The Arctic Ocean has reached a critical state, which leads to further irreversible changes. A new study by scientists at the University of Edinburgh has shown that the rapid reduction in sea ice has triggered chemical processes that deprive water of a key nutrient – nitrates for plankton, which even huge whales feed on.
Melting of ice in the ocean. Photo: Vadim Kantor / PORA Photobank
This hidden shift has led to massive and potentially irreversible transformations in the ocean, disrupting the food chain from the bottom up, affecting all species of fauna, from fish and birds to marine mammals, and weakening the Arctic Ocean’s ability to absorb carbon from the atmosphere.
In recent years, scientists have observed significant changes in the number of wild animal populations in the Arctic, but the main reasons for these changes have not been fully understood. The researchers tried to find answers by examining oceanographic research data collected over more than 20 years.
The analysis revealed a turning point that began around 2009: since that period, nitrate levels in waters leaving the Arctic Ocean have been steadily decreasing. This coincided with a period of rapid acceleration of ice melting.
The disappearance of the ice sheet has opened vast shallow areas of the ocean to sunlight. This accelerated the natural but destructive process, during which nitrates in the sediments began to turn into nitrogen gas and irrevocably leave the ocean.
Shallow-water shelf zones occupy almost half of the area of the Arctic Ocean, which makes this process particularly significant. Nitrates are food for microscopic algae (phytoplankton) that feed on zooplankton (shrimps, crustaceans, and others). They, in turn, feed on fish, and then on seals, dolphins and, finally, polar bears.
A decrease in nitrate concentration changes the structure of the plankton community itself, giving an advantage to less productive species, which reduces water productivity. In addition, phytoplankton absorb carbon dioxide, and the weakening of its growth reduces the ability of the ocean to retain carbon, exacerbating the climate crisis.
Since these changes are related to the ongoing reduction of sea ice, researchers believe that the Arctic Ocean is unlikely to return to its former state.
For many years, it was expected that the release of Arctic ice would lead to a rapid growth of phytoplankton due to the influx of light to the water. However, the reality turned out to be different – the ocean switched to a nutrient restriction system.
This has far-reaching implications for marine ecosystems, food chains, and the role of the Arctic in Earth’s climate. The detected changes indicate that the ecosystem has passed a critical point and irreversible negative changes have begun.
By Anna Shchetinina
