MOSCOW, October 26. /TASS/. Scientists of the Shirshov Institute of Oceanology (the Russian Academy of Sciences) for the first time in the world conducted studies to see how life on the Arctic Ocean's bottom changes at various depths, press service of the Russian Ministry of Science and Higher Education said.
"The distribution of life in depth is called "vertical" or "bathymetric", and normally it is surveyed within certain regions or seas," the press service said. "In the recent study, the scientists have conducted such an analysis for the first time in the entire Arctic Ocean and with a vast coverage of depths - from 14 to 5,416 meters. The scientists used both their original data obtained from about 150 stations and a large spectrum of published information."
When speaking about the applied significance of obtained results, the scientists note that the understanding of how life is distributed in the Arctic Ocean depths may be used to assess environmental impacts from economic activities. For example, in forecasting environmental risks associated with the Northern Sea Route operations, or with laying deep-water pipelines.
The studies have found that the greater the depth, the smaller is the number of animals living on the bottom. For example, the number of invertebrates decreases in the range from about 3,000 to 130 per a square meter, and the biomass decreases from 40 g to 1 g of "raw weight" per a square meter. The species richness, that is, the number of species, which behave in a more complicated manner: at first, it grows and reaches a peak at a depth of 100 to 600 meters, and then gradually decreases with depth.
"Why at all do the "sets" of animals in the ocean change with the depth? This question does not have a straightforward answer. However, every species has its own "vertical distribution range", with certain upper and lower distribution levels. What affects them? Most likely, a complex of reasons, among which are environmental factors (temperature, salinity, soil type, organic matter content in sediment, etc.) and interaction with other species living "in the neighborhood," the press service quoted the institute's Deputy Director on ecology of seas and oceans Andrey Gebruk as saying.
Vertical distribution ranges
This complex of such factors forms "areas of vertical distribution" of marine animal species, the scientist said. Deep-sea animal species many have various vertical ranges: some live within the first hundreds of meters, others prefer several thousand meters in depth.
"The most difficult and challenging task is to trace the depths horizons, where the boundaries of the ranges become "distinct": for some species this may be the lower limit of distribution, for others - the upper one. Such zones point to the most important universal boundaries of distribution in nature, that is, to biogeographic boundaries of certain species," the scientist said.
Inside the Arctic Ocean scientists have identified several depth horizons with similar sets of species and prevailing forms. These horizons were named "lower shelf", "upper slope", "lower slope" and "abyssal". They encircle the entire ocean, and are located one under another. The survey's most important result is that the scientists have managed to clarify positions of boundaries between these belts, or, in other words, positions of the main boundaries in life distribution in depth.
The first important boundary (between the "shelf - lower slope" and the "upper slope") was registered a depth of 450-900 meters. This boundary separates the shelf fauna from the continental slope fauna). In other areas of the World Ocean, this boundary is normally much higher - at a depth of about 200 meters. The second important boundary (between the "lower slope" and the "abyssal") in the Arctic Ocean is located at a depth of 1,700-2,100 meters. It separates the slope fauna from the abyssal (oceanic bottom) fauna. In the World Ocean, this boundary usually lies much deeper, at a depth of about 3,000 meters.
The vertical life distribution patterns found at the bottom of the Arctic Ocean turned out to be universal for the entire basin. As yet, scientists cannot explain what caused such a discrepancy in vertical boundaries' positions in the Arctic Ocean and in the World Ocean. Among such reasons could be a unique ice regime, and the peculiarities of primary products formation, as well as the most powerful freshwater outflow into the ocean by the North's rivers.