Who brought 800 cattle to the Azores around AD? Who lit big fires there around 850? And which people left behind human poo molecules dating back to the eleventh century in a lake in the Azores?

All of these questions are raised in a particularly comprehensive study of the sediment in five freshwater lakes on five islands of the Azores. This archipelago is located in the middle of the Atlantic Ocean, 1,500 km west of Portugal and 2,000 km southeast of Canadian Newfoundland, the easternmost tip of North America.

In the fifteenth century the islands were colonized by Portuguese explorers and they are still part of that country. According to 15th century Portuguese writings, the Azores were then uninhabited and covered with dense forest, but the sediment study published this week by a large international team in the PNAS now comes to very different conclusions. Partly on the basis of analysis of the prevailing Atlantic winds in the early Middle Ages, the researchers, led by Pedro Raposeiro (University of the Azores), strongly suspect that those early inhabitants of the Azores must have been Normans, the only seafarers from the Atlantic region who were then capable of distant ocean voyages.

Icelandic literature

In Icelandic literature much can be found about Viking voyages to Iceland in the ninth century and to Greenland and Newfoundland in the tenth and eleventh centuries, but nothing is known about colonization of more southern Atlantic areas such as the Azores.

Yet there is since 2014 a direct medieval link known between Scandinavia and the Azores, even though in principle it only concerns the DNA of mice – a species that does not originally occur on the island and must therefore have arrived there by ships. The DNA of the mice that now live in the Azores clearly shows that their origin is in Southern Europe, but there is also an unmistakable signal in the mouse DNA that indicates that they also have ancestors from Scandinavia. which, according to mutation calculations, must have arrived in the Azores sometime around 1100.

That there must have been habitation on the Atlantic islands for the Portuguese has already been deduced from the discovery from about a thousand-year-old mouse bones on the island of Madeira (which is not part of the Azores, but is ‘near’, 500 km south-east, towards the African coast). There has also always been the intriguing fact that the Azores could already be found on numerous maps from the late fourteenth century before their ‘official discovery’ by Portuguese navigators between 1425 and 1452. Sometimes there is even a connection between the name of Madeira (Portuguese for wood) and the Markland (‘forest land’) from the Norwegian literature on the exploration of North America. There is no doubt that Markland was somewhere in America, but the name may have influenced the Italian namesake of the island in the fourteenth century. The oldest mention from 1351, in an Italian atlas, is Island of the timber (wood island). Incidentally, there is no source for meetings with possible Norwegian-speaking islanders on Madeira.


With all these conjectures and speculations, the highly detailed molecular analysis of lake sediments in the Azores is a welcome reinforcement of the ideas about pre-Portuguese habitation of the Azores. Due to the stratification of the sediments, the finds of organic molecules, soot particles and pollen can be dated fairly well.

The first sign of human entry is the appearance of the organic poo molecule 5B-stigmastanol around AD 700 in Lake Peixinho on Pico Island and around 850 in Lake Caldeirão on Corvo – direct evidence of the presence of cattle, sheep or goats. It’s not clear whether the presence of livestock — and the people who brought it to the islands — was directly continuous, but at least from the tenth century onwards, this cattle dung molecule has been a permanent presence in the lake sediment.

At that time, clear indications appeared in the sediment that the inhabitants set forest fires to create meadows: a strong increase in soot particles and grass pollen, with a decrease in tree pollen. In the eleventh century, the coprostanol molecule appears in the sediment of Lake Peixinho and later also of Lake Azul on São Michel: a substance that is very abundant in human faeces, and therefore, according to the researchers, a very clear indication. constitutes human presence. They also admit that coprostanol is also found in the poop of other omnivores. In the fifteenth century, the arrival of the Portuguese can also be clearly read in the sediment: even more forest fires, even more grass and even more poop molecules.

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