“White ice, for example, forms when the water surface freezes, thaws, and freezes repeatedly,” said Hans-Peter Grossart, head of the Aquatic Microbial Ecology research group at the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB). Stechlin site in Brandenburg. He took part in the study that sampled frozen lakes. According to the researchers, the findings should give reason to reconsider the rules for entering ice surfaces.
Even lay people can recognize white ice, Grossart explains: “Because of the air it contains, it has a lower density and a rougher surface, which slows you down when skating.” The more frequent occurrence of this type of ice is linked to the fact that winter temperatures no longer rise above zero during the day and cold periods do not last as long as they used to.
Black ice is already rare nowadays. “When a lake freezes overnight at sub-zero temperatures, ice is black. Clear, mirror-smooth beautiful ice – great for skating.”
The study, led by Sweden’s Uppsala University and involving Grossart, was published this summer in the journal Nature Communications. For this purpose, ice sheet samples were repeatedly taken and analyzed from 31 lakes in 10 countries in the northern hemisphere during the winter of 2020/21. Long-term data for the two lakes dating back to 1971 and 1996, respectively, were available and used for comparison.
The studies were carried out during a period said to be one of the warmest winters since 1880. In most cases, therefore, unstable white ice was found during this time, which at times made up the entire ice sheet. The rate of white ice also increased during the winter due to snowfall and perpetual freezing, mostly at night. It has been observed that fatal crashes usually occur at the end of the season, before the melting and unsustainable ice sheet melts.
When the research team took a sample at Dagow Lake, near Stechlin in Brandenburg, they were surprised at how thin the ice sheet they found was, only around ten centimeters, mostly white ice. “There were several hundred people in the lake at the time. So it’s easy to overstate the payload.”
According to the researchers’ estimates, black ice can carry ten times the load of a piece of white ice of the same thickness and size. As a result, if there is a large amount of white ice, there is a much higher risk of collapse despite the deceptively strong ice thickness.
Grossart said of the current study’s findings: “It’s scary to see how much systems have changed.” Ice quality also has consequences on the ecology of lakes, as the light transmittance is different. White ice, for example, provides less light, which alters the photosynthesis of algae and ultimately affects the entire food chain.
Long-term records also show a rapid decline in the number of days lakes freeze in winter, the researchers said. Many lakes are expected to remain permanently ice-free this century. (SDA)