Decline of the Arctic sea ice causing phytoplankton from the oceans farther north

According to new research, the phytoplankton blooms that form the basis of the marine food web are spreading northwards in ice-free waters, where they have never seen each other before.

A new study based on satellite imagery of the color of the ocean reveals that spring blooms of phytoplankton in the Arctic Ocean, which did not exist before, spread to north at a rate of 1 degree of latitude per decade. Although blooms and large phytoplankton blasts have not occurred previously in this region, phytoplankton was present in the low-biomass central Arctic basin. The study also revealed that the primary productivity of phytoplankton, or the rate at which phytoplankton converted sunlight into chemical energy, increased during spring bloom.

According to the authors of the study, the decline of the Arctic sea ice in recent decades has given way to open water areas where phytoplankton can develop, leading to their northward expansion. Researchers do not know what effect this expansion will have on the food web, but the results suggest that the decline in ice cover has an unpredictable impact on marine ecosystems.

If sea ice continues to degrade, it could lead to a springtime phytoplankton bloom further north and further increase primary productivity. According to the study, these changes could affect the fate of the Arctic Ocean as a carbon source or carbon sink.

"If the pack ice disappears completely in summer, it will have consequences for the spring phytoplankton bloom," said Sophie Renaut, Ph.D. student at Laval University in Quebec City, Canada, and lead author of the new study. Letters of geophysical research, a journal of the American Geophysical Union. "We can not predict exactly how this will evolve, but we are almost certain that this will have dramatic consequences for the entire ecosystem."

Phytoplankton in the ecosystem

Phytoplankton is a microscopic organism that lives in water, consumes carbon dioxide and releases oxygen through photosynthesis. In this process, they convert sunlight into chemical energy. Phytoplankton form the basis of the marine food web, indirectly feeding everything from small fish to whales of several tons.

Phytoplankton growth depends on the availability of carbon dioxide, sunlight, nutrients, water temperature and salinity, depth of water and grazing animals , according to NASA's Earth Observatory. When conditions are ideal, growth of the phytoplankton population can explode or bloom. Although a bloom may last several weeks, the life span of an individual phytoplankton rarely exceeds a few days.

Phytoplankton in the Arctic Ocean usually flowers every spring. In the past, phytoplankton blooms were virtually absent from higher arctic latitudes because these areas are generally covered with sea ice. In recent decades, sea ice has declined, fragmented earlier in the spring, or declined. forming at all in some areas of the Arctic.

In the new study, Renaut and his colleagues wanted to know if recent declines in sea ice had had an effect on spring blooms of phytoplankton. They used satellite observations of the color of the ocean – which provide estimates of biomass and primary productivity of phytoplankton – to track changes in proliferation each spring from 2003 to 2013.

They found that spring blooms extend further north and increase in primary productivity. In spring and summer, net primary productivity in the Arctic Ocean increased by 31% between 2003 and 2013, according to the study. The researchers also found that these blooms in the Barents and Kara seas in northern Russia stretched northward at a rate of 1 degree of latitude per decade.

Unexpected effects of the decline of sea ice

The melting of sea ice that occurs earlier in the season creates larger open-water areas that act as incubators for phytoplankton growth and lengthen their growing season, according to Renaut.

The authors suspect that spring blooms may one day spread into the central Arctic basin, which encompasses almost all north of 80 degrees latitude. Primary productivity, however, would likely remain low due to a lack of nutrients. Less ice cover means that spring bloom and proliferation under ice may also compete for light and nutrients, changing the flow of the marine ecosystem. The results suggest a significant change in this region, which has never been devoid of ice cover.

"The polar regions – the Southern Ocean and the Arctic Ocean – are really important because they play a crucial role in regulating the global climate," said Renaut. "If the sea ice disappears completely in summer in the Arctic Ocean, as we have been predicting for a few decades, it will have an impact on the ecosystem, but also probably on the climate."

Patricia Yager, a professor of marine science at the University of Georgia, who did not participate in the new study, said earlier growth of algal blooms observed in some areas could have significant effects if the animals are not yet ready to graze the phytoplankton.

"Such a mismatch over time could result in major changes in the Arctic food web, affecting not only local animals and people living there, but also the global population of migratory animals that depend on these Arctic resources," Yager said. "What's happening in the Arctic does not stay in the Arctic."

Cécile Rousseaux, a researcher at the Universities Space Research Association, who did not participate in the new study, said the study advanced research in this area by investigating the productivity of phytoplankton in different regions of the world. Arctic, cover have on the biochemical cycle of the Arctic Ocean. Rousseaux however noted that the study had limitations.

"It is also important to remember that we are currently limited by the amount of data available to study these changes," said Rousseaux. Longer time series of satellite data will allow us to confirm whether these trends in phytoplankton productivity

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