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Blue rings found in the stems of trees and bushes in Norway point to a historic cold period in the late 1800s, but the exact cause of this climatic event remains unclear, scientists say.
Researchers suspect volcanic eruptions in Central and South America may have led to cold summers in Norway between 1877 and 1902, forming peculiar blue rings in Scandinavian trees and shrubs.
A new study published in Frontiers in Plant Science assessed samples from 25 Scots pine trees and 54 common juniper shrubs from a site high on Mount Iškoras in northern Norway.
These samples and shrubs revealed several characteristic “blue rings”, representing the years when they did not grow properly due to the cold climate.
Trees require warm periods in a year to grow properly without which their cell walls don’t solidify for that year. When the cells growing in a particular year do not solidify, they create “blue rings” when the wood samples are dyed.
Since trees and shrubs live for hundreds of years, studying their blue rings allows researchers to spot cold summers.
“Blue rings look like unfinished growth rings and are associated with cold conditions during the growing season,” Agata Buchwal, co-author of the study from Adam Mickiewicz University in Poland, said. In the sampled trees, researchers found that blue rings were common between 1902 and 1877.
Around 96 per cent of pine trees and 70 per cent of juniper shrubs revealed blue rings from 1902 and 84 per cent of trees and 36 per cent of shrubs from 1877.
“In general, we found more blue rings in trees than in shrubs. Shrubs seem to be more adapted to cooling events than trees, which is probably why shrubs are found further north,” Dr Buchwal said.
Since such cold periods can potentially weaken the trees, researchers warn that if the phenomenon persists over several years, it could make them “susceptible to mechanical damage or disease”.
Previous research has linked cold 1902 temperatures in Scandinavia to the volcanic eruption of Mount Pelée in the Caribbean.
Some studies have also found links between the cold Norwegian summer of 1877 and the eruption of Cotopaxi in Ecuador. But researchers say “there is no other evidence” to link the volcanic eruption with temperatures in Norway that year.
“1902’s cold June could be related to the eruption of Mount Pelée in May. Similarly, the late June eruption of Cotopaxi aligns with 1877’s cold August, but there is no other reported evidence for related cooling in northern Norway after this eruption,” scientists say.
“This blue ring could also be due to another, as-yet-unidentified, factor.”
Source: independent.co.uk
