Lake Baikal is the largest freshwater lake in the world, with an average depth of over 5000 feet down and is 25 million years old so is therefore not only the deepest lake but oldest.

Lake Baikal contains roughly 20% of the world's surface fresh water that is unfrozen and is located in the south of the Russian region of Siberia, has provided scientists with insight into the ways that climate change affects water temperature, which in turn affects life in the lake.

The study is published in the journal PLoS ONE today. The research team discovered many climate variability signals, called teleconnections, in the data. For example, changes in Lake Baikal water temperature correlate with monthly variability in El Ni?o indices, reflecting sea surface temperatures over the Pacific Ocean tens of thousands of kilometers away. At the same time, Lake Baikal's temperatures are influenced by strong interactions with Pacific Ocean pressure fields described by the Pacific Decadal Oscillation.

The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N. During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs.

The scientists found that seasonality of Lake Baikal's surface water temperatures relate to the fluctuating intensity and path of the jet stream on multiple time scales. Although the lake has warmed over the past century, the changing of seasons was not found to trend in a single direction, such as later winters.

The climate indices reflect alterations in jet stream strength and trajectory, and these dynamics collectively appear to forecast seasonal onset in Siberia about three months in advance, according to the study.

Lake Baikal's seasonality also tracked decadal-scale variations in the Earth's rotational velocity. The speed of the Earth's rotation determines the length of a day, which differs by milliseconds from day to day depending on the strength of atmospheric winds, including the jet stream. This scale of variability was also seen to affect the timing variability in seasonal lake warming and cooling, reinforcing the mechanistic role of the jet stream.

"Remarkably, the temperature record that reflects all these climate messages was collected by three generations of a single family of Siberian scientists, from 1946 to the present, and the correlation of temperature with atmospheric dynamics is further confirmation that this data set is of exceptionally high quality," said Katz who is another author.