Lake Ohrid, between Albania and North Macedonia, is one of Europe’s oldest and deepest lakes. Lakes like this usually only last a few hundred thousand years before they become filled with sediments, but this doesn’t seem to be the case for Ohrid as it is much older. Now, its age has allowed researchers to open a window into the past of the Mediterranean Basin.
As reported in Nature, scientists were able to gain an insight into what the climate was like over the past 1.36 million years in the mid-to-north Mediterranean. The researchers have shown that during warm, interglacial periods, the winter rainfall in the Med has been in phase with the occurrence of African summer monsoons.
"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," co-author Dr Alexander Francke, from the University of Wollongong, said in a statement.
"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."
The team collected sediments in a place where the lake is 245 meters (804 feet) deep. They drilled 568 meters (1863 feet) into the sediments and were able to reconstruct the climate history of the lake over its entire existence.
By combining the data with climate model simulations, they were able to gain insights into the climate in the central-northern Mediterranean. The region is characterized by wet winters and dry summers and this is linked to its interaction with the tropical African climate, especially in terms of the warming of the sea's surface.
"This climate system would be fairly stable during the summer and autumn until the temperatures decrease in winter and cold air from the north causes the whole system to become unstable and this low-pressure system moves eastwards towards the Balkan Peninsula and promotes rainfall in the winter months," Dr Francke explained.
But it is not just about the past. Climate models have encountered difficulties in predicting how the human-made climate crisis will affect the Med in the coming years. Some point at wetter winters, others at drier ones. This new data will be key to refining the models and providing clues to what the future holds for the Mediterranean.