A biological island in the ice
Lake Baikal's extreme age and isolation have created an unparalleled evolutionary laboratory. Of the more than 2,600 recorded species in the lake, about two-thirds are endemic, meaning they exist nowhere else on the planet. This massive body of water, technically a rift lake, is located in a continental rift zone where the Earth's crust is slowly pulling apart.
The most famous resident is the Baikal seal, or nerpa (Pusa sibirica). It is the world's only exclusively freshwater seal. How its marine ancestors arrived in this landlocked Siberian lake is a topic of scientific debate, with theories pointing to ancient connections to the Arctic Ocean during a previous ice age. These seals have adapted to the unique environment with unusually large eyes for hunting in the clear, deep water.
The nerpa's primary food source is the golomyanka (Comephorus baikalensis), another local marvel. This translucent, scaleless fish is about 30% fat and gives birth to live young, which is unusual for fish. It lives in the deep, cold waters and is a large portion of the lake's fish biomass. The lake's food web also depends on a tiny endemic crustacean, Epischura baikalensis, which makes up the bulk of the zooplankton and filters the lake's water, contributing to its clarity. In winter, visibility can extend down to 40 meters.
Water, ice, and neutrinos
The water in Lake Baikal is clear but also highly oxygenated, even at its greatest depths. This is a rare quality for such a deep lake and lets a complex ecosystem thrive throughout the entire water column, from the surface to the abyssal floor over a mile below. The lake bottom even features hydrothermal vents, similar to those found in deep oceans, which support unique communities of organisms.
During the five months of winter, the lake surface freezes into an ice sheet up to 1.5 meters thick. The extreme temperature differences between the air and the water cause the ice to crack and expand, producing loud, resonant sounds that have been compared to booms, clicks, and laser blasts.
This combination of extreme depth, water clarity, and a protective ice cover has made Baikal an good location for a different kind of science: particle physics. The Baikal-GVD (Gigaton Volume Detector) is one of the world's largest neutrino telescopes. It uses the pure lake water as a natural detector. Arrays of light-sensitive optical modules are lowered deep into the lake to spot the faint flashes of Cherenkov radiation produced when high-energy neutrinos from space interact with water molecules.