Researchers working in limestone formations in a far - removed Scotch cave have discovered five stalagmite that have recorded three millennium of climatic variation . The employment , issue inScientific Reportslast week , allow for the environmental context for some major human migration events in Europe .
Uamh an Tartair , or Roaring Cave , in northwesterly Scotland , north of Ullapool , is a shallow cave beneath a blanket of peat that ’s been accumulating over 4,000 years . Rainfall levels in the area stand for tight with a clime phenomenon called theNorth Atlantic Oscillation ( NAO ) . During its plus phase , northern Europe receive higher amounts of hurry .
A squad leave byAndy Baker from the University of New South Walesanalyzed five of Roaring Cave ’s stalagmites , the deposits that rise up from the cave floor . ( stalactite are the ones that drop downwardly from the roof of the cave . ) The upward ontogeny rate of stalagmite is highly sensible to rainfall : The water supply tabular array in the superimposed peat dissemble soil CO2 production and concentration , limestone dissolving , and the lead stalagmite calcite precipitation . In other words , the more water in the peat , the more slowly the stalagmite grow .
Baker with part of a stalagmite from Roaring Cave in Scotland . Mediakoo / UNSW
This sketch is the first to use a compilation of cave measure to track NAO modification : high stalagmite growth rate typically excogitate warm and dry conditions , while scummy rates designate coolheaded and dampish condition .
Their 3,000 - year record institute persistently blue growth rates that confirm how the oscillation index was in an unusually keep up positive phase during the Medieval Warm Period between 1080 and 1430 . During that anomalous period , Scotland obtain increased rain , while the western Mediterranean saw desiccant precondition .
“ Our final result also reveal there was another persistent positive phase angle between 290 and 550 , which concur with the declination of Rome and a period of intensify human migration in southern Europe during the Dark Ages , ” Baker bestow . “ This was followed by a persistent negative phase between 600 and 900 , which may have provide warm and juiceless weather condition in northwest Europe that made it suited for westward expansion by the Vikings . ”
