The City of the Southern Ocean Large floating ice shelves appear to harbor blooms of phytoplankton, a discovery that could revolutionize our understanding of Antarctica’s ecosystems and their impact on climate change.
The key to the growth of phytoplankton is photosynthesis, and the key to photosynthesis is sunlight – and until now scientists didn’t think there was much chance for plankton to thrive in the dark under the Antarctic ice shelves.
However, they have recently discovered phytoplankton blooms under the Arctic ice, which are formed when the ice breaks up, changes climate, shrinks, and melts water. This prompted researchers to look at Antarctica again.
The field work was carried out using floating measuring instruments, which were collected together with satellite data of sea ice and output from climate models to estimate the amount of phytoplankton that can pass under the ice, hidden from view.
“We found that almost all of the samples that floated under the Antarctic sea ice were growing in phytoplankton before the sea ice arrived,” says Christopher Horvat, a geophysicist at the University of Auckland in New Zealand.
“Most of the time, we saw big flowers.”
These floats can measure themselves and take stealthy action when approaching the ice when it detects that the water is too cold. Here, they were tasked with measuring levels of chlorophyll-a pigment and particulate backscatter, both indicators of phytoplankton.
Between 2014 and 2021, a total of 51 floats were tested at 2,197 times under the ice. This massive amount of data was collected in 79 consecutive measurements for analysis, while satellite images provided a record of ice cover.
“We found that 50 percent or more of the Antarctic under ice can support ice flowers, because the ice in the Southern Ocean has floes, and small areas of open water allow light and thus photosynthetic life,” he says. Horvat. .
Where sea levels have reached full and near-record levels, 88 percent of sea levels have begun to rise, and sea ice levels have begun to rise significantly.
There is some uncertainty in the data due to the time lag between sampling and logging – an uncertainty that future studies should remove – but the scientists who conducted the study say there is good, definitive evidence that the blooms are occurring.
Since phytoplankton communities are made up of tiny algae, they often represent the bottom of the ocean’s food supply – variations in their availability and distribution can have a significant impact on all marine life in the area.
The next step for the researchers will be to gather more information, and see how plankton blooms may affect other forms of life under the ice. It should also help us understand how the ice is shrinking due to global warming.
“The upper crust moves to where the harvest is, and if it’s under the ice, one would expect the food to follow,” says Horvat.
Research has been published in Frontiers in Marine Science.
