Swiss Alps Have Influenced Europe's Climate Since the Miocene

Switzerland's highest peaks in the geologically young central Alps have been this high for quite some time, as a new study shows. 15 million years ago Europe's own mountain range was at least as high as today. Scientists at the Biodiversity and Climate Research Centre (BiK-F), the Goethe University in Frankfurt and the ETH Zurich compared the isotopic ratios of water and oxygen in rocks in the Alps and Alpine foreland and were able to determine the height of the peaks in the past. The study was recently published in Earth and Planetary Science Letters.

Interestingly, the history of the topography of the European Alps, which are certainly the best-studied mountain range in the world, is virtually unknown. A new study is likely to reveal more, as it shows the topography of the central Alps seen today has its roots 15 million years ago. At that time the highest peaks in Switzerland were between 2,850 and 3,350 metres high. As such, the mountain range was on average even higher than today. "This leads us to conclude that the bulk of Alpine topography was built over 15 million years ago, when Europe collided with Africa and the accretion rates exceeded removal by erosion at the same time," explains Marion Campani, the lead author of the study at the Biodiversity and Climate Research Centre (BiK-F).
Alps have influenced precipitation in southern Europe for 15 million years
High mountain ranges form a natural obstacle for moist air masses and can affect the climate on both sides of it. Their height is the decisive factor. The new findings therefore lead to conclusions about precipitation patterns in southern Europe and Eurasia and indirectly about conditions for the development of entire ecosystems in the Mediterranean as well. This means that the Alps as they have towered this region for the past 15 million years have determined the transport of precipitation since then from the Atlantic toward central Europe and Eurasia. Therefore the mountain range had a crucial effect on the climate in the eastern Mediterranean. "In the past this region was repeatedly threatened by drought and is a hotspot for water shortages associated with global warming. If you want to understand the climate of the past and derive projections from the future of the region from it, you can't avoid the Alps," says Prof. Dr. Andreas Mulch, BiK-F and Goethe University Frankfurt.
Previous height determined by geochemical traces of precipitation
How high mountains were during their history can be reconstructed by means of oxygen isotopes. Preserved in rocks, they store information about precipitation in the past over millions of years. This works because both elements occur as differently weighted isotopes. With increasing amounts of precipitation the proportion of heavy isotopes of oxygen systematically decreases. So the ratio of heavy to light isotopes in ancient rainwater tells you how high the area was the precipitation fell unto at a particular period. In a novel approach the researchers compared for the first time precipitation from the Alpine foreland (which were approximately at sea level at the time) and from the former highland areas of the Alps. Thus they were able to determine the relative difference in the height of the mountains compared to the planes. "In addition, mountains over a certain height are capable of influencing the climate and continental rainfall patterns themselves. Which is why we also have to consider the moisture source so we can take account of initial changes in the composition and amount of precipitation in the isotope analysis," says Campani about the method of the study.

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