulder blade, or scapula, recovered from Richmond in North Yorkshire. The bone, found in 1864 and held in the collections of the Yorkshire Museum, was sampled in collaboration with the museum and dated by Dr Thibaut Devièse at the University of Oxford as part of the Natural Environment Research Council funded Decline of the Bear project, led by Professor Hannah O’Regan of the University of Nottingham. The result was unexpectedly late, placing the animal firmly in the medieval period and demonstrating that bears were present in northern England immediately after the Norman Conquest.

Professor O’Regan emphasised the wider significance of the finding. Bear baiting was an important social and economic activity in early modern England, and the study demonstrates that it has much longer roots than scholars had appreciated. According to O’Regan, this is the first study of the medieval origins of the practice, and the new radiocarbon date on the Richmond bear shows that bears were widespread very early in the medieval period. The research team also surveyed documents such as the Domesday Book, along with other historical records and medieval manuscripts, for references to bears, building a documentary dataset that complements the skeletal evidence and allows the movements and ownership of the animals to be traced through the centuries.

One of the most evocative documentary discoveries concerns Richmond itself. The town appears in one of the earliest known references to a named medieval bearward, the professional keeper responsible for the care and exhibition of a performing bear. The record names Spenellus, a bearward who lived at Richmond in the early 1200s, providing a rare human face for a trade that must otherwise be reconstructed from bones and passing mentions. Bearwards appear increasingly often in later medieval records, leading dancing and fighting bears through towns and fairs, and the Richmond reference shows that this profession, with its distinctive title and its itinerant economy, was already established within a century and a half of the Conquest. For Lewis, the discovery underscores the richness of the documentary record once it is read alongside the archaeology.

The visual record adds a further dimension. Historians have long puzzled over images of dancing and performing bears sketched into the margins of medieval manuscripts, wondering how often ordinary people actually encountered these animals. The new study is the first to combine such imagery systematically with archaeological and documentary sources, and it identifies an even earlier and more famous image: a bear baiting scene depicted in the lower margin of the Bayeux Tapestry, the eleventh century embroidery that narrates the Norman conquest of England. That a baiting scene should appear in a work produced for the Norman elite is consistent with the study’s broader argument that the spectacle arrived in England with the conquerors, embedded in their culture of aristocratic display and public festivity.

The Richmond scapula also carries a lesson about the value of museum collections. The bone lay in storage for more than a century and a half before modern radiocarbon dating revealed its significance, and Lewis argues that the case demonstrates the importance of keeping samples and re-examining old collections, because there is still much more to learn from material gathered by antiquarians in the nineteenth century. As the AHRC funded Box Office Bears project, through which Lewis and O’Regan are jointly investigating the medieval roots of baiting culture, continues, the team expects more bones in museum drawers across Britain and France to yield dates and isotopic signatures that could map the trade in live bears in still finer detail. What is already clear, however, is that the chained bears of Shakespeare’s Bankside had ancestors in the England of William the Conqueror, transported across the sea, carried along the roads of a newly conquered kingdom, and fought before crowds who found in the spectacle a shared, enduring and very medieval form of entertainment.

Baiting spectacles of this kind were not unique to bears. Medieval England also hosted bull baiting and cock fighting, and the same towns that accommodated travelling bears often staged other animal contests, suggesting a broader culture of blood sports in which the bear occupied a particularly prestigious place because of its exotic origins. The need to import every animal from the continent meant that each bear represented a substantial investment, and its survival in the pit mattered economically as well as morally to its keeper.

The study also illustrates how radiocarbon dating can overturn long held assumptions about museum specimens. Bones recovered by antiquarians were frequently catalogued with only vague provenance, and without scientific dating many medieval bear remains could easily have been misassigned to earlier periods when bears were still native to Britain. A precise date on a single scapula was enough to anchor the entire northern distribution of the evidence to the decades following the Conquest.

For archaeologists, the distinction between bones from live animals and those from imported meat or hides is crucial. Remains showing signs of captivity, such as those found in urban contexts far from any plausible wild population, indicate living animals kept for display rather than carcasses traded for their pelts. It is this distinction that allows the ten sites in the study to be read as evidence of a trade in performing bears rather than simply a commerce in animal products, and that gives the documentary references to bearwards their material confirmation.

Subject of Research: The medieval origins of bear baiting and the importation of live brown bears into Norman and later medieval England

Article Title: Bear baiting became more common following Norman invasion

Article References: Bear baiting became more common following Norman invasion. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: bear baiting, Norman Conquest, medieval England, brown bears, radiocarbon dating, Bayeux Tapestry, Domesday Book, bearward, Richmond scapula, Cardiff University, University of Nottingham, medieval archaeology

The institution behind this mobility was the nabo system, the circuit of seasonal imperial camps through which the Liao empire (907–1125) and, in modified form, the Jurchen-led Jin dynasty (1115–1234) conducted much of their politics. Instead of fixing the state in one capital, the emperor moved with his entire government through an annual rhythm of encampments, each staged in a landscape suited to the season. The spring nabo was positioned around the shallow lakes and wetlands of the Songnen Plain in what is now western Jilin Province, where the imperial party fished, hunted waterfowl, received envoys and held feasts. Court chronicles such as the Liaoshi and the Jinshi record both the spectacle and the machinery that sustained it: animals flowed in from state-managed imperial herds, from tribute levied on subordinate tribes and neighboring polities, and through procurement organized by officials who traveled with the court. Historians have long read these passages as evidence of a flexible, multi-channel provisioning economy. What no text could demonstrate is whether that system operated on the ground—inside one camp, in the bones and chemistry of the animals themselves.

Houmingzi, a locality within the spring nabo site complex on the lake margin near Chagan Lake in Qian’an County, supplies that ground truth. Excavated in 2016 by archaeologists from Jilin University and the Jilin Provincial Institute of Cultural Relics and Archaeology, the site sits in one of Northeast China’s most environmentally constrained landscapes: the Songnen Plain is a mosaic of saline-alkaline soils, marshes and grassland whose grazing capacity swings sharply between seasons and years. Radiocarbon dating of the deposit anchors the assemblage within the Liao–Jin era, matching the historical lifetime of the royal spring encampments. The setting drives the study’s central logic. A locality used only seasonally, on a shoreline with limited carrying capacity, could not plausibly have reared the volume of domestic animals represented in its refuse; any such accumulation must represent animals moved in from elsewhere, whether herded alongside the traveling court or dispatched to meet it. The bone deposit therefore reads as a ledger of provisioning rather than a portrait of local herding, and that distinction is what makes it archaeologically powerful.

The first line of evidence was classical zooarchaeology. Every fragment was identified to taxon, abundance was quantified with standard measures such as the number of identified specimens and the minimum number of individuals, and the survival of particular skeletal elements was recorded. Kill-off patterns—the ages at which animals died—were reconstructed from tooth eruption and wear stages and from the fusion timing of limb-bone epiphyses, the standard tools for distinguishing herds managed for meat, milk, traction or breeding. Cut marks, chop marks and other carcass-processing traces were mapped across the bones and screened against taphonomic damage from weathering, carnivore activity and recovery bias. The outcome was unambiguous: mortality profiles and butchery patterns were taxon-specific. Cattle, sheep, horses and pigs were not treated as interchangeable meat units; each species was slaughtered at different ages, processed in different ways and consumed under different conventions, implying that each taxon entered the camp through a distinct logic of supply and use.

The second line of evidence came from the animals’ own chemistry. The team extracted bone collagen and measured its stable carbon and nitrogen isotope ratios, expressed as δ¹³C and δ¹⁵N. Because collagen turns over slowly, bone integrates diet over roughly the final years of an animal’s life, so every measurement preserves a pre-death dietary archive. Carbon isotopes separate two photosynthetic worlds: C₃ plants, the trees, shrubs and cool-season grasses that dominate the region’s natural vegetation, and C₄ plants such as millet, a staple of the Liao–Jin world. Nitrogen isotopes climb with trophic level and can flag foddering on animal by-products or other distinctive feeds. Only collagen that passed strict quality controls—adequate yield and atomic carbon-to-nitrogen ratios within accepted windows—entered the analysis, a safeguard against the diagenetic alteration that can silently corrupt ancient samples. AMS radiocarbon dates, calibrated against the IntCal20 curve, fixed the assemblage chronologically within the era of the royal camps, tying the chemistry to the Liao–Jin period.

The isotope data split the assemblage into two very different groups. The wild animals, few in number but essential as a local reference, broadly reflect the C₃-based environment of the surrounding region, sketching what locally raised fauna should look like. Sheep occupy a comparatively narrow δ¹³C range, a pattern consistent with flocks raised under relatively uniform grazing regimes before they reached the camp. Cattle, horses and pigs behave altogether differently: each of these species shows marked intraspecific variation, with individual animals scattered across the isotopic spectrum. That spread cannot be produced by a single herd on a single pasture under a single feeding strategy. It means individual animals arrived carrying distinct pre-death feeding histories—different pastures, different fodder, plausibly different herder communities. Combined with the species-specific kill-off and processing patterns, the chemistry indicates that different animals were funneled into the camp through different channels and consumed according to different conventions.

Those converging channels are the heart of the finding. At a seasonally occupied lake-margin camp that could not have reared such quantities of livestock itself, animals with divergent carbon isotope signatures almost certainly originated in more than one ecological or management background. The researchers interpret Houmingzi as a point of concentration and consumption: a node where livestock raised elsewhere was gathered to sustain a mobile political center. The inference is structural as well as chemical, because a seasonal camp on the saline-alkaline shores of the Songnen Plain lacked the carrying capacity to supply the cattle, sheep, horses and pigs its deposits contain. The conclusion aligns closely with the historical record, which documents a multi-channel provisioning framework for the Liao court—state herds, tribute from subordinate groups and locally arranged procurement—administered by officials attached to the moving household. The refuse of a single encampment now shows that this framework left a measurable fingerprint in bone.

The study also extends the archaeology of Inner Asian empire into an underexamined setting. Because power in these polities resided in moving assemblies rather than fixed cities, provisioning was spatially separated from production, and the supply systems behind it are notoriously difficult to detect. Most isotopic work on elite provisioning has therefore focused on permanent capitals—among them a recent investigation at medieval Karabalgasun in Mongolia, which used zooarchaeological and isotopic evidence to examine the pastoral provisioning of Uyghur elites in an urban environment. Houmingzi offers the complementary and far rarer case: zooarchaeological and isotopic evidence from within a locality of a mobile royal camp, where the encampment itself, not a walled city, was the seat of power for the season. The results show that even a temporary court sat atop a logistics network capable of assembling and differentiating large volumes of livestock, moving the study of imperial supply from urban centers into the mobile political landscape of the steppe frontier.

The authors are careful about what the evidence cannot yet say. Carbon and nitrogen isotopes record feeding histories rather than birthplaces, so they cannot establish whether a given animal came from imperial herds, a tribute consignment or a market transaction, and the specific origins and supply channels behind the isotopic variation remain unresolved. The wild-fauna sample is also small, leaving the local isotopic baseline broad rather than fine-grained. The way forward is clearly defined: strontium isotope analysis of tooth enamel, which fingerprints the geology of an animal’s home range; sequential sampling of dental tissues, which tracks seasonal movement and dietary change across an individual’s life; and systematic comparison with faunal assemblages from other nabo localities and from the permanent settlements and capitals of the Liao and Jin worlds. Together, these approaches could convert the camp’s differential chemistry into an actual map of supply routes across Northeast China.

Even with those limits, the findings change how a chapter of imperial history can be read. The Khitan and Jurchen courts that moved through the Songnen Plain did not travel light: they carried with them, or summoned to meet them, a hinterland of herders and tribute payers whose animals converged on the lakeshore each spring. At Houmingzi, that hinterland is visibly non-uniform—sheep arrived on one dietary regime, cattle and horses on several, pigs on others—so that every animal carried the chemical record of the routes and management systems that delivered it. In butchered bone and collagen chemistry, archaeologists have recovered the ledger of a state in motion, and with it confirmation that the most sophisticated infrastructure of a nomadic empire may have been the provisioning system that traveled quietly beside it, assembled species by species long before the first imperial pot went on the fire.