Jääkaldade

Jääkaldade refers to a phenomenon observed in cold climates where water bodies freeze from the bottom up. This contrasts with the more common freezing of lakes and rivers from the surface down. The primary reason for this inversion is the unique property of water: its maximum density occurs at approximately 4 degrees Celsius. As the surface water cools, it becomes denser and sinks, while warmer, less dense water rises. This process continues until the entire water column reaches 4 degrees Celsius.

Once the water temperature drops below 4 degrees Celsius, further cooling causes the water to become less dense. This colder water then stays at the surface, where it eventually freezes. The ice formation begins at the surface and progresses downwards, but the initial cooling and convection currents drive the temperature to 4 degrees Celsius throughout the water column before surface freezing becomes dominant. Jääkaldade is therefore a consequence of this density anomaly and the resultant convection.

This phenomenon can be observed in various freshwater environments, including lakes and ponds, particularly those that are relatively shallow or have a significant source of cold, dense water entering from below. The process is a key factor in the survival of aquatic life during winter. By freezing from the bottom up, it can leave a layer of unfrozen water at the surface or a mix of ice and water, which allows fish and other organisms to continue to exist. Understanding jääkaldade is important for limnology and aquatic ecology in regions experiencing harsh winters.