Using strontium isotope ratios to try to determine the origin of victims of the transAtlantic slave trade.

Between the fifteenth to nineteenth centuries, at least 12.5 million people were abducted from sub-Saharan Africa and taken as slaves to the Americas, and to a lesser extent Europe, the largest forced migration in Human history. This has had a profound impact on the demographics, economics, and politics of both Africa and the Americas, and while is some ways the process was well-documented (we have, for example, documented records of the voyages of at least 30 079 vessels which were involved in the slave trade, including records of ports they visited and the number of captives they transported), we know very little about the identities of the individuals involved and their actual points of origin.

Recent studies have used genetic information from archaeological remains from the Caribbean, Brazil, North America, St Helena, and South Africa, have had some success in determining the populations from which individuals descended, this cannot tell us where they a person was born or brought up.

Strontium isotopes (specifically the ratio between the isotopes strontium⁸⁷ and strontium⁸⁶) in water are largely determined by bedrock, as well as rainfall and geomorphology, and is taken up and incorporated into biomineralized tissues, such as tooth and bone. Importantly, these ratios remain stable over archaeological timescales, enabling archaeologists to use them to determine the origin of Human and Animal remains, as long as a geological reference map, with the isotope ratios present in appropriate locations, is available. 

In sub-Saharan Africa, strontium isotope ratios have been used to trace the migration routes of large Mammals, and to determine the origin of ivory seized from smugglers, as well as to analyse landscape use by early Hominins, but has been under-used in other spheres, such as historical archaeology, largely because data on strontium isotope ratios are not available for large areas of the continent, and in particular much of West and West-Central Africa, the areas from which the overwhelming majority of slaves were taken to the New World. This is in part due to the high cost associated with carrying out strontium isotope testing over large areas, with the added complication that some parts of the continent are plagued by ongoing conflicts and political instability, making the necessary fieldwork difficult and dangerous.

In a paper published in the journal Nature Communications on 30 December 2024, a team of scientists led by Xueye Wang of the Center for Archaeological Science at Sichuan University and the Anthropology Department at the University of California Santa Cruz, present strontium isotope ratios from 778 new environmental studies from 24 African countries, mostly in West and West-Central Africa, which they combine with 1488 previously published strontium isotope ratios from other studies, to build a more detailed map of strontium isotope ratios across sub-Saharan Africa. These are then compared to ratios obtained from Human remains at two cemeteries in the Americas associated with African slaves, the Anson Street African Burial Ground in Charleston, South Carolina, and the Pretos Novos Cemetery in Rio de Janeiro, Brazil.

Strontium⁸⁷/strontium⁸⁶ ratios in Africa range from 0.70381 to 0.87810, a far higher range than is known from any other continent studied. Some areas have a high proportion of radiogenic strontium⁸⁷, notably those areas with an underlying Archaean bedrock, such as Angola, Zimbabwe, Zambia, western Tanzania, northern South Africa, Côte d'Ivoire, Liberia, Sierra Leone, and southwestern Mali. Other areas have a very low level of strontium⁸⁷, particularly areas of East Africa covered by Mesozoic-Cainozoic volcanic rocks, and areas of South Africa covered by flood basalts, as these tend to generate soils with a high cation exchange capacity and clay content. Strontium ratios are also affected by precipitation levels and elevation, both of which impact the weathering rate of silicate rocks.

Geological map and sampling locations. (a) Simplified geological map. (b) Map showing the environmental sampling locations from this study and previously published work. The sampling locations focused on filling gaps in West Africa, West-Central Africa, and parts of South Africa, covering all major geological units across the African continent south of the Sahara. Wang et al. (2024).

Strontium isotope ratios were analysed for five individuals from the Anson Street African Burial Ground for which genetic analysis had been used to determine a population-of-origin, and five individuals from the Pretos Novos Cemetery, for which this data was not available, but oxygen isotope ratios, which can be used to determine diet, were.

Two of the Anson Street African Burial Ground individuals had previously been determined to be of West-Central African origin, both of which produced strontium isotope ratios consistent with an origin in eastern-central Angola. The remaining three individuals were all determined to be from West Africa by genetic analysis. The first of these produced a strontium isotope ratio which indicates that they could have originated from a wide area, including large regions of Liberia, Côte d’Ivoire, Guinea, Sierra Leone, and Mali. The remaining two individuals showed much higher levels of radiogenic strontium, consistent with having come from either a 100 km stretch of the coast of southern Côte d’Ivoire and Ghana, or from the eastern part of Guinea.

Four of the five individuals from the Pretos Novos Cemetery produced strontium isotope ratios consistent with having come from different regions of Angola or South-East Africa, while the fifth produced a result consistent with having come from parts of Guinea, Nigeria, Cameroon, or South Africa. 

Oxygen isotope ratios suggest that this individual grew up in a region where the main crops were C₄ Plants. This would exclude the 'Rice Coast' of West Africa, which runs from Guinea Bissau through Guinea into western Côte d’Ivoire, or the vegecultural zone of southern West Africa, where the predominant crops are Manioc, Yams, and other C₃ root vegetables, but would include parts of central Nigeria where the main crops are Sorghum and Millet, and parts of northern Cameroon where different areas would have grown Sorghum and Millet or Maize (itself introduced from the Americas by European traders). Potentially, a South African could have also had a diet dominated by C₄ Plants, which are easily grown in many places there, but Wang et al. consider this less likely, given the much larger number of slaves taken from West Africa to Brazil.

The four other individuals from Pretos Novos Cemetery are hypothesized to have come from different parts of Angola based upon strontium isotope ratios. This was supported by the oxygen isotope analysis, which suggests they did not share common dietary habits in early life. This is consistent with the known agricultural practices in Angola at the time, with different regions emphasizing the cultivation of manioc and other root crops, or maize and millet.

Wang et al. are confident that improved groundwater sampling from a wider area of Africa would have the potential to greatly improve our ability to determine the origin of African remains from the New World. With the limited sampling available, they were able to provide approximate locations of origin for ten individuals from two well-studied burial grounds, one in the United States and the other in Brazil, and while their answers cannot be taken as 100% reliable at this stage, none of them contradict data from previous studies, nor do they suggest improbable points of origin for the individuals examined.

There are still some notable gaps in the strontium ratio maps used by Wang et al. most notably Namibia and the Sahel Region. Wang et al. identify these regions as being sparsely populated, and therefore unlikely to have been heavily targeted by slavers. This is probably true for Namibia, where the most habitable areas are separated from the coat be large areas of desert, but certainly isn't true for the Sahel Region, which was home to powerful states such as the Mali Empire, and where travellers such as Mungo Park recorded extensive activity by slavers. Sampling is also limited for Mozambique, from where historical records show that at least half a million people were taken as slaves in the first half of the nineteenth century. The method is further limited in that it can only trace the origins of people born and raised in Africa, anyone raised in the Americas will have a strontium isotope signal from there, no matter where their parents came from.

Wang et al. also note that an improved isotope map for Africa, particularly if it includes other elements, such as oxygen, hydrogen, sulphur, and carbon, has the potential to improve not just our ability to identify the origins of Human remains from archaeological contexts, but also items such as smuggled wildlife and timber. It also has the ability to improve our understanding of wildlife migrations, or historic dispersals, including those of species extinct today. Moreover, it also has the ability to help identify the thousands of African migrants who perish in the Mediterranean Sea during their passage to southern Europe, something which has been described as potentially the greatest humanitarian disaster in Europe since the Second World War.

See also...

Using strontium isotope ratios to determine the origin of textiles from archaeological sites in Nubia.

The manufacture of textiles by pre-industrial societies was typically a demanding, multi-stage process, which involved obtaining fibres from an Animal or Plant, spinning it into a thread, and weaving it into a cloth, with dyes potentially being added at different stages to achieve colours or patterns. As such, textiles from archaeological sites can be important sources of information about the societies that produced them, giving evidence about trade routes and manufacturing techniques, as well as the social status, gender and age of the wearer. 

Textiles from archaeological sites in Sudan have been studied since the early twentieth century, with material recovered from many sites in the mid Nile Valley. Wool and cotton are the most common fibres in these archaeological assemblages. Linen is also present, but in much lower quantities. Silk has never been produced in Sudan, so any silk discovered there can automatically be assumed to have been imported. Spinning of threads in Sudan was almost exclusively done in the S-direction (anticlockwise), while woven cloths were usually plain tabbies (a plain weave, with warp and weft threads crossing at right angles to form a criss-cross pattern) or weft-facing tabbies (cloths in which the warp is covered up by multiple, complimentary weft layers, enabling the building up of a pattern, which is typically angular in nature), often having bands or stripes in different shades.

However, determining the origin of fabrics from archaeological sites is complex, as plain and weft-facing tabbies are widely manufactured, and the textiles recovered from archaeological sites are typically very fragmentary. Even spinning direction is of limited use, as even in areas where the majority of spinning is done in one direction, the presence of local communities or even individual spinners doing the opposite cannot be excluded.

In a paper published in the Journal of African Archaeology on 11 August 2022, Magdalena Wozniak of the Department of African Studies at the University of Warsaw, and Zdzislaw Belka of the Isotope Research Unit at Adam Mickiewicz University, present the results of a study which used strontium isotope ratios to determine the origin of cotton and wool fragments from Late Antiquity and the Early Medieval Period recovered from archaeological sites in the Middle Nile Valley.

Strontium isotope ratios in water are strongly linked to local geology, and can be preserved in the tissues of Animals and Plants, making them a powerful tool in archaeology. Strontium isotopes have been used to track the movements of ancient Human and Animal groups, as well as tracing ancient trade routes by determining the origin of stone tools, glass, and textiles. This technique requires an understanding of the ratio of the isotopes strontium⁸⁷ and strontium⁸⁶ in the geology of the area, both locally and regionally. Armed with this it is possible to determine whether or not a material (in this case fabric) was manufactured locally, and in some cases where a non-local item originated from. Both Animals and Plants (the producers of wool and cotton) take up strontium from the environment in the ratios at which they are present, without any fractionation, with the strontium isotope ratios found in their tissues reflecting a mixture of that found in the bedrock and overlying soil as well as that from ground and surface water. However, the different ecologies of Animals and Plants mean that even when they live in the same area, they will have slightly different isotopic ratios.

Although obtaining an accurate strontium isotope ratio only requires about 100-150 mg of material, the desiccated and friable nature of most archaeological fabrics means that the process typically leads to the destruction of one or two square centimetres of fabric, so the choice of materials sacrificed must be made very carefully.

Wozniak and Belka used four textile samples from recent excavations near the fourth cataract, made available for the study by the Polish Academy of Sciences, as well as three samples provided by the Sudan National Museum and the National Corporation for Antiquities and Museums in Khartoum. All bar one of these was from a burial site, and all are of either wool or cotton. The sample was chosen to include samples which were presumed to be of both local manufacture and imported. None of the samples showed signs of decomposition or degradation, making it unlikely that they had had their isotope signatures overwritten by strontium from groundwater after being buried, something which can be a severe problem in wetter climates, but is less so in arid Nubia.

The first sample chosen, NT1, was a section of decorated warp-faced woollen fabric (woollen fabric in which the threads are packed together closely, hiding the weft) with roughly 14-16 warp threads and 8 weft threads per cm². This fragment was recovered from the bottom of a funerary chamber beneath Tumulus 24 in the El-Ar 1 cemetery, near the El-Ar village in Shamkhiya District. The El-Ar 1 cemetery has been dated to the 2-3rd centuries AD, with decorated fabrics being very rare there.

Fragment of warp-faced wool tabby, sample NT1. Magdalena Wozniak in Wozniak & Belka (2022).

The second fragment used, NT2, is a piece of dark brown plain tabby woollen fabric, woven from S-spun threads, recovered from the El-Ar 4 Christian cemetery, and which could indicate a date anywhere between the sixth and fifteenth centuries AD. The fragment has 8-9 warp and 7 weft threads per cm², and comes from a section of shroud, which is in turn likely to have been a cloak or blanket used by the buried person and re-used as a shroud upon their death.

Fragment of the wool shroud, sample NT2. Magdalena Wozniak in Wozniak & Belka (2022).

Sample NT6 is a course wool plain tabby, woven with 8 warp and 8 weft threads per cm², taken from the shroud of a naturally mummified body (i.e. preserved by burial in a dry environment, rather than Human intervention). The fragment is brown in colour, and very desiccated. The mummy was buried in a supine position, with hands resting on hips, which is indicative of a Christian burial, again implying the 6th-15th centuries AD.

Close-up of mummy’s shroud, sample NT6. Magdalena Wozniak in Wozniak & Belka (2022).

Sample NT7 is a section of woollen kilim (woven tapestry rug). This has a dense weave with 7 warp threads and 32 weft threads per cm², and is woven in the slit-tapestry style, which creates the same pattern on both sides. The warp is a 2-ply z-spun (clockwise) cream wool, while the weft is single-ply z-spun wool in a variety of colours, including red, green, blue, orange, yellow and pink, giving a pattern of geometric and floral designs against a red background. The kilim was discovered in the town of Meinarti near the 2nd cataract in 1963, and has been dated to the 14th century AD.

Fragment of wool kilim from Meinarti, sample NT7, before conservation. Magdalena Wozniak in Wozniak & Belka (2022).

Sample NT3 is a piece of weft-faced tabby cotton cloth from the El-Ar 4 Christian cemetery. The threads are S-spun and of a golden colour, with the weft threads thicker than the warp threads, and a thread-density of 11 warp threads and 19 weft threads per cm². This is a common, medium-quality cloth type at archaeological sites on the Middle Nile.

Fragment of cotton tabby, sample NT3. Magdalena Wozniak in Wozniak & Belka (2022).

Sample NT4 is a fragment of cotton plain tabby from a Late Antique (2nd to 5th century AD) burial site at El-Ar. It is comprised of Z-spun white threads with traces of blue, green, and red pigments, probably a sign of resist dying (dying a finished fabric, while using wax or a similar substance to control which parts of the fabric the dye reaches), and a thread density of 22-24 threads per cm² for both warp and weft.

Bi-coloured threads from the cotton tabby, sample NT4. Magdalena Wozniak in Wozniak & Belka (2022).

Sample NT5 comes from the shroud of a naturally mummified body of unknown providence in the collection of the National Corporation for Antiquities and Museums. The textile is desiccated, low density, cotton tabby with a thread count of 8 warps and 8-9 wefts per cm². The threads are Z-spun, and have a golden colour. This mummy was also preserved in a supine position, with hands on hips, indicating a Christian burial, between the 6th and 15th centuries AD.

Fragment of cotton tabby woven from Z-spun threads, sample NT5. Magdalena Wozniak in Wozniak & Belka (2022).

Precambrian rocks of the Arabian-Nubian shield are widely exposed between the 2nd and 5th cataracts of the Nile. These exposures show a large variety of magmatic and metamorphic rocks, separated by suture zones with small occurrences of ophiolites and deep-water sedimentary rocks. To the west of the Nile Valley these are bordered by younger sedimentary rocks, predominantly Silurian sandstones. These rocks are overlain unconformably by the rocks of the Nubian Sandstone, which spreads across much of northern Africa, and includes a range of continental, esturine and marine sediments (predominantly sandstones), which in Sudan are predominantly of Cretaceous age. These Nubian Sandstone deposits have been mostly eroded away in the northeast of the country, exposing the underlying Precambrian basement, but extensive exposures are still present in the Bayuda Desert in the south, and the area to the west of the Nile. Tertiary Basalt rocks, which have intruded into these overlying strata, are exposed in the south of the country, around Abu Hamad. The floodplains of Nile Valley is also home to an extensive succession of Tertiary Sediments. 

Simplified geological map of northern Sudan. Red asterisks  indicate places where the investigated wool and cotton textiles were found. Numbers refer to the samples numbers. Inset shows the location of the study area. Wozniak & Belka (2022).

The volcanic rocks of the Precambrian basement of northern Sudan have strontium⁸⁷/strontium⁸⁶ ratios in the range 0.7024 to 0.7071, while the plutonic and metamorphic rocks of the basement have ratios in the range 0.7158 to 1.0039. The Cretaceous sediments of the Nubian Sandstone have strontium isotope ratios reflective of those of the basement rocks, with two clusters of values, around 0.7070 and 0.7160.

The alluvial sediments of the Desert Nile Valley are dominated by material derived from the Blue Nile and Atbara rivers, which drain from the Ethiopian Highlands, an area dominated by Cainozoic Volcanic rocks. These sediments have isotopic ratios in the range 0.7047 to 0.7076, a range which includes that of modern Nile water, at 0.7062. Nile muds dating from the end of the African Humid Period, about 45 000 years ago, show a strontium isotope ratio of 0.7052–0.7057, while those dating from between 1000 BC and 500 AD (i.e. between 3000 and 1500 years ago) show an isotope range of 0.7058–0.7076.

Samples NT1, NT2, and NT6 are all low-density woollen tabbies made from S-spun threads, technologically consistent with local manufacture. Sample NT1 contains cream and dark wool, used to make a pattern, while NT1 and NT6 are made entirely of undyed, dark wool. Lighter, cream-coloured wools are rare in the El-Ar assemblage, which may reflect the genetic structure of the local flocks (i.e. many brown Sheep and few cream Sheep). Alternatively, the local Sheep of the period may have been entirely brown, with cream wool being an imported commodity.

Sample NT7 is quite different from these, made up of coloured, Z-spun threads woven together using the split-tapestry technique to produce a decorative pattern, which is likely to indicate that this was an imported item. Furthermore, furthermore, the red dye used on some of the wool appears to have been treated with a lac dye, derived from the Scale Insect, Laccifer lacca, which is found in South and Southeast Asia and South China, but quite alien to the Nubia, where red dyes were traditionally derived from the Madder Plant. This apparently non-local item dates from the 14th century, a time when Meinarti was occupied by the Beni Ikrima, a nomadic group from the Maghreb region.

All four wool samples yielded strontium isotopic ratios within the range 0.7075 to 0.7084. In order to better compare these to the local environment, Wozniak and Belka also obtained strontium isotope ratios from Sheep and/or Goat remains (the two are hard to tell apart) from several archaeological sites between the 2nd and 4th cataracts. All of these remains are known to be older than the wool samples, dating to between 2500 and 500 BC, and gave isotopic ratios in the range 0.7068 to 0.7082 (one set of remains gave a much higher reading, of 0.7109, though this is likely to indicate that the Animal was of non-local origin).

Diagram showing the strontium isotope signatures of the  investigated wool textiles (yellow spots; numbers refer to sample numbers) in comparison to Strontium isotope  composition of Ovis/Capra remains found in the region  between the 2nd and 4th cataracts. Wozniak & Belka (2022).

Three of the investigated wool samples, NT1, NT6, and NT7, had isotopic ratios entirely consistent with archaeologically derived Sheep/Goat remains from the region, and the fourth, NT2, fell only slightly outside this range, and still within the range of Cattle and Human remains from the Desert Nile Valley.

Of the three cotton samples, only one, NT3, was made of a yarn spun in an anticlockwise, S-direction, typical of local manufacture in Nubia or Egypt. The other two, NT4 and NT5, were spun in a clockwise, Z-direction, which may indicate non-local manufacture. One of these, NT4, also shows signs of a resist-dying technique, not known in Nubia in the 2nd-5th centuries AD, but common in textiles from India during this period.

These three samples show a narrow isotope ratio range, from 0.7084 to 0.7086, which makes it likely that they were derived from crops grown within a limited geographical area. As a crop, cotton requires a rather specific set of conditions, with a hot dry climate, and large amounts of available water for several months of the year. This can be provided in the Nile Valley between the confluence of the White and Blue Niles and the 2nd cataract, although water and plants derived from this region show isotope ratios below 0.7075, ruling this region out as an origin point for the cotton in the study. Cotton is also grown around the Nile Delta, and ancient cotton fibres and seeds have been recovered from other sites along the Lower Nile, suggesting that cotton may have once been grown more widely. Strontium isotopic signatures are not available for sediments from all of these areas, but the isotopic signature of the Nile water, at about 0.7069, makes it unlikely that any of these floodplains have an isotopic ratio above about 0.7075. Similarly, the sediments of the Atabara and Blue Nile valleys have average isotope ratios between 0.7041 and 0.7060. All of these locations therefore seem unlikely as a point of origin for the cotton used to make the textiles included in the study. 

However, cotton grown in the Western Desert of lower Nubia typically has an isotopic value of about 0.7085, and limestones from the Western Desert of Egypt can have strontium isotope signatures in the range 0.7077 to 0.7078. Cotton is known to have been grown in this region in the 2nd-3rd centuries AD, using irrigation systems which drew upon shallow groundwater reservoirs, supplied by rainwater that had filtered through Eocene carbonates, which could conceivably produce a cotton with a strontium isotopic signature of about 0.7085.

Cotton is also known to have been produced in Meroe, on the lower White Nile to the south of Khartoum, during the Roman period, although both the water and plants from this region tend to have a higher isotopic ratio than the cotton from the study, excluding this region as a point of origin. 

Diagram showing the strontium isotope composition of the investigated cotton textiles (green spots; numbers refer to samples) in comparison to Sr isotope composition of selected elements of the natural environment in the Nile and White valleys. Wozniak & Belka (2022).

There is strong evidence for the production of cotton in Egypt and Sudan in Roman and later times, but the possibility of material also being imported from further afield should not be ruled out. Cotton was widely cultivated in India and on the Arabian Peninsula during antiquity, and both raw cotton and finished textiles could easily have been imported to Nubia via the Red Sea. Cotton seeds and textiles excavated at Mleiha in the modern United Arab Emirates have been shown to have originated from western India by their strontium isotope ratios. Unfortunately, strontium isotope information is only available for a few locations on the Arabian Peninsula or from India or Pakistan. However, several regions would be compatible with the isotope signatures obtained from the cotton samples, including the lower Indus River Basin, in India and Pakistan, the Kathijawar Peninsula on the west coast of India, the area covered by modern Kuwait, and the Oman Peninsula.

The isotope signatures obtained from the wool samples from archaeological sites in the Nubian Nile Valley all support a local origin. This is also supported by the technological features of three of the samples, NT1, NT2, and NT6, but not the fourth, NT7. This sample, a kilim rug from 14th century Meinarti, appears to have been made with a technology entirely alien to this part of the Nile Valley. However, it also dates from a time when the city of Meinarti was occupied by an alien group, the Beni Ikrima, who originated from the Maghreb region. Since the Maghreb has a geology with similar strontium isotopic ratios to that of northern Sudan, it is possible that the kilim was brought to the area by the Beni Ikrima from their homeland. However, it is also possible that the kilim was made locally by Beni Ikrima craftspeople from wool obtained from local, Nubian, flocks. Wozniak and Belka conclude that, given the available isotopic evidence, the more likely scenario is that the kilim was made locally, contrary to previous expectations.

In contrast, the isotopic signature of the cotton samples examined fits poorly with an origin in the Nile Valley. The samples all have very similar isotopic signatures, which seems to imply a common origin, although this is at odds with the different spinning techniques used. One of the samples, NT3, has an isotopic signature that fits well with the Dakhla/Kharga oasis in the Egyptian Western Desert, which has previously been identified as a possible site of ancient cotton cultivation. This piece also shows a technology consistent with production in the Nile Valley, notably an S-spun yarn. Importing cotton textiles from an oasis in the Western Desert would only make sense if local, Nubian, production was failing to meet demand. The frequency of cotton fabrics from archaeological sites in Nubia has been observed to have dropped during the Late Antique and Early Medieval periods, so this is not implausible, although an alternative explanation could be that the deceased person for whom this item was used as a shroud had travelled during their lifetime, either moving from the Western Desert to Nubia and bringing the cloth with them, or at some point visiting the Western Desert and obtaining the item there.

Sample NT4, on the other hand, appears much more likely to be of Indian origin, where a block printing technique using resist dying was common at this time. The isotopic signature of this sample matches that of the Kathijawar Peninsula on the west coast of India, leading Wozniak and Belka to conclude that this item was most likely imported from India. This adds evidence to the inclusion of the area around the 4th cataract into long distance trade networks, something previously indicated by the discovery of glass beads of foreign manufacture in the region.

Sample NT5 also appears to be non-local in origin, with a Z-spinning technique having been used, and a non-local isotopic signature. However, there is insufficient evidence to give a precise origin for this fragment at this time, with possible points of origin including  Indus River basin in Pakistan, the west coast of India, Kuwait, and the Oman Peninsula.

Although Wozniak and Belka were not able to determine the point of origin of all the fabrics in the study, their study shows the potential for determining the origin of ancient fabrics using strontium isotope ratios. The development of a wider data set of strontium isotope values for textiles could add to the information obtained by examining the technological aspects of textile-making, to provide a better understanding of the manufacture of and trade in cloth in the ancient world.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

Using strontium isotope analysis to identify the origins of cremated human remains from Stonehenge.

Stonehenge is an internationally renowned Neolithic monument located on Salisbury Plain in Wiltshire, southern England, thought to have been constructed between 4000 and 5000 years ago.. The monument comprises a ring of standing stones, each of which is about 4 m high and 2.1 m wide, and weighs about 25 tonnes, known as the Sarsen Stones, thought to be derived from Marlborough Downs, about 30 km away, within which is a ring of smaller stones, the Blue Stones, which have been identified as having been sourced from Mynydd Preseli (Preseli Hill) in Pembrokeshire, west Wales, around 240 km away. The site has been the subject of numerous archaeological excavations, and, between 1919 and 1926, a total of 58 sets of cremated Human remains were found within the complex, within a series of pits known as 'Aubry Holes' after the seventeenth century antiquarian John Aubrey who first noted them.

Stonehenge. Gareth Wiscombe/Flikr/Wikimedia Commons.

In a paper published in the journal Scientific Reports on 2 August 2018, Christophe Snoeck of the School of Archaeology at the University of Oxford, and Analytical, Environmental & Geo-Chemistry at the Vrije Universiteit Brussel, John Pouncett, also of the School of Archaeology at the University of Oxford, Philippe Claeys and Steven Goderis, also of Analytical, Environmental & Geo-Chemistry at the Vrije Universiteit Brussel, Nadine Mattielli of the G-Time Laboratory at the Université Libre de Bruxelles, Mike Parker Pearson and Christie Willis of the Institute of Archaeology at University College London, Antoine Zazzo of the Unité Mixte de Recherche ‘Archéozoologie, Archéobotanique: Sociétés, Pratiques et Environnements’ at the Sorbonne Universités, and Julia Lee-Thorp and Rick Schultin, again of the School of Archaeology at the University of Oxford, describe the results of a study which uses strontium isotope analysis to attempt to uncover the geographical origin of the cremated remains.

Strontium isotopes in water vary with local geology, and are incorporated in tooth and bone, providing a record of where people have lived. Strontium isotope levels in tooth enamel become fixed at about puberty, reflecting the isotopic content of the water consumed at this time, unlike bone where the isotope content varies with water consumed throughout the life of the individual, and are often used not just in archaeology but in the identification of modern remains by forensic scientists, in those working with war graves and similar sites. 

However, the strontium signature of tooth enamel is almost invariably destroyed by cremation, which causes the enamel to shatter and break down. As an alternative, Snoeck et al. extracted strontium isotopes from bone fragments that have survived cremation. The strontium isotope ratio in bone does not become fixed at puberty as it does in tooth enamel, but continues to change over the lifetime of the individual, but it does provide an average reading of the foods eaten over the last decade or so before death, giving some idea where that individual was living.

Cremated occipital bone fragments from Stonehenge. Snoeck et al. (2018).

Snoeck et al. carried out analyses on bone fragments from 25 individuals, and compared them to the isotope ratios of the chalk geology of the Salisbury Plain,as well as plant samples from eight locations in West Wales, and previously published modern plant, water and dentine data from around Britain.

Fifteen of the tested individuals produced results consistent with having lived and died in the region around Stonehenge, however the remaining ten were clearly not local, and had strontium isotope ratios consistent with having lived in Devon, West Wales, or some more distant location outside the study set (such as Ireland, Scotland or continental Europe).

Biologically available strontium (BASr) baseline (left – mean and right – 1 SD), generated using the Spatial Join and Polygon to Raster tools in ArcGIS Desktop 10.6. Based upon British Geological Survey map Geology 625k.

Snoek et al. also not that the ratio of carbon isotopes in the local and non-local individuals was different. Carbon isotope ratios from bone or tooth enamel are generally assumed to represent the diet of an individual rather than where they lived, and since there is thought to have been little variation in the diet of Neolithic peoples across Britain, might be expected to be similar in all of the Stonehenge individuals. 

However, the carbon isotope ratios of cremated remains are known to be reset by the cremation process, with bone fragments absorbing carbon from the wood used in the cremation process. Carbon ratios in wood reflect the environment in which the tree which produced the wood was living, with wood produced by trees from open woodland distinct from wood from trees from more densely wooded environments. During the time when Stonehenge was constructed southern England, including Salisbury Plain and Devon, is thought to have been only lightly wooded, while the west of Wales is reconstructed as having been covered by dense woodland. This suggests that the non-local individuals found at Stonehenge both lived and were cremated in West Wales, with their remains being later transported to the site to be buried.

See also...

Follow Sciency Thoughts on Facebook.

Interpreting the life history of the Egtved Girl.

The ‘Egtved Girl’ was excavated near Egtved in Denmark in 1921, one of a series of Bronze Age burials in Oak coffins placed within barrows (raised burial mounds) in the area dated to between 1000 and 1500 BC. Egtved Girl was between 16 and 18 years old at the time of her death, and buried in an Oak coffin dated dedrochronologically (i.e. using tree rings) to 3400 years ago. The interior of the coffin was flooded with slightly acidified water, which had led to good preservation of the sort tissues, but dissolution of the skeleton with only dental enamel remaining. She was dressed in well-made woollen clothing including a short corded skirt and a short blouse, interpreted as a sign of a high social status (as are Oak coffins and burial mounds), with a leather belt with a large disk-shaped bronze ornament, which has been suggested may indicate she was a priestess of a Nordic Sun-worshiping cult, and a variety of other grave goods. A small container was placed by her head, containing the cremated remains of a child thought to have been aged 5-6.

In a paper published in the journal Scientific Reports on 21 May 2015, a group of scientists led by Karin Margarita Frei of the National Museum of Denmark and the Danish National Research Foundation’s Centre for Textile Research at the University of Copenhagen describe the results of a multi-disciplinary investigation into the Egtved Girl remains, intended to elucidate her movements during her lifetime.

A photo of the remains of a Bronze Age high status female found inside an oak-coffin in a monumental burial barrow at Egtved, Denmark. The Egtved Girl’s garments are extremely well preserved and her exceptional wool costume consists of several wool textile pieces as well as a disc-shaped bronze belt plate, symbolizing the sun. Roberto Fortuna/National Museum of Denmark. Frei et al. (2015).

Attempts to extract DNA from the hair of Egtved Girl failed, probably due to the acidic conditions inside the coffin, which is not a good environment for DNA preservation. However isotopic ratio analysis proved to be much more applicable and was applied to a number of tissues and fibres from the burial. Strontium has two stable isotopes, strontium-86 (⁸⁶Sr) and strontium-87 (⁸⁷Sr), and the ratio of these in tissues is derived from that in groundwater where a person or animal lives, which in turn is determined by the local geology.

The first strontium isotope ratio test was carried out on the enamel of the first lower left molar. This is laid down between birth and 3-4 years of age, and its isotopic ratio is subsequently fixed for life. The enamel yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71187; this is very high compared to the value obtained from soil in the Egtved area, which yielded results ranging from 0.70852 to 0.70874, indicating that the girl had not spent her childhood in the area. Such high values are not found anywhere in Denmark with the exception of the (remote) island of Bornholm, but are found in other areas of Europe, such as southern Scandinavia, southern Germany, France and much of the UK.

Next an isotope ratio from a fragment of occipital bone from the cremated child. Bone, unlike tooth enamel, is constantly replaced throughout life, albeit at a slow rate, so isotopic information obtained from it is typically an average of the ingested ratio over the last few years of life. In this instance the bone fragment yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71190, comparable to that obtained from the tooth but incompatible with local soil values, indicating that the child too had come from outside the area.

Frei et al. then took a hair from the scalp of Egtved Girl from analysis. Hair is constantly produced by the body, and the isotope ratio within a piece of hair remains fixed at the point when it grew. This means that a long hair can contain a record of the isotopic composition of ingested strontium for months or even years. A 23 cm length of hair was obtained from the girl, and divided into four lengths of about 6 cm each. The hair segment closest to the scalp, thought to have been produced in the last 4-6 months of life, yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71229, again not close to anything found in the Egtved area, suggesting that she had spent this part of her life away from the area, but the middle two segments, thought to represent a period of at least nine months, produced ratios of 0.71028 and 0.71086 slightly high for the Egtved area, but certainly compatible with her having lived in Denmark for this period and possibly having had spent some of her time close to the burial site. The final fragment, thought to have been produced at least 13 to 23 months prior to death, yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71255, again incompatible with her having lived in Denmark for this part of her life. Taken together these results suggest a fair amount of mobility on the part of Egtved Girl during the last two years of her life.

An additional study of the microstructure of Egtved Girl’s hair suggested that she had gone through several periods of sharply reduced protein intake during the period when it was growing, but an attempt to obtain DNA for analysis from the hair failed (which is unsurprising given the acid environment inside the girl’s coffin).

Next Frei et al. took a series of samples from one of Egtved Girl’s fingernails for analysis. Isotopic levels in nails are laid down in a similar way to those in hairs, though nails are rather slower growing, giving a more detailed glimpse into the last moths of life. The nail samples are thought to represent a period covering the last 4-6 months of life (similar to the first 6 cm of hair), and yielded ⁸⁶Sr/⁸⁷Sr ratios of 0.71235 to 0.71240, similar to that obtained from the youngest hair, and again incompatible with the period having been spent in Denmark.

Drawing depicting the sampling strategy to reconstruct a high-resolution life-mobility-timeline of the Egtved Girl. Tooth enamel was sampled to reconstruct the first years of her life, segments of scalp hair to reconstruct, at least, the 23 final months of her life as well as segments of one of her fingernails to reconstruct the final approximately 6 month of her life. Marie Louise Andersson/National Museum of Denmark in Frei et al. (2015).

The clothing of Egtved Girl was made of high quality woollen material. Fibres from this were also analysed, yielding ⁸⁶Sr/⁸⁷Sr ratios ranging from 0.71168 to 0.71551, indicating that the material had also originated from outside Denmark. However fibres from a woollen cord from the container with the cremated remains of the child yielded results ranging from 0.70982 to 0.71044, consistent with local manufacture.

The majority of ⁸⁶Sr/⁸⁷Sr ratios recovered from Egtved Girl and associated remains exceed 0.711, to high for anywhere within Denmark, or within several hundred kilometres of its border, but consistent with a wide range of areas within Europe. The grave goods found with the body are archaeologically consistent with a culture found in the period from southern Germany to southern Scandinavia, in which alliances between chieftainships are believed to have been cemented by marriages to high-ranking women, leading to a high level of mobility among women of noble status. Egtved Girl appears to have moved long distances several times within the last two years of her life, and had travelled from an area outside of Denmark shortly prior to her death. Based upon the strontium isotope ratios in her tissues and the nature of her grave goods, Frei et al. suggest that it is most likely that she originated from the Black Forest region of southwestern Germany.

Map showing the location of the Egtved burial site (red dot). Borders of the nearest areas with bioavailable ⁸⁷Sr/⁸⁶Sr values that potentially fit the tooth enamel, the child’s bone, wool garments and oxhide belonging to the Egtved find are marked with green lines and arrows. Of these regions the Black Forest area (red ellipse) appears to be the most plausible place of origin as constrained by the multiple strontium isotope codes contained in materials from the Egtved find combined with the archaeological artefact record patterns. Marie Louise Andersson/National Museum of Denmark in Frei et al. (2015).

See also…

Evidence of Leprosy in from an early Anglo Saxon grave from Essex, England.

Leprosy is caused by the Bacterium Mycobacterium leprae; it is fatal, incurable without modern antibiotics and causes serious disfigurations prior to death...

 Philistine and Hellenistic remains from the Iron Age city of Ashdod-Yam on the southern Mediterranean coast of Israel.

The Philistine Kingdom of Ashdod fell under the...

The first dairy farmers in Finland.

Dairy farming (keeping Mammals in order to consume their milk or products derived from it) spread through Europe as part of the ‘Neolithic Package’ of technologies, which originated in the Middle East...

Follow Sciency Thoughts on Facebook.