Rubbish heaps left behind by Greenland’s medieval Norse settlers are revealing new details about farming, livestock and everyday life. Researchers have found that microbial traces can survive in archaeological deposits for centuries, offering another way to investigate how people lived in medieval Greenland.
A new study has examined microbial DNA preserved in middens across Greenland, some representing thousands of years of human activity. Among them are rubbish heaps and surrounding soils associated with Norse settlements, where researchers found distinctive biological signatures connected with livestock, human activity and decomposing organic material.
Published in Frontiers in Microbiology, the research examined archaeological deposits left by Paleo-Inuit populations, medieval Norse settlers and Inuit from the early colonial period. The study focused primarily on whether microorganisms preserved in permafrost might present a danger as Greenland warms, but its results also demonstrate how microbes can provide evidence about activities that took place at archaeological sites centuries ago.
Greenland’s Norse settlements date from roughly the 10th to 15th centuries. The settlers established farming communities in southwestern Greenland and raised domestic livestock. Their rubbish accumulated in middens containing materials such as animal bones, excrement, mollusc shells and artefacts, creating deposits that archaeologists can use to investigate diet, habits and everyday life.
“Here we show that the risk of release of ancient pathogens from ancient middens on Greenland is currently low,” said Dr Frank Møller Aarestrup, a professor at the National Food Institute of Denmark Technical University and corresponding author of the study. “Rather, we found that these middens in the cold Arctic acted like long-term natural experiments. Human- and animal-associated bacterial signals, including opportunistic bacteria and bacteria carrying antibiotic resistance genes, have remained detectable in them many centuries later as the legacy of human activity: for example, livestock farming by the ancient Norse.”
Microbial traces of a medieval farm
Sampling locations and layout of the Norse settlement sites studied in Greenland. Image: Maccario et al. / Frontiers in Microbiology / CC BY
Researchers collected samples during fieldwork in Greenland and used DNA sequencing to reconstruct the bacterial communities preserved within them. Altogether, the study compared 78 midden samples with 143 samples from surrounding soils. The midden material represented several periods of Greenland’s settlement history.
For the medieval Norse period, the researchers examined 34 midden samples from Kapisillit, on the coast of Kapisillit Fjord about 80 kilometres east-northeast of Nuuk. They did not restrict their investigation to the rubbish heap itself. Another 50 samples came from the settlement’s infields, which were used as winter enclosures for livestock, while 30 came from outfields used for summer grazing. A further 48 outfield samples were taken near Norse settlements around Narsarsuaq in southern Greenland.
This allowed researchers to compare microbial signatures from different parts of the medieval farming landscape. The communities varied according to their archaeological context, with samples clustering according to whether they came from middens, infields, outfields, surface deposits or deeper material. The researchers found that the microbial communities were therefore structured by what had taken place at particular locations rather than being uniform across the landscape.
The medieval rubbish itself also produced distinctive results. Norse-period middens at Kapisillit associated with decomposing bones contained comparatively high proportions of unidentified Proteobacteria and Clostridiaceae. More generally, the researchers found that both the age of a midden and the type of material deposited there affected which bacterial signatures remained detectable.
Across all of the middens included in the study, researchers identified 1,207 bacterial species, with between nine and 202 detected in individual samples. Many organisms could only be identified at broader taxonomic levels, something the researchers say highlights how poorly described the microbial communities of Arctic soils and archaeological deposits remain.
The midden samples were generally richer in host-associated bacteria than surrounding soils. Some were organisms associated with human and animal intestinal microbiomes, providing a microbial trace of waste, carcasses and other material deposited by the people who once occupied these sites.
There was also evidence of antimicrobial resistance genes throughout the archaeological landscape. At the Norse sites, researchers detected resistance genes that could have originated both naturally in soils and through faecal or livestock inputs. Significantly, their distribution was not confined to rubbish heaps: the researchers found them in middens, infields and outfields, suggesting that these microbial traces extended across the wider Norse farm landscape.
Centuries preserved in the cold
Microbial community structure in samples from the Greenland sites, showing the relative abundance of the 47 most abundant bacterial orders. Image: Maccario et al. / Frontiers in Microbiology / CC BY
The study also demonstrates how long biological traces of human activity can remain detectable in Greenland.
The oldest Paleo-Inuit middens had bacterial communities more similar to ordinary soils, suggesting that the microbial imprint of people and animals gradually diminishes. The medieval Norse middens nevertheless retained distinctive signatures centuries after the settlements themselves were abandoned. The researchers suggest that cold temperatures and water-saturated conditions have contributed to this preservation.
There is an important limitation to what these findings can tell us. The researchers did not carry out the specialised authentication procedures necessary to establish conclusively that individual DNA fragments themselves are ancient. They therefore caution that the results should be understood as preserved microbial DNA signatures in archaeological deposits, rather than proof of authenticated ancient microbiomes or that the microorganisms themselves remain alive.
The findings nevertheless suggest another potential source of evidence for archaeologists. Animal bones, artefacts and other visible remains have long made middens valuable records of past communities. Microbial signatures can add another layer, potentially helping researchers distinguish between different activities and areas within settlements.
What happens when the permafrost thaws?
Part of Kapisillit in Nuup Kangerlua in summer – photo by Vikebe / Wikimedia Commons
The study’s original purpose was partly prompted by a modern concern: what happens to microbes preserved in archaeological deposits as Greenland’s permafrost thaws?
Arctic temperatures are increasing considerably faster than the global average, exposing archaeological sites to thawing, erosion and changing precipitation. Many Greenlandic middens are also situated near coastlines, making them vulnerable to erosion and the loss of archaeological material into the sea.
The researchers therefore examined whether midden-associated microbes were spreading into the surrounding environment. At the eroding Paleo-Inuit site of Sermermiut, they followed bacterial communities from the midden through the erosion front, cliff and beach sediments and finally into the tidal zone. The microbial composition changed rapidly with distance from the midden and was eventually replaced by marine communities.
“The microbiome in thawing permafrost appeared to be rapidly replaced by local contemporary environmental microbes once released into run-offs,” observed co-author Dr Saria Otani, an associate professor at the National Food Institute.
The study therefore found little evidence that potentially harmful midden-associated microbes are currently spreading over substantial distances. The authors conclude that their dispersal appears to be highly localised.
That does not mean the situation will remain unchanged. As warming and erosion continue, archaeological deposits are likely to become increasingly exposed, and the researchers argue that microbial monitoring could become part of future work at Arctic archaeological sites.
For medievalists, however, the research offers another reason to pay close attention to Greenland’s rubbish. Centuries after the Norse settlements disappeared, the biological traces left in their middens, livestock enclosures and grazing grounds are providing a new way to reconstruct the workings of a medieval Greenland farm.
The article. “Microbial composition of archaeological middens: tracing human footprints through centuries in Greenland’s ancient settlements,” by Lorrie Maccario, Saria Otani, Judit Szarvas, Louise Hindborg Mortensen, Bo Elberling, Kirstine Eiby Møller, Christian Edelfelt Koch Madsen, Frank M. Aarestrup and Anders Priemé, is published in Frontiers in Microbiology. Click here to read it.
Top Image: The field research in Greenland. Image credit: Louise Hindborg Mortensen
Rubbish heaps left behind by Greenland’s medieval Norse settlers are revealing new details about farming, livestock and everyday life. Researchers have found that microbial traces can survive in archaeological deposits for centuries, offering another way to investigate how people lived in medieval Greenland.
A new study has examined microbial DNA preserved in middens across Greenland, some representing thousands of years of human activity. Among them are rubbish heaps and surrounding soils associated with Norse settlements, where researchers found distinctive biological signatures connected with livestock, human activity and decomposing organic material.
Published in Frontiers in Microbiology, the research examined archaeological deposits left by Paleo-Inuit populations, medieval Norse settlers and Inuit from the early colonial period. The study focused primarily on whether microorganisms preserved in permafrost might present a danger as Greenland warms, but its results also demonstrate how microbes can provide evidence about activities that took place at archaeological sites centuries ago.
Greenland’s Norse settlements date from roughly the 10th to 15th centuries. The settlers established farming communities in southwestern Greenland and raised domestic livestock. Their rubbish accumulated in middens containing materials such as animal bones, excrement, mollusc shells and artefacts, creating deposits that archaeologists can use to investigate diet, habits and everyday life.
“Here we show that the risk of release of ancient pathogens from ancient middens on Greenland is currently low,” said Dr Frank Møller Aarestrup, a professor at the National Food Institute of Denmark Technical University and corresponding author of the study. “Rather, we found that these middens in the cold Arctic acted like long-term natural experiments. Human- and animal-associated bacterial signals, including opportunistic bacteria and bacteria carrying antibiotic resistance genes, have remained detectable in them many centuries later as the legacy of human activity: for example, livestock farming by the ancient Norse.”
Microbial traces of a medieval farm
Researchers collected samples during fieldwork in Greenland and used DNA sequencing to reconstruct the bacterial communities preserved within them. Altogether, the study compared 78 midden samples with 143 samples from surrounding soils. The midden material represented several periods of Greenland’s settlement history.
For the medieval Norse period, the researchers examined 34 midden samples from Kapisillit, on the coast of Kapisillit Fjord about 80 kilometres east-northeast of Nuuk. They did not restrict their investigation to the rubbish heap itself. Another 50 samples came from the settlement’s infields, which were used as winter enclosures for livestock, while 30 came from outfields used for summer grazing. A further 48 outfield samples were taken near Norse settlements around Narsarsuaq in southern Greenland.
This allowed researchers to compare microbial signatures from different parts of the medieval farming landscape. The communities varied according to their archaeological context, with samples clustering according to whether they came from middens, infields, outfields, surface deposits or deeper material. The researchers found that the microbial communities were therefore structured by what had taken place at particular locations rather than being uniform across the landscape.
The medieval rubbish itself also produced distinctive results. Norse-period middens at Kapisillit associated with decomposing bones contained comparatively high proportions of unidentified Proteobacteria and Clostridiaceae. More generally, the researchers found that both the age of a midden and the type of material deposited there affected which bacterial signatures remained detectable.
Across all of the middens included in the study, researchers identified 1,207 bacterial species, with between nine and 202 detected in individual samples. Many organisms could only be identified at broader taxonomic levels, something the researchers say highlights how poorly described the microbial communities of Arctic soils and archaeological deposits remain.
The midden samples were generally richer in host-associated bacteria than surrounding soils. Some were organisms associated with human and animal intestinal microbiomes, providing a microbial trace of waste, carcasses and other material deposited by the people who once occupied these sites.
There was also evidence of antimicrobial resistance genes throughout the archaeological landscape. At the Norse sites, researchers detected resistance genes that could have originated both naturally in soils and through faecal or livestock inputs. Significantly, their distribution was not confined to rubbish heaps: the researchers found them in middens, infields and outfields, suggesting that these microbial traces extended across the wider Norse farm landscape.
Centuries preserved in the cold
The study also demonstrates how long biological traces of human activity can remain detectable in Greenland.
The oldest Paleo-Inuit middens had bacterial communities more similar to ordinary soils, suggesting that the microbial imprint of people and animals gradually diminishes. The medieval Norse middens nevertheless retained distinctive signatures centuries after the settlements themselves were abandoned. The researchers suggest that cold temperatures and water-saturated conditions have contributed to this preservation.
There is an important limitation to what these findings can tell us. The researchers did not carry out the specialised authentication procedures necessary to establish conclusively that individual DNA fragments themselves are ancient. They therefore caution that the results should be understood as preserved microbial DNA signatures in archaeological deposits, rather than proof of authenticated ancient microbiomes or that the microorganisms themselves remain alive.
The findings nevertheless suggest another potential source of evidence for archaeologists. Animal bones, artefacts and other visible remains have long made middens valuable records of past communities. Microbial signatures can add another layer, potentially helping researchers distinguish between different activities and areas within settlements.
What happens when the permafrost thaws?
The study’s original purpose was partly prompted by a modern concern: what happens to microbes preserved in archaeological deposits as Greenland’s permafrost thaws?
Arctic temperatures are increasing considerably faster than the global average, exposing archaeological sites to thawing, erosion and changing precipitation. Many Greenlandic middens are also situated near coastlines, making them vulnerable to erosion and the loss of archaeological material into the sea.
The researchers therefore examined whether midden-associated microbes were spreading into the surrounding environment. At the eroding Paleo-Inuit site of Sermermiut, they followed bacterial communities from the midden through the erosion front, cliff and beach sediments and finally into the tidal zone. The microbial composition changed rapidly with distance from the midden and was eventually replaced by marine communities.
“The microbiome in thawing permafrost appeared to be rapidly replaced by local contemporary environmental microbes once released into run-offs,” observed co-author Dr Saria Otani, an associate professor at the National Food Institute.
The study therefore found little evidence that potentially harmful midden-associated microbes are currently spreading over substantial distances. The authors conclude that their dispersal appears to be highly localised.
That does not mean the situation will remain unchanged. As warming and erosion continue, archaeological deposits are likely to become increasingly exposed, and the researchers argue that microbial monitoring could become part of future work at Arctic archaeological sites.
For medievalists, however, the research offers another reason to pay close attention to Greenland’s rubbish. Centuries after the Norse settlements disappeared, the biological traces left in their middens, livestock enclosures and grazing grounds are providing a new way to reconstruct the workings of a medieval Greenland farm.
The article. “Microbial composition of archaeological middens: tracing human footprints through centuries in Greenland’s ancient settlements,” by Lorrie Maccario, Saria Otani, Judit Szarvas, Louise Hindborg Mortensen, Bo Elberling, Kirstine Eiby Møller, Christian Edelfelt Koch Madsen, Frank M. Aarestrup and Anders Priemé, is published in Frontiers in Microbiology. Click here to read it.
Top Image: The field research in Greenland. Image credit: Louise Hindborg Mortensen
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