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Sept. 3 (UPI) -- After five years of drilling in Lake Ohrid, Europe's oldest lake, scientists have extracted sediment cores comprising more than a million years of climate history. The climate timeline, unprecedented in length, revealed a unique connection between the Mediterranean climate and the African monsoon.
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Researchers began studying Lake Ohrid, which is located between Albania and North Macedonia, more than 15 years ago. In 2013, scientists began drilling. The deepest drilling, which occurred several hundred feet beneath the lake's surface, penetrated more than 1,800 feet underground.
As sediment cores were extracted over the last five years, scientists analyzed their layers for insights into the Mediterranean's climate, like changes in annual precipitation levels. By comparing the geologic data with the predictions of climate models, scientists were able to calibrate their simulations of climate patterns in the Mediterranean and elsewhere, as well as make connections between different changes -- shifts in temperature and rainfall, for example.
"This way, our research helps us to better understand the causes of rain phases and to more accurately assess the effects of climate change for future predictions," Bernd Wagner, University of Bern geologist, said in a news release.
During their analysis of Lake Ohrid sediments, scientists found evidence of a correlation between periods of warming and increased winter precipitation in the northern Mediterranean. The research -- published this week in the journal Nature -- also showed warmer temperatures triggered the development of low pressure systems over the western Mediterranean, particularly during autumn. The pattern correlated neatly with the strength and timing of the African monsoon.
"We discovered a teleconnection between the African monsoon and winter precipitation in the Mediterranean region, so between tropical climate systems and rainfall in the mid-latitudes thousands of kilometers away," said Alexander Francke, a research fellow at Wollongong University in Australia. "Whenever incoming solar radiation from the sun is enhanced in the northern hemisphere you have this northward migration of the tropical climate system and we see increased rainfall in winter at Lake Ohrid. We see this mechanism consistently over the past 1.3 million years."
Researchers were also able to precisely date the lake's origins.
"We have shown that the lake formed exactly 1.36 million years ago and has existed continuously ever since," said Bern geologist Hendrik Vogel. "We were thrilled when we realized that we had retrieved one of the longest and most complete lake sediment cores from the oldest lake in Europe. Getting the chance to obtain high-resolution regional climate data for a period of over 1.3 million years is the dream of every climate researcher."
