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.

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More than 100 people dead after a series of landslides and flash floods hit the city of Petrópolis in Rio de Janeiro State, Brazil.

One hundred and seventeen people are now known to have died and more than one hundred and forty more are still missing after a series of landslides and flash floods hit the Brazilian city of Petrópolis in Rio de Janeiro State on Tuesday 15 February 2022. The incident happened following a rainstorm which brought more than a month's rain in three hours, making it the worst such storm recorded in the state since 1932. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. In the worst incident over 80 homes were destroyed by a single landslide that hit the neighbourhood of Morro da Oficina. In addition to the dead many hundreds more have been injured and/or displaced from their homes, with many of the displaced now staying in temporary accommodation in schools, sports centres, and other civic buildings.

 

A landlide which swept through the Morro da Oficina area of Petrópolis on 15 February 2022, destroying more than 80 homes. Reuters.

Southern Brazil has a rainy season that lasts from October to March, with peak rains from mid-November to mid-January, however, this year's rains have been exceptionally strong. Brazil has suffered a string of flood-related disasters in recent years, most notably in 2011, when over 800 people died. The country has a rapidly growing population, with little effective urban planning, which has led to sprawling urban developments springing up with little thought to natural hazards, and in particular poorer neighbourhoods often expanding up unstable hillsides, with the result that when floods occur (which is not unusual) communities are often quickly overwhelmed. This year's exceptional rains have led to more widespread flooding, which may also persist for longer, and there is a distinct danger that without determined action the death toll may exceed that of 2011. Such events are becoming increasingly common in Brazil, something which many climatologists are citing as direct evidence of global warming.

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Landslides kill at least 24 in Brazil.

At least twenty four people have died in a series of landslips in the Brazilian states of São Paulo and Rio de Janeiro on Tuesday 3 March 2020. The incidents were triggered by a large storm hitting the coastal areas of the two states, brining with it 280 mm of rain in just 12 hours. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. As well as the known fatalities at least 30 people are missing and several hundred have been displaced from their homes, making it likely that the number of fatalities will rise. The majority of the deaths occurred in São Paulo State, where nineteen people have died, including a mother and her child who became trapped beneath the rubble of their home following a landslide, and two firefighters who were killed when a second landslip hit the same area as they were trying to rescue them. A further five fatalities have been recorded in Rio de Janeiro State.

House displaced from its foundations by a landslide in the municipality of Guarujá in São Paulo State, Brazil, on 3 March 2020. AFP/Getty Images.

Southern Brazil has a rainy season that lasts from Ocotober to March, with peak rains from mid-November to mid-January, however, this year's rains have been exceptionally strong. Brazil has suffered a string of flood-related disasters in recent years, most notably in 2011, when over 800 people died. The country has a rapidly growing population, with little effective urban planning, which has led to sprawling urban developments springing up with little thought to natural hazards, and in particular poorer neighborhoods often expanding up unstable hillsides, with the result that when floods occur (which is not unusual) communities are often quickly overwhelmed. This years exceptional rains have led to more widespread flooding, which may also persist for longer, and there is a distinct danger that without determined action the death toll may exceed that of 2011.

 The aftermath of a landslide in the  Baixada Santista Metropolitan Area of  São Paulo State, Brazil, on 3 March 2020. São Paulo Civil Defense.

This extreme weather may be linked to an El Niño wearther system over the Pacific Ocean. The El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.

 

 

Movements of air masses and changes in precipitation in an El Niño weather system. Fiona Martin/NOAA.

 

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Inbiomyia azevedoi: A new species of Inbiomyiid Fly from the Atlantic Forest in southeastern Brazil.

Inbiomyiid Flies are a curious group of True Flies, Dipters, first discovered in 2006. They are small in size, with the largest recorded specimens being about 1.6 mm in length, and generally very dark in colour. Inbiomyiid Flies are restricted to the tropical forests of the Americas but little is known about their biology. Large, flattened eggs have been found within the bodies of females, but what they are laid upon is unclear. To date only twelve species have been discovered, all of which have been placed within a single genus, Inbiomyia.

In a paper published in the American Museum Novitates on 12 Auguat 2019, Paula Raile Riccardi of the Departamento de Entomologia at the Museu Nacional do Rio de Janeiro, and Dalton de Souza Amorim of the Departamento de Biologia at the Universidade de São Paulo, describe a new species of Inbiomyiid Fly from the Atlantic Forest in southeastern Brazil.

The new species is named Inbiomyia azevedoi, in honour of Leonardo Henrique Gil Azevedo of the Museu Nacional do Rio de Janeiro, who collected most of the specimens from which the species is described. These specimens comprise eight males and seventeen males caught in the Parque Nacional de Itatiaia in Rio de Janeiro State, and one female caught in the Parque Nacional do Caparaó in Espírito Santo State, all caught with Malaise (fine net) traps. They are between 1.75 and 1.8 mm in length with wings that are 2.1 to 2.2 mm long.

Inbiomyia azevedoi, female. Riccardi & Amorim (2019).

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Platydoris guarani: A new species of Nudibranch Sea Slug from Brazil.

Nudibranch Sea Slugs are marine Gastropod Molluscs that lose their shells during their larval stage. Like other Sea Slugs (not all of which are closely related) they are often colourful and have feathery external gills, and while often hard to tell apart from these other Sea Slug groups, can be distinguished by morphological examination. All Sea Slugs are externally biliterally symetrical, however Nudibraches are Opisthobranches (members of the same Gastropod group as the terrestrial Pulmonate Snails), and lack internal symmetry. This is manifested externally in the positioning of the sexual openings, with both male and female openings on the right side of the body. Almost all Nudibranches are benthic (live on the sea floor or other surfaces) and are found from the intertidal zone to the abyssal ocean floors, though most species are found on shallow tropical reefs.

The Nudibranch Platydoris angustipes is considered to be widespread in the western Atlantic, being found from the Caribbean in the north, south to the coast of Brazil and east as far as Ascension Island. However, the species was described from specimens collected in the Caribbean (the US Virgin Islands) and shows considerable morphological variation across its range, so it is not completely certain that it whether all populations assigned to Platydoris angustipes are in fact the same species.

In a paper published in the journal Zoological Systematics on 2 January 2018, Patricia Lima and Luiz Ricardo Simone of the Museu de Zoologia da Universidade de São Paulo describe a new, cryptic, species of Platydoris from the coast of Rio de Janeiro State in Brazil.

Cryptic species are species that closely resemble other species, and cannot be separated by simple, non-invasive examination. While taxonomists have known about cryptic species for a long time, it was not realised how numerous such species were until taxonomists began to use genetics to determine relationships between species, about twenty years ago. The presence of cryptic species can have a profound influence on conservation efforts, as ‘species’ thought to be wide ranging with large populations and broad environmental tolerances can turn out to be complexes of closely related but reproductively isolated species, each with a smaller population and distribution, and narrower range of environmental tolerances.

The Brazilian and Caribbean populations of Platydoris angustipes have previously been suggested to be different in several ways, including the colour and shape of the body, the length of the foot, the covering of the dorsal surface, the nature of the oral tentacles, and the number of gills branches. However, Lima and Simone found that all these features are variable in both populations, and that while the two populations show different frequencies of all these traits, none of them could be reliably used to assess which population an individual specimen came from.

Nevertheless, it did prove possible to different the two populations, based upon on several important morphological differences. Firstly, the shape of the radula (tongue) is different in the two populations, with the Caribbean populations having a straight-sided radula and the Brazilian populations having a radula distinctively wider at the base (radula shape is considered an important diagnostic feature in all Gastropod groups). Secondly, the renal vesicles (kidneys) of the Brazilian population are much larger. Thirdly the digestive tract of the two populations is arranged differently, with the Brazilian population having shorter odontophore muscles and a shorter cecum. Finally, the reproductive systems of the two populations are quite different, with the Brazilian population lacking spines on either the penis or vagina, unlike the Caribbean population, and indeed any previously described species of Platydoris. The structure of the reproductive tract is particularly important for establishing species boundaries in all animal groups that mate internally (as opposed to releasing eggs and sperm into the environment), as populations with different reproductive apparatus typically cannot mate.

The radula of (left) a specimen of Platydoris angustipes from the US Virgin Islands, and (right) Platydoris sp. from Rio de Janeiro State, Brazil. Scale bars are 100 μm. Lima & Simone (2018).

The new species is named Platydoris guarani, in honour of the Guarani indigenous people of Rio de Janeiro State. These Sea Slugs are typically about 60 mm in length and 40 mm in width, with a rounded body, and are usually orange in colour with a white ribbon around their edges, and a row of brown spots just above this. The dorsal surface is covered in small tubercles, and the gills typically have six white branchial leaves.

Platydoris guarani, living animals. (A) Dorsal view, specimen from Papagaio, Cabo Frio, Rio de Janeiro. (B) Same specimen in ventral view. (C) Living animal with spawning, specimen from Enseada da Meia Lua, Cabo Frio, Rio de Janeiro. Vinícius Padula in Lima & Simone (2018).

Lima and Simone suggest that all Brazilian populations of ‘Platydoris angustipes’ should in fact be assigned to ‘Platydoris guarani’, but are uncertain as to the status of the Ascension Island populations, and suggest that this should be investigated in the future.

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Landslide kills at least ten in Rio de Janeiro State, Brazil.

Ten people, including a three-year-old boy have been confirmed dead following a landslide in the city of Niterói in Rio de Janeiro State, Brazil, on Saturday 10 November 2018. A further four people are missing following the event, with eleven having been rescued alive. The incident occurred after days of heavy rain in the area, when part of a muddy slope collapsed onto a group of residential properties, carrying with it several large boulders. andslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.

The scene of a landslide that killed at least ten people in Rio de Janeiro State, Brazil, on Saturday 10 November 2018. EPA.

November sees the start of the rainy season in southern Brazil, a country that has suffered a string of flood and landslide related disasters in recent years. The country has a rapidly growing population, with little effective urban planning, which has led to sprawling urban developments springing up with little thought to natural hazards, and in particular poorer neighbourhoods often expanding up unstable hillsides, with the result that when floods occur (which is not unusual) communities are often quickly overwhelmed. 

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Poeciloderrhis spp.: Six new species of Giant Cockroaches from Brazil.

Giant Cockroaches, Blaberidae, are generally large Cockroaches, reaching between 10 and 60 mm, with spines on their middle and rear legs. There are about 660 known species from across the globe, many of which give birth to live young.

In a paper published in the jounrnal Zoologia on 22 March 2018, Leonardo de Oliveira Cardoso da Silva and Sonia Maria Lopes of the Department of Entomology at the Museu Nacional of the Universidade Federal do Rio de Janeiro, describe six new species of Giant Cockroaches from Brazil, all of which are placed in the genus Poeciloderrhis.

The first new species described is named Poeciloderrhis aureolatus, in reference to their yellow-brown colour. The species is described from nineteen male and ten female specimens, collected in Rio de Janeiro and Minas Gerais states. The females are on average larger than the males, though the largest specimens of both sexes are about the same size, with females reaching 45.4-45.7 mm in length, compared to 41.6-45.7 mm in the males. These Cockroaches have triangular heads with black eyes and robust spines on all legs.

Poeciloderrhis aureolatus, male (top) and female (bottom). Scale bars 5.6 mm (top) and 6.0 mm (bottom). Silva & Lopes (2018).

The second new species is named Poeciloderrhis mediansclerostylatus, meaning 'stylus shaped median sclerite' in reference to a detail of the male genitalia. This species is described from a single male specimen collected in Rio de Janeiro State. This is 30 mm in length and shiny brown in colour, with a triangular head, dark brown eyes and strong spines on all legs.

Poeciloderrhis mediansclerostylatus, male specimen. Scale bar is 5.6 mm. Silva & Lopes (2018).

The third new species is named Poeciloderrhis diamantinensis, in reference to the municipality of Diamantino in Mato Grosso State, where this species was first discovered. The species is described from twelve male specimens from Mato Grosso, Rondônia and Goiás states. These range from 22.1 to 24.5 mm in length and are a shiny light brown colour with triangular heads, dark brown eyes, and strong spines on all legs.

Poeciloderrhis diamantinensis, male specimen. Scale bar is 3.4 mm. Silva & Lopes (2018).

The fourth new species is named Poeciloderrhis itatiaiensis, in reference to the Parque Nacional de Itatiaia, in Rio de Janeiro State, where the species was discovered. The species is described from a single male specimen, light brown in colour and 48.9 mm in length, with black eyes, a triangular head and spines on all legs.

Poeciloderrhis itatiaiensis, male specimen. Scale bar is 6.7 mm. Silva & Lopes (2018).

The fifth new species described is named Poeciloderrhis vanzolinii, in honour of herpetologist Paulo Emilio Vanzolini, who collected the specimen from which the species is described, a male from São Paulo State. This specimen is 27.5 mm in length, and shiny light brown in colour with dark brown eyes, a triangular head and strong spines on all legs.

Poeciloderrhis vanzolinii, male specimen. Scale bar is 3.5 mm. Silva & Lopes (2018).

The final new species described is named Poeciloderrhis penduloides, meaning 'pendulum shaped; in reference to the male genetalia. This species is described from a single male specimen collected in Rio de Janeiro State. This specimen is 26.9 mm in length and shiny light brown in colour, with brown eyes, a triangular head and spines on all limbs.

Poeciloderrhis penduloides, male specimen. Scale bar is 4.7 mm. Silva & Lopes (2018).

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