The temperature prevailing hundreds, and even thousands of years ago, you can know, among others examining the cores of lake sediments. Polish Scientists have examined almost 11,000 years of history Lake Żabińskie. – In our reconstruction, modern climate warming is perfectly visible. It reached the values previously unheard of in the Holocene. What is even more important, the growth rate in the last 90 years is unprecedented. According to our reconstruction, it reached an average of 0.28 ° C per decade – says prof. Wojciech Tylmann, one of the authors of the study published in Geophysical Research Letters (Zander et al., 2024).
Prof. Tylmann in an interview with “Science of the Climate” explains that this is another of the evidence on the dominant influence of man on the shaping of the modern climate of the Earth. – There is no doubt that emissions gases greenhouse contribute to temperature increases. Science does not have another explanation today that would explain it – emphasizes an expert from the Faculty of Oceanography and Geography of the University of Gdańsk. However, the main reason for conducting the study was something different.
The warmer, the greater the variability
Climate forecasts not only indicate that due to greenhouse gas emissions, the Earth will become warmer. They also suggest that the warmer the planet is, the greater the temperature variability (on a long -term scale). The researchers who looked at the history of Lake Żabiński wanted to check whether such a relationship actually occurred in the past. And it turned out that yes.
– Our reconstruction shows that during the Holocene thermal maximum (approx. 9-5 thousand years ago) temperature variability was indeed greater than in the colder periods of Holocene. It can therefore be assumed that in the future during the man -caused and progressive insulation will be similar – explains prof. Tylmann.
Lake history, climate history
In the database regarding temperature changes in the last 12 thousand. There are over 1.3 thousand years. various types of reconstruction of historical climatic conditions. Many of them are made on the basis of sediment analyzes. Most, however, use data with time resolution up to 50 or 100 years. Just a few dozen reconstructions have a resolution of 20 years or less.
In the case of Lake Żabiński, the analysis is even more accurate, because each analyzed sediment sample represented a period of three years. The researchers wanted to assess whether it was possible to demonstrate differences in decaded temperature variability.
The results show not only that today the lake is the warmest and warms the fastest in its history. They also show such significant climatic events as the Little Ice Age or medieval climate anomaly.
Our reconstruction is one of the few in the world that operates such high time resolution. Thanks to this, we could look at what is not visible in other reconstructions
– emphasizes prof. Tylmann. But how are such reconstructions at all?
20 meters of sediment
In most cases, sediments at the bottom of the lake are subject to more or more disorders, which makes them disappear for the next years. Sometimes, however, they behave intact. This is the case with the lake located in Masuria, in which the layers of the annual sludge increases can be seen – and divided into the season.
– In spring and summer, a light layer, i.e. calcium -rich in carbonate, accumulates, and in autumn and winter a dark layer, in which the remains of organisms living in water and other organic remains dominate. Such two layers are so -called Varnish, or settlement postponed in one calendar year. The principle of determining the age of the sediment by counting the WARW [warwochronologia] So it is similar to counting the age of the tree with the help of incremental jars – explains in an interview with “Science of the Climate” prof. Tylmann.
In the case of Żabiński Lake, scientists with specialized drilling equipment stuck the appropriate samples into the bottom of the lake. In this way, they took the cores with sediment reaching almost 20 m long (in the same way, e.g. the past of glaciers is examined). The samples were analyzed using the XRF scanning method, which does not destroy deposits and allows you to achieve a very high resolution of measurements. Thanks to this, as many as 50 measurements of the content of elements could be made in each centimeter.
Calcium will tell you the truth
Calcium carbonate was the indicator that scientists were the most. – The increase in temperature increases the efficiency of precipitating calcium carbonate, which makes more to the bottom. Therefore, layers of sediment and higher calcium carbonate content can represent warmer periods, and those in which it is less – cooler periods – explains prof. Tylmann.
Researchers chose this indicator based on the conclusions of previous research, which has been carried out for several years in the case of Żabiński Lake. They showed that there is a statistical relationship between calcium carbonate content in sediments and meteorological conditions. When the same was confirmed by data analysis for the last 60 years, scientists already knew that the content of calcium carbonate is crucial to understand the history of the Żabiński Lake.
The article comes from the portal Science about the climate