“Borealization” of the Arctic Ocean as a new reality | Polarjournal
The Arctic Ocean covers an area of almost 14 million square kilometres, surrounded by continents and which is covered (to a large extent) by ice. Since it has only two inputs/outputs, it is usually divided into a Eurasian and Amerasian area, separated by the Lomonossov ridge, which also change which change in different ways, according to the study. Photo: Michael Wenger

The Arctic Ocean, the smallest of all oceans, has so far been explored only marginally. But the faster melting ice sheet also paves the way for science to study the change drivers and their effects more closely. An international research team has now found that the masses of water flowing into the basins of the Arctic Ocean from the south bring stronger and deeper changes than previously thought.

The study, conducted under Finnish-American leadership, examined how the now warmer waters affect the two different basins of the Arctic Ocean and what influences match with observations made. It was shown that in the Eurasian area of the ocean, the warmer, more salty water of the Atlantic ensures that the previously stable cold and somewhat more fresh-water upper layer of the Arctic Ocean slowly dissolves and slightly warmer deep water reaches the surface, where the sea ice then melts even faster.

“In many respects, the Arctic Ocean now looks like a new ocean”

Professor Igor Polyakov, University of Alaska Fairbanks
Picture: Courtesy of the University of Alaska Fairbanks

On the Amerasian side, it is the other way around, as the invading Pacific water is less salty than the Arctic Ocean. Together with the increased freshwater inputs from rivers (through more rain), a more stable separation layer is created here, which prevents the water masses from the depth from mixing and thus achieves a reduction in the productivity of the region. “In many respects, the Arctic Ocean now looks like a new ocean,” explains lead author Professor Igor Polyakov, an oceanographer at the University of Alaska Fairbanks.

The borealization of the Arctic Ocean is no longer a theoretical model, but has already begun. On the Pacific side of the ocean, saithe (also called Pollock) has now migrated to the Chukchi Sea and in such quantities that fishing is worthwhile.

The authors of the study were able to draw on satellite data from 1981 to 2017 on the development of sea ice. They also used the simultaneous oceanographic data, which are continuously collected in the Arctic Ocean. They were also able to incorporate the geochemical data to determine productivity into their work. “The goal of our research was to illustrate the part of Arctic climate change driven by anomalous influxes of oceanic water from the Atlantic Ocean and the Pacific Ocean, a process which we refer to as borealization,” explains Igor Polyakov. The authors were surprised that this change reaches to great depths.

The changes that have already begun are affecting food webs and can accelerate another step towards a new Arctic reality. But many questions remain as to how the effects of physical, geochemical and biological changes will look in detail.

The impact of this Arctic ocean borealization also has serious consequences for species composition in the Arctic Ocean. This is because the mixture creates a kind of biological pump with more nutrients from the depths and the surface becomes more biologically productive for more heat-loving organisms from the south. These then displace the adapted Arctic inhabitants into areas that are not yet subject to the effects. But these regions are becoming smaller and the new species are spreading faster. An example of this is the large amount of pollock or saithe, which have now been registered in the Bering Sea and the Chukchi Sea. As a result, the entire food web gets mixed up and top predators such as seals and polar bears lose not only their habitat, but also their food sources. Although polar bears, for example, are highly adaptable, such changes can come too quickly and put already weakened populations at greater risk. And man, too, will have to adapt to the new reality.

Dr Michael Wenger, PolarJournal

Link to the study: Polyakov et al (2020) Front Mar Sci 7 (491) Borealization of the Arctic Ocean in Response to Anomalous Advection from Sub-Arctic Seas; https://doi.org/10.3389/fmars.2020.00491

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