Antarctica sea ice may be hiding the plankton blooms

Underwater photo of Iceberg in the Antarctica Peninsula’s Southern Ocean.

The icy climate at the bottom of the world isn’t exactly the kind of place you’d expect to be teeming with life, but a recent study reveals it might be a little more hospitable than it seems.

Researchers looking at sea ice in the Southern Ocean of the region have discovered signs of extensive phytoplankton blooms buried beneath it, which seem to be defying the lack of light to grow in its icy waters.

The team, led by Dr. Christopher Horvat of Brown University and the University of Auckland, was taken aback by the results because it was believed that the Southern Ocean’s sea ice was too dense to permit any light to penetrate to the ocean below.

Because phytoplankton require light to exist, it was thought that the thick and deep ice cover typical of an Antarctica winter was essentially incompatible with this form of life.

As sunshine bathes the upper layers of the ocean, these blooms can be seen after the Antarctica sea ice starts to recede in the spring. However, the scientists’ interest in this phenomena was sparked by an increase in Arctic under-ice phytoplankton bloom observations, which they attribute to anthropogenic alterations to the sea ice.

Between 2014 and 2021, the scientists deployed floats to sample the conditions in the water column beneath Antarctica’s compact sea ice in the spring and summer. 88% of the time-series data demonstrated a spike in phytoplankton prior to the retreat of the sea ice, while 26% revealed what constitutes an under-ice bloom.

A group of phytoplankton in Antarctica’s sea ice. Photo: Cnet

“We found that nearly all examples of floats profiling under Antarctic sea ice record increases in phytoplankton before sea ice retreats,” told Horvat. “In many cases, we observed significant blooms.”

The researchers was able to determine the size and concentration of the phytoplankton by monitoring the colors and particulate backscatter that they released. The research has limitations, such as the inability of the floats to precisely monitor their sampling positions beneath the sea ice, but the researchers believe the body of data is substantial enough.

“It is possible some of the high productivity events might be recorded in regions with low sea ice cover,”  said Horvat. “Because the time we observe these blooms is close to when sea ice retreats, it is also possible some of the phytoplankton come from processes occurring outside of the sea ice zone, though we consider this unlikely given the sheer number of high-productivity measurements we found.”

According to the report of New Atlas, the scientists used data from NASA’s ICESat-2 spacecraft, which was launched in 2018 to precisely measure ice coverage at the poles to within the width of a pencil, to get a sense of how widespread the phenomena might be. The scientists ICESat-2 observations and climate models, and discovered that a large section of it housed conditions suitable to under-ice phytoplankton blooms.

“We used a new data product derived from a new NASA satellite, the ICESat-2 laser altimeter, to understand the compactness of ice around Antarctica, and with a suite of global climate models considered how much light reached the upper ocean,” he said. “We found that 50% or more of the under-ice Antarctic might support under-ice blooms, because sea ice in the Southern Ocean is comprised of discrete floes, and small areas of open water permit light and therefore photosynthetic life.”

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