What is hidden beneath Antarctic ice, White Walkers?

NASA's Earth Observing System has revealed that Antarctic sea ice lets in enough light for hidden phytoplankton to flourish in the Southern Ocean.

According to those responsible for the study, published in the journal Frontiers in Marine Science, it was previously thought that the dense sea ice prevented light from passing beyond its lower layers, so there were no necessary conditions for phytoplankton to emerge.

This is because sunlight is their main source of energy, therefore, as there is a lower incidence of it, it is not possible for these aquatic organisms to reproduce.

Previously, these algal blooms had been observed to develop as soon as the ice began to melt, as this action led to more light and more iron-rich freshwater. However, in this new research, considerable amounts of phytoplankton were recorded long before the iceberg thawed.

Until now it was thought that the compact sea ice of the Southern Ocean blocked all light reaching the sea below, preventing phytoplankton, the tiny algae that are the basis of aquatic food webs, from growing there because, the less light there is, the less the phytoplankton will be able to photosynthesise and, therefore, there will be less phytoplankton, which will greatly limit life under the ice.

life under the ice

The tiny photosynthetic algae that account for about 50% of the primary production of our planet's oceans, that is, the transformation of sunlight into organically available energy, are known as phytoplankton.

Phytoplankton blooms occur when algae reproduce rapidly due to an overabundance of available nutrients in their environment, appearing as voluminous blue-green eddies. However, phytoplankton needs a basic “fuel” for their reproduction: sunlight. Because of this, phytoplankton blooms are usually confined to the upper layer of the oceans, because in that context the sunlight is stronger and hits directly.

So while the Arctic and Antarctic have nutrient-rich waters and host massive phytoplankton blooms during the summer, when ice covers a smaller percentage of the oceans, this burst of life recedes rapidly and perishes by the time the colder months arrive of the year. The growth of sea ice in winter and little access to sunlight determine their fate.

The same phenomenon at both poles

Now, a scientific expedition that was dedicated to studying an area of ​​the Arctic in the Chukchi Sea, between Siberia and Alaska, found abundant phytoplankton in the waters near the seabed. According to a paper published in Live Science, University of Tokyo scientist Takuhei Shiozaki and his team concluded that sea ice forms later in the year as a result of climate change, allowing phytoplankton to receive sufficient sunlight to continue developing at those depths.

Along the same lines, a study led by Christopher Horvat, a researcher at Brown University in Rhode Island, USA, revealed that phytoplankton can also thrive under Antarctic sea ice. Horvat and his colleagues determined that 50% or more of Antarctica could support phytoplankton blooms under the ice, according to a paper published in Frontiers.

Hidden ecosystems?

Measuring under compacted sea ice with complete or near complete coverage of the water below, the scientists found that 88% of the measurement sequences recorded an increase in phytoplankton prior to sea ice retreat, and 26% met the criteria for flowering under the ice.

By making measurements under packed sea ice with complete or near complete coverage of the water below, the scientists found that 88% of the measurement sequences recorded an increase in phytoplankton prior to sea ice retreat, and 26% met the criteria

Consequently, both findings force the development of new expeditions and investigations that can obtain details about the new conditions for the growth of these underwater blooms, based on the changes generated at the environmental level. At the same time, the scientists highlighted that phytoplankton could support hidden ecosystems totally unknown until today, opening a new world to the eyes of science.

"It's possible that some of the high-productivity events are in regions with low sea ice cover," Horvat says. "Since the time we see these blooms are close to when the sea ice retreats, it's also possible that some of the phytoplankton comes from processes that occur outside the sea ice zone, although we consider this unlikely given the large number of high-productivity measurements we found."

The implications for Antarctic ecosystems could be significant. "The upper trophic levels migrate to where the productivity is, and if it's under the ice, you would expect the food web to follow," Horvat says.

For this reason, they believe that further research is needed to understand how these hidden ecosystems work and whether phytoplankton blooms attract predators and prey under the ice.

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