Russian Geographer Assesses Parameters of Ancient Rivers in Western Siberia

Река Обь. Фото: Андрей Гребнев, участник конкурса РГО "Самая красивая страна".

What were the rivers of Western Siberia like in the relatively recent past – in the Late Glacial period about 16-18 thousand years ago? The answer to this interesting question was given by the reconstruction of the hydrological regime of ancient watercourses, done by Aleksey Sidorchuk, lead researcher at the Research Laboratory of Soil Erosion and Fluvial Processes of the Geographical Faculty of Moscow State University. It turned out that paleorivers were much wider and fuller than modern ones. For example, the annual total flow of the Ob into the Arctic Ocean was about three times higher than current figures.

Wide winding channels of ancient Siberian rivers were first discovered at the end of the 19th century. They were significantly larger than modern ones in the same drainage basins. Initially, this was explained by local factors, but later it became clear that this phenomenon has a global distribution and is due to the climatic conditions of the past, which differed from the current ones.

In his research paper, the author used methods of quantitative paleohydrology based on morphological indicators: size, proportions, patterns of development.

"Morphometric dependencies based on the geometry of the riverbed and developed for modern rivers are also valid for ancient rivers. According to these dependencies, the width of the river is a power function of water flow. The width of the paleorivers was determined using satellite images. By reverse recalculation, the daily intensity of water intake from snowmelt was obtained, which turned out to be five times higher than the current one. It follows from this that the total annual flow of fresh water into the Arctic Ocean was several times larger than the modern one," Aleksey Sidorchuk noted.


На космическом снимке видны древние излучины в пойме реки Кулунда. Фото: географический факультет МГУ.

In general, the size of river basins on the West Siberian Plain in the past did not differ much from today. However, the rivers carried much more water into the ocean and were 2-16 times wider.

According to calculations, the total annual flow of the Ob into the ocean was about 1,000 km3. This is three times higher than the current figures. During the last deglaciation, the river was a significant source of fresh water entering the Arctic Ocean. At that time, the air temperature in summer during the snowmelt was the same as it is now, and the winter temperature was lower by 8-10°C. The total amount of precipitation has increased and redistributed throughout the year: there is more of it in the winter months. The permafrost boundary was 15° south of the modern one (it is more than 1,500 km).

More information about the study can be found in the article of the science journal Water.