6 June 2019

Publication in Scientific Reports

Rotation of the earth causes currents in Lake Garda

Lake Garda (Wikimedia Commons)

The earth’s rotation has surprising effects on narrow, deep lakes such as Lake Garda. Utrecht physicists Sebastiano Piccolroaz and Henk Dijkstra and researchers from the University of Trento conclude this on the basis of measurements in Lake Garda and a simulation model. The researchers published their results this week in Scientific Reports.

Lake Garda from space (Wikimedia Commons)

The rotation of the earth influences the water currents in the lake, which in turn influence the transfer of oxygen between the water surface and deep water layers. This is an important insight, because climate change can lead to the development of water layers without oxygen in narrow, deep lakes such as Lake Garda. Such so-called anoxic layers can have major consequences for local ecosystems.

Secondary current

When the wind blows along the main axis of Lake Garda – from the northeast to the southwest or vice versa – the rotation of the earth causes a secondary current that moves the water from one coast to another. This causes a difference in water temperature between the eastern and western coasts and the transport of oxygen, nutrients and other substances between the surface of the water and deeper water layers. “This phenomenon is familiar in coastal areas of oceans and large lakes,” the researchers said. “Because of the small size of Lake Garda, we didn't expect to see it here as well.”

Turbulence microstructure profilers used for the monitoring (photo by Sebastiano Piccolroaz)

Coriolis effect

Due to this secondary current, cold water rises along the east side of the lake, while the warmer water moves down along the west side. This current is caused by the interaction between the geometry of the lake and the coriolis effect: due to the rotation of the earth, currents in the northern hemisphere bend to the right, and in the southern hemisphere to the left. Between February and April, when the lake’s water temperature is at its lowest, this effect even causes water to mix all the way to the bottom of the lake, at a depth of 350 metres.

 

Monitoring in the snow, 28 February 2018 (photo by Alessandro Bottazzi)

Publication

Importance of planetary rotation for ventilation processes in deep elongated lakes: Evidence from Lake Garda (Italy)
Sebastiano Piccolroaz*, Marina Amadori, Marco Toffolon, Henk A. Dijkstra*
Scientific Reports, 5 July 2019, DOI 10.1038/s41598-019-44730-1
* affiliated with Utrecht University